Reversible Structural Changes and High-Rate Capability of Li3PO4

Article Cite This: J. Phys. Chem. C 2018, 122, 16607−16612

pubs.acs.org/JPCC

Reversible Structural Changes and High-Rate Capability of Li3PO4‑Modified Li2RuO3 for Lithium-Rich Layered Rocksalt Oxide Cathodes Sou Taminato,† Masaaki Hirayama,*,† Kota Suzuki,† KyungSu Kim,† Kazuhisa Tamura,‡ and Ryoji Kanno†

Downloaded via KAOHSIUNG MEDICAL UNIV on July 28, 2018 at 12:35:56 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

†

Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan ‡ Japan Atomic Energy Agency, Synchrotron Radiation Research Center, Kansai Research Establishment 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan S Supporting Information *

ABSTRACT: Lithium-rich layered rocksalt oxides are promising cathode materials for lithium-ion batteries, owing to their high charge−discharge capacities of over 250 mA h g−1. However, their poor rate capability remains to be addressed. Here, we investigate the effects of surface modification by amorphous Li3PO4 on the structures and electrochemical reactions in the surface region of an epitaxial Li2RuO3(010) film electrode fabricated by pulsed laser deposition. Structural characterization using surface X-ray diffraction (XRD), hard X-ray photoemission spectroscopy, and neutron reflectometry shows that surface modification by 3 nm thick Li3PO4 resulted in the partial substitution of P for Li in the surface region of Li2RuO3. The modified (010) surface exhibits better rate capability at 20 C (41% of the discharge capacity at 0.3 C) compared to the unmodified surface (5% of that at 0.3 C). In situ surface XRD confirmed that highly reversible structural changes occurred at the modified surface during lithium (de)intercalation, whereas the unmodified surface showed irreversible structural changes. These results demonstrate that this surface modification stabilizes the crystal structure in the surface region, and it can improve the rate capability of lithium-rich layered rocksalt oxide cathodes.

■

INTRODUCTION

electrolyte interface, which can be caused by decomposition of the electrolyte at high voltage regions over 4.5 V versus Li/Li+. Recently, we found that the lithium-rich layered oxide Li2RuO3 exhibits poor rate capability under low-voltage operation conditions (≤4 V), where electrolyte decomposition does not readily occur.17 Direct observation of the surface structures revealed an irreversible phase change on the (010) surface during the initial electrochemical process, and the reconstructed phase limited lithium (de)intercalation at the electrode/electrolyte interface. This surface reconstruction

Lithium-rich layered oxides with the formula xLi2MO3−(1 − x)LiMO2 (where M indicates 3d and/or 4d transition metals) have attracted significant attention as promising intercalation cathodes for use in lithium batteries because they allow discharge capacities of over 250 mA h g−1.1−4 However, these materials show poor rate capabilities when compared to LiCoO2,5−7 making it difficult for them to replace conventional layered rocksalt cathodes [Li(Co,Ni,Mn)O2]. There have been several reports of improving the rate capabilities of lithium-rich layered oxide electrodes through surface coating with oxides, phosphates, or carbons.8−16 In these studies, the surface coatings were believed to enhance the electronic conductivity and/or suppressed the formation of a highly resistive solid © 2018 American Chemical Society

Received: May 18, 2018 Revised: June 25, 2018 Published: June 27, 2018 16607

DOI: 10.1021/acs.jpcc.8b04723 J. Phys. Chem. C 2018, 122, 16607−16612

Article

The Journal of Physical Chemistry C

potentiostatic method using a potentiostat (Ivium, Compactstat). The XRD patterns were observed in air at 4.0 V after charging and 3.0 V after discharging. Whereas the out-of-plane 060 and 13-3 diffraction peaks corresponded to crystal structure changes in the bulk region, the in-plane 202 and 004 peaks collected at a low glancing angle corresponded to surface structural changes.17,27 To the small peak shifts observed for in-plane diffraction due to the strong constraint by the substrate lattice,24,25 we calibrated the diffraction angles of Li2RuO3 using the diffraction peaks of the SrTiO3 substrate (a = 3.901 Å28) with no lithium intercalation characteristics.

therefore has a pronounced effect on the power characteristics of lithium-rich layered cathodes during battery operation. On the basis of these findings, it is essential to establish effective treatment methods to control the surface structural changes and elucidate the mechanism for the development of the lithium-rich layered oxide cathodes. In this paper, we examine the effects of surface modification on the surface structure and lithium intercalation properties of the Li2RuO3(010) plane. A 3 nm thick amorphous Li3PO4 layer was fabricated by pulsed laser deposition (PLD) to modify the surface of epitaxial Li2RuO3(010) films. The structure of the pristine Li3PO4/Li2RuO3 film was characterized by X-ray diffraction (XRD) and hard X-ray photoelectron spectroscopy (HAX-PES). The surface structural changes during cycling were observed using in situ surface XRD measurements. The modified surface showed superior stability compared to the unmodified one, providing a stable and reversible intercalation reaction field and thus enhancing the rate capability.

■

RESULTS AND DISCUSSION The Li2RuO3 and Li3PO4 layers were about 14.5 and 2.7 nm thick, respectively (see Figure S1 in the Supporting Information). The Li3PO4-modified film has (010) and (206) orientations along the out-of-plane ⟨110⟩ and in-plane ⟨110⟩ directions of the (110) substrate, respectively, including rutile-type RuO2 as the impurity phase (see Figure S2). The lattice parameters are a = 5.068(9) Å, b = 8.829(3) Å, c = 9.772(4) Å, and β = 100.59(10)°, which are similar to those of the unmodified film [a = 5.07(17) Å, b = 8.82(3) Å, c = 9.77(2) Å, and β = 99.7(2)°].17 The similarity in the lattice parameters indicates that the surface modification with amorphous Li3PO4 did not affect the crystal structure in the Li2RuO3 bulk. Figure 1 shows the surface XRD patterns of 004 and 202 peaks for unmodified and Li 3 PO 4 -modified Li2RuO3(010) films before cell construction, respectively. Both surface diffraction peaks have slightly larger d-values for the Li3PO4-modified film than the unmodified film. This

■

EXPERIMENTAL SECTION Li2RuO3(010) films were synthesized on 0.5 wt % Nb-doped SrTiO3 (110) substrates (10 mm × 10 mm × 0.5 mm, Crystal Base Co., Ltd.) using PLD as described elsewhere.17 Amorphous Li3PO4 was deposited on the Li2RuO3 films using the following PLD conditions: oxygen pressure, PO2 = 3.3 Pa; distance between the substrate and target, d = 70 mm; laser frequency, f = 10 Hz; deposition time, td = 10 min; energy density, E = 150 mJ; and temperature, T = 293 K. The crystal structure and thickness of the pristine film were characterized by XRD and X-ray reflectivity (XRR) measurements using an X-ray diffractometer (Rigaku ATX-G) with Cu Kα1 radiation, respectively. The oxidation states of the Ru ions were determined from the Ru 3p HAX-PES spectra acquired at SPring-8 BL46XU, using a hemispherical electron energy analyzer (Scienta, R-4000) with an incident photon energy level of approximately 7940 eV. The spectra were collected at two take-off angles (TOAs) of 8° and 80°. The escape depths of the photoelectrons decrease as the TOA becomes smaller. Thus, X-ray photoelectron spectra collected at TOAs of 8° and 80° would reveal the surface- and bulk-enhanced structural information, respectively.18 To investigate the depth profile of lithium content in the Li2RuO3 film electrode, neutron reflectometry (NR) was performed using a time-of-flight reflectometer (SOFIA) installed at J-PARC BL16.19−21 The Parratt32 program, which applies Parratt’s method,22 was used for the reflectivity data analysis.23 The charge−discharge characteristics were examined using 2032-type coin cells assembled with the films as the cathodes, lithium foil anodes, and 1 mol dm−3 LiPF6 in a 3:7 mixture of ethylene carbonate/ diethyl carbonate as the electrolyte. Crystal structure changes during the electrochemical reactions were investigated by in situ surface XRD using a diffractometer installed on the BL14B1 beamline at SPring8.17,24,25 An X-ray beam at the wavelength of 0.82518 Å (15 keV) was employed. The measurements were performed using reciprocal coordinate systems (H, K, L), with two components (H and K) parallel to the surface and a third (L) normal to the surface.26 To investigate the surface structural changes, the inplane XRD patterns were collected with an incident angle half of the critical angle θc, at which the penetration depth of the Xray (15 keV) was calculated to be 2.6 nm (at 0.08°). Deintercalation and intercalation were induced by the

Figure 1. XRD patterns of the in-plane (a) [H, −2H] and (b) [H, 0] peaks for the unmodified17 and Li3PO4-modified Li2RuO3(010) films under the pristine condition. 16608

DOI: 10.1021/acs.jpcc.8b04723 J. Phys. Chem. C 2018, 122, 16607−16612

Article

The Journal of Physical Chemistry C

no significant changes in the oxidation state of Ru in Li2RuO3. In contrast, the intensity of O 1s peaks at 531.7 eV increased after the Li3PO4 modification. This peak could be assigned to the P−O bonding in the PO43− unit.30−32 The lattice expansion without Ru valence change after Li3PO4 modification suggests that substitution of P component for Li and/or decrease in Li and O contents possibly occurred upon contact with Li3PO4. Because the O 1s spectrum cannot distinguish between the unsubstituted and phosphorus-substituted Li2RuO3 lattice, the detailed structural modification of Li2RuO3 surface by Li3PO4 was investigated using NR. Figure 3 shows the neutron reflectivity spectra of both the observed and calculated curves plotted as functions of the scattering vector, Qz = 4π sin θ/λ (λ is the neutron wavelength and θ is the glancing angle). The reflectivity curve for the unmodified film is simulated with the best goodness using a three-layer model composed of the Al2O3 substrate, the Li2RuO3 film, and a surface layer (Li2CO3 and/or LiOH). In contrast, a four-layer model with an interfacial layer (Li2RuO3-2) between Li2RuO3 and the Li3PO4 layer provided the best goodness of simulation for the Li3PO4-modified film (see Figure S4). Scattering length density (SLD) profiles were calculated using the refined thickness values, the SLD, and roughness in each layer. The SLD value of 3.88 × 10−4 nm−2 for unmodified Li2RuO3 film is in good agreement with that of Li2RuO3 (ICSD# 78721; 3.90 × 10−4 nm−233). In contrast, the Li3PO4-modified surface has a larger SLD value of 4.09 × 10−4 nm−2 than the electrode bulk (and unmodified film). This is due to an increase in the element having positive scattering lengths for neutrons in the Li2RuO3 lattice at the electrode surface and/or a decrease in the element having negative scattering lengths. These results suggest that the modification causes the substitution of P for Li in the Li2RuO3 surface (the scattering lengths for Li and P are −1.9 and 5.13 fm, respectively). The Li and P compositions in the Li2RuO3 surface region were estimated using the SLD value, the formula of Li2−5xPxRuO3, and a lattice volume of 434.3(4) Å3 determined from NR, HAX-PES, and XRD, respectively. The value of x in the formula was estimated to be 0.11, indicating the formation of Li1.45P0.11RuO3 phase at the Li2RuO3 surface region after Li3PO4 modification. Figure 4a shows the charge−discharge curves of the Li3PO4modified Li2RuO3(010) film between 3.0 and 4.0 V at 0.3 C. Two plateau regions were observed at around 3.4 and 3.6 V,

indicates that the crystal structure in the surface region of Li2RuO3 was changed by surface modification. Figure 2 shows the Ru 3p3/2 and O 1s HAX-PES spectra of the unmodified and Li3PO4-modified Li2RuO3(010) films

Figure 2. (a) Ru 3p3/2 and (b) O 1s HAX-PES spectra of unmodified and Li3PO4-modified Li2RuO3(010) films on Nb:SrTiO3(110), collected using the photoelectron TOA of 8°. The binding energies were calibrated according to the Au 4f7/2 core level spectrum.

collected at TOA = 8° (those collected at TOA = 80° are similar and shown in Figure S3). The Ru 3p3/2 and O 1s peaks of the Li2RuO3 film were observed at 463 and 529.5 eV, respectively. The peaks of the RuO2 impurity could not be distinguished in the spectra because RuO2 has binding energies very similar to those of Li2RuO3 (e.g., Ru 3p3/2 at 462.6 eV).29 No shifts in the Ru 3p3/2 peaks were observed in the bulk and surface spectra after the modification with Li3PO4, indicating

Figure 3. (a) NR data of the unmodified and Li3PO4-modified Li2RuO3 films prepared on the Al2O3(0001) substrate. Refined neutron SLD profiles of (b) unmodified and (c) Li3PO4-modified Li2RuO3 films are also shown. 16609

DOI: 10.1021/acs.jpcc.8b04723 J. Phys. Chem. C 2018, 122, 16607−16612

Article

The Journal of Physical Chemistry C

unmodified film (5% of the 0.3 C value), revealing that the surface modification improves the power characteristics of the Li2RuO3 film. To better understand the origin of such superior rate capability of the modified surface, its structural changes during the electrochemical reactions were investigated by the surface XRD experiment. Figure 5 shows the in situ XRD patterns of the modified Li2RuO3(010) film in its pristine condition and during the electrochemical processes. The bulk (060 and 13-3) and surface (202 and 004) peaks all shifted to higher angles with decreased intensities during the first charging, and the opposite changes happened during the first discharge. In Figure 5c, an additional peak appeared at H = 1.84 on the first charge to 4.0 V and disappeared after the first discharge, corresponding to the reversible phase change at the electrode surface during the lithium (de)intercalation processes. The reversible changes of all diffraction peaks during the subsequent cycles confirm the high stability of the bulk and surface structures in the Li3PO4-modified Li2RuO3(010) film. Previously, we reported structural changes in the unmodified (010) film.17 In that case, although the reversible structural changes proceeded in the bulk region, an irreversible phase transition occurred on the surface during electrochemical cycling. The (010) surface showed much lower rate capability than the (001) surface, on which no irreversible phase transition occurred. Thus, lithium diffusion through the reconstructed surface is the rate-determining step for lithium intercalation in Li2RuO3 electrodes. The present study reveals that Li3PO4 modification suppresses the irreversible structural change in the (010) surface and improves the rate capability of lithium intercalation. This result provides direct evidence of the strong impact of the surface structure on the rate capability. Currently, it is widely believed that surface coating could suppress electrode dissolution and/or excessive decomposition of electrolyte species, by preventing direct contact between the electrode surface and the electrolyte.35−37 In contrast, despite its low coverage on the surface, an ultrathin coating layer (0.5− 1 nm thick) improves the electrochemical performance of the intercalation electrodes similar to thicker layers (≥10 nm).38 Our results here indicate that the decrease in contact area by surface coating is not a crucial factor in the high stability because the Li2RuO3 surface maintained sufficient contact with the electrolyte through the thin, amorphous Li3PO4 layer (3 nm). Furthermore, the structural characterization of the pristine film using surface XRD, HAX-PES, and XRR analyses clarifies that phosphorus substitutes for lithium in the Li2RuO3 surface after modification with Li3PO4. The structural reconstruction occurs at the Li2RuO3 surface, accompanied by atomic diffusion when it is in contact with Li3PO4. The total energies estimated from first-principles calculation indicate that the P atom prefers to substitute for the Li atom in the transition-metal layer, which could suppress the migration of transition metal from this layer to the lithium layer upon charging.39 The migration of transition metals is a factor in preventing lithium re-intercalation into the crystal lattice, resulting in irreversible phase change. The suppression of transition-metal migration by phosphorus substitution could provide a reversible phase transition at the modified surface, in contrast to the unmodified one. In light of these speculations, the Li3PO4 phase likely has a role in stabilizing the surface structure in the electrochemical reaction field. Moreover, the elemental substitution into the bulk crystal lattice is known to be a suitable method for improving the structural stability

Figure 4. (a) Charge−discharge curves of Li 3PO4-modified Li2RuO3(010) film operating at 0.3 C. (b) Variations in discharge capacity retention with charge−discharge C rates.

which are associated with multiphasic reactions of Li2−xRuO3.33 The initial charge and discharge capacities of the film are 155 and 113 mA h g−1, respectively. A large irreversible capacity is often observed for nanosized film electrodes at the first cycle because the small amount of active material makes the side reactions quite prominent.34 In the following cycles, the modified film delivered high coulombic efficiency, with a capacity retention of >99% over 30 cycles. Figure 4b presents the rate capabilities of the modified film operated at different C-rates. The discharge capacity at 20 C was 48 mA h g−1, which was 41% of that at 0.3 C. After cycling at 20 C, the electrode recovered to deliver a high capacity of 119 mA h g−1. The unmodified film exhibited first charge and discharge capacities of 150 and 120 mA h g−1, respectively, with an irreversible capacity of 30 mA h g−1,17 and also delivered high Coulombic efficiency of >99% over 30 cycles. Table 1 summarizes the charge−discharge characteristics of Table 1. Charge−Discharge Characteristics of Li2RuO3(010) Films before and after Li3PO4 Modification characteristics initial discharge capacity at 0.3 C (mA h g−1) capacity retention at the 30th cycle (%) average discharge potential at the 30th cycle (V) rate capability at 20 C rate (%)

unmodified Li2RuO3(010)a

Li3PO4-modified Li2RuO3(010)

120

113

98

>99

3.48

3.50

5

41

a

Electrochemical data of unmodified Li2RuO3(010) are taken from ref 17.

the unmodified17 and Li3PO4-modified Li2RuO3(010) films. No significant differences were observed in the discharge capacities and the reaction voltages when operating at low current density. It is consistent with the result that the bulk structure of the Li2RuO3 film was unaffected by the surface modification. However, the modified electrode showed higher capacity retention at 20 C (41% of the value at 0.3 C) than the 16610

DOI: 10.1021/acs.jpcc.8b04723 J. Phys. Chem. C 2018, 122, 16607−16612

Article

The Journal of Physical Chemistry C

Figure 5. In situ XRD patterns and fitting peaks of Li3PO4-modified Li2RuO3(010) films along the out-of-plane (a) [0,0,L] and (b) [0,K,K] and the in-plane [(c) [H, 0] and (d) [H, −2H]] directions of the SrTiO3(110) substrate. Patterns were obtained in air (before), after the initial charging and discharging, and after several cycles.

during electrochemical cycling.39−41 However, the results here demonstrate that elemental substitution in the surface structure alone, instead of in the bulk, is more effective for providing stable lithium intercalation for the Li-rich layered cathode materials.

ORCID

Sou Taminato: 0000-0002-9327-6422 Kota Suzuki: 0000-0002-2473-0724 Notes

■

The authors declare no competing financial interest.

■

CONCLUSIONS The surface modification of lithium-rich layered material Li2RuO3 film with amorphous Li3PO4 improved the rate capability of lithium intercalation into the film. A phosphorusdoped phase (Li2−5xPxRuO3) was formed only at the surface region on the Li2RuO3(010) film after Li3PO4 modification. The discharge capacity of the modified film at 20 C was 48 mA h g−1, which was 41% of the value of that at 0.3 C. The modified film also showed high Coulombic efficiency, with a capacity retention of >99% over 30 cycles. In situ surface XRD analysis confirmed highly reversible structure changes on the modified surface during electrochemical cycling. The modification of Li2RuO3 surface by the Li3PO4 phase stabilized the electrode for lithium intercalation reaction. Such stabilization of the crystal structure at the electrochemical interface is crucial for developing lithium-rich layered rocksalt cathodes with high power densities.

■

ACKNOWLEDGMENTS The research was partially supported by a Grant-in-Aid for Scientific Research (S), Grant-inAid for Scientific Research (A) and Grant-in-Aid for Scientific Research (C) from the Japan Society for the Promotion of Science (Grant no.: 17H06145, 25248051, 16K05929). The synchrotron XRD and HAX-PES experiments were performed with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (proposal nos. 2010A3672, 2011A1866, 2011B1863, and 2012A1615). The NR experiments were performed as projects approved by the Japan Proton Accelerator Research Complex (2012A0108).

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.8b04723. Structural characterizations of the unmodified and Li3PO4-modified films (X-ray reflectometry, XRD, and HAX-PES), structural model using neutron reflectivity analysis, and charge−discharge curves (C-rate dependence) (PDF)

■

REFERENCES

(1) Lu, Z.; MacNeil, D. D.; Dahn, J. R. Layered Li[Nix]Co1−2xMnx]O2 Cathode Materials for Lithium-Ion Batteries. Electrochem. SolidState Lett. 2001, 4, A191−A194. (2) Sathiya, M.; Abakumov, A. M.; Foix, D.; Rousse, G.; Ramesha, K.; Saubanère, M.; Doublet, M. L.; Vezin, H.; Laisa, C. P.; Prakash, A. S.; et al. Origin of Voltage Decay in High-Capacity Layered Oxide Electrodes. Nat. Mater. 2014, 14, 230−238. (3) Yabuuchi, N.; Yoshii, K.; Myung, S.-T.; Nakai, I.; Komaba, S. Detailed Studies of a High-Capacity Electrode Material for Rechargeable Batteries, Li2MnO3−LiCo1/3Ni1/3Mn1/3O2. J. Am. Chem. Soc. 2011, 133, 4404−4419. (4) Mori, D.; Kobayashi, H.; Okumura, T.; Nitani, H.; Ogawa, M.; Inaguma, Y. XRD and XAFS study on structure and cation valence state of layered ruthenium oxide electrodes, Li 2 RuO 3 and Li2Mn0.4Ru0.6O3 , upon electrochemical cycling. Solid State Ionics 2016, 285, 66−74. (5) Li, H.; Shen, L.; Zhang, X.; Nie, P.; Chen, L.; Xu, K. Electrospun Hierarchical Li4Ti4.95Nb0.05O12/Carbon Composite Nanofibers for High Rate Lithium Ion Batteries. J. Electrochem. Soc. 2012, 159, A116−A120.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +81-45-9245403. Fax: +81-45-924-5403. 16611

DOI: 10.1021/acs.jpcc.8b04723 J. Phys. Chem. C 2018, 122, 16607−16612

Article

The Journal of Physical Chemistry C (6) Wang, J.; Yao, X.; Zhou, X.; Liu, Z. Synthesis and Electrochemical Properties of Layered Lithium Transition Metal Oxides. J. Mater. Chem. 2011, 21, 2544−2549. (7) Choi, J.; Manthiram, A. Structural and electrochemical characterization of the layered LiNi0.5-yMn0.5-yCo2yO2 (0 ≤ 2y ≤ 1) cathodes. Solid State Ionics 2005, 176, 2251−2256. (8) Liu, J.; Manthiram, A. Functional surface modifications of a high capacity layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode. J. Mater. Chem. 2010, 20, 3961−3967. (9) Liu, J.; Wang, Q.; Reeja-Jayan, B.; Manthiram, A. Carbon-coated high capacity layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathodes. Electrochem. Commun. 2010, 12, 750−753. (10) Li, H.; Zhou, H. Enhancing the Performances of Li-Ion Batteries by Carbon-Coating: Present and Future. Chem. Commun. 2012, 48, 1201−1217. (11) Qiao, Q. Q.; Zhang, H. Z.; Li, G. R.; Ye, S. H.; Wang, C. W.; Gao, X. P. Surface modification of Li-rich layered Li(Li0.17Ni0.25Mn0.58)O2 oxide with Li-Mn-PO4 as the cathode for lithium-ion batteries. J. Mater. Chem. A 2013, 1, 5262−5268. (12) Kang, S.-H.; Thackeray, M. M. Enhancing the rate capability of high capacity xLi2MnO3·(1−x)LiMO2 (M = Mn, Ni, Co) electrodes by Li-Ni-PO4 treatment. Electrochem. Commun. 2009, 11, 748−751. (13) Wang, Q. Y.; Liu, J.; Murugan, A. V.; Manthiram, A. High capacity double-layer surface modified Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode with improved rate capability. J. Mater. Chem. 2009, 19, 4965−4972. (14) Xia, Y.; Zhu, H.; Liang, C.; Xiao, Z.; Gan, Y.; Zhang, J.; Tao, X.; Huang, H.; Zhang, W. Synthesis and electrochemical properties of LiMnPO4 -modified Li[Li0.2Mn0.534Co0.133Ni0.133]O2 cathode material for Li-ion batteries. Electrochim. Acta 2017, 235, 1−9. (15) Xu, M.; Chen, Z.; Li, L.; Zhu, H.; Zhao, Q.; Xu, L.; Peng, N.; Gong, L. Highly crystalline alumina surface coating from hydrolysis of aluminum isopropoxide on lithium-rich layered oxide. J. Power Sources 2015, 281, 444−454. (16) Xu, M.; Chen, Z.; Zhu, H.; Yan, X.; Li, L.; Zhao, Q. Mitigating capacity fade by constructing highly ordered mesoporous Al2O3/ polyacene double-shelled architecture in Li-rich cathode materials. J. Mater. Chem. A 2015, 3, 13933−13945. (17) Taminato, S.; Hirayama, M.; Suzuki, K.; Kim, K.; Zheng, Y.; Tamura, K.; Mizuki, J.; Kanno, R. Mechanistic studies on lithium intercalation in a lithium-rich layered material using Li2RuO3epitaxial film electrodes and in situ surface X-ray analysis. J. Mater. Chem. A 2014, 2, 17875−17882. (18) Zheng, Y.; Hirayama, M.; Taminato, S.; Lee, S.; Oshima, Y.; Takayanagi, K.; Suzuki, K.; Kanno, R. Reversible lithium intercalation in a lithium-rich layered rocksalt Li2RuO3 cathode through a Li3PO4 solid electrolyte. J. Power Sources 2015, 300, 413−418. (19) Mitamura, K.; Yamada, N. L.; Sagehashi, H.; Torikai, N.; Arita, H.; Terada, M.; Kobayashi, M.; Sato, S.; Seto, H.; Goko, S.; et al. Novel Neutron Reflectometer SOFIA at J-PARC/MLF for In-situ Soft-interface Characterization. Polym. J. (Tokyo, Jpn.) 2013, 45, 100− 108. (20) Yamada, N. L.; Torikai, N.; Mitamura, K.; Sagehashi, H.; Sato, S.; Seto, H.; Sugita, T.; Goko, S.; Furusaka, M.; Oda, T.; et al. Design and Performance of Horizontal-type Neutron Reflectometer SOFIA at J-PARC/MLF. Eur. Phys. J. Plus 2011, 126, 1−13. (21) Hirayama, M.; Shibusawa, T.; Yamaguchi, R.; Kim, K.; Taminato, S.; Yamada, N. L.; Yonemura, M.; Suzuki, K.; Kanno, R. Neutron reflectometry analysis of Li4Ti5O12/organic electrolyte interfaces: characterization of surface structure changes and lithium intercalation properties. J. Mater. Res. 2016, 31, 3142−3150. (22) Parratt, L. G. Surface Studies of Solids by Total Reflection of XRays. Phys. Rev. 1954, 95, 359−369. (23) Hirayama, M.; Yonemura, M.; Suzuki, K.; Torikai, N.; Smith, H.; Watkinsand, E.; Majewski, J.; Kanno, R. Surface Characterization of LiFePO4 Epitaxial Thin Films by X-ray/Neutron Reflectometry. Electrochemistry 2010, 78, 413−415. (24) Kim, K.; Toujigamori, T.; Suzuki, K.; Taminato, S.; Tamura, K.; Mizuki, J.; Hirayama, M.; Kanno, R. Characterization of Nano-Sized

Epitaxial Li4Ti5O12(110) Film Electrode for Lithium Batteries. Electrochemistry 2012, 80, 800−803. (25) Hirayama, M.; Ido, H.; Kim, K.; Cho, W.; Tamura, K.; Mizuki, J.; Kanno, R. Dynamic Structural Changes at LiMn2O4/Electrolyte Interface during Lithium Battery Reaction. J. Am. Chem. Soc. 2010, 132, 15268−15276. (26) Ocko, B. M.; Wang, J.; Davenport, A.; Isaacs, H. In situx-ray reflectivity and diffraction studies of the Au(001) reconstruction in an electrochemical cell. Phys. Rev. Lett. 1990, 65, 1466−1469. (27) Taminato, S.; Hirayama, M.; Suzuki, K.; Tamura, K.; Minato, T.; Arai, H.; Uchimoto, Y.; Ogumi, Z.; Kanno, R. Lithium intercalation and structural changes at the LiCoO2 surface under high voltage battery operation. J. Power Sources 2016, 307, 599−603. (28) Abramov, Y. A.; Tsirelson, V. G.; Zavodnik, V. E.; Ivanov, S. A.; I. D, B. The chemical bond and atomic displacements in SrTiO3 from X-ray diffraction analysis. Acta Crystallogr., Sect. B: Struct. Sci. 1995, 51, 942−951. (29) Sarma, D. D.; Rao, C. N. R. XPES Studies of Oxides of Secondand Third-Row Transition Metals Including Rare Earths. J. Electron Spectrosc. Relat. Phenom. 1980, 20, 25−45. (30) Zhang, H. Z.; Qiao, Q. Q.; Li, G. R.; Gao, X. P. PO43− polyanion-doping for stabilizing Li-rich layered oxides as cathode materials for advanced lithium-ion batteries. J. Mater. Chem. A 2014, 2, 7454−7460. (31) Appapillai, A. T.; Mansour, A. N.; Cho, J.; Shao-Horn, Y. Microstructure of LiCoO2with and without “AlPO4” Nanoparticle Coating: Combined STEM and XPS Studies. Chem. Mater. 2007, 19, 5748−5757. (32) Lv, Y.; Yu, L.; Huang, H.; Liu, H.; Feng, Y. Preparation, characterization of P-doped TiO2 nanoparticles and their excellent photocatalystic properties under the solar light irradiation. J. Alloys Compd. 2009, 488, 314−319. (33) Kobayashi, H.; Kanno, R.; Kawamoto, Y.; Tabuchi, M.; Nakamura, O.; Takano, M. Structure and lithium deintercalation of Li2−xRuO3. Solid State Ionics 1995, 82, 25−31. (34) Okubo, M.; Hosono, E.; Kim, J.; Enomoto, M.; Kojima, N.; Kudo, T.; Zhou, H.; Honma, I. Nanosize Effect on High-Rate Li-Ion Intercalation in LiCoO2 Electrode. J. Am. Chem. Soc. 2007, 129, 7444−7452. (35) Kim, Y.; Veith, G. M.; Nanda, J.; Unocic, R. R.; Chi, M.; Dudney, N. J. High voltage stability of LiCoO2 particles with a nanoscale Lipon coating. Electrochim. Acta 2011, 56, 6573−6580. (36) Lu, Y.-C.; Mansour, A. N.; Yabuuchi, N.; Shao-Horn, Y. Probing the Origin of Enhanced Stability of “AlPO4” Nanoparticle Coated LiCoO2 during Cycling to High Voltages: Combined XRD and XPS Studies. Chem. Mater. 2009, 21, 4408−4424. (37) Kim, Y. J.; Kim, H.; Kim, B.; Ahn, D.; Lee, J.-G.; Kim, T.-J.; Son, D.; Cho, J.; Kim, Y.-W.; Park, B. Electrochemical Stability of Thin-Film LiCoO2Cathodes by Aluminum-Oxide Coating. Chem. Mater. 2003, 15, 1505−1511. (38) Park, J. S.; Mane, A. U.; Elam, J. W.; Croy, J. R. Amorphous Metal Fluoride Passivation Coatings Prepared by Atomic Layer Deposition on LiCoO2 for Li-Ion Batteries. Chem. Mater. 2015, 27, 1917−1920. (39) Wang, Z. Q.; Wu, M. S.; Xu, B.; Ouyang, C. Y. Improving the electrical conductivity and structural stability of the Li2MnO3 cathode via P doping. J. Alloys Compd. 2016, 658, 818−823. (40) Komaki, H.; Kitajo, A.; Okada, S. Cathode Properties of PDoped Li2MnO3. Abstract #684, Honolulu PRiME 2012; The Electrochemical Society, 2012. (41) Xiao, P.; Deng, Z. Q.; Manthiram, A.; Henkelman, G. Calculations of Oxygen Stability in Lithium-Rich Layered Cathodes. J. Phys. Chem. C 2012, 116, 23201−23204.

16612

DOI: 10.1021/acs.jpcc.8b04723 J. Phys. Chem. C 2018, 122, 16607−16612