Welcome to Dr. Sun's Nanomaterials and Energy Group

Size-dependent Surface Phase Change of Lithium Iron Phosphate during Carbon Coating. J. Wang, J. Yang, Y. Tang, J. Liu, Y. Zhang, G. Liang, M. Gauthier, Y. K. Chen, M. Banis, X. Li, R. Li, J. Wang, T. -K. Sham, X. Sun, Nat. Commun. 5 (2014) 3145

View PDF

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 and extremely high stability during the carbon coating process, whereas microscale particles display a directly 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.  dfsfs

Superior Catalytic Activity of Nitrogen-doped Graphene Cathode for High Performance Sodium-Air Batteries. Y. Li, H. Yadegari, X. Li, M. Banis, R. Li, X. Sun, Chem. Commun. (2013), 49, 11731

View PDF

Nitrogen-doped graphene nanosheets (N-GNSs) displayed a discharge capacity two times greater than their pristine counterpart, as well as superior electrocatalytic activity as a cathode material for sodium–air batteries. The enhanced performance of N-GNSs is attributed to the active sites introduced by nitrogen doping.

Atomic Layer Deposition of Solid-State Electrolyte Coated Cathode Materials with Superior High-Voltage Cycling Behavior for Lithium Ion Battery Application. X. Li, J. Liu, M. Banis, A. Lushington, R. Li, M. Cai, X. Sun, Energy Environ. Sci. 7 (2) (2014) 768

View PDF

LiNi1/3Co1/3Mn1/3O2 (NMC) is a highly promising cathode material for use in lithium ion batteries; unfortunately, its poor cycling performance at high cutoff voltages hinders its commercialization. In this study, for the first time, we employ atomic layer deposition (ALD) to coat lithium tantalum oxide, a solid-state electrolyte, with varying thicknesses on NMC in an attempt to improve battery performance.

Layer by Layer Assembly of Sandwiched Graphene/SnO2 Nanowire/Carbon Nanostructures with Ultrahigh Lithium Ion Storage Properties D. Wang, J. Yang, X. Li, D. Geng, R. Li, M. Cai, T.-K. Sham, X. Sun, Energy Environ. Sci. 6 (2013) 2900

View PDF

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.

Challenges and Opportunities of Nanostructured Materials for Aprotic Rechargeable Lithium-oxygen Batteries J. Wang, Y. Li, X. Sun. Nano Energy 2 (2013) 443

View PDF

Rechargeable lithium–air (O2) batteries have received much attention due to their extremely high theoretical energy densities, which far exceeds that of current lithium-ion batteries. The considerable high energy densities come from (i) pure metal lithium as anode and (ii) the cathode oxidant, oxygen, which comes from the surrounding air. However, there are still many scientific and technical challenges especially nanomaterial challenges to overcome before it turns into reality. In this review, the fundamental principles and understanding of the electrochemical reaction in the aprotic lithium–air batteries are first presented.

Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition S. Sun , G. Zhang, N. Gauquelin, N. Chen, J. Zhou, S. Yang, W. Chen, X. Meng, D. Geng, M. Banis, R. Li, S. Ye, S. Knights, G. Botton, T.-K. Sham, X. Sun, Sci. Rep., 3 (2013) 1775.

View PDF

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle.

Porous Dendritic Platinum Nanotubes with Extremely High Activity and Stability for Oxygen Reduction Reaction G. Zhang, S. Sun, M. Cai, Y. Zhang, R. Li, X. Sun, Sci. Rep., 3 (2013) 1526.

View PDF

Controlling the morphology of Pt nanostructures can provide opportunities to greatly increase their activity and stability. Porous dendritic Pt nanotubes were successfully synthesized by a facile, cost-effective aqueous solution method at room temperature in large scale. These unique structures are porous, hollow, hierarchical, and single crystalline, which not only gives them a large surface area with high catalyst utilization, but also improves mass transport and gas diffusion.

LiFePO4/graphene as a Superior Cathode Material for Rechargeable Lithium Batteries: Impact of Stacked Graphene and Unfolded Graphene J. Yang, J. Wang, Y. Tang, D. Wang, X. Li, Y. Hu, R. Li, G. Liang, T.-K. Sham, X. Sun, Energy Environ. Sci. 6 (2013) 1521

View PDF

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 LiFePO4particle to be attached to the conducting layer, which could greatly enhance the electronic conductivity, thereby realizing the full potential of the active materials.

Tin Oxide with Controlled Morphology and Crystallinity by Atomic Layer Deposition onto Graphene Nanosheets for Enhanced Lithium Storage X. Li, X. Meng, J. Liu, D. Geng, Y. Zhang, M. Banis, Y. Li, R. Li, X. Sun, M. Cai, M. Verbrugge, Adv. Funct. Mater. 22 (2012) 1647

View PDF

As one of the most promising negative electrode materials in lithium-ion batteries (LIBs), SnO2 experiences intense investigation due to its high specific capacity and energy density, relative to conventional graphite anodes. In this study, for the first time, atomic layer deposition (ALD) is used to deposit SnO2, containing both amorphous and crystalline phases, onto graphene nanosheets (GNS) as anodes for LIBs. The resultant SnO2-graphene nanocomposites exhibit a sandwich structure, and, when cycled against a lithium counter electrode, demonstrate a promising electrochemical performance. It is demonstrated that the introduction of GNS into the nanocomposites is beneficial for the anodes by increasing their electrical conductivity and releasing strain energy: thus, the nanocomposite electrode materials maintain a high electrical conductivity and flexibility.

Understanding and Recent Development of Carbon Coating on LiFePO4 Cathode Material for Lithium-ion Batteries J. Wang, R. Li, X. Sun, Energy Environ. Sci., 5 (2012) 5163-5185.

View PDF

Olivine-structured LiFePO4 has been the focus of research in developing low cost, high performance cathode materials for lithium ion batteries. Various processes have been developed to synthesize LiFePO4 or C/LiFePO4 (carbon coating on LiFePO4), and some of them are being used to mass produce C/LiFePO4 at the commercial or pilot scale. Due to the low intrinsic electronic and ionic conductivities of LiFePO4, the decrease of particle size and the nano-layer of carbon coating on LiFePO4 particle surfaces are necessary to achieve a high electrochemical performance. Significant progress has been made in understanding and controlling phase purity, particle size and carbon coating of the C/LiFePO4 composite material in the past. However, there are still many challenges in achieving a high quality product with high consistency.

Interaction of Carbon Coating on LiFePO4: Local Visualization Study of the Influence of Impurity Phases. J. Wang, J. Yang, Y. Zhang, Y. Li, M. N. Banis, X. Li, R. Li, X. Sun, G. Liang, Adv. Funct. Mater., 23 (2013) 806

View PDF

Carbon coating is a proven successful approach for improving the conductivity of LiFePO4 used in rechargeable Li-ion batteries. Different impurity phases can be formed during LiFePO4 synthesis. Here, a direct visualization of the impact of impurity phases in LiFePO4 on a carbon coating is presented; they are investigated on a model material using various surface-characterization techniques. By using polished ingot model materials, impurity phases can be clearly observed, identified, and located on the surface of the sample by scanning electron microscopy (SEM), focused-ion-beam lithography (FIB), high-resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy. During the carbon-coating process, the phosphorus-rich phase is found to have an inhibiting effect (or no positive catalytic effect) on carbon formation, while iron-rich phases (mainly iron phosphides) promote carbon growth by contributing to more carbon deposition and a higher graphitic carbon content. This finding, and the methodological evaluation here, will help us to understand and reveal the influencing factors of impurity phases on the basic carbon-deposition process to obtain high-performance LiFePO4 material for future energy-storage devices.

Atomic Layer Deposition of Lithium Tantalate Solid-State Electrolytes. J. Liu, M. Banis, X. Li, A. Lushington, M. Cai, R. Li, T.-K. Sham, X. Sun, J. Phys. Chem. C 117 (2013) 20260

View PDF

3D all-solid-state microbatteries are promising onboard power systems for autonomous devices. The fabrication of 3D microbatteries needs deposition of active materials, especially solid-state electrolytes, as conformal and pinhole free thin films in 3D architectures, which has proven very difficult for conventional deposition techniques, such as chemical vapor deposition and physical vapor deposition. Herein, we report an alternative technique, atomic layer deposition (ALD), for achieving ideal solid-state electrolyte thin films for 3D microbatteries. Lithium tantalate solid-state electrolytes, with well-controlled film composition and film thickness, were grown by ALD at 225 °C using subcycle combination of 1 × Li2O + n × Ta2O5 (1 ≤ n ≤ 10).

Emerging Applications of Atomic Layer Dposition for Lithium-ion Battery Studies. X. Meng, X.-Q. Yang, X. Sun, Adv. Mater., 24 (2012) 3589

View PDF

Lithium-ion batteries (LIBs) are used widely in today's consumer electronics and offer great potential for hybrid electric vehicles (HEVs), plug-in HEVs, pure EVs, and also in smart grids as future energy-storage devices. However, many challenges must be addressed before these future applications of LIBs are realized, such as the energy and power density of LIBs, their cycle and calendar life, safety characteristics, and costs. Recently, a technique called atomic layer deposition (ALD) attracted great interest as a novel tool and approach for resolving these issues. In this article, recent advances in using ALD for LIB studies are thoroughly reviewed, covering two technical routes: 1) ALD for designing and synthesizing new LIB components, i.e., anodes, cathodes, and solid electrolytes, and; 2) ALD used in modifying electrode properties via surface coating. This review will hopefully stimulate more extensive and insightful studies on using ALD for developing high-performance LIBs.

A New Highly Durable Pt Nanocatalyst for PEM Fuel Cells: the Multiarmed Star-like Nanowire Single Crystal. S. Sun, G. Zhang, D. Geng, Y. Chen, R. Li, M. Cai, X. Sun, Angew. Chem. Int. Ed. 50 (2011) 422

View PDF

Carbon-supported multiarmed starlike Pt nanowires (see SEM picture) are highly active and stable electrocatalysts for proton-exchange membrane fuel cells. This novel nanostructure shows much improved activity and durability over the current commercial Pt/C catalyst made of Pt nanoparticles.

Superior Energy Capacity of Graphene Nanosheets for Nonaqueous Lithium-Oxygen Battery. Y. Li, J. Wang, X. Li, D. Geng, R. Li, X. Sun, Chem. Commun. 47 (2011) 9438

View PDF

Graphene nanosheets (GNSs) were synthesized and used as cathode active materials in a nonaqueous lithium-oxygen battery.  

The GNSs electrode delivered an extremely high discharge capacity in comparison to carbon powders, which is attributed to its unique morphology and structure.

Superior Cycle Stability of Nitrogen-doped Graphene Nanosheets as Anode for Lithium Ion Batteries. X. Li, D. Geng, Y. Zhang, X. Meng, R. Li, X. Sun, Electrochem. Commun., 13 (2011) 822

View PDF

The specific capacity of nitrogen-doped graphene nanosheet (N-GNS) evidently increases with charge/discharge cycles, exhibiting superior electrochemical performance. N-GNS presented a specific capacity of 684 mAh g− 1 in the 501st cycles while only 452 mAh g− 1 in the 100th cycle, accounting for higher cycling stability and larger specific capacity in comparison to a pristine graphene and a commercialized graphite anode. The obtained significant improvement is attributed to the incorporated nitrogen to graphene planes with a result of more structural defects during cycling.

High Oxygen-reduction Activity and Durability of Nitrogen-doped Graphene. D. Geng, Y. Chen, Y. Chen, Y. Li, R. Li, X. Sun, S. Ye, S. Knights, Energy Environ. Sci. 4 (2011) 760

View PDF

Structural and Morphological Control, Nitrogen Incorporation and Stability of Aligned Nitrogen-Doped Carbon Nanotubes. H. Liu, Y. Zhang, R. Li, X. Sun, D. Désilets, H. Abou-Rachid, Carbon 48 (2010) 1498

View PDF

Nitrogen-doped carbon nanotubes (CNx–NTs) were prepared using a floating catalyst chemical vapor deposition method. Melamine precursor was employed to effectively control nitrogen content within the CNx–NTs and modulate their structure. X-ray photoelectron spectroscopy (XPS) analysis of the nitrogen bonding demonstrates the nitrogen-incorporation profile according to the precursor amount, which indicates the correlation between the nitrogen concentration and morphology of nanotubes. With the increase of melamine amount, the growth rate of nanotubes increases significantly, and the inner structure of CNx–NTs displayed a regular morphology transition from straight and smooth walls (0 at.% nitrogen) to cone-stacked shapes or bamboo-like structure (1.5%), then to corrugated structures (3.1% and above). Both XPS and CHN group results indicate that the nitrogen concentration of CNx–NTs remained almost constant even after exposing them to air for 5 months, revealing superior nitrogen stability in CNTs. Raman analysis shows that the intensity ratio of D to G bands (ID/IG) of nanotubes increases with the melamine amount and position of G-band undergoes a down-shift due to increasing nitrogen doping. The aligned CNx–NTs with modulated morphology, controlled nitrogen concentration and superior stability may find potential applications in developing various nanodevices such as fuel cells and nanoenergetic functional components.

High Loading of Pt Nanoparticles on Carbon Nanotubes as Electrodes for PEM Fuel Cells. M. Saha, R. Li, X. Sun, J. Power Sources 177 (2008) 314 View PDF     Composite electrodes consisting of Pt nanoparticles-supported on multiwalled carbon nanotubes grown directly on carbon paper (Pt/CNTs/carbon paper) have been synthesized by a new method using glacial acetic acid as a reducing agent. Transmission electron microscopy (TEM) images show that the Pt nanoparticles with high density and relative small in size (2–4 nm) were monodispersed on the surface of CNTs. X-ray photoelectron spectroscopy (XPS) analysis indicates that the glacial acetic acid acts as a reducing agent and has the capability of producing a high density of oxygen-containing functional groups on the surface of CNTs that leads to high density and monodispersion of Pt nanoparticles. Compared with standard Pt/C electrode, the Pt/CNT/carbon paper composite electrodes exhibit higher electrocatalytic activity for methanol oxidation reaction and higher single-cell performance in a H2/O2 fuel cell.

An Electrochemical Avenue to Blue Luminescencent Nanocrystals from Multiwalled Carbon Nanotubes (MWCNTs). J. Zhou, C. Booker, R. Li, X. Zhou, T.-K. Sham, X. Sun, Z. Ding, J. Am. Chem. Soc. 129 (2007) 744

View PDF

We have developed a method by employing electrochemistry to convert MWNTs into highly efficient luminescent carbon NCs, which can be easily dispersed in various solvents. It is anticipated that these NCs will find a wealth of applications in biology labeling and optoelectronic devices.

Notice to the web visitors:
Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the publisher and the web site owner.