Description

The manufacture of Li-battery will go through 5 parts, which are coating, winding, inserting,

sealing and formation. Coating is meant to separate the active electrode materials from other

parts, and winding will gather the electrodes. Inserting and sealing part can provide a case for the electrode and fill the fuel——electrolyte into the case, then seal it to keep it enclosed. Finally, the

formation procedure will activate the battery into a useable state, and test the battery carefully.

Currently, most research studies on Li-battery have been focused on diverse active electrode materials and suitable electrolytes for high cutoff voltage applications, especially the nickel-rich and/or cobalt-free cathode materials and Si or Li metal anode materials and their associated electrolytes. Progress in Li-battery manufacturing lags behind and not much progress has been made, although manufacturing contributes about 25% of the cost of Li-battery[2]. Currently, the manufacturing of Li-battery still needs to go through slurry mixing, coating, drying, calendering, slitting, vacuum drying, jelly roll fabrication (stacking for pouch cells and winding for cylindrical and prismatic cells), welding, packaging, electrolyte filling, formation, and aging, a multi-staged process being adopted by industry[3].

Figure 1 introduces the current state-of-the-art battery manufacturing process, which includes three major parts: electrode preparation, cell assembly, and battery electrochemistry activation. First, the active material (AM), conductive additive, and binder are mixed to form a uniform slurry with the solvent. For the cathode, N-methyl pyrrolidone (NMP) is normally used to dissolve the binder, polyvinylidene fluoride (PVDF), and for the anode, the styrene-butadiene rubber (SBR) binder is dissolved in water with carboxymethyl cellulose (CMC). The slurry is then pumped into a slot die, coated on both sides of the current collector (Al foil for cathode and Cu foil for the anode), and delivered to drying equipment to evaporate the solvent. The common organic solvent (NMP) for cathode slurry is toxic and has strict emission regulations. Thus a solvent recovery process is necessary for the cathode production during drying and the recovered NMP is reused in battery manufacturing with 20%–30% loss[4]. For the water-based anode slurry, the harmless vapor can be exhausted to the ambient environment directly. The following calendering process can help adjust the physical properties (bonding, conductivity, density, porosity, etc.) of the electrodes. After all these processes, the finished electrodes are stamped and slitted to the required dimension to fit the cell design. The electrodes are then sent to the vacuum oven to remove the excess water. The moisture level of the electrodes will be checked after drying to ensure the side reaction and corrosion in the cell are minimized.

After the electrodes are well prepared, they are sent to the dry room with dried separators for cell production. The electrodes and separator are winded or stacked layer by layer to form the internal structure of a cell. The aluminum and copper tabs are welded on the cathode and anode current collector, respectively. The most common welding method is ultrasonic welding, and some manufacturers may choose resistance welding for their cell design. The cell stack is then transferred to the designed enclosure, which does not have a consistent standard currently. Each manufacturer has their preference depending on the purpose of the cells. The enclosure is filled with electrolyte before the final sealing and completes the cell production.

Before delivering the cells to the end product manufacturers, the electrochemistry activation steps are applied to these cells to enable operation stability. A stable solid-electrolyte interface (SEI) layer can prevent the irreversible consumption of electrolyte and protect the anode from overpotential during fast charging, which can result in forming Li dendrites[5]. The formation and aging process starts from charging the cells to a relatively low voltage (e.g., 1.5V) to protect the copper current collector from corrosion, followed by a rest session for electrolyte wetting. The cells are charged/discharged under a low rate such as C/20, and then the rate will be gradually increased to ensure a stable SEI layer on the surface of the anode[6]. The gas generated from the formation process needs to be discharged for safety concerns. After or during formation cycles, the cells are stored on the aging shelves for complete electrolyte wetting and SEI stabilization. Another degassing step is arranged before the cells are finally sealed for future applications. Depending on the formation protocol and aging temperature, this step normally lasts several weeks.

Manufacturing This page is part of the collection 'Li-Metal Battery'.

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