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Ag-carbon composite interlayers have been reported to enable Li-free (anodeless) cycling of solid-state batteries. Here, we report structural changes in the Ag-graphite interlayer, showing that on charge, Li intercalates electrochemically into graphite, subsequently reacting chemically with Ag to form Li-Ag alloys. Discharge is not the reverse of charge but rather passes through Li-deficient Li-Ag phases. At higher charging rates, Li intercalation into graphite outpaces the chemical reactions with Ag, delaying the formation of the Li-Ag phases and resulting in more Li metal deposition at the current collector. At and above 2.5 mA·cm−2, Li dendrites are not suppressed. Ag nanoparticles do not suppress dendrites more effectively than does an interlayer of graphite alone. Instead, Ag in the carbon interlayer results in more homogeneous Li and Li-Ag formation on the current collector during charge.

Ether solvent based electrolytes exhibit excellent performance with sodium battery anodes, outperforming the carbonate electrolytes that are routinely used with the analogous lithium-ion battery. Uncovering the mechanisms that facilitate this high performance for ether electrolytes, and conversely diagnosing the causes of the poor cycling with carbonate electrolytes, is crucial for informing the design of optimized electrolytes that promote fully reversible sodium cycling. An important contributor to the performance difference has been suggested to be the enhanced elasticity of the ether-derived solid–electrolyte interphase (SEI) layer, however experimental demonstration of exactly how this translates to improving the microscopic dynamics of a cycled anode remain less explored. Here, we reveal how this more elastic SEI prevents gas evolution at the interface of the metal anode by employing operando electrochemical transmission electron microscopy (TEM) to image the cycled electrode–electrolyte interface in real time. The high spatial resolution of TEM imaging reveals the rapid formation of gas bubbles at the interface during sodium electrostripping in carbonate electrolyte, a phenomenon not observed for the higher performance ether electrolyte, which impedes complete Na stripping and causes the SEI to delaminate from the electrode. This non-conformal and inflexible SEI must thus continuously reform, leading to increased Na loss to SEI formation, as supported by mass spectrometry measurements. The more elastic ether interphase is better able to maintain conformality with the electrode, preventing gas formation and facilitating flat electroplating. Our work shows why an elastic and flexible interphase is important for achieving high performance sodium anodes.

Polymers designed with a specific combination of electrochemical, mechanical, and chemical properties could help overcome challenges limiting practical all-solid-state batteries for high-performance next-generation energy storage devices. In composite cathodes, comprising active cathode material, inorganic solid electrolyte, and carbon, battery longevity is limited by active particle volume changes occurring on charge/discharge. To overcome this, impractical high pressures are applied to maintain interfacial contact. Herein, block polymers designed to address these issues combine ionic conductivity, electrochemical stability, and suitable elastomeric mechanical properties, including adhesion. The block polymers have “hard-soft-hard”, ABA, block structures, where the soft “B” block is poly(ethylene oxide) (PEO), known to promote ionic conductivity, and the hard “A” block is a CO2-derived polycarbonate, poly(4-vinyl cyclohexene oxide carbonate), which provides mechanical rigidity and enhances oxidative stability. ABA block polymers featuring controllable PEO and polycarbonate lengths are straightforwardly prepared using hydroxyl telechelic PEO as a macroinitiator for CO2/epoxide ring-opening copolymerization and a well-controlled Mg(II)Co(II) catalyst. The influence of block polymer composition upon electrochemical and mechanical properties is investigated, with phosphonic acid functionalities being installed in the polycarbonate domains for adhesive properties. Three lead polymer materials are identified; these materials show an ambient ionic conductivity of 10–4S cm–1, lithium-ion transport (tLi+0.3–0.62), oxidative stability (>4 V vs Li+/Li), and elastomeric or plastomer properties (G′ 0.1–67 MPa). The best block polymers are used in composite cathodes with LiNi0.8Mn0.1Co0.1O2active material and Li6PS5Cl solid electrolyte–the resulting solid-state batteries demonstrate greater capacity retention than equivalent cells featuring no polymer or commercial polyelectrolytes.

Investigation of lithium-oxygen cells on discharge using a mixture of16O16O and18O18O gases, showed that O–O bond cleavage occurs during disproportionation of LiO2to O2and Li2O2, detected by the presence of isotopic16O18O. The formation of singlet oxygen,1O2, was also monitored during disproportionation. While only 4.5% of oxygen was found to undergo bond cleavage and scrambling of oxygen atoms, more than 40% of the singlet oxygen produced during disproportionation came from the scrambling pathway, making it a major source of singlet oxygen generation in lithium-oxygen batteries. Our results demonstrate that Li2O2formation occurs predominantly by disproportionation, and by controlling the pathway of this step, it may be possible to suppress1O2formation, a species that has been implicated in the degradation of lithium-oxygen batteries.

Supercapacitor represents an important electrical energy storage technology with high-power performance and superior cyclability. However, currently commercialized supercapacitors still suffer limited energy densities. Here we report an unprecedentedly respiring supercapacitor with chlorine gas iteratively re-inspires in porous carbon materials, that improves the energy density by orders of magnitude. Both electrochemical results and theoretical calculations show that porous carbon with pore size around 3 nm delivers the best chlorine evolution and adsorption performance. The respiring supercapacitor with multi-wall carbon nanotube as the cathode and NaTi

Solid-state batteries (SSBs) using lithium (Li) metal anodes and solid-state electrolytes (SSEs) can offer both improved energy densities and, by removing flammable liquid electrolytes, improved safety. The argyrodite-type Li6PS5Cl ceramic is an attractive candidate SSE material because of its high ionic conductivity (>1 mS cm−1) at room temperature and relatively ductile mechanical properties. However, interface contact issues between the SSE and Li metal hamper the practical development of solid-state Li metal batteries. In this work, we show that the interfacial resistance between the Li6PS5Cl SSE and Li metal anode can be reduced to as low as 1.3 Ω cm2 in symmetric cells by introducing a thin amorphous and Li-ion conducting lithium phosphorus oxynitride (LiPON) interlayer. We demonstrate that this interlayer improves the wetting behaviour of the Li6PS5Cl SSE, and helps form an effective conformal interfacial contact between the Li6PS5Cl SSE and Li metal. LiPON coated Li6PS5Cl symmetric cells with reduced interfacial resistance exhibit stable Li plating/stripping cycling for over 1000 h at 0.5 mA cm−2, and a dramatically improved critical current density of 4.1 mA cm−2 at 30 °C. These results demonstrate a reliable thin-film coating strategy for improving contact between the SSEs and Li metal anodes, stabilizing interfaces and realizing the practical application of solid-state Li metal batteries.

The sodium-air battery offers a sustainable, high-energy alternative to lithium-ion batteries. Discharge in the cell containing glyme-based electrolytes can lead to formation of large cubic NaO2 particles via a solution-precipitation mechanism. While promising, high rates result in sudden death. The exact nature of the discharge product has been a matter of contention, and Na2O2 has never been directly detected in a dry glyme Na?O2 cell. If Na2O2 were to form during discharge in the Na?O2 cell it would have a detrimental impact on cell performance. Here we show that Na2O2 forms during discharge at high overpotential in the glyme-based Na?O2 batteries. Na2O2 formation is confirmed by spectroscopic and electrochemical analysis and electron microscopy demonstrates that it results in thin insulating films at the electrode surface. The formation of these thin films results in rapid cell death during discharge, introducing an inherent chemical limitation to the Na?O2 battery.

Lithium-metal anodes with high theoretical capacity and ultralow redox potential are regarded as a "holy grail" of the next-generation energy-storage industry. Nevertheless, Li inevitably reacts with conventional liquid electrolytes, resulting in uneven electrodeposition, unstable solid electrolyte interphase, and Li dendrite formation that all together lead to a decrease in active lithium, poor battery performance, and catastrophic safety hazards. Here, we report a unique nonporous gel polymer electrolyte (NP-GPE) with a uniform and dense structure, exhibiting an excellent combination of mechanical strength, thermal stability, and high ionic conductivity. The nonporous structure contributed to a uniform distribution of lithium ions for dendrite-free lithium deposition, and Li/NP-GPE/Li symmetric cells can maintain an extremely low and stable polarization after cycling at a high current density of 10 mA cm-2. This work provides an insight that the NP-GPE can be considered as a candidate for practical applications for lithium-metal anodes.

Summary Li-metal batteries have been emerging as attractive technologies for electrical energy storage and conversion by virtue of the ultrahigh theoretical specific capacity of lithium. However, the undesirable Li-dendrite growth upon prolonged cycling gives rise to thermal runaway, inducing tremendous safety concerns that impede the development of the technology. In general, Li nucleation and growth behavior significantly changes when the operating condition is modified through modulating temperature or thermodynamic energy to produce regulated lithium depositions. Herein, this perspective takes these two key factors as an example to emphasize the importance of thermodynamic understandings of the Li-dendrite issue. The key challenges and corresponding strategies for designing advanced dendrite-free Li-metal anodes with respect to thermodynamic factors are also discussed as fundamental guidance for future development.

Multivalent cation rechargeable batteries, including those based on Ca, Mg, Al, etc., have attracted considerable interest as candidates for beyond Li-ion batteries. Recent developments have realized promising electrolyte compositions for rechargeable Ca batteries; however, an in-depth understanding of the Ca plating and stripping behavior and the mechanisms by which adverse dendritic growth may occur remains underdeveloped. In this work, via in situ transmission electron microscopy, we have captured the real-time nucleation, growth, and dissolution of Ca and the formation of dead Ca and demonstrated the critical role of current density and the solid-electrolyte interphase layer in controlling the plating morphology. In particular, the interface was found to influence Ca deposition morphology and can lead to Ca dendrite growth under unexpected conditions. These observations allow us to propose a model explaining the preferred conditions for reversible and efficient Ca plating.

Developing safe and high-energy-density lithium metal batteries (LMBs) are considered as the focus of next-generation rechargeable batteries. However, the inevitable lithium reacting with the liqui...

Summary An advantageous solid electrolyte/liquid electrolyte interface is crucial for the implementation of a protected lithium anode in liquid electrolyte cells. Li6.5La3Zr1.5Ta0.5O12 (LLZTO) garnet electrolytes are among the few solid electrolytes that are stable in contact with lithium metal. We show LLZTO is unstable in contact with the organic carbonate-based Li+ liquid electrolyte used in conventional Li-ion cells. The interfacial resistance between LLZTO and LiPF6 in (CH2O)2CO: OC(OCH3)2 (1:1 v/v) increases with time due to the growth of a lithium-ion-conducting solid electrolyte interphase (SEI) at the surface of the ceramic electrolyte. The interphase is composed of Li2CO3, LiF, Li2O, and organic carbonates. Even at a rate of 5 mA cm−2, a 3 V potential drop occurs across the LLZTO/liquid electrolyte interface. A practical LLZTO membrane (thickness ∼10 μm), in contact with a lithium anode, gives a potential loss of ∼16 mV, less than 1% of the resistance of the SEI.

Correction for ‘Interfacial modification between argyrodite-type solid-state electrolytes and Li metal anodes using LiPON interlayers’ by Jin Su et al., Energy Environ. Sci., 2022, 15, 3805–3814, https://doi.org/10.1039/D2EE01390H.

Correction for ‘The role of an elastic interphase in suppressing gas evolution and promoting uniform electroplating in sodium metal anodes’ by Chen Gong et al., Energy Environ. Sci., 2023, 16, 535–545, https://doi.org/10.1039/D2EE02606F.

The positive material has been one of the research hotspots in lithium–oxygen batteries. Carbon is the most widely used material due to its cheap price, high conductivity, low weight, and structura...

The large-scale application of lithium-sulfur batteries (LSBs) has been impeded by the shuttle effect of lithium-polysulfides (LiPSs) and sluggish redox kinetics since which lead to irreversible capacity decay and low sulfur utilization. Herein, a hierarchical interlayer constructed by boroxine covalent organic frameworks (COFs) with high Li

It remains a great challenge to explore desirable cathodes for sodium-ion batteries to satisfy the ever-increasing demand for large-scale energy storage systems. In this Letter, we report a NASICON-structured Na4MnCr(PO4)3 cathode with high specific capacity and operation potential. The reversible access of the Mn2+/Mn3+ (3.75/3.4 V), Mn3+/Mn4+ (4.25/4.1 V), and Cr3+/Cr4+ (4.4/4.3 V vs Na/Na+) redox couples in a Na4MnCr(PO4)3 cathode endows a distinct three-electron redox reaction during the insertion/extraction process. The highly stable NASICON structure with a small volume variation upon cycling ensures long-time cycling stability (73.3% capacity retention after 500 cycles within the potential region of 2.5-4.6 V). The impedance analysis and interface characterization indicate that the evolution of a cathode electrolyte interphase at high potential is correlated with the capacity fading, while the robustness of the NASICON framework is redemonstrated.

The solid electrolyte interphase (SEI), a complex layer that forms over the surface of electrodes exposed to battery electrolyte, has a central influence on the structural evolution of the electrode during battery operation. For lithium metallic anodes, tailoring this SEI is regarded as one of the most effective avenues for ensuring consistent cycling behavior, and thus practical efficiencies. While fluoride-rich interphases in particular seem beneficial, how they alter the structural dynamics of lithium plating and stripping to promote efficiency remains only partly understood. Here, operando liquid-cell transmission electron microscopy is used to investigate the nanoscale structural evolution of lithium electrodeposition and dissolution at the electrode surface across fluoride-poor and fluoride-rich interphases. The in situ imaging of lithium cycling reveals that a fluoride-rich SEI yields a denser Li structure that is particularly amenable to uniform stripping, thus suppressing lithium detachment and isolation. By combination with quantitative composition analysis via mass spectrometry, it is identified that the fluoride-rich SEI suppresses overall lithium loss through drastically reducing the quantity of dead Li formation and preventing electrolyte decomposition. These findings highlight the importance of appropriately tailoring the SEI for facilitating consistent and uniform lithium dissolution, and its potent role in governing the plated lithium's structure.

Intercalation transition metal oxides (ITMO) have attracted great attention as lithium-ion battery negative electrodes due to high operation safety, high capacity and rapid ion intercalation. However, the intrinsic low electron conductivity plagues the lifetime and cell performance of the ITMO negative electrode. Here we design a new carbon-emcoating architecture through single CO2activation treatment as demonstrated by the Nb2O5/C nanohybrid. Triple structure engineering of the carbon-emcoating Nb2O5/C nanohybrid is achieved in terms of porosity, composition, and crystallographic phase. The carbon-embedding Nb2O5/C nanohybrids show superior cycling and rate performance compared with the conventional carbon coating, with reversible capacity of 387 mA h g−1at 0.2 C and 92% of capacity retained after 500 cycles at 1 C. Differential electrochemical mass spectrometry (DEMS) indicates that the carbon emcoated Nb2O5nanohybrids present less gas evolution than commercial lithium titanate oxide during cycling. The unique carbon-emcoating technique can be universally applied to other ITMO negative electrodes to achieve high electrochemical performance.

Given the high cost and poisoning issues of Pt, developing Pd-based catalysts as substitutes is highly essential. Although substantial progress has been made, the synthesis of Pd-based electrocatalysts with both high activity and stability in the oxygen reduction reaction (ORR) remains a challenge. In this work, we prepared Pd-Ag nanowires with up to micro-sized length and a diameter of ∼17 nm via a facile modified polyol method. The obtained Pd-Ag nanowires (NWs) exhibit interlaced features and are rich in grain boundary defects. Due to the continuous grain boundaries in the one-dimensional (1D) structure and the optimized composition, the synthesized Pd1Ag1 NWs show half-wave potential of 0.897 V and mass activity of 0.103 A mg-1 in alkaline media toward ORR, higher than those of both state-of-the-art Pt/C and other Pd-Ag counterparts. Significantly, after stability tests over 5000 cycles, Pd1Ag1 NWs shows a 2 mV positive shift, much better than that of Pt/C, exhibiting striking stability for ORR. This work may provide an avenue to construct advanced catalysts by surface defect engineering.

Single-atom cobalt-nitrogen-carbon (Co-N-C) has emerged as one of the most promising electrocatalysts for the oxygen reduction reaction (ORR) as it has the utmost atomic utilization efficiency and may avoid possible Fenton reactions. Herein, we report dual carbon-supported single-atom cobalt with the unusual Co-N coordination number of three (Co-N3-C) as an efficient catalyst for the ORR. The combination of experiments and density functional theory calculations reveal that the Co-N3-C would experience an activation process and be favorable to lowering the energy barriers of the intermediates, leading to accelerated reaction kinetics. The as-prepared Co-N3-C catalyst exhibited unprecedented ORR activity with a half-wave potential of 0.891 V versus reversible hydrogen electrode and outstanding stability under alkaline conditions, not only outperforming the previously reported Co-based catalysts but also surpassing state-of-the-art Pt/C catalyst. The current work may provide a new insight into the engineering of the single-atom coordination environment to improve the catalytic activity.

Niobium dioxide (NbO2) features a high theoretical capacity and an outstanding electron conductivity, which makes it a promising alternative to the commercial graphite negative electrode. However, studies on NbO2 based lithium-ion battery negative electrodes have been rarely reported. In the present work, NbO2 4 nanoparticles homogeneously embedded in carbon matrix are synthesized using a dental resin monomer (bisphenol A glycidyl dimethacrylate, Bis-GMA) as solvent and carbon source and niobium ethoxide (NbETO) as the precursor. Thermal polymerization and calcination under Ar/H2 atmosphere at 900 °C are applied, to synthesize the NbO2/carbon nanohybrid in a facile scalable way. It is revealed that a low Bis-GMA/NbETO mass ratio (from 1:1 to 1:2) enables the conversion of Nb (V) to Nb (IV) due to increased porosity induced by alcoholysis reaction between the NbETO and Bis-GMA. The fundamental mechanisms responsible for the formation of NbO2 are elaborated, which involve the reduction of Nb (V) by in situ generated carbon monoxide. The as-prepared NbO2/carbon nanohybrid delivers a reversible capacity of 225 mA h g-1 after 500 cycles at 1 C rate with the Coulombic efficiency of more than 99.4 % in the cycles. Various experimental and theoretical approaches including solid state NMR, ex situ XRD, differential electrochemical mass spectrometry, and density functional theory (DFT) are utilized to understand the fundamental lithiation/delithiation mechanisms of the NbO2/carbon nanohybrid. The results suggest that the NbO2/carbon nanohybrid bearing high capacity, long cycle life and low gas-evolution is promising for lithium storage applications.

The use of solid electrolyte separators has the potential to revolutionise the safety of batteries by removing the need for flammable liquid electrolytes, as well as improve their energy densities by enabling the use of lithium metal anodes.1 However, significant challenges need to be overcome before solid-state batteries (SSBs) are able to compete with the performance of conventional Li-ion batteries, with many of these challenges occurring at the interfaces of the solid electrolyte. To enable the use of a Li metal anode, the challenges of the anode/solid electrolyte interface must be surmounted, the most significant of these being contact loss on battery discharge and dendrite infiltration into the solid electrolyte on charge.2–4 In addition, new hybrid approaches utilising both liquid and solid electrolyte must be explored. A promising approach to integrating a cathode into a SSB is a hybrid cell in which the solid electrolyte and cathode are separated by a conventional liquid electrolyte. This overcomes the problem of creating and maintaining intimate contact between two ceramic phases during cycling. However, in these hybrid cells a new interface, the solid electrolyte/liquid electrolyte interface, is introduced.5,6 In our recent work, we have assessed the stability of this interface and tracked the growth of solid electrolyte interphase (SEI) with time by a variety of techniques including electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and galvanostatic cycling (Figure 1).7 These results lead to conclusions as to the feasibility of such an interface in a SSB. Figure 1: Schematic of a hybrid solid electrolyte/liquid electrolyte cell set over i) an SEM showing SEI growth at the interface and ii) a graph showing increase in resistance with time due to the development of this SEI, obtained by EIS To enable the use of an energy dense Li metal anode, solid electrolyte separators must be impervious to penetration by dendrites. However, dendrite penetration of ceramic electrolytes is observed during charge (i.e. plating the Li metal anode) above a critical rate of current, termed the critical current density on plating (CCP). Better understanding how dendrites grow and the factors that affect critical current densities is of vital importance to enable rational design of materials and to make informed choices for operating conditions of a SSB. Our current research seeks to approach this challenge in two ways; to achieve a better mechanistic understanding of Li ingress into solid electrolytes by studying the process of plating Li metal, and to understand and prevent Li/solid electrolyte contact loss during the stripping process. Results from studies on both dendrite growth and contact loss will be presented. The stripping process has been investigated in Li/Li6PS5Cl/Li and Na/Na-β’’-alumina/Na cells, revealing the formation of voids above a critical current density on stripping (CCS). Studies utilising 3-electrode cells, cross-sectional SEM and operando X-ray CT showed that that above CCS voids form and grow, leading to higher local current densities at the remaining areas of contact, leading to dendrite formation on plating.3,8 For both solid electrolytes, CCS was observed to be < CCP. This means that CCS rather than to CCP limits the rate at which it is possible to cycle a SSB. CCS is found to be dependent on the rate of creep of the metal anode. In this context, realistic operating conditions which can increase this rate of creep during battery operation will be discussed. J. Janek and W. G. Zeier, Nat. Energy, 1, 16141 (2016). M. J. Wang, R. Choudhury, and J. Sakamoto, Joule, 1–14 (2019) J. Kasemchainan et al., Nat. Mater., 18, 1105–1111 (2019) K. Kerman, A. Luntz, V. Viswanathan, Y.-M. Chiang, and Z. Chen, J. Electrochem. Soc., 164, A1731–A1744 (2017) T. Abe, F. Sagane, M. Ohtsuka, Y. Iriyama, and Z. Ogumi, J. Electrochem. Soc., 152, A2151 (2005). M. Weiss et al., Electrochem. Energy Rev., 3, 221–238 (2020) J. Liu et al., Joule, 4, 101–108 (2020). D. Spencer Jolly et al., ACS Appl. Mater. Interfaces, 12, 678-685 (2020) Figure 1

Discharge by a surface route at the cathode of an aprotic metal-O2 battery typically results in surface passivation by the non-conducting oxide product. This leads to low capacity and early cell death. Here we investigate the cathode discharge reaction in the potassium-O2 battery and demonstrate that discharge by a surface route is not limited to growth of thin (1 μm product layer, far in excess of that possible in the related lithium-O2 battery. These results demonstrate a high-capacity surface route in a metal-O2 battery for the first time and the insights revealed here have significant implications for the design of the K-O2 battery.

Lithium–oxygen cells, in which lithium peroxide forms in solution rather than on the electrode surface, can sustain relatively high cycling rates but require redox mediators to charge. The mediators are oxidised at the electrode surface and then oxidise lithium peroxide stored in the cathode. The kinetics of lithium peroxide oxidation has received almost no attention and yet is crucial for the operation of the lithium–oxygen cell. It is essential that the molecules oxidise lithium peroxide sufficiently rapidly to sustain fast charging. Here, we investigate the kinetics of lithium peroxide oxidation by several different classes of redox mediators. We show that the reaction is not a simple outer-sphere electron transfer and that the steric structure of the mediator molecule plays an important role. The fastest mediator studied could sustain a charging current of up to 1.9 A cm–2, based on a model for a porous electrode described here., The kinetics of Li2O2 oxidation is of high importance to the operation of Li–O2 batteries. Here the authors work on different types of mediators revealing the dependence of the kinetics on the nature of the redox active site and its steric hindrance.

Although multivalent cation batteries based on magnesium, calcium or aluminium are technologically attractive, the metal anode still represents a challenge. It is now demonstrated that significant quantities of calcium can be plated and stripped at room temperature with low polarization. There is considerable interest in multivalent cation batteries, such as those based on magnesium, calcium or aluminium1,2,3,4,5,6,7,8,9,10,11. Most attention has focused on magnesium. In all cases the metal anode represents a significant challenge. Recent work has shown that calcium can be plated and stripped, but only at elevated temperatures, 75 to 100 °C, with small capacities, typically 0.165 mAh cm−2, and accompanied by significant side reactions7. Here we demonstrate that calcium can be plated and stripped at room temperature with capacities of 1 mAh cm−2 at a rate of 1 mA cm−2, with low polarization (∼100 mV) and in excess of 50 cycles. The dominant product is calcium, accompanied by a small amount of CaH2 that forms by reaction between the deposited calcium and the electrolyte, Ca(BH4)2 in tetrahydrofuran (THF). This occurs in preference to the reactions which take place in most electrolyte solutions forming CaCO3, Ca(OH)2 and calcium alkoxides, and normally terminate the electrochemistry. The CaH2 protects the calcium metal at open circuit. Although this work does not solve all the problems of calcium as an anode in calcium-ion batteries, it does demonstrate that significant quantities of calcium can be plated and stripped at room temperature with low polarization.

The Li–O 2 cell performance is largely limited by the insulating and insoluble nature of Li 2 O 2 . Here the authors report that dual mediators decouple the electrochemical reactions at the cathode from the formation and decomposition of Li…

Rechargeable battery such as Li-ion battery will be the main focus worldwide for decades to come. However, energy storage beyond the capabilities of Li-ion technologies are becoming increasingly important to satisfy society’s future energy storage needs. One such alternative is aprotic Li-air (O2) battery with its theoretical specific energy several times higher than that of Li-ion. However, many challenges including early cell death, high overpotential and poor cycle life need to be addressed before its commercialisation. Fundamental studies of the processes at the positive electrode have shown that this is a result of passivating Li2O2 film at the electrode surface. It is generally accepted that solution growth of discharge product Li2O2 is required to achieve high rates and capacities. One way to achieve solution mechanism is use of high donor or acceptor number electrolytes, however, such electrolytes are less stable towards the reactive oxygen species in aprotic Li-O2 cell. Here, we discuss our new strategies to use redox mediators as soluble catalysts, to reduce O2 to Li2O2 by halving the overpotential on discharge, without forming passivating films and with less side reactions in ether solvents, while on charge Li2O2 can be oxidized rapidly to O2 even when the former is not in contact with the electrode surface, Fig. 1. As a result, cycling of an aprotic Li-O2 cell has been demonstrated with rates and capacities of several mA and mAh cm-2 respectively. The advantages and disadvantages of redox mediators during cycling and decomposition of carbon electrode will be discussed. Figure 1: Schematics of positive electrode reactions on discharge and charge in the presence of dual mediators. Figure 1

LiMn 2 O 4 spinel was prepared by a hydrothermal method using α-MnO 2 nanotubes as precursor at 180 °C, a temperature much lower than that in previously reported methods. It is nanoporous with a pore size of about 40–50 nm and a BET surface area of 9.76 m 2 g −1 . It exhibits a high specific capacitance of 189 F g −1 at 0.3 A g −1 as a cathode for an aqueous supercapacitor. Even at 12 A g −1 , it still has a capacitance of 166 F g −1 . After 1500 cycles, there is no evident capacity fading. The LiMn 2 O 4 cathode can deliver an energy density of 31.9 Wh kg −1 at 3480 W kg −1 and even maintain 19.4 Wh kg −1 at about 5100 W kg −1 based on the mass of LiMn 2 O 4 .

In this study, a novel single-ion conducting polymer electrolyte, lithium polyvinyl alcohol oxalate borate (LiPVAOB), from the reaction of poly(vinyl alcohol) (PVA) with different molar ratio of boric acid, oxalic acid and lithium carbonate was prepared. The prepared materials were characterized by Fourier transformation infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG), differential thermal analysis (DTA), electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry. Ionic conductivity of these polymer electrolytes from adding an assistant (about 20 wt.% propylene carbonate) is dependent on molar ratio of the reactants and can up to 6.11 × 10 −6 S cm −1 at ambient temperature. Their electrochemical window can be stable up to 7 V ( vs . Li + /Li), which is of great attraction for high voltage lithium ion batteries with high energy density.

A novel single-ion polymer electrolyte, LiPAAOB (lithium oxalate polyacrylic acid borate), was prepared with different ratio of polyacrylic acid, boric acid, lithium hydroxide and oxalic acid. The obtained membranes were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetry and differential thermal analysis. After absorbing 3% solvent (propylene carbonate), the as-prepared LiOPAAB presents a single ion conductive behavior. Its ionic conductivity at ambient temperature can be up to 2.3×10−6 S cm−1 and electrochemical window can be stable up to 7.0 V (vs. Li+/Li), which is of great attraction for 5 V lithium ion batteries with high energy density. Keywords: Lithium ion batteries, Polymer electrolyte, Single-ion conductor, Ionic conductivity

1–4 ] However, super-capacitors deliver an unsatisfactory energy density. Intensive efforts have been devoted to the enhancement of their energy density to make it comparable to that of rechargeable batteries. Among the supercapacitor electrode materials, pseudocapacitive transition-metal oxides and electronically conducting polymers based on faradic redox charge storage have attracted signifi cant attention because of their higher energy density than those of electrochemical double-layer capacitive carbon materials.

Interest in the rechargeable Li-O2 battery is driven by its high theoretical specific energy (3500 Whkg-1).1-2 However, a number of challenges face the realization of practical devices.3-10 Overcoming these challenges requires an understanding of the reactions and processes in the cell, especially at the electrodes. Our focus has been on the reaction at the positive electrode: O2 + 2e- + 2Li+ = Li2O2 This simple reaction belies the complexity of the problems during charge and discharge. Li2O2, is an insulating solid, if it grows on the electrode surface it can only do so to a thickness of approx. 6 to 7 nm. The resulting passivation leads to low rates and low capacities.11 If Li2O2 grows from solution, passivation is avoided, leading to high rates and capacities.12 The solvent donor number is an important factor in controlling which pathway, surface film or solution growth, occurs. Low donor number ethers promote surface films while high donor numbers result in solution growth. Unfortunately, high donor number solvents are more susceptible to decomposition by the reactive O2 - nucleophile (the intermediate in the O2/Li2O2 reaction is LiO2).13 We show that using redox mediator molecules to shuttle electrons between the electrode surface and solution, Li2O2 can be formed and decomposed in solution even in low donor number solvent like ethers.14 As a result, rates and capacities of several mA and mAh cm-2 respectively are observed. The impact of the mediators on solvent and electrode stability will be discussed in the context of the mechanism of Li2O2 formation and decomposition. Ultimately, the Li-O2 cell must operate in air. The effect of H2O in the gas stream and hence in the electrolyte solution on the mechanism of O2/Li2O2 and the effect on cell performance are important. The influence of H2O on the O2 reduction mechanism will be considered. REFERENCES [1] D. Aurbach; B.D. McCloskey; L.F. Nazar; P.G. Bruce, Nature Energy 2016, 1, 16128. [2] J.W. Choi; D. Aurbach, Nature Reviews Materials 2016, 1, 16013. [3] N. Mahne; B. Schafzahl; C. Leypold; M. Leypold, et al., Nature Energy 2017, 2, 17036. [4] K.U. Schwenke; M. Metzger; T. Restle; M. Piana, et al., Journal of The Electrochemical Society 2015, 162 (4), A573-A584. [5] D. Grübl; B. Bergner; D. Schröder; J. Janek, et al., The Journal of Physical Chemistry C 2016, 120 (43), 24623-24636. [6] H.-D. Lim; B. Lee; Y. Zheng; J. Hong, et al., Nature Energy 2016, 1 (6), 16066. [7] B.D. McCloskey; D. Addison, ACS Catalysis 2017, 7 (1), 772-778. [8] S. Ganapathy; J.R. Heringa; M.S. Anastasaki; B.D. Adams, et al., The Journal of Physical Chemistry Letters 2016. [9] A.I. Belova; D.G. Kwabi; L.V. Yashina; Y. Shao-Horn, et al., The Journal of Physical Chemistry C 2017, 121 (3), 1569-1577. [10] D. Krishnamurthy; H.A. Hansen; V. Viswanathan, ACS Energy Letters 2016, 1 (1), 162-168. [11] V. Viswanathan; K.S. Thygesen; J.S. Hummelshoj; J.K. Norskov, et al., Journal of Chemical Physics 2011, 135 (21), 214704. [12] L. Johnson; C. Li; Z. Liu; Y. Chen, et al., Nature Chemistry 2014, 6 (12), 1091-1099. [13] A. Khetan; A. Luntz; V. Viswanathan, The Journal of Physical Chemistry Letters 2015, 6 (7), 1254-1259. [14] X. Gao; Y. Chen; L.R. Johnson; Z.P. Jovanov, et al., Nature Energy 2017, 2, 17118.

Multivalent-ion batteries are receiving significant attention as potential post-lithium ion energy storage devices, such as Mg, Ca, etc.1-6 Among them, calcium has a potential much closer to Li (0.17 V vs. Li) and its natural abundance in the Earth’s crust make calcium cells potentially attractive. However, the major problem of calcium anodes is their tendency to reduce the organic electrolyte solvents forming passivating surface films such as CaO and CaCO3 that inhibit further plating.2,8-9 Recent studies showed calcium deposition under elevated temperatures, 75 to 100 °C, however with significant side reactions.5 Here, our recent studies show that calcium can be plated and stripped at room temperature with capacities of 1 mAh cm-2 at a rate of 1 mA cm-2, with low polarization (100 mV), in excess of 50 cycles and with low side reactions, Fig.1. The key role of the electrolyte, Ca(BH4)2 in tetrahydrofuran (THF), will be discussed. Figure 1. Galvanostatic Ca plating/stripping load curves in Ca(BH4)2 in THF at the rate of 1 mA cm-2. Inset shows variation of coulombic efficiency with cycle number. References: Aurbach D., Lu Z., Schechter A., Gofer Y., Gizbar H., Turgeman R., et al. Prototype systems for rechargeable magnesium batteries. Nature, 407, 724-727 (2000). Aurbach D., Skaletsky R., Gofer Y. The Electrochemical-Behavior of Calcium Electrodes in a Few Organic Electrolytes. J Electrochem Soc, 138, 3536-3545 (1991). Lin M. C., Gong M., Lu B. G., Wu Y. P., Wang D. Y., Guan M. Y., et al. An ultrafast rechargeable aluminium-ion battery. Nature, 520, 324-328 (2015). Muldoon J., Bucur C. B., Gregory T. Quest for Nonaqueous Multivalent Secondary Batteries: Magnesium and Beyond. Chem Rev, 114, 11683-11720 (2014). Ponrouch A., Frontera C., Barde F., Palacin M. R. Towards a calcium-based rechargeable battery. Nat Mater, 15, 169-172 (2016). Yoo H. D., Shterenberg I., Gofer Y., Gershinsky G., Pour N., Aurbach D. Mg rechargeable batteries: an on-going challenge. Energ Environ Sci, 6, 2265-2279 (2013). Muldoon J., Bucur C. B., Oliver A. G., Sugimoto T., Matsui M., Kim H. S., et al. Electrolyte roadblocks to a magnesium rechargeable battery. Energ Environ Sci, 5, 5941-5950 (2012). Hayashi M., Arai H., Ohtsuka H., Sakurai Y. Electrochemical characteristics of calcium in organic electrolyte solutions and vanadium oxides as calcium hosts. J Power Sources, 119, 617-620 (2003). Canepa P., Gautam G. S., Hannah D. C., Malik R., Liu M., Gallagher K. G., et al. Odyssey of Multivalent Cathode Materials: Open Questions and Future Challenges. Chem Rev, 117, 4287-4341 (2017). Figure 1

This paper describes the internal structure of Au-Pd nanoparticles exhibiting newly discovered three-layer core/shell morphology, which is composed of an evenly alloyed inner core, an Au-rich intermediate layer, and a Pd-rich outer shell. By exploitation of spatially resolved imaging and spectroscopic and diffraction modes of transmission electron microscopy (TEM), insights were gained on the composition of each one of the observed three layers, indicating a significant extent of intimate alloy among the monometallic elements.

On discharge, the Li–O2 battery can form a Li2O2 film on the cathode surface, leading to low capacities, low rates and early cell death, or it can form Li2O2 particles in solution, leading to high capacities at relatively high rates and avoiding early cell death. Achieving discharge in solution is important and may be encouraged by the use of high donor or acceptor number solvents or salts that dissolve the LiO2 intermediate involved in the formation of Li2O2. However, the characteristics that make high donor or acceptor number solvents good (for example, high polarity) result in them being unstable towards LiO2 or Li2O2. Here we demonstrate that introduction of the additive 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) promotes solution phase formation of Li2O2 in low-polarity and weakly solvating electrolyte solutions. Importantly, it does so while simultaneously suppressing direct reduction to Li2O2 on the cathode surface, which would otherwise lead to Li2O2 film growth and premature cell death. It also halves the overpotential during discharge, increases the capacity 80- to 100-fold and enables rates >1 mA cmareal−2 for cathodes with capacities of >4 mAh cmareal−2. The DBBQ additive operates by a new mechanism that avoids the reactive LiO2 intermediate in solution.

Li-ion and related battery technologies will be important for years to come. However, society needs energy storage that exceeds the capacity of Li-ion batteries. We must explore alternatives to Li-ion if we are to have any hope of meeting the long-term needs for energy storage. One such alternative is the Li-air (O2) battery, Fig. 1; its theoretical specific energy exceeds that of Li-ion, but many hurdles face its realization.[1-5] One spin-off of the recent interest in rechargeable Li-O2 batteries, based on aprotic electrolytes is that it has highlighted the importance of understanding the fundamental processes at the positive electrode within the battery.[6- 12 ] Based on these studies, it is generally accepted that a solution growth mechanism will be required to achieve high rates and capacities. One way to achieve discharge in solution is use of high donor or acceptor number (DN/AN) electrolytes, which might be less stable towards LiO2 and Li2O2 than their low DN/AN counterparts. To solve this dilemma, a reduction mediator was introduced into the low DN/AN electrolyte to encourage the discharge in solution. By forming an intermediate complex, it suppresses the direction reduction to Li2O2 on surface and thus leads to higher capacity on discharge with higher rates. Furthermore, if Li2O2 is formed in solution a charge mediator will be required, as the traditional electrode configuration is unable to oxidize the product. The implication of this is complete solution phase cycling where solid Li2O2is simply a storage material for lithium ions and electrons. REFERENCES [1]. Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J.-M. Nature Materials 2012, 11, 19. [2]. Lu, Y. C.; Gallant, B. M.; Kwabi, D. G.; Harding, J. R.; Mitchell, R. R.; Whittingham, M. S.; Shao-Horn, Y. Energy & Environmental Science 2013, 6, 750. [3]. Black, R.; Adams, B.; Nazar, L. F. Advanced Energy Materials 2012, 2, 801. [4]. Girishkumar, G.; McCloskey, B.; Luntz, A. C.; Swanson, S.; Wilcke, W. The Journal of Physical Chemistry Letters 2010, 1, 2193. [5]. Li, F.; Zhang, T.; Zhou, H. Energy & Environmental Science 2013, 6, 1125. [6]. Horstmann, B.; Gallant, B.; Mitchell, R.; Bessler, W. G.; Shao-Horn, Y.; Bazant, M. Z. The Journal of Physical Chemistry Letters 2013, 4, 4217. [7]. Hummelshoj, J. S.; Luntz, A. C.; Norskov, J. K. The Journal of Chemical Physics 2013, 138, 034703. [8]. McCloskey, B. D.; Scheffler, R.; Speidel, A.; Girishkumar, G.; Luntz, A. C. The Journal of Physical Chemistry C 2012, 116, 23897. [9]. Trahan, M. J.; Mukerjee, S.; Plichta, E. J.; Hendrickson, M. A.; Abraham, K. M. Journal of The Electrochemical Society 2013, 160, A259. [10]. Sharon, D.; Etacheri, V.; Garsuch, A.; Afri, M.; Frimer, A. A.; Aurbach, D. The Journal of Physical Chemistry Letters 2012, 4, 127. [11]. Jung, H. G.; Kim, H. S.; Park, J. B.; Oh, I. H.; Hassoun, J.; Yoon, C. S.; Scrosati, B.; Sun, Y. K. Nano Letters 2012, 12, 4333. [12]. Zhai, D.; Wang, H. H.; Yang, J.; Lau, K. C.; Li, K.; Amine, K.; Curtiss, L. A. Journal of the American Chemical Society 2013, 135, 15364.

Li-ion and related battery technologies will be important for years to come. However, society needs energy storage that exceeds the capacity of Li-ion batteries. We must explore alternatives to Li-ion if we are to have any hope of meeting the long-term needs for energy storage. One such alternative is the Li-air (O2) battery; its theoretical specific energy exceeds that of Li-ion, but many hurdles face its realization.[1-5] One spin-off of the recent interest in rechargeable Li-O2 batteries, based on aprotic electrolytes is that it has highlighted the importance of understanding the fundamental electrochemistry at the positive electrode within the battery.[6-15] The challenges of obtaining efficient, reversible charge and discharge are well-documented in the field. Here, we describe how our recent studies into the electrochemical mechanism of O2 reduction to form Li2O2 at the positive electrode might allow us to design new strategies to overcome these limitations;[16]For example, exploiting the effect of solvent donor number, Fig. 1. We will describe our resent results using redox mediators to facilitate the electrochemistry along with the implications of the results for the future of rechargeable Li-O2 batteries. REFERENCES [1]. Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J.-M. Nature Materials 2012, 11, 19. [2]. Lu, Y. C.; Gallant, B. M.; Kwabi, D. G.; Harding, J. R.; Mitchell, R. R.; Whittingham, M. S.; Shao-Horn, Y. Energy & Environmental Science 2013, 6, 750. [3]. Black, R.; Adams, B.; Nazar, L. F. Advanced Energy Materials 2012, 2, 801. [4]. Girishkumar, G.; McCloskey, B.; Luntz, A. C.; Swanson, S.; Wilcke, W. The Journal of Physical Chemistry Letters 2010, 1, 2193. [5]. Li, F.; Zhang, T.; Zhou, H. Energy & Environmental Science 2013, 6, 1125. [6]. Adams, B. D.; Radtke, C.; Black, R.; Trudeau, M. L.; Zaghib, K.; Nazar, L. F. Energy & Environmental Science 2013, 6, 1772. [7]. Horstmann, B.; Gallant, B.; Mitchell, R.; Bessler, W. G.; Shao-Horn, Y.; Bazant, M. Z. The Journal of Physical Chemistry Letters 2013, 4, 4217. [8]. Hummelshoj, J. S.; Luntz, A. C.; Norskov, J. K. The Journal of Chemical Physics 2013, 138, 034703. [9]. McCloskey, B. D.; Scheffler, R.; Speidel, A.; Girishkumar, G.; Luntz, A. C. The Journal of Physical Chemistry C 2012, 116, 23897. [10]. Mitchell, R. R.; Gallant, B. M.; Shao-Horn, Y.; Thompson, C. V. The Journal of Physical Chemistry Letters 2013, 4, 1060. [11]. Trahan, M. J.; Mukerjee, S.; Plichta, E. J.; Hendrickson, M. A.; Abraham, K. M. Journal of The Electrochemical Society 2013, 160, A259. [12]. Sharon, D.; Etacheri, V.; Garsuch, A.; Afri, M.; Frimer, A. A.; Aurbach, D. The Journal of Physical Chemistry Letters 2012, 4, 127. [13]. Jung, H. G.; Kim, H. S.; Park, J. B.; Oh, I. H.; Hassoun, J.; Yoon, C. S.; Scrosati, B.; Sun, Y. K. Nano Letters 2012, 12, 4333. [14]. Peng, Z.; Freunberger, S. A.; Hardwick, L. J.; Chen, Y.; Giordani, V.; Barde, F.; Novak, P.; Graham, D.; Tarascon, J. M.; Bruce, P. G. Angewandte Chemie International Edition 2011, 50, 6351. [15]. Zhai, D.; Wang, H. H.; Yang, J.; Lau, K. C.; Li, K.; Amine, K.; Curtiss, L. A. Journal of the American Chemical Society 2013, 135, 15364. [16]. Johnson, L.; Li, C. ; Liu, Z.; Chen, Y.; Freunberger, S. A.; Ashok, P.; Praveen, B.; Dholakia, K.; Tarascon, J-M.; Bruce, P. G. Nature Chemistry 2014, 6, 1091. Figure 1

We report on the structure and magnetic properties of a silver and carbon nanocomposite. The as-synthesized nanocomposite consists of a matte-black powder composed of Ag nanoparticles encapsulated in carbon nanospheres ($\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ diameter) that are interconnected in necklace-like structures. Magnetic measurements of the Ag and C nanocomposite, in its powder form, showed weak ferromagnetic behavior up to at least room temperature with a coercive field of $389\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}$ at $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $103\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}$ at $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, from which we estimate magnetic ordering up to $425\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. However, pressing the $\mathrm{Ag}\text{\ensuremath{-}}\mathrm{C}$ powder samples into tablets suppressed the ferromagnetism; the pressed samples instead exhibited diamagnetic behavior. Chemical analysis with EDS and trace metal analysis with ICP-MS indicated that there are no magnetic contaminants in the sample. Therefore, we attribute the ferromagnetism to the carbon nanospheres and propose a model for the observed magnetism. We also measured a pronounced peak in the magnetization between 50 and $90\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ that was completely suppressed when measurements were made upon cooling; we attribute this peak to a first-order spin reorientation.

A hybrid of V2O5 nanowires and MWCNTs coated with polypyrrole (PPy) was prepared as an anode material for ARLBs. The hybrid shows a good electrochemical reversibility since the PPy coating can effectively prevent the dissolution of the reduced vanadium ions.

In this work, bismuth nanoparticles were synthesized when a precursor, sodium bismuthate, was exposed to an electron beam at room temperature in a transmission electron microscope (TEM). The irradiation effects were investigated in situ using selected-area electron diffraction, high-resolution transmission electron microscopy and x-ray energy dispersive spectroscopy. After the electron irradiation, bismuth nanoparticles with a rhombohedral structure and diameter of 6 nm were observed. The average particle size increased with the irradiation time. The electron-induced reduction is attributed to the desorption of oxygen ions. This method offers a one-step route to synthesize bismuth nanoparticles using electron irradiation, and the particle size can be controlled by the irradiation time.