Na-ion Battery Applications Research Articles

Silicene for Na-ion battery applications

Na-ion batteries are promising candidates to replace Li-ion batteries in large scale applications because of the advantages in natural abundance and cost of Na. Silicene has potential as the anode in Li-ion batteries but so far has not received attention with respect to Na-ion batteries. In this context, freestanding silicene, a graphene-silicene-graphene heterostructure, and a graphene-silicene superlattice are investigated for possible application in Na-ion batteries, using first-principles calculations. The calculated Na capacities of 954 mAh/g for freestanding silicene and 730 mAh/g for the graphene-silicene superlattice (10% biaxial tensile strain) are highly competitive and potentials of against the Na/Na potential exceed the corresponding value of graphite. In addition, the diffusion barriers are predicted to be .

Atomic Layer Deposition of HfO2 at Anode/Electrolyte Interface for Stable Anodes in Li and Na Ion Battery Applications

Recently, atomic layer deposition (ALD) has emerged as a promising and powerful technique to fabricate nanostructured electrodes and improve electrode/electrolyte interface in energy storage devices such as Li and Na ion batteries. In this project, we have deposited an electrochemically inert oxide material, hafnium oxide (HfO2), on different anode materials. We demonstrate that a nanoscale layer of HfO2 on zero dimensional (0D) SnO2 nanospheres, one dimensional (1D) MoO3 nanorods and two dimensional (2D) MoS2 nanosheets significantly improves the cyclic stability, when these materials were applied as anode in Li ion batteries. Moreover, HfO2 coated MoS2 nanosheets were tested as anode material in Na ion batteries and, after 50 charge/discharge cycles, HfO2 coated MoS2 electrodes retained 91% of the initial capacity and bare MoS2 electrodes retained only 63%. Most importantly, the mechanism of capacity retention was explained by ex situ high resolution transmission electron microscopy (HRTEM), electrical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and X-ray diffraction. We showed that capacity retention is directly related to the degree of crystallinity retention after charge/discharge process. For instance, in case of MoO3, ex-situ HRTEM analysis showed that after 50 charge/discharge cycles, the crystal structure of bare MoO3 electrodes degrades severely while HfO2 preserves the crystal structure during charge/discharge process. Furthermore, it was found that thickness and amorphous nature of HfO2 layer plays critical role because Li+ ions has to diffuse through this layer. In summary, a mechanistic insight into capacity retention after HfO2 coating has been provided by post – electrochemical ex-situ analysis.

Dependence of Electrochemical Properties on Structure and Deeper Understanding of Sodium Insertion in Hard Carbons Used As Anode for Sodium-Ion Batteries

Nowadays, Lithium ion (Li-ion) batteries are present in many applications such as mobile phones, computers, power tools, hybrid electric (HEV) and electric (EV) vehicles. However abundance, cost and especially accessibility of lithium will be able to bring some issues for Li-ion development in the future [1]. This leads the scientist community to go back to sodium ion battery research, which decreased significantly after Li ion battery success in the 90’s. Sodium seems to be an interesting alternative to lithium because of its abundance and availability. However, in order to be competitive against other technologies, capacity, rate capability and cycle life should be improved [2]. Carbon for Na-ion battery applications has been extensively studied in the literature [3,4] whatever its form: hard carbon, carbon black, carbon nanospheres or nanotubes, carbon fibers and graphene. Especially for hard carbons the main problems reported in literature are a high first irreversible capacity and a poor cyclability. For example, Ding et al.[5] tested carbon made from peat (organic matter) pyrolysis and they obtained a reversible capacity of 255 mAh.g-1 after 200 cycles with a current density equal to 50 mA.g-1 and an initial coulombic efficiency reaching 60%. Recently Sun et al.[6] have synthesized hard carbon from shaddock peel pyrolysis. The pyrolysis temperature was varied from 800 to 1400°C and the best performances were obtained for the temperature 1200°C: the material exhibited a very high reversible capacity of around 400 mAh.g-1 with a good stability over 200 cycles and a first coulombic efficiency of 68%. Even though hard carbon structure and sodium ion insertion into these materials were studied, especially by Dahn’s group in 2000 [7,8,9], insertion mechanisms are still in debate in the literature. Dahn and coworkers developed a card-house model with two different mechanisms: in the galvanostatic curve, the sloppy part corresponds to sodium intercalation between graphene sheets and the low voltage plateau is related to the sodium insertion in micropores. Lately Bommier et al. [10] have proposed another point of view concerning this model based on ab initio calculations: the low voltage plateau is due to intercalation into sites around the defective carbon surface. In this presentation we proposed to develop two parts. The first part exhibits the dependence of electrochemical performances on hard carbon structure. All hard carbon samples are made from the same organic precursor, cellulose. The final pyrolysis temperature is varied from 700°C to 1600°C. The samples are fully characterized with both usual techniques such as X-ray diffraction, scanning electron microcopy and N2 adsorption and more advanced tools such as small-angle X-ray scattering (SAXS) and transmission electron microscopy. The different parameters obtained from all these characterization methods (d002, specific surface area, radius of gyration and crystallite size) can be linked to the electrochemical performances as indicated in the figure. Samples pyrolysed from 1300°C to 1600°C showed a reversible capacity equal to 300 mAh.g-1 at C/10 rate (where C=372 mA.g-1) with an excellent stability in cycling and a very good initial coulombic efficiency reaching 84%. The second part of the presentation aims to deeper understand sodium insertion mechanisms in these disordered structures. To distinguish the different mechanisms hard carbons are discharged at different potentials and analyzed with SAXS and impedance spectroscopy.

RGO/Stibnite Nanocomposite as a Dual Anode for Lithium and Sodium Ion Batteries

RGO/Sb2S3 nanocomposite has been investigated in this study as a dual anode material for Li- and Na-ion battery applications. The stibnite phase of Sb2S3, and its rGO composite have been obtained from a molecular complex, Sb(SCOPh)3 or its rGO mixture by solid state decomposition or hydrothermal treatment. The pristine sample consists of micron sized particles with rod-like morphology while the rGO composite is made of nanoparticles of Sb2S3 embedded in rGO sheets. Electrochemical lithium and sodium storage properties of the prepared materials have been investigated using galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy studies. The rGO composite demonstrates better lithium storage capacity than the pristine sample owing to enhanced conductivity. In addition, the rGO sheets act as a buffer for volume change during lithium/sodium cycling resulting in a better energy storage.

Selenides Based Sodium Superionic Conductors

All-solid-state Na-ion batteries that operate at or close to room temperature are a promising next-generation battery technology with enhanced safety and reduced manufacturing cost. An indispensable component of this technology is the solid state electrolyte that allows rapid shuttling of the mobile cation (i.e., Na+) between the cathode and anode. However, there are very few fast Na-ion conductors with ionic conductivity approaching that of the liquid counterparts (i.e., 1 mS cm-1). Compared to oxides and sulfides, selenides form a huge unexplored chemical space for fast ionic conductor discovery. Based upon ionic size considerations, selenide-based compounds may provide a more suitable structural framework for the rapid diffusion of the much larger Na+ cations compared with Li+. This consideration led us to an extensive search of fast Na-ion conductors in the Se-based chemical space via high-throughput computational screening, and has identified cubic Na3PSe4 as one of the most promising candidates. In this work, we present the synthesis and structural characterization of Na3PSxSe4-x (x = 0, 1, 2, 3, 4). The structures of these phases are determined from high-resolution synchrotron X-ray diffraction data, which allow us to unambiguously identify a tetragonal-to-cubic phase transition with increasing Se concentration in Na3PSxSe4-x. The Na-ion conductivity and activation energy for Na-ion diffusion were further characterized via variable temperature impedance spectroscopy, from which a negative correlation between the activation barrier and Se concentration can be established. Of particular note is that the x = 4 end member (i.e., cubic Na3PSe4) possesses a room-temperature ionic conductivity exceeding 0.1 mS cm-1, and does not require high temperature sintering to minimize grain boundary resistance, making it a promising solid-state electrolyte candidate for all-solid-state Na-ion battery applications. These experimental results were complemented by ab initio computation through which we demonstrate an intriguing interplay between the tetragonal-to-cubic phase transition, defect formation, and Na+ migration. This work has two important implications for future studies in related fields: (1) selenide based compounds represent a promising platform for the discovery of new fast Na-ion conductors; and (2) the current study opens up new opportunities for the exploration of Se and/or S based battery chemistry, such as the construction of all-solid-state Na/Se battery.

Layered-to-Rock-Salt Transformation in Desodiated NaCrO2

O3 layered sodium transition metal oxides (i.e., NaMO2, M = Ti, V, Cr, Mn, Fe, Co or Ni) are a promising class of cathode materials for Na-ion battery applications. These materials, however, all suffer from severe capacity decay when a large amount of Na is extracted from the hosts. Understanding the causes of this capacity decay is the key to fully unlock the potential of these materials for battery applications. In this work, we elaborate the capacity fading mechanism for one of the compounds in this class, i.e., NaCrO2. The (de)sodiation processes of NaCrO2 were first characterized by in situ XRD. Using a slow cycling rate (C/50), a phase diagram of NaxCrO2 close to thermodynamic equilibrium could be constructed. Ex situ synchrotron XRD and electron diffraction were then performed on samples that were charged to selected stages of charge. Through these and additional ab initio computation, we demonstrate that NaxCrO2 (0 < x < 1) remains in the layered structure framework without Cr migration up to a composition of Na0.4CrO2. Further removal of Na beyond this composition will trigger a layered to rock-salt transformation converting the P'3-Na0.4CrO2 to a rock-salt CrO­2 phase, which is responsible for the capacity fade of NaCrO2. This structural transformation proceeds via the formation of an intermediate O3-CrO2 phase that contains Cr in both Na and Cr slabs. It is intriguing to note that intercalation of alkaline ions (i.e., Na+ and Li+) into the rock-salt CrO2 is actually possible, albeit in a limited amount (~0.2 per formula). Preventing the layered to rock-salt transformation is of uttermost importance to improve the cyclibility of NaCrO2. Possible strategies for circumventing this detrimental phase transition will be proposed. We believe insights obtained in this work can be potentially applied to other O3 type of Na and Li transition metal oxides, and can serve as strong basis for future materials design of NaCrO2 based cathodes.

Layered-to-Rock-Salt Transformation in Desodiated NaxCrO2 (x 0.4)

O3 layered sodium transition metal oxides (i.e., NaMO2, M = Ti, V, Cr, Mn, Fe, Co, Ni) are a promising class of cathode materials for Na-ion battery applications. These materials, however, all suffer from severe capacity decay when the extraction of Na exceeds certain capacity limits. Understanding the causes of this capacity decay is critical to unlocking the potential of these materials for battery applications. In this work, we investigate the structural origins of capacity decay for one of the compounds in this class, NaCrO2. The (de)sodiation processes of NaCrO2 were studied both in situ and ex situ through X-ray and electron diffraction measurements. We demonstrate that NaxCrO2 (0 < x < 1) remains in the layered structural framework without Cr migration up to a composition of Na0.4CrO2. Further removal of Na beyond this composition triggers a layered-to-rock-salt transformation, which converts P′3-Na0.4CrO2 into the rock-salt CrO2 phase. This structural transformation proceeds via the formation of a...

Development of ionic liquid mediated novel polymer electrolyte membranes for application in Na-ion batteries

Polymer electrolyte membranes based on polymer PEO, ionic liquid, 1-butyl-3-methylimidazolium methylsulfate (BMIM-MS), and salt, sodium methylsulfate (NaMS), were prepared and characterized by SEM, XRD, TGA/DTGA, DSC, ac impedance spectroscopy and cyclic voltammetry.

Computational and Experimental Investigations of Na-Ion Conduction in Cubic Na3PSe4

All-solid-state Na-ion batteries that operate at or close to room temperature are a promising next-generation battery technology with enhanced safety and reduced manufacturing cost. An indispensable component of this technology is the solid-state electrolyte that allows rapid shuttling of the mobile cation (i.e., Na+) between the cathode and anode. However, there are very few fast Na-ion conductors with ionic conductivity approaching that of the liquid counterparts (i.e., 1 mS cm–1). In this work, we present the synthesis and characterization of a fast Na-ion conductor, cubic Na3PSe4. This material possesses a room-temperature ionic conductivity exceeding 0.1 mS cm–1 and does not require high-temperature sintering to minimize grain boundary resistance, making it a promising solid-state electrolyte candidate for all-solid-state Na-ion battery applications. On the basis of density functional theory, nudged elastic band, and molecular dynamics investigations, we demonstrate that the framework of cubic Na3PSe...

A Perylene Diimide Crystal with High Capacity and Stable Cyclability for Na-Ion Batteries.

Organic Na-host materials have are now actively pursued as an attractive alternative to conventional transition-metal compounds for development of sustainable sodium ion batteries; however, most of the organic compounds reported so far suffer from their low reversible capacity and poor cyclability. Here, we report a simple perylene diimide, 3,4,9,10-perylene-bis(dicarboximide) (PTCDI), which demonstrates remarkable electrochemical performances as an organic cathode for Na-ion batteries. With the high density of redox-active carbonyl groups in a stable π-conjugated structure, the PTCDI molecule can undergo a two-electron redox reaction with reversible insertion/extraction of 2 Na(+) ions per molecular unit, demonstrating a high capacity of 140 mAh g(-1), a strong rate performance with a reversible capacity of 103 mAh g(-1) at 600 mA g(-1) (5 C,1 C = 120 mA g(-1)) and a long-term cyclability with 90% capacity retention over 300 cycles. Because this PTCDI material is commercially available and nontoxic, it may serve as a new alternative cathode for Na-ion battery applications.

Nanostructured polystyrene/polyaniline/graphene hybrid materials for electrochemical supercapacitor and Na-ion battery applications

In this work, nanostructured polystyrene/polyaniline/reduced graphene oxide (PS–PANI/rGO) hybrid materials based on in situ reduction of graphene oxide with ascorbic acid and self-assembly have been successfully prepared for electrochemical supercapacitor and Na-ion battery applications. The supercapacitor based on the PS–PANI/rGO as an electrode material exhibits a specific capacitance of 180 F g−1 at a current density of 0.5 A g−1 from −0.4 to 1.0 V and a high energy density of 49 W h kg−1 at the power density of 352.8 W kg−1. Moreover, the nanostructured PS–PANI/rGO has a good cycle stability (74 % capacitance retention after 5000 cycles), indicating its future potential application in electrochemical energy storage. The material is further used as an anode in Na-ion batteries, and the results show that the porous nanostructured PS–PANI/rGO delivers a high capacity of 155 mA h g−1 and keeps over 150 charge–discharge cycles at a constant current of 100 mA g−1 (0.5 C).

In situ monitoring of TiO2(B)/anatase nanoparticle formation and application in Li-ion and Na-ion batteries

A facile method is used to synthesise TiO2(B) for use in Li- and Na-ion batteries.

Investigation of Na2/3Ni1/3Ti2/3O2 as Novel Bi-Functional Electrode Material for Non-Aqueous, Room Temperature Na-Ion Batteries

Developing long life, low-cost energy storage solutions based on earth abundant minerals is crucial for renewable energy sources, smart electric grid networks, portable electronics and automotive sector. Na-ion batteries, engineered to operate under ambient conditions with non-aqueous electrolytes, offer much promise in that they do not have resource constraints1and by selecting appropriate materials they can be fabricated into high voltage electrochemical cells, similar to Li-ion chemistry. The objective of the current work is to study the electrochemical properties of a new oxide material with the composition Na2/3Ni1/3Ti2/3O2 (SNTL)2 as a “bi-functional” intercalation-type electrode for Na-ion battery applications. The presence of two transition metals in this layered oxide enables us to activate two redox couples (Ni2+/3+ and Ti4+/3+) of different species in the same material and thereby provides the opportunity to use it as anode or cathode depending on the potential window. This approach of making both electrodes (anode and cathode) using the same material can simplify electrode design and potentially reduce manufacturing costs for commercial applications. The solid state synthesis conditions of SNTL have been optimized to make phase-pure oxide with minimal particle size as shown in Figure 1a and Figure 1b. Galvanostatic cycling shows that up to 50% of sodium ions can be removed reversibly by oxidizing nickel from 2+ to higher oxidation state without any significant capacity loss. This contributes to a sloping voltage profile in the range of 3-4.2 V (Figure 1c) with solid solution-type mechanism involving no phase transitions. Sodium insertion into pristine SNTL, due to its sodium deficient nature, activates the Ti4+/3+ redox couple. This leads to again a sloping voltage profile with an average voltage of 0.7 V vs. Na/Na+ as shown in Figure 1d. The reaction has been confirmed to be of solid solution-type using ex-situ XRD measurements. Thus, SNTL can be used to fabricate 3V intercalation-based Na-ion batteries. Wet chemistry-based synthetic routes (sol gel) are being currently explored to reduce the particle size, decrease the diffusion length scale of electrons and thereby improve the electrochemical performance under higher currents. Fabrication and testing of solid state batteries using SNTL material as active electrodes (anode and cathode) and Na3Zr2P1Si2O12 material (NASICON)3as fast sodium conducting solid electrolyte is also currently under progress.

Electrochemical Properties of Electrodeposited Sn Anodes for Na-Ion Batteries

Introduction Over the past few decades, Li-ion batteries (LIBs) have been widely used as power sources for mobile electronic products and power tools, and nowadays a much effort has been focused on the use of these batteries in large-scale applications such as electric vehicles, hybrid electric vehicles and electrical energy storage (EES) devices. However, because the amount of the Li resources would not be sufficient to meet industrial needs in the long term, the expansion of the LIBs market takes concern on the sustainable supply of Li and the raising of the Li prices. Accordingly, in recent years, rechargeable Na-ion batteries (SIBs) have received great attention as a possible alternative to replace LIBs. Owing to the abundant resource, low cost and a relatively low redox potential (0.3 V above that of Li/Li+), NIBs are expected to be a near-term alternative for large-scale systems such as grid storages [1].Despite the high specific capacity, pure Na metal is inappropriate as an anode material for practical applications of NIBs because the dendiritc deposition of sodium during charging can cause the severe safety problems as well as the reduced capacity and increasing electrode impedance. To overcome these problems, the research for finding suitable electrode materials which have high specific capacity, low irreversible loss, high coulombic efficiency and long cycle life for SIBs have been extensively conducted. Among the various candidate materials, Sn is one of the most attractive anode materials because of its high theoretical capacity and low reaction potential. When assuming complete sodiation of Sn into Na15Sn4, the capacity of Sn is approximately 847 mAh g-1[1], which is substantially higher than the reversible capacity of carbonaceous materials (approximately 250 mAh g-1) [2]. In this study, the electrochemical performance and the sodiation/desodiation mechanisms of electrodeposited Sn were investigated based on previous studies. Herein, two Sn electrodes that have completely different morphologies and crystal structures were prepared by electrodeposition, and their electrochemical properties for Na-ion battery applications were examined, with an emphasis on the effects of the morphology and the phase structure of Sn on the cyclability of the electrodes. Experimental. Two different Sn electrodes were prepared by electrodeposition from different electrolytes. The electrodeposition of Sn was performed in a two-electrode cell that consists of a smooth Cu sheet as the cathode and a Sn plate as the anode. A constant current density of -10 mAcm-2 was applied for 4 min at room temperature. The electrochemical properties of the Sn electrodes were investigated using Swagelok-type cells assembled in an Ar-filled glove box. The cell is composed of a sheet of the Sn electrode (with an area of 1 cm2) and a Na metal film (with an area of 1 cm2) without using a separator. The electrolyte was anhydrous propylene carbonate (PC) containing 1 M NaClO4 and 0.5 vol.% fluoroethylene carbonate (FEC). The charge/discharge characteristics of the electrode were galvanostatically examined at a current density of 50 mA g-1 between 0.001 and 0.65 V (vs. Na/Na+). Results and discussion. Two Sn electrodes that have completely different morphologies and crystal structures were successfully prepared by electrodeposition. One consists of coarse and isolated particles, but the other exhibits a compact thin layer composed of fine grains. Both electrodes showed excellent reversibility via three conjugated sodiation/desodiation reactions. Nevertheless, the particle-type Sn electrode had the poor cycle performance due to the electrical isolation of the active materials. In contrast, the layer-type Sn electrode showed a stable cycle performance in which the charge capacity was maintained at 607.51 mAh g-1after 40 cycles, which corresponds to 98.21% of its initial charge capacity. The difference in the cyclability of the electrodes was attributed to the morphology of the Sn electrodeposits and to the bond between Sn and the Cu substrate.

Atom-Level Understanding of the Sodiation Process in Silicon Anode Material.

Despite the exceptionally large capacities in Li ion batteries, Si has been considered inappropriate for applications in Na ion batteries. We report an atomic-level study on the applicability of a Si anode in Na ion batteries using ab initio molecular dynamics simulations. While crystalline Si is not suitable for alloying with Na atoms, amorphous Si can accommodate 0.76 Na atoms per Si atom, corresponding to a specific capacity of 725 mA h g(-1). Bader charge analyses reveal that the sodiation of an amorphous Si electrode continues until before the local Na-rich clusters containing neutral Na atoms are formed. The amorphous Na0.76Si phase undergoes a volume expansion of 114% and shows a Na diffusivity of 7 × 10(-10) cm(2) s(-1) at room temperature. Overall, the amorphous Si phase turns out quite attractive in performance compared to other alloy-type anode materials. This work suggests that amorphous Si might be a competitive candidate for Na ion battery anodes.

Low Voltage Sodium Intercalation in NaxNix/2Ti1-x/2O2 (0.5 ≤ x ≤ 1.0)

The NaxNix/2Ti1-x/2O2 (0.5 ≤ x ≤ 1.0) series of layered oxides were found to be remarkably stable to 0 V vs. Na and have a reversible low intercalation voltage plateau at 0.7 V. In situ X-ray diffraction measurements confirmed the low voltage intercalation mechanism. The low voltage plateau increases in capacity as x is decreased with the x = 0.6 composition having a reversible capacity of 100 mAh/g or 394 Ah/L between 0.005 and 2 V. Higher capacities may be possible in materials which can tolerate more vacancies in the sodium layer. Such layered transition metal titanates may represent a new class of negative electrode materials for applications in Na-ion batteries.

Self-doped polypyrrole with ionizable sodium sulfonate as a renewable cathode material for sodium ion batteries

A Na-host cathode is developed by grafting the polypyrrole chains with ionizable sodium sulfonate. Due to the immobile p-doping of organic anions, the self-doped polymer can act as a Na-host for reversible Na insertion-extraction reaction, thus offering a low cost and renewable organic cathode for Na ion battery applications.

Single-crystal FeFe(CN)6 nanoparticles: a high capacity and high rate cathode for Na-ion batteries

Prussian blue analogues are actively explored as low cost and high capacity cathodes for Na ion batteries; however, their applications are hindered by low capacity utilization and poor cyclability of these compounds. Here we show that this problem can be solved by controlling the purity and crystallinity of the Prussian blue lattices. As a model compound, single-crystal FeIIIFeIII(CN)6 nanoparticles are synthesized and found to have a sufficiently high capacity of 120 mA h g−1, an exceptional rate capability at 20 C and superior cyclability with 87% capacity retention over 500 cycles, showing great promise for Na ion battery applications. More significantly, these results provide a new insight into the intercalation chemistry of Prussian blue analogues and open new perspectives to develop Na storage cathodes for widespread applications of electric energy storage.

Synthesis and electrochemical behaviors of layered Na0.67[Mn0.65Co0.2Ni0.15]O2 microflakes as a stable cathode material for sodium-ion batteries

Stable Na+ ion storage cathodes with adequate reversible capacity are now greatly needed for enabling Na-ion battery technology for large scale and low cost electric storage applications. In light of the superior Li+ ion storage performance of layered oxides, pure P2-phase Na0.67[Mn0.65Ni0.15Co0.2]O2 microflakes are synthesized by a simple sol–gel method and tested as a Na+ ion storage cathode. These layered microflakes exhibit a considerably high reversible capacity of 141 mA h g−1 and a slow capacity decay to 125 mA h g−1 after 50 cycles, showing much better cyclability than previous NaMnO2 compounds. To further enhance the structural and cycling stability, we partially substituted Co3+ by Al3+ ions in the transition-metal layer to synthesize Na0.67[Mn0.65Ni0.15Co0.15Al0.05]O2. As expected, the Al-substituted material demonstrates a greatly improved cycling stability with a 95.4% capacity retention over 50 cycles, possibly serving as a high capacity and stable cathode for Na-ion battery applications.

Carbon coated hollow Na2FePO4F spheres for Na-ion battery cathodes

Carbon coated porous hollow Na2FePO4F (C/Na2FePO4F) spheres with 500 nm diameter and 80 nm wall thickness are synthesized by a one-step template-free ultrasonic spray pyrolysis process using sucrose as the carbon source. Nano-sized porous hollow C/Na2FePO4F spheres allow electrolyte to penetrate into the hollow structure, and thus the electrochemical reaction can take place on both the outside and inside surface and in the pores. Also, the carbon coating on Na2FePO4F hollow spheres enhances the electronic conductivity and charge transfer reaction kinetics. The unique carbon coated porous hollow C/Na2FePO4F cathodes deliver 89 mAh g−1 capacity at a low rate of 0.1C, and 75 mAh g−1 at 1C, and maintains 33% of capacity at 9C. After 750 cycles at 1C, C/Na2FePO4F cathodes can still provide 60 mAh g−1, which is 80% of initial capacity. The significant advance in electrochemical performance of hollow C/Na2FePO4F spheres combined with mature aerosol spray synthesis technology make these carbon coated porous hollow C/Na2FePO4F spheres very promising as cathode materials for practical applications in Na-ion batteries.