A detailed thermal study of usual LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2, LiMn_2O_4 and LiFePO_4 cathode materials for lithium ion batteries

摘要

The thermal stabilities of delithiated LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2 (L523), delithiated LiMn_2O_4 (LMO), and delithiated LiFePO_4 (LFP) for lithium ion batteries with bare electrode, solvent and different concentration of electrolyte under delithiated state have been investigated by using differential scanning calorimetry (DSC) and ex X-ray diffraction (XRD). The LFP has the best thermal stability, follows by the LMO and then the L523. The existing of solvent facilitates the decomposition of materials. The addition of Li salt in solvent can further accelerate the thermal decomposition of LMO and LFP; but hold back the decomposition of L523 at some extent that although the total reaction heat grown by 297 J g~(−1), the first exothermic peak (ca. 279 °C) moves backwards comparing with L523 and solvent coexisting system (ca. 255.7 °C). As increasing the ratio of electrode material quality to electrolyte, the total exothermic quantity of L523 and LMO becomes large, meanwhile the unit mass exothermic quantity of the L523 varies with little dropping tendency, and that of the LMO decreases obviously. However, for the LFP, the total exothermic quantity decreases and the unit mass exothermic quantity decreases more obviously. Also, the XRD patterns of the three samples at ambient temperature and after 350 °C processing with existing of solvent or electrolyte suggest that the L532, LMO and LFP suffer evident structure changes since their pristine peaks become broader, weaker and splitting or disappearing at high temperature.