JP5032800B2 - Positive electrode for lithium secondary battery and lithium secondary battery using the same - Google Patents

Positive electrode for lithium secondary battery and lithium secondary battery using the same Download PDF

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JP5032800B2
JP5032800B2 JP2006177760A JP2006177760A JP5032800B2 JP 5032800 B2 JP5032800 B2 JP 5032800B2 JP 2006177760 A JP2006177760 A JP 2006177760A JP 2006177760 A JP2006177760 A JP 2006177760A JP 5032800 B2 JP5032800 B2 JP 5032800B2
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lithium
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秀治 武澤
肇 西野
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Panasonic Holdings Corp
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Matsushita Electric Industrial Co Ltd
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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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Description

本発明は、釘刺し試験における信頼性に優れ、かつ高容量なリチウム二次電池用正極およびそれを用いたリチウム二次電池に関する。   The present invention relates to a positive electrode for a lithium secondary battery having excellent reliability and high capacity in a nail penetration test and a lithium secondary battery using the same.

リチウム二次電池はノート型パソコンや携帯用通信機器などの駆動用電源として用いられている。近年では、電子機器のポータブル化やコードレス化が進展するに伴って、高容量化や小型軽量化の要望がますます強くなっている。これに伴い、電極材料の改良や変更あるいは電池構造の改善などによってリチウム二次電池はますます高容量化してきている。一方、高容量化に伴いエネルギー密度も増加するため、内部短絡試験等において大きなエネルギーが放出された場合の信頼性を向上させる要請もきわめて大きくなっている。それゆえ、このような試験時における高い信頼性と高容量とを両立させたリチウム二次電池が強く求められている。   Lithium secondary batteries are used as driving power sources for notebook computers and portable communication devices. In recent years, as electronic devices have become more portable and cordless, demands for higher capacity, smaller size, and lighter weight have increased. Accordingly, the capacity of lithium secondary batteries has been increasing due to improvements and changes in electrode materials or improvements in battery structure. On the other hand, since the energy density increases as the capacity increases, there is an increasing demand for improving the reliability when large energy is released in an internal short circuit test or the like. Therefore, there is a strong demand for a lithium secondary battery that achieves both high reliability and high capacity during such tests.

内部短絡時の信頼性を調べる試験の１つとして、電池に釘を刺す内部短絡試験（以下、釘刺し試験と略記）が行われる。エネルギー密度の高いリチウム二次電池は、釘刺し試験において内部短絡により正極が熱分解を始めた場合には、大きなエネルギーを放出して熱暴走により電池が過熱される。従って、釘刺し試験におけるリチウム二次電池の過熱は正極の熱安定性に大きく影響されることになる。   As one of tests for checking reliability at the time of internal short circuit, an internal short circuit test (hereinafter, abbreviated as nail penetration test) in which a nail is inserted into a battery is performed. In the case of a lithium secondary battery having a high energy density, when the positive electrode starts to thermally decompose due to an internal short circuit in the nail penetration test, the battery is overheated due to thermal runaway by releasing large energy. Therefore, overheating of the lithium secondary battery in the nail penetration test is greatly influenced by the thermal stability of the positive electrode.

正極の熱安定性は、正極に用いられる活物質の熱安定性に依存する。リチウム二次電池の正極に用いられる活物質としては、層状構造を有するＬｉＣｏＯ2やＬｉＮｉＯ2、スピネル構造を有するＬｉＭｎ2Ｏ4などのリチウムを含有する複合酸化物が知られている。これらのリチウム含有複合酸化物は、それぞれ電気化学的特性および熱安定性が異なっている。 The thermal stability of the positive electrode depends on the thermal stability of the active material used for the positive electrode. As active materials used for the positive electrode of a lithium secondary battery, lithium-containing composite oxides such as LiCoO 2 and LiNiO 2 having a layered structure and LiMn 2 O 4 having a spinel structure are known. These lithium-containing composite oxides have different electrochemical characteristics and thermal stability.

例えば、ＬｉＮｉＯ2などのリチウムニッケル酸化物は可逆容量が１８０〜２００（ｍＡｈ／ｇ）あり、その他のリチウム含有酸化物に比べ容量密度は大きいが、発熱開始温度は低く、熱安定性は低い。そのため、これを正極活物質として用いたリチウム二次電池は、釘刺し試験において過熱しやすい傾向にある。 For example, lithium nickel oxide such as LiNiO 2 has a reversible capacity of 180 to 200 (mAh / g), and has a larger capacity density than other lithium-containing oxides, but has a low heat generation start temperature and low thermal stability. Therefore, the lithium secondary battery using this as a positive electrode active material tends to be overheated in the nail penetration test.

そこで、高容量を維持しながら正極の熱安定性を改善するため、熱分解時の酸素放出抑制を目的にＬｉＮｉＯ2のＮｉの一部を他元素に置換したリチウム含有酸化物を正極活物質として用いたリチウム二次電池や、リチウムニッケル酸化物とこれよりも熱安定性の高いリチウム含有酸化物とを組合せてこれらを活物質として正極を構成したリチウム二次電池が提案されている。 Therefore, in order to improve the thermal stability of the positive electrode while maintaining a high capacity, a lithium-containing oxide in which a part of Ni in LiNiO 2 is replaced with another element for the purpose of suppressing oxygen release during thermal decomposition is used as the positive electrode active material. There have been proposed lithium secondary batteries used and lithium secondary batteries in which a positive electrode is formed using a combination of lithium nickel oxide and a lithium-containing oxide having higher thermal stability as an active material.

例えば、特許文献１が提案するリチウム二次電池の正極は、集電基材の表面にリチウム含有酸化物を正極活物質として含む２層以上の合剤層を有し、合剤層の最表層に発熱開始温度の高い正極活物質を用いている。この従来技術は、釘刺し試験において、負極を貫通し負極電位になった釘が正極に接触した瞬間にその正極の最表面に大電流が流れてジュール熱が発生し、その熱によって正極が熱分解することを防止している。
特開２００３−０３６８３８号公報 For example, the positive electrode of the lithium secondary battery proposed in Patent Document 1 has two or more mixture layers containing a lithium-containing oxide as a positive electrode active material on the surface of the current collecting base material, and the outermost layer of the mixture layer A positive electrode active material having a high heat generation starting temperature is used. In this prior art, in a nail penetration test, a large current flows through the outermost surface of the positive electrode at the moment when the nail that penetrates the negative electrode and has a negative potential contacts the positive electrode, and Joule heat is generated. Prevents disassembly.
JP 2003-036838 A

ところで、釘刺し試験は、異物等により発生し得る内部短絡を意図的に発生させて電池の過熱の有無を調査することを目的としている。従って、釘刺し試験はできるだけ過酷な使用環境を想定した内部短絡条件の下で行うことが望ましい。例えば、釘刺し試験では、釘刺しの速度が遅い場合には、速い場合よりも確実に内部短絡が発生し、短絡部位に電流が集中するため、電池が過熱状態になりやすい。高容量化が進められるリチウム二次電池では、特に、このような内部短絡条件下で行う釘刺し試験においても過熱のないことが求められる。   By the way, the purpose of the nail penetration test is to intentionally generate an internal short circuit that may be caused by a foreign object or the like to investigate whether or not the battery is overheated. Therefore, it is desirable to perform the nail penetration test under internal short-circuit conditions assuming a harsh usage environment. For example, in a nail penetration test, when the nail penetration speed is slow, an internal short circuit occurs more reliably than when the nail penetration speed is high, and the current concentrates at the short circuit site, so the battery tends to overheat. A lithium secondary battery whose capacity is being increased is required not to be overheated even in a nail penetration test performed under such internal short circuit conditions.

しかしながら、本発明者等によるリチウム二次電池についての詳細な研究によれば、例えば特許文献１に開示されたようなリチウム二次電池用正極を用いても、そのような過酷な内部短絡条件下で行う釘刺し試験において、リチウム二次電池の過熱を大幅に抑制することはできなかった。   However, according to detailed studies on lithium secondary batteries by the present inventors, even if a positive electrode for a lithium secondary battery as disclosed in Patent Document 1 is used, for example, such severe internal short circuit conditions are used. In the nail penetration test performed in step 1, overheating of the lithium secondary battery could not be significantly suppressed.

本発明はこのような事情に鑑みてなされたものであり、過酷な使用環境を想定した内部短絡条件の下で行う釘刺し試験においても、リチウム二次電池の過熱を確実に抑制し得るリチウム二次電池用正極を提供すること、およびそれを用いて、信頼性に優れ、かつ高容量なリチウム二次電池を提供することを課題とする。   The present invention has been made in view of such circumstances, and in a nail penetration test performed under an internal short-circuit condition assuming a harsh usage environment, the lithium secondary battery can reliably suppress overheating of the lithium secondary battery. It is an object of the present invention to provide a positive electrode for a secondary battery and to provide a lithium secondary battery having excellent reliability and high capacity using the positive electrode.

上記課題を解決した本発明の一局面は、集電基材と前記集電基材上に複数の合剤層からなる正極塗膜とを備え、前記正極塗膜は正極活物質として発熱開始温度が異なる２種以上のリチウム含有化合物を含有し、前記２種以上のリチウム含有化合物のうち少なくとも１種のリチウム含有化合物は３００℃以上の発熱開始温度を有し、前記集電基材に最も近い第１合剤層中に、前記発熱開始温度が３００℃以上のリチウム含有化合物を少なくとも１種含有するリチウム二次電池用正極である。   One aspect of the present invention that has solved the above problems includes a current collecting base material and a positive electrode coating film composed of a plurality of mixture layers on the current collecting base material, wherein the positive electrode coating film serves as a positive electrode active material, and a heat generation start temperature. 2 or more types of lithium-containing compounds different from each other, and at least one lithium-containing compound among the two or more types of lithium-containing compounds has an exothermic onset temperature of 300 ° C. or higher and is closest to the current collecting base material In the first mixture layer, the positive electrode for a lithium secondary battery contains at least one lithium-containing compound having a heat generation start temperature of 300 ° C. or higher.

低速、例えば５ｍｍ／ｓ程度の釘刺し速度での釘刺し試験における内部短絡による発熱機構についての本発明者等の検討によれば、内部短絡による熱エネルギーが最も大きく放出される部位は、負極を貫通し負極電位になった釘が最初に接触する正極合剤の最表層ではなく、正極の集電基材あるいは正極の集電基材と正極塗膜の界面部分であることが明らかとなった。   According to the inventors' investigation of the heat generation mechanism due to internal short circuit in the nail penetration test at a low speed, for example, a nail penetration speed of about 5 mm / s, the region where the largest amount of thermal energy is released by the internal short circuit is the negative electrode. It became clear that it was not the outermost layer of the positive electrode mixture that the nail that penetrated and became negative potential first contacted, but the interface part of the positive electrode current collector substrate or the positive electrode current collector substrate and the positive electrode coating film .

すなわち、内部短絡によって、主として正極集電基材と負極集電基材との導通によるジュール熱が発生し、この熱がリチウム二次電池を過熱させる。ジュール熱の熱量はジュールの法則に従い、短絡時の電流（以下、短絡電流と略記）の２乗に比例する。この関係に基づけば、内部短絡箇所の抵抗（以下、短絡抵抗と略記）が小さくなると短絡電流が流れやすくなり、発生するジュール熱は高くなると考えられる。ここで正極の集電基材として一般に用いられているアルミニウム箔の比抵抗は２．７５×１０-6Ω・ｃｍであり、一般的な正極合剤層の比抵抗（約１０〜１０4Ω・ｃｍ）に比べてはるかに小さい。 That is, due to the internal short circuit, Joule heat is generated mainly due to conduction between the positive electrode current collecting base material and the negative electrode current collecting base material, and this heat causes the lithium secondary battery to overheat. The amount of Joule heat is proportional to the square of the current at the time of short circuit (hereinafter abbreviated as short circuit current) according to Joule's law. Based on this relationship, it is considered that when the resistance at the internal short circuit location (hereinafter abbreviated as “short circuit resistance”) becomes small, a short circuit current easily flows and the generated Joule heat increases. Here, the specific resistance of an aluminum foil generally used as a positive electrode current collecting base material is 2.75 × 10 −6 Ω · cm, and the specific resistance of a general positive electrode mixture layer (about 10 to 10 4 Ω).・ Much smaller than cm).

従って、釘が比抵抗の大きい正極合剤層の表層部と接触したときよりも正極集電基材のアルミニウム箔と接触したときに、大きな短絡電流が流れて高いジュール熱が発生すると考えられた。   Therefore, it was thought that when the nail was in contact with the aluminum foil of the positive electrode current collector base material, higher Joule heat was generated when the nail was in contact with the surface layer portion of the positive electrode mixture layer having a large specific resistance. .

本発明の上記一局面はこの知見に基づいてなされたものである。   The one aspect of the present invention has been made based on this finding.

すなわち、正極塗膜を複数の合剤層から構成し、釘刺し試験における内部短絡により高いジュール熱が発生する集電基材に最も近い第１合剤層中に、発熱開始温度が３００℃以上のリチウム含有化合物を少なくとも１種含有させることにより、内部短絡による正極の発熱が確実に抑制され正極の熱暴走が最小限にとどめられる。そして、本発明の正極塗膜は、発熱開始温度が３００℃以上のリチウム含有化合物以外の他のリチウム含有化合物、すなわち発熱開始温度は低いものの容量密度が大きい他のリチウム含有化合物を含有させることができるため、正極全体としては高容量を達成することができる。その結果、釘刺し試験における電池の過熱を確実に抑制でき、かつ高容量なリチウム二次電池用正極の提供が可能となる。   That is, the positive electrode coating film is composed of a plurality of mixture layers, and the heat generation start temperature is 300 ° C. or higher in the first mixture layer closest to the current collecting base material that generates high Joule heat due to an internal short circuit in the nail penetration test. By containing at least one lithium-containing compound, heat generation of the positive electrode due to an internal short circuit is surely suppressed, and thermal runaway of the positive electrode is minimized. The positive electrode coating film of the present invention may contain another lithium-containing compound other than the lithium-containing compound having an exotherm starting temperature of 300 ° C. or higher, that is, another lithium-containing compound having a high capacity density but a low exotherm starting temperature. Therefore, high capacity can be achieved as the whole positive electrode. As a result, overheating of the battery in the nail penetration test can be reliably suppressed, and a high capacity positive electrode for a lithium secondary battery can be provided.

また、第１合剤層は、正極活物質として発熱開始温度が３００℃以上のリチウム含有化合物に加えて、それ以外の他のリチウム含有化合物を含有してもよいが、その場合は、発熱開始温度が３００℃以上のリチウム含有化合物の含有量が、それ以外の他のリチウム含有化合物の含有量より多いことが好ましい。これにより、内部短絡による正極の発熱を確実に抑制することができ、同時に高容量を達成することができる。   In addition, the first mixture layer may contain other lithium-containing compound as a positive electrode active material in addition to the lithium-containing compound having a heat generation start temperature of 300 ° C. or higher. It is preferable that the content of the lithium-containing compound having a temperature of 300 ° C. or higher is higher than the contents of other lithium-containing compounds. Thereby, the heat_generation | fever of the positive electrode by an internal short circuit can be suppressed reliably, and high capacity | capacitance can be achieved simultaneously.

さらに、第１合剤層は、正極活物質として実質的に発熱開始温度が３００℃以上のリチウム含有化合物のみを含有することが好ましい。釘刺し試験における内部短絡により高いジュール熱が発生する第１合剤層中に、発熱開始温度が３００℃以上のリチウム含有化合物のみを含有させることにより、第１合剤層の厚みを薄くすることができるとともに、内部短絡による正極の発熱を更に確実に抑制することができる。   Furthermore, it is preferable that the first mixture layer contains substantially only a lithium-containing compound having a heat generation starting temperature of 300 ° C. or more as a positive electrode active material. To reduce the thickness of the first mixture layer by including only a lithium-containing compound having an exotherm starting temperature of 300 ° C. or higher in the first mixture layer that generates high Joule heat due to an internal short circuit in the nail penetration test. In addition, heat generation of the positive electrode due to an internal short circuit can be more reliably suppressed.

本発明の他の局面は、集電基材上に形成される正極塗膜が、正極活物質として発熱開始温度が異なる２種以上のリチウム含有化合物を含有し、２種以上のリチウム含有化合物のうち少なくとも１種のリチウム含有化合物は３００℃以上の発熱開始温度を有し、正極塗膜の表層側から集電基材側に向かう厚み方向において、前記発熱開始温度が３００℃以上のリチウム含有化合物が増加するリチウム二次電池用正極である。   In another aspect of the present invention, the positive electrode coating film formed on the current collecting base material contains two or more lithium-containing compounds having different heat generation start temperatures as the positive electrode active material, Among them, at least one lithium-containing compound has a heat generation start temperature of 300 ° C. or higher, and the heat generation start temperature is 300 ° C. or higher in the thickness direction from the surface layer side of the positive electrode coating film to the current collecting base material side. Is a positive electrode for a lithium secondary battery.

正極塗膜の表層側から集電基材側に向かって厚み方向に、発熱開始温度が３００℃以上のリチウム含有化合物を増加させ、釘刺し試験における内部短絡により高いジュール熱が発生する集電基材に最も近い正極塗膜部分に、発熱開始温度が３００℃以上のリチウム含有化合物を最も高く含有させることにより、内部短絡による正極の発熱を確実に抑制して正極の熱暴走を最小限にとどめることができる。同時に、正極塗膜の表層側に向かって厚み方向に、発熱開始温度が３００℃以上のリチウム含有化合物以外の他のリチウム含有化合物、すなわち発熱開始温度は低いものの容量密度が大きい他のリチウム含有化合物を増加させることができるため、内部短絡による正極の発熱を抑制しつつ高容量を達成することができる。その結果、釘刺し試験における電池の過熱を確実に抑制でき、かつ高容量なリチウム二次電池用正極の提供が可能となる。   A current collecting group in which a lithium-containing compound having a heat generation starting temperature of 300 ° C. or more is increased in the thickness direction from the surface layer side of the positive electrode coating film toward the current collecting substrate side, and high Joule heat is generated due to an internal short circuit in a nail penetration test By containing the highest lithium-containing compound with a heat generation start temperature of 300 ° C or higher in the positive electrode paint film part closest to the material, the heat generation of the positive electrode due to an internal short circuit is surely suppressed and the thermal runaway of the positive electrode is minimized. be able to. At the same time, in the thickness direction toward the surface layer side of the positive electrode coating film, other lithium-containing compounds other than lithium-containing compounds having an exothermic start temperature of 300 ° C. or higher, that is, other lithium-containing compounds having a low capacity of heat generation but a large capacity density Therefore, it is possible to achieve a high capacity while suppressing the heat generation of the positive electrode due to an internal short circuit. As a result, overheating of the battery in the nail penetration test can be reliably suppressed, and a high capacity positive electrode for a lithium secondary battery can be provided.

また、集電基材と最も近い正極塗膜部分は、正極活物質として実質的に発熱開始温度が３００℃以上のリチウム含有化合物のみを含有することが好ましい。釘刺し試験における内部短絡により高いジュール熱が発生する集電基材と最も近い正極塗膜部分に、発熱開始温度が３００℃以上のリチウム含有化合物のみを含有させることにより、内部短絡による正極の発熱を一層確実に抑制することができ、かつ高容量を確実に確保することができる。   Moreover, it is preferable that the positive electrode coating film part nearest to the current collecting substrate contains substantially only a lithium-containing compound having a heat generation start temperature of 300 ° C. or more as a positive electrode active material. Heat generation of the positive electrode due to an internal short circuit by including only a lithium-containing compound having a heat generation start temperature of 300 ° C. or higher in the positive electrode coating film part closest to the current collecting base material that generates high Joule heat due to an internal short circuit in the nail penetration test Can be more reliably suppressed, and a high capacity can be reliably ensured.

本発明の他の局面は、上記のリチウム二次電池用正極と負極及び非水電解質を備えたリチウム二次電池である。本発明のリチウム二次電池用正極を用いることにより、釘刺し試験における信頼性に優れ、かつ高容量なリチウム二次電池が得られる。   Another aspect of the present invention is a lithium secondary battery including the above-described positive and negative electrodes for a lithium secondary battery and a non-aqueous electrolyte. By using the positive electrode for a lithium secondary battery of the present invention, a lithium secondary battery having excellent reliability and high capacity in a nail penetration test can be obtained.

本発明のリチウム二次電池用正極は、釘刺し試験におけるリチウム二次電池の過熱を確実に抑制することができ、これを用いることにより、釘刺し試験における信頼性に優れ、かつ高容量なリチウム二次電池が得られる。   The positive electrode for a lithium secondary battery of the present invention can reliably suppress overheating of the lithium secondary battery in the nail penetration test, and by using this, the lithium in the nail penetration test is excellent in reliability and high capacity. A secondary battery is obtained.

以下、本発明の実施の形態について詳細に説明する。   Hereinafter, embodiments of the present invention will be described in detail.

＜実施の形態１＞
本実施の形態に係るリチウム二次電池用正極は、集電基材と、前記集電基材上に複数の合剤層からなる正極塗膜とを備えたものであって、正極塗膜は、正極活物質として発熱開始温度が異なる２種以上のリチウム含有化合物を含有し、２種以上のリチウム含有化合物のうち、少なくとも１種のリチウム含有化合物は３００℃以上の発熱開始温度を有し、集電基材に最も近い第１合剤層中に、前記発熱開始温度が３００℃以上のリチウム含有化合物を少なくとも１種含有するものである。 <Embodiment 1>
The positive electrode for a lithium secondary battery according to the present embodiment includes a current collecting base material and a positive electrode coating film composed of a plurality of mixture layers on the current collecting base material. And containing two or more lithium-containing compounds having different heat generation start temperatures as the positive electrode active material, and of the two or more lithium-containing compounds, at least one lithium-containing compound has a heat generation start temperature of 300 ° C. or higher. The first mixture layer closest to the current collecting base material contains at least one lithium-containing compound having a heat generation start temperature of 300 ° C. or higher.

本実施の形態に係るリチウム二次電池用正極について、図を用いて説明する。   A positive electrode for a lithium secondary battery according to the present embodiment will be described with reference to the drawings.

図１は本実施の形態に係るリチウム二次電池用正極の一例を示す模式断面図である。   FIG. 1 is a schematic cross-sectional view showing an example of a positive electrode for a lithium secondary battery according to the present embodiment.

図１のリチウム二次電池用正極は、集電基材１の上に正極塗膜２が形成され、正極塗膜２は集電基材に最も近い第１合剤層３およびその外層側を構成する合剤層４の２層から構成されている。図１は第１合剤層の外層側を構成する合剤層が１層の場合を示すが、第１合剤層の外層側を構成する合剤層は２層以上形成されていてもよい。２層の合剤層からなる正極塗膜２は、正極活物質として発熱開始温度が異なる２種のリチウム含有化合物を含有し、２種のリチウム含有化合物のうち１種のリチウム含有化合物は３００℃以上の発熱開始温度を有する。そして、集電基材に最も近い第１合剤層３は発熱開始温度が３００℃以上のリチウム含有化合物５を含有する。合剤層４はそれ以外の他のリチウム含有化合物６、すなわち発熱開始温度はより低いが容量密度が大きい他のリチウム含有化合物を含有する。なお、第１合剤層３はリチウム含有化合物５に加えて他のリチウム含有化合物６を含有してもよい。また、合剤層４は他のリチウム含有化合物６に加えてリチウム含有化合物５を含有してもよい。   In the positive electrode for a lithium secondary battery in FIG. 1, a positive electrode coating film 2 is formed on a current collecting base material 1, and the positive electrode coating film 2 has a first mixture layer 3 closest to the current collecting base material and its outer layer side. It is comprised from the 2 layers of the mixture layer 4 to comprise. Although FIG. 1 shows the case where the mixture layer constituting the outer layer side of the first mixture layer is one layer, two or more mixture layers constituting the outer layer side of the first mixture layer may be formed. . The positive electrode coating film 2 comprising two mixture layers contains two types of lithium-containing compounds having different heat generation start temperatures as the positive electrode active material, and one type of lithium-containing compound of the two types of lithium-containing compounds is 300 ° C. It has the above heat generation start temperature. And the 1st mixture layer 3 nearest to a current collection base material contains the lithium containing compound 5 whose heat_generation | fever start temperature is 300 degreeC or more. The mixture layer 4 contains another lithium-containing compound 6 other than that, that is, another lithium-containing compound having a lower heat generation start temperature but a larger capacity density. The first mixture layer 3 may contain another lithium-containing compound 6 in addition to the lithium-containing compound 5. The mixture layer 4 may contain a lithium-containing compound 5 in addition to the other lithium-containing compound 6.

上記形態の正極であれば、釘刺し試験時に負極電位を帯びた釘が集電基材１に達して内部短絡により高いジュール熱が発生した場合でも、この集電基材１に最も近い第１合剤層３に含まれるリチウム含有化合物５は３００℃以上の発熱開始温度を有するため、正極の熱暴走が抑制されて電池のさらなる過熱を免れることができる。そして、合剤層４は、第１合剤層３に含まれるリチウム含有化合物よりも発熱開始温度が低い他のリチウム含有化合物６を含んでいても、比抵抗の高い第１合剤層３によって集電基材１との直接的な接触を免れているため、熱暴走にいたる心配はない。さらに、合剤層４に含まれる他のリチウム含有化合物６は容量密度が大きいため、高容量を達成することができる。   In the case of the positive electrode of the above configuration, even when a nail having a negative electrode potential reaches the current collecting base material 1 during the nail penetration test and high Joule heat is generated due to an internal short circuit, the first closest to the current collecting base material 1 Since the lithium-containing compound 5 contained in the mixture layer 3 has a heat generation starting temperature of 300 ° C. or higher, thermal runaway of the positive electrode is suppressed and further overheating of the battery can be avoided. And even if the mixture layer 4 contains the other lithium containing compound 6 with a heat_generation | fever starting temperature lower than the lithium containing compound contained in the 1st mixture layer 3, the 1st mixture layer 3 with a high specific resistance is used. Since direct contact with the current collecting base material 1 is avoided, there is no fear of thermal runaway. Furthermore, since the other lithium containing compound 6 contained in the mixture layer 4 has a large capacity density, a high capacity can be achieved.

本発明において、集電基材に最も近い第１合剤層が含有するリチウム含有化合物は、３００℃以上の発熱開始温度を有するものであればよい。およそ正極活物質として使用し得るリチウム含有化合物をその発熱開始温度で分けるとすると、約２５０〜３００℃をはさんで、それより高温側すなわち３００℃以上の発熱開始温度を有するリチウム含有化合物と、それより低温側すなわち２５０℃以下の発熱開始温度を有するリチウム含有化合物とに略二分することができる。本発明者等の検討によれば、発熱開始温度が３００℃以上のリチウム含有化合物を含有する第１合剤層であれば、低速での釘刺し試験において、正極集電基材および正極集電基材と第１合剤層の界面で高いジュール熱が発生しても、第１合剤層での発熱が抑制されるため、電池の過熱を防止することができる。   In this invention, the lithium containing compound which the 1st mixture layer nearest to a current collection base material contains should just have the heat_generation | fever start temperature of 300 degreeC or more. If the lithium-containing compound that can be used as the positive electrode active material is roughly divided by its exothermic start temperature, the lithium-containing compound having an exothermic start temperature of about 250 to 300 ° C. and higher temperature side, that is, 300 ° C. or higher, It can be roughly divided into a lithium-containing compound having a lower temperature side, that is, an exothermic start temperature of 250 ° C. or lower. According to the study by the present inventors, in the case of the first mixture layer containing a lithium-containing compound having a heat generation starting temperature of 300 ° C. or higher, in the nail penetration test at a low speed, the positive electrode current collector base material and the positive electrode current collector Even if high Joule heat is generated at the interface between the base material and the first mixture layer, heat generation in the first mixture layer is suppressed, so that overheating of the battery can be prevented.

ここで、本発明におけるリチウム含有化合物の発熱開始温度は、例えば以下のようにして測定することができる。所定の製造方法によって得たリチウム含有化合物から測定する場合には、これに導電剤、結着剤を加えてシート状の電極を作製し、それを作用極とする評価用セルにおいて所定の電圧まで充電した後の正極活物質をサンプリングし、示差走査熱量計（ＤＳＣ）で測定する。また、作製したリチウム二次電池から測定する場合には、所定の電圧まで充電したリチウム二次電池を分解して正極活物質を回収し、ＤＳＣで測定する。測定条件は試料を１０℃／分の昇温速度で昇温し、得られたＤＳＣのプロファイルがベースラインから立ち上がる温度を発熱開始温度とする。一般的には発熱開始温度が高く高温時の結晶構造が安定しているリチウム含有化合物の方が正極活物質の熱分解反応が起こりにくく、従って発熱開始温度は正極活物質の熱安定性を評価し得る主要な指標である。   Here, the heat generation start temperature of the lithium-containing compound in the present invention can be measured, for example, as follows. When measuring from a lithium-containing compound obtained by a predetermined production method, a sheet-like electrode is prepared by adding a conductive agent and a binder to this, and up to a predetermined voltage in an evaluation cell using this as a working electrode. The positive electrode active material after charging is sampled and measured with a differential scanning calorimeter (DSC). Moreover, when measuring from the produced lithium secondary battery, the lithium secondary battery charged to the predetermined voltage is decomposed | disassembled, positive electrode active materials are collect | recovered, and it measures by DSC. The measurement condition is that the temperature of the sample is raised at a rate of 10 ° C./min, and the temperature at which the obtained DSC profile rises from the baseline is defined as the heat generation start temperature. In general, a lithium-containing compound with a high exothermic start temperature and a stable crystal structure at a high temperature is less prone to thermal decomposition of the positive electrode active material. Therefore, the exothermic start temperature evaluates the thermal stability of the positive electrode active material. It is a major indicator that can.

本発明においては、集電基材に最も近い第１合剤層が含有する発熱開始温度が３００℃以上のリチウム含有化合物は、１種でもよく、また２種以上であってもよい。１種が用いられる場合は、発熱開始温度が３００℃以上のリチウム含有化合物の中でも、より高い、例えば４００℃以上の発熱開始温度を有するリチウム含有化合物が好ましい。発熱開始温度が３００℃以上のリチウム含有化合物を２種以上用いる場合は、内部短絡による正極の発熱を確実に抑制する観点から、例えば４００℃以上の発熱開始温度を有するリチウム含有化合物の含有量を多くすることが好ましい。   In the present invention, the lithium-containing compound having a heat generation start temperature of 300 ° C. or higher contained in the first mixture layer closest to the current collecting base material may be one kind or two or more kinds. When one type is used, among lithium-containing compounds having an exothermic start temperature of 300 ° C. or higher, a lithium-containing compound having a higher exothermic start temperature, for example, 400 ° C. or higher is preferable. When using two or more lithium-containing compounds having an exotherm starting temperature of 300 ° C. or higher, the content of the lithium-containing compound having an exothermic starting temperature of, for example, 400 ° C. or higher is selected from the viewpoint of reliably suppressing the heat generation of the positive electrode due to internal short circuit It is preferable to increase it.

第１合剤層中には、正極活物質として発熱開始温度が３００℃以上のリチウム含有化合物に加えて、それ以外の発熱開始温度がより低い他のリチウム含有化合物を含有してもよい。その場合は、内部短絡による正極の発熱を抑制する観点から、発熱開始温度が３００℃以上のリチウム含有化合物の含有量が、それ以外の他のリチウム含有化合物の含有量より多いことが好ましい。さらに、第１合剤層中のリチウム含有化合物のうち、発熱開始温度が３００℃以上のリチウム含有化合物が８０質量％以上含まれることがより好ましい。更に好ましくは９０質量％以上であり、最も好ましくは１００質量％である。   In the first mixture layer, in addition to the lithium-containing compound having a heat generation start temperature of 300 ° C. or more as the positive electrode active material, other lithium-containing compounds having a lower heat generation start temperature may be contained. In that case, from the viewpoint of suppressing the heat generation of the positive electrode due to an internal short circuit, the content of the lithium-containing compound having a heat generation start temperature of 300 ° C. or higher is preferably higher than the content of other lithium-containing compounds. Furthermore, it is more preferable that 80% by mass or more of the lithium-containing compound having a heat generation start temperature of 300 ° C. or higher is included among the lithium-containing compounds in the first mixture layer. More preferably, it is 90 mass% or more, Most preferably, it is 100 mass%.

本発明においては、第１合剤層の外層側を構成する１層以上の合剤層は、発熱開始温度が３００℃以上のリチウム含有化合物以外の他のリチウム含有化合物、すなわち発熱開始温度は３００℃未満であるが容量密度が大きい他のリチウム含有化合物を含有する。第１合剤層の外層側を構成する１層以上の合剤層が含有する前記他のリチウム含有化合物は１種でもよく、また２種以上であってもよい。例えば、第１合剤層の外層側を構成する合剤層が１層であれば、その層に前記他のリチウム含有化合物を１種含有しても、２種以上を含有してもよい。また、第１合剤層の外層側を構成する合剤層が２層以上であれば、その各層にそれぞれ異なる発熱開始温度を有する前記他のリチウム含有化合物を１種以上含有してもよい。   In the present invention, the one or more mixture layers constituting the outer layer side of the first mixture layer have a lithium-containing compound other than the lithium-containing compound having a heat generation start temperature of 300 ° C. or higher, that is, a heat generation start temperature of 300. It contains other lithium-containing compounds that are less than ° C but have a large capacity density. The other lithium-containing compound contained in one or more mixture layers constituting the outer layer side of the first mixture layer may be one kind or two or more kinds. For example, if the mixture layer constituting the outer layer side of the first mixture layer is one layer, the layer may contain one type of the other lithium-containing compound or two or more types. Moreover, if the mixture layer which comprises the outer layer side of a 1st mixture layer is two or more layers, you may contain 1 or more types of the said other lithium containing compound which has a different heat_generation | fever starting temperature in each layer, respectively.

第１合剤層の外層側を構成する１層以上の合剤層中には、発熱開始温度が３００℃以上のリチウム含有化合物が含有されていてもよい。その場合は、高容量化を図る観点から、発熱開始温度は３００℃未満であっても容量密度が大きい他のリチウム含有化合物の含有量が、発熱開始温度が３００℃以上のリチウム含有化合物の含有量より多いことが好ましい。前記他のリチウム含有化合物は８０質量％以上含まれることがより好ましく、更に好ましくは９０質量％以上である。   One or more mixture layers constituting the outer layer side of the first mixture layer may contain a lithium-containing compound having a heat generation start temperature of 300 ° C. or more. In that case, from the viewpoint of increasing the capacity, the content of other lithium-containing compounds having a large capacity density even when the heat generation starting temperature is less than 300 ° C. is contained in the lithium-containing compound having a heat generation starting temperature of 300 ° C. or higher. More than the amount is preferred. The other lithium-containing compound is more preferably contained in an amount of 80% by mass or more, and still more preferably 90% by mass or more.

なお、本発明においては、複数の合剤層からなる正極塗膜の最表層中に、実質的に発熱開始温度が３００℃以上のリチウム含有化合物のみが含有されていてもよい。例えば、高速での釘刺し試験において、負極を貫通した釘が正極に接触した瞬間にその正極の最表面に大電流が流れてジュール熱が発生した場合でも、その熱による正極の熱分解を防止することができる。   In the present invention, only the lithium-containing compound having a heat generation start temperature of 300 ° C. or higher may be contained in the outermost layer of the positive electrode coating film composed of a plurality of mixture layers. For example, in a high-speed nail penetration test, even when a large current flows through the outermost surface of the positive electrode and Joule heat is generated at the moment when the nail that penetrates the negative electrode contacts the positive electrode, thermal decomposition of the positive electrode due to the heat is prevented. can do.

本発明においては、第１合剤層中に発熱開始温度が３００℃以上のリチウム含有化合物を含有させることによって、釘刺し試験における内部短絡による高いジュール熱の発生を効果的に抑制することができるため、集電基材上の複数の合剤層の内、第１合剤層の厚みを薄くしてもよい。更に、第１合剤層の厚みを薄くすることにより、その外層側を構成する１層以上の合剤層の厚みを相対的に厚くして、そこに容量密度が大きい他のリチウム含有化合物を高濃度で含有させてもよい。   In the present invention, the generation of high Joule heat due to an internal short circuit in the nail penetration test can be effectively suppressed by including a lithium-containing compound having an exotherm starting temperature of 300 ° C. or higher in the first mixture layer. Therefore, you may make the thickness of a 1st mixture layer thin among the some mixture layers on a current collection base material. Further, by reducing the thickness of the first mixture layer, the thickness of one or more mixture layers constituting the outer layer side is relatively increased, and another lithium-containing compound having a large capacity density is added thereto. It may be contained at a high concentration.

第１合剤層の平均厚みは、集電基材の片面で０．５〜２０μｍの範囲にまで薄くすることができ、２〜１５μｍとするのが好ましく、５〜１０μｍとするのが更に好ましい。また、第１合剤層の平均厚みとその外層（１層以上）の平均厚みとの比は、０．５：１００〜２０：１００の範囲にあることが好ましく、５：１００〜１８：１００の範囲にあることが更に好ましい。   The average thickness of the first mixture layer can be reduced to a range of 0.5 to 20 μm on one side of the current collecting base material, preferably 2 to 15 μm, and more preferably 5 to 10 μm. . Moreover, it is preferable that ratio of the average thickness of a 1st mixture layer and the average thickness of the outer layer (one or more layers) exists in the range of 0.5: 100-20: 100, 5: 100-18: 100. More preferably, it is in the range.

本発明において、発熱開始温度が３００℃以上のリチウム含有化合物としては、リチウムマンガン系酸化物、リチウムニッケルコバルトマンガン系酸化物、及びオリビン型リン酸リチウム系化合物からなる群から選ばれる１種を、好ましいリチウム含有化合物として例示することができる。これらのリチウム含有化合物は発熱開始温度が高いのみならず、熱分解しにくい結晶構造を有する点で好ましい。   In the present invention, the lithium-containing compound having an exotherm starting temperature of 300 ° C. or higher is selected from the group consisting of lithium manganese oxide, lithium nickel cobalt manganese oxide, and olivine type lithium phosphate compound, It can be illustrated as a preferable lithium-containing compound. These lithium-containing compounds are preferable not only because they have a high heat generation starting temperature but also have a crystal structure that is difficult to thermally decompose.

本発明において、これらのリチウム含有化合物はいずれも、低速での釘刺し試験において、短絡による電池電圧の降下をほぼ抑制する優れた効果を有することが示された。その効果に基づいて、これらのリチウム含有化合物を用いたリチウム二次電池用正極は釘刺し試験におけるリチウム二次電池の過熱を確実に抑制し得ることがわかる。   In the present invention, it has been shown that all of these lithium-containing compounds have an excellent effect of substantially suppressing a drop in battery voltage due to a short circuit in a nail penetration test at a low speed. Based on the effect, it can be seen that the positive electrode for a lithium secondary battery using these lithium-containing compounds can reliably suppress overheating of the lithium secondary battery in the nail penetration test.

更に、低速での釘刺し試験で内部短絡を発生させた場合にジュール熱の発生により電池電圧が低下するが、上記のリチウム含有化合物はその低下を抑制するだけでなく、短絡時の最低電圧よりも高い電圧に回復する性質を有する。このため、短絡時の最低電圧と回復時の電圧との電位差を利用して充放電を制御することもできる。   In addition, when an internal short circuit occurs in a low-speed nail penetration test, the battery voltage decreases due to the generation of Joule heat, but the above lithium-containing compound not only suppresses the decrease, but also exceeds the minimum voltage at the time of the short circuit. Have the property of recovering to a higher voltage. For this reason, charging / discharging can also be controlled using the potential difference between the lowest voltage at the time of a short circuit and the voltage at the time of recovery.

リチウムマンガン系酸化物としては、ＬｉＭｎ2Ｏ4で表されるスピネル構造型のリチウムマンガン酸化物を用いることが好ましい。このリチウムマンガン酸化物は発熱開始温度が高いのみならず（上記測定方法によれば３２０℃である）、熱分解温度が高く、分解時の酸素放出量も少ないため熱安定性が高い。また、リチウムマンガン系酸化物のサイクル特性を向上させるために、Ｍｎの一部がＣｒ、Ｆｅ、Ｍｇ、Ａｌなどの他元素に置換されたリチウムマンガン系酸化物を用いてもよい。 As the lithium manganese oxide, it is preferable to use a spinel structure type lithium manganese oxide represented by LiMn 2 O 4 . This lithium manganese oxide not only has a high heat generation start temperature (320 ° C. according to the above measurement method), but also has a high thermal decomposition temperature and a small amount of oxygen released at the time of decomposition, and thus has high thermal stability. Further, in order to improve the cycle characteristics of the lithium manganese oxide, a lithium manganese oxide in which a part of Mn is substituted with another element such as Cr, Fe, Mg, Al may be used.

リチウムニッケルマンガンコバルト系酸化物は、リチウムマンガン系酸化物の組成物中に、さらにニッケルおよびコバルトを含有させたものである。リチウムニッケルマンガンコバルト系酸化物としては、化学式ＬｉaＮｉ1-(b+c)ＭｎbＣｏcＯ2（ただし、１≦ａ≦１．２であり、０．１≦ｂ≦０．５であり、０．１≦ｃ≦０．５である）で表されるリチウムニッケルマンガンコバルト酸化物を用いることが好ましい。この組成のリチウムニッケルマンガンコバルト酸化物は安定した特性を有するだけでなく安価に得ることができる。ここで、ａ値は１≦ａ≦１．２であることが好ましい。１以上の場合、原料として用いるリチウム塩が十分であるために酸化ニッケル、酸化コバルトなどの電気化学的に不活性な不純物の存在がより確実に抑えられ、容量低下を誘発しにくい。またａ値が１．２以下の場合、原料として用いるリチウム塩が過剰に存在することがないためにリチウム化合物が不純物として残存することがより確実に抑えられ、同様に容量低下を誘発しにくい。なお、前記ａ値は未充電時の組成である。また、ｂ値は０．１≦ｂ≦０．５であることが望ましい。０．１以上であると熱安定性向上の効果がより確実に得られ、０．５以下であれば容量低下が生じにくいからである。更に、ｃ値は０．１≦ｃ≦０．５であることが望ましい。０．１以上であると結晶構造がより安定化してサイクル特性上の懸念が生じにくく、０．５以下では容量低下が生じにくいからである。例えば、ＬｉＮｉ1/3Ｍｎ1/3Ｃｏ1/3Ｏ2で表されるリチウムニッケルマンガンコバルト酸化物の発熱開始温度は、上記測定方法によれば３０５℃である。 The lithium nickel manganese cobalt-based oxide is a lithium manganese-based oxide composition further containing nickel and cobalt. The lithium nickel manganese cobalt-based oxide has a chemical formula Li a Ni 1- (b + c) Mn b Co c O 2 (where 1 ≦ a ≦ 1.2, 0.1 ≦ b ≦ 0.5 Yes, it is preferable to use lithium nickel manganese cobalt oxide represented by 0.1 ≦ c ≦ 0.5. The lithium nickel manganese cobalt oxide having this composition has not only stable characteristics but also can be obtained at low cost. Here, the a value is preferably 1 ≦ a ≦ 1.2. In the case of 1 or more, since the lithium salt used as a raw material is sufficient, the presence of electrochemically inactive impurities such as nickel oxide and cobalt oxide can be more reliably suppressed, and the capacity reduction is unlikely to be induced. When the a value is 1.2 or less, the lithium salt used as a raw material does not exist excessively, so that the lithium compound can be more reliably prevented from remaining as an impurity, and similarly it is difficult to induce a decrease in capacity. The a value is the composition when not charged. The b value is preferably 0.1 ≦ b ≦ 0.5. This is because if it is 0.1 or more, the effect of improving the thermal stability can be obtained more reliably, and if it is 0.5 or less, the capacity is hardly lowered. Furthermore, the c value is preferably 0.1 ≦ c ≦ 0.5. If it is 0.1 or more, the crystal structure is further stabilized and it is difficult to cause a concern about cycle characteristics, and if it is 0.5 or less, the capacity is hardly reduced. For example, the heat generation start temperature of lithium nickel manganese cobalt oxide represented by LiNi 1/3 Mn 1/3 Co 1/3 O 2 is 305 ° C. according to the measurement method.

オリビン型リン酸リチウム系化合物としては、ＬｉＭｅＰＯ４（ただし、ＭｅはＣｏ、Ｎｉ、Ｆｅ、及びＭｎから選ばれる少なくとも１種である）で表されるオリビン型リン酸リチウム化合物が好ましい。オリビン型リン酸リチウム化合物は、熱分解しにくい結晶構造を有するのみならず、きわめて高い発熱開始温度を有する。例えば、ＬｉＦｅＰＯ４はきわめて高い発熱開始温度を有し、上記測定方法によれば４００℃以上でも発熱開始は観測されない。これは、ＬｉとＦｅが八面体を占有しＰが四面体を占有する中で、酸素原子が六方最密充填構造を取るオリビン型結晶構造に由来すると考えられる。 The olivine-type lithium phosphate compound is preferably an olivine-type lithium phosphate compound represented by LiMePO 4 (where Me is at least one selected from Co, Ni, Fe, and Mn). The olivine-type lithium phosphate compound not only has a crystal structure that is difficult to be thermally decomposed, but also has a very high exothermic starting temperature. For example, LiFePO 4 has a very high heat generation start temperature, and according to the measurement method, no heat generation start is observed even at 400 ° C. or higher. This is considered to be derived from an olivine type crystal structure in which oxygen atoms take a hexagonal close-packed structure while Li and Fe occupy an octahedron and P occupies a tetrahedron.

本発明において、発熱開始温度が３００℃以上のリチウム含有化合物以外の他のリチウム含有化合物としては、リチウムコバルト系酸化物およびリチウムニッケル系酸化物からなる群から選ばれる少なくとも１種を、好ましいリチウム含有化合物として挙げることができる。   In the present invention, the other lithium-containing compound other than the lithium-containing compound having an exotherm starting temperature of 300 ° C. or higher is preferably at least one selected from the group consisting of lithium cobalt oxides and lithium nickel oxides. It can be mentioned as a compound.

リチウムコバルト系酸化物としては、ＬｉＣｏＯ2、またはＬｉaＣｏ1-(b+c)ＭｇbＭcＯ2（ただし、１≦ａ≦１．０５で、０．００５≦ｂ≦０．１０で、０．００５≦ｃ≦０．１０であり、ＭはＡｌ、Ｓｒ、及びＣａから選ばれる少なくとも１種である）で表されるリチウムコバルト系酸化物を用いることが好ましい。ここで、リチウム量を示すａ値が１以上の場合、原料として用いるリチウム塩が十分であるために酸化コバルトなどの電気化学的に不活性な不純物の存在が抑えられ、容量低下を誘発しにくい。ａ値が１．０５以下の場合、原料として用いるリチウム塩が過剰に存在することがないためにリチウム化合物が不純物として残存することが抑えられ、同様に容量低下を誘発しにくくなる。なお、前記ａ値は未充電時の組成である。また、ｂ値が０．００５≦ｂ≦０．１０の範囲にある場合、Ｍｇの効果として高温時の結晶構造の安定性が向上し、熱安定性がより向上する。さらに充放電に伴う膨張収縮による格子歪・構造破壊および粒子の割れに起因する放電容量の低下が緩和できるので、サイクル特性がより向上する。更に、ｃ値が０．００５以上の場合は、結晶構造が安定し、熱安定性が向上する。ｃ値が０．１０以下の場合は、容量低下を生じにくい。例えば、ＬｉＣｏＯ2の発熱開始温度およびＬｉＣｏ0.98Ｍｇ0.02Ｏ2で表されるリチウムコバルト系酸化物の発熱開始温度は、上記測定方法によれば、それぞれ２０２℃および２０８℃である。 Examples of the lithium cobalt oxide include LiCoO 2 or Li a Co 1- (b + c) Mg b McO 2 (where 1 ≦ a ≦ 1.05 and 0.005 ≦ b ≦ 0.10. 0.005 ≦ c ≦ 0.10, and M is at least one selected from Al, Sr, and Ca). Here, when the a value indicating the amount of lithium is 1 or more, since the lithium salt used as a raw material is sufficient, the presence of electrochemically inactive impurities such as cobalt oxide is suppressed, and it is difficult to induce a decrease in capacity. . When the a value is 1.05 or less, since the lithium salt used as a raw material does not exist excessively, it is suppressed that the lithium compound remains as an impurity, and similarly it is difficult to induce a decrease in capacity. The a value is the composition when not charged. Moreover, when b value exists in the range of 0.005 <= b <= 0.10, stability of the crystal structure at the time of high temperature improves as an effect of Mg, and thermal stability improves more. Further, since the reduction in discharge capacity due to lattice strain / structural destruction and particle cracking due to expansion / contraction associated with charge / discharge can be alleviated, cycle characteristics are further improved. Further, when the c value is 0.005 or more, the crystal structure is stabilized and the thermal stability is improved. When the c value is 0.10 or less, the capacity is hardly reduced. For example, the exothermic start temperature of LiCoO 2 and the exothermic start temperature of a lithium cobalt oxide represented by LiCo 0.98 Mg 0.02 O 2 are 202 ° C. and 208 ° C., respectively, according to the measurement method.

リチウムニッケル系酸化物としては、ＬｉaＮｉ1-(b+c)ＣｏbＭcＯ2（ただし、１≦ａ≦１．０５で、０．1≦ｂ≦０．３５で、０．００５≦ｃ≦０．３０であり、ＭはＡｌ、Ｓｒ、及びＣａから選ばれる少なくとも１種である）で表されるリチウムニッケル系酸化物を用いることが好ましい。この組成とすることにより、高容量密度ながら充放電に伴う結晶構造変化が大きく可逆性が悪いＬｉＮｉＯ2ベースの活物質としての物性を改善することができる。このリチウムニッケル酸化物はＬｉＣｏＯ2ベースの活物質材料に比べて安価であり、特に大型電池用途への正極活物質材料としても有用である。ここで、ａ値が１以上の場合、原料として用いるリチウム塩が十分であるために酸化ニッケル、酸化コバルトなどの電気化学的に不活性な不純物の存在が抑えられ、容量低下を誘発しにくくなる。ａ値が１．０５以下の場合、原料として用いるリチウム塩が過剰に存在することがないためにリチウム化合物が不純物として残存することが抑えられ、同様に容量低下を誘発しにくくなる。なお、前記ａ値は未充電時の組成である。また、ｂ値は０．１０≦ｂ≦０．３５であることが望ましい。０．１以上であると上述した効果がより確実に得られ、０．３５以下であれば容量低下を生じにくい。更に、ｃ値が０．００５以上の場合は熱安定性が向上し、ｃ値が０．３以下の場合は容量低下を生じにくい。リチウムニッケル系酸化物として、例えば、ＬｉＮｉ0.82Ｃｏ0.15Ａｌ0.03Ｏ2で表されるリチウムニッケル系酸化物の発熱開始温度は、上記測定方法によれば２１５℃である。 Lithium nickel-based oxides include Li a Ni 1- (b + c) Co b McO 2 (where 1 ≦ a ≦ 1.05, 0.1 ≦ b ≦ 0.35, 0.005 ≦ c ≦ 0.30, and M is preferably at least one selected from Al, Sr, and Ca). By adopting this composition, the physical properties as an active material based on LiNiO 2 that has a large capacity density and a large change in crystal structure accompanying charge / discharge and poor reversibility can be improved. This lithium nickel oxide is cheaper than an active material based on LiCoO 2 and is particularly useful as a positive electrode active material for large battery applications. Here, when the a value is 1 or more, since the lithium salt used as a raw material is sufficient, the presence of electrochemically inactive impurities such as nickel oxide and cobalt oxide is suppressed, and it is difficult to induce a decrease in capacity. . When the a value is 1.05 or less, since the lithium salt used as a raw material does not exist excessively, it is suppressed that the lithium compound remains as an impurity, and similarly it is difficult to induce a decrease in capacity. The a value is the composition when not charged. The b value is preferably 0.10 ≦ b ≦ 0.35. The effect mentioned above is more reliably acquired as it is 0.1 or more, and if it is 0.35 or less, a capacity | capacitance fall will not produce easily. Furthermore, when the c value is 0.005 or more, the thermal stability is improved, and when the c value is 0.3 or less, the capacity is hardly lowered. As the lithium nickel oxide, for example, the heat generation start temperature of a lithium nickel oxide represented by LiNi 0.82 Co 0.15 Al 0.03 O 2 is 215 ° C. according to the above measurement method.

本実施の形態に係るリチウム二次電池用正極は、例えば、次のようにして作製することができる。   The positive electrode for a lithium secondary battery according to the present embodiment can be produced, for example, as follows.

発熱開始温度が３００℃以上のリチウム含有化合物、例えばオリビン型リン酸リチウム系化合物の一定量に、正極結着剤及び導電剤等を加えて撹拌し、正極合剤ペーストを作製する。別に、発熱開始温度が３００℃以上のリチウム含有化合物以外の他のリチウム含有化合物、例えばリチウムコバルト系酸化物を含有する正極合剤ペーストを同様に作製する。集電基材（例えばアルミニウム箔）の表面にオリビン型リン酸リチウム系化合物を含有する正極合剤ペーストを塗布、乾燥し、第１合剤層とする。その上に、リチウムコバルト系酸化物を含有する正極合剤ペーストを塗布、乾燥する。乾燥後の塗膜を圧延すれば、例えば２層の正極合剤層からなる塗膜を有する正極板が得られる。   A positive electrode binder paste is prepared by adding a positive electrode binder and a conductive agent to a certain amount of a lithium-containing compound having an exothermic starting temperature of 300 ° C. or higher, for example, an olivine type lithium phosphate compound, to prepare a positive electrode mixture paste. Separately, a positive electrode mixture paste containing a lithium-containing compound other than the lithium-containing compound having an exotherm starting temperature of 300 ° C. or higher, for example, a lithium cobalt-based oxide, is similarly prepared. A positive electrode mixture paste containing an olivine-type lithium phosphate compound is applied to the surface of a current collecting substrate (for example, an aluminum foil) and dried to form a first mixture layer. On top of that, a positive electrode mixture paste containing a lithium cobalt oxide is applied and dried. If the dried coating film is rolled, for example, a positive electrode plate having a coating film composed of two positive electrode mixture layers can be obtained.

正極の集電基材としては、用いる正極材料の充放電電位において化学変化を起こさない電子伝導体であれば特に限定されない。一般的に集電基材として用いられる材料はアルミニウム（Ａｌ）である。また、例えば、チタン（Ｔｉ）、ステンレス鋼（ＳＵＳ）、炭素、導電性樹脂などを用いてもよい。さらに、ＡｌやＳＵＳの表面にカーボンあるいはＴｉを処理させたものを用いることができる。特に、コストや加工性、安定性の面から、ＡｌあるいはＡｌ合金が好ましい。これらの材料の表面を酸化して用いることもできる。また、表面処理により集電基材表面に凹凸を付けることも可能である。また、ＰＥＴなどの樹脂シート上にＡｌやＴｉを蒸着などにより薄膜として付けたものを用いることもできる。形状は、フォイルの他、フィルム、シート、ネット、パンチされたもの、ラス体、多孔質体、発泡体、繊維群、不織布体の成形体などを用いることができる。厚みは、特に限定されないが、１〜５０μｍのものが好ましい。   The current collecting base material of the positive electrode is not particularly limited as long as it is an electron conductor that does not cause a chemical change at the charge / discharge potential of the positive electrode material to be used. A material generally used as a current collecting base is aluminum (Al). Further, for example, titanium (Ti), stainless steel (SUS), carbon, conductive resin, or the like may be used. Furthermore, the surface of Al or SUS treated with carbon or Ti can be used. In particular, Al or an Al alloy is preferable from the viewpoints of cost, workability, and stability. The surface of these materials can be oxidized and used. It is also possible to make the current collecting substrate surface uneven by surface treatment. Moreover, what attached Al or Ti as a thin film by vapor deposition etc. on resin sheets, such as PET, can also be used. As the shape, a film, a sheet, a net, a punched product, a lath body, a porous body, a foamed body, a fiber group, a non-woven body molded body, and the like can be used in addition to the foil. The thickness is not particularly limited, but is preferably 1 to 50 μm.

本発明の正極塗膜は、上述の正極活物質および必要に応じて結着剤、導電剤を溶媒に混練、分散させた合剤ペーストを正極集電基材上に塗布し、乾燥後、圧延することによって作製することができる。また、スパッタなどの真空成膜プロセスを用いて作製することもできる。必要に応じて、これらを組み合わせることもできる。   The positive electrode coating film of the present invention is obtained by applying a mixture paste prepared by kneading and dispersing a positive electrode active material and, if necessary, a binder and a conductive agent in a solvent onto a positive electrode current collector substrate, drying, rolling It can produce by doing. Moreover, it can also be produced using a vacuum film formation process such as sputtering. These can be combined as necessary.

合剤ペースト中に添加する結着剤は、熱可塑性樹脂、熱硬化性樹脂のいずれであってもよい。例えば、ポリエチレン、ポリプロピレン、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）、スチレンブタジエンゴム（ＳＢＲ）をはじめとする一般に用いられる樹脂を用いることができる。これらの材料は単独又は混合物として用いることができる。   The binder added to the mixture paste may be either a thermoplastic resin or a thermosetting resin. For example, commonly used resins such as polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and styrene butadiene rubber (SBR) can be used. These materials can be used alone or as a mixture.

合剤ペースト中に添加する導電剤としては、電子伝導性材料を用いることができる。例えば、天然黒鉛（鱗片状黒鉛など）、人造黒鉛、膨張黒鉛などのグラファイト類、アセチレンブラック、ケッチェンブラック等のカ−ボンブラック類、炭素繊維、金属繊維などの導電性繊維類、銅、ニッケル等の金属粉末類およびポリフェニレン誘導体などの有機導電性材料を挙げることができる。これらは、単独で用いてもよく、複数種を組み合わせて用いてもよい。これらの導電剤のなかで、微粒子で導電性の高いアセチレンブラック、ケッチェンブラックなどのカーボンブラック類が好ましい。導電剤の添加量は、本発明の効果を損なわない限りにおいて特に限定されない。   As the conductive agent added to the mixture paste, an electron conductive material can be used. For example, natural graphite (such as flake graphite), graphite such as artificial graphite and expanded graphite, carbon black such as acetylene black and ketjen black, conductive fibers such as carbon fiber and metal fiber, copper, nickel And metal conductive materials such as polyphenylene derivatives and the like. These may be used alone or in combination of two or more. Among these conductive agents, carbon blacks such as acetylene black and ketjen black, which are fine and highly conductive, are preferable. The addition amount of the conductive agent is not particularly limited as long as the effects of the present invention are not impaired.

合剤ペーストの作製に用いられる溶媒としては、Ｎ−メチル−２−ピロリドン（ＮＭＰ）等の有機溶媒を用いることができるが、これに限定されない。   As a solvent used for preparation of the mixture paste, an organic solvent such as N-methyl-2-pyrrolidone (NMP) can be used, but is not limited thereto.

正極活物質および必要に応じて用いられる導電剤、結着剤を溶剤に混練、分散させてペースト状合剤を作製する方法は、特に限定されるものではない。例えば、プラネタリーミキサー、ホモミキサー、ピンミキサー、ニーダー、ホモジナイザー等を用いることができる。これらを単独、或いは組み合わせて使用することも可能である。また、上記合剤ペーストの混練分散時に、増粘剤、各種分散剤、界面活性剤、安定剤等を必要に応じて添加することも可能である。   The method for producing a paste-like mixture by kneading and dispersing a positive electrode active material and, if necessary, a conductive agent and a binder in a solvent is not particularly limited. For example, a planetary mixer, a homomixer, a pin mixer, a kneader, a homogenizer, or the like can be used. These can be used alone or in combination. Moreover, it is also possible to add a thickener, various dispersing agents, surfactants, stabilizers and the like as needed during the kneading and dispersing of the mixture paste.

集電基材上への塗布、乾燥、圧延は、特に限定されるものではない。塗布は、上記のように混錬分散させたペースト状の合剤を、例えば、スリットダイコーター、リバースロールコーター、リップコーター、ブレードコーター、ナイフコーター、グラビアコーター、ディップコーター等を用いて、容易に塗布し塗着させることができる。乾燥は自然乾燥が好ましいが、生産性を考慮すると７０℃〜２００℃の温度で乾燥させるのが好ましい。圧延は、ロールプレス機によって所定の厚みになるまで、圧延するのが好ましい。   Application, drying, and rolling on the current collecting substrate are not particularly limited. Application is easy using the paste-like mixture kneaded and dispersed as described above, for example, using a slit die coater, reverse roll coater, lip coater, blade coater, knife coater, gravure coater, dip coater, etc. Can be applied and applied. Drying is preferably natural drying, but considering productivity, it is preferable to dry at a temperature of 70 ° C to 200 ° C. The rolling is preferably performed until a predetermined thickness is reached by a roll press.

本発明のリチウム二次電池は、上記のようにして作製されるリチウム二次電池用正極および負極を、セパレータを介して対向させ、それを巻回または積層した電極体を作製し、この電極体を非水電解質とともに電池ケース内に封入することにより作製される。   The lithium secondary battery of the present invention produces an electrode body in which a positive electrode and a negative electrode for a lithium secondary battery produced as described above are opposed to each other through a separator, and wound or laminated. Is encapsulated in a battery case together with a non-aqueous electrolyte.

負極は特に限定されない。負極活物質としては、例えば、黒鉛などの炭素系材料、シリコン（Ｓｉ）、スズ（Ｓｎ）などを含む金属、合金、あるいは酸化物、炭化物、窒化物材料、塩など既に知られたものを単独であるいは組み合わせて用いることができる。負極は、例えば、負極活物質、必要により結着剤、導電剤、増粘剤を溶媒に混練、分散させて調製したペーストを銅製の集電基材上に所定厚みとなるように塗布し、乾燥、圧延後、裁断することにより作製される。   The negative electrode is not particularly limited. As the negative electrode active material, for example, a carbon-based material such as graphite, a metal, an alloy containing silicon (Si), tin (Sn), or the like, or an already known material such as an oxide, carbide, nitride material, or salt is used alone. Or in combination. The negative electrode is, for example, a paste prepared by kneading and dispersing a negative electrode active material, if necessary, a binder, a conductive agent, and a thickener in a solvent, and applying the paste to a predetermined thickness on a copper current collector. It is produced by cutting after drying and rolling.

非水電解質としては、液体電解質だけでなく、ゲル状あるいは固体の電解質であってもよい。液体電解質としては、非水溶媒に溶質および必要に応じて添加剤が溶解されたものが用いられる。非水溶媒には、エチレンカーボネート、ジメチルカーボネート、メチルエチルカーボネート等の炭酸エステルが好ましく用いられるが、これらに限定されない。非水溶媒は２種以上を組み合わせて用いることが好ましい。溶質には、ＬｉＰＦ６，ＬｉＢＦ４等のリチウム塩が好ましく用いられるが、これらに限定されない。添加剤としては、例えば、ビニレンカーボネート、シクロヘキシルベンゼン等を用いることができる。 The non-aqueous electrolyte may be not only a liquid electrolyte but also a gel or solid electrolyte. As the liquid electrolyte, a solution in which a solute and, if necessary, an additive are dissolved in a nonaqueous solvent is used. As the non-aqueous solvent, carbonate esters such as ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate are preferably used, but are not limited thereto. It is preferable to use a combination of two or more non-aqueous solvents. Lithium salts such as LiPF 6 and LiBF 4 are preferably used as the solute, but are not limited thereto. As the additive, for example, vinylene carbonate, cyclohexylbenzene, or the like can be used.

セパレータとしては、特に限定されないが、ポリエチレン、ポリプロピレン等のポリオレフィン樹脂からなる微多孔フィルムを用いることができる。   Although it does not specifically limit as a separator, The microporous film which consists of polyolefin resins, such as polyethylene and a polypropylene, can be used.

本発明のリチウム二次電池は、コイン型、ボタン型、シート型、積層型、円筒型、偏平型、角型、電気自動車等に用いる大型のものなどいずれの形状にも適用できる。   The lithium secondary battery of the present invention can be applied to any shape such as a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, a square type, a large type used for an electric vehicle and the like.

＜実施の形態２＞
本実施の形態に係るリチウム二次電池用正極は、集電基材上に形成される正極塗膜が、正極活物質として発熱開始温度が異なる２種以上のリチウム含有化合物を含有し、２種以上のリチウム含有化合物のうち少なくとも１種のリチウム含有化合物は３００℃以上の発熱開始温度を有し、正極塗膜の表層側から集電基材側に向かう厚み方向において、前記発熱開始温度が３００℃以上のリチウム含有化合物が増加するものである。 <Embodiment 2>
In the positive electrode for a lithium secondary battery according to the present embodiment, the positive electrode coating film formed on the current collecting substrate contains two or more lithium-containing compounds having different heat generation start temperatures as the positive electrode active material. Among the above lithium-containing compounds, at least one lithium-containing compound has a heat generation start temperature of 300 ° C. or higher, and the heat generation start temperature is 300 in the thickness direction from the surface layer side of the positive electrode coating film to the current collecting base material side. Lithium-containing compounds at or above ° C will increase.

本実施の形態に係るリチウム二次電池用正極について、図を用いて説明する。なお、集電基材、活物質等は実施の形態１と同様であるため、重複する部分は省略し、異なる部分について説明する。   A positive electrode for a lithium secondary battery according to the present embodiment will be described with reference to the drawings. In addition, since a current collection base material, an active material, etc. are the same as that of Embodiment 1, the overlapping part is abbreviate | omitted and a different part is demonstrated.

図２は本実施の形態に係るリチウム二次電池用正極の一例を示す模式断面図である。   FIG. 2 is a schematic cross-sectional view showing an example of a positive electrode for a lithium secondary battery according to the present embodiment.

集電基材１の上に、正極塗膜２が形成され、正極塗膜２は正極活物質として発熱開始温度が異なる２種のリチウム含有化合物５及び６を含有し、２種のリチウム含有化合物のうち１種のリチウム含有化合物５は３００℃以上の発熱開始温度を有する。そして、正極塗膜２の表層側から集電基材側に向かう厚み方向において、発熱開始温度が３００℃以上のリチウム含有化合物５が増加する。   A positive electrode coating film 2 is formed on the current collecting substrate 1, and the positive electrode coating film 2 contains two lithium-containing compounds 5 and 6 having different heat generation start temperatures as a positive electrode active material, and includes two lithium-containing compounds. Among them, one lithium-containing compound 5 has an exothermic onset temperature of 300 ° C. or higher. Then, in the thickness direction from the surface layer side of the positive electrode coating film 2 toward the current collecting base material side, the lithium-containing compound 5 having a heat generation start temperature of 300 ° C. or more increases.

上記形態の正極であれば、釘刺し試験において釘が集電基材１に接触して内部短絡により高いジュール熱が発生した場合でも、集電基材１に最も近い正極塗膜部分は、発熱開始温度が３００℃以上のリチウム含有化合物５を最も多く含有するため、正極の熱暴走を抑制し電池のさらなる過熱を免れることができる。同時に、正極塗膜の表層側に向かう厚み方向において、他のリチウム含有化合物、すなわち発熱開始温度は低いが容量密度が大きい他のリチウム含有化合物６が増加することになるため、高容量を達成することができる。その結果、釘刺し試験における電池の過熱を確実に抑制でき、かつ高容量なリチウム二次電池用正極を提供することが可能となる。   In the case of the positive electrode in the above form, even when the nail contacts the current collecting base material 1 in the nail penetration test and high Joule heat is generated due to an internal short circuit, the positive electrode coating film portion closest to the current collecting base material 1 generates heat. Since most of the lithium-containing compound 5 having a starting temperature of 300 ° C. or higher is contained, thermal runaway of the positive electrode can be suppressed and further overheating of the battery can be avoided. At the same time, in the thickness direction toward the surface layer side of the positive electrode coating film, another lithium-containing compound, that is, another lithium-containing compound 6 having a low heat generation start temperature but a large capacity density is increased, so that a high capacity is achieved. be able to. As a result, overheating of the battery in the nail penetration test can be reliably suppressed, and a high capacity positive electrode for a lithium secondary battery can be provided.

３００℃以上の発熱開始温度を有するリチウム含有化合物は、正極塗膜の表層側から集電基材側に向かう厚み方向において、段階的に増加してもよく、連続的に増加してもよい。   The lithium-containing compound having an exotherm starting temperature of 300 ° C. or more may increase stepwise or continuously in the thickness direction from the surface layer side of the positive electrode coating film toward the current collecting base material side.

正極塗膜に含まれる発熱開始温度が異なる２種以上のリチウム含有化合物のうち、発熱開始温度が３００℃以上のリチウム含有化合物の含有率は、集電基材に最も近い正極塗膜部分においては、正極の熱暴走を抑える観点から、６０質量％以上であることが好ましく、８０質量％以上であることが更に好ましく、９０質量％以上であることが特に好ましく、１００質量％であることが最も好ましい。また、前記２種以上のリチウム含有化合物のうち発熱開始温度が３００℃以上のリチウム含有化合物以外の他のリチウム含有化合物の含有率は、集電基材から最も遠い正極塗膜の最表層側部分においては、正極の容量密度を上げる観点から、６０質量％以上であることが好ましく、８０質量％以上であることが更に好ましく、９０質量％以上であることが特に好ましい。   Among the two or more types of lithium-containing compounds having different heat generation start temperatures contained in the positive electrode coating film, the content of the lithium-containing compound having a heat generation start temperature of 300 ° C. or higher is From the viewpoint of suppressing thermal runaway of the positive electrode, it is preferably 60% by mass or more, more preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 100% by mass. preferable. The content of the other lithium-containing compound other than the lithium-containing compound having an exotherm starting temperature of 300 ° C. or higher among the two or more lithium-containing compounds is a portion on the outermost layer side of the positive electrode coating film farthest from the current collecting substrate. In view of increasing the capacity density of the positive electrode, it is preferably 60% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

本実施の形態に係るリチウム二次電池用正極、すなわち正極塗膜が発熱開始温度の異なる２種以上のリチウム含有化合物を含有し、正極塗膜の表層側から集電基材側に向かう厚み方向において、発熱開始温度が３００℃以上のリチウム含有化合物が増加する正極塗膜を有する正極は、例えば、次のようにして作製することができる。   The positive electrode for a lithium secondary battery according to the present embodiment, that is, the positive electrode coating film contains two or more lithium-containing compounds having different heat generation start temperatures, and the thickness direction from the surface layer side of the positive electrode coating film toward the current collecting base material side The positive electrode having a positive electrode coating film in which the lithium-containing compound having an exotherm starting temperature of 300 ° C. or higher increases can be produced, for example, as follows.

正極活物質として、発熱開始温度が３００℃以上のリチウム含有化合物、例えばオリビン型リン酸リチウム系化合物と、それ以外の他のリチウム含有化合物、例えばリチウムコバルト系酸化物との合計量を一定として配合比率を変えた混合物のそれぞれに、正極結着剤及び導電剤等を加えて撹拌し、正極合剤ペーストを作製する。集電基材（アルミニウム箔）の表面にオリビン型リン酸リチウム系化合物の配合比率が最も高い正極合剤ペーストを塗布、乾燥する、その上に、オリビン型リン酸リチウム系化合物の配合比率が低い正極合剤ペーストを塗布、乾燥する。更に、その上に、オリビン型リン酸リチウム系化合物の配合比率が最も低い正極合剤ペースト、すなわちリチウムコバルト系酸化物の配合比率が最も高い正極合剤ペーストを塗布、乾燥する。得られた塗膜を圧延すれば、例えば、正極塗膜の表層側から集電基材側に向かう厚み方向において、オリビン型リン酸リチウム系化合物が段階的に増加する正極塗膜を有する正極板が得られる。   Formulated as a positive electrode active material with a constant total amount of a lithium-containing compound having an exotherm starting temperature of 300 ° C. or higher, such as an olivine-type lithium phosphate compound, and another lithium-containing compound such as a lithium cobalt-based oxide. A positive electrode binder, a conductive agent, and the like are added to each of the mixtures with different ratios and stirred to prepare a positive electrode mixture paste. Apply the positive electrode mixture paste with the highest blending ratio of the olivine-type lithium phosphate compound on the surface of the current collector base (aluminum foil) and dry it. On top of that, the blending ratio of the olivine-type lithium phosphate compound is low. Apply positive electrode mixture paste and dry. Further, a positive electrode mixture paste having the lowest mixing ratio of the olivine type lithium phosphate compound, that is, a positive electrode mixture paste having the highest mixing ratio of the lithium cobalt oxide is applied and dried. If the obtained coating film is rolled, for example, a positive electrode plate having a positive electrode coating film in which the olivine-type lithium phosphate compound gradually increases in the thickness direction from the surface layer side of the positive electrode coating film to the current collecting base material side Is obtained.

また、上記の正極作製方法において、正極合剤ペーストを塗布し、乾燥前に他の正極合剤ペーストを塗布する方法を使用することもできる。例えば、オリビン型リン酸リチウム系化合物の配合比率が最も高い正極合剤ペーストの一定量に、オリビン型リン酸リチウム系化合物の配合比率が最も低い正極合剤ペーストの同量を、所定の時間をかけて撹拌しながら少しずつ加え、添加の過程で得られる配合比率が漸次異なる正極合剤ペーストを順次塗布し、その後に乾燥する。このようにして得られた塗膜を圧延すれば、正極塗膜の表層側から集電基材側に向かう厚み方向において、オリビン型リン酸リチウム系化合物が連続的に増加する正極塗膜を有する正極板が得られる。   Moreover, in said positive electrode preparation method, the method of apply | coating positive mix paste and apply | coating another positive mix paste before drying can also be used. For example, to a certain amount of the positive electrode mixture paste with the highest mixing ratio of the olivine type lithium phosphate compound, the same amount of the positive electrode mixture paste with the lowest mixing ratio of the olivine type lithium phosphate compound is used for a predetermined time. The mixture is added little by little with stirring, and positive electrode mixture pastes having different blending ratios obtained in the course of addition are sequentially applied and then dried. If the coating film thus obtained is rolled, it has a positive electrode coating film in which the olivine type lithium phosphate compound continuously increases in the thickness direction from the surface layer side of the positive electrode coating film toward the current collecting base material side. A positive electrode plate is obtained.

上記のようにして得られる本実施の形態に係るリチウム二次電池用正極は、実施の形態１と同様に、セパレータを介して負極に対向させ、それを巻回または積層した電極体を作製し、この電極体を非水電解質とともに電池ケース内に封入すれば、本発明のリチウム二次電池が作製される。   The positive electrode for a lithium secondary battery according to the present embodiment obtained as described above is made to face the negative electrode through a separator and wound or laminated to produce an electrode body as in the first embodiment. If this electrode body is enclosed in a battery case together with a nonaqueous electrolyte, the lithium secondary battery of the present invention is produced.

以上、本発明が詳細に説明されたが、上記の説明は全ての局面において例示であって、本発明はそれらに限定されるものではない。例示されていない無数の変形例が、本発明の範囲から外れることなく想定され得るものと解される。   As mentioned above, although this invention was demonstrated in detail, said description is an illustration in all the aspects, Comprising: This invention is not limited to them. It is understood that countless variations that are not illustrated can be envisaged without departing from the scope of the present invention.

以下に、本発明に関する実施例が示されるが、本発明はこれらの実施例に限定されるものではない。   Examples relating to the present invention are shown below, but the present invention is not limited to these examples.

（ｉ）正極活物質の調製
ａ−１乃至ａ−６の正極活物質を、それぞれ以下の方法にて調製した。 (I) Preparation of positive electrode active material The positive electrode active materials a-1 to a-6 were prepared by the following methods, respectively.

（ｉ−１）ａ−１
Ｌｉ2ＣＯ3とＣｏＣＯ3とを所定のモル比で混合し、９００℃下で１０時間焼成した後
で粉砕、分級し、化学式ＬｉＣｏＯ2で表される正極活物質ａ−１を得た。 (I-1) a-1
Li 2 CO 3 and CoCO 3 were mixed at a predetermined molar ratio, calcined at 900 ° C. for 10 hours, pulverized and classified to obtain a positive electrode active material a-1 represented by the chemical formula LiCoO 2 .

（ｉ−２）ａ−２
０．９８ｍｏｌ／リットルの濃度で硫酸コバルトを含み、０．０２ｍｏｌ／リットルの濃度で硫酸マグネシウムを含む水溶液を、反応槽に連続供給し、液のｐＨが１０〜１３になるように反応槽に水酸化ナトリウムを滴下しながら、活物質の前駆体を合成し十分に水洗し乾燥させた。その結果、Ｃｏ0.98Ｍｇ0.02（ＯＨ）2からなる水酸化物を得た。この前駆体と炭酸リチウムとを、リチウムとコバルトとマグネシウムとのモル比が、１：０．９８：０．０２になるように混合し、混合物を６００℃で１０時間仮焼成し、粉砕した。次いで、粉砕された焼成物を９００℃で再度１０時間焼成し、粉砕、分級し、化学式ＬｉＣｏ0.98Ｍｇ0.02Ｏ2で表される正極活物質ａ−２を得た。 (I-2) a-2
An aqueous solution containing cobalt sulfate at a concentration of 0.98 mol / liter and containing magnesium sulfate at a concentration of 0.02 mol / liter is continuously supplied to the reaction vessel, and water is added to the reaction vessel so that the pH of the solution becomes 10-13. While adding sodium oxide dropwise, an active material precursor was synthesized, sufficiently washed with water and dried. As a result, a hydroxide composed of Co 0.98 Mg 0.02 (OH) 2 was obtained. This precursor and lithium carbonate were mixed so that the molar ratio of lithium, cobalt and magnesium was 1: 0.98: 0.02, and the mixture was calcined at 600 ° C. for 10 hours and pulverized. Next, the pulverized fired product was fired again at 900 ° C. for 10 hours, pulverized and classified to obtain a positive electrode active material a-2 represented by the chemical formula LiCo 0.98 Mg 0.02 O 2 .

（ｉ−３）ａ−３
０．８２ｍｏｌ／リットルの濃度で硫酸ニッケルを含み、０．１５ｍｏｌ／リットルの濃度で硫酸コバルトを調整した水溶液さらに０．０３ｍｏｌ／リットルの濃度で硫酸アルミニウムを調整した水溶液を、反応槽に連続供給し、液のｐＨが１０〜１３になるように反応槽に水酸化ナトリウムを滴下しながら、活物質の前駆体を合成し十分に水洗し乾燥させた。その結果、Ｎｉ0.82Ｃｏ0.15Ａl0.03（ＯＨ）2からなる水酸化物を得た。この前駆体と炭酸リチウムとを、リチウムとニッケルとコバルトとアルミニウムとのモル比が、１：０．８２：０．１５：０．０３になるように混合し、混合物を酸素雰囲気下５００℃で７時間仮焼成し、粉砕した。次いで、粉砕された焼成物を８００℃で再度１５時間焼成し、粉砕、分級し、化学式ＬｉＮｉ0.82Ｃｏ0.15Ａｌ0.03Ｏ2で表される正極活物質ａ−３を得た。 (I-3) a-3
An aqueous solution containing nickel sulfate at a concentration of 0.82 mol / liter, cobalt sulfate adjusted at a concentration of 0.15 mol / liter, and an aqueous solution adjusted with aluminum sulfate at a concentration of 0.03 mol / liter were continuously supplied to the reaction vessel. While adding sodium hydroxide dropwise to the reaction vessel so that the pH of the solution was 10-13, the active material precursor was synthesized, sufficiently washed with water and dried. As a result, a hydroxide composed of Ni 0.82 Co 0.15 Al 0.03 (OH) 2 was obtained. This precursor and lithium carbonate were mixed so that the molar ratio of lithium, nickel, cobalt, and aluminum was 1: 0.82: 0.15: 0.03, and the mixture was heated at 500 ° C. in an oxygen atmosphere. It was calcined for 7 hours and pulverized. Next, the pulverized fired product was fired again at 800 ° C. for 15 hours, pulverized and classified to obtain a positive electrode active material a-3 represented by the chemical formula LiNi 0.82 Co 0.15 Al 0.03 O 2 .

（ｉ−４）ａ−４
硫酸ニッケルと硫酸マンガンと、硫酸コバルトを等モル濃度で調整した水溶液を、反応槽に連続供給し、液のｐＨが１０〜１３になるように反応槽に水酸化ナトリウムを滴下しながら、活物質の前駆体を合成し十分に水洗し乾燥させた。その結果、Ｎｉ1/3Ｍｎ1/3Ｃｏ1/3（ＯＨ）2からなる水酸化物を得た。この前駆体と炭酸リチウムとを、リチウムとニッケルとマンガンとコバルトとのモル比が、３：１：１：１になるように混合し、混合物を酸素雰囲気下５００℃で７時間仮焼成し、粉砕した。次いで、粉砕された焼成物を８００℃で再度１５時間焼成し、粉砕、分級し、化学式ＬｉＮｉ1/3Ｍｎ1/3Ｃｏ1/3Ｏ2で表される正極活物質ａ−４を得た。 (I-4) a-4
An aqueous solution prepared by continuously supplying nickel sulfate, manganese sulfate, and cobalt sulfate in equimolar concentrations to the reaction vessel, and dropping sodium hydroxide into the reaction vessel so that the pH of the solution is 10 to 13, the active material The precursor was synthesized, washed thoroughly with water and dried. As a result, a hydroxide composed of Ni 1/3 Mn 1/3 Co 1/3 (OH) 2 was obtained. This precursor and lithium carbonate were mixed so that the molar ratio of lithium, nickel, manganese, and cobalt was 3: 1: 1: 1, and the mixture was calcined at 500 ° C. for 7 hours in an oxygen atmosphere. Crushed. Next, the pulverized fired product was fired again at 800 ° C. for 15 hours, pulverized, and classified to obtain a positive electrode active material a-4 represented by the chemical formula LiNi 1/3 Mn 1/3 Co 1/3 O 2 . .

（ｉ−５）ａ−５
二酸化マンガンと炭酸リチウムとを、リチウムとマンガンとのモル比が、１：２になるように混合し、混合物を空気雰囲気下８５０℃で１０時間焼成し、粉砕、分級し、化学式ＬｉＭｎ2Ｏ4で表される正極活物質ａ−５を得た。 (I-5) a-5
Manganese dioxide and lithium carbonate are mixed so that the molar ratio of lithium to manganese is 1: 2, the mixture is fired at 850 ° C. for 10 hours in an air atmosphere, pulverized and classified, and the chemical formula LiMn 2 O 4 The positive electrode active material a-5 represented by these was obtained.

（ｉ−６）ａ−６
炭酸リチウムＬｉ2ＣＯ3、シュウ酸鉄ＦｅＣ2Ｏ4・２Ｈ2Ｏ、リン酸水素二アンモニウム（ＮＨ4）2ＨＰＯ4をそれぞれ化学量論比０．５：１．０：１．０となるように秤量した後、乳鉢を用いてよく混合し、Ａｒ−Ｈ2雰囲気下６００℃で１５時間焼成して化学式ＬｉＦｅＰＯ４で表される正極活物質ａ−６を得た。 (I-6) a-6
Lithium carbonate Li 2 CO 3 , iron oxalate FeC 2 O 4 .2H 2 O, diammonium hydrogen phosphate (NH 4 ) 2 HPO 4 have a stoichiometric ratio of 0.5: 1.0: 1.0, respectively. After being weighed in this manner, the mixture was thoroughly mixed using a mortar and fired at 600 ° C. for 15 hours in an Ar—H 2 atmosphere to obtain a positive electrode active material a-6 represented by the chemical formula LiFePO 4.

ここで、上記のようにして調製した正極活物質ａ−１〜ａ−６の充電状態の熱安定性を、ＤＳＣ（ＲＩＧＡＫＵ ＴＡＳ３００）を用いて以下のようにして評価した。まず、正極活物質ａ−１〜ａ−６の８５重量部に、導電剤としてアセチレンブラックを１０重量部、結着剤としてＰＴＦＥを５重量部混合し、成形して、シート状の電極を作製した。その電極を作用極に、対極にはＬｉ金属を用いた評価用セルにおいて、０．２ｍＡ／ｃｍ２の定電流で４．２５Ｖまで充電した後の正極を適当量サンプリングし、消防用ＳＵＳ製パンに密閉した。昇温速度は１０℃／分で行った。ＤＳＣのプロファイルがベースラインから立ち上がる温度を発熱開始温度とした。以上の条件で得られた発熱開始温度はａ−１が２０２℃、ａ−２が２０８℃、ａ−３が２１５℃、ａ−４が３０５℃、ａ−５が３２０℃であった。ａ−６は４００℃以上でも発熱開始を観測することはできなかった。 Here, the thermal stability of the charged state of the positive electrode active materials a-1 to a-6 prepared as described above was evaluated using DSC (RIGAKU TAS300) as follows. First, 85 parts by weight of the positive electrode active materials a-1 to a-6 are mixed with 10 parts by weight of acetylene black as a conductive agent and 5 parts by weight of PTFE as a binder, and then molded to produce a sheet-like electrode. did. In an evaluation cell using Li electrode for the working electrode and Li electrode for the counter electrode, an appropriate amount of the positive electrode after sampling to 4.25 V with a constant current of 0.2 mA / cm 2 was sampled, and a SUS pan for fire fighting Sealed. The heating rate was 10 ° C./min. The temperature at which the DSC profile rises from the baseline was defined as the heat generation start temperature. The heat generation starting temperatures obtained under the above conditions were 202 ° C. for a-1, 208 ° C. for a-2, 215 ° C. for a-3, 305 ° C. for a-4, and 320 ° C. for a-5. It was not possible to observe the onset of exotherm of a-6 even at 400 ° C. or higher.

（ｉｉ）正極合剤ペーストの作製
上記の方法で得られた正極活物質ａ−１〜ａ−６を用いて、以下に示す正極合剤ペーストを作製した。 (Ii) Production of positive electrode mixture paste Using the positive electrode active materials a-1 to a-6 obtained by the above method, the following positive electrode mixture paste was produced.

（ｉｉ−１）ａ−１１
正極活物質ａ−１を３ｋｇと、正極結着剤として呉羽化学（株）製のＰＶＤＦを１２重量％含むＮＭＰ溶液０．５ｋｇと、導電剤としてアセチレンブラック９０ｇと、適量のＮＭＰとを、プラネタリーミキサーにて攪拌し、正極合剤ペーストａ−１１を作製した。 (Ii-1) a-11
3 kg of positive electrode active material a-1, 0.5 kg of NMP solution containing 12% by weight of PVDF manufactured by Kureha Chemical Co., Ltd. as a positive electrode binder, 90 g of acetylene black as a conductive agent, and an appropriate amount of NMP The mixture was stirred with a Lee mixer to prepare positive electrode mixture paste a-11.

（ｉｉ−２）ａ−２１
正極活物質ａ−１をａ−２に代えた以外は、正極合剤ペーストａ−１１と同様の方法で、正極合剤ペーストａ−２１を作製した。 (Ii-2) a-21
A positive electrode mixture paste a-21 was produced in the same manner as the positive electrode mixture paste a-11 except that the positive electrode active material a-1 was replaced with a-2.

（ｉｉ−３）ａ−３１
正極活物質ａ−１をａ−３に代えた以外は、正極合剤ペーストａ−１１と同様の方法で、正極合剤ペーストａ−３１を作製した。 (Ii-3) a-31
A positive electrode mixture paste a-31 was produced in the same manner as the positive electrode mixture paste a-11 except that the positive electrode active material a-1 was replaced with a-3.

（ｉｉ−４）ａ−４１
正極活物質ａ−１をａ−４に代えた以外は、正極合剤ペーストａ−１１と同様の方法で、正極合剤ペーストａ−４１を作製した。 (Ii-4) a-41
A positive electrode mixture paste a-41 was produced in the same manner as the positive electrode mixture paste a-11 except that the positive electrode active material a-1 was replaced with a-4.

（ｉｉ−５）ａ−５１
正極活物質ａ−１をａ−５に代えた以外は、正極合剤ペーストａ−１１と同様の方法で、正極合剤ペーストａ−５１を作製した。 (Ii-5) a-51
A positive electrode mixture paste a-51 was produced in the same manner as the positive electrode mixture paste a-11, except that the positive electrode active material a-1 was replaced with a-5.

（ｉｉ−６）ａ−６１
正極活物質ａ−１を正極活物質ａ−３とａ−４との重量比２：１の混合物に代えた以外は、正極合剤ペーストａ−１１と同様の方法で、正極合剤ペーストａ−６１を作製した。 (Ii-6) a-61
The positive electrode mixture paste a-11 was the same as the positive electrode mixture paste a-11 except that the positive electrode active material a-1 was replaced with a mixture of the positive electrode active materials a-3 and a-4 in a weight ratio of 2: 1. -61 was produced.

（ｉｉ−７）ａ−７１
正極活物質ａ−１を正極活物質ａ−３とａ−５との重量比３：１の混合物に代えた以外は、正極合剤ペーストａ−１１と同様の方法で、正極合剤ペーストａ−７１を作製した。 (Ii-7) a-71
The positive electrode mixture paste a-11 was the same as the positive electrode mixture paste a-11 except that the positive electrode active material a-1 was replaced with a mixture of the positive electrode active materials a-3 and a-5 in a weight ratio of 3: 1. -71 was produced.

（ｉｉ−８）ａ−８１
正極活物質ａ−１をａ−６に代えた以外は、正極合剤ペーストａ−１１と同様の方法で、正極合剤ペーストａ−８１を作製した。 (Ii-8) a-81
A positive electrode mixture paste a-81 was produced in the same manner as the positive electrode mixture paste a-11, except that the positive electrode active material a-1 was replaced with a-6.

（ｉｉｉ）正極の作製
上記の方法で得られた正極合剤ペーストａ−１１〜ａ−８１を用いて、以下に示す正極を作製した。 (Iii) Production of positive electrode Using the positive electrode mixture pastes a-11 to a-81 obtained by the above method, the following positive electrodes were produced.

（ｉｉｉ−１）ｂ−１
正極集電基材である厚み１５μｍのアルミニウム箔の両面に、まず正極合剤ペーストａ−４１を塗布し、乾燥した。その上から正極合剤ペーストａ−１１を塗布し、乾燥後の塗膜をローラで圧延して２種類の合剤層からなる正極塗膜を形成した。この後、アルミニウム箔および正極塗膜からなる極板の厚みを１６３μｍに制御し、正極板ｂ−１を作製した。正極活物質ａ−１を含む表層側の合剤層の平均厚みは両面で１２８μｍ、正極活物質ａ−４を含む集電基材側の合剤層の平均厚みは両面で２０μｍであった（第１合剤層の平均厚みとその外層の平均厚みとの比は、１６：１００）。 (Iii-1) b-1
First, positive electrode mixture paste a-41 was applied to both surfaces of a 15 μm-thick aluminum foil as a positive electrode current collector, and dried. The positive electrode mixture paste a-11 was applied from above, and the dried coating film was rolled with a roller to form a positive electrode coating film composed of two types of mixture layers. Thereafter, the thickness of the electrode plate made of the aluminum foil and the positive electrode coating film was controlled to 163 μm to produce the positive electrode plate b-1. The average thickness of the mixture layer on the surface layer side containing the positive electrode active material a-1 was 128 μm on both sides, and the average thickness of the mixture layer on the current collecting substrate side containing the positive electrode active material a-4 was 20 μm on both sides ( The ratio of the average thickness of the first mixture layer to the average thickness of the outer layer is 16: 100).

（ｉｉｉ−２）ｂ−２
アルミニウム箔の両面に、まず正極合剤ペーストａ−４１を塗布乾燥し、その上に正極合剤ペーストａ−２１を塗布乾燥した以外は、正極ｂ−１と同様の方法で正極ｂ−２を作製した。正極活物質ａ−２を含む表層側の合剤層の平均厚みは両面で１２５μｍ、正極活物質ａ−４を含む集電基材側の合剤層の平均厚みは両面で２０μｍであった（第１合剤層の平均厚みとその外層の平均厚みとの比は、１６：１００）。 (Iii-2) b-2
The positive electrode mixture b-2 was coated and dried on both surfaces of the aluminum foil, and the positive electrode mixture paste a-21 was coated and dried thereon. Produced. The average thickness of the mixture layer on the surface layer side containing the positive electrode active material a-2 was 125 μm on both sides, and the average thickness of the mixture layer on the current collecting substrate side containing the positive electrode active material a-4 was 20 μm on both sides ( The ratio of the average thickness of the first mixture layer to the average thickness of the outer layer is 16: 100).

（ｉｉｉ−３）ｂ−３
アルミニウム箔の両面に、まず正極合剤ペーストａ−４１を塗布乾燥し、その上に正極合剤ペーストａ−３１を塗布乾燥した以外は、正極ｂ−１と同様の方法で正極ｂ−３を作製した。正極活物質ａ−３を含む表層側の合剤層の平均厚みは両面で１２５μｍ、正極活物質ａ−４を含む集電基材側の合剤層の平均厚みは両面で２０μｍであった。 (Iii-3) b-3
The positive electrode b-3 was coated on the both sides of the aluminum foil by the same method as the positive electrode b-1, except that the positive electrode mixture paste a-41 was first applied and dried, and then the positive electrode mixture paste a-31 was applied and dried thereon. Produced. The average thickness of the mixture layer on the surface layer side containing the positive electrode active material a-3 was 125 μm on both sides, and the average thickness of the mixture layer on the current collecting substrate side containing the positive electrode active material a-4 was 20 μm on both sides.

（ｉｉｉ−４）ｂ−４
アルミニウム箔の両面に、まず正極合剤ペーストａ−５１を塗布乾燥し、その上に正極合剤ペーストａ−３１を塗布乾燥した以外は、正極ｂ−１と同様の方法で正極ｂ−４を作製した。正極活物質ａ−３を含む表層側の合剤層の平均厚みは両面で１３０μｍ、正極活物質ａ−５を含む集電基材側の合剤層の平均厚みは両面で１５μｍであった（第１合剤層の平均厚みとその外層の平均厚みとの比は、１２：１００）。 (Iii-4) b-4
First, positive electrode mixture paste a-51 was applied and dried on both surfaces of the aluminum foil, and then positive electrode mixture paste a-31 was applied and dried thereon. Produced. The average thickness of the mixture layer on the surface layer side containing the positive electrode active material a-3 was 130 μm on both sides, and the average thickness of the mixture layer on the current collecting substrate side containing the positive electrode active material a-5 was 15 μm on both sides ( The ratio of the average thickness of the first mixture layer to the average thickness of the outer layer is 12: 100).

（ｉｉｉ−５）ｂ−５
アルミニウム箔の両面に、まず正極合剤ペーストａ−４１を塗布乾燥し、その上に正極合剤ペーストａ−６１を塗布乾燥した以外は、正極ｂ−１と同様の方法で正極ｂ−５を作製した。正極活物質ａ−３とａ−４の混合物を含む表層側の合剤層の平均厚みは両面で１３０μｍ、正極活物質ａ−４を含む集電基材側の合剤層の平均厚みは両面で１５μｍであった。 (Iii-5) b-5
The positive electrode b-5 was applied to the both surfaces of the aluminum foil in the same manner as the positive electrode b-1, except that the positive electrode mixture paste a-41 was first applied and dried, and then the positive electrode mixture paste a-61 was applied and dried thereon. Produced. The average thickness of the mixture layer on the surface layer side containing the mixture of the positive electrode active materials a-3 and a-4 is 130 μm on both sides, and the average thickness of the mixture layer on the current collecting substrate side containing the positive electrode active material a-4 is on both sides 15 μm.

（ｉｉｉ−６）ｂ−６
アルミニウム箔の両面に、まず正極合剤ペーストａ−５１を塗布乾燥し、その上に正極合剤ペーストａ−７１を塗布乾燥した以外は、正極ｂ−１と同様の方法で正極ｂ−６を作製した。正極活物質ａ−３とａ−５の混合物を含む表層側の合剤層の平均厚みは両面で１３０μｍ、正極活物質ａ−５を含む集電基材側の合剤層の平均厚みは両面で１５μｍであった。 (Iii-6) b-6
The positive electrode b-6 was coated on the both sides of the aluminum foil by first applying and drying the positive electrode mixture paste a-51, and then the positive electrode mixture paste a-71 was coated and dried thereon by the same method as the positive electrode b-1. Produced. The average thickness of the mixture layer on the surface layer side containing the mixture of the positive electrode active material a-3 and a-5 is 130 μm on both sides, and the average thickness of the mixture layer on the current collecting substrate side containing the positive electrode active material a-5 is double sided 15 μm.

（ｉｉｉ−７）ｂ−７
アルミニウム箔の両面に、正極合剤ペーストａ−５１のみを塗布乾燥した以外は、正極ｂ−１と同様の方法で正極ｂ−７を作製した。正極活物質ａ−５を含む合剤層の平均厚みは１４０μｍであった。 (Iii-7) b-7
A positive electrode b-7 was produced in the same manner as the positive electrode b-1, except that only the positive electrode mixture paste a-51 was applied and dried on both surfaces of the aluminum foil. The average thickness of the mixture layer containing the positive electrode active material a-5 was 140 μm.

（ｉｉｉ−８）ｂ−８
アルミニウム箔の両面に、正極合剤ペーストａ−３１のみを塗布乾燥した以外は、正極ｂ−１と同様の方法で正極ｂ−８を作製した。正極活物質ａ−３を含む合剤層の平均厚みは１４５μｍであった。 (Iii-8) b-8
A positive electrode b-8 was produced in the same manner as the positive electrode b-1, except that only the positive electrode mixture paste a-31 was applied and dried on both surfaces of the aluminum foil. The average thickness of the mixture layer containing the positive electrode active material a-3 was 145 μm.

（ｉｉｉ−９）ｂ−９
アルミニウム箔の両面に、まず正極合剤ペーストａ−３１を塗布乾燥し、その上に正極合剤ペーストａ−５１を塗布乾燥した以外は、正極ｂ−１と同様の方法で正極ｂ−９を作製した。正極活物質ａ−５を含む表層側の合剤層の平均厚みは両面で１５μｍ、正極活物質ａ−３を含む集電基材側の合剤層の平均厚みは両面で１３０μｍであった。 (Iii-9) b-9
The positive electrode b-9 was coated on the both surfaces of the aluminum foil by first applying and drying the positive electrode mixture paste a-31, and then the positive electrode mixture paste a-51 was coated and dried thereon by the same method as the positive electrode b-1. Produced. The average thickness of the mixture layer on the surface layer side containing the positive electrode active material a-5 was 15 μm on both sides, and the average thickness of the mixture layer on the current collecting substrate side containing the positive electrode active material a-3 was 130 μm on both sides.

（ｉｉｉ−１０）ｂ−１０
アルミニウム箔の両面に、まず正極合剤ペーストａ−８１を塗布乾燥し、その上に正極合剤ペーストａ−３１を塗布乾燥した以外は、正極ｂ−１と同様の方法で正極ｂ−１０を作製した。正極活物質ａ−３を含む表層側の合剤層の平均厚みは両面で１４０μｍ、正極活物質ａ−６を含む集電基材側の合剤層の平均厚みは両面で１０μｍであった（第１合剤層の平均厚みとその外層の平均厚みとの比は、７：１００）。 (Iii-10) b-10
The positive electrode mixture paste a-81 was first applied and dried on both surfaces of the aluminum foil, and then the positive electrode mixture paste a-31 was applied and dried thereon. Produced. The average thickness of the mixture layer on the surface layer side containing the positive electrode active material a-3 was 140 μm on both sides, and the average thickness of the mixture layer on the current collecting substrate side containing the positive electrode active material a-6 was 10 μm on both sides ( The ratio of the average thickness of the first mixture layer to the average thickness of the outer layer is 7: 100).

（ｉｉｉ−１１）ｂ−１１
アルミニウム箔の両面に対し、正極合剤ペーストａ−４１に、１分間かけて同量の正極合剤ペーストａ−３１を少しずつ加え、撹拌しながら、添加の過程で得られる配合比率が漸次異なる正極合剤ペーストを順次塗布し、その後に乾燥した。その他は正極ｂ−１と同様の方法により、正極塗膜の表層側から集電基材側に向かう厚み方向において、正極活物質ａ−４が連続的に増加する（正極活物質ａ−３が連続的に減少する）正極ｂ−１１を作製した。正極塗膜の平均厚みは両面で１５０μｍであった。 (Iii-11) b-11
With respect to both surfaces of the aluminum foil, the same amount of the positive electrode mixture paste a-31 is gradually added to the positive electrode mixture paste a-41 over 1 minute, and the mixing ratio obtained in the addition process is gradually different while stirring. The positive electrode mixture paste was sequentially applied and then dried. Otherwise, the positive electrode active material a-4 continuously increases in the thickness direction from the surface layer side of the positive electrode coating film to the current collecting base material side in the same manner as the positive electrode b-1 (the positive electrode active material a-3 is A positive electrode b-11, which decreases continuously, was prepared. The average thickness of the positive electrode coating film was 150 μm on both sides.

（ｉｖ）負極の作製
（ｉｖ−１）ｃ−１
負極活物質として人造黒鉛３ｋｇと、負極結着剤として日本ゼオン（株）製の「ＢＭ−４００Ｂ（商品名）」（スチレン−ブタジエン共重合体の変性体を４０重量％含む水性分散液）７５ｇと、増粘剤としてＣＭＣを３０ｇと、適量の水とを、プラネタリーミキサーにて攪拌し、負極合剤塗料を調製した。この塗料を負極集電基材である厚さ１０μｍの銅箔の両面に、負極リード接続部を除いて塗布し、乾燥後の塗膜をローラで圧延して負極板とした。この際、銅箔および負極合剤層からなる極板の厚みを１８０μｍに制御した。 (Iv) Production of negative electrode (iv-1) c-1
Artificial graphite 3 kg as a negative electrode active material and 75 g of “BM-400B (trade name)” (an aqueous dispersion containing 40% by weight of a modified styrene-butadiene copolymer) manufactured by Nippon Zeon Co., Ltd. as a negative electrode binder. Then, 30 g of CMC as a thickener and an appropriate amount of water were stirred with a planetary mixer to prepare a negative electrode mixture paint. This paint was applied to both sides of a 10 μm thick copper foil as a negative electrode current collector, excluding the negative electrode lead connecting portion, and the dried coating film was rolled with a roller to obtain a negative electrode plate. Under the present circumstances, the thickness of the electrode plate which consists of copper foil and a negative mix layer was controlled to 180 micrometers.

（ｉｖ−２）ｃ−２
Ｓｉ（純度９９．９９９％、フルウチ化学製、インゴット）を黒鉛製坩堝の中に入れた。集電基材シートとなる電解Ｃｕ箔（古河サーキットフォイル（株）製、厚さ１８μｍ）を、真空蒸着装置内に設置した水冷ローラに貼り付けて固定した。その直下にＳｉを入れた黒鉛製坩堝を配置し、坩堝とＣｕ箔の間に酸素ガスを導入するノズルを設置し、酸素ガス（日本酸素製 純度９９．７％）の流量を２０ｓｃｃｍ（１分間に２０ｃｍ３流れる流量）に設定して真空蒸着装置内に酸素を導入した。電子銃を用いて、真空蒸着を行った。蒸着条件は加速電圧−８ｋＶ、電流５００ｍＡとした。 (Iv-2) c-2
Si (purity 99.999%, manufactured by Furuuchi Chemical, ingot) was placed in a graphite crucible. An electrolytic Cu foil (made by Furukawa Circuit Foil Co., Ltd., thickness 18 μm) serving as a current collecting base sheet was attached and fixed to a water-cooled roller installed in a vacuum deposition apparatus. A graphite crucible containing Si is arranged immediately below, a nozzle for introducing oxygen gas is installed between the crucible and the Cu foil, and the flow rate of oxygen gas (purity 99.7%, manufactured by Nippon Oxygen) is 20 sccm (1 minute) The flow rate was set to 20 cm 3 , and oxygen was introduced into the vacuum deposition apparatus. Vacuum deposition was performed using an electron gun. The deposition conditions were an acceleration voltage of -8 kV and a current of 500 mA.

負極片面あたりの活物質からなる膜の厚さは約１８μｍであった。またこの負極に含まれる酸素量を燃焼法によって測定したところ、ＳｉＯ０．３で示される組成になることが判明した。 The thickness of the film made of the active material per one surface of the negative electrode was about 18 μm. Further, when the amount of oxygen contained in the negative electrode was measured by a combustion method, it was found that the composition represented by SiO 0.3 was obtained.

（ｖ）非水電解質の調製
エチレンカーボネート（ＥＣ）とジメチルカーボネート（ＤＭＣ）とエチルメチルカーボネート（ＥＭＣ）とを体積比２：３：３で含む非水溶媒の混合物に、ＬｉＰＦ６を１ｍｏｌ／Ｌの濃度で溶解し、非水電解質とした。 (V) Preparation of non-aqueous electrolyte LiPF 6 was added at 1 mol / L to a mixture of non-aqueous solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) at a volume ratio of 2: 3: 3. To give a non-aqueous electrolyte.

（ｖｉ）円筒形電池の作製
まず、超音波溶接で正極にアルミニウムからなる正極リードを取り付けた。同様に負極に銅からなる負極リードを取り付けた。その後、正負極間に両極板より幅が広い帯状の微多孔性ポリエチレン製セパレータを介在させ、円筒状に捲回して極板群を構成した。極板群の上下にそれぞれポリプロピレン製の絶縁リングを配して電池ケースに挿入し、電池ケースの上部に段部を形成した後、上述した電解液を注入し、封口板で密閉して直径１８ｍｍ、総高６５ｍｍの円筒形電池を作製した。 (Vi) Production of Cylindrical Battery First, a positive electrode lead made of aluminum was attached to the positive electrode by ultrasonic welding. Similarly, a negative electrode lead made of copper was attached to the negative electrode. Thereafter, a strip-shaped microporous polyethylene separator having a width wider than the both electrode plates was interposed between the positive and negative electrodes and wound into a cylindrical shape to form a plate group. Polypropylene insulation rings are arranged on the upper and lower sides of the electrode plate group and inserted into the battery case. After the step is formed on the upper part of the battery case, the above-described electrolyte is injected, sealed with a sealing plate, and 18 mm in diameter. A cylindrical battery having a total height of 65 mm was produced.

ここで、正極にｂ−１〜ｂ−６およびｂ−１０を用い、負極にｃ−１を用いたものをそれぞれ実施例１〜７とし、正極にｂ−３およびｂ−１０を用い、負極にｃ−２を用いたものをそれぞれ実施例８および９とし、正極にｂ−１１を用い、負極にｃ−１を用いたものを実施例１０とした。なお、正極にｂ−７〜ｂ−９を用い、負極にｃ−１を用いたものをそれぞれ比較例１〜３とした。   Here, b-1 to b-6 and b-10 were used for the positive electrode, and c-1 was used for the negative electrode as Examples 1 to 7, respectively, and b-3 and b-10 were used for the positive electrode. Examples using c-2 as the examples were designated as Examples 8 and 9, respectively, using b-11 as the positive electrode and c-1 as the negative electrode as Example 10. Comparative examples 1 to 3 were prepared using b-7 to b-9 for the positive electrode and c-1 for the negative electrode, respectively.

これらの電池について、所定の充放電を行った後、以下の評価を行った。   About these batteries, after performing predetermined charging / discharging, the following evaluation was performed.

（電池容量測定）
各電池を以下の条件で充放電した。放電容量を表１に示した。
定電流充電：１６８０ｍＡ、終止電圧４．２Ｖ
定電圧充電：終止電流２４０ｍＡ、休止時間３０分
定電流放電：電流４８０ｍＡ、終止電圧３．０Ｖ、休止時間３０分 (Battery capacity measurement)
Each battery was charged and discharged under the following conditions. The discharge capacity is shown in Table 1.
Constant current charging: 1680 mA, final voltage 4.2 V
Constant voltage charging: end current 240 mA, rest time 30 minutes Constant current discharge: current 480 mA, end voltage 3.0 V, rest time 30 minutes

（釘刺し試験条件）
容量測定後の電池に対し、この容量測定と同条件で充電し、２０℃環境下の温度槽の中で５ｍｍ／ｓの速度で鉄製の釘（直径１．９ｍｍ）を電池に貫通させた。その際の電池電圧をモニタリングし、釘によって電池が短絡を開始して１秒後の電池電圧およびその間に観測された電池電圧の極小値を測定した。なお、各電池の短絡直前の電池電圧は４．１７Ｖであった。 (Nail penetration test conditions)
The battery after the capacity measurement was charged under the same conditions as the capacity measurement, and an iron nail (diameter 1.9 mm) was passed through the battery at a speed of 5 mm / s in a temperature bath in a 20 ° C. environment. The battery voltage at that time was monitored, and the battery voltage one second after the battery started short-circuiting by the nail and the minimum value of the battery voltage observed during that time were measured. In addition, the battery voltage just before the short circuit of each battery was 4.17V.

結果を表１に示した。   The results are shown in Table 1.

Figure 0005032800
Figure 0005032800

実施例１〜４および７〜９のリチウム二次電池用正極は、アルミニウム箔上に合剤層をそれぞれ２層形成し、各層はそれぞれ発熱開始温度が異なるリチウム含有化合物を１種含有し、アルミニウム箔に最も近い第１合剤層中に、発熱開始温度が３００℃以上のリチウム含有化合物を含有する。具体的には、第１合剤層に、実施例１〜３および８はリチウムニッケルマンガンコバルト酸化物を、実施例４はリチウムマンガン酸化物を、実施例７および９はオリビン型リン酸リチウム化合物を、それぞれ含有する。   In the positive electrodes for lithium secondary batteries of Examples 1 to 4 and 7 to 9, two mixture layers were formed on the aluminum foil, each layer containing one type of lithium-containing compound having a different heat generation starting temperature, and aluminum. The first mixture layer closest to the foil contains a lithium-containing compound having an exotherm starting temperature of 300 ° C. or higher. Specifically, in the first mixture layer, Examples 1 to 3 and 8 are lithium nickel manganese cobalt oxide, Example 4 is lithium manganese oxide, and Examples 7 and 9 are olivine type lithium phosphate compounds. Is contained respectively.

実施例５、６及び１０のリチウム二次電池用正極では、正極塗膜の表層側から集電基材側に向かう厚み方向において、発熱開始温度が３００℃以上のリチウム含有化合物が増加する。具体的には、実施例５では、リチウムニッケルマンガンコバルト酸化物の含有率が３３％から１００％に、実施例６では、リチウムマンガン酸化物の含有率が２５％から１００％にそれぞれ段階的に増加し、実施例１０では、リチウムニッケルマンガンコバルト酸化物の含有率が連続的に増加する。   In the positive electrodes for lithium secondary batteries of Examples 5, 6 and 10, the lithium-containing compound having a heat generation start temperature of 300 ° C. or more increases in the thickness direction from the surface layer side of the positive electrode coating film to the current collecting base material side. Specifically, in Example 5, the content of lithium nickel manganese cobalt oxide is changed from 33% to 100%, and in Example 6, the content of lithium manganese oxide is gradually increased from 25% to 100%. In Example 10, the content of lithium nickel manganese cobalt oxide is continuously increased.

これらの実施例ではいずれも、合剤層が発熱開始温度の低いリチウムニッケル酸化物のみを含有する比較例２と比較して、釘刺し試験において、短絡による電池電圧の降下を抑制する優れた効果が認められた。   In each of these examples, compared with Comparative Example 2 in which the mixture layer contains only lithium nickel oxide having a low heat generation start temperature, an excellent effect of suppressing a drop in battery voltage due to a short circuit in the nail penetration test. Was recognized.

特に、３００℃以上の発熱開始温度を有するリチウム含有化合物の中でも、オリビン型リン酸リチウム化合物には優れた電圧降下抑制効果が認められた（実施例７および９）。   In particular, among lithium-containing compounds having an exotherm starting temperature of 300 ° C. or higher, the olivine-type lithium phosphate compound has an excellent voltage drop suppressing effect (Examples 7 and 9).

釘刺し試験におけるこの高い電圧降下抑制効果は、正極の集電基材に最も近い第１合剤層または集電基材と最も近い正極塗膜部分に発熱開始温度が３００℃以上のリチウム含有化合物を含有させることによって、釘刺し試験時に内部短絡により高いジュール熱が発生した場合でもリチウム二次電池の過熱を確実に抑制し得ることを示す。   This high voltage drop suppression effect in the nail penetration test is due to the lithium-containing compound having a heat generation start temperature of 300 ° C. or higher in the first mixture layer closest to the current collector base material or the positive electrode coating film portion closest to the current collector base material. It is shown that the overheating of the lithium secondary battery can be reliably suppressed even when high Joule heat is generated due to an internal short circuit during the nail penetration test.

また、比較例３では、アルミニウム箔に最も近い第１合剤層が発熱開始温度の低いリチウムニッケル酸化物を含有し、第１合剤層の外層が発熱開始温度の高いリチウムマンガン酸化物を含有する。比較例３は、形式的には実施例４と２層の合剤層が含有するリチウム含有化合物が入れ替わる形となっているが、それにより、釘刺し試験において電圧降下抑制はほとんど認められず、釘刺し試験時の信頼性が低いことが明らかである。   In Comparative Example 3, the first mixture layer closest to the aluminum foil contains lithium nickel oxide having a low heat generation start temperature, and the outer layer of the first mixture layer contains lithium manganese oxide having a high heat generation start temperature. To do. Comparative Example 3 has a form in which the lithium-containing compound contained in the mixture layer of Example 4 and the two layers is interchanged in form, but almost no voltage drop suppression is observed in the nail penetration test, It is clear that the reliability during the nail penetration test is low.

更に、実施例１〜１０の構成によるリチウム含有化合物はいずれも、比較例２および３と比較して、短絡による電池電圧の低下を抑制するだけでなく、短絡時の最低電圧（電池電圧極小値）よりも高い電圧（１秒後の電池電圧）に回復する効果が認められた。すなわち、正極の集電基材に最も近い第１合剤層または集電基材と最も近い正極塗膜部分に発熱開始温度が３００℃以上のリチウム含有化合物を含有させることにより、短絡時の最低電圧と回復時の電圧との電位差を利用して充放電を制御することもできる。   Furthermore, all of the lithium-containing compounds according to the configurations of Examples 1 to 10 not only suppress the decrease in battery voltage due to a short circuit as compared with Comparative Examples 2 and 3, but also the lowest voltage at the time of the short circuit (battery voltage minimum value). ) Was recovered to a higher voltage (battery voltage after 1 second). That is, by including a lithium-containing compound having a heat generation starting temperature of 300 ° C. or higher in the first mixture layer closest to the current collecting base material of the positive electrode or the positive electrode coating film portion closest to the current collecting base material, Charging / discharging can also be controlled using the potential difference between the voltage and the voltage at the time of recovery.

一方、発熱開始温度が３００℃以上のリチウムマンガン酸化物のみで正極を構成した比較例１では、釘刺し試験においては高い電圧降下抑制を示したが、リチウムマンガン酸化物は容量密度が低いために電池容量が低下した。   On the other hand, in Comparative Example 1 in which the positive electrode was composed only of lithium manganese oxide having an exotherm starting temperature of 300 ° C. or higher, high voltage drop suppression was shown in the nail penetration test, but lithium manganese oxide has a low capacity density. Battery capacity has dropped.

本発明のリチウム二次電池用正極は、釘刺し試験におけるリチウム二次電池の過熱を確実に抑制することができるので、これを用いることにより、釘刺し試験における信頼性に優れ、かつ高容量なリチウム二次電池が提供される。本発明のリチウム二次電池は、携帯情報端末、携帯電子機器、家庭用小型電力貯蔵装置、自動二輪車、電気自動車、ハイブリッド電気自動車等に用いることができる。   The positive electrode for a lithium secondary battery of the present invention can reliably suppress overheating of the lithium secondary battery in the nail penetration test, and by using this, the reliability in the nail penetration test is excellent and the capacity is high. A lithium secondary battery is provided. The lithium secondary battery of the present invention can be used for portable information terminals, portable electronic devices, small household power storage devices, motorcycles, electric vehicles, hybrid electric vehicles, and the like.

本発明の実施の形態１に係るリチウム二次電池用正極の一例を示す模式断面図である。It is a schematic cross section which shows an example of the positive electrode for lithium secondary batteries which concerns on Embodiment 1 of this invention. 本発明の実施の形態２に係るリチウム二次電池用正極の一例を示す模式断面図である。It is a schematic cross section which shows an example of the positive electrode for lithium secondary batteries which concerns on Embodiment 2 of this invention.

符号の説明Explanation of symbols

１ 集電基材
２ 正極塗膜
３ 第１合剤層
４ 合剤層
５〜６ 正極活物質 DESCRIPTION OF SYMBOLS 1 Current collection base material 2 Positive electrode coating film 3 1st mixture layer 4 Mixture layer 5-6 Positive electrode active material

Claims (10)

集電基材と、前記集電基材上に正極塗膜とを備えたリチウム二次電池用正極であって、
前記正極塗膜は、正極活物質として発熱開始温度が異なる２種以上のリチウム含有化合物を含有し、
前記２種以上のリチウム含有化合物のうち、少なくとも１種のリチウム含有化合物は３００℃以上の発熱開始温度を有し、
前記正極塗膜の表層側から集電基材側に向かう厚み方向において、前記発熱開始温度が３００℃以上のリチウム含有化合物が増加することを特徴とするリチウム二次電池用正極。 A positive electrode for a lithium secondary battery comprising a current collecting base material and a positive electrode coating film on the current collecting base material,
The positive electrode coating film contains two or more lithium-containing compounds having different heat generation start temperatures as a positive electrode active material,
Of the two or more lithium-containing compounds, at least one lithium-containing compound has an exothermic onset temperature of 300 ° C. or higher,
The positive electrode for a lithium secondary battery, wherein a lithium-containing compound having a heat generation start temperature of 300 ° C. or higher increases in a thickness direction from a surface layer side of the positive electrode coating film toward a current collecting base material side. 前記集電基材と最も近い正極塗膜部分は、正極活物質として前記発熱開始温度が３００℃以上のリチウム含有化合物のみを含有することを特徴とする請求項１に記載のリチウム二次電池用正極。 Nearest positive Gokunurimaku portion and the current collector substrate is a lithium secondary battery according to claim 1, wherein the heat generation starting temperature of the positive electrode active material is characterized in that it contains only the lithium-containing compound described above 300 ° C. Positive electrode. 前記発熱開始温度が３００℃以上のリチウム含有化合物が、リチウムマンガン系酸化物、リチウムニッケルコバルトマンガン系酸化物、及びオリビン型リン酸リチウム系化合物からなる群から選ばれる１種である請求項１または２に記載のリチウム二次電池用正極。 The lithium-containing compound of the heat generation starting temperature of 300 ° C. or higher, lithium manganese oxide, lithium nickel-cobalt-manganese-based oxide, and which is a kind claim 1 or selected from the group consisting of olivine-type lithium phosphate compound 2. The positive electrode for a lithium secondary battery according to 2. 前記リチウムマンガン系酸化物が、ＬｉＭｎ2Ｏ4で表されるリチウムマンガン酸化物である請求項３に記載のリチウム二次電池用正極。 The positive electrode for a lithium secondary battery according to claim 3 , wherein the lithium manganese-based oxide is a lithium manganese oxide represented by LiMn 2 O 4 . 前記リチウムニッケルコバルトマンガン系酸化物が、ＬｉaＮｉ1-(b+c)ＭｎbＣｏcＯ2
（ただし、１≦ａ≦１．２であり、０．１≦ｂ≦０．５であり、０．１≦ｃ≦０．５である）で表されるリチウムニッケルマンガンコバルト酸化物である請求項３に記載のリチウム二次電池用正極。 The lithium nickel cobalt manganese-based oxide is Li a Ni 1- (b + c) Mn b Co c O 2
(However, 1 ≦ a ≦ 1.2, 0.1 ≦ b ≦ 0.5, and 0.1 ≦ c ≦ 0.5) Item 4. The positive electrode for a lithium secondary battery according to Item 3 . 前記オリビン型リン酸リチウム系化合物が、ＬｉＭｅＰＯ４（ただし、ＭｅはＣｏ、Ｎｉ、Ｆｅ、及びＭｎから選ばれる少なくとも１種である）で表されるオリビン型リン酸リチウム化合物である請求項３に記載のリチウム二次電池用正極。 The olivine-type lithium phosphate compound, LiMePO 4 (although, Me is Co, Ni, Fe, and at least one selected from Mn) in claim 3 is an olivine-type lithium phosphate compound represented by The positive electrode for lithium secondary batteries as described. 前記発熱開始温度が３００℃以上のリチウム含有化合物以外の他のリチウム含有化合物が、リチウムコバルト系酸化物およびリチウムニッケル系酸化物からなる群から選ばれる少なくとも１種である請求項１〜６の何れか１項に記載のリチウム二次電池用正極。 Other lithium-containing compounds other than the lithium-containing compound of the heating start temperature of 300 ° C. or higher, any of claims 1 to 6 is at least one selected from the group consisting of lithium cobalt oxide and lithium nickel-based oxide 2. A positive electrode for a lithium secondary battery according to claim 1. 前記リチウムコバルト系酸化物が、ＬｉＣｏＯ2、またはＬｉaＣｏ1-(b+c)ＭｇbＭcＯ2（ただし、１≦ａ≦１．０５で、０．００５≦ｂ≦０．１０で、０．００５≦ｃ≦０．１０であり、ＭはＡｌ、Ｓｒ、及びＣａから選ばれる少なくとも１種である）で表されるリチウムコバルト系酸化物である請求項７に記載のリチウム二次電池用正極。 The lithium cobalt oxide is LiCoO 2 or Li a Co 1- (b + c) Mg b McO 2 (where 1 ≦ a ≦ 1.05 and 0.005 ≦ b ≦ 0.10. The lithium secondary oxide according to claim 7 , wherein 0.005 ≦ c ≦ 0.10, and M is at least one selected from Al, Sr, and Ca. Battery positive electrode. 前記リチウムニッケル系酸化物が、ＬｉaＮｉ1-(b+c)ＣｏbＭcＯ2（ただし、１≦ａ≦１．０５で、０．1≦ｂ≦０．３５で、０．００５≦ｃ≦０．３０であり、ＭはＡｌ、Ｓｒ、及びＣａから選ばれる少なくとも１種である）で表されるリチウムニッケル系酸化物である請求項７に記載のリチウム二次電池用正極。 The lithium nickel-based oxide is Li a Ni 1- (b + c) Co b McO 2 (where 1 ≦ a ≦ 1.05, 0.1 ≦ b ≦ 0.35, 0.005 The positive electrode for a lithium secondary battery according to claim 7 , wherein ≦ c ≦ 0.30, and M is at least one selected from Al, Sr, and Ca. 請求項１〜９の何れか１項に記載のリチウム二次電池用正極、負極、及び非水電解質を備えるリチウム二次電池。 A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to any one of claims 1 to 9 , a negative electrode, and a nonaqueous electrolyte.
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