Research On Preparation And Performance Of KAlSi₂O₆-Aluminosilicate Saggar Material For Resisting Corrosion Of Ternary Anode Materials

The aluminosilicate saggar employed for the calcination of ternary lithium battery anode materials(Li Ni_xCo_yMn_1-x-yO₂,LNCM)has a short service life,which results from the Li⁺penetration and corrosion reactions with aluminosilicate phases.To improve the corrosion resistance and increase the service life of the saggar,KAlSi O₄and KAlSi₂O₆?referred to as KAS₂ and KAS₄,respectively?with excellent corrosion resistance were synthesized in this work.The corrosion resistance mechanism of KAS₄?KAS₂?to LNCM was revealed.Using KAS₄?KAS₂?as the anti-corrosion component,mullite-KAS₄ core-shell structure composite was constructed through the preparation of protective layers composed of KAS₄ on the surface of mullite particles.Effects of the composite on the corrosion resistance and physical properties of mullite-corundum saggar materials were also investigated in this work.Furthermore,KAS₄ was used to modify natural aluminosilicates containing higher Si O₂ content–andalusite?Si O₂?40wt%?and solid waste coal gangue?Si O₂?60 wt%?.The andalusite-and coal gangue-KAS₄ composites with core-shell structure were designed and studied in terms of the stability and corrosion resistance.To achieve the principle of high quality,low cost,less energy consumption and CO₂ emission,aluminosilicate saggers were also prepared by replacing mullite with the designed composites,and were studied in terms of the corrosion resistance and physical properties.The main research contents and results are given as follow:The interfacial reactions between KAS₂ and KAS₄ and LNCM materials were investigated at temperatures ranging from 800 to 1100°C.It was found that KAS₂ and KAS₄ did not chemically react with LNCM precursors or the LNCM material.This can be ascribed to its difficult for Li⁺to enter the crystal structure of KAS₂ and KAS₄through forming solid solution.The result reveals that KAS₂ and KAS₄ exhibit superior corrosion resistance to Li⁺,which can be used as anti-corrosion components of the saggar for calcining LNCM.Based on the principle that KAS₂ can react with mullite to form in-situ KAS₄,the mullute-KAS₄ core-shell structure was designed and constructed through introducing KAS₂ into the mullite-corundum saggar material.The stability of the core-shell structure and its influence on the corrosion resistance and physical properties of the saggar material were studied.The mullite-KAS₄ core-shell structure can remain stable at the LNCM calcining temperature.The KAS₄ shell completely isolates the interaction between mullite and LNCM,thereby giving the saggar material more excellent corrosion resistance.The formation of in-situ KAS₄ shell would produce 4.88%volume expansion,causing some micropores or microcracks generated in the structure,which is helpful to alleviate thermal stress and then beneficial for improving the thermal shock resistance of the saggar material.Meanwhile,the KAS₄ shell structure could promote the combination of aggregates and matrixes,improving the structural strength of the saggar material.When the addition content of the in-situ KAS₄ ranges from 8.3 to 12.4wt%,the mullite-corundum-KAS₄ saggar material has significantly improved corrosion resistance,and possesses higher cold and hot strength as well as enhanced thermal shock resistance at the same time.The andalusite-KAS₄ composite with core-shell structure were constructed,and the aluminosilicate saggar materials prepared by the composites were studied in terms of the phase composition,microstructure and properties.Andalusite has a more serious corrosion reaction with LNCM compared with mullite due to its higher Si O₂ content.Based on the andalusite-KAS₄ core-shell structure design,KAS₄ shell was constructed on the surface of andalusite particles.And the designed KAS₄ shell can remain stable with the andalusite phase,which effectively improved the corrosion resistance of andalusite.After firing at 1450?,the andalusite-KAS₄-corundum saggar materials were prepared,and the andalusite-KAS₄core-shell structure remains stable during the firing.When the designed KAS₄ content ranges from 6 wt%to 9 wt%in the composites,the used andalusite?1-0 mm?can be completely wrapped by the in-situ KAS₄,giving the prepared saggars good corrosion resistance.Compared to the mullite-corundum saggar material,the andalusite-KAS₄-corundum material has better sinterability,higher cold and hot strength as well as in an identical thermal shock resistance.The calcined coal gangue-KAS₄ composite with core-shell structure was constructed,and the aluminosilicate saggar materials prepared by the composites were studied in term of the phase,structure and properties.Due to the highest Si O₂ content,the coal gangue?after the calcination?has the most serious corrosion reaction with LNCM compared with mullite and andalusite.By designing the coal gangue-KAS₄composite with core-shell structure,the corrosion resistance of the coal gangue is dramatically improved due to the protection effect of the KAS₄ shell.In the constructed core-shell structure,a transition layer composed of K?Al_xSi_y?O_z materials was formed between the core and shell,which can remain stable during the calcination of LNCM.After firing at 1350?,the andalusite-KAS₄-corundum saggar materials were prepared.However,because of the diffusion of K element,the thickness of the KAS₄shell reduced whereas the thickness of the transition layer increased,revealing that the coal gangue-KAS₄ core-shell structure is weak.The diffusion reaction caused a stronger sinterability and improved the structure strength of the saggar material.When the KAS₄ content in the composites was about 9 wt%,the coal gangue-KAS₄ core-shell structure in the prepared saggar can be retained,giving the saggar material good corrosion resistance.At the same time the saggar samples exhibit higher cold and hot strength and better thermal shock resistance than the saggar materials prepared by the mullite and andalusite-KAS₄ composites.In this work,using KAS₄?or KAS₂?as the anti-corrosion component,by designing aluminosilicate-KAS₄ core-shell structure composites,the corrosion resistance of aluminosilicate materials is dramatically enhanced.And with the decrease of Si O₂ in the aluminosilicate,the designed core-shell structure tends to be more stable.Through adjusting the KAS₄ content in the core-shell structure and sintering process of the saggar materials,the designed andalusite/coal gangue-KAS₄ is expected to replace mullite to prepare aluminosilicate saggar with excellent corrosion resistance to LNCM and sound performance,which has important practical value for energy conservation,emission reduction,waste utilization and cost reduction.