Phase engineering of cobalt hydroxide toward cation intercalation.

Multi-cation intercalation in aqueous and neutral media is promising for the development of high-safety energy storage devices. However, developing a new host matrix for reversible cation intercalation as well as understanding the relationship between cation intercalation and the interlayer structure is still a challenge. In this work, we demonstrate layered cobalt hydroxides as a promising host for cation interaction, which exhibit high metal ion (Li+, Na+, K+, Mg2+ and Ca2+) storage capacities after phase transformation. Moreover, it is found that α-Co(OH)2 with an intercalated structure is more conducive to phase transition after electrochemical activation than β-Co(OH)2. As a result, the activated α-Co(OH)2 delivers four times higher capacity in multi-cation storage than activated β-Co(OH)2. Meanwhile, the α-Co(OH)2 after activation also shows an ultralong cycle life with capacity retention of 93.9% after 5000 cycles, which is also much superior to that of β-Co(OH)2 (∼74.8%). Thus, this work displays the relationship between cation intercalation and the interlayer structure of layered materials, which is important for designing multi-ion storage materials in aqueous media.