Lithium-ion cell design involves making a series of critical decisions related to electrode compositions, coat weights, porosities, current collectors, separators, electrolytes, and connection tags to achieve the desired cell safety and performance properties.
The study by Lain et al. provided insights into the design limitations faced when developing high power Vs high energy lithium-ion cells. While academic investigations often focus on active material design, this study aims to shed light on the equally critical aspects of cell design and engineering for high-power lithium-ion cells. The researchers conducted a comparative analysis of various commercial LIBs, focusing on the differences between high energy density and high-power density cells. By disassembling and examining 9 different cells, they identified design features that aligned with expectations and discovered some unexpected findings.
Design Decisions and Trade-offs Findings
1. Electrodes: To achieve higher power density, lower coat weights, lower areal capacities, smaller active particles, and higher cathode porosities are used. All the examined electrodes were heavily calendared, indicating a common practice to enhance performance.
2. Tag Configuration: It was expected that high power cells would use more tags, but most cells (eight out of nine) used the same three tag configuration. Only the A123 M1A cell, designed for high power, had two symmetrically located tags.
3. Separators: Thinner separators benefit both energy density and power density. Manufacturers have been reducing separator thickness while ensuring safety. The separators selected for the cells were deemed the best available at the time of design.
4. Current Collectors: The thicknesses of current collectors did not follow any specific design trend and were likely influenced by component availability at the time of design. The high-power Sony VTC5A cell had thicker current collectors and tags compared to the high energy Sony VTC6 cell, despite both being designed in the same year.