High‐Performance Li‐O₂ Batteries Enabled by Dibenzo‐24‐Crown‐8 Aldehyde Derivative as Electrolyte Additives

Abstract

Aprotic Li‐O2 batteries (LOB) with high theoretical energy density usually experience cathode clogging by insoluble Li2O2, along with high charge overpotential from its insulating nature. A dibenzo‐24‐crown‐8 aldehyde derivative (DB24C8A) is employed as an additive to enhance the binding strength with Li+, hence promoting the solubility of Li2O2. The generated [DB24C8A•Li+] avoids the parasitic reactions caused by reactive O2−. Thus, the LOB achieves a large discharge capacity of 6939 mAh g−1 at 200 mA g−1 and a high Li2O2 yield (≈93%). Moreover, DB24C8A facilitates the efficient decomposition of Li2O2 via Li+ coordination during the charge process, reducing the charge overpotential to 0.77 V and prolonging the lifetime of the LOB over 213 cycles at 1000 mAh g−1 and 500 mA g−1. This work provides a novel approach to boost the performance of LOB by incorporation of crown ether‐based compounds to regulate the Li2O2 growth and decomposition pathway.

Enhancing the Reaction Kinetics and Reversibility of Li–O2 Batteries by Multifunctional Polymer Additive

“…An illustration of fitting equivalent circuit is represented as the inset. Much lower charge transfer impedance value (R ct ) with PTFEMA-contained electrolyte (136 Ω; base electrolyte: 165 Ω) after 20 cycles supports an accelerated charge transfer and enhanced electrochemical kinetic in Li-O 2 cell, [6,36] which is consistent with the experimental and analytical results of enhanced OER process (Figures 2g and 3d,e). The accumulation of incompletely decomposed Li 2 O 2 product and poor conductivity of side products (such as Li 2 CO 3 ) on the cathode side can result in the passivation of GDL and growth of charge-transfer resistance, causing an increased chargetransfer impedance in EIS plot.…”

“…A negative adsorption energy value (∆ E ad = −7.8 eV) of optimized GDL‐PTFEMA structure can be obtained (Figure 2b), which indicates not only thermodynamic feasibility but also strong adsorption behavior between GDL and PTFEMA (GDL‐PTFEMA). [ 19,36 ] The negative adsorption energy (∆ E ad = −0.89 eV) of the PTFEMA‐Li + complex further confirms the ability of PTFEMA to solvate Li + (Figure 2c). PTFEMA molecules dissolved in the electrolyte can be uniformly adsorbed on the GDL substrate due to the strong interaction.…”

“…[34,35] As the mass fraction of PTFEMA in base electrolyte increases, a downfield shift can be observed, indicating a weak shielding effect on Li + . [36] It confirms the solvability of PTFEMA to Li + . DFT calculation by Vienna ab-initio simulation package (VASP) was then conducted to deeply explore the interaction between PTFEMA and Li + .…”

“…The accumulation of incompletely decomposed Li 2 O 2 product and poor conductivity of side products (such as Li 2 CO 3 ) on the cathode side can result in the passivation of GDL and growth of charge-transfer resistance, causing an increased chargetransfer impedance in EIS plot. [36,39,41] Hence, PTFEMA-present Li-O 2 cell with low R ct value also implies good reversibility of Li 2 O 2 and by-product accumulation suppression during cycling. 1 H NMR spectra measurement of D 2 O-extracted cathodic plate and separator from corresponding cycled Li-O 2 cell (20 cycles) is further carried out to investigate possible byproducts during cycling.…”

Lithium Salt Dissociation Promoted by 18‐Crown‐6 Ether Additive toward Dilute Electrolytes for High Performance Lithium Oxygen Batteries

“…The most obvious promotion effect was observed in cell with the 100‐18C6 electrolyte. Moreover, the oxidation peak ascribed to electrolyte or KB cathode decomposition shifted to higher potential of 4.438 V in cell with 100‐18C6 electrolyte, compared with 4.371 V in the cell without additive, indicating the broadened electrochemical stability of 100‐18C6 electrolyte [17] . Figure 2k shows the EIS results of cells with 100‐18C6 electrolyte after first discharging and charging.…”