In situ formation of partially carbonized polyvinylpyrrolidone as a green binder for high-voltage Li-ion battery cathode with improved electrochemical performance

Abstract

We propose the in situ formation of partially carbonized polyvinylpyrrolidone (PC-PVP) as a green binder for high-voltage LiNi0.5Mn1.5O4 (LNMO) cathodes. A mixture of water and ethanol with an equal volume ratio is shown to enable a more uniform dispersion of LNMO particles in the active material matrix with fewer crevices rather than pure water or pure ethanol. Conformal coverage of LNMO with PC-PVP can be achieved through a stepwise thermal process, which not only enhances the electrical conductance of the cathode material but also protects the electrode surface from overreaction with the electrolyte at high voltages. This can be attributed to the coral reef-like structure of the PC-PVP coating layer, which offers abundant electrical contact without sacrificing ion transport pathways. In addition, the specific nitrogen-containing groups of PC-PVP promote ion transport within the electrode. Furthermore, a carbon paper (CP) substrate is introduced as a current collector to support the PC-PVP/LNMO material layer and to establish a good interconnection. Owing to these features, the PC-PVP/LNMO/CP electrode outperforms the PVDF/LNMO/Al counterpart in terms of high-voltage cycling stability and rate capability. The improved electrode performance is supported by the reduced cathode–electrolyte interphase (CEI) resistance, which corresponds to mitigated electrolyte decomposition and stable CEI formation.