Cell Integration Evolution and Busbar Connection Solutions

 As the new energy vehicle (NEV) industry rapidly evolves, the traction battery has become the core component of the vehicle. Its integration architecture directly affects energy density, space utilization, driving range, and system safety, making battery integration a key area of technological competition.

From traditional module-based designs to vehicle-level structural integration, battery architectures have gradually evolved from separate assembly to structural integration. Meanwhile, the electrical connection system—responsible for transferring energy between cells—has become increasingly critical. The selection and process design of copper and aluminium busbars now play a key role in ensuring stable battery operation and supporting different integration architectures.

Drawing on RHI’s experience in battery connection technologies, the following outlines the evolution of cell integration and the corresponding busbar connection solutions.

1. Battery Cell Integration Architectures in EVs

Battery integration focuses on optimizing the structure between cells, modules, battery packs, and the vehicle platform. The main architectures include CTM, CTP, and CTC/CTB, each representing a different level of integration.

(1) CTM (Cell to Module): The Traditional Architecture

CTM was the earliest mainstream battery architecture. Individual cells are first assembled into standardized modules, and multiple modules are then integrated into a battery pack with structural components and housing.

Advantages

• Mature and widely validated technology

• High reliability and stable performance

• Modular structure supports standardized production

• Faulty modules can be replaced individually, reducing maintenance cost and downtime

Limitations

• Additional structures such as module housings, side plates, and fasteners increase redundancy

• Battery pack space utilization is typically around 40%

• Limited space for cells restricts energy density and vehicle range improvements

(2) CTP (Cell to Pack): Module-Free Integration

CTP is a major upgrade from CTM. It removes the module layer and integrates cells directly into the battery pack through optimized structural and layout design.

This architecture has become a mainstream solution widely adopted by leading battery manufacturers and automakers.

Advantages

• Space utilization increases to over 60%

• Higher energy density and longer driving range

• Fewer components and simplified manufacturing

• Lower production cost and improved assembly efficiency

Note

CTP does not eliminate structural support entirely. Stability is maintained through cell bundling, structural adhesives, and optimized mechanical structures.

(3) CTC / CTB: Cell-to-Vehicle Structural Integration

CTC (Cell to Chassis) and CTB (Cell to Body) represent a further step beyond CTP, where the battery system becomes deeply integrated with the vehicle structure.

(4) CTC (Cell to Chassis)

CTC integrates the battery system directly into the vehicle chassis, allowing cells to function as structural elements.

Key features:

• Eliminates the traditional battery pack housing
• Reduces structural redundancy and vehicle weight
• Maximizes space utilization
• Requires high standards for chassis strength, sealing, and protection

(5) CTB (Cell to Body)

In CTB architecture, the battery pack top cover is integrated with the vehicle body floor.

Key benefits:

• The battery acts as both an energy system and a structural component
• Improved body torsional rigidity and vehicle safety
• Increased interior space utilization

(6) Architecture Comparison

• Integration level: CTC/CTB > CTP > CTM

• Space utilization & energy density: CTC/CTB highest, CTP moderate, CTM lowest

• Technical complexity: CTC/CTB > CTP > CTM

• Serviceability: CTM > CTP > CTC/CTB

Automakers select architectures based on vehicle positioning, cost targets, and service strategy.

2. Busbar Connection Solutions for Battery Systems

As battery integration evolves, connection systems must meet higher requirements for conductivity, structural adaptability, durability, and reliability.

As a specialized battery connection solution provider, RHI offers customized copper and aluminium busbar solutions for CTM, CTP, and CTC/CTB architectures.

(1) Cell-Level Connections: Lightweight Conductive Components

At the cell level, compact conductive components are used to connect cell tabs to primary current collectors. Typical materials include:

• Copper foil

• Aluminium foil

• Aluminium busbars

• Copper tabs

Different cell formats require different busbar structures and materials.

Prismatic Cells

Busbars commonly use 1060-O aluminium, which offers good conductivity and formability.

However, pure aluminium cannot be used directly at the bolted terminal interface. Copper–aluminium composite materials or dissimilar metal welding are required.

Pouch Cells

Busbars are typically U-shaped connectors made from T2 copper.

(2) Tab Connections

In many designs:

• One end is laser welded to the aluminum tab

• The other end is bolted to copper terminals

Reliable copper–aluminium joining is achieved using processes such as:

• Friction welding

• Electron beam welding

• Ultrasonic welding

These components are thin, flexible, and highly conductive, making them suitable for dense cell layouts. They enable reliable welding with low heat generation and stable current transmission, reducing the risk of overheating or weak joints.

(3) Module and Pack-Level Busbar Solutions

Module-to-Module Connections

Flexible connections such as extruded flexible copper or aluminium busbars help absorb relative movement, vibration, and assembly stress between modules.

Battery Pack Output Connections

High-current connections between the battery pack and the vehicle electrical system typically use rigid insulated busbars, manufactured with processes such as:

• Heat shrink insulation

• PVC dip coating

• Powder coating

• Extruded insulation

3. Busbar Design Advantages

To support different battery integration architectures, RHI provides both rigid and flexible copper copper busbars.

(1) Reliable Insulation

Fully insulated busbars provide:

• High-voltage protection

• Short-circuit prevention

• Resistance to dust, moisture, oil, and temperature variations

(2) Structural Adaptability

• Rigid busbars provide strong mechanical support for main circuits

• Flexible busbars absorb vibration and adapt to complex installation layouts

(3) Stable Electrical Performance

• High-purity copper and aluminum ensure excellent conductivity

• Precision forming supports automated assembly

• Low resistance reduces heat generation and improves service life

Conclusion

As battery integration technologies continue to evolve, the reliability of electrical connections becomes increasingly critical.

RHI specializes in battery connection technologies, including forming, insulation and welding. We offer customized solutions for CTM, CTP and CTC/CTB architectures, optimizing both electrical performance and structural integration.

Through strict quality control and environmental testing—including thermal cycling, vibration, and humidity tests—RHI products are designed for reliable performance under demanding automotive conditions.

RHI ELECTRIC | Battery Interconnection Solutions