Negative differential resistance as a critical indicator for the discharge capacity of lithium-oxygen batteries

Yoko Hase,Takashi Harada,Yasuhiro Komori,Shuji Nakanishi,Takayoshi Kusumoto,Kazuhide Kamiya,Tohru Shiga,Juntaro Seki

doi:10.1038/s41467-019-08536-z

Abstract

In non-aqueous lithium-oxygen batteries, the one-electron reduction of oxygen and subsequent lithium oxide formation both occur during discharge. This lithium oxide can be converted to insulating lithium peroxide via two different pathways: a second reduction at the cathode surface or disproportionation in solution. The latter process is known to be advantageous with regard to increasing the discharge capacity and is promoted by a high donor number electrolyte because of the stability of lithium oxide in media of this type. Herein, we report that the cathodic oxygen reduction reaction during discharge typically exhibits negative differential resistance. Importantly, the magnitude of negative differential resistance, which varies with the system component, and the position of the cathode potential relative to the negative differential resistance determined the reaction pathway and the discharge capacity. This result implies that the stability of lithium oxide on the cathode also contributes to the determination of the reaction pathway.

Highlights

IntroductionIn the case that the equilibrium lies to the left, the LiO2* can undergo a second reduction to form insulating Li2O2 on the cathode surface (known as the surface pathway): LiOÃ2 þ Liþ þ eÀ ! Li2O2: ð4Þ
In the case that the equilibrium lies to the left, the LiO2* can undergo a second reduction to form insulating Li2O2 on the cathode surface: LiOÃ2 þ Liþ þ eÀ ! Li2O2: ð4Þ
The Gutmann donor number (DN) of the solvent, which is an index of Lewis basicity, is an important factor affecting the equilibrium, and it has been reported that there is a positive correlation between the discharge capacity and the DN value of the solvent[29]

Summary

Introduction

In the case that the equilibrium lies to the left, the LiO2* can undergo a second reduction to form insulating Li2O2 on the cathode surface (known as the surface pathway): LiOÃ2 þ Liþ þ eÀ ! Li2O2: ð4Þ. Kwabi et al reported that the cathode potential is another important factor that determines the equilibrium[37] Considering these results, it is evident that the main parameters that decide between the solution pathway and the surface pathway have not yet been elucidated. In the case of the system with large NDR, the discharge capacity is found to change dramatically as the positional relationship between NDR and the discharge potential is varied This result suggests that it appears that the adsorption/desorption of the inhibitor is closely related to the stability of LiO2* on the cathode. These findings provide valuable insights regarding the importance of the stability of LiO2* in determining the discharge properties of Li–O2 batteries

Methods

Results

Conclusion