LiPAA with Short-chain Anion Facilitating Li2Sx (x ≤ 4) Reduction in Lean-electrolyte Lithium-sulfur Battery

Lean electrolyte usage in lithium-sulfur battery (LSB) meets the demand of the high energy density. However, lean condition makes the electrolyte-related interface discrete, leading to retardation of ion transfer that depends on interfaces. Consequently, electrochemical reactions face restraint. Herein, lithium polyacrylate acid (LiPAA) with short-chain anions (molecular weight of 2000) is introduced into the cathode. Because of the polysulfide (PS)-philic instinct of the short-chain PAA anions, short-chain PS is captured inside of the cathode. In addition, LiPAA supplies Li+ to the short-chain PS captured. The strong interaction between Li2S4 and LiPAA effectively decreases Li2S4 migration to the anode during discharging. In a sense, the ion mass transfer pattern is thus changed comparing to traditional long-way mode between cathode and anode. Galvanostatic intermittent titration technique (GITT) proves that the interfacial reaction resistance is greatly decreased in the region where Li2Sx (x <= 4) reduction contributes most. In the same time, the reversibility of electrochemical reduction/oxidation is improved. Owing to the accelerated Li2Sx (x <= 4) reduction, Li implanting of only 0.3 wt.% plus O introduction up to 1.4 wt.% enables the LSB perform well even with 1/4 of regular electrolyte dosage (5 mu L mg(-1)) and high-sulfur loading (4.2 mg cm(-2)), increasing its rate capacity C-0.8/0.5 from 52.6% (without the LiPAA) to 92.3% (with the LiPAA) as well as a capacity of 518.7 mAh g(-1) after 400 cycles at 0.8 mA cm(-2).

Automated summary

In this study, the introduction of LiPAA anions into the cathode of lithium-sulfur batteries successfully addressed the issue of ion transfer limitations, as well as improving the reversibility of electrochemical reduction/oxidation. The new electrolyte design not only accelerated sulfur reduction, but also allowed the LSB to perform well under reduced electrolyte dosage and high sulfur loading conditions.