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热电池是一种以固态熔盐作为电解质的一次性储备电源，因其高比能量和比功率，能够在严苛的环境下正常放电，成为现代武器（战略战术导弹，鱼雷，核武器等）不可替代的军用电源，其技术水平与高端国防武器装备发展息息相关。日新月异的军事工业对热电池提出了越来越苛刻的性能要求，具有高能量输出、高比功率、微型化小型化的电池体系成为军用电源的研究重点。而热电池中正极材料性能是影响热电池性能的关键因素，目前我国实际应用到型号的正极材料多为FeS2和CoS2，其中FeS2材料热稳定性差、电导率低，CoS2材料放电电压低，成本高，实际应用正极材料种类少导致热电池产品单一，不能满足不同军事领域对多样化热电池体系的需求。另外，热电池制备工艺仍采用传统的粉末压片工艺，存在工艺繁琐，制得电池体积大，活性材料利用率较低等问题。更重要的是，该制备工艺严重制约单体电池向小型化和微型化方向发展。本文针对正极材料单一问题，设计合成新型材料NiS2和Fe0.5Co0.5S2，并对高电压正极材料NiCl2材料进行改性研究；针对制备技术落后问题，将丝网印刷工艺用于单体电池的制备实现电池薄膜化，不仅克服传统粉末压片工艺的不足，提高活性材料的利用率和电池的比容量，并且使得电池的小型化和微型化成为可能。具体的研究内容和结果如下： （1）一元硫化物正极材料制备与电化学性能研究 通过控制合成温度采用高温固相法制备的一元硫化物FeS2、CoS2和NiS2物相单一、结晶结构良好。同一条件放电测试发现，NiS2放电性能处于FeS2和CoS2之间，可用作中等电压中长寿命热电池正极材料，丰富正极材料的种类。而且，高温固相法生产工艺简单，生产周期短，单次产量高，适合作为工程化生产的制备方法。 （2）新型复合硫化物Fe0.5Co0.5S2正极材料制备与电化学性能研究通过高温固相法和液相法分别合成复合硫化物正极材料Fe0.5Co0.5S2。将其进行放电测试发现，电压截止到1.25 V，固相法和液相法合成的Fe0.5Co0.5S2单体电池的放电比容量为1547.17 As?g-1和1872.89 As?g-1皆高于FeS2体系电池放电比容量，结合了FeS2高电压和CoS2高电导率的优势。另外，液相法合成的Fe0.5Co0.5S2在物理性能和放电性能上都优于固相法合成的材料。设计合成的新型复合硫化物Fe0.5Co0.5S2，尤其是液相法合成的Fe0.5Co0.5S2，是FeS2较为理想的替代材料。 （3）高电压NiCl2正极材料制备与改性研究 采用高温升华处理得到比表面积大、结构疏松的片状NiCl2材料，改善了NiCl2紧凑的结构，提高电化学活性。为缓解溢流现象，用LiF-LiBr-KBr替代LiF-LiCl-LiBr后电解质NiCl2体系单体电池的放电时间提高2.57倍。为提高NiCl2材料的导电率，一种方法是通过机械球磨方法在升华NiCl2中掺杂导电剂镍粉，电池的激活时间由7.57 s缩短至0.23 s，电池内阻也显著降低；另一种方法是泡沫镍基体替代传统不锈钢基体，放电过程中泡沫镍既充当基体又作为导电剂，NiCl2体系单体电池放电电压可达2.55 V，电压截止到1.5 V，电池的比容量为684.61 As?g-1，是不锈钢基NiCl2单体电池比容量的2.29倍。因此，改性后的NiCl2克服了自身的缺陷是高电压高能量输出电池正极材料理想的选择。 （4）薄膜单体电池制备与电化学性能研究 采用丝网印刷法制备出厚度为50 μmCoS2薄膜正极，该薄膜具有良好机械性能和柔韧性。CoS2薄膜正极与压片正极单体电池的放电比容量分别为2092.61 As?g-1和1076.65 As?g-1，CoS2薄膜正极活性物质利用率为66.70%。在CoS2薄膜正极基础上制备的CoS2/LiF-LiCl-LiBr复合薄膜，复合薄膜厚度仅为300 μm，极大地减小了电池的厚度和减轻了电池的重量，不仅使电池小型化和微型化成为可能，而且可以满足高新技术武器对高电压、高比容量热电池的需求。另外，薄膜单体电池的脉冲承载能力比压片电池提升30%，适合短时间内需要改变功率的热电池体系。;Thermal battery is a kind of one-time reserve power supply with solid molten salt as electrolyte. Because it can discharge normally in harsh environment with high specific energy and power, thermal batteries become an irreplaceable military power supply for modern weapons (strategic and tactical missiles, torpedoes, nuclear weapons). Its technical level is closely related to the development of high-end national defense weapons and equipment. Battery system with high energy output, high specific power and miniaturization has become the focus of military power supply research. The cathode material is the main limiting factor to improve the discharge performance of thermal batteries. At present, the two most widely used cathode materials in our country are FeS2 and CoS2. However, FeS2 material has poor thermal stability and low conductivity, while CoS2 has low discharge voltage and high cost. Fewer kinds of cathode materials in practical application lead to a single product of thermal batteries, which can not meet the requirements of diversified thermal batteries in different military fields. In addition, the traditional powder pressing process is still used in the preparation of thermal batteries, which has many problems, such as cumbersome process, large battery volume and low utilization of active materials. More importantly, the preparation process severely limits the miniaturization and miniaturization of batteries. Aiming at the single problem of cathode material, this paper designs and synthesizes new materials NiS2 and Fe0.5Co0.5S2, and modifies high voltage cathode material NiCl2. Aiming at the problem of backward preparation technology, screen printing process is applied to the preparation of single cell to realize the thin film of thermal battery, which not only overcomes the shortcomings of traditional powder pressing technology, but also improves the utilization of active materials and specific capacity of batteries. It also makes it possible to miniaturize and miniaturize batteries. Here are the main research contents and results. (1) Preparation and electrochemical properties of monosulfide cathode materials The monosulfides FeS2, CoS2 and NiS2 with single phase and good crystalline structure were prepared by high temperature solid-state method at controlled synthesis temperature. It was found that the discharge performance of NiS2 was between FeS2 and CoS2 under the same condition. So, NiS2 could be used as cathode material for medium voltage and long life thermal batteries, enriching the types of cathode materials. Moreover, the high-temperature solid-state method is simple in production process, short in production cycle and high in single output, which is suitable for engineering production. (2) Preparation and electrochemical properties of a new Fe0.5Co0.5S2 cathode material for thermal batteries Composite sulfide Fe0.5Co0.5S2 used as cathode material in thermal batteries can be prepared through traditional high-temperature solid-state method and liquid phase method, which combines precipitation and high temperature sulfuration. Compared with Fe0.5Co0.5S2 synthesized by high-temperature solid-state method (S-Fe0.5Co0.5S2), the Fe0.5Co0.5S2 synthesized by liquid phase method (L-Fe0.5Co0.5S2) had higher decomposition temperature, smaller size and larger specific surface area. The thermal battery employing L-Fe0.5Co0.5S2 as cathode exhibited excellent electrochemical properties, delivering a specific capacity of 1872.89 As?g-1. More importantly, the discharge performances of Fe0.5Co0.5S2 prepared by two different methods were better than that of FeS2, exhibiting higher material utilization and discharge specific capacity. Based on its excellent electrochemical properties, Fe0.5Co0.5S2 compound, especially synthesized by liquid phase method, is a promising cathode material for thermal batteries. (3) Preparation and modification of high voltage NiCl2 cathode material High specific surface area and loose sheet NiCl2 material was obtained by high temperature sublimation, which improved the compact structure and electrochemical activity of NiCl2. To alleviate the overflow phenomenon, the discharge time of NiCl2 single cell with LiF-LiBr-KBr instead of LiF-LiCl-LiBr electrolyte was increased by 2.57 times. In order to improve the conductivity of NiCl2 materials, one way was to add conductive agent Ni powder to sublimate NiCl2 by mechanical ball milling. The activation time of 7.57 s was shortened to 0.23 s, and the internal resistance of the battery was also significantly reduced. Another method was to replace the traditional stainless steel substrate with foam nickel substrate. The NiCl2-based single cell with nickel foam substrate exhibited a 2.55 V discharge voltage and a specific capacity of 684.61 As?g-1 with the cut-off voltage of 1.5 V. For comparison, the NiCl2 single cell with stainless steel substrate was also discharged, demonstrating a 2.43 V discharge voltage and a specific capacity of 299.39 As?g-1. These significant improvements can be attributed to the excellent impregnation of NiCl2 into the high-porosity nickel metal foam wherein the nickel metal foam acts as conductive agent and substrate. Therefore, the modified NiCl2 overcomes its own shortcomings and is an ideal choice for cathode material of high voltage and high energy output batteries. (4) Preparation and electrochemical performance of thin film single cell The thin film CoS2 cathode with thickness of 50 μm was prepared by screen printing process，possessing good mechanical properties and flexibility. The discharge specific capacities of single cells with CoS2 film cathode and pressed cathode were 2092.61 As?g-1 and 1076.65 As?g-1, respectively. The utilization of active substances of CoS2 thin film cathode was 66.70%. The CoS2/LiF-LiCl-LiBr composite thin film was prepared on the basis of the CoS2 film cathode, whose thickness was 300 μm. The film single cell can reduce the thickness and weight of the battery, which makes the miniaturization of the battery possible and meets the needs of high-tech weapons for high voltage and high specific power thermal batteries. In addition, the pulse carrying capacity of thin film single cell was 30% higher than that of pellet single cell, which is suitable for the thermal battery system that needs to change power in a short time.
|胡静. 热电池新型正极材料的制备与薄膜化工艺的研究[D]. 中国科学院大学,2019.|
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