JP2023128175A - Positive electrode active substance for secondary battery, positive electrode for secondary battery and secondary battery - Google Patents

Abstract

To provide a secondary battery which can obtain excellent capacity characteristics and excellent load characteristics.SOLUTION: An active substance contained in a positive electrode active substance layer of a secondary battery includes a central part for occluding and discharging an electrode reaction substance, and a coating part provided thereon. The central part includes a polycrystalline substance where two or more crystal grains are bonded to each other, and a grain boundary between the two crystal grains bonded to each other. The coating part coats the surface of the central part and the grain boundary, and includes a substrate layer and a surface layer in order from a side closer to the central part. The substrate layer includes a reactant of first metal alkoxide having no metal atom-carbon atom bond in one molecule, and a reactant of second metal alkoxide having two or more metal atom-carbon atom bonds in one molecule. The surface layer includes third metal alkoxide having one metal atom-carbon atom bond in one molecule, and the third metal alkoxide is bonded to at least one of the reactant of the first metal alkoxide and the second metal alkoxide.SELECTED DRAWING: Figure 8

Description

The present technology relates to a positive electrode active material for a secondary battery, a positive electrode for a secondary battery, and a secondary battery.

BACKGROUND OF THE INVENTION As various electronic devices such as mobile phones have become widespread, secondary batteries are being developed as power sources that are small and lightweight and can provide high energy density. This secondary battery includes an electrolytic solution together with a positive electrode (positive electrode for secondary battery) and a negative electrode, and the positive electrode contains a positive electrode active material (positive electrode active material for secondary battery).

Various studies have been made regarding the configuration of secondary batteries. Specifically, large-sized positive electrode active material particles made of a polyanionic compound and carbon, and carbon composites of small-sized positive electrode active material particles made of a polyanionic compound and carbon are used (for example, (See Patent Document 1.) A lithium-transition metal composite oxide powder coated with a coating layer having a Si/transition metal surface composition ratio of 80% or more is used (see, for example, Patent Document 2). A positive electrode active material having a layer surface-treated with a silane coupling agent (surface-treated layer) is used (see, for example, Patent Document 3). A positive electrode active material in which particles made of a polyanionic compound and carbon are coated with a lipophilic treatment agent is used (see, for example, Patent Document 4). A positive electrode active material obtained from particles containing a positive electrode material capable of intercalating and deintercalating lithium ions, a silane coupling agent capable of bonding with the positive electrode material, and a polymer compound capable of bonding with the silane coupling agent. (For example, see Patent Document 5.)

Japanese Patent Application Publication No. 2011-034776 Japanese Patent Application Publication No. 2012-199101 Japanese Patent Application Publication No. 2012-169249 JP2011-049161A Japanese Patent Application Publication No. 2013-191539

Although various studies have been made regarding the configuration of secondary batteries, the capacity characteristics and load characteristics are still insufficient, so there is room for improvement.

Therefore, there is a need for a positive electrode active material for a secondary battery, a positive electrode for a secondary battery, and a secondary battery that can provide excellent capacity characteristics and excellent load characteristics.

A positive electrode active material for a secondary battery according to an embodiment of the present technology includes a center portion that occludes and releases an electrode reactant, and a coating portion provided on the surface of the center portion. The central portion includes a polycrystalline body in which two or more crystal grains are bonded to each other, and has a grain boundary between the two crystal grains bonded to each other. The covering portion covers each of the surface and grain boundaries of the center portion, and includes a base layer and a surface layer in order from the side closer to the center portion. The base layer contains a reactant of a first metal alkoxide having no metal atom-carbon bond in one molecule and a reactant of a second metal alkoxide having two or more metal atom-carbon bonds in one molecule. . The surface layer contains a third metal alkoxide having one metal atom-carbon atom bond in one molecule, and the third metal alkoxide reacts with at least one of the reactant of the first metal alkoxide and the second metal alkoxide. combined.

A positive electrode for a secondary battery according to an embodiment of the present technology includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material for a secondary battery, and the positive electrode active material for a secondary battery includes the present technology described above. It has a configuration similar to that of the positive electrode active material for a secondary battery according to the embodiment.

A secondary battery according to an embodiment of the present technology includes a positive electrode for a secondary battery, a negative electrode, and an electrolyte, and the positive electrode for a secondary battery has the same structure as the positive electrode for a secondary battery according to an embodiment of the present technology described above. They have similar configurations.

According to a positive electrode active material for a secondary battery, a positive electrode for a secondary battery, or a secondary battery according to an embodiment of the present technology, the positive electrode active material for a secondary battery has a central portion that occludes and releases an electrode reactant, and a covering portion ( The coating portion covers the surface of the center and the grain boundaries, respectively, and the underlayer contains a reactant of the first metal alkoxide and a reactant of the second metal alkoxide. superior capacity because the surface layer includes a third metal alkoxide, and the third metal alkoxide is bonded to at least one of the reactant of the first metal alkoxide and the second metal alkoxide. characteristics and excellent load characteristics can be obtained.

Note that the effects of the present technology are not necessarily limited to the effects described here, and may be any of a series of effects related to the present technology described later.

FIG. 1 is a cross-sectional view showing the configuration of a positive electrode active material for a secondary battery in an embodiment of the present technology. FIG. 2 is a cross-sectional view showing a detailed configuration of the positive electrode active material for a secondary battery shown in FIG. 1. FIG. FIG. 2 is a schematic diagram showing an enlarged structure near the surface of the positive electrode active material for a secondary battery shown in FIG. 1. FIG. FIG. 2 is another schematic diagram showing an enlarged structure near the surface of the positive electrode active material for a secondary battery shown in FIG. 1. FIG. FIG. 2 is a cross-sectional view showing a detailed configuration of a positive electrode active material for a secondary battery according to a comparative example. FIG. 2 is a cross-sectional view for explaining problems of a positive electrode active material for a secondary battery according to a comparative example. FIG. 2 is a cross-sectional view for explaining the advantages of a positive electrode active material for a secondary battery in an embodiment of the present technology. FIG. 1 is a perspective view showing the configuration of a secondary battery in an embodiment of the present technology. 9 is a cross-sectional view showing the configuration of the battery element shown in FIG. 8. FIG. FIG. 2 is a block diagram showing the configuration of an application example of a secondary battery.

Hereinafter, one embodiment of the present technology will be described in detail with reference to the drawings. The order of explanation is as follows.

1. Positive electrode active material for secondary batteries 1-1. Configuration 1-2. Operation 1-3. Manufacturing method 1-4. Action and effect 2. Secondary battery (positive electrode for secondary battery)
2-1. Configuration 2-2. Operation 2-3. Manufacturing method 2-4. Action and effect 3. Modification example 4. Applications of secondary batteries

<1. Cathode active material for secondary batteries>
First, a positive electrode active material for a secondary battery (hereinafter simply referred to as "positive electrode active material") according to an embodiment of the present technology will be described.

The positive electrode active material described here is a material that absorbs and releases an electrode reactant, and is used as a constituent material of a positive electrode mounted in a secondary battery. Details of the secondary battery using the positive electrode active material will be described later.

The type of electrode reactant is not particularly limited, but specifically light metals such as alkali metals and alkaline earth metals. Specific examples of alkali metals include lithium, sodium, and potassium, and specific examples of alkaline earth metals include beryllium, magnesium, and calcium.

In the following, a case where the electrode reactant is lithium will be exemplified. That is, the positive electrode active material described below is a material that intercalates and desorbs lithium, and in the positive electrode active material, lithium is intercalated and desorbed in an ionic state.

<1-1. Configuration>
FIG. 1 shows a cross-sectional configuration of a positive electrode active material 100, which is a positive electrode active material according to an embodiment of the present technology, and FIG. 2 shows a detailed cross-sectional configuration of the positive electrode active material 100 shown in FIG. There is. Each of FIGS. 3 and 4 schematically shows an enlarged structure near the surface of the positive electrode active material 100 shown in FIG.

However, in FIG. 1, the cross-sectional shape of the positive electrode active material 100 is circular, and in FIG. 2, the cross-sectional shape of the positive electrode active material 100 is polygonal. Further, in FIG. 3, the configuration of the covering portion 120 is shown using a diagram, and in FIG. 4, the configuration of the covering portion 120 is shown using a chemical formula together with the diagram.

As shown in FIG. 1, the positive electrode active material 100 is in the form of a plurality of particles and includes a center portion 110 and a covering portion 120. That is, the positive electrode active material 100 is a coated particle in which the surface of the center portion 110 is coated with the coating portion 120.

[Central part]
As shown in FIG. 1, the central portion 110 is a portion of the positive electrode active material 100 that intercalates and deintercalates lithium, and includes one or more types of lithium-containing compounds. Although FIG. 1 shows a case where the cross-sectional shape of the central portion 110 is circular, the cross-sectional shape of the central portion 110 is not particularly limited and may be any other shape such as an ellipse.

This lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements. However, the lithium-containing compound may further contain one or more other elements as constituent elements. The type of other element is not particularly limited as long as it is an element other than lithium and transition metal elements, but specifically, it is an element belonging to Groups 2 to 15 in the long period periodic table.

The type of lithium-containing compound is not particularly limited, but specifically includes oxides, phosphoric acid compounds, silicic acid compounds, and boric acid compounds. Specific examples of oxides include LiNiO ₂ , LiCoO ₂ , LiCo _0.98 Al _0.01 Mg _0.01 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ and LiMn ₂ O ₄ . Specific examples of phosphoric acid compounds include LiFePO ₄ , LiMnPO ₄ and LiFe _0.5 Mn _0.5 PO ₄ .

Here, as shown in FIG. 2, the central portion 110 includes two or more crystal grains 111, and thus includes a polycrystalline body in which the two or more crystal grains 111 are bonded to each other. Thereby, the cross-sectional shape of the central portion 110 is a polygon.

Each of the two or more crystal grains 111 has a surface 111X and a grain boundary 111Y. The surface 111X is a surface (exposed surface) that does not exist between two crystal grains 111 that are bonded to each other. The grain boundary 111Y is a surface (non-exposed surface) existing between two crystal grains 111 that are bonded to each other, that is, a bonding surface (interface) between the two crystal grains 111.

Thereby, the center portion 110 containing the polycrystalline body has a plurality of surfaces 111X and a plurality of grain boundaries 111Y. However, in FIG. 2, only two crystal grains 111 and one grain boundary 111Y are shown to simplify the illustration.

[Coated part]
As shown in FIG. 1, the covering portion 120 is provided on the surface 111X of the center portion 110, and thus covers the surface 111X of the center portion 110. However, the covering portion 120 may cover the entire surface 111X, or may cover only a part of the surface 111X. In the latter case, a plurality of covering portions 120 may cover the surface 111X at a plurality of locations separated from each other.

In particular, as shown in FIG. 2, the covering portion 120 not only covers the surface 111X but also the grain boundaries 111Y. As a result, each surface 111X of two or more crystal grains 111 is covered with the covering part 120, and two crystal grains 111 adjacent to each other are covered with a part of the covering part 120 covering the grain boundary 111Y. are connected to each other through the parts.

Further, as shown in FIGS. 3 and 4, the covering portion 120 includes a base layer 121 and a surface layer 122 in order from the side closer to the center portion 110. That is, the covering portion 120 has a two-layer structure in which a base layer 121 and a surface layer 122 are arranged in order from the side closest to the center portion 110.

The covering portion 120 described here includes the base layer 121 and the surface layer 122 as described above, and therefore, as described below, the covering portion 120 includes a first metal alkoxide reactant, a second metal alkoxide reactant, and a third metal alkoxide reactant. It is an organic-inorganic hybrid film containing metal alkoxide.

(base layer)
The base layer 121 contains a reactant of a first metal alkoxide and a reactant of a second metal alkoxide.

As shown in FIGS. 3 and 4, this base layer 121 is a layer that has a network structure as described later, and more specifically, it is a film-like layer that covers the surface of the center portion 110. be.

The reason why the covering part 120 includes the base layer 121 is because the ionic conductivity of the positive electrode active material 100 is improved even if the covering part 120 is provided on the surface 111X of the central part 110. In this case, as will be described later, since each of the first metal alkoxide reactant and the second metal alkoxide reactant has a plurality of pores 121K, the Lithium ions become more mobile.

(First metal alkoxide)
The first metal alkoxide contains in one molecule one or more metal alkoxides that do not have a metal atom-carbon atom bond. Thereby, the first metal alkoxide contains one metal atom to which one or more alkoxy groups are bonded. The type of metal atom is not particularly limited as long as it is a metal atom that can form a metal alkoxide.

Specifically, the first metal alkoxide contains a compound represented by formula (1). This is because the reactant of the first metal alkoxide is easily formed, so that the base layer 121 is easily formed stably.

M1-(OR1) _a ...(1)
(M1 is any one of a silicon atom, a titanium atom, an aluminum atom, and a zirconium atom. R1 is an alkyl group having 1 to 10 carbon atoms and a group represented by formula (100). Either. a is 3 or 4. However, two R1's adjacent to each other may be bonded to each other.)

-CR11=CH-C(=O)-R12...(100)
(R11 is an alkyl group having 1 to 10 carbon atoms. R12 is an alkyl group having 1 to 30 carbon atoms, an alkoxy group having 1 to 30 carbon atoms, and 1 to 30 carbon atoms. It is any alkenyloxy group having a carbon number.)

The type of metal atom (M1) is not particularly limited as long as it is a silicon atom, a titanium atom, an aluminum atom, or a zirconium atom, but a silicon atom is particularly preferred. This is because a reactant of the first metal alkoxide is more easily formed.

The alkyl group (R1) is a monovalent group composed of carbon and hydrogen, and may be linear or branched with one or more side chains. Specific examples of alkyl groups include methyl, ethyl, propyl and butyl groups.

However, the type of alkyl group having 3 or more carbon atoms can be arbitrarily selected. Specifically, taking a propyl group having 3 carbon atoms as an example, the propyl group may be an n-propyl group or an isopropyl group. Further, taking a butyl group having 4 carbon atoms as an example, the butyl group may be an n-butyl group, a sec-butyl group, an isobutyl group, or a tert-butyl group.

Since the value of a is determined according to the valence of the metal atom (M1), it is the same value as the valence of the metal atom (M1). As a result, as mentioned above, when the metal atom (M1) is any one of silicon atom, titanium atom, aluminum atom, and zirconium atom, the value of a becomes 3 or 4, so the first metal Alkoxides contain 3 or 4 alkoxy groups (OR1).

When the value of a is 3, the three types of R1 may be the same or different. Of course, only some of the three R1 may be of the same type. Furthermore, when the value of a is 4, the types of the four R1s may be the same or different. Of course, only some of the four R1s may be of the same type.

Note that, since any two of the three R1s that are adjacent to each other are bonded to each other, the first metal alkoxide may form a ring containing any two R1s that are bonded to each other. Furthermore, since any two of the four R1s that are adjacent to each other are bonded to each other, the first metal alkoxide may form a ring containing any two R1s that are bonded to each other.

The alkoxy group (R12) is a monovalent group composed of carbon, hydrogen, and oxygen, and like the alkyl group described above, it may be linear or branched with one or more side chains. It may be in the form of Specific examples of alkoxy groups include methoxy, ethoxy, propoxy and butoxy groups. Note that the alkoxy group is sometimes referred to as an alkyloxy group.

The alkenyloxy group (R12) is a monovalent group composed of carbon, hydrogen, and oxygen and has one carbon-carbon double bond (>C=C<), and like the above-mentioned alkyl group, it is It may be chain-like or branched having one or more side chains. Specific examples of alkenyloxy groups include vinyloxy and allyloxy groups.

Specific examples of the first metal alkoxide when the metal atom (M1) is a silicon atom include Si-(OCH ₃ ) ₄ , Si-(OC ₂ H ₅ ) ₄ , Si-(OC ₃ H ₇ ) ₄ and Si -(OC ₄ H ₉ ) ₄ , etc.

Specific examples of the first metal alkoxide when the metal atom (M1) is a titanium atom are not particularly limited, but include Ti-(OCH ₃ ) ₄ , Ti-(OC ₂ H ₅ ) ₄ , Ti-(OC ₃ H ₇ ) ₄ and Ti-(OC ₄ H ₉ ) ₄ .

Specific examples of the first metal alkoxide when the metal atom (M1) is an aluminum atom are not particularly limited, but include Al-(OCH ₃ ) ₃ , Al-(OC ₂ H ₅ ) ₃ , Al-(OC ₃ H ₇ ) ₃ and Al-(OC ₄ H ₉ ) ₃ .

Specific examples of the first metal alkoxide when the metal atom (M1) is a zirconium atom include, but are not limited to, Zr-(OCH ₃ ) ₄ , Zr-(OC ₂ H ₅ ) ₄ , Zr-(OC ₃ H ₇ ) ₄ and Zr-(OC ₄ H ₉ ) ₄ .

The structure of the reactant of the first metal alkoxide is not particularly limited. Here, taking as an example the case where the metal atom (M1) is a silicon atom and more specifically the first metal alkoxide is Si-(OC ₂ H ₅ ) ₄ , the reactant of the first metal alkoxide has a configuration expressed by equation (11).

In the first metal alkoxide reactant, silicon atoms are bonded to each other via oxygen atoms, as shown in formula (11), so the first metal alkoxide reactant has multiple silicon atoms - Contains oxygen atomic bonds.

In this case, silicon atoms and oxygen atoms are bonded alternately to form a plurality of rings. As a result, spaces (pores 121K) are provided inside each ring, so the reactant of the first metal alkoxide has a plurality of pores 121K. Therefore, the reactant of the first metal alkoxide has a network structure formed by silicon atoms and oxygen atoms.

Of course, although a specific configuration is not shown here, even when the metal atom (M1) is a titanium atom, the reactant of the first metal alkoxide contains a plurality of titanium atom-oxygen atom bonds. Therefore, it has a network structure in which a plurality of pores 121K are provided.

Similarly, in the case where the metal atom (M1) is an aluminum atom, the reactant of the first metal alkoxide contains a plurality of aluminum atom-oxygen atom bonds, so it forms a network with a plurality of pores 121K. It has the structure of

Similarly, in the case where the metal atom (M1) is a zirconium atom, the reactant of the first metal alkoxide contains a plurality of zirconium atom-oxygen atom bonds, so it forms a network with a plurality of pores 121K. It has the structure of

(Second metal alkoxide)
The second metal alkoxide contains one or more metal alkoxides having two or more metal atom-carbon atom bonds in one molecule. Thereby, the second metal alkoxide contains two or more metal atoms that are bonded to each other via carbon chains and to each of which one or more alkoxy groups are bonded. That is, two or more metal atoms are bonded to each other via a carbon chain, and one or more alkoxy groups are bonded to each of the two or more metal atoms.

The type of carbon chain is not particularly limited as long as it is a chain hydrocarbon group that can bond to two or more metal atoms. The type of metal atom is not particularly limited as long as it is a metal atom that can form a metal alkoxide.

Among these, since the second metal alkoxide contains a silicon atom as a metal atom, it is preferable that the second metal alkoxide has two or more silicon atom-carbon atom bonds in one molecule. This is because the reactant of the second metal alkoxide is likely to be easily and stably formed.

Specifically, the second metal alkoxide contains one or more of the compounds represented by each of formulas (2) to (4). This is because the reactant of the second metal alkoxide is easily formed, so that the base layer 121 is easily formed stably.

(R3O) ₃ -Si-R2-Si-(OR4) ₃ ...(2)
(R2 is an alkylene group having 1 to 20 carbon atoms. Each of R3 and R4 is an alkyl group having 1 to 10 carbon atoms.)

(OR8) ₃ -Si-R5-NH-R6-NH-R7-Si-(OR9) ₃ ...(3)
(Each of R5 to R7 is an alkylene group having 1 to 20 carbon atoms. Each of R8 and R9 is an alkyl group having 1 to 10 carbon atoms.)

(R10) ₂ -Si-(OR11) ₂ ...(4)
(Each of R10 and R11 is an alkyl group having 1 or more and 10 or less carbon atoms.)

Details regarding the alkyl group (R3, R4, R8 to R11) are as described above.

The alkylene group (R2, R5 to R7) is a divalent group composed of carbon and hydrogen, and like the alkyl group described above, it may be linear or have one or more side chains. It may have a branched shape. Specific examples of alkylene groups include methylene, ethylene, propylene, and butylene groups.

However, the type of alkylene group having 3 or more carbon atoms can be arbitrarily selected. Specifically, taking a propylene group having 3 carbon atoms as an example, the propylene group may be an n-propylene group or an isopropylene group. Further, taking a butylene group having 4 carbon atoms as an example, the butylene group may be an n-butylene group, a sec-butylene group, an isobutylene group, or a tert-butylene group.

The three types of R3 may be the same or different. Of course, only two of the three R3 types may be the same type. What has been described here also applies to each of the three R4s, three R8s, three R9s, two R10s, and two R11s. Furthermore, what has been explained here also applies to R5 to R7.

Specific examples of the second metal alkoxide shown in formula (2) are (H ₃ CO) ₃ -Si-C ₂ H ₄ -Si-(OCH ₃ ) ₃ , (H ₃ CO) ₃ -Si-C ₄ H ₈ -Si-(OCH ₃ ) ₃ , (H ₃ CO) ₃ -Si-C ₆ H ₁₂ -Si-(OCH ₃ ) ₃ and (H ₅ C ₂ O) ₃ -Si-C ₂ H ₄ -Si- (OC ₂ H ₅ ) ₃ and the like.

A specific example of the second metal alkoxide shown in formula (3) is (H ₃ CO) ₃ -Si-C ₂ H ₄ -NH-C ₂ H ₄ -NH-C ₂ H ₄ -Si-(OCH ₃ ). ₃ and (H ₅ C ₂ O) ₃ -Si-C ₂ H ₄ -NH-C ₂ H ₄ -NH-C ₂ H ₄ -Si-(OC ₂ H ₅ ) ₃ .

Specific examples of the second metal alkoxide shown in formula (4) include (H ₃ C) ₂ -Si-(OCH ₃ ) ₃ and (H ₅ C ₂ ) ₂ -Si-(OC ₂ H ₅ ) _3. be.

The structure of the reactant of the second metal alkoxide is not particularly limited. Here, taking as an example the case where the second metal alkoxide shown in formula (2) is (H ₅ C ₂ O) ₃ -Si-C ₂ H ₄ -Si-(OC ₂ H ₅ ) ₃ , The second metal alkoxide reactant has a configuration represented by formula (21).

In the second metal alkoxide reactant, as shown in formula (21), formula (11) is satisfied, except that some silicon atoms are bonded to each other via alkylene groups, which are carbon chains. It has a structure similar to that of the reactant of the first metal alkoxide shown.

That is, in the reactant of the second metal alkoxide, some of the silicon atoms are bonded to each other via oxygen atoms, so the reactant of the second metal alkoxide contains multiple silicon atom-oxygen bonds. I'm here. In addition, in the second metal alkoxide reactant, other silicon atoms are bonded to each other via alkylene groups, so the second metal alkoxide reactant contains multiple silicon atom-carbon atom bonds. There is.

In this case, silicon atoms and oxygen atoms are bonded to each other, and silicon atoms are bonded to each other via alkylene groups, so that a plurality of rings are formed. As a result, a space (pore 121K) is provided inside each ring, so the reactant of the second metal alkoxide has a plurality of pores 121K, similar to the reactant of the first metal alkoxide. There is. Therefore, the reactant of the second metal alkoxide has a network structure formed by silicon atoms, oxygen atoms, and carbon atoms.

In this second metal alkoxide reactant, compared to the first metal alkoxide reactant, the pore size of the pores 121K increases due to the spacer 121S (alkylene group) interposed between some silicon atoms. are doing. This allows lithium ions to move more easily through the pores 121K in the second metal alkoxide reactant.

Note that the reactant of the second metal alkoxide may not be combined with the reactant of the first metal alkoxide, or may be combined with the reactant of the first metal alkoxide.

(Surface layer)
The surface layer 122 contains one or more of the third metal alkoxides, and is bonded to the base layer 121 as shown in FIGS. 3 and 4. As a result, the surface layer 122 is a layer having a plurality of hydrocarbon chains 122N described later as a matrix, and more specifically, a whisker-like layer extending radially from the center portion 110 in a plurality of directions. be.

The reason why the covering portion 120 includes the surface layer 122 is that the surface layer 122 is used to improve the filling property of the positive electrode active material 100. In this case, as described later, the third metal alkoxide has a plurality of hydrocarbon chains 122N, so the surface free energy of the surface layer 122 decreases. This improves the slipperiness of the surface 111X of the positive electrode active material 100, making it easier to densely fill the plurality of positive electrode active materials 100.

In addition, the coating portion 120 (base layer 121 and surface layer 122) covers the surface 111X and the grain boundaries 111Y of the center portion 110, which improves slipperiness not only on the surface 111X but also on the grain boundaries 111Y. Because it does. This makes it easier for the plurality of positive electrode active materials 100 to be more densely packed while ensuring ionic conductivity in the positive electrode active material 100.

(Third metal alkoxide)
The third metal alkoxide contains one or more metal alkoxides having one metal atom-carbon atom bond in one molecule. Thereby, the third metal alkoxide contains one metal atom to which each of one alkyl group and one or more alkoxy groups is bonded. The type of metal atom is not particularly limited as long as it is a metal atom that can form a metal alkoxide.

This third metal alkoxide is bonded to one or both of the reactant of the first metal alkoxide and the second metal alkoxide contained in the base layer 121, and more specifically, Bonded to silicon atoms.

Specifically, the third metal alkoxide contains a compound represented by formula (5). This is because the third metal alkoxide is easily bonded to one or both of the reactant of the first metal alkoxide and the second metal alkoxide, and thus the surface layer 122 is easily formed stably.

R12-Si-(OR13) ₃ ...(5)
(R12 is an alkyl group having 8 to 30 carbon atoms. R13 is an alkyl group having 1 to 10 carbon atoms.)

Details regarding the alkyl group (R12, R13) are as described above. The three types of R13 may be the same or different. Of course, only two of the three R13 types may be the same.

Specific examples of the third metal alkoxide are H ₁₇ C ₈ -Si-(OCH ₃ ) ₃ , H ₂₁ C ₁₀ -Si-(OCH ₃ ) ₃ , H ₃₃ C ₁₆ -Si-(OCH ₃ ) ₃ , H ₄₁ C ₂₀ --Si-(OCH ₃ ) ₃ and H ₆₁ C ₃₀ Si-(OCH ₃ ) ₃ and the like.

Here, taking as an example the case where the third metal alkoxide is H ₃₃ C ₁₆ Si-(OC ₃ H ₇ ) ₃ , the third metal alkoxide is added to the base layer as shown in FIGS. 3 and 4. It is bonded to one or both of the first metal alkoxide reactant and the second metal alkoxide reactant contained in 121.

Specifically, one end of the third metal alkoxide is bonded to a silicon atom included in the base layer 121. Further, the other end of the third metal alkoxide (-C ₁₆ H ₃₃ which is a plurality of hydrocarbon chains 122N) extends in a direction away from the base layer 121. As a result, the plurality of hydrocarbon chains 122N extend radially from the base layer 121 and are arranged while being separated from each other with intervals. Therefore, the third metal alkoxide has a radial structure composed of a plurality of hydrocarbon chains 122N. Note that Y in FIG. 4 represents a part of the third metal alkoxide, and more specifically represents the alkyl group (R12) shown in formula (5).

(Configuration conditions)
Regarding this positive electrode active material 100, it is preferable that the structural conditions described below are satisfied.

(Weight ratio R1)
First, the weight ratio R1 (weight %), which is the ratio of the weight M1 of the first metal alkoxide reactant to the weight M120 of the coating part 120, is not particularly limited, but is preferably 5.0 weight % to 85.0 weight %. Preferably, it is % by weight. This is because the network structure derived from the first metal alkoxide is more likely to be formed, so that the base layer 121 can be easily and stably formed. This weight ratio R1 is calculated based on the formula R1=(M1/M120)×100. However, the value of the weight ratio R1 is a value obtained by rounding off the value to the second decimal place.

(Weight ratio R2)
Second, the weight ratio R2 (weight %), which is the ratio of the weight M2 of the second metal alkoxide reactant to the weight M120 of the coating portion 120, is not particularly limited, but is preferably 1.0 weight % to 40.0 weight %. Preferably, it is % by weight. This is because the network structure derived from the second metal alkoxide is more likely to be formed, so that the base layer 121 can be easily and stably formed. This ratio R2 is calculated based on the formula R2=(M2/M120)×100. However, the value of the weight ratio R2 is a value obtained by rounding off the value to the second decimal place.

(Weight ratio R3)
Thirdly, the weight ratio R3 (weight %), which is the ratio of the weight M3 of the third metal alkoxide to the weight M120 of the coating portion 120, is not particularly limited, but is preferably 5.0 weight % to 90.0 weight %. It is preferable that there be. This is because a radial structure originating from the third metal alkoxide is more likely to be formed, so that the surface layer 122 can be easily and stably formed. This ratio R3 is calculated based on the formula R3=(M2/M120)×100. However, the value of the weight ratio R3 is a value obtained by rounding off the value to the second decimal place.

(Weight ratio R4)
Fourthly, the weight ratio R4 (weight %), which is the ratio of the weight M120 of the covering part 120 to the sum M100 of the weight M110 of the center part 110 and the weight M120 of the covering part 120, is not particularly limited, but is preferably 0. The amount is preferably 0.010% to 2.000% by weight. Since the proportion of the coating portion 120 in the positive electrode active material 100 is optimized, the ion conductivity of the positive electrode active material 100 is sufficiently improved while ensuring the amount of intercalation and desorption of lithium, and the filling property of the positive electrode active material 100 is improved. This is because the results are sufficiently improved. This ratio R4 is calculated based on the formula R4=(M120/M100)×100. However, the value of the weight ratio R4 is a value obtained by rounding off the value to the fourth decimal place.

(Thickness ratio R5)
Fifth, when comparing the thickness T111X of the covering part 120 covering the surface 111X and the thickness T111Y of the covering part 120 covering the grain boundary 111Y, it is found that the thickness T111Y is smaller than the thickness T111X. The thickness ratio R5 (%) is not particularly limited, but is preferably 10% to 100%. This is because the sliding properties of the grain boundaries 111Y are sufficiently improved, so that the filling properties of the positive electrode active material 100 are sufficiently improved. This ratio R5 is calculated based on the formula R5=(T111Y/T111X)×100.

Note that the procedure for calculating the thickness ratio R5 is as explained below. Below, a case where a secondary battery using the positive electrode active material 100 is used will be explained. This secondary battery includes a positive electrode active material layer including a plurality of positive electrode active materials 100.

First, the secondary battery is disassembled to recover the positive electrode including the positive electrode active material 100, and then the positive electrode is cut to expose the cross section of the positive electrode active material layer. The method for cutting the positive electrode is not particularly limited, but specifically, ion milling or the like is used.

Subsequently, the cross section of the positive electrode active material layer is observed using a scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDX) or the like to obtain an observation result (electron micrograph). The observation magnification can be arbitrarily set as long as it can measure each of the thicknesses T111X and T111Y.

Next, the thickness T111X of the covering portion 120 covering the surface 111X is calculated based on the electron micrograph. In this case, after measuring the thickness T111X at 10 different locations, the average value of the 10 thicknesses T111X is calculated.

Next, the thickness T111Y of the covering portion 120 covering the grain boundary 111Y is calculated based on the electron micrograph. In this case, after measuring the thickness T111Y at 10 different locations, the average value of the 10 thicknesses T111Y is calculated.

Finally, the thickness ratio R5 is calculated based on the calculation results of the thicknesses T111X and T111Y.

<1-2. Operation＞
In this positive electrode active material 100, lithium is released from the center portion 110 during an electrode reaction, and at the same time, the lithium is occluded in the center portion 110. In this case, as described above, lithium is intercalated and released in an ionic state.

<1-3. Manufacturing method＞
When manufacturing the positive electrode active material 100, first, a plurality of core parts 110 (powdered lithium-containing compound) are prepared. As described above, this central portion 110 includes a polycrystalline body (surface 111X and grain boundaries 111Y) in which a plurality of crystal grains 111 are bonded to each other.

Subsequently, the plurality of centers 110, the first metal alkoxide, the second metal alkoxide, and the third metal alkoxide are placed in the alkaline solvent, and then the alkaline solvent is stirred. The type of alkaline solvent is not particularly limited as long as it is one or more types of alkaline solvents, but specifically, it is a mixture of ethanol and aqueous ammonia.

As a result, the plurality of core portions 110 are dispersed in the alkaline solvent, and each of the first metal alkoxide, second metal alkoxide, and third metal alkoxide is dissolved, so that a preparation solution is prepared. In this preparation solution, the plurality of centers 110 are dispersed in an alkaline solution in which each of the first metal alkoxide, the second metal alkoxide, and the third metal alkoxide are dissolved, so that the alkaline solution covers the center parts 110. Adheres to surfaces.

Subsequently, after the plurality of central parts 110 are filtered out from the preparation solution, the plurality of central parts 110 are washed using a cleaning solvent. The type of cleaning solvent is not particularly limited as long as it is one or more organic solvents, but specifically, it is acetone.

Finally, the plurality of center parts 110 are dried by heating the plurality of center parts 110.

In this case, the first metal alkoxide, the second metal alkoxide, and the third metal alkoxide react with each other on the surface of the central portion 110. As a result, a base layer 121 containing a reactant of the first metal alkoxide and a reactant of the second metal alkoxide is formed, and a surface layer 122 containing the third metal alkoxide is formed. Further, since one or both of the first metal alkoxide reactant and the second metal alkoxide reactant and the third metal alkoxide are bonded to each other, the surface layer 122 is connected to the base layer 121.

Therefore, the covering portion 120 including the base layer 121 and the surface layer 122 is formed on the surface of the center portion 110, so that the positive electrode active material 100 is completed.

In this case, by adjusting various conditions such as the amounts of the first metal alkoxide, the second metal alkoxide, and the third metal alkoxide, the stirring conditions of the alkaline solvent, and the heating conditions of the plurality of center portions 110, the surface The covering portion 120 is formed to cover not only the grain boundary 111X but also the grain boundary 111Y.

Note that although a dipping method was used to manufacture the positive electrode active material 100, other methods may be used. Specific examples of other methods include coating methods and spraying methods. When using the coating method, the preparation solution is applied to the surface of the center portion 110, and when using the spray method, the preparation solution is sprayed onto the surface of the center portion 110.

<1-4. Action and effect>
According to this positive electrode active material 100, the positive electrode active material 100 includes a center portion 110 and a covering portion 120 (base layer 121 and surface layer 122), and the covering portion 120 covers the surface 111X of the center portion 110 and the grain boundaries. 111Y. Further, the base layer 121 contains a reactant of a first metal alkoxide and a reactant of a second metal alkoxide, and the surface layer 122 contains a third metal alkoxide, and the third metal alkoxide is a reactant of a first metal alkoxide. bonded to one or both of the reactant and the second metal alkoxide. Therefore, excellent capacity characteristics and excellent load characteristics can be obtained for the reasons explained below.

FIG. 5 shows a detailed cross-sectional configuration of a positive electrode active material 200, which is a positive electrode active material for a secondary battery according to a comparative example, and corresponds to FIG. FIG. 6 shows a cross-sectional configuration corresponding to FIG. 5 in order to explain the problems of the positive electrode active material 200. FIG. 7 shows a cross-sectional configuration corresponding to FIG. 2 in order to explain the advantages of the positive electrode active material 100.

As shown in FIG. 5, the positive electrode active material 200 of the comparative example includes a center portion 110 and a covering portion 120, but the covering portion 120 does not cover the grain boundaries 111Y but only the surface 111X. The structure is similar to that of the positive electrode active material 100 (FIG. 2) of this embodiment, except for the following.

In the positive electrode active material 200 of the comparative example, as shown in FIG. 5, the covering portion 120 covers the surface 111X. In this case, as described above, even if the covering portion 120 is provided on the surface 111 The filling properties are improved.

However, the covering portion 120 does not cover the grain boundaries 111Y. As a result, as shown in FIG. 6, the positive electrode active material 200 is broken, and when the two crystal grains 111 are separated from each other at the grain boundary 111Y, the bonding surface 111Z not covered by the covering portion 120 is exposed. This bonding surface 111Z is a so-called bulk surface of the crystal grain 111. The cause of the cathode active material 200 cracking is when a cathode active material layer containing the cathode active material 200 is pressed in the step of forming a cathode using the cathode active material 200.

In this case, due to the large friction of the bonding surface 111Z, the slipperiness when the crystal grains 111 come into contact with each other is significantly reduced, so that the filling property of the positive electrode active material 200 is significantly reduced. That is, when a positive electrode active material layer including a plurality of positive electrode active materials 200 is pressed, it becomes difficult for the plurality of positive electrode active materials 200 to be arranged densely, so that the volume density of the positive electrode active material layer decreases.

Moreover, if the bonding surface 111Z having high reactivity is exposed, the electrolyte may interact with the bonding surface 111Z during an electrode reaction, more specifically, during charging and discharging of a secondary battery equipped with an electrolyte together with the positive electrode active material 200. react. This accelerates the decomposition reaction of the electrolytic solution during the electrode reaction.

For these reasons, although ionic conductivity is ensured in the positive electrode active material 200, the volume density of the positive electrode active material layer decreases due to a decrease in the filling property of the positive electrode active material 200, and the electrolyte Due to the reaction with the bonding surface 111Z, the decomposition reaction of the electrolytic solution is promoted. Therefore, it is difficult to obtain excellent capacity characteristics and excellent load characteristics in a secondary battery using the positive electrode active material 200.

In contrast, in the positive electrode active material 100 of this embodiment, as shown in FIG. 2, the coating portion 120 covers not only the surface 111X but also the grain boundaries 111Y. In this case, as described above, even if the covering portion 120 is provided on the surface 111 The filling properties are improved.

In this case, the covering portion 120 covers not only the surface 111X but also the grain boundaries 111Y. As a result, as shown in FIG. 7, even if the two crystal grains 111 are separated from each other at the grain boundary 111Y due to the cracking of the positive electrode active material 200, the bonding surface 111Z is still covered by the covering portion 120. The bonding surface 111Z is not exposed.

Therefore, due to the low friction of the surface layer 122, the slipperiness when the crystal grains 111 come into contact with each other is significantly improved, so that the filling properties of the positive electrode active material 100 are significantly improved. That is, when a positive electrode active material layer including a plurality of positive electrode active materials 100 is pressed, the plurality of positive electrode active materials 100 tend to be arranged densely, so that the volume density of the positive electrode active material layer increases.

Furthermore, even if the covering portion 120 covers the grain boundaries 111Y, as described above, lithium ions can easily move through the plurality of pores 121K, so that the lithium intercalation and desorption performance is ensured. This ensures the ion diffusivity in the grain boundary 111Y and makes it difficult for the interfacial resistance of the grain boundary 111Y to increase.

Furthermore, since the highly reactive bonding surface 111Z is not exposed, the electrolytic solution does not react with the bonding surface 111Z during charging and discharging of a secondary battery including an electrolytic solution together with the positive electrode active material 200. This suppresses the decomposition reaction of the electrolytic solution during the electrode reaction.

From these facts, while the ionic conductivity is ensured in the positive electrode active material 100, the volume density of the positive electrode active material layer increases due to the improvement in the filling property of the positive electrode active material 100, and the electrolyte is bonded. Since it does not react with the surface 111Z, the decomposition reaction of the electrolytic solution is suppressed. Therefore, in a secondary battery using the positive electrode active material 100, excellent capacity characteristics and excellent load characteristics can be obtained.

In particular, if one or more alkoxy groups are bonded to one metal atom in the first metal alkoxide, a reactant of the first metal alkoxide having a network structure is likely to be easily formed. Therefore, the base layer 121 is more likely to be stably formed, so that higher effects can be obtained.

In addition, if two or more metal atoms in the second metal alkoxide are bonded to each other via carbon chains and one or more alkoxy groups are bonded to each of the two or more metal atoms, a network-like structure may be formed. A reactant of the second metal alkoxide having the structure is likely to be easily formed. Therefore, the base layer 121 is more likely to be stably formed, so that higher effects can be obtained.

Furthermore, if one alkyl group and one or more alkoxy groups are each bonded to one metal atom in the third metal alkoxide, the third metal alkoxide having a radial structure is likely to be easily formed. Therefore, since the surface layer 122 is easily formed stably, higher effects can be obtained.

Further, if the first metal alkoxide contains the compound shown in formula (1), a reactant of the first metal alkoxide is likely to be easily and stably formed, so that higher effects can be obtained. In this case, if the metal atom (M1) in formula (1) is a silicon atom, the reactant of the first metal alkoxide is likely to be formed more easily and stably, so that even higher effects can be obtained. can.

Furthermore, if the second metal alkoxide contains two or more silicon atom-carbon atom bonds in one molecule, the reaction product of the second metal alkoxide will be easily and stably formed, resulting in higher effects. Obtainable. In this case, if the second metal alkoxide contains one or more of the compounds shown in formulas (2) to (4), the reaction product of the second metal alkoxide can be formed more easily and stably, so even higher effects can be obtained.

Moreover, if the third metal alkoxide contains the compound shown in formula (5), the third metal alkoxide is likely to be easily and stably formed, so that higher effects can be obtained.

Furthermore, if the weight ratio R1 is 5.0% by weight to 85.0% by weight, a network structure derived from the first metal alkoxide is likely to be formed. Therefore, the base layer 121 can be easily and stably formed, so that higher effects can be obtained.

Further, if the weight ratio R2 is 1.0% by weight to 40.0% by weight, a network structure derived from the second metal alkoxide is likely to be formed. Therefore, the base layer 121 can be easily and stably formed, so that higher effects can be obtained.

Further, if the weight ratio R3 is 5.0% to 90.0% by weight, a radial structure derived from the third metal alkoxide is likely to be formed. Therefore, the surface layer 122 is easily and stably formed, so that higher effects can be obtained.

Further, when the weight ratio R4 is 0.010% to 2.000% by weight, the ratio of the coating portion 120 in the positive electrode active material 100 is optimized. Therefore, while the amount of intercalation and desorption of lithium is ensured, the ionic conductivity is sufficiently improved and the filling property is also sufficiently improved, so that even higher effects can be obtained.

Further, when the thickness ratio R5 is 10% to 100%, the slipperiness of the grain boundaries 111Y is sufficiently improved. Therefore, since the filling properties of the positive electrode active material 100 are sufficiently improved, higher effects can be obtained.

<2. Secondary battery (positive electrode for secondary battery)>
Next, a secondary battery according to an embodiment of the present technology using the above-described positive electrode active material will be described.

Note that the positive electrode for a secondary battery according to an embodiment of the present technology (hereinafter simply referred to as a "positive electrode") is a part (one component) of the secondary battery described here, so the following regarding the positive electrode will be explained below.

Below, as mentioned above, the case where the electrode reactant is lithium will be exemplified. A secondary battery whose battery capacity is obtained by utilizing intercalation and desorption of lithium is a so-called lithium ion secondary battery.

<2-1. Configuration>
8 shows a perspective configuration of the secondary battery, and FIG. 9 shows a cross-sectional configuration of the battery element 20 shown in FIG. 8. However, in FIG. 8, the exterior film 10 and the battery element 20 are shown separated from each other, and the cross section of the battery element 20 along the XZ plane is shown by a broken line. In FIG. 9, only a part of the battery element 20 is shown.

As shown in FIGS. 8 and 9, this secondary battery includes an exterior film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42. The secondary battery described here is a laminate film type secondary battery using a flexible or pliable exterior member (exterior film 10).

[Exterior film and sealing film]
As shown in FIG. 8, the exterior film 10 is an exterior member that houses the battery element 20, and has a sealed bag-like structure with the battery element 20 housed inside. Thereby, the exterior film 10 accommodates an electrolyte together with a positive electrode 21 and a negative electrode 22, which will be described later.

Here, the exterior film 10 is a single film-like member, and is folded in the folding direction F. This exterior film 10 is provided with a recessed portion 10U (so-called deep drawn portion) for accommodating the battery element 20.

Specifically, the exterior film 10 is a three-layer laminate film in which a fusing layer, a metal layer, and a surface protection layer are laminated in this order from the inside, and the outer peripheral edges of the fusing layers facing each other are , the exterior films 10 are fused together in the folded state. The adhesive layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protective layer contains a polymer compound such as nylon.

However, the structure (number of layers) of the exterior film 10 is not particularly limited, and may be one or two layers, or four or more layers.

The sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

The sealing film 41 is a sealing member that prevents outside air from entering the exterior film 10. Note that the sealing film 41 contains a polymer compound such as polyolefin that has adhesiveness to the positive electrode lead 31, and a specific example of the polyolefin is polypropylene.

The structure of the sealing film 42 is the same as that of the sealing film 41 except that it is a sealing member that has adhesiveness to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as polyolefin that has adhesiveness to the negative electrode lead 32.

[Battery element]
As shown in FIGS. 8 and 9, the battery element 20 is a power generating element that includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown), and is housed inside the exterior film 10. has been done.

This battery element 20 is a so-called wound electrode body. That is, the positive electrode 21 and the negative electrode 22 are stacked on each other with the separator 23 in between, and are wound around the winding axis P while facing each other with the separator 23 in between. This winding axis P is a virtual axis extending in the Y-axis direction.

The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the three-dimensional shape of the battery element 20 is flat, the shape of the cross section of the battery element 20 that intersects the winding axis P (the cross section along the It has a defined flat shape. The long axis J1 is a virtual axis that extends in the X-axis direction and has a longer length than the short axis J2. Further, the short axis J2 is a virtual axis that extends in the Z-axis direction intersecting the X-axis direction and has a length smaller than the long axis J1. Here, since the three-dimensional shape of the battery element 20 is a flat cylindrical shape, the cross-sectional shape of the battery element 20 is a flat, substantially elliptical shape.

(positive electrode)
As shown in FIG. 9, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B.

The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. This positive electrode current collector 21A includes a conductive material such as a metal material, and a specific example of the metal material is aluminum.

Here, the positive electrode active material layer 21B is provided on both surfaces of the positive electrode current collector 21A, and includes one or more types of positive electrode active materials capable of intercalating and deintercalating lithium. However, the positive electrode active material layer 21B may be provided only on one side of the positive electrode current collector 21A on the side where the positive electrode 21 faces the negative electrode 22.

Note that the positive electrode active material layer 21B may further contain one or more of other materials such as a positive electrode binder and a positive electrode conductive agent. The method for forming the positive electrode active material layer 21B is not particularly limited, but specifically, it may be one or more of coating methods.

The configuration of the positive electrode active material is similar to the configuration of the positive electrode active material 100 described above. However, the positive electrode active material layer 21B may further include any one type or two or more types of other positive electrode active materials. The configuration of the other positive electrode active materials is similar to the configuration of the center portion 110.

The positive electrode binder contains one or more of synthetic rubber, polymer compounds, and the like. Specific examples of synthetic rubber include styrene butadiene rubber, fluorine rubber, and ethylene propylene diene. Specific examples of the polymer compound include polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

The positive electrode conductive agent contains one or more types of conductive materials such as carbon materials, and specific examples of the carbon materials include graphite, carbon black, acetylene black, and Ketjen black. . However, the conductive material may be a metal material, a polymer compound, or the like.

(Negative electrode)
As shown in FIG. 9, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B.

The negative electrode current collector 22A has a pair of surfaces on which the negative electrode active material layer 22B is provided. This negative electrode current collector 22A includes a conductive material such as a metal material, and a specific example of the metal material is copper.

Here, the negative electrode active material layer 22B is provided on both sides of the negative electrode current collector 22A, and includes one or more types of negative electrode active materials capable of inserting and extracting lithium. However, the negative electrode active material layer 22B may be provided only on one side of the negative electrode current collector 22A on the side where the negative electrode 22 faces the positive electrode 21.

Note that the negative electrode active material layer 22B may further contain one or more of other materials such as a negative electrode binder and a negative electrode conductive agent. The method for forming the negative electrode active material layer 22B is not particularly limited, but specifically, any one of a coating method, a gas phase method, a liquid phase method, a thermal spraying method, a firing method (sintering method), etc. There are two or more types.

The type of negative electrode active material is not particularly limited, but specifically, it may be one or both of a carbon material and a metal-based material. This is because high energy density can be obtained.

Specific examples of carbon materials include easily graphitizable carbon, non-graphitizable carbon, and graphite (natural graphite and artificial graphite).

A metal-based material is a material containing as a constituent element one or more of metal elements and metalloid elements that can form an alloy with lithium. Specific examples of the metal elements and metalloid elements are: , silicon and tin. This metallic material may be a single substance, an alloy, a compound, a mixture of two or more types thereof, or a material containing phases of two or more types thereof. Specific examples of metal-based materials include TiSi ₂ and SiO _x (0<x≦2, or 0.2<x<1.4).

The details regarding each of the negative electrode binder and the negative electrode conductive agent are the same as the details regarding each of the positive electrode binder and the positive electrode conductive agent.

(Separator)
As shown in FIG. 9, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and prevents contact (short circuit) between the positive electrode 21 and negative electrode 22. Allows lithium ions to pass through. This separator 23 contains a high molecular compound such as polyethylene.

(electrolyte)
The electrolyte is a liquid electrolyte. This electrolytic solution is impregnated into each of the positive electrode 21, negative electrode 22, and separator 23, and contains a solvent and an electrolyte salt.

Here, the solvent contains one or more types of non-aqueous solvents (organic solvents), and the electrolytic solution containing the non-aqueous solvent is a so-called non-aqueous electrolytic solution. This nonaqueous solvent includes esters and ethers, and more specifically includes carbonate ester compounds, carboxylic ester compounds, and lactone compounds. This is because the dissociability of the electrolyte salt and the mobility of ions are improved.

Carbonic ester compounds are cyclic carbonic esters and chain carbonic esters. Specific examples of the cyclic carbonate include ethylene carbonate and propylene carbonate, and specific examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate.

The carboxylic acid ester compound is a chain carboxylic acid ester. Specific examples of chain carboxylic acid esters include ethyl acetate, ethyl propionate, propyl propionate, and ethyl trimethylacetate.

Lactone compounds include lactones. Specific examples of lactones include γ-butyrolactone and γ-valerolactone.

In addition to lactone compounds, the ethers may include 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane.

The electrolyte salt contains one or more light metal salts such as lithium salts. Specific examples of lithium salts include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), and lithium bis(fluorosulfonyl)imide (LiN). (FSO ₂ ) ₂ ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF ₃ SO ₂ ) ₂ ), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF ₃ SO ₂ ) ₃ ), bis(oxalato)boro These include lithium oxide (LiB(C ₂ O ₄ ) ₂ ), lithium monofluorophosphate (Li ₂ PFO ₃ ), and lithium difluorophosphate (LiPF ₂ O ₂ ). This is because high battery capacity can be obtained.

The content of the electrolyte salt is not particularly limited, but specifically, it is 0.3 mol/kg to 3.0 mol/kg relative to the solvent. This is because high ionic conductivity can be obtained.

In addition, the electrolytic solution may further contain any one type or two or more types of additives. The types of additives are not particularly limited, but specifically include unsaturated cyclic carbonates, halogenated cyclic carbonates, sulfonic esters, phosphoric esters, acid anhydrides, nitrile compounds, and isocyanate compounds.

Specific examples of unsaturated cyclic carbonate esters include vinylene carbonate, vinylethylene carbonate, and methyleneethylene carbonate. Specific examples of the halogenated cyclic carbonate ester include monofluoroethylene carbonate and difluoroethylene carbonate. Specific examples of sulfonic acid esters include propane sultone and propene sultone. Specific examples of phosphoric acid esters include trimethyl phosphate and triethyl phosphate. Specific examples of acid anhydrides include succinic anhydride, 1,2-ethanedisulfonic anhydride, and 2-sulfobenzoic anhydride. Specific examples of nitrile compounds include succinonitrile. A specific example of the isocyanate compound is hexamethylene diisocyanate.

[Positive lead and negative lead]
As shown in FIGS. 8 and 9, the positive electrode lead 31 is a positive terminal connected to the positive electrode current collector 21A of the positive electrode 21, and is led out from inside the exterior film 10. This positive electrode lead 31 includes a conductive material such as a metal material, and a specific example of the conductive material is aluminum. Although the shape of the positive electrode lead 31 is not particularly limited, specifically, it is either a thin plate shape or a mesh shape.

As shown in FIGS. 8 and 9, the negative electrode lead 32 is a negative electrode terminal connected to the negative electrode current collector 22A of the negative electrode 22, and is led out from inside the exterior film 10. This negative electrode lead 32 includes a conductive material such as a metal material, and a specific example of the conductive material is copper. Here, the details regarding the lead-out direction and shape of the negative electrode lead 32 are the same as the lead-out direction and shape of the positive electrode lead 31.

<2-2. Operation＞
When charging the secondary battery, in the battery element 20, lithium is released from the positive electrode 21, and at the same time, the lithium is inserted into the negative electrode 22 via the electrolyte. On the other hand, when the secondary battery is discharged, lithium is released from the negative electrode 22 in the battery element 20, and the lithium is inserted into the positive electrode 21 via the electrolyte. During these charging and discharging operations, lithium is intercalated and released in an ionic state.

<2-3. Manufacturing method>
When manufacturing a secondary battery, each of the positive electrode 21 and the negative electrode 22 is manufactured and an electrolytic solution is prepared according to the example procedure described below, and then the positive electrode 21, the negative electrode 22, and the electrolytic solution are used. While assembling the secondary battery, a stabilization process is performed on the assembled secondary battery.

[Preparation of positive electrode]
First, a paste-like positive electrode mixture slurry is prepared by adding a mixture of a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent (positive electrode mixture) to a solvent. This solvent may be an aqueous solvent or an organic solvent. Subsequently, a positive electrode active material layer 21B is formed by applying a positive electrode mixture slurry to both surfaces of the positive electrode current collector 21A. Finally, the positive electrode active material layer 21B may be compression molded using a roll press machine or the like. In this case, the positive electrode active material layer 21B may be heated or compression molding may be repeated multiple times. Thereby, the positive electrode active material layers 21B are formed on both sides of the positive electrode current collector 21A, so that the positive electrode 21 is manufactured.

[Preparation of negative electrode]
The negative electrode 22 is formed by the same procedure as the positive electrode 21 described above. Specifically, first, a paste-like negative electrode mixture slurry is prepared by adding a mixture (negative electrode mixture) in which a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent are mixed together into a solvent. Subsequently, a negative electrode active material layer 22B is formed by applying a negative electrode mixture slurry to both surfaces of the negative electrode current collector 22A. Finally, the negative electrode active material layer 22B may be compression molded. Thereby, the negative electrode active material layers 22B are formed on both sides of the negative electrode current collector 22A, so that the negative electrode 22 is manufactured.

[Preparation of electrolyte]
Add electrolyte salt to the solvent. As a result, the electrolyte salt is dispersed or dissolved in the solvent, so that an electrolytic solution is prepared.

[Assembling the secondary battery]
First, the positive electrode lead 31 is connected to the positive electrode current collector 21A of the positive electrode 21 using a joining method such as welding, and the negative electrode lead 31 is connected to the negative electrode current collector 22A of the negative electrode 22 using a joining method such as welding. Connect.

Subsequently, the positive electrode 21 and the negative electrode 22 are laminated with each other via the separator 23, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound to produce a wound body (not shown). This wound body has a configuration similar to that of the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with an electrolytic solution. Subsequently, the rolled body is pressed using a press or the like to shape the rolled body into a flat shape.

Subsequently, after the wound body is housed inside the recessed portion 10U, the exterior films 10 (fusion layer/metal layer/surface protection layer) are folded to face each other. Next, by bonding the outer peripheral edges of two sides of the mutually opposing fusion layers using an adhesive method such as a heat fusion method, a wound body is formed inside the bag-shaped exterior film 10. to store.

Finally, after injecting the electrolytic solution into the interior of the bag-shaped exterior film 10, the outer peripheral edges of the remaining one side of the fusion layer are bonded to each other using an adhesive method such as a heat fusion method. In this case, a sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32.

As a result, the wound body is impregnated with the electrolytic solution, so that the battery element 20, which is a wound electrode body, is produced, and the battery element 20 is sealed inside the bag-shaped exterior film 10, so that the secondary The battery is assembled.

[Stabilization of secondary batteries]
Charge and discharge the assembled secondary battery. Various conditions such as environmental temperature, number of charging/discharging times (number of cycles), and charging/discharging conditions can be set arbitrarily. As a result, a film is formed on each surface of the positive electrode 21 and the negative electrode 22, so that the state of the secondary battery is electrochemically stabilized. Thus, the secondary battery is completed.

<2-4. Action and effect>
According to this secondary battery, the positive electrode 21 includes a positive electrode active material, and the positive electrode active material has the same configuration as the positive electrode active material 100 described above. Therefore, for the same reason as explained regarding the positive electrode active material 100, the volume density of the positive electrode active material layer 21B increases and the decomposition reaction of the electrolyte is suppressed while ensuring ionic conductivity in the positive electrode active material. , excellent capacity characteristics and excellent load characteristics can be obtained.

In particular, if the secondary battery is a lithium ion secondary battery, a sufficient battery capacity can be stably obtained by utilizing intercalation and desorption of lithium, so that higher effects can be obtained.

In addition, according to the positive electrode 21, the positive electrode 21 includes a positive electrode active material, and the positive electrode active material has a configuration similar to that of the positive electrode active material 100 described above. Therefore, for the same reason as explained regarding the positive electrode active material 100, excellent capacity characteristics and excellent load characteristics can be obtained in a secondary battery using the positive electrode 21.

Other functions and effects regarding the secondary battery and the positive electrode 21 are the same as those regarding the positive electrode active material 100 described above.

<3. Modified example>
Next, a modification of the above-described secondary battery will be described.

The configuration of the secondary battery can be changed as appropriate, as described below. However, the series of modifications described below may be combined with each other.

[Modification 1]
A separator 23, which is a porous membrane, was used. However, although not specifically illustrated here, a laminated separator including a polymer compound layer may also be used.

Specifically, the laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer provided on one or both sides of the porous membrane. This is because the adhesion of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, so winding misalignment of the battery element 20 is suppressed. This makes it difficult for the secondary battery to swell even if a decomposition reaction of the electrolyte occurs. The polymer compound layer contains a polymer compound such as polyvinylidene fluoride. This is because polyvinylidene fluoride and the like have excellent physical strength and are electrochemically stable.

Note that one or both of the porous membrane and the polymer compound layer may contain any one type or two or more types of the plurality of insulating particles. This is because the plurality of insulating particles promote heat dissipation when the secondary battery generates heat, thereby improving the safety (heat resistance) of the secondary battery. The insulating particles contain one or more of inorganic materials, resin materials, and the like. Specific examples of inorganic materials include aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of the resin material include acrylic resin and styrene resin.

When producing a laminated separator, a precursor solution containing a polymer compound, a solvent, etc. is prepared, and then the precursor solution is applied to one or both sides of the porous membrane. In this case, instead of applying the precursor solution to the porous membrane, the porous membrane may be immersed in the precursor solution. Further, a plurality of insulating particles may be added to the precursor solution.

Even when this laminated separator is used, the same effect can be obtained because lithium ions can move between the positive electrode 21 and the negative electrode 22. In this case, in particular, as described above, the safety of the secondary battery is improved, so higher effects can be obtained.

[Modification 2]
An electrolytic solution, which is a liquid electrolyte, was used. However, although not specifically illustrated here, an electrolyte layer that is a gel-like electrolyte may also be used.

In the battery element 20 using an electrolyte layer, a positive electrode 21 and a negative electrode 22 are stacked on each other with a separator 23 and an electrolyte layer in between, and the positive electrode 21, negative electrode 22, separator 23, and electrolyte layer are wound. This electrolyte layer is interposed between the positive electrode 21 and the separator 23 and also between the negative electrode 22 and the separator 23. However, the electrolyte layer may be interposed only between the positive electrode 21 and the separator 23, or may be interposed only between the negative electrode 22 and the separator 23.

This electrolyte layer contains a polymer compound together with an electrolyte solution, and the electrolyte solution is held by the polymer compound. This is because electrolyte leakage is prevented. The structure of the electrolytic solution is as described above. The polymer compound includes polyvinylidene fluoride and the like. When forming an electrolyte layer, a precursor solution containing an electrolytic solution, a polymer compound, a solvent, etc. is prepared, and then the precursor solution is applied to one or both surfaces of each of the positive electrode 21 and the negative electrode 22.

Even when this electrolyte layer is used, the same effect can be obtained because lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer. In this case, in particular, as described above, leakage of the electrolytic solution is prevented, so that higher effects can be obtained.

<4. Applications of secondary batteries>
Finally, the uses (application examples) of secondary batteries will be explained.

The use of the secondary battery is not particularly limited. A secondary battery used as a power source may be a main power source or an auxiliary power source in electronic devices, electric vehicles, and the like. The main power source is a power source that is used preferentially, regardless of the presence or absence of other power sources. The auxiliary power source may be a power source used in place of the main power source, or may be a power source that can be switched from the main power source.

Specific examples of uses of the secondary battery are as described below. Electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals. Backup power supplies and storage devices such as memory cards. Power tools such as power drills and power saws. This is a battery pack installed in electronic devices. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric vehicles (including hybrid vehicles). A power storage system such as a household or industrial battery system that stores power in case of an emergency. In these applications, one secondary battery or a plurality of secondary batteries may be used.

The battery pack may include single cells or assembled batteries. An electric vehicle is a vehicle that runs using a secondary battery as a driving power source, and may be a hybrid vehicle that also includes a driving source other than the secondary battery. In a home power storage system, home electrical appliances and the like can be used by using the power stored in a secondary battery, which is a power storage source.

Here, an example of the use of the secondary battery will be specifically explained. The configuration described below is just an example and can be modified as appropriate.

FIG. 10 shows a block configuration of a battery pack that is an application example of a secondary battery. The battery pack described here is a battery pack (so-called soft pack) using one secondary battery, and is installed in electronic devices such as smartphones.

This battery pack includes a power source 51 and a circuit board 52, as shown in FIG. This circuit board 52 is connected to a power source 51 and includes a positive terminal 53, a negative terminal 54, and a temperature detection terminal 55.

Power source 51 includes one secondary battery. In this secondary battery, the positive electrode lead is connected to the positive electrode terminal 53, and the negative electrode lead is connected to the negative electrode terminal 54. This power source 51 is connected to the outside via a positive terminal 53 and a negative terminal 54, so that it can be charged and discharged. The circuit board 52 includes a control section 56 , a switch 57 , a heat sensitive resistance element (so-called PTC element) 58 , and a temperature detection section 59 . However, the PTC element 58 may be omitted.

The control unit 56 includes a central processing unit (CPU), memory, and the like, and controls the operation of the entire battery pack. This control unit 56 performs detection and control regarding the usage state of the power source 51.

Note that when the voltage of the power source 51 (secondary battery) reaches the overcharge detection voltage or overdischarge detection voltage, the control unit 56 disconnects the switch 57 so that no charging current flows through the current path of the power source 51. Do it like this. The overcharge detection voltage is not particularly limited, but is specifically 4.20V±0.05V, and the overdischarge detection voltage is not particularly limited, but specifically is 2.40V±0.10V. It is.

The switch 57 includes a charging control switch, a discharging control switch, a charging diode, a discharging diode, and the like, and switches whether or not the power supply 51 is connected to an external device in accordance with an instruction from the control unit 56. This switch 57 includes a field effect transistor (MOSFET) using a metal oxide semiconductor, and each of the charging current and the discharging current is detected based on the ON resistance of the switch 57.

The temperature detection section 59 includes a temperature detection element such as a thermistor. The temperature detection section 59 measures the temperature of the power supply 51 using the temperature detection terminal 55 and outputs the temperature measurement result to the control section 56 . The temperature measurement result measured by the temperature detection unit 59 is used when the control unit 56 performs charging/discharging control during abnormal heat generation and when the control unit 56 performs correction processing when calculating the remaining capacity.

An example of the present technology will be described.

<Experimental Examples 1 to 7 and Comparative Examples 1 to 5>
As explained below, after manufacturing the positive electrode active material 100 shown in FIGS. 1 to 4 and manufacturing the secondary battery (laminate film type lithium ion secondary battery) shown in FIGS. 8 and 9, , and evaluated the characteristics of the secondary battery.

[Manufacture of positive electrode active material]
A positive electrode active material 100 was manufactured using a dipping method according to the procedure described below.

First, 6 g of ammonia water (concentration = 28% by weight) was added to 25 g of ethanol, and then the ethanol was stirred. As a result, aqueous ammonia was dispersed in ethanol, so an alkaline solvent was obtained.

Subsequently, 35 g of the plurality of core parts 110 (powdered lithium cobalt oxide (LiCoO ₂ ), which is a lithium-containing compound) is added to the alkaline solvent, and then the first metal alkoxide, the second metal alkoxide, and the third metal alkoxide are added to the alkaline solvent. Added metal alkoxide. Subsequently, the alkaline solvent was stirred (stirring time = 120 minutes) in a room temperature environment (temperature = 20°C). This prepared a preparatory solution.

As the first metal alkoxide, Si-(OC ₂ H ₅ ) ₄ (TES) was used. As the second metal alkoxide, (H ₃ CO) ₃ -Si-C ₂ H ₄ -Si-(OCH ₃ ) ₃ (BTESE) or (H ₃ CO) ₃ -Si-C ₆ H ₁₂ -Si-(OCH ₃ ) ₃ (BTESH) was used. H ₃₃ C ₁₆ Si-(OCH ₃ ) ₃ (HDTMS) was used as the third metal alkoxide.

In this case, the amounts of each of the first metal alkoxide, second metal alkoxide, and third metal alkoxide were adjusted so that the weight ratios R1 to R4 (wt%) each had the values shown in Table 1. .

Subsequently, the preparation solution was filtered to collect the plurality of centers 110 on the surfaces of which the preparation solution was adhered, and then the plurality of centers 110 were washed using a cleaning solvent (acetone).

Subsequently, the plurality of center parts 110 were dried by heating them (heating temperature = 80° C. and heating time = 120 minutes). As a result, a base layer 121 containing a reactant of the first metal alkoxide and a reactant of the second metal alkoxide, and a surface layer 122 containing a third metal alkoxide are formed on the surface 111X of the center portion 110 and the grain boundaries 111Y, respectively. It was done. That is, a covering portion 120, which is an organic-inorganic hybrid film including a base layer 121 and a surface layer 122, was formed.

Thus, a positive electrode active material 100 including a central portion 110 and a covering portion 120 (base layer 121 and surface layer 122) was manufactured (Examples 1 to 7).

The thickness ratio R5 (%) is as shown in Table 1. When manufacturing the positive electrode active material 100, the time period for immersing the plurality of core parts 110 in an alkaline solvent containing a first metal alkoxide, a second metal alkoxide, and a third metal alkoxide should be set to be sufficiently long. As a result, the covering portion 120 was formed so as to cover not only the surface 111X but also the grain boundary 111Y. In this case, the thickness ratio R5 was changed by changing the amounts of each of the first metal alkoxide, the second metal alkoxide, and the third metal alkoxide, the stirring time of the alkaline solvent, and the like.

For comparison, a positive electrode active material was manufactured using the same procedure except that one of the first metal alkoxide, second metal alkoxide, and third metal alkoxide was not used (Comparative Example 1-3). When the second metal alkoxide was not used, the surface layer 122 was not formed.

Further, for comparison, a positive electrode active material was manufactured by the same procedure except that all of the first metal alkoxide, second metal alkoxide, and third metal alkoxide were not used (Comparative Example 4). In this case, the covering portion 120 was not formed.

Furthermore, for comparison, the positive electrode active layer was formed using the same procedure except that the coating portion 120 (base layer 121 and surface layer 122) was not formed on the grain boundary 111Y and the coating portion 120 was formed only on the surface 111X. A material was produced (Comparative Example 5). In this case, the time for immersing the plurality of core parts 110 in the alkaline solvent containing the first metal alkoxide, the second metal alkoxide, and the third metal alkoxide is shortened, and the stirring time of the alkaline solvent is shortened (specifically The coating portion 120 was formed so as to cover only the surface 111X without covering the grain boundaries 111Y by setting the stirring time to 30 minutes or less. The fact that the thickness ratio R5 is 0% means that the grain boundary 111Y is not covered by the covering portion 120.

[Preparation of secondary battery]
A secondary battery was produced according to the procedure described below.

(Preparation of positive electrode)
First, 90 parts by mass of a positive electrode active material, 5 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 5 parts by mass of a positive electrode conductive agent (Ketjen Black) were mixed together to form a positive electrode mixture. Subsequently, the positive electrode mixture was added to an organic solvent (N-methyl-2-pyrrolidone), and the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. Next, a positive electrode mixture slurry is applied to both sides of the positive electrode current collector 21A (aluminum foil with a thickness of 15 μm) using a coating device, and then the positive electrode mixture slurry is dried to form a positive electrode active material layer. 21B was formed. Subsequently, the positive electrode active material layer 21B was compression molded using a roll press machine (roll temperature = 130°C, linear pressure = 0.7 t/cm, press speed = 10 m/min). Finally, the positive electrode current collector 21A on which the positive electrode active material layer 21B was formed was cut into a strip shape (width = 48 mm, length = 300 mm). In this way, the positive electrode 21 was manufactured.

(Preparation of negative electrode)
First, 90 parts by mass of a negative electrode active material (artificial graphite, which is a carbon material) and 10 parts by mass of an N-methyl-2-pyrrolidone solution (concentration = 20% by weight) containing polyamic acid were mixed together. A paste-like negative electrode mixture slurry was prepared by stirring the N-methyl-2-pyrrolidone solution. Next, the negative electrode mixture slurry was applied to both sides of the negative electrode current collector 22A (copper foil with a thickness of 15 μm) using a bar coater (gap = 35 μm), and then the coating film of the negative electrode mixture slurry was dried ( Temperature = 80°C). Subsequently, the coating film was compression-molded using a roll press machine, and then heated (heating time = 700° C., heating time = 3 hours) to form the negative electrode active material layer 22B. Finally, the negative electrode current collector 22A on which the negative electrode active material layer 22B was formed was cut into a strip shape (width = 50 mm, length = 310 mm). In this way, the negative electrode 22 was manufactured.

(Preparation of electrolyte)
After adding an electrolyte salt (lithium hexafluorophosphate (LiPF ₆ )) to the solvent (ethylene carbonate, which is a cyclic carbonate, and ethyl methyl carbonate, which is a chain carbonate), the solvent was stirred. In this case, the mixing ratio (weight ratio) of the solvent was set to ethylene carbonate: ethyl methyl carbonate = 50; 50, and the content of the electrolyte salt was set to 1 mol/l (= 1 mol/dm ³ ) to the solvent. . In this way, an electrolytic solution was prepared.

(Assembling secondary battery)
First, the positive electrode lead 31 (aluminum foil) was welded to the positive electrode current collector 21A of the positive electrode 21, and the negative electrode lead 32 (copper foil) was welded to the negative electrode current collector 22A of the negative electrode 22. Subsequently, the positive electrode 21 and the negative electrode 22 are laminated with each other via the separator 23 (a microporous polyethylene film having a thickness of 25 μm), and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound. A rotating body was created. Subsequently, the rolled body was pressed using a press machine to shape the rolled body so that the cross-sectional shape was flat.

Subsequently, after folding the exterior film 10 (fusion layer/metal layer/surface protection layer) so as to sandwich the rolled body housed in the recessed part 10U, the outer periphery of two sides of the adhesive layer is folded. The rolled body was housed inside the bag-shaped exterior film 10 by heat-sealing them together. The exterior film 10 includes a fusion layer (a polypropylene film with a thickness of 30 μm), a metal layer (an aluminum foil with a thickness of 40 μm), and a surface protection layer (a nylon film with a thickness of 25 μm). Moisture-proof aluminum laminate films were used that were laminated in this order from the inside.

Finally, after injecting the electrolytic solution into the interior of the bag-shaped exterior film 10, the outer peripheral edges of the remaining one side of the adhesive layer were thermally fused together in a reduced pressure environment. In this case, a sealing film 41 (a polypropylene film with a thickness of 5 μm) is inserted between the outer film 10 and the positive electrode lead 31, and a sealing film is inserted between the outer film 10 and the negative electrode lead 32. 42 (polypropylene film with thickness = 5 μm) was inserted. As a result, the wound body was impregnated with the electrolytic solution, so that the battery element 20 was formed. Therefore, since the battery element 20 was sealed inside the exterior film 10, a secondary battery was assembled.

(Stabilization of secondary batteries)
The secondary battery was charged and discharged for one cycle in a normal temperature environment (temperature = 20°C). The charging and discharging conditions were the same as the charging and discharging conditions used when examining cycle characteristics, which will be described later. As a result, a film was formed on each surface of the positive electrode 21 and the negative electrode 22, so that the state of the secondary battery was stabilized. Thus, the secondary battery was completed.

[Characteristics evaluation of secondary batteries]
When the capacity characteristics and load characteristics of the secondary battery were evaluated, the results shown in Table 1 were obtained.

(capacitance characteristics)
Here, instead of measuring the capacity of the secondary battery, the volume density (g/cm ³ ) of the positive electrode active material layer 21B, which is an index representing the filling property of the positive electrode active material that greatly affects the capacity, was investigated. In this case, after measuring dimensions such as the thickness (cm) of the positive electrode active material layer 21B using a height meter and also measuring the weight of the positive electrode active material layer 21B, the volume is determined based on the dimensions and weight. The density was calculated.

(Load characteristics)
When examining the load characteristics, first, the discharge capacity (first cycle discharge capacity) was measured by charging and discharging the secondary battery in a normal temperature environment (temperature = 20° C.). When charging, charge at a constant current with a current of 0.5A until the voltage reaches 4.2V, and then at that voltage of 4.2V until the current reaches 1/10 of the initial value (0.05A). Charged at constant voltage. During discharging, constant current discharge was performed at a current of 0.2 A until the voltage reached 3.0 V.

Subsequently, the discharge capacity (second cycle discharge capacity) was measured by charging and discharging the secondary battery in the same environment. The charging and discharging conditions were the same as those for the first cycle, except that the current during discharging was changed to 0.1C. This 0.1C is a current value equivalent to 0.1C when the discharge capacity of the first cycle is 1C, and more specifically, it is a current value that completely discharges the discharge capacity of the first cycle in 10 hours. be.

Subsequently, the discharge capacity (discharge capacity at the third cycle) was measured by charging and discharging the secondary battery in the same environment. The charging and discharging conditions were the same as those for the first cycle, except that the current during discharging was changed to 2C. This 2C is a current value corresponding to 2C when the discharge capacity of the first cycle is 1C, and more specifically, it is a current value that allows the discharge capacity of the first cycle to be completely discharged in 0.5 hours.

Finally, load maintenance rate (%) = (3rd cycle discharge capacity (discharge current = 2C) / 2nd cycle discharge capacity (discharge current = 0.1C)) x 100.

[Consideration]
As shown in Table 1, the volume density and load maintenance rate each varied greatly depending on the configuration of the positive electrode active material.

Specifically, when the surface layer 122 containing the third metal alkoxide was not formed because the third metal alkoxide was not used to form the covering portion 120 (Comparative Example 1), the volume density and the load Both retention rates decreased.

Further, since the first metal alkoxide or the second metal alkoxide was not used to form the covering portion 120, the base layer 121 containing the reactant of the first metal alkoxide and the reactant of the second metal alkoxide was not formed. In the cases (Comparative Examples 2 and 3), the load maintenance rate decreased, and in some cases, the volume density also decreased.

Furthermore, when all of the first metal alkoxide, second metal alkoxide, and third metal alkoxide were used to form the covering part 120, but the covering part 120 was formed to cover only the surface 111X (comparison In Example 5), a high load maintenance rate was obtained, but the volume density was reduced.

On the other hand, when all of the first metal alkoxide, second metal alkoxide, and third metal alkoxide are used to form the covering portion 120 (Examples 1 to 7), the reaction of the first metal alkoxide A base layer 121 containing a reactant of a metal and a second metal alkoxide was formed, and a surface layer 122 containing a third metal alkoxide was also formed. Furthermore, the covering portion 120 was formed to cover not only the surface 111X but also the grain boundary 111Y. As a result, not only a high volume density was obtained, but also a high load maintenance rate.

In this case, in particular, a series of trends were obtained, which will be explained below.

First, the weight ratio R1 is 5.0% to 85.0% by weight, the weight ratio R2 is 1.0% to 40.0% by weight, and the weight ratio R3 is 5.0% to 85.0% by weight. At 90.0% by weight, not only a sufficient volume density was obtained, but also a sufficient load maintenance rate.

Second, when the weight ratio R4 was 0.010% to 2.000% by weight, not only a sufficient volume density was obtained, but also a sufficient load maintenance rate.

Thirdly, when the thickness ratio R5 was 10% to 100%, the volume density was further increased while maintaining a high load maintenance rate.

[summary]
From the results shown in Table 1, the positive electrode active material 100 includes a center portion 110 and a covering portion 120 (base layer 121 and surface layer 122), and the covering portion 120 forms a surface 111X of the center portion 110 and a grain boundary 111Y. The base layer 121 contains a reactant of a first metal alkoxide and a reactant of a second metal alkoxide, and the surface layer 122 contains a third metal alkoxide. was bonded to one or both of the first metal alkoxide reactant and the second metal alkoxide, high volume densities and high load retention rates were obtained. Therefore, it was possible to obtain excellent capacity characteristics and excellent load characteristics in the secondary battery.

Although the present technology has been described above with reference to one embodiment and an example, the configuration of the present technology is not limited to the configuration described in the one embodiment and example, and can be variously modified.

Specifically, the case where the battery structure of the secondary battery is a laminate film type has been described. However, the battery structure of the secondary battery is not particularly limited, and may be cylindrical, square, coin-shaped, button-shaped, or the like.

Furthermore, the case where the element structure of the battery element is a wound type has been described. However, the element structure of the battery element is not particularly limited, and may be a stacked type, a 99-fold type, or the like. In this laminated type, the positive electrode and the negative electrode are stacked on each other, and in the 99-fold type, the positive electrode and the negative electrode are folded in a zigzag pattern.

Furthermore, although the case where the electrode reactant is lithium has been described, the electrode reactant is not particularly limited. Specifically, the electrode reactants may be other alkali metals, such as sodium and potassium, or alkaline earth metals, such as beryllium, magnesium, and calcium, as described above. In addition, the electrode reactant may be other light metals such as aluminum.

Since the effects described in this specification are merely examples, the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with the present technology.

21... Positive electrode, 21B... Positive electrode active material layer, 22... Negative electrode, 100... Positive electrode active material, 110... Center, 111... Crystal grain, 111X... Surface, 111Y... Grain boundary, 120... Covering portion, 121... Base layer, 122...Surface layer.

Claims (13)

A central part that absorbs and releases electrode reactants;
and a coating provided on the surface of the central portion,
The central portion includes a polycrystalline body in which two or more crystal grains are bonded to each other, and has a grain boundary between the two crystal grains bonded to each other,
The coating portion covers each of the surface and the grain boundaries of the center portion, and includes a base layer and a surface layer in order from the side closer to the center portion,
The base layer is a reactant of a first metal alkoxide that does not have a metal atom-carbon bond in one molecule, and a reactant of a second metal alkoxide that has two or more metal atom-carbon bonds in one molecule. including;
The surface layer contains a third metal alkoxide having one metal atom-carbon atom bond in one molecule,
The third metal alkoxide is bonded to at least one of the reactant of the first metal alkoxide and the second metal alkoxide,
Cathode active material for secondary batteries. The first metal alkoxide includes one metal atom to which one or more alkoxy groups are bonded,
The second metal alkoxide includes two or more metal atoms that are bonded to each other via a carbon chain and to each of which one or more alkoxy groups are bonded,
The third metal alkoxide includes one metal atom to which each of one alkyl group and one or more alkoxy groups is bonded.
The positive electrode active material for a secondary battery according to claim 1. The first metal alkoxide includes a compound represented by formula (1),
The positive electrode active material for a secondary battery according to claim 1 or 2.
M1-(OR1) _a ...(1)
(M1 is any one of a silicon atom, a titanium atom, an aluminum atom, and a zirconium atom. R1 is an alkyl group having 1 to 10 carbon atoms and a group represented by formula (100). Either. a is 3 or 4. However, two R1's adjacent to each other may be bonded to each other.)
-CR11=CH-C(=O)-R12...(100)
(R11 is an alkyl group having 1 to 10 carbon atoms. R12 is an alkyl group having 1 to 30 carbon atoms, an alkoxy group having 1 to 30 carbon atoms, and 1 to 30 carbon atoms. It is any alkenyloxy group having a carbon number.) The M1 is a silicon atom,
The positive electrode active material for a secondary battery according to claim 3. The second metal alkoxide has two or more silicon atom-carbon atom bonds in one molecule,
The positive electrode active material for a secondary battery according to claim 1 or 2. The second metal alkoxide contains at least one compound represented by each of formulas (2) to (4),
The positive electrode active material for a secondary battery according to claim 5.
(R3O) ₃ -Si-R2-Si-(OR4) ₃ ...(2)
(R2 is an alkylene group having 1 to 20 carbon atoms. Each of R3 and R4 is an alkyl group having 1 to 10 carbon atoms.)
(OR8) ₃ -Si-R5-NH-R6-NH-R7-Si-(OR9) ₃ ...(3)
(Each of R5 to R7 is an alkylene group having 1 to 20 carbon atoms. Each of R8 and R9 is an alkyl group having 1 to 10 carbon atoms.)
(R10) ₂ -Si-(OR11) ₂ ...(4)
(Each of R10 and R11 is an alkyl group having 1 or more and 10 or less carbon atoms.) The third metal alkoxide includes a compound represented by formula (5),
The positive electrode active material for a secondary battery according to claim 1 or 2.
R12-Si-(OR13) ₃ ...(5)
(R12 is an alkyl group having a carbon number of 8 or more and 30 or less. R13 is an alkyl group having a carbon number of 1 or more and 10 or less.) The ratio of the weight of the first metal alkoxide reactant to the weight of the coating portion is 5.0% by weight or more and 85.0% by weight or less,
The ratio of the weight of the second metal alkoxide reactant to the weight of the coating portion is 1.0% by weight or more and 40.0% by weight or less,
The ratio of the weight of the third metal alkoxide to the weight of the coating portion is 5.0% by weight or more and 90.0% by weight or less,
The positive electrode active material for a secondary battery according to any one of claims 1 to 7. The ratio of the weight of the covering portion to the sum of the weight of the center portion and the weight of the covering portion is 0.010 weight % or more and 2.000 weight % or less,
The positive electrode active material for a secondary battery according to any one of claims 1 to 8. The ratio of the thickness of the covering portion covering the grain boundary to the thickness of the covering portion covering the surface is 10% or more and 100% or less,
The positive electrode active material for a secondary battery according to any one of claims 1 to 9. Equipped with a positive electrode active material layer,
The positive electrode active material layer includes the positive electrode active material for a secondary battery according to any one of claims 1 to 10.
Positive electrode for secondary batteries. A secondary battery comprising the positive electrode for a secondary battery according to claim 11, a negative electrode, and an electrolyte. A lithium ion secondary battery,
The secondary battery according to claim 12.

Images