PACK Module Knowledge Series ① - Basic Understanding of PACK

A battery PACK (also known as a battery pack) is not a single battery but a complete energy system composed of battery cells, structural components, a thermal management system, electrical components, and a BMS (Battery Management System). If battery cells are compared to "individual family members," then PACK is the "entire family" - not only having members but also "family rules" (safety protection) to maintain the family's operation, a "heating/cooling system" (thermal management), and a "communication network" (electrical connection).

Here is an intuitive example:
A single lithium - ion battery cell in your mobile phone is like a piece of chocolate.
Stacking several pieces of chocolate according to rules (series and parallel connection), and adding a simple package, you get a "module" (similar to a chocolate gift box).
Then, by equipping this gift box with a temperature monitor, a safety lock, and a charging interface, it becomes a "PACK" (equivalent to a smart - enabled chocolate gift box that can tell you how many pieces are left and whether it will melt).

The core function of PACK is to transform scattered battery cells into "directly usable energy" and solve three key problems:

A qualified PACK consists of "hardware + software", and each part has a clear division of labor. Just like the forwards, midfielders, defenders, and goalkeepers of a football team, they need to cooperate with each other to win the game.

1. Battery Cell Module: The "Heart" of PACK

• Prismatic Cells: Resembling "chocolate bricks", they are regular and easy to stack. BYD's Blade Battery is a typical example, which is suitable for electric vehicles.
• Cylindrical Cells: Similar to "cans", they have a high energy density. Tesla's 4680 battery uses this type, and it has good heat dissipation performance.
• Pouch Cells: Like "bagged potato chips", they are lightweight and flexible in shape, and are often used in consumer electronics such as mobile phones and tablets.

• Series connection increases the voltage (for example, for a 3.7V battery cell, 100 series connections result in 370V).
• Parallel connection increases the capacity (for example, for a 2Ah battery cell, 10 parallel connections result in 20Ah).

2. Electrical System: The "Blood Vessels and Nerves" of PACK

• High - Voltage System: Resembling the "main artery", the wire harnesses and connectors for transmitting electrical energy must be able to withstand voltages above 1000V, and the current - carrying capacity is ≥ 200A (equivalent to being able to power 20 air conditioners simultaneously). Tesla's high - voltage wire harnesses are made of nickel - plated copper with a resistance ≤ 5mΩ to reduce power loss.
• Low - Voltage System: Similar to the "neural network", it consists of thin signal wires and is responsible for transmitting the voltage and temperature data of the battery cells to the BMS. To prevent interference, the wire harness is wrapped with an aluminum foil shielding layer, just like the wire wearing an "anti - magnetic suit".

3. Thermal Management System: The "Air Conditioner" of PACK

• Liquid - Cooling System: It dissipates heat through the coolant in the pipes and is suitable for high - power scenarios (such as electric vehicles). The liquid - cooling plate of CATL's Kirin Battery is designed at the bottom of the battery cells, which can control the temperature difference within ±2°C.
• Air - Cooling System: It uses a fan to blow cold air for heat dissipation. It has a low cost but poor efficiency and is often used in energy storage PACKs (such as home energy storage battery cabinets).
• Phase - Change Material (PCM): Similar to an "ice pack", it melts and absorbs heat when the temperature exceeds 40°C to prevent local overheating and is often used in PACKs in extreme environments.

4. Structural Components: The "Skeleton and Armor" of PACK

• Box: It is made of aluminum alloy or composite materials. The protection level is at least IP67 (it can be immersed in 1 - meter - deep water for 30 minutes without water ingress) and must also be able to resist impacts (for example, it does not deform during an electric vehicle collision). The battery box of NIO ET7 uses carbon - fiber composite materials, which is 30% lighter than traditional aluminum alloy.
• End Plates/Side Plates: They are clamped on both sides of the battery cells to resist the expansion force during the charging and discharging of the battery cells (the expansion rate of lithium iron phosphate battery cells is about 3%, and a pre - tightening force of 5kN is required for fixation).
• Explosion - Proof Valve: When the internal pressure of PACK is too high (such as gas generation during thermal runaway), it will automatically burst to relieve pressure and avoid explosion, similar to the safety valve of a pressure cooker.

5. Software System: The "Brain" of PACK

• Monitoring: Real - time collection of battery cell voltage (accuracy ±1mV), temperature (accuracy ±0.5°C), and current.
• Decision - Making: When an abnormality is detected (such as a battery cell voltage > 4.3V), it immediately cuts off the charging and discharging circuit.
• Optimization: Through the equalization algorithm, it makes the battery cell capacities consistent (for example, "discharging" the excess capacity of a battery cell with more 电量).
  A PACK without software is like a car without a driver - no matter how good the hardware is, it cannot drive safely.

III. Classification of PACK: Different "Custom - Made" Versions for Different Scenarios

1. Classification by Structure: The Evolution from "Traditional" to "Module - less"

• Traditional Modular PACK: It has a three - layer structure of battery cells → modules → PACK, similar to a "matryoshka doll". The advantage is that it is convenient for maintenance (a single module can be replaced if it is damaged), and the disadvantage is that it takes up a large volume (the module casing takes up space). Volkswagen's ID. series uses this type, with a volume utilization rate of about 60%.
• CTP (Cell to Pack): It removes the modules, and the battery cells directly form the PACK, like "putting chocolates directly into the gift box". The volume utilization rate is increased to 70 - 80%. CATL's Kirin Battery and BYD's Blade Battery both use CTP technology, which can increase the range of electric vehicles by more than 10%.
• CTC/CTB (Cell to Chassis/Body): It integrates the PACK with the device structure (such as the chassis of an electric vehicle), like "integrating the chocolate gift box with the table". The volume utilization rate exceeds 80%. Tesla's 4680 battery's CTC technology can easily make the range of electric vehicles exceed 1000 kilometers.

2. Classification by Application Scenario: Each with Its "Strengths"

• Automotive - Grade PACK: It pursues "high energy + safety".
  The energy density is ≥ 160Wh/kg (which can enable an electric vehicle to travel more than 500 kilometers), supports fast charging (above 4C, charging to 80% in 10 minutes), and must pass strict tests such as nail penetration and extrusion (it should not catch fire when pierced by a nail). Representative products: CATL's Kirin Battery, LG Chem's 4680 PACK.
• Energy Storage PACK: It pursues "long life + stability".
  The cycle life is ≥ 6000 times (it can be charged and discharged once a day for 16 years). It does not pursue a too - high energy density (as long as it is sufficient), but it needs to support cluster management (hundreds or thousands of PACKs working in coordination). Representative products: Tesla Megapack (with a capacity of 1.3MWh), Sungrow's 1500V energy storage PACK.
• Consumer Electronics PACK: It pursues "compact + lightweight".
  The volume is usually < 1000cm³ (smaller than a shoebox), the weight is < 500g, and the voltage is 3.7 - 7.4V (suitable for mobile phones and laptops). For example, the PACK of Apple's MacBook uses pouch cells, which can be inserted into the ultra - thin body and has a capacity of 100Wh (providing an 18 - hour battery life).

IV. Why is PACK Considered a "Technical Task"?

• Balancing Act: Finding the optimal solution among energy density, safety, and cost (for example, adding heat dissipation will increase the cost but can extend the lifespan).
• Consistency: Ensuring that hundreds or thousands of battery cells "work synchronously" (if one battery cell is 5% worse, the performance of the entire PACK will be reduced).
• Adaptability: Operating stably in extremely cold conditions of - 40°C or extremely hot conditions of 60°C (for example, the electric vehicle PACKs in Northeast China need a stronger heating system).