Lithiation-induced conductivity modulation in Prussian blue interlayer for stable Li/garnet solid-state batteries

The garnet-based solid-state batteries have the potential advantages of high energy density and safety. However, the poor solid–solid contact and Li dendrite growth at the anode interface lead to uneven Li deposition or short circuit, which hinders their practical application. Here, we propose a Prussian blue (PB) interlayer to improve the interface contact and charge transfer between Li anode and garnet electrolyte by lithiation-induced conductivity modulation. This mixed-conducting interlayer with unique 3D open framework enables a well welded interface with enhanced lithiophilicity and uniform Li diffusion. The Li/garnet interface resistance is significantly reduced. This lithiated PB interlayer is highly durable with invariable thickness during cycling, leading to a highly stable cycling of Li plating/stripping and corresponding LiFePO₄ full cells without dendrite growth. The dual modulation of ion and electron transports in an integrated structure without phase segregation through thermal or electrochemical lithiation provides a solution to the challenge of solid–solid interfaces and the development of practical solid-state batteries.