Two strain modes and transition point of 18650 lithium-ion battery at different charging rates

Abstract

The safety issues of lithium-ion batteries are one of the biggest obstacles restricting the development of lithium-ion batteries. Excessive charging rate is not conducive to extending the cycle life of lithium-ion batteries. However, there is a lack of research on the upper limit of the charging rate of lithium batteries. The strain of the battery can reflect the change of the internal material during the charging process. The purpose of this study is to explore the charging rate of the strain transition point of lithium-ion batteries and the strain characteristics of the batteries after exceeding this rate. The experiments conducted at different rates and temperatures on battery strain revealed that the transition point of strain in the battery occurs at a rate of 2C. When the charging rate is lower than 2C, the battery strain increases monotonically, which is similar to the step response of the first-order system. When the charging rate exceeds 2C, the battery strain experiences excessive strain due to severe lithium plating, showing a step response similar to a second-order system with a spike representing an overshoot phenomenon. As the charging rate continues to increase, the overshoot peak of the battery ‘s strain becomes more obvious. The experimental results confirm that the charging rate of the 18,650 ternary lithium-ion battery used in the experiment should not exceed 2C, as it would lead to excessive strain in the battery.