Research Of Long Cycling Life LiMn₂O₄-Li₄Ti₅O₁₂ Power Lithium-ion Battery For Electric Vehicle

Lithium-ion battery has been widely used in portable electronic products and is developing as the power for electric vehicles（EV）due to its advantages of small size,light weight,long cycling life,no pollution,high energy density,no memory effect,ect.The EVs require the batteries possess better safety and power performance,lower cost,which is controlled by the electrode material,thus the development of high-performance electrode material is particularly important.The spinel LiMn₂O₄ shows the advantages of high potential,better safety performance,low cost and no pollution,which is considered as the ideal cathode material for the power lithium ion battery.Li₄Ti₅O₁₂ anode material shows the advantages of superior safety performance,stable structure,easy preparation and low cost,which meets the demand of some kind of EVs.This paper investigatied the synthesis,modification and perfprmance of LiMn₂O₄ and Li₄Ti₅O₁₂ further fabricates and preparation the LiMn₂O₄-Li₄Ti₅O₁₂ lithium ion battery system and its electrochemical performance is tested.The results are as following :（1）The lithium manganese oxide cathode material synthesized by solid-state reaction method was compared with commercial lithium manganese oxide material.The results shows that the initial specific discharge capacity and coulombic efficiency and taht after 50 cycles of LiMn₂O₄ thus-prepared is 113.6m Ah g^-1vs.89% and106.7m Ah g^-1vs.99.4%,respectively.In comparison,the corresponding data of commercialized LiMn₂O₄ is 108.3m Ah g^-1vs.89.1% and 101.5m Ah g^-1vs.96.6%,respecitively.These results show that the LiMn₂O₄ thus prepared shows higher reversible capacity and coulombic efficiency and better cycling stability.（2）Li₄Ti₅O₁₂ materials were synthesized by spray drying assisted high temperature（3）solid reaction using lithium acetate and nano-TiO₂ as main raw materials.Furthermore,the surface is coated by C,C-Cu and C-Ag to obtain Li₄Ti₅O₁₂/C,Li₄Ti₅O₁₂/C-Cu and Li₄Ti₅O₁₂/C-Ag composites.The results show that the structural stability and crystallinity of Li₄Ti₅O₁₂ are improved by coating.The results also show that the reversible capacity is improved from 165 m Ah g^-1 of Li₄Ti₅O₁₂ to 169 m Ah g^-1of Li₄Ti₅O₁₂/C,185 m Ah g^-1 of Li₄Ti₅O₁₂/C-Cu and 189 m Ah g^-1 of Li₄Ti₅O₁₂/C-Ag,respectively.The corresponding capacity at 20 C is improved from 98 m Ah g^-1 to 125,136 and 113 m Ah g^-1 respectively.The reasons for the performance improvement are the electronic conductivity and ion diffusion ability are improved by coating and thus the rate performance and cycling stability is improved.The effect of metal coating on the performance of is Li₄Ti₅O₁₂ further investigated and the results show that the coating only imrpoves the electronic conductivity of surface rather than bulk,thus the electrode without conductive carbon shows much poor performance but can be improved by first discharge at low current density and further larger current density.（3）The soft package cell is prepared by LiMn₂O₄ as cathode and Li₄Ti₅O₁₂ as anode.The results show that the discharge capacities of the initial and after 50 cycles are11.48 and 11.23 Ah,respectively,with a capacity retention rate of 97.8%.These results show that the cell can be developed as a battery with super long cycling life.