硝酸根添加剂提升钠金属电池循环稳定性

Nitrate additive facilitates cycling stability of sodium metal batteries

钠金属电池由于金属钠具有的高比能量密度和低电极电势特性极具发展潜力,然而,传统的碳酸酯类电解液与钠金属之间持续反应,导致电池的循环稳定性能不理想。添加剂策略是一种提升电解液性能的简单有效策略,通过盐包盐策略成功制备了NaNO_(3)作为添加剂的酯类电解液。DFT计算和NMR测试结果表明,NO_(3)^(-)将进入Na+溶剂化鞘层内侧,在钠金属负极优先还原。对于钠金属界面的SEM和XPS表征结果及电化学测试显示,NO_(3)^(-)的还原构建了含氮的SEI界面,助力均匀稳定的钠金属沉积剥离行为。Na_(3)V_(2)(PO_(4))_(3)(NVP)与钠金属负极组装的钠离子电池在NO_(3)^(-)改性的酯类电解液中可获得超长稳定循环,在2 C(1 C=110 mA/g)下循环了2000次后容量保持率高达89.9%,在5 C下循环1000次后容量保持率为97.4%。

Sodium metal batteries have great potential due to high specific energy density and low electrode potential characteristics of metallic sodium.However,traditional carbonate-based electrolytes react continuously with sodium metal,leading to unsatisfactory cycling stability of the battery.The additive strategy is a simple and effective approach to enhance electrolyte performance.By employing a salt-in-salt strategy,NaNO_(3) was successfully introduced as an additive in ester-based electrolytes.Density functional theory(DFT)calculations and nuclear magnetic resonance(NMR)tests indicate that NO_(3)^(-)enters the solvation sheath of Na+and is preferentially reduced at the surface of sodium metal.SEM and XPS characterization results of the sodium metal interface and electrochemical tests show that the reduction of NO_(3)^(-)forms an N(nitrogen)-containing solid-electrolyte interphase(SEI)interface,promoting uniform deposition and stripping behavior of sodium metal.Na_(3)V_(2)(PO_(4))_(3)(NVP)||Na batteries in NO_(3)^(-)-modified ester-based electrolytes exhibit exceptionally long-term stable cycling.After 2000 cycles at 2 C(1 C=110 mA/g),the capacity retention rate remains as high as 89.9%,and after 1000 cycles at 5 C,the capacity retention rate reaches 97.4%.