Investigation Of Si-based Composite Polymer Electrolytes And Application In Secondary Batteries

Recent research reports about different types of polymer electrolytes were reviewed and research development of PEO-based polymer electrolytes was further summarized in this paper. It is necessary and important for all solid-state lithium polymer batteries to develop all kinds of PEO-based polymer electrolytes capable of combining high ionic conductivity at room temperature, large lithium ion transfer number, and superior interfacial stability towards Li anode, easy preparation process, good mechanical properties, and wide electrochemical stability windows. This paper focused on investigating the effect of various Si-based fillers on the conductivity of PEO-LiClO₄ polymer electrolytes. Surface morphology, structure, thermal properties and electrochemical performance of PEO-based polymers were characterized by physical methods such as SEM,FTIR,XRD,DSC combined with electrochemical techniques.In the second chapter, all solid-state PEO-LiClO₄ polymer electrolytes were prepared by solvent evaporation technique, using PEO as base and LiClO₄ as lithium salt, respectively. The polymer electrolyte with higher conductivity and better mechanical properties was obtained under the optimized preparation conditions, that is, the molecular weight of polyethylene oxide (M_v) =100,000, the molar ratio of EO and Li (EO/Li) =20, the formation temperature of membrane 50℃.In the third chapter, PE0-LiC104-AGM composite polymer electrolytes were prepared using modified absorptive glass mat (AGM) as filler. SEM images showed that the addition of Li salt and modified AGM may improve the surface morphology of CPE. The results of FTIR spectroscopy, XRD and DSC indicated that the inclusion of LiClO₄ salt and the addition of AGM filler can reduce the crystallinity of PEO. It is concluded that the addition of AGM plays two roles in PEO-based CPEs, namely, interruption of the PEO recrystallization and reinforcement of CPEs, accordingly enhancing room temperature ionic conductivity of CPEs and improving its mechanical strength and electrochemical stability at high temperatures. In the fourth chapter, nano-sized fumed silica and SBA-15 molecular sieve were modified by silanization reaction. SEM results presented that modified SiO₂ compounds with hydrophobic -Si(CH₃)₃ or 3-glycidyloxypropyl groups have less particle aggregation and can be easily dispersed into PEO-based polymer electrolytes. XRD and DSC results proved that modified filler can effectively reduce the crystallinity of PEO through the Lewis acid-base interactions, resulting in obvious enhancement in the ionic conductivity of PEO-based polymer electrolytes from room temperature to 80℃.In the fifth chapter, ZB-SBA-15 molecular sieve was synthesized by the introduction of super strong acid ZrO₂, B₂O₃ with the characteristic of severe lack of electron and SBA-15 with special mesoporous channels. The results of SEM, FTIR, XRD and DSC indicated that the modified fillers can reduce the crystallinity of the corresponding samples by lowering PEO particle size. Moreover, modified fillers can also hold the stability of the interface between electrolytes and anode materials and increase the electrochemical stability window of the electrolytes through the Lewis acid-base interactions between modified fillers and PEO chains.In the sixth chapter, all solid-state lithium polymer batteries were assembled by using PEO-LiClO₄-10% ZB-SBA-15 polymer electrolyte as separator and electrolyte, LiCoO₂ as cathode materials and lithium foil as anode, and their electrochemical performance were tested. It was found that the reversible capacity of the assembled polymer batteries is larger than 93% of the capacity of the corresponding batteries with liquid electrolyte at a rate of 0.1C and at room temperature.In the seventh chapter, polysiloxane-based gel electrolyte (PBGE) was prepared and investigated as a new gel electrolyte for valve-regulated lead-acid (VRLA) batteries. The addition of PBGE improves the utilization efficiency of positive active material (PAM) in AGM-PBGE hybrid batteries and thus enhances the battery capacity compared with the AGM-CSGE reference batteries. Cyclic overdischarge tests showed that the AGM-PBGE hybrid batteries have superior recharge and discharge during partial-state-of-charge (PSoC). It was also found that the greatly enhanced electrochemical performance of the AGM-PBGE batteries may be due to higher charge efficiency, good conductivity with lower internal resistance and the open three-dimensional network structure of the polyelectrolyte. The results of failure mode analysis indicated that the softening and shedding of positive active material are the main causes of failure for the two gel batteries.