Situating the stage for solid-state battery success

Accelerating new battery technologies through university, national laboratory and industry partnerships. The importance of promoting knowledge and knowledge transfer through private-public funded collaborative efforts, avoiding the common death valleys of risky start-up companies, where important intellectual property and development know-how are lost. Setting the stage for solid-state battery success … Battery researchers and other engineers from University of California San Diego,

Battery researchers and other engineers at the University of California San Diego, in collaboration with LG Energy Solutions, have published a forward-looking perspective article in the journal Joule.

In the paper, the researchers describe three categories of engineering challenges that must be addressed to transition all-solid-state batteries from the laboratory toward large-scale industrial production.  These three challenges are precursors, processing and stress.

The research and thought leadership featured in the article was made possible by funding from the US National Science Foundation (NSF) as well as a collaborative effort between engineers at UC San Diego and LG Energy Solutions through the Frontier Research Laboratory program.

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Engineering and scalability challenges remain

The drivers of this article are recent scientific developments that have paved the way for all-solid-state batteries with significantly higher energy densities than conventional lithium ion batteries.  Some of these advances include the use of thicker dry cathode electrodes, as well as fully metallic alloys or alkali metal anodes.  With these and related advances, the remaining massive challenges lie in engineering and scalability, both in terms of manufacturing batteries in sufficiently large form factors and in terms of manufacturing these batteries in large quantities.

Precursors, processing, and pressure are highlighted as three areas where engineering challenges must be addressed to make major strides toward consumer success for all-solid-state batteries.

Precursors of solid electrolytes

For all solid-state batteries to compete in consumer markets, they must be cost competitive ($ per kWh).  One obstacle to this is solid electrolytes, which are the key enabling technology for all solid-state batteries.  Currently, the cost of solid electrolytes per kilogram is two orders of magnitude higher than that of liquid electrolytes.

The two main drivers of the high cost of solid electrolytes are: 1) immature supply chains for precursors;  and 2) lack of understanding of scalable synthesis methods for solid electrolytes.

Beyond raw material costs, the Joule perspective authors discuss solid electrolyte synthesis and conditioning steps.  They demonstrate that with proper optimization and handling under dry room conditions, the time and resources required to produce these materials can be significantly reduced and ensure they are up to spec.

Processing

Much of the work performed today on all solid-state batteries is still done manually.  The tools and infrastructure that support the scalable processing and integration of solid electrolytes into the composite layers required in a battery do not yet exist.  Instead, adapting to each process requires intense customization.

To overcome this, the engineers who wrote the new vision at Joule designed processes to adopt lithium-ion-compatible machines in the production of all-solid-state batteries.  In a striking example in the article, Z-stacking of solid electrolyte sheets and electrodes was demonstrated. Z-stacking is a common technique used in lithium ion batteries but was not previously thought possible in all solid state batteries.

stress

Due to the solid nature of the materials in the chemistry used in all-solid-state batteries, poor contact at the interfaces is usually compensated for by applying a high stack stress on the battery.  These high stack pressure requirements are often criticised when discussing the use of all-solid-state batteries in electric vehicles.  The authors highlight a severe lack of knowledge of the factors that determine stack stress at the module to pack level, as well as its effects on energy density efficiency losses.

To work to address this gap in knowledge, the authors share key considerations for all solid-state battery module design.  They highlight that beyond the specific value of stress that the battery community has often focused on, attention should be paid to stress uniformity and how stress can be maintained while the battery is operating.

what next

The engineering challenges in the precursors, processing and pressure categories are, without a doubt, daunting.  This is especially true in a university research environment.

Battery research at universities is often focused on the discovery and innovative use of materials on a small scale.  This type of research often does not include the resources needed to scale the findings so that they are easily relevant for transfer to industry.  Additionally, the authors suggest that current academic evaluation systems provide limited incentives for university scientists to bridge this gap.  As battery start-up companies attempt to fill the scalability gap between university and industry, this leads to various forms of information protection, engineering practice and valuable knowledge lost through failed iterations.

In these and related ways, the all-solid-state battery field currently faces an efficiency gap when it comes to solving and sharing the tough engineering challenges that stand in the way of large-scale use of all-solid-state batteries across a wide variety of industries.

The authors of the perspective article in Joule argue that when it comes to all-solid-state batteries, the gap between university research and large-scale production must be bridged through methods that do not rely solely on start-up companies.

U.S.  One way the authors argue is to leverage more of the research infrastructure and expertise of national laboratories.  In fact, the U.S.  National laboratories have infrastructure that can support a wide range of research, from small-scale projects conducted at universities to large pilot-scale projects.  These types of mid-level laboratories can be best utilised by university and industry researchers to pursue relevant research.

This will lead to more open and dynamic research and innovation ecosystems for all solid-state battery development.  In these types of ecosystems, researchers from universities, US national laboratories, start-ups, and established industry players are able to benefit more from pre-competitive engineering advances in precursors, processing, and pressure to move the entire field.  Next,