Method for producing lithium desorption-type β-phase Li x V 2 O 5 (x<0.22) and lithium insertion-type β'-phase Li x V 2 O 5 (x>0.49) with a non-electrochemical topotactic reaction step, thermoelectric conversion material, and positive electrode active material.

Abstract

β-phase Li x Lower limit of lithium concentration and β' phase Li for V2O5 (0.22 ≤ x ≤ 0.37) x The objective is to obtain a positive electrode active material with a high thermoelectric performance factor and close to the fully charged and fully discharged states of a lithium-ion battery by decreasing and increasing the lithium concentration upper limit of V2O5 (0.44 ≤ x ≤ 0.49) in both phases, without using electrochemical methods, while maintaining the V2O5 skeletal structure of both phases. [Solution] β-Li x V2O5 (0.22 ≤ x ≤ 0.37) or β'-Li x By performing a non-electrochemical topotactic reaction on V2O5 (0.44 ≤ x ≤ 0.49) by adding an oxidizing agent or reducing agent, lithium-desorbed β-Li x V2O5 (x<0.22) and lithium-intercalated β'-Li x Provides V2O5 (x>0.49).

Description

Technical Field

[0001] The present invention relates to a method for producing lithium - desorbed β - phase Li x V2O5 (x < 0.22) and lithium - inserted β'-phase Li x V2O5 (x > 0.49), a thermoelectric conversion material, and a positive electrode active material.

Background Art

[0002] Renewable energies such as hydropower, wind power, and solar power are primary energy sources that are free from problems such as depletion, greenhouse gas emissions, and radioactive waste. The construction of a society based on these energies is one of the most important issues for humanity. Since this energy involves problems such as regional uneven distribution and temporal fluctuations, for its stable utilization, it is essential to improve the performance of thermoelectric conversion materials, which are energy conversion devices, and high - performance devices such as lithium - ion secondary batteries, which are energy storage devices.

[0003] As vanadium oxides that can be thermoelectric conversion materials, monoclinic β - phase Li x V2O5 (0.2 ≦ TIFF0007832610000002.tif141702) etc. are known. The thermoelectric performance factor (P = S 2 / ρ) obtained from the electrical resistivity (ρ) and the thermoelectric power (S) is on the order of 10 -5 Wm -1 K -2 at room temperature and shows a tendency to increase with an increase in temperature. Here, the lithium concentration range of the above - mentioned β - phase Li x V2O5 is correctly 0.22 ≦ x ≦ 0.37 as described later.

[0004] As a positive electrode active material of vanadium oxide having lithium - ion secondary battery performance, Li x V2O5 (0.1 ≦ x ≦ 0.3) produced at a temperature of 973K or higher is known (Patent Document 3). The flat potential is about 2.7V, and the capacitance in the range of an output potential of 2V or more is at most 250 Ahkg -1It is said that Li x V2O5 (0.1 ≤ x ≤ 0.3) is not a single phase, but rather a β-phase Li 0.3 V2O5, orthorhombic V2O5, and orthorhombic α-phase Li x This is a multiphase system of V2O5 (x ≤ 0.04).

[0005] Nearly single-phase β-phase Li 0.32 A lithium secondary battery using V2O5 as the positive electrode active material has a flat potential of approximately 2.7V, and a maximum discharge capacity of 320Ahkg in the range of output potential above 1.5V after initial charging. -1 It is said (Non-Patent Document 3). However, the phase in the discharge state is the crystal structure of the β phase. TIFF0007832610000003.tif8170 Patent Document 4). The charge-discharge characteristics of lithium secondary batteries using the ω phase as the positive electrode active material are complex, and although various studies have been conducted, they have not yet been elucidated.

[0006] Li x V2O5 exists as a high-temperature synthesized phase in the form of a β phase and a monoclinic β' phase. These are produced at temperatures above 673 K during a heat treatment process of the raw material mixture, with lithium concentration ranges of 0.22 ≤ x ≤ 0.37 and 0.44 ≤ x ≤ 0.49, respectively (Non-Patent Document 5). β phase Li x V2O5 (hereinafter, β -Li x V2O5, or simply the β phase, and β' phase Li x V2O5 (hereinafter, β' -Li x Regarding the crystal structure of V2O5 (or simply the β' phase), the V2O5 framework structures of both phases are similar, but the lithium ion sites are significantly different. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2008-53542 [Patent Document 2] Japanese Patent Publication No. 2018-157018 [Patent Document 3] Japanese Patent Publication No. 2-12769 [Non-patent literature]

[0008] [Non-Patent Document 1] M. Onoda and T. Sato, J. Phys. Soc. Jpn. 86, 124801 (2017). [Non-Patent Document 2] M. Onoda and M. Onoda,Phys.Rev.B73,104108(2006). [Non-Patent Document 3] J. Jiang, Z. Wang, and L. Chen, J. Phys. Chem. C 111, 10707 (2007). [Non-Patent Document 4] C. Delmas, S. Brethes, and M. Menetrier, J. Power Sources 34, 113 (1991). [Non-Patent Document 5] J. Galy, J. Solid State Chem. 100, 229 (1992), and the references cited therein. [Overview of the project] [Problems that the invention aims to solve]

[0009] Thermoelectric conversion candidate substance β-Li x The thermoelectric merit factor of V2O5 at room temperature is 10 -5 Wm -1 K -2 This is the current order, but further improvements are needed before it can be put into practical use.

[0010] As described later, β-Li x V2O5 and β'-Li x The high-temperature limit of the thermoelectric power (S) of V2O5 is explained by a spin model associated with the vanadium-oxygen-vanadium (VOV) molecular orbital, which exhibits a behavior in which the absolute value of the thermoelectric power increases with decreasing lithium concentration. That is, β-Li xIn V2O5, reducing the lithium concentration below the normal lower limit increases the absolute value of the thermoelectric power, and a high thermoelectric performance factor can be expected.

[0011] β-Li x The discharge capacity of a lithium-ion secondary battery using V2O5 as the positive electrode active material, after initial charging, is approximately 320 Ah / kg. -1 However, the initial charging process presents a practical application challenge. When considering applications such as implantable cardiac defibrillators that use lithium metal as the negative electrode, a high-capacity positive electrode active material for lithium-ion primary or secondary batteries that does not require this charging process is desirable. In the following, unless otherwise specified, lithium-ion primary and secondary batteries will be collectively referred to as lithium-ion batteries.

[0012] β-Li x In V2O5, the initial discharge capacity is reduced because some vanadium ions are reduced. Therefore, if the lithium concentration can be reduced below the normal lower limit while maintaining the β-phase V2O5 framework structure, without using electrochemical methods, and the vanadium ions can be relatively oxidized, a high initial discharge capacity can be expected, making it suitable for use in implantable cardiac defibrillators and other applications.

[0013] In lithium-ion secondary batteries, when a lithium-ion-free material such as graphite is used as the negative electrode during battery assembly, the positive electrode active material needs to be in a discharged state to compensate for lithium ions. If the positive electrode active material is not sufficiently discharged, it becomes necessary to add a sacrificial lithium source.

[0014] The present invention has been made in view of the above problems, and β-Li x V2O5 and β'-Li x In V2O5, while maintaining the V2O5 framework structure of both phases, the lower limit of lithium concentration in the β phase (x=0.22; hereafter, x) is reached. c1 A method for reducing the lithium concentration of the β' phase (x=0.49; hereafter, x c2 The objective is to construct a method for increasing (represented by ). [Means for solving the problem]

[0015] As a result of diligent research, the inventors have found that β-Li can be extracted without the use of electrochemical methods. x V2O5(x c1 (≤x ≤ 0.37) and β'-Li x V2O5(0.44≦x≦x c2 ) While maintaining the V2O5 framework structure, lithium-desorbed β-Li x V2O5(x <x c1 ) and lithium-intercalated β'-Li x V2O5(x>x c2 We succeeded in creating it.

[0016] The present invention provides lithium-desorbed β-Li x V2O5(x <x c1 ) and lithium-intercalated β'-Li x V2O5(x>x c2 The manufacturing method of ) is β-Li x V2O5(x c1 (≤x ≤ 0.37) and β'-Li x V2O5(0.44≦x≦x c2 The process includes the steps of preparing ) and desorbing and inserting lithium ions from them.

[0017] In the aforementioned process of desorption and insertion of lithium ions, a non-electrochemical topotactic reaction is carried out at near room temperature on the β or β' phase. This reaction, without the use of electrochemistry, desorbs, inserts, or substitutes some elements while maintaining the basic crystalline framework, resulting in a phase in which kinetic stability is prioritized over thermodynamic stability. Hereinafter, this preparation method will be referred to as the soft chemistry method. [Effects of the Invention]

[0018] By using the manufacturing method of the present invention, it is possible to provide a material that exhibits a high thermoelectric performance factor.

[0019] By using the manufacturing method of the present invention, the positive electrode active material β-Li in the recharged state of a lithium-ion battery can be obtained without using an electrochemical method. xV2O5(x <x c1 ) can be provided.

[0020] By using the manufacturing method of the present invention, the positive electrode active material β'-Li in the final discharge state of a lithium-ion battery can be obtained without using an electrochemical method. x V2O5(x>x c2 ) can be provided. [Brief explanation of the drawing]

[0021] [Figure 1(a)] Crystal structure of lithium-desorbed β-Li0.13V2O5 at 293K, projected along the monoclinic b-axis using the polyhedron method. [Figure 1(b)] Oxygen coordination of lithium ions. [Figure 2] X-ray powder diffraction patterns of β-LixV2O5 (x=0, 0.18, 0.25) and β'-LixV2O5 (x=0.45, 2.25). Here, the column of checkmarks below each pattern represents the calculated diffraction angle. The abbreviations SS, EC, and SC represent the manufacturing methods of the substances, meaning solid-phase reaction, electrochemical, and soft chemical methods, respectively. [Figure 3] Composition dependence of monoclinic lattice constants of β-LixV2O5 and β'-LixV2O5 in the lithium concentration range x ≤ xc2. Here, the dotted line represents the result of applying Vegard's rule to data of the β phase prepared by solid-phase reaction and soft chemical methods, and the gray area represents the region of the normal β phase and β' phase prepared only by solid-phase reaction (first step of the manufacturing method). [Figure 4] Temperature dependence of electrical resistivity of β-LixV2O5 and β'-LixV2O5. Empty and solid symbols represent data for the cooling and heating processes, respectively. Solid and dotted lines represent calculated values ​​for the Hopping model and the 3D Variable-Range Hopping (3d-VRH) model. [Figure 5] Temperature dependence of the thermoelectric power of β-LixV2O5 and β'-LixV2O5. Empty and solid symbols represent data for the cooling and heating processes, respectively. The solid line represents the calculated values ​​of the hopping model. [Figure 6]Composition dependence of the thermoelectric power of β-LixV2O5 and β'-LixV2O5 at 294K and 200K. Here, the solid line represents the high-temperature limit based on the spin model associated with the molecular d orbitals of VOV, and the gray region shows the regions of the normal β phase and β' phase, which were prepared by solid-phase reaction methods only. [Figure 7] Composition dependence of the thermoelectric performance factor at 294K for β-LixV2O5 and β'-LixV2O5. Here, the gray region represents the regions of the normal β phase and β' phase, which were prepared solely by solid-phase reaction. [Figure 8] Block diagram of electrochemical measurements. [Figure 9(a)] The capacitance dependence of the potential of a lithium-ion secondary battery using β-Li0.25V2O5 as the positive electrode active material after the start of discharge. Here, the horizontal axis (|Δx|) represents the absolute amount of change in lithium concentration. [Figure 9(b)] The capacitance dependence of the potential of a lithium-ion secondary battery using β-Li0.25V2O5 as the positive electrode active material after the start of charging. Here, the horizontal axis represents the absolute amount of change in lithium concentration. [Modes for carrying out the invention]

[0022] The following will describe in detail compositions to which the present invention is applied, with reference to the figures as appropriate. Note that the drawings used in the following description may be enlarged for convenience in order to clearly illustrate the features of the present invention, and the dimensional ratios of each component may differ from those of the actual components. Furthermore, the materials, dimensions, etc., exemplified in the following description are merely examples, and the present invention is not limited to them. It can be implemented with appropriate modifications without altering the essence of the invention.

[0023] (composition) The composition produced by the manufacturing method of the present invention is lithium-desorbed β-Li x V2O5(x <x c1 ) and lithium-intercalated β'-Li x V2O5(x>x c2 Figure 1(a) shows lithium-desorbed β-Li 0.13This is the crystal structure of V2O5 at 293K, projected along the monoclinic b-axis using the polyhedron method. Three crystallographically non-equivalent vanadium atoms (V1, V2, V3) form a distorted oxygen polyhedron. Here, the polyhedron units of V1, V2, and V3 atoms are characterized by the V1O6 octahedron, V2O6 octahedron, and V3O5 pyramid, respectively, and their linkage forms the V2O5 framework. From the ground state wavefunction of each vanadium ion, molecular d-orbitals are formed in the V2-O1-V2 unit and V1-O5-V3 unit in the ac-plane, respectively, forming a one-dimensional chain in the b-axis direction. Figure 1(b) shows the oxygen coordination of the lithium atom.

[0024] The V2O5 skeletal structure of the composition is known as β-Li x V2O5(x c1 (≤x ≤ 0.37) or β' -Li x V2O5(0.44≦x≦x c2 ) is qualitatively the same. However, because the lithium concentration is different from the normal concentration range, there are differences in the lattice constant, atomic parameters, and interatomic bond distances, and clear differences also appear in the following electrical resistivity or thermoelectric power.

[0025] β-Li x The lithium concentration of V2O5 is x c1 Further reduction results in a higher thermoelectric performance factor. This is because β-Li x V2O5 and β'-Li x This is because the high-temperature limit of the thermoelectric power (S) of V2O5 can be explained by the spin model associated with the VOV molecular d orbital, and its composition dependence is given by |S|∝log[2(1-x) / x]. c1 Further reduction will increase the absolute value of the thermoelectric power, thereby increasing the thermoelectric performance factor.

[0026] Lithium-desorbed β-Li x In V2O5, the lithium concentration is x c1 Because it is lower, when used as a lithium-ion battery, it can maximize the potential and electrical capacity of the lithium-ion battery. This is β-Lix The lower limit of lithium concentration in V2O5 is x c1 In this case, the vanadium ions are partially reduced and partially discharged, whereas lithium desorption type β-Li x The lithium concentration of V2O5 is x <x c1 This is because the vanadium ions are relatively oxidized.

[0027] Lithium-intercalated β'-Li x In V2O5, the lithium concentration is x c2 Because it is more efficient, it can be used as the positive electrode active material in lithium-ion secondary batteries with a graphite negative electrode without the need to add a lithium sacrificial source.

[0028] (Method of manufacturing the composition) The manufacturing method of the present invention is known as β-Li x V2O5(x c1 (≤x ≤ 0.37) and β'-Li x V2O5(0.44≦x≦x c2 The first step is to prepare ) and then lithium desorption type β-Li x V2O5(x <x c1 ) and lithium-intercalated β'-Li x V2O5(x>x c2 The process consists of a first step and a second step for producing ). The first step is, for example, a solid-phase reaction method, which consists of a mixing step of a lithium (Li) source, a vanadium (V) source, or a lithium-vanadium (Li-V) source containing both lithium and vanadium, and a heat treatment step for the resulting mixture. The second step is a soft chemical method step that carries out a non-electrochemical topotactic reaction.

[0029] [1st process (mixing process)] β-Li x V2O5 and β'-Li x In the mixing process for preparing V2O5, two or more sources are used from the lithium source, vanadium source, and lithium-vanadium source mentioned above, such that the molar ratio of Li, V, and O in the β phase and β' phase is x:2:5, and the lithium concentration range of each phase is x c10 ≤ x ≤ 0.37, 0.44 ≤ x ≤ x c2 Prepare a mixture adjusted to satisfy the above conditions.

[0030] The lithium source is, for example, a group consisting of lithium carbonate (Li2CO3), lithium nitrate (LiNO3), lithium oxide (Li2O), lithium hydroxide (LiOH), lithium chloride (LiCl), and lithium sulfate (Li2SO4).

[0031] The vanadium source is, for example, a group consisting of vanadium pentoxide (V2O5), vanadium dioxide (VO2), vanadium trioxide (V2O3), and ammonium metavanadate (NH4VO3).

[0032] The lithium-vanadium source is, for example, a group consisting of lithium metavanadate (LiVO3), trilithium vanadate (Li3VO4), lithium tetravanadate (Li4V2O7), etc.

[0033] [First step (heat treatment step)] Heat-treat the mixture prepared above in a vacuum or an inert gas. The heat treatment temperature is preferably between 923 K and 973 K.

[0034] [Second step] For β-Li x V2O5 (x c1 ≤ x ≤ 0.37) or β'-Li x V2O5 (0.44 ≤ x ≤ x c2 ), add an oxidizing agent to produce lithium-desorbed β-Li x V2O5 (x < x c1 ). For β'-Li x V2O5 (x > x c2 ), add a reducing agent to produce lithium-inserted β'-Li

[0035] The oxidizing agent contains at least one selected from the group consisting of, for example, bromine (Br2), nitrosyl tetrafluoroborate (NOBF4), nitronium tetrafluoroborate (NO2BF4), sulfuric acid (H2SO4), hydrochloric acid (HCl), and nitric acid (HNO3).

[0036] The reducing agent contains at least one selected from the group consisting of, for example, n-butyllithium (C4H9Li), sec-butyllithium, tert-butyllithium, and lithium aluminum hydride (LiAlH4).

[0037] As described above, the preferred embodiments of the present invention have been described in detail. However, the present invention is not limited to specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Examples

[0038] Hereinafter, examples of the present invention will be described. Note that the present invention is not limited only to the following examples.

[0039] (Crystal Structure) [Sample Synthesis] The reagents used in the synthesis are shown in Table 1. β-Li x V2O5 (x c1 ≦x≦0.37) and β'-Li x V2O5 (0.44≦x≦x c2 ) were prepared using the solid-state reaction method. For example, a mixture consisting of x / 3 mol of Li3VO4, x / 4 mol of V2O3, and 1 - 5x / 12 mol of V2O5 in molar ratio was vacuum-sealed in a quartz tube and then prepared by holding at a constant temperature within the temperature range of 923K to 973K for 24 h. Here, Li3VO4 was prepared in advance by heating and holding a mixture consisting of 3 mol of Li2CO3 and 1 mol of V2O5 in air at 923K for 20 h. Also, V2O3 was prepared in advance by heating and holding V2O5 in a mixed gas of hydrogen and nitrogen at 973K for 24 h to 48 h.

[0040] [Table 1]

[0041] β-Li prepared using a solid-phase reaction method x V2O5 and β'-Li x The chemical composition of V2O5, although detailed analysis results are omitted here, agreed within the range of standard deviation with the crystal structure analysis results obtained using a four-axis X-ray diffractometer, as will be shown later.

[0042] Lithium-desorbed β-Li x V2O5(x <x c1 ) was prepared using a soft chemical method. β-Li obtained by solid-phase reaction was used as a raw material. 0.25 V2O5 and an appropriate amount of Br2 were added to acetonitrile (CH3CN), stirred, and then the sample was dried under reduced pressure. The compositions of the obtained polycrystalline and single crystals were determined based on crystal structure analysis using inductively coupled plasma emission spectrometry (ICP) and a four-axis X-ray diffractometer, respectively.

[0043] Lithium-intercalated β'-Li x V2O5(x>x c2 ) was prepared using a soft chemical method. β-Li obtained by solid-phase reaction was used as a raw material. 0.25 V2O5 is converted to n-hexane (C6H 14 The sample was dispersed in (a solution), an appropriate amount of n-C4H9Li was added, and after stirring, the sample was dried under reduced pressure. The composition of the resulting polycrystalline material was based on the initial values.

[0044] [Phase identification] X-ray powder diffraction was performed on samples obtained by solid-phase reaction, soft chemistry, and the electrochemical method described later, using a Rigaku Ultima+ diffractometer. The X-ray source was CuKα. An example of the measurement results is shown in Figure 2. Here, the abbreviations SS, EC, and SC represent the preparation or manufacturing method of the substance, meaning solid-phase reaction, electrochemical method, and soft chemistry method, respectively. From the X-ray powder diffraction pattern, the lithium concentration range x <x c1 It was revealed that the β phase is maintained in this case. On the other hand, x > x c2Therefore, although the diffraction peak broadening is significant due to the high concentration of lithium ions inserted, we clarified that the β' phase is maintained as the dominant phase.

[0045] [Lattice constant] Based on the above results, the lithium concentration range x ≤ x was determined. c2 Figure 3 shows the composition dependence of the lattice constant in the given state. Here, the lattice constants prepared by the solid-phase reaction method are 0.25 ≤ x ≤ x c2 Regarding the composition of the polycrystalline sample, the charging concentration of lithium was used because the difference between the charging concentration and the analytical concentration was 0.01 or less. The compositions of the polycrystalline and single-crystal samples prepared by the soft chemistry method were determined according to the ICP analysis values ​​and crystal structure analysis values, respectively. On the other hand, x>x prepared by the soft chemistry method c2 The polycrystalline composition is the initial value. The lithium concentration of the polycrystalline sample prepared by electrochemical method was evaluated from measured electron transfer values. Lithium concentration range x ≤ x c2 The behavior of the lattice constants of the β-phase and β'-phase differs significantly. This can be attributed to the difference in Li-saturation. The known lithium concentration range of the β-phase (x c1 For x ≤ 0.37, as the lithium concentration decreases, the a-axis and β-angle decrease, while the b-axis increases. The change in the c-axis is small. These trends are observed in the lithium concentration range (x) of the newly prepared lithium-desorbed β-phase using the soft chemistry method. <x c1 This also holds true in the case of x=0. As shown by the dotted line in Figure 3, the lattice constant at x=0 expected by applying Vegard's law is close to the value of the sample prepared by electrochemical method. In other words, the lithium concentration range of the β phase is extended to close to x=0. Lithium concentration range 0.44 ≤ x ≤ x c2 The composition dependence of the lattice constant of the β' phase in x=2.25 can be attributed to the anharmonic thermal vibrations of lithium ions, although detailed analysis results are omitted. On the other hand, the lattice constants of the lithium-inserted β' phase at x=2.25 are a=15.385(4)Å, b=3.64(3)Å, c=10.107(5)Å, β=104.8(3)°, V=547(4)Å 3 That was the assessment.

[0046] [Crystal structure] Using a Nonius CAD4 diffractometer and MoKα radiation, X-ray quadraaxial diffraction measurements were performed at 293 K up to θ = 80° on single crystals prepared by soft chemistry and single crystals prepared by solid-phase reaction with x = 0.25 and 0.44. As shown in Table 2, after refining the atomic coordinates using the full matrix least squares method, the lithium concentrations of these samples were determined to be x = 0.13 (2), 0.26 (2), and 0.43 (3). Atomic coordinates and equivalent isotropic temperature factor U at 293K for x=0.13(2) eq , as well as the anisotropic displacement parameter U ij This is shown in Table 3. The crystal structure at this time is shown in Figure 1. Figure 1(a) shows the lithium-desorbed β-Li 0.13 This is the crystal structure of V2O5 at 293K, projected along the monoclinic b-axis using the polyhedron method. Three crystallographically non-equivalent vanadium atoms (V1, V2, V3) form a distorted oxygen polyhedron. Here, the polyhedron units of V1, V2, and V3 atoms are represented as the V1O6 octahedron, V2O6 octahedron, and V3O5 pyramid, respectively. From their ground state wave functions, it can be seen that the V2-O1-V2 unit and V1-O5-V3 unit in the ac plane form molecular d orbitals, respectively. As shown in Figure 1(b), the lithium atom takes oxygen 5-coordinate and is located on the mirror plane within the tunnel of the V2O5 framework.

[0047] [Table 2]

[0048] [Table 3]

[0049] [Transportation characteristics: Electrical resistivity] β-Li x b-axis direction and β'-Li of V2O5 (x=0.13, 0.25, 0.30) single crystal sample xThe DC electrical resistivity (ρ) of polycrystalline V2O5 (x=0.45, 0.49) samples was measured in the temperature range of 80K to 300K. Figure 4 shows the reciprocal of the absolute temperature T. -1 This is a semi-logarithmic plot of electrical resistivity for each composition. The resistivity of all compositions exhibits nonmetallic behavior. TIFF0007832610000007.tif11170, and it is large in the β' phase. T>T c The temperature dependence of resistivity in follows a hopping model due to its polaron-like properties. The fit results for a single crystal sample are shown by the solid line in Figure 4. Except for x=0.13, T c The resistivity near x increases more than expected from the above equation as the temperature decreases, whereas at x=0.13 it behaves in the opposite way. The temperature dependence of resistivity in the low-temperature region curves upward, and T c The following results can be best explained by the 3D variable hopping (3d-VRH) model.

[0050] [Transport properties: thermoelectric power] β-Li x b-axis direction and β'-Li of V2O5 (x=0.13, 0.25, 0.30, 0.33) single crystal sample x The thermoelectric power (S) of a polycrystalline V2O5 (x=0.45, 0.49) sample was measured in the temperature range of 80K to 300K. Figure 5 shows the temperature dependence of the thermoelectric power. The value of the thermoelectric power is negative, suggesting that the carriers are electronic. The absolute value of the thermoelectric power at room temperature decreases with increasing lithium concentration. T>T c While the temperature change is weak, T <T c Then it is strong. Similar to the results for electrical resistivity, the T of the β phase c The temperature history of the thermoelectric power is small in the β' phase, while it is large in the β' phase. T>T c The thermoelectric power of the material could be explained by the hopping model, as shown by the solid line in the figure.

[0051] Figure 6 shows the composition dependence of thermoelectric power at 294K and 200K. From the analysis of magnetic properties, although experimental results and details of the investigation are omitted, it has been revealed that the correlation effect of polarons is strong, so a high-temperature limit model of thermoelectric power that takes spin degrees of freedom into account is effective. The solid lines in the figure represent the high-temperature limit values ​​of thermoelectric power based on molecular d orbitals on the V2-O1-V2 unit and V1-O5-V3 unit described in the crystal structure section, and the results, including the data for x=0.13, which is the lithium-desorbed β phase, were well explained.

[0052] β-Li x V2O5 and β'-Li x Figure 7 shows the composition dependence of the thermoelectric performance factor of V2O5 at 294 K. The factor is highest for the lithium-desorbed β phase with x=0.13, and is 10 at room temperature. -4 Wm -1 K -2 We demonstrated that it is of the order of magnitude. Since the temperature dependence of electrical resistivity in the high-temperature region follows a hopping model, resistivity decreases exponentially with increasing temperature, so the thermoelectric performance factor is expected to become even larger.

[0053] [Charge / discharge characteristics] β-Li 0.25 The charge-discharge characteristics of V2O5 were tested. The positive electrode was β-Li 0.25 The electrode consists of V2O5 (weight = 72.165 mg), polytetrafluoroethylene (PTFE) as a binder, acetylene black as a conductive additive, and carbon, with lithium metal foil as the negative electrode. The electrolyte is LiPF6 (molar concentration 1 mol L). -1 The solvent EC:DEC ratio was 1:1 (V / V%). Using these, a simple battery cell (Figure 8, Table 4) was assembled and electrochemical tests were performed (C rate ≈ 1 / 48).

[0054] [Table 4] TIFF0007832610000009.tif31170

[0055] The capacitance (Q) dependence of the potential (φ) after discharge and charging initiation is shown in Figures 9(a) and 9(b), respectively. The upper horizontal axis of each figure corresponds to the absolute amount of change in lithium concentration (|Δx|). From the results in Figure 9(a), it can be seen that in the initial discharge process, the capacity is approximately 300 Ah kg in the range of a flat potential of approximately 2.7 V and an output potential of 2 V or higher. -1 During the charging process after discharge, the capacity is approximately 260 Ah kg. -1 I confirmed it.

[0056] From the results in Figure 9(b), β-Li 0.25 Approximately 0.25 moles of lithium ions are desorbed per 1 mole of V2O, resulting in a charge capacity of approximately 30 Ah / kg. -1 This confirmed that β-Li x This suggests the existence of a composition where x=0 in V2O5.

[0057] From the results in Figures 9(a) and (b), the discharge capacity after charging starts is approximately 330 Ahkg at an output power of 2V or higher. -1 That is the case.

[0058] The X-ray powder diffraction pattern after the measurement in Figure 9(b) was close to the β-phase pattern, as shown in Figure 2. That is, the crystal structure at x=0 is the known orthorhombic α-phase Li x It became clear that the structure shown in Figure 1(a) was maintained, rather than a V2O5 (x≦0.04) type structure. Furthermore, the determined lattice constants matched the extrapolated values ​​to x=0 predicted from the results of Vegard's law applied to the composition dependence of the lattice constants of the β phase obtained by solid-phase reaction and soft chemistry methods (dotted line in the figure), as shown in Figure 3.

[0059] The X-ray powder diffraction pattern after the initial discharge measurement in Figure 9(a) closely corresponded to the β' phase pattern, as shown in Figure 2. The broadening of the diffraction peaks was significant due to the high concentration of lithium ions inserted.

[0060] Lithium-desorbed β-Li x V2O5(x=0.13 <x c1 ) and lithium-intercalated β'-Lix V2O5(x=2.25>x c2 The vanadium ions in these materials have valencies close to 5 and 4, respectively, making them positive electrode active materials that closely resemble the fully charged and fully discharged states of a lithium-ion battery.

[0061] Lithium-desorbed β-Li x V2O5(x=0.13 <x c1 The detailed crystal structure of ) was determined, and it was found that it has a high thermoelectric transformation factor, and β-Li x V2O5(x c1 We demonstrated that the structure of the positive electrode active material corresponds to a structure close to the fully charged state of a lithium-ion battery with positive electrode active material Li (≤x ≤ 0.37). Furthermore, we demonstrated the structure of the positive electrode active material Li in the fully discharged state of a lithium-ion battery. x The main phase of V2O5 (x=2.25) is the β' phase, and this is a lithium-intercalated β'-Li prepared using a soft chemical method. x The present invention was completed by demonstrating that it is almost identical to V2O5 (x=2.25).

Claims

【Request Item 1】 β-Li ｘ V ２ O ５ (0.22 ≤ x ≤ 0.37) and β'-Li ｘ V ２ O ５ A first step of preparing (0.44 ≤ x ≤ 0.49), and a second step of performing a non-electrochemical topotactic reaction by adding an oxidizing agent or a reducing agent, for a lithium extraction type β-Li ｘ V ２ O ５ (0 ≤ x < 0.22) and a lithium insertion type β'-Li ｘ V ２ O ５ manufacturing method (0.49 < x ≤ 2.25). 【Request Item 2】 The first step described above includes a mixing step of adjusting a lithium source, a vanadium source, or a lithium-vanadium source so that the molar ratio of Li, V, and O in β-Li x V 2 O 5 (0.22 ≤ x ≤ 0.37) and β'-Li x V 2 O 5 (0.44 ≤ x ≤ 0.49) is x:2:5, and a heat treatment step, which is the lithium desorption type β-Li according to claim 1. ｘ V ２ O ５ (0 ≤ x < 0.22) and lithium-intercalated β'-Li ｘ V ２ O ５ A method for manufacturing (0.49 < x ≤ 2.25). 【Request Item 3】 The lithium desorption type β-Li according to claim 2, wherein the temperature in the heat treatment step is 923K or more and 973K or less. ｘ V ２ O ５ (0 ≤ x < 0.22) and lithium-intercalated β'-Li ｘ V ２ O ５ A method for manufacturing (0.49 < x ≤ 2.25). 【Request Item 4】 β-Li ｘ V ２ O ５ A thermoelectric material where (0 ≤ x < 0.22).

5. β-Li having a C lattice ｘ V ２ O ５ The positive electrode active material for a lithium-ion battery where (0 ≤ x < 0.22). 【Request Item 6】 β'-Li ｘ V ２ O ５ The positive electrode active material of a lithium-ion battery where (0.49 < x ≤ 2.25).

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