Poly (ethylene oxide) (PEO) polymer electrolytes are promising candidates for next-generation rechargeable lithium batteries. However, the poor interfacial stability between 4 V cathodes and PEO electrolytes impedes their applications in 4 V lithium batteries with high energy density. Here, we demonstrate a facile and effective strategy to enhance the interfacial stability by the synergy of Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) coating on the cathode surface, and salt combination in the electrolyte, even with a cut-off voltage of 4.25-4.4 V vs. Li⁺/Li. Nano-LAGP coated Li|PEO|LiCoO₂ cell delivers stable cycling with a capacity retention of 81.9%/400 cycles and 84.7%/200 cycles at 60 ^oC when charged to 4.25 and 4.3 V in pure polyether electrolyte, respectively. Steady cycling is also demonstrated at room temperature and with LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) cathode. This work offers a viable and scalable approach to improve the stability between PEO electrolytes and 4 V cathodes and open up new possibilities for practical application of 4 V lithium metal batteries.

聚（环氧乙烷）（PEO）聚合物电解质是下一代可再充电锂电池的有前途的候选者。但是，4 V阴极和PEO电解质之间的不良界面稳定性阻碍了它们在具有高能量密度的4 V锂电池中的应用。在这里，我们展示了一种简便有效的策略，通过在阴极表面上的Li _1.5 Al _0.5 Ge _1.5（PO ₄）₃（LAGP）涂层和电解质中的盐结合物协同作用来增强界面稳定性，即使采用相对于Li ⁺ / Li的4.25-4.4 V截止电压。纳米LAGP涂覆的Li | PEO | LiCoO ₂当在纯聚醚电解质中分别充电至4.25和4.3 V时，该电池可在60 ^o C时提供稳定的循环，容量保持率分别为81.9％/ 400次和84.7％/ 200次。在室温和使用LiNi _0.5 Co _0.2 Mn _0.3 O ₂（NCM523）阴极的情况下也显示出稳定的循环。这项工作提供了一种可行且可扩展的方法，以改善PEO电解质和4 V阴极之间的稳定性，并为4 V锂金属电池的实际应用开辟了新的可能性。