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The cycling stability of O3‐type NaNi1/3Fe1/3Mn1/3O2 (NFM) as a commercial cathode material for sodium ion batteries (SIBs) is still a challenge. In this study, the Ni/Fe/Mn elements are replaced successfully with tantalum (Ta) in the NFM lattice, which generated additional delocalized electrons and enhanced the binding ability between the transition metal and oxygen, resulting in suppressed lattice distortion during charging and discharging. This caused significant mitigation of voltage decay and improved cycle stability within the potential range of 2.0–4.2 V. The optimized Na(Ni1/3Fe1/3Mn1/3)0.97Ta0.03O2 sample achieved a reversible capacity of 162.6 mAh g−1 at a current rate of 0.1 C and 73.2 mAh g−1 at a high rate of 10 C. Additionally, the average charge/discharge potential retention reached 98% after 100 cycles, significantly mitigating the voltage decay. This work demonstrates a significant contribution towards the practical utilization of NFM cathodes in the SIBs energy storage field. [ABSTRACT FROM AUTHOR]

As one of the most promising cathodes for sodium-ion batteries (SIBs), the layered transition metal oxides have attracted great attentions due to their high specific capacities and facile synthesis. However, their applications are still hindered by the problems of poor moisture stability and sluggish Na+ diffusion caused by intrinsic structural Jahn—Teller distortion. Herein, we demonstrate a new approach to settle the above issues through introducing K+ into the structures of Ni/Mn-based materials. The physicochemical characterizations reveal that K+ induces atomic surface reorganization to form the birnessite-type K2Mn4O8. Combining with the phosphate, the mixed coating layer protects the cathodes from moisture and hinders metal dissolution into the electrolyte effectively. Simultaneously, K+ substitution at Na site in the bulk structure can not only widen the lattice-spacing for favoring Na+ diffusion, but also work as the rivet to restrain the grain crack upon cycling. The as achieved K+-decorated P2-Na0.67Mn0.75Ni0.25O2 (NKMNO@KM/KP) cathodes are tested in both coin cell and pouch cell configurations using Na metal or hard carbon (HC) as anodes. Impressively, the NKMNO@KM/KP||Na half-cell demonstrates a high rate performance of 50 C and outstanding cycling performance of 90.1% capacity retention after 100 cycles at 5 C. Furthermore, the NKMNO@KM/KP||HC full-cell performed a promising energy density of 213.9 Whkg−1. This performance significantly outperforms most reported state-of-the-art values. Additionally, by adopting this strategy on O3-NaMn0.5Ni0.5O2, we further proved the universality of this method on layered cathodes for SIBs. [ABSTRACT FROM AUTHOR]

A micro-cubic Prussian blue (PB) with less coordinated water is first developed by electron exchange between graphene oxide and PB. The obtained reduced graphene oxide–PB composite exhibited increased redox reactions of the Fe sites and delivered ultrahigh specific capacity of 163.3 mA h g−1 (30 mA g−1) as well as excellent cycle stability as a cathode in sodium-ion batteries. [ABSTRACT FROM AUTHOR]

Rational engineering of the microstructure and interfacial properties of nano-metal oxides materials is critical to realize their practical use in batteries. This work reports a detailed study on how structural and chemical interplay in a robust 3D crumpled MXene protected SnO2 core–shell system contributes to performance as an anode in lithium-ion batteries. Our results show that the compact conductive MXene shell can provide robust protection against the large volume change and aggregation of SnO2, providing excellent structural stability. Further analyses show that rich surface groups on the MXene can not only enable strong interfacial interactions through Sn–O–Ti bonds to grant electrical contacts, but also provide a pseudocapacitive contribution for fast and stable lithium storage. Furthermore, a conformal SEI formed outside the MXene can build a stable protective interface and prevent further consumption of electrolyte simultaneously. As a result, the SnO2@MXene composite delivered a high specific capacity of 829.4 mAh g−1 at a current density of 0.2 A g−1, and exhibited an excellent cycling stability (533.9 mAh g−1 after 500 cycles at 1 A g−1). The strategy reported here for synthesizing a core–shell MXene based material can be promising for the development of high-performance anode materials for next-generation LIBs. [ABSTRACT FROM AUTHOR]

Considering the natural abundance and low cost of sodium resources, sodiumion batteries (SIBs) have received much attention for large-scale electrochemical energy storage. However, smart structure design strategies and good mechanistic understanding are required to enable advanced SIBs with high energy density. In recent years, the exploration of advanced cathode, anode, and electrolyte materials, as well as advanced diagnostics have been extensively carried out. This review mainly focuses on the challenging problems for the attractive battery materials (i.e., cathode, anode, and electrolytes) and summarizes the latest strategies to improve their electrochemical performance as well as presenting recent progress in operando diagnostics to disclose the physics behind the electrochemical performance and to provide guidance and approaches to design and synthesize advanced battery materials. Outlook and perspectives on the future research to build better SIBs are also provided. [ABSTRACT FROM AUTHOR]

In operando XRD and TXM‐XANES approaches demonstrate that structure evolution in NaNi1/3Fe1/3Mn1/3O2 during cycling follows a continuous change, and the formation of a nonequilibrium solid solution phase in the existence of two phases. An O3′ and P3′ monoclinic phase occur, and redox couples of Ni3+/Ni4+ and Fe3+/Fe4+ are mainly responsible in the charge voltage range from 4.0 to 4.3 V. [ABSTRACT FROM AUTHOR]

Retraction of 'Prussian blue without coordinated water as a superior cathode for sodium-ion batteries' by Dezhi Yang et al., Chem. Commun., 2015, 51, 8181–8184, https://doi.org/10.1039/C5CC01180A. [ABSTRACT FROM AUTHOR]

A micro-cubic Prussian blue (PB) without coordinated water is first developed by electron exchange between graphene oxide and PB. The obtained reduced graphene oxide–PB composite exhibited complete redox reactions of the Fe sites and delivered ultrahigh electrochemical performances as well as excellent cycling stability as a cathode in sodium-ion batteries. [ABSTRACT FROM AUTHOR]

The O3‐type NaNi0.5Mn0.5O2 (NM) layered cathode in sodium ion batteries (SIBs) undergoes structural distortion and capacity degradation during cycling, which seriously hinders its practical application. Herein, lanthanum (La) is employed as a dopant in O3‐NaNi0.5Mn0.5‐xLaxO2 (NML) cathodes, which triggered an “atomic knife” effect, reducing particle size, and stabilizing crystal structure. The larger La ions generated structural strain during grain growth at high temperatures, hindering the movement of grain boundaries and refining the size of NML particles. Comprehensive characterizations illuminated La doping‐induced atomic site occupancy and phase transformations within NML. A competitive phase formation between layered NML and perovskite LaMnO3 (LMO) is observed. Spontaneously formed perovskite LMO provides surface protection. Moreover, strong La─O bonds expand the Na interlayer spacing, enhancing Na+‐ion diffusion. Consequently, NML cathodes exhibit superior long‐term cycling stability and ultrahigh rate capacities compared to pristine NM cathode and most currently reported layered cathodes for SIBs. [ABSTRACT FROM AUTHOR]

In this work, a facile strategy is proposed to synthesize hierarchical hollow rod‐like Mn‐doped Prussian blue (R‐PB) using MnO2 nanosheets as a self‐sacrifice template. The as prepared R‐PB with low contents of vacancies and coordinated water, and high content of sodium, exhibits appealing electrochemical performance as a cathode for sodium ion batteries (SIBs) achieving a high discharge capacity of 117.3 mAh g−1 and a capacity retention of 98.5% after 200 cycles at 1 C. Moreover, the specific capacity reaches 111.5 mAh g−1 at 5 C with a Coulombic efficiency (CE) of 93.8%. The high capacity, superior cycling stability, and enhanced kinetics of Na+ migration of R‐PB are attributed to the positive effect of doped Mn ions and the hierarchical hollow rod‐like structure. The doped Mn ions in R‐PB activate the redox of FeLS(C) in the high voltage region to reach a high capacity. The unique hierarchical hollow rod‐like structure provides a buffer space for the volume change during the insertion/extraction of sodium ions, enlarges the contact area between the electrode materials and electrolyte, and enhances the apparent diffusion coefficient of sodium ions in electrode materials. A hierarchical hollow rod‐like Mn‐doping Prussian blue (R‐PB) is prepared via a facile MnO2 nanosheet self‐sacrifice template method. As a cathode for sodium ion batteries, R‐PB exhibits superior cycling stabilities and rate capabilities. The capacity retention is as high as 98% after 300 cycles at a high current of 5 C. [ABSTRACT FROM AUTHOR]

Layered transition metal dichalcogenides are promising as lithium and/or sodium storage materials for lithium and sodium (Li/Na) ion batteries. However they always exhibit limited rate capability and long-term cycling stability, due to the fact that their 2D structures are easily restacking and agglomeration during cycling process and further result poor electrochemical reversibility. Herein, hierarchical Co 1/3 Mo 2/3 S 2 /graphene nanocomposites without CoS x and MoS 2 impurities have been synthesized via one-pot solvothermal process. The incorporation of Co into MoS 2 at atomic level can not only give rise to thinner and smaller nanosheets in the nanocomposites than MoS 2 /graphene nanocomposites, but also significantly decrease the size of in-situ formed MoS 2 /CoS x nanoparticles during electrochemical conversion process, which can greatly promoting the ion diffusion and suppressing the aggregation of active materials. Furthermore, the conductivity of Co 1/3 Mo 2/3 S 2 /graphene nanocomposites can be enhanced from 0.46 S m −1 (MoS 2 /graphene) to 1.39 S m −1 via changing the semiconducting MoS 2 to metallic Co 1/3 Mo 2/3 S 2 . The simultaneously optimized electron conductivity and ions diffusion dynamics of Co 1/3 Mo 2/3 S 2 /graphene nanocomposites can effectively improve the reversibility of electrochemical conversion reactions. A capacity of 940 mAh g −1 and 529 mAh g −1 can be maintained at 3200th cycle (2 A g −1 ) in lithium-ion batteries and 200th cycle (1 A g −1 ) in sodium-ion batteries, respectively. [ABSTRACT FROM AUTHOR]

Prussian blue analogues have been intensely investigated as promising cathode materials for sodium-ion batteries owing to their high capacities, easy synthesis and low cost. However, the poor cycling performance due to the presence of lattice defects and the structural deterioration when exposed to humid air hinder their practical application. Herein we report an effective surface modification method to tackle these issues. A Zinc-zeolitic imidazolate framework (ZIF-8) modified PB sample is prepared by in-situ growth via simple wet chemical reaction. The obtained PB@ZIF-8 composite with a ZIF-8 coating layer of ∼70 nm thickness on the 2–5 μm PB particle surface shows excellent cycling stability with reversible capacity of 106.5 mAh g−1 at 1C charge-discharge rate and a remarkable capacity retention of 96.7 % after 500 cycles. Furthermore, the PB@ZIF-8 composite shows excellent storage stability owing to its moisture-proof property. After exposure to high humidity air (RH=70 %) for 24 h or storage for 180 days in a bottle filled with air of relative humidity RH=40 %, the PB@ZIF-8 sample still maintains excellent cycling performance. ZIF-8 coating layer not only acts as a shield for PB particles against the electrolyte corrosion, but also resists the H 2 O attacking in humid environment. [ABSTRACT FROM AUTHOR]

Abstract Sodium-ion pouch cells with up to 1000 cycles are presented by using a NaNi 1/3 Fe 1/3 Mn 1/3 O 2 cathode, a hard carbon anode, and a functional electrolyte. The functional electrolyte is composed of 1 M NaPF 6 dissolved in a 1:1 (v/v) mixed solvent of propylene carbonate (PC) and ethyl methyl carbonate (EMC) with 3–4 wt% of two or three additives, including fluoroethylene carbonate (FEC), prop-1-ene-1,3-sultone (PST), and 1,3,2-Dioxathiolane-2,2-dioxide (DTD). It is shown that the capacity retentions of the cells increase to 84.4% and 92.2% after 1000 cycles for electrolytes containing FEC-PST bi-additive and FEC-PST-DTD tri-additive, respectively, as compared with that containing FEC single additive. Using X-ray photoelectron spectroscopy, inductively coupled plasma optical, and transmission electron microscopy, post-mortem analyses on the surface of the cycled electrodes indicate that PST and DTD are beneficial to the anode by forming an organic compound rich solid electrolyte interphase (SEI), and to the cathode by forming a dense and thick cathode electrolyte interphase (CEI) that consequently prevents transition metal ions from dissolving into electrolyte. Highlights • Long cycle life of sodium-ion pouch cells is obtained by using optimized electrolyte. • Multiple additives electrolyte is for the Na x Ni 1/3 Fe 1/3 Mn 1/3 O 2 //hard carbon system. • The capacity retention of cells comes up to 92% after 1000 cycles. • SEI on the anode and CEI on the cathode are forming to protect electrodes. [ABSTRACT FROM AUTHOR]

In this work, rubidium and cesium ions are studied as electrolyte additives for sodium-ion batteries. It is shown that adding small amount of Rb + and Cs + into the electrolyte significantly modifies the chemical composition of solid electrolyte interphase (SEI) on hard carbon (HC) surfaces, which results in a significant increase in the ionic conductivity and stability of the SEI. The results of this work show that a 0.05 M addition in the form of MPF 6 (M = Rb or Cs) can increase the capacity retention of the Na/HC cells to 95.3% and 97.1% by the Rb + and Cs + ions, respectively, from 80.6% of the control cell after 100 cycles. [ABSTRACT FROM AUTHOR]

Prussian blue and its analogues have been intensively studied as potential electrode materials for sodium ion batteries. In this work, a prussian blue sample was prepared by a simple precipitation method and the electrochemical performance of the prussian blue (PB) cathode was investigated at various temperatures and in different voltage ranges. When cycled in the voltage range of 2.0 − 4.0 V vs. Na/Na + , the PB cathode exhibited initial discharge capacities of 135.4 mAh g −1 (55 °C), 128.5 mAh g −1 (25 °C) and 99.2 mAh g −1 (-10 °C) at 10 mA g −1 . The PB cathode showed good cycling stability at low temperature, however the cycling capacity degraded remarkably at elevated temperature. CV test indicated that the capacity fade was mainly due to the side reactions on the electrode-electrolyte interface at near 4.0 V vs. Na/Na + . XPS and FTIR analyses revealed several types of compounds formed on the cathode surface which indicated the complexity of the side reactions. Controlling the high cut-off voltage at 3.8 V vs. Na/Na + significantly improved the cycling stability of the PB electrode. The PB cathode delivered 1C rate reversible capacity of 100.0 mAh g −1 in 2.0 − 3.8 V vs. Na/Na + with outstanding capacity retention of 98.2% after 300 cycles. [ABSTRACT FROM AUTHOR]

Highlights: [•] P2-Na2/3[Ni1/3Mn2/3]O2 was synthesized via spray drying method and a two step solid state process. [•] Cycling performance of P2-Na2/3[Ni1/3Mn2/3]O2 cathode was studied in different voltage ranges. [•] The prepared material showed excellent reversibility between 2.0V and 4.0V with good capacity retention. [•] Cycled in 2.0–4.5V, the crystal structure of P2-Na2/3[Ni1/3Mn2/3]O2 was irreversibly damaged. [•] The discharge capacities increased to 134.7mAg−1 (0.1C) and 107.8mAg−1 (1C), cycled in 1.6–3.8V. [ABSTRACT FROM AUTHOR]

[Display omitted] • AlF 3 coated nanoscaled Na 3.12 Fe 2.44 (P 2 O 7) 2 @CNTs is synthesized. • Carbon nanotubes build highly conductive networks. • The AlF 3 layer facilitates the formation of cathode-electrolyte interphase film. • AlF 3 coating improves materials structural stability at high temperatures. Sodium ion batteries (SIBs) are applied to the field of energy storage due to their unique advantages, however, large scale energy storage equipment, also requires low cost, good cycling performance, safety performance and good environmental adaptation performance, in order to cope with various climatic conditions. The polyanionic material Na 3.12 Fe 2.44 (P 2 O 7) 2 (NFPO) is considered to be an excellent cathode material for SIBs due to its unique large frame work structure and good thermal stability, leading to good cycle stability and a wide working temperature. Nevertheless, poor intrinsic conductivity of the material brings about large polarization, resulting in low electrochemical reversibility. Especially in high temperature environment, the electrolyte aggravates the erosion of the material and increases the side reactions, making the cycle stability worse. In this study, nanoscale NFPO composites are synthesized by an optimized sol–gel method, while the interface is modified using AlF 3 , to achieve resistance to surface oxidation and corrosion. Impressively, these modified materials exhibit high-temperature electrochemical properties due to the thermal stability and interfacial protection of AlF 3. At 60 °C, it provides a discharge capacity of 130 mAh g−1 at 0.1C, still has a discharge capacity of 100.4 mAh g−1 at 10C, a capacity retention rate of 96.3% after 400 cycles, and has excellent long-term cycling performance (70% capacity retention rate after 6000 cycles at 50C). This work demonstrates the effectiveness of the interfacial modification and provides an impactful strategy for the design of batteries at high temperatures. [ABSTRACT FROM AUTHOR]

Na 4 Fe 3 (PO 4) 2 P 2 O 7 (NFPP) is known as a cathode material with great potential for sodium ion batteries (SIBs) due to its thermodynamic stability, considerable theoretical capacity and small volume change. However, its inherent poor conductivity leads to low discharge capacity and poor cycle stability, which greatly limits its widespread and practical application. In this work, a Mn2+ doped NFPP together with the graphene modification, is proposed. It is found that the optimal Na 4 Fe 2.7 Mn 0.3 (PO 4) 2 P 2 O 7 /rGO(Mn0.3-NFPP/rGO) can provide an initial discharge capacity of 131.5 mAh g−1 at 0.1C, (1C = 129mAh g−1) also an excellent rate performance (70.2 mAh g−1 at 50C) and good long cycle stability (97.2% capacity retention after 2000 cycles at 10C) can be obtained. Impressively, the as-prepared Mn0.3-NFPP/rGO also shows excellent low-temperature performance, at −20 °C, it demonstrates a discharge capacity of 85.3 mAh g−1 at 0.2C and good rate performance. Density functional theory (DFT) calculation shows that Mn2+ doping reduces the Na + migration energy barrier, and also narrows the bandgap of the NFPP lattice, which is beneficial to improve the Na+ diffusion kinetics and conductivity. In addition, the doping of Mn2+ can further help to improve its structural stability during the long cycling process. [Display omitted] • Mn-doped Na 4 Fe 3 (PO 4) 2 (P 2 O 7) together with graphene modification is proposed. • Mn2+ doping reduces the Na + migration energy barrier. • Mn2+ doping narrows the bandgap of Na 4 Fe 3 (PO 4) 2 (P 2 O 7). • The Na + migration is facilitated by Mn2+ doping, particularly at low temperature. [ABSTRACT FROM AUTHOR]

MnFe@NiFe Prussian blue analogue with enhanced electrochemical performance was prepared via a facile in situ ion-exchange strategy. • PBM@PBN with high energy density and superior cycling stability was synthesized. • ICP results proved that Mn ions dissolution was inhibited by PBN coating. • Ex-situ XRD proved the PBM@PBN undergoes a reversible structural change. Sodium manganese hexacyanoferrate (PBM) is one of the most promising cathode materials for sodium-ion batteries due to its high theoretical capacity, high voltage, and low cost. However, its cycling performance is limited by serious Mn ions dissolution during Na+ insertion/extraction. In this work, a facile in situ ion-exchange strategy is developed to synthesize sodium manganese hexacyanoferrate coated by sodium nickel hexacyanoferrate (PBM@PBN). The as-prepared PBM@PBN showed superior cyclic stability and enhanced rate capability. PBM@PBN exhibited a high reversible capacity of 126.9 mAh g−1 (1 C), with a capacity retention of 74.3% after 800 cycles. ICP results proved that superior cyclic stability was attributed to the inhibition of Mn ions dissolution by PBN coating. Besides, PBM@PBN also exhibited enhanced rate capability, and it delivered a high capacity of 87.2 mAh g−1 at 10 C. Ex -situ XRD proved that the PBM@PBN undergoes a reversible structural change (monoclinic ↔ cubic/tetragonal) during the whole cycle. PBN coating inhibited the PBM from suffering serious Mn ions dissolution during Na+ insertion/extraction, thus ensured the framework stability of PBM during long-term cycling and contributed to the excellent electrochemical performance. The simple preparation of PBM@PBN makes it accessible for large-scale applications. [ABSTRACT FROM AUTHOR]

• Non-flammable electrolyte with TMP and F-EPE improves the safety of SIB. • TMP/F-EPE electrolyte stabilizes the interface of NFM cathode during all processes. • The cycling life of NFM/HC pouch cell increases by using TMP/F-EPE electrolyte. Despite their beneficial effect on battery safety, non-flammable electrolytes often have an adverse side effect on the electrochemical performance of lithium and sodium ion batteries due to their poor compatibility with the electrodes. In this paper, we report a new non-flammable electrolyte consisting of trimethyl phosphate (TMP) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (F-EPE) as non-flammable solvents and fluoroethylene carbonate (FEC) as additive with different concentration of Na salts, and a EC-DEC-FEC electrolyte was also prepared as baseline electrolyte. The flammability and non-flammability of the prepared electrolytes was tested. It is shown that the prepared electrolyte not only increases the capacity (129.9 vs. 122.5 mAh g−1 of baseline electrolyte) of NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM) cathode but also stabilizes the cyclability (70.8% retention after 500 cycles) of NFM/HC (HC: hard carbon) pouch cells. The dissolution of pristine NaNi 1/3 Fe 1/3 Mn 1/3 O 2 cathode material in different solvents and electrolytes, and the XPS patterns of the cycled NFM cathode in the prepared electrolytes were also studied to understand the capacity fading mechanism. These results indicate that this new non-flammable electrolyte holds great potential for application in rechargeable sodium-ion batteries. [ABSTRACT FROM AUTHOR]