Shi-Xi Zhao

Effect of the morphology of Li–La–Zr–O solid electrolyte coating on the electrochemical performance of spinel LiMn1.95Ni0.05O3.98F0.02 cathode materials

Lithium ion solid electrolyte Li7La3Zr2O12 (LLZO) coated LiMn1.95Ni0.05O3.98F0.02 cathode materials with controllable coating morphology were prepared via a sol–gel route and subsequently heat treated at different temperatures. The effect of the morphology of Li–La–Zr–O solid electrolyte coating on the electrochemical performance of spinel LiMn1.95Ni0.05O3.98F0.02 cathode materials was investigated by XRD, SEM, TEM and electrochemical tests. The results showed the coating did not change the spinel structure of LiMn1.95Ni0.05O3.98F0.02 cathode materials, as the atoms of coating material can only adhere to the surface of the octahedral grain rather than enter the spinel lattice. Heat annealing temperature has a significant effect on the microstructure of the LLZO coating layer. At a lower heat annealing temperature (400 °C), the coating forms a reticulation, whereas at the mid-temperature (600 °C), it exhibits a more uniform and continuous layer; moreover, when the heat treatment temperature increases to a high level (800 °C), the coating exists as discontinuous nanoparticles rather than as a layer. Among all coating forms, the continuous coating layer formed at 600 °C shows the best electrochemical performance.

Synthesis and electrochemical performance of rod-like spinel LiMn2O4 coated by Li–Al–Si–O solid electrolyte

Li1.05Co0.1Mn1.9O3.95F0.05 rods with a spinel structure were synthesized by a topochemical conversion route, and a Li–Al–Si–O (LASO) glassy solid electrolyte was used to modify the surface of the cathode material. The structure and electrochemical properties were investigated using X-ray diffraction, scanning electron microscope, transmission electron microscope and electrochemical tests. XRD, SEM and TEM observations show that Li1.05Co0.1Mn1.9O3.95F0.05 materials have a single crystal of cubic spinel structure and exhibit a rod-like morphology with a diameter of 400–500 nm. The electrochemical results indicate that LASO-coated Li1.05Co0.1Mn1.9O3.95F0.05 rods exhibit an excellent rate capability and cycle stability at elevated temperatures and high rates. The initial discharge capacity of the LCMOF-rod-LASO sample is 93.9 mA h g−1 under 10 C at 55 °C, and the capacity retention ratio is higher than 96% after 200 cycles. Even under 15 C at 55 °C, the cathode material shows a high capacity of 87 mA h g−1. The cyclic voltammograms and impedance spectra results reveal that the LASO coating enhances the kinetics of the lithium-ion diffusion through the surface layer and the charge transfer reaction, improving the electrochemical activity of the cathode. Thus, the LASO-coated Li1.05Co0.1Mn1.9O3.95F0.05 rods have shown potential for high power applications in lithium ion batteries.

A novel pseudocapacitance mechanism of elm seed-like mesoporous MoO3−x nanosheets as electrodes for supercapacitors

Pseudocapacitance is induced by surface or near surface redox, ion intercalation or underpotential deposition processes. A given electrochemically active material usually has only one of the above mechanisms. In this study, we synthesized elm seed-like mesoporous MoO3−x nanosheets, which possess both redox and intercalation faradic mechanisms. This novel pseudocapacitance mechanism causes a high capacitance of 1480 F g−1 at 5 A g−1 and outstanding cycling performance where the capacitance does not decay but increases slightly up to 10 000 cycles at a scan rate of 100 mV s−1. Here, we clarified that the tunnel structure of MoO3−x and its special electrochemical kinetics towards H+ generate this mechanism. This faradic mechanism could achieve a higher degree of utilization of the active-sites thus resulting in excellent electrochemical performance.

Impact of lithium excess on the structural and electrochemical properties of the LiNi0.5Mn1.5O4 high-voltage cathode material

LiNi0.5Mn1.5O4-based cathode materials are synthesized by a one-step nonaqueous co-precipitation method. Appropriate excess lithium ions can extrude transition metal ions out of tetrahedral 8a sites, which could have a higher effect on the rate performance of LiNi0.5Mn1.5O4 than the well-known factor, i.e. cationic order degree in 16d octahedral sites.

Effect of Ni substitution on structural stability, micromorphology, and electrochemical performance of Li2MnSiO4/C cathode materials

The chief drawback of Li2MnSiO4 cathode materials is structural instability deriving from the transformation of [MnO4] tetrahedra to [MnO6] octahedra during oxidation from Mn(II) to Mn(III) and the Jahn–Teller effect especially from Mn(III) to Mn(IV). Based on the theory that Ni2+ could keep the [NiO4] ligand unchanged and stable during oxidation/reduction, [NiO4] tetrahedra may behave as a regional structural framework to support the total crystal lattice and alleviate structural distortion partially. In this paper we synthesize nano-Li2Mn1−xNixSiO4/C samples with a small amount of Ni as the dopant via a hydrothermal route. Firstly, we discuss the existential state of Ni through XPS spectra, and demonstrate that both Ni2+ and metallic Ni coexist, especially Ni2+ could improve structural stability. The influence of Ni doping on morphology, structural stability, and electrochemical performance is discussed through Raman spectroscopy and electrochemical tests below. It is confirmed that there exists an optimal Ni content under which the optimal performance is displayed. In our work, the optimum Ni content is 5.0%, and the maximal discharge capacity achieved is 235 mA h g−1 for the 5.0% Ni doped sample in the first cycle.

Serration behaviours in metallic glasses with different plasticity

Abstract We present a statistical study of serration behaviours in Pd77.5Cu6Si16.5, Ti41Zr25Be26Ag8, Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 and Fe50Ni30P13C7 metallic glasses with different plasticity. The four samples show similar serration patterns in the beginning of yielding, and different patterns during later loading. These results indicate that the shear band initiation process in metallic glasses follow some similar dynamics. And the later serration process follows different dynamics and will lead to different plasticity. Here we interpret these serration behaviours from a perspective of inhomogeneity. The different serration patterns and shear band dynamics could be reasonably understood. The serration pattern of the Fe-based sample suggests that the brittleness of metallic glasses might result from a lower degree of inhomogeneity, and a less tendency of forming shear band intersections. This study might provide new experimental evidences for different micro-structures (or inhomogeneity) and dynamic behaviours in metallic glasses with different plasticity.

Enhanced electrochemical performance of bulk type oxide ceramic lithium batteries enabled by interface modification

The interface issue is one of the severe problems in all-solid-state (ASS) batteries, especially for oxide-type batteries with a full ceramic structure. Rigid interfacial contact between electrodes and electrolyte and poor mechanical properties of ceramics limit the choices of applicable materials and fabrication processes for ASS batteries. In this report, a bulk type ASS lithium battery with an initial discharge capacity of 112.7 mA h g−1 is successfully fabricated. A garnet-structured Li6.75La3Zr1.75Ta0.25O12 (LLZO-Ta) ceramic pellet is used as the solid electrolyte. A slurry of a composite cathode consisting of Li[Ni0.5Co0.2Mn0.3]O2, In2(1−x)Sn2xO3, Li3BO3, and polyvinylidene fluoride was tape-cast on the LLZO-Ta pellet and annealed to improve the interfacial contact among the particles in the composite cathode as well as between the composite cathode and the electrolyte pellet. Without the surface modification of a Li[Ni0.5Co0.2Mn0.3]O2 active material, an obvious degradation of discharge capacity due to polarization is observed during cycling. When a layer of a Li–Ti–O precursor is coated on the surface of Li[Ni0.5Co0.2Mn0.3]O2 particles, in situ spinel Li[Ti0.1Mn0.9]2O4 is formed at the surface after annealing, leading to an enhancement of discharge capacity of the battery and great improvement for cycling stability. This novel method of interface modification reduces the interfacial polarization with an enhanced Li+ transfer between the cathode and the electrolyte. Our experimental results reveal that the interface engineering by means of reasonable regulation on the surface constituent of electrode materials can effectively improve the capacity and cycling stability of ASS lithium batteries.

Synthesis of petal-like δ-MnO2 and its catalytic ozonation performance

Petal-like δ-MnO2 microspheres were successfully synthesized by a very simple hydrothermal method with potassium permanganate (KMnO4) as the only raw material. By adjusting the initial concentration of KMnO4 solution and the time of the hydrothermal reaction, the morphology and crystallinity of δ-MnO2 can be controlled. The synthesized δ-MnO2 microspheres were characterized by XRD, SEM, TEM, TG/DSC, BET, ICP-AES and XPS. The catalytic ozonation performance of δ-MnO2 prepared by a hydrothermal reaction at 160 °C for 24 h using 0.1 mol L−1 KMnO4 solution was tested. Its catalytic activity is excellent. The degradation efficiencies of bisphenol A and ibuprofen using 0.1 g L−1 δ-MnO2 as the catalyst were 68.2% and 68.5% in 20 min reaction time. The results were much better than those of individual ozone treatment and with commercial MnO2 as the catalyst. The formation of hydroxyl radicals was not the main reason for the rapid degradation of organic compounds in the catalytic reaction with δ-MnO2 as the catalyst. The strong interaction among the catalyst surface, ozone and organic molecules was the important reason for catalysis based on the related experimental results.

Improving the electrochemical performance of LiFePO 4 /C by doping magnesium trisilicate

This work studies the effect of doping with magnesium trisilicate for LiFePO₄/C cathode materials by a solid-state method. The samples were synthesized by two-step processing. Firstly, it was heated at 360 °C for 10 hours and then was calcined at 700°C for 10 hours. All the annealing processing was carried out in argon atmosphere. The phase structure, morphology and element distribution of prepared samples were characterized by XRD and scanning electron microscope and energy dispersive spectrometer. The results show that Mg²⁺and Si⁴⁺ co-doped LiFe_0.99Mg_0.01P_0.985Si_0.015O₄/C cathode materials exhibit higher capacity and rate capability than the unsubstituted LiFePO₄/C cathode. For example, LiFe_0.99Mg_0.01P_0.985Si_0.015O₄/C exhibit discharge capacity of 146 mAh·g^-1 compared to 140mAh·g^-1 for unsubstituted LiFePO₄/C at 0.5C. Especially, at 5C rate, the discharge capacity of LiFe_0.99Mg_0.01P_0.985Si_0.015O₄/C was remarkably exceeded that of unsubstituted LiFePO₄/C cathode materials. The better performances of the cathode were attributed to the increase of electronic conductivity and the improved migration of lithium ion.

Hierarchical porous Li4Ti5O12–TiO2 composite anode materials with pseudocapacitive effect for high-rate and low-temperature applications

Dual-phase hierarchical porous Li4Ti5O12–TiO2 (HP LTO–TO) microspheres were synthesized using a topochemical conversion method and used as an anode material in high power lithium ion batteries, particularly for use in low temperature applications. The HP LTO–TO microspheres are composed of ultra-thin nanosheets with a large specific surface area for interface intercalation reactions and also to provide a much reduced diffusion path for both electrons and lithium ions. The HP LTO–TO electrode was found to exhibit excellent low-temperature cycling capability and rate performance. The discharge capacities of HP LTO–TO under a current rate of 0.2C reached 167 mA h g−1 at 25 °C, 143 mA h g−1 at 0 °C, 130 mA h g−1 at −10 °C, and 94 mA h g−1 at −40 °C. A discharge capacity of 77 mA h g−1 is readily attainable at −20 °C at a high current rate of 5C. The aforementioned high capacity and rate performance at low temperature can be partially attributed to the novel hierarchical porous dual phase microsphere structure made up of thin nanosheets. It is also hypothesized that the co-existence of dual LTO and TO phases may create cation vacancies and/or result in a favorable interface between LTO and TO that permit fast charge and ion transport, even at very low temperatures. This can be attributed to the fact that HP LTO–TO has a relatively low activation energy for Li+ diffusion and a fast surface faradaic reaction, which benefits from the abundant dual-phase interfaces and grain boundaries, as well as the large specific surface area.