Preparation Of High-performance LiMnPO₄Cathode Material From Hollow-sphere Li₃PO₄

Olivine framed LiMnPO4is one of the most promising cathode material for high-energy lithium ion batteries duo to its high energy density (170mAh·g-1), high thermal stability and high voltage (vs. Li/Li+). However, the intrinsically low electronic and ionic conductivity limit its application. For the purpose of improving the electrochemical performances of LiMnPO4, a delicate polyol-assisted hydrothermal method is devised to synthesize phase pure LiMnPO4from the pre-prepared hollow-sphere Li3PO4. The detailed works are as follows:The precursor Li3PO4was synthesized by precipitation, then the influence of the stirring rate, reaction temperature and feeding speed on the morphology, particle size, composition and phase were investigate by SEM、TEM、XRD and ICP. The tests results show that the reaction temperature has a considerably influence on the particle size of Li3PO4, and the hollow-sphere Li3PO4can be synthesized when the optimal condition was600rpm,60℃and1.7mL/min. The SEM and TEM results also show that the secondary particles’diameters are varying from200nm to500nm, and the primary particles’diameters are all less than50nm.Basing on the pre-prepared Li3PO4precursor, we devised a delicate poloy-assisted hydrothermal method to synthesize the high-performance nanoscale LiMnPO4cathode material, and confirmed the optimal condition by studying the influence of mixed solvents’molar ratio "X", hydrothermal time "i", calcinations temperature "T", high calcinations temperature time "t" and carbon contend "sucrose wt%" on the morphology, character and electrochemical properties of LiMnPO4. The tests results show that the irregular flaky LiMnPO4synthesized when X=2,t=24h,T=600℃,t=3h and sucrose wt%=30%gave the best overall electrochemical performance. The excellent capacity retention of all the LiMnPO4prepared by poloy-assisted hydrothermal method were not expected but obtained after cycling50times at0.1C:all the capacity retention were more than90%, and the highest one was96%, all which were far bigger than that of the blank sample (78%). The greatly improved performance can be attributed to the new synthesis method, which results in nanocrystalline LiMnPO4and a particular morphology to shorten Li+diffusion pathway.Moreover, the phase pure hollow-sphere LiMnPO4was firstly synthesized when X=0.78. And12group comparative tests were devised to confirm the reason of the unique character generation. After investigation the crystal changes of LiMnP04, which is prepared at different reaction time, by XRD testing technology it was found that the formation of the hollow-sphere character is controlled by reaction rate, while the reaction rate is depended on the value of H2O/DEG molar ratio.