Lithium–metal fluoride batteries promise significantly higher energy density than the state‐of‐the‐art lithium‐ion batteries and lithium–sulfur batteries. Unfortunately, commercialization of metal fluoride cathodes is prevented by their high resistance, irreversible structural change, and rapid degradation. In this study, a substantial boost in metal fluoride (MF) cathode stability by designing nanostructure with two layers of protective shells—one deposited ex situ and the other in situ is demonstrated. Such methodology achieves over 90% capacity retention after 300 charge–discharge cycles, producing the first report on FeF₃ as a cathode material, where a very high capacity utilization in combination with excellent stability is approaching the level needed for practical applications of FeF₃. The cathode solid electrolyte interphase (CEI) containing lithium oxalate and BF bond containing anions is found to effectively protect the cathode material from direct contact with electrolytes, thus greatly suppressing the dissolution of Fe. Quantum chemistry and molecular dynamics calculations provide unique insights into the mechanisms of CEI layer formation. As a result, this work not only demonstrates unprecedented performance, but also provides the reader with a better fundamental understanding of electrochemical behavior of MF cathodes and the positive impact observed with the application of a lithium bis(oxalato)borate salt in the electrolyte.

中文翻译：

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具有双重表面保护的锂铁（III）氟化物电池

锂金属氟化物电池的能量密度远高于最新的锂离子电池和锂硫电池。不幸的是，金属氟化物阴极的高电阻，不可逆的结构变化和快速降解阻止了其商业化。在这项研究中，通过设计具有两层保护壳的纳米结构，可以显着提高金属氟化物（MF）阴极的稳定性，一层为非原位沉积，另一层为原位沉积。这种方法在300次充放电循环后可实现90％以上的容量保持率，这是有关FeF ₃作为正极材料的首份报告，在此报告中，非常高的容量利用率以及出色的稳定性已接近FeF ₃实际应用所需的水平。。发现含有草酸锂和含有BF键的阴离子的阴极固体电解质中间相（CEI）可有效保护阴极材料免于直接与电解质接触，从而极大地抑制了Fe的溶解。量子化学和分子动力学计算提供了对CEI层形成机理的独特见解。结果，这项工作不仅展示了空前的性能，而且还为读者提供了对MF阴极的电化学行为以及在电解质中使用双（草酸硼酸）硼酸锂盐观察到的积极影响的更好的基本理解。