| The cathode material is one of the important factors restricting the development of high-power and long-life lithium-ion batteries.The silicate cathode material Li2MnSiO4 has attracted wide attention because of its high theoretical capacity(333 mAh·g-1),low price and environmental protection.However,Li2MnSiO4 has the disadvantages of low conductivity,difficult preparation of pure phase materials and unstable structure during cycling.In view of these shortcomings,Li2MnSiO4 cathode material was prepared by hydrothermal method.The effects of reaction conditions on the purity,morphology and grain size of Li2MnSiO4 were studied;Improvement of electrochemical properties of Li2MnSiO4 by carbon-coated modification.At the same time,the effects of reaction conditions on the structure and electrochemical properties of Li2MnSiO4/C were studied;The intrinsic transport characteristics of Li2MnSiO4 are further studied.?1?Li2MnSiO4 cathode material was prepared by ball milling assisted hydrothermal method using lithium silicate,lithium hydroxide and manganese chloride as precursors.XRD measurements and calculations show that Li2MnSiO4 with high purity,good crystallinity and small grain size can be synthesized when the reaction temperature is 270°C,the reaction time is 24 h and the precursor concentration is 2 mol·L-1.SEM shows that the sample particles with irregular cuboid morphology,and the particle size distribution was in the range of 150-250nm.TEM shows that the crystal lattice of Li2MnSiO4 samples is orderly arranged and has good crystallinity.?2?Li2MnSiO4 was carbon coated by ball milling assisted sintering method.XRD,EIS and charge discharge test results show that When the carbon source is sucrose,the calcination temperature is 700°C,the calcination time is 10 h,and the amount of carbon coating is 10%,the prepared Li2MnSiO4/C has high purity,good crystallinity,high capacity,good cycling stability and low charge transfer resistance.The sample for the first time in the 0.1 C(the current density is 33.3 mA·g-1)discharge capacity is 156.6 mAh·g-1,Kulun high efficiency up to 92.4%,after 50 cycles,the discharge capacity is 80.8 mAh·g-1,the capacity retention rate is51.6%.The charge transfer impedance of the sample is about 79.6?and the diffusion coefficient of lithium ion is 5.07×10-1515 cm2·s-1.?3?Transport characteristics of Li2MnSiO4 and Li2MnSiO4/C samples were tested by electrochemical workstation.The results show that the charge transfer impedance Rctt of Li2MnSiO4 is about 3.1×106?,and the charge conductivity?ctt is about 1.607×10-88 S·cm-1.Among them,the ionic conductivity?i and the electronic conductivity?e are 5.86×10-99 S·cm-1and 1.021×10-88 S·cm-1,respectively,at room temperature?20°C?.By studying the effect of carbon coating reaction conditions on the conductivity of Li2MnSiO4/C,the results show that when the carbon source is sucrose,the calcination temperature is 700°C,the calcination time is 10 h,and the carbon coating amount is 10%,the charge transfer resistance of Li2MnSiO4/C sample is the smallest,about 1.76×104?,and the conductivity?ctt is about 2.827×10-66 S·cm-1. |
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