Construction of Uniform Cobalt-Based Nanoshells and Its Potential for

Jun 27, 2018 - Geballe Laboratory for Advanced Materials, Stanford University, Stanford , California 94305 , United States. △ College of Physics and...
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Construction of Uniform Cobalt-Based Nanoshells and Its Potential for Improving Li-Ion Battery Performance Jun-Yu Piao,†,‡,§ Xiao-Chan Liu,†,⊥ Jinpeng Wu,∥,# Wanli Yang,∥ Zengxi Wei,△ Jianmin Ma,△ Shu-Yi Duan,‡,§ Xi-Jie Lin,‡,§ Yan-Song Xu,‡,§ An-Min Cao,*,‡,§ and Li-Jun Wan*,‡,§

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CAS Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences (ICCAS), Beijing 100190, China § University of Chinese Academy of Sciences (UCAS), Beijing 100049, China ⊥ Shandong Provincial Key Laboratory for Special Silicone - Containing Materials, Advanced Materials Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250014, China ∥ Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States # Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, United States △ College of Physics and Electronics, Hunan University, Changsha 410022, China S Supporting Information *

ABSTRACT: Surface cobalt doping is an effective and economic way to improve the electrochemical performance of cathode materials. Herein, by tuning the precipitation kinetics of Co2+, we demonstrate an aqueous-based protocol to grow uniform basic cobaltous carbonate coating layer onto different substrates, and the thickness of the coating layer can be adjusted precisely in nanometer accuracy. Accordingly, by sintering the cobalt-coated LiNi0.5Mn1.5O4 cathode materials, an epitaxial cobalt-doped surface layer will be formed, which will act as a protective layer without hindering charge transfer. Consequently, improved battery performance is obtained because of the suppression of interfacial degradation. KEYWORDS: lithium-ion batteries, cobalt, surface doping, coating, LiNi0.5Mn1.5O4

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becomes an efficient and economic choice for the optimizations of cathode materials. According to the previously reported synthetic routes,12,13 it is logical to infer that surface Co-doped cathode materials will be achieved by sintering the cathode particles coated with Co based coating layers. The capability of constructing uniform and thickness-controllable Co-based coating layers is the key to realizing the surface Co doping protocol. Atomic layer deposition (ALD) technique has been used to construct uniform Co3O4 layers on different substrates where their thickness could be adjusted precisely.15,16 Unfortunately, because of the extremely high cost and the limitation in the yield, there are huge obstacles to the industrial application of the ALD technique.17 In the meantime, solution based coating route could be an appealing choice because of its high feasibility and low cost.18 However, because of the fast precipitation kinetics of Co2+ (Ksp[Co(OH)2] = 2 × 10−16),19 it is quite difficult to achieve a mild nucleation and growth precipitation process, leading to the formation of independent

ecause of the scientific and technological development and the support of policy, electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) are believed to play a significant role in alleviating energy and environment problems.1−3 As the main energy storage component for EVs and PHEVs, it is a challenge for lithium-ion batteries (LIBs) to meet the ever increasing demand of higher energy density, which is primarily determined by the cathode materials.4,5 Cathode materials with higher energy density usually suffer from their intrinsic drawbacks originate from either the high working voltage or unstable crystal structure, especially at the delithiated state.6 Therefore, proper modification is necessary for optimizing high-energy-density cathode materials for their practical use. Co doping has been reported to be helpful for optimizing the electrochemical performance of cathode materials due to the alleviated variation of lattice parameters during cycling and the increased electronic/ionic conductivity,7−9 especially at high temperature and high rate.10 However, the relatively high price of cobalt makes it uneconomic to dope Co at bulk level.11 Recently, a surface doping strategy has been proposed to be effective for improving the battery performance of cathode materials.12,13 Considering the significant role of a controlled surface,5,14 doping Co only on the surface naturally © XXXX American Chemical Society

Received: May 23, 2018 Accepted: June 27, 2018 Published: June 27, 2018 A

DOI: 10.1021/acsami.8b08528 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces particles instead of coating layers.20 Moreover, it is also a great challenge to ensure the uniformity and the thickness adjustability of the coating layer, which is critical to control the surface chemistry of the Co doped cathode materials. Therefore, it is of great importance to find a controllable and feasible way to deposit Co element, and form a uniform layer on the surface of cathode materials. Herein, we developed an aqueous-based protocol of constructing uniform basic cobaltous carbonate coating layer with a thickness adjustable in nanometer accuracy, and achieved surface cobalt doped 5 V spinel LiNi0.5Mn1.5O4 (LNMO) materials by sintering the cobalt coated LNMO particles. We selected LNMO as the representative of cathode materials because of its high energy density and serious interfacial problems originated from its high working voltage,5 which is suitable for demonstrating the effects of the surface cobalt doping strategy. Such feasible and controllable coating method endows us the capability to deposit proper amount of cobalt element evenly onto the surface of the pristine LNMO particles, which is able to ensure the uniformity of the surface doping layer after heat treatment and the precise control of the doping content. Such a well-designed surface does not negatively affect the charge transfer and the specific capacity of the LNMO materials. Indeed, an enhanced battery performance is achieved because of the alleviation of interfacial degradation. This study suggests that the surface cobalt doping strategy is promising in the stabilization of high-energy-density cathode materials of LIBs. Taking SiO2 nanospheres as an example for demonstrating our newly developed coating protocol. First, the pristine SiO2 nanospheres were obtained from the hydrolysis of tetraethyl orthosilicate according to a standard Stöber method.21 The transmission electron microscopy (TEM) image showed that the diameter of these SiO2 nanospheres was around 240 nm (Figure 1a). The coating layer was constructed through the hydrolysis of cobalt acetate in urea solution, and the thickness of the uniform coating layer could be adjusted by simply tuning the reaction time. In general, a longer hydrolysis time would lead to thicker coating layer (Figure 1b−d). Because of the alkalescent nature of the solution, the SiO2 nanospheres

might be partially dissolved when the reaction time was extended. Further synthesis efforts revealed that the construction of the uniform nanoshells could be ascribed to the effective control of the precipitation kinetics of Co2+, which was achieved by using urea to ensure the mild increase in the pH value. According to the LaMer’s Law,20 keeping a balance between nucleation and growth kinetics of the precipitate was eccential for achieving a hecterogeneous core−shell structure. After removing the SiO2 core, hollow spheres would be obtained (Figure 2a). As shown in Figure 2b, the X-ray

Figure 2. (a) STEM image of hollow spheres obtained from removing the SiO2 core of the coated SiO2 spheres. (b) XRD pattern of the hollow spheres mentioned in panel a. The XRD result indicated that the hollow spheres were basic cobaltous carbonate (PDF No. 48− 4083). (c) Co mapping of the hollow spheres mentioned in panel a. (d) O mapping of the hollow spheres mentioned in panel a.

diffraction (XRD) pattern showed that the coating layer was crystalline with a composition of basic cobaltous carbonate (PDF No. 48−4083), which matched well with the elemental mapping (Figure 2c, d). Encouragingly, such coating protocol could be well extended to different core materials, including oxides and organics. Figure 3a, b and Figure S1 showed the representing TEM images of the LNMO particles and phenolic resin nanospheres. In particular, the pristine LNMO sample (Figure 3a) was obtained through a sol−gel protocol,22 and the phenolic resin nanospheres were synthesized following our previous work (Figure S1a).23,24 Through a similar coating process, a coating layer would be formed on the surface of LNMO particles (Figure 3b) and phenolic resin nanospheres (Figure S1b). For the coated LNMO sample, because of the loose and unstable nature of the basic cobaltous carbonate coating layer, further heat treatment was necessary to achieve a stable surface for the protection of cathode materials. As shown in Figure 3c, LNMO sample with a clean surface (denote as Co-LNMO) would be obtained after sintering the LNMO particles coated with 12 nm of basic cobaltous carbonate. Thus, a surface reaction would take place during the sintering process and the Co element would diffuse into the surface of LNMO particles consequently. The corresponding high resolution TEM

Figure 1. (a) TEM image of the SiO2 nanospheres. (b−d) TEM image of the SiO2 nanospheres coated by basic cobaltous carbonate with different thickness. B

DOI: 10.1021/acsami.8b08528 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Figure 3. (a) TEM image of pristine LNMO particles. (b) TEM images of LNMO particles coated with 12 nm of basic cobaltous carbonate. (c) TEM image of Co-LNMO particles with an inset of HRTEM image. (d−g) Elemental mapping of a Co-LNMO particle. (h) STEM-HAADF image of the surface structure of Co-LNMO. (i) Schematic illustration of the surface cobalt doping strategy.

cathode materials, we studied the battery performance of CoLNMO by galvanostatic methods. Figure 4a compared the representative charge/discharge curves of pristine LNMO and Co-LNMO sample. Both the two samples showed characteristic 4.7 V plateaus originated from the redox of Ni.26 As the plateau voltage of Co4+/Co3+ was around 5.1 V in spinel type cathodes,27,28 the highly oxidative Co4+ would not be formed when the cell cycled in the range from 3.0 to 5.0 V. Accordingly, the doped Co element was electrochemically inactive in this circumstance and was not able to contribute to the specific capacity. We did not observe noticeable differences in charge/discharge profiles of the first cycle between the two samples, indicated that doping small amount of Co on the surface would not obviously affect the intrinsic electrochemical properties of LNMO. The most prominent contribution for surface doping was found to be the optimized cycling stability. After 100 cycles, the pristine LNMO sample showed much more severe specific capacity decay than Co-LNMO (Figure 4a), which could be further confirmed by the electrochemical performance at multiple cycling stages (Figure 4b). Moreover, an obvious change in plateau voltage could be observed for the cycled LNMO electrode, indicating a severe polarization which had been attributed to the electrode/electrolyte interfacial degradation.29 To have better understanding on the capacity degradation, electrochemical impedance spectroscopy (EIS) was employed to probe the interfacial issues associated with the surface reactions.29 The EIS spectra were shown in Figure 4c, which had been fitted using the equivalent circuit exhibited in the inset.30 The fitting result was provided in Table S2. As shown in Figure 4c, after 100 cycles, a great increase in impedance (from 172.1 Ω to 368.9 Ω) was observed for the pristine LNMO sample while the Co-LNMO sample showed a much reduced impedance increase (from 172.3 Ω to 252.7 Ω), revealing a much alleviated electrode/electrolyte interface deterioration process for Co-LNMO.29 This conclusion could be further confirmed by the enhanced rate performance for Co-LNMO (Figure 4d). Notably, by adjusting the thickness of the coating layer before sintering, different amount of Co would be introduced onto the surface of LNMO (Figure S4). Although LNMO sample with higher Co dopant amount

(HRTEM) image showed no significant change in the crystalline structure according to the measured (111) lattice spacing (inset in Figure 3c). The signal of Co could be detected in X-ray photoelectron spectroscopy (XPS), confirming the presence of Co on the surface of Co-LNMO (Figure S2a). To further characterize the distribution of Co, we carried out energy dispersive spectrum (EDS) analysis on the CoLNMO sample. As shown in Figure 3d−g, the results of the EDS analysis clearly revealed that the element of Co was enriched on the surface of Co-LNMO, indicating the surface cobalt doping nature of Co-LNMO. Besides, the inductively coupled plasma atomic emission spectroscopy (ICP-AES) based elemental analysis showed that the amount of Co was 0.81 wt % in Co-LNMO sample (Table S1). Moreover, the nearly unchanged Mn and Ni XPS peaks before and after doping Co on the surface indicated that the introduction of Co would not affect the chemical valence of the Mn and Ni (Figure S2b, c). We also examined the crystal structure of CoLNMO by X-ray diffraction (XRD). As shown in Figure S3, Co-LNMO and pristine LNMO had almost identical peaks corresponding to Fd3̅m space group (PDF No. 80−2162), confirmed that the spinel structure would keep unchanged in bulk level. To have better understanding of the atomic structure of the surface cobalt doped sample, we used the aberration-corrected scanning TEM in a high-angle angular dark-field (STEM-HAADF) mode to obtain the corresponding atomic scale images. Figure 3h was the STEM-HAADF image of Co-LNMO along the [110]spinel crystallographic direction. It was evident that the heavy atoms formed typical diamond shape both on the surface and in the body, which suggested that the Co ions were doped in the 16d sites of the spinel lattices.25 The surface cobalt doping process was schematically summarized in Figure 3i. After the heat treatment, the basic cobaltous carbonate coating layer would disappear and the Co ions would be driven into the 16d sites on the surface of the spinel LNMO particles, forming a cobalt doped surface layer. Meanwhile, the interior of these particles would remain unaffected. To examine the effectiveness of the surface Co doping strategy for the surface stabilization of high-energy -density C

DOI: 10.1021/acsami.8b08528 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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exhibited an optimized cycling performance at elevated temperature (55 °C) as well (Figure S5b), indicating a much increased thermal stability for the surface Co doped sample. Furthermore, we also investigated the Mn dissolution during long time cycling, which had been considered to be responsible for the fatigue of LNMO cathode,31,32 using the ICP-AES. As shown in Table S3, the Co-doped surface was more effective for suppressing Mn dissolution than the original spinel structure, indicating that the Co-doped surface would endow Co-LNMO a higher resistance against structural degradation. Aside from the structural degradation, the parasitic reactions happened on the electrode/electrolyte interface were also considered as a decisive factor for the degradation of LIBs.5,14,29 In order to directly confirm the stabilization effect of the surface Co doping, we further characterize the contrast of the surface chemistry with and without Co doping upon extended electrochemical cycling. For such purpose, synchrotron-based soft X-ray absorption spectroscopy (sXAS) in its surface sensitive total electron yield (TEY) mode is employed, which provides chemical information on the electrode surface with around 10 nm probe depth.33,34 As shown in Figure 4, LNMO and Co-LNMO exhibit almost identical lineshapes for the Ni-L3 (Figure 4e), Mn-L3 (Figure 4f), and O-K (Figure 4g) edges before cycling (Pristine). However, after 200 cycles, the spectra show significant contrast between the two systems especially after charged to high voltage (Ch). For Ni, the spectra of the undoped LNMO are dominated by Ni(II) features at both the discharged and charged states after 200 cycles (Figure 4e), indicating the formation of electrochemically inactive low-valence Ni(II) on the surface, as previously reported on various cathode surfaces.26,35,36 In contrast, the Co-LNMO electrode exhibits obvious line shape change from the Ni2+/4+ redox even after 200 cycles, as revealed by the Ni(IV) feature at the charged state,26 indicating a surface much inert from parasitic reaction products. Such a surface stabilization effect in our Co-doped system is consistently but more clearly shown by the Mn-L3 spectra (Figure 4f). The charged LNMO electrode showed a prominent low-energy feature that is characteristic to Mn(II) species. Note that finding low-valence Mn at charged (oxidized) state is seemingly counterintuitive, which is actually the direct evidence of parasitic surface reactions with electrolyte and the formation of a low-valence TM surface layer at high potential, as often observed on high-voltage cathode surfaces.35 Again, such a surface reaction is completely suppressed in our Co-LNMO system, where Mn(IV) features dominate the sXAS data at charged state (Figure 4f). Consistently, the suppression of surface reaction and surface layer formation at high voltage of Co-LNMO is also indicated by the O-K spectra, in contrast with the untreated LNMO electrodes (Figure 4g). The peak intensity in the range of 530−535 eV, which corresponds to hybridization features of TM and oxygen states,37 substantially decreases after cycling for the LNMO, indicating again a surface layer formation related to the electrolyte decomposition with the products showing in O-K sXAS at high energies (535−545 eV).35,36 However, for the cycled CoLNMO sample, the O-K edge spectrum maintains its overall line shape, revealing a much stable cathode surface even after long cycles. Therefore, all the sXAS results consistently and directly show that surface cobalt doping will stabilize the CoLNMO surface and effectively suppress the typical parasitic reactions involved in high voltage electrochemical operations, which contribute to the decrease in impedance growth and the

Figure 4. (a) Charge and discharge profiles of 1st and 100th cycle. The data was collected at 0.1 C. (b) Cycling performance at 0.1 C. (c) EIS spectra collected before cycling and after 100 cycles at 0.1 C with the frequency range of 0.1 Hz to 100 kHz. Inset is the equivalent circuit used for fitting the impedance spectra, Re, Rct, Cdl, and Zw represents the electrolyte impedance, charge transfer impedance, double layer capacitance, and Warburg diffusion impedance, respectively. (d) Electrochemical performance at different rates. (e− g) The sXAS TEY spectra of LNMO and Co-LNMO electrodes obtained before cycling and after 200 cycles at charged state (200Ch) and discharged state (200D). (e) Ni L3-edge TEY spectra. The Ni(IV) signal of LNMO at charged state disappears and is covered by electrochemically inactive Ni(II) signals after 200 cycles, but clearly displays in the spectrum of Co-LNMO. (f) Mn L3-edge TEY spectra. The LNMO electrode exhibited much higher intesity surface Mn(II) signal at charged state after 200 cycles, compared with a clean surface of the Co-LNMO. (g) O K-edge TEY spectra. Compared with the Co-LNMO system, the pre-edge peak attributed to the TM-O hybridization was strongly suppressed after 200 cycles, indicating a surface layer formation from parasitic reactions with electrolyte for LNMO.

exhibited good cycling performance, the slashed specific capacity and sluggish charge transfer prevented the practical use of this sample (Figure 4b, c). Thus, introducing excess amount of electrochemically inert element on the surface would surely deteriorate the battery performance. However, lower Co dopant amount was not sufficient for the protection of LNMO, leading to a relatively faster capacity fading during cycling (Figure 4b). Therefore, tuning the Co amount on the surface was critical for achieving good electrochemical performance. We found that doping Co on the surface would contribute to the stabilization of LNMO materials. Differential scanning calorimetry (DSC) analysis revealed that the surface modified LNMO had a higher decomposition temperature with less heat released (Figure S5a). Meanwhile, the Co-LNMO sample D

DOI: 10.1021/acsami.8b08528 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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(3) Konarov, A.; Myung, S.-T.; Sun, Y.-K. Cathode Materials for Future Electric Vehicles and Energy Storage Systems. ACS Energy Lett. 2017, 2 (3), 703−708. (4) Kang, K. S.; Meng, Y. S.; Breger, J.; Grey, C. P.; Ceder, G. Electrodes with High Power and High Capacity for Rechargeable Lithium Batteries. Science 2006, 311 (5763), 977−980. (5) Ma, J.; Hu, P.; Cui, G. L.; Chen, L. Q. Surface and Interface Issues in Spinel LiNi0.5Mn1.5O4: Insights into a Potential Cathode Material for High Energy Density Lithium Ion Batteries. Chem. Mater. 2016, 28 (11), 3578−3606. (6) Goodenough, J. B.; Kim, Y. Challenges for Rechargeable Li Batteries. Chem. Mater. 2010, 22 (3), 587−603. (7) Jang, M.-W.; Jung, H.-G.; Scrosati, B.; Sun, Y.-K. Improved CoSubstituted, LiNi0.5−xCo2xMn1.5−xO4 Lithium Ion Battery Cathode Materials. J. Power Sources 2012, 220, 354−359. (8) Zhu, W.; Liu, D.; Trottier, J.; Gagnon, C.; Guerfi, A.; Julien, C. M.; Mauger, A.; Zaghib, K. Comparative studies of the phase evolution in M-doped LixMn1.5Ni0.5O4 (M = Co, Al, Cu and Mg) by in-situ X-ray diffraction. J. Power Sources 2014, 264, 290−298. (9) Arunkumar, T. A.; Manthiram, A. Influence of Lattice Parameter Differences on the Electrochemical Performance of the 5 V Spinel LiMn1.5‑yNi0.5‑zMy+zO4 (M = Li, Mg, Fe, Co, and Zn). Electrochem. Solid-State Lett. 2005, 8 (8), A403−A405. (10) Ito, A.; Li, D.; Lee, Y.; Kobayakawa, K.; Sato, Y. Influence of Co Substitution for Ni and Mn on the Structural and Electrochemical Characteristics of LiNi0.5Mn1.5O4. J. Power Sources 2008, 185 (2), 1429−1433. (11) Radin, M. D.; Hy, S.; Sina, M.; Fang, C.; Liu, H.; Vinckeviciute, J.; Zhang, M.; Whittingham, M. S.; Meng, Y. S.; Van der Ven, A. Narrowing the Gap between Theoretical and Practical Capacities in Li-Ion Layered Oxide Cathode Materials. Adv. Energy Mater. 2017, 7 (20), 1602888. (12) Lu, J.; Zhan, C.; Wu, T.; Wen, J.; Lei, Y.; Kropf, A. J.; Wu, H.; Miller, D. J.; Elam, J. W.; Sun, Y. K.; Qiu, X.; Amine, K. Effectively Suppressing Dissolution of Manganese from Spinel Lithium Manganate via a Nanoscale Surface-Doping Approach. Nat. Commun. 2014, 5, 5693. (13) Piao, J.-Y.; Duan, S.-Y.; Lin, X.-J.; Tao, X.-S.; Xu, Y.-S.; Cao, A.M.; Wan, L.-J. Surface Zn Doped LiMn2O4 for an Improved High Temperature Performance. Chem. Commun. 2018, 54 (42), 5326− 5329. (14) Lee, K. T.; Jeong, S.; Cho, J. Roles of Surface Chemistry on Safety and Electrochemistry in Lithium Ion Batteries. Acc. Chem. Res. 2013, 46 (5), 1161−1170. (15) Donders, M. E.; Knoops, H. C. M.; van de Sanden, M. C. M.; Kessels, W. M. M.; Notten, P. H. L. Remote Plasma Atomic Layer Deposition of Co3O4 Thin Films. J. Electrochem. Soc. 2011, 158 (4), G92−G96. (16) Huang, B.; Yang, W.; Wen, Y.; Shan, B.; Chen, R. Co3O4Modified TiO2 Nanotube Arrays via Atomic Layer Deposition for Improved Visible-Light Photoelectrochemical Performance. ACS Appl. Mater. Interfaces 2015, 7 (1), 422−431. (17) Elam, J. W.; Dasgupta, N. P.; Prinz, F. B. ALD for Clean Energy Conversion, Utilization, and Storage. MRS Bull. 2011, 36 (11), 899− 906. (18) Duan, S.-Y.; Piao, J.-Y.; Zhang, T.-Q.; Sun, Y.-G.; Liu, X.-C.; Cao, A.-M.; Wan, L.-J. Kinetically Controlled Formation of Uniform FePO4 Shells and Their Potential for Use in High-Performance Sodium Ion Batteries. NPG Asia Mater. 2017, 9 (7), e414. (19) Gayer, K. H.; Garrett, A. B. The Solubility of Cobalt Hydroxide, Co(OH)2, in Solutions of Hydrochloric Acid and Sodium Hydroxide at 25°. J. Am. Chem. Soc. 1950, 72 (9), 3921−3923. (20) Lamer, V. K.; Dinegar, R. H. Theory, Production and Mechanism of Formation of Monodispersed Hydrosols. J. Am. Chem. Soc. 1950, 72 (11), 4847−4854. (21) Stober, W.; Fink, A.; Bohn, E. Controlled Growth of Monodisperse Silica Spheres in the Micron Size Range. J. Colloid Interface Sci. 1968, 26 (1), 62−69.

improvement in rate performance. Such a surface effect ensures a more stable surface structure and chemistry that is favorable for extended electrochemical cycles. In summary, we developed a simple but effective synthetic protocol to control the formation of basic cobaltous carbonate nanoshells with precisely tunable thickness on different core materials by modulating its growth kinetics in solution. In particular, we extended such protocol to spinel LNMO, which was a promising cathode material for LIBs with relatively high energy density. By sintering the basic cobaltous carbonate coated LNMO particles, Co ions would be doped into their surface lattice. Our experimental data revealed that proper amount of Co dopant on the surface was critical for strengthening the surface chemistry of cathode materials while maintaining the mobility of Li+ and electrons, which would lead to the good cycling performance without the sacrifice of specific capacity. Our synchrotron-based sXAS results reveal directly a much more stable surface over hundreds of electrochemical cycles. Such surface Co doping strategy provided an alternative perspective for the optimization of high-energy-density LIB systems.

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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/acsami.8b08528. Materials and methods and supplemental figures and tables, including the synthetic process, TEM images, XPS patterns, XRD patterns, high-temperature properties, results of the ICP-AES tests, and fitting results of the EIS tests (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (A.-M.C.). *E-mail: [email protected] (L.-J.W.). ORCID

Wanli Yang: 0000-0003-0666-8063 An-Min Cao: 0000-0001-9280-4337 Li-Jun Wan: 0000-0002-0656-0936 Author Contributions †

J.-Y.P. and X.-C.L. contributed equally. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant XDA09010101) and the National Natural Science Foundation of China (Grant 51672282). This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under Contract DE-AC02-05CH11231.

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REFERENCES

(1) Armand, M.; Tarascon, J. M. Building better batteries. Nature 2008, 451 (7179), 652−657. (2) Dunn, B.; Kamath, H.; Tarascon, J. M. Electrical Energy Storage for the Grid: A Battery of Choices. Science 2011, 334 (6058), 928− 935. E

DOI: 10.1021/acsami.8b08528 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Letter

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DOI: 10.1021/acsami.8b08528 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX