JP2015037008A - Electrode active material layer for nonaqueous electrolyte secondary battery, and method for manufacturing the same - Google Patents

Electrode active material layer for nonaqueous electrolyte secondary battery, and method for manufacturing the same Download PDF

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JP2015037008A
JP2015037008A JP2013167284A JP2013167284A JP2015037008A JP 2015037008 A JP2015037008 A JP 2015037008A JP 2013167284 A JP2013167284 A JP 2013167284A JP 2013167284 A JP2013167284 A JP 2013167284A JP 2015037008 A JP2015037008 A JP 2015037008A
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active material
electrode active
material layer
porosity
secondary battery
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北吉　雅則
Masanori Kitayoshi
雅則 北吉
崇資 三浦
Takashi Miura
崇資 三浦
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Toyota Motor Corp
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract

PROBLEM TO BE SOLVED: To provide an electrode active material layer for a nonaqueous electrolyte secondary battery which enables the effective increase in the battery capacity.SOLUTION: An electrode active material layer 20 for a nonaqueous electrolyte secondary battery is formed on a current collector 10. The electrode active material layer has a porosity which is changed so as to increase stepwise or continuously along the thickness direction from the current collector 10 toward the surface 20S. The inclination of the porosity in the thickness direction is 3.5-4.0%/10 μm. It is preferable that the electrode active material layer 20 has a laminate structure including a plurality of layers different from one another in porosity.

Description

本発明は、非水電解質二次電池用の電極活物質層とその製造方法に関するものである。   The present invention relates to an electrode active material layer for a non-aqueous electrolyte secondary battery and a method for producing the same.

リチウムイオン二次電池等の非水電解質二次電池は、プラグインハイブリッド車（ＰＨＶ）あるいは電気自動車（ＥＶ）等の用途に利用されている。
非水電解質二次電池は、一対の電極である正極および負極と、これらの間を絶縁するセパレータと、非水電解質とを備える。 Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries are used in applications such as plug-in hybrid vehicles (PHV) or electric vehicles (EV).
A nonaqueous electrolyte secondary battery includes a positive electrode and a negative electrode that are a pair of electrodes, a separator that insulates between them, and a nonaqueous electrolyte.

非水電解質二次電池用の電極（正極または負極）の構造としては、集電体とその上に形成された電極活物質層（正極活物質層または負極活物質層）とを含む積層構造が知られている。
容積当たりのエネルギー密度を向上させることを考慮すれば、電極活物質層は厚い方が好ましい。しかしながら、例えば厚みが７０〜９０μｍである厚膜の電極活物質層では、活物質とＬｉイオン等の伝導イオンとの反応は、活物質と非水電解質とが接触しやすい電極活物質層の表層で集中的に起こる。集電体側の活物質は伝導イオンとは接触しがたく、有効に活用されないため、電極活物質層の厚みに見合った電池容量の向上を得ることが難しい。
また、電極活物質層の表層で反応が集中する結果、電池容量が低下する恐れもある。例えば正極の場合、放電時において、正極活物質層の表層で反応が集中し、その部分で塩濃度が低下して反応抵抗が上昇し、放電容量が低下する恐れがある。 As a structure of the electrode (positive electrode or negative electrode) for the nonaqueous electrolyte secondary battery, a laminated structure including a current collector and an electrode active material layer (positive electrode active material layer or negative electrode active material layer) formed thereon is used. Are known.
In consideration of improving the energy density per volume, it is preferable that the electrode active material layer is thick. However, for example, in the case of a thick electrode active material layer having a thickness of 70 to 90 μm, the reaction between the active material and conductive ions such as Li ions causes the surface layer of the electrode active material layer to easily contact the active material and the nonaqueous electrolyte. Happens intensively. Since the active material on the current collector side is difficult to contact with the conductive ions and is not effectively used, it is difficult to improve the battery capacity corresponding to the thickness of the electrode active material layer.
Further, as a result of the reaction concentration on the surface layer of the electrode active material layer, the battery capacity may be reduced. For example, in the case of the positive electrode, during the discharge, the reaction concentrates on the surface layer of the positive electrode active material layer, and there is a possibility that the salt concentration decreases at that portion, the reaction resistance increases, and the discharge capacity decreases.

特許文献１には、集電体側の空隙率が表面側の空隙率より小さい電極活物質層が開示されている（請求項８）。
特許文献１の段落００１８には、「電解質側の領域の空隙率を大きくしておくことにより、電解液浸透時初期の電解液の浸透速度を大きくすることができ、空隙率が一様の場合より、短時間でまたは空隙なく電極活物質層に電解液を浸透することができる」ことが記載されている。 Patent Document 1 discloses an electrode active material layer in which the current collector-side porosity is smaller than the surface-side porosity (Claim 8).
Paragraph 0018 of Patent Document 1 states that “by increasing the porosity of the electrolyte-side region, the permeation rate of the initial electrolyte can be increased, and the porosity is uniform. Thus, it is described that the electrolytic solution can penetrate into the electrode active material layer in a short time or without voids ”.

特開平09-320569号公報Japanese Unexamined Patent Publication No. 09-320569

しかしながら、特許文献１には、空隙率を厚み方向にどのように変化させることが好ましいか、具体的に記載されていない。そのため、電池容量の向上効果を効果的に得ることは難しい。
本発明者が空隙率の厚み方向の変化について実際に検討を行ったところ、空隙率の厚み方向の変化によっては電池容量の向上効果が効果的に得られないことが分かった。 However, Patent Document 1 does not specifically describe how the porosity is preferably changed in the thickness direction. For this reason, it is difficult to effectively obtain the effect of improving the battery capacity.
When the inventor actually examined the change in the thickness direction of the porosity, it was found that the effect of improving the battery capacity could not be effectively obtained by the change in the thickness direction of the porosity.

本発明は上記事情に鑑みてなされたものであり、電池容量を効果的に増大することが可能な非水電解質二次電池用の電極活物質層を提供することを目的とするものである。   This invention is made | formed in view of the said situation, and it aims at providing the electrode active material layer for nonaqueous electrolyte secondary batteries which can increase battery capacity effectively.

本発明の非水電解質二次電池用の電極活物質層は、
集電体上に形成された非水電解質二次電池用の電極活物質層であって、
前記集電体側から表面側に向けて厚み方向に、空隙率が段階的または連続的に大きくなるように変化しており、
空隙率の厚み方向の傾斜度合が３．５〜４．０％／１０μｍを充足するものである。 The electrode active material layer for the non-aqueous electrolyte secondary battery of the present invention is
An electrode active material layer for a non-aqueous electrolyte secondary battery formed on a current collector,
In the thickness direction from the current collector side toward the surface side, the porosity is changed stepwise or continuously increased,
The degree of inclination of the porosity in the thickness direction satisfies 3.5 to 4.0% / 10 μm.

本明細書において、「空隙率の厚み方向の傾斜度合」は、集電体側から表面側に向けて、１０μｍおきの空隙率の増加量を示したものである。
集電体側から表面側に向かう厚み方向の位置をｘ（μｍ）で表し、厚み方向の位置ｘ（μｍ）における空隙率をｙ（％）で表すとする。任意の位置ｘ１（μｍ）における空隙率をｙ１（％）とし、ｘ１＋１０（μｍ）の位置における空隙率をｙ１＋α（％）としたとき、本発明の非水電解質二次電池用の電極活物質層では、αが３．５〜４．０（％）の範囲内にある。 In the present specification, the “degree of inclination of the porosity in the thickness direction” indicates an increase in the porosity every 10 μm from the current collector side to the surface side.
The position in the thickness direction from the current collector side to the surface side is represented by x (μm), and the porosity at the position x (μm) in the thickness direction is represented by y (%). The electrode active material layer for the nonaqueous electrolyte secondary battery of the present invention when the porosity at an arbitrary position x1 (μm) is y1 (%) and the porosity at a position x1 + 10 (μm) is y1 + α (%) Then, α is in the range of 3.5 to 4.0 (%).

本発明の非水電解質二次電池用の電極活物質層は、空隙率の異なる複数層の積層構造を有することが好ましい。   The electrode active material layer for a non-aqueous electrolyte secondary battery of the present invention preferably has a multi-layered laminated structure with different porosity.

本発明によれば、電池容量を効果的に増大することが可能な非水電解質二次電池用の電極活物質層を提供することができる。   ADVANTAGE OF THE INVENTION According to this invention, the electrode active material layer for nonaqueous electrolyte secondary batteries which can increase battery capacity effectively can be provided.

本発明に係る非水電解質二次電池の構成例を示す模式全体図である。It is a schematic whole view which shows the structural example of the nonaqueous electrolyte secondary battery which concerns on this invention. 図１の非水電解質二次電池における電極積層体の模式断面図である。It is a schematic cross section of the electrode laminated body in the nonaqueous electrolyte secondary battery of FIG. 本発明に係る一実施形態の電極の構造を示す模式断面図である。It is a schematic cross section which shows the structure of the electrode of one Embodiment which concerns on this invention.

「非水電解質二次電池」
図１及び図２に、本発明に係る非水電解質二次電池の構成例を示す。図１は模式全体図、図２は電極積層体の模式断面図である。 "Nonaqueous electrolyte secondary battery"
1 and 2 show a configuration example of a nonaqueous electrolyte secondary battery according to the present invention. FIG. 1 is a schematic overall view, and FIG. 2 is a schematic cross-sectional view of an electrode laminate.

図１に示す非水電解質二次電池１は、外装体（電池容器）１１内に、電極積層体２０と非水電解質（符号略）とが収容されたものである。
図２に示すように、電極積層体２０は、正極２１と負極２２とがこれらを絶縁するセパレータ２３を介して積層されたものである。
外装体１１の外面には、外部接続用の２個の外部端子（プラス端子及びマイナス端子）１２が設けられている。 A non-aqueous electrolyte secondary battery 1 shown in FIG. 1 is one in which an electrode stack 20 and a non-aqueous electrolyte (not shown) are accommodated in an exterior body (battery container) 11.
As shown in FIG. 2, the electrode laminate 20 is obtained by laminating a positive electrode 21 and a negative electrode 22 with a separator 23 insulating them.
Two external terminals (a plus terminal and a minus terminal) 12 for external connection are provided on the outer surface of the exterior body 11.

本発明は、非水電解質二次電池用の電極活物質層に関する。
本発明の電極活物質層は、正極活物質層でも負極活物質層でもよい。
本発明の電極活物質層は集電体上に形成されており、集電体側から表面側に向けて厚み方向に、空隙率が段階的または連続的に大きくなるように変化したものである。
本発明の電極活物質層は、空隙率の厚み方向の傾斜度合が３．５〜４．０％／１０μｍを充足する。 The present invention relates to an electrode active material layer for a non-aqueous electrolyte secondary battery.
The electrode active material layer of the present invention may be a positive electrode active material layer or a negative electrode active material layer.
The electrode active material layer of the present invention is formed on the current collector, and changes so that the porosity increases stepwise or continuously in the thickness direction from the current collector side to the surface side.
In the electrode active material layer of the present invention, the degree of slope of the porosity in the thickness direction satisfies 3.5 to 4.0% / 10 μm.

上記構成を有する本発明の電極活物質層では、例えば総厚が７０〜９０μｍである厚膜であっても、非水電解質が表面側から集電体側の全体に渡って電極活物質層内に浸透しやすい。そのため、表面側から集電体側の全体に渡って、活物質が伝導イオンと良好に接触し、電極活物質層の厚みに見合った電池容量を得ることができる。
本発明は、総厚が７０〜９０μｍである厚膜の電極活物質層に好ましく適用でき、電極活物質層の厚膜化による電池容量の向上効果が得られる。 In the electrode active material layer of the present invention having the above configuration, for example, even if it is a thick film having a total thickness of 70 to 90 μm, the nonaqueous electrolyte is contained in the electrode active material layer from the surface side to the entire current collector side. Easy to penetrate. Therefore, the active material is in good contact with the conductive ions from the surface side to the entire current collector side, and a battery capacity corresponding to the thickness of the electrode active material layer can be obtained.
The present invention can be preferably applied to a thick electrode active material layer having a total thickness of 70 to 90 μm, and an effect of improving battery capacity by obtaining a thick electrode active material layer can be obtained.

正極活物質層であれば、放電時において、正極活物質層の表層での反応集中による表層での塩濃度の低下と反応抵抗の上昇が抑制され、放電容量の向上効果が得られる。
負極活物質層であれば、充電容量の向上効果が得られる。 If it is a positive electrode active material layer, at the time of discharge, the fall of the salt concentration by the reaction concentration in the surface layer of a positive electrode active material layer and the raise of reaction resistance will be suppressed, and the improvement effect of discharge capacity will be acquired.
If it is a negative electrode active material layer, the improvement effect of charge capacity will be acquired.

本発明の電極活物質層は、空隙率の異なる複数層の積層構造を有することが好ましい。
図３は、本発明に係る一実施形態の電極の模式断面図である。この電極は、非水電解質二次電池１における正極２１または負極２２である。
図３に示すように、非水電解質二次電池１における正極２１または負極２２は、集電体１１０上に、集電体１１０側から第１層１２１〜第９層１２９の積層構造を有する電極活物質層１２０が形成されたものである。
図中、符号Ｓは電極活物質層の表面である。
図示例では、電極活物質層１２０は９層構造を有しているが、積層数は適宜設計できる。 The electrode active material layer of the present invention preferably has a multilayer structure having a plurality of different porosity.
FIG. 3 is a schematic cross-sectional view of an electrode according to an embodiment of the present invention. This electrode is the positive electrode 21 or the negative electrode 22 in the nonaqueous electrolyte secondary battery 1.
As shown in FIG. 3, the positive electrode 21 or the negative electrode 22 in the nonaqueous electrolyte secondary battery 1 is an electrode having a laminated structure of a first layer 121 to a ninth layer 129 on the current collector 110 from the current collector 110 side. An active material layer 120 is formed.
In the figure, symbol S is the surface of the electrode active material layer.
In the illustrated example, the electrode active material layer 120 has a nine-layer structure, but the number of layers can be designed as appropriate.

電極活物質層１２０は、空隙率の厚み方向の傾斜度合が３．５〜４．０％／１０μｍを充足する。
例えば、層１２１〜１２９がいずれも１０μｍ厚である場合、層１２２〜１２９の空隙率はいずれも直下層の空隙率より３．５〜４．０％小さく設計される。
層１２１〜１２９の厚みは、任意に設計される。層１２１〜１２９の厚み方向中心の位置ｘ（μｍ）とその位置における空隙率ｙ（％）とをプロットしたとき、空隙率ｙの変化が３．５〜４．０％／１０μｍになるよう、厚み方向の空隙率の変化が設計される。 The electrode active material layer 120 satisfies a degree of inclination of the porosity in the thickness direction of 3.5 to 4.0% / 10 μm.
For example, when the layers 121 to 129 are all 10 μm thick, the porosity of the layers 122 to 129 is designed to be 3.5 to 4.0% smaller than the porosity of the immediately lower layer.
The thicknesses of the layers 121 to 129 are arbitrarily designed. When plotting the position x (μm) at the center in the thickness direction of the layers 121 to 129 and the porosity y (%) at the position, the change in the porosity y is 3.5 to 4.0% / 10 μm. The change in porosity in the thickness direction is designed.

電極活物質層１２０全体の厚み方向中心の空隙率（図３の例では、第５層１２５の空隙率）は、特に空隙率に傾斜を持たせない従来の電極活物質層の空隙率と同様に設計される。
電極活物質層１２０全体の厚み方向中心の空隙率は、２８〜３２％が好ましい。
電極活物質層１２０全体の厚み方向中心の空隙率を従来同様として空隙率に傾斜を持たせた場合、空隙率の厚み方向の傾斜度合が３．５％／１０μｍより小さいと、表層の空隙率が充分に大きくならず、この部分で塩濃度が低下して反応抵抗が上昇し、電池容量が低下する恐れがある。また、空隙率の厚み方向の傾斜度合が４．０％／１０μｍより大きいと、集電体１１０側の空隙率を充分に大きくできず、この部分で塩濃度が低下して反応抵抗が上昇し、電池容量が低下する恐れがある。
空隙率の厚み方向の傾斜度合を３．５〜４．０％／１０μｍとすることで、集電体１１０側から表面Ｓ側の全体に渡って空隙率が充分に確保され、電極活物質層１２０の厚みに見合った電池容量を得ることができる。 The porosity at the center in the thickness direction of the entire electrode active material layer 120 (in the example of FIG. 3, the porosity of the fifth layer 125) is the same as that of the conventional electrode active material layer that does not have an inclination in the porosity. Designed to.
The porosity at the center in the thickness direction of the entire electrode active material layer 120 is preferably 28 to 32%.
When the porosity at the center in the thickness direction of the entire electrode active material layer 120 is inclined as in the conventional case, if the slope of the porosity in the thickness direction is less than 3.5% / 10 μm, the porosity of the surface layer Is not sufficiently large, the salt concentration is lowered at this portion, the reaction resistance is increased, and the battery capacity may be reduced. Further, if the slope of the porosity in the thickness direction is larger than 4.0% / 10 μm, the porosity on the current collector 110 side cannot be sufficiently increased, and the salt concentration is lowered and the reaction resistance is increased at this portion. Battery capacity may be reduced.
By setting the slope of the porosity in the thickness direction to 3.5 to 4.0% / 10 μm, a sufficient porosity is secured from the current collector 110 side to the entire surface S side, and the electrode active material layer A battery capacity corresponding to the thickness of 120 can be obtained.

非水電解質二次電池としては、リチウムイオン二次電池等が挙げられる。
以下、リチウムイオン二次電池を例として、主な構成要素について説明する。 Examples of the non-aqueous electrolyte secondary battery include a lithium ion secondary battery.
Hereinafter, main components will be described by taking a lithium ion secondary battery as an example.

（正極）
正極は、公知の方法により、アルミニウム箔などの正極集電体に正極活物質を塗布して、製造することができる。
公知の正極活物質としては特に制限なく、例えば、ＬｉＣｏＯ２、ＬｉＭｎＯ２、ＬｉＭｎ２Ｏ４、ＬｉＮｉＯ２、ＬｉＮｉｘＣｏ（１−ｘ）Ｏ２、およびＬｉＮｉｘＣｏｙＭｎ（１−ｘ−ｙ）Ｏ２等のリチウム含有複合酸化物等が挙げられる（式中、０＜ｘ＜１、０＜ｙ＜１）。 (Positive electrode)
The positive electrode can be manufactured by applying a positive electrode active material to a positive electrode current collector such as an aluminum foil by a known method.
Known no particular limitation on the positive electrode active material, for example, LiCoO 2, LiMnO 2, LiMn 2 O 4, LiNiO 2, LiNi x Co (1-x) O 2, and LiNi x Co y Mn (1- x-y And lithium-containing composite oxides such as O 2 (where 0 <x <1, 0 <y <1).

例えば、Ｎ−メチル−２−ピロリドン等の分散剤を用い、上記の正極活物質と、炭素粉末等の導電助剤と、ポリフッ化ビニリデン（ＰＶＤＦ）等の結着剤とを混合および混練して、ペーストを得、このペーストをアルミニウム箔等の集電体上に塗布し、乾燥し、プレス加工して、正極活物質層を形成することができる。   For example, using a dispersing agent such as N-methyl-2-pyrrolidone, mixing and kneading the positive electrode active material, a conductive aid such as carbon powder, and a binder such as polyvinylidene fluoride (PVDF). The paste is obtained, and the paste is applied onto a current collector such as an aluminum foil, dried, and pressed to form a positive electrode active material layer.

（負極）
負極活物質としては特に制限なく、Ｌｉ／Ｌｉ＋基準で２．０Ｖ以下にリチウム吸蔵能力を持つものが好ましく用いられる。負極活物質としては、黒鉛等の炭素、金属リチウム、リチウム合金、リチウムイオンのド−プ・脱ド−プが可能な遷移金属酸化物／遷移金属窒化物／遷移金属硫化物、及び、これらの組合わせ等が挙げられる。 (Negative electrode)
The negative electrode active material is not particularly limited, and a material having a lithium storage capacity of 2.0 V or less on the basis of Li / Li + is preferably used. As the negative electrode active material, carbon such as graphite, metallic lithium, lithium alloy, transition metal oxide / transition metal nitride / transition metal sulfide capable of doping / dedoping lithium ions, and these A combination etc. are mentioned.

負極は例えば、公知の方法により、銅箔などの負極集電体に負極活物質を塗布して、製造することができる。
例えば、水等の分散剤を用い、負極活物質と、変性スチレン−ブタジエン共重合体ラテックス等の結着剤と、必要に応じてカルボキシメチルセルロースＮａ塩（ＣＭＣ）等の増粘剤とを混合して、ペーストを得、このペーストを銅箔等の集電体上に塗布し、乾燥し、プレス加工して、負極を得ることができる。 The negative electrode can be produced, for example, by applying a negative electrode active material to a negative electrode current collector such as a copper foil by a known method.
For example, using a dispersant such as water, a negative electrode active material, a binder such as a modified styrene-butadiene copolymer latex, and a thickener such as carboxymethyl cellulose Na salt (CMC) are mixed as necessary. Thus, a paste can be obtained, and this paste can be applied onto a current collector such as a copper foil, dried, and pressed to obtain a negative electrode.

（空隙率の傾斜方法）
正極および／または負極の製造において、集電体上へのペーストの塗布・乾燥・プレス加工の工程を複数回繰り返すことで、積層構造の電極活物質層を形成できる。この際、各層のプレス圧条件を変更することで、各層の空隙率を変化させることができる。各層のペースト組成は同一でも非同一でもよい。
複数層を積層する際のプレス圧を集電体側から表面側に向けて段階的に弱めることで、集電体側から表面側に向けて段階的に空隙率を大きくすることができる。
複数層を積層する際にプレス圧を変化させる場合、必要に応じてペースト塗布量を変化させて各層の厚みを所望厚に調整する。 (Porosity slope method)
In the production of the positive electrode and / or the negative electrode, the electrode active material layer having a laminated structure can be formed by repeating the process of applying, drying, and pressing the paste on the current collector a plurality of times. At this time, the porosity of each layer can be changed by changing the press pressure condition of each layer. The paste composition of each layer may be the same or non-identical.
By gradually decreasing the pressing pressure when laminating a plurality of layers from the current collector side toward the surface side, the porosity can be increased stepwise from the current collector side toward the surface side.
When the press pressure is changed when laminating a plurality of layers, the paste coating amount is changed as necessary to adjust the thickness of each layer to a desired thickness.

（非水電解質）
非水電解質としては公知のものが使用でき、液状、ゲル状もしくは固体状の非水電解質が使用できる。
例えば、プロピレンカーボネ−トあるいはエチレンカーボネ−ト等の高誘電率カーボネート溶媒と、ジエチルカーボネート、メチルエチルカーボネート、ジメチルカーボネート等の低粘度カーボネート溶媒との混合溶媒に、リチウム含有電解質を溶解した非水電界液が好ましく用いられる。 (Nonaqueous electrolyte)
As the non-aqueous electrolyte, known ones can be used, and liquid, gel-like or solid non-aqueous electrolytes can be used.
For example, a lithium-containing electrolyte is dissolved in a mixed solvent of a high dielectric constant carbonate solvent such as propylene carbonate or ethylene carbonate and a low viscosity carbonate solvent such as diethyl carbonate, methyl ethyl carbonate, or dimethyl carbonate. A water electrolysis solution is preferably used.

混合溶媒としては例えば、エチレンカーボネート（ＥＣ）／ジメチルカーボネート（ＤＭＣ）／エチルメチルカーボネート（ＥＭＣ）、およびエチレンカーボネート（ＥＣ）／ジエチルカーボネート（ＤＥＣ）等の混合溶媒が好ましく用いられる。
リチウム含有電解質としては例えば、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣｌＯ４、ＬｉＡｓＦ６、Ｌｉ２ＳｉＦ６、ＬｉＯＳＯ２ＣｋＦ（２ｋ＋１）（ｋ＝１〜８の整数）、ＬｉＰＦｎ｛ＣｋＦ（２ｋ＋１）｝（６−ｎ）（ｎ＝１〜５の整数、ｋ＝１〜８の整数）等のリチウム塩、およびこれらの組合わせが挙げられる。 As the mixed solvent, for example, a mixed solvent such as ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) and ethylene carbonate (EC) / diethyl carbonate (DEC) is preferably used.
Examples of the lithium-containing electrolyte include LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , Li 2 SiF 6 , LiOSO 2 C k F (2k + 1) (k = 1 to 8), LiPF n {C k F (2k + 1) )} (6-n) ( n = 1~5 integer, k = 1 to 8 integer) lithium salts such as, and combinations thereof.

（セパレータ）
セパレータは、正極と負極とを電気的に絶縁し、かつリチウムイオンが透過可能な膜であればよく、多孔質高分子フィルムが好ましく使用される。
セパレータとしては例えば、ＰＰ（ポリプロピレン）製多孔質フィルム、ＰＥ（ポリエチレン）製多孔質フィルム、あるいは、ＰＰ（ポリプロピレン）−ＰＥ（ポリエチレン）の積層型多孔質フィルム等のポリオレフィン製多孔質フィルムが好ましく用いられる。 (Separator)
The separator may be a film that electrically insulates the positive electrode and the negative electrode and is permeable to lithium ions, and a porous polymer film is preferably used.
As the separator, for example, a porous film made of polyolefin such as a porous film made of PP (polypropylene), a porous film made of PE (polyethylene), or a laminated porous film of PP (polypropylene) -PE (polyethylene) is preferably used. It is done.

（外装体（電池容器））
外装体としては公知のものが使用できる。
二次電池の型としては、円筒型、コイン型、角型、あるいはフィルム型（ラミネート型）等があり、所望の型に合わせて外装体を選定することができる。 (Exterior body (battery container))
A well-known thing can be used as an exterior body.
As a type of the secondary battery, there are a cylindrical type, a coin type, a square type, a film type (laminate type), and the like, and an exterior body can be selected according to a desired type.

以上説明したように、本発明によれば、電池容量を効果的に増大することが可能な、非水電解質二次電池用の電極活物質層を提供することができる。   As described above, according to the present invention, it is possible to provide an electrode active material layer for a non-aqueous electrolyte secondary battery that can effectively increase battery capacity.

本発明に係る試験例について説明する。   Test examples according to the present invention will be described.

（試験例１〜６）
試験例１〜６では、正極の製造条件を変更する以外は同一条件として、リチウムイオン二次電池を製造した。 (Test Examples 1-6)
In Test Examples 1 to 6, lithium ion secondary batteries were manufactured under the same conditions except that the positive electrode manufacturing conditions were changed.

＜正極＞
正極活物質として、下記式で表される３元系のリチウム複合酸化物を用意した。
ＬｉＮｉ１／３Ｍｎ１／３Ｃｏ１／３Ｏ２
導電助剤として、アセチレンブラック（電気化学工業（株）社製ＨＳ−１００）を用意した。
結着剤として、ＰＶＤＦ（（株）クレハ社製ＫＦポリマー♯１１２０）を用意した。
分散剤として、Ｎ−メチル−２−ピロリドン（（株）和光純薬工業社製）を用意した。
上記原料をプラネタリミキサーを用いて混合および混練して、ペーストを得た。まず、正極活物質と導電助剤とを混合した後、結着剤を加えて混練し、最後に分散剤を加えて混練した。
原料比は以下の通りとした。
活物質／導電助剤／結着剤／分散剤＝９１／６／３／７２．４（質量比）
上記ペーストを集電体であるアルミニウム箔上にコンマコーターを用いて０．８ｍ／ｍｉｎの条件で塗布した。これを１８０℃で５分間乾燥した後、プレス機を用いてプレス加工して、第１層を形成した。
ペーストの塗布、乾燥、およびプレスの工程を複数回繰り返し、計９層の積層構造からなる電極活物質層（集電体側から第１層〜第９層）を形成した。各層の厚みはいずれも１０μｍとし、総厚は９０μｍとした。
いずれの例においても、各層のペースト組成は同一とした。
試験例１については、第１層〜第９層におけるペーストの塗布量とプレス圧条件を特に変えず、各層の空隙率を厚み方向に一定とした。
試験例２〜９については、第１層〜第９層におけるプレス圧条件を変えることで、各層の空隙率を厚み方向に変化させた。試験例２〜９では、複数層を積層する際のプレス圧を集電体側から表面側に向けて段階的に弱めて、集電体側から表面側に向けて段階的に空隙率を大きくした。プレス圧に合わせてペーストの塗布量を調整することで、各層の厚みを１０μｍに調整した。
いずれの試験例においても、中心の第５層の空隙率は３１％とし、かつ、第１層〜第９層の平均空隙率は３１％とした。
各試験例における、第１層〜第９層の空隙率、総厚、平均空隙率、および空隙率の傾斜度合を表１に示す。 <Positive electrode>
As the positive electrode active material, a ternary lithium composite oxide represented by the following formula was prepared.
LiNi 1/3 Mn 1/3 Co 1/3 O 2
Acetylene black (HS-100 manufactured by Denki Kagaku Kogyo Co., Ltd.) was prepared as a conductive aid.
As a binder, PVDF (KF polymer # 1120 manufactured by Kureha Co., Ltd.) was prepared.
N-methyl-2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.) was prepared as a dispersant.
The raw materials were mixed and kneaded using a planetary mixer to obtain a paste. First, after mixing a positive electrode active material and a conductive support agent, a binder was added and kneaded, and finally a dispersant was added and kneaded.
The raw material ratio was as follows.
Active material / conductive aid / binder / dispersant = 91/6/3 / 72.4 (mass ratio)
The paste was applied onto an aluminum foil as a current collector using a comma coater under the condition of 0.8 m / min. After drying this at 180 degreeC for 5 minute (s), it pressed using the press machine and formed the 1st layer.
The paste application, drying, and pressing steps were repeated a plurality of times to form electrode active material layers (first to ninth layers from the current collector side) having a total of nine layers. Each layer had a thickness of 10 μm and a total thickness of 90 μm.
In any example, the paste composition of each layer was the same.
For Test Example 1, the amount of paste applied in the first to ninth layers and the press pressure conditions were not particularly changed, and the porosity of each layer was made constant in the thickness direction.
About Test Examples 2-9, the porosity of each layer was changed in the thickness direction by changing the press pressure conditions in the first layer to the ninth layer. In Test Examples 2 to 9, the press pressure when laminating a plurality of layers was gradually reduced from the current collector side toward the surface side, and the porosity was increased stepwise from the current collector side toward the surface side. The thickness of each layer was adjusted to 10 μm by adjusting the amount of paste applied according to the press pressure.
In any of the test examples, the porosity of the central fifth layer was 31%, and the average porosity of the first to ninth layers was 31%.
Table 1 shows the porosity, total thickness, average porosity, and slope of the porosity of each of the first to ninth layers in each test example.

＜負極＞
負極活物質として、黒鉛を用いた。
分散剤として水を用い、上記の負極活物質と、結着剤である変性スチレン−ブタジエン共重合体ラテックス（ＳＢＲ）と、増粘剤であるカルボキシメチルセルロースＮａ塩（ＣＭＣ）とを混合および混練して、ペーストを得た。
上記ペーストを集電体である銅箔上に塗布し、１８０℃で５分間乾燥し、プレス機を用いてプレス加工して、負極を得た。 <Negative electrode>
Graphite was used as the negative electrode active material.
Using water as a dispersant, the negative electrode active material, a modified styrene-butadiene copolymer latex (SBR) as a binder, and a carboxymethyl cellulose Na salt (CMC) as a thickener are mixed and kneaded. To obtain a paste.
The said paste was apply | coated on the copper foil which is an electrical power collector, it dried at 180 degreeC for 5 minute (s), and it pressed using the press machine, and obtained the negative electrode.

＜セパレータ＞
ＰＰ（ポリプロピレン）／ＰＥ（ポリエチレン）／ＰＰ（ポリプロピレン）の３層積層構造を有する多孔質フィルムからなる市販のセパレータを用意した。 <Separator>
A commercially available separator made of a porous film having a three-layer laminated structure of PP (polypropylene) / PE (polyethylene) / PP (polypropylene) was prepared.

＜非水電解質＞
エチレンカーボネート（ＥＣ）／ジエチルカーボネート（ＤＥＣ）＝１／１（体積比）を溶媒とし、電解質としてリチウム塩であるＬｉＰＦ６を１ｍｏｌ／Ｌの濃度で溶解して、非水電解液を調製した。 <Nonaqueous electrolyte>
A nonaqueous electrolytic solution was prepared by dissolving LiPF 6 which is a lithium salt as an electrolyte at a concentration of 1 mol / L using ethylene carbonate (EC) / diethyl carbonate (DEC) = 1/1 (volume ratio) as a solvent.

＜リチウムイオン二次電池の製造＞
上記の正極と負極とセパレータとラミネート型外装体とを用い、公知方法により、電池セルを製造した。その後、セル内に非水電解液を注入して、リチウムイオン二次電池を製造した。 <Manufacture of lithium ion secondary batteries>
Using the above positive electrode, negative electrode, separator, and laminate type outer package, a battery cell was produced by a known method. Thereafter, a non-aqueous electrolyte was injected into the cell to produce a lithium ion secondary battery.

＜充放電試験＞
各試験例において得られたリチウムイオン二次電池について、充放電試験を実施した。
２５℃で、４．１Ｖ（ｖｓ.Ｌｉ／Ｌｉ＋）まで充電した後、３Ｖまで放電したときの放電容量を求めた。
電流密度２Ｃと電流密度８Ｃの２条件で試験を行った。
試験例１の放電容量を１００％としたときの、各試験例の各評価条件における放電容量の向上率を求めた。 <Charge / discharge test>
The lithium ion secondary battery obtained in each test example was subjected to a charge / discharge test.
After charging to 4.1 V (vs. Li / Li +) at 25 ° C., the discharge capacity when discharged to 3 V was determined.
The test was conducted under two conditions of current density 2C and current density 8C.
When the discharge capacity of Test Example 1 was assumed to be 100%, the improvement rate of the discharge capacity under each evaluation condition of each Test Example was determined.

評価結果を表１に示す。
集電体側から表面側に向けて厚み方向に空隙率を段階的に大きくなるように変化させ、かつ、空隙率の厚み方向の傾斜度合を３．５〜４．０％／１０μｍの範囲内とした試験例３〜５では、空隙率に変化を持たせなかった試験例１に対して、大きな放電容量の向上効果が見られた。
空隙率の厚み方向の傾斜度合を３．５％／１０μｍ未満とした試験例２、および、空隙率の厚み方向の傾斜度合を４．０％／１０μｍ超とした試験例６では、放電容量の向上効果が不充分であった。
試験例２では、表層の空隙率が不充分であったため、この部分で塩濃度が低下して反応抵抗が上昇し、放電容量が低下したと考えられる。
試験例６では、集電体側の空隙率が不充分であったため、この部分で塩濃度が低下して反応抵抗が上昇し、放電容量が低下したと考えられる。
空隙率の厚み方向の傾斜度合を３．５〜４．０％／１０μｍの範囲内とすることで、電極活物質層を厚膜としたことによる電池容量の向上効果が効果的に得られることが分かった。 The evaluation results are shown in Table 1.
The porosity is changed so as to increase stepwise in the thickness direction from the current collector side to the surface side, and the slope of the porosity in the thickness direction is within a range of 3.5 to 4.0% / 10 μm. In Test Examples 3 to 5, a large discharge capacity improvement effect was observed compared to Test Example 1 in which the porosity was not changed.
In Test Example 2 in which the slope of the porosity in the thickness direction was less than 3.5% / 10 μm and Test Example 6 in which the slope of the porosity in the thickness direction was over 4.0% / 10 μm, the discharge capacity was The improvement effect was insufficient.
In Test Example 2, since the porosity of the surface layer was insufficient, it is considered that the salt concentration decreased at this portion, the reaction resistance increased, and the discharge capacity decreased.
In Test Example 6, since the porosity on the current collector side was insufficient, it was considered that the salt concentration decreased in this portion, the reaction resistance increased, and the discharge capacity decreased.
By increasing the slope of the porosity in the thickness direction within the range of 3.5 to 4.0% / 10 μm, the effect of improving the battery capacity due to the thick electrode active material layer can be effectively obtained. I understood.

Figure 2015037008
Figure 2015037008

本発明の非水電解質二次電池用の負極は、プラグインハイブリッド車（ＰＨＶ）あるいは電気自動車（ＥＶ）に搭載されるリチウムイオン二次電池等に好ましく適用できる。   The negative electrode for a non-aqueous electrolyte secondary battery of the present invention can be preferably applied to a lithium ion secondary battery mounted on a plug-in hybrid vehicle (PHV) or an electric vehicle (EV).

１ 非水電解質二次電池
１１ 外装体（電池容器）
１２ 外部端子
２０ 電極積層体
２１ 正極
２２ 負極
２３ セパレータ
１１０ 集電体
１２０ 電極活物質層
１２１〜１２９ 電極活物質層の各層 1 Nonaqueous electrolyte secondary battery 11 Exterior body (battery container)
DESCRIPTION OF SYMBOLS 12 External terminal 20 Electrode laminated body 21 Positive electrode 22 Negative electrode 23 Separator 110 Current collector 120 Electrode active material layers 121-129 Each layer of an electrode active material layer

Claims (4)

集電体上に形成された非水電解質二次電池用の電極活物質層であって、
前記集電体側から表面側に向けて厚み方向に、空隙率が段階的または連続的に大きくなるように変化しており、
空隙率の厚み方向の傾斜度合が３．５〜４．０％／１０μｍである、非水電解質二次電池用の電極活物質層。 An electrode active material layer for a non-aqueous electrolyte secondary battery formed on a current collector,
In the thickness direction from the current collector side toward the surface side, the porosity is changed stepwise or continuously increased,
An electrode active material layer for a non-aqueous electrolyte secondary battery, wherein the slope of the porosity in the thickness direction is 3.5 to 4.0% / 10 μm. 空隙率の異なる複数層の積層構造を有する、請求項１に記載の非水電解質二次電池用の電極活物質層。   The electrode active material layer for a nonaqueous electrolyte secondary battery according to claim 1, which has a multi-layer laminated structure having different porosity. 総厚が７０〜９０μｍである、請求項１または２に記載の非水電解質二次電池用の電極活物質層。   The electrode active material layer for a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the total thickness is 70 to 90 µm. 請求項２に記載の非水電解質二次電池用の電極活物質層の製造方法であって、
前記集電体上に対する電極活物質を含むペーストの塗布、乾燥、およびプレス加工の工程を繰り返して、前記複数層を積層する工程を有し、
前記複数層を積層する際のプレス圧を前記集電体側から前記表面側に向けて段階的に弱める、非水電解質二次電池用の電極活物質層の製造方法。 A method for producing an electrode active material layer for a non-aqueous electrolyte secondary battery according to claim 2,
The step of applying the paste containing the electrode active material on the current collector, drying, and pressing are repeated to laminate the plurality of layers.
The manufacturing method of the electrode active material layer for nonaqueous electrolyte secondary batteries which weakens the press pressure at the time of laminating | stacking the said multiple layers gradually from the said collector side toward the said surface side.
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WO2021117550A1 (en) 2019-12-13 2021-06-17 パナソニックＩｐマネジメント株式会社 Non-aqueous electrolyte secondary battery
WO2023054096A1 (en) * 2021-09-30 2023-04-06 パナソニックＩｐマネジメント株式会社 Electrode for secondary batteries, and secondary battery
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