Flame retardant encapsulation in MOFs: A promising universal approach for enhancing battery performance

As one of the key components in a lithium-ion battery, separator plays an important role in guaranteeing the battery safety in practical application. However, polyolefin-based battery separators are prone to causing safety problems, such as internal short circuit and thermal runaway, due to their poor thermal stability, low melting point and flammable nature. In this work, a unique capsule structure with a zeolitic imidazolate framework-8 (ZIF-8) as the shell and flame retardant (FR) as the core was designed by a one-step in-situ growth method. The porous ZIF-8 shell can successfully prevent the flame retardant, i.e., hexachlorocyclotriphosphazene (HCCP) from decomposing into electrolyte, therefore, retaining the electrochemical performance. When fire accident occurs, the ZIF-8 shell collapses and releases the HCCP before further damage could take place to the battery. The results show that ZIF-8/FR-50@PP keeps 98 % area retention rate at 190 °C, and the self-extinguishing time (SET) is 2 s. The Li//NCM-811 cells based on ZIF-8/FR-50@PP deliver a remarkable discharge capacity of 50 mAh·g−1 even at 10C, and a high capacity retention of 68 % at 1C over 300 cycles. This work provides a new design strategy for high safety and good performance battery.