# Novel Q-Carbon Anodes for Sodium-Ion Batteries
## 3 Results and Discussion
Q1 exhibits initial discharge and charge capacities of 344.5 mAh\(\cdot\)g\({}^{-1}\) and 279.8 mAh\(\cdot\)g\({}^{-1}\), respectively, with a columbic efficiency of 81%. After the 4 th cycle, the coulombic efficiency increases to above 99%, with the reversible capacity gradually decreasing. The capacity retention is 63% (6 cells; 152.07 \(\pm\) 14 mAh\(\cdot\)g\({}^{-1}\)) at the end of 200 cycles. Q2 provides an initial columbic efficiency of 58% with an initial discharge capacity of 427.5 mAh\(\cdot\)g\({}^{-1}\) and charge capacity of 247.98 mAh\(\cdot\)g\({}^{-1}\). After eight cycles, the coulombic efficiency increases to above 99% while the capacity remains stable. The capacity retention was found to be 74% (6 cells: 166.22 \(\pm\) 4 mAh\(\cdot\)g\({}^{-1}\)) at the end of 200 cycles. The cycling was performed on five cells of each type and all cells showed similar performance. The discharge capacity for Q1 and Q2 was 152.078 \(\pm\) 15 mAh\(\cdot\)g\({}^{-1}\) and 164.18 \(\pm\) 9 mAh\(\cdot\)g\({}^{-1}\). CV and rate experiments were also performed two times to confirm performance. The ICE and final capacity of Q1 and Q2 cells are reported in Table S1. Figure 1a,b show the charge/discharge profile of the first three cycles for Q1 and Q2 carbon, respectively. Notice the larger leftward shift between the 1 st and 2 nd; the 3 rd discharge curve is larger for Q2 than Q1 carbon, which is due to the higher surface area of Q2, which leads to extensive SEI formation and lower initial columbic efficiency. Figure 1c,d show the charge/discharge profile of the 1 st, 50 th, 100 th, 150 th, and 200 th for Q1 and Q2 carbon. It is noticed that the discharge curves for the 1 st, 50 th, 100 th, 150 th, and 200 th cycle of Q1 carbon keeps shifting to the left, signifying its faster capacity fade over Q2. As a comparison, the cycling profiles for Q2 are close to each other, indicating superior cycling stability. For both Q1 and Q2, the curve can be divided into three sloping regions, with the first region being 0 to 0.22 V, the next being 0.22 to 1 V, and the last being the 1 to 3 V region. The absence of a flat voltage plateau at low voltage shows the absence of a graphitic region or \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**d\({}_{002}\) (Å)**} & \multirow{2}{*}{**LC\({}_{002}\) (nm)**} & \multirow{2}{*}{**I\({}_{d}\)/I\({}_{g}\)**} & \multicolumn{2}{c}{**Micropore**} & \multicolumn{2}{c}{**Mesopore**} & \multirow{2}{*}{**BET Surface**} & \multirow{2}{*}{**d**} \\  & & & & **Volume** & **Volume** & **Area (m\({}^{2}\)\(\cdot\)g\({}^{-1}\))** & & **(nm)** \\ \hline Q1 & 3.629 & 6.81 & 4.37 & 0.002 & 0.005 & 8.7 & 74.3 \\ \hline Q2 & 3.801 & 6.51 & 2.067 & 0.0228 & 0.0225 & 82.24 & 146.1 & 488.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Structural parameters of Q1 and Q2 carbon. Pore structure characterization and BET surface area for Q1 and Q2 carbon. Figure 1: Charge/discharge capacities and columbic efficiencies for (**a**) Q1 and (**b**) Q2 carbon; Charge/discharge profile at different cycles for (**c**) Q1 and (**d**) Q2. nano-pores in both Q1 and Q2 [30]. As noted from the Raman spectra, the slower quench from higher temperature for Q1 leads to the formation of larger particles with low surface area. In addition, slower undercooling might also provide a longer time for closure of the micropores, resulting in lower porosity. Both the lower porosity and surface area suppress irreversible capacity, leading to the formation of thinner solid-electrolyte interface (SEI) layers on the electrode surface and a higher ICE [30]. As a comparison, the rapid quench of Q2 leads to a higher porosity, high surface area, large irreversible capacity loss and a low ICE. The difference of cycling stability of Q1 and Q2 can be ascribed to their difference in \(\mathrm{I_{d}}/\mathrm{I_{g}}\) ratio, which is 4.37 for Q1 and 2.067 for Q2.