The rapid evolution of lithium-ion battery (LIB) technology is fundamentally reshaping energy storage for electric vehicles and grid-scale applications. However, this progress is intrinsically linked to a critical challenge: managing the substantial heat generated during operation. Excessive temperature rise accelerates capacity fade, shortens lifespan, and, in severe cases, can trigger thermal runaway—a catastrophic failure mode involving fire and explosion. An effective battery management system (BMS) is paramount, and its thermal management subsystem is a cornerstone for ensuring safety, performance, and longevity. Among various cooling strategies, phase change material (PCM)-based passive thermal management has garnered significant interest due to its simplicity, low energy consumption, and high heat absorption capacity.
Traditional organic PCMs, like paraffin wax, are widely studied but present a severe safety paradox: they are highly flammable. In a failing battery system, these materials can act as fuel, exacerbating thermal runaway fires. This critical flaw has redirected research towards non-flammable alternatives. Inorganic phase change materials (IPCMs), particularly salt hydrates, offer a compelling solution with high volumetric latent heat, suitable phase change temperatures, low cost, and inherent fire resistance. Their integration into a battery management system could significantly enhance safety protocols. Yet, their practical application has been hampered by persistent drawbacks: leakage upon melting, supercooling, phase separation, and loss of crystallization water, which degrade thermal stability and shape integrity over cycles.
To overcome these barriers, we have developed and investigated a novel Composite Inorganic Phase Change Material (CIPCM). Our design operates on two scales. At the microscale, the salt hydrate core is encapsulated within a synthesized silica (SiO₂) shell via an inverse emulsion interfacial polymerization process. This microencapsulation effectively addresses leakage and improves cyclic stability. At the macroscale, these microcapsules are integrated into a flexible ethylene-vinyl acetate (EVA) copolymer skeleton using a solvent evaporation method. This framework provides shape stability, allowing the CIPCM to be molded into flexible sheets that can conform to complex battery geometries, a crucial feature for practical integration into a battery pack managed by a BMS. The resulting material exhibits a consistent phase change temperature around 48.5°C with a latent heat of approximately 89 kJ/kg.
While experimental validation on small modules is essential, comprehensive performance evaluation for large-scale battery packs is constrained by high costs, safety risks, and logistical complexity. Parametric studies, crucial for optimizing the battery management system design, become prohibitively difficult through experimentation alone. Therefore, we employ numerical simulation as a powerful complementary tool. This study leverages COMSOL Multiphysics to construct a three-dimensional coupled electro-thermal model of a battery module integrated with our CIPCM. This approach allows for systematic, cost-effective, and safe exploration of the CIPCM’s thermal management performance under a wide range of operational parameters, providing vital data to guide the design of real-world BMS strategies.
The core of our model is a module of cylindrical 18650-type lithium-ion batteries, each wrapped with a layer of CIPCM. The primary heat transfer pathway is as follows: heat generated within the battery is conducted to the adjacent CIPCM layer, which absorbs it as latent heat during phase change. Subsequently, heat is dissipated from the outer surfaces of the CIPCM to the environment via natural convection and radiation. The model incorporates key thermophysical properties of the CIPCM, as summarized in Table 1.
| Parameter | Value | Unit |
|---|---|---|
| Density ($\rho_{pcm}$) | 0.951 $\pm$ 0.42 | g/cm³ |
| Phase Change Temperature ($T_{pc}$) | 48.5 $\pm$ 1.3 | °C |
| Latent Heat ($L_{pcm}$) | 88.87 $\pm$ 2.2 | kJ/kg |
| Thermal Conductivity ($k_{pcm}$) | 0.216 $\pm$ 0.004 | W/(m·K) |
| Specific Heat Capacity ($C_{p,pcm}$) | 3.152 $\pm$ 0.21 | kJ/(kg·K) |
The battery’s heat generation is a critical input. We use a widely adopted electro-thermal model where the volumetric heat generation rate ($\dot{Q}_{gen}$) during discharge is given by:
$$\dot{Q}_{gen} = \frac{I}{V_{cell}} (V_{ocv} – V_{cell} – T_{cell} \frac{dV_{ocv}}{dT})$$
where $I$ is the current, $V_{cell}$ is the terminal voltage, $V_{ocv}$ is the open-circuit voltage, and $T_{cell}$ is the battery temperature. The entropic heat term $T_{cell} \frac{dV_{ocv}}{dT}$ is significant for lithium-ion chemistry. The governing energy equation for the battery and the CIPCM domain (excluding phase change) is:
$$\rho C_p \frac{\partial T}{\partial t} = \nabla \cdot (k \nabla T) + \dot{Q}_{gen}$$
For the CIPCM, the phase change process is modeled using the apparent heat capacity method, where the latent heat effect is incorporated into an effective heat capacity over a small temperature range around $T_{pc}$.
We first validated our electro-thermal model against experimental data from a single cell under 2C and 3C discharge rates. The simulated surface temperature curves showed excellent agreement with measurements, with a discrepancy of less than 5%, confirming the accuracy of our heat generation model and boundary conditions. This validated framework forms the basis for all subsequent parametric studies on the multi-cell module.
The visual representation above conceptualizes a battery management system where thermal management is a critical component. Our simulation studies essentially quantify the performance of the CIPCM block within such a system. We systematically investigated the influence of three key parameters: discharge rate (C-rate), CIPCM layer thickness ($\delta$), and ambient temperature ($T_{amb}$). These parameters are central to the operational logic of any BMS.
The primary metric for evaluation is the maximum temperature ($T_{max}$) within the battery module. Compared to mere natural air convection, the inclusion of a 5 mm thick CIPCM layer demonstrated substantial cooling benefits. The results are compelling: at 1C, 2C, and 3C discharge rates, the CIPCM reduced $T_{max}$ by 4.9°C, 12.0°C, and 20.6°C, respectively. The temperature evolution with CIPCM typically shows three distinct phases: a pre-phase-change temperature rise, a temperature plateau during the CIPCM’s latent heat absorption, and a post-melting temperature rise. The duration of the plateau is a direct indicator of the active cooling period provided by the CIPCM, a feature highly desirable for a passive BMS.
The thickness of the CIPCM layer ($\delta$) is a major design variable, trading off cooling performance against volume and weight penalties in the battery pack. Our simulations explored $\delta$ from 2 mm to 11 mm. The relationship between performance and thickness is non-linear and highly dependent on C-rate. The data is best analyzed by observing the plateau phase and the final $T_{max}$.
| C-rate | $\delta$ = 2 mm | $\delta$ = 3 mm | $\delta$ = 5 mm | $\delta$ = 8 mm | $\delta$ = 11 mm |
|---|---|---|---|---|---|
| 1C | 60.5 °C | 55.8 °C | 50.1 °C | 47.3 °C | 45.2 °C |
| 2C | 90.8 °C | 75.6 °C | 58.6 °C | 53.1 °C | 50.8 °C |
| 3C | >100 °C* | 88.4 °C | 62.8 °C | 57.5 °C | 54.9 °C |
*Temperature exceeded safe limits before discharge completion.
As seen in Table 2, increasing $\delta$ from 2 mm to 5 mm dramatically improves thermal management, especially at higher C-rates. For 2C and 3C, the plateau period extends significantly, preventing dangerous temperature spikes. This is because the increased mass of CIPCM provides more latent heat capacity to absorb the battery’s total generated heat. However, diminishing returns are observed beyond $\delta$ = 5 mm. While further cooling is achieved, the incremental gain is small (only 2-5°C reduction from 5 mm to 11 mm). This is attributed to the relatively low thermal conductivity of the CIPCM ($k_{pcm}$). As the layer thickens, heat cannot rapidly diffuse to the outer regions of the CIPCM within the fixed discharge time, leaving a portion of the material unutilized. Therefore, from a BMS design perspective targeting optimal energy density, a thickness of 5 mm represents a effective compromise for standard operating conditions (25°C ambient, up to 3C discharge).
The effectiveness of a passive thermal management system is inherently tied to the operating environment. A BMS must account for varying climatic conditions. We simulated the performance of the 5 mm CIPCM under different ambient temperatures ($T_{amb}$: 15°C, 25°C, 35°C, 45°C). The results indicate that the CIPCM’s capability to limit $T_{max}$ degrades as $T_{amb}$ rises, particularly at high C-rates. At 1C discharge, the 5 mm layer maintains temperatures below 55°C across all tested $T_{amb}$. However, at 3C, while effective at 25°C, it struggles at 45°C, allowing $T_{max}$ to enter a risky region (>60°C). This occurs because a higher $T_{amb}$ reduces the temperature gradient driving heat dissipation from the CIPCM to the environment, causing heat to accumulate within the module.
This finding necessitates adaptive design. For aggressive driving cycles (high C-rate) in hot climates, the BMS design must incorporate a larger thermal buffer. Our simulations provide guidance for such scenarios: to maintain safe temperatures (<60°C) under a 45°C ambient at 3C discharge, the CIPCM thickness needs to be increased to approximately 9 mm. We can formalize a simplified relationship for the required latent heat capacity per battery ($Q_{req}$) under steady-high-power conditions, ignoring transient effects for initial sizing:
$$Q_{req} \approx I \cdot (V_{ocv} – V_{cutoff}) \cdot t_{discharge} – \int_{t_0}^{t_{discharge}} hA(T_{pcm}(t)-T_{amb}) dt$$
where $V_{cutoff}$ is the discharge cutoff voltage, $t_{discharge}$ is the discharge time, $h$ is the convective coefficient, and $A$ is the dissipative surface area. The mass of CIPCM required is then $m_{pcm} = Q_{req} / L_{pcm}$. This underscores that the BMS thermal strategy cannot be one-size-fits-all but must be tailored to the worst-case operational profile.
| Scenario (C-rate, $T_{amb}$) | Recommended $\delta$ | Key Rationale for BMS Design |
|---|---|---|
| Mild (1C, ≤35°C) | 3 – 5 mm | Sufficient for normal operation, optimizes pack energy density. |
| Standard (2-3C, 25°C) | 5 mm | Balances performance and space utilization for typical dynamic loads. |
| Severe (3C, ≥35°C) or Fast-Charging | 7 – 9 mm | Required to prevent thermal saturation and maintain safety margins under stress. |
The integration of CIPCM into a commercial battery management system presents both opportunities and challenges. Its passive nature simplifies the BMS architecture by reducing or eliminating the need for pumps, fans, and complex liquid cooling loops, thereby enhancing reliability and reducing parasitic energy draw. The material’s flexibility aids in assembly, allowing it to be positioned around cells and within pack voids. Most importantly, its non-flammability adds a crucial layer of safety, potentially slowing thermal runaway propagation—a paramount concern for the BMS’s safety management unit.
However, significant hurdles remain for widespread adoption. The additional volume and mass of the CIPCM negatively impact the overall energy density of the battery pack, a key metric for electric vehicles. This necessitates careful optimization, as our studies show. Manufacturing complexity and cost of the microencapsulated, shape-stable CIPCM are currently higher than for simple cooling plates. Long-term durability and performance degradation over thousands of cycles need further validation. Finally, the BMS must now account for the thermal state of the CIPCM itself. While it doesn’t require active control, algorithms could potentially use temperature data to infer when the CIPCM is fully melted (saturated), indicating a reduced thermal safety margin, which could trigger a derating of power by the BMS to prevent overheating.
Future work should focus on enhancing the thermal conductivity ($k_{pcm}$) of the CIPCM composite to mitigate the diminishing returns with thickness. This could involve advanced additives like graphene or oriented graphite foams. Furthermore, hybrid systems combining CIPCM with a low-power active cooling system (e.g., miniaturized fans or thermoelectric devices) could be managed by an intelligent BMS. The BMS would activate the active component only when the CIPCM approaches saturation during extreme conditions, optimizing the trade-off between cooling performance and energy consumption. Multi-objective optimization algorithms are needed to simultaneously solve for CIPCM thickness, battery spacing, and cooling strategy to maximize pack-level energy density and thermal safety.
In conclusion, our development and numerical analysis of a shape-stable Composite Inorganic Phase Change Material present a significant step towards safer, high-performance battery thermal management. The simulation studies provide a robust quantitative framework for integrating this material into a Battery Management System. We have demonstrated that CIPCM can effectively suppress temperature rise under various loads, with its optimal thickness being a function of the anticipated discharge rate and ambient temperature. While challenges in integration and energy density persist, the unique combination of passive operation, shape adaptability, and non-flammability makes CIPCM a highly promising candidate for next-generation BMS designs, particularly where safety is the foremost priority. The insights from this parametric simulation work offer essential guidance for engineers to tailor and optimize CIPCM-based thermal management solutions for specific application profiles.