JP7532898B2 - Positive electrode and storage element - Google Patents
Positive electrode and storage element Download PDFInfo
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- JP7532898B2 JP7532898B2 JP2020090716A JP2020090716A JP7532898B2 JP 7532898 B2 JP7532898 B2 JP 7532898B2 JP 2020090716 A JP2020090716 A JP 2020090716A JP 2020090716 A JP2020090716 A JP 2020090716A JP 7532898 B2 JP7532898 B2 JP 7532898B2
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- positive electrode
- active material
- electrode active
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- 238000003860 storage Methods 0.000 title claims description 33
- 239000000758 substrate Substances 0.000 claims description 92
- 239000007774 positive electrode material Substances 0.000 claims description 73
- 239000011164 primary particle Substances 0.000 claims description 50
- 239000011163 secondary particle Substances 0.000 claims description 47
- 239000000203 mixture Substances 0.000 claims description 45
- -1 lithium transition metal Chemical class 0.000 claims description 37
- 229910052744 lithium Inorganic materials 0.000 claims description 29
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- 239000002905 metal composite material Substances 0.000 claims description 22
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- 229910052759 nickel Inorganic materials 0.000 claims description 11
- 229910052748 manganese Inorganic materials 0.000 claims description 9
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 4
- 229910017052 cobalt Inorganic materials 0.000 claims description 4
- 239000010941 cobalt Substances 0.000 claims description 4
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 4
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Images
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
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- Electric Double-Layer Capacitors Or The Like (AREA)
- Cell Electrode Carriers And Collectors (AREA)
- Battery Electrode And Active Subsutance (AREA)
Description
本発明は、正極及び蓄電素子に関する。 The present invention relates to a positive electrode and a storage element.
リチウムイオン二次電池に代表される非水電解質二次電池は、エネルギー密度の高さから、パーソナルコンピュータ、通信端末等の電子機器、自動車等に多用されている。上記非水電解質二次電池は、一般的には、セパレータで電気的に隔離された一対の電極と、この電極間に介在する非水電解質とを有し、両電極間でイオンの受け渡しを行うことで充放電するよう構成される。また、非水電解質二次電池以外の蓄電素子として、リチウムイオンキャパシタや電気二重層キャパシタ等のキャパシタ、非水電解質以外の電解質が用いられた蓄電素子等も広く普及している。 Non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc., due to their high energy density. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and is configured to charge and discharge by transferring ions between the two electrodes. In addition, as storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium ion capacitors and electric double layer capacitors, and storage elements using electrolytes other than non-aqueous electrolytes, etc. are also widely used.
蓄電素子に用いられる正極は、正極基材に正極合材層が積層された構造を有するものが一般的である。正極基材としては、導電性等の点からアルミニウム製の箔が広く使用されている。また、通常、正極を製造する際、塗工及び乾燥により正極基材上に正極合材層を形成した後、見かけの密度を高めるなどのために正極合材層に対してプレスがなされる。しかし、正極基材上に正極合材層を形成していない部分がある場合、このプレスによって正極合材層を形成した部分の反りや正極合材層を形成していない部分のたわみが生じることがある。そこで、プレスに伴う反りやたわみの発生の抑制等のために、正極基材としてＡ３００３等の高強度のアルミニウム合金製の箔を用いることがある。また、さらに高強度のリチウムイオン二次電池正極集電体用アルミニウム合金製の箔の開発も進められている（特許文献１参照）。 The positive electrode used in the energy storage element generally has a structure in which a positive electrode composite layer is laminated on a positive electrode substrate. Aluminum foil is widely used as the positive electrode substrate because of its electrical conductivity. In addition, when manufacturing a positive electrode, a positive electrode composite layer is usually formed on the positive electrode substrate by coating and drying, and then the positive electrode composite layer is pressed to increase the apparent density. However, if there is a portion on the positive electrode substrate where the positive electrode composite layer is not formed, this pressing may cause warping of the portion where the positive electrode composite layer is formed and bending of the portion where the positive electrode composite layer is not formed. Therefore, in order to suppress the occurrence of warping and bending due to pressing, a foil made of a high-strength aluminum alloy such as A3003 may be used as the positive electrode substrate. In addition, development of an even higher-strength aluminum alloy foil for lithium-ion secondary battery positive electrode current collectors is also underway (see Patent Document 1).
上記のような高強度のアルミニウム合金製の正極基材を用いて作製された正極は、一般的な強度の純アルミニウム製の正極基材を用いて作製された正極に対して、電気抵抗が大幅に増加する場合がある。 Positive electrodes made using high-strength aluminum alloy positive electrode substrates such as those described above may have a significantly higher electrical resistance than positive electrodes made using pure aluminum positive electrode substrates of average strength.
本発明は、以上のような事情に基づいてなされたものであり、その目的は、高強度のアルミニウム合金製の正極基材を用いた場合に電気抵抗が大幅に増加するという不都合が改善された正極、及びこの正極を備える蓄電素子を提供することである。 The present invention was made based on the above circumstances, and its purpose is to provide a positive electrode that overcomes the disadvantage of a large increase in electrical resistance when a positive electrode substrate made of a high-strength aluminum alloy is used, and an energy storage element that includes this positive electrode.
本発明の一態様は、アルミニウムを含有する正極基材と、上記正極基材に積層され、正極活物質を含有する正極合材層とを備え、上記正極基材の引張強さが２３０Ｎ／ｍｍ２以上であり、上記正極活物質は、一次粒子径に対する二次粒子径の比が５以下である二次粒子を含む蓄電素子用の正極（Ａ）である。 One aspect of the present invention is a positive electrode (A) for an energy storage element, comprising: a positive electrode substrate containing aluminum; and a positive electrode mixture layer laminated on the positive electrode substrate and containing a positive electrode active material, wherein the positive electrode substrate has a tensile strength of 230 N/ mm2 or more; and the positive electrode active material contains secondary particles having a ratio of secondary particle diameter to primary particle diameter of 5 or less.
本発明の他の一態様は、アルミニウムを含有する正極基材と、上記正極基材に積層され、正極活物質を含有する正極合材層とを備え、上記正極基材の引張強さが２３０Ｎ／ｍｍ２以上であり、上記正極活物質は、実質的に凝集していない一次粒子を含む蓄電素子用の正極（Ｂ）である。 Another aspect of the present invention is a positive electrode (B) for an energy storage element, comprising: a positive electrode substrate containing aluminum; and a positive electrode mixture layer laminated on the positive electrode substrate and containing a positive electrode active material, wherein the positive electrode substrate has a tensile strength of 230 N/ mm2 or more, and the positive electrode active material contains primary particles that are not substantially aggregated.
本発明の他の一態様は、当該正極（Ａ）又は当該正極（Ｂ）を備える蓄電素子である。 Another aspect of the present invention is a storage element including the positive electrode (A) or the positive electrode (B).
本発明の一態様によれば、高強度のアルミニウム合金製の正極基材を用いた場合に電気抵抗が大幅に増加するという不都合が改善された正極、及びこの正極を備える蓄電素子を提供することができる。 According to one aspect of the present invention, it is possible to provide a positive electrode that overcomes the disadvantage of a significant increase in electrical resistance when a positive electrode substrate made of a high-strength aluminum alloy is used, and an energy storage element that includes this positive electrode.
初めに、本明細書によって開示される正極及び蓄電素子の概要について説明する。 First, we will provide an overview of the positive electrode and the energy storage element disclosed in this specification.
本発明の一態様に係る正極は、アルミニウムを含有する正極基材と、上記正極基材に積層され、正極活物質を含有する正極合材層とを備え、上記正極基材の引張強さが２３０Ｎ／ｍｍ２以上であり、上記正極活物質は、一次粒子径に対する二次粒子径の比が５以下である二次粒子を含む蓄電素子用の正極（Ａ）である。 A positive electrode according to one aspect of the present invention is a positive electrode (A) for an energy storage element, comprising: a positive electrode substrate containing aluminum; and a positive electrode mixture layer laminated on the positive electrode substrate and containing a positive electrode active material, wherein the positive electrode substrate has a tensile strength of 230 N/ mm2 or more; and the positive electrode active material contains secondary particles having a ratio of secondary particle diameter to primary particle diameter of 5 or less.
当該正極（Ａ）は、高強度のアルミニウム合金製の正極基材を用いた場合に電気抵抗が大幅に増加するという不都合が改善されている。上記のような効果が生じる理由は定かではないが、以下の理由が推測される。一般的な正極の製造においては、正極基材上に正極合材層を形成し、この正極合材層をプレスすることにより、正極合材層中の正極活物質の粒子が正極基材に食い込み、これにより十分な導電性が確保されると考えられる。しかし、正極基材が高強度のアルミニウム合金製である場合、一般的なアルミニウム製の正極基材よりも硬いため、正極活物質の粒子が正極基材に食い込みにくい。そのため、正極合材層をプレスした際に、正極活物質の粒子が正極基材に食い込むよりも、二次粒子である正極活物質が粉砕しやすく、正極合材層の見かけの密度が高まりやすくなる。その結果、正極活物質の粒子が正極基材に食い込みにくいため、十分な導電性が確保されず電気抵抗が大幅に増加すると考えられる。これに対し、本発明の一態様に係る正極（Ａ）においては、正極活物質が、一次粒子径に対する二次粒子径の比が５以下である二次粒子を含んでいる。このような二次粒子は、多数の一次粒子が凝集してなる一般的な正極活物質の粒子と異なり、比較的少数の一次粒子から形成されたものであるため、プレスした際にも粒子自体の粉砕が生じにくく、高強度のアルミニウム合金製の正極基材に対しても食い込みやすい。このため、本発明の一態様に係る正極（Ａ）においては、正極合材層と正極基材との間で十分な導電性が確保され、高強度のアルミニウム合金製の正極基材を用いた場合に電気抵抗が大幅に増加するという不都合が改善されると推測される。このため、当該正極（Ａ）によれば、電気抵抗の増加を抑制しつつ、正極の反りやたわみが生じ難くなるという、高強度のアルミニウム合金製の正極基材を用いることによる利点を享受することができる。 The positive electrode (A) has been improved from the inconvenience of a significant increase in electrical resistance when a high-strength aluminum alloy positive electrode substrate is used. The reason for the above effect is unclear, but the following reasons are presumed. In the manufacture of a general positive electrode, a positive electrode composite layer is formed on a positive electrode substrate, and the positive electrode composite layer is pressed, so that the particles of the positive electrode active material in the positive electrode composite layer bite into the positive electrode substrate, which is considered to ensure sufficient electrical conductivity. However, when the positive electrode substrate is made of a high-strength aluminum alloy, it is harder than a general aluminum positive electrode substrate, so that the particles of the positive electrode active material do not bite into the positive electrode substrate. Therefore, when the positive electrode composite layer is pressed, the positive electrode active material, which is a secondary particle, is more likely to be crushed than the particles of the positive electrode active material bite into the positive electrode substrate, and the apparent density of the positive electrode composite layer is more likely to increase. As a result, it is considered that the particles of the positive electrode active material do not bite into the positive electrode substrate, so that sufficient electrical conductivity is not ensured and the electrical resistance increases significantly. In contrast, in the positive electrode (A) according to one embodiment of the present invention, the positive electrode active material contains secondary particles having a ratio of secondary particle diameter to primary particle diameter of 5 or less. Unlike particles of a general positive electrode active material formed by agglomeration of a large number of primary particles, such secondary particles are formed from a relatively small number of primary particles, so that the particles themselves are less likely to be crushed when pressed, and are easily embedded in a positive electrode substrate made of a high-strength aluminum alloy. Therefore, in the positive electrode (A) according to one embodiment of the present invention, sufficient conductivity is ensured between the positive electrode mixture layer and the positive electrode substrate, and it is presumed that the inconvenience of a significant increase in electrical resistance when a positive electrode substrate made of a high-strength aluminum alloy is used is improved. Therefore, according to the positive electrode (A), it is possible to enjoy the advantage of using a positive electrode substrate made of a high-strength aluminum alloy, that is, the increase in electrical resistance is suppressed while the positive electrode is less likely to warp or bend.
なお、「引張強さ」は、ＪＩＳ－Ｚ－２２４１（２０１１年）に準拠して測定される値である。
正極活物質の「一次粒子径」とは、走査型電子顕微鏡（ＳＥＭ）において観察される正極活物質の粒子を構成する任意の５０個の一次粒子における各粒子径の平均値である。一次粒子とは、上記ＳＥＭでの観察において、外観上に粒界が観測されない粒子である。一次粒子の粒子径は、次のようにして求める。一次粒子の最小外接円の中心を通り最も短い径を短径とし、上記中心を通り短径に直交する径を長径とする。長径と短径との平均値を粒子径とする。最も短い径が２本以上存在する場合、直交する径が最も長いものを短径とする。
正極活物質の「二次粒子径」とは、ＪＩＳ－Ｚ－８８１５（２０１３年）に準拠し、正極活物質の粒子を溶媒で希釈した希釈液に対しレーザ回折・散乱法により測定した粒径分布に基づき、ＪＩＳ－Ｚ－８８１９－２（２００１年）に準拠し計算される体積基準積算分布が５０％となる値（Ｄ５０：メジアン径）である。
The "tensile strength" is a value measured in accordance with JIS-Z-2241 (2011).
The "primary particle diameter" of the positive electrode active material is the average value of the particle diameters of any 50 primary particles constituting the particles of the positive electrode active material observed under a scanning electron microscope (SEM). A primary particle is a particle in which no grain boundary is observed in appearance when observed under the SEM. The particle diameter of a primary particle is determined as follows. The shortest diameter passing through the center of the minimum circumscribing circle of the primary particle is defined as the minor diameter, and the diameter passing through the center and perpendicular to the minor diameter is defined as the major diameter. The average value of the major diameter and the minor diameter is defined as the particle diameter. When there are two or more shortest diameters, the diameter perpendicular to the minor diameter is defined as the minor diameter.
The "secondary particle diameter" of the positive electrode active material is a value (D50: median diameter) at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured in accordance with JIS-Z-8815 (2013) using a laser diffraction/scattering method for a diluted solution obtained by diluting particles of the positive electrode active material with a solvent.
本発明の他の一態様に係る正極は、アルミニウムを含有する正極基材と、上記正極基材に積層され、正極活物質を含有する正極合材層とを備え、上記正極基材の引張強さが２３０Ｎ／ｍｍ２以上であり、上記正極活物質は、実質的に凝集していない一次粒子を含む蓄電素子用の正極（Ｂ）である。 A positive electrode according to another embodiment of the present invention is a positive electrode (B) for an energy storage element, comprising: a positive electrode substrate containing aluminum; and a positive electrode mixture layer laminated on the positive electrode substrate and containing a positive electrode active material, wherein the positive electrode substrate has a tensile strength of 230 N/ mm2 or more; and the positive electrode active material contains primary particles that are not substantially aggregated.
当該正極（Ｂ）においても、高強度のアルミニウム合金製の正極基材を用いた場合に電気抵抗が大幅に増加するという不都合が改善されている。この理由は定かではないが、上述した正極（Ａ）と同様の理由が推測される。すなわち、当該正極（Ｂ）が、実質的に凝集していない一次粒子を正極活物質として含有することから、プレスした際にも粒子自体の粉砕が生じにくく、高強度のアルミニウム合金製の正極基材に対して食い込みやすい。このため、本発明の一態様に係る正極（Ｂ）においては、正極合材層と正極基材との間で十分な導電性が確保され、高強度のアルミニウム合金製の正極基材を用いた場合に電気抵抗が大幅に増加するという不都合が改善されると推測される。 In the positive electrode (B), the disadvantage of a large increase in electrical resistance when a positive electrode substrate made of a high-strength aluminum alloy is used is also improved. The reason for this is unclear, but it is presumed to be the same as that of the positive electrode (A) described above. That is, since the positive electrode (B) contains substantially non-aggregated primary particles as the positive electrode active material, the particles themselves are less likely to be crushed when pressed, and are more likely to bite into the positive electrode substrate made of a high-strength aluminum alloy. For this reason, in the positive electrode (B) according to one embodiment of the present invention, sufficient conductivity is ensured between the positive electrode mixture layer and the positive electrode substrate, and it is presumed that the disadvantage of a large increase in electrical resistance when a positive electrode substrate made of a high-strength aluminum alloy is used is improved.
正極活物質が「実質的に凝集していない一次粒子である」とは、正極合材層から正極活物質を採取し、バインダを除去した状態で正極活物質の粒子をＳＥＭで観察したとき、複数の一次粒子が凝集せずに独立して存在していることをいう。以下、「実質的に凝集していない一次粒子」又は「一次粒子径に対する二次粒子径の比が５以下である二次粒子」を「単粒子系粒子」とも称する。 The positive electrode active material is "primary particles that are substantially not aggregated" means that when the positive electrode active material is taken from the positive electrode mixture layer, the binder is removed, and the particles of the positive electrode active material are observed with an SEM, and multiple primary particles exist independently without aggregation. Hereinafter, "primary particles that are substantially not aggregated" or "secondary particles whose secondary particle diameter ratio to primary particle diameter is 5 or less" are also referred to as "single particle system particles".
上記正極活物質が、ニッケルと、コバルトと、マンガン又はアルミニウムとを含むリチウム遷移金属複合酸化物であることが好ましい。このようなリチウム遷移金属複合酸化物を用いることで、エネルギー密度を高くすることなどができる。また、このようなリチウム遷移金属複合酸化物は、一般的に多数の一次粒子が凝集してなる二次粒子の形態で製造され、使用される場合が多い。このため、本発明の一実施形態において、正極活物質に上記リチウム遷移金属複合酸化物を用いることで、このリチウム遷移金属複合酸化物が有する高いエネルギー密度等の利点に加え、単粒子系粒子であることによる高強度のアルミニウム合金製の正極基材を用いた場合に電気抵抗が大幅に増加するという不都合の改善効果を兼ね備える良好な機能が発揮でき得る。 The positive electrode active material is preferably a lithium transition metal composite oxide containing nickel, cobalt, and manganese or aluminum. By using such a lithium transition metal composite oxide, it is possible to increase the energy density. In addition, such lithium transition metal composite oxides are generally manufactured and used in the form of secondary particles formed by agglomeration of a large number of primary particles. Therefore, in one embodiment of the present invention, by using the lithium transition metal composite oxide as the positive electrode active material, in addition to the advantages of the high energy density of this lithium transition metal composite oxide, it is possible to exhibit a good function that combines an improvement effect on the inconvenience of a large increase in electrical resistance when using a positive electrode substrate made of a high-strength aluminum alloy due to the fact that it is a single-particle particle.
上記二次粒子の一次粒子径に対する二次粒子径の比が１．５以下であることが好ましい。このように、単粒子系粒子の中でも一次粒子により近い粒子を用いることで、高強度のアルミニウム合金製の正極基材を用いた場合に電気抵抗が大幅に増加するという不都合の改善効果を高めることができる。 It is preferable that the ratio of the secondary particle diameter to the primary particle diameter of the secondary particles is 1.5 or less. In this way, by using particles that are closer to primary particles among the single particle particles, it is possible to improve the effect of improving the inconvenience of a significant increase in electrical resistance when a positive electrode substrate made of a high-strength aluminum alloy is used.
本発明の一態様に係る蓄電素子は、当該正極（Ａ）又は正極（Ｂ）を備える蓄電素子である。当該蓄電素子は、高強度のアルミニウム合金製の正極基材を有する正極を用いた場合に電気抵抗が大幅に増加するという不都合が改善されている。従って、当該蓄電素子によれば、電気抵抗の増加を抑制しつつ、プレスに伴う正極の反りやたわみが生じ難いという、高強度のアルミニウム合金製の正極基材を用いることによる利点を享受することができる。 The energy storage element according to one aspect of the present invention is an energy storage element including the positive electrode (A) or the positive electrode (B). The energy storage element improves upon the disadvantage of a significant increase in electrical resistance when a positive electrode having a positive electrode substrate made of a high-strength aluminum alloy is used. Therefore, with the energy storage element, it is possible to enjoy the advantage of using a positive electrode substrate made of a high-strength aluminum alloy, that is, the positive electrode is less likely to warp or bend due to pressing, while suppressing the increase in electrical resistance.
以下、本発明の一実施形態に係る正極及び蓄電素子について、順に説明する。 The positive electrode and the storage element according to one embodiment of the present invention will be described below.
＜正極＞
本発明の一実施形態に係る正極は、正極基材、及びこの正極基材に直接又は中間層を介して積層される正極合材層を有する。当該正極は、蓄電素子用の正極である。
<Positive electrode>
A positive electrode according to one embodiment of the present invention has a positive electrode substrate and a positive electrode mixture layer laminated on the positive electrode substrate directly or via an intermediate layer. The positive electrode is a positive electrode for an electric storage element.
正極基材は、導電性を有する。「導電性」を有するとは、ＪＩＳ－Ｈ－０５０５（１９７５年）に準拠して測定される体積抵抗率が１０７Ω・ｃｍ以下であることを意味し、「非導電性」とは、上記体積抵抗率が１０７Ω・ｃｍ超であることを意味する。また、正極基材の形状は、通常、シート状又は板状であり、薄く打ち延ばされてシート状に形成された箔であることが好ましい。 The positive electrode substrate is conductive. Being "conductive" means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7 Ω·cm or less, and being "non-conductive" means that the volume resistivity is more than 10 7 Ω·cm. The shape of the positive electrode substrate is usually a sheet or plate, and is preferably a foil formed into a sheet by thinly rolling it out.
正極基材は、アルミニウムを含有する。正極基材の材質は、純アルミニウム及びアルミニウム合金のいずれであってもよいが、強度の点からアルミニウム合金であることが好ましい。 The positive electrode substrate contains aluminum. The material of the positive electrode substrate may be either pure aluminum or an aluminum alloy, but an aluminum alloy is preferable from the viewpoint of strength.
正極基材の引張強さは２３０Ｎ／ｍｍ２以上であり、２４０Ｎ／ｍｍ２以上が好ましく、２５０Ｎ／ｍｍ２以上がより好ましく、２６０Ｎ／ｍｍ２以上がさらに好ましい。このような高強度の正極基材を用いることで、プレスを経ても、反りやたわみが少ない良好な正極となる。この引張強さの上限は、例えば３２０Ｎ／ｍｍ２であってよく、３００Ｎ／ｍｍ２又は２８０Ｎ／ｍｍ２であってもよい。正極基材としては、ＪＩＳ－Ｈ－４０００（２０１４年）又はＪＩＳ－Ｈ－４１６０（２００６年）に規定されるＡ１０００系、Ａ３０００系、Ａ１Ｎ３０系等の純アルミニウム製及びアルミニウム合金製の箔等の中から、引張強さが２３０Ｎ／ｍｍ２以上の市販品等を用いることができる。 The tensile strength of the positive electrode substrate is 230 N / mm 2 or more, preferably 240 N / mm 2 or more, more preferably 250 N / mm 2 or more, and even more preferably 260 N / mm 2 or more. By using such a high-strength positive electrode substrate, a good positive electrode with little warping or bending is obtained even after pressing. The upper limit of this tensile strength may be, for example, 320 N / mm 2 , or may be 300 N / mm 2 or 280 N / mm 2. As the positive electrode substrate, a commercially available product having a tensile strength of 230 N / mm 2 or more can be used from among pure aluminum and aluminum alloy foils such as A1000 series, A3000 series, and A1N30 series as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).
正極基材の平均厚さは、３μｍ以上５０μｍ以下が好ましく、５μｍ以上４０μｍ以下がより好ましく、８μｍ以上３０μｍ以下がさらに好ましく、１０μｍ以上２５μｍ以下が特に好ましい。正極基材の平均厚さを上記の範囲とすることで、正極基材の強度を高めつつ、蓄電素子の体積当たりのエネルギー密度を高めることができる。正極基材及び後述する負極基材の「平均厚さ」とは、所定の面積の基材を打ち抜いた際の打ち抜き質量を、基材の真密度及び打ち抜き面積で除した値をいう。 The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the energy storage element. The "average thickness" of the positive electrode substrate and the negative electrode substrate described below refers to the value obtained by dividing the punched mass when a substrate of a given area is punched out by the true density and punched area of the substrate.
中間層は、正極基材の表面の被覆層であり、炭素粒子等の導電性粒子を含むことで正極基材と正極合材層との接触抵抗を低減する。中間層の構成は特に限定されず、例えば樹脂バインダ及び導電性粒子を含有する組成物により形成できる。 The intermediate layer is a coating layer on the surface of the positive electrode substrate, and contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode composite layer. The composition of the intermediate layer is not particularly limited, and it can be formed, for example, from a composition containing a resin binder and conductive particles.
正極合材層は、正極活物質を含むいわゆる正極合材から形成される。また、正極合材層を形成する正極合材は、必要に応じて導電剤、バインダ、増粘剤、フィラー等の任意成分を含む。 The positive electrode mixture layer is formed from a so-called positive electrode mixture that contains a positive electrode active material. In addition, the positive electrode mixture that forms the positive electrode mixture layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as necessary.
本発明の一実施形態において、正極活物質は、一次粒子径に対する二次粒子径の比が５以下である二次粒子αを含む。このような二次粒子αを用いることで、高強度のアルミニウム合金製の正極基材を用いた場合に電気抵抗が大幅に増加するという不都合が改善される。 In one embodiment of the present invention, the positive electrode active material contains secondary particles α in which the ratio of the secondary particle diameter to the primary particle diameter is 5 or less. By using such secondary particles α, the disadvantage of a significant increase in electrical resistance when a positive electrode substrate made of a high-strength aluminum alloy is used is improved.
二次粒子αの一次粒子径に対する二次粒子径の比は、５以下であり、３以下が好ましく、２以下がより好ましく、１．５以下がさらに好ましく、１．２以下がよりさらに好ましく、１．１未満が特に好ましい。二次粒子αの一次粒子径に対する二次粒子径の比が上記上限以下であることにより、当該正極における導電性に係る改善効果がより高まる。 The ratio of the secondary particle diameter to the primary particle diameter of the secondary particles α is 5 or less, preferably 3 or less, more preferably 2 or less, even more preferably 1.5 or less, even more preferably 1.2 or less, and particularly preferably less than 1.1. When the ratio of the secondary particle diameter to the primary particle diameter of the secondary particles α is equal to or less than the above upper limit, the effect of improving the conductivity of the positive electrode is further enhanced.
二次粒子αの一次粒子径に対する二次粒子径の比の下限は、１であってよい。なお、一次粒子径の測定方法と二次粒子径の測定方法との違いから、二次粒子αの一次粒子径に対する二次粒子径の比の下限は、１未満、例えば０．９であってもよい。 The lower limit of the ratio of the secondary particle diameter to the primary particle diameter of the secondary particles α may be 1. Note that, due to differences in the methods for measuring the primary particle diameter and the secondary particle diameter, the lower limit of the ratio of the secondary particle diameter to the primary particle diameter of the secondary particles α may be less than 1, for example 0.9.
本発明の他の実施形態において、正極活物質は、実質的に凝集していない一次粒子βを含む。このような場合も、高強度のアルミニウム合金製の正極基材を用いた場合に電気抵抗が大幅に増加するという不都合が改善される。 In another embodiment of the present invention, the positive electrode active material contains primary particles β that are substantially non-aggregated. In such a case, the disadvantage of a large increase in electrical resistance when using a positive electrode substrate made of a high-strength aluminum alloy is also improved.
上記一次粒子βに関し、例えば、ＳＥＭにおいて観察される任意の５０個の正極活物質の粒子中、一次粒子βの数は、２５個超であることが好ましく、３０個以上であることがより好ましく、４０個以上であることがさらに好ましい。一次粒子βの含有量が多い場合、当該正極における導電性に係る改善効果がより高まる。 Regarding the primary particles β, for example, among any 50 particles of the positive electrode active material observed under SEM, the number of primary particles β is preferably more than 25, more preferably 30 or more, and even more preferably 40 or more. When the content of primary particles β is high, the effect of improving the conductivity of the positive electrode is further enhanced.
二次粒子αの一次粒子径及び一次粒子βの一次粒子径（すなわち一次粒子βの粒子径）としては、例えば０．１μｍ以上２０μｍ以下が好ましく、１μｍ以上１２μｍ以下がより好ましく、３μｍ以上８μｍ以下がさらに好ましく、４．５μｍ以上がよりさらに好ましい。二次粒子αの二次粒子径（すなわち二次粒子αの粒子径）としては、例えば０．１μｍ以上２０μｍ以下が好ましく、１μｍ以上１５μｍ以下がより好ましく、３μｍ以上１０μｍ以下がさらに好ましく、４μｍ以上８μｍ以下がよりさらに好ましい。これらの粒子径（一次粒子径及び二次粒子径）を上記範囲とすることで、導電性がより高まり、高強度のアルミニウム合金製の正極基材を用いた場合に電気抵抗が大幅に増加するという不都合がより改善される。 The primary particle diameter of the secondary particles α and the primary particle diameter of the primary particles β (i.e., the particle diameter of the primary particles β) are, for example, preferably 0.1 μm or more and 20 μm or less, more preferably 1 μm or more and 12 μm or less, even more preferably 3 μm or more and 8 μm or less, and even more preferably 4.5 μm or more. The secondary particle diameter of the secondary particles α (i.e., the particle diameter of the secondary particles α) is, for example, preferably 0.1 μm or more and 20 μm or less, more preferably 1 μm or more and 15 μm or less, even more preferably 3 μm or more and 10 μm or less, and even more preferably 4 μm or more and 8 μm or less. By setting these particle diameters (primary particle diameter and secondary particle diameter) within the above ranges, the conductivity is further increased, and the inconvenience of a significant increase in electrical resistance when a positive electrode substrate made of a high-strength aluminum alloy is used is further improved.
正極活物質には、単粒子系粒子（二次粒子α又は一次粒子β）以外の他の正極活物質が含まれていてもよい。但し、正極合材層に含まれる全ての正極活物質に対する単粒子系粒子の含有量は、８０質量％以上が好ましく、９０質量％以上がより好ましく、９９質量％以上がさらに好ましく、実質的に１００質量％であることがよりさらに好ましい。すなわち、当該正極においては、正極活物質として単粒子系粒子（二次粒子α又は一次粒子β）のみを用いることが特に好ましい。これにより、高強度のアルミニウム合金製の正極基材を用いた場合に電気抵抗が大幅に増加するという不都合をより十分に改善することができる。 The positive electrode active material may contain other positive electrode active materials besides the single particle particles (secondary particles α or primary particles β). However, the content of the single particle particles relative to all the positive electrode active materials contained in the positive electrode composite layer is preferably 80 mass% or more, more preferably 90 mass% or more, even more preferably 99 mass% or more, and even more preferably substantially 100 mass%. In other words, it is particularly preferable to use only single particle particles (secondary particles α or primary particles β) as the positive electrode active material in the positive electrode. This makes it possible to more fully improve the disadvantage of a significant increase in electrical resistance when a positive electrode substrate made of a high-strength aluminum alloy is used.
所定粒子径の正極活物質の粒子（単粒子系粒子）は、公知の方法により製造することができ、一次粒子径等は製造条件によって制御することができる。また、所定粒子径の正極活物質の粒子は、市販品を用いてもよい。活物質の製造工程において、焼成温度を高温にしたり焼成時間を長時間にしたりするなどして、複数の一次粒子を焼結させて粒子径を大きくすることが可能である。 Positive electrode active material particles (single particle particles) of a specified particle size can be manufactured by known methods, and the primary particle size, etc. can be controlled by manufacturing conditions. In addition, the positive electrode active material particles of a specified particle size may be commercially available products. In the manufacturing process of the active material, it is possible to increase the particle size by sintering multiple primary particles, for example, by increasing the firing temperature or lengthening the firing time.
正極活物質の粒子を構成する正極活物質の材料（種類）としては、公知の正極活物質の中から適宜選択できる。リチウムイオン二次電池用の正極活物質としては、通常、リチウムイオンを吸蔵及び放出することができる材料が用いられる。正極活物質としては、例えば、α－ＮａＦｅＯ２型結晶構造を有するリチウム遷移金属複合酸化物、スピネル型結晶構造を有するリチウム遷移金属複合酸化物、ポリアニオン化合物、カルコゲン化合物、硫黄等が挙げられる。α－ＮａＦｅＯ２型結晶構造を有するリチウム遷移金属複合酸化物として、例えば、Ｌｉ［ＬｉｘＮｉ１－ｘ］Ｏ２（０≦ｘ＜０．５）、Ｌｉ［ＬｉｘＮｉγＣｏ１－ｘ－γ］Ｏ２（０≦ｘ＜０．５、０＜γ＜１）、Ｌｉ［ＬｉｘＣｏ１－ｘ］Ｏ２（０≦ｘ＜０．５）、Ｌｉ［ＬｉｘＮｉγＭｎ１－ｘ－γ］Ｏ２（０≦ｘ＜０．５、０＜γ＜１）、Ｌｉ［ＬｉｘＮｉγＭｎβＣｏ１－ｘ－γ－β］Ｏ２（０≦ｘ＜０．５、０＜γ、０＜β、０．５＜γ＋β＜１）、Ｌｉ［ＬｉｘＮｉγＣｏβＡｌ１－ｘ－γ－β］Ｏ２（０≦ｘ＜０．５、０＜γ、０＜β、０．５＜γ＋β＜１）等が挙げられる。スピネル型結晶構造を有するリチウム遷移金属複合酸化物として、ＬｉｘＭｎ２Ｏ４、ＬｉｘＮｉγＭｎ２－γＯ４等が挙げられる。ポリアニオン化合物として、ＬｉＦｅＰＯ４、ＬｉＭｎＰＯ４、ＬｉＮｉＰＯ４、ＬｉＣｏＰＯ４、Ｌｉ３Ｖ２（ＰＯ４）３、Ｌｉ２ＭｎＳｉＯ４、Ｌｉ２ＣｏＰＯ４Ｆ等が挙げられる。カルコゲン化合物として、二硫化チタン、二硫化モリブデン、二酸化モリブデン等が挙げられる。これらの材料中の原子又はポリアニオンは、他の元素からなる原子又はアニオン種で一部が置換されていてもよい。 The material (type) of the positive electrode active material constituting the particles of the positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium ion secondary battery, a material capable of absorbing and releasing lithium ions is usually used. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO 2 type crystal structure, lithium transition metal composite oxides having a spinel type crystal structure, polyanion compounds, chalcogen compounds, sulfur, and the like. Examples of lithium transition metal composite oxides having an α-NaFeO 2 type crystal structure include Li[Li x Ni 1-x ]O 2 (0≦x<0.5), Li[Li x Ni γ Co 1-x-γ ]O 2 (0≦x<0.5, 0<γ<1), Li[Li x Co 1-x ]O 2 (0≦x<0.5), Li[Li x Ni γ Mn 1-x-γ ]O 2 (0≦x<0.5, 0<γ<1), Li[Li x Ni γ Mn β Co 1-x-γ-β ]O 2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), Li[Li x Ni γ Co β Al 1-x-γ-β ]O 2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), etc. Examples of lithium transition metal composite oxides having a spinel crystal structure include Li x Mn 2 O 4 and Li x Ni γ Mn 2-γ O 4 , etc. Examples of polyanion compounds include LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 , Li 3 V 2 (PO 4 ) 3 , Li 2 MnSiO 4 , and Li 2 CoPO 4 F, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide, etc. Atoms or polyanions in these materials may be partially substituted with atoms or anion species consisting of other elements.
正極活物質としては、リチウム遷移金属複合酸化物が好ましく、ニッケルと、コバルトと、マンガン又はアルミニウムとを含むリチウム遷移金属複合酸化物がより好ましく、ニッケルと、コバルトと、マンガンとを含むリチウム遷移金属複合酸化物がさらに好ましい。このリチウム遷移金属複合酸化物は、α－ＮａＦｅＯ２型結晶構造を有することが好ましい。このようなリチウム遷移金属複合酸化物を用いることで、エネルギー密度を高くすることなどができる。より具体的には、α－ＮａＦｅＯ２型結晶構造を有するリチウム遷移金属複合酸化物としては、下記式（１）で表される化合物が好ましい。
Ｌｉ１＋ｘＭｅ１－ｘＯ２ ・・・（１）
式（１）中、Ｍｅは、Ｎｉと、Ｃｏと、Ｍｎ又はＡｌとを含む金属（Ｌｉを除く）である。０≦ｘ＜１である。
As the positive electrode active material, a lithium transition metal composite oxide is preferable, a lithium transition metal composite oxide containing nickel, cobalt, and manganese or aluminum is more preferable, and a lithium transition metal composite oxide containing nickel, cobalt, and manganese is even more preferable. This lithium transition metal composite oxide preferably has an α-NaFeO 2 type crystal structure. By using such a lithium transition metal composite oxide, it is possible to increase the energy density. More specifically, as the lithium transition metal composite oxide having an α-NaFeO 2 type crystal structure, a compound represented by the following formula (1) is preferable.
Li 1+x Me 1-x O 2 ...(1)
In formula (1), Me is a metal (excluding Li) including Ni, Co, Mn, and Al, and 0≦x<1.
式（１）中のＭｅは、実質的にＮｉ、Ｃｏ及びＭｎの三元素、又はＮｉ、Ｃｏ及びＡｌの三元素から構成されていることが好ましく、Ｎｉ、Ｃｏ及びＭｎの三元素から構成されていることがより好ましい。但し、Ｍｅは、その他の金属が含有されていてもよい。 Me in formula (1) is preferably substantially composed of the three elements Ni, Co, and Mn, or the three elements Ni, Co, and Al, and more preferably composed of the three elements Ni, Co, and Mn. However, Me may contain other metals.
電気容量がより大きくなることなどの観点から、式（１）で表される化合物における各構成元素の好適な含有量（組成比）は以下の通りである。なお、モル比は、原子数比に等しい。 From the viewpoint of achieving a larger electric capacity, the preferred contents (composition ratios) of the constituent elements in the compound represented by formula (1) are as follows. Note that the molar ratio is equal to the atomic ratio.
式（１）中、Ｍｅに対するＮｉのモル比（Ｎｉ／Ｍｅ）の下限としては、０．１が好ましく、０．２、０．３又は０．４がより好ましい場合もある。一方、このモル比（Ｎｉ／Ｍｅ）の上限としては、０．９が好ましく、０．８、０．７、０．６、０．５、０．４又は０．３がより好ましい場合もある。 In formula (1), the lower limit of the molar ratio of Ni to Me (Ni/Me) is preferably 0.1, and in some cases 0.2, 0.3, or 0.4 is more preferable. On the other hand, the upper limit of this molar ratio (Ni/Me) is preferably 0.9, and in some cases 0.8, 0.7, 0.6, 0.5, 0.4, or 0.3 is more preferable.
式（１）中、Ｍｅに対するＣｏのモル比（Ｃｏ／Ｍｅ）の下限としては、０．０１が好ましく、０．１又は０．２がより好ましい場合もある。一方、このモル比（Ｃｏ／Ｍｅ）の上限としては、０．５が好ましく、０．４又は０．３がより好ましい場合もある。 In formula (1), the lower limit of the molar ratio of Co to Me (Co/Me) is preferably 0.01, and in some cases 0.1 or 0.2 is more preferable. On the other hand, the upper limit of this molar ratio (Co/Me) is preferably 0.5, and in some cases 0.4 or 0.3 is more preferable.
式（１）中、Ｍｅに対するＭｎのモル比（Ｍｎ／Ｍｅ）の下限としては、０．０５が好ましく、０．１又は０．２がより好ましい場合もある。Ｍｅに対するＡｌのモル比（Ａｌ／Ｍｅ）が０でない場合は、このモル比（Ｍｎ／Ｍｅ）は０であってもよい。一方、このモル比（Ｍｎ／Ｍｅ）の上限としては、０．６が好ましく、０．４又は０．３がより好ましい場合もある。 In formula (1), the lower limit of the molar ratio of Mn to Me (Mn/Me) is preferably 0.05, and in some cases 0.1 or 0.2 is more preferable. When the molar ratio of Al to Me (Al/Me) is not 0, this molar ratio (Mn/Me) may be 0. On the other hand, the upper limit of this molar ratio (Mn/Me) is preferably 0.6, and in some cases 0.4 or 0.3 is more preferable.
式（１）中、Ｍｅに対するＡｌのモル比（Ａｌ／Ｍｅ）の下限としては、０．０１が好ましく、０．０２又は０．０３がより好ましい場合もある。Ｍｅに対するＭｎのモル比（Ｍｎ／Ｍｅ）が０でない場合は、このモル比（Ａｌ／Ｍｅ）は０であってもよい。一方、このモル比（Ａｌ／Ｍｅ）の上限としては、０．３が好ましく、０．２又は０．１がより好ましい場合もある。 In formula (1), the lower limit of the molar ratio of Al to Me (Al/Me) is preferably 0.01, and in some cases 0.02 or 0.03 is more preferable. When the molar ratio of Mn to Me (Mn/Me) is not 0, this molar ratio (Al/Me) may be 0. On the other hand, the upper limit of this molar ratio (Al/Me) is preferably 0.3, and in some cases 0.2 or 0.1 is more preferable.
式（１）中、Ｍｅに対するＬｉのモル比（Ｌｉ／Ｍｅ）、即ち、（１＋α）／（１－α）は、１（α＝０）であってもよく、１．０超（α＞０）又は１．１以上が好ましい場合もある。一方、このモル比（Ｌｉ／Ｍｅ）の上限としては、１．６が好ましく、１．４又は１．２がより好ましい場合もある。 In formula (1), the molar ratio of Li to Me (Li/Me), i.e., (1+α)/(1-α), may be 1 (α=0), or may be preferably greater than 1.0 (α>0) or 1.1 or greater. On the other hand, the upper limit of this molar ratio (Li/Me) is preferably 1.6, and in some cases 1.4 or 1.2 is more preferable.
なお、リチウム遷移金属複合酸化物の組成比は、次の方法により完全放電状態としたときの組成比をいう。まず、蓄電素子を、０．０５Ｃの電流で通常使用時の充電終止電圧となるまで定電流充電し、満充電状態とする。３０分の休止後、０．０５Ｃの電流で通常使用時の下限電圧まで定電流放電する。解体し、正極を取り出し、金属リチウム電極を対極とした試験電池を組み立て、正極活物質１ｇあたり１０ｍＡの電流値で、正極電位が２．０Ｖ ｖｓ．Ｌｉ／Ｌｉ＋となるまで定電流放電を行い、正極を完全放電状態に調整する。再解体し、正極を取り出す。ジメチルカーボネートを用いて、取り出した正極に付着した非水電解質を十分に洗浄し、室温にて一昼夜乾燥後、正極活物質のリチウム遷移金属複合酸化物を採取する。採取したリチウム遷移金属複合酸化物を測定に供する。蓄電素子の解体から測定までの作業は露点－６０℃以下のアルゴン雰囲気中で行う。ここで、通常使用時とは、当該蓄電素子について推奨され、又は指定される充放電条件を採用して当該蓄電素子を使用する場合であり、当該蓄電素子のための充電器が用意されている場合は、その充電器を適用して当該蓄電素子を使用する場合をいう。 The composition ratio of the lithium transition metal composite oxide refers to the composition ratio when the battery is fully discharged by the following method. First, the storage element is charged at a constant current of 0.05C until the end-of-charge voltage during normal use is reached, and the battery is fully charged. After a 30-minute pause, the battery is discharged at a constant current of 0.05C to the lower limit voltage during normal use. The battery is disassembled, the positive electrode is removed, and a test battery is assembled with a metallic lithium electrode as the counter electrode. A constant current discharge is performed at a current value of 10 mA per 1 g of positive electrode active material until the positive electrode potential becomes 2.0 V vs. Li/Li + , and the positive electrode is adjusted to a fully discharged state. The battery is disassembled again, and the positive electrode is removed. The nonaqueous electrolyte attached to the removed positive electrode is thoroughly washed using dimethyl carbonate, and the battery is dried at room temperature for one day and night, and then the lithium transition metal composite oxide of the positive electrode active material is collected. The collected lithium transition metal composite oxide is subjected to measurement. The work from disassembly of the energy storage element to measurement is carried out in an argon atmosphere with a dew point of -60° C. or less. Here, normal use refers to the case where the energy storage element is used under the charge/discharge conditions recommended or specified for the energy storage element, and in the case where a charger for the energy storage element is provided, the charger is used to use the energy storage element.
好適なリチウム遷移金属複合酸化物としては、例えばＬｉＮｉ１／３Ｃｏ１／３Ｍｎ１／３Ｏ２、ＬｉＮｉ３／５Ｃｏ１／５Ｍｎ１／５Ｏ２、ＬｉＮｉ１／２Ｃｏ１／５Ｍｎ３／１０Ｏ２、ＬｉＮｉ１／２Ｃｏ３／１０Ｍｎ１／５Ｏ２、ＬｉＮｉ８／１０Ｃｏ１／１０Ｍｎ１／１０Ｏ２、ＬｉＮｉ０．８Ｃｏ０．１５Ａｌ０．０５Ｏ２等を挙げることができる。 Suitable examples of lithium transition metal composite oxides include LiNi1 / 3Co1 / 3Mn1 / 3O2 , LiNi3/5Co1/ 5Mn1/5O2 , LiNi1 / 2Co1 / 5Mn3 / 10O2 , LiNi1 / 2Co3 / 10Mn1 / 5O2 , LiNi8/ 10Co1/10Mn1/10O2 , and LiNi0.8Co0.15Al0.05O2 .
正極活物質の材料は、１種を単独で用いてもよく、２種以上を混合して用いてもよい。なかでも、正極活物質は、リチウム遷移金属複合酸化物を、使用する全正極活物質のうち５０質量％以上（好ましくは７０から１００質量％、より好ましくは８０から１００質量％）の割合で含有することが好ましく、実質的にリチウム金属複合酸化物のみからなる正極活物質を用いることがより好ましい。 The material for the positive electrode active material may be used alone or in combination of two or more. In particular, the positive electrode active material preferably contains lithium transition metal composite oxide in a proportion of 50% by mass or more (preferably 70 to 100% by mass, more preferably 80 to 100% by mass) of the total positive electrode active material used, and it is more preferable to use a positive electrode active material consisting essentially of lithium metal composite oxide.
正極合材層における正極活物質の含有量は、８０質量％以上９９質量％以下が好ましく、８５質量％以上９８質量％以下がより好ましく、９０質量％以上９７質量％以下がより好ましい。正極合材層における正極活物質の含有量を上記範囲とすることで、導電性及びエネルギー密度をバランスよく高めることができる。 The content of the positive electrode active material in the positive electrode composite layer is preferably 80% by mass or more and 99% by mass or less, more preferably 85% by mass or more and 98% by mass or less, and even more preferably 90% by mass or more and 97% by mass or less. By setting the content of the positive electrode active material in the positive electrode composite layer within the above range, it is possible to increase the conductivity and energy density in a balanced manner.
導電剤は、導電性を有する材料であれば特に限定されない。このような導電剤としては、例えば炭素質材料、金属、導電性セラミックス等が挙げられる。炭素質材料としては、黒鉛化炭素、非黒鉛化炭素、グラフェン系炭素等が挙げられる。非黒鉛化炭素としては、カーボンナノファイバー、ピッチ系炭素繊維、カーボンブラック等が挙げられる。カーボンブラックとしては、ファーネスブラック、アセチレンブラック、ケッチェンブラック等が挙げられる。グラフェン系炭素としては、グラフェン、カーボンナノチューブ（ＣＮＴ）、フラーレン等が挙げられる。導電剤の形状としては、粉状、繊維状等が挙げられる。導電剤としては、これらの材料の１種を単独で用いてもよく、２種以上を混合して用いてもよい。また、これらの材料を複合化して用いてもよい。例えば、カーボンブラックとＣＮＴとを複合化した材料を用いてもよい。これらの中でも、電子伝導性及び塗工性の観点よりカーボンブラックが好ましく、中でもアセチレンブラックが好ましい。 The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, conductive ceramics, and the like. Examples of carbonaceous materials include graphitized carbon, non-graphitized carbon, graphene-based carbon, and the like. Examples of non-graphitized carbon include carbon nanofiber, pitch-based carbon fiber, carbon black, and the like. Examples of carbon black include furnace black, acetylene black, ketjen black, and the like. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerene, and the like. Examples of the conductive agent include powder and fiber. As the conductive agent, one of these materials may be used alone, or two or more of them may be mixed and used. These materials may also be used in combination. For example, a material in which carbon black and CNT are combined may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity and coatability, and acetylene black is particularly preferred.
正極合材層における導電剤の含有量は、１質量％以上１０質量％以下が好ましく、３質量％以上９質量％以下がより好ましい。導電剤の含有量を上記の範囲とすることで、蓄電素子のエネルギー密度を高めることができる。 The content of the conductive agent in the positive electrode composite layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent in the above range, the energy density of the storage element can be increased.
バインダとしては、例えばフッ素樹脂（ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）等）、ポリエチレン、ポリプロピレン、ポリアクリル、ポリイミド等の熱可塑性樹脂；エチレン－プロピレン－ジエンゴム（ＥＰＤＭ）、スルホン化ＥＰＤＭ、スチレンブタジエンゴム（ＳＢＲ）、フッ素ゴム等のエラストマー；多糖類高分子等が挙げられる。 Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), and fluororubber; polysaccharide polymers, etc.
正極合材層におけるバインダの含有量は、１質量％以上１０質量％以下が好ましく、３質量％以上８質量％以下がより好ましく、５質量％以下がさらに好ましい場合もある。バインダの含有量を上記下限以上とすることで、活物質を安定して保持することができる。また、バインダの含有量を上記上限以下とすることで、正極活物質の含有量を増やし、エネルギー密度を高めることができる。 The binder content in the positive electrode composite layer is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 8% by mass or less, and in some cases even more preferably 5% by mass or less. By setting the binder content to the above lower limit or more, the active material can be stably held. Furthermore, by setting the binder content to the above upper limit or less, the content of the positive electrode active material can be increased, and the energy density can be increased.
増粘剤としては、カルボキシメチルセルロース（ＣＭＣ）、メチルセルロース等の多糖類高分子が挙げられる。また、増粘剤がリチウムと反応する官能基を有する場合、予めメチル化等によりこの官能基を失活させておくことが好ましい。増粘剤を使用する場合、正極合材層における増粘剤の含有量は、５質量％以下、さらには１質量％以下とすることが好ましい。ここで開示される技術は、正極合材層が増粘剤を含まない態様で好ましく実施され得る。 Examples of thickeners include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. In addition, when the thickener has a functional group that reacts with lithium, it is preferable to deactivate this functional group in advance by methylation or the like. When a thickener is used, the content of the thickener in the positive electrode mixture layer is preferably 5 mass % or less, and more preferably 1 mass % or less. The technology disclosed herein can be preferably implemented in an embodiment in which the positive electrode mixture layer does not contain a thickener.
フィラーは、特に限定されない。フィラーとしては、ポリプロピレン、ポリエチレン等のポリオレフィン、二酸化ケイ素、酸化アルミニウム、二酸化チタン、酸化カルシウム、酸化ストロンチウム、酸化バリウム、酸化マグネシウム、アルミノケイ酸塩等の無機酸化物、水酸化マグネシウム、水酸化カルシウム、水酸化アルミニウム等の水酸化物、炭酸カルシウム等の炭酸塩、フッ化カルシウム、フッ化バリウム、硫酸バリウム等の難溶性のイオン結晶、窒化アルミニウム、窒化ケイ素等の窒化物、タルク、モンモリロナイト、ベーマイト、ゼオライト、アパタイト、カオリン、ムライト、スピネル、オリビン、セリサイト、ベントナイト、マイカ等の鉱物資源由来物質又はこれらの人造物等が挙げられる。フィラーを使用する場合、正極合材層におけるフィラーの含有量は、５質量％以下、さらには１質量％以下とすることが好ましい。ここで開示される技術は、正極合材層がフィラーを含まない態様で好ましく実施され得る。 The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, aluminum oxide, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, poorly soluble ion crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof. When a filler is used, the content of the filler in the positive electrode mixture layer is preferably 5% by mass or less, and further preferably 1% by mass or less. The technology disclosed herein can be preferably implemented in an embodiment in which the positive electrode mixture layer does not contain a filler.
正極合材層は、Ｂ、Ｎ、Ｐ、Ｆ、Ｃｌ、Ｂｒ、Ｉ等の典型非金属元素、Ｌｉ、Ｎａ、Ｍｇ、Ａｌ、Ｋ、Ｃａ、Ｚｎ、Ｇａ、Ｇｅ、Ｓｎ、Ｓｒ、Ｂａ等の典型金属元素、Ｓｃ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｍｏ、Ｚｒ、Ｎｂ、Ｗ等の遷移金属元素を正極活物質、導電剤、バインダ、増粘剤及びフィラー以外の成分として含有してもよい。 The positive electrode composite layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.
正極合材層の見かけの密度としては、２．５ｇ／ｃｍ３以上４．５ｇ／ｃｍ３以下が好ましく、２．８ｇ／ｃｍ３以上４．０ｇ／ｃｍ３以下がより好ましい。正極合材層の見かけの密度が上記下限以上であることで、エネルギー密度を高めることなどができる。一方、見かけの密度が上記上限以下である正極合材層は、一般的なプレス装置等によって効率的に製造することができる。なお、正極合材層の見かけの密度とは、正極合材層の質量（ｇ）を見かけの体積（ｃｍ３）で除することによって求められる値である。正極合材層の見かけの体積は、正極合材層の平均厚さと面積との積である。正極合材層の平均厚さは、任意の５ヶ所で測定した厚さの平均値とする。 The apparent density of the positive electrode mixture layer is preferably 2.5 g/cm 3 or more and 4.5 g/cm 3 or less, and more preferably 2.8 g/cm 3 or more and 4.0 g/cm 3 or less. When the apparent density of the positive electrode mixture layer is equal to or more than the lower limit, the energy density can be increased. On the other hand, a positive electrode mixture layer having an apparent density equal to or less than the upper limit can be efficiently manufactured by a general press device or the like. The apparent density of the positive electrode mixture layer is a value obtained by dividing the mass (g) of the positive electrode mixture layer by the apparent volume (cm 3 ). The apparent volume of the positive electrode mixture layer is the product of the average thickness and area of the positive electrode mixture layer. The average thickness of the positive electrode mixture layer is the average value of the thicknesses measured at any five points.
正極の作製は、例えば正極基材に直接又は中間層を介して、正極合材ペーストを塗布し、乾燥させることにより、未プレスの正極合材層を形成すること、及び未プレスの正極合材層が形成された未プレス正極をプレスすることにより行うことができる。正極合材ペーストには、正極活物質、及び任意成分である導電剤、バインダ等、正極合材層を構成する各成分が含まれる。正極合材ペーストには、通常さらに分散媒が含まれる。 The positive electrode can be produced, for example, by applying a positive electrode composite paste to a positive electrode substrate directly or via an intermediate layer, drying the paste to form an unpressed positive electrode composite layer, and then pressing the unpressed positive electrode on which the unpressed positive electrode composite layer has been formed. The positive electrode composite paste contains the components that make up the positive electrode composite layer, including the positive electrode active material, and optional components such as a conductive agent and a binder. The positive electrode composite paste usually also contains a dispersion medium.
上記プレスは、未プレスの正極合材層表面を加圧することにより行われる。上記プレスは、従来公知のプレス装置によって行うことができる。このプレスにより、正極活物質の粒子の少なくとも一部が正極基材に食い込み、良好な導電性を確保することができると推測される。 The pressing is performed by applying pressure to the surface of the unpressed positive electrode composite layer. The pressing can be performed using a conventional pressing device. It is presumed that this pressing allows at least a portion of the particles of the positive electrode active material to penetrate into the positive electrode substrate, ensuring good electrical conductivity.
＜蓄電素子＞
本発明の一実施形態に係る蓄電素子は、正極、負極及び電解質を有する。以下、蓄電素子の一例として、非水電解質二次電池（以下、単に「二次電池」ともいう。）について説明する。上記正極及び負極は、通常、セパレータを介して積層又は巻回により交互に重畳された電極体を形成する。この電極体は容器に収納され、この容器内に非水電解質が充填される。上記非水電解質は、正極と負極との間に介在する。また、上記容器としては、二次電池の容器として通常用いられる公知の金属容器、樹脂容器等を用いることができる。
<Electricity storage element>
The electric storage element according to one embodiment of the present invention has a positive electrode, a negative electrode, and an electrolyte. Hereinafter, a non-aqueous electrolyte secondary battery (hereinafter, simply referred to as a "secondary battery") will be described as an example of an electric storage element. The positive electrode and the negative electrode are usually stacked or wound alternately with a separator interposed therebetween to form an electrode body. This electrode body is housed in a container, and the container is filled with a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. In addition, as the container, a known metal container, a resin container, or the like that is usually used as a container for a secondary battery can be used.
（正極）
当該二次電池に備わる正極は、上述した本発明の一実施形態に係る正極である。
(Positive electrode)
The positive electrode of the secondary battery is the positive electrode according to one embodiment of the present invention described above.
（負極）
上記負極は、負極基材、及びこの負極基材に直接又は中間層を介して積層される負極合材層を有する。上記中間層は正極の中間層と同様の構成とすることができる。
(Negative electrode)
The negative electrode has a negative electrode substrate and a negative electrode mixture layer laminated on the negative electrode substrate directly or via an intermediate layer. The intermediate layer may have the same structure as the intermediate layer of the positive electrode.
負極基材は、正極基材と同様の構成とすることができるが、材質としては、銅、ニッケル、ステンレス鋼、ニッケルメッキ鋼等の金属又はそれらの合金が用いられ、銅又は銅合金が好ましい。つまり、負極基材としては銅箔が好ましい。銅箔としては、圧延銅箔、電解銅箔等が例示される。 The negative electrode substrate can have the same structure as the positive electrode substrate, but the material used is a metal such as copper, nickel, stainless steel, or nickel-plated steel, or an alloy thereof, with copper or a copper alloy being preferred. In other words, copper foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.
負極基材の平均厚さは、２μｍ以上３５μｍ以下が好ましく、３μｍ以上３０μｍ以下がより好ましく、４μｍ以上２５μｍ以下がさらに好ましく、５μｍ以上２０μｍ以下が特に好ましい。負極基材の平均厚さを上記の範囲とすることで、負極基材の強度を高めつつ、二次電池の体積当たりのエネルギー密度を高めることができる。 The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, even more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per volume of the secondary battery.
負極合材層は、一般的に負極活物質を含むいわゆる負極合材から形成される。また、負極合材層を形成する負極合材は、必要に応じて導電剤、バインダ、増粘剤、フィラー等の任意成分を含む。導電剤、バインダ、増粘剤、フィラー等の任意成分は、正極合材層と同様のものを用いることができる。負極合材層は、実質的に金属Ｌｉ等の負極活物質のみからなる層であってもよい。 The negative electrode mixture layer is generally formed from a so-called negative electrode mixture that contains a negative electrode active material. The negative electrode mixture that forms the negative electrode mixture layer also contains optional components such as a conductive agent, binder, thickener, and filler as necessary. The optional components such as a conductive agent, binder, thickener, and filler can be the same as those in the positive electrode mixture layer. The negative electrode mixture layer may be a layer that is substantially composed of only a negative electrode active material such as metallic Li.
負極合材層は、Ｂ、Ｎ、Ｐ、Ｆ、Ｃｌ、Ｂｒ、Ｉ等の典型非金属元素、Ｌｉ、Ｎａ、Ｍｇ、Ａｌ、Ｋ、Ｃａ、Ｚｎ、Ｇａ、Ｇｅ、Ｓｎ、Ｓｒ、Ｂａ等の典型金属元素、Ｓｃ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｍｏ、Ｚｒ、Ｔａ、Ｈｆ、Ｎｂ、Ｗ等の遷移金属元素を負極活物質、導電剤、バインダ、増粘剤、フィラー以外の成分として含有してもよい。 The negative electrode composite layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.
負極活物質としては、公知の負極活物質の中から適宜選択できる。例えばリチウムイオン二次電池用の負極活物質としては、通常、リチウムイオンを吸蔵及び放出することができる材料が用いられる。負極活物質としては、例えば、金属Ｌｉ；Ｓｉ、Ｓｎ等の金属又は半金属；Ｓｉ酸化物、Ｔｉ酸化物、Ｓｎ酸化物等の金属酸化物又は半金属酸化物；Ｌｉ４Ｔｉ５Ｏ１２、ＬｉＴｉＯ２、ＴｉＮｂ２Ｏ７等のチタン含有酸化物；ポリリン酸化合物；炭化ケイ素；黒鉛（グラファイト）、非黒鉛質炭素（易黒鉛化性炭素又は難黒鉛化性炭素）等の炭素材料等が挙げられる。これらの材料の中でも、黒鉛及び非黒鉛質炭素が好ましい。負極合材層においては、これら材料の１種を単独で用いてもよく、２種以上を混合して用いてもよい。 The negative electrode active material can be appropriately selected from known negative electrode active materials. For example, as the negative electrode active material for a lithium ion secondary battery, a material capable of absorbing and releasing lithium ions is usually used. Examples of the negative electrode active material include metal Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; titanium-containing oxides such as Li 4 Ti 5 O 12 , LiTiO 2, and TiNb 2 O 7 ; polyphosphate compounds; silicon carbide; carbon materials such as graphite and non-graphitic carbon (easily graphitized carbon or non-graphitizable carbon). Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode mixture layer, one of these materials may be used alone, or two or more may be mixed and used.
「黒鉛」とは、充放電前又は放電状態において、エックス線回折法により決定される（００２）面の平均格子面間隔（ｄ００２）が０．３３ｎｍ以上０．３４ｎｍ未満の炭素材料をいう。黒鉛としては、天然黒鉛、人造黒鉛が挙げられる。安定した物性の材料を入手できるという観点で、人造黒鉛が好ましい。 "Graphite" refers to a carbon material having an average lattice spacing (d 002 ) of the (002) plane determined by X-ray diffraction before charging and discharging or in a discharged state of 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of obtaining a material with stable physical properties.
「非黒鉛質炭素」とは、充放電前又は放電状態においてエックス線回折法により決定される（００２）面の平均格子面間隔（ｄ００２）が０．３４ｎｍ以上０．４２ｎｍ以下の炭素材料をいう。非黒鉛質炭素としては、難黒鉛化性炭素や、易黒鉛化性炭素が挙げられる。非黒鉛質炭素としては、例えば、樹脂由来の材料、石油ピッチまたは石油ピッチ由来の材料、石油コークスまたは石油コークス由来の材料、植物由来の材料、アルコール由来の材料等が挙げられる。 "Non-graphitic carbon" refers to a carbon material in which the average lattice spacing (d002) of the ( 002 ) plane, as determined by X-ray diffraction before charging and discharging or in a discharged state, is 0.34 nm or more and 0.42 nm or less. Examples of non-graphitic carbon include carbon that is difficult to graphitize and carbon that is easy to graphitize. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.
ここで、炭素材料の「放電状態」とは、負極活物質として炭素材料を含む負極を作用極として、金属リチウム電極を対極として用いた単極電池において、開回路電圧が０．７Ｖ以上である状態をいう。開回路状態での金属リチウム対極の電位は、Ｌｉの酸化還元電位とほぼ等しいため、上記単極電池における開回路電圧は、Ｌｉの酸化還元電位に対する炭素材料を含む負極の電位とほぼ同等である。つまり、上記単極電池における開回路電圧が０．７Ｖ以上であることは、負極活物質である炭素材料から、充放電に伴い吸蔵放出可能なリチウムイオンが十分に放出されていることを意味する。 Here, the "discharged state" of the carbon material refers to a state in which the open circuit voltage is 0.7 V or more in a single-electrode battery using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and a metallic lithium electrode as the counter electrode. Since the potential of the metallic lithium counter electrode in the open circuit state is approximately equal to the redox potential of Li, the open circuit voltage in the single-electrode battery is approximately equal to the potential of the negative electrode containing the carbon material relative to the redox potential of Li. In other words, an open circuit voltage of 0.7 V or more in the single-electrode battery means that sufficient lithium ions that can be absorbed and released during charging and discharging have been released from the carbon material, which is the negative electrode active material.
「難黒鉛化性炭素」とは、上記ｄ００２が０．３６ｎｍ以上０．４２ｎｍ以下の炭素材料をいう。 The term "non-graphitizable carbon" refers to a carbon material having the above d002 of 0.36 nm or more and 0.42 nm or less.
「易黒鉛化性炭素」とは、上記ｄ００２が０．３４ｎｍ以上０．３６ｎｍ未満の炭素材料をいう。 The term "graphitizable carbon" refers to a carbon material having the above d002 of 0.34 nm or more and less than 0.36 nm.
負極活物質の形態が粒子（粉体）の場合、負極活物質の平均粒径は、例えば、１ｎｍ以上１００μｍ以下とすることができる。負極活物質が例えば炭素材料である場合、その平均粒径は１μｍ以上１００μｍ以下が好ましい場合がある。負極活物質が、金属、半金属、金属酸化物、半金属酸化物、チタン含有酸化物、ポリリン酸化合物等である場合、その平均粒径は、１ｎｍ以上１μｍ以下が好ましい場合がある。負極活物質の平均粒径を上記下限以上とすることで、負極活物質の製造又は取り扱いが容易になる。負極活物質の平均粒径を上記上限以下とすることで、合材層の導電性が向上する。粉体を所定の粒径で得るためには粉砕機や分級機等が用いられる。また、負極活物質が金属Ｌｉの場合、その形態は箔状又は板状であってもよい。なお、負極活物質の平均粒径は、二次粒子径であり、上述した正極活物質の二次粒子径の測定方法に準じて測定される値である。 When the negative electrode active material is in the form of particles (powder), the average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is, for example, a carbon material, the average particle size may be preferably 1 μm or more and 100 μm or less. When the negative electrode active material is a metal, a semi-metal, a metal oxide, a semi-metal oxide, a titanium-containing oxide, a polyphosphate compound, or the like, the average particle size may be preferably 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to the above lower limit or more, the negative electrode active material can be easily manufactured or handled. By setting the average particle size of the negative electrode active material to the above upper limit or less, the conductivity of the composite layer is improved. In order to obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. In addition, when the negative electrode active material is metal Li, the form may be a foil or a plate. The average particle size of the negative electrode active material is the secondary particle size, and is a value measured in accordance with the above-mentioned method for measuring the secondary particle size of the positive electrode active material.
負極合材層における負極活物質の含有量は、例えば負極合材層が負極合材から形成されている場合、６０質量％以上９９質量％以下が好ましく、９０質量％以上９８質量％以下がより好ましい。負極活物質の含有量を上記の範囲とすることで、負極合材層の高エネルギー密度化と製造性を両立できる。負極活物質が金属Ｌｉである場合、負極合材層における負極活物質の含有量は９９質量％以上であってよく、１００質量％であってよい。 When the negative electrode mixture layer is formed from a negative electrode mixture, the content of the negative electrode active material in the negative electrode mixture layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material in the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode mixture layer. When the negative electrode active material is metallic Li, the content of the negative electrode active material in the negative electrode mixture layer may be 99% by mass or more, or may be 100% by mass.
（セパレータ）
セパレータは、公知のセパレータの中から適宜選択できる。セパレータとして、例えば、基材層のみからなるセパレータ、基材層の一方の面又は双方の面に耐熱粒子とバインダとを含む耐熱層が形成されたセパレータ等を使用することができる。セパレータの基材層の材質としては、例えば、織布、不織布、多孔質樹脂フィルム等が挙げられる。これらの材質の中でも、強度の観点から多孔質樹脂フィルムが好ましく、非水電解質の保液性の観点から不織布が好ましい。セパレータの基材層の材料としては、シャットダウン機能の観点から例えばポリエチレン、ポリプロピレン等のポリオレフィンが好ましく、耐酸化分解性の観点から例えばポリイミドやアラミド等が好ましい。セパレータの基材層として、これらの樹脂を複合した材料を用いてもよい。
(Separator)
The separator can be appropriately selected from known separators. For example, a separator consisting of only a base layer, a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both sides of the base layer, etc. can be used as the separator. Examples of the material of the base layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these materials, a porous resin film is preferable from the viewpoint of strength, and a nonwoven fabric is preferable from the viewpoint of the liquid retention of the non-aqueous electrolyte. As the material of the base layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of shutdown function, and polyimide and aramid are preferable from the viewpoint of oxidation decomposition resistance. A material obtained by combining these resins may be used as the base layer of the separator.
耐熱層に含まれる耐熱粒子は、大気下で室温から５００℃に加熱したときの質量減少が５％以下であるものが好ましく、大気下で室温から８００℃に加熱したときの質量減少が５％以下であるものがさらに好ましい。加熱したときの質量減少が所定以下である材料として無機化合物が挙げられる。無機化合物として、例えば、酸化鉄、酸化ケイ素、酸化アルミニウム、酸化チタン、チタン酸バリウム、酸化ジルコニウム、酸化カルシウム、酸化ストロンチウム、酸化バリウム、酸化マグネシウム、アルミノケイ酸塩等の酸化物；水酸化マグネシウム、水酸化カルシウム、水酸化アルミニウム等の水酸化物；窒化アルミニウム、窒化ケイ素等の窒化物；炭酸カルシウム等の炭酸塩；硫酸バリウム等の硫酸塩；フッ化カルシウム、フッ化バリウム等の難溶性のイオン結晶；シリコン、ダイヤモンド等の共有結合性結晶；タルク、モンモリロナイト、ベーマイト、ゼオライト、アパタイト、カオリン、ムライト、スピネル、オリビン、セリサイト、ベントナイト、マイカ等の鉱物資源由来物質又はこれらの人造物等が挙げられる。無機化合物として、これらの物質の単体又は複合体を単独で用いてもよく、２種以上を混合して用いてもよい。これらの無機化合物の中でも、二次電池の安全性の観点から、酸化ケイ素、酸化アルミニウム、又はアルミノケイ酸塩が好ましい。 The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500°C in air, and more preferably have a mass loss of 5% or less when heated from room temperature to 800°C in air. Examples of materials that have a mass loss of a predetermined amount or less when heated include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ion crystals such as calcium fluoride and barium fluoride; covalent crystals such as silicon and diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of the safety of the secondary battery.
セパレータの空孔率は、強度の観点から８０体積％以下が好ましく、放電性能の観点から２０体積％以上が好ましい。ここで、「空孔率」とは、体積基準の値であり、水銀ポロシメータでの測定値を意味する。 The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured using a mercury porosimeter.
セパレータとして、ポリマーと非水電解質とで構成されるポリマーゲルを用いてもよい。ポリマーとして、例えば、ポリアクリロニトリル、ポリエチレンオキシド、ポリプロピレンオキシド、ポリメチルメタアクリレート、ポリビニルアセテート、ポリビニルピロリドン、ポリフッ化ビニリデン等が挙げられる。ポリマーゲルを用いると、漏液を抑制する効果がある。セパレータとして、上述したような多孔質樹脂フィルム又は不織布等とポリマーゲルを併用してもよい。 As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyvinylidene fluoride, etc. Using a polymer gel has the effect of suppressing leakage. As the separator, a polymer gel may be used in combination with the porous resin film or nonwoven fabric as described above.
（非水電解質）
非水電解質としては、公知の非水電解質の中から適宜選択できる。非水電解質には、非水電解液を用いてもよい。非水電解液は、非水溶媒と、この非水溶媒に溶解されている電解質塩とを含む。
(Non-aqueous electrolyte)
The nonaqueous electrolyte may be appropriately selected from known nonaqueous electrolytes. The nonaqueous electrolyte may be a nonaqueous electrolyte solution. The nonaqueous electrolyte solution includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent.
非水溶媒としては、公知の非水溶媒の中から適宜選択できる。非水溶媒としては、環状カーボネート、鎖状カーボネート、カルボン酸エステル、リン酸エステル、スルホン酸エステル、エーテル、アミド、ニトリル等が挙げられる。非水溶媒として、これらの化合物に含まれる水素原子の一部がハロゲンに置換されたものを用いてもよい。 The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylate esters, phosphate esters, sulfonate esters, ethers, amides, and nitriles. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds are substituted with halogens may also be used.
環状カーボネートとしては、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート（ＢＣ）、ビニレンカーボネート（ＶＣ）、ビニルエチレンカーボネート（ＶＥＣ）、クロロエチレンカーボネート、フルオロエチレンカーボネート（ＦＥＣ）、ジフルオロエチレンカーボネート（ＤＦＥＣ）、スチレンカーボネート、１－フェニルビニレンカーボネート、１，２－ジフェニルビニレンカーボネート等が挙げられる。これらの中でもＥＣが好ましい。 Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.
鎖状カーボネートとしては、ジエチルカーボネート（ＤＥＣ）、ジメチルカーボネート（ＤＭＣ）、エチルメチルカーボネート（ＥＭＣ）、ジフェニルカーボネート、トリフルオロエチルメチルカーボネート、ビス（トリフルオロエチル）カーボネート等が挙げられる。これらの中でもＤＭＣ及びＥＭＣが好ましい。 Examples of chain carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, DMC and EMC are preferred.
非水溶媒として、環状カーボネート及び鎖状カーボネートの少なくとも一方を用いることが好ましく、環状カーボネートと鎖状カーボネートとを併用することがより好ましい。環状カーボネートを用いることで、電解質塩の解離を促進して非水電解液のイオン伝導度を向上させることができる。鎖状カーボネートを用いることで、非水電解液の粘度を低く抑えることができる。環状カーボネートと鎖状カーボネートとを併用する場合、環状カーボネートと鎖状カーボネートとの体積比率（環状カーボネート：鎖状カーボネート）としては、例えば、５：９５から５０：５０の範囲とすることが好ましい。 As the non-aqueous solvent, it is preferable to use at least one of a cyclic carbonate and a chain carbonate, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. By using a cyclic carbonate, it is possible to promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. By using a chain carbonate, it is possible to keep the viscosity of the non-aqueous electrolyte low. When a cyclic carbonate and a chain carbonate are used in combination, it is preferable that the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is, for example, in the range of 5:95 to 50:50.
電解質塩としては、公知の電解質塩から適宜選択できる。電解質塩としては、リチウム塩、ナトリウム塩、カリウム塩、マグネシウム塩、オニウム塩等が挙げられる。これらの中でもリチウム塩が好ましい。 The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, etc. Among these, lithium salts are preferred.
リチウム塩としては、ＬｉＰＦ６、ＬｉＰＯ２Ｆ２、ＬｉＢＦ４、ＬｉＣｌＯ４、ＬｉＮ（ＳＯ２Ｆ）２等の無機リチウム塩、ＬｉＳＯ３ＣＦ３、ＬｉＮ（ＳＯ２ＣＦ３）２、ＬｉＮ（ＳＯ２Ｃ２Ｆ５）２、ＬｉＮ（ＳＯ２ＣＦ３）（ＳＯ２Ｃ４Ｆ９）、ＬｉＣ（ＳＯ２ＣＦ３）３、ＬｉＣ（ＳＯ２Ｃ２Ｆ５）３等のハロゲン化炭化水素基を有するリチウム塩等が挙げられる。これらの中でも、無機リチウム塩が好ましく、ＬｉＰＦ６がより好ましい。 Examples of the lithium salt include inorganic lithium salts such as LiPF6 , LiPO2F2 , LiBF4 , LiClO4 , and LiN( SO2F ) 2 , and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3 , LiN( SO2CF3 ) 2 , LiN ( SO2C2F5 ) 2 , LiN( SO2CF3 )( SO2C4F9 ), LiC (SO2CF3 ) 3 , and LiC( SO2C2F5 ) 3 . Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred .
非水電解液における電解質塩の含有量は、０．１ｍｏｌ／ｄｍ３以上２．５ｍｏｌ／ｄｍ３以下であると好ましく、０．３ｍｏｌ／ｄｍ３以上２．０ｍｏｌ／ｄｍ３以下であるとより好ましく、０．５ｍｏｌ／ｄｍ３以上１．７ｍｏｌ／ｄｍ３以下であるとさらに好ましく、０．７ｍｏｌ／ｄｍ３以上１．５ｍｏｌ／ｄｍ３以下であると特に好ましい。電解質塩の含有量を上記の範囲とすることで、非水電解液のイオン伝導度を高めることができる。 The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol/dm 3 or more and 2.5 mol/dm 3 or less, more preferably 0.3 mol/dm 3 or more and 2.0 mol/dm 3 or less, even more preferably 0.5 mol/dm 3 or more and 1.7 mol/dm 3 or less, and particularly preferably 0.7 mol/dm 3 or more and 1.5 mol/dm 3 or less. By setting the content of the electrolyte salt in the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.
非水電解液は、添加剤を含んでもよい。添加剤としては、例えばビフェニル、アルキルビフェニル、ターフェニル、ターフェニルの部分水素化体、シクロヘキシルベンゼン、ｔ－ブチルベンゼン、ｔ－アミルベンゼン、ジフェニルエーテル、ジベンゾフラン等の芳香族化合物；２－フルオロビフェニル、ｏ－シクロヘキシルフルオロベンゼン、ｐ－シクロヘキシルフルオロベンゼン等の上記芳香族化合物の部分ハロゲン化物；２，４－ジフルオロアニソール、２，５－ジフルオロアニソール、２，６－ジフルオロアニソール、３，５－ジフルオロアニソール等のハロゲン化アニソール化合物；無水コハク酸、無水グルタル酸、無水マレイン酸、無水シトラコン酸、無水グルタコン酸、無水イタコン酸、シクロヘキサンジカルボン酸無水物；亜硫酸エチレン、亜硫酸プロピレン、亜硫酸ジメチル、硫酸ジメチル、硫酸エチレン、スルホラン、ジメチルスルホン、ジエチルスルホン、ジメチルスルホキシド、ジエチルスルホキシド、テトラメチレンスルホキシド、ジフェニルスルフィド、４，４’－ビス（２，２－ジオキソ－１，３，２－ジオキサチオラン）、４－メチルスルホニルオキシメチル－２，２－ジオキソ－１，３，２－ジオキサチオラン、チオアニソール、ジフェニルジスルフィド、ジピリジニウムジスルフィド、パーフルオロオクタン、ホウ酸トリストリメチルシリル、リン酸トリストリメチルシリル、チタン酸テトラキストリメチルシリル等が挙げられる。これら添加剤は、１種を単独で用いてもよく、２種以上を混合して用いてもよい。 The non-aqueous electrolyte may contain additives. Examples of additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexyl benzene, and cyclohexyl benzene. Examples of the additives include hexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, and tetrakistrimethylsilyl titanate. These additives may be used alone or in combination of two or more.
非水電解液に含まれる添加剤の含有量は、非水電解液全体の質量に対して０．０１質量％以上１０質量％以下が好ましく、０．１質量％以上７質量％以下がより好ましく、０．２質量％以上５質量％以下がさらに好ましく、０．３質量％以上３質量％以下が特に好ましい。添加剤の含有量を上記の範囲とすることで、高温保存後の容量維持性能又は充放電サイクル性能を向上させたり、安全性をより向上させたりすることができる。 The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass. By setting the content of the additive within the above range, it is possible to improve the capacity retention performance or charge/discharge cycle performance after high-temperature storage, and to further improve safety.
非水電解質には、固体電解質を用いてもよく、非水電解液と固体電解質とを併用してもよい。 The non-aqueous electrolyte may be a solid electrolyte, or a non-aqueous electrolyte may be used in combination with a solid electrolyte.
固体電解質としては、リチウム、ナトリウム、カルシウム等のイオン伝導性を有し、常温（例えば１５℃から２５℃）において固体である任意の材料から選択できる。固体電解質としては、例えば、硫化物固体電解質、酸化物固体電解質、及び酸窒化物固体電解質、ポリマー固体電解質等が挙げられる。 The solid electrolyte can be selected from any material that has ionic conductivity such as lithium, sodium, calcium, etc., and is solid at room temperature (e.g., 15°C to 25°C). Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, polymer solid electrolytes, etc.
硫化物固体電解質としては、リチウムイオン二次電池の場合、例えば、Ｌｉ２Ｓ－Ｐ２Ｓ５、ＬｉＩ－Ｌｉ２Ｓ－Ｐ２Ｓ５、Ｌｉ１０Ｇｅ－Ｐ２Ｓ１２等が挙げられる。 Examples of sulfide solid electrolytes for lithium ion secondary batteries include Li 2 S—P 2 S 5 , LiI—Li 2 S—P 2 S 5 , and Li 10 Ge—P 2 S 12 .
本実施形態の二次電池（蓄電素子）は、高強度のアルミニウム合金製の正極基材を有する正極を用いた場合に電気抵抗が大幅に増加するという不都合が改善されている。従って、当該二次電池は、高出力用途にも好適に適用することができる。当該二次電池は、高出力用途として例えば、電気自動車（ＥＶ）、ハイブリッド自動車（ＨＥＶ）、プラグインハイブリッド自動車（ＰＨＥＶ）等の自動車用電源等に好適に用いられる。 The secondary battery (energy storage element) of this embodiment improves on the disadvantage that electrical resistance increases significantly when a positive electrode having a positive electrode substrate made of a high-strength aluminum alloy is used. Therefore, the secondary battery can be suitably applied to high-output applications. The secondary battery is suitably used for high-output applications such as automotive power sources for electric vehicles (EVs), hybrid vehicles (HEVs), plug-in hybrid vehicles (PHEVs), etc.
本実施形態の二次電池の形状については特に限定されるものではなく、例えば、円筒型電池、ラミネートフィルム型電池、角型電池、扁平型電池、コイン型電池、ボタン型電池等が挙げられる。 The shape of the secondary battery of this embodiment is not particularly limited, and examples include cylindrical batteries, laminated film batteries, square batteries, flat batteries, coin batteries, button batteries, etc.
当該二次電池（蓄電素子）は、例えば、正極を作製すること、負極を作製すること、非水電解質を調製すること、正極及び負極を、セパレータを介して積層又は巻回することにより交互に重畳された電極体を形成すること、正極及び負極（電極体）を容器に収容すること、並びに上記容器に上記非水電解質を注入することを備える製造方法により製造することができる。注入後、注入口を封止することにより当該二次電池を得ることができる。 The secondary battery (electric storage element) can be manufactured by a manufacturing method that includes, for example, preparing a positive electrode, preparing a negative electrode, preparing a non-aqueous electrolyte, forming an electrode body in which the positive and negative electrodes are alternately stacked by stacking or rolling them with a separator interposed therebetween, housing the positive and negative electrodes (electrode body) in a container, and injecting the non-aqueous electrolyte into the container. After injection, the injection port is sealed to obtain the secondary battery.
図１に角型電池の一例としての蓄電素子１を示す。なお、同図は、容器内部を透視した図としている。セパレータを挟んで巻回された正極及び負極を有する電極体２が角型の容器３に収納される。正極は正極リード４１を介して正極端子４と電気的に接続されている。負極は負極リード５１を介して負極端子５と電気的に接続されている。
Figure 1 shows an
＜蓄電装置の構成＞
本実施形態の蓄電素子は、電気自動車（ＥＶ）、ハイブリッド自動車（ＨＥＶ）、プラグインハイブリッド自動車（ＰＨＥＶ）等の自動車用電源、パーソナルコンピュータ、通信端末等の電子機器用電源、又は電力貯蔵用電源等に、複数の蓄電素子１を集合して構成した蓄電ユニット（バッテリーモジュール）として搭載することができる。この場合、蓄電ユニットに含まれる少なくとも一つの蓄電素子に対して、本発明の一実施形態に係る技術が適用されていればよい。
<Configuration of Power Storage Device>
The energy storage element of this embodiment can be mounted as an energy storage unit (battery module) formed by assembling a plurality of
図２に、電気的に接続された二以上の蓄電素子１が集合した蓄電ユニット２０をさらに集合した蓄電装置３０の一例を示す。蓄電装置３０は、二以上の蓄電素子１を電気的に接続するバスバ（図示せず）、二以上の蓄電ユニット２０を電気的に接続するバスバ（図示せず）等を備えていてもよい。蓄電ユニット２０又は蓄電装置３０は、一以上の蓄電素子の状態を監視する状態監視装置（図示せず）を備えていてもよい。
Figure 2 shows an example of a
＜その他の実施形態＞
本発明は、上記実施形態に限定されるものではなく、本発明の要旨を逸脱しない範囲内において種々変更を加えてもよい。例えば、ある実施形態の構成に他の実施形態の構成を追加することができ、また、ある実施形態の構成の一部を他の実施形態の構成又は周知技術に置き換えることができる。さらに、ある実施形態の構成の一部を削除することができる。また、ある実施形態の構成に対して周知技術を付加することができる。
<Other embodiments>
The present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the scope of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or a well-known technique. Furthermore, a part of the configuration of one embodiment may be deleted. Also, a well-known technique may be added to the configuration of one embodiment.
上記実施形態では、蓄電素子が充放電可能な非水電解質二次電池（例えばリチウムイオン二次電池）として用いられる場合について説明したが、蓄電素子の種類、形状、寸法、容量等は任意である。本発明の正極及び蓄電素子は、種々の非水電解質二次電池、電気二重層キャパシタ又はリチウムイオンキャパシタ等のキャパシタにも適用できる。また、本発明の正極及び蓄電素子は、電解質が非水電解質以外の電解質である蓄電素子にも適用できる。 In the above embodiment, the case where the storage element is used as a chargeable and dischargeable non-aqueous electrolyte secondary battery (e.g., a lithium ion secondary battery) has been described, but the type, shape, size, capacity, etc. of the storage element are arbitrary. The positive electrode and storage element of the present invention can also be applied to various non-aqueous electrolyte secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors. The positive electrode and storage element of the present invention can also be applied to storage elements in which the electrolyte is an electrolyte other than a non-aqueous electrolyte.
以下、実施例によって本発明をさらに具体的に説明するが、本発明は以下の実施例に限定されるものではない。 The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.
以下に用いた正極活物質及び正極基材を示す。
・正極活物質Ａ：正極活物質であるＬｉＮｉ０．６Ｃｏ０．２Ｍｎ０．２Ｏ２の粒子
一次粒子径４．０μｍ、二次粒子径４．４μｍ、二次粒子径／一次粒子径＝１．１
・正極活物質Ｂ：正極活物質であるＬｉＮｉ０．６Ｃｏ０．２Ｍｎ０．２Ｏ２の粒子
一次粒子径１．９μｍ、二次粒子径８．９μｍ、二次粒子径／一次粒子径＝４．７
・正極活物質Ｃ：正極活物質であるＬｉＮｉ０．６Ｃｏ０．２Ｍｎ０．２Ｏ２の粒子
一次粒子径５．０μｍ、二次粒子径５．１μｍ、二次粒子径／一次粒子径＝１．０
・正極活物質Ｘ：正極活物質であるＬｉＮｉ０．６Ｃｏ０．２Ｍｎ０．２Ｏ２の粒子
一次粒子径０．６μｍ、二次粒子径８．５μｍ、二次粒子径／一次粒子径＝１３．４
・正極基材ａ：アルミニウム合金箔Ａ３００３（引張強さ２７０Ｎ／ｍｍ２）
・正極基材ｘ：アルミニウム箔Ａ１０８５（引張強さ１８０Ｎ／ｍｍ２）
The positive electrode active material and positive electrode substrate used are shown below.
Positive electrode active material A: Positive electrode active material LiNi0.6Co0.2Mn0.2O2 particles Primary particle diameter 4.0 μm , secondary particle diameter 4.4 μm, secondary particle diameter/primary particle diameter = 1.1
Positive electrode active material B: Positive electrode active material LiNi0.6Co0.2Mn0.2O2 particles Primary particle diameter 1.9 μm , secondary particle diameter 8.9 μm, secondary particle diameter/primary particle diameter = 4.7
Positive electrode active material C: Positive electrode active material LiNi0.6Co0.2Mn0.2O2 particles Primary particle diameter 5.0 μm , secondary particle diameter 5.1 μm, secondary particle diameter/primary particle diameter = 1.0
Positive electrode active material X: Positive electrode active material LiNi0.6Co0.2Mn0.2O2 particles Primary particle diameter 0.6 μm , secondary particle diameter 8.5 μm, secondary particle diameter/primary particle diameter = 13.4
Positive electrode substrate a: Aluminum alloy foil A3003 (tensile strength 270 N/mm 2 )
Positive electrode substrate x: Aluminum foil A1085 (tensile strength 180 N/mm 2 )
［実施例１］
（正極の作製）
正極活物質として上記正極活物質Ａ、導電剤としてカーボンブラック、及びバインダとしてポリフッ化ビニリデン（ＰＶＤＦ）を用いた。正極活物質ＡとカーボンブラックとＰＶＤＦとの質量比を９４：３：３とした混合物に、Ｎ－メチル－ピロリドン（ＮＭＰ）を適量加えて粘度を調整し、正極合材ペーストを作製した。この正極合材ペーストを、上記正極基材ａの表面に塗布し、乾燥することにより正極合材層を作製した。その後、ロールプレスを行い、正極合材層の見かけの密度を３．２ｇ／ｃｍ３とした実施例１の正極を得た。
[Example 1]
(Preparation of Positive Electrode)
The positive electrode active material A was used as the positive electrode active material, carbon black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder. A suitable amount of N-methyl-pyrrolidone (NMP) was added to a mixture of the positive electrode active material A, carbon black, and PVDF in a mass ratio of 94:3:3 to adjust the viscosity, and a positive electrode composite paste was prepared. This positive electrode composite paste was applied to the surface of the positive electrode substrate a, and dried to prepare a positive electrode composite layer. Thereafter, roll pressing was performed to obtain a positive electrode of Example 1 in which the apparent density of the positive electrode composite layer was 3.2 g/cm 3 .
［実施例２、３、比較例１、参考例１から３、参考比較例１］
正極活物質の種類及び正極基材の種類を表１に示す通りとしたこと以外は実施例１と同様にして、実施例２、３、比較例１、参考例１から３及び参考比較例１の各正極を作製した。
[Examples 2 and 3, Comparative Example 1, Reference Examples 1 to 3, and Reference Comparative Example 1]
The positive electrodes of Examples 2 and 3, Comparative Example 1, Reference Examples 1 to 3, and Reference Comparative Example 1 were prepared in the same manner as in Example 1, except that the types of positive electrode active materials and the types of positive electrode substrates were as shown in Table 1.
［評価］
（表面抵抗）
得られた各正極について、正極合材層上に抵抗率計（三菱化学アナリテック製「Ｌｏｒｅｓｔａ－ＥＰ ＭＣＰ－Ｔ３６０）の二探針プローブを押し当て、表面抵抗を測定した。測定された表面抵抗を表１に示す。
また、高強度ではないアルミニウム製の正極基材（正極基材ｘ）を用いた参考例又は参考比較例の表面抵抗（Ｒｘ）に対する、正極基材を高強度のアルミニウム合金製の正極基材（正極基材ａ）に替えた実施例又は比較例の表面抵抗（Ｒａ）の増加率（（（Ｒａ－Ｒｘ）／Ｒｘ）×１００％）をあわせて表１に示す。
[evaluation]
(Surface Resistance)
For each of the obtained positive electrodes, a two-probe probe of a resistivity meter ("Loresta-EP MCP-T360" manufactured by Mitsubishi Chemical Analytech) was pressed against the positive electrode mixture layer to measure the surface resistance. The measured surface resistance is shown in Table 1.
Table 1 also shows the rate of increase ((R a -R x )/R x ) x 100%) of the surface resistance (R a ) of an example or comparative example in which the positive electrode substrate was replaced with a positive electrode substrate made of a high-strength aluminum alloy (positive electrode substrate a) relative to the surface resistance (R x ) of a reference example or comparative example in which a positive electrode substrate made of aluminum (positive electrode substrate x ) that is not high strength was used.
比較例１と参考比較例１との対比から、一次粒子径に対する二次粒子径の比が大きい正極活物質Ｘを用いた場合、高強度ではないアルミニウム製の正極基材ｘを用いた参考比較例１の正極に対して、高強度のアルミニウム合金製の正極基材ａを用いた比較例１の正極の抵抗は大幅に増加していることがわかる（抵抗増加率５４％）。 Comparing Comparative Example 1 with Reference Comparative Example 1, it can be seen that when using a positive electrode active material X with a large ratio of secondary particle diameter to primary particle diameter, the resistance of the positive electrode of Comparative Example 1, which uses a positive electrode substrate a made of a high-strength aluminum alloy, is significantly increased (resistance increase rate: 54%) compared to the positive electrode of Reference Comparative Example 1, which uses a positive electrode substrate x made of aluminum that is not high strength.
一方、実施例１から３と参考例１から３との対比から、正極活物質として単粒子系粒子（正極活物質ＡからＣ）を用いた場合、高強度ではないアルミニウム製の正極基材ｘを用いた参考例１から３の各正極に対する、高強度のアルミニウム合金製の正極基材ａを用いた実施例１から３の各正極の抵抗増加率は小さい（抵抗増加率１７から２９％）。すなわち、実施例１から３の各正極は、高強度のアルミニウム合金製の正極基材を用いた場合に電気抵抗が大幅に増加するという不都合が改善されていることがわかる。 On the other hand, a comparison between Examples 1 to 3 and Reference Examples 1 to 3 shows that when single-particle particles (positive electrode active materials A to C) are used as the positive electrode active material, the resistance increase rate of each of the positive electrodes of Examples 1 to 3 using a positive electrode substrate a made of a high-strength aluminum alloy is small (resistance increase rate 17 to 29%) compared to each of the positive electrodes of Reference Examples 1 to 3 using a positive electrode substrate x made of aluminum that is not high strength. In other words, it can be seen that each of the positive electrodes of Examples 1 to 3 has improved the inconvenience of a large increase in electrical resistance when a positive electrode substrate made of a high-strength aluminum alloy is used.
本発明は、パーソナルコンピュータ、通信端末等の電子機器、自動車などの電源として使用される非水電解質蓄電素子、及びこれに備わる正極などに適用できる。 The present invention can be applied to nonaqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles, as well as to the positive electrodes provided therein.
１ 蓄電素子
２ 電極体
３ 容器
４ 正極端子
４１ 正極リード
５ 負極端子
５１ 負極リード
２０ 蓄電ユニット
３０ 蓄電装置
Claims (4)
上記正極基材に積層され、正極活物質を含有する正極合材層と
を備え、
上記正極基材の引張強さが２３０Ｎ／ｍｍ２以上であり、
上記正極活物質は、一次粒子径に対する二次粒子径の比が１．５以下である二次粒子を含む蓄電素子用の正極。 A positive electrode substrate containing aluminum;
a positive electrode mixture layer that is laminated on the positive electrode substrate and contains a positive electrode active material,
The positive electrode substrate has a tensile strength of 230 N/mm2 or more ;
The positive electrode active material is a positive electrode for an electricity storage element, which contains secondary particles having a ratio of secondary particle diameter to primary particle diameter of 1.5 or less.
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| JP2001243949A (en) | 2000-02-28 | 2001-09-07 | Toyota Central Res & Dev Lab Inc | Lithium transition metal composite oxide for positive electrode active material of lithium secondary battery, method for producing the same, and lithium secondary battery using the same |
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| JP2009064560A (en) | 2006-08-29 | 2009-03-26 | Toyo Aluminium Kk | Aluminum alloy foil for current collector |
| JP2008150651A (en) | 2006-12-15 | 2008-07-03 | Mitsubishi Alum Co Ltd | Aluminum alloy foil with excellent bending resistance for lithium-ion battery electrode material, and its manufacturing method |
| JP2012021205A (en) | 2010-07-16 | 2012-02-02 | Kobe Steel Ltd | Hardened aluminum foil for battery collector |
| JP2015067872A (en) | 2013-09-30 | 2015-04-13 | 日立金属株式会社 | Electrolytic aluminum foil, electrode using the same and electricity storage device |
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