Enhancing solid-state battery performance with spray-deposited gradient composite cathodes

Solid state electrolytes, which replace flammable liquid ones, are seen as being key to deployment of safe and high capacity batteries based on lithium metal anodes. Yet these materials often suffer from poor electrode/electrolyte contact which limits Li+ transport and active material utilisation. To overcome these barriers, effective methods to intimately connect active materials and electrolytes must be developed and demonstrated. In this work gradient composite cathodes of lithium iron phosphate (LFP) and polyethylene oxide (PEO) were manufactured using spray deposition to remove the planar electrode/electrolyte interface in solid-state batteries with polymeric electrolytes. These graded cathodes achieved ten times lower resistance and superior cycle life and rate testing performance compared to ungraded cathodes made in the same way. Graded composite cathodes maintained stable capacity after 80 cycles and functioned well at rates up to 2C, whereas ungraded composite cathodes failed to deliver any useable capacity after 80 cycles and at rates higher than C/5. Hence, this work acts as a demonstration that simple electrode structuring can have a significant impact on cell performance, offering a route towards the stabilization of solid-state batteries in real-world applications.