Gareth Hinds

In-operando high-speed tomography of lithium-ion batteries during thermal runaway

Prevention and mitigation of thermal runaway presents one of the greatest challenges for the safe operation of lithium-ion batteries. Here, we demonstrate for the first time the application of high-speed synchrotron X-ray computed tomography and radiography, in conjunction with thermal imaging, to track the evolution of internal structural damage and thermal behaviour during initiation and propagation of thermal runaway in lithium-ion batteries. This diagnostic approach is applied to commercial lithium-ion batteries (LG 18650 NMC cells), yielding insights into key degradation modes including gas-induced delamination, electrode layer collapse and propagation of structural degradation. It is envisaged that the use of these techniques will lead to major improvements in the design of Li-ion batteries and their safety features.

Investigating lithium-ion battery materials during overcharge-induced thermal runaway: an operando and multi-scale X-ray CT study

Catastrophic failure of lithium-ion batteries occurs across multiple length scales and over very short time periods. A combination of high-speed operando tomography, thermal imaging and electrochemical measurements is used to probe the degradation mechanisms leading up to overcharge-induced thermal runaway of a LiCoO2 pouch cell, through its interrelated dynamic structural, thermal and electrical responses. Failure mechanisms across multiple length scales are explored using a post-mortem multi-scale tomography approach, revealing significant morphological and phase changes in the LiCoO2 electrode microstructure and location dependent degradation. This combined operando and multi-scale X-ray computed tomography (CT) technique is demonstrated as a comprehensive approach to understanding battery degradation and failure.

Quantifying Bulk Electrode Strain and Material Displacement within Lithium Batteries via High-Speed Operando Tomography and Digital Volume Correlation

Tracking the dynamic morphology of active materials during operation of lithium batteries is essential for identifying causes of performance loss. Digital volume correlation (DVC) is applied to high‐speed operando synchrotron X‐ray computed tomography of a commercial Li/MnO2 primary battery during discharge. Real‐time electrode material displacement is captured in 3D allowing degradation mechanisms such as delamination of the electrode from the current collector and electrode crack formation to be identified. Continuum DVC of consecutive images during discharge is used to quantify local displacements and strains in 3D throughout discharge, facilitating tracking of the progression of swelling due to lithiation within the electrode material in a commercial, spiral‐wound battery during normal operation. Displacement of the rigid current collector and cell materials contribute to severe electrode detachment and crack formation during discharge, which is monitored by a separate DVC approach. Use of time‐lapse X‐ray computed tomography coupled with DVC is thus demonstrated as an effective diagnostic technique to identify causes of performance loss within commercial lithium batteries; this novel approach is expected to guide the development of more effective commercial cell designs.

Stress corrosion cracking of steam turbine disc steel––measurement of the crack-tip potential

Abstract In situ measurements have been made of the crack-tip potential in a fatigue-precracked compact tension specimen of a 3% NiCrMoV steam turbine disc steel immersed in simulated steam condensate environments at 90 °C. Despite high corrosion potentials of 0.1 V saturated calomel electrode (SCE) the extent of crack-tip anodic polarisation was very constrained, a limiting potential of about −0.61 V SCE being attained. Surprisingly, adding chloride up to 1500 ppb, or separately sulphate at 406 ppb, had no impact on the tip potential and its variation with corrosion potential, compared with pure water. Increasing the pH of initially neutral pure water also had no significant effect.

Chemistry of Concentrated Salts Formed by Evaporation of Seawater on Duplex Stainless Steel

Abstract An investigation has been made of the solution chemistry associated with the concentrated solutions formed by seawater evaporation on hot duplex stainless steel (DSS) and super duplex stai...

Degradation Study by Start-Up/Shut-Down Cycling of Superhydrophobic Electrosprayed Catalyst Layers Using a Localized Reference Electrode Technique

Degradation of a polymer electrolyte membrane fuel cell (PEMFC) with electrosprayed cathode catalyst layers is investigated during cyclic start-up and shut-down events. The study is carried out within a single cell incorporating an array of reference electrodes that enables measurement of cell current as a function of local cathode potential (localized polarization curves). Accelerated degradation of the cell by start-up/shut-down cycling gives rise to inhomogeneous performance loss, which is more severe close to the gas outlet and occurs predominantly during start-up. The degradation consists primarily of loss of cathode catalyst activity and increase in cell internal resistance, which is attributed to carbon corrosion and Pt aggregation in both anode and cathode. Cells with an electrosprayed cathode catalyst layer show lower degradation rates during the first 100 cycles, compared with those of a conventional gas diffusion electrode. This difference in behavior is attributed to the high hydrophobicity of the electrosprayed catalyst layer microstructure, which retards the kinetics of corrosion of the carbon support. In the long term, however, the degradation rate is dominated by the Pt/C ratio in the cathode catalyst layer.

Technical Note: Measurement of pH in Concentrated Brines

Abstract To resolve reported discrepancies between pH values of concentrated brines measured in the laboratory and those predicted by thermodynamic models, extensive measurements have been carried out to compare the performance of several different types of a glass pH electrode against a standard hydrogen electrode (SHE). The results demonstrate that the use of glass electrodes to measure pH in concentrated sodium chloride solutions gives a misleadingly low indication of pH, and may introduce errors of up to 0.2 pH units. This small difference is usually not significant but if the target pH is near a step-change in corrosion behavior then consideration should be given to adopting the SHE as back-up.

Identifying the Cause of Rupture of Li‐Ion Batteries during Thermal Runaway

Abstract As the energy density of lithium‐ion cells and batteries increases, controlling the outcomes of thermal runaway becomes more challenging. If the high rate of gas generation during thermal runaway is not adequately vented, commercial cell designs can rupture and explode, presenting serious safety concerns. Here, ultra‐high‐speed synchrotron X‐ray imaging is used at >20 000 frames per second to characterize the venting processes of six different 18650 cell designs undergoing thermal runaway. For the first time, the mechanisms that lead to the most catastrophic type of cell failure, rupture, and explosion are identified and elucidated in detail. The practical application of the technique is highlighted by evaluating a novel 18650 cell design with a second vent at the base, which is shown to avoid the critical stages that lead to rupture. The insights yielded in this study shed new light on battery failure and are expected to guide the development of safer commercial cell designs.

Influence of Weld Preparation Procedure and Heat Tinting on Sulfide Stress Corrosion Cracking of Duplex Stainless Steel

Corrosion resistant alloys, such as duplex stainless steel (DSS), are increasingly the material of choice for oilfield applications as a result of the trend toward more extreme temperature, higher pressure, and elevated levels of hydrogen sulfide. However, the susceptibility of such materials to localized corrosion and sulfide stress cracking (SSC) is a major consideration, particularly in the vicinity of welds. Here we investigate the effect of surface preparation and oxygen content in the backing gas during welding on the pitting and SSC susceptibility of 22Cr DSS. Four-point bend testing of welded specimens under conditions close to the pass/fail boundary revealed a greater tendency for pitting as a function of oxygen content in the backing gas. Pitting was concentrated in the heat-tinted region, whereas cracking was mainly observed in the adjacent coarse ground parent material, with surface defects from the grinding process acting as primary crack initiation sites. The results demonstrate that control...

Effect of Pigging Damage on Sulfide Stress Corrosion Cracking of Corrosion Resistant Alloys

Hard wire brush pigging of oil and gas pipelines is often used to remove deposits and maintain flow efficiency but there is uncertainty as to whether the resulting mechanical damage could introduce a risk of localized corrosion or stress corrosion cracking. In this study, three different corrosion resistant alloys (CRAs) commonly used in oil and gas pipelines were subjected to surface abrasion at different levels of severity to simulate the damage experienced during pigging. Resistance to sulfide stress corrosion cracking under representative sour oilfield conditions was then evaluated using the four-point bend test method. No increase in susceptibility to stress corrosion cracking as a result of the simulated pigging process was observed under a range of conditions close to the pass/fail boundary for each material. Furthermore, under more severe conditions, surface abrasion inhibited local initiation and propagation of cracks on 25Cr superduplex stainless steel, with a ground surface finish, as a result ...