PERformance and SEcurity for high POtentiality LIthium/Sulfur batteries – PERSEPOLIS

The development of rechargeable batteries is of considerable importance due to the increasing energy consumption of portable devices. Over the past 20 years, lithium-ion batteries have been under intense research due to their advantages such as high energy density, high operating voltage and low self-discharge rate. However, the gravimetric energy density of such Li-ion batteries is known to be limited to 250 Wh.kg-1, which is not enough to meet the ideal electric vehicle requirements for instance. Moreover, most of positive electrode materials are toxic, expensive, and usually have safety issues.

Elemental sulfur is a promising positive electrode material for lithium batteries due to its high theoretical specific capacity of about 1675 mAh.g-1 of sulfur material. The discharge potential is around 2.1 V (vs. Li+/Li), and the complete Li/S system should allow to reach a gravimetric energy density close to 500 Wh.kg-1. In addition, elemental sulfur is readily available and non-toxic, advantages that should allow to produce cheap and safe high energy batteries.

This technology has attracted attention of the electrochemistry community for many years. However, this promising system still suffers from several drawbacks: low discharge capacity, poor cycle life, low coulombic efficiency, high self-discharge and use of the highly reactive lithium metal negative electrode, which may lead to dendrites formation, short-circuits and explosions.

The objective of the PERSEPOLIS project will be to improve the lithium/sulfur system. More particularly, the project will aim at developing a protection for lithium metal negative electrode in order to prevent the dendrites formation as well as to improve the system performances. Thus, the project objective will be dual:
• The first goal will be related to safety: the negative electrode protection should prevent the dendrites formation, thus improving the safety of lithium metal electrode during cycling.
• The second goal will be related to performances: the negative electrode protection should help to decrease self-discharge and to improve the coulombic efficiency simultaneously.

To this purpose, three different strategies will be considered in this project to protect the lithium metal electrode: organic protections will be developed by looking at efficient polymer layers and electrolyte additives; inorganic protective layers will also be investigated by looking at ceramic electrolyte materials; finally, both organic and inorganic solutions will be combined in order to provide a multilayered solution that would further improve electrochemical performances. The developed protective layer solutions will then be tested in full lithium/sulfur cells and thoroughly characterized.