Emanuel Peter Roth

Advanced technology development program for lithium-ion batteries : thermal abuse performance of 18650 Li-ion cells.

Li-ion cells are being developed for high-power applications in hybrid electric vehicles currently being designed for the FreedomCAR (Freedom Cooperative Automotive Research) program. These cells offer superior performance in terms of power and energy density over current cell chemistries. Cells using this chemistry are the basis of battery systems for both gasoline and fuel cell based hybrids. However, the safety of these cells needs to be understood and improved for eventual widespread commercial application in hybrid electric vehicles. The thermal behavior of commercial and prototype cells has been measured under varying conditions of cell composition, age and state-of-charge (SOC). The thermal runaway behavior of full cells has been measured along with the thermal properties of the cell components. We have also measured gas generation and gas composition over the temperature range corresponding to the thermal runaway regime. These studies have allowed characterization of cell thermal abuse tolerance and an understanding of the mechanisms that result in cell thermal runaway.

Thermal characterization of Li-ion cells using calorimetric techniques

The thermal stability of Li-ion cells with intercalating carbon anodes and metal oxide cathodes was measured as a function of state of charge and temperature for two advanced cell chemistries. Cells of the 18650 design with Li/sub x/CoO/sub 2/ cathodes (commercial Sony cells) and Li/sub x/Ni/sub 0.8/Co/sub 0.2/O/sub 2/ cathodes were measured for thermal reactivity. Accelerating rate calorimetry (ARC) was used to measure cell thermal runaway as a function of state of charge (SOC), microcalorimetry was used to measure the time dependence of thermal output, and differential scanning calorimetry (DSC) was used to study the thermal reactivity of the individual components. Thermal decomposition of the anode solid electrolyte interphase (SEI) layer occurred at low temperatures and contributes to the initiation of thermal runaway. Low temperature reactions from 40/spl deg/C-70/spl deg/C were observed during the ARC runs that were SOC dependent. These reactions measured in the microcalorimeter decayed over time with power-law dependence and were highly sensitive to SOC and temperature. ARC runs of aged and cycled cells showed complete absence of these low-temperature reactions but showed abrupt exothermic spikes between 105-135/spl deg/C. These results suggest that during aging the anode SEI layer is decomposing from a metastable state to a stable composition that is breaking down at elevated temperatures.

Thermal abuse studies on lithium ion rechargeable batteries

The thermal stability of Li-ion cells with intercalating carbon anodes and metal oxide cathodes was measured as a function of state of charge and temperature for two advanced cell chemistries. Cells of the 18650 design with Li/sub x/CoO/sub 2/ cathodes (commercial SONY cells) and Li/sub x/Ni/sub 0.85/Co/sub 0.15/O/sub 2/ cathodes were measured for thermal reactivity in the open circuit cell condition. Calorimetric techniques of differential scanning calorimetry (DSC) and accelerating rate calorimetry (ARC) were used to characterize these cells in both full cell configuration and as individual electrode components. The effects of thermal aging on cell thermal response were also investigated.

Advanced inactive materials for improved lithium-ion battery safety.

This report describes advances in lithium-ion battery safety by use of alternative electrolytes and separators. Electrolytes based on hydrofluoro ether solvents and sulfonimide salts were characterized to determine electrochemical performance, thermal stability, and decomposition products. Flammability of these electrolytes was also tested under known cell failure mode conditions. Separators based on high melting temperature polymers and ceramics were developed by fiber spinning, casting, and vapor deposition techniques. Resulting high melt integrity separators show good electrochemical performance and improved thermal stability compared to commercial polyolefin separator materials.

Development and characterization of li-ion batteries for the freedomCAR advanced technology development program

High-power 18650 Li-ion cells have been developed for hybrid electric vehicle applications as part of the DOE FreedomCAR Advanced Technology Development (ATD) program. Cells have been developed for high-power, long-life, low-cost and abuse tolerance conditions. The thermal abuse response of advanced materials and cells were measured and compared. Cells were constructed for determination of abuse tolerance to determine the thermal runaway response and flammability of evolved gas products during venting. Advanced cathode and anode materials were evaluated for improved tolerance under abusive conditions. Calorimetric methods were used to measure the thermal response and properties of the cells and cell materials up to 450 oC. Improvements in thermal runaway response have been shown using combinations of these materials. Keywords-Li-ion, abuse tolerance, hybrid vehicles, safety