Preparation And Electrochemical Properties Of Nanostructured LiMn₂O₄ And LiMn₂O₄/Carbon Nanocomposites

Spinel LiMn2O4 is regarded as one of the most attractive cathode materials for transportation and large-scale batteries due to its low cost, environmental friendliness, good structural stability, and much improved safety. Improvement of the energy density and power density of the lithium-ion batteries is urgently required with the rapid development of electric vehicles and portable electronic devices..However, bulk LiMn2O4 suffers from poor rate capability due to the sluggish Li ion diffusion and limited electrical conductivity. to improve the rate capability of LiMn2O4 cathode. One method is to reduce the particle size from micrometer to nanometer so that electron and Li ion diffusion paths can be shortened. Another method is to add conductive additives to the cathode materials to improve their electrical conductivity.Phase pure and nanocrystalline LiMn2O4 possessing a particle size of 10-20nm have been prepared at a temperature as low as 180℃ by one-pot hydrothermal synthesis.with an excess concentration of Li:Mn precursor ratio (2:1).the LiMn2O4 nanoparticle electrode exhibits good cathode performance with high specific capacity, But the rate capability still too low for high power application.A one-step hydrothermal method has been developed to synthesize LiMn2O4/ graphene nanosheets (GNS) nanocomposite. The morphological and structural characterizations show that phase pure and well-crystallized LiMn2O4 nanoparticles with particle size distributed between 10 and 20 nm are uniformly anchored on the GNS. The LiMn2O4/GNS nanocomposite electrode exhibits superior cathode performance with high specific capacity, good cycling stability and rate capability as compared to the bare LiMn2O4 nanoparticle electrode. The combination of the LiMn2O4 nanoparticles and highly conductive GNS greatly enhances the kinetics of charge transfer of the electrode, which leads to good rate capability and large specific capacity. The flexible GNS can buffer the volume stain of LiMn2O4 grains associated with Jahn-Teller distortion and reduce the Mn dissolution into the electrolyte. which leads to improved cycling stability.The synthesis of highly crystallized ultrafine LiMn2O4/carbon nanotube (CNT) nanocomposite has been demonstrated by a one-step hydrothermal treatment using cheap reagents and with a short synthesis time of 5 h. Structural characterizations show that the material is phase pure, well crystallized, retains a spinel type structure with particle size distributed between 10 and 20 nm. The three-dimensional network formed by the carbon nanotubes provides the material with a higher electronic conductivity and also prevents agglomeration between the nanosized LiMn2O4 particles. the LiMn2O4/CNT nanocomposite with unique structural and morphological features exhibits superior high-rate capability and long term cycling stability, delivering discharge capacities of 127 mAhg-1(93% retention) after500 cycles at 1C rate and 72 mAhg-1 (74% retention) even after 1000 cycles at rates as high as 20C, as illustrated in this paper and holds promise for applications in electric traction.