Preparation Of Novel Activated Carbons And Their Electrochemical Performance

Carbon materials have been widely used as electrode materials in electrochemical energy system, which is due to it's rich raw materials, simple preparation, advantageous physico-chemical properties and good electrochemical performance. In this paper, novel activated carbon, which is applied in supercapacitors and lithium ion batteries, has been prepared from peanuts shell, tea seed shell and phenol-melamine-formaldehyde resin by activation with different reagent, such as K2CO3 or the mixed gas of oxygen and nitrogen. This paper mainly includes such following parts:1. Novel activated carbon has been prepared from peanuts shell and tea seed shell by activation with K2CO3. The optimum preparation of activated carbon from peanuts shell is as follows:the weight ratio of K2CO3 to peanuts shell is 1:1, the heating rate is 7℃min-1, the activation temperature is 800℃, and the activation time is 1 h. The optimum preparation of activated carbon from tea seed shell is as follows:the weight ratio of K2CO3 to tea seed shell is 1:2, the heating rate is 4℃min-1, the activation temperature is 800℃. and the activation time is 2 h. After activation, the specific surface area of both kinds of activated carbon is sharply increased, which is up to 1297 m2 g-1and 1272 m2 g-1 respectively, and the electrochemical performance is obviously improved, the specific capacitance is up to 155 F g-1 and 150 F g-1 respectively, which suggest that they may be promising candidates for supercapacitors.2. A novel activated carbon has been prepared by carbonization and activation of phenol-melamine-formaldehyde resin which is synthesized by the condensation polymerization method. The yield of phenol-melamine-formaldehyde resin is up to 98.2%, and the optimum synthesis is as follows:the mol ratio of phenol and melamine to formaldehyde is 2:1:2, pH=3, the reaction temperature is 75℃, and the reaction time is 10 h. The optimum preparation of carbonization sample is as follows: the heating rate, the carbonization temperature and time are 7℃min-1,700℃and 1 h respectively. The optimum preparation of activation sample is as follows:the heating rate, the activation temperature and time are 4℃min-1,400℃and 1 h respectively. Phenol-melamine-formaldehyde resin shows evenly distributed buff powder, and the diameter of particles is approximately 120 nm. After carbonization and activation, samples still show similarly excellent morphology with the precursor. The high specific capacitance is up to 213 F g-1, which is attributed to the synergetic effects of the developed specific surface area and heteroatom polar functional groups. The specific capacitance retained 99% of the original one after 10000 cycles, which suggest that it may be promising candidates for supercapacitors.3. The novel activated carbon derived from carbonization and then activation of phenol-melamine-formaldehyde resin, has been used as anode material for lithium secondary battery. The capacity is up to 917 mAh g-1 for the first discharge process, which may be attributed to nitrogen atomic functionalities, high surface area and the increased microporosity. After 20 cycles, coulombic efficiency is still over 90% and reversible capacity reaches approximate 251 mAh g-1, which indicates that activation can improve the cycle life.