How to assemble lithium batteries?

Introduction

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The production of lithium-ion (Li-ion) batteries is a complex process that involves several key steps, each crucial for ensuring the final battery’s quality and performance. In this article, we will walk you through the Li-ion cell production process, providing insights into the cell assembly and finishing steps and their purpose. Additionally, we will highlight that you can find more information about equipment for Li-ion battery manufacturing on Sovema Group’s website.

Picture credits: Sovema Group

Step 1: Cell Assembly – Electrode Shaping

What is Electrode Shaping?

The cell assembly process begins with finished electrode reels. In pouch and prismatic cells with stacked electrodes, anodes and cathodes are separated from the electrode daughter rolls and cut to size, leaving the current collector as a tab.

Details:

• The electrode cutting can be done through punching (mechanical separation) or laser (thermal separation).

Why Punching?

• Precision
• Affordable initial investment
• Advised for all scales, from labs to mass production

Why Laser?

• Easy format changeover
• Flexibility
• Advised for mass production and well-supported labs

Manufacturing Key Focus Points:

• LASER: The electrode shaping area is subject to heat and requires fume aspiration.
• PUNCHING: Quality issues can arise from burrs on the cutting edge due to tool wear.

Step 2: Cell Assembly – Electrode Stacking

What is Electrode Stacking?

In pouch cells and some prismatic cells, anodes, separator sheets, and cathodes are stacked together in a repeated cycle until the required number of layers is reached.

Details:

• Electrode and separator stacking can use a Z-folding process or a single sheet stacking process.

Manufacturing Key Focus Points:

• Perfect alignment of electrodes and the separator
• Delicate handling of the electrodes to avoid damage to the surface or edges

Step 3: Cell Assembly – Tab Welding

What is Tab Welding?

Between the stacking/winding and packaging stages, the electrical contacting tabs are welded to the electrode current collectors.

Details:

• Different welding methods are used based on cell types (pouch, prismatic, or cylindrical).

Manufacturing Key Focus Points:

• Welding tightness
• Avoid excessive thermal stress during welding

Picture Credits: Sovema Group

Step 4: Cell Assembly – Packaging (Pouch Cells)

What is Packaging for Pouch Cells?

Once tabs are welded, the cell stack is inserted into the pouch foil. It involves forming a cavity, inserting the stack, sealing, and trimming the excess material.

Manufacturing Key Focus Points:

• Precision of the pouch cavity
• Uniformity of sealing temperature and pressure
• Avoid excessive thermal stress during sealing

Picture Credits: Sovema Group

Step 5: Cell Assembly – Packaging (Prismatic and Cylindrical Cells)

What is Packaging for Prismatic and Cylindrical Cells?

For these cells, the jelly roll is inserted into metal cans after welding tabs. It involves carving a groove, inserting insulators, and welding.

Manufacturing Key Focus Points:

• Avoid excessive thermal stress during welding
• Delicate handling of the jelly roll

Step 6: Cell Assembly – Electrolyte Filling

What is Electrolyte Filling?

Electrolyte is dispensed into cells, ensuring proper wetting under vacuum conditions. It’s a critical step due to safety and quality considerations.

Manufacturing Key Focus Points:

• Dry room required
• Filling parameters for homogeneous electrolyte distribution
• High hazard level control
• Precise control of electrolyte quantity

Step 7: Cell Finishing – Formation

What is Formation?

Formation is the first charge of the cell, crucial for Solid Electrolyte Interface (SEI) layer formation and battery performance.

Manufacturing Key Focus Points:

• Environmental temperature control
• Efficiency and regenerative technology for cost-effectiveness

Step 8: Cell Finishing – Degassing

What is Degassing?

Gas formed during charging, especially in pouch cells, is removed through degassing and sealing.

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Manufacturing Key Focus Points:

• Gas disposal
• Full gas removal from the cell
• Vacuum conditions and dry room requirements

Step 9: Cell Finishing – Aging

What is Aging?

Aging is the final quality control step. Cells are stored and monitored under controlled temperatures.

Manufacturing Key Focus Points:

• Environmental temperature control
• Aging time can be a bottleneck

In conclusion, the production of Li-ion batteries involves a series of meticulously controlled steps, each vital to ensuring the battery’s performance, safety, and reliability.

For more information about equipment for Li-ion battery manufacturing, visit Sovema Group’s website.

1. Lithium Battery Assembly Methods:

- Preparing materials and tools: Required materials include lithium battery cells, protection circuit boards, wires, battery clamps, and battery pack casings.

- Checking materials: Ensure the lithium battery cells and protection circuit boards are in good condition and meet specifications.

- Connecting the protection circuit board: Properly connect the protection circuit board to the lithium battery cells.

- Securing the protection circuit board: Fix the protection circuit board in place to prevent loosening or shifting.

- Connecting wires: Attach wires to the positive and negative terminals as needed.

- Assembling the battery pack: Place the assembled lithium battery cells in the battery pack casing.

2. Precautions for Lithium Batteries:

- Prevent overcharging and over-discharging to maintain battery performance.

- Avoid overheating by controlling the battery's temperature within a safe range.

- Prevent short circuits by avoiding contact between metallic or conductive objects with the battery's positive and negative terminals.

- Protect against vibration and shock to avoid damage to the battery structure and performance.

- Store unused batteries in a dry, well-ventilated environment with appropriate temperature and humidity levels.

- Handle abnormal situations like heating, leaking, or smoking by immediately discontinuing use and following safety guidelines for disposal.

Prismatic cell

3. Explanation of Lithium Battery Parameters:

- Capacity (Ah): Indicates the battery's energy storage and discharge capacity.

- Voltage (V): Represents the potential difference between the battery's positive and negative terminals.

- Maximum Charge and Discharge Current (A): Denotes the maximum continuous current the battery can supply without overheating.

- Cycle Life: Indicates the number of charge and discharge cycles a battery can endure while maintaining 80% capacity.

- Self-Discharge Rate: Measures the rate at which the battery discharges when not in use.

Assembling and using lithium batteries requires careful handling and adherence to safety guidelines. Choosing quality materials, ensuring secure connections, and taking precautions during assembly are essential for safety and performance. Additionally, understanding the various battery parameters helps in selecting and using lithium batteries for different applications effectively.

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