Polypropylene (PP) separators are widely used in lithium-ion battery (LIBs) separators due to their excellent mechanical properties, high resistance of electrolyte corrosion, superior ionic permeability, easy processability, and low cost. However, PP separators have poor affinity with electrolytes and lack the function of inhibiting lithium dendrite growth, which limits the performance of LIBs. In this paper, polypropylene/polydopamine (PP-PDA_x) composite separator was rapidly prepared by solution polymerization under the catalytic action of sodium periodate (SP), and its properties were systematically studied. The results show that when the modification time is 4 h and the deposition amount of PDA nanoparticles is 0.075 mg·cm^-2, that is, the PP-PDA₄ separator has the maximum electrolyte absorption rate of 324%, the contact angle drops to 9°, and it also exhibits the best electrochemical performance with an ionic conductivity of 0.51 mS·cm^-1. When a LiFePO₄/PP-PDA₄ separator/Li coin-type battery is assembled, the discharge capacity can still remain at 113.9 mAh·g^-1 after 100 cycles at 1C. In addition, the PP-PDA₄ separator shows a remarkable ability to inhibit lithium dendrite growth.

1.2 g of Tris was dissolved in deionized water, and adding hydrochloric acid solution to adjust pH to 8.5 dissolved a certain amount of dopamine hydrochloride in the prepared Tris buffer solution. The polypropylene separator was rolled into a column and immersed in the solution for 5 min to make the surface of the polypropylene septum was evenly wetted on separator. Added Sodium periodate to the solution and fully steep for 2, 4 h, and 6 h. After that, PP-PDA_x separators were be obtained after drying.

In this paper, the optimal sample is PP-PDA₄ that the polydopamine deposition is 0.075 mg·cm^-2, PP separator as a control group. PP-PDA₄ electrolyte contact angle decreased 82% to 9°, the tensile strength increased from 101 MPa to 110 MPa. And tested the separators electrochemical performance, the ionic conductivity increased from 0.26 mS·cm^-1 to 0.51 mS·cm^-1. Introduced positive and negative electrode materials to assemble the full cell, and the discharge specific capacity of PP-PDA₄ was the highest, which was up to 128.2 mAh·g^-1, and tested the rate performance of the full cell in the range of voltage from 2.5 V to 4.2 V, and the current density from 0.2 C to 2C. the discharge capacity of PP-PDA₄ is increased by 9%, 17%, 30%, and 9% compared with PP at 0.5, 1, 2 C, and 0.2 C. Finally, assembled Li/separator/Li batteries to evaluated the ability of PP-PDA₄ to inhibit lithium dendrites, and PP-PDA₄ could work stably for 400 h and maintain at a lower voltage polarization. Meanwhile, the SEM photographs of the lithium film after cycling showed that the lithium deposition was more uniform.

In summary, PP-PDA_x separator were synthesized rapidly via solution polymerization catalyzed by SP. This strategy exploits the intrinsic properties of PDA to enhance the affinity between the separator and the electrolyte, thereby markedly improving electrochemical performance and concurrently inhibiting lithium dendrite formation. Under the catalytic effect of SP, the optimum modification time is only 4 h. This treatment not only improves wettability but also significantly boosts electrochemical performance, without compromising the separator's integrity.