Francesco Piccirillo

Keeping the battery temperature below a reasonable limit of 50 °C is a primary objective of battery thermal management systems (BTMSs). Accordingly, the battery available operating time (BAOT) can be defined as the time required for the battery maximum temperature to reach 50 °C, which could be adopted as a key indicator for safe and efficient operation. BAOT can be improved through different BTMS configurations. This work focuses on passive solutions, aiming to increase BAOT without requiring pumping power. The study numerically investigates the combined use of phase change materials (PCMs) and fins to evaluate their effectiveness in terms of time percentage improvement (TPI). A preliminary analysis is conducted to assess the need for PCMs and fins at three discharge rates, namely 1C, 3C, and 5C. The results indicate that PCMs are required under all operating conditions, while the use of fins is not always advantageous; in particular, at 1C, fins lead to a reduction in BAOT. The analysis then focuses on the 3C and 5C cases, where topology-optimized fins are employed to dump temperatures under these stress conditions. Three fin arc lengths (ψ_fin) and eight diffusion coefficients (R_f) are examined. The optimized fin configurations increase BAOT, achieving maximum TPIs of 10.61% and 7.69% for the 3C and 5C cases, respectively, both corresponding to ψ_fin = 2.75 mm and R_f = 0.10 mm. At 5C, BAOT is limited to only a few seconds; therefore, configurations with PCMs arranged in series are also analyzed using different combinations of four selected PCMs. When coupled with optimized fins, the PCM-in-series solutions yield further improvements, with maximum TPIs of 22.92% for 3C and 62.50% for 5C compared to the single-PCM configuration coupled with optimized fins. The results also show that the optimal diffusion coefficient and PCM arrangement strongly depend on the discharge rate.

Purpose: Thermal management is essential to ensure the performance and safety of lithium-ion batteries, and effective heat dissipation helps prevent excessive temperature rise. This study aims to explore advanced passive thermal management strategies by developing a coupled electrochemical–thermal model to investigate the effectiveness of different phase change material (PCM) configurations: internal (within a hollow mandrel), external (surrounding the cell) and combined internal/external placement. The objective is to contain temperature rise while optimizing battery pack dimensions. In addition, a parametric analysis on the external PCM thickness is carried out to identify optimal design solutions for space-constrained applications. Design/methodology/approach: An 18650 lithium cobalt oxide (LCO) battery (3.7 V, 2.6 Ah) is studied, combining a multiscale pseudo-two-dimensional electrochemical model with a two-dimensional axis-symmetric thermal domain. Sodium thiosulfate pentahydrate is selected as PCM and modeled with an enthalpy-based method to account for latent heat effects. Equal PCM volume is used to compare internal and external configurations. Findings: The internal/external PCM configuration delays the battery critical temperature of 50 °C by up to 120.5%, compared to the case without PCM. External- and internal-only PCM provide delays of 58.6% and 40.5%, respectively. The parametric study shows that, to maintain a safe operating temperature of 45°C, an optimal PCM thickness of 1.66 mm is required for the internal/external layout versus 1.96 mm for the external-only case, corresponding up to a 5.4% battery pack volume saving. Originality/value: This work highlights the benefit of internal PCM integration in lithium-ion batteries, improving both thermal buffering and spatial efficiency. The findings offer guidance for designing compact, passively cooled battery systems.

In this paper, strategies to model thermo-electrochemical mechanisms occurring in Li-ion batteries are introduced. Two models are presented. The first consists in a numerical model suitable for finite-element method (FEM) simulations. The numerical model was validated by comparing simulation results with experimental data. The second model concerns fast and accurate simulations in a SPICE-compatible software package; such a model is denoted as macrocircuit and accounts for the main thermo-electrochemical effects of batteries. The macrocircuit was (i) validated with FEM simulation results and (ii) proven to be effective in simulations of practical circuits based on batteries. Although both the above modeling strategies were applied on a commercial product, they are suitable for batteries in any technology.

Nowadays, accurately predicting the operating temperature field in Li-Ion batteries is fundamental to properly design thermal management solutions to avoid phenomena like aging or thermal runaway. Specific approaches to describe the thermal behavior of Li-ion pouch battery cells have been investigated and the findings have been organized as a two-part manuscript. In particular, in this paper, corresponding to the Part I of the study, finite element simulations will be performed, based on the solution of 2D Laplace equation for potential field, and on 3D transient heat conduction equation to predict the temperature accounting for heat source term for the multiphysics coupling. In order to perform an exhaustive parametric analysis, correlations between some parameters like resistances or entropy coefficients, are mandatory. In this contribution, heat transfer predictions on a Li-Ion pouch cell are presented. Various regressions have been performed to obtain electric resistance evolution with SOC, while for the entropy coefficient different regressions have been compared too. Results are shown to be in excellent agreement with available literature data, highlighting that temperatures are generally much higher close to the tabs mainly due to the local increase in the current density. Finally, a parametric analysis for the exterior heat transfer coefficient has been carried out to underline the importance of an appropriate thermal management in such applications. The presented approach will be used to validate the SPICE-compatible battery model described in Part II.

This paper belongs to a two-part study dealing with thermal effects in Li-ion pouch battery cells. Here, a SPICE-compatible battery model suited for circuit-based simulations is presented. The model accounts for the thermo-electrochemical mechanisms taking place in batteries. Since it provides fast, yet accurate, results, the approach is aimed at supporting designers of electric/electronic systems based on storage supplies. Although the proposed solution can be applied to a generic product, a Li-ion pouch battery cell in nickel-manganese-cobalt was considered as a case study. The model accuracy is verified by comparing PSPICE results with those obtained through the 3-D finite-element method simulations described in Part I.