LiNi_(3/8)Co_(2/8)Mn_(3/8)O_2正极材料氟掺杂改性研究

Fluorine Doping of LiNi_(3/8)Co_(2/8)Mn_(3/8)O_2 Cathode Material for Lithium-ion Batteries

以共沉淀氢氧化物为前驱体制备了F-掺杂化合物LiNi3/8Co2/8Mn3/8O2-yFy(y:0,0.05,0.10,0.20),采用XRD、XPS、SEM、循环伏安(CV)、充放电测试、DSC等表征了其结构与性能.结果表明,F-掺杂置换部分O2-生成固溶体,不改变样品中过渡金属离子的价态. F-掺杂量y为0.05、0.10时,比容量不受影响,但在充放电过程中ch方向膨胀率由未掺杂样的2.06％分别下降至1.017％、1.018％,改善了其结构稳定性与循环寿命,30周后容量保持率分别达97.5％、96.2％;而y增至0.20时,离子混乱度升高,且颗粒间烧结过于严重,内阻增加,使容量与循环特性再度恶化.F-掺杂还促进材料烧结,使该材料粒径通过粉碎分级控制成为可能,有利于该材料电极的制备.另外,F-掺杂也使LiNi3/8Co2/8Mn3/8O2热稳定性得到一定程度改善.

The layered LiNi3/8Co2/8Mn3/8O2-yFy(y=0, 0.05, 0.10, 0.20) samples were prepared by using the co-precipitated hydroxide as precursor, and characterized by means of XRD, XPS, SEM, cyclic voltammetry, charge/discharge tests, DSC etc techniques. The results show that fluorine doping can not induce the valence change of transition metal ions in LiNi3/8Co2/8Mn3/8O2-yFy samples. The samples with y=0.05, 0.10 show better cycling performance with no expense of capacity compared with undoped one, 97.5%, 96.2% capacity retention respectively after 30 cycles can be reached. The ch lattice expanding of samples with y=0.05, 0.10 reduces from 2.06% of undoped one to 1.017%, 1.018% respectively when lithium is de-intercalated, contributing to the improvement of structure stability and electrochemical cycle character. However, the sample with y=0.20 exhibits lower capacity and faster capacity fading upon cycling, due to high cation disordering and internal impedance. Fluorine doping also accelerates agglomeration of particles of the samples, enhancing operability of electrode preparation of the cathodes. In addition, fluorine-doped samples have better thermal stability than LiNi3/8Co2/8Mn3/8O2.