Preparations Of Polymer Electrolytes And Their Applications In Polymer Li-ion Battery

Polymer lithium ion battery (PLIB) not only possesses the advantages of high energy density, long cycle life and friendliness with environment, but also has advantages of improved safety and design flexibility in cell dimension compared with the liquid electrolyte Li-ion batteries. Thus, PLIB has attracted much research attention and becomes a highlight of development of advanced chemical power sources in recent years. This work was concentrated on some technical problems encountered in manufacturing of PLIB. The main results are summarized as follows:1. In order to improve the mechanical strength of the conventional plasticized polymer electrolytes, a membrane-supported composite polymer electrolyte was developed, by casting a layer of PVDF-based polymer solution on a microporous polyolefin membrane (celgard2300). And the effects of the solution viscosity and composition on the structural and electrochemical properties of this composite polymer electrolyte were also characterized by SEM and impedance measurements. The results showed, in comparison with conventional plasticized polymer electrolyte, this composite polymer electrolyte not only possesses enhanced mechanical strength and dimensional stability, but also has higher ionic conductivity, facilitating for practical applications for polymer lithium ion batteries.2. In order to simplify the manufacturing process of PLIB, an in-situ thermal polymerization method was proposed to fabricate the PLIBs, which was carried out by directly filling the precursor solution composed of a curable monomer, a thermal initiator and an organic liquid electrolyte into the battery core, and then thermally initiating the internalpolymerization to solidify the pouched cell. Since this in-situ polymerization method does not require any complicated processes such as plasticizing, film making and extraction, and it can be simply and conveniently used for manufacturing PLIBs at industrial scale.3. A gel polymer electrolyte (GPE) was prepared by in-situ polymerization of 1, 3-butanediol diacrylate (BDDA) in the EC/EMC/DMC electrolytesolution and the effects of the precursor-solution compositions and the polymerization conditions on the mechanical and electrochemical properties of the GPEs were also investigated. The results showed that the GPEs prepared using in-situ polymerization method have high room temperature conductivities above 3. 0X10 3 S ? cm"1, wide electrochemical window (>4. 5 V) and sufficient mechanical strength with the polymer content ^ 10%.4. In order to evaluate the actual feasibility of the in-situ thermal polymerization method in practical lithium ion batteries, the LiCo02/MCMB polymer cells were assembled and their electrochemical properties were evaluated at various charge-discharge rate and temperatures. The results showed that the PLIB cells prepared using in-situ thermal polymerization method have almost the same electrochemical performances as conventional liquid lithium ion batteries.