Sincere: Selective ion-conductive ceramic electrolytes

Lead Research Organisation: Imperial College London
Department Name: Materials

Abstract

Li-stuffed garnet electrolytes are poised to provide a breakthrough in battery technology since they can deliver the adequate Li-conductivity and the safety and cycle life required for the commercialisation of high-energy density batteries (i.e. high voltage Li-ion and Li-metal batteries). However, these garnet electrolytes, if they are not processed properly, suffer from severe moisture-sensitivity that leads to drastic degradation of their transport and microstructural properties - a problem that has not been universally recognised in the field. This fast degradation, which occurs even at room temperature, has so far hindered fundamental studies aimed at identifying and optimising the modes of lithium transport within the crystal lattice and the grain boundaries. Furthermore, measurements of the interfacial resistances reflect those of the decomposition products, rather than the intrinsic properties of the garnets themselves. We have developed a unique t setup that will allow a strict control of the moisture during the processing and characterization of the garnets. Our work, to date, has shown a three-fold enhancement in lithium-ion conductivity, if the degradation-related problems are addressed. The aim of this project is threefold: a) Reveal the optimum intrinsic Li-mobility in Li7-nxAxV(n-1)xLa3Zr2O12 (V = lithium vacancy) garnets b) Investigate the electrode/garnet interfaces and c) Analyse the degradation under moisture-controlled conditions to evaluate the potential use of the garnets in Li-air cells.

Planned Impact

The development of safe, long life, high energy density secondary batteries is one of the most important challenges in materials science towards safeguarding quality of life for future generations. On the one hand, it will reduce fossil fuel dependency and its associated greenhouse gas emission levels, helping to fulfill targets set by the Climate Change Act for the UK to cut its emissions by at least 80% from 1990 levels by 2050. On the other hand, the successful realisation of such high capacity batteries will allow the production of long-range electric transport requiring mobile storage and release of electrical energy and will support the utilization of green power sources more efficiently for stationary applications. Solid electrolytes such as lithium-conducting garnet ceramic oxides have the potential to provide the breakthrough in battery technology that we seek since they are able to deliver the required safety and stability properties. However, there are some aspects relating to the adequate understanding of Li-conduction paths and degradation processes in these systems that remain unknown, hindering their optimization and integration in commercial batteries. This project represents a unique and timely opportunity to unveil the intrinsic Li conductivity in garnets and to understand and improve the interfacial resistance of the solid electrolyte/electrode interfaces. It will provide invaluable information for optimising the Li-conduction pathways in these materials that will allow the design and production of the best possible ceramic electrolytes to be used in secondary batteries. Furthermore, the project aims to establish a universal procedure for the suitable processing of Li-ceramics that will prevent their degradation and optimise their performance in batteries (i.e. via tuning of the microstructural and electrochemical properties). This will not only have a great impact on the knowledge of these complex and interesting systems but also has potential economic benefits through the introduction of procedures for the commercialization of solid state batteries.
 
Description The project has allowed to following discoveries:
The potential use of garnet solid electrolytes for Li batteries is greatly dependent on the composition of the garnet and the processing route.
Cubic dense electrolytes with Li content equal or higher to 6.5 per formula unit is fundamental to achieve the highest Li mobilities.
Microstructure control is fundamental since generally, grain boundaries have higher Li mobility than grains and therefore, smaller grains leading to a higher density of grain boundaries are beneficial for fast Li ion dynamics.
The control of the chemical composition in the surface, grains and grain boundaries is of paramount importance to achieve the highest Li mobility and to control degradation problems related to corrosion with H2O and CO2 and Li dendrite growth upon cycling. The dopant used for the stabilisation of the cubic garnet seems to have a great effect on this.
The effect of the Li-H exchange in the Li ion dynamics has been chemically and electrochemically analysed probing a very important deterioration of three orders of magnitude due to the Li-H exchange in grain and grain boundaries
A new method has been proposed for the study of Li diffusion using 6Li trace diffusion experiments
Exploitation Route The findings of this project have been fundamental for the award of the following projects, wich aims to develop solid state batteries to achieve safer and more efficient batteries for transport and stationary applications
EPSRC ICSF "Genesis: garnet electrolytes for new energy storage integrated solutions" EP/R024006/1 CoI (£ 754,4k)
EPSRC Platform grant "Understanding the critical role of interfaces and surfaces in energy materials" EP/R002010/1 CoI (£1.3M)
EPSRC JSPS Core to Core Core "Solid Oxide Interfaces for Faster Ion Transport (SOIFIT)" EP/P026478/1 CoI (£1M)
EPSRC Supergen Energy Storage Challenge "Next Generation solid state Lithium Batteries" EP/P003532/1 CoI (£1.74M)
MIT-Imperial Seed Fund "Control of Interfaces for Increasing the Power Density and Durability of Solid State Batteries" PI (£34.85k)

Furthermore, this project has implements protocols for the use of surface analysis facilities to characterise solid state batteries in situ and in operando conditions helping for the creation of a new surface analysis equipment called "High Five" for which I have been awarded EPSRC Strategic Equipment "High Five: Resolution, Sensitivity, in operando Control, Ultra High Vacuum and Ion Sectioning in a Single Instrument" PI (£1.725M)
Sectors Energy,Environment

 
Description EPSRC ICSF Genesis
Amount £754,400 (GBP)
Funding ID EP/R024006/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 10/2017 
End 09/2020
 
Description Strategic equipment grant
Amount £1,725,000 (GBP)
Funding ID EP/P029914/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 09/2017 
End 09/2020
 
Description Supergen Energy Storage Challenge
Amount £1,740,000 (GBP)
Funding ID EP/P003532/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 12/2016 
End 11/2019
 
Description MIT Seed Fund 
Organisation Massachusetts Institute of Technology
Country United States 
Sector Academic/University 
PI Contribution We have established a collaboration to look at cathode-garnet electrolyte interfaces. at Imperial we provide with the garnet electrolyte and analyse the surface and interfacial chemical properties by using surface analysis techniques
Collaborator Contribution At MIT the gorth by sputtering the cathodes on the garnet electrolyte and measure high pressure XPS and XANES in synchrotron facilities at USA
Impact So far we have developed a protocol for in-situ characterization of the cathode/electrolyte interfaces under Temperature and bias
Start Year 2016