Publish Group. b) Histogram of H 2 O clusters in the hydrate melt. Reproduced with permission. [44] Copyright 2019, American Chemical Society. c) Potential window depending on the type of the electrodes and the salt concentration of the electrolytes. Reproduced with permission. [45] Copyright 2019, American Chemical Society. d) Schematic images of the distinctive reductive stabilities of the hydrate-melt electrolyte on Al and Pt electrode surfaces. Reproduced with permission. [46] Copyright 2020, American Institute of Physics.

density and high output power is being considered indispensable for both portable electronic devices and electric vehicles. However, limited lithium reserves and increased mining difficulty cannot meet the expanded needs for LIBs in largescale energy-storage systems (EESs). [1][2][3] In recent years, sodium-ion batteries (SIBs) emerge as a promising candidate for EESs owing to the high abundance and low cost of sodium resources. In spite of a similar intercalation chemistry to LIBs, SIBs afford a lower energy density and sluggish sodium intercalation/deintercalation kinetics which are regarded as the main obstacles to its widespread use. [4][5][6][7] Hence, considerable efforts have been made to search suitable electrode materials for SIBs.Cathode materials play a dominant role in determining the energy density, cost, and safety of SIBs, consequently become the focus of the current research. Nevertheless, only several types of materials, including transition-metal oxides, [8][9][10] Prussian blue analogues, [11,12] and polyanionic compounds, [4,13,14] show their potential application in SIBs. Compared to the other two types of cathode materials, polyanionic compounds with robust open frameworks have received significant attention due to their high structural and thermal stability, which are beneficial for a long lifespan and high safety. Generally, the exploration of available polyanionic cathodes has concentrated on vanadium-and ironbased compounds. Several NASICON-type vanadium-based materials, such as Na 3 V 2 (PO 4 ) 3 , [15,16] Na 7 V 4 (P 2 O 7 ) 4 PO 4 , [17] and Na 3 (VO) 2 (PO 4 ) 2 F, [18] exhibit high operating voltage, favorable energy density, fast sodium-ion transport and long cycle life, thus making them comparable to the cathodes of LIBs. However, the use of expensive and toxic V element remains a barrier to their practical applications. [19,20] Instead, employing earth-abundant and non-toxic iron as the redox center in the polyanionic compounds can lower the manufacturing cost and advance the environmental friendliness, which will accelerate the commercialization of SIBs.The great success of the commercial application of LiFePO 4 in LIBs encouraged researchers to seek for electrochemical active Na-Fe-PO 4 material for SIBs. [21] However, unlike its lithium analogue, NaFePO 4 does not crystallize in the olivine structure, and only some unconventional synthetic Sodium-ion battery has been considered as one of the most promising power sources for large-scale energy storage systems due to its similar electrochemistry to the lithium-ion battery and the crust abundance of Na resources. Essentially, developing low-cost electrode materials along with a facile and economical synthesis procedure is critically important to promote the commercialization of sodium-ion batteries. However, applicable cathode materials capable of being massively produced are still scarcely reported to date. Herein, a green and scalable synthesis approach is developed to obtain Na 3 Fe 2 (PO 4 )P 2 O 7 (NFPP)/rGO composite by usi...

Rechargeable aqueous zinc-ion batteries (ZIBs) have been regarded as a promising battery technology for stationary energy storage applications due to high safety, long-term sustainability, and low cost. The main challenge for ZIBs is the lack of robust structure to accommodate repeated ion insertion/extraction in aqueous solutions. In contrast to transition metal oxides cathodes (MnO2, V2O5), iron-based polyanionic compounds have rigid structure and open framework, hence may serve as compatible cathodes for aqueous batteries. However, only several iron-based polyanionic cathodes such as Na4Fe3(PO4)2P2O7, have received scant attentions to date, not to mention that their underlying complex reaction mechanisms in aqueous solutions have not yet been clearly revealed. In this work, we identify the Na+/Zn2+ cointercalation mechanism of Na4Fe3(PO4)2P2O7 in zinc-ion batteries by both experimental spectra and DFT calculations. Benefiting from the synergistic chemistry, the Na4Fe3(PO4)2P2O7 demonstrates enhanced structural stability and ion diffusion kinetics upon the Na+/Zn2+ cointercalation in comparison with single metal ion (only Na+ or Zn2+) storage reaction, hence a high-power density (6.73 kW kg–1) and long cycle life (54.6% after 5000 cycles) are exhibited. In particular, the prominent reaction kinetics endows the battery with low-temperature (−30 °C) operation capability (capacity retention of 87.6%).

Sodium‐ion battery (SIB) is considered as a revolutionary technology toward large‐scale energy storage applications. Developing cost‐effective cathode material as well as economical synthesis procedure is a key challenge for its commercialization. Herein, we develop a facile and economic strategy to simultaneously remove rust from the surface of carbon steel and achieve porous and hollow spherical Na4Fe3(PO4)2P2O7/C (HS‐NFPP/C). Benefiting from the desirable structure that fastens the electronic/ionic transportation and effectively accommodates the volume expansion/contraction during discharge/charge process, the as‐prepared cathode exhibits outstanding rate capability and ultralong cycle life. An extraordinarily high‐power density of 32.3 kW kg−1 with an ultrahigh capacity retention of 89.7% after 10 000 cycles are achieved. More significantly, the 3 Ah HC||HS‐NFPP/C full battery manifests impressive cycling stability. Therefore, this work provides an economical and sustainable approach for the massive production of high‐performance Na4Fe3(PO4)2P2O7 cathode, which can be potentially commercialized toward SIB applications.image

A facile and easily scaled‐up polymer‐pyrolysis method is developed to synthesize porous coralline LiVO3 as cathodes for lithium‐ion batteries (LIBs). Polyacrylates of Li and V are used as the precursor compounds. The nanostructured LiVO3 delivers a high specific capacity of 307.6 mAh g−1 with a remarkable capacity retention of 80.6% after 100 cycles. In addition, a high energy density close to 800 Wh kg−1 as well as a competitive power density of ∼4500 W kg−1 are attained. Such excellent lithium storage performance derives from its porous nanoarchitecture, which not only supplies numerous active sites for electrochemical reactions, and shortens Li‐ions diffusion distance, but also provides enough void space to buffer the volume change during lithium intercalation and deintercalation. Therefore, the porous coralline LiVO3 justifies its potential practical application as an alternative to high energy and high power electrode materials for lithium‐ion batteries. The simple approach opens up a new way to fabricate other types of porous coralline energy storage materials.