JP7513652B2 - Method for manufacturing a negative electrode and a negative electrode - Google Patents
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Description
本発明は、負極の製造方法及び負極に関する。 The present invention relates to a method for producing a negative electrode and a negative electrode.
非水電解質二次電池の負極を構成する負極活物質層は、負極集電体上に形成された負極合剤層を圧縮等することにより形成することが知られている（例えば、特許文献１及び２等）。 It is known that the negative electrode active material layer constituting the negative electrode of a non-aqueous electrolyte secondary battery is formed by compressing the negative electrode mixture layer formed on the negative electrode current collector (for example, Patent Documents 1 and 2, etc.).
非水電解質二次電池では、当該電池の充放電時に負極活物質層を備える負極の膨化量が増大することがあった。 In non-aqueous electrolyte secondary batteries, the amount of swelling of the negative electrode having the negative electrode active material layer sometimes increases during charging and discharging of the battery.
本開示の目的は、負極活物質層を備える負極の膨化を抑制できる負極の製造方法及び負極を提供することにある。 The objective of this disclosure is to provide a method for manufacturing a negative electrode that can suppress swelling of a negative electrode having a negative electrode active material layer, and a negative electrode.
〔１〕 負極集電体と負極活物質層とを有する負極の製造方法であって、
前記負極集電体上に形成された負極合剤層を圧縮することにより、前記負極活物質層を形成する工程を含み、
前記負極合剤層は、負極材料を含み、
前記負極材料は、黒鉛粒子の含有量が７０質量％以上である負極活物質を含み、
前記黒鉛粒子の比表面積は、１．０ｍ２／ｇ以上２．５ｍ２／ｇ以下であり、
前記黒鉛粒子を一軸方向に密度１．７ｇ／ｃｍ３まで圧粉するために必要な成形圧力は、２０ＭＰａ以下である、負極の製造方法。
〔２〕 前記負極活物質は、さらにＳｉ含有粒子を含む、〔１〕に記載の負極の製造方法。
〔３〕 前記Ｓｉ含有粒子は、炭素ドメインと、サイズが５０ｎｍ以下であるケイ素ドメインとを含むＳｉＣ粒子を含み、
前記ＳｉＣ粒子中の酸素含有量は、７質量％以下である、〔２〕に記載の負極の製造方法。
〔４〕 前記Ｓｉ含有粒子の平均粒子径Ｄ５０は、前記黒鉛粒子の平均粒子径Ｄ５０の０．１５倍以上０．３０倍以下である、〔２〕又は〔３〕に記載の負極の製造方法。
〔５〕 前記黒鉛粒子の平均粒子径Ｄ５０は、８μｍ以上２５μｍ以下である、〔１〕～〔４〕のいずれかに記載の負極の製造方法。
〔６〕 前記黒鉛粒子のＸ線回折によるピーク強度Ｉ（００４）及びピーク強度Ｉ（１１０）に基づいて算出した比Ｉ（００４）／Ｉ（１１０）は、３．５以上である、〔１〕～〔５〕のいずれかに記載の負極の製造方法。
〔７〕 前記負極材料は、さらに、バインダ及び繊維状炭素を含む、〔１〕～〔６〕のいずれかに記載の負極の製造方法。
〔８〕 前記繊維状炭素は、単層カーボンナノチューブを含む、〔７〕に記載の負極の製造方法。
〔９〕 前記バインダは、スチレンブタジエンラバー（ＳＢＲ）、カルボキシメチルセルロース（ＣＭＣ）、及びポリアクリル酸（ＰＡＡ）からなる群より選択される１種以上を含む、〔７〕又は〔８〕に記載の負極の製造方法。
〔１０〕 負極集電体と負極活物質層とを有する負極であって、
前記負極活物質層は、黒鉛粒子の含有量が７０質量％以上である負極活物質を含み、
前記負極活物質層の比表面積は、１．０ｍ２／ｇ以上３．０ｍ２／ｇ以下である、負極。
〔１１〕 前記負極活物質は、さらにＳｉ含有粒子を含む、〔１０〕に記載の負極。
[1] A method for producing a negative electrode having a negative electrode current collector and a negative electrode active material layer, comprising the steps of:
a step of compressing the negative electrode mixture layer formed on the negative electrode current collector to form the negative electrode active material layer;
The negative electrode mixture layer contains a negative electrode material,
The negative electrode material includes a negative electrode active material having a graphite particle content of 70 mass% or more,
The specific surface area of the graphite particles is 1.0 m 2 /g or more and 2.5 m 2 /g or less,
a molding pressure required for compressing the graphite particles in one axial direction to a density of 1.7 g/cm 3 is 20 MPa or less.
[2] The method for producing a negative electrode according to [1], wherein the negative electrode active material further contains Si-containing particles.
[3] The Si-containing particles include SiC particles including carbon domains and silicon domains having a size of 50 nm or less;
The method for producing a negative electrode according to [2], wherein the oxygen content in the SiC particles is 7 mass% or less.
[4] The method for producing a negative electrode according to [2] or [3], wherein the average particle diameter D50 of the Si-containing particles is 0.15 to 0.30 times the average particle diameter D50 of the graphite particles.
[5] The method for producing a negative electrode according to any one of [1] to [4], wherein the graphite particles have an average particle diameter D50 of 8 μm or more and 25 μm or less.
[6] The method for producing a negative electrode according to any one of [1] to [5], wherein a ratio I(004)/I(110) calculated based on a peak intensity I(004) and a peak intensity I(110) by X-ray diffraction of the graphite particles is 3.5 or more.
[7] The method for producing a negative electrode according to any one of [1] to [6], wherein the negative electrode material further contains a binder and fibrous carbon.
[8] The method for producing a negative electrode according to [7], wherein the fibrous carbon includes a single-walled carbon nanotube.
[9] The method for producing a negative electrode according to [7] or [8], wherein the binder contains one or more selected from the group consisting of styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polyacrylic acid (PAA).
[10] A negative electrode having a negative electrode current collector and a negative electrode active material layer,
the negative electrode active material layer contains a negative electrode active material having a graphite particle content of 70 mass% or more,
The negative electrode, wherein the specific surface area of the negative electrode active material layer is 1.0 m 2 /g or more and 3.0 m 2 /g or less.
[11] The negative electrode according to [10], wherein the negative electrode active material further contains Si-containing particles.
本開示によれば、負極活物質層を備える負極の膨化を抑制できる負極の製造方法及び負極を提供できる。 The present disclosure provides a method for manufacturing a negative electrode that can suppress swelling of a negative electrode having a negative electrode active material layer, and a negative electrode.
（負極の製造方法）
図１は、実施形態の負極の製造方法を示すフローチャートである。本実施形態の負極の製造方法は、非水電解質二次電池（以下「本電池」ともいう。）が有する負極を製造する方法である。負極は、負極集電体と負極活物質層とを有する。本実施形態の負極の製造方法は、負極集電体上に形成された負極合剤層を圧縮することにより、負極活物質層を形成する工程を含む。負極合剤層は負極材料を含む。
(Method of Manufacturing Negative Electrode)
FIG. 1 is a flow chart showing a method for manufacturing a negative electrode according to an embodiment. The method for manufacturing a negative electrode according to the present embodiment is a method for manufacturing a negative electrode included in a non-aqueous electrolyte secondary battery (hereinafter also referred to as "the present battery"). The negative electrode includes a negative electrode current collector and a negative electrode active material layer. The method for manufacturing a negative electrode according to the present embodiment includes a step of forming a negative electrode active material layer by compressing a negative electrode mixture layer formed on the negative electrode current collector. The negative electrode mixture layer includes a negative electrode material.
負極活物質層を形成する工程は、さらに、負極材料を用いて負極合剤スラリーを形成する工程、負極集電体上に負極合剤スラリーを塗布することにより負極合剤層を形成する工程を含んでいてもよい。 The process of forming the negative electrode active material layer may further include a process of forming a negative electrode mixture slurry using a negative electrode material, and a process of forming a negative electrode mixture layer by applying the negative electrode mixture slurry onto a negative electrode current collector.
負極材料は、黒鉛粒子の含有量が７０質量％以上である負極活物質を含み、さらにバインダ及び繊維状炭素を含んでいてもよい。負極活物質は、黒鉛粒子のみを含んでいてもよく、黒鉛粒子に加えて、さらにＳｉ含有粒子を含んでいてもよい。 The negative electrode material includes a negative electrode active material having a graphite particle content of 70% by mass or more, and may further include a binder and fibrous carbon. The negative electrode active material may include only graphite particles, or may further include Si-containing particles in addition to the graphite particles.
負極活物質の総量に対する黒鉛粒子の含有量は、７０質量％以上１００質量％以下であってもよく、好ましくは８０質量％以上９７質量％以下であり、より好ましくは９０質量％以上９５質量％以下である。負極活物質の総量に対するＳｉ含有粒子の含有量は、０質量％以上３０質量％以下であってもよく、好ましくは３質量％以上２０質量％以下であり、より好ましくは５質量％以上１０質量％以下である。負極活物質中の黒鉛粒子の含有量が上記の範囲内である場合、後述する比表面積及び成形圧力の黒鉛粒子を含む負極合剤層を圧縮することにより、圧密性に優れた負極活物質層を得ることができる。また、負極活物質層の比表面積が増加することを抑制できる。 The content of the graphite particles relative to the total amount of the negative electrode active material may be 70% by mass or more and 100% by mass or less, preferably 80% by mass or more and 97% by mass or less, and more preferably 90% by mass or more and 95% by mass or less. The content of the Si-containing particles relative to the total amount of the negative electrode active material may be 0% by mass or more and 30% by mass or less, preferably 3% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 10% by mass or less. When the content of the graphite particles in the negative electrode active material is within the above range, a negative electrode active material layer having excellent compactibility can be obtained by compressing the negative electrode mixture layer containing the graphite particles with the specific surface area and molding pressure described later. In addition, an increase in the specific surface area of the negative electrode active material layer can be suppressed.
黒鉛粒子は、天然黒鉛であってもよく、人造黒鉛であってもよい。黒鉛粒子は、表面に非晶質炭素の被覆層を有していてもよい。負極活物質に含まれる黒鉛粒子は１種であってもよく、２種以上であってもよい。負極活物質に含まれる黒鉛粒子が２種以上である場合、黒鉛粒子の含有量は、２種以上の黒鉛粒子の総量をいう。 The graphite particles may be natural graphite or artificial graphite. The graphite particles may have a coating layer of amorphous carbon on the surface. The graphite particles contained in the negative electrode active material may be of one type or of two or more types. When the graphite particles contained in the negative electrode active material are of two or more types, the content of the graphite particles refers to the total amount of the two or more types of graphite particles.
黒鉛粒子の比表面積（ＢＥＴ）は、１．０ｍ２／ｇ以上２．５ｍ２／ｇ以下であり、より好ましくは１．２ｍ２／ｇ以上２．０ｍ２／ｇ以下である。黒鉛粒子の比表面積は、０．５ｍ２／ｇ以上３．５ｍ２／ｇ以下であってもよい。負極材料に含まれる黒鉛粒子が２種以上である場合、２種以上の黒鉛粒子を混合した混合物の比表面積をいう。黒鉛粒子の比表面積は、全自動比表面積計を用い、所定の質量の黒鉛粒子をセル内に挿入して測定を行って算出する。 The specific surface area (BET) of the graphite particles is 1.0 m 2 /g or more and 2.5 m 2 /g or less, more preferably 1.2 m 2 /g or more and 2.0 m 2 /g or less. The specific surface area of the graphite particles may be 0.5 m 2 /g or more and 3.5 m 2 /g or less. When the negative electrode material contains two or more types of graphite particles, the specific surface area refers to the specific surface area of a mixture of two or more types of graphite particles. The specific surface area of the graphite particles is calculated by inserting a predetermined mass of graphite particles into a cell and measuring using a fully automatic specific surface area meter.
黒鉛粒子を一軸方向に密度１．７ｇ／ｃｍ３まで圧粉するために必要な成形圧力は、２０ＭＰａ以下であり、好ましくは１８ＭＰａ以下であり、通常５ＭＰａ以上である。黒鉛粒子の上記成形圧力は、３０ＭＰａ以下であってもよい。黒鉛粒子の上記成形圧力は、次の手順で算出できる。まず、底面の面積が一定である筒状の容器に所定量の黒鉛粒子を投入し、自動粉体抵抗測定システムを用いて、容器内の黒鉛粒子を一軸方向に圧粉したときの荷重及び変位を測定する。容器内の黒鉛粒子を密度１．７ｇ／ｃｍ３まで圧粉するために必要な荷重に基づいて上記成形圧力を算出する。 The molding pressure required to compress the graphite particles in one axial direction to a density of 1.7 g/ cm3 is 20 MPa or less, preferably 18 MPa or less, and usually 5 MPa or more. The molding pressure of the graphite particles may be 30 MPa or less. The molding pressure of the graphite particles can be calculated by the following procedure. First, a predetermined amount of graphite particles is placed in a cylindrical container with a constant bottom area, and an automatic powder resistivity measuring system is used to measure the load and displacement when the graphite particles in the container are compressed in one axial direction. The molding pressure is calculated based on the load required to compress the graphite particles in the container to a density of 1.7 g/ cm3 .
上記成形圧力は、黒鉛粒子を密度１．７ｇ／ｃｍ３という高い密度まで圧粉する際に必要となる圧力を表す。負極の製造方法では、負極材料を含む負極合剤層を圧縮して負極活物質層を形成する。負極材料に含まれる黒鉛粒子として比表面積の小さい黒鉛粒子を用いても、負極活物質層を形成する際の負極合剤層の圧縮によって黒鉛粒子が割れると、負極活物質層中の黒鉛粒子の比表面積が増加する。これによって、負極活物質層の比表面積が大きくなると、本電池の充放電により負極が膨化しやすくなる。 The above molding pressure represents the pressure required to compress the graphite particles to a high density of 1.7 g/ cm3 . In the method for manufacturing the negative electrode, a negative electrode mixture layer containing a negative electrode material is compressed to form a negative electrode active material layer. Even if graphite particles with a small specific surface area are used as the graphite particles contained in the negative electrode material, if the graphite particles are broken by compression of the negative electrode mixture layer when forming the negative electrode active material layer, the specific surface area of the graphite particles in the negative electrode active material layer increases. If the specific surface area of the negative electrode active material layer increases as a result, the negative electrode is more likely to swell due to charging and discharging of the battery.
一方、本実施形態の負極材料に含まれる黒鉛粒子は、比表面積及び上記成形圧力が上記の範囲にある。そのため、負極材料を含む負極合剤層を圧縮しても、黒鉛粒子が割れにくいため、圧縮後に負極活物質層の比表面積が増加することを抑制できる。これにより、本電池の充放電によって負極が膨化することを抑制できる。 On the other hand, the graphite particles contained in the negative electrode material of this embodiment have a specific surface area and the molding pressure in the above range. Therefore, even if the negative electrode mixture layer containing the negative electrode material is compressed, the graphite particles are not likely to break, so that an increase in the specific surface area of the negative electrode active material layer after compression can be suppressed. This makes it possible to suppress the expansion of the negative electrode due to charging and discharging of the battery.
黒鉛粒子の上記成形圧力は、黒鉛粒子のタップ密度から導き出せるパラメータではないと考えられる。一般的なタップ密度は低荷重域の圧力で測定される値であり、上記成形圧力のように黒鉛粒子を１．７ｇ／ｃｍ３という高い密度に圧粉するような高荷重域の圧力で測定される値ではないためである。したがって、タップ密度が大きい黒鉛粒子であっても、上記成形圧力を小さくできるとは限らない。 The compaction pressure of the graphite particles is not considered to be a parameter that can be derived from the tap density of the graphite particles. This is because a typical tap density is a value measured at a pressure in a low load range, and is not a value measured at a pressure in a high load range such as the compaction pressure described above, where the graphite particles are compressed to a high density of 1.7 g/ cm3 . Therefore, even if the graphite particles have a high tap density, the compaction pressure described above cannot necessarily be reduced.
黒鉛粒子の平均粒子径Ｄ５０は、５μｍ以上３０μｍ以下であってもよく、好ましくは８μｍ以上２５μｍ以下であり、１０μｍ以上２５μｍ以下であってもよい。本明細書における平均粒子径Ｄ５０は、体積基準の粒度分布において粒子径が小さい方からの頻度の累積が５０％になる粒子径である。黒鉛粒子の平均粒子径Ｄ５０が上記の範囲内であることにより、負極合剤層を圧縮する際に黒鉛粒子の比表面積が増加しにくくなる。体積基準の粒度分布は、レーザ回折式粒度分布測定装置（島津製作所製の「ＳＡＬＤ－２２００」等）により測定できる。 The average particle diameter D50 of the graphite particles may be 5 μm or more and 30 μm or less, preferably 8 μm or more and 25 μm or less, and may be 10 μm or more and 25 μm or less. In this specification, the average particle diameter D50 is the particle diameter at which the cumulative frequency from the smallest particle diameter in the volumetric particle size distribution is 50%. By having the average particle diameter D50 of the graphite particles within the above range, the specific surface area of the graphite particles is less likely to increase when the negative electrode mixture layer is compressed. The volumetric particle size distribution can be measured using a laser diffraction particle size distribution measuring device (such as Shimadzu Corporation's "SALD-2200").
黒鉛粒子のＸ線回折によるピーク強度Ｉ（００４）及びピーク強度Ｉ（１１０）に基づいて算出した比Ｉ（００４）／Ｉ（１１０）で表される黒鉛粒子の配向度は、好ましくは３．０以上であり、より好ましくは３．５以上であり、４．０以上であってもよい。ピーク強度Ｉ（００４）は、黒鉛粒子のＸ線回折の００４回折線から求めた面間隔ｄ００４のピーク強度である。ピーク強度Ｉ（１１０）は、黒鉛粒子のＸ線回折の１１０回折線から求めた面間隔ｄ１１０のピーク強度である。黒鉛粒子が配向性に優れていると、ベーサル面（配向面）でのへき開粉砕が生じやすくなるため、負極合剤層を圧縮する際に黒鉛粒子の比表面積が増加しにくく、負極活物質層の比表面積が大きくなりにくい。 The degree of orientation of the graphite particles, represented by the ratio I(004)/I(110) calculated based on the peak intensity I(004) and peak intensity I(110) by X-ray diffraction of the graphite particles, is preferably 3.0 or more, more preferably 3.5 or more, and may be 4.0 or more. The peak intensity I(004) is the peak intensity of the interplanar spacing d 004 obtained from the 004 diffraction line of the X-ray diffraction of the graphite particles. The peak intensity I(110) is the peak intensity of the interplanar spacing d 110 obtained from the 110 diffraction line of the X-ray diffraction of the graphite particles. When the graphite particles have excellent orientation, cleavage and crushing on the basal plane (orientation plane) are likely to occur, so that the specific surface area of the graphite particles is unlikely to increase when the negative electrode mixture layer is compressed, and the specific surface area of the negative electrode active material layer is unlikely to increase.
Ｓｉ含有粒子は、例えばケイ素単体の粒子、ＳｉＯｘ粒子、ＳｉＣ（多孔質炭素粒子内にケイ素のナノ粒子が分散されたもの）粒子等が挙げられ、好ましくはＳｉＣ粒子である。Ｓｉ含有粒子は、表面が非晶質炭素により被覆されていてもよい。Ｓｉ含有粒子の平均粒子径Ｄ５０は、好ましくは２μｍ以上８μｍ以下であり、より好ましくは３μｍ以上５μｍ以下である。 The Si-containing particles include, for example, particles of simple silicon, SiOx particles, and SiC (porous carbon particles with silicon nanoparticles dispersed therein) particles, and are preferably SiC particles. The surface of the Si-containing particles may be coated with amorphous carbon. The average particle diameter D50 of the Si-containing particles is preferably 2 μm or more and 8 μm or less, and more preferably 3 μm or more and 5 μm or less.
ＳｉＣ粒子は、炭素ドメインと、サイズが５０ｎｍ以下であるケイ素ドメインとを含み、ＳｉＣ粒子中の酸素含有量が７質量％以下であることが好ましい。このようなＳｉＣ粒子を含むことにより、ＳｉＣ粒子の割れを抑制することができ、酸素含有量が少ないため電池容量を向上できる。ＳｉＣ粒子に含まれる酸素は、炭素ドメインに含まれていてもよく、ケイ素ドメインに含まれていてもよく、両方に含まれていてもよい。ケイ素ドメインのサイズは、集束イオンビーム（ＦＩＢ）加工により取り出した負極活物質層を透型過電子顕微鏡（ＴＥＭ）で観察し、エネルギー分散型Ｘ線分析（ＥＤＸ）マッピングにより元素（Ｓｉ，Ｃ）を確認した後、明視野像（ＢＦ像）の高角度散乱暗視野像（ＨＡＡＤＦ像）で確認した形状及び得られるコントラストから判断できる。酸素含有量は、酸素分析装置を用い、不活性ガス中の加熱溶融法により抽出した酸素量により決定できる。ＳｉＣ粒子の平均粒子径Ｄ５０は、好ましくは２μｍ以上８μｍ以下であり、より好ましくは３μｍ以上５μｍ以下である。ＳｉＣ粒子は内部に空隙を有していてよく、空隙率は好ましくは５体積％以上である。ＳｉＣ粒子は、表面が非晶質炭素により被覆されていてもよい。 The SiC particles preferably contain a carbon domain and a silicon domain having a size of 50 nm or less, and the oxygen content in the SiC particles is 7 mass% or less. By containing such SiC particles, cracking of the SiC particles can be suppressed, and the battery capacity can be improved due to the low oxygen content. The oxygen contained in the SiC particles may be contained in the carbon domain, the silicon domain, or both. The size of the silicon domain can be determined from the shape and contrast confirmed in the high angle scattering dark field image (HAADF image) of the bright field image (BF image) after observing the negative electrode active material layer extracted by focused ion beam (FIB) processing with a transmission electron microscope (TEM) and confirming the elements (Si, C) by energy dispersive X-ray analysis (EDX) mapping. The oxygen content can be determined by the amount of oxygen extracted by a heating and melting method in an inert gas using an oxygen analyzer. The average particle diameter D50 of the SiC particles is preferably 2 μm or more and 8 μm or less, more preferably 3 μm or more and 5 μm or less. The SiC particles may have voids therein, and the porosity is preferably 5% by volume or more. The surfaces of the SiC particles may be coated with amorphous carbon.
負極活物質が黒鉛粒子及びＳｉ含有粒子を含む場合、Ｓｉ含有粒子の平均粒子径Ｄ５０は、黒鉛粒子の平均粒子径Ｄ５０の０．１０倍以上０．３５倍以下であることが好ましく、０．１５倍以上０．３０倍以下であることがより好ましい。負極活物質がＳｉ含有粒子を含む場合、Ｓｉ含有粒子の平均粒子径Ｄ５０が上記の範囲内であることにより、負極合剤層の圧縮により、負極活物質が割れて負極活物質層の比表面積が増加すること抑制できる。また、本電池の充放電に伴ってＳｉ含有粒子が膨張収縮することによって発生する内部ストレスを緩和できる。これにより、負極活物質がＳｉ含有粒子を含む場合であっても、本電池の充放電により負極が膨化することを抑制できる。 When the negative electrode active material contains graphite particles and Si-containing particles, the average particle diameter D50 of the Si-containing particles is preferably 0.10 to 0.35 times the average particle diameter D50 of the graphite particles, and more preferably 0.15 to 0.30 times. When the negative electrode active material contains Si-containing particles, by having the average particle diameter D50 of the Si-containing particles within the above range, it is possible to suppress the negative electrode active material from cracking due to compression of the negative electrode mixture layer, thereby suppressing an increase in the specific surface area of the negative electrode active material layer. In addition, it is possible to alleviate internal stress caused by the expansion and contraction of the Si-containing particles accompanying the charging and discharging of the battery. As a result, even when the negative electrode active material contains Si-containing particles, it is possible to suppress the expansion of the negative electrode due to the charging and discharging of the battery.
負極材料は、上記したように、バインダ及び繊維状炭素を含むことができる。バインダとしては、スチレンブタジエンラバー（ＳＢＲ）、カルボキシメチルセルロース（ＣＭＣ）、及びポリアクリル酸（ＰＡＡ）等が挙げられる。繊維状炭素としては、カーボンナノチューブ（ＣＮＴ）が挙げられる。繊維状炭素を含むことにより、負極活物質間の導電パスを維持しやすくなり、本電池の耐久性を向上できる。 As described above, the negative electrode material may contain a binder and fibrous carbon. Examples of binders include styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polyacrylic acid (PAA). Examples of fibrous carbon include carbon nanotubes (CNT). By including fibrous carbon, it becomes easier to maintain the conductive path between the negative electrode active materials, and the durability of the battery can be improved.
ＳＢＲの含有量は、負極材料の総量に対して好ましくは０．５質量％以上５．０質量％以下であり、より好ましくは１．０質量％以上３．０質量％以下である。ＣＭＣの含有量は、負極材料の総量に対して好ましくは０．３質量％以上３．０質量％以下であり、より好ましくは０．５質量％以上１．５質量％以下である。ＰＡＡの含有量は、負極材料の総量に対して好ましくは０．５質量％以上５．０質量％以下であり、より好ましくは１．０質量％以上３．０質量％以下である。上記でいう負極材料の総量は、負極活物質層を構成する成分の総量をいう。 The content of SBR is preferably 0.5% by mass or more and 5.0% by mass or less, more preferably 1.0% by mass or more and 3.0% by mass or less, based on the total amount of the negative electrode material. The content of CMC is preferably 0.3% by mass or more and 3.0% by mass or less, more preferably 0.5% by mass or more and 1.5% by mass or less, based on the total amount of the negative electrode material. The content of PAA is preferably 0.5% by mass or more and 5.0% by mass or less, more preferably 1.0% by mass or more and 3.0% by mass or less, based on the total amount of the negative electrode material. The total amount of the negative electrode material referred to above refers to the total amount of the components constituting the negative electrode active material layer.
ＣＮＴは、単層カーボンナノチューブ（ＳＷＣＮＴ）であることが好ましい。ＳＷＣＮＴは、炭素六角網面が１層で１本の円筒形状を構成する炭素ナノ構造体である。ＳＷＮＣＴの長さは０．０１μｍ以上５μｍ以下であることができ、ＳＷＣＮＴの径は５０ｎｍ以下であることが好ましく、１５ｎｍ以下であることがより好ましい。 The CNT is preferably a single-walled carbon nanotube (SWCNT). SWCNT is a carbon nanostructure in which a single layer of carbon hexagonal mesh planes forms a single cylindrical shape. The length of the SWCNT can be 0.01 μm or more and 5 μm or less, and the diameter of the SWCNT is preferably 50 nm or less, and more preferably 15 nm or less.
負極材料を用いて負極合剤スラリーを形成する工程では、負極活物質の周囲を、バインダであるＣＭＣ及び／又はＰＡＡで被覆するために、負極活物質とＣＭＣ及び／又はＰＡＡとを混練する工程を行うことが好ましい。負極活物質とＣＭＣ及び／又はＰＡＡとの混練は、固練りで行うことが好ましい。固練りを行う際に、混練する成分の混合物に加わる圧力負荷を最適化する方法としては、混合物の分散溶媒率（例えば、水分率）を調整し、理想固形分率を算出する方法が挙げられる。理想固形分率は、例えば次のように決定することができる。まず、規定組成の負極活物質の粉体（例えば、黒鉛粒子とＳｉ含有粒子との混合粉体）に分散溶媒（水）を添加した混合物を用意する。この混合物に混練に必要となるトルクが最大となる分散溶媒率（水分率）をＡ０［％］とし、分散溶媒率Ａ０［％］に相当する負極活物質の粉体１００ｇあたりの分散溶媒量（水分量）をＡ１［ｍＬ］とすると、最大のトルクを与える理想固形分率Ｂ０［％］は下記式によって算出できる。
Ｂ０［％］＝１００－Ａ０＝｛１００／（１００＋Ａ１）｝×１００
In the process of forming the negative electrode mixture slurry using the negative electrode material, it is preferable to perform a process of kneading the negative electrode active material with CMC and/or PAA as a binder in order to cover the periphery of the negative electrode active material. It is preferable to knead the negative electrode active material with CMC and/or PAA by solid kneading. When performing solid kneading, a method of optimizing the pressure load applied to the mixture of the components to be kneaded includes a method of adjusting the dispersion solvent ratio (e.g., moisture ratio) of the mixture and calculating the ideal solid content ratio. The ideal solid content ratio can be determined, for example, as follows. First, a mixture is prepared by adding a dispersion solvent (water) to a powder of a negative electrode active material of a specified composition (e.g., a mixed powder of graphite particles and Si-containing particles). If the dispersion solvent percentage (moisture percentage) at which the torque required for kneading this mixture is maximized is A0 [%], and the amount of dispersion solvent (moisture content) per 100 g of negative electrode active material powder corresponding to the dispersion solvent percentage A0 [%] is A1 [mL], then the ideal solid content percentage B0 [%] that gives the maximum torque can be calculated by the following formula.
B0 [%] = 100 - A0 = {100/(100 + A1 )} x 100
負極合剤スラリーを形成する工程は、さらに、負極活物質とＣＭＣ及び／又はＰＡＡとを混練して得た混練体に、ＣＭＣ及び／又はＰＡＡ以外のバインダ（例えば、ＳＢＲ）及び分散溶媒を添加して、希釈混合する工程を含むことができる。この希釈混合する工程を経て、負極合剤スラリーを形成できる。 The process of forming the negative electrode mixture slurry may further include a process of adding a binder other than CMC and/or PAA (e.g., SBR) and a dispersion solvent to the mixture obtained by kneading the negative electrode active material with CMC and/or PAA, and diluting and mixing the mixture. Through this diluting and mixing process, the negative electrode mixture slurry can be formed.
負極合剤スラリーを負極集電体上に塗布することにより負極合剤層を形成する工程は、負極集電体上の負極合剤スラリーを乾燥することによって負極合剤層を形成できる。負極合剤層を形成する工程は、負極集電体上に塗布した負極合剤スラリーを乾燥する前に、当該負極合剤スラリーの磁力配向処理を行う工程を行ってもよい。磁力配向処理を行う工程では、負極合剤スラリーに含まれる黒鉛粒子の配向面（ベーサル面）を、負極平面に対して垂直方向に近づくように配向させることが好ましい。負極材料に含まれる黒鉛粒子として、配向性の高い黒鉛粒子を用いた場合、本電池の充放電により、黒鉛粒子の配向面（ベーサル面）の膨張収縮が大きくなりやすい。この配向面を、負極平面に対して垂直方向に磁力配向させることにより、本電池の充放電に生じる負極の膨化を抑制できる。 In the process of forming the negative electrode mixture layer by applying the negative electrode mixture slurry onto the negative electrode current collector, the negative electrode mixture layer can be formed by drying the negative electrode mixture slurry on the negative electrode current collector. In the process of forming the negative electrode mixture layer, a process of performing a magnetic orientation process on the negative electrode mixture slurry before drying the negative electrode mixture slurry applied onto the negative electrode current collector may be performed. In the process of performing the magnetic orientation process, it is preferable to orient the orientation surface (basal surface) of the graphite particles contained in the negative electrode mixture slurry so that it approaches a direction perpendicular to the negative electrode plane. When highly oriented graphite particles are used as the graphite particles contained in the negative electrode material, the expansion and contraction of the orientation surface (basal surface) of the graphite particles tends to increase due to charging and discharging of the battery. By magnetically orienting this orientation surface in a direction perpendicular to the negative electrode plane, the swelling of the negative electrode caused by charging and discharging of the battery can be suppressed.
磁力配向処理を行う工程の後、負極集電体上の負極合剤スラリーを乾燥して負極合剤層を形成する。このようにして得られた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、負極を製造できる。上記した負極合剤スラリーを形成する工程において、負極活物質の周囲をＣＭＣ及び／又はＰＡＡで被覆することにより、負極合剤層の圧縮時に負極活物質を滑りやすくできる。これにより、負極合剤層を圧縮して得られる負極活物質層の比表面積の増加を抑制できる。 After the magnetic orientation process, the negative electrode mixture slurry on the negative electrode current collector is dried to form a negative electrode mixture layer. The negative electrode mixture layer thus obtained is compressed to form a negative electrode active material layer, thereby manufacturing a negative electrode. In the process of forming the negative electrode mixture slurry described above, the negative electrode active material is coated with CMC and/or PAA, which makes it easier for the negative electrode active material to slide when the negative electrode mixture layer is compressed. This makes it possible to suppress an increase in the specific surface area of the negative electrode active material layer obtained by compressing the negative electrode mixture layer.
（負極）
本実施形態の負極は、負極集電体と負極活物質層とを有する。負極活物質層は、黒鉛粒子の含有量が７０質量％以上である負極活物質を含む。負極活物質は、さらにＳｉ含有粒子を含んでいてもよい。負極活物質に含まれる黒鉛粒子及びＳｉ含有粒子は、上記負極の製造方法で説明した黒鉛粒子及びＳｉ含有粒子であってもよい。負極活物質層に含まれる黒鉛粒子の含有量及びＳｉ含有粒子の含有量は、上記で説明した負極材料に含まれるそれぞれの含有量と同じとすることができる。
(Negative electrode)
The negative electrode of this embodiment has a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer contains a negative electrode active material having a graphite particle content of 70 mass% or more. The negative electrode active material may further contain Si-containing particles. The graphite particles and Si-containing particles contained in the negative electrode active material may be the graphite particles and Si-containing particles described in the manufacturing method of the negative electrode. The content of the graphite particles and the content of the Si-containing particles contained in the negative electrode active material layer may be the same as the respective contents contained in the negative electrode material described above.
負極活物質層は、さらに、バインダ及び繊維状炭素を含むことができる。負極活物質層に含まれるバインダの含有量及び繊維状炭素の含有量は、上記で説明した負極材料に含まれるそれぞれの含有量と同じとすることができる。 The negative electrode active material layer may further include a binder and fibrous carbon. The binder content and fibrous carbon content contained in the negative electrode active material layer may be the same as the respective contents contained in the negative electrode material described above.
負極活物質層の比表面積（ＢＥＴ）は、１．０ｍ２／ｇ以上３．０ｍ２／ｇ以下であり、好ましくは１．２ｍ２／ｇ以上２．５ｍ２／ｇ以下である。負極活物質層の比表面積は、全自動比表面積計を用いて、所定のサイズに裁断した負極をセル内に挿入して測定を行い、負極活物質層の質量あたりの値として算出する。上記比表面積を有する負極活物質層は、例えば、上記した負極の製造方法によって得ることができる。 The specific surface area (BET) of the negative electrode active material layer is 1.0 m 2 /g or more and 3.0 m 2 /g or less, preferably 1.2 m 2 /g or more and 2.5 m 2 /g or less. The specific surface area of the negative electrode active material layer is measured by inserting the negative electrode cut to a predetermined size into a cell using a fully automatic specific surface area meter, and calculated as a value per mass of the negative electrode active material layer. The negative electrode active material layer having the above specific surface area can be obtained, for example, by the above-mentioned method for producing a negative electrode.
負極活物質層の厚みは、好ましくは１００μｍ以上２６０μｍ以下であり、より好ましくは１２０μｍ以上２００μｍ以下である。 The thickness of the negative electrode active material layer is preferably 100 μm or more and 260 μm or less, and more preferably 120 μm or more and 200 μm or less.
負極活物質層の充填密度は、好ましくは１．２０ｇ／ｃｍ３以上１．７０ｇ／ｃｍ３以下であり、より好ましくは１．４５ｇ／ｃｍ３以上１．６５ｇ／ｃｍ３以下である。負極活物質層の空隙率は、２０％以上３５％以下であることが好ましい。負極活物質層の充填密度は、負極活物質層の目付量［ｇ／ｍ２］を厚みで除して算出することができる。負極活物質層の空隙率［％］は、｛１－（充填密度／２．２）｝×１００として算出できる。 The packing density of the negative electrode active material layer is preferably 1.20 g/cm 3 or more and 1.70 g/cm 3 or less, more preferably 1.45 g/cm 3 or more and 1.65 g/cm 3 or less. The porosity of the negative electrode active material layer is preferably 20% or more and 35% or less. The packing density of the negative electrode active material layer can be calculated by dividing the basis weight [g/m 2 ] of the negative electrode active material layer by the thickness. The porosity [%] of the negative electrode active material layer can be calculated as {1-(packing density/2.2)}×100.
（非水電解質二次電池）
本電池は、上記した負極を備えることができる。本電池は通常、負極、正極、及びセパレータを有する電極体と、電解液とを有する。本電池は、電極体と電解質とを収容する外装体を含むことができる。電極体と外装体との間には、電極ホルダーとしての樹脂シートが配置されていてもよい。電極体の厚みをＴとし、外装体（ケース）の一対の側壁の間の距離をＤとするとき、Ｔ／Ｄは、好ましくは１０以上２００以下であり、より好ましくは２０以上１００以下である。後述するように、本電池は負極活物質層の膨化が抑制されているため、上記範囲のＴ／Ｄであっても電極体の膨張を許容することができる。本電池は、角型電池であることが好ましい。
(Non-aqueous electrolyte secondary battery)
The present battery may include the above-mentioned negative electrode. The present battery usually includes an electrode body having a negative electrode, a positive electrode, and a separator, and an electrolyte. The present battery may include an exterior body that houses the electrode body and the electrolyte. A resin sheet may be disposed between the electrode body and the exterior body as an electrode holder. When the thickness of the electrode body is T and the distance between a pair of side walls of the exterior body (case) is D, T/D is preferably 10 to 200, more preferably 20 to 100. As described later, the present battery is capable of allowing the expansion of the electrode body even when T/D is within the above range, since the expansion of the negative electrode active material layer is suppressed. The present battery is preferably a prismatic battery.
電極体は、負極の負極活物質層と正極の正極活物質層とがセパレータを介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ることが好ましい。 The electrode body has a structure in which a negative electrode active material layer of a negative electrode and a positive electrode active material layer of a positive electrode are laminated with a separator interposed therebetween. The electrode body may be of a wound type or a laminated type. It is preferable that the electrode body be a flat electrode body.
負極は、上記したように負極集電体上に形成された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。 The negative electrode has a negative electrode active material layer formed on a negative electrode current collector as described above. The negative electrode current collector is, for example, a metal foil made of a copper material such as copper or a copper alloy.
セパレータは、本電池の分野で公知の材料を用いることができる。セパレータは、基材層と、基材層上に形成された耐熱層とを有することが好ましい。基材層は、好ましくはポリオレフィンで構成され、より好ましくはポリエチレンで構成される。耐熱層は、セラミック粒子等の無機粒子と、アクリル系バインダー、フッ素ポリマー系バインダー、及びスチレンブタジエンゴム（ＳＢＲ）等のバインダとを含むことが好ましい。耐熱層は、負極及び正極に接着するための接着層であってもよく、耐熱層上に接着層が形成されていてもよい。 The separator may be made of a material known in the field of batteries. The separator preferably has a substrate layer and a heat-resistant layer formed on the substrate layer. The substrate layer is preferably made of polyolefin, more preferably polyethylene. The heat-resistant layer preferably contains inorganic particles such as ceramic particles, and a binder such as an acrylic binder, a fluoropolymer binder, and styrene butadiene rubber (SBR). The heat-resistant layer may be an adhesive layer for adhering to the negative electrode and the positive electrode, or an adhesive layer may be formed on the heat-resistant layer.
正極及び電解質は、本電池の分野で公知の材料を用いることができる。 The positive electrode and electrolyte can be made of materials known in the field of batteries.
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。
〔実施例１〕
（負極の作製）
負極活物質として表１に示す黒鉛粒子、及び、Ｓｉ含有粒子としてＳｉＣ粒子を用い、バインダとしてカルボキシメチルセルロース（ＣＭＣ）及びポリアクリル酸（ＰＡＡ）を用い、これらをドライミックスして混合粉体を得た。混合粉体に、繊維状炭素としてのＳＷＣＮＴ（固形分率２質量％の水溶性ペースト）及び分散媒としての水を投入して固練り混練し（固形分率：６２．５％）、混練体を得た。混練体に、バインダとしてのスチレンブタジエンラバー（ＳＢＲ）及び分散溶媒としての水を投入して希釈混合し、負極合剤スラリーを得た。負極合剤スラリーは、黒鉛粒子：ＳｉＣ粒子：ＳＷＣＮＴ：ＣＭＣ：ＰＡＡ：ＳＢＲ＝９０：１０：０．５：１：２：２（質量比）となるように、撹拌造粒機を用いて調製した。固練り時の固形分率は、上記した理想固形分率Ｂ０［％］を算出することにより決定した。
The present disclosure will be described more specifically below with reference to examples and comparative examples.
Example 1
(Preparation of negative electrode)
Graphite particles shown in Table 1 were used as the negative electrode active material, and SiC particles were used as the Si-containing particles. Carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) were used as the binder, and these were dry-mixed to obtain a mixed powder. SWCNT (a water-soluble paste with a solid content of 2% by mass) as fibrous carbon and water as a dispersion medium were added to the mixed powder, and the mixture was kneaded and kneaded (solid content: 62.5%) to obtain a kneaded body. Styrene butadiene rubber (SBR) as a binder and water as a dispersion solvent were added to the kneaded body, and the mixture was diluted and mixed to obtain a negative electrode mixture slurry. The negative electrode mixture slurry was prepared using a stirring granulator so that the graphite particles: SiC particles: SWCNT: CMC: PAA: SBR = 90: 10: 0.5: 1: 2: 2 (mass ratio). The solid content rate during the kneading was determined by calculating the ideal solid content rate B 0 [%] described above.
負極集電体としての銅箔（厚み１０μｍ）上に、負極合剤スラリーを塗布して乾燥し、圧縮することにより負極活物質層を形成し、これを所定の寸法に加工して負極とした。負極を真空乾燥した後、負極活物質層の目付量及び負極の厚みを測定したところ、それぞれ２２０ｇ／ｍ２及び１５２μｍであった。負極活物質層の充填密度（＝目付量／厚み）は１．５５ｇ／ｃｍ３であり、空隙率（＝｛１－（充填密度／２．２）｝×１００）は３０％であった。
（正極の作製）
正極活物質としてのリチウムニッケルコバルトマンガン複合酸化物（ＮＣＭ）１００質量部に対し、導電材としてのアセチレンブラック（ＡＢ）１質量部、及び、バインダとしてのポリフッ化ビニリデン（ＰＶＤＦ）１質量部を混合して正極合剤を用意した。正極合剤及びＮ－メチル－２－ピロリドン（ＮＭＰ）を混合して、ペースト状の正極合剤スラリーを作製した。正極集電体としてのアルミニウム箔（厚み１５μｍ）上に正極合剤スラリーを塗布し乾燥して圧縮した後、これを所定の寸法に加工して正極とした。
The negative electrode mixture slurry was applied onto a copper foil (thickness 10 μm) as a negative electrode current collector, dried, and compressed to form a negative electrode active material layer, which was then processed to a predetermined size to form a negative electrode. After the negative electrode was vacuum-dried, the basis weight of the negative electrode active material layer and the thickness of the negative electrode were measured, and were found to be 220 g/m 2 and 152 μm, respectively. The packing density (= basis weight/thickness) of the negative electrode active material layer was 1.55 g/cm 3 , and the porosity (= {1-(packing density/2.2)}×100) was 30%.
(Preparation of Positive Electrode)
A positive electrode mixture was prepared by mixing 1 part by mass of acetylene black (AB) as a conductive material and 1 part by mass of polyvinylidene fluoride (PVDF) as a binder with 100 parts by mass of lithium nickel cobalt manganese composite oxide (NCM) as a positive electrode active material. The positive electrode mixture and N-methyl-2-pyrrolidone (NMP) were mixed to prepare a paste-like positive electrode mixture slurry. The positive electrode mixture slurry was applied to an aluminum foil (thickness 15 μm) as a positive electrode current collector, dried and compressed, and then processed to a predetermined size to form a positive electrode.
（電池の作製）
正極及び負極のそれぞれにリードを取り付け、セパレータを介して正極と負極とを積層して電極体を作製した。電極体をアルミニウムラミネートフィルムで構成される外装体内に挿入し、電解液を注入し、外装体の開口部を封止して電池を得た。電解液は、エチレンカーボネート（ＥＣ）とエチルメチルカーボネート（ＥＭＣ）とジメチルカーボネート（ＤＭＣ）とを体積比でＥＣ：ＥＭＣ：ＤＭＣ＝２０：４０：４０で含む混合溶媒に、リチウム塩としてのＬｉＰＦ６を１ｍｏｌ／Ｌの濃度で溶解させたものを用いた。外装体の側壁間の距離Ｄと電極体の厚みＴとの比Ｔ／Ｄは２０であった。
(Battery Construction)
A lead was attached to each of the positive and negative electrodes, and the positive and negative electrodes were laminated via a separator to prepare an electrode body. The electrode body was inserted into an exterior body made of an aluminum laminate film, an electrolyte was injected, and the opening of the exterior body was sealed to obtain a battery. The electrolyte was a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC=20:40:40, in which LiPF 6 as a lithium salt was dissolved at a concentration of 1 mol/L. The ratio T/D of the distance D between the side walls of the exterior body and the thickness T of the electrode body was 20.
〔実施例２～４、比較例１及び２〕
表１に示す黒鉛粒子及びＳｉ含有粒子を用いたこと以外は、実施例１の手順で電池を作製した。
[Examples 2 to 4, Comparative Examples 1 and 2]
A battery was fabricated in the same manner as in Example 1, except that the graphite particles and Si-containing particles shown in Table 1 were used.
［比表面積の測定］
（黒鉛粒子の比表面積の測定）
全自動比表面積計Macsorb Model-1201（Ｎ２ガスを使用）を用い、所定の質量の黒鉛粒子をセル内に挿入して測定を行い、単位質量あたりの比表面積（ＢＥＴ）を算出した。結果を表１に示す。
[Measurement of specific surface area]
(Measurement of the specific surface area of graphite particles)
A fully automatic specific surface area meter Macsorb Model-1201 (using N2 gas) was used to insert a specified mass of graphite particles into a cell, and measurements were performed to calculate the specific surface area per unit mass (BET). The results are shown in Table 1.
（負極活物質層の比表面積の測定）
全自動比表面積計Macsorb Model-1201（Ｎ２ガスを使用）を用い、所定のサイズに裁断した負極をセル内に挿入して測定を行った。測定後、超音波洗浄により負極活物質層を剥離して負極集電体の質量を測定し、負極活物質層の質量あたりの比表面積（ＢＥＴ）を算出した。結果を表１に示す。
(Measurement of Specific Surface Area of Negative Electrode Active Material Layer)
Using a fully automatic specific surface area meter Macsorb Model-1201 (using N2 gas), the negative electrode cut to a predetermined size was inserted into a cell and measured. After the measurement, the negative electrode active material layer was peeled off by ultrasonic cleaning, the mass of the negative electrode current collector was measured, and the specific surface area (BET) per mass of the negative electrode active material layer was calculated. The results are shown in Table 1.
［黒鉛粒子の成形圧力の測定］
底面の面積が一定である筒状の容器に所定量の黒鉛粒子を投入し、自動粉体抵抗測定システムMCP-PD600を用いて、容器内の黒鉛粒子を一軸方向に圧粉したときの荷重及び変位を測定した。容器内の黒鉛粒子を密度１．７ｇ／ｃｍ３まで圧粉するために必要な荷重に基づいて成形圧力を算出した。結果を表１に示す。
[Measurement of compaction pressure of graphite particles]
A given amount of graphite particles was placed in a cylindrical container with a fixed bottom area, and the load and displacement were measured when the graphite particles in the container were compressed in one axial direction using an automatic powder resistivity measuring system MCP-PD600. The compacting pressure was calculated based on the load required to compress the graphite particles in the container to a density of 1.7 g/ cm3 . The results are shown in Table 1.
［黒鉛粒子の配向度の測定］
全自動多目的Ｘ線回折装置Rigaku_SmartLab（使用Ｘ線：Ｃｕ－Ｋα、スキャン範囲：２０～１１０°）を用い、黒鉛粒子のＸ線回折プロファイルを取得した。面間隔ｄ００４のピーク強度Ｉ（００４）及び面間隔ｄ１１０のピーク強度Ｉ（１１０）から、黒鉛粒子の配向度である比Ｉ（００４）／Ｉ（１１０）を算出した。結果を表１に示す。
[Measurement of the degree of orientation of graphite particles]
An X-ray diffraction profile of the graphite particles was obtained using a fully automated multipurpose X-ray diffractometer Rigaku_SmartLab (X-ray used: Cu-Kα, scan range: 20-110°). The ratio I( 004 )/I(110), which is the degree of orientation of the graphite particles, was calculated from the peak intensity I(004) of the interplanar spacing d 004 and the peak intensity I(110) of the interplanar spacing d 110. The results are shown in Table 1.
［負極厚みの評価］
電池の作製で用いた負極の厚みを初期の厚みとした。温度２５℃の環境下において、上記で作製した電池のＣＣＣＶ充電（充電電流０．４Ｃ、終止電圧４．２Ｖ、終止電流０．１Ｃ）及びＣＣ放電（放電電流０．４Ｃ、終止電圧２．５Ｖ）を１サイクルとして、３００サイクルの充放電を行った。その後、電池を２．５Ｖまで放電し、アルゴン雰囲気下で解体し、負極を取り出した。取り出した負極をＤＭＣ（ジメチルカーボネート）に浸漬して洗浄した後、乾燥して負極の厚みを測定し、３００サイクル後の厚みとした。下記式にしたがって負極の厚みの変化率を算出した。結果を表１に示す。
厚みの変化率［％］＝｛（３００サイクル後の厚み／初期の厚み）－１｝×１００
[Evaluation of negative electrode thickness]
The thickness of the negative electrode used in the preparation of the battery was taken as the initial thickness. In an environment at a temperature of 25° C., the battery prepared above was charged and discharged 300 times, with CCCV charging (charging current 0.4 C, end voltage 4.2 V, end current 0.1 C) and CC discharging (discharging current 0.4 C, end voltage 2.5 V) as one cycle. Thereafter, the battery was discharged to 2.5 V, disassembled under an argon atmosphere, and the negative electrode was removed. The removed negative electrode was immersed in DMC (dimethyl carbonate) and washed, then dried to measure the thickness of the negative electrode, which was taken as the thickness after 300 cycles. The rate of change in the thickness of the negative electrode was calculated according to the following formula. The results are shown in Table 1.
Thickness change rate [%] = {(thickness after 300 cycles/initial thickness) - 1} x 100
比較例１の負極材料に含まれる黒鉛粒子の成形圧力は、実施例１～４の負極材料に含まれる黒鉛粒子の成形圧力よりも大きい。そのため、負極合剤層を圧縮したときの圧密性に劣り、負極合剤層の圧縮により黒鉛粒子が割れて負極活物質層の比表面積が増加し、厚み変化率が大きくなったと考えられる。比較例２の負極材料に含まれる黒鉛粒子の比表面積は、実施例１～４の負極材料に含まれる黒鉛粒子の比表面積よりも大きい。そのため、負極活物質層の比表面積も大きく、厚み変化率が大きくなったと考えられる。実施例４の負極材料は、実施例１～３の負極材料に比較すると、Ｓｉ含有粒子の平均粒子径Ｄ５０と黒鉛粒子の平均粒子径Ｄ５０との比が大きい。そのため、実施例４では、負極合剤層の圧縮により負極活物質層の比表面積が増加しやすく、また、電池の充放電に伴ってＳｉ含有粒子が膨張収縮することによって発生する内部ストレスが緩和されにくく、実施例１～３に比較すると厚み変化率が大きくなったと考えられる。 The molding pressure of the graphite particles contained in the negative electrode material of Comparative Example 1 is greater than the molding pressure of the graphite particles contained in the negative electrode material of Examples 1 to 4. Therefore, the compaction property when the negative electrode mixture layer is compressed is inferior, and it is considered that the graphite particles are broken by the compression of the negative electrode mixture layer, the specific surface area of the negative electrode active material layer increases, and the thickness change rate is large. The specific surface area of the graphite particles contained in the negative electrode material of Comparative Example 2 is greater than the specific surface area of the graphite particles contained in the negative electrode material of Examples 1 to 4. Therefore, it is considered that the specific surface area of the negative electrode active material layer is also large, and the thickness change rate is large. Compared to the negative electrode materials of Examples 1 to 3, the negative electrode material of Example 4 has a large ratio of the average particle diameter D50 of the Si-containing particles to the average particle diameter D50 of the graphite particles. Therefore, in Example 4, the specific surface area of the negative electrode active material layer is likely to increase due to compression of the negative electrode mixture layer, and the internal stress generated by the expansion and contraction of the Si-containing particles accompanying the charging and discharging of the battery is difficult to alleviate, which is thought to result in a larger thickness change rate compared to Examples 1 to 3.
Claims (10)
前記負極集電体上に形成された負極合剤層を圧縮することにより、前記負極活物質層を形成する工程を含み、
前記負極合剤層は、負極材料を含み、
前記負極材料は、黒鉛粒子の含有量が７０質量％以上である負極活物質を含み、
前記黒鉛粒子の比表面積は、１．０ｍ２／ｇ以上２．５ｍ２／ｇ以下であり、
前記黒鉛粒子を一軸方向に密度１．７ｇ／ｃｍ３まで圧粉するために必要な成形圧力は、２０ＭＰａ以下である、負極の製造方法。 A method for producing a negative electrode having a negative electrode current collector and a negative electrode active material layer, comprising the steps of:
a step of compressing the negative electrode mixture layer formed on the negative electrode current collector to form the negative electrode active material layer;
The negative electrode mixture layer contains a negative electrode material,
The negative electrode material includes a negative electrode active material having a graphite particle content of 70 mass% or more,
The specific surface area of the graphite particles is 1.0 m 2 /g or more and 2.5 m 2 /g or less,
a molding pressure required for compressing the graphite particles in one axial direction to a density of 1.7 g/cm 3 is 20 MPa or less.
前記ＳｉＣ粒子中の酸素含有量は、７質量％以下である、請求項２に記載の負極の製造方法。 The Si-containing particles include SiC particles including carbon domains and silicon domains having a size of 50 nm or less;
The method for producing a negative electrode according to claim 2 , wherein the oxygen content in the SiC particles is 7 mass % or less.
前記負極活物質層は、黒鉛粒子の含有量が７０質量％以上である負極活物質を含み、
前記負極活物質は、さらにＳｉ含有粒子を含み、
前記負極活物質層の比表面積は、１．０ｍ２／ｇ以上３．０ｍ２／ｇ以下である、負極。 A negative electrode having a negative electrode current collector and a negative electrode active material layer,
the negative electrode active material layer contains a negative electrode active material having a graphite particle content of 70 mass% or more,
The negative electrode active material further includes Si-containing particles,
The negative electrode, wherein the specific surface area of the negative electrode active material layer is 1.0 m 2 /g or more and 3.0 m 2 /g or less.
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