JP2024088363A - Negative electrode plate and lithium ion secondary battery - Google Patents
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims description 23
- 229910001416 lithium ion Inorganic materials 0.000 title claims description 23
- 239000000203 mixture Substances 0.000 claims abstract description 87
- 239000007773 negative electrode material Substances 0.000 claims abstract description 86
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 69
- 229910002804 graphite Inorganic materials 0.000 claims abstract description 52
- 239000010439 graphite Substances 0.000 claims abstract description 52
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- 229910010584 LiFeO2 Inorganic materials 0.000 description 1
- 229910052493 LiFePO4 Inorganic materials 0.000 description 1
- 229910002099 LiNi0.5Mn1.5O4 Inorganic materials 0.000 description 1
- 229910015009 LiNiCoMnO2 Inorganic materials 0.000 description 1
- 229910003005 LiNiO2 Inorganic materials 0.000 description 1
- 229910001228 Li[Ni1/3Co1/3Mn1/3]O2 (NCM 111) Inorganic materials 0.000 description 1
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- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- FKQOMXQAEKRXDM-UHFFFAOYSA-N [Li].[As] Chemical compound [Li].[As] FKQOMXQAEKRXDM-UHFFFAOYSA-N 0.000 description 1
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Abstract
【課題】高温保存耐久性に優れ、入出力特性にも優れた二次電池を提供することができる負極板を提供する。
【解決手段】負極板は、負極集電体と負極活物質層とを有する。負極活物質層は、負極活物質及び結着材を含む負極合剤層から形成される。負極活物質は、黒鉛粒子の表面を非晶質炭素で被覆した非晶質コート黒鉛を含む。非晶質コート黒鉛の吸油量は４０ｃｃ／１００ｇ以上５３ｃｃ／１００ｇ以下である。負極集電体上に形成した負極合剤層を圧力１９０ＭＰａで圧縮したときの負極合剤層の密度は、１．５５ｇ／ｃｃ以上１．７６ｇ／ｃｃ以下である。
【選択図】なし
The present invention provides a negative electrode plate capable of producing a secondary battery having excellent high-temperature storage durability and excellent input/output characteristics.
[Solution] The negative electrode plate has a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is formed from a negative electrode mixture layer containing a negative electrode active material and a binder. The negative electrode active material contains amorphous coated graphite in which the surfaces of graphite particles are coated with amorphous carbon. The amorphous coated graphite has an oil absorption of 40 cc/100 g or more and 53 cc/100 g or less. When the negative electrode mixture layer formed on the negative electrode current collector is compressed at a pressure of 190 MPa, the density of the negative electrode mixture layer is 1.55 g/cc or more and 1.76 g/cc or less.
[Selection diagram] None
Description
本発明は、負極板、及びそれを含むリチウムイオン二次電池に関する。 The present invention relates to a negative electrode plate and a lithium-ion secondary battery including the same.
リチウムイオン二次電池では、負極板の反応面積を増加させると、入出力特性（ハイレート特性）が改善する一方でサイクル耐久性が低下し、負極板の反応面積を減少させると、サイクル耐久性が改善する一方で入出力特性が低下する傾向にある。このようにリチウムイオン二次電池の入出力特性とサイクル耐久性とはトレードオフの関係にあるため、これらを両立することは難しい。入出力特性及びサイクル耐久性に優れたリチウムイオン二次電池を得るために、黒鉛粒子を非晶質炭素等の結晶性の低い炭素材料で被覆した負極活物質を用いることがある（特許文献１及び２等）。 In lithium-ion secondary batteries, increasing the reaction area of the negative plate improves the input/output characteristics (high-rate characteristics) but reduces cycle durability, while decreasing the reaction area of the negative plate tends to improve cycle durability but reduce input/output characteristics. As such, there is a trade-off between the input/output characteristics and cycle durability of lithium-ion secondary batteries, and it is difficult to achieve both. In order to obtain lithium-ion secondary batteries with excellent input/output characteristics and cycle durability, a negative electrode active material in which graphite particles are coated with a carbon material with low crystallinity, such as amorphous carbon, may be used (Patent Documents 1 and 2, etc.).
特許文献１には、負極活物質の材料物性を調整することにより、リチウムイオン二次電池の電池特性が向上することが開示されている。特許文献２には、負極活物質の材料物性とともに、非水電解液に含まれる特定の支持塩の含有量を調整することにより、リチウムイオン二次電池の電池特性が向上することが開示されている。 Patent Document 1 discloses that the battery characteristics of a lithium-ion secondary battery are improved by adjusting the material properties of the negative electrode active material. Patent Document 2 discloses that the battery characteristics of a lithium-ion secondary battery are improved by adjusting the content of a specific supporting salt contained in the non-aqueous electrolyte, in addition to the material properties of the negative electrode active material.
上記のように、負極活物質として非晶質炭素等の炭素材料で被覆した黒鉛粒子を用いることにより、リチウムイオン二次電池の入出力特性及びサイクル耐久性を向上することができる。しかし、負極板は通常、負極活物質と結着材等とを混合して得られた負極合剤スラリーを、集電体上に塗布して乾燥し、圧縮することによって作製される。このような加工工程を経ると負極活物質の材料物性が変化することがある。そのため、負極板の製品設計にあたり、負極活物質の材料物性のみならず、当該負極活物質を用いて得られる負極板の物性も考慮する必要がある。 As described above, by using graphite particles coated with a carbon material such as amorphous carbon as the negative electrode active material, the input/output characteristics and cycle durability of a lithium-ion secondary battery can be improved. However, a negative electrode plate is usually produced by mixing the negative electrode active material with a binder and applying a negative electrode mixture slurry onto a current collector, drying it, and compressing it. This processing step can cause the material properties of the negative electrode active material to change. Therefore, when designing a negative electrode plate, it is necessary to consider not only the material properties of the negative electrode active material, but also the properties of the negative electrode plate obtained using the negative electrode active material.
本開示は、高温で保存したときにも放電容量を良好に維持できる高温保存耐久性に優れ、入出力特性にも優れた二次電池を提供することができる負極板、及び、リチウムイオン二次電池の提供を目的とする。 The present disclosure aims to provide a negative electrode plate and a lithium-ion secondary battery that can provide a secondary battery with excellent high-temperature storage durability that can maintain a good discharge capacity even when stored at high temperatures and excellent input/output characteristics.
本開示は、以下の負極板及びリチウムイオン二次電池を提供する。
〔１〕 負極集電体と負極活物質層とを有する負極板であって、
前記負極活物質層は、負極活物質及び結着材を含む負極合剤層から形成され、
前記負極活物質は、黒鉛粒子の表面を非晶質炭素で被覆した非晶質コート黒鉛を含み、
前記非晶質コート黒鉛の吸油量は、４１ｃｃ／１００ｇ以上５３ｃｃ／１００ｇ以下であり、
前記負極集電体上に形成した前記負極合剤層を圧力１９０ＭＰａで圧縮したときの前記負極合剤層の密度は、１．５５ｇ／ｃｃ以上１．７６ｇ／ｃｃ以下である、負極板。
〔２〕前記結着材は、セルロース系結着材及びスチレンブタジエンゴムのうちの少なくとも一方を含む、〔１〕に記載の負極板。
〔３〕 前記結着材は、セルロース系結着材を含む、〔２〕に記載の負極板。
〔４〕 前記負極活物質層の単位質量あたりの比表面積は、１．７７ｍ２／ｇ以上２．０５ｍ２／ｇ以下である、〔１〕～〔３〕のいずれかに記載の負極板。
〔５〕 前記黒鉛粒子は、人造黒鉛である、〔１〕～〔４〕のいずれかに記載の負極板。
〔６〕 前記負極板は、リチウムイオン二次電池用負極板である、〔１〕～〔５〕のいずれかに記載の負極板。
〔７〕 〔１〕～〔５〕のいずれかに記載の負極板を含む、リチウムイオン二次電池。
The present disclosure provides the following negative electrode plate and lithium ion secondary battery.
[1] A negative electrode plate having a negative electrode current collector and a negative electrode active material layer,
The negative electrode active material layer is formed of a negative electrode mixture layer including a negative electrode active material and a binder,
The negative electrode active material includes amorphous-coated graphite in which the surface of a graphite particle is coated with amorphous carbon,
The oil absorption of the amorphous coated graphite is 41 cc/100 g or more and 53 cc/100 g or less,
a density of the negative electrode mixture layer when the negative electrode mixture layer formed on the negative electrode current collector is compressed at a pressure of 190 MPa is 1.55 g/cc or more and 1.76 g/cc or less.
[2] The negative electrode plate according to [1], wherein the binder includes at least one of a cellulose-based binder and a styrene-butadiene rubber.
[3] The negative electrode plate according to [2], wherein the binder includes a cellulose-based binder.
[4] The negative electrode plate according to any one of [1] to [3], wherein the specific surface area per unit mass of the negative electrode active material layer is 1.77 m 2 /g or more and 2.05 m 2 /g or less.
[5] The negative electrode plate according to any one of [1] to [4], wherein the graphite particles are artificial graphite.
[6] The negative electrode plate according to any one of [1] to [5], which is a negative electrode plate for a lithium ion secondary battery.
[7] A lithium ion secondary battery comprising the negative electrode plate according to any one of [1] to [5].
本開示の負極板によれば、優れた高温保存耐久性を有しながらも入出力特性がさらに改善されたリチウムイオン二次電池を提供することができる。 The negative electrode plate disclosed herein can provide a lithium-ion secondary battery that has excellent high-temperature storage durability while also exhibiting improved input/output characteristics.
（負極板）
本実施形態の負極板は、負極集電体と負極活物質層とを有する。負極板は通常、負極集電体の片面又は両面に負極活物質層を有する。負極集電体は例えば、銅及び銅合金等の銅材料を用いて構成された金属箔である。負極板は、二次電池用の負極板であることができ、特にリチウムイオン二次電池用の負極板であることができる。
(Negative plate)
The negative electrode plate of this embodiment has a negative electrode current collector and a negative electrode active material layer. The negative electrode plate usually has a negative electrode active material layer on one or both sides of the negative electrode current collector. The negative electrode current collector is, for example, a metal foil made of a copper material such as copper or a copper alloy. The negative electrode plate can be a negative electrode plate for a secondary battery, and in particular, can be a negative electrode plate for a lithium ion secondary battery.
負極活物質層は、負極活物質及び結着材を含む負極合剤層から形成される。そのため、負極活物質層も負極活物質及び結着材を含む。負極合剤層は、負極板が有する負極活物質層を形成するために負極集電体上に形成される層である。後述するように負極集電体上に負極合剤スラリーを塗布して乾燥し、圧縮して負極活物質層を形成する場合、負極合剤層は、塗布した負極合剤スラリーを乾燥した後であって圧縮する前の層である。負極活物質層は上記のように通常、負極合剤層を圧縮することにより形成される。負極活物質層及び負極合剤層はいずれも、少なくとも負極活物質及び結着材を含んでいればよく、繊維状炭素等の導電助剤を含んでいてもよい。 The negative electrode active material layer is formed from a negative electrode mixture layer containing a negative electrode active material and a binder. Therefore, the negative electrode active material layer also contains a negative electrode active material and a binder. The negative electrode mixture layer is a layer formed on the negative electrode current collector to form the negative electrode active material layer of the negative electrode plate. As described below, when the negative electrode mixture slurry is applied to the negative electrode current collector, dried, and compressed to form the negative electrode active material layer, the negative electrode mixture layer is a layer after the applied negative electrode mixture slurry is dried and before compression. The negative electrode active material layer is usually formed by compressing the negative electrode mixture layer as described above. Both the negative electrode active material layer and the negative electrode mixture layer need only contain at least the negative electrode active material and the binder, and may contain a conductive assistant such as fibrous carbon.
負極活物質は、黒鉛粒子の表面を非晶質炭素で被覆した非晶質コート黒鉛を含む。非晶質コート黒鉛を含む負極活物質層を備えた負極板を用いることにより、負極活物質がリチウムイオンの吸蔵及び放出を良好に行うことができ、電解質の分解物等が負極活物質表面に堆積してリチウムイオンの吸蔵及び放出を阻害することを抑制することができる。これにより、入出力特性に優れ、高温で保存したときにも放電容量を良好に維持できる高温保存耐久性にも優れる二次電池を得ることができる。 The negative electrode active material includes amorphous-coated graphite, which is a graphite particle whose surface is coated with amorphous carbon. By using a negative electrode plate having a negative electrode active material layer that includes amorphous-coated graphite, the negative electrode active material can absorb and release lithium ions well, and it is possible to prevent electrolyte decomposition products and the like from accumulating on the surface of the negative electrode active material and impeding the absorption and release of lithium ions. This makes it possible to obtain a secondary battery that has excellent input/output characteristics and high-temperature storage durability that can maintain a good discharge capacity even when stored at high temperatures.
非晶質コート黒鉛に含まれる黒鉛粒子は、人造黒鉛であってもよく、天然黒鉛であってもよく、これらの両方であってもよいが、人造黒鉛であることが好ましい。人造黒鉛は、天然黒鉛に比べると硬度が大きく変形しにくいため、負極合剤層を圧縮したときに非晶質コート黒鉛の非晶質炭素が割れることを抑制できる。これにより、後述する負極合剤層の圧縮密度を、後述する範囲に調整しやすくなる。 The graphite particles contained in the amorphous coated graphite may be artificial graphite, natural graphite, or both, but artificial graphite is preferable. Artificial graphite is harder and less likely to deform than natural graphite, so that the amorphous carbon of the amorphous coated graphite can be prevented from cracking when the negative electrode mixture layer is compressed. This makes it easier to adjust the compressed density of the negative electrode mixture layer, which will be described later, to the range described later.
非晶質コート黒鉛に含まれる非晶質炭素は、アモルファス構造を有する炭素材料をいい、例えばカーボンブラックや活性炭等が挙げられる。非晶質炭素は、黒鉛粒子の表面の一部を被覆してもよく、黒鉛粒子の表面全体を被覆してもよい。黒鉛粒子の表面を被覆する非晶質炭素の厚みは、例えば１ｎｍ以上１μｍ以下であってもよい。非晶質コート黒鉛は、例えば、黒鉛粒子とピッチとを混合し、ピッチを焼成して炭素化することによって得ることができる。 The amorphous carbon contained in the amorphous-coated graphite refers to a carbon material having an amorphous structure, such as carbon black or activated carbon. The amorphous carbon may cover a part of the surface of the graphite particle, or may cover the entire surface of the graphite particle. The thickness of the amorphous carbon covering the surface of the graphite particle may be, for example, 1 nm or more and 1 μm or less. The amorphous-coated graphite can be obtained, for example, by mixing graphite particles with pitch and baking the pitch to carbonize it.
非晶質コート黒鉛の吸油量は、４０ｃｃ／１００ｇ以上５３ｃｃ／１００ｇ以下であり、好ましくは４１ｃｃ／１００ｇ以上５１ｃｃ／１００ｇ以下であり、より好ましくは４３ｃｃ／１００ｇ以上５０ｃｃ／１００ｇ以下であり、さらに好ましくは４５ｃｃ／１００ｇ以上５０ｃｃ／１００ｇ以下である。非晶質コート黒鉛の吸油量が上記した範囲内であることにより、非晶質コート黒鉛の表面に過剰に結着材が吸着し、リチウムイオンの吸蔵及び放出を阻害することを抑制できるため、二次電池の入出力特性をさらに改善することができる。 The oil absorption of the amorphous coated graphite is 40cc/100g or more and 53cc/100g or less, preferably 41cc/100g or more and 51cc/100g or less, more preferably 43cc/100g or more and 50cc/100g or less, and even more preferably 45cc/100g or more and 50cc/100g or less. By having the oil absorption of the amorphous coated graphite within the above range, it is possible to suppress excessive adsorption of the binder on the surface of the amorphous coated graphite, which would inhibit the absorption and release of lithium ions, thereby further improving the input/output characteristics of the secondary battery.
非晶質コート黒鉛の吸油量は、次の手順で算出することができる。まず、非晶質コート黒鉛にアマニ油を２ｃｃ／ｍｉｎの添加速度で添加したときの粘度特性の変化をトルク検出器により検出し、その出力をトルクに換算する。続いて、得られたトルクのうちの最大トルクの７０％に相当するトルクが発生したときのアマニ油の添加量を、非晶質コート黒鉛１００ｇ当たりの添加量に換算し、これを非晶質コート黒鉛の吸油量として算出する。トルク検出器としては、例えば株式会社あさひ総研製「Ｓ－５００」を用いることができる。 The oil absorption of amorphous coated graphite can be calculated by the following procedure. First, the change in viscosity characteristics when linseed oil is added to the amorphous coated graphite at an addition rate of 2 cc/min is detected by a torque detector, and the output is converted into torque. Next, the amount of linseed oil added when a torque equivalent to 70% of the maximum torque is generated is converted into the amount added per 100 g of amorphous coated graphite, and this is calculated as the oil absorption of the amorphous coated graphite. As a torque detector, for example, the "S-500" manufactured by Asahi Research Institute Co., Ltd. can be used.
非晶質コート黒鉛の吸油量は、例えば、非晶質コート黒鉛の粒径、タップ密度、比表面積（ＢＥＴ）、及び形状からなる群より選ばれる１つ以上を調整することにより、調整することができる。 The oil absorption of the amorphous coated graphite can be adjusted, for example, by adjusting one or more of the following: particle size, tap density, specific surface area (BET), and shape of the amorphous coated graphite.
負極活物質層に含まれる負極活物質のうち、上記した吸油量を有する非晶質コート黒鉛の含有量は、負極活物質の総量に対して、８０質量％以上であってもよく、９０質量％以上であってもよく、９５質量％以上であってもよく、１００質量％であってもよい。負極活物質層が２種以上の負極活物質を含む場合、負極活物質の総量は２種以上の負極活物質の合計量をいう。 The content of the amorphous coated graphite having the above-mentioned oil absorption amount in the negative electrode active material contained in the negative electrode active material layer may be 80 mass% or more, 90 mass% or more, 95 mass% or more, or 100 mass% based on the total amount of the negative electrode active material. When the negative electrode active material layer contains two or more types of negative electrode active materials, the total amount of the negative electrode active materials refers to the combined amount of the two or more types of negative electrode active materials.
負極集電体上に形成した負極合剤層を圧力１９０ＭＰａで圧縮したときの負極合剤層の密度（以下、「負極合剤層の圧縮密度」ともいう。）は、１．５５ｇ／ｃｃ以上１．７６ｇ／ｃｃ以下であり、好ましくは１．５６ｇ／ｃｃ以上１．７５ｇ／ｃｃ以下であり、より好ましくは１．５７ｇ／ｃｃ以上１．７３ｇ／ｃｃ以下であり、さらに好ましくは１．５８ｇ／ｃｃ以上１．７０ｇ／ｃｃ以下である。負極合剤層の圧縮密度が１．５５ｇ／ｃｃ以上であることにより、負極板を用いた二次電池を高容量化しやすい。負極合剤層の圧縮密度が１．７６ｇ／ｃｃ以下であることにより、負極合剤層を圧縮成形して負極活物質層を形成する際に、非晶質コート黒鉛の非晶質炭素が割れにくくなると考えられる。これにより、負極活物質層の単位質量当たりの比表面積（ＢＥＴ）が増大することを抑制することができ、高温保存耐久性に優れた二次電池が得られやすくなる。このように、本実施形態の負極板では、負極活物質の材料物性のみならず負極合剤層を圧縮したときの物性も考慮して負極板を設計しているため、入出力特性に優れ、高温保存耐久性にも優れる二次電池が得られやすい。 The density of the negative electrode mixture layer when the negative electrode mixture layer formed on the negative electrode current collector is compressed at a pressure of 190 MPa (hereinafter also referred to as the "compressed density of the negative electrode mixture layer") is 1.55 g/cc or more and 1.76 g/cc or less, preferably 1.56 g/cc or more and 1.75 g/cc or less, more preferably 1.57 g/cc or more and 1.73 g/cc or less, and even more preferably 1.58 g/cc or more and 1.70 g/cc or less. When the compressed density of the negative electrode mixture layer is 1.55 g/cc or more, it is easy to increase the capacity of a secondary battery using the negative electrode plate. When the compressed density of the negative electrode mixture layer is 1.76 g/cc or less, it is thought that the amorphous carbon of the amorphous coated graphite is less likely to crack when the negative electrode mixture layer is compression-molded to form the negative electrode active material layer. This makes it possible to suppress an increase in the specific surface area (BET) per unit mass of the negative electrode active material layer, making it easier to obtain a secondary battery with excellent high-temperature storage durability. In this way, the negative electrode plate of this embodiment is designed taking into consideration not only the material properties of the negative electrode active material but also the properties when the negative electrode mixture layer is compressed, making it easier to obtain a secondary battery with excellent input/output characteristics and excellent high-temperature storage durability.
負極合剤層の圧縮密度は、負極集電体上に負極合剤層を形成し、負極集電体と負極合剤層とを積層した積層体を圧力１９０ＭＰａで圧縮し、負極合剤層の目付量（単位面積当たりの固形分量）及び圧縮後の負極合剤層の厚みに基づいて算出する。具体的には、まず、負極集電体と負極合剤層との積層体を直径２０ｍｍの円形に打抜き、質量を測定して負極合剤層の目付量［ｍｇ／１０ｃｍ２］を算出する。続いて、打抜いた積層体に油圧プレス機を用いて６０ｋＮの荷重を付与して３０秒間保持することにより、積層体を圧力１９０ＭＰａで圧縮する。圧縮後の積層体の負極合剤層の厚み［μｍ］を算出し、負極合剤層の圧縮密度［ｇ／ｃｃ］（＝負極合剤層の目付量［ｍｇ／１０ｃｍ２］／負極合剤層の厚み［μｍ］）を算出する。 The compression density of the negative electrode mixture layer is calculated based on the basis weight (solid content per unit area) of the negative electrode mixture layer and the thickness of the negative electrode mixture layer after compression, by forming a negative electrode mixture layer on the negative electrode current collector and compressing the laminated body obtained by laminating the negative electrode current collector and the negative electrode mixture layer at a pressure of 190 MPa. Specifically, the laminated body of the negative electrode current collector and the negative electrode mixture layer is first punched into a circle having a diameter of 20 mm, and the mass is measured to calculate the basis weight [mg/10 cm 2 ] of the negative electrode mixture layer. Then, the punched laminated body is compressed at a pressure of 190 MPa by applying a load of 60 kN using a hydraulic press and holding it for 30 seconds. The thickness [μm] of the negative electrode mixture layer of the laminated body after compression is calculated, and the compression density [g/cc] of the negative electrode mixture layer (= basis weight [mg/10 cm 2 ]/thickness [μm] of the negative electrode mixture layer) is calculated.
負極合剤層の圧縮密度は、例えば、非晶質コート黒鉛を構成する黒鉛粒子の種類、非晶質炭素の種類、非晶質炭素の熱処理温度、負極合剤層中の負極活物質の含有量、結着剤の種類等により、調整することができる。上記したように、非晶質コート黒鉛の黒鉛粒子として人造黒鉛を用いることにより、負極合剤層を圧縮して負極活物質層を形成するときに非晶質炭素を割れることを抑制できるため、負極合剤層の圧縮密度を上記の範囲に調整しやすくなる。 The compressed density of the negative electrode mixture layer can be adjusted, for example, by the type of graphite particles constituting the amorphous coated graphite, the type of amorphous carbon, the heat treatment temperature of the amorphous carbon, the content of the negative electrode active material in the negative electrode mixture layer, the type of binder, etc. As described above, by using artificial graphite as the graphite particles of the amorphous coated graphite, it is possible to suppress cracking of the amorphous carbon when the negative electrode mixture layer is compressed to form the negative electrode active material layer, and therefore it is easy to adjust the compressed density of the negative electrode mixture layer to the above range.
負極板における負極活物質層の単位質量当たりの比表面積（ＢＥＴ）は、好ましくは１．７７ｍ２／ｇ以上２．０５ｍ２／ｇ以下であり、より好ましくは１．７９ｍ２／ｇ以上２．００ｍ２／ｇ以下であり、さらに好ましくは１．８０ｍ２／ｇ以上１．９９ｍ２／ｇ以下である。負極活物質層の単位質量当たりの比表面積は、負極板を１ｍｍ×１ｍｍの大きさに切り出してガラス容器に入れ、全自動比表面積計により窒素（Ｎ２）ガスの吸脱着量から比表面積［ｍ２］を求め、単位質量あたりの比表面積［ｍ２／ｇ］を算出すればよい。全自動比表面積計としては、例えばＭＯＵＮＴＥＣＨ社製「Ｍａｃｓｏｒｂ ＨＭ ｍｏｄｅｌ－１２０８」を用いることができる。 The specific surface area (BET) per unit mass of the negative electrode active material layer in the negative electrode plate is preferably 1.77 m 2 /g or more and 2.05 m 2 /g or less, more preferably 1.79 m 2 /g or more and 2.00 m 2 /g or less, and even more preferably 1.80 m 2 /g or more and 1.99 m 2 /g or less. The specific surface area per unit mass of the negative electrode active material layer may be calculated by cutting the negative electrode plate into a size of 1 mm x 1 mm and placing it in a glass container, determining the specific surface area [m 2 ] from the adsorption and desorption amount of nitrogen (N 2 ) gas using a fully automatic specific surface area meter, and calculating the specific surface area [m 2 /g] per unit mass. As the fully automatic specific surface area meter, for example, "Macsorb HM model-1208" manufactured by MOUNTECH Co., Ltd. can be used.
一般に、負極活物質層の単位質量当たりの比表面積が大きくなると、二次電池の入力抵抗は小さくなり入出力特性が改善するが、二次電池の高温保存耐久性が低下する傾向にある。逆に、負極活物質層の単位質量当たりの比表面積が小さくなると、二次電池の高温保存耐久性が改善するが、二次電池の入出力特性が低下する傾向にある。そのため、負極活物質層の単位質量当たりの比表面積の増加を抑制しながら、二次電池の入力抵抗を小さくすることができれば、優れた高温保存耐久性を有しながらも、入出力特性がさらに改善された二次電池を得ることができると考えられる。本実施形態の負極板は、負極合剤層の圧縮密度及び非晶質コート黒鉛の吸油量を上記した特定の範囲に調整していため、これらの物性が調整されていないものの単位質量当たりの比表面積が同程度の負極活物質層を用いた二次電池に比較すると、高温保存耐久性を維持しながらも、入出力特性がさらに改善された二次電池を得ることができる。 In general, when the specific surface area per unit mass of the negative electrode active material layer is increased, the input resistance of the secondary battery is decreased and the input/output characteristics are improved, but the high-temperature storage durability of the secondary battery tends to decrease. Conversely, when the specific surface area per unit mass of the negative electrode active material layer is decreased, the high-temperature storage durability of the secondary battery is improved, but the input/output characteristics of the secondary battery tend to decrease. Therefore, if the input resistance of the secondary battery can be reduced while suppressing the increase in the specific surface area per unit mass of the negative electrode active material layer, it is considered that a secondary battery having excellent high-temperature storage durability and further improved input/output characteristics can be obtained. In the negative electrode plate of this embodiment, the compressed density of the negative electrode mixture layer and the oil absorption of the amorphous coated graphite are adjusted to the above-mentioned specific range, so that compared to a secondary battery using a negative electrode active material layer with a similar specific surface area per unit mass even though these physical properties are not adjusted, a secondary battery with further improved input/output characteristics can be obtained while maintaining high-temperature storage durability.
負極活物質は、少なくとも、上記した吸油量を有する非晶質コート黒鉛を含んでいればよく、上記した吸油量の範囲外の非晶質コート黒鉛、及び／又は、非晶質コート黒鉛以外の他の負極活物質を含んでいてもよい。他の負極活物質としては、人工黒鉛又は天然黒鉛等の黒鉛（グラファイト）、ハードカーボン、ソフトカーボン等といった非晶質コート黒鉛以外の炭素（Ｃ）原子を含む炭素系活物質；ケイ素（Ｓｉ）、錫（Ｓｎ）、アンチモン（Ｓｂ）、ビスマス（Ｂｉ）、チタン（Ｔｉ）、ゲルマニウム（Ｇｅ）からなる群から選択される元素を含む金属単体又は金属酸化物等の金属元素を含む金属系活物質が挙げられる。ケイ素元素を含むＳｉ系活物質としては、ケイ素単体、ＳｉＯｘ、ＬｉｘＳｉｙＯｚ等が挙げられる。 The negative electrode active material may contain at least amorphous coated graphite having the above-mentioned oil absorption amount, and may contain amorphous coated graphite outside the above-mentioned oil absorption amount range, and/or other negative electrode active materials other than amorphous coated graphite. Examples of other negative electrode active materials include carbon-based active materials containing carbon (C) atoms other than amorphous coated graphite, such as graphite (graphite) such as artificial graphite or natural graphite, hard carbon, soft carbon, etc.; and metal-based active materials containing metal elements such as metal simple substances or metal oxides containing elements selected from the group consisting of silicon (Si), tin (Sn), antimony (Sb), bismuth (Bi), titanium (Ti), and germanium (Ge). Examples of Si-based active materials containing silicon elements include silicon simple substance, SiOx, LixSiyOz, etc.
結着材としては、カルボキシメチルセルロース（ＣＭＣ）、メチルセルロース（ＭＣ）、ヒドロキシプロピルセルロース等のセルロース系結着材；スチレンブタジエンゴム（ＳＢＲ）、ポリアクリル酸（ＰＡＡ）、アクリロニトリルブタジエンゴム（ＮＢＲ）、ポリフッ化ビニリデン（ＰＶｄＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）等が挙げられる。結着材は、セルロース系結着材及びＳＢＲのうちの少なくとも一方を含むことが好ましく、両方を含んでいてもよい。セルロース系結着材は、ＣＭＣであることが好ましい。ＣＭＣ及びＰＡＡは、酸の形態であってもよく、塩の形態であってもよい。 Examples of binders include cellulose-based binders such as carboxymethyl cellulose (CMC), methyl cellulose (MC), and hydroxypropyl cellulose; styrene butadiene rubber (SBR), polyacrylic acid (PAA), acrylonitrile butadiene rubber (NBR), polyvinylidene fluoride (PVdF), and polytetrafluoroethylene (PTFE). The binder preferably contains at least one of a cellulose-based binder and SBR, and may contain both. The cellulose-based binder is preferably CMC. CMC and PAA may be in the form of an acid or a salt.
負極活物質層に含まれる結着材の含有量は、負極活物質層の総量に対して、０．５質量％以上１０質量％以下であってもよく、１．０質量％以上８．０質量％以下であってもよく、１．５質量％以上５．０質量％以下であってもよい。負極活物質層が２種以上の結着材を含む場合、結着材の含有量は、２種以上の結着材の合計含有量をいう。 The content of the binder contained in the negative electrode active material layer may be 0.5% by mass or more and 10% by mass or less, 1.0% by mass or more and 8.0% by mass or less, or 1.5% by mass or more and 5.0% by mass or less, relative to the total amount of the negative electrode active material layer. When the negative electrode active material layer contains two or more types of binders, the content of the binder refers to the total content of the two or more types of binders.
導電助剤としては、繊維状炭素、カーボンブラック（例えば、アセチレンブラック、ケッチェンブラック）、コークス、活性炭等の炭素材料が挙げられる。繊維状炭素としては、カーボンナノチューブ（以下、「ＣＮＴ」ともいう。）が挙げられる。ＣＮＴは、単層カーボンナノチューブ（ＳＷＣＮＴ）であってもよく、２層カーボンチューブ（ＤＷＣＮＴ）等の多層カーボンナノチューブであってもよい。 Examples of conductive additives include carbon materials such as fibrous carbon, carbon black (e.g., acetylene black, ketjen black), coke, and activated carbon. Examples of fibrous carbon include carbon nanotubes (hereinafter also referred to as "CNT"). CNTs may be single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes such as double-walled carbon tubes (DWCNTs).
（負極板の製造方法）
負極板は例えば、負極集電体上に、負極合剤スラリーを塗布して乾燥することにより負極合剤層を形成し、負極集電体上の負極合剤層を圧縮して負極活物質層を形成することにより、得ることができる。負極合剤層の圧縮は、例えば、負極集電体と負極合剤層とを積層した積層体をロールプレス機でプレスすることによって行えばよい。
(Method of manufacturing negative electrode plate)
The negative electrode plate can be obtained, for example, by applying a negative electrode mixture slurry onto a negative electrode current collector, drying the slurry to form a negative electrode mixture layer, and compressing the negative electrode mixture layer on the negative electrode current collector to form a negative electrode active material layer. The compression of the negative electrode mixture layer can be performed, for example, by pressing a laminate obtained by stacking the negative electrode current collector and the negative electrode mixture layer with a roll press machine.
負極合剤スラリーは、負極活物質、結着材、及び分散媒を含み、これらを混合することによって得ることができる。負極合剤スラリーは、上記した吸油量の範囲内にある非晶質コート黒鉛を含む。負極合剤スラリーに含まれる分散媒としては、イオン交換水等の水が挙げられる。負極合剤スラリーは、上記した吸油量の範囲内にある非晶質コート黒鉛以外の負極活物質を含んでいてもよく、導電助剤を含んでいてもよい。負極合剤スラリーが含んでいてもよい負極活物質及び結着材としては、上記で説明したものが挙げられる。 The negative electrode mixture slurry contains a negative electrode active material, a binder, and a dispersion medium, and can be obtained by mixing these. The negative electrode mixture slurry contains amorphous coated graphite within the above-mentioned oil absorption range. Examples of the dispersion medium contained in the negative electrode mixture slurry include water such as ion-exchanged water. The negative electrode mixture slurry may contain a negative electrode active material other than amorphous coated graphite within the above-mentioned oil absorption range, and may also contain a conductive assistant. Examples of the negative electrode active material and binder that may be contained in the negative electrode mixture slurry include those described above.
負極合剤スラリーは、例えば次の工程で調製することができる。まず、非晶質コート黒鉛と、セルロース系結着材等の結着材の一部と、必要に応じて導電助剤とをドライブレンドした後、分散媒を加えて高い固形分量で混練する固練りを行い、非晶質コート黒鉛の表面に結着材を付着させる。続いて、分散媒をさらに加えて、上記した固練りでの固形分量よりも低い固形分量で混練し、結着材が表面に付着した非晶質コート黒鉛が分散媒に分散させる。その後、必要に応じて、残りの結着材を添加して混練することにより、負極合剤スラリーを得る。 The negative electrode mixture slurry can be prepared, for example, by the following process. First, the amorphous coated graphite is dry-blended with a portion of the binder, such as a cellulose-based binder, and optionally with a conductive assistant. A dispersion medium is then added and kneaded with a high solid content to adhere the binder to the surface of the amorphous coated graphite. Next, further dispersion medium is added and kneaded with a lower solid content than the solid content in the above-mentioned kneading, and the amorphous coated graphite with the binder adhered to its surface is dispersed in the dispersion medium. Then, if necessary, the remaining binder is added and kneaded to obtain the negative electrode mixture slurry.
（リチウムイオン二次電池）
リチウムイオン二次電池は、上記で説明した負極板を含むことができる。リチウムイオン二次電池は通常、上記した負極板、正極板、及びセパレータを有する電極体と、電解液とを有する。リチウムイオン二次電池は、電極体と電解質とを収容する外装体をさらに含むことができる。
(Lithium-ion secondary battery)
The lithium ion secondary battery may include the negative electrode plate described above. The lithium ion secondary battery usually includes an electrode assembly having the negative electrode plate, the positive electrode plate, and a separator described above, and an electrolyte. The lithium ion secondary battery may further include an exterior body that contains the electrode assembly and the electrolyte.
電極体は、負極板の負極活物質層と正極板の正極活物質層とがセパレータを解して積層された構造を有する。電極体は、巻回型であってもよく、積層型であってもよい。電極体は偏平状の電極体であってもよい。 The electrode body has a structure in which a negative electrode active material layer of a negative electrode plate and a positive electrode active material layer of a positive electrode plate are laminated with a separator interposed therebetween. The electrode body may be of a wound type or a laminated type. The electrode body may be of a flat electrode body.
正極板は、正極集電体と、正極集電体上に形成された正極活物質層とを有する。正極集電体は、例えば、アルミニウム及びアルミニウム合金等のアルミニウム材料を用いて構成された金属箔である。正極活物質層は、正極活物質を含む。正極活物質としては公知の材料を用いることができ、層状系又はスピネル系等のリチウム遷移金属酸化物（例えば、ＬｉＮｉＣｏＭｎＯ２、ＬｉＮｉＯ2、ＬｉＣｏＯ2、ＬｉＦｅＯ2、ＬｉＭｎ2Ｏ4、ＬｉＮｉ0.5Ｍｎ1.5Ｏ4、ＬｉＣｒＭｎＯ4、ＬｉＦｅＰＯ4、ＬｉＮｉ1/3Ｃｏ1/3Ｍｎ1/3Ｏ2）が挙げられる。 The positive electrode plate has a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode current collector is, for example, a metal foil made of an aluminum material such as aluminum or an aluminum alloy. The positive electrode active material layer includes a positive electrode active material. A known material can be used as the positive electrode active material, and examples of the positive electrode active material include layered or spinel lithium transition metal oxides (e.g., LiNiCoMnO2 , LiNiO2 , LiCoO2 , LiFeO2 , LiMn2O4 , LiNi0.5Mn1.5O4 , LiCrMnO4 , LiFePO4 , LiNi1 / 3Co1 / 3Mn1 / 3O2 ).
正極活物質層は、正極活物質以外の添加剤として、結着材及び導電助剤等を含むことができる。結着材としては、スチレンブタジエンゴム（ＳＢＲ）、ポリフッ化ビニリデン（ＰＶｄＦ）、及びポリテトラフルオロエチレン（ＰＴＦＥ）等が挙げられる。導電助剤としては、繊維状炭素、カーボンブラック（アセチレンブラック、ケッチェンブラック等）、コークス、活性炭等の炭素材料が挙げられる。繊維状炭素は、上記で説明したものが挙げられる。 The positive electrode active material layer may contain additives other than the positive electrode active material, such as a binder and a conductive assistant. Examples of the binder include styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), and polytetrafluoroethylene (PTFE). Examples of the conductive assistant include carbon materials such as fibrous carbon, carbon black (acetylene black, ketjen black, etc.), coke, and activated carbon. Examples of the fibrous carbon include those described above.
正極活物質層は、正極活物質及び添加剤を含む正極合剤を分散媒と混合して調製した正極合剤スラリーを、正極集電体に塗布して乾燥し、圧縮することにより形成することができる。分散媒としては、Ｎ－メチル－２－ピロリドン（ＮＭＰ）が挙げられる。 The positive electrode active material layer can be formed by mixing a positive electrode mixture containing a positive electrode active material and an additive with a dispersion medium to prepare a positive electrode mixture slurry, applying the slurry to a positive electrode current collector, drying the slurry, and compressing the slurry. Examples of the dispersion medium include N-methyl-2-pyrrolidone (NMP).
セパレータとしては、ポリエチレン、ポリプロピレン、ポリエステル、セルロース、ポリアミド等の樹脂からなる多孔質シート（フィルム、不織布等）が挙げられる。多孔質シートは、単層構造であってもよく、２層以上の多層構造であってもよい。 Examples of the separator include porous sheets (films, nonwoven fabrics, etc.) made of resins such as polyethylene, polypropylene, polyester, cellulose, and polyamide. The porous sheet may have a single-layer structure or a multi-layer structure of two or more layers.
電解質としては、非水電解液が挙げられ、例えば、有機溶媒等の非水溶媒中に支持塩を含有させたものが挙げられる。電解質は、さらに負極活物質層及び／又は正極活物質層の表面に良好な皮膜を形成したり、過充電時の安定性を確保したりするために、ビニレンカーボネート（ＶＣ）、シクロヘキシルベンゼン（ＣＨＢ）、及び、ＣＨＢの変性体からなる群より選ばれる１種又は２種以上の添加剤を含んでいてもよい。 The electrolyte may be a non-aqueous electrolyte, for example, a non-aqueous solvent such as an organic solvent containing a supporting salt. The electrolyte may further contain one or more additives selected from the group consisting of vinylene carbonate (VC), cyclohexylbenzene (CHB), and modified forms of CHB, in order to form a good film on the surface of the negative electrode active material layer and/or the positive electrode active material layer, and to ensure stability during overcharging.
非水溶媒としては例えば、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）、ジメチルカーボネート（ＤＭＣ）、エチルメチルカーボネート（ＥＭＣ）、ジエチルカーボネート（ＤＥＣ）、γ－ブチロラクトン（γ－ＢＬ）、スルホラン、アセトニトリル、１，２－ジメトキシエタン（ＤＭＥ）、１，３－ジメトキシプロパン、ジエチルエーテル、テトラヒドロフラン、２－メチルテトラヒドロフランからなる群より選ばれる１種又は２種以上が挙げられる。 Examples of non-aqueous solvents include one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), γ-butyrolactone (γ-BL), sulfolane, acetonitrile, 1,2-dimethoxyethane (DME), 1,3-dimethoxypropane, diethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran.
支持塩としては例えば、過塩素酸リチウム（ＬｉＣｌＯ４）、六フッ化リン酸リチウム（ＬｉＰＦ６）、ホウフッ化リチウム（ＬｉＢＦ４）、六フッ化砒素リチウム（ＬｉＡｓＦ６）、トリフルオロメタスルホン酸リチウム（ＬｉＣＦ３ＳＯ３）、及びビストリフルオロメチルスルホニルイミドリチウム［ＬｉＮ（ＣＦ３ＳＯ２）２］からなる群より選ばれる１種又は２種以上が挙げられる。 Examples of the supporting salt include one or more selected from the group consisting of lithium perchlorate (LiClO 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium borofluoride (LiBF 4 ), lithium arsenic hexafluoride (LiAsF 6 ), lithium trifluoromethansulfonate (LiCF 3 SO 3 ), and lithium bistrifluoromethylsulfonylimide [LiN(CF 3 SO 2 ) 2 ].
外装体は、例えばアルミニウム層を有するラミネートシート等を用いて、電極体の外表面を覆う大きさ及び形状に形成すればよい。 The exterior body may be formed into a size and shape that covers the outer surface of the electrode body, for example using a laminate sheet having an aluminum layer.
以下、実施例及び比較例を示して本開示をさらに具体的に説明する。
〔比較例１～９、実施例１～４〕
（負極合剤スラリーの調製）
微少量混練機（ＰＲＩＭＩＸ社製「ハイビスミックス２Ｐ－１型」）を用いて、水を分散媒とした負極合剤スラリーを調製した。負極合剤スラリーは、表１に示す負極活物質／カルボキシメチルセルロース（ＣＭＣ）／スチレンブタジエンゴム（ＳＢＲ）＝９８．３／０．７／１．０（質量比）の配合比となるように次の手順で調製した。まず、表１に示す負極活物質と、結着材としてのＣＭＣとを、回転数２５ｒｐｍで１０分間ドライブレンドした後、水を加えて回転数６０ｒｐｍで７．５分間混練し（固練り）、混練体を得た。この混練体にさらに水を加えて回転数６０ｒｐｍで５分間混練することにより、ＣＭＣが付着した負極活物質が水に分散した分散体を得た。この分散体に、ＳＢＲを添加し、回転数６０ｒｐｍで５分間混練して負極合剤スラリーを得た。
The present disclosure will be described more specifically below with reference to examples and comparative examples.
[Comparative Examples 1 to 9, Examples 1 to 4]
(Preparation of negative electrode mixture slurry)
A negative electrode mixture slurry was prepared using a micro-mixer (PRIMIX "Hibismix 2P-1 type"). The negative electrode mixture slurry was prepared in the following procedure so that the mixing ratio of the negative electrode active material/carboxymethyl cellulose (CMC)/styrene butadiene rubber (SBR) shown in Table 1 was 98.3/0.7/1.0 (mass ratio). First, the negative electrode active material shown in Table 1 and CMC as a binder were dry-blended at a rotation speed of 25 rpm for 10 minutes, and then water was added and kneaded at a rotation speed of 60 rpm for 7.5 minutes (solid kneading) to obtain a kneaded body. Water was further added to this kneaded body and kneaded at a rotation speed of 60 rpm for 5 minutes to obtain a dispersion in which the negative electrode active material to which CMC was attached was dispersed in water. SBR was added to this dispersion and kneaded at a rotation speed of 60 rpm for 5 minutes to obtain a negative electrode mixture slurry.
（負極集電体と負極合剤層との積層体の作製）
負極集電体として、厚み１０μｍの銅（Ｃｕ）箔を準備した。この銅箔の両面に、負極合剤スラリーを塗布し乾燥させて負極合剤層を形成し、負極集電体と負極合剤層とを積層した積層体を得た。負極合剤スラリーの塗布量は、負極活物質層の容量を正極活物質層の容量で除した値（負極活物質層の容量／正極活物質層の容量）が、すべての実施例及び比較例で同じとなるように調整した。負極合剤層の目付量（銅箔上に塗布した負極合剤スラリーの単位面積当たりの固形分量）は、２５５ｍｇ／１０ｃｍ２以上２６５ｍｇ／１０ｃｍ２以下の範囲内で調整した。すべての実施例及び比較例において、正極板の正極活物質層の容量は同じとなるように調整した。
(Preparation of Laminate of Negative Electrode Current Collector and Negative Electrode Mixture Layer)
A copper (Cu) foil having a thickness of 10 μm was prepared as the negative electrode current collector. The negative electrode mixture slurry was applied to both sides of the copper foil and dried to form a negative electrode mixture layer, and a laminate was obtained in which the negative electrode current collector and the negative electrode mixture layer were laminated. The amount of the negative electrode mixture slurry applied was adjusted so that the value obtained by dividing the capacity of the negative electrode active material layer by the capacity of the positive electrode active material layer (capacity of the negative electrode active material layer/capacity of the positive electrode active material layer) was the same in all examples and comparative examples. The weight of the negative electrode mixture layer (the solid content per unit area of the negative electrode mixture slurry applied on the copper foil) was adjusted within a range of 255 mg/10 cm 2 or more and 265 mg/10 cm 2 or less. In all examples and comparative examples, the capacity of the positive electrode active material layer of the positive electrode plate was adjusted to be the same.
（負極板の作製）
上記で得た積層体を小型のロールプレス機を用いて圧縮し、密度が１．５６ｇ／ｃｃである負極活物質層を形成することにより、負極板を得た。ロールプレス機による圧縮では、上記密度の負極活物質層が得られる厚みを下記式に基づいて算出し、算出した厚みの負極活物質層が得られるように、上記ロールプレス機の圧縮荷重及びロール間の隙間の大きさ（ギャップ（ｇａｐ））を調整した。
負極活物質層の密度［ｇ／ｃｃ］
＝負極合剤層の目付量［ｍｇ／１０ｃｍ２］／負極活物質層の厚み［μｍ］
(Preparation of negative electrode plate)
The laminate obtained above was compressed using a small roll press machine to form a negative electrode active material layer with a density of 1.56 g/cc, thereby obtaining a negative electrode plate. In the compression using the roll press machine, the thickness at which the negative electrode active material layer with the above density was obtained was calculated based on the following formula, and the compression load of the roll press machine and the size of the gap between the rolls (gap) were adjusted so that the negative electrode active material layer with the calculated thickness was obtained.
Density of negative electrode active material layer [g/cc]
= Weight per unit area of negative electrode mixture layer [mg/10 cm 2 ]/Thickness of negative electrode active material layer [μm]
（正極合剤スラリーの調製）
微少量混練機（ＰＲＩＭＩＸ社製「ハイビスミックス２Ｐ－１型」）を用いて、Ｎ－メチル－２－ピロリドン（ＮＭＰ）を分散媒とした正極合剤スラリーを調製した。正極合剤スラリーは、正極活物質（リチウムニッケルコバルトマンガン複合酸化物（ＮＣＭ））／導電助剤（カーボンブラック）／結合材（ポリフッ化ビニリデン（ＰＶｄＦ））＝９７．５／１．５／１．０（質量比）の配合比となるように調製した。
(Preparation of Positive Electrode Mixture Slurry)
A positive electrode mixture slurry was prepared using a micro-mixer (PRIMIX Corporation, "Hibismix 2P-1 type") with N-methyl-2-pyrrolidone (NMP) as a dispersion medium. The positive electrode mixture slurry was prepared to have a mixture ratio of positive electrode active material (lithium nickel cobalt manganese composite oxide (NCM))/conductive assistant (carbon black)/binder (polyvinylidene fluoride (PVdF)) = 97.5/1.5/1.0 (mass ratio).
（正極板の作製）
正極集電体として、厚み１３μｍのアルミニウム（Ａｌ）箔を準備した。このアルミニウム箔の両面に、正極合剤スラリーを塗布し乾燥させて正極合剤層を形成し、正極集電体と正極合剤層とを積層した積層体を得た。この積層体を小型のロールプレス機を用いて圧縮して正極活物質層を形成し、正極板を得た。
(Preparation of positive electrode plate)
An aluminum (Al) foil having a thickness of 13 μm was prepared as a positive electrode current collector. A positive electrode mixture slurry was applied to both sides of the aluminum foil and dried to form a positive electrode mixture layer, and a laminate was obtained in which the positive electrode current collector and the positive electrode mixture layer were laminated. The laminate was compressed using a small roll press machine to form a positive electrode active material layer, and a positive electrode plate was obtained.
（試験セル（ラミネートセル）の作製）
上記で作製した負極板及び正極板のそれぞれにリードを取り付けた。セパレータを介して負極活物質層と正極活物質層とが対向するように、リードを取り付けた電極板を積層して、電極体を得た。アルミニウムラミネートシートで構成される外装体に電極体を収容して電解質を注入した後、外装体の開口部を封止して、ラミネートセルとしての試験セルを得た。電解質は、支持塩として１．１５ＭのＬｉＰＦ６、非水溶媒としてエチレンカーボネート（ＥＣ）／エチルメチルカーボネート（ＥＭＣ）／ジメチルカーボネート（ＤＭＣ）＝３０／３０／４０（体積比）の混合溶媒、及び、添加剤として、混合溶媒の総質量に対して１．０質量％のビニレンカーボネート（ＶＣ）を混合して調製した。
(Preparation of test cell (laminate cell))
A lead was attached to each of the negative and positive electrode plates prepared above. The electrode plates with the lead attached were laminated so that the negative and positive active material layers faced each other via the separator to obtain an electrode body. The electrode body was housed in an exterior body made of an aluminum laminate sheet, and an electrolyte was injected, and then the opening of the exterior body was sealed to obtain a test cell as a laminate cell. The electrolyte was prepared by mixing 1.15M LiPF 6 as a supporting salt, a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) = 30 / 30 / 40 (volume ratio) as a non-aqueous solvent, and 1.0 mass% vinylene carbonate (VC) with respect to the total mass of the mixed solvent as an additive.
［負極活物質の吸油量の測定］
２枚羽根（高速側の回転数：１２５ｒｐｍ、低速側の回転数：６２．５ｒｐｍ）によって撹拌されている負極活物質２０ｇに、添加速度２ｃｃ／ｍｉｎでアマニ油を添加した。このときの粘度特性の変化を、トルク検出器（株式会社あさひ総研製「Ｓ－５００」）で検出し、その出力をマイクロコンピュータでトルクに換算した。得られたトルクのうちの最大トルクの７０％に相当するトルクが発生したときのアマニ油の添加量を、負極活物質１００ｇ当たりの添加量に換算し、これを負極活物質の吸油量［ｃｃ／１００ｇ］として算出した。結果を表１に示す。
[Measurement of oil absorption of negative electrode active material]
Linseed oil was added at an addition rate of 2 cc/min to 20 g of negative electrode active material being stirred by two blades (high-speed rotation speed: 125 rpm, low-speed rotation speed: 62.5 rpm). The change in viscosity characteristics at this time was detected by a torque detector ("S-500" manufactured by Asahi Research Institute Co., Ltd.), and the output was converted to torque by a microcomputer. The amount of linseed oil added when a torque equivalent to 70% of the maximum torque of the obtained torque was generated was converted to the amount added per 100 g of negative electrode active material, and this was calculated as the oil absorption amount of the negative electrode active material [cc/100 g]. The results are shown in Table 1.
［負極合剤層の圧縮密度の測定］
負極集電体上に形成した負極合剤層を圧力１９０ＭＰａで圧縮したときの負極合剤層の密度（負極合剤層の圧縮密度）は、上記で作製した負極集電体と負極合剤層との積層体を用いて行った。具体的には、この積層体を直径２０ｍｍの円形に打抜いた後、質量を測定し、負極合剤層の目付量を算出した。打抜いた積層体に油圧プレス機を用いて６０ｋＮの荷重を付与して３０秒間保持することにより、積層体を圧力１９０Ｍｐａで圧縮した。その後、圧縮後の積層体の負極合剤層の厚みを測定した。負極合剤層の目付量［ｍｇ／１０ｃｍ２］及び負極合剤層の厚み［μｍ］から、下記式に基づいて負極合剤層の圧縮密度［ｇ／ｃｃ］を算出した。結果を表１に示す。
負極合剤層の圧縮密度［ｇ／ｃｃ］
＝（負極合剤層の目付量［ｍｇ／１０ｃｍ２］）／（負極合剤層の厚み［μｍ］）
[Measurement of Compressed Density of Negative Electrode Mixture Layer]
The density of the negative electrode mixture layer when the negative electrode mixture layer formed on the negative electrode current collector was compressed at a pressure of 190 MPa (compressed density of the negative electrode mixture layer) was measured using the laminate of the negative electrode current collector and the negative electrode mixture layer prepared above. Specifically, the laminate was punched into a circle with a diameter of 20 mm, and then the mass was measured to calculate the basis weight of the negative electrode mixture layer. The punched laminate was compressed at a pressure of 190 MPa by applying a load of 60 kN using a hydraulic press and holding it for 30 seconds. Thereafter, the thickness of the negative electrode mixture layer of the compressed laminate was measured. The compressed density [g/cc] of the negative electrode mixture layer was calculated based on the following formula from the basis weight [mg/10 cm 2 ] of the negative electrode mixture layer and the thickness [μm] of the negative electrode mixture layer. The results are shown in Table 1.
Compressed density of negative electrode mixture layer [g/cc]
= (area weight of negative electrode mixture layer [mg/10 cm 2 ])/(thickness of negative electrode mixture layer [μm])
［負極活物質層の単位質量当たりの比表面積（ＢＥＴ）の測定］
負極板を１ｍｍ×１ｍｍの大きさに切り出して測定用のガラス容器に入れた。全自動比表面積測定装置（ＭＯＵＮＴＥＣＨ社製「Ｍａｃｓｏｒｂ ＨＭ ｍｏｄｅｌ－１２０８」）を用いて、窒素（Ｎ２）ガスの吸脱着量から比表面積［ｍ２］を求めた。この比表面積［ｍ２］を負極活物質層の質量［ｇ］で除して（比表面積［ｍ２］／負極活物質層の質量［ｇ］）、負極活物質層の単位質量当たりの比表面積［ｍ２／ｇ］を算出した。結果を表１に示す。
[Measurement of specific surface area per unit mass (BET) of negative electrode active material layer]
The negative electrode plate was cut into a size of 1 mm x 1 mm and placed in a glass container for measurement. Using a fully automatic specific surface area measuring device ("Macsorb HM model-1208" manufactured by MOUNTECH), the specific surface area [m 2 ] was obtained from the amount of adsorption and desorption of nitrogen (N 2 ) gas. This specific surface area [m 2 ] was divided by the mass [g] of the negative electrode active material layer (specific surface area [m 2 ]/mass [g] of the negative electrode active material layer) to calculate the specific surface area per unit mass of the negative electrode active material layer [m 2 /g]. The results are shown in Table 1.
［試験セルの入力抵抗の評価］
試験セルをＳＯＣ（state of charge）を５０％に調整した後、試験セルを定電流で充電し、充電開始から５秒経過した時点での電圧を記録した。これを、定電流での充電を複数の電流値で実施することにより、Ｉ（電流）に対してＶ（電圧）をプロットし、その傾きから、充電開始から５秒経過時点の入力抵抗（Ｖ／Ｉ）［ｍΩ］を算出した。入力抵抗の値が小さいほど、入出力特性に優れていることを示す。結果を表１に示す。
[Evaluation of the input resistance of the test cell]
After adjusting the SOC (state of charge) of the test cell to 50%, the test cell was charged at a constant current, and the voltage at 5 seconds after the start of charging was recorded. By performing constant current charging at multiple current values, V (voltage) was plotted against I (current), and the input resistance (V/I) [mΩ] at 5 seconds after the start of charging was calculated from the slope. The smaller the input resistance value, the better the input/output characteristics. The results are shown in Table 1.
［試験セルの高温保存耐久性の評価］
試験セルを、ＳＯＣが順に０％、１００％、０％となるように充放電し、初期の放電容量を測定した後、試験セルのＳＯＣを９５％に調整した。続いて、試験セルを温度６０℃の恒温槽に入れ、３０日間放置する高温保存試験を行った。高温保存試験後に恒温槽から試験セルを取り出してＳＯＣを０％にした後、再びＳＯＣが順に０％、１００％、０％となるように充放電し、高温保存試験後の放電容量を測定した。下記式にしたがって高温保存時の放電容量維持率を算出した。高温保存時の放電容量維持率の値が大きいほど、高温保存耐久性に優れていることを示す。結果を表１の放電容量維持率の欄に示す。
高温保存時の放電容量維持率［％］
＝（高温保存試験後の放電容量／初期の放電容量）×１００
[Evaluation of high-temperature storage durability of test cells]
The test cell was charged and discharged so that the SOC was 0%, 100%, and 0% in sequence, and the initial discharge capacity was measured, and then the SOC of the test cell was adjusted to 95%. Next, the test cell was placed in a thermostatic chamber at a temperature of 60° C. and left for 30 days to perform a high-temperature storage test. After the high-temperature storage test, the test cell was removed from the thermostatic chamber and the SOC was set to 0%, and then the test cell was charged and discharged again so that the SOC was 0%, 100%, and 0% in sequence, and the discharge capacity after the high-temperature storage test was measured. The discharge capacity retention rate during high-temperature storage was calculated according to the following formula. The higher the value of the discharge capacity retention rate during high-temperature storage, the better the high-temperature storage durability. The results are shown in the column of discharge capacity retention rate in Table 1.
Discharge capacity retention rate when stored at high temperature [%]
= (discharge capacity after high temperature storage test/initial discharge capacity) x 100
Claims (7)
前記負極活物質層は、負極活物質及び結着材を含む負極合剤層から形成され、
前記負極活物質は、黒鉛粒子の表面を非晶質炭素で被覆した非晶質コート黒鉛を含み、
前記非晶質コート黒鉛の吸油量は、４０ｃｃ／１００ｇ以上５３ｃｃ／１００ｇ以下であり、
前記負極集電体上に形成した前記負極合剤層を圧力１９０ＭＰａで圧縮したときの前記負極合剤層の密度は、１．５５ｇ／ｃｃ以上１．７６ｇ／ｃｃ以下である、負極板。 A negative electrode plate having a negative electrode current collector and a negative electrode active material layer,
The negative electrode active material layer is formed of a negative electrode mixture layer containing a negative electrode active material and a binder,
The negative electrode active material includes amorphous-coated graphite in which the surface of a graphite particle is coated with amorphous carbon,
The oil absorption of the amorphous coated graphite is 40 cc/100 g or more and 53 cc/100 g or less,
a density of the negative electrode mixture layer when the negative electrode mixture layer formed on the negative electrode current collector is compressed at a pressure of 190 MPa is 1.55 g/cc or more and 1.76 g/cc or less.
A lithium ion secondary battery comprising the negative electrode plate according to any one of claims 1 to 5.
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JP2024088363A true JP2024088363A (en) | 2024-07-02 |
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