52 Chapter 5 very damaging to the company and the industry as a whole, because it was one of the major drivers that led A123 Systems ultimately filing bankruptcy in the US. This second failure was a process failure, in that it is believed that there had been a miscalibration problem with one of their welding machines during the cell production process which created the possibility for latent failures in the cells in the future (Rousch, 2012).
Now these are both good companies with very good products, and there have been other expensive recalls in the battery world so do not let me lead you astray in thinking that these are not quality products, but these examples emphasize the needs for robust quality control and reliability planning in the battery industry, as the industry is in very early stages of commercialization. Design for Reliability/Design for Service Much like all other engineering fields, DFR and design for service (DFS) are two important processes that must be integrated very early into the lithium-ion electronic safety and security design process.
DFR is the use of a systematic and concurrent engineering process which is integrated throughout the entire product development cycle and is focused on achieving product reliability and durability over the products lifetime. Described in the Reliability Edge quarterly newsletter, DFR is a systematic, streamlined, concurrent engineering program in which reliability engineer- ing is weaved into the total development cycle. (ReliaSoft, 2014, p. 1) DFR is not a single process but rather a series of processes such as failure modes effects analysis (FMEA), test to failure (TTF), accelerated life testing, voice of the customer (VOC), and design of experiments (DOE) among many others.
The main challenge with implementing these tools is that they are mainly focused on using historical data in order to predict future results, and with lithium-ion battery systems that presents some challenges as there is very little historical data on systems that are this large. While there is a large amount of data on lithium-ion battery in portable power products like laptop computers and cell phones it does not always scale up directly to the larger systems. DFS essentially involves evaluating the designs at the very early stages looking for solutions to improve the serviceability of the energy storage system.
In some cases this may involve using a mechanical fastener to interconnect the cells. This allows for the ability to replace a single cell, thereby making it the smallest replaceable unit (SRU). However, there are also challenges with this strategy that must be evaluated, such as the risk of the fasteners loosening over time and creating a failure mode in that manner. Other battery manufacturers look at welding the cells together instead of using fasteners. This approach makes the “module” the SRU, making it a much more expensive part. However, by welding the cells, there is a smaller