Sustainable Development Goals
Abstract/Objectives
Lithium-ion batteries (LIB) have been one of the most promising energy storage systems. The high energy efficiency of LIBs may also allow their use in various electric grid applications. It will contribute to build an energy-sustainable economy. Transition metal oxides have attracted vast interest in LIBs as an anode material. This is attributed to their higher theoretical capacity than commercial graphite, natural abundance leading to lower cost, environmental friendliness, and high safety. Other than the improvements of electrode materials, an alternative approach is to focus on altering electrolyte compositions, which determines the power density, the battery, reliability, and the formation of the solid electrolyte interface (SEI) layer. In this study, MnO2 powders are used as anode materials for LIBs with four organic electrolyte combinations. Investigate their effects on the electrochemical properties and SEI layer characteristics. The result of this work suggests a better commercial organic electrolyte for LIBs with MnO2 anodes. And facilitates the commercialization of transition metal oxide anodes in LIB applications. source: https://pubs.acs.org/doi/10.1021/acs.jpcc.0c09022
Results/Contributions

In this study, MnO2 powder was used as anode material for Li-ion batteries, combined with four organic electrolytes, including 1 M LiPF6+EC/DEC=1:1 (vol %)、LiPF6+EC/EMC=1:1 (vol %)、LiPF6+EC/DMC/DEC=1:1:1 (vol %)、LiPF6+EC/DEC=1:1 (vol %)+10 wt% FEC. According to the results of the lithium-ion battery charge-discharge cycle, the overall performance from the best to the worst is EC/DEC>EC/DMC/DEC>EC/EMC.

It is speculated that the possibility of the electrolyte solvent tends to decompose in descending order of EC/EMC>EC/DEC/DMC>EC/DEC. From the dQ/dV analysis and cyclic voltammetry analysis results, the reaction potential of MnO2 in each electrolyte does not change significantly. And FEC seems to be able to inhibit the secondary decomposition of the electrolyte.

From the results of electrochemical impedance analysis, the electrolyte has a great influence on the impedance of the SEI layer with long cycles. The impedance from high to low is EC/EMC>EC/DEC/DMC>EC/DEC>EC/DEC+FEC. The SEI layer impedance has a great influence on the cycle stability. The higher the SEI layer impedance, the worse the cycle stability. The results also show that FEC can effectively reduce the SEI layer impedance and improve the cycle stability. It can be seen from the results of chemical analysis electron energy spectrum analysis that the difference in Coulombic efficiency in the first cycle may be related to the relative content of Li2CO3 generated in the SEI layer. FEC will be decomposed into VC in the first cycle and polymerized into carbonic acid polymer. And covers the surface of MnO2 and acts as a buffer layer for the volume expansion of MnO2 to improve cycle performance. In addition, FEC can also prevent the erosion of Li2O in the SEI layer and improve the transport of lithium ions in the SEI layer.

Finally, this study concluded that EC/DEC performed the best, and further addition of FEC could enhance the cyclic capacitance performance of the MnO2 anode, although the effect would be weakened during long cycles. Overall, it is still suitable as an electrolyte for lithium-ion batteries with MnO2 as the anode.

 

source:

https://pubs.acs.org/doi/10.1021/acs.jpcc.0c09022

Keywords
Lithium-ion batteryTransition metal oxideManganese oxideOrganic electrolyteSolid electrolyte interface
References