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ACS materials letters 4(2), 418 - 423 (2022). doi:10.1021/acsmaterialslett.1c00817, High-entropy ceramics are attracting large interest because of their unique materials properties. Nevertheless, the effect of entropy on the lithium transport remains largely elusive. Here, we report, for the first time, about medium- and high-entropy polyanionic lithium superionic conductors crystallizing in the F–43m space group and adopting the so-called argyrodite structure. The Li6PS5[Cl0.33Br0.33I0.33], Li6P[S2.5Se2.5][Cl0.33Br0.33I0.33], and Li6.5[Ge0.5P0.5][S2.5Se2.5][Cl0.33Br0.33I0.33] materials were structurally characterized using complementary synchrotron and neutron scattering techniques in combination with 31P magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. We show that, in contrast to other high-entropy ceramics, an unequal distribution of elements over the respective crystallographic sites occurs in these materials. Using electrochemical impedance spectroscopy (EIS) and 7Li pulsed field gradient (PFG) NMR spectroscopy, we demonstrate that introducing entropy (compositional disorder) marginally affects the room-temperature ionic conductivity (∼10–3 S cm–1) but instead lowers the activation energy for conduction to 0.22 eV. Our results emphasize the possibility of increasing entropy in polyanionic materials, thereby opening up compositional space for the search of Li-ion conductors with unprecedented properties., Published by ACS Publications, Washington, DC

In search of high-performance solid electrolytes, various materials have been discovered in the past, approaching or even exceeding the ionic conductivity of conventional liquid electrolytes. Among the reported classes of superionic electrolytes for solid-state battery applications, lithium thiophosphates appear to be the most promising owing to their high ionic conductivity and mechanical softness. A recent example is the Li

Large-scale industrial application of all-solid-state-batteries (ASSBs) is currently hindered by numerous problems. Regarding thiophosphate-based ASSBs, interfacial reactions with the solid electro...

All-inorganic solid-state batteries (SSBs) currently attract much attention as next-generation high-density energy-storage technology. However, to make SSBs competitive with conventional Li-ion batteries, several obstacles and challenges must be overcome, many of which are related to interface stability issues. Protective coatings can be applied to the electrode materials to mitigate side reactions with the solid electrolyte, with lithium transition metal oxides, such as LiNbO3 or Li2ZrO3, being well established in research. In addition, it has been recognized lately that carbonates incorporated into the coating may also positively affect the interface stability. In this work, we studied the effect that surface carbonates in case of Li2ZrO3-coated Li1+x(Ni0.6Co0.2Mn0.2)1-xO2 (NCM622) cathode material have on the cyclability of pellet stack SSB cells with Li6PS5Cl and Li4Ti5O12 as a solid electrolyte and an anode, respectively. Both carbonate-rich and carbonate-poor hybrid coatings were produced by altering the synthesis conditions. The best cycling performance was achieved for carbonate-deficient Li2ZrO3-coated NCM622 due to decreased degradation of the argyrodite solid electrolyte at the interfaces, as determined by ex situ X-ray photoelectron spectroscopy and in situ differential electrochemical mass spectrometry. The results emphasize the importance of tailoring the composition and nature of protective coatings to improve the cyclability of bulk SSBs.

Solid-state batteries (SSBs) currently attract great attention as a potentially safe electrochemical high-energy storage concept. However, several issues still prevent SSBs from outperforming today's lithium-ion batteries based on liquid electrolytes. One major challenge is related to the design of cathode active materials (CAMs) that are compatible with the superionic solid electrolytes (SEs) of interest. This perspective, gives a brief overview of the required properties and possible challenges for inorganic CAMs employed in SSBs, and describes state-of-the art solutions. In particular, the issue of tailoring CAMs is structured into challenges arising on the cathode-, particle-, and interface-level, related to microstructural, (chemo-)mechanical, and (electro-)chemical interplay of CAMs with SEs, and finally guidelines for future CAM development for SSBs are proposed.

Solid-state batteries (SSBs) are a promising next step in electrochemical energy storage but are plagued by a number of problems. In this study, we demonstrate the recurring issue of mechanical degradation because of volume changes in layered Ni-rich oxide cathode materials in thiophosphate-based SSBs. Specifically, we explore superionic solid electrolytes (SEs) of different crystallinity, namely glassy 1.5Li2S-0.5P2S5-LiI and argyrodite Li6PS5Cl, with emphasis on how they affect the cyclability of slurry-cast cathodes with NCM622 (60% Ni) or NCM851005 (85% Ni). The application of a combination of ex situ and in situ analytical techniques helped to reveal the benefits of using a SE with a low Young’s modulus. Through a synergistic interplay of (electro)chemical and (chemo)mechanical effects, the glassy SE employed in this work was able to achieve robust and stable interfaces, enabling intimate contact with the cathode material while at the same time mitigating volume changes. Our results emphasize the importance of considering chemical, electrochemical, and mechanical properties to realize long-term cycling performance in high-loading SSBs.

Inorganic solid-state batteries are attracting significant interest as a contender to conventional liquid electrolyte-based lithium-ion batteries but still suffer from several limitations. The search for advanced coatings for protecting cathode materials in solid-state batteries to achieve interfacial stability is a continuing challenge. In the present work, the surface of an industrially relevant Ni-rich LiNi$_x$Co$_y$Mn$_z$O$_2$ cathode material, NCM-851005 (85 % Ni), was modified by applying a coating containing Li, Nb and Zn, aiming at a composition Li$_6$ZnNb$_4$O$_14$, by means of sol-gel chemistry. Detailed characterization using scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy and nano-beam electron diffraction showed that the surface layer after heating in O$_2$ at 500 °C contains Li$_3$NbO$_4$ nanocrystals and Li$_2$CO$_3$, with Zn presumably acting as a dopant. The protective coating on the NCM-851005 secondary particles significantly increased the cycling performance (reversible capacity, rate capability etc.) and stability of full cells using argyrodite Li$_6$PS$_5$Cl as solid electrolyte. Interestingly, the level of improvement is superior to that achieved with conventional LiNbO$_3$ coatings.

In recent years, the search for glassy and ceramic Li+ superionic conductors has received significant attention, mainly due to the renaissance of interest in all-solid-state batteries. Here, we report the mechanochemical synthesis of metastable Li7GeS5Br, which is, to the best of our knowledge, the first compound of the Li2S-GeS2-LiBr system. Applying combined synchrotron X-ray diffraction and neutron powder diffraction, we show Li7GeS5Br to crystallize in the F43m space group and to be isostructural with argyrodite-type Li6PS5Br, but with a distinct difference in the S2-/Br- site disorder (and improved anodic stability). Electrochemical impedance spectroscopy indicates an electrical (ionic) conductivity of 0.63 mS cm-1 at 298 K, with an activation energy for conduction of 0.43 eV. This is supported by temperature-dependent 7Li pulsed-field gradient-nuclear magnetic resonance spectroscopy measurements. Overall, the results demonstrate that novel (metastable) argyrodite-type solid electrolytes can be prepared via mechanochemistry that are not accessible by conventional solid-state synthesis routes.

Gas evolution in conventional lithium-ion batteries using Ni-rich layered oxide cathode materials presents a serious issue that is responsible for performance decay and safety concerns, among others. Recent findings revealed that gas evolution also occurred in bulk-type solid-state batteries. To further clarify the effect that the electrolyte has on gassing, we report in this work-to the best of our knowledge-the first study comparing gas evolution in lithium-ion batteries with NCM622 cathode material and different electrolyte types, specifically solid (β-Li3PS4 and Li6PS5Cl) versus liquid (LP57). Using isotopic labeling, acid titration, and in situ gas analysis, we show the presence of O2 and CO2 evolution in both systems, albeit with different cumulative amounts, and possible SO2 evolution for the lithium thiophosphate-based cells. Our results demonstrate the importance of considering gas evolution in solid-state batteries, especially the formation and release of highly corrosive SO2, due to side reactions with the electrolyte.

Lithium–silicon compounds are used as active material in the negative electrodes of Li-ion batteries. The knowledge of Li diffusion in these materials is of importance for the optimization of charg...

Bulk-type all-solid-state batteries (SSBs) are receiving much attention as next-generation energy storage technology with potentially improved safety and higher power and energy densities (over a w...

ASSBs (all-solid-state batteries) are promoted as an energy dense and safe alternative to current Li-ion batteries (LIBs) and attract great interest from academia and industry. In contrast to LIBs, which employ a liquid organic electrolyte, they utilize a solid electrolyte. This substitution promises to eliminate the flammability of the battery and to simplify the cell design. While recent research efforts have concentrated on miniaturizing and eventually even removing the anode host material in batteries, the relative portion of the cathode needs to be maximized, as cathodes are the only component that can increase energy density by increasing its fraction. In a simplified view, the cathode kinetics are determined by the cathode microstructure, the volume fractions of the constituents and the properties of electrolyte and cathode active material (CAM). Liquid electrolytes can easily penetrate porous composite cathodes, but rigid SEs can not do the same, resulting in residual porosity in the cathode. This porosity can lower active interface area between CAM and SE, and increase tortuosity of ionic and electronic charge transport pathways. Sufficient ionic and electronic transport pathways in composite cathode structures are, however, essential because cathode active material particles that are either electronically or ionically isolated cannot contribute to the charging or discharging process. We analyse the requirements for SSB cathodes and determine charge transport bottlenecks by impedance spectroscopy of a reference system consisting of a thiophosphate based solid electrolyte and a nickel rich layered CAM. Different cathode microstructures are analysed and their charge transport properties are quantified as partial conductivities. From the obtained partial conductivities, we calculated tortuosity factors and correlated them to cell performance with complementary cycling data of all-solid-state batteries in order to determine charge transport bottlenecks. We find, that ionic charge transport and consequently cathode kinetics are highly dependent on the SE particle size distribution In addition, we analyse the requirements for CAMs for SSBs and develop design principles for different CAM types that aim to further increase cathode performance.

Lithium‐ion batteries (LIBs), which utilize a liquid electrolyte, have established prominence among energy storage devices by offering unparalleled energy and power densities coupled with reliable electrochemical behavior. The development of solid‐state batteries (SSBs), utilizing a solid electrolyte layer for ionic conduction between the electrodes, could potentially offer further performance improvements in key areas such as energy density and safety. However, to date, SSBs remain unable to match the performance of their liquid counterparts. In light of renewed interest in accelerating the development of alternative energy storage devices, herein, a current overview of operando characterization techniques applied to solid‐state cells and related experimental setups is presented. Operando techniques, which allow materials to be studied as part of a dynamic system, have significantly advanced understanding of LIBs, and they offer the same potential for SSBs. To address this, a selection of analytical tools for probing interfacial/bulk electrochemical processes is highlighted and their advantages and challenges for studying various aspects of SSB chemistry are described. Finally, a perspective on how different techniques could support the future development of advanced SSBs is provided.

A room temperature, atomic-layer-deposition-like coating strategy for NCM811 (80% Ni) is reported. Trimethylaluminum is shown to readily react with adsorbed moisture, leading both to Al2O3 surface layer formation on NCM811 and to trace H2O removal in a single treatment step. Even more importantly, the cycling performance of pouch cells at 45 8C is greatly improved.

This short perspective summarizes recent findings on the role of residual lithium present on the surface of layered Ni-rich oxide cathode materials in liquid- and solid-electrolyte based batteries, with emphasis placed on the carbonate species. Challenges and future research opportunities in the development of carbonate-containing protective nanocoatings for inorganic solid-state battery applications are also discussed.

All-inorganic solid-state batteries (SSBs) currently attract much attention as next-generation high-density energy-storage technology. However, to make SSBs competitive with conventional Li-ion batteries, several obstacles and challenges must be overcome, many of which are related to interface stability issues. Protective coatings can be applied to the electrode materials to mitigate side reactions with the solid electrolyte, with lithium transition metal oxides, such as LiNbO

While still premature as an energy storage technology, bulk solid-state batteries are attracting much attention in the academic and industrial communities lately. In particular, layered lithium metal oxides and lithium thiophosphates hold promise as cathode materials and superionic solid electrolytes, respectively. However, interfacial side reactions between the individual components during battery operation usually result in accelerated performance degradation. Hence, effective surface coatings are required to mitigate or ideally prevent detrimental reactions from occurring and having an impact on the cyclability. In the present work, we examine how surface carbonates incorporated into the sol–gel-derived LiNbO3 protective coating on NCM622 [Li1+x(Ni0.6Co0.2Mn0.2)1–xO2] cathode material affect the efficiency and rate capability of pellet-stack solid-state battery cells with β-Li3PS4 or argyrodite Li6PS5Cl solid electrolyte and a Li4Ti5O12 anode. Our research data indicate that a hybrid coating may in fact be beneficial to the kinetics and the cycling performance strongly depends on the solid electrolyte used.

In recent years, investigations into improving the performance of bulk-type solid-state batteries (SSBs) have attracted much attention. This is due, in part, to the fact that they offer an opportunity to outperform the present Li-ion battery technology in terms of energy density. Ni-rich Li$_{1+x}$(Ni$_{1-y-z}$Co$_{y}$Mn$_{z}$)$_{1-x}$O$_{2}$ (NCM) and lithium-thiophosphate-based solid electrolytes appear to be a promising material combination for application at the cathode side. Here, we report about exploratory investigations into the 1.5Li$_{2}$S/0.5P$_{2}$S$_{5}$/LiI phase system and demonstrate that a glassy solid electrolyte has more than an order of magnitude higher room-temperature ionic conductivity than the crystalline counterpart, tetragonal Li$_{4}$PS$_{4}$I with the P4/nmm space group (∼1.3 versus ∼0.2 mS cm$^{-1}$). In addition, preliminary results show that usage of the glassy 1.5Li$_{2}$S–0.5P$_{2}$S$_{5}$–LiI in pellet stack SSB cells with an NCM622 (60% Ni content) cathode and a Li$_{4}$Ti$_{5}$O$_{12}$ anode leads to enhanced capacity retention when compared to the frequently employed argyrodite Li$_{6}$PS$_{5}$Cl solid electrolyte. This indicates that, apart from interfacial instabilities, the stiffness (modulus) of the solid electrolyte and associated mechanical effects may also impact significantly the long-term performance. Moreover, SSB cells with the glassy 1.5Li$_{2}$S–0.5P$_{2}$S$_{5}$–LiI and high-loading cathode (∼22 mg$_{NCM622}$ cm$^{-2}$) manufactured using a slurry-casting process are found to cycle stably for 200 cycles at C/5 rate and 45 °C, with areal capacities in excess of 3 mA h cm$^{-2}$.

Measures to improve the cycling performance and stability of bulk-type all-solid-state batteries (SSBs) are currently being developed with the goal of substituting conventional lithium-ion battery ...

The formation of gaseous side products in liquid electrolyte-based lithium-ion batteries has been intensively studied in recent years and identified as being one of the sources of degradation (an indication of electrolyte and electrode instabilities). Herein, we demonstrate, to our knowledge for the first time, that gassing can also arise in all-solid-state battery cells made of Ni-rich layered oxide cathode materials and thiophosphate-based solid electrolytes. Combining isotopic labeling, titration for quantitative carbonate determination, and operando gas analysis, our findings reveal the evolution of CO2 stemming from carbonate species on the cathode surface as well as O2 from the bulk of the oxide cathode at potentials above 4.5 V with respect to Li+/Li, among others.

The search for high Li-ion conducting ceramics has regained tremendous interest triggered by the renaissance of the all-solid-state battery. Within this context we herein reveal the impact of structural polymorphism of lithium copper pyroborate Li6CuB4O10 on its ionic conductivity. Using combined in situ synchrotron X-ray and neutron powder diffraction, a structural and synthetic relationship between α- and β-Li6CuB4O10 could be established and its impact on ionic conductivity evolution was followed using electrochemical impedance spectroscopy. We show that the high temperature form of Li6CuB4O10 exhibits a high Li-ion conductivity (2.7 mS cm–1 at 350 °C) and solve its crystal structure for the first time. Our results emphasize the significant impact of structural phase transitions on ionic conductivity and show possible high Li-ion mobility within borate based compounds.

Measures to improve the cycling performance and stability of bulk-type all-solid-state batteries (SSBs) are currently being developed with the goal of substituting conventional Li-ion battery (LIB) technology. As known from liquid electrolyte based LIBs, layered oxide cathode materials undergo volume changes upon (de)lithiation, causing mechanical degradation due to particle fracture, among others. Unlike solid electrolytes, liquid electrolytes are somewhat capable of accommodating morphological changes. In SSBs, the rigidity of the materials used typically leads to adverse contact loss at the interfaces of cathode material and solid electrolyte during cycling. Hence, designing zero- or low-strain electrode materials for application in next-generation SSBs is desirable. In the present work, we report on novel Co-rich NCMs, NCM361 (60% Co) and NCM271 (70% Co), showing minor volume changes up to 4.5 V vs Li+/Li, as determined by operando X-ray diffraction and pressure measurements of LIB pouch and pelletized SSB cells, respectively. Both cathode materials exhibit good cycling performance when incorporated into SSB cells using argyrodite Li6PS5Cl solid electrolyte, albeit their morphology and secondary particle size have not yet been optimized.

All-solid-state batteries (SSBs) are attracting widespread attention as next-generation energy storage devices, potentially offering increased power and energy densities and better safety than liquid electrolyte-based Li-ion batteries. Significant research efforts are currently underway to develop stable and high-performance bulk-type SSB cells by optimizing the cathode microstructure and composition, among others. Electronically conductive additives in the positive electrode may have a positive or negative impact on cyclability. Herein, it is shown that for high-loading (pelletized) SSB cells using both a size- and surface-tailored Ni-rich layered oxide cathode material and a lithium thiophosphate solid electrolyte, the cycling performance is best when low-surface-area carbon black is introduced.

The implementation of all-solid-state batteries (ASSBs) is regarded as an important step toward next-generation energy storage systems, in particular for electric vehicles and portable electronics. This may be achieved through application of layered Ni-rich oxide cathode materials such as Li1+x(Ni1–y–zCoyMnz)1–xO2 (NCM) with high specific capacity and thiophosphate-based solid electrolytes. Here, the profound effect that the secondary particle size of the cathode active material has on the capacity of ASSB cells comprising NCM622 (60% Ni), β-Li3PS4, and In anode is demonstrated. We show the benefits of using small particles (d ≪ 10 μm), allowing virtually full charge capacity. This finding is rationalized through galvanostatic charge–discharge tests and complementary ex situ and operando X-ray diffraction experiments combined with Rietveld refinement analysis. Our results indicate the importance of considering and avoiding electrochemically inactive electrode material in bulk-type ASSBs, which we show usi...

Li tracer self-diffusion was studied in amorphous lithium–silicon compounds which are important as negative electrodes in Li-ion batteries. Experiments were done on LixSi/6LixSi (LixSi, x ∼ 0.02 and x ∼ 0.06) thin-film heterostructures using secondary ion mass spectrometry. The diffusivities follow the Arrhenius law in the temperature range between 140 and 325 °C, both with an activation energy of (1.42 ± 0.03) eV, while the Li-richer samples show 1 order of magnitude higher diffusivities. A trap-limited diffusion mechanism is suggested, explaining this result with a lower concentration of unsaturated traps. A discussion against the literature suggests a strong lithium concentration dependence of diffusivities also for higher x.

Cell reports 2(6), 100465 (2021). doi:10.1016/j.xcrp.2021.100465, Laboratory research into bulk-type solid-state batteries (SSBs) has been focused predominantly on powder-based, pelletized cells and has been sufficient to evaluate fundamental limitations and tailor the constituents to some degree. However, to improve experimental reliability and for commercial implementation of this technology, competitive slurry-cast electrodes are required. Here, we report on the application of an approach guided by design of experiments (DoE) to evaluate the influence of the type/content of polymer binder and conductive carbon additive on the cyclability and processability of Li$_{1+x}$(Ni$_{0.6}$Co$_{0.2}$Mn$_{0.2}$)$_{1−x}$O$_2$ (NCM622) cathodes in SSB cells using lithium thiophosphate solid electrolytes. The predictions are verified by charge-discharge and impedance spectroscopy measurements. Furthermore, structural changes and gas evolution are monitored via X-ray diffraction and differential electrochemical mass spectrometry, respectively, in an attempt to rationalize and support the DoE results. In summary, the optimized combination of polymer binder and conductive carbon additive leads to high electrochemical performance and good processability., Published by Elsevier, [New York, NY]

Chemical communications 55(75), 11223 - 11226 (2019). doi:10.1039/C9CC04453A, Determining the state-of-charge of all-solid-state batteries via bothex situ and operando X-ray diffraction, rather than by electrochemicaltesting (may be strongly affected by electrically isolated/inactivematerial, irreversible side reactions, etc.), is reported. Specifically,we focus on bulk-type cells and use X-ray diffraction data obtainedon a liquid electrolyte-based Li-ion cell as the reference standardfor changes in lattice parameters with (de)lithiation., Published by Soc., Cambridge

All-solid-state batteries (SSBs) are considered as next-generation energy storage technology with the possibility of higher energy and power densities as well as safety compared to conventional lithium-ion batteries [1]. SSBs with sulfidic solid electrolytes (SEs) as a component are thought to be the closest towards practical implementation [2] despite widely reported side reactions at the cathode active material (CAM)/SE interface. Advances in coating technology have helped suppress these detrimental reactions to a certain extent [3]. We demonstrate the use of differential electrochemical mass spectrometry (DEMS) on evaluating the stability of a protective surface coating [4]. Analysis of the gas evolved provides insights into possible reaction mechanisms at the CAM/SE interface. DEMS was also used to investigate the practical safety performance of sulfide-based SSBs with respect to possible harmful gas evolution such as H2S and SO2 [5]. Key Words: All-solid-state battery, differential electrochemical mass spectrometry, electrochemical energy storage References Janek, W. Zeier, Nat. Energy, 1 (2016) 16141. J. Nam, D. Y. Oh, S. H. Jung, Y. S. Jung, J. Power Sources, 375 (2018) 93–101. -Y. Kim, F. Strauss, T. Bartsch, J. H. Teo, T. Hatsukade, A. Mazilkin, J. Janek, P. Hartmann, T. Brezesinski, Chem. Mater., 31 (2019) 9664 – 9672. Bartsch, F. Strauss, T. Hatsukade, A. Schiele, A-Y. Kim, P. Hartmann, J. Janek, T. Brezesinski, ACS Energy Lett., 3 (2018) 2539–2543. Strauss, J. H. Teo, A. Schiele, T. Bartsch, T. Hatsukade, P. Hartmann, J. Janek, T. Brezesinski, ACS Appl. Mater. Interfaces, 12 (2020), 20462–20468.

In the ongoing search for new negative electrode materials for lithium-ion batteries, amorphous silicon with a theoretical specific capacity of almost 4000 mA h g−1 is still one of the most promising candidates. In order to optimize cycling behavior, prelithiation of silicon is discussed as possible solution. Yet, little is known about kinetics in the Li-Si system, especially with a low lithium content. Using neutron reflectometry as a tool, lithium permeation through amorphous LixSi layers was probed during annealing. From the results a lithium permeability (diffusivity×solubility) of P=(3.3±0.9)×10−21 m2 s−1 is derived for LixSi (x≈0.1), which is identical to that of pure amorphous silicon.

In the search for new cathode materials for Li-ion batteries, borate (BO33-) based compounds have gained much interest during the last two decades due to the low molecular weight of the borate polyanions which leads to active materials with increased theoretical capacities. In this context we herein report the electrochemical activity versus lithium and the ionic conductivity of a diborate or pyroborate B2O54- based compound, Li6CuB4O10. By combining various electrochemical techniques with in situ X-ray diffraction, we show that this material can reversibly insert/deinsert limited amounts of lithium (~0.3 Li+) in a potential window ranging from 2.5 to 4.5 V vs. Li+/Li0. We demonstrate, via electron paramagnetic resonance (EPR), that such an electrochemical activity centered near 4.25 V vs. Li+/Li0 is associated with the Cu3+/Cu2+ redox couple, confirmed by density functional theory (DFT) calculations. Another specificity of this compound lies in its different electrochemical behavior when cycled down to 1 V vs. Li+/Li0 which leads to the extrusion of elemental copper via a conversion type reaction as deduced by transmission electron microscopy (TEM). Lastly, we probe the ionic conductivity by means of AC and DC impedance measurements as a function of temperature and show that Li6CuB4O10 undergoes a reversible structural transition around 350 °C, leading to a surprisingly high ionic conductivity of ~1.4 mS cm-1 at 500 °C.

Conversion type materials, in particular metal fluorides, have emerged as attractive candidates for positive electrodes in next generation Li-ion batteries (LIBs). However, their practical use is being hindered by issues related to reversibility and large polarization. To minimize these issues, a few approaches enlisting the anionic network have been considered. We herein report the electrochemical properties of bismuth oxyborate Bi

International audience; Conversion type materials, in particular metal fluorides, have emerged as attractive candidates for positive electrodes in next generation Li-ion batteries (LIBs). However, their practical use is being hindered by issues related to reversibility and large polarization. To minimize these issues, a few approaches enlisting the anionic network have been considered. We herein report the electrochemical properties of bismuth oxyborate Bi4B2O9 and show that this compound reacts with lithium via a conversion reaction leading to a sustained capacity of 140 mA h g−1 when cycled between 1.7 and 3.5 V vs. Li+/Li0 while having a surprisingly small polarization (∼300 mV) in the presence of solely 5% in weight of a carbon additive. These observations are rationalized in terms of charge transfer kinetics via complementary XRD, HRTEM and NMR measurements. This finding demonstrates that borate based conversion type materials display rapid charge transfer with limited carbon additives, hence offering a new strategy to improve their overall cycling efficiency.

We present experiments based on neutron reflectometry in combination with 29Si/natSi isotope multilayers in order to investigate the self-diffusion in amorphous silicon. Such experiments allow the detection of diffusion processes in the amorphous state on length scales below 10 nm. First results at 650 °C show a continuous decrease of the artificial Bragg peak produced by the multilayer, corresponding to a diffusivity of (1.1 ± 0.4) x 10-20 m2/s on a length scale of 2 - 7 nm. The diffusivity is not time-dependent for annealing times between 3 min and 1 h. Compared to recent measurements in silicon single crystals by the same method, the diffusivity is higher by a factor of about 105.

Self-diffusion in thin nanocrystalline Pt films was investigated using secondary ion mass spectrometry. Our experiments are motivated by recent investigations on stress relaxation where self-diffusion of Pt is supposed to play an important role, especially at temperatures below 250 °C and annealing times of a few hours. For the diffusion experiments, double layers of natPt/194Pt were deposited on oxidized silicon wafers using ion beam sputtering. At 180 °C no significant diffusion induced broadening of the profiles could be observed even after an annealing time of 64 h. However, the concentration of 195Pt in the top layer decreases slightly after an annealing time of 16 h and remains constant for higher annealing times. At 600 °C a broadening of the profiles was observed after an annealing time of 5 minutes. From our results we conclude that at 180 °C only atoms in the grain boundaries are mobile. After about 16 h the isotopes in the grain boundaries are completely interdiffused. From the change of the 195Pt concentration in the top layer we estimate the amount of grain boundary phase in the Pt films to be about 5 %. The broadening of the profile after annealing at 600 °C is attributed to bulk diffusion.

Amorphous lithium–silicon compounds are promising materials in order to improve pure silicon as a high-capacity anode material in lithium-ion batteries. We demonstrated that it is possible to produce amorphous LixSi (x ≈ 0.4) thin films by reactive ion-beam co-sputtering of a segmented solid state target composed of metallic lithium and elemental silicon. At the surface a graded LixSiOy layer of some nanometer thickness is formed by contact with air which seems to prevent decomposition of the LixSi.

In the search for new cathode materials for sodium ion batteries, the exploration of polyanionic compounds has led to attractive candidates in terms of high redox potential and cycling stability. Herein we report the synthesis of the two new sodium transition-metal pentaborates Na

International audience; In the search for new cathode materials for sodium ion batteries, the exploration of polyanionic compounds has led to attractive candidates in terms of high redox potential and cycling stability. Herein we report the synthesis of two new sodium transition metal pentaborates Na 3 MB 5 O 10 (M = Fe, Co), where Na 3 FeB 5 O 10 represents the first sodium iron borate reported at present. By means of synchrotron X-ray diffraction, we reveal a layered structure consisting of pentaborate B 5 O 10 groups connected through M 2+ in tetrahedral coordination, providing possible three-dimensional Na-ion migration pathways. Inspired by these structural features we examined the electrochemical performances versus sodium and show that Na 3 FeB 5 O 10 is active at an average potential of 2.5 V vs. Na + /Na 0 , correlated to the Fe 3+ /Fe 2+ redox couple as deduced from ex situ Mössbauer measurements. This contrasts with Na 3 CoB 5 O 10 which is electrochemical inactive. Moreover, we show that their electrochemical performances are kinetically limited as deduced by complementary AC/DC conductivity measurements, hence confirming once again the complexity in designing highly performant borate-based electrodes.

The present Letter reports on self-diffusion in amorphous silicon. Experiments were done on $^{29}\mathrm{Si}/^{\text{nat}}\mathrm{Si}$ heterostructures using neutron reflectometry and secondary ion mass spectrometry. The diffusivities follow the Arrhenius law in the temperature range between 550 and $700\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ with an activation energy of $(4.4\ifmmode\pm\else\textpm\fi{}0.3)\text{ }\text{ }\mathrm{eV}$. In comparison with single crystalline silicon the diffusivities are tremendously higher by 5 orders of magnitude at about $700\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, which can be interpreted as the consequence of a high diffusion entropy.