Zhicheng Ju

One-pot hydrothermal synthesis of Nitrogen-doped graphene as high-performance anode materials for lithium ion batteries

Nitrogen-doped (N-doped) graphene has been prepared by a simple one-step hydrothermal approach using hexamethylenetetramine (HMTA) as single carbon and nitrogen source. In this hydrothermal process, HMTA pyrolyzes at high temperature and the N-doped graphene subsequently self-assembles on the surface of MgO particles (formed by the Mg powder reacting with H2O) during which graphene synthesis and nitrogen doping are simultaneously achieved. The as-synthesized graphene with incorporation of nitrogen groups possesses unique structure including thin layer thickness, high surface area, mesopores and vacancies. These structural features and their synergistic effects could not only improve ions and electrons transportation with nanometer-scale diffusion distances but also promote the penetration of electrolyte. The N-doped graphene exhibits high reversible capacity, superior rate capability as well as long-term cycling stability, which demonstrate that the N-doped graphene with great potential to be an efficient electrode material. The experimental results provide a new hydrothermal route to synthesize N-doped graphene with potential application for advanced energy storage, as well as useful information to design new graphene materials.

Direct Synthesis of Few-Layer F-Doped Graphene Foam and Its Lithium/Potassium Storage Properties

Heteroatom-doped graphene is considered a potential electrode materials for lithium-ion batteries (LIBs). However, potassium-ion batteries (PIBs) systems are possible alternatives due to the comparatively higher abundance. Here, a practical solid-state method is described for the preparation of few-layer F-doped graphene foam (FFGF) with thickness of about 4 nm and high surface area (874 m(2)g(-1)). As anode material for LIBs, FFGF exhibits 800 mAh·g(-1) after 50 cycles at a current density of 100 mA·g(-1) and 555 mAh·g(-1) after 100 cycles at 200 mA·g(-1) as well as remarkable rate capability. FFGF also shows 165.9 mAh·g(-1) at 500 mA·g(-1) for 200 cycles for PIBs. Research suggests that the multiple synergistic effects of the F-modification, high surface area, and mesoporous membrane structures endow the ions and electrons throughout the electrode matrix with fast transportation as well as offering sufficient active sites for lithium and potassium storage, resulting in excellent electrochemical performance. Furthermore, the insights obtained will be of benefit to the design of reasonable electrode materials for alkali metal ion batteries.

One‐Pot Hydrothermal Synthesis of FeMoO4 Nanocubes as an Anode Material for Lithium‐Ion Batteries with Excellent Electrochemical Performance

Metal molybdates nanostructures hold great promise as high-performance electrode materials for next-generation lithium-ion batteries. In this work, the facial design and synthesis of monodisperse FeMoO4 nanocubes with the edge lengths of about 100 nm have been successfully prepared and present as a novel anode material for highly efficient and reversible lithium storage. Well-defined single-crystalline FeMoO4 with high uniformity are first obtained as nanosheets and then self-aggregated into nanocubes. The morphology of the product is largely controlled by the experimental parameters, such as the reaction temperature and time, the ratio of reactant, the solution viscosity, etc. The molybdate nanostructure would effectively promote the insertion of lithium ions and withstand volume variation upon prolonged charge/discharge cycling. As a result, the FeMoO4 nanocubes exhibit high reversible capacities of 926 mAh g(-1) after 80 cycles at a current density of 100 mA g(-1) and remarkable rate performance, which indicate that the FeMoO4 nanocubes are promising materials for high-power lithium-ion battery applications.

Phosphorus and oxygen dual-doped graphene as superior anode material for room-temperature potassium-ion batteries

The intercalation of potassium ions into graphitic carbon materials has been demonstrated to be feasible while the electrochemical performance of the potassium-ion battery (PIB) is still unsatisfactory. More effort should be made to improve the specific capacity and achieve superior rate capability. Functional phosphorus and oxygen dual-doped graphene (PODG) is introduced as the anode for PIB, made by a thermal annealing method using triphenylphosphine and graphite oxide as precursors. It exhibits high specific capacity and ultra-long cycling stability, delivers a capacity of 474 mA h g−1 at 50 mA g−1 after 50 cycles and retains a capacity of 160 mA h g−1 at 2000 mA g−1 after 600 cycles. The superior electrochemical performance of PODG is mainly due to the large interlayer spacing caused by phosphorus and oxygen dual-doping, which facilitates potassium-ion insertion and extraction. Furthermore, the ultrathin and wrinkled features structure leads to a continuous and efficient supply of vacancies and defects for potassium storage.

Direct synthesis of 3D hierarchically porous carbon/Sn composites via in situ generated NaCl crystals as templates for potassium-ion batteries anode

It has been approved that embedding potassium ions into graphitic carbon interlayer is possible. The intercalation of potassium ions into graphite has been demonstrated feasible while the electrochemical performance of potassium ion battery (PIB) is still unsatisfying. Herein, an in situ formed NaCl serving as hierarchical templates and supporting the formation of 3D polymer–Sn complex is reported. The polymer–Sn complex is heat-treated to obtain a 3D Carbon/Sn network constructed by porous films. In particular, the large specific surface area of the composite and the Sn nanoparticles homogeneously embedded in 3D hierarchically porous carbon shells result in an excellent potassiation/depotassiation performance. Under the optimal conditions (650 °C), the 3D hierarchically porous carbon/Sn composite (3D-HPCS) as an anode material of PIBs demonstrates a high reversible capacity of 276.4 mA h g−1 at 50 mA g−1 (100 cycles) with coulombic efficiency of over 96%. This interesting method can provide new avenues to other high-capacity anode material systems that are subject to significant volume expansion.

Co2+xTi1−xO4 nano-octahedra as high performance anodes for lithium-ion batteries

Single crystal Co2+xTi1−xO4 nano-octahedra enclosed by {111} planes with an average edge length of 200 nm were synthesized via a one-step hydrothermal approach using economical TiO2 as a titanium source. The structure of Co2+xTi1−xO4 is actually an inverse spinel solid solution with an excess amount of Co. As anode materials for lithium-ion batteries (LIBs), the Co2+xTi1−xO4 electrode delivered a high specific capacity of over 766.5 mA h g−1 at the current density of 100 mA g−1 after 60 cycles; moreover, it provided stable rate capability and lithium storage performance at the high current density of 680 mA h g−1 after 400 cycles at 1000 mA g−1. This excellent electrochemical performance is mainly derived from the atomic-level combination of two active materials (CoO and TiO2 matrix) via different lithium storage mechanisms (conversion reaction and insertion/extraction, respectively) after the initial discharge process. In particular, the nanostructured TiO2 matrix formed after the first cycle in the electrode would alleviate large volume changes and avoid rapid capacity fading, which could endow Co2+xTi1−xO4 electrodes with excellent structural stability.

Phosphorus Particles Embedded in Reduced Graphene Oxide Matrix to Enhance Capacity and Rate Capability for Capacitive Potassium-Ion Storage

Early studies indicate that graphite is feasible as the negative electrode of a potassium-ion battery, but its electrochemical performance still cannot meet the demands of applications. More efforts should be focused on increasing the specific capacity and improving the rate capability in the meantime. Thus, stainless-steel autoclave technology has been utilized to prepare phosphorus nanoparticles encapsulated in reduced graphene oxide matrix as the electrode materials for a potassium-ion battery. As a result, the composite matrix affords high reversible capacities of 354 and 253 mA h g-1 at 100 and 500 mA g-1 , respectively. The superior electrochemical performance is mainly because the composite matrix possesses better electronic conductivity and a robust structure, which can promote the electron-transfer performance of the electrode. Furthermore, phosphorus particles can contribute to the high capacity through an alloying mechanism. In addition, the silklike, ultrathin, film composite with a high surface area is conducive to capacitive potassium-ion storage, which plays a more important role in rate performance and a high current density capability.