Design And Performance Study Of High-temperature Battery Separator/electrolyte

High-temperature batteries are widely used in aerospace,military weapons,oil and gas exploration,large-scale energy storage and other scenarios.Due to their high electrode reactivity and high ion conductivity at high temperatures,high-temperature batteries can have high power density,which is unmatched performance advantage of other batteries.Thermal battery(heat activated battery)is a common high-temperature battery,it ignites the internal heating material by activating the system,and the battery heats up to about 500℃ to melt the electrolyte inside the battery into a liquid ion-conducting state,and then outputs electrical energy to electrical appliances.Electrolyte is one of the key factors of thermal battery performance.The electrolyte sheet is made by mixing molten salt and MgO according to the proportion and then pressed.In order to ensure sufficient mechanical strength of the electrolyte sheet and a good positive and negative barrier effect,The volume fraction of the non-ion MgO in the electrolyte sheet is usually not less than 30%,which makes the electrolyte sheet thick and the ionic conductivity show certain limitations.The introduction of inorganic fiber fabric as the separator of the thermal battery can further improve the performance of the electrolyte part of the thermal battery.In addition,the activation and working temperature of the molten salt system of the thermal battery are usually above 400℃,which increases the cost of the battery and limits the application scenarios of the thermal battery.Based on this,the following studies have been carried out.The main research contents and conclusions are as follows:The high-temperature stable SiC fiber fabric is introduced as the separator of the thermal battery,and the SiC fiber surface is uniformly covered with MgO particles by a simple precursor conversion method,and obtain SiC@MgO composite separator,which increases the affinity of the SiC fiber to the molten electrolyte salt and the roughness of the fiber surface.Through the infiltration test in the LiCl-KCl electrolyte,it is found that the adsorption of the electrolyte of the SiC@MgO composite separator is 1.5 times that of the pure SiC fiber.And because the SiC fiber is stable at high temperature,the assembled Li(B)|LiCl-KCl|FeS2 battery containing the composite separator realizes normal discharge at high temperature and the battery internal resistance is only 0.2846Ω.The dense PE film is used to wrap the electrolyte of the polymer system to reduce the activation and working temperature of the thermal battery.A PE film with a thickness of 8 μm is used to wrap and isolate LiTFSi-PEO with EO:Li+=15,and the whole is used as the electrolyte part of the battery.At room temperature,the ion-conducting part of the electrolyte is sealed and does not show conductivity.When the temperature rises to the melting point of the PE film(130℃),the PE film melts and the internal ion path conducts shows the ion conductivity,and ion conductivity of the electrolyte system is 1.52×10-4 S cm-1 at 150℃.In addition,the electrolyte system is used in the V2O5|LiTFSi/PEO-PE|Li primary battery,and the battery realizes activation and operation at a lower temperature of 132℃.The power advantage of lithium-ion batteries in high-temperature scenarios can solve the mileage concerns of electric vehicles to a certain extent,and there are many high-temperature application scenarios of lithium-ion batteries.So,we have prepared silicon carbide(SiC)-fiber-supported alumina(Al2O3)pure inorganic composite separator(A@S ceramic separator)through a simple casting method,which is applied to lithium-ion batteries in high-temperature scenarios.A high-temperature stable SiC fiber-reinforced alumina separator,compared with traditional polyolefin separators,it can completely ignore the effect of temperature,and there is no heat shrinkage even under more severe electrolyte immersion conditions.When using with 1M LiDFOB/PC electrolyte,its conductivity at 120℃ reached 5.12 mS cm-1,which is 3 times higher than room temperature.With the high conductivity at high temperature and the high electrode reactivity,LFP(LiFePO4)battery containing the separator can maintain a capacity of 138 mAh g-1 for 200 cycles at a rate of 20 C.In addition,it also shows excellent flexibility,which provides good conditions for it in the actual production of battery assembly.