表面包覆改善球形Ni(OH)_2高温性能的研究

Coating of Spherical Ni(OH)_2 Cathode Materials for Ni-MH Batteries at Elevated Temperature

采用Yb/Co氢氧化物共沉淀包覆方法和Ca3(PO4)2与Co(OH)2分别沉淀分层包覆方法在球形Ni(OH)2的表面进行了均匀的包覆。前者利用CoSO4,YbCl3和NaOH溶液进行共沉淀包覆,后者是先在球形Ni(OH)2的表面沉淀包覆Ca3(PO4)2,然后再沉淀包覆Co(OH)2。结果显示,两种包覆方法均能有效地提高球形Ni(OH)2的高温(60℃)性能。按照Yb/Co=0.75%:2%共沉淀包覆的试样制成AA型电池后,在60℃下1C放电的容量保持率达到常温下的90%。而2%Ca3(PO4)2与2%Co(OH)2分层包覆后的球形Ni(OH)2制成AA型电池后,在60℃下1C放电的容量保持率达到常温下的81%。未包覆和仅用Co(OH)2包覆的球形Ni(OH)2制成的AA型电池,在60℃下1C放电的容量保持率分别只有46%和48%。通过循环伏安测试表明,利用表面包覆的方法可以增大正极材料Ni(OH)2在高温下的氧化电位、析氧电位和两者之间的电位差,从而提高了材料在高温下的电化学性能。

Ytterbium hydroxide, Calcium phosphate and cobalt hydroxide were used for surface modification of spherical Ni（OH）2 to improve its high temperature performance. The Yb/Co coated spherical Ni（OH）2 was prepared by co-precipitation of Co/Yb hydroxide on the surface of spherical Ni（OH）2 from COSO4, YbCl3 and NaOH solutions. The Ca3（PO4）2 and Co（OH）2 coated Ni（OH）2 were prepared by precipitation of Ca3（PO4）2 on the surface of spherical Ni（OH）2, followed by precipitation of Co（OH）2 on its surface. The capacity retentions of the sealed AA-sized Ni-MH using 2%Co/0.75%Yb hydroxide coated and 2%Ca/2%Co coated spherical Ni（OH）2 reached 90% and 81%, respectively, at 60℃, where the capacity retentions for un-coated and only Co（OH）2 coated Ni（OH）2 were only 46% and 48%, respectively. The cyclic voltammetry analysis showed that for the Ni（OH）2, the oxidation potential, the oxygen evolution potential and the difference between them increased after the coating both at room temperature and high temperature, leading to an increase of the charging efficiency of Ni（OH）2 and improvement of the electrochemical performance at high temperature.