Surface Modification And Characterization Of Polypropylene Separator In Lithium-ion Battery

Polypropylene(PP) separator used in the Lithium-ion battery has stable chemical property, corrosion resistance and its tiny pores have self-closing function when temperature reach a certain degree. But polypropylene separator has a disadvantage of poor heat resistance, the pores of conventional polypropylene membrane are uneven, at the same time, its ability to taking in electrolyte is poor, the lithium-ion battery has bad performance at high rate, surely its long cycle capacity should be to improve, so should the safety performance.In order to improve the performance of heat resistance、liquid absorption and fluid retention and the state of the membrane pores within the PP separator, to improve the long cycle performance and high-rate charge-discharge performance of the lithium-ion battery, this article makes use of the superior bond strength and adhesion of dopamine(DA) produced from the oxidation and polymerization process and thereby improves the binding strength between inorganic ceramic materials(SiO2 nanoparticles, SiO2 nano--tubes, SiO2 hollow spheres) and PP membrane, then fix them on the surface of PP separator, in this way, a SiO2/polydopamine(PDA)/PP composite membrane is produced successfully, finally explores the structure and electrochemistry properties of different composite membranes.The results showed that, compared with PP membrane, different kinds of SiO2 nanoparticles/PDA/PP composite membrane showed good performance of lyophilicity(composite membrane’s average contact angle was 51.5±1°), liquid absorption and fluid retention, at the current density of 548 m A/g,after 100 cycles,the Li Co O2 / Li half-cells assembled by composite membrane showed initial charge a discharge capacity of 160.8 m Ah/g(PP membrane was 152.3 m Ah/g), capacity fading rate of 43.4%(polypropylene membrane was 43.7%) and better cycle stability; at 0.2C rate, half cell assembled by different formulations of the composite membrane exhibited excellent charge-discharge characteristics, at the rate of 0.2C~1C, half cell assembled by composite membrane has better battery performance, but poor high-rate charge-discharge characteristics between the rate of 2C and 8C.Different kinds of SiO2 nanotube/PDA/PP composite film also showed good performance of lyophilicity(composite membrane’s average contact angle was 50.5±2°, liquid absorption and fluid retention, when the mass ratio of SiO2 nanotubes and dopamine was 2:1 or 3:2, composite film has excellent heat resistance; half cell assembled by composite membrane showed higher initial charge-discharge capacity(158.1 m Ah/g) and less capacity decay rate(35.1%) at the current density of 548 m A/g; it also showed good cycle stability at 0.2C~2C rate, its discharge capacity is higher than the half-cell assembled by polypropylene film, but poor high-rate charge-discharge characteristics at the rate of 2C~8C.Different kinds of SiO2 hollow sphere/PDA/PP composite membranes also showed good performance of lyophilicity(composite membrane’s average contact angle was 44.8±1°), liquid absorption and fluid retention, the half cells assembled by composite membrane, at the current density of 548 m A/g, 1370 m A/g, 2192 m A/g, exhibited good cycle stability and a high initial charge and discharge capacity after 100 charging and discharging cycles; at 0.2C~8C rate, half cell assembled by SiO2 hollow sphere/PDA/PP composite films showed a distinct advantage of better rate performance, especially high rate discharge performance.