Positive electrode active material

Abstract

Provided is a positive electrode active material having a layered rock salt structure and having a higher initial charge capacity than conventional positive electrode active materials. The positive electrode active material is formed by adding an additive containing a boron element to a lithium composite oxide having a layered rock salt structure represented by Li2Mn1-xNixO3 (0 < = x < 1) or a precursor of the lithium composite oxide, so that the amount of boron is more than 0.00075 equivalents and 0.2 equivalents or less relative to the total 1 equivalents of Mn and Ni in the lithium composite oxide, and then heating and sintering.

Description

Technical Field

[0001] This invention relates to positive electrode active materials. Background Technology

[0002] In recent years, the demand for lithium-ion rechargeable batteries has further increased due to their applications in electric vehicles, large-scale energy storage systems, and equipment requiring high energy density.

[0003] Therefore, lithium-rich nickel-manganese oxides with layered structures that can exhibit high capacity have attracted attention (e.g., Patent Document 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2011-129269 Summary of the Invention

[0007] However, the lithium-rich nickel-manganese oxide in Patent Document 1 has a small initial charging capacity. In order to achieve the target high capacity, it needs to be activated by repeated charge-discharge cycles of about dozens of times, leaving room for further improvement.

[0008] Therefore, the purpose of this invention is to provide a positive electrode active material with a layered rock salt structure and a larger initial charging capacity than in the past.

[0009] One solution of the present invention to solve the above-mentioned problems is a positive electrode active material, which is a positive electrode active material in Li2Mn 1－x Ni x The lithium composite oxide with a layered rock salt structure represented by O3 (0≤x<1) or the precursor of the above lithium composite oxide is made by adding an additive containing boron, such that the boron content relative to the total Mn and Ni of the above lithium composite oxide is greater than 0.00075 equivalents and less than 0.2 equivalents, and then sintering it by heating.

[0010] The term "precursor to lithium complex oxides" refers to substances produced before the formation of lithium complex oxides.

[0011] According to this scheme, since an additive containing boron is added to the lithium composite oxide or the precursor of the lithium composite oxide, the amount of boron relative to the total Mn and Ni of the above-mentioned lithium composite oxide is greater than 0.00075 equivalents and less than 0.2 equivalents, thus forming a structure with a layered rock salt type, the initial charging capacity is greater than before.

[0012] A preferred embodiment is to add the above-mentioned additive to the above-mentioned lithium composite oxide or the precursor of the above-mentioned lithium composite oxide, such that the boron content is 0.005 equivalent to 0.1 equivalent relative to the total Mn and Ni of the above-mentioned lithium composite oxide, and then heat and sinter it.

[0013] The preferred method is to heat and sinter the material at a temperature above 850°C.

[0014] The preferred embodiment is that the charging curve of the lithium metal reference voltage relative to the charging capacity during the initial constant current charging at a current density of 10 mA / g has a peak value in the range of 4.7V to 4.8V.

[0015] The preferred approach is to charge the battery with a constant current density of 10 mA / g until it reaches 4.8V under the lithium metal reference, and then charge it with a constant voltage while maintaining the lithium metal reference of 4.8V until the current density decays to 1 mA / g. At this point, the initial charge capacity per 1g is more than 250mAh / g.

[0016] The preferred method is to charge the lithium metal reference to 4.8V at a constant current density of 10mA / g, charge it to 4.8V at the lithium metal reference, charge it to 1mA / g at a constant voltage while maintaining the lithium metal reference, and then discharge it to 2.0V at the lithium metal reference at a constant current density of 10mA / g. At this time, the initial discharge capacity per 1g is more than 150mAh / g.

[0017] A preferred embodiment is that, after 10 charge-discharge cycles, the discharge capacity per 1g in the 10th discharge action is less than 1.5 times the discharge capacity per 1g in the first discharge action. The charge-discharge cycle consists of a charging action and a discharging action. The charging action involves charging with a constant current density of 10mA / g until reaching 4.8V under the lithium metal reference, and then charging with a constant voltage while maintaining the 4.8V under the lithium metal reference until the current density decreases to 1mA / g. The discharging action involves discharging with a constant current density of 10mA / g until reaching 2.0V under the lithium metal reference.

[0018] The preferred embodiment is that the above-mentioned additive contains lithium tetraborate.

[0019] In a preferred embodiment, a portion of Mn and / or Ni in the aforementioned lithium composite oxide is replaced by boron.

[0020] A preferred embodiment is that a boron compound is attached to the aforementioned lithium composite oxide.

[0021] As long as the above solutions are included within the technical scope of this invention, they can be subordinate to each other, refer to a part of the structure, or replace a part of the structure.

[0022] The positive electrode active material according to the present invention has a larger initial charging capacity than in the past, even though it has a layered rock salt structure. Attached Figure Description

[0023] Figure 1 This is a schematic representation of a cross-section of a lithium-ion secondary battery according to the first embodiment of the present invention.

[0024] Figure 2 The graphs are shown to represent the charge-discharge curves of Example 1 and Comparative Example 1 of the present invention. (a) shows the charge-discharge curve of Example 1, and (b) shows the charge-discharge curve of Comparative Example 1. Detailed Implementation

[0025] The embodiments of the present invention will now be described in detail.

[0026] like Figure 1 As shown, the lithium-ion secondary battery 1 of the first embodiment of the present invention includes a positive electrode 2, a negative electrode 3, an electrolyte 5 and a separator 6, and an external load 7 can be connected to the positive electrode 2 and the negative electrode 3.

[0027] like Figure 1 As shown, the positive electrode 2 is obtained by stacking a positive electrode active material layer 11 on the positive electrode current collector 10, and is an intercalation electrode in which lithium ions can be inserted and detached.

[0028] The positive electrode active material layer 11 has a positive electrode active material 20, a conductive additive, and a binder.

[0029] The negative electrode 3 is obtained by stacking a negative electrode active material layer 13 on the negative electrode current collector 12, and is an intercalation electrode in which lithium ions can be inserted and detached.

[0030] The negative electrode active material layer 13 contains negative electrode active material 21, conductive additives, and binders.

[0031] like Figure 1 As shown in the enlarged view, the positive electrode active material 20 is a coated positive electrode active material on the surface of the oxide active material 30 with a coating layer 31.

[0032] <Oxide Active Substance 30>

[0033] The oxide active material 30 is preferably a lithium-ion conductive active material, and the average potential for lithium desorption and insertion relative to the deposition potential of Li (also expressed as vs. Li) + The operating potential of the oxide active material 30 is preferably 4.5V to 5.0V based on elemental lithium metal.

[0034] The potential (hereinafter also referred to as voltage) for lithium-ion insertion and deintercalation reactions (vs. Li + For example, the voltage at the beginning and end of a plateau can be determined by measuring the charge-discharge characteristics of a half-cell using an oxide active material 30 as the working electrode and lithium metal as the counter electrode. When there are two or more plateaus, the lowest plateau voltage is 4.5V (vs. Li). + / Li) or above is acceptable, with the highest voltage plateau being 5.0V (vs. Li) + The following is acceptable: / Li)

[0035] The oxide active material 30 has a layered rock salt type crystal structure represented by the following formula (1), and uses lithium-rich lithium manganese nickel oxide as the basic framework.

[0036] Li2Mn 1－x Ni x O3(0≤x<1)···(1)

[0037] The oxide active material 30 is preferably a layered rock salt type lithium manganese nickel oxide in which a portion of the positions are replaced by boron, and more preferably it is composed of a layered rock salt type lithium manganese nickel boron oxide represented by the following formula (2).

[0038] Li 2+y Mn 1－x Ni x－y B y O 3－ x + 2y···(2)

[0039] (In the formula, 0<x<1, 0<y<1, 0≤x-y<1.)

[0040] <Covering layer 31>

[0041] The coating layer 31 preferably contains at least boron and is composed of boron oxide or lithium boron compound.

[0042] <Negative Electrode Active Material 21>

[0043] There are no particular limitations on the negative electrode active material 21; for example, lithium titanate can be used.

[0044] <Conductive additives>

[0045] There are no particular limitations on the conductive additives used in the positive electrode active material layer 11 and / or the negative electrode active material layer 13, but carbon materials are preferred.

[0046] The carbon material is preferably selected from at least one of natural graphite, artificial graphite, vapor-grown carbon fiber, carbon nanotubes, acetylene black, Ketjen black and furnace black.

[0047] The amount of conductive additive contained in the positive electrode active material layer 11 is preferably 1 to 30 parts by weight relative to 100 parts by weight of the positive electrode active material 20.

[0048] The amount of conductive additive contained in the negative electrode active material layer 13 is preferably 1 to 30 parts by weight relative to 100 parts by weight of negative electrode active material 21.

[0049] If it falls within the above range, it can ensure the conductivity of the active material layers 11 and 13, maintain the adhesion to the adhesive, and fully obtain the adhesion to the current collectors 10 and 12.

[0050] <Adhesive>

[0051] The adhesive used in the positive electrode active material layer 11 and / or the negative electrode active material layer 13 is not particularly limited. For either of the active material layers 11 and 13, at least one selected from polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber, polyimide and their derivatives can be used.

[0052] The amount of binder contained in the positive electrode active material layer 11 is preferably 1 to 30 parts by weight relative to 100 parts by weight of the positive electrode active material 20.

[0053] The amount of binder contained in the negative electrode active material layer 13 is preferably 1 to 30 parts by weight relative to 100 parts by weight of negative electrode active material 21.

[0054] If it falls within the above range, the adhesion between the active materials 20 and 21 and the conductive additives can be maintained, and sufficient adhesion with the current collectors 10 and 12 can be obtained.

[0055] <Current collectors 10, 12>

[0056] The current collectors 10 and 12 are not particularly limited, but aluminum or aluminum alloys are preferred given their stability under both positive and negative electrode reaction atmospheres.

[0057] Current collectors 10 and 12 can also be current collectors obtained by coating the surface of metals other than aluminum (copper, SUS, nickel, titanium and their alloys) with metals that do not react at the potential of positive electrode 2 and negative electrode 3.

[0058] <Electrolyte 5>

[0059] Electrolyte 5 is not particularly limited as long as it has lithium-ion conductivity. It can be a non-aqueous electrolyte in which the solute is dissolved in a non-aqueous solvent, or a gel electrolyte obtained by impregnating a polymer with a non-aqueous electrolyte in which the solute is dissolved in a non-aqueous solvent. Electrolyte 5 can be in solid form or a solid electrolyte.

[0060] Electrolyte 5 can be pre-included in positive electrode 2, negative electrode 3 and separator 6, or it can be added after the separator 6 is arranged between positive electrode 2 and negative electrode 3 and then wound or stacked.

[0061] <Isolation Component 6>

[0062] The separator 6 only needs to be an insulating structure that is placed between the positive electrode 2 and the negative electrode 3 and can contain the electrolyte 5.

[0063] Examples of insulating materials 6 include nylon, cellulose, polysulfone, polyethylene, polypropylene, polybutene, polyacrylonitrile, polyimide, polyamide, polyethylene terephthalate, and fabrics, nonwovens, microporous membranes, etc., made of two or more of these materials.

[0064] The separator 6 may also contain various plasticizers, antioxidants, flame retardants, or be coated with metal oxides, etc.

[0065] Next, the manufacturing method of the lithium-ion secondary battery 1 according to this embodiment will be described.

[0066] The manufacturing method of the lithium-ion secondary battery 1 in this embodiment mainly consists of an active material forming process for forming a positive electrode active material 20, a positive electrode forming process for forming a positive electrode 2, a negative electrode forming process for forming a negative electrode 3, and a secondary battery assembly process for assembling the positive electrode 2, the negative electrode 3 and the electrolyte 5. The negative electrode forming process and the secondary battery assembly process are the same as conventional processes, so the description is omitted.

[0067] <Active Substance Formation Process>

[0068] The active substance formation process consists of a mixing process and a heating process.

[0069] (Mixed Process)

[0070] The mixing process is a process of mixing additives containing boron into lithium composite oxides or lithium composite oxide precursors to form a mixture.

[0071] The lithium composite oxide used in the mixing process is a lithium-rich lithium manganese nickel oxide that is a precursor of oxide active material 30 and has a layered rock salt-type crystal structure represented by the following formula (3).

[0072] Li2Mn 1－x Ni x O3(0≤x<1)···(3)

[0073] In addition, the precursor of the lithium composite oxide used in the mixing process is the precursor of the manganese nickel oxide represented by the above formula (3) and includes lithium material containing lithium, manganese material containing manganese and nickel material containing nickel.

[0074] Lithium materials can be made as long as they contain lithium; there are no special restrictions. For example, lithium carbonate and lithium hydroxide can be used.

[0075] Manganese materials can be any materials that contain manganese; there are no special restrictions. For example, manganese oxide, manganese carbonate, and manganese sulfate can be used.

[0076] Nickel materials can be made as long as they contain nickel; there are no special restrictions. For example, nickel oxide and nickel sulfate can be used.

[0077] It should be noted that the precursor for lithium composite oxides can also be a manganese-nickel material containing manganese and nickel elements, instead of manganese and nickel materials.

[0078] The additives used in the mixing process can be any additives containing boron, without any particular restrictions. For example, lithium tetraborate (Li2B4O7) can be used.

[0079] The amount of additives added in the mixing process is such that the amount of boron in the additive is greater than 0.00075 equivalents and less than 0.2 equivalents relative to the total Mn and Ni of the lithium composite oxide, preferably 0.0005 equivalents to 0.1 equivalents.

[0080] (Heating process)

[0081] The heating process is a process in which the mixture obtained in the mixing process is heated in an oxygen atmosphere to form the positive electrode active material 20.

[0082] The heating temperature in the heating process is the sintering temperature of the mixture, which is above 850℃.

[0083] The heating temperature in the heating process can be set appropriately according to the heating time, but it is preferably below 1200°C.

[0084] The heating time in the heating process can be set appropriately according to the heating temperature, preferably 6 hours or more, and more preferably 10 hours or more.

[0085] The heating time in the heating process is preferably less than 48 hours, more preferably less than 36 hours, and even more preferably less than 24 hours.

[0086] <Positive electrode formation process>

[0087] The positive electrode formation process consists of a positive electrode coating process and a positive electrode drying process.

[0088] (Positive electrode coating process)

[0089] The positive electrode coating process is a process of mixing the positive electrode active material 20 obtained through the active material formation process with conductive additives and binders to make a positive electrode mixture, and then coating the positive electrode mixture onto the positive electrode current collector 10.

[0090] For ease of fabrication of the positive electrode 2 and the negative electrode 3, the adhesive used in the positive electrode coating process is preferably dissolved or dispersed in a non-aqueous solvent or in water.

[0091] Non-aqueous solvents are not particularly limited, but examples include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate, and tetrahydrofuran. Dispersants and thickeners may also be added to these.

[0092] (Positive electrode drying process)

[0093] The positive electrode drying process is a process of drying the positive electrode current collector 10, which has been coated with positive electrode agent in the positive electrode coating process, to form the positive electrode 2.

[0094] The positive electrode 2 formed by the above positive electrode formation process is assembled together with the negative electrode 3 formed by the negative electrode formation process in the same way as before and the electrolyte 5 to complete the lithium-ion secondary battery 1.

[0095] Next, the physical properties of the positive electrode 2 used in the lithium-ion secondary battery 1 of this embodiment during charging and discharging will be explained.

[0096] It should be noted that the following physical properties are described in the case of alternating charging and discharging operations at 25°C in an inactive gas atmosphere: the charging operation involves charging with a constant current density of 10 mA / g to reach 4.8V based on lithium metal, and then charging with a constant voltage while maintaining 4.8V based on lithium metal until the current density decreases to 1 mA / g; the discharging operation involves discharging with a constant current density of 10 mA / g to 2.0V based on lithium metal. Furthermore, the charging and discharging process begins with a charging operation, and one charging operation and one discharging operation are combined to constitute one cycle.

[0097] For the positive electrode 2, during the first charging operation, the charging curve representing the lithium metal reference voltage relative to the charging capacity preferably has a peak value in the range of 4.7V to 4.8V.

[0098] For the positive electrode 2, during the first charging operation, the charging capacity of each 1g of positive electrode active material 20 is preferably 250mAh / g or more, and particularly preferably 280mAh / g or more.

[0099] For the positive electrode 2, in the first discharge operation, the discharge capacity of each 1g of positive electrode active material 20 is preferably 150mAh / g or more, and more preferably 170mAh / g or more.

[0100] For the positive electrode 2, when two charge-discharge cycles have been performed, the charging capacity of 1g of positive electrode active material 20 in the second charging operation is preferably 0.75 times or less than the charging capacity of 1g of positive electrode active material 20 in the first charging operation.

[0101] For the positive electrode 2, when two charge-discharge cycles have been performed, in the second charging operation, the charging capacity of each 1g of positive electrode active material 20 is preferably 0.5 times or more, more preferably 0.55 times or more, relative to the charging capacity of each 1g of positive electrode active material 20 in the first charging operation.

[0102] For the positive electrode 2, when two charge-discharge cycles have been performed, in the second discharge operation, the discharge capacity of each 1g of positive electrode active material 20 is preferably 1.2 times or less, more preferably 1.15 times or less, compared with the discharge capacity of each 1g of positive electrode active material 20 in the first discharge operation.

[0103] For the positive electrode 2, during two charge-discharge cycles, in the second discharge operation, the discharge capacity of each 1g of positive electrode active material 20 is preferably 0.8 times or more, more preferably 0.9 times or more, and even more preferably 1 times or more.

[0104] For the positive electrode 2, when 10 charge-discharge cycles have been performed, the charging capacity of 1g of positive electrode active material 20 in the 10th charging operation is preferably 0.85 times or less than the charging capacity of 1g of positive electrode active material 20 in the first charging operation.

[0105] For the positive electrode 2, when 10 charge-discharge cycles have been performed, the charging capacity of 1g of positive electrode active material 20 in the 10th charging operation is preferably 0.5 times or more, more preferably 0.55 times or more, relative to the charging capacity of 1g of positive electrode active material 20 in the first charging operation.

[0106] For the positive electrode 2, when 10 charge-discharge cycles have been performed, in the 10th discharge operation, the discharge capacity of each 1g of positive electrode active material 20 is preferably 1.5 times or less, more preferably 1.3 times or less, and even more preferably 1.2 times or less, relative to the discharge capacity of each 1g of positive electrode active material 20 in the first discharge operation.

[0107] For the positive electrode 2, when 10 charge-discharge cycles have been performed, in the 10th discharge operation, the discharge capacity of each 1g of positive electrode active material 20 is preferably 0.8 times or more, more preferably 0.9 times or more, and even more preferably 1 times or more.

[0108] According to the positive electrode active material 20 of this embodiment, since an additive containing boron is added to the lithium composite oxide or the precursor of the lithium composite oxide, the amount of boron relative to the total Mn and Ni of the lithium composite oxide is greater than 0.00075 equivalents and less than 0.2 equivalents. Therefore, even if it has a layered rock salt type structure, the initial charging capacity is greater than that of the past.

[0109] Furthermore, according to the positive electrode active material 20 of this embodiment, an additive containing boron is added to a layered rock-salt type lithium composite oxide or a precursor of a lithium composite oxide, such that the amount of boron relative to the total Mn and Ni of the aforementioned lithium composite oxide is greater than 0.00075 equivalents and less than 0.2 equivalents, and the material is calcined at a temperature of 850°C or higher. Therefore, compared to a layered rock-salt type lithium composite oxide without additives and a layered rock-salt type lithium composite oxide with a small amount of additives (less than 0.00075 equivalents), it has high charge and discharge capacity, approaches a stable state during the second charging cycle, and achieves a discharge capacity close to that of the stable state during the charge and discharge cycles following the second charging cycle.

[0110] In the above embodiments, the positive electrode active material 20 is coated with a coating layer 31 on the surface of the oxide active material 30, but the present invention is not limited thereto. The positive electrode active material 20 may also not be coated with a coating layer 31 on the surface of the oxide active material 30.

[0111] In the above embodiment, a separator 6 is sandwiched between the positive electrode 2 and the negative electrode 3, but the present invention is not limited thereto. If the electrolyte 5 is a solid electrolyte, the separator 6 may not be provided.

[0112] As long as the above embodiments are included within the technical scope of the present invention, the constituent components can be freely replaced or added between the embodiments.

[0113] Example

[0114] The present invention will now be specifically described with reference to embodiments. It should be noted that the present invention is not limited to the following embodiments and may be implemented with appropriate modifications without altering its essential principles.

[0115] (Example 1)

[0116] First, weigh 20 g of Ni / Mn intermediate (manufactured by Tosoh Corporation, Ni:Mn = 1:3), 14.04 g (188.13 mmol), and 0.0697 g (0.4121 mmol) of lithium tetraborate (manufactured by Tokyo Chemical Industry Co., Ltd.), and mix them in an automatic mortar for 60 minutes to form a mixed powder. Specifically, the mixture was prepared such that the amount of boron relative to the total equivalent of Mn and Ni was 0.0075 equivalents.

[0117] Next, the mixed powder was filled into an alumina sintering container and heated at 900°C for 12 hours in an air atmosphere using a muffle furnace (manufactured by Yamato Scientific Co., Ltd., FP411). Then, it was allowed to cool naturally inside the furnace to obtain the positive electrode active material of lithium nickel manganese oxide.

[0118] Next, a slurry is prepared by dispersing a mixture of the obtained positive electrode active material, acetylene black as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder, comprising 88 parts by weight, 6 parts by weight, and 6 parts by weight respectively based on the solid content concentration, in N-methyl-2-pyrrolidone (NMP).

[0119] It should be noted that the above-mentioned adhesive is an adhesive solution of N-methyl-2-pyrrolidone (NMP) with a solid component concentration of 5% by weight. To facilitate the coating process described later, NMP was further added to adjust the viscosity.

[0120] The above slurry was coated onto a 15 μm aluminum foil, dried in an oven at 120°C, and then further vacuum dried at 170°C to produce a positive electrode, which was used as Example 1.

[0121] (Example 2)

[0122] In Example 1, lithium tetraborate was mixed to make the amount of boron 0.0375 equivalents relative to the total amount of Mn and Ni when forming the mixed powder, and otherwise the same procedure was followed. This is referred to as Example 2.

[0123] (Example 3)

[0124] In Example 1, when forming the mixed powder, lithium tetraborate was mixed so that the amount of boron was 0.075 equivalents relative to the total of Mn and Ni, and otherwise the same procedure was followed. This is referred to as Example 3.

[0125] (Comparative Example 1)

[0126] In Example 1, lithium tetraborate was not added, but otherwise the same procedure was followed as Comparative Example 1. That is, in Comparative Example 1, the amount of boron relative to the total 1 equivalent of Mn and Ni was 0.

[0127] (Comparative Example 2)

[0128] In Example 1, lithium tetraborate was mixed to make the amount of boron 0.00075 equivalents relative to the total amount of Mn and Ni when forming the mixed powder, and otherwise the same procedure was followed. This was used as Comparative Example 2.

[0129] (Cyclic performance evaluation)

[0130] Inside the glove box, the positive electrode of Example 1 and Comparative Example 1 was used as the working electrode, and lithium metal was used as the counter electrode. These electrodes were stacked in sequence as positive electrode / separator / lithium metal and arranged in the test cell. A non-aqueous electrolyte (ethylene carbonate / propylene carbonate / ethyl methyl carbonate = 15 / 15 / 70 (volume ratio), lithium hexafluorophosphate LiPF6: 1 mol / L) was added to the test cell to make a half cell.

[0131] The manufactured half-cell is connected to a charging and discharging device (manufactured by Hokuto Electric Co., Ltd., HJ1005SD8) and subjected to charging and discharging cycles.

[0132] In an environment of 25℃, the following charging and discharging actions were repeated 10 times alternately: the charging action was to charge the battery with a constant current density of 10mA / g until the battery voltage reached the upper limit voltage of 4.8V, and then charge it with a constant voltage while maintaining the voltage at 4.8V until the current density decreased to 1mA / g; the discharging action was to discharge the battery with a constant current density of 10mA / g, and stop discharging when the battery voltage reached the lower limit voltage of 2.0V.

[0133] It should be noted that charging and discharging begins with the charging action, and one charging action and one discharging action are combined to form one cycle.

[0134] The charge-discharge curves of Example 1 and Comparative Example 1 are shown below. Figure 1 The evaluation results are shown in Table 1.

[0135] Table 1

[0136]

[0137] As shown in Table 1, in Examples 1-3, the charging and discharging capacities were significantly improved compared to Comparative Example 1 without boron in any of the cycles from the 1st to the 10th. On the other hand, although Comparative Example 2 included boron, its charging and discharging capacities decreased compared to Comparative Example 1. Therefore, it is believed that if too little boron is added, the charging and discharging capacities will decrease, and an appropriate amount of boron needs to be added to improve both.

[0138] In Example 1, the ratio of the charging capacity of the second cycle to the charging capacity of the first cycle (hereinafter also referred to as the two-cycle charging capacity change rate) was 0.7, which was a smaller value than the two-cycle charging capacity change rate (0.8) of Comparative Example 1.

[0139] In Examples 2, 3 and Comparative Example 2, the rate of change of capacity after two cycles of charging was smaller than that of Comparative Example 1.

[0140] In Example 1, the ratio of the discharge capacity of the second cycle to the discharge capacity of the first cycle (hereinafter also referred to as the two-cycle discharge capacity change rate) was 1.1, which was a smaller value than the two-cycle discharge capacity change rate (1.2) of Comparative Example 1.

[0141] In Examples 2 and 3, the rate of change of discharge capacity after two cycles was smaller than that of Comparative Example 1, while the rate of change of discharge capacity after two cycles in Comparative Example 2 was not different from that in Comparative Example 1.

[0142] In Example 1, the ratio of the charging capacity of the 10th cycle to the charging capacity of the 1st cycle (hereinafter also referred to as the 10-cycle charging capacity change rate) was 0.8, which was a smaller value than the 10-cycle charging capacity change rate (1.3) of Comparative Example 1.

[0143] In Examples 2, 3 and Comparative Example 2, the rate of change of capacity after 10 charging cycles was smaller than that of Comparative Example 1.

[0144] Compared with Comparative Example 2, Examples 1-3 showed a smaller value of 0.3 or more for the rate of change of capacity after 10 charging cycles.

[0145] In Example 1, the ratio of the discharge capacity of the 10th cycle to the discharge capacity of the 1st cycle (hereinafter also referred to as the 10-cycle discharge capacity change rate) was 1.3, which was a smaller value than the 10-cycle discharge capacity change rate (2.0) of Comparative Example 1.

[0146] In Examples 2, 3 and Comparative Example 2, the rate of change of discharge capacity after 10 cycles was smaller than that of Comparative Example 1.

[0147] Compared with Comparative Example 2, Examples 1-3 showed a smaller value of 0.4 or more for the rate of change of discharge capacity after 10 cycles.

[0148] like Figure 2 As shown in (b), in Comparative Example 1, the charging curve increases monotonically, and no peak is observed in the range of 4.7V to 4.8V. In contrast, as shown in [the diagram], Figure 2As shown in (a), in Example 1, a peak was observed in the charging curve in the range of 4.7V to 4.8V.

[0149] In Comparative Example 1, such as Figure 2 As shown in (b), the capacity gradually changes towards the 10th cycle through repeated charging and discharging. In contrast, in Example 1, as... Figure 2 As shown in (a), the capacity obtained in the second charging cycle is close to that of the tenth cycle, and the charging and discharging curves after the second cycle become highly reproducible shapes.

[0150] Based on the above results, it can be concluded that by using Li2Mn 1－x Ni x Adding boron-containing additives to the precursor of a layered rock salt-type lithium composite oxide (represented by O3, 0 ≤ x < 1) such that the boron content is greater than 0.00075 equivalents relative to the total Mn and Ni of the lithium composite oxide, and sintering at a temperature above 850°C, results in higher initial charge and discharge capacities compared to the layered rock salt-type lithium composite oxide without additives. It approaches a stable state in the second charging cycle, and subsequent charging and discharging cycles yield discharge capacities close to those in the stable state.

[0151] Symbol Explanation

[0152] 20 Positive electrode active material

[0153] 30 Oxide Active Substances

[0154] 31 Covering layer

Claims

1. A positive electrode active material, in Li2Mn 1－x Ni x The lithium composite oxide with a layered rock salt structure represented by O3 (0≤x<1) or the precursor of the lithium composite oxide is supplemented with an additive containing boron, such that the boron content relative to the total Mn and Ni of the lithium composite oxide is greater than 0.00075 equivalents and less than 0.2 equivalents, and then heated and sintered.

2. The positive electrode active material according to claim 1, wherein, The additive is added to the lithium composite oxide or the precursor of the lithium composite oxide, such that the boron content is 0.005 equivalent to 0.1 equivalent relative to the total Mn and Ni of the lithium composite oxide, and then heated and sintered.

3. The positive electrode active material according to claim 1 or 2, wherein, It is formed by heating and sintering at a temperature above 850℃.

4. The positive electrode active material according to claim 1 or 2, wherein, The charging curve, which indicates that the lithium metal reference voltage versus charging capacity has a peak value in the range of 4.7V to 4.8V when the lithium metal is charged at a constant current density of 10mA / g for the first time, is a constant current charging curve.

5. The positive electrode active material according to claim 1 or 2, wherein, The device is charged with a constant current at a current density of 10 mA / g until it reaches 4.8V under the lithium metal reference. While maintaining the 4.8V under the lithium metal reference, it is charged with a constant voltage until the current density decays to 1 mA / g. At this point, the initial charge capacity per 1g is more than 250mAh / g.

6. The positive electrode active material according to claim 5, wherein, The lithium metal reference voltage is 4.8V at a constant current density of 10mA / g. While maintaining the lithium metal reference voltage of 4.8V, the lithium metal reference voltage is 4.8V. The lithium metal reference voltage is then maintained at a constant voltage until the current density decreases to 1mA / g. Finally, the lithium metal reference voltage is 2.0V at a constant current density of 10mA / g. At this point, the initial discharge capacity per 1g is more than 150mAh / g.

7. The positive electrode active material according to claim 1 or 2, wherein, After 10 charge-discharge cycles, the discharge capacity per 1g in the 10th discharge action is less than 1.5 times the discharge capacity per 1g in the first discharge action. The charge-discharge cycle consists of a charging action and a discharging action. The charging process involves charging with a constant current density of 10 mA / g until the lithium metal reference voltage of 4.8V is reached, and then charging with a constant voltage while maintaining the lithium metal reference voltage of 4.8V until the current density decreases to 1 mA / g. The discharge action is to discharge at a constant current density of 10 mA / g to 2.0V based on lithium metal.

8. The positive electrode active material according to claim 1 or 2, wherein, The additive contains lithium tetraborate.

9. The positive electrode active material according to claim 1 or 2, wherein, In the lithium composite oxide, a portion of Mn and / or Ni is replaced by boron.

10. The positive electrode active material according to claim 1 or 2, wherein, Boron compounds are attached to the lithium composite oxide.

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