Anionic metal-organic framework modified separator boosting efficient Li-ion transport

Abstract

Low lithium ion (Li+) mobility and thermal stability of polyolefin separator are crucial obstacles that limit the utilization of Li metal electrodes in the age of rapid acceleration toward high-energy-density rechargeable batteries. Herein, we report anionic metal-organic frameworks (MOFs) modified separator to overcome the barriers. By grafting –SO3− group onto the Universitetet i Oslo (UIO) structure, the anionic MOFs nanoparticles are synthesized (noted as UIO-SOLi). The UIO-SOLi is adhered on the surface of Celgard 2400 via polyacrylic acid (PAA) to fabricate the modified separator (UIOSOL@PP). The MOFs coating optimizes the wettability and thermal stability of the pristine separator. Negatively charged moieties –SO3− within the pore surface electrostatically repel anions while facilitate the transport of Li+, thus achieving a high Li+ transference number (tLi+) of 0.82. The effective Li+ transport relieves the concentration polarization, regulates the Li+ flow and realizes the uniform deposition of lithium. By implementing the UIOSOL@PP separator, the LiFePO4|Li cells deliver superior rate performance and cycling lifespan that renders a high discharge capacity retention of 155 mAh g−1 over 600 cycles at 1C. These results indicate that anionic MOFs modified separator is a promising strategy to modulate Li+ flow and assist with efficient long-term operation of lithium metal batteries.