Synthesis And Electrochemical Study Of The Electrode Materials For Lithium Ion Batteries Through Polystyrene Template Method

The development of the Li-ion battery has been limited by its electrode materials, which is one of the key technologies of the Li-ion battery system. It is well known that the performances of electrode materials are greatly influenced by the synthesis methods. Solid state method,which is used in industry widely,consumes more power and wastes more time than others. Moreover,the as-prepared materials agglomerate seriously and their crystals and particles are difficult to be well controlled leading to the degradation of the materials'performances.In this paper, we successfully prepared a series of electrode materials for lithium ion batteries using polystyrene (PS) template by use of its effects of spatial confinement and control. The results show that polystyrene template can control particle size, morphology and structure of the electrode materials and thus optimize the physical and electrochemical properties of materials.This study includes the main aspects as following:1. Synthesis of ordered macroporous LiMn₂O₄ spinel material using PS as a template. The XRD results show that LiMn₂O₄ has a spinel structure. The synthesis temperature influences the structure, morphology and electrochemical performances of the electrode materials. It is found that the spinel LiMn₂O₄ synthesized at 700oC for 3h displays excellent electrochemical performances. Its specific capacity is 113.8 mAh/g at first cycle when charged/discharged between 3.0 and 4.3 V at 1C, and remains 86.6% of its initial capacity after 100 cycles. In addition, the as-prepared material can also deliver a specific capacity of 90 mAh/g at 2C showing a good high rate compability and a stable cycling performance. The kinetic characteristics and the electrochemical performances of the synthesized LiMn₂O₄ are investigated and the diffusion coefficient of lithium intercalation in LiMn₂O₄ has been calculated.2. Synthesis of spinel LiNi0.5Mn_1.5O₄ high-voltage electrode material using PS as a template. After a lot of trials, we successfully synthesized the macroporous and sub-micron LiNi_0.5Mn_1.5O₄ materials. The synthesis conditions is defined by thermal analysis (DTA, TGA), and the crystal structure is defined by powder X-ray diffraction (XRD). The morphology is obsvered by scanning electron microscopy (SEM). The electrochemical properties of the prepared materials are measured by cyclic voltammetry (CV) and charge-discharge. The optimal synthesis temperature is 900 oC. The resultant LiNi_0.5Mn_1.5O₄ delivers a specific capacity of 102 mAh/g at first cycle, and remains a specific capacity of 90.1 mAh/g after 186 cycles, which is 88.3% of the initial capacity, when charged/discharged between 3.5 and 5.0 V at 0.5 C. The results show that LiNi_0.5Mn_1.5O₄ prepared by the template method possesses good cycling performance.3. Synthesis of other lithium storage materials such as LiCO₂, LiFePO₄, Co₃O₄ and NiO using PS as template. By controlling the synthesis temperature, sintering time, heating rate and particle size of polymer templates, we can obtain these materials with novel morphology, small particles and the perfect crystal. The crystal structure of various products are defined by powder X-ray diffraction (XRD), the morphology is obsvered by scanning electron microscopy (SEM). The electrochemical properties of these obtained materials are investigated initially by cyclic voltammetry (CV) and charge-discharge.