Controllable Synthesis And Supercapacitive Properties Of α-Co（OH）₂

Supercapacitors (electrochemical capacitors) have exhibited potential applications in many fields because of their high power density, excellent cycling stability and rapid charge-discharge rates. a-Co(OH)2 has a similar structure as hydrotalcite and a high specific area. Thus, it has a wide application prospect as an electrode active material of supercapacitors.This thesis focuses on the following three aspects of a-Co(OH)2.1. Firstly, the influences of anion exchange and phase transformation on the supercapacitive properties of α-Co(OH)2 were studied. NO3-, CH3COO- and SO42-intercalated a-Co(OH)2 has the same morphology, structure and d-spacing as starting Cl- intercalated a-Co(OH)2. The resultant α-Co(OH)2 exhibited better rate capability and cycling stability after intercalation using NO3- and SO42-. a-Co(OH)2 was phase transformed to β-form and other cobalt phases after soaking in alkaline solution at room temperature, leading to a dramatic decrease in the specific capacitance of a-Co(OH)2.2. The effects of interlayer anions, d-spacing and thermal treatment on the supercapacitive properties of a-Co(OH)2 were explored. NO3- and SO42- could be successfully anion-exchanged into the interlayer space of dodecyl sulfate (DS) intercalated α-Co(OH)2 with the morphology and structure reserved. However, there was an obvious difference in their d-spacings, increasing with the order of NO3-, SO42- and DS. The specific capacitance decreased with NO3-, SO42- and DS intercalated a-Co(OH)2. However, their cycling stability improved with the same order. DS intercalated a-Co(OH)2 was transformed into CoO after anneal at 450 and 500 ℃ in N2. It would be a mixtrure of CoO and Co3O4 at 550 ℃ in N2. After thermal treatment, the specific capacitance of the product reduced greatly, but the cyclic stability improved.3. Finally, the effects of Co/Ni ratios on the supercapacitive properties of a-form hydroxides were investigated. α-form CoxNi1-x hydroxides had similar hydrotalcite structure to a-Co(OH)2 and exhibited better electrochemical performance than pure a-Co(OH)2 after being tested by XRD, FTIR and electrochemical performance when x≠0. An asymmetric supercapacitor packaged using Co0.6Ni0.4 hydroxide had a high energy density of 23.5 W h kg-1 at a power density of 412.5 W kg-1.