Integrated cut and place module for high productive manufacturing of lithium-ion cells

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Abstract

A main reason for the high costs of lithium-ion cells is the complexity of the assembly process. Especially, creating the cell stack is an inefficient process due to an immature handling and aligning of the limp electrodes and separators. This paper focuses therefore on the methodical development of a functionally integrated assembly module that combines cutting and handling of electrode sheets to increase stacking accuracy, process reliability and productivity. Based on an analysis of requirements and functions, a technical solution has been identified and will be illustrated. At the end, the realized module is described and its performance is proven by experimental validation.

Introduction

Due to the global shortage of fossil resources the electrification of the power train becomes more and more the centre of attention for the automobile manufacturers [1]. The biggest challenge here is to develop powerful and cost-efficient energy storage systems [2]. In the short and medium term, lithium-ion batteries offer the greatest potential in this regard because of their high energy and power density [3]. Only their high price that is especially driven by the assembling of the single battery cells is currently hampering the successful breakthrough of electromobility [4]. At the moment, the assembly of single cells accounts for nearly 50% of the overall battery system costs [5]. In order to achieve the cost objectives of the automotive industry, it is necessary to improve the technologies used to manufacture the Li-ion battery cells. Increasing the productivity of the available facilities and an increase in yields in production are, above all, considered to be the most important factors on the road to success. At the same time, the highest quality requirements have to be fulfilled in order to avoid negative effects on the expected lifetime and capacity of the cells.

This article describes a possibility of increasing the productivity while at the same time reducing the cost for the assembling of lithium-ion pouch cells. Requirements for optimizing the cell stack creation are deduced from the deficits in the cell production according to the current state of the art. Based on this, the approach of the cut and place module and its technical implementation will be presented. After that, the realized setup and the findings for validating the approach are presented before finally discussing different alternatives for the overall system configuration.

Section snippets

State of the art

When assembling stack cells, the single functional layers which are still separate material webs at the beginning, have to be processed to form a proper cell stack. During this process, the extremely thin and limp anodes, cathodes and separators have to be put on top of each other always alternating and in a repetitive sequence until they reach a defined number of electrodes according to the desired cell capacity [6].

Four competitive procedures are known for the production of stack cells

Design of the cut and place module

A first step in developing the required module involved a comparison of technologies at which the achievable cutting edge qualities of the different methods were compared with each other. Based on these results, numerous solution principles could be worked out which finally led to an overall design of the cut and place module. The final step was the installation and start-up of the module for validating the developed approach.

Validation

To examine the accuracy of the placed electrode below the machine module measurements concerning the deviation of the gripper in x and y direction were carried out after performing several work cycles. The results are depicted in Fig. 8.

The diagram reveals that the deviations between the gripper and its ideal position do not exceed 8 μm in the moment of depositing an electrode. The reachable repeatability during the positioning of the electrodes runs below the allowed tolerance of ±0.1 mm by

System configuration for automated stacking

Apart from the filling of a shaft magazine, the developed cut and place module may also be used as a component of an integrated system for stacking. Two different system configurations are presented in Fig. 10a and b.

Fig. 9a shows the principle of z-folding with two cut and place modules, one for the anode and one for the cathode. Compared to the current solutions regarding z-folding [8], this concept represents a significant simplification of system engineering since stacking robots and steps

Summary

A new machine module for cutting and precisely placing single sheet electrodes has been designed and realized avoiding deficits that prevail in current manufacturing systems for lithium-ion pouch cells. A functionally integrated cut and place module could be designed which allows the cutting and highly accurate handling of single sheet electrodes without any elaborate steps of examination or alignment. Finally, a validation of the reachable depositing accuracy has been conducted with a hardware

Acknowledgements

This work has been funded in the framework of the project ‘Competence E’. We thank the German Ministry of Economy for the support.

References (12)

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