Study On The Novel Cathode And Anode Materials For Lithium Battery

Elemental sulfur has been proposed as promising cathode materials for the next generation of high-performance rechargeable lithium batteries due to their high theoretical capacity. However, they exhibit low utilization and fast capacity fades in lithium batteries due to their electrically and ionically insulated nature as well as solvent-solubility. Therefore, the cathode material must be well combined with a conductive agent when prepared as an electrode.In this study, three types of sulfur composite materials were prepared, that is: active carbon-sulfur composites, conductive polymer-sulfur composites and oxide-sulfur composites, which can be used as advanced cathode materials for rechargeable lithium batteries. The structure of the prepared cathode material was characterized by XRD.The electrochemical performance of sulfur composite electrodes was investigated by galvanostatic charge/discharge, cycling voltammetry methods and AC impedance.Sulfur-carbon composites were prepared by thermal treatment. The composites with favorable sulfur contents exhibited high specific capacity up to 1057.8 mAh/g in the initial cycle and a stable reversible capacity approximately 400 mAh/g.Oxide-sulfur cathode materials have been synthesized by mechanical milling or chemical aggradation, using mixture of oxides (V₂O₅, TiO₂, and CeO₂) and elemental sulfur. Combined with gel polymer electrolyte, the V₂O₅-S composites exhibited high specific capacity up to 844.68 mAh·g!(-1) in the initial cycle and a stable reversible capacity approximately 696.71 mAh·g^-1 after 30 cycle numbers. The discharge capacity of TiO₂-S is 600.83 mAh·g^-1 in the first cycle and 419.34 mAh·g^-1 in the 30th cycle. CeO₂-sulfur composites were prepared by depositing CeO₂ on the surface of sulfur power. The results indicated that the appending of CeO₂ formed a thin layer over sulfur particles. The initial capacity of CeO₂-sulfur composite was as high as 731.25 mAh·g^-1. The capacity was still 468.39 mAh·g^-1 after 30 charge-discharge cycles. EIS results showed that CeO₂-coating could suppress the electrochemical reaction resistant.Conductive polymer-sulfur composites were containing polyaniline-sulfur composites and poly ethylene oxide-sulfur composites.A novel conducting sulfur-polyaniline composite material was prepared by the chemical polymerization method .When the cathode materials are cycled at 0.2mA·cm^-2, the polyaniline/sulfur composites containing 15% polyaniline can delivered 1134.01mAh·g^-1 at the first discharge which is 82.42% higher than that of bare sulfur, the capacity was still 526.89 mAh·g^-1 after 30 charge-discharge cycles. When the discharge current density reaches up to 0.3mA·cm^-2, 0.4mA·cm^-2, the capacity of polyaniline/sulfur composites are 704.81mAh·g^-1,194.77mAh·g^-1 respectively. Poly (ethylene oxide) -sulfur composite was prepared by the thermal treatment method. The cathode with poly (ethylene oxide)-sulfur composite material shows the improvement of not only the charge-discharge capacity but also cycle durability.When the ratio of poly (ethylene oxide) and sulfur is 1:3, the cmposites can delivered 843.45mAh·g^-1 at the first discharge,after 30 cycles, the discharge capacity was 438.64 mAh·g^-1.The lithium titanium oxide Li₄Ti₅O₁₂ as anode material for lithium ion battery is regarded as a"zero strain"material. The lithium ion battery using Li₄Ti₅O₁₂ material as anode material is suitable for electric vehicle (EV) and power storage battery.In this paper, Li₄Ti₅O₁₂ was synthesized by amorphous titanium dioxide TiO₂ and Li₂CO₃ as lithium sources. Influential factors such as temperature, materials, time and proportion of reactants were researched. Pure spinel Li₄Ti₅O₁₂ can be synthesized by solid phase reaction at 800℃for about 24h, with excessive 8% Li₂CO₃. investigated. The results showed that the initial discharge capacity was 163mAh·g^-1, after 60 cycles, the specific capacity was 156.0mAh·g^-1, Its cycle retention rate after 60 cycles was 95.6%.Li₄Ti₅O₁₂ modified by C was obtained by solid state reaction. The system used LiCoO₂ as cathode was characterized. The results showed that, the battery's initial discharge specific energy was 122.9mAh·g^-1 with the current density 0. 1 mA·cm^-2, and decreased only by 3.43% after 100 cycles. The capacity was decreased as current density increased. But the rate of decrease was declined.Spinel Li₄Ti₅O₁₂ was modified by SnO₂ by physical and chemical procedures respectively. Both of the two procedures were compared with pure Li₄Ti₅O₁₂ to find the favorable way that could improve the performance.The experiments demonstrate that the physical procedure could restrain the bulk swell of Sn effectively and delivered promising electrochemical performance. After 15 cycles, its capacity is 207.7 mAh·g^-1。Li₄Ti₅O₁₂ was modified by doped Sb₂O₃. The composites materials Li₄Ti_5-xSb_xO₁₂ were characterized by constant current charge-discharge, cyclic voltammetry and electrochemical impedance spectrum. And the possible principle of reaction was proposed. The results showed that, when x=1, the initial discharge specific energy was 595.84mAh·g^-1 and the initial charge-discharge efficiency was only 45.7%.. After 20 cycles, the specific energy was still 249.57mAh·g^-1 which showed better cyclicity and can be a kind of preferable lithium ion battery.