JP6321520B2 - Negative electrode for sodium ion secondary battery, method for producing the same, and sodium ion secondary battery - Google Patents
Negative electrode for sodium ion secondary battery, method for producing the same, and sodium ion secondary battery Download PDFInfo
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- JP6321520B2 JP6321520B2 JP2014223391A JP2014223391A JP6321520B2 JP 6321520 B2 JP6321520 B2 JP 6321520B2 JP 2014223391 A JP2014223391 A JP 2014223391A JP 2014223391 A JP2014223391 A JP 2014223391A JP 6321520 B2 JP6321520 B2 JP 6321520B2
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- 229910001415 sodium ion Inorganic materials 0.000 title claims description 32
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 title claims description 29
- 238000004519 manufacturing process Methods 0.000 title claims description 10
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- 239000007773 negative electrode material Substances 0.000 claims description 38
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- IYPQZXRHDNGZEB-UHFFFAOYSA-N cobalt sodium Chemical compound [Na].[Co] IYPQZXRHDNGZEB-UHFFFAOYSA-N 0.000 description 1
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- 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
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- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Description
本発明は、ナトリウムイオン二次電池用負極およびその製造方法並びにナトリウムイオン二次電池に関する。 The present invention relates to a negative electrode for a sodium ion secondary battery, a manufacturing method thereof, and a sodium ion secondary battery.
リチウムイオン二次電池は高電圧、高容量を有することから、携帯電話やノートパソコン等の小型電子機器だけでなく、電気自動車やハイブリッド自動車等の自動車用電源や電力貯蔵用の分散電源として広く使用されている。 Lithium-ion secondary batteries have high voltage and high capacity, so they are widely used not only for small electronic devices such as mobile phones and laptop computers, but also as power sources for automobiles such as electric vehicles and hybrid vehicles, and as distributed power sources for power storage. Has been.
リチウムイオン二次電池は、その正極にリチウム含有遷移金属複合酸化物を用い、電解質塩にも種々のリチウム塩を用いている。しかし、リチウムはその産地が偏在する稀少金属元素であり、リチウムに代わる、より安価で入手の容易な材料が求められている。これに対し、同じアルカリ金属元素であるナトリウムを用いたナトリウムイオン二次電池に対する期待が高まっている。ナトリウム(Na)は地殻中に多く存在し,海水中にも高濃度に含まれていることから,これを電荷担体とするナトリウムイオン二次電池はリチウムイオン二次電池と比較し資源的な制約がないという大きな利点がある。 Lithium ion secondary batteries use a lithium-containing transition metal composite oxide for the positive electrode and various lithium salts for the electrolyte salt. However, lithium is a rare metal element whose production area is unevenly distributed, and there is a need for a cheaper and easily available material that can replace lithium. On the other hand, expectation for a sodium ion secondary battery using sodium which is the same alkali metal element is increasing. Since sodium (Na) is abundant in the crust and contained in seawater at a high concentration, sodium ion secondary batteries using this as a charge carrier are more resource-constrained than lithium ion secondary batteries. There is a big advantage that there is no.
しかしながら、NaイオンはLiイオンの1.4倍もの直径を有していることから、現行のリチウムイオン二次電池用負極活物質であるグラファイトの層間に電気化学的に挿入させることが困難という問題がある。そのため、Naを電気化学的に挿入−脱離できる負極活物質が求められている。同じ炭素系材料でも低結晶性であるため層間距離がグラファイトより広いハードカーボンを使用することで、可逆的にNaが挿入・脱離することが見出されてきた(例えば特許文献1)。しかし、ハードカーボンはサイクル安定性には優れるものの、250〜300mAh/g程度の理論容量しか期待できないため(例えば非特許文献1)、さらなる高容量化が可能な負極活物質を用いた負極が望まれている。 However, since Na ions have a diameter 1.4 times that of Li ions, it is difficult to insert them between graphite layers, which are current negative electrode active materials for lithium ion secondary batteries. There is. Therefore, a negative electrode active material capable of electrochemically inserting and removing Na is required. Since the same carbon-based material is low in crystallinity, it has been found that Na is reversibly inserted and desorbed by using hard carbon whose interlayer distance is wider than that of graphite (for example, Patent Document 1). However, although hard carbon is excellent in cycle stability, only a theoretical capacity of about 250 to 300 mAh / g can be expected (for example, Non-Patent Document 1), so a negative electrode using a negative electrode active material capable of further increasing the capacity is desired. It is rare.
本発明は、上記の課題を解決するものであり、さらなる容量およびサイクル特性の向上の可能なナトリウムイオン二次電池用負極およびその製造方法並びにナトリウムイオン二次電池を提供することを目的とした。 The present invention has been made to solve the above problems, and has an object to provide a negative electrode for a sodium ion secondary battery, a method for producing the same, and a sodium ion secondary battery that can further improve capacity and cycle characteristics.
本発明者らは、上記の課題を解決すべく鋭意検討する過程で、SiクラスターがSiO2媒体中に分散した構造を有する負極活物質を含む負極が高い容量と優れたサイクル特性を有することを見出して本発明を完成させたものである。すなわち、本発明のナトリウムイオン二次電池用負極は、SiクラスターがSiO2媒体中に分散した構造を有する負極活物質を含むことを特徴とする。 In the process of earnestly examining the above problems, the present inventors have found that a negative electrode including a negative electrode active material having a structure in which Si clusters are dispersed in a SiO 2 medium has high capacity and excellent cycle characteristics. The present invention has been found and completed. That is, the negative electrode for sodium ion secondary batteries of the present invention is characterized in that it includes a negative electrode active material having a structure in which Si clusters are dispersed in a SiO 2 medium.
また、本発明のナトリウムイオン二次電池用負極の製造方法は、SiクラスターがSiO2媒体中に分散した構造を有する負極活物質をガスデポジション法を用いて集電体上に堆積させて負極活物質層を形成することを特徴とする。 Further, the negative electrode active material for sodium ion secondary battery according to the present invention is manufactured by depositing a negative electrode active material having a structure in which Si clusters are dispersed in a SiO 2 medium on a current collector using a gas deposition method. An active material layer is formed.
また、本発明のナトリウムイオン二次電池は、正極と負極と電解液を有するナトリウムイオン二次電池であって、前記負極がSiクラスターがSiO2媒体中に分散した構造を有する負極活物質を含むことを特徴とする。 The sodium ion secondary battery of the present invention is a sodium ion secondary battery having a positive electrode, a negative electrode, and an electrolyte, and the negative electrode includes a negative electrode active material having a structure in which Si clusters are dispersed in a SiO 2 medium. It is characterized by that.
本発明によれば、さらなる容量およびサイクル特性の向上の可能なナトリウムイオン二次電池を提供することが可能となる。 According to the present invention, it is possible to provide a sodium ion secondary battery capable of further improving capacity and cycle characteristics.
以下、図面等を参照して本発明を詳細に説明する。
本発明のナトリウムイオン二次電池用負極は、SiクラスターがSiO2媒体中に分散した構造を有する負極活物質を含むことを特徴とするものである。
Hereinafter, the present invention will be described in detail with reference to the drawings.
The negative electrode for a sodium ion secondary battery according to the present invention includes a negative electrode active material having a structure in which Si clusters are dispersed in a SiO 2 medium.
(負極)
本発明の負極は、集電体と、該集電体上に形成された負極活物質層とを有し、負極活物質層を構成する負極活物質は、SiクラスターがSiO2媒体中に分散した構造を有する。
Siクラスターは、結晶質Siの微粒子であり、それがSiO2媒体、具体的には非晶質SiO2に分散した構造を有する。本発明の負極活物質は、X線回折法によりその構造を確認することができ、SiクラスターはSiの結晶ピークにより、非晶質SiO2は回折角2θが23度付近のブロードなピークにより確認することができる。また、Siクラスターの結晶子サイズは、微分散の観点から、1〜300nm、好ましくは1〜150nm、より好ましくは1〜20nmである。結晶子サイズは、(220)面の回折ピークの半値幅から算出したものを用いることができる。
(Negative electrode)
The negative electrode of the present invention has a current collector and a negative electrode active material layer formed on the current collector, and the negative electrode active material constituting the negative electrode active material layer has Si clusters dispersed in the SiO 2 medium. Has the structure.
Si clusters are fine particles of crystalline Si, and have a structure in which they are dispersed in a SiO 2 medium, specifically, amorphous SiO 2 . The structure of the negative electrode active material of the present invention can be confirmed by an X-ray diffraction method. Si clusters are confirmed by Si crystal peaks, and amorphous SiO 2 is confirmed by broad peaks having a diffraction angle 2θ of around 23 degrees. can do. The crystallite size of the Si cluster is 1 to 300 nm, preferably 1 to 150 nm, more preferably 1 to 20 nm from the viewpoint of fine dispersion. As the crystallite size, one calculated from the half-value width of the diffraction peak on the (220) plane can be used.
SiO2媒体中のSiクラスターの含有量は、高い充放電容量を確保するとともにサイクル性を確保する観点から、負極活物質の12〜48質量%、好ましくは22〜42質量%、より好ましくは25〜39質量%である。ここで、Siクラスターの含有量は、電子エネルギー損失分光法により算出することができる。 The content of Si clusters in the SiO 2 medium is 12 to 48% by mass of the negative electrode active material, preferably 22 to 42% by mass, more preferably 25 from the viewpoint of ensuring high charge / discharge capacity and ensuring cycleability. It is -39 mass%. Here, the Si cluster content can be calculated by electron energy loss spectroscopy.
SiクラスターがSiO2媒体中に分散した構造を有する材料としては、一般式SiOx(x=0.5〜1.6)で表される酸化ケイ素化合物や、Siクラスター/SiO2複合膜等を挙げることができる。前記の酸化ケイ素化合物は、ケイ素の酸化、二酸化ケイ素の還元、あるいはケイ素と二酸化ケイ素との反応により製造することができる。前記の酸化ケイ素化合物の具体例としては一酸化ケイ素SiOを挙げることができる。また、Siクラスター/SiO2複合膜としては、気相成膜法を用いてSiO2マトリックス中にナノスケールのSi結晶を分散させたもので、例えばSiO2基板上にスパッタリングによりナノスケールのSiを分散させた複合膜を挙げることができる。なお、xは上記の電子エネルギー損失分光法を用いて算出することができる。また、x=0.5〜1.6は、上記の12〜48質量%に、x=0.7〜1.3は、上記の22〜42質量%に、x=0.8〜1.2は、上記の25〜39質量%に相当する。 Examples of the material having a structure in which Si clusters are dispersed in the SiO 2 medium include silicon oxide compounds represented by the general formula SiO x (x = 0.5 to 1.6), Si cluster / SiO 2 composite films, and the like. be able to. The silicon oxide compound can be produced by oxidation of silicon, reduction of silicon dioxide, or reaction between silicon and silicon dioxide. Specific examples of the silicon oxide compound include silicon monoxide SiO. As the Si cluster / SiO 2 composite film, nanoscale Si crystals are dispersed in a SiO 2 matrix using a vapor deposition method. For example, nanoscale Si is sputtered on a SiO 2 substrate. A dispersed composite membrane can be mentioned. Note that x can be calculated using the above-described electron energy loss spectroscopy. Further, x = 0.5 to 1.6 is 12 to 48% by mass, x = 0.7 to 1.3 is 22 to 42% by mass, and x = 0.8 to 1. 2 corresponds to the above 25-39% by mass.
一酸化ケイ素SiOには、例えば二酸化ケイ素とケイ素を加熱して得られる気体のSiOを冷却して得られる粉末状のものを用いることができる。SiOの平均粒径は、20μm以下、好ましくは5μm以下、より好ましくは5μm〜0.1μmである。なお、この粉末状のSiOについては、非晶質のSiO2がSiO4四面体の三次元網目構造を形成し,この構造中にSiクラスターが微分散した構造が形成されることを、本発明者は報告している(H. Sakaguchi et al., J. Electrochem. Soc., 151 (2004) A1572)。 As the silicon monoxide SiO, for example, a powdery one obtained by cooling gaseous SiO obtained by heating silicon dioxide and silicon can be used. The average particle diameter of SiO is 20 μm or less, preferably 5 μm or less, and more preferably 5 μm to 0.1 μm. As for the powdery SiO, amorphous SiO 2 forms a three-dimensional network structure of SiO 4 tetrahedrons, and a structure in which Si clusters are finely dispersed is formed in the present invention. Reported (H. Sakaguchi et al., J. Electrochem. Soc., 151 (2004) A1572).
本発明の負極の製造方法は特に限定されない。例えばスラリー法を用いることができる。この場合、上記の負極活物質に、バインダー、溶媒、必要に応じて炭素材等の導電材を添加して混練して電極スラリーを調製し、それを集電体上に塗布し、その後乾燥することにより負極を作製することができる。電極スラリー中の負極活物質は40重量%以上とすることが好ましい。バインダーには、フッ化ビニリデン重合体やその共重合体等の公知のフッ素含有重合体、ポリアクリル酸およびそのNa塩並びにその共重合体等のアクリル酸系重合体、カルボキシメチルセルロース等のセルロース誘導体を用いることができる。 The manufacturing method of the negative electrode of the present invention is not particularly limited. For example, a slurry method can be used. In this case, a binder, a solvent, and, if necessary, a conductive material such as a carbon material are added to the negative electrode active material and kneaded to prepare an electrode slurry, which is applied onto a current collector and then dried. Thus, a negative electrode can be produced. The negative electrode active material in the electrode slurry is preferably 40% by weight or more. The binder includes a known fluorine-containing polymer such as a vinylidene fluoride polymer and a copolymer thereof, polyacrylic acid and an Na salt thereof, an acrylic acid polymer such as a copolymer thereof, and a cellulose derivative such as carboxymethyl cellulose. Can be used.
また、本発明においては、ガスデポジション法を用いて負極を作製することもできる。ガスデポジション法では、バインダーが不要であることから負極中の活物質濃度を大きくすることができるのでエネルギー密度を向上させることが可能である。また、負極活物質層と集電体間との密着性が向上し、負極活物質の剥離が抑制されてサイクル特性の向上が期待でき、さらに接触抵抗の低下により、電池の内部抵抗の低減も可能となる。以下、ガスデポジション法について詳細に説明する。 Moreover, in this invention, a negative electrode can also be produced using a gas deposition method. In the gas deposition method, since no binder is required, the active material concentration in the negative electrode can be increased, so that the energy density can be improved. In addition, the adhesion between the negative electrode active material layer and the current collector is improved, the negative electrode active material is prevented from being peeled off, and the cycle characteristics can be improved, and the internal resistance of the battery can be reduced by reducing the contact resistance. It becomes possible. Hereinafter, the gas deposition method will be described in detail.
(ガスデポジション法)
ガスデポジション法により粉末原料を基材(集電体)に担持させることによって、負極活物質層を形成する。かかる負極活物質層は、従来の圧着法、気相析出法、メッキ法等による緻密で均質な層とは異なり、厚み方向及び層の面方向の密度が不均一になっている。これにより、ナトリウムイオンが負極活物質層に挿入される際に発生する応力を緩和ないしは解消することができる結果、充放電特性、サイクル特性等の向上を図ることができる。
(Gas deposition method)
A negative electrode active material layer is formed by supporting a powder raw material on a base material (current collector) by a gas deposition method. Such a negative electrode active material layer has a non-uniform density in the thickness direction and the surface direction of the layer, unlike a dense and homogeneous layer formed by a conventional pressure bonding method, vapor phase deposition method, plating method or the like. As a result, stress generated when sodium ions are inserted into the negative electrode active material layer can be relieved or eliminated. As a result, charge / discharge characteristics, cycle characteristics, and the like can be improved.
ガスデポジション法は、粉末原料とキャリアガスとを用いることによりエアロゾルを発生させ、これを基材上に噴射することにより膜を形成する方法である。 The gas deposition method is a method of forming a film by generating an aerosol by using a powder raw material and a carrier gas and injecting it onto a substrate.
図6は、ガスデポジション法に用いる装置の構造の一例を示す模式図である。所定の初期圧力を有するキャリアガス1を粉末原料2とともに導管3中でエアロゾル化した後、このエアロゾルを、減圧装置4によって真空状態に保持されたチャンバ5内に設置された基材6の表面へ向けて、導管3の先端に取り付けたノズル7から噴出させる。
FIG. 6 is a schematic diagram showing an example of the structure of an apparatus used for the gas deposition method. After the
ガスデポジション法は、公知の方法に従って実施することができる。本発明では、次のような条件とすることが望ましい。すなわち、キャリアガスとしては、例えばアルゴンガス、窒素ガス等の不活性ガスを用いることが好ましい。また、圧力差(装置内圧力とガスのゲージ圧との差)は、3×105〜1×106Pa程度とすることが好ましい。さらに、基材とノズルとの距離は5〜30mm程度とすることが好ましい。 The gas deposition method can be performed according to a known method. In the present invention, the following conditions are desirable. That is, as the carrier gas, it is preferable to use an inert gas such as argon gas or nitrogen gas. The pressure difference (difference between the pressure in the apparatus and the gas gauge pressure) is preferably about 3 × 10 5 to 1 × 10 6 Pa. Furthermore, the distance between the substrate and the nozzle is preferably about 5 to 30 mm.
ガスデポジション法により粉末原料を担持する場合、その担持量は要求される電極特性に応じて適宜設定することができる。一般的には、担持量を0.5〜20mg/cm2程度とすれば良い。また、電極活物質層の厚さは、1〜6μm、好ましくは1〜4μmとすることができる。1μmより小さいと、十分な容量が得られず、また10μmより大きいと剥離し易くなり好ましくない。 When the powder raw material is supported by the gas deposition method, the amount supported can be appropriately set according to the required electrode characteristics. In general, the supported amount may be about 0.5 to 20 mg / cm 2 . The thickness of the electrode active material layer can be 1 to 6 μm, preferably 1 to 4 μm. If it is smaller than 1 μm, a sufficient capacity cannot be obtained, and if it is larger than 10 μm, it tends to peel off, which is not preferable.
また、ガスデポジション法を実施する場合、1回の噴射で電極活物質層を形成しても良いが、複数回にわたり噴射しても良い。複数回の噴射による場合は、多層構造を有する電極活物質層が形成されるが、このような構造も本発明に含まれる。 Further, when the gas deposition method is performed, the electrode active material layer may be formed by one injection, but may be injected a plurality of times. In the case of multiple injections, an electrode active material layer having a multilayer structure is formed, and such a structure is also included in the present invention.
用いる基材の種類は特に限定されない。例えば、銅、ニッケル、アルミニウム等の導電性材料を用いることができる。その形状も特に限定されるものではなく、例えば箔、シート等の形態で使用することができる。基材の厚みは、例えば1〜50μm程度とすれば良い。 The kind of base material to be used is not particularly limited. For example, a conductive material such as copper, nickel, or aluminum can be used. The shape is not particularly limited, and can be used in the form of, for example, a foil or a sheet. The thickness of the substrate may be about 1 to 50 μm, for example.
ガスデポジション法に用いる粉末原料は、上記の負極活物質を用いる。粉末原料の平均粒径は、ガスデポジション法が行える範囲であれば特に制限されないが、平均粒径0.1〜50μm、好ましくは0.1〜10μmである。なお、平均粒径はD50であり、例えばレーザー回折散乱式粒度分布測定装置を用いて測定することができる。 The negative electrode active material is used as the powder raw material used in the gas deposition method. The average particle size of the powder raw material is not particularly limited as long as the gas deposition method can be performed, but the average particle size is 0.1 to 50 μm, preferably 0.1 to 10 μm. The average particle diameter is D 50, it can be measured using for example a laser diffraction scattering particle size distribution measuring apparatus.
粉末原料の調製には、公知の機械的粉砕方法を用いることができる。微粉砕の可能な、メカニカルアロイング法やメカニカルミリング法を用いることが好ましい。メカニカルアロイング法及びメカニカルミリング法は、公知の条件に基づいて実施することができる。例えば、所定の粉末原料となるように調合された出発原料をボールミルに投入し、ミリングを実行すれば良い。ボールミルとしては、遊星型ボールミル等の公知の装置を使用することができる。また、ミリングは、乾式又は湿式のいずれであっても良いが、特に乾式であることが望ましい。ミリングの条件は、所望の粉末原料の性状等に応じて適宜設定することができる。一般的には室温(特に0〜50℃)で回転数100〜500rpm程度とすればよい。ミリングの雰囲気は、アルゴンガス、窒素ガス等の不活性ガス雰囲気とすることが望ましい。 For the preparation of the powder raw material, a known mechanical pulverization method can be used. It is preferable to use a mechanical alloying method or a mechanical milling method that can be finely pulverized. The mechanical alloying method and the mechanical milling method can be performed based on known conditions. For example, a starting material prepared so as to become a predetermined powder material may be charged into a ball mill and milling may be performed. A known device such as a planetary ball mill can be used as the ball mill. The milling may be either dry or wet, but it is particularly desirable that the milling be dry. Milling conditions can be appropriately set according to the properties of the desired powder raw material. In general, the rotational speed may be about 100 to 500 rpm at room temperature (especially 0 to 50 ° C.). The milling atmosphere is preferably an inert gas atmosphere such as argon gas or nitrogen gas.
粉末原料には、必要に応じて他の成分を配合することもできる。例えば、導電性材料(銀、銅、アルミニウム、ニッケル、アセチレンブラック、ケッチェンブラック等)等が含まれていても良い。導電性材料を含む場合、その含有量は特に限定的ではないが、通常は粉末原料中50重量%以下、好ましくは5〜30重量%である。 Other ingredients can be blended in the powder raw material as necessary. For example, a conductive material (silver, copper, aluminum, nickel, acetylene black, ketjen black, or the like) may be included. When the conductive material is included, the content is not particularly limited, but is usually 50% by weight or less, preferably 5 to 30% by weight in the powder raw material.
(正極)
正極は、正極活物質、集電体、および電極活物質を集電体に結着させるバインダー、および必要に応じて導電材とから構成される。
(Positive electrode)
The positive electrode includes a positive electrode active material, a current collector, a binder that binds the electrode active material to the current collector, and, if necessary, a conductive material.
正極活物質は、ナトリウムイオンの挿入・脱離が可能であれば特に限定されないが、ナトリウム含有遷移金属複合酸化物が好ましい。例えば、ナトリウムマンガン複合酸化物、ナトリウム鉄複合酸化物、ナトリウムニッケル複合酸化物、ナトリウムコバルト複合酸化物、ナトリウムマンガンチタン複合酸化物、ナトリウムニッケルチタン複合酸化物、ナトリウムニッケルマンガン複合酸化物、ナトリウム鉄マンガン複合酸化物、等を挙げることができる。また、ナトリウム鉄リン酸化合物、ナトリウムマンガンリン酸化合物、ナトリウムコバルトリン酸化合物等も挙げることができる。 The positive electrode active material is not particularly limited as long as it can insert and desorb sodium ions, but a sodium-containing transition metal composite oxide is preferable. For example, sodium manganese composite oxide, sodium iron composite oxide, sodium nickel composite oxide, sodium cobalt composite oxide, sodium manganese titanium composite oxide, sodium nickel titanium composite oxide, sodium nickel manganese composite oxide, sodium iron manganese Examples include composite oxides. Moreover, a sodium iron phosphate compound, a sodium manganese phosphate compound, a sodium cobalt phosphate compound, etc. can be mentioned.
正極は、例えば、正極活物質と導電剤とバインダーとを溶剤を用いて混練分散して電極スラリーを得、該スラリーを集電体に塗布することによって作製できる。バインダーには、フッ化ビニリデン重合体やその共重合体等の公知のフッ素含有重合体、ポリアクリル酸およびそのNa塩並びにその共重合体等のアクリル酸系重合体、カルボキシメチルセルロース等のセルロース誘導体を用いることができる。 The positive electrode can be produced, for example, by kneading and dispersing a positive electrode active material, a conductive agent, and a binder using a solvent to obtain an electrode slurry, and applying the slurry to a current collector. The binder includes a known fluorine-containing polymer such as a vinylidene fluoride polymer and a copolymer thereof, polyacrylic acid and an Na salt thereof, an acrylic acid polymer such as a copolymer thereof, and a cellulose derivative such as carboxymethyl cellulose. Can be used.
(電解液)
電解液には、電解質を有機溶媒に溶解した非水電解液を用いる。有機溶媒には、環状カーボネート、環状エステルおよび鎖状カーボネートから選択される1種の溶媒または2種以上の混合溶媒を用いることができる。環状カーボネートとしては、エチレンカーボネートやプロピレンカーボネートを挙げることができる。また、環状エステルとしては、γ―ブチロラクトンを挙げることができる。また、鎖状カーボネートとしては、ジメチルカーボネートやジエチルカーボネートを挙げることができる。また、電解質には、NaPF6、NaBF4、NaClO4、NaAsF6、NaCF3SO3、Na(CF3SO2)2N、Na(C2F5SO2)2N、およびNa(CF3SO2)3C等から選択される1種以上の電解質を用いることができる。また、非水電解液に代えて、その非水電解液を含有する高分子ゲル電解質や、ナトリウムイオン導電性を有する高分子固体電解質に上記の電解質を含有させた高分子固体電解質を用いることもできる。
(Electrolyte)
As the electrolytic solution, a nonaqueous electrolytic solution in which an electrolyte is dissolved in an organic solvent is used. As the organic solvent, one kind of solvent selected from cyclic carbonates, cyclic esters and chain carbonates, or two or more kinds of mixed solvents can be used. Examples of the cyclic carbonate include ethylene carbonate and propylene carbonate. Examples of the cyclic ester include γ-butyrolactone. Examples of the chain carbonate include dimethyl carbonate and diethyl carbonate. In addition, the electrolyte includes NaPF 6 , NaBF 4 , NaClO 4 , NaAsF 6 , NaCF 3 SO 3 , Na (CF 3 SO 2 ) 2 N, Na (C 2 F 5 SO 2 ) 2 N, and Na (CF 3 One or more electrolytes selected from SO 2 ) 3 C and the like can be used. In place of the non-aqueous electrolyte, a polymer gel electrolyte containing the non-aqueous electrolyte or a polymer solid electrolyte in which the above electrolyte is contained in a polymer solid electrolyte having sodium ion conductivity may be used. it can.
また、本発明においては、電解液にフルオロ基を有する飽和環状カーボネートを添加してもよい。サイクル特性を向上させることが可能となる。フルオロ基を有する飽和環状カーボネートとしては、フルオロエチレンカーボネート、ジフルオロエチレンカーボネート等を挙げることができる。フルオロ基を有する飽和環状カーボネートの割合は、電解液の少なくとも1体積%、好ましく5〜30体積%である。 In the present invention, a saturated cyclic carbonate having a fluoro group may be added to the electrolytic solution. The cycle characteristics can be improved. Examples of the saturated cyclic carbonate having a fluoro group include fluoroethylene carbonate and difluoroethylene carbonate. The ratio of the saturated cyclic carbonate having a fluoro group is at least 1% by volume, preferably 5 to 30% by volume of the electrolytic solution.
(セパレータ)
セパレータには、微多孔膜や不織布を用いることができ、組成としてはポリエステル系ポリマー、ポリオレフィン系ポリマー、エーテル系ポリマー、ガラス繊維等を挙げることができる。
(Separator)
As the separator, a microporous film or a non-woven fabric can be used. Examples of the composition include polyester polymers, polyolefin polymers, ether polymers, and glass fibers.
(ナトリウムイオン二次電池の製造方法)
本発明の負極を用いてナトリウムイオン二次電池を作製することができる。ナトリウムイオン二次電池は、少なくとも、正極と負極、正極と負極を隔離するセパレータ、電解液、および電池容器で構成される。
(Method for manufacturing sodium ion secondary battery)
A sodium ion secondary battery can be produced using the negative electrode of the present invention. The sodium ion secondary battery includes at least a positive electrode and a negative electrode, a separator that separates the positive electrode and the negative electrode, an electrolytic solution, and a battery container.
ナトリウムイオン二次電池の製造は公知の方法を用いて行うことができる。例えば、正極と負極をセパレータを介して積層し、平面状の積層体あるいは巻き取って巻回体とする。その積層体または巻回体を金属製または樹脂製の電池容器に収容し、密封する。密封時に開口部を設けて、電解液を注入してその開口部を封止して二次電池を得る。 A sodium ion secondary battery can be manufactured using a known method. For example, a positive electrode and a negative electrode are laminated via a separator, and a planar laminate or a wound body is obtained. The laminated body or wound body is accommodated in a metal or resin battery container and sealed. An opening is provided at the time of sealing, an electrolytic solution is injected, and the opening is sealed to obtain a secondary battery.
実験例1
(負極活物質)
SiO(和光純薬工業製)(SiOx:x=1.00)をジルコニアボール(φ15mm)との重量比が1:65になるようにジルコニアポットに封入し、室温、回転速度380rpmで10分、20分、60分機械的粉砕を行った(以下、粉砕時間をミリング時間という)。
Experimental example 1
(Negative electrode active material)
SiO (manufactured by Wako Pure Chemical Industries, Ltd.) (SiOx: x = 1.00) was sealed in a zirconia pot so that the weight ratio with zirconia balls (φ15 mm) was 1:65, and at room temperature for 10 minutes at a rotation speed of 380 rpm. Mechanical grinding was performed for 20 minutes and 60 minutes (hereinafter, the grinding time is referred to as milling time).
(負極の製造)
粉砕したSiO粉末を原料として、ガスデポジション法を用いてSiO粉末を集電体の銅箔上に堆積させて負極を得た。銅箔の厚さは20μmである。また前処理としてリン酸を用いて銅箔表面の電解研磨を行った。なお、ガスデポジション法の条件は以下の通りである。
ノズル−基板間距離:10mm
圧力差:7×105Pa
ノズル径:直径0.8mm
キャリアガス:He(6N)
製膜面積:0.5×0.5×πcm2
析出量:55〜68μg
(Manufacture of negative electrode)
Using the pulverized SiO powder as a raw material, the SiO powder was deposited on the copper foil of the current collector using a gas deposition method to obtain a negative electrode. The thickness of the copper foil is 20 μm. Moreover, the electrolytic polishing of the copper foil surface was performed using phosphoric acid as a pretreatment. The conditions for the gas deposition method are as follows.
Nozzle-substrate distance: 10 mm
Pressure difference: 7 × 10 5 Pa
Nozzle diameter: 0.8mm diameter
Carrier gas: He (6N)
Film forming area: 0.5 × 0.5 × πcm 2
Precipitation amount: 55 to 68 μg
(コインセル作製)
上記の負極と、対極として金属ナトリウム箔(厚さ約1mm)、セパレータとしてポリプロピレン系セパレータ(旭化成製ND420)を用い、電解液を注入して、2032型コインセルを作製した。電解液には、以下の3種を用いた。
電解液A:1M NaTFSA/PC
(TFSA:ビス(トリフルオロメタンスルホニル)アミド)
(PC:プロピレンカーボネート)
電解液B:1M NaFSA/PC
(FSA:ビス(フルオロスルホニル)アミド)
電解液C:1M NaPF6/EC:DMC(50:50vol.%)
(EC:エチレンカーボネート)
(DMC:ジメチルカーボネート)
(Coin cell production)
A 2032 type coin cell was manufactured by injecting an electrolytic solution using the above negative electrode, a metal sodium foil (thickness: about 1 mm) as a counter electrode, and a polypropylene separator (ND420 manufactured by Asahi Kasei) as a separator. The following three types of electrolytes were used.
Electrolyte A: 1M NaTFSA / PC
(TFSA: bis (trifluoromethanesulfonyl) amide)
(PC: Propylene carbonate)
Electrolyte B: 1M NaFSA / PC
(FSA: Bis (fluorosulfonyl) amide)
Electrolyte C: 1M NaPF6 / EC: DMC (50:50 vol.%)
(EC: ethylene carbonate)
(DMC: dimethyl carbonate)
上記のコインセル作製は、すべて、露点−100℃以下、酸素濃度1ppm以下のアルゴン雰囲気のグローブボックス中で行った。 The above coin cells were all produced in an argon atmosphere glove box having a dew point of −100 ° C. or lower and an oxygen concentration of 1 ppm or lower.
(充放電測定)
室温で、電位範囲0.005〜3.000V(vs.Na/Na+)、電流密度50mA/gで行った。
(Charge / discharge measurement)
At room temperature, the potential range was 0.005 to 3.000 V (vs. Na / Na + ) and the current density was 50 mA / g.
(分析)
負極活物質のX線回折(XRD)測定は、X線回折装置(リガク製:UltimaIV)を用いて行った。また、負極活物質の粒度分布は、レーザー回析式粒度分布測定装置(島津製作所製:SALD−2300)を用いて行った。
(analysis)
X-ray diffraction (XRD) measurement of the negative electrode active material was performed using an X-ray diffraction apparatus (manufactured by Rigaku: Ultimate IV). Moreover, the particle size distribution of the negative electrode active material was performed using a laser diffraction particle size distribution measuring apparatus (manufactured by Shimadzu Corporation: SALD-2300).
(結果)
図1は、負極活物質にSiO粉末を用いた負極を含むコインセルの第1回目の充放電曲線であり、図2はサイクル数と放電容量の関係を示すグラフであり、電解液には電解液A(1M NaTFSA/PC)を用いた。また、表1に所定のサイクル回数における放電容量の値を示す。また、図3は、SiO粉末のXRDパターンである。図4は、SiO粉末の粒径分布を示すグラフである。xの値を用いて算出した原料SiO粉末中のSiクラスターの含有量は、32質量%である。
なお、比較としてSi粉末(和光純薬工業製)とSn粉末(高純度化学研究所製)を負極活物質として用いた。
(result)
FIG. 1 is a first charge / discharge curve of a coin cell including a negative electrode using SiO powder as a negative electrode active material, and FIG. 2 is a graph showing the relationship between the number of cycles and the discharge capacity. A (1M NaTFSA / PC) was used. Table 1 shows the value of the discharge capacity at a predetermined number of cycles. FIG. 3 is an XRD pattern of the SiO powder. FIG. 4 is a graph showing the particle size distribution of the SiO powder. The content of Si clusters in the raw material SiO powder calculated using the value of x is 32% by mass.
For comparison, Si powder (manufactured by Wako Pure Chemical Industries) and Sn powder (manufactured by High Purity Chemical Laboratory) were used as the negative electrode active material.
表1に示すように、ミリング時間10分のSiO粉末を用いた場合、1回目の放電容量として220mAh/g、そして120回目でも170mAh/gという高い放電容量を有していた。また、ミリング時間を長くすると、放電容量は低下したが、これは、図1に示すようにSiが低放電容量であること、および図3に示すようにミリング時間とともに結晶子サイズの大きなSiの割合が増加したためと考えられる。なお、X線回折法で測定したSiO中のSiの結晶子サイズは、ミリング時間10分、20分、60分の場合、それぞれ12nm、104nm、170nmであった。結晶子サイズは(220)面の回折ピークの半値幅より算出した。また、SiO粉末の平均粒径は、ミリング時間10分、20分、60分の場合、それぞれ5.4μm、4.1μm、7.6μmであった。60分のミリングでは、粒子の凝集が起こりサイズが増大することを走査型電子顕微鏡観察により確認している. As shown in Table 1, when SiO powder having a milling time of 10 minutes was used, the first discharge capacity was 220 mAh / g, and the 120th discharge capacity was 170 mAh / g. Further, when the milling time is lengthened, the discharge capacity is reduced. This is because Si has a low discharge capacity as shown in FIG. 1, and the fact that Si having a large crystallite size with the milling time as shown in FIG. This is probably because the ratio increased. The crystallite size of Si in SiO measured by X-ray diffraction method was 12 nm, 104 nm, and 170 nm, respectively, when the milling time was 10 minutes, 20 minutes, and 60 minutes. The crystallite size was calculated from the half-value width of the diffraction peak on the (220) plane. The average particle diameter of the SiO powder was 5.4 μm, 4.1 μm, and 7.6 μm when the milling time was 10 minutes, 20 minutes, and 60 minutes, respectively. It was confirmed by scanning electron microscope observation that particle aggregation occurred and size increased in 60-minute milling.
図5は、ミリング時間10分のSiO粉末を負極活物質に用い、異なる3種の電解液A(1M NaTFSA/PC)、B(1M NaFSA/PC)、C(1M NaPF6/EC:DMC)を用いたコインセルの第1回目の充放電曲線を示している。電解液A、電解液B、電解液Cを用いた場合、第1回目の放電容量として、それぞれ、220mAh/g、110mAh/g、185mAh/gの値が得られた。電解液A、B、Cの中では、電解液A(1M NaTFSA/PC)を用いた場合に最も高い放電容量が得られた。 FIG. 5 shows the use of SiO powder having a milling time of 10 minutes as a negative electrode active material, and three different electrolytes A (1M NaTFSA / PC), B (1M NaFSA / PC), and C (1M NaPF 6 / EC: DMC). The 1st charge / discharge curve of the coin cell using is shown. When the electrolytic solution A, the electrolytic solution B, and the electrolytic solution C were used, values of 220 mAh / g, 110 mAh / g, and 185 mAh / g were obtained as the first discharge capacity, respectively. Among the electrolytic solutions A, B, and C, the highest discharge capacity was obtained when the electrolytic solution A (1M NaTFSA / PC) was used.
上記の実験例の結果から明らかなように、Siクラスターを有するSiOをナトリウムイオン二次電池の負極活物質として用いることが可能であることを本発明者らは世界で初めて明らかにした。充放電の機構については限定されるものではないが、例えば以下の機構が考えられる。従来、SiはLiと合金化することは知られているが、Naと合金化することは知られていなかった。SiとNaとの合金化反応が進行し、NaSiの化合物相が形成されているものとすると、理論容量として954mAh/gが期待できる。また、SiOがコンバージョン反応を示すとすると、以下の反応が進行すると考えられる。この場合、理論容量としては1220mAh/gが期待できる。
ここで、コンバージョン反応とは、例えば、リチウムイオン二次電池における金属Liとの反応を例にとり説明すると、微細構造を有する金属酸化物(MO)が充電(Li吸蔵)時のLiとの反応で金属Mと熱力学的に安定なLi2Oとに分相し、放電(Li脱離)時に一部のLi2OがLiに分解され再びMOが形成される反応である。ナトリウムイオン二次電池においても、SiOがNaとの間でコンバージョン反応を行い、充電(Na吸蔵)時のNaとの反応で金属Siと熱力学的に安定なNa2Oとに分相し、放電(Na脱離)時に一部のNa2OがNaに分解され再びSiOが形成されるものと考えられる。なお、詳細については検討中である。
As is clear from the results of the above experimental examples, the present inventors have revealed for the first time in the world that SiO having Si clusters can be used as a negative electrode active material of a sodium ion secondary battery. Although the charging / discharging mechanism is not limited, for example, the following mechanism can be considered. Conventionally, Si is known to alloy with Li, but it has not been known to alloy with Na. Assuming that an alloying reaction between Si and Na proceeds and a compound phase of NaSi is formed, a theoretical capacity of 954 mAh / g can be expected. If SiO exhibits a conversion reaction, the following reaction is considered to proceed. In this case, 1220 mAh / g can be expected as the theoretical capacity.
Here, the conversion reaction will be described by taking, for example, a reaction with metal Li in a lithium ion secondary battery as an example. It is a reaction with Li during charging (Li occlusion) of a metal oxide (MO) having a fine structure. This is a reaction in which phase separation is performed between the metal M and thermodynamically stable Li 2 O, and a part of Li 2 O is decomposed into Li during discharge (Li desorption) to form MO again. Also in the sodium ion secondary battery, SiO undergoes a conversion reaction with Na, and phase separation into metal Si and thermodynamically stable Na 2 O by reaction with Na during charging (Na storage), It is considered that a part of Na 2 O is decomposed into Na during discharge (Na desorption) and SiO is formed again. Details are under consideration.
SiクラスターがSiO2媒体中に分散した構造を有する材料を負極活物質として用いることにより、高容量でサイクル特性に優れたナトリウムイオン二次電池の実用化に大きく寄与することができる。 Use of a material having a structure in which Si clusters are dispersed in a SiO 2 medium as a negative electrode active material can greatly contribute to the practical use of a sodium ion secondary battery having high capacity and excellent cycle characteristics.
1 キャリアガス
2 粉末原料
3 導管
4 減圧装置
5 チャンバ
6 基材
7 ノズル
DESCRIPTION OF
Claims (7)
前記負極が、SiクラスターがSiO2媒体中に分散した構造を有する負極活物質を含む該ナトリウムイオン二次電池。 A sodium ion secondary battery having a positive electrode, a negative electrode, and an electrolyte,
The sodium ion secondary battery, wherein the negative electrode includes a negative electrode active material having a structure in which Si clusters are dispersed in a SiO 2 medium.
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