正极材料的同步辐射技术锂离子和钠离子电池表征
Summary
我们描述了使用同步辐射X射线吸收光谱（XAS）和X-射线衍射（XRD）技术，以探测在锂离子和钠离子电池的电极材料的嵌入/脱嵌过程的细节。无论是在就地和移地实验来了解有关设备的运行结构行为
Abstract
层间化合物等过渡金属氧化物或磷酸盐是在锂离子和钠离子电池中最常用的电极材料。在插入或除去碱金属离子，该化合物中的过渡金属的氧化还原状态的变化和结构转变诸如相变和/或晶格参数的增加或减少发生。这些行为反过来确定电池势如型材，速率能力和循环寿命的重要特征。极亮和可调X射线同步辐射产生的允许快速采集，提供有关这些进程的相关信息的高分辨率数据。在散装的材料，如相变转化，可以使用X-射线衍射（XRD）进行直接观察，而X-射线吸收光谱（XAS）给出了关于本地电子和几何结构（ 例如，改变的氧化还原状态和键信息升engths）， 在执行上操作的细胞原位实验，因为它们允许的材料的电化学性质和结构性质之间的直接相关性是特别有用的。这些实验是耗时的，并且可以是具有挑战性的设计，由于在半电池构造中使用的碱金属的阳极的反应性和空气的灵敏度，和/或从其他细胞成分和硬件信号干扰的可能性。由于这些原因，很适合开展易地实验（ 如从部分充电或循环细胞收获电极）在某些情况下。在这里，我们提出了详细的方案编制双方易地和就地样品中涉及同步辐射实验和演示如何将这些实验完成。
Introduction
锂离子电池的消费电子产品目前全世界命令$ 11十亿市场( http://www.marketresearch.com/David-Company-v3832/Lithium-Ion-Batteries-Outlook-Alternative-6842261/ )并且是首选新兴车辆应用例如插电式混合电动车（PHEV汽车）和电动汽车（EV）。类似物，这些设备利用钠离子，而不是锂都还处于早期发展阶段，但被认为是大规模储能（ 即电网应用）基于成本和供应安全参数1，2吸引力。两个双插系统的工作原理相同;碱金属离子作为主体结构，并且经过插入过程在不同电位的两个电极之间穿梭。电化学电池本身是RELatively简单，包括对集流器，通过与通常由溶解在有机溶剂中（ 图1）的混合物的盐的电解溶液饱和的多孔膜隔开的复合正极和负极的。石墨和钴酸锂是最常用的负电极和正电极，分别为锂离子电池。几种可供选择的电极材料也已被开发为特定的应用程序，包括的LiMn 2 O 4尖晶石，LiFePO 4的具有橄榄石结构的变体，和NMC（的LiNi x的Mn x坐标1 – 2个 O 2的化合物）为阳性，和硬碳，李4的Ti 5 O 12，和锂与锡的底片3合金。高压材料，如的LiNi 0.5锰1.5 O 4，新的高容量材料，如分层，分层复合材料（ 如 XLI 2的MnO <子> 3·（1-x）的锰酸锂镍0.5 0.5 O 2），过渡金属，可以进行氧化还原状态的多个变化，和Li-Si合金阳极是目前激烈的研究课题，并在成功部署，应化合物提高锂离子电池的实际能量密度进一步。另一个类的材料，被称为转换电极，其中过渡金属的氧化物，硫化物或氟化物被可逆地还原为金属元素和锂盐，也在考虑用作电池的电极（主要作为替代阳极）4。基于钠的设备，硬碳，合金，NASICON结构，以及钛酸盐正在被研究用作阳极和各种过渡金属氧化物和聚阴离子化合物作为阴极。
由于锂离子和钠离子电池并非基于固定化学品，其性能特点很大的不同取决于对T他认为电极雇用。电极的氧化还原行为决定的电位分布，速率能力，以及设备的循环寿命。常规的粉末X-射线衍射（XRD）技术可被用于原始材料和循环电极易地测量的初始结构表征，但实际的考虑因素，例如低信号强度和所需的收集数据的相对长的时间限制的信息的量可以在放电和充电过程中获得。相比之下，同步辐射的高亮度和短的波长（ 例如 λ= 0.97在斯坦福同步辐射一个LightSource的光束线11-3），结合运用高通量图像探测器，采集许可证的高分辨率数据，对样本少至10秒。 原位工作在传输模式中执行对电池组件进行充电和放电在密封包装袋透明的X射线，而无需停止运行采集数据。其结果是，电极的结构变化，可以观察到“时间快照”作为细胞周期，并且可以比使用常规技术来获得更多的信息。
X射线吸收光谱（XAS），有时也被称为X-射线吸收精细结构（XAFS）给出了关于材料的本地电子和几何结构的信息。在XAS实验中，光子的能量被调谐到所调查的特定元素的特征吸收边缘。最常用的电池材料，这些能量相当于感兴趣的过渡金属的K边缘（1S轨道），但软X光吸收实验，调整到O，F，C，B，N和第一行的第l 2,3边缘过渡金属有时也进行了易地样品5。通过XAS实验产生的光谱可以被分成若干个区INCT地区，包含不同的信息（见Newville，M.，基础XAFS的， http://xafs.org/Tutorials?action=AttachFile&do=get&target=Newville_xas_fundamentals.pdf ）。主要特征，包括吸收边缘，并延伸大约30-50电子伏特超越是在X射线吸收近边结构（XANES）区，并指出了电离的阈值，以连续态。这包含了吸收剂的氧化态和配位化学的信息。光谱的更高能量部分被称为扩展X-射线吸收精细结构（EXAFS）区域，并对应于所喷射的光电子关闭相邻原子的散射。这个区域的傅里叶分析给出短程结构信息，如键长和键的数量和类型邻近离子。 Preedge采用了characterist以下一些化合物的IC吸收的能量也有时会出现。这些从偶极禁电子跃迁产生的空束缚态的八面体几何形状，或在四面体那些偶极允许的轨道杂化效应，往往可以关联到吸收离子（ 例如是否是四面体或八面体配位）的局部对称性6。
XAS是研究混合金属等系统的NMC确定初始氧化还原状态以及过渡金属离子在脱锂及锂化过程进行氧化还原一个特别有用的技术。在几个不同的金属的数据可以在一次实验中迅速地获得和解释是相当简单的。与此相反，穆斯堡尔谱是有限的，以在电池材料（主要是Fe和Sn）的使用仅几个金属。而磁测量也可以用于确定氧化态，磁性耦合效应可以并发症德解释特别是对于复合氧化物如NMC的。
精心策划和执行的就地和迁地保护同步加速器X射线衍射和X光吸收实验给予补充信息，并允许在比什么可以通过常规技术获得正常的电池操作发生在电极材料的结构变化更完整的画面形成。这反过来，给出了什么支配着设备的电化学行为更深入的了解。
Protocol
Representative Results
Discussion
的XANES数据分析表明，随着国产的LiNi x坐标1-2X锰×○2（0.01≤X≤1）的化合物，含有Ni 2 +，Co 3 +和Mn 4 + 10上的LiNi最近原位 XAS研究0.4钴0.15铝0.05的Mn 0.4 O 2表明，Ni 2 +的氧化，镍3 +和最终的Ni 4 +脱锂过程中，但涉及的Co 3 +的氧化还原过程提供一些容量，即使在低的状态-的电荷，违背先前的假设<sup…
Disclosures
The authors have nothing to disclose.
Acknowledgements
这项工作是由助理秘书长能源效率和可再生能源，能源的美国能源部车辆技术合同号DE-AC02-05CH11231办公室的支持。这项研究的部分进行了在斯坦福同步辐射一个LightSource，为SLAC国家加速器实验室一局和斯坦福大学经营了科学的能源办公室，美国能源部科学用户设施的办公室。该SSRL结构分子生物学项目是由生物和环境研究的美国能源部办公室的支持，并通过健康，国家研究资源中心，生物技术计划（P41RR001209）全国学院。
Materials
| Equipment | |||
| Inert atmosphere glovebox | Vacuum Atmospheres | Custom order, contact vendors | Used during cell assembly and to store alkali metals and moisture sensitive components. (http://vac-atm.com) |
| Inert atmosphere glovebox | Mbraun | Various sizes (single, double) available, many options such as mini or heated antechambers oxygen/water removal systems, shelving, electrical feedthroughs, etc. (http://www.mbraunusa.com) | |
| X-ray powder diffractometer (XRD) | Panalytical | X'Pert Powder | X'Pert is a modular system. Many accessories available for specialized experiments. (www.panalytical.com) |
| X-ray powder diffractometer (XRD) | Bruker | Bruker D2 Phaser | Bruker D2 Phaser is compact and good for routine powder analyses. (www.bruker.com) |
| Scanning Electron Microscope (SEM) | JSM7500F | High resolution field emission scanning electron microscope with numerous customizable options. JEOL (http://www.jeolusa.com) Low cost tabletop versions also available. Contact vendor for options. | |
| Pouch Sealer | VWR | 11214-107 | Used to seal pouches for in situ work. (https://us.vwr.com) |
| Manual crimping tool | Pred Materials | HSHCC-2016, 2025, 2032, 2320 | Used to seal coin cells. Match size to coin cell hardware. (www.predmaterials.com) |
| Coin cell disassembling tool | Pred Materials | Contact vendor | Used to take apart coin cells to recover electrodes for ex situ work. Needlenose pliers can also be used. Cover ends with Teflon tape to avoid shorting cells. (www.predmaterials.com) |
| Film casting knives | BYK Gardner | 4301, 4302, 4303, 4304,4305,2325, 2326,2327,2328, 2329 | Used to cast electrodes films from slurries. Different sizes available, with either metric or English gradations. Bar film or Baker-type applicators and doctor blades are less versatile but lower cost options. Can be used by hand or with automatic film applicators. (https://www.byk.com) |
| Doctor blades, Baker applicators | Pred Materials | Baker type applicator and doctor blade. Film casting knives also available. | Used to cast electrodes films from slurries. Different sizes available, with either metric or English gradations. Bar film or Baker-type applicators and doctor blades are less versatile but lower cost options. Can be used by hand or with automatic film applicators. (www.predmaterials.com) |
| Automatic film applicator | BYK Gardner | 2101, 2105, 2121, 2122 | Optional. Used with bar applicators, doctor blades, or film casting knives for automatic electrode film production. Films can also be made by hand but are less uniform. (https://www.byk.com) |
| Automatic film applicator | Pred Materials | Contact vendor | Optional. Used with bar applicators, doctor blades, or film casting knives for automatic electrode film production. Films can also be made by hand but are less uniform. (www.predmaterials.com) |
| Potentiostat/Galvanostat | Bio-Logic Science Instruments | VSP | Portable 5 channel computer-controlled potentiostat/galvanostat used to cycle cells for in situ experiments. (http://www.bio-logic.info) |
| Potentiostat/Galvanostat | Gamry Instruments | Reference 3000 | Portable single channel computer-controlled potentiostat/galvanostat used to cycle cells for in situ experiments. (www.gamry.com) |
| The Area Diffraction Machine | Free download | Used for analysis of 2D diffraction data. Mac and Windows versions available. http://code.google.com/p/areadiffractionmachine/ | |
| IFEFFIT | Free download | Suite of interactive programs for XAS analysis, including Hephaestus, Athena, and Artemis. Available for Mac, Windows, and UNIX. http://cars9.uchicago.edu/ifeffit/ | |
| SIXPACK | Free download | XAS analysis program that builds on IFEFFIT. Windows and Mac versions. http://home.comcast.net/~sam_webb/sixpack.html | |
| CelRef | Free download | Graphical unit cell refinement. Windows only. http://www.ccp14.ac.uk/tutorial/lmgp/celref.htm and http://www.ccp14.ac.uk/ccp/web-mirrors/lmgp-laugier-bochu/ | |
| Reagent/Material | |||
| Electrode active materials | various | Synthesized in-house or obtained from various suppliers. | |
| Synthetic flake graphite | Timcal | SFG-6 | Conductive additive for electrodes. (www.timcal.com) |
| Acetylene black | Denka | Denka Black | Conductive additive for electrodes. (http://www.denka.co.jp/eng/index.html) |
| 1-methyl-2-pyrrolidinone (NMP) | Sigma-Aldrich | 328634 | Used to make electrode slurries. (www.sigmaaldrich.com) |
| Al current collectors | Exopack | z-flo 2650 | Carbon-coated foils. Coated on one side. (http://www.exopackadvancedcoatings.com) |
| Al current collectors | Alfa-Aesar | 10558 | 0.025 mm (0.001 in) thick, 30 cm x 30 cm (12 in x 12 in), 99.45% (metals basis), uncoated (http://www.alfa.com) |
| Cu current collectors | Pred Materials | Electrodeposited Cu foil | For use with anode materials for Li-ion batteries. (www.predmaterials.com) |
| Lithium foil | Rockwood Lithium | Contact vendor | Anode for half cells. Available in different thicknesses and widths. Reactive and air sensitive. Store and handle in an inert atmosphere glovebox under He or Ar (reacts with N2). (www.rockwoodlithium.com) |
| Lithium foil | Sigma-Aldrich | 320080 | Anode for half cells. Available in different thicknesses and widths. Reactive and air sensitive. Store and handle in an inert atmosphere glovebox under He or Ar (reacts with N2). (www.sigmaaldrich.com) |
| Sodium ingot | Sigma-Aldrich | 282065 | Anodes for half cells. Can be extruded into foils. Reactive and air sensitive. Store and handle in an inert atmosphere glovebox under He only. (www.sigmaaldrich.com) |
| Electrolyte solutions | BASF | Selectilyte P-Series contact vendor | Contact vendor for desired formulations. (http://www.catalysts.basf.com/p02/USWeb-Internet/catalysts/en/content/microsites/catalysts/prods-inds/batt-mats/electrolytes) |
| Dimethyl carbonate (DMC) | Sigma-Aldrich | 517127 | Used to wash electrodes for ex situ experiments. (www.sigmaaldrich.com) |
| Microporous separators | Celgard | 2400 | Polypropylene membranes (http://www.celgard.com) |
| Coin cell hardware (case, cap, gasket) | Pred Materials | CR2016, CR2025, CR2320, CR2032 | Match size to available crimping tool, Al-clad components also available. (www.predmaterials.com) |
| Wave washers | Pred Materials | SUS316L | (www.predmaterials.com) |
| Spacers | Pred Materials | SUS316L | (www.predmaterials.com) |
| Ni and Al pretaped tabs | Pred Materials | Contact vendor | Sizes subject to change. Inquire about custom orders. (www.predmaterials.com) |
| Polyester pouches | VWR | 11214-301 | Used to seal electrochemical cells for in situ work. Avoid heavy duty pouches because of strong signal interference. (https://us.vwr.com) |
| Kapton film | McMaster-Carr | 7648A735 | Used to cover electrodes for ex situ experiments, 0.0025 in thick (www.mcmaster.com) |
| Helium, Argon and 4-10% hydrogen in helium or argon | Air Products | contact vendor for desired compositions and purity levels | Helium or argon used to fill glovebox where cell assembly is carried out and alkali metal is stored. (http://www.airproducts.com/products/gases.aspx) |
| Do not use nitrogen because it reacts with lithium. Use only helium if sodium is being stored. Purity level needed depends on whether the glovebox is equipped with a water and oxygen removal system. Hydrogen mixtures needed to regenerate water/oxygen removal system, if present or any other suitable gas supplier |
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