Preparation And Lithium Storage Properties Of Molybdenum-based Oxide Anode Materials

Molybdenum-based oxides?including molybdenum oxides and molybdate compounds?have unique topological structure,abundant molybdenum valences and various phase compositions,which are considered as potential anode materials for lithium-ion batteries.However,most of the molybdenum-based oxides have intrinsic poor conductivity?rate performance?and volume change caused by lithium ion insertion and removal,which leads to the failure of active materials from the collector?reversible capacity?,thus limiting their practical application.Therefore,how to improve the conductivity and structural stability of molybdenum-based oxides,and then improve their rate performance and reversible capacity is the main task of this paper.In this paper,ammonium molybdate was used as molybdenum source to controllably synthesize molybdenum-based oxides with different phases via solvothermal-heat treatment and one-step heat treatment.The relationship between the structure and properties of the products was thoroughly analysed by structural characterization and electrochemical performance test.The main research conclusions are as follows:?1?Using ammonium molybdate as molybdenum source,the precursor was firstly obtained by solvothermal reaction adjusting the volume ratio of water-saving/anhydrous ethanol,then the precursor was pyrolyzed in Ar inert atmosphere to obtain the target product MoO_x(Mo₄O₁₁/MoO₂).In this system,Mo₄O₁₁ and MoO₂ both have considerable theoretical specific capacity(1050mAh·g^-1,838 mAh·g^-1)and metal-like conductivity(5×10⁵ S·m^-1,8.3×10⁵S·m^-1).The two-phase hierarchical system works synergistically,thus overcoming the shortcomings that single-phase molybdenum oxide has few active centers or single electronic conduction path.The Mo₄O₁₁/MoO₂electrode can reach discharge capacity of 939 mAh·g^-1 over 80 cycles at 0.1A·g^-1 and 624 mAh·g^-1 over 100 cycles at 1 A·g^-1.?2?Plate-like structured molybdenum trioxide?MoO₃?with rich well-developed?040?crystal facets was successfully synthesized by one-step heat treatment using ammonium molybdate as molybdenum source and glucose as structural modified agent.This plate-like MoO₃ electrodes can deliver discharge capacity as high as 1452 mAh·g^-1 over 370 charge/discharge cycles.The excellent electrochemical lithium storage performance is mainly attributed to the plate-like structure of MoO₃ and its marginal micro-stripping layer.Firstly,the plate-like structure can provide a high proportion of highly reactive?040?crystal surfaces to be effective reaction sites.Secondly,the marginal micro-exfoliated layer exerts its effectiveness in the direction perpendicular to the?040?crystal plane,this structure is conducive to the intercalation of lithium ions.?3?The composites that?NH₄?₂Mo₄O₁₃ particles embedded in nitrogen-doped porous carbon(?NH₄?₂Mo₄O₁₃/NC)were in-situ synthesized by one-step heat treatment using ammonium molybdate as molybdenum source and glucose as carbon source,in which the compound?NH₄?₂Mo₄O₁₃ has high Li⁺/e^-acceptability and intrinsic structural stability,besides,the N-doped porous carbon matrix is formed of stacked nanosheets with in-plane pores that is in favor of the electrolyte percolation and serves as an elastic conductive network.The as-prepared?NH₄?₂Mo₄O₁₃/NC as anode for LIBs exhibits significantly excellent reversible capacity of 1151 mAh·g^-1 at 0.1 A·g^-1 over350 cycles.