At present, the mainstream commercial lithium-ion batteries are mainly divided into three categories according to the package form: soft pack, square and cylinder, the internal composition of the soft-packed lithium battery (positive electrode, negative electrode, separator, electrolyte) is not much different from that of square and cylindrical lithium batteries, the biggest difference is that the soft-packed battery uses aluminum-plastic composite film as the outer casing, and the square and cylindrical battery uses metal The material acts as a casing.