Mechanical integrity issues such as particle cracking are considered one of the leading causes of structural deterioration and limited long-term cycle stability for Ni-rich cathode materials of ...Li-ion batteries. Indeed, the detrimental effects generated from the crack formation are not yet entirely addressed. Here, applying physicochemical and electrochemical ex situ and in situ characterizations, the effect of Co and Mn on the mechanical properties of the Ni-rich material are thoroughly investigated. As a result, we successfully mitigate the particle cracking issue in Ni-rich cathodes via rational concentration gradient design without sacrificing the electrode capacity. Our result reveals that the Co-enriched surface design in Ni-rich particles benefits from its low stiffness, which can effectively suppress the formation of particle cracking. Meanwhile, the Mn-enriched core limits internal expansion and improve structural integrity. The concentration gradient design also promotes morphological stability and cycling performances in Li metal coin cell configuration.
Historically long accepted to be the singular root cause of capacity fading, transition metal dissolution has been reported to severely degrade the anode. However, its impact on the cathode behavior ...remains poorly understood. Here we show the correlation between capacity fading and phase/surface stability of an LiMn
O
cathode. It is revealed that a combination of structural transformation and transition metal dissolution dominates the cathode capacity fading. LiMn
O
exhibits irreversible phase transitions driven by manganese(III) disproportionation and Jahn-Teller distortion, which in conjunction with particle cracks results in serious manganese dissolution. Meanwhile, fast manganese dissolution in turn triggers irreversible structural evolution, and as such, forms a detrimental cycle constantly consuming active cathode components. Furthermore, lithium-rich LiMn
O
with lithium/manganese disorder and surface reconstruction could effectively suppress the irreversible phase transition and manganese dissolution. These findings close the loop of understanding capacity fading mechanisms and allow for development of longer life batteries.
Solid-state reaction has been widely adopted as a low-cost and scalable approach to synthesize inorganic materials for industrial applications. However, a special caution must be paid to carefully ...control the synthesis condition in order to obtain final products with desired structure and physical/chemical properties. In this work, LiCoO2 was investigated as a model material to illustrate the complexity of the solid-state reaction, as well as its condition control. Taking the advantage of the high flux and high penetration capability of synchrotron X-ray source, in-situ high-energy X-ray diffraction was deployed to investigate the structural evolution of materials during the solid-state reaction while ex-situ high-resolution X-ray diffraction was utilized to quantify the residual microstrains of LiCoO2. It is shown that the microstrain is a sensitive indicator to probe the completeness of the solid-state reactions, and that it also provides a more quantitative way to establish the structure-property relationship of materials. It can serve as a sensitive indicator for the rational design of synthesis process for functional materials.
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•Impurities influence the electrochemical performance.•Lattice strain occurs at the heterogeneous phase boundary.•Microstrain analysis is sensitive to probe the strained structure.
An efficient synthesis is used for the first time to prepare CuO/reduced graphene oxide nanocomposite anode materials for lithium ion batteries. Initially, copper oxide (CuO) nanoparticles are ...synthesized via a simple, facile and inexpensive microwave-assisted method within short reaction times (<20 min) and subsequent heat treatment at 500 °C for 5 h. The obtained pure CuO nanoparticles are mixed with 10 wt% of graphene nanosheets by the use of spex mill for 1 min. By short-time spex-milling, a unique CuO/reduced graphene oxide nanocomposite is obtained with a microstructure of multi-scale CuO nanoparticles homogeneously dispersed in a graphene matrix. The synthesized samples are characterized using X-ray diffraction and field-emission transmission electron microscopy studies. The spex-milled nanocomposite anode exhibits better electrochemical performance with higher reversible capacity and excellent cyclability in comparison with pure CuO nanoparticles. The initial discharge capacity of the pure CuO nanoparticles and their nanocomposite are 785.2 mAh g−1 and 1043.3 mAh g−1 with reversible capacity retention of 392.1 mAh g−1 and 516.4 mAh g−1 after 45 cycles respectively. The excellent electrochemical performance of CuO/reduced graphene oxide nanocomposite can be attributed to their unique structures, which intimately combine the conductive graphene nanosheets network with uniformly dispersed CuO nanoparticles.
► Copper oxide (CuO) nanoparticles were synthesized by low cost facile microwave-assisted method. ► Nanocomposite was synthesized by short-time spex-milling of CuO and 10 wt% graphene nanosheets. ► Nanocomposite anode exhibited high rate capability and excellent cyclic stability. ► Excellent performance can be attributed to synergistic effect between CuO and reduced graphene. ► Simple, low cost and short-time synthesis is attractive for practical application in large scale.
In response to the ever-increasing global demand for viable energy-storage systems, sodium and potassium batteries appear to be promising alternatives to lithium ion batteries because of the ...abundance, low cost and environmental benignity of sodium/potassium. Electrical energy storage via ion-intercalation reactions in crystalline electrodes is critically dependent on the sizes of the guest ions. Herein, we report on the use of a porous amorphous iron phosphate synthesized using ambient temperature strategies as a potential host that stores electrical energy through the feasible insertion of mono-/di-/tri-valent ions. A combination of ex situ studies reveals the existence of a reversible amorphous-to-crystalline transition in this versatile electrode during electrochemical reactions with monovalent sodium, potassium and lithium. This reconstitutive reaction contributes to realizing specific capacities of 179 and 156 mAhg-1 versus sodium and potassium at current densities of 10 and 5 mAg-1 , respectively. This finding facilitates the feasible development of several amorphous electrodes with similar phase behavior for energy-storage applications.
•A study on Mo6+-doped TiO2 as a high performance anode material.•Mo6+ doping significantly influence the crystal structure and particle sizes.•The electrical conductivity is significantly improved ...by Mo6+ doping.•Mo-doped TiO2 exhibits better electrochemical performances than undoped sample.•Mo doping creates the Ti4+ vacancies in the lattice and generates more free holes.
The effects of molybdenum (Mo6+) doping on the electrochemical properties of anatase-type titanium dioxide (TiO2) were investigated. The Mo6+-doped TiO2 samples were prepared using a simple and cost-effective solvothermal method with the doping levels of 1, 3, and 5wt%, followed by annealing at a low temperature of 300°C for 5h. High-resolution synchrotron X-ray diffraction and electron microscopy were conducted to know the structural and morphological properties of doped TiO2 samples. The dopant significantly suppresses the growth of TiO2 grains and reduces the particles sizes, which can also improve markedly the performance and stability of charge/discharge cycles. The particles sizes are in the range of 115–250nm and 5–10nm for undoped and Mo-doped TiO2 nanoparticle samples, respectively. Electrochemical results show that the Mo6+-doped TiO2 nanoparticle samples display a significantly lower charge transfer resistance, higher rate capability and excellent reversibility. Author’s believed that the high rate performance offered by Mo-doped TiO2 nanoparticle electrodes may be attributed to the enhanced electronic and ionic conductivity, which are achieved by increasing the number of Ti4+ vacancies in the lattice via Mo6+ doping, which may lead to the generation of more free holes in the doped p-type semiconductor. The increased hole concentration in the valence band can contribute to the electrical conductivity of the doped sample.
Hierarchical meso-/macroporous anatase TiO2 was synthesized by the hydrolysis of a titanium metal-organic framework precursor followed by calcination in air. This unique porous feature enables the ...superior rate capability and excellent cycling stability of anatase TiO2 as an anode for rechargeable lithium-ion batteries.
We present a facile and cost-effective urea-assisted auto-combustion method for synthesizing pure MgFe2O4 nanoparticle and MgFe2O4/graphene nanocomposite samples followed by annealing at 600 degree C ...for 5h under N2 atmosphere. The X-ray diffraction pattern confirmed the single phase formation for both samples. The obtained morphology of the nanocomposite sample shows that the MgFe2O4 nanoparticles are highly dispersed on conductive graphene nanosheets with particle size in the range of 50-100nm. When applied as an anode material, MgFe2O4/graphene nanocomposite electrode shows a high reversible charge capacity of 764.4mAhg-1 at 0.04C over 60 charge/discharge cycles and in spite of that it also retained a capacity of 219.9mAhg-1 at high current rate of 4.2C. The obtained result is much better than the synthesized pure MgFe2O4 nanoparticle electrode. The excellent electrochemical performance of the MgFe2O4/graphene nanocomposite electrode can be attributed to the strong favorable synergistic interaction between MgFe2O4 and reduced graphene nanosheets, which supplied a large number of accessible active sites for Li+-ion insertion and short diffusion length for both Li+ ions and electrons. In addition, the graphene nanosheets in the nanocomposite electrode provide high conductivity and accommodate the large volume expansion/contraction during cycling, resulting in high capacity and long cycling stability.
Undoped and 2 wt% vanadium (V5+) doped TiO2 samples are prepared in polyol medium by low-temperature solvothermal method. The as-prepared samples are annealed at 400 °C for 5 h in an air atmosphere ...to increase the crystallinity. The XRD pattern shows that pure anatase TiO2 is formed in both the doped and undoped samples. The maximum sizes of nanoparticles are found to be 300 nm and 15 nm with spherical shaped morphology for undoped TiO2 and V5+ doped TiO2 samples respectively. In addition, 2 wt% V5+ doped sample exhibits excellent electrochemical performance with high reversible specific capacity and excellent rate capability compared to the undoped case. This improvement can be attributed to the substitution of the Ti4+ ions by V5+ ions in the TiO2 lattice and create more Ti4+ vacancies in the lattice. This action may lead to the generation of apparently more number of free holes in the doped p-type semiconductor. Therefore, the increased hole concentration in the valence band can contribute to the electrical conductivity of the doped sample. Vanadium doping also influences the sample crystallinity and reduces the particle size, which provides a larger active surface area than that of undoped TiO2.
•A study on V5+ doped TiO2 as a high performance anode for lithium ion battery.•V5+ doping significantly influence the crystal structure and particle sizes.•The electronic conductivity is largely improved through V5+ doping.•V5+ doping greatly increased both the reversible capacity and cycling stability of TiO2.
In this work, almost pure NaxCoO2 (x=0.71) sample has been prepared via a solid-state route. The stoichiometric composition has been estimated by ICP-AES analysis and the Rietveld refinement ...performed on the respective XRD pattern led to an orthorhombic structure in the Cmcm space group with a=2.83218(3)Å, b=4.89983(4)Å, and c=10.92334(14)Å. The insertion/deinsertion of sodium into the well-crystallized particles leads to capacities as high as 70.4mAhg−1 with an initial Coulombic efficiency of 90%, and excellent capacity retention of almost ~100% after the 90th cycle between a 2.0 and 3.5V voltage window for a 0.08C–rate. The insertion ratio (x) varied between 0.592 and 0.673 during the deinsertion/insertion process within NaxCoO2. The voltage profile shows numerous voltage steps being mainly associated to the slight ordering of the Na ions within the layers. By coupling the electrochemical process with an in-situ X-ray diffraction experiment, the c-axis and a-axis peak positions such as (002), (004) and (100) are shifted with the accompanying deintercalation/intercalation of sodium, suggesting that the extracted sodium has been reversibly occupied with a small variation in sodium composition ranges due to peculiar Na+/vacancy ordering.
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