Rate Performance Research Articles

Ion-Conducting and Stretchable Organogel Polymer Interface Layer for Stabilizing Lithium Metal Anodes via In Situ Polymerization Strategy.

The uncontrollable growth of lithium dendrites and the unstable interface of the lithium metal anode/electrolyte inhibit potential large-scale applications of lithium metal batteries. The polymer artificial solid-electrolyte interface layer shows potential for the homogeneity of ion flux toward a lithium metal electrode. Herein, we design an ionic conductive and stretchable organogel polymer layer as the artificial protective layer via in situ polymerization on an active lithium metal anode, which can accommodate volume changes and maintain enhanced interfacial contact with the electrode. The propylene carbonate and the long alkyl ether in the polymer protective layer contribute to the inducing of uniform Li deposition and enhance ion transport. In addition, the in situ polymerization membrane adheres tightly to the lithium metal anode, which can effectively eliminate the barriers of ionic transport at heterogeneous interfaces and has stretchable strength tending to suppress Li dendrites. As a result, the Li/Li symmetric cell with this artificial polymeric protect layer can stably cycle for over 800 h under 1 mA cm-2 without increased polarization voltage, while the corresponding lithium metal/LiFePO4 full battery delivers high-capacity retention of 102.6, 127.7, and 136.7% after 244, 862, and 976 cycles at 0.3, 1, and 2 C. Furthermore, the lithium metal battery equipped with this artificial layer also shows longer cycling life and higher reversible specific capacity (130.24 mAh g-1) under 1 C and enhanced rate performance than bare Li battery.

Insight into the Role of Closed-Pore Size on Rate Capability of Hard Carbon for Fast-Charging Sodium-Ion Batteries.

The sluggish Na ion diffusion kinetics and Na metal plating in hard carbon negative electrodes restrict the fast-charging of sodium-ion batteries, which is intricately entwined with the crystal structure and pore structure. Here, the pore structures of hard carbon materials are focused on and reveal that the pore size significantly affects the Na-filling potentials during the sodiation process. Specifically, the micro closed pores exhibit higher Na-filling potentials, which reduces risks of Na metal plating at high current densities, thus enabling improved rate performance. As a result, the optimized hard carbon with closed micropores (1.6nm) achieves an initial capacity exceeding 400 mAh g-1 at 20mA g-1 and a plateau retention rate of 73.3% at a current density of 500mA g-1. Paired with P2-type layered oxide positive electrodes, the 2.2 Ah pouch cell shows 10min charging for ≈90% of the capacity and ≈90% capacity retention after 1500 cycles at a 6C rate. This work establishes a bridge between pore size and rate performance, offering guidance for the design of fast-charging sodium-ion batteries.

Asking questions matters: comparing the effect of learning through dialogue with peers, ChatGPT, and intelligent tutoring system

ABSTRACT The ways students learn through dialogue are diversifying, in terms of whom they engage with and how. With the recent advancement of AI chatbots like ChatGPT, learners can leverage aspects of dialogue, such as asking and answering questions, without a peer or instructor being present. Given the lack of experimental studies validating their effect, this study compares three dialogue conditions involving Peer, ChatGPT, and Intelligent Tutoring System. A chat interface was developed where students could exchange questions with a Peer, ask questions to a GPT agent, or answer questions displayed by an ITS agent. After reading a biology passage, 114 university students from Republic of Korea solved two practice items and then engaged in dialogue with their respective counterparts about what they had studied. Finally, they were instructed to re-answer the practice items and solve two new isomorphic test problems. The Peer and GPT groups, where students could ask questions, demonstrated significantly higher post-dialogue performance in both absolute score and conditional correct rate compared to the ITS group, which only answered questions. The number of questions asked and the level of trust in the dialogue were positively correlated with individual differences in performance. Our findings highlight the importance of asking questions over asking many when learning through dialogue, laying the groundwork for designing more effective interactive learning systems.

Effects of LATP Particle Size on the Residual Moisture of Separator Coating and the Performance of NCM811 Batteries.

Li1+xAlxTi2-x(PO4)3 (LATP) is a NASICON-type solid electrolyte that presents stability in aqueous media and high ion conductivity. With these advantages, it is expected to be used as a cathode and separator coating material for lithium-ion batteries to improve battery performance. However, it also displays a high level of residual moisture introduction due to its strong water absorption. Meanwhile, LATP particle size is a key influential factor for the residual moisture level and thereby produces an impact on the battery performance. In this research, we prepared three different particle sizes of LATP (100, 500, and 1000 nm) to investigate their effects as separator coatings on residual moisture and NCM811 battery performance. The results indicate that the water absorption of LATP is much higher than that of Al2O3 with the same particle size; the use of nanoscale LATP keeps the residual moisture of the LATP/PE separator rather high. When the particle size is in the range of 100-1000 nm, the battery's cycling performance gradually deteriorates with the decrease of the particle size, among which the degradation of rate performance is more noticeable. More importantly, the research finds that LATP particles coated with polydopamine (PDA) can effectively reduce the coating's residual moisture. After being coated with PDA, LATP particles with a particle size of 1000 nm result in the residual moisture content within the composite separator decreasing from 2136 to 408 ppm, thereby contributing to the optimal performance of NCM811||Li and NMC811||C batteries.

Active-Site-Switching in Medium-Entropy Metal Sulfides for Wide-Temperature High-Power Zn-Air Pouch Cells.

Quasi-solid-state Zn-air pouch cells (QZPCs) promise a high energy-to-cost ratio while ensuring inherent safety. However, addressing the challenges associated with exploring superior energy-wise cathode catalysts along with their activity origin, and the super-ionic electrolytes remains a fundamental task. Herein, the realistic high-performance QZPCs are contrived, underpinned by a robust NiVFeCo medium-entropy metal sulfides (MESs) bifunctional air cathode with a record-low potential polarization of 0.523V, paired with a sodium polyacrylate-ionic liquid hydrogel exhibiting exceptional conductivity (234 mS cm-1) and water retention (93.8% at 7 days) at room temperature as the super-ionic conductor electrolyte. Through combined studies of in situ Raman, ex situ X-ray absorption fine structure analysis, and theoretic calculations, an intriguing adaptive active-sites-switching mechanism of the MESs cathode during discharging/charging processes is unveiled, revealing a dynamic role transition of Co and Ni active sites in the reversible oxygen electrocatalysis. Consequently, the persistent low cathode polarization and super ion-conductive electrolyte endorse QZPCs an excellent rate performance from 1 to 100mA cm-2 at room temperature. Moreover, an impressively high cell-level energy density of 105Wh kgcell -1 with an ultra-long cycle lifespan of 4000 cycles at 5mA cm-2 and a low temperature of -30°C is achieved.

Silicon Hysteresis and Voltage Relaxation Phenomena: Implications on the Characterization of Anode Overpotentials

Abstract Silicon anode active materials for lithium-ion batteries are becoming increasingly relevant for industrial applications. However, their material-intrinsic voltage hysteresis and voltage relaxation behavior is not fully understood and introduces challenges to the modeling of the material for battery management systems. Here, we characterize the hysteresis and voltage relaxation behavior of an electrode for which the capacity is almost exclusively attributed to the silicon active material, which is based on silicon micro-particles. By comparing it to a common graphite electrode, we highlight the unusual behavior of silicon at open-circuit voltage (OCV) conditions: the voltage relaxes significantly more strongly than what could be explained by the removal of ohmic, kinetic, and mass-transport overpotentials. Furthermore, it appears that during OCV conditions there is a reversible build-up of additional overpotentials which disappear after a subsequent (de)lithiation for a small increment of the overall capacity. By comparing the rate performance to impedance measurements and current-interrupt experiments, we find that relative differences of the potentials under load can be characterized similarly for silicon and graphite, but for experiments where the silicon OCV potential is compared to a potential under load, artefacts can be introduced to the analysis that can lead to an overestimation of electrode resistances.

Construction of NiCoSe2 nanosheets supported on CuNi2S4 nanospheres for advanced hybrid supercapacitors.

Construction of NiCoSe2 nanosheets supported on CuNi2S4 nanospheres for advanced hybrid supercapacitors.

Flip-GFDM complexity reduction for a power-efficient visible light communication system

Visible light communication (VLC) has emerged as a promising solution to the limitations of traditional radio frequency systems, leveraging LEDs for high-speed, interference-free data transmission. However, optical orthogonal frequency division multiplexing (OFDM) techniques such as Flip-OFDM face challenges including high peak-to-average power ratio (PAPR) and spectral inefficiency. This study introduces what we believe to be a novel flip-generalized frequency division multiplexing waveform (Flip-GFDM), named non-Hermitian Flip-GFDM (NH-Flip-GFDM), designed to reduce complexity. By eliminating Hermitian symmetry and halving the IFFT/FFT size, the proposed approach achieves significant computational savings, with about a 50% reduction in complexity. Simulation results reveal that NH-Flip-GFDM maintains comparable symbol error rate (SER) and bit error rate (BER) performance to traditional Flip-GFDM while reducing PAPR by approximately 2 dB over Flip-OFDM. These improvements position NH-Flip-GFDM as a power-efficient and cost-effective solution for next-generation VLC systems.

Preparation of Co3S4/rGO composites and their supercapacitor performances

Graphene, with its two-dimensional structure, offers high mechanical flexibility and excellent conductivity, but its tendency to stack and aggregate in practical applications reduces the effective surface area, resulting in rapid capacity degradation. To overcome this, we in situ grow rod-like Co3S4 structures on graphene oxide graphene oxide (rGO), forming a highly conductive and mechanically stable composite. The Co3S4 nanoparticles serve as active sites for redox reactions, significantly improving the specific capacitance, while the rGO matrix enhances electron transport and mitigates the issues of volume expansion during charge/discharge cycles. The Co3S4/rGO composite is synthesized via a two-step hydrothermal process, and the effects of sulfuration temperature and time on electrochemical performance are systematically explored. The results show that the Co3S4/rGO-160-8 composite, synthesized at 160 °C for eight hours, achieves a specific capacitance of 1442.5 F·g-1 at 1 A·g-1 and exhibits a capacity retention of 93.3% after 5000 cycles at 4 A·g-1. Furthermore, the Co3S4/rGO-160-8//activated carbon asymmetric supercapacitor delivers an energy density of 47.0 Wh·kg-1 at 749.8 W·kg-1 power density, with only an 8.9% capacity loss after 5000 cycles, demonstrating excellent cycling stability. This novel composite material offers a promising approach for high-performance supercapacitors, balancing high energy density, excellent rate performance, and long-term stability.

A biomimetic host from a poultry bone structure enables dendrite‐free lithium deposition

AbstractLithium metal anode is one of the ideal anode materials for the next generation of high‐energy‐density battery systems. Unfortunately, the uneven nucleation of Li leads to dendrite growth and volume changes during cycling, resulting in poor electrochemical performance and potential safety hazards, which hinder its practical application. In this work, a low‐cost chicken‐bone‐derived carbon material (CBC) with a biomimetic structure was designed and synthesized using a simple one‐step carbonization method. Combining theoretical calculations and experimental results, the self‐doped N and S heteroatoms in CBC are demonstrated to effectively reduce the binding energy with Li atoms and lower the nucleation overpotential. After uniform nucleation, the Li metal grows in a spherical shape without dendrites, which is related to the reduction of the local current density inside the biomimetic crosslinking structure of CBC. Benefiting from this favorable Li growth behavior, the Li@CBC electrode achieves ultra‐low nucleation overpotential (15.5 mV at 0.1 mA cm−2) and superdense lithium deposition (zero volume expansion rate at a capacity of 2 mAh cm−2) without introducing additional lithiophilic sites. The CBC retains a high Coulombic efficiency of over 98% in 479 cycles (1 mA cm−2 and 1 mAh cm−2) when applied in a half‐cell with Li, and shows an excellent rate and cycling performance when applied in a full cell with LiFePO4 as the cathode.

Voltage Regulation via Covalent Bond Strength to Increase Energy Density for Safe Fast‐Charging Lithium‐Ion Batteries

AbstractSafe fast‐charging anodes with high operating voltage, such as Li4Ti5O12 (≈1.55 V) and TiNb2O7 (≈1.65 V), compromise the full‐cell output voltage (2.3 V) to ensure safety, limiting the energy density. Lowering anode potential can effectively enhance energy density while maintaining safety; however, the mechanisms behind require further exploration. Here, methods are proposed to lower voltage by enhancing the M–L covalent bonding, achieved by reducing coordination number, electron‐donating inductive effects, or utilizing pseudo‐Jahn–Teller effect distortion. Using LiLaTiO4 as a model anode, the pseudo‐Jahn–Teller effect distortion of TiO6 octahedra is explored to show how it adds covalency to Ti–O bonds, lowing the potential (≈0.3 V). Moreover, bulk LiLaTiO4 exhibits excellent rate performance (181 mAh g−1 at 1 A g−1, 122 mAh g−1 at 10 A g−1) and good cycling stability (retention rate of 73% after 6000 cycles at 5 A g−1). NCM811//LiLaTiO4 full cell demonstrates exceptionally high‐power performance (118.4 mAh g−1 at 10 C and 95.6 mAh g−1 at 20 C), achieving a voltage of 3.6 V, 57% higher than the 2.3 V, enhancing energy density to levels of graphite‐LiFePO4 systems. These improvements are attributed to lithium storage sites with low hopping energy barriers and the structure stability of Ruddlesden–Popper perovskite, offering new insights for safe fast‐charging anodes.

Self-Compartmented Electrolyte Design for Stable Cycling of Lithium Metal Batteries under Extreme Conditions.

Electrolyte is the key component dictating lithium battery performance, especially under extreme conditions such as fast cycling and low temperatures. However, conventional electrolyte design principles, which generally rely on a homogeneous mixture of solvents, salts, and functional additives, fail to simultaneously meet the requirements for both anodic/cathodic interfacial stability and bulk ion-transport kinetics in lithium metal batteries. Herein, we present a self-compartmented electrolyte design methodology. Lithium 4,5-dicyano-2-(trifluoromethyl)imidazol-1-ide (LiTDI), featuring the ability to selectively self-assemble on the cathode/electrolyte interface, compartmented the electrolyte into a heterogonous one. Close to the cathode side, LiTDI could induce an interfacial high-concentration region, where the anion-rich solvation structure facilitates the formation of a stable cathode-electrolyte interphase (CEI). In the bulk, the electrolyte maintains a low concentration with low viscosity, ensuring fast ion transport and superior rate performance. Li||NCM811 cells achieve over 500 stable cycles with 80.3% capacity retention and deliver 169.3mAhg-1 at a 10C discharge rate. Under low-temperature conditions (-20°C), the cells maintained outstanding stability over 700 cycles at 0.5C charge/discharge, achieving capacity retention of 96.6% and an average Coulombic efficiency of 99.2%. This work provides a new electrolyte design paradigm, addressing the critical challenges of LMBs for high-voltage and low-temperature applications.

Self‐Compartmented Electrolyte Design for Stable Cycling of Lithium Metal Batteries under Extreme Conditions

AbstractElectrolyte is the key component dictating lithium battery performance, especially under extreme conditions such as fast cycling and low temperatures. However, conventional electrolyte design principles, which generally rely on a homogeneous mixture of solvents, salts, and functional additives, fail to simultaneously meet the requirements for both anodic/cathodic interfacial stability and bulk ion‐transport kinetics in lithium metal batteries. Herein, we present a self‐compartmented electrolyte design methodology. Lithium 4,5‐dicyano‐2‐(trifluoromethyl)imidazol‐1‐ide (LiTDI), featuring the ability to selectively self‐assemble on the cathode/electrolyte interface, compartmented the electrolyte into a heterogonous one. Close to the cathode side, LiTDI could induce an interfacial high‐concentration region, where the anion‐rich solvation structure facilitates the formation of a stable cathode–electrolyte interphase (CEI). In the bulk, the electrolyte maintains a low concentration with low viscosity, ensuring fast ion transport and superior rate performance. Li||NCM811 cells achieve over 500 stable cycles with 80.3% capacity retention and deliver 169.3 mAh g−1 at a 10C discharge rate. Under low‐temperature conditions (−20 °C), the cells maintained outstanding stability over 700 cycles at 0.5C charge/discharge, achieving capacity retention of 96.6% and an average Coulombic efficiency of 99.2%. This work provides a new electrolyte design paradigm, addressing the critical challenges of LMBs for high‐voltage and low‐temperature applications.

Environmentally Benign and Long Cycling Mn-Ion Full Batteries Enabled by Hydrated Eutectic Electrolytes and Polycarbonyl Conjugated Organic Anodes.

Aqueous rechargeable manganese (Mn)-ion batteries have recently emerged as a promising candidate for multivalent ion rechargeable batteries. However, challenges remain, particularly in expanding the electrolyte's voltage window and identifying compatible anode materials. Herein, we introduce a Mn-ion full battery comprising a nickel hexacyanoferrate (NiHCF) cathode, a perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) anode, and a novel hydrated eutectic electrolyte formulated from Mn(ClO4)2·6H2O and acetamide. This electrolyte composition, optimized for molar ratio, provides a stable solvation structure that suppresses water reactivity and supports high ionic conductivity, as confirmed by spectroscopic and molecular dynamics analyses. The PTCDI anode facilitates highly reversible Mn2+ storage via a unique enolization redox reaction, delivering exceptional rate capability and cycling stability. As a result, the NiHCF||PTCDI full battery achieves a 1.2 V plateau, excellent rate performance (up to 5.0 A g-1), and long cycling life with 95.6% capacity retention over 1200 cycles at 1.0 A g-1. This study proposes a feasible strategy for the construction of environment-friendly, long-life and low-cost aqueous Mn-ion full batteries, offering a sustainable and high-performance solution for future energy storage applications.

MoS2@C-Modified Separator as an Efficient Polysulfide Barrier for High-Performance Li-S Batteries.

Due to the promising energy density (2800 Wh kg-1) and high theoretical specific capacity (1675 mAh g-1), there has been significant research interest in lithium-sulfur batteries (LSBs) recently. However, the shuttle effect and sluggish redox kinetics impede the commercial application of LSBs. In this work, a MoS2@C interlayer-modified commercial polypropylene (PP) (MoS2@C-PP) separator is designed to improve the electrochemical performance of LSBs. The active sites provided by MoS2 are conducive to enhancing the absorption of polysulfide lithium and improving the electrochemical performance. The N-doped carbon not only facilitates electrolyte penetration but also enhances ion transfer to promote reaction kinetics. Additionally, the formation of C-S bonds significantly reduces the shuttle effect. These factors largely accelerate the redox kinetics and decrease the shuttle effect, thereby improving the electrochemical performance of LSBs. As a consequence, the LSB with the MoS2@C-PP separator achieves a high discharge capacity of 860.5 mAh g-1 at 0.5 C after 200 cycles and a superior rate performance of 711.5 mAh g-1 at 2 C. This work offers a promising direction for enhancing the electrochemical performance of LSBs through separator modification .

Hybrid Flying Foxes and Enhanced Whale Algorithm‐Based Cluster Optimization Method for Efficient Stable Routing in Vehicular Ad Hoc Networks (VANETs)

ABSTRACTVehicular ad hoc network (VANET) is an indispensable entity to diversified number of intelligent transportation system (ITS)–enabled technologies. But network scalability, frequent topology changes, and high mobility are the major problems due to the sparse distribution of vehicles especially in highways and constantly changing vehicular network topology. Maintenance of stable route in the network between the vehicles is a herculean task as its failure increases the probability of instability. This establishment of stable routes is essential in VANETs for efficiently utilizing the computational resources such that desirable degree of quality of service (QoS) can be achieved. This stable route determination can be attained by addressing the factors of energy balancing, coverage, connectivity, and load balancing for the purpose of guaranteeing the sensed data from all the points of target to the base stations in a reliable manner. In this paper, hybrid flying foxes and enhanced whale algorithm (HFFEWA)–based cluster optimization method is proposed for attaining sustained routing that establishes stable cluster construction during the routing process. This HFFEWA adopted the factors of route along the highway, velocity, number of nodes, and communication range into the fitness function for minimizing the degree of randomness. It specifically used flying fox optimization algorithm (FFOA) for exploring the search space more eminently such that global clusters could be constructed with maximized diversity. On the other hand, enhanced whale algorithm (EWA) is adopted for preventing the issue of premature convergence. It is also proposed with the capability of well‐balanced exploration and exploitation that explores and exploits the search space such that it can be used in generating optimal number of cluster heads (CHs). The simulation results of this HFFEWA conducted different vehicular density confirmed an improved network lifetime of 19.42% with the stabilized cluster construction of 32.18%, better than the competitive approaches. The evaluation of HFFEWA under different network size confirmed better performance in packet delivery rate, end‐to‐end delay, and packet loss.

Might tiger beetles serve as effective predators of fire ants? Preliminary investigations using the golden-spotted tiger beetle, Cosmodela aurulenta (Fabricius)

Abstract The red imported fire ant, Solenopsis invicta Buren is listed as one of the most invasive alien insect pests and the fifth costliest worldwide. Sustainable and long-term management of S. invicta is achievable using natural enemy insects. So far, parasitic Pseudacteon flies (Diptera: Phoridae) are the most studied natural enemies of S. invicta, but their low parasitism rate make eradication of S. invicta very difficult. Natural predators of S. invicta are scarcely reported. In this study, we evaluated the control potential of a natural predator, the golden-spotted tiger beetle, Cosmodela aurulenta (Fabricius) against S. invicta. The theoretical maximum daily predation of C. aurulenta adults to small and large S. invicta workers were 29.1545 and 12.4533, respectively. The predation functional responses of C. aurulenta adults on small and large S. invicta workers fit the Holling’s type II predator–prey equation. Intraspecific competition and mutual interference among C. aurulenta adults preying on small and large S. invicta workers were detected. C. aurulenta adults showed obvious preference for small S. invicta workers and rapid self-defense reaction on S. invicta worker attack. When fed on Tenebrio molitor Linnaeus (Coleoptera: Tenebrionidae) larvae, C. aurulenta adults had significantly higher survival rate and reproductive performance than when fed on S. invicta. Our study exploited a natural predator, C. aurulenta, for management of S. invicta and laid a foundation for the mass production of the predator.

Piperazine-Linked Phthalocyanine Covalent Organic Frameworks for Efficient Anodic Lithium Storage.

Organic anode materials have been considered as promising electrodes for achieving low-cost and sustainable lithium-ion batteries (LIBs). However, organic materials face challenges, such as inadequate cycling stability and sluggish reaction kinetics, leading to an unsatisfactory LIB performance. Covalent organic frameworks (COFs) possess a porous and designable structure coupled with exceptional stability, making them promising candidates for anode electrodes in LIBs to address the challenges. Herein, two piperazine-linked conjugated phthalocyanine-based COFs (named CoPc-BTM-COF and CoPc-DAB-COF) were fabricated from reacting hexafluorophthalocyanine cobalt(II) (CoPcF16) with 1,2,4,5-benzenetetramine (BTM) and 3,3'-diaminobenzidine (DAB), respectively. Powder X-ray diffraction and electron microscopy analyses in combination with theoretical simulation reveal their crystalline nature with sql net and AA arranged stacking pattern. The pore sizes of these two Pc-COFs are 1.62 and 1.90 nm according to theoretical simulation and N2 sorption measurement, which facilitates their rapid transport of Li+ ions. The immersion experiments disclose their remarkable stability. These advantages, together with their conjugated nitrogen-rich skeletal structures, lead to outstanding anodic Li+ storage capabilities, exceptional rate performance, and favorable cycling stability. In particular, both Pc-COFs exhibit high capacities of 877 and 669 mAh g-1 at 100 mA g-1, superior to most reported organic LIB anodes, showing promising application potential in high-performance LIBs.

Noncovalent Interactions Promoted Kinetics in Perylene Diimide-Based Aqueous Zn-Ion Batteries: An Operando Attenuated Total Reflection Infrared Study.

Perylene-based organic anodes, as an alternative to metallic Zn for aqueous Zn-ion batteries, store Zn2+ through a Zn enolate coordination mechanism, which potentially bypasses challenges such as dendrite and hydroxide formation associated with a Zn anode. However, organic anodes exhibit low electrical conductivity and show a low rate performance. Molecular aggregation of conjugated aromatics plays a key role in the electrical conductivity of this class of material, and it is important to understand their impact on the battery rate performance. In this work, we combined electrochemistry and in situ attenuated total reflection infrared characterization to demonstrate the dominating role of aggregates in perylene-based electrodes in the enhancement of the electrode kinetics. We demonstrated the use of noncovalent interaction to form a supermolecular network that exhibits more than 4 orders of magnitude increase in the electron transfer rate, and provides nearly doubled charge storage capacity. The aggregation of perylene units was driven by π-π stacking and hydrogen bonding between the active material and a mediator, ethylene diamine. We showed that, in practice, this additive-mediated aggregation can occur during solution process at a moderate temperature.

Ti-Doped, Mn-Based Polyanionic Compounds of Na4Fe1.2Mn1.8(PO4)2P2O7 for Sodium-Ion Battery Cathode

Na4Fe3(PO4)2P2O7 (NFPP) is recognized as a prospective electrode for sodium-ion batteries (SIBs) because of its structure stability, economic viability and environmental friendliness. Nevertheless, its commercialization is constrained by low operating voltage and limited theoretical capacity, which result in a power density significantly inferior to that of LiFePO4. To address these limitations, in this work, we first designed and synthesized a series of Mn-doped NFPP to enhance its operating voltage, inspired by the successful design of LiFe1-xMnxPO4 cathodes. This approach was implemented to enhance the operating voltage of the material. Subsequently, the optimized Na4Fe1.2Mn1.8(PO4)2P2O7 (1.8Mn-NFMPP) sample was selected for further Ti-doped modification to enhance its cycle durability and rate performance. The final Mn/Ti co-doped Na4Fe1.2Mn1.7Ti0.1(PO4)2P2O7 (0.1Ti-NFMTPP) material exhibited a high operating voltage of ~3.6 V (vs. Na+/Na) in a half cell, with an outstanding reversible capacity of 122.9 mAh g−1 at 0.1 C and remained at 90.6% capacity retention after 100 cycles at 0.5 C. When assembled into a coin-type full cell employing a commercial hard carbon anode, the optimized cathode material exhibited an initial capacity of 101.7 mAh g−1, retaining 86.9% capacity retention over 50 cycles at 0.1 C. These results illustrated that optimal Mn/Ti co-doping is an effective methodology to boost the electrochemical behavior of NFPP materials, achieving mitigation of the Jahn–Teller effect on the Mn3+ and Mn dissolution problem, thereby significantly improving structural stability and cycling performance.