Study On Preparation And Capacity Fade Of High Capacity 18650 Li-ion Battery

In this paper, we used LixCoO2 and LiNixCoyMn1-x-yO2 as cathode active materials, carbonaceous mesophase spherules (CMS) as anode active material to prepare 18650 lithium-ion second batteries. The influence on properties of batteries due to change of technological conditions were studied, and reasons for capacity fade were investigated as well.The results show that the properties of batteries are mainly influenced by charge/discharge schedule. When the top limit of charge voltage is too high, the capacity per gram of electrode material decreases suddenly with the cycling. Besides, if not activated during the initial charge period, the capacity of battery comes to the maximum value after several cycles. Larger the density per area, lower the initial charge/discharge efficiency. When electrolytes is not enough, the constant voltage charge period take a longer time. The utility ratio of electrode materials decreases as well. At the same time, the battery resistance increases and the cycle life decreases due to the decrease of the paths of Li-ion transportation. The properties of batteries come to a stable state when appropriate electrolytes are injected into batteries. In our experiment, 0.3g electrolytes per 100mAh is the best. The capacity of batteries is related to the ratio of cathode and anode closely. During the battery design, the designed capacity of anode should be larger than that of cathode, but not too much, since the forming of excess SEI membrane consumes a large number of lithium-ions. The cycle life is also influenced by the ratio between cathode and anode capacity. The resistance of the batteries increases with the cycling due to the interface resistance between the particles of cathode materials and electrolytes increases. The unlevelness of thickness of the electrode makes partial cathode active materials surplus, and results in capacity fade.