The Investigation of Electrolyte Oxidation and Film Deposition Characteristics at High Potentials in a Carbonate-Based Electrolyte Using Pt Electrode

Abstract

High voltage positive electrodes for lithium ion batteries have suffered from continuous oxidation of the electrolyte during cycling, which largely offsets the benefits of high energy and power densities. In this work, the electrolyte oxidation and concomitant film deposition/dissolution behaviors were investigated on Pt electrode by using linear sweep voltammetry (LSV), electrochemical quartz crystal microbalance (EQCM), and X-ray photoelectron spectroscopy (XPS). Two characteristics were identified. First, film deposition is relatively unfavorable at higher potentials (>4.7 V vs. Li/Li + ) because the oxidation products are mostly gaseous or soluble species. Second, the concentration of inorganic species decreases in the surface film as the potential increases, which is likely dissolved by HF or polar species. The dominance of gaseous or soluble products and the partial dissolution of the surface film, are two characteristics which hamper passivation of the electrode surface, leading to severe electrolyte oxidation at the high potentials.

Decoupling Interfacial Reactions at Anode and Cathode by Combining Online Electrochemical Mass Spectroscopy with Anode‐Free Li‐Metal Battery

“…Carbonate electrolytes also electrochemically oxidize at the cathode surface above 4.3 V and causes to release gases such as CO 2 and CO at the cathode side. [ 13 ] As a result, the evolved gases due to chemical and electrochemical oxidation of electrolytes at the cathode side cannot be decoupled easily. However, the evolution of O 2 is insignificant in the second and third cycles, and cannot enough to be detectable.…”

“…[ 6–9 ] It has been reported that the interfacial reactions upon charging of Li/NMC and graphite/NMC cells with carbonate electrolytes generate CO 2 , CO, H 2 and C 2 H 4 gases. [ 3,7,9–13 ] Nevertheless, the main source of hydrogen (H 2 ) gas at the early stage of solid–electrolyte‐interphase (SEI) formation is the reduction of residual trace H 2 O at the anode surface with the formula of H 2 O + e − → OH − + ½ H 2 . [ 7,8,14 ]…”

Anodic decomposition of surface films on high voltage spinel surfaces—Density function theory and experimental study

“…1a), which is also suggested for oxidation on Pt surfaces. 16 Electrolytes with fluorinated solvent molecules exhibits increased anodic stability. 7,8 This behavior is not inconsistent with our hypothesis, because CEI formed from fluorinated molecules should also be more stable against oxidation than CEI formed from standard organic battery electrolytes.…”

“…Based on these computational and experimental findings, we adopt an alternative view of high voltage cathode interfacial reactions which has already been suggested for oxidation on Pt surfaces 16 (Fig. 1a).…”

“…5 EC and DMC oxidation has been proposed to lead to formation of thin cathode electrolyte interphase (CEI) films. 1,[6][7][8][9][10][11][12][13][14][15][16][17] While the existence of CEI films on cathode surfaces has long been confirmed at modest voltages, [12][13][14]17 questions remain about the origin of CEI species. 18,19 Although extensive spectroscopic and imaging studies have been conducted, the structure and function of CEI on cathode oxide material surfaces remain poorly understood.…”