Synthesis and characterization of urchin-like Mn 0.33 Co 0.67 C 2 O 4 for Li-ion batteries: Role of SEI layers for enhanced electrochemical properties

Achieving ultrastability and efficient lithium storage capacity with high-energy iron(II) oxalate anode materials by compositing Ge nano-conductive sites

Transition metal oxalates (TMOxs, represented by iron oxalate) have attracted considerable interest in anode materials due to their excellent lithium storage properties and consistent cyclic performance. Although investigations into their electrochemical capabilities and lithium storage mechanisms are gradually deepening, the complex and varied electrochemical reactions in the initial cycle, poor inherent conductivity, and high irreversible capacity constrain their further development. Herein, to solve the above-mentioned problems, we controlled the hydrothermal synthesis conditions of iron oxalate with the assistance of organic solvents, which induced the growth of iron oxalate crystals with nano Ge metal as the core. The metal Ge space sites compounded to the stacked iron oxalate particles act as conductive nodes and metal frames, which enhances both the strength of iron oxalate samples and electronic conductivity and lithium-ion diffusion inside the electrode materials. This special structure enhances the electrochemical activity of iron oxalates and improves their lithium storage capability. The iron oxalate @ nano Ge metal composite (FCO@Ge-1) exhibits an excellent cycling performance and an appreciable reversible specific capacity (1090 mA h g^-1 after 200 cycles at 1 A g^-1). The obvious polarization and variation of the electrochemical reaction in the initial cycle of iron oxalate are reduced by compositing nano Ge metal. It is demonstrated that nano Ge metal can promote reversible capacity retention from 67.72% to 80.69% in the early cycles. The distinctive structure of iron oxalate @ nano Ge metal composite provides a fresh pathway to enhance oxalate electrochemical reversible lithium storage activity and develop high-energy electrode material by constructing composite space conductive sites.

High Pseudocapacitance-Driven CoC2 O4 Electrodes Exhibiting Superior Electrochemical Kinetics and Reversible Capacities for Lithium-Ion and Lithium-Sulfur Batteries

In this study, cuboid-like anhydrous CoC₂ O₄ particles (CoC₂ O₄ -HK) are synthesized through a potassium citrate-assisted hydrothermal method, which possess well-crystallized structure for fast Li⁺ transportation and efficient Li⁺ intercalation pseudocapacitive behaviors. When being used in lithium-ion batteries, the as-prepared CoC₂ O₄ -HK delivers a high reversible capacity (≈1360 mAh g^-1 at 0.1 A g^-1 ), good rate capability (≈650 mAh g^-1 at 5 A g^-1 ) and outstanding cycling stability (835 mAh g^-1 after 1000 cycles at 1 A g^-1 ). Characterizations illustrate that the Li⁺ -intercalation pseudocapacitance dominates the charge storage of CoC₂ O₄ -HK electrode, together with the reversible reaction of CoC₂ O₄ +2Li⁺ +2e^- →Co+Li₂ C₂ O₄ on discharging and charging. In addition, CoC₂ O₄ -HK particles are also used together with carbon-sulfur composite materials as the electrocatalysts for lithium-sulfur (Li-S) battery, which displays a gratifying sulfur electrochemistry with a high reversibility of 1021.5 mAh g^-1 at 2 C and a low decay rate of 0.079% per cycle after 500 cycles. The density functional theory (DFT) calculations show that CoC₂ O₄ /C can regulate the adsorption-activation of reaction intermediates and therefore boost the catalytic conversion of polysulfides. Therefore, this work presents a new prospect of applying CoC₂ O₄ as the high-performance electrode materials for rechargeable Li-ion and Li-S batteries.

Proton solvent-controllable synthesis of manganese oxalate anode material for lithium-ion batteries

Manganese oxalates with different structures and morphologies were prepared by the precipitation method in a mixture of dimethyl sulfoxide (DMSO) and proton solvents. The proton solvents play a key role in determining the structures and morphologies of manganese oxalate. Monoclinic MnC2O4·2H2O microrods are prepared in H2O-DMSO, while MnC2O4·H2O nanorods and nanosheets with low crystallinity are synthesized in ethylene glycol-DMSO and ethanol-DMSO, respectively. The corresponding dehydrated products are mesoporous MnC2O4 microrods, nanorods, and nanosheets, respectively. When used as anode material for Li-ion batteries, mesoporous MnC2O4 microrods, nanorods, and nanosheets deliver a capacity of 800, 838, and 548 mA h g-1 after 120 cycles at 8C, respectively. Even when charged/discharged at 20C, mesoporous MnC2O4 nanorods still provide a reversible capacity of 647 mA h g-1 after 600 cycles, exhibiting better rater performance and cycling stability. The electrochemical performance is greatly influenced by the synergistic effect of surface area, morphology, and size. Therefore, the mesoporous MnC2O4 nanorods are a promising anode material for Li-ion batteries due to their good cycle stability and rate performance.

Synthesis of Co0.5 Mn0.1 Ni0.4 C2 O4 ⋅n H2 O Micropolyhedrons: Multimetal Synergy for High-Performance Glucose Oxidation Catalysis

Owing to the synergy between metals, trimetal oxalate micropolyhedrons have been synthesized by means of a room-temperature coprecipitation strategy. The effect of their nanoscale size on their electrochemical performance toward glucose oxidation was investigated. In particular, the Co_0.5 Mn_0.1 Ni_0.4 C₂ O₄ ⋅n H₂ O micropolyhedrons illustrated prominent electrocatalytic activity for the glucose oxidation reaction. Additionally, the Co_0.5 Mn_0.1 Ni_0.4 C₂ O₄ ⋅n H₂ O micropolyhedrons, when used as an electrode material, illustrated an excellent lower limit of detection (1.5 μm), a wide detection concentration range (0.5-5065.5 μm), and a high sensitivity (493.5 μA mm^-1  cm^-2 ). Further analysis indicated that the effectively improved conductivity may have been due to the small size of the materials, and it was easier to form a flat film when Nafion was coated onto the glassy carbon electrode.

Conversion Chemistry of Cobalt Oxalate for Sodium Storage

Conversion electrodes, which can realize high capacities by employing the wider valence states of transition metals, are investigated for sodium storage and applied for rechargeable sodium-ion batteries (SIBs). Importantly, this work is a first report for the sodium storage ability and related storage mechanism in oxalate compounds, specifically cobalt oxalate (CoC₂O₄) nanorods. The nanorods are intimately blended with acetylene black powders to achieve sufficient electrical conductivity (∼10^-3 S cm^-1). The resulting C-CoC₂O₄ electrode delivers an initial capacity of about 330 mA h (g-CoC₂O₄)^-1 at a rate of 0.2 C (60 mA g^-1) and preserves 75% of the initial capacity over 200 cycles. A high charge (oxidation) capacity, ∼111 mA h g^-1, was achieved even at 30 C (9000 mA g^-1). This remarkable electrode performance is reported for the first time for metal oxalate compounds tested for Na cells, to the best of our knowledge. X-ray diffraction, transmission electron microscopy, and time-of-flight secondary-ion mass spectroscopy analyses lead to the proposal of a new sodium storage mechanism. For this mechanism, CoC₂O₄ is converted into Co metal involving with the creation of Na₂C₂O₄ on discharge (reduction), and the Co metal is recovered to CoC₂O₄ on charge. The employed electroconducting carbon is likely to provide good electron conduction paths, which enables fast conversion on both discharge and charge. A full cell comprised of the C-CoC₂O₄ anode and carbon-coated NaCrO₂ cathode exhibits good retention capacity over prolonged cycling, with retention of about 84.7% of the first capacity [107 mA h (g-NaCrO₂)^-1] for 300 cycles, and is active at a rate of 5 C (550 mA g^-1), with a capacity of 79.5 mA h g^-1. This result demonstrates the potential of applying C-CoC₂O₄ as an anode material for rechargeable SIBs.

New Fe₂O₃-Clay@C Nanocomposite Anodes for Li-Ion Batteries Obtained by Facile Hydrothermal Processes

New iron-oxide-based anodes are prepared by an environmentally-friendly and low-cost route. The analysis of the composition, structure, and microstructure of the samples reveals the presence of a major hematite phase, which is accompanied by a certain concentration of an oxyhydroxide phase, which can act as a "lithium-reservoir". By using sodium alginate as a binder, the synthesized anodes display superior electrochemical response, i.e., high specific capacity values and high stability, not only versus Li but also versus a high voltage cathode in a full cell. From these bare materials, clay-supported anodes are further obtained using sepiolite and bentonite natural silicates. The electrochemical performance of such composites is improved, especially for the sepiolite-containing one treated at 400 °C. The thermal treatment at this temperature provides the optimal conditions for a synergic nano-architecture to develop between the clay and the hematite nanoparticles. High capacity values of ~2500 mA h g-1 after 30 cycles at 1 A g-1 and retentions close to 92% are obtained. Moreover, after 450 cycles at 2 A g-1 current rate, this composite electrode displays values as high as ~700 mA h g-1. These results are interpreted taking into account the interactions between the iron oxide nanoparticles and the sepiolite surface through hydrogen bonds. The electrochemical performance is not only dependent on the oxidation state and particle morphology, but the composition is revealed as a key feature.

Significantly Improving Lithium-Ion Transport via Conjugated Anion Intercalation in Inorganic Layered Hosts

Layered hydroxides (LHs) have emerged as an important class of functional materials owing to their unusual physicochemical properties induced by various intercalated species. While both the electrochemistry and interlayer engineering of the materials have been reported, the role of interlayer engineering in improving the Li-ion storage of these materials remains unclear. Here, we rationally introduce pillar ions with conjugated anion dicarboxylate groups, cobalt oxalate ions ([CoOx₂]^2-), into the interlayers of Co(OH)₂ nanosheets [denoted as I-Co(OH)₂ NSs]. The pillar ion guarantees excellent structural stability, high electrical conductivity, and accelerated Li-ion diffusion. The structure delivers high-rate cycling performance for lithium-ion batteries. This work provides insights for the design of LH-based high-performance electrode materials by a rational interlayer-engineering strategy.

High-Crystallinity Urchin-like VS4 Anode for High-Performance Lithium-Ion Storage

VS₄ anode materials with controllable morphologies from hierarchical microflower, octopus-like structure, seagrass-like structure to urchin-like structure have been successfully synthesized by a facile solvothermal synthesis approach using different alcohols as solvents. Their structures and electrochemical properties with various morphologies are systematically investigated, and the structure-property relationship is established. Experimental results reveal that Li⁺ ion storage behavior in VS₄ significantly depends on physical features such as the morphology, crystallite size, and specific surface area. According to this study, electrochemical performance degrades on the order of urchin-like VS₄ > octopus-like VS₄ > seagrass-like VS₄ > flower-like VS₄. Among them, urchin-like VS₄ demonstrates the best electrochemical performance benefiting from its peculiar structure which possesses large surface area that accommodates the volume change to a certain extent, and single-crystal thorns that provide fast electron transportation. Kinetic parameters derived from EIS spectra and sweep-rate-dependent CV curves, such as charge-transfer resistances, Li⁺ ion apparent diffusion coefficients and stored charge ratio of capacitive and intercalation contributions, both support this claim well. In addition, the EIS measurement was conducted during the first discharge/charge process to study the solid electrolyte interface (SEI) formation on urchin-like VS₄ and kinetics behavior of Li⁺ ion diffusion. A better fundamental understanding on Li⁺ storage behavior in VS₄ is promoted, which is applicable to other vanadium-based materials as well. This study also provides invaluable guidance for morphology-controlled synthesis tailored for optimal electrochemical performance.

Doping of Ni and Zn Elements in MnCO3 : High-Power Anode Material for Lithium-Ion Batteries

Herein, Ni and Zn elements are doped simultaneously in MnCO₃ and microspheric Mn_x Ni_y Zn_z CO₃ is successfully obtained. Atomic mapping images reveal that the Ni and Zn elements have been successfully doped in MnCO₃ and thus the prepared sample is not a mixture of MnCO₃ , NiCO₃ , and ZnCO₃ . It is the first time that the atomic mapping images of ternary transition metal carbonates have been demonstrated so far. The scanning transmission electron microscopy - annular bright field (STEM-ABF) image successfully confirms the formation of oxygen vacancies in Mn_x Ni_y Zn_z CO₃ , which is beneficial to improve the electrical conductivity. The evolution of the microstructure from crystal to amorphization during cycling process confirmed by the fast Fourier transform patterns effectively lowers the overpotential of the conversion reaction and accelerates the conversion between Mn²⁺ and much higher valence of Mn element, contributing to the superior capacity of Mn_x Ni_y Zn_z CO₃ electrode. As anode material for lithium-ion batteries, the prepared Mn_x Ni_y Zn_z CO₃ exhibits excellent long-term cycling stability and outstanding rate performance, delivering the superior reversible discharge capacities of 1066 mA h g^-1 at 500 mA g^-1 after 500 cycles and 760 mA h g^-1 at 1 A g^-1 after 1000 cycles. It is the first time that Mn_x Ni_y Zn_z CO₃ has been synthesized and used as anode for lithium-ion batteries so far.

The role of graphene in nano-layered structure and long-term cycling stability of MnxCoyNizCO3 as an anode material for lithium-ion batteries

The prepared nano-layered Mn_xCo_yNi_zCO₃/graphene composite as an anode material for lithium-ion batteries demonstrated long-term cycling stability and perfect rate performance.