Charge storage performances of micro-supercapacitor predominated by two-dimensional (2D) crystal structure

Abstract How to develop a high-energy-density supercapacitor still remains a big challenge to us. Herein, we employ two new “anion intercalation materials” to fabricate the asymmetric micro-supercapacitor with a high energy density. It is found that both [Bi 6 O 6 (OH) 3 ](NO 3 ) 3 ·1.5H 2 O and Bi 2 O(OH) 2 SO 4 electrodes show high charge/discharge rates and excellent cycling stabilities (99.7% and 95.1% capacitance retention after 10,000 cycles, repecticely). Amazingly, the micro-supercapacitors fabricated by [Bi 6 O 6 (OH) 3 ](NO 3 ) 3 ·1.5H 2 O and Bi 2 O(OH) 2 SO 4 display the high energy densities of 0.125 and 0.048 mWh cm −3 at a power density of 53 mWcm −3 . In consideration of a lower BET area (1 m 2  g −1 ) and a higher electric resistance (1.06 Ω) of [Bi 6 O 6 (OH) 3 ](NO 3 ) 3 ·1.5H 2 O than those (2.2 m 2  g −1 , 0.78 Ω) of Bi 2 O(OH) 2 SO 4 , the higher energy density of [Bi 6 O 6 (OH) 3 ](NO 3 ) 3 ·1.5H 2 O is mainly attributed to the unique two-dimensional (2D) extended [Bi 2 O(OH) 2 2+ ] n layer structure that favors for charge insertion. This contribution demonstrates that it is the crystal structure of material but not conventional BET area and electrical conductivity that decides the electrochemical performances of micro-supercapacitors, which has been unknown before. We can expect that unique two-dimensional (2D) extended layer material could be a new candidate for next-generation supercapacitor.