Bachelor of Science, Fudan University (2010)
Doctor of Philosophy, University of California Berkeley (2015)
Yi Cui, Postdoctoral Faculty Sponsor
Shell-Protective Secondary Silicon Nanostructures as Pressure-Resistant High-Volumetric-Capacity Anodes for Lithium-Ion Batteries.
The nanostructure design of a prereserved hollow space to accommodate 300% volume change of silicon anodes has created exciting promises for high-energy batteries. However, challenges with weak mechanical stability during the calendering process of electrode fabrication and poor volumetric energy density remain to be solved. Here we fabricated a pressure-resistant silicon structure by designing a dense silicon shell coating on secondary micrometer particles, each consisting of many silicon nanoparticles. The silicon skin layer significantly improves mechanical stability, while the inner porous structure efficiently accommodates the volume expansion. Such a structure can resist a high pressure of over 100 MPa and is well-maintained after the calendering process, demonstrating a high volumetric capacity of 2041 mAh cm-3. In addition, the dense silicon shell decreases the surface area and thus increases the initial Coulombic efficiency. With further encapsulation with a graphene cage, which allows the silicon core to expand within the cage while retaining electrical contact, the silicon hollow structure exhibits a high initial Coulombic efficiency and fast rise of later Coulombic efficiencies to >99.5% and superior stability in a full-cell battery.
View details for PubMedID 30339401
- Fundamental study on the wetting property of liquid lithium ENERGY STORAGE MATERIALS 2018; 14: 345–50
Lithium metal stripping beneath the solid electrolyte interphase.
Proceedings of the National Academy of Sciences of the United States of America
Lithium stripping is a crucial process coupled with lithium deposition during the cycling of Li metal batteries. Lithium deposition has been widely studied, whereas stripping as a subsurface process has rarely been investigated. Here we reveal the fundamental mechanism of stripping on lithium by visualizing the interface between stripped lithium and the solid electrolyte interphase (SEI). We observed nanovoids formed between lithium and the SEI layer after stripping, which are attributed to the accumulation of lithium metal vacancies. High-rate dissolution of lithium causes vigorous growth and subsequent aggregation of voids, followed by the collapse of the SEI layer, i.e., pitting. We systematically measured the lithium polarization behavior during stripping and find that the lithium cation diffusion through the SEI layer is the rate-determining step. Nonuniform sites on typical lithium surfaces, such as grain boundaries and slip lines, greatly accelerated the local dissolution of lithium. The deeper understanding of this buried interface stripping process provides beneficial clues for future lithium anode and electrolyte design.
View details for DOI 10.1073/pnas.1806878115
View details for PubMedID 30082382
Engineering stable interfaces for three-dimensional lithium metal anodes.
2018; 4 (7): eaat5168
Lithium metal has long been considered one of the most promising anode materials for advanced lithium batteries (for example, Li-S and Li-O2), which could offer significantly improved energy density compared to state-of-the-art lithium ion batteries. Despite decades of intense research efforts, its commercialization remains limited by poor cyclability and safety concerns of lithium metal anodes. One root cause is the parasitic reaction between metallic lithium and the organic liquid electrolyte, resulting in continuous formation of an unstable solid electrolyte interphase, which consumes both active lithium and electrolyte. Until now, it has been challenging to completely shut down the parasitic reaction. We find that a thin-layer coating applied through atomic layer deposition on a hollow carbon host guides lithium deposition inside the hollow carbon sphere and simultaneously prevents electrolyte infiltration by sealing pinholes on the shell of the hollow carbon sphere. By encapsulating lithium inside the stable host, parasitic reactions are prevented, resulting in impressive cycling behavior. We report more than 500 cycles at a high coulombic efficiency of 99% in an ether-based electrolyte at a cycling rate of 0.5 mA/cm2 and a cycling capacity of 1 mAh/cm2, which is among the most stable Li anodes reported so far.
View details for PubMedID 30062125
- Quantitative investigation of polysulfide adsorption capability of candidate materials for Li-S batteries ENERGY STORAGE MATERIALS 2018; 13: 241–46
Vertically Aligned and Continuous Nanoscale Ceramic-Polymer Interfaces in Composite Solid Polymer Electrolytes for Enhanced Ionic Conductivity.
Among all solid electrolytes, composite solid polymer electrolytes, comprised of polymer matrix and ceramic fillers, garner great interest due to the enhancement of ionic conductivity and mechanical properties derived from ceramic-polymer interactions. Here, we report a composite electrolyte with densely packed, vertically aligned, and continuous nanoscale ceramic-polymer interfaces, using surface-modified anodized aluminum oxide as the ceramic scaffold and poly(ethylene oxide) as the polymer matrix. The fast Li+ transport along the ceramic-polymer interfaces was proven experimentally for the first time, and an interfacial ionic conductivity higher than 10-3 S/cm at 0 °C was predicted. The presented composite solid electrolyte achieved an ionic conductivity as high as 5.82 * 10-4 S/cm at the electrode level. The vertically aligned interfacial structure in the composite electrolytes enables the viable application of the composite solid electrolyte with superior ionic conductivity and high hardness, allowing Li-Li cells to be cycled at a small polarization without Li dendrite penetration.
View details for PubMedID 29727578
An Aqueous Inorganic Polymer Binder for High Performance Lithium-Sulfur Batteries with Flame-Retardant Properties
ACS CENTRAL SCIENCE
2018; 4 (2): 260–67
Lithium-sulfur (Li-S) batteries are regarded as promising next-generation high energy density storage devices for both portable electronics and electric vehicles due to their high energy density, low cost, and environmental friendliness. However, there remain some issues yet to be fully addressed with the main challenges stemming from the ionically insulating nature of sulfur and the dissolution of polysulfides in electrolyte with subsequent parasitic reactions leading to low sulfur utilization and poor cycle life. The high flammability of sulfur is another serious safety concern which has hindered its further application. Herein, an aqueous inorganic polymer, ammonium polyphosphate (APP), has been developed as a novel multifunctional binder to address the above issues. The strong binding affinity of the main chain of APP with lithium polysulfides blocks diffusion of polysulfide anions and inhibits their shuttling effect. The coupling of APP with Li ion facilitates ion transfer and promotes the kinetics of the cathode reaction. Moreover, APP can serve as a flame retardant, thus significantly reducing the flammability of the sulfur cathode. In addition, the aqueous characteristic of the binder avoids the use of toxic organic solvents, thus significantly improving safety. As a result, a high rate capacity of 520 mAh g-1 at 4 C and excellent cycling stability of ∼0.038% capacity decay per cycle at 0.5 C for 400 cycles are achieved based on this binder. This work offers a feasible and effective strategy for employing APP as an efficient multifunctional binder toward building next-generation high energy density Li-S batteries.
View details for DOI 10.1021/acscentsci.7b00569
View details for Web of Science ID 000426613700018
View details for PubMedID 29532026
View details for PubMedCentralID PMC5833002
Strong texturing of lithium metal in batteries
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2017; 114 (46): 12138–43
Lithium, with its high theoretical specific capacity and lowest electrochemical potential, has been recognized as the ultimate negative electrode material for next-generation lithium-based high-energy-density batteries. However, a key challenge that has yet to be overcome is the inferior reversibility of Li plating and stripping, typically thought to be related to the uncontrollable morphology evolution of the Li anode during cycling. Here we show that Li-metal texturing (preferential crystallographic orientation) occurs during electrochemical deposition, which governs the morphological change of the Li anode. X-ray diffraction pole-figure analysis demonstrates that the texture of Li deposits is primarily dependent on the type of additive or cross-over molecule from the cathode side. With adsorbed additives, like LiNO3 and polysulfide, the lithium deposits are strongly textured, with Li (110) planes parallel to the substrate, and thus exhibit uniform, rounded morphology. A growth diagram of lithium deposits is given to connect various texture and morphology scenarios for different battery electrolytes. This understanding of lithium electrocrystallization from the crystallographic point of view provides significant insight for future lithium anode materials design in high-energy-density batteries.
View details for DOI 10.1073/pnas.1708224114
View details for Web of Science ID 000415173300045
View details for PubMedID 29087316
View details for PubMedCentralID PMC5699048
- Stitching h-BN by atomic layer deposition of LiF as a stable interface for lithium metal anode SCIENCE ADVANCES 2017; 3 (11)
Reactivation of dead sulfide species in lithium polysulfide flow battery for grid scale energy storage
2017; 8: 462
Lithium polysulfide batteries possess several favorable attributes including low cost and high energy density for grid energy storage. However, the precipitation of insoluble and irreversible sulfide species on the surface of carbon and lithium (called "dead" sulfide species) leads to continuous capacity degradation in high mass loading cells, which represents a great challenge. To address this problem, herein we propose a strategy to reactivate dead sulfide species by reacting them with sulfur powder with stirring and heating (70 °C) to recover the cell capacity, and further demonstrate a flow battery system based on the reactivation approach. As a result, ultrahigh mass loading (0.125 g cm-3, 2 g sulfur in a single cell), high volumetric energy density (135 Wh L-1), good cycle life, and high single-cell capacity are achieved. The high volumetric energy density indicates its promising application for future grid energy storage.Lithium polysulfide batteries suffer from the precipitation of insoluble and irreversible sulfide species on the surface of carbon and lithium. Here the authors show a reactivation strategy by a reaction with cheap sulfur powder under stirring and heating to recover the cell capacity.
View details for DOI 10.1038/s41467-017-00537-0
View details for Web of Science ID 000409458000016
View details for PubMedID 28878273
View details for PubMedCentralID PMC5587700
2017; 17 (3): 1741-1747
Intercalation of exotic atoms or molecules into the layered materials remains an extensively investigated subject in current physics and chemistry. However, traditionally melt-growth and chemical interaction strategies are either limited by insufficiency of intercalant concentrations or destitute of accurate controllability. Here, we have developed a general electrochemical intercalation method to efficaciously regulate the concentration of zerovalent copper atoms into layered Bi2Se3, followed by comprehensive experimental characterization and analyses. Up to 57% copper atoms (Cu6.7Bi2Se3) can be intercalated with no disruption to the host lattice. Meanwhile the unconventional resistance dip accompanied by a hysteresis loop below 40 K, as well as the emergence of new Raman peak in CuxBi2Se3, is a distinct manifestation of the interplay between intercalated Cu atoms with Bi2Se3 host. Our work demonstrates a new methodology to study fundamentally new and unexpected physical behaviors in intercalated metastable materials.
View details for DOI 10.1021/acs.nanolett.6b05062
View details for PubMedID 28218538
- Electrochemical Control of Copper Intercalation into Nanoscale Bi(2)Se3 NANO LETTERS 2017; 17 (3): 1741-1747
Nanoscale Nucleation and Growth of Electrodeposited Lithium Metal.
2017; 17 (2): 1132-1139
Lithium metal has re-emerged as an exciting anode for high energy lithium-ion batteries due to its high specific capacity of 3860 mAh g(-1) and lowest electrochemical potential of all known materials. However, lithium has been plagued by the issues of dendrite formation, high chemical reactivity with electrolyte, and infinite relative volume expansion during plating and stripping, which present safety hazards and low cycling efficiency in batteries with lithium metal electrodes. There have been a lot of recent studies on Li metal although little work has focused on the initial nucleation and growth behavior of Li metal, neglecting a critical fundamental scientific foundation of Li plating. Here, we study experimentally the morphology of lithium in the early stages of nucleation and growth on planar copper electrodes in liquid organic electrolyte. We elucidate the dependence of lithium nuclei size, shape, and areal density on current rate, consistent with classical nucleation and growth theory. We found that the nuclei size is proportional to the inverse of overpotential and the number density of nuclei is proportional to the cubic power of overpotential. Based on this understanding, we propose a strategy to increase the uniformity of electrodeposited lithium on the electrode surface.
View details for DOI 10.1021/acs.nanolett.6b04755
View details for PubMedID 28072543
- Self-healing SEI enables full-cell cycling of a silicon-majority anode with a coulombic efficiency exceeding 99.9% ENERGY & ENVIRONMENTAL SCIENCE 2017; 10 (2): 580-592
- High-Performance Lithium Metal Negative Electrode with a Soft and Flowable Polymer Coating ACS ENERGY LETTERS 2016; 1 (6): 1247-1255