WO2015072111A1 - Treatment agent for cathode active material, cathode active material composite, method for producing cathode active material composite, cathode, and electricity storage device - Google Patents

Abstract

The objective of the present invention is to provide a technology that can suppress degradation of a storage battery. That which is able to capture sodium and sulfur is used as a treatment agent for treating a Li-transition metal cathode active material containing lithium and a transition metal. The treatment agent is used in a gel form, and the treatment agent is effective because the Li-transition metal cathode active material contains sodium and sulfur as impurities.

Description

Treatment agent for positive electrode active material, positive electrode active material complex, method for producing positive electrode active material complex, positive electrode and power storage device

The present invention relates to a treatment agent for a positive electrode active material used in a power storage device such as a lithium ion secondary battery, a positive electrode active material composite treated with the treatment agent, a method for producing the positive electrode active material composite, and the treatment The present invention relates to a positive electrode using an agent and a power storage device using the positive electrode.

2. Description of the Related Art Power storage devices represented by lithium ion secondary batteries and lithium secondary batteries are conventionally known. The battery capacity of the power storage device may decrease as the power storage device deteriorates over time. And the technique which suppresses degradation of such an electrical storage apparatus is regarded as important when developing an electrical storage apparatus.

As a positive electrode active material for a power storage device, a material containing lithium and a transition metal is known. Hereinafter, a positive electrode active material containing lithium and a transition metal is referred to as a Li-transition metal-based positive electrode active material as necessary. The Li-transition metal-based positive electrode active material generally contains sulfate and sodium hydroxide as part of the raw material (see, for example, Patent Document 1). The Li-transition metal-based positive electrode active material using such raw materials contains sodium (Na) and sulfur (S) as impurities, and these impurities remain in the vicinity of the surface of the Li-transition metal-based positive electrode active material. there is a possibility. However, there are cases where Na and S remaining in the vicinity of the surface of the Li-transition metal-based positive electrode active material can be elements that adversely affect the battery. That is, Na and S can cause deterioration of the power storage device.

JP 2013-144625 A

The present invention has been made in view of the above circumstances, and an object thereof is to provide a technology capable of suppressing deterioration of a power storage device.

As a result of intensive studies, the inventors of the present invention have formulated a positive active material layer by blending a specific treatment agent with a Li-transition metal-based positive electrode active material. It was found that Na and S were trapped. The inventors of the present invention have also found that deterioration of the power storage device can be suppressed by using a positive electrode including a positive electrode active material treated with the treating agent. Furthermore, it has been found that the treatment agent remains as an adhering material on the surface of the positive electrode active material and the adhering material can contribute to suppression of deterioration of the power storage device. Hereinafter, the positive electrode active material treated with the treatment agent is referred to as a positive electrode active material composite as necessary.

The treating agent for positive electrode active material of the present invention that solves the above problems is
A treating agent for treating a Li-transition metal-based positive electrode active material containing lithium and a transition metal,
The Li-transition metal-based positive electrode active material contains sodium and sulfur as impurities,
The treatment agent is capable of capturing the sodium and sulfur.

Moreover, the first positive electrode active material composite of the present invention that solves the above problems is
An adhering material containing an oxide having at least one element selected from the group consisting of Group 3 to Group 5 elements, sulfur, and phosphorus is adhered to the surface of the positive electrode active material.

In addition, the second positive electrode active material composite of the present invention that solves the above problems is
An adhesion material containing at least one selected from the group consisting of Group 3 to Group 5 elements, sulfur, and phosphorus is attached to the surface of the positive electrode active material;
The positive electrode active material is a Li-transition metal-based positive electrode active material containing lithium and a transition metal,
The sulfur is derived from the positive electrode active material.

The method for producing the positive electrode active material composite is represented by the chemical formula: (MO) ₂ P ₂ O ₇ (M is at least one selected from the group consisting of Group 3 to Group 5 elements). A positive electrode active material composite preparation step of heat-treating an active material-gel composite containing a metal phosphate oxide and water gel and a positive electrode active material,
At least one of the gel and the positive electrode active material is a method containing sulfur.

The positive electrode of the present invention that solves the above problems includes any of the positive electrode active material composites of the present invention described above.

The power storage device of the present invention that solves the above-described problems includes any of the positive electrodes of the present invention described above.

The treatment agent for positive electrode active material of the present invention can capture Na and S contained in the Li-transition metal-based positive electrode active material, and suppresses adverse effects on the power storage device due to Na and S, that is, deterioration of the power storage device. obtain. Moreover, according to the positive electrode of the present invention, deterioration of the power storage device can be suppressed. The power storage device of the present invention is excellent in deterioration resistance.

2 is a SEM image of a positive electrode active material treated with the treating agent of Example 1. FIG. 4 is an EDS analysis result regarding a Zr element of a positive electrode active material treated with the treating agent of Example 1. 3 is an EDS analysis result regarding a P element of the positive electrode active material treated with the treating agent of Example 1. 3 is an EDS analysis result regarding S element of the positive electrode active material treated with the treating agent of Example 1. It is an EDS analysis result regarding Na element of the positive electrode active material processed with the processing agent of Example 1. It is a powder X-ray-diffraction (XRD) result of the deposit | attachment in the sample for confirmation tests. _{(ZrO) 2} thermogravimetry of P 2 _{O 7:} is a graph showing the (Thermogravimetry TG) results. 10 shows a TEM image and a STEM analysis result of the positive electrode active material composite of Example 8. FIG. 3 shows a TEM image and a STEM analysis result of the positive electrode active material composite of Example 11.

Hereinafter, modes for carrying out the present invention will be described. Unless otherwise specified, the numerical range “a to b” described in this specification includes the lower limit “a” and the upper limit “b”. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.

If necessary, the treatment agent for the Li-transition metal positive electrode active material of the present invention is simply referred to as a treatment agent. Moreover, the positive electrode containing the positive electrode active material composite material of this invention is called the positive electrode of this invention. The method for producing the positive electrode of the present invention is referred to as the production method of the present invention. Furthermore, a power storage device including the positive electrode of the present invention is referred to as a power storage device of the present invention.

<Positive electrode active material>
As described above, the Li-transition metal-based positive electrode active material to be treated by the treating agent of the present invention contains lithium and a transition metal. The positive electrode of the present invention and the power storage device of the present invention that are treated with the treating agent of the present invention may include a Li-transition metal-based positive electrode active material as at least a part of the positive electrode active material. A positive electrode active material other than the material may be included. Furthermore, the positive electrode active material composite, positive electrode, and power storage device of the present invention described later do not necessarily need to contain a Li-transition metal-based positive electrode active material as the positive electrode active material.

Li- transition metal-based positive active material, for _{example, Li a Ni b Co c Mn} d D e O f layered compounds are preferably used. Note that 0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 <e <1, 1.7 ≦ f ≦ 2.1, D requires S, and Li, Fe, Cr, Cu Zn, Ca, Mg, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, and La may be included. As this type of Li-transition metal-based positive electrode active material, for example, a material containing two or more selected from nickel element (Ni), cobalt element (Co) and manganese element (Mn) is preferably used. Those containing all of Co and Mn are more preferably used.

In addition, as the Li-transition metal-based positive electrode active material, Li ₂ MnO ₃ which is also a layered compound may be used. Other Li-transition metal-based positive electrode active materials include solid solutions composed of spinels such as LiMn ₂ O ₄ and Li ₂ Mn ₂ O ₄ , and mixtures of spinels and layered compounds, LiM ² PO ₄ , LiM ² VO _4. Another example is a polyanionic compound represented by Li ₂ M ² SiO ₄ (wherein M ² is selected from at least one of Co, Ni, Mn, and Fe). ^{_{Moreover, LiFePO 4 F LiM 3 PO 4}} F (M 3 is a transition metal) tavorite based compound represented by such as the ^LiM 3 _BO 3, such LiFeBO ^{₃ (M} ₃ is a transition metal) borate compound represented by It can be cited as a Li-transition metal-based positive electrode active material. The metal oxide used as the Li-transition metal positive electrode active material only needs to contain a lithium element and a transition metal element. For example, the above composition formula may be a basic composition, and a metal element included in the basic composition may be substituted with another metal element.

As the positive electrode active material other than the Li-transition metal-based positive electrode active material that can be used in combination with the Li-transition metal-based positive electrode active material, a material that does not contain a charge carrier may be selected. The charge carrier refers to lithium ions that contribute to charge / discharge. Examples of the positive electrode active material other than the Li-fiber metal positive electrode active material and including no charge carrier include, for example, sulfur alone (S), a compound in which sulfur and carbon are combined, a metal sulfide such as TiS ₂ , Examples thereof include oxides such as V ₂ O ₅ and MnO ₂ , polyaniline and anthraquinone, compounds containing these aromatics in the chemical structure, and conjugated materials such as conjugated diacetate-based organic substances. In addition, other known materials that can be used as the positive electrode active material can also be used. Further, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, phenoxyl, etc. may be adopted as the positive electrode active material. Furthermore, only a positive electrode active material other than these Li-transition metal-based positive electrode active materials may be used as the positive electrode active material. In this case, at least S may be intentionally added to the positive electrode active material.

The Li-transition metal-based positive electrode active material contains Na and S as impurities. The Li-transition metal-based positive electrode active material may contain Na and S as elements. For example, S may exist as sulfate ions. Na may be present as Na carbonate or NaOH. Alternatively, Na may be present as Li contained in the layered compound described above is replaced with Na. Na and S referred to below are concepts including these.

Na and S contained in the Li-transition metal-based positive electrode active material may be contained in the Li-transition metal-based positive electrode active material in any process. That is, as described above, it may be inevitably included in the manufacturing process of the Li-transition metal-based positive electrode active material, or may be unavoidably included. The term “impurity” as used herein means that Na and S are not mainly involved in occlusion and release of lithium ions as charge carriers, and the amounts thereof are not particularly limited. However, if these impurities are excessive, the adverse effect on the power storage device is great, which is not preferable. Therefore, the Li-transition metal-based positive electrode active material to be processed preferably contains an impurity in an amount smaller than the content of the transition metal element. Of course, since these impurities can cause deterioration of the power storage device, the smaller the content of impurities, the better.

Further, a part of Na and / or S desorbed from the Li-transition metal positive electrode active material may be present together with the Li-transition metal positive electrode active material. Alternatively, a part of Na and / or S used as a raw material at the time of manufacture but not constituting the Li-transition metal positive electrode active material may be present together with the Li-transition metal positive electrode active material without being removed. . Furthermore, at least S may be intentionally added to the Li-transition metal-based positive electrode active material. The timing of addition is not particularly limited, and it may be added during the production process of the Li-transition metal-based positive electrode active material, or may be added to the Li-transition metal-based positive electrode active material after production.

In any case, not only Na and / or S constituting a part of the Li-transition metal-based positive electrode active material, but also Na and / or S present together with the Li-transition metal-based positive electrode active material will be described later. It can become a processing target of a processing agent.

<Treatment agent for Li-transition metal positive electrode active material>
The treatment agent of the present invention is not particularly limited as long as it can capture Na and S, and any treatment agent may be used, but it should not adversely affect the power storage device. Specific examples include phosphoric acid compounds. Preferably, the treating agent of the present invention is a gel containing zirconium phosphate oxide represented by (ZrO) ₂ P ₂ O ₇ and water, as will be described later. As will be described in detail in Examples, according to this type of treatment agent, when an electrode is produced, Na and S can be captured in a gel state, that is, in a water-containing state, and a state in which Na and S are retained after drying can be maintained. . The positive electrode active material treated with the treating agent of the present invention is a composite of an adhering material having the treating agent as a precursor and a positive electrode active material, and includes supplemented S in the adhering material.

The processing agent is a phosphoric acid compound _(ZrO) is good containing phosphoric acid zirconium oxide represented by the ₂ P _{2 O 7.} All of the phosphoric acid compound in the treating agent may be (ZrO) ₂ P ₂ O ₇ , but the treating agent may contain a phosphoric acid compound other than (ZrO) ₂ P ₂ O ₇ . As the phosphate compound other than (ZrO) ₂ P ₂ O ₇ , a compound having a phosphate skeleton can be used. The phosphate skeleton here means a structure in which at least three Os are bonded to P, one O is double-bonded to P, and the other at least two Os are bonded to H. The compound having the phosphate skeleton is particularly preferably zirconium phosphate oxide. Specifically, at least one selected from ZrOHPO ₄ , Zr (HPO ₄ ) ₂ , NH ₄ Zr ₂ (PO ₄ ) ₃ , Zr ₂ O (PO ₄ ) ₂ , Zr ₃ (PO ₄ ) ₄ may be mentioned. it can.

The treatment agent of the present invention may be used in any state, but is preferably used in a gel form. Here, the gel form refers to a solid state containing moisture. In addition, a processing agent may contain polar solvents other than water. Examples of the polar solvent include those having a high polarity such as ethanol, methanol, n-propanol, acetone, and dioxane.

By using the treatment agent of the present invention in the form of a gel, there is an advantage that Na and S adhering to the surface of the Li-transition metal-based positive electrode active material can easily come into contact with the treatment agent. In addition, in order to make a processing agent into a gel form, it is preferable to produce | generate a processing agent in water. For example, when the treating agent is zirconium phosphate oxide, gel zirconium phosphate oxide (that is, treating agent) can be obtained by reacting a zirconium source and a phosphate source in water and filtering. In this case, zirconium compounds such as ZrO (NO ₃ ) ₂ .2H ₂ O and ZrOCl ₂ may be used alone or in combination as a zirconium source. Further, as the phosphoric acid source, phosphoric acid compounds such as (NH ₄ ) ₂ HPO ₄ , NH ₄ H ₂ PO ₄ , and H ₃ PO ₄ may be used singly or in combination.

As the treatment agent, one containing another element instead of Zr may be selected. Examples of the element replacing Zr include at least one metal element selected from the group consisting of Group 3 elements, Group 4 elements, and Group 5 elements. More preferably, the metal element is at least one selected from Zr, La, Y, Ti, Ta, and Nb. In this case, the adhering material precursor is represented by the chemical formula: (M ¹ O) ₂ P ₂ O ₇ (M ¹ is at least ^one selected from the group consisting of Group 3 to Group 5 elements). . At least one element selected from the group consisting of Group 3 to Group 5 elements combines with oxygen and forms a compound with phosphoric acid. That is, it can be said that the compound contains an oxide having at least one element selected from the group consisting of Group 3 to Group 5 elements, and P. The compound contains water and forms an amorphous gel. Further, as will be described later, the gel is considered to be crystallized by introducing S during heat treatment or the like.

The above-mentioned compound of Group 3 to Group 5 metal element and phosphoric acid is a precursor of the adhering material. Hereinafter, as necessary, the precursor of the adhesive material is referred to as an adhesive material precursor. Moreover, an above-described gel contains an adhesion material precursor and water, and is equivalent to the processing agent in this invention. This gel is called a treatment agent gel. The treatment agent gel is not only a treatment agent supplemented with S and Na, but also heat treated together with the supplemented S to constitute an adhesive material.

If the treatment agent is zirconium phosphate oxide, the treatment agent gel contains zirconium phosphate oxide and water, and most of the zirconium phosphate oxide exists as a hydrate in the treatment agent gel. The zirconium phosphate oxide is particularly preferably (ZrO) ₂ P ₂ O ₇ . The use of _{(ZrO) 2} P _{2 O 7-hydrate} as a treatment agent gels, on the surface of the positive electrode active material deposited material adheres to the adhering member precursor _{(ZrO) 2 P 2 O 7} . Presence of this adhering material is considered to modify the positive electrode active material and thus suppress deterioration of the power storage device.

Although details are unknown, it is thought that a compound having (ZrO) ₂ P ₂ O ₇ as a basic skeleton of the structure may have excellent ionic conductivity. That is, (ZrO) ₂ P ₂ O _{7 which} is an adhering material precursor can form a compound having excellent ion conductivity. Therefore, an adhering material using (ZrO) ₂ P ₂ O ₇ as a part of the material also has ion conductivity. It is considered excellent. Furthermore, the positive electrode active material (that is, the positive electrode active material composite material) formed by adhering the adhering material to the surface is also considered to have excellent ion conductivity. And it is thought that the battery resistance of an electrical storage apparatus reduces by containing the said positive electrode active material composite material in a positive electrode.

Furthermore, by using (ZrO) ₂ P ₂ O ₇ as an adhesive precursor, it is considered that side reactions occurring on the electrode surface are suppressed. That is, it is considered that (ZrO) ₂ P ₂ O _{7 which} is an adhesive material precursor suppresses a side reaction occurring on the electrode surface when it exists on the electrode surface. As a result, in the power storage device using (ZrO) ₂ P ₂ O ₇ as the positive electrode, the initial charge / discharge efficiency is improved and the storage characteristics are improved. This is supported by the test results disclosed in the patent application filed by the present applicant (Japanese Patent Application No. 2013-016851). Since (ZrO) ₂ P ₂ O ₇ contributes to side reaction suppression in this way, the adhesive material using (ZrO) ₂ P ₂ O ₇ as a precursor also contributes to side reaction suppression, and as a result, the initial stage of the power storage device. Contributes to improved charge / discharge efficiency and storage characteristics. In addition, although S is introduced into the adhesive material in the present invention, it is considered that (ZrO) ₂ P ₂ O ₇ without introduction of S partially remains in the adhesive material. This remaining (ZrO) ₂ P ₂ O ₇ is also considered to exhibit excellent ion conductivity and suppress side reactions occurring on the electrode surface.

Also, the adhering material prevents direct contact between the positive electrode active material and the electrolyte. For this reason, the presence of the adhering material reduces the decomposition of the electrolytic solution caused by the contact between the positive electrode active material and the electrolytic solution. This also improves the cycle characteristics of the power storage device. By these cooperation, the positive electrode of the present invention can suppress deterioration of the power storage device, and the power storage device of the present invention is hardly deteriorated.

By the way, the adhering material having (ZrO) ₂ P ₂ O ₇ as a precursor has a partial structure derived from (ZrO) ₂ P ₂ O ₇ . As will be described later, this partial structure can be confirmed by XRD (powder X-ray diffraction). Therefore, the adhesion material having (ZrO) ₂ P ₂ O ₇ as a precursor can be referred to as zirconium oxide based on this partial structure. In addition, it is estimated that the said adhering material has further the partial structure which P and O couple | bonded, and the partial structure which S and O couple | bonded.

More specifically, the adhering material having (ZrO) ₂ P ₂ O ₇ as a part of the material is presumed to be a compound represented by the chemical formula: (ZrO) _w P ₂ O _x (SO _y ) _z. The In this formula, w, x, y, and z are numbers exceeding 0, respectively. Furthermore, it is considered that 1.8 <w <2.2, 6 <x <8, 0 <y ≦ 4, and 0 <z. Similarly, it can be said that the adhering material containing Group 3 to Group 5 metal other than Zr has a partial structure in which the metal and O are bonded. Therefore, it can be said that the adhesive material in the present invention is a metal oxide. Further, even when the metal is other than Zr, it is presumed that the adhesion material in the present invention has a partial structure in which P and O are bonded and a partial structure in which S and O are bonded.

<Method for producing positive electrode>
The production method of the present invention includes a step of obtaining the above-described positive electrode active material composite. This process is called a positive electrode active material composite preparation process. In the positive electrode active material composite preparation step, a positive electrode active material is brought into contact with a gel containing an adhesive precursor and water (that is, a treatment agent gel), and the active material-gel composite containing the gel and the positive electrode active material is heat-treated. It is a process to do. At least one of the treating agent gel and the positive electrode active material used here contains S. For example, when the positive electrode active material contains S, S contained in the positive electrode active material moves to the treatment agent gel and constitutes the adhesive material together with the adhesive material precursor. More specifically, it is considered that S in the treatment agent gel is introduced into the adhesive precursor as the water evaporates during the heat treatment, and constitutes the adhesive.

It is considered that introduction of S into the adhesive material precursor hardly occurs when the adhesive material precursor is not used in a gel form. That is, when an adhesive precursor and S (for example, sulfate ions as an S source) coexist in a treatment liquid that is excessively present and not in a gel state, S is preferentially dissolved in water. For this reason, when water is removed from the processing solution by filtration or the like, S is also lost from the processing solution together with water. For this reason, in this case, it is difficult to introduce a sufficient amount of S into the adhesive precursor. For example, if the treatment liquid containing excessive water is heat-treated for a long time, it is considered that S dissolved in water moves from water to the adhering material precursor as the water evaporates. The method is inferior in production efficiency. The production method of the present invention has an advantage that S can be efficiently introduced into the adhesive precursor by bringing S into contact with the gel-like adhesive precursor.

S may be included in the positive electrode active material as an unavoidable impurity or may be added to the treatment agent gel. As described above, since the Li-transition metal-based positive electrode active material contains S as an unavoidable impurity or the like, the Li-transition metal-based positive electrode active material is used as the positive electrode active material, and S derived from the positive electrode active material is used as an adhesive precursor. It is more efficient to introduce it into the body.

<Positive electrode>
The positive electrode includes a current collector and a positive electrode active material layer provided on the current collector. The positive electrode active material layer includes a Li-transition metal-based positive electrode active material and a treatment agent, and may include additives such as a binder and a conductive additive. Hereinafter, the positive electrode will be described, but the same applies to the negative electrode in a power storage device described later.

The binder plays a role of connecting the positive electrode active material to the surface of the current collector. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. it can.

Further, a polymer having a hydrophilic group may be employed as the binder. Examples of the hydrophilic group of the polymer having a hydrophilic group include a phosphate group such as a carboxyl group, a sulfo group, a silanol group, an amino group, a hydroxyl group, and a phosphate group.

The blending ratio of the binder in the positive electrode active material layer is preferably a positive electrode active material: binder = 1: 0.005 to 1: 0.3 in mass ratio. This is because when the amount of the binder is too small, the moldability of the positive electrode is lowered, and when the amount of the binder is too large, the energy density of the positive electrode is lowered.

Conductive aid is added to increase the conductivity of the positive electrode. Therefore, the conductive auxiliary agent may be optionally added when the positive electrode has insufficient conductivity, and may not be added when the positive electrode has sufficiently high conductivity. The conductive auxiliary agent may be any chemically inert electronic high conductor, such as carbon black, graphite, acetylene black, ketjen black (registered trademark), vapor grown carbon fiber (Vapor Growth Carbon, carbonaceous fine particles). Fiber: VGCF) and various metal particles are exemplified. These conductive assistants can be added to the positive electrode active material layer alone or in combination of two or more. The mixing ratio of the conductive additive in the positive electrode active material layer is preferably positive electrode active material: conductive auxiliary agent = 1: 0.01 to 1: 0.5 in terms of mass ratio. This is because if the amount of the conductive auxiliary is too small, an efficient conductive path cannot be formed, and if the amount of the conductive auxiliary is too large, the formability of the positive electrode active material layer is deteriorated and the energy density of the electrode is lowered.

In order to form the positive electrode active material layer on the current collector, the positive electrode active material is applied to the surface of the current collector using a dip coating method, a doctor blade method, a spray coating method, a curtain coating method, or the like. It ’s fine. Specifically, a positive electrode active material, and, if necessary, a positive electrode active material layer forming composition (so-called positive electrode mixture, in the case of a negative electrode, a negative electrode mixture) containing a binder and a conductive additive are prepared, and this composition An appropriate solvent is added to the product to form a paste, which is applied to the surface of the current collector and then dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried product may be compressed.

[Current collector]
The current collector in the power storage device of the present invention is a chemically inert electronic high conductor that keeps a current flowing through the electrode during discharging or charging of the power storage device. Examples of the current collector include at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, and molybdenum, or an alloy thereof. Is done. For example, stainless steel can be selected.

The current collector can take the form of a foil, a sheet, a film, a line, a rod, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. Further, a coat layer may be formed on the surface of the current collector. As the material for the coat layer, a material having excellent conductivity is preferably selected. The same applies to the negative electrode.

<Power storage device>
The power storage device of the present invention includes a negative electrode, an electrolytic solution, and, if necessary, a separator in addition to the positive electrode of the present invention.

[Negative electrode]
Similar to the positive electrode, the negative electrode includes a current collector and a negative electrode active material layer provided on the current collector. The negative electrode active material layer includes a negative electrode active material and may include additives such as a binder and a conductive additive.

As the negative electrode active material, a general material that can occlude and release charge carriers can be used. For example, when the power storage device is a lithium ion secondary battery, a material capable of inserting and extracting lithium ions may be selected as the negative electrode active material. More specifically, any element (single element) that can be alloyed with a charge carrier such as lithium, an alloy containing the element, or a compound containing the element may be used.

Specifically, as the negative electrode active material, a group 14 element such as Li, carbon, silicon, germanium or tin, a group 13 element such as aluminum or indium, a group 12 element such as zinc or cadmium, 15 such as antimony or bismuth, etc. A group element, an alkaline earth metal such as magnesium and calcium, and a group 11 element such as silver and gold may be employed alone. When silicon or the like is employed as the negative electrode active material, one silicon atom reacts with a plurality of lithiums, so that a high capacity active material is obtained. On the other hand, however, problems such as significant expansion and contraction of the volume of the negative electrode active material may occur with the insertion and extraction of lithium. Therefore, in order to reduce the fear, it is also preferable to employ an alloy or a compound in which another element such as a transition metal is combined with a simple substance such as silicon as the negative electrode active material.

Specific examples of the alloy or compound include tin-based materials such as Ag—Sn alloy, Cu—Sn alloy and Co—Sn alloy, carbon-based materials such as various graphites, SiO _x (disproportionated into silicon simple substance and silicon dioxide). Examples thereof include silicon-based materials such as 0.3 ≦ x ≦ 1.6), silicon alone, or composites obtained by combining silicon-based materials and carbon-based materials. Further, as the negative electrode active material, oxides such as Nb ₂ O ₅ , TiO ₂ , Li ₄ Ti ₅ O ₁₂ , WO ₂ , MoO ₂ , Fe ₂ O ₃ , or Li _3-x M _x N (M = Co Nitride represented by Ni, Cu) may be employed. One or more of these materials can be used as the negative electrode active material.

[Electrolyte]
The electrolyte solution is not particularly limited as long as the electrolyte solution corresponds to the type of power storage device. For example, if the power storage device of the present invention is a non-aqueous electrolyte secondary battery, an electrolytic solution obtained by dissolving a supporting electrolyte (supporting salt) in an organic solvent may be used. For example, when the power storage device is a lithium ion secondary battery, the organic solvent is an aprotic organic solvent such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl At least one selected from methyl carbonate (EMC) and the like can be preferably selected. In this case, as the supporting electrolyte, it is preferable to use a lithium metal salt that is soluble in an organic solvent. For example, the supporting electrolyte is selected from the group consisting of LiPF ₆ , LiBF ₄ , LIASF ₆ , LiI, LiClO ₄ , and LiCF ₃ SO _3. It is preferable to use at least one kind. The supporting electrolyte is preferably dissolved in the organic solvent at a concentration of about 0.5 mol / L to 1.7 mol / L.

[Separator]
A separator is used in the power storage device as necessary. The separator separates the positive electrode and the negative electrode and allows the charge carrier to pass while preventing a short circuit of current due to contact between the two electrodes. As separators, natural resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polymer), polyester, polyacrylonitrile and other polysaccharides, cellulose, amylose and other polysaccharides, fibroin, keratin, lignin and suberin Examples thereof include porous bodies, nonwoven fabrics, and woven fabrics using one or more electrically insulating materials such as polymers and ceramics. The separator may have a multilayer structure.

セ パ レ ー タ Separator is sandwiched between the positive electrode and the negative electrode described above as necessary to obtain an electrode body. The electrode body may be any of a stacked type in which a positive electrode, a separator and a negative electrode are stacked, or a wound type in which a positive electrode, a separator and a negative electrode are sandwiched. After connecting the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal connected to the outside using a current collecting lead or the like, an electrolytic solution is added to the electrode body to obtain a power storage device It is possible.

The power storage device of the present invention can be applied as various power storage devices such as a secondary battery and a capacitor. The power storage device of the present invention may be charged and discharged within a voltage range suitable for the type of active material contained in the electrode.

The shape of the power storage device of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be employed.

The use of the power storage device of the present invention is not particularly limited, and examples thereof include various home appliances driven by electric power, such as personal computers and portable communication devices, office equipment, industrial equipment, and vehicles.

(Example)
The present invention will be specifically described below based on examples and comparative examples. The present invention is not limited to the following examples and comparative examples. In the following, unless otherwise specified, “part” means part by mass, and “%” means mass%.

Example 1
The treatment agent of Example 1 and the method for producing the treatment agent will be described below. The power storage device of Example 1 is a lithium ion secondary battery that is a kind of non-aqueous electrolyte secondary battery. The treating agent of Example 1 is zirconium phosphate using ZrO (NO ₃ ) ₂ .2H ₂ O as a zirconium source and (NH ₄ ) ₂ HPO ₄ as a phosphoric acid source.

First, ZrO (NO ₃ ) ₂ .2H ₂ O and (NH ₄ ) ₂ HPO ₄ were dissolved in pure water so that the molar ratio of Zr and P was 1: 1. This solution was stirred at room temperature or room temperature for 60 minutes. In the solution under stirring, a gel-like white powder was produced as a precipitate. By filtering this precipitate, a treatment agent gel containing zirconium phosphate oxide and water was recovered. Since the treatment agent gel is only filtered and forms a gel, it naturally includes a certain amount of water. This gel is a treatment agent for treating the positive electrode active material. This gel was used as the treating agent of Example 1.

The positive electrode active material was added to the treating agent gel obtained in the above step and stirred to mix the gel and the positive electrode active material to obtain a positive electrode active material-gel composite. As the positive electrode active material, LiNi _0.5 Co _0.2 Mn _0.3 O ₂ which is a kind of Li-transition metal positive electrode active material was used. Although not shown in the general formula, this positive electrode active material contains trace amounts of Na and S as inevitable impurities. More specifically, the positive electrode active material and the treatment agent gel are mixed with the mass of the positive electrode active material: (the mass of the treatment agent gel, that is, the mass sum of water and zirconium phosphate oxide) = 99.9: 0.1. Weighed out and mixed in a mortar. The amount of zirconium phosphate oxide added at this time was 0.1 mass% when the total mass of the positive electrode active material, zirconium phosphate oxide and water was 100 mass%.

At this time, it is considered that impurities (that is, Na and S) present on the surface of the positive electrode active material are dissolved in water contained in the treatment agent gel and then irreversibly captured by zirconium phosphate oxide. At this time, ethanol may be added according to the viscosity of the mixture so that the treating agent gel and the positive electrode active material are sufficiently kneaded and contacted.

Here, when water is added for viscosity adjustment, even Li contained in the positive electrode active material may be dissolved in water and trapped by the treatment agent. For this reason, it is preferable to select a non-aqueous medium such as ethanol as the viscosity adjusting medium. A mixture of the positive electrode active material and the treating agent gel, that is, the active material-gel composite was dried at 120 ° C. for 6 hours. Through the above steps, a positive electrode active material composite treated with the treating agent of Example 1 was obtained. This positive electrode active material composite was used as the positive electrode active material composite of Example 1. Note that water-insoluble S may also be present on the surface of the positive electrode active material. Water-insoluble S does not dissolve in water contained in the treatment agent gel, but may be taken into zirconium phosphate oxide during heat treatment.

This positive electrode active material was subjected to elemental analysis at an accelerating voltage of 15 kV by energy dispersive X-ray analysis (EDS: Energy dispersive X-ray spectroscopy). An SEM image of the positive electrode active material treated with the treating agent of Example 1 is shown in FIG. In addition, FIGS. 2 to 5 show EDS analysis results of the positive electrode active material treated with the treating agent of Example 1. FIG. Specifically, FIGS. 2 to 5 show the results of elemental analysis at the same position as the position enclosed by the ellipse in FIG. 1, more specifically, the position enclosed by the rectangle within the ellipse. More specifically, FIG. 2 shows an analysis result regarding the Zr element, and a white portion in the drawing is a portion where the Zr element exists. FIG. 3 shows the analysis result regarding the P element, and the white portion in the figure is the portion where the P element exists. FIG. 4 shows the analysis result regarding the S element, and the white part in the figure is the part where the S element exists. FIG. 5 shows the analysis results regarding the Na element, and the white part in the figure is the part where the Na element exists.

From the SEM image in FIG. 1, it can be seen that the positive electrode active material composite of Example 1 has a large number of particulate substances. This material is a positive electrode active material (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ). Then, according to FIG. 1, it can be seen that the _LiNi 0.5 _Co 0.2 _Mn 0.3 _{O 2} of particulate of different materials looks are present in the portion surrounded by a circle.

Also, according to FIG. 2, it can be seen that the Zr element is confirmed at the same position where the substance exists. Furthermore, according to FIG. 3, it can be seen that the P element is further confirmed at the same position where the substance exists. That is, the results shown in FIGS. 1 to 3 indicate that the substance is a compound containing Zr and P, that is, zirconium phosphate oxide.

Also, according to FIG. 4, it can be seen that the S element is confirmed at the same position where zirconium phosphate is present. Furthermore, according to FIG. 5, it can be seen that Na element is further confirmed at the same position where zirconium phosphate oxide is present. 4 and 5, it can be seen that the S element and the Na element are mainly present inside the block of zirconium phosphate oxide. That is, the results shown in FIGS. 1 to 5 indicate that Na and S are present together with zirconium phosphate oxide and are mainly trapped inside the zirconium phosphate oxide.

(Example 2)
The treatment method of Example 2 was the same as that of Example 1 except that the positive electrode active material: hydrated zirconium phosphate oxide was mixed at a mass ratio of 99.5: 0.5. A substance complex was obtained.

Example 3
In the treatment method of Example 3, the positive electrode active material and the water-containing zirconium phosphate oxide (that is, the treatment agent gel) are mixed into the positive electrode active material: water-containing zirconium phosphate oxide = 99.0: 1.0. A positive electrode active material composite of Example 32 was obtained in the same manner as in Example 1 except that the ratio was mixed.

(Comparative Example 1)
LiNi _0.5 Co _0.2 Mn _0.3 O ₂ that was not treated with the treating agent was used as the positive electrode active material of Comparative Example 1.

[Lithium ion secondary battery]
Using the positive electrode active material composites of Examples 1 to 3 and the positive electrode active material of Comparative Example 1, lithium ion secondary batteries were produced.

First, the positive electrode active material composites of Examples 1 to 4 or the positive electrode active material of Comparative Example 1, polyvinylidene fluoride (PVdF) as a binder, and AB as a conductive additive were respectively added to the positive electrode active material composite (or the positive electrode). Active material): binder: conducting aid = 94: 3: 3 is mixed at a mass ratio, and N-methyl-2-pyrrolidone (NMP) as a solvent is further added and mixed to obtain a paste-like positive electrode mixture. Obtained. This paste-like positive electrode mixture was applied to a current collector using a doctor blade. As the current collector, an aluminum foil with a thickness of 20 μm was used. The current collector and the positive electrode mixture applied to the current collector were dried at 80 ° C. for 20 minutes to volatilize and remove NMP. The current collector and the positive electrode mixture after drying were compressed using a roll press. By this step, the aluminum foil and the active material layer were firmly bonded. The bonded product was heated at 120 ° C. for 6 hours using a vacuum dryer, and cut into a predetermined shape to obtain a positive electrode.

By drying at 80 ° C. and vacuum drying at 120 ° C. in the positive electrode preparation step, moisture contained in the treatment agent gel together with zirconium phosphate oxide, that is, adhering water contained in zirconium phosphate oxide is Almost all transpiration, and only the zirconium phosphate from which Na and S were trapped remained in the positive electrode mixture.

Graphite was used as the negative electrode active material. As the binder, a mixture of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) at a mass ratio of 1: 1 was used. Ketjen black (KB) was used as a conductive aid. A negative electrode active material, a binder, and a conductive additive are mixed at a mass ratio of negative electrode active material: binder: conductive aid = 97: 2: 1, and an appropriate amount of ion-exchanged water is added and mixed to form a slurry-like material. A negative electrode mixture was obtained. This negative electrode mixture was applied to a current collector using a doctor blade. A copper foil having a thickness of 20 μm was used as the current collector. The current collector and the negative electrode mixture applied to the current collector were dried and compressed in the same manner as the positive electrode described above, further vacuum dried, and then cut into a predetermined shape to obtain a negative electrode.

As the organic solvent for the electrolytic solution, an organic solvent mixed at a volume ratio of ethylene carbonate (EC): diethyl carbonate (DEC) = 3: 7 was used. LiPF ₆ was used as the supporting salt. This supporting salt was dissolved in an organic solvent so as to be 1 M to obtain an electrolytic solution.

A laminated lithium ion secondary battery was manufactured using the positive electrode, the negative electrode, and the electrolytic solution. Specifically, a rectangular sheet (thickness 25 μm) made of a resin film having a three-layer structure of polypropylene / polyethylene / polypropylene was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then the electrolyte solution was poured into the bag-like laminated film. Thereafter, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. Note that the positive electrode and the negative electrode have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery. Through the above steps, lithium ion secondary batteries of Examples 1 to 3 and Comparative Example 1 were obtained.

[Preservation test]
The lithium ion secondary batteries of Examples 1 to 3 and Comparative Example 1 were subjected to a storage test. Specifically, each battery was charged to 4.32 V and stored at 60 ° C. for 20 days. The discharge capacity was measured before and after the storage test. The rate at the time of measurement was 0.33C, the discharge start voltage was 4.5V, and the discharge end voltage was 3.0V. In addition, 1C means the electric current value which completes discharge in 1 hour by CC discharge (constant current discharge). The percentage of the discharge capacity after the storage test with respect to the discharge capacity before the storage test was determined to obtain the capacity maintenance rate. Table 1 shows capacity retention ratios of the lithium ion secondary batteries of Examples 1 to 3 and Comparative Example 1.

As shown in Table 1, all of the lithium ion secondary batteries of Examples 1 to 3 using the positive electrode active material treated with the treating agent exhibited a high capacity retention rate. Compared to this, the capacity retention rate of the lithium ion secondary battery of Comparative Example 1 using the untreated positive electrode active material was a low value. That is, the lithium ion secondary batteries of Examples 1 to 3 using the positive electrode active material treated with the treating agent are compared with the lithium ion secondary battery of Comparative Example 1 using the untreated positive electrode active material. The lithium ion secondary battery was hardly deteriorated. From this result, it can be said that the deterioration of the lithium ion secondary battery can be suppressed by treating the positive electrode active material with the treatment agent of the present invention.

Also, if the amount of treatment agent added is in the range of 0.1 to 1.0% by mass, it can be said that it is very effective for suppressing deterioration of the lithium ion secondary battery. In addition, when the addition amount of a processing agent is less than 0.05 mass%, it is somewhat inferior to the deterioration effect of a lithium ion secondary battery. Therefore, it can be said that the addition amount of the treatment agent may be 0.05% by mass or more. Moreover, when the addition amount of a processing agent exceeds 1.0 mass%, when producing the slurry of positive electrode compound material, a slurry will be easy to gelatinize. Therefore, when the positive electrode manufacturing workability is taken into consideration, it can be said that the addition amount of the treatment agent is preferably 1.0% by mass or less. Therefore, the preferable addition amount of the additive is 0.05% by mass or more and 1.0% by mass or less.

From a different viewpoint, in the lithium ion secondary batteries of Examples 1 to 3 in which the treating agent and the adhering material made of S were adhering to the positive electrode active material, the lithium ion secondary batteries of Examples 1 to 3 did not have the adhering material. It can be said that suppression of deterioration was seen compared with the lithium ion secondary battery.

By the way, the treating agent used in Examples 1 to 3 is a gel containing an adhesive precursor and water, and the adhesive precursor (that is, zirconium phosphate oxide) has a chemical formula: (ZrO) ₂ P consisting of compounds represented by ₂ O _7. (ZrO) ₂ P ₂ O ₇ may be a commercially available product, or may be produced as in the examples.

That is, a hydrate of (ZrO) ₂ P ₂ O ₇ is obtained by dissolving ZrO (NO ₃ ) ₂ .2H ₂ O and (NH ₄ ) ₂ HPO ₄ .6H ₂ O at a fixed ratio in pure water. It can be deposited. The precipitated hydrate of (ZrO) ₂ P ₂ O ₇ is in a gel state (in other words, a state having poor crystallinity), and contains (ZrO) ₂ P ₂ O _{7 which} is zirconium phosphate oxide and water. If this gel is heat-treated at a temperature of 150 ° C. or higher, the moisture contained therein is reduced. In particular, if the dried gel is baked at 400 ° C. or higher, it is considered that the crystal water of (ZrO) ₂ P ₂ O ₇ hydrate is almost eliminated and the crystallinity is increased.

[Confirmation test]
LiNi _0.5 Co _0.2 Mn _0.3 O ₂ having an average particle diameter of 10 μm was prepared as a positive electrode active material.

As in Example 1, ZrO (NO ₃ ) ₂ .2H ₂ O and (NH ₄ ) ₂ HPO ₄ .6H ₂ O were purified so that the molar ratio of Zr to P was Zr: P = 1: 1. It was dissolved in water to obtain zirconium phosphate oxide. Then, to obtain a treating solution was added to _LiNi 0.5 _Co 0.2 _Mn 0.3 _{O 2} in the solution. The amount of LiNi _0.5 Co _0.2 Mn _0.3 O ₂ added is such that (ZrO) ₂ P ₂ O ₇ is 100% by mass of LiNi _0.5 Co _0.2 Mn _0.3 O _2. The amount was 0.1% by mass.

Thereafter, the mixture was stirred for 1 hour, the treated liquid after the suction was filtered by suction, and the slurry-like filtrate was heat-treated with a 120 ° C. dryer for 12 hours. The filtrate obtained by evaporating water was pulverized using a pestle and mortar, placed in a crucible, and further heat-treated at 400 ° C. for 5 hours. After the heat treatment at 400 ° C., the sample was pulverized with a pestle and a mortar so that the average particle size was about 10 μm to obtain a sample for a confirmation test.

The manufacturing method of this sample is different from the manufacturing methods of Examples 1 to 3 in that the positive electrode active material is not contacted with the previously prepared gel-like zirconium phosphate oxide. However, this sample is formed by adhering a deposit made of zirconium phosphate to the positive electrode active material. Further, the partial structure of zirconium phosphate oxide in the deposit of this sample is highly likely to coincide with the partial structure of zirconium phosphate oxide in the deposits obtained by the manufacturing methods of Examples 1 to 3.

The deposit on this sample was analyzed by powder X-ray diffraction (XRD) (SmartLab, Rigaku). The analysis results are shown in FIG. 6 together with the analysis results of ZrP ₂ O ₇ and (ZrO) ₂ P ₂ O ₇ . From the position of the peak shown in FIG. 6, it was confirmed that the deposit on the sample had a partial structure containing zirconium oxide. That is, the zirconium phosphate oxide used in Examples 1 to 3 is not ZrP ₂ O ₇ but (ZrO) ₂ P ₂ O ₇ , and the adhesive obtained in Examples 1 to 3 Was confirmed to have a partial structure containing zirconium oxide.

[Thermogravimetry (TG) of (ZrO) ₂ P ₂ O ₇ ]
(ZrO) ₂ P ₂ O ₇ for TG measurement was prepared by the following method. In pure water _{ZrO (NO 3) 2 · 2H} 2 O and _{(NH 4)} 2 and _{HPO 4 · 6H 2 O Zr:} P = 1: 1 and so as to put and the solution stirred and dissolved. The mixture was stirred for 1 hour. The solution was filtered with suction, and the filtrate was dried in a dryer at 120 ° C. for 12 hours. This was used as a sample for TG measurement.

The thermogravimetric change of the sample was measured with a thermal analyzer manufactured by TA Instruments. In the TG measurement, the weight change of the sample is measured by raising the temperature from room temperature to 700 ° C. at a constant speed. The original mass was taken as 100%, the mass at each temperature was measured, and the mass at each temperature was compared with the original mass and displayed in%. The TG measurement results are shown in FIG.

As can be seen in FIG. 7, the mass of (ZrO) ₂ P ₂ O ₇ decreased in two steps as the temperature was increased. That is, in the temperature range from room temperature to 150 ° C., the mass of (ZrO) ₂ P ₂ O ₇ decreased at a substantially constant rate, and the decrease in mass once became moderate near 150 ° C. In the temperature range from 150 ° C. to 500 ° C., the mass of (ZrO) ₂ P ₂ O ₇ again decreased at a substantially constant rate. And the change of mass was not seen so much above 500 degreeC. The decrease in mass of (ZrO) ₂ P ₂ O ₇ in the temperature range from room temperature to around 150 ° C. is due to the weight loss due to the desorption of adhering water that was present in the gel and adhered to (ZrO) ₂ P ₂ O _7. I guess. On the other hand, the mass reduction of _{(ZrO) 2} P _{2 O 7} at 0.99 ° C. or higher 500 ° C. or less of the temperature _range, that's mass reduction due to _{the (ZrO) 2} P ₂ crystal water contained in the _{O 7} is eliminated Guessed.

That is, from this result, it was found that the water contained in the gel-like (ZrO) ₂ P ₂ O ₇ was at least partially desorbed at a temperature of 150 ° C. or higher and almost all was desorbed at 400 ° C. or higher.

Example 4
The treating agent of Example 4 was the same zirconium phosphate oxide as that of Example 1. The positive electrode active material A used in the treatment method of Example 4 is LiNi _0.5 Co _0.2 Mn _0.3 O ₂ which is a kind of Li-transition metal positive electrode active material. This positive electrode active material A contains trace amounts of Na and S as inevitable impurities. Moreover, content of S of this positive electrode active material A was 0.06 mass%. LiOH and Li ₂ CO ₃ , which are a kind of Li compound, were attached to the surface of the positive electrode active material A. The adhesion amount of LiOH was 0.13% by mass, and the adhesion amount of Li ₂ CO ₃ was 0.23% by mass. In addition, the adhesion amount here is mass ratio which made the total amount of the positive electrode active material crude product containing impurities, such as Na, S, and Li compound, 100 mass%.

The positive electrode active material A described above was added to a treatment agent gel containing zirconium phosphate oxide and water. The amount of zirconium phosphate oxide added at this time was the mass of the positive electrode active material A: (mass of water and zirconium phosphate oxide) = 99.9: 0.1. A mixture of the positive electrode active material A and the treating agent gel, that is, the active material-gel composite was heated at 120 ° C. for 6 hours to perform a one-step heat treatment. The positive electrode active material composite of Example 4 was obtained through the above steps.

(Example 5)
The treating agent of Example 5 was the same zirconium phosphate oxide as that of Example 1. In Example 5, the same positive electrode active material A as in Example 4 was used.

The amount of zirconium phosphate oxide added in the treatment method of Example 5 was the mass of the positive electrode active material A: (mass of water and zirconium phosphate oxide) = 99.9: 0.1. A mixture of the positive electrode active material A and the treating agent gel was first heated at 120 ° C. for 6 hours, and then heated at 400 ° C. for 6 hours to perform two-stage heat treatment. The positive electrode active material composite of Example 5 was obtained through the above steps.

(Example 6)
The treating agent of Example 6 was the same zirconium phosphate oxide as that of Example 1. In Example 6, the same positive electrode active material A as in Example 4 was used.

The amount of zirconium phosphate oxide added in the treatment method of Example 6 was mass of positive electrode active material A: (mass of water and zirconium phosphate oxide) = 99.9: 0.5. The mixture of the positive electrode active material A and the treatment agent gel was subjected to one-stage heat treatment in the same manner as in Example 4. The positive electrode active material composite of Example 6 was obtained through the above steps.

(Example 7)
The treating agent of Example 7 was the same zirconium phosphate oxide as that of Example 1. In Example 7, the same positive electrode active material A as in Example 4 was used.

The addition amount of zirconium phosphate oxide in the treatment method of Example 7 was mass of positive electrode active material A: (mass sum of water and zirconium phosphate oxide) = 99.9: 0.5. The mixture of the positive electrode active material A and the treatment agent gel was subjected to two-stage heat treatment in the same manner as in Example 5. The positive electrode active material composite of Example 7 was obtained through the above steps.

(Comparative Example 2)
The positive electrode active material of Comparative Example 2 was the same positive electrode active material A as used in Example 4. The positive electrode active material of the comparative collar 2 is not subjected to treatment with a treatment agent.

(Example 8)
The treating agent of Example 8 was the same zirconium phosphate oxide as that of Example 1. The positive electrode active material B used in the treatment method of Example 8 is LiNi _0.5 Co _0.2 Mn _0.3 O ₂ which is a kind of Li-transition metal positive electrode active material. This positive electrode active material B contains trace amounts of Na and S as inevitable impurities. Further, the content of S in the positive electrode active material B was 0.11% by mass. The amount of LiOH deposited on the positive electrode active material B was 0.06% by mass, and the amount of Li ₂ CO ₃ deposited was 0.12% by mass.

In Example 8, the addition amount of zirconium phosphate oxide was the mass of the positive electrode active material B: (mass sum of water and zirconium phosphate oxide) = 99.9: 0.1. The mixture of the positive electrode active material B and the treatment agent gel was subjected to one-stage heat treatment in the same manner as in Example 4. The positive electrode active material composite of Example 8 was obtained through the above steps.

Example 9
The treating agent of Example 9 was the same zirconium phosphate oxide as that of Example 1. In Example 9, the same positive electrode active material B as in Example 8 was used.

In Example 9, the addition amount of zirconium phosphate oxide was the mass of the positive electrode active material B: (mass sum of water and zirconium phosphate oxide) = 99.9: 0.1. The mixture of the positive electrode active material B and the treatment agent gel was subjected to two-stage heat treatment in the same manner as in Example 5. The positive electrode active material composite of Example 9 was obtained through the above steps.

(Example 10)
The treating agent of Example 10 was the same zirconium phosphate oxide as that of Example 1. In Example 10, the same positive electrode active material B as in Example 8 was used.

In Example 10, the addition amount of zirconium phosphate oxide was the mass of the positive electrode active material B: (mass sum of water and zirconium phosphate oxide) = 99.9: 0.5. The mixture of the positive electrode active material B and the treatment agent gel was subjected to one-stage heat treatment in the same manner as in Example 4. The positive electrode active material composite of Example 10 was obtained through the above steps.

(Example 11)
The treating agent of Example 11 was the same zirconium phosphate oxide as that of Example 1. In Example 11, the same positive electrode active material B as in Example 8 was used.

In Example 11, the addition amount of zirconium phosphate oxide was the mass of the positive electrode active material B: (mass sum of water and zirconium phosphate oxide) = 99.9: 0.5. The mixture of the positive electrode active material B and the treatment agent gel was subjected to two-stage heat treatment in the same manner as in Example 5. The positive electrode active material composite of Example 11 was obtained through the above steps.

[Lithium ion secondary battery]
Production method of lithium ion secondary batteries of Examples 1 to 3 and Comparative Example 1 using the positive electrode active material composites of Examples 8 to 11 and the positive electrode active materials of Comparative Examples 2 and 3 Lithium ion secondary batteries of Examples 8 to 11, Comparative Example 2 and Comparative Example 3 were produced by the same method as described above.

[Preservation test]
The lithium ion secondary batteries of Examples 8 to 11, Comparative Example 2 and Comparative Example 3 were subjected to a storage test. Specifically, each battery was charged to 4.32 V and stored at 60 ° C. for 6 days. Thereafter, the lithium ion secondary battery was CCCV charged (constant current constant voltage charging) under the conditions of a charge rate of 1C, a charge end voltage of 4.5V, and 2.5 hours. And the discharge capacity (namely, capacity after a test) of the lithium ion secondary battery after charge was measured. The lithium ion secondary battery before storage was similarly charged to 4.5 V, and the discharge capacity (that is, the initial capacity) was measured. The measurement conditions were a discharge rate of 0.33 C, a discharge start voltage of 4.5 V, a discharge end voltage of 3.0 V, and a CCCV discharge of 5 hours.

The percentage of the discharge capacity after the storage test with respect to the discharge capacity before the storage test was determined to obtain the capacity maintenance rate. Table 2 shows the capacity retention rates of the lithium ion secondary batteries of Examples 8 to 11, Comparative Example 2 and Comparative Example 3. In Table 2, the initial capacity (mAh / g) refers to the discharge capacity of each lithium ion secondary battery before the storage test. The post-test capacity (mAh / g) refers to the discharge capacity after the storage test.

As shown in Table 2, the power storage devices of Example 4 and Example 5 in which the treatment agent was used in an amount of 0.1% by mass maintained the capacity compared to the power storage device of Comparative Example 2 that did not use the treatment agent. Excellent rate. Similarly, the power storage devices of Example 8 and Example 9 in which the treatment agent was used in an amount of 0.1% by mass are superior in capacity retention rate compared to the power storage device of Comparative Example 3 in which no treatment agent was used. From this result, it can be said that the positive electrode active material composite of the present invention obtained by treatment with the treatment agent can suppress the deterioration of the power storage device as compared with the untreated positive electrode active material.

In addition, as shown in Table 2, in terms of improving the capacity retention ratio after storage, if the amount of the treatment agent is excessive, the deterioration suppressing effect is less likely to appear compared to the case where an untreated positive electrode active material is used. There is a case. This is presumably because the amount of the adhering material itself finally formed on the surface of the positive electrode active material particles is related to the amount of S contained in the adhering material.

For example, the positive electrode active material B shown in Table 2 has not only a large amount of S but also a small amount of Li ₂ CO _{3 on the} surface of the positive electrode active material. Li ₂ CO ₃ prevents contact between the positive electrode active material, S contained in the positive electrode active material, and the adhesive precursor. Therefore, when the positive electrode active material B is used, it is considered that the efficiency of taking in the S of the adhesive precursor is improved. For this reason, when the positive electrode active material B is used, as the amount of the treatment agent increases and the amount of the adhering material precursor increases, the effect of suppressing the deterioration of the power storage device increases.

Furthermore, the material state of the adhering material formed after the heat treatment is predicted to change depending on the amount of S contained, and it is considered that the Li ion conductivity is particularly changed. Since the adhering material of the present invention has excellent Li ion conductivity, even if it adheres to the active material surface, it does not hinder the movement of Li ions, so that it can absorb and release Li ions with high efficiency while protecting the positive electrode active material. A possible positive electrode is realized and the life characteristics are improved. However, the adhering material containing excessive S is expected to be in a state where excessive S interferes with the conduction of Li ions. As a result, when the adhering material contains an excessive amount of S, even if the positive electrode active material can be protected by the adhering material, there is a possibility that the efficiency of absorbing and releasing Li is reduced in the positive electrode. As a result, the battery capacity is likely to be reduced.

And, in order to improve the capacity maintenance ratio after storage, it is considered that there is an optimum range for the S content of the adhering material. It is considered that the preferable range of the S content is determined according to the amount of phosphoric acid oxidation Zr that governs the molecular structure of the adhering material. Specifically, it is considered that the S content of the adhering material is preferably 5 to 20 (atomic%). This is a ratio in which P, Zr, and S are 100 atomic%. More preferably, the S content is in the range of 8 to 16 atomic%, and more preferably in the range of 10 to 14 atomic%.

As shown in Example 6 of Table 2, when the S content is small, the capacity retention rate is improved even if the amount of the treatment agent is increased. Therefore, it can be said that the amount of the treating agent can be appropriately set according to the amount of S in the active material-gel complex.

Also, from the results in Table 2, it can be seen that the heating method during the heat treatment also affects the capacity retention rate after the storage test. That is, the capacity retention rate after storage differs between the case where the one-step heat treatment is performed at 120 ° C. and the case where the two-step heat treatment is performed at 120 ° C. → 400 ° C. Considering only the improvement of the capacity retention rate after storage, it is preferable to perform a one-step heat treatment. The temperature of the first stage heat treatment is preferably around 120 ° C., specifically 100 ° C. or more and 150 ° C. or less. The temperature of the second stage heat treatment is preferably higher than 150 ° C. and around 400 ° C., specifically 180 ° C. or higher and 500 ° C. or lower.

The positive electrode active material composite of Example 8 and the positive electrode active material composite of Example 11 were each imaged with a TEM (Transmission Electron Microscope). The TEM image of the positive electrode active material composite of Example 8 and the result of STEM analysis described later are shown in FIG. 8, and the TEM image of the positive electrode active material composite of Example 11 and the result of STEM analysis are shown in FIG.

In the TEM images, the area surrounded by a square was further analyzed by STEM (Scanning Transmission Electron Microscope). There is an adhering material in this portion, and the content of each element in the adhering material can be analyzed by STEM. Furthermore, Table 3 shows the content of each element in the adhering material of the positive electrode active material composites of Example 8 and Example 11. “Element content (%)” in Table 3 is a value where the sum of the element contents of Zr, P and S is 100%. Hereinafter, as necessary, the adhering material of the positive electrode active material composite of each example is abbreviated as the adhering material of each example.

As shown in FIGS. 8 and 9, the adhesive material of Example 11 had a greater intensity ratio of S peak (II) to P and Zr peaks (I) than the adhesive material of Example 8. In other words, the adhesive material of Example 11 has a higher elemental content of S relative to P and Zr than the adhesive material of Example 8. Specifically, in the adhesive material of Example 11, {(P element content + Zr element content) / 2} :( S element content) = 3.5: 1, whereas Example 8 In the adhering material, {(P element content + Zr element content) / 2} :( S element content) = 1.8: 1. That is, the adhesive material of Example 11 has about 3.5 atoms of P and Zr per S of one atom. On the other hand, the adhesive of Example 8 has about 1.8 atoms of P and Zr per S of one atom. This is considered to be caused by the amount of the treating agent and the heat treatment conditions when manufacturing each positive electrode active material composite.

That is, the adhesive material of Example 11 uses a larger amount of treatment agent during the manufacture than the adhesive material of Example 8. For this reason, as described above, it is considered that S contained in the positive electrode active material particles moves to the surface of the positive electrode active material and is further taken into the treatment agent to constitute a part of the adhering material. Moreover, since the adhesive material of Example 11 was heat-treated in two stages of low temperature and high temperature, and the adhesive material of Example 8 was heat-treated only in one stage of low temperature, the above-described movement of S It is estimated that this also occurs in the heating process.

Further, as described in the section of _[(ZrO) thermogravimetry of ₂ P 2 _{O 7],} by heating at 400 around ℃ was heat-treated in two _steps, crystallization of _{(ZrO) 2} P _{2 O 7} Progresses. At this time, S is considered to be firmly integrated into the crystal structure derived from (ZrO) ₂ P ₂ O ₇ . Specifically, it is speculated that S is chemically bonded to (ZrO) ₂ P ₂ O ₇ . For this reason, it is considered that the two-stage heat treatment causes the adhering material to have a regular crystal structure, and the path of Li ions inside the adhering material is configured regularly, and as a result, the diffusibility of Li is improved. The adhering material after the first stage heat treatment is excellent in Li ion conductivity as described above, but is considered to be in a state of poor regularity in terms of structure. Specifically, the adhering material after the first stage heat treatment is excellent in the function of capturing and transmitting Li ions, but the structure regularity is poor. For this reason, there are few passages through which Li ions can easily pass inside the adhering material, and it is considered that the adhering material does not have sufficient Li ion diffusibility. Therefore, it is considered that the diffusibility of Li ions inside the adhering material can be improved by performing the second heat treatment to promote the crystallization of the adhering material.

Furthermore, according to Table 2, a larger initial capacity was obtained in the case where the heat treatment was performed in two stages than in the case where the heat treatment was performed in one stage in all cases. Than the initial capacity has increased. This can be understood to be due to the above-described effect of improving the diffusibility of Li ions. That is, it can be said that the second stage heat treatment has an effect of improving the initial capacity. On the other hand, it is predicted from Table 2 that excessive crystallization deteriorates the Li ion conductivity and deteriorates the life characteristics.

That is, the S content of the positive electrode active material, the amount of the treating agent, and the temperature of the heat treatment can be appropriately set according to the characteristics required for the power storage device. In any case, the positive electrode and the power storage device of the present invention have the effect of improving the initial capacity derived from the adhering material and suppressing the life deterioration.

Claims (25)

1. A treating agent for treating a Li-transition metal-based positive electrode active material containing lithium and a transition metal,
   The Li-transition metal-based positive electrode active material contains sodium and sulfur as impurities,
   The treatment agent is a treatment agent for a Li-transition metal-based positive electrode active material capable of capturing the sodium and sulfur.
2. The treatment agent for a Li-transition metal-based positive electrode active material according to claim 1, wherein the treatment agent is in a gel form.
3. The treatment agent for a Li-transition metal-based positive electrode active material according to claim 1 or 2, wherein the treatment agent contains a phosphate compound.
4. The Li-transition metal-based positive electrode according to any one of claims 1 to 3, wherein the Li-transition metal-based positive electrode active material includes two or more selected from nickel, cobalt, and manganese as a transition metal. Treatment agent for active material.
5. The treatment agent for a Li-transition metal-based positive electrode active material according to any one of claims 1 to 4, wherein the treatment agent contains zirconium phosphate oxide.
6. A current collector and a positive electrode active material layer provided on the current collector,
   6. The positive electrode active material layer includes a Li-transition metal-based positive electrode active material containing lithium and a transition metal, and a treatment agent for a Li-transition metal-based positive electrode active material according to any one of claims 1 to 5. And a positive electrode.
7. A positive electrode active material composite in which an adhering material containing at least one element selected from the group consisting of Group 3 to Group 5 elements, sulfur, and phosphorus is attached to the surface of the positive electrode active material Wood.
8. The adhering material includes a metal phosphate oxide represented by a chemical formula: (MO) ₂ P ₂ O ₇ (M is at least one selected from the group consisting of Group 3 to Group 5 elements) as a precursor. The positive electrode active material composite according to claim 7.
9. The positive electrode active material composite according to claim 8, wherein the positive electrode active material composite is obtained by heat-treating an active material-gel composite containing a positive electrode active material and a gel containing the precursor and water.
10. The positive electrode active material is a Li-transition metal-based positive electrode active material containing lithium and a transition metal,
    The positive electrode active material composite according to any one of claims 7 to 9, wherein the sulfur is derived from the positive electrode active material.
11. The positive electrode active material composite according to any one of claims 7 to 10, wherein the Group 3 to Group 5 elements are Zr, La, Y, Ti, Ta, and Nb.
12. The positive electrode active material composite according to claim 10 or 11, wherein the Li-transition metal-based positive electrode active material contains two or more kinds selected from nickel, cobalt, and manganese as a transition metal.
13. An adhesion material containing at least one selected from the group consisting of Group 3 to Group 5 elements, sulfur, and phosphorus is attached to the surface of the positive electrode active material;
    The positive electrode active material is a Li-transition metal-based positive electrode active material containing lithium and a transition metal,
    The positive electrode active material composite in which the sulfur is derived from the positive electrode active material.
14. 14. The positive electrode active material composite according to claim 13, wherein at least one selected from the group consisting of the Group 3 to Group 5 elements constitutes an oxide.
15. The adhering material includes a metal phosphate oxide represented by a chemical formula: (MO) ₂ P ₂ O ₇ (M is at least one selected from the group consisting of Group 3 to Group 5 elements) as a precursor. The positive electrode active material composite according to claim 13 or 14.
16. 16. The positive electrode active material composite according to claim 15, wherein the positive electrode active material composite is obtained by heat-treating an active material-gel composite containing a positive electrode active material and a gel containing the precursor and water.
17. The positive electrode active material composite according to any one of claims 13 to 16, wherein the Group 3 to Group 5 elements are Zr, La, Y, Ti, Ta, and Nb.
18. The positive electrode active material composite according to any one of claims 13 to 17, wherein the Li-transition metal-based positive electrode active material includes two or more selected from nickel, cobalt, and manganese as a transition metal.
19. A gel comprising a metal phosphate oxide represented by a chemical formula: (MO) ₂ P ₂ O ₇ (M is at least one selected from the group consisting of Group 3 to Group 5 elements) and water, and a positive electrode A positive electrode active material composite preparation step of heat-treating an active material-gel composite containing the active material,
    A method for producing a positive electrode active material composite in which at least one of the gel and the positive electrode active material contains sulfur.
20. The positive electrode active material composite according to claim 19, wherein in the positive electrode active material composite preparation step, the active material-gel composite is heated to 100 ° C or higher and 150 ° C or lower, and then heated to 180 ° C or higher and 500 ° C or lower. Manufacturing method.
21. The positive electrode active material is a Li-transition metal-based positive electrode active material containing lithium and a transition metal,
    The method for producing a positive electrode active material composite according to claim 19 or 20, wherein the sulfur is derived from the positive electrode active material.
22. The method for producing a positive electrode active material composite according to any one of claims 19 to 21, wherein the Group 3 to Group 5 elements are Zr, La, Y, Ti, Ta, and Nb.
23. 23. The method for producing a positive electrode active material composite according to claim 21, wherein the Li-transition metal-based positive electrode active material contains two or more selected from nickel, cobalt, and manganese as a transition metal.
24. A current collector and a positive electrode active material layer provided on the current collector,
    A positive electrode comprising the positive electrode active material composite according to any one of claims 7 to 18.
25. A power storage device including the positive electrode according to claim 6 or 24.

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