Analyze the factors affecting the life of lithium batteries

　　The service life of lithium batteries is a indicator that must be paid attention to in the use of lithium ion batteries. Generally speaking, the service life of lithium -ion batteries is mainly affected by two factors: 1) use time; 2) the number of cycles. According to the attenuation rate of lithium ion batteries, the attenuation rate of the battery can be divided into early linear attenuation rates and later non -linear attenuation rates. The typical feature of the non -linear decline process is that the capacity of the battery has decreased significantly in a short period of time. This is what we usually call capacity diving, which is very unfavorable to the use of batteries and steps.

　　In the experiment, the battery used by Simonf.schuster was E-One Moli Energy's IHR20250A battery. The cathode material is NMC material, the anode material is graphite, and the nominal capacity is 1.95AH. In the experiment, the effects of voltage windows, charging ratios, discharge rates, and temperature on the non -linear attenuation of batteries. The specific experiments are arranged as shown in the following table.

　　The main results are as follows:

　　1. The impact of working voltage windows on the growth of the negative SEI film is that due to the width of the electrochemical window, the dissolution of the transition metal element is enhanced, and the dissolved transition metal element is migrated to the negative surface, which accelerates the growth of the negative electrode transition metal film. The results showed that the negative polarization conditions accelerated the decline of lithium, so the negative polarization precipitated lithium in advance, resulting in non -linear attenuation earlier.

　　2. The impact of charging and discharge multiplication rate

　　Because the non -linear attenuation of lithium ion batteries is mainly caused by the precipitation of lithium metals on the negative surface, the charging and discharge current is closely related to the occurrence of non -linear attenuation of lithium ion batteries. The battery charging at a 1C rate shows the trend of non -linear attenuation from the beginning, but if we reduce the charging current to 0.5C, the time node of the battery is that the non -linear decay will be greatly delayed. The impact of the discharge current on the non -linear attenuation of the battery can almost ignore it. This is mainly because as the charging current increases, the polarization of the negative electrode has also increased significantly, which leads to the significant increase in the risk of lithium from the negative electrode. The precipitated porous metal metal promotes the decomposition of electrolytes and accelerate. The decline in negative dynamic performance leads to an early occurrence of non -linear decay.

　　3. The effect of temperature

　　Temperature has a very important impact on the dynamic characteristics of negative electrode, so temperature also has an important impact on the time of battery non -linear attenuation.

　　A non -linear decline at the latest battery in a 35 ° C cycle. If we reduce the battery's voltage window to 3.17-4.11V, the battery attenuation rate of the early 35 ° C and 50 ° C cycle was relatively consistent, but the battery that circulated at 35 ° C at the end of life began to show non-linear decline. This is mainly due to the deterioration of the dynamic conditions of the battery at low temperature, which makes the negative electrode easier to be analyzed as lithium, which accelerates the growth of the SEI membrane, resulting in further deterioration of negative dynamic conditions, resulting in non -linearity of early lithium -ion batteries.

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