Hongbo Shu

Suppressed capacity/voltage fading of high-capacity lithium-rich layered materials via the design of heterogeneous distribution in the composition

Lithium-rich layered materials, Li1+xM1−xO2 (M = Mn, Ni, Co), have been under intense investigation as high-performance cathode materials for lithium ion batteries due to their high discharge capacity, low cost and environmental benignity. Unfortunately, the practical uses of these oxides have so far been hindered by their severe capacity and voltage fading during high voltage cycling (>4.5 V vs. Li/Li+). In an attempt to overcome these problems, herein, a novel lithium-rich Li1.14[Mn0.60Ni0.25Co0.15]0.86O2 microsphere with heterogeneous distribution in the composition has been reasonably designed and successfully synthesized via a co-precipitation method. The chemical composition in the spherical particle is gradually altered by increasing the Mn concentration while reducing the Co content from the particle center to the outer layer. At the same time, the Ni content remains almost constant throughout the particle. The coin cell with the heterogeneous cathode material delivers a high discharge capacity of over 230 mA h g−1 between 2.0 V and 4.6 V, and shows excellent cyclic stability due to the continuous increase of the stable tetravalent Mn towards the outer surface of the spherical particles, corresponding to 93.8% capacity retention after 200 cycles at 0.5 C. More importantly, the as-prepared material exhibits a significantly lower discharge voltage decay compared with conventional materials, which may mainly be ascribed to the suppression of the layered-to-spinel transformation in the Co-rich/Mn-depleted regions of the spherical particle. The capacity and voltage fading of the lithium-rich layered material are simultaneously suppressed by the special architecturual design, and the results here will shed light on developing cathode materials with special structures and superior electrochemical properties for high-performance lithium ion batteries.

Porous hollow α-Fe2O3@TiO2 core–shell nanospheres for superior lithium/sodium storage capability

Porous hollow α-Fe2O3@TiO2 core–shell nanospheres for use as anode materials in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) have been successfully fabricated by a simple template-assisted method, which has been rarely reported before. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 adsorption–desorption isotherms reveal that the as-prepared α-Fe2O3@TiO2 is composed of a hollow inner cavity and an outer shell with massive mesopores. This porous hollow structure is capable of buffering the large volume variation of α-Fe2O3 during cycling and preventing the electrode from pulverization and aggregation, as well as providing sufficiently large interstitial space within the crystallographic structure to host alkalis (Li and Na). As a consequence, this hybrid composite exhibits outstanding electrochemical properties, e.g., high specific capacity, excellent cyclability, satisfactory rate performance, and splendid initial coulombic efficiency for both LIBs and SIBs.

Synthesis and characterization of a Li-rich layered cathode material Li1.15[(Mn1/3Ni1/3Co1/3)0.5(Ni1/4Mn3/4)0.5]0.85O2 with spherical core–shell structure

A Li-rich layered cathode material Li1.15[(Ni1/3Co1/3Mn1/3)0.5(Ni1/4Mn3/4)0.5]0.85O2 with a spherical core–shell structure was firstly synthesized by a co-precipitation route. In this material, the Li1.15[Ni1/3Co1/3Mn1/3]0.85O2 core was completely encapsulated by a Li1.15[Ni1/4Mn3/4]0.85O2 shell. The structure and morphology of the as-prepared core–shell structured material were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results indicate that the core–shell structured material has a typical layered structure with the existence of a Li2MnO3-type integrated component. Spherical morphologies with an inner core and outer shell layer are clearly observed by SEM. A half cell using the core–shell structured cathode material showed a high capacity of 242 mA h g−1 at a rate of 0.1 C in a voltage range of 2.0–4.8 V. Especially, the core–shell structured cathode material represents excellent lithium intercalation stability compared to the Li1.15[Mn1/3Co1/3Mn1/3]0.85O2 core, and an improved rate capability compared to the Li1.15[Ni1/4Mn3/4]0.85O2 shell. A synergetic effect of the positive attributes of the two materials is achieved by the formation of the core–shell architecture. Therefore, the as-prepared core–shell structured Li1.15[(Mn1/3Ni1/3Co1/3)0.5(Ni1/4Mn3/4)0.5]0.85O2 is very effective for improving the electrochemical behavior of Li-rich layered cathode materials in the high-performance lithium ion batteries.

A facile synthesis of Fe3O4 nanoparticles/graphene for high-performance lithium/sodium-ion batteries

In this study, a facile, simple, and inexpensive co-precipitation method is used to fabricate diamond-like Fe3O4 nanoparticle/graphene composites for use as lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) electrode materials. In our synthesis, high-temperature treatment and complicated procedures and apparatus are avoided. Physical characterizations reveal that the as-prepared product is composed of a large fraction of diamond-like Fe3O4 nanoparticles uniformly distributed on thin graphene nanosheets. Compared to bare Fe3O4 and most of the previously reported studies, the as-obtained Fe3O4/graphene composite exhibits greatly enhanced electrochemical properties for both LIBs and SIBs, including excellent reversible capacity, superior cyclability and good rate performance. Specifically, when tested as an anode for LIBs, the Fe3O4/graphene composite shows specific capacity of 1430 mA h g−1 after 100 cycles at 200 mA g−1. The initial discharge capacity tested in SIBs is 855 mA h g−1, and after 40 cycles, the discharge capacity stabilizes at ∼210 mA h g−1 for 250 cycles. The excellent performance can be attributed to the greatly improved electrical conductivity, large surface area and excellent stability of the electrode material.

Facile synthesis and performances of nanosized Li2TiO3-based shell encapsulated LiMn1/3Ni1/3Co1/3O2 microspheres

LiMn1/3Ni1/3Co1/3O2 microspheres covered by a nanosized Li2TiO3-based shell are prepared by a facile synthesis method. First, a controllable TiO2 nano-layer is grown on the surface of a spherical Mn1/3Ni1/3Co1/3CO3 precursor, and then the resultant TiO2@LiMn1/3Ni1/3Co1/3O2 hybrid is synchronously transformed in situ into a hierarchical Li2TiO3@LiMn1/3Ni1/3Co1/3O2 microsphere through a solid-phase reaction. It has been found that the hierarchical Li2TiO3@LiMn1/3Ni1/3Co1/3O2 microspheres exhibit a good rate capability with a discharge capacity of 92.3 mA h g−1 even at higher rates of 20 C between 3.0 and 4.3 V. Besides, they possess excellent cyclic stability especially at high rates, with a capacity retention of 90.3% after 500 cycles at a 20 C rate. The enhanced electrochemical performance of the hierarchical Li2TiO3@LiMn1/3Ni1/3Co1/3O2 at high rates is attributed to the stable and fast Li+-conductor characteristic of the nanosized Li2TiO3-based shell. Thus, the Li2TiO3@LiMn1/3Ni1/3Co1/3O2 microspheres will be a promising cathode material for lithium-ion batteries with high power density and excellent cycling performance.

Spherical concentration-gradient LiMn1.87Ni0.13O4 spinel as a high performance cathode for lithium ion batteries

A novel spherical concentration-gradient material with an average composition of LiMn1.87Ni0.13O4 is successfully synthesized via a co-precipitation route, in which the homogeneous LiMn2O4 core is encapsulated by a continuously Ni increasing concentration-gradient layer, and the composition of the outmost layer of the spherical LiMn1.87Ni0.13O4 is LiMn1.5Ni0.5O4. The physicochemical and electrochemical performances of the spherical LiMn1.87Ni0.13O4 sample are investigated by X-ray diffraction (XRD) and electrochemical tests, and using a scanning electron microscope (SEM) with an energy-dispersive X-ray spectroscope (EDXS). The results show that the LiMn1.87Ni0.13O4 sample has a typical Fd3m spinel structure. It can be found from the cross-sectional SEM images and EDXS analysis that the LiMn1.87Ni0.13O4 particles are quite homogeneous without any apparent gap between the inner core and the outer concentration-gradient layer. Especially, the LiMn1.87Ni0.13O4 sample has excellent performance at an elevated temperature. It delivers a discharge capacity of 108.2 mA h g−1 between 3.0 and 4.4 V vs. Li/Li+ with a retention of 90.2% over 200 cycles at a rate of 0.5 C (74 mA g−1) at 55 °C. Besides, it has an exceptional capacity of 129.1 mA h g−1 between 3.0 and 4.9 V with a retention of 91.9% over 100 cycles at a rate of 0.5 C at 55 °C. Apparently, the LiMn1.87Ni0.13O4 sample shows excellent capacity stability even at an elevated temperature, i.e. 55 °C, where a traditional LiMn2O4 sample inevitably fails. Thus, the LiMn1.87Ni0.13O4 sample with a homogeneous LiMn2O4 core material and an isotropy concentration-gradient outer layer shell will be a promising cathode material for advanced lithium ion batteries.

Sheet-like structure FeF3/graphene composite as novel cathode material for Na ion batteries

A sheet-like structure FeF3/graphene composite is successfully synthesized by a novel and facile sol–gel method. The structure and electrochemical performance of the as-synthesized FeF3/graphene composite are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and electrochemical measurement. The results indicate that the FeF3 nanosheets are loaded on the surface of the graphene sheets to form the sheet-like structure hybrid. Fourier transform infrared (FTIR) spectrum confirms that C–F bonds exist in FeF3/graphene composite, and it further indicates that a chemical bond between FeF3 and graphene has been formed and FeF3 can preferably stick to the surface of the graphene. The FeF3/graphene composite as cathode material of rechargeable Na ion batteries (NIB) exhibits a fairly high initial discharge capacity of 550 mA h g−1 at 0.1 C, and it still keeps a capacity of 115 mA h g−1 after 50 cycles at 0.3 C at a range of 1.0–4.0 V for NIB.

Self-assembly synthesis and electrochemical performance of Li1.5Mn0.75Ni0.15Co0.10O2+δ microspheres with multilayer shells

Novel Li1.5Mn0.75Ni0.15Co0.10O2+δ microspheres with hierarchical multilayer shells were rationally designed and successfully prepared through a layer-by-layer self-assembly deposit with a co-precipitation process. The microsphere with multilayer shells consists of a Li1.5Mn0.75Ni0.25O2+δ inner core and hierarchical multilayer shells. The structure and electrochemical properties of the spherical Li1.5Mn0.75Ni0.15Co0.10O2+δ cathode material with multilayer shells are evaluated and compared to those of the conventional Li1.5Mn0.75Ni0.15Co0.10O2+δ cathode material with the same chemical composition as the multilayer spherical cathode material. The results show that the spherical cathode material with multilayer shells delivers a high discharge capacity of 257.8 mA h g−1 at a rate of 0.1 C with an outstanding capacity retention of 96.1% after 100 cycles at 0.5 C between 2.0 and 4.6 V. Especially, the spherical cathode material with multilayer shells exhibits an improved rate capability with a capacity of 102.7 mA h g−1 even at a high discharge rate of 10 C, and it is apparently superior to the conventional Li1.5Mn0.75Ni0.15Co0.10O2+δ cathode material (64.9 mA h g−1). Thus, the reasonable design for function and structure of cathode materials will be significant for improving the lithium ion battery performance.

An Fe3O4@(C–MnO2) core–double-shell composite as a high-performance anode material for lithium ion batteries

An Fe3O4@(C–MnO2) composite with a cube-like core–double-shell structure has been successfully designed and prepared by a combination of the hydrothermal method and a layer-by-layer (LBL) self-assembly technique. This novel hybrid composite was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy and electrochemical tests. It has been found that this material has a cube-like morphology with a core–double-shell structure. Compared with the bare α-Fe2O3 and Fe3O4–C materials, the as-prepared composite has a significantly enhanced electrochemical performance, with a high capacity, good rate capability, and excellent cycling stability as an anode material for lithium ion batteries (LIBs). At a current density of 100 mA g−1, the as-obtained Fe3O4@(C–MnO2) composite electrode delivers a reversible capacity exceeding 1000 mA h g−1 and retains 979 mA h g−1 after 150 cycles. In contrast, the discharge capacities of the bare α-Fe2O3 and Fe3O4–C show only 111 mA h g−1 and 282 mA h g−1 at a current density of 100 mA g−1 after 150 cycles, respectively. This improved electrochemical performance can be attributed to the high theoretical capacity and larger specific surface area of the MnO2 layer, as well as the high electrical conductivity of the carbon layer, which acts as both the linker and the stabilizer between Fe3O4 and MnO2.

Preparation and performance of β-MnO2 nanorod @ nanoflake (Ni, Co, Mn) oxides with hierarchical mesoporous structure

The rational design and facile synthesis of transition metal oxides are necessary to improve their application in supercapacitors. Herein three kinds of hierarchical mesoporous structured transition metal oxides, which are composed of a β-MnO2 nanorod core and one of three different nanosheet hybrid (Ni, Co, Mn) oxide shells, are facilely synthesized via a novel in situ nucleation and growth of transition metal oxides on the surface of the β-MnO2 nanorods. The crystallographic analyses demonstrated that the three kinds of hybrid oxide shells consisted of cobalt manganese oxide (CMO), nickel manganese oxide (NMO), and nickel cobalt manganese oxide (NCMO). These transition metal oxides are evaluated as electrodes for high performance supercapacitors (SCs). The results reveal that β-MnO2@CMO exhibits a good rate capability of 35% capacity retention even at 20 A g−1, while β-MnO2@NMO displays a high pseudocapacitance of 560 F g−1 at 1 A g−1. However, β-MnO2@NCMO combined the advantages of both β-MnO2@CMO and β-MnO2@NMO, and exhibits a high specific capacitance of 675 F g−1 at 1 A g−1 with excellent rate performance (about 30% capacity retention at 20 A g−1) and cycling stability (83% capacity retention after 3000 cycles). The improved electrochemical performance can be attributed to the unique hierarchical architecture and the synergistic effect of different components.