共沉淀中热力学耦合对正极材料电化学性能的影响

Coupling Effects of Thermodynamics in Co-precipitation on Electrochemical Performance of Cathode Materials

以共沉淀法制备钠离子层状氧化物正极材料NaNi_(0.4)Mn_(0.4)Fe_(0.2)O_(2),采用Al^(3+)有效控制和平衡共沉淀反应的过程.考察了加入Al元素带来的热力学耦合效应及对正极材料电化学性能的影响.结果表明,在Mn^(2+),Ni^(2+)和Fe^(2+)离子共存的环境中,由于Al^(3+)更高的过饱和度和更负的吉布斯自由能变(ΔG)所产生的热力学耦合效应,显著改变了溶液离子之间的沉淀驱动力,加速Ni^(2+)和Mn^(2+)的沉淀并抑制Fe^(3+)的沉淀.Na[Ni_(0.4)Mn_(0.4)Fe_(0.2)]_(0.995)Al_(0.005)O_(2)正极材料表现出优异的电化学性能,这归因于引入Al^(3+)制备得到高质量的前驱体([0.4MnCO_(3)·0.4NiCO_(3)·0.2Fe(OH)_(3)]_(0.995)·0.005Al(OH)_(3)).

The sodium ion layered oxide cathode material NaNi_(_(0.4))Mn_(0.4)Fe_(0.2)O_(2)was synthesized by the co-precipitation method,and Al^(3+)was used to effectively control and balance the co-precipitation reaction process.The thermodynamic coupling effect brought by the addition of Al element and its influence on electrochemical performance of cathode materials were investigated.In an environment where Mn^(2+),Ni^(2+)and Fe^(3+)ions coexist,owing to the thermodynamic coupling effect,the superior high supersaturation of Al^(3+)and the more negative change in the Gibbs free energy(ΔG)can efficiently changes the precipitation driving force between the solution ions,accelerating the precipitation of Ni^(2+)and Mn^(2+)ions and inhibiting the precipitation of Fe^(3+)ions.The obtained Na[Ni_(0.4)Mn_(0.4)Fe_(0.2)]_(0.995) Al _(0.005) O_(2)cathode material has demonstrated excellent electrochemical performance which can be attributed to the high quality precursor([_(0.4)MnCO_(3)·_(0.4)NiCO_(3)·_(0.2)Fe(OH)_(3)]_(0.995)·0.005Al(OH)_(3))brought about by the introduction of Al^(3+).