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Solid-State Li-Ion Batteries Using Fast, Stable, Glassy Nanocomposite Electrolytes for Good Safety and Long Cycle-Life Guoqiang Tan,†,‡ Feng Wu,*,†,§ Chun Zhan,‡ Jing Wang,†,§ Daobin Mu,†,§ Jun Lu,*,‡ and Khalil Amine‡ †

School of Materials Science and Engineering, Beijing Institute of Technology, Beijing Key Laboratory of Environmental Science and Engineering, Beijing 100081, China ‡ Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 S. Cass Avenue, Lemont, Illinois 60439, United States § Collaborative Innovation Center of Electric Vehicles in Beijing, Beijing 100081, China S Supporting Information *

ABSTRACT: The development of safe, stable, and long-life Li-ion batteries is being intensively pursued to enable the electrification of transportation and intelligent grid applications. Here, we report a new solid-state Li-ion battery technology, using a solid nanocomposite electrolyte composed of porous silica matrices with in situ immobilizing Li+conducting ionic liquid, anode material of MCMB, and cathode material of LiCoO2, LiNi1/3Co1/3Mn1/3O2, or LiFePO4. An injection printing method is used for the electrode/ electrolyte preparation. Solid nanocomposite electrolytes exhibit superior performance to the conventional organic electrolytes with regard to safety and cycle-life. They also have a transparent glassy structure with high ionic conductivity and good mechanical strength. Solid-state full cells tested with the various cathodes exhibited high specific capacities, long cycling stability, and excellent high temperature performance. This solid-state battery technology will provide new avenues for the rational engineering of advanced Li-ion batteries and other electrochemical devices. KEYWORDS: Silica matrix, ionic liquid, nanocomposite, solid electrolyte, full cell, Li-ion battery

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safe, suffer from low conductivities and insufficient electrode− electrolyte interfaces for high power applications.18−21 Despite significant research in this area, there remains a need for improved electrolyte materials that can be easily incorporated into solid-state LIBs without expensive synthesis cost or a complex fabrication process. Solid-state ion-conducting composite systems, which are based on in situ immobilizing ionic liquids (ILs) within organic, inorganic, or hybrid porous matrices, offer a wide choice of electrolyte materials for solid-state LIBs.9,10,22−28 In these composites, generally, the ILs always maintain their liquid dynamics, so they are responsible for ion conducting and other electrochemical properties; the porous matrices provide abundant channels to confine ILs while maintaining good mechanical properties, so the composites look like solid materials. Such solid composite electrolytes also have been previously shown to reduce lithium dendrite formation and proliferation in lithium metal batteries.10,20 Herein, we report on a solid-state Li-ion configuration using porous silica matrices

ince the commercialization of the LiCoO2/graphite system by Sony in 1991, Li-ion batteries (LIBs) have been used heavily in consumer electronics worldwide, and their use is expanding to electric vehicles and other high power transportation applications as their prices continue to decline.1−3 With the currently rapid development of the electric and energy industries, there is growing demand for LIBs with higher energy/power densities, longer lifetimes, and better safety. Recently, solid-state LIBs have been proposed to achieve significant improvement over the state-of-the-art LIBs, which contain organic electrolytes.4−10 In the solid-state LIBs, one important component that needs to be improved to make it more suitable for high performance applications is the electrolyte material. Generally, high Li+ ion mobility and a wide voltage window are required for high energy applications, efficient charge and discharge with a minimum of power loss to resistive heating, and good structural stability and electrode− electrolyte interface compatibility to guarantee battery safety.11−14 However, up to now, very few solid electrolytes have been developed with the above combination of performance parameters. For example, polymer solid electrolytes prevent leakage but do not solve the flammability issue due to their organic nature of thermal degradation;15−17 inorganic solid electrolytes, which are solvent free and thus keep batteries © XXXX American Chemical Society

Received: December 22, 2015 Revised: January 22, 2016

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Figure 1. Schematic of the synthetic route and structural composition of the SiO2/[BMI][TFSI]/LiTFSI nanocomposite electrolytes.

Table 1. Nanocomposites: Composition, Pore Volumes, Pore Diameters, and Surface Areas sample compositions (in relative molar ratios) sample

TEOS

LiTFSI

HCOOH

[BMI][TFSI]

Vpor [cm3·g−1]

D [nm]

SBET [m2·g−1]

NE-0 NE-1 NE-2 NE-3 NE-4 ILE-3

1 1 1 1 1 0

0.5 0.5 0.5 0.5 0.5 0.5

8.7 8.7 8.7 8.7 8.7 0

0.0 0.5 1.0 1.5 2.0 1.5

0.63 1.14 1.75 1.52 1.38

3 6 8 10 12

1000 780 1080 950 860

combined with in situ immobilizing Li+-conducting ILs as the solid-electrolyte separator; mesocarbon microbeads (MCMB) as anode material; and LiCoO2 (LCO), LiNi1/3Co1/3Mn1/3O2 (NCM), or LiFePO4 (LFP) as cathode material. We investigate the electrochemical performance of these systems and also their structural compositions, dynamic features, and electrochemical mechanisms. The Li+-conducting IL we investigated is [BMI][TFSI]/ LiTFSI, where [BMI][TFSI] is 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonylimide), and LiTFSI is lithium trifluoromethanesulfonate. This liquid was incorporated into mesoporous silica matrices via a nonaqueous sol−gel route (Figure 1). The resulting composite possesses a transparent glass shape, abundant internal cross-linking networks, hybrid solid/liquid nanocompositions, and fluid-like dynamics (Figures S1 and S2, Supporting Information). These properties result in excellent structural and electrochemical properties, including stable mechanical strength, good thermal stability, high ionic conductivity, and wide voltage window (Figures S2 and S3). To take advantage of these attractive properties, we incorporate the nanocomposite electrolytes as solid-electrolyte separators into LIBs, thus creating a new solid-state Li-ion cell configuration. We characterize the battery properties and find that they are promising candidates for the next generation of rechargeable batteries. Hereafter, we refer to the Li+-conducting IL electrolytes ([BMI][TFSI]/LiTFSI) as ILEs, and the nanocomposite electrolytes (SiO2/[BMI][TFSI]/LiTFSI) as NEs. The solidstate Li-ion full cells composed of an LCO, NCM, or LFP cathode, NE solid electrolyte, and MCMB anode are referred to as LCO/NE/MCMB, NCM/NE/MCMB, and LFP/NE/ MCMB, respectively. The NEs were synthesized using a nonaqueous sol−gel procedure, as shown in Figure 1 and discussed in Methods

(Supporting Information). Predeterminded amounts of the asprepared ILEs were directly blended with a mixture of tetraethoxysilane (TEOS) and formic acid (HCOOH), then stored 30 min so that the gelation produced NEs with a range of ILE loadings. Scanning electron microscopy (SEM) and N 2 sorption−desorption measurements (Figure S1) confirmed that the nanosilica particles cross-link as a porous matrix, which possesses abundant networks and high open porosity. It is noteworthy that the average pore diameter and pore dispersion significantly increase as the ILE/TEOS molar ratio increases. Table 1 shows the compositions, specific surface areas, total pore volumes, and average pore diameters of the five NEs studied after removal of the ILE. Also shown is the composition of the one ILE sample studied for comparison. The NEs look like glass monoliths (Figure S1H) and are transparent, smooth, and homogeneous, without obvious volume shrinkage during aging and drying owing to the negligible vapor pressure of ILs. Table S1 shows the mechanical parameters of NEs measured by the three-point bending technique, which indicates fracture strength in the range of 0.69−0.85 MPa, and a Young modulus in the range of 57.3−63.8 MPa. The mechanical strength decreases as increasing the ILE content because more ILE yields much looser structure. The nanocomposites can be easily processed into various sizes and shapes by a simple fabrication process, allowing their flexible incorporation into electrical devices. Figure 2 shows an optical photograph, SEM images, transmission electron microscopy (TEM) images, and a molecular structural representation for the thin films of NE-2. The round thin films were directly formed in stainless steel molds with thickness of about 0.5 mm, which are the thinnest films we used for assembly of the half-cells. They appear to be transparent, smooth, homogeneous, and crack-free (Figure 2A). B

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Figure 2. Structure and morphology of NE-2 thin films. (A) Optical photograph; (B) surface and (C) cross-sectional SEM images of the film washed out the ILE; (D,E) TEM images of the pure silica matrix; and (F) schematic diagram showing 3D mesoporous structure.

state 7Li nuclear magnetic resonance (NMR) measurements, as shown in Figure S2. The XRD patterns (Figure S2A) show a structural comparison for all samples. The ILE shows two obvious peaks at 12.6° and 19.5°, which indicate that [BMI][TFSI] is purely monophasic. The ions are associated as ion pairs in the liquid state.29 While the ILE is confined in NEs, the peaks show no shift, only a gradually decreasing intensity with reduced ILE content. The silica matrix is devoid of any sharp peaks, except a broad peak at 15°−30°, indicating an amorphous structure. The FT-IR spectra (Figure S2B) provide considerable insight into the chemical structure of NEs. The ILE spectrum shows various characteristic peaks associated with the [BMI][TFSI] structure. Table S2 gives the peak wavelengths. The FT-IR spectrum for the silica matrix shows two strong bands at 797 and 1060 cm−1, which are attributed to Si−O−Si bending and asymmetric stretching vibrations, respectively. The two weak bands at 960 and 1200 cm−1 are due to the stretching vibrations of various Si−O−Si bonds of silicate networks.30−32 The NE-2 spectrum is found to be a good superposition of those of the ILE and silica matrix. No significant changes are observed in the individual spectrum, suggesting that strong interactions, such as hydrogen bonding between the ILE and silica networks, are not

These features are significantly important for solid-state electrolytes to avoid short circuit and, hence, the safety issues in batteries. The surface (Figure 2B) of the thin film after removing the ILE shows a ravine-like cross-linked structure, and its cross-section (Figure 2C) shows a porous network consisting of a large number of silica nanoparticles. The TEM images (Figure 2D,E) show the pore structure and morphology of the matrix. The fabrication method yields a controllable mesoporous silica matrix composed of numerous worm-like interconnected channels and nanopores. The average pore diameter of the NE-2 sample is about 8 nm, while the ion sizes of [BMI][TFSI] are calculated to be 1.01 and 0.79 nm in the longest dimension for the BMI+ and TFSI− ions, respectively. Because the ion sizes are smaller than the pore sizes, we assume that, in the NEs, ILEs are entrapped as liquid-state “microspheres” in the mesoporous silica matrix at the nanometer scale. Hence, the NEs are pictured as two interpenetrating continuous mesoporous matrices of silica and ILEs intermingled at the molecular scale (Figure 2F). The structural compositions and dynamics of NEs were elucidated by the X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and solidC

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298 K

333 K

373 K

473 K

activation energy E [eV] (333−473 K)

electrochemical window (V vs Li+/Li)

NE-1 NE-2 NE-3 NE-4 ILE-3

1.19 2.85 3.15 3.57 5.21

4.85 7.88 9.17 10.8 13.3

10.7 16.9 19.0 22.8 29.1

36.0 57.2 64.7 70.7 77.0

0.25 0.23 0.22 0.21 0.20

4.0 3.9 3.9 3.8 3.7

prevalent in the NEs. Thus, we believe that the ILE is physically entrapped in silica nanopores, rather than chemically bound to silica networks. Similar structure and mechanism analyses have been reported in previous literature.10,33,34 The FT-IR spectra indicate that the ILEs are physically confined in interconnected channels and pores rather than chemically bound to the silica. Thus, scarcely any strong chemical interactions can restrict the molecular mobility by forming high kinetic barriers and causing high activation energies to retard ion transfer. Solid-state 7Li NMR spectra of NEs (Figure S2C) confirm their liquid dynamics. Compared to the pristine LiTFSI, the NEs show a distinctive change. The number and intensity of the spinning sidebands in the 7Li MAS NMR spectra together with the line width of the signal in the static 7Li NMR spectra are drastically reduced. Generally, the spinning sidebands indicate the quadrupolar coupling of the 7Li nuclei due to the dynamics of Li+ ions; while the line width of the static 7Li NMR signal represents the homo- and heteronuclear dipolar interactions. A close inspection of the line widths and the almost complete loss in spinning sideband intensities indicate a high Li+ dynamic mobility within the porous networks.10,35 It is also found that both the static 7Li NMR line width and residual spinning sideband intensities gradually decrease with increasing the ILE content, showing a corresponding increase in Li+ mobility. This result demonstrated that Li+ ions possess almost fluid-like dynamics in NEs, which contain high ILE content. Both TGA and DSC (Figure S2D−F) reveal the thermodynamic characteristics of NE-1 to NE-4 and ILE. The TGA results show that the NEs are thermally stable up to 390 °C, which is slightly higher than that of the liquid ILEs due to their confinement effect on ILE. Moreover, the degradation temperature (T5% or T10%) of the NEs (inset, Figure S2D) gradually increase with decreasing ILE content in NEs; that is to say, the thermal stability of NEs, to some extent, is dependent on the confinement effect on ILE caused by the pore sizes. It is noteworthy that 12−23 wt % of silica skeleton remains, suggesting that the weight of ILE in NE is 3−7 times higher than that of the silica. This finding indicates that a great deal of ILE is confined in silica matrices. The DSC results show a dramatic change in the NE: both crystallization and melting grow stronger with increasing ILE content in NE, that is to say, the confined ILE exhibits almost fluid-like dynamics in NE, and this fluid dynamics property is beneficial for ion transfer. High ionic conductivity and good electrochemical stability are prerequisites for solid-state electrolytes. Table 2 and Figure S3 illustrate the ionic conductivities and electrochemical windows (V vs Li+/Li) for the NEs and ILE-3 samples. The results show that the NEs exhibit attractive room-temperature ionic conductivities of 1.2−3.6 × 10−3 S·cm−1 at all ILE loadings. The temperature dependence of the conductivity at high (T > 50 °C) temperatures follows an Arrhenius behavior (Figure 3) with activation energies of EA = 0.23 ± 0.2 eV, which are mainly attributed to the improved fluid dynamics of

Figure 3. Arrhenius plots of ionic conductivity of the ILE-3 and NEs.

confined ILEs under high temperatures. While Vogel− Fulcher−Tammann (VFT) fitting curves (Figure S3B) at low (T < 50 °C) temperatures imply that the motion of the ions is controlled by the molecular relaxation and by exaggerated swinging motions of SiO2−IL−TFSI tethered to nanoparticles. Linear sweep voltammograms (LSV) (Figure S3C) and cyclic voltammograms (CV) (Figure S3D) indicate stable electrochemical windows of 3.9 ± 0.1 V vs Li+/Li. Such high ionic conductivity and stable electrochemical window should help enable the practical application of NEs in LIBs. The above results indicate that the mechanical strength and stabilities of the NEs gradually decreased with increasing ILE content; by contrast, the Li+ dynamic mobility and conduction properties increased with increasing ILE content. Among the NEs, NE-2 and NE-3 possess optimized comprehensive properties and thus are considered as the most suitable solidstate electrolytes for lithium-ion batteries. Two approaches were used to assemble the solid-state Li-ion cells. One is the conventional method of battery assembly: stacking an as-prepared NE thin film on a cathode, followed by a metal Li electrode to form a half cell. The other method is injection printing, i.e., using a syringe to print a layer of NE solvent precursor onto the as-prepared anodes and cathodes, then after gelation, drying them under vacuum at 100 °C. Several layers are required to obtain NEs with enough thickness about 30 μm to act as a solid electrolyte separator. Then, the NE-coated cathodes and anodes are stacked face to face in a coin cell to form a solid-state full cell. All of these cells are aged at 35 °C for 24 h before electrochemical testing. This aging can promote the penetration of electrolyte into the electrode bulk to achieve a good wetting electrode−electrolyte contact, which avoids high polarization. In addition, the injection printing results in electrodes and electrolytes that are mixed uniformly, which improves the interface compatibility, reduces the interfacial resistance, and promotes charge transfer. Figure 4 shows the initial charge−discharge profiles and cycling performance of the half cells with cathodes of LCO, D

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Figure 4. Electrochemical characterization of NEs in half cells. Initial charge−discharge profiles and cycling performance of LiCoO2/NEs/Li cells (A,D), LiCo1/3Ni1/3Mn1/3O2/NEs/Li cells (B,E), and LiFePO4/NEs/Li cells (C,F) worked at 30 °C and at C/10 rate. (In this and subsequent figures, the half cells are assembled using a conventional battery assembly method described in battery structural design; all cells are cycling at 30 °C.)

Figure 5. High temperature electrochemical characterization of NEs in Li/LiFePO4 half cells. Electrochemical impedance spectra of the LiFePO4/ NE-2/Li (A) and LiFePO4/NE-3/Li (B) cells before charging/discharging at different temperatures. High temperature cycling performance of the LiFePO4/NE-2/Li (C) and LiFePO4/NE-3/Li (D) cells worked at 55 °C at a current density of C/10 rate (insert: electrochemical impedance spectra of cells discharged to 2.5 V after selected cycles at 55 °C).

mainly attributed to the improved charge transfer in the electrode−electrolyte interface by increasing their wetting properties. The highest discharge capacities were achieved by

NCM, and LFP and the four NE compositions. It is noteworthy that the specific capacities of all these cells are gradually increasing with higher ILE content in the NEs. This finding is E

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Figure 6. Structural schematic of full cells and their electrochemical characterization. Charge−discharge profiles and cycling performance of LiCoO2/ NE-3/MCMB cells (A,D), LiCo1/3Ni1/3Mn1/3O2/NE-3/MCMB cells (B,E), and LiFePO4/NE-3/MCMB cells (C,F) worked at 30 °C and at C/10 rate. (In this figure, the full cells are assembled using an injection printing method described in battery structural design; all cells are cycling at 30 °C.)

the three half cells with NE-4: namely, 140.9, 148.7, and 149.6 mAh g−1 for LCO/NE-4/Li, NCM/NE-4/Li, and LFP/NE-4/ Li, respectively. Stable cycling performance was also observed for all these cells over 50 cycles, as shown in Figures 4D−F. Among these cells, the LFP/NE/Li cells always exhibit the best cycle stability, which is attributed to the LFP yielding the lowest charge/discharge voltage plateau. The NEs and their interfaces with the cathode are more stable in the lower voltage plateau. More comparisons of electrochemical performance for these half cells are shown in Table S3. Because of their high ionic conductivity and improved interface compatibility at high temperature, the half cells exhibit good high temperature performance. Figure 5 shows the electrochemical impedance spectroscopy (EIS) profiles and cycle performance of LFP/NE-2/Li and LFP/NE-3/Li at high

temperatures. Figure 5A,B gives the EIS profiles for cells heated from 25 °C to 30, 40, and 55 °C and then cooled to 40, 30, and 25 °C in a stepwise manner. At each step the temperature is maintained for 5 h to allow for the cell stabilization. As shown, the cell resistance gradually decreases with increasing temperature, caused by the improved conductivity and charge transfer. This suggests that the cell may have better charge−discharge performance at high temperature than at ambient. Moreover, the cell resistance almost recovers its original value when it is cooled to its initial temperature. This confirms the good thermal stability of these cells. Figure 5C,D shows that the specific capacity and Coulombic efficiency of LFP/NE/Li cells at 55 °C are higher than those at ambient. The LFP/NE-2/Li cell delivers an initial discharge capacity of 153.7 mAh g−1 and maintains a capacity retention of 151.3 mAh g−1 after 51 cycles. F

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Figure 7. Structure and morphology of cycled electrodes. SEM images and EDX elemental mapping of the cycled LiCoO2 (A), LiCo1/3Ni1/3Mn1/3O2 (B), LiFePO4 (C), and MCMB (D) electrodes after 100 cycles.

always have a little lower voltage plateau and larger polarization voltage differences than half cells. Also note that the Coulombic efficiency of all cells is decreasing with cycling number, especially in the final cycle stage, which is mainly ascribed to the increased polarization. The improved performance for the half and full cells is due to two important characteristics of this solid-state design. The first is the fluid-like dynamics, which ensure fast Li+ ion conduction in NEs and favorable charge transfer at electrode/electrolyte interfaces. The NEs consist of two interpenetrating continuous networks of silica and ILE intermingled at the molecular scale. The porous silica matrix affords high absorption capacity of ILE and provides good mechanical strength, so it looks like a solid glass. The ILE molecules in NEs exhibit a continuous liquid phase behavior, fluid-like dynamics, thus affording high ionic conductivity and good wettability. Figure S4 shows SEM images for an NCM/NE-3 layered structure with good compatibility, thanks to the low viscosity and good wetting properties of the ionogel precursor sol. Hence, the solid-state battery exhibits high reversible capacity and Coulombic efficiency. The second characteristic is the accommodation of structural change over long-term cycling, which retains the structural integrity of the electrodes and NEs, and also stabilizes the solid−electrolyte interphase (SEI) on the electrode/electrolyte interface. Figure 7 shows the structure and morphology of cycled electrodes in full cells after 100 cycles. The LCO, NCM, and MCMB electrode materials show nearly perfect spherical micrometer-sized particles, without obvious cracks or destruction. Few nanosized silica networks are observed in the electrode pores. In contrast, in the LFP electrode, due to the same order of magnitude scale of LFP particles and silica particles, the nanosized NEs are immersed in the electrode and uniformly mixed with LFP. It is always hard to wash away the silica networks from the LFP electrode, so it looks like a dense network. The EDX elemental mapping also indicates that the Si element distribution in the LFP electrode is more uniform than that in other electrodes. The nanoscale uniform dispersion of LFP/NEs confirms the high efficiency charge transfer and

The performance improves as increasing the ILE content, as the LFP/NE-3/Li cell still delivers a high discharge capacity of 153.6 mAh g−1, with an average Coulombic efficiency above 98.5%, over 51 cycles. It is noteworthy that both the reversible capacity and Coulombic efficiency increase during the first 10 cycles, which are contributed by the initial activation of solidstate cells. Under 55 °C, the NEs exhibit better wettability than that at ambient, which greatly improves the interface compatibility and structural stability of the electrode/electrolyte. That is to say, increasing the operating temperature in a proper manner enhances the molecular mobility of the ILE, which is beneficial for faster ion transfer in solid electrolytes and easier charge transfer at the electrode−electrolyte interfaces. However, it is also observed that the Coulombic efficiency declines and the charge transfer resistance increases with long cycling, which are mainly due to the instability of LiFePO4 for the Fe dissolution from cathode when it cycled at 55 °C.36,37 Figure 6 shows the structure of the full cells (top) and their voltage profiles and cycling performance with NE-3 (graphs below). Owing to the improved interface compatibility and structural stability of the electrode/electrolyte layered materials prepared by injection printing, the full cells show superior performance to the half cells. As shown in Figure 6A,D, the LCO/NE-3/MCMB cell delivers an initial discharge capacity of 138.8 mAh g−1, an initial Coulombic efficiency of 90.6%, and a capacity retention of 84.0% after 100 cycles. As shown in Figure 6B,E, the NCM/NE-3/MCMB cell shows an initial discharge capacity of 143.0 mAh g−1, an initial Coulombic efficiency of 89.2%, and a capacity retention of 92.4% after 100 cycles. As shown in Figure 6C,F, for the LFP/NE-3/MCMB cell, the corresponding values increase to 144.6 mAh g−1, 93.9%, and 98.9%, respectively. Note that the LFP full cell with NE-3 shows the best battery performance, including largest reversible capacity, highest Coulombic efficiency, and best cycling performance, which are attributed to the LFP yielding the lowest charge/discharge voltage plateau and nanoscale effects of LFP particles discussed below in Figure 7. Because of the lithiation potential of MCMB (∼0.5 V vs Li/Li+),38 the full cells G

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minimal interfacial resistance. This is another reason for that the LFP cells thus exhibit the best electrochemical performance among three cathode materials. Figure S5 shows the large-scale structure and morphology of the NCM electrode and electrolyte for the NCM/NE-3/ MCMB cell operated for 100 cycles. Note that the NCM particles and silica networks both maintain good structural integrity, which confirms the good cycling performance. The volume change of electrodes in this solid-state battery is much less than that in conventional batteries containing organic electrolytes. Also, the accommodated structural change ensures that the SEI on the electrode is thin and stable. This mechanism not only decreases the loss of irreversible capacity but also improves the charge-transfer efficiency and cycling stability. An additional advantage of such solid-state battery technology is that the NEs can be processed easily to give various shapes and sizes, allowing their application in electrical devices, and their synthesis does not involve any complex equipment or processes, resulting in the potential for low cost and easy reproducibility in commercial production and promotion. In conclusion, we have developed a solid-state Li-ion full cell technology, which entails injection printing of silica−ILE nanocomposite electrolytes onto porous composite electrodes. This approach allows fabrication of high-performance solidstate batteries with improved safety and cycle-life. This special solid-state design also provides new avenues for the rational engineering of battery configurations for lithium-ion batteries, beyond lithium-ion batteries, and other electrochemical devices.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.nanolett.5b05234. Experimental details; mechanical property and conducitvity of the materials; FT-IR, XRD, BET, and SEM characterization of the materials (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Basic Research Program of China (2015CB251100). This work was also supported by the U.S. Department of Energy under Contract DE-AC0206CH11357 with the main support provided by the Vehicle Technologies Office, Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE). We especially thank the collaboration between Beijing Institute of Technology and Argonne National Laboratory under ChinaU.S. Electric Vehicle and Battery Technology Program.

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REFERENCES

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DOI: 10.1021/acs.nanolett.5b05234 Nano Lett. XXXX, XXX, XXX−XXX

Letter

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DOI: 10.1021/acs.nanolett.5b05234 Nano Lett. XXXX, XXX, XXX−XXX