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Na-based batteries have shown substantial progress in recent years and are promising candidates for mitigating the supply risks associated with Li-based batteries. In this Review, Na and Li batteries are compared in terms of fundamental principles and specific materials. Principles for the rational design of a Na battery architecture are discussed. Recent prototypes are surveyed to demonstrate that Na cells offer realistic alternatives that are competitive with some Li cells in terms of performance. Sodium batteries are promising candidates for mitigating the supply risks associated with lithium batteries. This Review compares the two technologies in terms of fundamental principles and specific materials, and assesses the performance of commercial prototype sodium cells.

Anode-free lithium metal batteries can maximize the energy density at the cell level. However, without the Li compensation from the anode side, it faces much more challenging to achieve a long cycling life with a competitive energy density than Li metal-based batteries. Here, we prolong the lifespan of an anode-free Li metal battery by introducing Li-rich Li2 [Ni0.8 Co0.1 Mn0.1 ]O2 into the cathode as a Li-ions extender. The Li2 [Ni0.8 Co0.1 Mn0.1 ]O2 can release a large amount of Li-ions during the first charging process to supplement the Li loss in the anode, then convert into NCM811, thus extending the lifespan of the battery without the introduction of inactive elements. By the benefit of Li-rich cathode and high reversibility of Li metal on Cu foil, the anode-free pouch cells enable to achieve 447 Wh kg-1 energy density and 84 % capacity retention after 100 cycles in the condition of limited electrolyte addition (E/C ratio of 2 g Ah-1 ).

Sodium metal batteries are attracting increasing attention on account of their high energy densities as well as the abundance of sodium-based resources. However, the uneven metallic deposition and dendrite formation during cycling hinder the application of sodium metal anodes. Carbon skeletons have been reported in the literature to mitigate the dendrite formation during the plating and stripping of metallic sodium. Still, the role played by different carbon structural features (i.e., pores vs. defects) and relative mechanisms are not well understood, preventing the controllable interface engineering at the anode side. Here, we have rationally designed the structural features of sustainable carbon skeletons from a renewable precursor to unveil the roles of defects and pores for metallic deposition. The obtained carbon skeleton with rich defects and negligible pores exhibits the best performance when applied to protect metal anodes. After long cycling (>1200 hours), the retained high Coulombic efficiency (∼99.9%) of the plating and stripping processes indicates the importance of defects for inducing uniform metallic deposition. Combined with different types of cathodes (e.g., Prussian blue and sulfur), “anode-less” sodium metal batteries with enhanced electrochemical performance are also demonstrated in terms of sustainability.

The sodium ion battery (NIB) is a promising alternative technology for energy storage systems because of the abundance and low cost of sodium in the Earth’s crust. However, the limited cycle life a...

O3-type layered oxide materials are being considered as one of the most promising cathodes for Na-ion batteries owing to their higher capacity, however, they usually suffer from structural damage at the highly desodiated state. To achieve the stable/high-capacity O3-type Na-ion cathodes, a series of Ni-rich O3–Na[NixFeyMn1-x-y]O2 (x ​= ​0.6, 0.7 and 0.8) oxide cathodes were successfully prepared and the phase transitions at high voltage were systematically investigated. Combined with the electrochemical measurements and structural characterizations, the structural transitions from O3 to O′3, P3, O3″ phases during the Na+ (de)intercalation process were demonstrated in the voltage range of 2.0–4.2 ​V. Moreover, several reasons for the high-voltage capacity decay are revealed: 1) the thermodynamic instability of high-voltage phase due to less Na+ in the crystal structure; 2) large volume change during the high-voltage phase evolution with inferior Na+ diffusion kinetics; 3) formation of microcracks and cathode-electrolyte interphase on the surface of cathode particles. To address the above issues, a reasonable upper cut-off voltage of 4.0 ​V was set to prevent the formation of O3″ phase and reduce electrolyte decomposition, which leads to a high reversible capacity of ~152 mAh g−1 (~467 ​Wh kg−1) with a superior capacity retention of ~84% after 200 cycles at 0.5C, showing great Na storage performance. This work provides insights on the relationship of the structure-property for the further development of high-performance Ni-rich O3-type Na-ion cathodes.

The insufficient ionic conductivity of oxide-based solid electrolytes and the large interfacial resistance between the cathode material and the solid electrolyte severely limit the performance of r...

The soft carbon precursor pitch, featured with low-cost and easy-availability, is regarded as a very promising candidate for the synthesis of carbonaceous anode. However, the Na-storage performance of pitch-derived carbon is strongly hindered by its highly graphitized structure, which mainly comes from the reordering during the fusion-state carbonization. To prevent the graphitization, herein, we propose an in-situ Mg(NO3)2·6H2O solidification strategy to convert the fusion-state to solid-state carbonization. The oxygen species and solid products generated from the decomposition of Mg(NO3)2·6H2O can retard the melting and reordering of pitch, thus tailoring the microstructure. The optimal sample displays outstanding overall performances in both half- and full-cells, with ~3-fold increase in capacity. Particularly, the carbon yield is significantly increased from 61% to 92% because less organic molecules can escape. The understandings gained in this work not only offer insights to adjust the carbonization process, but also provide solutions to obtain highly disordered carbon anodes from soft carbon precursors.

Efficient inorganic perovskite light-emitting devices (PeLEDs) with a vacuum-deposited CsPbBr3 emission layer were realized by introducing an ultrathin 2-phenylethanamine bromide interlayer. The PEA+ cations not only passivated the nonradiative defects by terminating on the CsPbBr3 surface but also regulated the charge transport to balance the hole and electron transport. Consequently, the PeLEDs exhibit significantly promoted performance with a turn-on voltage of 3 V, a maximum current efficiency of 14.64 cd A-1, and an external quantum efficiency of 4.10%. Our work would provide instructive guidance for realizing efficient PeLEDs based on a vacuum processing method via focusing on the interface modification between the perovskite layer and the carrier transport layer.

Owing to the smaller Stokes radius and desolvation energy of Na+ compared to those of Li+, an unusual ultralow-concentration electrolyte is proposed for Na-ion batteries to further reduce the cost ...

Nowadays, cost-efficient and high-power energy storage technologies are urgently required for extensive integration of intermittent wind and solar renewable energy. Complying with the simplification and acceleration principle, we designed a fast-charge Al organic battery in which ionic diffusion in anode materials and through the solid electrolyte interphase (SEI) process is simplified while the generation of charge-carrier ions at the cathode/anode interface and ion diffusion in cathode materials are accelerated. A prototype based on 2,3,5,6-tetraphthalimido-p-benzoquinone (TPBQ)–Al was successfully demonstrated with 100 mA h pouch cells displaying superior power capability, high energy density and excellent cycling stability. Moreover, extensive characterizations and DFT calculations predict the crystal structure and simulate the precise reaction pathway corresponding to the thermodynamic redox potential of TPBQ and consolidate our proposed AlCl2+ electrochemical surface-coordination and storage mechanism. We believe that our design philosophy by simplifying and accelerating kinetics would provide guidance for tailoring fast and affordable energy storage systems.

Owing to its unique structure, Chevrel phase (CP) is a promising candidate for applications in rechargeable multivalent (Mg and Al) batteries. However, its wide applications are severely limited by...

NASICON type material Na1+xZr2SixP3-xO12 is considered as an ideal option of solid-state electrolyte (SSE) material for solid-state Na batteries (SSNBs). However, the ionic conductivity of the material essentially needs to be further improved. Herein, a new strategy is proposed to enhance the ionic conductivity of NASICON material by adding NaF into the precursor, improving the ionic conductivity of classical Na3Zr2Si2PO12 from 4.5 × 10−4 S cm−1 to 1.7 × 10−3 S cm−1 at 25 °C with an activation energy of 0.28 eV. Furthermore, both qualitative and quantitative analysis are conducted by employing XRD, XPS, SEM, and solid-state NMR techniques to investigate the long-range and local structures as well as compositions for the prepared Na3Zr2Si2PO12-xNaF materials. It is revealed that with the addition of NaF into the precursor, the monoclinic phase of NASICON grains gradually transforms into rhombohedral phase with in-situ formed a ‘binder-like’ glassy phase around them, indicating NaF plays an important role in the modification of grain boundary and the improvement of the ionic conductivity. Moreover, the strategy is also applied to other NASICON system, achieving the optimum conductivity of 3.6 × 10−3 S cm−1 at 25 °C with an activation energy of 0.25 eV for the Na3.2Zr2Si2.2P0.8O12-0.5NaF, which is the highest ionic conductivity among previously reported NASICON-based materials. More importantly, our work provides a simple and low-cost approach to prepare high ionic conducting NASICON materials.

Batteries have experienced fast growing interests driven by new demands for covering a wide spectrum of application fields. The update of batteries heavily relies on materials innovation where the involvement of governments, research entities, and manufacturers will accelerate the course. In this perspective, we present an overview of the research and development of advanced battery materials made in China, covering Li-ion batteries, Na-ion batteries, solid-state batteries and some promising types of Li-S, Li-O2, Li-CO2 batteries, all of which have been achieved remarkable progress. In particular, most of the research work was under the support of the Strategic Priority Research Program, launched by Chinese Academy of Sciences in 2013. Based on the current status, the roadmap of the battery development within the next decade is provided to suggest possible directions for the future research.

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 NaNi0.12 Cu0.12 Mg0.12 Fe0.15 Co0.15 Mn0.1 Ti0.1 Sn0.1 Sb0.04 O2 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.

Summary Understanding structure-property chemistry of electrodes will be greatly helpful for developing advanced Na-ion batteries (NIBs). To search for promising electrodes, we employ chemical substitution in Na2/3TMO2 (TM = transition metal) layered compounds with different stacking modes: O3-Na2/3Mg1/3Ti2/3O2 and P2-Na2/3Mg1/3Mn2/3O2. Partial Ti-substituted Na2/3Mg1/3Ti1/6Mn1/2O2 enables significant improvements on electrochemical properties with respect to the stability of high-voltage plateau and total reversible capacity (∼230 mAh g−1). More than twice as much capacity is reserved in the high-voltage plateau area for the Ti-substituted cathode against non-Ti-substituted counterparts after the same cycles. The present work demonstrates that Ti substitution will decrease Mg and Mn ordering distribution in the pristine structure due to the intermediate size of Ti4+, which further increases the structural stability during Na+ deintercalculation and intercalculation. Additionally, Ti substitution leads to more localized electrons around oxygen ions in Mg–, Ti–, and Mn–O bonding, which can facilitate the charge-transfer reaction of oxygen redox. Our work provides new insights into structural chemistry on developing high-capacity, low-cost layered electrodes for NIBs.

High-capacity anode materials are one of the bottlenecks to further improve the energy density of Na-ion batteries (NIBs). Except for introducing more defects to increase the sloping capacity, tuni...

How to utilize oxygen redox chemistry in oxide electrodes is a promising challenge to realize high-capacity cathodes. Herein, we demonstrate an unexpected strategy, ‘decreasing transition metal (TM)’ to form TM deficiency, to activate non-bonding O 2p orbitals in charge compensation process for the A-deficient (A: alkali metal, e.g., Li, Na) oxide electrodes. Na0.653Mn0.929O2, as a model material, has been successfully prepared and shows an obvious voltage plateau at ~ 4.2 V, corresponding to the oxygen redox (O2-/(O2)n-) with a total capacity of ~ 210 mAh g−1. This proposed strategy reveals that the special structural and chemical features can effectively increase O 2p orbitals near the Fermi level, triggering oxygen oxidation prior to transition metal oxidation towards a high-valence state. Our results provide an insightful guide for the further development of high-capacity materials, particularly for Na-deficient NaxTMO2 (x≤1) electrodes in Na-ion batteries (NIBs).

Na-ion batteries (NIBs) have attracted significant attention owing to Na being an abundant resource that is uniformly distributed in the Earth’s crust. Several 3d transition metal (TM) ions have been thoroughly investigated as charge compensators in single or multiple composition systems to enhance the electrochemical performance of cathodes for the practical applications. In this review, the composition-structure-property relationship of Ni-based cathodes has been reviewed as a design perspective for NIB’s cathodes. The typical Ni-based cathode materials have been systematically summarized and comparatively analyzed, and it is demonstrated that Ni ions can be used to provide charge compensation. Moreover, Ni-based cathodes present high reversible capacity owing to the multi-electron redox reactions and suitable redox potential of Ni-ions redox. However, considering the abundance, cost, and hygroscopic properties of Ni element, the content of 0.15–0.35 per formula can be optimal for enhancing the performance of cathodes. Lastly, further perspectives on designing Ni-containing cathodes, including Ni-rich layered cathodes, have been discussed, which could promote the practical applications of NIBs for grid-scale energy storage in future.

Solid polymer electrolytes (SPEs) are considered as promising candidates for solid-state batteries. SPEs with a conventional solution casting technique have serious side reactions during charging b...

Aqueous K-ion batteries (AKIBs) are promising candidates for grid-scale energy storage due to their inherent safety and low cost. However, full AKIBs have not yet been reported due to the limited availability of suitable electrodes and electrolytes. Here we propose an AKIB system consisting of an Fe-substituted Mn-rich Prussian blue KxFeyMn1 − y[Fe(CN)6]w·zH2O cathode, an organic 3,4,9,10-perylenetetracarboxylic diimide anode and a 22 M KCF3SO3 water-in-salt electrolyte. The cathode achieves 70% capacity retention at 100 C and a lifespan of over 10,000 cycles due to the mitigation of phase transitions by Fe substitution. Meanwhile, the electrolyte can help decrease the dissolution of both electrodes owing to the lack of free water. The AKIB exhibits a high energy density of 80 Wh kg−1 and can operate well at rates of 0.1–20 C and over a wide temperature range (−20 to 60 °C). We believe that our demonstration could pave the way for practical applications of AKIBs for grid-scale energy storage. Intensive efforts are underway towards developing battery-based grid-scale storage technologies. Here, the authors report an aqueous K-ion battery that offers many attractive advantages over various battery alternatives.

Recently, sodium-ion batteries (SIBs), regarded as promising supplements for lithium-ion batteries (LIBs), especially in the large-scale energy storage field, are attracting more and more attention. However, the limited suitable cathode materials hinder the wide commercialization of SIBs. Given this aspect, in this work, a new layered oxide with 4d metal Tin was synthesized and investigated as cathode material for SIBs. Two optimized sodium-deficient O3-Na0.9Ni0.45Sn0.55O2 and O3-Na0.9Ni0.4Mn0.1Sn0.5O2 were selected for comprehensive investigation, both of which exhibited high operating voltage of around 3.45 V with smooth charge/discharge curves. In comparison, O3-Na0.9Ni0.4Mn0.1Sn0.5O2 shows a higher reversible capacity (65 mA h/g, 0.1 C), better rate capability and cycling stability than that of O3-Na0.9Ni0.45Sn0.55O2 (50 mA h/g, 0.1 C), indicating that a small amount of Mn-substitution can improve the electrochemical performance. This work presents a new possibility of discovering potential cathode candidates by exploring the Tin-based layered oxides.

As a supplement to lithium-ion batteries, the rate capability and cycling stability of sodium-ion batteries still need to be improved for practical applications. Here we report a novel poplar wood derived hard carbon anode, exhibiting a high specific capacity of 330 mAh/g and an initial Coulombic efficiency of 88.3% in half cells, and delivering a reversible specific energy of 212.9 Wh/kg (based on two-electrode masses) at 1 C and a long cycle life of 1200 cycles at 5 C when pairing with Na[Cu1/9Ni2/9Fe1/3Mn1/3] O 2 cathode in full cells. In addition, with the matched areal capacity of 2 mAh/cm2 and under the industrial level cathode loading of 20.5 mg/cm2, the capacity highly maintains at 2 C, and after 1400 cycles could almost fully recover by setting the current rate to C/10. This indicates sodium-ion batteries are approaching maturity.

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 NaNi1/3 Fe1/3 Mn1/3 O2 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.

Here, we report the synthesis of hard carbon materials (RH) made from natural rice husk through a single pyrolysis process and their application as an anode in sodium-ion batteries. The studies show that the electrochemical properties of RHs are affected by the treatment temperatures, which determine the materials morphology, in particular, their degree of graphitization and extent of continuous channels (nanovoids). The latter are accessible to sodium ions and significantly contribute to charge storage capacity of the produced anodes. The RHs obtained at 1600 °C deliver the highest reversible capacity of 276 mAh g−1 mainly due to insertion of sodium ions into the nanovoids. This work deepens the basic understanding of the influence of the carbonization temperature on the sodium storage mechanism.

NASICON- (Na superionic conductor-) based solid-state electrolytes (SSEs) are believed to be attracting candidates for solid-state sodium batteries due to their high ionic conductivity and prospectively reliable stability. However, the poor interface compatibility and the formation of Na dendrites inhibit their practical application. Herein, we directly observed the propagation of Na dendrites through NASICON-based Na 3.1 Zr 2 Si 2.1 P 0.9 O 12 SSE for the first time. Moreover, a fluorinated amorphous carbon (FAC) interfacial layer on the ceramic surface was simply developed by in situ carbonization of PVDF to improve the compatibility between Na metal and SSEs. Surprisingly, Na dendrites were effectively suppressed due to the formation of NaF in the interface when molten Na metal contacts with the FAC layer. Benefiting from the optimized interface, both the Na||Na symmetric cells and Na 3 V 2 (PO 4 ) 3 ||Na solid-state sodium batteries deliver remarkably electrochemical stability. These results offer benign reference to the maturation of NASICON-based solid-state sodium batteries.

Properties of the underlying hole transport layer (HTL) in perovskite light-emitting devices (PeLEDs) play a critical role in determining the optoelectronic performance through influencing both the charge transport and the quality of the active perovskite emission layer (EML). This work focuses on manipulating the carrier transport behavior and obtaining a high-quality EML film by tailoring the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL with previously unused amino alcohol 3-amino-1-propanol (3AP). The modified PEDOT:PSS rendered a deeper work function that is more suitable for the hole injection from the HTL to EML. More importantly, the 3AP-modified PEDOT:PSS film can induce a low-dimensional perovskite phase that can passivate the defects in the EML, resulting in a significantly improved light emission. Such ameliorations consequently result in a dramatical enhancement in performance of PeLED with a low turn-on voltage of 2.54 V, a maximum luminance of 23033 cd/m

Na-ion batteries have been considered promising candidates for stationary energy storage. However, their wide application is hindered by issues such as high cost and insufficient electrochemical performance, particularly for cathode materials. Here, we report a solvent-free mechanochemical protocol for the in-situ fabrication of sodium vanadium fluorophosphates. Benefiting from the nano-crystallization features and extra Na-storage sites achieved in the synthesis process, the as-prepared carbon-coated Na3(VOPO4)2F nanocomposite exhibits capacity of 142 mAh g−1 at 0.1C, higher than its theoretical capacity (130 mAh g−1). Moreover, a scaled synthesis with 2 kg of product was conducted and 26650-prototype cells were demonstrated to proof the electrochemical performance. We expect our findings to mark an important step in the industrial application of sodium vanadium fluorophosphates for Na-ion batteries., The high production cost and poor electrochemical performance of polyanionic cathode hinders their industrial application. Here, the authors report large-scale fabrication of sodium vanadium fluorophosphates and in situ construction of their carbon nanocomposites via a mechanochemical protocol.

A surface plasmon resonance (SPR) sensor based on a dual-side polished microstructured optical fiber (MOF) with a dual core is proposed for a large analyte refractive index (RI; na) detection range. Gold is used as a plasmonic material coated on the polished surface, and analytes can be directly contacted with the gold film. The special structure not only facilitates the fabrication of the sensor, but also can work in the na range of 1.42–1.46 when the background material RI is 1.45, which is beyond the reach of other traditional MOF-SPR sensors. The sensing performance of the sensor was investigated by the wavelength and amplitude interrogation methods. The detailed numerical results showed that the proposed sensor can work effectively in the na range of 1.35–1.47 and exhibits higher sensitivity in the na range of 1.42–1.43.

Reversibly intercalating ions into host materials for electrochemical energy storage is the essence of the working principle of rocking-chair type batteries. The most relevant example is the graphite anode for rechargeable Li-ion batteries which has been commercialized in 1991 and still represents the benchmark anode in Li-ion batteries 30 years later. Learning from past lessons on alkali metal intercalation in graphite, recent breakthroughs in sodium and potassium intercalation in graphite have been demonstrated for Na-ion batteries and K-ion batteries. Interestingly, some significant differences proved to exist for the intercalation of Na+ and K+ into graphite compared with the Li+ case. Such different host-guest interactions are unique depending on the host materials and electrolytes, which greatly contribute to a deeper understanding of intercalation-type electrode materials for next generation alkali metal ion batteries. This review summarizes significant advances from both experimental and theoretical calculations with a focus on comparing the intercalation of three alkali metal ions (Li+, Na+, K+) into graphite and aims to clarify the intimate host-guest relationships and the underlying mechanisms. New approaches developed to achieve favorable intercalation coupled with the challenges in this field are also discussed. We also extrapolate alkali metal ion intercalation in graphite to mono-/multi-valent ions in layered electrode materials, which will deepen the understanding of intercalation chemistry and provide guidance to explore new guests and hosts.

Layered Na-based oxides with the general composition of NaxTMO2 (TM: transition metal) have attracted significant attention for their high compositional diversity that provides tunable electrochemical performance for electrodes in sodium-ion batteries. The various compositions bring forward complex structural chemistry that is decisive for the layered stacking structure, Na-ion conductivity, and the redox activity, potentially promising new avenues in functional material properties. In this work, we have explored the maximum Na content in P2-type layered oxides and discovered that the high-content Na in the host enhances the structural stability; moreover, it promotes the oxidation of low-valent cations to their high oxidation states (in this case Ni2+). This can be rationalized by the increased hybridization of the O(2p)-TM(3d-eg*) states, affecting both the local TM environment as well as the interactions between the NaO2 and TMO2 layers. These properties are highly beneficial for the Na storage capabilities as required for cathode materials in sodium-ion batteries. It leads to excellent Na-ion mobility, a large storage capacity (>100 mAh g-1 between 2.0-4.0 V), yet preventing the detrimental sliding of the TMO2 layers (P2-O2 structural transition), as reflected by the ultralong cycle life (3000 (dis)charge cycles demonstrated). These findings expand the horizons of high Na-content P2-type materials, providing new insights of the electronic and structural chemistry for advanced cathode materials.

A new model material of Na0.6[Mg(II)0.3Mn(IV)0.7]O2, with only Mg2+ and Mn4+ in the transition metal layers, is synthesized for the research of anionic redox reaction. The material delivers a capacity of ∼130 mAh/g with a long plateau at ∼4.2 V in the initial charge profile, indicating anionic redox reaction (ARR) involved during the initial desodiation process. In the following cycles, the reversible capacity can reach a high value of ∼210 mAh/g, which is probably derived from the participation of both ARR and Mn3+/Mn4+ redox couples, further proving the charge compensation from ARR during the initial charge and following cycles. The designed cathode material without Mn3+ helps avoid the influence of oxygen activity from transition metals, enabling the investigation of ARR without other distractions.

Metallic sodium (Na) has been generally regarded as one of the most promising anode materials due to its high specific capacity and natural abundance. However, uneven deposition, large volume change, and dendrite growth during Na plating/stripping process severely restrict its feasibility for energy storage devices. Here we propose a copper nanowire-reinforced three-dimensional (3D) Cu foam current collector (CuNW-Cu) to achieve highly reversible Na storage. The in-situ growth of Cu nanowires can provide abundant active nucleation sites and reduce the local electric current by increasing surface area of the current collector, leading to homogeneous Na deposition. The Na metal anode can run for more than 1400 h (350 cycles) on CuNW-Cu with a low thickness variation of 2% and a stable voltage hysteresis of 25 mV. Moreover, controllable Na loading ranging from 2 to 12 mA h cm−2 can be plated into CuNW-Cu with a long steady life-span over 1000 h and a high Coulombic efficiency over 97.5% owing to the synergistic effect between copper nanowires and interconnected 3D porous Cu foam, which delivers an excellent compatibility for cathodes with different areal loadings. Our results indicate that this hierarchically nanostructured current collector holds great potential for next-generation Na-based batteries.

Summary The large-scale application of rechargeable batteries in electric vehicles and energy-storage systems is still hindered by their high cost, particularly from the active materials. Here we proposed a concept of integration of extraction-separation and materials-preparation to further reduce the materials' cost. The power of this concept was demonstrated by the large-scale room-temperature synthesis (150 g per batch) of multi-shelled Na3(VOPO4)2F microspheres based on in situ generated bubbles as soft templates. The as-prepared Na3(VOPO4)2F shows superior rate capability with discharge capacity of 81 mAh g−1 at 15 C current rate and capacity retention of 70% after 3,000 cycles. Ex situ UV-vis was first employed to characterize the variation of oxidation state for vanadium during the charging and discharging process. This is the first report of a rapid and facile large-scale room-temperature controllable synthesis of Na3(VOPO4)2F microspheres, and this approach could be extended to synthesize other similar compounds.

Na metal anode, benefiting from its high theoretical capacity and lowest electrochemical potential, is one of the most favorable candidates for future Na-based batteries with high energy density. Dendrite growth, volume change and high reactivity are the formidable challenges in terms of good cycling performance and high Coulombic efficiency as well as an expected safety guarantee of Na metal anode for the practical application. Solid electrolyte interphase (SEI) layer as an indispensable component of a battery, its formation and stability play the critical role in the feasibility of Na metal anode. In this review, we first discuss the current consideration and challenges of Na metal anode, and then summarize several strategies to suppress dendrite growth and improve electrochemical performance, including interface engineering, electrolyte composition, electrode construction, and so on. Finally, the conclusion and future perspective of potential development on Na metal anode are proposed.

Sodium-based rechargeable batteries are very promising energy storage and conversion systems owing to their wide availability and the low cost of Na resources, which is beneficial to large-scale electric energy storage applications in future. In the context of attempting to achieve high-energy densities and low cost, multi-electron reaction materials for both cathodes and anodes are attracting significant attention due to high specific capacities involved. Here, we present a brief review on recently reported multi-electron reaction materials for sodium-based batteries. We mostly concentrate on true multi-electron reactions that involve individually valence changes greater than one per redox center, but in addition include materials in the discussion, which undergo multi-electron processes per formula unit. The theoretical gravimetric and volumetric (expanded state) capacities are studied for a broad range of examples. Then, the practically achievable volumetric energy density and specific energy of Na cells with hard carbon, sodium (Na), and phosphorus (P) anodes are compared. For this purpose, various data are recalculated and referred to the same basis cell. The results show the potential superiority of the cells using multi-electron reaction materials and provide an intuitive understanding of the practically achievable energy densities in future Na-based rechargeable batteries. However, these multi-electron reaction materials are facing several key challenges, which are preventing their high-performance in current cells. In order to overcome them, general strategies from particle design to electrolyte modification are reviewed and several examples in both cathode and anode materials using such strategies are studied. Finally, future trends and perspectives for achieving promising Na-based batteries with better performance are discussed.

Sodium-ion batteries (NIBs) show great prospect on the energy storage applications benefiting from their low cost and the abundant Na resources despite the expected lower energy density compared with lithium-ion batteries (LIBs). To further enhance the competitive advantage, especially in energy density, developing the high-capacity carbon anode materials can be one of the effective approaches to realize this goal. Herein, we report a novel carbon anode made from charcoal with a high capacity of ∼400 mAh g−1, wherein about 85% (>330 mAh g−1) of its total capacity is derived from the long plateau region below ∼0.1 V, which differs from those of typical hard carbon materials (∼300 mAh g−1) in NIBs but is similar to the graphite anode in LIBs. When coupled with air-stable Na0.9Cu0.22Fe0.30Mn0.48O2 oxide cathode, a high-energy density of ∼240 Wh kg−1 is achieved with good rate capability and cycling stability. The discovery of this promising carbon anode is expected to further improve the energy density of NIBs towards large-scale electrical energy storage.

Layered transition metal oxides Nax MO2 (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 Na0.66 Mg0.34 Ti0.66 O2 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 Nax MO2 . 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.

Potassium ion batteries are potential energy storage devices owing to their low cost and good K+ diffusion kinetics due to the small Stoke's radius. Here, we report a layered TiS2 cathode material, demonstrating outstanding potassium storage cycling and rate performances in ether-based electrolyte, with a capacity of 80 mAh g−1 at 20 C and 63 mAh g−1 after 600 cycles (1.5–3.0 V, corresponding to 4.8 A g−1). The phase transitions during K ion intercalation at the atomic level are explored via High Resolution Transmission Electron Microscopy (HRTEM) and ex-situ X-ray diffraction (XRD) combined with Rietveld refinements. It undergoes a second-stage structure to be K0.11TiS2 and then first-stage K0.56TiS2. The K cations intercalate into trigonal prismatic sites with a sliding of Ti-S plane by 120 degree-rotation, rendering a 3 × 3 commensurate superstructure along the [001] zone. The K stage intercalation is in favor of a Daumas-Herold model rather than Rudorff model. This study demonstrates that the layer structure materials are promising candidates for high performances K-ion batteries and highlights the importance of improving electrochemical performances with electrolyte modification.

Garnet-type solid-state electrolytes (SSEs) are considered to be a good choice for solid-state batteries, yet the interfacial issues with metallic Li limit their applications. Herein, we propose an ultrasimple and effective strategy to enhance the interfacial connection between garnet SSEs and Li metal just by drawing a graphite-based soft interface with a pencil. Both experimental analysis and theoretical calculations confirm that the reaction between the graphite-based interfacial layer and metallic lithium forms a lithiated connection interface with good lithium-ionic and electronic conductivity. Compared to the reported interfacial materials, the graphite provides a soft interface with better ductility and compressibility. With improvement by this soft interface, the impedance of symmetric Li cells significantly decreases and the cell cycle is stable for over 1000 h. Moreover, a solid-state battery with Li-metal anode, ternary NCM523 cathode, and treated-garnet SSEs is fabricated and displays excellen...

Nanosized Na3PS4 solid electrolyte with an ionic conductivity of 8.44 × 10-5 S cm-1 at room temperature is synthesized by a liquid-phase reaction. The resultant all-solid-state FeS2/Na3PS4/Na batteries show an extraordinary high initial Coulombic efficiency of 95% and demonstrate high energy density of 611 Wh kg-1 at current density of 20 mA g-1 at room temperature. The outstanding performances of the battery can be ascribed to good interface compatibility and intimate solid-solid contact at FeS2 electrode/nanosized Na3PS4 solid electrolytes interface. Meanwhile, excellent cycling stability is achieved for the battery after cycling at 60 mA g-1 for 100 cycles, showing a high capacity of 287 mAh g-1 with the capacity retention of 80%.

Using stable inorganic solid electrolyte to replace organic liquid electrolyte could significantly reduce potential safety risks of rechargeable batteries. Na-superionic conductor (NASICON)-structured solid electrolyte is one of the most promising sodium solid electrolytes and can be employed in solid-state sodium batteries. In this work, a NASICON-structured solid electrolyte Na3.1Zr1.95Mg0.05Si2PO12 was synthesized through a facile solid-state reaction, yielding high sodium-ionic conductivity of 1.33 × 10−3 S·cm−1 at room temperature. The results indicate that Mg2+ is a suitable and economical substitution ion to replace Zr4+, and this synthesis route can be scaled up for powder preparation with low cost. In addition to electrolyte material preparation, solid-state batteries with Na3.1Zr1.95Mg0.05Si2PO12 as electrolyte were assembled. A specific capacity of 57.9 mAh·g−1 is maintained after 100 cycles under a current density of 0.5C rate at room temperature. The favorable cycling performance of the solid-state battery suggests that Na3.1Zr1.95Mg0.05Si2PO12 is an ideal electrolyte candidate for solid-state sodium batteries.

High ionic conductivity electrolyte and intimate interfacial contact are crucial factors to realize high-performance all-solid-state sodium batteries. Na2.9PS3.95Se0.05 electrolyte with reduced particle size of 500 nm is first synthesized by a simple liquid-phase method and exhibits a high ionic conductivity of 1.21 × 10–4 S cm–1, which is comparable with that synthesized with a solid-state reaction. Meanwhile, a general interfacial architecture, that is, Na2.9PS3.95Se0.05 electrolyte uniformly anchored on Fe1–xS nanorods, is designed and successfully prepared by an in situ liquid-phase coating approach, forming core–shell structured Fe1–xS@Na2.9PS3.95Se0.05 nanorods and thus realizing an intimate contact interface. The Fe1–xS@Na2.9PS3.95Se0.05/Na2.9PS3.95Se0.05/Na all-solid-state sodium battery demonstrates high specific capacity and excellent rate capability at room temperature, showing reversible discharge capacities of 899.2, 795.5, 655.1, 437.9, and 300.4 mAh g–1 at current densities of 20, 50, 100, ...

With the desirable energy densities, Li-rich layered cathodes have attracted great attention as potential candidates for next generation Li-ion batteries (LIBs). In this context, the Li-rich layered cathode Li[Li0.2Mn0.56Ni0.17Co0.07]O2 (LMNCO) is prepared and surface modified homogeneously with Li-conductive Li2SiO3 layer via a facile co-precipitation process. It is found that the 3 wt% Li2SiO3 modified Li-rich cathode delivers a specific capacity as high as 207 mAh g−1 after 50 cycles, which results from the interplay among the electrode, Li2SiO3 coating layer and the electrolyte. Further analysis indicates that the Li2SiO3 layer could effectively balance the exfoliation of surface alkaline speciation and the dissolution of surface transition metal to generate the Li Mn Ni Co Si O protection layer, which will beneficial to the Li surface diffusion kinetics and the electrochemical stability of Li-rich layered materials as well.

A novel Eu and F co-doped zinc oxide (EFZO) thin film has been prepared by ion-assisted electron beam evaporation. The effects of different atomic contents of Eu and F on the structural, optical, and electrical properties of EFZO films were investigated. Eu3+ and F− ions are successfully incorporated into the ZnO lattice by the substitution of Zn2+ and O2− sites, respectively. Simultaneously, F− ions also play an important role of filling oxygen vacancy defects. Eu3+ and F− ions serve cooperatively as charge donor centers and compensate for the deformation in the ZnO crystal structure produced by either Eu or F individual ions, thus resulting in improving crystalline quality and electrical properties as compared with single element doping. Complementarity of Eu3+ and F− doping is assumed to be conducive to the F− filling oxygen vacancy effect in consideration of the changes in lattice constant and electrical parameters with varying dopant contents in EFZO films. An optimized EFZO film shows an average visible optical transmittance of 82.9% and a resistivity of 5.7 × 10−4 Ω cm corresponding to a carrier density of 1.86 × 1020 cm−3 and a mobility of 58.8 cm2 V−1 s−1. Conventional organic light-emitting diodes based on the EFZO anode and inverted structural quantum dot light-emitting diodes based on the EFZO cathode have been designed and fabricated, both of which show equivalent or a little higher electroluminescence performance in comparison to the reference ITO-based devices. Our results indicate that Eu and F are effective co-doping elements for ZnO transparent conducting oxide films, and EFZO transparent electrodes have efficient hole and electron injection abilities. As a promising candidate for low cost and high-performance transparent conducting oxide (TCO) films, EFZO can be used for a variety of optoelectronic devices.

Anionic redox reaction (ARR) in lithium- and sodium-ion batteries is under hot discussion, mainly regarding how oxygen anion participates and to what extent oxygen can be reversibly oxidized and reduced. Here, a P3-type Na0.6[Li0.2Mn0.8]O2 with reversible capacity from pure ARR was studied. The interlayer O-O distance (peroxo-like O-O dimer, 2.506(3) Å), associated with oxidization of oxygen anions, was directly detected by using a neutron total scattering technique. Different from Li2RuO3 or Li2IrO3 with strong metal-oxygen (M-O) bonding, for P3-type Na0.6[Li0.2Mn0.8]O2 with relatively weak Mn-O covalent bonding, crystal structure factors might play an even more important role in stabilizing the oxidized species, as both Li and Mn ions are immobile in the structure and thus may inhibit the irreversible transformation of the oxidized species to O2 gas. Utilization of anionic redox reaction (ARR) on oxygen has been considered as an effective way to promote the charge-discharge capacity of the layered oxide cathodes for lithium- or sodium-ion batteries. The detailed mechanism of ARR, in particular how crystal structure affects and coordinates with the ARR, is not yet well understood. In the present work, a combination of X-ray and neutron total scattering measurements has been performed to study the structure of the prototype P3-type layered Na0.6[Li0.2Mn0.8]O2 with pure ARR. Unique structural characteristics, rather than prevailing knowledge of covalency of metal-oxygen, enable the stabilization of the crystal structure of Na0.6[Li0.2Mn0.8]O2 along with the ARR. This work suggests that reversible ARR can be manipulated by proper structure designs, thus to achieve high lithium or sodium storage in layered oxide cathodes. For P3-type Na0.6[Li0.2Mn0.8]O2 with relatively weak Mn-O covalent bonding, crystal structure factors play an important role in stabilizing the oxidized species, inhibiting the irreversible transformation of the oxidized species to O2 gas. The finding is important for better design of layered oxide positive materials with higher reversible capacity via the introduction of a reversible anionic redox reaction.

Rechargeable sodium-ion batteries with earth-abundant Fe/Mn based cathodes are a promising choice for grid-scale applications. However, the key candidate, P2-type Fe-based materials, suffers from severe voltage decay during battery operation due to Fe3+ migration to the neighboring tetrahedral sites. In this study, two Fe-based layered oxides, Na0.7[Cu0.15Fe0.3Mn0.55]O2 and Na0.7[Cu0.2Fe0.2Mn0.6]O2, were prepared. With a combination of in situ XRD, X-ray PDF, and hard and soft X-ray absorption, we demonstrate that the voltage decay in Fe-based layered oxides has dynamic origins. Drastic phase transition can be triggered by higher upper voltage limit, while partially irreversible Fe migration leads to voltage fading. With excess Cu doped into the crystal lattice, Fe migration can be considerably mitigated and therefore, structural stability can be maintained. Furthermore, Cu introduction brings about extra capacity via the correlation between transition metal elements and ligand oxygen, which may well compensate for capacity loss from inert impurity doping. Possible strategies for suppressing the detrimental voltage decay in battery cathodes can be proposed accordingly.

Significantly enhanced luminance and current efficiency for inorganic light-emitting devices have been obtained by tetrabutylammonium bromide (TBAB) additive into perovskite precursors. Reduced nonradiative defects primarily passivated by TBAB and increased exciton binding energy are responsible for improvement of PeLED performance. By employing a TBAB-treated interfacial layer, interface defects are reduced and it results in further promotion of electroluminescence performance of PeLED, including turn-on voltage of 2.6 V, brightness as high as 67 300 cd m−2, current efficiency of 22.5 cd A−1 and external quantum efficiency of 6.28%. Our results shed light on optimization of inorganic PeLEDs by focusing on the removal of defects both at the grain boundaries and the interfaces between carrier transport layers and perovskite emitting layers.

The ever-growing demand for advanced energy storage devices in portable electronics, electric vehicles and large scale power grids has triggered intensive research efforts over the past decade on lithium and sodium batteries. The key to improve their electrochemical performance and enhance the service safety lies in the development of advanced electrode, electrolyte, and auxiliary materials. Ionic liquids (ILs) are liquids consisting entirely of ions near room temperature, and are characterized by many unique properties such as ultralow volatility, high ionic conductivity, good thermal stability, low flammability, a wide electrochemical window, and tunable polarity and basicity/acidity. These properties create the possibilities of designing batteries with excellent safety, high energy/power density and long-term stability, and also provide better ways to synthesize known materials. IL-derived materials, such as poly(ionic liquids), ionogels and IL-tethered nanoparticles, retain most of the characteristics of ILs while being endowed with other favourable features, and thus they have received a great deal of attention as well. This review provides a comprehensive review of the various applications of ILs and derived materials in lithium and sodium batteries including Li/Na-ion, dual-ion, Li/Na-S and Li/Na-air (O2) batteries, with a particular emphasis on recent advances in the literature. Their unique characteristics enable them to serve as advanced resources, medium, or ingredient for almost all the components of batteries, including electrodes, liquid electrolytes, solid electrolytes, artificial solid-electrolyte interphases, and current collectors. Some thoughts on the emerging challenges and opportunities are also presented in this review for further development.

Organic materials, especially the carbonyl compounds, are promising anode materials for room temperature sodium-ion batteries owing to their high reversible capacity, structural diversity as well as eco-friendly synthesis from bio-mass. Herein, we report a novel anthraquinone derivative, C14H6O4Na2 composited with carbon nanotube (C14H6O4Na2-CNT), used as an anode material for sodium-ion batteries in ether-based electrolyte. The C14H6O4Na2-CNT electrode delivers a reversible capacity of 173 mAh g−1 and an ultra-high initial Coulombic efficiency of 98% at the rate of 0.1 C. The capacity retention is 82% after 50 cycles at 0.2 C and a good rate capability is displayed at 2 C. Furthermore, the average Na insertion voltage of 1.27 V vs. Na+/Na makes it a unique and safety battery material, which would avoid Na plating and formation of solid electrolyte interface. Our contribution provides new insights for designing developed organic anode materials with high initial Coulombic efficiency and improved safety capability for sodium-ion batteries.

Among the contenders in the new generation energy storage arena, all-solid-state batteries (ASSBs) have emerged as particularly promising, owing to their potential to exhibit high safety, high energy density and long cycle life. The relatively low conductivity of most solid electrolytes and the often sluggish charge transfer kinetics at the interface between solid electrolyte and electrode layers are considered to be amongst the major challenges facing ASSBs. This review presents an overview of the state of the art in solid lithium and sodium ion conductors, with an emphasis on inorganic materials. The correlations between the composition, structure and conductivity of these solid electrolytes are illustrated and strategies to boost ion conductivity are proposed. In particular, the high grain boundary resistance of solid oxide electrolytes is identified as a challenge. Critical issues of solid electrolytes beyond ion conductivity are also discussed with respect to their potential problems for practical applications. The chemical and electrochemical stabilities of solid electrolytes are discussed, as are chemo-mechanical effects which have been overlooked to some extent. Furthermore, strategies to improve the practical performance of ASSBs, including optimizing the interface between solid electrolytes and electrode materials to improve stability and lower charge transfer resistance are also suggested.