Ultrahigh-voltage lithium metal batteries based on cobalt-free LiNi0.5Mn1.5O4 (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 in the next-generation high energy density and sustainable batteries, due to the high theoretical energy density of ∼650 Wh kg-1, elimination of toxic Co element and intrinsic safety brought by LNMO spinel structure compared with the unstable layered oxides LiNixCoyMnzO2. However, their development is critically limited by the incompatibility between state-of-the-art carbonate electrolytes and the two aggressive electrodes. Herein, we synthesize a new electrolyte additive, i.e. 2,2-difluoroethyl methyl sulfone (FS), which could enable the ultrahigh-voltage lithium metal batteries to stably cycle in conventional carbonate electrolytes. On the cathode side, different from conventional electrolyte additives, FS could be selectively adsorbed on the LNMO surface and form a special assembled FS “buffer” layer, which could efficiently exclude the free carbonate molecules away from the cathode surface. Therefore, upon charging, the -CF2H group of FS is preferably anodically decomposed to form inorganics-rich CEI, which efficiently suppresses micro-fracture and transition metal dissolution of LNMO. On the anode side, the FS could also be preferably cathodically decomposed, resulting in an inorganics-rich SEI for the stable cycling of Li metal anode. Thus, carbonate electrolyte with FS additive enables the unprecedented high performance for cobalt-free 5V-class lithium metal batteries, i.e. 40 μm-Li/LNMO (loading=7 mg cm−2) full cell with high capacity retention of 84% even over 600 cycles at 1 C using commercial 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 capacity retention of 99% after 100 cycles at 0.25 C. Moreover, the Li/LNMO pouch cells, which has not been reported before to the best of our knowledge, is assembled and can operate stably for over 150 cycles.

中文翻译：

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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 LiNi0.5Mn1.5O4 (LNMO) 正极（5 V 级，相对于 Li+/Li）和锂金属负极（-3.04 V 相对于标准氢电极）的超高压锂金属电池吸引了广泛的关注。近年来，由于LNMO尖晶石结构具有~650 Wh kg-1的高理论能量密度、消除了有毒Co元素以及带来的本质安全性，作为下一代高能量密度和可持续电池的有希望的候选者而受到关注。不稳定的层状氧化物LiNixCoyMnzO2。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。在正极侧，与传统电解液添加剂不同，FS可以选择性地吸附在LNMO表面，并形成特殊组装的FS“缓冲”层，可以有效地将游离碳酸盐分子排除在正极表面之外。因此，充电时，FS的-CF2H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，从而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液使无钴5V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，使用商业碳酸盐基低浓度电解质，在 1 C 下循环 600 次后仍具有 84% 的高容量保持率。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 0.25 C 下循环 100 次后容量保持率为 99%。此外，Li/LNMO 软包电池具有据我们所知，之前没有报道过，组装后可以稳定运行超过 150 个周期。