Preparation And Characterization Of Heat-resistant Separator And Polymer Electrolyte For Lithium Battery

The novel thermostable polymer separator and polymer electrolyte for Lithium（ion） battery have been investigated. Two kinds of separators have designed and perapared, including heat-resistant thermoset resin based separator and inorganic-orgnic composite separator. Two kinds of polymer gel electrolytes have prepared, including glass-fiber supporting PVA-β-CN based electrolyte and shelf-crosslinking polyether electrolyte system. The chemical structure, thermal behavior, surface morphology and electrochemical performance have been investigated by FIIR, NMR, DSC, SEM and Electrochemical workstation, and further to probe the operation performance of the cells using the resultant separator and polymer electrolyte. To analysize the effection of the propotion of raw materials and preparation condition on the properties of separator or polymer electrolyte, with the purpose of maintaining good mechanical strength and electrochemical properties, as well as improving the themmal safety of the resultant separator and polymer electrolyte.1. A heat-resistant and flame retardant separator based on melamine formaldehyde resin（MFR） was prepared by reactive electrospinning. The resultant separator possessed higher ionc conductivity（0.79 mS/cm）, wider electrochemical window（4.7 V）, higher porosity（72%）, and superior liquid electrolyte wettability and retention against conventional PP separators. Moreover, the high thermal stable temperature（180 oC） in the case of static pressure and the high value of limited oxygen index（38%） could be potential to improve the safety characteristic of cells. Most importantly, the LiMn₂O₄/LiPF6/graphite cells with MFR separators revealed an improved cycle life against to the cells with commercial separators. The data of XPS and EDS indicated that the dissolved Mn²⁺ in electrolytes can be immobilized by MFR separator and thus suppressing deposition of Mn²⁺ on the surface of negative electrode. Notably, These characteristic endow MFR-based separator is a promising candidate for lithium-ion battery.2. The composite membrane of glass microfiber and polyimide wasprepared by papermaking methodand following dip-coating process to explore the feasibility as high performance separator of lithium ion battery（LIB）. It was demonstrated that the composite membranes, with a thickness of about 45 μm, possessed a significantly enhanced tensile strength and a modified porous structure, compared with that of pristine glass microfiber membrane. Impressive improvements in thermo-stability and flame retarding were achieved for composite membrane, with no shrinkage at the elevated temperature of 200 °C, even no burn on fire, compared with commercial polyolefin separators. Meanwhile, the composite membrane presented a favorable wettability and remarkable electrochemical stability incommercial liquid electrolyte. In addition, the battery tested results of Li FePO₄/Li and Li FePO₄/graphite cells proved the composite membrane was a promising separator with an improved rate capability. The cycle performance of cells at the elevated temperature of 120 °C demonstrated their excellent safety characteristic as separator in LIBs, indicating the composite membrane was a potential separator candidate for high power battery.3. A heat-resistant and rigid-flexible coupling glass-microfiber nonwoven supported cyanoethyl-β-polyvinyl alcohol composite polymer electrolyte membrane（GFMPE） has been successfully fabricated explored for high-performance lithium batteries. It was demonstrated that the GFMPE possessed enhanced mechanical property, superior dimensional thermostability（>200 oC）. In addition, Ethylene carbonate（EC）/Dimethyl carbonate（DMC） solvent soaked GFMPE exhibited a superior Li ion transport number of 0.86, wide electrochemical window up to 4.8 V vs Li+/Li and high ionic conductivity of 0.89 mS/cm at 25 oC. Moreover, LiCoO₂/graphite cells using such polymer electrolyte with EC:DMC（1:1, v/v） showed excellent cycling stability and superior rate capability at room temperature. It is important to note that the LiFePO₄/Li cell using GFMPE/ propylene carbonate（PC） can also operate very well at an elevated temperature of 120 oC. These fascinating results would endow GFMPE a very promising polymer electrolyte in high-performance lithium batteries with improved safety and reliablity.4. A flexible polymer electrolyte based on silicon methoxy polyether with shelf-crosslinking characteristic has been successfully prepared and explored for lithium batteries. It was found that this polyether can be shelf-cosslinked by mixed with Li BOB. It was demonstrated that the polymer electrolyte would reveal good combination performance（such as tensile strength and electrochemical properties） in the case of the 1/10 of LiBOB/TSPPG mole ratio at the temperature of 40 oC. The resultant polymer electrolyte possessed lower glass-transition temperature（-48 oC）, high ionic conductivity（10-5 S/cm）. For improving the ionic conductivity, another CSPE-based composite solid electrolyte doped with plastic crystal（N-CSPE） was also fabricated, and the PEO-based solid electrolyte as a comparison. It was demonstrated that the the LiFePO₄/Li cell using this polymer electrolytes（CSPE and N-CSPE） can also operate very well at the ambient temperature and an elevated temperature of 100 oC. Thus, the flexible crosslinked polymer electrolyte can be opened up a new kind of perspective for all-solid-state polymer electrolytes.In a word, we prepared the separators and polymer electrolytes with simple method or process, and the resultant samples possessed good properties, which were potential to be used for lithium battery for improving safety in practice.