乙基膦酸二乙酯基阻燃宽温域电解液在锂离子电池中的应用

Diethyl ethylphosphonate-based flame-retardant wide-temperature-range electrolyte in lithium-ion batteries

锂离子电池(lithium-ion batteries,LIBs)在电动汽车和电化学储能等领域有着广泛的应用。然而,商用碳酸酯电解液的低闪点和易燃烧给LIBs的应用拓展带来了安全隐患。通过引入低成本、不可燃的乙基膦酸二乙酯(diethyl ethylphosphonate,DEEP)阻燃剂,可以有效降低电解液燃烧的风险。然而,DEEP与Li+之间的相互作用强,容易导致DEEP进入Li+的第一溶剂化壳层,参与形成负极表面固态电解质界面(solid electrolyte interphase,SEI)。但是,DEEP还原分解形成的SEI电子屏蔽能力差,难以阻止溶剂分子在界面持续分解,导致石墨负极失效。本研究通过强配位溶剂碳酸乙烯酯和弱配位溶剂线性碳酸酯协同调节DEEP与Li^(+)的作用强度,降低了DEEP在Li^(+)的第一溶剂化壳层中的占比,抑制了DEEP在负极上的分解。在构筑的常规浓度(约1.15 mol/L)DEEP改性的碳酸酯电解液中,石墨负极稳定循环150圈后的容量保持率高达95.6%。此外,该电解液在-60℃下仍能保持良好的流动性,并且石墨/磷酸铁锂电池在-20℃下循环50圈后仍有49.3%的容量保持率。

Lithium-ion batteries are extensively used in various applications such as electric vehicles and electrochemical energy storage systems.However,safety concerns related to flammability and low flash point of commercial carbonate electrolytes limit their broad application.The incorporation of nonflammable flame-retardant diethyl ethylphosphonate(DEEP)into carbonate electrolytes has been shown to effectively reduce the risk of battery fires and explosions by mitigating electrolyte combustion.Nonetheless,the strong interaction between DEEP and Li+leads to the infiltration of DEEP into the first solvated shell layer of Li+,contributing to the formation of solid electrolyte interphase(SEI)on the graphite anode.The SEI formed through the reductive decomposition of DEEP provides inadequate electron shielding,failing to halt the ongoing decomposition at the interface and leading to the failure of graphite anodes in DEEP-modified carbonate electrolytes.To address this issue,this study adopts a synergistic strategy,using ethylene carbonate as a strong ligand solvent and linear carbonate as a weak ligand solvent.This approach aims to diminish the interaction strength between DEEP and Li^(+),decrease the proportion of DEEP in the first solvated shell layer of Li^(+),and reduce the decomposition of DEEP on the anode.In the developed DEEP-modified carbonate electrolyte with a conventional concentration(~1.15 mol/L),the graphite anode shows an impressive capacity retention of 95.6%after 150 cycles.In addition,the electrolyte remains fluid at-60℃,and the graphite/LiFePO_(4) battery retains 49.3%of its capacity after 50 cycles at-20℃.