Preparation Of Doped Microporous Carbons And Their Electrochemical Performance

Electrode materials are the main factor that influence the performance of the supercapacitors and lithium ion batteries. Carbon materials are widely used in metallurgy, ceramics, catalyst, gas absorbent and electrode materials due to their advantages such as relatively low cost, electrochemical stability, and work at wide range of temperature. Carbon materials have attracted much attention because of their structure performance can be significantly improved through introduction of heteroatom (such as nitrogen, oxygen, boron and phosphorous) groups. We have prepared polyaniline (PANI) and phenol-melamine-formaldehyde (PMF) based microporous activated carbons by chemical activation using K2CO3, ZnCl2and KOH as chemical agents. The morphology, surface chemical composition, and electrochemical properties of the as-prepared carbon materials were investigated by X-ray photoelectron spectroscopy and cyclic voltammetry, and so on. Carbon electrodes were applied in supercapacitor and lithium ion secondary batteries. The major contents of the paper are as follows:1. Two type of nitrogen-and oxygen-enriched microporous carbons were prepared from PANI by using K2CO3and ZnCl2as chemical agents, respectively. Orthogonal experiments were carried out to investigate the influence of conditions to the electrochemical properties of the carbons. The optimum technological condition for K2CO3activation:the activation temperature was600℃, the weight ratio of PANI to K2CO3was2:1and the heating rate was4℃min-1. The optimum technological condition for ZnCl2activation:the weight ratio of PANI to ZnCl2was1:1, the heating rate was10℃min-1and the activation temperature was700℃. After activation by K2CO3and ZnCl2, the specific surface area and total pore volume of the carbon materials with microporous structure increased remarkably. In addition, activated carbon still with relatively high content of nitrogen. Furthermore, the electrochemical performance of the carbon materials also increases obviously after activated by K2CO3and ZnCl2, the specific capacitance reached as high as210and174F g-1, respectively. After2,000cycles, the specific capacitance was still about89%and96.5%of the initial specific capacitance, respectively.2. A serials of microporous carbons were prepared by simple carbonization and activation of phenol-melamine-formaldehyde resin, which was synthesis under designed aqueous basic/acidic conditions. K2CO3, ZnCl2and KOH were used as chemical reagents. Orthogonal experiments were carried out to find out that the weight ratio of PMF to chemical reagents was the major factor which influence the capacitance of the samples. The specific capacitance of the optimum samples from KOH, K2CO3and ZnCl2activation were202,208and153F g-1, respectively. After activation, the specific surface area, total pore volume, and the oxygen-containing of the carbon materials increased remarkably. Owing to these, the obtained carbon materials cherished good electrochemical performance such as high specific capacitance, high energy and power densities and cycling stability. After20,000cycles at a current density of500mAg-1, the specific capacitance was still about98%of the initial specific capacitance. The specific capacitance decayed not obvious even at high current density of10A g-1. These demonstrated that activated carbons would be promising electrode materials for supercapacitors.3. The electrochemical properties of the PANI-based and PMF-based nitrogen-and oxygen-enriched microporous carbons as anode materials in lithium ion batteries were evaluated. The first discharge capacity of as-prepared carbons was much higher than the theoretical capacity of graphite. The first discharge capacity of the optimized PANI-based and PMF-based carbon was1108and2610mAh g-1, respectively. After20cycling tests, both microporous carbons showed a coulomb ic efficiency above90%, with a reversible capacity of603and716mAh g-1, respectively. These may be attributed to the high surface area with well-developed micropores, amorphous structure with low R value and the high nitrogen/oxygen content.