【作者】 姚文俐；

【导师】 杨军；

【作者基本信息】 上海交通大学 ， 应用化学， 2008， 博士

【摘要】 锂离子二次电池具有比能量高、工作电压高、循环寿命长、安全无污染等优点,已成为发展最快和最受重视的高能蓄电池。商业化石墨碳负极材料具有良好的循环性能,但比容量（300～350 mA h g-1）较低,不能满足高比能量电池的发展要求,迫切需要进行新型高容量负极材料的研究和探索。而过渡族金属钴氧化物（CoO、Co₃O₄）的比容量高达700～1000 mA h g-1,很有希望成为一种新型高容量锂离子二次电池负极材料。研究表明,无论钴氧化物纳米颗粒还是纳米管,首次容量损失较大（>30%）及快速的容量衰减限制了此类材料的实际应用。本文采用合成的六方β-Co（OH）2为模板制备了层片状CoO、Co₃O₄材料及其复合负极材料;另外,以酸化处理的碳纳米纤维为模板合成了Co（OH）₂-碳纳米纤维（Co（OH）₂-CNF）前驱体并制备了Co₃O₄-碳纳米纤维（Co₃O₄-CNF）复合负极材料。结果表明,合成的CoO、Co₃O₄及其复合材料很好地改善了电池的首次效率和循环性能。主要工作包括以下几方面:1.层片状氧化亚钴的制备及储锂性能研究。在无模板、无表面活性剂的水热条件下,控制反应条件合成了不同尺寸的六方β-Co（OH）₂材料;研究了初始硝酸钴浓度、反应溶液组成、反应温度、反应时间等实验参数对产物形貌的影响。以层片状β-Co（OH）2为模板制备了层片状CoO材料,系统研究了形貌尺寸对CoO材料储锂容量和循环性能的影响。平均直径约为15μm,厚度约6μm层片状CoO电化学性能要比单薄片及纳米CoO要好,100次循环后其容量保持在800 mA h g-1。2.纳米、层片状四氧化三钴负极材料制备及储锂性能研究。在异丙醇/水（体积比,1:1）溶液中,合成了α-Co（OH）2前驱体并煅烧制备了纳米Co₃O₄材料,研究了纳米Co₃O₄电化学储锂性能。同时,采用水热-热分解法制备了层片状Co₃O₄材料,研究了层片状Co₃O₄材料电化学性能。结果表明,平均直径约15μm,厚度4～10μm层片状Co₃O₄材料循环性能较好,100次循环后其容量稳定在600 mA h g-1左右。3.四氧化三钴-碳纳米纤维复合负极材料制备及电化学性能研究。以酸化处理碳纳米纤维为模板在异丙醇/水溶液中合成了Co（OH）2-CNF前驱体并煅烧制备了Co₃O₄-CNF复合负极材料。详细地研究了前驱体Co（OH）2-CNF煅烧温度对复合材料中Co₃O₄的晶形、尺寸、比表面积及物相转变的影响。Co₃O₄-CNF复合材料的比表面积及碳纳米纤维的含量强烈地影响该系列复合材料的电化学性能。作为锂离子电池负极材料,Co₃O₄-CNF（CNF的百分含量为24.3%）纳米复合材料显示了优良的储锂容量和循环性能（100次循环后容量仍超过880 mA h g-1）。4.层片状氧化钴/碳纳米纤维复合材料制备及储锂性能研究。以合成的β-Co（OH）₂/CNF前驱体在氩气或空气氛中煅烧分别制备了层片状CoO/CNF和Co₃O₄/CNF复合材料。层片状CoO/CNF复合材料具有良好的储锂循环性能和高倍率性能。在1 M LiPF6-EC: DMC （1:1,Vol）常规电解液中,与正极材料LiNi0.5Mn1.5O4组成全电池的首次放电平台约2.8 V左右,以CoO/CNF复合材料的重量计算,其首次放电容量为450 mA h g-1,很可能成为一种有希望的、新型高容量的锂离子负极材料。更多还原

【Abstract】 Lithium-ion batteries are considered as the most promising power sources because of their high potential, high energy density, long cycle life, no memory effect and environmental friendliness. The commercialized graphite-based anode materials exhibit excellent charge and discharge cycling performance, but their low specific capacity （300-350 mA h g?1） can’t satisfy the demand for the high energy density of batteries. Therefore, it is urgent to develop new anode materials with larger capacity. Owing to their high capacity of 700-1000 mA h g?1, transition metal cobalt oxides （CoO, Co₃O₄） are a new class of promising anode materials for rechargeable Li-ion batteries. As reported, the large irreversible capacity loss （>30%） in the first cycle and relatively fast capacity fading rate during electrochemical cycling of cobalt oxides nanoparticles and nanotubes limit their practical applications. In this thesis, we have successfully synthesized series of lamellar CoO and Co₃O₄ platelets as well as their composites prepared through as-synthesized hexagonalβ-Co（OH）₂ as templates. Moreover, Co₃O₄-carbon nanofiber （Co₃O₄-CNF） composites were also successfully prepared by calcination of Co（OH）2-carbon nanofiber （Co（OH）₂-CNF） precursors using acid-treated carbon nanofiber as templates. As a result, both the first cycle efficency and cycling performances have been greatly improved by using the prepared CoO, Co₃O₄ and their composites. The concrete research contents are summarized as following:1. Preparation and study on electrochemical performance of lamellar CoO materials as anode materials for lithium-ion batteries. Lamellar β-Co（OH）2 platelets with different dimensions were synthesized by a simple hydrothermal route without using surfactants or templates. The influence of reaction conditions, such as: Co（NO3）2 concentrations, composition of solutions, reaction time, reaction temperature, on the morphology and structure of the obtained products was investigated. Lamellar-type CoO platelets were prepared through thermal decomposition of lamellarβ-Co（OH）2 templates. As a typical example, the effect of the morphology and size of lamellar CoO platelets on the capacity and cycle-ability was systematically investigated. Lamellar CoO platelets with average tubular size of 15μm in diameter and 6μm thick showed larger capacities and much better electrochemical performance than monolayer CoO platelets and CoO nanoparticles. Even after 100 cycles, the reversible capacity of lamellar CoO platelets was still kept at 800 mA h g-1.2. Preparation of nanosized Co₃O₄ and lamellar Co₃O₄ and study on their lithium-storage performance. Co₃O₄ nanoparticles were prepared by the calcination ofα-Co（OH）2 precursors formed in isopropyl alcohol - water （1:1, v/v） solution. The electrochemical performance of Co₃O₄ nanoparticles was thoroughly studied. Furthermore, Lamellar Co₃O₄ platelets were prepared through thermal decomposition of lamellarβ-Co（OH）₂ synthesized by simple hydrothermal method. The lamellar Co₃O₄ platelet with average tubular size of 15μm in diameter and 4-10μm thick exhibited an excellent cycling performance, retaining a specific capacity of approximately 600 mA h g-1 after 100 cycles.3. Preparation and study on electrochemical performance of Co₃O₄-CNF composites as anode materials for lithium-ion batteries. Co₃O₄-CNF composites were prepared by the calcination of Co（OH）2-CNF precursors synthesized on acid-treated carbon nanofiber templates. The effects of the calcining temperature on the crystallinity, grain size, specific surface area of Co₃O₄ and phase transformation from Co₃O₄ to CoO were studied in detail. Both the specific surface area and CNF content in CNF-cobalt oxide composites dominated the electrochemical performance of these composites. As anode materials for lithium ion batteries, Co₃O₄-CNF （24.3 wt% CNF） composite showed excellent cyclability and high lithium-storage capacity （881 mAh g-1 after 100 cycles）.4. Preparation of lamellar cobalt oxide/carbon nanofiber （CNF） composite and study on their lithium-storage performance. Lamellar CoO/CNF composite or Co₃O₄/CNF composite have been prepared by caicining as-synthesizedβ-Co（OH）₂/CNF precursors under Ar flow or air atmosphere, respectively. The electrochemical lithium-storage performance of these composites was investigated detailedly. As a result, lamellar CoO/CNF composite electrodes showed excellent cyclability and high charge-discharge rate capability. A complete cell was assembled by lamellar CoO/CNF composite anode coupled with LiNi0.5Mn1.5O4 cathode in 1 M LiPF6-EC: DMC （1:1, Vol） electrolyte solution. The voltage profiles of the complete cell showed a long voltage plateau at about 2.8 V during the first discharge step. The first discharge capacity was 450 mA h g-1 based on the weight of the CoO/CNF composite. It could be a promising and high-capacity negative electrode material for advanced lithium-ion batteries.更多还原