WO2018084046A1

WO2018084046A1 - Lithium ion secondary battery, manufacturing method for same, and precursor for lithium ion secondary battery

Info

Publication number: WO2018084046A1
Application number: PCT/JP2017/038481
Authority: WO
Inventors: 阿部　浩史; 石澤　政嗣
Original assignee: マクセルホールディングス株式会社
Priority date: 2016-11-02
Filing date: 2017-10-25
Publication date: 2018-05-11

Abstract

Provided are a lithium ion secondary battery having excellent charge/discharge cycle characteristics, a manufacturing method for the same, and a precursor for constituting the lithium ion secondary battery. The precursor for a lithium ion secondary battery of the present invention is obtained by housing, in an outer casing, a negative electrode having a negative electrode mixture layer, a positive electrode having a positive electrode mixture layer, and a separator; wherein the negative electrode mixture layer contains at least a negative electrode active material doped with Li ions, the positive electrode mixture layer contains, as a positive electrode active material, a metal oxide constituted by Li and a metal M different from the Li, and the separator has a porous membrane (I) comprising mainly a thermoplastic resin, and a porous layer (II) comprising mainly a filler with a heat resistance temperature of 150°C or higher. The lithium ion secondary battery of the present invention is constituted by the precursor of the present invention and a non-aqueous electrolyte, and the molar ratio (Li/M) of the Li and the metal M different from the Li contained in the positive electrode active material when discharged under specific conditions is 0.8 to 1.05.

Description

Lithium ion secondary battery, its manufacturing method and lithium ion secondary battery precursor

The present invention relates to a lithium ion secondary battery having excellent charge / discharge cycle characteristics, a method for producing the same, and a precursor for constituting the lithium ion secondary battery.

Since lithium ion secondary batteries have high voltage and high capacity, there are great expectations for their development. Particularly recently, improvements have been made not only to positive electrode active materials and negative electrode active materials involved in battery reactions and non-aqueous electrolytes, but also to binders used in positive electrodes and negative electrodes.

For example, in Patent Documents 1 and 2, by using a copolymer of vinyl alcohol and an alkali metal neutralized ethylenically unsaturated carboxylic acid as a binder for the negative electrode mixture layer, the negative electrode active material can be removed or the negative electrode composite can be removed. A technique for suppressing peeling of the agent layer from the current collector has been proposed.

By the way, recently, a further increase in capacity has been desired for a lithium-ion secondary battery for portable devices that has been downsized and multifunctional, and in response to this, a negative electrode active material has been used as a widely used graphite. In addition, it is also considered to change to a material that can accommodate more Li, such as low crystalline carbon, Si (silicon), Sn (tin), etc. (hereinafter also referred to as “high capacity negative electrode material”). Yes.

However, since a high capacity negative electrode material generally has a very large volume change amount due to charging / discharging, there is a risk that the battery characteristics may be rapidly deteriorated by repeated charging / discharging.

For these reasons, in a non-aqueous secondary battery such as a lithium ion secondary battery using a high-capacity negative electrode material, a technique for solving the problem caused by the volume change of the negative electrode accompanying charge / discharge has been studied. For example, in Patent Document 3, as a binder for the negative electrode, SiO _x which is a high capacity negative electrode material and a conductive auxiliary agent are more firmly bonded than a conventionally used styrene butadiene rubber (SBR) or carboxymethyl cellulose (CMC). By using polyimide, polyamideimide, and polyamide that can be produced, it is possible to suppress the decrease in conductivity in the negative electrode mixture layer by separating the SiO _x particles from the conductive auxiliary agent due to charge / discharge of the battery, resulting in a decrease in battery characteristics. Non-aqueous secondary batteries that suppress the above have been proposed.

In addition, in a battery configured using a high-capacity negative electrode material, in general, among Li released from the positive electrode by charging, a large proportion of the lithium that is taken into the high-capacity negative electrode material and remains without being discharged at the next discharge, There is a tendency that the capacity that the battery originally has cannot be drawn out sufficiently.

In order to reduce the irreversible capacity of such a battery, the negative electrode (negative electrode mixture layer) is doped with Li ions (pre-doping) to increase the proportion of Li that can travel between the positive electrode and the negative electrode during charge / discharge of the battery. Technology is also being considered. As such a pre-doping technique of Li ions into the negative electrode, as described in Patent Document 4, in addition to means for pre-doping Li ions into the negative electrode in the battery (hereinafter sometimes referred to as “in-system pre-doping”). In addition, means for assembling a battery using a negative electrode pre-doped with Li ions in advance (hereinafter, pre-doping of Li ions into the negative electrode by such means may be referred to as “outside pre-doping”) has also been proposed.

International Publication No. 2014/207967 Japanese Patent Laying-Open No. 2015-8147 International Publication No. 2009/063902 JP 11-283670 A

In the means for configuring the battery using the negative electrode obtained through the pre-doping outside the system, it is easy to control the doping amount of Li ions, for example, the problem due to precipitation of Li dendrite that may occur due to excessive doping of Li ions On the other hand, there is a demerit that the hardness of the negative electrode is increased and the charge / discharge cycle characteristics of the battery are easily impaired.

The present invention has been made in view of the above circumstances, and the object thereof is a lithium ion secondary battery excellent in charge / discharge cycle characteristics, a method for producing the same, and a precursor for constituting the lithium ion secondary battery. Is to provide.

The precursor of the lithium ion secondary battery of the present invention that has achieved the above object has a negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder, a positive electrode active material and a positive electrode mixture layer containing a binder. A positive electrode and a separator are accommodated in an outer package, and the negative electrode mixture layer contains at least a negative electrode active material doped with Li ions, and the positive electrode mixture layer includes Li and a metal M other than Li. The separator contains a porous film (I) mainly composed of a thermoplastic resin and a filler mainly including a filler having a heat resistant temperature of 150 ° C. or higher. And a layer (II).

The lithium ion secondary battery of the present invention is composed of the precursor of the lithium ion secondary battery of the present invention and a non-aqueous electrolyte, and the voltage is 2.0 V at a discharge current rate of 0.1 C. When discharged to reach, the molar ratio (Li / M) between Li and the metal M other than Li contained in the positive electrode active material is 0.8 to 1.05.

The lithium ion secondary battery of the present invention uses a negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder, a step of doping the negative electrode active material with Li ions, and the negative electrode subjected to the step. A step of assembling a precursor of a lithium ion secondary battery; and a step of forming a lithium ion secondary battery using the precursor of the lithium ion secondary battery and a non-aqueous electrolyte. It can be manufactured by the manufacturing method (1).

Further, the lithium ion secondary battery of the present invention is obtained by the steps of producing a negative electrode having a negative electrode mixture layer containing a negative electrode active material doped with Li ions at least partially and a binder, and the above-described steps. A step of assembling a precursor of a lithium ion secondary battery using the negative electrode and a step of forming a lithium ion secondary battery using the precursor of the lithium ion secondary battery and a non-aqueous electrolyte. It can also be produced by the production method (2) of the invention.

According to the present invention, it is possible to provide a lithium ion secondary battery excellent in charge / discharge cycle characteristics, a method for producing the same, and a precursor for constituting the lithium ion secondary battery.

It is a top view which represents typically an example of the positive electrode which concerns on the lithium ion secondary battery of this invention. It is a top view which represents typically an example of the negative electrode which concerns on the lithium ion secondary battery of this invention. It is a top view which represents typically an example of the lithium ion secondary battery of this invention. FIG. 4 is a cross-sectional view taken along a line II in FIG. 3.

The lithium ion secondary battery of the present invention is configured using a negative electrode containing a negative electrode active material doped with Li ions by pre-doping outside the system.

The fact that the negative electrode active material in the negative electrode mixture layer of the negative electrode is pre-doped with Li ions means that when the battery is discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V, the positive electrode active material It can be grasped by the molar ratio (Li / M) between Li contained and a metal M other than Li. In the lithium ion secondary battery, the molar ratio Li / M is 0.8 or more and 1.05 or less. For example, in a battery including a negative electrode mixture layer containing a negative electrode active material not containing Li, and having a negative electrode in which Li ions are not pre-doped (and pre-doped) into the negative electrode active material, the molar ratio Li / M becomes smaller than the lower limit value.

Li-ion doped into the negative electrode active material by external pre-doping so that the molar ratio Li / M in the battery is 0.8 or more and 1.05 or less, when converted into the battery capacity, the irreversible capacity of the negative electrode active material and Same or less.

The composition analysis of the positive electrode active material when discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V can be performed using an ICP (Inductive Coupled Plasma) method as follows. First, 0.2 g of a positive electrode active material to be measured is collected and placed in a 100 mL container. Thereafter, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water are added in order and dissolved by heating. After cooling, the sample is further diluted 25 times with pure water, and calibrated using an ICP analyzer “ICP-757” manufactured by JARRELASH. The composition is analyzed by the line method. The composition amount can be derived from the obtained results. The molar ratio Li / M described in the examples described later is a value determined by this method.

The positive electrode active material for obtaining the molar ratio Li / M in this specification includes a positive electrode material in which the surface of the positive electrode active material particles described later is coated with a specific material (such as an Al-containing oxide). The amount of the metal contained in the specific material existing on the surface of the positive electrode material is also included in the amount of the metal M for obtaining the molar ratio Li / M.

Incidentally, the molar ratio Li / M will be described by taking Example 1 described later as an example. In Example 1, LiCo _0.9795 Mg _0.011 Zr _0.0005 Al _0.009 O ₂ of lithium cobalt oxide (A1) The cathode material (a1) having an Al-containing oxide film formed on the surface and the LiCo _0.97 Mg _0.012 Al _0.009 O ₂ lithium cobalt oxide (B1) surface formed with an Al-containing oxide film The positive electrode material (b1) is used, and the metal M other than Li at this time refers to Co, Mg, Zr, and Al. That is, after producing the lithium ion secondary battery, the battery after predetermined charge / discharge is disassembled, and the positive electrode material (mixture in this Example 1) is collected and analyzed from the positive electrode mixture layer to derive the molar ratio Li / M.

Using a negative electrode containing a negative electrode active material doped with Li ions by pre-doping outside the system, and adjusting the degree of doping of the Li ions so that the molar ratio Li / M in the positive electrode active material is within the above range If the battery is assembled, it is doped with an appropriate amount of Li ions to reduce the irreversible capacity of the negative electrode active material, so that, for example, generation of Li dendrite can be suppressed, and this generation can cause a short circuit of the battery. It can be suppressed well.

On the other hand, as described above, the negative electrode (the negative electrode mixture layer) containing the negative electrode active material doped with Li ions by pre-doping outside the system is increased in hardness. A negative electrode active material that requires doping of Li ions has a large amount of expansion / contraction due to charging / discharging of the battery, and a negative electrode mixture layer containing the same greatly expands / contracts along with charging / discharging of the battery. During this expansion, the negative electrode mixture layer damages the separator interposed between the positive electrode and a short circuit occurs. For this reason, in a battery having a negative electrode containing a negative electrode active material doped with Li ions by out-of-system pre-doping, capacity reduction is likely to occur due to repeated charge and discharge.

Therefore, in the lithium ion secondary battery of the present invention, a laminated type having a porous film (I) mainly composed of a thermoplastic resin and a porous layer (II) mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher. This separator was used. Such a laminated separator has higher strength than a polyolefin microporous membrane separator that is widely used in ordinary lithium ion secondary batteries, so that the hardness increases and the expanded negative electrode mixture layer It is hard to be damaged even if touched. Therefore, in the lithium ion secondary battery of the present invention, by using a negative electrode containing a negative electrode active material doped with Li ions by external pre-doping, while achieving high capacity by reducing the irreversible capacity of the negative electrode, It becomes possible to secure the excellent charge / discharge cycle characteristics by suppressing the occurrence of a fine short circuit due to repeated charge / discharge. Moreover, in the lithium ion secondary battery of this invention, since the damage | wound of the above separators can be suppressed, safety | security improves.

A negative electrode according to a lithium ion secondary battery has a negative electrode mixture layer containing a negative electrode active material and a binder. For example, the negative electrode mixture layer has a structure formed on one side or both sides of a current collector. Is.

As the negative electrode active material used for the negative electrode mixture layer, carbon materials such as graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon; Si or Sn simple substance; Si or Sn-containing alloy; Si or Sn-containing oxide; As the negative electrode active material, only one of these may be used, or two or more may be used in combination.

Among such negative electrode active materials, since the effect of the present invention becomes more remarkable, it is desirable to have a large amount of Li ions accepted and a large irreversible capacity. For example, a material containing Si and O as constituent elements ( However, the atomic ratio x of O with respect to Si is preferably 0.5 ≦ x ≦ 1.5 (hereinafter, this material may be referred to as “material S”).

Examples of the material S include materials containing Si and O as constituent elements and not containing Li as a constituent element, such as those represented by the composition formula SiO _x (0.5 ≦ x ≦ 1.5). Can be mentioned.

The SiO _x may contain Si microcrystal or amorphous phase. In this case, the atomic ratio of Si and O is a ratio including Si microcrystal or amorphous phase Si. That is, the SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and is dispersed in the amorphous SiO ₂ . In combination with Si, the atomic ratio x should satisfy 0.5 ≦ x ≦ 1.5. For example, in the case of a material in which Si is dispersed in an amorphous SiO ₂ matrix and the material has a molar ratio of SiO ₂ to Si of 1: 1, since x = 1, the structural formula is represented by SiO. . In the case of a material having such a structure, for example, in X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed, but when observed with a transmission electron microscope, the presence of fine Si Can be confirmed.

The material S preferably constitutes a composite that is combined with a carbon material. For example, the surface of the material S is preferably coated with the carbon material. In general, since the material S has poor conductivity, when using it as a negative electrode active material, a conductive material (conductive aid) is used from the viewpoint of securing good battery characteristics, and the material S and the conductive material in the negative electrode are electrically conductive. It is necessary to form an excellent conductive network by making good mixing and dispersion with the conductive material. In the case of a composite in which the material S is combined with a carbon material, for example, the conductive network in the negative electrode is better than when a material obtained by simply mixing the material S and a conductive material such as a carbon material is used. Formed.

Examples of the composite of the material S and the carbon material include a granulated body of the material S and the carbon material as well as the material S coated with the carbon material as described above.

As a carbon material that can be used for forming a composite with the material S, for example, low crystalline carbon, carbon nanotube, vapor grown carbon fiber, and the like are preferable.

The details of the carbon material include at least one selected from the group consisting of fibrous or coiled carbon materials, carbon black (including acetylene black and ketjen black), artificial graphite, graphitizable carbon, and non-graphitizable carbon. A seed material is preferred. A fibrous or coiled carbon material is preferable in that it easily forms a conductive network and has a large surface area. Carbon black (including acetylene black and ketjen black), graphitizable carbon, and non-graphitizable carbon have high electrical conductivity and high liquid retention. Even if the particles expand and contract, it is preferable in that it has a property of easily maintaining contact with the particles.

Among the carbon materials exemplified above, a fibrous carbon material is particularly preferable as a material used when the composite with the material S is a granulated body. The fibrous carbon material has a thin thread shape and high flexibility, so that it can follow the expansion and contraction of the material S that accompanies charging / discharging of the battery, and since the bulk density is large, This is because it can have many junctions. Examples of the fibrous carbon include polyacrylonitrile (PAN) -based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, and carbon nanotube, and any of these may be used.

In the composite of the material S and the carbon material, the ratio of the material S to the carbon material is preferably 3 parts by mass or more of the carbon material with respect to 100 parts by mass of the material S: 5 parts by mass or more. More preferably, it is more preferably 7 parts by mass or more, more preferably 20 parts by mass or less, and even more preferably 17 parts by mass or less. The reason is not clear, but when Li ions are doped, the charge / discharge cycle characteristics of the battery can be further improved by adjusting the ratio of the material S and the carbon material in the composite as described above. It becomes.

The composite of the material S and the carbon material can be obtained by, for example, the following method.

When the surface of the material S is coated with a carbon material to form a composite, for example, the particles of the material S and the hydrocarbon gas are heated in the gas phase, and are generated by thermal decomposition of the hydrocarbon gas. Carbon is deposited on the surface of the particles. Thus, according to the vapor deposition (CVD) method, the hydrocarbon-based gas spreads to every corner of the particle of the material S, and a thin and uniform film (carbon) containing a conductive carbon material on the particle surface. Since the material covering layer) can be formed, the conductivity of the particles of the material S can be imparted with good uniformity with a small amount of carbon material.

In the production of the material S coated with the carbon material, the processing temperature (atmosphere temperature) of the CVD method varies depending on the type of hydrocarbon gas, but is usually 600 to 1200 ° C., and more preferably 700 ° C. It is preferable that it is above, and it is still more preferable that it is 800 degreeC or more. This is because the higher the treatment temperature, the less the remaining impurities, and the formation of a coating layer containing carbon having high conductivity.

As the liquid source of hydrocarbon gas, toluene, benzene, xylene, mesitylene and the like can be used, but toluene that is easy to handle is particularly preferable. A hydrocarbon-based gas can be obtained by vaporizing them (for example, bubbling with nitrogen gas). Moreover, methane gas, acetylene gas, etc. can also be used.

In addition, when producing a granulated body of the material S and the carbon material, a dispersion liquid in which the material S is dispersed in a dispersion medium is prepared, sprayed and dried to obtain a granulated body including a plurality of particles. Make it. For example, ethanol or the like can be used as the dispersion medium. It is appropriate to spray the dispersion liquid in an atmosphere of 50 to 300 ° C. In addition to the above method, a granulated body of the material S and the carbon material can be produced also by a granulating method by a mechanical method using a vibration type or planetary type ball mill or rod mill.

If the average particle size of the material S is too small, the dispersibility of the material S may be reduced and the effects of the present invention may not be sufficiently obtained, and the material S has a large volume change associated with charging / discharging of the battery. If the average particle diameter is too large, the material S is likely to collapse due to expansion / contraction (this phenomenon leads to capacity degradation of the material S), and therefore it is preferably 0.1 μm or more and 10 μm or less.

The content of the composite in the total amount of the negative electrode active material contained in the negative electrode mixture layer is, for example, 0.5% by mass from the viewpoint of better securing the effect of increasing the battery capacity by using the composite. It is above, it is preferable that it is 10 mass% or more, it is more preferable that it is 20 mass% or more, and it is still more preferable to set it as 50 mass% or more. As described above, since only the composite may be used as the negative electrode active material, the preferable upper limit of the content of the composite in the total amount of the negative electrode active material contained in the negative electrode mixture layer is 100% by mass. is there.

The content of the negative electrode active material in the negative electrode mixture layer (total content of all negative electrode active materials) is preferably 80 to 99.5% by mass.

As the binder for the negative electrode mixture layer, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyimide, polyamide, polyamideimide, or the like can be used. However, it is preferable to use a copolymer having a unit represented by the following formula (1) and a unit represented by the following formula (2) [hereinafter referred to as “copolymer (A)”].

In the formula (2), R is hydrogen or a methyl group, and M ′ is an alkali metal element.

The copolymer (A) has a strong binding force and excellent flexibility as compared with, for example, SBR widely used as a binder for a negative electrode mixture layer of a lithium ion secondary battery. Therefore, even when a high-capacity negative electrode material such as the material S is used for the negative electrode active material, the negative electrode active material is easily detached from the negative electrode mixture layer and the negative electrode mixture layer and the current collector are peeled off. Can be suppressed.

Further, Li used for pre-doping of the negative electrode reacts with moisture to form lithium hydroxide, or from F and moisture contained in an electrolyte salt widely used for non-aqueous electrolytes of lithium ion secondary batteries. Hydrogen fluoride may be formed and these may cause deterioration of the binder of the negative electrode mixture layer. However, the copolymer (A) is highly resistant to these and hardly deteriorates.

Therefore, when the copolymer (A) is used for the binder of the negative electrode mixture layer, the negative electrode is hardly deteriorated, and the charge / discharge cycle characteristics of the lithium ion secondary battery are further improved.

Furthermore, by using the copolymer (A) as a binder for the negative electrode mixture layer, the load characteristics of the battery are also improved. This is thought to be because the negative electrode mixture layer using the copolymer (A) as a binder has a structure in which the nonaqueous electrolytic solution penetrates well inside. Moreover, by using the copolymer (A) as a binder, it is possible to highly suppress the precipitation of Li on the negative electrode surface that may occur with the use of the battery.

The copolymer (A) having the unit represented by the formula (1) and the unit represented by the formula (2) has a vinyl ester and at least one of an acrylate ester and a methacrylate ester as monomers. A copolymer obtained by polymerization can be obtained by saponification.

Examples of the vinyl ester for obtaining the copolymer (A) include vinyl acetate, vinyl propionate, and vinyl pivalate, and one or more of these can be used. Among these vinyl esters, vinyl acetate is more preferable.

The copolymer of vinyl ester and at least one of acrylic acid ester and methacrylic acid ester for obtaining copolymer (A) is a unit derived from monomers other than vinyl ester, acrylic acid ester and methacrylic acid ester. You may have.

The copolymer of vinyl ester and at least one of acrylic acid ester and methacrylic acid ester is a suspension in which polymerization is performed in a state where these monomers are suspended in an aqueous solution containing a polymerization catalyst and a dispersant, for example. Polymerization can be performed by a turbid polymerization method. As the polymerization catalyst at this time, organic peroxides such as benzoyl peroxide and lauryl peroxide; azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile; and the like can be used. In addition, the dispersant used in the suspension polymerization includes water-soluble polymers (polyvinyl alcohol, poly (meth) acrylic acid or a salt thereof, polyvinyl pyrrolidone, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, etc.), inorganic compounds (Calcium phosphate, magnesium silicate, etc.) can be used.

The temperature at which suspension polymerization is performed may be about −20 to + 20 ° C. with respect to the 10-hour half-life temperature of the polymerization catalyst, and the polymerization time may be several hours to several tens of hours.

Saponification of a copolymer of vinyl ester with at least one of acrylic acid ester and methacrylic acid ester uses an alkali (sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.) containing an alkali metal, and is aqueous. It can be performed in a mixed solvent of an organic solvent and water. By this saponification, the unit derived from the vinyl ester becomes a unit in which a hydroxyl group is directly bonded to the main chain of the copolymer [that is, a unit represented by the above formula (1)]. The unit derived from at least one monomer is a unit in which an alkali metal salt (group) of a carboxyl group is directly bonded to the main chain of the copolymer [that is, a unit represented by the formula (2)]. Therefore, examples of M ′ in the formula (2) include sodium, potassium, and lithium.

Examples of the aqueous organic solvent used for saponification include lower alcohols (such as methanol and ethanol), ketones (such as acetone and methyl ethyl ketone), and the like. The use ratio of the aqueous organic solvent to water is preferably 3/7 to 8/2 in terms of mass ratio.

The temperature at the time of saponification may be 20 to 60 ° C., and the time at that time may be about several hours.

The saponified copolymer may be taken out from the reaction solution, washed and then dried.

The unit represented by the formula (1) of the copolymer (A) obtained through the saponification has a structure in which an unsaturated bond of vinyl alcohol is opened and polymerized, The unit represented by (2) is an acrylate or methacrylate (hereinafter referred to as “(meth) acrylate” collectively, and acrylic acid and methacrylic acid are collectively referred to as “(meth) A structure in which an unsaturated bond of “acrylic acid” is polymerized by opening. Therefore, the copolymer (A) uses vinyl alcohol or (meth) acrylate as a monomer and is not obtained by copolymerizing these, but for convenience, “vinyl alcohol and (meth) It may also be referred to as an acrylate salt [a copolymer of (meth) acrylic acid alkali metal neutralized product].

In the copolymer (A), the composition ratio of the unit represented by the formula (1) and the unit represented by the formula (2) is the formula (1) when the total of these units is 100 mol%. Is preferably 5 mol% or more, more preferably 50 mol% or more, still more preferably 60 mol% or more, and preferably 95 mol% or less, and 90 mol%. The following is more preferable. That is, when the total of the unit represented by the formula (1) and the unit represented by the formula (2) is 100 mol%, the ratio of the unit represented by the formula (2) is 5 mol% or more. Is preferably 10 mol% or more, more preferably 95 mol% or less, more preferably 50 mol% or less, and still more preferably 40 mol% or less.

The content of the copolymer (A) in the negative electrode mixture layer suppresses the effects of its use (the effect of enhancing the load characteristics of the battery, the falling off of the negative electrode active material, and the peeling between the negative electrode mixture layer and the current collector). From the viewpoint of ensuring a good effect), the content is preferably 2% by mass or more, and more preferably 5% by mass or more. However, if the amount of the copolymer (A) in the negative electrode mixture layer is too large, it becomes difficult to adjust the density of the negative electrode mixture layer to a value described later, and the capacity and load characteristics of the battery are reduced. There is a fear. Therefore, the content of the copolymer (A) in the negative electrode mixture layer is preferably 15% by mass or less, and more preferably 10% by mass or less.

In the negative electrode mixture layer, together with the copolymer (A), binders used in the negative electrode mixture layer related to the negative electrode of ordinary lithium ion secondary batteries, for example, SBR, CMC, polyvinylidene fluoride (PVDF), etc. Can also be used. However, the content of the binder other than the copolymer (A) in the total amount of binder contained in the negative electrode mixture layer is preferably 50% by mass or less.

The negative electrode mixture layer may contain a conductive auxiliary as necessary. Examples of conductive assistants to be included in the negative electrode mixture layer include graphites such as natural graphite (scaly graphite, etc.), artificial graphite and the like; acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black and the like. -It is preferable to use carbon materials such as bon blacks; carbon fibers; and conductive fibers such as metal fibers; carbon fluorides; metal powders such as aluminum; zinc oxide; conductivity such as potassium titanate. Whiskers; conductive metal oxides such as titanium oxide; organic conductive materials such as polyphenylene derivatives; and the like can also be used. As the conductive assistant, those exemplified above may be used singly or in combination of two or more.

When the conductive additive is contained in the negative electrode mixture layer, the content of the conductive additive in the negative electrode mixture layer is preferably 10% by mass or less.

The negative electrode is, for example, a paste obtained by dispersing a negative electrode mixture containing a negative electrode active material and a binder and, if necessary, a conductive additive in a solvent such as N-methyl-2-pyrrolidone (NMP) or water. Or a slurry-like negative electrode mixture-containing composition (the binder may be dissolved in a solvent), which is applied to one or both sides of the current collector, dried, and then calendered as necessary. It can manufacture through the process of performing press processing, such as a process. However, the negative electrode is not limited to those manufactured by the above method, and may be manufactured by other methods.

As the negative electrode current collector, a copper or nickel foil, a punching metal, a net, an expanded metal, or the like can be used, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is 5 μm in order to ensure mechanical strength. Is desirable.

Further, a lead body for electrical connection with other members in the lithium ion secondary battery may be formed on the negative electrode according to a conventional method, if necessary.

The thickness of the negative electrode mixture layer (when the negative electrode mixture layer is provided on both sides of the current collector, the thickness per side) is preferably 10 to 100 μm.

The extra-system pre-doping of the negative electrode active material can be performed, for example, by the following (i) or (ii).

In-system pre-doping method (i)
A negative electrode manufactured using a negative electrode active material not doped with Li ions is used, and the negative electrode active material is doped with Li ions.

In the extra-system pre-doping method (i), the doping of Li ions into the negative electrode active material in the negative electrode mixture layer of the negative electrode is performed by, for example, biphenyl, polycyclic aromatic compounds (anthracene, naphthalene) in a solvent such as tetrahydrofuran or diethyl ether. Etc.), and the negative electrode is immersed in a solution in which p-benzoquinone, metal Li, etc. are dissolved, and then washed with a solvent and dried [hereinafter referred to as “out-of-system pre-doping method (i-1)”. ]. The doping amount of Li ions at this time can be controlled by adjusting the amount of each component in the solution. For example, the molar ratio Li / M may be adjusted so as to satisfy the preferred value.

Further, in the extra-system pre-doping method (i), a negative electrode (working electrode) and a lithium metal foil (counter electrode, including a lithium alloy foil) are immersed in a nonaqueous electrolytic solution, and a current is passed between them. In addition, the negative electrode active material in the negative electrode mixture layer can be doped with Li ions [hereinafter referred to as out-of-system pre-doping method (i-2)]. As the non-aqueous electrolyte, the same non-aqueous electrolyte for lithium ion secondary batteries (described in detail later) can be used. The doping amount of Li ions at this time can be controlled by adjusting the current density per area of the negative electrode (negative electrode mixture layer) and the amount of electricity to be energized. For example, the molar ratio Li / M has the preferred value. Adjust to meet.

Out-of-system pre-doping method (ii)
A negative electrode active material not doped with Li ions is directly doped with Li ions. In this case, by immersing a negative electrode active material (a negative electrode active material before Li ion doping) in place of the negative electrode in the solution in which the negative electrode described above in the description of the extra-system pre-doping method (i-1) is immersed. The negative electrode active material can be doped with Li ions.

When adopting this extra-system pre-doping method (ii), by using the negative electrode active material obtained by this (negative electrode active material doped with Li ions), by producing the negative electrode by the above method, A negative electrode containing a negative electrode active material doped with Li ions can be obtained. In this case, as the negative electrode active material used for the production of the negative electrode, a part or all of the negative electrode active material doped with Li ions by the external pre-doping method (ii) can be used. The ratio of the negative electrode active material doped with Li ions by the extra-system pre-doping method (ii) in the negative electrode active material used for the production of the negative electrode and the doping amount of Li ions into the negative electrode active material are, for example, the molar ratio Li / What is necessary is just to adjust so that M may satisfy | fill the said suitable value.

The negative electrode active material doped with Li ions by the extra-system pre-doping method (ii) preferably has a large acceptance amount of Li ions and a large irreversible capacity. For example, Li ions are added to a material containing Si and O as constituent elements. It is desirable to dope.

A positive electrode according to a lithium ion secondary battery has a positive electrode mixture layer containing a positive electrode active material and a binder. For example, the positive electrode mixture layer has a structure formed on one side or both sides of a current collector. And those composed of a positive electrode mixture layer (positive electrode mixture molded body).

As the positive electrode active material, a metal oxide (lithium-containing composite oxide) composed of Li and a metal M other than Li (Co, Ni, Mn, Fe, Mg, Al, etc.) is used. Examples of such lithium-containing composite oxides include lithium cobalt oxides such as LiCoO ₂ ; lithium manganese oxides such as LiMnO ₂ and Li ₂ MnO ₃ ; lithium nickel oxides such as LiNiO ₂ ; LiCo _1-x NiO Lithium-containing composite oxide having a layered structure such as ₂ ; Lithium-containing composite oxide having a spinel structure such as LiMn ₂ O ₄ and Li _4/3 Ti _5/3 O ₄ ; Lithium-containing composite oxide having an olivine structure such as LiFePO ₄ And oxides having the above-described oxide as a basic composition and substituted with various elements.

Among such positive electrode active materials, lithium cobalt oxide (lithium cobaltate) containing at least Co and at least one element M ¹ selected from the group consisting of Mg, Zr, Ni, Mn, Ti, and Al. ) Is preferred. The positive electrode material mixture layer more preferably contains a positive electrode material in which the surfaces of such lithium cobalt oxide particles are coated with an Al-containing oxide. When the positive electrode material is used, since the resistance at the positive electrode during battery charging can be increased, it is difficult for Li to precipitate at the negative electrode, so the composite in the negative electrode mixture layer Even if the proportion of the body is increased, the charge / discharge cycle characteristics of the lithium ion secondary battery can be further improved.

The lithium cobalt oxide is an element that includes Co, at least one element M ¹ selected from the group consisting of Mg, Zr, Ni, Mn, Ti, and Al, and other elements that may further be contained. when the group ^{M a,} is represented by the composition formula ^LiM a _{O 2.}

In the lithium cobalt oxide, the element M ¹ has an effect of increasing the stability of the lithium cobalt oxide in a high voltage region and suppressing the elution of Co ions, and the thermal stability of the lithium cobalt oxide. It also has the effect of increasing

In the lithium cobalt oxide, the amount of the element M ¹ is preferably such that the atomic ratio M ¹ / Co with Co is 0.003 or more from the viewpoint of more effectively exerting the above action, and 0.008 or more. It is more preferable that

However, when the amount of the element M ¹ in the lithium cobalt oxide is too large, too small amounts of Co, there is a possibility can not be sufficient action by these. Therefore, in the lithium cobaltate, the amount of the element M ¹ is preferably such that the atomic ratio M ¹ / Co with Co is 0.06 or less, and more preferably 0.03 or less.

In the lithium cobaltate, Zr adsorbs hydrogen fluoride that may be generated due to a fluorine-containing lithium salt (such as LiPF ₆ ) contained in the non-aqueous electrolyte, and suppresses deterioration of the lithium cobaltate. have.

Fluorine-containing lithium contained in the non-aqueous electrolyte if some moisture is inevitably mixed in the non-aqueous electrolyte used in the lithium ion secondary battery or if moisture is adsorbed by other battery materials Reacts with salt to produce hydrogen fluoride. When hydrogen fluoride is generated in the battery, the action causes deterioration of the positive electrode active material.

However, when the lithium cobaltate is synthesized so as to also contain Zr, Zr oxide is deposited on the surface of the particles, and this Zr oxide adsorbs hydrogen fluoride. Therefore, deterioration of the lithium cobalt oxide due to hydrogen fluoride can be suppressed.

In addition, when the positive electrode active material contains Zr, the load characteristics of the battery are improved. When the lithium cobalt oxide contained in the positive electrode material is two materials having different average particle diameters, the larger average particle diameter is lithium cobalt oxide (A), and the smaller average particle diameter is lithium cobalt oxide (B). And In general, when a positive electrode active material having a large particle size is used, the load characteristics of the battery tend to deteriorate. Therefore, among the positive electrode active materials constituting the positive electrode material, it is preferable that lithium cobaltate (A) having a larger average particle diameter contains Zr. On the other hand, lithium cobaltate (B) may contain Zr or may not contain it.

In the lithium cobaltate, the amount of Zr is such that the atomic ratio Zr / Co with Co is preferably 0.0002 or more, more preferably 0.0003 or more, from the viewpoint of better exerting the above action. Is more preferable. However, if the amount of Zr in the lithium cobalt oxide is too large, the amount of other elements decreases, and there is a possibility that the effects of these elements cannot be sufficiently ensured. Therefore, the amount of Zr in the lithium cobaltate is preferably such that the atomic ratio Zr / Co with Co is 0.005 or less, and more preferably 0.001 or less.

The lithium cobalt oxide includes Li-containing compounds (such as lithium hydroxide and lithium carbonate), Co-containing compounds (such as cobalt oxide and cobalt sulfate), Mg-containing compounds (such as magnesium sulfate), and Zr-containing compounds (such as zirconium oxide). compounds containing elements M ¹ (oxides, hydroxides, sulfates, etc.) can be mixed, synthesized, for example, by firing the raw material mixture. Incidentally, in synthesizing the lithium cobaltate with a higher purity, composite compound containing Co and the element M ¹ (hydroxides, oxides, etc.) and the like and Li-containing compound are mixed and firing the raw material mixture It is preferable.

The firing condition of the raw material mixture for synthesizing the lithium cobaltate can be, for example, 800 to 1050 ° C. for 1 to 24 hours, but once the temperature is lower than the firing temperature (for example, 250 to 850 ° C.). It is preferable to preheat by heating and holding at that temperature, and then to raise the temperature to the firing temperature to advance the reaction. There is no particular limitation on the preheating time, but it is usually about 0.5 to 30 hours. The atmosphere during firing can be an atmosphere containing oxygen (that is, in the air), a mixed atmosphere of an inert gas (such as argon, helium, or nitrogen) and oxygen gas, or an oxygen gas atmosphere. The oxygen concentration (volume basis) is preferably 15% or more, and more preferably 18% or more.

In the positive electrode material, the surface of the lithium cobalt oxide particles is coated with an Al-containing oxide (for example, 90 to 100% or more of the total area of the lithium cobalt oxide particle surface includes Al-containing oxides). Things are present). Examples of the Al-containing oxide covering the surface of the lithium cobalt oxide particles include Al ₂ O ₃ , AlOOH, LiAlO ₂ , and LiCo _1-w Al _w O ₂ (where 0.5 <w <1). Of these, only one of them may be used, or two or more of them may be used in combination. For example, when the surface of the lithium cobalt oxide is coated with Al ₂ O ₃ by a method described later, an Al-containing oxide containing elements such as Co, Li, and Al transferred from the lithium cobalt oxide in the Al ₂ O ₃ Although a film in which a part is mixed is formed, the film formed of an Al-containing oxide that covers the surface of the lithium cobaltate constituting the positive electrode material may be a film containing such a component. .

The average coating thickness of the Al-containing oxide according to the positive electrode material increases the resistance due to the inhibition of the Al-containing oxide in the positive and negative electrode active materials during charging and discharging of the battery according to the positive electrode material, From the viewpoint of further improving the charge / discharge cycle characteristics of the battery by suppressing Li deposition at the negative electrode and from the viewpoint of satisfactorily suppressing the reaction between the positive electrode active material according to the positive electrode material and the non-aqueous electrolyte, the thickness is 5 nm or more. It is preferable that the thickness is 15 nm or more. In addition, from the viewpoint of suppressing deterioration of the load characteristics of the battery due to the Al-containing oxide inhibiting the lithium ion in and out of the positive electrode active material during charging and discharging of the battery, the average coating of the Al-containing oxide according to the positive electrode material The thickness is preferably 50 nm or less, and more preferably 35 nm or less.

The “average coating thickness of the Al-containing oxide” as used herein refers to a cross section of the positive electrode material obtained by processing by the focused ion beam method, observed at a magnification of 400,000 times using a transmission electron microscope, Of the positive electrode material particles existing in the field of view of 500 × 500 nm, particles having a cross-sectional size within the average particle diameter (d ₅₀ ) ± 5 μm of the positive electrode material are arbitrarily selected for 10 fields, and for each field, Al It means the average value (number average value) calculated for all thicknesses (thicknesses at 100 locations) obtained by measuring the thickness of the coating film of the contained oxide at 10 arbitrary locations.

The specific surface area of the positive electrode material is preferably 0.1 m ² / g or more, more preferably 0.2 m ² / g or more, and preferably 0.4 m ² / g or less, More preferably, it is 0.3 m ² / g or less. When the specific surface area of the positive electrode material is in the above value, the resistance during charging / discharging of the battery is further increased, so that the charge / discharge cycle characteristics of the battery are further improved.

When the surface of the lithium cobalt oxide constituting the positive electrode material is coated with an Al-containing oxide or when Zr oxide is deposited on the surface of the lithium cobalt oxide particles, the positive electrode material is usually used. The surface becomes rough and the specific surface area increases. For this reason, the positive electrode material has a small specific surface area as described above if the properties of the Al-containing oxide film covering the surface of the lithium cobalt oxide particles are good in addition to a relatively large particle size. It is preferable because it is easy.

About the said lithium cobaltate which the said positive electrode material contains, one type may be sufficient, as above-mentioned, two materials from which an average particle diameter differs may be sufficient, and three or more from which an average particle diameter differs It may be a material.

In order to adjust the specific surface area of the positive electrode material to the above value, when one type of the lithium cobaltate is used, the average particle diameter of the positive electrode material is preferably 10 to 35 μm.

When two materials having different average particle diameters are used for the lithium cobalt oxide contained in the positive electrode material, the surface of lithium cobalt oxide (A) particles is coated with an Al-containing oxide, and the average particle diameter is 1 The positive electrode material (a) having a particle size of 40 μm and the surface of lithium cobalt oxide (B) particles are coated with an Al-containing oxide, the average particle diameter is 1 to 40 μm, and the positive electrode material (a) It is preferable that at least the positive electrode material (b) having a small average particle diameter is included. More preferably, it is an embodiment comprising large particles [positive electrode material (a)] having an average particle diameter of 24 to 30 μm and small particles [positive electrode material (b)] having an average particle diameter of 4 to 8 μm. When the positive electrode material contains the positive electrode material (a) and the positive electrode material (b), the ratio of the positive electrode material (a) in the total amount of the positive electrode material is preferably 75 to 90% by mass. As a result, not only can the specific surface area be adjusted, but also when the positive electrode mixture layer is pressed, the positive electrode material having a small particle size enters the gap between the positive electrode materials having a large particle size, so that the stress applied to the positive electrode mixture layer is entirely reduced. It is possible to disperse and to suppress the cracking of the positive electrode material particles satisfactorily, so that the action by the coating with the Al-containing oxide can be exhibited better.

The particle size distribution of the positive electrode material in the present specification means a particle size distribution obtained by a method for obtaining an integrated volume from particles having a small particle size distribution using a microtrack particle size distribution measuring apparatus “HRA9320” manufactured by Nikkiso Co., Ltd. . In addition, the average particle diameter of the positive electrode material and other particles (such as the material S) in the present specification is the volume-based integrated fraction when the integrated volume is obtained from particles having a small particle size distribution using the above-described apparatus. Means the value of 50% diameter (d ₅₀ ).

In order to coat the surface of the lithium cobalt oxide particles with an Al-containing oxide to form the positive electrode material, for example, the following method can be employed. In a lithium hydroxide aqueous solution having a pH of 9 to 11 and a temperature of 60 to 80 ° C., the lithium cobalt oxide particles are charged and dispersed by stirring, and Al (NO ₃ ) ₃ · 9H ₂ O and Aqueous ammonia for suppressing fluctuations in pH is added dropwise to produce an Al (OH) ₃ coprecipitate and adhere to the surface of the lithium cobalt oxide particles. Thereafter, the lithium cobalt oxide particles to which the Al (OH) ₃ coprecipitate is adhered are taken out from the reaction solution, washed, dried, and then heat-treated to form an Al-containing oxide on the surface of the lithium cobalt oxide particles. A film is formed to form the positive electrode material. The heat treatment of the lithium cobaltate particles to which the Al (OH) ₃ coprecipitate is deposited is preferably performed in the air atmosphere, and the heat treatment temperature is 200 to 800 ° C. and the heat treatment time is 5 to 15 hours. preferable. When the surface of the lithium cobalt oxide particles is coated with an Al-containing oxide by this method, the Al-containing oxide as a main component constituting the coating is changed to Al ₂ O ₃ or AlOOH by adjusting the heat treatment temperature. Or LiAlO ₂ or LiCo _1-w Al _w O ₂ (where 0.5 <w <1).

When the positive electrode material and another positive electrode active material are used, the continuous charge characteristics of the battery are further improved, and the charge / discharge cycle characteristics and storage characteristics of the lithium ion secondary battery using the positive electrode material at a high temperature Therefore, nickel acid containing Ni and Co and element M ² selected from the group consisting of Mg, Mn, Ba, W, Ti, Zr, Mo, and Al as the other positive electrode active material It is preferable to use lithium.

The lithium nickelate is represented by the chemical formula LiM ^b O ₂ when Ni, Co, and the element M ² , and other elements that may further be contained, are combined into an element group M ^b . when Ni of the total number of atoms in 100 mol% of the element group ^{M 2,} the amount of Co and the element ^{M 2,} respectively, expressed in s (mol%), t ( mol%) and u (mol%), 30 ≦ s ≦ 97, 0.5 ≦ t ≦ 40, 0.5 ≦ u ≦ 40 are preferable, and 70 ≦ s ≦ 97, 0.5 ≦ t ≦ 30, and 0.5 ≦ u ≦ 5 are more preferable. preferable.

The lithium nickelate, Li-containing compound (lithium hydroxide, etc. lithium carbonate), Ni-containing compound (such as nickel sulfate), Co-containing compound (cobalt sulfate, cobalt oxide, etc.), and containing the element M ^b as necessary The compound (oxide, hydroxide, sulfate, etc.) to be mixed can be mixed, and this raw material mixture can be fired. Incidentally, in synthesizing the lithium nickel oxide at a higher purity, Ni, complex compound containing a plurality of elements among the elements M ^b be contained if Co and the required (hydroxides, oxides, etc.), It is preferable to mix other raw material compounds (such as Li-containing compounds) and to fire this raw material mixture.

The firing conditions of the raw material mixture for synthesizing the lithium nickelate can also be set at, for example, 800 to 1050 ° C. for 1 to 24 hours, as in the case of the lithium cobaltate, but once lower than the firing temperature. It is preferable to heat up to a temperature (for example, 250 to 850 ° C.) and perform preliminary heating by holding at that temperature, and then raise the temperature to the firing temperature to advance the reaction. There is no particular limitation on the preheating time, but it is usually about 0.5 to 30 hours. The atmosphere during firing can be an atmosphere containing oxygen (that is, in the air), a mixed atmosphere of an inert gas (such as argon, helium, or nitrogen) and oxygen gas, or an oxygen gas atmosphere. The oxygen concentration (volume basis) is preferably 15% or more, and more preferably 18% or more.

When the positive electrode material and another positive electrode active material (for example, the lithium nickelate) are used as the positive electrode active material, the amount of the positive electrode material in a total of 100 mass% of the positive electrode material and the other positive electrode active material Is preferably 50% by mass or more, more preferably 80% by mass or more (that is, the amount of the other positive electrode active material used together with the positive electrode material is the same as that of the positive electrode material and the other positive electrode active material). The total content is preferably 50% by mass or less, and more preferably 20% by mass or less. Since only the positive electrode material may be used as the positive electrode active material, the preferred upper limit of the amount of the positive electrode material in the total of 100% by mass of the positive electrode material and the other positive electrode active material is 100% by mass. is there. However, in order to better ensure the continuous charge characteristics improvement effect of the battery by using the lithium nickelate, the amount of the lithium nickelate in a total of 100% by mass of the positive electrode material and the lithium nickelate, It is preferably 5% by mass or more, and more preferably 10% by mass or more.

Conductive aids for the positive electrode mixture layer include natural graphite (such as flake graphite), graphite such as artificial graphite (graphitic carbon material); acetylene black, ketjen black, channel black, furnace black, lamp black, thermal Carbon materials such as carbon black such as black; carbon fiber; Also, PVDF, polytetrafluoroethylene (PTFE), vinylidene fluoride-chlorotrifluoroethylene copolymer [P (VDF-CTFE)], SBR, CMC, etc. are preferably used as the binder for the positive electrode mixture layer. It is done.

The positive electrode is prepared, for example, by preparing a paste-like or slurry-like positive electrode mixture-containing composition in which a positive electrode active material (such as the above-mentioned positive electrode material), a conductive additive and a binder are dispersed in a solvent such as NMP. May be dissolved in a solvent), and this is applied to one or both sides of the current collector, dried, and then subjected to a press treatment such as a calender treatment as necessary.

However, the positive electrode is not limited to those manufactured by the above manufacturing method, and may be manufactured by other methods. For example, when the positive electrode is formed into a pellet-like positive electrode mixture molded body, the positive electrode is produced by a method of pressing a positive electrode mixture containing a positive electrode active material, a conductive additive, a binder, and the like into a pellet shape. can do.

The current collector can be the same as that used for the positive electrode of a conventionally known lithium ion secondary battery, such as aluminum foil, punching metal, net, expanded metal, etc. The thickness is preferably 5 to 30 μm.

As the composition of the positive electrode mixture layer and the positive electrode mixture molded body, the amount of the positive electrode active material (including the positive electrode material) is preferably 60 to 95% by mass, and the amount of the binder is 1 to 15% by mass. The amount of the conductive auxiliary is preferably 3 to 20% by mass. In the case of a positive electrode having a positive electrode mixture layer and a current collector, the thickness of the positive electrode mixture layer (thickness per one side of the current collector) is preferably 30 to 150 μm. On the other hand, in the case of a positive electrode comprising a positive electrode mixture molded body, the thickness is preferably 0.15 to 1 mm.

In a lithium ion secondary battery, a negative electrode (a negative electrode containing a negative electrode active material doped with Li ions by pre-doping outside the system) and a positive electrode are laminated body (laminated electrode body) laminated via a separator, or this laminated body. Is further used in the form of a wound body (wound electrode body) wound in a spiral shape.

As the separator, a laminated separator having a porous film (I) mainly composed of a thermoplastic resin and a porous layer (II) mainly including a filler having a heat resistant temperature of 150 ° C. or higher is used. Since such a separator has a high mechanical strength due to the action of the porous layer (II), the battery is charged / discharged while facing the negative electrode whose hardness has been increased by the pre-doping outside the system in the battery. Even if expansion / shrinkage of the agent layer occurs, it is difficult to be damaged, so that it is possible to suppress deterioration of battery characteristics due to charge / discharge. Furthermore, due to the large mechanical strength, it is considered that the laminated separator is unlikely to be distorted even when the battery is charged and discharged, and the adhesion between the negative electrode-separator-positive electrode can be maintained. With these actions, excellent charge / discharge cycle characteristics can be secured in the lithium ion secondary battery of the present invention.

The laminated separator has both shutdown characteristics and heat resistance (heat shrinkage resistance).

In this specification, “heat-resistant temperature is 150 ° C. or higher” means that deformation such as softening is not observed at least at 150 ° C.

The porous membrane (I) according to the separator is mainly for ensuring a shutdown function, and when the battery reaches or exceeds the melting point of the thermoplastic resin, which is the main component of the porous membrane (I), The thermoplastic resin related to the porous membrane (I) melts and closes the pores of the separator, and a shutdown that suppresses the progress of the electrochemical reaction occurs.

The thermoplastic resin that is the main component of the porous membrane (I) is preferably a resin having a melting point of 140 ° C. or lower, and specifically includes polyethylene. In addition, as the form of the porous membrane (I), a microporous membrane usually used as a battery separator or a dispersion containing polyethylene particles is applied to a substrate such as a nonwoven fabric and dried. Examples thereof include sheet-like materials such as those obtained. Here, among the total volume of the constituent components of the porous membrane (I) [the total volume excluding the void portion. The same applies to the volume content of the constituent components of the porous membrane (I) and the porous layer (II) according to the separator. ], The volume content of the resin whose main melting point is 140 ° C. or lower is 50% by volume or more, and more preferably 70% by volume or more. For example, when the porous membrane (I) is formed of the polyethylene microporous membrane, the volume content of the resin having a melting point of 140 ° C. or lower is 100% by volume.

The porous layer (II) according to the separator has a function of preventing a short circuit due to direct contact between the positive electrode and the negative electrode even when the internal temperature of the battery rises, and has a heat resistance temperature of 150 ° C. or higher. The function is secured by. That is, when the battery becomes high temperature, even if the porous membrane (I) shrinks, the porous layer (II) which does not easily shrink can cause the positive and negative electrodes directly when the separator is thermally shrunk. It is possible to prevent a short circuit due to the contact. In addition, since the heat-resistant porous layer (II) acts as a skeleton of the separator, thermal contraction of the porous membrane (I), that is, thermal contraction of the entire separator itself can be suppressed.

The filler related to the porous layer (II) has a heat resistant temperature of 150 ° C. or higher, is stable with respect to the non-aqueous electrolyte of the battery, and is electrochemically stable that is difficult to be oxidized and reduced within the battery operating voltage range. Any inorganic particles or organic particles may be used as long as they are fine, but fine particles are preferable from the viewpoint of dispersion and the like, and inorganic oxide particles, more specifically, alumina, silica, and boehmite are preferable. Alumina, silica, and boehmite have high oxidation resistance, and the particle size and shape can be adjusted to the desired numerical values, making it easy to control the porosity of the porous layer (II) with high accuracy. It becomes. In addition, the filler whose heat-resistant temperature is 150 degreeC or more may use the thing of the said illustration individually by 1 type, and may use 2 or more types together, for example.

The phrase “containing a filler having a heat resistant temperature of 150 ° C. or higher as a main component” of the porous layer (II) means that 70% by volume or more of the filler is included in the total volume of the constituent components of the porous layer (II). is doing. The amount of the filler in the porous layer (II) is preferably 80% by volume or more and more preferably 90% by volume or more in the total volume of the constituent components of the porous layer (II). By making the said filler in porous layer (II) high content as mentioned above, the thermal contraction of the whole separator can be suppressed favorably and high heat resistance can be provided.

The porous layer (II) preferably contains an organic binder to bind the fillers or bind the porous layer (II) and the porous membrane (I). From such a viewpoint, the suitable upper limit of the amount of filler (B) in the porous layer (II) is, for example, 99% by volume in the total volume of the constituent components of the porous layer (II). When the amount of the filler (B) in the porous layer (II) is less than 70% by volume, for example, it is necessary to increase the amount of the organic binder in the porous layer (II). There is a possibility that the pores of the layer (II) are filled with the organic binder, and the function as a separator is lost, for example.

As an organic binder used for the porous layer (II), the fillers or the porous layer (II) and the porous film (I) can be bonded well, are electrochemically stable, and are used for an electrochemical element. There is no particular limitation as long as it is stable with respect to the non-aqueous electrolyte. Specifically, fluororesin (such as PVDF), fluororubber, SBR, CMC, hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), poly N-vinylacetamide, Cross-linked acrylic resin, polyurethane, epoxy resin and the like can be mentioned. These organic binders may be used alone or in combination of two or more.

The laminated separator is, for example, a composition for forming a porous layer (II) containing, in the porous membrane (I), the filler, an organic binder, and the like, and a solvent (an organic solvent such as water and ketones) ( It can be manufactured by applying a slurry, paste, etc.) and then drying at a predetermined temperature to form the porous layer (II).

The laminated separator may have one or more each of the porous membrane (I) and the porous layer (II). Specifically, the porous layer (II) is disposed only on one side of the porous membrane (I) to form the laminated separator. For example, the porous layer (II) is formed on both sides of the porous membrane (I). May be used as the laminated separator. However, if the number of layers of the multilayer separator is too large, it is not preferable because the thickness of the separator is increased, which may increase the internal resistance of the battery or decrease the energy density. Is preferably 5 layers or less.

The thickness of the separator (the laminated separator and other separators) is preferably 6 μm or more and more preferably 10 μm or more from the viewpoint of more reliably separating the positive electrode and the negative electrode. On the other hand, if the separator is too thick, the energy density of the battery may be lowered. Therefore, the thickness is preferably 50 μm or less, and more preferably 30 μm or less.

Further, the thickness of the porous membrane (I) [the total thickness when a plurality of porous membranes (I) are present] is preferably 5 to 30 μm. Further, the thickness of the porous layer (II) [when there are a plurality of porous layers (II), the total thickness] is preferably 1 μm or more, more preferably 2 μm or more, and 4 μm or more. Further, it is preferably 20 μm or less, more preferably 10 μm or less, and further preferably 6 μm or less.

The porosity of the separator is preferably 30 to 70%. Furthermore, the average pore diameter of the separator is preferably 0.01 μm or more, more preferably 0.05 μm or more, and preferably 1 μm or less, more preferably 0.5 μm or less.

The separator preferably has an adhesive layer on one or both sides. When the separator and the electrode are integrated by the adhesive layer of the separator when forming the laminated electrode body or the wound electrode body, even if charging / discharging is repeated in a battery using such an electrode body, Since the shape change can be suppressed, the charge / discharge cycle characteristics of the battery are further improved. In the case of a battery using a flat wound electrode body having a flat cross section, the effect of improving the charge / discharge cycle characteristics by the adhesive layer is particularly remarkable.

The adhesive layer of the separator preferably contains an adhesive resin that exhibits adhesiveness when heated. In the case of an adhesive layer containing an adhesive resin, the separator and the electrode can be integrated by undergoing a step of pressing while heating the electrode body (heating press). The minimum temperature at which the adhesiveness of the adhesive resin develops is lower than the temperature at which shutdown occurs in the layers other than the adhesive layer in the separator [the melting point of the thermoplastic resin that is the main component of the porous membrane (I). Low temperature], specifically, it is preferably 60 ° C. or higher and 120 ° C. or lower.

By using such an adhesive resin, deterioration of the separator can be satisfactorily suppressed when the separator and the positive electrode and / or the negative electrode are integrated by heating and pressing.

Due to the presence of the adhesive resin, the peel strength obtained when a peel test at 180 ° between the electrode (for example, the negative electrode) constituting the electrode body and the separator is carried out is preferable in the state before the hot press. Is 0.05 N / 20 mm or less, particularly preferably 0 N / 20 mm (a state having no adhesive force), and a delayed tack property of 0.2 N / 20 mm or more after being heated and pressed at a temperature of 60 to 120 ° C. It is preferable to have.

However, if the peel strength is too strong, the electrode mixture layer (the positive electrode mixture layer and the negative electrode mixture layer) may peel from the current collector of the electrode, and the conductivity may be lowered. The peel strength according to the peel test at ° is preferably 10 N / 20 mm or less after being hot pressed at a temperature of 60 to 120 ° C.

In addition, the peel strength at 180 ° between the electrode and the separator referred to in this specification is a value measured by the following method. The separator and the electrode are each cut into a size of 5 cm in length and 2 cm in width, and the cut-out separator and the electrode are overlapped. When obtaining the peel strength in the state after being hot-pressed, a test piece is prepared by hot-pressing a 2 cm × 2 cm region from one end. The end of the test piece on the side where the separator and electrode are not heated and pressed is opened, and the separator and the negative electrode are bent so that these angles are 180 °. Thereafter, using a tensile tester, both the one end side of the separator opened at 180 ° of the test piece and the one end side of the electrode are gripped and pulled at a pulling speed of 10 mm / min. Measure the strength when peeled off. In addition, the peel strength of the separator and the electrode before heating press was determined by preparing a test piece in the same manner as above except that the separator and electrode cut out as described above were stacked and pressed without heating. The peel test is performed in the same manner as described above.

Therefore, the adhesive resin has almost no adhesiveness (stickiness) at room temperature (for example, 25 ° C), and the minimum temperature at which the adhesiveness is developed is less than the temperature at which the separator shuts down, preferably 60 ° C to 120 ° C. Those having tackiness are desirable. The temperature of the heating press when integrating the separator and the electrode is more preferably 80 ° C. or more and 100 ° C. or less at which the thermal contraction of the separator does not occur significantly, and the adhesiveness of the adhesive resin is exhibited. The minimum temperature is more preferably 80 ° C. or higher and 100 ° C. or lower.

As the adhesive resin having a delayed tack property, a resin that has almost no fluidity at room temperature, exhibits fluidity when heated, and has a property of being in close contact with a press is preferable. A resin of a type that is solid at room temperature, melts by heating, and exhibits adhesiveness by a chemical reaction can also be used as the adhesive resin.

The adhesive resin preferably has a softening point in the range of 60 ° C. or higher and 120 ° C. or lower with the melting point, glass transition point and the like as indices. The melting point and glass transition point of the adhesive resin can be measured, for example, by a method prescribed in JIS K 7121, and the softening point of the adhesive resin can be measured, for example, by a method prescribed in JIS K 7206.

Specific examples of such adhesive resins include, for example, low density polyethylene (LDPE), poly-α-olefin [polypropylene (PP), polybutene-1, etc.], polyacrylate ester, ethylene-vinyl acetate copolymer. (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer (EBA), ethylene-methyl methacrylate copolymer (EMMA), ionomer resin Etc.

Each resin, or a resin having adhesiveness at room temperature, such as SBR, nitrile rubber (NBR), fluorine rubber, or ethylene-propylene rubber, is used as a core, and the melting point and softening point are within the range of 60 ° C to 120 ° C It is also possible to use a resin having a core-shell structure with a resin as a shell as an adhesive resin. In this case, various acrylic resins and polyurethane can be used for the shell. Further, as the adhesive resin, one-pack type polyurethane, epoxy resin, or the like that exhibits adhesiveness in a range of 60 ° C. or higher and 120 ° C. or lower can be used.

As the adhesive resin, one of the above exemplified resins may be used alone, or two or more of them may be used in combination.

When an adhesive layer made of an adhesive resin and containing substantially no pores is formed, there is a risk that the non-aqueous electrolyte of the battery will be difficult to contact the surface of the electrode integrated with the separator. For this reason, it is preferable that a portion where the adhesive resin exists and a portion where the adhesive resin does not exist are formed on the surface where the adhesive resin exists in the positive electrode, the negative electrode, and the separator. Specifically, for example, the location where the adhesive resin is present and the location where the adhesive resin is not present may be alternately formed in a groove shape, and the location where the adhesive resin such as a circle is not present in a plan view is not present. A plurality may be formed continuously. In these cases, the locations where the adhesive resin is present may be regularly arranged or randomly arranged.

In addition, in the presence surface of the adhesive resin in the positive electrode, the negative electrode, and the separator, when forming the location where the adhesive resin is present and the location where the adhesive resin is not present, The area (total area) may be such that, for example, the peel strength at 180 ° after thermocompression bonding of the separator and the electrode is the above value, and depending on the type of adhesive resin used Specifically, the adhesive resin is preferably present in 10 to 60% of the surface area of the adhesive resin in plan view.

Further, in the presence of the adhesive resin, the basis weight of the adhesive resin improves the adhesion with the electrode. For example, the peel strength at 180 ° after the pressure bonding between the separator and the electrode is performed as described above. to adjust the value is preferably to 0.05 g / ^{m 2} or more, and more preferably set to 0.1 g / ^{m 2} or more. However, if the basis weight of the adhesive resin is too large in the presence of the adhesive resin, the electrode body becomes too thick, or the adhesive resin blocks the pores of the separator, and the movement of ions inside the battery is hindered. There is a risk. Therefore, the existing surface of the adhesive resin, the basis weight of the adhesive resin is preferably 1 g / m ² or less, more preferably 0.5 g / m ² or less.

The adhesive layer is composed of an adhesive layer forming composition (adhesive resin solution or emulsion) containing an adhesive resin and a solvent, on one or both sides of a laminate of the porous membrane (I) and the porous layer (II). It can form through the process of apply | coating to.

As the non-aqueous electrolyte solution related to the lithium ion secondary battery, for example, a solution prepared by dissolving a lithium salt in the following non-aqueous solvent can be used.

Non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone (γ-BL ), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), 1,3-dioxolane, formamide, dimethylformamide (DMF), dioxolane, acetonitrile, nitromethane, Methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative Aprotic organic solvents such as diethyl ether and 1,3-propane sultone can be used singly or as a mixed solvent in which two or more are mixed.

The lithium salt according to the non-aqueous electrolyte solution, for _{_{_{example, LiClO 4, LiPF 6, LiBF}}} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) 2, LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO 3 (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] At least one selected from the above. The concentration of these lithium salts in the non-aqueous electrolyte is preferably 0.6 to 1.8 mol / l, and more preferably 0.9 to 1.6 mol / l.

Non-aqueous electrolytes include vinylene carbonate, vinyl ethylene carbonate, acid anhydride, sulfonic acid for the purpose of further improving the charge / discharge cycle characteristics of the battery and improving safety such as high temperature storage and overcharge prevention. Additives (including these derivatives) such as esters, dinitriles, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, t-butylbenzene can also be added as appropriate.

Furthermore, as the non-aqueous electrolyte, a gel (gel electrolyte) obtained by adding a known gelling agent such as a polymer can be used.

When assembling a lithium ion secondary battery, a negative electrode containing a negative electrode active material doped with Li ions, a positive electrode and a separator are assembled into a precursor of a lithium ion secondary battery. A method of sealing the exterior body after putting the non-aqueous electrolyte in the exterior body can be employed. In the precursor of the lithium ion secondary battery, the negative electrode, the positive electrode, and the separator that are accommodated in the outer package can be prepared in advance as the electrode body. Moreover, the doping of Li ions into the negative electrode active material contained in the negative electrode can be performed by, for example, extra-system pre-doping (i) or (ii).

There is no particular limitation on the form of the lithium ion secondary battery. For example, any of a small cylindrical shape, a coin shape, a button shape, a flat shape, a square shape, a large size used for an electric vehicle, and the like may be used.

Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of positive electrode>
Li ₂ CO ₃ that is a Li-containing compound, Co ₃ O ₄ that is a Co-containing compound, Mg (OH) ₂ that is a Mg-containing compound, ZrO ₂ that is a Zr compound, and Al (OH that is an Al-containing compound ₃ ) was mixed in a mortar at an appropriate mixing ratio, then solidified into pellets, calcined in an air atmosphere (under atmospheric pressure) at 950 ° C. for 24 hours using an muffle furnace, and determined by the ICP method A lithium cobaltate (A1) having a composition formula of LiCo _0.9795 Mg _0.011 Zr _0.0005 Al _0.009 O ₂ was synthesized.

Next, 10 g of the lithium cobaltate (A1) is added to 200 g of a lithium hydroxide aqueous solution having a pH of 10 and a temperature of 70 ° C., and the mixture is stirred and dispersed. Then, Al (NO ₃ ) is added thereto. ) ₃ · _9H 2 O: and 0.0154G, and ammonia water to suppress variation in pH, was added dropwise over 5 hours, to produce a Al _{(OH) 3} coprecipitate, the lithium cobalt oxide (A1 ). Thereafter, the lithium cobalt oxide (A1) to which the Al (OH) ₃ coprecipitate is adhered is taken out from the reaction solution, washed, dried, and then heat-treated at 400 ° C. for 10 hours in an air atmosphere. Thus, an Al-containing oxide film was formed on the surface of the lithium cobalt oxide (A1) to obtain a positive electrode material (a1).

The average particle diameter of the obtained positive electrode material (a1) was measured by the above method and found to be 27 μm.

Li ₂ CO ₃ that is a Li-containing compound, Co ₃ O ₄ that is a Co-containing compound, Mg (OH) ₂ that is an Mg-containing compound, and Al (OH) ₃ that is an Al-containing compound are appropriately mixed. After mixing in a mortar, the mixture was hardened into pellets, baked at 950 ° C. for 4 hours in an atmospheric atmosphere (under atmospheric pressure) using a muffle furnace, and the composition formula obtained by ICP method was LiCo _0.97. Mg _0.012 Al _0.009 O ₂ lithium cobaltate (B1) was synthesized.

Next, 10 g of the lithium cobalt oxide (B1) is added to 200 g of lithium hydroxide aqueous solution: 200 having a pH of 10 and a temperature of 70 ° C., and dispersed by stirring. _{₃₎ 3} · _9H 2 O: and 0.077 g, and ammonia water to suppress variation in pH, was added dropwise over 5 hours, to produce a Al _{(OH) 3} coprecipitate, the lithium cobaltate ( It was made to adhere to the surface of B1). Thereafter, the lithium cobaltate (B1) to which the Al (OH) ₃ coprecipitate is adhered is taken out from the reaction solution, washed, dried, and then heat-treated at 400 ° C. for 10 hours in an air atmosphere. Then, an Al-containing oxide film was formed on the surface of the lithium cobalt oxide (B1) to obtain a positive electrode material (b1).

The average particle diameter of the obtained positive electrode material (b1) was measured by the above method and found to be 7 μm.

Then, the positive electrode material (a1) and the positive electrode material (b1) were mixed at a mass ratio of 85:15 to obtain a positive electrode material (1) for battery preparation. When the average coating thickness of the Al-containing oxide on the surface of the obtained positive electrode material (1) was measured by the above method, it was 30 nm. Moreover, when the composition of the film was confirmed by element mapping when measuring the average coating thickness, the main component was Al ₂ O ₃ . Furthermore, when the volume-based particle size distribution of the positive electrode material (1) was confirmed by the above method, the average particle diameter was 25 μm, and peak tops were observed at the respective average particle diameters of the positive electrode material (a1) and the positive electrode material (b1). Two peaks were observed with Moreover, it was 0.25 m < ² > / g when the BET specific surface area of positive electrode material (1) was measured using the specific surface area measuring apparatus by a nitrogen adsorption method.

Positive electrode material (1): 96.5 parts by mass, NMP solution containing binder (P (VDF-CTFE) at a concentration of 10% by mass): 20 parts by mass, and acetylene black as a conductive auxiliary agent: 1.5 parts by mass Part was kneaded using a biaxial kneader, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing paste. This paste is applied to both sides of an aluminum foil having a thickness of 15 μm, vacuum-dried at 120 ° C. for 12 hours, a positive electrode mixture layer is formed on both sides of the aluminum foil, press treatment is performed, and a predetermined size is obtained. This was cut to obtain a strip-like positive electrode. In addition, when applying the positive electrode mixture-containing paste to the aluminum foil, a part of the aluminum foil is exposed, and the positive electrode mixture-containing paste is applied to both sides of the aluminum foil. The applied part was also made into the application part. The thickness of the positive electrode mixture layer of the obtained positive electrode (the thickness per one side when the positive electrode mixture layer was formed on both surfaces of the aluminum foil) was 55 μm.

Forming the positive electrode mixture layer so that a part of the exposed portion of the aluminum foil (positive electrode current collector) protrudes so that the strip-like positive electrode having the positive electrode mixture layer formed on both surfaces of the aluminum foil becomes a tab portion. The part was punched out with a Thomson blade so as to have a substantially quadrangular shape with four corners being curved, and a positive electrode for a battery having a positive electrode mixture layer on both surfaces of the positive electrode current collector was obtained. FIG. 1 is a plan view schematically showing the battery positive electrode (however, in order to facilitate understanding of the structure of the positive electrode, the size of the positive electrode shown in FIG. 1 does not necessarily match the actual one). Not) The positive electrode 10 has a shape having a tab portion 13 punched out so that a part of the exposed portion of the positive electrode current collector 12 protrudes, and the shape of the formation portion of the positive electrode mixture layer 11 is a substantially rectangular shape with four corners curved. In the figure, the lengths a, b and c were 8 mm, 37 mm and 2 mm, respectively.

<Production of negative electrode>
Composite Si-1 whose surface of SiO is coated with a carbon material (average particle diameter is 5 μm, specific surface area is 8.8 m ² / g, and the amount of carbon material in the composite is 10 parts by mass with respect to 100 parts by mass of SiO: 100 parts by mass. Part by mass) was used as the negative electrode active material. A unit represented by the above formula (1) and a unit represented by the above formula (2), wherein R is hydrogen and M 'is potassium in the above formula (2). A copolymer (A) having a molar ratio of 6/4 to the unit represented by the formula (2) is dissolved in ion-exchanged water, and an aqueous solution having a copolymer (A) concentration of 8% by mass is obtained. Prepared. The negative electrode active material and carbon black were added to this aqueous solution and mixed by stirring to obtain a negative electrode mixture-containing paste. The composition ratio (mass ratio) of negative electrode active material: carbon black: copolymer (A) in this paste was 90: 2: 8.

The negative electrode mixture-containing paste is applied to a copper foil having a thickness of 10 μm and dried to form a negative electrode mixture layer on one side and both sides of the copper foil, and press treatment is performed to reduce the density of the negative electrode mixture layer. After adjusting to 1.2 g / cm ³ , it was cut to a predetermined size to obtain a strip-shaped negative electrode. In addition, when applying the negative electrode mixture-containing paste to the copper foil, a part of the copper foil was exposed, and the negative electrode mixture layer formed on both sides is the back side where the coating part is the application part Was also applied.

Working a negative electrode of the strip-shaped electrode, the metallic lithium as the counter electrode, these mixed at a volumetric ratio of 30:70 between the non-aqueous electrolyte (ethylene carbonate and diethyl carbonate, LiPF ₆ was dissolved at a concentration of 1 mol / l, An electrolyte bath filled with vinylene carbonate: 4 mass%, 4-fluoro-1,3-dioxolan-2-one: a solution added in an amount of 5 mass%) was loaded. Then, an out-of-system pre-doping method (i) in which an amount of electricity corresponding to 500 mAh / g per mass of the negative electrode active material is passed between the negative electrode and metallic lithium at a current density of 0.2 mA / cm ² per area of the negative electrode. ), The negative electrode active material in the negative electrode mixture layer was doped with Li ions.

The negative electrode after doping with Li ions was taken out from the electrolytic bath, washed with diethyl carbonate, and then dried by blowing dry air.

In order to make the strip-shaped negative electrode after drying into a tab part, a part of the exposed part of the copper foil (negative electrode current collector) protrudes, and the formation part of the negative electrode mixture layer has curved corners. The battery was punched with a Thomson blade so as to have a substantially square shape, and a negative electrode for a battery having a negative electrode mixture layer on both surfaces and one surface of the negative electrode current collector was obtained. FIG. 2 is a plan view schematically showing the battery negative electrode (however, in order to facilitate understanding of the structure of the negative electrode, the size of the negative electrode shown in FIG. 2 does not necessarily match the actual size). Not) The negative electrode 20 has a shape having a tab portion 23 punched out so that a part of the exposed portion of the negative electrode current collector 22 protrudes, and the shape of the formation portion of the negative electrode mixture layer 21 is a substantially square shape with four corners curved. In the figure, the lengths of d, e, and f were 9 mm, 38 mm, and 2 mm, respectively.

<Preparation of separator>
To 5 kg of plate boehmite (average particle diameter 1 μm, aspect ratio 10), 5 kg of ion-exchanged water and 0.5 kg of a dispersant (aqueous polycarboxylic acid ammonium salt, solid content concentration 40% by mass) are added, and the internal volume is 20 L. Dispersion was prepared by crushing for 10 hours with a ball mill with 40 rotations / minute. When a part of the treated dispersion was vacuum dried at 120 ° C. and observed with a scanning electron microscope (SEM), the shape of boehmite was almost plate-like. The average particle size of the boehmite after the treatment was 1 μm.

To 500 g of the above dispersion, 0.5 g of xanthan gum as a thickener and 17 g of a resin binder dispersion (modified polybutyl acrylate, solid content 45% by mass) as a binder were added and stirred for 3 hours with a three-one motor to obtain uniform porosity. A slurry for forming a quality layer (II) (solid content ratio 50 mass%) was prepared.

PE microporous film (thickness 10 μm, porosity 40%, average pore diameter 0.08 μm, PE melting point 135 ° C.), corona discharge treatment (discharge amount 40 W · min / m) ² ), and the slurry for forming the porous layer (II) is applied to the treated surface by a micro gravure coater and dried to form a porous layer (II) having a thickness of 2 μm on one side of the porous membrane (I). Formed.

Next, an aqueous solution (containing 20% by mass of polyacrylic acid) of a delayed tack type adhesive resin as an adhesive resin is applied to the porous film (I) side and the porous layer (II) side of the laminate. It was applied using a gravure coater and dried to obtain a separator (thickness 22 μm) having adhesive resin on both sides. In this separator, the total area of the adhesive resin existing portion on the surface where the adhesive resin is present is 30% of the area of the adhesive resin existing surface on the separator, and the basis weight of the adhesive resin is 0.5 g. / M ² .

<Battery assembly>
Two negative electrodes for a battery having a negative electrode mixture layer formed on one side of the negative electrode current collector, 16 negative electrodes for a battery having a negative electrode mixture layer formed on both sides of the negative electrode current collector, and a positive electrode mixture on both sides of the positive electrode current collector A laminate was formed using 17 positive electrodes for a battery having a layer formed thereon and the separator. In this laminate, a negative electrode for a battery in which a negative electrode mixture layer is formed on one side of a negative electrode current collector is disposed on the outermost part, and a positive electrode mixture layer is formed on both sides of the positive electrode current collector on the inner side thereof The positive electrode and the negative electrode for a battery having a negative electrode mixture layer formed on both surfaces were alternately arranged. One separator was interposed between each battery positive electrode and each battery negative electrode so that the porous layer (II) faced the positive electrode. Also, when laminating the battery positive electrode and the battery negative electrode, the tab parts of all the battery positive electrodes are on the same side, the tab parts of all the battery negative electrodes are on the same side, and the battery The side was different from the tab portion of the positive electrode.

Next, the tab portions of the battery positive electrodes in the laminate were welded together, and the tab portions of the battery negative electrodes in the laminate were welded together to obtain a laminated electrode body. Then, the laminated electrode body is inserted into the depression of a metal (aluminum) laminate film having a thickness of 0.15 mm, a width of 34 mm, and a height of 50 mm in which the depression is formed so that the electrode body can be accommodated thereon, A metal (aluminum) laminate film of the same size as described above was placed, and three sides of both metal laminate films were thermally welded. Then, from the remaining one side of both metal laminate films, LiPF ₆ was dissolved at a concentration of 1 mol / l in a non-aqueous electrolyte (a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 30:70), and vinylene carbonate: 4 And a solution added in an amount of 5% by mass, 4-fluoro-1,3-dioxolan-2-one: 5% by mass, adiponitrile: 0.5% by mass, and 1,3-dioxane: 0.5% by mass) Injected. Thereafter, the remaining one side of both metal laminate films was vacuum-sealed to produce a lithium ion secondary battery having a cross-sectional structure shown in FIG. 4 with the appearance shown in FIG.

Here, FIG. 3 and FIG. 4 will be described. FIG. 3 is a plan view schematically showing a lithium ion secondary battery, and FIG. 4 is a cross-sectional view taken along the line II of FIG. The lithium ion secondary battery 100 accommodates a laminated electrode body 102 and a non-aqueous electrolyte (not shown) in a metal (aluminum) laminate film outer package 101 constituted by two metal (aluminum) laminate films. The metal laminate film outer package 101 is sealed by heat-sealing the upper and lower metal laminate films at the outer periphery thereof. In FIG. 4, in order to avoid the complexity of the drawing, the layers constituting the metal laminate film outer package 101 and the positive electrode, the negative electrode, and the separator constituting the laminated electrode body are not shown separately. .

Each positive electrode of the laminated electrode body 102 is integrated by welding the tab portions together, and the integrated product of the welded tab portions is connected to the positive electrode external terminal 103 in the battery 100, although not shown. The negative electrode and the third electrode of the laminated electrode body 102 are also integrated by welding the tab portions, and the integrated product of the welded tab portions is connected to the negative electrode external terminal 104 in the battery 100. The positive electrode external terminal 103 and the negative electrode external terminal 104 are drawn out to the outside of the metal laminate film exterior body 101 so that they can be connected to an external device or the like.

(Example 2)
Corona discharge treatment (discharge amount 40 W · min / m ² ) was applied to one side of the same PE microporous membrane [porous membrane (I)] used in Example 1, and this treated surface was subjected to Example 1 The same slurry for forming the porous layer (II) as used was applied by a micro gravure coater and dried to form a porous layer (II) having a thickness of 4 μm on one side of the porous membrane (I). Got. A lithium ion secondary battery was produced in the same manner as in Example 1 except that this separator was used.

(Example 3)
Except for changing Al _(NO ₃₎ the amount of 3 · 9H ₂ O to 0.0026g was prepare a positive electrode material in the same manner as the positive electrode material (a1) (a2). With respect to the positive electrode material (a2) obtained, its average particle diameter was measured by means of the method as described before, thereby finding that it was 27 μm.

Also, except for changing the Al _(NO ₃₎ the amount of 3 · 9H ₂ O in 0.013g is to prepare a positive electrode material (b2) in the same manner as the positive electrode material (b1). With respect to the positive electrode material (b2) obtained, its average particle diameter was measured by means of the method as described before, thereby finding that it was 7 μm.

Next, the positive electrode material (a2) and the positive electrode material (b2) were mixed at a mass ratio of 85:15 to obtain a positive electrode material (2) for battery production. When the average coating thickness of the Al-containing oxide on the surface of the obtained positive electrode material (2) was measured by the above method, it was 5 nm. Moreover, when the composition of the film was confirmed by element mapping when measuring the average coating thickness, the main component was Al ₂ O ₃ . Further, when the volume-based particle size distribution of the positive electrode material (2) was confirmed by the above method, the average particle diameter was 25 μm, and peak tops were observed at the respective average particle diameters of the positive electrode material (a2) and the positive electrode material (b2). Two peaks were observed with Moreover, it was 0.25 m < ² > / g when the BET specific surface area of positive electrode material (2) was measured using the specific surface area measuring apparatus by a nitrogen adsorption method.

Then, a positive electrode was produced in the same manner as in Example 1 except that the positive electrode material (2) was used instead of the positive electrode material (1), and the lithium ion secondary was prepared in the same manner as in Example 2 except that this positive electrode was used. A battery was produced.

Example 4
Except for changing Al _(NO ₃₎ the amount of 3 · 9H ₂ O to 0.0256g was prepare a positive electrode material in the same manner as the positive electrode material (a1) (a3). With respect to the positive electrode material (a3) obtained, its average particle diameter was measured by means of the method as described before, thereby finding that it was 27 μm.

Also, except for changing the Al _(NO ₃₎ the amount of 3 · 9H ₂ O in 0.128g is to prepare a positive electrode material (b3) in the same manner as the positive electrode material (b1). With respect to the positive electrode material (b3) obtained, its average particle diameter was measured by means of the method as described before, thereby finding that it was 7 μm.

Next, the positive electrode material (a3) and the positive electrode material (b3) were mixed at a mass ratio of 85:15 to obtain a positive electrode material (3) for battery preparation. When the average coating thickness of the Al-containing oxide on the surface of the obtained positive electrode material (3) was measured by the above method, it was 50 nm. Moreover, when the composition of the film was confirmed by element mapping when measuring the average coating thickness, the main component was Al ₂ O ₃ . Furthermore, when the volume-based particle size distribution of the positive electrode material (3) was confirmed by the above method, the average particle diameter was 25 μm, and peak tops were observed at the respective average particle diameters of the positive electrode material (a3) and the positive electrode material (b3). Two peaks were observed with Moreover, it was 0.25 m < ² > / g when the BET specific surface area of positive electrode material (3) was measured using the specific surface area measuring apparatus by a nitrogen adsorption method.

Then, a positive electrode was produced in the same manner as in Example 1 except that the positive electrode material (3) was used instead of the positive electrode material (1), and a lithium ion secondary was prepared in the same manner as in Example 2 except that this positive electrode was used. A battery was produced.

(Example 5)
Lithium cobaltate (A1) and lithium cobaltate (B1) synthesized by the same method as in Example 1 were mixed at a mass ratio of 85:15 to obtain a positive electrode material (4) for battery production. It was.

Positive electrode material (4): 96.5 parts by mass; NMP solution containing P (VDF-CTFE) as a binder at a concentration of 10% by mass: 17 parts by mass; Acetylene black as a conductive auxiliary agent: 1.3 parts by mass Part and an alumina filler having an average particle size of 0.7 μm: 0.5 part by mass is kneaded using a biaxial kneader, and NMP is added to adjust the viscosity to prepare a positive electrode mixture-containing paste. Then, a positive electrode was produced in the same manner as in Example 1 except that this positive electrode mixture-containing paste was used, and a lithium ion secondary battery was produced in the same manner as in Example 2 except that this positive electrode was used.

(Example 6)
LiCoO _{2 as a} positive electrode active material: 96.5 parts by mass, NMP solution containing 10% by mass of P (VDF-CTFE) as a binder: 17 parts by mass, and acetylene black as a conductive auxiliary agent: 1. 3 parts by mass and alumina filler having an average particle size of 0.7 μm: 0.5 parts by mass are kneaded using a biaxial kneader, and NMP is added to adjust the viscosity to contain a positive electrode mixture. A paste was prepared, and a positive electrode was produced in the same manner as in Example 1 except that this positive electrode mixture-containing paste was used. A lithium ion secondary battery was produced in the same manner as in Example 2 except that this positive electrode was used. .

(Example 7)
Graphite A (graphite whose surface is not coated with amorphous carbon): 25% by mass and graphite B (graphite whose surface is made of natural graphite and coated with amorphous carbon using pitch as a carbon source) Yes, the average particle size is 10 μm): 25 mass% and composite Si-1: 50 mass% were mixed in a V-type blender for 12 hours to obtain a negative electrode active material. A strip-shaped negative electrode was prepared in the same manner as in Example 1 except that this negative electrode active material was used, and the strip-shaped negative electrode was formed in the same manner as in Example 1 except that the amount of electricity was 250 mAh / g per mass of the negative electrode active material. The negative electrode was doped with Li ions. And the lithium ion secondary battery was produced like Example 2 except having used this strip | belt-shaped negative electrode.

(Example 8)
The graphite A: 48% by mass, the graphite B: 48% by mass, and the Si-1: 4% by mass were mixed in a V-type blender for 12 hours to obtain a negative electrode active material. A strip-shaped negative electrode was produced in the same manner as in Example 1 except that this negative electrode active material was used, and the strip-shaped negative electrode was formed in the same manner as in Example 1 except that the amount of electricity was 50 mAh / g per mass of the negative electrode active material. The negative electrode was doped with Li ions. And the lithium ion secondary battery was produced like Example 2 except having used this strip | belt-shaped negative electrode.

Example 9
Composite Si-2 whose surface of SiO is coated with a carbon material (average particle size is 5 μm, specific surface area is 7.9 m ² / g, and the amount of carbon material in the composite is 5 for SiO: 100 parts by mass. A lithium ion secondary battery was produced in the same manner as in Example 2 except that (part by mass) was used as the negative electrode active material.

(Example 10)
Composite Si-3 whose surface of SiO is coated with a carbon material (average particle size is 5 μm, specific surface area is 9.9 m ² / g, and the amount of carbon material in the composite is 15 parts by mass with respect to 100 parts by mass of SiO: 100 parts by mass. A lithium ion secondary battery was produced in the same manner as in Example 1 except that (part by mass) was used as the negative electrode active material.

(Example 11)
Except that the amount of electricity supplied was 450 mAh / g per mass of the negative electrode active material, lithium ions were doped in the same manner as in Example 1 except that the strip-shaped negative electrode was doped with lithium ions and this negative electrode was used. A secondary battery was produced.

(Example 12)
Except that the amount of electricity was 550 mAh / g per mass of the negative electrode active material, lithium ions were doped in the same manner as in Example 1 except that the strip-shaped negative electrode was doped with Li ions and this negative electrode was used. A secondary battery was produced.

(Example 13)
The graphite A: 50% by mass and the graphite B: 50% by mass were mixed with a V-type blender for 12 hours to obtain a negative electrode active material. This negative electrode active material: 97 parts by mass, CMC: 1.5 parts by mass, and SBR: 1.5 parts by mass were mixed with ion-exchanged water to prepare a negative electrode mixture-containing paste. A belt-like negative electrode was prepared in the same manner as in Example 1 except that this negative electrode mixture paste was used, and the same as in Example 1 except that the amount of electricity passed was 30 mAh / g per negative electrode active material mass. The strip-shaped negative electrode was doped with Li ions. And the lithium ion secondary battery was produced like Example 2 except having used this strip | belt-shaped negative electrode.

(Comparative Example 1)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the same microporous membrane made of PE as that used in Example 1 as the porous membrane (I) was used as the separator.

(Comparative Example 2)
Except that the amount of electricity supplied was 0 mAh / g per mass of the negative electrode active material, the same treatment as in doping of Li ions into the strip-shaped negative electrode was performed in the same manner as in Example 1, and Example 2 was used except that this negative electrode was used. Similarly, a lithium ion secondary battery was produced.

(Comparative Example 3)
Except that the amount of electricity supplied was 650 mAh / g per mass of the negative electrode active material, lithium ions were doped in the strip-like negative electrode in the same manner as in Example 1 and lithium ion was obtained in the same manner as in Example 2 except that this negative electrode was used. A secondary battery was produced.

The following evaluations were performed on each of the lithium ion secondary batteries of Examples and Comparative Examples.

<Measurement of Li content in positive electrode active material>
Five lithium ion secondary batteries of Examples and Comparative Examples were each charged with a constant current of up to 4.4 V at a current value of 0.5 C, and subsequently reached a current value of 0.02 C at a constant voltage of 4.4 V. Charged until Thereafter, the battery was discharged at a discharge current rate of 0.1 C until the voltage reached 2.0V. And the metal laminate film exterior body was disassembled in the glove box, and only the positive electrode was taken out. After the positive electrode taken out was washed with diethyl carbonate, the positive electrode mixture layer was scraped out, and the composition ratio “Li / M” (Li: Li amount, M: metal other than Li) of the metal other than Li and Li by the ICP method described above. Amount) was calculated, and an average value of five positive electrodes was obtained.

<Charge / discharge cycle characteristics evaluation>
Five lithium ion secondary batteries of Examples and Comparative Examples (batteries different from those for Li / M calculation described above) were charged at a constant current of up to 4.4 V at a current value of 0.5 C, and then 4 The battery was charged at a constant voltage of 0.4 V until the current value reached 0.02C. Then, it discharged to 2.0V with the constant current of 0.2C, and calculated | required the initial discharge capacity.

After the initial discharge capacity measurement, the lithium ion secondary batteries (5 each) were charged at a constant current of up to 4.4V at a current value of 0.5C, and subsequently the current value was set at 0.02C at a constant voltage of 4.4V. Charged until it reached. Then, it discharged to 2.0V with the constant current of 0.2C, and calculated | required the initial discharge capacity. Next, each battery was charged with a constant current up to 4.4 V at a current value of 1 C, subsequently charged with a constant voltage of 4.4 V until the current value reached 0.05 C, and then 2. with a current value of 1 C. A series of operations for discharging to 0 V was taken as one cycle, and this was repeated 500 times. Each battery was subjected to constant current-constant voltage charging and constant current discharging under the same conditions as those for the initial discharge capacity measurement, and the discharge capacity was determined. Then, a value obtained by dividing these discharge capacities by the initial discharge capacities was expressed as a percentage to obtain a capacity maintenance ratio, and an average value of 5 pieces was calculated for each.

The evaluation results are shown in Table 1 together with the separator configuration related to each battery. In Table 1, a separator having the porous membrane (I) and the porous layer (II) is referred to as “laminated type”. Moreover, in Table 1, the capacity retention ratio at the time of charge / discharge cycle characteristic evaluation is shown as a relative value when the value of the battery of Comparative Example 1 is 100.

As shown in Table 1, the molar ratio Li / M in the positive electrode active material under a specific condition is set to an appropriate value using the negative electrode subjected to extra-system pre-doping, and the porous film (I) and the porous layer (II) The lithium ion secondary batteries of Examples 1 to 13 using the laminated separator having the characteristics are compared with the battery of Comparative Example 1 using the PE microporous membrane separator that is widely used in ordinary lithium ion secondary batteries. The capacity retention rate at the time of charge / discharge cycle characteristic evaluation was high, and the battery had excellent charge / discharge cycle characteristics.

On the other hand, the battery of Comparative Example 2 in which the molar ratio Li / M was too small using a negative electrode in which the doping of Li ions was not sufficiently progressed and the energization of the extra-predoping were not conducted during the extra-predoping. The battery of Comparative Example 3 in which the molar ratio Li / M was too large using a negative electrode in which the doping amount of Li ions was excessive by setting the amount of electricity had a low capacity retention rate at the time of charge / discharge cycle characteristics evaluation. Discharge cycle characteristics were inferior.

[Experimental example of a lithium ion secondary battery having a negative electrode containing a negative electrode active material doped with Li ions by an extra-system pre-doping method (ii)]
A negative electrode was produced in the same manner as in Example 1 except that the same composite Si-1 as used in Example 1 was doped with Li ions by the extra-system pre-doping method (ii) to obtain a negative electrode active material. And the lithium ion secondary battery was able to be produced favorably by carrying out similarly to Example 1 except having used this negative electrode, without performing the pre dope by an extrasystem pre dope method (i).

The present invention can be implemented in other forms as long as it does not depart from the spirit of the present invention. The embodiments disclosed in the present application are examples, and the present invention is not limited to these embodiments. The scope of the present invention is construed in preference to the description of the appended claims rather than the description of the above specification, and all modifications within the scope equivalent to the claims are construed in the scope of the claims. included.

The lithium ion secondary battery of the present invention can be applied to the same use as that of a conventionally known lithium ion secondary battery.

DESCRIPTION OF SYMBOLS 10 Positive electrode 11 Positive electrode mixture layer 12 Positive electrode collector 13 Tab part 20 Negative electrode 21 Negative electrode mixture layer 22 Negative electrode collector 23 Tab part 100 Lithium ion secondary battery 101 Metal laminated film exterior body 102 Laminated electrode body 103 Positive electrode external terminal 104 Negative external terminal

Claims

A negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder, a positive electrode having a positive electrode mixture layer containing a positive electrode active material and a binder, and a precursor of a lithium ion secondary battery in which a separator is housed in an exterior body Because
The negative electrode mixture layer contains at least a negative electrode active material doped with Li ions,
The positive electrode mixture layer contains a metal oxide composed of Li and a metal M other than Li as the positive electrode active material,
The separator has a porous membrane (I) mainly composed of a thermoplastic resin and a porous layer (II) mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher. Secondary battery precursor.
The precursor of a lithium ion secondary battery according to claim 1, wherein the negative electrode mixture layer contains a material S containing Si as the negative electrode active material.
The precursor of the lithium ion secondary battery according to claim 2, wherein the material S is SiO x (where 0.5 ≦ x ≦ 1.5).
The lithium ion secondary battery precursor according to claim 3, wherein the SiO x forms a composite with a carbon material.
The precursor of a lithium ion secondary battery according to claim 4, wherein the content of the composite in the total amount of the negative electrode active material contained in the negative electrode mixture layer is 5% by mass or more.
The negative electrode mixture layer contains a copolymer having a unit represented by the following formula (1) and a unit represented by the following formula (2) as the binder. A precursor of the lithium ion secondary battery according to 1.

[In the formula (2), R is hydrogen or a methyl group, and M ′ is an alkali metal element. ]
The positive electrode mixture layer includes a positive electrode material in which the surface of the positive electrode active material particles is coated with an Al-containing oxide, the average coating thickness of the Al-containing oxide is 5 to 50 nm, and the positive electrode material includes The positive electrode active material to be used is lithium cobalt oxide containing at least Co and at least one element M 1 selected from the group consisting of Mg, Zr, Ni, Mn, Ti and Al. The precursor of the lithium ion secondary battery in any one.
The precursor of a lithium ion secondary battery according to any one of claims 1 to 7, wherein the separator has an adhesive layer on one side or both sides.
A lithium ion secondary battery precursor according to any one of claims 1 to 8, and a non-aqueous electrolyte,
When discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V, the molar ratio (Li / M) between Li and metal M other than Li contained in the positive electrode active material is 0.8-1 .05, a lithium ion secondary battery.
A method for manufacturing the lithium ion secondary battery according to claim 9, comprising:
A step of doping the negative electrode active material with Li ions of a negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder;
Assembling a precursor of a lithium ion secondary battery using the negative electrode subjected to the step;
And a step of forming a lithium ion secondary battery using the precursor of the lithium ion secondary battery and a non-aqueous electrolyte.
A method for manufacturing the lithium ion secondary battery according to claim 9, comprising:
Producing a negative electrode having a negative electrode mixture layer containing a negative electrode active material doped with Li ions at least partially and a binder;
Assembling a precursor of a lithium ion secondary battery using the negative electrode obtained by the step;
And a step of forming a lithium ion secondary battery using the precursor of the lithium ion secondary battery and a non-aqueous electrolyte.