# Novel Q-Carbon Anodes for Sodium-Ion Batteries
## 3 Results and Discussion  
Figure 51a depicts the XRD patterns of the Q1 and Q2 carbon powders. The Q2 powder shows three broad 2\(\theta\) peaks at \(\sim\)10.5\({}^{\circ}\), \(\sim\)24.5\({}^{\circ}\), and 44\({}^{\circ}\), while the Q1 powder shows the latter two broad 2\(\theta\) peaks at \(\sim\)24.5\({}^{\circ}\) and 44\({}^{\circ}\). The 10.5\({}^{\circ}\) peaks correspond to (001) graphene oxide, which is formed because of higher oxygen concentrations in the environment during the processing of the Q2 powder. The 24.5\({}^{\circ}\) peak corresponds to a graphitic (002) XRD peak and is shifted lower by 1.3\({}^{\circ}\) in the Q1 powder. Both peaks are much lower than the characteristic 26.7\({}^{\circ}\) of (002) graphite, suggesting a defective structure for both carbons, with Q1 having higher defect densities. The full width at half maximum (FWHM) values are related to crystallite sizes of graphite and were found to be 6.81 and 6.51 nm, respectively. The d\({}_{002}\) was calculated to be 3.629 A and 3.801 A for the Q1 and Q2 carbon, respectively. The interlayer spacing d\({}_{002}\) is an important measure of carbon's microstructure and hence will significantly impact sodium-ion transport [29]. Figure 51b,c show the Raman spectra of the Q1 and Q2 carbon powders, respectively. Gaussian peak fitting is used for deconvolution of the peaks. In general, amorphous carbons have three peaks in the range 1000-1800 cm\({}^{-1}\); the first peak, D, at around 1320 cm\({}^{-1}\), the second peak, G, at around 1485 cm\({}^{-1}\), and the third peak, T, at around 1060 cm\({}^{-1}\). The D peak, G peak, and T peak correspond to the breathing mode of the sp\({}^{2}\) bonds due to the presence of defects in the structure, stretching of the sp\({}^{2}\) bonds present in the rings or chains, and vibrational mode of sp\({}^{3}\)-bonded carbon. The deconvoluted peaks ascribe I\({}_{\rm d}\)/I\({}_{\rm g}\) values of 4.37 and 2.067 for the Q1 and Q2 carbons, respectively. Generally, a higher I\({}_{\rm d}\)/I\({}_{\rm g}\) ratio means more sp\({}^{2}\) nature, indicating high disorder and a low graphitization degree. The current work shows the Raman results in Figure 51b,c, which are indicative of a higher sp\({}^{3}\) fraction in the Q2 phase (I\({}_{\rm d}\)/I\({}_{\rm g}\) = 2.067) than the Q1 phase (I\({}_{\rm d}\)/I\({}_{\rm g}\) = 4.37) because of the lower I\({}_{\rm d}\)/I\({}_{\rm g}\) ratios in Q2 than those in Q1. The obtained Raman I\({}_{\rm d}\)/I\({}_{\rm g}\) of Q2 matches with the Raman spectra of 80% sp\({}^{3}\)-bonded Q-carbon in previous papers [1,2]. The Q-carbon phase of \(\sim\)80% sp\({}^{3}\) was confirmed in previous works by EELS, XPS, and Raman [1,2]. N2 adsorption-desorption isotherms, as shown in Figure S2, were collected to investigate the micropores and surface area for the Q-carbons. The Brunauer-Emmett-Teller (BET) surface area [30], Barrett-Joyner-Halenda (BJH) [31], and cumulative mesopore volume are obtained from this data. The BET surface area and micropore and mesopore volume for Q1 are 8.7 m\({}^{2}\).g\({}^{-1}\), 0.002 cm\({}^{3}\).g\({}^{-1}\), and 0.005 cm\({}^{3}\).g\({}^{-1}\). The BET surface area and micropore and mesopore volume for Q2 are 82.24 m\({}^{2}\).g\({}^{-1}\), 0.0228 cm\({}^{3}\).g\({}^{-1}\), and 0.0225 cm\({}^{3}\).g\({}^{-1}\). Q1 has a low surface area and low mesopore volume, whereas Q2 has a higher surface area and mesopore volume. Particle size distribution was also measured using a laser diffractometer, as shown in Figure S3. The particle size for Q1 was 74.3 nm, whereas Q2 showed a wider bimodal distribution of particle sizes, concentrated at 146.1 nm and 488.7 nm. A summary of all structural properties of the Q1 and Q2 carbon are given in Table 2. The electrochemical performance of Q-carbons was evaluated using sodium half cells. Figure 1 shows the discharge (Na intercalation) and charge (Na deintercalation) capacities and coulombic efficiencies of the Q1 and Q2 carbons cycled at a current density of 124 mA\(\cdot\)g\({}^{-1}\).