JP5904096B2 - Current collector for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents

Current collector for lithium ion secondary battery and lithium ion secondary battery using the same Download PDF

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JP5904096B2
JP5904096B2 JP2012240321A JP2012240321A JP5904096B2 JP 5904096 B2 JP5904096 B2 JP 5904096B2 JP 2012240321 A JP2012240321 A JP 2012240321A JP 2012240321 A JP2012240321 A JP 2012240321A JP 5904096 B2 JP5904096 B2 JP 5904096B2
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current collector
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lithium ion
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JP2014089916A (en
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田中　一正
一正 田中
康之 川中
康之 川中
平林　幸子
幸子 平林
大石　昌弘
昌弘 大石
正樹 蘇武
正樹 蘇武
佐野　篤史
篤史 佐野
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TDK 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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    • Y02E60/10—Energy storage using batteries

Description

本発明は、リチウムイオン二次電池に用いる集電体、およびそれを用いたリチウムイオン二次電池に関するものである。   The present invention relates to a current collector used for a lithium ion secondary battery, and a lithium ion secondary battery using the current collector.

現在、リチウムイオン二次電池は、ニッケル電池、水素蓄電池などと比較して、軽量、高電圧、高容量であるため携帯電話、スマートフォン、モバイル用ノートパソコンなどの小型電子機器の電池として広く使用されている。   Currently, lithium ion secondary batteries are lighter, higher voltage, and higher capacity than nickel batteries, hydrogen storage batteries, etc., so they are widely used as batteries for small electronic devices such as mobile phones, smartphones, and mobile laptops. ing.

上記リチウムイオン二次電池は、正極、負極、正極と負極とを絶縁するセパレーター、及び正極と負極との間でイオンの移動を可能にするための電解液から構成されている。正極及び負極は、金属箔からなる集電体の両面に各種の活物質が塗布されてなるものである。例えば、正極として、コバルト酸リチウム等を含む活物質がアルミニウム箔よりなる集電体に塗布されてなるものが用いられ、一方、負極としては、黒鉛等を含む活物質が銅箔よりなる集電体に塗布されてなるものが用いられている。   The lithium ion secondary battery includes a positive electrode, a negative electrode, a separator that insulates the positive electrode from the negative electrode, and an electrolyte solution that allows ions to move between the positive electrode and the negative electrode. The positive electrode and the negative electrode are formed by applying various active materials to both surfaces of a current collector made of a metal foil. For example, a positive electrode is used in which an active material containing lithium cobaltate or the like is applied to a current collector made of aluminum foil, while a negative electrode is a current collector made of copper foil made of an active material containing graphite or the like. What is applied to the body is used.

近年、小型電子機器の消費電力の上昇により、更なる電池の高容量化が望まれており、負極活物質としても、上記黒鉛よりも多くのリチウムイオンを収容できる材料が注目されている。   In recent years, due to an increase in power consumption of small electronic devices, further increase in battery capacity has been desired, and a material that can accommodate more lithium ions than the above-mentioned graphite has attracted attention as a negative electrode active material.

このような材料として、例えばケイ素やスズなどが一例として挙げられ、特にケイ素は現在実用化されている黒鉛の理論容量３７２ｍＡｈ／ｇよりも遙かに高い理論容量４２００ｍＡｈ／ｇを示すことから、電池の小型化と高容量化において、最も期待される材料であり、近年多くの研究がなされている。   As such a material, for example, silicon and tin can be cited as an example. In particular, silicon exhibits a theoretical capacity of 4200 mAh / g which is much higher than the theoretical capacity of 372 mAh / g of graphite currently in practical use. It is the most promising material for reducing the size and increasing the capacity, and many studies have been made in recent years.

しかし、特に負極活物質としてケイ素を使用した場合、充放電によるリチウムイオンの吸蔵と放出に伴った電極の膨張と収縮の挙動が、黒鉛よりも顕著に大きくなる。したがって、ケイ素を負極活物質に用いたリチウムイオン二次電池では、充電と放電の繰り返しによって、負極が膨張と収縮を繰り返すため、負極に多大な応力が加わる。この応力により、負極は負極活物質層と集電体の間で剥離を生じたり、または図１に示す様な負極外周部の破れが生じ、最終的には電池容量の低下、およびサイクル特性の劣化が生じる恐れがある。   However, particularly when silicon is used as the negative electrode active material, the behavior of the expansion and contraction of the electrode accompanying the insertion and extraction of lithium ions by charging and discharging is significantly greater than that of graphite. Therefore, in a lithium ion secondary battery using silicon as a negative electrode active material, the negative electrode repeatedly expands and contracts due to repeated charging and discharging, so that a great amount of stress is applied to the negative electrode. Due to this stress, the negative electrode is peeled off between the negative electrode active material layer and the current collector, or the negative electrode outer periphery as shown in FIG. 1 is torn, eventually resulting in a decrease in battery capacity and cycle characteristics. Deterioration may occur.

このような問題に対し、特許文献１では、負極の集電体である銅箔の銅の粒子径を大きくし、かつ所定の空孔密度を有した銅箔を用いることで、電池のサイクル特性を改善させる手法が開示されている。   With respect to such a problem, in Patent Document 1, by using a copper foil having a predetermined pore density and a copper particle diameter of a copper foil that is a negative electrode current collector, the cycle characteristics of the battery are obtained. A technique for improving the above is disclosed.

具体的には、集電体である銅箔断面全体にわたって、断面の面積が２０μｍ２以上の結晶子が含まれ、さらに、上記断面全体に占める空孔は、０．００１〜１．００個／μｍ２の空孔密度とした集電体を用いてリチウムイオン二次電池を作製することで、充放電時の膨張収縮による結晶子間に生じる歪みが減少し、サイクル特性が向上するとしている。 Specifically, the entire cross-section of the copper foil as the current collector includes crystallites having a cross-sectional area of 20 μm 2 or more, and the number of holes occupied in the entire cross-section is 0.001 to 1.00 / By producing a lithium ion secondary battery using a current collector having a pore density of μm 2 , distortion generated between crystallites due to expansion and contraction during charge and discharge is reduced, and cycle characteristics are improved.

しかし、本発明者等の検討では、上記範囲の空孔密度を実際に銅箔に形成させた負極を電池に用いた場合、負極に破れや剥離が生じてしまい、最終的な電池として、良好なサイクル特性を得ることができなかった。   However, in the study by the present inventors, when a negative electrode in which the void density in the above range is actually formed on a copper foil is used for a battery, the negative electrode is torn or peeled off, which is good as a final battery. Cycle characteristics could not be obtained.

例えば集電体の空孔密度が０．０１個／μｍ２の負極を用いた電池では、充放電後の電池を分析したところ、負極に剥離が生じていた。これは集電体内の空孔が少ないため、集電体の柔軟性が乏しく、負極活物質が充放電によって膨張収縮した際に負極活物質と集電体の膨張収縮差を緩和できず、負極表面に大きな皺が多数形成されてしまい、最終的に剥離につながったものと考えられる。 For example, in a battery using a negative electrode having a current collector having a pore density of 0.01 / μm 2 , when the battery after charge / discharge was analyzed, peeling of the negative electrode occurred. This is because the current collector has few vacancies, and thus the current collector has poor flexibility, and when the negative electrode active material expands and contracts due to charge and discharge, the difference in expansion and contraction between the negative electrode active material and the current collector cannot be reduced. It is thought that many large wrinkles were formed on the surface, which eventually led to peeling.

一方、集電体の空孔密度が０．３５個／μｍ２の負極を用いた電池では、充放電後の負極において、一部で破れが生じていた。これは空孔密度が高い場合、負極活物質の膨張収縮に対して柔軟になったものの、その一方で空孔が多いことにより、負極そのものの抗張力が低下し、負極活物質層の膨張収縮による体積変動に耐えきれず、端部に破れが生じてしまったものと考えられる。 On the other hand, in a battery using a negative electrode having a current collector with a hole density of 0.35 / μm 2 , the negative electrode after charge / discharge was partially broken. This is because when the hole density is high, the negative electrode active material becomes flexible with respect to expansion and contraction. On the other hand, due to the large number of holes, the tensile strength of the negative electrode itself decreases, and the negative electrode active material layer expands and contracts. It is thought that the end portion was torn because the volume variation could not be withstood.

さらに集電体の空孔密度が０．０１〜０．３５個／μｍ２の範囲内の任意の空孔を有する負極を複数検討した結果においても、負極の剥離と破れを同時に改善することはできなかった。 Furthermore, even in the result of examining a plurality of negative electrodes having arbitrary pores in the range of the pore density of the current collector of 0.01 to 0.35 / μm 2 , it is possible to simultaneously improve the peeling and breaking of the negative electrode. could not.

特開２００８−４４６２号公報JP 2008-4462 A

本発明は、上記問題に対応するべく、電極の剥離や破れを防止し、ひいてはリチウムイオン二次電池としたときのサイクル特性の向上を目的とする。   In order to cope with the above-described problems, the present invention aims to prevent electrode peeling and tearing, and thus to improve cycle characteristics when a lithium ion secondary battery is obtained.

上記目的を達成するために、本発明に係る集電体は、内部に複数の空孔を有するリチウムイオン二次電池用の集電体であって、集電体の主面と交差する断面（以下、集電体断面ともいう。）において、前記集電体の主面側の表層部における空孔数比率は、前記集電体の中央部における空孔数比率よりも高いことを特徴とする。   In order to achieve the above object, a current collector according to the present invention is a current collector for a lithium ion secondary battery having a plurality of vacancies therein, and a cross section intersecting with a main surface of the current collector ( Hereinafter, it is also referred to as a current collector cross section.), The number of holes in the surface layer portion on the main surface side of the current collector is higher than the number of holes in the central portion of the current collector. .

上記集電体の構造により、電極の剥離や破れを防止し、ひいてはリチウムイオン二次電池としたときのサイクル特性の向上に寄与できる集電体となる。   Due to the structure of the current collector, the electrode can be prevented from being peeled off or torn, and as a result, the current collector can contribute to the improvement of cycle characteristics when a lithium ion secondary battery is obtained.

これは、集電体の断面において、比較的高い空孔数比率を持つ表層部が、充放電による活物質の膨張収縮変形に対して柔軟性を示し、これにより集電体に加わる応力を緩和し、さらに比較的低い空孔数比率を持つ中央部の抗張力により、活物質の収縮挙動にも対応することで、剥離や破れを防止するものと考えられる。   This is because the surface layer portion having a relatively high vacancy ratio in the cross section of the current collector is flexible to the expansion and contraction deformation of the active material due to charge and discharge, thereby relieving the stress applied to the current collector. Furthermore, it is considered that peeling and tearing can be prevented by coping with the shrinkage behavior of the active material by the tensile strength of the central portion having a relatively low porosity ratio.

なお、集電体の主面とは、シート状の集電体における対向する広い面のことをいう。   Note that the main surface of the current collector refers to a wide surface facing the sheet-shaped current collector.

また、本発明に係る集電体は、上記複数の空孔のうち、最大の空孔径となる空孔は、上記集電体厚みの１／４以下の空孔径で構成されていることが好ましい。さらに、上記空孔径は集電体を構成する金属の結晶粒子径よりも小さいことが好ましい。なお、上記空孔径は、集電体断面において空孔を円として規格化したときの円の直径を意味する。   Further, in the current collector according to the present invention, it is preferable that the hole having the largest hole diameter among the plurality of holes is configured with a hole diameter of 1/4 or less of the current collector thickness. . Furthermore, the pore diameter is preferably smaller than the crystal particle diameter of the metal constituting the current collector. In addition, the said hole diameter means the diameter of a circle | round | yen when a hole is normalized as a circle in a collector cross section.

また、上記複数の空孔は、集電体を構成する金属の複数の結晶粒子の粒子間に局所的に配置されていることが好ましい。この様な構成により、より充放電後の電極における剥離や破れをより抑制することができる。   Moreover, it is preferable that the plurality of pores are locally arranged between the plurality of metal crystal particles constituting the current collector. With such a configuration, peeling and tearing of the electrode after charge / discharge can be further suppressed.

本発明に係る上記集電体は、上記複数の結晶粒子を含み、上記集電体断面において、上記集電体の主面側における結晶粒子径が、上記集電体の中央部における結晶粒子径よりも小さいことが好ましい。つまり、主面側よりも中央部に比較的大きい粒子径が分布していることが好ましい。この様な構成により、充放電後の電極における剥離や破れを更に効果的に抑制することができる。
なお、上記結晶粒子径とは、集電体断面において結晶粒子を円として規格化したときの円の直径を意味する。 The current collector according to the present invention includes the plurality of crystal particles, and in the cross section of the current collector, the crystal particle diameter on the main surface side of the current collector is a crystal particle diameter in a central portion of the current collector. Is preferably smaller. In other words, it is preferable that a relatively large particle size is distributed in the central portion rather than the main surface side. With such a configuration, peeling and tearing in the electrode after charging and discharging can be further effectively suppressed.
The crystal particle diameter means the diameter of a circle when the crystal particle is normalized as a circle in the current collector cross section.

また、上記集電体は複数の結晶粒子を含み、上記複数の結晶粒子は、上記断面において、集電体内部の上記結晶粒子径が、上記中央部から上記表層部にかけ、徐々に小さくなっていることが好ましい。この様な構成により、さらに充放電後の電極における剥離や破れを抑制することができる。   In addition, the current collector includes a plurality of crystal particles, and the plurality of crystal particles have a crystal particle diameter inside the current collector that gradually decreases from the central portion to the surface layer portion in the cross section. Preferably it is. With such a configuration, peeling and tearing of the electrode after charge / discharge can be further suppressed.

特に、上記集電体は複数の結晶粒子を含み、上記表層部の上記結晶粒子の平均粒子径をＸとし、上記中央部の結晶粒子の平均粒子径をＹとするとき、Ｘ≦０．９Ｙの関係式を満たすことが好ましい。さらに、上記関係式において、より好ましくは０．６Ｙ≦Ｘ≦０．８Ｙの関係式を満たすことが好ましい。   In particular, when the current collector includes a plurality of crystal particles, the average particle diameter of the crystal particles in the surface layer portion is X, and the average particle diameter of the crystal particles in the center portion is Y, X ≦ 0.9Y It is preferable that the relational expression is satisfied. Further, in the above relational expression, it is more preferable to satisfy the relational expression of 0.6Y ≦ X ≦ 0.8Y.

本発明に係る集電体は、集電体内の空孔の配置を制御することにより、電極の剥離や破れを防止し、ひいてはリチウムイオン二次電池としたときのサイクル特性の向上が可能となる。   In the current collector according to the present invention, by controlling the arrangement of vacancies in the current collector, peeling and tearing of the electrodes can be prevented, and as a result, cycle characteristics when a lithium ion secondary battery is obtained can be improved. .

充放電によって生じる負極の破れを示した従来技術の模式図である。It is the schematic diagram of the prior art which showed the tear of the negative electrode produced by charging / discharging. 本実施形態の集電体断面における主面側表層部（上部）、主面側表層部（下部）、および中央部を説明した概略図である。It is the schematic explaining the main surface side surface layer part (upper part), the main surface side surface layer part (lower part), and the center part in the collector cross section of this embodiment. 本実施形態における集電体の熱処理状態を示す概略図である。It is the schematic which shows the heat processing state of the electrical power collector in this embodiment. 実施例１に示す集電体断面の反射電子像である。2 is a reflected electron image of a current collector cross section shown in Example 1. FIG. 図４の像を二値化処理した像である。It is the image which binarized the image of FIG. 本実施形態におけるリチウムイオン二次電池の電池要素を示す概略図である。It is the schematic which shows the battery element of the lithium ion secondary battery in this embodiment. 図６に示す電池要素の断面概略図である。FIG. 7 is a schematic cross-sectional view of the battery element shown in FIG. 6.

以下、本実施形態として、集電体、およびそれを用いたリチウムイオン二次電池について、具体例を挙げ説明する。なお、本発明は下記実施形態に示したものに限定されるものではなく、その要旨を変更しない範囲において適宜変更して実施できるものとする。   Hereinafter, as the present embodiment, a current collector and a lithium ion secondary battery using the current collector will be described with specific examples. In addition, this invention is not limited to what was shown to the following embodiment, In the range which does not change the summary, it shall change suitably.

本実施形態に係る集電体は、内部に複数の空孔を有するリチウムイオン二次電池用の集電体であって、集電体の主面と交差する断面において、前記集電体の主面側の表層部における空孔数比率は、前記集電体の中央部における空孔数比率よりも高いことを特徴としている。
このような内部構造により、充放電による膨張収縮時の電極の剥離や破れが効果的に改善され、膨張収縮が大きい負極活物質、例えばケイ素を使用した場合においても、剥離や破れの不具合が効果的に改善される。これにより、ひいてはリチウムイオン二次電池のサイクル特性が向上することになる。つまり充放電によるサイクル寿命が向上することになる。 The current collector according to the present embodiment is a current collector for a lithium ion secondary battery having a plurality of holes therein, and has a cross section intersecting with the main surface of the current collector. The surface area portion on the surface side has a vacancy number ratio that is higher than a vacancy number ratio in the central portion of the current collector.
Such an internal structure effectively improves electrode peeling and tearing during expansion and contraction due to charge and discharge, and even when a negative electrode active material having a large expansion and contraction, such as silicon, is used, the problem of peeling or tearing is effective. Improved. As a result, the cycle characteristics of the lithium ion secondary battery are improved. That is, the cycle life due to charge / discharge is improved.

なお、集電体の主面とは、シート状の集電体における、対向する広い面のことをいい、一方の主面のみを対象とする場合も、一方の主面及び他方の主面を対象とする場合も広く含む表現である。   The main surface of the current collector means a wide surface facing the sheet-shaped current collector. Even when only one main surface is targeted, one main surface and the other main surface are It is an expression that includes a wide range of cases.

本実施形態に係る集電体において、上記複数の空孔のうち、最大の空孔径となる空孔は、上記集電体厚みの１／４以下の空孔径で構成されていることが好ましい。この様な構成により、より充放電後の電極における剥離や破れを抑制することができる。   In the current collector according to the present embodiment, it is preferable that the hole having the largest hole diameter among the plurality of holes is configured with a hole diameter of ¼ or less of the current collector thickness. With such a configuration, peeling and tearing of the electrode after charge / discharge can be further suppressed.

このときの破れの原因として、詳細な理由は分かっていないが、上記空孔径が集電体厚みの１／４よりも大きい空孔径が存在すると、金属結晶粒子と金属結晶粒子との結合力が低下し、それが破れ等の起点となる可能性が生じるためと考えている。   Although the detailed reason is not known as the cause of the breakage at this time, when the pore diameter is larger than 1/4 of the current collector thickness, the bonding force between the metal crystal particles and the metal crystal particles is reduced. It is thought that it may decrease, and it may become the starting point of tearing.

さらに、上記空孔径は、上記結晶粒子径よりも小さいことが好ましい。   Furthermore, the pore diameter is preferably smaller than the crystal particle diameter.

また、本実施形態に係る集電体において、前記複数の空孔は、集電体を構成する金属の複数の結晶粒子の粒子間に局所的に配置されていることが好ましい。この様な構成により、より充放電後の電極における剥離や破れを抑制することができる。   In the current collector according to the present embodiment, it is preferable that the plurality of holes are locally arranged between the plurality of metal crystal particles constituting the current collector. With such a configuration, peeling and tearing of the electrode after charge / discharge can be further suppressed.

なお言うまでもないが、上記複数の空孔は、上記集電体断面において、上記表層部の空孔と上記中央部の空孔との相対的な関係が成り立てば十分であるが、全体として、上記空孔は集電体の断面積全体に対する比率において０．２％以上の空孔面積比率であることが好ましい。もちろんこの数値に限定されるわけではない。   Needless to say, the plurality of holes are sufficient if the relative cross-section between the surface layer hole and the central hole is established in the current collector cross section. It is preferable that the pores have a pore area ratio of 0.2% or more with respect to the total cross-sectional area of the current collector. Of course, it is not limited to this value.

また、集電体内部の空孔数比率を求めるに際し、上記表層部の範囲は、例えば、集電体断面を厚み方向に略３等分し、集電体の主面側に位置する３分の１の厚みの断面領域を表層部として上記空孔数比率を算出すればよい。したがって、集電体の一方の主面と他方の主面によって挟まれた領域は中央部となる。   Further, when determining the ratio of the number of vacancies inside the current collector, the range of the surface layer portion is, for example, 3 minutes that divides the current collector cross section into approximately three equal parts in the thickness direction and is located on the main surface side of the current collector. The above-mentioned ratio of the number of vacancies may be calculated with the cross-sectional area having a thickness of 1 as the surface layer. Therefore, a region sandwiched between one main surface and the other main surface of the current collector is a central portion.

さらに本実施形態の集電体は、複数の結晶粒子を持ち、上記複数の結晶粒子は、集電体断面において、その集電体の主面側の表層部における結晶粒子径が、集電体の中央部における結晶粒子径よりも小さいことが好ましい。この様な構成により、充放電後の電極における剥離や破れをさらに抑制することができる。   Furthermore, the current collector of the present embodiment has a plurality of crystal particles, and the plurality of crystal particles have a crystal particle diameter in a surface layer portion on the main surface side of the current collector in the cross section of the current collector. It is preferable that it is smaller than the crystal particle diameter in the central part. With such a configuration, peeling and tearing in the electrode after charge / discharge can be further suppressed.

また、上記集電体は複数の結晶粒子を含み、上記断面において、集電体内部の上記結晶粒子径が、上記中央部から上記表層部にかけ、徐々に小さくなっていることが好ましい。この様な構成により、さらに充放電後の電極における剥離や破れを抑制することができる。   The current collector includes a plurality of crystal particles, and in the cross section, the crystal particle diameter inside the current collector is preferably gradually decreased from the central portion to the surface layer portion. With such a configuration, peeling and tearing of the electrode after charge / discharge can be further suppressed.

特に、上記集電体は複数の結晶粒子を含み、上記表層部の結晶粒子の平均粒子径をＸとし、上記中央部の結晶粒子の平均粒子径をＹとするとき、Ｘ≦０．９Ｙの関係式を満たすことが好ましい。
さらに、上記関係式において、より好ましくは０．６Ｙ≦Ｘ≦０．８Ｙの関係式を満たすことが好ましい。 In particular, when the current collector includes a plurality of crystal particles, the average particle size of the crystal particles in the surface layer portion is X, and the average particle size of the crystal particles in the central portion is Y, X ≦ 0.9Y It is preferable to satisfy the relational expression.
Further, in the above relational expression, it is more preferable to satisfy the relational expression of 0.6Y ≦ X ≦ 0.8Y.

本実施形態における集電体の抗張力は、２００Ｎ／ｍｍ２以上のものを用いればよく、特に後述する実施例の集電体は熱処理工程を含むため、熱処理後の集電体の抗張力が、２００Ｎ／ｍｍ２以上を有する集電体が望ましい。 The tensile strength of the current collector in this embodiment may be 200 N / mm 2 or more. Particularly, the current collectors of the examples described later include a heat treatment step, and thus the tensile strength of the current collector after the heat treatment is 200 N. A current collector having / mm 2 or more is desirable.

抗張力に関しては、上記に限定するものではないが、我々のこれまでの種々の研究成果において、抗張力が２００Ｎ／ｍｍ２よりも小さい集電体を電極に用いた場合、充放電時の負極活物質（特にケイ素）の膨張収縮によって、破れが発生しやすくなる傾向にあったためである。つまり、本実施形態の集電体構造によって充放電後の負極の破れや負極活物質層の剥離、つまり脱落をより効果的に抑制するためには、少なからず所定の抗張力を有する集電体を用いることが望ましく、それによって本実施形態の効果がより好適に発揮されると考えられる。 With respect to the tensile strength, although not limited to the above, in various research results so far, when a current collector having a tensile strength of less than 200 N / mm 2 is used for the electrode, the negative electrode active material during charging and discharging This is because tearing tends to easily occur due to expansion and contraction of (especially silicon). In other words, in order to more effectively suppress the negative electrode breakage and the negative electrode active material layer peeling after the charge and discharge by the current collector structure of the present embodiment, that is, the falling off, a current collector having a predetermined tensile strength is used. It is desirable to use it, and it is thought that the effect of this embodiment is exhibited more suitably by it.

本実施形態における上記集電体として、銅箔のような金属箔を用いた場合、その銅箔の厚みは、特に限定するものではないが、さらに例えばケイ素を含有する材料を負極活物質層として用いたとき、４〜１００μｍの銅箔を好適に用いることができる。より好ましくは４〜２０μｍの銅箔を好適に用いることができる。   When a metal foil such as a copper foil is used as the current collector in the present embodiment, the thickness of the copper foil is not particularly limited. For example, a material containing silicon is used as the negative electrode active material layer. When used, a copper foil of 4 to 100 μm can be suitably used. More preferably, a copper foil of 4 to 20 μm can be suitably used.

銅箔厚みが４μｍよりも薄い集電体になると、銅箔の相対的な抗張力が弱くなる傾向にあり、負極活物質の充放電による膨張収縮応力によって、銅箔の破れや変形等が生じやすくなる可能性があるためである。   When the current collector is thinner than 4 μm, the relative tensile strength of the copper foil tends to be weakened, and the copper foil is easily broken or deformed due to expansion / contraction stress due to charging / discharging of the negative electrode active material. This is because there is a possibility of becoming.

また、上記銅箔の表面粗さＲａについても特に限定するものではないが、表面粗さが大きな集電体が好ましい。銅箔の表面粗さＲａとしては、０．１μｍ以上の銅箔を用いればよい。   Further, the surface roughness Ra of the copper foil is not particularly limited, but a current collector having a large surface roughness is preferable. As the surface roughness Ra of the copper foil, a copper foil of 0.1 μm or more may be used.

上述の集電体は、以下の製造方法により作製することができる。   The above-mentioned current collector can be produced by the following production method.

例えば、あらかじめ用意した金属箔からなる集電体を、その集電体よりも熱伝導性の低い基板にて集電体を挟みながら、所定温度の熱処理工程を経て作製する。この様な工程により、集電体を構成する金属の結晶粒子が粒成長し、上記熱処理によって、集電体内部に空孔が複数形成される。   For example, a current collector made of a metal foil prepared in advance is manufactured through a heat treatment step at a predetermined temperature while the current collector is sandwiched between substrates having lower thermal conductivity than the current collector. Through such a process, metal crystal particles constituting the current collector grow and a plurality of holes are formed inside the current collector by the heat treatment.

上記熱処理の際には、アルゴン、窒素雰囲気、または真空中での雰囲気において、集電体が酸化しない温度で処理することが好適である。
これは集電体表面が酸化してしまうと表面抵抗が上昇し、導電性の低下によって所望の電気容量よりも特性が低下してしまうためである。 The heat treatment is preferably performed at a temperature at which the current collector is not oxidized in an atmosphere of argon, nitrogen, or vacuum.
This is because when the surface of the current collector is oxidized, the surface resistance is increased, and the characteristics are lower than the desired electric capacity due to the decrease in conductivity.

また、上記熱処理工程は、集電体をそのまま熱処理してもよく、もしくは集電体の主面上に負極活物質層を塗布してから熱処理をしてもよい。
もし、集電体の主面上に負極活物質層を塗布してから熱処理を実施する場合では、上記負極活物質層に含まれているバインダーが完全に分解しない温度で熱処理することが望ましい。熱処理によって上記バインダーが過度に分解してしまうと、負極活物質同士の結着性が弱くなり、その結果、充放電による膨張収縮の際に、負極活物質が集電体から剥離しやすくなるためである。 Moreover, the said heat processing process may heat-process a collector as it is, or may heat-process, after apply | coating a negative electrode active material layer on the main surface of a collector.
If the heat treatment is performed after the negative electrode active material layer is applied on the main surface of the current collector, the heat treatment is preferably performed at a temperature at which the binder contained in the negative electrode active material layer is not completely decomposed. If the binder is excessively decomposed by heat treatment, the binding property between the negative electrode active materials becomes weak, and as a result, the negative electrode active material is easily peeled off from the current collector during expansion / contraction due to charge / discharge. It is.

上記集電体よりも熱伝導性の低い基板は、平滑な基板で対向して挟み込みながら熱処理をするのがよい。上記平滑な基板の材料は、セラミックス、金属、耐熱性ポリマーなどが挙げられ、特にセラミックスなどの熱伝導性が小さいものが好適に用いることができる。上記理由については、完全には解明できていないが、以下のように考察している。   A substrate having lower thermal conductivity than the current collector is preferably heat-treated while being sandwiched and opposed by a smooth substrate. Examples of the material for the smooth substrate include ceramics, metals, heat-resistant polymers, and the like, and those having low thermal conductivity such as ceramics can be preferably used. The reason for this is not fully understood, but is considered as follows.

集電体よりも熱伝導性の低い上記セラミックス基板を、対向させた状態で集電体を挟み込みながら熱処理することで、セラミックス基板と接する上記集電体表面近傍の熱伝導性が低下し、上記集電体表面の金属粒子の成長が、集電体中央近傍の金属粒子の成長よりも遅延される。つまり、中央近傍での金属粒子は、上記セラミックス基板に接していないため、表面近傍の金属粒子よりも粒成長が進行しやすいため、上記表面と中央における金属の結晶粒子径に差が生じやすくなる。この結晶粒子径の差、およびまたは粒成長速度の差によって、粒子と粒子との隙間に空孔が形成されやすくなり、本実施形態に係る集電体構造が得られていると考えている。   By heat-treating the ceramic substrate having a lower thermal conductivity than the current collector while sandwiching the current collector, the thermal conductivity in the vicinity of the surface of the current collector in contact with the ceramic substrate is reduced. The growth of the metal particles on the surface of the current collector is delayed from the growth of the metal particles near the center of the current collector. In other words, since the metal particles near the center are not in contact with the ceramic substrate, the grain growth is more likely to proceed than the metal particles near the surface, so that a difference in the crystal grain size of the metal between the surface and the center is likely to occur. . Due to the difference in the crystal particle diameter and / or the difference in the grain growth rate, it is considered that pores are easily formed in the gap between the particles, and the current collector structure according to the present embodiment is obtained.

さらに上述したとおり集電体の粒成長速度の差を利用することから、熱処理を行う際の昇温速度および降温速度も重要であり、急昇温、急降温の温度プロセスにて熱処理するものである。具体的には、１５〜４０℃／ｍｉｎの昇温および降温速度であることが好ましい。   Furthermore, since the difference in the grain growth rate of the current collector is used as described above, the rate of temperature increase and the rate of temperature decrease during heat treatment is also important, and heat treatment is performed in a temperature process of rapid temperature increase and decrease. is there. Specifically, it is preferable that the temperature is increased and decreased at a rate of 15 to 40 ° C./min.

また、上述したような平滑な基板で挟みながら熱処理をすることにより、集電体の熱伝導性の低い基板に接している面は、その面内で熱量を均一にすることができることから、集電体の表面を構成する金属粒子の粒子径を面内で略均一にすることができるため更に好ましい。   In addition, by performing heat treatment while sandwiching between the smooth substrates as described above, the surface of the current collector that is in contact with the substrate having low thermal conductivity can make the amount of heat uniform within the surface. It is further preferable because the particle diameter of the metal particles constituting the surface of the electric conductor can be made substantially uniform in the plane.

また、上記熱処理において、集電体よりも熱伝導性の低いセラミックス基板として、材質は、ジルコニア、アルミナ、ムライト、またはそれらの２種類以上からなる複合材、などを用いればよい。上記形状としては、緻密で空孔の少ない形状が好ましいが、多孔質な形状でも構わない。   In the heat treatment, as the ceramic substrate having lower thermal conductivity than the current collector, the material may be zirconia, alumina, mullite, or a composite material composed of two or more thereof. The shape is preferably a dense shape with few pores, but may be a porous shape.

また、上記基板は、集電体と同等、またはそれ以上のサイズであることが望ましく、さらに、集電体表面との接触を高めるために、上記基板の平滑度としては、反りの少ない、または無いものが好適であり、例えば１００μｍ以下の反りであることが好ましい。   In addition, the substrate is preferably the same size or larger than the current collector, and in order to improve contact with the current collector surface, the smoothness of the substrate is less warped, or Those having no warp are suitable, for example, warp of 100 μm or less is preferred.

以下、上述の集電体を用いてリチウムイオン二次電池を作製する際の好適な構成例を図面を用い詳細に説明する。ただし、以下の実施形態に限定されるものではない。なお、図面の寸法比率は図示の比率に限られるものではない。   Hereinafter, a preferred configuration example for producing a lithium ion secondary battery using the above-described current collector will be described in detail with reference to the drawings. However, it is not limited to the following embodiment. In addition, the dimensional ratio of drawing is not restricted to the ratio of illustration.

〈本実施形態におけるリチウムイオン二次電池の構成〉
図６に、本実施形態のリチウムイオン二次電池を構成する電池要素の模式的に示す。図７は、図６の断面を模式図である。図６及び図７のリチウムイオン二次電池は、リチウムイオンを吸蔵、放出する材料（正極活物質、負極活物質）を含む正極及び負極と、正極と負極との間にあってリチウムイオン伝導性を有する電解質が保持されたセパレーターから構成されている。その正極は、正極集電体の両面に正極活物質層を備えて構成されており、負極は、負極集電体の両面に負極活物質層を備えて構成されている。また正極集電体から正極タブが負極集電体から負極タブが引き出し電極として引き出されている。 <Configuration of lithium ion secondary battery in this embodiment>
In FIG. 6, the battery element which comprises the lithium ion secondary battery of this embodiment is typically shown. FIG. 7 is a schematic view of the cross section of FIG. The lithium ion secondary battery of FIGS. 6 and 7 has lithium ion conductivity between a positive electrode and a negative electrode including materials (positive electrode active material, negative electrode active material) that occlude and release lithium ions, and between the positive electrode and the negative electrode. It is comprised from the separator with which electrolyte was hold | maintained. The positive electrode is configured by including a positive electrode active material layer on both surfaces of the positive electrode current collector, and the negative electrode is configured by including a negative electrode active material layer on both surfaces of the negative electrode current collector. A positive electrode tab is drawn from the positive electrode current collector, and a negative electrode tab is drawn from the negative electrode current collector as a lead electrode.

図６に示しような電池要素は、図示されていないが、最終的に電解液と共に外装体に収納されリチウムイオン二次電池となる。   Although the battery element as shown in FIG. 6 is not shown in the figure, it is finally housed in an outer package together with the electrolytic solution to become a lithium ion secondary battery.

〈集電体〉
本実施形態の集電体は、上述したとおりであるが、材料として好適には、正極集電体としてはアルミニウム、ステンレス鋼、ニッケル、チタンまたはこれらの合金などの金属箔を用いることができ、負極集電体としては銅、ステンレス鋼、ニッケル、チタン、またはこれらの合金などの金属箔を用いることができる。特に、正極集電体としては、アルミニウム箔が好ましく、負極集電体としては、銅箔が好ましい。上記銅箔としては、銅であっても銅合金であってもよく、電解銅箔および圧延銅箔によって製造された箔が好適に用いられる。 <Current collector>
Although the current collector of the present embodiment is as described above, a metal foil such as aluminum, stainless steel, nickel, titanium, or an alloy thereof can be preferably used as the positive electrode current collector, As the negative electrode current collector, a metal foil such as copper, stainless steel, nickel, titanium, or an alloy thereof can be used. In particular, the positive electrode current collector is preferably an aluminum foil, and the negative electrode current collector is preferably a copper foil. As said copper foil, copper or a copper alloy may be sufficient and the foil manufactured with the electrolytic copper foil and the rolled copper foil is used suitably.

〈正極活物質〉
本実施形態におけるリチウムイオン二次電池用正極活物質としては、リチウム含有複合酸化物が用いられ、具体的には、以下に示す各材料、及びその材料を構成する各元素の組成比が異なる類似の材料が使用でき、コバルト酸リチウム（ＬｉＣｏＯ２）、マンガン酸リチウム（ＬｉＭｎ２Ｏ４）、ニッケルコバルト酸リチウム（ＬｉＮｉＣｏＯ２）、ニッケル酸リチウム（ＬｉＮｉＯ２）、リン酸鉄リチウム（ＬｉＦｅＰＯ４）、ＬｉＮｉＭｎＣｏＯ２、ＬｉＦｅＭｎＯ２、Ｌｉ２ＰｔＯ３、ＬｉＭｎＮｉＯ４、ＬｉＮｉＭｎＯ２、ＬｉＮｉＶＯ４、ＬｉＣｒＭｎＯ４、ＬｉＦｅ（ＳＯ４）３、ＬｉＣｏＶＯ４、ＬｉＣｏＰＯ４、などが挙げられる。また、この材料に限定することはなく、他にも、リチウムイオンを電気化学的に挿入および脱離する正極活物質材料であれば、特に制限はされない。 <Positive electrode active material>
As the positive electrode active material for the lithium ion secondary battery in the present embodiment, a lithium-containing composite oxide is used, and specifically, the following materials and similarities in which the composition ratio of each element constituting the material is different Materials such as lithium cobaltate (LiCoO 2 ), lithium manganate (LiMn 2 O 4 ), nickel lithium cobaltate (LiNiCoO 2 ), lithium nickelate (LiNiO 2 ), lithium iron phosphate (LiFePO 4 ), Examples include LiNiMnCoO 2 , LiFeMnO 2 , Li 2 PtO 3 , LiMnNiO 4 , LiNiMnO 2 , LiNiVO 4 , LiCrMnO 4 , LiFe (SO 4 ) 3 , LiCoVO 4 , and LiCoPO 4 . The material is not limited to this material, and any other positive electrode active material that electrochemically inserts and desorbs lithium ions is not particularly limited.

〈負極活物質〉
本実施形態におけるリチウムイオン二次電池用負極活物質としては、高容量が期待できる金属系材料が望ましく、具体的には、ケイ素、ケイ素化合物、金属スズ、スズ化合物、などが挙げられ、さらに上記活物質を２種類以上の混合物から構成されてもよい。特にケイ素と酸素からなるケイ素化合物が好ましい。また、負極活物質として、上記に挙げた材料に限定することはなく、他にも、リチウムイオンを電気化学的に挿入、脱離する材料であれば特に制限はされない。ただし、本実施形態の銅箔は、負極活物質の膨張、収縮に対して有効であるため、膨張収縮が大きい負極活物質に使用することで、その有効性が好適に発揮される。 <Negative electrode active material>
As the negative electrode active material for the lithium ion secondary battery in the present embodiment, a metal-based material that can be expected to have a high capacity is desirable, and specifically, silicon, silicon compounds, metal tin, tin compounds, and the like can be given. The active material may be composed of a mixture of two or more types. In particular, a silicon compound composed of silicon and oxygen is preferable. Further, the negative electrode active material is not limited to the above-described materials, and any other material that can insert and desorb lithium ions electrochemically is not particularly limited. However, since the copper foil of the present embodiment is effective for the expansion and contraction of the negative electrode active material, the effectiveness thereof is suitably exhibited by using it for the negative electrode active material having a large expansion and contraction.

また、本実施形態のリチウムイオン二次電池の正極活物質層、及び負極活物質層は、活物質材料（正極活物質材料、負極活物質材料）と、バインダーと、導電助剤とを含む塗料を集電体に塗布することによって形成することができる。   In addition, the positive electrode active material layer and the negative electrode active material layer of the lithium ion secondary battery of the present embodiment are paints that include an active material (positive electrode active material, negative electrode active material), a binder, and a conductive additive. Can be applied to the current collector.

〈導電助剤〉
正極活物質層および負極活物質層を構成する材料において、導電助剤として導電性材料を添加してもよい。このような導電性材料としては、リチウムイオン二次電池内において化学変化を起こさなければ特に限定されない。通常、黒鉛、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、炭素繊維、金属粉などの材料を、１種または２種以上用いることができる。 <Conductive aid>
In the materials constituting the positive electrode active material layer and the negative electrode active material layer, a conductive material may be added as a conductive additive. Such a conductive material is not particularly limited as long as no chemical change occurs in the lithium ion secondary battery. Usually, one or more materials such as graphite, carbon black, acetylene black, ketjen black, carbon fiber, and metal powder can be used.

〈バインダー〉
バインダーは、正極用バインダーとして、ポリフッ化ビリニデン（ＰＶＤＦ）、スチレンブタジエンゴム（ＳＢＲ）、カルボキシメチルセルロース（ＣＭＣ）などを用いることができる。一方、負極用バインダーとしては、機械的強度に優れたポリイミドやポリアミドイミドが好適に使用できる。ポリイミドをバインダーに選定した場合は、前駆体であるポリアミド酸を熱処理することにより、脱水縮合することで、ポリイミドを得ることができる。さらに上記ポリアミドイミドを用いる場合には、イミド化率が高いものが好ましい。 <binder>
As the binder, polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), or the like can be used as a positive electrode binder. On the other hand, as the negative electrode binder, polyimide or polyamideimide having excellent mechanical strength can be suitably used. When polyimide is selected as the binder, the polyimide can be obtained by dehydrating and condensing the precursor polyamic acid by heat treatment. Furthermore, when using the said polyamideimide, a thing with a high imidation ratio is preferable.

上記負極用バインダーとしては、上述したポリイミド、ポリアミドイミドを１種類のみ、またはそれらを併用してもよい。さらに、上記負極用バインダーの１種、または２種と、これ以外のバインダーとを組み合わせて併用してもよい。   As the negative electrode binder, only one kind of the above-described polyimide and polyamideimide may be used, or they may be used in combination. Furthermore, you may use together 1 type or 2 types of the said binder for negative electrodes, and a binder other than this in combination.

〈セパレーター〉
本実施形態のセパレーターとしては、ポリプロピレン、ポリエチレンなどのポリオレフィン、フッ素樹脂、などの多孔性フィルムが用いられる。ただし、これらに限定されることはなく、適宜最良なセパレーターを用いればよい。 <separator>
As the separator of the present embodiment, a porous film such as a polyolefin such as polypropylene or polyethylene, or a fluororesin is used. However, it is not limited to these, and the best separator may be used as appropriate.

〈電解質〉
本実施形態の電解質としては、下記の非水溶媒中に下記の無機イオン塩を溶解させることによって調製した電解液が挙げられる。 <Electrolytes>
Examples of the electrolyte of the present embodiment include an electrolytic solution prepared by dissolving the following inorganic ion salt in the following nonaqueous solvent.

上記非水溶媒としては、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）、ジエチルカーボネート（ＤＥＣ）、メチルエチルカーボネート（ＭＥＣ）、γ−ブチロラクトン、１，２−ジメトキシエタン、テトラヒドロフラン、２−メチルテトラヒドロフラン、ジメチルスルフォキシド、１，３−ジオキソラン、ホルムアミド、ジメチルホルムアミド、ジオキソラン、アセトニトリル、ニトロメタン、ギ酸メチル、酢酸メチル、リン酸トリエステル、トリメトキシメタン、ジオキソラン誘導体、スルホラン、３−メチル−２−オキサゾリジノン、プロピレンカーボネート誘導体、テトラヒドロフラン誘導体、ジエチルエーテル、１，３−プロパンサルトンなどの非プロトン性有機溶媒を、１種または２種以上を混合して用いることができる。   Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane , Dioxolane derivatives, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, diethyl ether, 1,3-propane salt An aprotic organic solvent such as tons, can be used alone or in combination.

無機イオン塩としては、Ｌｉ塩、例えば、ＬｉＣｌＯ４、ＬｉＢＦ４、ＬｉＰＦ６、ＬｉＣＦ３ＳＯ３、ＬｉＣＦ３ＣＯ２、ＬｉＡｓＦ６、ＬｉＳｂＦ６、ＬｉＢ１０Ｃｌ１０、低級脂肪族カルボン酸Ｌｉ、ＬｉＡｌＣｌ４、ＬｉＣｌ、ＬｉＢｒ、ＬｉＩ、クロロボランＬｉ、四フェニルホウ酸Ｌｉなどを、１種または２種以上用いることができる。 As the inorganic ion salt, Li salt, for example, LiClO 4, LiBF 4, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10, lower aliphatic carboxylic acids Li, LiAlCl 4 , LiCl, LiBr, LiI, chloroborane Li, Li tetraphenylborate, or the like can be used alone or in combination.

上記溶媒中に上記無機イオン塩が溶解された電解液の中でも、１，２−ジメトキシエタン、ジエチルカーボネートおよびメチルエチルカーボネートよりなる群から選ばれる少なくとも１種と、エチレンカーボネートまたはプロピレンカーボネートとを含む溶媒に、ＬｉＣｌＯ４、ＬｉＢＦ４、ＬｉＰＦ６、およびＬｉＣＦ３ＳＯ３よりなる群から選ばれる少なくとも１種の無機イオン塩を溶解した電解液が好ましい。電解液中の無機イオン塩の濃度は、例えば、０．２〜３．０ｍｏｌ／ｄｍ３が適当である。 Among the electrolytic solutions in which the inorganic ion salt is dissolved in the solvent, a solvent containing at least one selected from the group consisting of 1,2-dimethoxyethane, diethyl carbonate, and methyl ethyl carbonate, and ethylene carbonate or propylene carbonate In addition, an electrolytic solution in which at least one inorganic ion salt selected from the group consisting of LiClO 4 , LiBF 4 , LiPF 6 , and LiCF 3 SO 3 is dissolved is preferable. An appropriate concentration of the inorganic ion salt in the electrolytic solution is, for example, 0.2 to 3.0 mol / dm 3 .

さらに、電解液添加剤として一般的な、例えば、ビニレンカーボネート（ＶＣ）などを用いることも可能である。   Furthermore, it is also possible to use common vinylene carbonate (VC), for example, as an electrolytic solution additive.

〈リチウムイオン二次電池〉
作製した正極と負極は、セパレーターを介して積層又は巻回され、電池要素として外装体の中に挿入される。 <Lithium ion secondary battery>
The produced positive electrode and negative electrode are laminated or wound via a separator and inserted into the outer package as a battery element.

正極、負極、セパレーターを積層した電池要素を封入する外装体は、特に制限はなく、アルミニウムやステンレス製の缶、アルミニウムラミネート製のフィルムを外装体として適宜選択することができる。   The exterior body that encloses the battery element in which the positive electrode, the negative electrode, and the separator are stacked is not particularly limited, and an aluminum or stainless steel can or an aluminum laminate film can be appropriately selected as the exterior body.

この外装体の中に電池要素を挿入した後、所定の電解質が加えられる。   After the battery element is inserted into the outer package, a predetermined electrolyte is added.

この後、外装体を真空密封しリチウムイオン二次電池を得ることができる。   Thereafter, the outer package is vacuum-sealed to obtain a lithium ion secondary battery.

なお本発明に係るリチウムイオン二次電池の形状としては、特に制限はなく、例えば、円筒型、角型、コイン型、ラミネート型など、いずれであってもよい。   In addition, there is no restriction | limiting in particular as a shape of the lithium ion secondary battery which concerns on this invention, For example, any, such as a cylindrical shape, a square shape, a coin shape, a laminate type, may be sufficient.

〈リチウムイオン二次電池の作製方法〉
次に本実施形態のリチウムイオン二次電池の作製方法について説明する。 <Production method of lithium ion secondary battery>
Next, a method for manufacturing the lithium ion secondary battery of this embodiment will be described.

本実施形態の集電体は、図３に示す様に集電体よりも熱伝導性の低い基板にて集電体を挟みながら、所定温度の熱処理工程を経て作製する。この様な工程により、集電体を構成する金属粒子が粒成長し、上記熱処理によって、集電体に空孔が複数形成される。   As shown in FIG. 3, the current collector of this embodiment is manufactured through a heat treatment step at a predetermined temperature while sandwiching the current collector between substrates having lower thermal conductivity than the current collector. By such a process, the metal particles constituting the current collector grow, and a plurality of holes are formed in the current collector by the heat treatment.

〈集電体の準備〉
集電体として、例えば銅箔を、集電体よりも熱伝導率の低いセラミックス基板で挟み込み、５５０℃以下の温度において負極を熱処理する。上記の熱処理条件としては、２００〜５００℃の温度によって、真空中、窒素雰囲気中もしくはアルゴン雰囲気中で実施することが好ましい。 <Preparation of current collector>
As the current collector, for example, a copper foil is sandwiched between ceramic substrates having a lower thermal conductivity than the current collector, and the negative electrode is heat-treated at a temperature of 550 ° C. or lower. As said heat processing conditions, it is preferable to implement in a vacuum, nitrogen atmosphere, or argon atmosphere by the temperature of 200-500 degreeC.

上記熱処理によれば、集電体銅箔表面の粒成長が、集電体銅箔中央の粒成長よりも抑制され、粒成長速度の違いによって、粒界に空孔を形成しやすくなる。この理由としては明らかではないが、その理由の１つとして、セラミックス基板に接している銅箔表層部では、熱容量がセラミックス基板に奪われるため、銅箔表層部から中央部にかけて、熱分布の傾斜が生じることにより、銅箔の中央部よりも表層部の粒成長が抑制されるものと考えている。しかし、５５０℃よりも高い温度で熱処理した場合、上記熱分布の傾斜が小さくなり、集電体銅箔の表層部の粒成長速度と、中央部における粒成長速度に差ができにくくなるため、空孔数の差が比較的小さくなる傾向にある。したがって、集電体内の空孔数比率および表面部における空孔数比率が低下してしまい、その結果、負極活物質の膨張収縮が緩和されにくくなる可能性がある。   According to the heat treatment, the grain growth on the surface of the current collector copper foil is suppressed as compared with the grain growth at the center of the current collector copper foil, and it becomes easy to form vacancies at the grain boundaries due to the difference in the grain growth rate. The reason for this is not clear, but one of the reasons is that the heat capacity is lost to the ceramic substrate at the copper foil surface layer in contact with the ceramic substrate. It is considered that the grain growth of the surface layer part is suppressed rather than the center part of the copper foil. However, when heat treatment is performed at a temperature higher than 550 ° C., the gradient of the heat distribution becomes small, and it becomes difficult to make a difference between the grain growth rate of the surface layer part of the current collector copper foil and the grain growth rate in the center part. The difference in the number of holes tends to be relatively small. Therefore, the ratio of the number of holes in the current collector and the ratio of the number of holes in the surface portion are lowered, and as a result, there is a possibility that the expansion and contraction of the negative electrode active material is hardly relaxed.

〈負極の作製方法〉
より具体的な例として、負極活物質にケイ素を用いた負極の作製工程について、以下に説明する。まず塗料の重量比率において、負極活物質としてケイ素７０ｗｔ％（固形分全量中の含有量）と、上記導電助剤としてアセチレンブラック５ｗｔ％と、バインダーとしてポリイミド１５ｗｔ％をＮ−メチル−２−ピロリドン（以下、ＮＭＰという。）に溶解したラッカーと、溶剤としてＮＭＰとを混練して塗料を調製し、熱処理を行い準備した厚みが１０μｍの電解銅箔からなる負極集電体の両面に、例えばコンマロールコーターを用いて、所定の厚みを有する負極活物質層となる塗膜を形成し、乾燥炉内で１１０℃の大気雰囲気下でＮＭＰ溶媒を乾燥させた。なお、上記集電体の両面に塗布された負極活物質層となる塗膜の厚みは、両面とも同じ膜厚であることが望ましい。また上記負極集電体には、表面粗さＲａが０．１μｍ以上、抗張力が２００Ｎ／ｍｍ２以上、破断伸び率が１５％以下の電解銅箔を好適な条件として使用すればよい。なお、上記の負極集電体の抗張力および破断伸び率は、熱処理後の抗張力および破断伸び率を意味する。 <Method for producing negative electrode>
As a more specific example, a manufacturing process of a negative electrode using silicon as a negative electrode active material will be described below. First, in the weight ratio of the coating material, 70 wt% of silicon as the negative electrode active material (content in the total solid content), 5 wt% of acetylene black as the conductive auxiliary agent, and 15 wt% of polyimide as the binder were added with N-methyl-2-pyrrolidone ( (Hereinafter referred to as NMP)) NMP as a solvent and NMP as a solvent are kneaded to prepare a paint, heat treatment is carried out, and both sides of a negative electrode current collector made of an electrolytic copper foil having a thickness of 10 μm are prepared. Using a coater, a coating film serving as a negative electrode active material layer having a predetermined thickness was formed, and the NMP solvent was dried in an air atmosphere at 110 ° C. in a drying furnace. In addition, as for the thickness of the coating film used as the negative electrode active material layer apply | coated to both surfaces of the said collector, it is desirable that both surfaces are the same film thickness. For the negative electrode current collector, an electrolytic copper foil having a surface roughness Ra of 0.1 μm or more, a tensile strength of 200 N / mm 2 or more, and a breaking elongation of 15% or less may be used as suitable conditions. The tensile strength and breaking elongation of the negative electrode current collector mean the tensile strength and breaking elongation after heat treatment.

上記負極活物質が形成された負極は、ローラープレスすることで、電解銅箔の両面に負極活物質層となる塗膜を圧着させ、負極活物質層と電解銅箔との密着性を高めると同時に、所定の密度を有する負極シートを得ることができる。   When the negative electrode on which the negative electrode active material is formed is roller-pressed, a coating film to be a negative electrode active material layer is pressure-bonded on both surfaces of the electrolytic copper foil, and the adhesion between the negative electrode active material layer and the electrolytic copper foil is increased. At the same time, a negative electrode sheet having a predetermined density can be obtained.

上記プロセスにより作製した負極シートは、電極金型によって、所定の電極サイズに打ち抜き、本実施形態のリチウムイオン二次電池用の負極を得ることができる。このときの負極の面積は、正極の面積よりも大きいサイズであることが好ましい。負極の面積を、対向する正極の面積よりも大きくすることで、リチウムの析出による内部短絡の発生を防止することができる。   The negative electrode sheet produced by the above process can be punched into a predetermined electrode size by an electrode mold to obtain the negative electrode for the lithium ion secondary battery of this embodiment. The area of the negative electrode at this time is preferably larger than the area of the positive electrode. By making the area of the negative electrode larger than that of the opposing positive electrode, it is possible to prevent the occurrence of an internal short circuit due to lithium deposition.

さらに上記負極は、集電体銅箔を熱処理した温度以下の温度で熱処理し、活物質の粒子と集電体間および活物質の粒子間での密着性の向上に加え、バインダーによる結着力も加わり、密着性をさらに高めることができる。また、集電体の表面に一定の表面粗さを有していれば、その表面の凹凸部分にバインダーが入り込むことにより、バインダーと集電体の間にアンカー効果が働き、さらに密着性が向上する。そのため、リチウムの吸蔵、放出の際の活物質の体積の膨張収縮による集電体からの活物質層の剥離を抑制することができる。   Furthermore, the negative electrode is heat-treated at a temperature equal to or lower than the temperature at which the current collector copper foil is heat-treated, and in addition to improving the adhesion between the active material particles and the current collector and between the active material particles, the binder also has a binding force. In addition, adhesion can be further enhanced. Also, if the current collector surface has a certain surface roughness, the binder will enter the uneven surface of the current collector, so that the anchor effect will work between the binder and the current collector, and the adhesion will be improved. To do. Therefore, peeling of the active material layer from the current collector due to expansion and contraction of the volume of the active material during insertion and extraction of lithium can be suppressed.

〈正極の作製〉
塗料の重量比率において、上記正極活物質のコバルト酸リチウム（ＬｉＣｏＯ２）を９６ｗｔ％と、上記導電助剤としてケッチェンブラックを２ｗｔ％と、バインダーとしてポリフッ化ビニリデン（以下、ＰＶＤＦという。）を２ｗｔ％と、ＮＭＰとを混練して正極活物質層用の塗料を調製し、厚みが２０μｍのアルミニウム箔からなる集電体の両面に、コンマロールコーターを用いて、所定の厚みを有する正極活物質層の塗膜を塗布し、乾燥炉内で１１０℃の雰囲気下でＮＭＰ溶媒を乾燥させた。なお、上記集電体の両面に塗布された正極活物質の塗膜は同じ膜厚であることが望ましい。 <Preparation of positive electrode>
In the weight ratio of the paint, 96 wt% of the positive electrode active material lithium cobaltate (LiCoO 2 ), 2 wt% of ketjen black as the conductive auxiliary agent, and 2 wt% of polyvinylidene fluoride (hereinafter referred to as PVDF) as the binder. % And NMP are kneaded to prepare a coating material for a positive electrode active material layer, and a positive electrode active material having a predetermined thickness using a comma roll coater on both sides of a current collector made of an aluminum foil having a thickness of 20 μm. The layer coating was applied and the NMP solvent was dried in a drying oven at 110 ° C. atmosphere. In addition, it is desirable that the coating films of the positive electrode active material applied on both surfaces of the current collector have the same film thickness.

上記プロセスにより作製した正極をローラープレスすることで集電体の両面に圧縮成形し、集電体と正極活物質層との密着性を高めると同時に、所定の塗膜密度を有する正極シートを得た。   The positive electrode produced by the above process is compression-molded on both sides of the current collector by roller pressing to improve the adhesion between the current collector and the positive electrode active material layer, and at the same time, a positive electrode sheet having a predetermined coating film density is obtained. It was.

さらに正極シートは、金型によって、所定のサイズに打ち抜き、本実施形態のリチウムイオン二次電池用の正極を得た。   Furthermore, the positive electrode sheet was punched into a predetermined size with a mold to obtain a positive electrode for the lithium ion secondary battery of the present embodiment.

〈電池の組立て〉
上述した通りのプロセスにて作製した正極および負極を、セパレーターを介して、対向するように挟み込み、電池要素を作製した。これを電極体１層とし、同様の作製方法にて、３層積層された電池要素を作製した。
そして、この電池要素を、アルミニウムラミネートフィルムの外装体内に挿入して周囲の１箇所を除いてヒートシールすることにより閉口部を形成し、外装体内に所定量の電解液を注入した後に、残りの１箇所を減圧しながらヒートシールすることにより密封し、リチウムイオン二次電池を作製した。 <Battery assembly>
The positive electrode and the negative electrode produced by the process as described above were sandwiched so as to face each other through a separator, and a battery element was produced. This was used as one electrode body, and a battery element in which three layers were laminated was produced by the same production method.
Then, the battery element is inserted into the exterior body of the aluminum laminate film and heat-sealed except for one place around it to form a closed portion. After injecting a predetermined amount of electrolyte into the exterior body, One place was sealed by heat sealing while reducing the pressure to produce a lithium ion secondary battery.

さらに後述する実施例にて本発明をさらに詳細に述べる。ただし、下記実施例は、本発明を制限するものではない。   Further, the present invention will be described in further detail in the examples described later. However, the following examples do not limit the present invention.

（実施例１）
〈負極の作製〉
負極用の集電体として、厚さ１０μｍ、表面粗さＲａが０．１μｍ、抗張力４００Ｎ／ｍｍ２、破断伸び率が１０％の電解銅箔を、対向する２枚のジルコニアセラミックス基板で挟み込み、加熱炉内にて各所定の温度まで３０℃／ｍｉｎで高速昇温して負極を熱処理した。熱処理温度は、１５０、２００、３００、４００、５００、５５０℃とし、この設定した熱処理温度に到達した後は保持させずに室温まで高速で急冷させた。各温度で熱処理した負極をそれぞれ得た。また、上記の熱処理は窒素雰囲気中で実施した。 (Example 1)
<Preparation of negative electrode>
As a current collector for the negative electrode, an electrolytic copper foil having a thickness of 10 μm, a surface roughness Ra of 0.1 μm, a tensile strength of 400 N / mm 2 and a breaking elongation of 10% is sandwiched between two opposing zirconia ceramic substrates, The negative electrode was heat-treated at a high temperature of 30 ° C./min up to each predetermined temperature in a heating furnace. The heat treatment temperatures were 150, 200, 300, 400, 500, and 550 ° C., and after reaching the set heat treatment temperature, they were rapidly cooled to room temperature without being held. Negative electrodes heat-treated at each temperature were obtained. Moreover, said heat processing was implemented in nitrogen atmosphere.

塗料の重量比率において、負極活物質のケイ素粉末７０ｗｔ％（固形分全量中の含有量）と、上記導電助剤としてアセチレンブラック粉末５ｗｔ％と、バインダーとしてポリイミド１５ｗｔ％をＮ−メチル−２−ピロリドン（ＮＭＰ）に溶解したラッカーを混錬し、次いで溶剤としてＮＭＰを加えて所定の粘性に調整した塗料を作製した。   In the weight ratio of the paint, 70 wt% of the silicon powder of the negative electrode active material (content in the total solid content), 5 wt% of acetylene black powder as the conductive auxiliary agent, and 15 wt% of polyimide as the binder were N-methyl-2-pyrrolidone. A lacquer dissolved in (NMP) was kneaded, and then NMP was added as a solvent to prepare a coating material adjusted to a predetermined viscosity.

次に上記塗料を、上記種々の熱処理条件で処理した電解銅箔の両主面上に、コンマロールコーターを用いて厚み５μｍの負極活物質層となる塗膜を塗布し、乾燥炉内で１１０℃の大気雰囲気下で塗膜中のＮＭＰ溶媒を乾燥させた。なお、上記集電体の両面に塗布された負極活物質層の塗膜の厚みは同じ膜厚に調整されている。   Next, a coating film to be a negative electrode active material layer having a thickness of 5 μm was applied to both main surfaces of the electrolytic copper foil treated with the above-mentioned various heat treatment conditions using a comma roll coater, and the coating was performed in a drying furnace. The NMP solvent in the coating film was dried in an air atmosphere at 0 ° C. In addition, the thickness of the coating film of the negative electrode active material layer apply | coated to both surfaces of the said collector is adjusted to the same film thickness.

上記負極活物質層が塗布された負極をローラープレスすることで、電解銅箔の両面主面に負極活物質層を圧着させ、集電体の負極活物質層と電解銅箔との密着性を高めると同時に、所定の密度を有する負極シートを得た。   The negative electrode on which the negative electrode active material layer is applied is roller-pressed so that the negative electrode active material layer is pressure-bonded to the main surface on both sides of the electrolytic copper foil, and the adhesion between the negative electrode active material layer of the current collector and the electrolytic copper foil is improved. Simultaneously with the increase, a negative electrode sheet having a predetermined density was obtained.

上記負極シートを、電極金型によって、２１×３１ｍｍの電極サイズに打ち抜き、リチウムイオン二次電池用の負極を得た。   The negative electrode sheet was punched into an electrode size of 21 × 31 mm using an electrode mold to obtain a negative electrode for a lithium ion secondary battery.

得られた各負極は、活物質の粒子と集電体間および活物質の粒子間での密着性の向上と、バインダーによる結着性と機械的強度の向上を付与するために、集電体銅箔の熱処理温度以下の温度より低い温度５０、１００、１５０、２００、３００、３５０℃で熱処理した。   Each of the obtained negative electrodes has a current collector in order to improve adhesion between the active material particles and the current collector and between the active material particles, and to improve the binding property and mechanical strength by the binder. It heat-processed at the temperature 50, 100, 150, 200, 300, 350 degreeC lower than the temperature below the heat processing temperature of copper foil.

（比較例１）
〈負極の作製〉
負極の比較例として、ジルコニアセラミックス基板に挟み込まずに、昇温降温速度５℃／ｍｉｎを３００℃、４００℃で熱処理した集電体を作製し、それ以外は実施例１と同様の方法によって負極を作製した。 (Comparative Example 1)
<Preparation of negative electrode>
As a comparative example of the negative electrode, a current collector that was heat-treated at 300 ° C. and 400 ° C. at a temperature rising / falling rate of 5 ° C./min without producing a zirconia ceramic substrate was prepared. Was made.

〈正極の作製〉
次に、正極活物質層となる塗料の重量比率において、正極活物質のコバルト酸リチウム（ＬｉＣｏＯ２）を９６ｗｔ％と、導電助剤としてケッチェンブラックを２ｗｔ％と、バインダーとしてＰＶＤＦを２ｗｔ％と、塗料中の粉末の分散および塗料の粘土調剤としてＮＭＰを混練し、正極活物質用塗料を調整した。
厚みが２０μｍのアルミニウム箔からなる集電体の両面に、コンマロールコーターを用いて、所定の厚みを有する正極活物質層となる塗料を塗布し、乾燥炉内で１１０℃の雰囲気下で塗膜中のＮＭＰ溶媒を乾燥させた。なお、上記集電体の両面に塗布された正極活物質層の塗膜は同じ膜厚とした。 <Preparation of positive electrode>
Next, in the weight ratio of the coating material used as the positive electrode active material layer, the positive electrode active material lithium cobaltate (LiCoO 2 ) is 96 wt%, the ketjen black is 2 wt% as the conductive additive, and the PVDF is 2 wt% as the binder. Then, NMP was kneaded as a dispersion of the powder in the paint and a clay preparation of the paint to prepare a positive electrode active material paint.
Using a comma roll coater, both sides of a current collector made of an aluminum foil with a thickness of 20 μm are coated with a coating material to be a positive electrode active material layer having a predetermined thickness, and a coating film is applied in an atmosphere of 110 ° C. in a drying furnace. The NMP solvent in it was dried. In addition, the coating film of the positive electrode active material layer apply | coated on both surfaces of the said electrical power collector was made into the same film thickness.

そして上記正極活物質層をローラープレスすることで集電体の両面に圧縮成形し、集電体と正極活物質との密着性を高めると同時に、所定の塗膜密度を有する正極シートを得た。   Then, the positive electrode active material layer was compression-molded on both sides of the current collector by roller pressing to improve the adhesion between the current collector and the positive electrode active material, and at the same time, a positive electrode sheet having a predetermined coating film density was obtained. .

上記の正極シートは、電極金型によって、２０×３０ｍｍの電極サイズに打ち抜き、リチウムイオン二次電池用の正極を得た。   The positive electrode sheet was punched into an electrode size of 20 × 30 mm using an electrode mold to obtain a positive electrode for a lithium ion secondary battery.

〈電池の作製〉
上述の通り作製した各熱処理温度の負極および正極を、２３×３３ｍｍのサイズに金型で打抜いたポリオレフィン系の多孔質セパレーターを介して、対向するように挟み込み、電池要素を作製した。これを電極体１層とし、これを３層積層させた電池要素をそれぞれ作製した。
そして、上記電極体の正極のアルミニウム箔の活物質が設けられていない端部に、アルミニウム製の正極タブを取り付け、また負極の電解銅箔に活物質が設けられていない端部に、ニッケル製の負極タブを取り付け、この電極体を、アルミニウムラミネートフィルムの外装体内に挿入して周囲の１箇所を除いてヒートシールすることにより閉口部を形成し、外装体内にＥＣ／ＤＥＣが３：７の割合で配合された溶媒中に無機イオン塩として１Ｍ（ｍｏｌ／Ｌ）のＬｉＰＦ６が添加された電解液を注入した後に、残りの１箇所を真空中でヒートシールすることにより密封し、リチウムイオン二次電池を作製した。 <Production of battery>
The battery element was produced by sandwiching the negative electrode and the positive electrode produced at the respective heat treatment temperatures as described above so as to face each other through a polyolefin-based porous separator punched out with a mold to a size of 23 × 33 mm. This was used as an electrode body, and battery elements were produced by laminating three layers.
Then, an aluminum positive electrode tab is attached to the end of the electrode body where the positive electrode aluminum foil is not provided with an active material, and a nickel electrode is attached to the end of the negative electrode electrolytic copper foil where no active material is provided. A negative electrode tab was attached, and this electrode body was inserted into an aluminum laminate film exterior body and heat-sealed except for one peripheral portion to form a closed portion. EC / DEC was 3: 7 in the exterior body. After injecting an electrolyte solution in which 1M (mol / L) LiPF 6 was added as an inorganic ion salt in a solvent blended at a ratio, the remaining one place was sealed by heat sealing in a vacuum, and lithium ion A secondary battery was produced.

〈集電体断面における空孔径および金属粒子径の評価〉
上記の実施例１において、各温度で熱処理した集電体銅箔は、熱硬化性樹脂によって包埋し、６０℃の乾燥機で１時間乾燥させた。この樹脂埋めされた負極を、自動回転研磨機によってメッシュナンバーを１０００、１５００、２０００番の耐水研磨紙で研磨して負極断面を露出させた。その後、アルミナ粉末φ０．３μｍを用いてバフ研磨することで鏡面に仕上げた。 <Evaluation of pore diameter and metal particle diameter in current collector cross section>
In said Example 1, the collector copper foil heat-processed at each temperature was embedded with the thermosetting resin, and was dried with the 60 degreeC dryer for 1 hour. The negative electrode filled with the resin was polished with water-resistant abrasive paper having mesh numbers 1000, 1500 and 2000 by an automatic rotary polishing machine to expose the cross section of the negative electrode. Thereafter, it was finished to a mirror surface by buffing with alumina powder φ0.3 μm.

上記研磨によって断面出しした各負極サンプルは、フラットミリング（ＨＭ−３０００：日立ハイテクノロジー社）を用いて、研磨面をエッチングした。条件としては、加速電圧６Ｖ、Ａｒガスフロー：０．０７ｃｍ３／ｍｉｎ、傾斜角８５°、偏心量４ｍｍ、処理時間１０分にて、サンプルを回転させながらＡｒイオンビームを照射させ、微小な研磨傷を除去した。 Each negative electrode sample taken out by the above polishing was etched on the polished surface using flat milling (HM-3000: Hitachi High-Technology Corporation). The conditions were as follows: acceleration voltage 6V, Ar gas flow: 0.07 cm 3 / min, tilt angle 85 °, eccentricity 4 mm, treatment time 10 minutes, Ar ion beam was irradiated while rotating the sample, and fine polishing The wound was removed.

これらのサンプルは、Ａｕスパッタを２ｍｉｎ実施し、ＦＥ−ＳＥＭ（Ｓ−４７００；日立製作所社製）を用いて、集電体である電解銅箔断面の空孔および銅の結晶粒子を観察した。観察条件としては、加速電圧＝５．０ｋＶにて反射電子像にて、５００倍〜１００００倍の視野で観察を行った。また、電解銅箔断面の観察位置は任意５箇所を撮影し、集電体断面における空孔面積比率をそれぞれ算出し、その平均値を空孔面積比率とした。なお、上記空孔面積比率は下記の式によって算出し、集電体断面の反射電子像をモノクロに画像処理し、空孔部と銅箔部に二値化することで、空孔断面積を数値化した。
また、この画像処理によって、個々の空孔の空孔径の算出も行うことができる。空孔径は、個々の空孔の空孔断面積を用い、この断面積を真円として計算した直径を用いることとした。 These samples were subjected to Au sputtering for 2 minutes, and FE-SEM (S-4700; manufactured by Hitachi, Ltd.) was used to observe pores and copper crystal particles in the cross section of the electrolytic copper foil as a current collector. As an observation condition, observation was performed with a reflected electron image at an acceleration voltage of 5.0 kV and a field of view of 500 to 10,000 times. Moreover, the observation positions of the electrolytic copper foil cross section were photographed at arbitrary five locations, the pore area ratio in the current collector cross section was calculated, and the average value was taken as the pore area ratio. In addition, the hole area ratio is calculated by the following formula, the reflected electron image of the current collector cross section is subjected to monochrome image processing, and binarized into a hole portion and a copper foil portion, thereby obtaining a hole cross-sectional area. Digitized.
In addition, the hole diameter of each hole can be calculated by this image processing. As the hole diameter, the hole cross-sectional area of each hole was used, and the diameter calculated with this cross-sectional area as a perfect circle was used.

この画像処理は結晶粒子径の算出も行うことができる。
結晶粒子は、集電体断面の反射電子像から確認できるので、上述の様な二値化処理を行わないで、画像処理にて、個々の結晶粒子の粒子断面積を算出し、この断面積を真円として計算したときの直径を結晶粒子径とした。 This image processing can also calculate the crystal particle size.
Since the crystal particles can be confirmed from the reflected electron image of the current collector cross section, the cross-sectional area of each crystal particle is calculated by image processing without performing the binarization process as described above. The diameter when calculated as a perfect circle was taken as the crystal particle diameter.

〈空孔面積比率〉
空孔面積比率は下記式により求められる。
空孔面積比率（％）＝ （任意の銅箔断面における全空孔の断面積の合計（μｍ２））／（任意の銅箔断面積（μｍ２）） × １００ <Hole area ratio>
The pore area ratio is obtained by the following formula.
Hole area ratio (%) = (total cross-sectional area of all holes in an arbitrary copper foil cross section (μm 2 )) / (arbitrary copper foil cross-sectional area (μm 2 )) × 100

〈空孔数比率〉
さらに、各熱処理温度の銅箔断面において、上部と下部の表面層更にそれに挟まれた中央部の領域内にある空孔数をそれぞれカウントし、集電体断面内の全空孔数に対する各領域の空孔数比率を以下の式によって算出した。 <Void number ratio>
Furthermore, in the copper foil cross section at each heat treatment temperature, the number of holes in the upper and lower surface layers and the central area sandwiched between them is counted, and each area for the total number of holes in the current collector cross section is counted. The number ratio of holes was calculated by the following formula.

空孔数比率（％）＝ （任意の銅箔断面における上部または下部、またはそれら上部と下部に挟まれた中央部における空孔数）／（任意の銅箔断面に存在する全空孔数） × １００   Porosity ratio (%) = (number of vacancies at the top or bottom of any copper foil cross section, or at the center between the top and bottom) / (total number of vacancies present on any copper foil cross section) × 100

〈結晶粒子の平均粒子径〉
また、集電体断面の上部と下部における表層部の結晶粒子の平均粒子径（Ｘ）と、集電体断面の中央の結晶粒子の平均粒子径（Ｙ）は以下の方法によって算出した。 <Average particle diameter of crystal particles>
Moreover, the average particle diameter (X) of the crystal particle of the surface layer part in the upper part and the lower part of a collector cross section, and the average particle diameter (Y) of the crystal grain of the center of a collector cross section were computed with the following method.

集電体表層部の結晶粒子の平均粒子径（Ｘ）（単位はμｍ）は、上記集電体断面の任意の反射電子像の視野を５箇所用いて、それぞれの集電体断面における表層部を構成する結晶粒子を概ね横切る直線を引き、直線に横切る結晶粒子の幅：ｍ（単位はμｍ）をカウントし、測定長さ当たりの幅ｍから粒子径を求め、同様に測定する合計５つの視野の平均値から平均粒子径（Ｘ）を求めた。同様に集電体断面の中央に位置する金属粒子の平均粒子径（Ｙ）（単位はμｍ）も、上記集電体断面の任意の反射電子像の視野を５箇所用いて、集電体断面の主面と平行な直線を、集電体中央に引き、直線を横切る結晶粒子の幅：ｎ（単位はμｍ）をカウントし、測定長さ当たりの結晶粒子の幅ｎから粒子径を求め、同様に測定する合計５つ視野の平均値から平均粒子径（Ｙ）を求めた。   The average particle diameter (X) (unit: μm) of the crystal particles of the current collector surface layer is the surface layer part of each current collector cross section using five arbitrary reflected electron image fields of the current collector cross section. A straight line that substantially intersects the crystal grains constituting the sample is drawn, the width of the crystal grains that cross the straight line: m (unit: μm) is counted, the particle diameter is obtained from the width m per measurement length, and a total of five measurements are similarly performed. The average particle diameter (X) was determined from the average value of the visual field. Similarly, the average particle diameter (Y) (unit: μm) of the metal particles located at the center of the current collector cross section is also the current cross section of the current collector using five points of arbitrary reflected electron image fields of the current collector cross section. A straight line parallel to the main surface of the crystal is drawn to the center of the current collector, the width of the crystal particles crossing the straight line: n (unit: μm) is counted, and the particle diameter is obtained from the width n of the crystal particles per measurement length, The average particle diameter (Y) was determined from the average value of a total of five fields of view measured in the same manner.

なお、上記集電体断面の上部、下部、中央部とは、上述したとおり厚み方向に３等分した図２に示す領域である。   In addition, the upper part of the said collector cross section, the lower part, and the center part are the area | regions shown in FIG. 2 divided into 3 equal to the thickness direction as mentioned above.

〈サイクル特性、および電極変形の評価〉
〈５０サイクル後の放電容量維持率〉
上記作製したリチウムイオン二次電池は、下記に示す充放電試験条件によって充放電によるサイクル特性について評価した。充放電は２５℃にて実施した。充放電試験条件は、１．０Ｃの定電流で４．２Ｖになるまで定電流充電を行い、その後は１．０Ｃの定電流で電池電圧が２．５Ｖとなるまで放電し、上記を１サイクルとし、５０サイクル後の放電容量維持率を算出した。その結果をサイクル特性として評価した。
なお、言うまでもないが１Ｃとは公称容量値の容量を有する電池セルを定電流充電、または低電流放電して、ちょうど１時間で充放電が終了となる電流値のことであり、したがって、上記電流値は、電池の公称容量値で決定される。一例として、２．２Ａｈの公称容量値のセルでは １Ｃ＝２．２Ａとなる。
また、５０サイクル後の放電容量維持率は、下記式によって定義される。
５０サイクル後の放電容量維持率（％）＝（５０サイクル後の放電容量）／（１サイクル後の放電容量）×１００（％） <Evaluation of cycle characteristics and electrode deformation>
<Discharge capacity maintenance ratio after 50 cycles>
The produced lithium ion secondary battery was evaluated for cycle characteristics by charge / discharge under the following charge / discharge test conditions. Charging / discharging was performed at 25 degreeC. The charging / discharging test conditions were as follows: constant current charging until a constant current of 1.0 C was 4.2 V, then discharging until a battery voltage of 2.5 V was reached with a constant current of 1.0 C, and the above was performed for one cycle. The discharge capacity retention rate after 50 cycles was calculated. The results were evaluated as cycle characteristics.
Needless to say, 1C is a current value at which charging / discharging is completed in just one hour after constant current charging or low current discharging of a battery cell having a nominal capacity value. The value is determined by the nominal capacity value of the battery. As an example, for a cell with a nominal capacity value of 2.2 Ah, 1C = 2.2A.
Moreover, the discharge capacity maintenance rate after 50 cycles is defined by the following formula.
Discharge capacity maintenance ratio after 50 cycles (%) = (discharge capacity after 50 cycles) / (discharge capacity after 1 cycle) × 100 (%)

さらに５０サイクル終了した上記電池は、グローブボックス内で解体し、負極を取り出し、取り出した負極は、ジメチルカーボネート（ＤＭＣ）で洗浄し、６０℃で乾燥した後に負極の変形状態を判定した。なお、上記変形は、上記負極の皺、負極活物質の剥がれ、負極の破れを目視によって評価した。   Further, the battery after 50 cycles was disassembled in the glove box, the negative electrode was taken out, the negative electrode taken out was washed with dimethyl carbonate (DMC) and dried at 60 ° C., and then the deformation state of the negative electrode was judged. In addition, the said deformation | transformation evaluated visually the wrinkle of the said negative electrode, peeling of a negative electrode active material, and the tearing of a negative electrode.

〈実施例１の結果〉
実施例１の検討結果を表１に示す。５０サイクル後の放電容量維持率が、７５％以上の良好なサイクルを示したサンプルは、ジルコニアセラミックス基板で負極を挟み込みながら、１５０℃から５５０℃の範囲で熱処理したものであった。
上記負極サンプルを構成する集電体の構造形態を確認すると、銅箔断面の空孔面積比率が０．２％以上であり、また表層部の上部と下部の空孔数比率が、中央部の空孔面積比率以上であり、かつ上部および下部の少なくともどちらか一方の空孔数比率が、中央部の空孔数比率よりも大きい負極であることが分かった。さらに上記熱処理した集電体断面において、集電体の表層部の結晶粒子径Ｘ（単位はμｍ）は、中央部の結晶粒子径Ｙ（単位はμｍ）のよりも小さく、０．６Ｙ≦Ｘ≦０．９Ｙの関係式を満たしていた。そして、複数の空孔は結晶粒子間に存在していることも確認した。 <Results of Example 1>
The examination results of Example 1 are shown in Table 1. A sample having a good discharge capacity retention rate of 75% or more after 50 cycles was heat-treated in the range of 150 ° C. to 550 ° C. while sandwiching the negative electrode with a zirconia ceramic substrate.
When confirming the structure of the current collector constituting the negative electrode sample, the hole area ratio of the copper foil cross section is 0.2% or more, and the number of holes in the upper part and the lower part of the surface layer part is in the center part. It was found that the negative electrode had a pore area ratio that was equal to or greater than the hole area ratio, and at least one of the upper and lower hole ratios was larger than the hole ratio in the central part. Further, in the heat-treated current collector cross section, the crystal particle diameter X (unit: μm) of the surface layer portion of the current collector is smaller than the crystal particle diameter Y (unit: μm) of the central portion, and 0.6Y ≦ X The relational expression ≦ 0.9Y was satisfied. It was also confirmed that a plurality of vacancies exist between crystal grains.

また、比較例としてジルコニアセラミックス基板で挟み込まず３００℃と４００℃で熱処理した各サンプルでは、集電体断面の上部または下部のどちらか一方の空孔数比率が中央部のそれよりも同等以下となり、５０サイクル後の負極において、破れが多数みられた。また、皺が原因と思われる塗膜（負極活物質層）剥がれも見受けられた。   In addition, as a comparative example, in each sample heat-treated at 300 ° C. and 400 ° C. without being sandwiched between zirconia ceramic substrates, the ratio of the number of holes in either the upper part or the lower part of the current collector cross section is equal to or less than that in the central part. In the negative electrode after 50 cycles, many tears were observed. In addition, peeling of the coating film (negative electrode active material layer) that was thought to be caused by wrinkles was also observed.

上記本実施形態の集電体構造を成す代表形態として、表１に示した３００℃で熱処理した集電体断面（実施例１−３）の反射電子像を図４に示す。また、図４を画像処理して二値化した画像を図５に示す。   FIG. 4 shows a reflected electron image of a cross section of the current collector (Example 1-3) heat-treated at 300 ° C. shown in Table 1 as a representative form constituting the current collector structure of the present embodiment. FIG. 5 shows an image obtained by binarizing the image of FIG.

（実施例２）
〈負極および電池の作製〉
実施例１で使用した電解銅箔のうち、厚さが８μｍのものを用意し、その厚さ８μｍの銅箔を、ジルコニアセラミックス基板で挟み込みながら、熱処理温度、昇温、降温速度、熱処理保持時間を様々に変更し、負極集電体断面内の空孔面積比率が０．２％以上、かつ上記集電体断面における上部、または下部の空孔数と、中央の空孔数の比率が種々に異なった集電体銅箔を作製した。
上記得られた種々の集電体銅箔における空孔面積比率は１．０％以上であり、上部（下部）と中央部との空孔数相対比（集電体断面における上部、または下部の空孔数 ÷ 集電体断面における中央の空孔数）は、１．２〜１．６の範囲内であった。そして、上記集電体銅箔を負極集電体として用いた以外は、実施例１と同様に負極および電池を作製した。
なお、上記の相対比の算出式において、集電体断面における上部、または下部における空孔数は、空孔数の多い方を評価対象とした。 (Example 2)
<Production of negative electrode and battery>
Among the electrolytic copper foils used in Example 1, those having a thickness of 8 μm were prepared, and the heat treatment temperature, temperature rise, temperature drop rate, heat treatment holding time while sandwiching the 8 μm thick copper foil between the zirconia ceramic substrates The ratio of the hole area in the negative electrode current collector cross section is 0.2% or more, and the ratio of the upper or lower hole number and the central hole number in the current collector cross section is various. Different current collector copper foils were prepared.
The hole area ratio in the obtained various current collector copper foils is 1.0% or more, and the relative number of holes in the upper part (lower part) and the central part (upper or lower part of the current collector cross section). The number of holes divided by the number of holes in the center of the current collector cross section was in the range of 1.2 to 1.6. And the negative electrode and the battery were produced similarly to Example 1 except having used the said collector copper foil as a negative electrode collector.
In the above calculation formula for the relative ratio, the number of vacancies in the upper part or the lower part of the current collector cross section was evaluated with respect to the larger number of vacancies.

〈サイクル特性、および電極変形の評価〉
実施例２で作製した集電体銅箔を負極集電体として、実施例１と同様の工程を経て電池を作製し、５０サイクル後の放電容量維持率と５０サイクル後の負極の変形状態を実施例１と同様に評価した。 <Evaluation of cycle characteristics and electrode deformation>
Using the current collector copper foil produced in Example 2 as the negative electrode current collector, a battery was produced through the same steps as in Example 1, and the discharge capacity retention rate after 50 cycles and the deformation state of the negative electrode after 50 cycles were determined. Evaluation was performed in the same manner as in Example 1.

〈実施例２の結果〉
実施例２の結果を表２に示す。銅箔断面の上部（または下部）の空孔数と中央部の空孔数の相対比とサイクル放電容量維持率との関係を調べた結果、相対比が１．２〜１．６において、５０サイクル後の放電容量維持率は良好であることが分かった。 <Results of Example 2>
The results of Example 2 are shown in Table 2. As a result of investigating the relationship between the relative ratio of the number of vacancies in the upper part (or lower part) and the number of vacancies in the central part and the cycle discharge capacity retention rate of the copper foil cross section, the relative ratio was 1.2 to 1.6. It was found that the discharge capacity retention rate after cycling was good.

（実施例３）
〈負極および電池の作製〉
実施例１と同様の厚さ１０μｍの集電体銅箔を、ジルコニアセラミックス基板で挟み込みながら、熱処理温度、昇温、降温速度、熱処理保持時間を様々に変更し、負極集電体断面内の空孔面積比率が０．２％以上、かつ上記集電体断面における上部と下部の空孔数比率が、中央部の空孔数比率のそれ以上を有し、さらに上記集電体の最大空孔径（μｍ）が種々に異なった集電体銅箔を作製した。種々の熱処理条件で実施した結果、上記集電体内の最大空孔径は、０．１〜３．３μｍであった。これらの最大空孔径は、集電体厚みに対して、１／１００〜１／３の範囲内であった。
なお、上記集電体銅箔を負極集電体として用いた以外は、実施例１と同様の工程にて負極および電池を作製した。 (Example 3)
<Production of negative electrode and battery>
While the current collector copper foil having a thickness of 10 μm similar to that of Example 1 is sandwiched between zirconia ceramic substrates, the heat treatment temperature, the temperature rise, the temperature drop rate, and the heat treatment holding time are variously changed, and the empty space in the negative electrode current collector cross section is changed. The hole area ratio is 0.2% or more, and the upper and lower hole number ratio in the current collector cross-section has more than the hole number ratio in the central part, and further the maximum hole diameter of the current collector Current collector copper foils having different (μm) were prepared. As a result of carrying out under various heat treatment conditions, the maximum pore diameter in the current collector was 0.1 to 3.3 μm. These maximum pore diameters were in the range of 1/100 to 1/3 with respect to the current collector thickness.
In addition, the negative electrode and the battery were produced in the same process as Example 1 except having used the said collector copper foil as a negative electrode collector.

〈負極の集電体銅箔断面における空孔径の評価〉
上記熱処理した実施例３の負極集電体は、実施例１と同様に集電体断面を鏡面処理し、ＦＥ−ＳＥＭ（電界放射型走査型電子顕微鏡）により任意の集電体断面５箇所を反射電子像によって観察し、集電体断面内における各空孔の断面積を算出した。各空孔の断面積は、実施例１と同様に、集電体断面の反射電子像をモノクロに画像処理（二値化）することによって、各空孔の断面積を数値化した。このとき空孔は円と仮定し、円の直径を空孔径と定義し、算出した。 <Evaluation of pore diameter in current collector copper foil cross section of negative electrode>
The heat-treated negative electrode current collector of Example 3 was mirror-treated on the current collector cross section in the same manner as in Example 1, and an arbitrary current collector cross section of 5 locations was obtained by FE-SEM (field emission scanning electron microscope). The cross-sectional area of each hole in the current collector cross section was calculated by observation with a reflected electron image. As in Example 1, the cross-sectional area of each hole was quantified by subjecting the reflected electron image of the current collector cross-section to monochrome image processing (binarization). At this time, the hole was assumed to be a circle, and the diameter of the circle was defined as the hole diameter.

〈サイクル特性、および電極変形の評価〉
実施例３で作製した集電体銅箔を負極集電体として、実施例１と同様の工程を経て電池を作製し、５０サイクル後の放電容量維持率と５０サイクル後の負極の変形状態を実施例１と同様に評価した。 <Evaluation of cycle characteristics and electrode deformation>
Using the current collector copper foil produced in Example 3 as the negative electrode current collector, a battery was produced through the same steps as in Example 1, and the discharge capacity retention rate after 50 cycles and the deformation state of the negative electrode after 50 cycles were determined. Evaluation was performed in the same manner as in Example 1.

〈実施例３の結果〉
実施例３の結果を表３に示す。まず集電体厚みの、１／１００〜１／３までの全ての実施例は５０サイクル後の負極に破れはなかった。さらに５０サイクル後における放電容量維持率は、集電体銅箔断面内における最大空孔径が、集電体厚みの、１／１００〜１／３までの全ての実施例が７５％以上の高い維持率を示し、１／１００〜１／４までの実施例は、８０％以上の更に高い維持率を示していることが確認された。よって、集電体内における最大空孔径は、集電体厚みの１／４以下が好ましいことが分かった。なお、実施例内で観察されたすべての空孔径は、集電体の金属結晶粒子径よりも小さいことを確認した。 <Results of Example 3>
The results of Example 3 are shown in Table 3. First, in all examples of the current collector thickness from 1/100 to 1/3, the negative electrode after 50 cycles was not broken. Furthermore, the discharge capacity maintenance rate after 50 cycles is maintained at a high value of 75% or more in all examples where the maximum pore diameter in the cross section of the current collector copper foil is 1/100 to 1/3 of the current collector thickness. It was confirmed that the examples from 1/100 to 1/4 showed a higher maintenance ratio of 80% or more. Therefore, it was found that the maximum pore diameter in the current collector is preferably ¼ or less of the current collector thickness. In addition, it confirmed that all the void | hole diameters observed in the Example were smaller than the metal crystal particle diameter of a collector.

本発明に係るリチウムイオン二次電池は、ケイ素およびスズなどの高容量な負極活物質であっても、電極の破れ等を生じることなく、さらに良好なサイクル特性を示すことから、電池サイズの小型化、軽量化、薄層化に貢献することができ、主に小型電子機器の電池として広く利用することができる。   The lithium ion secondary battery according to the present invention shows a better cycle characteristic without causing electrode breakage even if it is a high-capacity negative electrode active material such as silicon and tin. It can contribute to reduction in size, weight and thickness, and can be widely used mainly as a battery for small electronic devices.

１ セラミックス基板
２ 集電体
1 Ceramic substrate 2 Current collector

Claims (6)

内部に複数の空孔を有するリチウムイオン二次電池用の銅箔からなる集電体であって、
前記集電体の厚みが４〜１００μｍであり、前記集電体の主面と交差する方向の断面において、
前記集電体の断面を厚み方向に３等分し、前記集電体の主面側に位置する３分の１の厚みの断面領域を表層部としたときに、
前記集電体の主面側の表層部における空孔数比率は、前記集電体の中央部における空孔数比率よりも高い集電体であって、
前記複数の空孔は、前記集電体を構成する複数の結晶粒子の粒子間に局所的に配置されていることを特徴とする集電体。 A current collector made of a copper foil for a lithium ion secondary battery having a plurality of holes therein,
The thickness of the current collector is 4 to 100 μm, and in the cross section in the direction intersecting with the main surface of the current collector,
When the cross section of the current collector is divided into three equal parts in the thickness direction, and a cross-sectional area having a thickness of one third located on the main surface side of the current collector is a surface layer portion,
The number-of-holes ratio in the surface layer portion on the main surface side of the current collector is a current collector higher than the number-of-holes ratio in the central part of the current collector,
The current collector is characterized in that the plurality of holes are locally arranged between a plurality of crystal particles constituting the current collector. 前記複数の空孔のうち、最大の空孔径となる空孔は、前記集電体の厚みの１／４以下の空孔径で構成されていることを特徴とする請求項１に記載の集電体。   2. The current collector according to claim 1, wherein a hole having a maximum hole diameter among the plurality of holes is configured with a hole diameter of ¼ or less of a thickness of the current collector. body. 前記集電体は、複数の結晶粒子を含み、前記断面において、
前記表層部における前記結晶粒子の平均結晶粒子径が、前記中央部における前記結晶粒子の平均結晶粒子径よりも小さいことを特徴とする請求項１乃至２のいずれか一項に記載の集電体。 The current collector includes a plurality of crystal particles, and in the cross section,
3. The current collector according to claim 1, wherein an average crystal particle diameter of the crystal particles in the surface layer portion is smaller than an average crystal particle diameter of the crystal particles in the central portion. . 前記集電体は、複数の結晶粒子を含み、前記断面において、
前記集電体内部の前記結晶粒子の平均結晶粒子径が、前記集電体の厚み方向において、前記中央部から前記表層部にかけ、徐々に小さくなっていることを特徴とする請求項１乃至３のいずれか一項に記載の集電体。 The current collector includes a plurality of crystal particles, and in the cross section,
The average crystal particle diameter of the crystal particles inside the current collector is gradually decreased from the central portion to the surface layer portion in the thickness direction of the current collector. The current collector according to any one of the above. 前記集電体は、複数の結晶粒子を含み、前記表層部の前記結晶粒子の平均結晶粒子径をＸとし、前記中央部の平均結晶粒子径をＹとしたとき、Ｘ≦０．９Ｙの関係式を満たすことを特徴とする請求項１乃至４いずれか一項に記載の集電体。   The current collector includes a plurality of crystal particles, where X is an average crystal particle diameter of the crystal particles in the surface layer portion, and Y is an average crystal particle size of the central portion, and X ≦ 0.9Y. The current collector according to claim 1, wherein an expression is satisfied. 請求項１乃至５のいずれか１項に記載の集電体を備えるリチウムイオン二次電池。   A lithium ion secondary battery provided with the electrical power collector of any one of Claims 1 thru | or 5.
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