Regulating Ion-Dipole Interactions in Weakly Solvating Electrolyte towards Ultra-Low Temperature Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are recognized as promising energy storage devices. However, they suffer from rapid capacity decay at ultra-low temperatures due to high Na+ desolvation energy barrier and unstable solid electrolyte interphase (SEI). Herein, a weakly solvating electrolyte (WSE) with decreased ion-dipole interactions is designed for stable sodium storage in hard carbon (HC) anode at ultra-low temperatures. 2-methyltetrahydrofuran with low solvating power is incorporated into tetrahydrofuran to regulate the interactions between Na+ and solvents. The reduced Na+-dipole interactions facilitate more anionic coordination in the first solvation sheath, which consistently maintains anion-enhanced solvation structures from room to low temperatures to promote inorganic-rich SEI formation. These enable WSE with a low freezing point of -83.3 °C and faster Na+ desolvation kinetics. The HC anode thus affords reversible capacities of 243.2 and 205.4 mAh g-1 at 50 mA g-1 at -40 and -60 °C, respectively, and the full cell of HC||Na3V2(PO4)3 yields an extended lifespan over 250 cycles with high capacity retention of ~100 % at -40 °C. This work sheds new lights on the ion-dipole regulation for ultra-low temperature SIBs.

Regulation of Coordination Chemistry for Ultrastable Layered Oxide Cathode Materials of Sodium-Ion Batteries.

Layered transition-metal (TM) oxide cathodes have attracted growing attention in sodium-ion batteries (SIBs). However, their practical implementation is plagued by Jahn-Teller distortion and irreversible cation migration, leading to severe voltage decay and structure instability. Herein, O3-Na0.898K0.058Ni0.396Fe0.098Mn0.396Ti0.092O2 (KT-NFM) is reported as an ultrastable cathode material via multisite substitution with rigid KO6 pillars and flexible TiO6 octahedra. The K pillars induce contracted TMO2 slabs and their strong Coulombic repulsion to inhibit Ni/Fe migration; and Ti incorporation reinforces the hybridization of Ni(3deg*)-O(2p) to mitigate the undesired O3-O'3 phase transition. These enable the reversible redox of Ni2+↔Ni3 . 20+ and Fe3+↔Fe3.69+ for 138.6 mAh g-1 and ultrastable cycles with >90% capacity retention after 2000 cycles in a pouch cell of KT-NFM||hard carbon. This will provide insights into the design of ultrastable layered cathode materials of sodium-ion batteries and beyond.

Dual-Function Presodiation with Sodium Diphenyl Ketone towards Ultra-stable Hard Carbon Anodes for Sodium-Ion Batteries.

Hard carbon (HC) is a promising anode material for sodium-ion batteries, yet still suffers from low initial Coulombic efficiency (ICE) and unstable solid electrolyte interphase (SEI). Herein, sodium diphenyl ketone (Na-DK) is applied to realize dual-function presodiation for HC anodes. It compensates the irreversible Na uptake at the oxygen-containing functional groups and reacts with carbon defects of five/seven-membered rings for quasi-metallic sodium in HC. The as-formed sodium induces robust NaF-rich SEI on HC in 1.0 M NaPF6 in diglyme, favoring the interfacial reaction kinetics and stable Na+ insertion and extraction. This renders the presodiated HC (pHC) with high ICE of ≈100 % and capacity retention of 82.4 % after 6800 cycles. It is demonstrated to couple with Na3 V2 (PO4 )3 cathodes in full cells to show high capacity retention of ≈100 % after 700 cycles. This work provides in-depth understanding of chemical presodiation and a new strategy for highly stable sodium-ion batteries.

Atomic Ruthenium-Riveted Metal-Organic Framework with Tunable d-Band Modulates Oxygen Redox for Lithium-Oxygen Batteries.

Non-aqueous Li-O2 batteries have aroused considerable attention because of their ultrahigh theoretical energy density, but they are severely hindered by slow cathode reaction kinetics and large overvoltages, which are closely associated with the discharge product of Li2O2. Herein, hexagonal conductive metal-organic framework nanowire arrays of nickel-hexaiminotriphenylene (Ni-HTP) with quadrilateral Ni-N4 units are synthesized to incorporate Ru atoms into its skeleton for NiRu-HTP. The atomically dispersed Ru-N4 sites manifest strong adsorption for the LiO2 intermediate owing to its tunable d-band center, leading to its high local concentration around NiRu-HTP. This favors the formation of film-like Li2O2 on NiRu-HTP with promoted electron transfer and ion diffusion across the cathode-electrolyte interface, facilitating its reversible decomposition during charge. These allow the Li-O2 battery with NiRu-HTP to deliver a remarkably reduced charge/discharge polarization of 0.76 V and excellent cyclability. This work will enrich the design philosophy of electrocatalysts for regulation of kinetic behaviors of oxygen redox.

Electrochemical impacts of sheet-like hafnium phosphide and hafnium disulfide catalysts bonded with reduced graphene oxide sheets for bifunctional oxygen reactions in alkaline electrolytes.

Non-noble metal-based catalysts with efficient catalytic activities for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are critical for energy conversion devices, including fuel cells and metal-air batteries. In this work, novel hafnium phosphide-reduced graphene oxide nanosheets (HfP-rGO NS) and hafnium disulfide-reduced graphene oxide nanosheets (HfS2-rGO NS) were synthesized and investigated as bifunctional electrocatalysts for OER and ORR. The prepared HfP-rGO NS and HfS2-rGO NS catalysts showed nanosheet structures, where the HfP or HfS2 nanosheet was closely packed with rGO. A unique methodology was adopted to lodge the non-metal oxide catalytic sheets (i.e., HfP and HfS2) over the rGO sheets, which positioned the oxide layer on the catalytic sheet surface for instant oxygen evolution. Low intensity X-ray diffraction patterns and Raman spectra confirmed the sheet-like structure of HfP-rGO NS and HfS2-rGO NS. Scanning electron microscope mapping images revealed that all elements (i.e., Hf, P, C and O for HfP-rGO NS and Hf, S, C and O for HfS2-rGO NS) were equally distributed in the synthesized heteroatomic nanosheets. Moreover, both the HfP-rGO NS and HfS2-rGO NS demonstrated excellent durability for both ORR and OER. This outperforms the most state-of-the-art non-precious-metal-based bifunctional catalysts, which is attributed to the synergistic effect of rGO and Hf-based catalysts. The different ORR and OER reaction potentials in HfP-rGO NS and HfS2-rGO NS likely result from the influence of HfP and HfS2.