同步辐射X-射线和中子衍射在储能材料研究中应用.docx

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1、Applications of synchrotron X-rays and neutrons diffraction in energy storage materials research【 摘 要 】 Abstract：Synchrotron X-ray and neutron diffraction facilities are very popular and indispensable scientific resources that provide powerfulinstrumentsandexperimentaltechniquesforboth fundamental a

2、nd applied researches around the world. X-rays and neutrons interact with matter in different and also complementary ways, and recently have been extensively used for studying energy storage materials at the electronic, atomic and molecular levels, and even extended to engineering scale. In this art

3、icle, we will briefly introduce synchrotronX-rayandneutronscatteringtechniquesandtheir difference, similarity and complementarity. Advantages of synchrotron high-energy X-rays will also be presented. The unique and powerful capacity of neutron scattering for hydrogen storage material study will be s

4、hown. We also present some examples ofin-situ/operando study of theatomicstructureevolutionofNa1Ni1/3Fe1/3Mn1/3O2and LiNi0.5Mn1.5O4activeelectrodematerialsduringsynthesisand electrochemical intercalation for sodium ion battery and lithium ion battery. Finally, the future perspectives of synchrotron

5、X-ray and neutron diffraction techniques in the field of materials science for energy storage technology will be discussed.【期刊名称】储能科学与技术【年(卷),期】2017(006)005【总页数】9【 关 键 词 】 Key words：synchrotron; X-ray; neutron diffraction; energy storage technology; electrode materialThe energy conservation law tell

6、s us that we cannot create or eliminate energy,we just store and convert energy from one type to another for our daily activities. Obviously, high efficient and environmentally benign energy conversion and storage technologies are highly desired and are the focus of growing research and development

7、efforts worldwide. However, physicsprinciplesoftensetuphighbarriersbetween performanceand safety, and many competing factors between stability and activity, capacity and cyclability, etc. in active energy materials. Basic knowledge at electronic, atomic and molecular levels is critical not only for

8、better understanding but also for future development of advanced energy materials. Synchrotron X-ray and neutron techniques play a very important role and have broad applications in energy storage materials research.Since the discovery of X-rays by W.C. ROENTGEN in late 1895, and neutron by J. CHADW

9、ICK in 1932, X-rays and neutrons have been widely used in various fields. Especially, the accelerator based synchrotron X- ray and spallation neutron sources have significantly advanced theirinstrumentational development and applications for research in almost all scientific and engineering discipli

10、nes. X-rays are electromagnetic waves and also called photons, while neutrons are subatomic particles.Both X-ray and neutron carry no charge and have spin. Table 1 lists some property and characteristics of X-rays and neutrons for reference. Generallyspeaking,X-raysinteractwithelectronsofatomsviathe

11、 electromagnetic interaction,while neutrons interact with atomic nuclei via very short-range strong nuclear forces, and also interact with unpaired electronic spins via the magnetic dipole interaction 1-5. Neutrons are important for studying magnetic materials, while X-rays can also probe spins via

12、very weak relativistic effects. Synchrotron X-ray techniques can be generally categorized into diffraction/scattering, spectroscopy and imaging/ tomography, which can be combined, time- resolved,polarization dependent, coherence related, furtherdetailed. Here we will be mainly focused on the elastic

13、 diffraction part for atomic structurecharacterization,althoughtheparticularapplicationof neutronscatteringinhydrogenstoragematerialswillbebriefly discussed later.1 BriefintroductiontosynchrotronX-rayandneutrondiffractionIn practice, one of the most important parameters in X-ray and neutron diffract

14、ion is the so-called scattering cross section, , where b is thescattering length, which measure the scattering power of X-rays and neutrons by an atom. Fig.1 shows the X-ray and thermal neutron scattering length of some selected elements. One can see that the X-ray scattering length is proportional

15、to the atomic number, because X-rays are interacting with electrons of atoms. X-ray scattering length at photon energy of 10 keV and 100 keV is also plotted for comparison, which indicates that with increasing photon energy the X-ray scattering length is reduced. This factor should be considered whe

16、n using synchrotron X-rays.In Fig.1, it also can be seen that the neutron scattering length of the sample element with different isotopes can be drastically different, like the hydrogen and deuterium, which even have a sign difference. Such a unique feature makes isotope substitution method very imp

17、ortant and useful in neutron scattering experiment. Vanadium has a nearly zero scattering length. This is why people often use vanadium for sample containers in many neutron scattering experiments.It is known that neutrons usually have much higher penetration capacity than X-rays, thus can be used t

18、o probe bulky samples, except those containing hydrogen or elements with large neutron absorption. But the availability of high-brilliance synchrotron high energy X-rays with tunable energy generated by high-energy synchrotron radiation sources has significantly advanced the field of materials resea

19、rch, especially forin-situ, operando, studies of function materials, in bulk forms or nanoscale structures, in realistic conditions and in real time. Fig.2(a) shows X-ray scattering cross section of lead as a function of photon energy. Below 1 MeV, the X-ray interactions with matter include the cohe

20、rent and incoherent scattering and the photoelectron effect, while the nuclear interactions occur at higher energy. Nowadays, X-rays with photon energy of above 40 keV are considered as high-energy (HE) X- rays. The weak scattering power of high-energy X-rays means a weak absorption, leading to a la

21、rge penetration power, as shown in Fig.2(b), from which one can see that the lab X-rays with Cu K radiation can only penetrate a few micron thick ion, while synchrotron HE X-rays with 115 keV can easily penetrate a few millimeter iron, showing bulk sample properties. On the other side, the weak scat

22、tering power of high-energy X-rays requires high flux and sometimes bulky samples, in order to perform high quality high-energy X-ray experiments.High-energy X-rays have many advantages like high penetration, low absorption, small scatteringangle and wide reciprocal space coverage etc. Such advantag

23、es make high-energy X-rays particularly suitable for in-situ operando investigation of advanced materials in complex sample environments, e.g. in low and high temperature, under magnetic, electric and stress field, high pressure or with combined external stimuli, or even in chemically hazardous, cor

24、rosive and radioactive conditions6-10.2 Application of neutron scattering for hydrogen containing materialsAt first, we want to emphasize a very important and unique feature in neutron scattering that is its ability of studying hydrogen containing materials. Hydrogen is the lightest element, which m

25、akes it very difficult for X-rays to probe hydrogen atoms in materials. Unfortunately, it is also very difficult for neutrons to see hydrogen, even it has a reasonable neutron scattering length (Fig.1). We have to point out that Fig.1 plots the coherent scattering length. Hydrogen has a huge incoher

26、ent scattering cross section, which gives rise to very high incoherent scattering background in neutron diffraction spectra of hydrogen- containing materials. In order for neutrons to see where hydrogen atoms are located in a compound or system, one has to replace hydrogen (H) by its isotope, deuter

27、ium (D).Neutron scattering plays an irreplaceableroleandprovidesfundamentalknowledgeinthis particular field.Hydrogen molecule is the simplest molecule with quantum states, in whichtwoprotonsareindistinguishablefermions,thushasan antisymmetric (AS) wave function. If the spins of the two protons are a

28、ntiparallel, it is called para-hydrogen. If the two spins are parallel, it is called ortho-hydrogen. From Table 1, one can see that the population ofpara- and othor-hydrogen is temperature dependent. The energy transfer from para-hydrogen to ortho-hydrogen in H2 solid is 14.7 meV, which is a fingerp

29、rint specifically for molecule hydrogen and its interaction with surroundings.We have employed neutron scattering techniques to in-situ investigate hydrogen storage capability andmechanism in carbon nanotubes and alsodynamicpropertiesofmetalhydrides11-12.Weuseda quasielastic neutron scattering (QENS

30、) instrument to monitor hydrogen adsorption in single walled carbon nanotube bundles. The QENS instrument can provide us rich information of hydrogen dynamic behavior and its interaction with absorbents. Molecular hydrogen has quantum rotational energy levels given by EJ=BJ(J+1), where J is the rota

31、tional quantum number and B the rotational constant (=7.35 meV for solid hydrogen). Fig.5 shows an inelastic neutron spectrum of H2 molecule adsorbed in carbon nanotubes. The shape peak at 14.5 meV corresponds to the quantum rotational transition from J=0 (para-) to J=1 (ortho-state) of the adsorbed

32、 hydrogen molecules, ambiguously indicating that molecule hydrogen is present. This peak becomes weaker and broader with increasing temperature, while the peak position remains almost unchanged. The observed transition energy of14.5 meV is slightly less than the 14.7 meV found in pure solid hydrogen

33、, implying that adsorbed hydrogen molecules encounterrelatively little hindrance for rotation, probably due to the weak Van der Waals interactions between hydrogen and carbon nanotubes. The linear increase of the peak width with temperature increase indicates that the hydrogen molecules become less

34、and less bound to the carbon nanotubes.3 In operando synchrotron X-ray study of sodium-ion batterymaterialsIn situ synchrotron X-ray diffraction (XRD) has proven to be a powerful technique to probe the sodium insertion mechanism in sodium ion batteries. We have used in situ/operando high-energy X-ra

35、y diffraction (HE-XRD)tounderstandthephasetransformationof NaNi1/3Fe1/3Mn1/3O2 materials during Na ion intercalation. During the operando experiments, high-energy X-rays are directed to transmit throughaperforated2032-typecoin-cellcontainingournewly synthesizedNaNi1/3Fe1/3Mn1/3O2materials.TheinsituH

36、E-XRD patterns of the NaNi1/3Fe1/3Mn1/3O2 during charge and discharge are illustrated in Fig.4.The in situ HE-XRD data clearly indicate the existence of a nonequilibrium solid-solution reaction during charging when the cut-off voltage of charge was set to 4.0 V as evident in Fig.4(a). During the dis

37、charge, the XRD pattern indicates an exact opposite electrode evolution compared with charge, suggesting that the phasetransformation of Na1Ni1/3Fe1/3Mn1/3O2 is reversible through an O3P3P3O3 sequence during cycling. We also can get the change in lattice parameters of Na1 Ni1/3Fe1/3Mn1/3O2 during cy

38、cling. Clearly, the structure of Na1Ni1/3Fe1/3Mn1/3O2 is very stable when cycled in the voltage range of 24.0 V.By contrast, as evident in Fig.4(b), the phase transformation of Na1 Ni1/3Fe1/3Mn1/3O2 is completely different whe n the cutoff voltage is set to 4.3 V. The phase change follows the sequen

39、ce of O3 to P3 when charged from 3.2 V to 4.0 V, but in the charge voltage range of 4.0 4.3 V, the (003) P3 shifts to higher angle and splits into two again. These two peaks eventually merge to a new (003) peak, indicating a new nonequilibrium phase, which is assigned to a monoclinic O3 phase consis

40、ting of a distorted lattice in comparison to an ideal hexagonal cell.Notethatatwo-phasereaction withthecoexistenceofP3 hexagonal and O3 monoclinic phases occurs in the charge voltage range of 4.0 4.1 V. In situ XRD shows a reversible evolution of O3 P3 O3 during charge. The lattice parameters in cri

41、tical phase change were calculatedandaresummarizedinTableS2oftheSupporting Information. The lattice parameters for such O3 monoclinic phases are a=8.5394 , b=5.3697 , and c=2.4631 . Interestingly, a single O3 monoclinic phase is maintained to cutoff voltage of 4.3 V. During discharge from 3.5 to 3.0

42、 V, the (003) peak shifts to a lower angle, andthe O3 monoclinic phase transforms to P3 monoclinic phase. The O3 phase is recovered via O3P3O3 during discharge.The nature of the structural evolution of P2-Na0.67Mn0.5Fe0.5O2 and P2-Na0.67Mn0.65Ni0.15Fe0.2O2upon cycling were studied by using combined

43、X-ray and neutron powder diffraction (XRPD and NPD) 14.The phase diagram of the two compositions as a function of sodium content is determined using operando diffraction experiments, and the structure of the unknown high voltage phase is solved by X-ray pair distribution function (PDF) analysis. The

44、 good fit between the average structure, determined by diffraction, and the measured PDF is a consequence of the low occupancies and weak scattering coefficient of sodium atoms. The structure of the high voltage phase of the nickel substituted oxide was similarly determined, using X-ray PDF analysis

45、 on a chemically oxidized “Z” -Na0.1Fe0.2Mn0.65Ni0.15O2 sample (Fig.5). ThesodiumcontentreachedbychemicaloxidationofP2- Na0.67Fe0.2Mn0.65Ni0.15O2 is slightly lower than what is achieved electrochemically.4 Complementary neutron and synchrotron study of high-voltage spinel cathode for lithium-ion bat

46、teriesResearch efforts are in progress world-wide to develop reliable, high- performance cathode materials for advanced lithium-ion batteries, paving the way to a secure and sustainable energy future. Among thecathode materials, LiCoO2 and LiTMO2 (TM is a mixture of transition metal elements and/or

47、Al), LiMn2O4 and LiFePO4 are the most widely used materials and stands for three different types of structures, such as layered-, spinel- and olivine-structure, respectively. To improve the energy and power density, one wants to increase the capacity and/or the operating voltage. LiNi0.5Mn1.5O4 is a

48、 type of spinel material with discharge voltage plateau around 4.7 V, which is among the highest ones. Among the claimed high voltage materials, LiNi0.5Mn1.5O4 is the fewdemonstrating goodcycle and calendarlife,being agood candidate for 5 V lithium ion batteries. However, the material produces by different synthesis methods demonstrate different electrochemical properties. It is known that, depending on the synthetic routes, LiNi0.5Mn1.5O4 has a structure of face-centered spinel (Fd3m) or primitive cubic crystal (P4332), where face-centered spinel (Fd3m) performance