关键词: 镍锰酸锂, 高电压, 循环寿命, 失效机理

Abstract: Due to the high specific energy and good cycle ability, secondary lithium-ion batteries have been adapted as the main power source for portable electronics in the past two decades. Recently this technology has been extended into the fast growing electric vehicle market. However such application posts further needs of battery technology advancement, especially higher energy density to ectend the driving range of electric vehicles. The higher energy density in batteries can be achieved by improving specific capacity of active materials or by increasing the working potential of the cathode materials. Among various high-voltage cathode materials, the spinel LiNi_0.5Mn_1.5O₄ has been investigated as a promising cathode material for Li-ion batteries with high energy density. In this paper, LiNi_0.5Mn_1.5O₄ / graphite and LiNi_0.5Mn_1.5O₄ / Li₄Ti₅O₁₂ are manufactured as the 32131-type cells, which offer more practical and reliable cell data compared with laboratory size coin-cells. The cathode electrode composite is LiNi_0.5Mn_1.5O₄ : SP : KS-6 : PVDF = 91.0 : 3.5 : 1.0 : 4.5, and the two anode electrodes are Li₄Ti₅O₁₂ : SP : KS-6 : PVDF = 90.0 : 4.0 : 1.0 : 5.0 and graphite : SP : CMC = 93.2 : 2.5 : 4.3, respectively. The cells are 7.5Ah (152 W·h/kg) for LiNi_0.5Mn_1.5O₄/graphite with N/P=1.1 and 5.5 A·h (81 W·h/kg) for LiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂ with N/P=0.9. The capacity retention is 90.1% for LiNi_0.5Mn_1.5O₄ /graphite after 250 cycles with 0.5 C charge/discharge rate at room temperature. For LiNi_0.5Mn_1.5O₄ /Li₄Ti₅O₁₂ cell, the capacity retention is 97.2% after 200 cycles with 1.0 C charge/1.5 C discharge rate at room temperature, the cycle performance is almost the same with LiNi_0.5Mn_1.5O₄/Li half cell. Therefore, the difference of cycle performance seems to be depended on the anodes. The capacity fading of the LiNi_0.5Mn_1.5O₄/graphite can be explained by the impact of Mn dissolution, and active Li⁺ loss in the full-cell system through continuous SEI formation (electrolyte reduction) prompted by Mn reduced on the surface of graphite. LiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂ cell whose capacity is limited by Li₄Ti₅O₁₂ anode showed almost no SEI and has better cycling performance.

Key words: LiNi0.5Mn1.5O4, high voltage, cycling performance, failure mechanism