Preparation And Modification Of Octahedral Spinel LiMn₂O₄ For Lithium-Ion Batteries

Aqueous lithium-ion battery is studied by researchers and shows a more extensive application prospect due to its environmental friendliness and high-power density.Spinel LiMn₂O₄,as a cathode material for lithium-ion batteries,is one of the most promising cathode materials for batteries with abundant reserves,low cost and easy synthesis.However,the biggest problem is capacity decay during cycles,which limits the development and application.Therefore,in this paper,the capacity attenuation of spinel LiMn₂O₄ can be reduced by the control of crystal plane orientation and surface coating,which could improve the cycling performance.The main research contents are as follows:（1）Octahedral lithium manganate O-LMO1 was synthesized using manganese carbonate（MnCO₃）as precursor and O-LMO1 showed excellent electrochemical performance in both aqueous and organic lithium-ion batteries.In an aqueous system,O-LMO1 sample exhibits the specific discharge capacity of 121.4 m Ah g^-1 at the current density of 0.1 A g^-1,and the capacity retention rate is 87%after 200 cycles under the same test condition.The capacity can keep 87%of the initial specific capacity after 500cycles when the current density is 1.0 A g^-1.In an organic system,the cycle retention rates of O-LMO1 can be able to keep 92%and 84%after 300 and 500 cycles at the current densities of 0.1 and 1.0 A g^-1,respectively.Through the preliminary study of the mechanism of capacity decay,it is proved that the octahedral structure mainly exposed to the（111）crystal plane is helpful to improve the cycle stability,which can inhibit the dissolution of Mnand enhance the structural stability.（2）Octahedral lithium manganate O-LMO2 was synthesized from manganese dioxide（MnO₂）as precursor,which exhibited good electrochemical properties in aqueous and organic lithium-ion batteries.In an aqueous lithium-ion battery,the discharge specific capacity of O-LMO2 sample is 107.6 m Ah g^-1 at 0.1 A g^-1,and the capacity retention rate after 200 cycles is 88%.And the capacity retention rate after 500cycles at 1.0 A g^-1 maintains 91%.In an organic lithium-ion battery,the specific discharge capacity of O-LMO2 reaches 100.9 m Ah g^-1 and maintains 89%after 300cycles at 0.1 A g^-1,and the capacity retention is 87%after 500 cycles at 1.0 A g^-1.（3）In order to further improve the cyclic performance of lithium manganate,a layer of lithium polyacrylate（LiPAA）was coated on the surface of O-LMO2 sample,and the obtained sample is named as LiPAA@LMO.In an aqueous lithium-ion battery,LiPAA@LMO sample displays the discharge specific capacity of 108.6 m Ah g^-1 under0.1 A g^-1.The capacity retention rate is 93%after 500 cycles,and the capacity does not decrease significantly after 500 cycles at 1.0 A g^-1.In an organic lithium-ion battery,the LiPAA@LMO sample has the specific discharge capacity of 95.0 m Ah g^-1 at the test condition of 0.1A g^-1.The capacity retention rate maintains 96%after 300 cycles,and the cycle stability is further improved.