Additive for lithium ion secondary battery positive electrode material, lithium ion secondary battery positive electrode material containing same, and lithium ion secondary battery

Abstract

The present invention addresses the problem of providing a novel additive for a positive electrode material capable of improving the performance of a lithium ion secondary battery, a lithium ion secondary battery positive electrode material including the same, and a lithium ion secondary battery. The improvement in performance refers to an increase in the performance of the lithium ion secondary battery when the positive electrode additive is added compared to when not added.　Provided are: an additive for a positive electrode material used in a nonaqueous electrolyte lithium ion secondary battery, the additive being a compound containing a rare earth element, boron, oxygen, and hydrogen, characterized in that the compound is amorphous; a lithium ion secondary battery positive electrode material including the same; and a lithium ion secondary battery.

Description

Additive for lithium ion secondary battery positive electrode material, lithium ion secondary battery positive electrode material containing the same, and lithium ion secondary battery

[0001] The present invention relates to an additive for a positive electrode material used in a lithium ion secondary battery, a positive electrode material for a lithium ion secondary battery containing the additive, and a lithium ion secondary battery.

[0002] In recent years, mobile information terminals such as mobile phones, laptops, and smartphones have rapidly become smaller and lighter, and lithium-ion secondary batteries, which are small, high-capacity sealed batteries, are widely used as their driving power sources.

[0003] Generally, a lithium ion secondary battery uses a negative electrode whose active material is a carbonaceous material or the like that can dope and dedop with lithium, and a positive electrode whose active material is a composite oxide of lithium and a transition metal oxide. The negative electrode and positive electrode current collectors are coated with the active material, respectively, and the electrodes are stacked with a separator between them, and then coated with an exterior material. Alternatively, the stacked electrodes are wound into a spiral shape and the resulting body is housed in a battery can.

[0004] To improve convenience, lithium-ion secondary batteries are required to have further improved performance. Typically, lithium-ion secondary batteries are required to be able to charge more quickly, have a larger discharge current, and have a longer life (maintain a high battery capacity even after repeated charge and discharge). To achieve this, various research and development efforts are being conducted.

[0005] Patent Document 1 relates to a nonaqueous electrolyte secondary battery using a positive electrode in which a composite oxide containing lithium and manganese is used as the positive electrode active material. Manganese elutes from the lithium manganate positive electrode active material, and various effects such as changes in the positive electrode active material, deposition of the eluted manganese on the negative electrode surface or separator, and deterioration of the electrolyte result in deterioration of the battery's cycle characteristics and a decrease in storage capacity. Patent Document 1 discloses that an oxide or carbonate of La or the like is included in the battery to reduce this manganese elution.

[0006] Patent Document 2 relates to a positive electrode active material for non-aqueous electrolyte secondary batteries, and aims to improve discharge performance at low temperatures. Specifically, it proposes a positive electrode active material in which a compound containing a rare earth element and silicic acid and / or boric acid is in contact with the surface of a lithium transition metal composite oxide. It discloses that the compound in contact with the surface reduces the activation energy for lithium ion acceptance between the lithium transition metal composite oxide and the electrolyte, improving ionic conductivity and thereby improving discharge performance at low temperatures.

[0007] Patent Document 3 relates to a positive electrode material for lithium-ion batteries, a manufacturing method thereof, and a lithium-ion battery, and aims to improve cycle characteristics. To that end, it proposes a manufacturing method for the positive electrode material, in which an additive is added to the starting materials, i.e., a Li raw material and a precursor containing Ni, Co, and Mn, and sintered at a temperature of 700°C or higher. It discloses that this increases the aspect ratio of the crystal grains of the positive electrode material, facilitating the insertion and extraction of lithium ions and improving cycle characteristics.

[0008] Japanese Patent Application Laid-Open No. 2000-311689 Japanese Patent No. 6233406 Special Publication No. 2023-515899

[0009] Although various research and development efforts have been made on lithium ion secondary batteries as described above, further improvements in performance are required.

[0010] The present invention aims to provide a novel cathode additive capable of improving the performance of lithium-ion secondary batteries, a lithium-ion secondary battery cathode material containing the same, and a lithium-ion secondary battery. Here, "improved performance" refers to the performance of a lithium-ion secondary battery improved when the cathode additive is added compared to when the cathode additive is not added. Specific examples of improved performance include an increase in discharge capacity during high-current discharge and suppression of an increase in internal resistance (impedance) after cycle testing.

[0011] In order to solve the above problems, the present inventors have conducted extensive research and have found that the performance of lithium ion secondary batteries can be improved by using a compound containing a rare earth element, boron, oxygen, and hydrogen as an additive for a positive electrode material used in lithium ion secondary batteries.

[0012] The present invention was completed based on these findings, and the gist of the invention is as follows.

[0013] (1) A cathode additive for use in a non-aqueous electrolyte lithium ion secondary battery, the cathode additive being a compound containing a rare earth element, boron, oxygen, and hydrogen, the compound being amorphous.

[0014] (2) The additive for a positive electrode material of a lithium ion secondary battery according to (1), characterized in that the molar ratio of the rare earth element to the boron is 85:15 to 10:90.

[0015] (3) The additive for a positive electrode material of a lithium ion secondary battery according to (1) or (2), characterized in that the mass loss rate measured by TG-DTA when the temperature is increased from 30°C to 1000°C at a temperature increase rate of 4°C / min is 3% or more and 35% or less.

[0016] (4) The additive for a positive electrode material of a lithium ion secondary battery according to any one of (1) to (3), characterized in that the rare earth element is one or more selected from the group consisting of yttrium, lanthanum, cerium, praseodymium, and neodymium.

[0017] (5) A positive electrode material for a lithium ion secondary battery, comprising the additive for a positive electrode material for a lithium ion secondary battery according to any one of (1) to (4) above, and a positive electrode active material.

[0018] (6) The positive electrode material for a lithium ion secondary battery according to (5), wherein the positive electrode active material contains at least one of nickel, cobalt, and manganese.

[0019] (7) A lithium ion secondary battery comprising the positive electrode material for lithium ion secondary batteries according to (5) above.

[0020] (8) A lithium ion secondary battery comprising the positive electrode material for lithium ion secondary batteries according to (6) above.

[0021] When the cathode additive of the present invention is added to a cathode material of a lithium ion secondary battery, the performance of the lithium ion secondary battery can be improved compared to when the additive is not added. Specifically, the performance improvement is an increase in capacity when the discharge voltage reaches 3.5 V during high-current discharge. The effects were compared for discharge capacity up to 3.5 V, which is the range of discharge voltage where the effect of voltage drop becomes clear. Furthermore, the increase in internal resistance (impedance) after cycle testing is suppressed.

[0022] FIG. 1 shows the peaks of the lanthanum boron complex compound in X-ray diffraction measurement (XRD, CuKα source). (Example 1)

[0023] Figure 2 shows the peaks of the hydroxyl group of the lanthanum-boron composite compound as measured by a Fourier transform infrared spectrophotometer (FT-IR). (Example 1) Figure 3 shows an example of comparing the internal resistance based on the size of the arc corresponding to the interfacial migration resistance of the positive electrode.

[0024] Hereinafter, embodiments of the present invention will be described in detail. These embodiments are merely examples of ways of carrying out the present invention, and should not be construed as limiting the present invention.

[0025] An additive for a positive electrode material of a lithium ion secondary battery, which is one embodiment of the present invention, is an additive for a positive electrode material used in a non-aqueous electrolyte lithium ion secondary battery, and is a compound containing a rare earth element, boron, oxygen, and hydrogen.

[0026] The positive electrode material of a lithium ion secondary battery is not particularly limited as long as it allows reversible insertion and release of lithium ions. Typical positive electrode materials include LiNiO ２ (lithium nickel oxide), LiCoO ２ (lithium cobalt oxide), LiMn ２ O ４ (lithium manganate), LiMn １－ｘ Fe ｘ P.O. ４ (lithium iron manganese phosphate) and composite materials thereof may also be used.

[0027] By adding the cathode material additive of this embodiment to the cathode material, various effects can be obtained, such as suppressing deterioration of the cathode material, improving ionic conductivity at the interface between the cathode material and the electrolyte, and extending the life of the lithium ion secondary battery, thereby improving the performance of the lithium ion secondary battery.

[0028] The cathode additive of this embodiment contains a rare earth element. A mixed solution containing a nonaqueous solvent, ethylene carbonate and diethyl carbonate, and a fluorine compound, such as a lithium salt, LiPF6 or LiBF4, may be used as an electrolyte for lithium-ion secondary batteries. The fluorine compound may react with moisture introduced from raw materials or moisture introduced during the battery manufacturing process to produce hydrofluoric acid. This acid may cause deterioration of the cathode material. The rare earth element contained in this embodiment is highly alkaline and therefore highly reactive with acidic substances. Therefore, the rare earth element reacts with hydrofluoric acid that may be produced in the electrolyte, resulting in the effect of suppressing deterioration of the cathode material.

[0029] The cathode additive of this embodiment contains boron, which reduces the activation energy for lithium ion acceptance between the cathode material and the electrolyte and improves ionic conductivity, thereby improving the performance of lithium ion secondary batteries.

[0030] The cathode additive of this embodiment contains oxygen. When the above-mentioned rare earth element or boron is added to the cathode material, it exists as a compound containing both of them and oxygen, a so-called composite oxide, rather than as they exist alone, and therefore has high stability. In a lithium ion secondary battery, it can exist stably even after repeated charge and discharge, and can achieve effects such as extending the life of the lithium ion secondary battery. In particular, by being a composite compound containing a rare earth element and boron, it is possible to enjoy the effects of both.

[0031] The additive for the positive electrode material of this embodiment contains hydrogen. Regarding the compound containing oxygen, a compound of boron and oxygen, so-called boron oxide (B ２ O ３) generally have high hygroscopicity. High hygroscopicity can lead to the introduction of moisture into the lithium-ion secondary battery, accelerating the deterioration of the lithium-ion secondary battery. Furthermore, boron oxide itself has poor pulverizability, making it difficult to microparticulate. The positive electrode additive of this embodiment is a compound containing hydrogen. That is, the compound is not a simple oxide but a complex compound containing hydrogen, and can also take the form of a hydroxide. This can suppress the hygroscopicity of the compound, thereby achieving effects such as extending the life of the lithium-ion secondary battery. Furthermore, in the manufacturing process of the lithium-ion secondary battery, there is also the advantage that the burden of moisture management, etc. can be reduced.

[0032] The hydrogen content of the compound can be confirmed by the following method. In the case of a compound containing hydrogen, Fourier transform infrared spectroscopy (FT-IR) shows a peak at 3750 to 2500 cm compared to a compound containing a hydroxyl group. -1 In the compound according to this embodiment, the inventors also observed a peak in the range of 3750 to 2500 cm -1 A peak was confirmed.

[0033] The FT-IR measurement was performed using a Shimadzu Fourier transform infrared spectrophotometer, IRTracer-100, in the wavenumber range of 7800 to 350 cm -1 Measurements were carried out.

[0034] The compound containing a rare earth element, boron, oxygen, and hydrogen, which is the additive for the positive electrode material of this embodiment, is amorphous.

[0035] Amorphous materials do not have a crystalline structure, and atoms are irregularly packed together, with fewer defects such as grain boundaries that hinder ion movement. Therefore, amorphous materials are more conducive to lithium ion diffusion than crystalline materials, so it is preferable for the additive to be an amorphous material.

[0036] The amorphous nature of the material can be confirmed by the following method. X-ray diffraction measurement (XRD, CuKα source) of an amorphous material results in an XRD pattern in which halo peaks, i.e., peaks attributable to crystalline materials, disappear and the background appears elevated, compared to a crystalline material. A similar XRD pattern was also confirmed for the compound according to this embodiment.

[0037] The X-ray diffraction measurement was carried out using an X-ray diffractometer MiniFlex 600 manufactured by Rigaku Corporation under the conditions of a step width of 0.01 deg, a scan speed of 2.0 deg / min, and a measurement speed angle.

[0038] According to one embodiment of the present invention, the molar ratio of rare earth element to boron in a compound serving as a cathode additive is preferably 85:15 to 10:90, more preferably 70:30 to 20:80, and even more preferably 50:50 to 30:70. The higher the molar ratio of rare earth element, the easier it is to react with acidic substances such as hydrofluoric acid, thereby enhancing the effect of suppressing deterioration of the cathode material. Furthermore, the higher the molar ratio of boron, the lower the activation energy for lithium ion acceptance between the cathode material and the electrolyte, improving ionic conductivity and thereby improving the performance of lithium-ion secondary batteries. However, excessively high molar ratios of either rare earth element or boron are undesirable because they result in the precipitation of lanthanum oxide or boric acid alone. Therefore, a composite compound with a molar ratio of rare earth element to boron of 85:15 to 10:90 is preferred. This allows the benefits of both elements to be enjoyed.

[0039] According to one embodiment of the present invention, the mass loss rate measured by TG-DTA when the cathode additive is heated from 30°C to 1000°C at a temperature increase rate of 4°C / min is 3% or more and 35% or less. The smaller the mass loss rate measured by TG-DTA, the higher the stability and the longer the life of the lithium-ion secondary battery. Typically, an increase in the internal resistance (impedance) of the battery after a cycle test is more likely to be suppressed. Preferably, the mass loss rate may be 32% or less, 30% or less, 25% or less, 20% or less, 17.5% or less, 15% or less, or 12% or less.

[0040] According to one embodiment of the present invention, the rare earth element contained in the compound serving as the cathode additive may be one or more selected from yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), and neodymium (Nd). The term "rare earth element" refers to a collective term for 17 elements: scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Generally, rare earth elements are known to have similar properties, and the rare earth element is not particularly limited in this embodiment of the present invention. On the other hand, since rare earth elements are scarce and have a low supply worldwide, one or more elements selected from yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), and neodymium (Nd) may be used in consideration of availability and cost.

[0041] Next, a method for producing an additive for a positive electrode of a lithium ion secondary battery, which is one embodiment of the present invention, will be described.

[0042] The additive for the positive electrode of a lithium ion secondary battery may be prepared by any method that can produce a compound that satisfies the requirements of the present invention. Examples include wet synthesis methods such as solid-state reaction, chemical vapor deposition, hydrothermal synthesis, and coprecipitation, as well as sol-gel and spray pyrolysis. An example of synthesis by a wet synthesis method is shown below.

[0043] First, the raw materials of the compounds contained in the additive are dissolved in water to prepare a raw material aqueous solution. Examples of the raw materials include water-soluble salts such as nitrates, oxides, chlorides, sulfates, and acetates. Specific examples of raw materials include boric acid as a boron source and nitrates of La, Pr, Sm, Nd, Gd, Yb, Ho, Ce, and Y as rare earth element sources. By dissolving these raw materials in water (preferably pure water or ion-exchanged water) at a predetermined molar ratio, an aqueous solution containing all the raw materials can be obtained. The dissolving and stirring methods are not particularly limited.

[0044] Next, a precipitant is added to the raw material aqueous solution to co-precipitate the compound raw materials, obtaining a precipitate (slurry). The precipitant, for example, controls the pH to a pH range in which rare earth element cations precipitate, and precipitation can be achieved by raising the pH (making it basic) by adding a basic compound such as ammonia water or hydroxides (NaOH, KOH, etc.). The resulting slurry is preferably heated to 70 to 90°C. The heating method is not particularly limited. Heating the slurry promotes olation and oxidation reactions in the precipitate. For example, the resulting slurry is heated to between 70 and 90°C and maintained at this temperature for 4 to 10 hours (aging). During the aging process, stirring operations commonly performed in the industry, such as stirring with a stirring blade or circulation using a pump, can also be performed, which is more preferable.

[0045] Alternatively, the raw aqueous solution may be heated and the precipitant added. Heating the raw aqueous solution changes the behavior of nucleation, which can change the aggregate structure of the precipitate.

[0046] The aged slurry is subjected to solid-liquid separation and washing. The means for the solid-liquid separation are not particularly limited, and industrially used equipment such as a centrifugal separator or a filter can be used. The washing operation is an operation for reducing nitride ions and chloride ions from the hydroxide slurry containing boric acid and rare earth element cations, which are the raw materials for the compound. For example, the hydroxide is dispersed in pure water, and then the washing operation is carried out using a centrifugal separator and a filter. This washing operation is preferably continued until the content of nitride ions and chloride ions in the hydroxide is reduced to 3% or less by mass.

[0047] The washed precipitate containing boric acid and rare earth element cations is then dried. The drying is carried out using an industrially used external heat or internal combustion drying device, for example, at a hot air or heater temperature of about 40 to 200°C. Spray drying can also be used. The drying yields a composite hydroxide containing boric acid and rare earth element cations, which is the raw material for the compound.

[0048] The composite hydroxide may optionally be subjected to heat treatment (sometimes referred to as calcination) at a higher temperature. Heat treatment (calcination) at a high temperature is expected to increase the stability of the compound and improve strength, and is therefore preferable. The conditions for the heat treatment (calcination) can be adjusted as appropriate. Typically, the lower limit of the heat treatment (calcination) temperature is equal to or higher than the drying temperature. From the viewpoint of obtaining the above-mentioned effects, a higher temperature is preferable, and the heat treatment (calcination) temperature may be 250°C or higher, or 300°C or higher. The upper limit of the heat treatment (calcination) temperature is not particularly limited as long as the amorphous nature of the composite hydroxide can be maintained. Typically, the upper limit may be 500°C or lower, 450°C or lower, or 400°C or lower. The heat treatment (calcination) time can be adjusted as appropriate to obtain the desired properties, and may typically be 1 hour or longer, preferably 3 hours or longer. Longer heat treatment (calcination) may saturate the obtained effects, so the heat treatment (calcination) may be limited to 5 hours or less. The atmosphere for the heat treatment (calcination) is not particularly limited and may be air or an inert atmosphere. The heat treatment (baking) may be performed on the compound alone or in a state where the compound is mixed with a positive electrode active material (as described below). The number of times the heat treatment (baking) is performed is not limited to one, and may be repeated multiple times as long as the amorphous state is maintained after the heat treatment (baking).

[0049] The composite hydroxide thus obtained may be pulverized to adjust the particle size as needed. The pulverization may be carried out using an industrially used pulverizing device such as a stamp mill, roller mill, jet mill, or ball mill, as long as the desired particle size can be adjusted.

[0050] The D50 (median diameter) of the secondary particles of the pulverized compound was measured using a wet particle size distribution measurement method. D50 is the particle diameter at which the cumulative volumetric frequency is 50%, and is also called the median diameter. The measurement method is as follows. The measurement sample is dispersed in an ethanol solvent and ultrasonically dispersed for 5 minutes using a US-300AT ultrasonic homogenizer manufactured by Nippon Seiki Seisakusho Co., Ltd. Next, D50 was measured using an MT3300 manufactured by Microtrac-Bell Corporation, assuming a particle refractive index of 2.17. From the perspective of obtaining a good mixture with the positive electrode active material, the particle diameter after pulverization should be D50 = 30 μm or less, preferably D50 = 10 μm or less, and more preferably D50 = 3 μm or less.

[0051] According to one embodiment of the present invention, there is provided a positive electrode material for lithium-ion secondary batteries. The positive electrode material includes the aforementioned additive for a positive electrode material for lithium-ion secondary batteries and a positive electrode active material. By adding the aforementioned additive for a positive electrode material for lithium-ion secondary batteries, which is one embodiment of the present invention, to a positive electrode material, it is possible to obtain effects such as suppressing deterioration of the positive electrode material, improving ionic conductivity at the interface between the positive electrode material and the electrolyte, and extending the life of the lithium-ion secondary battery, thereby improving the performance of the lithium-ion secondary battery.

[0052] The method of adding the additive to the positive electrode active material is not particularly limited, and the additive can be added to the positive electrode active material and mixed to obtain a positive electrode material. Addition and mixing can be performed using an industrial mixer such as a V-type mixer, a screw-type mixer, or an air mixer. Preferably, heat treatment is performed after mixing, and more preferably at 200 to 500°C. The heat treatment after mixing may also serve as heat treatment (firing) of the additive. From the viewpoint of improving adhesion between the additive and the positive electrode active material, heat treatment at 200°C or higher is preferred. Furthermore, from the viewpoint of maintaining the amorphous nature of the additive for lithium-ion secondary battery positive electrode material, heat treatment at 500°C or lower is preferred.

[0053] According to one embodiment of the present invention, the positive electrode active material may contain at least one of nickel, cobalt, and manganese. The positive electrode active material can be appropriately selected from known positive electrode active materials commonly used in lithium ion secondary batteries and all-solid-state batteries depending on the desired battery capacity, voltage, and characteristics. As the positive electrode active material, a material capable of absorbing and releasing lithium ions is usually used. From this perspective, the positive electrode active material may contain at least one of nickel, cobalt, and manganese. A typical positive electrode active material is lithium nickel oxide (LiNiO). ２ , lithium cobalt oxide LiCoO ２ , lithium manganese oxide LiMn ２ O ４ , lithium iron manganese phosphate LiMn １－ｘ Fe ｘ P.O. ４ , or lithium nickel oxide Li(Ni—Co—Mn)O, partially substituted with cobalt and manganese ２ may also be used.

[0054] Li(Ni-Co-Mn)O ２ is based on lithium nickel oxide, with a portion of the material replaced with cobalt and manganese, and is known as a ternary or NCM-based positive electrode active material. This is preferable because it can improve safety while reducing the amount of cobalt used, which is relatively expensive. Typically, the positive electrode active material is LiNi ０．５ Co ０．２ Mn ０．３ O ２ (NCM523) is an example.

[0055] According to one embodiment of the present invention, there is provided a lithium-ion secondary battery. The cathode material includes the aforementioned lithium-ion secondary battery cathode material. By including the aforementioned lithium-ion secondary battery cathode material according to one embodiment of the present invention, it is possible to obtain effects such as suppressing deterioration of the cathode material, improving ionic conductivity at the interface between the cathode material and the electrolyte, and extending the life of the lithium-ion secondary battery, thereby improving the performance of the lithium-ion secondary battery.

[0056] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0057] Example 1: Preparation of Cathode Additive. Ammonia water was added to a mixed solution of lanthanum nitrate aqueous solution and boric acid aqueous solution, adjusted to pH 7.0, and heated and stirred in a round-bottom flask at 80°C for 6 hours. The final La:B molar ratio was adjusted to 30:70. The precipitate was then removed from the heated slurry, washed with water, and dried at 60°C. The dried material was pulverized using a Jet Millco Jet System α-mkIV manufactured by Seishin Enterprise Co., Ltd. to obtain a lithium-ion secondary battery cathode additive with a particle size D50 = 1.8 μm. X-ray diffraction analysis of the product produced by this method confirmed its amorphous nature, as shown in Figure 1. Furthermore, this product was heated to 400°C in air and then subjected to X-ray diffraction analysis again; no peaks attributable to crystalline matter were detected, indicating its amorphous nature.

[0058] Preparation of Positive Electrode Active Material A composite hydroxide having a molar ratio of Ni:Mn:Co of 49:29:22 was used, and the total number of moles of Ni, Co, and Mn that can be contained in the composite hydroxide was set to M Ｔ As such, the M Ｔ The molar ratio of lithium to Ｔ The powder mixture was mixed with lithium carbonate so that the D50 was 1.05. The mixed powder was then fired in air at 870°C for 10 hours. Here, the particle diameter after firing was D50 = 5 μm, and the composition was Li １．０２ Ni ０．４８ Mn ０．２８ Co ０．２２ O ２ The molar ratio of the raw materials was adjusted so that

[0059] Preparation of Positive Electrode Composite Next, the additive obtained above was mixed with the positive electrode active material in a rocking mill manufactured by Seiwa Giken Co., Ltd. so that the amount of additive added was 1.0 mass % (amount of additive / total mass of positive electrode composite), and the mixture was heat-treated at 400° C. in air to obtain a positive electrode composite.

[0060] Battery Preparation The cathode mixture obtained above, acetylene black powder as a conductive material, and polyvinylidene fluoride (PVdF) as a binder (binding agent) were mixed in an N-methyl-2-pyrrolidone (NMP) solution in a mass ratio of 93:3.5:3.5 to prepare a cathode mixture slurry. The cathode mixture slurry was then applied to aluminum foil and dried at 140 ° C., after which the punched cathode was compressed at 28 MPa in a table press. The cathode was then vacuum dried at 120 ° C. to form a cathode plate, lithium metal foil was used as the anode, and 1 mol / L LiPF ６ The volume ratio of EC:DEC was 3:7, and a coin-type battery was assembled.

[0061] Example 2: Preparation of a positive electrode additive. Ammonia water was added to a mixed solution of lanthanum nitrate aqueous solution and boric acid aqueous solution, adjusted to pH 7.0, and heated and stirred in a round-bottom flask at 80°C for 6 hours. The final La:B molar ratio was adjusted to 30:70. The precipitate was then removed from the slurry after the heating reaction, washed with water, and dried at 60°C. The dried material was pulverized using a Jet Millco Jet System α-mkIV manufactured by Seishin Enterprise Co., Ltd. to obtain a positive electrode additive for lithium-ion secondary batteries with a particle size of D50 = 1.8 μm. This product was heated to 400°C in air and then subjected to X-ray diffraction analysis again. No peaks derived from crystalline materials were detected, indicating that the product was amorphous.

[0062] Preparation of Positive Electrode Active Material A composite hydroxide having a molar ratio of Ni:Mn:Co of 49:29:22 was used, and the total number of moles of Ni, Co, and Mn that can be contained in the composite hydroxide was set to M Ｔ As such, the M Ｔ The molar ratio of lithium to Ｔ The powder mixture was precisely mixed with lithium carbonate so that the sintering ratio was 1.05. The mixed powder was then fired at 870°C in air. １．０2 Ni ０．４８ Mn ０．２８ Co ０．２２ O ２ The molar ratio of the raw materials was adjusted so that

[0063] Next, the additive obtained above was mixed with the positive electrode active material in a rocking mill manufactured by Seiwa Giken Co., Ltd. so that the amount of additive added was 1.0 mass % (amount of additive / total amount of positive electrode composite), to obtain a positive electrode composite. The subsequent steps were the same as in Example 1, and a battery was fabricated.

[0064] Example 3: Preparation of Cathode Additive. Ammonia water was added to a mixed solution of lanthanum nitrate aqueous solution and boric acid aqueous solution, adjusted to pH 7.0, and heated and stirred in a round-bottom flask at 80°C for 6 hours. The final La:B molar ratio was adjusted to 10:90. The precipitate was then removed from the slurry after the heating reaction, washed with water, and dried at 60°C. The dried product was pulverized in a mortar and mortar using a Jet Millco Jet System α-mkIV manufactured by Seishin Enterprise Co., Ltd. to obtain a cathode additive for lithium-ion secondary batteries with a particle size D50 = 2.9 μm. This product was heated to 400°C in air and then subjected to X-ray diffraction analysis again. No peaks attributable to crystalline materials were detected, indicating an amorphous state. The following steps were repeated to fabricate a battery using the same procedure as in Example 1.

[0065] Example 4: Ammonia water was added to a mixed solution of lanthanum nitrate aqueous solution and boric acid aqueous solution, adjusted to pH 7.0, and heated and stirred in a round-bottom flask at 80°C for 6 hours. The final La:B molar ratio was adjusted to 50:50. The precipitate was then removed from the slurry after the heating reaction, washed with water, and dried at 60°C. The dried material was pulverized in a mortar and classified using a 45 μm mesh sieve to obtain an additive for a lithium-ion secondary battery cathode material with a particle size D50 = 18.3 μm. This product was heated to 400°C in air and then subjected to X-ray diffraction analysis again. No peaks attributable to crystalline materials were detected, indicating that the product was amorphous. The following steps were performed in the same manner as in Example 1 to fabricate a battery.

[0066] Example 5: Ammonia water was added to a mixed solution of lanthanum nitrate and boric acid solution, adjusted to pH 7.0, and heated and stirred in a round-bottom flask at 80°C for 6 hours. The final La:B molar ratio was adjusted to 80:20. The precipitate was then removed from the slurry after the heating reaction, washed with water, and dried at 60°C. The dried material was crushed in a mortar and classified using a 45 μm mesh sieve to obtain an additive with a particle size D50 = 19.0 μm. A battery was fabricated using the same process as in Example 1. This product was heated to 400°C in air and then subjected to X-ray diffraction analysis again. A slight peak due to crystalline lanthanum nitrate was detected, but the product was largely amorphous. A battery was fabricated using the same process as in Example 1.

[0067] Example 6: Ammonia water was added to a mixed solution of yttrium nitrate and boric acid solution, adjusted to pH 7.0, and heated and stirred at 80°C for 6 hours in a round-bottom flask. The final Y:B molar ratio was adjusted to 30:70. The precipitate was then removed from the slurry after the heating reaction, washed with water, and dried at 60°C. The dried material was pulverized in a mortar and classified using a 45 μm mesh sieve to obtain an additive with a particle size D50 = 17.0 μm. A battery was fabricated using the same process as in Example 1. This product was heated to 400°C in air and then subjected to X-ray diffraction analysis again. No peaks derived from crystalline materials were detected, indicating that the product was amorphous. A battery was fabricated using the same process as in Example 1.

[0068] Example 7: Ammonia water was added to a mixed solution of cerium nitrate and boric acid aqueous solution, adjusted to pH 7.0, and heated and stirred in a round-bottom flask at 80°C for 6 hours. The final molar ratio of Ce:B was adjusted to 30:70. The precipitate was then removed from the slurry after the heating reaction, washed with water, and dried at 60°C. The dried material was pulverized in a mortar and classified using a 45 μm mesh sieve to obtain an additive with a particle size D50 = 16.6 μm. A battery was fabricated using the same procedures as in Example 1. After heating this product to 400°C in air, X-ray diffraction was measured again, but no peaks attributable to crystalline matter were detected, indicating that the product was amorphous. A battery was fabricated using the same procedures as in Example 1.

[0069] Example 8: Ammonia water was added to a mixed solution of praseodymium nitrate and boric acid solution, the pH was adjusted to 7.0, and the mixture was heated and stirred at 80°C for 6 hours in a round-bottom flask. The final Pr:B molar ratio was adjusted to 30:70. The precipitate was then removed from the slurry after the heating reaction, washed with water, and dried at 60°C. The dried material was pulverized in a mortar and classified using a 45 μm mesh sieve to obtain an additive with a particle size D50 = 14.5 μm. A battery was fabricated using the same procedures as in Example 1. After heating this product to 400°C in air, X-ray diffraction was measured again, but no peaks attributable to crystalline materials were detected, indicating that the product was amorphous. A battery was fabricated using the same procedures as in Example 1.

[0070] Example 9: Ammonia water was added to a mixed solution of neodymium nitrate and boric acid aqueous solution, adjusted to pH 7.0, and heated and stirred in a round-bottom flask at 80°C for 6 hours. The final Nd:B molar ratio was adjusted to 30:70. The precipitate was then removed from the slurry after the heating reaction, washed with water, and dried at 60°C. The dried material was crushed in a mortar and classified using a 45 μm mesh sieve to obtain an additive with a particle size D50 = 14.6 μm. The following steps were repeated to fabricate a battery in the same manner as in Example 1. After heating this product to 400°C in air, X-ray diffraction measurements were performed again. No peaks attributed to crystalline lanthanum nitrate were detected, indicating that the product was amorphous. After heating this product to 400°C in air, X-ray diffraction measurements were performed again. A slight peak attributed to crystalline lanthanum nitrate was detected, but the product was largely amorphous. The following steps were repeated to fabricate a battery in the same manner as in Example 1.

[0071] (Comparative Example 1) Ammonia water was added to a mixed solution of lanthanum nitrate and boric acid aqueous solution to adjust the pH to 7.0, and the mixture was heated and stirred at 80°C for 6 hours in a round-bottom flask. At this time, the molar ratio of La:B in the finished product was adjusted to 30:70. Thereafter, a precipitate was taken out from the slurry after the heating reaction, washed with water, and then dried at 60°C. The dried product was pulverized in a mortar, classified using a sieve with 45 μm openings, and then calcined in air at 800°C to obtain crystalline LaBO having a particle size D50 of 8.1 μm. ３ and LaB ３ O ６A battery was fabricated in the same manner as in Example 2. The X-ray diffraction of the product fabricated in Comparative Example 1 was measured, and it was found that the compound was LaBO as shown in FIG. ３ and LaB ３ O ６ The presence of a peak confirmed that the material was crystalline.

[0072] Comparative Example 2 A battery was fabricated in the same manner as in Example 1, except that lanthanum oxide (manufactured by Jiangxi Jinshi Jiangxi Co., Ltd., D50=3 μm) was used as the positive electrode additive.

[0073] (Comparative Example 3) Boric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was pulverized using a fiber mixer MX-X701-T manufactured by Panasonic Corporation, and the pulverized material was classified using a sieve with a mesh size of 45 μm, and used as a positive electrode additive. The subsequent steps were the same as in Example 1, and a battery was fabricated.

[0074] Comparative Example 4 A battery was fabricated in the same manner as in Example 2, except that lanthanum oxide (manufactured by Jiangxi Jinshi Jiangxi Co., Ltd., D50=3 μm) was used as the positive electrode additive.

[0075] Comparative Example 5 Boric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was pulverized using a Panasonic fiber mixer MX-X701-T, and the pulverized material was sieved with a 45 μm mesh size sieve to be used as a positive electrode additive. The subsequent steps were the same as in Example 2 to fabricate a battery.

[0076] Comparative Example 6 A battery was fabricated in the same manner as in Example 2, except that no positive electrode additive was used.

[0077] The above battery was charged and discharged under the following conditions.

[0078] Battery Evaluation (Initial Activation, Rate Test) Evaluation of coin-type lithium secondary batteries was performed using an ELF1024 model charge / discharge device manufactured by Electrofield Corporation. A charge / discharge test was performed on the coin-type lithium secondary batteries in a thermostatic chamber at 25°C, with a reference rate of 150 mA / g at 1C, an upper limit of 4.2 V, and a lower limit voltage of 3.0 V. The prepared coin-type lithium secondary batteries were first placed in a thermostatic chamber at 25°C for 6 hours, after which initial activation was performed. Charging was performed at a rate of 30 mA / g (0.2C) with a constant current and voltage of 4.2 V, and charging was terminated when the current reached 2 mA / g. Discharging was performed at a rate of 30 mA / g (0.2C) with a lower limit voltage of 3.0 V. Initial activation was performed by repeating charge and discharge three times under these conditions. A 30-minute rest period was allowed after charging and discharging. Subsequently, charging was terminated when the current reached 2 mA / g at a rate of 30 mA / g and a constant current / voltage upper limit of 4.2 V, and discharge was terminated at a rate of 75 mA / g (0.5 C) with a discharge lower limit of 3.0 V, and charge and discharge were performed twice. After charging, a 30-minute pause was allowed after discharge. Then, charging was terminated when the current reached 2 mA / g at a rate of 30 mA / g and a constant current / voltage upper limit of 4.2 V, and discharge was terminated at a rate of 150 mA / g (1 C) with a discharge lower limit of 3.0 V, and charge and discharge were performed twice. After charging, a 30-minute pause was allowed after discharge. Then, charging was terminated when the current reached 2 mA / g at a rate of 30 mA / g and a constant current / voltage upper limit of 4.2 V, and discharge was terminated at a rate of 300 mA / g (2 C) with a discharge lower limit of 3.0 V, and charge and discharge were performed twice. After charging, a 30-minute pause was allowed after discharge. Thereafter, charging was terminated when the current reached 2 mA / g at a constant current / voltage rate of 30 mA / g and an upper limit of 4.2 V. Discharge was performed twice at a rate of 750 mA / g (5 C) with a lower limit discharge voltage of 3.0 V. The rest period after charging and discharging was 30 minutes. From the obtained charge / discharge test results, the discharge capacity (mAh / g) when the discharge voltage reached 3.5 V was calculated.

[0079] TG-DTA Measurement The mass reduction rate (%) of the positive electrode additives obtained in Examples 1 to 9 and Comparative Example 1 was measured by TG-DTA in the following manner.

[0080] A thermogravimetric analyzer STA2500 Regulus manufactured by Netsch was used, and nitrogen was introduced at 100 cm3 The sample was run at a flow rate of 1 / min and measured in an inert atmosphere from 30 to 1000°C at a temperature increase rate of 4°C / min. The mass loss rate (%) was calculated using the following formula: Mass loss rate (%) = [(Ml - M2) / Ml] x 100

[0081] As shown in Table 1, in a charge-discharge test of a coin-type lithium secondary battery, the positive electrodes using the rare earth element-boron composite compounds of Examples 1 to 9 as additives were compared to the positive electrodes using the additives of Comparative Examples 1 to 6. Although no significant difference was observed at 0.2 C to 1 C, the discharge capacity at a discharge voltage of 3.5 V was increased at 2 C to 5 C. Specific effects were 125 mAh / g or more at 2 C and 71 mAh / g or more at 5 C. This confirmed that the rate characteristics of lithium-ion secondary batteries were improved by the additives of one embodiment of the present invention. Furthermore, the positive electrode additives of Examples 1 to 9 exhibited a maximum mass loss rate (%) of 31.4% as measured by TG-DTA. This confirmed that the additives of one embodiment of the present invention have a certain degree of stability even in environments heated up to 1000°C.

[0082]

[0083] (Example 10) Preparation of Positive Electrode Additive Ammonia water was added to a mixed solution of lanthanum nitrate aqueous solution and boric acid aqueous solution, adjusted to pH 7.0, and heated and stirred in a round-bottom flask at 80°C for 6 hours. At this time, the molar ratio of the final La:B ratio was adjusted to 30:70. The precipitate was then removed from the slurry after the heating reaction, washed with water, and dried at 60°C. The dried material was pulverized using a Panasonic Fiber Mixer MX-X701-T, classified using a 1mm mesh sieve, and then heat-treated (calcined) at 400°C in air. The calcined material was pulverized using a Jet Millco Jet System α-mkIV manufactured by Seishin Enterprise Co., Ltd. to obtain a lithium-ion secondary battery positive electrode additive with a particle diameter of D50 = 2.3 μm. X-ray diffraction analysis of the product produced by this method confirmed that it was amorphous.

[0084] Preparation of Positive Electrode Active Material A composite hydroxide having a molar ratio of Ni:Mn:Co of 49:29:22 was used, and the total number of moles of Ni, Co, and Mn that can be contained in the composite hydroxide was set to M Ｔ As such, the M Ｔ The molar ratio of lithium to Ｔ The powder mixture was mixed with lithium carbonate so that the D50 was 1.05. The mixed powder was then fired in air at 870°C for 10 hours. Here, the particle diameter after firing was D50 = 5 μm, and the composition was Li １．０２ Ni ０．４８ Mn ０．２８ Co ０．２１ O ２ The molar ratio of the raw materials was adjusted so that

[0085] Preparation of Positive Electrode Composite Next, the additive obtained above was mixed with the positive electrode active material in a rocking mill manufactured by Seiwa Giken Co., Ltd. so that the amount of additive added was 1.0 mass % (amount of additive / total mass of positive electrode composite), and the mixture was heat-treated at 400° C. in air to obtain a positive electrode composite.

[0086] Battery Preparation The cathode mixture obtained above, acetylene black powder as a conductive material, and polyvinylidene fluoride (PVdF) as a binder (binding agent) were mixed in an N-methyl-2-pyrrolidone (NMP) solution in a mass ratio of 93:3.5:3.5 to prepare a cathode mixture slurry. The cathode mixture slurry was then applied to aluminum foil, dried at 140 ° C, and the punched cathode was compressed with a table press. The cathode was then vacuum dried at 120 ° C to form a cathode plate, lithium metal foil was used as the anode, and 1 mol / L LiPF ６ The volume ratio of EC to DEC was 3:7, and a coin-type battery was assembled.

[0087] Example 11: Preparation of Cathode Additive Ammonia water was added to a mixed solution of lanthanum nitrate aqueous solution and boric acid aqueous solution, adjusted to pH 7.0, and heated and stirred at 80°C for 6 hours in a round-bottom flask. The final La:B molar ratio was adjusted to 30:70. The precipitate was then removed from the slurry after the heating reaction, washed with water, and dried at 60°C. The dried material was then pulverized using a Panasonic Fiber Mixer MX-X701-T and classified using a 1mm mesh sieve. The dried material was then pulverized using a Seishin Enterprise Jet Millco Jet System α-mkIV to obtain a lithium-ion secondary battery cathode additive with a particle size of D50 = 1.5 μm. X-ray diffraction analysis of the product produced by this method confirmed that it was amorphous. The following steps were performed in the same manner as in Example 10 to prepare a battery.

[0088] Example 12 A battery was fabricated in the same manner as in Example 10, except that the positive electrode mixture was obtained without being subjected to heat treatment at 400° C. in air.

[0089] (Comparative Example 7) Ammonia water was added to a mixed solution of lanthanum nitrate and boric acid aqueous solution, the pH was adjusted to 7.0, and the mixture was heated and stirred at 80°C for 6 hours using a round-bottom flask. At this time, the molar ratio of the finished La:B ratio was adjusted to 30:70. Thereafter, the precipitate was removed from the slurry after the heating reaction, washed with water, and then dried at 60°C. The dried product was pulverized using a fiber mixer MX-X701-T manufactured by Panasonic Corporation, classified using a sieve with 1 mm openings, and then calcined at 800°C in air. Thereafter, the calcined product was pulverized using a Jet Millco Jet System α-mkIV manufactured by Seishin Enterprise Co., Ltd., to obtain LaBO having a particle size of D50 = 2.6 μm. ３ and LaB ３ O ６ A battery was fabricated in the same manner as in Example 10. The X-ray diffraction of the product fabricated in Comparative Example 7 was measured, and it was found that LaBO ３ and LaB ３ O ６ The presence of a peak confirmed that the material was crystalline.

[0090] Comparative Example 8 A battery was fabricated in the same manner as in Comparative Example 7, except that the positive electrode mixture was obtained without being subjected to heat treatment at 400° C. in air.

[0091] Comparative Example 9 A battery was fabricated in the same manner as in Example 10, except that no positive electrode additive was used.

[0092] The above battery was charged and discharged under the following conditions.

[0093] Cycle Test After initial activation and rate testing, a cycle test was performed. The coin-type lithium secondary battery was left standing in a thermostatic chamber at 45°C for 6 hours. Charging was performed at a rate of 75 mA / g (0.5C) with a constant current and voltage upper limit of 4.25V, and charging was terminated when the current reached 2 mA / g. Discharging was performed at a rate of 75 mA / g (0.5C) with a lower discharge voltage limit of 3.0V. The rest period after charging and discharging was 0 minutes. Under these conditions, charging and discharging were repeated 100 times.

[0094] Impedance Measurement The battery that had undergone 100 charge / discharge cycles was charged to half of the charge capacity at 100 cycles at a rate of 75 mA / g (0.5 C) in a thermostatic chamber at 25 ° C., and the charge rate (State of Charge, SOC) was set to 50%. Then, the internal resistance (impedance) was measured using a Biologic VSP model electrochemical measurement system in a thermostatic chamber at 25 ° C. The starting frequency was 200 kHz, the ending frequency was 10 mHz, and the sine wave amplitude was 10.0 mV. Measurements were repeated twice for each measurement frequency, and the average value was obtained. As shown in Figure 3, the internal resistance was compared based on the size of the arc corresponding to the interfacial migration resistance of the positive electrode.

[0095] TG-DTA Measurement The mass reduction rate (%) of the positive electrode additives obtained in Examples 10 to 12 and Comparative Examples 7 and 8 was measured by TG-DTA in the same manner as described above.

[0096] As shown in Table 2, the positive electrodes using the lanthanum boron composite compounds of Examples 10 to 12 as additives had lower internal resistance (impedance) after the multi-cycle charge-discharge test of the coin-type lithium secondary battery compared to the positive electrodes using the additives of Comparative Examples 7 to 9. This confirms that the additive of one embodiment of the present invention can suppress an increase in internal resistance (impedance) after multi-cycle charge-discharge of a lithium ion secondary battery, thereby contributing to extending the life of the lithium ion secondary battery.

[0097]

Claims

1. A cathode additive for use in non-aqueous electrolyte lithium-ion secondary batteries, the cathode additive being a compound containing a rare earth element, boron, oxygen, and hydrogen, characterized in that the compound is amorphous.

2. The additive for a positive electrode material of a lithium ion secondary battery according to claim 1, wherein the molar ratio of the rare earth element to the boron is 85:15 to 10:

90.

3. The additive for a positive electrode material of a lithium ion secondary battery according to claim 1, characterized in that the mass loss rate (%) measured by TG-DTA when heated from 30°C to 1000°C at a temperature increase rate of 4°C / min is 3% or more and 35% or less.

4. The additive for a positive electrode material of a lithium ion secondary battery according to claim 1, characterized in that the rare earth element is one or more elements selected from the group consisting of yttrium, lanthanum, cerium, praseodymium, and neodymium.

5. A positive electrode material for a lithium ion secondary battery, comprising the additive for a positive electrode material for a lithium ion secondary battery according to any one of claims 1 to 4, and a positive electrode active material.

6. The positive electrode material for a lithium ion secondary battery according to claim 5, wherein the positive electrode active material contains at least one of nickel, cobalt, and manganese.

7. A lithium ion secondary battery comprising the positive electrode material for lithium ion secondary batteries according to claim 5.

8. A lithium ion secondary battery comprising the positive electrode material for lithium ion secondary batteries according to claim 6.

Images