铜硫化合物作为锂电池正极材料的性能及机理研究

发布时间：2018-07-11 18:25

本文选题：锂电池 + 锂硫电池　；参考：《厦门大学》2014年硕士论文

【摘要】：锂硫(Li-S)电池具有成本低廉、环境友好、能量密度高等优点,是一种理想的下一代二次电池。现有的硫正极及相应的锂硫电池存在电极材料导电性差、电化学反应中间产物多硫化物溶解于电解液而引起的活性物质利用率低和循环寿命短等诸多问题。如何固硫,提高电极材料活性物质利用率,如何提高电极材料的电导率,提高循环稳定性,是锂硫电池研究开发的重要课题。硫元素(S)容易与过渡金属(M)形成稳定的金属硫化物(MS)。利用这一特性,在硫正极材料中加入过渡金属或者直接利用金属硫化物作为锂电池正极材料是一种有效的固硫策略。在金属硫化物中,硫化亚铜(Cu2S)材料导电性好,与硫化锂(Li2S)晶体结构极其相似,摩尔体积基本相等,并且其还原产物纳米铜的导电性优异。因此,硫化亚铜是一种非常具有潜力的锂电池材料。本论文研究了硫化亚铜作为锂电池正极材料的电化学性能及其反应机理,研究工作主要包括以下三个部分： (1)使用商品化的硫化亚铜(Cu2S)作为电极材料,测试了Cu2S半电池的电化学性能。该电极材料中含有Cu、CuS和Cu2S三种化合物,比容量为335mAh·g-1,200个充放电循环之后容量保持率为99.5%,具有优异的循环性能。但是该材料在循环初期阶段具有多种放电电压平台,不断循环过程中电压平台发生变化。为了探讨其中的电化学反应机理,本论文利用XRD、XPS和TEM分析手段对硫化亚铜材料的充放电过程进行表征。分析结果表明,当电极材料中含有足够量的Cu时,如采用铜箔集流体或添加过量铜粉,不同形态的S元素在充放电循环过程中全部逐渐转化为Cu2S晶体。此后充放电过程中只有一个单一的电化学反应,即Cu2S+Li(?)Li2S+Cu,表现为充放电过程中1.7V和1.85V两个特别平坦的电压平台。 (2)研究了不同粒径的Cu粉与S粉按不同比例反应生成Cu2S的过程。研究发现当铜硫摩尔比为3：1时,纳米铜粉和硫粉反应生成纯度较高的Cu2S,该材料具有优异的循环性能和固硫效果,100个循环容量保持率为83.3%；当铜硫摩尔比为2：1和1：1时,纳米铜粉和硫粉反应生成物中含有CuS,材料的循环性能和固硫效果较差,100个循环容量保持率分别为33.3%和14.5%。 (3)通过采用铜箔集流体并在电极材料中添加铜粉的方式研究了锂硫电池在充放电过程中Cu和S原位形成的硫化亚铜正极材料的电化学性能。该复合材料在0.5C倍率下充放电测试,首圈放电时单位硫质量的比容量高达1614.1mAh·g1-,硫的利用率高达91%;在2C倍率下充放电循环,第1000个循环的容量保持率为96.5%。通过本论文的研究发现,在锂硫电池充放电过程中,用金属Cu固定元素S元素从而在电极上形成导电性高的Cu2S材料,最终得到了一种硫利用率高、循环稳定性及倍率性能优异的含硫电极材料,说明Cu2S是一种非常具有潜力的储能材料。
[Abstract]:Li-S battery is an ideal next-generation secondary battery because of its advantages of low cost, friendly environment and high energy density. The existing sulfur positive electrode and its corresponding lithium-sulfur battery have many problems, such as poor conductivity of electrode materials, low utilization rate of active substances and short cycle life due to the dissolution of polysulfide, an intermediate product of electrochemical reaction, in the electrolyte. How to fix sulfur, improve the utilization ratio of active materials of electrode materials, improve the conductivity of electrode materials and improve the cycle stability is an important subject in the research and development of lithium-sulfur batteries. Sulfur (S) is easy to form stable metal sulfides (MS) with transition metals (M). It is an effective strategy to fix sulfur by adding transition metal to sulfur cathode material or directly using metal sulfide as cathode material for lithium battery. Cuprous sulfide (Cu _ 2S) has good electrical conductivity and is similar to lithium sulfide (Li _ 2S) crystal structure. The molar volume of Cu _ 2S is similar to that of lithium sulfide (Li _ 2S), and the reduction product of Cu _ 2S has excellent electrical conductivity. Therefore, cuprous sulfide is a promising lithium battery material. In this paper, the electrochemical performance and reaction mechanism of cuprous sulfide as cathode materials for lithium batteries were studied. The research work mainly includes the following three parts: (1) the commercial copper sulfide (Cu2S) was used as electrode material. The electrochemical performance of Cu 2S semilayer was tested. The electrode material contains three kinds of compounds, Cu-CuS and Cu2S. The specific capacity of the electrode is 335mAh g-1200 charge-discharge cycles, the capacity retention rate is 99.5, and it has excellent cycling performance. However, the material has a variety of discharge voltage platforms in the initial stage of the cycle, and the voltage platform changes continuously during the cycle. In order to investigate the electrochemical reaction mechanism, the charge-discharge process of cuprous sulfide materials was characterized by XRDX XPS and TEM. The results show that when sufficient amount of Cu is contained in the electrode material, if copper foil is used to collect the fluid or the excess copper powder is added, all the S elements in different forms are transformed into Cu _ 2S crystals during the charging and discharging cycle. After that, there is only one single electrochemical reaction in the charge-discharge process. That is, Cu _ 2S Li (?) Li _ 2S Cu, which is a very flat voltage platform of 1.7V and 1.85V during charge and discharge. (2) the process of Cu _ 2S formation from Cu _ 2O _ 2 powder and S powder in different proportion has been studied. When the molar ratio of copper to sulfur is 3:1, Cu _ 2S with high purity can be obtained by the reaction of nano-copper powder and sulfur powder. The material has excellent cycling performance and sulfur fixation effect, and the retention rate of 100 cycles capacity is 83.3%. When the molar ratio of copper to sulfur is 2:1 and 1:1, Due to the existence of CuS in the reaction product of nano-copper powder and sulfur powder, the recycling performance and sulfur fixation efficiency of the materials are poor, and the retention of 100 cyclic capacity is 33.3% and 14.575% respectively. (3) the copper powder is added to the electrode material by using copper foil to collect fluid and add copper powder to the electrode material. The electrochemical properties of copper sulfide cathode materials formed in situ by Cu and S during charging and discharging of Lithium-Sulphur batteries were studied in this paper. The specific capacity per unit sulfur mass of the composite is as high as 1614.1mAh g _ 1-and the utilization ratio of sulfur is 91g ~ (-1) at the first cycle of discharge, and the capacity retention rate of the 1000th cycle is 96.5% at 2C rate. Through the research in this paper, it is found that in the process of charging and discharging of lithium-sulfur battery, Cu is used to fix the element S to form a high conductivity Cu _ 2S material on the electrode, and a kind of high sulfur utilization ratio is obtained. Cu2S is a potential material for energy storage because of its excellent cycle stability and rate performance.
【学位授予单位】：厦门大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：O614.121;TM912

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