Coordinating Anions “to the Rescue” of the Lithium Ion Mobility in Ternary Solid Polymer Electrolytes Plasticized With Ionic Liquids

Abstract

Lithium salts with low coordinating anions such as bis(trifluoromethanesulfonyl)imide (TFSI) have been the state‐of‐the‐art for polyethylene oxide (PEO)‐based “dry” polymer electrolytes for 3 decades. Plasticizing PEO with TFSI‐based ionic liquids (ILs) to form ternary solid polymer electrolytes (TSPEs) increases conductivity and Li+ diffusivity. However, the Li+ transport mechanism is unaffected compared to their “dry” counterparts and is essentially coupled to the dynamics of the polymer host matrix, which limits Li+ transport improvement. Thus, a paradigm shift is hereby suggested: the utilization of more coordinating anions such as trifluoromethanesulfonyl‐N‐cyanoamide (TFSAM), able to compete with PEO for Li+ solvation, to accelerate the Li+ transport and reach a higher Li+ transference number. The Li–TFSAM interaction in binary and ternary TFSAM‐based electrolytes is probed by experimental methods and discussed in the context of recent computational results. In PEO‐based TSPEs, TFSAM drastically accelerates the Li+ transport (increases Li+ transference number by a factor 6 and the Li+ conductivity by 2–3) and computer simulations reveal that lithium dynamics are effectively re‐coupled from polymer to anion dynamics. Last, this concept of coordinating anions in TSPEs is successfully applied in LFP||Li metal cells leading to enhanced capacity retention (86% after 300 cycles) and an improved rate performance at 2C.

High Dielectric Poly(vinylidene fluoride)‐Based Polymer Enables Uniform Lithium‐Ion Transport in Solid‐State Ionogel Electrolytes

“…This performance is much better than the LFP/PVDF iono‐SPE/Li cell (7.9 %@1000 cycles, Figure 4d and S15b), and even superior to the LFP/LEs/Li cell (74.5 %@1000 cycles, Figure 4d and S15c). Compared to other LFP/iono‐SPE/Li cells reported in the literature, [12, 15, 42–51] the lifespan of our LFP/PTC iono‐SPE/Li cell is among the best. As summarized in Figure 5e and Table S2, the reported LFP/iono‐SPE/Li cells cannot cycle steadily for more than 800 times although some iono‐SPEs show quite high ionic conductivities (such as 1.22×10 −3 S cm −1 at 25 °C, [42] Table S2).…”

Hochdielektrischer Poly(vinylidenfluorid)‐basierter Ionogel‐Feststoffelektrolyt für den gleichmäßigen Lithium‐Ionen‐Transport

“…Diese Leistung ist viel besser als die der LFP/PVDF-Iono-SPE/Li-Zelle (7.9 % @ 1000 Zyklen, Abbildung 4d und S15b) und sogar denen einer LFP/ LEs/Li-Zelle überlegen (74.5 % @ 1000 Zyklen, Abbildung 4d und S15c). Wie in Abbildung 5e und Tabelle S2 zusammengefasst, können die publizierten LFP/iono-SPE/ Li-Zellen nicht stabil für mehr als 800 Zyklen zyklisie-ren, [12,15,[42][43][44][45][46][47][48][49][50][51] obwohl einige iono-SPEs eine relativ hohe ionische Leitfähigkeit aufweisen (wie z. B.…”

“…(c) EIS und (d) Langzeitzyklusleistung bei 1 C und 25 °C von LFP/PTC-Iono-SPE/Li-, LFP/PVDF-Iono-SPE/Li-und LFP/LEs/Li-Zellen. (e) Der Vergleich der Lebensdauer von symmetrischen LFP/PTC-Iono-SPE/Li-Zellen mit denen, die in der Literatur berichtet wurden [12,15,[42][43][44][45][46][47][48][49][50][51]. Langzeitzyklusleistung von (f) LFP/PTC-Iono-SPE/Li-Zellen bei 3 C und 5 C bei 25 °C und (g) NCM811/PTC-Iono-SPE/Li-Zellen bei 0.5 C und 25 °C.…”

A Scalable, Robust Polyvinyl‐Butyral‐Based Solid Polymer Electrolyte with Outstanding Ionic Conductivity for Laminated Large‐Area WO3–NiO Electrochromic Devices

“…[1,2] During ECD operation, electrons and positively charged ions (such as H + , Li + , and Na + ) are concurrently injected into and extracted from an electrochromic material at an externally applied voltage of 1-3 V, resulting in polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, and polymethyl methacrylate, PVB is not an inherently effective ion conductor. [22][23][24] Therefore, the ionic conductivity of PVB must be enhanced to realize a high-performance ECD electrolyte for lamination-related applications. Efforts that have been made in this regard [25][26][27][28][29][30][31][32][33][34] can be roughly classified into two categories (Table S1, Supporting Information).…”

“…However, unlike polymers such as polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, and polymethyl methacrylate, PVB is not an inherently effective ion conductor. [ 22–24 ] Therefore, the ionic conductivity of PVB must be enhanced to realize a high‐performance ECD electrolyte for lamination‐related applications. Efforts that have been made in this regard [ 25–34 ] can be roughly classified into two categories (Table S1, Supporting Information).…”