What Is the Use of Cell Grading Machine?

Cell Grading Machines are core quality control equipment in lithium battery manufacturing and PACK (battery pack) assembly processes. Their core function is to precisely cycle individual cells to measure key parameters such as capacity, voltage, and internal resistance, and then sort and classify cells with consistent performance into the same level (e.g., Grade A, Grade B, Grade C) to ensure that the subsequently assembled battery packs have extremely high consistency, safety, and lifespan.

I. Working Principle and Process of Cell Grading Machines

A cell grading machine is essentially a multi-channel, high-precision battery charge-discharge testing system. Its standard workflow typically includes the following 5 steps:

1. Loading and Clamping: The cell to be tested is placed in the channel and reliably contacted using pneumatic or mechanical clamps (usually high-precision four-wire clamps to eliminate contact resistance).

2. Pre-charging and Formation (Optional): Some equipment also has a formation function, performing initial activation on newly manufactured cells.

3. Standard Discharge and Charge Cycles:

1. Full Charge: Fully charge the cell using constant current-constant voltage (CC-CV) mode.
2. Rest: Allow the cell temperature and voltage to stabilize.
3. Full Discharge: Discharge to the cutoff voltage using constant current (CC) mode, accurately recording the discharge capacity and energy.

4. Parameter Acquisition and Data Analysis: High-precision sensors acquire real-time open-circuit voltage (OCV), AC/DC internal resistance (IR), temperature profile, and precise capacity of each cell throughout the entire cycle.

5. Grading and Sorting: The host computer software automatically determines the cell grade based on preset control standards (e.g., capacity error ≤ ± 1%, internal resistance error ≤ ± 2mΩ) and sorts the cells using LED indicators or an automated robotic arm.

II. What are the Classifications of Cell Grading Machines?

1. Classification by Cell Packaging Type

• Cylindrical Cell Grading Machine: Offers a large number of channels (typically 256, 512, or even more), compatible with 18650, 21700, 32140, and other specifications.
• Prismatic Lithium Battery Grading Machine: Features typically high single-channel current (e.g., 60A, 100A, 200A, or even 400A), equipped with pneumatic side pressure or flat clamps, primarily used for energy storage and power battery testing.
• Pouch Battery Grading Machine: Employs specialized alligator clips or needle clamps to prevent puncturing the aluminum-plastic film.

2. Classification by Core Technology

* Energy-Feedback Type: Currently the mainstream technology in the industry. Traditional equipment converts electrical energy into heat during discharge, which is both energy-intensive and requires extensive air conditioning for cooling. Feedback-type equipment uses a bidirectional AC/DC inverter module to convert the DC power generated by cell discharge into AC power, feeding it back to the internal or factory power grid, typically saving over 40% of energy.

* Conventional resistor-consuming type: Lower cost, but generates enormous heat during high-power charging and discharging, and is gradually being phased out.

III. Core Technical Indicators of Mainstream Industry Equipment

When purchasing or evaluating industrial-grade cell sorting machines, the following indicators are crucial:

1. Testing Accuracy: Typically requires voltage and current accuracy of ±0.05% to ±0.1% FS (full scale).
2. Channel Independence: Each channel must have an independent constant current and constant voltage source; a single point of failure should not affect the operation of other channels.
3. Power Failure Protection: The equipment must have an automatic data saving function. In the event of a sudden power outage, the test can resume from the previous step after power is restored, avoiding the test time being reset to zero and the test data becoming invalid.
4. Software Data Traceability: Supports generating professional charge/discharge curves (capacity-voltage curves, cycle life curves) and can interface with MES systems, achieving "one lithium battery, one code" quality traceability through barcode scanning.

IV. Why Use a Cell Grading Machine?

In battery packs (such as those in electric vehicles or large energy storage cabinets) composed of hundreds or thousands of cells connected in series and parallel, the "weakest link" principle applies:

1. If a low-capacity or high-internal-resistance "inferior cell" is mixed in, it will be the first to fully charge during charging, triggering the charging protection of the entire battery pack; conversely, it will be the first to discharge during discharging, causing the entire battery pack to stop working prematurely. 

2. Severe inconsistency can also lead to overcharging and overheating of individual cells, even causing thermal runaway and fire hazards.

Using a sorting machine to group cells with similar characteristics is the only industrially viable method to extend battery pack life and improve overall safety.

Conclusion

Cell grading machine plays a critical role in ensuring the performance, safety, and reliability of lithium battery cells before they are assembled into battery packs. By accurately testing key parameters such as capacity, voltage, internal resistance, and charge-discharge performance, manufacturers can effectively eliminate inconsistent cells and achieve better battery pack consistency, longer cycle life, and improved safety.

As a professional lithium battery manufacturing equipment supplier, ACEY New Energy provides high-precision Battery Capacity Tester solutions for different battery applications, including cylindrical cells, prismatic cells, and pouch cells. Our equipment features accurate testing performance, independent channels, advanced data management systems, and optional energy feedback technology to help customers improve production efficiency and reduce energy consumption.

Contact ACEY today to get professional technical support and a suitable cell grading solution for your lithium battery project.