Synthesis And Research Of Anode Materials For The Power Lithium Ion Batteries

Under the double influence of energy crisis and environmental pollution,Lithium-ion batteries are drawing more and more people's attention because of its advantages such as high energy,environmental protection and safety.Among all electrode materials,Li₄ Ti₅O₁₂is considered as next generation cathode material for lithium-ion batteries because it has better cycling performance,safety and fast charge capability.In this dissertation,spinel Li₄ Ti₅O₁₂anode materials were prepared by high temperature solid-state reaction.After synthesis process was optimized and materials surface was coated by carbon,the electrochemical properties of Li₄ Ti₅O₁₂ were improved remarkably.Besides,the high capacity Sn O₂ anode materials were fabricated by sol-gel method.By combining Sn O₂ materials with Li₄ Ti₅O₁₂materials,cycling performance of Sn O₂ and capacity performance of Li₄ Ti₅O₁₂ could be improved effectively.The specific work is as follows:In this paper,the Li₄ Ti₅O₁₂ materials were characterized by SEM,XRD and charge-discharge tests etc.The effects of different Ti-source and calcination technology on the material properties were analyzed and investigated.The results showed that the Li₄ Ti₅O₁₂materials have the best properties when using nano-sized Ti O₂ as the original material,and preheated at 500?for 4h followed by 800?for 8h.The as-prepared sample was well-crystallized single-phase,and its particle was uniform with the size from 200 to 300nm.At charge/discharge rate of 1C,3C and 5C,the first discharge capacities were 141.6m Ah/g,126.3m Ah/g and 115.9m Ah/g,respectively.Besides,technology optimization has been conducted on the one-step solid state method.The results showed that the ratio of raw materials Li/Ti and heat-treatment time had great influence on the electrochemical properties of the sample,the performance of the sample was best when the raw materials Li/Ti with the ratio of 0.86 were calcinated at 800?for 12h.Its first discharge capacity and initial coulombic efficiency were 169m Ah/g and 99.5%,and the discharge capacity at 5C increased from 50.9m Ah/g to 92.4m Ah/g.In order to improve the conductivity and rate performance of Li₄ Ti₅O₁₂ material,carbon-coated Li₄ Ti₅O₁₂ composites were prepared by three different solid phase synthetic methods.EDS and electrochemical measurement showed that the carbon were attached to the surface of the materials successfully,and the carbon content in the three composites were all around 5wt.%.The materials that had been coated showed better first discharge cycle capacity and capacity reached 175.5m Ah/g,173.1m Ah/g and 166.9m Ah/g respectively.Among the three materials,the Li₄ Ti₅O₁₂/C composite obtained through a post-coating route exhibits remarkable electrochemical properties with good conductivity,high lithium ion diffusion coefficient,good cyclic reversibility and high-rate discharge performance.At 55?,the electrochemical analyses showed that the discharge capacity remains at 162m Ah/g at 3 C rate.The high capacity Sn O₂ anode materials were fabricated by sol-gel method,and the effect of surfactant on the structure,morphology and electrochemical performance of the Sn O₂ anode material was investigated.The results showed that the Sn O₂ synthesized with a surfactant exhibited smaller dimension,higher specific surface area and improved charge-discharge performance.The initial discharge specific capacity of the sample was as high as 536.3m Ah/g at the current density of 0.1C at room temperature,and the capacity retention was 64.7%after 50 cycles.On the bases of the study on preparing the pure Sn O₂ materials,Sn O₂-Li₄ Ti₅O₁₂composite materials with different Sn O₂ contents?95wt.%and 5wt.%?were prepared by two different liquid-phase methods.Electrochemical measurement showed that adding small amount of Li₄ Ti₅O₁₂ material to Sn O₂ material,could effectively improve the cycle performance of the Sn O₂ anode.The capacity fading of composite was reduced in the first several cycles and delivered a stable capacity of 195m Ah/g after 50 cycles.In addition,adding Sn O₂ nanoparticles to Li₄ Ti₅O₁₂ material,could also improve the capacity performance of the Li₄ Ti₅O₁₂ anode.For the compound material,the initial dicharge capacity were originally 178.3m Ah/g?0.1C?at room temperature and fifty cycles later,it remained at174.7m Ah/g,the capacity was much better than before.