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Synchrotron radiation based techniques are powerful tools for battery research and allow probing a wide range of length scales, with different depth sensitivities and spatial/temporal resolutions. Operando experiments enable characterization during functioning of the cell and are thus a precious tool to elucidate the reaction mechanisms taking place. In this perspective, the current state of the art for the most relevant techniques (scattering, spectroscopy, and imaging) is discussed together with the bottlenecks to address, either specific for application in the battery field or more generic. The former includes the improvement of cell designs, multi-modal characterization and development of protocols for automated or at least semi-automated data analysis to quickly process the huge amount of data resulting from operando experiments. Given the recent evolution in these areas, accelerated progress is expected in the years to come, which should in turn foster battery performance improvements., The authors are grateful for funding through PTI+ TRANS-ENER+: “Alta Tecnología clave en la transición en el ciclo energético”, part of the CSIC program for the Spanish Recovery, Transformation and Resilience Plan funded by the Recovery and Resilience Facility of the European Union, established by the Regulation (EU) 2020/2094. ICMAB-CSIC members thank the Spanish Agencia Estatal de Investigación Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000917-S)., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

A simplified method is presented to extract the transport parameters of a liquid electrolyte solution from an experiment in a four-electrode cell. By observing that both polarisation and relaxation tend exponentially to a finite value with the same time constant, it becomes possible to precisely evaluate the limiting voltage attained upon polarisation though no steady state can be reached in practice, and use this input to evaluate the cation transference number as a function of the thermodynamic factor. This procedure simplifies the data analysis by avoiding complete fitting of the polarisation with a complicated numerical model. Such approach can favour the deployment of the four-electrode method to evaluate electrolyte transport parameters, which are crucial for the development of better performing batteries., Funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant Agreement No. 715087). We thank the Spanish Agencia Estatal de Investigacion Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000917-S). R.D. acknowledges support of the Beatriu de Pinos postdoctoral programme of the Government of Catalonia's Secretariat for Universities and Research of the Ministry of Economy and Knowledge (2017 BP 00187). We thank Charles Delacourt and Mohammad Farkhondeh for useful discussion., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Ca metal anode rechargeable batteries are seen as a sustainable high-energy density and high-voltage alternative to the current Li-ion battery technology due to the low redox potential of Ca metal...

Divalent cation based batteries are being considered as potential high energy density storage devices. The optimization of electrolytes for these technologies is, however, still largely lacking. Recent demonstration of the feasibility of Ca and Mg plating and stripping in the presence of a passivation layer or an artificial interphase has paved the way for more diverse electrolyte formulations. Here we exhaustively evaluate several Ca based electrolytes with different salts, solvents and concentrations, via measuring physico-chemical properties and using vibrational spectroscopy. Some comparisons with Mg and Li based electrolytes are made in order to highlight the unique properties of the Ca2+ cation. The Ca-salt solubility is found to be a major issue, calling for development of new highly dissociative salts. Nonetheless, reasonable salt solubility and dissociation was achieved using TFSI, BF4 and triflate anion based electrolytes and high permittivity solvents such as EC, PC, gBL and DMF. The local Ca2+ coordination is concentration dependent and rather complex, possibly involving bidentate coordination and participation of the nitrogen atom of DMF. The ionicity and the degree of ion-pair formation were both investigated and found to be strongly dependent on the nature of the cation, solvent donicity and salt concentration. The large ion-ion interaction energies of the contact ion-pairs, confirmed by DFT calculations, are expected to play a major role in the interfacial processes, and thus we here provide electrolyte design strategies to engineer the cation solvation and possibly improve the power performance of divalent battery systems., Funding from the European Union’s Horizon 2020 research and innovation program H2020 is acknowledged: European Research Council (ERC-2016-STG, CAMBAT grant agreement No. 715087), FETOPEN-1-2016-2017 (CARBAT, grant agreement No. 766617), and H2020-MSCA-COFUND-2016 (DOC-FAM, grant agreement No. 754397). A.P. is grateful to the Spanish Ministry for Economy, Industry and Competitiveness Severo Ochoa Program for Centers of Excellence in R&D (SEV-2015-0496). P.J. acknowledges financial support from the Swedish Energy Agency (contract #37671-1, Next Generation Batteries) and Chalmers Battery Initiative, part of the profile Materials for Energy Applications jointly managed by the Areas of Advance Materials Science and Energy at the Chalmers University of Technology, We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).

The development of practical multivalent-ion batteries critically depends on the identification of suitable positive electrode materials. To gain a better understanding of the intercalation chemistry of multivalent ions, model frameworks can be used to study the distinct specificities of possible multivalent ions, thus expanding our knowledge on the emerging “beyond Li battery” technology. Here, we compare the intercalation chemistry of Mg2+, Zn2+, and Ca2+ ions in a disordered layered-type structure featuring water interlayers and cationic vacancies as possible host sites. The thermodynamics of cation-inserted reactions performed on the model structure indicated that these reactions are thermodynamically favorable with Zn2+ being the least stable ion. Galvanostatic measurements confirmed that the structure is inactive toward Zn2+ intercalation, while Mg2+ can be reversibly inserted (0.37 Mg2+ per formula unit) with minor changes in the atomic arrangement, as demonstrated by pair distribution function analysis. Moreover, we demonstrate that nonsolvated Mg2+ was intercalated in the structure. Finally, the intercalation of Ca2+ performed at 100 °C with Ca(BF4)2 in propylene carbonate induced the collapse of the layered structure releasing water molecules that contribute to the degradation of the electrolyte, as revealed by the presence of CaF2 at the electrode level. The decomposition of the structure led to the formation of an electrochemically active phase featuring a strong long-range disorder, yet a short-range order close to that found in perovskite structures, particularly with corner-shared TiO6 octahedra. We, hence, hypothesize that defective CaTiO3-based perovskite could be explored as viable cathode materials for rechargeable Ca-based batteries., The research leading to these results received funding from the French National Research Agency under Idex@Sorbonne University for the Future Investments Program (no. ANR-11-IDEX-0004-02). Funding from the European Union’s Horizon 2020 research is acknowledged: European Research Council (ERC-2016-STG, CAMBAT grant agreement no. 715087). The work done at the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under contract no. DE-AC02-06CH11357. A.P. is grateful to the Spanish Ministry for Economy, Industry and Competitiveness Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496). We thank IMPC FR2482 for SEM-FEG and TEM instrumentation funded by CNRS, Sorbonne Université and C’Nano projets of Region Ile-de-France.

The currently emerging sodium-ion battery technology is in need of an optimized standard organic solvent electrolyte based on solid and directly comparable data. With this aim we have made a systematic study of “simple” electrolyte systems consisting of two sodium salts (NaTFSI and NaPF6) dissolved in three different alkyl carbonate solvents (EC, PC, DMC) within a wide range of salt concentrations and investigated: (i) their more macroscopic physico-chemical properties such as ionic conductivity, viscosity, thermal stability, and (ii) the molecular level properties such as ion-pairing and solvation. From this all electrolytes were found to have useful thermal operational windows and electrochemical stability windows, allowing for large scale energy storage technologies focused on load levelling or (to a less extent) electric vehicles, and ionic conductivities on par with analogous lithium-ion battery electrolytes, giving promise to also be power performant. Furthermore, at the molecular level the NaPF6-based electrolytes are more dissociated than the NaTFSI-based ones because of the higher ionic association strength of TFSI compared to PF6− while two different conformers of DMC participate in the Na+ first solvation shells – a Na+ affected conformational equilibrium and induced polarity of DMC. The non-negligible presence of DMC in the Na+ first solvation shells increases as a function of salt concentration. Overall, these results should both have a general impact on the design of more performant Na-conducting electrolytes and provide useful insight on the very details of the importance of DMC conformers in any cation solvation studies., We acknowledge funding received from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 646433 (NAIADES), the ALISTORE-ERI members for many fruitful discussions, and also the funding received from the Swedish Research Council the Swedish Energy Agency (#37671-1), the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, the Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496). DM especially acknowledges the European Union for a H2020 MSCA-IF grant no. 74343. PJ is grateful for the continuous financial support from several of Chalmers Areas of Advance: Materials Science, Energy, and Transport. We also acknowledge the computational resources provided by the Swedish National Infrastructure for Computing (SNIC) at Chalmers Centre for Computational Science and Engineering (C3SE). Author Information

Several Hard carbon||Na3V2(PO4)2F3 full-cells in 18650-format are assembled to demonstrate the possible use of SIBs in stationary applications. The cell aging process is investigated in two different conditions: (i) continuous cycling at different current rates, and (ii) storage at different states-of-charge at various temperatures. The obtained results reveal that the cell degradation depends strongly on the temperature, current rates applied in cycling conditions, or state-of-charge of the storage test. Under cycling conditions, the continuous sodiation/desodiation may induce significant mechanical deformation, leading to the detachment of active materials from the current collector. Furthermore, the post-mortem analysis shows that reaction rate and aging process are not homogeneous along the electrode roll. The XRD analysis shows that Na3V2(PO4)2F3 structure is robust; nevertheless, the material cannot recover the initial Na+ content as the cycling progresses, which is the main cause for capacity loss in the positive electrode. The solid-electrolyte interphase present on the hard carbon surface was characterised using XPS. The hard carbon electrode cannot be detected during this study, evidencing the formation of a relatively thick (>5 nm) passivating layer composed of carbonate salts and NaF, which are the main products of electrolyte decomposition., The authors acknowledge the European Commission for funding this work through the H2020 NAIADES project (LCE10-2014, Contract number 646433). LC, DC, PSC and LHBN thank the RS2E Network for the funding of LHBN's PhD thesis as well as the financial support of Région Nouvelle Aquitaine. LC, DC, PSC, LHBN, CC, and RD acknowledge the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01) for financial support. MRP and AP acknowledge Ministerio de Economía y Competititivad (Spain) for Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496). The authors thank E. Garitte (SAFT, France) for her helps to coordinate this project.

A study of the Solid Electrolyte Interphase (SEI) on hard-carbon (HC) electrodes in sodium half-cells is presented. Electrochemical performances over > 100 cycles were compared with two different salts (NaPF6, NaTFSI) and two different electrolyte additives (FEC, DMCF) in a mixture of EC and DMC solvents. The best electrochemical performances were observed with NaPF6 salt in conjunction with 3% FEC. The DMCF additive had a detrimental effect in all electrolyte combinations. The chemical characterization of the SEI was carried out by X-ray Photoelectron Spectroscopy (XPS) and showed that the best electrochemical behavior was related to an SEI composition based on sodium ethylene dicarbonate and NaF, whereas poorer electrochemical performances were associated to either low NaF or high Na2CO3 content. The results reported herein provide an insight on the SEI chemistry on hard carbon electrodes in sodium cells after long-term cycling, as a complement to previous studies dealing with the first cycles., Authors acknowledge the European Commission for funding through H2020 NAIADES project (LCE10–2014, grant nb. 646433). EI, MRP and AP acknowledge Ministerio de Economía y Competititivad (Spain) for Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496). This work has been done in the frame of the Doctoral Degree Program in Chemistry by the Universitat Autònoma de Barcelona. JF, CC and RD acknowledge Agence Nationale de la Recherche (ANR) for its “Investment for the Future” Program through I-SITE E2S-UPPA funding.

In this work, aprotic and protic ionic liquid (IL)-based electrolytes designed for calcium-based energy storage systems are investigated. We have shown that these electrolytes display good transport properties and electrochemical stabilities comparable with those of IL-based electrolytes proposed for lithium and sodium-based systems. The use of these electrolytes in electrochemical double layer capacitors (EDLCs) leads to the realization of devices displaying good capacitances paired with a high reversibility and stability. Their use in combination with TiS2 cathode appears more problematic as the cation of the ILs is inserting in the layered structure of this material during the charge process. In this latter case a careful design of the cation appears necessary to guarantee selective insertion of Ca2+ and reversible charge-discharge process., AB and TS wish to thank the Friedrich Schiller University of Jena for the financial support. Funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (ERC-2016-STG, CAMBAT grant agreement No 715087) is acknowledged. RD acknowledges support of the Beatriu de Pinós postdoctoral programme of the Government of Catalonia's Secretariat for Universities and Research of the Ministry of Economy and Knowledge (2017 BP 00187). A. Ponrouch is grateful to the Spanish Ministry for Economy, Industry and Competitiveness Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496). We thank Dr. R. Verrelli for providing us with TiS2 electrodes and for helpful discussion.

A comparative study of the electrochemical intercalation of Ca2+ and Mg2+ in layered TiS2 using alkylcarbonate-based electrolytes is reported, and for the first time, reversible electrochemical Ca2+ insertion is proved in this compound using both X-ray diffraction and differential absorption X-ray tomography at the Ca L2 edge. Different new phases are formed upon M2+ insertion that are structurally characterized, their amount and composition being dependent on M2+ and the experimental conditions. The first phase formed upon reduction is found to be the result of an ion-solvated intercalation mechanism, with solvent molecule(s) being cointercalated with the M2+ cation. Upon further reduction, new non-cointercalated calcium-containing phases seem to form at the expense of unreacted TiS2. The calculated activation energy barriers for Ca2+ migration in TiS2 (0.75 eV) are lower than those previously reported for Mg (1.14 eV) at the dilute limit and within the CdI2 structural type. DFT results indicate that the...

The electrochemical oxidation of a transition metal oxide through calcium extraction is achieved for the first time. The 1D framework of Ca3Co2O6 is maintained upon oxidation and the new phase formed exhibits a modulated structure. The process occurs at high potential and is partially reversible, which opens prospects for a calcium battery proof-of-concept.

This special collection contains a selection of research articles corresponding to contributions presented at Symposium C of the European Materials Science Meeting Edition 2019 that was held in Nice, France, from the 26th to the 31st of May 2019.

The cell potential of magnesium metal anode batteries is currently limited by the lack of stable and non-corrosive electrolytes. In a recent issue of Nature Chemistry, Son et al. demonstrated an artificial interphase on Mg anode that extends the electrolyte stability range while enabling magnesium transport. This approach paves the way for practical assessment of high-voltage cathodes and the assembly of high-energy-density Mg cells. Extension of the concept to other multivalent systems is also exciting.

Background Lean management aims to improve the performance of a company through the involvement of employees. It makes it possible to find the ideal conditions of functioning by optimising staff, equipment and sites, to add value with the least waste possible. The sterilisation activity is a production activity, which can be managed by lean management. Purpose The objectives are to schedule and optimize the recomposition flow, to redistribute resources, to pool skills and to prioritise emergencies. Material and methods A management engineer was assigned to help the sterilisation unit’s team to implement this project. After observation of the sterilisation activity and analysis of production data of the different surgical specialties resulting from the traceability software of the unit, an exercise in setting up a new organisation was carried out with all the agents. An interest in the use of Kanban to smooth the flow was demonstrated during these exercises. Results A redevelopment of the conditioning area was produced to limit movements. Islands of recomposition previously specific to a surgical unit, were redefined. The configuration of the conditioning area made it possible to create three production lines. To create three equivalent flows, the specialties were grouped according to their volumetrics and the complexity of the operating trays (OT). Each of the three resulting flows contained two blocks, and represented an activity of 2500 OT/month. Kanban labels were deposited on the OT in the washing zone, so the OT were handled in the conditioning area in order of arrival, according to the ‘First-In, First-Out’ principle. The restitution delay of the OT to surgical specialties decreased from 44 hours to 30 hours. The percentage of OT returned within the contractual deadlines increased from 72% to 85%. Conclusion The reorganisation of the sterilisation unit began on 16 July 2018. We can conclude that there was an improvement in productivity in terms of scheduling, fluidity and availability, reduction in the production pressure, redefinition of the true urgency, development of the concept of self-help and an increase in versatility through training. The project was presented to the general management of the University Hospital Centre in September 2018. A re-evaluation in 6 months is planned. References and/or acknowledgements https://ejhp.bmj.com/content/20/3/168 No conflict of interest.

Background The management of personal medical treatments of patients hospitalised in health facilities follows regulatory requirements. Failure to respect these requirements may result in iatrogenesis, with sometimes severe consequences for the patients. According to the High Authority of Health, not taking into consideration the personal treatment might lead to administrative mistakes which represent more than 57% of reported medication errors. In order to prevent these errors, a procedure and a technical data sheet have been designed to assist caregivers in the management of these medical treatments. Purpose The objective is to evaluate the caregiver’s level of knowledge of which documents in order to suggest ways of improvement. Material and methods This audit has been realised in order to assess how the medical staff follow these technical data sheets. The audit has been performed by a pharmacist student during 2 months, in eight randomly chosen services. An audit grid including 15 evaluated criteria was used. Results For this audit, 138 hospitalised patients were followed. At the time of their hospitalisation, 83.7% of the patients had personal treatment at home. Only 18.7% of these patients had their personal treatments prescribed in the hospital’s computer software. Regarding the management of these treatments, 47% of the wards had removed the personal treatment at the hospitalisation of the patients, and 38% identified and stored the treatments in a specific and secure place as indicated in the procedure. Seventy per cent of the patients actually took their treatment, while this fact had not been indicated in the prescription software by the responsible doctor. Regarding leaving the hospital, out of 10 outgoing patients, 54% left with a prescription including the updated personal treatment. Conclusion This audit allowed us to identify several problems, the lack of knowledge of the documents and insufficient training on computer software of the medical staff. Improvements are now being developed through communication campaigns concerning the data sheet and through training on the prescription software. A future assessment will be conducted to verify that the actions taken have had a positive effect. Reference and/or acknowledgements Patients personal treatment management in hospital: practices analysis and improvement opportunities. J Pharm Clin 2015;34. No conflict of interest.

Batteries based on Ca hold the promise to leapfrog ahead regarding increases in energy densities and are especially attractive as Ca is the 5th most abundant element in the Earth's crust. The viability of Ca metal anodes has recently been shown by approaches that either use wide potential window electrolytes at moderately elevated temperatures or THF-based electrolytes at room temperature. This paper provides realistic estimates of the practical energy densities for Ca-based rechargeable batteries at the cell level, calculated using open source models for several concepts. The results from the Ca metal anode batteries indicate that doubled or even tripled energy density as compared to the state-of-the-art Li-ion batteries is viable if a practical proof-of-concept can be achieved.

Among the different next-generation battery technologies, the ones based on divalent cations have recently gained particular attention due to their higher raw material availability and potentially higher energy density when compared with Li-ion. Such is the case of calcium, being the 5th most abundant element in the earth crust and having a standard redox potential only 170 mV above metallic lithium. However, the development of a secondary calcium-metal battery had been hampered by the lack of organic electrolytes allowing for reversible plating and stripping, which was only recently reported by our group and others employing different electrolyte formulations. The different electrolyte components – salt(s), solvent(s) and additive(s) – are expected to play a significant role in the operation of a calcium-metal battery. Here we will show how the solvation structure of the cation evolves in relation to the solvent employed and the concentration of the salt. Combining conductivity measurements with Raman spectroscopy data, a high tendency to form contact ion pairs is evidenced, which significantly affects the mobility of the ions in the liquid media. The use of different anions and their bonding strength with Ca2+ in solution will be discussed. Combined, the anion and solvent characteristics dictate the solvation of the cation, which in turn can affect the Ca plating and stripping kinetics. Additionally, the presence of electrolyte contaminants will be explored. The crucial yet very challenging drying of electrolyte containing Ca(BF4)2 in carbonate solvents will be presented. The difficulties to obtain anhydrous and contaminant free solutions from commercially available salts will be discussed and two alternative routes for anhydrous synthesis of the target salt will be presented.

New battery technologies have received increased attention in recent years, especially those based on the use of divalent cations such as calcium and magnesium. Their high abundance (calcium and magnesium being, respectively, the 5th and 8th most abundant element in the earth crust) and the possible safe use of metal anodes could result in more sustainable devices with lower cost and higher energy density systems when compared to Li-ion. Feasibility of plating/stripping of calcium metal has been demonstrated recently1 in very few organic electrolyte formulations. In all cases, some degree of electrolyte reduction and formation of passivation layer were reported. In particular, using Ca(BF4)2 in a mixture of carbonate solvents, a fully conformal passivation layer is formed at the surface of the metal anode.2 Yet this layer allows for Ca plating and stripping, thus exhibiting similar behavior as a solid electrolyte interphase (SEI). However, the nature and composition of such layer remain mostly unknown. In this communication, an in-depth analysis of the SEI will be presented. The influence of the electrolyte formulation (salt, solvent and additive) on the formation of the SEI and how it affects Ca plating and stripping kinetics were investigated. Among other technics, XPS, EELS and ToF-SIMS measurements allowed to detail the composition of the SEI. The homogeneity, the morphology and the microstructure were studied by means of TEM and FTIR microspectroscopy. Ponrouch, A. et al. Towards a calcium-based rechargeable battery. Nat. Mater. 15, 169 (2015). Forero-Saboya, J. et al. Understanding the nature of the passivation layer enabling reversible calcium plating. Energy Environ. Sci. 13, 3423–3431 (2020).

We present herein a systematic study of solvent co-intercalation during electrochemical reduction of titanium disulfide in lithium cells using state of the art in situ cells and synchrotron X-ray diffraction. To understand the role of the electrolyte components, four salts (LiBF4, LiBOB, LiPF6 and LiTFSI) and three solvents (ethylene carbonate, propylene carbonate and dimethyl carbonate) were investigated. Various types of in situ cells were assembled and X-ray diffraction patterns were collected in operando upon cycling. Co-intercalated phase formation was found to be triggered by the presence of propylene carbonate and to be electrochemically driven. This co-intercalated phase is formed in the early stages of reduction, with cell parameters a = 3.514 Å, c = 17.931 Å, corresponding approximately to a tripling of the pristine TiS2 cell along the c-axis. This phase does not seem to evolve upon further oxidation and hence induces an overall loss of capacity. Whereas the nature of the anion does not appear to influence the co-intercalated phase formation, the content of propylene carbonate in the electrolyte is clearly correlated to both its amount and the extent of capacity loss., The authors acknowledge funding from Ministry of Science and Innovation through grant MAT2017–86616-R, from the "Severo Ochoa" Programme for Centres of Excellence in R&D (CEX2019-000917-S). This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement N° 754397. The ALBA synchrotron is acknowledged for provision of beamtime within the in-house project program (proposals 2019013225 and 2020014004).

Hybrid electrolytes aimed at application in sodium-ion batteries (SIB) consisting of an organic solvent mixture (EC:PC) and different ionic liquids (ILs); EMImTFSI, BMImTFSI, and Pyr13TFSI, and with the NaTFSI salt providing the Naþ charge carriers have here been extensively studied. The physico-chemical and electrochemical characterisation includes ionic conductivity, viscosity, density, cation coordination and solvation, various safety measures, and electrochemical stability window (ESW). Hybrid electrolytes with 10e50% of IL content were found to have ionic conductivities on par with comparable organic solvent based electrolytes, but with highly enhanced safety properties. A systematic Raman spectroscopy study of the cation coordination and solvation before and after electrolyte safety tests by ignition suggest that IL cations and TFSI remain stable when ignited while organic solvents are consumed. Finally, the solid electrolyte interphase (SEI) formed when using hybrid electrolytes has both better mechanical and electrochemical stability than the SEI derived from pure IL based electrolytes. For a half-cell with a hard carbon (HC) electrode and a hybrid electrolyte with a composition of 0.8 m NaTFSI in EC0.45:PC0.45:- Pyr13TFSI0.10 encouraging results were obtained for IL based electrolytes e ca. 182 mAhg1 at C/10 over 40 cycles., We acknowledge the ALISTORE-ERI members for many fruitful discussions and the Swedish Research Council (VR), the Swedish Energy Agency (STEM), the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) and Ministerio de Ciencia e Innovacion (Spain, grant MAT2014-53500- R) for research funding. DM is grateful for a travel grant to ICMAB from Chalmers Area of Advance Energy. PJ acknowledges the continuous funding from several of Chalmers Areas of Advance: Energy, Materials Science, and Transport.

Density functional theory (DFT) calculations are used to investigate the basic electrochemical characteristics of Si-based anodes in calcium ion batteries (CIBs). The calculated average voltage of Ca alloying with fcc-Si to form the intermetallic CaxSi phases (0.5 b x ≤ 2) is of 0.4 V, with a volume variation of 306%. Decalciation of the lower Ca content phase, CaSi2, is predicted at an average voltage between 0.57 V (formation of Si-fcc, 65% volume variation) and 1.2 V (formation of metastable deinserted-Si phase, 29% volume variation). Experiments carried out in conventional alkyl carbonate electrolytes show evidence that electrochemical “decalciation” of CaSi2 is possible at moderate temperatures. The decalciation of CaSi2 is confirmed by different characterization techniques., We are grateful to the Toyota Battery Research division at Higashi Fuji (M6) for financial support. Diffraction experiments were performed at MSPD beamline at ALBA Synchrotron and the collaboration of François Fauth (ALBA staff) is sincerely acknowledged. ICMAB authors acknowledge the Spanish Ministry of Economy and Competitiveness (“Severo Ochoa” Programme for Centres of Excellence in R&D (SEV- 2015-0496)).

Various metals have been used as battery anodes in electrochemical cells ever since the birth of the batteries with Volta’s pile and in the first commercialized primary (Zn/MnO2, Leclanché 1866) and secondary (Pb/acid, Planté 1859) batteries. Li-MoS2 cells, employing Li metal anodes, with specific energies two to three times higher than both Ni/Cd and Pb/acid cells, were withdrawn from the market due to safety issues related to dendrites growth. Instead, electrodeposition of Mg and Ca appears to be less prone to dendrite formation.[1,2] Pioneering work by Aurbach et al. in the early 1990’s showed a surface-film controlled electrochemical behavior of Ca and Mg metal anodes in electrolytes with conventional organic solvents.[3,4] The lack of metal plating was attributed to the poor divalent cation migration through the passivation layer. Nevertheless, recent demonstration of Ca and Mg plating and stripping in the presence of a passivation layer or an artificial interphase [2,5,6] has paved the way for assessment of new electrolyte formulations with high resilience towards oxidation. However, several challenges remain to be tackled for the development of Ca and Mg based batteries.[7,8] Among these, the need for reliable electrochemical test protocols, mass transport limitations and high desolvation energies (due to strong cation-solvent and cation–anion interactions) are implied.[9, 10] Here, the reliability of electrochemical set-ups involving multivalent chemistries is discussed, and a systematic investigation on the impact of the electrolyte formulation on the cation solvation structure and transport is presented. References 1. M. Matsui, J. Power Sources, 196 (2011) 7048. 2. A. Ponrouch, C. Frontera, F. Bardé, M.R. Palacín, Nat. Mater., 15 (2016) 169. 3. D. Aurbach, R. Skaletsky, Y. Gofer, J. Electrochem. Soc.138 (1991) 3536. 4. Z. Lu, A. Schechter, M. Moshkovich, D. Aurbach, J. Electroanal. Chem. 466 (1999) 203. 5. D. Wang, X. Gao, Y. Chen, L. Jin, C. Kuss, P. G. Bruce, Nat. Mater. 17 (2018) 16. 6. S.-B. Son, T. Gao, S. P. Harvey, K. X. Steirer, A. Stokes, A. Norman, C. Wang, A. Cresce, K. Xu, C. Ban, Nat. Chem. 10 (2018) 532. 7. A. Ponrouch, M.R. Palacín, Current Opinion in Electrochemistry 9 (2018) 1. 8. A. Ponrouch, J. Bitenc, R. Dominko, N. Lindahl, P. Johansson, M.R. Palacin, Energy Storage Materials 20 (2019) 253. 9. D. S. Tchitchekova, D. Monti, P. Johansson, F. Bardé, A. Randon-Vitanova, M. R. Palacı́n, A. Ponrouch, J. Electrochem. Soc., 164 (2017) A1384. 10. J. D. Forero-Saboya, E. Marchante, R. B. Araujo, D. Monti, P. Johansson, A. Ponrouch, J. Phys. Chem. C (2019).

Divalent metal batteries have gained much attention recently given the high gravimetric capacities of calcium and magnesium metal electrodes (1340 and 2000 mAh/g respectively), and thus, holding promise as high energy density next-generation battery technologies. Although calcium metal possesses lower reduction potential (-2.76 V vs SHE) than magnesium (-2.38 V vs SHE), the development of calcium metal batteries has been hampered by the lack of electrolytes allowing for reversible electrodeposition. After the first demonstration of reversible calcium plating/stripping in and organic electrolyte based on Ca(BF4)2 in carbonate solvents [1], the attention devoted to calcium-based batteries have substantially increased. Recently, other electrolyte systems allowing for reversible plating/stripping were reported [2–4]. One of the crucial parameters to consider in the devolvement of divalent metal batteries is the presence of undesired impurities, particularly water, as it will affect greatly the surface chemistry of the calcium metal anode and prevent electrodeposition. As normally alkaline-earth metal salts are more hygroscopic that their alkaline counterparts, obtaining ultra-dry electrolytes is a key challenge which needs to be addressed. In the case of commercial Ca(BF4)2, most likely synthesised in aqueous solution, the water content is usually as high as 30wt%. In the present study we evaluate different drying methods and report on their effect on the stability of the BF4 - anion. The performance of the differently dried electrolytes with regard to the calcium electrodeposition is evaluated and discussed. An anhydrous synthetic route of Ca(BF4)2 will also be presented and compared to the commercially available salt. References 1. A. Ponrouch, C. Frontera, F. Bardé, and M. R. Palacín, Nat. Mater., 15, 169–172 (2016). 2. D. Wang et al., Nat. Mater., 17, 16–20 (2017). 3. Z. Li, O. Fuhr, M. Fichtner, and Z. Zhao-Karger, Energy Environ. Sci. (2019). 4. A. Shyamsunder, L. E. Blanc, A. Assoud, and L. F. Nazar, ACS Energy Lett., 4, 2271–2276 (2019).

This paper is part of the JES Focus Issue on Challenges in Novel Electrolytes, Organic Materials, and Innovative Chemistries for Batteries in Honor of Michel Armand., A comparative study of the reduction of TiS2 in diverse electrolyte formulations involving Ca(BF4)2 and Ca(TFSI)2 salts was carried out at different temperatures (from 25 °C to 100 °C). While for the former salt intercalation of calcium is only observed at high temperatures, calcium intercalated phases are also observed for the latter even at room temperature. The nature of the electrolyte does also have an impact on the relative amounts of the phases formed. Since Ca(TFSI)2 based electrolytes do not enable calcium plating, cycling was attempted using activated carbon as counterelectrode, and the reversibility of the process was ascertained. Even if corrosion of stainless steel current collectors and side reactions do still prevent proper cyclability, the results achieved should contribute to the establishment of reliable and viable cell set-up and methodology for the unambiguous study of the intercalation process in multivalent battery systems., Funding from the European Union's Horizon 2020 research and innovation programme H2020 FETOPEN-1-2016-2017 (CARBAT, grant agreement No. 766617) and ERC-2016-STG, (CAMBAT grant agreement No 715087) is gratefully acknowledged. Authors are grateful to the Spanish Ministry for Economy, Industry and Competitiveness Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496).

The electrochemical oxidation of a transition metal oxide through calcium extraction is achieved for the first time. The 1D framework of Ca3Co2O6 is maintained upon oxidation and the new phase formed exhibits a modulated structure. The process occurs at high potential and is partially reversible, which opens prospects for a calcium battery proof-of-concept.

[EN] The present invention relates to a calcium-based secondary cell containing: - an electrolyte arranged between the negative electrode and the positive electrode and comprising a calcium salt of a fluorine-containing anion of formula (XFn)m-, wherein n is a positive integer of at most 6 and m is a positive integer of at least 1 and m < n, - a positive-electrode active material at the positive electrode which is a one-dimensional structure accommodating Ca2+ ions and has the formula (1): Can+2Me1(n+1)-y-zMe2yMe3zO3n+3, wherein: Me1, Me2, Me3 are different transition metals; 1 ≤ n and n is not necessarily an integer; 0 ≤ y and y is not necessarily an integer; 0 ≤ z and z is not necessarily an integer, [FR] La présente invention porte sur un accumulateur à base de calcium contenant : - un électrolyte agencé entre l'électrode négative et l'électrode positive et comprenant un sel de calcium d'un anion contenant du fluor de formule (XFn)m", n étant un entier positif égal à 6 au plus et m étant un entier positif égal à au moins 1 et m < n, - un matériau actif d'électrode positive à l'électrode positive qui est une structure unidimensionnelle accueillant des ions Ca²⁺ et qui a la formule (1) : Can+2Me1(n+1)-y-zMe2yMe3zO3 n+3 (1) : Me1, Me2, Me3 étant des métaux de transition différents; 1 < n et n n'étant pas nécessairement un entier; 0 < y et y n'étant pas nécessairement un entier; 0 < z et z n'étant pas nécessairement un entier, Toyota Motor Europe, Consejo Superior de Investigaciones Científicas (España), A1 Solicitud de patente con informe sobre el estado de la técnica

Electrochemical performance of hard carbon (HC) prepared from sugar pyrolysis was investigated against sodium anodes at temperatures ranging from −15 °C up to 75 °C. Carbon coating was performed on HC decreasing its surface area and allowing significant improvement in terms of the first cycle coulombic efficiency and thus, irreversible capacity loss. Electrochemical performances of HC at various temperatures pointed at the IR drop of the cell being determinant for achieving the highest reversible capacity (450 mAh/g at C/10, 75 °C) and rate capability (340 mAh/g at 2C, 75 °C) ever reported. Stable cycling was also achieved at −15 °C with reversible capacity of ca. 265 mAh/g. Keywords: Na-ion batteries, Negative electrode, Hard carbon, Temperature, Electrolyte, Coating

Na2Ti3O7 is an interesting negative electrode material for sodium ion batteries given its electrochemical capacity and low operation potential. Unfortunately its prospects of practical application are hindered by an unacceptable capacity fading upon cycling. In this work we combine experiments and DFT calculations to investigate the origin of such a phenomenon. Different electrode technologies and different electrolytes have been targeted for electrochemical testing while the stability of Na2Ti3O7 and the fully reduced Na4Ti3O7 has been studied. The calculated elastic constants and vibrational modes support the mechanical and dynamical stability of the Na4Ti3O7 structure. In situ XRD measurements corroborate the reversibility of the insertion reaction as no structural damage is detected after 50 cycles. An intriguing reactivity of Na2Ti3O7 with the electrolyte upon storage is observed, which coupled to electrochemical measurements points to this being the main factor behind capacity fading.

The first review of the various electrolytes currently used and developed for sodium-ion batteries (SIBs), both in terms of materials and concepts, is presented. In contrast to the Li-ion battery (LIB), which is a mature technology for which a more or less unanimously accepted “standard electrolyte” exists: 1 M LiPF6 in EC/DMC, the electrolyte of choice for SIBs has not yet fully conformed to a standard. This is true for both materials: salts, solvents, or additives, and concept, using the main track of organic solvents or aiming for other concepts. SIB research currently prospers, benefitting from using know-how gained from 30 years of LIB R&D. Here the currently employed electrolytes are emphasized and their effects on practical SIB performance are outlined, scrutinizing the rationale for specific choices made, salts, solvents, additives, concentrations, etc. for each specific cell set-up and usage conditions.

A comprehensive study is reported entailing a comparison of Li, Na, K, Mg, and Ca based electrolytes and an investigation of the reliability of electrochemical tests using half-cells. Ionic conductivity, viscosity, and Raman spectroscopy results point to the cationsolvent interaction to follow the polarizing power of the cations, i.e. Mg2+ > Ca2+ > Li+ > Na+ > K+ and to divalent cation based electrolytes having stronger tendency to form ion pairs - lowering the cation accessibility and mobility. Both increased temperature and the use of anions with delocalized negative charge, such as TFSI, are effective in mitigating this issue. Another factor impeding the divalent cations mobility is the larger solvation shells, as compared to those of monovalent cations, that in conjunction with stronger solvent - cation interactions contribute to slower charge transfer and ultimately a large impedance of Mg and Ca electrodes. An important consequence is the non-reliability of the pseudo-reference electrodes as these present both significant potential shifts as well as unstable behaviors. Finally, experimental protocols in order to achieve consistent results when using half-cell set-ups are proposed.

The present invention relates to a calcium-based secondary cell comprising, as a positive-electrode active material, a titanium-based material comprising at least titanium (IV) and sulfide., Toyota Motor Europe, Consejo Superior de Investigaciones Científicas (España), A1 Solicitud de patente con informe sobre el estado de la técnica

We report on the hydrothermal synthesis of LiMn 1 − x Fe x PO 4 where x = 0.1, 0.2, 0.5, 0.8 and LiMn 0.9 Mg 0.1 PO 4 at 260 °C, using water–EMI_TFSI mixture as reacting medium. Electrochemical tests carried out in galvanostatic mode at 100 oC show that LiMn 0.5 Fe 0.5 PO 4 presents the best performance in terms of capacity (ca.120 mAh/g), therefore this capacity is equally parted between 3.5 and 4.1 V plateaus. This contrasts with LiMn 0.9 Mg 0.1 PO 4 which is more attractive energy density wise, as it exhibits a single reversible plateau having a capacity of 120 mAh/g at higher voltage (ca. 4.1 V vs. Li + /Li).

The performance of MnV2O6 (MnV) and its [{Mn(Bpy)}(VO3)2]≈(H2O)1.16 (MnBpy) and [{Mn(Bpy)0.5}(VO3)2]≈(H2O)0.62 (MnBpy0.5) hybrid derivative compounds was investigated against sodium and lithium counter electrodes. For MnV2O6 stable capacities of 850 mAh/g were achieved in lithium cells, the best value reported so far. The whole capacity is ascribed to a conversion reaction in which the amorphization of the compounds takes place. No significant differences in the capacities for the inorganic compound and the hybrid ones were observed. Interestingly, the potential hysteresis decreases in the hybrid compounds. The difference between Li and Na cell capacity most probably comes from the difference of standard potential of the two redox couples Li+/Li and Na+/Na of about ca. 0.3 V leading to an incomplete conversion reaction and thus lowers capacity in the case of Na cells. The Raman and IR ex-situ experiments after cycling indicate that the bipyridine organic ligands are completely decomposed during the electrochemical testing. The IR studies in MnV inorganic and MnBpy and MnBpy0.5 hybrid electrodes after the electrochemical cycling, suggest that the SEI formation and bipyridine degradation give rise to different aliphatic compounds.

Carbon coating on battery electrode active material powders is currently achieved through chemical procedures involving dispersing the powder in a liquid medium with a carbon precursor followed by thermolysis at high temperatures (ca. 700°C). This procedure has the drawback of not being applicable to materials which may decompose or reduce under such conditions. We present herein an alternative procedure based on physical deposition of carbon, carried out at room temperature under dry conditions, hence avoiding the limitations mentioned above and being generally applicable to any electrode active material. Homogeneous conformal coating was achieved and results are herein presented regarding improved electronic conductivity and limited side reactions recorded upon oxidation and reduction for carbon coated powder active materials in Li cells.

Storing electrochemical energy by means of fully reducing transition metal compounds to their metallic state is attractive due to the large amounts of charge that are produced. However, while more reversible than originally envisioned, electrochemical conversion reactions are accompanied by large inefficiencies. These inefficiencies are associated with hysteresis between the potentials of reduction and re-oxidation, as well as the loss of capacity when reversing back to the initial state. This work presents a series of results collected from different kinds of electroanalytical experiments. The use of data from conventional powder electrodes as well as thin films offered the opportunity to compare measurements of common occurrence in the literature with more sophisticated experiments carried out at higher temperature, which provided a complete picture of the kinetic nature of the processes involved. This picture is supportive of the thermodynamic nature of potential hysteresis, and indicates that coulombic inefficiencies stem from the low reversibility of the conversion reaction. Taken together, the results cast a clear light on the significant challenges that lie ahead if this kind of reactivity is to become technologically relevant in devices such as Li-ion batteries.

Raman spectroscopy is a powerful tool to study molecular level interactions in e.g. battery electrolytes. As cations and solvents interact, this affects the ion-pair formation and the nature of the solvation shells, which both are key factors affecting solution equilibria and ion transport. While Raman spectroscopy has been extensively used to study lithium-ion battery (LIB) electrolytes, studies on alternative battery technology electrolytes are scarce. Most concern sodium-ion batteries (SIB) and the interpretations are eased by the chemical similarity of Li and Na — both being monovalent. For divalent battery technologies such as Ca and Mg the differences in cation solvation can be expected to be larger, due to the fundamental differences between mono- and divalent ions, and prevents the full application of LIB electrolyte know-how and hence calls for further studies. The recently unveiled calcium battery technology [1] is today limited in scope of electrolytes, basically two compositions dominate [1, 2]. The lack of variety and understanding considerably slows down the Ca battery development, why more in depth analysis of the Ca2+ solvation is called for, to highlight issues hindering fast cation transport within the electrolytes. Here monovalent electrolytes composed of NaPF6 or NaTFSI dissolved in mixtures of ethylene carbonate (EC) and dimethyl carbonate (DMC), i.e. EC:DMC (1:1) were investigated for concentrations ranging from 0.3–1.0 M. They were selected based on the similarities with common LIB electrolytes either commercialized or extensively studied at the laboratory scale [3]. Divalent electrolytes composed of Ca(TFSI)2 and Ca(BF4)2 dissolved in a mixture of ethylene carbonate (EC) and propylene carbonate (PC), i.e. EC:PC (1:1) were chosen for their compatibility with available Ca electrodes [4, 5]. Both Raman spectroscopy and density functional theory calculations were employed to understand quantitatively how the speciation and solvation differ between these monovalent and divalent electrolytes, and ultimately how it could affect ion transport within both electrolytes and electrodes. In addition to the ion conductivities also the viscosities were measured to enable us to apply the fractional Walden rule [6] and qualitatively estimate the ion-pairing as function of both temperature and salt concentration. We observe that the solvation shell configurations change with the salt concentration for both multivalent and divalent formulations; the sizes of the divalent cationic complexes are nearly twice as large as the monovalent but the solvent coordination order is similar; EC tends to predominantly coordinate the cations, followed by PC or DMC. Finally, the Walden plots indicate that formation of contact ion-pairs (CIP) and/or aggregates (AGG) may be more likely for the BF4 based electrolytes, independent of the nature of the cation. References [1] A. Ponrouch, C. Frontera, F. Bardé, M.R. Palacín, Nature Materials, 15 (2016) 169-172. [2] D. Wang, X. Gao, Y. Chen, L. Jin, C. Kuss, P.G. Bruce, Nature Materials, 17 (2017) 16. [3] K. Xu, Chem Rev, 114 (2014) 11503-11618. [4] D.S. Tchitchekova, C. Frontera, A. Ponrouch, C. Krich, F. Bardé, M.R. Palacín, Dalton Transactions, 47 (2018) 11298-11302. [5] D.S. Tchitchekova, A. Ponrouch, R. Verrelli, T. Broux, C. Frontera, A. Sorrentino, F. Bardé, N. Biskup, M.E. Arroyo-de Dompablo, M.R. Palacín, Chemistry of Materials, 30 (2018) 847-856. [6] P. Walden, Z. Phys. Chem, 55 (1906) 207-249.

The study of intercalation compounds [1] led to the identification of redox reactions in host transition metal compounds involving reversible (usually topotactic) insertion and deinsertion of Mn+ ions. Studies with Li+ turned out to be a cornerstone in the development of the Li-ion battery technology [2] that has synergistically boosted portable electronics, while intercalation of multivalent cations (n>1) remained an academic curiosity. Yet, the current energy needs for batteries require significant improvement in energy density, beyond the capabilities of the traditional Li-ion technology, and multivalent cation chemistries represent a thrilling alternative in terms of the amount of energy that can be delivered. Ca metal based batteries have been almost unexplored as reversible plating and stripping of Ca with conventional organic electrolytes at moderate temperature was reported only recently [3,4]. The alkylcarbonate based electrolytes used in this work offer a wide electrochemical stability window, thus inciting the exploration of possible high voltage cathode materials with reliable electrochemical set-ups [5]. Development of potential multivalent host structures is challenging and the choice of cathode materials extremely limited, as divalent cation insertion/extraction is associated with sluggish solid state diffusion kinetics and high activation energies for the charge transfer kinetics. Layered intercalation compounds, with expandable interlayer space like TiS2, V2O5, MoO3, etc., are typically the most studied, but fundamental understanding of the reaction mechanisms in these phases is limited [6,7]. In this work we have explored the possibility of using Ca3Co2O6 cobaltite as Ca-based battery cathode [8]. The pristine compound has a 1D structure of CoO6 octahedra and prisms alternating along chains. By means of ex-situ synchrotron X-ray powder diffraction we have realized that Ca can be extracted by electrochemical methods driving to an incommensurate structure of the type Can+2Con+1O3n+3 (or, equivalently Ca1+xCoO3), characterized by the alternation of n octahedra and one prism along the Co-chain. The reversibility of the redox process seems to be rather limited in the present experimental conditions, indicating some kinetic or thermodynamic issues. Structurally related phases have been also explored as strategy for identifying alternative Ca2+ hosts. References: M.S. Whittingham, Prog. Solid St. Chem. (1978), 12, 41-99. G.E. Blomgren, J. Electrochem. Soc. (2017), 164, A5019-A5025. A. Ponrouch, C. Frontera, F. Bardé and M. R. Palacín, Nat. Mater. (2016), 15, 169-172. A. Ponrouch and M. R. Palacín, Current Opinion in Electrochemistry (2018), 9, 1-7. D. S. Tchitchekova, D. Monti, P. Johansson, F. Bardé, A. Randon-Vitanova, M. R. Palacín and A. Ponrouch, J. Electrochem. Soc. (2017), 164, A1384-A1392. D. S. Tchitchekova, A. Ponrouch, R. Verrelli, T. Broux, C. Frontera, A. Sorrentino, F. Bardé, M. E. Arroyo-de Dompablo and M. R. Palacín, Chem. Mater. (2018), 30, 847. R. Verrelli, A. P. Black, C. Pattanathummasid, D. S. Tchitchekova, A. Ponrouch, J. Oró-Solé, C. Frontera, F. Bardé, P. Rozier and M. R. Palacín, J. Power Sources (2018), 407, 162-172. D. S. Tchitchekova, C. Frontera, A. Ponrouch, C. Krich, F. Bardé and M. R. Palacín, Dalton Trans. (2018), 47, 11298-11302.

Due to serious concerns about future availability and price increase of lithium minerals, several alternatives have been investigated to substitute lithium-ion batteries in high demand applications. Divalent-cation chemistries, such as calcium and magnesium, promise a high energy capacity relying on much more abundant elements (5th and 8th, respectively, in the earth crust) than lithium (25th). Until recently, the development of such battery concepts was focused on electrolytes that do not form passivation films (solid electrolyte interphases - SEI) on the metal surface [1]. These electrolytes, however, suffer from a low stability towards oxidation and thus, limit the output voltage of the assembled cells. Previous works from our group demonstrated calcium plating and stripping in SEI-forming electrolytes at moderate temperatures [2]. Specifically, redox activity of calcium metal was observed in a Ca(BF4)2 electrolyte dissolved in a mixture of cyclic carbonates, while no activity was observed when TFSI was used as anion. The current study focuses on understanding the chemical composition differences between the SEI layers formed in the two systems analysed. A systematic characterization of the SEI formed on the Ca metal anode in various electrolyte formulations will be presented and the most suitable SEI compounds in terms of divalent cation mobility will be discussed. References [1] J. Muldoon, C. B. Bucur and T. Gregory, Chem. Rev., 2014, 114, 11683–11720. [2] A. Ponrouch, C. Frontera, F. Bardé and M. R. Palacín, Nat. Mater., 2016, 15, 169–172.

Batteries based on naturally abundant, light metal anodes (such as Ca and Mg) and multivalent ion host cathodes can potentially achieve very high energy densities at relatively low cost and environmental impact, thus representing a compelling alternative to currently available Li-ion systems. While reversible Ca metal plating and stripping in conventional alkyl carbonate based electrolytes has been accomplished [1,2], unraveling cathode materials with fast and reversible ion mobility at high operating voltages remains a major open challenge, mainly hampered by the slow diffusion kinetics in the solid state of multivalent ions. Thus, besides the exploration of new materials, revisiting traditional layered intercalation hosts appears as a very useful tool to gain further insight into the fundamentals of divalent ion intercalation. In this context, a thorough study of the electrochemical intercalation of Ca2+ in layered TiS2, in alkyl carbonate based electrolytes, is herein presented [3]. Fundamental insights on the insertion process are acquired through X-ray diffraction. Ca2+ insertion is unambiguously proved by using both X-ray diffraction and differential absorption X-ray tomography at the Ca L2 edge and the reversibility of the process is demonstrated at moderate temperature. Different phases can be formed upon reduction of pristine TiS2, whose amount and composition dependon the experimental conditions employed. A comparative study with Mg2+ containing electrolytes and other conventional intercalation hosts, such as V2O5, was also carried out. Careful examination of results highlights the potential relevance of side reactions in these system and the need to use several complementary characterization techniques to unambiguously assess divalent ion intercalation. [1]A. Ponrouch, C. Frontera, F. Bardé and M. R. Palacín, Nat. Mater. (2016), 15, 169. [2] A. Ponrouch, M. R. Palacín, Curr. Opin. Electrochem. (2018), 1. [3] Tchitchekova D.S., Ponrouch A., Verrelli R., Broux T., Frontera C., Sorrentino A., Biskup N., Arroyo-de Dompablo M.E., Bardé F., Palacín M.R., Chem. Mat. (2018), 30, 847.

Various metals have been used as battery anodes in electrochemical cells ever since the birth of the batteries with Volta’s pile and in the first commercialized primary (Zn/MnO2, Leclanché 1866) and secondary (Pb/acid, Planté 1859) batteries. Li-MoS2 cells, employing Li metal anodes, with specific energies two to three times higher than both Ni/Cd and Pb/acid cells, were withdrawn from the market due to safety issues related to dendrites growth. Instead, electrodeposition of Mg and Ca appears to be less prone to dendrite formation.[1,2] Pioneering work by Aurbach et al. in the early 1990’s showed a surface-film controlled electrochemical behavior of Ca and Mg metal anodes in electrolytes with conventional organic solvents.[3,4] The lack of metal plating was attributed to the poor divalent cation migration through the passivation layer. Nevertheless, recent demonstration of Ca and Mg plating and stripping in the presence of a passivation layer or an artificial interphase [2,5,6] has paved the way for assessment of new electrolyte formulations with high resilience towards oxidation. However, several challenges remain to be tackled for the development of Ca based batteries.[7] Among these, the need for reliable electrochemical test protocols, mass transport limitations and high desolvation energies (due to strong cation-solvent and cation–anion interactions) are implied.[8] Here, the reliability of electrochemical set-ups involving multivalent chemistries is discussed, and a systematic investigation on the impact of the electrolyte formulation on the cation solvation structure and transport is presented. Finally, a systematic characterization of the SEI formed on the Ca metal anode in various electrolyte formulations using complementary techniques allowed for the identification of the most suitable SEI compounds in terms of divalent cation mobility. Reference s : [1] M. Matsui, J. Power Sources, 196 (2011) 7048. [2]. A. Ponrouch, C. Frontera, F. Bardé, M.R. Palacín, Nat. Mater., 15 (2016) 169. [3] D. Aurbach, R. Skaletsky, Y. Gofer, J. Electrochem. Soc.138 (1991) 3536. [4] Z. Lu, A. Schechter, M. Moshkovich, D. Aurbach, J. Electroanal. Chem. 466 (1999) 203. [5] D. Wang, X. Gao, Y. Chen, L. Jin, C. Kuss, P. G. Bruce, Nat. Mater. 17 (2018) 16. [6] S.-B. Son, T. Gao, S. P. Harvey, K. X. Steirer, A. Stokes, A. Norman, C. Wang, A. Cresce, K. Xu, C. Ban, Nat. Chem. 10 (2018) 532. [7] A. Ponrouch, M.R. Palacín, Current Opinion in Electrochemistry 2018,doi.org/10.1016/j.coelec.2018.02.001. [8] D. S. Tchitchekova, D. Monti, P. Johansson, F. Bardé, A. Randon-Vitanova, M. R. Palacı́n, A. Ponrouch, J. Electrochem. Soc., 164 (2017) A1384. Figure 1: Scheme of a Ca metal anode-based battery with the main problems/ requirements outlined.[7] Figure 1

Na2Ti3O7 was recently reported to be highly promising as a negative electrode material for Na-ion batteries, thanks to its very low intercalation voltage (0.3 V vs Na+/Na0) and high capacity (200 mAh/g). The investigation of the redox mechanism in A2Ti3O7 (A = Li, Na) upon additional alkali ion intercalation concomitant to reduction of titanium is reported in this paper. Even if the low stability of the reduced phases (A2+xTi3O7) precluded a direct study, density functional theory (DFT) calculations allowed us to propose structural models for the reduced phases (A2+xTi3O7), which were further successfully confronted to the available experimental data. The alkali atoms are octahedrally coordinated in the reduced A2+xTi3O7 phase, so that the whole resulting structure can be considered rocksalt type. The very different potentials at which ion insertion is observed for A = Li or A = Na clearly prove that analogies between lithium and sodium systems cannot be taken for granted. In this case, such findings can ...

Electrochemical performance of hard carbon prepared from sugar pyrolysis was investigated against sodium anodes. Specific surface area and graphitization degree are determinant for achieving the highest reversible capacity ever reported (more than 300 mAh/g at C/10 after 120 cycles) with excellent rate capability. Such results were obtained using additive free EC:PC based electrolyte which appears to induce the formation of a more conducting solid electrolyte interphase (SEI) than that produced in the presence of 2% fluoroethylene carbonate (FEC). Keywords: Sodium ion batteries, Negative electrode, Hard carbon, Electrolyte, FEC additive

Arrays of Pt@RuO2 core–shell nanotubes were prepared by electrodeposition of RuO2 on Pt nanotubes and evaluated as electrochemical microsupercapacitor electrodes. Specific capacitance of ca. 1585 and 1280 F g − 1 RuO 2 is obtained at sweep rates of 2 and 500 mV s−1, respectively, demonstrating high utilization factor of RuO2 due to facilitated transport of protons and electrons. The specific geometric capacitance for the Pt@RuO2 core shell nanotubes electrode is 320 mF cm−2 at 2 mV s−1 and 256 mF cm−2 at 500 mV s−1.

The development of a rechargeable battery technology using light electropositive metal anodes would result in a breakthrough in energy density1. For multivalent charge carriers (Mn+), the number of ions that must react to achieve a certain electrochemical capacity is diminished by two (n = 2) or three (n = 3) when compared with Li+ (ref. 2). Whereas proof of concept has been achieved for magnesium3, 4, 5, the electrodeposition of calcium has so far been thought to be impossible6 and research has been restricted to non-rechargeable systems7, 8, 9, 10. Here we demonstrate the feasibility of calcium plating at moderate temperatures using conventional organic electrolytes, such as those used for the Li-ion technology. The reversibility of the process on cycling has been ascertained and thus the results presented here constitute the first step towards the development of a new rechargeable battery technology using calcium anodes., Authors are grateful to F. Fauth for his assistance during data collection at the ALBA Synchrotron. The authors thank the Toyota Battery Research division at Higashi Fuji (M6) for their financial support.