National Physical Laboratory

About: National Physical Laboratory is a facility organization based out in London, United Kingdom. It is known for research contribution in the topics: Dielectric & Thin film. The organization has 7615 authors who have published 13327 publications receiving 319381 citations.

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.

Some new methods for the numerical integration of ordinary differential equations

Abstract: The choice of a numerical method for the solution of ordinary differential equations depends on the associated boundary conditions. When all the boundary conditions are specified at one end of the range of integration, one of the well-known step-by-step methods will generally be used, while the method of relaxation is reserved for the case in which boundary conditions are specified at more than one point (1). In the latter, simple but inaccurate finite-difference formulae are used to provide a first approximation to the required solution; this approximation is then used to give an estimate of the errors involved in the use of the inaccurate formulae, and successive corrections are obtained until the full, accurate finite-difference equations are satisfied (1). The same principle is followed in this paper with regard to step-by-step methods, the main difference being the way in which approximate solutions are obtained. In relaxation methods simultaneous equations are solved, while in the use of the step-by-step methods suggested here successive pivotal values are built up by the use of recurrence relations. All the methods of this paper follow this principle, differing only in the method of obtaining a recurrence relation, and consequently in the form of the correction terms.

Sputtering yields of compounds using argon ions

Abstract: An analysis is made of published sputtering yield data for compounds using argon primary ions at normal incidence to evaluate the validity of simple predictive equations. These are sputtering yields at dynamical equilibrium. First, two archetypal compounds are analysed: GaAs with constituent elements of similar atomic number and weak preferential sputtering, and Ta2O5 with constituent elements of widely separate atomic number and strong preferential sputtering. The agreements of the sputtering yields predicted by the semi-empirical linear cascade theory are excellent when the appropriate parameters are interpolated, rather than using an average atomic number. The effect of preferential sputtering is included within the framework of the simple pair-bond theory. The average ratios of the data to the initial predictions for GaAs and Ta2O5 are 1.01 ± 0.06 and 1.00 ± 0.07, respectively. Extension of this analysis to a range of oxides shows that the heat of reaction of the oxidation process needs inclusion. It is here that the effect of preferential sputtering can lead to an expansion of the uncertainties. SiO2 is often used as a reference material and so the published yield data are analysed in detail. These show an extremely broad scatter and so new experimental data are measured. These new results are in the upper range of previous data and correlate with the semi-empirical theory with a scatter of only 9%. These correlations show that the semi-empirical linear cascade theory is excellent for predicting the energy dependence of the yield and can be excellent for absolute yields where the compound heat of formation is low.