层状锰酸锂衍生物的阳离子价态与锂电池的电化学性能研究

采用溶胶-凝胶法, 通过锂盐、镍盐、钴盐与锰盐生成锂镍钴锰氧化合物的前驱体, 随后采用高温固相法合成了Li(Mn_1/3Co_1/3Ni_1/3)O₂. 借助于X射线光电子能谱(XPS)、X射线衍射(XRD)、循环伏安(CV)及充放电测试等现代测试手段研究了材料的晶型结构、离子价态及电化学性能. 前驱体经950 ℃煅烧可获得晶体结构完整、晶胞参数为a＝0.2864 nm, c＝1.4235 nm的六方层状Li(Mn_1/3Co_1/3Ni_1/3)O₂化合物; XPS结果表明Li(Mn_1/3Co_1/3Ni_1/3)O₂化合物表面上的Mn, Ni和Co分别以Mn^4＋, Ni^2＋和Co^3＋存在; 材料的高温放电比容量比室温要高, 在55 ℃下, 在2.5～4.6 V电压范围内, 电流密度为28 mA/g时材料首次放电容量195 mAh/g, 循环10次后容量保持在170 mAh/g; 循环伏安曲线上3.7 V和4.4 V的氧化还原过程对应于Ni^2＋/4＋和Co^3＋/4＋氧化还原电对的反应.

Cationic Ion Value State of Layered Lithium Manganate Derivative and Electrochemical Properties of Lithium Battery

Abstract The cathode material for lithium batteries Li(Mn_1/3Co_1/3Ni_1/3)O₂ has been synthesized by sol-gel technique followed by high temperature solid state reaction. The crystalline structure, ionic value and electrochemical properties of the material were investigated via X-ray photoelectron spectra, X-ray diffraction, cyclic voltammetry and charge-discharge cycling. The hexagonal lattice parameters of the compound by calcining the precursor at 950 ℃ are: a＝0. 2864 nm, c＝1. 4235 nm. XPS studies indicate that the oxidation states of manganese, nickel and cobalt in the Li(Mn_1/3Co_1/3Ni_1/3)O₂ surface region are largely 4＋, 2＋ and 3＋ respectively with small content of Ni^2＋ ion. Initial discharge capacity of 195 mAh/g at 55 ℃ was obtained in the range 2.5～4.6 V and at a specific current of 28 mA/g and under the same conditions 170 mAh/g was retained at the end of the 10th cycles. From the voltage profile and cyclic voltammetry, the redox processes occurring at ～3.7 and ～4.4 V were assigned to the Ni^2＋/4＋ and Co^3＋/4＋ couples, respectively.