Muti-method Preparation And Doping Modification Of Li₂MnSiO₄ As Cathode Material For Lithium-ion Battery

As one kind of high capacity lithium ion cathode material, Li₂MnSiO₄ can deliver a much higher capacity, about 330 mAh g-1. Li₂MnSiO₄ has high thermal stability, low costs, and environmental benignancy. However, Li₂MnSiO₄ exhibits an extremely low electronic conductivity. And the two dimensional layer framework of Li₂MnSiO₄ will become unstable and the layer exfoliation readily occurs at full delithiation. The above drawbacks largely restricted its application. In this article, we have respectively studied the conditions of different method to prepare Li₂MnSiO₄. On the basis of the above, metal cations were incorporated into Li₂MnSiO₄ to improve its electrochemical property. The detailed works are as follows:Li₂MnSiO₄/C have been synthesized by polyol-assisted hydrothermal method, then the influences of the mixed solvents/water volume ratio, hydrothermal reaction temperature, lithium resources, calcination temperature were investigated by SEM and XRD. The results show that the the mixed solvents/water ratio has a considerably influence on the purity of the production, and the calcination temperature have a closely relationship with the morphology and the size of the production. Under the conditions of the mixed solvents/water of 25/45, hydrothermal reaction at 180 oC for 8 days, LiO H as lithium resources, calcination temperature of 650-700 oC for 10 h, the particle with highly crystalline nature and uniform morphology has been obtained. O n the basis of the conditions, Li₂ Lax Mn?1-x?SiO₄/C with high capacity has been synthesized. 1 at.% La³⁺ doped Li₂MnSiO₄ displays capacity of about 257 mAh g-1 corresponding to 1.55 lithium ion delivered. According to the results of EIS and CV, doping La³⁺ can accelerate lithium ion diffusion in the bulk material, and decress the polarization of material. The results of XRD and TEM of the cycled samples indicate that doping La³⁺ not only increases the capacity of Li₂MnSiO₄, but also inhibits the layer exfoliation to stabilize the two-dimensional structure during cycling, which leads to better electrochemical performance.Li₂MnSiO₄/C has also been synthesized by wet milling-assisted solid state method at a low temperture of 650?. The obtained particle has highly crystalline nature and uniform morphology. Ti4+ and Zn2+ have respectively incorporated into Li₂MnSiO₄ to improve its electrochemical performance. 3 at.% Ti4+ doped Li₂MnSiO₄ exhibits the highest discharge capacity of about 209.5 mAh g-1, much higher than that of the pure Li₂MnSiO₄ obtained by wet milling-assisted solid state method. 3 at.% Zn2+ doped Li₂MnSiO₄ was synthesized under the same conditions. Although the discharge capacity is not obviously increased, the cycle performance has been effectively improved. The results demonstrate that the doping effect is closely related to the valence state of dopant.