Study On Preparation And Al Doping Modication Of Nanosized LiMn₂O₄

Lithium ion batteries have been widely used in portable mobile devices,but further research is needed to meet the high power market demand.The rate performance is considered to be an important index to evaluate the cathode materials of power lithium ion batteries.Most of commercial lithium manganese oxide（LiMn₂O₄）materials are micron level,and its relatively large particle size is not conducive to the deintercalation/intercalation of lithium ions,which leads to poor rate performance.Hence,the particle size is reduced to nanometer level,which can be regard as an effective way to improve the rate performance of LiMn₂O₄ materials.However,the overmuch contact area between nanoparticles and electrolyte is easy to accelerate dissolution of manganese,which results in capacity attenuation and then shortens the service life.Furthermore,it is necessary to modify the nanosale LiMn₂O₄ materials,which can stabilize the lattice structure of materials,enhance cycle stability of materials,and prolong the battery life.This paper is mainly composed of two aspects of reserch.Firstly,two kinds of LiMn₂O₄ products with different sizes are synthesized by sol-gel method and solid state method,respectively.It is found that the nanosized LiMn₂O₄（SG-LMO）prepared by sol-gel method exhibits preferable electrochemical performance.The discharge capacity of SG-LMO is 85.5 m Ah g^-1at 5 C rate under ambient temperature,which occupies 71.7% of a capacity of 0.5 C.The capacity of nanosized LiMn₂O₄（SS-LMO）prepared by solid state method is 72.8 m Ah g^-1 at 5 C rate under ambient temperature,and the capacity retention rate is only 62.6% of the capacity of 0.5 C.The superior electrochemical performance of SG-LMO is mainly determined by the following points:（1）the reduced metal atom confused degree in lattice and the low I（111）/I（311）intensity ratio value stabilizes the spinel lattice structure stable,and suppresses Jahn-Teller effect and erosion rection of electrolyte;（2）the small particle size shortens the lithium ion diffusion path;（3）the low electrode polarization potential is conducive to insertion and extraction of lithium ions.Secondly,based on the excellent electrochemical performance of SG-LMO,this study exploits aluminum doping method to further heighten the cycling satbility of SG-LMO.LiAl_xMn_2-xO₄（x=0.00,0.05,0.10,0.15）materials are synthesized by adjusting the content of doped aluminum and their properties are explored.The results indicate that the LiAl₀.1Mn₁.9O₄ owns the preferable electrochemical property.At 25 oC,LiAl₀.1Mn₁.9O₄ delivers a capacity retention of 96.5% at 0.5 C rate after 200 cycles,which is obviously higher than undoped LiMn₂O₄（85.6%）.At 45 oC,LiAl₀.1Mn₁.9O₄ exhibits a higher capacity retention of 93.3% compared with undoped LiMn₂O₄（88.3%）at 0.5 C rate after 100 cycles.The above advantageous properties of SG-LMO could be attributed to the reason that the newly formed Al-O bond in the LiMn₂O₄ crystal structure is more stable than the intrinsic Mn-O,which effectively suppresses the occurrence of Mn dissolution and Jahn-Teller effect,and furthermore enhances the structure of the material.In this paper,the high performance nanosized aluminum doped LiMn₂O₄ could be used as cathode materials for high power lithium ion batteries,which provides the possibility to increase the battery charge-discharge rate and prolong service life.