Xihui Nan

Hollow-Cuboid Li3VO4/C as High-Performance Anodes for Lithium-Ion Batteries.

Li3VO4 has been demonstrated to be a promising anode material for lithium-ion batteries with a low, safe voltage and large capacity. However, its poor electronic conductivity hinders its practical application particularly at a high rate. This work reports that Li3VO4 coated with carbon was synthesized by a one-pot, two-step method with F127 ((PEO)100-(PPO)65-(PEO)100) as both template and carbon source, yielding a microcuboid structure. The resulting Li3VO4/C cuboid shows a stable capacity of 415 mAh g(-1) at 0.5 C and excellent capacity stability at high rates (e.g., 92% capacity retention after 1000 cycles at 10 C = 4 A g(-1)). The lithiation/delithiation process of Li3VO4/C was studied by ex situ X-ray diffraction and Raman spectroscopy, which confirmed that Li3VO4/C underwent a reversible intercalation reaction during discharge/charge processes. The excellent electrochemical performance is attributed largely to the unique microhollow structure. The voids inside hollow structure can not only provide more space to accommodate volume change during discharge/charge processes but also allow the lithium ions insertion and extraction from both outside and inside the hollow structure with a much larger surface area or more reaction sites and shorten the lithium ions diffusion distance, which leads to smaller overpotential and faster reaction kinetics. Carbon derived from F127 through pyrolysis coats Li3VO4 conformably and thus offers good electrical conduction. The results in this work provide convincing evidence that the significant potential of hollow-cuboid Li3VO4/C for high-power batteries.

Coherent Mn3O4-carbon nanocomposites with enhanced energy-storage capacitance

Nanostructured Mn3O4 was introduced to activated C (AC) by a novel sonochemical reaction, and the resulting nanocomposites were examined as supercapacitor electrodes. The sonication not only catalyzed the redox reaction but also promoted the diffusion of the precursors, causing the formation of coherent nanocomposites with Mn3O4 nanoparticles grown and uniformly distributed inside the mesopores of the AC. In addition, the extreme local condition in the sonochemical synthesis yielded an excessive amount of divalent manganese ions and oxygen vacancies. This novel microstructure endowed the sample with a superior performance, including a specific capacitance of 150 F/g compared with the value of 93 F/g for AC at a charge/discharge rate of 100 mA/g. A Li-ion capacitor delivered an energy density of 68 Wh/kg, compared with 41 Wh/kg for the AC capacitor at a power density of 210 W/kg.

MnO nanoparticles with cationic vacancies and discrepant crystallinity dispersed into porous carbon for Li-ion capacitors

MnO nanoparticles with cationic vacancies and discrepant crystallinity were prepared through a one-step hydrothermal synthesis followed by calcination at different temperatures. Glucose was used as both a reducing agent to introduce cationic vacancies with a content of ∼5.5% into MnO nanocrystals, and a carbon source to encapsulate MnO nanocrystals in a three dimensional porous framework. Cationic vacancies benefit phase transition in a conversion reaction, and together with a low degree of crystallinity, may also provide more void spaces for ion diffusion (3.37 × 10−13 cm2 s−1). Three dimensional porous carbon with a pore volume of 0.27 cm3 g−1 demonstrated a high electrical conductivity of 6.25 S cm−1 and offered fast pathways for charge transfer and penetration of the electrolyte. Such a synergistic structure endowed MnO with excellent electrochemical properties including a considerably enhanced capacity of 650 mA h g−1 at a current density of 1000 mA g−1. Li ion capacitors based on such a MnO anode and activated carbon cathode achieved the maximum energy density of 220 W h kg−1, and the capacitance retention was 95.3% after 3600 cycles at a rate of 5000 mA g−1.

Highly Efficient Storage of Pulse Energy Produced by Triboelectric Nanogenerator in Li3V2(PO4)3/C Cathode Li-Ion Batteries

Triboelectric nanogenerator (TENG) has been considered as a new type of energy harvesting technology, which employs the coupling effects of triboelectrification and electrostatic induction. One key factor having limited its application is the energy storage. In this work, a high performance Li3V2(PO4)3/C material synthesized by low-cost hydrothermal method followed with subsequent annealing treatment was studied to efficiently store the power generated by a radial-arrayed rotary TENG. Not only does the Li3V2(PO4)3/C exhibit a discharge capacity of 128 mAh g(-1) at 1 C with excellent cyclic stability (capacity retention is 90% after 1000 cycles at a rate of 5 C) in Li-ion battery, but also shows outstanding energy conversion efficiency (83.4%) compared with the most popular cathodic materials: LiFePO4 (74.4%), LiCoO2 (66.1%), and LiMn2O4 (73.6%) when it was charged by high frequency and large current electricity directly from by TENG.

Effects of Preinserted Na Ions on Li-Ion Electrochemical Intercalation Properties of V2O5

Na-preinserted V2O5 samples of NaxV2O5 (x = 0.00, 0.005, 0.01, or 0.02) were synthesized through sol-gel and freeze-drying routes and subsequent calcination. X-ray diffraction (XRD) results showed that all of the synthesized materials have typical orthorhombic structures without impurity phases. The lattice parameters were refined via the Rietveld refinement method, and the results suggested that the lattice parameters of preinserted samples increased in comparison with pristine V2O5. X-ray photoelectron spectroscopy (XPS) measurements demonstrated that the V(4+) concentration in the Na-preinserted V2O5 samples gradually increased as amount of sodium increased. Results from both XRD and XPS strongly suggested that Na ions indeed enter the interlamination position in the V2O5 crystal to expand the channels for Li-ion migration. NaxV2O5 samples exhibited improved electrochemical properties compared with those of pristine V2O5. Among all of the samples, Na0.01V2O5 delivered the highest reversible specific capacity, best cycling stability, and excellent rate capability. The analysis and discussion on ion diffusion revealed that the preinserted Na ions benefited the mobility of Li ions to improve the rate capabilities of electrodes.

Impacts of Surface Energy on Lithium Ion Intercalation Properties of V2O5

Oxygen vacancies have demonstrated to be one of the most effective ways to alter electrochemical performance of electrodes for lithium ion batteries, though there is little information how oxygen vacancies affect the electrochemical properties. Vanadium pentoxide (V2O5) cathode has been investigated to explore the relationship among oxygen vacancies, surface energy, and electrochemical properties. The hydrogen-treated V2O5 (H-V2O5) sample synthesized via thermal treatment under H2 atmosphere possesses a high surface energy (63 mJ m(-2)) as compared to that of pristine V2O5 (40 mJ m(-2)) and delivers a high reversible capacity of 273.4 mAh g(-1) at a current density of 50 mA g(-1), retaining 189.0 mAh g(-1) when the current density increases to 2 A g(-1). It also displays a capacity retention of 92% after 100 cycles at 150 mA g(-1). The presence of surface oxygen vacancies increases surface energy and possibly serves as a nucleation center to facilitate phase transition during lithium ion intercalation and deintercalation processes.

A new anode material for high performance lithium-ion batteries: V2(PO4)O/C

V2(PO4)O/C is a promising new anode material for lithium ion batteries with excellent electrochemical properties, synthesized by a facile one pot hydrothermal method, followed by a two-step calcination process. The composite can deliver a reversible capacity of 445 mA h g−1, 409 mA h g−1 and 382 mA h g−1 at 1.0, 1.5 and 2.0 A g−1. The capacity retentions of V2(PO4)O/C cycled at 1 and 5 A g−1 for 200 cycles are 90% and 80%, respectively. The excellent electrochemical properties are mainly attributed to the following three factors: (1) face-sharing [VO6] octahedral arrays endow the crystal with a high intrinsic electronic conductivity; (2) the good lithium ion diffusion coefficient of the material contributes for reducing electrochemical and concentration polarization in the charge–discharge process; and (3) porous microstructure and nanoscale particles not only permit effective contact between the electrolyte and active material, but also provide more space to accommodate volume change during the discharge/charge processes. The results in this study provide convincing evidence that V2(PO4)O/C has significant research value for future practical applications.

High performance lithium-sulfur batteries for storing pulsed energy generated by triboelectric nanogenerators

Storing pulsed energy harvested by triboelectric nanogenerators (TENGs) from ambient mechanical motion is an important technology for obtaining sustainable, low-cost, and green power. Here, we introduce high-energy-density Li-S batteries with excellent performance for storing pulsed output from TENGs. The sandwich-structured sulfur composites with multi-walled carbon nanotubes and polypyrrole serve as cathode materials that suppress the shuttle effect of polysulfides and thus preserve the structural stability of the cathode during Li-ion insertion and extraction. The charging time and energy storage efficiency of the Li-S batteries are directly affected by the rotation rates of the TENGs. The average storage efficiency of the batteries for pulsed output from TENGs can exceed 80% and even reach 93% at low discharge currents. The Li-S batteries also show excellent rate performance for storing pulsed energy at a high discharge current rate of 5 C. The high storage efficiency and excellent rate capability and cyclability demonstrate the feasibility of storing and exploiting pulsed energy provided by TENGs and the potential of Li-S batteries with high energy storage efficiency for storing pulsed energy harvested by TENGs.