[Show abstract][Hide abstract] ABSTRACT: A lithium nickel manganese oxide, O3-Li2/3Ni1/3Mn2/3O2, is synthesized from the precursor, P3-Na2/3Ni1/3Mn2/3O2, by a Na+/Li+ ion exchange reaction using molten salt. Post-heating at 300, 400, 500, 600, and 700 °C is carried out for 5 h in air. The products are characterized by powder XRD, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), SEM, 6Li-magic-angle-spinning-NMR, and electrochemical measurements. The charge/discharge profiles of O3-Li2/3Ni1/3Mn2/3O2, thermally treated at 500 °C, show a high-potential plateau region at 4.8 V. Furthermore, sloping voltage profiles are observed at an average voltage of 3.21 V. An initial discharge capacity of 257 mA h g-1 is obtained between 2.0 and 4.8 V with a current density of 15 mA g-1 at 25 °C. This capacity corresponds to 0.90 electron transfers per formula unit. This study shows that Post-heating of O3-Li2/3Ni1/3Mn2/3O2 is effective to improve its electrochemical properties.
[Show abstract][Hide abstract] ABSTRACT: The surface structures, high-voltage charging/discharging performances, and Li-ion transfer at the electrode/electrolyte interface of LiNi1/3Co1/3Mn1/3O2 coated with small amounts of Zr oxide by the sol-gel method were investigated. Island-like ZrO2 grains as well as grain-free (sea-like) zones were observed on the surfaces of the coated LiNi1/3Co1/3Mn1/3O2 samples. The ratio of the area of these sea-like zones to the total surface area of the LiNi1/3Co1/3Mn1/3O2 sample increased from 44 to 85% when the Zr oxide content was decreased from 1.0 to 0.125 wt%. A compound oxide phase containing Zr, Ni, Co, and Mn was formed uniformly on the sea-like zones; the depth of this phase was approximately 2 nm. The initial discharge capacities of the coated LiNi1/3Co1/3Mn1/3O2 samples were equal to that of bare LiNi1/3 Co1/3Mn1/3O2. Further, the cycling performances of the coated LiNi1/3Co1/3Mn1/3O2 samples were significantly higher, as were their discharge capacities and discharge voltages, while their charge-transfer resistances (Rct) were lower. It was also found that the coated LiNi1/3Co1/3Mn1/3O2 samples had lower activation energies (Ea) for charge transfer than the bare LiNi1/3 Co1/3Mn1/3O2. Thus, it can be surmised that the area and structure of the sea-like zones determined the Rct and Ea values and cycling performances of the coated LiNi1/3Co1/3Mn1/3O2 samples.
No preview · Article · Jan 2016 · Journal of The Electrochemical Society
[Show abstract][Hide abstract] ABSTRACT: A sol-gel method was used to fabricate Al-oxide coated LiNi1/3Co1/3Mn1/3O2 cathodes and their surface structure and high-voltage charge/discharge characteristics were evaluated with a view to their potential use in Li-ion batteries. Scanning transmission electron microscopy (STEM) revealed that a solid solution of LiAlO2-LiNi1/3Co1/3Mn1/3O2 is uniformly formed to a depth of several nanometers from the surface of Al-oxide coated LiNi1/3Co1/3Mn1/3O2. Furthermore, the discharge capacity and average discharge voltage of Al-oxide coated LiNi1/3Co1/3Mn1/3O2 is equal to or higher than uncoated LiNi1/3Co1/3Mn1/3O2 at a charge voltage of 4.5 to 4.9 V. It was also found that the Al-oxide coating significantly improves the cycle performance at a charge voltage of 4.5 to 4.7 V. A substantial fade in capacity observed during the cycling of bare LiNi1/3Co1/3Mn1/3O2 is attributed to an increase in polarization due to an increased charge transfer resistance (R-ct), which is indicative of degradation of the interface between the electrode and electrolyte. However, this increase in polarization and R-ct is effectively suppressed in the Al-oxide coated LiNi1/3Co1/3Mn1/3O2. This can be explained by an inhibition of the formation of a rock-salt-structured phase in the surface region of bare LiNi1/3Co1/3Mn1/3O2 during cycling, as confirmed by STEM and electron energy loss spectrometry. (C) The Author(s) 2015. Published by ECS.
Preview · Article · Nov 2015 · Journal of The Electrochemical Society
[Show abstract][Hide abstract] ABSTRACT: The cobalt-based fluorophosphate Li2CoPO4F positive electrode has the potential to obtain high energy density in a lithium ion battery since its theoretical capacity is 287 mAh•g−1 when two electrons can react reversibly. This material promises to charge/discharge with an extremely high redox-couple voltage of over 4.8 V vs Li/Li+. Bulk structural analyses including X-ray diffraction, Co K-edge X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) reveal that an orthorhombic LiβCoPO4F phase is produced from pristine Li2CoPO4F by a combination of solid-solution and two-phase reaction manners during the first charging process, and these phases reversibly transform during charge-discharge cycling. The results of 7Li MAS NMR and classical molecular dynamics simulations suggest that Li ions located at Li(1) sites insert/desert through a 1D diffusion path along the b axis, whereas those located at Li(2) and Li(3) sites are fixed. The aforementioned analyses were successfully performed with the enhancement of electrochemical properties by use of a fluoroethylene carbonate-based electrolyte instead of an ethylene carbonate-based one and reducing its volume. Further enhancement was achieved by adding SiO2 nanoparticles into the electrode slurry. The electrochemical results encourage the possibility of the desertion/insertion of more than one Li ion from/into Li2CoPO4F during electrochemical cycling.
No preview · Article · Apr 2015 · Chemistry of Materials
[Show abstract][Hide abstract] ABSTRACT: Single crystals of the ternary manganese vanadate AgMnVO4, were grown using AgVO3 flux. The structure was determined from single crystal X-ray diffraction data. The magnetic structure and properties of AgMnVO4 were characterized by magnetic susceptibility, specific heat, and low-temperature neutron powder diffraction measurements. AgMnVO4 crystallizes in the maricite-type structure with space group Pnma, a = 9.5393(12), b = 6.8132(9), c = 5.3315(7) Å and Z = 4. AgMnVO4 contains MnO4 chains made up of edge-sharing MnO6 octahedra, and these chains are interlinked by the VO4 and AgO4 tetrahedra. The specific heat measurements indicate a 3D-antiferromagnetic ordering at ~12.1 K and the neutron powder diffraction measurements at 5 K show that the Mn+2 magnetic moments are antiferromagnetically coupled within the chains which are antiferromagnetically coupled to each other.
Full-text · Article · Sep 2014 · Journal of Solid State Chemistry
[Show abstract][Hide abstract] ABSTRACT: The 5 wt.% Al2O3-coated Li1.20Mn0.55Ni0.16Co0.09O2 was prepared by the mechanochemical reaction. The optimal condition for sample preparation was determined to be the rotation speed of 2000 rpm and the reaction time of 5 min by SEM, XRD, and XANES measurements. Surface analysis using XANES data demonstrated that all the samples were rather uniformly covered with nano-Al2O3 particles. The pristine and 5 wt.% Al2O3-coated samples after the stepwise pre-cycling treatment showed the discharge capacity of 243 and 216 mAh/g at 323 K, respectively. Although the Al2O3-coated sample showed less discharge capacity compared with the pristine sample, the Al2O3-coated sample showed better discharge capacity retention compared with the pristine sample after 35 cycles at 323 K. These results demonstrate that the mechanochemical Al2O3-coating process is an effective way of improving the cycle performance at high temperature.
No preview · Article · Sep 2014 · Solid State Ionics
[Show abstract][Hide abstract] ABSTRACT: The new polymorph of Co2[PO4]F has been synthesized by a hydrothermal route. Its crystal structure was determined from single-crystal X-ray diffraction data. Co2[PO4]F crystallizes with the triplite-type structure, space group C2/c, a = 12.856(2), b = 6.4369(10), c = 9.6742(16) Å, β = 117.40(1) °, V = 710.7(2) Å3 and Z = 8. The structure consists of a 3D-framework buildup of condensed PO4 tetrahedra, and cobalt(II) polyhedra which form chains running along the  and  directions. The coordina-tion of the cobalt cations and the connectivity between the cobalt polyhedra are not well defined due to the disorder of the fluoride anions which form zigzag chains along . The theoretical ordering of the fluoride anions led to two different structural models, very similar to the triplite Cc-CoFe[PO4]F and the triploidite P21/c-Co2[PO4]F, and in which the cobalt atoms are five and six coordinated.
[Show abstract][Hide abstract] ABSTRACT: Bulk and surface structural changes induced in a Li5FeO4 positive electrode with a defect anti-fluorite type structure are examined during its initial charge–discharge cycle by various synchrotron-radiation analysis techniques, with a view to determining the contribution of oxygen to its electrochemical properties. Bulk structural analyses including XRD, Fe K-edge XANES and EXAFS reveal that pseudo-cubic lithium iron oxides (PC-LFOs), in the form of LiαFe(4−α)+O2, are formed during the first charging process instead of the decomposition of pristine Li5FeO4. Moreover, the relative volume of this PC-LFO phase varies nonlinearly according to the charging depth. At the same time, the surface lithium compounds such as Li2O cover over the PC-LFO phase, which also contribute to the overall electrochemical reaction, as measured from the O K-edge XANES operating in a surface-sensitive total-electron yield mode. The ratio of these two different reaction mechanisms changes with the depth during the first charging process, with this tendency causing variation in the subsequent discharge capacity retention in relation to the depth of the charging electron and/or temperature of this “Li-rich” positive electrode. Indeed, such behaviour is noted to be very similar to the specific electrochemical properties of Li2MnO3.
[Show abstract][Hide abstract] ABSTRACT: The new compound HP-Na2Co[PO4]F was synthesized by high pressure solid state reaction and its crystal structure was determined from single crystal X-ray diffraction data. The physical properties of HP-Na2Co[PO4]F were characterized by magnetic susceptibility, specific heat capacity, galvanometric cycling, and electrochemical impedance spectroscopy measurements. HP-Na2Co[PO4]F crystallizes with the space group P63/m, a = 10.5484(15), c = 6.5261(9) Å, V = 628.87(15) Å3 and Z = 6. The crystal structure consists of infinite chains of edge-sharing CoF2O4 octahedra. The latter are interconnected through the PO4 tetrahedra forming a 3D-Co[PO4]F-framework. The six coordinated sodium atoms are distributed over three crystallographic sites (2b, 6h, and 4f). The structure of HP-[Na11/3Na23/3Na32/3]Co[PO4]F is similar to [Na11/3Na23/3Sr1/3•1/3]Ge[GeO4]O. There is only one difference; Na3 occupies the 4f (1/3, 2/3, 0.0291) atomic position, whereas the Sr occupies the 2c (1/3, 2/3, 1/4) atomic position. The magnetic susceptibility follows a Curie-Weiss behavior above 50 K with Θ = -21 K indicating predominant antiferromagnetic interactions. The specific heat capacity and magnetization measurements show that HP-Na2Co[PO4]F undergoes a three-dimensional magnetic ordering at TN = 11.0(1) K. The ionic conductivity σ, estimated at 350 °C, is 1.5 10−7 S cm−1. The electrochemical cycling indicates that only one sodium ion could be extracted during the first charge in Na half-cell; however, the re-intercalation was impossible due to a strong distortion of the structure after the first charge to 5.0 V.
[Show abstract][Hide abstract] ABSTRACT: Solid electrolyte interphase (SEI) and Mn deposition formed on capacity-degraded graphite electrodes in commercially available Mn-based/Graphite lithium ion batteries were characterized using glow discharge-optical emission spectroscopy (GD-OES). The depth profile of the whole electrode showed a homogeneous distribution of Li and Mn except for the surface region at the initial state. With the progress of degradation, Li and Mn concentrations increased inhomogeneously in the depth-direction of the electrode; the Li and Mn concentrations were high in the outer layer and decreased with depth to the current collector in the degraded electrodes. The SEI layer deposited on the electrode surface was separately analyzed in detail. The GD-OES surface profile was explained by comparing to the XPS analysis results. The amount of Li deposited on the electrode surface was almost constant with the capacity degradation, though the Li concentration in the whole electrode increased along with the capacity degradation. In contrast, the amount of Mn deposition increased with the capacity degradation both in the surface deposition layer and in the whole electrode.
No preview · Article · Jun 2014 · Journal of The Electrochemical Society
[Show abstract][Hide abstract] ABSTRACT: In oxide electrolytes, crystalline phosphate with NASICON (NaSuper Ionic Conductor)-type structures such as Li1+xAlxTi2−x(PO4)3 (LATP) and Li1+xAlxGe2−x(PO4)3 (LAGP) are known as excellent Li ion conductors. Perovskite Li0.5−3xLa0.5+xTiO3 (LLT) exhibits the high level of bulk conductivity of 10−3 S cm−1, but LATP and LLT electrolytes have Ti element in crystalline structure, and thus transition metal such as Ti is easily reduced by lithium metal negative electrode; it is thus difficult for these electrolytes to use in lithium metal batteries.
Recently, we started the systematic study of crystal structure and the electrochemical properties of fluorophosphate phases which do not contain transition metal elements. Indeed, in the ternary phase diagram LiMgPO4-LiF-Li3PO4, two new lithium rich phases have been discovered (Li2Mg[PO4]FandLi9Mg3[PO4]4F3). Li2Mg[PO4]F crystallizes with the well-known Li2Ni[PO4]F-type structure, whereas the Li9Mg3[PO4]4F3 crystallizes with a new-type of structure. Li9Mg3[PO4]4F3 exhibits an ionic conductivity of 10-4 S cm-1 at 300 °C, which is much higher than that of Li3VO4 (σ300 °C =1.6x10-6 S cm-1), γ-Li3PO4 (σ300 °C =2.2 ´ 10-8 S cm-1) or Li2SO4 (σ300 °C =2 ´ 10-7 S cm-1). This new phase would be also of great interest as positive electrode for Li-ion batteries if Mg2+ could be replaced by Fe2+ or Mn2+cations .
 Crystal structures of the new fluorophosphates Li9Mg3[PO4]4F3 and Li2Mg[PO4]F and ionic conductivities of selected compositions, H. Ben Yahia, M. Shikano, T. Takeuchi, H. Kobayashi, M. Itoh, J. Mater. Chem. A (2014)DOI:10.1039/C3TA15264B.
[Show abstract][Hide abstract] ABSTRACT: Realization of all-solid-state lithium-ion batteries (ASS-LIB) consisting of non-flammable inorganic solid electrolytes is desired because of their high safety. To improve energy and power densities of the ASS-LIB, the decrease of the interfacial resistance between electrode and solid electrolyte is required as well as the synthesis of solid electrolyte with high lithium-ion conductivity and the development of high thermodynamically stable positive and negative electrode materials. Spark plasma sintering (SPS), by which sintered ceramics can be assembled at shorter time and lower temperature, would be one of the useful tools for designing the ASS-LIB since the by-products at the interface are inhibited as well as possible. Actually, Aboulaich et al. have first reported the charge-discharge profiles of Li3V2(PO4)3 or LiFePO4/Li1.5Al0.5Ge1.5(PO4)3/Li3V2(PO4)3ASS-LIB using the SPS technique .
LiCoPO4 has a high redox potential for lithium-ion (de-)intercalation of c.a. 4.8 V vs. Li/Li+ with a theoretical capacity of 167 mAh/g. However, this material shows the capacity fading during charge–discharge cycling in LiPF6 based electrolyte solutions as shown in inserted figure (b) because of a nucleophilic attack of F− anions on the P atoms of the electrode surface . Therefore, we assembled high-voltage LiCoPO4 positive electrodes with high-electrochemically-stable Li2O-TiO2-Al2O3-P2O5(LATP) solid electrolytes, and then analyzed electrochemical properties as ASS-LIB in present study.
A LiCoPO4 powder was prepared by sucrose-aided combustion reaction. The XRD pattern of synthesized powder indicated the olivine-type structure (S.G.: Pnma). Li2O-TiO2-Al2O3-P2O5 (LATP) powder was sintered at 1100 oC as solid electrolyte pellet. Then, the mixed pellet of LiCoPO4, LATP, acetylene black and polytetrafluoroethylene (33 : 33 : 17 : 17 (wt%)) was put on the both faces of the solid electrolyte pellet, and sintered at 700 oC by using SPS. The carbon sheets were used as current collector of the ASS-LIB. The electrochemical test was carried out at a constant current density of 0.12 mA/cm2 at 250 oC using a battery test device (Solartron 1470). The specific two-step plateaus of LiCoPO4 during charging process can be observed around 2.2 and 2.7 V as shown in figure (a). This result means that lithium-ion removed from LiCoPO4 in one electrode side and extracted from LATP in the other side. (The redox plateau of LATP is around 2.45 V vs. Li/Li+). However, a large potential drop and low capacity could be observed during discharging. After charging, the large resistance of 2800 Ω/cm2 at the interfaces was measured by AC impedance spectroscopy. In the presentation, we also discuss the ASS-LIB test results of LiCoPO4 mixed with Li3PO4, whichaided the contact between LCP electrode and LATP electrolyte during SPS.
 A. Aboulaich, R. Bouchet, G. Delaizir, V. Seznec, L. Tortet, M. Morcrette, P. Rozier, J. Tarascon, V. Viallet, M. Dollb, Adv. Energy Mater., 1, 179–183 (2011).
 E. Markevich, R. Sharabi, H. Gottlieb, V. Borgel, K. Fridman, G. Salitra, D. Aurbach, G. Semrau, M.A. Schmidt, N. Schall, C. Bruenig, Electrochem. Commun.,15 (2012) 22–25.
[Show abstract][Hide abstract] ABSTRACT: X-ray absorption near-edge structure (XANES) spectroscopy, which reveals the features of the electronic and local structure, of lithium manganese oxides LixMn2O4 (x = 0–2) was examined using first-principles calculations. Both the easily observable parts and the tiny peaks of the theoretical Mn K-edge XANES spectra agreed with the experimental spectra. From the theoretical results of two anti-ferromagnetic LiMn2O4 models, the contributions of the Mn3+ ion and Mn4+ ion centers to the XANES spectra differ due to the difference in the overlap between the Mn 4p partial density of state (PDOS) and the O 2p PDOS. Similar results can be also seen by comparing the theoretical XANES spectra and the PDOS between Li(Mn3+Mn4+)O4 and de-intercalated Li0.5(Mn3+0.5Mn4+1.5)O4 and Mn4+2O4 (λ-MnO2). The XANES spectral changes with the lithium ion displacement (six- to four-coordination) due to the phase transition (cubic Fdm LiMn2O4 to tetragonal I41/amd Li2Mn2O4) can be determined by the indirect contribution of the Li 2p PDOS to the Mn 4p PDOS via the O 2p PDOS.
[Show abstract][Hide abstract] ABSTRACT: The new compounds Li2Mg[PO4]F and Li9Mg3[PO4]4F3 have been synthesized by a solid state reaction route. The crystal structures were determined from single-crystal X-ray diffraction data. Li2Mg[PO4]F crystallizes with the orthorhombic Li2Ni[PO4]F structure, space group Pnma, a = 10.7874(3), b = 6.2196(5), c = 11.1780(4) Å, V = 721.13(10) Å3, and Z = 8, whereas Li9Mg3[PO4]4F3 crystallizes with hexagonal symmetry, space group P63, with a = 12.6159(6), c = 5.0082(4) Å, V = 690.32(7) Å3, and Z = 2. A merohedral twinning was taken into account for its structural refinement. The structure of Li2Mg[PO4]F contains MgO3F chains made up of edge-sharing MgO4F2 octahedra. These chains are interlinked by PO4 tetrahedra forming a 3D-Mg[PO4]F framework. The lithium atoms occupy mainly three distinct crystallographic sites. The structure of Li9Mg3[PO4]4F3 consists of corner-sharing MgO4F2 octahedra forming MgO4F chains running along the c axis. These chains are interlinked by PO4 tetrahedra forming a 3D-Mg3[PO4]4F3 framework with hexagonal and pentagonal tunnels, in which are located the Li atoms. This study reveals also a strong relationship between Li2Mg[PO4]F-, Mg1-xFexAl3[BO3][SiO4]O2- and P21/c-Li5V[PO4]2F2-structures; and between P63-Li9Mg3[PO4]4F3 and P21/c-Na2Mn[PO4]F. The ionic conductivities σ of the composite material Li6Mg4[PO4]3[SO4]F3 and Li9Mg3[PO4]4F3, estimated using electrochemical impedance spectroscopic analyses at 300 °C, are 3.9 10−5 and 10−4 S cm−1 with activation energies of 0.524 eV and 0.835 eV, respectively.
[Show abstract][Hide abstract] ABSTRACT: Depth profiling and quantification using glow discharge optical emission spectroscopy (GD-OES) were applied to a graphite electrode in a lithium ion battery. To improve the measurement time and reliability beyond conventional argon discharge plasma, reactive sputtering with the respective addition of oxygen (0.50% v/v O2 in Ar) and hydrogen (1.00% v/v H2 in Ar) was investigated. Samples contained dispersed 0-5 wt% LiF or 0-0.5 wt% Li3PO4 in graphite electrodes. Adding oxygen to argon plasma increased the sputtering rate and the sensitivity in quantitative analysis of lithium drastically. That unexpected depth profile was obtained for graphite electrode samples possibly because chemical etching by oxygen was inhomogeneous. In contrast, adding hydrogen to argon plasma exhibited benefits both for depth profiling and for quantifying Li for graphite electrode samples with a shorter measurement time and higher sensitivity than that of conventional pure argon discharge. Molecular spectra showed strong C-H and C-C bands, suggesting that formation of volatile material fragments of CH and CC increased with hydrogen addition during measurements. Surface analysis results with SEM and XPS showed that redeposition of sputtered materials and Ar+ ion implantation that occurred in pure argon plasma were also suppressed.
No preview · Article · Jan 2014 · Journal of Analytical Atomic Spectrometry
[Show abstract][Hide abstract] ABSTRACT: The title compounds were synthesized by a hydrothermal route from a 1:1 molar ratio of lithium fluoride and transition-metal acetate in an excess of water. The crystal structures were determined using a combination of powder and/or single-crystal X-ray and neutron powder diffraction (NPD) measurements. The magnetic structure and properties of Co(OH)F were characterized by magnetic susceptibility and low-temperature NPD measurements. M(OH)F (M = Fe and Co) crystallizes with structures related to diaspore-type α-AlOOH, with the Pnma space group, Z = 4, a = 10.471(3) Å, b = 3.2059(10) Å, and c = 4.6977(14) Å and a = 10.2753(3) Å, b = 3.11813(7) Å, and c = 4.68437(14) Å for the iron and cobalt phases, respectively. The structures consist of double chains of edge-sharing M(F,O)6 octahedra running along the b axis. These infinite chains share corners and give rise to channels. The protons are located in the channels and form O-H···F bent hydrogen bonds. The magnetic susceptibility indicates an antiferromagnetic ordering at ∼40 K, and the NPD measurements at 3 K show that the ferromagnetic rutile-type chains with spins parallel to the short b axis are antiferromagnetically coupled to each other, similarly to the magnetic structure of goethite α-FeOOH.
Preview · Article · Dec 2013 · Inorganic Chemistry
[Show abstract][Hide abstract] ABSTRACT: Thermal design and management are important for lithium-ion batteries (LIBs) to prevent thermal runaway under normal and abnormal conditions such as overcharge and short circuit. A sound understanding of the heat generation behaviors of LIBs is needed for their thermal design and management. Since battery characteristics such as capacity and power capability degrade with time and the number of cycles, one can infer that the amount of heat generated by LIBs may also be changed by this degradation. Calorimetry is an effective method of studying the heat generation mechanisms of LIBs. In this study, we apply calorimetry to characterize the heat generation behavior of LIBs during charging and discharging after degradation due to long-time storage. At low rates of charging and discharging, such as 0.1C, significant differences dependent on the degree of degradation are not observed. On the contrary, more degraded batteries exhibit greater heat generation related to overvoltage increase at high rates of charging and discharging, such as 1 C. The solution resistance increase is particularly striking in an LIB stored at 50 °C. The chief cause of this increase may be leakage of electrolyte solution, resulting in greater heat generation at high rates of charging and discharging.
No preview · Article · Dec 2013 · Journal of Power Sources