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Lithium Ion Batteries (LIBs) are widely used in research, industry and households, especially equipped in autonomous systems, such as mobile robots in air, land, or sea. More importantly, some of the environments are filled with nuclear radiation and with high temperature. The performance of LIBs in these environments are crucial to sustained operations of these systems. Unfortunately, how an LIB may degrade the operation of such systems has not been seriously studied in the field. Researches on LIBs material, performance, sustainability, etc. have been done through recent decades. Many kinds of cathode, electrolyte and anode material have been discovered and several configurations, like coin cells, cylinder cells, and prismatic cells have been developed for different operating conditions. The concern is still on the performance degradation and reliability when operating in radiation and high temperature environments such as in outer space exploration, to power robots in hot cell, and equipment for performing rescue or sampling missions at post-nuclear accidents. In this study, we designed an in situ methodology to monitor LIBs performance degradation when operating (cycling) under gamma radiation with a post-accident dose rate (~30krad/h), in terms of capacity fade and impedance rise. Coin cells were assembled using commercial cathode material and electrolyte, with Li as reference electrode. An ex-situ irradiation -testing protocol was also adopted in this study, as we were interested in investigating separate radiation effects on individual battery components. Additionally, the effect of radiation on battery materials may be different at various temperature environment, for example, in space or in a nuclear accident field. We have conducted battery performance under irradiation while heating (80 °C) or cooling (-40 °C). Ex situ studies, including cathode material X-ray diffraction (XRD), and characterizations with Fourier Transform Infrared (FTIR) spectroscopy, ultraviolet–visible spectroscopy (UV-vis) spectroscopy and electron paramagnetic resonance (EPR) will also be discussed.

We have recently developed a nondestructive method to visualize and quantify Li atom position in real-time using neutrons by a method referred to as neutron depth profiling (NDP). In situ NDP is an ideal technique for probing Li complex formation, accumulation and transport within the battery material during charge/discharge. Currently, our work is focused on understanding the effect of an electrochemical event to the materials’ storage properties. Specifically we report our recent work on the preferential Li nucleation, Li trapping and Li transport in intermetallic materials like LixSny, LixSiy and LixAly and intercalating materials like LiNiMnCoO3.

Introduction Lithium ion batteries (LIBs) are rechargeable batteries widely used in portable devices such as laptops, mobile phones and other electronic devices. Owing to their success and promising properties, LIBs are now being considered for storage and distribution of renewable energy sources, and in the automotive industry, for powering hybrid and plug-in vehicles. The increasing demands on batteries has stimulated the development of advanced materials, diagnostic tools and battery models that could lead to better performance in terms of storage capacity, kinetics, and long-term cyclability. A real-time quantification of Li transport using a non-destructive neutron method to measure the Li distribution upon charge and discharge of a Li-ion cell is reported here. In situ Neutron Depth Profiling (NDP) provides temporal and spatial measurement of Li and visualization of its transposition to guide materials development for efficient storage. Using in situNDP, we probed the onset of lithiation in a model Sn electrode and visualized the enrichment of Li atoms on the surface while monitoring the propagation of Li into the bulk. Energy density requirements for larger-scale applications would require higher storage capacity from both anodes and cathodes. Current graphite anode material in Li-ion batteries offers numerous advantages including good cycle life and relatively low cost. Increasing the storage capacity anodes require higher capacity materials. Sn, with its relatively high theoretical specific capacity of 959 mAh/g is a promising alternative anode material among other group IV elements. These intermetallic forming materials experiences volumetric expansions of ~300% upon charge, resulting in drastic capacity fade with time. Improvements in the complex architectures such as nanowires, 3D architecture, inactive core/active shell structures are often attributed to enhanced accommodation of the transformations that occur during cycling. However, the transport properties of lithium and their resulting distribution within the material are largely inferred using ex situand often invasive techniques. This paper will discuss recent efforts in using neutron depth profiling (NDP) to probe the distribution and dynamics of Li transport in Sn anodes during lithiation and delithiation processes. Experimental Half-cells with Sn foil as the working electrode (0.0125 mm thick, 97.4%, Goodfellow) in disk geometry (12 mm in diameter), metallic lithium (Chemetall Foote Corp) disc (12 mm in diameter) as a combined counter and reference electrode, a Celgard® separator (~ 25 mm), and electrolyte (1 M LiBF4 in 1:1 ethylene carbonate: dimethyl carbonate from Sigma Aldrich) were assembled in a modified CR2032 coin cells (MTI Corp) as depicted in Figure 1. Coin cell components were cleaned in acetone (≥ 99.5%) and methanol (≥ 99.8%) in sequence followed by overnight drying at 55 oC under vacuum. The coin cells were crimped using a manual hydraulic crimping machine (MSK-110, MTI Corp) equipped with a CR2032 die at pressures of 1100 – 1200 psi. The coin cells were modified with a 9.5 mm diameter hole on one of the casings to allow the placement of a Kapton® film (7.5 mm thickness) adhered to the casing via Kapton® tape (Bertech). The design of a “leak” free electrochemical cell is critical to the success of the experiment. The electrochemical cell remains functional and air free for weeks and remains “leak” free under vacuum (10-6 torr) for days. The handling and assembling of materials were performed in an Argon-filled glovebox (mBraun) with continuous detection of H2O < 0.5 ppm and O2< 0.5 ppm. After assembly, the coin cells were transported in a sealed, argon-filled desiccator. Electrochemical measurements were performed on a Gamry Potentiostat (Reference 600, Gamry Instruments). The mass of the electroactive Sn electrode was determined by weighing. Neutron depth profiling facility and measurements While the data presented in this paper was obtained using a “cold” neutron depth profiling ( NDP) facility at the National Institute of Standards and Technology’s (NIST) Center for Neutron Research (NCNR) (Gaithersburg, MD, USA), the preliminary testing and the optimization of the in situ electrochemical design were initially performed at the Ohio State University Research Reactor (OSURR) with a thermal equivalent fluence rate of 8.6 × 106 cm-2s-1 and a maximum beam diameter of 30 mm. The facility at NIST provides a well-collimated “cold” neutron (~5 meV) with thermal equivalent fluence rate of 1.0 × 109 cm-2s-1 and a nominal beam area of 110 mm2. Results and Discussion Figure 1. (a) CVs of a 200 nm Sn foil (WE) collected at 0.05 mV/s. (b) Li distribution from NDP of a thin Sn foil (ca. 12.5 um) as a function of charge. All electrochemical data were collected in 1 M LiPF6 in EC:DMC (1:1 wt) electrolyte.