Electrolytes for low temperature, high energy lithium metal batteries are expected to possess both fast Li⁺ transfer in the bulk electrolytes (low bulk resistance) and a fast Li⁺ de-solvation process at the electrode/electrolyte interface (low interfacial resistance). However, the nature of the solvent determines that the two always stand at either ends of the balance, and conventional electrolyte designs have to make a compromise to favor one at the expense of the other. Here, we address this irreconcilable dilemma using an “electric-field assisted self-assembly layer”, i.e. sodium perfluorooctanoate (NaPFO). Driven by the bias-potential, PFO⁻ anions dissolved in the electrolyte could reversibly self-assemble into a dense and ordered molecular layer at the cathode/electrolyte interface, which could protect the electrolyte from anodic degradation due to the high voltage and enable the stable cycling of LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) in ether-based electrolyte with an ultra-low freeing point. More importantly, the self-assembly of the PFO⁻ layer could aid the Li⁺ de-solvation behavior at the cathode/electrolyte interface, thus significantly lowering the interfacial resistance. Thus, with this reversible self-assembly layer on the cathode surface, low bulk resistance and low interfacial resistance are simultaneously achieved. Consequently, the tetrahydrofuran (THF)-based electrolyte containing NaPFO is applied to practical Li‖NMC811 pouch cells and achieves an unprecedented energy density of 122 W h kg⁻¹ (except taps and packing foil, same hereafter) at −85 °C, the highest reported power density of 318 W kg⁻¹ at a high current density of 4.1 mA cm⁻² at −60 °C, and can be recharged with stable performance (175 W h kg⁻¹ at 20th cycles) at −40 °C. This electric-field assisted self-assembly layer enables fine tuning of the micro-environment at the cathode–electrolyte interface, and provides a new design concept for the electrolyte of ultra-low temperature high voltage lithium-metal batteries.

中文翻译：

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超低温下具有高能量/功率密度的锂金属电池的可逆自组装分子层


用于低温、高能锂金属电池的电解质预计在本体电解质中具有快速的Li ⁺ 转移（低体电阻）和快速的Li ⁺ 去溶剂化过程。电极/电解质界面（低界面电阻）。然而，溶剂的性质决定了两者总是处于天平的两端，传统的电解质设计必须做出妥协，以牺牲另一种为代价，以偏向其中一种。在这里，我们使用“电场辅助自组装层”，即全氟辛酸钠（NaPFO）来解决这个不可调和的困境。在偏压驱动下，溶解在电解液中的 PFO ⁻ 阴离子可以在阴极/电解液界面可逆地自组装成致密且有序的分子层，从而保护电解液免受阳极降解。高电压，使 LiNi _0.8 Mn _0.1 Co _0.1 O ₂ (NMC811) 在醚基电解液中稳定循环超低自由点。更重要的是，PFO ⁻ 层的自组装有助于正极/电解质界面的 Li ⁺ 去溶剂化行为，从而显着降低界面电阻。因此，通过阴极表面上的这种可逆自组装层，可以同时实现低体电阻和低界面电阻。因此，含有NaPFO的四氢呋喃（THF）基电解质被应用于实用的Li‖NMC811软包电池，并在122 W h kg ⁻¹ （除了抽头和包装箔，下同）达到了前所未有的能量密度。 -85 °C，在 4 的高电流密度下，报道的最高功率密度为 318 W kg ⁻¹ 。-60 °C 时为 1 mA cm ⁻² ，-40 °C 时可再充电且性能稳定（第 20 次循环时为 175 W h kg ⁻¹ ）。这种电场辅助自组装层能够微调正极-电解质界面的微环境，为超低温高压锂金属电池电解质提供了新的设计理念。