WO2012117991A1

WO2012117991A1 - Negative electrode active material for lithium ion secondary cell, negative electrode for lithium ion secondary cell, and lithium ion secondary cell

Info

Publication number: WO2012117991A1
Application number: PCT/JP2012/054710
Authority: WO
Inventors: 俊夫谷; 西村　健; 島田　道宏; 阿部　英俊; 昌明久保田; 江黒　高志
Original assignee: 古河電気工業株式会社; 古河電池株式会社
Priority date: 2011-02-28
Filing date: 2012-02-27
Publication date: 2012-09-07
Also published as: KR20130119447A; TW201236249A; CN103370817A

Abstract

The present invention can provide a negative electrode active material for a lithium ion secondary cell can be provided, the material having a high capacity, a high charge and discharge efficiency, and exceptional cycle properties. This negative electrode active material is characterized in including silicon as a main component and at least 0.05 % by weight of element A, the atomic radius r_A of element A in relation to the atomic radius r_O of silicon satisfying the relationship │(r_A-r_O)/r_O│≤0.1. This negative electrode for a lithium ion secondary cell is obtained by applying the negative electrode active material to a collector or forming the material into a film on the collector.

Description

Negative electrode active material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery

The present invention relates to a negative electrode active material for a lithium ion secondary battery, a negative electrode using the same, and a lithium ion secondary battery, and in particular, has a high capacity, high charge / discharge efficiency, and charge / discharge It is related with the negative electrode active material which can implement | achieve the lithium ion secondary battery excellent in cycling characteristics, without peeling and removing from a collector even if it repeats.

Lithium ion secondary batteries are used mainly in portable devices, and higher capacities are required as the devices used become smaller and more multifunctional. However, the negative electrode active material used in the present lithium ion secondary battery is a carbon-based material such as artificial graphite or natural graphite, and has a theoretical capacity of 372 mAh / g, and a further increase in capacity cannot be expected. .

For this reason, a negative electrode using a metal material such as silicon (Si) or tin (Sn) having a larger theoretical capacity or an oxide material thereof has been proposed (for example, see Patent Document 1). Attention has been paid. These materials show a very high capacity in the initial few cycles, but by repeating charging and discharging, pulverization occurs due to expansion and contraction of the active material, and the negative electrode active material falls off the current collector. As compared with the carbon-based negative electrode active material, there is a problem that the cycle characteristics are inferior and the life is short.

Therefore, a proposal has been disclosed in which carbon nanofibers are grown on the surface of a Si-based active material, the strain during expansion and contraction of the negative electrode active material particles is relaxed by its elastic action, and the cycle life is improved (for example, Patent Document 2).

Also, a proposal has been made to form a hybrid alloy of an active material that can be alloyed with Li, such as Si or Sn, and an element that is not alloyed with Li, such as Cu or Fe (see, for example, Patent Document 3).

In addition, a method of forming a negative electrode by forming these materials as a thin film on a current collector by CVD, sputtering, vapor deposition, plating, or the like has been proposed. According to this thin film type negative electrode, it is possible to suppress pulverization of the negative electrode active material as compared with a conventional coated negative electrode prepared by applying a slurry containing a powdered negative electrode active material together with a binder or the like on a current collector, Furthermore, since the current collector and the active material can be integrated with good adhesion, it is known that the electron conductivity in the negative electrode is improved.

Furthermore, it has been proposed to form a negative electrode active material thin film on a foamed current collector to ensure battery capacity while maintaining higher adhesion between the current collector and the negative electrode active material. (For example, refer to Patent Document 4).

Japanese Patent Laid-Open No. 07-29602 JP 2006-244984 A JP 2005-78999 A JP 2004-71305 A

However, a conventional negative electrode in which a negative electrode active material is formed by applying a slurry-like coating liquid of a negative electrode active material, a conductive material, and a binder, and the negative electrode active material and the current collector are made of a resin having low conductivity. The binding force is weak because it is bound with a binding material and the amount of resin used must be kept to a minimum so that the internal resistance does not increase. For this reason, if the volume expansion of Si itself cannot be suppressed, problems such as pulverization and separation of the negative electrode active material during charge and discharge, cracks in the negative electrode, and decrease in conductivity between the active materials occur, resulting in a decrease in capacity. Resulting in. That is, the charge / discharge cycle characteristics are poor, and the secondary battery has a short life.

The invention described in Patent Document 2 does not suppress the volume expansion of Si itself, but binds the negative electrode active material and the current collector with a resin having insufficient bonding force. It has not been able to exert a sufficient effect for suppressing deterioration. Furthermore, since a carbon nanofiber production process is required, both productivity and economy are low. In addition, the technique described in Patent Document 3 is difficult to uniformly disperse nano-sized components, and the actual situation is that it cannot contribute to the improvement of charge / discharge cycle characteristics.

As described above, since Si, which is expected as a negative electrode active material, has a large volume change during charge and discharge, active material particles containing Si are liable to be cracked, and thus current collection within the particles is likely to deteriorate. Still, the shortcoming is that the cycle life is short.

In addition, although the thin film type negative electrode greatly improves the electrode characteristics, when a thin film having an active material amount that satisfies the actual capacity required for electronic devices such as personal computers and mobile phones is formed, the charge / discharge cycle characteristics deteriorate, There was a tendency for the serviceable life to be repeated. For this reason, when used in a lithium ion secondary battery, the amount of the active material is necessarily reduced, so that the application is limited and it is difficult to put it to practical use.

In the invention described in Patent Document 4, the use of the foamed current collector increases the thickness of the electrode. As a result, the energy density of the electrode and the energy density of the battery are reduced. It was. Further, since the edge portion of the foamed portion of the current collector is easily exposed during electrode processing, there is a problem that an internal short circuit is likely to occur through the thin separator.

The present invention has been made in view of the above-described problems. The object of the present invention is to provide a lithium ion battery that does not easily deteriorate even after repeated charge and discharge, has a long battery life, and provides a high charge and discharge capacity. A negative electrode active material for a secondary battery, a negative electrode using the negative electrode active material, and a lithium ion secondary battery having a long life and high energy density are provided.

As a result of intensive studies to achieve the above object, the present inventors have introduced a second element having an atomic radius as large as Si into a negative electrode active material mainly composed of silicon (Si). Therefore, insertion (charge) and desorption between the lattices of silicon active material without charging too much strain between the lattices or atoms of the negative electrode active material, and when charging / discharging Li ions with a small ion radius. It has been found that (discharge) can be easily generated without failure, and generation of useless irreversible capacity due to residual Li ions accompanying discharge after charging can be reduced. The present invention has been made based on these findings.

That is, the present invention provides the following inventions.
(1) An active material used for a negative electrode for a lithium ion secondary battery, which is composed of particles containing silicon as a main component and containing at least 0.05% by mass of element A, and the element with respect to the atomic radius r ₀ of silicon A negative electrode active material for a lithium ion secondary battery, wherein the atomic radius r _{A of A} satisfies a relationship of | (r _A −r ₀ ) / r ₀ | ≦ 0.1.
(2) The lithium ion according to (1), wherein the element A is at least one element selected from the group consisting of P, Cr, Mn, Fe, Co, Ni, Cu, and As Negative electrode active material for secondary batteries.
(3) The negative electrode active material for a lithium ion secondary battery according to (1), further comprising oxygen or fluorine.
(4) The negative electrode active material for a lithium ion secondary battery according to (1), wherein the particles have an average primary particle diameter of 10 nm to 5 μm.
(5) A nonaqueous electrolyte secondary battery comprising an active material layer formed by applying and drying a coating liquid containing the negative electrode active material described in (1) on one or both surfaces of a negative electrode current collector Negative electrode.
(6) A negative electrode current collector having protrusions on the surface, and a thin film negative electrode active material formed on the surface of the negative electrode current collector, containing silicon as a main component and containing at least 0.05% by mass of element A The element A is an element in which the atomic radius r _{A of the} element A with respect to the atomic radius r ₀ of silicon satisfies a relationship of | (r _A −r ₀ ) / r ₀ | ≦ 0.1. There is a negative electrode for a lithium ion secondary battery.
(7) The lithium ion according to (6), wherein the element A is at least one element selected from the group consisting of P, Cr, Mn, Fe, Co, Ni, Cu, and As Negative electrode for secondary battery.
(8) The negative electrode for a lithium ion secondary battery according to (6), wherein the negative electrode active material layer further contains oxygen or fluorine.
(9) The negative electrode current collector is a copper foil, and the surface of the copper foil on which the active material layer is provided is subjected to an electrolytic surface roughening treatment to provide a protrusion, and the surface roughness Rz is 1 μm. (6) The negative electrode for a lithium ion secondary battery according to (5) or (6), wherein
(10) The surface roughness Rz of the surface on which the active material layer is provided of the copper foil before the electrolytic surface-roughening treatment is 0.5 μm to 3 μm. Negative electrode for secondary battery.
(11) having a positive electrode capable of inserting and extracting lithium ions, a negative electrode according to (5) or (6), and a separator disposed between the positive electrode and the negative electrode, and having lithium ion conductivity A lithium ion secondary battery, wherein the positive electrode, the negative electrode, and the separator are provided in an electrolyte.

According to the present invention, a negative electrode active material that realizes a lithium-ion secondary battery having high capacity, high charge / discharge efficiency, and excellent cycle characteristics without being peeled off or removed from the current collector even after repeated charge / discharge. Substance materials can be obtained.

The cross-sectional schematic diagram which shows an example of the negative electrode for lithium ion secondary batteries which concerns on 1st Embodiment. The figure which shows the manufacturing apparatus of nanosize particle | grains. The figure which shows the mixer used for manufacture of the negative electrode which concerns on 1st Embodiment. The figure which shows the coater used for manufacture of the negative electrode which concerns on 1st Embodiment. The cross-sectional schematic diagram which shows an example of the negative electrode for lithium ion secondary batteries which concerns on 2nd Embodiment. The cross-sectional schematic diagram which shows an example of the lithium ion secondary battery which concerns on this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(1. Negative electrode for lithium ion secondary battery according to first embodiment)
First, a negative electrode for a lithium ion secondary battery according to an embodiment of the present invention will be described with reference to FIG.
In the negative electrode 1 for a lithium ion secondary battery of the present invention, a slurry-like coating liquid containing the negative electrode active material 3, the conductive material 4, and the binder 6 is applied to one or both surfaces of the negative electrode current collector 9 and dried. The active material layer 5 is formed. The negative electrode active material 3 in the present invention is characterized by comprising Si-based particles having a characteristic component structure.

(1-1. Configuration of negative electrode active material)
Therefore, embodiments of the negative electrode active material for a lithium ion secondary battery according to the present invention will be described in detail below.
The negative electrode active material for a lithium ion secondary battery of the present invention has a particulate form, and the particles contain silicon as a main component and at least an element A as a second element. Since silicon is an element that easily stores lithium, the particles also have lithium storage capacity. In addition, silicon has an advantage that the cost is relatively low among elements having lithium storage ability.

The element A is an element in which the atomic radius r _A approximates the atomic radius r ₀ (0.117 nm) of Si, and satisfies the relationship | (r _A −r ₀ ) / r ₀ | ≦ 0.1. . Filled atomic radius r ₀ of the atomic radius r _A and Si element A the above relationship, the element A has a Si comparable atomic radius, the element A in a system composed mainly of Si lattice or Si, There is a high possibility of substitution to a position substantially the same as the Si atom position of the Si lattice, or it is easy to form a compound with Si, and the Si lattice structure can exist in a stable state. On the other hand, when | (r _A −r ₀ ) / r ₀ | exceeds 0.1, an element having an atomic radius that is too small or too large compared to the atomic radius of Si is mainly composed of Si lattice or Si. It will be included in the system. Elements that are too large intrude into the interstitial position of Si and cause vacancies, causing excessive strain on the Si lattice. Elements that are too small also become excessive solid solubility limits and cause a large amount of diffusion. Giving excessive strain due to alloying. Such elements themselves do not contribute to the subsequent charge / discharge without inhibiting the electrochemical movement of Li ions or desorbing the alloyed Li ions entering the Si lattice during charging and desorbing during discharging. Therefore, there is a possibility of generating an irreversible capacity, which is not preferable as the negative electrode active material of the present invention.

As shown in Table 1 below, element A can be used by selecting one or more from the group of P, Cr, Mn, Fe, Co, Ni, Cu, Ga, Ge, As, Se, and Br. These elements A are elements that do not combine with Li, or elements that form a compound that has a small amount of occlusion of lithium even when combined with Li and does not cause a large density change compared to silicon. Volume expansion and contraction of silicon during discharge can be suppressed. The element A may form a compound with silicon, or may exist as a simple substance or a solid solution except for Fe. When the compound is formed, it does not matter whether it is crystalline or amorphous.

Furthermore, the element A is preferably at least one element selected from the group consisting of P, Cr, Mn, Fe, Co, Ni, Cu, and As. P, Cr, Mn, Fe, Co, Ni, Cu, and As are economical elements with relatively low costs and are practical. Furthermore, for elements other than P and As, Si and Si ₂ M type or SiM ₂ type compounds can be formed, and the effect of suppressing volume expansion and contraction is high.

More than 0.05% by mass of the above element A is contained in the particles. When a plurality of elements A are included, the total content of these elements is set to 0.05% by mass or more. By making the content 0.05% by mass or more, volume expansion / contraction of silicon during charge / discharge can be effectively suppressed. Although the upper limit of the content of the element A is not particularly defined, it can be arbitrarily determined within a range of less than 50% by mass in consideration of the lithium storage capacity of silicon and the like. Even if the amount of the element A is sufficiently smaller than that of Si, the effect of suppressing the volume expansion and contraction can be obtained.

The particles according to the present invention may further contain oxygen or fluorine as the third element. Although oxygen and fluorine have small atomic radii, as shown in Table 1 above, the ionic radius r _{A ′} is comparable in size to the atomic radius r ₀ (0.117 nm) of Si, causing extra strain. In addition, the change in the volume of silicon can be suppressed and the charge / discharge cycle life can be further improved without obstructing the penetration and desorption of Li ions. Oxygen and fluorine are combined and dispersed with a part of Li, and also have an effect of stabilizing the active material. As for Ag and Cd, although the ionic radius is comparable to the atomic radius r ₀ of Si, it does not form an ion-binding compound with Si, so the third element constituting the negative electrode active material of the present invention It is not preferable.

Note that oxygen and fluorine may be uniformly contained in the entire particle, or may be contained, for example, in part of the surface portion or the like. The oxygen and fluorine contents are preferably 0.5% by mass or more in order to maintain high charge / discharge characteristics, and the total with the element A content is preferably 50% by mass or less.

Such particles according to the present invention may have an average primary particle size of 10 nm to 5 μm. Some conventional negative electrode active material materials mainly composed of silicon suppress the influence of volume expansion and contraction by reducing the average particle diameter, but the particles constituting the negative electrode active material of the present invention are primary particles. Even if it is used from the nanometer order to the micrometer order of secondary particles, the effect can be sufficiently exhibited. Therefore, an active material having an appropriate size can be obtained according to the application and various purposes. For example, if the negative electrode active material is composed of nano-scale to sub-micron order particles having an average particle diameter of 10 nm, the Li ion conductivity and electron conductivity paths are short, and the current collecting property is good and easy to maintain. , Cycle characteristics can also be improved. In addition, for example, if the negative electrode active material is composed of particles of micron order to 5 μm level, a slurry-like coating liquid having excellent coating properties on the current collector surface can be prepared, and a thick film can be easily formed. Thus, a high actual capacity can be secured. The particles according to the present invention can also be used as secondary particles obtained by granulating primary particles. In this case, considering the practical thickness of the negative electrode active material layer when forming the negative electrode, the secondary particles The average particle size of the particles is preferably 20 μm or less, and more preferably about 5 μm or less. From the viewpoint of particle handling, the average particle size is preferably 10 nm or more.

The shape of the particles is not particularly limited, and may be, for example, a substantially spherical body or a linear body. Since the fine particles are usually present in an aggregated state, the average particle size of the particles here refers to the average particle size of the primary particles. The particle size can be measured by using image information of an electron microscope (SEM) and a volume-based median diameter of a dynamic light scattering photometer (DLS). For the average particle size, confirm the particle shape in advance using an SEM image, obtain the particle size by image analysis (for example, “A Image-kun” (registered trademark) manufactured by Asahi Kasei Engineering), or disperse the particles in a solvent to obtain DLS (for example, , DLS-8000 manufactured by Otsuka Electronics Co., Ltd.). If the fine particles are sufficiently dispersed and not agglomerated, almost the same measurement results can be obtained with SEM and DLS. In addition, even when the shape of the particle is a highly developed structure such as acetylene black, the average particle size is defined by the primary particle size here, and the average particle size can be obtained by image analysis of the SEM photograph. it can.

Also, the average particle size of secondary particles can be determined by image analysis of SEM photographs.

In the present invention, “having silicon as a main component” means that the silicon content is the largest among the elements constituting the particles, and the silicon content is preferably 50% by mass or more, more preferably 70%. It shows that it is at least mass%. The second element and the third element are the elements constituting the particles other than silicon, and the element group having a characteristic role is referred to as the second element or the third element. And there is no relationship with the content of both.

Note that the negative electrode active material of the present invention described above may have a crystalline structure that is crystalline, microcrystalline, amorphous, or a mixture thereof. This is because any crystalline form becomes amorphous by alloying with Li ions during charging.

(1-2. Production of negative electrode active material)
The method for producing the negative electrode active material of the present invention is not particularly limited, and for example, by using various known particle (powder) production methods, those having the composition and average particle diameter as described above can be produced. it can.

A typical example of the production of the nano-sized particles constituting the negative electrode active material is a gas phase synthesis method. For example, a raw material powder blended to have a desired composition by plasma CVD synthesis is turned into plasma, heated to the equivalent of 10,000 K, and then cooled, so that nano-sized particles having an average particle size of about 10 nm to about 100 nm The negative electrode active material of this invention which consists of can be manufactured.

Here, a specific example of a manufacturing apparatus used for manufacturing nano-sized particles will be described with reference to FIG. In the nanosize particle manufacturing apparatus 31 shown in FIG. 2, a high frequency coil 43 for generating plasma is wound around the upper outer wall of the reaction chamber 33. An AC voltage of several MHz is applied to the high frequency coil 43 from the high frequency power supply 45. A preferred frequency is 4 MHz. The upper outer wall around which the high-frequency coil 43 is wound is a cylindrical double tube made of quartz glass or the like, and cooling water is passed through the gap to prevent the quartz glass from melting by the plasma 47.

In addition, a sheath gas supply port 39 is provided in the upper part of the reaction chamber 33 together with the raw material powder supply port 35. The raw material powder 37 supplied from the raw material powder feeder is supplied into the plasma 47 through the raw material powder supply port 35 together with the carrier gas 42 (rare gas such as helium and argon). The sheath gas 41 is supplied to the reaction chamber 33 through the sheath gas supply port 39. Note that the raw material powder supply port 35 is not necessarily installed above the plasma 47 as shown in FIG. 2, and a nozzle can be installed in the lateral direction of the plasma 47. The raw material powder supply port 35 may be water-cooled with cooling water. Note that the properties of the raw material of the nano-sized particles supplied to the plasma 47 are not limited to powder, and a slurry-like coating liquid of raw material powder or a gaseous raw material may be supplied.

The reaction chamber 33 plays a role of maintaining the pressure in the plasma reaction part and suppressing the dispersion of the produced fine powder. The reaction chamber 33 is also water-cooled to prevent damage due to the plasma 47. A suction tube is connected to the side of the reaction chamber 33, and a filter 49 for collecting the synthesized fine powder is installed in the middle of the suction tube. The suction pipe connecting the reaction chamber 33 and the filter 49 is also water-cooled with cooling water. The pressure in the reaction chamber 33 is adjusted by the suction capability of a vacuum pump (VP) installed on the downstream side of the filter 49.

The method for producing nano-sized particles is a bottom-up method in which the nano-sized particles are deposited from plasma into a solid via a gas and a liquid, and thus become spherical at the droplet stage. On the other hand, in the top-down method of reducing large particles, such as the crushing method and the mechanochemical method, the shape of the particles is rugged and the shape is greatly different.
In addition, the nanosized particle which comprises the negative electrode active material which concerns on this invention is obtained by using mixed powder of each powder of Si and the element A for raw material powder. When there are a plurality of elements A, a mixed powder of a plurality of types of powders can be used.

A typical example of the production of micron-sized particles constituting the negative electrode active material is an atomizing method. For example, an alloy gas melted to have a desired composition by a gas atomizing method is used as an inert gas flow. The negative electrode active material of the present invention consisting of micron-sized particles of submicron to about 5 μm can be produced by supplying the liquid to the inside and quenching.

Furthermore, by exposing the obtained negative electrode active material material to an oxygen or fluorine atmosphere, the Si-based active material can be oxidized or fluorinated, and the negative electrode active material containing oxygen or fluorine as the third element The material can be manufactured. When oxygen is contained, it may be exposed to a heated air atmosphere.

(1-3. Effects of negative electrode active material)
According to the negative electrode active material of the present invention, in addition to silicon, the negative electrode active material material is composed of particles containing at least an element A having an atomic radius similar to that of silicon, and the element A is an excessively large strain between Si lattices or Si atoms. Without charge, insertion (charge) and desorption (discharge) between the Si-based active material lattices can be easily performed without any obstacles when charging and discharging Li ions having a small ion radius. Generation of useless irreversible capacity due to residual Li ions accompanying discharge can be reduced.

In addition, silicon expands in volume when lithium is occluded, while element A does not occlude lithium or is difficult to occlude, so there is little volume change and distortion due to expansion and contraction, and the reduction in discharge capacity during cycle characteristics is suppressed. A negative electrode active material is provided.
Furthermore, by including oxygen or fluorine having an ionic radius close to the Si atomic radius as the third element, a negative electrode active material having further improved charge / discharge cycle characteristics and battery life is provided.

This negative electrode active material can have an average particle size set in a wide range of 10 nm to 5 μm, and a negative electrode active material having a particle size according to the application can be easily adjusted.

(1-4. Production of negative electrode by slurry application)
The negative electrode for a lithium ion secondary battery of the present invention is obtained by applying and drying a slurry-like coating liquid containing the negative electrode active material of the present invention, a conductive material and a binder on one or both surfaces of a negative electrode current collector. Can be produced. For example, the negative electrode active material of the present invention, conductive material, binder, thickener, solvent, and other coating liquid materials are charged into a mixer and kneaded to form a slurry-like coating liquid. It can manufacture by apply | coating to an electric body and forming a negative electrode active material layer.

The solid distribution number of the coating liquid is 25 to 90% by mass of the negative electrode active material of the present invention, 0 to 70% by mass of the conductive material, 1 to 30% by mass of the binder, and 0 to 25% by mass of the thickener. Can be adjusted appropriately.

As the mixer, for example, a general kneader used for preparing a slurry-like coating liquid as shown in FIG. 3 can be used, and a coating liquid called a kneader, a stirrer, a disperser, a mixer, a ball mill, or the like. You may use the apparatus which can prepare. When preparing an aqueous coating solution, latex (fine rubber dispersion) such as styrene butadiene rubber (SBR) can be used as a binder, and carboxymethyl cellulose and methyl cellulose as thickeners. It is suitable to use polysaccharides such as 1 type or a mixture of 2 types or more. When an organic coating solution is prepared, polyvinylidene fluoride (PVdF) or the like can be used as a binder, and N-methyl-2-pyrrolidone can be used as a solvent.

The conductive material is a powder made of at least one conductive material selected from the group consisting of carbon, copper, tin, zinc, nickel, and silver. A single powder of carbon, copper, tin, zinc, nickel, or silver may be used, or a powder of each alloy may be used. For example, general carbon black such as furnace black and acetylene black can be used. In particular, when silicon is exposed on the surface of the negative electrode active material of the present invention, the conductivity becomes low, so it is preferable to add carbon nanohorn as a conductive material. Here, the carbon nanohorn (CNH) has a structure in which a graphene sheet is rounded into a conical shape, and the actual form is an aggregate of a shape like a radial sea urchin with many CNHs facing the apex to the outside. Exists as. The outer diameter of the sea urchin-like aggregate of CNH is about 50 nm to 250 nm. In particular, it is preferable to use CNH having an average particle size of about 80 nm.

The average particle size of the conductive material also refers to the average particle size of the primary particles. Even when the structure shape is highly developed such as acetylene black (AB), the average particle diameter can be defined by the primary particle diameter here, and the average particle diameter can be obtained by image analysis of the SEM photograph.

Further, both a particulate conductive material and a wire-shaped conductive material may be used. The wire-shaped conductive material is a wire made of a conductive material, and the conductive materials listed for the particulate conductive material can be used. As the wire-shaped conductive material, a linear body having an outer diameter of 300 nm or less, such as carbon fiber, carbon nanotube, copper nanowire, or nickel nanowire, can be used. By using a wire-shaped conductive material, it is easier to maintain electrical connection with the negative electrode active material, current collector, etc., improving current collection performance, increasing the fibrous material on the porous membrane-shaped negative electrode, and cracking the negative electrode Is less likely to occur. For example, it is conceivable to use AB or copper powder as the particulate conductive material, and to use vapor grown carbon fiber (VGCF: Vapor Carbon Carbon Fiber) as the wire-shaped conductive material. Note that only the wire-shaped conductive material may be used without adding the particulate conductive material.

The length of the wire-shaped conductive material is preferably 0.1 μm to 2 mm. The outer diameter of the conductive material is preferably 4 nm to 1000 nm, more preferably 25 nm to 200 nm. If the length of the conductive material is 0.1 μm or more, the length is sufficient to increase the productivity of the conductive material, and if the length is 2 mm or less, the coating liquid can be easily applied. Further, when the outer diameter of the conductive material is thicker than 4 nm, synthesis is easy, and when the outer diameter is thinner than 1000 nm, the coating liquid is easily kneaded. The measuring method of the outer diameter and length of the conductive material can be performed by image analysis by SEM.

The binder is a resin binder, and a fluorocarbon resin such as polyvinylidene fluoride (PVdF), a rubber system such as styrene butadiene rubber (SBR), or an organic material such as polyimide (PI) or acrylic is used. be able to.

Application of the coating liquid to the current collector can be performed by, for example, applying the coating liquid on one side of the current collector using a coater. As the coater, a general coating apparatus that can apply the coating liquid to the current collector can be used. For example, a roll coater as shown in FIG. 4, a coater using a doctor blade, a comma coater, a die coater, or the like. is there.

The current collector can be composed of a material that is not alloyed with lithium. For example, a foil made of at least one metal selected from the group consisting of copper, nickel, and stainless steel can be used. These metals may be used alone or in their respective alloys. The thickness is preferably about 4 μm to 35 μm, more preferably about 6 μm to 20 μm, depending on the application. From the viewpoint of the thinness, strength, conductivity, etc. of the foil, it is preferable to use a copper foil.

In the present invention, the negative electrode current collector is preferably one in which the surface of the copper foil is subjected to an electrolytic surface roughening treatment and a protrusion is provided. The surface roughness Rz of the current collector having the protrusions is preferably 1 μm to 6 μm. Since the negative electrode active material material expands by alloying with lithium, the surface shape of the current collector is made into an appropriate fine rough surface shape with a surface roughness Rz of 1 μm to 6 μm by electrolytic surface roughening treatment, and the specific surface area is increased. However, when the negative electrode is formed so that the amount of the active material per unit area is reduced, the stress due to expansion and contraction of the negative electrode active material is caused by the gap between the protrusions even when the volume change occurs in the negative electrode active material due to charge and discharge. Can be relaxed, and the cycle characteristics can be improved. Further, since the surface area is increased, the negative electrode active material layer formed on the surface of the current collector can be supported by the necessary amount as the negative electrode with good adhesion.

When the surface roughness Rz obtained by the electrolytic surface roughening treatment is less than 1 μm, the surface area of the current collector is not sufficiently large, so that the amount of the negative electrode active material that can be supported becomes insufficient, and the unit area per unit area Since the charge / discharge sites of the battery are reduced, the cycle characteristics are also deteriorated. If the surface roughness Rz due to the electrolytic surface roughening treatment exceeds 6 μm, the thickness of the current collector becomes too large, which adversely affects the formation of the negative electrode active material layer. For example, a jelly roll type cylindrical shape or a square shape Since it becomes difficult to put it into practical use as a current collector for a negative electrode of a lithium ion secondary battery, it is not preferable. The surface roughness Rz in the present invention is defined by the ten-point average roughness of Japanese Industrial Standard JIS B0601-1994.

Such protrusions are formed on the metal foil surface by wet (electroplating, electroless plating, chemical etching, electrochemical etching, etc.) methods, dry methods (evaporation, chemical ion deposition, etc.), painting, polishing, etc. It can be formed using a roughening treatment technique. In the present invention, it is shown as a desirable mode that a metal foil having a surface roughness Rz of 0.5 μm to 3 μm is subjected to electrolytic surface roughening treatment.

As the metal foil before the roughening treatment (so-called untreated foil), a double-sided glossy foil or a double-sided smooth foil formed by an electrolytic method or a rolling method can be used. The reason why the surface roughness Rz is 0.5 μm or more is because it is a small realistic roughness for a double-sided glossy foil or a double-sided smooth foil. If the surface roughness Rz exceeds 3 μm, the variation in roughness after the formation of protrusions increases. This is not preferable. In addition, even if it is an untreated foil, there is a surface roughness Rz of 1 μm or more, but the unevenness formed during the manufacture of the foil also includes gentle unevenness, ensuring adhesion with the active material layer Therefore, it is not preferable to use the untreated foil as it is. It is important to form irregularities with complicated shapes by roughening treatment. Furthermore, by subjecting the metal foil having a surface roughness in the above range to a roughening treatment, the protrusions formed on the current collector become uniform on the same surface and on both the front and back surfaces. It exhibits better adhesion, and the negative electrode active material layer is less likely to fall off, which can contribute to extending the life of the negative electrode and securing the actual capacity.

The electrolytic surface roughening treatment is to roughen the surface by forming a plating film having irregularities on the surface of the untreated foil. For example, a generally used roughening method by plating is used. be able to. That is, by electroplating using an aqueous copper sulfate solution by so-called burn plating to form a granular copper plating layer on the foil surface, a normal film-like plating (capsule) is formed on the granular copper plating layer. Protruding portions that prevent the particles from falling off can be formed. This burn plating is preferable because it allows uniform control and reproducibility of the plating layer and is excellent in quality control. In addition, for example, when the material of the current collector is copper, it is preferable because a protrusion having a complicated shape can be formed by electroplating. By using the electrolytic copper foil, it is possible to easily form a current collector with little variation.

Also, a rust-preventing layer can be formed on the current collector on which the protrusions are formed by nickel or zinc plating, chromate treatment, or silane coupling treatment. With this rust preventive layer, for example, it is possible to prevent or suppress deterioration over time from manufacture to stock and deterioration due to a high-temperature atmosphere during formation of the negative electrode active material layer. In addition, excessive diffusion between the current collector component and the negative electrode active material component is prevented, and this contributes to maintaining good adhesion. Practically, for the current collector on which the protrusions are formed, electroplating with such a known sulfate aqueous solution or the like, immersion treatment, displacement plating, functional surface treatment by vapor phase method, rust prevention treatment, It is preferable to perform any one or more of the adhesion improving treatments.

Next, the prepared coating solution is uniformly applied to the current collector, then dried at about 50 to 150 ° C., and passed through a roll press to adjust the thickness, whereby a negative electrode for a lithium ion battery can be obtained. .

(1-5. Effect of negative electrode for lithium ion secondary battery)
According to the present invention, since the negative electrode active material of the present invention is used, volume expansion during lithium ion occlusion is suppressed, pulverization and peeling of the negative electrode active material, generation of cracks in the negative electrode, and between the negative electrode active materials A negative electrode having a high capacity and a long life in which problems such as a decrease in conductivity are solved is provided.

According to the present invention, since the surface of the current collector is roughened, the bonding force between the negative electrode active material layer and the current collector is high, and the stress due to the expansion and contraction of the negative electrode active material is reduced. In addition, the cycle characteristics of the electrode can be improved.

(2. Negative electrode for lithium ion secondary battery according to second embodiment)
(2-1. Configuration of negative electrode for lithium ion secondary battery)
First, a negative electrode for a lithium ion secondary battery according to an embodiment of the present invention will be described with reference to FIG. A negative electrode 61 for a lithium ion secondary battery of the present invention comprises a negative electrode current collector 67 having a protrusion 65 on the surface, and a thin film negative electrode active material layer 63 formed on the surface of the negative electrode current collector 67. Have.
The negative electrode active material layer 63 in the present invention is made of a silicon-based thin film having a characteristic component structure, and a negative electrode current collector 67 having a specific form is used for the negative electrode active material layer 63. ing.

(2-2. Negative electrode active material layer)
The negative electrode active material layer 63 of the present invention is a thin film integrally formed on the surface of the negative electrode current collector 67 and contains silicon as a main component and at least an element A as a second element. Since silicon is an element that easily stores lithium, this negative electrode active material layer also has a high lithium storage capacity. In addition, silicon has an advantage that the cost is relatively low among elements having lithium storage ability.

Element A is contained in an amount of 0.05% by mass or more in the negative electrode active material layer. When a plurality of elements A are included, the total content of these elements is set to 0.05% by mass or more. By making the content 0.05% by mass or more, volume expansion / contraction of silicon during charge / discharge can be effectively suppressed. Although the upper limit of the content of the element A is not particularly defined, it can be arbitrarily determined within a range of less than 50% by mass in consideration of the lithium storage capacity of silicon and the like. Even if the amount of the element A is sufficiently smaller than that of Si, the effect of suppressing the volume expansion and contraction can be obtained.

The negative electrode active material layer according to the present invention may further contain oxygen or fluorine as the third element. Although oxygen and fluorine have small atomic radii, as shown in Table 1 above, the ionic radius r _{A ′} is comparable in size to the atomic radius r ₀ (0.117 nm) of Si, causing extra strain. In addition, the change in the volume of silicon can be suppressed and the charge / discharge cycle life can be further improved without obstructing the penetration and desorption of Li ions. Oxygen and fluorine are combined and dispersed with a part of Li, and also have an effect of stabilizing the active material. As for Ag and Cd, although the ion radius is comparable to the atomic radius r _{0 of} Si, it is difficult to form an ion-binding compound, so that the third active material layer constituting the negative electrode active material layer according to the present invention is formed. It is not preferable as an element.

Note that oxygen and fluorine may be uniformly contained in the entire active material layer, or may be contained, for example, in part of the surface portion or the like. The oxygen and fluorine contents are preferably 0.5% by mass or more in order to maintain high charge / discharge characteristics, and the total with the element A content is preferably 50% by mass or less.

Such a negative electrode active material layer according to the present invention is practically required to have a thickness of at least 1 μm or more, and has a thickness of about 1 μm to 6 μm for high energy density applications such as electronic equipment. It is desirable.

In the present invention, silicon as a main component means that the silicon content is the largest among the elements constituting the active material layer, and the silicon content is preferably 50% by mass or more, more preferably. Indicates 70% by mass or more. The second element and the third element are the elements constituting the particles other than silicon, and the element group having a characteristic role is referred to as the second element or the third element. And there is no relationship with the content of both.

The above-described negative electrode active material layer of the present invention may have a crystalline structure that is crystalline, microcrystalline, amorphous, or a state in which these are mixed. This is because any crystalline form becomes amorphous by alloying with Li ions during charging.

In addition, the method for forming the negative electrode active material layer according to the present invention is not particularly limited, and for example, by using various known film forming methods, a thin film having the composition and thickness as described above can be formed. it can. Specifically, for example, a sputtering method, a vapor deposition method, a CVD method, and the like can be exemplified. According to these methods, it is easy to form a uniform thin film.

(2-3. Negative electrode current collector)
The negative electrode current collector according to the present invention can be made of a material that is not alloyed with lithium. For example, a foil made of at least one metal selected from the group consisting of copper, nickel, and stainless steel can be used. These metals may be used alone or in their respective alloys. From the viewpoint of the thinness, strength, conductivity, etc. of the foil, it is preferable to use copper foil. Depending on the application, the current collector preferably has a thickness of about 4 μm to 35 μm, more preferably about 6 μm to 20 μm, excluding the protrusions.

The negative electrode current collector in the present invention has a protrusion. This protrusion is preferably provided by subjecting the surface of the copper foil to an electrolytic surface roughening treatment, and the surface roughness Rz is preferably 1 μm to 6 μm. This is because the negative electrode active material material expands by alloying with lithium, so that the surface shape of the current collector is an appropriate fine rough surface shape with a surface roughness Rz of 1 μm to 6 μm to increase the specific surface area, By forming the negative electrode so that the amount of the negative electrode active material per unit area is reduced, even when volume change occurs in the negative electrode active material layer due to charge / discharge, the negative electrode active material layer is expanded and contracted by the gap between the protrusions. This is because stress can be relaxed and cycle characteristics can be improved. Further, since the surface area is increased, the negative electrode active material layer formed on the surface of the current collector can be supported by the necessary amount as the negative electrode with good adhesion.

When the surface roughness Rz due to the protrusion is less than 1 μm, it is difficult to carry the negative electrode active material layer directly formed as a thin film on the current collector without peeling. Further, even if the negative electrode active material layer according to the present invention is used, the surface area of the current collector is not sufficiently large, so that the amount of the negative electrode active material that can be supported becomes insufficient, and the unit area is Since the charge / discharge sites of the battery are reduced, the cycle characteristics are also deteriorated. When the surface roughness Rz exceeds 6 μm, the thickness measured by the micrometer of the current collector becomes too large, which adversely affects the formation of the negative electrode active material layer. For example, a jelly-roll cylindrical or square lithium ion Since it becomes difficult to put it into practical use as a current collector for a negative electrode of a secondary battery, it is not preferable. The surface roughness Rz in the present invention is defined by the ten-point average roughness of Japanese Industrial Standard JIS B0601-1994.

Such protrusions are applied to the smooth surface of the metal foil by a wet (electroplating, electroless plating, chemical etching or electrochemical etching) method, a dry (evaporation, chemical ion deposition, etc.) method, and coating, It can be formed using a surface roughening technique such as polishing. In the present invention, it is shown as a desirable mode that a copper foil having a surface roughness Rz of 0.5 μm to 3 μm is subjected to an electrolytic surface roughening treatment.

As the metal foil before the roughening treatment (so-called untreated foil), a double-sided glossy foil or a double-sided smooth foil formed by an electrolytic method or a rolling method can be used. The reason why the surface roughness Rz is 0.5 μm or more is because it is a small realistic roughness for a double-sided glossy foil or a double-sided smooth foil. If the surface roughness Rz exceeds 3 μm, the variation in roughness after the formation of protrusions increases. This is not preferable. In addition, even if it is an untreated foil, there is a surface roughness Rz of 1 μm or more, but the unevenness formed during the manufacture of the foil also includes gentle unevenness, ensuring adhesion with the active material layer Therefore, it is not preferable to use the untreated foil as it is. It is important to form irregularities with complicated shapes by roughening treatment. Further, by subjecting the double-sided smooth foil having the above surface roughness to a roughening treatment, the protrusions formed on the current collector become uniform on the same surface and on both the front and back surfaces, and further with the negative electrode active material layer. Good adhesion is exhibited, and the negative electrode active material layer is less likely to fall off, which can contribute to extending the life of the negative electrode and securing the actual capacity.

The electrolytic surface roughening treatment is to roughen the surface by forming a plating film having irregularities on the surface of the untreated foil. For example, a generally used roughening method by plating is used. be able to. That is, by electroplating using an aqueous copper sulfate solution by so-called burn plating and forming a granular copper plating layer on the surface of the foil, an ordinary film-like plating ( The projection can be formed by performing capsule plating. This burn plating is preferable because it allows uniform control and reproducibility of the plating layer and is excellent in quality control. In addition, for example, when the material of the current collector is copper, it is preferable because a protrusion having a complicated shape can be formed by electroplating. By using the electrolytic copper foil, it is possible to easily form current collector projections with little variation.

(2-4. Effect of negative electrode for lithium ion secondary battery)
According to the negative electrode for a lithium ion secondary battery of the present invention, the negative electrode active material layer includes at least an element A having an atomic radius of the same size as that of silicon in addition to silicon. Insertion (charging) and desorption (discharging) between silicon-based active material lattices can be easily generated without any problems when charging / discharging Li ions with a small ion radius without giving too much strain between Si atoms. It is possible to reduce generation of useless irreversible capacity due to residual Li ions accompanying discharge after charging.

In addition, silicon expands in volume when lithium is occluded, while element A does not occlude lithium or is difficult to occlude, so there is little volume change and distortion due to expansion and contraction, and the reduction in discharge capacity during cycle characteristics is suppressed. Provided is a negative electrode for a lithium ion secondary battery.
Furthermore, by including oxygen or fluorine having an ionic radius close to the Si atomic radius as the third element, a negative electrode for a lithium ion secondary battery with improved charge / discharge cycle characteristics and battery life is provided.

Moreover, since the negative electrode current collector has a predetermined surface roughness, a negative electrode for a lithium ion secondary battery is provided in which the effect of the negative electrode active material layer as described above is sufficiently exhibited.

(3. Configuration of lithium ion secondary battery)
A lithium ion secondary battery according to an embodiment of the present invention will be described with reference to FIG. The lithium ion secondary battery 11 of the present invention is disposed between the positive electrode 13 capable of inserting and extracting lithium ions, the negative electrode 1 for a lithium ion secondary battery according to the present invention, and the positive electrode 13 and the negative electrode 1. The positive electrode 13, the negative electrode 1, and the separator 15 are provided in an electrolyte 17 having lithium ion conductivity.

(4. Positive electrode)
The positive electrode can be produced by directly applying and drying a composition of the positive electrode active material on a metal current collector such as an aluminum foil. The composition of the positive electrode active material can be prepared by mixing a positive electrode active material, a conductive additive, a binder, and a solvent.

(4-1. Positive electrode active material)
Any positive electrode active material can be used as long as it is generally used. For example, LiCoO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiNiO ₂ , LiCo _1/3 Ni _1/3 Mn _1/3. Compounds such as O ₂ and LiFePO ₄ .

(4-2. Conductive aid)
The conductive additive is a powder made of at least one conductive material selected from the group consisting of carbon, copper, tin, zinc, nickel, and silver. A single powder of carbon, copper, tin, zinc, nickel, or silver may be used, or a powder of each alloy may be used. For example, general carbon black such as furnace black and acetylene black can be used. Moreover, it is preferable to add carbon nanohorn as a conductive support agent. Here, the carbon nanohorn (CNH) has a structure in which a graphene sheet is rounded into a conical shape, and the actual form is an aggregate of a shape like a radial sea urchin with many CNHs facing the apex to the outside. Exists as. The outer diameter of the sea urchin-like aggregate of CNH is about 50 nm to 250 nm. In particular, CNH having an average particle size of about 80 nm is preferable.

The average particle size of the conductive aid refers to the average particle size of the primary particles. Even when the structure shape is highly developed such as acetylene black (AB), the average particle size is defined by the primary particle size here. The particle size can be measured by using image information of an electron microscope (SEM) and a volume-based median diameter of a dynamic light scattering photometer (DLS). For the average particle size, confirm the particle shape in advance using an SEM image, obtain the particle size by image analysis (for example, “A Image-kun” (registered trademark) manufactured by Asahi Kasei Engineering), or disperse the particles in a solvent to obtain DLS (for example, , DLS-8000 manufactured by Otsuka Electronics Co., Ltd.). If the fine particles are sufficiently dispersed and not agglomerated, almost the same measurement results can be obtained with SEM and DLS.

Also, both a particulate conductive aid and a wire-shaped conductive aid may be used. The wire-shaped conductive aid is a wire made of a conductive material, and the conductive materials listed in the particulate conductive aid can be used. As the wire-shaped conductive assistant, a linear body having an outer diameter of 300 nm or less, such as carbon fiber, carbon nanotube, copper nanowire, or nickel nanowire, can be used. By using a wire-shaped conductive aid, electrical connection with the negative electrode active material or current collector is easily maintained and current collection performance is improved, and fibrous material is increased in the porous membrane-shaped negative electrode. Cracks are less likely to occur. For example, it is conceivable to use AB or copper powder as the particulate conductive aid, and to use vapor grown carbon fiber (VGCF) as the wire-shaped conductive aid. In addition, you may use only a wire-shaped conductive support agent, without adding a particulate-form conductive support agent.

The length of the wire-shaped conductive assistant is preferably 0.1 μm to 2 mm. The outer diameter of the conductive aid is preferably 4 nm to 1000 nm, more preferably 25 nm to 200 nm. If the length of the conductive auxiliary agent is 0.1 μm or more, the length is sufficient to increase the productivity of the conductive auxiliary agent, and if the length is 2 mm or less, application of the slurry is easy. Further, when the outer diameter of the conductive auxiliary agent is larger than 4 nm, the synthesis is easy, and when the outer diameter is thinner than 1000 nm, the slurry is easily kneaded. The measuring method of the outer diameter and length of the conductive material can be performed by image analysis using SEM.

(4-3. Binder)
The binder is a resin binder, such as a fluororesin such as polyvinylidene fluoride (PVdF), a rubber system such as styrene butadiene rubber (SBR), and a polyimide (PI) or a water-soluble acrylic binder. Organic materials can be used.

(4-4. Solvent)
As the solvent, N-methyl-2-pyrrolidone (NMP), water or the like is used. At this time, the contents of the positive electrode active material, the conductive additive, the binder, and the solvent can be appropriately adjusted at a level usually used in a lithium ion secondary battery.

(4-5. Production of positive electrode)
The composition of the positive electrode active material adjusted as described above is uniformly applied to one surface of the current collector using, for example, a coater. As the coater, a general coating apparatus capable of applying the composition to the current collector can be used. For example, a coater using a roll coater or a doctor blade, a comma coater, or a die coater.

The current collector is a foil made of at least one metal selected from the group consisting of copper, nickel, and stainless steel. Each may be used alone or may be an alloy of each. The thickness is preferably 4 μm to 35 μm, more preferably 6 μm to 20 μm, although depending on the application.
After the composition of the positive electrode active material is applied, it is dried at about 50 to 150 ° C., and the positive electrode is obtained through a roll press in order to adjust the thickness.

(5. Separator)
Any separator can be used as long as it has a function of insulating electronic conduction between the positive electrode and the negative electrode and is usually used in a lithium ion secondary battery. For example, a microporous polyolefin film can be used.

(6. Electrolyte)
Various electrolytes and electrolytes having lithium ion conductivity can be used as the electrolyte. For example, an organic electrolytic solution (non-aqueous electrolytic solution), an inorganic solid electrolyte, a polymer solid electrolyte, or the like can be used.

Specific examples of the organic electrolyte solvent include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate; diethyl ether, dibutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol di Ethers such as butyl ether and diethylene glycol dimethyl ether; aprotic such as benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethylchlorobenzene, nitrobenzene Solvent, or two of these solvents Mixed solvent of the above can be cited.

The electrolyte of the organic electrolyte includes LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAlO ₄ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) A mixture of one or more electrolytes made of a lithium salt such as ₂ can be used.

It is desirable to add a compound capable of forming an effective solid electrolyte interface coating on the surface of the negative electrode active material as an additive to the organic electrolyte. For example, a substance having an unsaturated bond in the molecule and capable of reductive polymerization during charging, such as vinylene carbonate (VC), is added.

Also, a solid lithium ion conductor can be used in place of the organic electrolyte. For example, a solid polymer electrolyte in which the lithium salt is mixed with a polymer made of polyethylene oxide, polypropylene oxide, polyethyleneimine, or the like, or a polymer gel electrolyte in which a polymer material is impregnated with an electrolytic solution and processed into a gel shape can be used.

Further, lithium nitride, lithium halide, lithium oxyacid salt, Li ₄ SiO ₄ , Li ₄ SiO ₄ —LiI—LiOH, Li ₃ PO ₄ —Li ₄ SiO ₄ , Li ₂ SiS ₃ , Li ₃ PO ₄ —Li An inorganic material such as ₂ S—SiS _{2 or} a phosphorus sulfide compound may be used as the inorganic solid electrolyte.

(7. Assembly of lithium ion secondary battery)
In the lithium ion secondary battery of the present invention, a battery element is formed by arranging a separator between the positive electrode as described above and the negative electrode for a lithium ion battery of the present invention. After winding or stacking such battery elements into a cylindrical or rectangular battery case, an electrolyte is injected to obtain a lithium ion secondary battery.

Specifically, as shown in FIG. 2, in the lithium ion secondary battery 11 of the present invention, the positive electrode 13 and the negative electrode 1 are laminated in the order of separator-negative electrode-separator-positive electrode via the separator 15, The electrode plate group is formed by winding the positive electrode 13 so as to be on the inner side, and this is inserted into the battery can 19. The positive electrode 13 is connected to the positive electrode terminal 25 via the positive electrode lead 23, and the negative electrode 1 is connected to the battery can 19 via the negative electrode lead 21, and chemical energy generated inside the lithium ion secondary battery 11 is externally output as electric energy. It can be taken out. Next, the battery can 19 is filled with the electrolyte 17 so as to cover the electrode plate group, and then the upper end (opening) of the battery can 19 is composed of a circular lid plate and a positive electrode terminal 25 on the upper portion thereof, and a safety valve mechanism is provided therein. Can be manufactured by attaching a sealing body 27 containing a ring through an annular insulating gasket.

(8. Effect of the lithium ion secondary battery according to the present invention)
The lithium ion secondary battery according to the present invention is composed of particles containing Si having a higher capacity per unit volume than carbon and a second element having an atomic radius similar to that of Si, and generating irreversible capacity. Since the negative electrode active material is used to decrease the capacity, the capacity is larger than that of a conventional lithium ion secondary battery, and the particles are difficult to expand and contract and are not easily pulverized, so that the cycle characteristics are good.

In addition, since the negative electrode for a lithium ion secondary battery of the present invention has a high bonding force between the negative electrode active material layer and the current collector and can relieve stress due to expansion and contraction of the negative electrode active material, the cycle An economical lithium ion secondary battery having excellent characteristics is provided.

Hereinafter, the present invention will be specifically described with reference to examples and comparative examples.

[Example 1: A negative electrode active material is applied to produce a negative electrode]
(Preparation of current collector)
Electrolytic plating was performed on a 10 μm thick electrolytic copper foil (Furukawa Electric NC-WS foil, surface roughness Rz 1.5 μm) to produce a current collector with protrusions. The plating conditions are as follows.

(A) Bake plating for roughening treatment: In an electrolytic solution mainly composed of copper 30 g / dm ³ and sulfuric acid 150 g / dm ³ without heating, in a current density range of 10 to 20 A / dm ² , Cathodic electrolysis was carried out under conditions for obtaining a predetermined surface shape that was appropriately selected along with the electrolysis time and was determined in advance.
(B) a smooth-walled copper plating roughening treatment (capsules Plating): Copper 70 g / dm ^3, in an electrolytic solution was maintained at a liquid temperature of 40 ° C. as a main component of sulfuric acid 100 g / dm ^3, a current density of 5 ~ 10A / In the range of dm ² , cathode electrolysis was performed under conditions appropriately selected together with electrolysis time for obtaining a predetermined surface shape determined in advance together with the conditions of (a).

Furthermore, after forming an inorganic film of nickel and zinc on this copper foil and performing chromate treatment by cathode electrolysis using a known aqueous solution to form a film with a thickness of about nanometer, (meth) acryloxy-based silane cup Each rust-proofing layer was formed by dipping in an aqueous ring solution to obtain a current collector.

(Preparation of negative electrode active material 1)
As the negative electrode active material, nano-sized particles of Si, Si—B, Si—P, Si—Fe, and Si—Ni were produced using the plasma CVD apparatus of FIG. As raw materials, Si powder, B powder with an atomic radius of 0.09 nm, P powder with 0.11 nm, Fe powder with 0.12 nm, and Ni powder with 0.12 nm were mixed as appropriate. These mixed powders were dried, and nanosized particles were produced by continuously supplying them with a carrier gas into the Ar gas plasma generated in the reaction chamber.

Specifically, after the reaction chamber was evacuated with a vacuum pump, Ar gas was introduced to atmospheric pressure. This exhaustion and Ar gas introduction were repeated three times to exhaust the residual air in the reaction vessel. Thereafter, Ar gas was introduced into the reaction vessel as a plasma gas at a flow rate of 13 L / min, an AC voltage was applied to the high frequency coil, and high frequency plasma was generated by a high frequency electromagnetic field (frequency 4 MHz). The plate power at this time was 20 kW. Ar gas having a flow rate of 1.0 L / min was used as a carrier gas for supplying the raw material powder.
The obtained fine powder was subjected to a fine oxidation treatment for preventing dust explosion for 12 hours after production, and then collected with a filter.

(Preparation of negative electrode active material 2)
In addition, as a negative electrode active material, a molten alloy of a predetermined composition of Si—B or Si—P is prepared, and finely powdered by a known nitrogen gas atomizing method, and then a Si—P or Si—B based microparticle is prepared. Metric-size active material particles were obtained.

(Preparation of negative electrode active material 3)
The obtained negative electrode active material was subjected to atmospheric oxidation treatment in a thermostatic chamber heated to 180 ° C. to contain oxygen.

(Analysis of negative electrode active material composition)
For 2-3 components of the negative electrode active material, ICP (High Frequency Inductively Coupled Plasma Emission Spectroscopy) analysis was performed with an aqueous solution in which the material was dissolved for component quantification. The results are shown in Table 2 as the subcomponent concentration (mass%) in terms of the mass ratio of subcomponents when the total mass of the material is 100.

(Preparation of negative electrode)
The negative electrode active material prepared as described above was mixed using a ball mill in which 10% by mass of carbon black was mixed as a conductive material and the inside was replaced with nitrogen. The mixed powder and polyimide as a binder were mixed at a mass ratio of 95: 5, and then NMP (N-methyl-2-pyrrolidone) was added as a solvent and sufficiently kneaded to obtain a negative electrode coating solution.

This negative electrode coating solution was applied to a current collector to a thickness of 15 μm and baked at 300 ° C. for 10 minutes. Then, it was rolled to a density of 2 g / cm ³ with a roll press and punched into a 2 cm ² disk shape to obtain a negative electrode.

[Examples 1-1, 1-2]
A negative electrode using two kinds of nano-sized Si—P particles with different P concentrations synthesized by the plasma method as an active material was used as a test electrode for evaluation of electrochemical characteristics.

[Examples 1-3, 1-4]
The nano-sized Si—P particles of Example 1 were oxidized, and the electrochemical characteristics were evaluated using a negative electrode using Si—P—O particles into which oxygen was introduced as an active material.

[Example 1-5]
The micron-sized Si—P particles synthesized by the atomization method were oxidized, and the negative electrode using the Si—P—O particles introduced with oxygen as the active material was used as a test electrode, and the electrochemical characteristics were evaluated.

[Example 1-6]
The electrochemical characteristics were evaluated using a negative electrode using nano-sized Si—Fe particles synthesized by the plasma method as an active material as a test electrode.
[Example 1-7]
The electrochemical characteristics were evaluated using a negative electrode using nano-sized Si—Ni particles synthesized by the plasma method as an active material as a test electrode.

[Examples 1-8, 1-9]
Electrochemical characteristics were evaluated using a negative electrode using Si—Fe—O particles and Si—Ni—O particles obtained by oxidizing the Si—Fe and Si—Ni particles of Examples 4 to 5 as active material materials, respectively, as test electrodes. .

[Comparative Examples 1-1 to 1-3]
As a comparative example, a negative electrode using nano-sized Si simple particles, nano-sized Si—B particles, and micron-sized Si—B particles as active material materials was used for evaluation of electrochemical characteristics as test electrodes.

(Production of cell for evaluating electrochemical characteristics of silicon electrodes)
Using the silicon thin film plate as a working electrode, lithium metal as a counter electrode and a reference electrode, and a mixed solvent of ethylene carbonate + diethyl carbonate (1: 1 by volume) in which 1 mol of LiPF ₆ is dissolved as an electrolyte, Produced.

(Production of cell for evaluating electrochemical characteristics of silicon electrodes)
The obtained negative electrode was processed into a disk shape having a diameter of 20 mm, and used as a working electrode in electrochemical property evaluation. In addition, using a mixed solvent of ethylene carbonate + diethyl carbonate (1: 1 by volume) in which lithium metal is dissolved as a counter electrode and a reference electrode and 1 mol of LiPF ₆ is used as an electrolyte, these are put in a beaker together with a working electrode, A chemical characterization cell was fabricated.

(Evaluation of electrochemical characteristics of silicon electrode)
Next, a test for evaluating charge / discharge performance was performed using an electrochemical property evaluation cell. The process of scanning the potential of the working electrode in the base direction (reduction side) is called charging, and the process of scanning the potential of the working electrode in the noble direction (oxidation side) is called discharging.

First, the initial charge / discharge was performed at 0.1 CA, the charge was performed up to 0.02 V (until 0.05 CA was reached at a constant potential), and the discharge was performed up to 1.5 V. In the second and subsequent cycles, charging was performed at 0.2 CA at 0.02 V (until reaching 0.05 CA at a constant potential), and discharging was performed at 0.2 CA up to 1.5 V. The evaluation temperature was 25 ° C. Evaluation was made under such conditions, and the capacity retention rate was determined from the discharge capacity cycle of the first charge / discharge and the discharge capacity at the 50th cycle. The definition of the capacity maintenance rate is as follows.

Capacity retention ratio = (discharge capacity at the 50th cycle / discharge capacity at the first cycle) × 100
Table 2 shows the specifications of the negative electrode used as the test electrode and the capacity retention rate of the test evaluation result. The capacity shown in the table is the capacity per mass of silicon.

From the above results, the atomic radii of Examples 1-1 to 1-9 approximate to the atomic radius of Si (0.117 nm) as compared to the active material made of only Si of Comparative Example 1-1. The negative electrode using the active material containing the second element (P, Fe, Ni) satisfying the relationship of r _A −r ₀ ) / r ₀ | ≦ 0.1 has a capacity retention ratio of about It has been found that it can be increased more than twice. It can be determined that the current collector has a protrusion having an appropriate shape on the surface, has good adhesion to the active material, and contributes to the charge / discharge cycle life.

Also, from the results of Examples 1-3, 1-4, 1-5, 1-8, 1-9, it was confirmed that the active material material preferably contains oxygen molecules. In this case, an increase in the average particle diameter of the active material material due to the introduction of oxygen atoms does not greatly affect the capacity retention rate.

On the other hand, when the element (B) in which the atomic radius of Comparative Examples 1-2 to 1-3 does not satisfy the relationship of | (r _A −r ₀ ) / r ₀ | ≦ 0.1 is introduced, the capacity of the negative electrode is maintained. It was confirmed that the rate was greatly reduced.

In this embodiment, the case where P, Fe, Ni is used as the second element in the negative electrode active material and oxygen is used as the third element is shown. However, the negative electrode active material of the present invention is not limited to this. Absent. The second element only needs to be an element satisfying the relationship of at least an atomic radius of | (r _A −r ₀ ) / r ₀ | ≦ 0.1. In addition to P, Fe, Ni, for example, Cr, It is presumed that the same result can be obtained even when Co, Cu, or the like is used or fluorine is used as the third element.

In the present embodiment, as a method of roughening the current collector, baking plating and capsule plating are performed, but the method of forming the protrusions of the current collector of the present invention is not limited to this. If the technique can form a stable film having a protrusion having a predetermined surface roughness on the surface of the current collector, it is presumed that the same tendency result as in this example can be obtained.

[Example 2: A negative electrode is produced by forming a film on a current collector]
(Preparation of negative electrode for lithium ion secondary battery 1)
A negative electrode active material layer having a composition of Si, Si—P, Si—As, Si—B, and Si—N is formed on the surface of the current collector obtained in the same manner as in Example 1, A negative electrode for a secondary battery was produced. Specifically, the negative electrode active material layer was formed using a catalytic chemical vapor deposition (Cat-CVD) apparatus under the following conditions. First, for the formation of a Si thin film, monosilane gas is used as a source gas, the flow rate is 20 sccm, the current collector temperature is 250 ° C., the tungsten wire catalyst body temperature is 1800 ° C., and the basic conditions are appropriately formed according to the film thickness. The membrane time was adjusted.

Further, when P was contained as the second element, phosphine gas was supplied at a flow rate of 10 sccm or 1 sccm in addition to monosilane gas as a source gas. Similarly, in the case where As is contained as the second element, in addition to the monosilane gas, 10 sccm of arsine gas is used as the source gas, in the case of containing B, 10 sccm of diborane gas, and in the case of containing N, ammonia gas. 100 sccm was supplied.

(Preparation of negative electrode for lithium ion secondary battery 2)
When oxygen is added as a third element to the surface of the obtained current collector, a negative electrode active material layer having a composition of Si—PO is formed by reactive sputtering of Si containing oxygen, and lithium A negative electrode for an ion secondary battery was produced. Specifically, Si and P substrates having different oxygen contents were sputtered to form a desired ratio of active materials.

(Preparation of negative electrode for lithium ion secondary battery 3)
The negative electrode obtained using the above Cat-CVD apparatus was subjected to atmospheric oxidation treatment in a thermostatic chamber heated to 180 ° C. to contain oxygen.

[Examples 2-1 to 2-3]
Three negative electrode active material layers were formed on the current collector provided with the protrusions by changing the P content and thickness by the Cat-CVD method to obtain a negative electrode.
[Example 2-4]
A negative electrode active material layer containing Si and P was formed on the current collector provided with the protrusions by a Cat-CVD method, and further oxidized by a thermostatic bath to obtain a negative electrode containing Si, P, and O.
[Example 2-5]
The negative electrode of Example 2-3 was oxidized in a thermostatic bath to form a negative electrode active material layer containing Si, P, and O to obtain a negative electrode.
[Example 2-6]
A negative electrode active material layer containing Si, P, and O was formed on the current collector provided with the protrusions by reactive sputtering to obtain a negative electrode.
[Example 2-7]
A negative electrode active material layer containing Si and As was formed on the current collector provided with the protrusions by a Cat-CVD method to form a negative electrode.
[Example 2-8]
The negative electrode of Example 2-7 was oxidized in a thermostatic bath to form a negative electrode active material layer containing Si, As, and O to obtain a negative electrode.
[Example 2-9]
A negative electrode active material containing Si and P by a Cat-CVD method, which is different from Example 2-1, in which a copper foil having a smooth surface is subjected to a roughening treatment and has a protrusion but a small surface roughness. A layer was formed as a negative electrode.

[Comparative Example 2-1]
A negative electrode active material layer made of a simple substance of Si was formed on a copper foil provided with protrusions by a Cat-CVD method to obtain a negative electrode.
[Comparative Example 2-2]
A negative electrode active material layer containing Si and B was formed by a Cat-CVD method on the copper foil provided with the protrusions to obtain a negative electrode.
[Comparative Example 2-3]
A negative electrode active material layer containing Si and N was formed on a copper foil provided with a protrusion by a Cat-CVD method to form a negative electrode.
[Comparative Example 2-4]
A negative electrode active material layer containing Si and P was formed by a Cat-CVD method on a double-sided smooth copper foil (Rz 1.5 μm WS foil, untreated foil) not provided with a protrusion, thereby forming a negative electrode.

(Analysis of anode active material layer composition)
The cross section of the negative electrode active material layer of the produced negative electrode was analyzed using an X-ray microanalyzer (EPMA), and the two to three components were quantified by the ZAF correction method. The results are shown in Table 2 as subcomponent concentrations. The subcomponent concentration represents the ratio (mass%) of the subcomponent when the mass of all the components constituting the layer is 100.

(Evaluation of electrochemical characteristics of silicon electrode)
In the same manner as in Example 1, the capacity retention rate at the 50th cycle was measured.

(Silicon weight measurement)
For the prepared negative electrode, the weight of the current collector (including the protrusions) was taken from the total weight of the negative electrode to obtain the weight of silicon, and the results are shown in Table 3.

From the above results, the atomic radii of Examples 2-1 to 2-8 approximated the atomic radius of Si (0.117 nm) as compared with the negative electrode having an active material layer composed only of Si of Comparative Example 2-1. , | (R _A −r ₀ ) / r ₀ | ≦ 0.1, the negative electrode using the active material layer containing the second element (P, As) satisfies the capacity retention rate after 50 cycles of charge and discharge Was found to be significantly improved.

Further, from comparison between Example 2-2 and Example 2-9, the negative electrode active material layer according to the present invention has a remarkable discharge capacity and capacity retention ratio in combination with a current collector having a sufficiently large surface roughness Rz. It was confirmed that the charge / discharge cycle characteristics were further improved. The negative electrode of Example 2-9 had a discharge capacity and capacity maintenance comparable to the negative electrode of Comparative Example 2-1, although the film thickness and silicon mass were about half that of Comparative Example 2-1. Have a rate.

Furthermore, from the results of Examples 2-4 to 2-6 and 2-8, it was confirmed that the active material layer contains oxygen and has a higher capacity retention rate and is more desirable. From the results of Example 2-5, it was confirmed that a sufficient effect was exhibited even when the oxygen content was 0.7 mass%.

On the other hand, when an element (B, N) whose atomic radius does not satisfy the relationship of | (r _A −r ₀ ) / r ₀ | ≦ 0.1 is introduced from Comparative Examples 2-2 to 2-3, the negative electrode It was confirmed that the capacity maintenance rate of the battery greatly decreased.

Further, from the results of Comparative Example 2-4, it was found that the negative electrode active material layer could not be supported on the current collector unless the protrusions were formed on the surface of the current collector.

In this embodiment, the case where P and As are used as the second element constituting the negative electrode active material layer and oxygen is used as the third element is shown, but the negative electrode of the present invention is not limited to this. The second element only needs to be an element satisfying the relationship of at least an atomic radius of | (r _A −r ₀ ) / r ₀ | ≦ 0.1. In addition to P and As, for example, Fe, Ni, It is presumed that the same result can be obtained even when Cr, Co, Cu or the like is used or fluorine is used as the third element.

The preferred embodiment of the present invention has been described above, but the present invention is not limited to such an example. It is obvious that a person skilled in the art can come up with various changes or modifications within the scope of the technical idea disclosed in the present application, and it is understood that these also belong to the technical scope of the present invention. Is done.

DESCRIPTION OF SYMBOLS 1 ......... Negative electrode 3 ......... Active material 4 ......... Conductive material 5 ......... Active material layer 6 ......... Binder 7 ......... Protrusion 9 ......... Current collector 11 ......... Lithium Ion secondary battery 13 ......... Positive electrode 15 ... Separator 17 ... Electrolyte 19 ......... Battery can 21 ......... Positive lead 23 ......... Negative lead 25 ......... Positive terminal 27 ......... Sealing body 31 ... ... Nano-sized particle production equipment 33 ......... Reaction chamber 35 ......... Raw powder supply port 37 ......... Raw powder 39 ...... Sheath gas supply port 41 ...... Sheath gas 42 ......... Carrier gas 43 ......... High frequency coil 45 ......... High frequency power supply 47 ......... Plasma 49 ......... Filter 53 ......... Mixer 55 ......... Coating liquid 57 ......... Coating liquid raw material 59 ......... Coater 61 ......... Negative electrode 63 ......... Negative electrode active Material layer 65 ……… Protrusions 67 ……… Negative electrode current collector

Claims

An active material used for a negative electrode for a lithium ion secondary battery,
Consists of particles containing silicon as a main component and containing at least 0.05% by mass of element A,
The negative electrode active for a lithium ion secondary battery, wherein the atomic radius r A of the element A with respect to the atomic radius r 0 of silicon satisfies a relationship of | (r A −r 0 ) / r 0 | ≦ 0.1 Material material.
2. The lithium ion secondary battery according to claim 1, wherein the element A is at least one element selected from the group consisting of P, Cr, Mn, Fe, Co, Ni, Cu, and As. Negative electrode active material.
Furthermore, oxygen or fluorine is contained, The negative electrode active material for lithium ion secondary batteries of Claim 1 characterized by the above-mentioned.
2. The negative electrode active material for a lithium ion secondary battery according to claim 1, wherein the particles have an average primary particle diameter of 10 nm to 5 μm.
A negative electrode for a non-aqueous electrolyte secondary battery, comprising an active material layer formed by applying and drying a coating liquid containing the negative electrode active material according to claim 1 on one side or both sides of a negative electrode current collector.
A negative electrode current collector having protrusions on the surface; and a thin film negative electrode active material layer formed on the surface of the negative electrode current collector, containing silicon as a main component and containing at least 0.05% by mass of element A Have
The element A is an element in which the atomic radius r A of the element A with respect to the atomic radius r 0 of silicon satisfies a relationship of | (r A −r 0 ) / r 0 | ≦ 0.1. Negative electrode for lithium ion secondary battery.
The lithium ion secondary battery according to claim 6, wherein the element A is at least one element selected from the group consisting of P, Cr, Mn, Fe, Co, Ni, Cu, and As. Negative electrode.
The negative electrode for a lithium ion secondary battery according to claim 6, wherein the negative electrode active material layer further contains oxygen or fluorine.
The negative electrode current collector is a copper foil;
The surface of the copper foil on which the active material layer is provided is subjected to electrolytic surface roughening to provide a protrusion, and the surface roughness Rz is 1 μm to 6 μm. The negative electrode for lithium ion secondary batteries as described.
10. The lithium ion secondary battery according to claim 9, wherein the surface roughness Rz of the surface on which the active material layer is provided of the copper foil before the electrolytic surface roughening treatment is 0.5 μm to 3 μm. Negative electrode.
In an electrolyte having lithium ion conductivity, comprising: a positive electrode capable of inserting and extracting lithium ions; a negative electrode according to claim 5; and a separator disposed between the positive electrode and the negative electrode. A lithium ion secondary battery comprising the positive electrode, the negative electrode, and the separator.