多元素掺杂抑制正极材料的内应力积累

Multi-element doping inhibits the accumulation of internal stress in cathode material

高镍层状氧化物LiNi_(x)Mn_(y)Co_(1-x-y)O_(2) (NCM,x≥0.8)由于其高的能量密度和低廉的成本是锂离子电池(LIBs)最有前途的正极材料之一。提高NCM镍含量和截止电压可以提升正极材料的实际放电比容量,然而,高镍含量导致其表面残留大量的锂化合物,影响界面处锂离子的传输;同时长循环过程中产生的HF会溶解层状晶体结构中的过渡金属离子,使其电化学性能变差,严重阻碍了NCM大规模的实际应用。改善NCM的结构不稳定性可以通过掺杂来实现,在此,提出了一种协同掺杂改性策略,在NCM晶体内部同时掺杂Ta、Ti和Mg元素,3种元素的协同作用抑制了不可逆相变的发生,缓解了晶体内应力的积累。Ta@Ti@Mg改性的NCM在2.75~4.60 V,0.5 C循环100次后放电比容量为175.5 mAh/g,该协同掺杂策略为其它正极材料的改性提供了借鉴作用。

High-nickel layered oxide LiNi_(x)Mn_(y)Co_(1-x-y)O_(2) (NCM,x≥0.8)is one of the most promising cathode materials for lithium-ion batteries(LIBs)due to its high energy density and low cost.Increas‐ing nickel content and cut-off voltage of NCM can improve the actual specific discharge capacity of cathode materials.However,high nickel content leads to a large number of lithium compounds remain‐ing on the surface,which affects the transmission of lithium ions at the interface.At the same time,HF produced in the long cycle process will dissolve the transition metal ions in the layered crystal structure,making its electrochemical performance worse,which seriously hinders the practical application of NCM on a large scale.The structural instability of NCM can be improved by doping.Here,we report a synergistic doping modification strategy,in which Ta,Ti and Mg are doped inside NCM crystals at the same time.The synergistic effect of the three elements inhibits the occurrence of irreversible phase tran‐sition and alleviates the accumulation of internal stress in the crystals.The specific discharge capacity of Ta@Ti@Mg modified NCM is 175.5 mAh/g after 100 cycles of 2.75‒4.60 V and 0.5 C.This collabora‐tive doping strategy provides a reference for the modification of other cathode electrode materials.