O_(3)-NaNi_(0.4)Fe_(0.2)Mn_(0.4)O_(2)正极Na^(+)传输动力学及相变机制

Understanding the Na+transport kinetics and phase transition mechanism of O_(3)-NaNi_(0.4)Fe_(0.2)Mn_(0.4)O_(2) cathode materials

钠离子电池因其成本低廉、环境友好且与锂离子电池工作原理相似,在大规模储能领域极具应用潜力。作为决定电池能量密度的关键组成部分,O3型钠基层状过渡金属氧化物因高容量、合成简单等优势在众多正极材料中脱颖而出。然而,Na^(+)在O3结构中八面体位点间的迁移需克服较大的能垒,最终导致复杂反应相变的发生和容量快速衰减。因此,探究O3型正极材料电化学反应过程中Na^(+)脱嵌行为与结构演变的构效关系对开发高性能正极材料至关重要。本工作以O_(3)-NaNi_(0.4)Fe_(0.2)Mn_(0.4)O_(2)(O3-NFM)正极为研究对象,对其电化学性能、Na^(+)传输动力学性质及相变机制展开了系统研究。电化学测试结果表明,O3-NFM在充电至高压(4.3 V)时可脱出0.84 mol Na^(+),发挥约201.9 mAh/g的比容量,但可逆性欠佳。当截止电压为4.0 V时,该正极材料循环性能优异,原位XRD结果进一步证明了电化学反应过程中O3-P3/O3-P3-P3/O3-O3的可逆结构转变。循环伏安(CV)曲线和恒电流间歇滴定技术(GITT)结果表明其具有快速的钠离子扩散速率,从而表现出较好的倍率性能。本研究为探索以O3-NFM为基础的正极材料结构设计及性能调控提供了理论基础。

Sodium-ion batteries have promising potential in large-scale electric storage applications due to their low cost,environmental friendliness,and similar working principles to lithium-ion batteries.O3-type layered oxides are used as a cathode material that determines the energy density of SIBs and stand out from other cathodes due to their high capacity and ease of synthesis.However,the migration of Na^(+) between octahedral positions in the O3 phase must overcome a large energy barrier,which results in complex reaction phase transitions and rapid capacity decay.Therefore,the Na^(+) de-intercalation behavior and the structural evolution of O3-type structure should be explored before developing high-performance cathodes.Herein,we systematically investigated the electrochemical properties,Na^(+)transport kinetics,and phase transition mechanism of O_(3)-NaNi_(0.4)Fe_(0.2)Mn_(0.4)O_(2)(O3-NFM).The O3-NFM cathode delivered a capacity about 201.9 mAh/g(corresponding to 0.84 mol of Na^(+)extraction)when charged to 4.3 V.After the cut-off voltage is set to 4.0 V,O3-NFM can achieve a stable reversible cycle.The improved cycling performance between 2.0 V and 4.0 V can be ascribed to the reversible transformation of O3-P3/O3-P3-P3/O3-O3 structural evolution,as determined by in situ X-ray diffraction.A fast kinetics of the Na^(+) diffusion in the O3 structure was revealed by cyclic voltammetry and galvanostatic intermittent titration technique techniques,which contributes to a good rate performance.This work provides a theoretical basis for investigating the structure modification and material design based on O3-NFM cathodes.