Fast internal preheating of 4680 lithium-ion batteries in cold environments

Lithium-ion batteries are expected to operate within a narrow temperature window around room temperature for optimal performance and lifetime.Therefore,in cold environments,electric vehicle battery packs must be extensively preheated prior to charge or discharge.However,conventional preheating is accomplished externally,which is slow and thus significantly increases charging times.Recently,internal heating has been demonstrated as a potential solution to quickly and uniformly preheat a lithium-ion pouch cell.However,internal heating has not been evaluated in other battery formats such as cylindrical batteries.In this work,we present a numerical model of a 4680 battery with internal heaters for fast preheating in cold environments.The effects that the number of heater layers,heating duration,resting duration,environmental temperature,and boundary heat transfer coefficient have on the temperature heterogeneity of the battery were investigated.The results show that internal heating alone reduces the temperature variation within the battery by a factor of 5 compared to external heating,and by a factor of 20 when combining internal and external heating.This study further proves that internal preheating of lithium-ion batteries is a promising thermal management strategy,and provides guidance on potential design considerations and heating protocols to implement internal heating.

Heat transfer during droHeat transfer during droplet impact on a cold superhydrophobic surface via interfacial thermal mappingplet impact on a cold superhydrophobic surface via interfacial thermal mapping

Undesired heat transfer during droplet impact on cold surfaces can lead to ice formation and damage to renewable infrastructure,among others.To address this,superhydrophobic surfaces aim to minimize the droplet surface interaction thereby,holding promise to greatly limit heattransfer.However,the dropletimpact on such surfaces spans only a few milliseconds making it difficult to quantify the heat exchange at the droplet–solid interface.Here,we employ high-speed infrared thermography and a three-dimensionaltransient heat conductionCOMSOL modelto map the dynamic heat flux distribution during droplet impact on a cold superhydrophobic surface.The comprehensive droplet impact experiments for varying surface temperature,droplet size,and impacting height reveal that the heat transfer effectiveness(Q′)scales with the dimensionless maximum spreading radius as Q′∼(Rmax∕Ri)1.6,deviating from previous semi-infinite scaling.Interestingly,despite shorter contact times,droplets impacting from higher heights demonstrate increased heat transfer effectiveness due to expanded contact area.The results suggest that reducing droplet spreading time,as opposed to contact time alone,can be a more effective strategy for minimizing heat transfer.The results presented here highlight the importance of both contact area and contact time on the heat exchange between a droplet and a cold superhydrophobic surface.