Within the new energy sector, the battery pack serves as the pivotal component, transforming individual cells into energy blocks. It not only determines the battery’s energy density but also dictates its safety, lifespan, and the overall performance of the vehicle or energy storage system.

Let us break it down layer by layer:

Cell: The smallest energy storage unit, akin to the “flour” used in baking bread.

Module: Multiple cells connected in series and parallel, fitted with brackets and busbars, enabling independent maintenance. Comparable to ‘dough’.

PACK: Building upon modules, it incorporates BMS, busbars, interfaces, and casing to form a ‘plug-and-play’ energy unit. Like sliced bread ready for the table.

Evolution of the PACK

2012 VDA Module: 355mm, assembly efficiency approx. 55%

2016 MEB590: 590mm, efficiency increased to 65%

2020 CTP 3.0: Eliminated modules, efficiency approx. 70%

2024 CTC/CTB: Batteries directly integrated with chassis, achieving 73%–75% volume utilisation, though with increased maintenance complexity and insurance costs

This development trajectory clearly illustrates a trend: higher energy density and reduced redundant structures, yet imposing greater demands on manufacturing and maintenance.

PACK Production Process

Sorting: Cells undergo open-circuit voltage (OCV) testing after 24-hour rest; only those with voltage differences ≤2mV are grouped together.

Series/Parallel Connection: Aluminium terminals and nickel plates are fused via laser welding; weld pull strength ≥200N to prevent micro-cracks.

Sampling: Resistance <15mΩ; longer wires must be thickened to 0.5mm². Temperature sensor NTC10kΩ±1%. Incorrect wire sequencing directly triggers BMS alarms.

Ageing: Two charge-discharge cycles at 45°C and 0.5C to identify early-failure cells, commonly termed ‘burn-in’ in the industry. Target yield rate ≥99.5%.

BMS (Battery Management System)

Functional Chain: Data Acquisition → Balancing → Protection → Communication

Balancing Current:

Passive: 50–100mA, suitable for iron-lithium batteries

Active: 0.5–1A (parallelable up to 2A), suitable for ternary high-nickel batteries to prevent 8% lifespan reduction from excessive voltage differentials

Communication Methods:

CAN-FD (2Mbit/s) commonly used in passenger vehicles

Energy storage cabinets predominantly use RS-485+Modbus; a 120Ω terminating resistor is required for transmission distances exceeding 100m to prevent waveform reflection and ‘CRC errors’.

Thermal Management and Safety Design

Heat Transfer Path: Cell → Terminal → Aluminium Busbar → Liquid Cooling Plate, with thermal resistance <0.2K/W per layer

Liquid cooling velocity: 0.3–0.4 m/s, maintaining temperature differential within 5°C; higher speeds only increase pump power consumption

Safety systems:

Mechanical: Side impact ≥10g triggers fuse + SBR high-voltage disconnection within 2ms

Electrical: Dual relays for positive/negative terminals; ‘inductive pulse method’ detects cell adhesion

Thermal runaway: Upon single-cell activation, high-temperature gas is directed through rear ‘vent channels’ in the aluminium busbar, preventing adjacent cell contamination

Thermal insulation design

For cold regions (e.g., northern energy storage cabinets operating at -20°C):

Add 1cm aerogel to the PACK base

Reduces heating power consumption by approximately 30%

Summary

An exemplary PACK design must strike a balance between energy density, safety, thermal management, and maintainability. Regardless of the approach taken, the BMS, thermal management, and safety systems form the ‘invisible armour’ ensuring stable battery operation.

Highjoule(HJ Group) specialises in the R&D and application of energy storage systems. Our product portfolio encompasses cells, modules, PACKs, Battery Management Systems (BMS), and containerised energy storage solutions. We not only provide mature energy storage products for commercial, industrial, residential, and utility-scale applications but also deliver innovative solutions tailored to client needs, including residential wind-solar hybrid systems, customised PACK configurations, and mobile energy storage vehicles.

Leveraging years of expertise in the new energy sector, Highjoule(HJ Group) consistently adheres to a design philosophy prioritising high safety, reliability, and cost-effectiveness. We are committed to delivering more efficient and sustainable energy solutions for users worldwide.