Jinli Yang

Layer by layer assembly of sandwiched graphene/SnO2 nanorod/carbon nanostructures with ultrahigh lithium ion storage properties

Sandwiched structures consisting of carbon coated SnO2 nanorod grafted on graphene have been synthesized based on a seed assisted hydrothermal growth to form graphene supported SnO2 nanorods, followed by a nanocarbon coating. As a potential anode for high power and energy applications, the hierarchical nanostructures exhibit a greatly enhanced synergic effect with an extremely high lithium storage capability of up to 1419 mA h g−1 benefiting from the advanced structural features.

LiFePO4–graphene as a superior cathode material for rechargeable lithium batteries: impact of stacked graphene and unfolded graphene

In this work, we describe the use of unfolded graphene as a three dimensional (3D) conducting network for LiFePO4 nanoparticle growth. Compared with stacked graphene, which has a wrinkled structure, the use of unfolded graphene enables better dispersion of LiFePO4 and restricts the LiFePO4 particle size at the nanoscale. More importantly, it allows each LiFePO4 particle to be attached to the conducting layer, which could greatly enhance the electronic conductivity, thereby realizing the full potential of the active materials. Based on its superior structure, after post-treatment for 12 hours, the LiFePO4–unfolded graphene nanocomposite achieved a discharge capacity of 166.2 mA h g−1 in the 1st cycle, which is 98% of the theoretical capacity (170 mA h g−1). The composite also displayed stable cycling behavior up to 100 cycles, whereas the LiFePO4–stacked graphene composite with a similar carbon content could deliver a discharge capacity of only 77 mA h g−1 in the 1st cycle. X-ray absorption near-edge spectroscopy (XANES) provided spectroscopic understanding of the crystallinity of LiFePO4 and chemical bonding between LiFePO4 and unfolded graphene.

Hierarchically porous LiFePO4/nitrogen-doped carbon nanotubes composite as a cathode for lithium ion batteries

A porous composite of LiFePO4/nitrogen-doped carbon nanotubes (N-CNTs) with hierarchical structure was prepared by a sol–gel method without templates or surfactants. Highly conductive and uniformly dispersed N-CNTs incorporated into three dimensional interlaced porous LiFePO4 can facilitate the electronic and lithium ion diffusion rate. The LiFePO4/N-CNTs composites deliver a reversible discharge capacity of 138 mA h g−1 at a current density of 17 mA g−1 while the LiFePO4/CNTs composites only deliver 113 mA h g−1, demonstrating N-CNTs modified composites can act as a promising cathode for high-performance lithium-ion batteries.

Hierarchical nanostructured core-shell Sn@C nanoparticles embedded in graphene nanosheets: spectroscopic view and their application in lithium ion batteries.

Hierarchical carbon encapsulated tin (Sn@C) embedded graphene nanosheet (GN) composites (Sn@C-GNs) have been successfully fabricated via a simple and scalable one-step chemical vapor deposition (CVD) procedure. The GN supported Sn@C core-shell structures consist of a crystalline tin core, which is thoroughly covered by a carbon shell and more interestingly, extra voids are present between the carbon shell and the tin core. Synchrotron spectroscopy confirms that the metallic tin core is free of oxidation and the existence of charge redistribution transfer from tin to the carbonaceous materials of the shell, facilitating their intimate contact by chemical bonding and resultant lattice variation. The hybrid electrodes of this material exhibit a highly stable and reversible capacity together with an excellent rate capability, which benefits from the improved electrochemical properties of tin provided by the protective carbon matrix, voids and the flexible GN matrices.

Novel approach toward a binder-free and current collector-free anode configuration: highly flexible nanoporous carbon nanotube electrodes with strong mechanical strength harvesting improved lithium storage

In this work, we developed a novel flexible nanoporous carbon nanotube film to use as a binder-free and current collector-free anode electrode for lithium ion batteries, providing a new approach to flexible energy devices. The proposed novel anode configuration shows better cycling performance and rate capability than the conventional electrode architecture. Moreover, this unique configuration exhibits good flexibility and robust mechanical strength, which has the potential to be applied to flexible lithium ion batteries. Our findings may provide a new anode configuration for lithium ion batteries with improved cycling stability and rate capability.

Surface aging at olivine LiFePO4: a direct visual observation of iron dissolution and the protection role of nano-carbon coating

LiFePO4 has attracted much attention as a potential cathode material for advanced lithium-ion batteries due to its superior thermal stability. In spite of this, LiFePO4 still suffers from fast capacity fading at high temperature and/or moisture-contaminated electrolyte. The influence of moisture and the detailed corrosion mechanism is still not clear. Here, for the first time, we present a direct visual observation of the surface corrosion process at olivine LiFePO4 stored in moisture-contaminated electrolyte, and found the direct relationship between iron dissolution and LiFePO4 corrosion. By using the LiFePO4 ingot sample with a flat surface as model materials, iron dissolution and surface chemistry change can be clearly observed and identified by field-emission scanning electron microscopy (SEM), time-of-flight-secondary ion mass spectroscopy (TOF-SIMS), and X-ray absorption near-edge structure (XANES). These iron dissolutions at some corrosion sites evoked the overall LiFePO4 surface corrosion. A significant improvement of the surface stability of LiFePO4 was obtained by nano-carbon coating, and the carbon surface layer protects LiFePO4 from direct contact with corrosive medium, effectively restraining the surface corrosion and preserving the initial surface chemistry of LiFePO4.

In situ self-catalyzed formation of core–shell LiFePO4@CNT nanowires for high rate performance lithium-ion batteries

In situ self-catalyzed core–shell LiFePO4@CNT nanowires can be fabricated by a two-step synthesis, where one-dimensional LiFePO4 nanowires with a diameter of 20–30 nm were encapsulated into CNTs, and 3D conducting networks of CNTs were obtained from in situ carbonization of a polymer. LiFePO4@CNT nanowires deliver a capacity of 160 mA h g−1 at 17 mA g−1, and 65 mA h g−1 at 8500 mA g−1 (50 C, 1.2 minutes for charging and 1.2 minutes for discharging).

Atomic layer deposited coatings to significantly stabilize anodes for Li ion batteries: effects of coating thickness and the size of anode particles

A study of the effect of thickness of alumina coating on the electrochemical performances of various sizes of SnO2 electrodes has been systematically studied in this paper. It is found that the different volume changes in various sizes of SnO2 electrodes can be suppressed by optimized thickness of Al2O3 coating layers, with a range from less than 1 nm to up to 3 nm deposited by atomic layer deposition (ALD), which have significant impact on the electrochemical behaviour of the composites. The well-defined and optimized Al2O3 layer could not only relieve mechanical degradation and improve cycling stability, but also form an artificial solid electrolyte interphase (SEI) layer to prevent the chemical reaction between SnO2 and the electrolyte, leading to improved electrochemical performances compared with bare SnO2 electrodes.

Size-dependent surface phase change of lithium iron phosphate during carbon coating

Carbon coating is a simple, effective and common technique for improving the conductivity of active materials in lithium ion batteries. However, carbon coating provides a strong reducing atmosphere and many factors remain unclear concerning the interface nature and underlying interaction mechanism that occurs between carbon and the active materials. Here, we present a size-dependent surface phase change occurring in lithium iron phosphate during the carbon coating process. Intriguingly, nanoscale particles exhibit an extremely high stability during the carbon coating process, whereas microscale particles display a direct visualization of surface phase changes occurring at the interface at elevated temperatures. Our findings provide a comprehensive understanding of the effect of particle size during carbon coating and the interface interaction that occurs on carbon-coated battery material--allowing for further improvement in materials synthesis and manufacturing processes for advanced battery materials.

Atomic layer deposited Li4Ti5O12 on nitrogen-doped carbon nanotubes

Atomic layer deposition was used for the synthesis of ternary spinel Li4Ti5O12 compounds on nitrogen-doped carbon nanotubes, featuring its accurate tunability of elemental compositions.