Research On PMMA-TEGDMA Based Gel Polymer Electrolyte Of Lithium-ion Battery

Lithium-ion gel electrolyte is the key point to improve the safety performance of the battery. The gel electrolyte fixes the plasticizer (electrolyte) in the gap of the polymer tightly, thereby ensuring favorable safety. However, due to the existence of the matrix, the initial capacity, the cycle life and the discharging capacity under low temperature of the gel electrolyte differ significantly from those of commercialized lithium-ion battery. As PMMA-based gel electrolyte is one of the matrixes frequently researched, this paper is mainly focused on the factors influencing the initial capacity, the cycle life and the discharging capacity under low temperature after PMMA and TEGDMA are copolymerized.1. Optimizing the proportion of MMA and TEGDMA, and improving the conductivity and liquid absorption. The test result shows that the liquid absorption can be improved through the copolymerization of MMA and TEGDMA. For the copolymerization with10%MMA and5%TEGDMA, there is no free electrolyte in the gel electrolyte after60℃thermal polymerization. All the monomers polymerize totally, and the structure of plasticizers (electrolyte) did not change. The conductivity of the co-polymerized gel electrolyte is larger than4.7mS/cm.2. Established the suitable formation method of the PMMA-TEGDMA battery. Through adopting the cycle of the liquid injection-thermal polymerization-formation-discharge, not only the battery can be fabricated with low internal resistance, effective cycle, as well as high-capacity, but also the gel electrolyte are high performance.3. Investigating the effect of different solvents and lithium salts on the performance of the PMMA-TEGDMA based gel electrolyte. In the cyclic lactone, the EC is more conducive to improve the capa city and the cycle performance than the PC. For the chain ester, the DMC can improve the electrical conductivity and cycle performance, but decreases the initial capacity. DEC can improve initial capacity, but poor cycle performance, large internal resistance and low conductivity. The performance of the EMC is between DMC and DEC. In the test for the1Ah cobalt acid lithium batteries, as the LiPF6is replaced by0.1mol/L LiTFSI, the initial capacity battery increases75mAh, and the retention rate of100-weeks-capacity increases3.6%. While the battery and capacity cycle performance are poor as the LiPF6is replaced by0.1mol/L LiBF4.4. Researching the applications of the film forming additive VC, VEC,1,3-PS in PMMA-TEGDMA based gel electrolyte. When the1,3-PS, VEC was used alone for the film forming additives, the initial capacity of the battery is low and the cycle performance is lower than VC. As the1,3-PS or VEC and VC are used together, the cycle performance is improved significantly. The retention rate of100-weeks-capacity reaches90.1%, which is9.3%higher than the one with1%VC used alone.5. Researching the effect of EA and EP on the conductivity, internal resistance and low-temperature discharge performance. Adding20%EA or EP can improve the conductivity, and reduce the low-temperature discharge capacitive and internal resistance. In the battery discharge test in-20℃,20%EA is added, the0.2C discharge capacity,1.0C discharge capacity, and2.0C discharge capacity increase5%,43%and87%, respectively. And these properties increase10%,23%, and34%respectively as20%EP is added.