Studies On Synthesis And Performance Of Lithium Iron Silicate As Cathode Material

Lithium iron silicate of polyanionic structure has resource-rich,lower costing,more friendly for environment,low price and higher safety performance.The theoretical capacity of one lithium iron insertion and extraction is 166mA.h.g-1.If we can achieve two lithium ion insertion and extraction,the theoretical capacity can be get 332mA.h.g-1,which is considered one of the promosing cathode materials of development.But the low diffusion rate of lithium ion and lower ionic conductivity,caused its electrochemical performance poor and limited its commercial process development.Therefore,we need to shorten the diffusion path of lithium ion efficiently and increase the conductivity to improve battery performance.There are now methods of coating by carbon,synthesing nanoparticles and doping metals to improve their electrochemical properties.The main points of this article include:In the experiment,we use the conventional method of water-soluble high-temperature solid-phase to synthesize cathode material lithium iron silicate.By using the thermogravimetry-differential thermal analysis(TG-DTA),X-ray diffraction(XRD),scanning electron microscopy(SEM),ect methods and comparing material properties through different calcination temperature(750℃,800℃,850℃)10h synthetic,we determined that the best condition of calcination is temperature of 800℃ to 10h.Under the best conditions for the synthesis of materials the assembled cells were measured.Due to the large particles and uneven distribution,under the charge and discharge rate of 0.1C,the specific capacity is 65mA.h.g-1.Charge and discharge platform is not obvious and the charge transfer resistance is 4000.By using method of carbon packeting precurs and high temperature solid phase,making glucose as the carbon source,we synthesized Li2FeSiO4/C materialof carbon content(5%,10%,15%).And compared to not pure carbon-doped sample,the grain size of carbon-doped synthetic materials decreases,the battery charge and discharge specific capacity significantly improved and the platform is significant.We through different characterization methods,the carbon content of 10%Li2FeSiO4/C material indicated that the best material properties,which is uniform particle size,better battery performance cycle,and charge and discharge platform is significant.After 20 charge-discharge cycles,the discharge capacity was 105mA.h.g-1,charge transfer resistance,compared Li2FeSiO4/C,reduced to 340Ω.We use the Sol-gel way of assisted citric acid to synthesize Li2FeSiO4/C cathode materials.Through the TG--DTA,XRD,SEM,battery charge and discharge testing technology,via various calcination temperature(650℃,700℃,750℃)10h,compared to synthetic material properties,we identified that synthetic materials calcined at 700℃,10h show the best performance and the particles reach the nanoscale.Battery assembled by the materials has good cycle performance,capacity fading lowerand battery charging and discharging platform is significant.After 20 charge-discharge cycles,the discharge capacity stabilized at 145mA.h.g-1,exhibiting good electrochemical performance.Under the experimental basis of the citrate sol-gel synthesis assisted Li2FeSiO4/C,we studied the synthesis of Si-site 3%Cr-doped to synthesize Li2FeSi0.97Cr0.03O4/C cathode material.Its structure and electrochemical properties of the material performance is tested,and the performance of 3%Cr-doped silicon-site impacting Li2FeSiO4 is researched.From the XRD spectra of Li2FeSiO4 pure and doped samples of Cr Li2FeSi0.97Cr0.03O4/C synthetic point of view,the diffraction peaksbefore Cr-doped and after show little difference,this indicates that Cr has entered the crystal interior,and stabilized the crystal.By comparing the cycle performance of the battery,after 20 cycles,the discharge capacity of the doped samples is 150mA.h.g-1,which shows that the ratio cycling performance is well.Compared to Li2FeSiO4/C the capacity of Si-site 3%Cr-doped has increased,at the same time the charge transfer resistance of the material reduced and the material conductivity increased.