物理化学学报

所属专题: 钠离子储能材料和器件

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Na0.44MnO2在碱性溶液中的电化学机制

李慧1, 刘双宇1, 袁天赐2, 王博1, 盛鹏1, 徐丽1, 赵广耀1, 白会涛1, 陈新1, 陈重学3, 曹余良2   

  1. 1 全球能源互联网研究院有限公司, 先进输电技术国家重点实验室, 北京 102211;
    2 武汉大学化学与分子科学学院, 湖北省电源材料与技术重点实验室, 武汉 430072;
    3 武汉大学动力与机械学院, 水力机械过渡过程教育部重点实验室, 武汉 430072
  • 收稿日期:2019-05-06 修回日期:2019-06-02 发布日期:2019-06-10
  • 通讯作者: 曹余良 E-mail:ylcao@whu.edu.cn
  • 基金资助:
    国家电网公司(SGRIDGKJ[2017]841)、国家科技部(2016YFB0901500)和国家自然科学基金(21875171,21673165)资助项目

Electrochemical Mechanism of Na0.44MnO2 in Alkaline Aqueous Solution

LI Hui1, LIU Shuangyu1, YUAN Tianci2, WANG Bo1, SHENG Peng1, XU Li1, ZHAO Guangyao1, BAI Huitao1, CHEN Xin1, CHEN Zhongxue3, CAO Yuliang2   

  1. 1 State Key Laboratory of Advanced Power Transmission Technology, Global Energy Interconnection Research Institute Co. Ltd., Beijing 102211, P. R. China;
    2 Hubei Key Laboratory of Electrochemical Power Sources, College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, P. R. China;
    3 Key Laboratory of Hydraulic Machinery Transients, Ministry of Education, School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, P. R. China
  • Received:2019-05-06 Revised:2019-06-02 Published:2019-06-10
  • Contact: CAO Yuliang E-mail:ylcao@whu.edu.cn
  • Supported by:
    The project was supported by the Science and Technology Project of State Grid, China (SGRIDGKJ[2017]841), the National Key Research Program of China (2016YFB0901500) and the National Natural Science Foundation of China (21875171, 21673165).

摘要: Na0.44MnO2具有原料丰富、合成简单、无毒环境友好、结构稳定性高等优势,适合作为水溶液钠离子电池的正极材料。Na0.44MnO2在中性水溶液中的比容量较低(30-40 mAh·g-1),而采用碱性电解液可大大提高Na0.44MnO2的可逆比容量(80 mAh·g-1)。当我们扩宽碱性电池的充放电窗口(1.95-0.3 V)时,在1.0 V(vs Zn/Zn2+)附近出现一个宽的放电平台,且首周放电比容量高达275 mAh·g-1,远远超出其理论嵌钠容量(121 mAh·g-1)。本文我们通过对不同放电深度下的电极进行X射线粉末衍射仪(XRD)、扫描电子显微镜(SEM)和电感耦合等离子体发射光谱(ICP-AES)表征,研究其超额容量的放电机理。结果表明1.0 V以下的低电位放电过程可分为两个阶段:第一阶段为H+在隧道结构中的嵌入,此时隧道结构保持不变,放电曲线上表现为平台区;第二阶段为过量H+的嵌入引起隧道结构破坏,同时伴随着Mn(OH)2相的生成和Na+从结构中释放出来,放电曲线上表现为斜坡区。这一研究结果表明Na0.44MnO2在碱液中的可逆性与下限电位紧密相关,高稳定的Na0.44MnO2材料需要避免H+的嵌入。

关键词: 钠离子电池, Na0.44MnO2, 碱性电解液, 电化学机制, 质子嵌入

Abstract: In recent years, aqueous sodium-ion batteries (ASIBs) have experienced rapid development, and a series of cathode materials for ASIBs has been widely reported. Among these, Na0.44MnO2 possesses the most promising prospects due to its low cost, non-toxic nature, simple synthesis, and structural stability. However, the reported capacity of Na0.44MnO2 in aqueous electrolyte was~40 mAh·g-1 (less than its theoretical capacity of 121 mAh·g-1), which limits its practical applications. Recently, we developed a novel alkaline Zn-Na0.44MnO2 dual-ion battery using Na0.44MnO2 as the cathode, a Zn metal sheet as the anode, and a 6 mol L-1 NaOH aqueous solution as the electrolyte. In this system, the Na0.44MnO2 electrode presented excellent electrochemical performance with high reversible capacity (80.2 mAh·g-1 at 0.5C) and outstanding cycling stability (73% capacity retention over 1000 cycles at 10C) in alkaline aqueous electrolyte. When the negative potential window was extended to 0.3 V, the Na0.44MnO2 electrode delivered an incredibly high capacity of 345.5 mAh·g-1, which far exceeded the theoretical capacity, but the cycling performance was extremely poor. In that study, X-ray diffraction (XRD)and inductively coupled plasma-atomic emission spectrometry (ICP-AES) analyses revealed that de-intercalation of Na+ and formation of Mn(OH)2 occurred during the discharge process, but the detailed electrochemical mechanism and structural evolution of this process remained unclear. In this study, we used ICP-AES to analyze the elemental composition of discharge products at different discharge depths and found that a small amount of Na+ ions extracted from Na0.44MnO2 electrode since Discharge-120 (corresponding to the discharge capacity of 120 mAh·g-1), and the extraction rate increased gradually with increasing discharge depth. Scanning electron microscope (SEM) and XRD analyses were also carried out to characterize the morphology and phase changes of Na0.44MnO2 electrode during discharge. The results show that the discharge of Na0.44MnO2 electrode in the voltage range 1.95-0.3 V could be divided into the three following steps:(1) the potential range above 1.0 V:Na+ ions de-intercalate reversibly into the tunnel structure of Na0.44MnO2; this discharge mechanism is consistent with that in non-aqueous and neutral aqueous sodium ion batteries. (2) The initial platform region at 1.0 V:in this step, protons (H+) began to insert into the Na+-vacancies in NaxMnO2, and the tunnel structure of NaxMnO2 was still maintained. (3) Subsequent slope region:when the Na+-vacancies in the tunnel structure were fully occupied by protons, further intercalation led to intensification of charge repulsion in the crystal structure. thus, the tunnel structure collapsed to form a new Mn(OH)2 phase, accompanied by the release of Na+ from the structure. H+ has a smaller radius than Na+; therefore, it could insert into the smaller vacancies in Na0.44MnO2, resulting in higher specific capacity. However, the insertion of H+ will also cause structural damage, which seriously worsens the cycling stability of the Na0.44MnO2 electrode.

Key words: Sodium ion battery, Na0.44MnO2, Alkaline electrolyte, Electrochemical mechanism, Proton insertion

MSC2000: 

  • O646