Intense Spallation Neutron Source Research Articles

Operando Measurement of Solid Electrolyte Interphase Formation at Working Electrode of Li-Ion Battery by Time-Slicing Neutron Reflectometry

Introduction A solid-electrolyte interphase (SEI) is known to play a significant role on safety and durability of lithium ion batteries (LIBs). Here, the chemical composition of SEI has been usually determined with an ex-situ X-ray photoelectron spectroscopic analysis technique. However, there are few reports on the structural properties of SEI, such as thickness and density, and their variation with cyclic charge and discharge reactions, because of the difficulty for observing SEI with an in-situ manner. This means that we will never reach deep understanding of “alive” SEI and its formation mechanism through the work on “dead” SEI with ex-situ analytical techniques. Therefore, we have started to use neutron reflectivity (NR), as NR is a powerful technique for estimating thickness and density of an interface between solid and liquid. Furthermore, since the interfacial reaction is expected to occur within a few nanometer-thickness from the initial boundary between electrode and electrolyte, we naturally need a NR technique with more precise spatial resolution for such purpose than the past NRs. Fortunately, Japan Proton Accelerator Research Complex (J-PARC) is one of the most intense spallation neutron source, leading to the highest depth resolution of NR in the world. Here, we report the first operando measurement of the SEI formation during the initial charge, i.e. lithiation reaction in the carbon electrode of LIB using a combination of in situ NR and electrochemical analyses [1]. Experimental As an electrode for NR measurements, a carbon/titanium multi-layer film was deposited on a silicon substrate by a magnetron sputtering technique (Fig. 1). Here, the titanium layer is necessary to increase adhesive force between the carbon electrode and Si substrate. In a special electrochemical cell for in-situ NR measurements, the carbon/titanium film was a working electrode, a lithium foil was a counter electrode, 1 mol/L LiPF6 in a 1:1 (v/v) ratio of ethylene carbonate and diethyl carbonate was an electrolyte, and a microporous polyethylene membrane was a separator. Cyclic voltammetry (CV) was performed at a slow sweep rate of 0.2 mV/s between 3.3 and 0.05 V. In situ NR measurements were performed during the repeated charge and discharge, i.e. lithiation and delithiation cycles on the surface profile analysis reflectometer (SOFIA) at BL16 of Materials and Life Science Experimental Facility (MLF) in J-PARC (Proposal No.2015B0016). The NR spectrum was measured as a function of the momentum transfer, Qz = (4π/λ)sin θ, in the Qz range between 0.1 and about 0.45 nm-1. The obtained NR spectra were fitted with Motofit based on a Parratt formalism [2] [3]. Results and Discussion After the CV measurement, the morphology of the carbon surface was clearly changed as expected. Fig. 2 shows a color map of the reflectivity profiles in the Qz and time plane for the 1st and 2nd charge and discharge cycles in order to demonstrate the overall data for the present NR measurements. NR is found to drastically change at potentials between 1.5 and 0.05 V corresponding to the lithiation reaction, and between 0.05 and 2.5 V corresponding to the delithiation reaction. The change in NR along the Qz axis naturally reflects the formation and variation of SEI. Fig. 3 shows the Scattering length density (SLD) as a function of depth and time. The data were obtained by fitting the NR spectra with a four-layer model. The change in thickness of carbon electrode indicates the volumetric change induced by the lithiation and delithiation reactions into and from carbon. The decrease in SLD of carbon also supports the lithiation reaction into carbon, because Li exhibits a negative coherent scattering length. More correctly, as potential decreases from 1.5 to 0.05 V, the width of the carbon film increases from 67 to 83 nm. On the contrary, the boundary between electrode and electrolyte clearly changes with potential, indicating the formation of SEI. That is, as potential decreases from 1.0 V, SLD increases from 2.4 to 3.2 (x 10-4) nm-2, while the thickness increases from 18 to 36 nm at potential = 0.05 V during the initial lithiation reaction. This clearly demonstrates the growth of SEI during the lithiation reaction. Consequently, with NR measurements in the most intense neutron source, we have successfully observed the formation and growth of SEI at the boundary of the carbon electrode and liquid electrolyte during electrochemical charge and discharge reactions. Such measurements will provide an insight how to improve the performance of LIBs.

Design of hydrogen vent line for the cryogenic hydrogen system in J-PARC

As one of the main experimental facilities in J-PARC, an intense spallation neutron source (JSNS) driven by a 1-MW proton beam selected supercritical hydrogen at a temperature of 20 K and a pressure of 1.5 MPa as a moderator material. Moderators are controlled by a cryogenic hydrogen system that has a hydrogen relief system, which consists of high and low pressure stage of manifolds, a hydrogen vent line and a stack, in order to release hydrogen to the outside safely. The design of the hydrogen vent line should be considered to prevent purge nitrogen gas in the vent line from freezing when releasing the cryogenic hydrogen, to prevent moisture in the stack placed in an outdoor location from freezing, and to inhibit large piping temperature reduction at a building wall penetration. In this work, temperature change behaviors in the hydrogen vent line were analyzed by using a CFD code, STAR-CD. We determined required sizes of the vent line based on the analytical results and its layout in the building.

低温工学に関わる真空の物理と技術 スーパーインシュレータ（ポリイミド及びポリエステル）のγ線照射後のガス生成量と機械的特性

Japanese intense spallation neutron source (JSNS) driven by 3 GeV protons with power of 1 MW is constructed under the joint project of Japan Atomic Energy Agency and High Energy Accelerator Research Organization. Supercritical hydrogen of around 20K with 2 MPa is selected as a neutron moderator material and cryogenic hydrogen transfer lines are constructed from the moderators to the refrigerator. Then, a super insulator (SI) is adopted to reduce heat load in the hydrogen transfer lines. We performed irradiation test of SI using 60Co gamma ray to evaluate the irradiation effect. Two kinds of super insulator (polyimide and polyester) coated both sides by aluminum with thickness of 5 x 10-8 m were irradiated. After gamma ray irradiation, tensile test and gas yield measurement of super insulator were performed. Polyester based SI became brittle at about 10 MGy, on the other hand, polyimide based SI did not loss ductility so much even 80 MGy. Polyester based SI generated gas yield higher than that of polyimide based SI about one order of magnitude. We developed the gas analysis method by using a Q-mass and a mass-flow, providing to identify the unknown gas (i.e. H2O) effectively compared to a gas chromatography method.

Current Status of Position-Sensitive Neutron Detectors for Pulsed Neutron Sources

Nowadays, neutron detectors draw many attentions since new intense spallation neutron sources and new neutron optics are being realized. Conventional neutron detectors suffer from their poor count rate characteristics, position resolutions, and energy resolutions, etc. Since those properties are related one another in a complicated way, better design of the neutron detector engineering is required. Also, people anticipate new innovative technologies to overcome the current limitation of the detector performance. Future trends for neutron detectors are introduced in this paper.

スーパーインシュレーション(ポリイミド、ポリエステル)のγ線による耐放射線性試験(S08-2 極低温材料システム(2),S08 極低温・超電導材料システムの強度・機能特性)

Japanese intense spallation neutron source (JSNS) driven by 3 GeV protons with power of 1 MW is constructed under joint project of Japan Atomic Energy Research Institute and High Energy Accelerator Research Organization. Super insulator is adopted to reduce heat load in hydrogen transfer line of JSNS. We performed irradiation test of super insulator (SI) using ^<60>Co gamma ray to evaluate the irradiation effect. Two kinds of super insulator (polyimide and polyester) coated both side by aluminum with thickness of 5×10^<-8>m were irradiated. After gamma ray irradiation, we performed tensile test and gas analysis of super insulator. Polyester based SI became brittle at about 10 MGy, on the other hand, polyimide based SI did not loss ductility even over 60 MGy. Polyester based SI generated about 30 times higher gas yield than that of polyimide based SI. However, it was very small amount of gas yield even polyester based SI. Gas analysis method by Q-mass was very effective to identify the unknown gas (i.e. H_2O) to compare with gas chromatography.

Measurements of attenuation lengths through concrete and iron for neutrons produced by 800-MeV proton on tantalum target at ISIS

A deep penetration experiment through a thick bulk shield was performed at an intense spallation neutron source facility, ISIS, of the Rutherford Appleton Laboratory (RAL), United Kingdom. ISIS is a 800 MeV–200 μA proton accelerator facility. Neutrons are produced from a tantalum target, and are shielded with approximately 3-m thick steel and 1-m thick ordinary concrete. On top of the shield, we measured the neutron flux attenuation through concrete and iron shields, which were additionally placed up to 120-cm and 60-cm thickness, respectively, using activation detectors of graphite and bismuth. The attenuation lengths of concrete and iron for high-energy neutrons above 20 MeV were obtained from the 12C(n, 2n) 11C reaction of graphite.

Spallation neutron production and the current intra-nuclear cascade and transport codes

A recent renascent interest in energetic proton-induced production of neutrons originates largely from the inception of projects for target stations of intense spallation neutron sources, like the planned European Spallation Source (ESS), accelerator-driven nuclear reactors, nuclear waste transmutation, and also from the application for radioactive beams. In the framework of such a neutron production, of major importance is the search for ways for the most efficient conversion of the primary beam energy into neutron production. Although the issue has been quite successfully addressed experimentally by varying the incident proton energy for various target materials and by covering a huge collection of different target geometries --providing an exhaustive matrix of benchmark data-- the ultimate challenge is to increase the predictive power of transport codes currently on the market. To scrutinize these codes, calculations of reaction cross-sections, hadronic interaction lengths, average neutron multiplicities, neutron multiplicity and energy distributions, and the development of hadronic showers are confronted with recent experimental data of the NESSI collaboration. Program packages like HERMES, LCS or MCNPX master the prevision of reaction cross-sections, hadronic interaction lengths, averaged neutron multiplicities and neutron multiplicity distributions in thick and thin targets for a wide spectrum of incident proton energies, geometrical shapes and materials of the target generally within less than 10% deviation, while production cross-section measurements for light charged particles on thin targets point out that appreciable distinctions exist within these models.

High-pressure GEM operation aiming at thermal neutron detection

Experiments at the anticipated intense spallation neutron sources require neutron detection with typically millimeter position resolution. We are investigating the possibility of applying the gas electron multiplier (GEM) for this purpose. For efficient detection, /sup 3/He gas at up to 10 bar is required with some stopping gas at a differential pressure of 3-5 bar, i.e., high enough to sufficiently reduce the range of the neutron capture reaction products to achieve the required resolution. Due to the large initial charge deposition in the gas, only a small gain (10-100) is necessary. However, at the high pressures involved, it is not clear if even this can be achieved. We present first results of experiments using a range of gases, pressures, and, in this case, GEM hole sizes of 60 and 80 /spl mu/m to investigate this question. We observed the highest gain in an Ar/DME mixture, but this mixture does not meet the resolution criterion. The use of Xe (an effective stopping gas) in a Xe/DME mixture is ruled out, as no signal can be detected at pressures above 2 bar.

Measurement of deep penetration of neutrons produced by 800-MeV proton beam through concrete and iron at ISIS

A deep penetration experiment through a thick bulk shield was performed at an intense spallation neutron source facility, ISIS, of the Rutherford Appleton Laboratory (RAL), UK. ISIS is an 800 MeV–200 μA proton accelerator facility. Neutrons are produced from a tantalum target, which is shielded with approximately 3-m thick iron and 1-m thick ordinary concrete in the upward direction. On the top of the shield, we measured the neutron flux attenuation through concrete and iron shields which were additionally placed up to 1.2-m and 0.6-m thicknesses, respectively, using the activation detectors of graphite, bismuth, aluminum and the multi-moderator spectrometer inserted indium. The attenuation lengths of concrete and iron for high-energy neutrons above 20 MeV produced at 90° to the proton beam were obtained from the 12 C( n,2 n) 11 C reaction rates of graphite. The neutron spectra through concrete and iron were obtained by the unfolding analysis of the reaction rates of the 12 C( n,2 n) 11 C , 27 Al( n, α) 24 Na , 209 Bi( n,x n) 210−x Bi ( x=4–10) and 115 In( n, γ) 116m In in the energy range of thermal to 400 MeV.

Measurements of Neutron Attenuation through Iron and Concrete at ISIS

A deep penetration experiment through a thick bulk shield was performed at an intense spallation neutron source facility, ISIS, of the Rutherford Appleton Laboratory. ISIS is an 800MeV-200 μ A proton accelerator facility. Neutrons are produced from a tantalum target, and are shielded with approximately 3m thick iron and 1 m thick ordinary concrete. On the top of the shield, we measured the neutron flux attenuation through concrete and iron shields which were additionally placed up to 1.2 m and 0.6 m thicknesses, respectively, using activation detectors of carbon, aluminum and bismuth, and also indium-loaded multi-moderator spectrometer. The dose attenuation was simultaneously measured with the neutron and photon survey meters. The attenuation lengths of concrete and iron for high energy neutrons above 20MeV were obtained from the 12C(n,2n) reaction of carbon, and the neutron spectra penetrated through the additional shield and on the target shield top were obtained from the 12C(n,2n), 27Al(n,α) and 209Bi(n, xn) reactions, and multi-moderator spectrometer.We are now analyzing the measured results to compare with the shielding calculation.

Helium/Hydrogen Effects on the Properties of Materials for the APT Target/Blanket Region

Materials irradiated in the target/blanket region of the Accelerator Production of Tritium (APT) system will contain significantly more hydrogen and helium, for any given displacements per atom (dpa), than typically found in materials irradiated in a fission reactor. The individual effects of helium and hydrogen implantation and displacement damage on structural materials are relatively well established. Helium will increase the strength, decrease the ductility, reduce the creep and stress rupture properties, decrease the fatigue life and weldability, and promote swelling. Hydrogen will also adversely effect the mechanical properties and promote premature fracture along metallurgical interfaces. Displacement damage generally increases the strength and decreases the ductility of single-phase metals and alloys. The adverse effects of hydrogen and helium implantation may couple with displacement damage to limit component lifetime in the target/blanket region of the APT system. This paper provides a technical basis to rationalize potential synergistic effects among displacement damage and the hydrogen and helium embrittlement processes and suggests that such synergistic effects may be of significant importance to component performance in intense spallation neutron sources.

Future perspective of nuclear energy in Japan and the OMEGA program

Nowadays, about one third of the total electricity in Japan is supplied by nuclear power plants. It is estimated that the fraction of nuclear power will be increased much more in future. The primary nuclear policy of Japan adopts a uranium and plutonium fuel cycle system. The recovered plutonium will be recycled in light water reactors as MOX fuels in near future. Vitrified high-level radioactive wastes will be stored for 30 – 50 years prior to the ultimate geological disposal. On the other hand, in order to develop future technological possibilities in management and disposal of high-level radioactive wastes, the Atomic Energy Commission of Japan initiated the first phase of the OMEGA program, which is consisting of R&D activities on partitioning processes, transmutation systems, and related underlying technologies. Results of the first phase activities show an important possibility that the radiotoxicity of the original high-level radioactive wastes can be reduced to less than one hundredth after several hundreds years by using a process based on partitioning and transmutation. An intense spallation neutron source is evaluated to be one of the most effective neutron suppliers for the transmutation process. JAERI has been making a significant effort to develop a high power proton linac for an intense spallation neutron source, which can be utilized for demonstration of the transmutation process, and more widely utilized in fields of nuclear science and technology.

加速器の開発と工学的応用研究の現状

The status quo of the development of proton and electron accelerators and future plans on proposal are reviewed from the viewpoint of their applications to engineering problems. Their promising applications are discussed with the emphasis on utilizations of the nuclear spallation reaction caused by a high intensity beam. Topics included are: (1) fissile breeding with spallation neutrons (2) TRU. transmutation with high energy protons and neutrons, and (3) intense spallation neutron sources for basic and material science researches,