RESUMEN
The "solvent-in-salt" electrolytes for an aqueous system, including "water-in-salt" electrolytes and "bisolvent-in-salt" electrolytes, have shown significantly improved electrochemical stability toward low-voltage anodes and high-voltage cathodes. However, the heavy use of salt raises concerns of high cost, high viscosity, inferior wettability, and poor low-temperature performance. Herein, a "localized bisolvent-in-salt electrolyte" is proposed by introducing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) as the diluent to the high-concentration water/sulfolane hybrid (BSiS-SL) electrolytes, forming a ternary solvent-based electrolyte, Li(H2O)0.9SL1.3·TTE1.3 (HS-TTE). The introduction of TTE dilutes the compact ionic clusters, while the original primary Li+ solvation structure remains, and in the meantime, boosts the formation of a robust solid electrolyte interphase. As a result, a wide electrochemically stable window of 4.4 V is achieved. In comparison with the bisolvent BSiS-SL system, the trisolvent HS-TTE electrolyte exhibits a low salt concentration of 2.1 mol kg-1, resulting in drastically reduced viscosity, superb separator wettability, and largely improved low-temperature performance. The constructed 2.5 V Li4Ti5O12/LiMn2O4 cell shows an excellent capacity retention of 80.7% after 800 cycles, and the cell can even work at -30 °C. With these extraordinary advantages, the fundamental designing strategy of the HS-TTE electrolyte developed in this work can promote the practical applications of solvent-in-salt electrolytes.
RESUMEN
Lithium metal is the "holy grail" of anodes, capable of unlocking the full potential of cathodes in next-generation batteries. However, the use of pure lithium anodes faces several challenges in terms of safety, cycle life, and rate capability. Herein, a solution-processable conjugated microporous thermosetting polymer (CMP) is developed. The CMP can be further converted into a large-scale membrane with nanofluidic channels (5-6 Å). These channels can serve as facile and selective Li-ion diffusion pathways on the surfaces of lithium anodes, thereby ensuring stable lithium stripping/plating even at high areal current densities. CMP-modified lithium anodes (CMP-Li) exhibit cycle stability of 2550 h at an areal current density of 20 mA cm-2 . Furthermore, CMP is readily amenable to solution-processing and spray coating, rendering it highly applicable to continuous roll-to-roll lithium metal treatment processes. Pouch cells with CMP-Li as the anode and LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) as the cathode exhibits a stable energy density of 400 Wh kg-1 .
RESUMEN
Sluggish dynamics of polysulfide (LiPS) conversion leads to reduced utilization of active sulfur and rapid capacity decay. Introducing catalysts into lithium-sulfur battery systems is a feasible and imperative strategy to tackle this problem. Previous research studies have mainly been focused on selecting new catalysts and design functional structures to improve performance, and ignoring the interaction between catalysts and their carriers. Herein, by simply fabricating a high-efficiency ZnS quantum dot@graphene nanosheet catalyst (ZnS QD@rGO), we utilized enhanced interfacial electronic interaction to accelerate polysulfide conversion for high energy density Li-S batteries. With the smaller size of ZnS, the interfacial electronic interaction becomes more enhanced, which was evidenced by DFT calculations and XPS experiments. After mixing with sulfur, the electrodes achieved a high capacity of 857.8 mA h g-1 at 1 C and a retention of 91.2% after 300 cycles. Also, a sulfur cathode with a high actual capacity of â¼4.0 mA h cm-2 could be obtained, with no obvious capacity decay within 100 cycles. We believe that this strategy represents a new perspective on designing efficient high-load electrodes for Li-S batteries.
RESUMEN
Lithium-sulfur (Li-S) batteries are strong contenders among lithium batteries due to superior capacity and energy density, but the polysulfide shuttling effect limits the cycle life and reduces energy efficiency due to a voltage gap between charge and discharge. Here, we demonstrate that graphene foam impregnated with single-atom catalysts (SACs) can be coated on a commercial polypropylene separator to catalyze polysulfide conversion, leading to a reduced voltage gap and a much improved cycle life. Also, among Fe/Co/Ni SACs, Fe SACs may be a better option to be used in Li-S systems. By deploying SACs in the battery separator, cycling stability improves hugely, especially considering relatively high sulfur loading and ultralow SAC contents. Even at a metal loading of â¼2 µg in the whole cell, an Fe SAC-modified separator delivers superior Li-S battery performance even at high sulfur loading (891.6 mAh g-1, 83.7% retention after 750 cycles at 0.5C). Our work further enriches and expands the application of SACs catalyzing polysulfide blocking and conversion and improving round trip efficiencies in batteries, without side effects such as electrolyte and electrode decomposition.
