Lithium Borocarbide LiBC as an Anode Material for Rechargeable Li

Article Cite This: J. Phys. Chem. C 2018, 122, 18231−18236

pubs.acs.org/JPCC

Lithium Borocarbide LiBC as an Anode Material for Rechargeable LiIon Batteries De Li,†,§ Pengcheng Dai,∥ Yong Chen,§ Ruwen Peng,‡ Yang Sun,*,† and Haoshen Zhou*,†,‡

J. Phys. Chem. C 2018.122:18231-18236. Downloaded from pubs.acs.org by EASTERN KENTUCKY UNIV on 08/16/18. For personal use only.

†

Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Umezono, 1-1-1, Tsukuba 305-8568, Japan ‡ National Laboratory of Solid State Microstructures and Department of Energy Science and Engineering and Department of Physics, Nanjing University, Nanjing 210093, China § State Key Laboratory on Marine Resource Utilization in South China Sea; Hainan Provincial Key Laboratory of Research on Utilization of Si-Zr-Ti Resources; College of Materials Science and Chemical Engineering, Hainan University, 58 Renmin Road, Haikou 570228, China ∥ International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba 305-0044, Japan S Supporting Information *

ABSTRACT: Graphite is the dominant anode material for commercial Li-ion batteries, whereas developing other graphite-like anode material has never been practically achieved to date. Here, we perform computational and experimental studies to demonstrate the feasibility of graphite-like LiBC as a high-capacity anode material for Li-ion batteries. Electrochemical measurements suggest that LiBC can deliver a reversible specific capacity of 450 mAh g−1 with an average voltage of 1.4 V vs Li+/Li. Analogous to graphite, both the discharged and charged LiBC preserve the layered structure. As far as we know, this is the first realization of a graphite-like anode material for Li-ion battery, which will shed light on the development of other graphite derivatives for energy storage. be accommodated.15 Previous first-principles studies also predicted that the boron-doped graphite BC3 is potentially a high-capacity electrode for Li-ion batteries.16,17 Lately, King et al. have reported the synthesis of graphitic BC3; however, the reversible lithium-storage capacity is much less than the theoretically predicted value, presumably due to the disordered nature.18,19 Another graphite-like compound LiBC was synthesized by Wörle et al.20 and predicted to be a hightemperature superconductor after hole-doping (Li1−xBC, x ≈ 0.5).21 Inspired by the theoretical prediction, the Li1−xBC compounds have been synthesized via various methods.22−25 Recently, Xu et al. have theoretically predicted that the layered structure of Li1−xBC can be well preserved at x ≤ 0.75, with the calculated voltage of 2.3−2.5 V vs Li+/Li in a Li-ion battery.26 More recently, Langer et al. have investigated the electrochemical properties of LiBC electrode in a Li-ion cell, while experimental results suggested a poor battery performance.27 To date, the challenge remains to find a practical anode material for Li-ion battery with graphite-like structure.

1. INTRODUCTION Nowadays, Li-ion batteries have been utilized as power sources in most of the portable electronic devices, and they are also being integrated into electric vehicles and smart grid to reduce fossil energy consumptions.1 For commercial Li-ion batteries, graphite is the most widely used anode material with a moderate specific capacity of 372 mAh g−1.2 To obtain higher specific energy, much efforts have also been made to develop negative electrodes based on alloying reaction3 (e.g., silicon4,5 and tin6) or conversion reaction7 (e.g., CoO,8 Cr2O3,9 Fe3O4,1010 and Mn3O411). A major disadvantage of these high-capacity anodes is the mechanical fracture induced by large volume change, which leads to the loss of active material and the resulting rapid capacity fading.3 Despite a massive research effort, these high-capacity anode materials are still far from satisfactory for commercial Li-ion batteries. Given the commercial success of graphite anode, people have tried to develop graphite-like materials as alternative anodes for Li-ion batteries. Theoretically, a variety of graphite derivatives, e.g., BC3, C3N, and BC2N,12−14 can be obtained by atomic substitution in the graphite lattice. In the case of boron doping, the carbon lattice becomes electron-deficient due to the empty boron pz states and accordingly more Li atoms can © 2018 American Chemical Society

Received: April 23, 2018 Revised: July 1, 2018 Published: July 11, 2018 18231

DOI: 10.1021/acs.jpcc.8b03763 J. Phys. Chem. C 2018, 122, 18231−18236

Article

The Journal of Physical Chemistry C

separated from the working electrode by a Celgard 2400 porous polypropylene film, and the electrolyte is 1 M LiClO4 in ethylene carbonate/diethyl carbonate (EC/DEC with a volume ratio of 1:1). All of these components are stored in the glovebox, as well as the cell assembly. Galvanostatic measurements are carried out by a battery charge/discharge system from Hokuto Denko Corp. The morphologies and crystal structures of pristine samples are characterized by powder X-ray diffraction (XRD, Cu Kα radiation, Bruker D8 Advance diffractometer), scanning electron microscopy (SEM, LEO Gemini Supra 35), and transmission electron microscopy (TEM, JEM-3000F, JEOL Corp.). For ex situ characterization, the electrochemically treated LiBC electrode is disassembled from the coin cell, repetitively washed by DEC and then thoroughly dried in the glovebox. For the ex situ XRD experiment, the working electrode is quickly measured in the air condition. For the TEM measurement, the working electrode is ultrasonically dispersed in pure DEC to obtain separated LiBC particles as TEM specimens.

In this work, we revisit the hexagonal layered LiBC through combined computational and experimental studies and finally demonstrate the feasibility of LiBC as a high-capacity anode material for Li-ion battery. Density functional theory (DFT) calculation results indicate that the Li1−xBC is stable in the range of 0 < x < 0.5, with a calculated insertion voltage of ca. 1.0 V vs Li+/Li. Then, the well-crystallized LiBC is facilely synthesized by a high-temperature solid-state reaction, and it is experimentally proved to be an excellent anode material with a high specific capacity of 450 mAh g−1 in Li-ion batteries. According to ex situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations, both the discharged and charged states preserve the layered structure, resulting in a good cycle performance.

2. METHODS Our calculations were performed using the Vienna Ab initio Simulation Package (VASP)28,29 by the projector augmentedwave approach.30 Generalized gradient approximation in the parameterization of Perdew, Burke, and Ernzerhof (PBE)31 pseudopotential was used to describe the exchange correlation potential. Besides the standard DFT calculations, the vdWDF2 functional was used to account for the van der Waals (vdW) interaction.32−34 The Li (1s, 2s, 2p), B (2s, 2p), and C (2s, 2p) orbitals are treated as valence states. The supercell comprises 3 × 3 × 1 conventional unit cells, corresponding to 18 formula units of LiBC. A 5 × 5 × 5 mesh was used for kpoint sampling. The optimized lattice parameters of LiBC are a = 2.750 Å, c = 7.042 Å (PBE functional) and a = 2.757 Å, c = 7.138 Å (vdW-DF2 functional), consistent with previous calculation results26,35 and experimental values (a = 2.752 Å, c = 7.058 Å).36 The plane-wave cutoff was set to 520 eV. Geometry optimizations were performed by using a conjugate gradient minimization until all of the forces acting on ions were less than 0.01 eV Å−1 per atom. The insertion voltage is determined by V(x) = [E(Li1−x+ΔBC) − E(Li1−xBC)]/Δ, where E(Li1−x+ΔBC) and E(Li1−xBC) represent the total energies of Li1−x+ΔBC and Li1−xBC supercells, respectively. Using the optimized geometries of Li1−xBC, the force constants (Hessian matrix) were evaluated with density functional perturbation theory implemented in VASP,37 and subsequently the phonon frequencies were calculated using PHONOPY program.38 To synthesize LiBC, LiH (Wako Pure Chemical Industries, Ltd.), boron (amorphous powder, Sigma-Aldrich), and carbon (acetylene black) with a mole ratio of 1.05:1:1 are mixed and ground thoroughly in a glovebox filled with Ar gas. Afterward, the mixture is pressed into a small pellet. Then, the pellet is inserted into a reaction vessel (SUS316L bipass with Ta foil lining), one end of which is sealed with an SUS316L plug and the other end is separated from the pure Ar flow by a Ta foil. In an electrical tube furnace with 100 mL min−1 Ar gas flow, the pellet is calcined at 800 °C for 10 h to obtain the product LiBC. After cooling down, the product pellet is taken out from the reaction vessel, ground into powder in the glovebox, and stored in a vacuum condition. For the electrochemical test, a composite paste is firmly pressed on an SUS mesh (100 mesh) with a mass loading of ca. 5 mg cm−2 to make the working electrode, where the composite paste is prepared in the glovebox with 80 wt % LiBC, 10 wt % acetylene black, and 10 wt % poly(tetrafluoroethylene) (drying powders). In the coin-type battery (CR2032), the counter electrode of lithium metal is

3. RESULTS AND DISCUSSION Figure 1a illustrates the hexagonal layered structure of LiBC with P63/mmc symmetry. The BC layers are stacked along the

Figure 1. (a) Crystal structure of hexagonal LiBC with graphite-like structure, top view (left) and side view (right). The Li, B, and C atoms are denoted by the green, white, and brown spheres, respectively. (b) Calculated intercalation voltage at various Li contents. The vdW and PBE symbols refer to the DFT with and without vdW correction, respectively. The solid circle/square indicates a stable crystal structure (no imaginary frequency in the phonon dispersion), while the hollow circle/square suggests the structural instability.

c-axis with intercalated Li ions between them. Each hexagonal B3C3 ring is alternately connected by B and C atoms, and each Li ion is sandwiched by two opposite B3C3 rings. Analogous to the graphene, the BC sheet is formed by the B−C bonding in an sp2 configuration with each π-bonding orbital occupied by a C 2pz electron and a Li 2s electron transferred to the B 2pz orbital. For the stoichiometric LiBC, all interstices between the 18232


Article


LiBC sample is shorter in the a-axis and longer in the c-axis. According to the results reported by Fogg et al.,22 the a-axis decreases with decreasing Li content while the c-axis increases, indicating that our sample is actually lithium-deficient. The lithium deficiency could also be reflected from the black color of our LiBC sample, rather than the golden color of stoichiometric LiBC.44 Scanning electron microscopy (SEM) image shown in Figure 2b suggests an assembly of aggregated LiBC nanoparticles. The layered LiBC lattice can be characterized by the TEM image (Figure 2c), wherein BC layers stacked along the c-axis are observed clearly. Figure 2d depicts the TEM image viewed along the [201] direction, and the inset shows the selected area diffraction (SAD) pattern obtained by fast Fourier transform. The SAD spots can be indexed by the lattice vectors of a hexagonal layered structure. Depending on the above experiments and analysis, the synthesized sample is confirmed as lithium-deficient Li1−δBC with layered graphite-like structure. Next, we investigate the lithium-storage capability of asprepared Li1−δBC in a Li-ion cell. As shown in Figure 3a, the 1st discharge capacity is ca. 300 mAh g−1, which could be attributed to the active material Li1−δBC and the conductive additive acetylene black. As shown in Figure S2, the acetylene black delivers an initial discharging capacity of ca. 700 mAh g−1 and a reversible capacity of ca. 200 mAh g−1. The large

interlayer B3C3 rings have been occupied and thus no further Li intercalation is permitted. Li-ion deintercalation from LiBC lattice is expected to provide charge capacity for Li-ion batteries, and the corresponding voltage can be obtained by DFT calculations. Results in Figure 1b show that when x ranges from 0 to 4/9, the calculated voltage is predicted to be ca. 1.9 V vs Li+/Li. In the case of x ≥ 5/9, the value significantly increases to more than 2.3 V vs Li+/Li. Considering the van der Waals interactions, the average voltage for above two ranges are calculated to be 1.0 and 1.4 V, respectively. Furthermore, we examine the lattice stability of Li1−xBC at different Li contents by phonon calculations, which have been proved effective in predicting the structural stabilities.39−42 The calculated phonon spectra dispersion curves in Figure S1 show no imaginary frequency when x ≤ 4/9, indicating that the LiBC lattice is mechanically stable at high lithium concentration; when x ≥ 5/9, the imaginary phonon modes emerge and increase with increasing x, suggesting the structural instability in the case of overdelithiation. Combining the calculated voltage and phonon spectra, a close correlation between the increase in voltage and the structural instability can be identified. Accordingly, the average voltage of Li1−xBC for a reversible Li storage is predicted to be 1.0 V vs Li+/Li. Considering the supercell size in our simulations, the upper limit of x is actually between 4/9 and 5/9, consistent with some earlier reports that the Li1−xBC is stable up to ca. Li0.5BC.23−25 Our results regarding the insertion voltage is lower than those of the previous computational study by Xu et al.,26 probably due to the different functions adopted in the two works. By a high-temperature solid-state reaction, LiBC is synthesized from LiH, amorphous boron, and carbon (1.05:1:1 in mole ratio) in an argon atmosphere. In contrast to a previous report,43 acetylene black is adopted as the carbon precursor. According to the XRD patterns in Figure 2a, the asprepared sample mainly consists of hexagonal layered LiBC with a little impurity of certain Li−B compounds. The lattice parameters of LiBC are calculated to be 2.739 and 7.149 Å for a- and c-axes, respectively. Compared to the previously reported values (a = 2.752 Å, c = 7.058 Å),20 the as-prepared

Figure 3. (a) Initial discharge/charge/discharge curves of LiBC with a current of 30 mA g−1 in the voltage window between 0.05 and 2.5 V. (b) XRD patterns for pristine LiBC (1#), the initial discharged (2#), the first charged (3#), and the second discharged (4#), where the SUS304 peak comes from the current collector of stainless steel mesh.

Figure 2. (a) XRD patterns of LiBC synthesized from acetylene black. (b) SEM and (c, d) TEM images of pristine LiBC. The inset in (d) displays the selected area electron diffraction pattern viewed along the [201] direction. 18233


Article

The Journal of Physical Chemistry C irreversible capacity of the initial discharge is mainly due to the formation of solid electrolyte interphase film. Considering the 10 wt % acetylene black in our electrode, the corresponding contribution to the specific capacity should be 88 mAh g−1 in the initial discharge and 25 mAh g−1 in subsequent reversible cycles. To probe the structural change of Li1−δBC after lithium de/ intercalation, ex situ XRD is carried out to characterize the Li1−δBC electrode at different charge/discharge states. The symbols 1#, 2#, 3#, and 4# represent the pristine, initial discharged, first charged, and second discharged states, respectively. The XRD patterns for the four states are illustrated in Figure 3b. We note that except for the pristine state #1, the XRD patterns of the other three states are measured using the electrode and therefore have strong background noises. It can be seen that the (002) diffraction peak, which features a layered structure, is well preserved after the initial discharge (2#). In the subsequent charge process, the (002) peak still remains but weakened (3#), suggesting that the layered structure of LiBC is generally maintained while the crystallinity becomes poor upon lithium deintercalation. The weakened (002) peak resumes after the second discharge (4#), indicating that the reduced crystallinity can be restored once the Li-ions are reintercalated. The above phenomena further demonstrate the important role of Li atoms, which donate electrons to the B atoms, in stabilizing the crystal structure of layered LiBC. TEM images are also acquired for the discharged (2#) and charged (3#) LiBC electrodes, as shown in Figure S3. For the discharged state (2#), the BC layers are clearly observed, and the SAD pattern further verifies the hexagonal layered structure of LiBC. For the charged state (3#), the BC layers can also be observed, but not as ordered as that of the discharged state, consistent with the XRD results. The corresponding SAD pattern also suggests that the hexagonal LiBC lattice is preserved at the charged state. According to both XRD and TEM results, the hexagonal layered structure of LiBC is confirmed in both discharged and charged electrodes, while the crystallinity is relatively poor in the latter. In other words, the discharging product was fully lithiated LiBC and the charging product was partially delithiated LiBC (Li1−xBC) with poor crystallinity. The electrochemical properties of LiBC electrode are estimated in the Li-ion battery. Figure 4a shows the galvanostatic charge/discharge curves of a LiBC/Li cell for the first 10 cycles. A large voltage hysteresis between the charge and discharge curves can be observed. The average intercalation voltage is ca. 1.4 V vs Li+/Li, 0.4 V higher than the calculated value. Besides the intrinsic error of DFT approaches in evaluating the intercalation voltage, the reduced crystallinity of LiBC at charged state may also contribute to the deviation. After the initial cycle, the reversible capacity of LiBC is ca. 450 mAh g−1, which is higher than that of graphite (372 mAh g−1). Owing to the strong interaction between the Li 2s electron and the B 2pz orbital, the intercalation voltage of LiBC is relatively higher than that of graphite, which can avoid the safety concerns caused by the formation of dendritic deposits, at the cost of which the LiBC anode will make the full battery exhibit a lower working voltage than the graphite anode. Figure 4b shows the cycling performance of LiBC electrode after initial 10 cycles. Both the charge and discharge capacities are approximately 460 mAh g−1, exhibiting a high Coulombic efficiency close to 100%. During the 50 cycles, almost no

Figure 4. (a) First 10 discharge/charge cycles of LiBC electrode in the voltage window between 0.2 and 2.5 V at a current of 15 mA g−1. (b) Cycling performance of LiBC with a current of 60 mA g−1 in the voltage window between 0.05 and 2.5 V.

capacity fading is observed, indicating a high reversibility of the LiBC electrode. According to the electrochemical results, we could evaluate the lithium deficiency δ in as-prepared Li1−δBC. As shown in Figure 4a, the capacity of initial discharge is ca. 300 mAh g−1 with the electrochemical reaction as Li1−δBC + δLi+ + δe → LiBC and the reversible capacity of LiBC is 450 mAh g−1 with the electrochemical reaction as Li0.5BC + 0.5Li+ + 0.5e ↔ LiBC, thereby δ:0.5 = 300:450 and δ = 1/3. However, the capacity of initial discharge should be attributed to not only the active material Li1−δBC but also the conductive additive acetylene black. As shown in Figure S2, acetylene black delivers an initial discharging capacity of ca. 700 mAh g−1 and a reversible capacity of ca. 200 mAh g−1. Considering the 10 wt % acetylene black in our electrode, the corresponding contribution to the specific capacity should be 88 mAh g−1 in the initial discharge and 25 mAh g−1 in subsequent reversible cycles. Therefore, δ:0.5 = (300 − 88):(450 − 25) and δ = 1/4, when considering the contribution of acetylene black. From the above experiments and analysis, we demonstrate that the layered LiBC makes the first practical anode material for Li-ion battery possessing a graphite-like structure, with high specific capacity, appropriate voltage, and excellent cycle stability. However, LiBC exhibits a large voltage hysteresis during the charge/discharge processes, indicating a slow kinetics of Li-ion transport, which might be attributed to its varied crystallinity depending on Li-ion concentration. This disadvantage is anticipated to be overcome by further optimizing LiBC. In addition, it is the first achievement of controlling the lithium concentration of LiBC through an electrochemical method, which has the advantage of continuously variable relative to the previously reported direct synthesis or soft chemistry oxidation,45 facilitating the fundamental research on the physical properties of layered LiBC. 18234


Article


Their Application as a Negative Electrode for a Lithium Ion (Shuttlecock) Cell. J. Electrochem. Soc. 1993, 140, 2490−2498. (3) Obrovac, M. N.; Chevrier, V. L. Alloy Negative Electrodes for LiIon Batteries. Chem. Rev. 2014, 114, 11444−11502. (4) Li, H.; Huang, X. J.; Chen, L. Q.; Wu, Z. G.; Liang, Y. A High Capacity Nano Si Composite Anode Material for Lithium Rechargeable Batteries. Electrochem. Solid-State Lett. 1999, 2, 547− 549. (5) Chan, C. K.; Peng, H.; Liu, G.; McIlwrath, K.; Zhang, X. F.; Huggins, R. A.; Cui, Y. High-Performance Lithium Battery Anodes Using Silicon Nanowires. Nat. Nanotechnol. 2008, 3, 31−35. (6) Courtney, I. A.; Tse, J. S.; Mao, O.; Hafner, J.; Dahn, J. R. Ab Initio Calculation of the Lithium-Tin Voltage Profile. Phys. Rev. B 1998, 58, 15583−15588. (7) Reddy, M. V.; Rao, G. V. S.; Chowdari, B. V. R. Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries. Chem. Rev. 2013, 113, 5364−5457. (8) Poizot, P.; Laruelle, S.; Grugeon, S.; Dupont, L.; Tarascon, J. M. Nano-Sized Transition-Metal Oxides as Negative-Electrode Materials for Lithium-Ion Batteries. Nature 2000, 407, 496−499. (9) Hu, J.; Li, H.; Huang, X. J. Cr2 O 3-Based Anode Materials for Li-Ion Batteries. Electrochem. Solid-State Lett. 2005, 8, A66−A69. (10) Taberna, P. L.; Mitra, S.; Poizot, P.; Simon, P.; Tarascon, J. M. High Rate Capabilities Fe3o4-Based Cu Nano-Architectured Electrodes for Lithium-Ion Battery Applications. Nat. Mater. 2006, 5, 567− 573. (11) Wang, H.; Cui, L.-F.; Yang, Y.; Sanchez Casalongue, H.; Robinson, J. T.; Liang, Y.; Cui, Y.; Dai, H. Mn3o4−Graphene Hybrid as a High-Capacity Anode Material for Lithium Ion Batteries. J. Am. Chem. Soc. 2010, 132, 13978−13980. (12) Kouvetakis, J.; Kaner, R. B.; Sattler, M. L.; Bartlett, N. A Novel Graphite-Like Material of Composition Bc3, and Nitrogen-Carbon Graphites. J. Chem. Soc., Chem. Commun. 1986, 24, 1758−1759. (13) Sandré, É ; Pickard, C. J.; Colliex, C. What Are the Possible Structures for Cnx Compounds? The Example of C3n. Chem. Phys. Lett. 2000, 325, 53−60. (14) Liu, A. Y.; Wentzcovitch, R. M.; Cohen, M. L. Atomic Arrangement and Electronic Structure of Bc2n. Phys. Rev. B 1989, 39, 1760−1765. (15) Way, B. M.; Dahn, J. R. The Effect of Boron Substitution in Carbon on the Intercalation of Lithium in Lix(Bzc1-Z )6. J. Electrochem. Soc. 1994, 141, 907−911. (16) Kuzubov, A. A.; Fedorov, A. S.; Eliseeva, N. S.; Tomilin, F. N.; Avramov, P. V.; Fedorov, D. G. High-Capacity Electrode Material Bc3 for Lithium Batteries Proposed by Ab Initio Simulations. Phys. Rev. B 2012, 85, No. 195415. (17) Joshi, R. P.; Ozdemir, B.; Barone, V.; Peralta, J. E. Hexagonal Bc3: A Robust Electrode Material for Li, Na, and K Ion Batteries. J. Phys. Chem. Lett. 2015, 6, 2728−2732. (18) King, T. C.; Matthews, P. D.; Glass, H.; Cormack, J. A.; Holgado, J. P.; Leskes, M.; Griffin, J. M.; Scherman, O. A.; Barker, P. D.; Grey, C. P.; et al. Theory and Practice: Bulk Synthesis of C3b and Its H2- and Li-Storage Capacity. Angew. Chem., Int. Ed. 2015, 54, 5919−5923. (19) King, T. C.; Matthews, P. D.; Holgado, J. P.; Jefferson, D. A.; Lambert, R. M.; Alavi, A.; Wright, D. S. A Single-Source Route to Bulk Samples of C3n and the Co-Evolution of Graphitic Carbon Microspheres. Carbon 2013, 64, 6−10. (20) Wörle, M.; Nesper, R.; Mair, G.; Schwarz, M.; Von Schnering, H. G. Libc  a Completely Intercalated Heterographite. Z. Anorg. Allg. Chem. 1995, 621, 1153−1159. (21) Rosner, H.; Kitaigorodsky, A.; Pickett, W. E. Prediction of High Tc Superconductivity in Hole-Doped Libc. Phys. Rev. Lett. 2001, 88, No. 127001. (22) Fogg, A. M.; Meldrum, J.; Darling, G. R.; Claridge, J. B.; Rosseinsky, M. J. Chemical Control of Electronic Structure and Superconductivity in Layered Borides and Borocarbides: Understanding the Absence of Superconductivity in Lixbc. J. Am. Chem. Soc. 2006, 128, 10043−10053.

4. CONCLUSIONS In summary, combined computational and experimental studies are performed to demonstrate the feasibility of hexagonal layered LiBC as a high-capacity anode material for Li-ion battery. DFT calculations indicate that the Li1−xBC is stable in the range of 0 < x < 0.5 and predict an insertion voltage of ca. 1.0 V vs Li+/Li. Then, the lithium-deficient Li1−δBC has been facilely synthesized by a high-temperature solid-state reaction. Using the XRD and TEM characterizations, it is found that the hexagonal layered structure of LiBC is maintained during the electrochemical charge/ discharge, but accompanied by a reversible change in crystallinity. Implemented in a Li-ion cell, LiBC can deliver a reversible capacity of 450 mAh g−1, with excellent capacity retention and high Coulombic efficiency. The average voltage is 1.4 V vs Li+/Li, which is higher than theoretical prediction and presumably due to the reduced crystallinity at charged state. As far as we know, the layered LiBC proposed in this work is the first practical graphite-like borocarbide as an anode material for Li-ion batteries, which will shed light on the development of other graphite derivatives for energy storage.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.8b03763.

■

Phonon dispersion and TEM images for LiBC and electrochemical contribution of acetylene black (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (Y.S.). *E-mail: [email protected] (H.Z.). ORCID

De Li: 0000-0003-2836-6808 Pengcheng Dai: 0000-0002-7141-8477 Ruwen Peng: 0000-0003-0424-2771 Haoshen Zhou: 0000-0001-8112-3739 Author Contributions

D.L. carried out sample preparations and SEM/XRD/electrochemical measurements. Y.S. performed first-principles calculations. P.D. performed TEM imaging. D.L. and Y.S. analyzed the experimental data. D.L. and Y.S. wrote the paper. H.Z. supervised and coordinated the entire investigation. All authors contributed to the discussions. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank Jun Okagaki, Xizheng Liu, and Jin Yi for experimental support. This study was partially supported by the National Basic Research Program of China (2014CB932300) and the National Natural Science Foundation of China (21633003).

■

REFERENCES

(1) Armand, M.; Tarascon, J. M. Building Better Batteries. Nature 2008, 451, 652−657. (2) Ohzuku, T.; Iwakoshi, Y.; Sawai, K. Formation of Lithium Graphite Intercalation Compounds in Nonaqueous Electrolytes and 18235


Article


Solids to Formal Mixed Valency: The Case of Lixbc. Philos. Trans. R. Soc., A 2008, 366, 55−62.

(23) Bharathi, A.; Jemima Balaselvi, S.; Premila, M.; Sairam, T. N.; Reddy, G. L. N.; Sundar, C. S.; Hariharan, Y. Synthesis and Search for Superconductivity in Libc. Solid State Commun. 2002, 124, 423−428. (24) Fogg, A. M.; Chalker, P. R.; Claridge, J. B.; Darling, G. R.; Rosseinsky, M. J. Libc Electronic, Vibrational, Structural, and LowTemperature Chemical Behavior of a Layered Material Isoelectronic with Mgb2. Phys. Rev. B 2003, 67, No. 245106. (25) Nakamori, Y.; Orimo, S.-i. Synthesis and Characterization of Single Phase Lixbc (X = 0.5 and 1.0), Using Li Hydride as a Starting Material. J. Alloys Compd. 2004, 370, L7−L9. (26) Xu, Q.; Ban, C. M.; Dillon, A. C.; Wei, S. H.; Zhao, Y. F. FirstPrinciples Study of Lithium Borocarbide as a Cathode Material for Rechargeable Li Ion Batteries. J. Phys. Chem. Lett. 2011, 2, 1129− 1132. (27) Langer, T.; Dupke, S.; Dippel, C.; Winter, M.; Eekert, H.; Pottgen, R. Libc - Synthesis, Electrochemical and Solid-State Nmr Investigations. Z. Naturforsch., B: J. Chem. Sci. 2012, 67, 1212−1220. (28) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B 1996, 54, 11169−11186. (29) Kresse, G.; Furthmüller, J. Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comput. Mater. Sci. 1996, 6, 15−50. (30) Blöchl, P. E. Projector Augmented-Wave Method. Phys. Rev. B 1994, 50, 17953−17979. (31) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865−3868. (32) Dion, M.; Rydberg, H.; Schröder, E.; Langreth, D. C.; Lundqvist, B. I. Van Der Waals Density Functional for General Geometries. Phys. Rev. Lett. 2004, 92, No. 246401. (33) Lee, K.; Murray, É . D.; Kong, L.; Lundqvist, B. I.; Langreth, D. C. Higher-Accuracy Van Der Waals Density Functional. Phys. Rev. B 2010, 82, No. 081101. (34) Klimeš, J.; Bowler, D. R.; Michaelides, A. Van Der Waals Density Functionals Applied to Solids. Phys. Rev. B 2011, 83, No. 195131. (35) Lebègue, S.; Arnaud, B.; Rabiller, P.; Alouani, M.; Pickett, W. E. Quasiparticle Properties of the Possible Superconductor Materials Libc and Nabc. Europhys. Lett. 2004, 68, 846. (36) Yanagisawa, H.; Tanaka, T.; Ishida, Y.; Rokuta, E.; Otani, S.; Oshima, C. Phonon Dispersion Curves of Stable and Metastable Bc3 Honeycomb Epitaxial Sheets and Their Chemical Bonding: Experiment and Theory. Phys. Rev. B 2006, 73, No. 045412. (37) Baroni, S.; Giannozzi, P.; Testa, A. Green’s-Function Approach to Linear Response in Solids. Phys. Rev. Lett. 1987, 58, 1861−1864. (38) Togo, A.; Oba, F.; Tanaka, I. First-Principles Calculations of the Ferroelastic Transition between Rutile-Type and Cacl2-Type Sio2 at High Pressures. Phys. Rev. B 2008, 78, No. 134106. (39) Goel, P.; Gupta, M. K.; Mittal, R.; Rols, S.; Patwe, S. J.; Achary, S. N.; Tyagi, A. K.; Chaplot, S. L. Phonons, Lithium Diffusion and Thermodynamics of Limpo4 (M = Mn, Fe). J. Mater. Chem. A 2014, 2, 14729−14738. (40) Kang, S.; Mo, Y.; Ong, S. P.; Ceder, G. Nanoscale Stabilization of Sodium Oxides: Implications for Na−O2 Batteries. Nano Lett. 2014, 14, 1016−1020. (41) Lin, S.-H.; Kuo, J.-L. Towards the Ionic Limit of TwoDimensional Materials: Monolayer Alkaline Earth and Transition Metal Halides. Phys. Chem. Chem. Phys. 2014, 16, 20763−20771. (42) Louis, L.; Nakhmanson, S. M. Structural, Vibrational, and Dielectric Properties of Ruddlesden-Popper Ba2zro4 from First Principles. Phys. Rev. B 2015, 91, No. 134103. (43) Kudo, T.; Nakamori, Y.; Orimo, S. I.; Badica, P.; Togano, K. Hydrogen Effects on Synthesis Processes and Electrical Resistivities of Libc. J. Japan Inst. Metals 2005, 69, 433−438. (44) Zhao, L.; Klavins, P.; Liu, K. Synthesis and Properties of HoleDoped Li1−Xbc. J. Appl. Phys. 2003, 93, 8653−8655. (45) Fogg, A. M.; Darling, G. R.; Claridge, J. B.; Meldrum, J.; Rosseinsky, M. J. The Chemical Response of Main-Group Extended 18236


Lithium Borocarbide LiBC as an Anode Material for Rechargeable Li

Recommend Documents