Bioinspired OH-BNNS/aramid fiber separator with high mechanical and temperature-tolerant properties for lithium metal batteries

Battery separator is considered as an important component to avoid direct contact between cathode and anode. The development of separators with high mechanical properties and excellent thermal stability remains a key challenge. Here, free-standing hydroxylated boron nitride nanosheet (OH-BNNS)/aramid nanofiber (ANF) nanocomposite separators with nacre-like structure were prepared by combining high modulus ANF with OH-BNNS through sol-gel conversion process. The OH-BNNS/ANF separator with 20 wt% OH-BNNS loading offers benefits of excellent mechanical properties (strength: 114.86±3.47 MPa, modulus: 3.66±0.29 GPa), high decomposition temperature (507.8°C) as well as better electrolyte wettability (contact angle ˂5°) compared with commercial polypropylene (PP) separator. A layered structure formed by the overlapped OH-BNNS and ANF contributes to constructing uniform lithium-ion transport channels and suppressing the growth of lithium dendrites. Meanwhile, even under the aging condition of 120°C, the battery with 20 wt% OH-BNNS/ANF separator still maintains stable electrochemical performance and shows high thermal stability. As expected, the Li/lithium titanate (Li/LTO) battery using 20 wt% OH-BNNS/ANF as the separator achieves a capacity of 172.7 mAh g-1 with a high discharge capacity retention of 96.5% after 500 cycles, revealing the long-term cycle stability.