Polydopamine-modified cellulose-based composite separator for inhibiting dendritic growth of lithium metal batteries

The inhomogeneous pore structure and lack of polar groups in lithium metal battery separators lead to uneven transport of Li+ through the separator, the uneven flux of Li+, and eventually the formation of lithium dendrites. Therefore, to provide uniform Li+ transport and inhibit the growth of lithium dendrites, a polydopamine-modified cellulose membrane (PDA-CM) was created by oxidative self-polymerizing dopamine and binding it to the surface and interface of the cellulose membrane through hydrogen bonds. The successful preparation of the PDA-CM separator by PDA-modified cellulose membrane by hydrogen bonds was proved by the FT-IR test. TGA, thermal shrinkage test, tensile strength test, FESEM, and porosity test results indicated that neither the PDA-CM nor the CM separators shrank at 160 °C, the PDA-CM separator also had better tensile strength (Stress = 31.1 MPa), and uniform pores (Porosity = 54.95 %) with homogeneous Li+ flux. The polar functional groups (-NH- and -OH) in PDA improved the electrolyte uptake rate (Electrolyte uptake rate = 469.77 %), the electrolyte retention (Electrolyte retention = 409.04 %), and electrolyte wettability (Contact angle = 18.35°) of the separator and promoted the uniform distribution of Li+ through the PDA-CM separator. In addition, the PDA-CM separator had better ionic conductivity (1.54 × 10−3 S·cm−1) and lower impedance (849 Ω). The catechol on the PDA molecule created strong adhesion between the separator and the lithium metal, reduced the local tension on the surface of the lithium metal and inhibited dendrite growth. The lithium metal anode remained smooth after cycling. The lithium metal battery prepared by the PDA-CM separator showed decent cycle performance and remained a high capacity retention rate (90.48 %) after 100 cycles. This study provides a new solution for the modification of cellulose-based lithium metal battery separators, which can achieve uniform transmission of Li+, inhibit the growth of lithium dendrites, and improve battery performance.