High Performance Rechargeable Lithium-Iodine Batteries using Triiodide/Iodide Redox Couples in an Aqueous Cathode

Transcription

1 Supplementary Information High Performance Rechargeable Lithium-Iodine Batteries using Triiodide/Iodide Redox Couples in an Aqueous Cathode Yu Zhao, Lina Wang, and Hye Ryung Byon* Byon Initiative Research Unit (IRU), RIKEN Hirosawa 2-1, Wako, Saitama , Japan Correspondence and requests for materials should be addressed to H.R.B. ( 1

2 Supplementary Figure S1 Optical images of GC electrode surface in 1 M aqueous KI and corresponding CV curve. 2

3 Supplementary Figure S2 XRD pattern from NASICON-type LATP. The blue and red lines indicate the LiTi 2 (PO 4 ) 3 and AlPO 4 phases, respectively. 3

4 Supplementary Figure S3 Electrochemical charge/discharge curves of the prototype Li-I 2 batteries. (a) First (black) and second (red) cycles using 0.1 M of I 2 and 1 M of aqueous KI cathode at 2.5 ma cm -2 of current rate. The first discharge capacity, ~0.78 mah, was closed to the ideal value (~0.80 mah) while the charge capacity was decreased to ~0.62 mah. The second cycle showed ~100% Coulombic efficiency. (b) First cycle from tailored battery using 0.03 M of LiI added to 0.08 M of I 2 and 1 M of aqueous KI at 2.5 ma cm -2. It delivered and mah of charge/discharge capacity, respectively, providing ~99.7% Coulombic efficiency. 4

5 Supplementary Figure S4 Ionic conductivity (σ) as a function of the normalized charge/discharge capacity in the battery at 298 K. The σ(organic) is the ionic conductivity of the 1M LiPF 6 in EC/DMC and σ(latp) is the ionic conductivity of LATP. σ(i - 3 ), σ(i - ) and σ(li + ) is the ionic conductivity of I - 3, I - and Li ion, respectively, in the aqueous cathode. σ(j) is the required ionic conductivity to retain the applied current density of 2.5 ma cm -2. 5

6 Supplementary Figure S5 Charge/discharge profile of an I 2 saturated Li-I 2 battery. The total weight of the aqueous cathode is 0.3 g, and the corresponding anode weight is 0.008g. Thus, the energy density is 0.33 kwh kg -1. The Coulombic efficiency is over 97%. 6

7 a 4.5 b Potential / V vs. Li + /Li Capacity / mah charge discharge CE CE / % Capacity / mah Cycle No. Supplementary Figure S6 Electrochemical performance of the aqueous Li-I 2 batteries using 1 M of I 2 with 2 M of KI. (a) 20-times cycled charge/discharge profile at a current rate of 2.5 ma cm -2 and cut-off potential of V. (b) Corresponding charge/discharge capacity and Coulombic efficiency. The performance curves demonstrated excellent cyclic performance as approaching ~100% capacity retention and Coulombic efficiency. The discharge potentials were slightly decreased to 0.2 V during cycling due to high viscosity of aqueous cathode whilst the electrical efficiency was still high. The energy density in this condition was 0.33 kwh kg -1, which was little smaller than the one from smaller concentration (0.08 M) of I 2 (Figure 2a) and almost identical to the one from saturated concentration of I 2 (Figure S5). 7

8 Energy efficiency / % Cycle No. Supplementary Figure S7 Estimated energy efficiency from 100 cycled charge/discharge curves in Figure 2a. The energy efficiency was calculated from the ratio of the integrated area of the charge/discharge profiles. 8

9 Potential / V vs Li + /Li Current density / ma/cm 2 Supplementary Figure S8 Polarization graph from Figure 2c. The discharge potential shows a linear relationship with the current rate indicating the performance of the battery is dominated by the internal resistance of the battery. Further increasing of the current density leads to the decrease of discharge potential, thus hydrogen evolution occurs, which causes damage to LATP separator due to the increased internal pressure. 9

10 cycled cell as-prepared cell 600 Z'' / Ωm Hz 1 Hz Z' / Ωm Supplementary Figure S9 Nyquist plot of as-prepared (red) and 100-cycled (black) Li- I 2 batteries, presenting negligibly changed ionic resistance. The frequency ranges from Hz. 10

11 Supplementary Figure S10 EDS analysis of the Super P carbon current collector after 100 cycles. The carbon signal was from the Super P carbon and TEM grid coated with a thin carbon layer. The copper signal was from the TEM grid. The oxygen signal was probably from the physically adsorbed water or the function groups of the Super P carbon. No sign of residual I 2 or iodide was found. The inset was TEM image of analyzed region in Super P carbon. 11