Ultrahigh-voltage lithium metal batteries based on a cobalt-free LiNi_0.5Mn_1.5O₄ (LNMO) cathode (5 V-class, vs. Li⁺/Li) and lithium metal anode (−3.04 V vs. the standard hydrogen electrode) have attracted extensive attention in recent years as promising candidates for the next-generation high energy density and sustainable batteries owing to their high theoretical energy density of ∼650 W h kg⁻¹, elimination of toxic Co elements and intrinsic safety caused by the LNMO spinel structure compared with the unstable layered oxide LiNi_xCo_yMn_zO₂. However, their development is critically limited by the incompatibility between state-of-the-art carbonate electrolytes and the two aggressive electrodes. Herein, we synthesized a new electrolyte additive, i.e. 2,2-difluoroethyl methyl sulfone (FS), which could enable ultrahigh-voltage lithium metal batteries to stably cycle in conventional carbonate electrolytes. On the cathode side, unlike conventional electrolyte additives, FS could be selectively adsorbed on the LNMO surface and form a special assembled FS “buffer” layer, which could efficiently exclude free carbonate molecules away from the cathode surface. Therefore, upon charging, the –CF₂H group of FS is preferably anodically decomposed to form an inorganic-rich CEI, which efficiently suppresses the micro-fracture and transition metal dissolution of LNMO. On the anode side, FS could also be preferably cathodically decomposed, resulting in an inorganic-rich SEI for the stable cycling of the Li metal anode. Thus, carbonate electrolyte with the FS additive enables the unprecedented high performance of cobalt-free 5 V-class lithium metal batteries, i.e. a 40 μm-Li/LNMO (loading = 7 mg cm⁻²) full cell with a high capacity retention of 84% over 600 cycles at 1C using commercial a carbonate-based low-concentration electrolyte. The full cell consisting of a high-loading cathode (20 mg cm⁻²) and an ultrathin Li anode (40 μm) achieves a capacity retention of 99% after 100 cycles at 0.25C. Moreover, Li/LNMO pouch cells, which have not been reported before to the best of our knowledge, are assembled and can operate stably for over 150 cycles.

中文翻译：

---

合理的电解液添加剂分子设计赋予无钴5V级锂金属电池稳定的循环性能


基于无钴 LiNi _0.5 Mn _1.5 O ₄ (LNMO) 阴极（5 V 级，相对于Li ⁺ /Li）和锂金属阳极（−3.04 V相对于标准氢电极）的超高压锂金属电池近年来，由于其理论能量密度高达〜650 W h kg ^-1 、消除了有毒Co元素以及LNMO尖晶石带来的本质安全性，作为下一代高能量密度和可持续电池的有希望的候选者受到了广泛的关注结构与不稳定的层状氧化物LiNi _x Co _y Mn _z O ₂相比。然而，它们的发展受到最先进的碳酸盐电解质和两种腐蚀性电极之间的不相容性的严重限制。在此，我们合成了一种新型电解液添加剂，即2,2-二氟乙基甲基砜（FS），它可以使超高压锂金属电池在传统碳酸酯电解液中稳定循环。在阴极侧，与传统电解质添加剂不同，FS可以选择性地吸附在LNMO表面上，并形成特殊组装的FS“缓冲”层，该层可以有效地将游离碳酸盐分子排除在阴极表面之外。 因此，充电时，FS的-CF ₂ H基团优选发生阳极分解，形成富含无机物的CEI，从而有效抑制LNMO的微断裂和过渡金属溶解。在阳极侧，FS也可以优选地进行阴极分解，产生富含无机物的SEI，以实现锂金属阳极的稳定循环。因此，含有 FS 添加剂的碳酸盐电解质使无钴 5 V 级锂金属电池具有前所未有的高性能，即40 μm-Li/LNMO（负载 = 7 mg cm ^-2 ）全电池，容量保持率高达使用商用碳酸盐基低浓度电解质，在 1C 下进行 600 次循环后，效率为 84%。由高负载正极（20 mg cm ^-2 ）和超薄锂负极（40 μm）组成的全电池在0.25C下循环100次后容量保持率为99%。此外，据我们所知，以前从未报道过的Li/LNMO软包电池已组装完毕，并且可以稳定运行超过150个循环。