JP2004327330A - Electrode material for nonaqueous electrolyte secondary battery, manufacturing method of same, and nonaqueous electrolyte secondary battery using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with an excellent charging/discharging property, an electrode material for realizing the above secondary battery, and a manufacturing method of the electrode material for the nonaqueous electrolyte secondary battery. <P>SOLUTION: The electrode material for the nonaqueous electrolyte secondary battery is to be a porous material which can store and release Li reversibly, and the nonaqueous electrolyte secondary battery contains the above material as a negative electrode activator. The manufacturing method of the nonaqueous electrolyte secondary battery comprises (i) a process of forming a thin film (particles) of a material containing Si, and (ii) a process of forming a porous thin film (particles) by forming fine holes on the thin film (particles) through a positive electrode oxidation method. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０１１０】
【表２】

【０１１１】
表１および表２に示すように、空隙率が０％である（即ち、細孔が形成されていない）サンプル１−０を活物質として用いた二次電池に比べて、多孔質の電極材料であるサンプル１−１〜１−１７および２−１〜２−１６を活物質として用いた二次電池では、容量維持率が向上した。多孔質の電極材料を活物質として含むことによって、充放電サイクル特性により優れる二次電池が得られることがわかった。
【０１１２】
また、空隙率と容量維持率との関係を見てみると、電極材料の空隙率が４０％〜８５％の範囲において、二次電池の容量維持率がより向上した。また、なかでも、電極材料の空隙率が５０％〜８０％の範囲に、特に、６０％〜８０％の範囲において、二次電池の容量維持率がさらに改善する結果となった。
【０１１３】
平均空間直径と容量維持率との関係を見てみると、空隙率との関係にもよるが、平均空間直径が３０ｎｍ以下において、二次電池の容量維持率がより向上した。また、なかでも、平均空間直径が１０ｎｍ以下において、二次電池の容量維持率がさらに改善する結果となった。
【０１１４】
（実施例２）
実施例２では、陽極酸化法を用いて多孔質かつ薄膜状の電極材料を作製し、二次電池にした場合の充放電サイクル特性を評価した。
【０１１５】
実施例２における電極材料の作製方法を示す。
【０１１６】
最初に、Ｓｉからなる薄膜をエピタキシー法（原子層エピタキシー法）により作製した。成膜装置には、日本真空（株）製の超高真空装置を用い、圧力を１０^−８Ｐａ以下に保持した状態で、厚さ１００μｍの銅箔上にＳｉを含む材料の薄膜を形成した。原材料のガスには、Ｓｉ_２Ｈ_６を用いた。このとき、エピタキシー法を用いた一般的なＳｉ薄膜の成膜方法に準じて成膜温度を３５０℃とし、成膜速度を約０．１ｎｍ／ｓｅｃとした。また、得られた薄膜の厚さが、それぞれ約５μｍとなるように成膜時間を制御した。なお、本実施例において成膜温度とは、基板である銅箔の温度である。また、成膜速度は、得られた薄膜の膜厚と薄膜形成にかかった時間とから算出した平均の成膜速度である。
【０１１７】
次に、このようにして得た薄膜に対して、陽極酸化を行い、多孔質かつ薄膜状の電極材料を作製した。陽極酸化は以下のように行った。
【０１１８】
まず、薄膜を銅箔上に形成したまま、ＨＦとエタノールとの混合溶液（重量比１：１）中に漬けた。次に、電流密度を４ｍＡ／ｃｍ^２〜９２ｍＡ／ｃｍ^２の範囲で変化させて陽極酸化を行った。このとき、銅箔を陽極とし、Ｐｔメッシュを陰極とした。その後、銅箔と薄膜とを分離することによって、多孔質かつ薄膜状の電極材料を得ることができた。なお、Ｓｉの溶解量は、電気化学的に、電気量（電流×時間）に比例すると考えられる。
【０１１９】
実施例２では、形成時間を５分間としたサンプル（電流密度が異なるサンプル３−１〜３−８の８種類）と、３０分間としたサンプル（電流密度が異なるサンプル４−１〜４−９の９種類）との２系統のサンプルを作製した。また、エピタキシー法による成膜のみを行った（陽極酸化は行わない）サンプルを比較例として１種類（サンプル３−０）作製した。
【０１２０】
このようにして作製したサンプルに対し、実施例１と同様に、窒素ガス吸着法を用いて各サンプルの平均空間直径と空隙率とを測定した。
【０１２１】
図７および図８に、陽極酸化時における電流密度と、各サンプルの平均空間直径および空隙率との関係を示す。図７および図８に示すように、同じ電流密度であっても、形成時間によって、得られた電極材料の平均空間直径および空隙率は異なる結果となった。形成時間が長いほど、これらの値は大きくなる傾向にあった。また、形成時間が５分程度では、電流密度によらず、平均空間直径が１０ｎｍ以下の電極材料を得ることができた。一方、形成時間が３０分程度になると、低い電流密度の場合でも、平均空間直径がより大きい細孔が形成される傾向にあった。さらに、平均空間直径が１０ｎｍ以上になると、平均空間直径が増大する結果となった。
【０１２２】
作製した各サンプルに対して平均空間直径および空隙率の測定を行った後、上記各サンプルを用いて二次電池を作製し、実施例１と同様に、二次電池の充放電サイクル特性（容量維持率）の評価を行った。ただし、薄膜状の電極材料は、銅箔から分離した後に粉砕し、粒子状の電極材料とした。
【０１２３】
表３および表４に、各サンプルの平均空間直径および空隙率と、各サンプルを用いた二次電池の容量維持率を示す。
【０１２４】
【表３】

【０１２５】
【表４】

【０１２６】
表３および表４に示すように、空隙率が０％である（即ち、細孔が形成されていない）サンプル３−０を活物質として用いた二次電池に比べて、多孔質の電極材料であるサンプル３−１〜３−８および４−１〜４−９を活物質として用いた二次電池の方が、容量維持率が向上した。多孔質の電極材料を活物質として含むことによって、充放電サイクル特性により優れる二次電池が得られることがわかった。
【０１２７】
また、空隙率と容量維持率との関係を見てみると、電極材料の空隙率が４０％〜８５％の範囲において、二次電池の容量維持率がより向上した。また、なかでも、空隙率が５０％〜８０％の範囲、特に、６０％〜８０％の範囲において、さらに二次電池の容量維持率が向上した。
【０１２８】
平均空間直径と容量維持率との関係を見てみると、空隙率との関係にもよるが、平均空間直径が３０ｎｍ以下において、二次電池の容量維持率がより向上した。また、なかでも、平均空間直径が１０ｎｍ以下において、さらに二次電池の容量維持率が向上した。
【０１２９】
ここで、実施例１および実施例２で得られた全データについて、空隙率と容量維持率との関係を図９に、空隙率と平均空間直径との関係を図１０に示す。図９に示すように、電極材料の空隙率が４０％〜８５％の範囲で充放電サイクル特性に優れる二次電池が得られており、好ましくは５０％〜８０％の範囲、より好ましくは６０％〜８０％の範囲において、より充放電サイクル特性に優れる二次電池が得られていることがわかる。また、図９および図１０を比較すると、形成時間が３０分間のサンプルにおいて、平均空間直径が大きくなり過ぎた場合に、二次電池の容量維持率が低下していることがわかる。これは、細孔のサイズが大きくなることによって、電極材料に割れが生じやすくなったからではないかと考えられる。また、平均空間直径の観点から見てみると、同じ空隙率では、平均空間直径が小さいサンプルの方が、容量維持率が大きくなる傾向が見られた。
【０１３０】
【発明の効果】
以上説明したように、本発明によれば、充放電サイクル特性に優れる非水電解質二次電池と、上記二次電池を実現する非水電解質二次電池用電極材料を提供することができる。また、上記非水電解質二次電池用電極材料の製造方法を提供することができる。
【図面の簡単な説明】
【図１】本発明の非水電解質二次電池用電極材料の概念図である。
【図２】本発明の非水電解質二次電池用電極材料の一例を示す模式図である。
【図３】本発明の非水電解質二次電池用電極材料の別の一例を示す模式図である。
【図４】本発明の非水電解質二次電池の一例を示す模式断面図である。
【図５】実施例において測定した、電流密度と平均空間直径との関係を示す図である。
【図６】実施例において測定した、電流密度と空隙率との関係を示す図である。
【図７】実施例において測定した、電流密度と平均空間直径との関係を示す図である。
【図８】実施例において測定した、電流密度と空隙率との関係を示す図である。
【図９】実施例において測定した、空隙率と容量維持率との関係を示す図である。
【図１０】実施例において測定した、空隙率と平均空間直径との関係を示す図である。
【符号の説明】
１ 電極材料
２ マトリクス部
３ 細孔
１１ 正極
１２ 負極
１３ セパレータ
１４ 下部絶縁板
１５ ケース
１６ 上部絶縁板
１７ ガスケット
１８ 封口板
１９ 正極リード
２０ 負極リード[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrode material for a non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery using the same.
[0002]
[Prior art]
At present, carbon materials capable of reversibly occluding and releasing Li are widely used as electrode materials for lithium ion secondary batteries, which are one type of non-aqueous electrolyte secondary batteries. As a lithium ion secondary battery, a secondary battery including the above carbon material as an active material of a negative electrode is generally used. However, the theoretical capacity of graphite, which is an example of the carbon material, is 372 mAh / g, and there is a limit to increasing the capacity of a battery.
[0003]
At present, as an electrode material having a higher capacity than a carbon material such as graphite, a simple metal material or a simple nonmetal material which forms a compound with Li is known. For example, Si, Sn, Zn, etc., each having the formula, Li ₂₂ Si ₅ , Li ₂₂ Sn ₅ , And LiZn. The theoretical capacities of these materials are 4199 mAh / g, 993 mAh / g, and 410 mAh / g, respectively, which are larger than the theoretical capacities of carbon materials such as graphite.
[0004]
In addition, it is composed of a non-ferrous metal silicide composed of a transition element (for example, see Patent Document 1) or an intermetallic compound containing at least one element selected from Group 4B elements, P and Sb, and has a crystal structure of CaF ₂ A compound that is at least one type selected from the group consisting of a ZnS type, a ZnS type and an AlLiSi type (see, for example, Patent Document 2) has been proposed as an electrode material for a non-aqueous electrolyte secondary battery.
[0005]
[Patent Document 1]
JP-A-7-240201
[0006]
[Patent Document 2]
JP-A-9-63651
[0007]
[Problems to be solved by the invention]
However, the above-mentioned electrode material has a higher capacity than a carbon material such as graphite in an initial state, but may be deteriorated during repeated charging and discharging to lower the capacity. Although the cause of the decrease in capacity is not clear, the following reasons are considered. For example, the intermetallic compound described in Patent Document 2 is one kind of alloy, and expands during charging because Li is occluded in the alloy. On the contrary, at the time of discharge, Li is released from the inside of the alloy and contracts. That is, expansion and contraction are repeated for each charge and discharge, and it is considered that the deterioration gradually progresses due to the accumulation of distortion, the progress of miniaturization, and the like. It is considered that the same phenomenon occurs when a simple metal material or a simple nonmetal material is used as the electrode material.
[0008]
Such a phenomenon is considered to be particularly remarkable when the electrode material has a crystal structure. Further, when the electrode material is non-crystalline (for example, amorphous), although accumulation of strain and miniaturization are slightly suppressed, cracks on the order of μm may occur.
[0009]
In the invention described in JP-A-2002-83594, by forming the electrode material on the core material having irregularities, the cracks on the order of μm can be suppressed. In Japanese Patent Application Laid-Open No. 2002-289181, by disposing an undercoat layer between an electrode and a current collector, separation from the current collector due to expansion of the electrode material is avoided, and the above-described crack in the order of μm is prevented. Can be suppressed. However, it is difficult to eliminate the accumulation of strain at the atomic level and the progress of miniaturization by any of the methods, and there is a limit to the continuity of reversibility as a secondary battery.
[0010]
Therefore, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics and an electrode material for a non-aqueous electrolyte secondary battery realizing the secondary battery. It is another object of the present invention to provide a method for producing the electrode material for a non-aqueous electrolyte secondary battery.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, an electrode material for a non-aqueous electrolyte secondary battery of the present invention (hereinafter, also simply referred to as an electrode material) is an electrode material for a non-aqueous electrolyte secondary battery capable of reversibly occluding and releasing Li. And it is porous.
[0012]
In the electrode material for a non-aqueous electrolyte secondary battery of the present invention, the electrode material may include Si.
[0013]
In the electrode material for a non-aqueous electrolyte secondary battery of the present invention, the electrode material may be in the form of particles.
[0014]
In the electrode material for a non-aqueous electrolyte secondary battery of the present invention, the electrode material may be in the form of a thin film.
[0015]
In the electrode material for a non-aqueous electrolyte secondary battery of the present invention, the electrode material may include pores having an average space diameter in a range of 4 nm to 30 nm measured by a nitrogen gas adsorption method.
[0016]
In the electrode material for a non-aqueous electrolyte secondary battery of the present invention, the average space diameter of the pores may be in a range of 4 nm to 10 nm.
[0017]
In the electrode material for a non-aqueous electrolyte secondary battery of the present invention, the porosity of the electrode material measured by a nitrogen gas adsorption method may be in a range of 40% to 85%.
[0018]
In the electrode material for a non-aqueous electrolyte secondary battery of the present invention, the electrode material may be amorphous.
[0019]
Next, a non-aqueous electrolyte secondary battery of the present invention (hereinafter, also simply referred to as a secondary battery) contains any of the above-mentioned electrode materials for a non-aqueous electrolyte secondary battery as an active material of a negative electrode.
[0020]
Next, the method for producing an electrode material for a non-aqueous electrolyte secondary battery of the present invention is a method for producing an electrode material for a non-aqueous electrolyte secondary battery including an active material capable of reversibly occluding and releasing Li,
(I) forming a thin film of a material containing Si;
(Ii) forming a porous thin film by forming pores in the thin film using an anodic oxidation method.
[0021]
In the method for producing an electrode material for a nonaqueous electrolyte secondary battery according to the present invention, in the step (ii), the porous thin film having a porosity of 40% to 85% measured by a nitrogen gas adsorption method is used. It may be formed.
[0022]
Further, the method for producing an electrode material for a non-aqueous electrolyte secondary battery of the present invention is a method for producing an electrode material for a non-aqueous electrolyte secondary battery including an active material capable of reversibly occluding and releasing Li,
(I) a step of forming particles of a material containing Si;
(II) a step of forming porous particles by forming pores in the particles by using an anodizing method.
[0023]
In the method for producing an electrode material for a non-aqueous electrolyte secondary battery according to the present invention, in the step (II), the porous particles having a porosity in a range of 40% to 85% measured by a nitrogen gas adsorption method are used. It may be formed.
[0024]
In the method for producing an electrode material for a nonaqueous electrolyte secondary battery according to the present invention, in the step (ii) or the step (II), the average space diameter measured by a nitrogen gas adsorption method is in a range of 4 nm to 30 nm. Holes may be formed.
[0025]
In the method for producing an electrode material for a nonaqueous electrolyte secondary battery according to the present invention, the average space diameter of the pores may be in a range of 4 nm to 10 nm.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
In the present embodiment, an electrode material for a non-aqueous electrolyte secondary battery of the present invention will be described.
[0027]
The electrode material of the present invention is a non-aqueous electrolyte secondary battery electrode material capable of reversibly inserting and extracting Li, and is porous. With such an electrode material, deterioration of the electrode material due to charge / discharge cycles can be suppressed. In addition, by including such an electrode material as an active material of a negative electrode, a nonaqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0028]
Generally, an electrode used for a secondary battery is porous. If the electrode is porous, the non-aqueous electrolyte can penetrate into the inside of the electrode, so exchange of Li between the active material and the non-aqueous electrolyte that are arranged not only on the surface of the electrode but also inside it Becomes possible. However, in a conventional secondary battery, the entire electrode including a conductive agent and a binder in addition to the active material is merely porous.
[0029]
On the other hand, in the electrode material of the present invention, the electrode material (that is, the active material) itself is porous. FIG. 1 is a conceptual diagram showing the concept of the electrode material of the present invention. The electrode material 1 shown in FIG. 1 is porous and has countless pores 3. The adsorption and release of Li are performed in the matrix portion 2 of the electrode material 1. It is considered that such an electrode material can suppress the expansion within its own elastic limit due to the presence of the pores 3 even when Li is occluded. Therefore, even when the occlusion and release of Li are repeatedly performed, accumulation of strain at the atomic level of the electrode material, progress of miniaturization, cracking on the order of μm, and the like are suppressed, and deterioration of the electrode material due to charge / discharge cycles is suppressed. It is possible to suppress the occurrence of such a problem (when microfabrication or cracks occur, the nascent surface generated in the electrode material reacts irreversibly with Li, and the discharge capacity as an active material may decrease). FIG. 1 is only a conceptual diagram, and the shape of the electrode material 1, the shape of the pores 3 in the electrode material 1, the ratio of the pores 3 in the electrode material 1, and the like are not particularly limited. Specific ranges of the shapes and ratios of the pores 3 will be described later.
[0030]
The electrode material of the present invention may contain Si. As described above, the theoretical capacity of Si is 4199 mAh / g, which is larger than other materials. Further, it can be made of amorphous Si if necessary, and has such properties that it can be relatively easily made porous by an anodic oxidation method described later. Therefore, an electrode material having a higher capacity and less deterioration due to charge / discharge cycles can be obtained. Note that Si may be contained in the form of a Si compound. Examples of the Si compound include silicon carbide (SiC) and SiGe.
[0031]
The shape of the electrode material of the present invention is not particularly limited as long as it can constitute a secondary battery. For example, the electrode material may be particulate. FIG. 2 shows an example of such an electrode material. The electrode material 1 shown in FIG. 2 is particulate and has countless pores 3. The insertion and extraction of Li are performed by the matrix portion 2 of the electrode material 1. If the electrode material is in the form of particles in this way, even during expansion and contraction caused by the occlusion and release of Li, accumulation of strain at the atomic level of the electrode material, progress of miniaturization, cracking on the order of μm, etc. Can be further suppressed. For this reason, it is possible to provide an electrode material in which deterioration due to charge / discharge cycles is further suppressed.
[0032]
When the electrode material is particulate, the specific shape is not particularly limited, and may be, for example, a substantially spherical shape, a substantially ellipsoidal shape, or an irregular shape. Above all, if it is substantially spherical or substantially ellipsoidal, during the expansion and contraction caused by the occlusion and release of Li, the accumulation of strain at the atomic level of the electrode material and the progress of miniaturization, the order of μm Cracking and the like can be further suppressed. For this reason, it is possible to provide an electrode material in which deterioration due to charge / discharge cycles is further suppressed. When the electrode material is in the form of particles, in order to form a secondary battery, for example, similarly to a conventional secondary battery, an electrode may be formed by mixing with a binder or a conductive agent. A secondary battery using the electrode material of the present invention as an active material can be formed.
[0033]
When the electrode material is particulate, the average volume is, for example, 1.6 × 10 ⁶ nm ³ ~ 1.4 × 10 ⁵ μm ³ 1.6 × 10 ⁶ nm ³ ~ 1.6 × 10 ³ μm ³ Is preferable. When the shape of the electrode material is substantially spherical, the average particle size of the particles may be, for example, in the range of 0.1 μm to 45 μm, and preferably in the range of 0.1 μm to 10 μm. According to Hall-Petch's law applicable to substances within the elastic limit, it is considered that the strength of the electrode material can be further increased when the electrode material is in the form of particles smaller than the order of μm.
[0034]
Further, the electrode material of the present invention may be in the form of a thin film. FIG. 3 shows an example of such an electrode material. The electrode material 1 shown in FIG. 3 is in the form of a thin film and has countless pores 3. The insertion and extraction of Li are performed by the matrix portion 2 of the electrode material 1. When the electrode material is in the form of a thin film as described above, a secondary battery using the electrode material of the present invention as an active material can be formed by a method such as forming the electrode material directly on a conductive support material. . Therefore, a secondary battery having excellent charge / discharge cycle characteristics can be more easily obtained.
[0035]
When the electrode material is in the form of a thin film, its thickness may be, for example, in the range of 0.1 μm to 45 μm, and preferably in the range of 0.1 μm to 10 μm.
[0036]
In the examples shown in FIGS. 1 to 3, the shape of the pores 3 is not particularly limited, and for example, the cross section may be a circle, an ellipse, a triangle, a square, a polygon, or the like. The pores 3 may penetrate the electrode material 1 or may not penetrate.
[0037]
In the electrode material of the present invention, the average space diameter of the pores measured by the nitrogen gas adsorption method may be in the range of 4 nm to 30 nm. Especially, the range of 4 nm to 10 nm is preferable. When the average space diameter of the pores is in such a range, during the expansion and contraction caused by the occlusion and release of Li, accumulation of strain at the atomic level of the electrode material, progress of miniaturization, μm order Cracks and the like can be further suppressed. Therefore, by using such an electrode material, it is possible to obtain an electrode material in which deterioration due to charge / discharge cycles is further suppressed.
[0038]
Here, the nitrogen gas adsorption method and the average space diameter will be described. The nitrogen gas adsorption method is a method used for analyzing a sample having pores (a catalyst, an adsorbent, etc.). By performing a nitrogen gas adsorption method on these samples, the specific surface area, pore distribution, and the like of the samples can be measured.
[0039]
In order to determine the average space diameter, the pore distribution of the electrode material may be measured by a nitrogen gas adsorption method. A graph of the pore distribution is obtained in which the abscissa indicates the pore diameter and the ordinate indicates the distribution, and the value of the pore diameter which divides the area obtained by integrating this graph in the horizontal axis direction into exactly two equal parts (so-called , D ₅₀ ) May be the average space diameter. The method for obtaining the pore distribution of the electrode material is not particularly limited, and a general method may be used. Examples of specific measurement conditions will be described later in Examples. In order to determine the average space diameter from the measurement results of the pore distribution, mathematical processing may be performed.
[0040]
In the electrode material of the present invention, the porosity of the electrode material measured by the nitrogen gas adsorption method may be in a range of 40% to 85%. Further, the porosity of the electrode material is preferably in the range of 50% to 80%, more preferably in the range of 60% to 80%. When the porosity of the electrode material is in such a range, even during expansion and contraction caused by occlusion and release of Li, accumulation of strain at the atomic level of the electrode material, progress of miniaturization, and μm order Cracking and the like can be further suppressed. Therefore, by using such an electrode material, it is possible to obtain an electrode material in which deterioration due to charge / discharge cycles is further suppressed.
[0041]
The electrode material of the present invention may be amorphous. At the time of expansion and contraction caused by the occlusion and release of Li, accumulation of distortion at the atomic level of the electrode material, progress of miniaturization, cracking on the order of μm, and the like can be further suppressed. Therefore, by using such an electrode material, it is possible to obtain an electrode material in which deterioration due to charge / discharge cycles is further suppressed. Above all, it may be amorphous containing Si. As described above, since the theoretical capacity of Si is larger than that of other materials, a higher capacity electrode material can be used.
[0042]
The electrode material of the present invention can be manufactured, for example, by the method for manufacturing an electrode material for a nonaqueous electrolyte secondary battery of the present invention described later in Embodiment 2.
[0043]
(Embodiment 2)
In the present embodiment, a method for producing an electrode material for a non-aqueous electrolyte secondary battery of the present invention will be described.
[0044]
The method for producing an electrode material for a non-aqueous electrolyte secondary battery of the present invention is a method for producing an electrode material for a non-aqueous electrolyte secondary battery that can reversibly occlude and release Li,
(I) forming a thin film of a material containing Si;
(Ii) forming a porous thin film by forming pores in the formed thin film using an anodic oxidation method.
[0045]
By adopting such a manufacturing method, an electrode material in which deterioration due to charge / discharge cycles is suppressed can be obtained.
[0046]
In the step (i), a method of forming a thin film of a material containing Si is not particularly limited. For example, a thin film may be formed over a substrate. The method for forming a thin film of a material containing Si on a substrate is not particularly limited, and a generally used thin film growth method (regardless of solid-phase growth, liquid-phase growth, or vapor-phase growth) may be used. Reference example: "Illustrated thin film technology" p1, Baifukan (1999)). For example, there are an epitaxy method, a plasma CVD method, a thermal chemical vapor deposition method, a reactive sputtering method, and a photochemical vapor deposition method. Further, by using these methods, a thin film made of amorphous Si can be formed. When a thin film made of amorphous Si is formed, a porous and amorphous electrode material can be obtained by continuously performing the above-mentioned step (ii).
[0047]
The substrate on which the thin film is formed may be made of, for example, copper, nickel, or the like. The thickness of the substrate is not particularly limited as long as a thin film of a material containing Si can be formed on the substrate. For example, the thickness may be in the range of 10 μm to 200 μm.
[0048]
Raw materials for forming a thin film of a material containing Si are not particularly limited. When a thin film is formed on a substrate, it depends on the film forming method. ₄ (Silane) or Si ₂ H ₆ Etc. may be used.
[0049]
The thickness of the thin film to be formed is not particularly limited, and may be arbitrarily set as needed. For example, it is in the range of 0.1 μm to 45 μm.
[0050]
In the step (ii), a general method may be used for the anodic oxidation method (Reference: Electrochemistry of Silicon, Wiley-VCH, 2002). For example, the thin film formed in the step (i) is placed in a mixed solution of hydrogen fluoride (HF) and an organic solvent (ethanol, dimethylformamide (DMF), acetone, etc.), and current is applied using the thin film as an anode. do it. By applying a current, Si + 2H ₂ O + 4H ⁺ → SiO ₂ + 4HF → SiF ₄ + 2H ₂ The reaction of O and the like proceeds, and countless pores are formed in the thin film. Thus, a porous thin film can be formed.
[0051]
In the production method of the present invention, in the step (ii), a porous thin film having a porosity measured by a nitrogen gas adsorption method in a range of 40% to 85% may be formed. Preferably, a porous thin film having the porosity in the range of 50% to 80% may be formed, and more preferably, a porous thin film having the porosity in the range of 60% to 80%. May be formed. By adopting such a manufacturing method, it is possible to obtain an electrode material in which deterioration due to charge / discharge cycles is further suppressed.
[0052]
In the production method of the present invention, in the step (ii), pores having an average space diameter measured by a nitrogen gas adsorption method in a range of 4 nm to 30 nm may be formed. Preferably, pores having an average space diameter in the range of 4 nm to 10 nm may be formed. By adopting such a manufacturing method, it is possible to obtain an electrode material in which deterioration due to charge / discharge cycles is further suppressed.
[0053]
In the step (ii), in order to control the porosity and the average space diameter, for example, the current value, the reaction time, and the ratio of HF in the mixed solvent in the anodizing method may be controlled. Further, by controlling these parameters, the shape of the pores can be controlled. The specific value of the current is, for example, 0.5 mA / cm in current density with respect to the area of the film surface of the thin film. ² ~ 100mA / cm ² The reaction time is, for example, in a range of 5 min to 30 min, and the ratio of HF is, for example, in a range of 2 wt% to 45 wt%. More specific examples will be described later in Examples.
[0054]
The thin film formed in the step (ii) may be used, for example, as it is for an electrode. A secondary battery having excellent charge / discharge cycle characteristics can be obtained. When used as it is for an electrode, a conductive agent or the like may be applied to the surface as needed. When a thin film is formed on a substrate, the substrate may or may not be separated. For example, if a thin film is formed on a substrate made of a conductive support material, the substrate can be used as an electrode.
[0055]
The thin film formed in the step (ii) may be pulverized into particles, for example. It can be a porous and particulate electrode material. As described above, in the case of forming the particles, the electrodes may be formed by mixing with a binder or a conductive agent as necessary. A secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0056]
Further, the method for producing an electrode material for a non-aqueous electrolyte secondary battery of the present invention is a method for producing an electrode material for a non-aqueous electrolyte secondary battery that can reversibly occlude and release Li,
(I) a step of forming particles of a material containing Si;
(II) a step of forming porous particles by forming pores in the formed particles using an anodizing method.
[0057]
By adopting such a manufacturing method, an electrode material in which deterioration due to charge / discharge cycles is suppressed can be obtained.
[0058]
In the step (I), a method for forming particles of a material containing Si is not particularly limited. For example, a rapid solidification method, a mechanical alloying method (mechanical alloying method), a mechanical milling method, or the like may be used (references on the mechanical alloying method: Encyclopedia of Utilization of Metallic Materials, Industrial Research Association, 870 (1999)). If the rapid solidification method is used alone or in combination with the mechanical alloying method or the like, amorphous Si-containing particles can be obtained, and an electrode material in which deterioration due to charge / discharge cycles is further suppressed can be obtained. The rapid solidification method includes roll spinning, melt dragging, direct casting and rolling, spinning in liquid spinning, spray forming, gas spraying, wet spraying, splat, rapid solidification strip grinding, gas This is a method in which particles are formed by a spray splat method, a melt extraction method, a melt spinning method, a spray forming method, a rotating electrode method or the like, followed by rapid solidification.
[0059]
The raw material for forming the particles of the material containing Si is not particularly limited. For example, a raw material in which necessary constituent elements alone are mixed in a desired composition ratio, an alloy, a solid solution, an intermetallic compound, or the like having a desired composition ratio may be used.
[0060]
The shape and size of the particles to be formed are not particularly limited. For example, the shape may be a substantially spherical shape, a substantially elliptical shape, an irregular shape, or the like. The average volume is, for example, 1.6 × 10 ⁶ nm ³ ~ 1.4 × 10 ⁵ μm ³ 1.6 × 10 ⁶ nm ³ ~ 1.6 × 10 ³ μm ³ Is preferable. When the particles are substantially spherical, the average particle size may be, for example, in the range of 0.1 nm to 45 μm, and preferably in the range of 0.1 μm to 10 μm.
[0061]
In the step (II), a general method may be used for the anodic oxidation method. For example, the particles formed in the step (I) are placed in a mixed solution of hydrogen fluoride (HF) and an organic solvent (ethanol, dimethylformamide (DMF), acetone, etc.), and a current is applied using the particles as an anode. do it. At this time, for example, the particles may be pressed on a metal pellet made of indium (In) or the like and then put into a mixed solution. As the reaction proceeds, countless pores are formed in the particles. Thus, porous particles can be formed.
[0062]
In the anodization method, it is possible to form pores having an average spatial diameter on the order of nm. Since the conventional electrode material does not use an anodizing method (and a method similar thereto) at the time of manufacturing, it is a porous electrode material having pores on the order of nm like the electrode material of the present invention. It is considered not.
[0063]
In the production method of the present invention, in the step (II), porous particles having a porosity measured by a nitrogen gas adsorption method in a range of 40% to 85% may be formed. Preferably, porous particles having the porosity in the range of 50% to 80% may be formed, and more preferably, the porous particles having the porosity in the range of 60% to 80%. May be formed. By adopting such a manufacturing method, it is possible to obtain an electrode material in which deterioration due to charge / discharge cycles is further suppressed.
[0064]
In the production method of the present invention, in the step (II), pores having an average space diameter measured by a nitrogen gas adsorption method in a range of 4 nm to 30 nm may be formed. Preferably, pores having an average space diameter in the range of 4 nm to 10 nm may be formed. By adopting such a manufacturing method, it is possible to obtain an electrode material in which deterioration due to charge / discharge cycles is further suppressed.
[0065]
In the step (II), in order to control the porosity and the average space diameter, for example, in the same manner as in the step (ii), for example, the value of the current density in anodic oxidation, the reaction time, May be controlled by controlling the ratio of HF.
[0066]
The particles formed in the step (II) may be mixed with a binder, a conductive agent, or the like, if necessary, to form an electrode. A secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0067]
(Embodiment 3)
In the present embodiment, a non-aqueous electrolyte secondary battery of the present invention will be described.
[0068]
FIG. 4 is a schematic sectional view showing an example of the secondary battery of the present invention.
[0069]
The secondary battery shown in FIG. 4 can be obtained, for example, as follows. First, a positive electrode 11 and a negative electrode 12, which can occlude and release Li reversibly, are laminated via a separator 13, and the obtained laminate is wound. The wound laminate is placed in a case 5 provided with a lower insulating plate 14 at the bottom, filled entirely with an electrolyte having Li conductivity, and an upper insulating plate 16 is arranged. After that, the gasket 17 may be sealed with a sealing plate 18 provided on the periphery. Positive electrode 11 and negative electrode 12 are electrically connected to external terminals of the secondary battery by positive electrode lead 19 and negative electrode lead 20.
[0070]
At this time, by including the electrode material of the present invention as an active material of the negative electrode 12, a secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0071]
The negative electrode 12 containing the electrode material of the present invention as an active material will be described.
[0072]
The negative electrode 12 can be formed by, for example, applying an electrode mixture including the electrode material, the conductive agent, and the binder of the present invention to the surface of the negative electrode current collector. When the electrode material of the present invention is in the form of a thin film, for example, it may be formed by laminating the electrode material of the present invention on a conductive support material. In this case, a conductive agent or the like may be applied to the surface as needed.
[0073]
The conductive agent used for the negative electrode 12 is not particularly limited as long as the material has electronic conductivity. For example, graphites such as natural graphite (flaky graphite, etc.), artificial graphite, expanded graphite, carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber For example, conductive fibers such as metal fibers, metal powders such as copper, and organic conductive materials such as polyphenylene derivatives may be used. Especially, it is preferable to use artificial graphite, acetylene black, and carbon fiber. These materials may be mixed and used. Further, these materials may be mechanically coated on the surface of the electrode material. The amount of the conductive agent to be added to the negative electrode 12 is not particularly limited, and is, for example, in the range of 1 to 50 parts by weight, preferably 1 to 30 parts by weight, per 100 parts by weight of the electrode material. . Since the electrode material of the present invention has electron conductivity, it can function as a secondary battery without adding a conductive agent.
[0074]
As the binder used for the negative electrode 12, any of a thermoplastic resin and a thermosetting resin may be used as long as the state in which the electrode mixture is bound to the current collector can be maintained. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE), Polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoro Ethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, ethylene-acryl Acid copolymer Na ⁺ Ion crosslinked product, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid copolymer Na ⁺ Ion crosslinked product, ethylene-methyl acrylate copolymer, ethylene-methyl acrylate copolymer Na ⁺ Ion crosslinked product, ethylene-methyl methacrylate copolymer, ethylene-methyl methacrylate copolymer Na ⁺ An ionic cross-linker or the like may be used. These materials may be mixed and used.
[0075]
The current collector used for the negative electrode 12 is a material having electron conductivity, and is not particularly limited as long as it does not cause a chemical change in the secondary battery. For example, stainless steel, nickel, copper, titanium, carbon, a conductive resin, or copper or stainless steel surface-treated with carbon, nickel, or titanium may be used. Among them, copper and copper alloy are preferred. In addition, unevenness may be provided on the surface of the current collector by a surface treatment or the like. The shape of the current collector may be, for example, a foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foam, a fiber group molded body, or the like. The thickness of the current collector is not particularly limited, and is, for example, in a range of about 1 μm to 500 μm. These materials may be used as the support when the electrode material is in the form of a thin film (that is, the support can also serve as a current collector).
[0076]
A known general method may be used for a method for producing an electrode mixture including an electrode material, a conductive agent, a binder, and the like, and a method for applying the produced electrode mixture to a current collector.
[0077]
Next, the positive electrode 11 will be described.
[0078]
The positive electrode 11 can be formed, for example, by applying an electrode mixture containing a positive electrode active material capable of reversibly occluding and releasing Li, a conductive agent, a binder, and the like to the surface of the positive electrode current collector.
[0079]
The positive electrode active material used for the positive electrode 11 may be, for example, a metal oxide containing Li. The metal oxide containing Li is, for example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ A metal oxide represented by the following formula may be used. However, in the above formula, x is a value adjusted in the range of 0 <x ≦ 1 for example. The value of x is a value that increases or decreases due to charging and discharging of the secondary battery.
[0080]
The positive electrode active material used for the positive electrode 11 may be a chalcogenide of a transition metal, a vanadium oxide and a lithium compound thereof, a niobium oxide and a lithium compound thereof, or a conjugated polymer composed of an organic conductive material, in addition to the above metal oxides. And a chevrel phase compound. Further, a plurality of positive electrode active materials may be mixed and used. The average particle size when the positive electrode active material is in the form of particles is not particularly limited, and is, for example, in the range of 1 μm to 30 μm.
[0081]
The conductive agent used for the positive electrode 11 is not particularly limited as long as it is a material having electron conductivity and does not cause a chemical change in a potential region that the positive electrode active material can take. For example, graphite such as natural graphite (flaky graphite, etc.), artificial graphite, etc., carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and conductive materials such as carbon fiber and metal fiber Conductive fibers, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and organic conductive materials such as polyphenylene derivatives. It may be used. Especially, it is preferable to use artificial graphite and acetylene black. These materials may be mixed and used. The amount of the conductive agent to be added to the positive electrode 11 is not particularly limited, and is, for example, in a range of 1 part by weight to 50 parts by weight, and in a range of 1 part by weight to 30 parts by weight based on 100 parts by weight of the positive electrode active material. preferable.
[0082]
As the binder used for the positive electrode 11, for example, the same resin as the binder used for the above-described negative electrode may be used.
[0083]
The current collector used for the positive electrode 11 is not particularly limited as long as it is a material having electron conductivity and a material that does not cause a chemical change in a potential region that the positive electrode active material can take. For example, stainless steel, aluminum, titanium, carbon, a conductive resin, or stainless steel surface-treated with carbon or titanium may be used. Among them, aluminum and aluminum alloy are preferable. In addition, unevenness may be provided on the surface of the current collector by a surface treatment or the like. The shape and thickness of the current collector may be the same as those of the current collector used for the negative electrode 12.
[0084]
A known general method may be used for a method for manufacturing an electrode mixture including a positive electrode active material, a conductive agent, a binder, and the like, and a method for applying the manufactured electrode mixture to a current collector.
[0085]
Next, the electrolyte and the separator 13 used in the secondary battery of the present invention will be described.
[0086]
The electrolyte is not particularly limited as long as it has Li conductivity. For example, a non-aqueous electrolyte composed of a non-aqueous solvent and a lithium salt dissolved in the solvent may be used. In this case, the non-aqueous solvent is not particularly limited, and for example, ethylene carbonate, ethyl methyl carbonate, or the like may be used. The lithium salt is not particularly limited as long as it can be dissolved in the above non-aqueous solvent. ₆ May be used. The amount of the lithium salt dissolved in the non-aqueous solvent is not particularly limited, and is, for example, in the range of 0.2 mol / l to 2 mol / l, and preferably in the range of 0.5 mol / l to 1.5 mol / l. Note that the amount of the electrolyte added to the secondary battery may be arbitrarily set depending on the amounts of the positive electrode active material and the negative electrode active material and the size of the secondary battery.
[0087]
The separator 13 is not particularly limited as long as it has a high Li permeability, is not subject to corrosion or the like inside the battery, and has an electrical insulating thin film having a certain mechanical strength. For example, a microporous thin film having the above characteristics and generally used for a nonaqueous electrolyte secondary battery may be used. Specifically, for example, a sheet, nonwoven fabric, woven fabric, or the like made of an olefin-based polymer or glass fiber containing at least one resin selected from polypropylene and polyethylene may be used. When the battery reaches a certain temperature or higher due to a short circuit or the like, a separator having a function of increasing electric resistance by closing holes may be used.
[0088]
The thickness of the separator 13 is, for example, in a range of 10 μm to 300 μm. When the separator 13 is a microporous thin film, the average pore size is preferably in a range where the positive electrode and the negative electrode active material detached from the electrode, the binder, the conductive agent, and the like do not pass, for example, 0.01 μm １1 μm. Further, the average porosity of the separator 13 may be set according to the electrical insulating property and Li permeability of the material forming the separator 13, the thickness of the separator, and the like. For example, the range is 30 vol% to 80 vol%.
[0089]
Further, as the secondary battery of the present invention, in addition to the secondary battery having the structure shown in FIG. 4, a battery obtained by absorbing and holding a non-aqueous electrolyte comprising a non-aqueous solvent and a lithium salt in a polymer material is used as a positive electrode mixture. And a secondary battery having a structure in which a porous separator made of the above polymer material is integrated with a positive electrode and a negative electrode by being included in a negative electrode mixture. As the polymer material in this case, any material may be used as long as it has electrical insulation properties and can absorb and hold the non-aqueous electrolyte. For example, a copolymer of vinylidene fluoride and hexafluoropropylene may be used.
[0090]
The non-aqueous electrolyte secondary battery in the present invention is not particularly limited to a cylindrical type as shown in FIG. For example, it may be a coin type, a button type, a sheet type, a laminated type, a flat type, a square type, or a large type used for an electric vehicle or the like. Any shape can be used.
[0091]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples.
[0092]
(Example 1)
In Example 1, a porous and particulate electrode material was produced by using an anodic oxidation method, and charge / discharge cycle characteristics in the case of a secondary battery were evaluated.
[0093]
A method for manufacturing an electrode material in Example 1 will be described.
[0094]
First, particles made of Si were produced by a mechanical alloying method. Si ingot (coarse powder) as a raw material was put in a planetary ball mill container, and mechanical alloying was performed under the conditions of a rotation speed of 2800 rpm and a synthesis time of 20 hours. Thereafter, the obtained powder was classified by a sieve to obtain substantially spherical particles having an average particle size of 45 μm or less.
[0095]
Next, the particles thus obtained were subjected to anodic oxidation to produce a porous and particulate electrode material. Anodization was performed as follows.
[0096]
First, the particles were pressed on a pellet made of In and immersed in a mixed solution of HF and ethanol (weight ratio 1: 1). Next, the current density was set to 0.5 mA / cm. ² ~ 45mA / cm ² The anodic oxidation was performed in the range described above. At this time, the pellet was used as an anode and the Pt mesh was used as a cathode. Thereafter, by separating the pellets and the particles, a porous and particulate electrode material could be obtained. The amount of dissolved Si is considered to be electrochemically proportional to the amount of electricity (current × time).
[0097]
In Example 1, a sample in which the anodizing time (formation time) was 5 minutes (17 types of samples 1-1 to 1-17 having different current densities) and a sample in which 30 minutes were used (Sample 2 having different current densities) -1 to 2-16). In addition, one type (sample 1-0) of a sample subjected to only mechanical alloying (no anodic oxidation) was prepared as a comparative example.
[0098]
The average space diameter and the porosity of each sample were measured using the nitrogen gas adsorption method for the samples thus manufactured. The nitrogen gas adsorption method uses ASAP2010 (manufactured by Shimadzu Corporation, manufactured by Micromeritex Co., Ltd.), and the measurement conditions were as follows: pre-drying (degassing conditions) in vacuum, 130 ° C., 2 hours, sample amount 0.1 g, adsorption The gas went as nitrogen.
[0099]
5 and 6 show the relationship between the current density during anodization and the average space diameter and porosity of each sample. Note that “5 minutes” and “30 minutes” in FIGS. 5 and 6 indicate the formation time. The same applies to the following drawings.
[0100]
As shown in FIG. 5 and FIG. 6, even with the same current density, the average space diameter and porosity of the obtained electrode material differed depending on the formation time. These values tended to increase as the formation time increased. When the formation time was about 5 minutes, an electrode material having an average space diameter of 10 nm or less could be obtained regardless of the current density. On the other hand, when the formation time is about 30 minutes, even when the current density is low, pores having a larger average space diameter tend to be formed. Furthermore, when the average space diameter became 10 nm or more, the result was that the average space diameter sharply increased.
[0101]
After measuring the average space diameter and the porosity of each of the manufactured samples, a secondary battery was manufactured using each of the samples, and the charge / discharge cycle characteristics (capacity maintenance ratio) of the battery were evaluated.
[0102]
A method for manufacturing a secondary battery and an evaluation method will be described.
[0103]
The negative electrode was produced as follows. 20 parts by weight of acetylene black (AB) as a conductive agent and 5 parts by weight of polyvinylidene fluoride resin as a binder were mixed with 75 parts by weight of the prepared particulate electrode material. This mixture was dispersed in N-methyl-2-pyrrolidone to form a slurry, applied to a negative electrode current collector made of copper foil (thickness: 14 μm) at a thickness of 100 μm, dried, and then rolled to obtain a negative electrode.
[0104]
The positive electrode was produced as follows. For 85 parts by weight of lithium cobalt oxide powder, 10 parts by weight of AB as a conductive agent and 5 parts by weight of polyvinylidene fluoride resin as a binder were mixed. This mixture was dispersed in dehydrated N-methylpyrrolidinone to form a slurry, which was applied on a positive electrode current collector made of aluminum foil (thickness: 20 μm) at a thickness of 150 μm, dried, and then rolled to obtain a positive electrode.
[0105]
The negative electrode and the positive electrode prepared as described above, a microporous separator made of polyethylene, and LiPF in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio 1: 1) ₆ Was dissolved at a concentration of 1.5 mol / l with a non-aqueous electrolyte to produce a cylindrical secondary battery as shown in FIG. The secondary battery had a diameter of 18 mm and a height of 650 mm.
[0106]
Evaluation of the capacity and charge / discharge cycle characteristics of the secondary battery was performed as follows.
[0107]
A charge / discharge cycle in which the battery was charged at a constant current of 1000 mA in a thermostat at 20 ° C. until the battery voltage reached 4.2 V, and then discharged at a constant current of 1000 mA until the battery voltage reached 2.0 V was repeated. The charge / discharge cycle was performed 100 times. The discharge capacity at the second cycle was defined as the initial discharge capacity of the secondary battery, and the ratio of the discharge capacity at the 100th cycle to the initial discharge capacity was defined as the capacity retention rate of the secondary battery.
[0108]
Tables 1 and 2 show the average space diameter and porosity of each sample, and the capacity retention of the secondary battery using each sample.
[0109]
[Table 1]

[0110]
[Table 2]

[0111]
As shown in Tables 1 and 2, a porous electrode material was used as compared with a secondary battery using Sample 1-0 having an porosity of 0% (that is, no pores formed) as an active material. In the secondary batteries using Samples 1-1 to 1-17 and 2-1 to 2-16 as active materials, the capacity retention ratio was improved. It was found that by including a porous electrode material as an active material, a secondary battery having more excellent charge / discharge cycle characteristics was obtained.
[0112]
Looking at the relationship between the porosity and the capacity retention, the capacity retention of the secondary battery was further improved when the porosity of the electrode material was in the range of 40% to 85%. In particular, when the porosity of the electrode material is in the range of 50% to 80%, and particularly in the range of 60% to 80%, the capacity retention of the secondary battery is further improved.
[0113]
Looking at the relationship between the average space diameter and the capacity retention, the capacity retention of the secondary battery was further improved when the average space diameter was 30 nm or less, depending on the relationship with the porosity. In particular, when the average space diameter was 10 nm or less, the capacity retention of the secondary battery was further improved.
[0114]
(Example 2)
In Example 2, a porous and thin-film electrode material was prepared by using an anodic oxidation method, and the charge / discharge cycle characteristics in the case of a secondary battery were evaluated.
[0115]
A method for manufacturing an electrode material in Example 2 will be described.
[0116]
First, a thin film made of Si was formed by an epitaxy method (atomic layer epitaxy method). An ultra-high vacuum apparatus manufactured by Nihon Vacuum Co., Ltd. was used as the film forming apparatus. ^-8 With the pressure kept at Pa or lower, a thin film of a material containing Si was formed on a copper foil having a thickness of 100 μm. The raw material gas is Si ₂ H ₆ Was used. At this time, the film forming temperature was set to 350 ° C. and the film forming rate was set to about 0.1 nm / sec in accordance with a general Si thin film forming method using an epitaxy method. The film forming time was controlled so that the thickness of each of the obtained thin films was about 5 μm. In this embodiment, the film forming temperature is the temperature of the copper foil as the substrate. The film formation rate is an average film formation rate calculated from the thickness of the obtained thin film and the time required for forming the thin film.
[0117]
Next, the thin film thus obtained was subjected to anodic oxidation to produce a porous and thin-film electrode material. Anodization was performed as follows.
[0118]
First, the thin film was immersed in a mixed solution of HF and ethanol (weight ratio 1: 1) while being formed on the copper foil. Next, the current density was set to 4 mA / cm. ² ~ 92mA / cm ² The anodic oxidation was performed in the range described above. At this time, the copper foil was used as an anode and the Pt mesh was used as a cathode. Then, by separating the copper foil and the thin film, a porous and thin-film electrode material could be obtained. The amount of Si dissolved is considered to be electrochemically proportional to the amount of electricity (current × time).
[0119]
In Example 2, the sample was formed for 5 minutes (eight types of samples 3-1 to 3-8 having different current densities) and the sample was formed for 30 minutes (samples 4-1 to 4-9 having different current densities). 9 types) were prepared. As a comparative example, one type (sample 3-0) of a sample in which only a film was formed by the epitaxy method (no anodic oxidation was performed) was manufactured.
[0120]
The average space diameter and the porosity of each sample were measured using the nitrogen gas adsorption method in the same manner as in Example 1.
[0121]
7 and 8 show the relationship between the current density during anodization and the average space diameter and porosity of each sample. As shown in FIGS. 7 and 8, even with the same current density, the average space diameter and the porosity of the obtained electrode material differed depending on the formation time. These values tended to increase as the formation time increased. When the formation time was about 5 minutes, an electrode material having an average space diameter of 10 nm or less could be obtained regardless of the current density. On the other hand, when the formation time is about 30 minutes, even when the current density is low, pores having a larger average space diameter tend to be formed. Further, when the average space diameter became 10 nm or more, the average space diameter increased.
[0122]
After measuring the average space diameter and the porosity of each of the manufactured samples, a secondary battery was manufactured using each of the samples, and the charge / discharge cycle characteristics (capacity of the secondary battery were measured in the same manner as in Example 1. (Retention rate) was evaluated. However, the thin-film electrode material was pulverized after being separated from the copper foil to obtain a particulate electrode material.
[0123]
Tables 3 and 4 show the average space diameter and porosity of each sample, and the capacity retention rate of the secondary battery using each sample.
[0124]
[Table 3]

[0125]
[Table 4]

[0126]
As shown in Tables 3 and 4, compared to a secondary battery using a sample 3-0 having a porosity of 0% (that is, no pores formed) as an active material, a porous electrode material was used. The secondary batteries using Samples 3-1 to 3-8 and 4-1 to 4-9 as the active materials have improved capacity retention rates. It was found that by including a porous electrode material as an active material, a secondary battery having more excellent charge / discharge cycle characteristics was obtained.
[0127]
Looking at the relationship between the porosity and the capacity retention, the capacity retention of the secondary battery was further improved when the porosity of the electrode material was in the range of 40% to 85%. In particular, when the porosity was in the range of 50% to 80%, particularly in the range of 60% to 80%, the capacity retention of the secondary battery was further improved.
[0128]
Looking at the relationship between the average space diameter and the capacity retention, the capacity retention of the secondary battery was further improved when the average space diameter was 30 nm or less, depending on the relationship with the porosity. In particular, when the average space diameter was 10 nm or less, the capacity retention of the secondary battery was further improved.
[0129]
Here, for all data obtained in Example 1 and Example 2, FIG. 9 shows the relationship between the porosity and the capacity retention ratio, and FIG. 10 shows the relationship between the porosity and the average space diameter. As shown in FIG. 9, a secondary battery having excellent charge / discharge cycle characteristics is obtained when the porosity of the electrode material is in the range of 40% to 85%, preferably in the range of 50% to 80%, more preferably 60%. It can be seen that a secondary battery having more excellent charge / discharge cycle characteristics is obtained in the range of% to 80%. 9 and FIG. 10, it can be seen that in the sample in which the formation time is 30 minutes, when the average space diameter becomes too large, the capacity retention ratio of the secondary battery decreases. This is considered to be because the increase in the size of the pores easily caused cracks in the electrode material. In addition, from the viewpoint of the average space diameter, with the same porosity, a sample having a smaller average space diameter tended to have a larger capacity retention rate.
[0130]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics and an electrode material for a nonaqueous electrolyte secondary battery realizing the above secondary battery. In addition, a method for producing the electrode material for a non-aqueous electrolyte secondary battery can be provided.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of an electrode material for a non-aqueous electrolyte secondary battery of the present invention.
FIG. 2 is a schematic view showing one example of an electrode material for a non-aqueous electrolyte secondary battery of the present invention.
FIG. 3 is a schematic view showing another example of the electrode material for a non-aqueous electrolyte secondary battery of the present invention.
FIG. 4 is a schematic sectional view showing an example of a non-aqueous electrolyte secondary battery of the present invention.
FIG. 5 is a diagram showing a relationship between a current density and an average space diameter measured in an example.
FIG. 6 is a diagram illustrating a relationship between a current density and a porosity measured in an example.
FIG. 7 is a diagram showing a relationship between a current density and an average space diameter measured in an example.
FIG. 8 is a diagram showing the relationship between current density and porosity measured in the examples.
FIG. 9 is a diagram showing the relationship between the porosity and the capacity retention as measured in the examples.
FIG. 10 is a diagram showing the relationship between the porosity and the average space diameter measured in the examples.
[Explanation of symbols]
1 electrode material
2 Matrix section
3 pores
11 Positive electrode
12 Negative electrode
13 Separator
14 Lower insulating plate
15 cases
16 Upper insulating plate
17 Gasket
18 Sealing plate
19 Positive electrode lead
20 Negative electrode lead

Claims (15)

An electrode material for a non-aqueous electrolyte secondary battery capable of reversibly occluding and releasing Li, wherein the electrode material is a porous non-aqueous electrolyte secondary battery. The electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode material contains Si. The electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode material is in the form of particles. The electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode material is a thin film. The electrode material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the electrode material includes pores having an average space diameter measured by a nitrogen gas adsorption method in a range of 4 nm to 30 nm. The electrode material for a non-aqueous electrolyte secondary battery according to claim 5, wherein the average space diameter of the pores is in a range of 4 nm to 10 nm. The electrode material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein a porosity of the electrode material measured by a nitrogen gas adsorption method is in a range of 40% to 85%. The electrode material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein the electrode material is amorphous. A non-aqueous electrolyte secondary battery comprising the electrode material for a non-aqueous electrolyte secondary battery according to claim 1 as a negative electrode active material. A method for producing an electrode material for a non-aqueous electrolyte secondary battery capable of reversibly occluding and releasing Li,
(I) forming a thin film of a material containing Si;
(Ii) a step of forming a porous thin film by forming pores in the thin film using an anodic oxidation method, thereby producing an electrode material for a non-aqueous electrolyte secondary battery. The electrode material for a non-aqueous electrolyte secondary battery according to claim 10, wherein in the step (ii), the porous thin film having a porosity measured by a nitrogen gas adsorption method in a range of 40% to 85% is formed. Manufacturing method. A method for producing an electrode material for a non-aqueous electrolyte secondary battery capable of reversibly occluding and releasing Li,
(I) a step of forming particles of a material containing Si;
(II) a step of forming porous particles by forming pores in the particles by using an anodizing method, thereby producing an electrode material for a non-aqueous electrolyte secondary battery. The electrode material for a non-aqueous electrolyte secondary battery according to claim 12, wherein in the step (II), the porous particles having a porosity measured by a nitrogen gas adsorption method in a range of 40% to 85% are formed. Manufacturing method. The non-aqueous electrolyte secondary battery according to claim 10 or 12, wherein in the step (ii) or (II), pores having an average space diameter measured by a nitrogen gas adsorption method in a range of 4 nm to 30 nm are formed. Method of manufacturing electrode material for use. The method for producing an electrode material for a non-aqueous electrolyte secondary battery according to claim 14, wherein the average space diameter of the pores is in a range of 4 nm to 10 nm.

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