A Shuttle‐Free Solid‐State Cu−Li Battery Based on a Sandwich‐Structured Electrolyte

Abstract Cu−Li batteries leveraging the two‐electron redox property of Cu can offer high energy density and low cost. However, Cu−Li batteries are plagued by limited solubility and a shuttle effect of Cu ions in traditional electrolytes, which leads to low energy density and poor cycling stability. In this work, we rationally design a solid‐state sandwich electrolyte for solid‐state Cu−Li batteries, in which a deep‐eutectic‐solvent gel with high Cu‐ion solubility is devised as a Cu‐ion reservoir while a ceramic Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 interlayer is used to block Cu‐ion crossover. Because of the high ionic conductivity (0.55 mS cm −1 at 25 °C), wide electrochemical window (>4.5 V vs. Li + /Li), and high Cu ion solubility of solid‐state sandwich electrolyte, a solid‐state Cu−Li battery demonstrates a high energy density of 1 485 Wh kg Cu −1 and long‐term cyclability with 97 % capacity retention over 120 cycles. The present study lays the groundwork for future research into low‐cost solid‐state Cu−Li batteries.