Effect of Recharging Multiplicity on Decline of Lithium-ion Battery

Lithium-ion batteries in use with the increase in the number of charge and discharge, the capacity is gradually reduced, which is what we call decline, the intuitive feeling is that the electricity is less and less used. For example, when we first buy a cell phone, full power can be used all day, but as we use it, we can only support half a day of use. This is the decline in the capacity of lithium-ion batteries in use. This is easier for consumer electronics to replace faster, and we may have replaced new phones before the battery capacity declined too much. However, it is not so easy to solve for a durable product such as an electric car with a long life. In general, the service life of a car can reach about 10 years. During this period, it may take 1,000 to 2,000 charges(assuming every other day). Charge). In order to meet the consumer's demand for electric vehicles, it is necessary to put forward certain requirements for the life of the lithium ion battery of electric vehicles.

There are many factors that affect the life of lithium ion batteries. The use temperature, charging and discharging current, charging and discharging cut-off voltage and other factors will affect the decline and fall speed of lithium ion batteries. The mechanism that causes the decline of the capacity of lithium-ion batteries can also be divided into three categories: increased internal resistance and polarization, loss of positive and negative polar active substances, and loss of Li. Different external factors have different effects on these three. For example, the batteries of LiFePO4 materials generally have very good cycling performance, but research such as DerekN. Wong of the University of Texas at Arlington found that the conditions of use have an important influence on their cycle life. When Derek N. Wong performed 15C pulse discharge and 15C continuous discharge on the 26650 type LiFePO4 battery, respectively, the two discharge systems had completely different effects on the LiFePO4 battery. The capacity of the 15C pulsed discharge lithium iron phosphate battery decays very fast. After 40 times, 15C discharge can not be performed, but 1C discharge can still be performed. The decay rate of 1C discharge is 6 % / 20 times. The 15C continuous discharge battery capacity decays slowly, and 15C discharge can still be performed after 60 times, but the 1C multiple rate decays faster than the 15C pulse discharge, reaching 14 % / 20 times. Mechanism studies have shown that the 15C pulsed discharge battery contains more LiF in the negative SEI membrane, and LiF has greater obstacles to the diffusion of lithium ions, resulting in a rapid increase in the Li + diffusion impedance and charge exchange impedance of the battery. As a result, the polarization voltage of the battery is too large during the charging and discharging process, resulting in a rapid decline in the discharge capacity of LiFePO4.

The discharge system of lithium-ion batteries depends to a large extent on the user, and a good discharge system is not necessarily applicable to some users. However, the charging system is mainly controlled by the designer. Therefore, the study of the impact of the charging system on the decline of battery life can better guide our design of lithium-ion batteries. Yang Gao of Beijing Jiaotong University and others studied the effects of different charging systems on the lifetime decline of lithium-ion batteries, and studied its mechanism, and proposed a model for the lifetime decline of lithium-ion batteries. YangGao's research shows that when the charging current and cut-off voltage exceed a certain value, the decline of lithium ion batteries will be greatly accelerated. In order to reduce the decay rate of lithium ion batteries, different systems need to be targeted. Select the appropriate charge and discharge current and cut-off voltage.

The page contains the contents of the machine translation.