Morphology evolution of CoNi‐LDHs synergistically engineered by precipitant and variable cobalt for asymmetric supercapacitor with superior cycling stability

Cobalt–nickel layered double hydroxides (CoNi‐LDHs) have been extensively synthesized through precipitation methods for their application in supercapacitors (SC). However, the influence of precipitant quantity on both morphology evolution and SC performance has been an underexplored area. This study systematically examines the morphological changes in CoNi‐LDHs by varying the alkaline quantity and evaluates the performance of asymmetric SC. The findings reveal a progressive transformation in the morphology of CoNi‐LDHs with an increase in alkaline content, starting from nanorod (Co1Ni2(OH)2‐1HMA), progressing to nanorod/nansosheet composite (Co1Ni2(OH)2‐4HMA), and ultimately evolving into nanosheet (Co1Ni2(OH)2‐8HMA). This evolution is attributed to the synergetic effect of the precipitant and variable cobalt, which provides multiple valences and induces morphology evolution. The resulting LDHs demonstrate different SC performances: (1) Co1Ni2(OH)2‐1HMA exhibits a maximum capacitance of 1764 F/g, while Co1Ni2(OH)2‐4HMA and Co1Ni2(OH)2‐8HMA show values of 1460 F/g and 1676 F/g, respectively; (2) rate capabilities showcase percentages of 60.5% for Co1Ni2(OH)2‐1HMA, 83.1% for Co1Ni2(OH)2‐4HMA, and 66.3% for Co1Ni2(OH)2‐8HMA; (3) maximum energy densities are recorded at 72.1 Wh/kg for Co1Ni2(OH)2‐1HMA, 41.3 Wh/kg for Co1Ni2(OH)2‐4HMA, and 62.8 Wh/kg for Co1Ni2(OH)2‐8HMA. Particularly, Co1Ni2(OH)2‐8HMA exhibits superlong cycling stability, retaining approximately 99% capacitance after 25000 consecutive charge/discharge cycles at 7.0 A/g. This result underscores its significant potential for efficient energy storage applications.