Low Temperature Electrochemical Properties of Li[NixCoyMn1-x-y]O2 Cathode Materials for Lithium Batteries
Ni-rich Li[NixCoyMn1-x-y]O2 materials are promising due to their high capacity that exceeds 200 mAh g−1, which results from the Ni2+/3+/4+ and Co3+/4+ redox couples. In contrast, the high amount of Mn in the transition metal layer would not be favored in terms of capacity, due to the fact that the average oxidation state is tetravalent so that it does not solve the electrochemical reaction but instead provides structural stability upon cycling. However, the low temperature electrode performances of Ni-rich Li[NixCoyMn1-x-y]O2 are rarely reported in literature. Capacity fade is mainly related with slow transport of Li+ ions at low temperatures. Except this fact, capacity fade mechanism has not been elucidated further. This motivates us to explore optimal compositions of cathode that operate at extreme conditions. Since diffusion is governed by particle size of active material, we limit the particle sizes of active materials to 10–11 μm in diameter to minimize the particle size effect of the Li[NixCoyMn1-x-y]O2 (x:y:1-x-y=1/3:1/3:1/3, 0.5:0.2:0.3, 0.6:0.2:0.2, 0.70:0.15:0.15, 0.8:0.1:0.1, and 0.85:0.075:0.075 hereafter defined as x = 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85, respectively). Here, we introduce the electrochemical properties of Li[NixCoyMn1-x-y]O2 at low temperatures (0 ∼ −20◦C) and suggest possible factors that affect the low temperature properties.
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