Improving the Electrochemical Stability of a Polyester–Polycarbonate Solid Polymer Electrolyte by Zwitterionic Additives

Abstract

Rechargeable batteries with solid polymer electrolytes (SPEs), Li-metal anodes, and high-voltage cathodes like LiNi x Mn y Co z O 2 (NMC) are promising next-generation high-energy-density storage solutions. However, these types of cells typically experience rapid failure during galvanostatic cycling, visible as an incoherent voltage noise during charging. Herein, two imidazolium-based zwitterions, with varied sulfonate-bearing chain length, are added to a poly(ε-caprolactone- co -trimethylene carbonate):LiTFSI electrolyte as cycling-enhancing additives to study their effect on the electrochemical stability of the electrolyte and the cycling performance of half-cells with NMC cathodes. The oxidative stability is studied with two different voltammetric methods using cells with inert working electrodes: the commonly used cyclic voltammetry and staircase voltammetry. The specific effects of the NMC cathode on the electrolyte stability is moreover investigated with cutoff increase cell cycling (CICC) to study the chemical and electrochemical compatibility between the active material and the SPE. Zwitterionic additives proved to enhance the electrochemical stability of the SPE and to facilitate improved galvanostatic cycling stability in half-cells with NMC by preventing the decomposition of LiTFSI at the polymer–cathode interface, as indicated by X-ray photoelectron spectroscopy (XPS).

Alternatives to fluorinated binders: recyclable copolyester/carbonate electrolytes for high-capacity solid composite cathodes

“…This could be attributed to the TFSI anion forming unstable interphases with the cathode. 68,69 Further detailed investigations of this inorganic chemistry will form the focus of subsequent work. Regardless, this high cycling stability with LiFSI whilst still delivering a good initial capacity (183 mA h g −1 ) is promising.…”

Applications of Zwitterions and Zwitterionic Polymers for Li‐Ion Batteries

“…The effect of zwitterions on the maintenance of the chargedischarge capacity found in low-molecular-weight electrolyte systems was also reported in cells using polymers as electrolytes. [26,28,29,33,54] For example, two imidazolium-based zwitterions with different spacer chain length between cation and anion, Z11 and Z24, were added to a poly(ɛ-caprolactone-co-trimethylene carbonate)/(P9)/LiTFSA electrolyte to investigate their effect on the electrochemical stability of the electrolyte and the cycling performance of half-cells with a LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NCM111) cathode. [54] The concentra-tion of each zwitterion was 1.5 wt%, which is the saturated concentration of Z11 with a shorter spacer chain in P9/ LiTFSA.…”

“…[26,28,29,33,54] For example, two imidazolium-based zwitterions with different spacer chain length between cation and anion, Z11 and Z24, were added to a poly(ɛ-caprolactone-co-trimethylene carbonate)/(P9)/LiTFSA electrolyte to investigate their effect on the electrochemical stability of the electrolyte and the cycling performance of half-cells with a LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NCM111) cathode. [54] The concentra-tion of each zwitterion was 1.5 wt%, which is the saturated concentration of Z11 with a shorter spacer chain in P9/ LiTFSA. The inclusion of Z11 resulted in improved electrochemical stability compared to Z24.…”

Charting the course to solid‐state dual‐ion batteries

“…343,[353][354][355][356][357][358] Further improvement in the anodic stability of SPEs can be achieved using electrolyte additives and by surface coating of the graphite particles to generate stable CEI layers. [359][360][361][362][363][364][365] Solving these critical issues in SPEs will be a challenge worth pursuing.…”

“…In principle, fluorinated polymers such as PVdF, and nitrile‐containing should be able to extend the anodic stability of SPEs, as long as they can dissolve sufficiently high salt fraction 343,353‐358 . Further improvement in the anodic stability of SPEs can be achieved using electrolyte additives and by surface coating of the graphite particles to generate stable CEI layers 359‐365 . Solving these critical issues in SPEs will be a challenge worth pursuing.…”