FASTER LITHIUM-ION BATTERY CELL PRODUCTION PROCESS
In the production process chain of lithium-ion battery cells, the filling of the cell, consisting of multiple dosing and wetting steps, and its components with liquid electrolyte is eminent for the final product quality and cost. All the microscopic cavities of the electrodes and the separator have to be filled and wetted with electrolyte to take part in the charge exchange of the battery and hence achieve a high capacity. Unfortunately, this is a very time-consuming step followed by the formation, which is even more time consuming. This process comprises the first charging and discharging cycles of the cell. The solid electrolyte interphase formed in the process depletes electrolyte and lithium resulting in an irreversible capacity loss in the first cycles. Filling and formation are the reason for high throughput times in production. Together with the capacity loss, they result in high costs per Ah of the cells.
To reduce wetting time between filling and formation, and thereby the production costs, the formation in an electrolytic immersion bath is presented. Contrary to the state of the art, the combination of both processes promises a reduction of the throughput times in production. This process changes the conventional production chain. The packaging of the cell assembly is placed after the formation. Therefore, an extra sealing step (e.g. hardcase-cells) or degassing step (e.g. pouch-cells) becomes unnecessary.
In addition it is possible to prevent the capacity loss due to lithium depletion by ensuring an adequate lithium environment through the electrolyte. The invention describes the process design including protective gas, low pressure profile, sinking rate and electric charge rate. It is even possible to drain unnecessary electrolyte of the cell assembly after formation, reducing the weight of the cell.
- Reduced cost per Ah
- Higher throughput rates
- Less production steps
- Higher capacity at lower weight
A prototype station has been built to validate und evaluate the process.