Preparation Of BN Fiber Separator And Application Of Bn Fiber Separator In Li-FeS₂/CoS₂ Thermal Battery

Due to its short activation time,high specific energy and long storage time,thermal battery technique has been widely applied in series of guided weapons and advanced equipment.The separator of thermal battery,which plays a key role in the battery functioning,is considered to have a reasonable impact on the high-power,long-service-time thermal battery.The excellent thermodynamically stability,electronically insulation and chemically inertness are expected for the separator materials when assembled with molten salt electrolyte and corrosive Li-alloy anode.Based on the state-of-the-art MgO-powder separator processing and the precedent researches on BN felt separator,this paper mainly introduce a BN fiber composite separator prepared by precursor modification and heat treatment.Furthermore the relationship betweent the BN fiber separator and the electrolyte retention has been revealed in this paper.Also the impacts on two types of thermal battery of the BN fiber separator have been investigated in followed chapter.Firstly,the effect of precursor species and heat treatment on the separator composition,microstructureand electrolyte retention has been investigated.The results indicate that the MgO particles pyrolysed from Mg?NO₃?₂ disperse better than those pyrolysed from Mg?CH₃COO?₂ on the surface of BN fiber.The average diameter of MgO particles is 20nm.And the MgO particles pyrolysed from Mg?NO₃?₂can completely cover the surface of BN fiber.The conglomeration of MgO becomes rigid when the MgO content increasing.The main phase of the separator after analysis is BN and MgO.However when heating temperature is above 700?,the BN fiber oxidation dramatically increase and then Mg₃?BO₃?₂ phase can be detected,which threatens the properties of the BN fiber separator.The oxidation of BN fiber can be effectively controlled by the using inert gas atmosphere.Secondly,the electrolyte retention properties of BN fiber separator to LiCl-KCl,LiF-LiCl-LiBr and LIF-LiBr-KBr molten salt electrolyte have been studied.When the MgO content in the separator is controlled and employing one single electrolyte,the electrolyte retention is higher if the BN fiber is modified by Mg?NO₃?₂.This may contribute to the dispersing status of MgO particles on BN fiber.As for the three molten salt,the electrolyte retention of the separator reaches the highest to LiF-LiCl-LiBr electrolyte.When the MgO content is 30wt.%,the maximum mass gain of the separator is 221.1%.From the SEM of the separator,the molten salt observed in the micrographs totally coat on the BN fiber.The BN fiber separator show better wettability compared with pure BN separator,and meanwhile the structural intergrity remains stable after electrolyte impregnation.Thirdly,the effects of BN fiber separator on the battery discharging have been studied in this paper.In the Li-Al/LiCl-KCl/FeS₂thermal battery,the open circuit voltage stabilize at 2.301V with the BN fiber separator containing 25wt.%MgO.From the pulse discharging result,the total ohmic polarization of the battery is 0.45?.When the battery is discharged at 50mA,the voltage plateau holds at 1.66V for 2h.In the Li-B/LiF-LiCl-LiBr/CoS₂battery,the total ohmic polarization reaches the lowest when the MgO content in the separator is 30wt.%.After discharging,the phase analysis result only shows the XRD pattern of BN and MgO,which indicates a good chemical stability and structural intergrity of the BN fiber separator during discharge.