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The mechanism of battery capacity decay has been widely studied and reported. The influencing factors of battery capacity degradation are shared by Yunsheng Electronic Technology Co., Ltd. The main reasons are: the reduction of recyclable lithium caused by side reactions on the electrode surface; The secondary factor is the reduction of active substances (such as metal leaching, structural damage, material phase transition, etc.); An increase in battery impedance. And the negative electrode is related to many influencing factors in the attenuation mechanism mentioned above.
Research progress on negative electrode decay mechanism: Carbon materials, especially graphite materials, are the most widely used negative electrode materials in lithium-ion batteries. Although other negative electrode materials, such as alloy materials and hard carbon materials, are also widely studied, the research focuses mainly on morphology control and performance improvement of active materials, and there is relatively little analysis on the mechanism of capacity decay. Therefore, research on the mechanism of negative electrode attenuation is mostly focused on the attenuation mechanism of graphite materials. The attenuation of battery capacity includes the attenuation during storage and use. The attenuation during storage is usually related to changes in electrochemical performance parameters (impedance, etc.), while during use, in addition to changes in electrochemical performance, there are also changes in mechanical stress such as structural changes and lithium deposition phenomena.
The change in the interface between the negative electrode and electrolyte is widely recognized as one of the main causes of negative electrode decay in lithium-ion batteries. During the initial charging process of lithium batteries, the electrolyte is reduced on the negative electrode surface, forming a stable and protective passivation film (SEI film). Lithium ion batteries may experience performance degradation due to changes in the negative electrode/electrolyte interface during subsequent storage and use.
The thickening/composition change of SEI film 1.1 The gradual decrease in power performance of batteries during use is mainly related to the increase in electrode impedance. The increase in electrode impedance is mainly caused by the thickening of the SEI film and changes in its composition and structure.
Due to differences and limitations in characterization methods and testing conditions, the results from different research institutions may vary, making it difficult to determine the specific composition of SEI films. According to previous reports, the composition of SEI film mainly includes two types of compounds: inorganic (Li2CO3, LiF) and organic [(CH2OCO2Li) 2, ROCO2Li, ROLi]. The composition and thickness of SEI film are not constant during use or storage.
