Study On The Modification Of Spinel Lithium Manganese By Rare Earth Element Doping

The spinel manganic acid lithium is promising to be cathodes forLi-ion battery, due to its relatively high energy density and low toxicity.However, the capacity of spinel manganic acid lithium fades rapidly inthe charge-discharge cycle process. It has been suggested that thecapacity fading is due to Jahn-Teller distortion, dissolution of manganeseinto the electrolyte and decomposition of the electrolyte. This dissertationis intending to investigate the modification of spinel lithium manganesecathode material for lithium-ion batteries by ion doping, so as to improveits electrochemical performance.(1) The lanthanide ion La³⁺ or Sm³⁺, which has the much larger ionicradius than Mn³⁺, and has much stronger Mn-O bond energy and higheroctahedral site preference, were introduced to modify spinel lithiummanganese. Analysis the structure and electrochemical characterization ofLiMn_2-xMO₄( M represents the doping element ) spinel lithiummanganese cathode doped with La³⁺ and Sm³⁺.The experiment resultsshowed that the structure was more steady and the cycling performance was better than pure lithium manganese cathode by doping someelements. X in LiMn_2-xM_xO₄ must be under 0．02 otherwise the structurewould be changed at the same time discharge capacity decayed. Bycomparison, LiMn₁．98La₀．02O₄ and LiMn₁．99Sm₀．01O₄ show the bettercharacterization in cycle performance. The first discharge capacity is120mAh·g^-1 and 118．8 mAh·g^-1 , the capacity still keep 105．7 mAh·g^-1 and107 mAh·g^-1 after 50 cycle.(2) The cathode materials, LiM1_xM2_yMn_2-x-yO₄ (M1= Ni, Al, Co;M2=La, Sm) , for Lithium-ion battery doped with two elements weresynthesized by high temperature solid-state reaction method. X-raydiffraction and SEM showed that the material had a better spinel structureand the particle size were narrowly distributed, and the electrochemicaltest showed a great difference among the materials doped with differentelements. LiCo_0．08 La_0．02 Mn_1．9 O₄ has the best performance compared to theothers in the range of 3．0-4．3V. The first discharging capacity reached120mA·h/g, and the capacity still kept at 109mA·h/g after 50 cycles,which decayed only 7%.