Realizing Formation and Decomposition of Li2O2 on Its Own Surface with a Highly Dispersed Catalyst for High Round-Trip Efficiency Li-O2 Batteries

Li-Na Song,Lian-Chun Zou,Xiao-Xue Wang,Nan Luo,Ji-Jing Xu,Ji-Hong Yu

doi:10.1016/j.isci.2019.03.013

Abstract

SummaryThe rapid and effective formation and decomposition of Li2O2 during cycling is crucial to solve the problems associated with the practical limitation of lithium-oxygen (Li-O2) batteries. In this work, a highly dispersed electrocatalyst with Ru nanoclusters inside the special organic molecular cage (RuNCs@RCC3) through a reverse double-solvent method for Li-O2 batteries has been proposed for the first time. This RuNCs@RCC3 shows an effective catalyst enabling reversible formation and decomposition of the Li2O2 at the interface between the Li2O2 and the liquid electrolyte, rather than the sluggish solid-solid interface reactions on commonly used solid catalysts. As a result, the Li-O2 cells with RuNCs@RCC3 show enhanced electrochemical performance, including low overpotential (310 mV at a current density of 100 mA g−1), high specific capacity (15,068 mAh g−1), good rate capability (1,800 mAh g−1 at a current density of 2.8 A g−1), and especially superior cycle stability up to 470 cycles.

Highlights

Rechargeable lithium-oxygen (Li-O2) batteries can provide a theoretical energy density of 3,600 Wh kgÀ1, delivering five times the energy density of the state-of-the-art Li-ion batteries, which are promising for electric vehicle applications (Asadi et al, 2018; Gallant et al, 2013; Xu et al, 2017)
RCC3 can be synthesized by reducing CC3R to the corresponding dodecaamine cage RCC3 using NaBH4 with an yield close to 100% (Briggs and Cooper, 2017), which is further confirmed by Fourier transform infrared spectroscopy (FTIR, Figures S2 and 2D), 1H and 13C nuclear magnetic resonance (NMR) spectroscopy (Figures 2I, S3, and S4), mass spectrum (Figure S5), and elemental analysis (Table S1) (Liu et al, 2014a, 2014b)
CH2Cl2 molecules were encapsulated in RCC3 cages by the reverse double-solvent approach to disperse the Ru nanoclusters (RuNCs)@RCC3 in the electrolyte

Summary

Introduction

Rechargeable lithium-oxygen (Li-O2) batteries can provide a theoretical energy density of 3,600 Wh kgÀ1, delivering five times the energy density of the state-of-the-art Li-ion batteries, which are promising for electric vehicle applications (Asadi et al, 2018; Gallant et al, 2013; Xu et al, 2017). The discharge capacity and the rate capability have been effectively improved, the slow kinetics of the large insoluble Li2O2 decomposition during charge is still a daunting challenge, and more effort is needed. The insoluble Li2O2 particles covering the solid catalysts’ surface during discharging could lead to the degradation of the cathode due to the toxic effect on the catalyst. It would cause voltage polarization and slow the electrochemical kinetics at the solid (Li2O2)-solid catalyst interface with rare reaction sites during discharge/charge (Chang et al, 2017).

Methods

Results

Conclusion