Synthesis And Electrochemical Performance Of New Silicates/Chromate As Cathode Materials For Lithium Batteries

Orthosilicates are promising candidates for next generation of lithium ion batteries, due to their high theoretical capacity and excellent safety performance.In this work, Li₂MnSiO₄/C and Li₂Mn_0.5Fe_0.5SiO₄/C electrode materials were prepared by hydrothermal assisted sol-gel process.The structure character and electrochemical performance of the prepared materials were studied.Structure stability and the reason of the poor cyclic performance of the materials were investigated by ex-intu FTIR and ex-intu XRD.The Li₂MnSiO₄/C and Li₂Mn_0.5Fe_0.5SiO₄/C composite material prepared through hydrothermal assisted sol-gel process were iso-structure and the space group is orthorhombic system Pmn2₁.The Li₂MnSiO₄/C and Li₂Mn_0.5Fe_0.5SiO₄/C composite material shows a discharge capacity as high as 205.8 mAhg^-1(1.24 Li reversible exchange per unit formula) and 215.6 mAhg^-1(1.30 Li reversible exchange per unit formula).But more than 1.6 electrons exchange per unit Mn occurred in Li₂Mn_0.5Fe_0.5SiO₄.Actually,electrochemical performance of Mn was improved after the mixing Fe and Mn.And the GITT data showed the diffusion of lithium in Li₂Mn_0.5Fe_0.5SiO₄ was improved.The cyclic stability of Li₂MnSiO₄/C and Li₂Mn_0.5Fe_0.5SiO₄/C composite material were not good.But the cyclic stability in the first five cycles was improved after the mixing Fe and Mn.Ex-intu FTIR showed that the characteristic bands of[SiO₄]in Li₂MnSiO₄ shift to high wavenumber with the increasing of cycle numbers.Compared to Li₂MnSiO₄, the characteristic bands in Li₂Mn_0.5Fe_0.5SiO₄ were not changed.Ex-intu XRD showed that after the first cycle,the crystalline Li₂MnSiO₄ changed to an amorphous state,but the characteristic peaks in Li₂Fe_0.5Mn_0.5SiO₄ were partly stable.We conclude that after the mixing Fe and Mn,the structure stability of Li₂MnSiO₄ were improved.It proved that a better structure stability probably be obtained by the mixing Fe and Mn.Primary lithium batteries and lithium ion batteries play the same important role in modern life.CuCrO₄ was one of multistep reductions cathodes for primary lithium batteries;its theoretical capacity is about 744mAh/g.Here,we report an improved method to synthesize the CuCrO₄.In addition,a possible mechanism of the CuCrO₄ material upon discharging was discussed.A high capacity CuCrO₄ composite cathode material with good rate performance has been successfully prepared through an improved precipitation method.The material delivered high discharge capacities of 706 and 610 mAh/g at 10 and 200 mAg^-1,respectively.The sub-micron rod-like morphology and discharging product Cu are responsible for its good rate performance. Furthermore,the ex-intu FTIR and ex-intu XRD measurements demonstrated that during the reductions of CuCrO₄ accompanied with the intercalation of lithium ions, the crystalline CuCrO₄ transformed into an amorphous state or decomposed into other amorphous compounds during the first discharge process;and the newly formed discharging products include Cu₂O and Cu.