Atomic-scale regulation of anionic and cationic migration in alkali metal batteries

Pan Xiong,Javad Safaei,Zongwen Liu,Takayoshi Sasaki,Yunyan Wu,Xiuyun Zhang,Yifan Liu,Guoxiu Wang,Renzhi Ma,Junwu Zhu,Shijian Wang,Xin Wang,Bing Sun,Yoshio Bando,Fan Zhang

doi:10.1038/s41467-021-24399-9

Abstract

The regulation of anions and cations at the atomic scale is of great significance in membrane-based separation technologies. Ionic transport regulation techniques could also play a crucial role in developing high-performance alkali metal batteries such as alkali metal-sulfur and alkali metal-selenium batteries, which suffer from the non-uniform transport of alkali metal ions (e.g., Li+ or Na+) and detrimental shuttling effect of polysulfide/polyselenide anions. These drawbacks could cause unfavourable growth of alkali metal depositions at the metal electrode and irreversible consumption of cathode active materials, leading to capacity decay and short cycling life. Herein, we propose the use of a polypropylene separator coated with negatively charged Ti0.87O2 nanosheets with Ti atomic vacancies to tackle these issues. In particular, we demonstrate that the electrostatic interactions between the negatively charged Ti0.87O2 nanosheets and polysulfide/polyselenide anions reduce the shuttling effect. Moreover, the Ti0.87O2-coated separator regulates the migration of alkali ions ensuring a homogeneous ion flux and the Ti vacancies, acting as sub-nanometric pores, promote fast alkali-ion diffusion.

Highlights

The regulation of anions and cations at the atomic scale is of great significance in membranebased separation technologies
Multiple obstacles associated with both S and Se cathodes and alkali metal anodes have severely hindered their practical applications, especially the unwanted shuttle effect of soluble polysulfide/polyselenide (PS) intermediates and the formation of alkali metal dendrites, which originate from the uneven migration of PS anions and alkali metal cations[8,9,10]
The small cations can pass, while large anions are selectively excluded based on a size-sieving effect and electrical interaction between ions and membrane. b 2D nanosheets with sub-nanometer pores act as selective ionic sieves in alkali metal-S/Se batteries

Summary

Introduction

The regulation of anions and cations at the atomic scale is of great significance in membranebased separation technologies. At the anode side of alkali metal batteries (Fig. 1c), the negatively charged nanosheets offer strong electrostatic interaction for the efficient adhesion and homogeneous distribution of Li+/Na+ ion flux, resulting in reducing the growth of Li/Na metal deposition with adverse morphologies. The surface area mass loading and thickness of the Ti0.87O2 functional layers in the resultant Ti0.87O2/PP separator can be conveniently controlled by directly adjusting the volume of the nanosheet suspensions used in the vacuum filtration process.

Results

Conclusion