Cost–Effective Synthesis and Electrochemical Evaluation of Triphylite NaFePO₄ as a High–Performance Cathode Material for Sodium–Ion Batteries

Improved high-rate performance of Na3V2(PO4)3 with an atomic layer deposition-generated Al2O3 layer as a cathode material for sodium-ion batteries

Electrochemical performance and structural evolution of layered oxide cathodes materials for sodium-ion batteries: A review

Development of novel cathode materials for sodium-ion batteries with high capacity and excellent cyclic performance is an exciting and demanding research direction. Herein, we demonstrate the synthesis of NaV3O8 via a rheological phase reaction method. The crystal structure and morphology of synthesized NaV3O8 were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The NaV3O8 powder, calcined at moderate temperature (350 °C) with more uniform and smaller nanorod/nanoplate morphology, and larger d001 spacing, exhibited excellent electrochemical performance as cathode material in sodium ion batteries. A specific discharge capacity of 120 mAh g−1 was achieved at the current density of 120 mA g−1, with exceptional cyclic performance (discharge capacity of 95 mAh g−1 at the 500th cycle). In addition, the NaV3O8 cathode demonstrated excellent rate capability and delivered specific capacity of 80.8 mAh g−1 at current density of 300 mA g−1. The superior electrochemical performance corresponds to the structural stability and faster ionic diffusion. The preliminary results indicate that NaV3O8 can be an alternative cathode material for high-performance sodium-ion batteries.

Energy storage systems made from abundant materials are essential for the transition to a more sustainable economy. Although today lithium-ion batteries (LIBs) are the most popular battery technology, the growing demand and low availability of lithium, as well as the use of cobalt and other rare metals raise questions about the sustainability and long-term viability of LIB as the only energy storage solution. The high abundance of sodium content and relative similarity to LIBs, allows the sodium ion batteries (SIBs) to be considered as alternative for stationary energy storage [1]. However, the widespread adoption of SIB technology is hampered by many challenges, including the relatively low energy density compared to LIB. Lower energy density electrodes, such as Na2FeP2O7, are generally stable during cycling [2], while many higher energy density electrodes, such as NaxMnO2, have had a shorter cycle life [3]. In this work we show several possible solutions how to improve the electrochemical properties of the SIBs made of these cathode materials.The promising cathode material Na2FeP2O7 was studied to improve its electrical conductivity, which is often low in the case of sodium pyrophosphates. Solution synthesis was used to prepare pristine Na2FeP2O7 and Na2FeP2O7/C composite cathode materials for sodium-ion batteries, using glucose as a carbon source. While the pristine Na2FeP2O7 displays capacity of only 45 mAh/g due to the relatively large grain size, the addition of carbon increases the capacity to up to 92 mAh/g (95% of the theoretical 97 mAh/g capacity) with excellent rate capability, as 44 mAh/g capacity is still retained even at 20 C (1.94 A/g) current. The optimal content of carbon was found to be 4.8%. The initial capacity of 81 mAh/g is fully retained after 500 cycles at 1 C, indicating excellent cycle life of Na2FeP2O7/C. Electrochemical measurements were carried out in 1 M NaClO4 salt in propylene carbonate as electrolyte and show that the addition of 5 wt.% fluoroethylene carbonate solid electrolyte interphase stabilizing additive greatly benefits the rate and cycling performance of Na2FeP2O7/C as measured in half-cells [4].Na0,67MnO2 is another compound that is widely studied as cathode materials in sodium ion batteries. Currently polyvinylidene fluoride (PVDF) is the most popular binder choice. In our study, a novel tetrabutylammonium (TBA) alginate binder is used to prepare a Na0,67MnO2 electrode for sodium-ion batteries with improved electrochemical performance. The ageing of the electrodes has been characterized. TBA alginate-based electrodes are compared to PVDF and Na alginate-based electrodes and show favorable electrochemical performance, with gravimetric capacity values of up to 164 mAh/g, which is 6% higher than measured for the electrode prepared with PVDF binder. TBA alginate-based Na0,67MnO2 electrodes also display good rate capability and improved cyclability and their solid–electrolyte interface is similar to that of PVDF-based electrodes. As the only salt of alginic acid soluble in non-aqueous solvents, TBA alginate emerges as a good alternative to PVDF binder in battery applications where the water-based processing of electrode slurries is not feasible, such as the demonstrated case with Na0,67MnO2 [5].Overall, we have shown that binder and electrolyte selection can significantly improve the electrochemical properties of electrode materials for SIBs.The financial support of projects No. 1.1.1.2/VIAA/1/16/166 “Advanced materials for sodium Ion batteries” and No. lzp-2020/1-0391 “Advanced polymer – ionic liquid composites for sodium-ion polymer batteries” is greatly acknowledged. Institute of Solid-State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Program H2020-WIDESPREAD-01–2016-2017-Teaming Phase 2 under grant agreement No. 739508, project CAMART2. Vaalma, C.; Buchholz, D.; Weil, M.; Passerini, S. A cost and resource analysis of sodium-ion batteries. Nat. Rev. Mater. 2018, 3, 18013.Jin, T.; Li, H.; Zhu, K.; Wang, P.-F.; Liu, P.; Jiao, L. Polyanion-type cathode materials for sodium-ion batteries. Chem. Soc. Rev. 2020, 49, 2342.Lyu, Y.; Liu, Y.; Yu, Z.-E.; Su, N.; Liu, Y.; Li, W.; Li, Q.; Guo, B.; Liu, B. Recent advances in high energy-density cathode materials for sodium-ion batteries. Sustain. Mater. Technol. 2019, 21, e00098.Kucinskis, G.; Nesterova, I.; Sarakovskis, A.; Bikse, L.; Hodakovska, J.; Bajars, G. Electrochemical performance of Na2FeP2O7/C cathode for sodium-ion batteries in electrolyte with fluoroethylene carbonate additive. J. Alloys Compd. 2022, 895, 162656.Kucinskis, G.; Kruze, B.; Korde, P.; Sarakovskis, A.; Viksna, A.; Hodakovska, J.; Bajars, G. Enhanced Electrochemical Properties of Na67MnO2 Cathode for Na-Ion Batteries Prepared with Novel Tetrabutylammonium Alginate Binder. Batteries 2022, 8, 6. Figure 1

NASICON-type Na3V2(PO4)3 with a three-dimensional open framework structure has attracted wide attention, and it is regarded as one of the most promising cathode material for sodium-ion batteries. However, the low electronic conductivity restricts its charge–discharge capacity and electrochemical performance. With the purpose to solve this problem, polystyrene microspheres are applied in the preparation of cathode materials for sodium-ion batteries. Particular porous-structured Na3V2(PO4)3 composing of interlaced nanosheets is obtained samples by a simple hydrothermal-assisted sol–gel method via a self-sacrificed template (polystyrene microsphere). As expected, the as-prepared porous sample delivers a reversible capacity of 109.2 mAh g−1 at 0.2 C, an excellent rate performance (89.6 mAh g−1 at 50 C) and superior cyclic stability (retention of 94% over 500 cycles at 50 C). The outstanding rate and cyclic performance are attributed to its unique porous structure which is conducive to improve electron conductivity and facilitate the diffusion of sodium ions.

Cu-substituted Prussian white with low crystal defects as high-energy cathode materials for sodium-ion batteries

Sodium-ion batteries (SIBs) are seen as an emerging force for future large-scale energy storage due to their cost-effective nature and high safety. Compared with lithium-ion batteries (LIBs), the energy density of SIBs is insufficient at present. Thus, the development of high-energy SIBs for realizing large-scale energy storage is extremely vital. The key factor determining the energy density in SIBs is the selection of cathodic materials, and the mainstream cathodic materials nowadays include transition metal oxides, polyanionic compounds, and Prussian blue analogs (PBAs). The cathodic materials would greatly improve after targeted modulations that eliminate their shortcomings and step from the laboratory to practical applications. Before that, some remaining challenges in the application of cathode materials for large-scale energy storage SIBs need to be addressed, which are summarized at the end of this Outlook.

An O3-type NaNi0.5Mn0.3Ti0.2O2 compound as new cathode material for room-temperature sodium-ion batteries

NASICON-structured Na3V2(PO4)3 (NVP) is one of the most promising cathode material for rechargeable sodium-ion batteries. NVP is characterized by a robust 3D structural framework and a high operating potential; these properties have enabled it to be widely studied as a stable and high-energy density cathode material for sodium-ion batteries (SIBs).1-4 In the present study, we designed a Na3V1.6Cr0.4(PO4)3/C (NVCrP@C) cathode by implanting Cr into the crystal structure of NVP and simultaneously coating the surface of NVP with carbon for realizing high power density SIBs. NVP is fabricated using a low-cost pyro synthesis technique with the advantage of self-carbon-coating and nano sized particles are gained through this facile technique. The substitution of Cr with vanadium in the NVP structure significantly enhanced the structural stability of the electrode while the uniform and thin carbon layer improved the electrical conductivity. Interestingly, the NVCrP@C cathode showed high electrochemical activities with multiple V3+/4+/5+ redox reactions triggered by Cr3+ substitution in a wide voltage range (2.5–4.1 V). Consequently, the NVCrP@C cathode delivered excellent cycling stability over 500 cycles even at 15 C-rate and power capability up to 70 C-rate. References Y. Cao, L. Xiao, W. Wang, D. Choi, Z. Nie, J. Yu, L. V. Saraf, Z. Yang and J. Liu, Mater., 2011, 23, 3155-3160.M. Giot, L. C. Chapon, J. Androulakis, M. A. Green, P. G. Radaelli and A. Lappas, Rev. Lett., 2007, 99, 247211 M. H. Han, E. Gonzalo, G. Singh and T. Rojo, Energy Environ. Sci., 2015, 8, 81-102. H. Liu, J. Xu, C. Ma and Y. S. Meng, Chem. Comm., 2015, 51, 4693-4696

P2-type Na0.66Ni0.33–xZnxMn0.67O2 as new high-voltage cathode materials for sodium-ion batteries

P2-Na2/3[Fe1/2Mn1/2]O2 layered oxide is a promising high energy density cathode material for sodium-ion batteries. However, one of its drawbacks is the poor long-term stability in the operating voltage window of 1.5–4.25 V vs Na+/Na that prevents its commercialization. In this work, additional light is shed on the origin of capacity fading, which has been analyzed using a combination of experimental techniques and theoretical methods. Electrochemical impedance spectroscopy has been performed on P2-Na2/3[Fe1/2Mn1/2]O2 half-cells operating in two different working voltage windows, one allowing and one preventing the high voltage phase transition occurring in P2-Na2/3[Fe1/2Mn1/2]O2 above 4.0 V vs Na+/Na; so as to unveil the transport properties at different states of charge and correlate them with the existing phases in P2-Na2/3[Fe1/2Mn1/2]O2. Supporting X-ray photoelectron spectroscopy experiments to elucidate the surface properties along with theoretical calculations have concluded that the formed electrode-electrolyte interphase is very thin and stable, mainly composed by inorganic species, and reveal that the structural phase transition at high voltage from P2- to “Z”/OP4-oxygen stacking is associated with a drastic increased in the bulk electronic resistance of P2-Na2/3[Fe1/2Mn1/2]O2 electrodes which is one of the causes of the observed capacity fading.

Attempts to utilize lithium-ion batteries (LIBs) in large-scale electrochemical energy storage systems have achieved initial success, and solid-state LIBs using metallic lithium as the anode have also been well developed. However, the sharply increased demands/costs and the limited reserves of the two most important metal elements (Li & Co) for LIBs have raised concerns about future development. Sodium-ion batteries (SIBs) equipped with advanced cobalt-free cathodes show great potential in solving both "lithium panic" and "cobalt panic", and have made remarkable progress in recent years. In this review, we comprehensively summarize the recent advances of high-performance cobalt-free cathode materials for advanced SIBs, systematically analyze the conflicts of structural/electrochemical stability with intrinsic insufficiencies of cobalt-free cathode materials, and extensively discuss the strategies of constructing stable cobalt-free cathode materials by making full use of non-cobalt transition-metal elements and suitable crystal structures, all of which aim to provide insights into the key factors (e.g., phase transformation, particle cracks, crystal defects, lattice distortion, lattice oxygen oxidation, morphology, transition-metal migration/dissolution, and the synergistic effects of composite structures) that can determine the stability of cobalt-free cathode materials, provide guidelines for future research, and stimulate more interest on constructing high-performance cobalt-free cathode materials.

Closed-loop transformation of raw materials into high-value-added products is highly desired for the sustainable development of the society but is seldom achieved. Here, a low-cost, solvent-free and "zero-waste" mechanochemical protocol is reported for the large-scale preparation of cathode materials for sodium-ion batteries (SIBs). This process ensures full utilization of raw materials, effectively reduces water consumption, and simplifies the operating process. Benefiting from the synergistic effect between the cubic Prussian blue analogs (c-NFFHCF) and dehydrated polyanionic sulfates (m-NFS), the generated composite exhibits promising wide-temperature electrochemical performance and excellent practical application potential. The synergistic effect between m-NFS and c-NFFHCF in the composite is revealed through multiple in situ characterizations and density functional theory calculations. The proposed mechanochemical strategy can be scaled to a kilogram-grade level, providing a sustainable method for the value-added utilization of the by-products during Prussian blue analogs synthesis, advancing the design of "zero-waste" cathode materials for low-cost practical SIBs.

Graphene oxide wrapped Na3V2(PO4)3/C nanocomposite as superior cathode material for sodium-ion batteries

The growing demand for sustainable, high capacity, and cost-effective energy storage has intensified the search for new alternative electrode materials beyond lithium-ion batteries. In this study, we employed dispersion corrected density functional theory (DFT-D3) calculations to investigate the potential of benzimidazole monolayers as cathode materials for sodium-ion batteries (SIBs). Our findings reveal that a single Na ion preferentially adsorbs along the ring structure of benzimidazole with an adsorption energy of -1.74 eV. The benzimidazole functionalised hexaazatriphenylene (BIFHAT) system demonstrates a specific capacity of 478.47 mAh g-1 and an open circuit voltage (OCV) of 0.35 V while accommodating up to nine Na ions. To further enhance performance, we introduce strategic ring modifications and evaluate five distinct structural variations. Among these, the benzotriazole system exhibits superior sodium storage, supporting up to twelve Na ions with an exceptional capacity of 634.21 mAh g-1 and an OCV of 0.53 V. The results also indicate that increasing the Na-ion concentration systematically reduces the adsorption energy across all studied configurations. Furthermore, quantum theory of atoms in molecules (QTAIM) analysis confirms that Na ion adsorption with nitrogen or oxygen sites in the considered structures is predominantly governed by noncovalent interactions. These findings highlight the potential of structurally tuned benzimidazole-based systems as promising cathode materials for next generation SIBs, offering an efficient and sustainable alternative for energy storage applications.