JP6268708B2 - Positive electrode for lithium secondary battery and lithium secondary battery - Google Patents

Description

  The present invention relates to a lithium secondary battery using as an active material a material in which a polymer radical material is combined with a conductive agent on the surface of an active material, particularly on the surface of a lithium composite oxide.

  In recent years, portable electronic devices such as notebook computers and mobile phones have become multifunctional, including communication functions, video playback functions, and camera functions. There are various demands such as safety, miniaturization, and weight reduction for power storage devices used in such portable electronic devices, and characteristics such as high energy density, high output density, and high cycle stability are required. Yes.

  A lithium secondary battery using an electrode that is a mixture of an active material for a lithium secondary battery such as a lithium composite oxide and a polymer radical material such as a nitroxyl polymer compound utilizes the ion adsorption / desorption reaction of the polymer radical material. By doing so, it is expected that faster reaction, that is, higher input / output characteristics can be obtained. For example, Patent Document 1 proposes a power storage device containing a nitroxyl compound in a positive electrode as a high power power storage device. However, since the polymer radical material has low conductivity, it has been difficult to obtain high input / output characteristics as expected.

  On the other hand, as shown in Patent Document 2, for example, a polymer radical material and a conductive agent are combined in advance and mixed with an active material of a lithium secondary battery and a conductive agent that is not combined with a polymer radical material. It is said that the output characteristics of the electrode are improved as compared with those obtained by simply mixing the polymer radical material and the conductive agent without combining them.

JP 2002-304996 A JP 2007-213992 A

  However, the conductive agent combined with the polymer radical material has high cohesive force, and since it tends to disperse unevenly when it is kneaded and mixed with the active material of the lithium secondary battery to produce an electrode, the reaction of the electrode It is difficult to obtain higher output characteristics. In addition, if the charge / discharge cycle is repeated, the characteristics may deteriorate early.

  Therefore, an electrode in which a polymer radical material, a conductive agent, and a lithium composite oxide are uniformly dispersed is required.

  One embodiment of the present invention is characterized in that a conductive material and a polymer radical material having a radical partial structure in a reduced state are fused and combined on the surface of an active material for a lithium secondary battery. The present invention relates to an active material for a lithium secondary battery.

  According to the present invention, a lithium secondary battery having excellent load characteristics can be obtained.

  The present invention is characterized in that an active material of a lithium secondary battery, in particular, a material in which a polymer radical material and a conductive agent are combined on the surface of a lithium composite oxide is newly used for an electrode as an active material of a lithium secondary battery. It is said. Here, the composite means that the polymer radical material is fused with the conductive agent on the surface of the lithium composite oxide, and the lithium composite oxide, the conductive agent, and the polymer radical material are integrated. In addition, a conductive agent and a polymer radical material on the surface of a lithium composite oxide, or a composite of a conductive agent and a polymer radical material is simply applied to the surface of the lithium composite oxide without fusing the polymer radical material. It is distinguished from contact or a state in which it is bound by a binder other than the polymer radical material. On the other hand, the new composite active material is combined with a current collector or a newly applied conductive agent by a binder different from the polymer radical material used for the composite to form an electrode. . Here, when the electrode is formed, if the lithium composite oxide is not pre-complexed with the conductive agent and the polymer radical material, the cohesive force of the composite of the conductive agent and the polymer radical is high. The body tends to aggregate, and as a result, a non-uniform electrode in which only the complex is locally aggregated in the electrode is likely to be formed. On the other hand, when the lithium composite oxide is pre-complexed with the conductive agent and the polymer radical material, such agglomeration is unlikely to occur due to the interposition of the lithium composite oxide. The body, the newly added conductive agent, and the electrode in which the binder is uniformly dispersed are formed. As a result, the resistance of the electrode is lowered, and higher output characteristics can be obtained.

  The active material of the lithium secondary battery that is combined with the polymer radical material of the present invention preferably has a reaction potential close to that of the polymer radical material. Therefore, the active material of the lithium secondary battery that is combined with the polymer radical material is preferably used for the positive electrode.

(Positive electrode active material)
The positive electrode active material of the lithium secondary battery composited with the polymer radical material of the present invention is not particularly limited as long as it can be used as the positive electrode active material of the lithium secondary battery. LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiMn _0.5 Ni _0.5 O ₂ , LiNi _0.7 Co _0.2 Mn _0.1 O ₂ , LiFePO ₄ and other lithium composite oxides used as positive electrode active materials, and MnO Examples include metal oxides such as ₂ that do not contain lithium. In addition, any substance that electrochemically inserts and desorbs lithium can be used without limitation. Of these, LiFePO ₄ and LiMn ₂ O ₄ having a reaction potential close to that of the polymer radical material are preferable. A plurality of these positive electrode active materials may be mixed or compounded, and those combined with a polymer radical material in the positive electrode and uncomposited materials may be mixed.

(Polymer radical material)
The polymer radical material of the present invention is a nitroxyl polymer compound having a nitroxyl cation partial structure represented by the chemical formula (1) in an oxidized state and a nitroxyl radical partial structure represented by the chemical formula (2) in a reduced state. It is characterized by that.

  The nitroxyl polymer compound is preferably a polymer compound containing a cyclic nitroxyl structure represented by the following chemical formula (3) in a reduced state.

化学式（３）中、Ｒ_１〜Ｒ_４はそれぞれ独立にアルキル基を表し、それぞれ独立に直鎖状のアルキル基が好ましい。またラジカルの安定性の観点から、Ｒ_１〜Ｒ_４はそれぞれ独立に炭素数１〜４のアルキル基が好ましく、特にメチル基が好ましい。Ｘは化学式（３）が５〜７員環を形成するような２価の基を表し、少なくとも一部がポリマーの主鎖の一部を構成する。このようなＸの具体例として、例えば、−ＣＨ_２ＣＨ_２−、−ＣＨ_２ＣＨ_２ＣＨ_２−、−ＣＨ_２ＣＨ_２ＣＨ_２ＣＨ_２−、−ＣＨ＝ＣＨ−、−ＣＨ＝ＣＨＣＨ_２−、−ＣＨ＝ＣＨＣＨ_２ＣＨ_２−、−ＣＨ_２ＣＨ＝ＣＨＣＨ_２−が挙げられ、その中で隣接しない−ＣＨ_２−は、−Ｏ−、−ＮＨ−又は−Ｓ−によって置き換えられていてもよく、−ＣＨ＝は、−Ｎ＝によって置き換えられていてもよい。また環を構成する原子に結合した水素原子は、アルキル基、ハロゲン原子、＝Ｏ、エーテル基、エステル基、シアノ基、アミド基等により置換されていてもよい。

In the chemical formula (3), R _{1 to} R ₄ each independently represents an alkyl group, and each independently preferably a linear alkyl group. From the viewpoint of radical stability, R _{1 to} R ₄ are each independently preferably an alkyl group having 1 to 4 carbon atoms, and particularly preferably a methyl group. X represents a divalent group such that chemical formula (3) forms a 5- to 7-membered ring, and at least a part thereof constitutes a part of the main chain of the polymer. Specific examples of such X, for _{example, -CH 2 CH 2 -, -} CH 2 CH 2 CH 2 -, - CH 2 CH 2 CH 2 CH 2 -, - CH = CH -, - CH = CHCH 2 - , —CH═CHCH ₂ CH ₂ —, —CH ₂ CH═CHCH ₂ —, in which —CH ₂ — that is not adjacent may be replaced by —O—, —NH—, or —S—. Often, -CH = may be replaced by -N =. In addition, a hydrogen atom bonded to an atom constituting the ring may be substituted with an alkyl group, a halogen atom, ═O, an ether group, an ester group, a cyano group, an amide group, or the like.

Among them, particularly preferred cyclic nitroxyl structures are 2,2,6,6-tetramethylpiperidinoxyl radical represented by the chemical formula (6) and 2,2,5,5- It is selected from the group consisting of a tetramethylpyrrolidinoxyl radical and a 2,2,5,5-tetramethylpyrrolinoxyl radical represented by the chemical formula (8). In the chemical formulas (6) to (8), R _{1 to} R ₄ are the same as those in the chemical formula (3).

The cyclic nitroxyl structure represented by the chemical formula (3) constitutes a part of the polymer as a part of the side chain or main chain. That is, at least a part of X constitutes a part of the main chain of the polymer, and a side chain or a part of the main chain of the polymer as a structure in which at least one hydrogen bonded to the element forming the cyclic structure is removed. Exists. It is preferable that it exists in the side chain from the viewpoint of ease of synthesis. When present in the side chain, like the residue represented by the following chemical formula (9), —CH ₂ —, —CH═ constituting the ring member in the group X of the cyclic nitroxyl structure represented by the chemical formula (3) Alternatively, it is bonded to the main chain polymer by a residue X ′ obtained by removing hydrogen from —NH—.

化学式（９）中、Ｒ_１〜Ｒ_４は前記化学式（３）と同じであり、Ｘ’は前記化学式（３）のＸから水素を取った残基を表したものである。このとき用いられる主鎖ポリマーの構造としては特に制限はなく、どのようなものであっても、化学式（９）で示される残基が側鎖に存在していればよい。具体的には、次に挙げるポリマーに、化学式（９）で示される残基が付加したもの、又はポリマーの一部の原子又は基が、化学式（９）で示される残基によって置換されたものを挙げることができる。いずれの場合も、化学式（９）で示される残基が直接ではなく、適当な２価の基を中間に介して結合していてもよい。主鎖ポリマーの構造としては、例えば、ポリエチレン、ポリプロピレン、ポリブテン、ポリデセン、ポリドデセン、ポリヘプテン、ポリイソブテン、ポリオクタデセン等のポリアルキレン系ポリマー；ポリブタジエン、ポリクロロプレン、ポリイソプレン、ポリイソブテン等のジエン系ポリマー；ポリ（メタ）アクリル酸；ポリ（メタ）アクリロニトリル；ポリ（メタ）アクリルアミド、ポリメチル（メタ）アクリルアミド、ポリジメチル（メタ）アクリルアミド、ポリイソプロピル（メタ）アクリルアミド等のポリ（メタ）アクリルアミド類ポリマー；ポリメチル（メタ）アクリレート、ポリエチル（メタ）アクリレート、ポリブチル（メタ）アクリレート等のポリアルキル（メタ）アクリレート類；ポリフッ化ビニリデン、ポリテトラフルオロエチレン等のフッ素系ポリマー；ポリスチレン、ポリブロモスチレン、ポリクロロスチレン、ポリメチルスチレン等のポリスチレン系ポリマー；ポリビニルアセテート、ポリビニルアルコール、ポリ塩化ビニル、ポリビニルメチルエーテル、ポリビニルカルバゾール、ポリビニルピリジン、ポリビニルピロリドン等のビニル系ポリマー；ポリエチレンオキサイド、ポリプロピレンオキサイド、ポリブテンオキサイド、ポリオキシメチレン、ポリアセトアルデヒド、ポリメチルビニルエーテル、ポリプロピルビニルエーテル、ポリブチルビニルエーテル、ポリベンジルビニルエーテル等のポリエーテル系ポリマー；ポリメチレンスルフィド、ポリエチレンスルフィド、ポリエチレンジスルフィド、ポリプロピレンスルフィド、ポリフェニレンスルフィド、ポリエチレンテトラフルフィド、ポリエチレントリメチレンスルフィド等のポリスルフィド系ポリマー；ポリエチレンテレフタレート、ポリエチレンアジペート、ポリエチレンイソフタレート、ポリエチレンナフタレート、ポリエチレンパラフェニレンジアセテート、ポリエチレンイソプロピリデンジベンゾエート等のポリエステル類；ポリトリメチレンエチレンウレタン等のポリウレタン類；ポリエーテルケトン、ポリアリルエーテルケトン等のポリケトン系ポリマー；ポリオキシイソフタロイル等のポリ無水物系ポリマー；ポリエチレンアミン、ポリヘキサメチレンアミン、ポリエチレントリメチレンアミン等のポリアミン系ポリマー；ナイロン、ポリグリシン、ポリアラニン等のポリアミド系ポリマー；ポリアセチルイミノエチレン、ポリベンゾイルイミノエチレン等のポリイミン系ポリマー；ポリエステルイミド、ポリエーテルイミド、ポリベンズイミド、ポリピロメルイミド等のポリイミド系ポリマー；ポリアリレン、ポリアリレンアルキレン、ポリアリレンアルケニレン、ポリフェノール、フェノール樹脂、セルロース、ポリベンゾイミダゾール、ポリベンゾチアゾール、ポリベンゾキサジン、ポリベンゾキサゾール、オリカルボラン、ポリジベンゾフラン、ポリオキソイソインドリン、ポリフランテトラカルボキシル酸ジイミド、ポリオキサジアゾール、ポリオキシンドール、ポリフタラジン、ポリフタライド、ポリシアヌレート、ポリイソシアヌレート、ポリピペラジン、ポリピペリジン、ポリピラジノキノキサン、ポリピラゾール、ポリピリダジン、ポリピリジン、ポリピロメリチミン、ポリキノン、ポリピロリジン、ポリキノキサリン、ポリトリアジン、ポリトリアゾール等のポリアロマティック系ポリマー；ポリジシロキサン、ポリジメチルシロキサン等のシロキサン系ポリマー；ポリシラン系ポリマー；ポリシラザン系ポリマー；ポリホスファゼン系ポリマー；ポリチアジル系ポリマー；ポリアセチレン、ポリピロール、ポリアニリン等の共役系ポリマーを挙げることができる。なお、（メタ）アクリルとはメタクリル又はアクリルを意味する。この中で、電気化学的な耐性に優れている点で、ポリアルキレン系ポリマー、ポリ（メタ）アクリル酸、ポリ（メタ）アクリルアミド類ポリマー、ポリアルキル（メタ）アクリレート類、ポリスチレン系ポリマーを主鎖構造として有することが好ましい。主鎖とは、高分子化合物中で、最も炭素数の多い炭素鎖のことである。

In the chemical formula (9), R _{1 to} R ₄ are the same as those in the chemical formula (3), and X ′ represents a residue obtained by removing hydrogen from X in the chemical formula (3). There is no restriction | limiting in particular as a structure of the main chain polymer used at this time, Whatever is necessary, the residue shown by Chemical formula (9) should just exist in a side chain. Specifically, a polymer represented by the following chemical formula (9) is added to the following polymer, or a part of the polymer atom or group is substituted by a residue represented by the chemical formula (9) Can be mentioned. In any case, the residue represented by the chemical formula (9) may be bonded via an appropriate divalent group in the middle instead of directly. Examples of the structure of the main chain polymer include polyalkylene polymers such as polyethylene, polypropylene, polybutene, polydecene, polydodecene, polyheptene, polyisobutene, and polyoctadecene; diene polymers such as polybutadiene, polychloroprene, polyisoprene, and polyisobutene; (Meth) acrylic acid; poly (meth) acrylonitrile; poly (meth) acrylamide polymers such as poly (meth) acrylamide, polymethyl (meth) acrylamide, polydimethyl (meth) acrylamide, polyisopropyl (meth) acrylamide; polymethyl (meta ) Polyalkyl (meth) acrylates such as acrylate, polyethyl (meth) acrylate, polybutyl (meth) acrylate; polyvinylidene fluoride, polytetraph Fluoropolymers such as oloethylene; polystyrene polymers such as polystyrene, polybromostyrene, polychlorostyrene, and polymethylstyrene; polyvinyl acetate, polyvinyl alcohol, polyvinyl chloride, polyvinyl methyl ether, polyvinyl carbazole, polyvinyl pyridine, polyvinyl pyrrolidone, etc. Vinyl polymers: Polyethylene oxide, polypropylene oxide, polybutene oxide, polyoxymethylene, polyacetaldehyde, polymethyl vinyl ether, polypropyl vinyl ether, polybutyl vinyl ether, polybenzyl vinyl ether, and other polyether polymers; polymethylene sulfide, polyethylene sulfide, polyethylene Disulfide, polypropylene sulfide, polypheny Polysulfide polymers such as polyethylene sulfide, polyethylene tetrafluoride, polyethylene trimethylene sulfide; polyesters such as polyethylene terephthalate, polyethylene adipate, polyethylene isophthalate, polyethylene naphthalate, polyethylene paraphenylene diacetate, polyethylene isopropylidene dibenzoate; Polyurethanes such as methylene ethylene urethane; polyketone polymers such as polyether ketone and polyallyl ether ketone; polyanhydride polymers such as polyoxyisophthaloyl; polyamines such as polyethylene amine, polyhexamethylene amine and polyethylene trimethylene amine -Based polymers; polyamide polymers such as nylon, polyglycine, and polyalanine; polyacetylene Polyimine polymers such as minoethylene and polybenzoyliminoethylene; Polyimide polymers such as polyesterimide, polyetherimide, polybenzimide, and polypyromerimide; polyarylene, polyarylene alkylene, polyarylene alkenylene, polyphenol, phenol resin, Cellulose, polybenzimidazole, polybenzothiazole, polybenzoxazine, polybenzoxazole, oricalborane, polydibenzofuran, polyoxoisoindoline, polyfurantetracarboxylic acid diimide, polyoxadiazole, polyoxindole, polyphthalazine, polyphthalide, Polycyanurate, polyisocyanurate, polypiperazine, polypiperidine, polypyrazinoquinoxane, polypyrazole, polypyridazi , Polypyridine, polypyromellitimin, polyquinone, polypyrrolidine, polyquinoxaline, polytriazine, polytriazole and other polyaromatic polymers; polydisiloxane, polydimethylsiloxane and other siloxane polymers; polysilane polymers; polysilazane polymers; poly Examples thereof include phosphazene polymers; polythiazyl polymers; conjugated polymers such as polyacetylene, polypyrrole, and polyaniline. In addition, (meth) acryl means methacryl or acrylic. Of these, polyalkylene polymers, poly (meth) acrylic acid, poly (meth) acrylamide polymers, polyalkyl (meth) acrylates, and polystyrene polymers are the main chains because of their excellent electrochemical resistance. It is preferable to have as a structure. The main chain is a carbon chain having the largest number of carbon atoms in the polymer compound.

Among the nitroxyl polymer compounds exemplified above, as an example of a unit that is particularly preferably used, a polymer compound represented by the chemical structure of the following chemical formula (4) and / or (5), or a chemical structure thereof is repeated. Examples of the copolymer include as a unit. The chemical formula (4), (5), n is an integer of 1 or _more, R 1 to R ₄ are the same as those in the chemical formula (3), _{R 5} is hydrogen or methyl.

  The molecular weight of the nitroxyl polymer in the present invention is not particularly limited, but preferably has a molecular weight that does not dissolve in the electrolytic solution, and this varies depending on the combination with the solvent type of the electrolytic solution. Generally, the weight average molecular weight is 1,000 or more, preferably 10,000 or more, more preferably 20,000 or more, and generally 5,000,000 or less, preferably 500,000 or less. Moreover, the polymer containing the residue represented by the chemical formula (9) may be cross-linked, thereby improving the durability against the electrolytic solution.

  Moreover, although a nitroxyl polymer compound can be used independently, you may mix and use 2 or more types.

(Conductive agent)
The conductive agent of the present invention is not particularly limited as long as it can be used as a conductive agent for a lithium secondary battery. Conventionally used carbon materials such as carbon black represented by acetylene black, Carbon fiber typified by vapor grown carbon fiber or carbon nanofiber is used.

(Combination of active material, conductive agent, polymer radical material)
There is no particular limitation on the method of combining the active material for a lithium secondary battery, the conductive agent, and the polymer radical material of the present invention.

  For example, a polymer radical material is dissolved in a solvent such as N-methylpyrrolidone, a conductive agent and an active material for a lithium secondary battery such as a lithium composite oxide are added, and a surfactant or the like is added and stirred as necessary. Thereafter, the polymer radical material, the conductive agent, and the lithium composite oxide are simultaneously precipitated by dropwise addition to a poor solvent such as methanol. This is recovered by filtration and dried to obtain a lithium composite oxide in which the polymer radical material and the conductive agent are fused to the surface to form a composite.

  It is desirable to increase the fusion and combination of the polymer radical material and the conductive agent to the active material for the lithium secondary battery by heating during or after the drying step. The heating temperature at this time is preferably equal to or higher than the glass transition temperature of the polymer radical material, and more preferably higher by 10 ° C. than the glass transition temperature. Further, if the temperature is too high, the polymer radical material may be deteriorated, so that the temperature range is such that the polymer radical material does not deteriorate. Specifically, although it depends on the type of polymer radical material to be used, it is generally 130 ° C. or higher, more preferably 150 ° C. or higher, and preferably 250 ° C. or lower, more preferably 200 ° C. or lower. is there.

  Alternatively, a uniform mixture of an active material for a lithium secondary battery, a conductive agent, and a polymer radical material, for example, a mixture of a polymer radical material and a conductive agent and an active material for a lithium secondary battery is converted into a polymer radical material. The active material for lithium secondary batteries, the polymer radical material, and the conductive agent may be combined by heating to a glass transition temperature or higher.

  The composite active material for lithium secondary battery, polymer radical material, and conductive agent can be used by pulverizing and classifying as necessary to obtain a desired particle size.

  In the composite of the active material, conductive agent and polymer radical material of the lithium secondary battery of the present invention, the ratio of the area where the conductive agent and polymer radical material adhere to the surface area of the active material is preferably 5 to 50%. More preferably, it is 10-40%, More preferably, it is 10-20%. Similarly, the ratio of the adhesion thickness of the conductive agent and the polymer radical material to the particle size of the active material is preferably 1 to 50%, more preferably 5 to 30%, and still more preferably 5 to 10%. If these ratios are too low, the effect of the polymer radical reaction cannot be obtained, and if it is too high, the reaction of the active material is inhibited, so that high input / output cannot be obtained.

(Negative electrode active material)
The negative electrode active material of the lithium secondary battery of the present invention is not particularly limited as long as it can be used as the negative electrode active material of the lithium secondary battery. For example, it has been conventionally used as a negative electrode active material. Examples thereof include graphite, amorphous carbon, lithium titanate, titanium oxide, silicon and oxides and alloys thereof, germanium and alloys thereof, tin and oxides and alloys thereof, and the like. In addition, any substance that electrochemically inserts and desorbs lithium can be used without limitation. The shape of these materials is not particularly limited, and examples thereof include a thin film, a solidified powder, a fiber, and a flake. Moreover, these negative electrode active materials can be used individually or in combination.

(Binder)
In forming the positive electrode and the negative electrode, a binder can also be used. By using the binder, it is possible to strengthen the connection between the active materials, between the active material and the conductivity imparting agent, and between the active material or the conductivity imparting agent and the current collector. Examples of such a binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer rubber, Examples thereof include resin binders such as polypropylene, polyethylene, polyimide, partially carboxylated cellulose, and various polyurethanes.

(Current collector)
The current collector of the lithium secondary battery of the present invention is not particularly limited as long as it is formed from a metal that does not alloy with lithium. For example, aluminum that has been conventionally used as a positive electrode current collector, and a negative electrode current collector Examples include copper and alloys thereof, nickel, and the like.

(Electrolyte)
The solvent of the non-aqueous electrolyte used in the lithium secondary battery of the present invention is not particularly limited, but cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl A mixed solvent with a chain carbonate such as carbonate is exemplified. Further, mixed solvents of the above cyclic carbonate and ether solvents such as 1,2-dimethoxyethane and 1,2-diethoxyethane are also exemplified. The solute of the non-aqueous electrolyte is not particularly limited, and LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C) conventionally used for lithium secondary batteries. _{2 F 5 SO 2) 2,} LiN (CF 3 SO 2) (C 4 F 9 SO 2), LiC (CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) 3, LiAsF 6, LiClO 4, Examples thereof include Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , and mixtures thereof, but LiPF ₆ and LiBF ₄ that are easy to adsorb and desorb to a polymer radical material are particularly preferable. Furthermore, examples of the electrolyte include a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide and polyacrylonitrile with an electrolytic solution, and an inorganic solid electrolyte.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications within a range not changing the gist thereof. Is.

Example 1
(Preparation of positive electrode active material 1)
LiMn ₂ O ₄ , carbon fiber (Showa Denko VGCF-H) and a nitroxyl polymer compound (weight average molecular weight 28000) in which R _{1 to} R _{5 in} chemical formula (4) are methyl groups are in a ratio of 70:10:20. Was dissolved in N-methylpyrrolidone and stirred with a homogenizer to obtain a slurry. The slurry was gradually added to a large amount of methanol with stirring to precipitate a composite of LiMn ₂ O ₄ , carbon fiber, and nitroxyl polymer compound. The precipitate was filtered, heated to 150 ° C. with a vacuum drier, and then vacuum dried at 60 ° C. for 8 hours to obtain a composite solid, which was pulverized to obtain a positive electrode active material 1. When this active material was observed with an electron microscope, it was observed that the conductive agent and the polymer radical material were integrated on the surface of the LiMn ₂ O ₄ grains and fused to form a composite. . At this time, about 10 to 20% of the surface of the LiMn ₂ O ₄ grains was covered with the conductive agent and the polymer radical material, and the increase rate of the grain size was about 5 to 10%.

(Comparative Example 1)
(Preparation of positive electrode active material 2)
The same amount of carbon fiber as that of the positive electrode active material 1 and a nitroxyl polymer compound (weight average molecular weight 28000) in which R _{1 to} R _{5 in} the chemical formula (4) are methyl groups are dissolved in N-methylpyrrolidone and stirred with a homogenizer. A slurry was obtained. The slurry was gradually added to a large amount of methanol with stirring to precipitate a composite of carbon fiber and nitroxyl polymer compound. The precipitate was filtered, heated to 150 ° C. with a vacuum drier, and then vacuum dried at 60 ° C. for 8 hours to obtain a composite solid. The composite and the same amount of LiMn ₂ O ₄ as the positive electrode active material 1 were mixed and pulverized to obtain a positive electrode active material 2.

(Comparative Example 2)
(Preparation of positive electrode active material 3)
The same amount of LiMn ₂ O _{4 as the} positive electrode active material 1, carbon fiber, and a nitroxyl polymer compound (weight average molecular weight 28000) in which R _{1 to} R _{5 in} the chemical formula (4) are methyl groups are mixed, pulverized, and positive electrode active Material 3 was obtained.

(Preparation of positive electrode)
For each of the positive electrode active materials 1 to 3, a slurry was prepared in which water was used as a dispersion medium and mixed with positive electrode active material: acetylene black: binder (CMC + PTFE) = 92: 5: 3. It applied and dried on foil and obtained the positive electrode. The positive electrodes obtained from the positive electrode active materials 1 to 3 were defined as a positive electrode 1, a positive electrode 2, and a positive electrode 3, respectively.

(Preparation of negative electrode)
A slurry in which N-methylpyrrolidone is used as a dispersion medium and graphite: acetylene black: binder (PVdF) = 92: 4: 4 is prepared, and this is applied onto a copper foil by a doctor blade method and dried to form a negative electrode. Got.

(Preparation of electrolyte)
LiPF ₆ was dissolved in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 so as to be 1 mol / liter to prepare an electrolytic solution.

(Cycle test of small laminate cell)
The positive electrode is cut to a size of 2 cm × 2 cm and the negative electrode is cut to a size of 2.5 cm × 2.5 cm, and the positive electrode and the negative electrode are overlapped with a separator so that the active material application surfaces face each other, and inserted into an aluminum laminate outer package And the said electrolyte solution was inject | poured and the small laminated cell was produced.

  At 25 ° C., constant current charging was performed until 4.2 V at 1 mA, and then constant current discharging was performed until 2.5 V at 1 mA. Next, constant current charging was performed until the voltage became 4.2 V at 1 mA, and then constant current discharging was performed until the voltage became 2.5 V at 10 mA. At this time, the ratio (discharge load characteristics) of the discharge capacity at 10 mA and the discharge capacity at 1 mA in the third cycle was compared. The results are shown in Table 1.

表１によると、実施例１、比較例１、比較例２の順に放電負荷特性に優れた。比較例２は高分子ラジカル材料に対する電子導電性が低いために放電負荷特性が劣ったと考えられる。比較例１は比較例２に比べ優れた特性を示したが、実施例１が最も優れた。これは比較例１、実施例１とも、高分子ラジカル材料に対する電子導電性が正極内で高く維持され、なおかつ実施例１のほうが高分子ラジカル材料、導電剤、ＬｉＭｎ₂Ｏ₄が均一に正極内に分散し、抵抗が低くなって速い反応が可能になったためと考えられる。

According to Table 1, the discharge load characteristics were excellent in the order of Example 1, Comparative Example 1, and Comparative Example 2. Comparative Example 2 is considered to have inferior discharge load characteristics due to low electronic conductivity with respect to the polymer radical material. Comparative Example 1 showed superior characteristics compared to Comparative Example 2, but Example 1 was the most excellent. In both Comparative Example 1 and Example 1, the electronic conductivity with respect to the polymer radical material is maintained higher in the positive electrode, and in Example 1, the polymer radical material, the conductive agent, and LiMn ₂ O ₄ are uniformly distributed in the positive electrode. This is thought to be due to the fact that the reaction was reduced and the reaction became faster.

  According to the embodiment of the present invention, it is possible to provide a lithium secondary battery having excellent load characteristics. Therefore, the lithium secondary battery according to the embodiment of the present invention includes a power source for various portable electronic devices, an electric vehicle, a driving or auxiliary storage power source for a hybrid electric vehicle, a power storage device for various energy such as solar energy and wind power generation, Alternatively, it can be used as a storage power source for household electric appliances.

Claims (8)

On the surface of the lithium composite oxide, a conductive agent and a nitroxyl having a nitroxyl cation partial structure represented by the following chemical formula (1) in the oxidized state and a nitroxyl radical partial structure represented by the following chemical formula (2) in the reduced state An active material for a lithium secondary battery in which a polymer compound is fused and compounded, and a ratio of an adhesion thickness of the conductive agent and the nitroxyl polymer compound to a particle size of the lithium composite oxide is 1 to An active material for a lithium secondary battery, characterized by being 50%.

  The active material for a lithium secondary battery in which a conductive agent and a nitroxyl polymer compound are combined is combined with a current collector by a binder different from the nitroxyl polymer compound to form an electrode. An electrode for a lithium secondary battery using the active material for a lithium secondary battery according to claim 1.   A lithium secondary battery, wherein the electrode according to claim 2 is used for a positive electrode. On the surface of the lithium composite oxide, a conductive agent and a nitroxyl having a nitroxyl cation partial structure represented by the following chemical formula (1) in the oxidized state and a nitroxyl radical partial structure represented by the following chemical formula (2) in the reduced state characterized by complexing with fused polymer compound, for the particle diameter of the lithium composite oxide, the proportion of deposition thickness of the conductive agent the nitroxyl polymer compound is 1 to 50% lithium secondary A method for producing an active material for a secondary battery.

The lithium composite oxide, the nitroxyl polymer compound and the conductive agent are uniformly dissolved or dispersed in a solvent,
Simultaneously dissolving or dispersing the lithium composite oxide, the nitroxyl polymer compound and the conductive agent;
By drying the precipitated lithium composite oxide, the nitroxyl polymer compound and the conductive agent mixture, the conductive agent and the nitroxyl polymer compound are fused and combined on the surface of the lithium composite oxide. The manufacturing method of the active material for lithium secondary batteries of Claim 4 characterized by performing. The lithium composite oxide, the nitroxyl polymer compound and the conductive agent are uniformly dissolved or dispersed in a solvent,
Simultaneously dissolving or dispersing the lithium composite oxide, the nitroxyl polymer compound and the conductive agent;
By drying and heating the precipitated lithium composite oxide, the nitroxyl polymer compound and the conductive agent mixture, the conductive agent and the nitroxyl polymer compound are fused to the surface of the lithium composite oxide. Combined
6. The composite of the lithium composite oxide, the nitroxyl polymer compound, and the conductive agent is further increased by heating to a temperature higher than the glass transition temperature of the nitroxyl polymer compound, according to claim 4 or 5. Of manufacturing an active material for a lithium secondary battery. Lithium composite oxide, a nitroxyl polymer compound having a nitroxyl cation partial structure represented by the following chemical formula (1) in an oxidized state and a nitroxyl radical partial structure represented by the following chemical formula (2) in a reduced state and a conductive agent Uniformly dissolved or dispersed in the solvent,
Simultaneously dissolving or dispersing the lithium composite oxide, the nitroxyl polymer compound and the conductive agent;
By drying the precipitated lithium composite oxide, the nitroxyl polymer compound and the conductive agent mixture, the conductive agent and the nitroxyl polymer compound are fused and combined on the surface of the lithium composite oxide. A method for producing an active material for a lithium secondary battery.

The lithium composite oxide, the nitroxyl polymer compound and the conductive agent are uniformly dissolved or dispersed in a solvent,
Simultaneously dissolving or dispersing the lithium composite oxide, the nitroxyl polymer compound and the conductive agent;
By drying and heating the precipitated lithium composite oxide, the nitroxyl polymer compound and the conductive agent mixture, the conductive agent and the nitroxyl polymer compound are fused to the surface of the lithium composite oxide. Combined
The lithium according to claim 7, further comprising increasing the composite of the lithium composite oxide, the nitroxyl polymer compound, and the conductive agent by heating to a temperature higher than a glass transition temperature of the nitroxyl polymer compound. A method for producing an active material for a secondary battery.