CAS OpenIR
新型热电池正极材料的制备及电化学性能研究
郭胜楠
Subtype博士
Thesis Advisor朱永平
2019-07-01
Degree Grantor中国科学院大学
Degree Discipline材料学
Keyword热电池,正极材料,二硫化钨,三氟化铁,分级结构
Abstract

热电池是一次贮备电池的一种,以固态熔盐作为电解质,具有能够大功率放电、贮存时间长、能耐苛刻环境等优点,是国防科技和武器工业应用中重要的化学电源体系。新一代武器装备的发展对热电池的性能不断提出更高的需求。正极材料是热电池体系的重要组成部分,对热电池体系的性能有着决定性的影响。但是,目前能够实际应用的正极材料仅有FeS2、CoS2等几种硫化物,随着军事应用的快速更新换代,现有的正极材料已逐渐不能满足大比容量、高输出功率的电源体系的设计要求,亟需开发新型的高性能正极材料。针对现有热电池正极材料FeS2在导电性、热稳定性及CoS2在放电电压等方面的不足,本论文以探索发展高性能新型热电池正极材料为目的,沿高比容量和高电压两个方向,通过对现有正极材料进行掺杂改性及开发新型电化学体系,研究了镍钴锰三元硫化物、二硫化钨及铁基氟化物等正极材料的制备和电化学性能。主要进行了以下工作:(1)利用高温固相法合成了高电导率镍钴锰三元硫化物正极材料。按组分比例,命名为NCM333、NCM622、NCM811。结果显示,三元硫化物具有极好的导电性。其中,NCM811正极材料具有最优的性能,单体电池总极化约6 mΩ。在同一测试条件下进行放电时,NCM811具有比FeS2和CoS2更平稳的放电性能,截止电压1.5 V时,比容量为289.4 mA h g-1,与CoS2的297.2 mA h g-1基本相当。NCM811成本低廉,是比CoS2更合适的长寿命热电池正极材料。(2)利用高温固相法合成了大比容量片状WS2纳米材料。WS2具有极高的热稳定性,其热分解温度超过1200 °C。添加适量Li-Si合金粉对WS2进行预锂化,能够消除放电尖峰,成功将其应用于热电池。WS2单体电池的开路电压为1.43 V;截止电压1 V时,放电比容量为334.7 mA h g-1,单体电池的总极化约10-11 mΩ。片状WS2纳米正极材料的热稳定性极其优异,放电比容量远高于CoS2,是理想的新一代大比容量长寿命热电池正极材料。(3)利用液相法合成了分级结构高电压FeF3正极材料。通过研究反应温度、时间、反应物浓度及脱水温度等实验条件对FeF3晶体形貌的影响,制备了纳米尺寸颗粒组装成微米级长方体的分级结构(Hierarchical structure)FeF3多孔材料。FeF3材料具有优异的热稳定性,初始分解温度为800 °C。FeF3单体电池的开路电压为3.3 V。在电流密度为100 mA cm-2的条件下,FeF3单体电池的放电电压为3.2 V,分级结构使其具有稳定的高电压放电平台。截止电压为2 V时,放电时间为276 s,比容量为81.9 mA h g -1。通过在FeF3正极材料中添加1 wt. %的多壁碳纳米管作为导电剂,大幅提高了其电子导电性,使电池的总极化从45 mΩ降低至约10 mΩ,放电时间倍增至542 s。使用Co掺杂进一步改善了FeF3正极材料的导电性,使单体电池的总极化从10 mΩ降低至6-8 mΩ。其中Co掺杂5%样品放电时间长达813 s,比容量为241.1 mA h g -1,为FeF3-MWCNTs的1.5倍。分级结构FeF3正极材料具有“3 V”放电平台,通过掺杂改性大幅改善了导电性,使其成为理想的高电压大功率热电池正极材料。(4)使用NH4HF2和Fe2O3作为氟源和铁源,制备了铁基复合氟化物材料FeF2.2。固相法相对液相法更加安全,有利于大规模合成。FeF2.2热稳定性高,放电时具有协同放电作用,因此兼具FeF3的高电压和FeF2的高电导率,单体电池在电流密度100 mA cm-2下,初始放电电压为3 V,截止电压2 V时,放电时间为414 s,放电比容量为123 mA h g-1。但是由于固相法FeF2.2不具备高电压放电平台,需要对其颗粒形貌进行进一步优化。;Thermal batteries are a type of reserve primary battery, which adopt inorganic salts as electrolyte. Due to the excellent performance of high-power output, long shelf life and high stability, thermal batteries are the mostly used chemical power sources for military operations. In recent years, the ever-changing technological needs of military operations call for thermal batteries with better electrochemical performance. The electrochemical performance of thermal batteries depends on the properties of cathode materials. The mostly used cathodes are FeS2 and CoS2, which are insufficient in thermal stability, conductivity and discharge voltage for the demands of higher specific capacity and larger output energy. To solve these problems and achieve cathode materials with high specific capacity and high voltage, research works including the modification of the existing cathode materials and the exploitation of new and better cathode materials are carried out in this dissertation. Therefore, nickel-cobalt-magnesium ternary sulfide, tungsten disulfide and iron-based fluorides have had been synthesized and evaluated as the cathode materials for thermal batteries. The main works are as follows: (1) The nickel-cobalt-magnesium ternary sulfide were synthesized by high-temperature solid-reaction method.The samples are denoted as NCM 333, NCM622 and NCM 811 by reactant proportion. The results present that the NCM811 cathode has the best conductivity of about 6 mΩ. At the same discharge conditions, the NCM811 single cell has a smoother discharge curve than that of FeS2 and CoS2. With a cut-off voltage of 1.5 V, the specific capacity is 289.4 mA h g-1, which is almost the same as CoS2. The high conductivity, large specific capacity and low cost make NCM811 a better cathode material for long-life thermal batteries than CoS2.(2) The WS2 nanosheet was synthesized by a high-temperature solid reaction method. The WS2 nanosheet has a high thermal decomposition temperature higher than 1200 °C. The voltage transient can be eliminated by prelithiation with Li-Si alloy powder. The open circuit voltage (OCV) of WS2 single cell is 1.43 V. With a cut-off voltage of 1 V, the specific capacity is 334.7 mA h g-1. The total polarization is about 10-11 mΩ. The outstanding thermal stability and larger specific capacity enable WS2 the ideal new generation cathodes for long-life thermal batteries.(3) A hierarchical-structured anhydrous FeF3 sample with high voltage was synthesized.By controlling of reaction kinetic factors, FeF3 sample with microporous hierarchical structure was synthesized. The FeF3 sample has good thermal stability. The initial decomposition temperature is 800 °C. The OCV of FeF3 single cell is 3.3 V. At a current density of 100 mA cm-2, the FeF3 single cell exhibits an initial discharge voltage of 3.20 V. The hierarchical structure enables the flat voltage plateau at high level. The discharge time is 276 s and the specific capacity of 81.9 mA h g-1 with a cut-off voltage of 2.0 V. Subsequently, the 1 wt % multi-walled carbon nanotubes (MWCNTs) are adopted as the conductive agents, leading to a reduction of total polarization from 45 mΩ to 10 mΩ. The discharge time is doubled to 542 s. The Co-doped FeF3 samples are designed and synthesized to improve the conductivity furtherly. The total polarization of Co-doped single cell is reduced to 6-8 mΩ. The 5% doped samples has the longest discharge time of 813 s and the largest specific capacity of 241.1 mA h g-1, which is 1.5 times higher than that of pristine FeF3-MWCNTs cathode. Thus, the “3 V” level hierarchical structure FeF3 cathode, combined with good conductivity from MWCNTs and Co-doping, will be the ideal cathodic material for high-voltage and high-power thermal batteries.(4) The NH4HF2 and Fe2O3 are used to synthesize a kind of FeF3-FeF2 composite denoted as FeF2.2. The solid reaction method is safer and favorable for large-scale synthesis. FeF2.2 sample has good thermal stability and a synergistic discharge effect. At a current density of 100 mA cm-2, the initial discharge voltages of the FeF2.2 single cell is 3.0 V. The discharge time and specific capacities is 414s and 123 mA h g-1 with a cut-off voltage of 2 V. However, the crystal structure of FeF2.2 needs to be optimized to obtain a flat voltage plateau. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40633
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
郭胜楠. 新型热电池正极材料的制备及电化学性能研究[D]. 中国科学院大学,2019.
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