Polymer-Chelation Synthesis Of Ternary Cathode Materials For Lithium-Ion Battery

With high specific capacity,high voltage,low cost and environmental protection,ternary cathode materials Li(Ni1/3Co1/3Mn1/3)O2(NCM111)has become the focus of our research for cathode materials of lithium ion batteries.In this paper,a new preparation method,namely polymer-chelation synthesis,has been developed to prepare ternary cathode material.The complexed chelate agents of ethylenediaminetetraacetic acid(EDTA)and polyethyleneimine(PEI)could chelate all metal ions in one step,with intimate mixing at the atomic level,ensuring a homogeneous ion distribution in the product.The as-prepared NCM111 have a submicrometer size and high crystalline,delivering a good electrochemical performance.The major conclusions are summaried as follows.(1)A cost-effective approach has been developed to prepare layered NCM111 single-crystal cathodes with desired stoichiometry via a polymer-chelation chemical solution process.The sintering process of 500? pre-sintering for 5h and 850? high temperature sintering for 12h was determined to obtain compositionally homogeneous product.Since lithium could volatilize during high-temperature sintering,it was necessary to add an excessive amount of lithium,and the optimized Li ratio of 1.05 was determined.The as-prepared NCM111 had submicron size with average particle size of?250nm and very defined layered ?-NaFeO2 structure.The chemical state of Ni,Co and Mn in the as-prepared NCM111 were fully accorded with the theoretical valences of +2,+3 and +4,respectively.The exposure of a large number of electrochemically active {010} crystal planes and the low Li+/Ni2+ cation mixing increased the transmission efficiency of Li+ and improved the electrochemical performance.The as-prepared NCM111 had an initial discharge capacity of 186.1 mAh g-1 at a current density of 0.2 C in a voltage range of 2.8-4.5V,with a coulomb efficiency of 87.5%.The material delivered a good capacity retention rate of 80.1%after 100 cycles reached,as well as a good rate capacity with capacity of 102.7 mAh g-1 at 10 C.(2)The modification of NCM111 including Al3+,Nb5+ and Mg2+ bulk doping and the Al2O3 surface coating were performed to further improve the cycle stability and rate performance of the material.Both Al3+ doping and Al2O3 coating greatly improved the cycling stability of the material,with the capacity retention rate after 100 cycles of 86%for Al3+ doping and 85.2%for Al2O3 coating.The doping of Nb5+ or Mg2+ could increase significantly the discharge capacity as well as rate capability,in which Nb5+ doping improve the discharge specific capacity to 115 mAh g-1 at 10 C,while Mg2+ doping increase the discharge specific capacity to 122.6 mAh g-1.Owing to the flexibility of the chelating chemistry,the synthesis could be extended to prepare other multicomponent single-crystal cathodes with homogeneous composition and desired substation.