Lithium composite oxide, power storage device, and method for producing lithium composite oxide

Abstract

To further enhance charge / discharge characteristics of energy storage devices including discharge capacity, etc.SOLUTION: A lithium composite oxide used as an electrode active material for energy storage devices, contains lithium, metal element M (where M is one or more of Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga and Ge) and boron, wherein the XRD spectrum shows a peak pattern of a disordered rock salt structure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present specification discloses a lithium composite oxide, an electricity storage device, and a method for producing the lithium composite oxide. [Background technology]

[0002] Conventionally, the positive electrode active material used in lithium secondary batteries has been, for example, a material having the composition Li x M y A lithium-excess metal oxide active for a positive electrode having O2 (0.6≦y≦0.85 and 0≦x+y≦2) has been proposed (see, for example, Patent Document 1). When used in lithium secondary batteries, this oxide is said to be insensitive to cation disorder and to have a high reversible capacity. Furthermore, as a positive electrode active material for lithium secondary batteries, for example, a lithium molybdenum composite oxide having a rock salt structure has been proposed (see, for example, Patent Document 2). This composite oxide is said to have a good discharge capacity and discharge capacity retention rate due to its rock salt structure, which is a metastable phase. Furthermore, a positive electrode active material having a layered rock salt structure that exhibits high capacity has also been proposed (see, for example, Patent Documents 3 and 4). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-92958 [Patent Document 2] Japanese Patent Application Publication No. 2017-202954 [Patent Document 3] Special Publication No. 2019-523532 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-166291 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned Patent Document 1, Li 1.233 Mo 0.467Cr 0.3 However, Patent Document 2 claims that O2 exhibits a discharge capacity exceeding 280 mAh / g, but uses Cr, which is prone to inducing polyvalent state fluctuations. Cr is an element with a high environmental impact, posing significant practical limitations. Furthermore, Patent Document 2 claims that a composite oxide cathode material containing lithium and molybdenum in its composition is prepared by a mechanochemical method and exhibits a high discharge capacity exceeding 300 mAh / g. However, the discharge is performed under low voltage conditions with a minimum voltage range of 1.0 V during charge and discharge, and the actual discharge capacity practically usable as a full cell is expected to be approximately 150 mAh / g. Thus, while the above-mentioned document claims that the discharge capacity and other properties are good, they are still not sufficient, and further improvements are desired. In other words, a new composite oxide that can further improve charge and discharge characteristics such as discharge capacity is desired.

[0005] The present disclosure has been made in view of the above-mentioned problems, and has as its main object to provide a novel lithium composite oxide, an electricity storage device, and a method for producing a lithium composite oxide, which can further improve the charge-discharge characteristics, including the discharge capacity, of an electricity storage device. [Means for solving the problem]

[0006] As a result of intensive research to achieve the above-mentioned object, the present inventors have found that when a lithium composite oxide has a disordered rock salt structure and further contains boron, the discharge capacity can be further increased, and have completed the invention disclosed in this specification.

[0007] That is, the lithium composite oxide disclosed in the present specification is A lithium composite oxide used as an electrode active material for an electricity storage device, containing lithium, a metal element M (wherein M is one or more of Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, and Ge), and boron; The XRD spectrum shows the peak pattern of a disordered rock salt structure.

[0008] The electricity storage device disclosed in this specification comprises: a positive electrode having the above-described lithium composite oxide as a positive electrode active material; a negative electrode having a negative electrode active material; an ion conductive medium interposed between the positive electrode and the negative electrode and conducting lithium ions; It is equipped with the following.

[0009] The method for producing a lithium composite oxide disclosed in the present specification includes the steps of: A method for producing a lithium composite oxide used as an electrode active material for an electricity storage device, comprising: a preparation step of mixing and grinding raw materials containing at least an M source, which is a lithium composite oxide containing a metal element M (where M is one or more of Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, and Ge) and whose XRD spectrum shows a peak pattern of a disordered rock-salt structure, and a B source containing B, by a mechanochemical method to obtain a lithium composite oxide containing lithium, the metal element M, and boron and whose XRD spectrum shows a peak pattern of a disordered rock-salt structure; It includes: [Effects of the Invention]

[0010] The present disclosure provides a novel lithium composite oxide, an electricity storage device, and a method for producing the lithium composite oxide, which can further improve the charge / discharge characteristics, including the discharge capacity, of an electricity storage device. The reason for this effect is presumed to be as follows. For example, in a lithium composite oxide with a disordered rock-salt structure, the amorphous structure allows Li to move three-dimensionally, allowing Li to be reversibly inserted and removed even in a Li-excess composition, thereby achieving high capacity. Furthermore, boron is added to this disordered rock-salt structure composite oxide. Because boron has a smaller atomic radius than Li and the metal element M, it can form a planar tri-coordination with three oxygen atoms in the structure. As a result, some octahedral sites become vacant, creating excess Li insertion sites, which is presumed to improve the discharge capacity. [Brief explanation of the drawings]

[0011] [Figure 1]Schematic illustration of the crystal structures of LiMnO2 and Li2B4O7 with disordered rock-salt structure. [Figure 2] Schematic diagram showing an example of a disordered rocksalt structure doped with B. [Figure 3] FIG. 2 is a schematic diagram showing an example of the configuration of an electricity storage device 20. [Figure 4] 1 shows XRD measurement results of boron-containing lithium manganese composite oxides of Experimental Examples 3 and 6. [Figure 5] 1 shows initial charge-discharge curves for test cells of Experimental Examples 1 to 6. [Figure 6] Charging and discharging curves up to the 10th cycle of Experimental Example 3. [Figure 7] 1 shows the results of measurement of discharge capacity and coulomb efficiency up to the 30th cycle in Experimental Example 3. [Figure 8] 1 shows the results of examining the dependency of the initial discharge capacity on the B content in Experimental Examples 1 to 6. [Figure 9] Discharge curves and dQ / dV curves up to the 10th cycle for Reference Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0012] (lithium composite oxide) The lithium composite oxide of the present disclosure is used as an electrode active material for an electricity storage device. This lithium composite oxide contains lithium, a metal element M, and boron. The metal element M can be one or more of Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, and Ge, with Mn being more preferred. The disordered rock salt structure exhibits a peak pattern in an XRD spectrum with four diffraction peaks in the 2θ ranges of 35° to 39°, 42° to 48°, 62° to 68°, and 80° to 84°. Furthermore, due to the disordered (random) structure, the diffraction peaks are relatively broad, with the main peak at 2θ = 42° to 48° having a half-width of 1.5° or more and the peak at 2θ = 62° to 68° having a half-width of 2° or more.

[0013] This lithium composite oxide has the basic composition formula Li a Bx M y O 2-z A z It may be represented as such. However, M is one or more of Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, and Ge, A is one or more of F, Cl, Br, I, and S, and it may satisfy 0 < a < 2, 0 < x < 1, 0 < y < 1, and 0 ≤ z < 2. The content x of this boron (B) preferably satisfies 0.03 ≤ x ≤ 0.27, and more preferably satisfies 0.05 ≤ x ≤ 0.25. In the range of 0.03 ≤ x ≤ 0.27, it can exceed the theoretical capacity when assuming the use of the one-electron reaction of M 3+ / M 4+ and is preferable. Also, in the range of 0.05 ≤ x ≤ 0.25, it can exceed the maximum theoretical capacity converted from the amount of Li in the charge and is more preferable. Further, this lithium composite oxide is preferably a boron-containing lithium manganese composite oxide in which the metal element M is Mn. This fluorine-containing lithium composite oxide has the general formula Li a MB x Mn y O 2-z A z and may be represented as such.

[0014] When this lithium composite oxide is used as an electrode active material of an electric storage device, the initial discharge capacity is preferably 250 mAh / g or more. This initial capacity is more preferably larger, for example, 270 mAh / g or more is more preferable, 290 mAh / g or more is still more preferable, and 300 mAh / g or more is most preferable. This initial discharge capacity can be adjusted depending on the content x of B and the randomness of the rock salt structure.

[0015] (Method for producing lithium composite oxide) The manufacturing method of the present disclosure is the manufacturing method of the above-described lithium composite oxide used for the electrode active material of the power storage device. This manufacturing method may include, for example, an adjustment step of adjusting the structure of the composite oxide. Further, this adjustment step may include a raw material preparation process and a mixing and grinding process. In this manufacturing method, in the raw material preparation process, a lithium composite oxide having a disordered rock salt structure peak pattern, which is an M source, is produced by mechanically grinding a rhombic lithium composite oxide by a mechanochemical method. The lithium composite oxide having a disordered rock salt structure is, for example, represented by the basic composition formula Li a M y O 2-z A z wherein, in the basic composition formula, M is one or more of Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, and Ge, A is one or more of F, Cl, Br, I, and S, and 0 < a < 2, 0 < y < 1, 0 ≤ z < 2 are satisfied. In the raw material preparation process, a rhombic lithium composite oxide is produced while adjusting the firing conditions. In this process, LiMnO2 may be produced as the raw material lithium composite oxide. In this process, Li2MnO3 as the raw material is obtained by firing in the range of 800°C or higher and 1100°C or lower for 6 hours or longer and 15 hours or shorter. LiMnO2 can be obtained by blending Li2MnO3 and MnO in equimolar amounts and firing in the range of 900°C or higher and 1100°C or lower for 6 hours or longer and 24 hours or shorter in an inert atmosphere (for example, in Ar).

[0016] In the mixing and grinding process, at least a raw material containing the M source, which is the above-described lithium composite oxide having a disordered rock salt structure, and a B source containing B is mixed and ground by a mechanochemical method. In this process, the above-described lithium composite oxide and the B source are blended in a predetermined ratio, and mixed and ground while adjusting the grinding conditions. In this process, the basic composition formula Li a B x M y O 2-z A z(However, the raw materials are blended so as to fall within the range satisfying 0 < a < 2, 0 < x < 1, 0 < y < 1, and 0 ≤ z < 2). As the B source, for example, lithium borate (Li2B4O7) and the like can be mentioned. By this treatment, by mixing and pulverizing a lithium composite oxide having a disordered rock salt structure and lithium borate, it may be possible to obtain a boron-containing lithium composite oxide containing lithium, metal element M, and boron, and having an XRD spectrum showing a peak pattern of a disordered rock salt structure. In this production method, the ranges described for the above lithium composite oxide, such as the content x of B and the blending ratio of the raw materials, can be appropriately adopted. Also, in this treatment, it may be mixed and pulverized within the range of 2 hours or more and 40 hours or less. The mixing and pulverization can be carried out, for example, with a ball mill or a planetary ball mill, and it is particularly preferable to carry out with a planetary ball mill. In the planetary ball mill, the rotation speed may be appropriately set according to the volume for accommodating the raw materials. For example, a range of 400 rpm or more and 1000 rpm or less is preferable, a range of 500 rpm or more and 800 rpm or less is more preferable, and a range of 550 rpm or more and 650 rpm or less is more preferable. By performing such an adjustment step, the above-described lithium composite oxide can be produced.

[0017] FIG. 1 is an explanatory diagram of the crystal structures of LiMnO2 having a disordered rock salt structure and Li2B4O7. FIG. 1A is the crystal structure with LiMnO2 having a disordered rock salt structure as the M source. Also, FIG. 1B is the crystal structure of lithium borate as the B source. FIG. 2 is a schematic diagram showing an example of the crystal structure of a boron-containing lithium manganese composite oxide having a disordered rock salt structure, which is a product. Boron (B) added to the lithium manganese composite oxide has an atomic radius smaller than that of Li and Mn, and thus can form a planar three-coordination with three oxygens in the structure shown in FIG. 2. As a result, as shown by the dotted circle in FIG. 2, when a part of the octahedral sites becomes vacant, an excess insertion site for Li is generated, and it is considered that an improvement in capacity can be expected.

[0018] (Power storage device) The power storage device of the present disclosure includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an ion-conductive medium interposed between the positive electrode and the negative electrode and conducting lithium ions. This power storage device has the above-described lithium composite oxide as the positive electrode active material. This power storage device may also be a lithium secondary battery using metallic lithium or a lithium alloy as the negative electrode active material, a lithium ion secondary battery having a negative electrode active material that absorbs and releases lithium ions, or a hybrid capacitor having a negative electrode active material that absorbs and desorbs ions.

[0019] The positive electrode may be formed by mixing a positive electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like positive electrode mixture, applying it to the surface of a current collector, drying it, and compressing it to increase electrode density as needed. The conductive material contained in the positive electrode is not particularly limited as long as it is an electronically conductive material that does not adversely affect the battery performance of the positive electrode. For example, a mixture of one or more of graphite such as natural graphite (scale graphite, flake graphite) or artificial graphite, acetylene black, carbon black, ketjen black, carbon whiskers, needle coke, carbon fiber, and metals (copper, nickel, aluminum, silver, gold, etc.) can be used. Among these, carbon black and acetylene black are preferred as the conductive material from the viewpoints of electronic conductivity and coatability. The binder contained in the positive electrode serves to bind the active material particles and conductive material particles together. Examples of binders include fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber; thermoplastic resins such as polypropylene and polyethylene; ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, and natural butyl rubber (NBR), either alone or in combination. Water-based binders such as cellulose-based binders and aqueous dispersions of styrene butadiene rubber (SBR) can also be used. Examples of solvents that can be used to disperse the positive electrode active material, conductive material, and binder include organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. Alternatively, dispersants, thickeners, and the like can be added to water to form a slurry of the active material with a latex such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more kinds. Application methods include, for example, roller coating such as an applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. Any of these can be used to obtain a desired thickness and shape.Examples of current collectors include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymers, and conductive glass, as well as aluminum or copper whose surfaces have been treated with carbon, nickel, titanium, or silver to improve adhesion, conductivity, and oxidation resistance. These surfaces can also be subjected to oxidation treatment. Current collectors may be in the form of foils, films, sheets, nets, punched or expanded materials, laths, porous materials, foams, or fiber aggregates. The thickness of the current collector is, for example, 1 to 500 μm.

[0020] The negative electrode may be formed by closely adhering a negative electrode active material to a current collector. Alternatively, the negative electrode active material may be mixed with a binder and, if necessary, a conductive material, and an appropriate solvent added to form a paste of the negative electrode material. This paste is then applied to the surface of a current collector, dried, and, if necessary, compressed to increase electrode density. Examples of negative electrode active materials include inorganic compounds such as lithium, lithium alloys, and tin compounds; carbonaceous materials capable of absorbing and releasing lithium ions; composite oxides containing multiple elements; and conductive polymers. Examples of carbonaceous materials include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Among these, graphites such as artificial graphite and natural graphite are preferred because they have an operating potential close to that of metallic lithium, allow for charging and discharging at high operating voltages, suppress self-discharge when using a lithium salt as a supporting electrolyte, and reduce irreversible capacity during charging. Examples of composite oxides include lithium-titanium composite oxide and lithium-vanadium composite oxide. Of these, carbonaceous materials are preferred as negative electrode active materials from the standpoint of safety. The conductive materials, binders, solvents, etc. used in the negative electrode can be the same as those exemplified for the positive electrode. For the negative electrode current collector, copper, nickel, stainless steel, titanium, aluminum, baked carbon, conductive polymers, conductive glass, Al-Cd alloys, etc., as well as copper whose surface has been treated with carbon, nickel, titanium, silver, etc., can also be used to improve adhesion, conductivity, and reduction resistance. These surfaces can also be oxidized. The shape of the current collector can be the same as that of the positive electrode.

[0021] The ion-conducting medium may be a non-aqueous electrolyte solution containing a supporting salt containing lithium and a non-aqueous solvent. Examples of the solvent for the non-aqueous electrolyte solution include carbonates, esters, ethers, nitriles, furans, sulfolanes, and dioxolanes, and these can be used alone or in combination. Specific examples of carbonates include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate; chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate; cyclic esters such as γ-butyl lactone and γ-valerolactone; chain esters such as methyl formate, methyl acetate, ethyl acetate, and methyl butyrate; ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane; nitriles such as acetonitrile and benzonitrile; furans such as tetrahydrofuran and methyltetrahydrofuran; sulfolanes such as sulfolane and tetramethylsulfolane; and dioxolanes such as 1,3-dioxolane and methyldioxolane. Of these, a combination of a cyclic carbonate and a chain carbonate is preferred.

[0022] Examples of supporting salts include LiPF, LiBF, LiAsF, LiCF, SO, LiN(CF, SO), LiC(CF, SO), LiSbF, LiSiF, LiAlF, LiSCN, LiClO, LiCl, LiF, LiBr, LiI, and LiAlCl. From the viewpoint of electrical properties, it is preferable to use a combination of one or more salts selected from the group consisting of inorganic salts such as LiPF, LiBF, LiAsF, and LiClO, and organic salts such as LiCF, SO, LiN(CF, SO), and LiC(CF, SO). The concentration of this supporting salt in the nonaqueous electrolyte is preferably 0.1 mol / L to 5 mol / L, and more preferably 0.5 mol / L to 2 mol / L. When the concentration of the dissolving supporting electrolyte is 0.1 mol / L or more, a sufficient current density can be obtained, and when it is 5 mol / L or less, the electrolyte can be made more stable.

[0023] The power storage device of the present disclosure may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the power storage device, but examples thereof include polymer nonwoven fabrics such as polypropylene nonwoven fabrics and polyphenylene sulfide nonwoven fabrics, and thin microporous films of olefin resins such as polyethylene and polypropylene. These may be used alone or in combination.

[0024] The shape of the electricity storage device of the present disclosure is not particularly limited, and examples thereof include coin-shaped, button-shaped, sheet-shaped, laminated, cylindrical, flat, and rectangular shapes. Furthermore, a plurality of such electricity storage devices may be connected in series to form large devices for use in electric vehicles and the like. FIG. 3 is a schematic diagram showing an example of an electricity storage device 20 of this embodiment. This electricity storage device 20 includes a positive electrode sheet 23 in which a positive electrode mixture 22 is formed on a current collector 21, a negative electrode sheet 26 in which a negative electrode mixture 25 is formed on the surface of a current collector 24, a separator 28 provided between the positive electrode sheet 23 and the negative electrode sheet 26, and a nonaqueous electrolyte solution 29 filling the space between the positive electrode sheet 23 and the negative electrode sheet 26. This electricity storage device 20 is formed by sandwiching a separator 28 between a positive electrode sheet 23 and a negative electrode sheet 26, winding them up, and inserting them into a cylindrical case 32, with a positive electrode terminal 34 connected to the positive electrode sheet 23 and a negative electrode terminal 36 connected to the negative electrode sheet 26. The positive electrode mixture 22 contains, as a positive electrode active material, a composite oxide that contains lithium, a metal element M, and boron and whose XRD spectrum shows a peak pattern of a disordered rock salt structure.

[0025] The lithium composite oxide, its manufacturing method, and the energy storage device of this embodiment, as described above, can provide a novel material capable of further increasing discharge capacity. The reason for this effect is presumed to be as follows. For example, in a lithium composite oxide with a disordered rock-salt structure, the amorphous structure allows Li to move three-dimensionally, allowing Li to be reversibly inserted and removed even in a Li-excess composition, thereby achieving high capacity. Furthermore, boron is added to this disordered rock-salt structure composite oxide. Because boron has a smaller atomic radius than Li and the metal element M, it can form a planar three-coordinated structure with three oxygen atoms in the structure. As a result, it is presumed that some octahedral sites become vacant, creating excess Li insertion sites, thereby improving discharge capacity.

[0026] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present disclosure. [Example]

[0027] Specific examples of fabricating the lithium composite oxide and electricity storage device of the present disclosure will be described below as experimental examples, with Experimental Examples 1 to 5 corresponding to working examples and Experimental Example 6 corresponding to a comparative example.

[0028] (Preparation of synthetic raw materials) Orthorhombic LiMnO2 was placed in a zirconia pot under an Ar atmosphere and ground in a planetary ball mill to obtain a disordered rock-salt lithium-manganese composite oxide. The synthesis conditions were a 500 mL zirconia pot with 5 mm diameter zirconia balls, a rotation speed of 560 rpm, and mechanochemical treatment for 28 hours. The resulting disordered rock-salt lithium-manganese composite oxide was used as the M source described below.

[0029] (Experimental Examples 1 to 5) Disordered rock salt LiMnO2 as the M source and Li2B4O7 as the B source were mixed in an agate bowl, then sealed in a zirconia pot under an Ar atmosphere and crushed in a planetary ball mill to obtain a boron-containing lithium manganese composite oxide. The synthesis conditions were as follows: 5 mm diameter zirconia balls were placed in an 80 mL zirconia pot, and the mechanochemical treatment was carried out at 600 rpm for 36 hours. The basic formula was Li a B x M y O 2-z A z In the above, x=0.03, y=0.97, z=0 was designated as Experimental Example 1. Furthermore, x=0.08, y=0.93, z=0 was designated as Experimental Example 2. Furthermore, x=0.15, y=0.87, z=0 was designated as Experimental Example 3. Furthermore, x=0.23, y=0.80, z=0 was designated as Experimental Example 4. Furthermore, x=0.27, y=0.76, z=0 was designated as Experimental Example 5.

[0030] (Experimental Example 6) The disordered rock-salt type lithium manganese composite oxide in which x=0, y=0, and z=0 in the above basic formula was used as Experimental Example 6.

[0031] (X-ray diffraction measurement) Powder X-ray diffraction measurements were performed on the samples. Measurements were performed using an X-ray diffractometer (Rigaku Ultima IV) using CuKα radiation (wavelength 1.54051 Å). Measurements were performed at an applied voltage of 50 kV and a current of 40 mA. Measurements were recorded at a scanning rate of 5° / min over the 2θ angle range of 10° to 100°.

[0032] (Fabrication of bipolar evaluation cell) The resulting sample was used as the positive electrode active material. The active material was 70% by mass, Ketjen Black (ECP-600, manufactured by Mitsubishi Chemical Corporation) was 25% by mass as a conductive material, and polytetrafluoroethylene (PTFE, F-104, manufactured by Daikin Industries, Ltd.) was 5% by mass as a binder. The mixture was crushed and mixed in a mixer. The resulting dry mixture was formed into circular pellets with a diameter of 10 mm and pressed onto an aluminum expander to form a positive electrode. A lithium metal foil (300 μm thick) was used as the negative electrode. A polyethylene separator (E20MMS, manufactured by Tonen Chemical Co., Ltd.) impregnated with a nonaqueous electrolyte was sandwiched between the two electrodes to prepare a bipolar evaluation cell. The nonaqueous electrolyte was a 1M solution of LiPF6 in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 30 / 40 / 30.

[0033] (Charge / discharge test) Using the bipolar evaluation cell, constant current and constant voltage charge / discharge measurements were carried out at a current value of 20 mA / g in a temperature environment of 20° C., in a potential range of 4.8 V to 1.5 V relative to the lithium reference potential.

[0034] (Results and Discussion) The evaluation results of Experimental Examples 1 to 6 are summarized in Table 1. Table 1 summarizes the composition formula, phase classification by XRD, initial charge capacity, and initial discharge capacity of Experimental Examples 1 to 6. Figure 4 shows the XRD measurement results of the boron-containing lithium manganese composite oxides of Experimental Examples 3 and 6. Figure 5 shows the initial charge / discharge curves of the test cells of Experimental Examples 1 to 6, and Figures 5A to 5F show the measurement results of Experimental Examples 1 to 6, respectively. Figure 6 shows the charge / discharge curves up to the 10th cycle of Experimental Example 3. Figure 7 shows the measurement results of the discharge capacity and coulombic efficiency up to the 30th cycle of Experimental Example 3. Figure 8 shows the results of an investigation into the dependency of the initial discharge capacity on the B content of Experimental Examples 1 to 6.

[0035] Example 6: Disordered rocksalt Li synthesized using a planetary ball mill a As shown in Table 1 and Figure 5F, the initial discharge capacity of MnO2 was 227 mAh / g. In Experimental Example 6, a relatively high discharge capacity was shown, but it did not exceed 250 mAh / g. On the other hand, XRD analysis revealed that Experimental Examples 1 to 5, which were synthesized using LiMnO2 and Li2B4O7 as raw materials, exhibited a single disordered rock salt structure, as shown in Table 1 and Figure 4. In Experimental Example 3, Li a B 0.15 Mn 0.87 For O2, the initial charge capacity was 221 mAh / g, while the discharge capacity was 315 mAh / g, demonstrating high discharge capacities exceeding 250 mAh / g and even 300 mAh / g. In Experimental Example 3, as shown in Figure 6, the charge / discharge curve up to the 10th cycle showed a drop in capacity to 297 mAh / g in the second cycle, but there was almost no subsequent capacity degradation, demonstrating good performance. Furthermore, in Experimental Example 3, as shown in Figure 7, there was no noticeable degradation in capacity or coulombic efficiency up to the 30th cycle.

[0036] As shown in Figure 8, for the boron-containing lithium manganese composite oxide with varying amounts of B, the results for the materials are shown in Table 1 and Figure 4 as Experimental Examples 1 and 3. When the composition x of B was in the range of 0.03≦x≦0.27, a capacity of 270 mAh / g or more was exhibited. 3+ / M 4+This was found to be preferable because it exceeded the theoretical capacity assumed to utilize a single-electron reaction. Furthermore, when the composition x of B was in the range of 0.05≦x≦0.25, the capacity exceeded 300 mAh / g, exceeding the maximum theoretical capacity calculated from the amount of Li added. This increase in capacity is thought to be due to the following reasons: The amorphous structure of the disordered rock-salt lithium composite oxide allows for three-dimensional Li mobility, enabling reversible Li insertion and desorption even in Li-excess compositions, leading to high capacity. Furthermore, when boron is added to this disordered rock-salt composite oxide, its atomic radius is smaller than that of Li and the metal element M, so it can form a planar tri-coordinated structure with three oxygen atoms in the structure. As a result, some octahedral sites become vacant, creating excess Li insertion sites, further improving discharge capacity (see Figure 2).

[0037] (Consideration of the substitution effect of anion sites) The above-mentioned disordered rock salt LiMnO2, Li3PO4, and LiF were used as raw materials and mixed in an agate bowl at a predetermined ratio. The mixture was then sealed in an 80 mL zirconia pot together with zirconia balls having a diameter of 5 mm under an Ar atmosphere and pulverized in a planetary ball mill at 600 rpm for 36 hours to obtain the lithium composite oxides of Reference Examples 1 to 3. The raw material ratio was determined according to the basic composition formula Li a P x Mn y O 2-z F z The values ​​of x, y, and z in the above formula were adjusted to 0.04, 0.92, and 0.00, respectively, in Reference Example 1, 0.04, 0.74, and 0.37 in Reference Example 2, and 0.00, 0.80, and 0.40 in Reference Example 3. A bipolar evaluation cell was fabricated in the same manner as in the above-described experimental examples, and a charge-discharge test was performed.

[0038] Figure 9 shows the discharge curves and dQ / dV curves up to the 10th cycle for Reference Examples 1 and 2, with Figures 9A and 9C for Reference Example 1 and Figures 9B and 9D for Reference Example 2. Table 2 summarizes the compositions, phase classifications, and discharge capacities for Reference Examples 1 and 2. As shown in Table 2 and Figure 9, in Reference Examples 1 and 2, similar to the positive electrodes of the present disclosure, introducing phosphorus (P), which has a small atomic radius, into the cation site of the disordered rock-salt lithium-manganese composite oxide allows for excessive Li insertion, resulting in high capacity. In this case, as shown in Figure 9, introducing F into the anion site of the disordered rock-salt composite oxide further suppressed changes in the profile of the charge-discharge curve. Based on the same theory, it was also speculated that the introduction of halogen into the anion site would also result in high capacity and long life for lithium composite oxides containing halogen in their composition.

[0039] [Table 1]

[0040] [Table 2]

[0041] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present disclosure. [Industrial Applicability]

[0042] The lithium composite oxide, the electricity storage device, and the method for producing the lithium composite oxide disclosed in this specification can be used in the technical field of secondary batteries. [Explanation of symbols]

[0043] 20 electricity storage device, 21 current collector, 22 positive electrode composite layer, 23 positive electrode sheet, 24 current collector, 25 negative electrode composite layer, 26 negative electrode sheet, 28 separator, 29 non-aqueous electrolyte, 32 cylindrical case, 34 positive electrode terminal, 36 negative electrode terminal.

Claims

1. A lithium composite oxide used as an electrode active material for an electricity storage device, containing lithium, a metal element M (wherein M is one or more of Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, and Ge), and boron; The XRD spectrum shows the peak pattern of a disordered rock salt structure. Lithium composite oxide.

2. Basic composition formula Li a B x M y O 2-z A z (wherein M is one or more of Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, and Ge, and A is one or more of F, Cl, Br, I, and S, and 0<a<2, 0<x<1, 0<y<1, 0≦z<2 are satisfied).

3. The lithium composite oxide according to claim 2, wherein 0.03≦x≦0.27 is satisfied.

4. The lithium composite oxide according to claim 2 or 3, wherein 0.05≦x≦0.25 is satisfied.

5. The lithium composite oxide according to any one of claims 1 to 4, wherein the M contains at least Mn.

6. A positive electrode having the lithium composite oxide according to any one of claims 1 to 5 as a positive electrode active material; a negative electrode having a negative electrode active material; an ion conductive medium interposed between the positive electrode and the negative electrode and conducting lithium ions; An electricity storage device comprising:

7. The positive electrode has an initial discharge capacity of 250 mAh / g or more. The electricity storage device according to claim 6 .

8. A method for producing a lithium composite oxide used as an electrode active material for an electricity storage device, comprising: a preparation step of mixing and grinding raw materials including at least an M source, which is a lithium composite oxide containing a metal element M (where M is one or more of Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, and Ge) and showing a peak pattern of a disordered rock-salt structure in an XRD spectrum, and a B source containing B, by a mechanochemical method to obtain a lithium composite oxide containing lithium, the metal element M, and boron and showing a peak pattern of a disordered rock-salt structure in an XRD spectrum; A method for producing a lithium composite oxide comprising:

9. In the preparation step, LiMnO 2 and Li as the B source. 2 B 4 O 7 The method for producing a lithium composite oxide according to claim 8, wherein

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