JP7184421B2 - POSITIVE ACTIVE MATERIAL FOR NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY, NONAQUEOUS ELECTROLYTE SECONDARY BATTERY, METHOD FOR SELECTING ADDITIONAL ELEMENTS FOR LITHIUM METAL COMPOUND OXIDE, AND METHOD FOR MANUFACTURING POSITIVE ACTIVE MATERIAL FOR NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Law Announced at the 83rd Annual Meeting of The Electrochemical Society of Japan on March 23, 2016 The 83rd Annual Meeting of The Electrochemical Society of Japan on March 29, 2016 Presented at the convention

The present invention relates to a positive electrode active material for non-aqueous electrolyte secondary batteries, a non-aqueous electrolyte secondary battery, a method for selecting additive elements for lithium metal composite oxides, and a method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries.

2. Description of the Related Art In recent years, with the spread of mobile devices such as mobile phones and laptop computers, there is a strong demand for the development of small and lightweight secondary batteries with high energy density. Also, eco-friendly vehicles called XEVs are required to have higher capacity, and the demand for high-capacity secondary batteries is expected to increase significantly in the future. Furthermore, there is an increasing need for an improvement in the traveling distance per charge and a reduction in the size of eco-friendly automobiles, and a further increase in capacity is required.

Non-aqueous electrolyte secondary batteries are known as such high-capacity secondary batteries. A lithium ion secondary battery is a representative non-aqueous electrolyte secondary battery, and a lithium metal composite oxide is used as a positive electrode active material for the positive electrode material of the lithium ion secondary battery. Lithium-cobalt composite oxide (LiCoO ₂ ) is relatively easy to synthesize, and in a lithium-ion secondary battery using lithium-cobalt composite oxide as a positive electrode material, a high voltage of the 4V class can be obtained. It has been put to practical use as a material for practical use of a secondary battery having an energy density.

However, it is difficult to say that the lithium-cobalt composite oxide satisfactorily meets the demand for higher capacity, and alternative materials with higher capacity are being investigated. Among positive electrode active materials that can be substituted for lithium-cobalt composite oxides, lithium-nickel composite oxides (LiNiO ₂ ), which have high capacity and are advantageous in terms of cost due to their low content of expensive cobalt, have been attracting attention in recent years. It is

However, the lithium-nickel composite oxide has a problem that its crystal structure collapses during charging, heat generation and oxygen release are likely to occur, and its thermal stability is low. In addition, the non-aqueous electrolyte secondary battery uses an organic solvent as the electrolyte, and there is a problem that if the heat is excessively generated, it will react with the organic solvent and generate more heat. and improvements in the battery itself have prevented these problems. For this reason, it cannot be said that the advantages of lithium-nickel composite oxides, such as high capacity and low cost, are fully utilized.

In order to solve such problems, for example, Patent Document 1 discloses a positive electrode material for secondary batteries having a chemical composition formula of A _4-x B(PO ₄ ) ₂ as a main component, wherein A is an alkaline At least one element selected from metals, B is at least one element selected from transition metals capable of forming a polyvalent ion of two or more valences, and x is mainly a compound in the range of 0 ≤ x ≤ 4 A positive electrode material for a secondary battery has been proposed as a component. According to this proposal, it is possible to provide a positive electrode material having a highly safe phosphoric acid skeleton structure, a two- or more-dimensional lithium diffusion network, and a high electric capacity of one-electron reaction or more.

Further, in Patent Document 2, general formula: Lix(Ni1-yCoy)1-zMzO2 (0.98≦x≦1.1, 0.05≦y≦0.4, 0.01≦z≦0.2, M is one or two or more selected from the group consisting of Al, Mn, Ti and Mg). (2) lattice volume of 99.6 Å or more; (3) Ni—O bond distance of 1.8 Å or more; (4) Ni—Ni bond distance of 2.8 Å or more; - a Waller factor of 0.065 or greater; and (6) a Ni--Ni Debye-Waller factor of 0.066 or less. According to this proposal, it is possible to provide a positive electrode active material with excellent structural stability (thermal stability) and high discharge capacity (high energy density).

WO2012/164751 JP-A-2005-332713

However, although the positive electrode material disclosed in Patent Document 1 is a polyanion type positive electrode active material and is expected to have a high electric capacity, the electric capacity that can be actually charged and discharged is small. It is difficult to say that it is a positive electrode active material with a large capacity. On the other hand, it is difficult to say that the positive electrode active material disclosed in Patent Document 2 has sufficiently achieved the required high capacity, and high thermal stability and further high capacity are required.

The present invention has been made in view of the above problems. Manufacture of novel and improved positive electrode active material for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and positive electrode active material for non-aqueous electrolyte secondary battery capable of providing positive electrode active material for next battery The purpose is to provide a method.

One aspect of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium metal composite oxide, comprising lithium, a metal element, an oxygen element and an additive element, wherein the lithium metal composite oxide has a crystal structure of a layered rock salt type structure, the metal element constitutes the 3b site, nickel is included as the metal element, and the nickel content is 82 with respect to the total of the metal element and the additive element .3 to 90 atomic %, and the additive element has a bond distance between a nickel atom and an oxygen atom determined by first-principles calculation of the 3b site of the lithium metal composite oxide that does not contain the additive element. By substituting nickel atoms with the additive element, the element becomes shorter than before the substitution, and the content of the additive element is 0.5 to 3.0 atomic % with respect to the total of the metal element and the additive element. The nickel atom is substituted for the nickel atom at the 3b site, and the initial discharge capacity when used as a positive electrode active material for a 2032 type coin battery is 195 mAh/g or more.

At this time, in one aspect of the present invention, the lithium metal composite oxide further contains cobalt as the metal element, and the additional element has a bond distance between the cobalt atom and the oxygen atom determined by first-principles calculation. Alternatively, by substituting the nickel atom at the 3b site of the lithium metal composite oxide not containing the additive element with the additive element, the length of the element becomes shorter than before the replacement.

Further, in one aspect of the present invention, the additive element is the bond distance between the additive element and the oxygen atom obtained using the first-principles calculation when the nickel atom at the 3b site is substituted with the additive element. may be shorter than the bond distance between the nickel atom and the oxygen atom in the lithium metal composite oxide not containing the additive element.

Further, in one aspect of the present invention, the additive element may be boron.

According to another aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery comprising a positive electrode containing any one of the positive electrode active materials for non-aqueous electrolyte secondary batteries described above.

Further, still another aspect of the present invention is the above lithium metal composite oxide comprising lithium, a metal element, an oxygen element and an additive element in a lithium metal composite oxide for a positive electrode active material for a non-aqueous electrolyte secondary battery wherein the lithium metal composite oxide has a layered rock salt crystal structure, the metal element constitutes the 3b site, nickel is included as the metal element, and the first principle The bond distance between the nickel atom and the oxygen atom of the lithium metal composite oxide obtained by calculation is shorter than before substitution by substituting the nickel atom at the 3b site of the lithium metal composite oxide not containing the additive element. is selected as the additive element, and the first principle calculation shows that the additive element replaces 4 to 16% of the nickel atoms at the 3b site, and 30 to 80% of the lithium atoms at the 3a site are extracted. It is characterized in that calculation is performed in a state in which

In still another aspect of the present invention, the first-principles calculation sets the ratio of nickel atoms at the 3b site to cobalt atoms at 84:16, and the additive element replaces 8% of the nickel atoms at the 3b site, The calculation may be performed in a state in which two-thirds of the lithium at the 3a site is deficient.

At this time, in still another aspect of the present invention, a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium metal composite oxide comprising lithium, a metal element, an oxygen element and an additive element, comprising: A metal element salt containing a nickel salt so that the nickel content is 82.3 to 90 atomic % with respect to the total of the metal element and the additive element, and the additive element selected by any of the above selection methods. A mixed aqueous solution containing a compound such that the content of the additive element is 0.5 to 3.0 atomic % with respect to the total of the metal element and the additive element, and an aqueous solution containing ammonium ions are mixed and reacted. a crystallization step of crystallizing the nickel composite hydroxide by controlling the pH value of the reaction solution to be in the range of 11.0 to 12.5 with respect to the liquid temperature of 25° C.; After washing the nickel composite hydroxide, a drying step of drying, and firing a mixture obtained by mixing the dried nickel composite hydroxide and a lithium compound in an oxygen atmosphere to obtain the lithium metal composite oxide. and a baking step to obtain.

At this time, in still another aspect of the present invention, in the crystallization step, an alkaline aqueous solution is used for controlling the pH value, and at that time, the aqueous solution containing the ammonium ions and the alkaline aqueous solution are mixed in the reaction solution. to grow the particles of the nickel composite hydroxide.

In still another aspect of the present invention, the supply positions of the aqueous solution containing the ammonium ions and the alkaline aqueous solution are such that, in the vertical direction, the reaction solution moves from the deepest part of the stirring blades in the reaction solution to the deepest part of the stirring blades. In the horizontal direction, it may be between the outermost periphery and the center of the stirring blade and the outermost periphery of the stirring blade. good.

In still another aspect of the present invention, in the crystallization step, an alkaline aqueous solution is used for controlling the pH value, and at that time, the aqueous solution containing the ammonium ions and the alkaline aqueous solution are mixed to the level of the liquid surface of the reaction solution. The nickel composite hydroxide may be grown by supplying it to the liquid surface between the outer circumference and the position of 1/3 of the distance between the outer circumference and the center of the liquid surface.

In still another aspect of the present invention, the lithium metal composite oxide further contains cobalt as the metal element, and in the selecting step, the bond between the cobalt atom and the oxygen atom determined by first-principles calculation. By substituting the nickel atom at the 3b site of the lithium metal composite oxide that does not contain the additive element, an element that makes the distance shorter than before substitution may be selected as the additive element.

Further, in still another aspect of the present invention, the additional element may be boron.

In still another aspect of the present invention, in the crystallization step, the total concentration of the metal element and the additive element in the mixed aqueous solution may be 1.5 to 2.5 mol/L.

In still another aspect of the present invention, the firing temperature may be 650 to 950° C. in the firing step.

In still another aspect of the present invention, lithium hydroxide, lithium carbonate, or a mixture thereof may be used as the lithium compound in the firing step.

As described above, according to the present invention, it is possible to obtain a positive electrode active material for a non-aqueous electrolyte secondary battery that can achieve high capacity and has high thermal stability. Moreover, a non-aqueous electrolyte secondary battery having a positive electrode containing the positive electrode active material has a high capacity and excellent stability at high temperatures. Furthermore, the method for producing a positive electrode active material for non-aqueous electrolyte secondary batteries according to the present invention allows easy selection of the composition, is suitable for production on an industrial scale, and has a very high industrial value.

BRIEF DESCRIPTION OF THE DRAWINGS It is a flowchart which shows the outline of the manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries which concerns on one Embodiment of this invention. (A) and (B) are diagrams for explaining the supply positions of an aqueous solution containing ammonium ions and an alkaline aqueous solution in a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention. be. 1A and 1B are configuration diagrams of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention; FIG.

Preferred embodiments of the present invention will be described in detail below. It should be noted that the present embodiment described below does not unduly limit the content of the present invention described in the claims, and all of the configurations described in the present embodiment are essential as means for solving the present invention. not necessarily.

The present inventors have made intensive studies on increasing the capacity and improving the thermal stability of positive electrode active materials for non-aqueous electrolyte secondary batteries. By adding an element that shortens the bonding distance between each element that constitutes the 3b site and the oxygen atom, which is determined using one-principle calculation, oxygen is less likely to be released, making it possible to achieve both high capacity and high thermal stability. The present invention was completed by obtaining the knowledge of Hereinafter, the components and configuration of the positive electrode active material for non-aqueous electrolyte secondary batteries according to one embodiment of the present invention, and the method for producing the same will be described.

(1) Positive electrode active material for non-aqueous electrolyte secondary battery The positive electrode active material for non-aqueous electrolyte secondary battery according to one embodiment of the present invention is a lithium-metal composite oxide containing lithium, a metal element, and an additive element. It is a positive electrode active material for a non-aqueous electrolyte secondary battery consisting of a substance. In the present embodiment, the lithium metal composite oxide has a layered rock salt crystal structure, contains nickel as a metal element, and has a nickel content of 60 to 90 atomic % with respect to the total of the metal element and the additive element. and the additive element replaces the nickel atom at the 3b site of the lithium metal composite oxide containing no additive element with the bond distance between the nickel atom and the oxygen atom determined by first-principles calculation with the additive element. By doing so, it is an element that becomes shorter than before the substitution, and is characterized by being substituted with the nickel atom at the 3b site.

The lithium metal composite oxide that constitutes the positive electrode active material for non-aqueous electrolyte secondary batteries (hereinafter sometimes simply referred to as "positive electrode active material") has a crystal structure of a layered rock salt structure, and contains nickel as a metal element. and the content of nickel is 60 to 90 atomic % with respect to the total of the metal element and the additive element. When the lithium metal composite oxide having such a layered rock salt crystal structure and high nickel content is used in a non-aqueous electrolyte secondary battery (hereinafter sometimes simply referred to as "battery"), A high charge/discharge capacity (hereinafter sometimes referred to as “battery capacity”) can be realized. On the other hand, since the stability of the crystal structure is not high, oxygen is easily released from the crystal.

In the positive electrode active material according to one embodiment of the present invention, the bond distance between the nickel atom and the oxygen atom obtained using first-principles calculation is the nickel atom at the 3b site of the lithium metal composite oxide containing no additive element. It contains, as an additive element, an element that becomes shorter than the lithium metal composite oxide before replacement, that is, without the additive element, by substituting it with the additive element.

Shortening the bond distance between the nickel atom and the oxygen atom increases the bond strength between the nickel atom and the oxygen atom, improving the stability of the crystal structure. Oxygen release is suppressed and thermal stability is improved even when stored. Further, by calculating the bond distance by first-principles calculation, the change in the bond distance can be easily estimated.

However, the bond distance by first-principles calculation is based on the premise that the additive element replaces the nickel atom at the 3b site, and it is necessary to actually replace the nickel atom at the 3b site. . Such substitution with a nickel atom at the 3b site can be confirmed as a change in lattice constant, and in the positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention, the lattice constant increases. has been confirmed.

In addition, the lithium metal composite oxide further contains cobalt as a metal element, and the additive element is a lithium metal composite oxide that does not contain the additive element so that the bonding distance between the cobalt atom and the oxygen atom obtained by first-principles calculation is By substituting the nickel atom at the 3b site of with the additive element, it is preferable that the length becomes shorter than before the substitution.

By including cobalt as a metal element in this way, the thermal stability of the lithium metal composite oxide is further improved. From the viewpoint of achieving both battery capacity and thermal stability at a high level, the content of cobalt is preferably 3 to 20 atomic % with respect to the total of metal elements and additive elements contained in the lithium metal composite oxide. In addition to the bond distance between the nickel atom and the oxygen atom, the bond distance between the cobalt atom and the oxygen atom is shortened, thereby increasing the stability of the crystal structure and further improving the thermal stability. Lithium metal composite oxides such as lithium nickelate have high energy density but cannot be said to have high thermal stability. Therefore, in this embodiment, cobalt is added to stabilize the crystal structure and improve thermal stability. are improving.

Furthermore, the additive element is a lithium metal composite oxide that does not contain the additive element, and the bonding distance between the additive element and the oxygen atom obtained by first-principles calculation when the nickel atom at the 3b site is substituted with the additive element. is preferably shorter than the bond distance between the nickel atom and the oxygen atom of Thus, the fact that the bonding distance between the additive element and the oxygen atom is shorter than the bonding distance between the nickel atom and the oxygen atom indicates that the additive element itself has a high effect of suppressing oxygen release, and improves thermal stability. preferred to let

The content of the additive element is preferably 0.5 to 3.0 atomic % with respect to the total of the metal element and the additive element contained in the lithium metal composite oxide. As a result, substitution at the 3b site is possible while maintaining a highly crystalline state, and the effect of improving the thermal stability obtained by shortening the bond distance between the nickel atom and the oxygen atom of the lithium metal composite oxide is obtained. , is even higher, which is preferable. Also, by setting the content of the additive element within such a numerical range, the battery capacity can be maintained at a higher level, which is preferable. Furthermore, in the present embodiment, boron (B) is preferable as the additive element from the viewpoint that the effect of shortening the bond distance to improve the thermal stability is large and the adverse effect on the battery characteristics other than the thermal stability is small. .

The positive electrode active material according to one embodiment of the present invention suppresses a decrease in the high battery capacity of a lithium metal composite oxide with a high nickel content and improves the thermal stability, thereby improving the battery capacity and thermal stability. is compatible at a high level, and the initial discharge capacity when used as a positive electrode active material for a non-aqueous electrolyte secondary battery, for example, a 2032 type coin battery is 195 mAh / g or more, and the capacity of the battery is increased. It becomes possible. Thus, as described above, the positive electrode active material according to one embodiment of the present invention achieves both high battery capacity and thermal stability by adding elements, and other powder characteristics are generally non-uniform. The characteristics of the positive electrode active material for aqueous electrolyte secondary batteries can be applied.

(2) Method for producing positive electrode active material for non-aqueous electrolyte secondary battery FIG. 1 is a flowchart showing an outline of a method for producing a positive electrode active material for non-aqueous electrolyte secondary battery according to one embodiment of the present invention. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery comprising lithium and a lithium metal composite oxide containing a metal element and an additive element. is a manufacturing method. As shown in FIG. 1, the method for producing a positive electrode active material of this embodiment includes a selection step S11, a crystallization step S12, a drying step S13, and a baking step S14. Each step will be described in detail below.

The selection step S11 is a step of selecting an additive element using first-principles calculation. In the present embodiment, in the selection step S11, the bond distance between the nickel atom and the oxygen atom obtained using the first principle calculation replaces the nickel atom at the 3b site of the lithium metal composite oxide containing no additive element. Therefore, an element that becomes shorter than before substitution is selected as an additive element.

By performing first-principles calculation in this way, it is possible to estimate the bond distance between a nickel atom and an oxygen atom in a lithium metal composite oxide having a layered structure. Further, by substituting the additive element with the nickel atom at the 3b site of the lithium metal composite oxide, the bond distance between the nickel atom and the oxygen atom changes, and the bond between the case of substitution and the case of non-substitution find the distance. At this time, if the bond distance is reduced by substituting the nickel atoms with the atoms of the additive element, the bond strength between the nickel atoms and the oxygen atoms increases, and oxygen release is suppressed. Therefore, in the present embodiment, an element that reduces the bond distance by being substituted with a nickel atom is selected as an additive element.

Lithium-metal composite oxides may contain, for example, cobalt in addition to the additive element to replace nickel atoms at the 3b site. In such a case, the element contained other than the additive element may be substituted with the nickel atom with the 3b site in advance to estimate the bond distance, and the bond distance may be compared with the bond distance when the additive element is substituted. .

In addition, since the oxygen release is suppressed by reducing the bond distance between the cobalt atom and the oxygen atom, it is preferable to select the additive element by estimating the change in the bond distance. Furthermore, the fact that the bond distance between the additive element and the oxygen atom is shorter than the bond distance between the nickel atom and the oxygen atom is also useful for suppressing oxygen release, and the additive element can be selected by estimating the change in the bond distance. preferable.

The first-principles calculation calculates the physical properties of the system from the atomic number and crystal structure, and by solving the Schrödinger equation, the bond energy and bond distance can be estimated. There are various programs for calculation using first-principles calculation, but it is sufficient to estimate the bond distance from the crystal structure and atomic arrangement. For example, MeDeA-VASP manufactured by Materials Design can be used.

Regarding the change in the bond distance between the nickel or cobalt atom and the oxygen atom due to the additive element, and the bond distance between the additive element and the oxygen atom, similar results can be obtained regardless of the calculation conditions. In order to estimate the bond distance more clearly, for example, it is preferable to perform approximation by the GGA+U method in consideration of the electron correlation effect, with a planar truncation energy of 650 eV, k-point sampling of 6×6×2 (conventional cell), and the electron correlation effect.

In addition, the amount of substitution with nickel atoms of the additive element is introduced by replacing 4 to 16% of the nickel atoms at the 3b site, and 30 to 80% of the lithium atoms at the 3a site are extracted and deficient (SOC 30 to 80%) is preferable because the bond distance that affects the oxygen release in the charged state where the crystal becomes unstable can be estimated more clearly.

In the crystallization step S12, a mixed aqueous solution containing a metal element salt containing at least a nickel salt and a compound of an additive element is mixed with an aqueous solution containing ammonium ions to form a reaction solution, and the pH value of the reaction aqueous solution based on a liquid temperature of 25° C. is In this step, the nickel composite hydroxide is crystallized by controlling the range of 11.0 to 12.5. Through the crystallization step S12, a nickel composite hydroxide (hereinafter sometimes simply referred to as "composite hydroxide") that serves as a precursor of a lithium metal composite oxide is obtained.

Since the positive electrode active material according to one embodiment of the present invention is one in which the additive element is substituted for the nickel atom at the 3b site, in the state of the composite hydroxide, the additive element is a solid solution in the composite hydroxide, Alternatively, it is preferably contained uniformly as a dispersed state in the particles of the composite hydroxide. Therefore, in the crystallization step S12, it is preferable to co-precipitate the additive element with the hydroxide generated from the metal salt.

The composition of the composite hydroxide is inherited by the obtained positive electrode active material. Therefore, the composition of the metal element salt and the additive element in the mixed aqueous solution used for crystallization of the composite hydroxide is set to be the same as that of the positive electrode active material to be obtained. Depending on the composition of the composite hydroxide, it may react in the mixed liquid to form a solid when mixed. In such a case, an aqueous solution containing the metal element salt and the additive element may be separately supplied so that the composition in the reaction solution becomes the composition of the composite hydroxide. When adjusting the composition by coating the crystallized hydroxide with a metal salt that constitutes the composite hydroxide, the amount corresponding to the metal salt to be coated may be subtracted from the mixed aqueous solution to adjust the composition.

The total concentration of the metal element and additive element in the mixed aqueous solution is preferably 1.5 to 2.5 mol/L. This makes it possible to prevent deposition of metal element salts and additive element compounds in the mixed aqueous solution, thereby obtaining a composite hydroxide having a uniform composition. In addition, the particle size can be sufficiently grown to obtain a high filling property and the particle size can be stabilized.

The reaction aqueous solution is controlled so that the pH value is in the range of 11.0 to 12.5 based on the liquid temperature of 25°C. Thereby, the particle size of the composite hydroxide can be controlled to an appropriate size, and the filling property of the obtained positive electrode active material can be improved. If the pH value is less than 11 or more than 12.5, the particle size of the composite hydroxide becomes too small, and the filling property of the positive electrode active material may decrease, or the composition may become unstable. It is not preferable because it may not co-precipitate.

The temperature of the reaction aqueous solution is preferably kept constant within the range of 45 to 55°C, for example, the upper and lower limits of the temperature are preferably controlled within 5°C. This facilitates particle size control of the composite hydroxide. If the temperature of the reaction aqueous solution is outside the above temperature range, the composition may become unstable and oxidation may easily proceed. If the temperature is less than 45°C, the particle size may become too large, and if it exceeds 55°C, the particle size may become too small. Therefore, in the present embodiment, the temperature of the reaction aqueous solution is controlled so as to fall within such a temperature range.

The ammonium ion concentration in the reaction aqueous solution is preferably 5-25 mg/L, more preferably 5-15 mg/L. Thereby, particle size control can be facilitated by suppressing variation in particle size due to variation in pH value. Moreover, the sphericity of the composite hydroxide can be improved, and the filling property of the positive electrode active material can be improved.

In this embodiment, in the crystallization step S12, an alkaline aqueous solution is used to control the pH value, and at that time, it is preferable to supply the aqueous solution containing ammonium ions and the alkaline aqueous solution directly into the reaction solution. For example, an alkaline aqueous solution is supplied to the reaction solution by inserting a supply pipe into the reaction solution. As a result, local fluctuations in the pH value and the ammonium ion concentration are suppressed, the distribution of the additive element becomes uniform, and the distribution of the additive element in the formed primary particles also becomes uniform. Then, by uniformizing the distribution of the additive element in the composite hydroxide, the distribution of the additive element in the composite oxide is uniformized in the firing step S14, and a positive electrode active material with higher thermal stability can be obtained. .

FIGS. 2A and 2B illustrate the supply positions of an aqueous solution containing ammonium ions and an alkaline aqueous solution in a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention. It is a diagram for In order to prevent localized high-concentration areas from occurring as much as possible, for example, as shown in FIG. From the deepest part D1 of the stirring blade ₁₁ in the middle to the position D3 that is one _third of the distance L between the deepest part _D1 of the stirring blade 11 and the liquid surface _D2 of the reaction solution, and in the horizontal direction , the middle position _B2 between the outermost periphery B1 of the stirring blade ₁₁ and the center C to the outermost periphery _B1 of the stirring blade 11. As a result, the aqueous solution containing ammonium ions and the alkaline aqueous solution can be supplied to the position where the flow speed is the fastest in the vicinity of the stirring blade 11 where the flow speed of the reaction solution is high, so the formation of local high concentration regions is suppressed. A good composite hydroxide can be obtained. The term “the deepest part of the stirring blade” referred to here indicates the deepest part reached by the stirring blade 11 in the reaction solution in the reaction tank 10 .

For example, as shown in FIG. 2(B), in the crystallization step S13, the local pH value and Fluctuations in ammonium ion concentration are suppressed. The aqueous solution containing ammonium ions and the alkaline aqueous solution are placed from the outer periphery 12 (B ₃ ) of the liquid surface of the reaction solution to a position B ₄ that is one third of the distance W′ between the outer periphery 12 (B ₃ ) of the liquid surface and the center C. By supplying the additive element to the liquid surface between 2000 to 2000, the distribution of the additive element becomes uniform and the growth of the particles can be stabilized.

In order to further suppress local variations in pH value and ammonium ion concentration, a stirring blade 11 for stirring the reaction solution and its shaft 14 are installed on the central axis C of the reaction tank 10 used for crystallization. is preferred. As a result, the reaction solution in the reaction tank is uniformly stirred, and concentration fluctuations are further suppressed.

The supply positions of the aqueous solution containing ammonium ions and the alkaline aqueous solution are as described above. In addition, it is preferable to supply an aqueous solution containing the additive element.

In addition, it is preferable to keep the oxygen concentration in the reaction aqueous solution low since the additive element can be contained more uniformly in the composite hydroxide by suppressing the oxidation of the additive element. For example, by introducing an inert gas to the liquid surface of the reaction aqueous solution in the reaction vessel and sealing the reaction vessel or applying a positive pressure, it is possible to prevent oxygen from entering from outside the vessel and suppress oxidation. Furthermore, by suppressing oxidation, the particle density of the composite hydroxide is improved, and a positive electrode active material with a high energy density can be obtained, which is preferable.

The drying step S13 is a step of drying after washing the crystallized nickel composite hydroxide. Since the resulting composite hydroxide contains impurities, it is subjected to solid-liquid separation and washed with water, preferably ion-exchanged water, to remove impurities such as sodium and sulfate ions contained in the composite hydroxide. In order to remove impurities such as oxoacid ions such as sulfate ions, washing may be performed with an alkaline aqueous solution. It is then dried, preferably at a temperature in the range of 110-150°C. The drying temperature and time should be such that moisture can be removed.

In addition, a heat treatment step of heating the composite hydroxide after drying in the drying step S13 to a temperature in the range of 600 to 800 ° C. to convert it to a nickel composite oxide (hereinafter sometimes simply referred to as “composite oxide”). It is preferable to further have This heat treatment suppresses the generation of water vapor in the subsequent baking step S14 to promote the reaction with the lithium compound, and stabilizes the total of the metal elements and additive elements in the positive electrode active material and the ratio of lithium. be able to. Furthermore, the additive element can be uniformly diffused in the composite oxide, and the nickel atoms at the 3b site can be sufficiently substituted when the positive electrode active material is obtained.

If the heat treatment temperature in the heat treatment step is less than 600° C., the conversion to the composite oxide becomes insufficient, and the additive element may not diffuse uniformly in the composite oxide. On the other hand, if the heat treatment temperature exceeds 800° C., the particles of the composite oxide may be sintered to form coarse particles. Moreover, since much energy is required, it is industrially unsuitable. The atmosphere in which the heat treatment is performed is not particularly limited, and may be a non-reducing atmosphere containing oxygen.

Moreover, the heat treatment time may be set to a time that allows sufficient conversion to the composite oxide, and is preferably 1 to 12 hours. Furthermore, the equipment used for the heat treatment is not particularly limited as long as it can heat the composite hydroxide in a non-reducing atmosphere containing oxygen, preferably in an air atmosphere, and does not generate gas. An electric furnace or the like that does not require heat is preferably used.

The baking step S14 is a step of baking a mixture obtained by mixing the dried nickel composite hydroxide and the lithium compound in an oxygen atmosphere to obtain a lithium metal composite oxide. In the present embodiment, the composite hydroxide or composite oxide and the lithium compound are the ratio of the sum of the total number of atoms of the metal element and the additive element in the mixture (Me) to the number of lithium atoms (Li) ( Li/Me) is preferably 0.98-1.15, more preferably 1.01-1.09. That is, since Li/Me does not change before and after the firing step, Li/Me mixed in this mixing step becomes Li/Me in the positive electrode active material, so Li/Me in the mixture is the same as that in the positive electrode active material to be obtained. Mixed to be the same as Li/Me.

Mixing so that the Li/Me ratio is 1.01 to 1.09 promotes crystallization and further promotes substitution of nickel atoms at the 3b site with additional elements. If the Li/Me ratio is less than 1.01, lithium may remain without reacting with some of the oxides, failing to obtain sufficient battery performance. On the other hand, when the Li/Me ratio is more than 1.09, sintering is accelerated, and the particle size and crystallite size become large, and sufficient battery performance may not be obtained.

The lithium compound used to form the lithium mixture is not particularly limited, but for example, lithium hydroxide, lithium nitrate, lithium carbonate, or mixtures thereof are preferred because they are readily available. In particular, considering ease of handling and stability of quality, it is more preferable to use lithium hydroxide or lithium carbonate. Lithium hydroxide has high reactivity with the composite oxide, promotes crystallization, and further promotes substitution of nickel atoms at the 3b site with additional elements.

In addition, it is preferable that the lithium mixture is thoroughly mixed before firing. If the mixture is not sufficiently mixed, the Li/Me ratio may vary among individual particles, and problems such as insufficient battery characteristics may occur. Therefore, sufficient mixing is required before firing.

In addition, a general mixer can be used for mixing, for example, a shaker mixer, Loedige mixer, Julia mixer, V blender, etc. can be used. It is sufficient if the material particles and the lithium-containing material are sufficiently mixed.

Next, the mixture is fired in an oxygen atmosphere, that is, in an oxygen-containing atmosphere to obtain a lithium metal composite oxide. The firing temperature at this time is preferably 650 to 950.degree. C., more preferably 700 to 800.degree. This increases crystallinity and promotes substitution. In particular, a temperature of 700 to 800° C. is preferable because cation mixing can be suppressed and the crystallinity can be increased.

If the firing temperature is lower than 650° C., diffusion of lithium into the heat-treated particles is not sufficiently carried out, and surplus lithium or unreacted particles remain, or the crystal structure is not sufficiently arranged, so that the particles cannot be used in batteries. sufficient battery characteristics may not be obtained. On the other hand, if the firing temperature exceeds 950° C., intense sintering may occur between the composite oxide particles and abnormal grain growth may occur. When abnormal grain growth occurs, the particles after firing become coarse and the specific surface area decreases, so when used in a battery, the problem arises that the resistance of the positive electrode increases and the battery capacity decreases.

Also, the firing time is preferably at least 4 hours or more, more preferably 6 to 10 hours. If it is less than 4 hours, the production of the lithium metal composite oxide may not be sufficiently carried out.

When lithium hydroxide is used as the lithium compound, before firing, the temperature is lower than the firing temperature and is 350 to 800 ° C., preferably 450 to 780 ° C. for about 1 to 10 hours, preferably 3 to 10 hours. It is preferable to hold and calcine for 6 hours. That is, it is preferable to calcine at the reaction temperature of lithium hydroxide or lithium carbonate and the composite oxide. In this case, if the lithium hydroxide or lithium carbonate is held near the reaction temperature described above, the lithium hydroxide melts and the lithium is sufficiently diffused into the composite oxide, resulting in a uniform and highly crystalline lithium-metal composite oxide. can be obtained, and the replacement of the additive element can be promoted.

The atmosphere during firing is an atmosphere containing oxygen, that is, an oxidizing atmosphere. The oxygen concentration is preferably a mixed atmosphere of 18 to 100% by volume of oxygen and an inert gas. That is, calcination is preferably carried out in the atmosphere or in an oxygen stream. If the oxygen concentration is less than 18% by volume, the crystallinity of the lithium metal composite oxide may be insufficient. Therefore, firing in an air atmosphere is easy, which is more preferable.

The furnace used for firing is not particularly limited as long as it can heat the mixture in the atmosphere or oxygen stream. Furnaces are preferred and either batch or continuous furnaces can be used.

Also, the lithium metal composite oxide obtained by firing may be aggregated or slightly sintered. In this case, it may be pulverized to obtain the lithium metal composite oxide, that is, the positive electrode active material according to one embodiment of the present invention. In addition, crushing refers to applying mechanical energy to aggregates composed of a plurality of secondary particles generated by sintering necking between secondary particles during firing, so that the secondary particles themselves are divided into two without almost destroying them. It means the operation of separating the secondary particles and breaking up the aggregates.

(3) Non-aqueous electrolyte secondary battery A non-aqueous electrolyte secondary battery according to one embodiment of the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte, etc., and has the same components as those of a general non-aqueous electrolyte secondary battery. Consists of An example in which the non-aqueous electrolyte secondary battery according to one embodiment of the present invention is applied to a 2032-type coin battery will be described with reference to the drawings. 3(A) and 3(B) are configuration diagrams of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention. FIG. 3(A) is a perspective view, and FIG. FIG. 4 is a cross-sectional view taken along the line AA of FIG. 3(A);

A non-aqueous electrolyte secondary battery 1 according to one embodiment of the present invention is a 2032 type coin battery, and is composed of a case 2 and an electrode 3 accommodated in the case 2 . As shown in FIG. 3B, the case 2 has a hollow positive electrode can 2a with one end open, and a negative electrode can 2b arranged in the opening of the positive electrode can 2a. is placed in the opening of the positive electrode can 2a, a space for housing the electrode 3 is formed between the negative electrode can 2b and the positive electrode can 2a. The electrode 3 consists of a positive electrode 3a, a separator 3c, and a negative electrode 3b, which are stacked in this order, with the positive electrode 3a contacting the inner surface of the positive electrode can 2a and the negative electrode 3b contacting the inner surface of the negative electrode can 2b. It is accommodated in the case 2 so that it does.

As shown in FIGS. 3(A) and 3(B), the case 2 is provided with a gasket 2c, which electrically insulates between the positive electrode can 2a and the negative electrode can 2b. is fixed to maintain The gasket 2c also has the function of sealing the gap between the positive electrode can 2a and the negative electrode can 2b to airtightly and liquidtightly isolate the inside of the case 2 from the outside. Hereinafter, each component of the non-aqueous electrolyte secondary battery 1 according to one embodiment of the present invention will be described in detail.

(a) Positive Electrode Using the positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention, a positive electrode for a non-aqueous electrolyte secondary battery is produced, for example, as follows.

First, a powdery positive electrode active material, a conductive material, and a binder are mixed, and if necessary, activated carbon and a solvent for viscosity adjustment are added, and the mixture is kneaded to prepare a positive electrode mixture paste. The mixing ratio of each component in the positive electrode mixture paste is also an important factor that determines the performance of the non-aqueous electrolyte secondary battery. When the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 to 95 parts by mass, similar to the positive electrode of a general non-aqueous electrolyte secondary battery. is preferably 1 to 20 parts by mass, and the content of the binder is preferably 1 to 20 parts by mass.

The obtained positive electrode mixture paste is applied, for example, to the surface of a current collector made of aluminum foil and dried to scatter the solvent. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. Thus, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size according to the intended battery, and used for manufacturing the battery. However, the method for producing the positive electrode is not limited to the illustrated one, and other methods may be used.

In preparing the positive electrode, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black-based materials such as acetylene black and Ketjenblack (registered trademark), and the like can be used as the conductive agent.

The binder plays a role of binding the active material particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, and polyacrylic. An acid or the like can be used.

If necessary, the positive electrode active material, the conductive material, and the activated carbon are dispersed, and a solvent for dissolving the binder is added to the positive electrode mixture. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used. In addition, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(b) Negative electrode For the negative electrode, a negative electrode mixture made by mixing a binder with a negative electrode active material such as metal lithium or a lithium alloy, or a negative electrode active material capable of intercalating and deintercalating lithium ions, and adding an appropriate solvent to form a paste is added. is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as needed.

As the negative electrode active material, for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powdery carbon substances such as coke can be used. In this case, as the negative electrode binder, similar to the positive electrode, fluorine-containing resin such as PVDF can be used. Organic solvents can be used.

(c) Separator A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode from the negative electrode and holds the electrolyte, and may be a thin film of polyethylene, polypropylene, or the like, having a large number of minute pores.

(d) Non-Aqueous Electrolyte The non-aqueous electrolyte is prepared by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, and dipropyl carbonate; One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate, and the like, or a mixture of two or more thereof is used. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ and the like, and composite salts thereof can be used. Furthermore, the non-aqueous electrolytic solution may contain radical scavengers, surfactants, flame retardants, and the like.

(e) Shape and configuration of battery The shape of the non-aqueous electrolyte secondary battery according to one embodiment of the present invention, which is composed of the positive electrode, negative electrode, separator, and non-aqueous electrolytic solution described above, is cylindrical, Various types such as a laminated type can be used. Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolytic solution, and a positive electrode terminal communicating with the positive electrode current collector and the outside is formed. and between the negative electrode current collector and the negative electrode terminal leading to the outside using a current collecting lead or the like, and sealed in the battery case to complete the non-aqueous electrolyte secondary battery.

(f) Characteristics The non-aqueous electrolyte secondary battery using the positive electrode active material according to one embodiment of the present invention has a high capacity and excellent thermal stability. A non-aqueous electrolyte secondary battery using a positive electrode active material according to an embodiment of the present invention obtained in a particularly more preferable form has a high initial Discharge capacity is obtained, and the capacity is even higher. In addition, the release of oxygen from the positive electrode active material is suppressed, the thermal stability is high, and the safety is also excellent.

EXAMPLES The positive electrode active material for non-aqueous electrolyte secondary batteries according to one embodiment of the present invention will be described below in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Selection of additive elements)
For the selection of the additive element, the bonding distance between the nickel atom, the cobalt atom, or the additive element and oxygen calculated by first-principles calculation was used. The shorter the bonding distance between a nickel atom, a cobalt atom, or an additive element and an oxygen atom, the stronger the bond, and the less likely oxygen is released, which causes the thermal stability of the non-aqueous electrolyte secondary battery to deteriorate. For the first-principles calculation program, MeDeA-VASP manufactured by Materials Design was used, the cut-off energy of the plane wave was 650 eV, the k-point sampling was 6 × 6 × 2 (conventional cell), and the GGA + U method was used in consideration of the electron correlation effect. was approximated by The basic ratio of nickel atoms at the 3b site to cobalt atoms is 84:16, the additive element replaces 8% of the nickel atoms at the 3b site, and two-thirds of the lithium at the 3a site is deficient (SOC 66%). performed the calculations. Table 1 shows the bond distance between each element and oxygen determined by first-principles calculation. Boron (B), which shortens the distance between nickel atoms and oxygen compared to the undoped state, was selected as an additive element.

(Analysis of composition)
The compositions of the positive electrode active materials for nonaqueous electrolyte secondary batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were analyzed by ICP emission spectrometry.

(Battery capacity evaluation)
Using the positive electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 to 4, 2032 type coin batteries 1 as shown in FIGS. 3(A) and 3(B) were produced. This 2032-type coin battery 1 is composed of a case 2 and an electrode 3 housed in the case 2 .

The case 2 has a hollow positive electrode can 2a with one end open, and a negative electrode can 2b arranged in the opening of the positive electrode can 2a. , a space for accommodating the electrode 3 is formed between the negative electrode can 2b and the positive electrode can 2a. The electrode 3 consists of a positive electrode 3a, a separator 3c, and a negative electrode 3b, which are stacked in this order, with the positive electrode 3a contacting the inner surface of the positive electrode can 2a and the negative electrode 3b contacting the inner surface of the negative electrode can 2b. It is accommodated in the case 2 so that it does.

The case 2 is provided with a gasket 2c. The gasket 2c fixes the positive electrode can 2a and the negative electrode can 2b so as to maintain an electrically insulated state. The gasket 2c also has the function of sealing the gap between the positive electrode can 2a and the negative electrode can 2b to airtightly and liquidtightly isolate the inside of the case 2 from the outside.

This 2032 type coin battery 1 was produced as follows. First, 52.5 mg of the positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa to prepare the positive electrode 3a. . The produced positive electrode 3a was dried at 120° C. for 12 hours in a vacuum dryer. Using this positive electrode 3a, negative electrode 3b, separator 3c, and electrolytic solution, a coin-type battery 1 was produced in an Ar atmosphere glove box with a controlled dew point of -80°C.

For the negative electrode 3b, a negative electrode sheet in which a copper foil was coated with graphite powder having an average particle size of about 20 μm and polyvinylidene fluoride punched into a disc shape with a diameter of 14 mm was used. A polyethylene porous film having a film thickness of 25 μm was used for the separator 3c. The electrolytic solution used was an equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1M LiClO4 as the supporting electrolyte (manufactured by Toyama Pharmaceutical Co., Ltd.).

The 2032 type coin battery 1 was left for about 24 hours after it was produced, and after the open circuit voltage OCV (Open Circuit Voltage) was stabilized, the current density to the positive electrode was set to 0.1 mA/cm ² and the cutoff voltage was 4.8 V. After 1 hour of rest, the battery was discharged to a cutoff voltage of 2.5 V, and a charge/discharge test was performed to measure the discharge capacity. The initial discharge capacity was determined as the battery capacity. At this time, a multi-channel voltage/current generator (R6741A, manufactured by Advantest Co., Ltd.) was used to measure the charge/discharge capacity.

(Thermal stability evaluation)
A positive electrode active material is collected from a 2032-type coin battery after battery characteristics evaluation, the collected positive electrode active material is washed to remove the electrolyte, and dried using a gas chromatograph-mass spectrometer (GC-MS). , the oxygen release temperature was measured as a thermal stability evaluation. PY-2020iD manufactured by Frontier Lab was used as the thermal decomposition part of the GC-MS, and the temperature was raised from 100°C to 450°C at a temperature elevation rate of 10°C/min. GC-2010 manufactured by Shimadzu Corporation was used for the gas chromatograph, Ultraalloy manufactured by Frontier Lab was used for the column, and helium (140 kPa) was used for the carrier gas. The oven temperature was kept constant at 200°C. A QP-2010plus manufactured by Shimadzu Corporation was used as a mass spectrometer.

(Example 1)
Nickel sulfate, cobalt sulfate, and boric acid were dissolved in ion-exchanged water so that the atomic ratio of nickel:cobalt:boron was 83.2:15.8:1.0 to prepare 3 L of a 2 mol/L mixed aqueous solution. did. 1 L of an aqueous sodium hydroxide solution having a pH value of 13 based on a liquid temperature of 25° C. was put into a reaction vessel kept at 50° C., and ammonia water was added so that the ammonia concentration was 10 mg/L. While maintaining the temperature, pH value, and ammonia concentration, 40 ml of the raw material solution, ammonia water, and sodium hydroxide aqueous solution were supplied into the reactor to generate nuclei that grow to form particles.

After that, the pH value based on the liquid temperature of 25 ° C. was set to 11.3, and the remaining raw material solution, ammonia water, and sodium hydroxide solution were supplied over 4 hours while maintaining the temperature, pH value, and ammonia concentration, and nickel composite The hydroxide was crystallized. The crystallized nickel composite hydroxide was solid-liquid separated by filtration, washed with an aqueous sodium hydroxide solution and ion-exchanged water, and dried to obtain a nickel composite hydroxide as a precursor of a positive electrode active material. During crystallization, the supply position of the ammonia water and the aqueous sodium hydroxide solution is set to the vertical direction from the deepest part of the stirring blade in the reaction solution to the position 1/5 of the distance between the deepest part of the stirring blade and the liquid surface of the reaction solution. , in the horizontal direction, at an intermediate position between the outermost periphery and the center of the stirring blade.

Next, the precursor was heated to 700° C. in an air atmosphere and held for 6 hours for heat treatment to convert it into a nickel composite oxide. A nickel composite oxide and lithium hydroxide were mixed to form a mixture such that the ratio of the number of lithium atoms to the total number of nickel, cobalt, and boron atoms (Li/Me ratio) was 1.02. The obtained mixture was calcined at 500° C. for 4 hours in an air atmosphere, and then calcined at 760° C. for 12 hours to obtain a positive electrode active material. The obtained positive electrode active material was evaluated to obtain the initial discharge capacity and the oxygen release temperature. Table 2 shows the evaluation results.

(Example 2)
A positive electrode was prepared in the same manner as in Example 1, except that nickel sulfate, cobalt sulfate, and boric acid were dissolved in ion-exchanged water so that the atomic ratio of nickel:cobalt:boron was 82.3:15.7:2.0. An active material was obtained and evaluated. Table 2 shows the evaluation results.

(Example 3)
The position of the supply port for ammonia water and sodium hydroxide aqueous solution is set to the vertical direction from the deepest part of the stirring blade in the reaction solution to the position of 1/3 of the distance between the deepest part of the stirring blade and the liquid surface of the reaction solution. A positive electrode active material was obtained and evaluated in the same manner as in Example 1, except for the above. Table 2 shows the evaluation results.

(Example 4)
A positive electrode active material was prepared in the same manner as in Example 1, except that the ammonia water and the aqueous sodium hydroxide solution were supplied to the liquid surface of the reaction solution at a position one third of the distance from the outer periphery to the center of the liquid surface. I got it and evaluated it. Table 2 shows the evaluation results.

(Comparative example 1)
As a conventional technique without adding an additive element, a positive electrode was prepared in the same manner as in Example 1, except that nickel sulfate and cobalt sulfate were dissolved in ion-exchanged water so that the atomic ratio of nickel:cobalt was 84.0:16.0. An active material was obtained and evaluated. Table 2 shows the evaluation results.

(Comparative example 2)
Except that a mixed aqueous solution of nickel sulfate and cobalt sulfate dissolved in ion-exchanged water and an aqueous sodium silicate solution were supplied to the reaction tank so that the atomic ratio of nickel:cobalt:silicon = 83.2:15.8:1.0. A positive electrode active material was obtained and evaluated in the same manner as in Example 1. Table 2 shows the evaluation results.

(Comparative Example 3)
Except that a mixed aqueous solution of nickel sulfate and cobalt sulfate dissolved in ion-exchanged water and an aqueous sodium silicate solution were supplied to the reaction vessel so that the atomic ratio of nickel:cobalt:silicon = 82.3:15.7:2.0. A positive electrode active material was obtained and evaluated in the same manner as in Example 1. Table 2 shows the evaluation results.

(Comparative Example 4)
Except that a mixed aqueous solution of nickel sulfate and cobalt sulfate dissolved in ion-exchanged water and an aqueous sodium silicate solution were supplied to the reaction tank so that the atomic ratio of nickel:cobalt:silicon = 81.5:15.5:3.0. A positive electrode active material was obtained and evaluated in the same manner as in Example 1. Table 2 shows the evaluation results.

In Examples 1 to 4 in which boron was added as an additive element that shortens the bond distance between nickel atoms and oxygen atoms in the first-principles calculation, the initial discharge capacity was maintained at a high value of 195 mAh / g or more, and there was no additive element. Compared with Comparative Example 1, the oxygen release temperature is increased. In particular, in Example 2, it can be seen that the oxygen release temperature is greatly increased to 220° C. or higher. From this, it can be seen that by selecting boron as the additive element, the oxygen release temperature rises and the thermal stability is improved while maintaining a high battery capacity.

On the other hand, in Comparative Examples 2 to 4, silicon was added as an element that increases the bond distance between a nickel atom and an oxygen atom. getting worse. Moreover, compared with Examples 1, 3 and 4, the initial discharge capacity, which is an index of battery capacity, is also lower. From this, it can be seen that it is preferable to add boron as an additive element in order to raise the oxygen release temperature and improve the thermal stability while maintaining a high battery capacity.

The positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention can increase the oxygen release temperature while maintaining the battery capacity. Suitable for secondary batteries. Moreover, due to its high capacity, it is also useful as a positive electrode active material for non-aqueous electrolyte secondary batteries used as power sources for small portable devices.

Although the embodiments and examples of the present invention have been described in detail as described above, it should be understood by those skilled in the art that many modifications are possible without substantially departing from the novel matters and effects of the present invention. , will be easily understood. Accordingly, all such modifications are intended to be included within the scope of the present invention.

For example, a term described at least once in the specification or drawings together with a different, broader or synonymous term can be replaced with the different term anywhere in the specification or drawings. Also, the configuration and operation of the positive electrode active material for non-aqueous electrolyte secondary batteries are not limited to those described in the embodiments and examples of the present invention, and various modifications are possible.

S11 selection step S12 crystallization step S13 drying step S14 firing step 1 non-aqueous electrolyte secondary battery (2032 type coin battery) 2 case 2a positive electrode can 2b negative electrode can 2c gasket 3 electrode 3a positive electrode , 3b negative electrode, 3c separator, 10 reaction vessel, 11 stirring blade, 12 outer periphery, 13 supply pipe, 14 shaft, outermost periphery of B ₁ stirring blade, intermediate position between outermost periphery and center of B ₂ stirring blade, B ₃ liquid level Perimeter of B ₄ liquid surface, 1/3 point of the distance between the outer periphery and the center of the liquid surface, C center (central axis), D ₁ deepest part of the stirring blade, D ₂ liquid surface, D ₃ stirring Point 1/3 of the distance between the deepest part of the impeller and the liquid surface of the reaction solution, P supply position

Claims (16)

A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium metal composite oxide,
lithium;
a metallic element;
elemental oxygen;
Consists of additive elements,
The lithium metal composite oxide has a crystal structure of a layered rock salt type structure, the metal element constitutes the 3b site of the crystal structure of the layered rock salt type structure, nickel is included as the metal element, and the nickel is contained. The amount is 82.3 to 90 atomic % with respect to the total of the metal element and the additive element,
In addition, the additive element replaces the nickel atom at the 3b site of the lithium metal composite oxide that does not contain the additive element so that the bond distance between the nickel atom and the oxygen atom determined by first-principles calculation is the additive element. is an element that becomes shorter than before substitution, the content of the additive element is 0.5 to 3.0 atomic % with respect to the total of the metal element and the additive element, and the nickel at the 3b site A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the positive electrode active material has an initial discharge capacity of 195 mAh/g or more when used as a positive electrode active material for a 2032 type coin battery. The lithium metal composite oxide further contains cobalt as the metal element, and the additive element is a lithium metal composite that does not contain the additive element so that the bonding distance between the cobalt atom and the oxygen atom obtained by first-principles calculation is 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the nickel atom at the 3b site of the oxide is replaced with the additive element so that the element becomes shorter than before the replacement. The additive element is lithium that does not contain the additive element, and the bonding distance between the additive element and the oxygen atom obtained using the first principle calculation when the nickel atom at the 3b site is replaced with the additive element. 3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the bonding distance is shorter than the bonding distance between the nickel atom and the oxygen atom of the metal composite oxide. 4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein said additive element is boron. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4. A method for selecting an additive element for a lithium-metal composite oxide comprising lithium, a metal element, an oxygen element, and an additive element,
The lithium metal composite oxide has a crystal structure of a layered rock salt type structure, the metal element constitutes the 3b site of the crystal structure of the layered rock salt type structure, and nickel is included as the metal element,
The bond distance between the nickel atom and the oxygen atom of the lithium metal composite oxide obtained by first-principles calculation is replaced by replacing the nickel atom at the 3b site of the lithium metal composite oxide that does not contain the additive element. selecting an element that is shorter than before as the additional element ;
In the first-principles calculation, the additive element replaces 4 to 16% of the nickel atoms at the 3b site, and 30 to 80% of the lithium atoms at the 3a site are extracted and deficient. method of selecting additive elements for products. The lithium metal composite oxide further contains cobalt as the metal element, and the first-principles calculation sets the ratio of nickel atoms at the 3b site to cobalt atoms at 84:16, and the additive element is 8 of the nickel atoms at the 3b site. 7. The method for selecting an additive element for a lithium metal composite oxide according to claim 6, wherein the calculation is performed in a state in which two-thirds of lithium at the 3a site is deficient by substituting %. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium metal composite oxide comprising lithium, a metal element, an oxygen element and an additive element, comprising:
Selected by the metal element salt containing nickel salt and the selection method according to claim 6 or 7 so that the nickel content is 82.3 to 90 atomic % with respect to the total of the metal element and the additional element. A mixed aqueous solution containing a compound of an additive element so that the content of the additive element is 0.5 to 3.0 atomic % with respect to the total of the metal element and the additive element, and an aqueous solution containing ammonium ions are mixed. a crystallization step of forming a reaction solution and controlling the pH value of the reaction solution to be in the range of 11.0 to 12.5 based on a liquid temperature of 25° C. to crystallize the nickel composite hydroxide;
a drying step of washing and then drying the crystallized nickel composite hydroxide;
a firing step of firing a mixture obtained by mixing the dried nickel composite hydroxide and a lithium compound in an oxygen atmosphere to obtain the lithium metal composite oxide;
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: In the crystallization step, an alkaline aqueous solution is used to control the pH value, and at that time, the aqueous solution containing the ammonium ions and the alkaline aqueous solution are supplied to the reaction solution to obtain the nickel composite hydroxide. 9. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 8, wherein the particles are grown. The position where the aqueous solution containing ammonium ions and the alkaline aqueous solution are supplied is, in the vertical direction, from the deepest part of the stirring blade in the reaction solution to 3/3 of the distance between the deepest part of the stirring blade and the liquid surface of the reaction solution. 1 position, and in the horizontal direction, the non-aqueous electrolyte according to claim 9, characterized in that it is between the outermost circumference and the center of the stirring blade and the outermost circumference of the stirring blade. A method for producing a positive electrode active material for a secondary battery. In the crystallization step, an alkaline aqueous solution is used to control the pH value, and at that time, the aqueous solution containing ammonium ions and the alkaline aqueous solution are spread from the periphery of the liquid surface of the reaction solution to the periphery and center of the liquid surface. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 8, wherein the nickel composite hydroxide is grown by supplying it to the liquid surface between the positions of one third of the distance of manufacturing method. The lithium metal composite oxide further contains cobalt as the metal element,
In the selection method, the bond distance between the cobalt atom and the oxygen atom obtained by first-principles calculation replaces the nickel atom at the 3b site of the lithium metal composite oxide that does not contain the additive element, 12. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 8 to 11, wherein an element that makes the length shorter than before substitution is selected as the additional element. 13. The method for producing an active material for a non-aqueous electrolyte secondary battery according to any one of claims 8 to 12, wherein the additive element is boron. 14. The method according to any one of claims 8 to 13, wherein in the crystallization step, the total concentration of the metal element and the additive element in the mixed aqueous solution is 1.5 to 2.5 mol/L. A method for producing the positive electrode active material for a non-aqueous electrolyte secondary battery described. The method for producing an active material for a non-aqueous electrolyte secondary battery according to any one of claims 8 to 14, characterized in that the firing temperature is 650 to 950°C in the firing step. 16. The active material for a non-aqueous electrolyte secondary battery according to any one of claims 8 to 15, wherein in the firing step, lithium hydroxide, lithium carbonate, or a mixture thereof is used as the lithium compound. manufacturing method.

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