Glucose Assisted Low Temperature Liquid Phase Synthesis And Modification Of Nano LiMnPO₄: Towards Electrochemical Performance

With the development of society,industry,economic and environmental problems have become increasingly prominent.It is necessary to find a kind of battery,which can meet the requirmnts of high capacity and also are environmentally friendly.In the 1990 s,the lithium ion battery with high energy density was invented,compared with other batteries,lithium ion batteries have some advantages such as high capacity,high voltage,long cycle life,a wide range of work,low self discharge rate and environmentally friendly characterization,therefore,lithium ion batteries have become the most promising batteries.The cathode materials play an important role in the lithium ion battery system.The electrochemical performance depends much on the cathode materials.LiMnPO₄ with olivine structure has become the focus of research due to its high specific capacity,good cycle stability,excellent thermal stability,abundant materials and environmentally friendly nature.But the LiMnPO₄ material itself also has some disadvantages,for examble poor electronic conductivity and low ion diffusion coefficient.Based on the above,we have done some modified research in this thesis.Firstly,we synthesized the LiMnPO₄ nanoparticles with good dispersion by the glucose-assisted low-temperature liquid phase method.Then,the graphene oxide was coated on the surface of the nanoparticles,which act as a conductive layer.Finally,we doped with Fe in LiMnPO₄,in order to improve the electrochemical performance of particles.According to the above,we synthesized the LiMnPO₄?LiFePO₄/GO and LiMn_xFe_1-xPO4 samples,which were nanoparticles with good dispersibility and then they were made into LiMnPO₄/C?C-LiFePO₄/GO?LiMn_xFe_1-xPO4/C after being coated carbon.The samples were characterized with a variety of techniques such as X-ray diffractometry?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and Raman spectrum and so on.The Land battery test system and electrochemical workstation were taken to test the electrochemical performance.?1?The LiMnPO₄ particles with good dispersion were synthesized by glucose-assisted low temperature and liquid phase method.The particles were nano rod with a length of 60-80 nm and a diameter of 40-50 nm.The carbon was coated on nano rod homogeneously after high temperature carbon coating.Electrochemical test results show that the LiMnPO₄/C have the excellent electrochemical performance,the discharge specific capacity can reach 155.3 mAh g^-1,140 mAh g^-1,123.4 mAh g^-1 and 89.8 mAh g^-1 respectively at 0.05 C,0.1C,1C and 5C.In addition,the capacity can still remain at 147.5 mAh g^-1 after 50 cycles,the capacity retention rate was 95%.?2?The LiMnPO₄/GO was made in liquid phase with glucose assisted,which was turn into C-LMP/GO after high temperature coating.The discharge specific capacity can reach 167.63 mAh g^-1,160.5 mAh g^-1,153.17 mAh g^-1 and 110.2 mAh g^-1 respectively at 0.05 C,0.1C,1C and 5C.In addition,the capacity can still remain at 159.1 mAh g^-1 after 100 cycles,the capacity retention rate was 95%.The coulombic efficiency still can reach 99% after 100 cycles.?3?The pure phase LiMn_xFe_1-xPO4 particles with good crystallinity were obtained with glucose assisted.The research results showed that the LiMn_xFe_1-xPO4 exhibited excellent electrochemical performance when the value of x was 0.9.The discharge specific capacity of Li Mn0.9Fe0.1PO4 can reach 162.1 mAh g^-1,151.9 mAh g^-1,139.56 mAh g^-1 and 104.4 mAh g^-1 respectively at 0.05 C,0.1C,1C and 5C.The capacity can still remain at 153.5 mAh g^-1 after 50 cycles,the capacity retention rate was 94.5%.