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

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 (PO₄ )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.