Applications of polymers in lithium-ion batteries with enhanced safety and cycle life

Lithium-ion batteries (LIBs) exhibiting high capacity and energy density are in high demand in emerging markets such as electric vehicles and energy storage systems. However, these LIBs often show intrinsic shorter cycle life and higher risk of short circuit, which may result in thermal runaway and explosion. This work reviewed those polymers employed to improve cycling performance and safety of LIBs. First, some novel separator membranes, which prevent the direct contact of cathode with anode to induce disastrous short circuit, were developed with an aim at imparting safety to LIBs. For example, composite separators comprising ceramic and polymer show higher abuse tolerance for LIBs. Surface modification of the cathode active materials by polymers (e.g., polyimide (PI)) results in greatly enhanced electrochemical performance of LIBs, especially for layered LiNixCoyMnzO2. Another unique technology was developed, which involves coating reactive oligomer/polymer on the particle surface of cathode active materials to effectively limit the probability of short circuit and, eventually, thermal runaway of cells in an abusive environment. The fundamental mechanisms of the secondary oligomer/polymer reaction to form a dense highly cross-linked film on the pellet surface to inhibit thermal runaway were then discussed. This was followed by the last topic on polymer coated anodes used to suppress Li dendrite formation at the anode surface. Li dendrites may cause short circuit and capacity fading during cycling in LIBs. Some representative polymers including PI, polyurea and polycyanoacrylate that can greatly inhibit dendrite formation at anode surface were discussed.