Altering the Electrochemical Pathway of Sulfur Chemistry with Oxygen for High Energy Density and Low Shuttling in a Na/S Battery

In this work, we demonstrate that intrinsically altering the reaction pathway of a sulfur-based cathode with designed additional redox activities could simultaneously suppress polysulfide shuttling and enhance energy density. A new hybrid sulfur–oxygen chemistry was described for room-temperature Na/S batteries, where the solvated sodium–oxygen reaction in the electrolyte redirected the cathode chemistry via the formation of NaO2–Na2Sn (1n ≤ 4) clusters at the nanoscale. These intermediate oxy-sulfur species serve as an effective mediator to immobilize the polysulfide species and unlock high specific capacity from the hybrid cathode. This new cathode chemistry delivers a high reversible capacity of over 1400 mA h/g, low overpotential (∼250 mV), and stable cycling performance (over 800 mA h/g after 50 cycles). The judicious hybridization of oxygen and sulfur chemistries has resolved the persistent degradation that has been plaguing all sulfur-based cathodes and enabled a high energy and reversible Na/S battery at room temperature

Altering the Electrochemical Pathway of Sulfur Chemistry with Oxygen for High Energy Density and Low Shuttling in a Na/S Battery

In this work, we demonstrate that intrinsically altering the reaction pathway of a sulfur-based cathode with designed additional redox activities could simultaneously suppress polysulfide shuttling and enhance energy density. A new hybrid sulfur–oxygen chemistry was described for room-temperature Na/S batteries, where the solvated sodium–oxygen reaction in the electrolyte redirected the cathode chemistry via the formation of NaO2–Na2Sn (1n ≤ 4) clusters at the nanoscale. These intermediate oxy-sulfur species serve as an effective mediator to immobilize the polysulfide species and unlock high specific capacity from the hybrid cathode. This new cathode chemistry delivers a high reversible capacity of over 1400 mA h/g, low overpotential (∼250 mV), and stable cycling performance (over 800 mA h/g after 50 cycles). The judicious hybridization of oxygen and sulfur chemistries has resolved the persistent degradation that has been plaguing all sulfur-based cathodes and enabled a high energy and reversible Na/S battery at room temperature

Altering the Electrochemical Pathway of Sulfur Chemistry with Oxygen for High Energy Density and Low Shuttling in a Na/S Battery

In this work, we demonstrate that intrinsically altering the reaction pathway of a sulfur-based cathode with designed additional redox activities could simultaneously suppress polysulfide shuttling and enhance energy density. A new hybrid sulfur–oxygen chemistry was described for room-temperature Na/S batteries, where the solvated sodium–oxygen reaction in the electrolyte redirected the cathode chemistry via the formation of NaO2–Na2Sn (1n ≤ 4) clusters at the nanoscale. These intermediate oxy-sulfur species serve as an effective mediator to immobilize the polysulfide species and unlock high specific capacity from the hybrid cathode. This new cathode chemistry delivers a high reversible capacity of over 1400 mA h/g, low overpotential (∼250 mV), and stable cycling performance (over 800 mA h/g after 50 cycles). The judicious hybridization of oxygen and sulfur chemistries has resolved the persistent degradation that has been plaguing all sulfur-based cathodes and enabled a high energy and reversible Na/S battery at room temperature

High-Efficiency Zinc-Metal Anode Enabled by Liquefied Gas Electrolytes

The practical applications of rechargeable zinc metal batteries are prevented by poor Zn reversibility, which induces both inferior Coulombic efficiency (CE) and zinc dendrite growth that worsens at low temperatures because of deteriorated kinetics in both charge and mass transfer. Herein, a liquefied gas electrolyte based on a mixture of fluoromethane and difluoromethane is demonstrated, which displays an excellent conductivity (>3.4 mS cm–1) across a broad temperature range (−60 to +20 °C) and enables highly reversible Zn cycling with no evidence of shorting behavior at both room temperature and −20 °C for over 200 cycles (>400 h) with an average CE of >99.3% and 20% Zn utilization per cycle. Density functional theory calculations showed that such improvements benefited from a ZnF2-enriched interphase formed on the anode because of decomposition of the liquefied gas electrolyte. This electrolyte was verified in a Zn||Na2V6O16·1.63H2O cell with stable performance, where a similar ZnF2-rich interphase was also confirmed

Toward Unraveling the Origin of Lithium Fluoride in the Solid Electrolyte Interphase

The solid electrolyte interphase (SEI) is an integral part of Li-ion batteries and their performance, representing the key enabler for reversibility and also serving as a major source of capacity loss and dictating the cell kinetics. In the pervasive LiPF6-containing electrolytes, LiF is one of the SEI’s major components; however, its formation mechanism remains unclear. Electrochemically, two separate reduction pathways could lead to LiF, either via direct anion reduction or electrocatalytic transformation of HF. This work aims to shed light on understanding the role played by these pathways. In a multimodal experimental and theoretical approach, we carried out operando structural characterization on an inert model single crystalline N-doped SiC working electrode during voltammetric scans in LiPF6 baseline electrolytes and complemented these with ex situ chemical characterization. These results were supplemented by cyclic voltammetry measurements using a variety of electrolyte formulations under different cycling rates as well as quantum chemical calculations and Born–Oppenheimer molecular dynamics simulations. Our results reveal that the reductive formation of LiF in these systems is likely a combined mechanism, which concomitantly involves both direct anion reduction and electrocatalytic transformation of HF. Specifically, LiF nucleates via the electrocatalytic transformation of HF followed by significant anion reduction

Localized Hydrophobicity in Aqueous Zinc Electrolytes Improves Zinc Metal Reversibility

The rechargeability of aqueous zinc metal batteries is plagued by parasitic reactions of the zinc metal anode and detrimental morphologies such as dendritic or dead zinc. To improve the zinc metal reversibility, hereby we report a new solution structure of aqueous electrolyte with hydroxyl-ion scavengers and hydrophobicity localized in solvent clusters. We show that although hydrophobicity sounds counterintuitive for an aqueous system, hydrophilic pockets may be encapsulated inside a hydrophobic outer layer, and a hydrophobic anode–electrolyte interface can be generated through the addition of a cation-philic, strongly anion-phobic, and OH–-reactive diluent. The localized hydrophobicity enables less active water and less absorbed water on the Zn anode surface, which suppresses the parasitic water reduction; while the hydroxyl-ion-scavenging functionality further minimizes undesired passivation layer formation, thus leading to superior reversibility (an average Zn plating/stripping efficiency of 99.72% for 1000 cycles) and lifetime (80.6% capacity retention after 5000 cycles) of zinc batteries

Localized Hydrophobicity in Aqueous Zinc Electrolytes Improves Zinc Metal Reversibility

The rechargeability of aqueous zinc metal batteries is plagued by parasitic reactions of the zinc metal anode and detrimental morphologies such as dendritic or dead zinc. To improve the zinc metal reversibility, hereby we report a new solution structure of aqueous electrolyte with hydroxyl-ion scavengers and hydrophobicity localized in solvent clusters. We show that although hydrophobicity sounds counterintuitive for an aqueous system, hydrophilic pockets may be encapsulated inside a hydrophobic outer layer, and a hydrophobic anode–electrolyte interface can be generated through the addition of a cation-philic, strongly anion-phobic, and OH–-reactive diluent. The localized hydrophobicity enables less active water and less absorbed water on the Zn anode surface, which suppresses the parasitic water reduction; while the hydroxyl-ion-scavenging functionality further minimizes undesired passivation layer formation, thus leading to superior reversibility (an average Zn plating/stripping efficiency of 99.72% for 1000 cycles) and lifetime (80.6% capacity retention after 5000 cycles) of zinc batteries

Localized Hydrophobicity in Aqueous Zinc Electrolytes Improves Zinc Metal Reversibility

The rechargeability of aqueous zinc metal batteries is plagued by parasitic reactions of the zinc metal anode and detrimental morphologies such as dendritic or dead zinc. To improve the zinc metal reversibility, hereby we report a new solution structure of aqueous electrolyte with hydroxyl-ion scavengers and hydrophobicity localized in solvent clusters. We show that although hydrophobicity sounds counterintuitive for an aqueous system, hydrophilic pockets may be encapsulated inside a hydrophobic outer layer, and a hydrophobic anode–electrolyte interface can be generated through the addition of a cation-philic, strongly anion-phobic, and OH–-reactive diluent. The localized hydrophobicity enables less active water and less absorbed water on the Zn anode surface, which suppresses the parasitic water reduction; while the hydroxyl-ion-scavenging functionality further minimizes undesired passivation layer formation, thus leading to superior reversibility (an average Zn plating/stripping efficiency of 99.72% for 1000 cycles) and lifetime (80.6% capacity retention after 5000 cycles) of zinc batteries

A 63 <i>m</i> Superconcentrated Aqueous Electrolyte for High-Energy Li-Ion Batteries

A water-in-salt electrolyte (WiSE) offers an electrochemical stability window much wider than typical aqueous electrolytes but still falls short in accommodating high-energy anode materials, mainly because of the enrichment of water molecules in the primary solvation sheath of Li+. Herein, we report a new strategy in which a non-Li cosalt was introduced to alter the Li+-solvation sheath structure. The presence of an asymmetric ammonium salt (Me3EtN·TFSI) in water increases the solubility of LiTFSI by two times, pushes the salt/water molar ratio from 0.37 in WiSE to an unprecedented value of 1.13, and significantly suppresses the water activity in both bulk electrolyte and the Li+-solvation sheath. This new 63 m (mol kgsolvent–1) aqueous electrolyte (42 m LiTFSI + 21 m Me3EtN·TFSI) offers a wide potential window of 3.25 V and supports a 2.5 V aqueous Li-ion battery (LiMn2O4//Li4Ti5O12) to deliver a high energy density of 145 Wh kg–1 stably over 150 cycles