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Surface coating modification on a polyethylene separator serves as a promising way to meet the high requirements of thermal dimensional stability and excellent electrolyte wettability for lithium ion batteries (LIBs). In this paper, we report a new type of surface modified separator by coating polyvinylidene fluoride (PVDF) organic particles on traditional microporous polyethylene (PE) separators. The PE separator coated by PVDF particles (PE-PVDF separator) has higher porosity (61.4%), better electrolyte wettability (the contact angle to water was 3.28° ± 0.21°) and superior ionic conductivity (1.53 mS/cm) compared with the bare PE separator (51.2%, 111.3° ± 0.12°, 0.55 mS/cm). On one hand, the PVDF organic polymer has excellent organic electrolyte compatibility. On the other hand, the PVDF particles contain sub-micro spheres, of which the separator can possess a large specific surface area to absorb additional electrolyte. As a result, LIBs assembled using the PE-PVDF separator showed better electrochemical performances. For example, the button cell using a PE-PVDF as the separator had a higher capacity retention rate (70.01% capacity retention after 200 cycles at 0.5 C) than the bare PE separator (62.5% capacity retention after 200 cycles at 0.5 C). Moreover, the rate capability of LIBs was greatly improved as well—especially at larger current densities such as 2 C and 5 C.

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Abstract. The volume stability, freezing-thawing cycles, the resistance of chloride ions and sulfate attack of RPC with different content (0%, 40%, 100%) of silicon powder are investigated in this paper. The results demonstrate that the volume stability and the resistance of freezing-thawing for RPC with 40% silicon powder are improved because of a high compactness, whose shrinkage is only 350 × 10 -6 for 60 d and tends to this value after 60 d, and the relative dynamic modulus is more than 99% after 300 times of freezing-thawing cycles. Meanwhile, with a high content of active SiO2 and a low magnesium content, the resistance of chloride ions and sulfate attack of RPC with 40% silicon powder are improved attributing to a high compact structure and a low level of magnesium sulfate attack. This leads an increase of the compressive strength with 5.6% after 150 times of wetting-drying cycles in the solution with 5% Na2SO4.