Tiefeng Liu

Improvement of the electrochemical performance of carbon-coated LiFePO4 modified with reduced graphene oxide

In this work, carbon-coated LiFePO4 was further modified with reduced graphene oxide (RGO) using an ultrasonic-assisted rheological phase method coupled with carbothermal treatment. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and electrochemical methods were used to characterize the materials properties. The results showed that the composite material consisting of carbon-coated LiFePO4 and RGO sheets possesses a unique and effective three-dimensional “sheet-web” structure. In the structure, the LiFePO4 particle size can be maintained at nanosize to form abundant voids between the nanoparticles while the RGO sheets are significantly beneficial for Li+ diffusion. As a result, the electrochemical properties of the composite material have been greatly improved. A sample with 5 wt% RGO exhibited high specific capacity and superior rate performance with the discharge capacities of 160.4 mA h g−1 at 0.2 C and 115.0 mA h g−1 at 20 C. The sample also showed an excellent cycling stability with only about 10% capacity decay at 10 C after 1000 cycles.

A three dimensional SiOx/C@RGO nanocomposite as a high energy anode material for lithium-ion batteries

A co-modification strategy to improve the electrode performance of SiO-based materials through the use of a carbon coating layer and reduced graphene oxide (RGO) network has been developed. The as-synthesized SiOx/C@RGO nanocomposites showed excellent specific capacity, cycling performance and rate capability when used as an anode in lithium-ion batteries.

Ultrafast preparation of three-dimensional porous tin–graphene composites with superior lithium ion storage

Three-dimensional porous Sn–graphene composites have been prepared on Ni foam by an easy, binder-free, low-cost and ultrafast electrophoretic deposition method. The structure and morphology of the as-prepared composite material are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, high resolution transmission electron microscopy, field emission scanning electron microscopy and elemental analysis. The lithium storage performance of the three-dimensional porous Sn–graphene anode is evaluated by cyclic voltammetry, galvanostatic charge–discharge cycling, and electrochemical impedance spectroscopy measurements. Results show that the composite material with a graphene content of 6.1 wt% delivers a reversible capacity of 552 mA h g−1 after 200 cycles at a current density of 500 mA g−1. The synthetic approach presented in this work may provide a facile strategy for the preparation of three-dimensional porous metal–graphene composites.

The composite electrode of LiFePO4 cathode materials modified with exfoliated graphene from expanded graphite for high power Li-ion batteries

In recent years, copious papers have reported the fruitful modifications of LiFePO4-based composites and exhibited excellent electrochemical performance in terms of rate capability and cycling stability. Besides, the optimization of bulk electrodes are essential to keep pace with composites, by enhancement of the electronic and ionic transport to further improve the power performance of an electrode. Therefore, in this work, a facile strategy is adopted to fabricate a composite electrode with NMP as a solvent, containing large-size multilayer graphene, which is prepared by the exfoliation of economical expanded graphite under high power ultrasound in isopropyl alcohol. Active LiFePO4 nanograins, as well as conductive additives, are attached to the superior conductive graphene and thereby fast pathways are established as a “highway” for electronic transport in the bulk electrode. As a result, this composite electrode exhibits a lower polarization at high-rate charge–discharge processes. The operating flat voltage of 20 C rate is maintained at more than 3.0 V in one minute and its discharge capacity is up to 107.8 mA h g−1, representing a better energy density and power density.

The synergy effect on Li storage of LiFePO4 with activated carbon modifications

In this work, composite electrodes containing lithium iron phosphate (LiFePO4) and activated carbon (AC) were prepared by physically mixing LiFePO4 and AC with polyvinylidene fluoride (PVDF) as a binder and acetylene black (AB) as an electrically conductive agent. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), nitrogen sorption, four-probe conductivity and vibrating densitometer techniques were employed to characterize samples. The characterization results showed that the presence of AC increased the electrical conductivity, reduced the tap density, and modified the porosity of the resultant composite electrode materials. Electrochemical data demonstrated that the composite electrode displayed a significantly improved electrochemical performance in comparison with the pure LiFePO4 electrode. An electrode with 5 wt% AC exhibited specific discharge capacities of 70 mA h g−1 at 20 C and 100 mA h g−1 at 10 C without significant capacity decay after 400 cycles. Galvanostatic charge–discharge and cyclic voltammetry results revealed that energy was stored via both charge adsorption and lithium intercalation/deintercalation owing to the presence of both AC and LiFePO4 in the composite electrode. Electrochemical impedance spectroscopy (EIS) was used to investigate the charge–discharge kinetics and mechanism of the composite electrode. The EIS results demonstrated that the two different active materials (LiFePO4 and AC) displayed synergy in terms of both material structure and energy storage, contributing to the observed excellent electrochemical performance.

Carbon-coated single-crystalline LiFePO4 nanocomposites for high-power Li-ion batteries: the impact of minimization of the precursor particle size

In this work, a high-energy ball mill technique is designed to deal with bulk precursors and achieve particle size minimization. A large amount of the nano-sized precursor is achieved in a narrow particle size distribution of ca. 95 nm. We confirm that the dimensional size of the precursor has a significant influence on the final LiFePO4 particle size and that small grains of the precursor probably form single-crystalline nanoparticles during the calcination process. After carbothermal reduction, the carbon-coated single-crystalline LiFePO4 nanocomposites (nano-CS–LFP) are easily synthesized. Benefiting from the decreasing particle size, the specific surface area of nano-CS–LFP is up to 48.0 m2 g−1, which implies a higher interfacial contact area between the active particles and the electrolyte, as well as an increase in its capacitance capability. Besides, cyclic voltammetry curves of nano-CS–LFP reveal a better capability of reversible reactivity and a lower polarization. Galvanostatic charge–discharge results exhibit excellent rate performance with a discharge capacity of ca. 100 mA h g−1 at 10 °C and a stable cycling property with a capacity retention of ca. 90% after 1000 cycles. In addition, the rapid charge–discharge test over 60 seconds indicates an excellent pulse performance with a high current in a short time period. The combination of the merits of carbon coating and particle size minimization is responsible for the above improvements. Finally, this facile preparation strategy is favorable for the industrial production of economical LiFePO4 materials from lab synthesis.

Carbon nanotube decorated NaTi2(PO4)3/C nanocomposite for a high-rate and low-temperature sodium-ion battery anode

A sodium super-ionic conductor structure NaTi2(PO4)3 has been considered as a promising anode material for sodium-ion batteries. However, the inherent poor electronic and ionic kinetics leading to inferior rate and low-temperature performance severely restricts its extensive developments. In this work, we report a carbon nanotube decorated nano-NaTi2(PO4)3/C anode composite to achieve high-rate capability (116.8 mA h g−1 at 1C, 113.3 mA h g−1 at 10C and 103.4 mA h g−1 at 50C) and stable cyclability (about 98% capacity retention at 50C of 1000 cycles) as well as impressive low-temperature performance (about 65.2 mA h g−1 at 10C at a temperature of minus 20 °C). The carbon nanotube network not only improved electrolyte infiltration to decrease the internal diffusion resistance, but also provides fast transport pathways for electrons to enhance the poor electronic conductivity of the NaTi2(PO4)3 anodes. In view of the advantages of the electrode architecture design, we anticipate that the nanocomposites might be promising anode materials for long-life and low-temperature rechargeable sodium-ion batteries.

Facile controlled synthesis of a hierarchical porous nanocoral-like Co3S4 electrode for high-performance supercapacitors

A facile one-step hydrothermal process is developed to synthesize a porous nanocoral-like Co3S4, which directly grows on a three dimensional (3D) macroporous nickel (Ni) foam. The scanning electron microscopy (SEM) images reveal the uniform formation of a Co3S4 nanocoral cluster on Ni foam with a hierarchical porous structure. The crystal growth mechanism and factors that influence the formation of the coral-like Co3S4 directly on Ni foam have been further studied. The subsequent electrochemical measurements demonstrate that the nanocoral-like Co3S4 as a binder-free electrode for supercapacitors possesses a large specific capacitance as high as 1559 F g−1 at a current density of 0.5 A g−1 in 2.0 M KOH aqueous electrolyte. Moreover, to confirm its practical application, an asymmetric supercapacitor is assembled with the nanocoral-like Co3S4 electrode as the positive electrode and activated carbon (AC) as the negative electrode. Such a device achieves a high energy density of 60.1 W h kg−1 at a power density of 418.2 W kg−1 and maintains 38.5 W h kg−1 at a high power density of 3812.5 W kg−1, suggesting that the presented nanocoral-like Co3S4 electrode not only has potential for applying in high energy density fields, but also in high power density applications.

Corrosion resistance of nickel foam modified with electroless Ni–P alloy as positive current collector in a lithium ion battery

We provide a novel and facile idea to enhance the corrosion resistance of nickel foam and improve the life of a positive current collector in an electrolyte containing LiPF6 salt. The crystal Ni–P alloy was prepared via an electroless Ni–P technique, combined with subsequent thermal treatment. The as-prepared crystal alloy coatings exhibit excellent stability at high operating voltages as positive current collectors in lithium ion batteries.

Li3V2(PO4)3 as a cathode additive for the over-discharge protection of lithium ion batteries

Li3V2(PO4)3 has been used as a cathode additive to make lithium ion batteries (LIBs) retain a good electrochemical performance under over-discharge conditions. Its lower discharge voltage plateau effectively prevents the corrosion of anode collector-copper foil during the over-discharge progress. When 7 wt% Li3V2(PO4)3 is added to LiCoO2 through a “layer to layer” mode, the capacity retention ratio of the LIBs has raised from 49.55% to 95.91%.