A dendrite-blocking polyimide-meta-aramid separator with ultrahigh strength and thermostability for high-security lithium-ion battery

Commercial polyolefin-based separators broadly applied in lithium-ion batteries (LIBs) seriously affect the safety and development of LIBs due to the poor thermostability and electrolyte wettability caused by its low melting point and non-polar structure. In this work, a simple self-adsorption crosslinking technology is invented to fabricate polyimide-meta-aramid (PI-MA) separators with superior thermostability, wettability and safety. This technology utilizes the hydrogen bond adsorption and MA self-adhesive effect to realize the close encapsulation of MA on the surface of PI nanofiber and form a compact crosslinking structure. Specifically, the PI-MA separator has no significant deformation at 300 °C, while PP has completely melted and contracted at 200 °C. The PI-MA exhibits an electrolyte contact angle as low as 6.1° and the faster electrolyte diffusion rate in both horizontal and vertical directions. Moreover, in the long-term stripping/plating characterization, the lithium symmetric cell with PI-MA exhibits the stable cycle performance at a current density of 2 mA cm−2 for 1000 h. Using LiNi0.8Co0.1Mn0.1O2 (NCM811) as cathode, the cell with PI-MA has a capacity retention rate of 82.1 % in the 300-cycle test at 1C, much higher than 58.3 % of PP separator. Compared with the cell assembled with PP separator exploding at 56 min, the cell with PI-MA discharged stably to the cut-off voltage within 160 min at 120 °C.