Modification Of ZnMn₂O₄ Anode Material For Lithium-ion Battery

Recently,rechargeable lithium ion batteries?LIBs?,as energy storage devices,are wildly applied in hybrid electric vehicles?HEVs?,pure electric vehicles?EVs?and plug-in hybrid vehicles?PHEVs?.However,in these cases,consumers usually hope the vehicles could have a long cruising mileage and good safety,which requires the LIBs with the enhanced performances in terms of their energy density and safety.Most commercial LIBs are still using graphite as anode material due to its low cost,stable capacity,and long cycle life.However,the structure of graphite determines that its theoretical capacity is only 372 mA h g^-1and the practical capacity is near to 360 mA h g^-1.Thus,the demand for next-generation LIBs with higher capacity has stimulated efforts to develop new materials such as graphene,carbon nanotubes,Silicon,transition metal oxides,etc.Among those candidates,ZnMn₂O₄ attracts much attention due to its high capacity,low price and environmentally friendly.But low coulombic efficiency,unstably solid-electrolyte interface?SEI?,voltage hysteresis and low service life restricts the development of Zn Mn₂O₄.We want to modified ZnMn₂O₄ by doping and coating.The main contents of our research are as follows:1.Zn_1-xAl_xMn₂O₄ was synthesized by spray drying process following with annealing treatment.The nonequivalent-substitution of Al³⁺for Zn²⁺makes manganese into a mixed valence state by the charge compensation mechanism.Moreover,this presence of the charge compensation significantly upgrades the electrochemical performances of the Zn_1-xAl_xMn₂O₄,such as increasing the initial coulombic efficiency,stabilizing the cycleability as well as improving the rate capability.The sample with 2%Al doping shows the best performances whose first cycle coulombic efficiency is 69.6%and the reversible capacity is 597.7 mA h g^-11 after 100 cycles.Even at high current density of1600 mA g^-1,its retained capacity is still kept at 558 mA h g^-1.The electrochemical results demonstrated that the nonequivalent-substitution is a successful try for development of advanced anode material for high-performance LIBs.2.ZnMn_2-xAl_xO₄ was synthesized by the same method using the submission of Al³⁺for Mn³⁺.The electrochemical performances of ZnMn_2-xAl_xO₄ are unsatisfactory,which proves the improvement of the nonequivalent substitution of ZnMn₂O₄ reversely.By contrast,Sn can't be introduced into the ZnMn₂O₄ lattice through the same way.ZnMn₂O₄ with SnO₂impurity performs poor electrochemical performances.This work deepened the cognizance of ZnMn₂O₄.3.We plan to combine ZnMn₂O₄ and carbon as a composite to improve the electrochemical stability of ZnMn₂O₄.ZnMn₂O₄/C composites with different carbon sources were synthesized by hydrothermal method.The results show that using glucose or ascorbic acid as carbon source simply would form micrometer-size carbon sphere,which covered the ZnMn₂O₄ nanoparticles and performed poor electrochemical performances.We adjusted the pH of Vc solution to decrease the size of carbon sphere,then Vc is carbonized on the surface of ZnMn₂O₄ nanoparticles.ZnMn₂O₄/C composite shows a little lower discharge capacity during the first few cycles but better cycle stability and higher capacity retention ratio at high current density of 1600 mA g^-1.The amorphous carbon pulled down the theoretical capacity,But Vc was evenly distributed among the Zn Mn₂O₄ nanoparticles and formed interconnected conductive carbon film,so that Zn Mn₂O₄/C composite showed superior cycle performance and rate capability.This work deepened the cognizance of ZnMn₂O₄ once more.