Lithium Polysulfide Sparingly Solvating Electrolyte for Practical High Energy Density Lithium Sulfur Battery
Authors: Li Shanglin , Watanabe Masayoshi , Nomura Nao , Tatara Ryoichi , Liu Jiali , Ueno Kazuhide , Dokko Kaoru 
Published: December 2020

Safe and cheap rechargeable batteries with high energy density and long cycle performance are urgently required for the increasing market of portable electronic devices, electric vehicles (EV), and large-scale grid. Conventional lithium ion batteries (LIBs) based on Li-ion intercalation, which have been widely applied, could not satisfy the demand for higher energy density and greater driving range of EVs. Elemental sulfur, an inexpensive, abundantly available, and environmental-friendly material, has become one of the most promising positive electrode active materials because of its high theoretical specific capacity (1675 mAh g-1). Nevertheless, the commercialization of the rechargeable Li-S battery is still hindered by several main issues: the electronically insulating nature of sulfur and its discharge products (Li2S/Li2S2), the large volumetric expansion of 80% upon its full lithiation, the dissolution and shuttle effect of lithium polysulfide (LiPS).[1-4]

To achieve the practical application of Li-S battery, high energy density and stable cycling performance both need to be focused on. However, for the traditional ether-based electrolyte of 1,3–dioxolane (DOL), and dimethoxyethane (DME) as solvent that is commonly utilized for Li-S battery, severe dissolution of sulfur species from cathode and shuttle effect of LiPS causes a loss of active material and poor cycling stability. To realize the high energy density of Li-S battery, the amounts of electrolyte in the whole battery system need to be controlled. Unfortunately, it is difficult to reduce the electrolyte/sulfur ratio (E/S [mL electrolyte/mg sulfur]) when using the conventional DOL/DME electrolyte because the electrodeposition of the LiPS was found to be significantly slower at high LiPS concentration for a given deposition substrate.[5] Therefore, development of novel electrolytes is of great importance to establishing high energy density Li-S batteries. Here, we report electrochemical performance of Li-S battery using the LiPS sparingly solvating electrolytes.[6-8] Based on these electrolytes, several advantages have been revealed. Firstly, the solubility of LiPS was greatly suppressed, and thus stable charge-discharge with high Coulombic efficiency was achieved in the Li-S batteries. Second, by utilizing pouch cell, we have achieved a high energy density (> 300 Wh kg-1) for Li-S battery under an extremely low E/S ratio of 3.0 μL mg-1. Third, gassing behavior of the Li-S battery using the DOL/DME electrolyte, which indicates high safety risk, could also be obviously depressed.
To further improve the electrochemical performance of Li-S batteries based on LiPS sparingly solvating electrolytes with extremely low E/S ratios, we also explored sulfur electrode additives to improve the electrolyte wettability, various electrolyte additives to protect the lithium anode, and optimized making process for pouch cell. The detailed progress will be presented in the presentation.

Acknowledgements

This work was financially supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) of the Japan Science and Technology Agency (JST).

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