Innovation brings needed safety to large-format lithium-ion cells
By Steven Minnihan
The battery separator is often overlooked as technology developers look for innovation in the lithium-ion cell and module. There is good reason for this mentality since cell producers will yield better improvements by devoting their limited R&D dollars towards cathode, electrolyte, and battery management system enhancements.
Lux Research has previously reported that separator innovation offers relatively low improvements in cost or performance. For example, a dramatic 20% reduction in separator cost only yields a $12/kWh cost reduction in a vehicle battery pack, while a 20% reduction in cathode cost yields a $36/kWh cost reduction. Furthermore, R&D money spent on enhancing the separatorâ€™s impact on round-trip efficiency can be better spent by optimizing the inverter blocks to offer superior efficiency over a wider state of charge window.
While the separator does not appear to hold the key to battery cost reduction, it does play a crucial role in the batteryâ€™s safety, longevity, and stack capacity. These factors are compounded in large-format prismatic and wound cells popular in the grid, uninterruptable power supply, and mobility markets. In such large-format cells, the separator commonly exhibits heterogeneous temperatures over the surface area, as demonstrated by Sandia National Labs, while smaller cells common in the consumer industry commonly exhibit homogenous temperatures.