Localized High‐Concentration Electrolytes with Low‐Cost Diluents Compatible with Both Cobalt‐Free LiNiO₂ Cathode and Lithium‐Metal Anode

Abstract High‐nickel layered oxide cathodes and lithium‐metal anode are promising candidates for next‐generation battery systems due to their high energy density. Nevertheless, the instability of the electrode–electrolyte interphase is hindering their practical application. Localized high‐concentration electrolytes (LHCEs) present a promising solution for achieving uniform lithium deposition and a stable cathode–electrolyte interphase. However, the limited choice of diluents and their high cost are restricting their implementation. Four novel cost‐effective diluents and their performance with highly reactive LiNiO₂ cathode and Li‐metal anode are reported here. The results show that all the LHCE cells exhibit a Coulombic efficiency of >99.38% in Li | Cu cells and a capacity retention of >85% in Li | LiNiO₂ cells after 250 cycles. Advanced characterizations unveil that the stable cell operation is due to well‐tuned electrode–electrolyte interphases and Li deposition morphology. In addition, online electrochemical mass spectroscopy and differential scanning calorimetry reveal that the gas generation and heat‐release are greatly reduced with the LHCEs presented. Overall, the study provides new insights into the role of diluents in LHCEs and offers valuable guidance for further optimization of LHCEs for high energy density lithium‐metal batteries.