Lithium sulfur battery exploiting material design and electrolyte chemistry: 3D graphene framework and diglyme solution

Abstract

Herein we investigate a lithium sulfur battery suitably combining alternative cathode design and relatively safe, highly conducting electrolyte. The composite cathode is formed by infiltrating sulfur in a N-doped 3D graphene framework prepared by a microwave assisted solvothermal approach, while the electrolyte is obtained by dissolving lithium bis(trifluoromethane)sulfonimide (LiTFSI) in diethylene glycol dimethyl ether (DEGDME), and upgraded by addition of lithium nitrate (LiNO3) as a film forming agent.The particular structure of the composite cathode, studied in this work by employing various techniques, well enhances the lithium-sulfur electrochemical process leading to very stable cycling trend and specific capacity ranging from 1000 mAh g −1 at the highest 2 rate to 1400 mAh g −1 at the lowest one. The low resistance of the electrode/electrolyte interphase, driven by an enhanced electrode design and a suitable electrolyte, is considered one of the main reasons for the high performance which may be of interest for achieving a promising lithium-sulfur battery. Furthermore, the study reveals a key bonus of the cell represented by the low flammability of the diglyme electrolyte, while comparable conductivity and interface resistance, with respect to the most conventional solution used for the lithium sulfur cell.

Sulfur Loaded by Nanometric Tin as a New Electrode for High‐Performance Lithium/Sulfur Batteries

“…The data of Table indicate an overall resistance value ( R ) of the electrode/electrolyte interphase decreasing from about 370 Ω at the OCV to values as low as 5, 4, and 3 Ω after 1, 5, and 10 CV cycles, respectively . This remarkable resistance reduction, mentioned earlier as electrode activation, as well as the relevant change of the Nyquist plot shape can account for a significant variation of the electrode structure and characteristic upon the first charge/discharge cycle, which certainly merits further insights by specific techniques, such as ex situ XRD, and possibly in situ XRD, in situ SEM, or tomography, to be fully clarified . Such an activation process leads to very low electrode/electrolyte resistance values, which can actually allow optimal operation in lithium cell in terms of the delivered capacity and the rate capability …”

The Role of Current Collector in Enabling the High Performance of Li/S Battery

“…Both cells reveal the expected voltage signature, composed by two plateaus during discharge at about 2.3 and 2 V, and the corresponding plateaus during charge at about 2.2 V and 2.5 V, as already evidenced by cyclic voltammetry. The cell using the 3DNG−S on Al (Figure a) shows satisfactory capacities of about 810, 770, and 700 mAh g −1 at C/8, C/5 and C/3 rate, respectively (1 C=1675 mA g S −1 ) with a polarization lower than 0.4 V. These good performances are relevantly improved by the employment of GDL as the cathode support (Figure b), achieving the remarkable capacities of 1150, 1060, and 1000 mAh g −1 at C/8, C/5 and C/3 rate, respectively, and polarization lower than 0.2 V. It is worth mentioning that these performances are in line with our previous results on the 3DNG−S/GDL electrode using a different electrolyte media based on diglyme solvent …”

“…Figure (a, b) shows the CV curves of 3DNG−S using Al and GDL support, respectively. Both samples show during cathodic scan the two typical reduction peaks at about 2.3 and 2 V, corresponding to the conversion of S 8 ring to long‐chain (Li 2 S x , 4 ≤ x < 8) and short chain (Li 2 S x , x =1,2) lithium polysulfides, which are reversed during anodic scan into merged peaks at potential higher than 2.2 V, by multiple step oxidation process of the polysulfides into sulfur . However, the cell using 3DNG−S cast into Al support (Figure a) shows a different reaction kinetics, peak broadening, higher polarization, and lower current intensity with respect to the same sulfur composite cast onto GDL (Figure b).…”

“…The first one corresponds to the carbon matrix of the substrate and the second to C bound to F (CF 2 ) due to the Teflon‐type component of the GDL. It cannot be excluded that the presence of these functional groups into the GDL can positively affect the kinetics of the electrochemical process, since electron attracting atoms such as F and O actually limit the polysulfide dissolution from the cathode to the electrolyte . However further studies to clarify this aspect are required.…”

“…Very important factor influencing Li/S battery performance is the nature of the substrate used for the active material deposition, which actually improves the efficiency and the delivered capacity by the cell . Indeed, we have reported in previous works a variety of optimized sulfur composites benefitting of carbon nanotubes, and 3D‐graphene with improved performances in terms of delivered capacity, rate capability and stability, which were well promoted by the employment of a carbon paper, i. e., a gas diffusion layer (GDL), rather than conventional aluminum as the electrode support.…”