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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at any time at marketing@everexceed.com.
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