1.Battery material aging and decay

The materials inside lithium batteries mainly include: positive and negative electrode active materials, binders, conductive agents, current collectors, separators, and electrolytes. During the use of lithium batteries, these materials undergo a certain degree of decay and aging. Tang Zhiyuan et al. believed that the factors causing capacity decay in manganese acid lithium batteries include dissolution of the positive electrode material, phase changes in the electrode material, electrolyte decomposition, formation of an interfacial film, and corrosion of the current collector. Vetter et al. systematically and deeply analyzed the changes in the positive electrode, negative electrode, and electrolyte of the battery during cycling. The author believed that the formation and subsequent growth of the SEI film on the negative electrode would be accompanied by irreversible loss of active lithium, and the SEI film did not possess true solid electrolyte functionality. The diffusion and migration of substances other than lithium ions would lead to gas generation and particle rupture. In addition, changes in material volume during cycling and the precipitation of metal lithium would also lead to capacity loss.

2. Charge and discharge system 

The charge and discharge system mainly includes three aspects: charge and discharge method, rate, and cut-off conditions. Regarding the charge method, American scientist Mas proposed the concept of an optimal charging curve. He believed that the optimal charging current of a battery gradually decreases as the charging time increases, which can be expressed by the formula I=I0e-αt. In this formula, I represents the receivable charging current; I0 represents the maximum initial current at the time t=0; t represents the charging time; and α represents the decay constant. The relationship curve between I and t is shown in follow Figure.

3.Temperature

Different types of lithium batteries have different optimal operating temperatures, and both excessively high and low temperatures can have an impact on the service life of the batteries.

4.Cell Consistency

Battery packs typically consist of hundreds or even thousands of individual cells connected in series or parallel. In addition to the aforementioned factors influencing their cycle life, cell consistency is another crucial factor. Due to differences in materials and manufacturing processes, it is challenging to ensure the consistency of lithium-ion battery cells. In terms of materials, the uniformity of positive and negative electrode materials and electrolytes is crucial. Lithium batteries produced from the same materials and in the same batch often exhibit relatively better consistency.

In terms of manufacturing, the production process of lithium batteries is complex, involving multiple process parameters at each step. Poor control can lead to inconsistencies in parameters such as battery voltage, capacity, and internal resistance.

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