The lithium metal /solid electrolyte interface
Lead Research Organisation:
University of Oxford
Department Name: Materials
Abstract
The need for better batteries has never been greater. Many automotive manufacturers now believe that limitations in the performance of current lithium-ion batteries represent the greatest barrier to the electrification of transport. The energy density of lithium batteries is currently restricted by the cathode material, delivering ~ 160-180 mAh g-1. New high-energy-density cathode materials are much sought after to meet the increasing requirements of consumer electronics, electric vehicles and grid energy storage. Recently the need for batteries for electric vehicles has been accelerated by the announcements that several car companies will be fully electrified in the coming years.
Lithium batteries with solid electrolytes would transform safety and enable the use of a lithium metal anode delivering significantly higher energy density than current carbon based anodes. The jury is still out on whether silicon anodes, with the problematical volume changes, can deliver the cycleability required for automotive applications, making investigation of lithium anodes an imperative.
The challenge is the lithium metal/solid electrolyte interface. We need to understand the processes that occur at this interface: reactivity between the lithium metal and the solid electrolyte, the formation of solid electrode interface layers (SEI), including their composition and morphology, how to form dense ceramic solid electrolytes but with rough, porous surfaces to accommodate the lithium metal and increase the effective electrode/electrolyte interface area thus accessing higher effective charge discharge rates. Mastering the lithium metal/solid electrolyte interface is essential to enable all-solid-state batteries.
At Oxford we have all the tools necessary to carry out the study, including state-of-the-art electron microscopy, focused ion beam techniques to section cells, alternating current impedance equipment to understand electrical characteristics of the interface and correlated with the electron microscopy. We have sparked plasma synthesis for the densification of ceramics, X-ray photoelectron Spectroscopy(XPS) for identifying surface film compositions. This project will also focus on understanding the fundamental science behind this interface using advanced characterisation methods such X-ray Absorption Spectroscopy with both hard and soft X-rays (XAS), Resonant Inelastic X-Scattering (RIXS), X-ray diffraction, Nuclear Magnetic Resonance, Raman and Electrochemistry.
The student co-funded by JLR would synthesise ceramic electrolytes, such as the Garnets, fabricate cells, cycle them at different rates and temperatures, section the cells at different states of charge and cycle number, investigate the nature of the interface with the techniques described above then use the understanding to optimise the performance of the lithium metal/solid electrolyte interface. This project falls within the EPSRC Energy research area.
Lithium batteries with solid electrolytes would transform safety and enable the use of a lithium metal anode delivering significantly higher energy density than current carbon based anodes. The jury is still out on whether silicon anodes, with the problematical volume changes, can deliver the cycleability required for automotive applications, making investigation of lithium anodes an imperative.
The challenge is the lithium metal/solid electrolyte interface. We need to understand the processes that occur at this interface: reactivity between the lithium metal and the solid electrolyte, the formation of solid electrode interface layers (SEI), including their composition and morphology, how to form dense ceramic solid electrolytes but with rough, porous surfaces to accommodate the lithium metal and increase the effective electrode/electrolyte interface area thus accessing higher effective charge discharge rates. Mastering the lithium metal/solid electrolyte interface is essential to enable all-solid-state batteries.
At Oxford we have all the tools necessary to carry out the study, including state-of-the-art electron microscopy, focused ion beam techniques to section cells, alternating current impedance equipment to understand electrical characteristics of the interface and correlated with the electron microscopy. We have sparked plasma synthesis for the densification of ceramics, X-ray photoelectron Spectroscopy(XPS) for identifying surface film compositions. This project will also focus on understanding the fundamental science behind this interface using advanced characterisation methods such X-ray Absorption Spectroscopy with both hard and soft X-rays (XAS), Resonant Inelastic X-Scattering (RIXS), X-ray diffraction, Nuclear Magnetic Resonance, Raman and Electrochemistry.
The student co-funded by JLR would synthesise ceramic electrolytes, such as the Garnets, fabricate cells, cycle them at different rates and temperatures, section the cells at different states of charge and cycle number, investigate the nature of the interface with the techniques described above then use the understanding to optimise the performance of the lithium metal/solid electrolyte interface. This project falls within the EPSRC Energy research area.
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/R512060/1 | 01/10/2017 | 31/03/2023 | |||
| 1939654 | Studentship | EP/R512060/1 | 01/10/2017 | 30/09/2021 | Dominic Spencer Jolly |
| Description | What were the most significant achievements from the award? A significant achievement has been identifying a previously undescribed failure mechanism occurring at the Li metal anode / solid electrolyte interface during the process of discharging an all-solid-state battery (stripping the Li metal anode). When the mass transport of Li metal to the interface is not high enough to match the flux of Li-ions away from the interface under current load, this leads to the formation of interfacial voids. The growth of such voids leads to localisation of current and hence to short circuiting of the battery. We have demonstrated that the use of pressure can increase the rate of Li metal creep and hence prevent this failure from taking place. This is detailed in our recent Nature materials paper (see the Papers section). We have also shown that this mechanism occurs in sodium anodes, as detailed in our recent ACS Applied Materials and Interfaces paper. A second key finding was understanding the mechanism during charge/discharge of a promising anode-protective interlayer for "anodeless" solid-state batteries. These findings were recently published in the journal Joule (see papers section). The work focussed on understanding the structural changes within the interlayer, the deposition morphology of lithium and lithium alloy on the current collector, and understanding the critical currents at which these interlayers ceased to prevent lithium dendrite penetration into the solid electrolyte, resulting in cell failure. Other significant research outputs have included contributing to work that has used X-ray tomography to visualise dendrite growth through a solid-state battery. This work gains insights into the failure mechanism of solid-state batteries during charge and in particular fast-charging. This work is currently in-press in Nature Materials. I have also undertaken similar work identifying sodium dendrite growth in sodium anode all-solid-state batteries, this time utilising MRI to visualise the dendrite growth. This work has been published in Angewandte Chemie International Edition. To what extent were the award objectives met? If you can, briefly explain why any key objectives were not met. The award objectives have been met through this research as we have identified a reason for failure at the anode/solid electrolyte interface, and described a preventative measure to enable faster charging of both Li and Na anode all-solid-state batteries. This being said, there remains scope to take this project further and demonstrate further ways to prevent voiding an solid-state-batteries. How might the findings be taken forward and by whom? Further research on conditions by which the rate of creep of a metal anode can be increased during battery operation are currently underway by myself and a masters student in my group. |
| Exploitation Route | In solid-state academia, awareness of the consequences of our research is spreading, with Jeff Sakamoto having written a highlight in Nature Energy on our paper and the importance of using pressure when operating solid-state batteries. Outputs of this research will need to be understood by industry to bring all-solid-state battery products to market. |
| Sectors | Energy |
| Description | SOLBAT (The Faraday Institution) |
| Organisation | The Faraday Institution |
| Country | United Kingdom |
| Sector | Charity/Non Profit |
| PI Contribution | I have been colaborating with the SOLBAT Project on a work package on interfaces between metal anodes and solid electrolytes. Our contribution has been on understanding the failures that occur on stripping lithium and sodium metal anodes as described in our recent publications. This has involved cell design, synthesis, densification, surface treatment, EIS voltammetry, cycling, XPS, SEM and X-ray tomography. |
| Collaborator Contribution | Partners have contributed help with X-ray tomography techniques and analysis as well as fundamental understanding of the properties of Li and na metal under pressure. |
| Impact | 2 papers: one on Li and one on Na listed in the 'Papers@ section. This collaboration is between researchers in different fields of Materials science, engineering and chemistry research. |
| Start Year | 2018 |