Layered Sodium Transition Metal Oxides Research Articles

The effect of octahedral distortions on the electronic properties and magnetic interactions in O3 NaTMO2 compounds (TM = Ti-Ni & Zr-Pd).

The interplay between the coordination environment and magnetic properties in O3 layered sodium transition metal oxides (NaTMO2) is a fascinating and complex problem. Through detailed and comprehensive density functional investigations on O3 NaTMO2 compounds, we demonstrate that the TM ions in O3 NaMnO2, NaFeO2 and NaCoO2 adopt a high spin state. Structurally, NaMnO2 and NaPdO2 undergo Jahn–Teller distortions while NaNbO2 undergoes puckering distortion. Furthermore, in addition to Jahn–Teller distortion, NaPdO2 exhibits charge disproportionation as it contains Pd2+, Pd3+ and Pd4+ species. These distortions stabilize the inter-plane ferromagnetism. Additionally, the inter-plane ferromagnetic coupling is stabilized by kinetic p–d exchange mechanism in undistorted NaCoO2, NaNiO2 and NaTcO2. The intra-plane coupling in this family of compounds on the other hand was found to be generally weak. Only NaMnO2, NaNiO2 and NaTcO2 are predicted to show bulk ferromagnetism with estimated Curie temperatures below ∼50 K.

The Interaction between Cu and Fe in P2-Type NaxTMO2 Cathodes for Advanced Battery Performance

Recently, Cu element has been introduced into layered sodium transition metal oxides (NaxTMO2) as cathode materials for sodium ion batteries to engineer rate and cycling performance. To study the unique role provided by Cu, we designed, synthesized and tested four different compositions of P2-type Nax(MnyFezCo1-y-z)O2 and three compositions of P2-type Nax(MnyFezCu1-y-z)O2 cathode materials. When cycled in the full voltage range of 1.5∼4.5 V under different rates 0.1 C, 1 C and 10 C, the cyclability of MnFeCu-based compounds is better than that of MnFeCo-based ones. Using X-ray diffraction, we observed the P2 to O2-like phase transition of MnFeCu-based materials upon charging and studied its influence on battery performance. Limiting the P2-O2 phase transition delivers less capacity, but improves cyclability. By DFT simulations, we showed that different Na diffusivity and site preference in the high voltage phase contribute to the difference in the electrochemical performances of these cathode materials.

The NaxMoO2 Phase Diagram (1/2 ≤ x < 1): An Electrochemical Devil’s Staircase

Layered sodium transition metal oxides represent a complex class of materials that exhibit a variety of properties, for example, superconductivity, and can feature in a range of applications, for example, batteries. Understanding the structure–function relationship is key to developing better materials. In this context, the phase diagram of the NaxMoO2 system has been studied using electrochemistry combined with in situ synchrotron X-ray diffraction experiments. The many steps observed in the electrochemical curve of Na2/3MoO2 during cycling in a sodium battery suggest numerous reversible structural transitions during sodium (de)intercalation between Na0.5MoO2 and Na∼1MoO2. In situ X-ray diffraction confirmed the complexity of the phase diagram within this domain, 13 single phase domains with minute changes in sodium contents. Almost all display superstructure or modulation peaks in their X-ray diffraction patterns suggesting the existence of many NaxMoO2 specific phases that are believed to be characteri...

Dual Stabilization and Sacrificial Effect of Na2CO3 for Increasing Capacities of Na-Ion Cells Based on P2-NaxMO2 Electrodes

Sodium ion battery technology is gradually advancing and can be viewed as a viable alternative to lithium ion batteries in niche applications. One of the promising positive electrode candidates is P2 type layered sodium transition metal oxide, which offers attractive sodium ion conductivity. However, the reversible capacity of P2 phases is limited by the inability to directly synthesize stoichiometric compounds with a sodium to transition metal ratio equal to 1. To alleviate this issue, we report herein the in situ synthesis of P2-NaxMO2 (x ≤ 0.7, M = transition metal ions)-Na2CO3 composites. We find that sodium carbonate acts as a sacrificial salt, providing Na+ ion to increase the reversible capacity of the P2 phase in sodium ion full cells, and also as a useful additive that stabilizes the formation of P2 over competing P3 phases. We offer a new phase diagram for tuning the synthesis of the P2 phase under various experimental conditions and demonstrate, by in situ XRD analysis, the role of Na2CO3 as a ...

Honeycomb Compound Na3Ni2BiO6 As Positive Electrode Material for Na-Ion Battery

Introduction Layered sodium transition metal oxide materials are promising candidates as positive electrode for sodium ion batteries. Partial substitution of the transition metal with other metal could modify the crystal structure and electrochemistry of the materials. Honeycomb oxides such as Na3Ni2SbO6 have been studied and showed high energy density.1,2 In this study, honeycomb compound Na3Ni2BiO6 was synthesized and characterized in Na cells. Experimental Stoichiometric amounts of NiO, NaBiO3 and Na2CO3 powders were mixed by ball milling and pelletized. The pellets were heated at 700 ºC for 8 hours first then 750 ºC for 12 hours under oxygen to obtain Na3Ni2BiO6. Heated samples were transferred to Ar-filled glovebox immediately. Electrodes were made with active material, PVDF binder, carbon black at a ratio of 8:1:1 and dried under vacuum at 120 ℃ overnight. 1M NaPF6 in a solution of EC, DEC, FEC (volume ratio 3:6:1) was used as electrolyte and Na foil was used as counter/reference electrode. X-ray diffraction (XRD) patterns were measured with a Rigaku Ultima IV X-ray diffractometer equipped with a Cu anode X-ray tube and a diffracted beam monochromator. Results and discussion Figure 1 shows the XRD pattern of synthesized Na3Ni2BiO6. The structure resembles that of Rm α-NaFeO2 (space group 166), except for the honeycomb ordering at low angles not described by the Rm α-NaFeO2 structure (indicated by stars). The honeycomb structure is generated by the 2:1 ordering of edge sharing NiO6 and BiO6 in the a-b plane. An impurity phase of NiO was present (indicated by solid circles). Figure 2 shows the voltage curve of Na3Ni2BiO6 for the first 2 cycles in the voltage range of 1.5 V – 3.8 V and 1.5 V – 4.5 V. Na3Ni2BiO6 was found to have a reversible capacity of ~80 mAh/g, corresponding to the reversible removal of ~0.5 Na per NaNi2/3Bi1/3O2. It should be noted that the heavy atomic weight of Bi lowers the gravimetric capacity. The voltage curve is characterized by two flat plateaus located at ~3.3 V and ~3.5 V during charging, which is typical for Ni-compounds. The two plateaus are both reversible during discharging with a hysteresis of ~0.2 V. When the cell was cycled between 1.5 V – 4.5 V, another plateau with a capacity of ~20 mAh/g appears at ~4.3 V upon charging. However this plateau is not reversible, as can be seen by the similar discharge curve to that of cycled between 1.5 V – 3.8 V. The cycling performance, rate capability and structural changes during charge/discharge will also be discussed. Acknowledgments The authors acknowledge funding from NSERC and 3M Canada under the auspices of the Industrial Research Chair and Discovery grant programs.

Electrochemical Performance of NaNiCoMnO2 for Cathode Material in Sodium Ion Batteries

Lithium ion batteries have emerged as the best suited power source for portable electronics. They are also being considered as strong contenders to meet the energy demands of the transport sector. However lithium cannot be considered as an abundant element and its natural resources are unevenly distributed. Sodium-ion batteries (NIB) appear as a promising alternative to the well-established lithium batteries technology. Sodium natural resources are unlimited everywhere as sodium is the fourth most abundant element on earth. Layered sodium transition metal oxides, NaxMO2 (M = transition metals), appear as very interesting cathode materials. The interest in these layered oxides probably arose from their high capacities and ease of synthesis In this study, we synthesized NaNiCoMnO2 as the cathode material and its electrochemical performance was measured. Also the Na ion intercalation and deintercalation behavior was studied using Galvanostatic Intermittent Titration Technique(GITT) and Cyclic voltammetry (CV)

Solid-State NMR Study of the Paramagnetic P2-Na0.67Mn0.95Mg0.05O2 Na-Ion Battery Cathode

Lithium-ion batteries have been preferred to their sodium-ion counterparts for their higher energy density and operating voltages, but concerns about lithium shortage and rising costs have encouraged the scientific community to turn its attention to the more sustainable sodium-ion batteries (NIBs). Layered sodium transition metal oxides, such as P2-Na0.67Mn1-xMgxO2 (0≤x≤1)1, have a high theoretical capacity and are promising NIB cathodes. The structural stability required for long-term cycling remains a major challenge due to the ionic size of Na+ (70% larger than Li+), whilst intermediate phases with particular Na+/vacancy ordering patterns tend to form upon cycling. An understanding of the underlying structural and electronic processes occurring on charge and discharge is a necessary step towards devising higher performance electrode materials2. Solid-state Nuclear Magnetic Resonance (ssNMR) allows the local distortions and variations in the electronic structure and in oxidation states upon cycling to be investigated3. We present both ex situ and in situ 23Na NMR results on the P2-Na0.67Mn0.95Mg0.05O2 cathode. Paramagnetic interactions in P2-Na0.67Mn0.95Mg0.05O2 lead to large NMR shifts and very broad resonances. Fast magic angle spinning (MAS) ex situ NMR was performed to enhance the resolution and allow the signals from different local environments (with different chemical and hyperfine shifts) to be distinguished4. In order to follow the electrochemical processes in real time, and to gain insight into the underlying Na (de)intercalation mechanisms, we performed in situ ssNMR experiments on a P2-Na0.67Mn0.95Mg0.05O2//Na(s) half-cell. A schematic of the in situ bag cell is shown in Figure 1a5,6,7. In order to excite the 100 kHz wide static 23Na NMR signal observed for the pristine cathode film, we made use of the recently developed Automatic Tuning Matching Cycler (ATMC) in situ NMR approach8. The low intensity, broad cathode signal is difficult to observe due to complete overlap with the more intense signals arising from the electrolyte (1M NaTFSI in PC) and the Na metal anode2. We carried out a so-called T1 filter NMR experiment which takes advantage of the different relaxation behaviors of the various components of the bag cell to discriminate between the overlapping 23Na NMR signals. This lead to significant enhancement of the broad feature arising from the cathode. 23Na in situ NMR data measured upon initial charge at a rate of C/50 reveals an expected increase of the Na metal peak intensity due to the formation of Na-metal dendrites, and the disappearance of the broad cathode feature (see Figure 1b). These encouraging results show that in situ NMR can be applied to even extremely difficult systems - from an NMR perspective - such as paramagnetic materials2. Ongoing work focuses on the optimization of the electrochemical performances of the in situ cell to allow for multiple cycles and higher rates to be investigated. The conventional bag cell is replaced by a new cell design with increased pressure and sample size. We expect the techniques developed in this work to enable us to investigate a greater range of electrode materials using in situ NMR.

Layered P2-Nax[Mg, Ni, Mn]O2 Cathodes: What Are the Atomistic Effects of Cation Substitution?

Layered sodium transition metal oxides such as Nax[Ni, Mn]O2 with P2 oxygen stacking structure are potential cathode materials for sodium-ion batteries. The main challenge is that they tend to show many plateaux in the charge-discharge profile, indicating numerous phase transitions resulted from sodium orderings, which has adverse effects on cyclability. Recently it has been reported that the substitution of non-redox active cations, such as Mg2+, Li+ and Zn2+, for transition metal ions results in smooth charge-discharge profile and improved rate performance. In this work, the P2-Nax[Mg, Ni, Mn]O2 system is investigated by both ab-initio and interatomic potential molecular dynamics simulations in order to understand the role of Mg2+ substitution. Na-ion diffusivities and migration barriers are simulated, and the atomistic effects of Mg2+ are discussed.

Design and Investigation on Soft-Packed Sodium-Ion Batteries Based on Layered Sodium Transition Metal Oxide Cathodes

Sodium ion battery (SIB) technology is considered as an attractive alternative to lithium ion batteries for the large scale energy storage systems due to vast availability of sodium resource. Up to now, much research effort has been devoted to the exploration of advanced electrode materials for SIBs. In order to promote the industrialization of sodium ion batteries, we scale up the synthesis of layered oxides NaxMO2 (M: Fe, Mn, Ni, Cu, Ti) using facile hydroxide co-precipitation combined with following calcination method. The obtained cathode materials showed good rate performance and excellent cycling stability even at low temperature. The Nax(Fe0.5Mn0.5)O2 cathode showed excellent reversibility between 2.0 V and 4.0 V with reversible capacity of 100 mAh g-1 (0.1 C). After Ni doping, the Nax(Fe0.5Ni0.3Mn0.2)O2 cathode showed good rate performance and excellent cycling stability with an initial capacity of 130 mAh g-1 at 1C. When hard carbon was used as anode, we designed soft-packed batteries with capacities ranging from 0.5Ah to 5Ah. Electrochemical behaviors of the batteries at different temperatures were studied and thermal stability of these batteries was also evaluated. A 0.1KWh sodium ion battery pack was fabricated and evaluated as shown in Fig.1. The sodium ion packs can be assembled and used in portable energy storage device, household electrical energy storage, smart grid and low-speed electric vehicle, etc. The authors are grateful for the financial support of this work by the Natural Science Foundation of China (21573147, 21506123, 21336003) and the 973 Program of China (2014CB239700). Figure 1

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...

Thermal Stability Studies in Charged Layered Sodium Transition Metal Oxide Cathode Materials for Na-Ion Batteries

Layered alkali transition metal oxides (i.e., LiMO2 and NaMO2, M=transition metal) are the premier class of cathode materials in lithium- and sodium-ion battery system. The safety characteristics of LiMO2 cathode based LIBs are one of the most critical barriers to be overcome for the large scale application such as EV. One of the main reasons that might cause safety hazards of the LIB is associated with the thermal instability of charged Li1-xMO2 cathode materials, which is related to the occurrence of exothermic reactions between flammable electrolyte and liberating oxygen from charged Li1-xMO2 at high temperature. Based on the structural homology between the layered LiMO2 and NaMO2, we expect that the investigation of thermal stability of charged Na1-xMO2cathode materials is also important for the practical use of SIBs. However, few attentions have been paid on safety issue of SIBs. In this study, the thermal stability of charged Na1-xMO2 cathode materials is investigated by using combined in situ time-resolved X-ray diffraction and mass spectroscopy (TR-XRD/MS), which allows simultaneous observation of the structural changes and gas species that are evolved during thermal decomposition of charged cathode materials, especially O2 gas in our interest. In addition, the ex situ/in situ X-ray absorption spectroscopy (XAS) has been also utilized to look at the local and electronic structural changes occurring during thermal decomposition in an elemental selective way. By utilizing combined X-ray techniques, we are able to get better understanding of structural and electronic structure changes in charged cathode materials during thermal decomposition. In this presentation, the thermal decomposition behavior of charged Na1-xMO2(M=Co, Cr) cathodes will be covered. Acknowledgement The work done at Brookhaven National Lab. was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. DOE under Contract No. DE-SC0012704.

Effect of Cation Substitution on Air-Sensitivity and Structural Stability of P2-NaxMn1/2Fe1/2O2

Layeredsodium transition metal oxides have attracted a great deal of attention for research and development for Na battery applications in past few years because of their suitable energy densities and cost-effectiveness [1]. P2-Na2/3Mn1/2Fe1/2O2 is one of the most promising materials studied so far [2] composed of abundant and non-toxic elements, and delivers a high specific capacity of over 190 mAh g-1 with moderate capacity retention. Regarding structural stability, the Na2/3Mn1/2Fe1/2O2/Na cell demonstrates a smooth charge/discharge profile, except for a voltage plateau at around 4V. A P2-OP4 phase transition at the high voltage region has been reported, although the new phase was not structurally characterized [2], and a P2-P'2 phase transition at the low voltage region was very recently reported for this material [3]. As a drawback of sodium transition metal oxides, these materials are generally known to be sensitive to atmospheric conditions. Formation of surface sodium carbonate was reported for an O3 composition [4]. Some P2 phases are reported to accommodate water molecules in the interlayer space [5], and others are reported to oxidize forming cationic vacancies [6]. Reactivity of Na2/3Mn1/2Fe1/2O2 has not been addressed so far leading to discrepancies in published results. We will describe the air sensitivity of Na2/3Mn1/2Fe1/2O2 and its influence on its electrochemical properties. The effect of cation substitution on the evolution of the crystal structure, the electrochemical performance and enhancement of atmospheric stability will be discussed as well. In this study, pristine and cation substituted Na2/3[Mn1/2Fe1/2]O2 samples were synthesized by solid state methods. The uptake/evolution of gases by P2-Na2/3[Mn1/2Fe1/2]O2 were studied by thermaogravimetric analysis (TGA) coupled with mass spectroscopy (MS). Structural characterization was carried out by in-situ x-ray and ex-situ neutron powder diffraction. A procedure to reproducibly obtain material free from air contamination was developed. The effect of the air sensitivity on the electrochemical properties was studied using sodium half cells. Composite electrodes were prepared by mixing the active material with carbon black and PVDF (80:10:10) for both air exposed and protected samples and cycling these cathodes with an electrolyte comprised of 1M NaClO4 in PC with 2 vol. % 4-fluoro-1,3-dioxolan-2-one (FEC). Our TGA and MS studies along with neutron diffraction analysis of air-exposed samples (Figure 1), shows that the aging mechanism of the P2-Na2/3Mn1/2Fe1/2O2 in air is more complex than the simple intercalation of water molecules. We propose an original oxidation mechanism not reported to date, for any of the layered sodium oxides, to the best of our knowledge. This oxidation mechanism explains the different voltage profiles of air exposed/protected Na2/3Mn1/2Fe1/2O2. Figure 2 shows the two first cycles of “air-protected” vs. “air-exposed” pristine and cation substituted P2-Na2/3Mn1/2Fe1/2O2, clearly demonstrating the effect of exposure of the material to air on the electrochemical properties. The effect of cation substitution on the air-sensitivity of P2-Na2/3Mn1/2Fe1/2O2 and also its structural evolution during (de)intercalation of sodium ions will be discussed in this presentation. Acknowledgements This research was supported by the Natural Sciences and Engineering Council of Canada through their Discovery and Canada Research Chair programs. Reference [1] D. Kundu, E. Talaie, V. Duffort and L. F. Nazar, Angew. chem., Accepted. [2] N. Yabuuchi, M. Kajiyama, J. Iwatate, H. Nishikawa, S. Hitomi, R. Okuyama, R. Usui, Y. Yamada, S. Komaba, Nat . Mater., 11, 512 (2012). [3] B. M. de Boisse, D. Carlier, M. Guignard, L. Bourgeois, C. Delmas, Inorg. Chem., 53, 11197 (2014). [4] M. Sathiya, K. Hemalatha, K. Ramesha, J.M. Tarascon, A.S. Prakash, Chem. Mater., 24, 1846 (2012). [5] Z. Lu, J.R. Dahn, Chem. Mater., 13, 1252 (2001). [6] R. Stoyanova, D. Carlier, M. Sendova-Vassileva, M. Yoncheva, E. Zhecheva, D. Nihtianova, C. Delmas, J. Solid State Chem., 183, 1372 (2010). Figure 1

Olivine Type NaFePO4 Prepared By Electrochemical Delithiation for Sodium Ion Batteries

Nowadays, sodium batteries attracted great interest due to the low cost and the environmental abundance of the sodium. Layered sodium-transition metal oxides, i.e. NaMO2, have been widely investigated as cathode materials for these batteries [1]. However, although Dahn’s group showed the high thermal stability for NaCrO2recently, the results so far obtained are not encouraging since this cathode material suffers of poor cycle life and low thermal stability [2].Metal-phosphate based electrodes, such as Nasicon type Na3V2(PO4)3 and NaFePO4, are believed to be very promising alternative cathodes for sodium batteries [3]. Considerable attention has been addressed to maricite NaFePO4, a phase characterized by the presence of (PO4 3-) tetrahedra that totally surround the Na+ cations, namely a structure with no free channels for Na+ diffusion and accordingly with a poor electrochemical behavior in sodium cells [4]. The NaFePO4 phase with an olivine structure is expected to have better electrochemical properties, as suggested by recent studies conducted on chemically delithiated olivine LiFePO4 [5,6]. The results reported in the quoted references showed in fact that FePO4 heterosite can be obtained by a chemical Li-Na exchange process; the formed NaFePO4, however, could not be cycled due to severe decays in capacity presumably associated with the presence of residual Li in its crystal structure, as speculated by Zaghib’s group.In this work we show that, by adopting a refined, electrochemical process, the LiFePO4 can be successfully and efficiently totally converted in NaFePO4and demonstrate that this material can be used as cathode in a sodium battery having excellent performance in terms of cycle life and rate capability.The process of transformation of olivine LiFePO4 to FePO4 was conducted electrochemically with conditions such as to assure a full delithiation of LiFePO4 and its total exchange in FePO4 (see experimental section for details). Figure 1A shows the voltage profile of this first process, evolving on the expect 3.5V plateau and delivering a capacity almost matching the theoretical value [7], both evidences demonstrating that the transformation of LiFePO4 into FePO4 was indeed almost completed. The achievement of the reaction process is confirmed by the XRD analysis, Figure 1B black and red patterns (LiFePO4 peaks were neglibable), demonstrating that the olivine LiFePO4 phase (triphylite) is fully delithiated to form the olivine FePO4(heterosite, JCPDS card No. 42-0579, Pnma space group) phase.

Layered oxides as positive electrode materials for Na-ion batteries

Abstract

Electrochemical Performances of NaFePO4 Prepared By Electrochemical Delithiation for Sodium Batteries

Introduction Nowadays, sodium batteries attracted great interest due to the low cost and the environmental abundance of the sodium. Layered sodium-transition metal oxides, i.e. NaMO2, have been widely investigated as cathode materials for these batteries [1]. However, although Dahn’s group showed the high thermal stability for NaCrO2recently, the results so far obtained are not encouraging since this cathode material suffers of poor cycle life and low thermal stability [2].Metal-phosphate based electrodes, such as Nasicon type Na3V2(PO4)3 and NaFePO4, are believed to be very promising alternative cathodes for sodium batteries [3]. Considerable attention has been addressed to maricite NaFePO4, a phase characterized by the presence of (PO4 3-) tetrahedra that totally surround the Na+ cations, namely a structure with no free channels for Na+ diffusion and accordingly with a poor electrochemical behavior in sodium cells [4]. The NaFePO4 phase with an olivine structure is expected to have better electrochemical properties, as suggested by recent studies conducted on chemically delithiated olivine LiFePO4 [5,6]. The results reported in the quoted references showed in fact that FePO4 heterosite can be obtained by a chemical Li-Na exchange process; the formed NaFePO4, however, could not be cycled due to severe decays in capacity presumably associated with the presence of residual Li in its crystal structure, as speculated by Zaghib’s group.In this work we show that, by adopting a refined, electrochemical process, the LiFePO4 can be successfully and efficiently totally converted in NaFePO4and demonstrate that this material can be used as cathode in a sodium battery having excellent performance in terms of cycle life and rate capability. Results and discussion The process of transformation of olivine LiFePO4 to FePO4 was conducted electrochemically with conditions such as to assure a full delithiation of LiFePO4 and its total exchange in FePO4 (see experimental section for details). Figure 1A shows the voltage profile of this first process, evolving on the expect 3.5V plateau and delivering a capacity almost matching the theoretical value [7], both evidences demonstrating that the transformation of LiFePO4 into FePO4 was indeed almost completed. The achievement of the reaction process is confirmed by the XRD analysis, Figure 1B black and red patterns (LiFePO4 peaks were neglibable), demonstrating that the olivine LiFePO4 phase (triphylite) is fully delithiated to form the olivine FePO4(heterosite, JCPDS card No. 42-0579, Pnma space group) phase.