Lithium battery life is one of the most important factors for electric car buyers. How does a lithium battery charge? Aging always comes with failure, but to be fair, aging and failure are two concepts. Aging, which refers to the degradation of battery performance parameters over time, is a quantitative process, and the factors refer to the maximum available capacity, internal resistance and battery power. Failure is the process of the battery completely losing the ability to work, short in time, is a qualitative change. Summary of aging is an important cause of failure.
Factors affecting aging.
The best working temperature of energy resources is 15 ℃-35 ℃, but every day application, it is not possible to fully meet the battery’s needs, therefore, the most common conditions are affected by aging of the battery is high temperature, low temperature.
In addition to the environment, the components of the battery will also play a role in promoting or reducing aging, so the choice of cell charger and hard drive has a great impact. Under the action of the external factors listed above, the battery electrode and side reactions other than normal charging and purification occur during the electrochemical reaction, resulting in the phenomenon of old age.
A common aging process.
A specific description of the aging process is closely related to the selection of positive and negative electrode materials, electrolytes and diaphragm, so this article will describe the aging process in Ontario and will not explain some things in detail enough at this time.
1. High temperature aging.
50℃ to 60℃ is the limit of the maximum working temperature that the general lithium battery can provide. When an electrochemical reaction is carried out at a high temperature, the electrolyte is active and causes a destructive reaction, and the products produced are attached to the cathode material, which is the food of the cathode; the material of the cathode structure deteriorates, the lattice structure collapses due to the lack of sufficient material support, the free space for lithium ions decreases, the ability of the cathode to accept lithium ions decreases, causing death of the battery.
At the same time, these products reflected by the cathode material, floating in the electrolyte, can stick to the surface of the positive and negative electrodes. The surface of the electrode is covered with substances that cannot participate in the process of charging and discharging, which prevents the process of electrochemical processes and increases the resistance of the cell.
The effect of the high temperature process and aging usually occurs on the positive electrode, and the effect on the negative electrode is a small percentage.
2. Aging at low temperatures.
When the temperature reaches below 0 ℃, the performance of the Li-ion battery begins to be greatly affected by the low temperature. The SIE film, the passivation film of the reaction between the negative electrode material and the electrolyte causes the base to be produced, with a protective effect against negative factors.
The thickening of the SEI film makes it difficult for lithium ions to pass through the film layer and reach the cathode, which increases the internal resistance of the cell when combined with the reduction of conductive lithium ions.
When charging at low temperature, especially when the charging current is very high, another reaction occurs at the negative electrode – the breakdown of lithium monomer. At low temperature, the activity of lithium ions decreases and is not charged, causing lithium ions to accumulate around the negative electrode and cannot pass through the SEI film to reach the coating of the negative electrode, then put in ‘up electrode is not good, forming a. layer of pure lithium. This process usually occurs when charging at high temperatures and cannot be reversed. As the process accumulates, lithium monoliths continue to accumulate and dendrites continue to grow, increasing the risk of diaphragm perforation.
Lithium batteries work at a low temperature, aging problems often occur in poor electrodes, positive reactions are also present, but the effect is not important.
3. High-current charging and discharging.
Discharge and current more than the ability to discharge processing, on the other hand, the thermal effect of the current, resulting in the temperature of the battery itself, the effects of high temperature aging gradually become stronger; On the other hand, the high current makes the high lithium ion to be absorbed into the cathode material, which affects the stability of the material.
High discharge current, one problem of heat production and the cathode material damaged the stability problem. At the same time, more lithium ions are transferred to the negative electrode, than the capacity of the negative electrode, causing the inclusion of lithium monomers. Not only will he lose ability, but the risk of running for a long time increases, the injury is more serious.
4. Charging and charging across the range and low voltage.
Charging above the voltage and discharging below the voltage will cause the cathode material to change over time, which will reduce the free space to accept lithium ions and affect the maximum capacity of the cell.
5. Self-isolation.
Battery discharge occurs at anytime and anywhere, and the self-discharge process is aggravated when the temperature is high and the level of charge is high. The self-discharge process determines whether or not the capacity of the battery can be changed. The self-released product, attached to the surface of the electrode, blocks the lithium-ion channel and reduces the concentration of lithium-ion, which leads to the loss of the cell’s permanent capacity.
Aging module.
Li-ion batteries are connected in series and in order to form a module, and the aging of the module directly affects the aging of the single cell. Also, the aging of the cores leads to the destruction of the unity between the cores, which mean that the aging of the module increases as a function of the aging of the cores.
In addition to the main effect of aging, the module will also be affected by vibration and oxidation, as well as corrosion of the conductive parts, which will make the degree of aging worse. Between the middle of the module and the copper bar, and between the copper bar and the end of the module are kept in close contact by screwing or screwing the connection to ensure that the resistance is within the limit common sense. The increase in connection resistance brought about by vibration and oxidation changes the position of the resistance distribution within the module. These changes can affect the cell’s voltage detection results, which in turn affect the charge/discharge process and the cell’s measurement settings.
The harsh environment and excessive work schedules make the aging process more valuable and easier for researchers to observe. In fact, the aging process remains silent. There are two life cycles for cells, the calendar life and the cyclic life. With the name of the calendar life, we can experience the insomnia of old age. Therefore, research on the factors affecting the aging of electrical cores is only required to reduce the rapid aging caused by regular operation.
