Professional Education

  • Bachelor of Science, Peking University (2007)
  • Doctor of Philosophy, Peking University (2012)

Stanford Advisors

  • Yi Cui, Postdoctoral Faculty Sponsor

All Publications

  • Artificial Solid Electrolyte Interphase-Protected LixSi Nanoparticles: An Efficient and Stable Prelithiation Reagent for Lithium-Ion Batteries JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Zhao, J., Lu, Z., Wang, H., Liu, W., Lee, H., Yan, K., Zhuo, D., Lin, D., Liu, N., Cui, Y. 2015; 137 (26): 8372-8375


    Prelithiation is an important strategy to compensate for lithium loss in lithium-ion batteries, particularly during the formation of the solid electrolyte interphase (SEI) from reduced electrolytes in the first charging cycle. We recently demonstrated that LixSi nanoparticles (NPs) synthesized by thermal alloying can serve as a high-capacity prelithiation reagent, although their chemical stability in the battery processing environment remained to be improved. Here we successfully developed a surface modification method to enhance the stability of LixSi NPs by exploiting the reduction of 1-fluorodecane on the LixSi surface to form a continuous and dense coating through a reaction process similar to SEI formation. The coating, consisting of LiF and lithium alkyl carbonate with long hydrophobic carbon chains, serves as an effective passivation layer in the ambient environment. Remarkably, artificial-SEI-protected LixSi NPs show a high prelithiation capacity of 2100 mA h g(-1) with negligible capacity decay in dry air after 5 days and maintain a high capacity of 1600 mA h g(-1) in humid air (∼10% relative humidity). Silicon, tin, and graphite were successfully prelithiated with these NPs to eliminate the irreversible first-cycle capacity loss. The use of prelithiation reagents offers a new approach to realize next-generation high-energy-density lithium-ion batteries.

    View details for DOI 10.1021/jacs.5b04526

    View details for Web of Science ID 000357964400015

    View details for PubMedID 26091423

  • The synergetic effect of lithium polysulfide and lithium nitrate to prevent lithium dendrite growth NATURE COMMUNICATIONS Li, W., Yao, H., Yan, K., Zheng, G., Liang, Z., Chiang, Y., Cui, Y. 2015; 6


    Lithium metal has shown great promise as an anode material for high-energy storage systems, owing to its high theoretical specific capacity and low negative electrochemical potential. Unfortunately, uncontrolled dendritic and mossy lithium growth, as well as electrolyte decomposition inherent in lithium metal-based batteries, cause safety issues and low Coulombic efficiency. Here we demonstrate that the growth of lithium dendrites can be suppressed by exploiting the reaction between lithium and lithium polysulfide, which has long been considered as a critical flaw in lithium-sulfur batteries. We show that a stable and uniform solid electrolyte interphase layer is formed due to a synergetic effect of both lithium polysulfide and lithium nitrate as additives in ether-based electrolyte, preventing dendrite growth and minimizing electrolyte decomposition. Our findings allow for re-evaluation of the reactions regarding lithium polysulfide, lithium nitrate and lithium metal, and provide insights into solving the problems associated with lithium metal anodes.

    View details for DOI 10.1038/ncomms8436

    View details for Web of Science ID 000357176700002

    View details for PubMedID 26081242

  • Polymer Nanofiber-Guided Uniform Lithium Deposition for Battery Electrodes NANO LETTERS Liang, Z., Zheng, G., Liu, C., Liu, N., Li, W., Yan, K., Yao, H., Hsu, P., Chu, S., Cui, Y. 2015; 15 (5): 2910-2916


    Lithium metal is one of the most promising candidates as an anode material for next-generation energy storage systems due to its highest specific capacity (3860 mAh/g) and lowest redox potential of all. The uncontrolled lithium dendrite growth that causes a poor cycling performance and serious safety hazards, however, presents a significant challenge for the realization of lithium metal-based batteries. Here, we demonstrate a novel electrode design by placing a three-dimensional (3D) oxidized polyacrylonitrile nanofiber network on top of the current collector. The polymer fiber with polar surface functional groups could guide the lithium ions to form uniform lithium metal deposits confined on the polymer fiber surface and in the 3D polymer layer. We showed stable cycling of lithium metal anode with an average Coulombic efficiency of 97.4% over 120 cycles in ether-based electrolyte at a current density of 3 mA/cm(2) for a total of 1 mAh/cm(2) of lithium.

    View details for DOI 10.1021/nl5046318

    View details for Web of Science ID 000354906000021

    View details for PubMedID 25822282

  • Improved lithium-sulfur batteries with a conductive coating on the separator to prevent the accumulation of inactive S-related species at the cathode-separator interface ENERGY & ENVIRONMENTAL SCIENCE Yao, H., Yan, K., Li, W., Zheng, G., Kong, D., Seh, Z. W., Narasimhan, V. K., Liang, Z., Cui, Y. 2014; 7 (10): 3381-3390

    View details for DOI 10.1039/c4ee01377h

    View details for Web of Science ID 000342884300022

  • Ultrathin Two-Dimensional Atomic Crystals as Stable Interfacial Layer for Improvement of Lithium Metal Anode NANO LETTERS Yan, K., Lee, H., Gao, T., Zheng, G., Yao, H., Wang, H., Lu, Z., Zhou, Y., Liang, Z., Liu, Z., Chu, S., Cui, Y. 2014; 14 (10): 6016-6022

    View details for DOI 10.1021/nl503125u

    View details for Web of Science ID 000343016400082

  • Interconnected hollow carbon nanospheres for stable lithium metal anodes NATURE NANOTECHNOLOGY Zheng, G., Lee, S. W., Liang, Z., Lee, H., Yan, K., Yao, H., Wang, H., Li, W., Chu, S., Cui, Y. 2014; 9 (8): 618-623


    For future applications in portable electronics, electric vehicles and grid storage, batteries with higher energy storage density than existing lithium ion batteries need to be developed. Recent efforts in this direction have focused on high-capacity electrode materials such as lithium metal, silicon and tin as anodes, and sulphur and oxygen as cathodes. Lithium metal would be the optimal choice as an anode material, because it has the highest specific capacity (3,860 mAh g(-1)) and the lowest anode potential of all. However, the lithium anode forms dendritic and mossy metal deposits, leading to serious safety concerns and low Coulombic efficiency during charge/discharge cycles. Although advanced characterization techniques have helped shed light on the lithium growth process, effective strategies to improve lithium metal anode cycling remain elusive. Here, we show that coating the lithium metal anode with a monolayer of interconnected amorphous hollow carbon nanospheres helps isolate the lithium metal depositions and facilitates the formation of a stable solid electrolyte interphase. We show that lithium dendrites do not form up to a practical current density of 1 mA cm(-2). The Coulombic efficiency improves to ∼99% for more than 150 cycles. This is significantly better than the bare unmodified samples, which usually show rapid Coulombic efficiency decay in fewer than 100 cycles. Our results indicate that nanoscale interfacial engineering could be a promising strategy to tackle the intrinsic problems of lithium metal anodes.

    View details for DOI 10.1038/NNANO.2014.152

    View details for Web of Science ID 000340140100015

    View details for PubMedID 25064396

  • Electrochemical tuning of layered lithium transition metal oxides for improvement of oxygen evolution reaction NATURE COMMUNICATIONS Lu, Z., Wang, H., Kong, D., Yan, K., Hsu, P., Zheng, G., Yao, H., Liang, Z., Sun, X., Cui, Y. 2014; 5


    Searching for low-cost and efficient catalysts for the oxygen evolution reaction has been actively pursued owing to its importance in clean energy generation and storage. While developing new catalysts is important, tuning the electronic structure of existing catalysts over a wide electrochemical potential range can also offer a new direction. Here we demonstrate a method for electrochemical lithium tuning of catalytic materials in organic electrolyte for subsequent enhancement of the catalytic activity in aqueous solution. By continuously extracting lithium ions out of LiCoO2, a popular cathode material in lithium ion batteries, to Li0.5CoO2 in organic electrolyte, the catalytic activity is significantly improved. This enhancement is ascribed to the unique electronic structure after the delithiation process. The general efficacy of this methodology is demonstrated in several mixed metal oxides with similar improvements. The electrochemically delithiated LiCo0.33Ni0.33Fe0.33O2 exhibits a notable performance, better than the benchmark iridium/carbon catalyst.

    View details for DOI 10.1038/ncomms5345

    View details for Web of Science ID 000340615500036

    View details for PubMedID 24993836

  • Sulfur Cathodes with Hydrogen Reduced Titanium Dioxide Inverse Opal Structure ACS NANO Liang, Z., Zheng, G., Li, W., Seh, Z. W., Yao, H., Yan, K., Kong, D., Cui, Y. 2014; 8 (5): 5249-5256


    Sulfur is a cathode material for lithium-ion batteries with a high specific capacity of 1675 mAh/g. The rapid capacity fading, however, presents a significant challenge for the practical application of sulfur cathodes. Two major approaches that have been developed to improve the sulfur cathode performance include (a) fabricating nanostructured conductive matrix to physically encapsulate sulfur and (b) engineering chemical modification to enhance binding with polysulfides and, thus, to reduce their dissolution. Here, we report a three-dimensional (3D) electrode structure to achieve both sulfur physical encapsulation and polysulfides binding simultaneously. The electrode is based on hydrogen reduced TiO2 with an inverse opal structure that is highly conductive and robust toward electrochemical cycling. The relatively enclosed 3D structure provides an ideal architecture for sulfur and polysulfides confinement. The openings at the top surface allow sulfur infusion into the inverse opal structure. In addition, chemical tuning of the TiO2 composition through hydrogen reduction was shown to enhance the specific capacity and cyclability of the cathode. With such TiO2 encapsulated sulfur structure, the sulfur cathode could deliver a high specific capacity of ∼1100 mAh/g in the beginning, with a reversible capacity of ∼890 mAh/g after 200 cycles of charge/discharge at a C/5 rate. The Coulombic efficiency was also maintained at around 99.5% during cycling. The results showed that inverse opal structure of hydrogen reduced TiO2 represents an effective strategy in improving lithium sulfur batteries performance.

    View details for DOI 10.1021/nn501308m

    View details for Web of Science ID 000336640600118

  • Improving lithium-sulphur batteries through spatial control of sulphur species deposition on a hybrid electrode surface NATURE COMMUNICATIONS Yao, H., Zheng, G., Hsu, P., Kong, D., Cha, J. J., Li, W., Seh, Z. W., McDowell, M. T., Yan, K., Liang, Z., Narasimhan, V. K., Cui, Y. 2014; 5

    View details for DOI 10.1038/ncomms4943

    View details for Web of Science ID 000337505600002

  • Improving lithium-sulphur batteries through spatial control of sulphur species deposition on a hybrid electrode surface. Nature communications Yao, H., Zheng, G., Hsu, P., Kong, D., Cha, J. J., Li, W., Seh, Z. W., McDowell, M. T., Yan, K., Liang, Z., Narasimhan, V. K., Cui, Y. 2014; 5: 3943-?


    Lithium-sulphur batteries are attractive owing to their high theoretical energy density and reasonable kinetics. Despite the success of trapping soluble polysulphides in a matrix with high surface area, spatial control of solid-state sulphur and lithium sulphide species deposition as a critical aspect has not been demonstrated. Herein, we show a clear visual evidence that these solid species deposit preferentially onto tin-doped indium oxide instead of carbon during electrochemical charge/discharge of soluble polysuphides. To incorporate this concept of spatial control into more practical battery electrodes, we further prepare carbon nanofibers with tin-doped indium oxide nanoparticles decorating the surface as hybrid three-dimensional electrodes to maximize the number of deposition sites. With 12.5 μl of 5 M Li2S8 as the catholyte and a rate of C/5, we can reach the theoretical limit of Li2S8 capacity ~\n1,470 mAh g(-1) (sulphur weight) under the loading of hybrid electrode only at 4.3 mg cm(-2).

    View details for DOI 10.1038/ncomms4943

    View details for PubMedID 24862162

  • Electrochemical tuning of vertically aligned MoS2 nanofilms and its application in improving hydrogen evolution reaction PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Wang, H., Lu, Z., Xu, S., Kong, D., Cha, J. J., Zheng, G., Hsu, P., Yan, K., Bradshaw, D., Prinz, F. B., Cui, Y. 2013; 110 (49): 19701-19706


    The ability to intercalate guest species into the van der Waals gap of 2D layered materials affords the opportunity to engineer the electronic structures for a variety of applications. Here we demonstrate the continuous tuning of layer vertically aligned MoS2 nanofilms through electrochemical intercalation of Li(+) ions. By scanning the Li intercalation potential from high to low, we have gained control of multiple important material properties in a continuous manner, including tuning the oxidation state of Mo, the transition of semiconducting 2H to metallic 1T phase, and expanding the van der Waals gap until exfoliation. Using such nanofilms after different degree of Li intercalation, we show the significant improvement of the hydrogen evolution reaction activity. A strong correlation between such tunable material properties and hydrogen evolution reaction activity is established. This work provides an intriguing and effective approach on tuning electronic structures for optimizing the catalytic activity.

    View details for DOI 10.1073/pnas.1316792110

    View details for Web of Science ID 000327744900025

    View details for PubMedID 24248362

  • Designed CVD Growth of Graphene via Process Engineering ACCOUNTS OF CHEMICAL RESEARCH Yan, K., Fu, L., Peng, H., Liu, Z. 2013; 46 (10): 2263-2274

    View details for DOI 10.1021/ar400057n

    View details for Web of Science ID 000326123300009

  • MoSe2 and WSe2 nanofilms with vertically aligned molecular layers on curved and rough surfaces. Nano letters Wang, H., Kong, D., Johanes, P., Cha, J. J., Zheng, G., Yan, K., Liu, N., Cui, Y. 2013; 13 (7): 3426-3433


    Two-dimensional (2D) layered materials exhibit high anisotropy in materials properties due to the large difference of intra- and interlayer bonding. This presents opportunities to engineer materials whose properties strongly depend on the orientation of the layers relative to the substrate. Here, using a similar growth process reported in our previous study of MoS2 and MoSe2 films whose layers were oriented vertically on flat substrates, we demonstrate that the vertical layer orientation can be realized on curved and rough surfaces such as nanowires (NWs) and microfibers. Such structures can increase the surface area while maintaining the perpendicular orientation of the layers, which may be useful in enhancing various catalytic activities. We show vertically aligned MoSe2 and WSe2 nanofilms on Si NWs and carbon fiber paper. We find that MoSe2 and WSe2 nanofilms on carbon fiber paper are highly efficient electrocatalysts for hydrogen evolution reaction (HER) compared to flat substrates. Both materials exhibit extremely high stability in acidic solution as the HER catalytic activity shows no degradation after 15 000 continuous potential cycles. The HER activity of MoSe2 is further improved by Ni doping.

    View details for DOI 10.1021/nl401944f

    View details for PubMedID 23799638

  • MoSe2 and WSe2 Nanofilms with Vertically Aligned Molecular Layers on Curved and Rough Surfaces NANO LETTERS Wang, H., Kong, D., Johanes, P., Cha, J. J., Zheng, G., Yan, K., Liu, N., Cui, Y. 2013; 13 (7): 3426-3433

    View details for DOI 10.1021/nl401944f

    View details for Web of Science ID 000321884300069