Simulation of electrical and thermal characteristics of a short circuit inside a boehmite composite separator

Although lithium-ion batteries are widely used in the field of new energy, their thermal runaway hazard is a serious threat to safety, of which the internal short circuit caused by lithium dendrites piercing the separator is the core cause. This paper presents a 3D electrochemical-heat transfer coupling model of the ceramic composite separator (boehmite coating) to investigate the influence of lithium dendrite radius, spacing and coating thickness on internal short-circuit behavior. It is shown that the increase of lithium dendrite radius significantly exacerbates the short-circuit heat generation effect, and the peak temperature increases from 73.3 to 82.1 °C when the radius is increased from 5 to 100 μm, with a 2.5-fold increase in the total heat generation. When double dendrites are shorted in parallel, the peak temperature increases by 7.1% compared with single-point shorting, and the limited thermal diffusion at small pitches leads to high-temperature buildup. Optimizing the thickness of the separator coating, it is found that a 10 μm coating (total separator thickness of 30 μm) balances heat diffusion with resistance regulation: its maximum temperature and total heat production are below safe thresholds, and it reduces the risk of heat buildup by 20% compared to a 15 μm thick coating. This study uncovers the synergistic mechanism between dendrite parameters and separator coatings, proposing the design guideline of “dendrite spacing control + coating thickness 1 : 3 optimization.” It provides theoretical support and a quantitative foundation for the development of high-safety lithium-ion batteries.