JP2004213905A - Electrode material for nonaqueous electrolyte secondary battery, its manufacturing method, and nonaqueous electrolyte secondary battery using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having an excellent charge-discharge cycle characteristic; to provide an electrode material for a nonaqueous electrolyte secondary battery used for realizing the secondary battery; and to provide its manufacturing method. <P>SOLUTION: The electrode material for the nonaqueous electrolyte secondary battery can reversibly store and release Li, and contains a material containing Si. The spin density of the material measured by an electron spin resonance method is above 1×10<SP>15</SP>cm<SP>-3</SP>. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０１００】
表１に示すように、本実施例では、比較例として４サンプル（サンプルＮｏ．０−１から０−４）、実施例として１５サンプル（サンプルＮｏ．１−１から１−７、２−１から２−７および３−１）を準備した。以下、サンプルＮｏ．０−１から０−４の各サンプルを比較例群、サンプルＮｏ．１−１から１−７の各サンプルをサンプルＡ群、サンプルＮｏ．２−１から２−７の各サンプルをサンプルＢ群、サンプルＮｏ．３−１をサンプルＣ群とする。
【０１０１】
それぞれのサンプル群の作製方法を示す。
【０１０２】
比較例群の各サンプルは、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、Ｓｉ₂Ｈ₆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０．１ｎｍ／ｓｅｃ〜０．４ｎｍ／ｓｅｃの範囲とした。成膜速度は、原材料ガスの流量を０．１Ｌ／ｍｉｎ〜０．８Ｌ／ｍｉｎの範囲で調整することで制御した。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、ガスの流量は０℃、１気圧における標準状態に換算した流量であり、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。
【０１０３】
サンプルＡ群の各サンプルは、比較例群の各サンプルと同様に、エピタキシー法（原子層エピタキシー法）により作製した。比較例群と同様に、成膜装置には、日本真空（株）製の超真空装置を用い、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、同じくＳｉ₂Ｈ₆を用いた。このとき、サンプルＡ群では、比較例群に比べてより低温での成膜を行い、成膜温度を２８０℃〜１８０℃の範囲で変化させた。また、原材料ガスの流量を１．０Ｌ／ｍｉｎ〜２．０Ｌ／ｍｉｎの範囲で調整し、成膜速度を０．５ｎｍ／ｓｅｃ〜１０ｎｍ／ｓｅｃの範囲で制御した。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。
【０１０４】
サンプルＢ群の各サンプルは、プラズマＣＶＤ法により作製した。成膜装置には、日本真空（株）製のプラズマＣＶＤ装置を用い、厚さ１００μｍの銅箔上にＳｉを含む材料の薄膜を形成した。原材料のガスは、ＳｉＨ₄（シラン）およびＨ₂を用いた。ＲＦ励起周波数を１３．５６ＭＨｚ、原材料ガスの流量をそれぞれ１．０Ｌ／ｍｉｎ、全ガス圧を４Ｐａとした。このとき、サンプルＢ群では、成膜温度を表１に示す範囲で制御して成膜を行った。この制御によって、サンプルＢ群の各サンプル間では薄膜中の水素濃度が異なっていると考えられる。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。
【０１０５】
サンプルＣ群のサンプルは、プラズマＣＶＤ法を用いて成膜した後に、光照射を行うことにより作製した。具体的には、サンプルＢ群のサンプル２−６と同等のサンプルに対して、光照射を行うことにより作製した。よって、プラズマＣＶＤの条件は、サンプルＢ群と同一である。光照射の際には、Ｘｅランプを用いて、波長１０００ｎｍ以下の成分を含む白色光を、強度３００ｍＷ／ｃｍ²で３時間照射した。
【０１０６】
以下の表２に、各サンプルにおける動径分布比およびスピン密度の測定結果を示す。
【０１０７】
【表２】

【０１０８】
表２に示すように、比較例群の各サンプルに比べて、サンプルＡ群、Ｂ群、Ｃ群の各サンプルでは、動径分布比およびスピン密度が増加していることがわかる。よって、サンプルＡ群、Ｂ群、Ｃ群の各サンプルでは、作製したＳｉを含む電極材料中に原子オーダーの空隙が増加していると考えられる。また、サンプル２−６とサンプル３−１とを比較すると、光を照射することによって、動径分布比およびスピン密度の双方が増加していることがわかる。これは、Ｓｔａｅｂｌｅｒ−Ｗｒｏｎｓｋｉ効果により、上記電極材料中に含まれるＳｉのダングリングボンド密度が増加したためであると考えられる。
【０１０９】
ここで、表２の結果に基づき、図３に、各サンプルにおける動径分布比とスピン密度との関係を示す。図３に示すように、動径分布比が増加するに伴い、スピン密度も増加する傾向にあることがわかる。
【０１１０】
次に、以下の表３に、各サンプルを用いて作製した二次電池の初期放電容量と容量維持率とを示す。
【０１１１】
【表３】

【０１１２】
表３に示すように、初期放電容量は、比較例、実施例を含め、全てのサンプルでほぼ同様の値となっている。その値は、約２４００〜２４８０ｍＡｈであり、電極材料として黒鉛材料を用いた場合（およそ１８００ｍＡｈ程度）よりも高容量の二次電池とすることができた。
【０１１３】
表３の結果に基づき、図４に、各サンプルのスピン密度と、各サンプルを用いて作製した二次電池の容量維持率との関係を示す。図４に示すように、各サンプルのスピン密度が１×１０¹⁵ｃｍ^-3以上の範囲において、比較例群に比べて、作製した二次電池の容量維持率が上昇していることがわかる。また、各サンプルのスピン密度が１×１０¹⁶ｃｍ^-3以上の範囲において、作製した二次電池の容量維持率がより上昇しており、スピン密度が１×１０¹⁷ｃｍ^-3以上では作製した二次電池の容量維持率が９０％以上となることがわかる。このことから、各サンプルのスピン密度が上昇するに伴い、より充放電サイクル特性に優れる二次電池が得られることがわかる。
【０１１４】
同じく、表３の結果に基づき、図５に、各サンプルの動径分布比と、各サンプルを用いて作製した二次電池の容量維持率との関係を示す。図５に示すように、各サンプルの動径分布比が６以上の範囲において、比較例群に比べて、作製した二次電池の容量維持率が上昇していることがわかる。また、各サンプルの動径分布比が７以上の範囲において、作製した二次電池の容量維持率がより上昇しており、動径分布比が９以上では二次電池の容量維持率は９０％以上となることがわかる。このことから、各サンプルの動径分布比が上昇するに伴い、より充放電サイクル特性に優れる二次電池が得られることがわかる。
【０１１５】
また、図４および図５におけるサンプルＣ群の結果によれば、電極材料に光を照射することによって、作製した二次電池の動径分布比、スピン密度および容量維持率が大幅に上昇していることがわかる（図４および図５中の矢印参照）。よって、光の照射によって、より充放電サイクル特性に優れる二次電池が得られることがわかる。
【０１１６】
次に、図６に、各サンプルにおける成膜速度とスピン密度との関係を示す。エピタキシー法を用いて成膜した比較例群とサンプルＡ群とを比べると、成膜速度が０．５ｎｍ／ｓｅｃ以上の範囲において、スピン密度が増加していることがわかる。また、成膜速度が１．０ｎｍ／ｓｅｃ以上の範囲では、スピン密度はほぼ一定の値になっていることがわかる。よって、エピタキシー法を用いる場合、成膜速度を０．５ｎｍ／ｓｅｃ以上の範囲に上昇させることによって、よりスピン密度の大きい電極材料を得られることがわかる。
【０１１７】
サンプルＢ群について見てみると、プラズマＣＶＤ法ではエピタキシー法とは異なり、単原子層を積層することは困難であるが、成膜速度とスピン密度との関係は、ほぼサンプルＡ群と同じライン上に乗っていることがわかる。よって、プラズマＣＶＤ法においても、成膜速度を上昇させることで、よりスピン密度の大きい電極材料を得られることがわかる。また、サンプルＣ群の結果から、光を照射することによって電極材料のスピン密度が増加することがわかる（図６中の矢印参照）。
【０１１８】
次に、プラズマＣＶＤ法を用いた場合における、成膜温度と、得られた薄膜のスピン密度および得られた薄膜中に含まれる水素濃度との関係を調べた。
【０１１９】
サンプルＢ群と同様の作製方法を用い、成膜温度を２０℃から４００℃の範囲で変化させて、それぞれ厚さ約５μｍの薄膜を作製した。このとき、作製した薄膜の厚さをほぼ同一にするために、成膜時間の制御を行った。その結果を、図７および図８に示す。
【０１２０】
図７および図８によれば、成膜温度が上昇するにつれて、得られた薄膜中に含まれる水素濃度が減少していることがわかる。また、それに伴い、スピン密度も減少していることがわかる。上述したように、電極材料のスピン密度が上昇するほど、より充放電サイクル特性に優れる二次電池が得られると考えられるため、プラズマＣＶＤ法を用いた場合、成膜温度をより低温側（例えば、１００℃以下）にすればよいことがわかる。また、薄膜中の水素濃度が１原子％のときに、スピン密度は約１×１０¹⁶ｃｍ^-3のレベルにあることがわかる。
【０１２１】
【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】結晶性シリコンに対して測定した動径分布関数の一例を示す図である。
【図２】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３】実施例において測定した、各電極材料サンプルにおける動径分布比とスピン密度との関係を示す図である。
【図４】実施例において測定した、各電極材料サンプルにおける成膜速度とスピン密度との関係を示す図である。
【図５】実施例において測定した、成膜温度と薄膜中の水素濃度との関係を示す図である。
【図６】実施例において測定した、成膜温度とスピン密度との関係を示す図である。
【図７】実施例において測定した、各電極材料サンプルにおけるスピン密度と、各電極材料サンプルを用いて作製した二次電池の容量維持率との関係を示す図である。
【図８】実施例において測定した、各電極材料サンプルにおける動径分布比と、各電極材料サンプルを用いて作製した二次電池の容量維持率との関係を示す図である。
【符号の説明】
１ 正極
２ 負極
３ セパレータ
４ 下部絶縁板
５ ケース
６ 上部絶縁板
７ ガスケット
８ 封口板
９ 正極リード
１０ 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]
Conventionally, as an electrode material of a lithium ion secondary battery, which is one type of nonaqueous electrolyte secondary battery, a carbon material capable of reversibly occluding and releasing Li has been widely used. 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 a higher capacity electrode material for nonaqueous electrolyte secondary batteries is required.
[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 can form a compound with Li is known. For example, Si, Sn, Zn, etc., each having the formula, Li _{twenty two} Si _Five , Li _{twenty two} Sn _Five , 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 _Two 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, although the above-mentioned electrode material has a higher capacity than a carbon material such as graphite in an initial state, it may deteriorate during repeated charging and discharging, and the capacity may be reduced. 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 the alloy expands during charging because Li is occluded in the alloy. On the contrary, at the time of discharging, the alloy shrinks because Li is released from the inside of the alloy. That is, it is considered that the alloy repeatedly expands and contracts each time charge and discharge is performed, so that the strain gradually accumulates and the deterioration proceeds due to the progress of miniaturization. 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. However, in the above invention, it is considered difficult to suppress distortion, expansion and contraction at the atomic level due to occlusion and release of Li.
[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, the electrode material for a non-aqueous electrolyte secondary battery of the present invention is an electrode material for a non-aqueous electrolyte secondary battery capable of reversibly occluding and releasing Li (hereinafter, also simply referred to as “electrode material”). ) Comprising a material containing Si, wherein the spin density of the material measured by an electron spin resonance method is 1 × 10 ^Fifteen cm ^-3 That is all.
[0012]
In the above electrode material, the spin density is 1 × 10 ¹⁶ cm ^-3 It may be the above.
[0013]
Further, the electrode material for a non-aqueous electrolyte secondary battery of the present invention is an electrode material for a non-aqueous electrolyte secondary battery capable of reversibly occluding and releasing Li, and includes a material containing Si. Has a radial distribution ratio of 6 or more. Here, the radial distribution ratio refers to a peak area D in a radial distance range of 0.3 nm to 0.5 nm in a radial distribution function obtained by using the X-ray diffraction method for the material. ₁ With the peak area D in the range of the radial distance of 0.2 nm to 0.3 nm. _Two Is the value divided by
[0014]
In the above electrode material, the radial distribution ratio may be 7 or more.
[0015]
In the above electrode material, the material may be hydrogenated amorphous silicon.
[0016]
In the above electrode material, the material may contain hydrogen atoms in a range of 1 atomic% to 50 atomic%.
[0017]
In the above electrode material, the material may include Si having a dangling bond.
[0018]
The non-aqueous electrolyte secondary battery of the present invention (hereinafter, also simply referred to as “secondary battery”) contains any one of the above-mentioned electrode materials for a non-aqueous electrolyte secondary battery as a negative electrode active material.
[0019]
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 on a substrate;
(Ii) irradiating the material with light to increase the spin density of the material measured by an electron spin resonance method;
(Iii) separating the formed thin film from the substrate.
[0020]
In the above manufacturing method, in the step (ii), the spin density of the material may be 1 × 10 ¹⁶ cm ^-3 The number may be increased as described above.
[0021]
In the above-described manufacturing method, the step (i) may be performed by at least one method selected from an epitaxy method and a plasma CVD method.
[0022]
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.
[0023]
The electrode material of the present invention is a non-aqueous electrolyte secondary battery electrode material capable of reversibly occluding and releasing Li, including a material containing Si (silicon), and measured by an electron spin resonance method (ESR). Spin density of material is 1 × 10 ^Fifteen cm ^-3 That is all.
[0024]
The electrode material of the present invention is an electrode material for a non-aqueous electrolyte secondary battery capable of reversibly occluding and releasing Li, including a material containing Si, and having a radial distribution ratio of Si of 6 in the material. It may be the above. The radial distribution ratio will be described later.
[0025]
Specifically, the material containing Si is, for example, crystalline silicon or amorphous silicon into which defects or hydrogen are introduced.
[0026]
With such an electrode material, deterioration due to charge / discharge cycles can be suppressed. In addition, by including such an electrode material as an active material for a negative electrode, a nonaqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0027]
In the above electrode material, the spin density is 1 × 10 ¹⁶ cm ^-3 The spin density may be 1 × 10 ¹⁷ cm ^-3 More preferably. In the above-mentioned electrode material, the radial distribution ratio may be 7 or more, and more preferably, the radial distribution ratio is 9 or more. By using such an electrode material, deterioration due to charge / discharge cycles can be further suppressed. In addition, by including such an electrode material as an active material of a negative electrode, a nonaqueous electrolyte secondary battery having more excellent charge / discharge cycle characteristics can be obtained.
[0028]
Here, the spin density and the radial distribution ratio will be described.
[0029]
The spin density in this specification is a spin density measured by ESR, and its value reflects the number of unpaired electrons in the electrode material. For example, Si contained in the electrode material of the present invention has four bonds per atom. Focusing on a certain Si atom, if all the bonds of this Si atom are bonded to adjacent Si atoms, there is no unpaired electron in the noted Si atom, so that it is not included in the spin density. However, when the Si atom of interest has an unbonded bond (ie, when the Si atom has a dangling bond), for example, because another Si atom is not disposed adjacently, the unbonded Is an unpaired electron, so its number is included in the spin density. Therefore, it can be said that the more voids of the atomic order exist in the electrode material, the larger the value of the spin density obtained by ESR becomes.
[0030]
In addition, the radial distribution ratio in the present specification refers to a radial distribution function J (r) obtained by using an X-ray diffraction method (XRD) with respect to an electrode material, for a radial distance of 0.3 nm to 0.5 nm. Range peak area D ₁ With the peak area D in the range of the radial distance of 0.2 nm to 0.3 nm. _Two (Ie, D ₁ / D _Two ).
[0031]
First, an example of a method of obtaining a radial distribution function J (r) for an electrode material will be described.
[0032]
First, a sample to be subjected to XRD measurement is prepared. The sample may be prepared according to a general XRD measurement technique. Since XRD measurement is usually performed on the Si contained in the electrode material by a reflection method, for example, a powdery electrode is placed in a reflection type XRD holder so that the X-ray reflection surface is flat. What is necessary is just to set a material.
[0033]
Next, XRD measurement is performed on the prepared sample. The range of the measurement may be set, for example, in the range of 10 ° to 140 ° in the scattering angle 2θ. For example, a Mo target may be used as the X-ray source. In this manner, a scattering curve showing the relationship between the scattering angle and the intensity of the scattered X-ray at the scattering angle can be obtained.
[0034]
The scattering curve obtained by the XRD measurement includes coherent scattering reflecting the structural factor of the substance contained in the electrode material. The coherent scattering is calculated from the scattering curve obtained by the measurement, and the structure factor as a wave vector is obtained from the calculated coherent scattering. The method of obtaining the coherent scattering and the structure factor may follow a general calculation method. Finally, when the obtained structure factor is subjected to Fourier transform, a radial distribution function J (r) indicating a two-body correlation between atoms can be obtained. FIG. 1 shows an example of a radial distribution function measured for crystalline silicon.
[0035]
In the radial distribution function shown in FIG. 1, a first peak exists at a position where the radial distance r is about 0.23 nm. This peak substantially corresponds to the closest interatomic distance (first interatomic distance) of crystalline silicon. In addition, peaks are also observed at positions where the radial distance r is about 0.38 nm and about 0.45 nm, and these peaks show the second and third interatomic distances of crystalline silicon, respectively. It is thought that it almost corresponds.
[0036]
Here, a case where all the bonds of Si atoms in the electrode material are bonded to adjacent Si atoms, and a case where a gap of an atomic order partially exists in the electrode material will be considered. Compared to the case where the bonds of all Si atoms are bonded to adjacent Si atoms, in the case where there is a gap on the order of atoms, the distance between adjacent Si atoms becomes closer to the closest interatomic distance (about 0.23 nm). The probability of existence is reduced. Instead, it is considered that the probability that adjacent Si atoms exist at a distance of 0.3 nm or more increases. When this is replaced with the radial distribution function, the peak at the position where the radial distance is about 0.23 nm decreases, and the peaks at the positions where the radial distance is about 0.38 nm and about 0.45 nm increase. That is, in the radial distribution function, the peak area D in the range of 0.2 nm to 0.3 nm ₁ Decrease and the peak area D in the range of 0.3 nm to 0.5 nm _Two Increases. The radial distribution ratio in this specification is D _Two / D ₁ Therefore, it can be said that as the number of atomic-order voids in the electrode material increases, the value of the radial distribution ratio increases.
[0037]
As described above, an electrode material made of a simple metal material, a simple nonmetal material, an intermetallic compound, or the like repeatedly expands and contracts when occluding and releasing Li (that is, during charging and discharging). It is considered that the larger the volume change during expansion and contraction, the more easily the electrode material deteriorates due to accumulation of strain and miniaturization due to particle cracking.
[0038]
When Si is used as an electrode material, regardless of whether it is crystalline silicon or amorphous silicon, the closest interatomic distance is about 0.23 nm. When Si occludes Li, Li having an ionic radius of about 0.1 nm is inserted into the space of about 0.23 nm. Therefore, at the time of charging, in the vicinity of the inserted Li, Si atoms that have been adjacent at an interatomic distance of about 0.23 nm are separated from each other until the interatomic distance becomes 0.3 nm or more. On the contrary, at the time of discharge, Li is released, so that the distance between adjacent Si atoms returns to about 0.23 nm again. It is considered that such a phenomenon causes the electrode material to expand and contract in a macroscopic manner, and particle cracks and the like in a microscopic manner. When particle cracks occur in the electrode material, the nascent surface of the electrode material reacts with Li, and irreversible Li (that is, Li that does not contribute to the electrochemical reaction of the battery) is generated by incorporation of Li as a film on the nascent surface. Increase. When the irreversible Li increases, the discharge capacity of the battery decreases, and the charge / discharge cycle characteristics deteriorate.
[0039]
On the other hand, it is considered that the electrode material of the present invention has a higher percentage of voids in the atomic order in the electrode material than the conventional electrode material. In addition, it is considered that the distance between adjacent Si atoms is already 0.3 nm or more in the vicinity of the void before Li is occluded. Therefore, when Si absorbs Li, expansion can be suppressed more than in the conventional electrode material, for example, Li can be inserted into the gap. That is, it is possible to use an electrode material in which a change in volume due to charge and discharge is suppressed, and deterioration due to charge and discharge cycles can be suppressed. Specific examples of the spin density and the radial distribution ratio in the electrode material of the present invention will be described later in Examples. The electrode material of the present invention can be obtained, for example, by a method for manufacturing an electrode material described later in Embodiment Mode 2 and Examples.
[0040]
In the electrode material of the present invention, the material may be amorphous silicon. Further, the material may be hydrogenated amorphous silicon. In such an electrode material, deterioration due to charge / discharge cycles can be further suppressed. In addition, by including such an electrode material as an active material of a negative electrode, a nonaqueous electrolyte secondary battery having more excellent charge / discharge cycle characteristics can be obtained.
[0041]
If Si in the electrode material is amorphous, the distance between adjacent Si atoms increases stochastically due to crystal defects (lattice defects) and the like. Therefore, it is possible to provide an electrode material in which a change in volume due to charge and discharge is further suppressed. In the case of hydrogenated amorphous silicon, the distance between adjacent Si atoms can be further increased due to the presence of hydrogen. Therefore, it is possible to provide an electrode material in which a change in volume due to charge and discharge is further suppressed.
[0042]
In the electrode material of the present invention, the material may contain hydrogen atoms in a range of 1 atomic% to 50 atomic%. In particular, the material preferably contains hydrogen atoms in the range of 1 to 20 atomic%. Due to the presence of hydrogen, the distance between adjacent Si atoms can be further increased, and in the above range, an electrode material can be obtained in which deterioration due to charge / discharge cycles is further suppressed. If the content of hydrogen atoms is less than 1 atomic%, the effect of increasing the distance between adjacent Si atoms may be small. If the content is 50 atomic% or more, the electron conductivity of the electrode material may be reduced.
[0043]
In the electrode material of the present invention, the material may include Si having a dangling bond. Since Si has a dangling bond, the distance between adjacent Si atoms increases stochastically. Therefore, it is possible to provide an electrode material in which a change in volume due to charge and discharge is further suppressed. Therefore, with such an electrode material, deterioration due to charge / discharge cycles can be further suppressed.
[0044]
The electrode material of the present invention may contain an element other than Si as long as the electrode material does not prevent Li from reversibly occluding and releasing Li. For example, a group V element such as N, P, As, Sb, or Bi may be contained. The ratio of these elements contained in the electrode material, excluding Li, is, for example, 0.1% by mass or less. Further, the electrode material of the present invention may be a Si compound. Examples of the Si compound include silicon carbide (SiC) and SiGe.
[0045]
(Embodiment 2)
In the present embodiment, a method for producing an electrode material for a non-aqueous electrolyte secondary battery according to the present invention will be described.
[0046]
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 on a substrate;
(Ii) irradiating the material with light to increase the spin density of the material measured by an electron spin resonance method;
(Iii) separating the formed thin film from the substrate.
[0047]
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.
[0048]
In the step (i), a method for forming a thin film of a material containing Si on the substrate is not particularly limited. A generally used thin film growth method may be used (Reference example: “Illustrated thin film technology” p1, Baifukan (1999)). For example, an epitaxy method, a plasma CVD method, a thermal chemical vapor deposition method, a reactive sputtering method, a photochemical vapor deposition method, or the like may be used. Silicon "p31, Ohmsha (1993)).
[0049]
Among them, it is preferable to use the epitaxy method and the plasma CVD method. According to the epitaxy method, by changing the film-forming rate (for example, making it larger than the film-forming rate usually used for forming a Si thin film), it is possible to form voids on the order of atoms in the thin film. In addition, it is possible to control the ratio of the voids included in the thin film. Therefore, an electrode material with less deterioration due to charge / discharge cycles can be obtained. According to the plasma CVD method, voids on the order of atoms can be formed in the thin film. For example, an amorphous silicon thin film in which the ratio of lattice defects is controlled can be more easily formed. If necessary, it is also possible to insert atoms other than Si into the thin film. Specific examples using these methods will be described later in Examples.
[0050]
As the substrate, for example, copper, nickel, or the like may be used. 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 substrate may have a thickness in the range of 10 μm to 200 μm.
[0051]
Raw materials for forming a thin film of a material containing Si are not particularly limited as long as the thin film can be formed on a substrate. Although it differs depending on the film forming method, for example, SiH _Four (Silane), Si _Two H ₆ May be used. When a silane gas is used, a thin film of a material containing Si containing a hydrogen atom can be formed, and the proportion of a hydrogen atom in the thin film can be controlled. For example, a thin film of hydrogenated amorphous silicon can be formed.
[0052]
In the step (ii), the light applied to the material is not particularly limited as long as the light contains a component having a wavelength of 1000 nm or less. For example, light irradiation may be performed using sunlight, a Xe lamp, an Hg lamp, a halogen lamp, or the like. Note that the time for irradiating light is not particularly limited. What is necessary is just to set arbitrarily according to the intensity of the light to irradiate.
[0053]
When the light containing a material containing Si is irradiated with the light, a phenomenon occurs in which the physical properties of the material change (light deterioration). This photodegradation phenomenon is called the Staebler-Wronski effect (Reference: Appl. Phys. Lett., P. 292, 31 (1977), DL Staebler and CR Wronski). The photodegradation phenomenon is a phenomenon in which a Si-Si bond or a Si-H bond in a material containing Si is generated by phonon energy released when electrons and holes photoexcited by light irradiation perform nonradiative recombination. This is a phenomenon in which the silicon is cut and a dangling bond is formed in Si. Therefore, in the step (ii), if the material is irradiated with light, a dangling bond is formed in Si in the thin film, so that the distance between adjacent Si atoms increases stochastically (in the thin film, It is considered that voids of the atomic order are formed more, that is, the spin density and the radial distribution ratio of the material increase. Therefore, it is possible to obtain an electrode material in which deterioration due to charge / discharge cycles is further suppressed.
[0054]
In the step (ii), the spin density of the material is set to 1 × 10 ¹⁶ cm ^-3 The number may be increased as described above. It is considered that the spin density of the material is increased by the light irradiation. At this time, the spin density of the material is 1 × 10 ¹⁶ cm ^-3 By irradiating light as described above, it is possible to obtain an electrode material in which deterioration due to charge / discharge cycles is further suppressed.
[0055]
In the method for producing an electrode material of the present invention, the step (i) and the step (ii) may be alternately performed a plurality of times, if necessary, or the step (i) and the step ( Step ii) may be performed simultaneously.
[0056]
The method of separating the formed thin film from the substrate in the step (iii) is not particularly limited. For example, it may be mechanically separated.
[0057]
The separated thin film may be used as it is for a secondary battery, or may be used in a secondary battery after being processed into a powder by pulverization or the like. The shape of the electrode material of the present invention may be any shape as long as it can constitute a secondary battery.
[0058]
(Embodiment 3)
In the present embodiment, a non-aqueous electrolyte secondary battery using the electrode material for a non-aqueous electrolyte secondary battery of the present invention will be described.
[0059]
FIG. 2 is a schematic sectional view showing an example of the secondary battery according to the present invention.
[0060]
The secondary battery shown in FIG. 2 can be obtained, for example, as follows. First, a positive electrode 1 and a negative electrode 2 capable of reversibly inserting and extracting Li are laminated with a separator 3 interposed therebetween, and the obtained laminate is wound. The wound laminate is placed in a case 5 provided with a lower insulating plate 4 at the bottom, filled entirely with an electrolyte having Li conductivity, and an upper insulating plate 6 is arranged. Thereafter, the gasket 7 may be sealed with a sealing plate 8 provided on the periphery. Positive electrode 1 and negative electrode 2 are electrically connected to external terminals of the secondary battery by positive electrode lead 9 and negative electrode lead 10.
[0061]
At this time, by including the electrode material of the present invention as an active material of the negative electrode 2, a secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0062]
The negative electrode 2 containing the electrode material of the present invention as an active material will be described.
[0063]
The negative electrode 2 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.
[0064]
The conductive agent used for the negative electrode 2 is not particularly limited as long as it is a material having electron 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.
[0065]
The amount of the conductive agent added to the negative electrode 2 is not particularly limited. For example, the range is from 1 to 50 parts by weight, preferably from 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 the above conductive agent.
[0066]
As the binder used for the negative electrode 2, 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.
[0067]
Above all, styrene butadiene rubber, polyvinylidene fluoride, ethylene-acrylic acid copolymer, ethylene-acrylic 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 ⁺ Ionic cross-linkers are preferred.
[0068]
The current collector used for the negative electrode 2 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. For example, it is in the range of about 1 μm to 500 μm.
[0069]
As a method for manufacturing an electrode mixture including an electrode material, a conductive agent, a binder, and the like, and a method for applying the manufactured electrode mixture to a current collector, a known general method may be used.
[0070]
Next, the positive electrode 1 will be described.
[0071]
The positive electrode 1 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.
[0072]
As the positive electrode active material used for the positive electrode 1, for example, a metal oxide containing Li may be used. As the metal oxide containing Li, for example, Li _x CoO _Two , Li _x NiO _Two , Li _x MnO _Two 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.
[0073]
Examples of the positive electrode active material used for the positive electrode 1 include, in addition to the above metal oxides, transition metal chalcogenides, vanadium oxides and lithium compounds thereof, niobium oxides and lithium compounds thereof, and conjugated polymers composed of organic conductive materials. 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 particulate form is not particularly limited. For example, the range is 1 μm to 30 μm.
[0074]
The conductive agent used for the positive electrode 1 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, graphites such as natural graphite (such as flake graphite) and artificial graphite, carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, carbon fibers, metal fibers, and the like. Conductive fibers, carbon fluoride, metal powders such as 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 Etc. may be used. Especially, it is preferable to use artificial graphite and acetylene black. These materials may be mixed and used.
[0075]
The amount of the conductive agent to be added to the positive electrode 1 is not particularly limited. For example, the range is 1 to 50 parts by weight, preferably 1 to 30 parts by weight, based on 100 parts by weight of the positive electrode active material.
[0076]
As the binder used for the positive electrode 1, 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, a resin similar to the binder used for the above-described negative electrode may be used.
[0077]
The current collector used for the positive electrode 1 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, 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 2.
[0078]
As a method for preparing an electrode mixture including a positive electrode active material, a conductive agent and a binder, and a method for applying the prepared electrode mixture to a current collector, a known general method may be used.
[0079]
When the positive electrode 1 and the negative electrode 2 are incorporated in a secondary battery, it is preferable that the electrode mixture surface of the positive electrode 1 and the electrode mixture surface of the negative electrode 2 face each other with the separator 3 interposed therebetween.
[0080]
Next, the electrolyte and the separator 3 used in the secondary battery of the present invention will be described.
[0081]
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. For example, ethylene carbonate, ethyl methyl carbonate, or the like may be used. The lithium salt is not particularly limited as long as it dissolves in the non-aqueous solvent. For example, LiPF ₆ May be used. The amount of the lithium salt dissolved in the non-aqueous solvent is not particularly limited. For example, the range is 0.2 mol / l to 2 mol / l, and the range is preferably 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.
[0082]
The separator 3 is not particularly limited as long as it is an electrically insulating thin film having a large Li permeability, not being corroded inside the battery, and 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. 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.
[0083]
The thickness of the separator 3 is, for example, in a range of 10 μm to 300 μm. When the separator 3 is a microporous thin film, the average pore size is preferably in a range in which the positive electrode and negative electrode active materials detached from the electrode, the binder, the conductive agent, and the like do not pass. １1 μm. In addition, the average porosity of the separator 3 may be set according to the electrical insulation property and Li permeability of the material forming the separator 3, the thickness of the separator, and the like. For example, the range is 30 vol% to 80 vol%.
[0084]
As the secondary battery of the present invention, in addition to the secondary battery having the structure shown in FIG. 2, 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.
[0085]
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.
[0086]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.
[0087]
First, a method for evaluating an electrode material in this example will be described. In this example, the spin density and the radial distribution ratio of each manufactured electrode material were measured. Further, a secondary battery as shown in FIG. 2 was prepared using each of the prepared electrode materials, and the capacity and charge / discharge cycle characteristics of the obtained secondary battery were evaluated. The degree of deterioration of the electrode material was evaluated.
[0088]
The spin density of the electrode material was measured by ESR (EMX8-2.7, manufactured by Bruker). For the measurement, a sample in which the electrode material was powdered and sealed in an ampoule was used. A microwave of 9.2 GHz was applied to the sample, and the spin density was measured by sweeping a magnetic field near the spin resonance energy. Further, the g value (split constant) at the time of analysis was 2.0055. The electron spin center of this value is considered to be derived from a dangling bond.
[0089]
The radial distribution ratio of the electrode material was calculated by the following method. First, an XRD measurement was performed on the electrode material to calculate a radial distribution function of the electrode material. Next, mathematical processing was performed on the obtained radial distribution function to determine a radial distribution ratio.
[0090]
The XRD measurement for the electrode material was performed as follows. First, the electrode material was powdered and set in a reflection type XRD sample holder. Next, the sample holder was set in an XRD measuring device (X'PertMPD, manufactured by Philips), and X-rays were applied to the electrode material to measure its reflected XRD, thereby obtaining a scattering curve of the electrode material. At that time, Mo was used as a target as an X-ray source, and X-rays having a wavelength of 0.070930 nm were used. The measurement range of XRD was a range of 10 ° to 140 ° in scattering angle 2θ. Finally, a mathematical process such as Fourier transform was performed on the obtained scattering curve to calculate a radial distribution function of the electrode material.
[0091]
After evaluating the spin density and the radial distribution ratio for each of the manufactured electrode materials, a secondary battery was manufactured using each of the above electrode materials, and the battery characteristics (initial battery capacity and capacity retention ratio) were evaluated. Was done.
[0092]
A method for manufacturing a secondary battery and an evaluation method will be described.
[0093]
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 produced 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. The electrode material was used in the form of powder having an average particle size of about 10 μm.
[0094]
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.
[0095]
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.
[0096]
Evaluation of the capacity and charge / discharge cycle characteristics of the secondary battery was performed as follows.
[0097]
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 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 battery.
[0098]
Next, Table 1 shows a list of electrode materials used in this example.
[0099]
[Table 1]

[0100]
As shown in Table 1, in this example, 4 samples (sample Nos. 0-1 to 0-4) were used as comparative examples, and 15 samples (samples No. 1-1 to 1-7, 2-1) were used as examples. From 2-7 and 3-1) were prepared. Hereinafter, the sample No. Each sample of Nos. 0-1 to 0-4 was a comparative example group, and sample No. Each of Samples 1-1 to 1-7 was designated as Sample A, Sample No. Samples Nos. 2-1 to 2-7 were designated as Sample B group and Sample No. 3-1 is a sample C group.
[0101]
The method for producing each sample group will be described.
[0102]
Each sample of the comparative example group was produced 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 _Two H ₆ Was used. At this time, the film forming temperature was set to 350 ° C. and the film forming rate was set to a range of 0.1 nm / sec to 0.4 nm / sec according to a general Si thin film forming method using an epitaxy method. The film forming rate was controlled by adjusting the flow rate of the raw material gas in the range of 0.1 L / min to 0.8 L / min. 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 gas flow rate is a flow rate converted to a standard state at 0 ° C. and 1 atm. The film forming rate is an average film forming rate calculated from the thickness of the obtained thin film and the time required for forming the thin film. is there.
[0103]
Each sample of the sample A group was produced by an epitaxy method (atomic layer epitaxy method) in the same manner as each sample of the comparative example group. Similarly to the comparative example group, an ultra-vacuum device manufactured by Japan Vacuum Co., Ltd. ^-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 also Si _Two H ₆ Was used. At this time, in the sample A group, film formation was performed at a lower temperature than in the comparative example group, and the film formation temperature was changed in the range of 280 ° C to 180 ° C. In addition, the flow rate of the raw material gas was adjusted in the range of 1.0 L / min to 2.0 L / min, and the film formation rate was controlled in the range of 0.5 nm / sec to 10 nm / sec. The film forming time was controlled so that the thickness of each of the obtained thin films was about 5 μm.
[0104]
Each sample of the sample B group was manufactured by a plasma CVD method. As a film forming apparatus, a plasma CVD apparatus manufactured by Japan Vacuum Corporation was used to form a thin film of a material containing Si on a copper foil having a thickness of 100 μm. The raw material gas is SiH _Four (Silane) and H _Two Was used. The RF excitation frequency was 13.56 MHz, the flow rate of the raw material gas was 1.0 L / min, and the total gas pressure was 4 Pa. At this time, in the sample B group, the film formation was performed while controlling the film formation temperature within the range shown in Table 1. By this control, it is considered that the hydrogen concentration in the thin film is different between the samples in the sample B group. The film forming time was controlled so that the thickness of each of the obtained thin films was about 5 μm.
[0105]
Samples of Sample C group were formed by performing light irradiation after forming a film by a plasma CVD method. Specifically, it was produced by irradiating a sample equivalent to the sample 2-6 of the sample B group with light. Therefore, the conditions of the plasma CVD are the same as those of the sample B group. At the time of light irradiation, using a Xe lamp, white light containing a component having a wavelength of 1000 nm or less is emitted at an intensity of 300 mW / cm. ^Two For 3 hours.
[0106]
Table 2 below shows the measurement results of the radial distribution ratio and the spin density in each sample.
[0107]
[Table 2]

[0108]
As shown in Table 2, it can be seen that the radial distribution ratio and the spin density are increased in each of the samples of the group A, the group B, and the group C as compared with the samples of the comparative example group. Therefore, it is considered that in each of the samples of the sample A group, the group B, and the group C, the voids of the atomic order are increased in the manufactured electrode material containing Si. In addition, a comparison between Sample 2-6 and Sample 3-1 shows that irradiation with light increases both the radial distribution ratio and the spin density. This is considered to be because the dangling bond density of Si contained in the electrode material increased due to the Staebler-Wronski effect.
[0109]
Here, based on the results in Table 2, FIG. 3 shows the relationship between the radial distribution ratio and the spin density in each sample. As shown in FIG. 3, the spin density tends to increase as the radial distribution ratio increases.
[0110]
Next, Table 3 below shows the initial discharge capacity and the capacity retention of the secondary batteries manufactured using each sample.
[0111]
[Table 3]

[0112]
As shown in Table 3, the initial discharge capacity is almost the same in all the samples including the comparative example and the example. The value was about 2400 to 2480 mAh, and it was possible to obtain a secondary battery having a higher capacity than when a graphite material was used as the electrode material (about 1800 mAh).
[0113]
Based on the results in Table 3, FIG. 4 shows the relationship between the spin density of each sample and the capacity retention of a secondary battery manufactured using each sample. As shown in FIG. 4, the spin density of each sample was 1 × 10 ^Fifteen cm ^-3 Within the above range, it can be seen that the capacity retention ratio of the manufactured secondary battery is higher than that of the comparative example group. The spin density of each sample is 1 × 10 ¹⁶ cm ^-3 Within the above range, the capacity retention ratio of the fabricated secondary battery was further increased, and the spin density was 1 × 10 ¹⁷ cm ^-3 From the above, it can be seen that the capacity retention of the manufactured secondary battery is 90% or more. This indicates that a secondary battery having more excellent charge / discharge cycle characteristics can be obtained as the spin density of each sample increases.
[0114]
Similarly, based on the results in Table 3, FIG. 5 shows the relationship between the radial distribution ratio of each sample and the capacity retention ratio of a secondary battery manufactured using each sample. As shown in FIG. 5, when the radial distribution ratio of each sample is in the range of 6 or more, the capacity retention ratio of the manufactured secondary battery is higher than that of the comparative example group. Further, when the radial distribution ratio of each sample was 7 or more, the capacity retention rate of the manufactured secondary battery was further increased. When the radial distribution ratio was 9 or more, the capacity retention rate of the secondary battery was 90%. It turns out that it becomes above. This indicates that as the radial distribution ratio of each sample increases, a secondary battery having more excellent charge / discharge cycle characteristics can be obtained.
[0115]
According to the results of the sample C group in FIGS. 4 and 5, the irradiation of the electrode material with light significantly increased the radial distribution ratio, spin density, and capacity retention ratio of the manufactured secondary battery. (See the arrows in FIGS. 4 and 5). Therefore, it is found that a secondary battery having more excellent charge / discharge cycle characteristics can be obtained by light irradiation.
[0116]
Next, FIG. 6 shows the relationship between the film formation rate and the spin density in each sample. Comparing the comparative example group formed by the epitaxy method with the sample A group, it can be seen that the spin density increases when the film forming speed is in the range of 0.5 nm / sec or more. In addition, it can be seen that the spin density has a substantially constant value when the film forming speed is in the range of 1.0 nm / sec or more. Therefore, when the epitaxy method is used, it is found that an electrode material having a higher spin density can be obtained by increasing the film formation rate to a range of 0.5 nm / sec or more.
[0117]
Looking at the sample B group, unlike the epitaxy method, it is difficult to stack monoatomic layers in the plasma CVD method, but the relationship between the film formation rate and the spin density is almost the same as that in the sample A group. You can see that it is on top. Therefore, it can be understood that an electrode material having a higher spin density can be obtained by increasing the film formation rate also in the plasma CVD method. Further, from the results of the sample C group, it can be seen that the spin density of the electrode material is increased by light irradiation (see the arrow in FIG. 6).
[0118]
Next, the relationship between the film formation temperature, the spin density of the obtained thin film, and the concentration of hydrogen contained in the obtained thin film when the plasma CVD method was used was examined.
[0119]
Using the same manufacturing method as that of the sample B group, the film forming temperature was changed in the range of 20 ° C. to 400 ° C., and thin films having a thickness of about 5 μm were formed. At this time, the film formation time was controlled so that the thickness of the manufactured thin film was almost the same. The results are shown in FIG. 7 and FIG.
[0120]
7 and 8 that the concentration of hydrogen contained in the obtained thin film decreases as the film forming temperature increases. In addition, it can be seen that the spin density is also reduced accordingly. As described above, it is considered that as the spin density of the electrode material increases, a secondary battery having more excellent charge / discharge cycle characteristics can be obtained. , 100 ° C. or less). When the hydrogen concentration in the thin film is 1 atomic%, the spin density is about 1 × 10 ¹⁶ cm ^-3 It is understood that it is at the level of.
[0121]
【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 diagram showing an example of a radial distribution function measured for crystalline silicon.
FIG. 2 is a schematic sectional view showing an example of a non-aqueous electrolyte secondary battery of the present invention.
FIG. 3 is a diagram showing a relationship between a radial distribution ratio and a spin density in each electrode material sample measured in the examples.
FIG. 4 is a diagram showing a relationship between a film formation rate and a spin density in each electrode material sample measured in the examples.
FIG. 5 is a diagram showing the relationship between the film formation temperature and the hydrogen concentration in the thin film, measured in the examples.
FIG. 6 is a diagram illustrating a relationship between a film forming temperature and a spin density measured in an example.
FIG. 7 is a graph showing the relationship between the spin density of each electrode material sample measured in the example and the capacity retention of a secondary battery manufactured using each electrode material sample.
FIG. 8 is a diagram illustrating a relationship between a radial distribution ratio of each electrode material sample measured in the example and a capacity retention ratio of a secondary battery manufactured using each electrode material sample.
[Explanation of symbols]
1 positive electrode
2 Negative electrode
3 separator
4 Lower insulating plate
5 cases
6 Upper insulating plate
7 Gasket
8 Sealing plate
9 Positive electrode lead
10 Negative electrode lead

Claims (11)

An electrode material for a non-aqueous electrolyte secondary battery that can reversibly occlude and release Li,
An electrode material for a non-aqueous electrolyte secondary battery, comprising a material containing Si, wherein the material has a spin density of 1 × 10 ¹⁵ cm ⁻³ or more as measured by an electron spin resonance method. 2. The electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the spin density is 1 × 10 ¹⁶ cm ⁻³ or more. An electrode material for a non-aqueous electrolyte secondary battery that can reversibly occlude and release Li,
An electrode material for a non-aqueous electrolyte secondary battery, comprising a material containing Si, wherein a radial distribution ratio of Si in the material is 6 or more.
However, the radial distribution ratio, the peak area D ₁ of the range of radial distance 0.3nm~0.5nm in radial distribution functions obtained using X-ray diffraction method with respect to the material, radial distance is a value obtained by dividing the peak area D ₂ in the range of 0.2Nm～0.3Nm. The electrode material for a non-aqueous electrolyte secondary battery according to claim 3, wherein the radial distribution ratio is 7 or more. The electrode material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the material is hydrogenated amorphous silicon. The electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the material contains hydrogen atoms in a range of 1 atomic% to 50 atomic%. The electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the material includes Si having a dangling bond. A nonaqueous electrolyte secondary battery comprising the electrode material for a nonaqueous electrolyte secondary battery according to claim 1 as an active material of a negative electrode. 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 on a substrate;
(Ii) irradiating the material with light to increase the spin density of the material measured by an electron spin resonance method;
(Iii) a method of producing an electrode material for a non-aqueous electrolyte secondary battery, the method including a step of separating the formed thin film from the substrate. 10. The method for producing an electrode material for a non-aqueous electrolyte secondary battery according to claim 9, wherein in the step (ii), the spin density of the material is increased to 1 × 10 ¹⁶ cm ⁻³ or more. The method for producing an electrode material for a nonaqueous electrolyte secondary battery according to claim 9 or 10, wherein the step (i) is performed by at least one method selected from an epitaxy method and a plasma CVD method.

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