Cathode Material Research Articles

Charge-Compensation-Driven Failure Mechanism of Ni Redox in Fe-Rich Ni/Fe/Mn-Based O3-Type Layered Oxide Sodium-Ion Cathodes.

For cathode materials of sodium-ion batteries, O3-type Ni/Fe/Mn-based (Na-NFM) layered oxides have garnered extensive attention because of high economic viability, environmental friendliness, and the potential for high energy density. Among them, Fe-rich compositions exhibit higher initial charge capacity and lower bill-of-material costs, while they fade rapidly and exhibit low initial coulombic efficiency, hindering their commercialization prospects. In this work, we investigate the failure of Fe-rich Na-NFM materials through X-ray absorption spectroscopy methods. The results reveal a combined failure mechanism that encompasses not only the conventional theory of Fe migration but also an abnormal Ni-redox deterioration, which has not yet been reported. More factors related to the failure of Fe-rich Na-NFM layered oxides are discussed in detail. These findings are expected to inspire targeted research efforts toward Fe-rich Na-NFM materials, thereby accelerating the practical application of sodium-ion batteries.

Constructing Quasi‐Single Ion Conductors by a β‐Cyclodextrin Polymer to Stabilize Zn Anode

AbstractAqueous Zn‐ion batteries (AZIBs) are promising for the next‐generation large‐scale energy storage. However, the Zn anode remains facing challenges. Here, we report a cyclodextrin polymer (P‐CD) to construct quasi‐single ion conductor for coating and protecting Zn anodes. The P‐CD coating layer inhibited the corrosion of Zn anode and prevented the side reaction of metal anodes. More important is that the cyclodextrin units enabled the trapping of anions through host–guest interactions and hydrogen bonds, forming a quasi‐single ion conductor that elevated the Zn ion transference number (from 0.31 to 0.68), suppressed the formation of space charge regions and hence stabilized the plating/striping of Zn ions. As a result, the Zn//Zn symmetric cells coated with P‐CD achieved a 70.6 times improvement in cycle life at high current densities of 10 mA cm−2 with 10 mAh cm−2. Importantly, the Zn//K1.1V3O8 (KVO) full‐cells with high mass loading of cathode materials and low N/P ratio of 1.46 reached the capacity retention of 94.5 % after 1000 cycles at 10 A g−1; while the cell without coating failed only after 230 cycles. These results provide novel perspective into the control of solid‐electrolyte interfaces for stabilizing Zn anode and offer a practical strategy to improve AZIBs.

Tailoring Cationic Cobalt Vacancies in Molybdenum-Cobalt Selenide Derived from POM@ZIF-67 for Enhanced Electrocatalysis in Lithium-Oxygen Batteries.

Slow reaction kinetics during redox reactions limits the utilization of the high theoretical energy density of lithium-oxygen batteries (LOBs). Vacancy engineering, a potential strategy for modulating active sites, is critical in the development of high performance catalysts. This study investigates cobalt vacancies in Mo-CoSe2 nanoparticles created by selenization of phosphomolybdic acid (POM) embedded into zeolitic imidazolate framework-67 (ZIF-67). The nanomaterial exhibits an outstanding electrochemical performance, characterized by high specific capacitance and excellent cycle durability. The LOBs with cobalt vacancies in the Mo-CoSe2 electrode material exhibit a discharge capacity of 21 836 mAh g-1 at a current density of 100 mA g-1 and exhibit stable cycling performance over 194 cycles at 300 mA g-1. Additionally, density functional theory (DFT) calculations suggest that the presence of cobalt vacancies increases the distance between the surface selenium atoms and the subsurface cobalt atoms. In addition, cobalt vacancies modify the electronic structure of the d-orbitals, lowering the energy barriers of the reaction and accelerating the reaction kinetics by improving the adsorption of the reactants. The research introduces a strategy for the rational design of efficient cathode materials in LOBs.

Achieving High Stability and Capacity in Micron-Sized Conversion-Type Iron Fluoride Li-Metal Batteries.

Iron fluoride, a conversion-type cathode material with high energy density and low-cost iron, holds promise for Li-ion batteries but faces challenges in synthesis, conductivity, and cycling stability. This study addresses these issues by synthesizing micron-sized iron-fluoride using a simple solid-state synthesis. Despite a large particle size, a high capacity of 571mAhg-1 is achieved, which is attributed to the unique surface and internal pores within the iron-fluoride particles, which provided a large surface area. This is the first study to demonstrate the feasibility of using large iron fluoride particles to enhance the energy density of the electrode and achieve an iron fluoride full cell with high capacity. Also, the cause of the capacity fading is investigated. Electrode delamination from the current collector, which is the main cause of capacity fading in early cycles, is resolved using a carbon-coated aluminum (C/Al) current collector. Moreover,iron (Fe) dissolution and the deposition of dissolved Fe on the Li metal also contributed significantly to the degradation. Localized high-concentration electrolytes (LHCEs)suppress iron dissolution and Li dendrite growth, resulting in long-cycle stability for 300 cycles. This study provides insights into the further development of conversion-type metal fluorides across various compositions.

Progress and Prospects in Cathode Materials for Sodium-Ion Batteries: Synthesis, Characterization, and Engineering Aspects

Progress and Prospects in Cathode Materials for Sodium-Ion Batteries: Synthesis, Characterization, and Engineering Aspects

High rate capability performance of cobalt-free lithium-rich Li1.2Ni0.18Mn0.57Al0.05O2 cathode material synthesized via co-precipitation method

High rate capability performance of cobalt-free lithium-rich Li1.2Ni0.18Mn0.57Al0.05O2 cathode material synthesized via co-precipitation method

Facile synthesis of monoclinic (NH4)2V4O9 nanosheets for zinc-ion batteries

Aqueous zinc-ion batteries (ZIBs) are increasingly popular due to their low cost and high safety. However, the quest for cathode materials with robust internal structures and efficient ion transport pathways remains critical. In this study, we introduce a simple hydrothermal method to synthesize monoclinic (NH4)2V4O9 nanosheets, serving as a advanced cathode for ZIBs. This material demonstrates outstanding electrochemical properties, with a high specific capacity of 389 mAh g−1 at 0.1 A g−1, and retains 78.9 % capacity after 3000 cycles at 1 A g−1 and 77.3 % after 15,000 cycles at 5 A g−1. Additionally, it achieves an energy density of 325 Wh kg−1 at 101 W kg−1. In-depth electrochemical analysis reveals the structural stability during reversible Zn2+ ion intercalation/de-intercalation, underscoring the potential of (NH4)2V4O9 as a high-performance material for ZIBs.

Interface Engineering Induced by Low Ru Doping in Ni/Co@NC Derived from Ni-ZIF-67 for Enhanced Electrocatalytic Overall Water Splitting.

Electrochemical water splitting is a promising approach for hydrogen evolution reactions (HER); however, the oxygen evolution reaction (OER) remains a major bottleneck due to its high energy requirements. High-performance electrocatalysts capable of facilitating HER, OER, and overall water splitting (OWS) are highly needed to improve OER kinetics. In this work, we synthesized a trimetallic heterostructure of Ru, Ni, and Co incorporated into N-doped carbon (denoted as Ru/Ni/Co@NC) by first synthesizing Ni/Co@NC from Ni-ZIF-67 polyhedrons via high-temperature carbonization, followed by Ru doping using the galvanic replacement method. Benefiting from increased active surface sites, modulated electronic structure, and enhanced interfacial synergistic effects, Ru/Ni/Co@NC exhibited exceptional electrocatalytic performance for both HER and OER processes. The optimized Ru/Ni/Co@NC catalyst, with a minimal Ru mass ratio of ∼2.07%, demonstrated significantly low overpotential values of 34 mV for HER and 174 mV for OER at a current density of 10 mA/cm2 with corresponding Tafel slope values of 33.42 and 34.39 mV/dec, respectively. Further, the optimized catalyst was loaded onto carbon paper and used as anode and cathode materials for alkaline water splitting. Interestingly, a low cell voltage of just 1.44 V was obtained. The enhanced electrolytic performance was further elaborated by density functional theory (DFT) calculations, which confirmed that Ru doping in Ni/Co introduced additional active sites for H*, enhancing adsorption/desorption abilities for HER (ΔGH* = -0.30 eV), lowering water dissociation barrier (ΔGb = 0.49 eV) and reducing the energy barrier for the rate-determining step of OER (O* → OOH*) to 1.62 eV in an alkaline environment. These findings reflect the significant potential of ZIF-67-based catalysts in energy conversion and storage applications.

Elucidating the diffusion and interaction mechanisms of Zn2+ and H+ in MnO2 for aqueous zinc-ion batteries: A DFT study

MnO2 is a promising cathode material for aqueous zinc-ion batteries (AZIBs) with potential applications in large-scale energy storage systems. However, its practical use is hindered by poor cyclic stability and slow diffusion kinetics. Despite considerable efforts, success has been limited due to an unclear understanding of the intrinsic properties of Zn2⁺ and proton (H⁺) insertion into MnO2. This study investigates the predominant phases of MnO2—α, β, δ, and γ—and elucidates their reaction mechanisms using first-principles computational methods based on density functional theory (DFT). Our research reveals that H⁺ ions exhibit a higher initial insertion voltage compared to Zn2⁺ ions, but their diffusion in MnO2 is significantly impeded by strong interactions with oxygen. Additionally, H⁺ insertion partially obstructs Zn2⁺ ion migration. Furthermore, the insertion of Zn2⁺/H⁺ and the adsorption of H⁺ on the MnO2 surface are intricately linked to the dissolution process of manganese. This work significantly enhances our fundamental understanding of MnO2 as a cathode material for AZIBs.

Understanding the Relation Between Intrinsic Parameters of Substituents and Physical‐Chemical Properties of NVP

AbstractNASICON‐type Na3V2(PO4)3 (NVP) is regarded as an intriguing cathode material choice for sodium ion batteries (SIBs) due to its cycling stability and relatively high capacity. However, its voltage and electronic conductivity still need to be improved for larger‐scale fast‐charging applications (e.g. electric vehicles and mobile phones). In this work, we investigate the influence of Vanadium (V) substitution by other environmentally friendly, cheap, and/or high‐valent transition metal (TM) elements on the electrochemical performance of NVP. Density functional theory calculation was used to study the volume change, voltage, conductivity, and redox mechanism during charge/discharge of different compositions. It is found that a substitution of 50% of V by Mn, Mo or W ions resulting in Na3VMn(PO4)3 (NVMnP), Na3VMo(PO4)3 (NVMoP), and Na3VW(PO4)3 (NVWP) significantly alters the cathode materials’ physical and chemical properties, notably decreasing the band gap. In particular, NVMnP has lesser than 1 eV theoretical band gap and provides a higher voltage, while NVWP a much lower voltage in comparison to NVP. This means that NVMnP and NVWP can be promising cathode and anode materials respectively. This work also establishes a relation between fundamental properties of substituents (i.e. ionization energy and ionic size) and the overall performance of NVP.

Design Double Layered Anode for Stably Introducing Lithium Source to Achieve Sulfur‐Carbon Full Batteries

AbstractLithium‐sulfur batteries offer high energy density but face great safety and cycle life challenges due to the use of Li metal anode. Replacing the Li metal anode with pre‐lithiated carbon anodes can thoroughly address cycling stability and safety issues. Directly contacting Li foil with graphite electrode is one of the most efficient and simple strategy to introduce a high content of lithium source into the sulfur‐carbon full batteries. However, the 100% lithiation of the graphite anode through the direct contact method generates excessive heat and stress heterogeneity, which leads to electrode structure cracking and electrochemical properties fading. This study implements a double‐layer anode to mitigate these issues. A thin layer of hard carbon placed between graphite and Cu foil limits heat generation and stress heterogeneity due to its structural and electrochemical stability. Additionally, differing from traditional electrochemical lithiation, this method gains better solid electrolyte interphase (SEI) for the graphite anode after several cycles. This research highlights the mass production potential of coupling high energy density lithium source‐free cathode materials with various lithium source‐free anodes for constructing long‐cycle and high‐safety rechargeable batteries.

High-Entropy Layered Oxide Cathode Materials with Moderated Interlayer Spacing and Enhanced Kinetics for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) with low cost and environmentally friendly features have recently attracted significant attention for renewable energy storage. Sodium layer oxides stand out as a type of promising cathode material for SIBs owing to their high capacity, good rate performance, and high compatibility for manufacturing. However, the poor cycling stability of layer oxide cathodes due to structure distortion greatly impacts their practical applications. Herein, a high entropy doped Cu, Fe, and Mn-based layered oxide (HE-CFMO), Na0.95Li0.05Mg0.05Cu0.20Fe0.22Mn0.35Ti0.13O2 for high-performance SIBs, is designed. The HE-CFMO cathode possesses high-entropy transition metal (TM) layers with a homogeneous stress distribution, providing a moderated interlayer spacing to maintain the structure stability and enhance Na+ ion diffusion. In addition, Li doping in TM layers increases the Mn valence state, which effectively suppresses John-Teller effect, thus stabilizing the layered structure during cycling. Furthermore, the use of nontoxic and low-cost raw materials benefits future commercialization and reduces the risk of environmental pollution. As a result, the HE-CFMO cathode exhibits a super cycling performance with a 95% capacity retention after 300 cycles. This work provides a promising strategy to improve the structure stability and reaction kinetics of cathode materials for SIBs.

Synergistic effect of 2D covalent organic frameworks confined 0D carbon quantum dots film: Toward molecularly imprinted cathodic photoelectrochemical platform for detection of tetracycline

The development of high photoactive cathode materials combined with the formation of a stable interface are considered important factors for the selective and sensitive photoelectrochemical (PEC) detection of tetracycline (TC). Along these lines, in this work, a novel type II heterostructure composed of two-dimensional (2D) covalent organic frameworks confined to zero-dimensional (0D) carbon quantum dots (CDs/COFs) film was successfully synthesized using the rapid in-situ polymerization method at room temperature. The PEC signal of CDs/COFs was significantly amplified by improving the light absorption and electron transfer capabilities. Furthermore, a cathodic molecularly imprinted PEC sensor (MIP-PEC) for the detection of TC was constructed through fast in-situ Ultraviolet (UV) photopolymerization on the electrode. Finally, a “turn-off” PEC cathodic signal was achieved based on the selective recognition of the imprinted cavity and the mechanism of steric hindrance increase. Under optimal conditions, the proposed sensor demonstrated a wide linear relationship with TC in the concentration range of 5.00 × 10−12–1.00 × 10−5 M, with a detection limit as low as 6.00 × 10−13 M. Meanwhile, excellent stability, selectivity, reproducibility, and applicability in real river samples was recorded. Our work provides an effective and rapid in situ construction method for fabricating highly photoactive cathode heterojunctions and uniform stable selective MIP-PEC sensing interfaces, yielding accurate antibiotics detection in the environment.

Preparation of Single-Crystal Li-Rich Mn-Based Layered Oxides with Excellent Electrochemical Performance via Simple Stepwise High-Temperature Sintering.

Li-rich Mn-based layered oxides have attracted extensive attention in lithium-ion battery cathode materials due to their high specific capacity, wide operating voltage, and low cost. However, the large-scale production of single-crystal Li-rich Mn-based layered oxides remains a significant challenge. Herein, the morphology, structure, and electrochemical properties of a series of samples (Li1.2Ni0.13Co0.13Mn0.54O2) prepared by the solid-state method and the molten-salt flux method were assessed. Single-crystal particles exactly could be prepared by potassium chloride (KCl), but its electrochemical performance was inferior and the molten-salt flux method was too complicated for industry. Surprisingly, we found that water washing and annealing processes could enhance the cycling performance. Furthermore, single-crystal Li1.2Ni0.13Co0.13Mn0.54O2 with a particle size of 536 nm was successfully prepared by simple stepwise sintering (950 °C for 7 h, 1000 °C for 1 h, and 850 °C for 2 h), which delivered a specific capacity of 274.9 mAh·g-1 between 2.0 and 4.8 V at 0.1 C with 77.4% initial Coulombic efficiency and 82.1% capacity retention after 100 cycles at 0.1 C. This study may provide theoretical guidance for the industrial production of single-crystal Li-rich Mn-based layered oxides.

Modification of Lithium‐Rich Manganese Oxide Materials: Coating, Doping and Single Crystallization

AbstractThe increasing demand for portable electronics, electric vehicles and energy storage devices has spurred enormous research efforts to develop high‐energy‐density advanced lithium‐ion batteries (LIBs). Lithium‐rich manganese oxide (LRMO) is considered as one of the most promising cathode materials because of its high specific discharge capacity (>250 mAh g−1), low cost, and environmental friendliness, all of which are expected to propel the commercialization of lithium‐ion batteries. However, practical applications of LRMO are still limited by low coulombic efficiency, significant capacity and voltage decay, slow reaction kinetics, and poor rate performance. This review focus on recent advancements in the modification methods of LRMO materials, systematically summarizing surface coating with different physical properties (e. g., oxides, metal phosphates, metal fluorides, carbon, conductive polymers, lithium compound coatings, etc.), ion doping with different doping sites (Li sites, TM sites, O sites, etc.), and single crystal structures. Finally, the current states and issues, key challenges of the modification of LRMO are discussed, and the perspectives on the future development trend base on the viewpoint of the commercialization of LRMO are also provided.

Effective Upcycling of Degraded NCM Cathode Materials Assisted by Surface Engineering for High‐Performance Lithium‐Ion Batteries

AbstractLithium‐ion batteries (LIBs) with ternary oxide cathode materials are the prevalent energy storage devices for electric vehicles, and the huge amounts of spent LIBs pose severe challenges in terms of environmental impact and resource management. Particularly, the proper handling of degraded cathode materials is of central importance for the sustainable and closed‐loop development of LIBs industry. In this context, direct regeneration of degraded ternary oxides toward reusable high‐performance cathode materials is environmentally and economically favorable in contrast to present metallurgical recycling methods. In this work, a simple and effective two‐step method is demonstrated to regenerate the degraded NCM 622 (LiNi0.6Co0.2Mn0.2O2) materials by elemental compensation and structural restoration. Moreover, a multi‐functional LTO (Li4Ti5O12) surface coating is simultaneously designed to guarantee rapid Li+ diffusion and stable surface of the regenerated product. Therefore, the regenerated LTO‐coated NCM materials show excellent electrochemical performance; specifically, the initial discharge capacity (183.0 mAh g−1 at 0.1 C), rate capability (90.0 mAh g−1 at 10 C), and cycling stability (79.3% capacity retention after 200 cycles) are even comparable with those of fresh materials. The as‐established upcycling strategy may shed light on the value‐added recycling of degraded cathode materials and thereby a virtuous cycle of LIBs.

A Uniform Conductive Carbon Coating of Nitrogen‐Doped Carbon Improves the Electrochemical Performance of LiMn0.7Fe0.3PO4 Cathode Material for Lithium‐ion Batteries

AbstractThe practical application of LiMn1−xFexPO4 as a cathode material is hindered considerably by its poor electronic conductivity and slow lithium‐ion diffusion. In the present study, a uniform nitrogen‐doped carbon coating on LiMn0.7Fe0.3PO4 (LiMn0.7Fe0.3PO4@NC) was achieved using ethylene diamine tetraacetic acid (EDTA) as a chelating agent and carbon source. The nitrogen‐doped carbon layer enhanced the electronic conductivity and ionic diffusion of the LiMn0.7Fe0.3PO4 cathode. Furthermore, the uniform carbon layer prevented metal ion dissolution and stabilized the crystal structure. The resulting LiMn0.7Fe0.3PO4@NC‐2 sample demonstrated superior performance with a specific capacity of 152.5 mAh g−1 at 0.1 C and preserved 93.7 % of this capacity over 200 cycles at 1 C. Meanwhile, the LiMn0.7Fe0.3PO4@NC‐2 sample demonstrated a high Li+ diffusion coefficient (3.98×10−11 cm2 s−1) and electrical conductivity (1.47×10−2 S cm−1). This study presents a novel approach to designing high‐performance cathode materials using a cost‐effective and straightforward process.

Promoting Layered Oxide Cathodes Based on Structural Reconstruction for Sodium‐Ion Batteries: Reversible Phase Transition, Stable Interface Regulation, and Multifunctional Intergrowth Structure

AbstractLayered transition‐metal oxides (NaxTMO2) are one of the most promising cathode materials for sodium‐ion batteries due to their high theoretical specific capacities, good conductivity, and environmental friendliness. However, several key scientific issues of NaxTMO2 cathode materials still persist in practical applications: i) complex phase transitions during the charge/discharge process owing to the slip of the transition‐metal layer; ii) the tendency for the interface to react with the electrolyte, resulting in structure degradation, and iii) reactions between active materials and H2O as well as CO2 on exposure to air in the environment to form alkaline substances on the surface. To understand electrochemical storage mechanisms and solve these problems, several modification strategies of NaxTMO2 have been reported recently, including bulk doping, concentration gradient structure design, interface regulation, and intergrowth structure construction. This review focuses on reversible phase transitions, stable interface regulation, and multifunctional intergrowth structure of the NaxTMO2 material from the inside to the outside. The future research directions for NaxTMO2 are also analyzed, providing guidance for the development of commercial layered oxides for next‐generation energy storage systems.

Li2FeCl4 as a Cost-Effective and Durable Cathode for Solid-State Li-Ion Batteries.

Low-cost cathode materials with high energy density and good rate performance are critical for the development of next-generation solid-state Li-ion batteries (SSLIBs). Here, we report Li2FeCl4 as a cathode material for SSLIBs with highly reversible Li intercalation and deintercalation, a high operation voltage of 3.7 V vs Li+/Li, good rate capability, and good cycling stability with an 86% capacity retention after 6000 cycles. Operando synchrotron XRD reveals that the phase evolution of Li2FeCl4 during charge-discharge cycling involves both solid-solution and two-phase reactions, which maintains a very stable framework during Li insertion and extraction.

Microstructure regulation of WxV1-xO2(B) nanorods with improved electrochemical properties

VO2(B) is regarded as a highly promising cathode material for secondary batteries due to its outstanding theoretical specific capacity and unique expansion tunnel structure, which facilitates reversible insertion and extraction of metal ions. Nonetheless, inherent structural instability, suboptimal ion/electron transport, and constrained capacity resulting from low redox potentials pose challenges to its wider adoption. Hence, in this paper, we proposed a strategy for synthesizing gradient concentration-doped WxV1-xO2(B) nanorods via a one-step hydrothermal method to solve the above problems. The experimental results demonstrated that as the W ion content increased, all fabricated WxV1-xO2(B) nanorods exhibited a monoclinic crystal phase along with noticeable lattice distortion. The positron annihilation lifetime spectra indicated that vacancy clusters were the predominant defect types in WxV1-xO2(B) nanorods. The synergistic effects of grain sizes and vacancy defects contributed to the superior electrochemical performance observed in the W0.01V0.99O2(B) sample. The capacitor retention reached 88.76 % at 0.10 A/g after 1000 charge/discharge cycles. These results had provided experimental foundation for improving electrochemical properties of WxV1-xO2(B) in metal ion secondary batteries.