JP2017091818A - Electrode material, method for producing electrode material, electrode, and electricity storage device - Google Patents
Electrode material, method for producing electrode material, electrode, and electricity storage device Download PDFInfo
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- JP2017091818A JP2017091818A JP2015220790A JP2015220790A JP2017091818A JP 2017091818 A JP2017091818 A JP 2017091818A JP 2015220790 A JP2015220790 A JP 2015220790A JP 2015220790 A JP2015220790 A JP 2015220790A JP 2017091818 A JP2017091818 A JP 2017091818A
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 121
- 239000003575 carbonaceous material Substances 0.000 claims abstract description 103
- LSGOVYNHVSXFFJ-UHFFFAOYSA-N vanadate(3-) Chemical compound [O-][V]([O-])([O-])=O LSGOVYNHVSXFFJ-UHFFFAOYSA-N 0.000 claims abstract description 90
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- WQEVDHBJGNOKKO-UHFFFAOYSA-K vanadic acid Chemical compound O[V](O)(O)=O WQEVDHBJGNOKKO-UHFFFAOYSA-K 0.000 description 1
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Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Inorganic Compounds Of Heavy Metals (AREA)
- Carbon And Carbon Compounds (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
Description
本発明は、例えばリチウムイオン電池に用いられる電極材料、電極材料の製造方法、電極、および蓄電デバイスに関する。 The present invention relates to an electrode material used for, for example, a lithium ion battery, an electrode material manufacturing method, an electrode, and an electricity storage device.
従来より、電気化学素子負極用のリチウム吸蔵、放出活物質として、グラファイトやハードカーボン等の炭素材料が負極に使用されている。しかし、これらの炭素材料を用いた負極の電位は、金属リチウムの電位に近い電位でリチウムを吸蔵する。そのため、低温環境下において負極上に金属リチウムが析出し、デンドライト結晶が成長するおそれがある。デンドライト結晶が成長すると、電極間における内部短絡や、電解液の還元等を引き起こすことが懸念されている。 Conventionally, carbon materials such as graphite and hard carbon have been used for negative electrodes as lithium storage and release active materials for electrochemical element negative electrodes. However, the negative electrode using these carbon materials occludes lithium at a potential close to that of metallic lithium. Therefore, there is a possibility that metallic lithium is deposited on the negative electrode in a low temperature environment and dendrite crystals grow. When the dendrite crystal grows, there is a concern that it may cause an internal short circuit between the electrodes, reduction of the electrolyte, or the like.
そこで、近年では、金属リチウムの電位に対して１．５Ｖでリチウムを吸蔵・放出するチタン酸リチウムが注目されている。このようなチタン酸リチウムは、リチウムの析出や電解液の分解などの副反応が生じにくい。また、チタン酸リチウムは、リチウムイオンの挿入・離脱に伴う体積変化が少なく、容量劣化が起きにくいという特徴がある。ただし、チタン酸リチウムを負極として用いる場合には、電位が高いことからキャパシタを高電圧化するには限界がある。また、チタン酸リチウムの容量は、２００ｍＡｈ／ｇ以下であり、高容量化にも限界がある。 Therefore, in recent years, lithium titanate that absorbs and releases lithium at 1.5 V with respect to the potential of metallic lithium has attracted attention. Such lithium titanate is less susceptible to side reactions such as lithium deposition and electrolyte decomposition. In addition, lithium titanate has a feature that there is little volume change due to insertion / extraction of lithium ions, and capacity deterioration hardly occurs. However, when lithium titanate is used as the negative electrode, there is a limit to increasing the voltage of the capacitor because the potential is high. The capacity of lithium titanate is 200 mAh / g or less, and there is a limit to increasing the capacity.
従って、黒鉛等の炭素材料やチタン酸リチウムより容量が大きな材料であることが好ましい。このような特性を持つ材料が、電極材料として、特に負極に応用されることが望まれていた。 Accordingly, a material having a larger capacity than a carbon material such as graphite or lithium titanate is preferable. It has been desired that a material having such characteristics be applied as an electrode material, particularly to the negative electrode.
本発明は、上記課題を解決するために提案されたものであり、その目的は、高い充放電容量を有する電極材料、電極材料の製造方法、電極、および蓄電デバイスを提供することにある。 The present invention has been proposed to solve the above-described problems, and an object thereof is to provide an electrode material having a high charge / discharge capacity, a method for producing the electrode material, an electrode, and an electricity storage device.
本発明者らは、上記課題を解決すべく種々の検討を重ねた結果、Ｌｉ３ＶＯ４をはじめとする金属源と、炭素材料とを混合し、金属源にポリマー鎖を形成した後に焼成処理を施すことで、炭素材料上に微細な金属粒子が均一に担持されることを見出した。この金属粒子が担持された炭素材料を用いることにより、比較的高い充放電電位および充放電容量を有する電極材料が得られることを見出し、本発明を完成するに至った。 As a result of various studies to solve the above problems, the present inventors have mixed a metal source such as Li 3 VO 4 and a carbon material, and formed a polymer chain on the metal source, followed by firing treatment. It has been found that fine metal particles are uniformly supported on the carbon material by applying. It has been found that an electrode material having a relatively high charge / discharge potential and charge / discharge capacity can be obtained by using the carbon material carrying the metal particles, and the present invention has been completed.
すなわち、本発明に係る電極材料の製造方法は、バナジウム源とリチウム源を含む金属粒子源と、導電性炭素材料と、錯体配位子と、重合剤とが混合された混合溶液を作製する混合工程と、前記炭素材料の表面に前記金属粒子源を付着させ、バナジン酸リチウムの前駆体を生成する分散工程と、前記炭素材料上に付着したバナジン酸リチウムの前駆体にポリマー鎖を形成するポリマー鎖形成工程と、ポリマー鎖を形成したバナジン酸リチウムの前駆体が付着した前記炭素材料を加熱し、ポリマー鎖を除去する除去工程と、バナジン酸リチウムの前駆体が付着した前記炭素材料を焼成し、バナジン酸リチウムと前記炭素材料の複合材料を得る結晶化工程と、を有する。 That is, the method for producing an electrode material according to the present invention is a method for producing a mixed solution in which a metal particle source including a vanadium source and a lithium source, a conductive carbon material, a complex ligand, and a polymerization agent are mixed. A step of depositing the metal particle source on the surface of the carbon material to produce a lithium vanadate precursor, and a polymer forming a polymer chain on the lithium vanadate precursor deposited on the carbon material Heating the carbon material to which the precursor of lithium vanadate that has formed a polymer chain is attached, removing the polymer chain, and firing the carbon material to which the precursor of lithium vanadate is attached. And a crystallization step of obtaining a composite material of lithium vanadate and the carbon material.
また、本発明に係る電極材料は導電性炭素材料の表面にバナジン酸リチウムが担持され、バナジン酸リチウムの金属粒子の大きさが１００ｎｍ以下であることを特徴とする。 The electrode material according to the present invention is characterized in that lithium vanadate is supported on the surface of a conductive carbon material, and the size of the metal particles of lithium vanadate is 100 nm or less.
以上のような電極材料を用いて形成された電極、およびその電極を備えた蓄電デバイスも、本発明の一態様である。 An electrode formed using the electrode material as described above and an electricity storage device including the electrode are also one embodiment of the present invention.
本発明によれば、高い充放電容量を有する電極材料、電極材料の製造方法、電極、および蓄電デバイスを提供することができる。 ADVANTAGE OF THE INVENTION According to this invention, the electrode material which has high charging / discharging capacity | capacitance, the manufacturing method of an electrode material, an electrode, and an electrical storage device can be provided.
［１．構成］
以下、本発明に係る電極材料および電極材料を用いた電極の実施形態について詳細に説明する。
[1. Constitution]
Hereinafter, embodiments of an electrode material and an electrode using the electrode material according to the present invention will be described in detail.
（１）電極材料
電極材料は、金属粒子と導電性炭素材料を含む。電極材料は、炭素材料の表面に微細な金属粒子が均一に担持されている材料である。金属粒子は炭素材料と複合化されており、炭素材料の表面に金属粒子が結合している。結合とは、単に炭素材料と金属粒子が接触している状態ではなく、金属粒子が炭素材料上において結晶化することにより構造を共有化している状態を意味する。
(1) Electrode material The electrode material includes metal particles and a conductive carbon material. The electrode material is a material in which fine metal particles are uniformly supported on the surface of a carbon material. The metal particles are compounded with the carbon material, and the metal particles are bonded to the surface of the carbon material. The bond means not a state where the carbon material and the metal particles are in contact but a state where the metal particles are crystallized on the carbon material to share the structure.
金属粒子は、バナジン酸リチウム（Ｌｉ３ＶＯ４）である。バナジン酸リチウムは、金属リチウムの電位に対する電位が、例えば黒鉛より高く、チタン酸リチウムより低い材料である。具体的には、電位がＬｉ／Ｌｉ＋に対し、約１Ｖである。また、バナジン酸リチウムは、容量が黒鉛やチタン酸リチウムより大きい材料である。バナジン酸リチウムの理論容量は、約６００ｍＡｈ／ｇである。 The metal particles are lithium vanadate (Li 3 VO 4 ). Lithium vanadate is a material that has a potential higher than that of, for example, graphite and lower than that of lithium titanate, relative to the potential of metallic lithium. Specifically, the potential is about 1 V with respect to Li / Li + . Further, lithium vanadate is a material having a capacity larger than that of graphite or lithium titanate. The theoretical capacity of lithium vanadate is about 600 mAh / g.
バナジン酸リチウムは微細なナノ粒子であり、炭素材料の表面に分散して、均一に担持されている。バナジン酸リチウムの金属粒子は、凝集体を形成することもあるが、凝集体であっても微細な粒子として存在している。具体的には、金属粒子の凝集体の大きさは１００ｎｍ以下であり、特に好ましくは５０ｎｍ以下である。また、金属粒子の約８０％以上が、３０ｎｍ以下の微細なナノ粒子である。このようにナノ粒子化された微細な金属粒子は、粒子内部においても反応が生じやすく、リチウムイオンの拡散経路が短縮される。したがって、活物質の利用率が向上し、発現容量が拡大する。また、バナジン酸リチウムの面積あたりの粒子数は、５０〜２００個／９００ｎｍ２であることが好ましい。すなわち、バナジン酸リチウムは、炭素材料の表面に高い分散度で分散している。 Lithium vanadate is a fine nanoparticle and is dispersed and uniformly supported on the surface of the carbon material. The metal particles of lithium vanadate may form an aggregate, but even the aggregate exists as fine particles. Specifically, the size of the aggregate of metal particles is 100 nm or less, and particularly preferably 50 nm or less. Further, about 80% or more of the metal particles are fine nanoparticles of 30 nm or less. The fine metal particles that have been made into nanoparticles in this way are likely to react even inside the particles, and the diffusion path of lithium ions is shortened. Therefore, the utilization factor of the active material is improved and the expression capacity is expanded. The number of particles per area of lithium vanadate is preferably 50 to 200/900 nm 2 . That is, lithium vanadate is dispersed with a high degree of dispersion on the surface of the carbon material.
以上のような電極材料では、炭素材料と金属粒子が複合化され、炭素材料により電子パスが構築されるとともに、金属粒子の粒子成長が抑制される。したがって、電気伝導性が向上し、電極に用いた場合に出入力特性が向上される。金属粒子は、金属粒子源と炭素材料を混合し、金属粒子源にポリマー鎖を形成した後に焼成処理を施すことで炭素材料上に担持される。 In the electrode material as described above, the carbon material and the metal particles are combined, an electron path is constructed by the carbon material, and the particle growth of the metal particles is suppressed. Therefore, the electrical conductivity is improved, and the input / output characteristics are improved when used for electrodes. The metal particles are supported on the carbon material by mixing the metal particle source and the carbon material, forming a polymer chain in the metal particle source, and performing a baking treatment.
（金属粒子源）
焼成処理によりバナジン酸リチウムとなる金属粒子源は、バナジウム源とリチウム源を含む。バナジウム源とリチウム源は、モル比でＬｉ：Ｖ＝３：１となるように混合する。バナジウム源は、金属バナジウムとバナジウム含有化合物を含む。バナジウム含有化合物としては、メタバナジン酸塩（ＮＨ４ＶＯ３、ＮａＶＯ３、ＫＶＯ３等）、酸化バナジウム（Ｖ２Ｏ５、Ｖ２Ｏ４、Ｖ２Ｏ３、Ｖ３Ｏ４）、バナジウム（ＩＩＩ）アセチルアセトナート、バナジウム（ＩＶ）オキシアセチルアセトナート、オキシ三塩化バナジウム、四塩化バナジウム、三塩化バナジウム、ポリバナジン酸塩等を用いることができる。リチウム源としては、水酸化リチウム、水酸化リチウム水和物、酢酸リチウム、硝酸リチウム、炭酸リチウム、塩化リチウム、乳酸リチウム等のリチウム含有化合物を用いることができる。
(Metal particle source)
The metal particle source that becomes lithium vanadate by the baking treatment includes a vanadium source and a lithium source. The vanadium source and the lithium source are mixed so that the molar ratio is Li: V = 3: 1. The vanadium source includes metal vanadium and a vanadium-containing compound. Examples of vanadium-containing compounds include metavanadate (NH 4 VO 3 , NaVO 3, KVO 3, etc.), vanadium oxide (V 2 O 5 , V 2 O 4 , V 2 O 3 , V 3 O 4 ), vanadium (III ) Acetylacetonate, vanadium (IV) oxyacetylacetonate, vanadium oxytrichloride, vanadium tetrachloride, vanadium trichloride, polyvanadate and the like can be used. As the lithium source, lithium-containing compounds such as lithium hydroxide, lithium hydroxide hydrate, lithium acetate, lithium nitrate, lithium carbonate, lithium chloride, and lithium lactate can be used.
（炭素材料）
炭素材料は導電性を有し、特にカーボンナノチューブなどの繊維構造を有する繊維状炭素を好適に用いることができる。カーボンナノチューブは、単層カーボンナノチューブ（ＳＷＣＮＴ）及び多層カーボンナノチューブ（ＭＷＣＮＴ）の何れでもよい。他にも、中空シェル構造のカーボンブラックであるケッチェンブラック、アセチレンブラック等のカーボンブラック、無定形炭素、炭素繊維、天然黒鉛、人造黒鉛、活性炭、メソポーラス炭素のうちの一種又は複数種類を混合して使用することができる。炭素材料が繊維構造を有する場合（例えば、ＣＮＴ、カーボンナノファイバ（ＣＮＦ）や気相成長カーボンファイバ（ＶＧＣＦ））、繊維構造の分散及び均質化を目的として超高圧分散処理を施したものを使用しても良い。なかでも粒子径がナノサイズの炭素材料が好ましい。
(Carbon material)
The carbon material has electrical conductivity, and fibrous carbon having a fiber structure such as carbon nanotubes can be preferably used. The carbon nanotube may be either a single-walled carbon nanotube (SWCNT) or a multi-walled carbon nanotube (MWCNT). In addition, one or more of carbon blacks such as ketjen black and acetylene black, which are hollow shell carbon blacks, amorphous carbon, carbon fiber, natural graphite, artificial graphite, activated carbon, and mesoporous carbon are mixed. Can be used. When the carbon material has a fiber structure (for example, CNT, carbon nanofiber (CNF) or vapor-grown carbon fiber (VGCF)), one that has been subjected to ultra-high pressure dispersion treatment for the purpose of dispersion and homogenization of the fiber structure You may do it. Among these, a carbon material having a nano-sized particle size is preferable.
上記の金属粒子源は、錯体重合によりポリマー鎖が形成される。金属粒子源と炭素材料には、錯体重合のための錯体配位子と重合剤が混合される。 In the metal particle source, a polymer chain is formed by complex polymerization. A complex ligand and a polymerizing agent for complex polymerization are mixed in the metal particle source and the carbon material.
（錯体配位子）
錯体配位子としては、複数のカルボキシル基を有する有機化合物を用いる。例えば、トリカルボン酸のクエン酸を用いることが好ましい。他には、シュウ酸、マロン酸、コハク酸などのジカルボン酸を用いても良い。
(Complex ligand)
As the complex ligand, an organic compound having a plurality of carboxyl groups is used. For example, it is preferable to use tricarboxylic acid citric acid. In addition, dicarboxylic acids such as oxalic acid, malonic acid, and succinic acid may be used.
（重合剤）
重合剤としては、複数のヒドロキシル基を有するアルコールを用いる。例えば、エチレングリコールを用いることが好ましい。他には、プロピレングリコールなどの他の２価のアルコール、またはグリセリンなどの３価のアルコールを用いても良い。
(Polymerizer)
As the polymerization agent, an alcohol having a plurality of hydroxyl groups is used. For example, it is preferable to use ethylene glycol. In addition, other dihydric alcohols such as propylene glycol or trivalent alcohols such as glycerin may be used.
（２）電極
上記の本実施形態の電極材料は、正極及び負極にそれぞれ金属化合物を用いたリチウムイオン二次電池や、正極に活性炭、負極にリチウムイオンを可逆的に吸着／脱着可能な材料を用いたリチウムイオンキャパシタ等の蓄電デバイスに用いることができる。特に、リチウムイオン二次電池の負極のために好適に用いることができる。例えば、蓄電デバイスとして、正極と、上記電極材料を含む活物質層を有する負極と、負極と正極との間に配置された非水系電解液を保持したセパレータとを備えたリチウムイオン二次電池を提供することができる。
(2) Electrode The electrode material of the present embodiment includes a lithium ion secondary battery using a metal compound for each of the positive electrode and the negative electrode, and a material capable of reversibly adsorbing / desorbing lithium ions on the positive electrode and activated carbon on the positive electrode. It can be used for power storage devices such as the lithium ion capacitor used. In particular, it can be suitably used for a negative electrode of a lithium ion secondary battery. For example, as an electricity storage device, a lithium ion secondary battery including a positive electrode, a negative electrode having an active material layer containing the above electrode material, and a separator holding a non-aqueous electrolyte disposed between the negative electrode and the positive electrode Can be provided.
電極材料を、バインダーと混合および混練した後シート状に成形し、これを集電体に接合することで電極が形成される。電極材料とバインダーの混合液をドクターブレード法等によって集電体上に塗工し、乾燥することで電極を形成しても良い。また、電極材料を所定形状に成形し、集電体上に圧着することで電極を形成することもできる。 The electrode material is mixed and kneaded with a binder, then formed into a sheet shape, and this is joined to a current collector to form an electrode. An electrode may be formed by applying a mixed solution of an electrode material and a binder onto a current collector by a doctor blade method or the like and drying. Moreover, an electrode can also be formed by shape | molding electrode material into a predetermined shape and crimping | bonding it on a collector.
集電体としては、アルミニウム、銅、鉄、ニッケル、チタン、鋼、カーボン等の導電材料を使用することができる。特に、アルミニウムおよび銅を用いることが好ましい。高い熱伝導性と電子伝導性とを有しているからである。集電体の形状は、膜状、箔状、板状、網状、エキスパンドメタル状、円筒状等の任意の形状を採用することができる。 As the current collector, conductive materials such as aluminum, copper, iron, nickel, titanium, steel, and carbon can be used. In particular, it is preferable to use aluminum and copper. This is because it has high thermal conductivity and electronic conductivity. As the shape of the current collector, any shape such as a film shape, a foil shape, a plate shape, a net shape, an expanded metal shape, and a cylindrical shape can be adopted.
バインダーとしては、例えばフッ素系ゴム，ジエン系ゴム，スチレン系ゴム等のゴム類、ポリテトラフルオロエチレン，ポリフッ化ビニリデン等の含フッ素ポリマー、カルボキシメチルセルロース，ニトロセルロース等のセルロース、その他、ポリオレフィン樹脂、ポリイミド樹脂，アクリル樹脂、ニトリル樹脂、ポリエステル樹脂、フェノール樹脂、ポリ酢酸ビニル樹脂、ポリビニルアルコール樹脂、エポキシ樹脂などを挙げることができる。これらのバインダーは、単独で使用しても良く、２種以上を混合して使用しても良い。 Examples of binders include rubbers such as fluorine rubber, diene rubber, and styrene rubber, fluorine-containing polymers such as polytetrafluoroethylene and polyvinylidene fluoride, cellulose such as carboxymethyl cellulose and nitrocellulose, other polyolefin resins, polyimides Examples thereof include resins, acrylic resins, nitrile resins, polyester resins, phenol resins, polyvinyl acetate resins, polyvinyl alcohol resins, and epoxy resins. These binders may be used alone or in combination of two or more.
［２．電極材料の製造方法］
上記のような本実施形態の電極材料の製造方法は、以下の工程を含む。
（１）バナジウム源とリチウム源を含む金属粒子源、導電性炭素材料、錯体配位子、および重合剤とが混合された混合溶媒を作製する混合工程
（２）炭素材料の表面に金属粒子源を付着させ、バナジン酸リチウムの前駆体を生成する分散工程
（３）炭素材料上に付着したバナジン酸リチウムの前駆体にポリマー鎖を形成するポリマー鎖形成工程
（４）ポリマー鎖を形成したバナジン酸リチウムの前駆体が付着した炭素材料を加熱し、ポリマー鎖を除去する除去工程
（５）バナジン酸リチウムの前駆体が付着した炭素材料を焼成し、バナジン酸リチウムと炭素材料の複合材料を得る結晶化工程
[2. Method for manufacturing electrode material]
The manufacturing method of the electrode material of this embodiment as described above includes the following steps.
(1) Mixing step of preparing a mixed solvent in which a metal particle source including a vanadium source and a lithium source, a conductive carbon material, a complex ligand, and a polymerization agent are mixed. (2) A metal particle source on the surface of the carbon material. (3) A polymer chain forming step for forming a polymer chain on a lithium vanadate precursor deposited on a carbon material (4) A vanadic acid having a polymer chain formed thereon Removal step of heating the carbon material to which the lithium precursor is attached and removing the polymer chain (5) A crystal in which the carbon material to which the lithium vanadate precursor is attached is fired to obtain a composite material of lithium vanadate and the carbon material Process
（１）混合工程
混合工程では、バナジウム源とリチウム源を含む金属粒子源、炭素材料、錯体配位子、および重合剤を溶媒に添加し、混合溶液を作製する。溶媒に添加する材料の組成比は、例えば金属粒子源１０〜２０ｍｏｌ％、錯体配位子１０〜２０ｍｏｌ％、重合剤４０〜８０ｍｏｌ％とすることができる。また、金属粒子源と炭素材料の重量比は、８０：２０〜６０：４０とすると良い。溶媒は水を用いるが、イソプロピルアルコール等のアルコール類を用いても良い。他にも、例えば重合剤であるエチレングリコール溶液中に他の材料を添加しても良い。
(1) Mixing step In the mixing step, a metal particle source including a vanadium source and a lithium source, a carbon material, a complex ligand, and a polymerization agent are added to a solvent to prepare a mixed solution. The composition ratio of the material added to the solvent can be, for example, 10 to 20 mol% of the metal particle source, 10 to 20 mol% of the complex ligand, and 40 to 80 mol% of the polymerization agent. The weight ratio between the metal particle source and the carbon material is preferably 80:20 to 60:40. Water is used as the solvent, but alcohols such as isopropyl alcohol may be used. In addition, other materials may be added to, for example, an ethylene glycol solution that is a polymerization agent.
各材料が添加された水溶液を撹拌手段により混合することで、金属粒子源と錯体配位子により金属錯体が形成される。また、混合時において、一部の金属配位子のカルボキシル基と、一部の重合剤のヒドロキシル基との間でエステル化反応が起こり、ポリマー鎖が形成される。混合工程では、複数の水溶液を作製後、それらの溶液を混合することで上記の材料が添加された水溶液を得ても良い。例えば、金属粒子源と錯体配位子のみを水に添加して混合することで、金属錯体の形成を促すことができる。この水溶液を、例えばエチレングリコール水溶液と混合した後に、炭素材料を添加することもできる。撹拌手段は、マグネチックスターラー、電気モータ式撹拌機、エアモータ式撹拌機等を用いる。 A metal complex is formed by the metal particle source and the complex ligand by mixing the aqueous solution to which each material is added with a stirring means. Further, at the time of mixing, an esterification reaction occurs between the carboxyl groups of some metal ligands and the hydroxyl groups of some polymerizing agents, and a polymer chain is formed. In the mixing step, after preparing a plurality of aqueous solutions, an aqueous solution to which the above materials are added may be obtained by mixing the solutions. For example, formation of a metal complex can be promoted by adding only the metal particle source and the complex ligand to water and mixing them. The carbon material can be added after this aqueous solution is mixed with, for example, an aqueous ethylene glycol solution. As the stirring means, a magnetic stirrer, an electric motor type stirrer, an air motor type stirrer or the like is used.
（２）分散工程
分散工程では、炭素材料の表面に金属粒子源を付着させる。炭素材料の表面に金属粒子源を付着させる手法としては、メカノケミカル処理が挙げられる。メカノケミカル処理は、旋回する反応容器等を用いてずり応力や遠心力等の機械的エネルギーを与える処理である。メカノケミカル処理は、超遠心力処理（Ultra-Centrifugal force processing method：以下、ＵＣ処理という）等、ずり応力、遠心力、その他の機械的エネルギーを加えることができればよい。要するに、機械的エネルギーによって、炭素材料に金属粒子源を付着させ、炭素材料の表面上にバナジン酸リチウムの前駆体を生成できればよい。メカノケミカル処理は、金属粒子源及び炭素材料の微細化と高分散化処理を兼ねることもできる。
(2) Dispersing step In the dispersing step, a metal particle source is attached to the surface of the carbon material. A mechanochemical process is mentioned as a method of attaching a metal particle source to the surface of a carbon material. The mechanochemical treatment is a treatment for applying mechanical energy such as shear stress or centrifugal force using a rotating reaction vessel or the like. In the mechanochemical treatment, it is only necessary to apply shear stress, centrifugal force, and other mechanical energy such as ultra-centrifugal force processing method (hereinafter referred to as UC treatment). In short, it is only necessary that a metal particle source is attached to a carbon material by mechanical energy to generate a precursor of lithium vanadate on the surface of the carbon material. The mechanochemical treatment can also serve as a metal particle source and carbon material refinement and high dispersion treatment.
ＵＣ処理について図１を参照して説明する。図１に示す反応器は、開口部にせき板１−２を有する外筒１と、貫通孔２−１を有し旋回する内筒２からなる。この反応器の内筒２内部に反応物を投入し、内筒２を旋回することによってその遠心力で内筒２内部の反応物が内筒２の貫通孔２−１を通って外筒１の内壁１−３に移動する。この時反応物は内筒２の遠心力によって外筒１の内壁１−３に衝突し、薄膜状となって内壁１−３の上部へずり上がる。この状態では反応物には内壁１−３との間のずり応力と内筒２からの遠心力の双方が同時に加わり、薄膜状の反応物に大きな機械的エネルギーが加わることになる。この機械的なエネルギーが反応に必要な化学エネルギー、いわゆる活性化エネルギーに転化するものと思われる。これにより、短時間で反応が進行する。機械的エネルギーの満足する付与のためには、１５００Ｎ（ｋｇｍｓ−２）以上の遠心力を発生させることが望ましい。好ましくは６００００Ｎ（ｋｇｍｓ−２）以上である。 The UC process will be described with reference to FIG. The reactor shown in FIG. 1 includes an outer cylinder 1 having a cough plate 1-2 at an opening and an inner cylinder 2 having a through hole 2-1 and swirling. By putting the reactant into the inner cylinder 2 of this reactor and turning the inner cylinder 2, the reactant inside the inner cylinder 2 passes through the through-hole 2-1 of the inner cylinder 2 by the centrifugal force. Move to the inner wall 1-3. At this time, the reaction product collides with the inner wall 1-3 of the outer cylinder 1 by the centrifugal force of the inner cylinder 2, and forms a thin film and slides up to the upper part of the inner wall 1-3. In this state, both the shear stress between the inner wall 1-3 and the centrifugal force from the inner cylinder 2 are simultaneously applied to the reactant, and a large mechanical energy is applied to the thin-film reactant. It is considered that this mechanical energy is converted into chemical energy necessary for the reaction, so-called activation energy. Thereby, reaction advances in a short time. For satisfactory application of mechanical energy, it is desirable to generate a centrifugal force of 1500 N (kgms −2 ) or more. Preferably, it is 60000 N (kgms −2 ) or more.
メカノケミカル処理は、少なくとも２回の処理に分けて行うことができる。例えば、第１回目の処理では、バナジウム源と炭素材料とにずり応力と遠心力を加えて、炭素材料にバナジウム源を付着させる。そして、第２回目の処理では、リチウム源と、炭素材料の表面に付着されたバナジウム源とにずり応力と遠心力を加えて、炭素材料の表面上に形成されたバナジウムの基礎を基点にバナジン酸リチウムの前駆体を生成することができる。 The mechanochemical treatment can be performed in at least two separate treatments. For example, in the first treatment, shear stress and centrifugal force are applied to the vanadium source and the carbon material to adhere the vanadium source to the carbon material. In the second treatment, the vanadium is based on the basis of vanadium formed on the surface of the carbon material by applying shear stress and centrifugal force to the lithium source and the vanadium source attached to the surface of the carbon material. Lithium acid precursors can be produced.
以上のようなＵＣ処理では、繊維状の炭素材料のバンドルが解れ、炭素材料が溶液中に分散する。また、図２の（ａ）に示すように混合溶液中の金属錯体が微粒子化され、炭素材料の表面に均一に分散して吸着される。 In the UC treatment as described above, the bundle of fibrous carbon materials is unwound and the carbon materials are dispersed in the solution. Further, as shown in FIG. 2A, the metal complex in the mixed solution is made into fine particles, and is uniformly dispersed and adsorbed on the surface of the carbon material.
なお、分散方法としては、ＵＣ処理以外にも、ミキサー、ジェットミキシング（噴流衝合）、および超音波処理などを用いることができる。ミキサーによる分散方法では、混合溶液に対して、ビーズミル、ロッドミル、ローラミル、攪拌ミル、遊星ミル、振動ミル、ボールミル、ホモジナイザー、ホモミキサーなどにより、物理的な力を加え、混合溶液を撹拌する。炭素材料に対して外力を加えることで、凝集した炭素材料を細分化及び均一化し、バンドルを解すことができる。中でも粉砕力が得られる遊星ミル、振動ミル、ボールミルが好ましい。 In addition to the UC treatment, a mixer, jet mixing (jet collision), ultrasonic treatment, and the like can be used as the dispersion method. In the dispersion method using a mixer, a physical force is applied to the mixed solution by a bead mill, a rod mill, a roller mill, a stirring mill, a planetary mill, a vibration mill, a ball mill, a homogenizer, a homomixer, and the like to stir the mixed solution. By applying an external force to the carbon material, the aggregated carbon material can be subdivided and homogenized, and the bundle can be unwound. Among these, a planetary mill, a vibration mill, and a ball mill that can obtain a crushing force are preferable.
ジェットミキシングによる分散方法では、筒状のチャンバの内壁の互いに対向する位置に一対のノズルを設ける混合溶液を、高圧ポンプにより加圧し、一対のノズルより噴射してチャンバ内で正面衝突させる。これにより、炭素材料のバンドルが粉砕され、分散及び均質化することができる。ジェットミキシングの条件としては、圧力は１００ＭＰａ以上、濃度は５ｇ／ｌ未満が好ましい。 In the dispersion method by jet mixing, a mixed solution in which a pair of nozzles are provided at positions opposite to each other on the inner wall of a cylindrical chamber is pressurized by a high-pressure pump and sprayed from the pair of nozzles to cause a frontal collision in the chamber. Thereby, the bundle of carbon materials can be crushed and dispersed and homogenized. As conditions for jet mixing, the pressure is preferably 100 MPa or more and the concentration is less than 5 g / l.
（３）ポリマー鎖形成工程
ポリマー鎖形成工程では、ＵＣ処理を施した混合溶液を加熱し、炭素材料上に付着したバナジン酸リチウムの前駆体にポリマー鎖を形成する。例えば、ろ過により不純物を除去した混合溶液に対し、真空中において８０〜１５０℃で乾燥を行う。乾燥時間は１２〜２４時間とする。このポリマー鎖形成処理により、バナジン酸リチウムの前駆体に配位した錯体配位子のカルボン酸と、重合剤のヒドロキシル基のエステル化反応が進行する。また、重合剤のヒドロキシル基間において、重合（脱水縮合）が進行する。これらの反応により、図２（ｂ）に示すように多くのポリマー鎖が形成される。ポリマー鎖は、バナジン酸リチウムの前駆体単体に形成される態様と、バナジン酸リチウムの前駆体間に形成される態様を含む。以上のようなポリマー鎖形成工程により、バナジン酸リチウムの前駆体間にポリマー鎖が形成され、バナジン酸リチウムの前駆体同士が結合し凝集体が形成されることが防止される。すなわち、微細なバナジン酸リチウムの前駆体が、炭素材料の表面に均一に分散される。
(3) Polymer chain formation process In a polymer chain formation process, the mixed solution which performed UC process is heated, and a polymer chain is formed in the precursor of lithium vanadate adhering on a carbon material. For example, the mixed solution from which impurities have been removed by filtration is dried at 80 to 150 ° C. in a vacuum. The drying time is 12 to 24 hours. By this polymer chain formation treatment, esterification reaction of the carboxylic acid of the complex ligand coordinated to the precursor of lithium vanadate and the hydroxyl group of the polymerization agent proceeds. Further, polymerization (dehydration condensation) proceeds between the hydroxyl groups of the polymerization agent. By these reactions, many polymer chains are formed as shown in FIG. The polymer chain includes an embodiment in which the lithium vanadate precursor is formed alone and an embodiment in which the polymer chain is formed between the lithium vanadate precursors. By the polymer chain forming step as described above, polymer chains are formed between the lithium vanadate precursors, and the lithium vanadate precursors are prevented from being bonded to each other to form an aggregate. That is, the fine lithium vanadate precursor is uniformly dispersed on the surface of the carbon material.
（４）除去工程
除去工程では、ポリマー鎖を形成したバナジン酸リチウムの前駆体が付着した炭素材料を加熱し、ポリマー鎖を除去する。例えば、炭素材料に対し、大気雰囲気下において、３００〜３２０℃で加熱を行う。加熱時間は３~５時間とする。この加熱工程により、金属配位子と重合剤により形成されたポリマー鎖が熱分解し、除去される。したがって、炭素材料上には、微細な粒子であるバナジン酸リチウムの前駆体のみが残される。
(4) Removal Step In the removal step, the carbon material to which the precursor of lithium vanadate that has formed the polymer chain is heated is heated to remove the polymer chain. For example, the carbon material is heated at 300 to 320 ° C. in an air atmosphere. The heating time is 3 to 5 hours. By this heating step, the polymer chain formed by the metal ligand and the polymerization agent is thermally decomposed and removed. Therefore, only the precursor of lithium vanadate, which is fine particles, remains on the carbon material.
（５）結晶化工程
結晶化工程では、バナジン酸リチウムの前駆体の前駆体が付着した炭素材料を焼成し、バナジン酸リチウムと炭素材料の複合材料を得る。焼成過程において、図２（ｃ）に示すように、バナジン酸リチウムの前駆体が結晶化し、バナジン酸リチウムの金属粒子が炭素材料に担持される。加熱条件は、例えば、窒素雰囲気下において、５００〜９００℃で焼成を行う。焼成時間は０~５分とする。焼成過程では、室温から焼成温度まで急加熱することが好ましい。焼成時間０分とは、例えば３分かけて８００℃まで昇温し、８００℃に到達した時点で加熱を終了し自然冷却することを意味する。このような急加熱により、バナジン酸リチウムの結晶化が促進され粒子成長することが防止される。すなわち、粒径の小さなナノ金属粒子が維持される。
(5) Crystallization Step In the crystallization step, the carbon material to which the precursor of the lithium vanadate precursor is attached is fired to obtain a composite material of lithium vanadate and the carbon material. In the firing process, as shown in FIG. 2C, the precursor of lithium vanadate is crystallized, and the metal particles of lithium vanadate are supported on the carbon material. The heating condition is, for example, baking at 500 to 900 ° C. in a nitrogen atmosphere. The firing time is 0 to 5 minutes. In the firing process, rapid heating from room temperature to the firing temperature is preferred. The firing time of 0 minutes means that, for example, the temperature is raised to 800 ° C. over 3 minutes, and when the temperature reaches 800 ° C., heating is terminated and natural cooling is performed. Such rapid heating promotes crystallization of lithium vanadate and prevents particle growth. That is, nano metal particles having a small particle size are maintained.
また、急加熱は、酸素濃度が１０００ｐｐｍ程度の低酸素濃度の雰囲気下で行われることが好ましい。この条件で急加熱を行うと、炭素材料の酸化が阻止される。以上のような焼成工程により、バナジン酸リチウムが結晶化され、ナノ粒子であるバナジン酸リチウムが炭素材料に担持された複合材料が得られる。 The rapid heating is preferably performed in an atmosphere having a low oxygen concentration with an oxygen concentration of about 1000 ppm. When rapid heating is performed under these conditions, the oxidation of the carbon material is prevented. Through the baking process as described above, lithium vanadate is crystallized, and a composite material in which lithium vanadate as nanoparticles is supported on a carbon material is obtained.
［３．作用効果］
本実施形態の電極材料の製造方法が奏する作用効果は以下の通りである。
（１）バナジウム源とリチウム源を含む金属粒子源と、導電性炭素材料と、錯体配位子と、重合剤とが混合された混合溶液を作製する混合工程と、炭素材料の表面に金属粒子源を付着させ、バナジン酸リチウムの前駆体を生成する分散工程と、炭素材料上に付着したバナジン酸リチウムの前駆体にポリマー鎖を形成するポリマー鎖形成工程と、ポリマー鎖を形成したバナジン酸リチウムの前駆体が付着した炭素材料を加熱し、ポリマー鎖を除去する除去工程と、バナジン酸リチウムの前駆体が付着した炭素材料を焼成し、バナジン酸リチウムと炭素材料の複合材料を得る結晶化工程と、を有する。
[3. Effect]
The effect which the manufacturing method of the electrode material of this embodiment show | plays is as follows.
(1) A metal particle source containing a vanadium source and a lithium source, a mixing step for producing a mixed solution in which a conductive carbon material, a complex ligand, and a polymerizing agent are mixed, and metal particles on the surface of the carbon material. A dispersion step of attaching a source to produce a precursor of lithium vanadate, a polymer chain forming step of forming a polymer chain on the precursor of lithium vanadate attached on the carbon material, and a lithium vanadate having a polymer chain formed The carbon material with the precursor attached is heated to remove the polymer chain, and the carbon material with the lithium vanadate precursor attached is baked to obtain a composite material of lithium vanadate and carbon material. And having.
バナジン酸リチウムの前駆体にポリマー鎖を形成することで、金属粒子の前駆体同士が結合し凝集体が形成されることが防止される。そのため、ポリマー鎖を除去すると、微細なバナジン酸リチウムの前駆体が炭素材料上に残存する。このバナジン酸リチウムの前駆体が付着した炭素材料を焼成して複合材料を形成することにより、導電性炭素材料の表面にバナジン酸リチウムが担持させることができる。また、バナジン酸リチウムの金属粒子の大きさが１００ｎｍ以下である電極材料を得ることができる。 By forming a polymer chain in the lithium vanadate precursor, it is possible to prevent the metal particle precursors from being bonded to each other to form an aggregate. Therefore, when the polymer chain is removed, a fine lithium vanadate precursor remains on the carbon material. By baking the carbon material to which the precursor of lithium vanadate is adhered to form a composite material, lithium vanadate can be supported on the surface of the conductive carbon material. In addition, an electrode material having a metal particle size of lithium vanadate of 100 nm or less can be obtained.
（２）分散工程は、混合溶液を、旋回する反応容器内でずり応力と遠心力を加え、炭素材料の表面に金属粒子源を付着させる工程を含む。
分散工程にＵＣ処理を用いることにより、炭素材料のバンドルが解れ、炭素材料が溶液中に分散する。また、混合溶液中の金属錯体が微粒子化され、炭素材料の表面に均一に分散して吸着される。よって、バナジン酸リチウムを、炭素材料の表面に分散して均一に担持させることができる。
(2) The dispersion step includes a step of applying a shear stress and a centrifugal force to the mixed solution in a swirling reaction vessel to attach a metal particle source to the surface of the carbon material.
By using UC treatment in the dispersion step, the bundle of carbon materials is unwound and the carbon material is dispersed in the solution. Further, the metal complex in the mixed solution is made into fine particles, and is uniformly dispersed and adsorbed on the surface of the carbon material. Therefore, lithium vanadate can be uniformly dispersed and supported on the surface of the carbon material.
また、本実施形態の電極材料が奏する作用効果は以下の通りである。
（３）本実施形態の電極材料は、導電性炭素材料の表面にバナジン酸リチウムが担持され、バナジン酸リチウムの金属粒子の大きさが１００ｎｍ以下である。
Moreover, the effect which the electrode material of this embodiment show | plays is as follows.
(3) In the electrode material of the present embodiment, lithium vanadate is supported on the surface of the conductive carbon material, and the size of the lithium vanadate metal particles is 100 nm or less.
炭素材料に、１００ｎｍ以下のナノ粒子であるバナジン酸リチウムが担持されている。この微細なバナジン酸リチウムは、粒子内部まで反応しやすい状態であり、リチウムイオンの拡散経路が短縮される。したがって、活物質の利用率が向上し、発現容量が拡大する。すなわち、高い充放電容量を有する電極材料を提供することが可能となる。 Lithium vanadate, which is a nanoparticle of 100 nm or less, is supported on the carbon material. This fine lithium vanadate is in a state where it easily reacts to the inside of the particle, and the diffusion path of lithium ions is shortened. Therefore, the utilization factor of the active material is improved and the expression capacity is expanded. That is, an electrode material having a high charge / discharge capacity can be provided.
バナジン酸リチウムの電位は、Ｌｉ／Ｌｉ＋に対し、約１．０Ｖである。よって、リチウムの析出や電解液の分解などの副反応が生じにくい。また、バナジン酸リチウムの理論容量は、約６００ｍＡｈ／ｇである。バナジン酸リチウムは電気伝導性１０−１０Ｓ ｃｍ−１以下と低いが、バナジン酸リチウムのナノ粒子を炭素材料に担持させることで、電気伝導性が向上する。したがって、高い充放電容量と出入力特性を達成することができる。 The potential of lithium vanadate is about 1.0 V with respect to Li / Li + . Therefore, side reactions such as lithium deposition and electrolytic solution decomposition hardly occur. The theoretical capacity of lithium vanadate is about 600 mAh / g. Although lithium vanadate is low in electric conductivity of 10 −10 S cm −1 or less, electric conductivity is improved by supporting the lithium vanadate nanoparticles on a carbon material. Therefore, high charge / discharge capacity and input / output characteristics can be achieved.
（４）バナジン酸リチウムは、前記炭素材料の表面に分散して均一に担持されており、バナジン酸リチウムの面積あたりの粒子数は、５０〜２００個／９００ｎｍ２である。
バナジン酸リチウムが炭素材料の表面に分散して均一に担持されることにより、電気伝導性が向上する。そのため、電極材料を電極に用いた場合に、幅広い電流密度において充放電容量が向上し、高出入力特性が得られる。
(4) The lithium vanadate is dispersed and uniformly supported on the surface of the carbon material, and the number of particles per area of the lithium vanadate is 50 to 200/900 nm 2 .
Electrical conductivity is improved by lithium vanadate being dispersed and uniformly supported on the surface of the carbon material. Therefore, when an electrode material is used for the electrode, the charge / discharge capacity is improved over a wide current density, and high input / output characteristics are obtained.
（５）炭素材料は、繊維状炭素である。
繊維状炭素は導電性に優れている。そのため、炭素材料として繊維状炭素を用いることで、電気伝導性を向上させることが可能となる。
(5) The carbon material is fibrous carbon.
Fibrous carbon is excellent in conductivity. Therefore, electrical conductivity can be improved by using fibrous carbon as the carbon material.
以下、実施例に基づいて本発明をさらに詳細に説明する。なお、本発明は下記実施例に限定されるものではない。 Hereinafter, the present invention will be described in more detail based on examples. In addition, this invention is not limited to the following Example.
（実施例１）
本実施例では、以下の製造方法により、バナジン酸リチウムとカーボンナノチューブ（ＣＮＴ）の複合材料（Ｌｉ３ＶＯ４／ＣＮＴ）を生成した。
Example 1
In this example, a composite material (Li 3 VO 4 / CNT) of lithium vanadate and carbon nanotubes (CNT) was generated by the following manufacturing method.
バナジン酸リチウムの金属粒子源は、バナジウム源としてメタバナジン酸アンモニウム（ＮＨ４ＶＯ３）、リチウム源として水酸化リチウム（ＬｉＯＨ）溶液を用い、モル比でＬｉ：Ｖ＝３：１となるように混合した。ＣＮＴは、多層カーボンナノチューブを用いた。ＣＮＴの平均繊維径は、１１ｎｍであった。使用したバナジン酸リチウムの金属粒子源とＣＮＴの重量比率は、６０：４０であった。また、金属配位子としてクエン酸、重合剤としてエチレングリコールを用いた。バナジウム源に対し、クエン酸は１当量、エチレングリコールは４当量添加した。 As the metal particle source of lithium vanadate, ammonium metavanadate (NH 4 VO 3 ) is used as the vanadium source, and lithium hydroxide (LiOH) solution is used as the lithium source, and mixed so that the molar ratio is Li: V = 3: 1. did. As the CNT, a multi-walled carbon nanotube was used. The average fiber diameter of CNT was 11 nm. The weight ratio of the lithium vanadate metal particle source and the CNT used was 60:40. Further, citric acid was used as the metal ligand, and ethylene glycol was used as the polymerization agent. 1 equivalent of citric acid and 4 equivalents of ethylene glycol were added to the vanadium source.
具体的には、図３に示すように、第１の溶液として、メタバナジン酸アンモニウムとクエン酸を蒸留水（Ｈ２Ｏ）に添加し、マグネチックスターラーを用いて撹拌した。第１の溶液では、メタバナジン酸アンモニウムの金属錯体が形成される。また、第２の溶液として、エチレングリコールを蒸留水に添加し、マグネチックスターラーを用いて撹拌した。この第１の溶液と第２の溶液を混合し、さらにマグネチックスターラーを用いて撹拌した。第１の溶液と第２の溶液の混合溶液に、水酸化リチウム溶液、カーボンナノチューブ、および蒸留水を添加し、第３の溶液とした。 Specifically, as shown in FIG. 3, as a first solution, ammonium metavanadate and citric acid were added to distilled water (H 2 O), and the mixture was stirred using a magnetic stirrer. In the first solution, a metal complex of ammonium metavanadate is formed. Moreover, ethylene glycol was added to distilled water as a 2nd solution, and it stirred using the magnetic stirrer. The first solution and the second solution were mixed and further stirred using a magnetic stirrer. A lithium hydroxide solution, carbon nanotubes, and distilled water were added to the mixed solution of the first solution and the second solution to obtain a third solution.
この第３の溶液について、８０℃の環境下においてＵＣ処理を行った。ＵＣ処理では、図１に示すような反応器を用い、回転速度を５０ｍ／ｓとし、第３の溶液に５分間にわたって６６０００Ｎ（ｋｇｍｓ−２）の遠心力を与えた。このＵＣ処理では、ＣＮＴのバンドルが解れるとともに、金属錯体を有するバナジン酸リチウムの前駆体が微粒子化し、均一に分散した状態でＣＮＴの表面に付着することが促進されていると考えられる。 About this 3rd solution, UC process was performed in 80 degreeC environment. In the UC treatment, a reactor as shown in FIG. 1 was used, the rotational speed was 50 m / s, and a centrifugal force of 66000 N (kgms −2 ) was applied to the third solution for 5 minutes. In this UC treatment, it is considered that the bundle of CNTs is unraveled, and the precursor of lithium vanadate having a metal complex is atomized and adhered to the surface of the CNTs in a uniformly dispersed state.
次に、第３の溶液から不純物をろ過し、１３０℃において、終夜、真空乾燥を行った。この真空乾燥では、ＣＮＴの表面に付着したバナジン酸リチウムの前駆体を核に、クエン酸のカルボキシル基とエチレングリコールのヒドロキシル基との間でエステル化反応が進行し、ポリマー鎖が形成される。ポリマー鎖の形成により、バナジン酸リチウムの前駆体間にポリマー鎖が形成され、バナジン酸リチウムの前駆体同士が結合し凝集体が形成されることが防止されると考えられる。そのため、微細なバナジン酸リチウムの前駆体が、ＣＮＴの表面に均一に分散される。 Next, impurities were filtered from the third solution, and vacuum drying was performed at 130 ° C. overnight. In this vacuum drying, an esterification reaction proceeds between a carboxyl group of citric acid and a hydroxyl group of ethylene glycol with a precursor of lithium vanadate adhering to the surface of the CNT as a nucleus, and a polymer chain is formed. It is considered that the formation of the polymer chain prevents a polymer chain from being formed between the lithium vanadate precursors, and the lithium vanadate precursors are bonded to each other to form an aggregate. Therefore, the fine lithium vanadate precursor is uniformly dispersed on the surface of the CNT.
真空乾燥後のＣＮＴについて、３００℃で３時間、大気雰囲気下で加熱を行った。この３００℃での熱処理により、クエン酸およびエチレングリコールのエステル化により形成されたポリマー鎖が熱分解する。したがって、ＣＮＴの表面には、微細なバナジン酸リチウムの前駆体のみが残存する。 The CNT after vacuum drying was heated at 300 ° C. for 3 hours in an air atmosphere. By this heat treatment at 300 ° C., the polymer chain formed by the esterification of citric acid and ethylene glycol is thermally decomposed. Therefore, only a fine lithium vanadate precursor remains on the surface of the CNT.
その後、窒素雰囲気下において、８００℃で０分間焼成を行った。この焼成は、３分かけて８００℃まで昇温し、８００℃に到達した時点で加熱を終了し自然冷却した。この焼成により、バナジン酸リチウムの前駆体が結晶化し、ＣＮＴの表面にナノ粒子化したバナジン酸リチウムが結合している状態となる。以上のようにして、ナノ粒子化したバナジン酸リチウムがＣＮＴに担持された複合材料（Ｌｉ３ＶＯ４／ＣＮＴ）が得られた。 Thereafter, baking was performed at 800 ° C. for 0 minute in a nitrogen atmosphere. In this firing, the temperature was raised to 800 ° C. over 3 minutes, and when the temperature reached 800 ° C., the heating was terminated and the product was naturally cooled. By this firing, the precursor of lithium vanadate is crystallized, and the nano-sized lithium vanadate is bonded to the surface of the CNT. As described above, a composite material (Li 3 VO 4 / CNT) in which nanoparticulate lithium vanadate was supported on CNTs was obtained.
（実施例２）
上記第３の溶液についてＵＣ処理を行う代わりに、ホモジナイザーで撹拌した。それ以外は、実施例１と同様に作製した。
(Example 2)
The third solution was agitated with a homogenizer instead of performing UC treatment. Other than that, it produced similarly to Example 1. FIG.
（比較例１）
第１の溶液として、メタバナジン酸アンモニウムを蒸留水（Ｈ２Ｏ）に添加し、マグネチックスターラーを用いて撹拌した。第１の溶液に、水酸化リチウム溶液、カーボンナノチューブ、および蒸留水を添加し、第２の溶液とした。この第２の溶液について、上記のＵＣ処理以降の処理を行った。それ以外は、実施例１と同様に作製した。
(Comparative Example 1)
As a first solution, ammonium metavanadate was added to distilled water (H 2 O) and stirred using a magnetic stirrer. A lithium hydroxide solution, carbon nanotubes, and distilled water were added to the first solution to obtain a second solution. About this 2nd solution, the process after said UC process was performed. Other than that, it produced similarly to Example 1. FIG.
（１）電極材料の結晶構造解析
上記実施例１について、ＨＲＴＥＭ像を撮影し結晶構造を解析した。図４および５は、実施例１において得られたＣＮＴの表面にバナジン酸リチウムが結合した複合体を示すＨＲＴＥＭ像である。図４は全体像を、図５は部分拡大像を示す。図４から明らかな通り、ＣＮＴのバンドルが解れ、紐状のＣＮＴの一本一本にバナジン酸リチウムのナノ粒子が複数結合している。また、図５に示すように、バナジン酸リチウムのナノ粒子は結晶化している。
(1) Crystal structure analysis of electrode material About the said Example 1, the HRTEM image was image | photographed and the crystal structure was analyzed. 4 and 5 are HRTEM images showing a composite in which lithium vanadate is bonded to the surface of the CNT obtained in Example 1. FIG. 4 shows an overall image, and FIG. 5 shows a partially enlarged image. As is apparent from FIG. 4, the bundle of CNTs is unwound, and a plurality of lithium vanadate nanoparticles are bonded to each of the string-like CNTs. Further, as shown in FIG. 5, the nanoparticles of lithium vanadate are crystallized.
図４に示す領域１〜３について、それぞれバナジン酸リチウムについて、凝集体を含む粒子の大きさと面積あたりの粒子数を目視にて計測した結果を図６〜８に示す。図６〜８から明らかな通り、各領域において確認されたバナジン酸リチウムの粒子の大きさは、最も大きなものでも５０ｎｍ程度であった。また、図９に示すように、各領域における粒子数を計測したところ、領域１では計９９個、領域２では計９３個、領域３では計１８２個の粒子が確認された。すなわち、バナジン酸リチウムの面積あたりの粒子数は、５０〜２００個／９００ｎｍ２であった。領域１〜３における粒子の個数を合計したところ３７４個／２７００ｎｍ２であった。 About the area | regions 1-3 shown in FIG. 4, the result of having measured the magnitude | size of the particle | grains containing an aggregate and the particle | grain number per area visually about lithium vanadate is shown in FIGS. As is apparent from FIGS. 6 to 8, the size of the lithium vanadate particles confirmed in each region was about 50 nm even at the largest. As shown in FIG. 9, when the number of particles in each region was measured, a total of 99 particles in region 1, 93 particles in region 2, and 182 particles in region 3 were confirmed. That is, the number of particles per area of lithium vanadate was 50 to 200/900 nm 2 . The total number of particles in the regions 1 to 3 was 374/2700 nm 2 .
さらに、各領域において３０ｎｍ以下の微細なナノ粒子が存在する割合を算出した。その結果、領域１は約９０％、領域２は約７９％、領域３は約８９％が、３０ｎｍ以下の金属粒子を含んでいた。領域全体では、約８７％が３０ｎｍ以下の金属粒子であった。すなわち、実施例１の複合体は、金属粒子の約８０％以上が３０ｎｍ以下の微細なナノ粒子であることが確認された。以上より、実施例１のＬｉ３ＶＯ４／ＣＮＴでは、ＣＮＴの表面に微細なナノ粒子のバナジン酸リチウムが均一かつ高い分散度で担持された状態であることが分かった。 Further, the ratio of the presence of fine nanoparticles of 30 nm or less in each region was calculated. As a result, the region 1 was about 90%, the region 2 was about 79%, the region 3 was about 89%, and contained metal particles of 30 nm or less. In the entire region, about 87% were metal particles of 30 nm or less. That is, it was confirmed that about 80% or more of the metal particles were fine nanoparticles of 30 nm or less in the composite of Example 1. From the above, it was found that in Li 3 VO 4 / CNT of Example 1, fine nano-sized lithium vanadate was supported on the CNT surface uniformly and with a high degree of dispersion.
（２）電極材料の放電容量特性
実施例１、実施例２、および比較例１の電極材料を、バインダーとしてのポリフッ化ビニリデンＰＶＤＦとNMP共に攪拌してスラリー状にし、銅箔上に塗布し、作用電極Ｗ．Ｅ．とした。投入比率は、重量比にしてＬｉ３ＶＯ４／ＣＮＴ：ＰＶＤＦ＝９４：６であった。充放電特性は２０３２型コインセルにて評価した。リチウム金属を対極Ｃ．Ｅとして下蓋に貼り付けた。対極Ｃ．Ｅの上にセパレータ、ガスケット、Ｗ．Ｅ、スペーサー、スプリング、上蓋の順に載せ、かしめてセルを作製した。電解液は、１．０Ｍ六フッ化リン酸リチウム（ＬｉＰＦ６）／炭酸エチレン（ＥＣ）と炭酸ジメチル（ＤＥＣ）とし、これらを浸透させてセルとした。なお、体積比率でＥＣ：ＤＥＣ＝１：１であった。
(2) Discharge capacity characteristics of electrode material The electrode materials of Example 1, Example 2, and Comparative Example 1 were stirred together with polyvinylidene fluoride PVDF and NMP as a binder to form a slurry, and applied onto a copper foil. Working electrode W. E. It was. The input ratio was Li 3 VO 4 / CNT: PVDF = 94: 6 in terms of weight ratio. The charge / discharge characteristics were evaluated using a 2032 type coin cell. Lithium metal counter electrode C.I. Attached to the lower lid as E. Counter electrode C.I. E. Separator, gasket, W. E, a spacer, a spring, and an upper lid were placed in this order and caulked to produce a cell. The electrolyte was 1.0 M lithium hexafluorophosphate (LiPF 6 ) / ethylene carbonate (EC) and dimethyl carbonate (DEC), and these were infiltrated into a cell. The volume ratio was EC: DEC = 1: 1.
実施例１、実施例２、および比較例１の電極材料を用いて作製したセルを用いて、任意の電流密度において充放電を行った。図１０は、様々な電流密度における、各セルの活物質あたりの充電容量を示す。充放電容量の測定は、放電側(Lithiation)の電流値は０．１Ａｇ-1で固定し、充電側(De-lithitation)の電流値は ０．０１〜２０Ａｇ-1で３サイクルずつ変化させて行った。電位範囲は、０．５〜２．５Ｖ ｖｓ．Ｌｉ／Ｌｉ＋であった。 Using the cell produced using the electrode material of Example 1, Example 2, and the comparative example 1, it charged / discharged in arbitrary current densities. FIG. 10 shows the charge capacity per active material of each cell at various current densities. The charge / discharge capacity was measured by fixing the current value on the discharge side (Lithiation) at 0.1 Ag- 1 and changing the current value on the charge side (De-lithitation) in increments of 3 cycles from 0.01 to 20 Ag- 1. went. The potential range is 0.5 to 2.5 V vs. Li / Li + .
図１０からも明らかな通り、実施例１はいずれの電流密度においても、比較例１と比較して活物質あたりの充電容量が大きい。すなわち、実施例１では、充電容量が安定的に発現していることが分かる。また、実施例２は、特に１５Ａｇ−１以下の低レート側において、比較例１と比較して活物質あたりの充電容量が大きい。実施例１および２の電極材料では、電気伝導性の向上が、出入力特性の向上に寄与していると考えられる。また、バナジン酸リチウムがナノ粒子化されていることにより、リチウムイオンの拡散経路が短縮され、粒子内部まで反応が起こりやすい状態となっている。したがって、活物質利用率が向上し、発現容量が拡大していると考えられる。 As is clear from FIG. 10, the charge capacity per active material of Example 1 is larger than that of Comparative Example 1 at any current density. That is, in Example 1, it turns out that charge capacity is expressing stably. In addition, Example 2 has a larger charge capacity per active material than Comparative Example 1, particularly on the low rate side of 15 Ag −1 or less. In the electrode materials of Examples 1 and 2, it is considered that the improvement in electrical conductivity contributes to the improvement in input / output characteristics. In addition, since lithium vanadate is made into nanoparticles, the diffusion path of lithium ions is shortened, and the reaction is likely to occur inside the particles. Therefore, it is considered that the active material utilization rate is improved and the expression capacity is expanded.
１…外筒
１−２…せき板
１−３…内壁
２…内筒
２−１…貫通孔
DESCRIPTION OF SYMBOLS 1 ... Outer cylinder 1-2 ... Baffle 1-3 ... Inner wall 2 ... Inner cylinder 2-1 ... Through-hole
Claims (8)
前記炭素材料の表面に前記金属粒子源を付着させ、バナジン酸リチウムの前駆体を生成する分散工程と、
前記炭素材料上に付着したバナジン酸リチウムの前駆体にポリマー鎖を形成するポリマー鎖形成工程と、
ポリマー鎖を形成したバナジン酸リチウムの前駆体が付着した前記炭素材料を加熱し、ポリマー鎖を除去する除去工程と、
バナジン酸リチウムの前駆体が付着した前記炭素材料を焼成し、バナジン酸リチウムと前記炭素材料の複合材料を得る結晶化工程と、
を有することを特徴とする電極材料の製造方法。 A mixing step of preparing a mixed solution in which a metal particle source including a vanadium source and a lithium source, a conductive carbon material, a complex ligand, and a polymerization agent are mixed;
A dispersion step of attaching the metal particle source to the surface of the carbon material to generate a precursor of lithium vanadate;
A polymer chain forming step of forming a polymer chain on a precursor of lithium vanadate adhering to the carbon material;
Removing the polymer chain by heating the carbon material to which the precursor of lithium vanadate that has formed a polymer chain is attached; and
Calcination of the carbon material to which the precursor of lithium vanadate is adhered, and a crystallization step of obtaining a composite material of lithium vanadate and the carbon material;
A method for producing an electrode material comprising:
バナジン酸リチウムの金属粒子の大きさが１００ｎｍ以下であることを特徴とする電極材料。 Lithium vanadate is supported on the surface of the conductive carbon material,
An electrode material, wherein the metal particles of lithium vanadate have a size of 100 nm or less.
バナジン酸リチウムの面積あたりの粒子数は、５０〜２００個／９００ｎｍ２であることを特徴とする請求項４記載の電極材料。 Lithium vanadate is dispersed and uniformly supported on the surface of the carbon material,
The electrode material according to claim 4, wherein the number of particles per area of lithium vanadate is 50 to 200 particles / 900 nm 2 .
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