A Lithium-Sulfur Battery Using Binder-Free Graphene-Coated Aluminum Current Collector

Abstract

Lithium-sulfur battery of practical interest requires thin-layer support to achieve acceptable volumetric energy density. However, the typical aluminum current collector of Li-ion battery cannot be efficiently used in the Li/S system due to the insulating nature of sulfur and a reaction mechanism involving electrodeposition of dissolved polysulfides. We study the electrochemical behavior of a Li/S battery using a carbon-coated Al current collector in which the low thickness, the high electronic conductivity, and, at the same time, the host ability for the reaction products are allowed by a binder-free few-layer graphene (FLG) substrate. The FLG enables a sulfur electrode having a thickness below 100 μm, fast kinetics, low impedance, and an initial capacity of 1000 mAh g_S ^-1 with over 70% retention after 300 cycles. The Li/S cell using FLG shows volumetric and gravimetric energy densities of 300 Wh L^-1 and 500 Wh kg^-1, respectively, which are values well competing with commercially available Li-ion batteries.

Figure 1

(a) Transmission electron microscopy (TEM) image, (b) statistical lateral size distribution with Lorentzian fit, (c) atomic force microscopy (AFM) image, and (d) statistical thickness distribution of the FLG precursor. (e) Raman spectrum of the FLG precursor including graphite reference with (f) corresponding I(2D₁)/I(G) vs I(2D₂)/I(G) and (g) statistical Raman analysis of I(D)/I(G) vs FWHM(G). SEM images of (h) Al_FLGP_50 and (i) Al_FLGP_60 after coating and pressing. See Table 1 for the definition of the samples’ acronyms.

Figure 2

Cyclic voltammetry (CV) measurements with currents normalized to the weight of the sulfur in the electrodes using (a) bare Al, (b) Al_FLGP_50, and (c) Al_FLGP_60 in a potential window of 1.8–2.8 V vs Li⁺/Li at a scan rate of 0.1 mV s^–1. Nyquist plots of the electrochemical impedance spectroscopy (EIS) performed at the OCV, and upon the first and fifth CV cycle of sulfur electrodes coated on (d) bare Al, (e) Al_FLGP_50, and (f) Al_FLGP_60 in a frequency range from 500 kHz to 0.1 Hz using a signal amplitude of 10 mV. Electrolyte: DOL:DME (1:1 w:w), LiTFSI (1 mol kg^–1), LiNO₃ (1 mol kg^–1). Room temperature (25 °C). See Table 1 for samples’ acronyms.

Figure 3

Voltage profiles of Li/S cells cycled at a C/5 rate (1C = 1675 mA g_S^–1) using electrodes coated on (a) bare Al, (b) Al_FLGP_50, and (c) Al_FLGP_60. (d) Comparison of the corresponding discharge capacity trends upon cycling (left-side y-axis) and Coulombic efficiency (right-side y-axis). Electrolyte: DOL:DME (1:1 w:w), LiTFSI (1 mol kg^–1), LiNO₃ (1 mol kg^–1). Voltage window 1.9–2.8 V. Room temperature (25 °C). See Table 1 for samples’ acronyms.

Figure 4

(a) Gravimetric (mAh g^–1, left-side y-axis) and areal (mAh cm^–2, right-side y-axis) capacities of the Li/S cell cycled at a C/5 rate (1C = 1675 mA g_S^–1) using a S-Al_FLGP_50 cathode with an areal sulfur loading increased up to ∼4.4 mg cm^–2 (electrode geometric area of 1.54 cm²) and (b) voltage profile during a related cycle with the maximum capacity. Electrolyte: DOL:DME (1:1 w:w), LiTFSI (1 mol kg^–1), LiNO₃ (1 mol kg^–1). Voltage window 1.7–2.8 V. Room temperature (25 °C). See Table 1 for samples’ acronyms.