LiPAA with Short‐chain Anion Facilitating Li₂S_x (x ≤ 4) Reduction in Lean‐electrolyte Lithium–sulfur Battery

Abstract

on demand of high energy density, electrolytewetted interfaces slump. [5,6] Therefore, all interface-dependent processes, especially Li 2 S x (x ≤ 4) reduction, are exacerbated, [7][8][9] and a bluff attenuation of capacity will definitely show up after a few cycles. [10][11][12] In order to promote the electrochemical reactions at leanelectrolyte condition, modulating both transfer pattern and gathering pattern of ions (PS and Li + ) is an indispensable assistance, at least making PS migrate toward cathode preferentially, rather than shuttle.Prelithiation is proved to be effective in Coulombic efficiency increasing [13,14] and resistance decreasing. [12] Thereinto, direct lithium implantation in cathodes facilitates an even lithium dispersion. However, a reaction happened in LSB not only needs lithium enrichment, but also requires the participation of PS. Recent publications point out that O doping [15][16][17] and O vacancies [18,19] are specialized in PS affinities. Moreover, the high electronegativity of O-containing centers endows S cathode with improved electrolyte compatibility. [20,21] Inspired by those scientific results, we propose a strategy to boost LSB running in lean electrolyte. Providing that implanting some O-relevant electrolyte-philic species at sites adjacent to those lithium-contained zones, Li + and PS will appear side by side at one wetted interface and therefore lowering down the dependence of electrochemical reactions on the restricted ion transfer. In this work, direct lithium implant and Ocontaining site introduction are simultaneously realized by one chemical, lithium polyacrylic acid (LiPAA). Results and DiscussionActually, Mukra et al. [22] published a paper about LiPAA as a cathode binder in LSBs. It was synthesized by lithium hydroxide reacting with polyacrylic acid of 450,000 in molecular weight. Thanks to its longchain anion, the resulted LiPAA performs a satisfying substitution of PVDF, deserving function-plus binder for its extra supply of Li + . Comparing its Li 2 S 4 adsorption potential to that of a short-chain LiPAA, specially designed in our research, whose molecular weight is only ~2000 (Figure 1a), it is definite that LiPAA containing short-chain anion wins out, of course, the short-chain PAA do the same thing (Figure S1).

Polymers in Lithium–Sulfur Batteries

“…It is also difficult to achieve a high sulfur loading due to their insufficient adsorption sites. [ 34 ] In addition to the fabrication of sulfur composite cathodes, the modification of binders and design of multifunctional separators, [ 35 ] the introduction of interphases between the cathode and separator, [ 36 ] and the design of solid electrolyte [ 37 ] are also of great importance to suppress the shuttle effect, thereby synergistically improve the electrochemical performance of LSBs.…”