JP7521287B2 - Positive electrode active material particles, manufacturing method thereof, energy storage element, and energy storage device - Google Patents

Description

This disclosure relates to positive electrode active material particles, a manufacturing method thereof, an energy storage element, and an energy storage device.

Secondary batteries, such as lithium-ion secondary batteries, are used in personal computers, electronic devices such as communication terminals, automobiles, etc. due to their high energy density.

As a method for manufacturing a positive electrode used in the above-mentioned secondary battery, a method for manufacturing a positive electrode for a lithium-ion secondary battery has been disclosed in which a nitrogen-containing polymer is added to a dispersion in which a positive electrode active material capable of absorbing and releasing lithium and an organic acid are dissolved or dispersed in a solvent to obtain a composite paste, and the composite paste is applied to a current collector and dried (see JP 2018-113235 A).

JP 2018-113235 A

The positive electrode described in Patent Document 1 above cannot be said to have a high packing density of the positive electrode active material layer, and it is difficult to say that a lithium ion secondary battery using this positive electrode has a sufficiently high energy density.

In view of the above circumstances, the object of the present invention is to provide positive electrode active material particles with improved packing properties, a method for producing the same, and an energy storage element and an energy storage device that include the positive electrode active material particles.

The positive electrode active material particles according to one embodiment of the present invention comprise transition metal oxide particles and a compound having a carbon-phosphorus bond that is present on at least a portion of the surface of the transition metal oxide particles, and the carbon atom content relative to the phosphorus atom content in the compound having the carbon-phosphorus bond is 9 or more in atomic ratio.

Another aspect of the present invention relates to an energy storage element that includes an electrode assembly including a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container that contains the electrode assembly and the non-aqueous electrolyte, and the positive electrode contains the positive electrode active material particles.

An energy storage device according to another aspect of the present invention includes one or more of the energy storage elements.

A method for producing positive electrode active material particles according to another aspect of the present invention comprises contacting transition metal oxide particles with a phosphonic acid compound having a hydrocarbon group having 9 or more carbon atoms.

According to one aspect of the present invention, it is possible to provide positive electrode active material particles with improved packing properties, a method for producing such positive electrode active material particles, and an energy storage element and an energy storage device including the positive electrode active material particles.

FIG. 1 is an external perspective view showing one embodiment of an energy storage element. FIG. 2 is a schematic perspective view showing an embodiment of an electricity storage device formed by assembling a plurality of electricity storage elements.

First, we will provide an overview of the positive electrode active material particles, their manufacturing method, and the energy storage element and energy storage device disclosed in this specification.

The positive electrode active material particles according to one embodiment of the present invention comprise transition metal oxide particles and a compound having a carbon-phosphorus bond that is present on at least a portion of the surface of the transition metal oxide particles, and the carbon atom content relative to the phosphorus atom content in the compound having the carbon-phosphorus bond is 9 or more in atomic ratio.

The positive electrode active material particles have a specific compound having a carbon-phosphorus bond on at least a portion of the surface of the transition metal oxide particles, which reduces the repulsive force caused by the interaction between the positive electrode active material particles, thereby increasing the packing property of the positive electrode active material particles and thereby improving the packing density of the positive electrode active material layer. This improvement in packing density allows the positive electrode active material particles to improve the energy density of the energy storage element.

Here, it is preferable that the mass ratio of the phosphorus atoms is 0.06 mass% or more and 0.3 mass% or less with respect to the mass of the transition metal oxide particles.

When the mass ratio of the phosphorus atoms is within the above range relative to the mass of the transition metal oxide particles, the filling property of the positive electrode active material particles is further improved. Therefore, the positive electrode active material particles can further improve the energy density of the energy storage element.

Here, it is preferable that the compound having the carbon-phosphorus bond has a hydrocarbon group having 9 or more carbon atoms, and that the carbon atom that constitutes the carbon-phosphorus bond constitutes part of the hydrocarbon group.

When the compound having the carbon-phosphorus bond has the specific hydrocarbon group, the filling property of the positive electrode active material particles is further improved. Therefore, the positive electrode active material particles can further improve the energy density of the storage element.

Another aspect of the present invention relates to an energy storage element that includes an electrode assembly including a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container that contains the electrode assembly and the non-aqueous electrolyte, and the positive electrode contains the positive electrode active material particles.

Since the energy storage element contains the positive electrode active material particles, the energy density is improved as described above.

An energy storage device according to another aspect of the present invention includes one or more of the energy storage elements.

Since the energy storage device includes the energy storage element, the energy density is improved as described above.

A method for producing positive electrode active material particles according to another aspect of the present invention comprises contacting transition metal oxide particles with a phosphonic acid compound having a hydrocarbon group having 9 or more carbon atoms.

According to the method for producing positive electrode active material particles, the above-mentioned positive electrode active material particles can be produced. In other words, as described above, positive electrode active material particles with improved packing properties can be produced.

The following describes in detail the positive electrode active material particles according to one embodiment of the present invention, the manufacturing method of the positive electrode active material particles, the configuration of the energy storage element, the configuration of the energy storage device, the manufacturing method of the energy storage element, and other embodiments. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art.

<Positive electrode active material particles>
The positive electrode active material particles include transition metal oxide particles and a compound having a carbon-phosphorus bond present on at least a portion of the surface of the transition metal oxide particles (hereinafter also referred to as a "first compound"), in which the content of carbon atoms relative to the content of phosphorus atoms in the first compound is 9 or more in terms of atomic ratio.

(Transition metal oxide particles)
The transition metal oxide particles are particles of a transition metal oxide. The transition metal oxide can be appropriately selected from known transition metal oxides. The transition metal oxide is usually a transition metal oxide that can occlude and absorb lithium ions. Examples of such transition metal oxides include lithium transition metal composite oxides having an α- _NaFeO2 type crystal structure and lithium transition metal composite oxides having a spinel type crystal structure. etc. Examples of lithium transition metal composite oxides having an α-NaFeO ₂ type crystal structure include Li[Li _x Ni _1-x ]O ₂ (0≦x<0.5), Li[Li _x Ni _γ Co _{1-x -γ} ]O ₂ (0≦x<0.5, 0<γ<1), Li[Li _x Co _1-x ]O ₂ (0≦x<0.5), Li[Li _x Ni _γ Mn _{1 -x-γ} ]O ₂ (0≦x<0.5, 0<γ<1), Li[Li _x Ni _γ Mn _β Co _1-x-γ-β ]O ₂ (0≦x<0.5 , 0<γ, 0<β, 0.5<γ+β<1), Li[Li _x Ni _γ Co _β Al _1-x-γ-β ]O ₂ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), etc. Lithium transition metal complex having a spinel type crystal structure Examples of oxides include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _2-γ O _4. Atoms in these materials may be partially substituted with atoms of other elements. The surface of these materials may be coated with another material. As the transition metal oxide particles, one of these materials may be used alone, or two or more of them may be used in combination. .

Of these, the transition metal oxide particles preferably contain nickel. The transition metal oxide particles more preferably contain manganese or aluminum in addition to nickel, and may further preferably contain cobalt. The transition metal oxide particles are preferably lithium transition metal composite oxides having an α- _NaFeO2 type crystal structure. By using such transition metal oxide particles, the energy density of the energy storage element can be further increased.

As the lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, a compound represented by the following formula 1 is preferable.
Li _1+α Me _1-α O ₂ ...1
In formula 1, Me is a transition metal or a combination of a transition metal and aluminum. 0≦α<1.

Me in formula 1 may be one or more metals. Me preferably contains Ni, more preferably further contains Mn or Al, and may further preferably contain Co. Me is preferably substantially composed of the three elements Ni, Co, and Mn, or the three elements Ni, Co, and Al. The lower limit of the molar ratio of the total content of Ni, Co, and Mn, or the total content of Ni, Co, and Al in Me is preferably 0.9, and more preferably 0.99. The upper limit of the molar ratio of the total content of Ni, Co, and Mn, or the total content of Ni, Co, and Al in Me may be 1.

In formula 1, the lower limit of the molar ratio of Ni to Me (Ni/Me) is preferably 0.1, and more preferably 0.2. On the other hand, the upper limit of this molar ratio (Ni/Me) is preferably 0.9, and more preferably 0.8.

In formula 1, the lower limit of the molar ratio of Co to Me (Co/Me) may be 0, but is preferably 0.05, and more preferably 0.1. The upper limit of this molar ratio (Co/Me) is preferably 0.7, and more preferably 0.5.

In formula 1, the lower limit of the molar ratio of Mn to Me (Mn/Me) may be 0, but is preferably 0.05, and more preferably 0.1. The upper limit of this molar ratio (Mn/Me) is preferably 0.7, and more preferably 0.5.

In formula 1, the lower limit of the molar ratio of Al to Me (Al/Me) may be 0, but is preferably 0.01, and more preferably 0.03. The upper limit of this molar ratio (Al/Me) is preferably 0.1, and more preferably 0.05.

In formula 1, the molar ratio of Li to Me (Li/Me), i.e., (1+α)/(1-α), may be 1, but may be preferably 1 or more, 1.1 or more, or 1.2 or more. On the other hand, the upper limit of this molar ratio (Li/Me) is preferably 1.6, and more preferably 1.5.

The composition ratio of the lithium transition metal composite oxide refers to the composition ratio when the battery is fully discharged by the following method. First, the storage element is charged at a constant current of 0.05C until the end-of-charge voltage during normal use is reached, and the battery is fully charged. After a 30-minute pause, the battery is discharged at a constant current of 0.05C to the lower limit voltage during normal use. The battery is disassembled, the positive electrode is removed, and a test battery is assembled with a metallic lithium electrode as the counter electrode. A constant current discharge is performed at a current value of 10 mA per 1 g of positive electrode active material until the positive electrode potential becomes 2.0 V vs. Li/Li ⁺ , and the positive electrode is adjusted to a fully discharged state. The battery is disassembled again, and the positive electrode is removed. The nonaqueous electrolyte attached to the removed positive electrode is thoroughly washed using dimethyl carbonate, and the battery is dried at room temperature for one day and night, and then the lithium transition metal composite oxide of the positive electrode active material is collected. The collected lithium transition metal composite oxide is subjected to measurement. The work from disassembly of the energy storage element to measurement is carried out in an argon atmosphere with a dew point of -60° C. or less. Here, normal use refers to the case where the energy storage element is used under the charge/discharge conditions recommended or specified for the energy storage element, and in the case where a charger for the energy storage element is provided, the charger is used to use the energy storage element.

By setting the molar ratios of each of the constituent elements in formula 1 (Ni/Me), (Co/Me), (Mn/Me), (Al/Me) and (Li/Me) within the above ranges, the discharge capacity and thermal stability of the lithium transition metal composite oxide are improved.

Examples of lithium transition metal composite oxides include LiNi1 _{/ 3Co1 / 3Mn1 /3O2 ,} LiNi3 _/ 5Co1/ _{5Mn1 / 5O2 , LiNi1} / _2Co1 / _5Mn3 / _{10O2 , LiNi1/2Co3/10Mn1/5O2 , LiNi8 / 10Co1 /10Mn1/10O2 , and LiNi0.8Co0.15Al0.05O2 .}

The average particle size of the transition metal oxide particles is not particularly limited and can be set appropriately to meet the average particle size of the positive electrode active material particles described below.

(First Compound)
The first compound has a carbon-phosphorus bond, and the content of carbon atoms to the content of phosphorus atoms in the first compound is 9 or more in terms of atomic ratio.

The lower limit of the carbon atom content relative to the phosphorus atom content in the first compound may be 9, preferably 10, and more preferably 11, in terms of atomic ratio. The upper limit of the carbon atom content relative to the phosphorus atom content in the first compound is preferably 20, more preferably 16, and even more preferably 12, in terms of atomic ratio. When the carbon atom content is equal to or greater than the lower limit, a sufficient amount of carbon atoms is present on the surface of the transition metal oxide particles, and the repulsive force due to the interaction between the positive electrode active material particles is reduced, thereby improving the packing property of the positive electrode active material particles. On the other hand, when the carbon atom content is equal to or less than the upper limit, the total amount of phosphorus atoms and carbon atoms can be suppressed while exerting the effect of reducing frictional force, so that the content ratio of transition metal oxide particles in the positive electrode active material particles is relatively increased, and the energy density of the storage element can be further improved.

As such a first compound, it is preferable that the carbon atom constituting the carbon-phosphorus bond is a part of the hydrocarbon group, and that the first compound has a hydrocarbon group having 9 or more carbon atoms. When the carbon atom and the phosphorus atom are present on the surface of the transition metal oxide particle in such a form, the frictional force is further reduced and the filling property is improved.

Here, the term "hydrocarbon group" includes aliphatic hydrocarbon groups and aromatic hydrocarbon groups. The term "aliphatic hydrocarbon group" includes chain-like hydrocarbon groups and alicyclic hydrocarbon groups. This "hydrocarbon group" may be a saturated or unsaturated hydrocarbon group. The term "chain-like hydrocarbon group" refers to a hydrocarbon group that does not include a ring structure and is composed only of a chain structure, and includes both linear and branched hydrocarbon groups. The term "alicyclic hydrocarbon group" refers to a hydrocarbon group that includes only an alicyclic structure as a ring structure and does not include an aromatic ring structure, and includes both monocyclic alicyclic hydrocarbon groups and polycyclic alicyclic hydrocarbon groups. However, it is not necessary for the group to be composed only of an alicyclic structure, and it may include a chain structure as part of it. The term "aromatic hydrocarbon group" refers to a hydrocarbon group that includes an aromatic ring structure as a ring structure. However, it is not necessary for the group to be composed only of an aromatic ring structure, and it may include a chain structure or an alicyclic structure as part of it.

The lower limit of the number of carbon atoms in the hydrocarbon group is preferably 9, more preferably 10, and in some cases even more preferably 11. The upper limit of the number of carbon atoms in the hydrocarbon group is preferably 20, more preferably 16, and even more preferably 12. If the number of carbon atoms in the hydrocarbon group is equal to or greater than the lower limit, the filling property of the positive electrode active material particles can be improved. On the other hand, if the number of carbon atoms in the hydrocarbon group is equal to or less than the lower limit, the energy density of the energy storage element can be further improved.

The hydrocarbon group is preferably an aliphatic hydrocarbon group. In this case, the carbon atom that constitutes the carbon-phosphorus bond constitutes a part of the aliphatic hydrocarbon group. In other words, one or more carbon atoms of the aliphatic hydrocarbon group are bonded to a phosphorus atom to form a carbon-phosphorus bond. Examples of the aliphatic hydrocarbon group include an alkyl group, an alkenyl group, and an alkynyl group.

As mentioned above, the lower limit of the number of carbon atoms in the aliphatic hydrocarbon group is preferably 9, more preferably 10, and in some cases even more preferably 11. As mentioned above, the upper limit of the number of carbon atoms in the aliphatic hydrocarbon group is preferably 20, more preferably 16, and even more preferably 12. As the aliphatic hydrocarbon group, an alkyl group (saturated hydrocarbon group) having 9 to 20 carbon atoms is preferred, an alkyl group having 10 to 16 carbon atoms is more preferred, and an alkyl group having 10 to 12 carbon atoms is even more preferred.

The carbon-phosphorus bond is formed by a bond between a carbon atom of the hydrocarbon group and a phosphorus atom. An example of a source of the phosphorus atom is a phosphonic acid group (-P(=O)(OH) ₂ ). An example of a source of the carbon-phosphorus bond is a compound formed by bonding a carbon atom of the hydrocarbon group and a phosphorus atom of a phosphonic acid group (hereinafter also referred to as a "phosphonic acid compound"). In this case, the first compound may be the phosphonic acid compound, or may be a product derived from the phosphonic acid compound. An example of the product derived from the first compound is a decomposition product of the phosphonic acid compound.

As described above, examples of the hydrocarbon group of the phosphonic acid compound include aliphatic hydrocarbon groups. As described above, examples of the aliphatic hydrocarbon group include alkyl groups, alkenyl groups, and alkynyl groups. That is, examples of the phosphonic acid compound include alkylphosphonic acid, alkenylphosphonic acid, and alkynylphosphonic acid.

For example, alkylphosphonic acid is represented as CH ₃ (CH ₂ ) _n P(═O)(OH) _2. n is an integer of 0 or more. The lower limit of n is preferably 8 or more, more preferably 9 or more, and even more preferably 10 or more. The upper limit of n is preferably 19 or less, more preferably 15 or less, and even more preferably 11 or less. That is, as the alkylphosphonic acid, alkylphosphonic acid having 9 to 20 carbon atoms is preferable, alkylphosphonic acid having 10 to 16 carbon atoms is more preferable, and alkylphosphonic acid having 10 to 12 carbon atoms is even more preferable. Examples of such alkylphosphonic acid include nonylphosphonic acid, decylphosphonic acid, dodecylphosphonic acid, tetradecylphosphonic acid, hexadecylphosphonic acid, and octadecylphosphonic acid. Other examples of alkenylphosphonic acids having the same number of carbon atoms as above include 2-hexylallylphosphonic acid, nonenylphosphonic acid, dodecenylphosphonic acid, hexadecenylphosphonic acid, etc. Examples of alkynylphosphonic acids having the same number of carbon atoms as above include nonynylphosphonic acid, decynylphosphonic acid, dodecynylphosphonic acid, hexadecenylphosphonic acid, etc.

The first compound may further have groups other than those mentioned above.

The first compound is present on at least a portion of the surface of the transition metal oxide particle. For example, the first compound may be present on the entire surface of the transition metal oxide particle. For example, the first compound may be present on only a portion of the surface of the transition metal oxide particle.

It may be preferable that the first compound is present on at least a portion of the surface of the transition metal oxide particle, for example, that the first compound coats a portion or the entire surface of the transition metal oxide particle. That is, it may be preferable that the positive electrode active material particle has the transition metal oxide particle and a coating layer that coats the transition metal oxide particle, and that the coating layer contains the first compound.

As described above, the first compound may be present on a part or all of the surface of the transition metal oxide particle, and may also be present in part inside the transition metal oxide particle.

The lower limit of the mass ratio of the phosphorus atoms in the positive electrode active material particles is preferably 0.06 mass%, more preferably 0.08 mass%, and even more preferably 0.1 mass%, relative to the mass (100 mass%) of the transition metal oxide particles. The upper limit of the mass ratio of the phosphorus atoms in the positive electrode active material particles is preferably 0.3 mass%, more preferably 0.25 mass%, even more preferably 0.2 mass%, and particularly preferably 0.15 mass%, relative to the mass (100 mass%) of the transition metal oxide particles. By having the mass ratio of the phosphorus atoms in the above range, the filling property of the positive electrode active material particles can be further improved.

The content of the first compound can be appropriately set so that the mass ratio of phosphorus atoms to the mass of the transition metal oxide particles is within the above range.

The average particle size of the positive electrode active material particles is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material particles to the above lower limit or more, the positive electrode active material particles can be easily manufactured or handled. By setting the average particle size of the positive electrode active material particles to the above upper limit or less, the electronic conductivity of the positive electrode active material layer using the positive electrode active material particles is improved. In addition, when a composite of the positive electrode active material particles and other materials is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material particles. "Average particle size" means a value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by a laser diffraction/scattering method for a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

In order to obtain powder with a specified particle size, a pulverizer or a classifier is used. Examples of pulverizing methods include those using a mortar, ball mill, sand mill, vibrating ball mill, planetary ball mill, jet mill, counter jet mill, swirling airflow type jet mill, or a sieve. Wet pulverization in the presence of water or an organic solvent such as hexane can also be used during pulverization. As for classification methods, sieves and air classifiers are used as necessary for both dry and wet methods.

<Method of manufacturing positive electrode active material particles>
The method for producing the positive electrode active material particles includes contacting the transition metal oxide particles with a phosphonic acid compound (contact step).

(Transition metal oxide particles)
Examples of the transition metal oxide particles include the particles described in the above-mentioned "(Transition metal oxide particles)" in "<Positive electrode active material particles>".

(Phosphonic acid compounds)
Examples of the phosphonic acid compound include the same compounds as the phosphonic acid compounds described as the derivatives of the first compound in "(first compound)" of the above-mentioned "<Positive electrode active material particles>". That is, for example, examples of the phosphonic acid compound include alkyl phosphonic acid, alkenyl phosphonic acid, alkynyl phosphonic acid, and the like. As the phosphonic acid compound, a phosphonic acid compound having 9 to 20 carbon atoms is preferable, a phosphonic acid compound having 10 to 16 carbon atoms is more preferable, and a phosphonic acid compound having 10 to 12 carbon atoms is even more preferable. Examples of the alkyl phosphonic acid having such a carbon number include nonyl phosphonic acid, decyl phosphonic acid, dodecyl phosphonic acid, tetradecyl phosphonic acid, hexadecyl phosphonic acid, octadecyl phosphonic acid, and the like. Examples of the alkenyl phosphonic acid having the above carbon number include 2-hexylallyl phosphonic acid, nonenyl phosphonic acid, dodecenyl phosphonic acid, hexadecenyl phosphonic acid, and the like. Examples of alkynylphosphonic acids having the above carbon numbers include nonynylphosphonic acid, decynylphosphonic acid, dodecynylphosphonic acid, and hexadecynylphosphonic acid.

(Contacting step)
In this step, the transition metal oxide particles are contacted with the phosphonic acid compound. Specifically, the contact step may be, for example, a method of dropping a solution (aqueous solution, alcohol solution, etc.) of the phosphonic acid compound into a dispersion of the transition metal oxide particles and mixing with a conventionally known mixing device or the like. This mixing causes the transition metal oxide particles to be coated with the phosphonic acid compound. The mixing conditions are not particularly limited and can be appropriately set so that the transition metal oxide particles are covered with the phosphonic acid compound. After dropping the solution of the phosphonic acid compound into the dispersion of the transition metal compound particles and mixing, that is, after contacting the transition metal oxide particles with the phosphonic acid compound, a heat treatment may be performed. The dropping and mixing may also be performed while heating. The obtained positive electrode active material particles may be subjected to treatments such as drying and classification.

In addition to the above, in this process, the transition metal oxide particles and the phosphonic acid compound may be contacted by mixing the phosphonic acid compound with the positive electrode mixture paste. For example, the phosphonic acid compound is added to a positive electrode mixture paste in which the transition metal oxide particles, the conductive agent, and the binder are dispersed in a dispersion medium, and the mixture is stirred. When the phosphonic acid compound is added, the content of the transition metal oxide particles in the solid content (components other than the dispersion medium) of the positive electrode mixture paste is preferably as close to 100% by mass as possible. This is because the phosphonic acid compound can be more effectively prevented from remaining in areas other than the surface of the transition metal oxide particles in the positive electrode mixture.

<Configuration of Energy Storage Element>
An electric storage element according to one embodiment of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode and the negative electrode are usually stacked or wound with a separator interposed therebetween to form an electrode body. This electrode body is housed in a container, and the container is filled with a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. As an example of an electric storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as a "secondary battery") will be described.

(Positive electrode)
The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

The positive electrode substrate has electrical conductivity. Having "electrical conductivity" means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 ⁷ Ω·cm or less, and "non-electrically conductive" means that the volume resistivity is more than 10 ⁷ Ω·cm. As the material of the positive electrode substrate, metals such as aluminum, titanium, tantalum, stainless steel, and alloys thereof are used. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high electrical conductivity, and cost. Examples of the form of the positive electrode substrate include foil and vapor deposition film, and foil is preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, A1N30, and the like specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate while increasing the energy density per volume of the secondary battery. "Average thickness" refers to the value obtained by dividing the punched mass when a substrate of a given area is punched out by the true density and punched area of the substrate. The same definition is used when "average thickness" is used for other members, etc.

The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may include, for example, a binder and a conductive agent.

The positive electrode active material layer contains the positive electrode active material particles described above. The positive electrode active material layer may contain optional components such as a conductive agent, a binder, a thickener, and a filler, as necessary.

The positive electrode active material layer may further contain positive electrode active material particles other than the positive electrode active material particles having the compound having the carbon-phosphorus bond. The material of such other positive electrode active material particles can be appropriately selected from, for example, the transition metal oxides described above or known positive electrode active materials described below. However, the lower limit of the total content of the positive electrode active material particles in all the positive electrode active material particles contained in the positive electrode active material layer is preferably 90 mass %, more preferably 99 mass %. In this way, the effect of the present invention can be further enhanced by using only the positive electrode active material particles having the compound having the carbon-phosphorus bond as the positive electrode active material particles.

As the known positive electrode active material, a material capable of absorbing and releasing lithium ions is usually used. As the positive electrode active material, polyanion compounds, chalcogen compounds, sulfur, etc. are listed. As the polyanion compounds, LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F, etc. are listed. As the chalcogen compounds, titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. are listed. The atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more may be mixed and used.

The content of all positive electrode active material particles in the positive electrode active material layer is not particularly limited, but the lower limit is preferably 50% by mass, more preferably 80% by mass, and even more preferably 90% by mass. On the other hand, the upper limit of this content is preferably 99% by mass, and may be 98% by mass.

The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, conductive ceramics, and the like. Examples of carbonaceous materials include graphitized carbon, non-graphitized carbon, graphene-based carbon, and the like. Examples of non-graphitized carbon include carbon nanofiber, pitch-based carbon fiber, carbon black, and the like. Examples of carbon black include furnace black, acetylene black, ketjen black, and the like. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerene, and the like. Examples of the conductive agent include powder and fiber. As the conductive agent, one of these materials may be used alone, or two or more types may be mixed and used. These materials may also be used in combination. For example, a material in which carbon black and CNT are combined may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity and coatability, and acetylene black is preferred among them.

The content of the conductive agent in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent in the above range, the energy density of the secondary battery can be increased.

Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), and fluororubber; polysaccharide polymers, etc.

The binder content in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 9% by mass or less. By keeping the binder content within the above range, the active material can be stably maintained.

Examples of thickeners include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. If the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like.

The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ion crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and man-made products thereof.

The positive electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, and Ge, and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, Sn, Sr, Ba, and W as components other than the positive electrode active material particles, conductive agent, binder, thickener, and filler.

(Negative electrode)
The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode.

The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, are used as the material for the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the form of the negative electrode substrate include foil and vapor-deposited film, with foil being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, even more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per volume of the secondary battery.

The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as necessary. The optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified for the positive electrode above.

The negative electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, and Ge, and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, Sn, Sr, Ba, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

The negative electrode active material can be appropriately selected from known negative electrode active materials. As the negative electrode active material for lithium ion secondary batteries, a material capable of absorbing and releasing lithium ions is usually used. Examples of the negative electrode active material include metal Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; titanium-containing oxides such as Li ₄ Ti ₅ O ₁₂ , LiTiO _{2, and} TiNb ₂ O ₇ ; polyphosphate compounds; silicon carbide; carbon materials such as graphite and non-graphitic carbon (easily graphitized carbon or non-graphitizable carbon). Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more may be mixed and used.

"Graphite" refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of the (002) plane determined by X-ray diffraction before charging and discharging or in a discharged state of 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of obtaining a material with stable physical properties.

"Non-graphitic carbon" refers to a carbon material having an average lattice spacing (d002) of 0.34 nm or more and 0.42 nm or less of ( ₀₀₂ ) plane determined by X-ray diffraction before charging and discharging or in a discharged state. Examples of non-graphitic carbon include non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

Here, the "discharged state" refers to a state in which the open circuit voltage is 0.7 V or more in a single-electrode battery using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic Li as the counter electrode. Since the potential of the metallic Li counter electrode in the open circuit state is approximately equal to the redox potential of Li, the open circuit voltage in the single-electrode battery is approximately equal to the potential of the negative electrode containing the carbon material relative to the redox potential of Li. In other words, an open circuit voltage of 0.7 V or more in the single-electrode battery means that sufficient lithium ions that can be absorbed and released during charging and discharging have been released from the carbon material, which is the negative electrode active material.

The term "non-graphitizable carbon" refers to a carbon material having the above _d002 of 0.36 nm or more and 0.42 nm or less.

The term "graphitizable carbon" refers to a carbon material having the above _d002 of 0.34 nm or more and less than 0.36 nm.

The negative electrode active material is usually a particle (powder). The average diameter of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is, for example, a carbon material, the average diameter may be preferably 1 μm or more and 100 μm or less. When the negative electrode active material is a metal, a semi-metal, a metal oxide, a semi-metal oxide, a titanium-containing oxide, a polyphosphate compound, or the like, the average diameter may be preferably 1 nm or more and 1 μm or less. By setting the average diameter of the negative electrode active material to the above lower limit or more, the negative electrode active material can be easily manufactured or handled. By setting the average diameter of the negative electrode active material to the above upper limit or less, the electronic conductivity of the active material layer is improved. In order to obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverizing method and the classifying method can be selected, for example, from the methods exemplified for the positive electrode above.

The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer.

(Separator)
The separator can be appropriately selected from known separators. For example, a separator consisting of only a base layer, a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both sides of the base layer, etc. can be used as the separator. Examples of the material of the base layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these materials, a porous resin film is preferable from the viewpoint of strength, and a nonwoven fabric is preferable from the viewpoint of the liquid retention of the non-aqueous electrolyte. As the material of the base layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of shutdown function, and polyimide and aramid are preferable from the viewpoint of oxidation decomposition resistance. A material obtained by combining these resins may be used as the base layer of the separator.

Examples of the heat-resistant particles contained in the heat-resistant layer include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ion crystals such as calcium fluoride and barium fluoride; covalent crystals such as silicon and diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. As the inorganic compound, a single substance or a complex of these substances may be used alone, or two or more types may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, and aluminosilicate are preferred from the viewpoint of the safety of the storage element.

The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured using a mercury porosimeter.

As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyvinylidene fluoride, etc. Using a polymer gel has the effect of suppressing leakage. As the separator, a polymer gel may be used in combination with the porous resin film or nonwoven fabric as described above.

(Non-aqueous electrolyte)
The nonaqueous electrolyte may be appropriately selected from known nonaqueous electrolytes. The nonaqueous electrolyte may be a nonaqueous electrolyte solution. The nonaqueous electrolyte solution includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent.

The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylate esters, phosphate esters, sulfonate esters, ethers, amides, and nitriles. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds are substituted with halogens may also be used.

Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.

Examples of chain carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, EMC is preferred.

As the non-aqueous solvent, it is preferable to use a cyclic carbonate or a chain carbonate, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. By using a cyclic carbonate, it is possible to promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. By using a chain carbonate, it is possible to keep the viscosity of the non-aqueous electrolyte low. When a cyclic carbonate and a chain carbonate are used in combination, it is preferable that the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is, for example, in the range of 5:95 to 50:50.

The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, etc. Among these, lithium salts are preferred.

_{Examples of} the lithium salt include inorganic lithium salts such as _LiPF6 , _LiBF4 , _LiClO4 , and LiN( _{SO2F ) 2} , and lithium salts having a halogenated hydrocarbon _group such as _LiSO3CF3 , LiN( _SO2CF3 ) ₂ , LiN( _SO2C2F5 ) ₂ , _{LiN ( SO2CF3} ) _{( SO2C4F9} ), LiC( _SO2CF3 ) ₃ , and LiC( _SO2C2F5 ) _{3 .} Among these, inorganic lithium salts are preferred, _{and LiPF6 is} more preferred.

The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol/dm ³ or more and 2.5 mol/dm ³ or less, more preferably 0.3 mol/dm ³ or more and 2.0 mol/dm ³ or less, even more preferably 0.5 mol/dm ³ or more and 1.7 mol/dm ³ or less, and particularly preferably 0.7 mol/dm ³ or more and 1.5 mol/dm ³ or less. By setting the content of the electrolyte salt in the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

The non-aqueous electrolyte may contain additives. Examples of additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalic acid compounds such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); lithium difluorophosphate; aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2,5-difluoroanisole, and the like. halogenated anisole compounds such as 2,6-difluoroanisole, 3,5-difluoroanisole; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, and the like. These additives may be used alone or in combination of two or more.

The content of the additives contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass. By setting the content of the additives within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and to further improve safety.

A solid electrolyte may be used as the non-aqueous electrolyte, or a non-aqueous electrolyte solution and a solid electrolyte may be used in combination.

The solid electrolyte can be selected from any material that has ionic conductivity such as lithium, sodium, calcium, etc., and is solid at room temperature (e.g., 15°C to 25°C). Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, polymer solid electrolytes, etc.

Examples of sulfide solid electrolytes include Li ₂ S—P ₂ S ₅ , LiI—Li ₂ S—P ₂ S ₅ , and Li ₁₀ Ge—P ₂ S ₁₂ .

The shape of the energy storage element of this embodiment is not particularly limited, and examples thereof include a cylindrical battery, a laminate film battery, a square battery, a flat battery, a coin battery, and a button battery.
Fig. 1 shows an energy storage element 1 as an example of a prismatic battery. Note that this figure is a see-through view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound with a separator sandwiched therebetween is housed in a prismatic container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

<Configuration of Power Storage Device>
The energy storage element of this embodiment can be mounted as an energy storage unit (battery module) formed by assembling a plurality of energy storage elements 1 in a power source for an automobile such as an electric vehicle (EV), a hybrid vehicle (HEV), or a plug-in hybrid vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source, etc. In this case, it is sufficient that the technology of the present invention is applied to at least one energy storage element included in the energy storage device.
2 shows an example of an energy storage device 30 in which energy storage units 20, each of which is an assembly of two or more electrically connected energy storage elements 1, are further assembled. The energy storage device 30 may include a bus bar (not shown) that electrically connects the two or more energy storage elements 1, a bus bar (not shown) that electrically connects the two or more energy storage units 20, and the like. The energy storage units 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of the one or more energy storage elements.

<Method of manufacturing energy storage element>
The method for manufacturing the energy storage element of the present embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode body, preparing a non-aqueous electrolyte, and housing the electrode body and the non-aqueous electrolyte in a container. The preparation of the electrode body includes preparing a positive electrode and a negative electrode, and forming the electrode body by stacking or rolling the positive electrode and the negative electrode with a separator interposed therebetween.

The method of placing the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte, the non-aqueous electrolyte solution can be injected through an injection port formed in the container, and then the injection port can be sealed.

<Other embodiments>
The positive electrode active material particles, the electric storage element, the electric storage device, and the method for manufacturing the positive electrode active material particles of the present invention are not limited to the above-mentioned embodiments, and various modifications may be made within the scope of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a well-known technique. Furthermore, a part of the configuration of one embodiment can be deleted. Also, a well-known technique can be added to the configuration of one embodiment.

In the above embodiment, the case where the storage element is used as a chargeable and dischargeable non-aqueous electrolyte secondary battery (e.g., a lithium ion secondary battery) has been described, but the type, shape, size, capacity, etc. of the storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

[Comparative Example 1]
As the transition metal oxide particles _{, LiNi0.6Mn0.2Co0.2O2} particles were used. These transition metal oxide particles were used as _the positive _electrode active material particles.

[Examples 1 to 4 and Comparative Examples 2 to 7]
(Preparation of Positive Electrode Active Material Particles)
The same transition metal oxide particles as those in Comparative Example 1 were used. The transition metal oxide particles were mixed with the additive compound and N-methylpyrrolidone in the amounts shown in Table 1 using a rotation/revolution mixer (ARE-310 manufactured by THYNKY Corporation) to bring the additive compound into contact with the transition metal oxide particles. The mixing conditions were a rotation speed of 2000 rpm and a mixing time of 2 minutes and 30 seconds. The resulting mixture was heated at 110° C. to remove N-methylpyrrolidone, thereby producing the positive electrode active material particles of Examples 1 to 4 and Comparative Examples 2 to 7.

In Table 1, "C number" indicates the number of carbon atoms in the additive compound, "C/P ratio" indicates the ratio of the number of carbon atoms to the number of phosphorus atoms in the additive compound, "amount" indicates the amount (mol%) of the additive compound in relation to the transition metal oxide particles, and "P or Si mass ratio" indicates the mass ratio (mass%) of phosphorus atoms or silicon atoms in relation to the transition metal oxide particles. The values of "C/P ratio," "amount," and "P or Si mass ratio" are values calculated on the assumption that all of the additive compound used has reacted and bonded to the surface of the transition metal oxide particles.

(Measurement of Press Density)
The press density of the positive electrode active material particles of each Example and Comparative Example was measured in the following manner. 4 g of the positive electrode active material particles were filled in a pellet molding machine of φ20 mm, and a hydraulic press was used to pressurize the positive electrode active material pellets at 20 kN. The press density (apparent density) of the obtained positive electrode active material pellets was obtained by dividing the mass of the positive electrode active material pellets by the apparent volume. The apparent volume of the positive electrode active material pellets was obtained by the product of the area and the average thickness of the positive electrode active material pellets. The average thickness of the positive electrode active material pellets was the average value of the thicknesses at any five points of the positive electrode active material pellets. The results are shown in Table 1.

(Positive electrode active material capacity)
A storage element (secondary battery) was prepared using the positive electrode active material particles (transition metal oxide particles) of Comparative Example 1 in the following manner. Using NMP as a dispersion medium, the positive electrode active material particles, the conductive agent, and the binder were mixed so that the mass ratio in terms of solid content was 93:5:2 to obtain a positive electrode mixture paste. The positive electrode mixture paste was applied to one side of an aluminum foil as a positive electrode substrate, leaving an uncoated portion (a portion where the positive electrode active material layer is not formed), and dried at 100 ° C. to form a positive electrode active material layer on the positive electrode substrate. The application amount of the positive electrode mixture paste was 16 mg / cm ² in terms of solid content. Pressurized with a roll press so that the porosity of the positive electrode active material layer was 30%, and dried in a vacuum at 100 ° C. for 12 hours. In this way, a positive electrode was obtained.
A laminate cell (electricity storage element) was produced using the above positive electrode as a working electrode, metallic lithium as a counter electrode, a nonaqueous electrolyte solution in which _LiPF6 was dissolved at a concentration of 1 mol/ ^dm3 in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio 30:70), and a separator made of a polyethylene base material.
The discharge capacity was measured using the obtained storage element as follows. The battery was charged at a constant current of 0.1C to 4.25V at 25°C, and then charged at a constant voltage of 4.25V. The end condition of the charge was set to when the total charge time was 3 hours. After a 10-minute pause was provided after the charge, the battery was discharged at a constant current of 0.1C to 2.75V at 25°C. The above charge and discharge were repeated twice, and the value obtained by dividing the second discharge capacity by the mass of the positive electrode active material particles was taken as the "positive electrode active material capacity". The positive electrode active material capacity of Comparative Example 1 was 170mAh/g. The positive electrode active material capacity was similarly determined for the other Comparative Examples and Examples. At this time, the positive electrode active material capacity was calculated on the assumption that all of the additive compounds used reacted and bonded to the transition metal oxide particle surface, and the mass of the compound derived from this additive compound did not contribute to charge and discharge. The results are shown in Table 1.
In addition, the product of the press density and the capacity of the positive electrode active material was calculated for each of the examples and comparative examples. The results are shown in Table 1.

It was confirmed that the press density of the positive electrode active material particles of Examples 1 to 4, in which the first compound derived from each additive compound, i.e., a specific compound having a carbon-phosphorus bond, is present on at least a part of the surface of each transition metal oxide particle, is greater than that of Comparative Examples 1 to 7, which do not have the first compound on the surface. As a result, it was shown that the packing properties of Examples 1 to 4 are greater than those of Comparative Examples 1 to 7. In particular, a comparison of Comparative Examples 6 and 7 with Examples 1 and 2 shows that when the content of carbon atoms relative to the content of phosphorus atoms is 9 or more in terms of atomic ratio, the packing properties are further improved and the press density is increased. In addition, it was confirmed that the product of the press density and the positive electrode material capacity in Examples 1 to 4 is greater than that of Comparative Examples 1 to 7. As a result, it was shown that when a storage element such as a secondary battery is produced using the positive electrode active material particles of Examples 1 to 4, the energy density is improved.

On the other hand, when the amount of additive compound is increased as in Example 4 and the mass ratio of phosphorus atoms in the mass of the obtained positive electrode active material particles is increased, the press density is particularly high, but the mass ratio of phosphorus atoms and carbon atoms that do not contribute to charging and discharging increases, so that the energy density of a storage element such as a secondary battery using such positive electrode active material particles tends to decrease. In other words, it was found that by adjusting the mass ratio of phosphorus atoms to the mass of the transition metal oxide particles, etc., it is possible to improve the filling property while suppressing the content of compounds having carbon-phosphorus bonds that do not contribute to charging and discharging, and as a result, it is possible to increase the energy density of the storage element.

The present invention can be applied to storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles, as well as to the positive electrodes and positive electrode active materials provided therein.

Reference Signs List 1 Energy storage element 2 Electrode body 3 Container 4 Positive electrode terminal 41 Positive electrode lead 5 Negative electrode terminal 51 Negative electrode lead 20 Energy storage unit 30 Energy storage device

Claims (5)

Transition metal oxide particles;
a compound having a carbon-phosphorus bond and present on at least a portion of the surface of the transition metal oxide particle,
the content of carbon atoms relative to the content of phosphorus atoms in the compound having a carbon-phosphorus bond is 9 or more in terms of atomic ratio,
The positive electrode active material particles have a mass ratio of the phosphorus atoms of 0.06 mass % or more and 0.3 mass % or less relative to the mass of the transition metal oxide particles . the compound having a carbon-phosphorus bond has a hydrocarbon group having 9 or more carbon atoms,
2. The positive electrode active material particle according to claim 1 , wherein the carbon atom constituting the carbon-phosphorus bond constitutes a part of the hydrocarbon group. an electrode assembly including a positive electrode, a negative electrode, and a separator;
A non-aqueous electrolyte;
a container for accommodating the electrode assembly and a non-aqueous electrolyte;
3. An electric storage element, wherein the positive electrode contains the positive electrode active material particles according to claim 1. An electricity storage device comprising one or more electricity storage elements according to claim 3 . The method comprises contacting transition metal oxide particles with a phosphonic acid compound having a hydrocarbon group having 9 or more carbon atoms ,
The method for producing positive electrode active material particles , wherein a mass ratio of phosphorus atoms in the phosphonic acid compound is 0.06 mass % or more and 0.3 mass % or less with respect to the mass of the transition metal oxide particles .

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