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With the technological breakthrough in the energy density of lithium ion battery, increased production capacity and rapid decline in price, lithium ion battery pack has become the top choice of energy source for computers, communication products, consumer electronics and electric vehicles. In order to increase the mileage of electric vehicles, manufacturers continue to increase the energy density of cells to store more energy, and insert more cells into a limited space. However, the increase in cell energy density and the increase in the number of cells also raises the probability of thermal runaway of the lithium ion battery pack. Thermal runaway refers to an instantaneous large energy release phenomenon where the cell is short-circuited due to either an increase in temperature from operating, or an impact from an external force. If a single cell burns due to thermal runaway and the fire spreads to adjacent cells, this phenomenon is called "fire propagation". This research begins with the structural design and material of the lithium battery pack, focusing on the improvement in fire propagation protection of multi-strung lithium battery pack used in electric vehicles. The research method employs the common quality control DMAIC problem solving program, systematically analyzing the phenomenon of fire propagation and looking for opportunities to improve. The characteristic factor map is used to analyze the cause of fire propagation, and the orthogonal design and signal-to-noise (SN) ratio in the Taguchi method were used to carry out experimental design to improve the product quality. The research results show that the Six Sigma DMAIC problem solving program and the Taguchi method produced highly reliable results, and the design process was changed accordingly. The design verification process which requires each component to be protected from fire propagation is omitted, moving straight into product verification. On average, this improvement reduced product development time by 3 weeks, and the number of design verifications by 6 times, saving the company approximately NT 3.6 million designs verification costs a year. This research aims to inspire the industry, apply the theory of quality management to practice, promote Taiwan's industrial upgrading, and enhance the country’s competitiveness.
Keywords: Lithium battery module, fire propagation, lithium battery, Taguchi method, Six Sigma。
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