Revealing the key factors determining Ni(OH)2's electrochemical performance and hereby establishing a carbon shell-protected structure as high-performance electrode material for supercapacitors

Ni(OH)2 as a typical battery-type electrode material has the advantage of high theoretical specific capacity. However, its prominent disadvantages as for extremely low cycling stability and poor rate-performance seriously undermines its reputation as a promising electrode material of supercapacitors. We believe that the key factors of determining its electrochemical performance is still unclear, thus leading to the limited performance promotion by the so far microstructure-engineering strategies. In this work, we try to reveal the key factors determining Ni(OH)2's electrochemical performance by investigating the electrochemical behaviors of α-Ni(OH)2 and β-Ni(OH)2 with or without carbon shell prepared by a homologous mode. The results indicate that α-Ni(OH)2 and β-Ni(OH)2 have the identical electrochemical activity, and both follow the one-electron transfer mechanism. The structure damage of α-Ni(OH)2 is caused by two behaviors including dissolution-precipitation and dissolution-recrystallization, while that of β-Ni(OH)2 is induced just by the dissolution-recrystallization behavior. It is found that the structure damage caused by dissolution-precipitation behavior is inevitable and that caused by the dissolution-recrystallization behavior can be completely suppressed by the carbon shell. Based on the revealed key factors, the established carbon shell-protected β-Ni(OH)2 presents the extremely high cycling stability and promoted electrochemical performance. In view of this, we believe that this is the most possible solution for the issues of Ni(OH)2.