⚡ electrical engineering

Design and Analysis of Phase Change Material-based Battery Thermal Management System With Various Cell Configurations

This study demonstrates that optimizing the enclosure geometry of a passive phase change material-based battery thermal management system significantly enhances thermal performance, reducing peak cell temperature and improving temperature uniformity for high-rate 18650 LiFePO4/Graphite battery packs.

Original authors: ARUN KUMAR M, PERIYASAMY S, PARIMALA MURUGAVENI S

Published 2026-07-09

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: ARUN KUMAR M, PERIYASAMY S, PARIMALA MURUGAVENI S

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you have a group of 16 tiny, high-performance energy workers (batteries) packed tightly together in a box. When they work hard (discharge at a high rate), they get hot. If they get too hot, they get tired, break down, or even catch fire. If they get too hot in one spot but stay cool in another, the whole team gets out of sync.

This paper is about building a better "blanket" for these workers to keep them cool without using fans or pumps.

The Problem: The "Overheating Team"

The researchers were studying a specific type of battery (18650 LiFePO4) arranged in a 4x4 grid. When these batteries work at a high speed (3C discharge), they generate a lot of heat.

The Danger: If the temperature goes above 60°C (333 K), the batteries start to degrade.
The Old Way: Usually, we use fans or liquid cooling (active systems). But these need electricity, have moving parts that can break, and add weight.
The New Idea: Use a "Phase Change Material" (PCM). Think of this like a giant block of paraffin wax (similar to candle wax) surrounding the batteries.

The Magic of the "Wax Blanket"

Paraffin wax has a superpower: Latent Heat.

The Analogy: Imagine you are sweating. As your sweat evaporates, it cools you down without your body temperature rising immediately.
How it works: When the batteries get hot, the wax starts to melt. Melting requires a huge amount of energy. So, the wax "soaks up" the heat from the batteries to turn from solid to liquid, keeping the battery temperature steady for a long time. It's like a thermal sponge that soaks up heat instead of water.

The Catch: Regular paraffin wax is a poor conductor of heat (it's like a thick wool sweater; it keeps heat in). If you just dump wax around the batteries, the wax touching the batteries melts instantly, but the wax far away stays frozen. The "thermal sponge" isn't being used efficiently.

The Experiment: Trying Different "Box" Shapes

The researchers asked: Can we change the shape of the box holding the wax and batteries to make the heat spread better?

They designed 7 different layouts (Models 1 through 7) using computer software.

Model 1 (The Control): A simple, plain box with batteries spaced evenly.
Models 2–7: They moved the batteries around, changed the spacing, and created diagonal patterns to see if they could force the heat to travel deeper into the wax.

They used a powerful computer simulation (ANSYS Fluent) to act out these scenarios, treating the melting wax as a "porous sponge" that changes state.

The Winner: Model 6

After running thousands of simulations, Model 6 was the clear champion.

What was different? It had a specific arrangement of batteries that maximized the contact area between the hot batteries and the cool wax.
The Results:
- Cooler Batteries: The hottest battery in Model 6 was 6.1°C cooler than in the plain box.
- More Even: The temperature difference between the hottest and coolest battery was reduced by nearly 12%. This means the whole team stays in sync.
- Longer Protection: The wax in Model 6 took 70 seconds longer to fully melt. This gives the batteries more time to work before the "thermal sponge" is exhausted.
- Leftover Power: Even after the test, Model 6 still had 16.9% of its wax solid. This means it had a "reserve tank" of cooling power left over for the next time it gets hot.

Testing the "Super Blanket"

The researchers didn't just trust the computer; they built the real thing in a lab.

Validation: They ran the real batteries through the same tests. The real-world results matched the computer predictions almost perfectly (within 0.5% error).
Stress Test: They ran the batteries through 5 cycles of heating and cooling. The "super blanket" (Model 6) stayed stable, with the temperature rising only slightly (about 1°C) over 5 cycles, proving it doesn't wear out quickly.
Leak Test: They heated the wax until it melted and checked for leaks. The container held tight; no wax spilled, and the mass loss was negligible.

The Verdict

The paper concludes that you don't need expensive fans or pumps to cool these batteries. By simply rearranging the batteries inside a wax-filled box (specifically using the Model 6 design), you can:

Keep the batteries significantly cooler.
Keep the temperature even across the whole pack.
Extend the time the system can handle high power.
Do all this passively (no electricity needed for the cooling system itself).

It's like realizing that if you arrange your furniture in a room differently, the air circulates better and the room stays cooler, without needing to buy a new air conditioner.

Technical Summary: Design and Analysis of Phase Change Material-based Battery Thermal Management System With Various Cell Configurations

Problem Statement
The increasing adoption of lithium-ion batteries in electric vehicles and grid storage necessitates robust thermal management systems (BTMS). While lithium iron phosphate (LiFePO₄) cells offer superior stability, high discharge rates (≥2C) generate volumetric heat that can drive surface temperatures beyond the safe operating threshold of 333 K (60°C). This leads to accelerated capacity fade, electrolyte decomposition, and thermal non-uniformity ( $\Delta T_{max}$ ) across multi-cell modules, causing differential aging. Conventional active cooling methods introduce mechanical complexity and parasitic energy consumption. Passive Phase Change Material (PCM) systems, particularly using paraffin wax, offer a solution due to their high latent heat, yet they suffer from low thermal conductivity, which can lead to localized melting and underutilization of the PCM volume. This study addresses the challenge of optimizing the geometric arrangement of cells within a PCM enclosure to enhance heat distribution and thermal buffering without altering the external dimensions or total PCM volume.

Methodology
The research employed a comprehensive numerical and experimental approach:

Numerical Simulation: A transient Computational Fluid Dynamics (CFD) model was developed using ANSYS Fluent 2021 R2. The study simulated a 4×4 array of 16 cylindrical 18650 LiFePO₄/Graphite cells (18 mm diameter, 65 mm height) enclosed in paraffin wax.
Phase Change Modeling: The enthalpy-porosity method was utilized to model the solid-liquid phase transition, treating the mushy zone as a porous medium. The Carman-Kozeny relation governed the permeability in the solid region.
Geometric Variations: Seven distinct PCM enclosure geometries were designed in CREO Parametric 12. Model 1 served as a plain reference enclosure, while Models 2–7 featured varying internal cell arrangements (spacing, offsets, and channel clearances) to maximize the effective heat transfer area between cells and the PCM.
Validation and Convergence: Rigorous mesh independence (converged at 196,380 elements) and time step independence (1.0 s) studies were conducted. The simulation framework was validated against published benchmark data, showing a maximum deviation of 0.056% in peak temperature.
Experimental Verification: Physical laboratory experiments were conducted on the reference (Model 1) and the best-performing model (Model 6) using K-type thermocouples, a battery cycler, and an infrared thermal camera. Tests included 3C discharge/1C charge cycles, repeated cycling (5 cycles), and structural integrity/leakage tests.

Key Contributions

Systematic Geometric Optimization: The study systematically evaluated seven enclosure configurations, identifying that internal cell arrangement significantly influences thermal performance even when external dimensions and PCM volume remain constant.
Identification of Optimal Configuration: Model 6, featuring an optimized arrangement with maximum effective PCM contact area, was identified as the superior geometry.
Comprehensive Performance Metrics: The analysis moved beyond peak temperature to evaluate temperature non-uniformity ( $\Delta T_{max}$ ), effective buffering duration, and solid PCM reserve ( $\phi_{avg}$ ) at the end of discharge.
Robustness Verification: The study confirmed that the geometric advantages of the optimal model are sustained across a wide operating envelope (1C to 4C discharge rates) and through repeated charge-discharge cycles.

Results

Thermal Performance: At a 3C discharge rate, Model 6 reduced the peak cell temperature ( $T_{max}$ ) to 358.14 K, a reduction of 6.1 K (1.68%) compared to the reference Model 1 (364.22 K).
Uniformity and Buffering: Model 6 improved temperature non-uniformity by 11.7% ( $\Delta T_{max}$ reduced from 4.88 K to 4.31 K) and extended the effective PCM buffering duration by 70 seconds (from 240 s to 310 s).
PCM Utilization: At the end of discharge, Model 6 maintained a solid PCM fraction of 16.9% ( $\phi_{avg} = 0.831$ ), indicating a retained thermal reserve, whereas the reference model was nearly fully melted ( $\phi_{avg} = 0.980$ ).
Sensitivity Analysis: The performance advantage of Model 6 increased with discharge rate, achieving a temperature reduction of 3.0 K at 1C and 8.9 K at 4C.
Experimental Validation: Laboratory results for Model 6 showed deviations of less than 2.63% from simulation predictions for peak temperature, non-uniformity, and re-solidification time. Thermal management effectiveness reached 80.2% at 3C compared to bare cells.
Durability: Repeated cycling (5 cycles) resulted in a minimal temperature rise of 1.02 K for Model 6, and structural integrity tests confirmed no leakage or mass loss exceeding 0.12 g.

Significance
The paper demonstrates that optimizing the internal geometry of a PCM enclosure is a viable and effective passive thermal management strategy for high-rate lithium-ion battery applications. By improving the distribution of heat from the cell surfaces into the bulk PCM, the optimal configuration (Model 6) simultaneously lowers peak temperatures, enhances thermal uniformity, and extends the duration of thermal protection. The study confirms that such geometric modifications can be implemented without increasing system volume or complexity, offering a low-cost, maintenance-free solution that maintains thermal stability across varying discharge rates and repeated operational cycles. The findings provide a validated framework for designing passive BTMS that rely on paraffin wax, addressing the inherent limitations of low thermal conductivity through geometric optimization rather than material modification.