JP2019160802A - Lithium ion secondary battery - Google Patents

Abstract

To provide a lithium ion secondary battery which has a high cycle life even in the case of having a positive electrode including positive electrode active material which is activated with 4.4 V(vs Li/Li+) or higher.SOLUTION: A lithium ion secondary battery comprises: a positive electrode including positive electrode active material; a negative electrode including negative electrode active material; an electrolyte including a nonaqueous solvent and lithium salt; and a coat film formed on a surface of the positive electrode, and having a Li-containing phosphorus compound, in which relative element concentration ratio (Li/P) of lithium to phosphorus is 0.3 or more 4.0 or less, and relative element concentration ratio (M/P) of transition metal M included in the positive electrode surface to phosphorus is less than one.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary battery.

With the recent development of electronic technology and increasing interest in environmental technology, various electrochemical devices are used. In particular, as the demand for energy savings increases, expectations for electrochemical devices that can contribute to this increase. Conventionally, lithium ion secondary batteries, which are representative examples of power storage devices, have been mainly used as rechargeable batteries for portable devices, but in recent years, they are also expected to be used as batteries for hybrid vehicles and electric vehicles. In such a flow, high energy density is required.

In order to respond to such a demand for higher energy density, for example, a positive electrode material having a high lithium content that can be occluded / desorbed has been developed. For this purpose, various additives have been studied, and in order to improve safety and reliability, studies have been made to include a flame retardant in the electrolyte or to form an insulating layer on the electrode or separator. It has been broken.

In particular, recently, a battery using a high-capacity positive electrode or a battery driven at a high voltage using a high-potential positive electrode has been demanded as a measure for increasing the energy density. In order to achieve a higher voltage of the battery, it is necessary to use a positive electrode that operates at a high potential, specifically 4.4 V.
Various positive electrode active materials that operate even at (vsLi / Li ⁺ ) or more have been proposed (see, for example, Patent Document 1).

In a conventional lithium ion secondary battery that operates at a voltage of about 4 V, a nonaqueous electrolytic solution in which a lithium salt is dissolved in a nonaqueous solvent mainly composed of a carbonate-based solvent is widely used (for example, Patent Document 2). reference). As a feature of the electrolytic solution containing the carbonate-based solvent, it can be mentioned that, under a voltage of about 4 V, the balance between oxidation resistance and reduction resistance is excellent and lithium ion conductivity is excellent.

However, in a high-voltage lithium ion secondary battery having a positive electrode containing a positive electrode active material that operates at 4.4 V (vsLi / Li ⁺ ) or higher, a carbonate-based solvent or the like contained in the electrolyte solution is present on the positive electrode surface. This causes the problem of oxidative decomposition. This shortens the charge / discharge cycle life, decreases the charge / discharge capacity, and generates unnecessary gas. Various solutions to such performance degradation have been studied, and a system showing a certain effect has been found, but it is still not at a satisfactory level. Therefore, a method for suppressing the decomposition of the electrolytic solution under the high voltage has been studied, and a lithium ion secondary battery having a high voltage drive and a high cycle life is desired.

As a technique for solving such a problem with a positive electrode active material, Patent Document 3 proposes a method for obtaining a positive electrode in which the surface of the positive electrode active material is coated with a polyamide resin. Patent Document 4 includes Li _0.375 Co _0.25 Mn _0.375 O ₂ , Li _0.1 Co _0.8 Mn _0.1 O ₂ , LiNi _1/3 Co _1/3.
A method for producing a positive electrode active material in which particles of lithium-containing composite oxide such as Mn _1/3 O ₂ and particles of electrochemically inactive metal oxide such as ZrO ₂ are mixed has been proposed. Further, Patent Document 5 proposes a positive electrode active material in which a part of the surface of the primary particles of the positive electrode active material is coated with a Li metal oxide and the surface of the remaining primary particles is coated with a cubic metal oxide. Yes. Furthermore, Patent Document 6 discloses that Zr, Ti, Sn, Mg, Ba, Pb,
What is claimed is: 1. A method for producing a positive electrode active material, comprising: particles having fine particles of oxides of at least one metal element selected from Bi, Nb, Ta, Zn, Y, La, Sr, Ce, In and Al. Proposed.
On the other hand, as a technique for solving the above problem with an electrolytic solution, for example, Patent Document 7 proposes a method of improving cycle life using a silicon-containing additive. Patent Document 8 proposes a method of forming an electrode protective film using a phosphate ester-based compound having an unsaturated bond as an electrolyte solution additive.

JP 2000-515672 A JP-A-7-006786 JP 2010-129494 A JP-T-2006-512742 JP 2013-137947 A JP 2012-138197 A International Publication No. 2012/170688 JP2013-12442A

However, when the positive electrode obtained by the method of Patent Document 3 is used, the diffusion of lithium ions is hindered by the resin coating, and the rate characteristics are deteriorated. Moreover, the positive electrode active material obtained by the method of Patent Document 4 is a mixture of powders, and the metal oxide content in the actual positive electrode active material is large, so that a large amount of metal oxide needs to be added. Furthermore, the positive electrode active material obtained by the method of Patent Document 5 is insufficient in suppressing the decomposition reaction of the electrolytic solution, and tends to be unable to sufficiently suppress capacity deterioration particularly at high voltage and high temperature. Furthermore, the positive electrode active material obtained by the method of Patent Document 6 is insufficient in suppressing the decomposition reaction of the electrolytic solution, and may not sufficiently suppress capacity deterioration particularly at high voltage and high temperature. As described above, in the techniques described in Patent Documents 3 to 6, it has been proposed to suppress the decomposition reaction of the electrolytic solution by improving the positive electrode active material, but a high cycle life is realized when operating at a high voltage or high temperature. No battery is available.
The electrolytic solution used in the method of Patent Document 7 is not intended to act on the electrode, and the effect on the electrode is limited. Moreover, the method of patent document 8 improves a lifetime by electropolymerizing an additive on an electrode during charge and forming a protective film. However, the film actually formed by electrolytic polymerization is not disclosed, and the composition and form of the protective film that is effective in improving the life, or
The conditions for forming an effective protective film are not known. In addition, the charging / discharging conditions of the battery and the conditions suitable for carrying out the electropolymerization must be matched, and the effect is recognized only in a limited system.

The present invention has been made in view of such a problem, and a lithium ion secondary battery having a high cycle life even when a positive electrode containing a positive electrode active material that operates at 4.4 V (vsLi / Li ⁺ ) or higher is provided. The purpose is to provide.

As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that lithium ions that operate at a high voltage and exhibit a high cycle life by using a positive electrode in which a compound having a specific structure is formed on the positive electrode surface. The present inventors have found that a secondary battery can be achieved and have completed the present invention.

That is, the present invention is as follows.
[1]
A positive electrode containing a positive electrode active material;
A negative electrode containing a negative electrode active material;
An electrolyte solution containing a non-aqueous solvent and a lithium salt;
The transition metal M and phosphorus formed on the surface of the positive electrode and having a relative element concentration ratio (Li / P) between lithium and phosphorus of 0.3 to 4.0 and included in the surface of the positive electrode A film having a Li-containing phosphorus compound having a relative element concentration ratio (M / P) of less than 1;
A lithium ion secondary battery comprising:
[2]
The lithium ion secondary battery according to [1], wherein the Li-containing phosphorus compound is a Li-containing phosphate compound.
[3]
The positive electrode active material is a compound represented by the following general formula (1); a compound represented by the following general formula (6); and an oxide represented by the following general formula (2A); The lithium according to [1] or [2], which is a composite oxide with an oxide represented by the following formula (1), which is at least one selected from the group consisting of compounds represented by the following general formula (2): Ion secondary battery.
_{LiMn 2-x Ma x O 4} (1)
(In the formula, Ma represents one or more selected from the group consisting of transition metals, and 0.2 ≦ x ≦ 0.7.)
LiMO ₂ (6)
(In the formula, M represents one or more selected from transition metals and Al.)
Li ₂ McO ₃ (2A)
(In the formula, Mc represents one or more selected from the group consisting of transition metals.)
LiMdO ₂ (2B)
(In the formula, Md represents one or more selected from the group consisting of transition metals.)
_{zLi 2 McO 3 - (1-} z) LiMdO 2 (2)
(In the formula, Mc and Md are synonymous with those in the general formulas (2A) and (2B), respectively, and 0.1 ≦ z ≦ 0.9).
[4]
A compound (A) selected from the group consisting of a protonic acid having a phosphorus atom and a compound in which at least one hydrogen atom of the protonic acid having a phosphorus atom is substituted with an alkali metal atom or a trialkylsilyl group. The lithium ion secondary battery according to any one of [1] to [3].
[5]
The lithium ion secondary battery according to [4], wherein the compound (A) includes a compound represented by the following formula (A-1).
(In the formula, X represents a hydrogen atom, an alkali metal atom, or a trialkylsilyl group having 3 to 10 carbon atoms, n is an integer of 0 or 1, and R ₁ and R ₂ are each independently an OH group, an OLi group, and a substituted group. An alkyl group having 1 to 10 carbon atoms which may be substituted, an alkoxy group having 1 to 10 carbon atoms which may be substituted, or a siloxy group having 3 to 10 carbon atoms.
[6]
The ratio of the relative element concentration of lithium and phosphorus (Li / P) is 0.3 or more and 2.0 or less,
The lithium ion secondary battery according to any one of [1] to [5].
[7]
The ratio of relative element concentration of lithium and phosphorus (Li / P) is 0.3 or more and 2.0 or less,
And the lithium ion secondary battery in any one of [1]-[5] which has a striped structure in the said film.
[8]
The lithium ion secondary battery according to any one of [1] to [7], wherein the lithium-based positive electrode potential at full charge is 4.4 V (vsLi / Li ⁺ ) or more.
[9]
A positive electrode active material;
Formed on the surface of the positive electrode active material, and the ratio of the relative element concentrations of lithium and phosphorus (Li /
P) is 0.3 or more and 4.0 or less, and the transition metal M contained on the surface of the positive electrode active material
And a film having a Li-containing phosphorus compound having a relative element concentration ratio (M / P) of less than 1 and phosphorus,
A positive electrode material.

According to the present invention, it is possible to provide a lithium ion secondary battery that operates at a high voltage and exhibits a high cycle life.

FIG. 1 is a cross-sectional view schematically showing an example of a lithium ion secondary battery in the present embodiment.

Hereinafter, a form for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail with reference to the drawings as necessary. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be implemented with appropriate modifications within the scope of the gist thereof. The positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[Lithium ion secondary battery]
The lithium ion secondary battery (hereinafter also simply referred to as “battery”) of the present embodiment contains a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a non-aqueous solvent, and a lithium salt. The ratio of the relative concentration of lithium and phosphorus formed on the surface of the electrolyte and the positive electrode (Li
/ P) having a Li-containing phosphorus compound having a relative element concentration ratio (M / P) of less than 1 between the transition metal M and phosphorus contained on the surface of the positive electrode is 0.3 or more and 4.0 or less A coating. Since it is configured in this way, the lithium ion secondary battery of the present embodiment can operate even at a high voltage and can exhibit a high cycle life.

The lithium ion secondary battery in the present embodiment includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte containing a nonaqueous solvent and a lithium salt.

(Positive electrode)
The positive electrode containing the positive electrode active material is not particularly limited as long as it reversibly occludes / releases Li ions and acts as a positive electrode of a lithium ion secondary battery, and a known one can be used. The positive electrode active material is not particularly limited. For example, LiCoO ₂ , Li
NiO ₂ , LiMnO ₂ , LiNi _x Co _y Mn _z O ₂ (x + y + z = 2), LiNi _x Co _y A
_{l z O 2 (x + y} + z = 2) such as Limbo ₂ (Mb is Al or selected from transition metals)
In the layered-type oxide _{represented, LiMn 2 O 4, LiNi x} Mn y O 4 (x + y = 1) spinel type oxide represented _{by, zLi 2 McO 3 - (1} -z) LiMdO 2 (0.1 ≦ z ≦ 0.9, M
Preferable examples include a Li-excess layered oxide positive electrode active material represented by c and Md selected from transition metals.

The battery of this embodiment is 4.4V (vsLi / Li ⁺⁾ from the viewpoint of realizing a higher voltage.
It is more preferable to provide a positive electrode containing a positive electrode active material having a discharge capacity of 10 mAh / g or more at the above potential. Even when such a positive electrode is provided, the battery of this embodiment is useful in that it can improve the cycle life. Here, the positive electrode active material having a discharge capacity of 10 mAh / g or more at a potential of 4.4 V (vsLi / Li ⁺ ) or more is 4.4 V (vsLi / Li ⁺ ).
/ Li ⁺ ) is a positive electrode active material capable of causing charge and discharge reactions as a positive electrode of a lithium ion secondary battery at a potential equal to or higher than that, and the discharge capacity at constant current discharge of 0.1 C is 10 mAh with respect to 1 g of mass of the active material. That's it. Therefore, the positive electrode active material is 4.4 V (vsLi / Li ⁺
In determining whether or not the battery has a discharge capacity of 10 mAh / g or more at the above potential, 4.4 V (vsL) when a lithium ion secondary battery including a positive electrode containing the positive electrode active material is fully charged.
i / Li ⁺ ) or higher, it can be determined that the battery has a discharge capacity of 10 mAh / g or higher at a potential of 4.4 V (vs Li / Li ⁺ ) or higher. For such a positive electrode active material, the capacity may be 4.4 V (vsLi / Li ⁺ ) or less at the beginning of charging or at the end of discharging. From the viewpoint of increasing the capacity of the lithium ion secondary battery, a positive electrode active material having a discharge capacity of 10 mAh / g or more at a potential of 4.5 V (vsLi / Li ⁺ ) or more is more preferable.

As the positive electrode active material having a discharge capacity of 10 mAh / g or more at a potential of 4.4 V (vsLi / Li ⁺ ) or more, from the viewpoint of the structural stability of the positive electrode active material, the following general formula (
1) Spinel-type oxide which is a compound represented by the following formula; compound represented by the following general formula (6); compound represented by the following general formula (2A) and compound represented by the following general formula (2B) A Li-excess layered oxide positive electrode active material which is a compound represented by the following general formula (2); an olivine type positive electrode active material which is a compound represented by the following general formula (3); And the following general formula (4
And one or more positive electrode active materials selected from the group consisting of fluorinated olivine type positive electrode active materials, which are compounds represented by:
_{LiMn 2-x Ma x O 4} (1)
LiMO ₂ (6)
(In formula (6), M represents one or more selected from transition metals and Al.)
Li ₂ McO ₃ (2A)
LiMdO ₂ (2B)
_{zLi 2 McO 3 - (1-} z) LiMdO 2 (2)
LiMb _1-y Fe _y PO ₄ (3)
Li ₂ MePO ₄ F (4)

Here, in each of the above formulas, Ma represents one or more selected from the group consisting of transition metals, and 0.2
≦ x ≦ 0.7. Mc and Md each independently represent one or more selected from the group consisting of transition metals, and 0.1 ≦ z ≦ 0.9. Further, Mb represents one or more selected from the group consisting of Mn and Co, and 0 ≦ y ≦ 0.9. Furthermore, Me represents one or more selected from the group consisting of transition metals.

As the positive electrode active material having a discharge capacity of 10 mAh / g or more at a potential of 4.4 V (vsLi / Li ⁺ ) or more, more preferably a spinel oxide which is a compound represented by the general formula (1); Compound represented by the general formula (6): a composite oxide of the compound represented by the general formula (2A) and the compound represented by the general formula (2B), the general formula (2) Is one or more positive electrode active materials selected from the group consisting of Li-excess layered oxide positive electrode active materials.

Although it does not specifically limit as a spinel type oxide which is a compound represented by the said General formula (1), From a stability viewpoint, it is preferable that it is a compound represented by the following general formula (1a).
LiMn _2-x Ni _x O ₄ (1a)
In the general formula (1a), 0.2 ≦ x ≦ 0.7. The compound represented by the general formula (1) is more preferably a compound represented by the following general formula (1b).
LiMn _2-x Ni _x O ₄ (1b)
In the general formula (1b), 0.3 ≦ x ≦ 0.6. The compounds represented by the general formula (1) are more preferably LiMn _1.5 Ni _0.5 O ₄ and LiMn _1.6 Ni _0.4 O ₄ . Here, the spinel oxide represented by the general formula (1) is within a range of 10 mol% or less with respect to the number of moles of Mn atoms from the viewpoint of stability of the positive electrode active material, electronic conductivity, and the like. In addition to the above structure, it may further contain a transition metal or a transition metal oxide. The compound represented by the general formula (1) is used singly or in combination of two or more.

Although it does not specifically limit as a layered oxide positive electrode active material which is a compound represented by the said Formula (6), From a viewpoint of stability, it is an oxide represented by the following formula (6a) or the following formula (6b). More preferably.
_{LiMn 1-vw Co v Ni w} O 2 (6a)
_{LiNi 1-tu Co t Al u} O 2 (6b)
Here, in formula (6a), 0.1 ≦ v ≦ 0.4 and 0.1 ≦ w ≦ 0.8, and formula (6b)
Among them, 0.05 ≦ t ≦ 0.3 and 0.01 ≦ u ≦ 0.15. As an example, LiMn _1/3
Co _1/3 Mn _1/3 O ₂ , LiMn _0.1 Co _0.1 Ni _0.8 O ₂ , LiMn _0.3 Co _0.2 Ni _0.5 O ₂ ,
LiNi _0.3 Co _0.15 Al _0.05 O _{2 and the} like are preferable.

The Li-excess layered oxide positive electrode active material which is a compound represented by the general formula (2) is not particularly limited, but from the viewpoint of stability, it may be a compound represented by the following general formula (2a). preferable.
_{zLi 2 MnO 3 - (1-} z) LiNi a Mn b Co c O 2 (2a)
In the general formula (2a), 0.3 ≦ z ≦ 0.7, a + b + c = 1, 0.2 ≦ a ≦ 0.6,
It is 0.2 <= b <= 0.6 and 0.05 <= c <= 0.4. Among them, in the above formula (2a),
0.4 ≦ z ≦ 0.6, a + b + c = 1, 0.3 ≦ a ≦ 0.4, 0.3 ≦ b ≦ 0.4, 0.
A compound satisfying 2 ≦ c ≦ 0.3 is more preferable.

Although it does not specifically limit as an olivine type positive electrode active material which is a compound represented by the said General formula (3), From a viewpoint of stability and electronic conductivity, following General formula (3a) and following General formula (3
It is preferable that it is a compound represented by b).
LiMn _1-y Fe _y PO ₄ (3a)
LiCo _1-y Fe _y PO ₄ (3b)
In the above formulas (3a) and (3b), each independently satisfies 0.05 ≦ y ≦ 0.8.
The compounds represented by the general formula (3) can be used singly or in combination of two or more.

The fluorinated olivine-type positive electrode active material that is the compound represented by the general formula (4) is not particularly limited, but Li ₂ FePO ₄ F, Li ₂ MnPO ₄ F, and Li ₂ CoPO _{4 are used} from the viewpoint of stability.
F is preferred. The compound represented by the general formula (4) can be used alone or in combination of two or more.

The positive electrode active materials having a discharge capacity of 10 mAh / g or more at a potential of 4.4 V (vsLi / Li ⁺ ) or more can be used singly or in combination of two or more. Also,
As a positive electrode active material, 4.4V (vsLi / Li ⁺⁾ or more has only to have a 10 mAh / g or more discharge capacity potential, 10 mAh / g at 4.4V (vsLi / Li ⁺⁾ or more potential
A positive electrode active material having the above discharge capacity and 10 m at a potential of 4.4 V (vsLi / Li ⁺ ) or higher.
A positive electrode active material having no discharge capacity of Ah / g or more can also be used in combination. 4).
A typical example of the positive electrode active material that does not have a discharge capacity of 10 mAh / g or more at a potential of 4 V (vsLi / Li ⁺ ) or more is not particularly limited, and examples thereof include LiFePO ₄ .

The positive electrode active material in the present embodiment can be synthesized by the same method as a general inorganic oxide synthesis method. For example, a positive electrode active material containing an inorganic oxide can be obtained by firing a mixture in which metal salts (for example, sulfate and / or nitrate) are mixed at a predetermined ratio in an atmosphere environment containing oxygen. Alternatively, a carbonate and / or hydroxide salt is allowed to act on a solution in which the metal salt is dissolved to precipitate a hardly soluble metal salt, which is extracted and separated into lithium carbonate and / or hydroxide as a lithium source. After mixing lithium, the positive electrode active material containing an inorganic oxide can be obtained by baking in an atmosphere environment containing oxygen.

Here, an example of a method for manufacturing the positive electrode is described below. First, a paste containing a positive electrode mixture is prepared by dispersing, in a solvent, a positive electrode mixture obtained by adding a conductive additive or a binder to the positive electrode active material, if necessary. Next, this paste is applied to a positive electrode current collector and dried to form a positive electrode mixture layer, which is pressurized as necessary to adjust the thickness, whereby a positive electrode can be produced. Although it does not specifically limit as a positive electrode electrical power collector, For example, it shall consist of metal foils, such as aluminum foil or stainless steel foil.

(Film)
The lithium ion secondary battery in the present embodiment is formed on the surface of the positive electrode, the ratio of the relative element concentration of lithium and phosphorus (Li / P) is 0.3 or more and 4.0 or less, and the above A film having a Li-containing phosphorus compound having a relative element concentration ratio (M / P) of transition metal M and phosphorus contained in the positive electrode of less than 1 is provided. By allowing the Li-containing phosphorus compound to be present on the positive electrode surface,
The oxidative decomposition of the electrolytic solution can be suppressed, and the cycle performance of the battery can be greatly improved. Here, the Li-containing phosphorus compound is a phosphorus compound containing an Li element, and the relative element concentration of the Li-containing phosphorus compound is derived from the Li element and the phosphorus element by XPS (X-ray photoelectron spectroscopy) measurement. This can be confirmed by identifying the peak. As the Li-containing phosphorus compound,
From the viewpoint of improving cycle characteristics, a Li-containing phosphate compound is preferable. Here, the Li-containing phosphoric acid compound is a compound having a phosphoric acid structure and a Li element, and specifically, 1 in XPS.
A compound having a peak derived from 35 eV phosphoric acid and a peak derived from 56 eV Li is shown.

Regarding the Li-containing phosphorus compound on the positive electrode surface of the lithium ion secondary battery in this embodiment, the ratio of the relative element concentration of lithium and phosphorus (Li / P) is 0.3 or more and 4.0 or less, and XP
The relative element concentration ratio (M / P) of the transition metal M and phosphorus on the positive electrode surface by S measurement is less than 1.

Here, the positive electrode surface is a surface facing the negative electrode through a separator in the battery. The ratio (Li / P) of the relative element concentration of lithium and phosphorus in the Li-containing phosphorus compound on the positive electrode surface is
It can be measured using XPS (X-ray photoelectron spectroscopy). In XPS measurement, the composition of the surface portion having a depth of about several nm can be observed without being affected by the internal structure of the observation object. That is, it can be said that the relative element ratio of the positive electrode surface in the present embodiment is the relative element ratio of the surface portion observed by XPS.

When performing XPS measurement of the positive electrode surface, after removing the positive electrode from the battery, the immersion electrolyte for 1 minute or more was repeated three times with diethyl carbonate, so that the remaining electrolyte could be removed sufficiently, and the positive electrode active The film formed on the substance can be measured well.

In the present embodiment, the positive electrode having a Li-containing phosphorus compound on the surface has a binding force or affinity that does not remove even after washing with diethyl carbonate for 1 minute or more, and the Li-containing phosphorus compound is formed on the surface of the positive electrode. It represents what is being done.

In the present embodiment, the ratio of the relative element concentration of lithium and phosphorus (Li / P) is 0.3 or more and 4.0 or less. By setting Li / P to 0.3 or more, the Li-containing phosphorus compound film formed on the positive electrode active material has good Li ion conductivity, and by setting Li / P to 4.0 or less, The Li-containing phosphorus compound film formed on the positive electrode active material can maintain sufficient durability. From the viewpoint of ion conductivity of the film and durability of the film, Li / P is preferably 0.3 or more and 2.0 or less, more preferably 0.3 or more and 1.5 or less, and further preferably 0. .35 or more and 1.5 or less, more preferably 0.35 or more and 1.4 or less, and particularly preferably 0.35 or more and 1.2 or less.

In this embodiment, from the viewpoint of ion conductivity of the film and durability of the film, the ratio of the relative element concentration of lithium and phosphorus (Li / P) is 0.3 or more and 2.0 or less, and the active material surface layer It is preferable to have a striped structure in the vicinity of 30 nm. The striped structure is considered to be derived from the element distribution. For example, the structure can be observed by observing the cross section of the positive electrode surface portion with a transmission electron microscope (TEM).

In this embodiment, the relative element concentration ratio (M / P) of the transition metal M and phosphorus is less than 1.
The relative element concentration ratio (M / P) between the transition metal M and phosphorus of the Li-containing phosphorus compound on the surface of the positive electrode is:
It can be measured using XPS (X-ray photoelectron spectroscopy). Here, M represents a transition metal contained in the positive electrode active material, and when the positive electrode active material has a plurality of types of transition metals, the relative element concentration is the sum of the concentrations of the plurality of types of transition metals. For example, in the case of the positive electrode active material LiNi _0.5 Mn _1.5 O ₄ , M is the sum of the Ni concentration and the Mn concentration. Relative element concentration ratio of transition metal M and phosphorus (M
/ P) is considered to represent a state in which a certain amount or more of the Li-containing phosphorus compound film is formed on the positive electrode active material. For example, when a sufficient amount of the Li-containing phosphorus compound film is not formed on the positive electrode active material, the concentration of P decreases with respect to the concentration of M, so M / P exceeds 1. By making M / P less than 1, it is considered that the Li-containing phosphorus compound film is sufficiently formed on the positive electrode active material, and the oxidative decomposition of the electrolytic solution on the positive electrode can be suppressed, and the cycle performance is improved. From the viewpoint of improving cycle performance, M / P is preferably 0.95 or less, more preferably M / P is 0.9 or less, further preferably M / P is 0.8 or less, and even more preferably M / P. Is 0.7 or less. M / P is 0 when the positive electrode active material is completely covered with the Li-containing phosphorus compound film.

(Negative electrode)
The lithium ion secondary battery of this embodiment has a negative electrode containing a negative electrode active material. The negative electrode is not particularly limited as long as it can reversibly occlude / release Li ions and acts as a negative electrode of a lithium ion secondary battery, and a known one can be used. The negative electrode is
As described above, the negative electrode active material may contain one or more selected from the group consisting of materials capable of inserting and extracting lithium ions. That is, the negative electrode includes, as a negative electrode active material, a negative electrode active material including an element capable of forming an alloy with lithium, such as a carbon negative electrode active material, a silicon alloy negative electrode active material, and a tin alloy negative electrode active material; It is preferable to contain one or more negative electrode active materials selected from the group consisting of: a tin oxide negative electrode active material; and a lithium-containing compound typified by a lithium titanate negative electrode active material. These negative electrode active materials are used singly or in combination of two or more.

The carbon negative electrode active material in the present embodiment is not particularly limited. For example, hard carbon, soft carbon, artificial graphite, natural graphite, graphite, pyrolytic carbon, coke, glassy carbon, a fired body of an organic polymer compound, Examples include mesocarbon microbeads, carbon fibers, activated carbon, graphite, carbon colloid, and carbon black. Examples of the coke include pitch coke, needle coke, and petroleum coke. Moreover, the fired body of an organic polymer compound is obtained by firing and carbonizing a polymer material such as a phenol resin or a furan resin at an appropriate temperature.

The negative electrode active material containing an element capable of forming an alloy with lithium in the present embodiment is not particularly limited, and may be a metal or a semimetal alone, an alloy or a compound, or one of these. Or what has two or more types of phases in at least one part may be sufficient. In addition,
“Alloys” include those having one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. Further, the alloy may contain a nonmetallic element as long as it has metal properties as a whole.

Although it does not specifically limit as a metal element and a metalloid element, For example, titanium (Ti), tin (Sn), lead (Pb), aluminum (Al), indium (In), silicon (Si)
, Zinc (Zn), antimony (Sb), bismuth (Bi), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), hafnium (Hf), zirconium (Zr)
And yttrium (Y). Among these, the metal elements and metalloid elements of Group 4 or 14 in the long-period periodic table are preferable, and titanium, silicon, and tin are particularly preferable.

The negative electrode is obtained as follows, for example. First, a negative electrode mixture containing a negative electrode mixture is prepared by dispersing, in a solvent, a negative electrode mixture prepared by adding a conductive additive or a binder to the negative electrode active material, if necessary. Next, this paste is applied to a negative electrode current collector and dried to form a negative electrode mixture layer, which is pressurized as necessary to adjust the thickness, thereby producing a negative electrode. The negative electrode current collector is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.

In the production of the positive electrode and the negative electrode, the conductive aid used as necessary is not particularly limited, and examples thereof include carbon black such as graphite, acetylene black and ketjen black, and carbon fiber. The binder is not particularly limited, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene butadiene rubber, and fluorine rubber.

(Electrolyte)
The electrolytic solution used for the lithium ion secondary battery in the present embodiment contains a non-aqueous solvent. The non-aqueous solvent is not particularly limited and various solvents can be used. For example, an aprotic polar solvent is preferable. Specific examples thereof include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,
Cyclic carbonates such as 2-pentylene carbonate, 2,3-pentylene carbonate, trifluoromethylethylene carbonate, fluoroethylene carbonate and 4,5-difluoroethylene carbonate; lactones such as γ-butyrolactone and γ-valerolactone; cyclic such as sulfolane Sulfone; cyclic ethers such as tetrahydrofuran and dioxane; Chain carbonates; Nitriles such as acetonitrile; Dimethyl ether And chain ether carbonates such as methyl propionate; chain ether carbonate compounds such as dimethoxyethane. These can be used individually by 1 type or in combination of 2 or more types.

As the non-aqueous solvent in the present embodiment, from the viewpoint of ion conductivity, cyclic carbonate,
It is more preferable to use a carbonate-based solvent such as a chain carbonate. Further, it is more preferable to use a combination of a cyclic carbonate and a chain carbonate as the carbonate solvent. Although it does not specifically limit as a cyclic carbonate and various things can be used, For example, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate are preferable, and ethylene carbonate and propylene carbonate are more preferable.
The chain carbonate is not particularly limited, and various types can be used. For example, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate are preferable.

When the carbonate-based solvent in the present embodiment includes a combination of a cyclic carbonate and a chain carbonate, the mixing ratio of the cyclic carbonate and the chain carbonate is 1:10 to 5: 1 in terms of volume ratio from the viewpoint of ion conductivity. And is more preferably 1: 5 to 3: 1.

In the case of using the carbonate-based solvent in the present embodiment, another nonaqueous solvent such as acetonitrile or sulfolane can be further added as necessary from the viewpoint of improving the physical properties of the battery.

The electrolyte solution of the lithium ion secondary battery in the present embodiment contains a lithium salt. The electrolyte content of the lithium salt is preferably 1% by mass or more from the viewpoint of ion conductivity,
From the viewpoint of solubility at low temperatures, it is preferably 40% by mass or less. The lithium salt content is more preferably 5% by mass or more and 35% by mass or less, and further preferably 7% by mass or more and 30% by mass or less. In addition, the content of the lithium salt in the electrolyte solution included in the lithium ion secondary battery according to the present embodiment is based on the elements included in the lithium salt, for example, ¹⁹ F-NMR.
This can be confirmed by performing NMR measurement such as ³¹ P-NMR.

The structure of the lithium salt in the present embodiment is not particularly limited, but is preferably LiPF ₆ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOS from the viewpoint of ion conductivity.
O ₂ C _k F _{2k + 1} (k is an integer of 1 to 8), LiN (SO ₂ C _k F _{2k + 1} ) ₂ [k is an integer of 1 to 8]
, LiPF _n (C _k F _{2k + 1} ) _6-n [n is an integer of 1 to 5, k is an integer of 1 to 8], LiPF ₄ (C
₂ O ₂ ) ₂ and LiPF ₂ (C ₂ O ₂ ) ₂ , and more preferably LiPF ₆ . These electrolytes can be used singly or in combination of two or more.

The electrolyte used for the lithium ion secondary battery in the present embodiment includes a proton acid having a phosphorus atom and a compound in which at least one hydrogen atom of the proton acid having a phosphorus atom is substituted with an alkali metal atom or a trialkylsilyl group. It is preferable to contain the compound (A) selected from the group consisting of The protonic acid having a phosphorus atom may be a compound having a phosphorus atom in the molecule and a hydrogen atom that can dissociate as a proton, such as a halogen atom such as a fluorine atom or a chlorine atom, Group, organic group such as alkyl group, Si
, B, O, N, etc. may be contained. Further, a plurality of phosphorus atoms may be contained in the molecule like polyphosphoric acid. Although it does not specifically limit as a protonic acid which has a phosphorus atom, For example, phosphoric acid, phosphorous acid, pyrophosphoric acid, polyphosphoric acid, and phosphonic acid are mentioned preferably. Among these, from the viewpoint of the stability of the compound (A), more preferably phosphoric acid,
Phosphorous acid and phosphonic acid. These protonic acids may be substituted.

The compound (A) may be a compound in which at least one hydrogen atom of a protonic acid having a phosphorus atom is substituted with an alkali metal atom or a trialkylsilyl group. Although it does not specifically limit as said alkali metal atom, For example, a lithium atom, a sodium atom, and a potassium atom are mentioned preferably. From the viewpoint of improving the cycle performance, the alkali metal atom is particularly preferably a lithium atom. The trialkylsilyl group is -SiR3R4R5 (
R3 to R5 are substituents represented by an alkyl group). Although it does not specifically limit as a trialkylsilyl group, From a viewpoint of the chemical stability in a lithium ion secondary battery, -Si (C
_{H 3) 3, -Si (C} 2 H 5) 3, -Si (CHCH 2) 3, -Si (CH 2 CHCH 2) 3, -S
i (CF ₃ ) ₃ is more preferable, and —Si (CH ₃ ) ₃ is further preferable.

The compound (A) is more preferably a compound represented by the following formula (A-1) from the viewpoint of chemical stability in the battery.

(In formula (A-1), X represents a hydrogen atom, an alkali metal atom, or a trialkylsilyl group having 3 to 10 carbon atoms, n is an integer of 0 or 1, and R ₁ and R ₂ are each independently OH. Group, OLi group,
Alkyl group having 1 to 10 carbon atoms which may be substituted, 1 to 1 carbon atom which may be substituted
An alkoxy group having 0 or less and a siloxy group having 3 to 10 carbon atoms are shown. )

Here, n represents an integer of 0 or 1, and n is particularly preferably 1 from the viewpoint of the stability of the compound (A) in the electrolytic solution. In formula (A-1), X is more preferably an alkali metal atom or a trialkylsilyl group having 3 to 10 carbon atoms from the viewpoint of maintaining the discharge capacity of the battery.

In the formula (A-1), the alkyl group represents a structure in which a carbon atom is directly bonded to a P atom, and the alkyl group has not only an aliphatic group but also an aromatic ring such as a phenyl group or a benzyl group. It may be. Further, fluorine-substituted hydrocarbon groups such as a trifluoromethyl group in which all hydrogen atoms in the alkyl group are substituted with fluorine atoms are also included. The alkyl group may be substituted with various functional groups.

In formula (A-1), preferred examples of R ₁ and R _{2 as} the alkyl group are not particularly limited,
Aliphatic alkyl groups such as methyl, ethyl, vinyl, allyl, propyl, butyl, pentyl, hexyl, fluorohexyl, benzyl, phenyl, nitrile-substituted phenyl, fluorination An aromatic alkyl group such as a phenyl group can be mentioned. Among them, from the viewpoint of chemical stability, methyl group, ethyl group, allyl group (allyl)
Propyl group, butyl group, pentyl group, hexyl group, and fluorohexyl group are more preferable. The carbon number of the alkyl group is 1 to 10, 1 or more from the viewpoint of improving battery performance, and 10 or less from the viewpoint of affinity with the electrolytic solution. The carbon number of the alkyl group is preferably 2 or more and 10 or less, more preferably 3 or more and 8 or less.

In the formula (A-1), the alkoxy group indicates a structure in which a carbon atom is bonded to a P atom through an oxygen atom, and the alkoxy group is not only aliphatic, but also a phenoxy group, a benzylalkoxy group, and the like. It may be a structure having an aromatic ring. Also included are fluorine-substituted alkoxy groups such as trifluoroethyl groups and hexafluoroisopropyl groups in which hydrogen atoms in the alkoxy groups are fluorine-substituted. The alkoxy group may be substituted with various functional groups.

In the formula (A-1), preferred examples of the alkoxy groups of R ₁ and R ₂ are not particularly limited, but methoxy group, ethoxy group, vinyloxy group, allyloxy group, propoxy group, butoxy group, cyano group Examples thereof include aliphatic alkoxy groups such as hydroxy group, fluoroethoxy group and fluoropropoxy group, and aromatic alkoxy groups such as phenoxy group, benzylalkoxy group, nitrile substituted phenoxy group and fluorinated phenoxy group. Among them, from the viewpoint of chemical stability, methoxy group, ethoxy group, vinyloxy group, allyloxy group (all
yloxy), propoxy group, butoxy group, cyanohydroxy group, fluoroethoxy group,
A fluoropropoxy group is more preferred. The alkoxy group has 1 to 10 carbon atoms, 1 or more from the viewpoint of improving battery performance, and 10 or less from the viewpoint of affinity with the electrolytic solution. The number of carbon atoms of the alkoxy group is preferably 1 or more and 8 or less, more preferably 2 or more and 8 or less.

In the formula (A-1), a siloxy group indicates a structure in which a silicon atom is bonded to a P atom through an oxygen atom, and the siloxy group may contain a siloxane structure such as Si—O—Si—. Good. Although it does not specifically limit as a siloxy group, From a viewpoint of chemical stability, a trimethylsiloxy group, a triethylsiloxy group, a dimethylethylsiloxy group, a diethylmethylsiloxy group etc. are mentioned preferably. More preferably, it is a trimethylsiloxy group. The siloxy group has 3 to 10 carbon atoms, 1 or more from the viewpoint of improving battery performance, and 10 or less from the viewpoint of chemical stability. The carbon number of the siloxy group is preferably 3 or more and 8 or less, more preferably 3 or more and 6 or less. The number of silicon in the siloxy group is not particularly limited, but from the viewpoint of improving chemical stability and battery performance, the number of silicon atoms in the siloxy group is particularly preferably 1 or more and 2 or less, and most preferably 1.

Preferable specific examples of the compound (A) include, but are not particularly limited to, tris (trimethylsilyl) phosphate, tris (trimethylsilyl) phosphite, tris (triethylsilyl) phosphate, tetrakis pyrophosphate (trimethylsilyl), trimethylsilyl polyphosphate, Butyl phosphonate bis (trimethylsilyl), propyl phosphonate bis (trimethylsilyl),
Bis (trimethylsilyl) ethylphosphonate, monomethylbis (trimethylsilyl) phosphate, monoethylbis (trimethylsilyl) phosphate, mono (trifluoroethyl) bis (trimethylsilyl) phosphate, mono (hexafluoroisopropyl) bis (trimethylsilyl) phosphate, phosphorus Examples include lithium acid, lithium pyrophosphate, phosphoric acid, and pyrophosphoric acid. Among these, from the viewpoint of cycle life and gas generation suppression, tris (trimethylsilyl) phosphate
, Tris phosphite (trimethylsilyl), tetrakis pyrophosphate (trimethylsilyl),
Trimethylsilyl polyphosphate, bis (trimethylsilyl) butylphosphonate, bis (trimethylsilyl) propyl phosphonate, bis (trimethylsilyl) ethylphosphonate, monomethylbis (trimethylsilyl) phosphate, monoethylbis (trimethylsilyl) phosphate,
Mono (trifluoroethyl) bis (trimethylsilyl) phosphate, mono (hexafluoroisopropyl) bis (trimethylsilyl) phosphate, lithium phosphate, and phosphoric acid are more preferred, and tris (trimethylsilyl) phosphate, tris (trimethylsilyl) phosphite ), Tetrakis pyrophosphate (trimethylsilyl), trimethylsilyl polyphosphate, lithium phosphate,
Phosphoric acid is particularly preferred.

Further, the content of the compound (A) in the electrolytic solution is preferably 0.01% by mass or more and 10% by mass or less with respect to the mass of the electrolytic solution. From the viewpoint of obtaining a good cycle life in the lithium ion secondary battery, the content of the compound (A) is preferably 0.01% by mass or more,
From the viewpoint of battery output, it is preferably 10% by mass or less. More preferably 0.05% by mass
10 mass% or less, more preferably 0.1 mass% or more and 8 mass% or less, still more preferably 0.2 mass% or more and 5 mass% or less, particularly preferably 0.3 mass% or more and 4 mass% or less. . The compound (A) only needs to be present in the electrolytic solution, and does not necessarily have to be dissolved at the molecular level, and may exist in a dispersed state. In addition, content of the compound (A) in the electrolyte solution contained in a lithium ion secondary battery is based on the element contained in the said compound (A), for example, ¹ H-NMR, ¹¹ B-NMR, ¹³ C— NMR, ²⁹ Si-NMR, ³¹ P-NMR
It can confirm by performing NMR measurement, such as.

The electrolytic solution in the present embodiment contains at least one hydrogen atom of an oxo acid selected from protonic acid, sulfonic acid, and carboxylic acid having a phosphorus atom and / or a boron atom represented by the following formula (B-
It is preferable to contain the compound (B) substituted by the structure represented by 1).

(In formula (B-1), R ₁ , R ₂ and R ₃ each independently represents an organic group having 1 to 10 carbon atoms.)

In the electrolyte solution of the present embodiment, the protonic acid having a phosphorus atom may be a compound having a phosphorus atom in the molecule and a hydrogen atom that can be dissociated as a proton. In addition to halogen atoms such as atoms, organic groups such as alkoxy groups and alkyl groups, hetero atoms such as Si, B, O, and N may be contained. Further, a plurality of phosphorus atoms may be contained in the molecule like polyphosphoric acid. Preferred examples of the protonic acid having a phosphorus atom include phosphoric acid, phosphorous acid, pyrophosphoric acid, polyphosphoric acid, and phosphonic acid. Among these, phosphoric acid, phosphorous acid, and phosphonic acid are more preferable from the viewpoint of the stability of the compound (B). These protonic acids may be substituted.

In the electrolytic solution in the present embodiment, the proton acid having a boron atom may be a compound having a boron atom in the molecule and a hydrogen atom that can be dissociated as a proton. In addition to halogen atoms such as atoms, organic groups such as alkoxy groups and alkyl groups, hetero atoms such as Si, P, O, and N may be contained. Further, a plurality of boron atoms may be contained in the molecule. Preferred examples of the protonic acid having a boron atom include boric acid, boronic acid, and borinic acid. These protonic acids may be substituted.

In the electrolytic solution in the present embodiment, the sulfonic acid is a compound having a —SO ₃ H group (sulfonic acid group) in the molecule, and may have a plurality of sulfonic acid groups in the molecule. In the present embodiment, it can be made containing sulfuric acid (HOSO ₃ H). Although not particularly limited, preferred examples include methylsulfonic acid, ethylsulfonic acid, propylsulfonic acid, 1,2 ethanedisulfonic acid, trifluoromethylsulfonic acid, phenylsulfonic acid, benzylsulfonic acid, and sulfuric acid. .

In the electrolytic solution in the present embodiment, the carboxylic acid is a compound having a CO ₂ H group (carboxylic acid group) in the molecule, and may have a plurality of carboxylic acid groups in the molecule. Although it does not specifically limit as carboxylic acid, For example, acetic acid, trifluoroacetic acid, propionic acid, butyric acid, valeric acid, acrylic acid, methacrylic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, phthalic acid, isophthalic acid, Examples include terephthalic acid, salicylic acid, malonic acid, fumaric acid, succinic acid, glutaric acid, adipic acid, and itaconic acid. From the viewpoint of improving the cycle performance of the obtained lithium ion secondary battery, preferably benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, malonic acid, fumaric acid, succinic acid, glutaric acid,
Dicarboxylic acids such as adipic acid and itaconic acid, more preferably adipic acid, itaconic acid, succinic acid, isophthalic acid and terephthalic acid.

In the structure represented by the formula (B-1), R ₁ , R ₂ , and R ₃ each independently represent an organic group (hydrocarbon group) having 1 to 10 carbon atoms. This includes not only aliphatic hydrocarbon groups but also aromatic hydrocarbon groups such as phenyl groups. Further, a fluorine-substituted hydrocarbon group such as a trifluoromethyl group in which all hydrogen atoms in the hydrocarbon group are substituted with fluorine atoms is also included. Further, if necessary, halogen atoms such as fluorine atom, chlorine atom, bromine atom, nitrile group (—CN), ether group (—O—), carbonate group (—OCO ₂ —), ester group (—CO _2- ), carbonyl group (—CO—) sulfide group (—S—), sulfoxide group (—SO—), sulfone group (—SO ₂ —), urethane group (—NHCO ₂ —), etc. are introduced. be able to.

In the present embodiment, preferred examples of R ₁ , R ₂ , and R ₃ in formula (B-1) include methyl group, ethyl group, vinyl group, 1-methylvinyl group, propyl group, butyl group, and fluoromethyl. An aliphatic hydrocarbon group such as a group; aromatic hydrocarbon groups such as a benzyl group, a phenyl group, a nitrile-substituted phenyl group, and a fluorinated phenyl group. Among these, a methyl group, an ethyl group, a vinyl group, a 1-methylvinyl group, and a fluoromethyl group are more preferable from the viewpoint of chemical stability. Two Rs may be bonded to form a ring. Although it does not specifically limit, In order to form a ring, the example substituted by the substituted or unsubstituted saturated or unsaturated alkylene group is mentioned, for example.

In the present embodiment, R ₁ , R ₂ and R ₃ in formula (B-1) each independently represent 1 carbon atom.
To 10 organic groups (hydrocarbon groups), R1 and R2 from the viewpoint of miscibility with nonaqueous solvents
, R3 preferably has 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms.

From the viewpoint of chemical durability in the lithium ion secondary battery, the structure represented by the formula (B-1) includes —Si (CH ₃ ) ₃ , —Si (C ₂ H ₅ ) ₃ , —Si. (CHCH ₂ ) ₃ , —Si (C
H ₂ CHCH ₂ ) ₃ and —Si (CF ₃ ) ₃ are more preferable, and —Si (CH ₃ ) ₃ is further preferable.

In the electrolytic solution in the present embodiment, when the oxo acid has a plurality of hydrogen atoms, it is sufficient that at least one hydrogen atom is substituted with the structure represented by the formula (B-1). Further, the remaining hydrogen atoms not substituted with the formula (B-1) may exist as they are,
It may be substituted with a functional group other than the structure represented by the formula (B-1). Such a functional group is not particularly limited, and for example, a halogen-substituted or unsubstituted saturated or unsaturated hydrocarbon group having 1 to 20 carbon atoms can be preferably exemplified. The halogen-substituted or unsubstituted saturated or unsaturated hydrocarbon group is not particularly limited, and examples thereof include an alkyl group, an alkenyl group, an alkynyl group, an allyl group, and a vinyl group. Two hydrogen atom substituents may be bonded to form a ring. Although it does not specifically limit, In order to form a ring, the example substituted by the substituted or unsubstituted saturated or unsaturated alkylene group is mentioned, for example.

With respect to the electrolytic solution in this embodiment, at least one hydrogen atom of the oxo acid is represented by the formula (B-1
As a compound (B) substituted with a structure represented by the following formula (B-2) and / or the following formula (
The compound represented by B-3) is more preferable. By applying such a compound, even when a positive electrode containing a positive electrode active material that operates at 4.4 V (vs Li / Li ⁺ ) or higher is provided, the cycle performance tends to be further improved.

(In formula (B-2), M represents a P atom or a B atom. When M is a B atom, n is 0;
When M is a P atom, n represents an integer of 0 or 1. R ₁ , R ₂ and R ₃ each independently represents an organic group having 1 to 10 carbon atoms. R ₄ and R ₅ are each independently an OH group, an OLi group, an optionally substituted alkyl group having 1 to 10 carbon atoms, an optionally substituted alkoxy group having 1 to 10 carbon atoms, or an alkyl group having 3 to 10 carbon atoms. A siloxy group is shown. )

(In formula (B-3), R ₁ , R ₂ and R ₃ each independently represents an organic group having 1 to 10 carbon atoms. R ₆ is an optionally substituted organic group having 1 to 20 carbon atoms. Is shown.)

In the compound (B) represented by the formula (B-2), M represents a P atom or a B atom,
When B is a B atom, n is 0, and when M is a P atom, n represents an integer of 0 or 1. That is,
In the formula (4), when M is a B atom and n is 0, the compound (B) has a boric acid structure, and M
Is a P atom and n is 0, the compound (B) has a phosphorous acid structure, and when M is a P atom and n is 1, the compound (B) has a phosphoric acid structure. From the viewpoint of the stability of the electrolytic solution containing the compound (B), the structure of the following formula (B-4) in which M is a P atom is more preferable.

(In Formula (B-4), n is 0 or 1, and R ₁ , R ₂ , and R ₃ each independently represent 1 carbon atom.
To 10 organic groups. R ₄ and R ₅ are each independently an OH group, an OLi group, an optionally substituted alkyl group having 1 to 10 carbon atoms, an optionally substituted alkoxy group having 1 to 10 carbon atoms, or an alkyl group having 3 to 10 carbon atoms. A siloxy group is shown. )

Regarding the compound (B) represented by the formula (B-2), the alkyl group is a structure in which a carbon atom is directly bonded to an M atom, and is not particularly limited. However, the alkyl group is aliphatic only. Alternatively, a structure having an aromatic ring such as a phenyl group or a benzyl group may be used. Further, fluorine-substituted hydrocarbon groups such as a trifluoromethyl group in which all hydrogen atoms in the alkyl group are substituted with fluorine atoms are also included. The alkyl group may be substituted with various functional groups. If necessary, a halogen atom such as a fluorine atom, a chlorine atom or a bromine atom, a nitrile group (—CN), an ether group (—O—) , Carbonate group (—OCO ₂ —), ester group (—CO ₂ —), carbonyl group (—CO—) sulfide group (—S—), sulfoxide group (—SO—), sulfone group (—SO ₂ —) And a functional group such as a urethane group (—NHCO ₂ —) can be introduced.

Preferred examples of the alkyl group represented by R ₄ and R _{5 in} the formula (B-2) include a methyl group, an ethyl group,
Vinyl group, allyl group, propyl group, butyl group, pentyl group, hexyl group,
Examples thereof include an aliphatic alkyl group such as a fluorohexyl group, and an aromatic alkyl group such as a benzyl group, a phenyl group, a nitrile-substituted phenyl group, and a fluorinated phenyl group. Of these, methyl, ethyl, allyl, propyl, butyl, pentyl, hexyl, and fluorohexyl are more preferred from the viewpoint of chemical stability. The carbon number of the alkyl group is 1 to 10, 1 or more from the viewpoint of improving battery performance, and 10 or less from the viewpoint of affinity with the electrolytic solution. The alkyl group preferably has 2 or more and 10 or less carbon atoms, more preferably 3 carbon atoms.
It is 8 or less.

Regarding the compound (B) represented by the formula (B-2), the alkoxy group represents a structure in which a carbon atom is bonded to an M atom through an oxygen atom, and is not particularly limited. May have a structure having not only an aliphatic group but also an aromatic ring such as a phenoxy group and a benzylalkoxy group. Further, fluorine-substituted alkoxy groups such as a trifluoroethyl group or a hexafluoroisopropyl group in which a hydrogen atom in the alkoxy group is fluorine-substituted are also included. The alkoxy group may be substituted with various functional groups. If necessary, a halogen atom such as a fluorine atom, a chlorine atom, or a bromine atom, a nitrile group (—CN), an ether group (—O—) , Carbonate group (—OCO ₂ —), ester group (—CO ₂ —), carbonyl group (—CO—) sulfide group (—S—), sulfoxide group (—SO—), sulfone group (—S
Functional groups such as O ₂ —) and urethane groups (—NHCO ₂ —) can be introduced.

Preferred examples of R ₄ and R _{5 as} the alkoxy group in the formula (B-2) include a methoxy group, an ethoxy group, a vinyloxy group, an allyloxy group, a propoxy group, a butoxy group,
Examples thereof include aliphatic alkoxy groups such as cyanohydroxy group, fluoroethoxy group and fluoropropoxy group, and aromatic alkoxy groups such as phenoxy group, benzylalkoxy group, nitrile substituted phenoxy group and fluorinated phenoxy group. Of these, from the viewpoint of chemical stability, a methoxy group, an ethoxy group, a vinyloxy group, an allyloxy group, a propoxy group, a butoxy group, a cyanohydroxy group, a fluoroethoxy group, and a fluoropropoxy group are more preferable. The alkoxy group has 1 to 10 carbon atoms, 1 or more from the viewpoint of improving battery performance, and 10 or less from the viewpoint of affinity with the electrolytic solution. The number of carbon atoms of the alkoxy group is preferably 1 or more and 8 or less, more preferably 2 or more and 8 or less.

Regarding the compound (B) represented by the formula (B-2), the siloxy group shows a structure in which a silicon atom is bonded to an M atom through an oxygen atom, and is not particularly limited. May contain a siloxane structure such as Si—O—Si—. As the above siloxy group, from the viewpoint of chemical stability, a trimethylsiloxy group, a triethylsiloxy group,
Preferred examples include dimethylethylsiloxy group and diethylmethylsiloxy group. More preferably, it is a trimethylsiloxy group. The siloxy group has 3 to 10 carbon atoms, 1 or more from the viewpoint of improving battery performance, and 10 or less from the viewpoint of chemical stability. The siloxy group preferably has 3 to 8 carbon atoms, more preferably 3 to 6 carbon atoms. The number of silicon in the siloxy group is not particularly limited, but from the viewpoint of improving chemical stability and battery performance, the number of silicon atoms in the siloxy group is preferably 1 or more and 4 or less, more preferably 1 or more and 3 or less. More preferably, it is 1 or more and 2 or less, and particularly preferably 1.

In the compound (B) represented by the formula (B-2), R ₄ and R ₅ are each independently a hydroxyl group, an optionally substituted alkyl group having 1 to 10 carbon atoms, or an optionally substituted carbon number. An alkoxy group having 1 to 10 carbon atoms and a siloxy group having 3 to 10 carbon atoms are shown. From the viewpoint of solubility in an electrolytic solution, an alkyl group having 1 to 10 carbon atoms that may be substituted is preferably substituted. Preferred are an alkoxy group having 1 to 10 carbon atoms and a siloxy group having 3 to 10 carbon atoms. R ₄
More preferably, at least one of R ₅ has a functional group selected from an optionally substituted alkoxy group having 1 to 10 carbon atoms and a siloxy group having 3 to 10 carbon atoms.

In the compound (B) represented by the formula (B-2), R ₁ , R ₂ , and R ₃ each independently represent a hydrocarbon group having 1 to 10 carbon atoms, but R ₁ , R ₂ , R ₃ The preferred structure of is the formula (
It is the same as the preferable structure of R ₁ , R ₂ and R _{3 in} the structure represented by B-1).

In the compound (B) represented by the formula (B-3), R ₆ has 1 carbon atom which may be substituted.
To 20 hydrocarbon groups, the hydrocarbon group includes not only an aliphatic hydrocarbon group but also an aromatic hydrocarbon group such as a phenyl group. Further, a fluorine-substituted hydrocarbon group such as a trifluoromethyl group in which all hydrogen atoms in the hydrocarbon group are substituted with fluorine atoms is also included. Further, if necessary, halogen atoms such as fluorine atom, chlorine atom, bromine atom, nitrile group (—CN), ether group (—O—), carbonate group (—OCO ₂ —), ester group (—CO _2- ), carbonyl group (—CO—) sulfide group (—S—), sulfoxide group (
Functional groups such as —SO—), sulfone group (—SO ₂ —), and urethane group (—NHCO ₂ —) can be introduced. Here, the carbon number of R ₆ is 1 to 20, but is preferably 1 or more and 16 or less, more preferably 1 or more and 14 or less, from the viewpoint of improving the cycle performance of the obtained lithium ion secondary battery. .

In addition, R ₆ can preferably have a structure represented by the following formula (B-5). In this case, the basic skeleton of the compound (B) has a dicarboxylic acid derivative structure.

(In the formula (B-5), R ₇ represents an optionally substituted hydrocarbon group having 1 to 13 carbon atoms,
R ₈ represents an optionally substituted hydrocarbon group having 1 to 6 carbon atoms or an optionally substituted trialkylsilyl group having 3 to 6 carbon atoms. )

In the formula (B-5), R ₇ is preferably a methylene group, an ethylene group, a propylene group, a butylene group, a phenyl group, a fluoromethylene group, a fluoroethylene group, from the viewpoint of the chemical stability of the compound (B). Examples include a fluoropropylene group and a fluorobutylene group. Also, the formula (
In B-5), R ₈ is preferably a trialkylsilyl group such as a methyl group, an ethyl group, a vinyl group, an allyl group, a trimethylsilyl group, or a triethylsilyl group from the viewpoint of the chemical stability of the compound (B). Can be mentioned. More preferred are trialkylsilyl groups such as trimethylsilyl group and triethylsilyl group. In particular, when R ₈ is a trialkylsilyl group, the compound (B) has a structure represented by the following formula (B-6).

(In Formula (B-6), R ₁ , R ₂ and R ₃ each independently represents an organic group having 1 to 10 carbon atoms.)

Although it does not specifically limit as a compound (B) contained in the electrolyte solution of this embodiment, As a preferable specific example, phosphorous acid tris (trimethylsilyl), phosphorous acid tris (trimethylsilyl), phosphoric acid tris (triethylsilyl), Tetrakis pyrophosphate (trimethylsilyl)
, Trimethylsilyl polyphosphate, bis (trimethylsilyl) butylphosphonate, bis (trimethylsilyl) propyl phosphonate, bis (trimethylsilyl) ethylphosphonate, bis (trimethylsilyl) methylphosphonate, monomethylbis (trimethylsilyl) phosphate
Monoethylbis (trimethylsilyl) phosphate, mono (trifluoroethyl) bis (trimethylsilyl) phosphate, mono (hexafluoroisopropyl) bis (trimethylsilyl) phosphate, tris (trimethylsilyl) borate, bis (trimethylsilyl) sulfate, trimethylsilyl acetate, Bis (trimethylsilyl) oxalate, bis (trimethylsilyl) malonate
Bis (trimethylsilyl) succinate, bis (trimethylsilyl) itaconate, bis (trimethylsilyl) adipate, bis (trimethylsilyl) phthalate, bis (isophthalate)
Trimethylsilyl) and bis (trimethylsilyl) terephthalate. Among these, from the viewpoint of cycle life and gas generation suppression, tris (trimethylsilyl) phosphate
, Tris phosphite (trimethylsilyl), tetrakis pyrophosphate (trimethylsilyl),
Trimethylsilyl polyphosphate, bis (trimethylsilyl) butylphosphonate, bis (trimethylsilyl) propyl phosphonate, bis (trimethylsilyl) ethylphosphonate, bis (trimethylsilyl) methylphosphonate, monomethylbis (trimethylsilyl) phosphate,
Monoethylbisphosphate (trimethylsilyl) phosphate, mono (trifluoroethyl) bisphosphate (
Trimethylsilyl), mono (hexafluoroisopropyl) bis (trimethylsilyl) phosphate, bis (trimethylsilyl) succinate, bis (trimethylsilyl) itaconate, and bis (trimethylsilyl) adipate are more preferred. However, the compound (B) is not limited to the above.

The electrolyte solution in this embodiment contains 0.01% by mass or more of the compound (B) with respect to the electrolyte solution
It is preferable to contain 0% by mass or less. From the viewpoint of obtaining a good cycle life in the lithium ion secondary battery, the content of the compound (B) is preferably 0.01% by mass or more, and preferably 10% by mass or less from the viewpoint of battery output. From the same viewpoint, the content of the compound (B) is more preferably 0.03% by mass or more and 8% by mass or less, further preferably 0.1% by mass or more and 5% by mass or less, and particularly preferably 0.2% by mass. It is 4 mass% or less. In addition, content of the compound (B) in the electrolyte solution contained in a lithium ion secondary battery is the said compound (
Based on the elements contained in B), for example, ¹ H-NMR, ¹¹ B-NMR, ¹³ C-NMR, ²⁹
It can confirm by performing NMR measurement, such as Si-NMR and ³¹ P-NMR.

In addition, by definition, there is a compound (tris (trimethylsilyl) phosphate, etc.) that overlaps between the compound (B) and the compound (A). For example, tris (trimethylsilyl) phosphate is selected as the compound (B). In this case, the added amount of tris (trimethylsilyl) phosphate is not included in the content of the compound (A) described above.

The lithium ion secondary battery of this embodiment preferably includes a separator between the positive electrode and the negative electrode from the viewpoint of providing safety such as prevention of short circuit between the positive and negative electrodes and shutdown. As the separator, those similar to those provided in known lithium ion secondary batteries can be used, and among them, an insulating thin film having high ion permeability and excellent mechanical strength is preferable. Although it does not specifically limit as a separator, For example, a woven fabric, a nonwoven fabric, and a synthetic resin microporous membrane are mentioned, Among these, a synthetic resin microporous membrane is preferable. The microporous membrane made of synthetic resin is not particularly limited. For example, a polyolefin microporous membrane such as a microporous membrane containing polyethylene or polypropylene as a main component or a microporous membrane containing both of these polyolefins is suitable. Used. Non-woven fabric is not particularly limited, for example, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester,
A porous film made of heat-resistant resin such as aramid is used. The separator may be a single microporous membrane or a laminate of a plurality of microporous membranes, or may be a laminate of two or more microporous membranes.

The lithium ion secondary battery of the present embodiment includes, for example, a separator, a positive electrode and a negative electrode that sandwich the separator from both sides, and a positive electrode current collector that further sandwiches the laminate (disposed outside the positive electrode).
And a negative electrode current collector (arranged outside the negative electrode) and a battery exterior housing them. The laminate in which the positive electrode, the separator, and the negative electrode are laminated can be impregnated with the electrolytic solution in the present embodiment.

FIG. 1 is a schematic cross-sectional view showing an example of a lithium ion secondary battery in the present embodiment. A lithium ion secondary battery 100 shown in FIG. 1 includes a separator 110, a positive electrode 120 and a negative electrode 130 that sandwich the separator 110 from both sides, and a positive electrode current collector 140 that sandwiches a laminate thereof (arranged outside the positive electrode). And a negative electrode current collector 150 (arranged outside the negative electrode) and a battery outer case 160 for housing them. Positive electrode 120, separator 110, and negative electrode 130
Is laminated with the electrolytic solution of the present embodiment.

The lithium ion secondary battery of this embodiment can be produced using the above-described electrolytic solution, positive electrode, negative electrode, and, if necessary, a separator. For example, a plurality of positive electrodes in which a positive electrode and a negative electrode are wound in a laminated state with a separator interposed therebetween to be formed into a laminate having a wound structure, or they are alternately laminated by bending or laminating a plurality of layers. Then, the laminate is formed in a battery case (exterior), and the electrolytic solution of the present embodiment is injected into the case. Is immersed in the electrolytic solution and sealed, a lithium ion secondary battery can be produced. The shape of the lithium ion secondary battery in the present embodiment is not particularly limited, and for example, a cylindrical shape, an elliptical shape, a rectangular tube shape, a button shape,
A coin shape, a flat shape, a laminate shape, and the like are preferably employed.

[Battery manufacturing method]
Although it does not specifically limit as a manufacturing method of the lithium ion secondary battery in this embodiment,
Usually, it can manufacture by inject | pouring electrolyte solution and passing through processes called formation, such as charge / discharge and aging performed on desired conditions after sealing. The formation can also be referred to as a leaving step for stabilizing the battery performance by forming and modifying films on the positive and negative electrode surfaces. The formation step is not particularly limited as long as it is a step for performing treatment for stabilizing the initial performance of the electric storage element, and specifically, for example, a step for performing treatment such as repeated initial charging and charge / discharge. be able to. The formation process is
An aging step may be included. The aging process is not particularly limited as long as the battery is placed in a high temperature atmosphere for a predetermined period, and can be various processes.

The Li-containing phosphorus compound on the surface of the positive electrode of the lithium ion secondary battery in the present embodiment may be formed by any method, but is prepared by injecting an electrolytic solution containing the compound (A) as an example. And the desired Li containing phosphorus compound of this embodiment can be formed in the positive electrode surface by adjusting formation conditions. Preferable formation conditions include injecting the electrolyte solution, charging 50% or more of the full charge capacity at a current value of 0.3 C or less, and then temperature of 35 ° C. or more and 60 ° C. or less and 5 days or more and 10 days or less. It is to be stored in the period. By performing the formation under such conditions, the ratio of the relative element concentration of lithium and phosphorus is 0.3 or more and 4.0 or less, and the ratio of the relative element concentration of transition metal M and phosphorus (M / P) is less than 1. In addition to being able to form a film on the positive electrode, there is a tendency for both better ion conductivity and improved cycle performance to be achieved.

(Positive electrode material)
The positive electrode material in the present embodiment includes the positive electrode active material in the present embodiment and the film in the present embodiment. That is, the positive electrode material in the present embodiment is formed on the surface of the positive electrode active material and the positive electrode active material, and the ratio of the relative element concentrations of lithium and phosphorus (Li / P) is 0.3.
And a film having a Li-containing phosphorus compound having a relative element concentration ratio (M / P) of transition metal M and phosphorus of less than 1 that is 4.0 or less and that is included on the surface of the positive electrode active material. . As described above, the “positive electrode material” in the present specification refers to a positive electrode active material having a film on the surface.
The Li / P and M / P in the positive electrode material of the present embodiment can be obtained by XPS measurement as described above. Further, the Li / P in the positive electrode material of the present embodiment is preferably 0.3 or more and 2.0 or less, more preferably 0.3 or more and 1 from the same viewpoint as described above.
. 5 or less, more preferably 0.35 or more and 1.5 or less, still more preferably 0.35 or more and 1.4 or less, and particularly preferably 0.35 or more and 1.2 or less. Further, the M / P in the positive electrode material of the present embodiment is preferably 0.9 from the same viewpoint as described above.
5 or less, more preferably 0.9 or less, particularly preferably 0.8 or less, and most preferably 0.7 or less. In addition, it can be said that the lithium ion secondary battery of this embodiment is provided with the positive electrode for lithium ion secondary batteries containing the positive electrode material of this embodiment. Since it is comprised in this way, according to the positive electrode material of this embodiment, while being able to express a high voltage, a high cycle life can be expressed.

Hereinafter, the present embodiment will be described more specifically based on Examples and Comparative Examples, but the present embodiment is not limited to these Examples.

(1) Battery performance evaluation by lithium ion secondary battery using LiNi _0.5 Mn _1.5 O ₄ positive electrode [Example 1]
<Synthesis of positive electrode active material>
(Synthesis of LiNi _0.5 Mn _1.5 O ₄ )
Nickel sulfate and manganese sulfate in an amount of 1: 3 as the molar ratio of the transition metal element were dissolved in water to prepare a nickel-manganese mixed aqueous solution so that the total metal ion concentration was 2 mol / L. Subsequently, this nickel-manganese mixed aqueous solution was dropped into 1650 mL of a 2 mol / L sodium carbonate aqueous solution heated to 70 ° C. at an addition rate of 12.5 mL / min for 120 minutes. During dropping, air with a flow rate of 200 mL / min was bubbled into the aqueous solution while stirring. Thereby, a precipitated substance was generated, and the obtained precipitated substance was sufficiently washed with distilled water and dried to obtain a nickel manganese compound. The obtained nickel-manganese compound and lithium carbonate having a particle size of 2 μm were weighed so that the molar ratio of lithium: nickel: manganese was 1: 0.5: 1.5, and obtained after dry-mixing for 1 hour. The obtained mixture was fired at 1000 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material represented by LiNi _0.5 Mn _1.5 O ₄ .

<Preparation of positive electrode>
The positive electrode active material obtained as described above and graphite powder (TIM as a conductive auxiliary agent)
CAL, trade name “KS-6”) and acetylene black powder (Electrochemical Industry, trade name “HS-100”), and a polyvinylidene fluoride solution (made by Kureha,
Trade name “L # 7208”) was mixed at a mass ratio of 85: 5: 5: 5 in terms of solid content. To the obtained mixture, N-methyl-2-pyrrolidone as a dispersion solvent was added so as to have a solid content of 35% by mass and further mixed to prepare a slurry solution. This slurry-like solution was applied to one side of an aluminum foil having a thickness of 20 μm, and the solvent was dried and removed, followed by rolling with a roll press. The rolled product was punched into a disk shape having a diameter of 16 mm to obtain a positive electrode.

<Production of negative electrode>
Graphite powder (made by Osaka Gas Chemical Co., Ltd., trade name “OMAC1.2”) as the negative electrode active material
H / SS ") and another graphite powder (manufactured by TIMCAL, trade name" SFG6 "),
Styrene butadiene rubber (SBR) and a carboxymethyl cellulose aqueous solution were mixed as a binder at a solid content mass ratio of 90: 10: 1.5: 1.8. The resulting mixture is
It added to the water as a dispersion solvent so that solid content concentration might be 45 mass%, and the slurry-like solution was prepared. This slurry-like solution was applied to one side of a copper foil having a thickness of 18 μm, and the solvent was removed by drying, followed by rolling with a roll press. The rolled product was punched into a disk shape having a diameter of 16 mm to obtain a negative electrode.

<Preparation of electrolyte>
Solution containing 1 mol / L of LiPF ₆ salt in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 2 (manufactured by Kishida Chemical Co., Ltd., LBG00069)
To 9.8 g, tris (trimethylsilyl) phosphate as compound A in this embodiment (
An electrolytic solution A was obtained by dissolving 0.2 g of 275794) manufactured by Aldrich. The content of tris (trimethylsilyl) phosphate in the obtained electrolytic solution A was 2% by mass.

<Production of battery>
A laminate in which the positive electrode and the negative electrode produced as described above are superimposed on both sides of a separator (thickness 25 μm, porosity 50%, pore diameter 0.1 μm to 1 μm) made of a polypropylene microporous film is made of stainless steel. It was inserted into a disc-shaped battery case (exterior body) made by the manufacturer. There, the electrolyte A
Was immersed in the electrolytic solution A, and the battery case was sealed to prepare a lithium ion secondary battery before formation.

<Formation>
The obtained lithium ion secondary battery is housed in a thermostatic chamber set at 25 ° C. (trade name “PLM-73S” manufactured by Futaba Kagaku Co., Ltd.), and a charge / discharge device (manufactured by Asuka Electronics Co., Ltd., product name “ACD”). -0
1 ") and allowed to stand for 20 hours. The battery was then fully charged with a constant current of 0.2C. The fully charged state is a state in which the battery is charged at a constant current up to 4.8V and then charged at a constant voltage of 4.8V for 2 hours. Thereafter, the battery in a fully charged state (100% charged) was left in a 45 ° C. constant temperature bath (manufactured by Futaba Kagaku, trade name “PLM-73S”) for 7 days. Next, it is housed in a thermostat set at 25 ° C. (trade name “PLM-73S” manufactured by Futaba Kagaku Co., Ltd.) and connected to a charge / discharge device (trade name “ACD-01” manufactured by Asuka Electronics Co., Ltd.) 3. With a maximum current value of 0.3 C after standing for 2 hours.
After charging with 8V constant current and constant voltage, constant current was discharged to 3V with a current value of 0.2C.

<Battery performance evaluation>
The lithium ion secondary battery obtained through the above formation was housed in a thermostatic bath set to a 50 ° C. environment, connected to a charge / discharge device, and allowed to stand for 2 hours. Next, the battery was charged to 4.8 V with a constant current of 1.0 C and then charged with a constant voltage of 4.8 V for 1 hour. Next, the battery was discharged for 6 minutes at a constant current of 1.0 C, rested for 5 minutes, and then discharged to 3.0 V. This discharge has a final voltage of 6 minutes (V0)
The value (V1−V0) / I obtained by dividing the difference between the voltage (V1) after 2 seconds from the rest and the discharge current (I) was defined as the DC resistance (R1) of this battery. Then, after charging to 4.8V with a constant current of 1.0C, 4.8V
The battery was charged at a constant voltage for 1 hour and discharged to 3.0 V at a constant current of 1.0C. Furthermore, this series of charging / discharging was made into 1 cycle, 49 cycles charging / discharging was repeated, and 50 cycles of cycle charging / discharging was performed in total. Subsequently, the direct current resistance of the battery was measured by the same method as described above, and the direct current resistance R2 after 50 cycles was obtained. The discharge capacity per positive electrode active material mass in the first and 50th charge / discharge cycles, the DC resistance R1 before the charge / discharge cycle evaluation, and the DC resistance R2 after the 50th cycle were obtained. As a result, the initial DC resistance R1 of the battery is 20.2Ω, 50
R2 after the cycle was 62.0Ω. The discharge capacity in the first cycle is 119 mAh /
g, The discharge capacity at the 50th cycle was as high as 98 mAh / g, and the discharge capacity retention rate obtained by dividing the discharge capacity at the 50th cycle by the discharge capacity at the 1st cycle was as high as 82%.

<Analysis of coating>
Separately from the battery evaluation, the lithium ion secondary battery obtained through the formation was disassembled in an argon glove box and the positive electrode was taken out.
Washing was repeated 3 times for 2 minutes in 5 mL of diethyl carbonate, and then dried in an argon glove box. The dried positive electrode is introduced into an XPS measuring apparatus (ESCALAB250 manufactured by Thermo Fisher Co., Ltd.) without contact with the atmosphere, XPS measurement is performed, and the molar ratio Li / P of lithium and phosphorus on the positive electrode surface, and the molar ratio of transition metal and phosphorus M / P was determined. As a result, the Li / P ratio was 0.56 and M / P was 0.06. As XPS measurement conditions, the excitation source is mono. Using AlKα (15 kV × 10 mA), the analysis size is 1 mm,
The measurement was conducted under the conditions of SurveyScan of 0 to 1,100 eV, and NarrowScan of 20 eV. Moreover, when the cross section of the positive electrode surface part was observed with the transmission electron microscope, the striped structure was recognized.

[Example 2]
A lithium ion secondary battery before formation obtained by injecting the electrolytic solution A by the method described in Example 1 was produced, and formation was performed under the following conditions instead of the formation conditions of Example 1. That is, it is housed in a constant temperature bath set at 25 ° C., connected to a charge / discharge device,
Allowed to stand for 20 hours. The battery was then charged at 80% of full charge with a constant current of 0.2C.
Full charge is the amount of charge when charging at a constant current up to the rated voltage followed by charging for 2 hours at the constant voltage of the rated voltage. Thereafter, the 80% charged battery was left in a thermostat set at 45 ° C. for 7 days.
Next, it is housed in a thermostat set at 25 ° C., connected to a charging / discharging device, charged at a constant current of 4.8 V with a maximum current value of 0.3 C, and then constant current up to 3 V at a current value of 0.2 C. Discharged.

Next, the lithium ion secondary battery obtained through the formation was subjected to battery performance evaluation and XPS measurement by the method described in Example 1. As a result, the initial DC resistance R1 is 18.3.
Ω, R2 after 50 cycles was 60.2Ω. The discharge capacity of the first cycle is 120m
The discharge capacity at the 50th cycle was as high as 100 mAh / g, and the discharge capacity retention ratio obtained by dividing the 50th cycle discharge capacity by the first cycle discharge capacity was as high as 83%. . The element molar ratio of the positive electrode surface by XPS measurement is 0.66 for Li / P and 0.05 for M / P.
Met.

[Example 3]
Solution containing 1 mol / L of LiPF ₆ salt in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 2 (manufactured by Kishida Chemical Co., Ltd., LBG00069)
In 9.9 g, 0.1 g of tris (trimethylsilyl) phosphate represented by the formula (3) was dissolved to obtain an electrolytic solution B. The content of tris (trimethylsilyl) phosphate in the obtained electrolytic solution B was 1% by mass.

A lithium ion secondary battery before formation obtained by injecting the electrolytic solution B by the method described in Example 1 was produced, and formation was performed under the following conditions instead of the formation conditions of Example 1. That is, it accommodated in the thermostat set to 25 degreeC, connected to the charging / discharging apparatus, and left still for 20 hours. The battery was then charged at 80% of full charge with a constant current of 0.2C. Full charge is the amount of charge when charging at a constant current up to the rated voltage followed by charging for 2 hours at the constant voltage of the rated voltage. Thereafter, the 80% charged battery was left in a thermostat set at 45 ° C. for 7 days. Next, it is housed in a thermostat set at 25 ° C., connected to a charging / discharging device, charged at a constant current of 4.8 V with a maximum current value of 0.3 C, and then constant current up to 3 V at a current value of 0.2 C. Discharged.

Next, the lithium ion secondary battery obtained through the formation was subjected to battery performance evaluation and XPS measurement by the method described in Example 1. As a result, the initial DC resistance R1 of the battery is 1.
The DC resistance R2 after 6.2 Ω and 50 cycles was 59.0 Ω. The discharge capacity at the first cycle is as high as 121 mAh / g, the discharge capacity at the 50th cycle is as high as 102 mAh / g, and the discharge capacity maintenance ratio obtained by dividing the discharge capacity at the 50th cycle by the discharge capacity at the first cycle is 84
% Was a high value. The element molar ratio by XPS measurement on the positive electrode surface is Li / P ratio of 0.55.
, M / P was 0.05.

[Example 4]
A lithium ion secondary battery before formation obtained by injecting the electrolytic solution B by the method described in Example 1 was produced, and formation was performed under the following conditions instead of the formation conditions of Example 1. That is, it accommodated in the thermostat set to 25 degreeC, connected to the charging / discharging apparatus, and left still for 20 hours. The battery was then charged at 80% of full charge with a constant current of 0.2C. Thereafter, the 80% charged battery was left in a thermostat set at 45 ° C. for 3 days. Then 2
Housed in a thermostatic chamber set at 5 ° C., connected to a charging / discharging device, left for 2 hours, charged with a constant current of 4.8 V at a maximum current value of 0.3 C, and then up to 3 V with a current value of 0.2 C A constant current was discharged.

Next, the lithium ion secondary battery obtained through the formation was subjected to battery performance evaluation and XPS measurement by the method described in Example 1. As a result, the initial DC resistance R1 of the battery is 1.
The DC resistance R2 after 7.3Ω and 50 cycles was 62.3Ω. The discharge capacity at the first cycle is as high as 119 mAh / g, the discharge capacity at the 50th cycle is as high as 97 mAh / g,
The discharge capacity maintenance ratio obtained by dividing the discharge capacity at the 50th cycle by the discharge capacity at the first cycle is 82%.
And showed a high value. The element molar ratio Li / P on the positive electrode surface by XPS measurement was 0.4, and M / P was 0.1.

[Example 5]
A lithium ion secondary battery before formation obtained by injecting the electrolytic solution B by the method described in Example 1 was produced, and formation was performed under the following conditions instead of the formation conditions of Example 1. That is, it accommodated in the thermostat set to 25 degreeC, connected to the charging / discharging apparatus, and left still for 20 hours. The battery was then charged 50% of the full charge with a constant current of 0.2C. Thereafter, the 50% charged battery was left in a thermostat set at 45 ° C. for 7 days. Then 2
Housed in a thermostatic chamber set at 5 ° C., connected to a charging / discharging device, left for 2 hours, charged at a constant current of 4.8 V at a maximum current value of 0.3 C, and then 3 V at a current value of 0.2 C. Discharged up to a constant current.

Next, the lithium ion secondary battery obtained through the formation was subjected to battery performance evaluation and XPS measurement by the method described in Example 1. As a result, the initial DC resistance R1 of the battery is 1.
The DC resistance R2 after 5.4Ω and 50 cycles was 61.0Ω. The discharge capacity at the first cycle is as high as 120 mAh / g, the discharge capacity at the 50th cycle is as high as 98 mAh / g,
The discharge capacity maintenance ratio obtained by dividing the discharge capacity at the 50th cycle by the discharge capacity at the first cycle is 82%.
And showed a high value. The element molar ratio on the surface of the positive electrode measured by XPS is Li / P ratio is 0.49, M
/ P was 0.15.

[Example 6]
Solution containing 1 mol / L of LiPF ₆ salt in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 2 (manufactured by Kishida Chemical Co., Ltd., LBG00069)
In 9.95 g, 0.05 g of tris (trimethylsilyl) phosphate represented by the formula (3) was dissolved to obtain an electrolytic solution C. The content of tris (trimethylsilyl) phosphate in the obtained electrolytic solution C was 0.5% by mass.

A lithium ion secondary battery before formation obtained by injecting the electrolytic solution C by the method described in Example 1 was prepared, and formation was performed under the following conditions instead of the formation conditions of Example 1. That is, it accommodated in the thermostat set to 25 degreeC, connected to the charging / discharging apparatus, and left still for 20 hours. The battery was then charged at 80% of full charge with a constant current of 0.2C. Thereafter, the 80% charged battery was left in a constant temperature bath operating at 45 ° C. for 7 days. Next, it is housed in a thermostat set at 25 ° C., connected to a charging / discharging device, left for 2 hours, charged at a constant current of 4.8 V at a maximum current value of 0.3 C, and then a current value of 0.2 C. At a constant current of 3V.

Next, the lithium ion secondary battery obtained through the formation was subjected to battery performance evaluation and XPS measurement by the method described in Example 1. As a result, the initial DC resistance R1 of the battery is 1.
The DC resistance R2 after 5.0Ω and 50 cycles was 65.0Ω. The discharge capacity at the first cycle is as high as 118 mAh / g, the discharge capacity at the 50th cycle is as high as 95 mAh / g,
The discharge capacity maintenance ratio obtained by dividing the discharge capacity at the 50th cycle by the discharge capacity at the first cycle is 81%.
And showed a high value. Element molar ratio Li / P ratio on the positive electrode surface by XPS measurement is 0.37, M /
P was 0.82.

[Comparative Example 1]
A lithium ion secondary battery before formation obtained by injecting the electrolytic solution A by the method described in Example 1 was prepared, and formation was performed under the following conditions instead of the formation conditions of Example 1. That is, it accommodated in the thermostat set to 25 degreeC, connected to the charging / discharging apparatus, and left still for 20 hours. Next, the battery was fully charged with a constant current of 0.2 C and discharged at a constant current of 3 C with a current value of 0.2 C.

Next, the lithium ion secondary battery obtained through the formation was subjected to battery performance evaluation and XPS measurement by the method described in Example 1. As a result, the direct current resistance R1 of the battery is 25.
The DC resistance R2 after 2Ω and 50 cycles was 157.3Ω. The discharge capacity at the first cycle is 118 mAh / g, and the discharge capacity at the 50th cycle is as low as 80 mAh / g.
The discharge capacity retention ratio obtained by dividing the discharge capacity at the 0th cycle by the discharge capacity at the 1st cycle showed a low value of 68%. Element molar ratio Li / P ratio of positive electrode surface by XPS measurement is 0.24, M / P
Was 0.27.

[Comparative Example 2]
A lithium ion secondary battery before formation obtained by injecting the electrolytic solution A by the method described in Example 1 was prepared, and formation was performed under the following conditions instead of the formation conditions of Example 1. That is, it accommodated in the thermostat set to 25 degreeC, connected to the charging / discharging apparatus, and left still for 20 hours. The battery was then charged 80% with a constant current of 0.2C. Then
The 80% charged battery was left in a thermostat set at 25 ° C. for 7 days. Next, it is housed in a thermostat set at 25 ° C., connected to a charging / discharging device, charged at a constant current of 4.8 V with a maximum current value of 0.3 C, and then constant current up to 3 V at a current value of 0.2 C. Discharged.

Next, the lithium ion secondary battery obtained through the formation was subjected to battery performance evaluation and XPS measurement by the method described in Example 1. As a result, the battery resistance R1 is 27.0Ω.
After 50 cycles, it was 157Ω. The discharge capacity in the first cycle is 120 mAh / g, the discharge capacity in the 50th cycle is as low as 80 mAh / g, and the discharge capacity maintenance ratio obtained by dividing the discharge capacity in the 50th cycle by the discharge capacity in the first cycle is The value was as low as 67%. XPS
The element molar ratio Li / P ratio on the positive electrode surface as measured was 0.2, and M / P was 0.1.

[Comparative Example 3]
A lithium ion secondary battery before formation obtained by injecting the electrolytic solution B by the method described in Example 1 was produced, and formation was performed under the following conditions instead of the formation conditions of Example 1. That is, it accommodated in the thermostat set to 25 degreeC, connected to the charging / discharging apparatus, and left still for 20 hours. The battery was then fully charged with a constant current of 0.2C. Next, after charging at a constant current of 4.8 V with a maximum current value of 0.3 C, a constant current is discharged to 3 V at a current value of 0.2 C.

Next, the lithium ion secondary battery obtained through the formation was subjected to battery performance evaluation and XPS measurement by the method described in Example 1. As a result, the initial DC resistance R1 of the battery is 1.
The DC resistance after 6.4Ω and 50 cycles was 125.4Ω. The discharge capacity at the first cycle is 121 mAh / g, and the discharge capacity at the 50th cycle is as low as 85 mAh / g.
The discharge capacity retention ratio obtained by dividing the discharge capacity at the 0th cycle by the discharge capacity at the 1st cycle showed a low value of 70%. The element molar ratio Li / P on the positive electrode surface by XPS measurement was 0.18, and M / P was 0.19.

[Comparative Example 4]
An electrolyte solution D was obtained by adding 1 mol / L of LiPF ₆ salt to a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 2.

A lithium ion secondary battery before formation obtained by injecting the electrolytic solution D by the method described in Example 1 was produced, and formation was performed under the following conditions instead of the formation conditions of Example 1. That is, it accommodated in the thermostat set to 25 degreeC, connected to the charging / discharging apparatus, and left still for 20 hours. The battery was then fully charged with a constant current of 0.2C. Next, constant current discharge was performed up to 3 V at a current value of 0.2 C.

Next, the lithium ion secondary battery obtained through the formation was subjected to battery performance evaluation and XPS measurement by the method described in Example 1. As a result, the initial DC resistance R1 of the battery is 2
The DC resistance R2 after 4.6Ω and 50 cycles was 70.5Ω. The discharge capacity at the first cycle is 120 mAh / g, the discharge capacity at the 50th cycle is as low as 69 mAh / g,
The discharge capacity retention ratio obtained by dividing the discharge capacity at the 50th cycle by the discharge capacity at the first cycle is 58%.
And showed a low value. Element molar ratio Li / P ratio of the positive electrode surface by XPS measurement is 0.0, M / P
Was 3.0.

[Comparative Example 5]
A lithium ion secondary battery before formation obtained by injecting the electrolytic solution D by the method described in Example 1 was produced, and formation was performed under the following conditions instead of the formation conditions of Example 1. That is, it accommodated in the thermostat set to 25 degreeC, connected to the charging / discharging apparatus, and left still for 20 hours. The battery was then charged at 80% of full charge with a constant current of 0.2C. Full charge is the amount of charge when charging at a constant current up to the rated voltage followed by charging for 2 hours at the constant voltage of the rated voltage. Thereafter, the 80% charged battery was left in a thermostat set at 45 ° C. for 7 days. Next, it is housed in a thermostat set at 25 ° C., connected to a charging / discharging device, charged at a constant current of 4.8 V with a maximum current value of 0.3 C, and then constant current up to 3 V at a current value of 0.2 C. Discharged.

Next, the lithium ion secondary battery obtained through the formation was subjected to battery performance evaluation and XPS measurement by the method described in Example 1. As a result, the DC resistance R1 of the battery is 22.
The DC resistance R2 after 0Ω and 50 cycles was 68.0Ω. The discharge capacity at the first cycle is 122 mAh / g, the discharge capacity at the 50th cycle is as low as 75 mAh / g,
The discharge capacity retention ratio obtained by dividing the discharge capacity at the cycle by the discharge capacity at the first cycle showed a low value of 61%. The element molar ratio Li / P ratio on the positive electrode surface by XPS measurement was 0.01, and M / P was 2.8.

Table 1 shows the specifications of Examples 1 to 6 and Comparative Examples 1 to 5 described above and the results obtained for these.
It shows together with.

As can be seen from Table 1, it was confirmed that the lithium ion secondary battery including the desired film of the present embodiment can operate even at a high voltage and can exhibit a high cycle life.

(2) Battery performance evaluation by lithium ion secondary battery using LiNi _1/3 Mn _1/3 Co _1/3 O ₂ positive electrode [Example 7]
<Preparation of positive electrode>
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (manufactured by Nippon Kagaku Kogyo Co., Ltd.) as a positive electrode active material, acetylene black powder (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, and a polyvinylidene fluoride solution as a binder (Manufactured by Kureha Co., Ltd.) at a solid content mass ratio of 90: 6: 4, N-methyl-2-pyrrolidone as a dispersion solvent is added to a solid content of 40% by mass, and further mixed.
A slurry solution was prepared. This slurry-like solution was applied to one side of an aluminum foil having a thickness of 20 μm, and the solvent was removed by drying, followed by rolling with a roll press to obtain a positive electrode. The rolled product was punched into a disk shape having a diameter of 16 mm to obtain a positive electrode.

<Production of negative electrode>
Graphite powder (made by Osaka Gas Chemical Co., Ltd., trade name “OMAC1.2”) as the negative electrode active material
H / SS ") and another graphite powder (manufactured by TIMCAL, trade name" SFG6 "),
Styrene butadiene rubber (SBR) and a carboxymethyl cellulose aqueous solution were mixed as a binder at a solid content mass ratio of 90: 10: 1.5: 1.8. The resulting mixture is
It added to the water as a dispersion solvent so that solid content concentration might be 45 mass%, and the slurry-like solution was prepared. This slurry-like solution was applied to one side of a copper foil having a thickness of 18 μm, and the solvent was removed by drying, followed by rolling with a roll press. The rolled product was punched into a disk shape having a diameter of 16 mm to obtain a negative electrode.

<Production of battery>
A laminate in which the positive electrode and the negative electrode produced as described above are superimposed on both sides of a separator (thickness 25 μm, porosity 50%, pore diameter 0.1 μm to 1 μm) made of a polypropylene microporous film is made of stainless steel. It was inserted into a disc-shaped battery case (exterior body) made by the manufacturer. Next, 0.2 mL of the electrolytic solution C was injected therein, and the laminate was immersed in the electrolytic solution C. Then, the battery case was sealed to prepare a lithium ion secondary battery before formation.

<Formation>
The lithium ion secondary battery before formation obtained by injecting the electrolytic solution C as described above is housed in a thermostatic bath set to 25 ° C. (trade name “PLM-73S” manufactured by Futaba Kagaku Co., Ltd.)
The battery was connected to a charge / discharge device (trade name “ACD-01” manufactured by Asuka Electronics Co., Ltd.) and allowed to stand for 20 hours. The battery was then charged with 80% of the full charge at a constant current of 0.2C. The full charge amount is a charge amount when charging with a constant current up to 4.35V and subsequently charging with a constant voltage of 4.35V for 2 hours. Next, the 80% charged battery was set to 45 ° C. (Futaba Kagaku, trade name “P
LM-73S ") for 7 days. Next, a constant temperature bath set at 25 ° C. (manufactured by Futaba Science Co., Ltd.,
The product name “PLM-73S”) and the charge / discharge device (manufactured by Asuka Electronics Co., Ltd., product name “AC”)
D-01 ") and left at rest for 2 hours, and then charged at a constant current of 4.35V at a maximum current value of 0.3C, and then discharged at a constant current of 3C at a current value of 0.2C.

<Battery performance evaluation>
The lithium ion secondary battery obtained by the above formation was charged with a constant current of 1.0 C.
. Charge to 35V, then charge at a constant voltage of 4.35V for 1 hour, 3.0 at a constant current of 1.0C
Discharged to V. This series of charging / discharging was made into 1 cycle, and 49 cycles charging / discharging was repeated, and the cycle charging / discharging of 50 cycles was performed in total. The discharge capacity per mass of the positive electrode active material at the first cycle and the 50th cycle was confirmed. Further, a value (ΔV / I) obtained by dividing a difference (ΔV = V3−V4) between a voltage (V3) before discharge and a voltage (V4) 10 seconds after the start of discharge by a discharge current value.
As a direct current resistance value, the direct current resistance value R3 in the first cycle and the direct current resistance R4 in the 50th cycle were confirmed. As a result, the discharge capacity at the first cycle is as high as 160 mAh / g, 5
The discharge capacity at the 0th cycle was as high as 144 mAh / g, and the discharge capacity retention rate obtained by dividing the discharge capacity at the 50th cycle by the discharge capacity at the 1st cycle showed a high value of 90%. The DC resistance R3 at the first cycle was 7Ω, and the DC resistance R4 at the 50th cycle was as low as 10Ω.

The specifications of Example 7 described above and the results obtained for this are also shown in Table 2. The XPS measurement in Example 7 and the derivation of the element molar ratios Li / P and M / P on the positive electrode surface were performed in the same manner as in Example 1.

As can be seen from Table 2, it was confirmed that the lithium ion secondary battery including the desired film of the present embodiment can operate even at a high voltage and can exhibit a high cycle life.

The lithium ion secondary battery of the present invention has industrial applicability to various consumer equipment power supplies, automobile power supplies, and the like.

DESCRIPTION OF SYMBOLS 100 Lithium ion secondary battery 110 Separator 120 Positive electrode 130 Negative electrode 140 Positive electrode collector 150 Negative electrode collector 160 Battery exterior

Claims (9)

A positive electrode containing a positive electrode active material;
A negative electrode containing a negative electrode active material;
An electrolyte solution containing a non-aqueous solvent and a lithium salt;
The transition metal M and phosphorus formed on the surface of the positive electrode and having a relative element concentration ratio (Li / P) between lithium and phosphorus of 0.3 to 4.0 and included in the surface of the positive electrode A film having a Li-containing phosphorus compound having a relative element concentration ratio (M / P) of less than 1;
A lithium ion secondary battery comprising: The lithium ion secondary battery according to claim 1, wherein the Li-containing phosphorus compound is a Li-containing phosphate compound. The positive electrode active material is a compound represented by the following general formula (1); a compound represented by the following general formula (6); and an oxide represented by the following general formula (2A); The lithium ion 2 according to claim 1, which is a composite oxide with an oxide represented by the following formula (1), which is at least one selected from the group consisting of compounds represented by the following general formula (2): Next battery.
_{LiMn 2-x Ma x O 4} (1)
(In the formula, Ma represents one or more selected from the group consisting of transition metals, and 0.2 ≦ x ≦ 0.7.)
LiMO ₂ (6)
(In the formula, M represents one or more selected from transition metals and Al.)
Li ₂ McO ₃ (2A)
(In the formula, Mc represents one or more selected from the group consisting of transition metals.)
LiMdO ₂ (2B)
(In the formula, Md represents one or more selected from the group consisting of transition metals.)
_{zLi 2 McO 3 - (1-} z) LiMdO 2 (2)
(In the formula, Mc and Md are synonymous with those in the general formulas (2A) and (2B), respectively, and 0.1 ≦ z ≦ 0.9). A compound (A) selected from the group consisting of a protonic acid having a phosphorus atom and a compound in which at least one hydrogen atom of the protonic acid having a phosphorus atom is substituted with an alkali metal atom or a trialkylsilyl group; The lithium ion secondary battery of any one of Claims 1-3 contained. The lithium ion secondary battery according to claim 4, wherein the compound (A) includes a compound represented by the following formula (A-1).
(In the formula, X represents a hydrogen atom, an alkali metal atom, or a trialkylsilyl group having 3 to 10 carbon atoms, n is an integer of 0 or 1, and R ₁ and R ₂ are each independently an OH group, an OLi group, and a substituted group. An alkyl group having 1 to 10 carbon atoms which may be substituted, an alkoxy group having 1 to 10 carbon atoms which may be substituted, or a siloxy group having 3 to 10 carbon atoms. The ratio of the relative element concentration of lithium and phosphorus (Li / P) is 0.3 or more and 2.0 or less,
The lithium ion secondary battery of any one of Claims 1-5. The ratio of relative element concentration of lithium and phosphorus (Li / P) is 0.3 or more and 2.0 or less,
And the lithium ion secondary battery of any one of Claims 1-5 which has a striped structure in the said film. The lithium ion secondary battery according to any one of claims 1 to 7, wherein a positive electrode potential based on lithium at full charge is 4.4 V (vsLi / Li ⁺ ) or more. A positive electrode active material;
Formed on the surface of the positive electrode active material, and the ratio of the relative element concentrations of lithium and phosphorus (Li /
P) is 0.3 or more and 4.0 or less, and the transition metal M contained on the surface of the positive electrode active material
And a film having a Li-containing phosphorus compound having a relative element concentration ratio (M / P) of less than 1 and phosphorus,
A positive electrode material.