Competing for PET/PP/PI composite current collector base membrane technology route.

  At present, composite current collectors are one of the hot materials that have attracted much attention in the power battery industry. In terms of technical route selection, basic material selection and product application, the choice of PET and PP has an important impact on the technical route and application selection of finished products.

  Since 2021, the market has begun to widely promote the concept of "PET copper foil", because of its multiple potential advantages and huge market space, it has attracted rapid investment from many listed and non-listed companies. A few years ago, some leading lithium battery companies cooperated with material manufacturers to carry out a large number of composite current collector technology development and application development.

  Industry information shows that leading companies not only choose PET as the base material in the field of composite current collectors, but also continue to promote various routes such as PP and PI.

  Recently, some people think that in fact, PET cannot meet the requirements of long cycle life for power batteries, so it has been technically eliminated in practical applications. What are the facts?

  First of all, from the perspective of PET, PP, and PI based on the composite current collector process, that is, to evaluate the ability to adapt to vacuum coating combined with water electroplating, from the perspective of high temperature resistance and physical strength, PI belongs to the highest grade, and its melting point The temperature reaches above 360°C. However, due to the high cost of PI ultra-thin film at present and in the foreseeable few years, it cannot be directly selected as a material for mass production of composite current collectors.

  The temperature resistance and physical properties of PET are at the middle level, and its melting point reaches above 260°C. For applications that need to participate in high temperature and high current intensive processes, although challenging, it still has great feasibility. In addition, as a polar material, PET is easy to chemically bond with metal substances, so as to obtain a strong coating binding force.

  In contrast, PP film has low temperature resistance and physical strength, and its melting point is about 160°C. It is difficult to process, and due to its non-polar nature, there are great technical difficulties in forming a high-adhesion coating on the surface.

  From a chemical stability point of view, however, the opposite is true. PET, or polyethylene terephthalate, is physically stronger and easier to use as a substrate for coating processing, but it is prone to degradation in ethylene glycol, water, methanol, and ammonia. Methanol has been industrialized for many years and is still used to recycle PET photographic film. In addition, the presence of lithium alkoxides (components of the SEI film) that catalyze PET degradation at the negative end of the lithium battery can significantly promote the degradation of PET. In addition, even if the degradation of PET is not complete, as long as the surface of PET and copper film is slightly degraded, it will cause fundamental damage to PET copper foil.

  Therefore, when selecting a composite current collector material, it is necessary to comprehensively consider multiple factors such as the physical properties of the material, temperature resistance, chemical stability, and production costs to meet the requirements of power batteries and ensure product quality and performance.