V2O5-anchored Carbon Nanotubes for enhanced electrochemical energy storage M. Sathiyaa, A. S. Prakasha,*, K. Rameshaa, J-M. Tarasconb and A. K. Shuklac
CSIR Central Electrochemical Research Institute-Chennai Unit, CSIR-Madras Complex, Taramani, Chennai-600 113, India. b Laboratoire de Réactivité et Chimie des Solides, CNRS UMR 6007, 33, rue Saint Leu - Université de Picardie Jules Verne, 80039 Amiens, France c
Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560 012, India.
1. Supporting information S-1
Figure S-1, Structure of (a) crystalline V2O5 and (b) V2O5 xerogels. In crystalline V2O5, single layers of V2O5 are arranged in orderly manner whereas in V2O5 xerogel, bilayers of single V2O5 layers are arranged as stacks along the c-axis of monoclinic unit cell. Oxygen coordination of vanadium resembles a square pyramid
in both structures. Oxygen atoms shown between the layers represent oxygen of water molecules.
2. Supporting information S-2
1.81 Å (062)-V2O5
3.4 Å CNT- (002)
1.92 Å (-114) V2O5
Figure S-2, High resolution Transmission electron micrograph showing growth of (-114) plane of V2O5 parallel to (002) planes of CNT lattice. The (062) planes of V2O5 which are perpendicular to (-114) planes are also shown. S2
3. Supporting information S-3
Figure S-3, Cyclic voltammogram of crystalline V2O5 (sigma Aldrich) at a scan rate of 0.1mV/ sec. Cyclic voltammogram of crystalline V2O5 reveal four reduction peaks at ~3.25, 3.05, 2.2 and 1.5V in the first cathodic sweep. These peaks are attributed to phase transition of α- V2O5 to ξ, δ, γ and ω phase which is in good agreement with previous reports1. Formation of ω phase is irreversible and ω phase is cycling reversibly from second cycle onwards.
4. Supporting information S-4
Figure S-4. Plot showing linear relationship of logν vs log i for cathodic (discharge) and anodic (charge) sweeps of cyclic voltammogram. According to Cottrell equation, i= nFAC0j√D0/ √(πt). 2 It can be simplified as i= at-1/2 where ‘a’ is the collection of constants. Further, (Scan rate)1/2 can be used in place of t-1/2. Hence, current response for the voltammetric sweep follows the power law relationship, i= aνb, where a and b are adjustable parameters. Thus log i= log a+ b log ν, value of b can be calculated from the slope of straight obtained by plotting log i vs. log ν. Further, b= 0.5 for diffusion limited processes (i= aν1/2) and is unity for non diffusion limited processes (i= aν). Thus CV experiments were carried out at different scan rates of 0.1 to 5 mV/ sec and current S4
values at different potentials were plotted as a function of scan rate. From the slope of the straight line obtained, b- value is calculated during cathodic and anodic sweeps.
5. Supporting information S-5
Figure S-5. Dependence of slope ‘b’ (derived from linear fit of log i vs log ν) as a function of cell voltage. As explained in previous section (supporting information Fig. S4), value of b is calculated and is plotted as a function of voltage V. Slope b is comparatively lower at peak potentials indicating the dominance of diffusion limited intercalation. Whereas it is near to 1 at other potentials indicating more of capacitive contribution.
6. Supporting information S-6
Figure S-6. The plots of ν1/2 vs i/ν1/2 used for calculating constants a1 and a2 at different potentials. According to power law relationship, i= aν for non diffusion limited processes and i= aν1/2 for diffusion limited processes. Thus, total current i= aν+ aν1/2 and i(V)/ ν1/2 = a1ν1/2 + a2. Current values at different potentials were calculated from cyclic voltammogram at different scan rates of 0.1 to 5mV/ sec. Plots of i/ν1/2 vs. ν1/2 have been drawn at different potentials and from the straight line obtained value of a1 (slope) and a2 (intercept) are calculated.
7. Supporting information S-7
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