JP6132164B2 - Positive electrode for non-aqueous secondary battery and non-aqueous secondary battery - Google Patents
Positive electrode for non-aqueous secondary battery and non-aqueous secondary battery Download PDFInfo
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- JP6132164B2 JP6132164B2 JP2014091341A JP2014091341A JP6132164B2 JP 6132164 B2 JP6132164 B2 JP 6132164B2 JP 2014091341 A JP2014091341 A JP 2014091341A JP 2014091341 A JP2014091341 A JP 2014091341A JP 6132164 B2 JP6132164 B2 JP 6132164B2
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- positive electrode
- electrode active
- active material
- secondary battery
- aqueous secondary
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
- H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Description
本発明は、非水系二次電池用正極及び非水系二次電池に関する。 The present invention relates to a positive electrode for a non-aqueous secondary battery and a non-aqueous secondary battery.
非水系二次電池は、内部短絡時に、瞬時に多量の電流が流れて、電池発熱が生じるおそれがある。短絡の結果、電圧が急激に降下する。そこで、従来、第１正極活物質に、第１正極活物質よりも充放電電位が低く抵抗が高い第２正極活物質を混合したものを正極活物質として用いることで、正極内を大量の電流が急激に流れることを防止して、電池の内部短絡時に電圧降下を抑えることが行われている。たとえば、第１正極活物質としては、ＬｉＮＩｘＣｏｙＭｎｚＯ２（ｘ+ｙ+ｚ＝１）で表されるリチウム金属複合酸化物が用いられ、このリチウム金属複合酸化物に、第２正極活物質としてのＬｉＦｅＰＯ４を混合した正極活物質を用いることが提案されている（特許文献１〜６）。
In a non-aqueous secondary battery, when an internal short circuit occurs, a large amount of current flows instantaneously and there is a risk that battery heat will be generated. As a result of the short circuit, the voltage drops rapidly. Therefore, conventionally, a mixture of the first positive electrode active material and the second positive electrode active material having a lower charge / discharge potential and higher resistance than the first positive electrode active material is used as the positive electrode active material, so that a large amount of current is generated in the positive electrode. Is prevented from suddenly flowing to suppress a voltage drop when the battery is short-circuited internally. For example, as the first positive electrode active material, a lithium metal composite oxide represented by LiNI x Co y Mn z O 2 (x + y + z = 1) is used. It has been proposed to use a positive electrode active material mixed with LiFePO 4 as a positive electrode active material (
しかしながら、短絡時の急激な電圧降下をより効果的に抑制することが求められている。 However, it is required to more effectively suppress a rapid voltage drop during a short circuit.
本発明はかかる事情に鑑みてなされたものであり、短絡時の急激な電圧降下をより効果的に抑えることができる非水系二次電池用正極及び非水系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 it is an object to provide a positive electrode for a non-aqueous secondary battery and a non-aqueous secondary battery that can more effectively suppress a rapid voltage drop at the time of a short circuit. To do.
本発明者は、ＬｉＦｅＰＯ４などのように充放電電位の低い第２正極活物質の形状を工夫することで、さらに電圧降下の少ない非水系二次電池用正極を開発した。 The present inventor has developed a positive electrode for a non-aqueous secondary battery with a smaller voltage drop by devising the shape of the second positive electrode active material having a low charge / discharge potential such as LiFePO 4 .
本発明の非水系二次電池用正極は、第１正極活物質と、前記第１正極活物質よりも充放電電位の低い第２正極活物質とを有する非水系二次電池用正極であって、
前記第２正極活物質の長尺部分の平均長さをＬ１とし、前記第２正極活物質の短幅部分の平均長さをＬ２としたときのＬ１／Ｌ２の比率をアスペクト比とした場合、前記アスペクト比は１．５以上であることを特徴とする。
The positive electrode for a non-aqueous secondary battery according to the present invention is a positive electrode for a non-aqueous secondary battery having a first positive electrode active material and a second positive electrode active material having a charge / discharge potential lower than that of the first positive electrode active material. ,
When the average length of the long portion of the second positive electrode active material is L1, and the ratio of L1 / L2 is L2 when the average length of the short width portion of the second positive electrode active material is L2, The aspect ratio is 1.5 or more.
本発明の非水系二次電池用正極を備える非水系二次電池は、短絡時の急激な電圧降下をより効果的に抑えることができる。 A non-aqueous secondary battery including the positive electrode for a non-aqueous secondary battery of the present invention can more effectively suppress a rapid voltage drop at the time of a short circuit.
本発明の実施形態に係る非水系二次電池用正極及び非水系二次電池について詳細に説明する。 A positive electrode for a non-aqueous secondary battery and a non-aqueous secondary battery according to an embodiment of the present invention will be described in detail.
本発明の非水系二次電池用正極は、第１正極活物質と、前記第１正極活物質よりも充放電電位の低い第２正極活物質とを有する。第２正極活物質は、第１正極活物質よりも充放電電位が低いため、抵抗が高く、第２正極活物質での電子及び金属イオンの移動速度が遅い。第２正極活物質の形状は、アスペクト比が１．５以上である。後述の実施例に示すように、第２正極活物質のアスペクト比が１．５以上であるときは、アスペクト比が１．５未満であるときよりも、短絡時の電圧降下が少なくなる。その理由は定かではないが、以下のように考えられる。 The positive electrode for non-aqueous secondary batteries of this invention has a 1st positive electrode active material and a 2nd positive electrode active material whose charging / discharging electric potential is lower than the said 1st positive electrode active material. Since the charge / discharge potential of the second positive electrode active material is lower than that of the first positive electrode active material, the resistance is high, and the movement speed of electrons and metal ions in the second positive electrode active material is slow. The shape of the second positive electrode active material has an aspect ratio of 1.5 or more. As shown in the examples described later, when the aspect ratio of the second positive electrode active material is 1.5 or more, the voltage drop at the time of short circuit is smaller than when the aspect ratio is less than 1.5. The reason is not clear, but it is thought as follows.
図１（ａ）は本発明の第１正極活物質１と第２正極活物質２ａとの関係を示す説明図であり、第２正極活物質２ａのアスペクト比は１．５以上である場合を示す。図１（ｂ）は比較例の第１正極活物質１と第２正極活物質２ｂとの関係を示す説明図であり、第２正極活物質２ｂのアスペクト比は１．５未満である場合を示す。第２正極活物質２ａ、２ｂは、いずれも第１正極活物質１の間に介在している。本発明においては、第２正極活物質２ａはアスペクト比が１．５以上の粒子（図１（ａ））を形成しているため、アスペクト比が１．５未満である球形状の粒子（図１（ｂ））を形成している第２正極活物質２ｂよりも、扁平な形状である。扁平な第２正極活物質２ａと球状の第２正極活物質２ｂとが粒子１つ当たりの質量が同じである場合、扁平な第２正極活物質２ａが、球状の第２正極活物質２ｂよりも、第１正極活物質１間を遮る遮蔽面積が大きい。そのため、第１正極活物質同士の接触を効果的に防止できる。扁平な第２正極活物質２ａは、球状の第２正極活物質２ｂよりも、多くの電子及び金属イオンの移動速度を抑制する。よって、正極内の急激な電圧降下を効果的に抑制できる。
FIG. 1 (a) is an explanatory view showing the relationship between the first positive electrode
第２正極活物質の長尺部分の平均長さＬ１は、断面観察において、第２正極活物質の最も長い部分の平均長さを測定し、正極中の第２正極活物質の該長さの平均を求めることにより得られる。第２正極活物質の短幅部分の平均長さＬ２は、断面観察において、長尺部分の長尺方向に対して直交する方向のうち最も長い部分の長さを測定し、正極中の第２正極活物質の該長さの平均を求めることにより得られる。 The average length L1 of the long part of the second positive electrode active material is obtained by measuring the average length of the longest part of the second positive electrode active material in cross-sectional observation, and measuring the length of the second positive electrode active material in the positive electrode. It is obtained by calculating the average. The average length L2 of the short width portion of the second positive electrode active material is measured by measuring the length of the longest portion in the direction orthogonal to the long direction of the long portion in the cross-sectional observation. It is obtained by calculating the average of the length of the positive electrode active material.
断面観察とは、本発明の正極の断面を走査型電子顕微鏡鏡（ＳＥＭ）、透過型電子顕微鏡（ＴＥＭ）、電子線後方散乱回折（ＥＢＳＤ）などで測定して得られる画像に基づき、行えばよい。上記画像に対し、画像解析ソフトを用いて解析しても良い。 Cross-sectional observation is based on an image obtained by measuring the cross section of the positive electrode of the present invention with a scanning electron microscope (SEM), transmission electron microscope (TEM), electron beam backscatter diffraction (EBSD), or the like. Good. You may analyze the said image using image analysis software.
本発明において、「第２正極活物質のアスペクト比」は、第２正極活物質の長尺部分の平均長さＬ１と、第２正極活物質の短幅部分の平均長さＬ２との比率（Ｌ１／Ｌ２）をいう。 In the present invention, the “aspect ratio of the second positive electrode active material” is the ratio between the average length L1 of the long portion of the second positive electrode active material and the average length L2 of the short width portion of the second positive electrode active material ( L1 / L2).
第２正極活物質のアスペクト比は１．５以上である。第２正極活物質のアスペクト比は３以上であることがよく、さらには、５以上であることが好ましくは、特に８以上であることが望ましい。 The aspect ratio of the second positive electrode active material is 1.5 or more. The aspect ratio of the second positive electrode active material is preferably 3 or more, more preferably 5 or more, and particularly preferably 8 or more.
第２正極活物質の形状は、例えば、正極の走査型電子顕微鏡（ＳＥＭ）、透過型電子顕微鏡（ＴＥＭ）などにおいて観察される。ＳＥＭなどによる第２正極活物質の断面の写真では、第２正極活物質の具体形状は、例えば、長方形状、針形状、繊維形状、楕円形状などの平面的な形状として観察されることが多い。本明細書において、長方形状は、第２正極活物質の長尺部分の平均長さＬ１が短幅部分の平均長さＬ２に対して長い形状をいい、Ｌ２／Ｌ１の比が１．５以上３以下である形状をいう。針形状は、長尺部分の平均長さＬ１が短幅部分の平均長さＬ２に対して長方形状よりも更に長い形状をいい、Ｌ２／Ｌ１の比が３を超えて大きく１０以下である形状をいう。繊維形状は、長尺部分の平均長さＬ１が短幅部分の平均長さＬ２に対して針形状よりも更に長い形状をいい、Ｌ２／Ｌ１の比が１０を超えて大きい形状をいう。楕円形状は、長径と短径をもつ円をいい、長径は長尺部分の平均長さに相当し、短径は短幅部分の平均長さに相当する。上記の長方形、針形状、繊維形状、楕円形状のうち、第１正極活物質間を遮断するためには、針形状がよい。ＳＥＭ断面写真において、上記のように各種形状と観察された第２正極活物質は、立体的には、様々な形状を有しており、例えば、直方体形状、板形状、針形状、繊維形状などの形状を呈していることが多い。 The shape of the second positive electrode active material is observed, for example, with a positive electrode scanning electron microscope (SEM) or transmission electron microscope (TEM). In the photograph of the cross section of the second positive electrode active material by SEM or the like, the specific shape of the second positive electrode active material is often observed as a planar shape such as a rectangular shape, a needle shape, a fiber shape, an elliptical shape, or the like. . In this specification, the rectangular shape means a shape in which the average length L1 of the long portion of the second positive electrode active material is longer than the average length L2 of the short width portion, and the ratio of L2 / L1 is 1.5 or more. A shape that is 3 or less. The needle shape is a shape in which the average length L1 of the long portion is longer than the rectangular shape with respect to the average length L2 of the short width portion, and the ratio of L2 / L1 exceeds 3 and is 10 or less. Say. The fiber shape refers to a shape in which the average length L1 of the long portion is longer than the needle shape with respect to the average length L2 of the short width portion, and the L2 / L1 ratio is greater than 10. The elliptical shape refers to a circle having a major axis and a minor axis, the major axis corresponding to the average length of the long part, and the minor axis corresponding to the average length of the short part. Of the rectangle, needle shape, fiber shape, and ellipse shape, a needle shape is preferable for blocking between the first positive electrode active materials. In the SEM cross-sectional photograph, the second positive electrode active material observed in various shapes as described above has various shapes in three dimensions, for example, a rectangular parallelepiped shape, a plate shape, a needle shape, a fiber shape, and the like. Often has the shape of
第２正極活物質の長尺部分の平均長さＬ１は、０．１μｍ以上であることがよく、さらには、１μｍ以上であることが好ましく、５μｍ以上であることが最も好ましい。第２正極活物質の長尺部分の平均長さＬ１は、１０μｍ以下であることがよい。第２正極活物質の長尺部分の平均長さＬ１が短すぎると、第２正極活物質の第１正極活物質間を遮る遮蔽面積が少なく、電圧降下を抑える効果が少なくなるおそれがある。第２正極活物質の長尺部分の平均長さＬ１が長すぎると、電極プレス時に第２正極活物質が破壊されるおそれがある。 The average length L1 of the long portion of the second positive electrode active material is preferably 0.1 μm or more, more preferably 1 μm or more, and most preferably 5 μm or more. The average length L1 of the long portion of the second positive electrode active material is preferably 10 μm or less. If the average length L1 of the long portion of the second positive electrode active material is too short, the shielding area of the second positive electrode active material blocking the first positive electrode active material is small, and the effect of suppressing the voltage drop may be reduced. If the average length L1 of the long portion of the second positive electrode active material is too long, the second positive electrode active material may be destroyed during electrode pressing.
第２正極活物質は、第１正極活物質の間に分散していることが好ましい。第２正極活物質の第１正極活物質間を遮る遮蔽面積が大きくなり、短絡時の電圧降下を低減させることができる。 The second positive electrode active material is preferably dispersed between the first positive electrode active materials. The shielding area which shields between the 1st positive electrode active materials of a 2nd positive electrode active material becomes large, and can reduce the voltage drop at the time of a short circuit.
第１正極活物質は、一次粒子が凝集して二次粒子を形成していることがよい。第１正極活物質の二次粒子の平均粒径は、１μｍ以上１０μｍ以下であることがよく、更には、３μｍ以上８μｍ以下であることが好ましく、４μｍ以上７μｍ以下であることが最も好ましい。第１正極活物質の二次粒子の平均粒径が過小の場合には、第１正極活物質の比表面積が増大して電解液との副反応が増大し、寿命の悪化を生じることがある。第１正極活物質の二次粒子の平均粒径が過大の場合には、出力低下等の電池特性の悪化に加え、正極の大きさに影響を与えたり、二次電池を構成するセパレータを損傷したりするなどの不具合を生じることがある。なお、本明細書における第１正極活物質の二次粒子の平均粒径は、ＳＥＭなどを用いた断面観察で計測した場合の第１正極活物質の二次粒子の粒径の平均値を意味する。 In the first positive electrode active material, primary particles are preferably aggregated to form secondary particles. The average particle diameter of the secondary particles of the first positive electrode active material is preferably 1 μm or more and 10 μm or less, more preferably 3 μm or more and 8 μm or less, and most preferably 4 μm or more and 7 μm or less. When the average particle size of the secondary particles of the first positive electrode active material is too small, the specific surface area of the first positive electrode active material is increased, side reaction with the electrolyte is increased, and the life may be deteriorated. . When the average particle size of the secondary particles of the first positive electrode active material is excessive, it affects the size of the positive electrode and damages the separator that constitutes the secondary battery, in addition to the deterioration of battery characteristics such as output reduction. May cause malfunctions. In addition, the average particle diameter of the secondary particles of the first positive electrode active material in this specification means the average value of the particle diameters of the secondary particles of the first positive electrode active material when measured by cross-sectional observation using an SEM or the like. To do.
第２正極活物質の長尺部分の平均長さＬ１に対して、第１正極活物質の二次粒子の平均粒径をＬ３としたときに、Ｌ３に対するＬ１の比率（Ｌ１／Ｌ３）は０．０１以上１０以下であることがよく、さらには、０．１以上５以下であることが好ましく、０．１５以上１以下であることが最も好ましい。Ｌ３に対するＬ１の比率（Ｌ１／Ｌ３）が過小の場合には、第２正極活物質の第１正極活物質間を遮る遮蔽面積が少なくなり、短絡時の電圧降下を抑制する効果が低下するおそれがある。Ｌ３に対するＬ１の比率（Ｌ１／Ｌ３）が過大の場合には、第２正極活物質が壊れやすくなるおそれがある。 When the average particle diameter of the secondary particles of the first positive electrode active material is L3 with respect to the average length L1 of the long portion of the second positive electrode active material, the ratio of L1 to L3 (L1 / L3) is 0. It is good that it is 0.01 or more and 10 or less, more preferably 0.1 or more and 5 or less, and most preferably 0.15 or more and 1 or less. If the ratio of L1 to L3 (L1 / L3) is too small, the shielding area of the second positive electrode active material blocking between the first positive electrode active materials is reduced, and the effect of suppressing the voltage drop at the time of short circuit may be reduced. There is. When the ratio of L1 to L3 (L1 / L3) is excessive, the second positive electrode active material may be easily broken.
隣合う第１正極活物質の間には、隣合う第１正極活物質の中心間を結ぶ直線に対して直交する方向に第２正極活物質が配向して配置されていることが好ましい。第２正極活物質を最少使用量に抑えつつ、第１正極活物質間を、第２正極活物質で広い領域に渡って遮断することができる。短絡時の電圧降下を効果的に抑制できる。 It is preferable that the second positive electrode active material is arranged between the adjacent first positive electrode active materials in a direction orthogonal to a straight line connecting the centers of the adjacent first positive electrode active materials. The second positive electrode active material can be blocked over a wide area while the second positive electrode active material is suppressed to the minimum amount. The voltage drop at the time of a short circuit can be suppressed effectively.
本発明の正極において、第１正極活物質と第２正極活物質との合計質量を１００質量％としたときに、第２正極活物質は、２４．５質量％を超えて多く且つ３５質量％以下であることがよい。さらには、２４．５質量％を超えて多く２８．７質量％以下であることが好ましい。第２正極活物質が過少である場合には、第２正極活物質添加による短絡時の電圧降下低減効果が少なくなるおそれがある。第２正極活物質が３５質量％を超える場合には、正極全体の電池容量、入出力特性が低下するおそれがある。 In the positive electrode of the present invention, when the total mass of the first positive electrode active material and the second positive electrode active material is 100% by mass, the second positive electrode active material is more than 24.5% by mass and 35% by mass. It may be the following. Furthermore, it is preferable that it exceeds 24.5 mass% and is 28.7 mass% or less. If the second positive electrode active material is too small, the effect of reducing the voltage drop at the time of a short circuit due to the addition of the second positive electrode active material may be reduced. When the second positive electrode active material exceeds 35% by mass, the battery capacity and input / output characteristics of the entire positive electrode may be reduced.
第１正極活物質は、非水系二次電池の正極活物質として機能する材料である。第１正極活物質としては、非水系二次電池の正極活物質として機能する公知の材料を採用すれば良い。第１正極活物質は、例えばリチウムイオン二次電池の正極活物質として機能する材料を用いるとよい。この場合、リチウムイオンを吸蔵及び放出し得る正極活物質を第１正極活物質として用いることができる。具体的な第１正極活物質としては、例えば、リチウム金属複合酸化物が挙げられる。リチウム金属複合酸化物は、高容量である点から、層状岩塩構造の一般式：ＬｉａＮｉｂＣｏｃＭｎｄＤｅＯｆ（０．２≦ａ≦１．７、ｂ＋ｃ＋ｄ＋ｅ＝１、０≦ｅ＜１、ＤはＬｉ、Ｆｅ、Ｃｒ、Ｃｕ、Ｚｎ、Ｃａ、Ｍｇ、Ｚｒ、Ｓ、Ｓｉ、Ｎａ、Ｋ、Ａｌから選ばれる少なくとも１の元素、１．７≦ｆ≦２．１）で表される化合物（以下、「ＮＣＭ」ということがある。）が好ましい。 The first positive electrode active material is a material that functions as a positive electrode active material of a non-aqueous secondary battery. As a 1st positive electrode active material, what is necessary is just to employ | adopt the well-known material which functions as a positive electrode active material of a non-aqueous secondary battery. For example, a material that functions as a positive electrode active material of a lithium ion secondary battery may be used as the first positive electrode active material. In this case, a positive electrode active material that can occlude and release lithium ions can be used as the first positive electrode active material. Specific examples of the first positive electrode active material include a lithium metal composite oxide. The lithium metal composite oxide has a high capacity, and therefore has a general formula of a layered rock salt structure: Li a Ni b Co c Mn d De O f (0.2 ≦ a ≦ 1.7, b + c + d + e = 1, 0 ≦ e <1, D is at least one element selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K, and Al (1.7 ≦ f ≦ 2.1) The compound represented (hereinafter sometimes referred to as “NCM”) is preferred.
上記一般式：ＬｉａＮｉｂＣｏｃＭｎｄＤｅＯｆ（０．２≦ａ≦１．７、ｂ＋ｃ＋ｄ＋ｅ＝１、０≦ｅ＜１、ＤはＬｉ、Ｆｅ、Ｃｒ、Ｃｕ、Ｚｎ、Ｃａ、Ｍｇ、Ｚｒ、Ｓ、Ｓｉ、Ｎａ、Ｋ、Ａｌから選ばれる少なくとも１の元素、１．７≦ｆ≦２．１）において、ｂ、ｃ及びｄの値は、上記条件を満足するものであれば特に制限はないが、０＜ｂ＜１、０＜ｃ＜１、０＜ｄ＜１であるものが良く、また、ｂ、ｃ、ｄの少なくともいずれか一つが０＜ｂ＜８０／１００、０＜ｃ＜７０／１００、１０／１００＜ｄ＜１の範囲であることが好ましく、１０／１００＜ｂ＜６８／１００、１２／１００＜ｃ＜６０／１００、２０／１００＜ｄ＜６８／１００の範囲であることがより好ましく、２５／１００＜ｂ＜６０／１００、１５／１００＜ｃ＜５０／１００、２５／１００＜ｄ＜６０／１００の範囲であることがさらに好ましく、１／３≦ｂ≦５０／１００、２０／１００≦ｃ≦１／３、３０／１００≦ｄ≦１／３の範囲であることが特に好ましく、ｂ＝１／３、ｃ＝１／３、ｄ＝１／３、または、ｂ＝５０／１００、ｃ＝２０／１００、ｄ＝３０／１００であることが最も好ましい。 General formula: Li a Ni b Co c Mn d De O f (0.2 ≦ a ≦ 1.7, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca In the case of at least one element selected from Mg, Zr, S, Si, Na, K, and Al (1.7 ≦ f ≦ 2.1), the values of b, c, and d satisfy the above conditions. If there is no particular limitation, it is preferable that 0 <b <1, 0 <c <1, 0 <d <1, and at least one of b, c, d is 0 <b <80 / Preferably, the ranges are 100, 0 <c <70/100, 10/100 <d <1, 10/100 <b <68/100, 12/100 <c <60/100, 20/100 <d. <68/100 is more preferable, 25/100 <b <60/100, 15/10 <C <50/100, 25/100 <d <60/100 are more preferable, and 1/3 ≦ b ≦ 50/100, 20/100 ≦ c ≦ 1/3, 30/100 ≦ d. ≦ 1/3 is particularly preferable, and b = 1/3, c = 1/3, d = 1/3, or b = 50/100, c = 20/100, d = 30/100. Most preferably.
ａは、０．５≦ａ≦１．５の範囲内が好ましく、０．７≦ａ≦１．３の範囲内がより好ましく、０．９≦ａ≦１．２の範囲内がさらに好ましく、１≦ａ≦１．１の範囲内が特に好ましい。 a is preferably in the range of 0.5 ≦ a ≦ 1.5, more preferably in the range of 0.7 ≦ a ≦ 1.3, still more preferably in the range of 0.9 ≦ a ≦ 1.2, A range of 1 ≦ a ≦ 1.1 is particularly preferable.
ｅ、ｆについては一般式で規定する範囲内の数値であればよく、ｅ＝０、ｆ＝２を例示することができる。 For e and f, any numerical value within the range defined by the general formula may be used, and e = 0 and f = 2 can be exemplified.
また、第１正極活物質は、スピネル構造をもつリチウム金属複合酸化物であってもよい。スピネル構造を有するリチウム金属複合酸化物は、一般式：Ｌｉx(ＡyＭｎ2-y)Ｏ4（Ａは、Ｃａ、Ｍｇ、Ｓ、Ｓｉ、Ｎａ、Ｋ、Ａｌ、Ｐ、Ｇａ、Ｇｅから選ばれる少なくとも１の元素、及び遷移金属元素から選ばれる少なくとも１種の金属元素、０＜ｘ≦２．２、０＜ｙ≦１）で表されると良い。一般式の中のＡを構成し得る遷移金属元素は、例えば、Ｆｅ、Ｃｒ、Ｃｕ、Ｚｎ、Ｚｒ、Ｔｉ、Ｖ、Ｍｏ、Ｎｂ、Ｗ、Ｌａ、Ｎｉ、Ｃｏから選ばれる少なくとも１の元素であるとよい。スピネル構造をもつリチウム金属複合酸化物の具体例としては、ＬｉＭｎ２Ｏ４及びＬｉＮｉ０．５Ｍｎ１．５Ｏ４から選ばれる少なくとも一種であることがよい。 Further, the first positive electrode active material may be a lithium metal composite oxide having a spinel structure. The lithium metal composite oxide having a spinel structure has a general formula: Li x (A y Mn 2-y ) O 4 (A is Ca, Mg, S, Si, Na, K, Al, P, Ga, Ge) It is preferable that at least one element selected and at least one metal element selected from transition metal elements, 0 <x ≦ 2.2, 0 <y ≦ 1). The transition metal element that can constitute A in the general formula is, for example, at least one element selected from Fe, Cr, Cu, Zn, Zr, Ti, V, Mo, Nb, W, La, Ni, and Co. There should be. A specific example of the lithium metal composite oxide having a spinel structure is preferably at least one selected from LiMn 2 O 4 and LiNi 0.5 Mn 1.5 O 4 .
また、リチウム金属複合酸化物は、層状岩塩構造をもつものと、ＬｉＭｎ２Ｏ４等のスピネルとの混合物で構成される固溶体を含んでいてもよい。 The lithium metal composite oxide may contain a solid solution composed of a mixture of a layered rock salt structure and a spinel such as LiMn 2 O 4 .
第２正極活物質は、非水系二次電池の正極活物質として機能できる材料であって、上記第１正極活物質よりも充放電電位の低い材料である。本発明の非水系二次電池用正極を具備する非水系二次電池においては、第２正極活物質の充放電電位が第１正極活物質の充放電電位よりも低いため、実質的に第１正極活物質が正極の充放電の役割を担う。非水系二次電池用正極に第２正極活物質が存在すると、電池の正極と負極の短絡時であっても、電池の発熱をある程度抑制することができる。 The second positive electrode active material is a material that can function as a positive electrode active material of a non-aqueous secondary battery and has a lower charge / discharge potential than the first positive electrode active material. In the non-aqueous secondary battery comprising the positive electrode for a non-aqueous secondary battery of the present invention, the charge / discharge potential of the second positive electrode active material is lower than the charge / discharge potential of the first positive electrode active material. The positive electrode active material plays a role of charge / discharge of the positive electrode. When the second positive electrode active material is present in the positive electrode for the nonaqueous secondary battery, the heat generation of the battery can be suppressed to some extent even when the positive electrode and the negative electrode of the battery are short-circuited.
例えば、第１正極活物質がリチウム金属複合酸化物の場合、第２正極活物質としては、具体的に、リチウムホスフェート系材料、リチウムシリケート系材料を用いることができる。このうち、リチウムホスフェート系材料が好ましい。リチウムホスフェート系材料はオリビン型構造をもち、この材料を含む正極は、短絡により電圧降下した後に電圧が復帰するからである。 For example, when the first positive electrode active material is a lithium metal composite oxide, specifically, a lithium phosphate material or a lithium silicate material can be used as the second positive electrode active material. Of these, lithium phosphate materials are preferred. This is because the lithium phosphate material has an olivine structure, and the positive electrode including this material recovers its voltage after a voltage drop due to a short circuit.
リチウムホスフェート系材料は、一般式：ＬｉＭｈＰＯ４（ＭはＭｎ，Ｆｅ，Ｃｏ，Ｎｉ，Ｃｕ，Ｍｇ，Ｚｎ，Ｖ，Ｃａ，Ｓｒ，Ｂａ，Ｔｉ，Ａｌ，Ｓｉ，Ｂ，Ｔｅ及びＭｏから選ばれる少なくとも１の元素、０＜ｈ＜２）で表される材料を挙げることができる。 Lithium phosphate-based materials are represented by the general formula: LiM h PO 4 (M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, Te and Mo. A material represented by at least one selected element, 0 <h <2) may be mentioned.
具体的には、第２正極活物質として用いることができるリチウムホスフェート系材料は、ＬｉＦｅＰＯ４、ＬｉＭｎＰＯ４、ＬｉＶＰＯ４、ＬｉＮｉＰＯ４、ＬｉＣｏＰＯ４、ＬｉＴｅＰＯ４、ＬｉＶ２／３ＰＯ４、ＬｉＦｅ２／３ＰＯ４、ＬｉＭｎ７／８Ｆｅ１／８ＰＯ４を挙げることができる。第２正極活物質としては、特にＬｉＦｅＰＯ４が好ましい。その理由は次のとおりである。ＬｉＦｅＰＯ４は放電時に比較的平坦な放電曲線を示す。そうすると、仮に、リチウムイオン二次電池の正極と負極が短絡して急激な放電が生じたとしても、ＬｉＦｅＰＯ４の存在箇所では放電に伴う急激な電位差が生じない。そのため、電極内の他の箇所からの電荷移動を誘起しにくく、過電流の発生を抑制することができる。その結果、二次電池の発熱を好適に抑制することができる。 Specifically, lithium phosphate materials that can be used as the second positive electrode active material are LiFePO 4 , LiMnPO 4 , LiVPO 4 , LiNiPO 4 , LiCoPO 4 , LiTePO 4 , LiV 2/3 PO 4 , LiFe 2/3. PO 4 and LiMn 7/8 Fe 1/8 PO 4 can be mentioned. As the second positive electrode active material, LiFePO 4 is particularly preferable. The reason is as follows. LiFePO 4 exhibits a relatively flat discharge curve during discharge. Then, even if the positive electrode and the negative electrode of the lithium ion secondary battery are short-circuited and a sudden discharge occurs, a sudden potential difference associated with the discharge does not occur at the location where LiFePO 4 exists. Therefore, it is difficult to induce charge transfer from other parts in the electrode, and the occurrence of overcurrent can be suppressed. As a result, the heat generation of the secondary battery can be suitably suppressed.
第２正極活物質として用いることができるリチウムシリケート系材料は、組成式：Ｌｉ２＋ａ−ｂＡｂＭ１−βＭ’βＳｉ１＋αＯ４＋ｃ（式中、Ａは、Ｎａ、Ｋ、Ｒｂ、及びＣｓからなる群から選ばれた少なくとも一種の元素であり、Ｍは、Ｆｅ及びＭｎからなる群から選ばれた少なくとも一種の元素であり、Ｍ’は、Ｍｇ、Ｃａ、Ｃｏ、Ａｌ、Ｎｉ、Ｎｂ、Ｔｉ、Ｃｒ、Ｃｕ、Ｚｎ、Ｚｒ、Ｖ、Ｍｏ及びＷからなる群から選ばれた少なくとも一種の元素である。各添字は次のとおりである。０≦α≦０．２、０≦β≦０．５、０≦ａ＜１，０≦ｂ＜０．２，０＜ｃ＜０．３）で表されることが好ましい。上記組成式は、リチウムシリケート系材料の基本組成を示す。上記組成式の中の、Ｌｉ、Ａ、Ｍ、Ｍ’、Ｓｉ、Ｏの一部が他の元素で置換されていてもよい。他の元素で置換される場合には、容量に悪影響がない範囲で行われることが好ましい。不可避的に生じるＬｉ、Ａ、Ｍ、Ｍ’、Ｓｉ又はＯの欠損や化合物の酸化により、上記組成式からわずかにずれた組成をもつリチウムシリケート系材料も含む。リチウムシリケート系材料は、例えば、Ｌｉ２ＦｅＳｉＯ４、Ｌｉ２ＭｎＳｉＯ４、Ｌｉ２ＣｏＳｉＯ４、Ｌｉ２ＮｉＳｉＯ４が挙げられる。 The lithium silicate-based material that can be used as the second positive electrode active material has a composition formula: Li 2 + ab- Mb 1-β M′β Si 1 + α O 4 + c (where A represents Na, K, Rb, and At least one element selected from the group consisting of Cs, M is at least one element selected from the group consisting of Fe and Mn, and M ′ is Mg, Ca, Co, Al, Ni, Nb And at least one element selected from the group consisting of Ti, Cr, Cu, Zn, Zr, V, Mo and W. Each subscript is as follows: 0 ≦ α ≦ 0.2, 0 ≦ β. ≦ 0.5, 0 ≦ a <1, 0 ≦ b <0.2, 0 <c <0.3). The above composition formula indicates the basic composition of the lithium silicate material. A part of Li, A, M, M ′, Si, and O in the above composition formula may be substituted with another element. In the case of substitution with other elements, it is preferably performed within a range that does not adversely affect the capacity. Lithium silicate materials having a composition slightly deviating from the above composition formula due to unavoidable loss of Li, A, M, M ′, Si or O and oxidation of the compound are also included. Examples of the lithium silicate-based material include Li 2 FeSiO 4 , Li 2 MnSiO 4, Li 2 CoSiO 4 , and Li 2 NiSiO 4 .
前記第１正極活物質は、一般式：ＬｉａＮｉｂＣｏｃＭｎｄＤｅＯｆ（０．２≦ａ≦１．７、ｂ＋ｃ＋ｄ＋ｅ＝１、０≦ｅ＜１、ＤはＬｉ、Ｆｅ、Ｃｒ、Ｃｕ、Ｚｎ、Ｃａ、Ｍｇ、Ｚｒ、Ｓ、Ｓｉ、Ｎａ、Ｋ、Ａｌから選ばれる少なくとも１の元素、１．７≦ｆ≦２．１）で表される化合物であり、前記第２正極活物質は、リチウムホスフェート系材料からなることが好ましい。 The first positive electrode active material has a general formula: Li a Ni b Co c Mn d De O f (0.2 ≦ a ≦ 1.7, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, A compound represented by at least one element selected from Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K, and Al (1.7 ≦ f ≦ 2.1), The positive electrode active material is preferably made of a lithium phosphate material.
第２正極活物質としては、その表面を炭素材料で被覆したものを採用するのが好ましい。炭素材料は、導電性を有するとよく、例えば、アセチレンブラック（ＡＢ）、ケッチェンブラック（ＫＢ）、炭素材料ブラック、炭素材料ナノチューブ、グラフェーン、炭素材料繊維、黒鉛等を用いることができる。 As the second positive electrode active material, it is preferable to employ a material whose surface is coated with a carbon material. The carbon material is preferably conductive, and for example, acetylene black (AB), ketjen black (KB), carbon material black, carbon material nanotube, graphene, carbon material fiber, graphite, or the like can be used.
正極は、上記の第１正極活物質及び第２正極活物質を有する。正極は、上記の第１正極活物質及び第２正極活物質を有する正極活物質層と、正極活物質層で被覆された集電体とを有することが好ましい。 The positive electrode has the first positive electrode active material and the second positive electrode active material. The positive electrode preferably includes a positive electrode active material layer having the first positive electrode active material and the second positive electrode active material, and a current collector covered with the positive electrode active material layer.
正極活物質層全体を１００質量％としたときに、正極活物質層に含まれている上記の第１正極活物質及び第２正極活物質の合計質量は８５質量％以上９６質量％以下であることが好ましい。この正極活物質層を有する正極を電池に用いた場合には、十分な電池容量を発揮できる。 When the entire positive electrode active material layer is 100 mass%, the total mass of the first positive electrode active material and the second positive electrode active material contained in the positive electrode active material layer is 85 mass% or more and 96 mass% or less. It is preferable. When a positive electrode having this positive electrode active material layer is used for a battery, a sufficient battery capacity can be exhibited.
正極活物質層は、上記の第１正極活物質及び第２正極活物質を有し、更に必要に応じて添加剤を添加してもよい。添加剤としては、導電助剤、結着剤、分散剤などを挙げることができる。 A positive electrode active material layer has said 1st positive electrode active material and 2nd positive electrode active material, and may add an additive further as needed. Examples of the additive include a conductive additive, a binder, and a dispersant.
導電助剤は、電極の導電性を高めるために添加される。そのため、導電助剤は、電極の導電性が不足する場合に任意に加えればよく、電極の導電性が十分に優れている場合には加えなくても良い。導電助剤としては化学的に不活性な電子高伝導体であれば良く、炭素質微粒子であるカーボンブラック、黒鉛、アセチレンブラック、ケッチェンブラック（登録商標）、気相法炭素繊維（Vapor Grown Carbon Fiber：ＶＧＣＦ）、および各種金属粒子などが例示される。これらの導電助剤を単独または二種以上組み合わせて正極活物質層に添加することができる。 The conductive assistant is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be any chemically inert electronic high conductor, such as carbon black, graphite, acetylene black, ketjen black (registered trademark), vapor grown carbon fiber (Vapor Grown Carbon). Fiber: VGCF) and various metal particles are exemplified. These conductive assistants can be added to the positive electrode active material layer alone or in combination of two or more.
導電助剤はその形状が特に制限されるものではないが、その役割からみて、平均粒子径は小さいほうが好ましい。導電助剤の好ましい平均粒子径を挙げると、１０μｍ以下が良く、０．０１〜１μｍの範囲内がさらに好ましい。なお、導電助剤の平均粒子径は、一般的な粒度分布測定装置で計測した場合のＤ５０の値である。 The shape of the conductive auxiliary agent is not particularly limited, but it is preferable that the average particle diameter is small in view of its role. When the preferable average particle diameter of a conductive support agent is given, 10 micrometers or less are good and the inside of the range of 0.01-1 micrometer is more preferable. In addition, the average particle diameter of a conductive support agent is the value of D50 at the time of measuring with a general particle size distribution measuring apparatus.
正極活物質層における導電助剤の配合量を挙げると、０．５〜１０質量％の範囲内が好ましく、１〜７質量％の範囲内がより好ましく、２〜５質量％の範囲内が特に好ましい。 When the blending amount of the conductive additive in the positive electrode active material layer is given, it is preferably in the range of 0.5 to 10% by mass, more preferably in the range of 1 to 7% by mass, and particularly preferably in the range of 2 to 5% by mass. preferable.
結着剤は、正極活物質や導電助剤を集電体の表面に繋ぎ止める役割を果たすものである。結着剤としては、ポリフッ化ビニリデン、ポリテトラフルオロエチレン、フッ素ゴム等の含フッ素樹脂、ポリプロピレン、ポリエチレン等の熱可塑性樹脂、ポリイミド、ポリアミドイミド等のイミド系樹脂、アルコキシシリル基含有樹脂を例示することができる。また、結着剤として、親水基を有するポリマーを採用してもよい。親水基を有するポリマーの親水基としては、カルボキシル基、スルホ基、シラノール基、アミノ基、水酸基、リン酸基が例示される。親水基を有するポリマーの具体例として、ポリアクリル酸、カルボキシメチルセルロース、ポリメタクリル酸、ポリ（ｐ−スチレンスルホン酸）を挙げることができる。 The binder plays a role of connecting the positive electrode active material and the conductive additive to the surface of the current collector. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. be able to. Moreover, you may employ | adopt the polymer which has a hydrophilic group as a binder. Examples of the hydrophilic group of the polymer having a hydrophilic group include a carboxyl group, a sulfo group, a silanol group, an amino group, a hydroxyl group, and a phosphate group. Specific examples of the polymer having a hydrophilic group include polyacrylic acid, carboxymethylcellulose, polymethacrylic acid, and poly (p-styrenesulfonic acid).
正極活物質層における結着剤の配合量を挙げると、０．５〜１０質量％の範囲内が好ましく、１〜７質量％の範囲内がより好ましく、２〜５質量％の範囲内が特に好ましい。結着剤の配合量が少なすぎると組成物を正極活物質層とした場合に当該層の成形性が低下するおそれがある。また、結着剤の配合量が多すぎると、正極活物質層における正極活物質の量が減少するため、好ましくない。 The amount of the binder in the positive electrode active material layer is preferably in the range of 0.5 to 10% by mass, more preferably in the range of 1 to 7% by mass, and particularly preferably in the range of 2 to 5% by mass. preferable. If the blending amount of the binder is too small, the moldability of the layer may be lowered when the composition is used as a positive electrode active material layer. Moreover, when there are too many compounding quantities of a binder, since the quantity of the positive electrode active material in a positive electrode active material layer reduces, it is unpreferable.
集電体は、リチウムイオン二次電池の放電又は充電の間、電極に電流を流し続けるための化学的に不活性な電子高伝導体をいう。集電体としては、銀、銅、金、アルミニウム、マグネシウム、タングステン、コバルト、亜鉛、ニッケル、鉄、白金、錫、インジウム、チタン、ルテニウム、タンタル、クロム、モリブデンから選ばれる少なくとも一種、並びにステンレス鋼などの金属材料を例示することができる。集電体は公知の保護層で被覆されていても良い。 The current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, magnesium, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel Examples of such a metal material can be given. The current collector may be covered with a known protective layer.
集電体は箔、シート、フィルム、線状、棒状などの形態をとることができる。そのため、集電体として、例えば銅箔、ニッケル箔、アルミニウム箔、ステンレス箔などの金属箔を好適に用いることができる。集電体が箔、シート、フィルム形態の場合は、その厚みが１０μｍ〜１００μｍの範囲内であることが好ましい。 The current collector can take the form of a foil, a sheet, a film, a line, a bar, and the like. Therefore, metal foils, such as copper foil, nickel foil, aluminum foil, stainless steel foil, can be used suitably as a collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 10 μm to 100 μm.
本発明の非水系二次電池用正極を製造するために、以下のａ）工程からｃ）工程を行うとよい。 In order to produce the positive electrode for a non-aqueous secondary battery of the present invention, the following steps a) to c) may be performed.
ａ）工程は、第１正極活物質、該第１正極活物質よりも充放電電位の低い第２正極活物質、添加剤及び溶剤を混合し、分散液を製造する工程である。 The step a) is a step of producing a dispersion by mixing the first positive electrode active material, the second positive electrode active material having a lower charge / discharge potential than the first positive electrode active material, the additive and the solvent.
溶剤としては、具体的にＮ−メチル−２−ピロリドン（以下、「ＮＭＰ」と略す場合がある。）、ジメチルホルムアミド、ジメチルアセトアミド、メタノール、アセトン、メチルエチルケトン、メチルイソブチルケトン、シクロヘキサノン、酢酸メチル、酢酸エチル、及びテトラヒドロフランを例示できる。これらの溶剤は、１種類を単独で用いてもよく、２種類以上を併用してもよい。ａ）工程の分散液は、溶剤及び溶剤以外の固形分からなる。溶剤以外の固形分とは、第１正極活物質、第２正極活物質、並びに、必要に応じて用いられる結着剤、導電助剤及び分散剤等の添加剤をいう。ａ）工程の分散液において、分散液を１００質量％としたときに、溶剤以外の固形分の配合量は、３０〜９０質量％の範囲内が好ましく、５０〜８０質量％の範囲内がより好ましく、６０〜７０質量％の範囲が特に好ましい。 Specific examples of the solvent include N-methyl-2-pyrrolidone (hereinafter sometimes abbreviated as “NMP”), dimethylformamide, dimethylacetamide, methanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, acetic acid. Examples thereof include ethyl and tetrahydrofuran. These solvents may be used alone or in combination of two or more. The dispersion liquid of a) process consists of solid content other than a solvent and a solvent. Solid content other than a solvent means additives, such as a 1st positive electrode active material, a 2nd positive electrode active material, and a binder used as needed, a conductive support agent, and a dispersing agent. a) In the dispersion liquid in the step, when the dispersion liquid is 100% by mass, the blending amount of solids other than the solvent is preferably in the range of 30 to 90% by mass, more preferably in the range of 50 to 80% by mass. The range of 60 to 70% by mass is particularly preferable.
ａ）工程では、各成分を同時に又は順に加えて混合装置で混合すればよい。混合装置としては、混合攪拌機、ボールミル、サンドミル、ビーズミル、分散機、超音波分散機、ホモジナイザー、ホモミキサー、プラネタリーミキサー、遊星式攪拌脱泡装置を例示できる。混合装置における混合速度は、組成物の各成分が好適に分散若しくは溶解できる速度を適宜設定すればよい。 In the step a), the components may be added simultaneously or sequentially and mixed with a mixing device. Examples of the mixing apparatus include a mixing stirrer, a ball mill, a sand mill, a bead mill, a disperser, an ultrasonic disperser, a homogenizer, a homomixer, a planetary mixer, and a planetary stirring deaerator. What is necessary is just to set the mixing speed in a mixing apparatus suitably the speed | rate which each component of a composition can disperse | distribute or melt | dissolve suitably.
ｂ）工程は、ａ）工程で製造された分散液を集電体に塗布し、該分散液に含まれる前記溶剤を除去して、正極活物質層を形成する工程である。 The step b) is a step of forming a positive electrode active material layer by applying the dispersion liquid produced in the step a) to a current collector and removing the solvent contained in the dispersion liquid.
分散液を集電体に塗布する具体的な方法としては、ロールコート法、ディップコート法、ドクターブレード法、スプレーコート法、カーテンコート法などの従来から公知の方法を挙げることができる。 Specific methods for applying the dispersion to the current collector include conventionally known methods such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, and a curtain coating method.
そして、分散液に含まれる溶剤を除去する具体的な方法としては、加温条件及び／又は減圧条件で分散液の乾燥を行い、分散液に含まれる溶剤を気体として除去する方法を挙げることができる。 As a specific method for removing the solvent contained in the dispersion liquid, there is a method of drying the dispersion liquid under a heating condition and / or a reduced pressure condition and removing the solvent contained in the dispersion liquid as a gas. it can.
ｃ）工程：前記ｂ）工程で得られた正極活物質層を圧縮装置で圧縮する。圧縮装置としては、従来から公知のものを採用すればよい。具体的な圧縮装置としては、ロールプレス機、真空プレス機、水圧プレス機、油圧プレス機を挙げることができる。圧縮装置における圧縮圧力としては、例えば、１〜５０００ｋＮの範囲を挙げることができる。 c) Step: The positive electrode active material layer obtained in the step b) is compressed with a compression device. A conventionally known compressor may be used as the compression device. Specific examples of the compression device include a roll press, a vacuum press, a hydraulic press, and a hydraulic press. Examples of the compression pressure in the compression device include a range of 1 to 5000 kN.
上記のａ）工程からｃ）工程による正極の製造方法によれば、本発明の正極を簡素に得ることができる。この製造方法では、短絡時の電圧降下を効果的に抑制できる正極を製造できる。第１正極活物質表面に第２正極活物質を被覆する工程によっても、短絡時の電圧降下を抑制できるが、被覆工程を必要とし、製造工数が多くなる。上記の方法では、第１正極活物質と第２正極活物質とを混合するという簡素な方法で、第１正極活物質間に第２正極活物質を介在させることができる。 According to the method for producing a positive electrode from steps a) to c), the positive electrode of the present invention can be obtained simply. With this manufacturing method, a positive electrode capable of effectively suppressing a voltage drop at the time of a short circuit can be manufactured. Even by the step of coating the surface of the first positive electrode active material with the second positive electrode active material, the voltage drop at the time of a short circuit can be suppressed, but the coating step is required and the number of manufacturing steps increases. In the above method, the second positive electrode active material can be interposed between the first positive electrode active materials by a simple method of mixing the first positive electrode active material and the second positive electrode active material.
本発明の正極を採用して、非水系二次電池を製造できる。非水系二次電池は、電池構成要素として、正極、負極、セパレータ及び電解液を含む。 By employing the positive electrode of the present invention, a non-aqueous secondary battery can be manufactured. The non-aqueous secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolytic solution as battery components.
負極は、集電体と、集電体の表面に結着させた負極活物質層を有する。負極活物質層は負極活物質、並びに必要に応じて結着剤及び／又は導電助剤を含む。集電体、結着剤及び導電助剤は、正極で説明したものを採用すればよい。また、負極活物質層用の結着剤としてスチレン−ブタジエンゴムを採用しても良い。 The negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector. The negative electrode active material layer includes a negative electrode active material and, if necessary, a binder and / or a conductive aid. As the current collector, the binder, and the conductive additive, those described for the positive electrode may be adopted. Moreover, you may employ | adopt a styrene-butadiene rubber as a binder for negative electrode active material layers.
負極活物質としては、リチウムを吸蔵及び放出可能な炭素系材料、リチウムと合金化可能な元素、リチウムと合金化可能な元素を有する化合物、あるいは高分子材料などを例示することができる。 Examples of the negative electrode active material include a carbon-based material capable of inserting and extracting lithium, an element that can be alloyed with lithium, a compound having an element that can be alloyed with lithium, a polymer material, and the like.
炭素系材料としては、難黒鉛化性炭素、天然黒鉛、人造黒鉛、コークス類、グラファイト類、ガラス状炭素類、有機高分子化合物焼成体、炭素繊維、活性炭あるいはカーボンブラック類が例示できる。ここで、有機高分子化合物焼成体とは、フェノール類やフラン類などの高分子材料を適当な温度で焼成して炭素化したものをいう。 Examples of the carbon-based material include non-graphitizable carbon, natural graphite, artificial graphite, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and carbon blacks. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.
リチウムと合金化可能な元素としては、具体的にＮａ、Ｋ、Ｒｂ、Ｃｓ、Ｆｒ、Ｂｅ、Ｍｇ、Ｃａ、Ｓｒ、Ｂａ、Ｒａ、Ｔｉ、Ａｇ、Ｚｎ、Ｃｄ、Ａｌ、Ｇａ、Ｉｎ、Ｓｉ、Ｇｅ、Ｓｎ、Ｐｂ、Ｓｂ、Ｂｉが例示でき、特に、Ｓｉ又はＳｎが好ましい。 Specifically, elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si. , Ge, Sn, Pb, Sb, Bi can be exemplified, and Si or Sn is particularly preferable.
リチウムと合金化可能な元素を有する化合物としては、具体的にＺｎＬｉＡｌ、ＡｌＳｂ、ＳｉＢ４、ＳｉＢ６、Ｍｇ２Ｓｉ、Ｍｇ２Ｓｎ、Ｎｉ２Ｓｉ、ＴｉＳｉ２、ＭｏＳｉ２、 ＣｏＳｉ２、ＮｉＳｉ２、ＣａＳｉ２、ＣｒＳｉ２、Ｃｕ５Ｓｉ、ＦｅＳｉ２、ＭｎＳｉ２、ＮｂＳｉ２、ＴａＳｉ２、ＶＳｉ２、ＷＳｉ２、ＺｎＳｉ２、ＳｉＣ、Ｓｉ３Ｎ４、Ｓｉ２Ｎ２Ｏ、ＳｉＯｖ（０＜ｖ≦２）、ＳｎＯｗ（０＜ｗ≦２）、ＳｎＳｉＯ３、ＬｉＳｉＯ あるいはＬｉＳｎＯを例示でき、特に、ＳｉＯｘ（０．３≦ｘ≦１．６）が好ましい。また、リチウムと合金化反応可能な元素を有する化合物として、スズ合金（Ｃｕ−Ｓｎ合金、Ｃｏ−Ｓｎ合金等）などの錫化合物を例示できる。
Specific examples of compounds having elements that can be alloyed with lithium include ZnLiAl, AlSb, SiB 4 , SiB 6 , Mg 2 Si, Mg 2 Sn, Ni 2 Si, TiSi 2 , MoSi 2 , CoSi 2 , NiSi 2 , CaSi 2, CrSi 2, Cu 5 Si,
負極活物質は、Ｓｉ元素又はＳｉ化合物を有するとよい。Ｓｉ元素又はＳｉ化合物は、不可逆容量が大きい。また、充放電電位の低い第２正極活物質からは、第１正極活物質よりも先に、Ｌｉイオンが放出される。第２正極活物質から放出されたＬｉイオンは、負極活物質としてのＳｉ元素又はＳｉ化合物に吸蔵され、Ｓｉ元素又はＳｉ化合物の不可逆容量分を補う。このため、第２正極活物質よりも後に第１正極活物質から放出されたＬｉイオンは、Ｓｉ元素又はＳｉ化合物の可逆容量分として、可逆可能なプロトン伝達媒体として機能する。従って、不可逆容量の大きいＳｉ元素又はＳｉ化合物が負極活物質であっても、第１正極活物質自体の本来の電池容量を発揮することができる。 The negative electrode active material may contain Si element or Si compound. Si element or Si compound has a large irreversible capacity. In addition, Li ions are released from the second positive electrode active material having a low charge / discharge potential before the first positive electrode active material. Li ions released from the second positive electrode active material are occluded by the Si element or Si compound as the negative electrode active material, and make up for the irreversible capacity of the Si element or Si compound. For this reason, Li ions released from the first positive electrode active material after the second positive electrode active material function as a reversible proton transmission medium as the reversible capacity of the Si element or Si compound. Therefore, even if Si element or Si compound having a large irreversible capacity is the negative electrode active material, the original battery capacity of the first positive electrode active material itself can be exhibited.
負極活物質に用いられる高分子材料としては、具体的にポリアセチレン、ポリピロールを例示できる。 Specific examples of the polymer material used for the negative electrode active material include polyacetylene and polypyrrole.
セパレータは、正極と負極とを隔離し、両極の接触による電流の短絡を防止しつつ、リチウムイオンを通過させるものである。セパレータとしては、例えばポリテトラフルオロエチレン、ポリプロピレン若しくはポリエチレンなどの合成樹脂を１種又は複数用いた多孔質膜、又はセラミックス製の多孔質膜が例示できる。 The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit of current due to contact between the two electrodes. Examples of the separator include a porous film using one or more synthetic resins such as polytetrafluoroethylene, polypropylene, and polyethylene, or a ceramic porous film.
電解液は、非水溶媒と、非水溶媒に溶解された電解質とを有する。 The electrolytic solution has a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent.
非水溶媒としては、環状エステル類、鎖状エステル類、エーテル類等が使用できる。環状エステル類としては、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、ガンマブチロラクトン、ビニレンカーボネート、２−メチル−ガンマブチロラクトン、アセチル−ガンマブチロラクトン、ガンマバレロラクトンを例示できる。鎖状エステル類としては、ジメチルカーボネート、ジエチルカーボネート、ジブチルカーボネート、ジプロピルカーボネート、メチルエチルカーボネート、プロピオン酸アルキルエステル、マロン酸ジアルキルエステル、酢酸アルキルエステル等を例示できる。エーテル類としては、テトラヒドロフラン、２−メチルテトラヒドロフラン、１，４−ジオキサン、１，２−ジメトキシエタン、１，２−ジエトキシエタン、１，２−ジブトキシエタンを例示できる。電解液には、これらの非水溶媒を単独で用いてもよいし、又は、複数を併用してもよい。 As the non-aqueous solvent, cyclic esters, chain esters, ethers and the like can be used. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. These nonaqueous solvents may be used alone or in combination with the electrolyte.
電解質としては、ＬｉＣｌＯ４、ＬｉＡｓＦ６、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３、ＬｉＮ（ＣＦ３ＳＯ２）２等のリチウム塩を例示できる。 Examples of the electrolyte include lithium salts such as LiClO 4 , LiAsF 6 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , and LiN (CF 3 SO 2 ) 2 .
電解液としては、エチレンカーボネート、ジメチルカーボネート、プロピレンカーボネート、ジエチルカーボネートなどの非水溶媒に、ＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３などのリチウム塩を０．５ｍｏｌ／ｌから１．７ｍｏｌ／ｌ程度の濃度で溶解させた溶液を例示できる。 As an electrolytic solution, 0.5 mol / l to 1.7 mol of a lithium salt such as LiClO 4 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 in a nonaqueous solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and diethyl carbonate. A solution dissolved at a concentration of about 1 / l can be exemplified.
非水系二次電池を製造するために、正極および負極にセパレータを挟装させ電極体とする。電極体は、正極、セパレータ及び負極を重ねた積層型、又は、正極、セパレータ及び負極を捲いた捲回型のいずれの型にしても良い。正極の集電体および負極の集電体から外部に通ずる正極端子および負極端子までの間を、集電用リード等を用いて接続した後に、電極体に電解液を加えて非水系二次電池とするとよい。 In order to manufacture a non-aqueous secondary battery, a separator is sandwiched between a positive electrode and a negative electrode to form an electrode body. The electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched. After connecting between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal connected to the outside using a current collecting lead or the like, an electrolyte is added to the electrode body to add a non-aqueous secondary battery It is good to do.
非水系二次電池は車両に搭載することができる。非水系二次電池の中でもリチウムイオン二次電池は、大きな充放電容量を維持し、かつ優れたサイクル性能を有するため、これを搭載した車両は、高性能の車両となる。 The non-aqueous secondary battery can be mounted on a vehicle. Among non-aqueous secondary batteries, a lithium ion secondary battery maintains a large charge / discharge capacity and has excellent cycle performance, and thus a vehicle equipped with the lithium ion secondary battery is a high-performance vehicle.
車両としては、電池による電気エネルギーを動力源の全部または一部に使用する車両であればよく、例えば、電気自動車、ハイブリッド自動車、プラグインハイブリッド自動車、ハイブリッド鉄道車両、電動フォークリフト、電気車椅子、電動アシスト自転車、電動二輪車が挙げられる。 The vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source. For example, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric forklift, an electric wheelchair, and an electric assist. Bicycles and electric motorcycles are examples.
以上、本発明の実施形態を説明したが、本発明は、上記実施形態に限定されるものではない。本発明の要旨を逸脱しない範囲において、当業者が行い得る変更、改良等を施した種々の形態にて実施することができる。 As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.
以下に、実施例および比較例を示し、本発明をより具体的に説明する。なお、本発明は、これらの実施例によって限定されるものではない。以下において、特に断らない限り、「部」とは質量部を意味し、「％」とは質量％を意味する。 Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited by these Examples. In the following, unless otherwise specified, “part” means part by mass, and “%” means mass%.
（実施例１）
ａ）工程
第１正極活物質としてのＬｉＮｉ５／１０Ｃｏ２／１０Ｍｎ３／１０Ｏ２を準備した。このＬｉＮｉ５／１０Ｃｏ２／１０Ｍｎ３／１０Ｏ２の２次粒子の平均粒子径（Ｄ５０）は６μｍであった。針形状のＬｉＦｅＰＯ４を、炭素材料で被覆した。ＬｉＦｅＰＯ４と炭素材料の合計質量を１００質量％としたときに、ＬｉＦｅＰＯ４の配合比は、９７質量％であった。
Example 1
a) Step LiNi 5/10 Co 2/10 Mn 3/10 O 2 as a first positive electrode active material was prepared. The average particle diameter (D50) of the secondary particles of this LiNi 5/10 Co 2/10 Mn 3/10 O 2 was 6 μm. Needle-shaped LiFePO 4 was coated with a carbon material. When the total mass of LiFePO 4 and the carbon material was 100% by mass, the blending ratio of LiFePO 4 was 97% by mass.
ＬｉＮｉ５／１０Ｃｏ２／１０Ｍｎ３／１０Ｏ２の充放電電位は、Ｌｉ基準で３．９Ｖであり、ＬｉＦｅＰＯ４の充放電電位は、Ｌｉ基準で３．５Ｖであった。 The charge / discharge potential of LiNi 5/10 Co 2/10 Mn 3/10 O 2 was 3.9 V on the basis of Li, and the charge / discharge potential of LiFePO 4 was 3.5 V on the basis of Li.
遊星式攪拌脱泡装置を用いて、第１正極活物質としてのＬｉＮｉ５／１０Ｃｏ２／１０Ｍｎ３／１０Ｏ２を６７部、第２正極活物質として表面を炭素材料で被覆したＬｉＦｅＰＯ４を２７部、導電助剤として平均粒子径（Ｄ５０）０．０５〜０．１μｍのアセチレンブラック（ＡＢ）を３部、結着剤としてポリフッ化ビニリデン（ＰＶＤＦ）を３部、溶剤としてＮＭＰを全量で約５４部混合し、分散液とした。混合は、プラネタリーミキサーを用いて実施した。分散液中の第１正極活物質と第２正極活物質との合計質量を１００％としたときに、第１正極活物質の質量比は７１％であり、第２正極活物質の質量比は２９％である。 LiFePO 4 with 67 parts of LiNi 5/10 Co 2/10 Mn 3/10 O 2 as the first positive electrode active material and a surface coated with a carbon material as the second positive electrode active material using a planetary stirring and deaerator 27 parts, 3 parts of acetylene black (AB) having an average particle size (D50) of 0.05 to 0.1 μm as a conductive additive, 3 parts of polyvinylidene fluoride (PVDF) as a binder, and the total amount of NMP as a solvent About 54 parts were mixed to prepare a dispersion. Mixing was performed using a planetary mixer. When the total mass of the first positive electrode active material and the second positive electrode active material in the dispersion is 100%, the mass ratio of the first positive electrode active material is 71%, and the mass ratio of the second positive electrode active material is 29%.
ｂ）工程
集電体として厚み２０μｍのアルミニウム箔を準備した。該アルミニウム箔の表面に、ａ）工程で製造した分散液をのせ、ドクターブレードを用いて該分散液が膜状になるように塗布した。分散液を塗布したアルミニウム箔を８０℃で２０分間乾燥することで、ＮＭＰを揮発により除去し、アルミニウム箔表面に正極活物質層を形成させた。
b) Step An aluminum foil having a thickness of 20 μm was prepared as a current collector. The dispersion produced in step a) was placed on the surface of the aluminum foil, and applied using a doctor blade so that the dispersion became a film. The aluminum foil coated with the dispersion was dried at 80 ° C. for 20 minutes, whereby NMP was removed by volatilization, and a positive electrode active material layer was formed on the aluminum foil surface.
ｃ）工程
圧縮装置として、ロールプレス機（大野ロール株式会社）を用いた。圧縮装置にｂ）工程の正極活物質層が形成されたアルミニウム箔を配置した。圧縮装置を起動させ、正極活物質層を圧縮した。得られた正極を１２０℃で６時間、真空乾燥機で加熱し、所定の形状（４０ｍｍ×８０ｍｍの矩形状）に切り取り、実施例１の正極とした。
c) Process A roll press machine (Ono Roll Co., Ltd.) was used as the compression device. The aluminum foil in which the positive electrode active material layer of b) process was formed was arrange | positioned at the compression apparatus. The compression apparatus was started and the positive electrode active material layer was compressed. The obtained positive electrode was heated with a vacuum dryer at 120 ° C. for 6 hours, cut into a predetermined shape (40 mm × 80 mm rectangular shape), and used as the positive electrode of Example 1.
図２は、正極の断面を示す説明図である。この図２は、ＳＥＭ断面写真に基づいて描かれた図である。図２に示すように、第１正極活物質としてのＬｉＮｉ５／１０Ｃｏ２／１０Ｍｎ３／１０Ｏ２は、一次粒子が凝集して二次粒子を形成していた。断面観察時におけるＬｉＮｉ５／１０Ｃｏ２／１０Ｍｎ３／１０Ｏ２の二次粒子の平均粒径Ｌ３は６μｍであった。第２正極活物質として表面を炭素材料で被覆したＬｉＦｅＰＯ４は、断面観察時において、長尺部分の平均長さＬ１が１μｍであり、短幅部分の平均長さＬ２が０．３μｍであって、針形状の粒子であった。第２正極活物質のアスペクト比の平均は、３．３であった。第２正極活物質の全体の約半分はアスペクト比が５以上であり、第２正極活物質のいくつかはアスペクト比が５未満であった。正極のＳＥＭ断面写真では、一方向で切断した断面の平面状態のみが観察され、第２正極活物質の立体的な形状はわからない。一方向で切断した断面で現れた形状のアスペクト比が小さくても、他の方向で切断した断面に現れた形状のアスペクト比が大きい場合もある。また、正極の断面観察では、いくつかの第２正極活物質は、隣合う第１正極活物質の間の隙間に配置されており、第１正極活物質の中心間を通る直線に対して直交する方向に第２正極活物質が配向していた。第２正極活物質の長尺部分の平均長さＬｌと第１正極活物質の二次粒子の平均粒径Ｌ３の比率（Ｌ１／Ｌ３）は０．１７であった。 FIG. 2 is an explanatory view showing a cross section of the positive electrode. FIG. 2 is a drawing drawn based on a SEM cross-sectional photograph. As shown in FIG. 2, LiNi 5/10 Co 2/10 Mn 3/10 O 2 as the first positive electrode active material had primary particles aggregated to form secondary particles. The average particle diameter L3 of the secondary particles of LiNi 5/10 Co 2/10 Mn 3/10 O 2 during cross-sectional observation was 6 μm. LiFePO 4 whose surface is coated with a carbon material as the second positive electrode active material has an average length L1 of the long portion of 1 μm and an average length L2 of the short width portion of 0.3 μm during cross-sectional observation. It was needle-shaped particles. The average aspect ratio of the second positive electrode active material was 3.3. About half of the entire second positive electrode active material had an aspect ratio of 5 or more, and some of the second positive electrode active materials had an aspect ratio of less than 5. In the SEM cross-sectional photograph of the positive electrode, only the planar state of the cross section cut in one direction is observed, and the three-dimensional shape of the second positive electrode active material is not known. Even if the aspect ratio of the shape appearing in the cross section cut in one direction is small, the aspect ratio of the shape appearing in the cross section cut in the other direction may be large. Moreover, in the cross-sectional observation of the positive electrode, some second positive electrode active materials are arranged in the gaps between the adjacent first positive electrode active materials, and are orthogonal to the straight line passing between the centers of the first positive electrode active materials. The second positive electrode active material was oriented in the direction to be. The ratio (L1 / L3) of the average length L1 of the long portion of the second positive electrode active material to the average particle size L3 of the secondary particles of the first positive electrode active material was 0.17.
実施例１の正極を用いて、リチウムイオン二次電池を以下のとおり作製した。 Using the positive electrode of Example 1, a lithium ion secondary battery was produced as follows.
負極は以下のように作製した。負極活物質としてＳｉＯｘ（０．３≦ｘ≦１．６）及び天然黒鉛を用いた。結着剤としてポリアミドイミド（ＰＡＩ）を用いた。導電助剤としてアセチレンブラック（ＡＢ）を用いた。ＳｉＯｘ（０．３≦ｘ≦１．６）：天然黒鉛：ＡＢ：ＰＡＩが質量比で３２：５０：８：１０となるように混合し、ＮＭＰを加えて、スラリー状の負極合材調製液を得た。負極合材調製液を負極集電体としての厚み２０μｍのアルミニウム箔表面に塗布し、次いで、上記実施例１の正極と同様に、乾燥工程及び圧縮工程を経て、負極を得た。 The negative electrode was produced as follows. SiO x (0.3 ≦ x ≦ 1.6) and natural graphite were used as the negative electrode active material. Polyamideimide (PAI) was used as a binder. Acetylene black (AB) was used as a conductive aid. SiO x (0.3 ≦ x ≦ 1.6): natural graphite: AB: PAI is mixed at a mass ratio of 32: 50: 8: 10, and NMP is added to prepare a slurry-like negative electrode mixture. A liquid was obtained. The negative electrode mixture preparation liquid was applied to the surface of an aluminum foil having a thickness of 20 μm as a negative electrode current collector, and then, similarly to the positive electrode of Example 1, the negative electrode was obtained through a drying step and a compression step.
実施例１の正極及び上記負極を用いて、ラミネート型リチウムイオン二次電池を以下のとおり作製した。 Using the positive electrode of Example 1 and the negative electrode, a laminated lithium ion secondary battery was produced as follows.
正極および負極の間に、セパレータとしてポリプロピレン／ポリエチレン／ポリプロピレンの３層構造の樹脂膜からなる矩形状シート（５０×９０ｍｍ、厚さ２５μｍ）を挟装して極板群とした。この極板群を二枚一組のラミネートフィルムで覆い、三辺をシールした後、袋状となったラミネートフィルムに電解液を注入した。電解液としては、フルオロエチレンカーボネート（ＦＥＣ），エチレンカーボネート（ＥＣ）、エチルメチルカーボネート（ＥＭＣ）及びジメチルカーボネート（ＤＭＣ）を体積比４：２６：３０：４０で混合した溶媒にＬｉＰＦ6を１モル／Ｌ、ＬｉＢＯＢを０．０５モル／Ｌとなるよう溶解した溶液を用いた。その後、残りの一辺をシールすることで、四辺が気密にシールされ、極板群および電解液が密閉されたラミネート型リチウムイオン二次電池を得た。なお、正極および負極は外部と電気的に接続可能なタブを備え、このタブの一部はラミネート型リチウムイオン二次電池の外側に延出している。 A rectangular sheet (50 × 90 mm, thickness 25 μm) made of a resin film having a three-layer structure of polypropylene / polyethylene / polypropylene as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film. As an electrolytic solution, 1 mol of LiPF 6 was added to a solvent in which fluoroethylene carbonate (FEC), ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 4: 26: 30: 40. / L, a solution in which LiBOB was dissolved at 0.05 mol / L was used. Thereafter, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. Note that the positive electrode and the negative electrode have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery.
（比較例１）
本比較例１の正極は、球形状の第２正極活物質を用いている他は、実施例１と同様である。本比較例１の正極のＳＥＭ断面観察において、第２正極活物質の長尺部分の平均長さＬ１は２μｍであり、短幅部分の平均長さＬ２は２μｍであり、アスペクト比（Ｌ１／Ｌ２）は１であった。
(Comparative Example 1)
The positive electrode of Comparative Example 1 is the same as Example 1 except that a spherical second positive electrode active material is used. In the SEM cross-sectional observation of the positive electrode of Comparative Example 1, the average length L1 of the long portion of the second positive electrode active material is 2 μm, the average length L2 of the short width portion is 2 μm, and the aspect ratio (L1 / L2 ) Was 1.
本比較例１の正極を用いて、実施例１と同様にリチウムイオン二次電池を作製した。 A lithium ion secondary battery was produced in the same manner as in Example 1 using the positive electrode of Comparative Example 1.
（評価例１）
実施例１、比較例１のリチウムイオン二次電池につき、以下の方法で釘刺し試験を行い、内部短絡時のリチウムイオン二次電池の電圧挙動を測定した。
(Evaluation example 1)
About the lithium ion secondary battery of Example 1 and Comparative Example 1, the nail penetration test was done by the following method, and the voltage behavior of the lithium ion secondary battery at the time of an internal short circuit was measured.
リチウムイオン二次電池に対し、４．５Ｖの電位で安定するまで定電圧充電を行った。充電後のリチウムイオン二次電池（放電容量は３．６Ａｈ程度と見込まれる。）を、径２０ｍｍの孔を有する拘束板上に配置した。上部に釘が取り付けられたプレス機に拘束板を配置した。釘が拘束板上のリチウムイオン二次電池を貫通して、釘の先端部が拘束板の孔内部に位置するまで、釘を上部から下部に２０ｍｍ／ｓｅｃ．の速度で移動させた。釘貫通後の電池の表面温度を測定した。使用した釘の形状は径８ｍｍ、先端角度６０°であり、釘の材質はＪＩＳ Ｇ ４０５１で規定するＳ４５Ｃであった。図３には、釘刺し試験における電圧プロファイルを示した。同図において、横軸は、試験経過の時間（秒）を示し、縦軸は、電圧（正極と負極との間の電位差）を示した。 The lithium ion secondary battery was charged at a constant voltage until stabilized at a potential of 4.5V. The charged lithium ion secondary battery (the discharge capacity is expected to be about 3.6 Ah) was placed on a constraining plate having a hole with a diameter of 20 mm. A restraint plate was placed on a press machine with a nail attached to the top. Until the nail penetrates the lithium ion secondary battery on the restraining plate and the tip of the nail is located inside the hole of the restraining plate, the nail is 20 mm / sec. Moved at a speed of. The surface temperature of the battery after penetrating the nail was measured. The shape of the nail used was 8 mm in diameter and the tip angle was 60 °, and the material of the nail was S45C defined by JIS G 4051. FIG. 3 shows a voltage profile in the nail penetration test. In the figure, the horizontal axis represents the time (seconds) of the test elapsed, and the vertical axis represents the voltage (potential difference between the positive electrode and the negative electrode).
図３に示すように、実施例１の電池の電圧は、電池釘刺しにより、４．５Ｖから３．８Ｖまで瞬時に降下した。比較例１の電池の電圧は、４．５Ｖから３．４Ｖまで瞬時に降下した。実施例１の電池は、比較例１の電池よりも、釘刺し試験時の電圧降下が少なかった。実施例１及び比較例１の電池のいずれも、電圧降下後は、電圧が４Ｖまで復帰した。 実施例１の電池のように針形状の第２正極活物質を用いた電池は、球形状の第２正極活物質を用いたとき（比較例１）よりも、短絡時の電圧降下が少なかった。アスペクト比が１．５以上の第２正極活物質を用いた正極を備えた電池は、電圧降下が少なく、発熱量も少なくなることがわかった。 As shown in FIG. 3, the voltage of the battery of Example 1 dropped instantaneously from 4.5V to 3.8V by battery nail penetration. The voltage of the battery of Comparative Example 1 dropped instantaneously from 4.5V to 3.4V. The battery of Example 1 had less voltage drop during the nail penetration test than the battery of Comparative Example 1. In both the batteries of Example 1 and Comparative Example 1, the voltage returned to 4 V after the voltage drop. The battery using the needle-shaped second positive electrode active material like the battery of Example 1 had less voltage drop at the time of short circuit than when the spherical second positive electrode active material was used (Comparative Example 1). . It was found that the battery including the positive electrode using the second positive electrode active material having an aspect ratio of 1.5 or more has a small voltage drop and a small amount of heat generation.
（比較例２）
本比較例２の正極では、正極活物質のすべてが、第１正極活物質としてのＬｉＮｉ５／１０Ｃｏ２／１０Ｍｎ３／１０Ｏ２からなり、第２正極活物質は含んでいない。
(Comparative Example 2)
In the positive electrode of Comparative Example 2, all of the positive electrode active material is made of LiNi 5/10 Co 2/10 Mn 3/10 O 2 as the first positive electrode active material, and does not contain the second positive electrode active material.
比較例２の正極を用いて、実施例１のリチウムイオン二次電池と同様にリチウムイオン二次電池を作製した。このリチウムイオン二次電池について評価例１と同様の手法で釘刺し試験を行った。釘刺し直後に電池の電圧がＯ（ゼロ）に降下し、その後電圧は復帰しなかった。 Using the positive electrode of Comparative Example 2, a lithium ion secondary battery was fabricated in the same manner as the lithium ion secondary battery of Example 1. The lithium ion secondary battery was subjected to a nail penetration test in the same manner as in Evaluation Example 1. Immediately after nail penetration, the voltage of the battery dropped to O (zero), and then the voltage did not return.
Claims (5)
前記第２正極活物質の長尺部分の平均長さをＬ１とし、前記第２正極活物質の短幅部分の平均長さをＬ２としたときのＬ１／Ｌ２の比率をアスペクト比とした場合、前記アスペクト比は３以上であり、
前記第１正極活物質は、一般式：Ｌｉ ａ Ｎｉ ｂ Ｃｏ ｃ Ｍｎ ｄ Ｄ ｅ Ｏ ｆ （０．２≦ａ≦１．７、ｂ＋ｃ＋ｄ＋ｅ＝１、０＜ｂ＜１、０＜ｃ＜１、０＜ｄ＜１、０≦ｅ＜１、ＤはＬｉ、Ｆｅ、Ｃｒ、Ｃｕ、Ｚｎ、Ｃａ、Ｍｇ、Ｚｒ、Ｓ、Ｓｉ、Ｎａ、Ｋ、Ａｌから選ばれる少なくとも１の元素、１．７≦ｆ≦２．１）で表される化合物であり、
前記第２正極活物質は、一般式：ＬｉＭ ｈ ＰＯ ４ （ＭはＭｎ，Ｆｅ，Ｃｏ，Ｎｉ，Ｃｕ，Ｍｇ，Ｚｎ，Ｖ，Ｃａ，Ｓｒ，Ｂａ，Ｔｉ，Ａｌ，Ｓｉ，Ｂ，Ｔｅ及びＭｏから選ばれる少なくとも１の元素、０＜ｈ＜２）で表される材料であり、
前記第２正極活物質の前記長尺部分の平均長さＬ１は、１μｍ以上であり、
前記第１正極活物質は、二次粒子を形成してなり、
前記第１正極活物質の二次粒子の平均粒径をＬ３としたときに、前記第１正極活物質の二次粒子の平均粒径Ｌ３に対する前記第２正極活物質の前記長尺部分の平均長さＬ１の比率（Ｌ１／Ｌ３）は０．１５以上１０以下であり、
前記第１正極活物質と前記第２正極活物質との合計質量を１００質量％としたときに、前記第２正極活物質の配合比は、２４．５質量％を超えて多く且つ３５質量％以下であり、
前記第２正極活物質は、前記第１正極活物質の間に分散していることを特徴とする非水系二次電池用正極。 A positive electrode for a non-aqueous secondary battery comprising a first positive electrode active material and a second positive electrode active material having a charge / discharge potential lower than that of the first positive electrode active material,
When the average length of the long portion of the second positive electrode active material is L1, and the ratio of L1 / L2 is L2 when the average length of the short width portion of the second positive electrode active material is L2, The aspect ratio is 3 or more ;
The first positive electrode active material has the general formula: Li a Ni b Co c Mn d D e O f (0.2 ≦ a ≦ 1.7, b + c + d + e = 1,0 <b <1,0 <c <1, 0 <d <1, 0 ≦ e <1, D is at least one element selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K, Al, 1.7 ≦ f ≦ 2.1),
The second positive electrode active material has a general formula: LiM h PO 4 (M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, Te and It is a material represented by at least one element selected from Mo, 0 <h <2),
The average length L1 of the long portion of the second positive electrode active material is 1 μm or more,
The first positive electrode active material is formed with secondary particles,
When the average particle size of the secondary particles of the first positive electrode active material is L3, the average of the long portions of the second positive electrode active material with respect to the average particle size L3 of the secondary particles of the first positive electrode active material The ratio of the length L1 (L1 / L3) is 0.15 or more and 10 or less,
When the total mass of the first positive electrode active material and the second positive electrode active material is 100% by mass, the compounding ratio of the second positive electrode active material is more than 24.5% by mass and 35% by mass. And
The positive electrode for a non-aqueous secondary battery, wherein the second positive electrode active material is dispersed between the first positive electrode active materials.
前記第２正極活物質の前記長尺部分の平均長さＬ１は、１μｍ以上１０μｍ以下であり、
前記（Ｌ１／Ｌ３）は０．１７以上１０以下である請求項１又は２に記載の非水系二次電池用正極。 The aspect ratio is 3.3 or more;
The average length L1 of the long portion of the second positive electrode active material is 1 μm or more and 10 μm or less,
The positive electrode for a non-aqueous secondary battery according to claim 1, wherein the (L1 / L3) is 0.17 or more and 10 or less .
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