Study On Electrochemical Properties Of Li₂MSiO₄?M=Fe,Mn? As Anode Material For Lithium-ion Battery

Poly anionic compounds Li₂MSiO₄?M=Fe,Mn?,which practical application was severely limited by its inherent defects used as cathode,can be also used as anode materials for lithium-ion battery.And when used as anode material,Li₂MSiO₄ show more excellent cycle stability and rate capacity.Li₂MSiO₄?M = Fe,Mn?were studied mainly from material synthesis,electrochemical performance analysis,mechanism research in this article.The specific contents and research results are as follows:?1?Li₂MnSiO₄/C nanocomposites were prepared by modified sol-gel method with high purity.Amphiphilic carbon materials?ACM?were added by means of ball milling in the process of synthesizing Li₂MnSiO₄/C.And then,a three-dimensional network structure of conductive carbon layer was formed when ACM was calcined with Li₂MnSiO₄ precursor under high temperature.The final carbon content is about 13.4% in synthetic Li₂MnSiO₄/C nanocomposites.In order to study the reaction mechanism of the anode,Li₂MnSiO₄/C cathode was discussed for comparison.It was found that the electrochemical performance of Li₂MnSiO₄/C anode is better than that of the cathode with different charge-discharge mechanisms through the comparative experimental results.The initial discharge capacity of Li₂MnSiO₄/C cathode is 134 mAh/g at 0.05 C?16.6 mA/g?,66 mAh/g after 20 cycles;while the Li₂MnSiO₄/C anode delivered the first discharge capacity 658 mAh/g at a current density of 20 mA/g,459 mAh/g after 50 cycles.According to different electrochemical behaviors of Li₂MnSiO₄/C electrodes,different reaction mechanisms were proposed.mechanism of intercalation and de-intercalation mechanism for Li₂MnSiO₄/C cathode: Li₂MnSiO₄ ? Li++ LiMnSiO4+e-?1?;conversion mechanism for Li₂MnSiO₄/C anode: Mn + 3/2 Li2 O ? 1/2 Mn2O3 + 3Li+ + 3e-?2?,during the first discharging process,irreversible reaction occurred and Li₂MnSiO₄ decomposed into metal Mn,SiO and Li2 O,then reversible reactions occurred as equation?2?in the subsequent charging-discharging process.?2?With ferric nitrate as the source iron,colloidal SiO2 as silicon source,and ACM as carbon source,pure phase Li₂FeSiO₄/C nanocomposites were prepared by sol-gel method,and showed excellent cycle stability and rate performance used as anode for lithium-ion battery.The Li₂FeSiO₄ electrode delivered an initial discharge capacity of 569 mAh/g at the current density of 50 mA/g,and the capacity retention ratio was still 95.3% even after 60 cycles.Its possible reaction mechanism was raised from charge-discharge curves,cyclic voltammograms test,ex-situ XRD and HRTEM images analysis,which was similar to that of Li₂MnSiO₄/C anode.That was: Li₂FeSiO₄ + 2Li⁺ + 2e^– ? 2Li₂ O + Fe + SiO₂?3?;Fe + 3/2 Li₂ O???1/2 Fe₂O₃ + 3 Li⁺ + 3e^–?4?.