Abstract
For high-voltage cycling of lithium-ion batteries, a gel polymer Li-ion conductor layer, P(VDF-HFP)/LiTFSI (PHL) with high electrochemical stability has been coated on the surfaces of as-formed LiCoO2 (LCO) cathodes by a solution-casting technique at low temperature. An LCO cathode coated with around 3 μm thickness of the PHL ultrathin membrane, retains 88.4% of its original capacity (184.3 mA h g−1) after 200 cycles in the 3.0–4.6 V range with a standard carbonate electrolyte, while the non-coated one retains only 80.4% of its original capacity (171.5 mA h g−1). The reason for the better electrochemical behaviors and high-voltage cycling is related to the distinctive characteristics of the PHL coating layer that is compact, has highly-continuous surface coverage and penetrates the bulk of LCO, forming an integrated electrode. The PHL coating layer plays the role of an ion-conductive protection barrier to inhibit side reactions between the charged LCO surface and electrolyte, reduces the dissolution of cobalt ions and maintains the structural stability of LCO. Further, the PHL coated LCO cathode is well preserved, compared to the uncoated one which is severely cracked after 200 cycles at a charging cut-off voltage of 4.6 V.
Highlights
For the application of high energy-density lithium-ion batteries (LIBs), it is extremely attractive to research and develop cathode materials with large reversible capacity and high operating voltage.[1,2,3,4,5] Unlike high power-density materials such as LiNi1/ 3Co1/3Mn1/3O2,6,7 lithium cobalt oxide (LCO) still occupies a dominant position in the cathode materials of LIBs, because its advantages of high volumetric energy-density, facile fabrication process and well-balanced electrochemical performance
The electrochemical stability window of PHL gel polymer electrolyte (GPE) and liquid electrolyte (LE) at room temperature was compared by Linear sweep voltammetry (LSV)
The results show that PHL GPE has favorable electrochemical stability, which indicates that PHL GPE is a promising polymer electrolyte for higher voltage LIBs
Summary
For the application of high energy-density lithium-ion batteries (LIBs), it is extremely attractive to research and develop cathode materials with large reversible capacity and high operating voltage.[1,2,3,4,5] Unlike high power-density materials such as LiNi1/ 3Co1/3Mn1/3O2,6,7 lithium cobalt oxide (LCO) still occupies a dominant position in the cathode materials of LIBs, because its advantages of high volumetric energy-density, facile fabrication process and well-balanced electrochemical performance. 55% (a er 80 cycles) 83% (a er 60 cycles) 82% (a er 46 cycles) 33% (a er 200 cycles) 52% (a er 100 cycles) 64% (a er 50 cycles) 88.4% (a er 200 cycles) conducted directly on as-formed LCO cathode, instead of application to LCO powders. Following, based on morphological and structural characterization of the PHL layer-coated LCO cathode, advantageous effects of the PHL coating layer on cycling performance and structural stability of 4.6 V high-voltage LCO are investigated. The results show that the effective ion conductive barrier coating signi cantly enhances the cycling performance and structural stability of the LCO at high cut-off voltage of 4.6 V
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