Effect of microstructure change on resistance of spherical LiCoO2 to electrode degradation for proton intercalation

Lithium cobalt oxide (LCO) with layered crystal structure suffers the structural proton intercalation in aqueous electrolytes of low pH values, little information is available about the effect of microstructure change on the cycling stability of LCO in response to the proton intercalation. In this work, electrochemical properties of three kinds of LCO spheres with different microstructures are studied in neutral aqueous 0.5 M Li₂SO₄ solution. The investigated materials were obtained by calcining the spherical LCO precursors at various temperatures, which were synthesized via a modified solid phase method for lithiation of spherical Co₃O₄. Structure and morphology of materials were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). The spherical LCO prepared at lower temperature shows more superior electrochemical stability. Herein, the resistance of spherical LCO with a particular microstructure to the electrode degradation for the proton intercalation can be measured by the frequency of occurrences of greater-than-100% coulombic efficiencies during cycling. Meanwhile, the capability of retaining the capacity contribution from the order-to-disorder transformation of lithium ions on the hexagonal lattice of host site after the first-order phase transition was proposed to compare and investigate the cyclability of the three kinds of spherical LCO with different microstructures.     

Electrochemical performance of high specific capacity of lithium-ion cell LiV3O8//LiMn2O4 with LiNO3 aqueous solution electrolyte

The electrochemical performance of aqueous rechargeable lithium battery (ARLB) with LiV₃O₈ and LiMn₂O₄ in saturated LiNO₃ electrolyte is studied. The results indicate that these two electrode materials are stable in the aqueous solution and no hydrogen or oxygen produced, moreover, intercalation/de-intercalation of lithium ions occurred within the range of electrochemical stability of water. The electrochemical performance tests show that the specific capacity of LiMn₂O₄ using as the cathode of ARLB is similar to that of ordinary lithium-ion battery with organic electrolyte, which works much better than the formerly reported. In addition, the cell systems exhibit good cycling performance. Therefore, it has great potential comparing with other batteries such as lead acid batteries and alkaline manganese batteries.     

Performance improvement of pasted nickel electrodes with multi-wall carbon nanotubes for rechargeable nickel batteries

Carbon nanotubes (CNTs) were employed as a functional additive to improve the electrochemical performance of pasted nickel-foam electrodes for rechargeable nickel-based batteries. The nickel electrodes were prepared with spherical β-Ni(OH)₂ powder as the active material and various amounts of CNTs as additives. Galvanostatic charge/discharge cycling tests showed that in comparison with the electrode without CNTs, the pasted nickel electrode with added CNTs exhibited better electrochemical properties in the chargeability, specific discharge capacity, active material utilization, discharge voltage, high-rate capability and cycling stability. Meanwhile, the CNT addition also lowered the packing density of Ni(OH)₂ particles in the three-dimensional porous nickel-foam substrate, which could lead to the decrease in the active material loading and discharge capacity of the electrode. Hence, the amount of CNTs added to Ni(OH)₂ should be optimized to obtain a high-performance nickel electrode, and an optimum amount of CNT addition was found to be 3 wt.%. The superior electrochemical performance of the nickel electrode with CNTs could be attributed to lower electrochemical impedance and less γ-NiOOH formed during charge/discharge cycling, as indicated by electrochemical impedance spectroscopy and X-ray diffraction analyses. Thus, it was an effective method to improve the electrochemical properties of pasted nickel electrodes by adding an appropriate amount of CNTs to spherical Ni(OH)₂ as the active material.     

Rate capability of graphite materials as negative electrodes in lithium-ion capacitors

The lithium-ion exchange rate capability of various commercial graphite materials are evaluated using galvanostatic charge/discharge cycling in a half-cell configuration over a wide range of C-rates (0.1-60 C). The results confirm that graphite is capable of de-intercalating stored charge at high rates, but has a poor intercalating rate capability. Decreasing the graphite coating thickness leads to a limited rate performance improvement of the electrode. Reducing the graphite particle size shows enhanced C-rate capability but with increased irreversible capacity loss (ICL). It is demonstrated that the rate of intercalation of lithium-ions into the graphite is significantly limited compared with the corresponding rate of de-intercalation at high C-rates. For the successful utilisation of commercially available conventional graphite as a negative electrode in a lithium-ion capacitor (LIC), its intercalation rate capability needs to be improved or oversized to accommodate high charge rates.     

Preparation and electrochemical profile of Li0.33MnO2 nanorods as cathode material for secondary lithium batteries

We report the preparation of Li_0.33MnO₂ nanorods from γ-MnO₂ nanorods reacted with LiNO₃ by a low temperature solid-state reaction method. The Li_0.33MnO₂ nanorods tend to be oriented along the b-axis, and show an improved rate capability and cycling performance as positive electrode for lithium battery. It delivers a discharge capacity of 199 and 129 mAh/g at the current rate of 0.1 C (20 mA/g) and 2 C, respectively, and keeps 92% of initial capacity over 100 cycles. Li_0.33MnO₂ nanorods reduce both the electrode bulk resistance and charge-transfer resistance for lithium-ion intercalation. The advantage of nanorods results from good electrical conduction, appropriate length of nanorod and small volume expansion from appropriate orientations of tunnels structure.     

Characteristics of an aqueous rechargeable lithium battery (ARLB)

Electrochemical performance of an aqueous rechargeable lithium battery (ARLB) containing a LiV₃O₈ (negative electrode) and LiCoO₂ (positive electrode) in saturated LiNO₃ aqueous electrolyte was studied. These two electrode materials are stable in the aqueous solution and intercalation/deintercalation of lithium ions occurs within the window of electrochemical stability of water. The obtained capacity of this cell system is about 55 mAh/g based on the mass of the positive electrode, which is lower than the corresponding one in the non-aqueous lithium ion battery. However, its specific capacity can be compared with those of the lead acid and Ni-Cd batteries. In addition, initial results show that this cell system is good in cycling.     

Electrospinning combined with hydrothermal synthesis and lithium storage properties of ZnFe2O4-graphene composite nanofibers

ZnFe₂O₄-graphene composite nanofibers were prepared through electrospinning technique, then with graphene oxide by the facile solvothermal method to get the final products for the first time. The obtained ZnFe₂O₄ nanofibers composed of numerous same size nanoparticles wrapped by graphene sheets to form a unique nanostructure. When the ZnFe₂O₄-graphene electrode was evaluated as anode for lithium-ion batteries, good rate capability and long-term cycling stability could be achieved. The ZnFe₂O₄-graphene electrode exhibited a first discharge capacity of 2166 mAh g⁻¹ cycling at 0.05 C, remained an average reversible capacity of 1000 mAh g⁻¹ after 50 cycles, and kept the high rate capacities of 899, 822, 760 and 711 mAh g⁻¹ at the current rates of 0.5, 1, 2 and 5 C, respectively. The excellent electrochemical performance could be ascribed to the following reasons: the large electrochemical active surface area provided by the composite nanofibers; the graphene sheets decreased the internal resistance of the lithium-ion batteries, which resulted from the electrical conductivity of the graphene sheets; the graphene sheets as conductive network could effectively restrain the agglomeration of ZnFe₂O₄ nanopaiticals.     

Nanoparticles constructed mesoporous coral-like Mn2O3 as high performance anode for lithium-ion batteries

As well established, the morphology and architecture of electrode materials greatly contribute to the electrochemical properties. Herein, a novel structure of mesoporous coral-like manganese (III) oxide (Mn₂O₃) is synthesized via a facile solvothermal method coupled with the carbonization under air. When fabricated as anode electrode for lithium-ion batteries (LIBs), the as-prepared Mn₂O₃ exhibits good electrochemical properties, showing a high discharge capacity of 1090.4 mAh g^?1 at 0.1 A g^?1, and excellent rate performance of 410.4 mAh g^?1 at 2 A g^?1. Furthermore, it maintains the reversible discharge capacity of 1045 mAh g^?1 at 0.1 A g^?1 after 380 cycles, and 755 mAh g^?1 at 1 A g^?1 after 450 cycles. The durable cycling stability and outstanding rate performance can be attributed to its unique 3D mesoporous structure, which is favorable for increasing active area and shortening Li⁺ diffusion distance.     

Fabrication,structure, electrochemical properties and lithium-ion storage performance of Nd:BiVO4 nanocrystals

Nd:BiVO₄ nanocrystals were synthesized by an effective and simple approach. Nd was incorporated into BiVO₄ host to enhance electronic conductivity and lithium-ion diffusion kinetics, thus promoting the electrochemical performance. When employed as anode materials in lithium-ion batteries, a good cycling stability and high capacity of ~611 mAh g⁻¹ at 100 mA g⁻¹ were delivered. The work can be extensively employed for fabricating other electrode materials and promoting the electrochemical performance in energy storage correlative domains.     

Rapid and controllable synthesis of LiCoO2 cathode materials by reactive flash sintering

LiCoO₂ (LCO) has been widely adopted as the electrode for lithium-ion batteries (LIBs) which provide a solution for settling problems referring to energy and environment. The demand for rapid and controllable synthesis of LCO increases dramatically. In this work, reactive flash sintering (RFS), for the first time, was introduced to synthesize LCO rapidly and controllably based on simple oxide precursors. The as-prepared LCO, investigated by physicochemical property characterization, showed well-constructed and high crystallinity and controllable morphologies, in which the grain size varied with the magnitude of the applied limited current value, allowing for grain size modulation. Furthermore, the as-prepared LCO exhibited excellent performance in cyclic stability and rate capacity by contrast with that synthesized by the conventional solid-phase sintering method. This is admittedly attributed to better crystallinity and less lithium loss. Therefore, RFS provides a new approach for the manufacture of LCO electrode and has the potential to be applied to other electrode materials for LIBs.     

Electrochemical performance of spherical Li-rich LMNCO cathode materials prepared using a two-step spray-drying method

In this study we synthesized Li-rich Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ (LMNCO) as a composite cathode material through a two-step spray-drying method, using transition metal (TM) acetates and citric acid (CA, as a chelating agent) at various molar ratios and then calcining at various temperatures for various periods of time. This two-step spray-drying method created hierarchical nano/micro-sphere structures of the LMNCO cathode material. The LMNCO cathode exhibited the best electrochemical performance when synthesized with a TM:CA ratio of 3:2, a calcination temperature of 900 °C, and a calcination time of 5 h. This as-prepared LMNCO composite was then modified with polyimide (PI) at various weight ratios (PI/LMNCO = 0.5, 1.0, and 1.5 wt%) to improve its electrochemical properties. Among the various structures, the LMNCO cathode material coated with 1.0 wt% of PI at a layer thickness of approximately 1.88 nm achieved the best initial discharge capacities. This modified electrode also displayed enhanced cycle stability, with over 93.3 and 87.9% of the capacity retained after 30 cycles at 0.1C and 100 cycles at 1C, respectively. In comparison, the capacity retention of the unmodified LMNCO electrode measured under the same conditions was no more than 91.3% at 0.1C and 70.1% at 1C. Thus, surface modification with PI was an effective method for improving the coulombic efficiency, discharge capacity, and long-term cycling performance of the LMNCO cathode. Such PI-coated LMNCO composite cathode materials appear to be potential candidates for use in next-generation high-performance lithium-ion batteries.     

Wet-Chemical Synthesis and Electrochemical Properties of Ce-Doped FeVO4 for Use as New Anode Material in Li-ion Batteries

Ce-doped FeVO₄ nanocomposites were successfully synthesized using reverse micro-emulsion route. Thermal and microstructural characteristics were comprehensively investigated by simultaneous thermal analysis, X-ray diffraction (XRD), scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and laser particle size analyzer. Moreover, as the anode material of lithium-ion batteries, the electrochemical properties were studied by galvanostatic charge and discharge tests and electrochemical impedance spectroscopy. The thermal analysis illustrated that the triclinic crystal structure of FeVO₄ nanoparticles is formed at about 520 °C, which is confirmed by XRD and FT-IR results. Furthermore, the microstructural analyses revealed more regular particles and high specific surface area for wet-chemical derived FeVO₄:Ce, which decreases the diffusion pathway of the lithium ions during the insertion/extraction process. The electrochemical measurements indicated that the electrode cycling performance and rate retention ability of Ce-doped FeVO₄ are better than those of pure FeVO₄ due to the expansion of the crystal lattice, which provided more lattice space for lithium intercalation and de-intercalation. Consequently, the as-prepared Ce-doped FeVO₄ with relatively high specific and reversible capacity, thermal stability and satisfactory cycling performance is a promising candidate for use as a lithium batteries anode material.     

Origin of Capacity Fading in Nano-Sized Co3O4 Electrodes: Electrochemical Impedance Spectroscopy Study

Transition metal oxides have been suggested as innovative, high-energy electrode materials for lithium-ion batteries because their electrochemical conversion reactions can transfer two to six electrons. However, nano-sized transition metal oxides, especially Co₃O₄, exhibit drastic capacity decay during discharge/charge cycling, which hinders their practical use in lithium-ion batteries. Herein, we prepared nano-sized Co₃O₄ with high crystallinity using a simple citrate-gel method and used electrochemical impedance spectroscopy method to examine the origin for the drastic capacity fading observed in the nano-sized Co₃O₄ anode system. During cycling, AC impedance responses were collected at the first discharged state and at every subsequent tenth discharged state until the 100th cycle. By examining the separable relaxation time of each electrochemical reaction and the goodness-of-fit results, a direct relation between the charge transfer process and cycling performance was clearly observed.     

Facile microwave synthesis of CoFe2O4 spheres and their application as an anode for lithium-ion batteries

CoFe₂O₄ spheres were synthesized using a microwave-hydrothermal reaction and characterized by X-ray diffraction, electron microscopy, and electrochemical analysis. This simple synthesis method led to a uniform dispersion of nanosized building blocks in the spheres, which exhibit significantly improved cycling performance and rate capability in lithium cells. The excellent electrochemical performances of CoFe₂O₄ sphere are attributed to an increased lithium wetting property at the electrode–electrolyte interface, facile lithium-ion diffusion, and better alleviation of the structure pulverization during charge–discharge process.     

Niobium doping of Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials with enhanced structural stability and electrochemical performance

Lithium-rich layered oxides with high energy density have been intensively investigated as advanced lithium-ion batteries cathode materials. However, capacity degradation and voltage decay caused by irreversible lattice oxygen loss and structural transformation during cycling restrict their application. Herein, we proposed a high valance cations Nb⁵⁺ doping strategy and synthesized a series of Li_1.2Mn_0.54-x/3Ni_0.13-x/3Co_0.13-x/3Nb_xO₂ (x = 0, 0.01, 0.02 and 0.03) cathode materials. The effects of Nb⁵⁺ doping on crystallographic structure and electrochemical property were systematically studied. In virtue of the large ionic radii and strengthened Nb–O bonds, the doped samples present commendable structural stability and expanded interlayer spacing for Li-ions migration, which ensures the upgraded cyclic stability and rate performance. In particular, the electrode with x = 0.02 delivers a discharge specific capacity of 265.8 mAh g^-1 at 0.2 C with decelerated voltage decay, while 86.9% capacity are remained after long-term cycles. Moreover, excellent discharge specific capacity of 153.4 mAh g⁻¹ is still attained at 5 C accompanied with enhanced Li-ion diffusion kinetics.     

Electrochemical properties of mixed cathode consisting of μm-sized LiCoO2 and nm-sized Li[Co0.1Ni0.15Li0.2Mn0.55]O2 in lithium rechargeable batteries

In order to enhance the utilization of active cathode material in lithium rechargeable batteries, physical mixtures of μm-sized LiCoO₂ (LCO) and nm-sized Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ (LCMNO) were prepared by varying the LCO content, and the physical and electrochemical properties of lithium half-cells utilizing the mixed cathodes were characterized. Our main concern is the packing state between the microparticles and nanoparticles within the electrode, which influences the determination of the electrode density. We found that the electrode composed of 80 wt.% LCO and 20 wt.% LCMNO shows the best performance in capacity retention ratio and high-rate capability, which are comparable to those of LCMNO, due to the superior density in the electrode’s packing state over other samples.     

Reducing atmosphere improves the conductivity of NaTi2(PO4)3/C material for hybrid aqueous rechargeable lithium-ion battery anode

Hybrid aqueous rechargeable lithium-ion batteries (HARLIBs) have lower cost and better safety performance than conventional lithium-ion batteries (organic electrolytes). The challenge faced by HARLIBs are the narrow selection of anode and cathode materials, and overcoming the problems of capacity decay of anode and cathode materials in aqueous electrolytes. NaTi₂(PO₄)₃, which has a stable three-dimensional open framework structure, shows certain applicability in HARLIBs, but its inherent low electronic conductivity leads to poor utilization of active materials and inferior rate performance. In this article, we propose an experimental method that can improve the conductivity of NaTi₂(PO₄)₃/C, and study the electrochemical performance of NaTi₂(PO₄)₃/C aqueous half-cell and NaTi₂(PO₄)₃/C||LiMn₂O₄ hybrid aqueous full cell. The results show that Ti³⁺/oxygen vacancies can endow NaTi₂(PO₄)₃/C with higher conductivity and improve the specific capacity and rate capability (69 mAh·g^?1, 7C). At 1C, the second discharge specific capacity is 98.46 mAh·g^?1. After 100 cycles, the Rct was 2.92 × 10^?2 Ω. The NaTi₂(PO₄)₃/C//LiMn₂O₄ full cell can provide a discharge specific capacity of up to 101.07 mAh·g^?1. The synthesized NaTi₂(PO₄)₃/C material can be applied to the anode electrode of hybrid aqueous lithium-ion full cell.     

Influence of Ti and Fe doping on the structural and electrochemical performance of LiCo0.6Ni0.4O2 cathode materials for Li-ion batteries

The combination of lithium cobalt oxide (LCO) and lithium nickel oxide (LNO) property for Li-ion batteries (LIB) brings a very promising cathode material, LiCo_1?xNi_xO₂ with a high specific reversible capacity and good cycling behaviour. Nonetheless, high toxic Co content and an instability of Li⁺/Ni²⁺ interaction in LiCo_1?xNi_xO₂ crystal structure paved the way for some modification for the development of this potential material. In this research, the self-propagating combustion method is used to reduce 40% Co content of LCO by replacing it with 40% Ni content resulting in cathode material with the stoichiometry of LiCo_0.6Ni_0.4O₂ (LCN). To improve the stability of the LiCo_0.6Ni_0.4O₂ structure, 5% of Ti and Fe was substituted at the Co site of the LCN material. The effect of these different cation substitutions (Ti⁴⁺ and Fe³⁺) on the structural and electrochemical performance of layered LiCo_0.6Ni_0.4O₂ cathode materials was investigated. Rietveld refinement revealed that Fe doped material has the longest atomic distance Li–O in the structure that allow better Li⁺ diffusion during intercalation/deintercalation to give an excellent electrochemical performance (138 mAhg^?1). After 50th cycle, it is found that the discharge cycling for Ti and Fe substituted materials were improved by more than 5% compared to pristine material. Both Ti and Fe doped materials were also having less than 13% of capacity fading indicates that the substitution of some Co with Ti and Fe are stable and can retain their electrochemical properties.     

Electrooxidation and dischargeability of transition-metal borides as possible anodic materials in neutral aqueous electrolytes

A number of transition-metal borides were studied as anodic materials for neutral aqueous batteries. These borides are shown to have considerably high electrochemical activities in neutral electrolytes. The discharge capacities for TiB₂ reach 1,350 mAh g⁻¹ at a constant current density of 50 mA g⁻¹, exceeding those for all the metal electrodes reported so far. Amorphous CoB_x can deliver a discharge capacity of >650 mAh g⁻¹, and even simply ball-milled FeB_x can also give a discharge capacity of >200 mAh g⁻¹. These results suggest the possible use of boride compounds as a large family of new anodic materials for constructing neutral aqueous batteries with high electrochemical capacity and rate capability.     

Study of electrochemical performances of perovskite-type oxide LaGaO3 for application as a novel anode material for Ni-MH secondary batteries

In this paper, the perovskite-type oxide LaGaO₃, which is proposed as a novel anode material for Ni-MH secondary batteries, was synthesized by the sol–gel method. The electrochemical performance of the oxide was analyzed at temperature 328 K using chronopotentiometry, potentiodynamic polarization and chronoamperomertry techniques. During the first three of charge/discharge cycles, the discharge capacity of the oxide LaGaO₃ reaches its maximum value at 220 mAh g⁻¹ and thereafter decreases. The degradation of cycling stability of the oxide can be explained by the corrosion behavior of the electrode as a result of the decrease in the electroactive surface area of the electrochemical reaction with cycling. The kinetic results showed that both the exchange current density I₀ and the hydrogen diffusion coefficient D_H of the anode decrease with increasing state of charge, after activation, which can be ascribed to the change in the electrode surface when transforming from α to β phase. The whole electrochemical reactions of the electrode are governed by two important processes: charge-transfer reaction on the electrode surface and hydrogen atom diffusion within the bulk of the electrode.