Interactions Between Refractory Saggar Matrix And Ternary Li-ion Battery Cathode Materials

Compared with saggars for unary cathode LiCoO2/LiMn2O4/LiNiO2 materials,the saggar for ternary LiNi,CoyMn1-x-yO2(LNCM)materials are subjected to the higher operating temperature of 940 0C-1100 0C.The LiCoO2/LiMn2O4/LiNi)O2 chemical attack changed to a LiNiXCoyMn1-x-yO2(LNCM)multiple corrosion.More demanding industrial conditions lead to the degradation and shorter overall life-time of saggars.Additionally,the spalled saggar materials will be subsequently tapped out together into lithium-ion battery materials and thus contaminate the LNCM materials.In order to identify and understand the occurring degradation mechanisms of the mullite-based saggars,and explore new components that can improve the corrosion resistance performance.Post-mortem analyses on industrial worn saggars were firstly carried out.Based on the post-mortem analysis,laboratory scale tests were designed to understand the refractory degradation mechanisms and to determine the effect of specific process parameters on the interactions between mullite and LNCM materials.The interfacial reactions of cordierite(MgO·2Al2O3·5SiO2),forsterite(2MgO·SiO2)and magnesium aluminate spinel(MgO·Al2O3)with LNCM cathode materials at different temperatures were studied,and the corrosion resistance of saggar matrix that contain different levels of SiO2 were evaluated.The effect of temperature on the preparation of potassium aluminate(K20·11Al2O3)materials was explored.The interfacial reaction of corundum and potassium aluminate with LNCM cathode materials at different temperatures was investigated.The effect of potassium aluminate addition on the corrosion resistance,normal temperature strength,and the thermal shock resistance of saggar materials was studied.Firstly,the corrosion mechanism of mullite attacked by LNCM cathode materials was analyzed.Through the examination of the phase formation in the inner surface of the mullite-based saggar after industrial use and the investigation of the microstructure of the section,it was found that Li2O from LNCM cathode materials reacts with Al2O3 and SiO2 in the saggar material to form Al2O3-SiO2-based products of LiAlSiO4,y-LiAlO2 and LiAlSi2O4.In addition,NiO,CoO,and MnO from the LNCM cathode materials react with MgO and Al2O3 in the saggar material to form(Mg,Ni,Mn,Co)Al2O4 spinel.The thickness of Al2O3-SiO2-based reaction product layer reaches above 900 ?m.The volume expansions accompanied with the formation of these phases and the mismatch of thermal expansion between the newly-formed phases and mullite lead to the generation of cracks in Al2O3-SiO2-based phases layers in mullite saggars,resulting in the spalling of mullite-based saggars.The chemical reactions of mullite components at 800?.900?.1000 ? and 1100 0C were investigated.The results show that the high penetrating Li2O in LNCM cathode can infiltrate into mullite and reacts with mullite to produce ?-LiAlO2 and LiAlSiO4 at 800 0C and 900 ?.When the temperature is above 1000 ?,the amount of LiAlSiO4 increases significantly and(Ni,Co,Mn)Al2O4 spinel was generated,forming the obvious reaction interface.In the presence of both Al2O3 and SiO2,the reaction of Li2O with Al2O3 and SiO2 is the main chemical reaction of mullite corrosion,resulting in a large number of products,and the bulk density and thermal expansion coefficient are significantly different from those of mullite.This could be the main reason of mullite corrosion by LNCM cathode materials.Secondly,the interfacial reactions between cordierite(MgO·2Al2O3·5SiO2),forsterite(2MgO·SiO2)and magnesium aluminate spinel(MgO·Al2O3)and LNCM cathode materials at different temperatures were investigated,respectively.Cordierite has a high degree of reactivity with LNCM cathode materials,and the reaction products of LiAlSiO4 and(Co0.5Mg0.5)2SiO4 was obviously formed at 800 ? and 900 ? on the reaction interface.Though there is no serious chemical reaction between the forsterite and LNCM cathode materials at 800? and 900?,the interfacial reaction degree is higher,and the volume change caused by the reaction products formation is very large when the temperature is above 1000?.There is the least reaction between MgAl2O4 spinel and LNCM cathode materials is the lightest,even at 1100 ?,only a small amount of ?-LiAlO2 can be formed.Nevertheless,at high temperatures,MgO is easy to diffuse into LNCM cathode materials.Although incorporation of cordierite could increase the thermal shock resistance of saggar materials,but,the excessive addition will reduce the corrosion resistance.The forsterite can be used as the saggar material for calcining LNCM cathode materials,however,just suitable for the service temperatures below 1000 ?.The appropriate amount of magnesium aluminum spinel addition will improve corrosion and thermal shock resistance of mullite-based refractory saggars.A comparison of the corrosion reaction of cordierite,forsterite,and magnesium aluminum spinel with LNCM cathode materials proves that the higher SiO2 content would decrease the corrosion resistance.Thirdly,the high purity potassium aluminate with complete crystal growth was synthesized by solid-state reaction method at 1300?.The interfacial reactions of corundum and potassium aluminate with LNCM anode materials at different temperatures were studied.It was found that the corundum and potassium aluminate reacted similarly with LNCM cathode materials.There is almost no reaction at 800?,and only a small amount of ?-LiAlO2 was formed at 900 ?.When the temperature is above 1000 ?,the reactions of corundum and LNCM cathode material produce(Ni,Mn,Co)Al2O4,?-LiAlO2 and LiAl5O8,however,potassium aluminate and LNCM cathode materials only react to form just(Ni,Mn,Co)Al2O4 and ?-LiAlO2.It was found through microscopic structure and EDS element distribution that there was a clear interface reaction layer between the corundum particles and the LNCM at 1000? or higher temperature,which is accompanied by the generation of cracks,however,there is no obvious interface or cracks in potassium aluminate-LNCM mixture sample.It is proved that potassium aluminate has good resistance to chemical attack of LNCM anode materials.Finally,based on the investigation of interfical reaction between different saggar matrix and LNCM cathode materials,potassium aluminate was added to mullite-based saggars with different potassium aluminate contents of 3 wt%,6 wt%and wt9%,respectively.The effects of potassium aluminate addition on the corrosion resistance and physical-mechanical properties(bulk density,apparent porosity,strength,and thermal shock resistance)of the saggar materials were examined.The results show that the addition of potassium aluminate can reduce the diffusion depth of Ni,Co and Mn elements in LNCM cathode material to the saggar material,also reduce the generation of transverse cracks,and thus improve the corrosion resistance of saggar materials.The main contributions of this work include illumination of the corrosion mechanism of the mullite based saggar material by LNCM ternary lithium battery.It was found and clarified that the reaction of Li2O with Al2O3 and SiO2 in the mullite-based saggar is the main reason for the erosion.The interfacial reaction of different refractory saggar component with LNCM ternary lithium battery anode materials at 800?-1100 ? were systematically studied.The degree of chemical reactions between different saggar matrix and LNCM cathode materials have been compared,and the corrosion resistance of different refractory saggar matrix was evaluated.Potassium aluminate was firstly introduced as the saggar material component for LNCM materials calcination.It was found that the addition of potassium aluminate may enhance the corrosion resistance and thermal shock resistance of mullite based saggar materials.