Lithium-Sulfur Batteries

4 Anode–Electrolyte Interface

Mark Wild

OXIS Energy, E1 Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK

4.1 Introduction

In Chapter 1, we discussed the issue of side reactions and solid–electrolyte interface (SEI) formation at the lithium anode in a lithium sulfur cell. In addition to electroplating and electrodissolution of lithium in the core redox chemistry of the cell to release cations into the electrolyte, we note that in a typical construction the anode provides a source of reductant species, whilst excess lithium acts as a lightweight current collector and helps combat poor coulombic efficiency. Thus, the degradation of the anode is a significant contributor to reduced cycle life and limits application. If the energy density of a lithium–sulfur cell is set at 400 Wh kg⁻¹, the thickness of lithium metal is estimated at 25–50 μm (5–10 mAh cm⁻¹). Commercial foils are 70–130 μm in most cases.

Lithium is highly reactive and lightweight, making it an ideal candidate for a battery technology designed for high gravimetric energy density. Unfortunately, lithium reacts with many species it comes into contact with, forming unwanted side products. These unwanted side reactions do not add value and may lead to irreversible loss of lithium and other electrolyte components. Consumption of electrolyte or drying of the cell and or loss of lithium results in accelerated capacity fade.

Lithium has an extremely high theoretical specific capacity of 3860 mAh g⁻¹ and ...