The importance of cycle performance for Li-ion batteries needs no elaboration; in addition, on a macro level, longer cycle life means less resource consumption. Therefore, the factors that affect the cycle performance of lithium-ion batteries is a problem that every person related to the lithium industry has to consider. The following Wen Wu lists several factors that may affect the cycle performance of the battery for your reference.
Material type: The choice of material is the first element that affects the performance of lithium-ion batteries. Choose a poor cycle performance of the material, the process is reasonable, made and perfect, the cycle of the cell is bound to be unable to guarantee; choose a better material, even if the subsequent made a slight problem, the cycle performance may not be too bad (a lithium cobalt acid gram play only about 135.5mAh/g and lithium precipitation of the cell, 1C although more than a hundred dives but 0.5C, 500 times 90% or more. (A primary cell disassembled negative electrode with black graphite particles of the cell, the cycle performance is normal). From the material point of view, the cycle performance of a full battery is determined by the cycle performance of the positive electrode after matching with the electrolyte, the negative electrode after matching with the electrolyte of the two, the worse one. The poor cycling performance of the material may be due to the rapid change of the crystal structure during the cycling process, which prevents the completion of lithium embedding and de-lithiuming, or due to the inability of the active material and the corresponding electrolyte to generate a dense and uniform SEI film, which causes the premature side reaction between the active material and the electrolyte and the premature consumption of the electrolyte, thus affecting the cycling. In the core design, if one pole is confirmed to be made of a material with poor circulation performance, the other pole does not need to be made of a material with better circulation performance, which is wasteful.
Compaction of positive and negative electrodes: Although high compaction of positive and negative electrodes can improve the energy density of the core, it will also reduce the cycling performance of the material to some extent. From the theoretical point of view, the greater the compaction, the greater the damage to the structure of the material, which is the basis for ensuring that the lithium-ion battery can be recycled; in addition, it is difficult to ensure a higher amount of liquid retention for a higher positive and negative electrode compaction, which is the basis for the completion of the normal cycle or more cycles of the electrode.
Moisture: Excessive moisture will react with the positive and negative electrode active substances, destroy their structure and thus affect the cycle, while excessive moisture is also not conducive to the formation of SEI film. However, while traces of water are difficult to remove, traces of water can also ensure the performance of the core to some extent. Unfortunately, Wen Wu's personal experience in this area is almost zero, can not say much. Everyone interested can search the forum inside the information on this topic, or a lot.
Coated film density: a single variable to consider the impact of film density on the cycle is almost an impossible task. Inconsistencies in film density either bring about differences in capacity, or differences in the number of layers of core winding or lamination. For the same type of cell with the same capacity and material, lowering the film density is equivalent to adding one or more layers of winding or stacking, which corresponds to an increased diaphragm that can absorb more electrolyte to ensure cycling. Considering that a thinner film density can increase the multiplier performance of the cell, the baking and water removal of the electrode and bare cell will be easier, of course, the error in coating may be more difficult to control with a too thin film density, and the large particles in the active material may also negatively affect the coating and rolling, more layers means more foil and diaphragm, which means higher cost and lower energy density. Therefore, a balanced consideration is also needed when evaluating.
Negative overload: In addition to the impact of first irreversible capacity and coated film density deviation, the impact on cycling performance is also a consideration for negative overload. For lithium cobaltate plus graphite system, it is more common for the negative graphite to become the "short board" in the cycling process. If the cathode is not sufficient, the core may not precipitate lithium before cycling, but after cycling hundreds of times, the cathode structure changes little but the cathode structure is severely damaged and cannot fully receive the lithium ions provided by the cathode, thus precipitating lithium and causing a premature drop in capacity.
