In the service life of the power battery, most of the time is in a state of shelving. Generally, after a long period of shelving, the performance of the battery will decline, generally showing an increase in internal resistance, a decrease in voltage, and a decrease in discharge capacity. There are many factors that cause the degradation of battery performance, among which temperature, state of charge and time are the most obvious factors.

Analysis of the aging of LiFePO4 power batteries in different shelving states, it is believed that the aging mechanism is mainly the side reactions of the positive and negative electrodes and the electrolyte (relative to the side reactions of the positive electrode, the side reactions of the graphite negative electrode are heavier, mainly the decomposition of the solvent, SEI The growth of the film) consumes the active lithium ions, and at the same time, the overall impedance of the battery increases, and the loss of active lithium ions leads to the aging of the battery storage; and the capacity loss of LiFePO4 power batteries increases seriously with the increase of storage temperature, compared to The capacity loss is smaller as the stored state of charge increases.

Storage temperature has a great influence on the aging of LiFePO4 power battery, and the influence of storage state of charge is second; and a simple model is proposed. The capacity loss of LiFePO4 power batteries can be predicted based on factors related to storage time (temperature and state of charge ). In a certain SOC state, with the increase of the shelf time, the lithium in the graphite will diffuse to the edge, forming a complex complex with the electrolyte and electrons, resulting in an increase in the proportion of irreversible lithium ions , SEI thickening and conductivity. The increase in impedance caused by the decrease (inorganic components increase, some have a chance to re-dissolve) and decrease in the activity of the electrode surface together contribute to the aging of the battery.

Differential scanning calorimetry (DSC) did not find any reaction between LiFePO4 and different electrolytes (the electrolytes were LiBF4, LiAsF6 or LiPF6), regardless of the charged or discharged state, in the temperature range from room temperature to 85 °C. However, when LiFePO4 is immersed in the electrolyte of LiPF6 for a long time, it will still show a certain reactivity: because the rate of reaction to form the interface is very slow, there is still no passivation film on the surface of LiFePO4 after immersion for one month to prevent it from further reacting with the electrolyte.

In the shelving state, harsh storage conditions (high temperature and high state of charge) will increase the degree of self-discharge of the LiFePO4 power battery, making the aging of the battery more obvious.

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