X. Sun et al.
Transmission electron microscopy (TEM, JEOL JEM-2010FEF). While Raman (SENTERRA) and X-ray di®raction (XRD, XRD DI SYSTEM) were employed to identify the structure of MWCNTs. The morphology of the MWCNT papers was eval- uated by a scanning electron microscope (SEM, JEM-3010) to analyze the interface structure of the MWCNTs and cellulose. The MWCNT sheet resis- tance was measured by four-probe method with a multi-electrical measurement system (St2258C). Thermal gravity analysis (TGA) test was also per- formed to analyze the content of MWCNTs in the paper. And the surface area was precisely evaluated by the Brunauer – Emmett – Teller (BET) analysis.
conductive. Sora et al. proposed a direct spinning process to fabricate CNT ¯lm. It was used as both active material and current collector. And the bat- tery maintained a reversible speci¯c capacity of 446 mAh/g at a current density of 165 mA/g. 15 Ng et al. used a light weight free standing bucky paper in lithium ion battery. At a high current density of 3000 mA/g, the cell maintains a reversible speci¯c capacity of 200 mAh/g. 25 Most of the fab- ricating methods of CNT ¯lm or CNT paper are complicated, such as the chemical vapor deposition (CVD) method and spinning method. In addition, the CNT ¯lms and CNT papers are formed all by CNTs, which will cause a high cost when applied in lithium ion battery. In this study, a multiwalled carbon nanotube (MWCNT) paper consists of 50% MWCNTs and 50% cellulose was prepared by a traditional paper- making technology. The MWCNT paper displayed good electrical conductivity. The porous structure of the MWCN papers increased the interface areas and improved the electrolyte absorption capacity. This work aimed to evaluate the performance of the battery with MWCNT paper as anode. 2. Experiment 2.1. Preparation of MWCNT paper anodes The cellulose was applied as matrix material, and MWCNTs supplied by Whisker Nanotech Co. Ltd in China served as anode active material. Both were fully dispersed and mixed by high-speed shear and sand-milling in deionized water to form a suspension with a ratio of 1:1. Then the MWCNT paper were obtained by ¯ltrating the suspension with a vacuum pump. And the as-produced MWCNT paper (AMP) was obtained by peeling it o® from the ¯lter paper after drying for 12 h. The carbonized MWCNT paper (CMP) was prepared by carboni- zation treatment in a vacuum oven at a temperature of 1460 for 8 h. The MWCNT papers were rolled and tailored to a disk of 14 mm to be used as an anode electrode directly in lithium ion battery. 2.2. Characterization of MWCNTs and MWCNT paper MWCNTs were observed by ¯eld emission scann- ing electron microscopy (SEM, JSM-6701F) and
2.3. Assembling of cell and
electrochemical measurements The tailored MWCNT papers were used as working electrodes, and Li metal plate was used as the counter electrode. CR2025 coin-type cells were as- sembled in an Ar ¯lled glove box (MBRAUN LABSTAR, Germany) by stacking a porous poly- propylene separator. The liquid electrolyte was 1 M LiPF 6 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 in weight). The electrochemical characterization of the batteries was measured by cell tester (CT-3008W- 5V5mA-S4), and electrochemical impedance spec- troscopy (EIS) were operated on an electrochemical workstation (CHI 660B). The speci¯c capacity was calculated according to the mass of the MWCNTs in the MWCNT paper. With a cut-o® voltage window from 0 V to 0.5 V, the charging and discharging current density was set at 40 mA/g for gravimetric speci¯c capacity measurement. 3. Results and Discussion The SEM image in Fig. 1(a) shows that the MWCNTs have distinct one-dimension structure. TEM image of the MWCNTs is shown in Fig. 1(b). It can be observed that the MWCNTs have a straight and clear texture, which indicates high crystallinity. The XRD patterns of the raw and graphited MWCNTs are shown in Fig. 2(a). According to Bragg's equation, 002 peak and 101 peak are the characteristic graphite di®raction peaks of CNT. After graphitization at 2800 C, the graphited MWCNTs display a sharp carbon peak (002), which
1650120-2
Made with FlippingBook Annual report maker