High Working Potential Research Articles

Effect of the succinonitrile additive, electrode processing, and N/P ratios in the performance of high‐voltage lithium‐ion batteries using LiNi0.5Mn1.5O4 cathode

AbstractThe progressive improvement in the gravimetric energy density of lithium‐ion batteries (LIBs) leads to electrolyte design, positive electrode, and full‐cell optimization processes. The spinel lithium nickel manganese oxide (LiNi0.5Mn1.5O4, LNMO) is one of the potential candidates for the next generation of LIBs applied for electric vehicles due to high working potential (4.75 V vs. Li+/Li), affordable price, and environmental friendliness. Nevertheless, the degradation of cycling performance at high potential induces massive challenges for commercializing LNMO‐based batteries. This study investigated the impact of succinonitrile (SN), electrode processing, and N/P ratios to strengthen the LNMO half‐cell and graphite||LNMO full‐cell performance. According to the performance in half‐cell, the sample contained 85 wt% LNMO: 7.5 wt% C65: 7.5 wt% PVDF/NMP combining with the electrolyte 1.5 M LiPF6 in EC:EMC:DMC (2:1:7 – v/v) at 0.5 wt% SN seems to be the optimal condition for further full‐cell. In addition, the full‐cell with N/P = 1.3 displays a remarkable initial capacity of 118.75 mAh g−1, a Coulombic efficiency of 91.64%, and a superior gravimetric energy density of 537.71 mWh g−1. Moreover, it maintains a capacity retention of around 58% at the current density of 0.1C after 100 cycles. As a result, this study presents an optimal solution to augment the material's potential for commercialization in the immediate future.

Tunneling Proton Grotthuss Transfer Channels by Hydrophilic-Zincophobic Heterointerface Shielding for High-Performance Zn-MnO2 Batteries.

Hollandite-type manganese dioxide (α-MnO2) is recognized as a promising cathode material upon high-performance aqueous zinc-ion batteries (ZIBs) owing to the high theoretical capacities, high working potentials, unique Zn2+/H+ co-insertion chemistry, and environmental friendliness. However, its practical applications limited by Zn2+ accommodation, where the strong coulombic interaction and sluggish kinetics cause significant lattice deformation, fast capacity degradation, insufficient rate capability, and undesired interface degradation. It remains challenging to accurately modulate H+ intercalation while suppressing Zn2+ insertion for better lattice stability and electrochemical kinetics. Herein, proton Grotthuss transfer channels are first tunneled by shielding MnO2 with hydrophilic-zincophobic heterointerface, fulfilling the H+-dominating diffusion with the state-of-the-art ZIBs performance. Local atomic structure and theoretical simulation confirm that surface-engineered α-MnO2 affords to the synergy of Mn electron t2g-eg activation, oxygen vacancy enrichment, selective H+ Grotthuss transfer, and accelerated desolvation kinetics. Consequently, fortified α-MnO2 achieves prominent low current density cycle stability (≈100% capacity retention at 1C after 400 cycles), remarkable long-lifespan cycling performance (98% capacity retention at 20C after 12000 cycles), and ultrafast rate performance (up to 30C). The study exemplifies a new approach of heterointerface engineering for regulation of H+-dominating Grotthuss transfer and lattice stabilization in α-MnO2 toward reliable ZIBs.

Stabilization of Pd0 by Cu Alloying: Theory‐Guided Design of Pd3Cu Electrocatalyst for Anodic Methanol Carbonylation

AbstractElectrocatalytic carbonylation of CO and CH3OH to dimethyl carbonate (DMC) on metallic palladium (Pd) electrode offers a promising strategy for C1 valorization at the anode. However, its broader application is limited by the high working potential and the low DMC selectivity accompanied with severe methanol self‐oxidation. Herein, our theoretical analysis of the intermediate adsorption interactions on both Pd0 and Pd4+ surfaces revealed that inevitable reconstruction of Pd surface under strongly oxidative potential diminishes its CO adsorption capacity, thus damaging the DMC formation. Further theoretical modeling indicates that doping Pd with Cu not only stabilizes low‐valence Pd in oxidative environments but also lowers the overall energy barrier for DMC formation. Guided by this insight, we developed a facile two‐step thermal shock method to prepare PdCu alloy electrocatalysts for DMC. Remarkably, the predicted Pd3Cu demonstrated the highest DMC selectivity among existing Pd‐based electrocatalysts, reaching a peaked DMC selectivity of 93 % at 1.0 V versus Ag/AgCl electrode. (Quasi) in situ spectra investigations further confirmed the predicted dual role of Cu dopant in promoting Pd‐catalyzed DMC formation.

Stabilization of Pd0 by Cu Alloying: Theory-Guided Design of Pd3Cu Electrocatalyst for Anodic Methanol Carbonylation.

Electrocatalytic carbonylation of CO and CH3OH to dimethyl carbonate (DMC) on metallic palladium (Pd) electrode offers a promising strategy for C1 valorization at the anode. However, its broader application is limited by the high working potential and the low DMC selectivity accompanied with severe methanol self-oxidation. Herein, our theoretical analysis of the intermediate adsorption interactions on both Pd0 and Pd4+ surfaces revealed that inevitable reconstruction of Pd surface under strongly oxidative potential diminishes its CO adsorption capacity, thus damaging the DMC formation. Further theoretical modeling indicates that doping Pd with Cu not only stabilizes low-valence Pd in oxidative environments but also lowers the overall energy barrier for DMC formation. Guided by this insight, we developed a facile two-step thermal shock method to prepare PdCu alloy electrocatalysts for DMC. Remarkably, the predicted Pd3Cu demonstrated the highest DMC selectivity among existing Pd-based electrocatalysts, reaching a peaked DMC selectivity of 93 % at 1.0 V versus Ag/AgCl electrode. (Quasi) in situ spectra investigations further confirmed the predicted dual role of Cu dopant in promoting Pd-catalyzed DMC formation.

A review on realizing rechargeable batteries based on SOCl2/SO2 electrolyte systems

AbstractAs representative high‐energy density primary batteries, Li‐SOCl2 and Li‐SO2 batteries possess superiorities including high working potential, long temperature range, low self‐discharge rate and high safety compared with other conventional primary batteries. In spite of the high energy features, these devices have only been applied for single discharge rather than achieved energy cyclic utilization via recharge. Various modifying strategies have been put out concerning the two electrolyte systems to liberate theoretical energy storage capability as much as possible over decades. Nevertheless, reversible chemistry is also urgently required nowadays for these sulfur‐based electrolyte primary batteries to achieve transformation and upgrading. In the review, we collect some of the modification works for Li‐SOCl2 and Li‐SO2 primary batteries since their invention and successively introduce some of the opening research studies of secondary batteries, designed technologies of which are demonstrated through aspects through anode interface, cathode materials, and electrolyte composition. Finally, it is aiming to look further into the future development of the reversibility of the unique electrolyte systems.

High-performance flexible planner device featuring WS2 electrode and non-aqueous polymeric ionic electrolytes incorporated with ionic liquid and dual redox additives

Introducing redox-active species to enhance redox-activity at electrode–electrolyte interfaces, and designing the rational architecture of flexible supercapacitors comprising high-performance active materials and electrolytes with a wide potential window would be a key strategy to boost energy and power density. Herein, for the first time, we prepared an ionic liquid-based polymer electrolyte (IL/PE) by entrapping ionic liquid N-methyl-N-butyl pyrrolidinium bis (trifluoromethane sulfonyl) imide (P14TFSI)) in a polymer electrolyte Poly (diallyl dimethylammonium bis (trifluoromethane sulfonyl) imide (PDADMATFSI)) and blended with dual redox-additives (potassium iodide, KI and diphenylamine, DPA). The IL/PE with dual redox additives, demonstrates spectacular flexibility, high ionic conductivity (∼23.8 × 10−4 S cm−1), and stability in a wide potential window (∼5.9 V). A symmetrical interdigitated planner device is fabricated using dual redox-active IL/PE and flower-like WS2 electrode material. Benefiting from the synergistic effect of dual redox-active additive, the highest energy density of 47.86 µWh cm−2 at a power density of 3509 µW cm−2, and a high working potential (3 V) with excellent cycling stability upto 20,000 cycles has been achieved.

Iron‐Based Sulfate for Sodium‐Ion Batteries: Past, Present, and Future

Sodium‐ion batteries (SIBs) are crucial energy equipment that sustain low cost and better environmental benefit. Nevertheless, the practical energy density of SIBs is limited by cathode material. Over last decades, the iron‐based sulfate (IBS) has been extensively studied owing to its numerous advantages, including a large theoretical specific energy (over 100 Wh kg−1), high working potential (above 3.4 V), low cost, good structural stability, and environmental friendliness. Nevertheless, the application of IBS in SIBs is limited by its unsuitable electrolyte and low electronic/ionic conductivity. This review summarizes recently developed results on IBS materials for SIBs, ranging from the phase diagram–composition structure–electrochemical performance to modification research. A generalized summary of the future prospects of IBS‐based materials is also provided, with the hope of inspiring further advances in their application in SIBs.

Unlocking Prussian Blue Analogues Inert‐Site to Achieve High‐Capacity Ammonium Storage

AbstractAqueous ammonium‐ion batteries (AIBs) are considered a promising alternative for large‐scale energy storage due to their cost‐effectiveness and high safety. Prussian blue analogues (PBAs) are widely regarded as potential cathode materials for AIBs because of their high working potential and stable 3D framework. However, the low capacity of PBAs (≈60 mAh g−1 in the existing reported works) hinders their further development. Herein, the ion insertion is first proposed to double the capacity of PBAs by unlocking the inert‐site. Using NH4+‐rich copper hexacyanoferrate as a representative, trace amounts of induced ion in the electrolyte can change the electronic states of atoms at the inert site to achieve much higher capacity. What's more, the construction of NH4+‐rich high‐entropy Prussian blue (N‐HEPBA) further facilitates structural stability. N‐HEPBA unlocked by corresponding induced ions can exhibit an impressive specific capacity (129 mAh g−1 at 0.1 A g−1), which is the highest and approximately twice that of reported PBAs for aqueous AIBs. Meanwhile, it delivers excellent cycling stability with nearly 100% capacity retention achieved over 1000 cycles at 2 A g−1. This innovative unlocking method can provide an effective way to obtain high‐capacity PBAs in AIBs, thus promoting the development of large‐scale energy storage.

Phase engineering of Ni-Mn binary layered oxide cathodes for sodium-ion batteries

Nickel-manganese binary layered oxides with high working potential and low cost are potential candidates for sodium-ion batteries, but their electrochemical properties are highly related to compositional diversity. Diverse composite materials with various phase structures of P3, P2/P3, P2, P2/O3, and P2/P3/O3 were synthesized by manipulating the sodium content and calcination conditions, leading to the construction of a synthetic phase diagram for NaxNi0.25Mn0.75O2 (0.45 ≤ x ≤ 1.1). Then, we compared the electrochemical characteristics and structural evolution during the desodiation/sodiation process of P2, P2/P3, P2/O3, and P2/P3/O3-NaxNi0.25Mn0.75O2. Among them, P2/P3-Na0.75Ni0.25Mn0.75O2 exhibits the best rate capability of 90.9 mA h g−1 at 5 C, with an initial discharge capacity of 142.62 mA h g−1 at 0.1 C and a capacity retention rate of 78.25% after 100 cycles at 1 C in the voltage range of 2–4.3 V. The observed superior sodium storage performance of P2/P3 hybrids compared to other composite phases can be attributed to the enhanced Na+ transfer dynamic, reduction of the Jahn-teller effect, and improved reaction reversibility induced by the synergistic effect of P2 and P3 phases. The systematic research and exploration of phases in NaxNi0.25Mn0.75O2 provide new sights into high-performance nickel-manganese binary layered oxide for sodium-ion batteries.

Potassium Vanadium Fluorides as Positive Electrode Materials for K-Ion Batteries

Potassium-ion batteries (KIBs) have attracted much attention as a potential high-voltage and high-power secondary batteries due to a low standard electrode potential of K+/K in carbonate ester-based electrolytes and weak Lewis acidity of K+ (1). We reported the K+ ion extraction/insertion reactions in polyanionic compounds at a high average working potential of > 4 V vs. K+/K, which should be attributed to the inductive effect of anion(2)(3). However, the specific capacity of polyanionic compounds is often limited by the high mass of the redox-inactive polyanion framework. In this study, we focused on potassium-containing vanadium fluorides, which have high theoretical capacity.We first created a triangle phase diagram of K-V-F systems considering with their theoretical capacities, as shown in Fig. 1a. Based on the theoretical capacity and valence of V, K3VF6 was selected and synthesized, and its electrode behavior and structural changes associated with potassium extraction were investigated as a positive electrode material for KIBs.K3VF6 was synthesized through a mechanochemical method after mixing stoichiometric ratios of KF and VF3 with 10 wt% Ketjen black (KB) and calcined to enhance crystallinity. The calcination was performed in an argon atmosphere at 300 °C. The working electrodes were prepared by mixing the synthesized sample with conductive carbon (KB) and binder (PVdF) at a weight ratio of 8 : 1 : 1 and applying it to an Al foil. The charge-discharge tests were conducted using coin cells with the prepared positive electrode, K metal counter electrode, and 1.0 mol dm-3 KPF6/EC : PC = 1 : 1 (v/v) or 5.6 mol kg-1 KFSA/G3 electrolyte (4).The Rietveld refinement of the synchrotron XRD pattern of K3VF6 is shown in Figure 1b. All of the diffraction peaks, except for VO peaks, could be indexed to the tetragonal space group I4/m. The refinement showed good fitting with a low R wp value of 6.18 %. The diffusion barrier of K+ ions in K3VF6 was calculated to 0.77 and 0.89 eV along b-axis and c-axis, respectively, by the BVEL method.Figure 1c shows the initial charge/discharge curve of K3VF6 electrode. The electrode exhibited a plateau at about 3.7 V and an initial discharge capacity of about 95 mAh g-1, which corresponds to a one-electron reaction of V4+/3+ (Figure 1c).Figure 1d shows ex-situ XAFS measurements to investigate the variation of V valence state during charge/discharge. After being charged to 4.3 V, the white line peak shifted to the higher energy and the pre-edge peak became stronger than the pristine spectra, indicating oxidation of V from trivalent to tetravalent during charge. The white line and the pre-edge peaks of K3VF6 discharged to 2.0 V are almost identical to that of the pristine, showing reversible V3+/4+ redox. We will further discuss the structural changes during the K+ ion extraction/insertion process and the redox behavior of V in the presentation.

KxNayH(2‐x‐y)Ti2O5 for High‐Performance Lithium‐Ion Battery Anode with Li Dendrites‐Free Mechanism, Zero‐Strain Characteristic

AbstractConventional Li‐ion batteries equipped with graphite anodes suffer from poor rate performance and the risk of lithium dendrites, which constrain scale‐up applications. Among the promising candidates, spinel‐type Li4Ti5O12 is still subjected to low theoretical specific capacity, high working potential, and poor diffusion properties. Herein the KxNayH(2‐x‐y)Ti2O5 product is provided by reconstructing the chemical bonding idea, which exhibits enhanced specific capacity (323 mAh g−1), lower working potential (major capacity contribution < 1.5 V vs Li+/Li), higher diffusion coefficient (10−8.5–10−5 cm2 s−1), and long cycle stability. Further in/ex situ studies show that these excellent properties can be attributed to the combination of high capacitive contribution, unique “switching mechanism” to avoid lithium dendrite generation, and the zero‐strain properties. The findings provide new ideas and opportunities for the development of next generation titanate anode materials with desirable electrochemical properties.

Li2CO3 As the Parasitic Reaction Root for Exacerbated Material Degradation and Performance Deterioration of Ni-Rich Cathode

Nickel-rich transition metal oxides is widely regarded as promising cathode materials for high energy density lithium-ion batteries for emerging applications in electric vehicles. However, achieving high energy density in Ni-rich cathodes is generally accompanied with substantial obstacles of lifetime and safety. The major issues of Ni-rich cathodes at high working potentials are originated from the unstable cathode-electrolyte interface, while the underlying mechanism of parasitic reactions to material degradation at the surface of cathode materials is not well understood. In this work, we report the parasitic-reaction-driven structural degradation in LiNi0.83Mn0.1Co0.07O2 cathode by altering interfacial chemistry by synthesizing cathode material in different environments. Our home-build high precision leakage current (HpLC) system verifies that Li2CO3 impurity generated in harsh synthesis environment is a nature root of electrolyte decomposition and parasitic reactions on Ni-rich cathodes. Different rates of parasitic reactions are strongly correlated to drastic discrepancy in electrochemical performance of Ni83 cathodes at different synthesis conditions. The post-mortem characterizations reveal that parasitic reactions promote severe rock-salt phase transformation with more Ni reduction and O deficiency at the surface of cathode materials. This study suggests the significance of developing impurity-free and mitigated parasitic reactions in Ni-rich transition metal oxides for enabling high energy density. Acknowledgement Research at the Argonne National Laboratory was supported by the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office. Argonne National Laboratory is operated for the DOE Office of Science by UChicago Argonne, LLC, under Contract DE-AC02-06CH11357. Figure 1

Unveiling the parasitic-reaction-driven surface reconstruction in Ni-rich cathode and the electrochemical role of Li2CO3

Nickel-rich transition-metal oxides are widely regarded as promising cathode materials for high-energy-density lithium-ion batteries for emerging electric vehicles. However, achieving high energy density in Ni-rich cathodes is accompanied by substantial safety and cycle-life obstacles. The major issues of Ni-rich cathodes at high working potentials are originated from the unstable cathode-electrolyte interface, while the underlying mechanism of parasitic reactions towards surface reconstructions of cathode materials is not well understood. In this work, we controlled the Li2CO3 impurity content on LiNi0.83Mn0.1Co0.07O2 cathodes using air, tank-air, and O2 synthesis environments. Home-built high-precision leakage current and on-line electrochemical mass spectroscopy experiments verify that Li2CO3 impurity is a significant promoter of parasitic reactions on Ni-rich cathodes. The rate of parasitic reactions is strongly correlated to Li2CO3 content and severe performance deterioration of Ni83 cathodes. The post-mortem characterizations via high-resolution transition electron microscope and X-ray photoelectron spectroscopy depth profiles reveal that parasitic reactions promote more Ni reduction and O deficiency and even rock-salt phase transformation at the surface of cathode materials. Our observation suggests that surface reconstructions have a strong affiliation to parasitic reactions that create chemically acidic environment to etch away the lattice oxygen and offer the electrical charge to reduce the valence state of transition metal. Thus, this study advances our understanding on surface reconstructions of Ni-rich cathodes and prepares us for searching for rational strategies.

Ni-rich LiNixCoyM1-x-yO2 (NCM; M=Mn, Al) cathode materials for lithium-ion batteries: Challenges, mitigation strategies, and perspectives

Ni-rich LiNixCoyM1-x-yO2 (NCM; M = Mn, Al) cathodes have attracted much attention owing to their ability to provide high specific capacity of > 200 mAh g−1, high working potential (∼3.8 V vs. Li/Li+), and low cost, hence they are considered as preferred candidates for electric vehicle applications. Nevertheless, the commercialization of Ni-rich NCM cathodes is limited due to challenges of surface instability, structural mechanical failure and deteriorated thermal instability leading to cycling capacity fading. Cation mixing, gas release, residual of lithium, and dissolution of transition metals will also affect the electrochemical performance of Ni-rich cathodes which need to be addressed. The mitigation strategies to solve these challenges are doping to suppress the structural degradation and surface coating to improve interface stability. Herein, we present the recent comprehensive research works on Ni-rich cathodes for LIB, regarding challenges, mitigating strategies, and future perspectives to improve their electrochemical performance.

Low-Potential Operation of Direct Electron Transfer Biosensor Strip With Single-Walled Carbon Nanotubes and Flavin Adenine Dinucleotide Glucose Dehydrogenase

In this study, the low-potential operation (+0.05 V vs. Ag/AgCl) of a direct electron transfer (DET) glucose biosensor strip with a small-volume (2 μL) electrochemical capillary chamber is demonstrated. We constructed a DET formation in which de-bundled single-walled carbon nanotubes (SWCNTs) were placed near the reaction center pocket of flavin adenine dinucleotide glucose dehydrogenase (FAD-GDH). The DET biosensor has the advantage of long-term stability, unlike an electron transfer mediator, which is naturally reduced to cause sensing malfunction in a mediated electron transfer biosensor, adopted in commercial devices. However, DET biosensors still have a high working potential owing to their overpotential. In this article, we have resolved this issue via a very short interval (1 ms) voltage application (+0.4 V) that reduced the onset potential, in other words, enhanced the current owing to an enzymatic reaction. The DET biosensors had a sensitivity of 0.055 μA (mg/dl) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , a linear dynamic range of 0-750 mg/dL, and a detection limit of 0.9 mg/dL.

Influence of the Thermal Treatment on the Structure and Cycle Life of Copper Hexacyanoferrate for Aqueous Zinc-Ion Batteries

Copper hexacyanoferrate (CuHCF) has become an attractive Zn2+ insertion material as a positive electrode in aqueous zinc-ion batteries thanks to its high reversibility towards Zn2+ (de-)insertion, its simple, inexpensive and easily scalable synthesis route, its low toxicity, and its high working potential. It is known that the physiochemical properties of CuHCF can be modified by manipulating its synthesis parameters. However, the effect of these parameters on the material’s electrochemical performance and cycle life needs further investigation. Here, the structure and composition of CuHCF treated at different temperatures are studied through crystallographic, compositional, and thermogravimetric analyses. The resulting CuHCF powders were galvanostatically cycled to assess their electrochemical performance in relation to their annealing temperature. The results showed that the annealed CuHCF electrodes exhibited longer cycle life while maintaining a coulombic efficiency ≥ 99.5%. The longest cycle life was achieved by annealing the CuHCF electrodes at 100 °C.

Hollandite-type VO1.52(OH)0.77 nanorod arrays on carbon cloth toward the improvement of zinc diffusion

As cathodes for aqueous zinc ion batteries (ZIBs), vanadium-based materials have received a lot of attention in recent years because of their high theoretical capacities and suitable working potentials. However, the sluggish kinetics and volume expansion effects lead to their rapid capacity decay and poor rate performance. Herein, a novel strategy is proposed through the in-situ growth of one-dimensional hollandite-type VO1.52(OH)0.77 nanorod arrays on flexible carbon fiber cloth as ZIBs cathode material. The synergistic effect between the hollandite-type tunnel structure and the functional group-modified conductive collector, not only accelerates the charge transfer rate and increases zinc ion intercalation capacity but also enhances the structural stability of the electrode by improving the interface stability and alleviating the detachment between the VO1.52(OH)0.77 nanorod arrays and the conducting substrate during the charge/discharge process. Benefitting from these merits, as-prepared VO1.52(OH)0.77 achieves an impressive reversible capacity of 305.6 mAh g−1 at 100 mA g−1 and ultralong cyclic stability (96.4% retention over 1000 cycles). This work reveals a concise approach to the construction of hollandite-type and demonstrates that the structural stability of vanadium-based oxide cathodes can be significantly enhanced by elegant structural design, thereby improving their Zn ion storage performance.

Design of Phosphide Anodes Harvesting Superior Sodium Storage: Progress, Challenges, and Perspectives

AbstractSodium (Na) ion batteries (SIBs) are promising in stationary energy storage applications. Research is also afoot to seek suitable electroactive materials for use in SIBs. Recently, phosphides to be used in the anode for Na storage are particularly appealing due to their high specific capacities and low working potentials. The following matters are to deal with their inherent drawbacks of large volume variation and inferior interfacial stability upon Na insertion/extraction, which is believed to be largely responsible for capacity and cycling decay. Despite striking progress in addressing the above drawbacks, current studies on phosphides remain preliminary. In this review, an in‐depth understanding of phosphides regarding Na storage mechanism, capacity assessment, phase change, and reaction types is provided. The effective strategies and the sound designs of phosphides for Na storage are also discussed. Their correlations between electrochemical behavior and chemical/structural characteristics are analyzed, in a bid to sort out the basic ideas for the design of high‐performance phosphides that enable high‐energy and durable SIBs. Doubtless, the experience and knowledge gained from the research on phosphides are shared, and the strategies are expected to extend the scope beyond phosphides.

Epitaxial interface stabilizing iridium dioxide toward the oxygen evolution reaction under high working potentials

Epitaxial interface stabilizing iridium dioxide toward the oxygen evolution reaction under high working potentials

Lotus root-like porous Na2MnPO4F·Na3V2(PO4)2F3/C as a high-performance cathode material for sodium-ion batteries

Na 2 MnPO 4 F has become a promising cathode candidate for next generation sodium ion batteries by virtue of its high working potential and theoretical capacity, but its electrochemical performance is restricted by its low electronic conductivity and sluggish Na + diffusion. In this study, Na 3 V 2 (PO 4 ) 2 F 3 is introduced into the Na 2 MnPO 4 F cathode material to improve the electron/ionic conductivity by generating lattice defects and providing active sites for Na + transportation. The structure, morphology and electrochemical properties of x Na 2 MnPO 4 F· y Na 3 V 2 (PO 4 ) 2 F 3 /C materials are investigated thoroughly. It is found that the electrochemical performance of Na 2 MnPO 4 F is significantly elevated by the modification of Na 3 V 2 (PO 4 ) 2 F 3 . The optimized lotus root-like porous Na 2 MnPO 4 F·Na 3 V 2 (PO 4 ) 2 F 3 /C cathode material delivers the first specific discharge capacity of 126.6 mAh·g −1 at 0.05C, which is close to the theoretical specific capacity. Furthermore, the Na 2 MnPO 4 F·Na 3 V 2 (PO 4 ) 2 F 3 /C cathode material also presents good rate performance (76.9 mAh·g −1 at 1C rate), and remains 93.2% capacity retention after 400 cycles. This paper demonstrates a promising guide to construct Na 2 MnPO 4 F-based cathode materials with superior electrochemical performance for sodium ion batteries.