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.

Economy: Solid-state Li-ion batteries (SSLBs) represent the ultimate in battery safety, eliminating the flammable electrolyte. Industries where battery safety is paramount have initiated major R&D activities in this area. The solid-state electrolyte films developed as part of this programme will also enable a protected Li anode, useful for transformative beyond-Li technologies such as Li/air or Li/sulphur batteries. Smaller SSLBs can replace primary batteries in smaller devices (e.g. batteries on chips, sensors) where the lack of liquid electrolyte allows increasing compatibility with the device (e.g., chip, antennae). Our SSLB programme will generate new technology and IP in these emerging new fields, from materials production to methods of producing scaleable electrodes and devices. Importantly, new UK specialism and knowledge will be developed, advancing national capabilities. We build on considerable UK historical expertise in ceramics and solid-state ionics that has already made significant contributions to UK industry. Implementing new technologically-relevant multi-scale modelling paradigms will reduce UK industries' R&D costs by making possible computational prototyping and design. The economic impact of our research will lie in maintaining the UK's international leadership in synthesis, analysis, and modelling of cutting-edge energy-storage systems, ensuring that any resulting IP is retained, licensed and exploited by UK research groups and industry.

Society: It is hard to overstate the impact of a disruptive automotive battery technology. By displacing the internal combustion engine in vehicles, automotive SSLBs (and eventually Li-air and Li-sulphur batteries) would help meet the DECC's target of sourcing 10% of energy for transport from renewables by 2020 and facilitate greenhouse-gas emissions reduction of 80% by 2050. Li-ion battery development is strong enough here that David Willetts identified energy storage as one of the UK's Eight Great Technologies for Policy Exchange in 2013, recognizing that energy-storage R&D will enable the UK to gain from the global transition to new energy sources.

Public: The PI has a strong track record in engagement, appearing, for example, on the BBC Radio 4 programme "Putting Science to Work" in 2015, and working with the World Economic Forum to help write "Energy Harnessing: New Solutions for Sustainability and Growing Demand". All the CIs have considerable experience with public engagement, have presented research to such diverse groups as schoolchildren, science journalists, and members of parliament. Specifically, we will produce a hands-on annual presentation for the Cambridge Science Festival on "beyond Li-ion technologies", designed for children ages 4-12 and building on past successful hands-on projects in the Chemistry Department, where the children grew Zn dendrites in simplified Zn primary cells. We will work with Cambridge's Public Engagement office and Women in Science group to engage growing public interest in energy and nanotechnology and explain how fundamental science enables technology development in the energy area.

People: The project will train 3 PDRAs trained in best practices of materials synthesis and analysis, and 2 PDRAs in modelling of technologically relevant materials, including multi-scale modelling. By working in research teams, both theorists and experimentalists will be gain familiarity with their counterparts' techniques. These skills will be disseminated into academia/industry as the researchers continue in their careers. Direct knowledge of commercial relevance through interfacing with industry and end-use will provide relevant transferable-skills training for the researchers in this project. We will train a new generation of PDRAs and students, growing the battery expertise relating to battery characterisation, and materials in the UK, supporting future EV/ICT industries.