Phosphor-containing lithium ruthenium-based complex oxide, manufacturing method thereof, cathode for lithium ion secondary batteries using the same, and lithium ion secondary battery

Abstract

To provide a cathode active material having high discharge capacity and capable of stably manufacturing slurry, provide an anode of high discharge capacity using the anode active material, and provide a lithium ion secondary battery of high energy density using the cathode.SOLUTION: Provided is a phosphor-containing lithium ruthenium-based complex oxide for cathodes for lithium ion secondary batteries which contains Li atoms, Ru atoms, P atoms and O atoms derived from Li2RuO3 and Li3 PO4 and of which a molar ratio of the P atoms with respect to the Ru atoms (P / Ru molar ratio) is 0.05 or more and 1.0 or less. Also provided is a manufacturing method of the phosphor-containing lithium ruthenium-based complex oxide. Further, there are provided a cathode for lithium ion secondary batteries containing the phosphor-containing lithium ruthenium-based complex oxide and a lithium ion secondary battery including the cathode.SELECTED DRAWING: Figure 4-4

Description

[Technical field]

[0001] The present invention relates to a phosphorus-containing lithium ruthenium composite oxide for use in a positive electrode of a lithium ion secondary battery and a method for producing the same, and also to a positive electrode for a lithium ion secondary battery containing the phosphorus-containing lithium ruthenium composite oxide and a lithium ion secondary battery using the positive electrode. [Background technology]

[0002] Secondary batteries are widely used as power sources for portable electronic devices, and lithium-ion secondary batteries in particular are indispensable energy storage devices as they are lightweight and have high energy density. Furthermore, from the perspective of reducing environmental impact, their use as power sources for household appliances and electric vehicles is expanding. As these uses expand, there is a demand for lithium-ion secondary batteries with even higher capacities.

[0003] In order to obtain a lithium ion secondary battery with a higher discharge capacity, a lightweight positive electrode for the secondary battery with a high energy density is required. As a means for obtaining a lightweight positive electrode for a lithium ion secondary battery with a high energy density, there is a method of using a positive electrode material with a high energy density, a method of increasing the surface area by making the material into fine particles, or a method of increasing the electrode density.

[0004] Lithium compounds such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), and lithium iron phosphate (LiFePO4) have traditionally been used as positive electrode materials for lithium-ion secondary batteries. Various composite materials are being researched as alternative positive electrode materials.

[0005] For example, Patent Document 1 describes a lithium-ion secondary battery positive electrode material and a lithium-ion secondary battery made of a composite oxide in which iron and nickel are dissolved in a solid solution, the composite oxide having an average oxidation number of iron, nickel, and manganese within a specific range when raw materials having a specific composition range are used, a coprecipitation method from an aqueous solution is employed, and specific production conditions are adopted.

[0006] In addition, Patent Document 2 discloses LiA as a lithium-ion secondary battery active material having a high discharge capacity and a high energy density. x B 1-x PO4 (where A is at least one selected from Mn, Co, and Ni, B is at least one selected from Nb, Ni, V, Cr, and Fe, and 0 < x ≦ 1), a positive electrode active material for a lithium-ion secondary battery containing an olivine-type crystal represented by the formula, and characterized by containing an amorphous phase, is presented.

[0007] Furthermore, Non-Patent Document 1 reports an evaluation of Li2RuO3 as a positive electrode active material for a lithium-ion secondary battery.

[0008] In addition, in fields other than lithium-ion secondary batteries, for example, Non-Patent Document 2 reports an electrochemical analysis of Li2RuO3-Li2SO4 as a new positive electrode material for all-solid-state batteries, showing a high discharge capacity of 350 mAh / g. Also, Patent Document 3 discloses a structure containing Li2RuO3-Li2SO4 as an amorphous oxide-based positive electrode active material, which is a raw material for producing a positive electrode for an all-solid-state secondary battery that can exhibit a high conductivity even with a relatively thick film positive electrode.

[0009] As a method for increasing the surface area by miniaturizing particles and increasing the electrode density, for example, Patent Document 4 describes a technique for controlling the particle diameter of the constituent particles, and Patent Document 5 describes a technique for defining the composition of the particle diameter and the particle diameter within the active material to increase the active material density.

[0010] Regarding the increase in the energy density of the secondary battery body, for example, Non-Patent Document 3 describes that a lithium-ion secondary battery using LiNi 0.6 Mn 0.2 Co 0.2 O2 as a positive electrode active material can obtain a high energy density of 300 Wh / kg.

Prior Art Documents

Patent Documents

[0011] [Patent Document 1] JP 2013-212959 A [Patent Document 2] JP 2013-225495 A [Patent Document 3] International Publication No. 2017 / 169599 [Patent Document 4] JP 2017-130395 A [Patent Document 5] JP 2013-065467 A [Non-patent literature]

[0012] [Non-Patent Document 1] Solid State Ionics, 82(1995)25-31 [Non-Patent Document 2] ACS Appl. Energy Mater., 2019, 2, 1594-1599 [Non-Patent Document 3] NATURE ENERGY, Vol.4, JULY 2019,551-559 Summary of the Invention [Problem to be solved by the invention]

[0013] There is an urgent need to increase the capacity of secondary batteries, which are being used in a wide range of fields. In particular, the performance of the positive electrode of a secondary battery that is lightweight and has a high energy density is required for use as a driving power source for electric vehicles, drones, etc., and portable electronic devices, etc., and the performance of the positive electrode greatly contributes to the performance. Therefore, there is a strong demand for a positive electrode material that has a high discharge capacity and can stably produce a positive electrode with a high discharge capacity.

[0014] In particular, the performance of the positive electrode greatly contributes to the performance of the entire secondary battery. For example, in the secondary battery reported in Non-Patent Document 3, LiNi 0.6 Mn 0.2 Co0.2 Although O2 is used, the discharge capacity presented in the document is 185mAh / g. This is significantly lower than the theoretical capacity of 3,860mAh / g for Li used as the negative electrode, and it is believed that the energy density of the entire battery is limited by the discharge capacity of the positive electrode active material.

[0015] Even when the positive electrode described in Patent Document 1 is used in a lithium ion secondary battery, the 1st discharge capacity is 227 mAh / g or less. Patent Document 2 does not specifically describe the discharge capacity, but in view of the configuration, the discharge capacity is theoretically considered to be about 170 mAh / g. Also, in Patent Document 4, the initial discharge capacity of the manufactured coin cell is 212 mAh / g or less. In Patent Document 5, the discharge capacity is 188 mAh / g. The discharge capacity of the lithium ion secondary battery described in Non-Patent Document 1 is 160 mAh / g. These discharge capacities cannot be said to satisfy the recent demand for even higher discharge capacity (preferably 280 mAh / g or more).

[0016] In addition, the conventional method of increasing the surface area by fine particle size or increasing the electrode density can achieve the desired charge / discharge capacity, but when the particle size of the positive electrode active material is small, the particles are likely to aggregate, and therefore, even if an electrode having a positive electrode active material with a high charge / discharge capacity is used, the energy density and cycle characteristics may not be sufficiently improved. In addition, some of these positive electrode active materials may become an extremely unstable slurry using the conventional procedure, and there is also a problem that the electrode performance is not stable for each electrode and each lot of active material.

[0017] An all-solid-state battery using the positive electrode material described in Patent Document 3 has achieved a maximum discharge capacity of about 270 mAh / g. However, in Patent Document 3, the positive electrode for the all-solid-state battery is produced by pressing the positive electrode material, and this method may cause variation in the quality (discharge capacity) of the positive electrode for each production lot. In addition, when attempting to produce a positive electrode for a lithium-ion secondary battery using this positive electrode material, there is a high possibility that the slurry containing the positive electrode material will gel, so the positive electrode material cannot be simply used as it is for a positive electrode for a lithium-ion secondary battery that is not an all-solid-state battery. Therefore, the positive electrode material described in Patent Document 3 has a problem in that it is difficult to use it as a positive electrode material for a lithium-ion secondary battery that has a high discharge capacity and does not gel.

[0018] For example, in the case of an active material containing particles with a fine particle size as disclosed in Patent Document 4 and Patent Document 5, aggregation is particularly likely to occur, and therefore, even if an electrode having a positive electrode active material with a high charge / discharge capacity is used, the energy density and cycle characteristics may not be sufficiently improved.

[0019] In the Li2RuO3-Li2SO4 shown in Non-Patent Document 2, larger particles are obtained with an increase in the Li2SO4 content. That is, the particle size becomes smaller when the ratio of the S component is reduced. In general, when an active material, a conductive assistant, and a binder are mixed and stirred to prepare a slurry, the smaller the particle size of the active material, the more likely it is to gel. In the case of Li2RuO3-Li2SO4, for example, when Li2RuO3-Li2SO4 with a ratio of the S component of 0.1 is used as an active material to prepare a slurry, it is difficult to prepare a positive electrode due to severe gelation.

[0020] In view of the above, the object of the present invention is to provide a positive electrode active material that has a higher discharge capacity and allows stable slurry preparation (in other words, easy electrode preparation). It is also an object of the present invention to provide a positive electrode that is easy to prepare an electrode and has a high discharge capacity by using the positive electrode active material. It is also an object of the present invention to provide a lithium ion secondary battery with a high energy density by using the positive electrode. [Means for solving the problem]

[0021] As a result of intensive research, the inventors of the present application have found that a lithium ruthenium-based composite oxide containing a specific amount of phosphorus has a higher discharge capacity and is capable of producing a stable slurry, compared to electrode materials such as lithium nickel cobalt manganese oxide and lithium iron phosphate that have conventionally been used as positive electrode materials for lithium ion secondary batteries, or lithium ruthenate that does not contain phosphorus, and have thus completed the present invention.

[0022] That is, the present invention and its preferred embodiments are as follows: However, the present invention is not limited to the following. [1] A phosphorus-containing lithium ruthenium-based composite oxide for a positive electrode of a lithium ion secondary battery, comprising: A phosphorus-containing lithium ruthenium-based composite oxide comprising Li atoms, Ru atoms, P atoms, and O atoms derived from Li2RuO3 and Li3PO4, and having a molar ratio of the P atoms to the Ru atoms (P / Ru molar ratio) of 0.05 or more and 1.0 or less. [2] The phosphorus-containing lithium ruthenium composite oxide according to [1], having a particle size D10 of 0.47 μm or more and 1.0 μm or less. [3] (a) mixing Li3PO4 and Li2RuO3 so that the molar ratio of Li3PO4 to Li2RuO3 (Li3PO4 / Li2RuO3) is in the range of 0.05 to 1.0; (b) subjecting the mixture obtained in (a) to a dry grinding and mixing process in a dry air atmosphere below the dew point; A method for producing the phosphorus-containing lithium ruthenium-based composite oxide according to [1] or [2], comprising: [4] The manufacturing method according to [3], wherein the dew point is -20°C. [5] (c) prior to step (a), drying Li3PO4 and Li2RuO3 at a temperature of 110° C. or higher for 15 hours or more at a gauge pressure of −0.1 MPa or less; The method for producing a product according to [3] or [4], comprising: [6] A positive electrode for a lithium ion secondary battery, comprising the phosphorus-containing lithium ruthenium composite oxide according to [1] or [2]. [7] A lithium ion secondary battery comprising the positive electrode for lithium ion secondary batteries according to [6]. Effect of the Invention

[0023] According to the phosphorus-containing lithium ruthenium-based composite oxide of the present invention, it is possible to provide a positive electrode for a lithium ion secondary battery having a high discharge capacity of 280 mAh / g or more, and a high-energy density lithium ion secondary battery including the positive electrode for the lithium ion secondary battery.

[0024] Furthermore, the phosphorus-containing lithium ruthenium composite oxide of the present invention can prevent the gelation of the slurry, which is a problem in the manufacturing process of a positive electrode using particles with a small particle size, even when fine particles are formed as in the past, so that a stable positive electrode can be manufactured. Therefore, it is also suitable for densifying a positive electrode using particles with a small particle size, and it is possible to stably manufacture a positive electrode with a high energy density (energy density per volume). [Brief description of the drawings]

[0025] [Figure 1-1] 1 is a SEM image of Example 1. [Figure 1-2] 1 is an SEM image of Example 2. [Figure 1-3] 1 is a SEM image of Example 3. [Figure 1-4] 1 is a SEM image of Example 4. [Figure 1-5] 1 is an SEM image of Example 5. [Figure 1-6] 1 is an SEM image of Example 6. [Figure 1-7] 1 is an SEM image of Comparative Example 1. [Figure 1-8] 1 is an SEM image of Comparative Example 2. [Figure 2-1]1 shows the particle size distribution of Example 1. [Figure 2-2] 1 shows the particle size distribution of Example 2. [Figure 2-3] 1 shows the particle size distribution of Example 3. [Figure 2-4] 1 shows the particle size distribution of Example 4. [Figure 2-5] 1 is a particle size distribution of Example 5. [Figure 2-6] 1 is a particle size distribution of Example 6. [Diagram 2-7] 1 shows the particle size distribution of Comparative Example 1. [Figure 2-8] 4 is a particle size distribution of Comparative Example 2. [Figure 3-1] 1 shows the results of X-ray diffraction in Example 1. [Figure 3-2] 1 shows the results of X-ray diffraction in Example 2. [Figure 3-3] 1 shows the results of X-ray diffraction in Example 3. [Diagram 3-4] 1 shows the results of X-ray diffraction in Example 4. [Figure 3-5] 1 shows the results of X-ray diffraction in Example 5. [Diagram 3-6] 1 shows the X-ray diffraction results of Example 6. [Diagram 3-7] 1 shows the X-ray diffraction results of Comparative Example 1. [Diagram 3-8] This is the X-ray diffraction result of Li3PO4. [Diagram 3-9] X-ray diffraction results of the sample folder. [Figure 4-1] 2 is a charge / discharge curve of Example 1. [Figure 4-2] 2 is a charge / discharge curve of Example 2. [Figure 4-3] 1 shows charge and discharge curves of Example 3. [Figure 4-4] 1 shows charge and discharge curves of Example 4. [Figure 4-5] 1 shows charge and discharge curves of Example 5. [Figure 4-6] 1 shows charge and discharge curves of Example 6. [Diagram 4-7] 2 is a charge / discharge curve of Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The phosphorus-containing lithium ruthenium composite oxide of the present invention contains Li atoms, Ru atoms, P atoms, and O atoms derived from lithium ruthenate (LiRuO) and lithium phosphate (LiPO), and the molar ratio of the P atoms to the Ru atoms (P / Ru molar ratio) is 0.05 or more and 1.0 or less.

[0027] Specifically, it is a phosphorus-containing lithium ruthenium-based composite oxide produced by mixing lithium ruthenate (Li2RuO3) and lithium phosphate (Li3PO4) so ​​that the molar ratio of Li3PO4 to Li2RuO3 (Li3PO4 / Li2RuO3) is 0.05 or more and 1.0 or less, and then performing a dry grinding and mixing process in a low dew point atmosphere. In other words, the phosphorus-containing lithium ruthenium-based composite oxide contains Li atoms, Ru atoms, P atoms, and O atoms derived from the raw materials lithium ruthenate (Li2RuO3) and lithium phosphate (Li3PO4), and the molar ratio of the P atoms to the Ru atoms (P / Ru molar ratio) is 0.05 or more and 1.0 or less, and the form of the oxide does not matter. Therefore, the form of the phosphorus-containing lithium ruthenium-based composite oxide can be, for example, a compound formed from Li2RuO3 and Li3PO4 (whose composition formula is Li 2+x Ru 1-x P x O 3+x(0.05≦x≦0.5)), or may further contain unreacted Li2RuO3 and / or Li3PO4. Therefore, the phosphorus-containing lithium ruthenium-based composite oxide of the present invention has a different structure from the conventionally reported positive electrode active material represented by the composition formula Li2RuO3 (for example, Non-Patent Document 1). In addition, the phosphorus-containing lithium ruthenium-based composite oxide of the present invention also has a different structure from the conventionally reported positive electrode materials for lithium ion secondary batteries (for example, Patent Documents 1, 2, 4, and 5). The phosphorus-containing lithium ruthenium-based composite oxide of the present invention is particularly useful as a positive electrode for lithium ion secondary batteries, and has a high discharge capacity of 280 mAh / g or more. This is an electrode characteristic that exceeds that of Li2RuO3 in the above-mentioned Non-Patent Document and the positive electrode materials for lithium ion secondary batteries described in the above-mentioned Patent Documents.

[0028] The phosphorus-containing lithium ruthenium composite oxide of the present invention contains phosphorus at the above-mentioned predetermined molar ratio, and therefore, compared with conventional positive electrode materials for lithium ion secondary batteries, it is possible to stably prepare a slurry and has excellent electrode properties. When the molar ratio is 0.05 or more, when preparing a slurry using the phosphorus-containing lithium ruthenium composite oxide, the slurry can be prevented from gelling. Therefore, a stable electrode can be manufactured. When the molar ratio is 1.0 or less, the performance (particularly, the discharge capacity) of the positive electrode using the phosphorus-containing lithium ruthenium composite oxide can be improved.

[0029] From the viewpoint of slurry stability and cycle performance of a lithium ion secondary battery, it is preferable that the phosphorus-containing lithium ruthenium-based composite oxide of the present invention maintains a crystalline state as much as possible. On the other hand, due to the above-mentioned production process, it is difficult to completely remove the amorphous phase. The ratio of the crystalline portion contained in the phosphorus-containing lithium ruthenium-based composite oxide of the present invention is preferably 80% by weight or more, more preferably 95% by weight or more, and particularly preferably 99% by weight or more.

[0030] The phosphorus-containing lithium ruthenium composite oxide of the present invention preferably has a particle diameter D10 of 0.47 μm or more and 1.0 μm or less, more preferably 0.49 μm or more and 0.90 μm or less. In the present invention, the particle diameter D10 is a value at 10% of the passing portion cumulative. When the particle diameter D10 is 0.47 μm or more, when the phosphorus-containing lithium ruthenium composite oxide is used to prepare a slurry, gelation of the slurry due to particle aggregation can be more effectively prevented, and more stable electrode production is possible. In addition, when the particle diameter D10 is 1.0 μm or less, the electrode performance can be more effectively improved by increasing the surface area of ​​the electrode and increasing the electrode density. The particle diameter of the phosphorus-containing lithium ruthenium composite oxide of the present invention is mainly distributed in the range of 0.1 μm to 100 μm, but it is not necessarily necessary to specify the composition ratio by the particle diameter as described in Patent Documents 4 and 5. In addition, as described above, the phosphorus-containing lithium ruthenium composite oxide of the present invention allows stable slurry preparation. For example, when the phosphorus-containing lithium ruthenium-based composite oxide of the present invention and Li2RuO3 reported in Non-Patent Document 1 are prepared by a dry grinding process so as to have the same particle size distribution, a slurry can be easily prepared from the phosphorus-containing lithium ruthenium-based composite oxide of the present invention, whereas aggregation and gelation occur in the case of Li2RuO3, making it difficult to prepare a slurry by a general method.

[0031] The present invention also provides a method for producing a method for manufacturing a semiconductor device comprising the steps of: (a) mixing Li3PO4 and Li2RuO3 so that the molar ratio of Li3PO4 to Li2RuO3 (Li3PO4 / Li2RuO3) is in the range of 0.05 to 1.0; (b) subjecting the mixture obtained in (a) to a dry grinding and mixing process in a dry air atmosphere below the dew point; A method for producing the phosphorus-containing lithium ruthenium-based composite oxide, comprising: to provide.

[0032] (a) is a step of mixing Li3PO4 and Li2RuO3. In this mixing step, Li3PO4 and Li2RuO3 are mixed so that the molar ratio of Li3PO4 to Li2RuO3 (Li3PO4 / Li2RuO3) is in the range of 0.05 to 1.0. By mixing within this molar ratio range, the molar ratio of P atoms to Ru atoms contained in the obtained phosphorus-containing lithium ruthenium-based composite oxide (P / Ru molar ratio) can be set to 0.05 to 1.0. When the P / Ru molar ratio in the mixing step is 0.05 or more, when a slurry is prepared using the phosphorus-containing lithium ruthenium-based composite oxide, the slurry can be prevented from gelling. Therefore, a stable electrode can be manufactured. When the P / Ru molar ratio in the mixing step is 1.0 or less, the performance (particularly, the discharge capacity) of the positive electrode using the phosphorus-containing lithium ruthenium-based composite oxide can be improved.

[0033] (b) is a step of subjecting the mixture obtained in (a) to a dry grinding and mixing treatment in a dry air atmosphere below the dew point. There is no particular restriction on the method of the dry grinding and mixing treatment, but examples thereof include treatment using a planetary ball mill. The treatment using the planetary ball mill is not particularly limited as long as it is a commonly used treatment condition, but examples thereof include treatment under conditions of a rotation speed of 50 to 600 rpm, 6 minutes to 200 hours, and 1 kWh to 100 kWh per 1 kg of material mixture. In addition, in the dry grinding and mixing treatment, a desired rest time (interval) may be set, and treatments such as opening the container and removing deposits may be performed between treatments. By performing the rest time, opening the container, or removing deposits, the obtained phosphorus-containing lithium ruthenium-based composite oxide can be homogenized and stabilized. A specific example of a dry grinding and mixing process including rest periods, container opening, and removal of adhering matter is one in which 14 sets of continuous operation are performed, with one set being a one-hour grinding and mixing process, followed by a 30-minute rest, after which the container is opened in a dry air atmosphere, the adhering matter is removed, the container interior is returned to its original state, and the above process is repeated for another 14 sets.

[0034] (b) is carried out in a dry air atmosphere below the dew point. The upper limit of the dew point may be preferably -20°C, more preferably -50°C, and even more preferably -80°C. By carrying out the dry grinding and mixing treatment below the dew point, it is possible to stably obtain a phosphorus-containing lithium ruthenium-based composite oxide. In addition, by carrying out the dry grinding and mixing treatment in a dry air atmosphere, gelation and heat generation can be prevented when preparing a slurry using the obtained phosphorus-containing lithium ruthenium-based composite oxide, compared to the case of treatment in an inert gas atmosphere such as argon.

[0035] The production method of the present invention may further include the following (c): (c) prior to step (a), drying Li3PO4 and Li2RuO3 at a temperature of 110° C. or higher for 15 hours or longer at a gauge pressure of −0.1 MPa or lower; That is, (c) is a pre-drying step of the materials used in the above-mentioned manufacturing method. In the pre-drying step, Li3PO4 and Li2RuO3 are individually dried at a temperature of 110°C or higher for 15 hours or more using a vacuum dryer that has been degassed to a gauge pressure of -0.1 MPa or less. By performing the pre-drying under these conditions, the obtained phosphorus-containing lithium ruthenium-based composite oxide can be preferably homogenized and stabilized.

[0036] The drying conditions in (c) may be such that the dried material can be used in the manufacturing process below the dew point, but drying may also be performed at a higher temperature and / or for a longer period of time at a gauge pressure of -0.1 MPa or less. The drying temperature is preferably 120° C. or higher, more preferably 130° C. or higher. The drying time is preferably 24 hours or more, more preferably 32 hours or more.

[0037] The present invention provides a positive electrode for a lithium ion secondary battery, comprising the phosphorus-containing lithium ruthenium-based composite oxide. The positive electrode for a lithium ion secondary battery has a higher discharge capacity than conventional positive electrodes for lithium ion secondary batteries. In addition, the positive electrode for a lithium ion secondary battery is less likely to gel when a slurry is prepared, so that the quality of each production lot can be prevented from varying. The positive electrode for a lithium ion secondary battery may have the same composition as a conventional positive electrode for a lithium ion secondary battery, except that it contains the phosphorus-containing lithium ruthenium-based composite oxide, and is obtained by using materials and a production method used for conventional positive electrodes for lithium ion secondary batteries.

[0038] The method for producing the positive electrode for the lithium ion secondary battery of the present invention is not particularly limited, but for example, the phosphorus-containing lithium ruthenium-based composite oxide, the conductive assistant, and the binder are added to a dispersion medium to prepare a slurry, the slurry is applied to a positive electrode current collector, the dispersion medium is then evaporated, the slurry is dried, and the obtained electrode is rolled to a desired density. Examples of the conductive assistant include natural graphite, artificial graphite, acetylene black, ketjen black, denka black, carbon black, carbon nanotubes, and vapor-grown carbon fiber (VGCF). Examples of the adhesive include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polymethyl methacrylate, and polyethylene. Examples of the dispersion medium include N-methyl-2-pyrrolidone (NMP). Examples of the positive electrode current collector include aluminum foil.

[0039] The present invention also provides a lithium ion secondary battery including the positive electrode for lithium ion secondary batteries. The lithium ion secondary battery has a higher discharge capacity than conventional lithium ion secondary batteries. The lithium ion secondary battery can use the same separator, negative electrode, and electrolyte as conventional lithium ion secondary batteries, except for using the positive electrode for lithium ion secondary batteries. EXAMPLES

[0040] The present invention will be specifically described below. Note that the present invention is not limited in any way by the following examples.

[0041] [Example 1] (Preparation of lithium ruthenate (Li2RuO3)) 3.6g of ruthenium oxide and 2.2g of lithium carbonate were dried at 110℃ for 15 hours in a vacuum dryer with a gauge pressure of -0.1MPa or less. The dried ruthenium oxide and lithium carbonate were ground and mixed in a mortar to obtain mixed material 1. This mixed material 1 was pre-fired at 900℃ for 12 hours in a tubular furnace in a flow atmosphere of 800mL / min nitrogen and 200mL / min oxygen. After firing, mixed material 1 was ground and mixed in a mortar. Mixed material 1 after firing and grinding was fired at 1100℃ for 12 hours in a tubular furnace in a flow atmosphere of 800mL / min nitrogen and 200mL / min oxygen. After firing, mixed material 1 was further ground and mixed in a mortar to obtain lithium ruthenate.

[0042] (Preparation of lithium ruthenium composite oxide) The obtained lithium ruthenate (Li2RuO3) 4.08g and lithium phosphate (Li3PO4) 0.92g were ground and mixed in a mortar to obtain mixed material 2. Mixed material 2 was placed in a grinding container for a planetary ball mill together with crushing balls. The grinding container was controlled using an atmosphere-controlled container so that the atmosphere in the grinding container was dry air at -50℃ or less, which is below the dew point. Mixed material 2 was ground and mixed in a planetary ball mill (FRITSCH Planetary Ball Mill Classic Line P-6) at a revolution speed of 370 rpm for 1 hour, followed by a 30-minute break, which was repeated 50 times. During the grinding and mixing process, the grinding container was opened every 14 consecutive runs, and mixed material 2 attached to the inner wall of the grinding container was peeled off, and the grinding container and atmosphere-controlled container were reset, and the grinding and mixing process was continued. After the grinding and mixing process, the mixed material 2 was removed from the grinding vessel and ground in a mortar for 30 minutes to obtain a powdered product (a phosphorus-containing lithium ruthenium-based composite oxide with a molar ratio (P / Ru) of 0.24 / 0.76).

[0043] The powdered product was then dried at 130° C. for 15 hours or more in a vacuum dryer degassed to a gauge pressure of −0.1 MPa or less, to obtain a powdered phosphorus-containing lithium ruthenium composite oxide, which was the target positive electrode active material.

[0044] This final product was subjected to SEM observation (KEYENCE 3D Real Surface View Microscope VE-9800), particle size distribution measurement (HORIBA LA-950V2), and X-ray diffraction measurement (Rigaku SmartLab).

[0045] (Preparation of positive electrode) The above positive electrode active material, acetylene black and carbon nanotubes as conductive assistants, and a 12 wt% solution of polyvinylidene fluoride (PVDF) (Kureha KF Polymer W#1100) as a binder were weighed and mixed. Furthermore, NMP was added to adjust the solid component weight / total slurry weight ratio, while stirring with a revolution / rotation mixer (Thinky Awatori Rentaro AR-100) to prepare a slurry. Here, the amount of each component in the slurry was 94.4 wt% of the positive electrode active material, 0.4 wt% of acetylene black, 0.2 wt% of carbon nanotubes, and 5 wt% of PVDF, with the total solid component weight being 100 wt%, and the solid component weight / total slurry weight ratio was 58 wt%.

[0046] The slurry was applied to one side of an aluminum foil having a thickness of 10 μm, which was a positive electrode current collector, and the NMP in the coating film was evaporated on a hot plate set at 110° C. The aluminum foil on which the slurry was applied was then dried in an oven at 80° C. The dried aluminum foil was cut into strips, and the density of the mixture layer was adjusted to 2.4 g / cm using a roll press device. 3 The positive electrode sheet was formed by rolling so that the density of the mixture layer was 2.4 g / cm 3 The density is set to below 2.5 g / cm because the mixture layer is formed on only one side of the aluminum foil, and this is to prevent the electrode from warping due to rolling. If warping can be controlled by coating conditions such as double-sided coating, the density is not limited to the above, and can actually be 2.5 g / cm.3 Equivalent operation was confirmed for samples fabricated at higher densities.

[0047] (Making coin-cell batteries) The positive electrode sheet was punched into a circle with a diameter of 16 mm and immersed in the electrolyte. The positive electrode sheet was held for 1 minute with the gauge pressure reduced to -0.08 MPa, and then the gauge pressure was returned to atmospheric pressure to impregnate the inside of the positive electrode sheet with the electrolyte. A 1 mol / L LiPF6 solution was used as the electrolyte. This electrolyte was obtained by dissolving LiPF6 in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of EC:DEC = 3:7. The aluminum current collector foil of the positive electrode sheet was faced to the lower cover side, and the treated positive electrode sheet, separator, and metallic lithium were laminated in this order to prepare a coin battery for charge / discharge testing. The coin battery was assembled in an environment of -80°C, which is below the dew point temperature.

[0048] The separators used were Celgard #2400 (Hextra Celanese) or Hosen Co., Ltd. lithium ion secondary battery separator and Whatman glass fiber filter paper punched out to a diameter of 16.8 mm, and Celgard #2400 or Hosen Co., Ltd. lithium ion secondary battery separator layered on the Whatman glass fiber filter paper soaked in electrolyte. It has been confirmed that there is no difference in short-term battery operation even if only Celgard #2400, only Hosen Co., Ltd. lithium ion secondary battery separator, or only Whatman glass fiber filter paper is used.

[0049] [Example 2] The same procedure as in Example 1 was carried out to obtain a phosphorus-containing lithium ruthenium-based composite oxide with P / Ru=0.1 / 0.9, except that the amounts of lithium ruthenate and lithium phosphate were changed to those shown in Table 1. The positive electrode and coin-type battery were also produced in the same manner as in Example 1.

[0050] [Example 3] A phosphorus-containing lithium ruthenium-based composite oxide with P / Ru=0.4 / 0.6 was obtained in the same manner as in Example 1, except that the amounts of lithium ruthenate and lithium phosphate were changed to those shown in Table 1. The positive electrode and coin-type battery were also produced in the same manner as in Example 1.

[0051] [Example 4] The same procedure as in Example 1 was carried out except that the revolution speed of the planetary ball mill was set to 450 rpm, and a phosphorus-containing lithium ruthenium-based composite oxide with P / Ru=0.24 / 0.76 was obtained. The positive electrode and coin-type battery were also produced in the same manner as in Example 1.

[0052] [Example 5] The same procedure as in Example 1 was carried out except that the revolution speed of the planetary ball mill was set to 500 rpm, and a phosphorus-containing lithium ruthenium-based composite oxide with P / Ru=0.24 / 0.76 was obtained. The positive electrode and coin-type battery were also produced in the same manner as in Example 1.

[0053] [Example 6] The same procedure as in Example 2 was carried out except that the revolution speed of the planetary ball mill was set to 500 rpm, and a phosphorus-containing lithium ruthenium-based composite oxide with P / Ru=0.1 / 0.9 was obtained. The positive electrode and coin-type battery were also produced in the same manner as in Example 1.

[0054] [Comparative Example 1] Lithium ruthenate was prepared in the same manner as in Example 1. An electrode and a coin-type battery were prepared in the same manner as in Example 1, without pulverizing and mixing with lithium phosphate.

[0055] [Comparative Example 2] Lithium ruthenate was produced in the same manner as in Example 1. The lithium ruthenate was placed in a grinding container for a planetary ball mill together with crushing balls without being ground and mixed with lithium phosphate, and was further ground and mixed in the same manner as in Example 1 using an atmosphere-controlled container. After the grinding and mixing process was completed, grinding in a mortar and vacuum drying were performed in the same manner as in Example 1 to obtain lithium ruthenate with a small particle size. For this lithium ruthenate, gelation of the slurry occurred during the slurry preparation stage when producing a positive electrode sheet, and an electrode could not be produced.

[0056] [Comparative Example 3] A lithium-ruthenium composite oxide containing phosphorus with P / Ru=0.045 / 0.955 was obtained in the same manner as in Example 1, except that the amounts of lithium ruthenate and lithium phosphate were changed to those shown in Table 1. For this sample, gelation of the slurry occurred during the slurry preparation stage in the production of the positive electrode sheet, and an electrode could not be produced.

[0057] [Comparative Example 4] Except for using trilithium borate (Li3BO3) instead of lithium phosphate, a powder sample (Li3BO3 / Li2RuO3) was obtained in the same manner as in Example 1. For this powder sample, gelation of the slurry occurred during the slurry preparation stage when making the positive electrode sheet, and an electrode could not be made.

[0058] [Comparative Example 5] Except for using lithium sulfate (Li2SO4) instead of lithium phosphate, a powder sample (Li2SO4 / Li2RuO3) was obtained in the same manner as in Example 2. For this powder sample, gelation of the slurry occurred during the slurry preparation stage when making the positive electrode sheet, and an electrode could not be made.

[0059] [Comparative Example 6] Except for using lithium fluoride (LiF) instead of lithium phosphate, a powder sample (Li2RuO3 / LiF) was obtained in the same manner as in Example 2. For this powder sample, gelation of the slurry occurred during the slurry preparation stage when making the positive electrode sheet, and an electrode could not be made.

[0060] (Charge / discharge test) A charge-discharge test was performed using the prepared coin-type battery to measure the discharge capacity. The charge-discharge test was performed as follows. The capacity of the positive electrode active material was assumed to be 250 mAh / g, and the current value was set at 1 / 10 C (C rate). The charge was performed by constant current charging (CC charging) from 1.6 V to 4.5 V, and the discharge was performed by constant current discharging (CC discharging) from 4.5 V to 1.6 V. However, for Comparative Example 1, since normal charging and discharging could not be performed at 2 V or less, the charge was performed by constant current charging (CC charging) from 2 V to 4.5 V, and the discharge was performed by constant current discharging (CC discharging) from 4.5 V to 2 V. For Comparative Examples 2 to 6, gelation occurred at the slurry preparation stage, and an electrode could not be prepared, so the charge-discharge test was not performed on the coin-type battery. The results of the charge-discharge test are shown in Table 1 and Figures 4-1 to 4-7.

[0061] [Evaluation Results] Table 1 shows the mixture ratio of lithium ruthenate and lithium phosphate, the P / Ru molar ratio in the sample, the revolution number of the planetary ball mill, the presence or absence of gelation during slurry preparation, and the measurement results of D10 for each sample (excluding the samples of Comparative Examples 4 to 6). It also shows the initial discharge capacity of the samples from which electrodes could be fabricated. Furthermore, SEM images obtained by SEM observation are shown in Figures 1-1 to 1-8. Particle size distributions obtained by particle size distribution measurement are shown in Figures 2-1 to 2-8. The results of X-ray diffraction measurements are shown in Figures 3-1 to 3-9. For the Examples and Comparative Examples from which coin batteries could be fabricated, the results of charge and discharge tests are shown in Figures 4-1 to 4-7.

[0062] [Table 1]

[0063] From Table 1, it can be seen that when the molar ratio of P atoms to Ru atoms (P / Ru molar ratio) contained in the sample is 0.05 or more and 1.0 or less, an electrode can be produced without gelling during slurry preparation, and a button battery using the produced electrode has an initial discharge capacity of 287 mAh / g or more.

[0064] The charge and discharge curves of the coin type batteries prepared using the samples of Examples 1 to 6 and Comparative Example 1 in which gelation did not occur are shown in Figures 4-1 to 4-7. All of the batteries had problem-free charge and discharge curves, and it was confirmed that the positive electrodes prepared in Examples 1 to 6 were effective as positive electrodes for lithium ion secondary batteries. Table 1 also shows the initial discharge capacities of the coin type batteries of Examples 1 to 6 and Comparative Example 1. The lithium ion secondary batteries of Examples 1 to 6 obtained discharge capacities of 287 to 349 mAh / g. All of the Examples had high discharge capacities exceeding 280 mAh / g, and compared to Comparative Example 1, in which the discharge capacity was 263 mAh / g, it can be seen that the present invention is an extremely effective means for increasing the capacity of lithium ion secondary batteries.

[0065] As already mentioned, in the samples of Comparative Examples 2 to 6, gelation occurred during the slurry preparation stage, and it was not possible to prepare a positive electrode sheet. In Examples 1 to 6 and Comparative Example 1, the slurry could be prepared without gelation by the existing method, but in Comparative Example 2, gelation occurred by the same method, and it was not possible to prepare a slurry. In Comparative Example 2, an attempt was made to adjust the slurry composition to suppress the occurrence of gelation, but gelation occurred, and it was impossible to apply the slurry to the aluminum current collector foil with a blade.

[0066] It can be seen that Example 2 and Comparative Example 2 have the same D10, but in Example 2, which contains a predetermined amount of phosphorus, gelation does not occur during slurry preparation. Comparative Examples 1 and 2 were prepared with the same mixing ratio, but gelation did not occur in Comparative Example 1, whereas gelation occurred in Comparative Example 2, so it can be confirmed that D10 contributes to the gelation of the slurry. In addition, Figures 2-1 to 2-8 show the particle size distributions of the phosphorus-containing lithium ruthenium composite oxides of Examples 1 to 6 and the lithium ruthenate of Comparative Examples 1 and 2. In Examples 1 to 6, the particle size distribution state differs depending on the mixing ratio of lithium ruthenate and lithium phosphate and the grinding conditions of the planetary ball mill, but is distributed in the range of 0.1 μm to several tens of μm. On the other hand, in Comparative Example 1, as shown in Figure 2-7, the distribution range of particle sizes around 10 μm is relatively narrow. In each of the samples of Examples 1 to 6, it can be seen that the smaller the mixing ratio of lithium phosphate and the fewer the revolutions of the planetary ball mill, the more fine particles of 1 μm or less tend to increase, and the smaller the D10 value becomes.

[0067] 1-1 to 1-8 show SEM images of the phosphorus-containing lithium ruthenium composite oxides of Examples 1 to 6, which are positive electrode active materials, and the lithium ruthenate of Comparative Examples 1 and 2. The positive electrode active materials of Examples 1 to 6 and Comparative Example 2 are composed of a plurality of particles of 1 μm or less clumped together, while the lithium ruthenate of Comparative Example 1 is composed of one particle in which constituent particles of a clear shape exceeding 1 μm are linked together. It can be observed that the degree of particle clumping differs depending on the mixing ratio of the lithium ruthenate and lithium phosphate and the grinding conditions (number of revolutions) of the planetary ball mill.

[0068] 3-1 to 3-9 show the results of X-ray diffraction measurement for the phosphorus-containing lithium ruthenium-based composite oxides of Examples 1 to 6, the lithium ruthenate and lithium phosphate of Comparative Example 1, and the sample holder used in the X-ray diffraction measurement. It can be confirmed that the results of X-ray diffraction measurement for Examples 1 to 6 show profiles different from those of lithium ruthenate and lithium phosphate. In Examples 1 to 6, similar profiles are obtained except for the change in the peak near 22.1°. It can be seen that this peak near 22.1° changes depending on the mixture ratio of lithium phosphate in the phosphorus-containing lithium ruthenium-based composite oxide. In addition, from the profile of the sample holder in FIG. 3-9, the peaks near 16.8°, 18.2°, and 33.9° and the rise on the low angle side of 5° to 40° are thought to be due to the influence of the sample holder and the background during measurement. [Industrial Applicability]

[0069] According to the present invention, it is possible to obtain a positive electrode active material that has a higher discharge capacity than the positive electrode active material used in the conventional positive electrode for lithium ion secondary batteries and allows stable slurry preparation. This also makes it possible to provide a positive electrode for lithium ion secondary batteries with a high discharge capacity and a lithium ion secondary battery with a high energy density. Therefore, it is expected to be used in various fields where the use of secondary batteries is expanding, such as power sources for driving electric vehicles and drones, and portable electronic devices.

Claims

1. A phosphorus-containing lithium ruthenium composite oxide for a positive electrode of a lithium ion secondary battery, comprising: Li ２ RuO ３ and Li ３ P.O. ４ a molar ratio of the P atoms to the Ru atoms (P / Ru molar ratio) of 0.05 or more and 1.0 or less.

2. The phosphorus-containing lithium ruthenium composite oxide according to claim 1, having a particle diameter D10 of 0.47 μm or more and 1.0 μm or less.

3. (a) Li ３ P.O. ４ and Li ２ RuO ３ Li ２ RuO ３ Li for ３ P.O. ４ The molar ratio of (Li ３ P.O. ４ / Li ２ RuO ３ ) is in the range of 0.05 or more and 1.0 or less; (b) subjecting the mixture obtained in (a) to a dry grinding and mixing treatment in a dry air atmosphere at a temperature below the dew point; 3. A method for producing the phosphorus-containing lithium ruthenium-based composite oxide according to claim 1, comprising:

4. The method according to claim 3, wherein the dew point is −20° C.

5. (c) Before the step (a), Li ３ P.O. ４ and Li ２ RuO ３ drying the mixture at 110°C or higher for 15 hours or longer under a gauge pressure of -0.1 MPa or lower; The method of claim 3, comprising:

6. A positive electrode for a lithium ion secondary battery, comprising the phosphorus-containing lithium ruthenium composite oxide according to claim 1 or 2.

7. A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to claim 6.

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