The design of the cell arrangement in lithium battery packs is a core link that affects the energy density, heat dissipation efficiency, structural strength and safety of the battery system. It needs to be comprehensively weighed from four dimensions: cell characteristics, installation space, thermal management requirements and mechanical constraints. The following are the specific design ideas and implementation paths:

First, the core objective of battery cell arrangement

Increase volumetric energy density

By compact arrangement to reduce ineffective space, for instance, compressing the gap between battery cells from the traditional 5mm to 2mm, the volume utilization rate can be increased by 15% to 20%.

Optimize the heat dissipation path

Ensure that the heat dissipation channels between the battery cells are unobstructed to avoid local heat accumulation. For instance, in a parallel arrangement, the temperature difference between adjacent cells should be controlled within no more than 5℃.

Enhance structural stability

Disperse mechanical stress through arrangement methods. For instance, in vibration conditions, the arrangement design should ensure that the maximum stress difference between battery cells is ≤20% of the average stress.

Simplify manufacturing and maintenance

Reduce the complexity of the arrangement, such as decreasing the number of connection points of the battery cells (traditional series connection requires N-1 connection points, while modular parallel connection can reduce the number of connection points by more than 30%).

Second, classification of battery cell arrangement methods and key design points

1. Series arrangement (to increase voltage

Key design points

High consistency requirements for battery cells: Series battery cells must strictly match capacity and internal resistance (capacity difference ≤1%, internal resistance difference ≤5%), otherwise overcharging/overdischarging is likely to occur.

Connection redundancy design: Add a bypass switch in the series path. When a single cell fails, its connection can be cut off to avoid affecting the entire battery pack.

Applicable scenarios: High-voltage demand scenarios (such as power tools, energy storage systems).

2. Parallel arrangement (capacity increase

Key design points

Current balanced distribution: Shunt resistors or current sensors should be set up between parallel cells to ensure that the current distribution deviation is ≤10%.

Short-circuit protection design: Add an insulating layer (such as 0.1mm thick PET film) between parallel cells to prevent short circuits caused by cell expansion.

Applicable scenarios: High-current discharge scenarios (such as electric vehicle starting motors, drones).

3. Mixed arrangement (series + parallel)

Key design points

Modular design: The battery pack is divided into multiple "series modules", with each module connected in parallel within and in series between. For instance, a 32-cell battery pack with 4 parallel cells and 8 series cells can balance high voltage and large capacity.

Thermal management zoning: Independent heat dissipation design is carried out for the series modules, for example, each module is equipped with an independent liquid cooling channel to prevent the spread of thermal runaway.

Applicable scenarios: Complex working conditions (such as electric vehicles, hybrid ships).

4. Three-dimensional stacking arrangement (Improving space utilization

Key design points

Interlayer insulation and buffering: Add insulating pads (such as 0.2mm thick silicone pads) and buffering layers (such as 0.5mm thick honeycomb aluminum) between the stacked layers to prevent short circuits or mechanical damage caused by cell expansion.

Vertical heat dissipation channels: Reserve liquid cooling channels in the stacking direction (such as channel width ≥3mm) to ensure uniform heat dissipation between layers.

Applicable scenarios: Limited installation Spaces (such as drones, portable energy storage devices).

5. Irregular arrangement (Adapted to irregular Spaces)

Key design points

Customized battery cells: Use trapezoidal, L-shaped and other irregular-shaped battery cells to fill the edges of the installation space. For example, embedding trapezoidal battery cells in the grooves of the car chassis can increase the space utilization rate by 10% to 15%.

Flexible connectors: Use FPC (Flexible Circuit Board) or aluminum wire bonding instead of rigid busbars to adapt to the shape changes of battery cells.

Applicable scenarios: Irregular installation environments (such as car chassis, robot joints).

Third, the compatibility of the arrangement method with the type of battery cells

Cylindrical cell arrangement

Hexagonal tight arrangement: By arranging the hexagonal honeycomb structure, the space utilization rate can be increased to 78%-82% (while the traditional rectangular arrangement is only 64%).

Spiral heat dissipation channel: A spiral liquid cooling flow channel is designed in the gap between cylindrical cells, increasing the heat dissipation efficiency by more than 30%.

Square battery cells arranged

Interlaced stacking: Square battery cells are arranged in an interlaced "Z" shape to reduce the interlayer gap and increase the volumetric energy density by 10% to 15%.

Integration of end plates: The end plates of the battery pack are designed as an integrated liquid cooling plate and structural support, reducing the need for additional heat dissipation space.

Arrangement of pouch cells

Three-dimensional folding arrangement: By folding the pouch cells into a multi-layer structure and using liquid cooling plates for direct cooling, the volume energy density can reach over 400Wh/L.

Vacuum adsorption fixation: The pouch cells are fixed to the heat dissipation plate through vacuum adsorption to avoid the increase in thickness caused by the use of adhesives.

Fourth, the influence of arrangement methods on thermal management

The heat dissipation advantage of parallel arrangement

The current distribution between parallel cells is uniform, and the local heat generation is low. Air cooling or natural heat dissipation design can be adopted to reduce the volume of the liquid cooling system.

Case: The battery pack of a certain unmanned aerial vehicle is arranged in parallel and combined with air cooling for heat dissipation, increasing the volumetric energy density to 320Wh/L and reducing the weight by 20% compared to the traditional liquid cooling solution.

The heat dissipation challenge of series arrangement

The voltage difference between series cells is large, which can easily lead to local overheating. Therefore, the liquid cooling design needs to be strengthened (such as the flow channel width ≥5mm and the flow rate ≥0.5m/s).

Case: The battery pack of a certain electric vehicle is arranged in series. The volume of the liquid cooling system accounts for 15%, but the temperature difference of the battery cells is controlled within ≤3℃ through flow channel optimization.

Three-dimensional stacked arrangement thermal runaway protection

Add an aerogel insulation layer (0.5-1mm thick) between the stacked layers to extend the thermal runaway spread time to more than 30 minutes, buying time for escape.

Case: A certain energy storage battery pack was arranged in a three-dimensional stacked manner, combined with aerogel insulation and directional pressure relief valves, and passed the UL9540A thermal runaway test.

Fifth, the optimization of mechanical strength by the arrangement method

Interlaced stress dispersion

By arranging in a "Z" shape or a spiral pattern, the stress peak under vibration conditions can be reduced by 30% to 40%, thereby extending the battery pack's lifespan.

Case: The battery pack of a certain electric vehicle is arranged in an interlaced pattern. Under a vibration acceleration of 10g, the maximum stress difference between the battery cells is ≤15% of the average stress.

Modular arrangement of redundant design

The battery pack is divided into multiple independent modules, which are connected by flexible connectors. When one module is damaged, the others can still work normally.

Case: The battery pack of a certain ship is arranged in a modular way. After thermal runaway of a single module, the overall capacity loss is ≤20%, and there is no risk of spread.

Sixth, the design verification method for the arrangement mode

Three-dimensional simulation analysis

The heat dissipation efficiency under the arrangement of battery cells is simulated using CFD (Computational Fluid Dynamics), and the flow channel layout and battery cell spacing are optimized.

The structural strength of the arrangement under vibration and shock is verified through FEA (Finite Element Analysis) to avoid space waste caused by overdesign.

Rapid prototyping iteration

The 3D printing technology is adopted to create a scale model of the battery pack, verify the arrangement of the battery cells and the interference of the connecting parts, and shorten the development cycle by more than 50%.

The installation process of the battery pack in the vehicle environment is simulated through virtual assembly technology (such as CATIA V5) to detect spatial conflicts in advance.

Seventh, Typical Application cases

Electric vehicle battery pack

Before optimization: Traditional rectangular arrangement, with a volume energy density of 280Wh/L and a space utilization rate of 65%.

After optimization: By adopting a modular hybrid arrangement (4 in parallel ×8 in series), combined with three-dimensional stacking and liquid-cooled direct cooling, the volume energy density has been increased to 380Wh/L, and the space utilization rate has reached 85%.

Drone battery pack

Before optimization: Cylindrical cells are arranged flat, with a 10mm gap reserved for heat dissipation, and the volumetric energy density is 220Wh/L.

After optimization: It adopts a three-dimensional folded arrangement of soft-pack cells, combined with vacuum adsorption and air cooling for heat dissipation. The volume energy density has been increased to 320Wh/L, and the battery life has been extended by 40%.