Novel Lithium‐Sulfur Polymer Battery Operating at Moderate Temperature

Abstract

A safe lithium-sulfur (LiÀ S) battery employs a composite polymer electrolyte based on a poly(ethylene glycol) dimethyl ether (PEGDME) solid at room temperature. The electrolyte membrane enables a stable and reversible LiÀ S electrochemical process already at 50 °C, with low resistance at the electrode/ electrolyte interphase and fast Li + transport. The relatively low molecular weight of the PEGDME and the optimal membrane composition in terms of salts and ceramic allow a liquid-like LiÀ S conversion reaction by heating at moderately high temperature, still holding the solid-like polymer state of the cell. Therefore, the electrochemical reaction of the polymer LiÀ S cell is characterized by the typical dissolution of lithium polysulfides into the electrolyte medium during discharge and the subsequent deposition of sulfur at the electrode/electrolyte interphase during charge. On the other hand, the remarkable thermal stability of the composite polymer electrolyte (up to 300 °C) suggests a lithium-metal battery with safety content significantly higher than that using the common, flammable liquid solutions. Hence, the LiÀ S polymer battery delivers at 50 °C and 2 V a stable capacity approaching 700 mAh g S À 1 , with a steady-state coulombic efficiency of 98 %. These results suggest a novel, alternative approach to achieve safe, highenergy batteries with solid polymer configuration.

Scalable Composites Benefiting from Transition‐Metal Oxides as Cathode Materials for Efficient Lithium‐Sulfur Batteries

“…The above difference may be attributed to a faster kinetics of the Li-S conversion promoted by the nanometric TiO2 included in the latter composite with respect to the micrometric MnO2 in the former one. It is worth mentioning that the notable lithium polysulfides retention of the MnO2 may possibly limit the kinetics of the Li-S conversion and rate capability of the cell, [24] that is in line with the better rate capability of the S-TiO2 electrode observed in Fig. 5.…”

“…The above difference may be attributed to specific effects on the kinetics of the LiÀ S conversion promoted by the nanometric TiO 2 and the micrometric MnO 2 . Indeed, the notable lithium polysulfides retention ability of the MnO 2 may possibly slow down the LiÀ S conversion and limit the rate capability, [24] while the nanometric morphology of the TiO 2 (Figure S1 in Supporting Information) may actually boost the electrode kinetics and the cycling rate of the cell. On the other hand, both materials recover almost completely the pristine electrochemical response upon lowering the C-rate back to C/10 after 35 cycles, as SÀ MnO 2 delivers 995 mAh g S À 1 and SÀ TiO 2 1050 mAh g S À 1 that correspond to about 95 % of the respective initial capacity.…”

“…This "shuttle process" between the electrodes typically leads to an apparent charge without any energy storage, with active material loss, anode degradation, low coulombic efficiency, and capacity fading. [12,13] Several approaches have been undertaken to control the undesired processes ascribed to the soluble polysulfides during battery operation, including the use of sulfur-carbon composites, [14][15][16][17] inorganic cathode additives, [18][19][20] alternative binders, [21,22] polymer electrolytes, [23,24] electrolyte sacrificial agents, [25][26][27] as well as functional interlayers [28,29] and separators. [30,31] In particular, transition metal oxides of various nature and morphology have been thoroughly studied for possibly mitigating the polysulfides diffusion into the electrolyte, and improving of the LiÀ S cell behavior.…”

Glyme-based electrolytes: suitable solutions for next-generation lithium batteries

“…The polymer electrolyte showed high thermal stability and a stable interphase during the Li–S conversion process at 2.2 V vs. Li + /Li. 104 Besides, [Li(G 3 ) 4 ][TFSI] and [Li(G 3 ) 1 ][TFSI] complexes were investigated as electrolyte solutions possibly able to mitigate the polysulfide dissolution. Indeed, a Li–S cell using the [Li(G 3 ) 1 ][TFSI] complex delivered a discharge capacity higher than 700 mA h g S −1 with a coulombic efficiency above 98% over more than 400 cycles.…”

“…[83][84][85][86][87][88][89][90][91][92][93][94][95][96][97][98][99][100][101][102] This new technology is nowadays considered close to a practical application and holds the promise of a breakthrough in storable energy per unit mass. 103,104 Furthermore, the glyme-based solutions have been selected as the electrolytes of choice for the lithium-oxygen (Li-O2) cell, in which a lithiummetal anode is coupled with a gas diffusion layer electrode enabling the O2 electrochemical conversion thanks to an open design. Notably, this system could store even more energy than the Li-S cell and has been suggested as possible battery for future applications.…”