Dual Activation for Tuning N, S Co-Doping in Porous Carbon Sheets Toward Superior Sodium Ion Storage.

Porous carbon has been widely focused to solve the problems of low coulombic efficiency (ICE) and low multiplication capacity of Sodium-ion batteries (SIBs) anodes. The superior energy storage properties of two-dimensional(2D) carbon nanosheets can be realized by modulating the structure, but be limited by the carbon sources, making it challenging to obtain 2D structures with large surface area. In this work, a new method for forming carbon materials with high N/S doping content based on combustion activation using the dual activation effect of K2 SO4 /KNO3 is proposed. The synthesized carbon material as an anode for SIBs has a high reversible capacity of 344.44 mAh g-1 at 0.05 A g-1 . Even at the current density of 5 Ag-1 , the capacity remained at 143.08 mAh g-1 . And the ICE of sodium-ion in ether electrolytes is ≈2.5 times higher than that in ester electrolytes. The sodium storage mechanism of ether/ester-based electrolytes is further explored through ex-situ characterizations. The disparity in electrochemical performance can be ascribed to the discrepancy in kinetics, wherein ether-based electrolytes exhibit a higher rate of Na+ storage and shedding compared to ester-based electrolytes. This work suggests an effective way to develop doubly doped carbon anode materials for SIBs.

Advances in the regulation of kinetics of cathodic H+/Zn2+ interfacial transport in aqueous Zn/MnO2 electrochemistry.

Rechargeable aqueous Zn-MnO2 energy storage systems have attracted extensive attention owing to their high theoretical capacity and non-flammable mild aqueous electrolytes. Nevertheless, the complicated reaction mechanism of a MnO2-based cathode severely restricts its further development. Therefore, it is crucial to clarify the kinetics of H+/Zn2+ interfacial transport in the MnO2 cathode for realizing controllable regulation of interfacial ion transport and then realizing high capacity and long lifespan. Recently, based on different reaction mechanisms, various strategies have been employed to improve the performance of aqueous Zn/MnO2 cells, such as surface modifications and structural engineering. Herein, we systematically summarize the recent advances in the modulation of interfacial H+/Zn2+ transport and related redox kinetics to effectively improve the electrochemical responses. Furthermore, the challenges of designing novel MnO2 cathodes have also been prospected in detail to provide possible guidelines for the development of Zn/MnO2 batteries.

Simultaneous reversible tuning of H+ and Zn2+ coinsertion in MnO2 cathode for high-capacity aqueous Zn-ion battery.

Protons and zinc ions are generally regarded as charge carriers for rechargeable Zn/MnO2 batteries relying on cation coinsertion for their two-step redox energy storage. However, the irreversibility of H+ insertion and especially Zn2+ insertion unlocks the innate advantages of this scalable aqueous battery system such as high safety and low cost. Herein, an encapsulated structure with manganese hexacyanoferrate(II)-polypyrrole (MnHCF-PPy) composite thin films was in situ constructed within α-MnO2 nanofibers to modulate the interfacial charge transfer process and direct the consequent reversible H+ and Zn2+ insertion/extraction via a synergistic action. The PPy film promotes interfacial proton transfer for the fast conversion of MnO2 to MnOOH and suppresses cathode dissolution, whereas MnHCF with abundant interconnected open ion channels serves as a cation reservoir to facilitate continuous and reversible zinc ion transfer without the aggregation of ZnMn2O4 nanocrystals, leading to protected MnO2 cathodes with recorded high discharge capacity (263 mA h g-1 at 0.5 C), remarkable rate capability (179 mA h g-1 at 5 C), and long lifespan in ZnSO4 electrolyte. Moreover, a flexible solid-state Zn/MnO2 full cell was further demonstrated, which delivers a preferable energy density of 220 W h kgcathode-1, opening a new modus operandi towards advanced flexible batteries through interfacial engineering and device optimization.

Redox Catalysis Promoted Activation of Sulfur Redox Chemistry for Energy-Dense Flexible Solid-State Zn-S Battery.

In aqueous Zn-ion batteries, the intercalation chemistry often foil attempts at the realization of high energy density. Unlocking the full potential of zinc-sulfur redox chemistry requires the manipulation of the feedbacks between kinetic response and the cathode's composition. The cell degradation mechanism also should be tracked simultaneously. Herein, we design a high-energy Zn-S system where the high-capacity cathode was fabricated by in situ interfacial polymerization of Fe(CN)64--doped polyaniline within the sulfur nanoparticle. Compared with sulfur, the FeII/III(CN)64/3- redox mediators exhibit substantially faster cation (de)insertion kinetics. The higher cathodic potential (FeII(CN)64-/FeIII(CN)63- ∼ 0.8 V vs S/S2- ∼ 0.4 V) spontaneously catalyzes the full reduction of sulfur during battery discharge (S8 + Zn2FeII(CN)6 ↔ ZnS + Zn1.5FeIII(CN)6, ΔG = -24.7 kJ mol-1). The open iron redox species render a lower energy barrier to ZnS activation during the reverse charging process, and the facile Zn2+ intercalative transport facilitates highly reversible conversion between S and ZnS. The yolk-shell structured cathode with 70 wt % sulfur delivers a reversible capacity of 1205 mAh g-1 with a flat operation voltage of 0.58 V, a fade rate over 200 cycles of 0.23%/cycle, and an energy density of 720 Wh kgsulfur-1. A range of ex situ investigations reveal the degradation nature of Zn-S cells: aggregation of inactive ZnS nanocrystals rather than the depletion of Zn anode. Impressively, the flexible solid-state Zn battery employing the composite cathode was assembled, realizing an energy density of 375 Wh kgsulfur-1. The proposed redox electrocatalysis effect provides reliable insights into the tunable Zn-S chemistry.