Effects Of Kaslilite Addition On The Properties Of Saggars For Ternary Lithium Ion Battery Cathode Material Firing

Li?Ni_xCo_yMn_z?O₂?LNCM?materials have been industrially prepared through solid-state reactions using Li-,Ni-,Mn-and Co-bearing precursors.Mullite and cordierite saggars are commonly used for firing of LNCM during firing.However,serious corrosion often occurs,resulting in short service life of saggars.Furthermore,LNCM is contaminated due to the corrosion of refractory saggars.Therefore,it is of great significance to develop new types of saggar materials which can better resist the severe corrosion of LNCM and have a longer service life.It is noticed that in alkali-containing environment,corrosion products of Al₂O₃-SiO₂ refractories including potassium aluminosilicates such as kalsilite?KAlSiO₄,KAS₂?and leucite?KAlSi₂O₆?seem to be stable under high temperatures in a high alkaline environment.In addition,kalsilite and leucite have high melting points of1750°C and 1690°C,respectively.Due to the fact that K and Li elements are located in the same family in the periodic table,their compounds have similar chemical properties.Therefore,KAS₂ may have little reaction with LNCM and it would be a promising route to use these potassium aluminosilicates as anti-LNCM corrosion materials to improve the quality of saggars.At present,studies concerning the potential value of KAS₂ as saggar materials for LNCM calcination have not been reported.In this work,KAS₂ was synthesized using solid state reaction method.Then,the interface reaction between KAS₂ and four kinds of saggar mateials fine powders,and between KAS₂ and LNCM were studied.Finally,the influence of KAS₂ addition on the properties of saggar materials was determined.The potential of KAS₂ application in saggar materials for calcination of ternary lithium ion battery cathode materials was explored.Firstly,highly pure KAS₂ was synthesized by solid state method at 1200°C for 6h,using potassium carbonate,industrial alumina powder and silica fume as raw materials.Secondly,the reaction of KAS₂ with different kinds of saggar materials at 1370°C,the sintering temperature of saggar,was studied.The results indicate that,after heat treatment at 1370°C for 3 h,KAS₂ does not react with corundum and magnesia-alumina spinel;KAS₂ reacts with mullite but does not generate any phase with low melting points;KAS₂ reacts with cordierite and generates low melting point phase,resulting in serious deformation of the specimen.Therefore,KAS₂ may be used with corundum,magnesia-alumina spinel and mullite saggar materials,but not with cordierite.Thirdly,the reaction behavior of KAS₂ and LNCM between 800¹100°C,the calcination temperature of LNCM in industry,was studied.In this work,KAS₂ fine powder and LNCM material were mixed at the mass ratio of 7:3,pressed into cylindrical specimen and put into electric furnace for calcination between 800¹100°C.Based on XRD and EDS results,Al³⁺from KAS₂ diffuses into the LNCM crystal structure when firing temperature is above 900°C.When firing temperature reaches 1100°C,Ni²⁺,Co²⁺and Mn²⁺from LNCM diffuse into the KAS₂ crystal structure.As indicated in SEM micrographs,although KAS₂ has slight solid solution with LNCM,the interface between KAS₂ and LNCM is clear and no reaction layer is detected.Therefore,KAS₂ could be used in saggar materials for LNCM firing to improve the corrosion resistance of saggar.Fourthly,the effects of KAS₂ addition on properties of corundum-mullite and corundum-spinel material such as CCS,HMOR and TSR were determined.The results show that the CCS and HMOR of samples with 3%and 6%KAS₂ addition improve significantly.For corundum-mullite material,the improvement of sintering performance may be attributed to the bonding effect of the newly-generated potassium aluminosilicates.By comparison,the improvement of corundum-spinel sintering performance is possibily because of the generation of more liquid phase due to existance of KAS₂ in the system.However,the CCS of samples with 9%KAS₂ addition see a downward trend.This could be explained by the existance of KAS₂ or newly formed leucite,whose thermal expansion coefficients?TEC?are much higher than that of corundum,mullite and spinel.In the cooling process,excessive micro-cracks owing to mistaches of TEC generates,resulting in a reduction in strength.Finally,the effects of KAS₂ addition on anti-LNCM corrosion performance of corundum-mullite and corundum-spinel materials were studied.The results show that the corrosion section of corundum-mullite materials with different KAS₂ addition has similar 4 layered structure,that is,?Ni,Mn,Co?Al₂O₄ spinel layer,Al₂O₃-SiO₂ reaction layer,Al₂O₃-SiO₂ penetration layer and original saggar materials layer.By contrast,the corrosion section of corundum-spinel materials with different KAS₂ addition has similar 3 layered structure,that is,?Mg,Ni,Mn,Co?Al₂O₄ spinel layer,LiAl O₂ reaction layer and original saggar materials layer.KAS₂ seems to have weak influence on the anti-LNCM corrosion behaviors of saggar materials since the corrosion layers have similar structure for the same kind of saggar materials.Therefore,based on the short laboratory experiment time?24 h?,it is not possible to draw a definite conclusion on the relationship between KAS₂ addition and the anti-LNCM corrosion properities of saggar materials.