High-performance Cathode Materials Research Articles

Ultrathin V6O13 nanosheets assembled into 3D micro/nano structured flower-like microspheres for high-performance cathode materials of Li-ion batteries

Benefiting from its unique high theoretical capacity and energy density, V6O13 is considered an outstanding cathode candidate. Nevertheless, the lithium ions will form LixV6O13 when embedded in V6O13, resulting in volume expansion and crystal structure instability. For that reason, the construction of three-dimensional nanostructures is an awfully serviceable method to resolve the above problems. Herein, we adopt a green and convenient hydrothermal method to synthesize three-dimensional microsphere structure composed of nanoflakes, and flower-like V6O13 microspheres are synthesized by adjusting the concentration of nitric acid (HNO3). Meanwhile, the formation mechanism of flower-like V6O13 microspheres is investigated by controlling the hydrothermal reaction time and the concentration of HNO3. As a lithium-ion cathode material, flower-like V6O13 microspheres show an initial discharge specific capacity of up to 368.1 mAh/g at a current density of 0.1 A/g. There was still a discharge specific capacity of up to 313.1 mAh/g after 50 charge/discharge cycles, with a capacity retention rate of 85.1%. The flower-like V6O13 microsphere electrode also combines an excellent rate performance with a satisfactory cycling stability, which achieves a cycle retention rate of 80.2% even after 200 charge/discharge cycles, and an initial discharge specific capacity of 216.9 mA/g even at a high current density of 1 A/g. The results show that, benefitting from its large specific surface area and robust three-dimensional structure, the flower-like V6O13 microsphere electrode material exhibits excellent cycling performance, and the lithium-ion batteries which use it as the cathode material perform equally well in terms of high capacity and high rate.

Bimetallic MnMoO4 nanostructures on carbon fibers as flexible cathode for high performance zinc-ion batteries

Aqueous zinc ion batteries (ZIBs) are promising energy storage devices due to the advantageous features of Zn. However, developing suitable cathode materials with high performance is still an urgent task for the development of ZIBs. In this work, we report on the preparation of a flexible cathode for ZIBs consisting of carbon fiber supported MnMoO4 nanostructures protected with N-doped carbon coatings (CF/MnMoO4@NCs). The N-doped carbon coating on MnMoO4 nanostructures can buffer volume expansion of MnMoO4, and the CF and NCs with good electronic conductivity can facilitate quick electrons transportation in the CF/MnMoO4@NCs system. The optimized CF/MnMoO4@NCs cathode exhibits high capacity and good rate capability. Specifically, it delivers an outstanding discharge capacity of 663 mA h g−1 at a current density of 0.1 A/g after 100 cycles, and at a current density of 2 A/g, the cathode can still achieve a discharge capacity of 212 mA h g−1. This work expands the choice of cathode material and provides constructive direction on designing high-performance cathode materials for ZIBs.

Structure, Electrochemical, and Transport Properties of Li- and F-Modified P2-Na2/3Ni1/3Mn2/3O2 Cathode Materials for Na-Ion Batteries

The development of cobalt-free P2-Na2/3Ni1/3Mn2/3O2 cathodes is hampered by poor electrochemical performance, resulting from structural instability during high-voltage cycling. Herein, Li+ and F− ions are introduced simultaneously via a simple sol–gel method. The F not only enters the lattice but forms chemically stable NaF on the surface. The modified electrode delivered significantly better electrochemical performance than the pristine one, including much-enhanced capacity retention (64% vs. 36%, 100 cycles) at 0.5 C and a four-time higher capacity output at 10 C. The ex situ XRD and in situ Raman analysis revealed cyclability enhancement mechanisms in terms of inhibiting the P2–O2 phase transition and Na+/vacancy ordering. The conductivity measurements (based on AC impedance and DC polarization) and GITT analysis proved, on both bulk material and electrode levels, that Na+ conduction and, thus, rate performance is notably promoted by doping. The individual contribution of Li and F to the overall performance improvement was also discussed. Furthermore, a solid-state sodium-metal battery was successfully demonstrated with the modified cathode. The above results verify that Li+/F− incorporation can enable enhancements in both cyclability and rate capability of the P2-Na2/3Ni1/3Mn2/3O2 cathodes and are expected to provide a new perspective for the rational design of high-performance layered oxide cathode materials for progressive sodium-ion batteries.

MnO2@Co3O4 heterostructure composite as high-performance cathode material for rechargeable aqueous zinc-ion battery

MnO2@Co3O4 heterostructure composite as high-performance cathode material for rechargeable aqueous zinc-ion battery

One-Dimensional Covalent Organic Framework as High-Performance Cathode Materials for Lithium-Ion Batteries.

Covalent organic frameworks (COFs) have emerged as a new class of cathode materials for energy storage in recent years. However, they are limited to two-dimensional (2D) or three-dimensional (3D) framework structures. Herein, this work reports designed synthesis of a redox-active one-dimensional (1D) COF and its composites with 1D carbon nanotubes (CNTs) via in situ growth. Used as cathode materials for Li-ion batteries, the 1D COF@CNT composites with unique dendritic core-shell structure can provide abundant and easily accessible redox-active sites, which contribute to improve diffusion rate of lithium ions and the corresponding specific capacity. This synergistic structural design enables excellent electrochemical performance of the cathodes, giving rise to 95% utilization of redox-active sites, high rate capability (81% capacity retention at 10 C), and long cycling stability (86% retention after 600 cycles at 5 C). As the first example to explore the application of 1D COFs in the field of energy storage, this study demonstrates the great potential of this novel type of linear crystalline porous polymers in battery technologies.

Organopolysulfides as high-performance cathode materials for rechargeable aluminum-ion batteries

The development of aluminum-ion batteries (AIBs) is significantly confined by the limited high-performance cathode materials. Herein, organopolysulfides are investigated as active cathode materials to fabricate AIBs. A liquid-phase phenyl tetrasulfide (PTS) can deliver a capacity above 600 mAh g−1 after activation, with the maintenance of 253 mAh g−1 after 100 cycles. Owing to the different S locations, PTS shows several voltage plateaus and an average voltage of ∼0.7 V vs. Al3+/Al with no decay upon cycling. More importantly, the liquid PTS can serve as a high-Coulombic-efficiency cathode (∼99.88% ± 0.57% after stabilization), enlighting the design of high-efficiency and low-resistance conversion-type cathode materials for AIBs. By experimental characterizations accompanied by theoretical calculations, it is found that PTS undergoes stepwise reaction procedures during discharge with final products of Al2S3 and AlCl2-coordinated phenyl sulfide, and partially reforms with elemental S and other organopolysulfides during charge. This study demonstrates new opportunities for the design of high-efficiency conversion-type cathode materials for advanced AIBs.

Mechanism enhancement of V3O7/V6O13 heterostructures to achieve high-performance aqueous Zn-Ion batteries

Vanadium oxides are the most promising cathode materials for aqueous Zn-ion batteries (AZIBs). A major restriction of vanadium oxides in practical applications is their poor utilization due to the limited migration depth of Zn2+. Mechanism enhancement through modifying Zn2+ intercalation chemistry is the key to boost the performance of vanadium oxides, but yet has rarely been reported. Through a series of ex situ characterizations, we demonstrate here a new two-process reversible transition mechanism in V3O7/V6O13 heterostructures. We observe an unusual reversible transition between V3O7/V6O13 and Zn3V2O7(OH)2·2H2O (ZVO, also a known Zn2+ and proton intercalation material), both of which can be the active materials for subsequent energy storage. This suggests that the Zn2+ intercalation pressure can be shared by the two hosts at deep discharging, that is, the active materials may be better utilized as compared to the only host, which is conducive to improving the available capacity. In addition, the generated ZVO also aids in Zn2+/H+ diffusion due to its open layered structure and water-lubricated channels. With the advanced energy storage mechanism, 2D defective heterostructures, and a facile and energy-efficient synthesis, the V3O7/V6O13 nanosheets are expected to be a high-performance and mass-produced cathode material for commercial AZIBs.

Mg–Zn–Mn Oxide Systems for a Rechargeable Mg-Battery Cathode

Mn-based spinel-oxide cathode materials are promising for achieving high-energy-density rechargeable Mg batteries (RMBs). However, Mg insertion into them often induces unfavorable phase transformation due to the poor stability of λ-MnO2, leading to capacity fading during cycling. Defect spinel ZnMnO3, which can be regarded as ZnO-stabilized λ-MnO2, is an outstanding exception that allows highly reversible Mg insertion/extraction. To further understand its phase stability, here we investigate wide-range compositions in Mg–Zn–Mn oxide systems and show that the stability of the spinel structure can be significantly improved by compositionally incorporating stable XO (X = Zn, Mg) with λ-MnO2. In particular, (i) the equimolar mixing of XO and MnO2 is critical to obtaining a single-phase cubic spinel structure and (ii) a higher Zn/Mg ratio is effective for preventing the formation of an irreversible rock salt phase to decrease the overpotential during discharge/charge cycling. Consequently, Zn-rich Mg–Zn–Mn oxides with the cubic spinel structure delivered as high as 120 mAh/g discharge capacities repeatedly at an elevated temperature of 150 °C. This work provides a fundamental understanding of the phase stability of Mg–Zn–Mn oxide materials and insights into designing high-performance cathode materials for RMBs.

A Fresh One-Step Spray Pyrolysis Approach to Prepare Nickel-Rich Cathode Material for Lithium-Ion Batteries.

The Ni-rich layered cathode material LiNi0.8Co0.1Mn0.1O2 (NCM811) with high specific capacity and acceptable rate performance is one of the key cathode materials for high-energy-density lithium-ion batteries. Coprecipitation, the widely utilized method in the precursor synthesis of NCM811 materials, however, suffers long synthetic processes and challenges in uniform element distribution. The spray pyrolysis method is able to prepare oxide precursors in seconds where all transition-metal elements are well distributed, but the difficulty of lithium distribution will also arise when the lithium salts are added in the subsequent sintering process. Herein, a fresh one-step spray pyrolysis approach is proposed for preparing high-performance NCM811 cathode materials by synthesizing lithium-contained precursors in which all elements are well distributed at a molecular level. The precursors with folded morphology and exceptional uniformity are successfully obtained at a low pyrolysis temperature of 300 °C by an acetate system. Furthermore, the final products commendably inherit the folded morphology of the precursors and exhibit excellent cyclic retentions of 94.6% and 88.8% after 100 and 200 cycles at 1 C (1 C = 200 mA g-1), respectively.

The Strategy of Surface Oxygen Vacancy Stabilization for High-Performance Lithium-rich Cathode Materials

Lithium-rich materials exhibit high capacity and high voltage properties due to the charge compensation mechanism, but the disadvantages such as material voltage decay and poor cycling stability limit their practical application. The fixation and stabilizations of surface lattice oxygen is considered the most challenging problem the materials. We have successfully prepared a lithium-rich cathode material with a triad of oxygen vacancies, surface spinel and polyanionic SO4 2− doping by a mild surface pre-activation treatment, and systematically investigated the stabilization mechanism of surface oxygen vacancies in the materials. The VS-LR0.25 material with multiple stabilizations of oxygen vacancies exhibited excellent cycling stability and rate performance, with an initial Coulomb efficiency of 82.7%, and capacity retention of 95.1% after 200 cycles at 1 C.

Pillar strategy enhanced ion transport and structural stability toward ultra-stable KVPO4F cathode for practical potassium-ion batteries

KVPO4F (KVPF) is a promising cathode material for potassium-ion batteries (PIBs) because of its high operating voltage, high energy density, and excellent thermal stability. Nevertheless, the low kinetics and large volume change have been the major hurdles causing irreversible structural damage, high inner resistance, and poor cycle stability. Herein, a pillar strategy of Cs+ doping in KVPO4F is introduced to reduce the energy barrier for ion diffusion and volume change during potassiation/depotassiation, which significantly enhances the K+ diffusion coefficient and stabilizes the crystal structure of the material. Consequently, the K0.95Cs0.05VPO4F (Cs-5-KVPF) cathode exhibits an excellent discharge capacity of 104.5 mAh g−1 at 20 mA g−1 and a capacity retention rate of 87.9% after 800 cycles at 500 mA g−1. Importantly, Cs-5-KVPF//graphite full cells attain an energy density of 220 Wh kg−1 (based on the cathode and anode weight) with a high operating voltage of 3.93 V and 79.1% capacity retention after 2000 cycles at 300 mA g−1. The Cs-doped KVPO4F cathode successfully innovates the ultra-durable and high-performance cathode materials for PIBs, demonstrating its considerable potential for practical applications.

Covalency modulation enables stable Na-rich layered oxide cathodes for Na-ion batteries

As the analogs of Li-rich materials, Na-rich transition metal layered oxides are promising cathode materials for Na-ion batteries owing to their high theoretical capacity and energy density through cumulative cationic and anionic redox. However, most of the reported Na-rich cathode materials are mainly Ru- and Ir-based layered oxides, which limits the practical application. Herein, we report a Na-rich and Ru-doped O3-type Na1.1Ni0.35Mn0.55O2 cathode to mitigate this issue. By partially substituting Mn4+ with high-electronegativity Ru4+, the structural stability and electrochemical performance of the cathode are both greatly improved. It is validated that the high covalency of Ru–O bonds could harden the structural integrity with rigid oxygen framework upon cycling, leading to enhanced O3-P3 phase transition reversibility. Ru doping also induces an enlarged interlayer spacing to boost the Na+ diffusion kinetics for improved rate capability. In addition, benefiting from the large energetic overlap between Ru 4d and O 2p states, the reinforced Ru–O covalency enables highly reversible Ru4+/Ru5+ redox accompanied with more stable oxygen redox, leading to improved specific capacity and stability over cycling. Our present study provides a promising strategy for designing high-performance Na-rich layered oxide cathode materials through covalency modulation toward practical applications.

π-Conjugated N-heterocyclic compound with redox-active quinone and pyrazine moieties as a high-capacity organic cathode for aqueous zinc-ion batteries

Organic cathode materials have been widely used for aqueous zinc-ion batteries (ZIBs) due to their designable molecular structures and diverse redox groups. However, there are still many challenges that need to be overcome, such as limited specific capacity and utilization, inadequate electrical conductivity, unsatisfactory cycle durability and unclear charge storage mechanism. Herein, we report a π-conjugated N-heterocyclic compound containing dual-redox active groups (i.e. quinone and pyrazine), benzo[b]phenazine-6,11-dione (BPD), which are employed as a cathode material in aqueous ZIBs. The BPD cathode shows a high capacity of up to 429 mAh g−1 at 0.05 A g−1, 100 % capacity utilization and excellent cycling performance upon 10,000 cycles. The aqueous ZIB full cell with the BPD cathode delivers an energy density of 276 Wh kg−1, higher than the most previously reported organic cathode materials. Moreover, ex-situ characterizations, electrochemical experiments, and theoretical calculations, clearly illustrate that H+ and Zn2+ are co-inserted during the charge/discharge process. The high utilization and stability of BPD cathode is due to the high insolubility of both BPD and its discharge products. This work provides a reasonable strategy and unique perspective for the design and synthesis of novel high-performance organic cathode materials for aqueous ZIBs.

High-Performance Aqueous Zinc-Ion Batteries Enabled by Superlattice Intercalation Zn3V2O7-C Cathodes

Aqueous Zn-ion batteries (AZIBs) have received widespread attention for their advantages of environmental friendliness and high-safety, yet the development of high-performance AZIBs faces some critical issues, including exploring high-performance cathode materials with high electrical conductivity, high capacity, and stable crystal structures that may greatly affect the cycling stability and rate performance. Herein, we report a superlattice Zn3V2O7-C, which shows promising properties with high capacity and long-term stability as a conversion-type cathode material of AZIBs. The Zn||Zn3V2O7-C half-cells deliver a capacity of ∼210 mAh/g over 10, 000 charging/discharging cycles. A comprehensive investigation elucidates that the superlattice Zn3V2O7-C can provide more reactive sites, more stable structure, and more enhanced electrical conductivity for Zn2+ storage, thus benefiting the promotion of Zn2+ electrochemical and diffusion kinetics. The favorable characteristics of the designed cathode will pave an avenue for the development of promising electrodes for practical AZIBs.

Hexagonal Carbon Nanoplates Decorated with Layer-Engineered MoS2: High-Performance Cathode Materials for Zinc-Ion Batteries.

Hexagonal carbon nanoplates bearing MoS2 (HCN@MoS2) were synthesized using two-dimensional (2D) microporous organic polymers as templating materials. The layer number of MoS2 in HCN@MoS2 and the 2D morphology of composites were critical factors to achieve high-performance cathode materials for aqueous zinc-ion batteries. The best cathode performance was obtained with HCN@MoS2 bearing 2-3 layered MoS2 (HCN@MoS2-2), showing excellent discharge capacities of 602 mAh/g (@50 mA/g), 498 mAh/g (@0.1 A/g), and 328 mAh/g (@1 A/g). The promising electrochemical performance of HCN@MoS2-2 is attributable to the facilitated insertion of zinc ions into 2-3 layered MoS2 due to the reduced lattice energy and the efficient electrochemical utilization of composite materials.

Unraveling the relationship between Sr stoichiometry in Sr Fe1.5Mo0.5O6− and its catalytic performance for high-temperature CO2 electrolysis

The solid oxide electrolytic cell (SOEC) is one of the most promising energy conversion and storage devices, which could convert CO2 to CO with high Faradaic efficiency and production rate. However, the lack of active and stable cathode materials impedes their practical applications. Here we focus on the promising perovskite oxide cathode material Sr2Fe1.5Mo0.5O6−σ, with the aim of understanding how A-atom stoichiometry and catalytic performance are linked. We find that increasing the strontium content in the perovskite improves the chemisorption of CO2 on its surface, forming a SrCO3 phase. This hinders the charge transfer and oxygen exchange processes. Simultaneously, strontoium segregation to the cathode surface facilitates coking of the surface during CO2 electrolysis, which poisons the electrode. Consequently, a small number of Sr deficiencies are optimal for both electrochemical performance and long-term stability. Our results provide new insights for designing high-performance CO2 electrolysis cathode materials.

High-Performance Layered Ni-Rich Cathode Materials Enabled by Stress-Resistant Nanosheets.

Layered O3-type transition metal oxides are promising cathode candidates for high-energy-density Li-ion batteries. However, the structural instability at the highly delithiated state and low kinetics at the fully lithiated state are arduous challenges to overcome. Here, a facile approach is developed to make secondary particles of Ni-rich materials with nanosheet primary grains. Because the alignment of the primary grains reduces internal stress buildup within the particle during charge-discharge and provides straightforward paths for Li transport, the as-synthesized Ni-rich materials do not undergo cracking upon cycling with higher overall Li+ ion diffusion rates. Specifically, a LiNi0.75Co0.14Mn0.11O2 cathode with nanosheet grains delivers a high reversible capacity of 206 mAh g-1 and shows ultrahigh cycling stability, e.g., 98% capacity retention over 500 cycles in a full cell with a graphite anode.

LiFePO4@C/graphene composite and in situ prepared NaFePO4@C/graphene composite as high-performance cathode materials for electrochemical energy storage

LiFePO4@C/graphene composite and in situ prepared NaFePO4@C/graphene composite as high-performance cathode materials for electrochemical energy storage

Effective chemisorption of polysulfides through organic molecules for high-performance lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries with high theoretical energy density have been regarded as promising energy storage devices. However, the sluggish redox kinetics and shuttle effect of lithium polysulfides of sulfur cathodes remain obstacles to their development, especially with high sulfur content. Herein, we introduce the organic molecule of 3-amino-1,2,4-triazole (AT) on graphene (G) through π–π interactions as a sulfur host material to address the shuttle effect of lithium polysulfides. The molecular fragment of = N–CN– in AT as the active site can effectively anchor polysulfides existing as neutral molecules and free radicals in the electrolyte via “Li···N” interaction. Combined with the fast electron transport facilitated by the graphene, the redox kinetics of polysulfides is promoted. Thus, the electrochemical performance of Li–S batteries can be remarkably improved. The S/G-AT electrode displays excellent electrochemical performance in terms of a high initial capacity (1411 mAh/g at 0.2C), long-term cycling stability (799 mAh/g after 450 cycles at 1C), and superior rate performance (817 mAh/g at 10C). This study helps to utilize functional organic molecules for fabricating high-performance cathode materials for Li–S batteries.

Investigating the effect of pH on the growth of coprecipitated Ni0.8Co0.1Mn0.1(OH)2 agglomerates as precursors of cathode materials for Li-ion batteries

Understanding how the morphology and microstructure of secondary particles are affected by pH is essential to design spherical and dense hydroxide aggregates as precursors of high-performance cathode materials for lithium-ion batteries. To investigate the interplay between thermodynamic reaction conditions and the physicochemical properties of precursors, a chemical equilibrium model is used to describe the evolution of metal ammonia complexes. Furthermore, the formation and growth of aggregates are studied by monitoring the changes in surface morphologies and crystal structures of precursors at different reaction times. As the pH value varied, two notable phenomena occurred during crystal growth: the fast growth of grains in the early stage as the pH decreased and the layered growth of grains in the later stage with increased pH values. Such findings could be explained from the following two perspectives. First, the decrease in pH causes a significant increase in the complex ion concentration, thereby facilitating the growth of crystals along the [010] direction. Second, an increase in pH generally accelerates deprotonation of the crystal surface, thus strengthening the adsorption of complex ions on the crystal surface and promoting layer-by-layer growth of primary grains along the [001] direction.