Lithium nickel manganese composite oxide, positive electrode active material for lithium secondary battery, lithium secondary battery, and method for producing lithium nickel manganese composite oxide

Abstract

To provide a lithium nickel manganese composite oxide that can increase the capacity of lithium secondary batteries even with 4.8 V aging.SOLUTION: The present invention relates to a lithium nickel manganese composite oxide represented by general formula (1): LixNiyMnzO2 (in formula (1), w is 0.95≤w≤1.1, y is 0.45≤y≤0.5, z is 0.45≤z≤0.5, and y=z is satisfied), wherein Li contained in a transition metal layer does not form LiMn6, wherein the lithium nickel manganese composite oxide has a manganese-rich layer from surfaces of secondary particles to the inside of the secondary particles, wherein a ratio (Mn / Ni ratio) of the number of Mn atoms to the number of Ni atoms in the manganese-rich layer is 1.0 or more and 1.5 or less, and wherein the lithium nickel manganese composite oxide has a space group R-3m, an a-axis lattice constant of 2.87 Å to 2.90 Å, and a c-axis lattice constant of 14.28 Å to 14.32 Å.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a lithium nickel manganese composite oxide, a positive electrode active material for a lithium secondary battery, a lithium secondary battery, and a method for producing a lithium nickel manganese composite oxide.

Background Art

[0002] In recent years, research and development on secondary batteries that contribute to energy efficiency have been conducted in order to enable more people to access affordable, reliable, sustainable, and advanced energy. Most secondary batteries are lithium secondary batteries. In addition, secondary batteries including lithium secondary batteries are expected to be put into practical use as large-scale batteries such as hybrid vehicles and power load leveling systems in the future, and their importance is increasing.

[0003] For example, a lithium secondary battery mainly includes an electrode composed of a positive electrode and a negative electrode containing a material capable of reversibly occluding and releasing lithium, and a separator or a solid electrolyte containing a non-aqueous electrolyte.

[0004] Among these components, as an electrode active material, a lithium nickel manganese composite oxide (LiNi 0.5 Mn 0.5 O2) with Ni:Mn = 1:1 is known (see, for example, Non-Patent Document 1). It is known that when this lithium nickel manganese composite oxide is simply synthesized, its outermost surface is composed of a nickel-rich layer.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] By the way, in the technology related to secondary batteries, lithium nickel manganese composite oxide (LiNi) with a ratio of Ni:Mn=1:1 is used. 0.5 Mn 0.5 In order to increase the capacity of a lithium secondary battery equipped with a positive electrode containing a positive electrode active material mainly composed of O2, a challenge is that the secondary battery must be aged at a high upper voltage limit (5.0V) (see, for example, Non-Patent Documents 2 and 3).

[0007] To solve the above-mentioned problems, this invention aims to create a lithium nickel manganese composite oxide that can achieve high capacity in lithium secondary batteries even after aging at 4.8V, by preventing the formation of LiMn6 (see, for example, Non-Patent Document 3) in the transition metal layer of the lithium nickel manganese composite oxide and creating a manganese-rich surface. This will ultimately contribute to energy efficiency. [Means for solving the problem]

[0008] To achieve the above objective, the present invention provides the following means. [1] It consists of secondary particles formed by the aggregation of multiple primary particles, and the general formula is (1): Li x Ni y Mn z A lithium nickel manganese composite oxide represented by O2 (wherein equation (1), x is 0.95 ≤ w ≤ 1.1, y is 0.45 ≤ y ≤ 0.5, z is 0.45 ≤ z ≤ 0.5, and y = z), LiMn6 is not formed in the Li contained in the transition metal layer. The secondary particles have a manganese-rich layer extending from the particle surface to the interior of the particle, The ratio of the number of Mn atoms to the number of Ni atoms in the manganese-rich layer (Mn / Ni ratio) is 1.0 or more and 1.5 or less. A lithium nickel manganese composite oxide with space group R-3m, a-axis lattice constant of 2.87 Å to 2.90 Å, and c-axis lattice constant of 14.28 Å to 14.32 Å.

[0009] The lithium nickel manganese composite oxide of the present invention does not form LiMn6 in Li contained in the transition metal layer, has a manganese-rich layer on the surface, has a Mn / Ni ratio of 1.0 or more and 1.5 or less, has a space group of R-3m, an a-axis lattice constant of 2.87 Å to 2.90 Å, and a c-axis lattice constant of 14.28 Å to 14.32 Å. Therefore, by using it as a positive electrode active material of a secondary battery, aging at 4.8 V can increase the capacity of the lithium secondary battery.

[0010] [2] In the spectrum measured by solid lithium nuclear magnetic resonance analysis ([ 6 Li-MAS-NMR) using the magic angle sample rotation method, the lithium nickel manganese composite oxide described in [1] in which the peak attributed to LiMn6 does not exist at 1495 to 1505 ppm in Li contained in the transition metal layer.

[0011] Solid lithium nuclear magnetic resonance analysis using the magic angle sample rotation method ([ 6 Li-MAS-NMR), in the spectrum measured by, since the peak attributed to LiMn6 does not exist at 1495 to 1505 ppm in Li contained in the transition metal layer, the surface of the lithium nickel manganese composite oxide of the present invention is a manganese-rich layer.

[0012] [3] A positive electrode active material for a lithium secondary battery, which contains the lithium nickel manganese composite oxide described in [1] or [2] as a main component.

[0013] The positive electrode active material for a lithium secondary battery of the present invention contains the lithium nickel manganese composite oxide of the present invention as a main component. Therefore, by using it as a positive electrode active material of a lithium secondary battery, the capacity of the lithium secondary battery can be increased.

[0014] [4] A lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte, The lithium secondary battery, wherein the positive electrode contains a positive electrode active material containing the lithium nickel manganese composite oxide described in [1] or [2] as a main component.

[0015] The lithium secondary battery of the present invention can have a high capacity because the positive electrode contains a positive electrode active material mainly composed of the lithium nickel manganese composite oxide of the present invention.

[0016] The method for producing a lithium nickel manganese composite oxide according to [5][1] or [2], at least one of lithium and lithium compounds and Ni a Mn b Z α (Z is O or OH, a is 0 < a < 1, b is 0 < b < 1, a + b = 1, and α is a value that makes it electrically neutral.) A mixture of is heat-treated at 950 °C or higher and 1150 °C or lower for 1 minute or longer and 5 hours or shorter to react at least one of the lithium and lithium compounds with the Ni a Mn b Z α to obtain a powder in a first step, A second step of cooling the temperature of the powder to room temperature, A third step of immersing the powder in ion-exchanged water at 50 °C or higher and 100 °C or lower for 5 minutes or longer and 3 hours or shorter, A fourth step of drying the powder after immersion in ion-exchanged water, A fifth step of heat-treating the dried powder at 800 °C or higher and 950 °C or lower for 1 hour or longer and 24 hours or shorter, The method for producing a lithium nickel manganese composite oxide having

[0017] According to the method for producing a lithium nickel manganese composite oxide of the present invention, the lithium nickel manganese composite oxide of the present invention can be obtained.

Effects of the Invention

[0018] According to the present invention, it is possible to produce a novel lithium nickel manganese composite oxide. By using this lithium nickel manganese composite oxide as a positive electrode active material of a secondary battery and aging at 4.8 V, the lithium secondary battery can have a high capacity.

Brief Description of the Drawings

[0019] [Figure 1] This is a schematic partial cross-sectional view showing an example of a lithium secondary battery according to one embodiment of the present invention. [Figure 2] This figure shows the powder X-ray diffraction patterns of lithium nickel manganese composite oxides for Example 1, Comparative Example 1, and Comparative Example 2. [Figure 3] This figure shows the 6Li-MAS-NMR spectra of the lithium nickel manganese composite oxides of Example 1 and Comparative Example 1. [Figure 4] These are the charging curves for the lithium secondary batteries of Example 1 and Comparative Example 1. [Figure 5] This figure shows the powder X-ray diffraction patterns of Example 2, Comparative Example 3, and the lithium nickel manganese composite oxide of Comparative Example 3. [Figure 6] This figure shows the 6Li-MAS-NMR spectra of lithium nickel manganese composite oxides from Example 2 and Comparative Example 3. [Figure 7] These are the charge and discharge curves for lithium secondary batteries in Example 2 and Comparative Example 3. [Modes for carrying out the invention]

[0020] Embodiments of the present invention will be described in detail below.

[0021] [Lithium nickel manganese composite oxide] A lithium nickel manganese composite oxide according to one embodiment of the present invention contains secondary particles formed by the aggregation of multiple primary particles, and has a manganese-rich layer extending from the particle surface to the interior of the secondary particles. The central part is located inside the manganese-rich layer. The lithium nickel manganese composite oxide has a multilayer structure in which the composition of the interior (central part) of the secondary particles and the composition of the outer periphery (manganese-rich layer) are different. The ratio of the number of Mn atoms to the number of Ni atoms (Mn / Ni ratio) is higher in the outer periphery (manganese-rich layer) than in the interior (central part) of the secondary particles.

[0022] The lithium nickel manganese composite oxide of this embodiment has the general formula (1): Li x Ni y Mn z O2 is represented by equation (1), where w is 0.95 ≤ x ≤ 1.1, y is 0.45 ≤ y ≤ 0.5, z is 0.45 ≤ z ≤ 0.5, and y = z. Equation (1) above represents the overall composition of the lithium nickel manganese composite oxide.

[0023] In the above general formula (1), x, which represents the lithium content, is between 0.95 and 1.1. In the above general formula (1), y, which represents the nickel content, is between 0.45 and 0.5. In the above general formula (1), z, which represents the manganese content, is between 0.45 and 0.5. Furthermore, in the lithium nickel manganese composite oxide as a whole, the nickel and manganese content are equal (y=z).

[0024] The composition of the lithium nickel manganese composite oxide in this embodiment can be analyzed by inductively coupled plasma (ICP) emission spectroscopy.

[0025] When manufacturing the lithium nickel manganese composite oxide of this embodiment, the initial composition of lithium, nickel, and manganese may be maintained in the resulting lithium nickel manganese composite oxide, or it may change in the resulting lithium nickel manganese composite oxide. The difference in the composition of lithium, nickel, and manganese in the resulting lithium nickel manganese composite oxide from the initial composition of lithium, nickel, and manganese is thought to be due to the evaporation of lithium or the deficiency of lithium in the crystal structure during the manufacturing of the lithium nickel manganese composite oxide.

[0026] The lithium nickel manganese composite oxide of this embodiment has a multilayer structure in which the composition of the central part and the composition of the manganese-rich layer on the outer periphery are different, and the composition of the manganese-rich layer is adjusted so that the proportion of Mn is higher than that of the central part. In other words, the lithium nickel manganese composite oxide of this embodiment has a manganese-rich layer on the outermost surface. In the lithium nickel manganese composite oxide of this embodiment, the ratio of the number of Mn atoms to the number of Ni atoms in the manganese-rich layer (Mn / Ni ratio) is 1.0 or more and 1.5 or less, and preferably 1.0 or more and 1.4 or less. When the Mn / Ni ratio is within the above range, the cycle characteristics of a lithium secondary battery using the lithium nickel manganese composite oxide as the positive electrode active material are improved.

[0027] The thickness of the manganese-rich layer is preferably 200 nm or less, and more preferably 150 nm or less. The lower limit of the thickness of the manganese-rich layer may be 1 nm or more, or 3 nm or more. If the thickness of the manganese-rich layer is less than or equal to the upper limit, the manganese-rich layer does not hinder the movement of lithium ions, and the effect of improving the capacity of a secondary battery using lithium nickel manganese composite oxide as the positive electrode active material can be obtained.

[0028] The composition of the manganese-rich layer can be determined, for example, by qualitative and quantitative analysis using X-ray photoelectron spectroscopy (XPS). XPS allows for the analysis of the manganese-rich layer composition across the entire surface of a single particle (the secondary particle mentioned above). In other words, the analysis results obtained by XPS represent the composition across the entire surface of a single particle, not just a localized composition on the entire surface.

[0029] The lithium nickel manganese composite oxide of this embodiment is a rhombohedral layered compound having a crystalline structure with space group R-3m.

[0030] The crystal structure of the lithium nickel manganese composite oxide in this embodiment has a space group R-3m, with an a-axis lattice constant of 2.87 Å to 2.90 Å and a c-axis lattice constant of 14.28 Å to 14.32 Å. Therefore, lithium ions diffuse easily within the primary particles, resulting in low resistance.

[0031] To obtain a lithium nickel manganese composite oxide with lower resistance, the a-axis lattice constant is preferably 2.88 Å to 2.90 Å, and the c-axis lattice constant is preferably 14.29 Å to 14.31 Å.

[0032] The fact that the lithium nickel manganese composite oxide of this embodiment has an R-3m crystal structure is confirmed by performing powder X-ray diffraction (XRD) measurements and detecting the peak attributed to R-3m.

[0033] In the lithium nickel manganese composite oxide of this embodiment, solid-state lithium nuclear magnetic resonance analysis is performed using the magic angle sample rotation method. 6 In the spectrum measured by Li-MAS-NMR, the peak at 1495-1505 ppm in the Li contained in the transition metal layer is not at the level of LiMn6. 6 Spectra measured by Li-MAS-NMR and 7 The spectra measured by Li-MAS-NMR have different shapes. In the lithium nickel manganese composite oxide of this embodiment, 6 In the spectrum measured by Li-MAS-NMR, there is no peak at 1495-1505 ppm that is attributed to LiMn6.

[0034] The lithium nickel manganese composite oxide of this embodiment does not have a peak at 1495-1505 ppm in the Li contained in the transition metal layer that is due to LiMn6, has a manganese-rich layer on its surface, has a Mn / Ni ratio of 1.0 to 1.5, has a space group R-3m, an a-axis lattice constant of 2.87 Å to 2.90 Å, and a c-axis lattice constant of 14.28 Å to 14.32 Å. Therefore, by using it as the positive electrode active material for a secondary battery and aging it at 4.8 V, the capacity of the lithium secondary battery can be increased.

[0035] [Method for Producing Lithium Nickel Manganese Composite Oxide] The method for producing a lithium nickel manganese composite oxide according to this embodiment is the method for producing a lithium nickel manganese composite oxide according to the above-described embodiment. The method for producing a lithium nickel manganese composite oxide according to this embodiment includes at least one of lithium and a lithium compound and Ni a Mn b Z α (Z is O or OH, 0 < a < 1, 0 < b < 1, a + b = 1, and α is a value that makes it electrically neutral.) The mixture is heat-treated at 950°C or higher and 1150°C or lower for 1 minute or longer and 5 hours or shorter to react at least one of the lithium and the lithium compound with the Ni a Mn b Z α to obtain a powder, a second step of cooling the temperature of the powder to room temperature, a third step of immersing the powder in ion-exchanged water at 50°C or higher and 100°C or lower for 5 minutes or longer and 3 hours or shorter, a fourth step of drying the powder after immersion in ion-exchanged water, and a fifth step of heat-treating the dried powder at 800°C or higher and 950°C or lower for 1 hour or longer and 24 hours or shorter.

[0036] "First Step" In the first step, first, at least one of a predetermined amount of lithium and a lithium compound and a predetermined amount of Ni a Mn b Z α (Z is O or OH, 0 < a < 1, 0 < b < 1, a + b = 1, and α is a value that makes it electrically neutral.) are dispersed and mixed in a solvent such as ethanol. In the first step, not only wet mixing using a solvent but also dry mixing without using a solvent can be used to mix at least one of thium and a lithium compound and a predetermined amount of Ni a Mn b Z αThey may be mixed. In addition to LiOH·H2O, lithium compounds such as carbonates such as Li2CO3 and acetates such as CH3COOLi and CH3COOLi·2H2O can be used. For example, as a lithium nickel manganese composite oxide, LiNi 0.5 Mn 0.5 When synthesizing O2, based on stoichiometric ratios, Ni 0.5 Mn 0.5 Weigh out 3% by mass more LiOH·H2O than (OH)2. Also, as a lithium nickel manganese composite oxide, Li 1.1 Ni 0.45 Mn 0.45 When synthesizing O2, Li:Ni 0.5 Mn 0.5 LiOH·H2O and Ni in a starting composition of =1.25:0.80 0.5 Mn 0.5 Weigh out (OH)2.

[0037] Lithium and at least one lithium compound and Ni a Mn b Z α The mixture is filled into a crucible and the mixture is heat-treated. A platinum crucible or a gold crucible conforming to JIS standards is used as the crucible. For the heat treatment of the mixture, for example, a firing furnace is used.

[0038] The mixture placed in the crucible is heated to a heat treatment temperature at a heating rate of 2.5°C / min to 25°C / min. The heat treatment temperature is 950°C to 1150°C, preferably 1000°C to 1100°C.

[0039] The heat treatment atmosphere is not particularly limited and can include air (under an air atmosphere), oxygen flow, etc. An oxygen flow atmosphere is preferred for the heat treatment.

[0040] The heat treatment time can be set appropriately according to the heat treatment temperature, and is between 1 minute and 5 hours, preferably between 10 minutes and 3 hours, and more preferably between 10 minutes and 2 hours. Note that the heat treatment time refers to the time during which the heat treatment temperature is maintained.

[0041] "The second step" In the second step, the temperature of the powder obtained in the first step is cooled to room temperature (25°C). Methods for cooling after the heat treatment in the first step include natural cooling (cooling in a furnace) and slow cooling.

[0042] "The third step" The powder, cooled to room temperature, is immersed in deionized water. The temperature of the deionized water is between 50°C and 100°C. The immersion time (water treatment time) of the powder in the deionized water is between 5 minutes and 3 hours. If the temperature of the deionized water is high, the immersion time of the powder in the deionized water will be shorter. If the temperature of the deionized water is low, the immersion time of the powder in the deionized water will be longer.

[0043] "The fourth step" For drying the powder after immersion in deionized water, for example, a hot plate can be used.

[0044] The drying temperature of the powder is preferably between 100°C and 130°C.

[0045] The drying time for the powder is preferably 10 minutes or more and 30 minutes or less.

[0046] "The fifth step" The dried powder is placed in a crucible and heat-treated. For example, a calcination furnace is used for the heat treatment of the powder.

[0047] The heat treatment temperature is 800°C to 950°C, preferably 850°C to 900°C. The heat treatment temperature in the fifth step is preferably lower than the heat treatment temperature in the first step. Furthermore, a higher heat treatment temperature results in a shorter heat treatment time, while a lower heat treatment temperature results in a longer heat treatment time.

[0048] The heat treatment atmosphere is not particularly limited and can include air (air atmosphere), oxygen flow, etc. An oxygen flow atmosphere is preferred for the heat treatment.

[0049] The heat treatment time can be set appropriately according to the heat treatment temperature, and is between 1 hour and 24 hours, with 1 hour and 20 hours being preferable.

[0050] According to the method for producing lithium nickel manganese composite oxide of this embodiment, the lithium nickel manganese composite oxide of the above-described embodiment can be obtained.

[0051] [Active material for positive electrode in lithium secondary batteries] The positive electrode active material for a lithium secondary battery according to one embodiment of the present invention is used in the positive electrode of a lithium secondary battery and mainly consists of the lithium nickel manganese composite oxide of the above embodiment.

[0052] In the positive electrode active material for lithium secondary batteries of this embodiment, "mainly composed of" lithium nickel manganese composite oxide means that the content of said lithium nickel manganese composite oxide is 75% by mass or more, preferably 80% by mass or more, more preferably 90% by mass, and even more preferably 99% by mass. The positive electrode active material for lithium secondary batteries may contain components other than the main component, as long as the function of the present invention is not impaired.

[0053] The positive electrode active material for lithium secondary batteries of this embodiment may contain only one type of lithium nickel manganese composite oxide of the above embodiment, or it may contain two or more types of lithium nickel manganese composite oxide of the above embodiment, as long as it mainly consists of the lithium nickel manganese composite oxide of the above embodiment.

[0054] The positive electrode active material for lithium secondary batteries in this embodiment can be manufactured using the lithium nickel manganese composite oxide of the above-described embodiment. As described above, by using the lithium nickel manganese composite oxide of the above-described embodiment as the positive electrode active material, the capacity of the lithium secondary battery can be increased.

[0055] [Lithium-ion rechargeable battery] A lithium secondary battery according to one embodiment of the present invention is a lithium secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and other battery elements as optional, wherein the positive electrode contains a positive electrode active material mainly composed of the lithium nickel manganese composite oxide of the above embodiment.

[0056] The lithium secondary battery of this embodiment can use conventionally known battery elements of lithium secondary batteries, except that the positive electrode contains a positive electrode active material mainly composed of the lithium nickel manganese composite oxide of the above-described embodiment. The lithium secondary battery of this embodiment may have any of the following configurations: coin type, button type, cylindrical type, prismatic type, or laminate type.

[0057] Below, as an example of a lithium secondary battery according to this embodiment, a lithium secondary battery using an electrolyte (coin-type lithium secondary battery) will be described. Each battery element described below can also be applied to an all-solid-state lithium secondary battery that does not use an electrolyte.

[0058] Figure 1 is a schematic partial cross-sectional view showing an example of a lithium secondary battery according to this embodiment. In Figure 1, an example is shown where the lithium secondary battery of this embodiment is a coin-type lithium secondary battery. The lithium secondary battery 1 shown in Figure 1 comprises a negative electrode terminal 2, a negative electrode 3, a separator 4 impregnated with electrolyte, an insulating packing 5, a positive electrode 6, and a positive electrode casing 7.

[0059] As shown in Figure 1, the positive electrode casing 7 is positioned on the lower side, and the negative electrode terminal 2 is positioned on the upper side. The positive electrode casing 7 and the negative electrode terminal 2 form the outer shape of the lithium secondary battery 1. Between the positive electrode casing 7 and the negative electrode terminal 2, the positive electrode 6 and the negative electrode 3 are arranged in layers from the bottom. A separator 4 impregnated with electrolyte is interposed between the positive electrode 6 and the negative electrode 3 to separate them from each other. The positive electrode casing 7 and the negative electrode terminal 2 are electrically insulated by an insulating packing 5.

[0060] In the lithium secondary battery of this embodiment, a positive electrode composite material can be prepared by adding a conductive agent, a binder, etc., as needed to the positive electrode active material for lithium secondary batteries of the above embodiment, and then pressing this composite material onto a current collector to produce the positive electrode. Preferably, stainless steel mesh, aluminum foil, etc., can be used as the current collector. Preferably, acetylene black, ketchen black, etc., can be used as the conductive agent. Preferably, tetrafluoroethylene, polyvinylidene fluoride, etc., can be used as the binder.

[0061] The composition of the positive electrode active material, conductive agent, and binder in the positive electrode composite material is not particularly limited. The content of the conductive agent in the positive electrode composite material is preferably 1% to 15% by mass, and more preferably 0.1% to 5% by mass. The content of the binder in the positive electrode composite material is preferably 0.1% to 10% by mass, and more preferably 0.1% to 5% by mass. It is preferable to blend the positive electrode active material, conductive agent, and binder so that the remainder of the positive electrode composite material (the portion other than the positive electrode active material and conductive agent) becomes the positive electrode active material.

[0062] In the lithium secondary battery of this embodiment, as the counter electrode to the positive electrode, known materials that function as a negative electrode and are capable of intercalating and releasing lithium can be used, such as metallic materials like metallic lithium and lithium alloys, and carbon-based materials like graphite and MCMB (mesocarbon microbeads).

[0063] Separators, battery containers, and other components can utilize known battery elements.

[0064] As the electrolyte, known electrolytes such as liquid electrolytes and solid electrolytes can be used. For example, as the electrolyte, an electrolyte such as lithium perchlorate or lithium hexafluoride phosphate can be dissolved in a solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate (PC), or ethyl carbonate (DEC).

[0065] Furthermore, the all-solid-state lithium secondary battery can have the same structure as a known all-solid-state lithium secondary battery, except that it uses a positive electrode active material mainly composed of the lithium nickel manganese composite oxide described in the above embodiment.

[0066] In the case of all-solid-state lithium secondary batteries, the electrolyte can be a polymer-based solid electrolyte such as a polyethylene oxide-based polymer compound, a polymer compound containing at least one of a polyorganosiloxane chain or a polyoxyalkylene chain, or a sulfide-based solid electrolyte, oxide-based solid electrolyte, etc.

[0067] For the positive electrode of an all-solid-state lithium secondary battery, for example, a positive electrode mixture containing a solid electrolyte in addition to the positive electrode active material, conductive agent, and binder described above can be supported on a positive electrode current collector made of aluminum, nickel, stainless steel, or the like.

[0068] The lithium secondary battery of this embodiment can achieve high capacity because the positive electrode contains a positive electrode active material mainly composed of the lithium nickel manganese composite oxide of the above-described embodiment.

[0069] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Examples]

[0070] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0071] [Comparative Example 1] (Synthesis of lithium nickel manganese composite oxide) LiOH·H2O (manufactured by High Purity Chemicals Co., Ltd.) and Ni 0.5 Mn 0.5 Weigh (OH)2 in a molar ratio of 1:1, and considering the evaporation of Li, calculate Ni based on the stoichiometric ratio. 0.5 Mn 0.5The amount of LiOH·H2O was weighed so that it was 3 mass% more than (OH)2. LiOH·H2O and Ni 0.5 Mn 0.5 The total mass of (OH)2 was set to 2.1 g. These were dispersed and mixed in ethanol using a mortar. Then, LiOH·H2O and Ni 0.5 Mn 0.5 A mixture of (OH)2 was packed into a JIS standard platinum crucible (30 ml). Using a firing furnace (product name: KDF-75Plus, manufactured by Denken Co., Ltd.), the mixture packed into the platinum crucible was heated in air at a heating rate of 10 °C / min and fired at 1050 °C for 30 minutes.

[0072] (analysis) The chemical composition of the obtained samples was analyzed using an ICP emission spectrometer (product name: Agilent 5110 VDV, manufactured by Agilent Technologies). The results are shown in Table 1. As shown in Table 1, it was confirmed that Li:Ni:Mn = 1.0:0.50:0.50. Furthermore, the X-ray diffraction pattern of the obtained sample was measured using a powder X-ray diffractometer (product name: SmartLab, manufactured by Rigaku). Using each index and its interplanar spacing, the lattice constants were determined by the least squares method, yielding a = 2.88884 (4) and c = 14.3008 (2). The powder X-ray diffraction pattern is shown in Figure 2. The lattice constants are shown in Table 1. We also have an X-ray photoelectron spectroscopy (XPS) analyzer (product name: K-Alpha + The composition of the surface layer of the obtained sample was analyzed by quantitative analysis using a Thermo Fisher Scientific instrument. The results are shown in Table 1. As shown in Table 1, the Mn / Ni ratio in the surface layer was 1.05. Furthermore, the obtained samples were analyzed by Li-MAS-NMR (product name: AVANCE300, manufactured by Bruker). The results are shown in Figure 3. From the results shown in Figure 3, 6 In the Li-MAS-NMR spectrum, no peak was observed in the 1495–1505 ppm range.

[0073] [Comparative Example 2] (Synthesis of lithium nickel manganese composite oxide) LiNi obtained in Comparative Example 1 0.5 Mn 0.5 1.5 g of O2 was immersed for 5 minutes in 50 mL of deionized water heated to 90°C. After that, Li limit 0.5 Mn 0.5 The O2 sample was placed on a hot plate heated to 120°C and dried for 15 minutes.

[0074] (analysis) The chemical composition of the obtained sample was analyzed in the same manner as in Comparative Example 1. The results are shown in Table 1. As shown in Table 1, it was confirmed that Li:Ni:Mn = 0.96:0.50:0.50. Furthermore, the lattice constants of the obtained sample were determined in the same manner as in Comparative Example 1, and were found to be a = 2.88879 (3) and c = 14.2962 (3). The powder X-ray diffraction pattern is shown in Figure 2. The lattice constants are shown in Table 1. Furthermore, the composition of the surface layer of the obtained sample was analyzed in the same manner as in Comparative Example 1. The results are shown in Table 1. As shown in Table 1, the Mn / Ni ratio in the surface layer was 1.22.

[0075] [Example 1] (Synthesis of lithium nickel manganese composite oxide) LiNi obtained in Comparative Example 2 0.5 Mn 0.5 1.5 g of O2 was packed into a platinum crucible conforming to JIS standards. Using a firing furnace, the mixture packed into the platinum crucible was heated in air at a heating rate of 10°C / min and fired at 900°C for 15 hours.

[0076] (analysis) The chemical composition of the obtained sample was analyzed in the same manner as in Comparative Example 1. The results are shown in Table 1. As shown in Table 1, it was confirmed that Li:Ni:Mn = 0.96:0.50:0.50. Furthermore, the lattice constants of the obtained sample were determined in the same manner as in Comparative Example 1, and were found to be a = 2.89258 (5) and c = 14.3149 (4). The powder X-ray diffraction pattern is shown in Figure 2. The lattice constants are shown in Table 1. Furthermore, the composition of the surface layer of the obtained sample was analyzed in the same manner as in Comparative Example 1. The results are shown in Table 1. As shown in Table 1, the Mn / Ni ratio in the surface layer was 1.30. Furthermore, the obtained samples were analyzed by Li-MAS-NMR. The results are shown in Figure 3. From the results shown in Figure 3, 6 In the Li-MAS-NMR spectrum, no peak was observed in the 1495–1505 ppm range.

[0077] [Manufacturing of lithium secondary batteries] Comparative Example 1 LiNi 0.5 Mn 0.5 O2 or LiNi from Example 1 0.5 Mn 0.5 O2 is used as the positive electrode active material, with acetylene black as the conductive agent and polyvinylidene fluoride as the binder, at a weight ratio of 8 mg / cm³. 2 The mixture was prepared in a 1:1 ratio and coated onto aluminum foil to create the positive electrode. The coating area density was 4.5 mg / cm². 2 The volume density is 2.3 g / cm³. 3 A lithium secondary battery (coin-type cell) with the structure shown in Figure 1 was fabricated, with lithium metal as the counter electrode and lithium hexafluoride phosphate dissolved in a 1.2 mol / L solution of a mixed solvent (volume ratio 3:4:3) of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) as the electrolyte. The battery was fabricated according to known cell configuration and assembly methods.

[0078] [Charge / Discharge Test] The fabricated lithium secondary batteries were subjected to charge-discharge tests at a temperature of 25°C, with a current density of 10 mA / g (0.05 C) and a cutoff potential of 4.8 V to 2.5 V, to evaluate their charge-discharge characteristics. The charge-discharge test began with charging.

[0079] Figure 4 shows the charge-discharge curves for Comparative Example 1 and Example 1. In Figure 4, the voltage change during discharge (when lithium is inserted) is shown, where the cell voltage decreases as the capacity increases, and the voltage change during charging (when lithium is removed) is shown, where the cell voltage increases as the capacity increases.

[0080] As shown in Figure 4, the LiNi of Example 1 0.5 Mn 0.5 The lithium secondary battery using O2 as the positive electrode active material is similar to the LiNi battery in Comparative Example 1. 0.5 Mn 0.5 It was found that the capacity was lower than that of lithium secondary batteries using O2 as the positive electrode active material. As shown in Figure 4, it was confirmed that the capacity of lithium secondary batteries can be increased by appropriate heat treatment.

[0081] [Table 1]

[0082] [Comparative Example 3] (Synthesis of lithium nickel manganese composite oxide) LiOH·H2O (manufactured by High Purity Chemicals Co., Ltd.) and Ni 0.5 Mn 0.5 (OH)2, Li:Ni 0.5 Mn 0.5 The weighing was performed so that the ratio was 1.25:0.80. LiOH·H2O (manufactured by High Purity Chemicals Co., Ltd.) and Ni 0.5 Mn 0.5 The total mass of (OH)2 was set to 2.1 g. These were dispersed and mixed in ethanol using a mortar. Then, the mixture was packed into a JIS standard platinum crucible (30 ml). Using a firing furnace (product name: KDF-75Plus, manufactured by Denken), the mixture packed in the platinum crucible was heated in air at a heating rate of 10 °C / min and fired at 1050 °C for 10 minutes.

[0083] (analysis) The chemical composition of the obtained samples was analyzed using an ICP emission spectrometer (product name: Agilent 5110 VDV, manufactured by Agilent Technologies). The results are shown in Table 2. As shown in Table 2, it was confirmed that Li:Ni:Mn = 1.1:0.45:0.45. Furthermore, the X-ray diffraction pattern of the obtained sample was measured using a powder X-ray diffractometer (product name: SmartLab, manufactured by Rigaku). Using each index and its interplanar spacing, the lattice constants were determined by the least squares method, yielding a = 2.86878 (12) and c = 14.2532 (12). The X-ray diffraction pattern is shown in Figure 5. The lattice constants are shown in Table 2. We also have an X-ray photoelectron spectroscopy (XPS) analyzer (product name: K-Alpha + The composition of the surface layer of the obtained sample was analyzed by quantitative analysis using a Thermo Fisher Scientific instrument. The results are shown in Table 2. As shown in Table 2, the Mn / Ni ratio in the surface layer was 0.86. Furthermore, the obtained samples were analyzed by Li-MAS-NMR (product name: AVANCE300, manufactured by Bruker). The results are shown in Figure 6. From the results shown in Figure 6, 6 In the Li-MAS-NMR spectrum, no peak was observed between 1495 and 1505 ppm.

[0084] [Comparative Example 4] (Synthesis of lithium nickel manganese composite oxide) 1.5 g of the lithium nickel manganese composite oxide obtained in Comparative Example 1 was immersed for 5 minutes in 50 mL of deionized water heated to 90°C. Subsequently, the lithium nickel manganese composite oxide was placed on a hot plate heated to 120°C and dried for 15 minutes.

[0085] (analysis) The chemical composition of the obtained sample was analyzed in the same manner as in Comparative Example 3. The results are shown in Table 2. As shown in Table 2, it was confirmed that Li:Ni:Mn = 1.1:0.45:0.45. Furthermore, the lattice constants of the obtained sample were determined in the same manner as in Comparative Example 3, and were found to be a = 2.87713 (11) and c = 14.2801 (10). The X-ray diffraction pattern is shown in Figure 5. The lattice constants are shown in Table 2. Furthermore, the composition of the surface layer of the obtained sample was analyzed in the same manner as in Comparative Example 3. The results are shown in Table 2. As shown in Table 1, the Mn / Ni ratio in the surface layer was 0.87.

[0086] [Example 2] (Synthesis of lithium nickel manganese composite oxide) 1.5 g of the lithium nickel manganese composite oxide obtained in Comparative Example 3 was packed into a platinum crucible conforming to JIS standards. The sample packed in the platinum crucible was calcined in air using a calcination furnace at 950°C for 5 hours.

[0087] (analysis) The chemical composition of the obtained sample was analyzed in the same manner as in Comparative Example 3. The results are shown in Table 2. As shown in Table 1, it was confirmed that Li:Ni:Mn = 0.94:0.45:0.45. Furthermore, the lattice constants of the obtained sample were determined in the same manner as in Comparative Example 3, and were found to be a = 2.87909 (10) and c = 14.2908 (10). The X-ray diffraction pattern is shown in Figure 5. The lattice constants are shown in Table 2. Furthermore, the composition of the surface layer of the obtained sample was analyzed in the same manner as in Comparative Example 3. The results are shown in Table 2. As shown in Table 1, the Mn / Ni ratio in the surface layer was 1.35. Furthermore, the obtained samples were analyzed by Li-MAS-NMR in the same manner as in Comparative Example 3. The results are shown in Figure 6. From the results shown in Figure 6, 6 In the Li-MAS-NMR spectrum, no peak was observed between 1495 and 1505 ppm.

[0088] [Manufacturing of lithium secondary batteries] The lithium nickel manganese composite oxide of Comparative Example 3 or the lithium nickel manganese composite oxide of Example 2 was used as the positive electrode active material. Acetylene black was used as the conductive agent and polyvinylidene fluoride as the binder, and these were mixed in a weight ratio of 8:1:1. The mixture was then coated onto aluminum foil to produce a positive electrode. The coating area density was 4.5 mg / cm². 2 The volume density is 2.3 g / cm³. 3 A lithium secondary battery (coin-type cell) with the structure shown in Figure 1 was fabricated, with lithium metal as the counter electrode and lithium hexafluoride phosphate dissolved in a 1.2 mol / L solution of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3 as the electrolyte. The battery was fabricated according to known cell construction and assembly methods.

[0089] [Charge / Discharge Test] The fabricated lithium secondary batteries were subjected to charge-discharge tests at a temperature of 25°C, with a current density of 10 mA / g (0.05 C) and a cutoff potential of 4.8 V to 2.5 V, to evaluate their charge-discharge characteristics. The charge-discharge test began with charging.

[0090] Figure 7 shows the charge-discharge curves for Comparative Example 3 and Example 2. Figure 7 shows the voltage change during discharge (when lithium is inserted), where the cell voltage decreases as the capacity increases, and the voltage change during charging (when lithium is removed), where the cell voltage increases as the capacity increases.

[0091] As shown in Figure 7, the lithium secondary battery using the lithium nickel manganese composite oxide of Example 2 as the positive electrode active material was found to have a higher capacity than the lithium secondary battery using the lithium nickel manganese composite oxide of Comparative Example 3 as the positive electrode active material. From the results shown in Figure 7, it was confirmed that the lithium nickel manganese composite oxide of Example 2 can increase the capacity of lithium secondary batteries.

[0092] [Table 2] [Explanation of Symbols]

[0093] 1. Lithium-ion rechargeable battery 2 Negative terminal 3 negative electrode 4. Separator impregnated with electrolyte. 5. Insulating packing 6 Positive electrode 7 Positive electrode can

Claims

1. It consists of secondary particles formed by the aggregation of multiple primary particles, and the general formula is (1): Li ｘ Ni ｙ Mn ｚ A lithium nickel manganese composite oxide represented by O2 (wherein formula (1), x is 0.95 ≤ x ≤ 1.1, y is 0.45 ≤ y ≤ 0.5, z is 0.45 ≤ z ≤ 0.5, and y = z), In the transition metal layer, LiMn ６ Without forming, The secondary particles have a manganese-rich layer extending from the particle surface to the interior of the particle, The ratio of the number of Mn atoms to the number of Ni atoms in the manganese-rich layer (Mn / Ni ratio) is 1.30 or more and 1.35 or less. In the space group R-3m, the a-axis lattice constant is 2.87 Å to 2.90 Å, and the c-axis lattice constant is 14.28 Å to 14.32 Å. A lithium nickel manganese composite oxide in which, in the spectrum measured by solid-state lithium nuclear magnetic resonance analysis (6 Li-MAS-NMR) using the magic angle sample rotation method, there is no peak at 1495-1505 ppm in the Li contained in the transition metal layer that is attributable to LiMn 6.

2. A positive electrode active material for a lithium secondary battery, comprising the lithium nickel manganese composite oxide described in claim 1 as the main component.

3. A lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, A lithium secondary battery wherein the positive electrode contains a positive electrode active material mainly composed of the lithium nickel manganese composite oxide described in claim 1.

4. A method for producing a lithium nickel manganese composite oxide according to claim 1, At least one of lithium and lithium compounds and Ni ａ Mn ｂ Z α (Z is O or OH, a is 0 < a < 1, b is 0 < b < 1, a + b = 1, and α is a value that makes it electrically neutral.) A mixture of is heat-treated at 950 °C or higher and 1150 °C or lower for 1 minute or longer and 5 hours or shorter to react at least one of the lithium and lithium compounds with the Ni ａ Mn ｂ Z α to obtain a powder in a first step, A second step is to cool the powder to room temperature, A third step involves immersing the aforementioned powder in ion-exchanged water at a temperature of 50°C to 100°C for 5 minutes to 3 hours. A fourth step is to dry the powder after immersion in deionized water, A fifth step involves heat-treating the dried powder at a temperature of 800°C to 950°C for 1 hour to 24 hours. A method for producing a lithium nickel manganese composite oxide having the following characteristics.

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