XPS study on the STOBA coverage on Li(Ni_0.4 Co_0.2 Mn_0.4 )O₂ oxide in pristine electrodes

Abstract

The additive of self-terminated oligomers with hyper-branched architecture (STOBA) in Li(Ni 0.4 Co 0.2 Mn 0.4 )O 2 (LNCM) cathodes of lithium ion batteries improves the battery stability and capacity. In this study, the surface chemistry of pristine LNCM electrodes with and without the STOBA additive was analyzed by means of X-ray photoelectron spectroscopy and the surface morphology was observed by scanning electron microscopy. It was found that STOBA covers LNCM particles uniformly and the formation of chemical bonding between nitrogen atoms in STOBA and metallic atoms in LNCM was discovered. This bonding may cause the uniform coverage of STOBA on LNCM. The formation of STOBA layer on LNCM improves the coverage of the binder poly(vinylidene fluoride) and inhibits the formation of LiF. KEYWORDS cathode, Li(Ni 0.4 Co 0.2 Mn 0.4 )O 2 , lithium ion batteries, STOBA, XPS 1 | INTRODUCTION The performance of lithium ion batteries (LIBs) like conductivity and stability depends on the surface chemistry of electrodes. Additives in electrodes of LIBs play essential roles in controlling the surface chemistry. 1,2 For example, poly(vinylidene fluoride) (PVDF), one of the most important adhesives, 3 is commonly added into LIB cathodes to enhance the connection between active particles. The C─F ionic bonds in PVDF has evident dipole configuration that induces a strong intermolecular van der Waals force. The improved connection leads to better electrical and ionic conductivities. The investigation of the chemical state of atoms on the surface of electrodes with some additive is essential for inferring the cause of effect of the additive on the performance of LIBs.Just recently, a kind of chemicals called self-terminated oligomers with hyper-branched architecture (STOBA) 4 added in cathodes was found to promisingly enhance the safety of LIBs. [5][6][7] However, no study has been reported on the STOBA coverage on the electrodes. Recently, we have chemically analyzed the surface of Li(Ni 0.4 Co 0.2 Mn 0.4 )O 2 (LNCM) pristine cathodes without and with STOBA additive by means of X-ray photoelectron spectroscopy (XPS). In this paper, we report these results, compare them with SEM observations, and discuss the effects of PVDF and STOBA additives on the surface coverage of LNCM cathodes. | EXPERIMENTAL PROCEDURESThe LNCM cathodes were prepared using the following procedures and were handled in an oxygen-free glove box with an oxygen limit of 10 ppm. For cathodes without STOBA (LNCM + PVDF), LNCM powder produced by Industrial Technology Research Institute (ITRI) and PVDF (produced by KUREHA Chemical) were mixed in N-methyl pyrolidine (NMP) solvent. The suspension was stirred for 15 minutes.Conductive agents including KS6 (graphite plates, TIMCAL) and super P (carbon black particles, TIMCAL) were added to the suspension and stirred a further 15 minutes. The mass percentages of LNCM, PVDF, and conductive agents are 89%, 4%, and 7%, respectively. The mixed cathode slurry was coated on aluminum substrates and dried. For the cathode with t...

XPS Analysis of K-based Reference Compounds to Allow Reliable Studies of Solid Electrolyte Interphase in K-ion Batteries

“…Commonly used electrode additives (binders and carbon black) have also been reported for information (grey-color), based on previous work. 23,[25][26][27][28][29]…”

“…Figure thus summarizes the relative (red-written labels) and absolute (values read on axes) binding energies for the KIB electrolyte salts (in yellow) and the K-based reference compounds (organic in blue and inorganic in orange), as obtained in this work. Commonly used electrode additives (binders and carbon black) have also been reported for information (gray color), based on previous work. ,− …”

Interface Interaction Behavior of Self-Terminated Oligomer Electrode Additives for a Ni-Rich Layer Cathode in Lithium-Ion Batteries: Voltage and Temperature Effects

“…The reflection intensity of the modified electrodes decreased considerably compared with that of bare NMC622, which is ascribed to the interaction between oligomers and NMC622. As reported in a previous study, oligomers react with active materials and form −N–TM– bonds (TM stands for transition metal). In addition, during the treatment of the active material with organic additives, the TM encapsulates the free electrons from O and N and is oxidized. , Consequently, the TM (especially Ni 2+ and Ni 3+ in bare NMC) is oxidized to a higher valence through the reaction with the free radical (−C–O – ) generated from −CO– of the imide group.…”