Solid State Gradients: One Step Aqueous Spray Deposition of Novel Graduated Cathode/Solid Electrolyte Interfaces for Improved Solid State Batteries.

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Lithium ion batteries are a necessity of daily life, being used more than ever in increasing size and power for applications like handheld devices, large scale energy storage and transport. They also offer huge potential in our shift towards renewable energy, therefore the production and use of these batteries is set to increase dramatically.Solid state batteries (SSB’s) replace the liquid electrolyte with a solid. This offers more stability against lithium dendrite formation which is the main cause of battery short-circuiting and failure. Because of this, solid state electrolytes (SSE’s) may be the answer to the challenge of pure lithium anodes, which are the highest theoretical capacity anode, but are hampered by rapid dendrite formation. SSE’s can have higher gravimetric and volumetric capacity due to the reduced electrolyte content and also make for safer batteries, particularly under stress, as the flammable liquid electrolyte has been removed.This work demonstrates a new manufacturing method for SSB’s, that allows for the formation of a novel design of the electrode/electrolyte interface. Ultrasonic spray coating is the process of spraying a material layer by layer to form thin films. By graduating between two or more different materials a gradient can be manufactured.Current SSB’s are formed by separately manufacturing a cathode film and a solid electrolyte film, then assembling these on top of each other to make the battery. This can cause interface issues between the cathode and the SSE, particularly, areas of poor contact, poor solid electrolyte interface (SEI) formation and degradation of the cathode. All of these issues lead to higher resistance, lower capacity and higher degradation.This work shows that a spray deposited graduated combined cathode/SSE removes the interfacial issues seen in the literature to create a battery that has 10x lower resistance, longer cycle life, lower capacity loss and performs substantially better under high rate conditions. All of which are necessary to help solid state batteries become more real world applicable.This new manufacturing technique is the only known way to produce this structure in a cheap, industrially relevant way, and is easily expandable to a larger scale. On top of this, unlike standard manufacturing methods, the methodology is almost entirely water based, which removes costs of solvent recapture and increases safety.This layer by layer gradient deposition technique is also applicable to other areas of materials research and has been used on silicon anodes and lithium sulfur batteries, as well as membranes for direct air capture and fuel cells. Figure 1