Immersion cooling of lithium-ion batteries with dielectric fluids

这项博士计划将研究使用介电流体对锂离子电池(LIB)进行浸泡冷却的运行机制。LIB是消费电子、电动汽车(EVS)以及整合零排放可再生技术(如风能和太阳能)的关键使能技术。虽然它们的商业应用仍在继续，但它们的成本、性能和寿命仍需改进，才能在经济上广泛可行。从单个电池转换到电池组时成本的增加是由于额外集成了电池管理系统和热管理系统(TMS)等组件，其中热管理系统电流约占总电池组成本的20%。由于电池的性能和寿命是高度热耦合的，有效的设计是实现长期性能目标的关键。在功率密度方面，2035年的目标是12千瓦/千克，距离目前3千瓦/千克的性能还有很长的路要走，寿命约为15年，而目前的值约为8年。此外，未来的TM还必须能够在-40-80摄氏度的温度范围内运行，这意味着节省了第1页日期：05/11/2019 15：55：11打印日期：05/11/2019 16：01：31研究组织主管*=主主管必须开发替代水的冷却介质。目前，有一系列TM正在进行商业开发。最简单的方法是利用自然对流来拒绝LIBS运行产生的热量。这是日产Leaf采用的一种方法，虽然这是一种低成本的方法，但空气的自然对流有限的比热容量(~1kJ/kg.K)和对流换热系数(~1-10W/m2K)意味着电池可能会因为较高的温度运行而加速退化，并且由于达到热限制而功率能力有限。另一方面，特斯拉电池组使用铜管，它以蛇形图案排列在电池组的单个圆柱形电池周围，通过水来散热。这里的优点是水具有更高的比热容量(~1,000 kJ/kgk)。这种方法的缺点是增加了热管的重量，电池和冷却介质之间的热接触不佳，以及电池之间的冷却不均匀，这可能导致加速降解。研究努力研究了各种替代冷却方法，如使用石蜡等相变材料(PCM)。虽然这些相变材料确实具有非常好的比热容(~2,000 kJ/kgK)，这是由于与固-液相变相关的额外延迟能量(~200 kJ/kgK)，但它们在熔融状态一次的性能并不理想，因为当固体阻止冷却介质的循环时，相变材料的滞留性质不能很好地散热。受这些挑战的推动，这项工作将从根本上深入了解使用介电流体(包括商业上可获得的单相和双相流体)对LIB进行浸没冷却的可行性，但也将扩展到对壳牌目前正在开发的更多专利解决方案的研究。这将通过首先在COMSOL多物理中开发LiB的3D热耦合电化学模型来实现，以预测热产生特性以及性能和寿命影响。在汽车电池组中常见的大尺寸和多电池电池组中，产生的热量可能是高度不均匀的，了解这一点至关重要。该项目的见解将帮助壳牌为不断增长的电动汽车行业开发改进的电动液体，并增加有关使用单相/多相介质液体进行LIBS浸入式冷却的学术知识。

This PhD proposal will investigate the operational mechanisms around immersion cooling of lithium-ion batteries (LIBs)using dielectric fluids.LIBs are a key enabling technology for consumer electronics, electric vehicles (EVs) and for the integration of zeroemission renewable technologies such as wind and solar. Whilst their commercial adoption continues at pace, their cost,performance and lifetime still needs to be improved to be widely economically viable. Increases in the cost when translatingfrom a single cell to a battery pack are due to the additional integration of components such as battery managementsystems and thermal management systems (TMS), with the thermal management system current contributing to ca. 20% ofthe total pack cost. With the battery performance and lifetime being highly thermally coupled, the effective design of a TMSis critical for achieving long term performance targets. In terms of power density, the 2035 target is 12 kW/kg which is still along way away from the current performance of 3 kW/kg with a lifetime of ca. 15 years compared to current values of ca. 8years. To compound this, future TMSs must also be able to operate over a temperature range of -40-80 degC which meansPage 1 of4Date Saved: 05/11/2019 15:55:11Date Printed: 05/11/2019 16:01:31Research OrganisationSupervisor* = Main Supervisoralternative cooling media to water must be explored.Currently, there are a range of TMSs being commercially exploited. The simplest approach is the use of natural convectionto reject heat generated from the operation of LIBs. This is an approach taken by the Nissan Leaf, and whilst this is lowcost, the limited specific heat capacity (~1 kJ/kg.K) and convective heat transfer coefficient (~1-10 W/m2K) of the naturalconvection of air means that batteries can experience accelerated degradation due to higher temperature operation andalso limited power capabilities due to thermal limits being reached. Tesla battery packs on the otherhand use a copper tubewhich is arranged in a serpentine pattern around the individual cylindrical cells of its pack to pass water to remove the heat.The advantage here is that water has a much higher specific heat capacity (~1,000 kJ/kgK). The disadvantage of thisapproach is the additional weight of the heat pipes, the suboptimum thermal contact between the cells and the coolingmedia as well as uneven cooling between cells which can lead to accelerated degradation.Research efforts have investigated various alternative cooling methods such as the use of phase change materials (PCM)like Paraffin. Whilst these PCMs do have very good specific heat capacitances (~2,000 kJ/kgK) due to the additional latentheat energy (~200 kJ/kgK) associated with the phase change from solid-to-liquid, their performance once in the meltedstate is not ideal since PCMs do not dissipate heat well in part due to the stagnant nature of the materialwhen solid preventing circulation of the cooling media.Motivated by these challenges, this work will develop a fundamental insightinto the feasibility of immersive cooling of LIBsusing dielectric fluids including commercially available single and dualphase fluids but extending out to the investigation ofmore proprietary solutions currently being developed by Shell. This will be achieved by first developing a 3D thermallycoupled electrochemical model of a LIB in COMSOL multi-physics to predict the heat generationcharacteristics as well as the performance and lifetime implications. In large form factor and multi-cell battery packs,commonly found in automotive battery packs, the heat generation can be high heterogeneous and it is critical tounderstand this.The insights from this project will help Shell develop improved e-fluids for the growing EV industry and add to academicknowledge around the use of single/multi-phase dielectric fluids for immerson cooling of LIBs.