Construction of solid-liquid fluorine transport channel to enable highly reversible conversion cathodes

Keyi Chen; Meng Lei; Zhenguo Yao; Yongjian Zheng; Jiulin Hu; Chuanzhong Lai; Chilin Li

doi:10.1126/sciadv.abj1491

Construction of solid-liquid fluorine transport channel to enable highly reversible conversion cathodes

Sci Adv. 2021 Nov 5;7(45):eabj1491. doi: 10.1126/sciadv.abj1491. Epub 2021 Nov 3.

Authors

Keyi Chen^{1

2

3}, Meng Lei^{1

3}, Zhenguo Yao^{1

2}, Yongjian Zheng^{1

2

3}, Jiulin Hu^{1

2

3}, Chuanzhong Lai^{1

2

3}, Chilin Li^{1

2

3}

Affiliations

¹ State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 585 He Shuo Road, Shanghai 201899, China.
² Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.
³ CAS Key Laboratory of Materials for Energy Conversion, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201899, China.

Abstract

Conversion-type iron fluoride is a promising alternative cathode to intercalation oxides because of its higher energy density. However, its intrinsic solid-solid conversion is sluggish during repeated splitting and rebonding of metal-fluorine moieties. Here, we propose a solid-liquid conversion mechanism to activate the fluorine transport kinetics of iron oxyfluorides enabled by fluoride anion receptor of tris(pentafluorophenyl)borane (TPFPB). TPFPB promotes the dissociation of inert lithium fluoride and provides a facile fluorine transport channel at multiphase interfaces via the formation of solvated F⁻ intermediate therein. The construction of solid-liquid channel with fluorinated cathode electrolyte interface is the key for the achievement of FeO_0.3F_1.7 and FeO_0.7F_1.3 in terms of sustaining conversion reaction (with an energy efficiency approaching 80%) and high-rate performance (with reversible capacity of 320 mAh/g at 2 A/g). The cathode energy densities can reach 1100 Wh/kg for FeO_0.3F_1.7 and 700 Wh/kg for FeO_0.7F_1.3 under the power densities of 220 and 4300 W/kg, respectively.