Cathode Material For Na-ion Batteries Research Articles

Na0.67Mn0.33Ni0.33Co0.33O2: Effect of synthesis technique on competing P3 and P2 phases

In layered NaxTMO2 (TM = transition metal) common understanding attributes the emergence of P2 and P3 phases to the synthesis temperature. In this work, we show that the synthesis technique is the main responsible for these phases. We synthesize Na0.67Mn0.33Ni0.33Co0.33O2 with two techniques, solid-state and electrospinning, using two temperatures, 700 °C and 900 °C. Both electrospun samples sintered at 900 °C and 700 °C show single phase P2 and P3, respectively. Both solid-state synthesized samples at 900 °C and 700 °C show mixture of P2/P3. Electrochemical properties of the sample with only P3 phase has the highest initial capacity of 130 mAhg−1 at C/3 rate. The sample with only P2 phase has very stable cycle performance with 87 % capacity retention over 100 cycles consistent with its large interlayer separation. Our results show that the synthesis technique plays a crucial role in the crystal structure and the electrochemical performance of the layered cathode materials for Na-ion batteries.

Improving electrochemical performance of Na4MnV(PO4)3 cathode material through Ti substitution

• The synthesis of Na 3+x MnTi 1-x V x (PO 4 ) 3 is facile. • The structure evolution and electrochemical performance of Na 3+x MnTi 1-x V x (PO 4 ) 3 are revealed. • Na 3.7 MnTi 0.3 V 0.7 (PO 4 ) 3 exhibits excellent cycle stability and rate capability as cathode material for Na-ion battery. Mn-based NASICON (Na super ionic conductor)-typed compounds are potentially applied as cathode materials for Na-ion batteries. However, cycling instability and poor rate capability limits its large-scale application. Herein, Na 3+x MnTi 1-x V x (PO 4 ) 3 with various Ti/V ratios were synthesized. The influence of the Ti/V ratios on the composition, structure and electrochemical properties were investigated. With increasing with content of V, cell parameters a (and b) and cell volume increases. Among these materials, Na 3.7 MnTi 0.3 V 0.7 (PO 4 ) 3 exhibits the best cycle stability and rate capability (62.7 mAh/g at 5 C, 53.2 mAh/g at 10 C), demonstrating potential application as cathode material for Na-ion batteries.

Enhanced electrochemical performance of Na4MnCr(PO4)3@C cathode by multi-walled carbon nanotubes interconnection for Na-ion batteries

• The Na 4 MnCr(PO 4 ) 3 @C@MWCNTs composites are synthesized for sodium ion batteries. • 3D well-interconnected architecture was designed by implanting CNTs into NMCP@C. • MWCNTs can enhance the rate capability and cycling stability of Na 4 MnCr(PO 4 ) 3 @C . • With WS 2 as anode, electrochemical performances were tested in full batteries. The development of high energy density and stable cathode materials for Na-ion batteries is an enormous puzzle. NASICON-structured Na 4 MnCr(PO 4 ) 3 (NMCP) has been reported as a novel and viable cathode material lately. Nonetheless, the inferior rate property and disappointing cycle stability hinder its commercial usage. Herein, a series of NMCP@C structurally interconnected with multi-walled carbon nanotubes (NMCP@C@x%MWCNTs, x = 0, 5, 10 and 15) were produced via a simple sol–gel strategy followed by an annealing treatment. The results indicate that the MWCNTs network could contribute to improving the electrochemical properties by accelerating electronic conductivity and increasing ionic diffusion property. As expected, the optimal composite (NMCP@C@10%MWCNTs) delivers the specific capacity of 66.1 mAh/g at 500 mA g −1 and capacity retention of 61.8% after 100 cycles at 1000 mA g −1 , while the pristine NMCP@C presents the specific capacity of 2.8 mAh/g at 500 mA g −1 and capacity retention of 27.5% after 100 cycles at 1000 mA g −1 . Moreover, When NMCP@C@10%MWCNTs is applied as cathode to assemble full battery with WS 2 anode, this battery delivers an initial discharge capacity of 181.3 mAh/g , acquiring a superior energy density of ∼435 Wh kg −1 with a working voltage of ∼2.4 V. These findings demonstrate that the MWCNTs network is favorable for the electrochemical enhancement of Na 4 MnCr(PO 4 ) 3 @C, which offers a hopeful prospect for Na 4 MnCr(PO 4 ) 3 as a cathode for sodium-ion batteries in practical application.

Study of Synergistic Effects of Cu and Fe on P2-Type Na0.67MnO2 for High Performance Na-Ion Batteries.

P2-type Na0.67MnO2 with a stable structure and an open framework can provide numerous channels for fast Na+ de/intercalation, for which it is considered to be advantageous in application of the cathode material for Na-ion batteries. However, the complex phase transition occurring during cycling and the lattice distortion triggered by the Jahn-Teller effect severely restrict its development. Herein, the modified Na0.67MnO2 with Cu or Fe single-element doping as well as Cu and Fe double-element doping was synthesized by the sol-gel method, and the effects of doping on the crystal structure and electrochemical performances of Na0.67MnO2 were studied. It was demonstrated that the phase of the material did not change after the introduction of Cu and Fe elements, and the cycling stability and rate performance were greatly improved by Cu and Fe double-doping owing to their synergistic effect. The Na0.67Mn0.92Fe0.04Cu0.04O2 (NMFCO) cathode delivers discharge specific capacities of 110.5 mA h g-1 at 5 C and 91.8 mA h g-1 at 10 C and exhibits the high-capacity retention of 94.35% at 1 C and 90.68% at 5 C after 100 cycles. Overall, this study offers a guiding direction for accelerating the modification of P2-type Na0.67MnO2 as a cathode active material for high performance Na-ion batteries.

‘Aqueous Processed’ O3-Type Transition Metal Oxide Cathodes Enabling Long-Term Cyclic Stability for Na-Ion Batteries

Among the potential cathode material classes for Na-ion batteries, O3-type layered NaxTMO2s (TM => transition metal ion) are of importance due to their high starting Na-content (of ~1 per formula unit; x). However, the O3-type NaxTMO2s suffer from multiple structural phase transformations during electrochemical charge/discharge cycles, TM-dissolution into electrolyte [1-2] and, more importantly, inherent sensitivity to moisture [3]. The moisture sensitivity of these ‘layered’ NaxTMO2s necessitates the usage of toxic/hazardous non-aqueous solvents like N-Methyl-2-pyrrolidone (NMP) during electrode preparation. Against this backdrop, a carefully designed composition has been developed in this work, which addresses the aforementioned problems, in particular, the air/water-instability. Partial/complete substitution of Ti-ion for Mn-ion in Na(Li0.05Mn0.5-xTixNi0.30Cu0.10Mg0.05)O2 eliminated the presence of Mn3+ (which dissolves in electrolyte) at the particle surface, supressed increment in impedance and voltage hysteresis during electrochemical cycling and, thus, significantly improved cyclic stability of Ti-substituted O3-type layered NaxTMO2s. The Mn-containing Na-TM-oxides were found to be extremely unstable in terms of phase/structure retention upon exposure to air and water; progressively evolving O’3 and P3 phases due to spontaneous Na-loss and thereby forming undesired NaOH and Na2CO3 phases on the particle surface (see Fig. 1a), causing increase in electrochemical impedance. By contrast, no phase/structural change occurred upon partial/complete Ti-substitution (for Mn-ion), even after 40 days of air-exposure and 12 h of soaking, as well as stirring, in water (viz., very stringent hydration condition) (see Fig. 1b). Such excellent stability against hydration, which was partly due to reduced Na-ion ‘inter-slab spacing’ in the presence of Ti-ion, was not reported earlier for O3-type Na-TM-oxides. The excellent stability of the optimized O3-type NaTMO2 enables the usage of environment/health-friendly and economical ‘aqueous-binder’ (viz., Na-alginate) and water (as solvent) for electrode preparation. Overall, the ‘aqueous-processed’ cathode exhibits first cycle capacity of ~125 mAh/g (between 2-4 V; vs. Na/Na+), with smooth electrochemical cycling profiles (see Fig. 2a) and excellent long-term cyclic stability, with a capacity retention of ~56% after 750 cycles at C/5 (see Fig. 2b). Overall, the present work, as published in ref. [4], has established important correlations between the composition, structure (viz., reduction in ‘inter-slab spacing’), stability against hydration (viz., in air and water), feasibility for health/environmental-friendly ‘aqueous processing’ of electrodes, electrochemical impedance, stability of average voltages and cyclic stability of O3-type Na-TM-oxide based cathode materials for Na-ion batteries. Keywords: Na-ion battery; layered transition metal oxide cathode; air/water-stability; aqueous processing; electrochemical behaviour Reference s : [1] S. Komaba, N. Yabuuchi, T. Nakayama, A.Ogata and T. Ishikawa, Inorg.chem, 51, 6211–6220 (2012).[2] P. F. Wang, Y. You, Y. X. Yin and Y. G. Guo, J. Mater. Chem. A, 4, 17660–17664 (2016).[3] H. R. Yao, P. F. Wang, Y. Gong, J. Zhang, X. Yu, L. Gu, C. Ouyang, Y. X. Yin, E. Hu, X. Q. Yang, E. Stavitski, Y. G. Guo and L. J. Wan, J. Am. Chem. Soc., 139, 8440–8443 (2017).[4] B. S. Kumar, A. Pradeep, A. Dutta, A. Mukhopadhyay., J. Mater. Chem. A, 8, 18064-18078 (2020). Figure 1

Na2FeF4 as a stable cathode material for Na-ion batteries

In the search of cathode materials for Na-ion batteries, iron-based compounds have attracted much attention due to the abundant resource, easy access, and environmental friendliness of iron. Herein, we report the synthesis, structure, and electrochemistry of a previously unknown compound in the Na–Fe–F system, formulated as Na2FeF4. It is prepared by an easy and mild hydrothermal reaction with oxalate as a Fe2+ protector. Based on the single crystal x-ray diffraction analysis, it crystallizes in space group Pmcb with a = 3.255 (3) Å, b = 5.591(7) Å, and c = 9.557(1) Å. The crystal structure features edge-sharing FeF6 octahedra to form [FeF4]∞ chains with Na+ ions located between chains. In electrochemical investigations, it is demonstrated that the material can deliver a reversible capacity of ∼90 mAh g−1 for 300 cycles in the window of 1.5–4.3 V with redox reactions at ∼3.0 V (vs Na+/Na). Such an activity originates from the Fe3+/Fe2+ redox couple, confirmed by x-ray absorption spectra and first-principles calculations.

Effects of ball milling on Structure and Electrochemical Properties of Na4MnV(PO4)3

Na4MnV(PO4)3 is regarded as a promising candidate as cathode material for Na-ion batteries (SIB) due to its low cost and high energy density. However, it suffers from fast capacity decay upon cycles, hindering its further commercialization. The ball milling technology was adopted in this study to control the particle size of Na4MnV(PO4)3, and the correlation of electrochemical properties was investigated. With increasing ball milling time, particle size was greatly reduced. The material with 20 minutes of ball milling displayed the best cycling stability and rate capability. It delivered a reversible capacity of 77.1 mAh/g at 0.5 C after 80 cycles, much higher than that of pristine Na4MnV(PO4)3. The decreased particle size might be to blame for the enhanced electrochemical performance, which effectively increased the interfacial contact with the electrolyte and greatly reduced the length of Na-ion diffusion in active particles.

First-principles computational studies on Na+ diffusion in Li-doped P3-type NaMnO2 as cathode material for Na-ion batteries

First-principles computational studies on Na+ diffusion in Li-doped P3-type NaMnO2 as cathode material for Na-ion batteries

Effects of nitrogen and sulfur atom regulation on electrochemical properties of Na3V2(PO4)2F3 cathode material for Na-ion batteries

The cathode material Na3V2(PO4)2F3 of sodium-ion battery is well-known for its large number of ion migration channels and high working voltage. However, the electrochemical performance of Na3V2(PO4)2F3 is not very outstanding. Thus, in the present study, Na3V2(PO4)2F3 cathode materials were successfully synthesized by using the sol-gel method and mechanical milling method to enhance the electrochemical performance. The physicochemical properties of synthesized Na3V2(PO4)2F3 were investigated by using X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transition electron microscopy. X-ray diffraction spectroscopy indicates that the doping of nitrogen and sulfur did not alter the crystal form of Na3V2(PO4)2F3. Transition electron microscopy image shows that Na3V2(PO4)2F3 has a thin carbon layer, and x-ray photoelectron spectroscopy illustrates the successful doping of nitrogen and sulfur into the carbon layer. The cyclic voltammetry curves show that the nitrogen and sulfur co-doped Na3V2(PO4)2F3 samples have good reversibility and low polarization. Materials with 15% thiourea has a high discharge specific capacity (126.9 mA h g−1 at 0.2 C) at the first cycle and excellent cycle stability (126.3 mA h g−1 after 100 cycles, a capacity retention of 99.5%) among the synthesized cathode materials. In the present study, the electrochemical performance of the Na3V2(PO4)2F3 cathode material was enhanced by regulation of co-doping of nitrogen and sulfur atoms.

Xanthan gum as a water-based binder for P3-Na2/3Ni1/3Mn2/3O2

P3-Na2/3Ni1/3Mn2/3O2 (P3-NNM) is a promising cathode material for Na-ion batteries, although large volume expansions during cycling mean that challenges around suitable binders still remain. This study reports the use of xanthan gum as a water-soluble, easy to handle, and sustainable biopolymer binder in conjunction with a P3-Na2/3Ni1/3Mn2/3O2-positive electrode material. The conditions for recovering pristine P3-NNM powders, following water-based processing, are established, and the electrochemical performance of cells prepared using the xanthan gum binder are compared to the more traditional polyvinylidene fluoride. Comparable discharge capacities are observed regardless of the binder choice, at ca. 115 mA h g−1 (77 mAh g−1 after 50 cycles; 0.1 C between 2.0 and 4.2 V). The xanthan gum binder cells also show a similar rate capability and slightly higher capacities at faster c-rates vs. polyvinylidene fluoride, making xanthan gum a viable alternative to the traditional organic binders for water-stable cathode materials.

Influence of Li and Mg substitution on structural properties and electrochemical performance of Na x MnO2-based cathode material for Na-ion batteries

Influence of Li and Mg substitution on structural properties and electrochemical performance of Na_<i>x</i>MnO₂-based cathode material for Na-ion batteries

Cobalt-free copper-substituted Na(Ti,Mn,Ni,Cu)O2 layered oxide cathode materials for Na-ion batteries

This work presents the results of an investigation of the structural, transport (electronic and ionic components of electrical conductivity, chemical diffusion coefficients of sodium) and electrochemical properties of P2-Na0.67Ti0.67Ni0.33-yCuyO2 (y ​= ​0, 0.1) and P2-Na0.67Ti0.33Mn0.33Ni0.33-yCuyO2 (y ​= ​0, 0.1, 0.2) cathode materials. Both families of compounds possess structural and electronic transport properties that change significantly upon copper substitution. Substitution with 0.1 ​mol of copper makes it possible to increase the electronic component of conductivity by more than one order of magnitude. A correlation between transport properties and electrochemical performance is demonstrated. The most desirable electrochemical behaviour was observed for the copper-substituted Na0.67Ti0.67Ni0.23Cu0.1O2 and Na0.67Ti0.33Mn0.33Ti0.33Ni0.23Cu0.1O2 cathode materials. The initial capacity of the former was 98 mAh g−1 with 96% capacity retention after 60 cycles with varying current rate, while the latter was characterized by 96 mAh g−1 with 99% capacity retention.

Structural, Electronic, Mechanical, and Thermodynamic Properties of Na Deintercalation from Olivine NaMnPO4: First-Principles Study.

The impact of Na atom deintercalation on olivine NaMnPO4 was investigated in a first-principle study for prospective use as cathode materials in Na-ion batteries. Within the generalized gradient approximation functional with Hubbard (U) correction, we used the plane-wave pseudopotential approach. The calculated equilibrium lattice constants are within 5% of the experimental data. The difference in equilibrium cell volumes for all deintercalated phases was only 6%, showing that NaMPO4 is structurally more stable. The predicted voltage window was found to be between 3.997 and 3.848 V. The Na1MnPO4 and MnPO4 structures are likely to be semiconductors, but the Na0.75MnPO4, Na0.5MnPO4, and Na0.25MnPO4 structures are likely to be metallic. Furthermore, all independent elastic constants for NaxMPO4 structures were shown to meet the mechanical stability requirement of the orthorhombic lattice system.

Sodium vanadium hexacyanoferrate as a high-rate capability and long-life cathode material for Na-ion batteries

Na-ion batteries have gradually begun to be commercialized due to their advantages of lower cost and wide source of raw materials, but more excellent electrochemical performance is required to compete with lithium-ion batteries. In this work, sodium vanadium hexacyanoferrate (NaVHCF) was designed and synthesized as a Na-ion cathode material to exhibit excellent electrochemical performance. The results show that the capacity retention rate of 1000 cycles at 2.5C rate is 72 %, the Coulombic efficiency is 100 %, and the capacity retention rate of 5000 cycles at 25C high rate is 65 %. After activating at a low current density of 2.5C, it still has a capacity of 42 mAh g−1 after 2000 cycles at a high rate of 25C, and the capacity retention rate is 92 %. The analysis shows that the excellent rate and long cycling ability are related to the three-dimensional open structure and microporous structure of NaVHCF. During the long cycle, the diffusion coefficient of sodium ions gradually increases and the charge transfer resistance gradually decreases, which improves the battery lifespan. These results suggest that sodium-ion batteries are one step closer to commercial application.

Robust Artificial Interphases Constructed by a Versatile Protein-Based Binder for High-Voltage Na-Ion Battery Cathodes.

The multiple issues of unstable electrode/electrolyte interphases, sluggish reaction kinetics, and transition-metal (TM) dissolution have long greatly affected the rate and cycling performance of cathode materials for Na-ion batteries. Herein, a multifunctional protein-based binder, sericin protein/poly(acrylic acid) (SP/PAA), is developed, which shows intriguing physiochemical properties to address these issues. The highly hydrophilic nature and strong H-bond interaction between crosslinking SP and PAA leads to a uniform coating of the binder layer, which serves as an artificial interphase on the high-voltage Na4 Mn2 Fe(PO4 )2 P2 O7 cathode material (NMFPP). Through systematic experiments and theoretical calculations, it is shown that the SP/PAA binder is electrochemically stable at high voltages and possesses increased ionic conductivity due to the interaction between sericin and electrolyte anion ClO4 - , which can provide additional sodium-migration paths with greatly reduced energy barriers. Besides, the strong interaction force between the binder and the NMFPP can effectively protect the cathode from electrolyte corrosion, suppress Mn-dissolution, stabilize crystal structure, and ensure electrode integrity during cycling. Benefiting from these merits, the SP/PAA-based NMFPP electrode displays enhanced rate and cycling performance. Of note, the universality of the SP/PAA binder is further confirmed on Na3 V2 (PO4 )2 F3 . It is believed that the versatile protein-based binder is enlightening for the development of high-performance batteries.

Engineering hierarchical structure and surface of Na4MnV(PO4)3 for ultrafast sodium storage by a scalable ball milling approach

Polyanion-type Na4MnV(PO4)3 (NMVP) is attracting increasing attention as a cathode material for Na-ion batteries (NIBs) due to its high redox potential and crystal structure stability, while it is still suffering from poor intrinsic conductivity. Herein, to address such issue, a unique hierarchical bayberry-like NMVP@NC material, in which the ultra-small primary nanoparticles are embedded in N-doped carbon conductive network, is fabricated by a scalable ball milling approach. The optimum NMVP@NC electrode exhibits a high reversible capacity of 103.5 mAh g−1 at 0.5 C and maintains a desirable capacity of 82.4 mAh g−1 even at an ultrahigh rate of 100 C. After 1000 cycles at 5 C, a capacity retention ratio of 94.4% is achieved. The underlying electrochemical Na storage mechanism verified by the kinetic analysis and operando X-ray diffraction characterization reveals that the superior electrochemical performance should be attributed to the hierarchical structure with a facile ion/electron diffusion pathway and excellent interfacial compatibility. Moreover, a solid-solution and biphasic reaction mechanism for Na storage is confirmed in NMVP. Further demonstration of commercial soft carbon//NMVP@NC full cell manifests the good potential of as-prepared material for practical applications. Therefore, the NMVP@NC with rational architecture design is a considerable competitive cathode for the commercialization of NIB.

Perspective: Design of cathode materials for sustainable sodium-ion batteries

Manufacturing sustainable sodium ion batteries with high energy density and cyclability requires a uniquely tailored technology and a close attention to the economical and environmental factors. In this work, we summarized the most important design metrics in sodium ion batteries with the emphasis on cathode materials and outlined a transparent data reporting approach based on common metrics for performance evaluation of future technologies.Sodium-ion batteries are considered as one of the most promising alternatives to lithium-based battery technologies. Despite the growing research in this field, the implementation of this technology has been practically hindered due to a lack of high energy density cathode materials with a long cycle-life. In this perspective, we first provide an overview of the milestones in the development of Na-ion battery (NIB) systems over time. Next, we discuss critical metrics in extraction of key elements used in NIB cathode materials which may impact the supply chain in near future. Finally, in the quest of most promising cathode materials for the next generation of NIBs, we overlay an extensive perspective on the main findings in design and test of more than 295 reports in the past 10 years, exhibiting that layered oxides, Prussian blue analogs (PBAs) and polyanions are leading candidates for cathode materials. An in-depth comparison of energy density and capacity retention of all the currently available cathode materials is also provided. In this perspective, we also highlight the importance of large data analysis for sustainable material design based on available datasets. The insights provided in this perspective, along with a more transparent data reporting approach and an implementation of common metrics for performance evaluation of NIBs can help accelerate future cathode materials design in the NIB field.Graphical abstract

Designing a P2-type cathode material with Li in both Na and transition metal layers for Na-ion batteries

P2-type layered oxides have been considered as promising cathode materials for Na-ion batteries, but the capacity decay resulting from the Na+/vacancy ordering and phase transformation limits their future large-scale applications. Herein, the impact of Li-doping in different layers on the structure and electrochemical performance of P2-type Na0.7Ni0.35Mn0.65O2 is investigated. It can be found that Li ions successfully enter both the Na and transition metal layers. The strategy of Li-doping can improve the cycling stability and rate capability of P2-type layered oxides, which promotes the development of high-performance Na-ion batteries.

Structural and transport properties of P2-Type Na0.70Ni0.20Cu0.15Mn0.65O2 layered oxide

P2-type Layered oxides have attracted increasing attention recently as the cathode materials for Na-ion batteries with promising cyclability and good specific capacity. In this work, structural, electrical, and electrochemical properties of P2-type Na0.70Ni0.20Cu0.15Mn0.65O2 (NNCM) ceramic fabricated via a sol-gel method were investigated. The Rietveld refinement of the room temperature XRD diffraction data confirmed the formation of a single P2-type phase with space group P63/mmc for the powder calcined at 850 °C. Complex impedance spectroscopy was used to deconvolute the contributions of grains and grain boundaries to the overall conduction inside the sample. The room temperature conductivity of the grains and grain boundaries calculated for the NNCM ceramic sintered at 950 °C were estimated to be (5.25 ± 0.03) × 10−5 Scm−1 and (4.70 ± 0.05) × 10−6 Scm−1, respectively. The respective activation energies for the grain and grain boundary conduction were 0.189 ± 0.008 eV and 0.22 ± 0.01 eV, respectively. Moreover, NNCM exhibited a sodium-ion transference number of ≈0.86, suggesting that the conduction in this material is dominated by the Na-ions. The conduction mechanisms and related relaxations were also investigated using the dielectric and ac conductivity formalisms. NNCM showed specific capacities of 99 mAh/g and 74 mAh/g at 0.1C and 1C discharge rates, respectively, between 2 V and 4.25 V (vs. Na/Na+) with 95% capacity retained after 300 cycles at 1C.

Recent Progress of Cathode Materials for Na-ion batteries

Recently, many researchers focus on Na-ion batteries as an alternative to Li-ion batteries, owing to their low cost and high natural abundance. However, they suffer from low electrochemical performance and large volume expansion, which makes difficult to industrial application. Therefore, various strategies have been proposed to address the current issues, such as particle-size control, surface-coating, and application of electrode material with various crystal structures. Herein, we briefly introduce and discuss the recent research with development trend of cathode material for Na-ion batteries.