Synthesis and Electrochemical Studies of Carbon-modified LiNiPO4 as the Cathode Material of Li-ion Batteries

Well-crystallized olivine LiNiPO4 and carbon-modified LiNiPO4(LiNiPO4/C) were synthesized by a combined solvothermal and solid state reaction method using water-benzyl alcohol two-phase solvent. The structure and morphology of the prepared LiNiPO4 were systematically characterized by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The LiNiPO4 particles are up to around 2 nm in diameter while the particle size of LiNiPO4/C is about 100-200 nm. At a current rate of 0.05 C(1.00 C =167 mA/g, corresponding to one Li+ intercalation/deintercalation), LiNiPO4 and LiNiPO4/C presented a high initial specific capacity of 157 and 220 mA.h/g, respectively. The capacity of LiNiPO4/C is 72% larger than that of LiNiPO4 at 0.1 C. The LiNiPO4/C cathode exhibits a superior electrochemical performance in comparison with LiNiPO4, revealing that carbon modifying is an effective method to improve the ionic diffusion and electronic conductivity of cathode material LiNiPO4. Furthermore, lithium ion diffusion coefficients of LiNiPO4 and LiNiPO4/C are 1.80x10(-15) and 1.91 x 10(-14) cm(2)/s, respectively, calculated via the data from electrochemical impedance spectra.