LiPAA with Short-chain Anion Facilitating Li₂S_x (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 Li₂S_x (x ≤ 4) reduction contributes most. In the same time, the reversibility of electrochemical reduction/oxidation is improved. Owing to the accelerated Li₂S_x (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 μL 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.