Battery cells: How they are manufactured!

2024/07/24 – Climate protection is unthinkable without electromobility across all transport sectors. Electromobility, in turn, needs energy storage. We are familiar with lithium-ion batteries from smartphones, laptops, and e-bikes. They have also become indispensable in the field of energy storage systems, crucial for storing renewable energy and stabilizing the power grid and established themselves as the technology for traction batteries in electric cars. But how are high-voltage storage devices like lithium-ion battery packs actually manufactured? DRIVEN describes how SVOLT builds batteries: a complex process with many important factors.

Electrode Production

It all starts with chemistry: In a battery, electrodes must constantly move between the anode (negative pole) and the cathode (positive pole) during the charging and discharging process. In the first production step, the powdered raw materials of the electrodes are mixed with water and solvents to form pastes for the negative and positive poles, and then coated with an active material. For the anode, this is primarily graphite (carbon). For the cathode, it is a metal oxide consisting of, for example, nickel, cobalt, manganese, and lithium. Both pastes are applied in a very thin layer onto a carrier foil: the paste for the anode made of carbon onto a copper foil, and the paste for the cathode made of metals and rare earths onto an aluminum foil.

Since the foils are coated on both sides, they cannot be laid down. Therefore, they are dried in a floating state until the pastes are firmly bonded to the carrier material. The escaping solvents are collected and reused.

Next, the foil passes through a rotating rolling mill. With 200 tons of pressure, it ensures maximum compaction and uniform material thickness. Possible deviations are monitored by AI: differences of more than 0.004 millimeters from the specification lead to rejection. For comparison, a human hair is at least 12 times thicker.

After rolling, the foil is cut lengthwise into four narrow strips to fit into a battery cell. Clean cut edges are essential to ensure the battery cell’s performance. Every process step is checked with sensors: Are all dimensions and properties correct? Even the smallest deviations are detected and corrected by AI. Precision is especially important, so these production steps take place in a cleanroom environment – similar to the food or pharmaceutical industry. Contamination of the cells could lead to significant losses in battery performance.

Cell Production ("Assembly")

The electrode strip (also called a "coil") is cut to the correct length at the beginning of cell production. The same is done with a separator foil that separates the cathode and anode foils in the cell. With the foils cut to size, stacking begins. The two foils are alternately stacked on top of each other – separated by the separator foil. Once the desired cell thickness is reached, the anode and cathode are electrically connected to the cell’s negative and positive contacts.

Final Assembly & Electrolyte

The finished stack is then placed in a solid metal case and sealed with a lid. A liquid substance – the electrolyte – is injected into this pre-assembled cell under vacuum conditions to prevent air from entering. The electrolyte is the conductive medium that allows electrons to move between the anode and cathode.

Formation & Aging Process

The first charging and discharging of the cells is called formation. The final process step is aging, which takes several weeks and ensures the cell maintains its high-quality properties over a long period without degradation.

Longevity & Reuse

An important aspect: traction batteries for electric cars can have a second life. They are designed for greater longevity than many other components of electric vehicles, often lasting up to a million kilometers. After being removed from cars, they can continue to be used as stationary energy storage systems in power generation. Stationary energy storage is becoming increasingly important to balance grid fluctuations due to the increasing amount of green power in the grid.

SVOLT traction batteries contribute to climate protection not only during their first life in cars but also after their initial use, serving as valuable building blocks for the energy transition.