Multivalent batteries, particularly zinc-ion batteries (ZIBs), are promising candidates for high-energy-density energy storage. However, their development is hindered by a scarcity of suitable cathode materials capable of the reversible (de)intercalation of Zn2+. To address this challenge, we propose cation-disordered rocksalt (DRX) cathodes, which have demonstrated excellent performance in Li-ion batteries, as a versatile host framework for nonaqueous ZIBs. Specifically, a vacancy-containing Mn0.4Ti0.4O2 DRX cathode demonstrates a reversible capacity of 170 mAh g-1 in nonaqueous ZIBs. Our investigation reveals that the Zn2+ ionic diffusion mechanism within the DRX framework is intrinsically sluggish compared to monovalent ions like Li+ due to strong electrostatic repulsion. Therefore, to successfully unlock Zn2+ migration, we show that it is necessary to introduce cation vacancies into the host, which significantly reduces the ion migration barrier. Additionally, we suggest that anion engineering may further enhance diffusion kinetics. This work expands the cathode material landscape for ZIBs and provides general insights into the design of disordered hosts for multivalent ion storage.

Sulfide solid electrolytes have high ionic conductivities necessary to achieve high-rate solid-state cathodes at room temperature and low pressure. Cathode active materials generally require coatings to avoid deleterious oxidative decomposition reactions with the electrolyte. Coatings add cost and complexity to the manufacture. Here we decouple the effect of double and triple phase boundaries on the decomposition in the thick (i.e., ∼110 μm) uncoated solid state cathode. We show that more severe oxidative decomposition of solid electrolytes occurs when the cathode active materials, carbon, and the solid electrolyte coexist, highlighting the importance of the triple phase boundary concerning the decomposition. By regulating the electronic pathways at the triple phase boundary, a thick uncoated electrode at 1 mA cm-2 and 2 MPa stack pressure, delivers an initial areal capacity of ∼4.6 mAh cm-2 at 30 °C and ∼85% capacity retention after 500 cycles.

Voids form at the interface between the lithium metal anode and ceramic electrolyte of a solidstate battery when discharged at practical rates (current densities) and stack pressures, leading to voltage polarisation and ultimately cell failure. Contouring the interface can increase the current density at which polarisation occurs and voids form. An egg-box contoured topography with peak height and separation of 5 and 30 µm respectively at the Li/Li 6 PS 5 Cl interface, increases the discharge current at which voiding commences ten-fold, from 0.2 to 2 mA cm −2 for a 2 MPa stack pressure at 30 °C. In practical applications, cells are typically subjected to short periods at higher discharge rates, e.g. electric vehicle (EV) acceleration. Contoured cells at 2 MPa stack pressure can sustain pulsed currents of 3 mA cm −2 at 30 °C and 8 mA cm −2 at 60 °C without cell failure. To assess practically relevant discharge demands, the Worldwide Harmonised Light Vehicles Test Procedure (WLTP), which is designed to represent typical driving conditions that a passenger car would experience in real-world use, was translated into a sequence of discharge current profiles equivalent to approximately five hours of driving (3.31 mAh cm −2 ) involving currents as high as 9 mA cm −2 . At 2 MPa and 60 °C, an egg-box contoured Li/Li 6 PS 5 Cl can sustain the WLTP discharge sequence without polarisation, whereas a non-contoured interface polarises by 5 V before completing two cycles. These results serve to demonstrate the significance contouring the Li/solid electrolyte interfacial can play in raising discharge currents to practically relevant levels. The results stand in stark contrast to the effect of contouring on the critical current before dendrites form on charging, which is only increased by ~50%.

Solid-state NMR spectroscopy, when combined with first-principles density functional theory (DFT) calculations, offers a highly sensitive probe of atomic-scale structure and dynamics in solid-state ion conductors, enabling the characterisation of subtle features that govern ionic conductivity. However, current approaches for interpreting NMR spectra rely on a comparison with static DFT reference calculations, which are inadequate for materials exhibiting fast ion dynamics such as lithium battery solid electrolytes. Here, using room-temperature NMR measurements and first-principles calculations, we show that the standard static-structure approach fails to reproduce the experimental 35Cl isotropic chemical shift (δ iso) of the fast Li-ion conductor Li6PS5Cl and substantially overestimates the quadrupolar coupling constant (C Q). We show that this discrepancy can be resolved using only ten DFT calculations by sampling relaxed configurations representative of Li-ion diffusion from machine-learning molecular dynamics. Compared with vibrational motion, Li-ion hopping around Cl is shown to dominate the motional averaging through reorientation of the NMR tensors. This study therefore provides an efficient computational method to resolve the complexities of the NMR spectra of Li6PS5Cl, which can be widely applied to other ion-conducting solids.

Rechargeable batteries represent a key transformative technology for electric vehicles, portable electronics, and renewable energy. Yet, there are few nondestructive diagnostic techniques compatible with realistic commercial cell enclosures. Many battery failures result from the loss or chemical degradation of the electrolyte. In this work, we present measurements through battery enclosures that allow quantification of electrolyte amount and composition. The study employs instrumentation and techniques developed in the context of zero-to-ultralow-field nuclear magnetic resonance (ZULF NMR), with quantum magnetometers as the detection elements (atomic optically pumped magnetometers, OPMs, and superconducting quantum interference devices, SQUIDs, used in this work). In contrast to conventional NMR methodology, which suffers from skin-depth limitations, the reduced resonance frequencies in ZULF NMR make battery housing and electrodes transparent to the electromagnetic fields involved. As demonstrated here through simulation and experiment, both the solvent and lithium-salt components of the electrolyte (lithium hexafluorophosphate, LiPF6) signature can be quantified using our techniques. Further, we show that the ZULF-NMR apparatus and technique are compatible with measurements of pouch-cell batteries.

The lithium–air (oxygen) battery could offer significant improvements in gravimetric energy density compared to lithium-ion technology. 1 A major barrier to a practical device is the oxidative degradation of the electrolyte solution and the carbon at the positive electrode. 2 Recently, the lithium–oxygen field has been focused on the formation of singlet oxygen within the cell, its impact as a major source of degradation, and strategies to mitigate this. We have investigated the reactivity of components within the lithium–oxygen cell by exposure to photochemically generated singlet oxygen both with and without an oxidising potential. 3 This approach to screening electrolytes against singlet oxygen is described, where tetraglyme, lithium bis(trifluoromethanesulfonyl)imide, or carbon, standard lithium-oxygen cell components, are reviewed. The role singlet oxygen plays in degradation of the lithium–oxygen battery is discussed, as well as the perspective to refocus on the discovery of electrolyte solutions with stability against major antagonists. [1] Aurbach, D., McCloskey, B., Nazar, L. et al. Advances in understanding mechanisms underpinning lithium–air batteries., Nat. Energy., 1: 16128 ( 2016 ); [2] Jethwa, R. B., Mondal, S., Pant, B., Freunberger, S. A., To DISP or not? The Far-Reaching Reaction Mechanisms Underpinning Lithium-air batteries., Angew. Chem. Int. Ed., e202316476 ( 2023 ); [3] Zor, C, Jones, K. D., Rees, G. J., Yang, S., Pateman, A., Gao, X., Johnson, L. R., Bruce, P. G., Singlet oxygen is not the main source of electrolyte degradation in lithium oxygen batteries., Energy Environ. Sci .,17: 7355-7361 ( 2024 ) Figure 1

Zinc-ion (Zn-ion) batteries for practical applications face several challenges, some of which arise from the inevitable degradation of the Zn metal anode. The intrinsic thermodynamic instability of Zn metal anodes in mildly acidic Zn-ion batteries can trigger spontaneous interfacial corrosion, which leads to hydrogen evolution, the formation of byproducts, and the irreversible loss of active species during both storage and operation. Here, we delve into the intricate corrosion processes of the Zn metal anode in mildly acidic electrolytes. With the help of operando electrochemical liquid cell transmission electron microscopy, the self-dissolution of Zn is observed, and the capacity loss due to such corrosion behaviour during the cell rest period is quantified. This dissolution of Zn is found to be closely related to the initial pH value of the electrolyte and can be mitigated by pH adjustment through the slight addition of a pH buffer additive. The self-dissolution of Zn, which causes an increase in the local pH, is a prelude to the formation of corrosion byproducts that continues throughout the entire storage and cycling period. These corrosion issues are exacerbated by the presence of excess Zn metal in the system, suggesting that the feasibility of using excess Zn metal in Zn-ion batteries should be carefully evaluated. These findings further emphasise the importance of considering electrolyte pH in future electrolyte modification research, as well as its potential impacts on the stability of both the anode and cathode, and the shelf life of the entire battery.

Enabling recycling and improving performance are key challenges for next‐generation electrolytes for rechargeable batteries. Here, an equilibrium polymerization: trimethylene carbonate (TMC) ring‐opening polymerization, in the presence of lithium difluoro(oxalato)borate salt, is utilized to form an electrolyte in situ during coin cell fabrication for lithium batteries. This process creates a semi‐solid poly(trimethylene carbonate) electrolyte with high ambient ionic conductivity (0.52 mS cm −1 ), thermal stability ( T d, 5% = 160 °C), and oxidative stability up to 4.7 V. Using this electrolyte with commercial lithium iron phosphate cathodes, results in 97% capacity retention after 350 cycles at 2C, achieving theoretical capacities of 170 mAh g −1 at 0.1C. The cells retain excellent performance at high current densities (86 mAh g −1 at 4C). Post‐use, the polymer can be separated from the salt and selectively recycled to pure starting monomer (TMC) through a solid‐state chemical recycling process. The recycled monomer, when repolymerized to reform the polycarbonate electrolyte, yields cells with performance identical to the original. The exploitation of polymerization‐depolymerization equilibria offers a useful strategy for enhancing battery performance, ensuring effective material recycling, and advancing a circular economy.

Many battery applications target fast charging to achieve an 80 % rise in state of charge (SOC) in < 15 min. However, in the case of all-solid-state batteries (SSBs), they typically take several hours to reach 80 % SOC while retaining a high specific energy of 400 W h kg(cell)(-1). We specify design strategies for fast-charging SSB cathodes with long cycle life and investigate the fast-charging capability of a sulfide-based single crystal Li-Ni-Mn-Co oxide composite cathode. At 30 degrees C and charging at 15 mA cm(-2), a specific capacity of 150 mA h g(-1) was achieved in similar to 8 min, with 81 % capacity retention after 3000 cycles. Critically, a 3-electrode arrangement was used to avoid the common problem of overcharging at high current densities. By following the design strategy and optimized manufacturing, a 210 mu m thick cathode was able to be charged at an extraordinary current density of 50 mA cm(-2) to reach an areal capacity of 8 mA h cm(-2) in only 10 min, suggesting practical cathodes for SSBs with 400 W h kg(cell)(-1) may be within reach.

Disordered rocksalt cathodes deliver high energy densities, but they suffer from pronounced capacity and voltage fade on cycling. Here, we investigate fade using two disordered rocksalt lithium manganese oxyfluorides: Li3Mn2O3F2 (Li1.2Mn0.8O1.2F0.8), which stores charge by Mn2+/Mn4+ redox, and Li2MnO2F, where charge storage involves both Mn3+/Mn4+ and oxygen redox (O-redox). Li3Mn2O3F2 is reported for the first time. We identify the growth of an electronically resistive surface layer with cycling that is present in both Li2MnO2F and Li3Mn2O3F2 but more pronounced in the presence of O-redox. This resistive surface inhibits electronic contact between particles, leading to the observed voltage polarization and capacity loss. By increasing carbon loading in the composite cathode, it is possible to substantially improve the cycling performance. These results help to disentangle O-redox from other leading causes of capacity fading in Mn oxyfluorides and highlight the importance of maintaining electronic conductivity in improving capacity and voltage retention.

Li-rich disordered rocksalts are promising next-generation cathode materials for Li-ion batteries. Recent reports have shown it is also possible to obtain Na-rich disordered rocksalts, however, it is currently poorly understood how the knowledge of the structural and redox chemistry translates from the Li-rich to the Na-rich analogs. Here, the properties of Li2MnO2F and Na2MnO2F are compared, which have different ion sizes (Li+ = 0.76 vs Na+ = 1.02 Å) but the same disordered rocksalt structure and stoichiometry. It is found that Na2MnO2F exhibits lower voltage Mn- and O-redox couples, opening access to a wider compositional range within the same voltage limits. Furthermore, the intercalation mechanism switches from predominantly single-phase solid solution behavior in Li2MnO2F to a two-phase transition in Na2MnO2F, accompanied by a greater decrease in the average Mn─O/F bond length. Li2MnO2F retains its long-range disordered rocksalt structure throughout the first cycle. In contrast, Na2MnO2F becomes completely amorphous during charge and develops a local structure characteristic of a post-spinel. This amorphization is partially reversible on discharge. The results show how the ion intercalation behavior of disordered rocksalts differs dramatically when changing from Li- to Na-ions and offers routes to control the electrochemical properties of these high-energy-density cathodes.

Reversible redox center is essential for long-life electrode materials. Iron is an earth abundant element, in lithium-ion batteries, highly reversible Fe2+/Fe3+ redox in LiFePO4 has play important role as redox center, Fe3+/Fe4+ redox in lithium layer-structured oxides display poor electrochemical performance. In sodium ion batteries, Fe3+/Fe4+ redox in sodium layer-structured oxides are active, while the cycle performance of Fe- contained sodium layer-structured oxide cathode need to be further improved. Herein, A pure-phase layer- structured high entropy oxide O3-Na(MgCu)1/12(NiCoFeMnTi)1/6O2 is synthesized and investigated as cathode for sodium ion battery. A reversible phase-transition takes place during the charge/discharge process. Particu- larly, highly reversible Fe3+/Fe4+ redox is revealed by X-ray absorption fine structure (XAFS). The as-synthesized high entropy oxide delivers a discharge capacity of 146.6 mAh g-1 at 10 mA g-1 , and can retain 83.2 % of capacity after 700 cycles at 100 mA g-1 between 2.0 and 4.1 V vs. Na+/Na. In this work, Fe K-edge of Fe3+/Fe4+ redox displays rigid shift, HEO-MgCuNi could be a platform to investigate the fundamental property of Fe3+/Fe4+ redox.

Recently there has been much interest in developing and understanding the chemistries of lithium-rich materials with stoichiometric ratios of Li:TM > 1 1-2 where TM is a transition metal. These materials can deliver improved capacity by redox involving the anions in the structure (i.e. O 2- → O (2-n)- + ne - ) 3-5 to compensate Li + removal. However, to meet the needs of a globally electrified society, electrochemical storage systems not reliant on lithium are required. Sodium-ion technologies are a promising alternative, but Na-ion batteries typically exhibit lower energy densities. Na-rich cathode technologies offer the opportunity to overcome this. However, the greater ionic radius of sodium means that for it to occupy a TM site, as Li + does in Li-rich species, significant strain is induced. As such, most Na-rich species reported to date contain rare 2 nd and 3 rd -row transition metals Ru 6,7 and Ir 8 , whose more diffuse orbitals can accommodate the larger Na + ion. We have developed a synthetic approach which allows us to synthesise Na-rich materials using only earth abundant elements. These materials show great promise as the first industrially relevant Na-rich materials with the ability to undergo reversible (de)sodiation. Here our efforts to understand the charge compensation mechanism of these materials using various techniques including synchrotron spectroscopic (RIXS and XAS), and scattering (XRD and PDF) experiments are presented. From these studies we have resolved the charge compensation mechanism in these materials and demonstrated how it contrasts with that of Ru and Ir containing materials. This is critically valuable information for the rational design of energy materials as it reveals how we can control material behaviour through compositional tuning. References A. House, et al . Nat. Energy , 2021 , 6, 781–789 Sharpe, et al ., J. Am. Chem. Soc., 2020 , 142, 21799–21809 A. House , et al ., Nat. Energy, 2023 , 8, 351–360 A. House, et al ., Energy Environ. Sci., 2022 , 15, 376–383 A. House, et al ., Nature, 2020 , 577, 502–508 Tamaru et al. Electrochemistry Communications . 2013 , 33, 23–26 Mortemardde Boisse et al. Nat. Commun. 2016 7:11397 Perez et al. Chem.Mater . 2016 , 28, 8278−8288 Figure 1

Avoiding lithium dendrites at the lithium/ceramic electrolyte interface and as a result avoiding cell short-circuit when plating at practical current densities remains a significant challenge for all-solid-state batteries. Typically, values are limited to around 1 mA cm-2, even, for example, for garnets with a relative density of >99%. It is not obvious that simply densifying ceramic electrolytes will deliver high plating currents. Here we show that plating currents of 9 mA cm-2 can be achieved without dendrite formation, by densifying Argyrodite, Li6PS5Cl, to 99%. Changes in the microstructure of Li6PS5Cl on densification from 83 to 99% were determined by FIB-SEM tomography and used to calculate their effect on the critical current density (CCD). Not all changes in microstructure with densification act to increase CCD. While smaller pores and shorter cracks increase CCD, lower pore population and narrower cracks act to decrease CCD. Calculations show that the former changes dominate over the latter, predicating an overall increase in CCD, as observed experimentally.

The very high theoretical specific energy of the lithium-air (Li-O2) battery (3500 Wh kg-1) compared with other batteries makes it potentially attractive, especially for the electrification of flight. While progress has been made in realizing the Li-air battery, several challenges remain. One such challenge is achieving a high capacity to store charge at the positive electrode at practical current densities, without which Li-air batteries will not outperform lithium-ion. The capacity is limited by the mass transport of O2 throughout the porous carbon positive electrode. Here it is shown that by replacing the binder in the electrode by a polymer with the intrinsic ability to transport O2, it is possible to reach capacities as high as 31 mAh cm-2 at 1 mA cm-2 in a 300 µm thick electrode. This corresponds to a positive electrode energy density of 2650 Wh L-1 and specific energy of 1716 Wh kg-1, exceeding significantly Li-ion batteries and previously reported Li-O2 cells. Due to the enhanced oxygen diffusion imparted by the gas diffusion polymer, Li2O2 (the product of O2 reduction on discharge) fills a greater volume fraction of the electrode and is more homogeneously distributed.

The lithium-air (Li-O2) battery has the highest theoretical energy density (3500 Wh kg-1) of any rechargeable battery. Modelling has suggested more than 600 Wh kg-1 may be possible for the whole system, including air handling, making Li-O2 attractive for the electrification of aviation.(1) However, the development of the Li-O2 battery has faced many challenges since its inception, such as degradation and slow kinetics.(2) The discharge product at the cathode is Li2O2, which is electronically insulating and difficult to oxidise on re-charging.(3) To overcome the difficulties of direct electrochemical reactions involving an insulating solid, redox mediating molecules (RMs) were introduced such that the Li2O2 is formed and oxidised in the electrolyte solution in the pores of the cathode.(4) On charging the cell, the RM is oxidised at the surface of the cathode, and then diffuses to and oxidises Li2O2 within the cathode pores, releasing O2. It is desirable for the RM to operate at as low a voltage as possible, above the thermodynamic oxidation potential of Li2O2, to maximise energy efficiency during cycling. In our recent work, we have investigated the mechanism by which RMs oxidise Li2O2 particles.(5) The trend of oxidation rate with mediator potential follows Marcus theory with a maximum rate at +3.74 V. We show that following the initial outer-sphere one-electron oxidation of Li2O2, the dominant subsequent step is the disproportionation of LiO2 to 3O2, and not the one-electron oxidation of LiO2 to 1O2 or 3O2 (Fig. 1). We also show how RMs with different potentials affect the 1O2 yield and that this does not correlate well with degradation, casting doubt on whether 1O2 is the major source of degradation during charge. Our mechanism not only explains why the current generation of mediators cannot deliver high charging rates at sufficiently low potentials for good round-trip energy efficiency but also points the way to designing mediators that can deliver high rates at low charge voltages. W. J. Kwak, et al., Chem Rev, 2020, 120, 6626-6683. S. A. Freunberger, et al., Angew Chem Int Ed Engl, 2011, 50, 8609-8613. V. Viswanathan, et al., J Chem Phys, 2011, 135, 214704. Y. Chen, et al., Nat Chem, 2013, 5, 489-494. S. Ahn, et al., Nat Chem, 2023, 15, 1022-1029. Figure 1

One of the most important challenges facing long cycle life Li-O2 batteries is solvent degradation. Even the most stable ethers, such as CH3O(CH2CH2O)CH3, degrade to form products including Li2CO3, which accumulates in the pores of the gas diffusion electrode on cycling leading to polarisation and capacity fading. In this work, we examine the build-up and distribution of Li2CO3 within the porous gas diffusion electrode during cycling and its link to the cell failure. We also demonstrate that the removal of Li2CO3 by a redox mediator can partially recover the cell performance and extend the cycle life of a Li-O2 battery.