Masayoshi Matsuzaki, R. Tatara, K. Kubota, Kazutoshi Kuroki, Tomooki Hosaka, Kazuteru Umetsu, Nobuhiro Okada, Shinichi Komaba
Owing to their high discharge capacities, P2‐type transition metal layered oxides have attracted attention for use as positive electrode materials in Na‐ion batteries. However, owing to the Na‐deficient compositions of these oxides, additional Na+ must be supplied using a Na‐metal negative electrode to attain a high capacity in a half‐cell configuration. In this study, solid Na2CO3 powder was introduced into the P2‐Na2/3Fe1/2Mn1/2O2 composite positive electrode as a sacrificial salt to compensate for the Na deficiency. Na+ was supplied through the electrochemical oxidative decomposition of Na2CO3 during the initial charging process; the decomposition mechanism responsible for this process was investigated in detail. Online electrochemical mass spectrometry confirmed that Na2CO3 was oxidatively decomposed in combination with the decomposition of the ethylene carbonate electrolyte. This reaction produced CO2, wherein the carbon source was derived from both Na2CO3 and the electrolyte. Consequently, Na+ supplementation improved the reversible capacity of the Na‐ion full cell. This study offers practical insights and a mechanistic understanding of the pre‐doping technique for Na‐free negative electrodes. This approach also compensates for the irreversible reductive capacity in a process that can be easily applied to practical sodium‐ and lithium‐ion batteries and capacitors.
P2- 型过渡金属层状氧化物具有很高的放电容量，因此在钠离子电池中用作正极材料备受关注。然而，由于这些氧化物的成分缺 Na，必须使用 Na 金属负极提供额外的 Na+，才能在半电池配置中获得高容量。本研究在 P2-Na2/3Fe1/2Mn1/2O2 复合正极中引入了固体 Na2CO3 粉末作为牺牲盐，以弥补 Na 的不足。在初始充电过程中，通过 Na2CO3 的电化学氧化分解来提供 Na+，并详细研究了这一过程的分解机制。在线电化学质谱分析证实，Na2CO3 的氧化分解与碳酸乙烯酯电解质的分解相结合。这一反应产生了 CO2，其中碳源来自 Na2CO3 和电解质。因此，Na+的补充提高了Na-离子全电池的可逆容量。这项研究为无 Na 负极的预掺杂技术提供了实用的见解和机理上的理解。这种方法还能补偿不可逆还原容量，可轻松应用于实际的钠离子和锂离子电池及电容器。
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Adnane Bouzina, René Meng, Françoise Pillier, Hubert Perrot, O. Sel, Catherine Debiemme-Chouvy
Herein, the development and the characterization of an all‐solid state symmetrical and current collector‐free microsupercapacitor based on a new reduced graphene oxide‐polydopamine (rGO‐PDA) composite are reported. The rGO‐PDA composite is synthesized by a facile, eco‐friendly and scalable hydrothermal approach in the presence of dopamine which can not only contribute to the oxygen functional groups removal from graphene oxide but also polymerize onto the rGO sheets reducing their restacking and improving the wettability of the electrode. The optimized rGO‐PDA composite material exhibits excellent capacitance and cycling stability as well as an improved rate capability compared to the pristine rGO in Na2SO4 solution. This performance enhancement can be linked to the higher transfer kinetic and lower transfer resistance values of the ions involved in the charge storage process of rGO‐PDA, as determined by ac‐electrogravimetry. Furthermore, an all‐solid‐state microsupercapacitor was prepared employing the optimized rGO‐PDA composite as electrode material. Interdigitated electrodes were obtained thanks to a CO2 laser and a Na2SO4/PVA hydrogel was employed, no current collector was used. This device achieves a noteworthy energy density of 6.2mWh·cm‐3 at a power density of 0.22W·cm‐3. Moreover, it exhibits exceptional cycling stability, retaining 104% of its initial capacity even after undergoing 10,000 cycles at 2V·s‐1.
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Pub Date : 2021-12-01DOI: 10.26434/chemrxiv-2021-d77zd
Katharina Helmbrecht, H. Euchner, A. Gross
While the Mo6S8 chevrel phase is frequently used as cathode material in Mg--ion batteries, theoretical studies on this material are comparatively scarce. The particular structure of the Mo6S8 phase, with rather loosely connected cluster entities, points to the important role of dispersion forces in this material. However, so far this aspect has been completely neglected in the discussion of Mo6S8 as cathode material for mono- and multivalent-ion batteries. In this work we therefore have studied the impact of dispersion forces on stability and kinetics of Mo6S8 intercalation compounds. For this purpose, a series of charge carriers (Li, Na, K, Mg, Ca, Zn, Al) has been investigated. Interestingly, dispersion forces are observed to only slightly affect the lattice spacing of the chevrel phase, nevertheless having a significant impact on insertion voltage and in particular on the charge carrier mobility in the material. Moreover, upon varying the charge carriers in the chevrel phase, their diffusion barriers are observed to scale linearly with the ion size, almost independent of the charge of the considered ions. This indicates a rather unique and geometry dominated diffusion mechanism in the chevrel phase. The consequences of these findings for the ion mobility in the chevrel phase will be carefully discussed.
Mo6S8 chevrel相是镁离子电池常用的正极材料，但对该材料的理论研究相对较少。Mo6S8相的特殊结构，具有相当松散连接的簇实体，指出了色散力在该材料中的重要作用。然而，到目前为止，在Mo6S8作为单价和多价离子电池正极材料的讨论中，这方面完全被忽视了。因此，在这项工作中，我们研究了分散力对Mo6S8插层化合物稳定性和动力学的影响。为此，研究了一系列载流子(Li, Na, K, Mg, Ca, Zn, Al)。有趣的是，观察到色散力仅轻微影响切夫相的晶格间距，但对插入电压有显著影响，特别是对材料中的载流子迁移率。此外，在改变切夫相的载流子时，可以观察到它们的扩散势垒与离子大小成线性比例，几乎与所考虑的离子的电荷无关。这表明了一个相当独特的和几何主导的扩散机制，在chevrel阶段。我们将仔细讨论这些发现对离子迁移率的影响。
{"title":"Revisiting the chevrel phase: Impact of dispersion corrections on the properties of Mo6S8 for cathode applications","authors":"Katharina Helmbrecht, H. Euchner, A. Gross","doi":"10.26434/chemrxiv-2021-d77zd","DOIUrl":"https://doi.org/10.26434/chemrxiv-2021-d77zd","url":null,"abstract":"While the Mo6S8 chevrel phase is frequently used as cathode material in Mg--ion batteries, theoretical studies on this material are comparatively scarce. The particular structure of the Mo6S8 phase, with rather loosely connected cluster entities, points to the important role of dispersion forces in this material. However, so far this aspect has been completely neglected in the discussion of Mo6S8 as cathode material for mono- and multivalent-ion batteries. In this work we therefore have studied the impact of dispersion forces on stability and kinetics of Mo6S8 intercalation compounds. For this purpose, a series of charge carriers (Li, Na, K, Mg, Ca, Zn, Al) has been investigated. Interestingly, dispersion forces are observed to only slightly affect the lattice spacing of the chevrel phase, nevertheless having a significant impact on insertion voltage and in particular on the charge carrier mobility in the material. Moreover, upon varying the charge carriers in the chevrel phase, their diffusion barriers are observed to scale linearly with the ion size, almost independent of the charge of the considered ions. This indicates a rather unique and geometry dominated diffusion mechanism in the chevrel phase. The consequences of these findings for the ion mobility in the chevrel phase will be carefully discussed.","PeriodicalId":230836,"journal":{"name":"Batteries & Supercaps","volume":"67 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124578502","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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