What is a Battery Energy Storage System?
A battery energy storage system (BESS) consists of one or more batteries that store electrical energy for later use. The basic function of a battery storage system is to charge or store energy when there is an excess supply of electricity and discharge when there is a demand. This capability makes battery storage systems essential for balancing supply and demand, ensuring reliability, and improving the efficiency of power systems (Figure 1).
Figure 1. Battery Energy Storage System (BESS) for Grid Stabilization.
Batteries play an important role in modern energy infrastructure, including electric vehicles (EVs) and renewable energy grids. However, regulating the heat created during battery operation poses a substantial challenge that impacts performance, safety, and longevity, which is where Thermal Interface Materials (TIMs) come into play.
What are the different BESS assembly design configurations?
A BESS contains multiple technical components, including but not limited to battery cell packs (usually lithium-ion) and inverters, which convert direct current (DC) to alternating current (AC). There are also control systems for battery management, power conversion, and fire safety. These systems come in a variety of sizes. You may have a tiny BESS mounted in your garage to charge your electric vehicle. A domestic BESS that powers your home in an outage could be the size of a tiny fridge. Larger applications, such as a solar farm, need larger systems. The larger the BESS, the more difficult it is to enclose.
Module-Based Design: Cell to Tray Assembly & Cell to Cell Potting
Module-based battery systems are a common choice for EVs. In this design, each battery cells are bonded by a thermal adhesive material such as Honeywell TA3000 directly below the cooling plates (A) to provide both efficient heat transfer and structural support. These cell are then grouped into modules, then assembled into larger battery packs. After the battery pack assembly, thermal potting material is used to encapsulate individual battery cells. This method not only enhances thermal conductivity but also provides mechanical protection, reducing the risk of damage due to vibration or impact. This modular approach offers scalability, allowing systems to expand or contract based on need. It also simplifies maintenance, as individual modules can be serviced or replaced without disrupting the entire system.
Rack-Based Design: Module to Tray Assembly
Battery trays are typically used in stationary energy storage applications, such as grid storage or backup power systems. These systems stack battery modules in racks to create a large, integrated storage unit. Rack-based designs are known for their high capacity and modular integration, making it easy to expand by adding more racks.
Pack an Container-Based Designs: Cell to Plate Assembly
Pack-based battery systems integrate cells directly into a single battery pack without modular separation. These compact units are commonly used in portable electronics, power tools, and some EV applications. The simplified design of pack-based systems makes them ideal for space-constrained applications and cost-effective manufacturing.
Container-based battery systems are large-scale storage solutions often used for renewable energy integration and grid stabilization. These designs house multiple battery racks or packs within shipping containers or similar structures. Container-based systems are highly mobile, making them easy to transport to different sites, and they offer high capacity suitable for large-scale energy storage needs.
How are Thermal Gap Fillers used in Battery Energy Storage Assembly?
Gap fillers find application in battery cell assembly regardless of the configuration. For example, in module-based and pack-based designs where the cells are directly bonded to the cooling plates, gap fillers are introduced to fill the gaps between battery cells and the cooling mechanisms, creating an efficient pathway for heat transfer away from the cells. Moreover, gap fillers also provide mechanical support. For tray assembly, gap fillers are used to bridge the thermal interface between battery modules and the cooling trays. This ensures even heat distribution and prevents hotspots, which can compromise battery performance and safety.
In addition, many gap fillers also offer electrical insulation, preventing short circuits and enhancing the overall safety of the battery system.
What Materials can be used as Thermal Gap Fillers in BESS Design Assemblies?
To select the right thermal gap filler for the BESS assembly, range of properties should be considered to ensure optimal performance, safety, and ease of manufacturing. Other than their thermal properties, gap fillers needed to offer assembly stability functions and ease of application. These values below can serve as a guideline, but the exact specifications will depend on the specific material and application requirements:
| Thermal Properties | |
| Thermal Conductivity | 1.0–6.0 W/m⋅K With higher-end materials potentially reaching 10 W/m⋅K |
| Operating Temperature Range | -40 °C to 200 °C |
| Electrical Properties | |
| Dielectric Strength | > 10 kV/mm |
| Volume Resistivity | 1012 to 1015 Ω⋅cm |
| Dielectric Constant at 1 MHz | 310 at 1MHz |
| Mechanical Properties | |
| Compressibility | 10– 70% depends on application requirement |
| Shore Hardness | Shore 00: 30-80 |
| Tensile Strength | 0.2–2 MPa |
| Manufacturability | |
| Ease of application | Easily dispensable viscosity typically in the range of 100,000 to 1,000,000 cps |
Given the typical values above, Honeywell Hybrid gels are ideal materials for thermal gap fillers in BESS assemblies.
Honeywell Hybrid gel represents a unique substance that bridges the gap between liquid and solid states. Specifically engineered as a silicone polymer blended with low molecular siloxane and high thermal conductivity particles like alumina and aluminum nitride powder, hybrid thermal gels are designed to excel as thermal conductive gap fillers. They offer excellent dispensing capabilities and thixotropic properties, making them ideal for automated assembly processes. One of their key advantages lies in their ability to conform to intricate shapes while maintaining strong material cohesion and ensuring long-term thermal stability.
Honeywell offers both pre-cured one-part hybrid (HT series) and two-part hybrid (HLT series) that require mixing and curing, providing flexibility to match specific assembly needs. For battery assemblies that are vertically integrated, the two-part hybrid gel is more stable to apply, while for horizontal assembly, both one- and two-part hybrid gels can achieve assembly stability.
The usual thermal conductivity requirement for a single modular battery pack assembly thermal conductivity is up to 3.5 W/m⋅K. Some notable products that conform both thermal and structural requirements are one part: HT3500 & HT4500, two part: HLT 2000, HLT 3000, & HLT 3500.
For larger battery packs, such as container-based packs, thermal management is more demanding, with thermal conductivity requirements potentially exceeding 7 W/m⋅K. The unique alumina and alumina nitride fillers in hybrid gels can achieve such high thermal conductivity. Examples of these high thermal conductivity hybrid gels include:
| Battery Assembly Design | Hybrid Gel | Product | Thermal Conductivity [W/m⋅K] | Thermal Impedance [°C·cm²/W] |
| Singular Modular Battery Packs | One-part | HT-3500 | 3.5 | 0.35 |
| HT-4500 | 4.5 | – | ||
| Two-part | HLT-2000 | 2 | 0.66 | |
| HLT-3000 | 3 | 0.45 | ||
| HLT-3500 | 3.5 | 0.44 | ||
| Large Container-based Packs | One-part | HT-7000 | 7 | 1.41 |
| HT-10000 | 10 | – | ||
| Two-part | HLT-7000 | 7 | – | |
| HLT-10000 | 10 | – |
Thermal gap fillers are indispensable in the assembly of modern battery storage systems. These materials play a key role in maintaining the performance, safety, and longevity of batteries. As the demand for efficient and reliable energy storage solutions grows, the importance of advanced thermal management technologies like thermal gap fillers will continue.
An application-specific assessment can be conducted to recommend a suitable TIM application for each battery assembly technology. Contact us and our application engineers and in-house thermal experts will help you out with product selection for your application requirements.
