scispace - formally typeset
Search or ask a question
Author

Yi Cui

Other affiliations: KAIST, University of California, Berkeley, Harvard University  ...read more
Bio: Yi Cui is an academic researcher from Stanford University. The author has contributed to research in topics: Anode & Lithium. The author has an hindex of 220, co-authored 1015 publications receiving 199725 citations. Previous affiliations of Yi Cui include KAIST & University of California, Berkeley.


Papers
More filters
Journal ArticleDOI
TL;DR: A two-step approach for synthesis of LiMn1 xFexPO4 nanorods on reduced graphene oxide sheets stably suspended in solution, which shows improved specific capacities and rate capabilities of simple oxide nanomaterials grown on graphene as LIB anode materials.
Abstract: Olivine-type lithium transition-metal phosphates LiMPO4 (M=Fe, Mn, Co, or Ni) have been intensively investigated as promising cathode materials for rechargeable lithium ion batteries (LIBs) owing to their high capacity, excellent cycle life, thermal stability, environmental benignity, and low cost. However, the inherently low ionic and electrical conductivities of LiMPO4 seriously limit Li + insertion and extraction and charge transport rates in these materials. In recent years, these obstacles have been overcome for LiFePO4 by reducing the size of LiFePO4 particles to the nanoscale and applying conductive surface coatings such as carbon, which leads to commercially viable LiFePO4 cathode materials. Compared to LiFePO4, LiMnPO4 is an attractive cathode material owing to its higher Li intercalation potential of 4.1 V versus Li/Li (3.4 V for LiFePO4), providing about 20% higher energy density than LiFePO4 for LIBs. [14–19] Importantly, the 4.1 V intercalation potential of LiMnPO4 is compatible with most of the currently used liquid electrolytes. However, the electrical conductivity of LiMnPO4 is lower than the already insulating LiFePO4 by five orders of magnitude, making it challenging to achieve high capacity at high rates for LiMnPO4 using methods developed for LiFePO4. [14–19] Doping LiMnPO4 with Fe has been pursued to enhance conductivity and stability of the material in its charged form. Recently, Martha et al. have obtained improved capacity and rate performance for carbon-coated LiMn0.8Fe0.2PO4 nanoparticles synthesized by a high-temperature solid-state reaction. Graphene is an ideal substrate for growing and anchoring insulating materials for energy storage applications because of its high conductivity, light weight, high mechanical strength, and structural flexibility. The electrochemical performance of various electrode materials can be significantly boosted by rendering them conducting with graphene sheets. Recent work has shown improved specific capacities and rate capabilities of simple oxide nanomaterials (Mn3O4, Co3O4, and Fe3O4) grown on graphene as LIB anode materials. However, it remains a challenge to grow nanocrystals on graphene sheets in solution for materials with more sophisticated compositions and structures, such as LiMn1 xFexPO4, which is a promising but extremely insulating cathode material for LIBs. Herein we present a two-step approach for synthesis of LiMn1 xFexPO4 nanorods on reduced graphene oxide sheets stably suspended in solution. Fe-doped Mn3O4 nanoparticles were first selectively grown onto graphene oxide by controlled hydrolysis. The oxide nanoparticle precursors then reacted solvothermally with Li and phosphate ions and were transformed into LiMn1 xFexPO4 on the surface of reduced graphene oxide sheets. With a total content of 26 wt% conductive carbon, the resulting hybrid of nanorods and graphene showed high specific capacity and unprecedentedly high power rate for LiMn1 xFexPO4 type of cathode materials. Stable capacities of 132 mAhg 1 and 107 mAhg 1 were obtained at high discharge rates of 20C and 50C, which is 85% and 70% of the capacity at C/2 (155 mAhg ), respectively. This affords LIBs with both high energy and high power densities. This is also the first synthesis of LiMn0.75Fe0.25PO4 nanorods that have an ideal crystal shape and morphology for fast Li diffusion along the radial [010] direction of the nanorods. Figure 1 shows our two-step solution-phase reaction for the synthesis LiMn0.75Fe0.25PO4 nanorods on reduced graphene oxide (for experimental details, see the Supporting Information). The first step was to selectively grow oxide nanoparticles at 80 8C on mildly oxidized graphene oxide (mGO) stably suspended in a solution. Controlling the hydrolysis rate of Mn(OAc)2 and Fe(NO3)3 by adjusting the H2O/N,N-dimethylformamide (DMF) solvent ratio and the reaction temperature afforded selective and uniform coating of circa 10 nm nanoparticles of Fe-doped Mn3O4 (Supporting Information, Figure S1a; X-ray diffraction data in Figure S1b) on the mGO sheets without free growth of nanoparticles in solution. Importantly, our mGO was made by a modified Hummers method (Supporting Information), with which a sixfold lower concentration of KMnO4 oxidizer was used to afford milder oxidation of graphite. The resulting mGO sheets contained a lower oxygen content than Hummers GO (ca. 15% vs. ca. 30% measured by X-ray photoelectron spectroscopy (XPS) and Auger spectroscopy) and showed higher electrical conductivity when chemically reduced than [*] H. Wang, Y. Liang, H. Sanchez Casalongue, Y. Li, G. Hong, Prof. H. Dai Department of Chemistry Stanford University, Stanford, CA 94305 (USA) E-mail: hdai@stanford.edu Y. Yang, L. Cui, Prof. Y. Cui Department of Materials Science and Engineering Stanford University, Stanford, CA 94305 (USA) E-mail: yicui@stanford.edu [] These authors contributed equally to this work.

290 citations

Journal ArticleDOI
TL;DR: In this article, the efficacy of inexpensive, non-toxic mixed cation electrolyte systems for Li-ion batteries that otherwise provide the same benefits as current water-in-salt (WIS) electrolytes was disclosed.
Abstract: Electrolyte solutions are a key component of energy storage devices that significantly impact capacity, safety, and cost. Recent developments in “water-in-salt” (WIS) aqueous electrolyte research have enabled the demonstration of aqueous Li-ion batteries that operate with capacities and cyclabilities comparable with those of commercial non-aqueous Li-ion batteries. Critically, the use of aqueous electrolyte mitigates safety risks associated with non-aqueous electrolytes. However, the high cost and potential toxicity of imide-based WIS electrolytes limit their practical deployment. In this report, we disclose the efficacy of inexpensive, non-toxic mixed cation electrolyte systems for Li-ion batteries that otherwise provide the same benefits as current WIS electrolytes: extended electrochemical stability window and compatibility with traditional intercalation Li-ion battery electrode materials. We take advantage of the high solubility of potassium acetate to achieve the WIS condition in a eutectic mixture of lithium and potassium acetate with water-to-cation ratio as low as 1.3. Our work suggests an important direction for the practical realization of safe, low-cost, and high-performance aqueous Li-ion batteries.

289 citations

Journal ArticleDOI
TL;DR: In this article, the structural transformation of silicon nanowires when cycled against lithium was evaluated using electrochemical potential spectroscopy and galvanostatic cycling, and it was shown that limiting the voltage in the charge to 70 mV results in improved efficiency and cyclability compared to charging to 10 mV.

288 citations

Journal ArticleDOI
TL;DR: Cui et al. as discussed by the authors used cryo-electron microscopy to reveal a drastically different solid electrolyte interface nanostructure emerging at 60°C, which maintains mechanical stability, inhibits continuous side reactions and guarantees good cycling stability and low electrochemical impedance.
Abstract: Operations of lithium-ion batteries have long been limited to a narrow temperature range close to room temperature. At elevated temperatures, cycling degradation speeds up due to enhanced side reactions, especially when high-reactivity lithium metal is used as the anode. Here, we demonstrate enhanced performance in lithium metal batteries operated at elevated temperatures. In an ether-based electrolyte at 60 °C, an average Coulombic efficiency of 99.3% is obtained and more than 300 stable cycles are realized, but, at 20 °C, the Coulombic efficiency drops dramatically within 75 cycles, corresponding to an average Coulombic efficiency of 90.2%. Cryo-electron microscopy reveals a drastically different solid electrolyte interface nanostructure emerging at 60 °C, which maintains mechanical stability, inhibits continuous side reactions and guarantees good cycling stability and low electrochemical impedance. Furthermore, larger lithium particles grown at the elevated temperature reduce the electrolyte/electrode interfacial area, which decreases the per-cycle lithium loss and enables higher Coulombic efficiencies. The performance of Li-ion batteries deteriorates at elevated temperatures due to increased activity of electrode materials and parasitic reactions. Here Yi Cui and colleagues report much-improved battery cyclability at 60 °C and use cryo-electron microscopy to shed light on the origin of the phenomenon.

287 citations

Journal ArticleDOI
TL;DR: The understanding developed herein of how volume expansion and extent of lithiation can depend on nanomaterial structure is important for the improvement of Si-based anodes.
Abstract: With its high specific capacity, silicon is a promising anode material for high-energy lithium-ion batteries, but volume expansion and fracture during lithium reaction have prevented implementation. Si nanostructures have shown resistance to fracture during cycling, but the critical effects of nanostructure size and native surface oxide on volume expansion and cycling performance are not understood. Here, we use an ex situ transmission electron microscopy technique to observe the same Si nanowires before and after lithiation and have discovered the impacts of size and surface oxide on volume expansion. For nanowires with native SiO2, the surface oxide can suppress the volume expansion during lithiation for nanowires with diameters <∼50 nm. Finite element modeling shows that the oxide layer can induce compressive hydrostatic stress that could act to limit the extent of lithiation. The understanding developed herein of how volume expansion and extent of lithiation can depend on nanomaterial structure is imp...

285 citations


Cited by
More filters
Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

01 May 1993
TL;DR: Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems.
Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

29,323 citations

28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

18,940 citations