Polyanionic Cathode Research Articles

The Role of Fluorine in Polyanionic Cathode Materials for Sodium-Ion Batteries.

With the growing global demand for renewable energy and the increasing scarcity of lithium resources, sodium-ion batteries have received extensive attention and research as a potential alternative. Among many cathode materials for sodium-ion batteries, polyanion materials are favored for their high operating voltage, stable cycling performance, and good safety. However, the low electronic conductivity and low energy density of polyanionic materials limit their potential for large-scale commercial applications. To overcome this challenge, various strategies have been explored to improve their electrochemical performance. Among them, fluorine doping has been proven to be an effective means. In this study, we have systematically explored the effects of trace fluorine doping and mass fluorine substitution on the structure, dynamics, and electrochemistry of polyanionic cathode materials for sodium-ion batteries and deeply analyzed their reaction mechanisms. The analysis results show that trace fluorine doping can effectively improve the electronic conductivity of the material, thus enhancing its electrochemical performance. A large amount of fluorine substitution can effectively improve the voltage plateau of the material, thus enhancing its energy density. However, the environmental and safety challenges associated with the introduction of fluorine should also be addressed. Overall, the introduction of fluorine in polyanionic cathode materials can further optimize the electronic structure and electrochemical performance, thus realizing the wide application of high-performance sodium-ion batteries and making them a competitive battery technology.

Regulation of Coordination Chemistry To Accelerate Na+ Transfer Kinetics of Polyanionic Cathodes for Ultrastable Sodium-Ion Batteries.

Alluaudite-type iron-based sulfate structure (Na2+2xFe2-x(SO4)3) has attracted wide attention due to its high working voltage and low cost. However, their practical application is hindered by challenges such as limited reversible capacity and sluggish transfer kinetics. Herein, we proposed an anion substitution strategy to optimize iron-based sulfate cathode materials. The electrochemical characterization and theoretical calculations confirmed a reduction in the migration barrier of Na+ ions in various pathways. Besides, fluorine weakened the electron density of the crystal plane, thereby impeding the continuous side reaction of the electrolyte. As expected, the NFSF cathode can exhibit a capacity of 121.5 mAh g-1 at 12 mA g-1 and keep a high retention of 78.8% after 1000 cycles at 600 mA g-1. In addition, the NFSF-based cathode and hard carbon (HC)-based anode were assembled into a laboratory-scale pouch cell to demonstrate the electrochemical performance and practical applications.

A Phase-Transition-Free Sodium Vanadium Phosphate Cathode via Medium-Entropy Engineering for Superior Sodium Ion Batteries.

Na3V2(PO4)3, based on multi-electron reactions between V3+/V4+/V5+, is a promising cathode material for SIBs. However, its practical application is hampered by the inferior conductivity, large barrier of V4+/V5+, and stepwise phase transition. Herein, these issues are addressed by constructing a medium-entropy material (Na3.2V1.1Ti0.2Al0.2Cr0.2Mn0.2Ni0.1(PO4)3, ME-NVP) with strong ME─O bond and highly occupied Na2 sites. Benefiting from the medium-entropy effect, ME-NVP manifests a phase-transition-free reaction mechanism, two reversible plateaus at 3.4 (V3+/V4+) and 4.0V (V4+/V5+), and small volume change (2%) during Na+ insertion/extraction processes, as confirmed by comprehensive in/ex situ characterizations. Moreover, kinetics analysis illuminates the superior Na+ diffusion ability of ME-NVP. Thus, the ME-NVP cathode realizes remarkable rate capability of 67mA h g-1 at 50C and a long-term lifespan over 10000 cycles (capacity retention of 81.3%). Theoretical calculations further illustrate that the weak binding of Na+ ion in the channel is responsible for the rapid Na+ diffusion, accounting for the superior reaction kinetics. Moreover, rigid MEO6 octahedral and feasible rearrangement of Na+ ions can suppress the phase transition, thus endowing an ultrastable ME-NVP cathode. This work highlights the significant role of medium-entropy engineering in advancing the output voltage, cycling stability, and rate capability of polyanionic cathodes.

Doping of Sodium-Ion Cathodes for in-Situ Resource Utilization on the Moon and Mars

On-demand in-space and on-surface manufacturing of batteries is sought to deliver energy storage devices needed for sustained human presence on the Moon and Mars. In-situ resource utilization (ISRU) is a disruptive approach that reduces the dependence on launch payload weight and volume by utilizing the local available resources to maximize long-term sustainability of exploration where resupply may be infeasible or costly. In this study, candidate sodium-ion cathode compositions were designed within the elemental abundance limitations of the Moon and Mars, which support sodium-ion chemistry over lithium-ion due to the low abundance of lithium in regolith. Compositions were assessed for theoretical yield normalized capacity [mAh/kgfeedstock], which revealed that poly-anion type sodium-ion cathodes, which use elements such as P, V, Ni, and Co, are infeasible to attain from ISRU manufacturing. Manganese containing layered and tunnel-type cathode compositions and processing conditions were studied to explore the balance between specific energy density and cycling performance with elemental abundance, specifically searching for replacement of manganese. Study of tunnel-type cathodes found that a critical manganese content was required to stabilize the orthorhombic tunnel type structure with Pbam symmetry (Na0.44MnO2 type) over the NaTiFeO4 type Pnma symmetry, which showed degraded electrochemical performance. Tunnel-type cathodes exhibit higher theoretical yield at the expense of specific capacity and yield normalized capacity. Calculated differences in elemental abundance between the Moon and Mars revealed that compositions containing Ti are better suited for lunar ISRU due to the lower Ti abundance on Mars. Layered-type cathodes exhibit the highest specific capacity and yield normalized capacity, but require improvement in capacity retention. Modification of layered-type Na0.67Mn0.5Fe0.5O2 with the ISRU abundant dopants Al3+, Ti4+, and Mg2+ delivered phase pure Na0.67Mn0.5Fe0.44Al0.03Ti0.015Mg0.015O2 (NMFATM) after calcination. Modification with dopants significantly improved the specific capacity and capacity retention compared to the undoped material.

Unlocking advanced sodium storage performance: High-entropy modulates crystallographic sites with reversible multi-electron reaction

Poor migration dynamics and low energy density are the main challenges of Na3V2(PO4)3 as a cathode material for sodium ion batteries. Herein, a nanoscale polyhedron high-entropy cathode of Na3V1.47(Fe,Al,Ga,Mg,Mn)0.5Mo0.01Nb0.02(PO4)3 is designed to modify the crystal structure and enhance the electrons transfer. Distributed nanoparticles improve the electrolyte interface, promoting rapid migration of Na+, while the abundant specific surface area offers extra sites for Na+ storage. High entropy and multi-metal synergistic effects increase the number of occupied Na(1) and Na(2) sites, maintaining multiple redox couples (V3+/4+/5+ and Mn2+/3+/4+) and obtaining a reversible 2.18-electron reaction. Consequently, the high-entropy cathode of Na3V1.47(Fe,Al,Ga,Mg,Mn)0.5Mo0.01Nb0.02(PO4)3 delivers excellent specific capacity of 130.2 mAh g−1 at 0.5 C, achieving high energy density of 448.3 Wh kg−1, and exhibiting the capacity retention of 95 % after 500 cycles at 5 C and 86.5 % after 1000 cycles at 15 C, respectively. In situ XRD, ex situ XAS and DFT calculations reveal the influence of structural evolution, valence changes, and high-entropy effects on chemical kinetics. This study provides a guideline for designing advanced polyanionic phosphate cathode materials for sodium ion batteries.

Thermal Runaway of Na‐Ion Batteries with Na3V2O2(PO4)2F Cathodes

AbstractThe metal‐ion battery manufacturing growth rates increase attention to the safety issues. For promising sodium‐ion batteries, this topic has been studied in much less detail than for the lithium‐ion ones. Here, we explored the thermal runaway process of Na‐ion pouch cells with the Na3V2O2(PO4)2F (NVOPF)‐based cathode. The thermal runaway onset temperature for such cells is noticeably higher than that for the NMC‐based LIBs. We show that thermal runaway is triggered by the anode and the separator decomposition rather than by the processes at the cathode. The composition of the gas mixture released during thermal runaway process is similar to that for Li‐ion batteries. The results suggest that sodium‐ion batteries based on polyanionic cathodes can pave the way to safer metal‐ion energy storage technologies.

Insights into Tiny High‐Entropy Doping Promising Efficient Sodium Storage of Na3V2(PO4)2O2F toward Sodium‐Ion Batteries

AbstractBoth high operation voltage and theoretical capacity promise polyanion‐type fluorophosphate Na3V2(PO4)2O2F as a competitive cathode toward high‐energy‐density sodium‐ion batteries (SIBs). However, the intrinsic low kinetic characteristics seriously influence its high‐power property and service life. To well address this, a creative tiny high‐entropy (HE) doping methodology is purposefully developed to fabricate nanoscale Na3V1.94(Cr, Mn, Co, Ni, Cu)0.06(PO4)3O2F (NVPOF‐HE) as the advanced cathode materials for SIBs. The grain refinement effect induced by collaborative regulations from polyvinyl pyrrolidone and tiny HE heteroatomic doping is reasonably proposed for nanosizing particle dimension of NVPOF‐HE. Systematic experiments and theoretical calculations authenticate that the HE doping efficiently promotes the electronic/ionic transport and high‐voltage capacity contribution, and weakens the lattice expansion over Na+‐(de)intercalation processes. Thanks to the appealing virtues mentioned here, the nano NVPOF‐HE, compared to single‐ion/dual‐ion/triple‐ion doped cases, achieves even better Na+‐storage performance in terms of both high‐rate capacities and long‐term cycling stability. Furthermore, the NVPOF‐HE assembled full SIBs deliver a high materials‐level energy density of 463 Wh kg−1 and electrochemical stability of ≈93.8% capacity retention after 1000 cycles at 5 C rate. More essentially, the fundamental insights gained here provide a significant scientific and technological advancement in high‐performance and durable polyanionic cathodes toward next‐generation SIBs.

The Development and Prospect of Stable Polyanion Compound Cathodes in LIBs and Promising Complementers.

Cathode materials are usually the key to determining battery capacity, suitable cathode materials are an important prerequisite to meet the needs of large-scale energy storage systems in the future. Polyanionic compounds have significant advantages in metal ion storage, such as high operating voltage, excellent structural stability, safety, low cost, and environmental friendliness, and can be excellent cathode options for rechargeable metal-ion batteries. Although some polyanionic compounds have been commercialized, there are still some shortcomings in electronic conductivity, reversible specific capacity, and rate performance, which obviously limits the development of polyanionic compound cathodes in large-scale energy storage systems. Up to now, many strategies including structural design, ion doping, surface coating, and electrolyte optimization have been explored to improve the above defects. Based on the above contents, this paper briefly reviews the research progress and optimization strategies of typical polyanionic compound cathodes in the fields of lithium-ion batteries (LIBs) and other promising metal ion batteries (sodium ion batteries (SIBs), potassium ion batteries (PIBs), magnesium ion batteries (MIBs), calcium ion batteries (CIBs), zinc ion batteries (ZIBs), aluminum ion batteries (AIBs), etc.), aiming to provide a valuable reference for accelerating the commercial application of polyanionic compound cathodes in rechargeable battery systems.

Dynamic Lock-And-Release Mechanism Enables Reduced ΔG at Low Temperatures for High-Performance Polyanionic Cathode in Sodium-Ion Batteries.

Low-temperature synthesis of polyanionic cathodes for sodium-ion batteries is highly desirable but often plagued by prolonged reaction times and suboptimal crystallinity. To address these challenges, a novel self-adaptive coordination field regulation (SACFR) strategy based on a dynamic lock-and-release (DLR) mechanism is introduced. Specifically, urea is used as a DLR carrier during synthesis, which dynamically "locks" and "releases" vanadium ions for controlled release, simultaneously "locking" H+ ions to enhance phosphate group release, thereby creating a self-adaptive coordination field that can intelligently respond to real-time demands of the reaction system. This dynamic coordination behavior contributes to both an improvement in reaction kinetics and a significant reduction in Gibbs free energy change (ΔG). As a result, the kinetic efficiency and thermodynamic spontaneity of the reaction are greatly enhanced, enabling the efficient synthesis of high-crystalline Na3V2O2(PO4)2F (NVOPF) at 90 °C within just 3 hours. The as-prepared NVOPF cathode exhibits exceptional rate performance and ultra-stable cycling stability across a broad temperature range. Furthermore, the successful kilogram-scale synthesis underscores the practical potential of the innovative strategy. This work pioneers the regulation of coordination field chemistry for polyanionic cathode synthesis, providing transformative insights into material design.

Opportunities and Challenges of Multi-Ion, Dual-Ion and Single-Ion Intercalation in Phosphate-Based Polyanionic Cathodes for Zinc-Ion Batteries.

With the continuous development of science and technology, battery storage systems for clean energy have become crucial for global economic transformation. Among various rechargeable batteries, lithium-ion batteries are widely used, but face issues like limited resources, high costs, and safety concerns. In contrast, zinc-ion batteries, as a complement to lithium-ion batteries, are drawing increasing attention. In the exploration of zinc-ion batteries, especially of phosphate-based cathodes, the battery action mechanism has a profound impact on the battery performance. In this paper, we first review the interaction mechanism of multi-ion, dual-ion, and single-ion water zinc batteries. Then, the impact of the above mechanisms on battery performance was discussed. Finally, the application prospects of the effective use of multi-ion, dual-ion, and single-ion intercalation technology in zinc-ion batteries is reviewed, which has significance for guiding the development of rechargeable water zinc-ion batteries in the future.

Revealing the electrolyte suitability optimization and failure mechanism of sodium-ion pouch cells with Na3.5V1.5Mn0.5(PO4)3 polyanionic cathode

Polyanionic cathodes are promising for sodium-ion batteries (SIBs) in large-scale energy storage applications, but there is almost no research on the failure mechanisms of SIBs with polyanionic cathodes. Herein, we investigate the failure mechanisms of the pouch cells with the Na3.5V1.5Mn0.5(PO4)3 (NVMP) polyanionic cathode and hard carbon (HC) anode. Firstly, the sodium salts are studied in same electrolyte solvents by combining theoretical calculation and electrochemical tests, and NaClO4 is verified as suitable for NVMP//Na half-cells, while NaPF6 is optimal for the cells containing HC electrode. Secondly, the charging cut-off voltages significantly affect the cycling performance. For the NVMP pouch cells cycled within 1.5 ∼ 4.2 V, slight electrolyte oxidation occurs during the final stage of each charge cycle, leading to macroscopic “swelling” after 500 cycles. Finally, for the NVMP pouch cells cycled >3000 cycles within 1.5 ∼ 4.0 V, the main failure mechanism is the “sodium deficiency” and the irreversible deactivation of manganese ions in the waste NVMP cathode, rather than the oxidation of the spent separator or the “sodium precipitation” on the spent HC anode. This work addresses critical gaps in failure mechanism research and lays a foundation for the large-scale application of SIBs with polyanionic cathodes.

Local Electronic Structure Regulation Enabling Fluorophosphates Cathode with Improved Redox Potential and Reversible Capacity for Sodium-Ion Batteries.

Mn-based fluorophosphates have attracted much attention as cathodes for sodium-ion batteries owing to their high cost effectiveness, considerable capacity, and stable framework. However, the fascinating Mn3+/2+ redox couple suffers from inadequate activation due to the Mn-O covalent character and poor electronic conductivity, impeding its further applications. Herein, a local electronic structure regulation strategy is proposed to improve the Mn3+/2+ redox potential and reversible capacity simultaneously through introducing elements with low-energy 3d orbitals to expand the energy gap between the eg orbitals and Fermi energy of Na. Moreover, the 3d element substitution serves to narrow the band gap toward the improved intrinsic electronic conductivity. In comparison with pristine Na2Fe0.45Mn0.55PO4F, the as-prepared Na2Fe0.45Mn0.4V0.1PO4F cathode achieves an increase from 3.5 to 3.6 V in the high-voltage platform and an improvement in energy density from 330 to 361 Wh kg-1. This work inspires new ideas in adjusting the redox potential of polyanionic cathodes through deliberate regulation of the local electronic structure.

NaLiFe(C2O4)2: A polyanionic Li/Na-ion battery cathode exhibiting cationic and anionic redox

Recently, polyanionic compounds have received great interest as alternative cathode materials to conventional oxides due to their different advantages in cost, safety, structural stability, as well as being environmentally friendly. However, the vast majority of polyanionic materials reported so far rely exclusively upon the redox reaction of the transition metal for lithium/sodium transfer.The development of multielectron redox-active cathode materials is a top priority for achieving high energy density with long cycle life in the next-generation secondary battery applications. Triggering anion redox activity is a promising strategy to enhance the energy density of polyanionic cathode materials for Li/Na-ion batteries. In addition to transition metal redox activity, the oxalate group also shows redox behavior enabling reversible charge/discharge and high capacity without gas evolution.Herein, we report NaLiFe(C2O4)2 as a new positive electrode and use different characterization techniques such as Raman spectroscopy and Mössbauer analyses to characterise this dual-ion redox process experimentally. First-principles calculations also help to understand the interactions between the transition metal and the oxalate group as the main factor that modulates the cationic and polyanionic redox couples in these materials.

Identifying the β-to-α phase transition during the long cycling process in Na2FePO4F cathode

Na2FePO4F has emerged as a promising cathode for large-scale electrochemical energy storage, primarily due to its abundance of raw materials and distinctive two-dimensional ion channels. Counterintuitively, pristine Na2FePO4F lacks the long-term stability typically seen in polyanionic cathodes, which severely impedes its practical application. Traditionally, the origin of this problem has been only phenomenologically attributed to the poor intrinsic electronic conductivity and structural instability of Na2FePO4F. Here, we identify that rapid capacity fading of Na2FePO4F is closely related to the β-to-α phase transition during the long cycling process. Furthermore, we develop a practical high-entropy doping strategy and the corresponding microstructure engineering to mitigate the impact of the phase transition on the crystal structure, thereby increasing the capacity retention from 56 % to 94 % over 400 cycles at 0.5C in coin cell, and attain almost 100 % capacity retention after 300 cycles at 0.1C in pouch cell. Overall, this work unveils the mechanism of rapid capacity decay in Na2FePO4F and lays the groundwork for the rational design of durable polyanionic electrodes.

Demystifying In Situ Pyrolysis Chemistry for High-Performance Polyanionic Cathodes in Sodium-Ion Batteries.

The carbon coating strategy has emerged as an indispensable approach to improve the conductivity of polyanionic cathodes. However, owing to the complex reaction process between precursors of carbon and cathode, establishing a unified screening principle for carbonaceous precursors remains a technical challenge. Herein, we reveal that carbonaceous precursor pyrolysis chemistry undeniably influences the formation process and performance of Na3V2(PO4)3 (NVP) cathodes from in situ insights. By investigating three types of carbonaceous precursors, it is found that O/H-containing functional groups can provide more bonding sites for cathode precursors and generate a reducing atmosphere by pyrolysis, which is beneficial to the formation of polyanionic materials and a uniform carbon coating layer. Conversely, excessive pyrolysis of functional groups leads to a significant amount of gas, which is detrimental to the compactness of the carbon layer. Furthermore, the substantial presence of residual heteroatoms diminishes graphitization. In this case, it is demonstrated that carbon dots (CDs) precursors with suitable functional groups can comprehensively enhance the Na+ migration rate, reversibility, and interface stability of the cathode material. As a result, the NVP/CDs cathode displays outstanding capacity retention, maintaining 92% after 10,000 cycles at a high rate of 50 C. Altogether, these findings provide a valuable benchmark for carbon source selection for polyanionic cathodes.

Integrated rocksalt–polyanion cathodes with excess lithium and stabilized cycling

Integrated rocksalt–polyanion cathodes with excess lithium and stabilized cycling

High-entropy doping NASICON[sbnd]Cathode breaks the kinetic barriers and suppresses voltage hysteresis for sodium ion batteries

The NASICON-type Na3MnTi(PO4)3 material has garnered widespread attention for its stable three-dimensional structure, rapid sodium-ion transport channels and excellent thermal stability. However, its poor electronic conductivity, cyclic stability and structural decay during cycling have posed significant obstacles to its commercialization. Herein, a high-entropy doping Na3.12MnTi0.9(VFeMgCrZr)0.02(PO4)3 cathode was successfully synthesized, exhibiting a high reversible capacity of 169.6 mAh g-1 and a high energy density of over 500 Wh kg-1. The DFT and machine learning MD results show that benefiting from the high-entropy effect of multi-element synergy in HE-NMTP, the electronic conductivity and sodium ion diffusion kinetics are significantly improved. Simultaneously, the voltage hysteresis and energy loss are mitigated, while crystal structural stability is improved. Furthermore, the full-cell achieves an impressive energy density of 440 Wh kg-1 (for cathode) at 0.2C. These results demonstrate the advantages of the high-entropy doping cathode as a potential cathode material for sodium-ion batteries and provide a valuable strategy for other NASICON system cathodes as well as polyanion cathodes.

Enhancing Voltage Output in Polyanion‐Type Cathode Materials for Sodium Ion Batteries

AbstractSodium‐ion batteries (SIBs) are promising in several aspects due to their many advantages over lithium‐ion batteries. Among SIB's several outstanding attributes, its low cost, resource abundance, and potential safety make it suitable for large‐scale energy storage systems (ESS). Among the potential cathode materials, poly‐anionic cathode materials could be a better choice for their stability and safety in comparison to layered transition metal oxides and Prussian blue analogues (PBA). However, on the other hand, the conductivity as well as the available capacity of the polyanion compounds are still poor, which limits their applications; moreover, some polyanion cathode operate at low voltage, which reduces the energy density and raises the cost of the battery system. We here try to summarize the recent progress of polyanion compounds as cathode materials for SIB. These compounds are categorized based on the metal redox couple, including V‐, Cr‐, Mn‐, Fe‐, Co‐, and Ni‐polyanion compounds. Our attention is specifically drawn to properties such as reversible redox voltage, capacity, cycling stability, and sodium storage mechanisms. We also discuss the challenges and potential development strategies for the future.

Preparation and application of high-performance sodium-ion batteries cathode material Na3.6Fe2.6(PO4)1.6P2O7 with optimized sodium-iron ratio

Na4Fe3(PO4)2P2O7 (NFPP) has been developed as the most promising polyanion cathode for sodium-ion batteries due to its excellent electrochemical performance, high safety properties, and environmental friendliness. However, the electrochemically inactive impurity (m-NaFePO4) will inevitably generate during synthesis process, which decreases the practical capacity of NFPP significantly. In this paper, a novel Na3.6Fe2.6(PO4)1.6P2O7 cathode material with excellent performance is successfully exploited by optimizing sodium-iron ratio to reduce the formation of impurity phases. In a series of as-prepared materials with sodium-iron ratio between 1.33–1.50, Na3.6Fe2.6(PO4)1.6P2O7 exhibits the highest discharge specific capacity (110.3 mAh g−1 at 0.1C), best rate capability (84.4 mAh g−1 at 30 C) and cycle performance (78.2 % capacity retention after 3000 cycles at 20 C). Furthermore, 20 Kg of the Na3.6Fe2.6(PO4)1.6P2O7 cathode material is prepared by spray drying method, which has been successfully applied in sodium-ion pouch cells (12 Ah) with a commercial hard carbon as the anode materials. The assembled pouch cells display excellent cycle performance (82.4 % capacity retention after 2000 cycles at 1 C), rate capability (88 % capacity retention at 30 C) and low-temperature performance (74 % capacity retention at −40 °C).

Understanding the Role of Mn Substitution for Boosting High-Voltage Na4Fe3-xMnx(PO4)2P2O7 Cathode in Sodium-Ion Batteries.

Na4Fe3(PO4)2P2O7 is regarded as the most promising polyanionic cathode for sodium-ion batteries (SIBs) due to its superior structural stability, cost-effectiveness, and environmental benignity. However, the low operating voltage inevitably weakens its competitiveness in energy density. Previous works have tried to enhance its operating voltage by Mn doping, which draws on the design idea of LiFexMn1-xPO4 cathode for lithium-ion batteries, but with little success. In this context, uncovering the role of Mn substitution in Na4Fe3-xMnx(PO4)2P2O7 (NFMxPP) cathode is urgently needed. This work discloses the effect of Mn contents on the structure, sodium storage property, and reaction mechanism of NFMxPP cathode for the first time. Introducing a moderate amount of Mn (0.6 ≤ x ≤ 1.2) into NFMxPP can weaken the Fe-O bonding interaction, thus leading to the full utilization of Mn3+/Mn2+ redox couple. As the representative, NFM1.2PP cathode exhibited a high operating voltage of ≈3.3V with a reversible capacity of 109.2 mAh g-1. Note that a Hard carbon||NFM1.2PP full battery manifests considerably high-capacity retention of 92.3% over 1600 cycles. It is believed that an understanding of the role of Mn substitution in this work will promote the practical application of high voltage NFMxPP cathodes for SIBs.