JP2020077615A - Negative electrode active material for sodium ion secondary battery and manufacturing method thereof - Google Patents
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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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- 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
- Y02E60/13—Energy storage using capacitors
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Abstract
Description
本発明は、例えば、携帯型電子機器や電気自動車に用いられるナトリウムイオン二次電池用の負極活物質及びその製造方法に関する。 The present invention relates to a negative electrode active material for a sodium ion secondary battery used in, for example, portable electronic devices and electric vehicles, and a method for manufacturing the same.
近年、携帯型電子機器や電気自動車等の普及に伴い、リチウムイオン二次電池の開発が活発となっている。しかしながら、リチウムイオン二次電池に使用されるＬｉ資源の枯渇が懸念されており、この解決策としてＬｉイオンをＮａイオンに代替したナトリウムイオン二次電池が検討されている。 In recent years, with the spread of portable electronic devices, electric vehicles, and the like, development of lithium-ion secondary batteries has become active. However, there is a concern that the Li resources used in the lithium ion secondary battery will be depleted, and as a solution to this problem, a sodium ion secondary battery in which Li ions are replaced by Na ions is being studied.
ナトリウムイオン二次電池用の負極活物質として、理論容量の高いＳｉまたはＳｎを含有する材料が提案されている。しかしながら、ＳｉまたはＳｎを含む負極活物質を負極に使用した場合、ナトリウムイオンの挿入脱離反応の際に生じる負極活物質の膨張収縮による体積変化が大きいため、充放電の繰り返しに伴う負極活物質の崩壊が激しく、サイクル特性の低下が起こりやすいという問題がある。そこで、特許文献１では、サイクル特性を向上させるためにＢｉ２Ｏ３を含有する負極活物質が提案されている。 A material containing Si or Sn having a high theoretical capacity has been proposed as a negative electrode active material for a sodium ion secondary battery. However, when a negative electrode active material containing Si or Sn is used for the negative electrode, the negative electrode active material undergoes a large volume change due to expansion and contraction of the negative electrode active material that occurs during the insertion and desorption reaction of sodium ions. However, there is a problem that the deterioration of cycle characteristics is likely to occur. Therefore, Patent Document 1 proposes a negative electrode active material containing Bi 2 O 3 in order to improve cycle characteristics.
特許文献１に記載の負極活物質は、初回充電容量が初回放電容量に比べて大きく、初回不可逆容量が大きい（即ち初回充放電効率が小さい）という課題を有する。 The negative electrode active material described in Patent Document 1 has a problem that the initial charge capacity is larger than the initial discharge capacity and the initial irreversible capacity is large (that is, the initial charge / discharge efficiency is small).
本発明は以上のような状況に鑑みてなされたものであり、初回不可逆容量が低いナトリウムイオン二次電池用負極活物質及びその製造方法を提供することを目的とする。 The present invention has been made in view of the above circumstances, and an object thereof is to provide a negative electrode active material for a sodium ion secondary battery having a low initial irreversible capacity and a method for producing the same.
本発明のナトリウムイオン二次電池用負極活物質は、ＳｉＯ２、Ｂ２Ｏ３及びＰ２Ｏ５から選択される少なくとも一種を含有するマトリクス中に金属Ｂｉが析出してなる結晶化ガラスからなることを特徴とする。 The negative electrode active material for a sodium ion secondary battery of the present invention is made of crystallized glass in which a metal Bi is deposited in a matrix containing at least one selected from SiO 2 , B 2 O 3 and P 2 O 5. It is characterized by
Ｂｉ２Ｏ３を含有する負極活物質は、充放電に伴い下記の式（１）及び（２）の反応を起こす。まず、初回充電時に式（１）の反応が不可逆的に生じる。その後は、充放電に伴い式（２）の反応が繰り返し生じる。 The negative electrode active material containing Bi 2 O 3 causes the reactions of the following formulas (1) and (2) with charge and discharge. First, the reaction of the formula (1) occurs irreversibly during the first charge. After that, the reaction of formula (2) repeatedly occurs with charge and discharge.
Ｂｉ２Ｏ３＋６Ｎａ＋＋６ｅ− → ２Ｂｉ＋３Ｎａ２Ｏ・・・（１）
Ｂｉ＋３Ｎａ＋＋３ｅ− ←→ ＢｉＮａ３・・・（２）
Bi 2 O 3 + 6Na + + 6e − → 2Bi + 3Na 2 O (1)
Bi + 3Na + + 3e − ← → BiNa 3 (2)
Ｂｉ２Ｏ３を含有する負極活物質の充放電に伴い発生する初回不可逆容量は、初回の充電過程で正極活物質中のキャリアイオンであるＮａ＋と電子の一部が、Ｂｉ２Ｏ３を還元するための反応（１）に消費されることが原因であると考えられる。一方、本発明の負極活物質では、既に還元状態にある金属Ｂｉをマトリクス中に析出してなる構造を有しているため、反応（１）を省略することができ、初回不可逆容量を低減することができる。また、ＳｉＯ２、Ｂ２Ｏ３及びＰ２Ｏ５から選択される少なくとも一種を含有するマトリクスが緩衝材の役割を果たすため、反応（２）を繰り返すことにより生じるＢｉ成分の膨張収縮を緩和することができ、サイクル特性にも優れるという効果も奏する。 The initial irreversible capacity generated during charge and discharge of the negative electrode active material containing Bi 2 O 3 is that Na + , which is a carrier ion in the positive electrode active material in the first charge process, and part of the electrons are Bi 2 O 3 . It is considered that the cause is consumption in the reaction (1) for reduction. On the other hand, the negative electrode active material of the present invention has a structure in which the reduced metal Bi is deposited in the matrix, so that the reaction (1) can be omitted and the initial irreversible capacity is reduced. be able to. Further, since the matrix containing at least one selected from SiO 2 , B 2 O 3 and P 2 O 5 plays a role of a buffer material, the expansion and contraction of the Bi component caused by repeating the reaction (2) is relaxed. It also has the effect of being excellent in cycle characteristics.
本発明のナトリウムイオン二次電池用負極活物質は、酸化物換算のモル％で、Ｂｉ２Ｏ３ １５〜７５％、Ｐ２Ｏ５ ０〜４５％、ＳｉＯ２ ０〜６０％、Ｂ２Ｏ３ ０〜６０％、Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３ ２５〜８５％、Ｎａ２Ｏ ０〜５０％を含有することが好ましい。なお、「Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３」はＰ２Ｏ５、ＳｉＯ２及びＢ２Ｏ３の合量を意味する。
Negative active material for a sodium ion secondary battery of the present invention, in mole percent oxide equivalent, Bi 2 O 3 15~75%, P 2 O 5 0~45%,
本発明のナトリウムイオン二次電池用負極活物質は、酸化物換算のモル％で、さらにＦｅ２Ｏ３ ０〜２５％を含有することが好ましい。Ｆｅ２Ｏ３を含有させることにより、Ｂｉ２Ｏ３の還元が促進し、金属Ｂｉが析出しやすくなる。 The negative electrode active material for a sodium ion secondary battery of the present invention preferably contains 0 to 25% of Fe 2 O 3 in mol% in terms of oxide. By containing Fe 2 O 3 , the reduction of Bi 2 O 3 is promoted and the metal Bi is easily deposited.
本発明のナトリウムイオン二次電池用負極活物質の製造方法は、上記のナトリウムイオン二次電池用負極活物質を製造するための方法であって、Ｂｉ２Ｏ３を含有する酸化物材料に対し、還元性ガスを供給しながら加熱処理を行うことにより、Ｂｉ２Ｏ３を金属Ｂｉに還元する工程、を含むことを特徴する。このようにすれば、酸化物材料中のＢｉ２Ｏ３を効率よく金属Ｂｉに還元させることができ、所望の特性を有する負極活物質を容易に作製することができる。 A method for producing a negative electrode active material for a sodium ion secondary battery according to the present invention is a method for producing the above negative electrode active material for a sodium ion secondary battery, which is applied to an oxide material containing Bi 2 O 3. And a step of reducing the Bi 2 O 3 to the metal Bi by performing a heat treatment while supplying a reducing gas. By doing so, Bi 2 O 3 in the oxide material can be efficiently reduced to metal Bi, and the negative electrode active material having desired characteristics can be easily manufactured.
本発明のナトリウムイオン二次電池用負極活物質の製造方法は、還元性ガスが、体積％で、不活性ガス ９０〜９９．５％、Ｈ２ ０．５〜１０％を含有することが好ましい。 In the method for producing a negative electrode active material for a sodium ion secondary battery according to the present invention, the reducing gas preferably contains 90% to 99.5% of an inert gas and 0.5% to 10% of H 2 in volume%. ..
本発明の製造方法によれば、初回不可逆容量が低いナトリウムイオン二次電池用負極活物質を提供することが可能となる。 According to the manufacturing method of the present invention, it is possible to provide a negative electrode active material for a sodium ion secondary battery having a low initial irreversible capacity.
本発明のナトリウムイオン二次電池用負極活物質（以下、単に負極活物質ともいう）は、ＳｉＯ２、Ｂ２Ｏ３及びＰ２Ｏ５から選択される少なくとも一種を含有するマトリクス中に金属Ｂｉが析出してなる結晶化ガラスからなることを特徴とする。具体的には、本発明の負極活物質は、酸化物成分のモル％で、Ｂｉ２Ｏ３ １５〜７５％、Ｐ２Ｏ５ ０〜４５％、ＳｉＯ２ ０〜６０％、Ｂ２Ｏ３ ０〜６０％、Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３ ２５〜８５％、Ｎａ２Ｏ ０〜５０％を含有するものであることが好ましい。組成をこのように限定した理由を以下に説明する。なお、以下の組成の説明において、「％」は特に断りのない限り「モル％」を意味する。
The negative electrode active material for a sodium ion secondary battery of the present invention (hereinafter, also simply referred to as a negative electrode active material) is a metal Bi in a matrix containing at least one selected from SiO 2 , B 2 O 3 and P 2 O 5. It is characterized in that it consists of crystallized glass formed by depositing. Specifically, the negative electrode active material of the present invention, in mole percent on the oxide components, Bi 2 O 3 15~75%, P 2 O 5 0~45%,
Ｂｉ２Ｏ３はナトリウムイオンを吸蔵及び放出するサイトとなる活物質成分である。Ｂｉ２Ｏ３の含有量は１５〜７５％であることが好ましく、２０〜７０％であることがより好ましく、３０〜６５％であることがさらに好ましく、４０〜５５％であることが特に好ましい。Ｂｉ２Ｏ３の含有量が少なすぎると、負極活物質の単位質量当たりの充放電容量が低下しやすくなる。一方、Ｂｉ２Ｏ３の含有量が多すぎると、負極活物質中の非晶質成分が相対的に少なくなるため、充放電時のナトリウムイオンの吸蔵及び放出に伴う体積変化を緩和できずに、サイクル特性が低下しやすくなる。 Bi 2 O 3 is an active material component that serves as a site that occludes and releases sodium ions. The content of Bi 2 O 3 is preferably 15 to 75%, more preferably 20 to 70%, further preferably 30 to 65%, particularly preferably 40 to 55%. .. When the content of Bi 2 O 3 is too small, the charge / discharge capacity per unit mass of the negative electrode active material tends to decrease. On the other hand, if the content of Bi 2 O 3 is too large, the amount of amorphous components in the negative electrode active material becomes relatively small, so that the volume change due to storage and release of sodium ions during charge / discharge cannot be relaxed. , Cycle characteristics are likely to deteriorate.
Ｐ２Ｏ５は網目形成酸化物であり、Ｂｉ２Ｏ３におけるナトリウムイオンの吸蔵及び放出サイトを包括し、サイクル特性を向上させる作用がある。Ｐ２Ｏ５の含有量は０〜４５％であることが好ましく、０．１〜４２％であることがより好ましく、５〜４０％であることがさらに好ましく、１０〜３８％であることが特に好ましい。Ｐ２Ｏ５の含有量が多すぎると、耐水性が悪化しやすくなる。 P 2 O 5 is a network-forming oxide, and includes the storage and release sites of sodium ions in Bi 2 O 3 and has the action of improving cycle characteristics. The content of P 2 O 5 is preferably 0 to 45%, more preferably 0.1 to 42%, further preferably 5 to 40%, and further preferably 10 to 38%. Particularly preferred. If the content of P 2 O 5 is too large, the water resistance tends to deteriorate.
ＳｉＯ２も網目形成酸化物であり、Ｂｉ２Ｏ３におけるナトリウムイオンの吸蔵及び放出サイトを包括し、サイクル特性を向上させる作用がある。ＳｉＯ２の含有量は０〜６０％であることが好ましく、０．１〜５５％であることが好ましく、１〜５０％であることがより好ましく、５〜４０％であることがさらに好ましく、１０〜３０％であることが特に好ましい。ＳｉＯ２の含有量が多すぎると、イオン伝導度が低下し、放電容量が低下する傾向にある。 SiO 2 is also a network-forming oxide, and has a function of including the storage and release sites of sodium ions in Bi 2 O 3 and improving cycle characteristics. The content of SiO 2 is preferably 0 to 60%, preferably 0.1 to 55%, more preferably 1 to 50%, further preferably 5 to 40%, It is particularly preferably 10 to 30%. If the content of SiO 2 is too large, the ionic conductivity tends to decrease, and the discharge capacity tends to decrease.
Ｂ２Ｏ３も、網目形成酸化物としてＢｉ２Ｏ３におけるナトリウムイオンの吸蔵及び放出サイトを包括し、サイクル特性を向上させる作用がある。Ｂ２Ｏ３の含有量は、０〜８５％であることが好ましく、１０〜６０％であることがより好ましく、２０〜５５％であることがさらに好ましく、２５〜５０％であることが特に好ましく、２８〜４０％であることが最も好ましい。Ｂ２Ｏ３の含有量が多すぎると、Ｂｉ成分への配位結合が強くなり、初回充電容量が増加し、結果として初回不可逆容量が大きくなる傾向にある。 B 2 O 3 also has a function of improving cycle characteristics by including sodium ion storage and release sites in Bi 2 O 3 as a network-forming oxide. The content of B 2 O 3 is preferably 0 to 85%, more preferably 10 to 60%, further preferably 20 to 55%, and particularly preferably 25 to 50%. It is preferably 28 to 40%, and most preferably 28% to 40%. When the content of B 2 O 3 is too large, the coordination bond to the Bi component becomes strong, the initial charge capacity increases, and as a result, the initial irreversible capacity tends to increase.
Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３の含有量は、２０〜８５％であることが好ましく、２５〜６０％であることがより好ましく、２８〜５０％であることがさらに好ましく、２８〜４０％であることが特に好ましい。Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３の含有量が少なすぎると、充放電時のナトリウムイオンの吸蔵及び放出に伴うＢｉ原子の体積変化を緩和できず構造劣化を起こすため、サイクル特性が低下しやすくなる。一方、Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３の含有量が多すぎると、Ｂｉ成分が相対的に少なくなるため充放電容量が低下する傾向にある。 The content of P 2 O 5 + SiO 2 + B 2 O 3 is preferably from 20% to 85%, more preferably 25 to 60%, more preferably from 28 to 50%, 28-40 % Is particularly preferable. If the content of P 2 O 5 + SiO 2 + B 2 O 3 is too small, the volume change of Bi atoms due to the absorption and desorption of sodium ions during charge and discharge cannot be relaxed, and the structure is deteriorated, which deteriorates the cycle characteristics. It will be easier. On the other hand, if the content of P 2 O 5 + SiO 2 + B 2 O 3 is too large, the Bi component tends to be relatively small, and the charge / discharge capacity tends to decrease.
Ｎａ２Ｏは、Ｂｉ２Ｏ３成分以外の酸化物マトリクス（特にＰ２Ｏ５、ＳｉＯ２またはＢ２Ｏ３から構成される酸化物マトリクス）のイオン伝導性を向上させる成分である。Ｎａ２Ｏの含有量は０〜５０％であることが好ましく、１〜４５％であることがより好ましく、３〜４３％であることがさらに好ましく、５〜４０％であることが特に好ましく、７〜３５％であることが最も好ましい。Ｎａ２Ｏの含有量が多すぎると、Ｐ２Ｏ５、ＳｉＯ２またはＢ２Ｏ３とＮａ２Ｏからなる異種結晶が多量に形成され、サイクル特性が低下しやすくなる。 Na 2 O is a component that improves the ion conductivity of an oxide matrix other than the Bi 2 O 3 component (in particular, an oxide matrix composed of P 2 O 5 , SiO 2 or B 2 O 3 ). The content of Na 2 O is preferably 0 to 50%, more preferably 1 to 45%, further preferably 3 to 43%, particularly preferably 5 to 40%, Most preferably, it is 7 to 35%. When the content of Na 2 O is too large, a large amount of heterogeneous crystals composed of P 2 O 5 , SiO 2 or B 2 O 3 and Na 2 O are formed, and the cycle characteristics are likely to deteriorate.
上記成分以外にＦｅ２Ｏ３を含有させてもよい。Ｆｅ２Ｏ３は、Ｂｉ２Ｏ３の還元を促し金属Ｂｉを析出しやすくする成分である。Ｆｅ２Ｏ３の含有量は０〜２５％であることが好ましく、０．１〜２０％であることがより好ましく、０．３〜１９％であることがさらに好ましく、０．５〜１４％であることが特に好ましく、１〜９％であることが最も好ましい。Ｆｅ２Ｏ３の含有量が多すぎると、Ｂｉ２Ｏ３とＦｅ２Ｏ３からなる異種結晶（σ−Ｂｉ３．４３Ｆｅ０．５７Ｏ６）が多量に形成されサイクル特性が低下しやすくなる。 Fe 2 O 3 may be contained in addition to the above components. Fe 2 O 3 is a component that promotes the reduction of Bi 2 O 3 and facilitates the precipitation of metal Bi. The content of Fe 2 O 3 is preferably 0 to 25%, more preferably 0.1 to 20%, further preferably 0.3 to 19%, and 0.5 to 14%. Is particularly preferable and 1 to 9% is most preferable. When the content of Fe 2 O 3 is too large, a large amount of heterogeneous crystals (σ-Bi 3.43 Fe 0.57 O 6 ) composed of Bi 2 O 3 and Fe 2 O 3 are formed, and the cycle characteristics are likely to deteriorate. Become.
本発明の負極活物質は、上記成分以外に種々の成分を含有していてもよい。例えば、ＴｉＯ２、ＭｎＯ、ＣｕＯ、ＺｎＯ、ＭｇＯ、ＣａＯ、Ａｌ２Ｏ３を合量で０〜２５％、０〜２３％、０〜２１％、さらには０．１〜２０％の範囲で含有していてもよい。これらの成分を含有することにより、構造が無秩序になって非晶質材料が得られやすくなる。ただし、その含有量が多すぎると、上述の網目形成酸化物（Ｐ２Ｏ５、ＳｉＯ２またはＢ２Ｏ３）からなるネットワークが切断されやすくなり、結果的に、充放電に伴う負極活物質の体積変化を緩和できずサイクル特性が低下するおそれがある。 The negative electrode active material of the present invention may contain various components in addition to the above components. For example, TiO 2 , MnO, CuO, ZnO, MgO, CaO, and Al 2 O 3 are contained in a total amount of 0 to 25%, 0 to 23%, 0 to 21%, and further 0.1 to 20%. You may have. By containing these components, the structure becomes disordered and an amorphous material is easily obtained. However, if the content is too large, the network composed of the above-mentioned network-forming oxide (P 2 O 5 , SiO 2 or B 2 O 3 ) is likely to be broken, and as a result, the negative electrode active material accompanying charge and discharge is generated. Therefore, there is a risk that the cycle characteristics may be deteriorated due to the inability to reduce the volume change.
本発明の負極活物質は、内部に金属Ｂｉ粒子が析出している。金属Ｂｉ粒子は、ＣｕＫα線を用いた粉末Ｘ線回折測定によって同定することができる。具体的には、測定により得られた回折線プロファイルにおいて、２θ値２７．２°、３７．９°、３９．６°にピーク位置を有する回折線は、金属Ｂｉの結晶相（六方晶系、空間群Ｒ−３ｍ（１６６））に帰属することができる。 The negative electrode active material of the present invention has metal Bi particles deposited therein. The metal Bi particles can be identified by powder X-ray diffraction measurement using CuKα ray. Specifically, in the diffraction line profile obtained by the measurement, diffraction lines having peak positions at 2θ values of 27.2 °, 37.9 °, and 39.6 ° are the crystal phases of metal Bi (hexagonal system, Space group R-3m (166)) can be assigned.
回折線プロファイルにおいて金属Ｂｉの結晶相に帰属される回折線の半価幅が０．０１°以上であることが好ましく、０．０５°以上であることがより好ましく、０．０７°以上であることがさらに好ましく、０．１°以上であることが特に好ましい。回折線の半価幅が大きい場合は、負極活物質中の金属Ｂｉの結晶子サイズがナノオーダー（例えば０．１〜１００ｎｍ）となるため、充電反応によりナトリウムイオンを吸蔵しても体積膨張が起こりにくく、結果としてサイクル特性に優れる傾向がある。一方、回折線の半価幅が小さすぎる場合は、金属Ｂｉの結晶子サイズが大きくなる（例えばミクロンオーダー以上）ため、充電反応によりナトリウムイオンを吸蔵した際に、局所的に大きな体積膨張が起こり、サイクル特性が低下する傾向がある。 In the diffraction line profile, the full width at half maximum of the diffraction line assigned to the crystal phase of the metal Bi is preferably 0.01 ° or more, more preferably 0.05 ° or more, and 0.07 ° or more. It is more preferable that the angle is 0.1 ° or more. When the full width at half maximum of the diffraction line is large, the crystallite size of the metal Bi in the negative electrode active material is in the nano order (for example, 0.1 to 100 nm), and therefore the volume expansion does not occur even if sodium ions are occluded by the charging reaction. It tends to occur, and as a result, tends to have excellent cycle characteristics. On the other hand, when the half width of the diffraction line is too small, the crystallite size of the metal Bi becomes large (for example, on the order of microns or more), so that a large volume expansion locally occurs when the sodium ions are occluded by the charging reaction. However, the cycle characteristics tend to deteriorate.
負極活物質の結晶化度は５％以上であることが好ましく、３０％以上であることがより好ましく、５０％以上であることがさらに好ましい。結晶化度が大きいほど、初回不可逆容量を低減しやすくなる。ただし、結晶化度が大きすぎると、サイクル特性が低下する傾向がある。よって、サイクル特性を高める観点からは、結晶化度は９９％以下、特に９５％以下であることが好ましい。 The crystallinity of the negative electrode active material is preferably 5% or more, more preferably 30% or more, and further preferably 50% or more. The larger the crystallinity, the easier it is to reduce the initial irreversible capacity. However, if the crystallinity is too large, the cycle characteristics tend to deteriorate. Therefore, from the viewpoint of enhancing the cycle characteristics, the crystallinity is preferably 99% or less, particularly preferably 95% or less.
結晶化度は、ＣｕＫα線を用いた粉末Ｘ線回折測定によって得られる、２θ値で１０〜６０°の回折線プロファイルから求められる。具体的には、回折線プロファイルからバックグラウンドを差し引いて得られた全散乱曲線から、１０〜４５°におけるブロードな回折線（非晶質ハロー）をピーク分離して求めた積分強度をＩａ、１０〜６０°において検出される各結晶性回折線をピーク分離して求めた積分強度の総和をＩｃとした場合、結晶化度Ｘｃは次式から求められる。 The crystallinity is obtained from a diffraction line profile of 10 to 60 at a 2θ value obtained by powder X-ray diffraction measurement using CuKα ray. Specifically, the integrated intensity obtained by peak-separating the broad diffraction line (amorphous halo) at 10 to 45 ° from the total scattering curve obtained by subtracting the background from the diffraction line profile is Ia, 10 The crystallinity Xc is calculated from the following equation, where Ic is the total integrated intensity obtained by separating the peaks of the crystalline diffraction lines detected at -60 °.
Ｘｃ＝［Ｉｃ／（Ｉｃ＋Ｉａ）］×１００（％） Xc = [Ic / (Ic + Ia)] × 100 (%)
ここで、平均粒子径と最大粒子径は、それぞれ一次粒子のメジアン径でＤ５０（５０％体積累積径）とＤ９０（９０％体積累積径）を示し、レーザー回折式粒度分布測定装置により測定された値をいう。 Here, the average particle size and the maximum particle size are D 50 (50% volume cumulative diameter) and D 90 (90% volume cumulative diameter) in median diameter of primary particles, respectively, and measured by a laser diffraction type particle size distribution measuring device. This is the value that was set.
所定サイズの粉末を得るためには、一般的な粉砕機や分級機が用いられる。例えば、乳鉢、ボールミル、振動ボールミル、衛星ボールミル、遊星ボールミル、ジェットミル、篩、遠心分離、空気分級等が用いられる。 A general crusher or classifier is used to obtain powder of a predetermined size. For example, a mortar, a ball mill, a vibrating ball mill, a satellite ball mill, a planetary ball mill, a jet mill, a sieve, centrifugal separation, air classification, etc. are used.
負極活物質の形状は特に限定されないが、通常は粉末状である。負極活物質の平均粒子径は０．１〜２０μｍであることが好ましく、０．２〜１５μｍであることがより好ましく、０．３〜１０μｍであることがさらに好ましく、０．５〜５μｍであることが特に好ましい。また負極活物質の最大粒子径は１５０μｍ以下であることが好ましく、１００μｍ以下であることがより好ましく、最大粒子径７５μｍ以下であることがさらに好ましく、５５μｍ以下であることが特に好ましい。平均粒子径または最大粒子径が大きすぎると、充放電した際にナトリウムイオンの吸蔵及び放出に伴う負極活物質の体積変化を緩和できず、サイクル特性が著しく低下する傾向がある。一方、平均粒子径が小さすぎると、ペースト化した際に粉末の分散状態に劣り、均一な電極を製造することが困難になる傾向がある。また、析出した金属Ｂｉが大気中の酸素により酸化されやすくなる。 The shape of the negative electrode active material is not particularly limited, but is usually powdery. The average particle diameter of the negative electrode active material is preferably 0.1 to 20 μm, more preferably 0.2 to 15 μm, further preferably 0.3 to 10 μm, and 0.5 to 5 μm. Is particularly preferable. The maximum particle diameter of the negative electrode active material is preferably 150 μm or less, more preferably 100 μm or less, further preferably 75 μm or less, and particularly preferably 55 μm or less. When the average particle diameter or the maximum particle diameter is too large, the volume change of the negative electrode active material due to the absorption and desorption of sodium ions during charging / discharging cannot be relaxed, and the cycle characteristics tend to be remarkably deteriorated. On the other hand, if the average particle size is too small, the state of dispersion of the powder when formed into a paste is poor, and it tends to be difficult to manufacture a uniform electrode. Further, the deposited metal Bi is easily oxidized by oxygen in the atmosphere.
次に本発明の負極活物質の製造方法について説明する。本発明の負極活物質の製造方法は、Ｂｉ２Ｏ３を含有する酸化物材料に対し、還元性ガスを供給しながら加熱処理を行うことにより、Ｂｉ２Ｏ３を金属Ｂｉに還元する工程、を含むことを特徴する。 Next, a method for producing the negative electrode active material of the present invention will be described. The method for producing a negative electrode active material of the present invention includes a step of reducing Bi 2 O 3 to metal Bi by performing heat treatment on an oxide material containing Bi 2 O 3 while supplying a reducing gas, It is characterized by including.
Ｂｉ２Ｏ３を含有する酸化物材料は、ＳｉＯ２、Ｂ２Ｏ３及びＰ２Ｏ５から選択される少なくとも一種とＢｉ２Ｏ３を含有するものである。具体的には、モル％で、Ｂｉ２Ｏ３ １５〜７５％、Ｐ２Ｏ５ ０〜４５％、ＳｉＯ２ ０〜６０％、Ｂ２Ｏ３ ０〜６０％、Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３ ２５〜８５％、Ｎａ２Ｏ ０〜５０％を含有するものであることが好ましい。組成をこのように限定した理由は既述の通りであり、説明を割愛する。
The oxide material containing Bi 2 O 3 contains at least one selected from SiO 2 , B 2 O 3 and P 2 O 5 and Bi 2 O 3 . Specifically, in mol%, Bi 2 O 3 15~75% , P 2 O 5 0~45%,
酸化物材料は、例えば上述した組成となるように調製した原料粉末を例えば６００〜１２００℃で加熱溶融して、均質な溶融物にした後、冷却固化することにより製造される。得られた溶融固化物は、必要に応じて粉砕や分級等の後加工が施される。 The oxide material is produced, for example, by heating and melting raw material powder prepared so as to have the above-described composition at 600 to 1200 ° C. to form a homogeneous melt, and then cooling and solidifying. The obtained molten and solidified product is subjected to post-processing such as pulverization and classification, if necessary.
酸化物材料は非晶質であることが好ましく、それにより、ＳｉＯ２、Ｂ２Ｏ３及びＰ２Ｏ５から選択される少なくとも一種を含有する非晶質マトリクス中に金属Ｂｉが析出してなる、本発明の負極活物質が得やすくなる。 The oxide material is preferably amorphous, whereby the metal Bi is deposited in an amorphous matrix containing at least one selected from SiO 2 , B 2 O 3 and P 2 O 5. Therefore, the negative electrode active material of the present invention can be easily obtained.
酸化物材料の形状は、負極活物質と同様に通常は粉末状である。酸化物材料の平均粒子径は０．１〜２０μｍであることが好ましく、０．２〜１５μｍであることがより好ましく、０．３〜１０μｍであることがさらに好ましく、０．５〜５μｍであることが特に好ましい。また酸化物材料の最大粒子径は、１５０μｍ以下であることが好ましく、１００μｍ以下であることがより好ましく、７５μｍ以下であることがさらに好ましく、５５μｍ以下であることが特に好ましい。平均粒子径または最大粒子径が大きすぎると、得られる負極活物質の粒径も大きくなるため、上述のような不具合が発生する傾向がある。また、還元性ガスによりＢｉ２Ｏ３を金属Ｂｉに十分に還元できないおそれがある。一方、平均粒子径が小さすぎると、得られる負極活物質の粒径も小さくなるため、上述のような不具合が発生する傾向がある。 The shape of the oxide material is usually a powder, like the negative electrode active material. The average particle diameter of the oxide material is preferably 0.1 to 20 μm, more preferably 0.2 to 15 μm, further preferably 0.3 to 10 μm, and 0.5 to 5 μm. Is particularly preferable. The maximum particle size of the oxide material is preferably 150 μm or less, more preferably 100 μm or less, further preferably 75 μm or less, and particularly preferably 55 μm or less. If the average particle size or the maximum particle size is too large, the particle size of the obtained negative electrode active material also becomes large, and the above-mentioned problems tend to occur. Moreover, there is a possibility that Bi 2 O 3 cannot be sufficiently reduced to the metal Bi by the reducing gas. On the other hand, if the average particle size is too small, the particle size of the obtained negative electrode active material also becomes small, and the above-mentioned problems tend to occur.
加熱処理する際の温度は２５０℃以上であることが好ましく、３００℃以上であることがより好ましく、４００℃以上であることが特に好ましい。加熱温度が低すぎると、付与される熱エネルギーが少ないため、酸化物材料中のＢｉ２Ｏ３が金属Ｂｉに還元されにくくなる。なお、加熱温度の上限は特に限定されないが、高すぎると、還元された金属Ｂｉ粒子が粗大化しやすくなり、負極活物質のサイクル特性が著しく低下するおそれがある。よって、加熱温度は７００℃以下であることが好ましく、６００℃以下であることがより好ましい。 The temperature for the heat treatment is preferably 250 ° C or higher, more preferably 300 ° C or higher, and particularly preferably 400 ° C or higher. If the heating temperature is too low, the thermal energy applied is small, and thus Bi 2 O 3 in the oxide material is less likely to be reduced to the metal Bi. The upper limit of the heating temperature is not particularly limited, but if it is too high, the reduced metal Bi particles are likely to be coarsened, and the cycle characteristics of the negative electrode active material may be significantly deteriorated. Therefore, the heating temperature is preferably 700 ° C. or lower, and more preferably 600 ° C. or lower.
加熱時間は２０〜１０００分であることが好ましく、６０〜５００分であることがより好ましい。加熱時間が短すぎると、付与される熱エネルギーが少ないため、酸化物材料中のＢｉ２Ｏ３が金属Ｂｉに還元されにくくなる。一方、加熱時間が長すぎると、還元された金属Ｂｉ粒子が粗大化しやすくなり、負極活物質のサイクル特性が著しく低下するおそれがある。 The heating time is preferably 20 to 1000 minutes, more preferably 60 to 500 minutes. When the heating time is too short, the applied thermal energy is small, and thus Bi 2 O 3 in the oxide material is less likely to be reduced to the metal Bi. On the other hand, if the heating time is too long, the reduced metal Bi particles are likely to be coarsened, and the cycle characteristics of the negative electrode active material may be significantly deteriorated.
加熱処理には、電気加熱炉、ロータリーキルン、マイクロ波加熱炉、高周波加熱炉等を用いることができる。 For the heat treatment, an electric heating furnace, a rotary kiln, a microwave heating furnace, a high frequency heating furnace, or the like can be used.
還元性ガスとしては、Ｈ２、ＮＨ３、ＣＯ、Ｈ２Ｓ及びＳｉＨ４から選ばれる少なくとも一種のガスが挙げられる。取扱い性の観点から、Ｈ２、ＮＨ３及びＣＯから選ばれる少なくとも一種のガスが好ましく、特にＨ２が好ましい。 Examples of the reducing gas include at least one gas selected from H 2 , NH 3 , CO, H 2 S, and SiH 4 . From the viewpoint of handleability, at least one gas selected from H 2 , NH 3 and CO is preferable, and H 2 is particularly preferable.
還元性ガスとしてＨ２を使用する場合、爆発等の危険性を抑制するため、Ｎ２やＡｒ等の不活性ガスと混合して使用することが好ましい。不活性ガスとＨ２の混合割合は、体積％で、不活性ガス ９０〜９９．５％、Ｈ２ ０．５〜１０％であることが好ましい。例えばＮ２とＨ２の混合ガスの場合、体積％で、Ｎ２ ９０〜９９．５％、Ｈ２ ０．５〜１０％、Ｎ２ ９２〜９９％、Ｈ２ １〜８％、特にＮ２ ９６〜９９％、Ｈ２ １〜４％を含有することが好ましい。またＡｒとＨ２の混合ガスの場合、体積％で、Ａｒ ９０〜９９．５％、Ｈ２ ０．５〜１０％、Ａｒ ９２〜９９％、Ｈ２ １〜８％、特にＡｒ ９５〜９８％、Ｈ２ ２〜５％を含有することが好ましい。
When H 2 is used as the reducing gas, it is preferable to use it by mixing it with an inert gas such as N 2 or Ar in order to suppress the risk of explosion and the like. The mixing ratio of the inert gas and H 2 is preferably 90 to 99.5% by volume of inert gas and 0.5 to 10% of H 2 by volume. For example, in the case of a mixed gas of N 2 and H 2 , in volume%, N 2 90 to 99.5%, H 2 0.5 to 10%, N 2 92 to 99%, H 2 1 to 8%, particularly N 2. 2 96 to 99 percent, preferably contains
なお、加熱処理工程において酸化物材料（酸化物材料粉末）は軟化流動して凝集体を形成する傾向がある。酸化物材料が凝集体を形成すると、還元性ガスが酸化物材料全体にゆき渡りにくくなるため、酸化物材料の還元に長時間要する傾向がある。あるいは、生成した負極活物質粒子が粗大化して、電池特性が低下するおそれがある。そこで、酸化物材料を加熱処理する際に凝集防止剤を添加することが好ましい。このようにすれば、加熱処理時の酸化物材料の凝集を抑制でき、短時間で酸化物材料中のＢｉ２Ｏ３を金属Ｂｉに還元することが可能となる。 In the heat treatment step, the oxide material (oxide material powder) tends to soften and flow to form an aggregate. When the oxide material forms an agglomerate, it becomes difficult for the reducing gas to spread over the entire oxide material, and therefore it tends to take a long time to reduce the oxide material. Alternatively, the generated negative electrode active material particles may become coarse, and the battery characteristics may deteriorate. Therefore, it is preferable to add a coagulation inhibitor when the oxide material is heat-treated. This makes it possible to suppress the aggregation of the oxide material during the heat treatment and reduce Bi 2 O 3 in the oxide material to the metal Bi in a short time.
凝集防止剤としては、導電性カーボンやアセチレンブラック等の炭素材料が挙げられる。炭素材料は電子伝導性も有するため、負極活物質に導電性を付与することもできる。なかでも、電子伝導性に優れるアセチレンブラックが好ましい。 Examples of the aggregation preventing agent include conductive carbon and carbon materials such as acetylene black. Since the carbon material also has electronic conductivity, it is possible to give conductivity to the negative electrode active material. Of these, acetylene black, which has excellent electron conductivity, is preferable.
酸化物材料と凝集防止剤は、質量％で、酸化物材料 ８０〜９９．５％、凝集防止剤 ０．５〜２０％の割合で混合することが好ましい。このようにすれば、良好な初回充電特性と安定したサイクル特性を有する負極活物質が得やすくなる。 It is preferable that the oxide material and the aggregation preventive agent are mixed in a ratio of 80% to 99.5% by weight of the oxide material and 0.5% to 20% of the aggregation inhibitor in mass%. This makes it easy to obtain a negative electrode active material having good initial charge characteristics and stable cycle characteristics.
本発明の負極活物質に対し、結着剤や導電助剤を添加することにより負極材料として使用される。 It is used as a negative electrode material by adding a binder or a conductive additive to the negative electrode active material of the present invention.
結着剤としては、カルボキシメチルセルロース、ヒドロキシプロピルメチルセルロース、ヒドロキシプロピルセルロース、ヒドロキシエチルセルロース、エチルセルロース、ヒドロキシメチルセルロース等のセルロース誘導体、またはポリビニルアルコール等の水溶性高分子；熱硬化性ポリイミド、フェノール樹脂、エポキシ樹脂、ユリア樹脂、メラミン樹脂、不飽和ポリエステル樹脂、ポリウレタン等の熱硬化性樹脂；ポリフッ化ビニリデン等が挙げられる。 As the binder, carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, ethylcellulose, cellulose derivatives such as hydroxymethylcellulose, or water-soluble polymer such as polyvinyl alcohol; thermosetting polyimide, phenol resin, epoxy resin, Thermosetting resins such as urea resin, melamine resin, unsaturated polyester resin and polyurethane; polyvinylidene fluoride and the like.
導電助剤としては、アセチレンブラックやケッチェンブラック等の高導電性カーボンブラック、グラファイト等のカーボン粉末、炭素繊維等が挙げられる。 Examples of the conductive aid include highly conductive carbon black such as acetylene black and Ketjen black, carbon powder such as graphite, and carbon fiber.
蓄電デバイス用負極材料を、集電体としての役割を果たす金属箔等の表面に塗布することで蓄電デバイス用負極として用いることができる。 The negative electrode material for a power storage device can be used as a negative electrode for a power storage device by applying it to the surface of a metal foil or the like that functions as a current collector.
本発明のナトリウムイオン二次電池用負極活物質は、ナトリウムイオン二次電池に用いられる負極活物質と非水系電気二重層キャパシタ用の正極材料とを組み合わせたハイブリットキャパシタ等にも適用できる。 The negative electrode active material for a sodium ion secondary battery of the present invention can be applied to a hybrid capacitor in which a negative electrode active material used in a sodium ion secondary battery and a positive electrode material for a non-aqueous electric double layer capacitor are combined.
ハイブリットキャパシタであるナトリウムイオンキャパシタは、正極と負極の充放電原理が異なる非対称キャパシタの一種である。ナトリウムイオンキャパシタは、ナトリウムイオン二次電池用の負極と電気二重層キャパシタ用の正極を組み合わせた構造を有している。ここで、正極は表面に電気二重層を形成し、物理的な作用（静電気作用）を利用して充放電するのに対し、負極はナトリウムイオン二次電池と同様にＮａイオンの化学反応（吸蔵及び放出）により充放電する。 A sodium ion capacitor, which is a hybrid capacitor, is a kind of asymmetric capacitor in which the positive and negative electrode charging and discharging principles are different. The sodium ion capacitor has a structure in which a negative electrode for a sodium ion secondary battery and a positive electrode for an electric double layer capacitor are combined. Here, the positive electrode forms an electric double layer on the surface and is charged and discharged by utilizing a physical action (electrostatic action), whereas the negative electrode is a chemical reaction of Na ions (occlusion) like the sodium ion secondary battery. And discharge).
ナトリウムイオンキャパシタの正極には、活性炭、ポリアセン、メソフェーズカーボン等の高比表面積の炭素質粉末等からなる正極活物質が用いられる。一方、負極には、本発明の負極活物質を用いることができる。 For the positive electrode of the sodium ion capacitor, a positive electrode active material made of carbonaceous powder having a high specific surface area such as activated carbon, polyacene, mesophase carbon, or the like is used. On the other hand, the negative electrode active material of the present invention can be used for the negative electrode.
以下、本発明の負極活物質を実施例に基づいて詳細に説明するが、本発明はこれらの実施例に限定されるものではない。 Hereinafter, the negative electrode active material of the present invention will be described in detail based on examples, but the present invention is not limited to these examples.
（１）酸化物材料の作製
表１に示す組成となるように、各種酸化物、炭酸塩原料、リン酸塩原料等を用いて原料粉末を調製した。原料粉末を白金ルツボに投入し、電気炉を用いて大気雰囲気にて溶融を行った。なお、実施例１及び比較例１は７５０℃で３０分間の溶融を行い、実施例２〜５及び比較例２〜４は１１００℃で２０分間の溶融を行った。
(1) Preparation of Oxide Material Raw material powders were prepared using various oxides, carbonate raw materials, phosphate raw materials, etc. so as to have the composition shown in Table 1. The raw material powder was put into a platinum crucible and melted in an air atmosphere using an electric furnace. In addition, Example 1 and Comparative Example 1 performed melting at 750 ° C. for 30 minutes, and Examples 2-5 and Comparative Examples 2-4 performed melting at 1100 ° C. for 20 minutes.
次いで、溶融物を一対の冷却回転ローラー間に流し出すことにより、急冷しながら成形し、厚み０．１〜２ｍｍのフィルム状ガラスを得た。このフィルム状ガラスを、φ１〜３ｃｍのジルコニアボールを入れたボールミルを用いて１００ｒｐｍで３時間粉砕した後、目開き１２０μｍの樹脂製篩に通過させ、平均粒子径３〜１５μｍのガラス粗粉末（酸化物材料粗粉末）を得た。次いで、ガラス粗粉末を空気分級することで、平均粒子径２μｍかつ最大粒子径２８μｍのガラス粉末（酸化物材料粉末）を得た。 Next, the melt was cast out between a pair of cooling rotary rollers to form the film while quenching to obtain a film glass having a thickness of 0.1 to 2 mm. This film glass was crushed for 3 hours at 100 rpm using a ball mill containing zirconia balls of φ1 to 3 cm, and then passed through a resin sieve having an opening of 120 μm to obtain a glass coarse powder having an average particle diameter of 3 to 15 μm (oxidation). To obtain a crude powder). Then, the glass coarse powder was classified by air to obtain glass powder (oxide material powder) having an average particle diameter of 2 μm and a maximum particle diameter of 28 μm.
酸化物材料粉末について粉末Ｘ線回折測定することにより構造を同定したところ、非晶質であり、結晶は検出されなかった。 When the structure of the oxide material powder was identified by powder X-ray diffraction measurement, the structure was amorphous and no crystal was detected.
（２）負極活物質の作製
得られた酸化物材料を表１に記載の条件で加熱処理した。なお、実施例２は酸化物材料粉末に凝集防止剤として導電性カーボンブラック粉末（ＳｕｐｅｒＣ６５，Ｔｉｍｃａｌ社製）を、酸化物材料：凝集防止剤＝９５：５（質量％）の割合で予めボールミルを用いて混合したものを用いた。比較例１、２は加熱処理を行わなかった。
(2) Preparation of Negative Electrode Active Material The obtained oxide material was heat-treated under the conditions shown in Table 1. In Example 2, a conductive carbon black powder (Super C65, manufactured by Timcal) was added to the oxide material powder as an anti-agglomeration agent, and a ball mill was preliminarily used at a ratio of oxide material: anti-aggregation agent = 95: 5 (mass%). The mixture used was used. Comparative Examples 1 and 2 were not heat-treated.
次いで、加熱処理後の酸化物材料をメノウ乳鉢で解砕した後、目開き２０μｍの樹脂製篩に通過させ、平均粒子径３μｍの負極活物質粉末を得た。 Next, the oxide material after the heat treatment was crushed in an agate mortar and then passed through a resin sieve having an opening of 20 μm to obtain a negative electrode active material powder having an average particle diameter of 3 μm.
得られた負極活物質について粉末Ｘ線回折測定することにより構造を同定した。その結果を表１及び図１に示す。 The structure was identified by performing powder X-ray diffraction measurement on the obtained negative electrode active material. The results are shown in Table 1 and FIG.
（３）負極の作製
実施例１及び比較例１については、以下のようにして負極を作製した。得られた負極活物質と導電助剤（導電性カーボンブラック）と結着剤（ポリフッ化ビニリデン）を質量比で８５：１０：５の割合になるように秤量、混合してステンレス製メッシュに４０ＭＰａで圧着して負極を作製した。
(3) Preparation of Negative Electrode For Example 1 and Comparative Example 1, a negative electrode was prepared as follows. The obtained negative electrode active material, conductive additive (conductive carbon black), and binder (polyvinylidene fluoride) were weighed and mixed at a mass ratio of 85: 10: 5, and mixed with a stainless steel mesh at 40 MPa. Then, it was pressure-bonded to prepare a negative electrode.
実施例２〜５及び比較例２〜４については、以下のようにして負極を作製した。得られた負極活物質と導電助剤（導電性カーボンブラック）と結着剤（ポリフッ化ビニリデン）を質量比で８５：５：１０の割合になるように秤量し、脱水したＮ−メチルピロリドンに分散した後、自転・公転ミキサーで十分に撹拌してスラリー化した。次に、隙間７５μｍのドクターブレードを用いて、得られたスラリーを負極集電体である厚さ２０μｍの銅箔上にコートし、７０℃の乾燥機で真空乾燥後、一対の回転ローラー間に通してプレスすることにより電極シートを得た。この電極シートを電極打ち抜き機で直径１１ｍｍに打ち抜き、温度２００℃にて８時間、減圧下で乾燥させて円形の負極を得た。 For Examples 2 to 5 and Comparative Examples 2 to 4, negative electrodes were prepared as follows. The obtained negative electrode active material, conductive auxiliary agent (conductive carbon black), and binder (polyvinylidene fluoride) were weighed in a mass ratio of 85: 5: 10 to give dehydrated N-methylpyrrolidone. After being dispersed, the mixture was sufficiently stirred by a rotation / revolution mixer to form a slurry. Next, using a doctor blade having a gap of 75 μm, the obtained slurry was coated on a copper foil having a thickness of 20 μm, which is a negative electrode current collector, and vacuum dried with a dryer at 70 ° C., and then between a pair of rotating rollers. An electrode sheet was obtained by pressing through. This electrode sheet was punched out to a diameter of 11 mm with an electrode punching machine and dried under reduced pressure at a temperature of 200 ° C. for 8 hours to obtain a circular negative electrode.
（４）試験電池の作製
得られた負極と、７０℃で８時間減圧乾燥した直径１６ｍｍのポリプロピレン多孔質膜（ヘキストセラニーズ社製 セルガード＃２４００）からなるセパレータ、及び、対極である金属ナトリウムを積層し、電解液を染み込ませることにより試験電池を作製した。電解液には、１Ｍ ＮａＰＦ６溶液／ＥＣ：ＤＥＣ＝１：１（ＥＣ＝エチレンカーボネート、ＤＥＣ＝ジエチルカーボネート）を用いた。なお試験電池の組み立ては露点温度−７０℃以下のアルゴン環境で行った。
(4) Preparation of test battery The obtained negative electrode, a separator composed of a polypropylene porous membrane (Celgard # 2400 manufactured by Hoechst Celanese Co., Ltd.) having a diameter of 16 mm dried under reduced pressure at 70 ° C. for 8 hours, and metallic sodium as a counter electrode A test battery was prepared by stacking and impregnating with an electrolytic solution. As the electrolytic solution, 1M NaPF 6 solution / EC: DEC = 1: 1 (EC = ethylene carbonate, DEC = diethyl carbonate) was used. The test battery was assembled in an argon environment with a dew point temperature of −70 ° C. or lower.
（５）充放電試験
作製した試験電池に対し、３０℃で開回路電圧から０ＶまでＣＣ（定電流）充電（負極活物質へのナトリウムイオンの吸蔵）を行い、単位質量の負極活物質へ充電された電気量（初回充電容量）を求めた。次に、０Ｖから３ＶまでＣＣ放電（負極活物質からのナトリウムイオンの放出）させ、単位質量の負極活物質から放電された電気量（初回放電容量）を求めた。なお、Ｃレートは０．１Ｃとした。これらの結果から、初回不可逆容量（＝初回充電容量−初回放電容量）を求めた。結果を表１に示す。
(5) Charge / Discharge Test The prepared test battery was charged with CC (constant current) from open circuit voltage to 0 V at 30 ° C. (storage of sodium ion in negative electrode active material) to charge the negative electrode active material of unit mass. The amount of electricity (first charge capacity) was calculated. Then, CC discharge (release of sodium ions from the negative electrode active material) was performed from 0 V to 3 V, and the amount of electricity (initial discharge capacity) discharged from the negative electrode active material having a unit mass was determined. The C rate was 0.1C. From these results, the first irreversible capacity (= first charge capacity-first discharge capacity) was determined. The results are shown in Table 1.
表１に示すように、実施例１〜５の負極活物質は初回不可逆容量が２３８ｍＡｈ／ｇ以下と小さいのに対し、比較例１〜４の負極活物質は初回不可逆容量が２５４ｍＡｈ／ｇ以上と大きかった。 As shown in Table 1, the negative electrode active materials of Examples 1 to 5 had a small initial irreversible capacity of 238 mAh / g or less, whereas the negative electrode active materials of Comparative Examples 1 to 4 had an initial irreversible capacity of 254 mAh / g or more. It was great.
本発明の負極活物質は、例えば、移動体通信機器、携帯用電子機器、電動自転車、電動二輪車、電気自動車等の主電源等に使用されるナトリウムイオン二次電池用途に好適である。 INDUSTRIAL APPLICABILITY The negative electrode active material of the present invention is suitable for use in sodium ion secondary batteries used as a main power source for mobile communication devices, portable electronic devices, electric bicycles, electric motorcycles, electric vehicles, and the like.
Claims (5)
Ｂｉ２Ｏ３を含有する酸化物材料に対し、還元性ガスを供給しながら加熱処理を行うことにより、Ｂｉ２Ｏ３を金属Ｂｉに還元する工程、を含むことを特徴するナトリウムイオン二次電池用負極活物質の製造方法。 A method for producing the negative electrode active material for a sodium ion secondary battery according to any one of claims 1 to 3,
A sodium ion secondary battery comprising a step of reducing Bi 2 O 3 to metal Bi by performing heat treatment on an oxide material containing Bi 2 O 3 while supplying a reducing gas. For manufacturing negative electrode active material for automobile.
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| JP2010062424A (en) * | 2008-09-05 | 2010-03-18 | Toko Inc | Manufacturing method of electronic component |
| JP2015035290A (en) * | 2013-08-08 | 2015-02-19 | 日本電気硝子株式会社 | Negative electrode active material for electric power storage device, and method for manufacturing the same |
| JP2015198000A (en) * | 2014-04-01 | 2015-11-09 | 日本電気硝子株式会社 | Negative electrode active material for power storage device, negative electrode material for power storage device, and power storage device |
| JP2017050195A (en) * | 2015-09-03 | 2017-03-09 | 国立大学法人長岡技術科学大学 | Negative electrode active material for power storage device |
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| JPS55119355A (en) * | 1979-03-07 | 1980-09-13 | Sanyo Electric Co Ltd | Non-aqueous electrolyte battery |
| JP2010062424A (en) * | 2008-09-05 | 2010-03-18 | Toko Inc | Manufacturing method of electronic component |
| JP2015035290A (en) * | 2013-08-08 | 2015-02-19 | 日本電気硝子株式会社 | Negative electrode active material for electric power storage device, and method for manufacturing the same |
| JP2015198000A (en) * | 2014-04-01 | 2015-11-09 | 日本電気硝子株式会社 | Negative electrode active material for power storage device, negative electrode material for power storage device, and power storage device |
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