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...
To meet the demanding requirements in plug-in hybrid electric vehicles (PHEVs) or electric vehicles (EVs), higher energy density materials, such as the Li-rich, layered manganese-based oxides (LLOs) with the general formula xLi 2 MnO 3 ·(1-x)LiTMO 2 (TM = Mn, Ni, Co, etc.), are promising candidates as they possess higher reversible capacity (>250 mAh g −1 ), improved safety and much reduced cost. [4][5][6][7][8][9] Recent microscopic evidence reveals the intergrowth of rhombohedral LiTMO 2 (R-3m) and the monoclinic Li 2 MnO 3 -like layered structure (C/2m) at the atomic scale in the oxide grains. [10] The Li 2 MnO 3 component serves as an electrochemically active phase for Li storage when cycled above 4.5 V versus Li/Li + . [8,[11][12][13][14] Nevertheless, these LLO materials undergo steady voltage/capacity decay when cycled above 4.5 V, resulting in a substantial decrease of the cathode energy density. [15][16][17][18] The origin of voltage/capacity decay upon cycling stems from cation migration between TM layers and Li layers and subsequent phase transformation. [19,20] The cationic doping with other metallic cations (such as Mg, [21] Al, [22] Ti, [23] Sn, [24] Ru, [25] Y, [26] Zn, [27] etc.) and polyanion doping based on nonmetal elements, such as BO 4 5− , [28] SiO 4 4− , [29] PO 4 3-, [30] etc., have been employed to improve the cyclic durability by weakening the TM-O covalency in the oxygen closepacked structure. In addition, surface coatings using metal oxides, [31][32][33][34] fluorides and phosphates, [35][36][37] LiNiPO 4 and Li 3 VO 4 , [38][39][40] have been applied to protect the surface structure from side reactions with the electrolyte under high voltage and to restrain the layered-to-spinel transformation which occurs preferentially on the crystal surface and leads to capacity fading of LLO materials. However, the ionic dopants and coating materials are mostly electrochemically inactive, so the improved cycling stability is achieved at the expense of reduced specific capacity/energy density of the cathode. Moreover, a conformal and continuous coating on the surface of oxide particles is rather difficult to obtain practically. Hence, advancing the structural and cycling stability in both the bulk material and the surface structure through a simple way is highly desired for potential applications of LLO materials.Herein, we develop a novel LLO material with a nanoscaled spinel-like surface layer through gradient doping of polyanions Surface Structural Transition Induced by Gradient Polyanion-Doping in Li-Rich Layered Oxides: Implications for Enhanced Electrochemical PerformanceYing Zhao, Jiatu Liu, Shuangbao Wang, Ran Ji, Qingbing Xia, Zhengping Ding, Weifeng Wei,* Yong Liu, Peng Wang,* and Douglas G. Ivey Lithium-rich layered oxides (LLOs) exhibit great potential as high-capacity cathode materials for lithium-ion batteries, but usually suffer from capacity/ voltage fade during electrochemical cycling. Herein, a gradient polyaniondoping strategy is developed to initiate surface structural trans...
A Li-rich Layered@Spinel@Carbon heterostructured cathode material for LIBs, which comprises Li-rich layered core, a spinel interlayer and a carbon nano-coating.
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