JP6957846B2 - Positive electrode active material for non-aqueous electrolyte secondary battery and its manufacturing method, and non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery.

In recent years, with the widespread use of mobile devices such as mobile phones and notebook computers, the development of compact and lightweight secondary batteries having a high energy density has been strongly desired. In addition, an environment-friendly vehicle called XEV is also required to have a high capacity, and the demand for a high-capacity secondary battery is expected to increase significantly in the future. Further, there is an increasing need for improvement of the mileage per charge and miniaturization of environment-friendly automobiles, and further increase in capacity is required.

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

However, it cannot be said that the lithium cobalt composite oxide can sufficiently meet the demand for higher capacity, and alternative materials with higher capacity are being studied. Among the positive electrode active materials that can replace the lithium cobalt composite oxide, the lithium nickel composite oxide (LiNiO ₂ ), which has a high capacity and a low content of expensive cobalt and is advantageous in terms of cost, has been attracting attention in recent years. There is.

However, the lithium nickel composite oxide has a problem that the crystal structure is broken during charging, heat generation and oxygen release are likely to occur, and the thermal stability is low. Further, the non-aqueous electrolyte secondary battery uses an organic solvent as the electrolytic solution, and has a problem that if it generates heat excessively, it reacts with the organic solvent to further generate heat. For example, manganese or the like as in Patent Document 1. The heat-stabilizing element of is added to the lithium-nickel composite oxide to prevent these problems.

When other elements are added in this way, the high capacity, which is an advantage of the lithium nickel composite oxide, is sacrificed.

In order to compensate for such a decrease in capacity, for example, as in Patent Document 2, by lowering the void ratio of the secondary particles of the positive electrode active material and increasing the density, the positive electrode activity improves the volume capacity when made into a battery. The substance is provided.

Further, Patent Document 3 provides a method of reducing the porosity of the positive electrode active material to 2% or less by reducing the porosity of the precursor of the positive electrode active material to 15% or less.

Japanese Unexamined Patent Publication No. 2011-116580 Japanese Unexamined Patent Publication No. 2014-237573 JP-A-2015-164123

However, in the positive electrode active material of Patent Document 2, the porosity can be reduced only to about 5%, and it cannot be said that the density is sufficiently high, and the possibility of further increasing the capacity remains. ing.

Further, in the method of Patent Document 3, it is possible to obtain an active material having a particle size of secondary particles of several μm or less and a void ratio of 2% or less, but the void ratio of the precursor and the positive electrode active material. The correlation with is not sufficient, and a low void ratio is not obtained with an active material having a secondary particle size of about 5 μm or more.

The present invention has been made in view of the above problems, and a lithium nickel composite oxide-based positive electrode active material for a non-aqueous electrolyte secondary battery when used as a positive electrode active material for a non-aqueous electrolyte secondary battery is high. An object of the present invention is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that can be densified, a method for producing the same, and a non-aqueous electrolyte secondary battery.

One aspect of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery composed of a lithium metal composite oxide composed of secondary particles formed by agglomeration of primary particles, wherein lithium, a metal element, and the like. consists added elements, lithium metal composite oxide has a crystal structure of the layered rock-salt structure, comprising nickel and cobalt as the metal element, the content of nickel relative to the total of metal elements and additional element 79.8 a 90 atom%, the cobalt content is from 5 to 15.8 atomic% based on the total of metal elements and additive element, and additive elements is silicofluoride-containing, content of silicon, metal It is characterized in that it is 0.5 to 7 atomic% with respect to the total of the elements and the added elements, the void ratio of the secondary particles is 1% or less, and the crystallite diameter is 140 nm or less.

Another aspect of the present invention is a non-aqueous electrolyte secondary battery, which comprises a positive electrode containing the above-mentioned positive electrode active material for a non-aqueous electrolyte secondary battery.

In addition, another aspect of the present invention comprises lithium, a metal element, and an additive element , and the content of nickel as the metal element is 79.8 to 90 atomic% with respect to the total of the metal element and the additive element. The content of cobalt as a metal element is 5 to 15.8 atomic% with respect to the total of the metal element and the additive element, and the additive element is silicon, and the silicon content is that of the metal element and the additive element. A non-aqueous electrolyte secondary battery made of a lithium metal composite oxide having a total void ratio of 0.5 to 7 atomic%, a void ratio of secondary particles of 1% or less, and a crystallite diameter of 140 nm or less. A method for producing a positive electrode active material for use, in which a metal element salt aqueous solution containing at least a nickel salt and a cobalt salt, an additive element aqueous solution containing silicon, and an aqueous solution containing ammonium ions are mixed to prepare a reaction solution. Control using an alkaline aqueous solution so that the pH value based on a temperature of 25 ° C. is in the range of 11.0 to 12.5, and at that time, an aqueous solution containing ammonium ions and an alkaline aqueous solution are supplied into the reaction solution. A crystallization step for growing particles of the nickel composite hydroxide, a drying step for washing the crystallized nickel composite hydroxide and then drying, and mixing the dried nickel composite hydroxide and the lithium compound. It is characterized by including a firing step of calcining the obtained mixture in an oxygen atmosphere to obtain a lithium metal composite oxide.

According to the present invention, a positive electrode active material for a non-aqueous electrolyte secondary battery having excellent high-temperature stability and high-density secondary particles can be obtained. Further, the non-aqueous electrolyte secondary battery including the positive electrode containing the positive electrode active material is expected to be a safe and high-capacity secondary battery having excellent high-temperature stability and high density.

It is a flow chart which shows the outline of the manufacturing method of the positive electrode active material for a non-aqueous electrolyte secondary battery 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 the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention. be. (A) and (B) are block diagrams of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention. It is a scanning electron micrograph of the precursor of the positive electrode active material of Example 6. 6 is a scanning electron micrograph of a cross section of the positive electrode active material of Example 6. It is a scanning electron micrograph of the precursor of the positive electrode active material of Comparative Example 1. It is a scanning electron micrograph of the cross section of the positive electrode active material of Comparative Example 1. It is a scanning electron micrograph of the precursor of the positive electrode active material of Comparative Example 6. 6 is a scanning electron micrograph of a cross section of the positive electrode active material of Comparative Example 6.

Hereinafter, preferred embodiments of the present invention will be described in detail. It should be noted that the present embodiment described below does not unreasonably limit the content of the present invention described in the claims, and all of the configurations described in the present embodiment are indispensable as a means for solving the present invention. It is not something to do.

As a result of diligent studies on increasing the density of the positive electrode active material for a non-aqueous electrolyte secondary battery containing nickel and cobalt, the present inventors have found that the particle density can be improved by adding silicon, and completed the present invention. .. Hereinafter, the components and configurations of the positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, and the manufacturing method thereof will be described in the following order with reference to the drawings.
1. 1. Non-aqueous electrolyte Positive electrode active material for secondary batteries 2. Method for manufacturing positive electrode active material for non-aqueous electrolyte secondary batteries 2-1. Crystallization step 2-2. Drying process 2-3. Baking process 3. Non-aqueous electrolyte secondary battery

<1. Positive electrode active material for non-aqueous electrolyte secondary batteries>
The positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention is composed of secondary particles formed by agglomeration of primary particles, and is a lithium metal containing lithium, a metal element, and an additive element. It is a positive electrode active material for a non-aqueous electrolyte secondary battery made of a composite oxide. In the present embodiment, the lithium metal composite oxide has a crystal structure of a layered rock salt type structure, contains nickel and cobalt as metal elements, and has a nickel content of 60 to 90 with respect to the total of the metal elements and additive elements. The content of atomic% and cobalt is 5 to 30%, and silicon is contained as an additive element, and the content is 0.5 to 7 atomic% of silicon with respect to the total of the metal element and the additive element. Further, it is characterized in that the void ratio of the secondary particles is 1% or less. In the present specification, unless otherwise specified, the numerical range means "greater than or equal to the lower limit and less than or equal to the upper limit".

The lithium metal composite oxide constituting the positive electrode active material for a non-aqueous electrolyte secondary battery (hereinafter, may be simply referred to as “positive electrode active material”) has a crystal structure of a layered rock salt type structure, and nickel as a metal element. The content of nickel is 60 to 90 atomic% with respect to the total of the metal element and the additive element. When a lithium metal composite oxide having such a layered rock salt type crystal structure and a high nickel content is used in a non-aqueous electrolyte secondary battery (hereinafter, may be simply referred to as a “battery”). 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, the crystal structure is stabilized by containing 5 to 30% of cobalt, but the charge / discharge capacity is lower than that of the lithium nickel composite oxide.

In addition, a lithium metal composite oxide containing nickel and cobalt as metal elements usually has many voids in the secondary particles because the primary particles are aggregated to form secondary particles. This void reduces the volume density.

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention has a relatively large secondary particle diameter of 5 to 20 μm in which the porosity is increased by adding silicon to a lithium metal composite oxide containing nickel and cobalt. Also, a low porosity is achieved.

Silicon has the effect of lowering the void ratio by adding it, but the content of silicon is 0.5 to 7 atoms with respect to the total of the metal elements and the added elements contained in the lithium metal composite oxide, which is 0. It is preferably 5 to 3 atomic%. Porosity can be reduced to less than 1% by adding 0.5 atomic% or more of silicon. There is no upper limit to the amount of silicon added, but the amount should be 7 atomic% or less so that the strain of the crystal lattice does not increase and the battery characteristics do not deteriorate.

The metal element and the additive element may further contain elements other than the above-mentioned elements, for example, Mn, Al, Mg, Ti, Cr, Fe, Cu, Zn, Ca, V, Zr, Nb, Mo, At least one element selected from W can be used.

Further, the porosity of the secondary particles is 1% or less. Since the secondary particles have a particle structure in which the primary particles are densely aggregated, the secondary particles have an extremely high particle density and are a positive electrode active material having a high density. Therefore, when the positive electrode active material is used in the battery, the density per volume of the battery can be increased, and a battery having a high volume energy density can be obtained.

Here, the porosity inside the positive electrode active material, that is, the secondary particles is determined by analyzing an image (SEM image) observed by a scanning electron microscope (hereinafter, may be referred to as “SEM”). Can be done. For example, a positive electrode active material (secondary particles) is embedded in a resin or the like, an SEM image is taken in a state where cross-section observation is possible by cross-section polisher processing, etc., and image analysis software such as WinLoof 6.1.1 (trade name) is used. It can be obtained by detecting the void as a black portion and calculating the ratio of the area of the black portion to the total cross-sectional area of the secondary particles.

Further, by containing cobalt as a metal element as described above, the structure of the lithium metal composite oxide is stabilized, and the thermal stability is further improved. From the viewpoint of achieving both battery capacity and thermal stability at a high level, the cobalt content is 5 to 30 atomic% with respect to the total of the metal elements and additive elements contained in the lithium metal composite oxide, and is 5 to 20. It is preferably atomic%. A lithium metal composite oxide such as lithium nickelate has a high energy density, but cannot be said to have high thermal stability. Therefore, in the present embodiment, cobalt is added to stabilize the crystal structure and provide thermal stability. Is improving.

The lithium metal composite oxide preferably has an average particle size of 5 to 20 μm. By setting this average particle size within the above range, the filling property of the positive electrode active material is improved while maintaining the battery capacity, and a higher volume energy density can be obtained when used for the positive electrode of the battery. Here, the average particle size is D50, which means a particle size in which the number of particles in each particle size is accumulated from the smaller particle size side and the accumulated volume is 50% of the total volume of all particles. It can be measured using a diffraction / scattering particle size analyzer.

The lithium metal composite oxide preferably has a crystallite diameter of 140 nm or less, more preferably 10 to 130 nm. The crystal grain size is an index that affects the size of the primary particles. By controlling the crystallite size, the size of the primary particles is made appropriate, the density of the secondary particles is increased, and the positive electrode has a high particle density. Active material can be obtained. If the crystallite diameter is too small, the primary particles become too small, the number of voids between the primary particles increases significantly, and the particle density may decrease. On the other hand, if the crystallite diameter is too large, the primary particles become too large, the voids between the primary particles become large, and the particle density may decrease.

The lithium metal composite oxide preferably has an a-axis lattice constant of 0.2868 nm or more and a c-axis lattice constant of 1.4177 nm or more. By setting the a-axis and c-axis lattice constants in the above range, it is possible to prevent the distortion of the crystal lattice from becoming too large and maintain a high battery capacity. From the viewpoint of battery capacity, the a-axis lattice constant is more preferably 0.2868 to 0.2890 nm, and the c-axis lattice constant is more preferably 1.4177 to 1.4250 nm.

As described above, the positive electrode active material according to the embodiment of the present invention has both high battery capacity and thermal stability due to the additive element, as described above, and other powder characteristics are general non-existent. The characteristics of the positive electrode active material for an aqueous electrolyte secondary battery can be applied.

<2. Manufacturing method of positive electrode active material for non-aqueous electrolyte secondary batteries ＞
FIG. 1 is a flow chart showing an outline of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery composed of lithium and a lithium metal composite oxide containing a metal element and an additive element. It is a manufacturing method of. As shown in FIG. 1, the method for producing a positive electrode active material of the present embodiment includes a crystallization step S11, a drying step S12, and a firing step S13. Hereinafter, each step will be described in detail.

(2-1. Crystallization step)
In the crystallization step S11, an aqueous solution containing at least nickel and cobalt, an aqueous solution containing silicon, and an aqueous solution containing ammonium ions are mixed to prepare a reaction solution, and the pH value of the reaction solution based on a liquid temperature of 25 ° C. is 11.0 to 1. This is a step of crystallizing the nickel composite hydroxide in a range of 12.5. By the crystallization step S11, a nickel composite hydroxide (hereinafter, may be simply referred to as “composite hydroxide”) which is a precursor of the lithium metal composite oxide is obtained.

In the positive electrode active material according to the embodiment of the present invention, silicon, which is an additive element, is replaced with a nickel atom. Therefore, in the state of a composite hydroxide, the additive element is dissolved in the composite hydroxide. Alternatively, it is preferable that the composite hydroxide is uniformly contained in the particles in a dispersed state. Therefore, in the crystallization step S11, 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 resulting positive electrode active material. Therefore, the composition of the metal element salt and the additive element in the mixed aqueous solution used for crystallizing the composite hydroxide is the same as that of the positive electrode active material to be obtained. Depending on the composition of the composite hydroxide, when mixed, it may react in the mixed solution to form a solid. In such a case, an aqueous solution containing the metal element salt and the additive element may be individually supplied so that the composition in the reaction solution becomes the composition of the composite hydroxide. When the crystallized hydroxide is coated with a metal salt constituting the composite hydroxide to adjust the composition, the amount corresponding to the metal salt to be coated may be subtracted from the mixed aqueous solution for adjustment.

The total concentration of the metal element and the additive element in the mixed aqueous solution is preferably 1.5 to 2.5 mol / L. As a result, it is possible to prevent precipitation of metal element salts and compounds of additive elements in the mixed aqueous solution and obtain a composite hydroxide having a uniform composition. In addition, the particle size can be sufficiently grown to obtain high filling property and the particle size can be stabilized. As the aqueous solution of the additive element containing silicon, it is preferable to use an aqueous solution of sodium silicate or an aqueous solution of potassium silicate, and it is more preferable to use an aqueous solution of sodium silicate.

The reaction aqueous solution is controlled so that the pH value based on the liquid temperature of 25 ° C. is in the range of 11.0 to 12.5. 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 may become too small, the filling property of the positive electrode active material may decrease, or the composition may become unstable, and the additive element may be added. It is not preferable because it may not co-precipitate.

The temperature of the reaction aqueous solution is constant in 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 the control of the particle size of the composite hydroxide. If the temperature of the reaction aqueous solution is outside the above temperature range, the composition may become unstable or oxidation may easily proceed. Further, if the temperature is lower than 45 ° C., the particle size may become too large, and if the temperature exceeds 55 ° C., the particle size may become too small. Therefore, in the present embodiment, the temperature of the reaction aqueous solution is controlled to be within such a temperature range.

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

In the crystallization step S11, an aqueous solution containing ammonium ions and an alkaline aqueous solution are directly supplied into the reaction solution. For example, a supply tube is inserted into the reaction solution to supply an alkaline aqueous solution to the reaction solution. As a result, local fluctuations in pH value and ammonium ion concentration are suppressed, the distribution of silicon becomes uniform, and the growth of particles is stabilized. Due to the homogenization of the silicon distribution, the growth of the primary particles of the composite hydroxide into plate-like particles is appropriately suppressed, and the particles grow stably, so that the primary particles are densely aggregated and the secondary particles are densified. Is promoted. Therefore, the positive electrode active material obtained by using the composite hydroxide as a precursor can also have a particle structure having a high particle density.

FIG. 2A shows a supply position P of an aqueous solution containing ammonium ions and an alkaline aqueous solution (for example, from the supply pipe 13) in the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention. It is a figure for demonstrating one aspect. To prevent possible cause local high density portion, the supply position P of the aqueous solution and an alkaline aqueous solution containing ammonium ions, in the vertical direction, from the deepest D ₁ of the stirring blade 11 in the reaction solution, Between the deepest part D _{1 of the stirring blade 11 and the position D 3} which is one-third of the distance between the liquid level D _{2 of the reaction solution (that is, between D 1} and D ₃ in FIG. 2 (A)). In the horizontal direction, between the outermost circumference B ₁ of the stirring blade 11 and the intermediate position B _{2 of the} center C to the outermost circumference B _{1 of the stirring blade 11 (that is, between B 1} and B ₂ in FIG. 2 (A)). Is preferable. As a result, it is possible to supply the aqueous solution containing ammonium ions and the alkaline aqueous solution to the position where the flow velocity is the fastest in the vicinity of the stirring blade 11 where the flow velocity of the reaction solution is high, and the formation of a local high concentration region is suppressed. A good composite hydroxide can be obtained.

Further, by supplying an aqueous solution containing ammonium ions and an alkaline aqueous solution to the liquid surface where the flow velocity of the reaction solution is high, local fluctuations in pH value and ammonium ion concentration can be suppressed. FIG. 2B shows the supply positions (for example, from the supply pipe 13) of the aqueous solution containing ammonium ions and the alkaline aqueous solution in the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to another embodiment of the present invention. It is a figure for demonstrating one aspect of P. In another embodiment of the present invention, between the outer periphery of the liquid surface of the reaction solution 12 (B _3), to the outer periphery 12 (B ₃₎ and 1 position-third of the distance between the center C B ₄ of the liquid surface _{By supplying the liquid surface (that is, between B 3} and B ₄ in FIG. 2 (B)), the distribution of silicon becomes uniform and the growth of particles is stabilized.

In order to further suppress fluctuations in local pH value and ammonium ion concentration, it is preferable to install a stirring blade 11 and its shaft 14 for stirring the reaction solution on the central axis C of the reaction tank 10 used for crystallization. .. As a result, the reaction solution in the reaction vessel is uniformly agitated, and the fluctuation of the concentration is further suppressed.

The supply positions P of the aqueous solution containing ammonium ions and the alkaline aqueous solution are as described above, but in order to promote the homogenization of the silicon distribution, silicon is similarly supplied to the aqueous solution containing ammonium ions and the alkaline aqueous solution. It is preferable to supply an aqueous solution of additive elements containing.

Further, it is preferable to keep the oxygen concentration in the reaction aqueous solution low because the compound hydroxide can be contained more uniformly by suppressing the oxidation of the additive element. For example, by introducing an inert gas into the liquid surface of the reaction aqueous solution in the reaction tank to seal the reaction tank or set the pressure to positive, it is possible to prevent the invasion of oxygen from the outside of the tank and suppress oxidation. Further, by suppressing oxidation, the particle density of the composite hydroxide is improved, and a positive electrode active material having a high energy density can be obtained, which is preferable.

(2-2. Drying process)
The drying step S12 is a step of washing the crystallized nickel composite hydroxide and then drying it. Since the obtained composite hydroxide contains impurities, it is solid-liquid separated 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 of oxoacid ion such as sulfate ion, it may be washed with an alkaline aqueous solution. Then, it is preferably dried at a temperature in the range of 110 to 150 ° C. The drying temperature and time may be such that moisture can be removed.

Further, a heat treatment step of heating the composite hydroxide after drying in the drying step S12 to a temperature in the range of 600 to 800 ° C. to convert it into a nickel composite oxide (hereinafter, may be simply referred to as “composite oxide”). It is preferable to have more. By this heat treatment, the generation of water vapor in the firing step S13, which is a subsequent step, is suppressed to promote the reaction with the lithium compound, and the total of the metal elements and additive elements in the positive electrode active material and the ratio of lithium are stabilized. be able to. Further, silicon, which is an additive element, can be uniformly diffused in the composite oxide so that when the positive electrode active material is obtained, it is sufficiently replaced with nickel atoms.

If the heat treatment temperature in the heat treatment step is less than 600 ° C., the conversion to the composite oxide is insufficient, and the additive elements may not be uniformly diffused in the composite oxide. On the other hand, when the heat treatment temperature exceeds 800 ° C., the particles of the composite oxide may be sintered and coarse particles may be generated. In addition, it is not industrially suitable because it requires a lot of energy. The atmosphere in which the heat treatment is performed is not particularly limited, and may be a non-reducing atmosphere containing oxygen, but it is preferably performed in an air atmosphere that can be easily performed.

The heat treatment time may be a time that allows sufficient conversion to the composite oxide, preferably 1 to 12 hours. Further, the equipment used for the heat treatment is not particularly limited as long as the composite hydroxide can be heated in a non-reducing atmosphere containing oxygen, preferably in an air atmosphere, and gas generation is generated. An electric furnace or the like is preferably used.

(2-3. Baking process)
The firing step S13 is a step of obtaining a lithium metal composite oxide by firing a mixture obtained by mixing the dried nickel composite hydroxide and the lithium compound in an oxygen atmosphere. 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 (Me) in the mixture to the number of atoms of lithium (Li) (Li). Li / Me) is preferably mixed so as to be 0.98 to 1.15, more preferably 1.01 to 1.09. That is, since Li / Me does not change before and after the firing step, the Li / Me mixed in this mixing step becomes Li / Me in the positive electrode active material, so that the Li / Me in the mixture is in the positive electrode active material to be obtained. It is mixed so as to be the same as Li / Me.

By mixing so that the Li / Me ratio is 1.01 to 1.09, crystallization is promoted, and the substitution of the nickel atom and the additive element silicon is further promoted. If the Li / Me ratio is smaller than 1.01, lithium may remain without reacting with some oxides and sufficient battery performance may not be obtained. On the other hand, if the Li / Me ratio is larger than 1.09, sintering is promoted, the particle size and crystallite diameter 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 a mixture thereof is preferable in that it is easily available. In particular, considering ease of handling and stability of quality, it is more preferable to use lithium hydroxide or lithium carbonate. Lithium hydroxide is highly reactive with the composite oxide, crystallization is promoted, and the substitution of the nickel atom with the additive element silicon is further promoted.

The lithium mixture is preferably sufficiently mixed before firing. If the mixing is not sufficient, Li / Me may vary among the individual particles, which may cause problems such as when sufficient battery characteristics cannot be obtained. Therefore, it is necessary to mix the particles sufficiently before firing.

In addition, a general mixer can be used for mixing, for example, a shaker mixer, a ladyge mixer, a julia mixer, a V blender, or the like can be used, and composite oxidation can be used to the extent that the skeleton of heat-treated particles and the like is not destroyed. It suffices if the physical particles and the substance containing lithium are sufficiently mixed.

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

If the firing temperature is less than 650 ° C., lithium is not sufficiently diffused into the heat-treated particles, excess lithium and unreacted particles remain, and the crystal structure is not sufficiently arranged, so that the battery is used. In this case, sufficient battery characteristics may not be obtained. On the other hand, if the firing temperature exceeds 950 ° C., the composite oxide particles may be violently sintered and abnormal grain growth may occur. When abnormal grain growth occurs, the particles after firing become coarse and the specific surface area decreases. Therefore, when used in a battery, there arises a problem that the resistance of the positive electrode increases and the battery capacity decreases.

The firing time is preferably at least 4 hours or more, more preferably 6 to 10 hours. In less than 4 hours, the formation of the lithium metal composite oxide may not be sufficient.

When lithium hydroxide is used as the lithium compound, it is preferably lower than the firing temperature and at a temperature of 350 to 800 ° C., preferably 450 to 780 ° C. for about 1 to 10 hours before firing the lithium mixture. Is preferably held for 3 to 6 hours and calcined. That is, it is preferable to perform calcining at the reaction temperature of lithium hydroxide or lithium carbonate and the composite oxide. In this case, if lithium hydroxide or lithium carbonate is held near the above reaction temperature, lithium hydroxide is melted and lithium is sufficiently diffused into the composite oxide, so that uniform and highly crystalline lithium metal composite oxidation is performed. The product can be obtained and the substitution of additive elements can be promoted.

The atmosphere at the time of 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, firing is preferably performed in the atmosphere or 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 the 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 an oxygen stream, but from the viewpoint of keeping the atmosphere in the furnace uniform, electricity that does not generate gas is used. A furnace is preferable, and either a batch type or a continuous type furnace can be used.

In addition, the lithium metal composite oxide obtained by firing may be agglutinated or slightly sintered. In this case, it may be crushed, whereby a lithium metal composite oxide, that is, a positive electrode active material according to an embodiment of the present invention can be obtained. In addition, crushing means that mechanical energy is applied to an agglomerate composed of a plurality of secondary particles generated by sintering necking between secondary particles during firing, and the secondary particles themselves are hardly destroyed. It refers to the operation of separating the next particles and disassembling the agglomerates.

<3. Non-aqueous electrolyte secondary battery ＞
The non-aqueous electrolyte secondary battery according to an embodiment of the present invention comprises a positive electrode containing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the above-described embodiment of the present invention, a negative electrode, a non-aqueous electrolyte solution, and the like. The battery structure itself is composed of the same components as a general non-aqueous electrolyte secondary battery. Hereinafter, each component of the non-aqueous electrolyte secondary battery according to the 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 the above-described embodiment of the present invention, for example, a positive electrode for a non-aqueous electrolyte secondary battery is produced as follows.

First, a powdered positive electrode active material, a conductive material, and a binder are mixed, and if necessary, activated carbon, a solvent for viscosity adjustment and the like are added, and the mixture is kneaded to prepare a positive electrode mixture paste. The mixing ratio of each of the positive electrode mixture pastes is also an important factor in determining 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 and the conductive material is similar to the positive electrode of a general non-aqueous electrolyte secondary battery. It is desirable that the content of the binder is 1 to 20 parts by mass and the content of the binder is 1 to 20 parts by mass.

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

In producing the positive electrode, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black material such as acetylene black, Ketjen black (registered trademark), or the like can be used as the conductive agent.

The binder plays a role of binding the active material particles, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, and polyacrylic acid. Acids and 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. Specifically, as the solvent, 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 The negative electrode is a negative electrode mixture made into a paste by mixing a binder with a metallic lithium, a lithium alloy, or a negative electrode active material capable of occluding and desorbing lithium ions, and adding an appropriate solvent. Is applied to the surface of a metal foil current collector such as copper, dried, and if necessary, compressed to increase the electrode density.

As the negative electrode active material, for example, a calcined product of an organic compound such as natural graphite, artificial graphite, or phenol resin, or a powdered material of a carbon substance such as coke can be used. In this case, as the negative electrode binder, a fluororesin such as PVDF can be used as in the positive electrode, and as a solvent for dispersing these active substances and the binder, N-methyl-2-pyrrolidone or the like can be used. An organic solvent can be used.

(C) Separator A separator is sandwiched between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and a thin film such as polyethylene or polypropylene, which has a large number of fine pores, can be used.

(D) Non-aqueous electrolyte solution The non-aqueous electrolyte solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of the organic solvent 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, and tetrahydrofuran and 2-. One selected from ether compounds such as methyl tetrahydrofuran and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sulton, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate are used alone or in combination of two or more. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) _2, etc., and a composite salt thereof can be used. Further, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant and the like.

(E) Battery Shape and Configuration The shape of the non-aqueous electrolyte secondary battery according to the embodiment of the present invention composed of the positive electrode, the negative electrode, the separator and the non-aqueous electrolyte solution described above is cylindrical. Various types such as a laminated type can be used. Regardless of the shape, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte solution to impregnate the positive electrode body with a non-aqueous electrolyte solution to communicate with the positive electrode current collector and the positive electrode terminal to the outside. The negative electrode current collector and the negative electrode terminal leading to the outside are connected to each other by using a current collecting lead or the like, and sealed in a battery case to complete a non-aqueous electrolyte secondary battery.

(F) Characteristics The non-aqueous electrolyte secondary battery using the positive electrode active material according to the embodiment of the present invention has a high capacity and excellent thermal stability. When the non-aqueous electrolyte secondary battery using the positive electrode active material according to the embodiment of the present invention obtained in a particularly preferable form is used for the positive electrode of a 2032 type coin battery, for example, the composition and manufacturing method are optimized. If this is done, a high initial discharge capacity of 195 mAh / g or more can be obtained, and the capacity is even higher.

Hereinafter, the positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. The method for analyzing the metal contained in the positive electrode active material and the various evaluation methods for the positive electrode active material in Examples and Comparative Examples are as follows.

(1) Composition analysis: Measured by ICP emission spectrometry.

(2) Average particle size D50: Performed by a laser diffraction / scattering type particle size distribution measuring device (Microtrac HRA, manufactured by Nikkiso Co., Ltd.).

(3) Crystallite diameter and lattice constant: Calculated from a diffraction chart obtained by an X-ray diffraction (XRD) diffractometer (X'Pert PRO manufactured by PANalytical Co., Ltd.). The crystallite diameter was calculated from the peak of the (003) plane by Scherrer's formula. The lattice constant was obtained by Rietveld analysis of the diffraction chart.

(4) Void ratio: A positive electrode active material (secondary particles) was embedded in a resin, and cross-section polisher processing was performed to make it possible to observe a cross section with a scanning electron microscope (SEM). For the void ratio, an SEM image of the cross section is taken, and the void is detected as a black portion using image analysis software such as WinLoof 6.1.1 (trade name), and the void ratio is determined by measuring the black portion with respect to the total cross-sectional area of the secondary particles. It was obtained by calculating the ratio of the area. Further, for the porosity of the positive electrode active material, 20 cross sections of secondary particles having an average particle size of 80% or more were randomly selected, and the porosities of the cross sections of those secondary particles were measured. The average porosity, which is the average value, was used.

(5) Initial discharge capacity: The battery capacity was evaluated by the following method.
(Battery capacity evaluation)
An example in which the non-aqueous electrolyte secondary battery according to the embodiment of the present invention is applied to a 2032 type coin battery will be described with reference to the drawings. 3A and 3B are structural views of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, FIG. 3A is a perspective view, and FIG. 3B is FIG. 3A. It is a cross-sectional view taken along the line AA. Using the positive electrode active materials obtained in Examples 1 to 8 and Comparative Examples 1 to 6, a 2032 type coin battery 1 as shown in FIG. 3 was produced.

The 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 positive electrode can 2a that is hollow and has one end opened, and a negative electrode can 2b that is arranged in the opening of the positive electrode can 2a. When the negative electrode can 2b is 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 is composed of a positive electrode 3a, a separator 3c, and a negative electrode 3b, and is laminated so as to be arranged in this order. The positive electrode 3a contacts the inner surface of the positive electrode can 2a, and the negative electrode 3b contacts the inner surface of the negative electrode can 2b. It is housed in the case 2 so as to do so.

The case 2 is provided with a gasket 2c, and is fixed by the gasket 2c so as to electrically maintain an insulating state between the positive electrode can 2a and the negative electrode can 2b. Further, the gasket 2c also has a function of sealing the gap between the positive electrode can 2a and the negative electrode can 2b to seal the inside and the outside of the case 2 in an airtight and liquid-tight manner.

This 2032 type coin battery 1 was manufactured 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 a positive electrode 3a. .. The prepared positive electrode 3a was dried at 120 ° C. for 12 hours in a vacuum dryer. Using the positive electrode 3a, the negative electrode 3b, the separator 3c, and the electrolytic solution, a coin-type battery 1 was produced in a glove box having an Ar atmosphere with a dew point controlled at −80 ° C.

For the negative electrode 3b, graphite powder having an average particle diameter of about 20 μm punched into a disk shape having a diameter of 14 mm and a negative electrode sheet coated with polyvinylidene fluoride on a copper foil were used. Further, as the separator 3c, a polyethylene porous membrane having a film thickness of 25 μm was used. As the electrolytic solution, an equal amount mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) using _{1M LiClO 4 as a supporting electrolyte (manufactured by Tomiyama Pure Chemical Industries, Ltd.) was used.}

After the 2032 type coin battery 1 is manufactured and left to stand for about 24 hours, after the open circuit voltage OCV (Open Circuit Voltage) stabilizes, the current density with respect to the positive electrode is set to 0.1 mA / cm ² and the cutoff voltage is 4.8 V. A charge / discharge test was conducted to measure the discharge capacity when the battery was charged until the battery capacity became 2.5 V after a one-hour rest period, and the initial discharge capacity was determined as the battery capacity. At this time, a multi-channel voltage / current generator (manufactured by Advantest Co., Ltd., R6741A) was used to measure the charge / discharge capacity.

(Example 1)
A mixed aqueous solution of 2 mol / L in which nickel sulfate and cobalt sulfate were dissolved in ion-exchanged water was prepared so that the atomic ratio was nickel: cobalt = 84.0: 16.0. In a reaction vessel kept at 50 ° C., 1 L of an aqueous sodium hydroxide solution having a pH value of 13 based on a liquid temperature of 25 ° C. was placed, and aqueous ammonia was added so that the ammonia concentration became 10 mg / L. While maintaining the temperature, pH value, and ammonia concentration, 40 ml of the raw material solution, aqueous ammonia, and aqueous sodium hydroxide solution were supplied into the reaction vessel 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 while maintaining the temperature, pH value, and ammonia concentration, the remaining raw material solution, aqueous ammonia, aqueous sodium hydroxide solution, and nickel: cobalt: silicon = 83. An aqueous sodium silicate solution was supplied over 2 hours so as to have a ratio of .2: 15.8: 1.0, and the nickel composite hydroxide was crystallized. The crystallized nickel composite hydroxide was separated into solid and liquid 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. Through crystallization, the supply position of aqueous ammonia and sodium hydroxide solution shall be one-fifth of the distance from the deepest part of the stirring blade in the reaction solution to the deepest part of the stirring blade and the liquid level of the reaction solution in the vertical direction. In the horizontal direction, the position was set between the outermost circumference and the center of the stirring blade.

Next, the precursor was heated to 700 ° C. in the air atmosphere, held for 6 hours and heat-treated to convert it into a nickel composite oxide. A nickel composite oxide and lithium hydroxide were mixed to prepare a mixture so that the ratio of the number of atoms of lithium to the total number of atoms of nickel, cobalt and silicon (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 determine the initial discharge capacity. The evaluation results are shown in Table 1.

(Example 2)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the supply time of the raw material solution after nucleation was formed, aqueous ammonia, aqueous sodium hydroxide solution, and aqueous sodium silicate solution was set to 4 hours. The evaluation results are shown in Table 1.

(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 was 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. The evaluation results are shown in Table 1.

(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 vessel so that the atomic ratio was 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 2. The evaluation results are shown in Table 1.

(Example 5)
Except for supplying a mixed aqueous solution in which nickel sulfate and cobalt sulfate were dissolved in ion-exchanged water and an aqueous sodium silicate solution so that the atomic ratio was 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. The evaluation results are shown in Table 1.

(Example 6)
Except for supplying a mixed aqueous solution in which nickel sulfate and cobalt sulfate were dissolved in ion-exchanged water and an aqueous sodium silicate solution so that the atomic ratio was 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 2. The evaluation results are shown in Table 1. Further, FIG. 4 shows a scanning electron micrograph of the precursor of the positive electrode active material of Example 6, and FIG. 5 shows a scanning electron micrograph of the positive electrode active material of Example 6.

(Example 7)
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 was nickel: cobalt: silicon = 80.6: 15.4: 4.0. , A positive electrode active material was obtained and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

(Example 8)
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 was nickel: cobalt: silicon = 79.8: 15.2: 5.0. , A positive electrode active material was obtained and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

(Example 9)
Except that the supply position of the aqueous ammonia and sodium hydroxide solution was set to one-third of the distance from the deepest part of the stirring blade in the reaction solution to the deepest part of the stirring blade and the liquid level of the reaction solution in the vertical direction. A positive electrode active material was obtained and evaluated in the same manner as in Example 6. The evaluation results are shown in Table 1.

(Example 10)
A positive electrode active material was obtained and evaluated in the same manner as in Example 6 except that aqueous ammonia and an aqueous sodium hydroxide solution were supplied to the liquid surface at a position of 1/4 of the distance from the outer periphery to the center of the liquid surface of the reaction solution. .. The evaluation results are shown in Table 1.

(Comparative Example 1)
As a conventional technique in which no additive element is added, except that a mixed aqueous solution of nickel sulfate and cobalt sulfate dissolved in ion-exchanged water is supplied to the reaction vessel so that the atomic ratio is nickel: cobalt = 84.0: 16.0. , A positive electrode active material was obtained and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. Further, FIG. 6 shows a scanning electron micrograph of the precursor of the positive electrode active material of Comparative Example 1, and FIG. 7 shows a scanning electron micrograph of the positive electrode active material of Comparative Example 1.

(Comparative Example 2)
As a conventional technique in which no additive element is added, except that a mixed aqueous solution of nickel sulfate and cobalt sulfate dissolved in ion-exchanged water is supplied to the reaction vessel so that the atomic ratio is nickel: cobalt = 84.0: 16.0. , A positive electrode active material was obtained and evaluated in the same manner as in Example 2. The evaluation results are shown in Table 1.

(Comparative Example 3)
Except for supplying only a mixed aqueous solution in which nickel sulfate, cobalt sulfate, and boric acid were dissolved in ion-exchanged water so that the atomic ratio was nickel: cobalt: boron = 83.2: 15.8: 1.0. , A positive electrode active material was obtained and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

(Comparative Example 4)
Except for supplying only a mixed aqueous solution in which nickel sulfate, cobalt sulfate, and boric acid were dissolved in ion-exchanged water so that the atomic ratio was nickel: cobalt: boron = 83.2: 15.8: 1.0. , A positive electrode active material was obtained and evaluated in the same manner as in Example 2. The evaluation results are shown in Table 1.

(Comparative Example 5)
Except for supplying only a mixed aqueous solution in which nickel sulfate, cobalt sulfate, and boric acid were dissolved in ion-exchanged water so that the atomic ratio was nickel: cobalt: boron = 82.3: 15.7: 2.0. , A positive electrode active material was obtained and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

(Comparative Example 6)
Except for supplying only a mixed aqueous solution in which nickel sulfate, cobalt sulfate, and boric acid were dissolved in ion-exchanged water so that the atomic ratio was nickel: cobalt: boron = 82.3: 15.7: 2.0. , A positive electrode active material was obtained and evaluated in the same manner as in Example 2. The evaluation results are shown in Table 2. Further, FIG. 8 shows a scanning electron micrograph of the precursor of the positive electrode active material of Comparative Example 6, and FIG. 9 shows a scanning electron micrograph of the positive electrode active material of Comparative Example 6.

In Comparative Example 1 and Comparative Example 2 in which no additive element was added, the porosity of the secondary particles was in the 2% range regardless of the particle size, but in Examples 1 to 10 to which silicon was added, the porosity was not related to the particle size. A high density secondary particle positive electrode active material was formed with a porosity of less than 1%. When the amount of silicon added is 3 atomic% or less with respect to the total of metal elements and added elements, the positive electrode of extremely high-density secondary particles having a void ratio of 0.5% or less regardless of the particle size. The active material was formed.

On the other hand, in Comparative Examples 3 to 6 to which boron was added, the porosity was as high as 1% or more, and when boron was 2 atomic%, the porosity increased to nearly 10%.

4 and 5 are scanning electron micrographs of the positive electrode active material precursor and the positive electrode active material of Example 6, and FIGS. 6 and 7 are the positive electrode active material precursor and the positive electrode activity of Comparative Example 1. 9 is a scanning electron micrograph of the substance, and FIGS. 8 and 9 are scanning electron micrographs of the precursor of the positive electrode active material and the positive electrode active material of Comparative Example 6. As can be seen from these figures, the non-aqueous system according to the embodiment of the present invention of Example 6 in which the amount of silicon added is 0.5 atomic% to 7 atomic% with respect to the total of the metal element and the added element. The positive electrode active material for an electrolyte secondary battery has fewer voids and a higher density than the figures of Comparative Example 1 in which silicon is not added and Comparative Example 6 in which boron is added instead of silicon. I understand.

In the positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, voids can be reduced by adding silicon, and a very high density positive electrode active material can be obtained. It is a useful technology for forming a non-aqueous electrolyte secondary battery with a large capacity, and is expected to be applied to the positive electrode active material of a non-aqueous electrolyte secondary battery for automobiles and mobiles.

Although each embodiment and each embodiment of the present invention have been described in detail as described above, those skilled in the art will be able to make many modifications that do not substantially deviate from the new matters and effects of the present invention. , Will be easy to understand. Therefore, all such modifications are included in the scope of the present invention.

For example, a term described at least once in a specification or drawing with a different term in a broader or synonymous manner may be replaced by that different term anywhere in the specification or drawing. Further, the composition and operation of the positive electrode active material for the non-aqueous electrolyte secondary battery are not limited to those described in each embodiment and each embodiment of the present invention, and various modifications can be carried out.

S11 crystallization step, S12 drying step, S13 firing step, 1 non-aqueous electrolyte secondary battery (2032 type coin cell), 2 case, 2a positive electrode can, 2b negative electrode can, 2c gasket, 3 electrode, 3a positive electrode, 3b negative electrode, 3c separator, 10 reaction tank, 11 stirring blade, 12 outer circumference, 13 supply pipe, 14 shaft, B ₁ outermost circumference of _{stirring blade, B 2} intermediate position between outermost circumference and center of stirring blade, B ₃ outer circumference of liquid surface, B one-third position of the distance between the outer periphery and the center of the liquid surface from the outer periphery of the ₄ liquid surface, C the center (central axis), the deepest portion, D ₂ liquid surface of D ₁ stirring blade deepest portion of the D ₃ agitation wings One-third of the distance between the deepest part of the stirring blade and the liquid level of the reaction solution, P supply position, W length of the stirring blade, W'distance from the outer circumference to the center of the liquid level, L Distance from the deepest part to the liquid level

Claims (13)

A positive electrode active material for a non-aqueous electrolyte secondary battery made of a lithium metal composite oxide composed of secondary particles formed by agglomeration of primary particles.
With lithium
With metal elements
It consists of added elements,
The lithium metal composite oxide has a crystal structure of a layered rock salt type structure, contains nickel and cobalt as the metal elements, and the content of the nickel is 79.8 with respect to the total of the metal elements and the additive elements. It is ~ 90 atomic%, and the content of the cobalt is 5 to 15.8 atomic% with respect to the total of the metal element and the additive element.
And the additional element is a silicofluoride-containing content of the silicon is 0.5 to 7 atomic% of the total of the metal element and the additive element,
Further, a positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that the void ratio of the secondary particles is 1% or less and the crystallite diameter is 140 nm or less. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the silicon content is 0.5 to 3 atomic%. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the lithium metal composite oxide has a particle size of 5 to 20 μm. The non-aqueous electrolyte according to any one of claims 1 to 3, wherein the lithium metal composite oxide has an a-axis lattice constant of 0.2868 nm or more and a c-axis lattice constant of 1.4177 nm or more. Positive electrode active material for secondary batteries. The positive electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the lithium metal composite oxide has a void ratio in the secondary particles of 0.5% or less as observed in a cross section. Active material. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for the non-aqueous electrolyte secondary battery according to any one of claims 1 to 5. It is composed of lithium, a metal element, and an additive element , and the content of nickel as the metal element is 79.8 to 90 atomic% with respect to the total of the metal element and the additive element, and the content of cobalt as the metal element. The amount is 5 to 15.8 atomic% with respect to the total of the metal element and the additive element, and the additive element is silicon, and the content of the silicon is the metal element and the additive element. A non-aqueous electrolyte secondary battery made of a lithium metal composite oxide having a total void ratio of 0.5 to 7 atomic%, a void ratio of secondary particles of 1% or less, and a crystallite diameter of 140 nm or less. It is a method for producing a positive electrode active material for use.
An aqueous solution of a metal element salt containing at least a nickel salt and a cobalt salt, an aqueous solution of an additive element containing silicon, and an aqueous solution containing ammonium ions are mixed to prepare a reaction solution, and the pH value of the reaction solution based on a liquid temperature of 25 ° C. is 11. It is controlled by using an alkaline aqueous solution so as to be in the range of 0 to 12.5, and at that time, an aqueous solution containing ammonium ions and an alkaline aqueous solution are supplied into the reaction solution to produce nickel composite hydroxide particles. The crystallization process to grow and
A drying step of washing the crystallized nickel composite hydroxide and then drying it,
A firing step of obtaining the lithium metal composite oxide by firing a mixture obtained by mixing the dried nickel composite hydroxide and a lithium compound in an oxygen atmosphere.
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises. The positive electrode activity for a non-aqueous electrolyte secondary battery according to claim 7, wherein in the crystallization step, silicon is 0.5 to 3 atomic% with respect to the total of the metal element and the additive element. Method of manufacturing the substance. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 7 or 8, wherein the concentration of the aqueous metal element solution is 1.5 to 2.5 mol / L in the crystallization step. Manufacturing method. In the crystallization step, the supply positions of the aqueous solution containing ammonium ions and the alkaline aqueous solution are, in the vertical direction, from the deepest part of the stirring blade in the reaction solution to the deepest part of the stirring blade and the liquid of the reaction solution. The claim is to be between a position of one-third of the distance from the surface, and in the horizontal direction, from an intermediate position between the outermost circumference and the center of the stirring blade to the outermost circumference of the stirring blade. Item 8. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Items 7 to 9. In the crystallization step, the supply position of the aqueous solution containing ammonium ions and the alkaline aqueous solution is from the outer periphery of the liquid surface of the reaction solution to a position of one-third of the distance between the outer periphery and the center of the liquid surface. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 7 to 9, wherein the solution is supplied to the liquid surface between the two. The method for producing an active material for a non-aqueous electrolyte secondary battery according to any one of claims 7 to 11, wherein in the firing step, the firing temperature is set to 650 to 950 ° C. Production of the active material for a non-aqueous electrolyte secondary battery according to any one of claims 7 to 12, wherein lithium hydroxide, lithium carbonate, or a mixture thereof is used as the lithium compound in the firing step. Method.

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