JP2021044093A - Production method of positive electrode active material for nonaqueous electrolyte secondary battery - Google Patents

Abstract

To provide a production method of a positive electrode active material which enables the formation of a nonaqueous electrolyte secondary battery of a high energy density.SOLUTION: A production method of a positive electrode active material for a nonaqueous electrolyte secondary battery comprises the steps of: preparing a first lithium transition metal oxide containing lithium and nickel, and having a layered structure in which the nickel ratio is 0.7 or larger, and the lithium ratio is 0.95 up to 1.05; bringing the first lithium transition metal oxide into contact with a liquid medium and then, removing at least part of the liquid medium to obtain a second lithium transition metal oxide of which the lithium ratio is 0.90 or larger and smaller than 1; mixing the second lithium transition metal oxide with lithium hydroxide to obtain a mixture in which the lithium ratio is 1 to 1.15; and performing a heat treatment on the mixture at a temperature of 460°C up to 750°C to obtain a third lithium transition metal oxide. The third lithium transition metal oxide has a layered structure, in which the lithium ratio is 1 up to 1.15, and the nickel ratio is 0.7 or larger and smaller than 0.99.SELECTED DRAWING: None

Description

The present disclosure relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.

High energy densities are required for electrode active materials for non-aqueous electrolyte secondary batteries used in large power equipment such as electric vehicles. In order to obtain a high energy density, the charge capacity of the positive electrode active material and the filling property of the positive electrode active material in the positive electrode plate are important, and further improvement of the charging capacity and the filling property is required.

In relation to the above, Patent Document 1 proposes a technique of washing a lithium transition metal composite oxide that requires nickel with water by a specific method to remove substances that may cause gas generation such as lithium carbonate. ing.

Japanese Unexamined Patent Publication No. 2003-017054

One aspect of the present disclosure is to provide a method for producing a positive electrode active material capable of constructing a non-aqueous electrolyte secondary battery having a high energy density.

The first aspect comprises lithium and nickel, and the nickel ratio, which is the molar ratio of nickel to the total number of moles of metals other than lithium in the composition, is 0.7 or more, and the ratio of lithium to the total number of moles of metals other than lithium is 0.7 or more. A first lithium transition metal oxide having a layered structure having a lithium ratio of 0.95 or more and 1.05 or less, which is a molar ratio, was prepared, and the first lithium transition metal oxide was brought into contact with a liquid medium. After that, at least a part of the liquid medium is removed to obtain a second lithium transition metal oxide having a lithium ratio of 0.90 or more and less than 1, and the second lithium transition metal oxide and lithium hydroxide are used. To obtain a mixture having a lithium ratio of 1 or more and 1.15 or less, and to heat the mixture at a temperature of 460 ° C. or more and 750 ° C. or less to obtain a third lithium transition metal oxide. It is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery containing. The third lithium transition metal oxide has a layered structure, has a lithium ratio of 1 or more and 1.15 or less, and has a nickel ratio of 0.7 or more and less than 1.

According to one aspect of the present disclosure, it is possible to provide a method for producing a positive electrode active material capable of forming a non-aqueous electrolyte secondary battery having a high energy density.

In the present specification, the term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes. Is done. Further, the content of each component in the composition means the total amount of the plurality of substances present in the composition when a plurality of substances corresponding to each component are present in the composition, unless otherwise specified. Further, the lithium ratio means the molar ratio of lithium to the total number of moles of metals other than lithium in the composition of the lithium transition metal oxide, the positive electrode active material or the mixture. Similarly, the nickel ratio means the molar ratio of nickel to the total number of moles of metals other than lithium in the composition of the lithium transition metal oxide, positive electrode active material or mixture. Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments shown below exemplify a method for producing a positive electrode active material for embodying the technical idea of the present invention, and the present invention is limited to the method for producing a positive electrode active material shown below. Not done.

[Manufacturing method of positive electrode active material for non-aqueous electrolyte secondary batteries]
The method for producing a positive electrode active material for a non-aqueous secondary battery (hereinafter, also simply referred to as a positive electrode active material) contains lithium and nickel, and the nickel ratio, which is the molar ratio of nickel to the total number of moles of metals other than lithium in the composition, is Prepare a first lithium transition metal oxide having a layered structure having a lithium ratio of 0.7 or more and a molar ratio of lithium to the total number of moles of metals other than lithium of 0.95 or more and 1.05 or less. After the preparatory step and the contact of the first lithium transition metal oxide with the liquid medium, at least a part of the liquid medium is removed to oxidize the second lithium transition metal having a lithium ratio of 0.90 or more and less than 1. A cleaning step of obtaining a product, a mixing step of mixing a second lithium transition metal oxide and lithium hydroxide to obtain a mixture having a lithium ratio of 1 or more and 1.15 or less, and a mixing step of 460 ° C. or higher and 750 ° C. A heat treatment step of obtaining a third lithium transition metal oxide by heat treatment at the following temperature is included. The obtained third lithium transition metal oxide has a layered structure, has a lithium ratio of 1 or more and 1.15 or less, and has a nickel ratio of 0.7 or more and less than 1.

Generally, a lithium transition metal composite oxide having a high nickel ratio of 0.7 or more can obtain an excellent charge capacity, but it is said that its synthesis is difficult. The lithium transition metal composite oxide is synthesized as a heat-treated product of a mixture of the transition metal composite oxide and the lithium compound, but in the synthesis of the lithium transition metal composite oxide having a high nickel ratio, the ratio of the lithium compound in the mixture is large. There is a need to. However, if the ratio of the lithium compound in the mixture is increased, the unreacted lithium compound may remain in the obtained heat-treated product. When a secondary battery is constructed using a positive electrode active material containing an unreacted lithium compound, the electrolyte may be decomposed during charging and cause gas generation. On the other hand, when the unreacted lithium compound is removed by a washing treatment, the filling property of the obtained positive electrode active material is lowered, and the lithium compound is eluted from the inside of the lithium transition metal composite oxide particles to the particle surface, resulting in the result. In some cases, the desired charge capacity could not be achieved.

In the method for producing a positive electrode active material according to the present embodiment, after the heat-treated product is washed, lithium hydroxide is added and the heat-treated product is heat-treated at a predetermined temperature to reduce the content of unreacted lithium compounds. It is possible to suppress the decrease in filling property and the elution of lithium. Thereby, an excellent charging capacity can be achieved when the secondary battery is constructed by using the obtained positive electrode active material.

Preparation Step In the preparation step, a first lithium transition metal oxide containing lithium and nickel, having a nickel ratio of 0.7 or more, a lithium ratio of 0.95 or more and 1.05 or less, and having a layered structure is prepared. To do. Here, the nickel ratio is the molar ratio of nickel to the total number of moles of metals other than lithium in the composition of the first lithium transition metal oxide. The lithium ratio is the molar ratio of lithium to the total number of moles of metals other than lithium in the composition of the first lithium transition metal oxide. The first lithium transition metal composite oxide may be appropriately selected from commercially available products and prepared, or may be newly prepared and prepared according to the preparation method as described below.

The first method for preparing a lithium transition metal composite oxide includes, for example, a precursor preparation step of preparing a precursor and a synthesis step of synthesizing a first lithium transition metal composite oxide from the precursor and a lithium compound. You can go out. The first lithium transition metal composite oxide may be composed of, for example, secondary particles composed of a plurality of primary particles containing the lithium transition metal composite oxide.

In the precursor preparation step, a precursor containing a nickel-containing composite oxide is prepared. The precursor may be appropriately selected from commercially available products and prepared, or a nickel-containing composite oxide having a desired constitution may be prepared and prepared by a conventional method.

As a method for obtaining a nickel-containing composite oxide having a desired composition, a method of mixing a raw material compound (hydroxide, carbonic acid compound, etc.) according to a target composition and decomposing it into a nickel-containing composite oxide by heat treatment, or a solvent can be used. A co-precipitation method in which a soluble raw material compound is dissolved in a solvent, a precipitate is obtained according to the desired composition by adjusting the temperature, adjusting the pH, adding a complexing agent, etc., and a nickel-containing composite oxide is obtained by heat treatment of the precipitate. And so on. Hereinafter, an example of a method for producing a nickel-containing composite oxide (hereinafter, also simply referred to as a composite oxide) will be described.

The method for obtaining a composite oxide by the co-precipitation method includes a seed generation step of adjusting the pH of a mixed solution containing metal ions at a desired composition ratio to obtain seed crystals, and a desired seed crystal growth method. A crystallization step of obtaining a composite hydroxide having characteristics and a step of heat-treating the obtained composite hydroxide to obtain a composite oxide can be included. For details of the method for obtaining such a composite oxide, for example, JP-A-2003-292322, JP-A-2011-116580 and the like can be referred to.

In the seed formation step, a liquid medium containing seed crystals is prepared by adjusting the pH of the mixed solution containing nickel ions in a desired composition ratio, for example, from 11 to 13. The seed crystal can include, for example, a hydroxide containing nickel in a desired ratio. The mixed solution can be prepared by dissolving the nickel salt in water in a desired ratio. Examples of the nickel salt include sulfates, nitrates, hydrochlorides and the like. In addition to the nickel salt, the mixed solution may contain other metal salts in a desired composition ratio, if necessary. The temperature in the seed production step can be, for example, 40 ° C to 80 ° C. The atmosphere in the seed production step can be a low-oxidizing atmosphere, for example, the oxygen concentration can be maintained at 10% by volume or less.

In the crystallization step, the produced seed crystal is grown to obtain a nickel-containing precipitate having desired properties. For seed crystal growth, for example, nickel ions and, if necessary, other metal ions are added to a liquid medium containing the seed crystals while maintaining the pH at, for example, 7 to 12.5, preferably 7.5 to 12. This can be done by adding a mixed solution containing the mixture. The addition time of the mixed solution is, for example, 1 hour to 24 hours, preferably 3 hours to 18 hours. The temperature in the crystallization step can be, for example, 40 ° C to 80 ° C. The atmosphere in the crystallization step is the same as that in the seed formation step.

The pH in the seed formation step and the crystallization step can be adjusted by using an acidic aqueous solution such as a sulfuric acid aqueous solution or a nitric acid aqueous solution, an alkaline aqueous solution such as sodium hydroxide aqueous solution, or ammonia water.

In the crystallization step, it is desirable to control the particle size of the precipitate. The particle size of the precipitate can be controlled by adjusting the temperature, pH, stirring speed and the like of the reaction field. Further, since the tendency changes depending on the shape of the container for accommodating the reaction field, the starting raw material, the charging speed of the starting raw material into the reaction field, and the like, it can be appropriately adjusted according to the actual conditions. Further, the particle size of the precipitate can be controlled by the aging time after the precipitation of the precipitate starts, the stirring speed, and the like. Also in this case, since the tendency differs depending on the shape of the reaction vessel, it can be appropriately adjusted according to the actual conditions.

In the step of obtaining the composite oxide, the precipitate containing the composite hydroxide obtained in the crystallization step is heat-treated to obtain the composite oxide. The heat treatment can be performed by heating the composite hydroxide at a temperature of, for example, 500 ° C. or lower, preferably 350 ° C. or lower. The heat treatment temperature is, for example, 100 ° C. or higher, preferably 200 ° C. or higher, and the heat treatment time can be, for example, 0.5 hour to 48 hours, preferably 5 hours to 24 hours. The atmosphere of the heat treatment may be the atmosphere or an atmosphere containing oxygen. The heat treatment can be performed using, for example, a box furnace, a rotary kiln furnace, a pusher furnace, a roller harsquill furnace, or the like.

The resulting composite oxide may contain other metal elements in addition to nickel. Examples of other metals include Co, Mn, Al, Zr, W, Nb, Mo, Ti and the like, and at least one selected from the group consisting of these is preferable, and at least Co, Mn and Al may be contained. preferable. When the composite oxide contains a metal other than nickel, the mixed aqueous solution for obtaining the precipitate may contain other metal ions in a desired composition. Thereby, nickel and other metals are impregnated in the precipitate, and the precipitate is heat-treated to obtain a composite oxide having a desired composition.

The average particle size of the composite oxide is, for example, 2 μm or more and 30 μm or less, preferably 4 μm or more and 25 μm or less. The average particle size of the composite oxide is a volume average particle size, and is a value at which the volume integrated value from the small particle size side in the cumulative particle size distribution based on the volume obtained by the laser scattering method is 50%.

In the synthesis step, a mixture containing lithium obtained by mixing a composite oxide and a lithium compound is heat-treated at a temperature of 550 ° C. or higher and 1000 ° C. or lower to obtain a heat-treated product. The resulting heat-treated product has a layered structure and contains a lithium transition metal composite oxide containing nickel.

Examples of the lithium compound to be mixed with the composite oxide include lithium hydroxide, lithium carbonate, lithium oxide and the like. The particle size of the lithium compound used for mixing is, for example, 0.1 μm or more and 100 μm or less, preferably 2 μm or more and 20 μm or less, as a 50% particle size of the cumulative particle size distribution based on the volume.

The molar ratio of lithium to the total number of moles of metal elements constituting the composite oxide in the mixture is, for example, 0.95 or more and 1.2 or less. The composite oxide and the lithium compound can be mixed, for example, by using a high-speed shear mixer or the like.

The mixture may further contain metals other than lithium and nickel. Examples of other metals include Zr, Ti, Mg, Ta, Nb, Mo, W and the like, and at least one selected from the group consisting of these is preferable. When the mixture contains a metal other than lithium and nickel, the mixture can be obtained by mixing a simple substance of the other metal or a metal compound together with the composite oxide and the lithium compound. Examples of the metal compound containing other metals include oxides, hydroxides, chlorides, nitrides, carbonates, sulfates, nitrates, acetates, oxalates and the like.

When the mixture contains other metals, the ratio of the total number of moles of metal elements constituting the composite oxide to the total number of moles of other metals is, for example, 1: 0.015 to 1: 0.1. It is preferably 1: 0.025 to 1: 0.05.

The heat treatment temperature of the mixture is, for example, 550 ° C. or higher and 1000 ° C. or lower, preferably 600 ° C. or higher and 950 ° C. or lower, and more preferably 700 ° C. or higher and 800 ° C. or lower. The heat treatment of the mixture may be carried out at a single temperature or at multiple temperatures. When the heat treatment is performed at a plurality of temperatures, for example, the first temperature can be held for a predetermined time, then the temperature can be further raised, and the second temperature can be held for a predetermined time. The first temperature is, for example, 200 ° C. or higher and 600 ° C. or lower, and the second temperature is, for example, 600 ° C. or higher and 900 ° C. or lower. The heat treatment time is, for example, 0.5 hours to 48 hours, and when the heat treatment is performed at a plurality of temperatures, it can be 0.2 hours to 47 hours, respectively.

The atmosphere of the heat treatment may be the atmosphere or an atmosphere containing oxygen. The heat treatment can be performed using, for example, a box furnace, a rotary kiln furnace, a pusher furnace, a roller harsquill furnace, or the like.

In the composition of the first lithium transition metal composite oxide obtained above, the nickel ratio, which is the molar ratio of nickel to the total number of moles of metals other than lithium, is 0.7 or more and less than 1, preferably 0.8 or more. It is 0.95 or less. The lithium ratio, which is the molar ratio of lithium to the total number of moles of metals other than lithium, is 0.95 or more and 1.05 or less, preferably 0.98 or more and 1.04 or less. The nickel ratio and the lithium ratio can be measured by, for example, an inductively coupled plasma emission spectrophotometer, and the same applies to other metal components.

The first lithium transition metal composite oxide may contain cobalt in addition to nickel. When the first lithium transition metal composite oxide contains cobalt, the molar ratio of cobalt to the total number of moles of metals other than lithium is, for example, 0.4 or less, preferably 0.01 or more and 0.2 or less. Yes, more preferably 0.03 or more and 0.15 or less. The first lithium transition metal composite oxide may contain manganese. When the lithium transition metal composite oxide contains manganese, the molar ratio of manganese to the total number of moles of metals other than lithium is, for example, 0.2 or less, preferably 0.01 or more and 0.1 or less. The first lithium transition metal composite oxide may contain aluminum. When the lithium transition metal composite oxide contains aluminum, the molar ratio of aluminum to the total number of moles of metals other than lithium is, for example, 0.15 or less, preferably 0.005 or more and 0.06 or less, and more. It is preferably 0.01 or more and 0.05 or less.

The first lithium transition metal composite oxide may have, for example, a composition represented by the following formula (1).
^{_{Li a Ni x Co y M 1}} Z M 2 w O 2 (1)
In the formula, 0.95 ≦ a ≦ 1.05, 0.7 ≦ x <1, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.5, 0 ≦ w ≦ 0.05, x + y + z + w ≦ 1 are satisfied. .. M ¹ is at least one selected from the group consisting of Al and Mn, and M ² is at least one selected from the group consisting of Mg, Ti, Zr, W, Ta, Nb and Mo.

The volume-based particle size distribution of the first lithium transition metal composite oxide may have a single peak or may have a plurality of (for example, two) peaks. When the particle size distribution of the first lithium transition metal composite oxide shows a single peak, the volume average particle size of the first lithium transition metal composite oxide is, for example, 2 μm or more and 25 μm or less, preferably 3 μm or more. It is 24 μm or less.

Further, when the particle size distribution of the first lithium transition metal composite oxide has two peaks, the first lithium transition metal composite oxide is of two types of lithium transition metal composite oxides having different volume average particle sizes. It may be a mixture. When the first lithium transition metal composite oxide is a mixture, the volume average particle size of one lithium transition metal composite oxide is, for example, 2 μm or more and 6 μm or less, preferably 3 μm or more and 5 μm or less. The volume average particle size of the other lithium transition metal composite oxide is, for example, 10 μm or more and 25 μm or less, preferably 18 μm or more and 23 μm or less. Further, the mixing ratio may be, for example, 3.5: 6.5 to 1.5: 8.5, where "the one having a small volume average particle diameter": "the one having a large volume average particle diameter". By combining lithium transition metal composite oxides having different volume average particle diameters, the filling rate of the positive electrode active material in the positive electrode can be further improved, and the energy density as a secondary battery can be improved.

Cleaning step In the cleaning step, after contacting the first lithium transition metal composite oxide with the liquid medium, at least a part of the liquid medium is removed, and the lithium ratio is 0.90 or more and less than 1. Obtain a lithium transition metal composite oxide. Here, the lithium ratio is the molar ratio of lithium to the total number of moles of metals other than lithium contained in the second lithium transition metal composite oxide. The cleaning step is, for example, a step of removing at least a part of the unreacted lithium compound contained in the first lithium transition metal composite oxide.

The liquid medium used in the washing step may be any medium that can dissolve the unreacted lithium compound. Specific examples of the liquid medium include so-called water such as pure water, ion-exchanged water, distilled water, and ultrafiltered water. The liquid medium may contain components other than water, if necessary. Examples of components other than water include alkali metal salts such as lithium salt, sodium salt, and potassium salt. Examples of the anion component of the alkali metal salt include sulfate ion, nitrate ion, acetate ion and the like. When the liquid medium contains a component other than water, the content thereof is, for example, 5% by mass or less, and more preferably 3% by mass or less. Further, the liquid medium does not have to contain components other than water.

The contact temperature between the first lithium transition metal composite oxide and the liquid medium is, for example, 0 ° C. or higher and 45 ° C. or lower, preferably 5 ° C. or higher and 30 ° C. or lower. The contact time is, for example, 10 minutes or more and 2 hours or less, preferably 30 minutes or more and 1 hour or less. The amount of liquid in the liquid medium used for contact is, for example, 0.8 times or more and 4 times or less, preferably 1 time or more and 3 times or less with respect to the mass of the first lithium transition metal composite oxide.

The contact between the first lithium transition metal composite oxide and the liquid medium may be carried out by charging the first lithium transition metal composite oxide into the liquid medium to prepare a slurry. When contacting as a slurry, the solid content concentration of the slurry is, for example, 20% by mass or more and 60% by mass or less, preferably 25% by mass or more and 50% by mass or less. Further, the contact may be carried out by passing a liquid medium through the first lithium transition metal composite oxide held in a funnel or the like.

In the cleaning step, after contact with the liquid medium, a drying treatment is performed to remove at least a part of the liquid medium from the mixture of the second lithium transition metal composite oxide and the liquid medium. The drying treatment can be performed by heat drying, air drying, vacuum drying or the like. The drying temperature in the case of heat drying is, for example, 80 ° C. or higher and 300 ° C. or lower, preferably 120 ° C. or higher and 250 ° C. or lower. The drying time is, for example, 1 hour or more and 10 hours or less, preferably 2 hours or more and 6 hours or less. The amount of water contained in the second lithium transition metal composite oxide after the drying treatment is, for example, 0.3% by mass or less, preferably 0.1% by mass or less.

The lithium ratio of the second lithium transition metal composite oxide obtained in the washing step is 0.90 or more and less than 1, preferably 0.95 or more and less than 1. Here, the lithium ratio is the molar ratio of lithium to the total number of moles of metals other than lithium contained in the second lithium transition metal composite oxide. When the lithium ratio in the second lithium transition metal composite oxide is within the above range, both battery characteristics and high filling property can be achieved.

Mixing Step In the mixing step, the second lithium transition metal composite oxide and lithium hydroxide are mixed to obtain a mixture having a lithium ratio of 1 or more and 1.15 or less. Here, the lithium ratio is the total molar ratio of lithium to the total number of moles of metals other than lithium contained in the mixture. The lithium ratio in the mixture is preferably 1.00 or more and 1.08 or less, and more preferably 1.02 or more and 1.06 or less.

In the mixing step, lithium hydroxide is used as the lithium compound. The purity of lithium hydroxide used in the mixing step is, for example, 95% by mass or more, preferably 99% by mass or more. When lithium hydroxide is used as the lithium compound and the lithium ratio of the mixture is within the above range, for example, in the subsequent heat treatment step, the primary particles constituting the lithium transition metal composite oxide are sufficiently grown to have a specific surface area. Can be reduced and the Ni disorder can be reduced.

Here, Ni disorder means a chemical disorder of transition metal ions (nickel ions) that should occupy the original site in the crystal lattice of the lithium transition metal composite oxide. In the layered structure lithium transition metal composite oxide, the lithium ion that should occupy the site represented by 3b (3b site, the same applies hereinafter) and the transition metal ion that should occupy the 3a site are replaced when expressed by the Wyckoff symbol. Is typical. The Ni disorder inhibits the diffusion of lithium ions in the lithium transition metal composite oxide and becomes a resistance, which may have an influence such as a decrease in charge / discharge capacity at a practical current density and a decrease in output characteristics. Further, the smaller the Ni disorder, the higher the initial efficiency tends to be.

The mixture may contain other components in addition to the second lithium transition metal composite oxide and lithium hydroxide. Examples of other components include lithium peroxide, lithium oxide, lithium carbonate and the like. When the mixture contains other components, the content of the other components is, for example, 5% by mass or less, preferably 1% by mass or less or less than 1% by mass. The mixture may consist substantially of a second lithium transition metal composite oxide and lithium hydroxide. Here, "substantially" means not excluding other components that are inevitably mixed.

Heat Treatment Step In the heat treatment step, the mixture containing the second lithium transition metal composite oxide and lithium hydroxide is heat-treated at 460 ° C. or higher and 750 ° C. or lower to obtain a third lithium transition metal composite oxide. By heat-treating a mixture having a lithium ratio of 1 or more and 1.15 or less at a predetermined temperature, for example, the primary particles constituting the lithium transition metal composite oxide are sufficiently grown and the specific surface area is lowered. In addition, Ni disorder decreases. As a result, the filling property of the positive electrode active material in the positive electrode is improved, and the energy density in the secondary battery is improved.

The heat treatment temperature may be 460 ° C. or higher and 750 ° C. or lower, preferably 600 ° C. or higher and lower than 750 ° C., and more preferably 650 ° C. or higher and 740 ° C. or lower. The atmosphere of the heat treatment may be an oxygen-containing atmosphere or may be in the air. The heat treatment time is, for example, 1 hour or more and 10 hours or less, preferably 2 hours or more and 5 hours or less. The heat-treated product obtained in the heat treatment step may be subjected to a crushing treatment, a classification treatment, or the like, if necessary.

The third lithium transition metal composite oxide obtained by the heat treatment step has a layered structure, has a lithium ratio of 1 or more and 1.15 or less, and a nickel ratio of 0.7 or more and less than 1. Here, the lithium ratio is the molar ratio of lithium to the total number of moles of metals other than lithium contained in the third lithium transition metal composite oxide. The lithium ratio of the third lithium transition metal composite oxide is preferably 1.00 or more and 1.08 or less, and more preferably 1.02 or more and 1.06 or less. The nickel ratio is the molar ratio of nickel to the total number of moles of metals other than lithium contained in the third lithium transition metal composite oxide. The nickel ratio in the third lithium transition metal composite oxide is preferably 0.7 or more and 0.99 or less, and more preferably 0.80 or more and 0.96 or less.

The third lithium transition metal composite oxide may contain cobalt in addition to nickel. When the third lithium transition metal composite oxide contains cobalt, the molar ratio of cobalt to the total number of moles of metals other than lithium is, for example, 0.4 or less, preferably 0.01 or more and 0.2 or less. Yes, more preferably 0.03 or more and 0.15 or less. The third lithium transition metal composite oxide may contain manganese. When the lithium transition metal composite oxide contains manganese, the molar ratio of manganese to the total number of moles of metals other than lithium is, for example, 0.2 or less, preferably 0.01 or more and 0.1 or less. The third lithium transition metal composite oxide may contain aluminum. When the lithium transition metal composite oxide contains aluminum, the molar ratio of aluminum to the total number of moles of metals other than lithium is, for example, 0.15 or less, preferably 0.005 or more and 0.06 or less, and more. It is preferably 0.01 or more and 0.05 or less.

When the lithium transition metal composite oxide contains nickel, cobalt, and at least one of manganese and aluminum, the content ratio of nickel, cobalt, manganese and aluminum Ni: Co: (Mn + Al) is, for example, molar. The standard can be 6: 2: 2, 6: 2: (1.5 + 0.5), 8: 1: 1, 8: 1: (0.5 + 0.5), and the like.

The third lithium transition metal composite oxide may have, for example, a composition represented by the following formula (2).
^{_{Li a Ni x Co y M 1}} Z M 2 w O 2 (2)
In the formula, 1 ≦ a ≦ 1.15, 0.7 ≦ x <1, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.5, 0 ≦ w ≦ 0.05, and x + y + z + w ≦ 1 are satisfied. M ¹ is at least one selected from the group consisting of Al and Mn, and M ² is at least one selected from the group consisting of Mg, Ti, Zr, W, Ta, Nb and Mo.

By applying the positive electrode active material containing the third lithium transition metal composite oxide to the positive electrode of the non-aqueous electrolyte secondary battery, the charge / discharge capacity can be improved, and the non-aqueous electrolyte secondary battery having a high energy density can be improved. Can be configured. The positive electrode active material can be contained in the positive electrode active material layer arranged on the current collector to form a positive electrode. That is, the present invention includes a positive electrode active material, an electrode for a non-aqueous electrolyte secondary battery containing the positive electrode active material, and a non-aqueous electrolyte secondary battery including the electrode.

[Electrodes for non-aqueous electrolyte secondary batteries]
The electrode for a non-aqueous electrolyte secondary battery includes a current collector and a positive electrode active material layer which is arranged on the current collector and contains a positive electrode active material for a non-aqueous electrolyte secondary battery manufactured by the above-mentioned production method. A non-aqueous electrolyte secondary battery provided with such an electrode has a good charge / discharge capacity and can achieve a high energy density.

Examples of the material of the current collector include aluminum, nickel, stainless steel and the like. The positive electrode active material layer is formed by applying a positive electrode mixture obtained by mixing the above positive electrode active material, a conductive material, a binder, etc. together with a solvent onto a current collector, and performing a drying treatment, a pressure treatment, or the like. Can be formed. Examples of the conductive material include natural graphite, artificial graphite, acetylene black and the like. Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, and polyamide acrylic resin.

[Non-aqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery includes the electrode for the non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery includes an electrode for a non-aqueous electrolyte secondary battery, a negative electrode for a non-aqueous secondary battery, a non-aqueous electrolyte, a separator, and the like. Regarding the negative electrode, non-aqueous electrolyte, separator and the like in the non-aqueous electrolyte secondary battery, for example, JP-A-2002-075367, JP-A-2011-146390, JP-A-2006-12433 (these are disclosure thereof). Those for non-aqueous electrolyte secondary batteries described in (the entire contents thereof are incorporated in the present specification by reference) and the like can be appropriately used.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. First, a method for measuring physical properties in the following Examples and Comparative Examples will be described.

For the average particle size, a laser diffraction type particle size distribution measuring device (SALD-3100 manufactured by Shimadzu Corporation) is used to measure the volume-based cumulative particle size distribution, and the volume accumulation from the small particle size side corresponds to 50%. The particle size to be used was determined and used as the volume average particle size (D50).

The specific surface area was measured by a nitrogen gas adsorption method (Maxorb Model-1201 manufactured by Mountech Co., Ltd.) and a gas adsorption method using nitrogen gas (one-point method) based on the BET method.

The pellet density was measured as follows using a mold consisting of two upper and lower molds. A columnar recess having a diameter of 20 mm was formed in the upper central portion of the lower mold, and 3 g of the positive electrode active material was uniformly filled in the recess. On the positive electrode active material filled in the recess, the upper mold formed according to the shape of the recess was placed. A pressure of ^{2.1 ton / cm 2} was applied to the upper mold for 30 seconds. The same operation of applying pressure was performed twice. Pellets made of positive electrode active material were formed inside the mold, and the pellet density (g / cm ³ ) was calculated by measuring the thickness of the pellets. The higher the pellet density, the better the filling property.

The value of the disorder of the nickel element (Ni disorder amount) was determined by the following procedure by the X-ray diffraction method. The X-ray diffraction spectrum (tube current 200 mA, tube voltage 45 kV) of the obtained lithium transition metal composite oxide was measured by CuKα rays. Based on the obtained X-ray diffraction spectrum, the composition model _{Li 1-d Ni d MeO 2} (Me is a transition metal other than nickel in the lithium transition metal composite oxide) as, lithium transition metal composite oxide, Structural optimization was performed by Rietbelt analysis using Lietan2000 software. As a result of the structural optimization, the calculated percentage of d was taken as the Ni disorder amount.

(Example 1)
Preparation process Seed generation process 1
Nitrogen gas was circulated in the reaction vessel while adding 1 kg of water and stirring, and the temperature in the vessel was set to 70 ° C. After maintaining the oxygen concentration in the reaction vessel space at 10% by volume or less, 60 g of a 12.5 mass% ammonia aqueous solution was added to adjust the pH value of the solution in the reaction vessel to 12 or more. Next, a nickel sulfate solution and a cobalt sulfate solution are mixed, and nickel and cobalt are contained at a molar ratio of 85:15 (Ni: Co), and the mixed aqueous solution has a total ion concentration of nickel and cobalt of 1.7 mol / L. Was prepared. While stirring the solution in the reaction vessel, 0.01 L of the prepared mixed aqueous solution was added to prepare a liquid medium containing seed crystals.

Crystallization step 1
After the seed formation step 1, 0.007 mol of 25% mass sodium hydroxide and 0.01 mol of the mixed aqueous solution were added into the reaction vessel at a constant flow rate while maintaining the temperature at 70 ° C.18. It took more than an hour to put in. The pH at this time was maintained at 11.0 to 12.0. The volume average particle diameter D50 of the obtained nickel cobalt hydroxide was 24 μm. Next, the generated precipitate was washed with water and filtered to obtain a composite hydroxide. The obtained composite hydroxide was heat-treated at 320 ° C. for 12 hours in an air atmosphere to obtain a composite oxide having a composition ratio of Ni: Co = 85: 15.

Synthesis step 1
The obtained composite oxide, lithium hydroxide and aluminum hydroxide were mixed so as to have Li :( Ni + Co): Al = 1.02: 0.96: 0.04 to obtain a raw material mixture. The obtained raw material mixture was heat-treated in the air at 730 ° C. for 4 hours to obtain a sintered body. After the heat treatment, it was dispersed. As described above, a lithium transition metal composite oxide A1 having a volume average particle diameter D50 of 22 μm and _{a composition represented by Li 1.02} Ni _0.820 Co _0.140 Al _0.04 O _{2 was obtained.}

Seed generation step 2
Nitrogen gas was circulated in the reaction vessel while adding 2 kg of water and stirring, and the temperature in the vessel was set to 45 ° C. After maintaining the oxygen concentration in the reaction vessel space at 10% by volume or less, 39 g of a 25 mass% sodium hydroxide aqueous solution was added to adjust the pH value of the solution in the reaction vessel to 12 or more. Next, a nickel sulfate solution and a cobalt sulfate solution are mixed, and nickel and cobalt are contained at a molar ratio of 85:15 (Ni: Co), and the mixed aqueous solution has a total ion concentration of nickel and cobalt of 1.7 mol / L. Was prepared. While stirring the solution in the reaction vessel, 0.06 L of the prepared mixed aqueous solution was added to prepare a liquid medium containing seed crystals.

Crystallization step 2
After the seed formation step 2, while maintaining the temperature at 45 ° C., 0.02 mol of 25% mass sodium hydroxide and 0.01 mol of the mixed aqueous solution were added into the reaction vessel at a constant flow rate of 18 respectively. It took more than an hour to put in. The pH at this time was maintained at 11.0 to 12.0. The volume average particle size D50 of the obtained nickel cobalt hydroxide was 4.5 μm. Next, the generated precipitate was washed with water and filtered to obtain a composite hydroxide. The obtained composite hydroxide was heat-treated at 320 ° C. for 12 hours in an air atmosphere to obtain a composite oxide having a composition ratio of Ni: Co = 85: 15.

Synthesis step 2
The obtained composite oxide, lithium hydroxide and aluminum hydroxide were mixed so as to have Li :( Ni + Co): Al = 1.02: 0.96: 0.04 to obtain a raw material mixture. The obtained raw material mixture was heat-treated in the air at 730 ° C. for 4 hours to obtain a sintered body. After the heat treatment, it was dispersed. As described above, a lithium transition metal composite oxide A2 having a volume average particle diameter D50 of 4 μm and _{a composition represented by Li 1.02} Ni _0.820 Co _0.140 Al _0.04 O _{2 was obtained.}

The lithium transition metal composite oxide A1 obtained above and the lithium transition metal composite oxide A2 were mixed at a ratio of 7: 3 and represented by Li _1.02 Ni _0.820 Co _0.140 Al _0.04 O ₂ . A first lithium transition metal composite oxide A having the composition to be obtained was obtained. The lithium ratio of the first lithium transition metal composite oxide A (hereinafter, also referred to as the first Li ratio) was 1.02.

Cleaning Step The obtained first lithium transition metal oxide A was added to a cleaning container containing 1.5 times the amount of pure water by mass ratio, and the mixture was stirred for 30 minutes. Then, the solid phase was dehydrated and dried at 150 ° C. for 10 hours. As a result, a second lithium transition metal composite oxide having a composition represented _{by Li 0.98} Ni _0.820 Co _0.140 Al _0.04 O _{2 was obtained.} The lithium ratio of the second lithium transition metal composite oxide (hereinafter, also referred to as the second Li ratio) was 0.98.

Mixing Step and Heat Treatment Step Lithium hydroxide was added to the obtained second lithium transition metal composite oxide so as to have Li :( Ni + Co + Al) = 0.02: 1, and the mixture was mixed and stirred to obtain a mixture. The obtained mixture is heat-treated in the air at 700 ° C. for 10 hours to form a third lithium transition metal composite oxidation having a composition represented by _{Li 1.00} Ni _0.820 Co _0.140 Al _0.04 O _2. A positive electrode active material E1 containing a substance was obtained. The lithium ratio of the third lithium transition metal composite oxide (hereinafter, also referred to as the third Li ratio) was 1.00.

(Example 2)
The same as in Example 1 except that the amount of lithium hydroxide in the mixing step was changed to Li: (Ni + Co + Al) = 0.04: 1 and the heat treatment temperature in the heat treatment step was changed to 500 ° C. , Li _1.03 Ni _0.820 Co _0.140 Al _0.04 O ₂ was obtained as a positive electrode active material E2 containing a third lithium transition metal composite oxide having a composition represented by O 2. The third Li ratio was 1.03.

(Example 3)
_{Li 1.02} Ni _0.820 Co _0.140 Al in the same manner as in Example 1 except that the amount of lithium hydroxide in the mixing step was changed to Li: (Ni + Co + Al) = 0.04: 1. A positive electrode active material E3 containing a third lithium transition metal composite oxide having a composition represented by _0.04 O _{2 was obtained.} The third Li ratio was 1.02.

(Comparative Example 1)
The second lithium transition metal composite oxide in Example 1 is heat-treated at 250 ° C. for 10 hours to form lithium having a composition represented by _{Li 0.97} Ni _0.820 Co _0.140 Al _0.04 O _2. A positive electrode active material C1 containing a transition metal composite oxide was obtained.

(Comparative Example 2)
The second lithium transition metal composite oxide in Example 1 is heat-treated at 700 ° C. for 10 hours, and the lithium transition has a composition represented by _{Li 0.98} Ni _0.820 Co _0.140 Al _0.04 O _2. A positive electrode active material C2 containing a metal composite oxide was obtained.

(Comparative Example 3)
Synthesis step 1
The composite oxide obtained in the crystallization step 1 of Example 1, lithium hydroxide and aluminum hydroxide were mixed so as to have Li :( Ni + Co): Al = 1.10: 0.96: 0.04. Except for this, in the same manner as in the synthesis step 1 of Example 1, the volume average particle diameter D50 is 22 μm, and the composition is represented by _{Li 1.10} Ni _0.820 Co _0.140 Al _0.04 O _2. A lithium transition metal composite oxide B1 was obtained.

Synthesis step 2
The composite oxide obtained in the crystallization step 2 of Example 1, lithium hydroxide and aluminum hydroxide were mixed so as to have Li :( Ni + Co): Al = 1.10: 0.96: 0.04. Except for this, in the same manner as in the synthesis step 2 of Example 1, the volume average particle diameter D50 is 4 μm, and the composition is represented by _{Li 1.10} Ni _0.820 Co _0.140 Al _0.04 O _2. A lithium transition metal composite oxide B2 was obtained.

The lithium transition metal composite oxide B1 obtained above and the lithium transition metal composite oxide B2 were mixed at a ratio of 7: 3 and represented by Li _1.10 Ni _0.820 Co _0.140 Al _0.04 O ₂ . A lithium transition metal composite oxide B3 having the composition to be obtained was obtained.

Cleaning Step The obtained lithium transition metal composite oxide B3 was washed with pure water in the same manner as in the cleaning step of Example 1, and then dried to perform Li _1.00 Ni _0.820 Co _0.140 Al _0. A lithium transition metal composite oxide B4 having a composition represented by ₀₄ O _{2 was obtained.}

Heat Treatment Step The obtained lithium transition metal composite oxide B4 is heat-treated at 250 ° C. for 10 hours to form lithium having a composition represented by _{Li 1.00} Ni _0.820 Co _0.140 Al _0.04 O _2. A positive electrode active material C3 containing a transition metal composite oxide was obtained.

(Comparative Example 4)
Mixing step and heat treatment step Lithium hydroxide was added to the lithium transition metal composite oxide B4 obtained in Comparative Example 3 so as to have Li :( Ni + Co + Al) = 0.04: 1, and after mixing and stirring, 700 in the air. Heat treatment was performed at ° C. for 10 hours to obtain a positive electrode active material C4 containing a lithium transition metal composite oxide having a composition represented by _{Li 1.04} Ni _0.820 Co _0.140 Al _0.04 O _2.

The specific surface area, pellet density and nickel disorder of the positive electrode active materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were measured. The measurement results are shown in Table 1.

<Making evaluation batteries>
Using the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 4, respectively, a non-aqueous electrolyte secondary battery for evaluation was obtained in the following manner.

[Manufacturing of positive electrode plate]
92 parts by mass of the positive electrode active material obtained above, 3 parts by mass of acetylene black, and 5 parts by mass of polyvinylidene fluoride were dispersed in N-methylpyrrolidone to obtain a positive electrode slurry. The obtained positive electrode slurry was applied to a current collector made of aluminum foil, dried, cut into a predetermined size, and compression-molded with a press to obtain a positive electrode electrode plate.

[Preparation of non-aqueous electrolyte solution]
Ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 3: 7 to obtain a mixed solvent. Lithium hexafluorophosphate was dissolved in the obtained mixed solvent so as to have a concentration of 1.0 mol / L to obtain a non-aqueous electrolytic solution.

[Assembly of non-aqueous electrolyte secondary battery]
After attaching the lead electrode to the positive electrode plate obtained above, vacuum drying was performed at 110 ° C. Next, the positive electrode plate was wrapped with a separator made of porous polyethylene, which was stored in a bag-shaped laminate pack and placed in an argon dry box. A metal Li foil cut to a predetermined size was attached to a SUS plate with a lead in an argon dry box to obtain a negative electrode plate. After arranging the positive and negative electrode plates and storing them in a laminate pack, the non-aqueous electrolyte solution obtained above is injected and sealed, and a laminate-type non-aqueous electrolyte secondary battery (unipolar cell) is used as an evaluation battery. ) Was obtained. The following battery characteristics were evaluated using the obtained evaluation battery.

<Evaluation of charge capacity and energy density>
Constant current constant voltage charging was performed with a charging voltage of 4.3 V and a charging current of 0.2 C (1 C is a current value at which discharge can be completed in 1 hour from a fully charged state), and the charge capacity Qc was measured. ^{The energy density (mAh / cm 3} ) was obtained from the product of the measured charge capacity Qc and the pellet density P. The measurement results are shown in Table 1.

The evaluation batteries constructed by using the positive electrode active materials of Examples 1 to 3 obtained by the specific manufacturing methods from Table 1 are compared with the evaluation batteries constructed by using the positive electrode active materials of Comparative Examples 1 to 4. It was confirmed that the energy density was improved. Further, in the evaluation battery constructed by using the positive electrode active material of Example 3, the energy is increased by setting the heat treatment temperature to 700 ° C. as compared with the evaluation battery constructed by using the positive electrode active material of Example 2. It was confirmed that the density was further improved.

Claims (6)

The nickel ratio, which is the molar ratio of nickel to the total number of moles of metals other than lithium in the composition containing lithium and nickel, is 0.7 or more, and the ratio of lithium, which is the molar ratio of lithium to the total number of moles of metals other than lithium. To prepare a first lithium transition metal oxide having a layered structure having a value of 0.95 or more and 1.05 or less.
After contacting the first lithium transition metal oxide with the liquid medium, at least a part of the liquid medium is removed to obtain a second lithium transition metal oxide having a lithium ratio of 0.90 or more and less than 1. That and
The second lithium transition metal oxide and lithium hydroxide are mixed to obtain a mixture having a lithium ratio of 1 or more and 1.15 or less.
The mixture is heat treated at a temperature of 460 ° C. or higher and 750 ° C. or lower to obtain a third lithium transition metal oxide.
The third lithium transition metal oxide has a layered structure, has a lithium ratio of 1 or more and 1.15 or less, and has a nickel ratio of 0.7 or more and less than 1. Method of manufacturing active material. The production method according to claim 1, wherein the temperature of the heat treatment is 600 ° C. or higher and lower than 750 ° C. The production method according to claim 1 or 2, wherein the liquid medium contains water. The first lithium transition metal oxide contains cobalt, and the molar ratio of cobalt to the total number of moles of metals other than lithium in the composition is 0.4 or less, according to any one of claims 1 to 3. Manufacturing method. The first lithium transition metal oxide contains at least one of aluminum and manganese, and the ratio of the total number of moles of aluminum and manganese to the total number of moles of metals other than lithium in the composition is 0.5 or less. The production method according to any one of 1 to 4. The production method according to any one of claims 1 to 5, wherein the third lithium transition metal oxide has a composition represented by the following formula.
^{_{Li a Ni x Co y M 1}} z M 2 w O 2
(In the formula, 1 ≦ a ≦ 1.15, 0.7 ≦ x <1, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.5, 0 ≦ w ≦ 0.05, x + y + z + w ≦ 1, M ¹ Is at least one selected from the group consisting of Al and Mn, and M ² is at least one selected from the group consisting of Mg, Ti, Zr, W, Ta, Nb and Mo).