Investigation On Mechanochemically Assisted Fast Solid-state Synthesis Of Nano LiCoO₂

Superfine LiCoO2 powders,featured with higher specific area,shorter distance for embedding and escape and higher diffusivity,have become an important positive material for Li ion batteries.They are usually synthesized from the chemical routes.In the papper,a novel route for the preparation of superfine LiCoO2 powders by low temperature solid reaction is developed.1,Effects of precursors(LiOH-Co(OH)2,Li2C03-Co(OH)2,Li2C03-CoCO3 and Li2CO3-Co3O4)on the phase constitutions and morphologies of the powders synthesized by the low-temperature solid reaction are invstigated.The LT-LiCoO2 powders are obtained.The activated carbonates are decomposed into Co3O4 at first and then play a role in synthetic reactions.The as-prepared LT-LiCoO2 powders are about 50nm in diameter and they become coarsening with a prolonged reaction time.2.High energy ball milling is beneficial to the decomposition of the carbonates.Ball milling can elevate the thermal decomposition rate of CoCO3 and lower the starting decomposition temperature.The as-milled powders are refined from 4?m to 50nm in size.These nano-scale Co3O4 powders can rapidly react with the Li sources.Ball milling of carbonate precursors can not only achieve activation but also assure the lattice completeness of the Co3O4 phase.Moreever,the surperfine LiCoO2 powders can be obtained at low temperature and short time.3.Effects of ball milling and solid reaction parameters on the phase constitution and morphologies on the as-prepared powders are studied.Being the milling additive,etharol can bring about obvious refinement of the precursors.The pure LiCoO2 powders can be prepared with the Li/Co ration of 1 in the precursors.The higher sintering temperature and the prolonged sintering time lead to the agglomeration and coaring of the as-prepared powders.The transition from LT-LiCoO2 to HT-LiCoO2 can be realized after sintering at 900? for lh or 3h.Moreover,the nano-scale powders with high surface finish quality are obtained.4.The solid reaction mechanisms for rapid synthesis of LiCoO2 powders is larified.Firstly,the powders of carbonate precursors are refined to the nano-scale level by high energy ball milling and thus crystal defects are obviously increased.Therefore,the atomic mixture of the raw materials is achieved.Secondly,the nano-scale CoCO3 powders are thermally decomposed into the nano-scale Co3O4 during sintering at low temperature(<300?).The activated Li2CO3 is melted at first and then is decomposed into Li2O at 600 ?.The melt of Li2CO3-Li2O-LiOH is diffused in the crystal lattice of Co3O4 and the reaction and the growth of LT-LiCoO2 occur,with the grain size of 50nm?100nm.Thirdly,the HT-LiCoO2 powders are formed by the atomic rearrangement of LT-LiCoO2 during sintering at high temperature and the nano-scale particles are fused into secondary paricles with the particle size of 400nm-500nm.5.The superfine HT-LiCoO2 powders are prepared by the optimized parameters and their electrochemical properties are tested.The powders prepared with the as-milled powders(600?/3h-900?/lh,3h)as the raw materials exhibit good electrochemical properties.