P2型层状氧化物正极的人工界面层构筑及储钠性能

Artificial interface layer construction and sodium storage performance of P2-type layered oxide cathode

P2型Na_(2/3)Ni_(1/3)Mn_(2/3)O_(2)(P2-NNMO)工作电压高、安全性好、成本低,是有潜力的钠离子电池正极材料。针对P2-NNMO正极钠不足和P2-NNMO正极与电解液的界面问题,通过化学预钠化法(P2-NNMO正极和联苯钠的自发反应),构造了一种富含无机物的人工界面层,可使外源性的钠嵌入氧化物正极层间。结果表明:预钠化形成的人工界面层含有的NaF,可有效缓解正极材料被有机溶剂侵蚀及过渡金属的溶出;同时人工界面层也改善了钠离子的扩散动力学。改性后的正极(P2-NNMO@CEI)在电压为2~4 V、电流密度为20 mA/g的条件下,放电比容量为95.1 mA·h/g、首次库伦效率为88.5%;在50 mA/g下循环280次后容量保持率为84.2%。该研究为层状氧化物正极表面改性提供了一种有效方法,也为电极材料的界面设计提供了新的思路和方向。

P2-type Na_(2/3)Ni_(1/3)Mn_(2/3)O_(2)(P2-NNMO)has high working voltage,good safety,and low cost,making it a promising cathode material for sodium ion batteries.To solve the problem of sodium deficiency of P2-NNMO cathode and the interface between P2-NNMO cathode and electrolyte,an inorganicrich artificial interface layer was constructed on P2-NNMO cathode via a chemical presodiation method(spontaneous redox reaction between P2-NNMO cathode and sodium biphenyl),with which extra sodium ions insert the oxide cathode host structure.The results showed that the artificial interface layer formed by presodiation contained NaF,shielded cathode material solvent corrosion and transition metal dissolution,and improved the diffusion kinetics of Na+.The modified cathode(P2-NNMO@CEI)delivered the discharge specific capacity of 95.1 mA∙h/g and the coulombic efficiency of 88.5%within the voltage of 2~4 V at the current density of 20 mA/g and possessed capacity retention of 84.2%after 280 cycles at the current density of 50 mA/g.This study provided an effective method for surface modification of layered oxide cathode and further provided a new concept and direction for designing interfaces of electrode materials toward real applications.