Development of high-performance cathode materials for lithium-ion batteries

Abstract

Cathode materials have been the bottleneck for the development of more advanced lithium-ion batteries due to their lower specific capacity. Lithium-rich manganese-based layered oxides (_xLi₂MnO₃·_1-xLiMO₂, M=Ni, Co or Mn, 0 <x< 1) and nickel-rich layered oxides (LiNi_xMn_yCo_zO₂, x+y+z=1, x≥0.5) have gained significant attention due to their high specific capacity and moderate cost. In this work, i) Li_1+xMn_0.54Co_0.13Ni_0.13O₂ (0.12≤x≤0.28) and LiNi_0.5Mn_0.3Co_0.2O₂ were synthesized via the co-precipitation and high-temperature sintering method. Spherical transition metal carbonate precursor (Mn_0.675Ni_0.1625Co_0.1625CO₃) was successfully obtained by a home-made continuous stirring tank reactor (CSTR) system. The tailor-made precursors were used for the systematic study of the impacts of lithium to transition metal ratio in Li_1+xMn_0.54Co_0.13Ni_0.13O₂ on electrochemical performance. The best performance was achieved on Li_1.12Mn_0.54Co_0.13Ni_0.13O₂. ii) Conventional coatings such as Al₂O₃ and carbon may not be applicable to surface modification of LiNi_0.85Mn_0.05Co_0.1O₂. Reductive agents should be avoided to prevent the reduction of transition metal cations which could lead to cation disordering or even severe phase change. The oxidative chemical vapor deposition process was shown as a promising method to coat a conductive polymer layer on LiNi_0.85Mn_0.05Co_0.1O₂. iii) LiNi_0.5Mn_0.3Co_0.2O₂ materials with a high rate capacity was also synthesized. The concentration of complexing agent, pH of synthesis solution, and temperature at different stages of the co-precipitation process were tuned to fabricate flower-like precursors. The specific capacity of the synthesized high-power LiNi_0.5Mn_0.3Co_0.2O₂ was 145.1 mAh/g at 5C, which was 20% higher than that of commercial one. The unique porous structure of secondary particle benefits high energy output at high rates as well as the cycling performance.

Date of Award	2019
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology