Research On Corrosion Resistance Of Refractory Materials For Synthesizing Cathode Materials Of Lithium Battery

With the gradual development of Li-ion battery cathode materials from unary cathode materials to ternary cathode materials,saggars used for calcining ternary cathode materials are subjected to more severe corrosion than ever.This is because the lithium source of the ternary cathode material is more aggressive and the calcination time is longer.In order to improve the service performance of saggars and reduce extra resource waste and environmental pollution,the corrosion resistance of refractory materials used for the synthesis of ternary cathode materials for lithium batteries was explored in this paper.Firstly,in order to improve the corrosion resistance of the material from corrosion mechanism aspect,four kinds of refractories?cordierite-mullite,Si₃N₄-SiC,SiO₂-SiC,and recrystallized SiC?were selected as the objects.The corrosion reaction between these refractories and the ternary cathode materials was studied by simulating the service conditions,respectively.After that,the phase and microstructure of the refractories were analyzed by XRD and SEM,respectively.It was found that:?1?After corrosion test at 780°C for 20h,the order of corrosion resistance of refractories is recrystallized SiC>Si₃N₄-SiC>SiO₂-SiC>cordierite-mullite.The thickness of the reaction layer was 0.00mm,1.54mm,2.52mm and 3.32mm after corrosion test,respectively.?2?During the corrosion test,Al₂O₃,SiO₂ in cordierite-mullite materials react with Li₂O,NiO,CoO and MnO in ternary cathode materials to form a reaction layer,which gradually damages the material.?3?For three SiC containing refractories,the main reason for corrosion is that SiO₂in the material or formed by oxidation will react with Li₂O in the ternary cathode material to form the lithium silicate compound,which makes the materials gradually erode.The amount of SiO2 in the material or the speed of formation is the main factor to determine the corrosion resistance of the material.The oxidation rate of recrystallized SiC is slower than that of Si₃N₄,so the recrystallized SiC presents better corrosion resistance.Since the SiO₂-SiC material itself contains SiO₂,it is easier to react with Li₂O,as a result it presents the worst corrosion resistance among the three SiC containing refractories.It can be seen from the foregoing research that reducing the porosity of the materials,preventing Li₂O from penetrating into the materials,and avoiding or reducing the reaction between the material components and Li₂O are effective methods to improve the corrosion resistance of the material.For this reason,the cordierite-mullite and the recrystallized SiC materials were modified by impregnation treatment.At the same time,the effects of different impregnating agents?MgSO₄·7H₂O,Mg?H₂PO₄?₂ and alumina sol?,impregnation time and times on the properties and microstructures of the materials were studied in this paper.The porosity reduction and the corrosion resistance were used to characterize the impregnating effect.At last,the phase composition of the impregnated refractories and the microstructure of the refractories after corrosion were analyzed by XRD and SEM,respectively.It was found that:?1?The impregnation treatment can effectively improve the corrosion resistance of cordierite-mullite and recrystallized SiC.Compared with MgSO₄·7H₂O saturated aqueous solution or Mg?H₂PO₄?₂ suspension,aluminum sol presents better effects to improve the corrosion resistance of the material.When aluminum sol is used as the impregnating agent,the impregnation times are 3 times and the impregnation time is 20minutes,the material presents the best corrosion resistance.?2?When the refractory is impregnated with aluminum sol,the impregnating substance enters the sample and fills some pores of the material.When the impregnating substance is decomposed into alumina by heating,the alumina contacts with Li₂O and reacts with volume expansion,which can further block the pores of the sample and prevents Li₂O from penetrating into sample.Thus,the corrosion resistance of the material was improved effectively.