Wang Sun

Three-dimensional graphene–Co3O4 cathodes for rechargeable Li–O2 batteries

A three-dimensional (3D) graphene–Co3O4 electrode was prepared by a two-step method in which graphene was initially deposited on a Ni foam with Co3O4 then grown on the resulting graphene structure. Cross-linked Co3O4 nanosheets with an open pore structure were fully and vertically distributed throughout the graphene skeleton. The free-standing and binder-free monolithic electrode was used directly as a cathode in a Li–O2 battery. This composite structure exhibited enhanced performance with a specific capacity of 2453 mA h g−1 at 0.1 mA cm−2 and 62 stable cycles with 583 mA h g−1 (1000 mA h gcarbon−1). The excellent electrochemical performance is associated with the unique architecture and superior catalytic activity of the 3D electrode.

Ultrastrong Polyoxyzole Nanofiber Membranes for Dendrite-Proof and Heat-Resistant Battery Separators

Polymeric nanomaterials emerge as key building blocks for engineering materials in a variety of applications. In particular, the high modulus polymeric nanofibers are suitable to prepare flexible yet strong membrane separators to prevent the growth and penetration of lithium dendrites for safe and reliable high energy lithium metal-based batteries. High ionic conductance, scalability, and low cost are other required attributes of the separator important for practical implementations. Available materials so far are difficult to comply with such stringent criteria. Here, we demonstrate a high-yield exfoliation of ultrastrong poly(p-phenylene benzobisoxazole) nanofibers from the Zylon microfibers. A highly scalable blade casting process is used to assemble these nanofibers into nanoporous membranes. These membranes possess ultimate strengths of 525 MPa, Youngs moduli of 20 GPa, thermal stability up to 600 °C, and impressively low ionic resistance, enabling their use as dendrite-suppressing membrane separators in electrochemical cells. With such high-performance separators, reliable lithium-metal based batteries operated at 150 °C are also demonstrated. Those polyoxyzole nanofibers would enrich the existing library of strong nanomaterials and serve as a promising material for large-scale and cost-effective safe energy storage.

Facile Synthesis of Hierarchical Porous Three-Dimensional Free-Standing MnCo2O4 Cathodes for Long-Life Li—O2 Batteries

Hierarchical porous three-dimensional MnCo2O4 nanowire bundles were obtained by a universal and low-cost hydrothermal method, which subsequently act as a carbon-free and binder-free cathode for Li-O2 cell applications. This system showed a high discharge capacity of up to 12 919 mAh g-1 at 0.1 mA cm-2 and excellent rate capability. Under constrained specific capacities of 500 and 1000 mAh g-1, Li-O2 batteries could be successfully operated for over 300 and 144 cycles, respectively. Moreover, their charge voltage was markedly decreased to about 3.5 V. Their excellent electrochemical performance is proposed to be related to the conductivity enhancements resulting from the hierarchical interconnected mesoporous/macroporous weblike structure of the hybrid MnCo2O4 cathode, which facilitated the electron and mass transport. More importantly, after 2 months of cycling, the microstructure of the cathode was maintained and a recyclability of over 200 cycles of the reassembled Li-O2 cells was achieved. The effects of the level of electrolyte and corrosion of the lithium anode during long-term cycling on the electrochemical property of Li-O2 cells have been explored. Furthermore, the nucleation process of the discharge product morphology has been investigated.

Synthesis and characterization of B-site Ni-doped perovskites Sr2Fe1.5−xNixMo0.5O6−δ (x = 0, 0.05, 0.1, 0.2, 0.4) as cathodes for SOFCs

Sr2Fe1.5−xNixMo0.5O6−δ (x = 0, 0.05, 0.1, 0.2, 0.4) (SFNM) materials have been synthesized by a sol–gel combustion method and studied towards application as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). The crystal structure, microstructure, thermal expansion, element valence, conductivity and electrochemical properties have been characterized as a function of Ni content. The symmetrical structure of the cubic lattice in perovskite oxides is confirmed. SFNM powders possess the 3D interconnected network microstructure composed of nanoparticles. An increasing Ni substitution results in the unit cell shrinkage and the increase of thermal expansion coefficient (TEC). Furthermore, X-ray photoelectron spectroscopy (XPS) analysis shows that Ni basically exhibits a low oxidation state (Ni2+). Doped Ni2+ affects the equilibrium between Fe3+/Mo5+ and Fe2+/Mo6+, which is directly related to the conductivity. The SFNM conductivity was apparently improved, reaching 60 S cm−1 at 450 °C when x = 0.1, which is more than twice that of the Sr2Fe1.5Mo0.5O6−δ (SFM) sample. In addition, Sr2Fe1.4Ni0.1Mo0.5O6−δ (SFN0.1M) cathodes showed excellent electrochemical performance and lowest interface polarization resistance (Rp). The Rp of the SFN0.1M cathode was approximately 50% of that of the SFM cathode. Moreover, the maximum power densities of a single cell based on the SFN0.1M cathode were 0.92, 1.27 W cm−2 at 700, 750 °C, respectively. The SFNM material is a type of potential cathode for IT-SOFCs.

Investigation into the effect of Fe-site substitution on the performance of Sr2Fe1.5Mo0.5O6−δ anodes for SOFCs

Ni-substituted Sr2Fe1.5−xNixMo0.5O6−δ (SFNM) materials have been investigated as anode catalysts for intermediate temperature solid oxide fuel cells. Reduced samples (x = 0.05 and 0.1) maintained the initial perovskite structure after reduction in H2, while metallic nickel particles were detected on the grain surface for x = 0.2 and 0.3 using transmission electron microscopy. Temperature programmed reduction results indicate that the stable temperature for SFNM samples under reduction conditions decreases with Ni content. In addition, X-ray photoelectron spectroscopy analysis suggests that the incorporation of Ni affects the conductivity of SFNM through changing the ratios of Fe3+/Fe2+ and Mo6+/Mo5+. Sr2Fe1.4Ni0.1Mo0.5O6−δ shows the highest electrical conductivity of 20.6 S cm−1 at 800 °C in H2. The performance of this anode was further tested with electrolyte-supported cells, giving 380 mW cm−2 at 750 °C in H2, hence demonstrating that Ni doping in the B-site is beneficial for Sr2Fe1.5Mo0.5O6−δ anode performance.

Inspired by the “tip effect”: a novel structural design strategy for the cathode in advanced lithium–sulfur batteries

Inspired by the “tip effect”, we demonstrate that hollow cupric oxide spheres (HCOS) built from abundant protrusive crystal strips can be used as an effective host for Li–S batteries. The battery based on this novel host retained an excellent cycle performance over 500 cycles and delivered an improved rate capability.

Achieving high specific capacity of lithium-ion battery cathodes by modification with “N–O˙” radicals and oxygen-containing functional groups

Enhancing the cathode capacity of lithium ion batteries (LIBs) has been one strategy to improve the energy density of batteries for electric vehicle applications, because of the limitation of inorganic cathode capacity. Here, we developed a new strategy to construct high capacity cathodes by using NMP pyrolysis to grow oxygen-containing functional groups on the Super P carbon black (SP) surface coated on commercial LiFePO4 (cLFP). Structural characterization using electron spin resonance (ESR) and X-ray photoelectron spectroscopy (XPS) showed that “N–O˙” and “CO” groups were present on the SP surface of cLFP@SP. The redox reaction occurred on these oxygen-containing functional groups and provided the excess capacity, allowing the composite cLFP@SP to achieve a capacity of 190 mA h g−1, which is higher than the theoretical maximum capacity of 170 mA h g−1. This work provides a new approach for enhancing cathode capacity by incorporating suitable “N–O˙” radicals and oxygen-containing functional groups on the surface of cathodes.

Hierarchical hollow nanofiber networks for high-performance hybrid direct carbon fuel cells

Herein, we demonstrated a new strategy for the development of Ce0.6Mn0.3Fe0.1O2 hierarchically structured porous hollow nanofibers tailored as efficient anodes for hybrid direct carbon fuel cells. The cell based on the as-optimized anode delivered an excellent electrochemical performance and achieved a good long-term stability.

A heterogenized Ni-doped zeolitic imidazolate framework to guide efficient trapping and catalytic conversion of polysulfides for greatly improved lithium–sulfur batteries

While lithium–sulfur (Li–S) batteries are poised to be the next generation of high-density energy storage devices, the intrinsic polysulfide shuttle has limited their practical applications. In order to fundamentally solve the problem, a well-designed host to simultaneously meet the requirements for both sufficient surface reaction and efficient conversion of polysulfides is urgently demanded. Herein, a 3D heterogeneous sulfur host, termed Ni-ZIF-8@CC, is fabricated by in situ deposition of nickel-doped zeolitic imidazolate framework-8 (Ni-ZIF-8) on carbon cloth (CC). Spectroscopic investigations show that polysulfides can be strongly adsorbed by the Ni-ZIF-8@CC host through the synergy between Ni–S and Li–N interactions, which is also verified by DFT simulations. The doped electrocatalytically active nickel species could furthermore significantly facilitate the kinetics of polysulfide redox reaction, attributed to fast lithium ion diffusion and reduced polarization potential. By combining these advantages, the electrodes exhibit a high areal capacity of up to 6.04 mA h cm−2 together with excellent cycling stabilities.

Preparation and Performance Characterization of a Large Area ScSZ Electrolyte Substrate

A thin ScSZ electrolyte with a large area was synthesized using the tape-casting method. The conductivity of 0.095 S cm-1 at 800°C was achieved. The maximum power density of a single cell reached 368 mW cm-1 at 800°C. To make a large electrolyte battery more suitable, our study improves the casting method of preparing a dense, porous electrolyte substrate that promotes surface roughness of the electrolyte. However, it is difficult to control the thickness of the substrate, meaning that further improvements are needed.