1. Energy Storage and Conversion

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• Introduction

Rechargeable batteries are critical to our life and also play a significant role in power supplies for various electric vehicles. The increasing demands of high energy batteries require the development of high capacity electrode materials and high voltage cathodes. In this field, our research has been focused on developing next-generation efficient advanced cathodes/anode for Li ion batteries and beyond lithium ion batteries (e.g, Sodium ion batteries, Li-sulfur batteries). For instance, in our previous efforts, we develop a novel atomic-level multiple-element method to dope the LCO crystal structure with multiple elements. The resulting doped LiCoO2 can withstand the increase in cell potential and still allow efficient lithium ion transport at high voltage, which exhibits extraordinary electrochemical performance: a high capacity of 190 mAh/g, approaching 70% of theoretical specific capacity of LiCoO2; a long cyclability (96% capacity retention over 50 cycles with a cut-off voltage of 4.5 V vs Li/Li+); and significantly enhanced rate capability. Such performance is the result of the combined effects of multiple doping elements on structural stability and lithium ion diffusion, which is supported via various electrochemical studies and synchrotron-based characterization. Especially, during the high voltage range, the O3-O6(H1-3)-O1 and order/disorder phase transition has been greatly suppressed.

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So in the my future study, our research will continue to focus on new cathodes such as  high-voltage LiCoO2, the lithium-rich layered metal oxides,Ni-rich cathode materials, etc; anode (Si, Li metal; hard carbon and SnO2 etc); solid state electrolytes and polymer based additives. Their synthetic, structural, electrochemical, property-structure-performance relationship,and safety properties will be studied extensively via a variety of characterization techniques, especially the advanced synchrotron and neutron scattering techniques. 

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• Research Topic

1. High-Capacity Cathode/Anode Materials

2. High-Voltage Cathode Materials

3. New Na-ion electrode materials 

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• Further Reading

1. "Graphene-Modified Nanostructured Vanadium pentoxide Hybrids  with Extraordinary Electrochemical Performance for Li-Ion  Batteries" Qi Liu, et al., Nature Communications, 2015, 6, 6127.  [View]

2. "Approaching the Capacity Limit of Lithium Cobalt Oxide in Lithium Ion Batteries via Lanthanum and Aluminum Doping". Qi Liu, et al., Nature Energy, 2018, 3, 936-943.  [View]

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2. Battery Safety

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• Introduction

The safety of Li ion battery is critical for its application. In 2013, the safety incident of Li ion batteries caused the damage to a multi-million dollar system in Boeing 787. Very recently, the explosion incidents of Li ion batteries in Electrical Vehicles have attracted much media and legal attention. To mitigate the safety problem, it is of scientific and engineering importance to understand the Li insertion/extraction mechanism and failure mechanism during the normal cycle. In our previous effort, we were working on the investigation of the Li ion battery failure mechanism for LiFePO4 so that we could get the fundamental understanding of what are the causes of the failure and how the failure was evolving. Several papers have been published in this field (JECS. 2015, 162, A2195, ACS Applied Materials Interfaces., 2014, 6, 3282, JECS. 2014, 161, A620, JECS. 2013, 160, A793, JECS. 2012, 159, A678, ACS Applied  Materials and Interface, 2018, 10, 4622). 

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Any failure is rooted in the materials structural change of Li ion batteries. Our hypotheses were: (1) Li+ ion may deposit as Li metal on the anode (cathode) as the anode is overcharged. The metallic Li may react with electrolyte or form dendrites to cause the internal short-circuit. (2) Li+ ion diffusion within the solid electrode may be hindered by the micro-structural change, (collapse of lattice due to mechanical expansion/contraction). The structure deterioration might cause the slow increase of diffusion resistance which was slowly evolving into a diffusion barrier causing the increase of internal impedance. In my future study, our research will continue to focus on developing advanced diagnostics to determine Li-ion cell failure mechanism; performing fundamental studies of safety issue of Li-ion and Na-ion batteries. Typically, the advanced synchrotron and neutron scattering techniques will be applied. The electrochemical experiment coupled with the in situ X-rays/neutron should be able to provide the information on the structure-property-performance of Li ion battery and elucidate the failure mechanism. The results will be used to develop an early detection and protection system to prevent the occurrence of the Li ion battery failure.

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• Research Topic

1. Taking a Comprehensive and Systematic Approach to Study the Failure Mechanism of LIBs

2. Developing an Early Detection and Protection System to prevent the Occurrence of the LIBs Failure

 

• Further Reading

1. "Failure Study of Commercial LiFePO4 Cells in Over-Discharge Conditions Using Electrochemical Impedance  Spectroscopy". Yadong Liu, Qi Liu, et al., Journal of the Electrochemical Society, 2015, 161, A620-            A632.  [View]

2. "Capacity Fading Mechanism of The Commercial 18650 LiFePO4-Based Lithium-ion batteries: An In-situ Time-Resolved High-Energy Synchrotron XRD study". Qi Liu et al., ACS Applied  Materials and Interface, 2018, 10, 4622-4629.  [View]

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3. Phase Transition

 

• Introduction

Novel advanced synchrotron X-ray techniques for Phase Transformation electrode. Phase transformation electrodes (such as LiFePO4, V2O5, NaFePO4, Na3Ti3(PO4)3 and NaVOPO4 ) have been recognized as the next generation electrode materials for Li-ion batteries or sodium ion batteries. However, the mechanism of the related performance is still not fully understood due to lack of in situ, non-destructive techniques to study the Li+/Na+ insertion/deinsertion mechanism in those materials. In my previous effort, utilizing the advanced synchrotron techniques, the dynamic chemical and structural changes of LiFePO4 in the commercial 18650 cells has been clearly clarified, and the proposed dual-phase solid-solution mechanism can explain the remarkable rate capability of LiFePO4 in commercial cells (ACS Applied Materials Interfaces., 2014, 6, 3282). Combining the synchrotron XRD and Spectroscopy techniques, the lithium ion insertion behavior and phase transition behavior have also been clarified for V2O5 (Electrochimica Acta., 2014, 136, 318) and VO2(B) (Nano Energy, 2017, 36, 197-205).

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So in my future study, I will develop and utilize the advanced synchrotron X-ray/neutron techniques, including diffraction, small-angle scattering, spectroscopy and imaging at different national user facilities (e.g. Advanced Photon Source in Argonne National Lab, National Synchrotron Light Source II at Brookhaven National Lab, and Advanced Light Source in Lawrence Berkeley National Lab, China Spallation Neutron Source at Dongguan ), coupled with the existing electroanalytical techniques to study the phase transformation process and interfacial processes during the realistic operational conditions.

 

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• Research Topic

1. The Phase Transformation Processes/behavior

2. The Interfacial Processes

 

• Further Reading

1. "Rate-Dependent, Li Ion Insertion/Deinsertion Behavior of LiFePO4 Cathodes in Commercial 18650 LiFePO4 Cells" Qi Liu, et al., ACS Applied Materials Interfaces, 2014, 6, 3282-3289.  [View]

2. "Revealing Mechanism Responsible for Structural Reversibility of Single Crystal VO2 Nanorods upon Lithiation/Delithiation". Qi Liu, et al., Nano Energy, 2017, 36, 197-205.  [View]

 

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4. Multimodal Synchrotron Techniques​

 

• Introduction

Synchrotron radiation is a source of electromagnetic radiation usually produced by a storage ring, for scientific and technical purposes. In this field, my research has been mainly focused on developing/building new synchrotron capabilities to solve the challenges for energy community as well as other research communities who require robust multimodal characterizations (XRD, spectroscopy and imaging). For an instance, In my previous effort, as the key investigator I have been involved in developing two synchrotron techniques as list below: 

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1) Framework for Integrating Multi-Modal Imaging of Materials for Energy Storage: improving batteries requires understanding of the interaction of many materials at multiple length scales at different electrochemical reaction stages. To address this challenge, I built a new x-ray projection microscope (XPM) with a combination of four different X-ray techniques and use it to investigate battery materials. The XPM will allow for in situ characterization of batteries with nano-CT, nano-XRD, nano-XRF and nano-XAS detections (X4 microscope). X4 will take advantage of fast temporal resolution of full-field imaging-based nano-CT to identify regions of interest (ROIs) in sample materials. XRD, XRF, and XAS will then be performed at the ROIs at nano scale. The tools developed in this project will constitute a revolutionary leap in the addressing of fundamental questions in energy storage research.  In my future research, I will take advantage of those novel capabilities and established standard data analysis tools to investigate the most fundamental questions in batteries research such as a) Formation and features of solid electrolyte interphase (SEI) in Li-ion batteries; b) Formation and growth mechanism of lithium dendrite during cycling.

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2) Integration of Scalable Microwave Reactor with High-Energy X-ray Beamline for High Throughput Screening of Energy Nanomaterials Synthesis: Microwave chemistry has been considered as a greener way to synthesize materials. However, the fast reaction kinetics present in microwave heating, and the design of microwave reactors makes in situ studying the real-time evolution of colloidal nanoparticles very difficult. This challenge significantly hinders our understanding of the reaction kinetics as well as the precise control over properties of the synthesized nanoparticles. In my previous effort, I successfully integrated a microwave reactor with a high energy X-ray synchrotron beamline. The established research platform makes us, for the first time, to capture the rapid kinetics of nanocrystal formation in large, statistically relevant solutions. Comprehensive data analysis reveals two different types of reaction kinetics corresponding to the nucleation and growth of the Ag nanoparticles. (Nano Letters., 2016, 16(1), 715-720). Importantly, in the future, the established research plateau at beamline 1-ID-E, APS can also help me further understand the complex nucleation and growth mechanisms involved in the formation of colloidal nanoparticles and thus enabling better design and synthesis of nanoparticles with improved quality and properties.

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• Research Topic

1. Formation and Features of Solid Electrolyte Interphase (SEI) in Li- Ion Batteries

2. Formation and Growth Mechanism of Lithium Dendrite during Cycling

3. Understanding the Complex Nucleation and Growth Mechanisms Involved in the Formation of Colloidal Nanoparticles

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• Further Reading

1. "Quantifying Nucleation and Growth Kinetics of Microwave Nanochemistry Enabled by In-Situ High-Energy X-Ray Scattering". Qi Liu, et al., Nano Letters, 2016, 16, 715-720.  [View]

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