Communication Cite This: Chem. Mater. 2017, 29, 8958-8962
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P′2-Na2/3Mn0.9Me0.1O2 (Me = Mg, Ti, Co, Ni, Cu, and Zn): Correlation between Orthorhombic Distortion and Electrochemical Property Shinichi Kumakura,† Yoshiyuki Tahara,† Syuhei Sato,† Kei Kubota,†,‡ and Shinichi Komaba*,†,‡ †
Department of Applied Chemistry, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan Elements Strategy Initiative for Catalysts & Batteries (ESICB), Kyoto University, Nishikyo-ku, Kyoto 615-8245, Japan
‡
S Supporting Information *
S
replacement of Mn with different metal elements and compare their electrochemical properties. The distortion is highly correlated with average oxidation state of manganese varied by divalent metals (MgII, NiII, CuII, and ZnII), a trivalent metal (CoIII), and a tetravalent metal (TiIV). The effects of metal substitution and lattice distortion on electrochemical properties are discussed, and Cu-doping successfully improves both cycle and rate performance. P′2-Na2/3Mn0.9Me0.1O2 (Me = Mg, Ti, Mn, Co, Ni, Cu, and Zn) samples were synthesized by a solid-state reaction, and the detailed synthesis method is described in the Supporting Information. Figure 1a shows X-ray diffraction (XRD) patterns of synthesized P′2-Na2/3MnO2 and Na2/3Mn0.9Me0.1O2 (Me = Mg, Ti, Co, Ni, Cu, and Zn) samples which are hereinafter denoted by Mn-NMO (undoped P′2-Na2/3MnO2), Mg-NMO, Ti-NMO, Co-NMO, Ni-NMO, Cu-NMO, and Zn-NMO, respectively. All diffraction peaks in the patterns can be indexed as a P′2-type layered structure (S.G. Cmcm) without any crystalline impurity. Synchrotron XRD and Rietveld analysis also proves the single phase for Cu- and Zn-NMOs (see Supporting Information, Figure S1 and Table S1 for Rietveld results). A schematic illustration of P′2-type crystal structure and in-plane arrangement of an orthorhombic lattice is shown in Figure 1b. If the bortho/aortho ratio equals √3, hexagonal setting is proper to express the crystal structure. When CJTD induces distortion in the orthorhombic lattice by b-axial elongation and/or a-axial shrinkage, the degree of an in-plane distortion is defined as δ in bortho/aortho = (1 + δ)√3 to express how the orthorhombic lattice is distorted from hexagonal one.10 Indeed, the bortho/aortho ratio for Mn-NMO becomes 1.87, namely, distortion degree δ is ca. 8%. The partial substitution for manganese significantly affects the distortion. Lattice parameter and the defined distortion of the obtained samples are summarized in Table S2. Although minor contribution of ionic radii of dopants to the distortion is observed in Figure S2, the interesting dependency of distortion degree on concentration of MnIII is found in Figure 1c. Relation between δ and the molar ratio of MnIII to total metal amount, MnIII/(Mn + Me), is plotted by reasonably assuming the valence such as MgII, NiII, CuII, ZnII, CoIII, and TiIV coexistent with MnIII and MnIV. Linear relation between δ and MnIII/(Mn + Me) except Cu-NMO proves that MnIII is a key factor leading CJTD. Compared to doping with NiII, MgII, and ZnII, CuII doping
ince the high energy Li-ion battery appeared as a power source of portable electronic devices in 1991, the application field of rechargeable batteries is continuously expanding, e.g. in electric vehicles and electrical energy storage (EES).1 The important issue of EES is to satisfy the requirement of both lower cost and higher energy density for rechargeable batteries; thus, the Na-ion battery (NIB) is recently attracting much attention due to its large reversible capacity and abundant resources of required metal elements. For higher energy NIBs, many efforts have been devoted to develop high-capacity positive electrode materials such as layered oxides and polyanion compounds.2 In particular, P2type layered oxides are one of the most promising candidates to achieve large capacity, high working voltage, and low material cost. For example, P2-type NaxFe1/2Mn1/2O2 consisting only of earth abundant elements demonstrates high reversible capacity of 190 mAh g−1.3 Although layered oxides of NaxMnO2 (x = 1− 2/3) have been intensively studied since 19714 because of abundance of Mn among 3d transition metals, studies on (electro-)chemical and physical properties of P2−Na2/3MnO2 suffered from difficulty in its single phase synthesis, low energy density, and poor cycle stability.5−10 In consequence, the current trend of study on P2−Na2/3MnO2 materials for NIB is metal substitution for Mn, such as electrochemically active metals FeIII, NiII,III, CoIII, and CuII 3,11−19 and inactive cations LiI, MgII, AlIII and ZnII.6,7,20−27 Another notable feature of P2− Na2/3MnO2 is existence of crystal polymorphs. In addition to the hexagonal system observed for most P2-type materials, it is also possible for Na2/3MnO2 to crystallize into an orthorhombic system. The lattice distortion from hexagonal to orthorhombic systems is induced by cooperative Jahn−Teller distortion (CJTD) derived from six-coordinated high spin MnIII (t2g3− eg1). The distorted structure, which is an analogue of P2-type structures, is categorized as P′2-Na2/3MnO2.28,29 Very recently, our group reported the single-phase samples of P′2- and P2− Na2/3MnO2, which exhibit different stoichiometry and the P′2type one having a lattice distortion demonstrates the superior electrochemical performance.10 Although the distortion in insertion materials is generally considered to be disadvantageous for electrode performance, quantitative understanding of how CJTD affects electrochemical properties such as reversibility, kinetics of sodium diffusion, and long-cycle stability is of great importance to realize high capacity performance of MnIII-based oxide materials for high energy density NIBs. In this study, we demonstrate the systematic synthesis of differently distorted P′2-Na2/3MnO2 samples by partial © 2017 American Chemical Society
Received: July 3, 2017 Revised: October 10, 2017 Published: October 10, 2017 8958
DOI: 10.1021/acs.chemmater.7b02772 Chem. Mater. 2017, 29, 8958−8962
Communication
Chemistry of Materials
Figure 1. (a) XRD patterns for Na2/3Mn0.9Me0.1O2, (b) schematic illustration of P′2 structure, and (c) lattice distortion vs MnIII concentration of P′2-Na2/3Mn0.9Me0.1O2. P2−Mn represents undistorted P2−Na2/3MnO2 containing Mn defect.10 Figure 2. Charge/discharge curves and SEM images for P′2-type Na2/3Mn0.9Me0.1O2.
results in significant distortion, which is due to extra Jahn− Teller distortion caused by six-coordinated CuII (t2g6-eg3). Consequently, we successfully obtained P′2-Na2/3Mn0.9Me0.1O2 samples having different distortion. Their electrochemical properties are investigated in nonaqueous Na cells, and initial charge/discharge curves are compared in Figure 2. Galvanostatic charge/discharge cutoff voltages are set to 4.4/1.5 V at a current rate of 10 mA g−1 corresponding nearly C/20 (1 C = 200 mAh g−1) for all samples. Because SEM images shown in Figure 2 indicate that morphology of every sample is platelet with a similar particle size of ∼5 μm, their electrochemical properties should not be influenced by the particle morphology. All samples show high reversible capacity beyond 200 mAh g−1 corresponding to reversible extraction/insertion of 0.8 mol Na per formula. NiNMO delivers the largest reversible capacity of 227 mAh g−1 because of additional capacity from NiII/IV redox reaction. MnNMO shows multiple stepwise curves on charge/discharge. These steps are derived from two major structural changes and several phase transitions originating from Na/vacancy and Mn charge orderings.10 All metal-doped samples, however, have smooth charge/discharge curves, which are generally beneficial for practical applications. Metal substitution for manganese induces charge-disorder into the transition-metal layer30 and thus suppresses phase transition related to long-range ordering of both Na/vacancy and MnIII/IV charge. Consequently, the structural change during sodium extraction/insertion is remarkably influenced by the metal substitution. To further investigate the influence of metal substitution on the electrochemical reactions, dQ/dV plots and rate and cycle performances are compared among the doped samples. dQ/dV plots of
first discharge and second charge are shown in Figure 3a. For Mn-NMO, the largest peak at 2.3 V upon discharge is assigned to the two-phase reaction of P′2 (P′2-I) and another P′2 (P′2II) phases.10 All doped samples show the similar largest peaks at around 2.3 V, indicating the same two-phase reactions are observed. The two-phase reaction is originated from first-order transition between two P′2 phases with different CJTD. P′2-II appears by Na insertion in the range of x > 0.7 in NaxMO2 and shows higher distortion in the lattice than P′2-I. Representative distortion of P′2-I is that of as-prepared powder in Figure 1c, and the distortion degrees of P′2-II for Mn- and Cu-NMO are 13.1 and 10.1%, respectively (obtained from ex situ XRD patterns in Figure S3). Redox potential during the two-phase reaction is directly reflected by the difference between formation energy of P′2-I and -II with the different degree of CJTD. Figure 3b shows the relation between dQ/dV peak voltage vs distortion degree of as-prepared powder samples. Clearly, the plots prove that the less distorted material shows lower potential of the two-phase reaction. Note that this trend is not consistent with oxidation state of Mn because of obvious differences among divalent dopant samples Ni-, Cu-, and ZnNMO. This result shows correlation between CJTD and electrochemical reactions via modulated electronic state by metal substitution in Na2/3Mn0.9Me0.1O2. During extensive 50 cycles, the correlation is confirmed to be maintained without any apparent irreversible phase change. 8959
DOI: 10.1021/acs.chemmater.7b02772 Chem. Mater. 2017, 29, 8958−8962
Communication
Chemistry of Materials
electrochemically active Mn(III) centers in the material and hence less CJTD upon Mn(III) to Mn(IV) oxidation on charge and discharge. However, Cu-NMO exhibits exceptional property among them as only Cu-NMO achieves both good cycle stability and high rate property. Such an exceptional electrochemical behavior of Cu-NMO is possibly related with exceptionally high CJTD of Cu-NMO, as described in Figure 1c. CJTD for electrode materials has been well-discussed in lithium manganese spinel since 1983,31 and Li insertion into LiMn2O4 is known to cause severe capacity degradation due to local lattice strain.32 In contrast, CJTD in doped P′2Na2/3MnO2 materials behaves differently, and highly distorted Ti-/Co-/Cu-NMO show reversible electrochemical reaction as mentioned above. The electrochemical observation of CJTD can attract attention in solid state chemistry. In addition, the positive effect of CJTD on battery performance with reversible Na insertion provides a new insight of designing electrode materials. Electronic state of transition metals and structural evolution during Na extraction/insertion were examined to understand exceptional behavior of electrode performance for Cu-NMO. Figure 4a shows XANES spectra of Mn K-edge of pristine, fully
Figure 3. (a) dQ/dV plot of first discharge (bottom side) and second charge (upper side); (b) plot of main peak voltage in dQ/dV vs distortion degree; (c) discharge rate properties; and (d) capacity retention vs rate capability plots for Na2/3Mn0.9Me0.1O2.
Figure 3c compares discharge-rate capability for Na2/3Mn0.9Me0.1O2 samples. Mn-NMO shows inferior rate property, especially above 1 C rate, and those of Ti- and CoNMO are even worse than Mn-NMO. On the other hand, Mg-, Ni-, and Zn-NMOs, classified in a less distorted group, exhibit better rate performance. Interestingly, capacity retention test gave us the opposite tendency, i.e. Ti- and Co-NMOs are better than Mg-, Ni-, and Zn-NMOs in terms of cycle stability (Figure S4). Electrochemical properties of the samples and the relationship between capacity maintenance as Q2C/Q0.05C ratio and capacity retention at 50th cycle for Na2/3Mn0.9Me0.1O2 samples are summarized in Figure 3d and Table S3, respectively. Basically, the linear relationship appears, indicating trade-off relationship between cycle stability and rate capability. Ti-/Co-/Cu-NMO have relatively large distortion with less phase transition than Mn-NMO, and thus, higher structural stability against Na extraction/insertion is expected, while less distorted samples Mg-/Ni-/Zn-NMO are more likely to suffer from local strain between distorted and undistorted MO2 octahedra. Comparison of rate capability among doped samples is generally difficult because of many possible scenarios such as change of bulk conductivity,19 change of surface, including structural change and deposits,18 etc. Normalized rate performance, 0.1−2 C vs C/20, is shown in Figure S5, and the different is distinct above C/2. Worse rate capability of Ti-/Co-/MnNMO can be related to structural change associated with loss of CJTD by Na extraction, and the detailed phase transitions are discussed with in situ XRD data later. Another aspect of better rate property for Mg-/Ni-/Zn-NMO is that a higher average Mn oxidation state due to divalent dopants leads to more dilute
Figure 4. XANES spectra of (a) Mn and (b) Cu K-edge for Na2/3Mn0.9Cu0.1O2 and operando XRD contour maps of (c) MnNMO and (d) Cu-NMO in the initial cycle recorded from the left to right side.
charged, and fully discharged electrodes. Mn K-edge shifts to higher energy by charge and then shifts back to energy by discharge lower than that of the pristine state. Cu K-edge spectra shown in Figure 4b, however, hardly change or even slightly shift to the opposite direction, i.e. toward lower and higher energy upon charge and discharge, respectively, in contrast to Cu II/III redox reaction observed in P2− Na2/3Cu1/3Mn2/3O2.15 Therefore, we conclude that MnIII/IV 8960
DOI: 10.1021/acs.chemmater.7b02772 Chem. Mater. 2017, 29, 8958−8962
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redox couple is responsible for electrochemical activity for CuNMO. CuII is electrochemically inactive, and the electronic state of copper is slightly changed via oxide ions bonding with neighbor Mn. Recently, Li et al. reported that Jahn−Teller active FeIV ions assist Na conduction on charged state in O3type layered oxides due to local lattice flexibility and soft-mode buckling of FeIVO2 octahedra.33,34 Electrochemically inactive and Jahn−Teller active CuII ions are able to act as stabilizer of distorted structure at charged state and promote Na conduction on charge/discharge. Figures 4c and d shows the contour maps of operando XRD patterns for Mn-NMO and Cu-NMO during initial charge and discharge. For Mn-NMO, P′2 structure shows steep structural change into OP4 structure at x < 0.25 in NaxMO2, which is also seen in the dQ/dV plot (Figure 3a) at 3.5 V upon charge. On the other hand, Cu-NMO shows that P′2 structure is being kept until full charge to x ∼ 0.16 in NaxMO2 (4.4 V), and another structural change, probably continuous transition from P2 to O2 phase, is found as a single-phasic reaction. The existence of electrochemically inactive CuII, which is wellintegrated in the lattice, resulting in the large distortion, stabilizes P′2 structure and suppresses capacity degradation during cycling. Ex situ XRD patterns are consistent with the operando XRD results, and coexistence of P′2 and P2−O2 intergrowth phase is found at 4.4 V (Figure S3). In summary, the electrochemically inactive and Jahn−Teller active feature of CuII ions enables achievement of superior rate and cycle properties of P′2-Na2/3MnO2 by providing more flexibility to the structure and acting as a buffer against steep structural changes. Detailed analyses of stoichiometry, supper structure, phase transition, magnetic properties, and so on are under investigation for the P′2-Na2/3Mn0.9Me0.1O2 system. Single phases of P′2-Na2/3Mn0.9Me0.1O2 were successfully obtained for a variety of dopants (Me = Mg, Ti, Co, Ni, Cu, and Zn). CJTD of P′2-Na2/3Mn0.9Me0.1O2 was systematically changed by the amount of MnIII ions via di/tri/tetravalent metal dopants. Because of Jahn−Teller active CuII, P′2Na2/3Mn0.9Cu0.1O2 possesses anomalous distortion compared to other samples with divalent-metal dopants. We emphasize that CJTD is not always disadvantageous for sodium insertion materials. The distortion was found to be one of the key factors to understand good electrochemical properties of P′2Na2/3Mn0.9Me0.1O2. Namely, P′2-Na2/3Mn0.9Cu0.1O2 demonstrates both good cycle life and rate capability as the copper doping would provide better structural stability of the framework oxide against Na extraction/insertion and significant CJTD, which should further enhance superior sodium diffusion. We will study the effect of cooperative distortion by Jahn− Teller effect on the phase stability of MnIII-based oxides to design high-performance sodium insertion materials for higher energy density NIBs.
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Communication
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Shinichi Komaba: 0000-0002-9757-5905 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was partly financially supported by Umicore. The synchrotron radiation experiments were performed at the BL02B2 of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal 2014B1820). The synchrotron X-ray absorption work was done under the approval of the Photon Factory Program Advisory Committee (Proposals 2012G149 and 2012G594).
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REFERENCES
(1) Dunn, B.; Kamath, H.; Tarascon, J. M. Electrical Energy Storage for the Grid: A Battery of Choices. Science 2011, 334, 928−935. (2) Yabuuchi, N.; Kubota, K.; Dahbi, M.; Komaba, S. Research development on sodium-ion batteries. Chem. Rev. 2014, 114, 11636− 82. (3) Yabuuchi, N.; Kajiyama, M.; Iwatate, J.; Nishikawa, H.; Hitomi, S.; Okuyama, R.; Usui, R.; Yamada, Y.; Komaba, S. P2-type NaxFe1/2Mn1/2O2 made from earth-abundant elements for rechargeable Na batteries. Nat. Mater. 2012, 11, 512−517. (4) Parant, J.-P.; Olazcuaga, R.; Devalette, M.; Fouassier, C.; Hagenmuller, P. NaxMnO phases. J. Solid State Chem. 1971, 3, 1−11. (5) Caballero, A.; Hernán, L.; Morales, J.; Sánchez, L.; Santos Peña, J.; Aranda, M. A. G. Synthesis and characterization of high-temperature hexagonal P2-Na0.6MnO2 and its electrochemical behaviour as cathode in sodium cells. J. Mater. Chem. 2002, 12, 1142−1147. (6) Yabuuchi, N.; Hara, R.; Kajiyama, M.; Kubota, K.; Ishigaki, T.; Hoshikawa, A.; Komaba, S. New O2/P2-type Li-Excess Layered Manganese Oxides as Promising Multi-Functional Electrode Materials for Rechargeable Li/Na Batteries. Adv. Energy Mater. 2014, 4, 1301453. (7) Billaud, J.; Singh, G.; Armstrong, A. R.; Gonzalo, E.; Roddatis, V.; Armand, M.; Rojo, T.; Bruce, P. G. Na0.67Mn1−xMgxO2 (0 ≤ x ≤ 0.2): a high capacity cathode for sodium-ion batteries. Energy Environ. Sci. 2014, 7, 1387−1391. (8) Clément, R. J.; Bruce, P. G.; Grey, C. P. ReviewManganeseBased P2-Type Transition Metal Oxides as Sodium-Ion Battery Cathode Materials. J. Electrochem. Soc. 2015, 162, A2589−A2604. (9) Ortiz-Vitoriano, N.; Drewett, N.; Gonzalo, E.; Rojo, T. High performance manganese-based layered oxide cathodes: overcoming the challenges of sodium ion batteries. Energy Environ. Sci. 2017, 10, 1051−1074. (10) Kumakura, S.; Tahara, Y.; Kubota, K.; Chihara, K.; Komaba, S. Sodium and Manganese Stoichiometry of P2-Type Na2/3MnO2. Angew. Chem., Int. Ed. 2016, 55, 12760−12763. (11) Lu, Z.; Dahn, J. R. Situ X-Ray Diffraction Study of P2Na2/3[Ni1/3Mn2/3]O2. J. Electrochem. Soc. 2001, 148, A1225−A1229. (12) Yoshida, H.; Yabuuchi, N.; Kubota, K.; Ikeuchi, I.; Garsuch, A.; Schulz-Dobrick, M.; Komaba, S. P2-type Na2/3Ni1/3Mn2/3‑xTixO2 as a new positive electrode for higher energy Na-ion batteries. Chem. Commun. (Cambridge, U. K.) 2014, 50, 3677−80. (13) Yabuuchi, N.; Hara, R.; Kubota, K.; Paulsen, J. M.; Kumakura, S.; Komaba, S. A new electrode material for rechargeable sodium batteries: P2-type Na2/3[Mg0.28Mn0.72]O2 with anomalously high reversible capacity. J. Mater. Chem. A 2014, 2, 16851−16855. (14) Xu, S.-Y.; Wu, X.-Y.; Li, Y.-M.; Hu, Y.-S.; Chen, L.-Q. Novel copper redox-based cathode materials for room-temperature sodiumion batteries. Chin. Phys. B 2014, 23, 118202.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.7b02772. Experimental details, Rietveld refinement, lattice parameters, relation with ionic radii and distortion, ex situ XRD patterns, cycle stability, normalized rate performance, and the full list of electrode performances (PDF) 8961
DOI: 10.1021/acs.chemmater.7b02772 Chem. Mater. 2017, 29, 8958−8962
Communication
Chemistry of Materials (15) Mason, C. W.; Lange, F.; Saravanan, K.; Lin, F.; Nordlund, D. Beyond Divalent Copper: A Redox Couple for Sodium Ion Battery Cathode Materials. ECS Electrochem. Lett. 2015, 4, A41−A44. (16) Li, Y.; Yang, Z.; Xu, S.; Mu, L.; Gu, L.; Hu, Y.-S.; Li, H.; Chen, L. Air-Stable Copper-Based P2-Na7/9Cu2/9Fe1/9Mn2/3O2 as a New Positive Electrode Material for Sodium-Ion Batteries. Adv. Science 2015, 2, 1500031. (17) Lee, D. H.; Xu, J.; Meng, Y. S. An advanced cathode for Na-ion batteries with high rate and excellent structural stability. Phys. Chem. Chem. Phys. 2013, 15, 3304−12. (18) Wang, X.; Tamaru, M.; Okubo, M.; Yamada, A. Electrode Properties of P2−Na2/3MnyCo1−yO2 as Cathode Materials for SodiumIon Batteries. J. Phys. Chem. C 2013, 117, 15545−15551. (19) Bucher, N.; Hartung, S.; Franklin, J. B.; Wise, A. M.; Lim, L. Y.; Chen, H.-Y.; Weker, J. N.; Toney, M. F.; Srinivasan, M. P2− NaxCoyMn1−yO2(y= 0, 0.1) as Cathode Materials in Sodium-Ion Batteries - Effects of Doping and Morphology To Enhance Cycling Stability. Chem. Mater. 2016, 28, 2041−2051. (20) Kim, D.; Kang, S. H.; Slater, M.; Rood, S.; Vaughey, J. T.; Karan, N.; Balasubramanian, M.; Johnson, C. S. Enabling Sodium Batteries Using Lithium-Substituted Sodium Layered Transition Metal Oxide Cathodes. Adv. Energy Mater. 2011, 1, 333−336. (21) Buchholz, D.; Vaalma, C.; Chagas, L. G.; Passerini, S. Mgdoping for improved long-term cyclability of layered Na-ion cathode materials − The example of P2-type NaxMg0.11Mn0.89O2. J. Power Sources 2015, 282, 581−585. (22) Hemalatha, K.; Jayakumar, M.; Bera, P.; Prakash, A. S. Improved electrochemical performance of Na0.67MnO2 through Ni and Mg substitution. J. Mater. Chem. A 2015, 3, 20908−20912. (23) Wu, X.; Guo, J.; Wang, D.; Zhong, G.; McDonald, M. J.; Yang, Y. P2-type Na0.66Ni0.33−xZnxMn0.67O2 as new high-voltage cathode materials for sodium-ion batteries. J. Power Sources 2015, 281, 18−26. (24) Clement, R. J.; Billaud, J.; Armstrong, A. R.; Singh, G.; Rojo, T.; Bruce, P. G.; Grey, C. P. Structurally stable Mg-doped P2Na2/3Mn1‑yMgyO2 sodium-ion battery cathodes with high rate performance: insights from electrochemical, NMR and diffraction studies. Energy Environ. Sci. 2016, 9, 3240−3251. (25) Kang, W.; Yu, D. Y.; Lee, P. K.; Zhang, Z.; Bian, H.; Li, W.; Ng, T. W.; Zhang, W.; Lee, C. S. P2-Type NaxCu0.15Ni0.20Mn0.65O2 Cathodes with High Voltage for High-Power and Long-Life SodiumIon Batteries. ACS Appl. Mater. Interfaces 2016, 8, 31661−31668. (26) Kwon, M. S.; Lim, S. G.; Park, Y.; Lee, S. M.; Chung, K. Y.; Shin, T. J.; Lee, K. T. P2 Orthorhombic Na0.7[Mn1‑xLix]O2+y as Cathode Materials for Na-Ion Batteries. ACS Appl. Mater. Interfaces 2017, 9, 14758−14768. (27) Pang, W.; Zhang, X.; Guo, J.; Li, J.; Yan, X.; Hou, B.; Guan, H.; Wu, X. P2-type Na2/3Mn1‑xAlxO2 cathode material for sodium-ion batteries: Al-doped enhanced electrochemical properties and studies on the electrode kinetics. J. Power Sources 2017, 356, 80−88. (28) Paulsen, J. M.; Dahn, J. R. Studies of the layered manganese bronzes, Na2/3 [Mn1‑x Mx ]O2 with M = Co, Ni, Li, and Li2/3 [Mn1‑x Mx ]O2 prepared by ion-exchange. Solid State Ionics 1999, 126, 3−24. (29) Stoyanova, R.; Carlier, D.; Sendova-Vassileva, M.; Yoncheva, M.; Zhecheva, E.; Nihtianova, D.; Delmas, C. Stabilization of overstoichiometric Mn4+ in layered Na2/3MnO2. J. Solid State Chem. 2010, 183, 1372−1379. (30) Wang, Y.; Xiao, R.; Hu, Y. S.; Avdeev, M.; Chen, L. P2Na0.6[Cr0.6Ti0.4]O2 cation-disordered electrode for high-rate symmetric rechargeable sodium-ion batteries. Nat. Commun. 2015, 6, 6954. (31) Thackeray, M. M.; David, W. I. F.; Bruce, P. G.; Goodenough, J. B. LITHIUM INSERTION INTO MANGANESE SPINELS. Mater. Res. Bull. 1983, 18, 461−472. (32) Thackeray, M. M. MANGANESE OXIDES FOR LITHIUM BATTERIES. Prog. Solid State Chem. 1997, 25, 1−71. (33) Li, X.; Wang, Y.; Wu, D.; Liu, L.; Bo, S.-H.; Ceder, G. Jahn− Teller Assisted Na Diffusion for High Performance Na Ion Batteries. Chem. Mater. 2016, 28, 6575−6583. (34) Goodenough, J. B. JAHN-TELLER PHENOMENA IN SOLIDS. Annu. Rev. Mater. Sci. 1998, 28, 1−27. 8962
DOI: 10.1021/acs.chemmater.7b02772 Chem. Mater. 2017, 29, 8958−8962
