The Preparation Of LiFePO₄ Cathode Material And Its Application In Lithium Ion Batteries

In the past decades,the greenhouse effect and overexploited fossil fuel resources encourage people to continuely explore the sustainable/renewable energy and electrical transportation devices.Developing such technology depends on the promotion of energy store efficency.The lithium batteries now have been widely applied in portable electronic devices.Exploiting the low cost and high safety electrode materials becomes the critical point in the development of lithium ion batteries.LiFePO₄ cathode material has drawn great interests due to its advantages whatever in scholar or in industry application.Its high theoretical capacity(170 mA h g^-1)and some other vitues such as a high safety,environmental benignity as well as a low toxicity make it a promising cathode material for lithium ion batteries.But its instrinct disadvantages such as the poor elctroconductivity and weak ion diffusivity also cause its weak rate performance and poor cycle ability at large current densities.The carbon coating technology was adopted to increase the LiFePO₄ cathode material.The electrochemical ploymerization was performed to coat a thin and uniform carbon source derived from polyaniline on the surface of the MWCNT decorated nano-LiFePO₄ particles.Meanwhile,the dense stacking of LiFePO₄particles via the hydrothermal method and the thin but homogeneous carbon layer also ensure the comparative high tap intensity of such composite.The introduce of MWCNT gets the electron transfer in all directions and decreases the ion diffusion distance,which leads eminent electrochemical behaviors for such cathode material.The porous LiFePO₄ composite with a complete conduct layer was also prepared via sol-gel technique.The particles can keep in a good contact and make the better permeation between the electrode material and electrolyte,which can alleviate the polarization phenomenon.As a result,the ion diffuse distance is enormously decreased in some degree.Finally,the enhanced cycle and rate performances were achieved.The LiFePO₄ products with different morphologies were prepared by adding different phosphorous sources.Among them the disk products with the least thickness and ion diffusion distance present the most excellent electrochemical performance.The assembly from the the lamellas layer guartees the eletron transfer in all directions and the maximum ion diffusivity ability.Such LiFePO₄ cathode material has overwhelming advantages in low cost and environmental benigntivity.Comparing with the full LiFePO₄ battery,the half battery has some lethal defects such as some safety problems.Herein,TiO₂ serves as the counter electrode and the full battery was fabricated.Considering the TiO₂ anode material suffers from the poor eletron conductivity,weak ion diffusivity ability,low capacity and unstable property during the cycle process.The nano-TiO₂ nanoparticles were embededed into porous the N modified graphene sheets,which prevents the pulverization of the active materials during the reaction process as well as enhancing the cycle ability.Besides,the modification of N increases the capacity of such TiO₂ anode material.