Next Generation Solid-State Batteries

Solid-state Li-ion batteries (SSLBs) represent the ultimate in battery safety, eliminating the flammable organic electrolyte. The SSLB would find potential uses in industries where battery safety is paramount, such as the automotive industry (in cars, e-bikes and buses) and also in smaller applications where the elimination of the liquid electrolyte results in more ready compatibility with other devices, e.g., a battery on a chip or sensor. These batteries can compete with traditional lithium ion batteries in terms of volumetric energy density but they suffer from low power density. Very recently several viable inorganic solid Li-ion conducting electrolytes been identified with conductivities approaching those of liquids, which motivates this research proposal. Strategies for lowering interfacial resistances, particularly between the electrolyte and electrodes, and for building inherently scaleable devices that can be cycled multiple times, without mechanical failure, are now urgently required to produce practical devices. This multi-institutional project brings together experienced, world-leading researchers from the University of Cambridge, the University of Oxford, and Imperial College with distinct but complementary expertise to attack a number of challenging critical issues in this field. Two classes of these solid electrolytes, oxide garnets and sulphide glass ceramics, have been found to have very high room-temperature ionic conductivities. A number of characteristics have been identified that may provide either relative benefits or disadvantages: higher-modulus materials may cycle more stably in batteries; tougher materials may be more easily brought into industrial practice; polycrystalline character may limit apparent bulk-transport rates, lowering power efficiency; interfaces may be chemically unstable, affecting long-term state of health; etc. We propose to implement fundamental studies that shed light on the relative benefits and disadvantages of the oxide and sulphide ion-conductor paradigms, using the Li6.55Ga0.15*0.3La3Zr2O12 (* = vacancy) (LLZO) garnet and the P2S5-Li2S (PSLS) glass ceramic as model materials. The project centres around three experimental work packages that focus on 1) quantifying bulk properties and making them reproducible; specifically, issues of moisture and carbon-dioxide sensitivity of the electrolytes will be addressed to produce films with reduced resistances at the interfaces between particles. LLZO and PSLS films will be contrasted, and transport through them will be investigated via a number of in operando (in situ) metrologies, e.g., 6Li tracer and NMR studies in close concert with theoretical studies of ionic transport. 2) illustrating chemistry of the solid-electrolyte/Li two-dimensional interface and probing its morphological stability over time; we seek to identify the critical parameters needed to mitigate Li-metal dendrite formation and growth, and which allow smooth Li-plating on the electrolyte surface. 3) producing tailored, cohesive three-dimensional interfaces with complex morphologies that do not crack on extensive cycling. The development of materials with much larger electrode/electrolyte contact areas will increase Li+ exchange between phases within the electrode, increasing rate performance. A multiscale modelling effort cuts across the 3 work packages, aiming to produce fundamental physical insight, synthesize experimental outputs, and guide experimental design. The goals for the theory portion are unique in the sense that the models will aim for true 'multiscale' character, integrating atomistic and continuum perspectives. Overall, the project aims to provide new new strategies to improve the performance of SSLBs but will also result in new electrolyte designs that are suitable for to protect Li metal in other so-called "beyond Li-ion" batteries such as Li-air and Li-S and smaller batteries for internet communications technologies.