The role of impurities on electrochemical properties of LiFePO₄ cathode material

LiFePO₄, one of the attractive cathode materials for lithium ion batteries, is obtained by lithiation of pre-synthesized FePO₄ using lithium carbonate as lithium source. Inexpensive reducing agent glucose was used for the reduction process. Glucose acted as a conductive additive as well. Lithium ion conductive impurity phase can be attributed to the capacity improvement in LiFePO₄ with carbon coating. The off-stoichiometric Li_xFePO₄ (x=1.005, 1.010) was synthesized to generate a conductive pyrophosphate layer. An electron conductive layer with carbon coating was also concurrently formed by carbothermal reduction of glucose. It is observed that the electrochemical property improves with increasing amount of lithium pyrophosphate impurity phase. This observable fact may be due to accelerating lithium ion diffusion on the lithium ion conductive lithium pyrophosphate layer. XRD and SEM observation show that the Li _xFePO₄/C composite has good crystallinity and well-dispersed particles of 200-300 nm size. The Li_xFePO ₄/C (x=1.010) composite shows a high discharge capacity of 150 mAh g^-1 and 136 mAh g^-1 at rates of 0.1 C and 1 C respectively with satisfactory capacity retention.