JP2007299764A5 - - Google Patents

Description

Energy device and manufacturing method thereof

  The present invention relates to an energy device and a manufacturing method thereof.

  The lithium ion secondary battery includes a negative electrode current collector, a negative electrode active material, an electrolyte, a separator, a positive electrode active material, and a positive electrode current collector as main components. The lithium ion secondary battery plays a major role as an energy source for mobile communication devices and various AV devices. Along with miniaturization of devices and higher performance, lithium ion secondary batteries are being downsized and increased in energy density, and many efforts have been made to improve each element constituting the battery.

  For example, Patent Document 1 discloses that a high energy density can be realized by using, as a positive electrode active material, an amorphous oxide obtained by heating, melting, and rapidly cooling a mixed powder of a specific transition metal oxide. It is disclosed.

  In Patent Document 2, a transition metal oxide containing lithium is used as a positive electrode active material, a compound containing a silicon atom is used as a negative electrode active material, and the weight of the positive electrode active material is larger than the weight of the negative electrode active material. Can increase battery capacity and cycle life.

Further, Patent Document 3 discloses using an amorphous silicon thin film as a negative electrode active material. As a result, a larger amount of lithium can be occluded than when carbon is used, and it is expected that the capacity can be increased.
JP-A-8-78002 Japanese Unexamined Patent Publication No. 2000-12092 JP 2002-83594 A

  However, when an amorphous silicon thin film is used as a negative electrode material for a lithium ion secondary battery, the amorphous silicon thin film has a large amount of occlusion of lithium, but also has a large expansion / contraction amount during charge / discharge. Ensuring characteristics is an issue. The amorphous silicon thin film can be formed by a vacuum film forming process such as sputtering or vapor deposition. In order to increase the capacity, it is necessary to increase the thickness of the amorphous silicon thin film, which is the negative electrode active material, to some extent according to the thickness of the positive electrode. However, when the thickness of the amorphous silicon thin film is increased, the battery capacity increases, but the cycle characteristics tend to deteriorate, and it is difficult to achieve both large capacity and cycle characteristics.

  The present invention solves the above-mentioned problems of the conventional technology, and provides an energy device having a thin film mainly composed of silicon as a negative electrode active material and having both a large capacity and cycle characteristics, and a method for manufacturing the same. Objective.

In order to achieve the above object, an energy device of the present invention is an energy device including a current collector layer and a negative electrode active material thin film provided on the current collector layer directly or through an underlayer. , wherein the negative electrode active material thin film have a multilayer structure comprising two or more silicon thin film containing silicon as a main component, between the silicon thin film adjacent, there is an intermediate layer containing a low melting point of elemental silicon And

The energy device manufacturing method of the present invention is a method for manufacturing an energy device in which a negative electrode active material thin film and a positive electrode active material thin film face each other through a layer that does not exhibit electron conduction, and is directly on a current collector layer. or wherein the step of forming by a vacuum deposition method the negative electrode active material thin film through the base layer, and forming the positive electrode active material thin film, the formation of the negative electrode active material thin film was over time division look containing two or more silicon deposition step, between two or more of the silicon deposition step, a step of forming an intermediate layer containing a low melting point of elemental silicon and wherein the free Mukoto.

  According to the energy device and the manufacturing method thereof of the present invention, deterioration of cycle characteristics can be prevented even if the negative electrode active material layer is thickened according to the thickness of the positive electrode active material layer. As a result, an energy device having both a large capacity and cycle characteristics can be realized.

  The energy device of the present invention includes a current collector layer and a negative electrode active material thin film provided on the current collector layer directly or via an underlayer. The negative active material thin film has a multilayer structure including two or more silicon thin films containing silicon as a main component.

  When a silicon thin film is formed by a vacuum film formation method or the like, silicon generally forms columnar particles having a substantially inverted truncated cone shape with the thickness direction as the central axis direction. When the thickness of the silicon thin film is increased in order to increase the battery capacity, the height of the substantially inverted frustoconical particles increases, and as a result, the diameter thereof becomes coarse. When charging / discharging is performed using a silicon thin film as a negative electrode active material of a lithium ion secondary battery, insertion / extraction of lithium ions is repeated in the silicon thin film, and silicon particles repeatedly expand / contract. If silicon particles with a large diameter are present in the silicon thin film, the expansion / contraction of the silicon particles causes separation at the interface between the silicon thin film and the negative electrode current collector layer, distortion and destruction of the silicon particles, and cycle characteristics are improved. Reduce.

  In the present invention, since the negative electrode active material thin film has a multilayer structure of two or more silicon thin films, even if the thickness of the negative electrode active material thin film is increased, the number of silicon thin films can be increased per layer. The increase in thickness of the silicon thin film can be prevented. Therefore, the silicon particle diameter does not become coarse in the silicon thin film. Therefore, even if the negative electrode active material thin film is thickened, deterioration of cycle characteristics can be prevented. As a result, an energy device having both a large capacity and cycle characteristics can be realized.

  In the present invention, “containing silicon as a main component” means that the silicon content is 50 at% or more. In order to improve the battery capacity, the silicon content is desirably 70 at% or more, more desirably 80 at% or more, and most desirably 90 at% or more. This is because the higher the silicon content, the better the battery capacity.

  The silicon thin film preferably has columnar particles whose longitudinal direction is the thickness direction, and the columnar particles are preferably discontinuous between the silicon thin films adjacent in the thickness direction. Thereby, generation | occurrence | production of the silicon particle which the diameter coarsened can be suppressed. Therefore, even if silicon particles expand / shrink due to insertion / extraction of lithium ions due to repeated charge / discharge, peeling at the interface between the silicon thin film and the negative electrode current collector layer, and distortion and destruction of the silicon particles can be suppressed. As a result, deterioration of cycle characteristics can be prevented.

  It is preferable that an interface layer exists between the adjacent silicon thin films. Thereby, since the columnar particles sandwiching the interface layer can be made discontinuous, the generation of silicon particles having a coarse diameter can be suppressed.

  It is preferable that a compound of silicon and a gaseous element exists in the interface layer. Thereby, the columnar particles sandwiching the interface layer can be more reliably discontinuous.

  The compound is preferably a nitride or an oxide. Such a compound can be easily formed during the formation of a silicon thin film, and discontinuous silicon columnar particles can be reliably formed.

  Alternatively, an intermediate layer in which silicon is less than 50 at% may exist between the adjacent silicon thin films. Thereby, since the columnar particles sandwiching the intermediate layer can be made discontinuous, the generation of silicon particles having a coarse diameter can be suppressed.

  The intermediate layer preferably contains lithium. Thereby, since an intermediate | middle layer can complement lithium ion, battery capacity can be increased.

  The intermediate layer is preferably a discontinuous film or an island shape. This facilitates the movement of ions, so that the cycle characteristics can be improved.

  The intermediate layer preferably contains an element having a melting point lower than that of silicon. Thereby, formation of a discontinuous film or an island-shaped intermediate layer is facilitated.

  It may be preferable that a part of silicon contained in the silicon thin film is an oxide. The silicon oxide here does not include silicon oxide contained in the interface layer existing between silicon thin films adjacent in the thickness direction. It means that silicon oxide is contained in an intermediate region excluding the upper and lower interface layers in the thickness direction. When the silicon content in the silicon thin film is large and the battery capacity is large, the degree of expansion / contraction of the silicon thin film during charge / discharge increases, and the cycle characteristics may deteriorate. If the silicon thin film contains silicon oxide, the silicon oxide has little expansion / contraction during charging / discharging, so that expansion / contraction of the silicon thin film during charging / discharging can be suppressed, and cycle characteristics can be improved. it can.

  Next, a method for manufacturing an energy device according to the present invention is a method for manufacturing an energy device in which a negative electrode active material thin film and a positive electrode active material thin film face each other through a layer that does not exhibit electronic conduction, The method includes a step of forming the negative electrode active material thin film by a vacuum film forming method directly or through an underlayer, and a step of forming the positive electrode active material thin film. The formation of the negative electrode active material thin film includes two or more silicon deposition steps divided with time.

  By dividing the silicon deposition process into multiple times over time to form a single negative electrode active material thin film, it is easy to form discontinuous silicon columnar particles in the thickness direction in this single negative electrode active material thin film it can. Therefore, even if the thickness of the negative electrode active material thin film is increased, an increase in the dimension in the thickness direction of the substantially inverted truncated cone-shaped silicon particles can be prevented by increasing the number of silicon deposition steps. Therefore, the silicon particle diameter does not become coarse in the negative electrode active material thin film. Therefore, even if the negative electrode active material layer is thickened, deterioration of cycle characteristics can be prevented. As a result, an energy device having both a large capacity and cycle characteristics can be realized.

  Here, the “vacuum film forming method” includes various vacuum thin film manufacturing processes such as a vapor deposition method, a sputtering method, a CVD method, an ion plating method, and a laser ablation method. An optimum film formation method can be selected according to the type of the thin film. A thin negative electrode active material thin film can be efficiently produced by a vacuum film formation method. As a result, a small and thin energy device can be obtained.

  It is preferable to perform a surface modification treatment on the surface of the silicon thin film mainly containing the formed silicon during the two or more silicon deposition steps. By the surface modification treatment, an interface layer that makes the silicon columnar particles discontinuous can be easily formed in the negative electrode active material layer. Accordingly, generation of silicon particles having a coarse diameter can be suppressed.

  The surface modification treatment is preferably gas introduction to the surface of the silicon thin film. Such surface modification treatment can be easily performed in a vacuum film forming method.

  The gas preferably contains nitrogen or oxygen as a main component. Thereby, the silicon particles formed before and after the surface modification treatment can be easily made discontinuous by a simple method.

  It is preferable to ionize or plasma the gas. Thereby, the silicon particles formed before and after the surface modification treatment can be made more reliable and discontinuous.

  Alternatively, an intermediate layer in which silicon is less than 50 at% may be formed between two or more silicon deposition steps. Thereby, since the columnar particles in the silicon thin film formed before and after the formation of the intermediate layer can be made discontinuous, generation of silicon particles having a coarse diameter can be suppressed.

  Subsequent to the silicon deposition step, the intermediate layer is preferably formed by a vacuum film formation method in a vacuum atmosphere. By performing the silicon deposition step and the intermediate layer forming step without destroying the vacuum atmosphere, the adhesion between layers can be improved and peeling can be prevented, so that the battery capacity can be prevented from decreasing. Moreover, a negative electrode active material thin film can be efficiently formed by performing any process by the vacuum film-forming method.

  Preferably, the intermediate layer is formed by a vacuum film formation method in a vacuum atmosphere, and then the silicon deposition step is performed. By performing the intermediate layer forming step and the silicon deposition step without destroying the vacuum atmosphere, the adhesion between the layers can be improved and peeling can be prevented, so that a reduction in battery capacity can be prevented. Moreover, a negative electrode active material thin film can be efficiently formed by performing any process by the vacuum film-forming method.

  The intermediate layer preferably contains an element having a melting point lower than that of silicon. Thereby, a discontinuous film or an island-shaped intermediate layer can be easily formed by heating during film formation or after film formation. By forming such an intermediate layer, the movement of ions is facilitated, so that the cycle characteristics can be improved.

  When the melting point of the material for forming the intermediate layer is Tm (° C.), it is preferable to maintain the film formation surface temperature at the time of forming the intermediate layer at Tm / 3 (° C.) or higher. Thereby, a discontinuous film or an island-shaped intermediate layer can be formed efficiently.

  Or after forming the said intermediate | middle layer, you may heat the said intermediate | middle layer more than the melting | fusing point. This also makes it possible to easily form a discontinuous film or an island-shaped intermediate layer.

  The silicon deposition process is preferably performed in an inert gas or nitrogen atmosphere. As a result, it is possible to prevent the silicon columnar particles adjacent in the direction parallel to the surface to be deposited from merging and growing to increase the silicon particle diameter. As a result, the degree of expansion / contraction of the silicon particles during charging / discharging becomes intense, and it is possible to suppress deterioration in cycle characteristics. As the atmospheric gas, argon is most preferable from the viewpoints of practicality and the remarkable effects described above.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
An energy device according to Embodiment 1 of the present invention will be described.

  The energy device according to the first embodiment includes a positive electrode current collector in which a positive electrode active material is formed on both sides, a separator as a layer that does not exhibit electronic conduction, and a negative electrode current collector in which a negative electrode active material is formed on both sides. Is wound in a battery can, and the battery can is filled with an electrolyte solution. The cylindrical can is wound with the separator interposed between the positive electrode current collector and the negative electrode current collector.

  As the positive electrode current collector, Al, Cu, Ni, stainless steel foil or net having a thickness of 10 to 80 μm can be used. Alternatively, a polymer substrate such as polyethylene terephthalate or polyethylene naphthalate having a metal thin film formed on the surface can be used.

  The positive electrode active material needs to be able to enter and exit lithium ions, and includes lithium-containing transition metal oxides including transition metals such as Co, Ni, Mo, Ti, Mn, and V, and conductivity aids such as acetylene black. It is also possible to use a mixed paste in which an agent and a binder such as nitrile rubber, butyl rubber, polytetrafluoroethylene, and polyvinylidene fluoride are mixed.

  As the negative electrode current collector, a foil, net, or the like of Cu, Ni, stainless steel having a thickness of 10 to 80 μm can be used. Alternatively, a polymer substrate such as polyethylene terephthalate or polyethylene naphthalate having a metal thin film formed on the surface can be used.

  The separator is preferably excellent in mechanical strength and ion permeability, and polyethylene, polypropylene, polyvinylidene fluoride, and the like can be used. The pore diameter of the separator is, for example, 0.01 to 10 μm, and the thickness thereof is, for example, 5 to 200 μm.

As an electrolytic solution, a solution in which an electrolyte salt such as LiPF ₆ , LiBF ₄ , or LiClO ₄ is dissolved in a solvent such as ethylene carbonate, propylene carbonate, methyl ethyl carbonate, hexafluoromethyl acetate, or tetrohydrofuran is used. I can do it.

  As the battery can, a metal material such as stainless steel, iron, aluminum, or nickel-plated steel can be used, but a plastic material can also be used depending on the battery application.

  The negative electrode active material is a silicon thin film containing silicon as a main component. The silicon thin film is preferably amorphous or microcrystalline, and can be formed by a vacuum film formation method such as sputtering, vapor deposition, or CVD.

[ Reference Examples 1 to 3, Comparative Example 1]
A reference example corresponding to the first embodiment will be described.

First, a method for manufacturing a positive electrode will be described. Li ₂ CO ₃ and CoCO ₃ were mixed at a predetermined molar ratio and synthesized by heating at 900 ° C. in the atmosphere to obtain LiCoO ₂ . This was classified to 100 mesh or less to obtain a positive electrode active material. 100 g of this positive electrode active material, 10 g of carbon powder as a conductive agent, 8 g of polytetrafluoroethylene dispersion as a binder, and pure water were mixed to form a paste. This positive electrode active material-containing paste was applied to both sides of a 15 μm-thick strip-shaped aluminum foil as a positive electrode current collector and dried to obtain a positive electrode.

  A strip-shaped copper foil having a thickness of 30 μm was used as the negative electrode current collector, and a silicon thin film was formed as a negative electrode active material on both surfaces by sputtering. Details will be described later.

  As the separator, a belt-like porous polyethylene having a thickness of 25 μm and wider than the positive electrode current collector and the negative electrode current collector was used.

  A positive electrode lead made of the same material was attached to the positive electrode current collector by spot welding. Further, a negative electrode lead made of the same material as the negative electrode current collector was attached by spot welding.

These were overlapped so that a separator was interposed between the positive electrode and the negative electrode obtained as described above, and wound in a spiral shape. Polypropylene insulation plates are arranged on the upper and lower surfaces of this cylindrical wound product, respectively, and housed in a bottomed cylindrical battery can, and a step is formed in the vicinity of the opening of the battery can. Then, an equal volume mixed solution of ethylene carbonate and diethyl carbonate in which LiPF ₆ was dissolved at a concentration of 1 × 10 ³ mol / m ³ was poured into a battery can, and the opening was sealed with a sealing plate to obtain a lithium ion secondary battery. It was.

  A method for forming a silicon thin film as a negative electrode active material will be described with reference to FIG.

  A vacuum film forming apparatus 10 shown in FIG. 1 includes a vacuum chamber 1 that is partitioned vertically by a partition wall 1a. In a room (conveying chamber) 1b above the partition wall 1a, a separating roll 11, a cylindrical can roll 13, a separating roll 14, and conveying rolls 12a and 12b are arranged. A first sputter film formation source 51, a gas introduction nozzle 55, and a second sputter film formation source 52 are disposed in a chamber (thin film formation chamber) 1c below the partition wall 1a. A mask 4 is provided at the center of the partition wall 1a, and the lower surface of the can roll 13 is exposed to the thin film formation chamber 1c through the opening of the mask 4. The inside of the vacuum chamber 1 is maintained at a predetermined degree of vacuum by a vacuum pump 16.

  The strip-shaped negative electrode current collector 5 squeezed out from the scooping roll 11 is sequentially transported by the transporting roll 12 a, the can roll 13, and the transporting roll 12 b, and scraped off by the scooping roll 14. In this process, particles such as atoms, molecules, or clusters (hereinafter referred to as “sputtered particles”) generated from the first sputter deposition source 51 and the second sputter deposition source 52 pass through the mask 4 of the partition wall 1a. Thus, the thin film 6 is formed on the surface of the negative electrode current collector 5 running on the can roll 13. A first sputter film formation source 51, a gas introduction nozzle 55, and a second sputter film formation source 52 are arranged facing the negative electrode current collector 5 from the upstream side to the downstream side in the transport direction. The gas introduction nozzle 55 extends in the vicinity of the can roll 13 over the entire width of the negative electrode current collector 5 in the width direction (perpendicular to the paper surface of FIG. 1). Therefore, the gas introduction nozzle 55 functions as a second mask, and prevents sputtered particles from being deposited on a region of the outer surface of the can roll 13 facing the gas introduction nozzle 55. Therefore, first, sputtered particles from the first sputter film forming source 51 are mainly deposited on the surface of the negative electrode current collector 5, and sputtered particles from the second sputtered film forming source 52 are mainly deposited for a short time. accumulate.

In Reference Example 1, by using such an apparatus, silicon is sputtered by argon ions in each of the first sputter film formation source 51 and the second sputter film formation source 52, and the copper foil as the negative electrode current collector 5 is formed. Then, a silicon thin film having a thickness of 8 μm was formed. The deposition rate of the silicon thin film was set to approximately 2 nm / s. Both the first sputter deposition source 51 and the second sputter deposition source 52 used DC magnetron sputtering. No gas was introduced from the gas introduction nozzle 55 during film formation.

In Reference Example 2, a silicon thin film was formed in the same manner as Reference Example 1 except that N ₂ gas was introduced from the gas introduction nozzle 55 at 0.05 Pa · m ³ / s during film formation.

In Reference Example 3, a silicon thin film was formed in the same manner as in Reference Example 1 except that O ₂ gas was introduced at 0.05 Pa · m ³ / s from the gas introduction nozzle 55 during film formation.

In Comparative Example 1, the second sputter deposition source 52 and the gas introduction nozzle 55 were removed, and only the first sputter deposition source 51 was used, and the negative electrode current collector 5 was run so that the deposition rate was the same as in Reference Example 1. A silicon thin film having a thickness of 8 μm was formed in the same manner as in Reference Example 1 except that the speed was adjusted.

2A to 2D schematically show SEM photographs in which the cross sections in the thickness direction of the silicon thin films (negative electrode active material thin films) of Comparative Example 1, Reference Examples 1, 2, and 3 are sequentially shown. FIG. In each figure, the lower side of the paper is the negative electrode current collector (copper foil) 5 side, and the upper side is the surface of the silicon thin film.

  In Comparative Example 1 (FIG. 2A), silicon particles grow as substantially inverted frustoconical columnar particles while the particle diameter gradually increases from the interface with the negative electrode current collector, and particles near the surface of the silicon thin film. The largest diameter.

On the other hand, in Reference Examples 1 to 3 (in order of FIGS. 2B to 2D), the silicon particles are similarly grown as columnar particles having a substantially inverted truncated cone shape. The silicon particle growth is discontinuous. The discontinuity of particle growth is more prominent in Reference Examples 2 and 3 (FIGS. 2C and 2D) in which gas is introduced. The positions in the thickness direction of the portions where the silicon particles are discontinuous are substantially the same for all the silicon particles. In Reference Examples 1 to 3, the silicon thin film is divided by the interface layer 50 which is the discontinuous portion, and has a two-layer structure in the vertical direction. The layer below the interface layer 50 (copper foil side) is a silicon thin film mainly formed by the first sputter film formation source 51, and the layer above the interface layer 50 is mainly formed by the second sputter film formation source 52. It is considered to be a formed silicon thin film. Since the silicon particles in the layer above the interface layer 50 newly start growing from the interface layer 50 in a substantially inverted truncated cone shape, the particle diameter in the vicinity of the surface of the silicon thin film is smaller than that in Comparative Example 1. . In addition, each silicon thin film of Reference Examples 1 to 3 and Comparative Example 1 is amorphous or microcrystalline without any significant peak corresponding to silicon crystal being detected by X-ray diffraction measurement (CuKα, 40 kV). Could be estimated.

3 is a view showing an Auger depth profile of the silicon thin film (negative electrode active material thin film) of Reference Example 1. FIG. The Auger depth profile was measured using a SAM670 manufactured by Philips. The acceleration voltage of the electron gun was 10 kV, the irradiation current was 10 nA, and the measurement was performed with the acceleration voltage of the etching ion gun of 3 kV and the sputtering rate of 0.4 nm / s. The “depth from the film surface” on the horizontal axis in the figure is the same as the sample, using the sputter rate obtained by measuring the step formed by sputter etching of the same Si film and Cu film with the step meter. The sputter etching time was obtained by converting into the etching depth in the thickness direction. As can be seen from FIG. 3, in Reference Example 1 in which no gas was introduced during film formation, a remarkable discontinuity of the composition could be confirmed to the extent that a slight argon peak was observed at a position corresponding to the interface layer. There wasn't. In FIG. 2 (B), the discontinuity of the particle growth is observed because the silicon particle growth may be discontinuous even by a slight gas adhesion that cannot be detected by the Auger depth profile or can be detected in a trace amount. Suggests that.

4 is a diagram showing an Auger depth profile of the silicon thin film (negative electrode active material thin film) of Reference Example 2. FIG. As can be seen from FIG. 4, in Reference Example 2 exposed to the N ₂ gas atmosphere between the film formation by the first sputter film formation source 51 and the film formation by the second sputter film formation source 52, this corresponds to the interface layer. A peak of nitrogen distribution is detected at the position. That is, silicon nitride exists in the interface layer. Reference Example 2 suggests that if silicon nitride is formed during the formation of the silicon thin film, the growth of silicon particles is likely to be discontinuous.

Although not shown, the silicon thin film (negative electrode active material thin film) of Reference Example 3 exposed to an O ₂ gas atmosphere between the film formation by the first sputter film formation source 51 and the film formation by the second sputter film formation source 52. ), As in FIG. 4, a peak of oxygen distribution was detected at a position corresponding to the interface layer. That is, silicon oxide was present in the interface layer. From Reference Example 3, it was found that the possibility that the growth of silicon particles becomes discontinuous also increases when silicon oxide is formed during the formation of the silicon thin film.

The lithium ion secondary batteries formed in Reference Examples 1 to 3 and Comparative Example 1 were subjected to a charge / discharge cycle test at a test temperature of 20 ° C., a charge / discharge current of 3 mA / cm ² , and a charge / discharge voltage range of 4.2 V to 2.5 V. went. The ratio of the discharge capacity after 50 cycles and after 200 cycles with respect to the initial discharge capacity was determined as the battery capacity retention rate (cycle characteristics). The results are shown in Table 1.

As can be seen from Table 1, in Reference Examples 1 to 3, in which the growth of silicon particles is discontinuous in the interface layer at the center in the thickness direction, there is no interface layer, and the growth of silicon particles over the entire range in the thickness direction. Compared to Comparative Example 1 in which the battery capacity is continuous, the battery capacity retention rate after 50 cycles and after 200 cycles is large. Further, as a result of introducing a gas between the film formation by the first sputter film formation source 51 and the film formation by the second sputter film formation source 52, Reference Example 2 in which discontinuity in the growth of silicon particles is recognized more remarkably. , 3 has a better battery capacity maintenance rate than Reference Example 1 in which no gas is introduced.

It is considered that the discontinuity of the silicon particles improves the battery capacity retention rate (cycle characteristics) for the following reason. As described above, in the silicon thin film formed by the vacuum film formation method, silicon forms columnar particles having a substantially inverted truncated cone shape with the thickness direction as the central axis direction. When this silicon thin film is used as the negative electrode active material of a lithium ion secondary battery, the insertion / extraction of lithium ions is repeated by charge / discharge, and the silicon particles repeatedly expand / contract. This causes peeling at the interface between the silicon thin film and the negative electrode current collector layer, distortion and destruction of the silicon particles, and lowers the battery capacity retention rate (cycle characteristics). When the thickness of the silicon thin film is increased to increase the battery capacity, the cycle characteristics decrease because the silicon particles grow and the maximum diameter increases as the thickness increases, so the mutual interference between the silicon particles increases. It is thought that it is to do. As in Reference Examples 1 to 3, when an interfacial layer that discontinuizes the growth of silicon particles is formed in the silicon thin film, the silicon particles newly start growing from the interfacial layer. Accordingly, an increase in the maximum diameter of the silicon particles is suppressed, and mutual interference between the silicon particles is suppressed. For this reason, a favorable battery capacity maintenance rate (cycle characteristic) is obtained.

  Thus, a multilayer silicon thin film including two or more silicon thin films containing silicon as a main component can be obtained by forming an interface layer in the silicon thin film that makes the columnar particle shape of silicon discontinuous. When such a multilayer silicon thin film is used as a negative electrode active material layer of a lithium ion secondary battery, cycle characteristics are not deteriorated even if the total thickness of the negative electrode active material layer is increased. Therefore, it is possible to provide an energy device that achieves both increased battery capacity and cycle characteristics.

By reacting the gas introduced from the gas introduction nozzle 55 with ionization or plasma, the reactivity between the introduced gas and the thin film particles increases, and the gas introduction effect can be enhanced. The ionization of the introduced gas can be realized by adding an ion source or plasma source function to the gas introduction nozzle 55. As the ion source, various types such as a hot cathode type and a hollow cathode type can be used, and the method is not particularly limited. When introducing the oxygen gas, it is preferable to devise such as using a mixed gas with an inert gas so that the hot cathode does not deteriorate due to oxidation. The applied voltage for generating plasma may be direct current, alternating current, or high frequency. Even when the introduced gas is ionized or plasmaized, the same effects as in Reference Examples 2 and 3 can be obtained in terms of cross-sectional SEM shape, Auger depth profile, and battery capacity retention rate (cycle characteristics), but capacity maintenance after 200 cycles. The rate was improved by about 2% compared to Reference Examples 2 and 3. This is thought to be due to the ionization and plasmatization of the introduced gas, which increases the reactivity between the introduced gas and the thin film particles and enhances the gas introduction effect of discontinuous growth of silicon particles.

[Examples 1 and 2 and Comparative Example 2]
The actual施例that corresponds to the first embodiment will be described.

First, a method for manufacturing a positive electrode will be described. Li ₂ CO ₃ and CoCO ₃ were mixed at a predetermined molar ratio and synthesized by heating at 900 ° C. in the atmosphere to obtain LiCoO ₂ . This was classified to 100 mesh or less to obtain a positive electrode active material. 100 g of this positive electrode active material, 12 g of carbon powder as a conductive agent, 10 g of polytetrafluoroethylene dispersion as a binder, and pure water were mixed to form a paste. This positive electrode active material-containing paste was applied to both sides of a strip-shaped aluminum foil having a thickness of 25 μm as a positive electrode current collector and dried to obtain a positive electrode.

  A strip-shaped copper foil having a thickness of 20 μm was used as a negative electrode current collector, and a silicon thin film was formed on both sides thereof as a negative electrode active material by a vacuum deposition method. Details will be described later.

  As the separator, a belt-like porous polyethylene having a thickness of 35 μm and wider than the positive electrode current collector and the negative electrode current collector was used.

  A positive electrode lead made of the same material was attached to the positive electrode current collector by spot welding. Further, a negative electrode lead made of the same material as the negative electrode current collector was attached by spot welding.

These were overlapped so that a separator was interposed between the positive electrode and the negative electrode obtained as described above, and wound in a spiral shape. Polypropylene insulation plates are arranged on the upper and lower surfaces of this cylindrical wound product, respectively, and housed in a bottomed cylindrical battery can, and a step is formed in the vicinity of the opening of the battery can. Then, an equal volume mixed solution of ethylene carbonate and diethyl carbonate in which LiPF ₆ was dissolved at a concentration of 1 × 10 ³ mol / m ³ was poured into a battery can, and the opening was sealed with a sealing plate to obtain a lithium ion secondary battery. It was.

  A method for forming a silicon thin film as a negative electrode active material will be described with reference to FIG.

  In the apparatus of FIG. 5, instead of the first sputter film formation source 51, the gas introduction nozzle 55, and the second sputter film formation source 52, the first vapor deposition source 61, the intermediate layer vapor deposition source 65, 1 differs from the apparatus of FIG. 1 in that the second vapor deposition source 62 is disposed. In FIG. 5, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

  The strip-shaped negative electrode current collector 5 squeezed out from the scooping roll 11 is sequentially transported by the transporting roll 12 a, the can roll 13, and the transporting roll 12 b, and scraped off by the scooping roll 14. In this process, particles such as atoms, molecules, or clusters (hereinafter referred to as “evaporated particles”) generated from the first deposition source 61, the intermediate layer deposition source 65, and the second deposition source 62 are referred to as the mask 4 of the partition wall 1a. The thin film 6 is formed by adhering to the surface of the negative electrode current collector 5 running on the can roll 13. A first vapor deposition source 61, an intermediate vapor deposition source 65, and a second vapor deposition source 62 are arranged facing the negative electrode current collector 5 from the upstream side to the downstream side in the transport direction. The intermediate layer evaporation source 65 extends in the vicinity of the can roll 13 over the entire width of the negative electrode current collector 5 in the width direction (perpendicular to the paper surface of FIG. 5). Accordingly, the intermediate layer deposition source 65 functions as a second mask, and the first layer 61 and the second deposition source 62 to the region of the outer surface of the can roll 13 that the intermediate layer deposition source 65 is opposed to. Prevent deposition of evaporated particles. Therefore, first, the evaporated particles from the first evaporation source 61 are mainly deposited on the surface of the negative electrode current collector 5, then the evaporated particles from the intermediate layer evaporation source 65 are mainly accumulated, and finally the second evaporation source 62. Evaporated particles from the deposit are mainly deposited.

In Examples 1 and 2 , using such an apparatus, silicon was electron beam evaporated from the first vapor deposition source 61 and the second vapor deposition source 62, respectively, and the thickness was deposited on the copper foil as the negative electrode current collector 5. A 6 μm silicon thin film was formed. The deposition rate of the silicon thin film was set to approximately 0.1 μm / s. As the first vapor deposition source 61 and the second vapor deposition source 62, a 270-degree deflection electron beam vapor deposition source was used.

Furthermore, in Example 1 , aluminum was deposited from the intermediate layer deposition source 65. The amount of aluminum deposited was equivalent to the formation of a thin film having a thickness of 0.1 μm when only aluminum was deposited.

In Example 2 , lithium was deposited from the intermediate layer deposition source 65. The amount of lithium deposited was equivalent to the formation of a thin film having a thickness of 0.1 μm when only lithium was deposited.

In Comparative Example 2, the second vapor deposition source 62 and the intermediate layer vapor deposition source 65 are removed, and only the first vapor deposition source 61 is used, and the traveling speed of the negative electrode current collector 5 is the same as in the first and second embodiments. A silicon thin film having a thickness of 6 μm was formed in the same manner as in Examples 1 and 2 except that the above was adjusted.

6A to 6C are diagrams schematically showing SEM photographs in which cross sections in the thickness direction of the silicon thin films (negative electrode active material thin films) of Comparative Example 2, Examples 1 and 2 are sequentially taken. is there. In each figure, the lower side of the paper is the negative electrode current collector (copper foil) 5 side, and the upper side is the surface of the silicon thin film.

  In Comparative Example 2 (FIG. 6A), silicon particles grow as substantially inverted frustoconical columnar particles while gradually increasing the particle diameter from the interface with the negative electrode current collector, and near the surface of the negative electrode active material. The largest particle size.

On the other hand, in Examples 1 and 2 (in order, FIGS. 6B and 6C), the silicon particles are similarly grown as columnar particles having a substantially inverted truncated cone shape. The growth of silicon particles is discontinuous on both sides of a layer (intermediate layer) 60 having a slight thickness. The silicon thin film is divided by the intermediate layer 60 and has a two-layer structure in the vertical direction. The lower layer (copper foil side) of the intermediate layer 60 is a silicon thin film formed mainly by the first vapor deposition source 61, and the intermediate layer 60 is an aluminum thin film formed by the intermediate vapor deposition source 65 (Example 1 ). Alternatively, it is a lithium thin film (Example 2 ), and the layer above the intermediate layer 60 is considered to be a silicon thin film formed mainly by the second evaporation source 62. Since the silicon particles in the layer above the intermediate layer 60 start to newly grow in a substantially inverted truncated cone shape from the intermediate layer 60, the particle diameter in the vicinity of the surface of the silicon thin film is smaller than that in Comparative Example 2. . The silicon thin films of Examples 1 and 2 and Comparative Example 2 are either amorphous or microcrystalline with no significant peaks corresponding to silicon crystals detected by X-ray diffraction measurement (CuKα, 40 kV). Could be estimated.

7 is a diagram showing an Auger depth profile of the silicon thin film (negative electrode active material thin film) of Example 1. FIG. As can be seen from FIG. 7, in Example 1 where aluminum is formed during the formation of the silicon thin film, a significant aluminum peak is detected at a position corresponding to the intermediate layer. Example 1 suggests that when an aluminum thin film is formed during the formation of a silicon thin film, the possibility of discontinuous growth of silicon particles increases.

Although not shown, in Example 2 where lithium is formed during the formation of a silicon thin film (negative electrode active material thin film), a lithium peak is detected at a position corresponding to the intermediate layer, as in FIG. It was done. From Example 2 , it was found that the possibility that the growth of silicon particles becomes discontinuous also increases when the lithium thin film is formed during the formation of the silicon thin film.

When the Auger depth profile of Example 1 and the Auger depth profile of Example 2 were compared, the peak distribution of lithium of Example 2 was gentler than that of aluminum of Example 1 . This is presumably because lithium atoms are smaller and lighter than aluminum atoms and thus have a strong tendency to disperse during and after film formation.

The lithium ion secondary batteries formed in Examples 1 and 2 and Comparative Example 2 were charged and discharged at a test temperature of 20 ° C., a charge / discharge current of 7.5 mA / cm ² , and a charge / discharge voltage range of 4.2 V to 2.5 V. A test was conducted. The ratio of the capacity after 50 cycles and after 200 cycles with respect to the initial discharge capacity was determined as the battery capacity retention rate (cycle characteristics). The results are shown in Table 2.

As can be seen from Table 2, in Examples 1 and 2 where the growth of silicon particles is discontinuous in the middle layer in the middle of the thickness direction, the growth of silicon particles is performed over the entire range in the thickness direction without the presence of the middle layer. Compared to Comparative Example 2 in which the battery capacity is continuous, the battery capacity retention rate after 50 cycles and after 200 cycles is large.

Further, when comparing the initial discharge capacity, Example 1 and Comparative Example 2 were almost the same, but Example 2 was about 5% higher in capacity than Example 1 . This is presumably because part of the lithium constituting the intermediate layer played a role of supplementing some lithium ions that could not move freely in the silicon thin film for some reason after the first charge.

  As described above, by forming an intermediate layer in the silicon thin film that makes the silicon columnar particle shape discontinuous, a multilayer silicon thin film including two or more silicon thin films containing silicon as a main component can be obtained. When such a multilayer silicon thin film is used as a negative electrode active material layer of a lithium ion secondary battery, cycle characteristics are not deteriorated even if the total thickness of the negative electrode active material layer is increased. Therefore, it is possible to provide an energy device that achieves both increased battery capacity and cycle characteristics.

(Embodiment 2)
An energy device according to a second embodiment of the present invention will be described.

  An example of a schematic configuration of the energy device according to the second embodiment of the present invention is shown in FIG. In the energy device of the present embodiment, the battery element 20 is laminated on the substrate 22. In the battery element 20, a positive electrode current collector 27, a positive electrode active material 26, a solid electrolyte 25 as a layer that does not exhibit electronic conduction, a negative electrode active material 24, and a negative electrode current collector 23 are formed in this order. In FIG. 8, the substrate 22 is disposed on the positive electrode current collector 27 side of the battery element 20, but may be disposed on the negative electrode current collector 23 side.

  Examples of the substrate 22 include polyimide (PI), polyamide (PA), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), other polymer films, stainless metal foil, nickel, copper, aluminum, and other metals. A flexible material such as a metal foil containing an element can be used. Furthermore, various shapes of silicon, glass, ceramic, plastic, and the like can be used, and in the present invention, the material and shape of the substrate are not particularly limited. What is necessary is just to select suitably according to the characteristic calculated | required by an energy device.

  As the positive electrode current collector 27, for example, a metal represented by nickel, copper, aluminum, platinum, platinum-palladium, gold, silver, titanium, or ITO (indium-tin oxide) can be used. Depending on the final form of the energy device, when the substrate 22 is disposed on the positive electrode side and a conductive material is used as the substrate 22, the positive electrode current collector 27 is omitted and the substrate 22 also functions as the positive electrode current collector 27. Can be made.

  As the positive electrode active material 26, for example, lithium cobaltate, lithium nickelate, or the like can be used. However, the material of the positive electrode active material 26 of the present invention is not limited to the above, and other materials can also be used.

As the solid electrolyte 25, a material having ionic conductivity and small enough to have negligible electronic conductivity can be used. Especially when the energy device is a lithium ion secondary battery, since lithium ions are mobile ions, Li ₃ PO ₄ and, mixed with nitrogen to Li ₃ PO ₄ (or part of the elements of Li ₃ PO ₄ A solid electrolyte made of a material (LiPON: typical composition is Li _2.9 PO _3.3 N _0.36 ) or the like obtained by substituting with nitrogen is preferable because of its excellent lithium ion conductivity. Similarly, a solid electrolyte made of a sulfide such as Li ₂ S—SiS ₂ , Li ₂ S—P ₂ S ₅ , Li ₂ S—B ₂ S ₃ is also effective. Furthermore, solid electrolytes obtained by doping these solid electrolytes with lithium halides such as LiI and lithium oxyacid salts such as Li ₃ PO ₄ are also effective. The material of the solid electrolyte 25 of the present invention is not limited to the above, and other materials can be used as the solid electrolyte 25. By using a solid electrolyte as the electrolyte, it is not necessary to take countermeasures against liquid leakage which are essential in the conventional liquid electrolyte, and the energy device can be easily reduced in size and thickness.

  As the negative electrode active material 24, a silicon thin film having a multilayer structure including two or more silicon thin films containing silicon as a main component can be used.

  As the negative electrode current collector 23, a metal represented by, for example, nickel, copper, aluminum, platinum, platinum-palladium, gold, silver, ITO (indium-tin oxide) is used similarly to the positive electrode current collector 27. I can do it. Depending on the final form of the energy device, when the substrate 22 is disposed on the negative electrode side and a conductive material is used as the substrate 22, the negative electrode current collector 23 is omitted and the substrate 22 also functions as the negative electrode current collector 23. Can be made.

  The product form of the energy device is not particularly limited, and various types are conceivable. For example, what laminated | stacked the battery element 20 shown in FIG. 8 on the flexible long board | substrate 22 may be wound by flat form as shown in FIG. At this time, a plate-shaped inner core 31 may be disposed on the inner periphery of the wound body 30.

  FIG. 10 is a perspective view of the planar energy device shown in FIG. In FIG. 10, reference numeral 32 denotes a pair of external electrodes provided at both ends of the wound body 30. As the material of the external electrode 32, various conductive materials such as nickel, zinc, tin, solder alloy, and conductive resin can be used. As the formation method, thermal spraying, plating, coating, or the like can be used. The negative electrode current collector 23 is electrically connected to one external electrode 32, and the positive electrode current collector 27 is electrically bonded to the other external electrode 32. At this time, it is necessary to pattern the formation regions in the width direction (winding center direction) of the negative electrode current collector 23 and the positive electrode current collector 27 so that the pair of external electrodes 32 are insulated from each other.

  FIG. 11 is a cross-sectional view showing another product form of the energy device. In FIG. 11, reference numeral 35 denotes a pair of external electrodes. The negative electrode current collector 23 is electrically connected to one external electrode 35, and the positive electrode current collector 27 is electrically bonded to the other external electrode 35. The The material and the formation method are the same as those of the external electrode 32 shown in FIG.

  Reference numeral 36 denotes a fuse portion provided in the vicinity of the connection portion between the negative electrode current collector 23 and the external electrode 35 and in the vicinity of the connection portion between the positive electrode current collector 27 and the external electrode 35. The fuse part 36 functions as a safety device that prevents the occurrence of ignition or the like by cutting off the overcurrent when the overcurrent flows and preventing the ignition. In the present embodiment, the fuse portion 36 is provided in the negative electrode current collector 23 and the positive electrode current collector 27, but only one of them may be provided.

  12A is a plan view illustrating an example of the fuse portion 36, and FIG. 12B is a cross-sectional view taken along line 12B-12B in FIG. A fuse portion 36 is formed on the current collectors 23 and 27 by giving a pattern that narrows the width of the portion where current flows. When an overcurrent flows, the fuse portion 36 generates heat due to Joule heat and melts to cut off the overcurrent. Therefore, it is possible to prevent a serious situation such as ignition from occurring. The configuration of the fuse portion 36 is not limited to FIGS. 12A and 12B. For example, the fuse portion 36 may be configured by partially reducing the thickness of the negative electrode current collector 23 and the positive electrode current collector 27. Alternatively, the fuse part may be formed by forming a different material having a large temperature coefficient of electrical resistance in a specific pattern in the negative electrode current collector 23 and the positive electrode current collector 27. Since the temperature coefficient of the electric resistance of the dissimilar material is larger than the temperature coefficient of the electric resistance of the negative electrode current collector 23 and the positive electrode current collector 27, the resistance value of the dissimilar material increases if the temperature of the fuse portion 36 slightly increases during overcurrent. Increases rapidly. Therefore, as a result of current flowing in the material of the negative electrode current collector 23 and the positive electrode current collector 27 other than the dissimilar materials in the fuse part 36, the fuse part 36 generates heat due to Joule heat and melts, resulting in overcurrent. Shut off.

  In FIG. 11, reference numeral 37 denotes a protective layer provided for the purpose of mechanical protection, improvement of moisture resistance, prevention of delamination, and the like. Although the material of the protective layer 37 is not specifically limited, For example, surface treatment agents, such as a silane coupling agent, light or a thermosetting resin, a metal, a metal oxide, a metal nitride etc. can be used. As a forming method, a wet process such as coating, dipping (dipping) or spraying, or a dry process such as vapor deposition or sputtering can be employed. Further, the protective layer 37 may be a multilayer composite film made of different or similar materials. The protective layer 37 can be formed on the outer surface of the energy device excluding the external electrode 35. Depending on the material of the substrate 22, the protective layer 37 may not be formed on the surface of the substrate 22 as shown in FIG. 11.

  Furthermore, the energy device may be configured by repeatedly stacking the battery elements 20 as many times as necessary.

[Examples 3 and 4 and Comparative Example 3]
An example corresponding to the second embodiment will be described.

  A polyimide film with a thickness of 25 μm is used as the substrate 22, and a nickel film with a thickness of 0.5 μm is stacked as the positive electrode current collector 27 and a lithium cobalt oxide with a thickness of 8 μm is stacked as the positive electrode active material 26 on the polyimide film. Further, a lithium phosphate solid electrolyte 25 having a thickness of 2 μm was laminated by a vacuum deposition method.

  Thereafter, a 5 μm silicon thin film was formed as the negative electrode active material 24 on the surface of the solid electrolyte 25. Details will be described later.

  Next, nickel having a thickness of 0.5 μm was formed as the negative electrode current collector 23 on the surface of the negative electrode active material 24 to obtain a strip-like laminate having the laminated structure shown in FIG.

  This is wound into a flat plate shape, and a pair of external electrodes 33 is formed so as to be electrically connected to the positive electrode current collector 27 and the negative electrode current collector 23, respectively, and a flat plate lithium ion as shown in FIG. A secondary battery was obtained.

  A method for forming a silicon thin film as the negative electrode active material 24 will be described with reference to FIG.

  In the apparatus of FIG. 13, a deposition source 71 and an intermediate layer deposition source 75 are arranged in the thin film formation chamber 1 c instead of the first sputter deposition source 51, the gas introduction nozzle 55, and the second sputter deposition source 52. 1 is different from the apparatus of FIG. In FIG. 13, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

  The strip-shaped substrate 22 on which the positive electrode current collector 27, the positive electrode active material 26, and the solid electrolyte 25 are formed is squeezed out from the scooping roll 11, and transported in turn by the transporting roll 12a, the can roll 13, and the transporting roll 12b. It is scraped off by the scraping roll 14. In this process, particles such as atoms, molecules, or clusters (hereinafter referred to as “evaporated particles”) generated from the vapor deposition source 71 and the intermediate layer vapor deposition source 75 pass through the mask 4 of the partition wall 1 a and are on the can roll 13. The thin film 6 is formed by adhering to the surface of the solid electrolyte 25 of the substrate 22 running on the substrate. Opposite to the substrate 22, a vapor deposition source 71 and an intermediate layer vapor deposition source 75 are arranged. An intermediate layer vapor deposition source 75 is disposed at a substantially central position in the traveling direction of the substrate 22 in the vaporized particle flow emitted from the vapor deposition source 71 and passing through the mask 4. The intermediate layer deposition source 75 extends in the vicinity of the can roll 13 over the entire width of the substrate 22 in the width direction (perpendicular to the paper surface of FIG. 13). Therefore, the intermediate layer vapor deposition source 75 functions as a second mask, and prevents the evaporation particles from being deposited from the vapor deposition source 71 on the outer surface of the can roll 13 in the region facing the intermediate layer vapor deposition source 75. Therefore, first, the evaporated particles from the vapor deposition source 71 are mainly deposited on the surface of the solid electrolyte 25 of the substrate 22, and then the vaporized particles from the intermediate layer vapor deposition source 75 are mainly deposited, and again the vaporized particles from the vapor deposition source 71. Is mainly deposited.

In Examples 3 and 4 , using such an apparatus, silicon is evaporated from the vapor deposition source 71 and copper-aluminum material (melting point Tm = 548 ° C.) is vaporized from the intermediate layer vapor deposition source 75 by a vacuum vapor deposition method. A negative electrode active material 24 having a multilayer structure with a total thickness of 5 μm was formed.

Furthermore, in Example 3 , the outer peripheral surface temperature of the can roll 13 when forming the negative electrode active material 24 was maintained at 20 ° C. by circulating a heat storage medium (not shown) inside the can roll 13.

Moreover, in Example 4 , it carried out similarly to Example 3 except having maintained the outer peripheral surface temperature of the can roll 13 at the time of formation of the negative electrode active material 24 at 280 degreeC.

In Comparative Example 3, the intermediate layer deposition source 75 is removed, only the deposition source 71 is used, the temperature of the outer peripheral surface of the can roll 13 during the formation of the negative electrode active material 24 is maintained at 20 ° C., and a single layer structure having a thickness of 5 μm The negative electrode active material 24 was formed in the same manner as in Example 3 .

FIGS. 14A and 14B are diagrams schematically showing SEM photographs in which cross-sections in the thickness direction of the negative electrode active material (silicon thin film) 24 of Examples 3 and 4 are taken in order. In each figure, the lower side of the paper is the solid electrolyte 25 side, and the upper side is the surface of the negative electrode active material 24.

In Examples 3 and 4 (in order of FIGS. 14A and 14B), the silicon particles grow as substantially inverted frustoconical columnar particles while the particle diameter gradually increases from the interface with the solid electrolyte 25. However, the growth of silicon particles is discontinuous on both sides of a layer (intermediate layer) 70 having a slight thickness present in the central portion in the thickness direction. The negative electrode active material 24 is divided by the intermediate layer 70 and has a two-layer structure in the vertical direction. The intermediate layer 70 is a copper-aluminum thin film formed by the intermediate layer deposition source 75. Since the silicon particles in the layer above the intermediate layer 70 newly start growing from the intermediate layer 70 in a substantially inverted truncated cone shape, the particle diameter increases near the surface of the negative electrode active material (silicon thin film) 24. It is suppressed.

Furthermore, in the negative electrode active material 24 (Example 3 , FIG. 14A) formed with the outer peripheral surface temperature of the can roll 13 being 20 ° C., the intermediate layer 70 is a continuous film. It was found that in the negative electrode active material 24 formed at a temperature of 280 ° C. (Example 4 , FIG. 14B), the intermediate layer 70 was divided into a network shape or an island shape instead of a continuous film. This is presumably because the melting point of the copper-aluminum-based material is lower than that of silicon, so that when a thin film is formed at a high temperature, it is easily divided into a network or islands. The division of the intermediate layer 70 recognized in the comparison between the example 3 and the example 4 is not limited to the case where the intermediate layer 70 is made of a copper-aluminum material, and similarly when other low melting point materials are used. confirmed.

Moreover, after forming the negative electrode active material 24 on the same conditions as Example 3 , it heated at 280 degreeC, cooled, and when the SEM photograph of the cross section of thickness direction was image | photographed, Example 4 (FIG.14 (B)) Similarly to the intermediate layer 70 of FIG. That is, it was confirmed that an intermediate layer divided into a mesh shape or an island shape can be obtained by heating after forming a continuous intermediate film made of a low melting point material.

  In addition, although illustration is abbreviate | omitted, in the comparative example 3 which does not use the intermediate | middle layer vapor deposition source 75, similarly to the comparative example 2 (FIG.6 (A)), a silicon particle gradually has a particle diameter from the interface with the solid electrolyte 25. While increasing, it grew as a substantially inverted truncated cone-shaped columnar particle, and the particle diameter was the largest in the vicinity of the surface of the negative electrode active material 24.

The lithium ion secondary batteries obtained in Examples 3 and 4 and Comparative Example 3 were subjected to a charge / discharge cycle test at a test temperature of 20 ° C., a charge / discharge current of 3 mA / cm ² , and a charge / discharge voltage range of 4.2 V to 2.5 V. went. The ratio of the capacity after 50 cycles and after 200 cycles with respect to the initial discharge capacity was determined as the battery capacity retention rate (cycle characteristics). The results are shown in Table 3.

As can be seen from Table 3, in Examples 3 and 4 , in which the growth of silicon particles is discontinuous in the middle layer in the middle of the thickness direction, the growth of silicon particles is performed over the entire range in the thickness direction without the presence of the middle layer. Compared to Comparative Example 3 in which the battery capacity is continuous, the battery capacity retention rate after 50 cycles and after 200 cycles is large.

In Table 3, there is no significant difference in cycle characteristics between Example 3 in which the intermediate layer is a continuous film and Example 4 in which the intermediate layer is a split film.

Capacity maintenance rate after 50 cycles in the case of performing charge and discharge were the charge and discharge rate to 5C and high speed, excellent in Example 4 and 65% in Example 4 while the Example 3 was 58% Results were obtained. This is probably because the movement of ions in the negative electrode active material 24 is facilitated by dividing the intermediate layer into a network shape or an island shape.

  In this example, the two-layered negative electrode active material 24 was formed using one vapor deposition source 71, but the two-layered negative electrode active material 24 was formed using two vapor deposition sources as shown in FIG. It may be formed.

  In the first and second embodiments, the negative electrode active material thin film (silicon thin film) is directly provided on the surface of the current collector layer. However, the present invention is not limited to this, and the surface of the current collector layer is not limited thereto. It may be provided via the provided underlayer. The underlayer may be, for example, a layer for the purpose of strengthening the adhesive force between the current collector layer and the negative electrode active material thin film (silicon thin film), rust prevention treatment, or the like. -A copper thin film or a chromate treatment layer can be used. Or the layer formed by the surface treatment mentioned later may be sufficient.

  In the first and second embodiments, the negative electrode active material thin film (silicon thin film) is formed by sputtering or vapor deposition. However, the present invention is not limited to this. Other vacuum film forming methods may be used, and even in this case, the same effect can be obtained.

  Moreover, although the negative electrode active material thin film shown in the above embodiment has a two-layer structure composed of two silicon thin films, the present invention is not limited to this and may have a multilayer structure of three or more layers. . By using a multi-layer structure, an improvement in cycle characteristics, which is an effect of the present invention, can be obtained. The thickness per layer of the silicon thin film is preferably 12 μm or less, more preferably 6 μm or less, and particularly preferably 2 μm or less. When the thickness per layer of the silicon thin film exceeds 12 μm, the particle diameter of the columnar particles is increased in the silicon thin film, and the cycle characteristics are remarkably deteriorated. Therefore, when the thickness per layer exceeds 12 μm, the negative electrode active material thin film is multilayered, and the cycle characteristics are improved as compared with the case where the negative electrode active material thin film is not divided into multiple layers. Issues remain. The number of layers of the negative electrode active material thin film can be set according to the thickness of the negative electrode active material thin film to be formed.

  The diameter of a typical silicon particle obtained in the above-mentioned embodiment is about 2 to 15 μm before expansion by lithium occlusion. Usually, each silicon particle is composed of a plurality of silicon particles of 1 to 6 μm. It becomes. However, the silicon particle diameter in the present invention is not limited to this.

Further, the copper foil used as the negative electrode current collector in Examples 1 and 2 and Reference Examples 1 to 3 may be subjected to a surface treatment. Surface treatments that can be applied to copper foil include zinc plating, tin, copper, nickel, or cobalt-zinc alloy plating, formation of a coating layer using an azole derivative such as benzotriazole, chromic acid or dichromic acid Formation of a chromium-containing film by a solution containing a salt or a combination thereof can be used. Or it can replace with copper foil and what gave the copper coating to the surface of the other base material can also be used. You may perform said surface treatment on the surface of this copper coating.

  Although not mentioned in the description of the above embodiments and examples, it is desirable to form a silicon thin film in an inert gas or nitrogen atmosphere. The atmospheric gas may be introduced toward the film formation surface (the opening of the mask 4 in the above embodiment), or introduced so as to reach the entire inside of the vacuum chamber (the thin film forming chamber 1c in the above embodiment). However, it is more efficient and preferable to introduce it toward the film formation surface.

  By forming the silicon thin film in such an atmospheric gas, it is possible to prevent the silicon columnar particles adjacent to each other in the direction parallel to the film formation surface from growing and growing and the silicon particle diameter from becoming coarse. As a result, the degree of expansion / contraction of silicon particles during charging / discharging becomes severe, and it is possible to suppress deterioration of cycle characteristics. According to the experiments by the present inventors, a graph showing detailed experimental results is omitted, but the battery capacity maintenance rate of the energy device is reduced to 80% by forming a silicon thin film in the above gas atmosphere. The number of charge / discharge cycles increased by 15 to 50%, for example.

A preferable introduction amount of the gas is set according to the film forming condition of the silicon thin film, particularly the thin film deposition rate R (nm / s). For example, when the gas is introduced toward the film formation surface, the gas introduction amount Q (m ³ / s) per 100 mm of the film formation width is 1 × 10 ⁻¹⁰ × R to 1 × 10 ⁻⁶ × R. In particular, it is preferably 1 × 10 ⁻⁹ × R to 1 × 10 ⁻⁷ × R. If the amount of gas introduced is too small, the above effect cannot be obtained. Conversely, if the amount of gas introduced is too large, the deposition rate of the silicon thin film will decrease.

  As the gas to be used, argon is most preferable from the viewpoints of practicality and the remarkable effects described above.

  Moreover, it may be preferable that a part of silicon contained in the silicon thin film is an oxide. When the silicon content in the silicon thin film is large and the battery capacity is large, the degree of expansion / contraction of the silicon thin film during charge / discharge increases, and the cycle characteristics may deteriorate. If the silicon thin film contains silicon oxide, the silicon oxide has little expansion / contraction during charging / discharging, so that expansion / contraction of the silicon thin film during charging / discharging can be suppressed, and cycle characteristics can be improved. it can. For example, it is preferable to form a film so that 20 to 50% of silicon contained in the silicon thin film is an oxide. According to the experiments by the present inventors, the graph showing the detailed experimental results is omitted, but the silicon thin film contains silicon oxide, so that the battery capacity retention rate of the energy device is 80% depending on the silicon thin film. For example, the number of charge / discharge cycles to be reduced to 10% increased by 10 to 140%.

  A part of silicon can be converted into an oxide by, for example, introducing an oxygen-based gas in the vicinity of the film formation surface and reacting with silicon atoms during the formation of a silicon thin film in a vacuum atmosphere. . In order to enhance the reactivity, it is effective to use ozone, or to apply energy by plasma or substrate potential.

A preferable introduction amount of the gas is set according to the film forming condition of the silicon thin film, particularly the thin film deposition rate R (nm / s). For example, when the gas is introduced toward the film formation surface, the gas introduction amount P (m ³ / s) per 100 mm of the film formation width is 1 × 10 ⁻¹¹ × R to 1 × 10 ⁻⁵ × R. In particular, it is preferably 1 × 10 ⁻¹⁰ × R to 1 × 10 ⁻⁶ × R, more preferably 1 × 10 ⁻⁹ × R to 1 × 10 ⁻⁷ × R. However, the gas introduction amount P is not limited to this, depending on the equipment configuration. If the amount of gas introduced is too small, the above effect cannot be obtained. On the other hand, if the amount of gas introduced is too large, the entire silicon thin film becomes an oxide and the battery capacity decreases.

  The field of application of the energy device of the present invention is not particularly limited, but it can be used as a secondary battery for a thin, lightweight, small portable device, for example.

It is sectional drawing which showed schematic structure of one Embodiment of the apparatus used for manufacture of the energy device of this invention. (A)-(D) is the figure which represented typically the SEM photograph of the cross section of the negative electrode active material thin film in the comparative example 1, reference examples 1, 2, and 3 in order. It is an element distribution map of the thickness direction of the negative electrode active material thin film of the reference example 1 of this invention. It is an element distribution map of the thickness direction of the negative electrode active material thin film of the reference example 2 of this invention. It is sectional drawing which showed schematic structure of another embodiment of the apparatus used for manufacture of the energy device of this invention. (A)-(C) is the figure which represented typically the SEM photograph of the cross section of the negative electrode active material thin film in the comparative example 2, Example 1 , and 2, in order. It is an element distribution map of the thickness direction of the negative electrode active material thin film of Example 1 of this invention. It is a schematic sectional drawing which shows an example of a structure of the principal part of the energy device which concerns on Embodiment 2 of this invention. It is a schematic sectional drawing which shows an example of the product form of the energy device which concerns on Embodiment 2 of this invention. It is a schematic perspective view of the product form of the energy device shown in FIG. It is a schematic sectional drawing which shows another example of the product form of the energy device which concerns on Embodiment 2 of this invention. 12A is a plan view showing an example of the fuse portion in the energy device of the present invention, and FIG. 12B is a cross-sectional view taken along line 12B-12B in FIG. It is sectional drawing which showed schematic structure of further another embodiment of the apparatus used for manufacture of the energy device of this invention. (A), (B) is the figure which represented typically the SEM photograph of the cross section of the negative electrode active material thin film in Example 3, 4 in order.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Vacuum chamber 1a ... Partition 1b ... Transfer chamber 1c ... Thin film formation chamber 4 ... Mask 5 ... Negative electrode collector 6 ... Thin film 10 ... Vacuum Film forming apparatus 11 ... unwinding rolls 12a, 12b ... transport roll 13 ... can roll 14 ... take-up roll 16 ... vacuum pump 20 ... battery element 22 ... substrate 23 .. Negative electrode current collector 24... Negative electrode active material 25... Solid electrolyte 26... Positive electrode active material 27. External electrode 35 ... external electrode 36 ... fuse portion 37 ... protective layer 50 ... interface layer 51 ... first sputter deposition source 52 ... second sputter deposition source 55 Gas introduction nozzle 60 ... intermediate layer 61 ... first vapor deposition source 62 ... second vapor deposition source 65 ... intermediate layer vapor deposition source 7 ... intermediate layer 71 ... vapor deposition source 75 ... middle layer deposition source

Claims (12)

An energy device comprising a current collector layer and a negative electrode active material thin film provided directly or via an underlayer on the current collector layer,
The negative electrode active material thin film have a multilayer structure comprising two or more silicon thin film containing silicon as a main component,
An energy device comprising an intermediate layer containing an element having a melting point lower than that of silicon between adjacent silicon thin films . The silicon thin film has columnar particles whose longitudinal direction is the thickness direction,
The energy device according to claim 1, wherein the columnar particles are discontinuous between the silicon thin films adjacent in the thickness direction. The energy device according to claim 1 , wherein the intermediate layer includes aluminum . The energy device according to claim 1 , wherein the intermediate layer is a discontinuous film. The energy device according to claim 1 , wherein the intermediate layer has an island shape.   The energy device according to claim 1, wherein a part of silicon contained in the silicon thin film is an oxide. A method for producing an energy device in which a negative electrode active material thin film and a positive electrode active material thin film face each other through a layer not exhibiting electronic conduction,
A step of forming the negative electrode active material thin film on the current collector layer directly or through an underlayer by a vacuum film forming method, and a step of forming the positive electrode active material thin film,
The formation of the negative electrode active material thin film is observed including a time divided two or more silicon deposition step,
Between two or more of the silicon deposition process, the manufacturing method of the energy device, characterized in including Mukoto forming an intermediate layer containing a low melting point of elemental silicon. The method for manufacturing an energy device according to claim 7, wherein the intermediate layer contains aluminum. The method for manufacturing an energy device according to claim 7 , wherein the intermediate layer is formed by a vacuum film formation method in a vacuum atmosphere, and the silicon deposition step is subsequently performed. The energy according to claim 7 , wherein when the melting point of the material for forming the intermediate layer is Tm (° C.), the deposition surface temperature during the formation of the intermediate layer is maintained at Tm / 3 (° C.) or more. Device manufacturing method. The method of manufacturing an energy device according to claim 7 , wherein after forming the intermediate layer, the intermediate layer is heated to a melting point or higher. The method for manufacturing an energy device according to claim 7 , wherein the silicon deposition step is performed in an inert gas or nitrogen atmosphere.