具有增强界面稳定性的阻燃型电解液用于实际锂金属电池

Flame-retardant electrolyte with boosted interfacial stability for practical Li metal batteries

开发匹配高电压正极的锂金属电池是实现高能量存储系统的关键.因此,研发可以同时为锂金属负极和高电压正极产生稳定界面相的先进电解液非常必要.LiNO_(3)作为高效的固体电解质界面相添加剂被广泛应用于醚基电解液中,然而其在碳酸脂类电解液中的低溶解性严重限制了其在高压锂金属电池中的应用.本文利用磷酸三甲酯助溶剂提高LiNO_(3)在碳酸乙基甲酯/氟代碳酸乙烯酯电解液中的溶解度,并赋予电解液阻燃性能.此外,通过添加双草酸硼酸锂(LiBOB)进一步提高正负极的界面稳定性.结果表明,该电解液对锂金属负极和高电压层状氧化物正极均具有较高的兼容性.在2.8–4.3 V电压范围内,Li||LiCoO_(2)和Li||LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)电池在1.2 mA cm^(-2)电流密度下循环300周后的容量保持率分别为80.2%和84.2%.更令人惊喜的是,负/正极容量比为3.33的Li||NCM811电池在相同的充放电条件下循环150周后的容量保持率仍高达~80%.本论文对富含LiNO_(3)的阻燃型高压电解液的研究将为通过界面相调控研发安全的高比能锂金属电池提供理论指导.

Developing Li metal batteries(LMBs) with highvoltage cathodes is crucial for realizing high energy storage systems. Thus, advanced electrolytes that can derive stable interphases for both Li anode and high-voltage cathodes are highly desired. LiNO_(3) has been widely used as an efficient additive for solid electrolyte interphases in ether-based electrolytes, but its poor solubility in carbonate-based electrolytes limits its application in high-voltage LMBs. Herein, trimethyl phosphate was proposed as co-solvent in ethyl methyl carbonate/fluoroethylene carbonate electrolyte to endow the electrolyte with high LiNO3 solubility and flame-retardant properties. Additionally, lithium bis(oxalato) borate was added to improve the interfacial stability at both the anode and the cathode sides. As a result, the obtained electrolyte exhibited high compatibility towards both Li metal anode and high-voltage layered cathodes. After cycled between 2.8±4.3 V at a current density of 1.2 mA cm^(-2) for 300 times, Li||LiCoO_(2) and Li||LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811) full cells delivered high capacity retention of 80.2% and 84.2%, respectively. More amazingly, the Li||NCM811 cell with a negative-to-positive capacity ratio of 3.33 still remained a capacity retention of~80% after 150 cycles under the same charge/discharge conditions. The understanding of this fire-retardant, high-voltage electrolyte enriched with LiNO3 inspires the development of safe and high energy LMBs through interphases regulation.