BEST reports from the Advanced Automotive Battery Conference where technical editor Dr Mike McDonagh finds discrepancies between marketing information and research organisations’ claims for solid-state battery development.
As a virtual delegate at the conference, I found it easy to find my way around. The planning facility allowed me to construct my own personal agenda, which removed the effort of keeping my own schedule and times. So, a thumbs up from me for this virtual event.
As the technical editor for BEST, my main interest was the current status of battery technology development. I chose a mix of research and manufacturing organisations’ presentations, as representative of the current status.
The main focus of the conference, unsurprisingly, was centred around EVs. In this category, the main topics were: fast charging, driving range, cost, and safety. The most prominent chemistry of EV battery technology? Yes, of course, solid-state lithium-ion. Runner up in this category was anodic silicon.
All-solid-state lithium-based batteries seem to be the way forward for most companies looking for a safe, high-energy-density power source that can be charged in minutes. It seems a logical enough approach to remove flammable electrolytes and prevent dendrite growth, plus the use of a metal anode, to provide more coulombs and therefore increase the runtime for a vehicle.
What is curious is the gap between the marketing information of some companies— who claim to be producing or are about to commercially manufacture lithium solid-state batteries (SSBs)— and the research organisations who are at the cutting edge of this technology. In the latter case, we still see the R&D projects designed to resolve the many problems created by the design, operation and manufacture of solid-state batteries.
Creating a solid electrolyte
The logical step to creating a solid electrolyte that is conducting, has a low-resistance bond with the electrodes, prevents dendrite growth, and withstands the volume changes of charging and discharging electrodes is easier to define than to achieve. The paper by Ying Shirley Meng, professor of nanoengineering at the University of San Diego sets out the problems and current status of this ambition quite succinctly. In her presentation, Meng considered the structural materials and the manufacturing requirements of an all-solid-state battery (ASSB) with a lithium metal anode.
One aspect of ASSBs is the need to maintain a good cell pressure to ensure a good electrolyte/electrode contact. The problems of achieving this were demonstrated by placing a lithium plated anode under various stack pressures. The results of these tests showed, surprisingly, that the lowest stack pressure prevented short circuits (Fig 1).
Other electrodes were considered, with silicon ticking many of the requirement boxes for EV use. These were its low cost ($2,000 per ton), high energy performance, mechanical robustness, and interfacial stability. Whilst it does have its downsides in liquid electrolytes, it seems to perform well in the solid state, accepting lithiation after the formation of the SEI. Types of solid electrolyte, including sulfides, were briefly compared and discussed. The overall conclusion of Meng was that there are still areas to be resolved, namely: obtaining suitable precursors for manufacture, the processability of the materials and the cell operating pressure.
Close to commercialisation
Looking to the industry as a measure of how close to commercialisation companies are with the ASSB design, the presentation by Josh Buettner-Garrett of Solid Power, seemed representative of the state of the industry. Claiming to be the ‘leader in all-solid-state batteries’, the presentation went on to list the company’s credentials, achievements, industry partners— such as Ford and BMW— and its road map for future developments. At present they are concentrating on manufacturing a solid electrolyte.
Like the University of San Diego, and other organisations, they favour a sulphide-based approach to meet commercial EV requirements. They have a variety of cell chemistries undergoing prototyping trials. These include: silicon-based anodes (low cost with high charge rates plus low-temperature operation), lithium metal anodes (high energy density), NMC type cathodes, both intercalation and conversion types (Fig 2). Solid Power’s pilot-scale equipment is compatible with that used for standard commercial lithium-ion production processes. Their plan is to license their technology to existing battery producers. They are planning, with a new manufacturing facility, to increase their capacity to produce proprietary SE material for formal qualification testing in 2022.
In contrast to Solid Power’s claims, Lisa Hsu, a director of Prologium Technology, claims her firm is the most advanced and will be market-ready in 2022. The company asserted that their products will be full-scale, solid-state EV batteries, based on their patented technological breakthroughs. These include their active safety mechanism (ASM), an undisclosed ceramic solid electrolyte (LCB), and their bipolar-like packing of individual cells (CTP).
The patented CTP architecture is designed to improve energy density and reduce cost (Fig 3). The slides showed impressive credentials, with 16 years of R&D plus third-party validation of pouch cells by an OEM, in 2013. Its technological advantages are the ASM, which the company claim actively blocks thermal runaway, LCB, a solid-state ceramic oxide electrolyte solution to the poor interface adhesion problems and their CTP and MAB packing that improves space efficiency and therefore energy density. Most of this has been put together in their current commercial operation, which they say produces and sells up to 60Ah cells. In fact, they claim that their MAB combined with their improved electrode materials can give a volumetric energy density of 437-693Wh/l. It will be interesting to see if their prediction of the mass production capability of at least half a GWh/y in 2022 will be met.
The wheel of fortune
An automotive battery conference would not be complete without a presentation on the status of lithium-ion battery recycling. The ReCell Centre of Argonne National Laboratories has been busy developing methods of removing spent cathode material from lithium-ion batteries, then cleaning and re-lithiating the black mass in a closed-loop recycling system. The presentation by its deputy director Bryant Polzin covered the methods they had been investigating for removal and re-lithiation of the cathode materials.
As we have come to expect from Argonne, the work was carried out in conjunction with an industry partner. This included building cells from the processed material then testing their performance. The presentation provided several new processes, each following the direct recycling route. The solvent Y process where the electrode is delaminated and the PDF binder is removed (Fig 4), and the five methods for re-lithiation of the black mass were described. Polzin showed that after extraction and de-lithiation that the recovered EOL cathode material was almost indistinguishable from virgin material.
The methods of re-lithiation: thermal solid-state, hydrothermal, redox mediator, ionothermal, electrochemical are under ongoing investigation. At present they are considered as two categories, room temperature operation and those that require heat. For reasons of cost and reducing carbon footprint, the room temperature processes are preferred. Formation results for cells manufactured using these methods, compared to baseline material, showed C/10 discharge capacities very close to those of the baseline virgin product. Process modelling revealed that this direct cathode-to-cathode recycling should be cheaper than conventional recycling processes— both hydro and pyro methods— regardless of the re-lithiation technology chosen. The current position is that further work is being carried out to improve the processes, particularly the Redox and E-chem methods. ReCell is continuing its work to optimise the material performance and process costs.