Ni^(2+)替代对LiFePO_4正极材料电化学性能的影响

Effect of Ni^(2+) Substitution on the Electrochemical Performance of LiFePO_4

利用炭热还原法合成了橄榄石型LiFe1-x Nix PO4/C(x=0.0,0.1,0.3,0.5)正极材料,并系统研究了Ni2+替代对材料电化学性能的影响。充放电循环、循环伏安和交流阻抗测试,结果表明Ni2+替代部分Fe2+可以显著改善LiFePO4材料的电化学性能。在0.2 C(1 C=170.0 mA·g-1)电流密度下,LiFe0.9Ni0.1PO4/C的放电比容量达到160 mAh·g-1。LiFe1-x Nix PO4/C电化学性能的改善归因于材料电导率的提高和电荷传输电阻的降低。利用第一性原理对LiFe1-x Nix PO4/C的电子结构进行了研究,结果表明Ni2+的铁位替代能够提高体系的电子电导性。LiFe0.875Ni0.125PO4的结构最稳定,带隙最小,导电性能最好。

LiFez.xNixPO4/C （x=0.0, 0.1, 0.3, 0.5）cathode materials were synthesized by a carbothermal reduction technique and the effect of Ni2＋ substitution on the electrochemical perforrnanees were systematically investigated. The results reveal that the cycle performance and electrochemical reversibility of LiFePO4 are remarkably improved with the substitution of Fe2＋ ions by Ni2＋ ions and LiFeo.gNioAPO4/C demonstrates good electrochemical performances with discharge capacity of 160 mAh＇gl at a discharge rate of 0.2 C （1 C=170.0 mA.gl）. The improvement of the reversible capacity and the high C-rate performance of LiFePO4 could be attributed to the enhancement of the electronic conductivity and the decrease of the charge transfer resistance. The first-principle calculations were employed to investigate the electronic structures of the LiFel-xNixPO4/C composites. The Lattice parameters, total energies, density of states have were also studies in details. The results show that the electronic conductivity of the Ni2＋-doped materials can be improved to certain extent. LiFe0.a75NioA25PO4 has the most stable structure, the smallest band gap and the best conductivity.