NiMH No. 7 battery

Research on NiMH No. 7 battery self-discharge and over-discharge

Research on self-discharge and over-discharge of lithium-ion batteries. As the energy density of lithium-ion batteries is further improved and the cost is further reduced, they have been widely used in electric vehicles and energy storage. The consistency of self-discharge and over-discharge of lithium-ion batteries is very important for the life and reliability of electric vehicles and energy storage systems. The research results on self-discharge and over-discharge of lithium-ion batteries in recent years are reviewed from the aspects of the formation mechanism, influencing factors and detection methods of self-discharge and over-discharge of lithium-ion batteries.

Research on self-discharge of lithium-ion batteries

Self-discharge is a phenomenon in which the capacity of the NiMH No. 7 battery is naturally lost during storage, which is generally manifested as a decrease in open circuit voltage after a period of storage. Lithium-ion NiMH No. 7 battery self-discharge can be divided into physical self-discharge and chemical self-discharge according to the reaction type. From the impact of self-discharge on the NiMH No. 7 battery, some people divide self-discharge into two categories: self-discharge in which the loss of capacity can be reversibly compensated and self-discharge in which the loss of capacity cannot be reversibly compensated. Usually, the capacity loss caused by physical self-discharge is reversible, while the capacity loss caused by chemical self-discharge is irreversible.

Lithium-ion batteries are widely used in various instruments and electric vehicles as energy systems due to their pollution-free, high specific energy, and long cycle life. The existence of lithium-ion NiMH No. 7 battery self-discharge not only causes the loss of NiMH No. 7 battery energy itself, but also reduces the life of lithium-ion NiMH No. 7 battery packs due to the inconsistency of self-discharge between batteries. The rapid decay of capacity causes a large error in the prediction of the NiMH No. 7 battery state of charge (SOC) by the NiMH No. 7 battery management system (BMS), and the electric vehicle control strategy fails, resulting in over-discharge of the electric vehicle NiMH No. 7 battery system.

Causes of lithium-ion NiMH No. 7 battery self-discharge

1. Causes of reversible capacity loss: The cause of reversible capacity loss is the occurrence of a reversible discharge reaction, which is consistent with the normal discharge reaction of the NiMH No. 7 battery. The difference is that the normal discharge electron path is an external circuit and the reaction speed is very fast; the self-discharge electron path is an electrolyte and the reaction speed is very slow.

2. Causes of irreversible capacity loss: When an irreversible reaction occurs inside the NiMH No. 7 battery, the capacity loss caused is irreversible capacity loss. The types of irreversible reactions that occur include: irreversible reactions between the positive electrode and the electrolyte, irreversible reactions between the negative electrode material and the electrolyte, irreversible reactions caused by impurities in the electrolyte itself, and irreversible reactions caused by micro-short circuits caused by impurities during manufacturing.

The self-discharge rate is an important parameter for measuring the life of lithium-ion batteries. The self-discharge process occurs inside the NiMH No. 7 battery and is related to the NiMH No. 7 battery materials and processes, and changes with changes in ambient temperature, storage time, and state of charge. Rapid detection of lithium-ion NiMH No. 7 battery self-discharge can shorten the time period for self-discharge parameter measurement and improve its accuracy. Self-discharge detection can be applied to NiMH No. 7 battery combination technology, and in practical applications, it provides new theoretical data for NiMH No. 7 battery consistency research and sorting work, thereby improving the performance of lithium-ion batteries.

Research on over-discharge phenomenon of lithium-ion batteries

When the NiMH No. 7 battery discharges the internal stored electricity and the voltage reaches a certain value, it will continue to discharge, which will cause over-discharge. The discharge cut-off voltage is usually determined based on the discharge current. Overdischarge of batteries may bring disastrous consequences to batteries, especially high current overdischarge or repeated overdischarge. Generally speaking, overdischarge will increase the internal pressure of the NiMH No. 7 battery, damage the reversibility of the positive and negative active materials, and even if charged, the capacity can only be partially restored and will be significantly attenuated.

In order to ensure that some lithium ions remain in the graphite layer after discharge, the minimum discharge termination voltage must be strictly limited, that is, lithium-ion batteries cannot be overdischarged. The discharge termination voltage is usually 3.0V/cell, and the minimum cannot be lower than 2.5V/cell. The length of NiMH No. 7 battery discharge time is related to the NiMH No. 7 battery capacity and discharge current. NiMH No. 7 battery discharge time (hours) = NiMH No. 7 battery capacity/discharge current; the discharge current of lithium-ion batteries should not exceed 3 times the NiMH No. 7 battery capacity, otherwise the NiMH No. 7 battery will be damaged.

Impact of overdischarge of lithium-ion batteries

1. The termination voltage value specified in the NiMH No. 7 battery standard is the voltage value reached when the NiMH No. 7 battery is continuously discharged; but in actual use, it is mostly intermittent discharge, so even if the discharge reaches the specified termination voltage value, overdischarge often occurs.

2. After the NiMH No. 7 battery is discharged to the termination voltage, the NiMH No. 7 battery voltage will automatically increase after standing for several minutes to half an hour. This misleads users into thinking that the NiMH No. 7 battery can continue to discharge, thus causing the NiMH No. 7 battery to be over-discharged.

3. Although the NiMH No. 7 battery capacity can be increased compared to the previous time by periodic treatment charging and discharging, continuous excessive deep discharge will not only fail to further activate the active substances that have not participated in the reaction, but on the contrary will cause positive grid corrosion and the conversion of part of α-PbO2 to β-PbO2, which will inevitably shorten the NiMH No. 7 battery cycle life. The deeper the discharge depth, the faster the NiMH No. 7 battery capacity decreases, the more obvious the side effects of over-discharge and periodic treatment appear, and the shorter the NiMH No. 7 battery cycle life.

At present, most electronic products use lithium-ion batteries. Since its advent in 1990, lithium-ion batteries have developed rapidly and widely used in society due to their excellent performance, and lithium-ion NiMH No. 7 battery manufacturers have also achieved the largest scale of development. Do not charge lithium-ion batteries to 100% full, let alone use up the power. When conditions permit, try to keep the NiMH No. 7 battery power near half full, and the smaller the charging and discharging amplitude, the better.

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