Cleanliness requirements of high-voltage vehicle batteries

The challenge of e-mobility: The cleanliness requirements of high-voltage vehicle batteries call for a rethink and the inclusion of new extraction methods. A service provider for surface cleanliness supports manufacturers in the development.

All OEMs are currently faced with the challenge of bringing high-voltage vehicle batteries to series production readiness in a very short time. Especially due to the fact that battery technology is new territory for many companies and not yet an "everyday business", many questions regarding the specification and analysis of particulate contaminants remain unanswered internally. CleanControlling therefore supports several OEMs and TIER1 in the development and industrialization of HV-vehicle batteries to achieve a stringent and target-oriented concept of specification and analysis of technical cleanliness.

Due to the variety of potential damage mechanisms caused by particulate contaminants, but also the component dimension, a rethinking is required regarding the specification of cleanliness limits, the integral consideration of technical cleanliness in assembly, as well as the application of new extraction methods.

Current vehicle batteries are complex, mechatronic systems, which consist of different assemblies. Some relevant properties such as the component size of up to 2 meters, the accessibility to cleanliness-critical areas, the use of electrical and electronic components, components that would be destroyed by liquid contact and, last but not least, high voltages and energy densities put the extraction methods known and established from VDA19 to the test. The sum of these characteristics makes an overall analysis of all surfaces according to the established methods of VDA19.1 almost impossible, which means that the state of cleanliness cannot simply be determined after complete assembly in an extraction cabinet according to the methods of VDA19.1. The component dimensions alone and the high stresses and energy densities make this impossible. This makes it necessary to replace the "closed-loop" control loop with an "open-loop" strategy (see Figure 1).

The "open-loop strategy" reconciles the cleanliness requirements of the critical component areas with the analyzability of the areas. For this purpose, the critical component areas were identified and evaluated in several workshops based on the damage mechanisms, and then individual limits for particulate contamination were defined and validated. Each of these test points was selected and defined in such a way that they could be sampled directly in production during the corresponding assembly step and the analyzed battery could be further installed and delivered.

In order to be able to carry out the analysis of the relevant test areas non-destructively directly in the assembly, the suction extraction process was found and defined. This method allows dry and non-destructive extraction of confined component areas by guiding a nozzle adapted to the component along the relevant component surface and loosening the particulate contamination by the appropriate combination of mechanical and fluidic cleaning factors. (see Figure 3)

In the assembly process, the partially assembled batteries can be stopped at defined intervals and the corresponding test areas extracted using the C|PS² suction extraction system. (see figure 2). The battery can then be reintroduced into the series assembly process and further processed. In the suction extraction system, the dissolved contamination is selectively deposited on a filter or in a laboratory glass and can subsequently be analyzed and evaluated using the analysis methods known from VDA 19.1.

The "open-loop" strategy makes it possible to obtain battery system cleanliness values at the neuralgic points directly in the assembly process, to detect deviations and to define optimization or remedial measures at short notice. A step toward greater process reliability, process knowledge and functional safety in the manufacturing process and operation of vehicle batteries. (OM-4/23)