Iron-based Prussian blue analogs are promising low-cost and easily prepared cathode materials for sodium-ion batteries. Their materials quality and electrochemical performance are heavily reliant on the precipitation process. Here we report a controllable precipitation method to synthesize high-performance Prussian blue for sodium-ion storage. Characterization of the nucleation and evolution processes of the highly crystalline Prussian blue microcubes reveals a rhombohedral structure that exhibits high initial Coulombic efficiency, excellent rate performance, and cycling properties. The phase transitions in the as-obtained material are investigated by synchrotron in situ powder X-ray diffraction, which shows highly reversible structural transformations between rhombohedral, cubic, and tetragonal structures upon sodium-ion (de)intercalations. Moreover, the Prussian blue material from a large-scale synthesis process shows stable cycling performance in a pouch full cell over 1000 times. We believe that this work could pave the way for the real application of Prussian blue materials in sodium-ion batteries.

Applications of room‐temperature–sodium sulfur (RT‐Na/S) batteries are currently impeded by the insulating nature of sulfur, the slow redox kinetics of sulfur with sodium, and the dissolution and migration of sodium polysulfides. Herein, a novel micrometer‐sized hierarchical S cathode supported by FeS2 electrocatalyst, which is grown in situ in well‐confined carbon nanocage assemblies, is presented. The hierarchical carbon matrix can provide multiple physical entrapment to polysulfides, and the FeS2 nanograins exhibit a low Na‐ion diffusion barrier, strong binding energy, and high affinity for sodium polysulfides. Their combination makes it an ideal sulfur host to immobilize the polysulfides and achieve reversible conversion of polysulfides toward Na2S. Importantly, the hierarchical S cathode is suitable for large‐scale production via the inexpensive and green spray‐drying method. The porous hierarchical S cathode offers a high sulfur content of 65.5 wt%, and can deliver high reversible capacity (524 mAh g−1 over 300 cycles at 0.1 A g−1) and outstanding rate capability (395 mAh g−1 at 1 A g−1 for 850 cycles), holding great promise for both scientific research and real application.

Owing to the natural abundance and low cost of sodium resources, sodium‐ion batteries (SIBs) have drawn considerable attention for state‐of‐the‐art power storage devices over the last few years. To enable advanced SIBs with a brighter future, great effort has been made, not only through optimizing the electrode materials, but also with rationally designing various electrolyte systems. Among the available electrolyte systems, organic electrolytes, especially those based on esters as well as ethers, are the most promising ones for practical application in the foreseeable future, due to their numerous inherent advantages. This review is concerned with the recent research progresses on organic electrolytes for SIBs, focusing on ether‐based and ester‐based ones.

and are considered as a new generation of energy storage devices to replace lithium ion batteries (LIBs) in certain applications. [1][2][3][4][5][6][7][8][9][10][11] Hitherto, the commercialization of SIBs has been held back, however, by their low energy density and unsatisfactory cycle life. The cathode, as much as the anode, also plays an important role in the final performance of the battery. Thus, it is crucial to develop cathode candidates with both high energy density and stable cycle life for sodium ion storage.It is accepted that the energy density is determined by the specific capacity and the voltage plateau of an electrode. The commercial cathode materials for LIBs can deliver 510-700 Wh kg −1 energy density with a potential plateau of 3.4-4.1 V (3.4 V for LiFePO 4 and 4.1 V for spinel LiMn 2 O 4 ) and high specific capacity of over 150 mAh g −1 . In comparison, most of the cathode candidates reported for SIBs show a potential plateau below 3.2 V and a capacity below 110 mAh g −1 , delivering energy density lower than 350 Wh kg −1 . [12][13][14][15][16][17] Exceptionally, the sodium superionic conductor Na 3 V 2 (PO 4 ) 3 presented a 3.4 V potential plateau and 115 mAh g −1 capacity; Na 3 (VO 1−x PO 4 ) 2 F 1+2x (0 < x < 1) showed 3.8-3.9 V average voltage and 120-130 mAh g −1 capacity. [18][19][20][21][22] Honeycomb-layered Na 3 Ni 2 SbO 6 provided an average working potential at 3.3 V and a high capacity of ≈120 mAh g −1 . Moreover, Na 3 Ni 2 SbO 6 showed superior rate capability and excellent cycling performance. [23,24] In the long run, however, these cathode materials containing toxic elements (V and Sb) are not suitable for commercial SIBs because commercialization also requires electrode materials to possess the properties of environmental friendliness and low cost in addition to excellent electrochemical performance.Recently, Prussian blue analogues (PBAs) have attracted much attention owing to their low cost and environmentalfriendliness. [6,[25][26][27][28] The PBAs utilized for electrode materials can be classified into three groups, that is, hexacyanoferrates (ATFe(CN) 6 ), hexacyanomanganates (ATMn(CN) 6 ), and hexacyanocobaltates (ATCo(CN) 6 , where A = K, Na; T = Fe, Mn, Ni, Co). Among them, hexacyanoferrates, in particular, have been put under the spotlight due to their nonpoisonous raw material ferrocyanide (Na 4 Fe(CN) 6 or K 3 Fe(CN) 6 ), while the raw materials K 3 Mn(CN) 6 for hexacyanomanganate and K 3 Co(CN) 6 for hexacyanocobaltate are harmful and toxic. In the case of Mn-based hexacyanoferrate Na x MnFe(CN) 6 (NMHFC) has been attracting more attention as a promising cathode material for sodium ion storage owing to its low cost, environmental friendliness, and its high voltage plateau of 3.6 V, which comes from the Mn 2+ /Mn 3+ redox couple. In particular, the Na-rich NMHFC (x > 1.40) with trigonal phase is considered an attractive candidate due to its large capacity of ≈130 mAh g −1 , delivering high energy density. Its unstable cycle life, however, is holding back its practica...

Prussian blue analogs (PBAs) are promising cathode materials for sodium‐ion batteries (SIBs) due to their low‐cost, similar energy density comparable with that of LiFePO4 in lithium‐ion batteries, and long cycle life. Nevertheless, crystal water (≈10 wt%) in PBAs from aqueous synthesis environments can bring significant side effects in real SIBs, especially for calendar life and high temperature storage performance. Therefore, it is of great importance to eliminate crystal water in PBAs for future commercial applications. Herein, a facile heat‐treatment method is reported in order to remove water from Fe‐based PBAs. Although the heat‐treated sample can be easily rehydrated in air, it still exhibits a stable cycling performance over 2000 times under controlled charge cut‐off voltage. In situ synchrotron high‐temperature powder X‐ray diffraction demonstrates that the as‐prepared sample is maintained at a new trigonal phase after dehydration. Moreover, the redox reaction of low‐spin Fe2+/Fe3+ is activated and the high‐temperature storage performance of as‐prepared sample is significantly improved after removal of water.