Bote Zhao

Binder-free α-MoO3 nanobelt electrode for lithium-ion batteries utilizing van der Waals forces for film formation and connection with current collector

We demonstrate a facile and effective way for the fabrication of a flexible, homogeneous and neat α-MoO3 thin-film electrode for lithium-ion batteries with high performance without using any binder and conductive additives. Single-crystalline α-MoO3 nanobelts with uniform width of around 200 nm and length at the micrometer level are first synthesized by a simple water-based hydrothermal route. The as-obtained α-MoO3 slurry is then directly deposited onto a copper foil current collector by the doctor blade method. The formation of the α-MoO3 film and its good adhesion to the current collector is realized via van der Waals attraction forces through a drying process. The structure and morphology of the α-MoO3 nanobelt particles and thin-film electrode are systematically characterized by XRD, Raman spectra, TEM, SEM and XPS techniques, and the electrochemical properties are investigated by CV and constant current discharge–charge test techniques. The α-MoO3 film electrode exhibits a reversible specific capacity of ∼1000 mA h g−1 at 50 mA g−1 and a stable capacity retention of 387–443 mA h g−1 at 2000 mA g−1, indicating its high Li storage capacity, superior rate performance and good cycling stability. The electrode material, as well as the fabrication technique, is highly promising for practical use in high energy and power density lithium-ion batteries.

Dramatically enhanced reversibility of Li2O in SnO2-based electrodes: the effect of nanostructure on high initial reversible capacity

The formation of irreversible Li2O during discharge is believed to be the main cause of large capacity loss and low Coulombic efficiency of oxide negative electrodes for Li batteries. This assumption may have misguided the development of high-capacity SnO2-based anodes in recent years. Here we demonstrated that contrary to this perception, Li2O can indeed be highly reversible in a SnO2 electrode with controlled nanostructure and achieved an initial Coulombic efficiency of ∼95.5%, much higher than that previously believed to be possible (52.4%). In situ spectroscopic and diffraction analyses corroborate highly reversible electrochemical cycling, suggesting that the interfaces and grain boundaries of nano-sized SnO2 may suppress the coarsening of Sn and enable the conversion between Li2O and Sn to amorphous SnO2 when de-lithiated. These results provide important insight into the rational design of high-performance oxide electrodes for Li-ion batteries.

High-Performance Energy Storage and Conversion Materials Derived from a Single Metal–Organic Framework/Graphene Aerogel Composite

Metal oxides and carbon-based materials are the most promising electrode materials for a wide range of low-cost and highly efficient energy storage and conversion devices. Creating unique nanostructures of metal oxides and carbon materials is imperative to the development of a new generation of electrodes with high energy and power density. Here we report our findings in the development of a novel graphene aerogel assisted method for preparation of metal oxide nanoparticles (NPs) derived from bulk MOFs (Co-based MOF, Co(mIM)2 (mIM = 2-methylimidazole). The presence of cobalt oxide (CoOx) hollow NPs with a uniform size of 35 nm monodispersed in N-doped graphene aerogels (NG-A) was confirmed by microscopic analyses. The evolved structure (denoted as CoOx/NG-A) served as a robust Pt-free electrocatalyst with excellent activity for the oxygen reduction reaction (ORR) in an alkaline electrolyte solution. In addition, when Co was removed, the resulting nitrogen-rich porous carbon-graphene composite electrode (denoted as C/NG-A) displayed exceptional capacitance and rate capability in a supercapacitor. Further, this method is readily applicable to creation of functional metal oxide hollow nanoparticles on the surface of other carbon materials such as graphene and carbon nanotubes, providing a good opportunity to tune their physical or chemical activities.

Facile Mechanochemical Synthesis of Nano SnO2/Graphene Composite from Coarse Metallic Sn and Graphite Oxide: An Outstanding Anode Material for Lithium‐Ion Batteries

A facile method for the large-scale synthesis of SnO2 nanocrystal/graphene composites by using coarse metallic Sn particles and cheap graphite oxide (GO) as raw materials is demonstrated. This method uses simple ball milling to realize a mechanochemical reaction between Sn particles and GO. After the reaction, the initial coarse Sn particles with sizes of 3-30 μm are converted to SnO2 nanocrystals (approximately 4 nm) while GO is reduced to graphene. Composite with different grinding times (1 h 20 min, 2 h 20 min or 8 h 20 min, abbreviated to 1, 2 or 8 h below) and raw material ratios (Sn:GO, 1:2, 1:1, 2:1, w/w) are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy and transmission electron microscopy. The as-prepared SnO2 /graphene composite with a grinding time of 8 h and raw material ratio of 1:1 forms micrometer-sized architected chips composed of composite sheets, and demonstrates a high tap density of 1.53 g cm(-3). By using such composites as anode material for LIBs, a high specific capacity of 891 mA h g(-1) is achieved even after 50 cycles at 100 mA g(-1).

A tailored double perovskite nanofiber catalyst enables ultrafast oxygen evolution

Rechargeable metal–air batteries and water splitting are highly competitive options for a sustainable energy future, but their commercialization is hindered by the absence of cost-effective, highly efficient and stable catalysts for the oxygen evolution reaction. Here we report the rational design and synthesis of a double perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+δ nanofiber as a highly efficient and robust catalyst for the oxygen evolution reaction. Co-doping of strontium and iron into PrBaCo2O5+δ is found to be very effective in enhancing intrinsic activity (normalized by the geometrical surface area, ∼4.7 times), as validated by electrochemical measurements and first-principles calculations. Further, the nanofiber morphology enhances its mass activity remarkably (by ∼20 times) as the diameter is reduced to ∼20 nm, attributed to the increased surface area and an unexpected intrinsic activity enhancement due possibly to a favourable eg electron filling associated with partial surface reduction, as unravelled from chemical titration and electron energy-loss spectroscopy.

A novel method to enhance rate performance of an Al-doped Li4Ti5O12 electrode by post-synthesis treatment in liquid formaldehyde at room temperature

An amenable method for improving rate performance of Li4Ti4.85Al0.15O12 electrode by post-synthesis treatment in formaldehyde aqueous solution at room temperature is introduced. The as-prepared samples are characterized by XRD, BET, SEM, HR-TEM, XPS and electronic conductivity measurement. The treatment causes no noticeable change on the phase structure and has only little effect on the specific surface area and particulate morphologies. It also only slightly decreases the lithium ion diffusion coefficient. However, it substantially increases the electronic conductivity due to the creation of Ti3+ in the oxide lattice. The post-synthesis treatment for a period of 4 h effectively increases the capacity at 10 C rate for Li4Ti4.85Al0.15O12 from 125 mA h g−1 for the untreated sample to 160 mA h g−1, and the electrode performance is also fairly stable. This method is highly attractive for synthesis of high-performance Li4Ti5O12 electrodes owing to its simplicity, energy saving and efficiency. As a general method, post-synthesis treatment using formaldehyde may be applicable to other electrodes.

Synthesis of well-crystallized Li4Ti5O12 nanoplates for lithium-ion batteries with outstanding rate capability and cycling stability

As a lithium-intercalation material, high crystallinity is important for Li4Ti5O12 to achieve good capacity and cycling stability, while a large surface area and a short lithium diffusion distance are critical to increase rate capacity. In this study, well-crystallized Li4Ti5O12 nanoplates with outstanding electrochemical performance were facially prepared through a two-step hydrothermal preparation with benzyl alcohol–NH3·H2O (BN) as the solvent and a subsequent intermediate-temperature calcination at 500 °C for 2 h in air. To support the superiority of benzyl alcohol–NH3·H2O (BN) for hydrothermal synthesis, ethanol–NH3·H2O (EN) was also comparatively studied as solvent. In addition, different hydrothermal reaction times were tried to locate the optimal reaction time. The nature of as-prepared Li4Ti5O12–BN (LTO–BN) and Li4Ti5O12–EN (LTO–EN) was characterized by XRD, N2 adsorption/desorption tests, SEM, TEM and TGA-DSC. Compared with EN, the BN hydrothermal solvent facilitated the formation of nanosheet-Li4Ti5O12 with wall thicknesses of 8–15 nm and better crystallization. After a 6 h hydrothermal reaction at 180 °C and subsequent calcination, well-crystallized Li4Ti5O12–BN nanoplates were produced, which demonstrate a superior discharge capacity of 160 mA h g−1, even at 40 C, maintaining a capacity of 88.8% compared with that at 1 C. The nanoplates also exhibited excellent cycling stability, retaining a discharge capacity of 153 mA h g−1 after 1000 charge–discharge cycles at 10 C.

Solution combustion synthesis of high-rate performance carbon-coated lithium iron phosphate from inexpensive iron (III) raw material

A facile way for the synthesis of LiFePO4 composite using a solution combustion technique based on the glycine–nitrate process with inexpensive iron (III) as the raw material is introduced. Pure phase LiFePO4 was obtained at an optimal glycine to LiFePO4 ratio of 4:1. To further increase the electrode performance, sucrose is applied as an organic carbon source. The introduction of sucrose after the auto-combustion is found to be the most effective way in improving electrode performance. The as-synthesized LiFePO4/C sample contained about 2.86 wt.% carbon shows an attractive discharge capacity of about 160 mA h g−1 at a 0.1 C rate and retains a capacity of 110 mA h g−1 at a 5 C rate. In addition, the electrodes show excellent cycling performance during the 90 cycles at various rates. The rate limiting step for the electrode reaction is explored with the chronoamperometry technique and it demonstrates the surface kinetics is effectively improved for the LiFePO4 electrode modified with a proper amount of carbon.

Amorphous V–O–C composite nanofibers electrospun from solution precursors as binder- and conductive additive-free electrodes for supercapacitors with outstanding performance

Flexible V-O-C composite nanofibers were fabricated from solution precursors via electrospinning and were investigated as free-standing and additive-free film electrodes for supercapacitors. Specifically, composite nanofibers (V0, V5, V10 and V20) with different vanadyl acetylacetonate (VO(acac)2) contents of 0, 5, 10 and 20 wt% with respect to polyacrylonitrile (PAN) were prepared. The composite nanofibers were comparatively studied using XRD, Raman spectroscopy, XPS, N2 adsorption-desorption, FE-SEM, TEM and S-TEM. The vanadium element was found to be well-dispersed in the carbon nanofibers, free from the formation of an aggregated crystalline phase, even in the case of V20. A specific surface area of 587.9 m(2) g(-1) was reached for V10 after calcination, which is approximately twice that of the vanadium-free carbon nanofibers (V0, 300.9 m(2) g(-1)). To perform as an electrode for supercapacitors in an aqueous electrolyte, the V10 film delivered a specific capacitance of 463 F g(-1) at 1 A g(-1). V10 was also able to retain a specific capacitance of 380 F g(-1), even at a current density of 10 A g(-1). Additionally, very stable cycling stability was achieved, maintaining an outstanding specific capacitance of 400 F g(-1) at 5 A g(-1) after charge-discharge cycling 5000 times. Thus, V-O-C composite nanofibers are highly attractive electrode materials for flexible, high-power, thin film energy storage devices and applications.

Harnessing the concurrent reaction dynamics in active Si and Ge to achieve high performance lithium-ion batteries

Advanced composite electrodes containing multiple active components are often used in lithium-ion batteries for practical applications. The performance of such heterogeneous composite electrodes can in principle be enhanced by tailoring the concurrent reaction dynamics in multiple active components for promoting their collective beneficial effects. However, the potential of this design principle has remained uncharted to date. Here we develop a composite anode of Cu/Si/Ge nanowire arrays, where each nanowire consists of a core of Cu segments and a Si/Ge bilayer shell. This unique electrode architecture exhibited a markedly improved electrochemical performance over the reference Cu/Si systems, demonstrating a stable capacity retention (81% after 3000 cycles at 2C) and doubled specific capacity at a rate of 16C (1C = 2 A g−1). By using in situ transmission electron microscopy and electrochemical testing, we unravel a novel reaction mechanism of dynamic co-lithiation/co-delithiation in the active Si and Ge bilayer, which is shown to effectively alleviate the electrochemically induced mechanical degradation and thus greatly enhance the long-cycle stability of the electrode. Our findings offer insights into a rational design of high-performance lithium-ion batteries via exploiting the concurrent reaction dynamics in the multiple active components of composite electrodes.