The Effect and Mechanism of Fast Charging on the Performance of Graphite Negative Electrode in Mobile Phone Batteries

　　With the rapid development of fast charging technology for mobile phone batteries, the charging rate of mobile phones is becoming faster and faster. While enjoying the benefits of fast charging for mobile phones, we still have a small question in our hearts. Does fast charging have an impact on the lifespan of lithium-ion batteries? Firstly, let's understand what the charging rate is. Generally speaking, lithium-ion batteries are described by the rate of charge. For example, 1C rate refers to the battery being fully charged within 1 hour, while 2C rate refers to fully charging the battery within 0.5 hours. This means that the higher the rate, the faster the charging rate, and the charging time is the reciprocal of the charging rate. After understanding the definition of charging rate, we can further understand the impact of fast charging on lithium-ion batteries.

　　Generally speaking, rapid charging can lead to an increase in internal resistance and a decrease in capacity of lithium-ion batteries. We need to understand the mechanism behind this now. At present, the main negative electrode material for commercial lithium-ion batteries is graphite materials. The use of graphite materials has largely solved the problem of dendrite precipitation in metal lithium negative electrodes, greatly improving the safety of lithium-ion batteries and enabling their commercial application. At present, common graphite negative electrode materials include natural graphite, artificial graphite, and other types. During the charging process of lithium-ion batteries, Li+migrates from the positive electrode to the negative electrode and embeds into the layered structure of the graphite material, forming LiC6 compounds, making the negative electrode appear golden. The lithium intercalation process of the negative electrode mainly includes the diffusion of Li+in the electrolyte and SEI film, the charge exchange on the surface of the negative electrode, and the diffusion of Li in the solid phase. These processes will directly affect the charging rate of lithium-ion batteries. During the charging process of lithium-ion batteries, the negative electrode undergoes concentration polarization and electrochemical polarization, both of which result in the potential of the negative electrode being lower than its actual steady-state potential. Moreover, as the charging rate increases, polarization will further worsen. This will exacerbate the occurrence of side reactions, and on the other hand, it will lead to the formation of metal lithium coatings and lithium dendrites on the surface of the negative electrode, leading to safety issues and a decrease in capacity of lithium-ion batteries.

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