Battery Cathode Research Articles

Fluorinated functional groups enhanced composite in-situ gel electrolytes for high voltage cathode of quasi solid-state lithium battery

Gel electrolyte is an ideal system for improving the cycling stability and safety of lithium metal battery. However, traditional gel system with acrylic ester system is still not suitable for high-voltage battery system limited by its intrinsic structure and unstable interface. The polymer structures with -CF3 modified acrylic ester are proposed to improve the stability of both structure and interface in high-voltage battery systems. The LiF-rich anode-electrolyte interface assisted by fluorine contained in-situ gel electrolyte ensures stable cycling of lithium anode. The quasi-solid state lithium battery assembled with the LiFePO4 can still achieve a capacity retention rate of 81.2 % after 900 cycles at a rate of 1 C. Furthermore, the uniform organic cathode-electrolyte interface constructed by crosslinked -CF3 modified polymer effectively inhibits the corrosion of HF on the cathode material. The interaction between the anion and solvent molecules prevents the continuous decomposition reaction of the electrolyte on the surface of the LiCoO2 cathode at high voltage, which guarantees LiCoO2 battery can still achieve a capacity retention rate of 82.1 % after 500 cycles at a voltage of 4.45V. Design of fluorine contained in-situ polymer gel electrolyte could promote the development of quasi solid-state battery in practical industrial application.

Boosting the Structural Reversibility of Layered Oxide Cathode for Realizing Long-Term Cycle Life Through Electronic Structure Regulation.

O3-type layered oxide cathode exhibits great application potential for practical sodium-ion batteries, due to its cost-effectiveness, abundant sodium and manganese resources, and high theoretical capacity. However, the irreversible phase transition, coupled with rapid capacity decay, which is primarily attributed to the Jahn-Teller effect of Mn3+, remains a significant bottleneck for commercial application. Additionally, the sluggish kinetics during the (de)sodiation process require urgent improvement. Herein, an electronic structure regulation strategy is proposed by low-valence Li/Cu co-substitution to address these issues. The roles of Li/Cu on the electronic structure, structural evolution, and electrochemical properties in the Na0.96Ni0.22Fe0.2Mn0.5Li0.04Cu0.04O2 (NFMLC) cathode are comprehensively explored through systematic in situ/ex situ characterization techniques and theoretical calculations. The results reveal that this strategy effectively activates more Ni2+/3+ and Fe3+/4+ redox reactions above 2.5V, while suppressing Mn3+/4+ redox activity below 2.5V, thereby achieving highly structural reversibility. Therefore, the NFMLC electrode displays excellent long-term cycling stability (81.5% capacity retention after 2000 cycles at 5 C), and significantly enhanced rate performance (from 45.5% to 80.4% under a ratio of 5 C to 0.5 C). This work provides a valuable perspective on the design of low-cost, long-life, and high-performance layered oxide cathodes for practical sodium-ion batteries.

Accelerating Li-Ion Diffusion in LiFePO4 by Polyanion Lattice Engineering.

Despite the widespread commercialization of LiFePO4 as cathodes in lithium-ion batteries, the rigid 1D Li-ion diffusion channel along the [010] direction strongly limits its fast charge and discharge performance. Herein, lattice engineering is developed by the planar triangle BO3 3- substitution on tetrahedron PO4 3- to induce flexibility in the Li-ion diffusion channels, which are broadened simultaneously. The planar structure of BO3 3- may further provide additional paths between the channels. With these synergetic contributions, LiFe(PO4)0.98(BO3)0.02 shows the best performance, which delivers the high-rate capacity (66.8 mAhg-1 at 50 C) and long cycle stability (ultra-low capacity loss of 0.003% every cycle at 10 C) at 25°C. Furthermore, excellent rate performance (34.0 mAhg-1 at 40 C) and capacity retention (no capacity loss after 2500 cycles at 10 C) at -20°C are realized.

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.

A facile self-saturation process enabling the stable cycling of a small molecule menaquinone cathode in aqueous zinc batteries.

Small quinone molecules are promising cathode materials for aqueous zinc batteries. However, they experience fast capacity decay due to dissolution in electrolytes. Herein, we introduce a simple methyl group to a naphthoquinone (NQ) cathode and demonstrate a facile self-saturation strategy. The methyl group exhibits hydrophobic properties together with light weight and a weak electron-donation effect, which allows a good balance among cycling stability, capacity and voltage for cathode materials. The resulting menadione (Me-NQ) presents around one-third solubility of NQ. The former thus rapidly reaches saturation in the electrolyte during cycling, which suppresses subsequent dissolution. Thanks to this process, the Me-NQ cathode preserves 146 mA h g-1 capacity after 3500 cycles at 5 A g-1, far exceeding 88 mA h g-1 for NQ. Me-NQ also delivers a stabilized capacity of 316 mA h g-1 at 0.1 A g-1 with only 0.05 V lower average redox voltage than NQ. The co-storage of Zn2+ and H+ with the redox reactions on the carbonyl sites of Me-NQ is revealed.

Electrolyte-triggered in-situ polymerization of multi-site organic cathodes for superior-longevity cation-anion co-storage secondary batteries

Organic electrodes are promising as next-generation energy storage materials owing to their diverse structures, low mass, and environmental friendliness. Nevertheless, the dissolution and degradation of organic active species in electrolytes are remaining obstacles to their authentic commercialization. Herein, we report an instantaneous in-situ upgrading strategy to convert multi-site organic cathode materials, e.g., 1-aminoanthraquinone (1-AAQ) and 1,5-diaminoanthraquinone (1,5-DAAQ), into poly(1-aminoanthraquinone) (PAAQ) and poly(1,5-diaminoanthraquinone) (PDAAQ) simply by dropping the electrolyte during battery assembly without extra operations. The remarkable chemistry is essentially a chemical polymerization process of redox-active organic monomers triggered by the electrolyte containing magnesium bis(hexamethyldisilazide) (Mg(HMDS)2) as an initiator. Notably, due to the π-conjugated polymer chain with inhibited dissolution, high conductivity, and improved stability, the as-obtained PDAAQ cathode delivered a high specific capacity (254 mAh/g at 100 mA/g), superior rate performance (83 mAh/g at 2000 mA/g), and excellent cycling stability for over 8000 cycles accompanied by an average capacity decay of only 0.0026 % per cycle. Detailed characterizations further explore the kinetic behaviors and verify a reversible hybrid cation–anion co-redox mechanism of PDDAQ cathode, which involves reversible Mg2+ cation insertion/extraction on AQ units and anion doping/de-doping reactions on the PANI backbones. Density functional theory (DFT) computations demonstrate the optimized structure of the discharged products and indicate that Mg2+ preferably interact with two carbonyls oxygen atoms and nitrogen atom for both PAAQ and PDAAQ. This study demonstrates an intriguing in-situ chemical-polymerization synthetic approach for preparing multi-site organic electrode materials that compromise structure optimization and synthetic efforts, offering great promise for high-performance and sustainable secondary batteries.

Improving the Performance of the Layered Nickel Manganese Oxide Cathode of Sodium-Ion Batteries by Direct Coating with Sodium Niobium Oxide.

This research highlights the efficacy of NaNbO3 as a coating for P2-Na2/3Ni1/3Mn2/3O2 cathodes in sodium-ion batteries. The coating enhances the kinetic behavior and cyclability of the electrochemical cells, as shown by electrochemical measurements. XRD analysis indicates that Nb does not incorporate into the cathode structure, implying a physical interaction between the coating and the cathode material. XRF analysis and EDX mapping confirm the actual composition and uniform dispersion of elements throughout the sample, while the electron micrographs evidence the occurrence of NaNbO3 particles modifying the surface of the layered oxide. The Ni4+/Ni3+ and Ni3+/Ni2+ redox pairs, along with the partially reversible oxidation of oxide to peroxide anions, contribute significantly to cell capacity, as revealed by XPS spectra. This last effect and the appearance of a co-intercalated phase at high voltage are positive factors to provide fast kinetics. Cyclic voltammograms show that samples coated with 2-3% NaNbO3 have superior rate capability, with high capacitive response and apparent diffusion coefficients. These samples also have low impedance at the electrode-electrolyte interface, which helps deliver a high capacity at 5C. Further cycling at 1C shows improved cyclability in the bare and 3% coated samples, due to their higher diffusion coefficients on charging. Notably, the 3% NaNbO3-coated sample exhibits excellent cyclability below 0 °C, making it a promising cathode material for sodium-ion batteries.

Boosting the synergistic activation of δ-MnO2 as cathode for aqueous zinc-ion batteries through Ni, Co co-doping

Layered δ-MnO2 is regarded as a promising cathode material for high-performance aqueous zinc-ion batteries (AZIBs) due to the sufficient interlayer spacing for the accommodation and migration of charge carriers. However, the sluggish activation process limits the reversible capacity, thus prevent their application. In this study, Ni-Co co-doped layered δ-MnO2 was designed to enhance ion diffusion capability and cycling stability. The influencing mechanism of Ni and Co on the long activation process are proposed by a comparative analysis between single doping and co-doping approaches. Specifically, the optimized co-doped δ-MnO2 maintained a high specific capacity of 200.2 mAh·g−1 with a capacity retention of 97.40 % after 700 cycles at 1 A·g−1. The co-doping approach exhibited a synergistic effect in suppressing Mn dissolution and enhancing ion diffusion capability. These findings provide new directions on boosting the synergistic activation process of manganese oxide and shed lights on the rational design of low-cost and high-safe batteries.

Polar Covalent Triazine Frameworks as High-Performance Potassium Metal Battery Cathodes.

The exploration of potassium metal batteries (PMBs) has been intensified, leveraging potassium's abundant availability, low redox potential, and small Stokes radius. Covalent triazine frameworks (CTFs) stand out for their accessible nitrogen sites and customizable structures, making them attractive electrode materials. Nonetheless, there is a lack of established design principles to guide the development of high-performance PMBs using CTFs. In this work, CTFs consisting of different monomers are used as PMB cathodes to investigate the structure-performance correlation. The electronic structure analysis reveals the polar characteristic of a CTF derived from the tetracyanoquinodimethane monomer, setting it apart with superior capacity (161 mAhg-1 at 0.1A g-1), rate performance (85 mAhg-1 at 5 Ag-1), and stability (capacity retention of 81% after 1000 cycles) over three non-polar counterparts in PMBs. Calculations based on density functional theory support the exceptional performance with increased K+ adsorption energy. Ultimately, among multifaceted factors, the polarity of CTF is the leading element that determines the K+ storage capability. These findings pave the way for the development of prudent CTF electrodes for high-performance PMBs.

Next-generation cathodes for calcium-ion batteries: Leveraging NASICON structures for enhanced stability and energy density

This study focuses on developing a high-performance, stable cathode for calcium-ion batteries (CIBs) using a sodium superionic conductor (NASICON) structure to match the energy density and safety standards of current lithium- and sodium-ion batteries. Given the relatively sparse database of CIB materials compared with their lithium and sodium counterparts, expanding the range of new candidates is essential for developing high-performance batteries. To address this, we employed density functional theory (DFT) calculations, which provide a quantum-mechanical description of the electronic properties of materials, to construct a highly reliable database. To improve the accuracy and efficiency, we integrated machine learning interatomic potential with DFT to stabilize the NASICON-type structures, CaxNaV’yV’’2-yBzP3-zO12, where x = 0.8, 0.5, 0; y = 1, 0.5; z = 0.5, 0; V’ and V’’ are transition metals that support stable doped configurations at the V- and P-sites. From the initial 176 candidates, the top 10 materials that facilitate stable structures were identified based on selection criteria focusing on formation energy < 0 eV/atom, energy above hull = 0 eV/atom, gravimetric capacity ≥ 150 mAh/g, -1% ≤ volume change ≤ 1%, and 3 ≤ average voltage ≤ 4.5 V. This approach advances CIB technology and outlines effective strategies for dopant selection to optimize battery cathodes, configuring a framework for future advancements in battery technology.

High-voltage and highly reversible redox chemistry of in situ cross-linked polydiphenylamine as an aqueous zinc battery cathode

Organic redox-active materials are promising electrode candidates for the next generation of rechargeable batteries owing to their versatile redox chemistry, sustainability, and potential low cost. Here, we present polydiphenylamine as a moderately high-voltage (1.25 V vs. Zn) and highly reversible organic cathode for aqueous zinc batteries. As revealed by cyclic voltammetry and spectroscopic analysis, the chemical oxidation–derived diphenylamine dimer electrochemically transforms into a cross-linked polymeric material during the first electrochemical oxidation (charge), which then operates by p-doping/dedoping redox of the amine center and a pseudocapacitor-like solid-state charge storage mechanism during the subsequent discharge-charge cycles. With an 80 wt% active loading, the polymer cathode delivers a specific capacity of 138 mAh/g at 100 mA/g, with 73% retention over 1000 cycles at a 99.8% Coulombic efficiency. Excellent rate capability is evidenced by 87 mAh/g capacity at 400 mA/g and highly stable cycling of over 1200 cycles under variable current rates. Facile one-step synthesis, fast charge storage kinetics, and attractive electrochemical performance establish polydiphenylamine as a notable organic cathode candidate for aqueous zinc batteries.

3D Tunnel Copper Tetrathiovanadate Nanocube Cathode Achieving Ultrafast Magnesium Storage Reactions through a Charge Delocalization and Displacement Mechanism.

Rechargeable magnesium batteries are attractive candidates for large-scale energy storage applications because of the low cost and high safety, but the scarcity and inferior performance of the cathode materials are hindering the development. In the present study, a kind of copper tetrathiovanadate (Cu3VS4) cathode is designed and developed with a comprehensive consideration of the chemical and electronic structures. The vanadium and sulfur atoms form chemical bonds with high covalent proportion, facilitating electron delocalization via the vanadium-sulfur bonds. This reduces the interaction with the bivalent magnesium cation and induces the coredox of vanadium and sulfur. The crystal structure of Cu3VS4 has interlaced 3D tunnels for solid-state magnesium cation transport. The Cu3VS4 cathode shows a high capacity of 350 mA h g-1 at 100 mA g-1, an outstanding rate performance of 67 mA h g-1 at 10 A g-1, and stable cycling for 1000 cycles at 5 A g-1 without obvious capacity fading. Prominently, a high areal mass load of 3.5 mg cm-2 could be achieved without obvious rate capability decay, which is quite favorable to pair with the high-capacity magnesium metal anode in practical application. The mechanism investigation and theoretical computation demonstrate that Cu3VS4 undergoes first a magnesium intercalation and then a displacement reaction, during which the crystal structure is maintained, assisting the reaction reversibility and cycling stability. All the copper, vanadium, and sulfur elements experience redox and contribute to the high capacity. Moreover, the weakened interaction with magnesium cations, well-kept 3D cation transport tunnels, and high electronic conductivity result in the superior rate performance and high areal active material loading. The present study develops a high-performance cathode for rechargeable magnesium batteries and reveal the design principle based on both of chemical and electronic structures.

Nanofibrous Covalent Organic Frameworks as the Cathode, Separator, and Anode for Batteries with High Energy Density and Ultrafast-Charging Performance.

To meet the demand for longer driving ranges and shorter charging times of power equipment in electric vehicles, engineering fast-charging batteries with exceptional capacity and extended lifespan is highly desired. In this work, we have developed a stable ultrafast-charging and high-energy-density all-nanofibrous covalent organic framework (COF) battery (ANCB) by designing a series of imine-based nanofibrous COFs for the cathode, separator, and anode by Schiff-base reactions. Hierarchical porous structures enabled by nanofibrous COFs were constructed for enhanced kinetics. Rational chemical structures have been designed for the cathode, separator, and anode materials, respectively. A nanofibrous COF (AA-COF) with bipolarization active sites and a wider layer spacing has been designed using a triphenylamine group for the cathode to achieve high voltage limits with fast mass transport. For the anode, a nanofibrous COF (TT-COF) with abundant polar groups, active sites, and homogenized Li+ flux based on imine, triazine, and benzene has been synthesized to ensure stable fast-charging performance. As for the separator, a COF-based electrospun polyacrylonitrile (PAN) composite nanofibrous separator (BB-COF/PAN) with hierarchical pores and high-temperature stability has been prepared to take up more electrolyte, promote mass transport, and enable as high-temperature operation as possible. The as-assembled ANCB delivers a high energy density of 517 Wh kg-1, a high power density of 9771 W kg-1 with only 56 s of ultrafast-charging time, and high-temperature operational potential, accompanied by a 0.56% capacity fading rate per cycle at 5 A g-1 and 100 °C. This ANCB features an ultralong lifespan and distinguished ultrafast-charging performance, making it a promising candidate for powering equipment in electric vehicles.

Roadmap for the Development of Transition Metal Oxide Cathodes for Rechargeable Zinc-Ion Batteries

Roadmap for the Development of Transition Metal Oxide Cathodes for Rechargeable Zinc-Ion Batteries

Multiwalled carbon nanotubes decorated ɛ-MnO2 nanoflowers cathode with oxygen defect for aqueous zinc-ion batteries

As a potential cathode for aqueous zinc-ion batteries, the low electrical conductivity and poor electrochemical kinetics of MnO2 limit its further development and application. Herein, multiwalled carbon nanotubes decorated MnO2 nanoflowers with hexagonal structure (ɛ-MnO2/MWCNTs) were synthesized by one-step co-precipitation method. The ɛ-MnO2/MWCNTs inherit the advantages of highly conductive MWCNTs and nanostructured MnO2, thus showing excellent zinc-ion storage capacity. The ɛ-MnO2/MWCNTs display high invertible capacity of 335.6 mAh/g at 0.2 A/g after 150 cycles, and long-term capacity of 115.7 mAh/g at 2.0 A/g after 4000 cycles. The results of kinetics tests further reveal that the MWCNTs decoration can reduce polarization of MnO2 and accelerate its reaction kinetics. Thanks to these merits, the ɛ-MnO2/MWCNTs hold great potential for high performance eco-friendly batteries cathode material.

Enhanced cyclability and energy density of mid-nickel layered oxide cathode material LiNi0.55Mn0.25Co0.20O2 by niobium doping via solvothermal method

Ni-based layered oxide materials are among the most promising cathode materials for the next generation of lithium-ion batteries due to their higher energy capacity. However, capacity decay occurs due to degradation mechanisms that reduce the electrochemical performance of this type of material. This work aims to synthesize Nb-doped LiNi0.55Mn0.25Co0.20O2 (Nb-NCM) materials via the solvothermal method to enhance the cyclability and energy density of the layered oxide cathode. The effects of Nb doping on the microstructure and the electrochemical performance of the cathodes are investigated. The introduction of the contents of Nb expands the structural lattice parameters and decreases the Li+/Ni2+ cation mixing degree of the NCM cathode. Furthermore, the Nb doping enhances the electrochemical activity of LiNi0.55Mn0.25Co0.20O2, increasing its initial discharge capacity to 169.61 mAhg−1 when 1% of Nb was used as a dopant (1%Nb-NCM) in contrast to the capacity of 149.45 mAhg−1 presented by the pristine material. The modified 1.0%Nb-NCM material also exhibits remarkable cycling performance with a capacity retention of 92.7% after 100 cycles at the rate of 1 C (2.8–4.3 V). This work suggests a rational strategy for high-performance cathode for lithium-ion batteries, proposing the extension of Nb doping to enhance Ni-mid material's cyclability.

Sol-gel-based synthesis of high-capacity-NaCoO2 cathode for advanced sodium-ion batteries

This study presents a successful synthesis of phase-pure P2-NaCoO2 by improving the sol-gel-based calcination temperature, yielding a highly crystalline, well-ordered material having P63/mmc hexagonal symmetry, ideal for reversible sodium-ion batteries (SIBs). Advanced physicochemical techniques confirm its pure hexagonal crystal structure along with the desired stoichiometry. NaCoO2 in Na/1M-NaClO4/NaCoO2 cell demonstrates multiple redox peaks for Co3+/Co4+ redox couple, signifying stable multiphase transitions during charge/discharge cycles and exhibiting exceptional structural and electrochemical stability. The cell demonstrates a high discharge specific-capacity of 155.85 mAh/g at 0.1C with outstanding discharge capacity retention of 136.98, 100.6, 84.78, 78.31, and 72.46 mAh/g at the C-rates of 0.15, 0.2, 0.3, 0.5, and 1.0C, respectively, outperforming previously reported values. It shows a remarkable discharge-energy density of 466.04 Wh/kg at 0.1C. Additionally, the small solution and charge transfer resistance with extremely low double-layer capacitance signifies its excellent electrolyte conductivity and potential for high energy density and slow discharge application. These results imply that NaCoO2 is a high-performance and high-capacity cathode material for lightweight and compact SIBs.

Enhanced Cycling Stability and Rate Capability of Al2O3-Coated NaNi1/3Fe1/3Mn1/3O2 Cathodes for Sodium-Ion Batteries

Enhanced Cycling Stability and Rate Capability of Al2O3-Coated NaNi1/3Fe1/3Mn1/3O2 Cathodes for Sodium-Ion Batteries

Experimental and computational insights into oxygen vacancy-rich MoO2-x/N-doped carbon nanowires as high-performance cathode for magnesium batteries and magnesium-lithium hybrid batteries

This work aims to develop efficient cathode materials for magnesium based batteries, which are considered promising next-generation energy storage and conversion devices. One major challenge in magnesium based batteries is the strong Coulomb interaction between magnesium ions and cathode materials, which hinders ion storage and diffusion. To overcome this, we designed and synthesized oxygen vacancy-rich MoO2-x/N-doped carbon nanowires (MoO2-x-NC-NWS). The materials were prepared through a controlled synthesis process, ensuring the incorporation of N-doped carbon and oxygen vacancies, which play crucial roles in improving magnesium ion diffusion and storage. The prepared MoO2-x-NC-NWS demonstrated superior energy storage performance, achieving a capacity of 64 mAh/g in magnesium batteries and 263 mAh/g in magnesium-lithium hybrid batteries at a current density of 50 mA/g. Theoretical calculations further confirmed that oxygen vacancies enhance the diffusion capabilities of magnesium and lithium ions, thereby improving the overall energy storage performance. Therefore, the controllable synthesis of defects such as oxygen vacancies and the development of composite cathode materials are clearly effective strategies for enhancing the performance of magnesium-based battery cathodes. Meanwhile, this rational design of MoO2-based nanostructures provides valuable insights into the development of high-performance cathode materials for magnesium-based energy storage systems.

Modified structure of vanadium oxide via cadmium doping and in-situ activation for high-performance aqueous zinc ion storage

Vanadium oxides are promising cathode materials for aqueous zinc-ion batteries, but they suffer from severe crystal collapse and poor electrical/ionic conductivity. Herein, we successfully synthesized the designed cadmium-doped, carbon-coated vanadium oxide precursor with abundant oxygen vacancies (Cd0.015V2O3-x@C) using a straightforward one-pot thermal reduction method, followed by in-situ activation to form a high-performance cathode material, Cd0.004V2O5-y·nH2O@C. We find that the interlayered water dramatically reduces the electrostatic force between zinc ions and V2O5-y layers, meanwhile, abundant oxygen vacancies and cadmium doping alter the material’s band structure, resulting in enhanced electronic and ionic conductivities. Leveraging these advantages, the phase transitioned Cd0.004V2O5-y·nH2O@C cathode delivers a remarkably high capacity of 420 mAh/g (0.2 A/g), an excellent rate capability of 198 mAh/g (20.0 A/g), and an outstanding capacity retention of 78.5 % after 3500 cycles (20 A/g). This synergistic structure modification strategy of elemental doping and in-situ activation offers a novel approach to design high-performance vanadium oxide-based cathodes for advanced aqueous batteries.