Letter pubs.acs.org/NanoLett
Probing the Degradation Mechanisms in Electrolyte Solutions for LiIon Batteries by in Situ Transmission Electron Microscopy Patricia Abellan,*,† B. Layla Mehdi,† Lucas R. Parent,† Meng Gu,‡ Chiwoo Park,§ Wu Xu,∥ Yaohui Zhang,∥,⊥ Ilke Arslan,∥ Ji-Guang Zhang,∥ Chong-Min Wang,‡ James E. Evans,‡ and Nigel D. Browning† †
Fundamental and Computational Sciences Directorate and ‡Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States § Department of Industrial and Manufacturing Engineering, Florida State University, Tallahassee, Florida 32306, United States ∥ Energy and Environmental Directorate, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States ⊥ Center for Condensed Matter Science and Technology, Department of Physics, Harbin Institute of Technology, Harbin 150001, People’s Republic of China S Supporting Information *
ABSTRACT: Development of novel electrolytes with increased electrochemical stability is critical for the next generation battery technologies. In situ electrochemical fluid cells provide the ability to rapidly and directly characterize electrode/electrolyte interfacial reactions under conditions directly relevant to the operation of practical batteries. In this paper, we have studied the breakdown of a range of inorganic/ salt complexes relevant to state-of-the-art Li-ion battery systems by in situ (scanning) transmission electron microscopy ((S)TEM). In these experiments, the electron beam itself caused the localized electrochemical reaction that allowed us to observe electrolyte breakdown in real-time. The results of the in situ (S)TEM experiments matches with previous stability tests performed during battery operation and the breakdown products and mechanisms are also consistent with known mechanisms. This analysis indicates that in situ liquid stage (S)TEM observations could be used to directly test new electrolyte designs and identify a smaller library of candidate solutions deserving of more detailed characterization. A systematic study of electrolyte degradation is also a necessary first step for any future controlled in operando liquid (S)TEM experiments intent on visualizing working batteries at the nanoscale. KEYWORDS: In situ TEM, liquid stage, Li-ion battery, electrolyte, Lithium salt
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(scanning) transmission electron microscopy ((S)TEM) are at the forefront of the diagnostic effort on Li-ion batteries.1−10 Currently, (S)TEM is the only experimental technique that gives in operando information at the scale of the active particles used during the operation of Li-ion batteries. Two main strategies have been followed for the characterization of battery materials using in situ (S)TEM: the use of a “nanobattery” fabricated by focused ion beam (FIB) and including solid electrolytes1,10 and the use of single nanowire electrodes with vacuum compatible ionic liquids.2,3,9 Because of the high vacuum required for TEM observations, the use of volatile organic electrolytes relevant to modern batteries has long been avoided.11,12 However, with the development of liquid stages imaging liquids in the electron microscope has now become a
o address the increasing demand for efficient energy storage systems, advanced lithium (Li)-ion batteries with high energy output are developed using high-voltage and highcapacity electrodes together with a new generation of nonaqueous electrolytes. A fundamental understanding of the processes that rule the battery operation and determine performance is a critical component in the development process. This requires noninvasive characterization/diagnostic tools that can be implemented in situ or in operando at the active particle size level, that is, the nanoscale, with the goal of directly observing the processes that occur during battery operation (such as lithium and electron transport within the electrode active material, electrode−electrolyte interfacial reactions, and electrolyte degradation). Because of the possibility of directly monitoring dynamic processes, in situ imaging characterization techniques, such as nuclear magnetic resonance (NMR) imaging, X-ray or Raman spectroscopic imaging, in situ atomic force microscopy (AFM), and in situ © 2014 American Chemical Society
Received: November 18, 2013 Revised: February 7, 2014 Published: February 21, 2014 1293
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routine technique and the field of in situ liquid electron microscopy has already evolved to the point that quantitative information can be obtained about processes such as nanoparticle growth from solution.13−15 This approach has already allowed for direct observation of beam sensitive systems such as macromolecular complexes16,17 and soft materials18,19 and of processes that span from the electrochemical deposition of metals,20,21 growth of different nanostructures,13,14,22−25 and most recently the lithiation/delithiation of silicon nanowire electrodes during battery cycling.26 In situ liquid (S)TEM associated with microfabrication techniques can potentially foster a paradigm shift in the characterization of Li-ion battery materials by probing the realtime transformation of active material primary particles and side reactions like the electrochemical degradation of electrolytes. In order to obtain quantitative information using liquid stage (S)TEM, the effect of the electron dose on the electrolyte must be understood and quantified. This is most critical for the three following interconnected processes: (1) lithium exchange at the electrode material/electrolyte interface, (2) Li transport within the material, and (3) the stability of the electrolyte. The latter is the focus of the study reported here. The stability of the electrolytes investigated here by in situ (S)TEM correlates with electrochemical trends reported in the literature, suggesting that this technique could potentially give new insights into the reduction/degradation processes that take place during the operation of Li-ion batteries. Using in situ liquid STEM, we explore the stability of five different electrolytes commonly used for Li-ion and Li−O2 battery applications.27,28 Three of the electrolyte mixtures investigated contained lithium hexafluoroarsenate (LiAsF6) salt. This lithium salt is known to be easily electrochemically reduced29,30 (1.15 V vs Li/Li+ on glassy carbon). For this work, we have investigated the degradation of LiAsF6 salt dissolved in three different organic solvents: (1) 1,3-dioxolane (DOL), (2) dimethyl carbonate (DMC), and (3) a mixture of DMC and ethylene carbonate (EC). We also studied lithium triflate (LiTf) in dimethyl sulfoxide (DMSO) and lithium hexafluorophosphate (LiPF6) in EC/DMC, two electrolytes used, respectively, in rechargeable Li−O2 batteries28 and as a baseline electrolyte for next generation Li-ion batteries.27 Fortunately LiPF6 is known to decompose in a similar way as LiAsF6 to form a highly reactive Lewis acid, PF5,7,27 whereas the LiTf/ DMSO electrolyte is known to be very resistant to reduction reactions31 due to the functional group triflate (CF3SO3−) acting as an extremely stable polyatomic anion and a prototypical super leaving group. The in situ investigation of the degradation of the different electrolytes has been performed using an environmental liquid stage (Hummingbird Scientific, Lacey, WA, USA) in an aberration corrected STEM where two silicon nitride (SiNx) membranes supported on Si chips enclose the liquid sample and provide an electron transparent viewing area, Figure 1a. When the high-energy imaging electrons (300 kV) irradiate the solution, primary and secondary scattering occurs within the solution generating radicals and solvated electrons. For the case of a simple salt dissolved in an aqueous solution, the electron beam essentially acts as a reducing agent, where the created radicals, such as the aqueous electrons, induce the reduction of metallic cations to grow metallic nanoparticles from solution.32,33 In more complex solutions, such as Li battery electrolytes, the solvated electrons, e−sol, and other radical
Figure 1. (a) Schematic of the windowed-cell used in the fluid stage. Spacers separating the chips in combination with the membrane bulging due to the pressure differential with the microscope vacuum determine the total fluid path length. (b) Example of a simple process induced by electron irradiation on an electrolyte. One-electron reduction mechanism of the AsF6 component in electrolytes containing the LiAsF6 salt induced by the solvated electrons, followed by possible subsequent recombination with Li+ into LiF. (c) Valence band EELS of 1 molar LiTf in DMSO, LiAsF6 in EC/DMC, LiAsF6 in DMC, and LiAsF6 in DOL recorded after the experiments shown in this work in a nearby nonreacted area. Thickness, as a function of numbe of mean free paths (λ), is given for each plot.
species induced by the electron-beam will interact through secondary chemical reactions with the salt and solvent. Figure 1b depicts an example of a likely reaction occurring between e−sol and an electrolyte solution containing the salt LiAsF6. The overall reductive decomposition of the LiAsF6 electrolyte salt on carbonaceous anodes is reported to be LiAsF6 + 2e− + 2Li+ → AsF3 + 3LiF.27,30 Figure 1b illustrates both processes with the reduction reaction of AsF6− by the electron beam-induced e−sol and the subsequent recombination of F− with Li+ to form solid LiF molecules. The rate constant for the reaction of solvated electrons with AsF6− is high (Ke= 9 × 109 M−1 s−1), approaching values for diffusion-controlled reactions,34 and indicates that AsF6− is a kinetically unstable component. Once the Lewis Acid AsF3 is formed at a high rate, precipitation of LiF can occur by a simple combination of the F− anion with Li+ cation. LiF is indeed a component frequently observed on electrode surfaces after battery cycling in electrolytes containing fluorinated salts like LiAsF6 or LiPF6.35 Hence we believe a similar behavior should occur during STEM illumination and act as a proof-of-principle that this approach could probe electrolyte stability. In order to verify the presence of liquid during the experiments and estimate the fluid path thickness of the organic carbonate electrolyte samples investigated by STEM, valence band electron energy loss spectroscopy (EELS) was used. Figure 1c shows EELS spectra of four of the different electrolytes investigated, recorded after finishing the in situ STEM damage experiments (shown in Figure 2). The total SiNx-liquid thickness was estimated in terms of relative inelastic mean-free-path, λ, by calculating the ratio of the integrated intensities of the unscattered electrons (intensity of the zero loss peak, I0) to the total number of electrons, including the inelastically scattered electrons (I), and solving the equation I/ 1294
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Figure 2 shows six different time series of bright-field (BF) STEM images corresponding to the five electrolyte solutions investigated and also showing the EC/DMC solvent alone (Supporting Information Movies S1−S6). A consistent electron dose per frame (f) of 13.7 e−/nm2f was used for all the experiments (using identical beam current, dwell time, and magnification). The series of frames in Figure 2a−c corresponds to the degradation of the three electrolyte solutions containing the LiAsF6 salt, dissolved in DOL (a), DMC (b), and EC/DMC (c). In all cases, except for the LiTf salt in DMSO and pure EC/DMC, the time evolution with increasing cumulative dose caused an electron-beam induced breakdown of the electrolytes. The stability of the LiTf salt when dissolved in the nonaqueous polar solvent DMSO and exposed to a high amount of solvated electrons was not surprising as this electrolyte has previously shown high stability.28 To ensure that the observed lack of degradation products when imaging the LiTf:DMSO mixture was not a result of improper focus, the edge of the window was recorded as a reference. Apart from the LiTf, all other salt containing solutions tested showed some evidence of degradation, although the specific rates, products, and mechanisms varied and depend on the saltsolvent combination. To evaluate the role of the organic solvents on the formation rate of the degradation products we performed in situ STEM experiments on LiAsF6 in three different solvents (see Figure 2a−c). The degradation of LiAsF6 in DOL when exposed to e−sol starts from the first frame (Figure 2a), forming ∼100 nm particles after 60 s total exposure time, that evolve into nanorods and also much smaller particles with brighter pixel intensity. The fact that nanorods are forming and grow continuously suggests that the organic has not degraded and is still acting to allow preferential growth along one axis. From the corresponding EELS spectrum (Figure 1c), a main component of these degradation products appears to contain arsenic (see Supporting Information) that could exist as either AsF3 or fully reduced As0 and are both common degradation products found in the SEI layer for LiAsF6-based electrolytes.34 For both LiAsF6 in DMC (Figure 2b) and LiAsF6 in EC/ DMC (Figure 2c), growth of rounded nanoparticles is observed instead of nanorods as seen in the presence of DOL. However, when the cosolvent EC is mixed with DMC (Figure 2c), the particle growth appears slower. The most apparent difference is that the breakdown of LiAsF6 in DMC occurs through two distinct degradation mechanisms. Once the rounded nanoparticles achieve a stable size of 200 nm, a second growth process initiates and occurs at a much faster rate. High area coverage is achieved with all solvents, the highest being observed with DOL. Because LiPF6 decomposes in a similar way as LiAsF6 to form a highly reactive Lewis acid, we also investigated its stability in EC/DMC to test the effect of the salt. Figure 2d shows the decomposition of LiPF6 in EC/DMC over time under the same dose conditions as used for the LiAsF6 in the same solvent. Compared to LiAsF6, the LiPF6 mixture appears more stable as evidenced by the presence of smaller and fewer nanoparticles. This trend was suggested previously due to the lower bimolecular rate constant for reduction of PF6 versus AsF6.34,39 Finally, to separate the contribution of the salt and the solvent, a mixture of EC/DMC in the absence of salt has also been tested. For this latter system, no obvious decomposition is observed even after 7 min of continuous beam exposure, suggesting that the decom-
Figure 2. e−-beam induced breakdown of different electrolytes upon e−-beam irradiation. (a−e) Cropped BF STEM images showing the time evolution of five different electrolyte solutions for the same dose values per image (13.7 e−/nm2f|) at exposure times of t = 3.2 s, 60 s, 131 s, and a longer time (different for each system). Images (a−c) correspond to solution of 1 molar LiAsF6 dissolved in (a) DOL, (b) DMC, and (c) EC/DMC (1:2, v:v). Images in (d) correspond to 1 molar LiPF6 in EC/DMC (1:2, v:v). (e) Sequential images from 1 molar LiTf in DMSO showing a high stability of the electrolyte upon electron beam irradiation for an extended period of time. (f) Frames from a data set probing the stability of the solvent EC/DMC for the same dose conditions as above over 7 min of continuous irradiation. The magnification for all data sets was M = 20000×, pixel-dwell time was 3 μs, total frame time accounting for STEM imaging flyback was 3.78 s, calibrated beam current 12 pA, and image size was 1024 × 1024 pixels. (g) TEM images of an irradiated area of the LiAsF6 in DMC mixture after separating and washing the Si chips for performing postmortem analysis. Low-magnification (left) and high-resolution TEM and consequent fast Fourier transform of the irradiated area shows the presence of LiF nanocrystals.
I0 = e(−t/λ) .36 This approach for estimating the thickness of a material has been previously applied to the study of aqueous solutions within the liquid cell.37 For all measurements, the fluid thickness stayed below t ∼ 6.5 λ, which previous studies have found to be sufficiently thin for obtaining valence information from the EELS.38 Spectra were recorded adjacent to the scan areas for the damage studies whenever possible in order to record the signal of a pure liquid phase (a full description of the EELS analysis is provided in the Supporting Information). 1295
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Figure 3. Two distinct degradation processes observed in LiAsF6 in DMC. (a) Series of cropped BF STEM frames from an in situ movie of continuous electron beam irradiation of 1 molar LiAsF6 in DMC electrolyte at a dose per frame of 3.4 e−/nm2f (M = 10000×, 3 μs pixel-dwell time, 3.78s frame time accounting for the STEM image flyback, 12pA beam current and 1024 × 1024 pixel image size). (b) Simultaneous HAADF STEM image and associated intensity line profiles (c) for primary growth (blue box) and secondary growth (red box). (d) Plots of particle diameter evolution over time using multitarget particle tracking method for LiAsF6 in DMC sample. The blue curves are the fitting for the primary growth and the red curves are the fitting for the secondary growth. The left plot is for the lower dose rate experiment (panel a data set) and the right plot is for the higher dose rate experiment (Figure 2b data set).
LiAsF6 in DMC at a dose per frame of 3.4 e−/nm2f, 4× smaller than that used in Figure 2b (achieved by a 2× reduction in imaging magnification). In the same manner as is observed in Figure 2b, nucleation and growth of primary particles occurs within the first few frames of electron-beam illumination. The formation of larger, secondary particles (indicated with white arrows) is coincident with the stabilization of size and shape of the smaller, primary particles, indicating a serial correlation between two growth processes. HAADF STEM images (Figure
position of the salt triggers a domino cascade reaction involving both the salt and the solvent, consistent with previous observations.7,40 To further understand the two-stage degradation/growth process of LiAsF6 in DMC by electron beam irradiation, we have used quantitative image analysis (Figure 3), as developed previously for tracking and quantifying nanoparticle growth and interactions.15 Figure 3a displays an additional series of BF STEM frames from an in situ movie of the degradation of 1296
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consistent with previous electrochemical stability tests with LiTf showing the highest stability against degradation at the dose conditions used here. Electrolytes containing the salt LiAsF6 show fast degradation under the electron beam, being consistent with the high reactivity reported for LiAsF6. Additionally, all three LiAsF6-based electrolytes displayed formation of nanoparticles as degradation products that was expected due to the known formation of LiF particles from these electrolytes during previous tests.35 The work carried out in this study is critical for in operando liquid (S)TEM experiments of working batteries at the nanoscale, where any observations of the battery processes must be free of e−-beam artifacts. Additional information can be extracted by combining in situ results with careful post mortem analyses of the reaction products formed during the experiment, making sure to couple particles observed by in situ imaging and spectroscopy (see Supporting InformationFigure S2 for the structural analysis of nanocrystalline LiF observed ex situ in a washed, previously irradiated SiNx chip). Furthermore, once the effect of the imaging electrons is fully calibrated, this approach could potentially provide insights into the degradation mechanisms that occur during the first stages of SEI formation. As a point of interest, Peled et al. previously reported that Li battery electrolyte materials which have a low Ke form SEI at lower potential versus Li/Li+, while those having high Ke will form at higher ESEI (versus Li/Li+). Therefore, a correlation between rate constants (Ke) of the reaction of solvated electrons with electrolyte components, and SEI formation voltage (ESEI) and composition has been previously demonstrated using X-ray photoelectron spectroscopy.34 It is intriguing to consider the possibility that one day in the near future in situ (S)TEM could possibly be used to study these processes through direct visualization and in real-time with the intent of optimizing current state-of-the-art and next generation electrolytes where additives are incorporated to form a SEI with controlled properties and with an emphasis on the formation of stable decomposition products at high potential.27 Materials and Methods. Solvents EC, DMC, and DOL and lithium salts LiAsF6, LiTf, and LiPF6, all in battery grade, were purchased from BASF Battery Materials (Independence, OH, U.S.A.). DMSO (anhydrous, ≥99.9%) was acquired from Sigma-Aldrich and was further dried with preactivated molecular sieves prior to use. Electrolyte solutions of 1 molar lithium salt in different solvents were prepared inside an MBraun glovebox filled with purified argon. In situ degradation STEM data sets and EELS spectra were acquired using an 80−300 kV FEI probe Cs-corrected Titan electron microscope equipped with an electron gun monochromator and a Gatan Quantum ERS spectrometer. HRTEM images were performed using an 80−300 kV FEI image Cscorrected environmental electron microscope in high-vacuum mode. All the images were taken using 300 kV. A Hummingbird Scientific fluid stage was used for all liquid experiments performed. Two silicon chips with silicon nitride membranes of thicknesses 50 (Hummingbird Scientific), 30, and 10 nm (Norcada, Inc.) were used to image the electrolytes LiAsF6 in DMC and in EC/DMC, LiPF6 in EC/DMC, and the solvent EC/DMC (50 nm), LiAsF6 in DOL (30 nm), and LiTf in DMSO (10 nm). The moisture level was controlled using a glovebox with argon environment to prevent LiPF6 in EC/ DMC from forming reactive hydrofluoric acid, HF, in the presence of water.7
3b), acquired simultaneously to the BF images, provided information into the relative atomic number and thickness of the primary and secondary particles, which approximated their chemical compositions. Intensity line profiles (Figure 3c) taken across the small particles (primary growth process) and large particles (secondary growth process) demonstrate that despite being considerably larger in projected diameter, and presumably thicker in the z-dimension, the secondary particles had essentially equal pixel intensity to the smaller primary particles. We believe that the secondary particles are therefore likely to be polymerized organic (small Z-number), while the small primary particles are likely to be inorganic material (high Znumber). This observation was supported by post mortem analysis in Figure 2g, where after harvesting, separating, and washing the chips used during the in situ experiment a structured organic coating was seen in the same area as individual LiF nanocrystals indicating both polymerization of organics and inorganic crystallization occurred in the same field of view. Quantitative multitarget particle tracking statistical analysis of the raw BF STEM movies41 (details of the analysis are provided in the Materials and Methods and Figure S1) yielded plots (Figure 3d) of the projected particle diameter over time for each individual particle in the data sets from Figures 3a and 2b (left and right, respectively). The average growth curves for both the primary particles (blue curve) and the secondary particles (red curve) fit power law growth behavior, given by rparticle ∼ tβ, where β is the growth exponent (unitless). For primary particle growth β ≅ 0.1 (Figure 3a data set) and β ≅ 0.2 (Figure 2b data set), which are consistent with β-values reported previously for hindered, diffusion-limited growth of inorganic nanoparticles during in situ liquid STEM irradiation (β ∼ 0.13 for Ag).13 The secondary growth seen at the lower dose rate condition (Figure 3a data set) has β ≅ 0.5, which happens to be the β-value predicted by the Lifshitz−SlyozovWagner (LSW) growth model for reaction limited growth. However, at the larger dose rate (Figure 2b data set) the secondary growth has β ≅ 0.7, which is significantly larger than β expected for inorganic growth by the LSW model, again suggesting that the secondary particles are likely composed of polymerized organic matter, rather than inorganic growth. By comparing these two data sets, we see that the imaging electron dose rate influences the growth exponents for both the primary and secondary particles, as well as the time required for the initiation of the secondary growth process (40 s for higher dose, and 96 s for lower dose). However, for both dose conditions the initiation of secondary growth occurs at the same stabilized average primary particle size (dparticle ∼ 200 nm). In summary, we have shown that the electron-beam in the STEM can be used as an effective tool for evaluating stability and degradation in battery electrolytes by allowing us to directly visualize the reductive decomposition of the electrolyte components. Using in situ liquid (S)TEM, we are able to directly observe a sequence of interconnected degradation mechanisms (see Figure 3) that otherwise could only be inferred from post mortem analysis40,42 (chromatography). The in situ approach presented here can potentially be used to scan new libraries of electrolytes in order to more rapidly develop and identify next-generation electrolytes. A calibration of the effect of electron dose on the formation of insoluble species will be important to fully understand the action of electrolytes additives. Furthermore, each electrolyte behaved differently under the electron-beam, and the in situ stability studies are 1297
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by the Ralph E. Powe Junior Faculty Enhancement Award. P.A. thanks Dr. Ivan T. Lucas for helpful discussions.
The electron current measured in the screen dose-meter of the microscope was calibrated to obtain the exact electron current values at the sample plane using an analytical holder with incorporated faraday cup (Gatan, Inc.). The electron dose per frame (electrons/(nm2f)), where f stands for frame in the in situ movie, is calculated by multiplying the calibrated beam current at the sample, ie (C/s), by the frame time and dividing by the size of the viewing area as follows: (ie*tf)/(e*A), where A is the scan area (nm2), e is the elementary charge (C/ electron) and tf is the frame time. Further details on the calculation of the electron dose rate, image acquisition, sample loading, and choice of microscope parameters can be found in previous publications.13,22,43,44 The multitarget particle tracking approach has been previously applied to the analysis of video frames of silver nanoparticles grown using in situ liquid STEM15 and has provided insights into the differences in growth across lengths scales. First, an image segmentation algorithm was applied to successive images in order to extract a set of image pixel locations for nanoparticles,45 and an object tracking algorithm is applied for associating the pixel locations over multiple time frames.46 Further details can be found in refs 15 and 41.
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(1) Yamamoto, K.; Iriyama, Y.; Asaka, T.; Hirayama, T.; Fujita, H.; Fisher, C. A. J.; Nonaka, K.; Sugita, Y.; Ogumi, Z. Angew. Chem., Int. Ed. 2010, 49, 4414−4417. (2) Wang, C. M.; Xu, W.; Liu, J.; Choi, D. W.; Arey, B.; Saraf, L. V.; Zhang, J. G.; Yang, Z. G.; Thevuthasan, S.; Baer, D. R.; Salmon, N. J. Mater. Res. 2010, 25, 1541−1547. (3) Wang, C. M.; Xu, W.; Liu, J.; Zhang, J. G.; Saraf, L. V.; Arey, B. W.; Choi, D. W.; Yang, Z. G.; Xiao, J.; Thevuthasan, S.; Baer, D. R. Nano Lett. 2011, 11, 1874−1880. (4) Klett, M.; Giesecke, M.; Nyman, A.; Hallberg, F.; Lindstrom, R. W.; Lindbergh, G.; Furo, I. J. Am. Chem. Soc. 2012, 134, 14654−14657. (5) Wang, J.; Chen-Wiegart, Y.-c. K.; Wang, J. Chem. Commun. 2013, 49, 6480−6482. (6) Lucas, I. T.; Pollak, E.; Kostecki, R. Electrochem. Commun. 2009, 11, 2157−2160. (7) Lux, S. F.; Lucas, I. T.; Pollak, E.; Passerini, S.; Winter, M.; Kostecki, R. Electrochem. Commun. 2012, 14, 47−50. (8) Novak, P.; Goers, D.; Hardwick, L.; Holzapfel, M.; Scheifele, W.; Ufhiel, J.; Wursig, A. J. Power Sources 2005, 146, 15−20. (9) Huang, J. Y.; Zhong, L.; Wang, C. M.; Sullivan, J. P.; Xu, W.; Zhang, L. Q.; Mao, S. X.; Hudak, N. S.; Liu, X. H.; Subramanian, A.; Fan, H. Y.; Qi, L. A.; Kushima, A.; Li, J. Science 2010, 330, 1515−1520. (10) Brazier, A.; Dupont, L.; Dantras-Laffont, L.; Kuwata, N.; Kawamura, J.; Tarascon, J. M. Chem. Mater. 2008, 20, 2352−2359. (11) Liu, X. H.; Liu, Y.; Kushima, A.; Zhang, S.; Zhu, T.; Li, J.; Huang, J. Y. Adv. Energy Mater. 2012, 2, 722−741. (12) Liu, X. H.; Huang, J. Y. Energy Environ. Sci. 2011, 4, 3844−3860. (13) Woehl, T. J.; Evans, J. E.; Arslan, L.; Ristenpart, W. D.; Browning, N. D. ACS Nano 2012, 6, 8599−8610. (14) Liao, H. G.; Cui, L. K.; Whitelam, S.; Zheng, H. M. Science 2012, 336, 1011−1014. (15) Woehl, T. J.; Park, C.; Evans, J. E.; Arslan, I.; Ristenpart, W. D.; Browning, N. D. Nano Lett. 2014, 14, 373−8. (16) Evans, J. E.; Jungjohann, K. L.; Wong, P. C. K.; Chiu, P.-L.; Dutrow, G. H.; Arslan, I.; Browning, N. D. Micron 2012, 43, 1085− 1090. (17) Mirsaidov, U. M.; Zheng, H. M.; Casana, Y.; Matsudaira, P. Biophys. J. 2012, 102, L15−L17. (18) Huang, T. W.; Liu, S. Y.; Chuang, Y. J.; Hsieh, H. Y.; Tsai, C. Y.; Wu, W. J.; Tsai, C. T.; Mirsaidov, U.; Matsudaira, P.; Chang, C. S.; Tseng, F. G.; Chen, F. R. Soft Matter 2013, 9, 8856−8861. (19) Proetto, M. T.; Rush, A. M.; Chien, M. P.; Abellan Baeza, P.; Patterson, J. P.; Thompson, M. P.; Olson, N. H.; Moore, C. E.; Rheingold, A. L.; Andolina, C.; Millstone, J.; Howell, S. B.; Browning, N. D.; Evans, J. E.; Gianneschi, N. C. J. Am. Chem. Soc. 2014, 136, 1162−1165. (20) Williamson, M. J.; Tromp, R. M.; Vereecken, P. M.; Hull, R.; Ross, F. M. Nat. Mater. 2003, 2, 532−536. (21) White, E. R.; Singer, S. B.; Augustyn, V.; Hubbard, W. A.; Mecklenburg, M.; Dunn, B.; Regan, B. C. ACS Nano 2012, 6, 6308− 6317. (22) Evans, J. E.; Jungjohann, K. L.; Browning, N. D.; Arslan, I. Nano Lett. 2011, 11, 2809−2813. (23) Zheng, H. M.; Claridge, S. A.; Minor, A. M.; Alivisatos, A. P.; Dahmen, U. Nano Lett. 2009, 9, 2460−2465. (24) Jungjohann, K. L.; Bliznakov, S.; Sutter, P. W.; Stach, E. A.; Sutter, E. A. Nano Lett. 2013, 13, 2964−2970. (25) Parent, L. R.; Robinson, D. B.; Cappillino, P. J.; Hartnett, R. J.; Abellan, P.; Evans, J. E.; Browning, N. D.; Arslan, I. Chem. Mater. 2014, 26, 1426−1433. (26) Gu, M.; Parent, L. R.; Mehdi, B. L.; Unocic, R. R.; McDowell, M. T.; Sacci, R. L.; Xu, W.; Connell, J. G.; Xu, P.; Abellan, P.; Chen, X.; Zhang, Y.; Perea, D. E.; Evans, J. E.; Lauhon, L. J.; Zhang, J.-G.; Liu, J.; Browning, N. D.; Cui, Y.; Arslan, I.; Wang, C.-M. Nano Lett. 2013, 13, 6106−6112.
ASSOCIATED CONTENT
S Supporting Information *
Details on the analysis of the energy loss spectra; supporting movies (S1−S7) of the in situ degradation of the different electrolytes induced by the electron beam, supporting Figure S1 showing examples of movie frames where the image segmentation algorithm was applied and histograms of the growth exponent distribution and Figure S2 showing a lowmagnification TEM image of an irradiated area displaying a jelly mixture of phases and HRTEM analysis of nanocrystalline LiF grains after the degradation experiments. This material is available free of charge via the Internet at http://pubs.acs.org.
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REFERENCES
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The electrolytes used in this work were prepared with the support from Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by DOE, Office of Science, Basic Energy Sciences. The work involving development of in situ stages was supported by the Chemical Imaging Initiative; under the Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy (DOE) under Contract DE-AC05-76RL01830. A portion of the research was performed using the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. C.P. was supported by the National Science Foundation (NSF), Division of Civil, Mechanical, and Manufacturing Innovation (CMMI) under contract NSFCMMI-1334012, by Florida State University (FSU), Committee on Faculty Research Support (COFRS) award 032968 and 1298
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dx.doi.org/10.1021/nl404271k | Nano Lett. 2014, 14, 1293−1299
