LiCoO2/Graphite Cells with Localized High Concentration Carbonate Electrolytes for Higher Energy Density

Xin Ma,Huajun Zhao,Peng Zhang,Shang-Sen Chi,Guangzhao Zhang,Zhongbo Liu,Qingrong Wang,Yunxian Qian,Chaoyang Wang,Jun Wang,Yonghong Deng

doi:10.3390/liquids1010005

Abstract

Widening the working voltage of lithium-ion batteries is considered as an effective strategy to improve their energy density. However, the decomposition of conventional aprotic electrolytes at high voltage greatly impedes the success until the presence of high concentration electrolytes (HCEs) and the resultant localized HCEs (LHCEs). The unique solvated structure of HCEs/LHCEs endows the involved solvent with enhanced endurance toward high voltage while the LHCEs can simultaneously possess the decent viscosity for sufficient wettability to porous electrodes and separator. Nowadays, most LHCEs use LiFSI/LiTFSI as the salts and β-hydrofluoroethers as the counter solvents due to their good compatibility, yet the LHCE formula of cheap LiPF6 and high antioxidant α-hydrofluoroethers is seldom investigated. Here, we report a unique formula with 3 mol L−1 LiPF6 in mixed carbonate solvents and a counter solvent α-substituted fluorine compound (1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether). Compared to a conventional electrolyte, this formula enables dramatic improvement in the cycling performance of LiCoO2//graphite cells from approximately 150 cycles to 1000 cycles within the range of 2.9 to 4.5 V at 0.5 C. This work provides a new choice and scope to design functional LHCEs for high voltage systems.

Highlights

Over the past 30 years, a secondary lithium battery has been developed as a vital energy storage strategy in daily life for its high energy density, environmentally friendly property and excellent cycle capability
All the components for localized HCEs (LHCEs) were stored in a glove box filled with Ar atmosphere
The purpose of counter solvent aims to decrease the viscosity of high concentration electrolytes (HCEs) without any disturb to the solvent shell structure [29,44], which can be proved by simple physical prop

Summary

Introduction

Over the past 30 years, a secondary lithium battery has been developed as a vital energy storage strategy in daily life for its high energy density, environmentally friendly property and excellent cycle capability. The boom of electric vehicles requires battery chemistry with higher power and energy density to afford longer service time under various operating conditions [1,2]. In this regard, two main strategies have been proposed to improve the battery energy density. Silicon/carbon [3,4], silicon [5,6], lithium metal [7,8] and anode free system [9,10] have been comprehensively and intensively investigated. The other method is the increase of the battery operating voltage by charging layered oxides such as lithium cobalt oxide (LiCoO2 , LCO), lithium nickel cobalt manganese oxides to higher cut-off voltage [11], or employing high-voltage cathode

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Results

Conclusion