Thermal and electrochemical stability of cathode materials in solid polymer electrolyte

Thermal stability of cathode materials, including LiCoO2, LiNiO2, LiMn2O4, V2O5, V6O13, and LixMnO2 in contact with poly(ethylene oxide) (PEO) based s olid polymer electrolyte was systemically investigated by means of thermal analysis in combination with X-ray diffraction technique (XRD). The differe ntial scanning calorimetry (DSC) analysis showed significant exothermic rea ction of both LiNiO2 and LiCoO2 in contact with the polymer electrolyte. Li Mn2O4 was less reactive compared with LiNiO2 and LiCoO2. V2O5, V6O13, and L ixMnO2 were also found less reactive, especially in their discharge states. The XRD results indicated that the thermal decomposition products of the c athode material were the low valance metal oxides, suggesting the exothermi c reaction was an oxidation reaction of the polymer electrolyte with active material. The decomposition temperature is somehow dependent on the potent ial of the cathode active materials. Cyclic voltammetry reveals that PEO ba sed solid polymer electrolyte is stable up to 5.0 V versus Li/Li+ at a bloc king electrode, whereas it decomposes at ca 3.8 V when contacted with a car bon composite electrode, (C) 2001 Elsevier Science B.V. All rights reserved .