Consulting on technical cleanliness of high-voltage battery systems

Due to the variety of potential damage mechanisms caused by particulate impurities, but also the component dimension, a rethink is necessary with regard to the specification of cleanliness limits, the integral consideration of technical cleanliness in assembly, as well as the application of new extraction methods.

All OEMs are currently facing the challenge of developing and industrializing high-voltage vehicle batteries 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 internal questions regarding the influence of impurities on functionality remain unanswered. CleanControlling therefore supports several OEMs in the development and industrialization of HV vehicle batteries to minimize the risk of failure due to particulate contamination.

Known damage mechanisms newly combined

Modern vehicle batteries are mechatronic systems which are usually composed of many individual battery modules, which in turn consist of many cells. This results in voltages during the assembly of the batteries which are in the range of HV technology and often exceed 500 V. For this very reason, the minimum distances for clearance and creepage distances are of particular importance. DIN EN 60664-1 VDE 0110-1 "Insulation coordination for electrical equipment in low-voltage systems" already specifies the handling and calculation of clearances and creepage distances. Although this is done taking into account the degree of contamination, these do not yet provide any information regarding the particle lengths or widths known from VDA19.1, which can be easily specified and which could allow a truly quantified result to be included in the calculation. This makes it all the more necessary to consider the product design and the resulting damage mechanisms individually.

Furthermore, static seals are also used in battery systems, which are already known with the know-how of technical cleanliness in media circuits, e.g. in the combustion engine, and which can be transferred and mastered to battery technology.

Completely new requirements arise due to the high current densities e.g. at all HV contact points in a battery. There, metallic impurities in combination with the high current densities cause bimetallic corrosion, which decomposes the contact materials and components by an accelerated electrochemical process. In the worst case, this leads to a strong thermal development within the battery due to the reduction of the electrical transmission surface. Motivation enough to initially and fundamentally analyse, evaluate and subsequently improve these damage mechanisms in the complete battery concept.

For this purpose, robustness workshops were already carried out in the early B-sample phase, in which the battery - which at that time was only available as a digital model - was "taken apart" down to the smallest component in the workshops and examined and evaluated with regard to the resulting damage potential in the installation. Similarly, in the workshops, most of which were held directly with developers and nominated suppliers, robustness-promoting measures in product design could be recommended and discussed. The adjustments to the product design identified in the workshops tripled the harmful particle sizes in some areas of the battery. This increase in robustness leads directly to a reduction of the cleanliness requirement and is consequently significantly noticeable in the procurement costs of some components, but also significantly in the costs for production-related measures, such as logistics, building construction and the production line.

"The costs for measures to achieve technical cleanliness, which were originally planned in the concept, could be reduced by a medium 7-digit sum as a result of the project..." says a quality manager of an OEM. In addition, it was possible to divide the entire battery into several cleanliness areas with cleanliness limit values that are functionally precisely matched to them.