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This paper presents the results of an analysis using the direct current internal resistance (DCIR) method on a nickel-cobalt-manganese oxide (NCM)-based battery with a nominal capacity of 55.6 Ah. The accelerated degradation test was performed on V0G, V1G, and V2G patterns, representing existing simple power supply, smart charging control, and bi-directional charge/discharge control, respectively. We assumed V0G, V1G, and V2G patterns and conducted charging and discharging experiments according to the set conditions. According to the pattern repetition, changes in the internal resistance of DCIR and AC-impedance were analyzed and battery deterioration was diagnosed. By comparing DCIR and AC-impedance, we confirmed that the changes in internal resistance has a similar trend. In particular, we propose a new DCIR analysis method in the “stop-operation” part rather than the traditional DCIR method. In the case of traditional DCIR method, time is required for the battery to stabilize. However, the newly proposed DCIR analysis method has the advantage of diagnosing the deterioration of the battery during system operation by analyzing the internal resistance without the stabilization time of the battery.

The freezing phenomena in supercooled liquid droplets are important for many engineering applications. For instance, a theoretical model of this phenomenon can offer insights for tailoring surface coatings and for achieving icephobicity to reduce ice adhesion and accretion. In this work, a mathematical model and hybrid numerical–analytical solutions are developed for the freezing of a supercooled droplet immersed in a cold air stream, subjected to the three main transport phenomena at the interface between the droplet and the surroundings: convective heat transfer, convective mass transfer and thermal radiation. Error-controlled hybrid solutions are obtained through the extension of the generalized integral transform technique to the transient partial differential formulation of this moving boundary heat transfer problem. The nonlinear boundary condition for the interface temperature is directly accounted for by the choice of a nonlinear eigenfunction expansion base. Also, the nonlinear equation of motion for the freezing front is solved together with the ordinary differential system for the integral transformed temperatures. After comparisons of the solution with previously reported numerical and experimental results, the influence of the related physical parameters on the droplet temperatures and freezing time is critically analysed.

C/SiO 2 composite derived from rice husks (RHs) have gained significant attention in developing abundant anode materials for sodium-ion batteries due to their unique features, simple synthesis process without using additional sources of silica and carbon, and affordable price. Despite the extensive research reported, a part of the expensive hard carbon, the choice of anode materials still needs to be improved, leading to challenges in commercializing SIBs. In this study, full-cell C/SiO 2 ǁNa 3 V 2 (PO 4 ) 3 was optimized for the assembly conditions, achieving the highest and most stable capacity. In detail, the N/P ratio survey using pre-sodiation C/SiO 2 materials is the remaining factor. Besides, evaluations of the diffusion process kinetics in C/SiO 2 have been conducted through Electrochemical Impedance Spectroscopy (EIS) and Galvanostatic Intermittent Titration Technique (GITT) studies. Within the pre-sodiation anode, full-cell C/SiO 2 ǁNa 3 V 2 (PO 4 ) 3 at N/ P  ∼ 1.2 offers the highest capacity of 126.3 mAh.g − 1 and capacity retention of 83.7% after 50 cycles. Moreover, other electrochemical evaluation techniques were also used in this study, such as EIS ex-situ, CV, C-rate, and GCPL. Finally, with the information from this study, the optimization of Na-ion battery assembly conditions from material C/SiO 2 has been explored, opening a new future for cost-effective batteries. Graphical Abstract

A NASICON-based Na3V2(PO4)2F3 (NVPF) cathode material is reported herein as a potential symmetric cell electrode material. The symmetric cell was active from 0 to 3.5 V and showed a capacity of 85 mAh/g at 0.1 C. With cycling, the NVPF symmetric cell showed a very long and stable cycle life, having a capacity retention of 61% after 1000 cycles at 1 C. The diffusion coefficient calculated from cyclic voltammetry (CV) and the galvanostatic intermittent titration technique (GITT) was found to be ~10−9–10−11, suggesting a smooth diffusion of Na+ in the NVPF symmetric cell. The electrochemical impedance spectroscopy (EIS) carried out during cycling showed increases in bulk resistance, solid electrolyte interphase (SEI) resistance, and charge transfer resistance with the number of cycles, explaining the origin of capacity fade in the NVPF symmetric cell. Finally, the postmortem analysis of the symmetric cell after 1000 cycles at a 1 C rate indicated that the intercalation/de-intercalation of sodium into/from the host structure occurred without any major structural destabilization in both the cathode and anode. However, there was slight distortion in the cathode structure observed, which resulted in capacity loss of the symmetric cell. The promising electrochemical performance of NVPF in the symmetric cell makes it attractive for developing long-life and cost-effective batteries.

In semi-auxetic sandwich plates, the Poisson’s ratio varies from positive value to negative and vice versa in the thickness direction. The elastic modulus can also be variable throughout the thickness, as previously applied to other composite materials. Considering variable mechanical properties in a sandwich plate, the buckling load may significantly increase. For the first time, this study investigates how the buckling load of symmetric three-layer semi-auxetic sandwich plates (a core and two faces) is enhanced. The rectangular sandwich plates’ edges are simply supported or fully clamped and are subjected to in-plane (combined biaxial and shear) loads. Their buckling equation is developed and solved using classical plate theory and applying the generalized integral transform technique (GITT). As the geometry and material are symmetrical relative to the sandwich plate midplane, the buckling load (coefficient) is obtained through an eigenvalue problem. The GITT gives more accurate and quicker results than the finite element analysis developed in the commercial software ABAQUS. The results show that the minimum buckling coefficient depends only on Poisson’s ratio distribution pattern throughout sandwich plate thickness. Furthermore, if the absolute value of core Poisson’s ratio is less than the faces, the buckling coefficient increases and vice versa. As the variations can approximately coincide with the saddle surface of a hyperbolic paraboloid, a concise formula is innovatively proposed to predict the buckling coefficient quickly. The suggested formula represents satisfactory results when the core and faces Poisson’s ratios are between − 0.5 and 0.3.

The chemical diffusion coefficient in LiNi 1/3 Mn 1/3 Co 1/3 O 2 was determined via the galvanostatic intermittent titration technique in the voltage range 3 to 4.2 V. Calculated diffusion coefficients in these layered oxide cathodes during charging and discharging reach a minimum at the open-circuit voltage of 3.8 V and 3.7 V vs. Li/Li + , respectively. The observed minima of the chemical diffusion coefficients indicate a phase transition in this voltage range. The unit cell parameters of LiNi 1/3 Mn 1/3 Co 1/3 O 2 cathodes were determined at different lithiation states using ex situ crystallographic analysis. It was shown that the unit cell parameter variation correlates well with the observed values for chemical diffusion in NMC cathodes; with a notable change in absolute values in the same voltage range. We relate the observed variation in unit cell parameters to the nickel conversion into the trivalent state, which is Jahn-Teller active, and to the re-arrangement of lithium ions and vacancies.

This paper presents an innovative and efficient methodology for the determination of the solid-state diffusion coefficient in electrode materials with phase transitions for which the assumption of applying the well-known formula from the work of Weppner et al. is not satisfied. This methodology includes a k-means machine learning screening of Galvanostatic Intermittent Titration Technique (GITT) steps, whose outcomes feed a physics-informed algorithm, the latter involving a pseudo-two-dimensional (P2D) electrochemical model for carrying out the numerical simulations. This methodology enables determining, for all of the 47 steps of the GITT characterization, the dependency of the Na+ diffusion coefficient as well as the reaction rate constant during the sodiation of an NVPF electrode to vary between 9 × 10−18 and 6.8 × 10−16 m2·s−1 and between 2.7 × 10−14 and 1.5 × 10−12 m2.5·mol−0.5·s−1, respectively. This methodology, also validated in this paper, is (a) innovative since it presents for the first time the successful application of unsupervised machine learning via k-means clustering for the categorization of GITT steps according to their characteristics in terms of voltage; (b) efficient given the considerable reduction in the number of iterations required with an average number of iterations equal to 8, and given the fact the entire experimental duration of each step should not be simulated anymore and hence can be simply restricted to the part with current and a small part of the rest period; (c) generically applicable since the methodology and its physics-informed algorithm only rely on “if” and “else” statements, i.e., no particular module/toolbox is required, which enables its replication and implementation for electrochemical models written in any programming language.

Conventional applications of the Galvanostatic Intermittent Titration Technique (GITT) and EIS for estimating chemical diffusivity in battery electrodes face issues such as insufficient relaxation time to reach equilibrium, excessively long pulse durations that violate the short-time diffusion assumption, and the assumption of sequential electrode reaction and diffusion processes. In this work, a quasi-equilibrium criterion of 0.1 mV h−1 was applied to NMC622 electrodes, yielding 8–9 h relaxations below 3.8 V, but above 3.8 V, voltage decayed linearly and indefinitely, even upon discharging titration, showing unusual nonmonotonic relaxation behavior. The initial 36-s transients of a 10-min galvanostatic pulse and diffusion impedance in series with the electrode reaction yielded consistent diffusivity values. However, solid-state diffusion in spherical active particles within porous electrodes, where ambipolar diffusion occurs in the pore electrolyte with t+=0.3, requires a physics-based three-rail transmission line model (TLM). The corrected diffusivity may be three to four times higher. An analytic two-rail TLM approximating the three-rail numerical model was applied to temperature- and frequency-dependent EIS data. This approach mitigates parameter ambiguity and unphysical correlations in EIS. Physics-based EIS enables the identification of multistep energetics and the diagnosis of performance and degradation mechanisms.

The working principle of lithium-ion batteries lies in the intercalation of lithium ions in electrode active materials, which exhibit either solid-solution or phase-separating behaviour. This study presents a comparative analysis of the electrochemical responses of these two classes of active materials using a multi-particle phase-field model, the structure and description of which are designed to promote easy interpretation by non-modelling experts. Current pulses and open-circuit relaxations, such as those in the galvanostatic intermittent titration technique (GITT), are simulated for different solid-state diffusion coefficients and particle size distributions. The distinct electrode potential responses are explained through the dynamic intra- and inter-particle lithium distributions and their interplay with active material thermodynamics. In solid-solution active materials, numerical results indicate that the solid-state diffusion coefficient tends to be underestimated by the GITT. In phase-separating active materials, current pulses instead generate a shrinking-core lithium distribution along the particle radius (e.g. the Li-rich phase at the particle surface and the Li-poor phase at the particle centre), so that only the phase nucleated at the particle surface can be electrochemically probed in terms of its diffusion and kinetic properties. Such a shrinking-core distribution represents a quasi-equilibrium configuration for a phase-separating active material, resulting in fast electrode potential relaxation upon current interruption and impeding any inter-particle lithium exchange. In fact, while small particles lithiate faster for both active materials during current pulses, the rest phases enable lithium homogenisation among the particles of a solid-solution active material, which can be adequately simulated using a single equivalent particle radius. In contrast, the absence of inter-particle lithium exchange at open circuit in phase-separating active materials may result in over-lithiation of small particles. This poses limitations to single-particle modelling for phase-separating active materials and highlights the need for carefully calibrated rest phases in pulse fast-charging protocols to facilitate inter-particle lithium exchange when the electrode is in an out-of-equilibrium configuration.

Battery models are one of the most important tools for understanding the behaviour of batteries. This is particularly important for the fast-moving electrical vehicle industry, where new battery chemistries are continually being developed. The main limiting factor on how fast battery models can be developed is the experimental technique used for collection of data required for model parametrisation. Currently, this is a very time-consuming process. In this paper, a fast novel parametrisation testing technique is presented. A model is then parametrised using this testing technique and compared to a model parametrised using current common testing techniques. This comparison is conducted using a WLTP (worldwide harmonised light vehicle test procedure) drive cycle. As part of the validation, the experiments were conducted at different temperatures and repeated using two different temperature control methods: climate chamber and a Peltier element temperature control method. The new technique introduced in this paper, named AMPP (accelerated model parametrisation procedure), is as good as GITT (galvanostatic intermittent titration technique) for parametrisation of ECMs (equivalent circuit models); however, it is 90% faster. When using experimental data from a climate chamber, a model parametrised using GITT was marginally better than AMPP; however, when using experimental data using conductive control, such as the ICP (isothermal control platform), a model parametrised using AMPP performed as well as GITT at 25 °C and better than GITT at 10 °C.