What are the factors that affect the cycling performance of lithium-ion batteries?

Materials

Material selection is the first factor affecting the performance of lithium-ion batteries. If you choose the battery material with poor cycle performance, even if the process is reasonable and the production is perfect, the cycle of the cell can not be guaranteed. And with better materials, the cycle performance may not be too bad even if there are some problems in the subsequent production process.

From the material point of view, the cycling performance of a battery depends on the cathode and anode, which have the worse cycling performance when matched with the electrolyte. If the material cycle performance is not good. On the one hand, the crystal structure may change too fast during the cycle, so that the released and received of lithium ion cannot be completed. On the one hand, it may lead to the failure of the active material and the corresponding electrolyte to generate a dense and uniform SEI film, resulting in premature side reactions between the active material and the electrolyte, resulting in rapid electrolyte consumption and thus affecting the cycling performance.

Therefore, in the design of the cell, if either the positive or negative electrode is confirmed to choose the material with poor cycle performance, then the other one does not need to choose the material with good cycle performance. Because only the material of positive and negative electrode is selected at the same time, it can show its performance.

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The degree of compaction of cathode and anode

Excessive compaction of positive and negative electrodes can improve the energy density of the cell, but it will also reduce the recycling performance of the material to a certain extent. Theoretically, the greater the compaction, the greater the damage to the structure of the material. But the structure of the material is fundamental to ensuring that lithium-ion batteries can be recycled. In addition, it is difficult to ensure high electrolyte retention for the cell with high positive and negative electrode compaction, and the electrolyte retention is also the basis for the cell to complete the normal cycle or more cycles.

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Moisture

Excessive moisture will react with positive and negative active substances, destroy their structure and affect the circulation. At the same time, excessive moisture is not conducive to the formation of SEI film. However, on the one hand, trace water is difficult to remove, on the other hand, trace water can also ensure the performance of the cell to a certain extent.

In LCO - graphite batteries, for example. When the moisture of the battery is less than 0.015%, the first discharge capacity of the battery has only a small change. When the battery moisture is in the range of 0.015% ~ 0.04%, the first discharge capacity of the battery decreases with the increase of moisture in the battery. According to the research, when the moisture in the battery is less than 0.015%, the alkyl lithium carbonate generated by the one-electron reduction process can also react with the trace amount of water in the electrolyte to form lithium carbonate. When CO2 is generated, new chemical reactions take place on the negative surface at low potential. In conclusion, the appropriate amount of water is conducive to the formation of Li2CO3 dominated, stable, uniform and dense SEI film. When the SEI film completely covers the negative electrode, the irreversible reaction stops immediately. In addition, when the moisture is in the range of 0.0150% ~ 0.04%, the lithium ion consumption increases and the charge and discharge capacity of the battery decreases, which has a negative effect on it.