New Measurement Method for Direct Cooled Power Electronic with Transmission Fluids

Power Electronic (PE) will play an essential role in future drive concepts. Nowadays, mainly water/glycol-based cooling media are used to cool PE. Due to their high electrical conductivity (EC), water/glycol-based coolants cannot be used for direct cooling of the electrical components. Direct cooling concepts with dedicated transmission fluids show potential usage of fluid in direct contact with electrified parts. This results in special requirements for the fluids and materials. The aimed action as a coolant requires a defined measurement and characterization of fluid properties and heat transfer in order to assess the cooling ability of a fluid. The purpose of the work was to develop a new measurement setup based on the thermal transient method with which the thermal requirements of cooling fluids for a direct cooling concept can be assessed. With this method, relevant transmission fluids have been tested and the thermal performance compared to indirect cooling effect of water/glycol is discussed. The result of the work is that the measurement method is very well suited for the application-related evaluation of the fluids. Direct oil cooling with transmission fluids could increase heat transfer coefficient by a factor of 3 to 8, compared to the indirect cooing with water/glycol as cooling media.

Dendrite-accelerated thermal runaway mechanisms of lithium metal pouch batteries

High-energy-density lithium metal batteries(LMBs)are widely accepted as promising next-generation energy storage systems.However,the safety features of practical LMBs are rarely explored quantitatively.Herein,the thermal runaway behaviors of a 3.26 Ah(343 Wh kg^(−1))Li|LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2)pouch cell in the whole life cycle are quantitatively investigated by extended volume-accelerating rate calorimetry and differential scanning calorimetry.By thermal failure analyses on pristine cell with fresh Li metal,activated cell with once plated dendrites,and 20-cycled cell with large quantities of dendrites and dead Li,dendrite-accelerated thermal runaway mechanisms including reaction sequence and heat release contribution are reached.Suppressing dendrite growth and reducing the reactivity between Li metal anode and electrolyte at high temperature are effective strategies to enhance the safety performance of LMBs.These findings can largely enhance the understanding on the thermal runaway behaviors of Li metal pouch cells in practical working conditions.