Chromium Doping As A New Approach To Improve The Cycling Performance At High Temperature Of 5 V Lini_(0.5)mn_(1.5)o_4-based Positive Electrode

摘要

LiCr_(2γ)Ni_(1.5-γ)Mn_(1.5-γ)O4 (0< Y ≤ 0.2) spinels have been synthesized by a sucrose-aided combustion method. Two sets of Cr-doped samples have been obtained by heating the "as-prepared" samples at 700 and 900 C for 1 h. X-ray diffraction and thermogravimetric data show that pure and single phase spinels with similar lattice parameter have been synthesized. The homogeneity and the sub-micrometric particle size of the spinels have been shown by SEM and TEM. The main effect of the temperature is to increase the particle size from ≈50 to≈500 nm, on heating from 700 to 900 C. The study of the influence of Cr-dopant content and thermal treatment on the electrochemical properties at 25 C and at 55 C has been carried out by galvanostatic cycling in Li-cells. The discharge capacity (≈l30mAhg~(-1)) does not noticeably change with the synthesis conditions; but the cycling performances are strongly modified. Key factors that control the cycling performances have been determined. The most highlighted result is that spinels heated at 900 C with Y≤0.1 have very high capacity retention at 55 C (>96% after 40 cycles, cyclability >99.9% by cycle) indicating that metal doping is a new approach to prepare 5 V LiNi_(0.5)Mn_(1.5)O_5-based cathodes with excellent cycling performances at high temperature.