Analysis of the Interphase on Carbon Black Formed in High Voltage Batteries

Reza Younesi,Søren Bredmose Simonsen,Kristina Edström,Ane Sælland Christiansen,Poul Norby,Johan Hjelm,Roberto Scipioni,Duc-The Ngo

doi:10.1149/2.0761507jes

Reza Younesi, Søren Bredmose Simonsen + Show 6 more

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https://doi.org/10.1149/2.0761507jes

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Abstract

Carbon black (CB) additives commonly used to increase the electrical conductivity of electrodes in Li-ion batteries are generally believed to be electrochemically inert additives in cathodes. Decomposition of electrolyte in the surface region of CB in Li-ion cells at high voltages up to 4.9 V is here studied using electrochemical measurements as well as structural and surface characterizations. LiPF6 and LiClO4 dissolved in ethylene carbonate:diethylene carbonate (1:1) were used as the electrolyte to study irreversible charge capacity of CB cathodes when cycled between 4.9 V and 2.5 V. Synchrotron-based soft X-ray photoelectron spectroscopy (SOXPES) results revealed spontaneous partial decomposition of the electrolytes on the CB electrode, without applying external current or voltage. Depth profile analysis of the electrolyte/cathode interphase indicated that the concentration of decomposed species is highest at the outermost surface of the CB. It is concluded that carboxylate and carbonate bonds (originating from solvent decomposition) and LiF (when LiPF6 was used) take part in the formation of the decomposed species. Electrochemical impedance spectroscopy measurements and transmission electron microscopy results, however, did not show formation of a dense surface layer on CB particles.

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Carbon black (CB) are generally thought of being an electrochemically inert additive in cathodes, but few studies have investigated the role of CBs at high voltages and have indicated that CBs exhibit irreversible electrochemical reactions resulting in appreciable irreversible charge capacities.[10,11,12,13,14,15,16,17,18]
Synchrotron-based soft X-ray photoelectron spectroscopy (SOXPES) results revealed that spontaneous decomposition of electrolyte solution (LiPF6 dissolved in EC:DEC) occurs in the surface region of carbon black particles stored in the electrolyte in the absence of external potential and current

Summary

Introduction

Users may download and print one copy of any publication from the public portal for the purpose of private study or research. CBs are generally thought of being an electrochemically inert additive in cathodes, but few studies have investigated the role of CBs at high voltages and have indicated that CBs exhibit irreversible electrochemical reactions resulting in appreciable irreversible charge capacities.[10,11,12,13,14,15,16,17,18] This charge capacity is attributed to oxidation reactions, anodic degradation of aprotic electrolytes on the surface of CBs, side reactions involving binder and salt, and intercalation of anions such as PF6− (partly reversible) and solvent molecules into graphitic layers.[10,11,12,13,14,15,16,17,18,19] The oxidation voltage, decomposition products, and possible formation of a surface layer are dependent on the chemistry of electrolyte and the surface area and the surface functional groups of CBs.[10,11,12,13,14] This is similar, but not identical, to the concept of formation of solid electrolyte interphase (SEI) on anodes. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract)

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