Investigating the Interfacial Chemistry of Organic Electrodes in Li- and Na-Ion Batteries

Abstract

Organic compounds are increasingly being investigated as electrode materials for Li-or Na-ion batteries. Even though their gravimetric capacity can challenge that of their inorganic counterparts, a number of problems need further attention, not least their chemical and electrochemical stability toward the electrolyte systems. There has been speculation that several of these issues have their origin in the formation of a less stable solid electrolyte interphase (SEI) layer and its evolution during battery cycling. We here present the very first thorough characterization of the organic electrode material SEI layer using hard X-ray photoelectron spectroscopy (HAXPES), for both Li-and Na-based electrodes. Dilithium and disodium benzenediacrylates have been used for battery construction and investigated electrochemically followed by HAXPES measurements after contact with the electrolyte and after cycling. The Na-based electrodes react spontaneously with the electrolyte, and the SEI layer is dominated by inorganic species with continuous salt degradation during cycling. The Li-based electrodes display an SEI layer with primarily organic species from solvent degradation products appearing only after cycling and increasing in amount with the number of electrochemical cycles.

Electrolytes, SEI Formation, and Binders: A Review of Nonelectrode Factors for Sodium‐Ion Battery Anodes

“…Additionally, the Na‐based SEI eschewed the long (CH 2 ) x  hydrocarbon chains found in the Li‐based SEI, instead of favoring carbonates, and other‐CO rich species, which could explain for the formation of a thicker, and more homogeneous SEI layer. A later study by Brandell and co‐workers confirmed the findings of the thicker, more homogenous SEI layer, showing that the Na SEI contains a significantly higher content of inorganic components, as compared to the Li‐based SEI, which has a higher concentration of organic components . This suggests two things: first, that the Li‐based environment is less reactive, as the SEI is still composed of organic solvent molecules.…”

“…A later study by Brandell and co-workers confirmed the findings of the thicker, more homogenous SEI layer, showing that the Na SEI contains a significantly higher content of inorganic components, as compared to the Li-based SEI, which has a higher concentration of organic components. [79] This suggests two things: first, that the Li-based environment is less reactive, as the SEI is still composed of organic solvent molecules. Additionally, it also suggests that the Na counter electrode used in the experiment may play an outsized role in the formation of the SEI, as side reactions between the Na counter electrode and the electrolyte would explain the shift towards a more inorganic SEI layer.…”

Improvement of the Cycle Performance of LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4 </sub> Cathode Active Materials by In-Situ Coating with Poly(3,4-Ethylenedioxythiophene)

“…Rechargeable lithium-ion batteries are now expected to put into use in hybrid electric vehicles (HEVs) and electric vehicles (EVs) [1] [2]. Unfortunately, the specific energy density of the present commercialized lithium-ion battery can hardly meet the requirements for practical applications [3].…”

An Ionic Liquid/Poly(vinylidene fluoride‐co‐hexafluoropropylene) Gel‐Polymer Electrolyte with a Compatible Interface for Sodium‐Based Batteries

“…After 100 cycles, the Rct value remained stable at 402.7 Ω. From Figure S7, Supporting Information, the F1s peaks at NaF (684.2 eV), [43] TFSI (687.9 eV), and CÀ F 2 (688.9 eV) indicate that NaÀ F and NaÀ FÀ IL species are present. After 100 cycles, the Rct value remained stable at 551.2 Ω.…”