High-performance Cathode Materials Research Articles

Preparation of Ni–Zn dual-doped polyhedral LiMn2O4 for endurable cycling lithium ion batteries at high rate

Jahn-Teller distortion and manganese dissolution are always the dominant problem of attenuating long cyclic performance and rate capacity of spinel LiMn2O4 cathode materials. Herein, a Ni–Zn dual-doping strategy is proposed to synthesize various LiNi0.05ZnxMn1.95-xO4 (x = 0–0.05) materials via a solid phase combustion method. All the as-prepared Ni–Zn co-doping materials have a good spinel structure with Fd3m space group and present unique polyhedron morphology with exposed (111) facets, which is conductive to relieving the manganese dissolution and Jahn-Teller effect. Moreover, the Ni–Zn co-doping gives rise to the extended Li–O bond and increased cell volume, hence boosting the favorable intercalation and deintercalation kinetics of Li+ ions. Consequently, the optimized LiNi0·05Zn0·02Mn1·93O4 cathode exhibits good electrochemical performance with the initial discharge capacity of 127.30 mAh g−1 and capacity retention of 70% after 1000 cycles at 1 C. At 5 C, an ultra-long cycle stability with a capacity retention of 61% is obtained up to 1800 cycles. Even at the high current rates of 10 C and 20 C, the relatively high first discharge capacities of 106.50 mAh g−1 and 99.40 mAh g−1 are also delivered, respectively. The Ni–Zn co-doping polyhedral LiMn2O4 will provide a solution for developing high-performance cathode materials in lithium ion battery.

Heterogeneous doping-induced surface reconstruction toward high-performance LiNiO2 cathode materials for lithium-ion batteries

Heterogeneous doping-induced surface reconstruction toward high-performance LiNiO2 cathode materials for lithium-ion batteries

Outstanding Electrochemical Performance of Ni-Rich Concentration-Gradient Cathode Material LiNi0.9Co0.083Mn0.017O2 for Lithium-Ion Batteries.

The full-concentrationgradient LiNi0.9Co0.083Mn0.017O2 (CG-LNCM), consisting of core Ni-rich LiNi0.93Co0.07O2, transition zone LiNi1-x-yCoxMnyO2, and outmost shell LiNi1/3Co1/3Mn1/3O2 was prepared by a facile co-precipitation method and high-temperature calcination. CG-LNCM was then investigated with an X-ray diffractometer, ascanning electron microscope, a transmission electron microscope, and electrochemical measurements. The results demonstrate that CG-LNCM has a lower cation mixing of Li+ and Ni2+ and larger Li+ diffusion coefficients than concentration-constant LiNi0.9Co0.083Mn0.017O2 (CC-LNCM). CG-LNCM presents a higher capacity and a better rate of capability and cyclability than CC-LNCM. CG-LNCM and CC-LNCM show initial discharge capacities of 221.2 and 212.5 mAh g-1 at 0.2C (40 mA g-1) with corresponding residual discharge capacities of 177.3 and 156.1 mAh g-1 after 80 cycles, respectively. Even at high current rates of 2C and 5C, CG-LNCM exhibits high discharge capacities of 165.1 and 149.1 mAh g-1 after 100 cycles, respectively, while the residual discharge capacities of CC-LNCM are as low as 148.8 and 117.9 mAh g-1 at 2C and 5C after 100 cycles, respectively. The significantly improved electrochemical performance of CG-LNCM is attributed to its concentration-gradient microstructure and the composition distribution of concentration-gradient LiNi0.9Co0.083Mn0.017O2. The special concentration-gradient design and the facile synthesis are favorable for massive manufacturing of high-performance Ni-rich ternary cathode materials for lithium-ion batteries.

Al2O3-coated LiNi0.8Co0.15Al0.05O2/graphene composite as a high-performance cathode material for lithium-ion battery

A cathode material composite containing Al2O3-coated LiNi0.8Co0.15Al0.05O2 (NCA) and graphene was prepared via a combination of ultrasonication and mechanical ball milling. No changes were observed in the crystalline structure of this material relative to the bare and Al2O3-coated LiNi0.8Co0.15Al0.05O2 materials based on the XRD spectrum. SEM images indicated that graphene was well distributed between the active material particles. The composite material was compared with the bare and Al2O3-coated active materials by electrochemical tests to evaluate its performance in the lithium-ion battery. The resistance values of the solid-electrolyte interphase layer and charge transfer were investigated during cycling by electrochemical impedance spectroscopy. The composite material provided the lowest resistance values with high stability during cycling. The capacity retention of the composite material was 27.7% more in comparison to the bare material during 50 cycles of charge/discharge at a 0.5C rate. Remarkably, the rate capability was improved by using the composite material, with a specific capacity of over 130.9 mAh g–1 at a 3C rate, which means delivering 62.9 mAh g–1 more capacity than the bare NCA. Graphene improved capacity retention and rate capability through the creation of a protective layer on the particles and providing a conductive medium in the electrode structure.

Advanced hybrid supercapacitors assembled with beta-Co(OH)2 microflowers and microclews as high-performance cathode materials

Supercapacitors (SCs) have received increasing attention thanks to their high power density, cyclic stability, and quick charging capability. Herein, a battery-type beta-Co(OH)2 electrode materials including two types of microstructures of nanosheets-assembled microflowers (MFs) and nanowires-based microclews (MCs) have been prepared through a three-step synthetic method, which contains an initial solvothermal reactions, aging the precursor in water, and final hydrothermal treatment. The mixed solvent of glycerol and isopropanol with different volume ratio in the first solvothermal stage has a crucial impact on the formation of different microstructures. Both the MFs and MCs possess huge surface area, and may provide abundant electro-active sites for further Faradic reactions. After they were tested in different electrode systems, it was found that the β-Co(OH)2 MFs presented a specific capacity of 396.5 C g−1 (1 A g−1) along with a rate of 81.2% at 10 A g−1, and the MCs exhibited an inferior capacity of 303.9 C g−1. In order to further assess the potential of practical applications in SCs, a hybrid supercapacitor (HSC) device was designed by choosing activated carbon (AC) as negative electrode. The β-Co(OH)2 MFs//AC device exhibited 158.6 C g−1 and an energy density (Ed) of 43.6 W h kg−1. In contrast, the β-Co(OH)2 MCs//AC HSC showed lower Ed of 34.1 W h kg−1 at 954.7 W kg−1. Both HSCs exhibited brilliant cycling stability over 5000 continuous cycles at 6 A g−1. Such impressive electrochemical response of β-Co(OH)2 MFs & MCs makes them the suitable candidates to assemble advanced HSC devices with high-performance, and may anticipate their promising application prospect in the near future.

Building a high-performance organic cathode material containing electron-withdrawing groups for lithium-ion batteries

The capacity of cathode materials is one of the main factors to limit the performance of lithium-ion batteries (LIBs), so it is urgent to develop high-performance cathode materials. Herein, trinitrohexaazatrinaphythylene (TNHATN) including an electron-withdrawing group (nitro, -NO2) was synthesized by the condensation reaction between hexaketocyclohexane and 4-nitro-o-phenylenediamine, and it was first investigated as a cathode material for lithium-ion batteries. The TNHATN electrode displays a high discharge specific capacity of 355.7 mAh g−1 at 0.05 A g−1 and a superior cycling stability, having the capacity retention of 97.9 % after 200 cycles. The excellent behaviors may be ascribed to its π-conjugated structure including electron-withdrawing groups and multiple redox active sites. The experimental results reveal the redox active sites are pyrazine nitrogen atoms and oxygen atoms from nitro groups. This work confirms that it is an effective route to introduce an electron-withdrawing group into a π-conjugated compound for obtaining high-performance organic cathode materials of LIBs.

Artificial interface modification of Ni-rich ternary cathode material to enhance electrochemical performance for Li-ion storage through RF-plasma-assisted technique

Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) is a promising high-performance cathode material for large-scale Li-ion storage applications. However, devices consisting of Ni-rich materials are less thermally stable, and several factors hinder their use in practical high-energy–density applications. Herein, an approach for plasma-modified NCM811 with TiN is proposed to effectively improve the electrochemical performance and stabilize the cathode–electrolyte interface reaction. In addition, the following aspects are systematically investigated using different techniques: (i) physicochemical properties; (ii) Li storage performance, particularly, cyclic/rate capacity, kinetic behavior of the lithium-ion diffusivities, and electrical conductivity; and (iii) key factor for improving the electrochemical performance through ex-situ/in-situ investigations. The NCM811-TiN/graphite pouch cell displays a high reversible capacity of 17.5 mAh and sustains over 200 cycles at 1C. Comprehensive characterization and probes indicate that the TiN interface with the NCM electrode enhances thermal stability, cyclic capacity, and rate stability without changing the bulk structure and morphology. Hence, these findings facilitate the practical use of safe and high-energy–density Li-ion batteries.

Preparation of long cycle lifespan spinel LiMn2O4 cathode material by a dual-modified strategy

Spinel LiMn2O4 has been identified as a cathode material with extensive application potential for Li-ion batteries. However, during cycling, the Jahn−Teller effect and Mn dissolution have a substantial impact on its specific capacity and cycle span. Herein, combining Fe and Cr elements co-doping with single crystal truncated octahedron morphology is proposed to solve these problems. The Fe−Cr co-doping markedly restrains the Jahn−Teller effect, and promotes the development of crystal and selective growth of crystal surfaces in spinel LiMn2O4. The high exposure (111) surfaces of the truncated octahedron reduce the dissolution of Mn, and a tiny proportion of (110) and (100) surfaces increase the diffusion channels of Li+. HAADF-STEM characterization indicates that the Fe and Cr elements largely replace the Mn atoms at the octahedral 16d site. Because of these advantages, the optimal LiFe0.05Cr0.08Mn1.95-xO4 (LFCMO-8) delivers excellent electrochemical performance with 119.6 mAh·g−1 discharge capacity and 78.1% capacity retention after 500 cycles at 1 C. At comparatively higher current densities of 20 C and 30 C, the superior capacity retention ratios of 79.8% and 87.3% are still achieved after 2000 cycles. Even at 40 C, the LFCMO-8 sample can still reach 98.8% capacity retention rate after 2000 cycles. After 1000 cycles at 5 C, the LFCMO-8 sample still maintained a capacity retention of 45.4% at high temperature (55 °C). ICP-OES test combined with a V-shaped tube device indicates that the Mn dissolution of LCFMO-8 only accounted for 11.8% of LiFe0.05Mn1.95O4 (LFMO). This study serves as a meaningful reference for the preparation of high-performance LiMn2O4 cathode materials.

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.