An ion-exchange strategy to eliminate anion impurities within LDH structure for refined NCA cathode materials

Abstract

The Ni-rich NCA precursor (Ni_0.80Co_0.15Al_0.05(OH)₂), synthesized via co-precipitation using sulfate salt, contains anions such as SO₄²⁻ within the layered double hydroxide (LDH) structure to compensate for the high oxidation state of Al³⁺. In particular, the inserted anions can deteriorate the performance of cathode materials by generating Li₂SO₄ during calcination, which induces particle agglomeration and disrupts the formation of a crystal structure. In this study, we explored an ion-exchange strategy using chloride ions to remove sulfate ions, since chloride ions easily volatilize during calcination. As a result, the synthesized NCA cathode represents superior rate capability and capacity retention by decreasing resistance, retaining a well-ordered crystal structure, and suppressing side reactions. These results underscore the importance of anion control in Ni-rich cathode materials with the LDH structure.