Electrochemically Stable, High Transference Number Lithium Bis(malonato)borate Polymer Solution Electrolytes

Abstract

Implementation of next-generation Li-ion batteries based on high-voltage cathodes requires the development of new electrolytes that are stable over wide electrochemical potential windows. High lithium-ion transference number (t Li+) electrolytes, in which most of the ionic current is carried by Li+, offer additional opportunities to improve the efficiencies of such batteries by minimizing unproductive anion motion. Herein, we report the synthesis and characterization of solution electrolytes based on poly­(lithium bis­(nonenylmalonato)­borate) (P­(LiBNMB)) with molecular weights M n = 2.7–55 kg/mol and dispersities Đ = M w/M n = 1.6–3.2. Cyclic voltammetry studies reveal that propylene carbonate (PC) solutions of P­(LiBNMB) are electrochemically stable up to 5.2 V (versus Li/Li+). Electrochemical impedance spectroscopy (EIS) studies indicate that the total ionic conductivities of these P­(LiBNMB)/PC solution electrolytes with [Li+] ≈ 0.10 M are nearly M n-invariant with σ = 0.31–0.39 mS/cm. Complementary ion diffusivity measurements by 1H and 7Li NMR diffusion ordered spectroscopy (DOSY) and potentiostatic polarization also reveal that they exhibit high t Li+ = 0.77–0.98. Thus, semidilute solutions of oligomeric salts comprising as few as 21 monomer units unexpectedly display t Li+ > 0.90 with σ = 0.34 mS/cm.

Transference Number Determination in Poor-Dissociated Low Dielectric Constant Lithium and Protonic Electrolytes

“…The role of the inorganic filler itself as a cation conductivity promotor was studied as well by the same research group [ 160 ]. Copolymer electrolytes [ 161 , 162 , 163 , 164 , 165 ], a crosslinked system based on methoxy compounds [ 155 , 166 , 167 , 168 ], plasticized electrolytes or polymers enhanced by mesoporous ceramic fillers [ 45 , 61 ] were successfully analyzed by Bruce–Vincent method. Reasonable values of transference number were obtained as well for quasi liquid systems like ionic liquids [ 169 , 170 , 171 ] or much more complex systems with porous polymeric membrane enhancing cationic conductivity [ 172 , 173 , 174 ].…”

Organoboron‐Containing Polymer Electrolytes for High‐Performance Lithium Batteries

“…[31] Hence, PEs with high Li + transference number are highly desirable. [26] The Li + transference number of PEs can be increased by incorporating nano-fillers, [32][33][34] single-ion conductors, [35,36] porous materials (MOFs), [37,38] and boron moieties [39][40][41] into the polymer matrixes. Among these strategies, the introduction of boron moieties is a facile and effective scheme to increase the Li + transference number.…”

Impact of Frictional Interactions on Conductivity, Diffusion, and Transference Number in Ether- and Perfluoroether-Based Electrolytes

“…[26][27][28][29]33,[38][39][40][41] Many recent publications emphasize the importance of another transport property, the transference number. 25,29,[42][43][44][45][46][47][48][49] In seminal work in 1987, Bruce and Vincent proposed a simple method for measuring the transference number. 50,51 They recognized that the transference number thus obtained is correct only in the case of ideal dilute electrolytes.…”

“…It is common in the literature, though not universal, 12,43,52 to focus on frictional interactions between the cation and the solvent to explain trends in the cation transference number. By analyzing our data using Newman's concentrated solution theory, we determine that at high salt concentrations, the differences in t 0 + are due to differences in , 0 Dwhich characterizes frictional interactions between the anion and the solvent chain.…”