Search

Na superionic conductor of Na3MnTi(PO4)3 only containing high earth‐abundance elements is regarded as one of the most promising cathodes for the applicable Na‐ion batteries due to its desirable cycling stability and high safety. However, the voltage hysteresis caused by Mn2+ ions resided in Na+ vacancies has led to significant capacity loss associated with Mn reaction centers between 2.5–4.2 V. Herein, the sodium excess strategy based on charge compensation is applied to suppress the undesirable voltage hysteresis, thereby achieving sufficient utilization of the Mn2+/Mn3+ and Mn3+/Mn4+ redox couples. These findings indicate that the sodium excess Na3.5MnTi0.5Ti0.5(PO4)3 cathode with Ti4+ reduction has a lowest Mn2+ occupation on the Na+ vacancies in its initial composition, which can improve the kinetics properties, finally contributing to a suppressed voltage hysteresis. Based on these findings, it is further applied the sodium excess route on a Mn‐richer phosphate cathode, which enables the suppressed voltage hysteresis and more reversible capacity. Consequently, this developed Na3.6Mn1.15Ti0.85(PO4)3 cathode achieved a high energy density over 380 Wh kg−1 (based on active substance mass of cathode) in full‐cell configurations, which is not only superior to most of the phosphate cathodes, but also delivers more application potential than the typical oxides cathodes for Na‐ion batteries. [ABSTRACT FROM AUTHOR]

The rhombohedral sodium manganese hexacyanoferrate (MnHCF) only containing cheap Fe and Mn metals was regarded as a scalable, low‐cost, and high‐energy cathode material for Na‐ion batteries. However, the unexpected Jahn‐teller effect and significant phase transformation would cause Mn dissolution and anisotropic volume change, thus leading to capacity loss and structural instability. Here we report a simple room‐temperature route to construct a magical CoxB skin on the surface of MnHCF. Benefited from the complete coverage and the buffer effect of CoxB layer, the modified MnHCF cathode exhibits suppressed Mn dissolution and reduced intergranular cracks inside particles, thereby demonstrating thousands‐cycle level cycling lifespan. By comparing two key parameters in the real energy world, i.e. cost per kilowatt‐hours and cost per cycle‐life, our developed CoxB coated MnHCF cathode demonstrates more competitive application potential than the benchmarking LiFePO4 for Li‐ion batteries. [ABSTRACT FROM AUTHOR]

Heteroatom doping has been proved to effectively enhance the sloping capacity, nevertheless, the high sloping capacity almost encounters a conflict with the disappointing initial Coulombic efficiency (ICE). Herein, we propose a heteroatom configuration screening strategy by introducing a secondary carbonization process for the phosphate‐treated carbons to remove the irreversible heteroatom configurations but with the reversible ones and free radicals remaining, achieving a simultaneity between the high sloping capacity and ICE (≈250 mAh g−1 and 80 %). The Na storage mechanism was also studied based on this "slope‐dominated" carbon to reveal the reason for the absence of the plateau. This work could inspire to distinguish and filter the irreversible heteroatom configurations and facilitate the future design of practical "slope‐dominated" carbon anodes towards high‐power Na‐ion batteries. [ABSTRACT FROM AUTHOR]

The irreversible consumption of sodium at the anode side during the first cycle prominently reduces the energy density of Na‐ion batteries. Different sacrificial cathode additives have been recently reported to address this problem; however, critical issues such as by‐products (e.g., CO2) release during cycling and incompatibility with current battery fabrication procedures potentially deteriorate the full‐cell performance and prevent the practical application. Herein, an additive‐free self‐presodiation strategy is proposed to create lattice‐coherent but component‐dependent O3‐NaxTMMnO2 (TM = transition metal ion(s)) cathodes by a quenching treatment rather than the general natural cooling. The quenching material preserves higher Mn3+ and Na+ content, which is able to release Na+ via Mn3+ oxidation to compensate for sodium consumption during the initial charge while adopting other TM to provide the capacity in the following cycles. Full cells fabricated with hard carbon anode and this material as both cathode and sodium supplement reagent have a nearly 9.4% cathode mass reduction, around 9.9% energy density improvement (from 233 to 256 Wh kg−1), and 8% capacity retention enhancement (from 76% to 84%) after 300 cycles. This study presents the route to rational design cathode materials with sodium reservoir property to simplify the presodiation process as well as improve the full‐cell performance. [ABSTRACT FROM AUTHOR]

Safety requirements stimulate Na-based batteries to evolve from high-temperature Na–S batteries to room-temperature Na-ion batteries (NIBs). Even so, NIBs may still cause thermal runaway due to the external unexpected accidents and internal high activity of electrodes or electrolytes, which has not been comprehensively summarized yet. In this review, we summarize the significant advances about the failure mechanisms and related strategies to build safer NIBs from the selection of electrodes, electrolytes and the construction of electrode/electrolyte interfaces. Considering the safety risk, the thermal behaviors are emphasized which will deepen the understanding of thermal stability of different NIBs and accelerate the exploitation of safe NIBs. [ABSTRACT FROM AUTHOR]

Material innovation on high‐performance Na‐ion cathodes and the corresponding understanding of structural chemistry still remain a challenge. Herein, we report a new concept of high‐entropy strategy to design layered oxide cathodes for Na‐ion batteries. An example of layered O3‐type NaNi0.12Cu0.12Mg0.12Fe0.15Co0.15Mn0.1Ti0.1Sn0.1Sb0.04O2 has been demonstrated, which exhibits the longer cycling stability (ca. 83 % of capacity retention after 500 cycles) and the outstanding rate capability (ca. 80 % of capacity retention at the rate of 5.0 C). A highly reversible phase‐transition behavior between O3 and P3 structures occurs during the charge‐discharge process, and importantly, this behavior is delayed with more than 60 % of the total capacity being stored in O3‐type region. Possible mechanism can be attributed to the multiple transition‐metal components in this high‐entropy material which can accommodate the changes of local interactions during Na+ (de)intercalation. This strategy opens new insights into the development of advanced cathode materials. [ABSTRACT FROM AUTHOR]

Replacing the commonly used nonaqueous liquid electrolytes in rechargeable sodium batteries with polymer solid electrolytes is expected to provide new opportunities to develop safer batteries with higher energy densities. However, this poses challenges related to the interface between the Na‐metal anode and polymer electrolytes. Driven by systematically investigating the interface properties, an improved interface is established between a composite Na/C metal anode and electrolyte. The observed chemical bonding between carbon matrix of anode with solid polymer electrolyte, prevents delamination, and leads to more homogeneous plating and stripping, which reduces/suppresses dendrite formation. Full solid‐state polymer Na‐metal batteries, using a high mass loaded Na3V2(PO4)3 cathode, exhibit ultrahigh capacity retention of more than 92 % after 2 000 cycles and over 80 % after 5 000 cycles, as well as the outstanding rate capability. [ABSTRACT FROM AUTHOR]

The comprehensive performance of carbon anodes for Na‐ion batteries (NIBs) is largely restricted by their inferior rate capability and safety issues. Herein, a slope‐dominated carbon anode is achieved at a low temperature of 800 °C, which delivers a high reversible capacity of 263 mA h g−1 at 0.15C with an impressive initial Coulombic efficiency (ICE) of 80 %. When paired with the NaNi1/3Fe1/3Mn1/3O2 cathode, the reversible capacity at 6C is still 75 % of that at 0.15C, and 73 % of the capacity is retained after 1000 cycles at 3C. The enhanced Na storage performance could be attributed to the unique microstructure with randomly oriented short carbon layers and the relatively higher defect concentration. Given its robustness, such a low‐temperature carbonization strategy could also be applicable to other precursors and provide a new opportunity to design slope‐dominated carbon anodes for high safety, low‐cost NIBs with excellent ICE and superior rate capability. Positive energy: The slope‐dominated carbon anode produced by the inverse low‐temperature strategy shows great potential for low‐cost and high‐safety Na‐ion batteries in terms of high specific capacity, impressive ICE, superior rate capability, and long cycle stability, without any doping, nano‐sizing, or pore‐creating procedures. [ABSTRACT FROM AUTHOR]

Abstract: Layered transition metal oxides NaxMO2 (M=transition metal) with P2 or O3 structure have attracted attention in sodium‐ion batteries (NIBs). A universal law is found to distinguish structural competition between P2 and O3 types based on the ratio of interlayer distances of the alkali metal layer d(O‐Na‐O) and transition‐metal layer d(O‐M‐O). The ratio of about 1.62 can be used as an indicator. O3‐type Na0.66Mg0.34Ti0.66O2 oxide is prepared as a stable anode for NIBs, in which the low Na‐content (ca. 0.66) usually undergoes a P2‐type structure with respect to NaxMO2. This material delivers an available capacity of about 98 mAh g−1 within a voltage range of 0.4–2.0 V and exhibits a better cycling stability (ca. 94.2 % of capacity retention after 128 cycles). In situ X‐ray diffraction reveals a single‐phase reaction in the discharge–charge process, which is different from the common phase transitions reported in O3‐type electrodes, ensuring long‐term cycling stability. [ABSTRACT FROM AUTHOR]

Batteries and supercapacitors are critical devices for electrical energy storage with wide applications from portable electronics to transportation and grid. However, rechargeable batteries are typically limited in power density, while supercapacitors suffer low energy density. Here, a novel symmetric Na-ion pseudocapacitor with a power density exceeding 5.4 kW kg−1 at 11.7 A g−1, a cycling life retention of 64.5% after 10 000 cycles at 1.17 A g−1, and an energy density of 26 Wh kg−1 at 0.585 A g−1 is reported. Such a device operates on redox reactions occurring on both electrodes with an identical active material, viz., Na3V2(PO4)3 encapsulated inside nanoporous carbon. This device, in a full-cell scale utilizing highly reversible and high-rate Na-ion intercalational pseudocapacitance, can bridge the performance gap between batteries and supercapacitors. The characteristics of the device and the potentially low-cost production make it attractive for hybrid electric vehicles and low-maintenance energy storage systems. [ABSTRACT FROM AUTHOR]

Li‐SO2 batteries have a high energy density but bear serious safety problems that are associated with pressurized SO2 and flammable solvents in the system. Herein, a novel ambient Li‐SO2 battery was developed through the introduction of ionic liquid (IL) electrolytes with tailored basicities to solvate SO2 by reversible chemical absorption. By tuning the interactions of ILs with SO2, a high energy density and good discharge performance with operating voltages above 2.8 V were obtained. This strategy based on reversible chemical absorption of SO2 in IL electrolytes enables the development of the next generation of ambient Li‐SO2 batteries. [ABSTRACT FROM AUTHOR]

Abstract: This work studies a novel rechargeable all-solid-state Ag battery by using AgI nanoplates in unusual polytype phases as solid Ag electrolytes, Ag as anode and TiTe2 as cathode. Sufficiently high conductivity at room temperature (ca. 2.2×10−3 Scm−1) of the polytype AgI nanoplates leads to a successful battery operation even at room temperature, which is not at all possible in the case of commercial AgI. The working temperature of the batteries with a high current density (up to 2500μAcm−2) using high-temperature modification of AgI (α-AgI) with conductivity >10−1 Scm−1 can be lowered as much as by ∼50°C (from 150°C to 100°C) due to the anomalous phase transition to α-phase (a large hysteresis) of the polytype nanoplates. Not only are the cycling and rate performance of the Ag batteries remarkable, but also the novel electrolyte (AgI nanoplates) promises the miniaturization into nanoscaled batteries (nano-batteries). [Copyright &y& Elsevier]

Highlights from the article: Sodium-Ion Batteries: Hard-Soft Carbon Composite Anodes with Synergistic Sodium Storage Performance (Adv. Funct. Keywords: closed pores; hard carbon; sodium-ion batteries; soft carbon; synergistic effect Closed pores, hard carbon, sodium-ion batteries, soft carbon, synergistic effect.

Abstract: A Na3V2(PO4)3 sample coated uniformly with a layer of 6nm carbon has been successfully synthesized by a one-step solid state reaction. This material shows two flat voltage plateaus at 3.4V vs. Na+/Na and 1.63V vs. Na+/Na in a nonaqueous sodium cell. When the Na3V2(PO4)3/C sample is tested as a cathode in a voltage range of 2.7–3.8V vs. Na+/Na, its initial charge and discharge capacities are 98.6 and 93mAh/g. The capacity retention of 99% can be achieved after 10 cycles. The electrode shows good cycle performance and moderate rate performance. When it is tested as an anode in a voltage range of 1.0–3.0V vs. Na+/Na, the initial reversible capacity is 66.3mAh/g and the capacity of 59mAh/g can be maintained after 50 cycles. These preliminary results indicate that Na3V2(PO4)3/C is a new promising material for sodium ion batteries. [Copyright &y& Elsevier]

Na-rich Prussian white NaMHCF was prepared by regulating precursors water content based on a mechanochemical protocol. Its interstitial water can be further reduced by rising drying temperature and thus the electrochemical performance was greatly improved. [Display omitted] • Na-rich Prussian white cathodes were synthesized via a mechanochemical protocol. • Precursors crystal water plays an important role for the formation of NaMHCF. • The interstitial H 2 O can be greatly reduced via increasing drying temperature. • NaMHCF with less interstitial H 2 O shows an improved stability and rate capacity. • NaMHCF/NaTi 2 (PO 4) 3 shows a high-rate capacity and ultra-stable cycle performance. Prussian blue analogs (PBAs) with rigid open framework are promising low-cost and easily prepared cathodes for Na-ion batteries. However, their electrochemical performances are hindered from the crystal vacancies and interstitial water in a traditional aqueous co-precipitation process. Herein, we explore a solvent-free mechanochemical protocol to prepare a monoclinic Na 1.94 Mn[Fe 0.99 (CN) 6 ] 0.95 ·□ 0.05 ·1.92H 2 O via regulating the crystal water in precursors. The interstitial water of NaMHCF can be further reduced through increasing the drying temperature. Ex-situ XRD confirms that the monoclinic phase transformed to the rhombohedral structure during the first cycle, and a highly reversible multi-phase evolution among rhombohedral, cubic, and Na-poor phase upon Na+ (de)intercalations occurred from the second cycle on. Finally, it delivers a specific capacity of 168.8 mA h g−1 with a stable average voltage of 3.44 V at 10 mA g−1, showing ultra-high rate capability (127 mA h g−1 at 2000 mA g−1) and cycling stability (87.6% capacity retention after 100 cycles at 100 mA g−1) for half cells. For the full cell of NaMHCF/NaTi 2 (PO 4) 3 , it can deliver an ultra-stable cycle performance, retaining 84% capacity after 500 cycles at 100 mA g−1. Our work provides a facile avenue to prepare monoclinic NaMHCF with low water and vacancies for high-performance Na-ion batteries. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries have been explored extensively due to its abundant reserve and low cost. However, reports on full symmetric battery with the same electrode materials are relatively less than asymmetrical battery. In this work, symmetric sodium-ion battery based on layered P 2-Na 0.67 [Zn x Mn 1- x ]O 2 (x = 0.1, 0.2, 0.28, 0.34) as both positive and negative electrode materials are studied comprehensively. This active material shows two electrochemical working windows with reversible lattice oxygen redox and Mn4+/Mn3+ redox couple. The positive side Na 0.67 [Zn 0.28 Mn 0.72 ]O 2 provides a highly reversible capacity of 170 mAh g−1 at 0.05C (10 mA g−1) between 2.0–4.2 V and outstanding capacity retention of 77.2% after 100 cycles. Na 0.67 [Zn 0.28 Mn 0.72 ]O 2 electrode also exhibits excellent rate performance up to a high rate of 5C which is the best among the pure anionic-redox based cathodes. In addition, an average voltage of about 2.0 V versus Na+/Na is obtained as negative electrode material, with a reversible capacity of 99 mAh g−1. This full symmetric battery also exhibits excellent rate performance and cycle stability which are related to Zn doping. As a cost-effective element, zinc has been used as inactive atom to induce the anionic redox and enhance the crystal structure. This is the first time to explore symmetric sodium-ion battery with anionic redox. [ABSTRACT FROM AUTHOR]