JP2008293969A - Electrode for lithium secondary battery, lithium-ion secondary battery, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve durability at the charging/discharging of a lithium secondary battery by the use of a material containing tin for a negative electrode active material. <P>SOLUTION: The electrode for the lithium secondary battery is provided with a sheet-like current collector and an active material layer carried by the current collector. The active material layer includes a plurality of columnar particles having at least one bent part and containing tin elements. The electrode is capable of absorbing and discharging lithium. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode for a lithium secondary battery, a lithium ion secondary battery, and a method for producing the same, and particularly relates to an electrode for a lithium secondary battery in which an active material layer contains a tin element.

  In recent years, with the development of portable devices such as personal computers and mobile phones, the demand for batteries as power sources has increased. A battery used for the above applications is required to be used at room temperature, and at the same time, a high energy density and excellent cycle characteristics are required.

In response to this requirement, high-capacity active materials have been newly developed in each of the positive electrode and the negative electrode. Among them, a simple substance, oxide or alloy of silicon (Si) or tin (Sn) capable of obtaining a very high capacity is considered promising as a negative electrode active material. In addition, Li-containing composite oxides such as LiNiO ₂ are considered promising as positive electrode active materials.

  However, an active material having a high ability to occlude and release lithium has a large expansion and contraction during charging and discharging. Therefore, the electrode including the current collector is greatly distorted and tends to be wrinkled or cut. Further, a space is generated between the electrode and the separator, and the charge / discharge reaction tends to be non-uniform. Therefore, there is a concern that the battery may cause local characteristic deterioration.

  In order to solve such a problem, it has been proposed to provide a space in the negative electrode for relaxing the expansion stress of the active material. This proposal is intended to suppress negative electrode distortion and undulation, and to suppress deterioration of cycle characteristics. For example, Patent Document 1 proposes forming silicon columnar particles on a current collector. Further, Patent Document 2 proposes to perform pattern forming in which an active material that forms an alloy with lithium is regularly arranged on a current collector. Patent Documents 3 and 4 propose that the columnar particles forming the negative electrode active material are inclined with respect to the normal direction of the current collector surface.

  In each of Patent Documents 1 and 2, an active material is formed in a columnar structure upright in the normal direction of a sheet-like current collector. Therefore, most of the active material does not face the counter electrode active material but faces the exposed portion of the electrode current collector. For example, when the negative electrode has a columnar structure, lithium supplied from the positive electrode active material at the time of charging is not occluded by the negative electrode active material, but tends to precipitate on the exposed portion of the negative electrode current collector. As a result, during discharge, lithium is not efficiently released from the negative electrode, and charge / discharge efficiency is reduced.

  According to Patent Document 3 and Patent Document 4, it is possible to obtain a positive electrode or negative electrode active material layer while relaxing expansion of the active material. In terms of capacity retention, Patent Document 3 or Patent Document 4 is superior to Patent Document 1 and Patent Document 2.

  Patent Document 5 proposes a method for growing spiral columnar particles, although it is not a method for producing a negative electrode for a lithium secondary battery. The spiral columnar particles are formed on the substrate by vapor deposition. At that time, the tilt angle of the substrate is continuously changed with respect to the incident direction of the vapor by the rotation of two orthogonal axes.

As a technique for forming an alloy thin film such as an Sn alloy, a flash vapor deposition method using an alloy as a vapor deposition source and a multi-source vapor deposition method in which alloy elements are put in separate vapor deposition sources and each vapor deposition source is vaporized separately are known. (Non-Patent Document 1).
JP 2003-303586 A JP 2004-127561 A JP-A-2005-196970 JP-A-6-187994 US Pat. No. 5,866,204 Basic Technology of Thin Films, Second Edition, University of Tokyo Press, 1987, p49

  However, the columnar particles are subjected to stress at the contact portion between the active material and the current collector due to the expansion of the active material that occurs during charging. When the thickness of the active material layer is increased to increase the energy density, the normal component of the stress increases. When the columnar particles are inclined (in the case of Patent Document 3 and Patent Document 4), this stress is concentrated on the contact portion between the columnar particles and the current collector. Therefore, when the charge / discharge cycle is repeated over a long period of time, stress is repeatedly applied to the contact portion between the columnar particles and the current collector, and cracks are likely to occur.

  Further, the columnar particles tend to grow gradually in the width direction (the direction of the intersecting line between the plane perpendicular to the incident direction of the vapor of the material supply source and the plane parallel to the current collector). In the direction perpendicular to the width direction, a sufficient gap can be provided between the particles, but in the width direction, a sufficient gap cannot be provided. Therefore, when the thickness of the active material layer is increased in order to obtain a large energy density, the electrode is distorted, wrinkled, or cut.

  Here, FIG. 1 and FIG. 2 are conceptual views of a part of an electrode that includes a current collector 2 and an active material layer 1 carried on the current collector 2, and the active material layer includes a plurality of columnar particles 3. Indicate. FIG. 1 is a cross-sectional view perpendicular to the width direction of the columnar particles 3. FIG. 2 is a cross-sectional view parallel to the width direction of the columnar particles 3 and corresponds to the side view of FIG.

  An electrode for a lithium secondary battery of the present invention includes a sheet-like current collector and an active material layer carried on the current collector, and the active material layer has a plurality of columnar particles having at least one bent portion. The columnar particles contain a tin element and can store and release lithium. The columnar particles contain, for example, tin element by containing at least one selected from the group consisting of simple tin, tin alloy and tin oxide.

The angle θ ₁ formed by the growth direction of the columnar particles from the bottom of the columnar particles (that is, the contact portion between the current collector and the columnar particles) to the first bent portion and the normal direction of the current collector is 10 ° or more, It is preferably less than 90 °.
The growth direction of the columnar particles from the nth bent portion to the (n + 1) th bent portion counting from the bottom of the columnar particles (that is, the contact portion between the current collector and the columnar particles), and the normal direction of the current collector, Is θ _{n + 1} and n is an integer of 1 or more, the θ _{n + 1} is preferably 0 ° or more and less than 90 °.

The columnar particles may have only one bent portion or a plurality of bent portions.
The columnar particles can have a zigzag shape or a spiral shape.
The porosity P of the active material layer is preferably 10% ≦ P ≦ 70%.
The present invention also relates to a lithium secondary battery including the above electrode, a counter electrode, and an electrolyte having lithium ion conductivity interposed therebetween.

  In addition, when changing the inclination angle of a board | substrate variously like patent document 4, for example, columnar particle | grains can be made to grow helically. Therefore, it is considered that the growth of the columnar particles in the width direction can be suppressed. However, in an actual manufacturing process, it is not easy to change the tilt angle of the substrate in various ways. In particular, when a long current collector is unwound from a roll to continuously produce an electrode and then wound with a roll, it is difficult to change the inclination angle of the current collector in the course of manufacturing the electrode.

  Therefore, the present invention, from another viewpoint, the first step of depositing the active material constituent element by causing the active material constituent element to enter the sheet-like current collector at a first incident angle of + 10 ° to + 70 °. And a second step of causing the active material constituent element to enter the sheet-like current collector and depositing the active material constituent element at a second incident angle of −10 ° to −70 °, and the active material constituent element Proposes a method of manufacturing an electrode for a lithium ion secondary battery containing a tin element.

The active material constituent element can include one or more elements. In the first step and the second step, one or more identical elements or groups of elements can be deposited. However, the active material constituent element includes a tin element.
In addition, the incident direction of particle | grains becomes reverse by the case where an incident angle is + and-.

  For example, the first step includes causing the active material constituent element generated from the material supply source at the first position and the second position to enter the surface of the current collector at the first incident angle, and the second step includes: Including the active material constituent element generated from the material supply source at the first position and the second position on the surface of the current collector at the second incident angle.

For example, according to the present invention, the material source is evaporated sequentially or alternately in the first position and the second position, and the vapor of the generated material source is incident on the surface of the sheet-like current collector. It includes a method for producing an electrode for a lithium secondary battery that forms an active material layer carried on a current collector by being deposited.
When the material source includes the first element and the second element, the present invention includes a manufacturing method in which the first element is evaporated at the first position and the second element is evaporated at the second position. In this case, the first element and the second element may be evaporated sequentially or alternately.

  The first position and the second position are, for example, positions that are symmetric with respect to a plane perpendicular to the surface of the current collector. Here, the surface perpendicular to the surface of the current collector preferably passes through the center in the longitudinal direction of the sheet-shaped current collector.

  Here, the bent portion means a point where the growth direction of grains (grains) becomes discontinuous. Specifically, when the grain growth direction is represented by a curve, a point at which the derivative of the curve is discontinuous (that is, the inflection point of the derivative curve) is a bent portion. A curve representing the growth direction of the particles can be obtained by, for example, analyzing a cross-sectional SEM photograph of the columnar particles. From the cross-sectional SEM photograph, the growth direction of the columnar particles from the current collector toward the surface of the active material layer can be determined.

  In the present invention, the normal direction of the current collector means a direction perpendicular to the surface of the current collector and away from the surface of the current collector. The surface of the current collector often has irregularities when viewed microscopically, but is flat according to visual observation, so that the normal direction of the current collector is uniquely determined.

  The angle formed by the growth direction of the columnar particles and the normal direction of the current collector can be determined using, for example, an electron microscope (SEM or the like). When using an electron microscope, for example, the active material layer is cut in parallel with the normal direction of the current collector and in parallel with the growth direction of the columnar particles so as to obtain a cut surface as shown in FIG. Observe the cross section.

The angles θ ₁ and θ ₂ formed by the growth direction of the columnar particles and the normal direction of the current collector are preferably measured for at least 10 columnar particles and the average value thereof is obtained. In FIG. 4, the angles θ ₁ and θ ₂ formed by the growth direction of the columnar particles and the normal direction of the current collector are evaluated as follows: an electrode immediately after manufacture, an electrode included in an unused battery immediately after manufacture, It is preferable to use an electrode included in a battery that is charged and discharged only 10 times or less.

  When the active material layer containing tin element occludes and releases lithium, the columnar particles are subjected to stress due to expansion and contraction of the active material layer. However, according to the present invention, such stress can be dispersed in the bent portion. Therefore, stress concentration at the interface between the columnar particles and the current collector (the bottom of the columnar particles) can be alleviated, and cracks in the columnar particles can be made difficult to occur. Thereby, the connection between the active material layer and the current collector is maintained.

  Furthermore, when viewed from the normal direction on the counter electrode side, the exposed portion of the current collector constituting the electrode of the present invention can be remarkably reduced. As a result, even when lithium supplied from the counter electrode during charging is deposited on the exposed portion of the current collector, the amount of deposited lithium is reduced. Therefore, lithium is efficiently released from the electrode during discharge, and charge / discharge efficiency is improved.

  According to the manufacturing method of the present invention, the incident direction of the vapor from the material supply source to the current collector can be alternately switched between two inclination directions. In addition, since such an operation can be performed by controlling the installation position of the material supply source, there is no need to install a rotating shaft movable in a plurality of directions on the substrate.

  According to the method of the present invention, it is possible to incline the incident direction of the vapor from the material supply source into the current collector in one direction and also in the direction orthogonal to the direction. Thus, when the columnar particles are inclined with respect to the normal direction of the current collector, a sufficient gap can be provided also in the width direction of the columnar particles. Thus, the bent portion not only disperses the stress, but the gap relaxes the expansion stress during charging. Thereby, distortion of an electrode, a wrinkle, and cutting | disconnection can be suppressed and the charge / discharge cycle characteristic of a lithium secondary battery can be improved.

Hereinafter, the present invention will be described with reference to the drawings. However, the present invention is not limited to the following contents as long as it has the features described in the claims.
FIG. 3 is a perspective view conceptually showing the electrode 10 for a lithium secondary battery according to Embodiment 1 of the present invention. The electrode 10 includes a sheet-like current collector 11 and an active material layer 12 capable of inserting and extracting lithium supported on the current collector 11. The active material layer 12 is composed of a plurality of columnar particles 13 having at least one bent portion. The columnar particles 13 contain a tin element by containing at least one selected from the group consisting of a simple tin, a tin alloy and a tin oxide, for example. The columnar particles 13 start from the contact portion (the bottom portion of the columnar particles) between the current collector 11 and the columnar particles 13 and continuously extend toward the surface of the active material layer through the bent portion.

FIG. 4 is an enlarged sectional view of a part of the electrode 20 for a lithium secondary battery of the present invention. In FIG. 4, the columnar particle 23 has two bent portions. Portion of the contact portion between the current collector 21 of the columnar particles 23 from (the bottom of the columnar particles) to the first bent portion (first columnar portion) has a growth direction D _1. The growth direction D ₁ forms an angle θ ₁ with the normal direction D of the surface of the current collector 21. θ ₁ is 10 ° or more and less than 90 °. Portion from the first bend to the second bend (second columnar portion) has a growth direction D _2. The growth direction D ₂ forms an angle θ ₂ with the normal direction D of the surface of the current collector. Portion from the second bent portion to the distal end of the columnar particles (third columnar portion) has a growth direction D _3. The growth direction D ₃ forms an angle θ ₃ with the normal direction D of the current collector surface.

Although the case where there are three columnar portions has been described with reference to FIG. 4, a case where the number of columnar portions further increases will be generally described. Angle θ _{n + 1} (n is an integer of 1 or more) formed by the growth direction of the columnar portion from the n-th bent portion to the (n + 1) -th bent portion counted from the starting point of growth and the normal direction of the current collector ) Is generally 0 ° or more and less than 90 °. Here, the starting point of growth is the contact portion between the current collector and the columnar particles (the bottom of the columnar particles). The growth direction of the columnar particles is a direction in which the columnar particles continuously extend from the growth starting point through the bent portion toward the surface of the active material layer. In the case of FIG. 4, the angle formed by the growth direction D ₂ of the second columnar portion, which is the region from the first bent portion to the second bent portion, and the normal direction D of the current collector corresponds to θ ₂ . To do.

  FIG. 5 shows the form of columnar particles having a plurality of bent portions when each columnar portion is shortened. In the active material layer 202 formed on the surface of the current collector 201, the columnar particle 203 has seven columnar portions d1 to d7 having different growth directions. The growth direction of each columnar part is D1-D7. Such columnar particles 203 can be obtained by performing a plurality of stages of deposition by changing the tilt angle.

  When each columnar part is short like the electrode 200, the columnar part is a layer rather than a columnar. The present invention also includes a form in which each columnar portion is rather layered like the electrode 200. Even in such a case, it can be confirmed by various analysis methods that the growth direction of the particles changes almost periodically and is bent. That is, even when each columnar part is short, if the microscopic observation is performed, the bent part and the columnar part can be clearly grasped. For example, by observing a cross section of the electrode 200 parallel to the normal direction of the current collector 201 with an SEM, a bent portion and a columnar portion (or a layered portion) can be confirmed. In addition, cross-sectional observation becomes easy by grind | polishing the cross section of an electrode and performing a chemical etching.

FIG. 6 shows an embodiment of another electrode for a lithium secondary battery of the present invention. The electrode 30 includes a sheet-like current collector 31 and an active material layer 32 supported on the current collector. The active material layer 32 includes a plurality of columnar particles 33 having one bent portion. First columnar portion from the contact portion of the current collector 31 of the columnar particles 33 to the first bend has a growth direction D _4. The growth direction D ₄ forms an angle θ ₁ with the normal direction D of the surface of the current collector 31. The second columnar portion from the first bend to a second bend has a growth direction D _5. The growth direction D ₅ forms an angle θ ₂ with the normal direction D of the surface of the current collector. Again, the growth direction D ₄ to D ₅ of the columnar section need not be present in one plane. Therefore, when viewed from the normal direction of the current collector, each columnar portion may be bent in a different direction. A preferable range of the angles θ ₁ and θ ₂ formed by each columnar portion and the normal direction of the current collector is the same as that of the electrode 20 in FIG.

  FIG. 7 shows an electron micrograph (SEM photograph) of a part of an electrode including columnar particles having a bent portion. According to the observation results, the active material layer is composed of columnar particles having bent portions as shown in FIG.

  When the columnar particle 33 contains a tin element, the columnar particle 33 expands when lithium is occluded. At that time, stress is generated in the columnar particles 33 due to expansion. In the battery, since the positive electrode and the negative electrode face each other with the separator interposed therebetween, the stress in the thickness direction of the active material layer is particularly large. When the columnar particles have a bent portion, this stress is concentrated and applied to the active material-current collector interface, but when the columnar particles have a bent portion, the stress is dispersed in the surface direction at the bent portion. Therefore, the stress applied to the bottom of the columnar particles is relaxed. As a result, the stress existing at the interface between the columnar particles and the current collector is reduced, and the progress of cracks is suppressed. As a result, even when the charge / discharge cycle is repeated, the active material is unlikely to drop out, and the deterioration of the battery characteristics is suppressed.

  In order to increase the capacity, it is necessary to increase the thickness of the active material layer. In the case of the present invention, increasing the thickness of the active material layer corresponds to growing columnar particles longer. It is desirable from the viewpoint of stress dispersion that the longer the columnar particles, the greater the number of bent portions. For example, in the case of columnar particles having a height in the normal direction of the current collector of 10 μm or more, it is desirable to have at least one bent portion. Further, in the case of columnar particles having a height in the normal direction of the current collector of 50 μm or more, it is desirable to have at least two or more bent portions.

The growth direction of each columnar part (in the case of FIG. 4, D _{1 to} D ₃ ) does not need to exist in the same plane. When viewed from the normal direction of the current collector, each columnar portion may be bent in a different direction. When the columnar particles have a plurality of bent portions, the columnar particles preferably have a zigzag shape. According to the zigzag shape, the stress in one direction concentrated on the contact portion between the columnar particles and the current collector can be dispersed in another direction, and the stress can be efficiently relieved. In addition, when the columnar particles have a zigzag shape, the columnar particles desirably have a spiral shape. According to the spiral shape, the stress applied to the contact portion between the columnar particles and the current collector can be more efficiently relaxed.

FIG. 8 shows still another embodiment of the electrode for a lithium secondary battery of the present invention. The electrode 40 includes a sheet-like current collector 41 and an active material layer 42 supported on the current collector. The active material layer 42 is composed of a plurality of columnar particles 43 having one bent portion. First columnar portion from the contact portion of the current collector 41 of the columnar particles 43 to the first bend has a growth direction D _6. The growth direction D ₆ forms an angle θ ₁ with the normal direction D of the surface of the current collector 41. Further, the second columnar portion from the first bent portion to the second bent portion has a growth direction D ₇ . The growth direction D ₇ forms an angle θ ₂ with the normal direction D of the surface of the current collector. Again growth direction D ₆ to D ₇ of the columnar section need not be present in one plane. When viewed from the normal direction, each columnar portion may be bent in a different direction. Therefore, a preferable range of the angles θ ₁ and θ ₂ formed by each columnar portion and the normal direction of the current collector is the same as that of the electrode 20 in FIG. In addition, FIG.3, FIG.4, FIG.5, FIG.6, FIG.7 and FIG. 8 do not restrict | limit the shape of columnar particle | grains. The shape of the columnar particles is not particularly limited.

  From the viewpoint of securing a large contact area between the electrolyte and the active material and relieving stress due to expansion of the active material, the active material layer is desired to have a predetermined porosity. The porosity P of the active material layer can be obtained from the weight and thickness of the active material layer having a certain area and the true density of the active material. Further, the porosity P can be measured more accurately by a method using a porosimeter by gas adsorption or mercury intrusion.

  The porosity P of the electrode is approximately 10% ≦ P ≦ 70% depending on how much the active material expands when lithium is occluded. If the porosity P is 10% or more, it is considered sufficient to relieve stress due to expansion and contraction of the columnar particles. Therefore, an abundant electrolyte in contact with the granular particles can be secured. From the viewpoint of suppressing capacity reduction during high-speed charge / discharge, the porosity P is more preferably 30% ≦ P ≦ 60%. Even if the porosity P exceeds 70%, it can be suitably used as an electrode depending on the use of the battery.

  If the thickness of the active material layer (in the case of FIG. 4 t) is 0.1 μm or more, the energy density can be secured, and if it is 100 μm or less, the rate at which each columnar particle is shielded by other columnar particles is kept low. be able to. Moreover, if the thickness of an active material layer is 100 micrometers or less, since the current collection resistance from columnar particles can be suppressed, it is advantageous for charging / discharging at a high rate. Therefore, the thickness of the active material layer is preferably 0.1 μm ≦ t ≦ 100 μm. Furthermore, it is particularly preferable that 1 μm ≦ t ≦ 50 μm from the viewpoint of suppressing temperature rise during high-speed charge / discharge.

  The shape of the cross section perpendicular to the growth direction of the columnar particles (hereinafter referred to as cross section C) is not particularly limited. Further, the shape of the cross section C may change in the length direction of the columnar particles. However, from the viewpoint of preventing the columnar particles from cracking or detaching from the current collector when the columnar particles expand, the cross section C is preferably substantially circular. The diameter d of the cross section C is approximately 100 μm or less. The diameter d of the cross-section C is preferably 1 to 50 μm from the viewpoint of high strength and high reliability by miniaturization. In addition, when the cross-section C of columnar particles is substantially circular, the diameter d is calculated | required as an average value of the diameter of arbitrary 2-10 columnar particles, for example. Here, the diameter of the columnar particles is determined by the center height. The center height means the center height of the columnar particles in the normal direction of the current collector. The diameter d is a diameter perpendicular to the growth direction of the columnar particles.

  A plurality of columnar particles adjacent to each other may coalesce during growth. However, since the individual columnar particles have different growth starting points, they are separated in the vicinity of the surface of the current collector, and the growth state of the particles is also different. Therefore, a boundary can be observed between the combined individual columnar particles. Therefore, it is possible to determine the diameter d of each columnar particle.

  The preferable state of the active material when measuring the porosity, thickness, and diameter of the columnar particles of the active material layer includes lithium corresponding to the irreversible capacity and lithium corresponding to the reversible capacity. It is desirable to measure in a state where there is no reversible capacity (a state where the reversible capacity is 0), that is, a complete discharge state. The completely discharged state corresponds to a state where the volume of the active material layer in the completed battery is minimum.

  When measuring the porosity of the negative electrode, the thickness of the active material layer, and the diameter of the columnar particles without lithium corresponding to the irreversible capacity, by correcting the measured values, Obtainable. For example, the porosity P of the active material layer containing no lithium can be measured using a mercury porosimeter. In this case, the value of the porosity P is corrected using the volume difference ΔV between the volume of the fully discharged active material layer containing lithium corresponding to the irreversible capacity and the volume of the active material layer not containing lithium at all. The porosity P ′ containing lithium corresponding to the irreversible capacity is obtained from P ′ = P−ΔV.

  In the present invention, the columnar particles can contain an element capable of forming a solid solution with tin in addition to tin. Examples of such elements include cobalt, nickel, zinc, copper, iron, manganese, chromium, titanium, vanadium, and indium. These may be used alone for the active material, or may be used in combination of plural kinds.

Examples of the active material that forms the columnar particles include Sn alone, Sn alloy, and Sn oxide. Similar to tin, high-capacity materials include Si alone, Si alloys, SiO _{x, and the} like. From the viewpoint of process cost, an active material containing tin is desirable. These may constitute an active material layer alone, or a plurality of types may simultaneously constitute an active material layer. The tin oxide preferably has a composition represented by the general formula (1): SnO _x (where 0 <x <2). The x value indicating the content of oxygen element is more preferably 0.01 ≦ x ≦ 1.

  The columnar particles may be single crystal particles of an active material or polycrystalline particles including crystallites (crystal grains) of a plurality of active materials. Further, the columnar particles may be particles containing fine crystals of an active material having a crystallite size of 100 nm or less, and more preferably particles containing a uniform amorphous active material.

  In the present invention, the constituent material of the sheet-like current collector is not particularly limited. As the negative electrode current collector, copper is generally suitable. For example, an electrolytic copper foil or an electrolytic copper alloy foil is used. An electrolytic copper foil whose surface is roughened, a rolled copper foil whose surface is roughened, and the like are also used. Titanium, nickel, stainless steel, etc. are also suitable for the current collector. The current collector is preferably produced by an electrolytic method. The thickness of each current collector is not particularly limited, but is generally 1 to 50 μm, for example.

  The sheet-like current collector desirably has irregularities on the surface carrying the active material layer. The specific value of the surface roughness Rz (ten-point average height) of the current collector is preferably in the range of 0.1 to 30 μm, more preferably 0.3 to 15 μm. When the surface roughness Rz is less than 0.1 μm, it may be difficult to provide a space between the columnar particles adjacent to each other. The surface roughness Rz is defined in Japanese Industrial Standard (JISB 0601-1994) and can be measured by, for example, a commercially available surface roughness meter.

  The electrode for a lithium secondary battery of the present invention can be manufactured using a manufacturing apparatus 50 as shown in FIGS. 9A and 9B, for example. 9B is a cross-sectional view taken along line BB in FIG. 9A. The manufacturing apparatus 50 includes a chamber 56 for realizing a vacuum atmosphere, a fixing base 54 for fixing the current collector 51, a target 55 containing a material supply source 59, and an electron beam (not shown) as a heating means for the target. A).

  In the case of forming an active material layer containing tin oxide, tin oxide may be used as a material supply source, but a gas introduction part for introducing oxygen gas into the chamber may be provided. The manufacturing apparatus 50 includes a nozzle 52 that discharges gas and a pipe 53 that introduces gas into the nozzle 52 from the outside. For example, when depositing an active material containing SnO in a columnar shape, SnO may be used as a material supply source, but tin alone may be used and high-purity oxygen gas may be released from the nozzle 52. However, the degree of vacuum in the chamber is preferably adjusted to about 1 Pa.

  When forming an active material layer containing a tin alloy, there are general methods such as flash vapor deposition using a tin alloy as a vapor deposition source, and multi-source vapor deposition methods in which alloy elements are placed in separate vapor deposition sources and each vapor deposition source is vaporized separately. Can be used.

The electrode of the present invention is produced, for example, by the following procedure.
The current collector 51 is fixed to the fixed base 54, the fixed base 54 is rotated around the tilt rotation shaft 57, and the fixed base 54 is installed so as to form an angle α with the horizontal plane. The rotation shaft 57 is an axis that is parallel to the fixed base 54 and the horizontal plane and passes through the center C of the fixed base 54. Here, the horizontal plane is a plane perpendicular to the vapor scattering direction of the material supply source from the target 55 toward the fixed base 54. The active material is deposited while the fixing base 54 is fixed at the angle α. Next, the fixing base 54 is rotated 180 degrees clockwise around the rotation shaft 58 and fixed. The rotation shaft 58 is an axis that is perpendicular to the current collector surface and passes through the center C of the fixed base 54. In this state, the active material is further deposited. Further, the fixing base 54 is fixed by rotating clockwise by 180 degrees about the rotation shaft 58, and the active material is continuously deposited. By such a procedure, columnar particles having two bent portions as shown in FIG. 4 are obtained. The angle formed by the first columnar portion and the second columnar portion of the columnar particles with the normal direction of the current collector surface is controlled by the angle α formed by the fixed base 54 and the horizontal plane.

  When the columnar particles are formed in a spiral shape, a device that rotates the fixed base 54 around the rotation shaft 58 is used. First, the current collector is fixed to the fixed base 54, the fixed base 54 is rotated about the rotation shaft 57, and the fixed base 54 is installed so as to form an angle α with the horizontal plane. Then, the current collector 51 is rotated around the rotation shaft 58 during the deposition of the active material. During the deposition of the active material, the angle α formed by the fixed base 54 and the horizontal plane is kept constant. At this time, columnar particles having a spiral shape are obtained by rotating the current collector 51 at a speed proportional to the deposition rate of the active material.

  FIG. 10 is a schematic cross-sectional view of a stacked lithium secondary battery which is an example of the lithium secondary battery of the present invention. The battery 60 includes an electrode plate group including a positive electrode 61, a negative electrode 62, and a separator 63 interposed therebetween. The electrode group and the electrolyte having lithium ion conductivity are accommodated in the exterior case 64. The separator 63 is impregnated with an electrolyte having lithium ion conductivity. The positive electrode 61 includes a positive electrode current collector 61a and a positive electrode active material layer 61b supported on the positive electrode current collector 61a. The negative electrode 62 includes a negative electrode current collector 62a and a negative electrode active material supported on the negative electrode current collector 62a. It consists of a material layer 62b. One end of a positive electrode lead 65 and a negative electrode lead 66 is connected to the positive electrode current collector 61 a and the negative electrode current collector 62 a, respectively, and the other end is led out of the exterior case 64. The opening of the outer case 64 is sealed with a resin material 67.

  The positive electrode active material layer 61b releases lithium ions during charging, and occludes lithium ions released from the negative electrode active material layer 62b during discharge. The negative electrode active material layer 62b occludes lithium ions released from the positive electrode active material during charging, and releases lithium ions during discharge.

  In a stacked battery, three or more layers including a positive electrode and a negative electrode may be stacked. At this time, a positive electrode having a positive electrode active material layer on both sides or one side and a negative electrode having a negative electrode active material layer on both sides or one side are used. However, all the positive electrode active material layers are opposed to the negative electrode active material layer, and all the negative electrode active material layers are opposed to the positive electrode active material layer.

  The inclination state of each region (each columnar portion or layered portion) divided by the bent portion of the columnar particles may be the same in all active material layers, or may be different for each active material layer. Furthermore, the same electrode may contain columnar particles having different inclination states of the columnar portions. In the case of an electrode having active material layers on both sides, in the columnar particles on both sides, the inclined state of each columnar part may be the same or different.

Various solid electrolytes and non-aqueous electrolytes are used as the lithium ion conductive electrolyte used in the present invention. As the non-aqueous electrolyte, a solution obtained by dissolving a lithium salt in a non-aqueous solvent is preferably used. The composition of the nonaqueous electrolytic solution is not particularly limited. The separator and the outer case are not particularly limited, and materials used in various forms of lithium secondary batteries can be used without particular limitation.
FIG. 10 shows an example of a stacked battery, but the present invention can naturally be applied to a cylindrical battery or a square battery having a spiral (winding) electrode group.

  11A and 11B show another apparatus for manufacturing an electrode for a lithium secondary battery of the present invention. The manufacturing apparatus 90 has the same configuration as the manufacturing apparatus 50 of FIGS. 9A and 9B except for the installation position of a target 95 including a material supply source and an electron beam apparatus (not shown) that is a heating means thereof. Therefore, the fixed base 54 can be rotated around the rotation shaft 57 so as to form an angle α with the horizontal plane. The installation position of the target 95 is movable between the first position 98 and the second position 99. The first position 98 and the second position 99 are symmetrical positions with respect to a plane that passes through the center C of the fixed base 54 and is orthogonal to the rotation shaft 57.

  An angle β1 formed by a direction U vertically below the center C of the fixed base 54 and a direction from the center C toward the first position can be set in a range of angles of 0 ° or more and less than 90 °. Similarly, the angle β2 formed by the direction U and the direction from the center C toward the second position can be set within an angle range of 0 ° or more and less than 90 °. However, when the fixed base 54 forms an angle α with the horizontal plane, the angles β1 and β2 are α × 0.2 ≦ β1 ≦ α × 0.8 and α × 0.2 ≦ β2 ≦ α × 0. The range of 8 is preferable, and the ranges of α × 0.35 ≦ β1 ≦ α × 0.65 and α × 0.35 ≦ β2 ≦ α × 0.65 are more preferable.

  FIG. 11A shows a state where the target 95 exists at the first position. FIG. 11B shows a state where the target 95 exists at the second position. The target 95 is moved alternately between the first position 98 and the second position 99 to evaporate the material source alternately at the first position 98 and the second position 99. As a result, the direction of incidence of the vapor of the material supply source from the first position to the current collector and the direction of incidence from the second position to the current collector are respectively rotation axes with respect to the normal direction of the current collector. Inclined in 57 axial directions. The angle α formed by the fixed base 54 with the horizontal plane can be set to 0 ≦ α <90 °, for example. The angle α may be 0 °.

  When the fixing base 54 forms an angle α larger than 0 ° with the horizontal plane, the columnar particles are inclined in the direction opposite to the rotation direction of the rotation shaft 57 with respect to the normal direction of the current collector. Furthermore, the incident direction of the vapor of the material supply source on the current collector forms an angle β1 and β2 with the direction U, whereby the axis of rotation 57 is inclined.

  By depositing the active material on the current collector by the method as described above, the incident direction of the vapor of the material supply source can be changed variously. Therefore, columnar particles having a bent portion can be easily grown. Moreover, a gap can be effectively formed between the adjacent columnar particles due to the influence of the shadows on the surface of the current collector. As a result, the expansion stress of the active material during charging can be effectively dispersed. Further, according to the above method, it is convenient in that columnar particles having a bent portion can be formed only by controlling the position of the target even when the fixing base 54 is fixed.

  12A and 12B show still another manufacturing apparatus for an electrode for a lithium secondary battery of the present invention. The manufacturing apparatus 100 has the same configuration as the manufacturing apparatus 50 of FIGS. 9A and 9B except for the installation position of a target including a material supply source and an electron beam apparatus (not shown) that is a heating means thereof. The manufacturing apparatus 100 includes two targets 105a and 105b. The installation positions of the targets 105a and 105b are a first position 108 and a second position 109, respectively. The first position 108 and the second position 109 are symmetrical positions with respect to a plane that passes through the center C of the fixed base 54 and is orthogonal to the rotation shaft 57. The angle β1 (or β2) formed by the direction U vertically below the center C of the fixed base 54 and the direction from the center C toward the first position (or second position) is the manufacturing apparatus of FIGS. 11A and 11B. 90.

  Targets 105a and 105b can be shielded separately by shutters 107a and 107b, respectively. FIG. 12A conceptually shows a state where the target 105a is shielded by the shutter 107a. FIG. 12B conceptually shows a state where the target 105b is shielded by the shutter 107b. Note that only one shutter that is movable between the first position 98 and the second position 99 may be installed. The targets 107a and 105b are alternately shielded by the shutter 107a and the shutter 107b, and the material supply source is evaporated from the unshielded target. By such a method, columnar particles having a bent portion can be formed as in the case of using the manufacturing apparatus 90.

  FIG. 13 shows still another manufacturing apparatus for the electrode for the lithium secondary battery of the present invention. The manufacturing apparatus 110 has the same configuration as the manufacturing apparatus 50 of FIGS. 9A and 9B except for a target including a material supply source. That is, the first position 118 and the second position 119 are symmetrical positions with respect to a plane that passes through the center C of the fixed base 54 and is orthogonal to the rotation shaft 57. An angle β1 (β2) formed by a direction U vertically below the center C of the fixed base 54 and a direction from the center C toward the first position (or the second position) is the manufacturing apparatus 90 of FIGS. 11A and 11B. It is the same.

  The target 115 has a width from the first position 118 to the second position 119. Both ends of the target 115 correspond to the first position 118 and the second position 119, respectively. By changing the irradiation position of the electron beam, a part or the whole of the target 115 can be heated. The irradiation position of the electron beam is controlled, and the material supply source is alternately evaporated at the first position and the second position. By such a method, columnar particles having a bent portion can be formed as in the case of using the manufacturing apparatus 90.

  In the manufacturing apparatus 110 of FIG. 13, one electron beam device is installed at each of the first position 118 and the second position 119, and the first position 118 and the second position 119 are alternately irradiated with the electron beam, Similar effects can be obtained.

The same effect can be obtained by fixing the material supply source and rotating or tilting the fixing base for fixing the current collector in the biaxial direction. However, when a long current collector is unwound from a roll to continuously produce an electrode and then wound with a roll, it is difficult to variously change the inclination angle of the current collector during the production of the electrode. On the other hand, in the case of a manufacturing apparatus like FIGS. 11-13, the inclination angle of a collector can be easily changed variously only by controlling the installation position of a material supply source and the timing of evaporation.
EXAMPLES Next, although this invention is demonstrated concretely based on an Example, a following example does not limit this invention.

Example 1
A stacked lithium secondary battery as shown in FIG. 10 was produced.
(I) Production of positive electrode 10 g of lithium cobaltate (LiCoO ₂ ) powder having an average particle diameter of about 10 μm as a positive electrode active material, 0.3 g of acetylene black as a conductive agent, and polyvinylidene fluoride powder as a binder. 8 g and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were sufficiently mixed to prepare a positive electrode mixture paste.

  The obtained paste was applied to one side of a positive electrode current collector 61a made of an aluminum foil having a thickness of 20 μm, dried and then rolled to form a positive electrode active material layer 61b. Thereafter, the positive electrode was cut into a predetermined shape. In the obtained positive electrode, the positive electrode active material layer carried on one side of the aluminum foil had a thickness of 50 μm and a size of 30 mm × 30 mm. A lead was connected to the back surface of the current collector without the positive electrode active material layer.

(Ii) Production of Negative Electrode A negative electrode was produced using a vapor deposition apparatus (manufactured by ULVAC, Inc.) as shown in FIGS. 9A and 9b. The negative electrode current collector 51 (62a in FIG. 10) was fixed to the fixed base 54, and a tungsten filament with a crucible was installed vertically below the fixed base 54. The crucible was filled with 99.99% pure tin (manufactured by Kanto Chemical Co., Inc.) as a material supply source 59.

  As the negative electrode current collector, an electrolytic copper foil (manufactured by Furukawa Circuit Foil Co., Ltd.) having a thickness of 35 μm and cut to a size of 40 mm × 40 mm and having a surface roughness Rz of 10 μm was used. The fixing base 54 on which the negative electrode current collector was fixed was first inclined to form an angle α of 70 ° with the horizontal plane, and tin was vapor-deposited for 10 minutes in this state (first vapor deposition step). As vapor deposition conditions, the current flowing through the filament was set to 60A. Thereafter, the fixed base 54 was rotated 180 ° clockwise around the rotation shaft 58, and in this state, tin was vapor-deposited under the same conditions for 10 minutes (second vapor deposition step).

  Thus, the negative electrode active material layer which consists of tin was formed on copper foil, and negative electrode 1A was obtained. Thereafter, the negative electrode 1A was cut into a size of 31 mm × 31 mm. A lead terminal was connected to the back surface of the current collector having no negative electrode active material layer.

The cross section of the negative electrode 1A was observed from various angles with an electron microscope (SEM).
As a result of observation, it was found that the negative electrode active material layer was composed of columnar particles having one bent portion. The angle θ1 formed by the first columnar portion from the contact portion of the columnar particle with the current collector to the bent portion and the normal direction of the current collector surface is 45 °, and the second columnar shape from the bent portion to the tip of the columnar particle The angle θ2 formed by the portion with the normal direction of the current collector surface was also 45 °. The thickness t of the negative electrode active material layer was 5.5 μm, and the center-to-center distance (pitch) between the columnar particles adjacent to each other was 15 μm. The diameter at the center height of the columnar particles was 4 μm.

  Next, the porosity P of the negative electrode 1A was measured as follows. On one side of a 3 cm × 3 cm size copper foil (surface roughness Rz = 10 μm, thickness 35 μm), tin columnar particles were uniformly formed under the same conditions as described above to prepare a sample of the negative electrode 1A. The weight of the copper foil was subtracted from the weight of the obtained sample to determine the weight of the active material layer, the film thickness of tin was measured, and the density of the active material layer was determined. The obtained density was divided by the true density of tin, and the void ratio P, which is the ratio of voids to the total volume, was found to be 46%.

Hereinafter, the physical properties of the negative electrode 1A are summarized.
Active material composition: Sn
Angle θ1: 45 ° formed by the first columnar portion and the normal direction of the current collector surface
Angle θ2: 45 ° formed by the second columnar portion and the normal direction of the current collector surface
Active material layer thickness t: 5.5 μm
Distance between centers of adjacent columnar particles: 15 μm
Columnar particle diameter: 4 μm
Current collector surface roughness Rz: 10 μm
Porosity P: 46%

(Iii) Production of test battery A positive electrode active material layer and a negative electrode active material layer were opposed to each other through a separator made of a polyethylene microporous film having a thickness of 20 μm manufactured by Asahi Kasei Co., Ltd. to form a thin electrode plate group. This electrode group was inserted into an outer case made of an aluminum laminate sheet together with the electrolyte. As the electrolyte, a nonaqueous electrolytic solution in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 1 and LiPF ₆ was dissolved at a concentration of 1.0 mol / L was used. The non-aqueous electrolyte was impregnated in the positive electrode active material layer, the negative electrode active material layer, and the separator, respectively. Thereafter, with the positive electrode lead and the negative electrode lead led out to the outside, the end portion of the outer case 64 was welded while vacuum decompression to complete a test battery. The obtained test battery is referred to as battery 1A.

<< Comparative Example 1 >>
A negative electrode was produced in the following manner.
As the negative electrode current collector, an electrolytic copper foil having a thickness of 35 μm and a surface roughness Rz of 10 μm (manufactured by Furukawa Circuit Foil Co., Ltd.) was used. Using a manufacturing apparatus as shown in FIGS. 9A and 9B, tin was deposited on the negative electrode current collector. The copper foil was fixed to the fixing base 54, the angle α formed by the fixing base and the horizontal plane was set to 0 °, and the copper foil was horizontally installed. As vapor deposition conditions, the current flowing through the filament was set to 60A. The deposition time was set to 5 minutes. Thus, the negative electrode active material layer which consists of tin was formed on copper foil, and the negative electrode 1B was obtained.

Similarly to the negative electrode 1A, the cross section of the negative electrode 1B was observed with an electron microscope (SEM).
As a result of observation, as shown in FIG. 14, it was found that the negative electrode active material layer was composed of a dense Sn film containing columnar particles having no bent portion. The thickness t of the obtained active material layer was 5.2 μm, and the diameter of the granular particles was 6.5 μm. Further, when the porosity P of the negative electrode 1B was determined by the same method as that of the negative electrode 1A, it was 14%.

Hereinafter, the physical properties of the negative electrode 1B are summarized.
Active material composition: Sn
The angle θ between the columnar particles and the normal direction of the current collector: 0 °
Active material layer thickness t: 5.2 μm
Columnar particle diameter: 6.5 μm
Porosity P: 14%

  The negative electrode 1B was cut into a size of 31 mm × 31 mm, and a lead terminal was connected to the back surface of the current collector not having the negative electrode active material layer. A test battery 1B was produced in the same manner as in Example 1 except that the negative electrode thus obtained was used.

[Evaluation methods]
The batteries 1A and 1B were each housed in a constant temperature room at 20 ° C. and charged by a constant current constant voltage method. Here, the battery is charged at a constant current of 1C rate (1C is a current value that can use up the entire battery capacity in 1 hour) until the battery voltage reaches 4.2V, and after reaching 4.2V, the current value is The battery was charged at a constant voltage until reaching 0.05C. After charging, the battery was paused for 20 minutes, and then discharged at a constant current of 1C until the battery voltage reached 2.5V. Furthermore, re-discharge was performed at a current value of 0.05 C until the battery voltage reached 2.5V. After the re-discharge, it was paused for 20 minutes.

  The above charging / discharging was repeated 100 cycles. (I) At the beginning of the cycle, the ratio of the discharge capacity to the charge capacity was determined as a percentage value as the charge / discharge efficiency. Further, (ii) the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the beginning of the cycle was obtained as a percentage value as the capacity retention rate. The results are shown in Table 1.

  From Table 1, the capacity maintenance rate of the battery 1A was improved as compared with the battery 1B. The capacity retention rate has been greatly improved because the columnar particles have a bent portion, so that the active material layer can have voids to relieve stress and connect the negative electrode active material and the current collector. This is probably because of

Example 2
As shown in FIG. 11A and FIG. 11B, a vapor deposition apparatus (manufactured by ULVAC, Inc.), that is, an apparatus similar to the manufacturing apparatus 50 of FIG. A negative electrode was prepared using the same. The negative electrode current collector 51 (62a in FIG. 9) was fixed to the fixed base 54, and targets 105a and 105b placed in a carbon crucible were installed below the fixed base 54. At that time, the targets 105a and 105b were placed at first and second positions symmetrical with respect to a plane passing through the center C of the fixed base 54 and orthogonal to the rotation shaft 57.

  An angle b1 formed by a direction U vertically below the center C of the fixed base 54 and a direction from the center C toward the first position, and an angle formed by the direction U and a direction directed from the center C toward the second position. Each b2 was 30 °.

  Each of the targets 105a and 105b is filled with 99.99% purity tin (manufactured by Kanto Chemical Co., Ltd.) and 99.99% purity cobalt (manufactured by Kanto Chemical Co., Ltd.) as a material supply source. An apparatus (not shown) was used to heat the material source.

  As the negative electrode current collector, an electrolytic copper foil (manufactured by Furukawa Circuit Foil Co., Ltd.) having a thickness of 35 μm and cut to a size of 40 mm × 40 mm and having a surface roughness Rz of 10 μm was used. The fixing base 54 to which the negative electrode current collector was fixed was first inclined so as to form an angle α of 70 ° with the horizontal plane. Further, the target 105b installed at the second position was shielded by the shutter 107b. In this state, tin was evaporated from the target 105a placed at the first position for 10 minutes, and an active material was vapor-deposited for 10 minutes (first vapor deposition step).

  Thereafter, in a state where the target 105a installed at the first position was shielded by the shutter 107a, cobalt was evaporated from the target 105b installed at the second position, and an active material was deposited for 5 minutes (second deposition process).

  Thereafter, the fixed base 54 was rotated 180 ° clockwise around the rotation shaft 58. Further, the target 105b installed at the second position was shielded by the shutter 107b. In this state, tin was evaporated from the target 105a installed at the first position, and was vapor-deposited for 10 minutes under the same conditions (third vapor deposition step).

  Thereafter, cobalt was evaporated from the target 105b installed at the second position while the target 105a installed at the first position was shielded by the shutter 107a again, and an active material was deposited for 5 minutes (fourth deposition process). .

The acceleration voltage of the electron beam irradiated to each target was set to -8 kV, the emission of the target 105a was set to 250 mA, and the emission of the target 105b was set to 500 mA.
The vapor of tin and cobalt could be deposited as a laminated film on the negative electrode current collector installed on the fixed base 54. Then, the obtained laminated film was heat-treated in a 200 ° C. vacuum oven for 24 hours. In this way, a negative electrode active material layer made of a tin-cobalt alloy was formed to obtain a negative electrode 2A. The negative electrode 2A was cut into a size of 31 mm × 31 mm. A lead terminal was connected to the back surface of the current collector having no negative electrode active material layer.

The negative electrode 2A was observed from various angles with an electron microscope (SEM).
As a result of observation, it was found that the negative electrode active material layer was composed of columnar particles having one bent portion. The angle θ1 formed by the first columnar portion from the contact portion of the columnar particle with the current collector to the bent portion and the normal direction of the current collector surface is 45 °, and the second columnar shape from the bent portion to the tip of the columnar particle The angle θ2 formed by the portion with the normal direction of the current collector surface was also 45 °. The thickness t of the negative electrode active material layer was 6.5 μm, and the distance (pitch) between the centers of the columnar particles adjacent to each other was 12 μm. The diameter at the center height of the columnar particles was 5.0 μm.

As a result of quantifying the amount of Co contained in the obtained negative electrode active material layer by ICP analysis, the composition of the tin-cobalt alloy was SnCo _0.3 . From the XRD analysis results, the presence of the CoSn ₃ phase was confirmed.

Next, the porosity P of the negative electrode 2A was measured as follows.
Sn columnar particles were uniformly formed on one side of a 3 cm × 3 cm size copper foil (surface roughness Rz = 10 μm, thickness 35 μm) under the same conditions as above to prepare a sample of the negative electrode 2A. The weight of the copper foil was subtracted from the weight of the obtained sample, the weight of the active material layer was determined, the thickness was measured, and the density was determined. The obtained density was divided by the true density of the tin alloy having the composition obtained by ICP analysis, and the porosity P, which is the ratio of the voids to the total volume, was found to be 48%.

Hereinafter, the physical properties of the negative electrode 2A are summarized.
Composition of active material: SnCo _0.3
Angle θ1: 45 ° formed by the first columnar portion and the normal direction of the current collector surface
Angle θ2: 45 ° formed by the second columnar portion and the normal direction of the current collector surface
Active material layer thickness t: 6.5 μm
Distance between centers of adjacent columnar particles: 12 μm
Columnar particle diameter: 5.0 μm
Porosity P: 48%
A test battery 2A was produced in the same manner as in Example 1 except that the negative electrode thus obtained was used.

<< Comparative Example 2 >>
A negative electrode was produced in the following manner.
As the negative electrode current collector, an electrolytic copper foil having a thickness of 35 μm and a surface roughness Rz of 10 μm (manufactured by Furukawa Circuit Foil Co., Ltd.) was used. A laminated film of tin and cobalt was deposited on the negative electrode current collector using a manufacturing apparatus as shown in FIGS. 11A and 11B. The copper foil was fixed to the fixing base 54, the angle α formed by the fixing base and the horizontal plane was set to 0 °, and the copper foil was horizontally installed. As the deposition conditions, the acceleration voltage of the electron beam applied to each target was set to -8 kV, the target 105a emission was set to 250 mA, and the target 105b emission was set to 500 mA.

  The target 105b installed at the second position was shielded by the shutter 107b. In this state, tin was evaporated from the target 105a placed at the first position for 10 minutes, and an active material was vapor-deposited for 10 minutes (first vapor deposition step).

  Thereafter, in a state where the target 105a installed at the first position was shielded by the shutter 107a, cobalt was evaporated from the target 105b installed at the second position, and an active material was deposited for 5 minutes (second deposition process).

  The vapor of tin and cobalt could be deposited as a laminated film on the negative electrode current collector installed on the fixed base 54. Then, the obtained laminated film was heat-treated in a 200 ° C. vacuum oven for 24 hours. In this way, a negative electrode active material layer made of a tin-cobalt alloy was formed to obtain a negative electrode 2B. The negative electrode 2B was cut into a size of 31 mm × 31 mm. A lead terminal was connected to the back surface of the current collector having no negative electrode active material layer.

The negative electrode 2B was observed from various angles with an electron microscope (SEM).
As a result of observation, it has been found that the active material layer is composed of a dense alloy film including granular particles having no bent portion. Similarly, when the composition of the alloy was determined by ICP analysis, a composition of SnCo _0.32 was obtained. The thickness t of the obtained active material layer was 6.6 μm, and the diameter of the granular particles was 5.4 μm. Further, when the porosity P of the negative electrode 1B was determined by the same method as 1A, it was 16%.

The physical properties of the negative electrode 2B are summarized below.
Composition of active material: SnCo _0.32
The angle θ between the columnar particles and the normal direction of the current collector: 0 °
Active material layer thickness t: 6.6 μm
Particle size of particles on the grain: 5.4 μm
Porosity P: 16%
A test battery 2B was produced in the same manner as in Example 1 except that the negative electrode thus obtained was used.

  Battery 2A and battery 2B were evaluated under the same conditions as in the above evaluation method. Table 2 shows the results of charge / discharge efficiency and capacity retention rate.

  From Table 2, the capacity maintenance rate of the battery 2A is improved as compared with the battery 2B. This is presumably because the active material layer of the negative electrode 2A had sufficient voids, and the expansion stress due to charging could be relaxed. Furthermore, since the columnar particles have a bent portion, the stress at the contact portion between the negative electrode active material and the current collector is also relaxed.

  The present invention can be applied to various forms of lithium secondary batteries, but is particularly useful in lithium secondary batteries that require high capacity and good cycle characteristics. The shape of the lithium secondary battery to which the present invention is applicable is not particularly limited, and may be any shape such as a coin shape, a button shape, a sheet shape, a cylindrical shape, a flat shape, and a square shape. Further, the form of the electrode plate group including the positive electrode, the negative electrode, and the separator may be a wound type or a laminated type. The size of the battery may be small for a small portable device or large for an electric vehicle. The lithium secondary battery of the present invention can be used for a power source of, for example, a portable information terminal, a portable electronic device, a small electric power storage device for home use, a motorcycle, an electric vehicle, a hybrid electric vehicle, etc., but the application is not particularly limited.

It is sectional drawing of a part of conventional electrode for lithium secondary batteries. It is a side view of the electrode of FIG. It is a perspective view which shows notionally the electrode for lithium secondary batteries which concerns on one Embodiment of this invention. It is a cross-sectional enlarged view of a part of an electrode for a lithium secondary battery according to an embodiment of the present invention. It is a cross-sectional enlarged view of a part of an electrode for a lithium secondary battery according to another embodiment of the present invention. It is a partial cross-sectional enlarged view of the electrode for lithium secondary batteries which concerns on another embodiment of this invention. It is a part of SEM photograph of the negative electrode for lithium secondary batteries which concerns on one Embodiment of this invention containing the columnar particle | grains which have a bending part. It is a cross-sectional enlarged view of a part of an electrode for a lithium secondary battery according to still another embodiment of the present invention. It is the schematic which shows an example of the manufacturing apparatus of the electrode for lithium secondary batteries. It is the BB sectional view taken on the line of FIG. 9A. It is a longitudinal cross-sectional view of an example of a laminated lithium secondary battery. It is the schematic which shows another example of the manufacturing apparatus of the electrode for lithium secondary batteries. It is the schematic which shows another state of the manufacturing apparatus of FIG. 11A. It is the schematic which shows another example of the manufacturing apparatus of the electrode for lithium secondary batteries. It is the schematic which shows another state of the manufacturing apparatus of FIG. 12A. It is the schematic which shows another example of the manufacturing apparatus of the electrode for lithium secondary batteries. It is a SEM photograph of a part of negative electrode for lithium secondary batteries containing the columnar particle | grains which do not have a bending part.

Explanation of symbols

1, 12, 22, 202, 32, 42 Active material layer 2, 11, 21, 201, 31, 41, 51 Current collector 3, 13, 23, 33, 43 Columnar particle 10, 20, 200, 30, 40 Negative electrode 50, 90, 100, 110 Vapor deposition device 52 Nozzle 53 Piping 54 Fixing base 55, 95, 105a, 105b, 115 Target 56 Chamber 57 Substrate tilt axis 58 Rotating axis 59 Material supply source 60 Battery 61 Positive electrode 61a Positive electrode current collector 61b Positive electrode active material layer 62 Negative electrode 62a Negative electrode current collector 62b Negative electrode active material layer 98, 108, 118 First position of target 99, 109, 119 Second position of target 107a Shutter (first position)
107b Shutter (second position)

Claims (14)

A sheet-like current collector, and an active material layer carried on the current collector,
The active material layer includes a plurality of columnar particles having at least one bent portion,
The said columnar particle | grain is an electrode for lithium secondary batteries which contains a tin element and can occlude and discharge | release lithium. The angle θ ₁ formed by the growth direction of the columnar particles from the bottom of the columnar particles to the first bent portion and the normal direction of the current collector is 10 ° or more and less than 90 °. Electrode for lithium secondary battery. The angle formed by the growth direction of the columnar particles from the n-th bent portion to the (n + 1) -th bent portion counted from the bottom of the columnar particles and the normal direction of the current collector is θ _{n + 1} , 3. The electrode for a lithium secondary battery according to claim ₁ , wherein when n is an integer of 1 or more, the θ _{n + 1} is 0 ° or more and less than 90 °.   The electrode for a lithium secondary battery according to any one of claims 1 to 3, wherein the columnar particles have two or more bent portions.   The electrode for a lithium secondary battery according to claim 4, wherein the columnar particles have a zigzag shape.   The electrode for a lithium secondary battery according to claim 4, wherein the columnar particles have a spiral shape.   The electrode for a lithium secondary battery according to claim 1, wherein a porosity P of the active material layer is 10% ≦ P ≦ 70%.   The columnar particles further include an element M capable of forming a solid solution with tin, and the element M is at least selected from the group consisting of cobalt, nickel, zinc, copper, iron, manganese, chromium, titanium, vanadium, and indium. The electrode for a lithium secondary battery according to any one of claims 1 to 7, which is one type.   A lithium secondary battery comprising the electrode for a lithium secondary battery according to any one of claims 1 to 8, a counter electrode, and an electrolyte having lithium ion conductivity interposed therebetween. A first step of depositing the active material constituent element by causing the active material constituent element to enter the sheet-like current collector at a first incident angle of + 10 ° to + 70 °;
A second step of depositing the active material constituent element by causing the active material constituent element to enter the sheet-like current collector at a second incident angle of −10 ° to −70 °;
The manufacturing method of the electrode for lithium ion secondary batteries in which the said active material structural element contains a tin element. The first step includes causing the active material constituent element generated from the material supply source at the first position and the second position to enter the surface of the current collector;
11. The lithium secondary according to claim 10, wherein the second step includes causing the active material constituent element generated from the material supply source at the first position and the second position to enter the surface of the current collector. Manufacturing method of battery electrode.   The method for producing an electrode for a lithium secondary battery according to claim 11, wherein the first position and the second position are symmetrical with respect to a plane perpendicular to the surface of the current collector.   The active material constituent element includes a first element and a second element, the first element is evaporated at the first position, and the second element is evaporated at the second position. Manufacturing method of electrode for lithium secondary battery.   The method for producing an electrode for a lithium secondary battery according to claim 13, wherein the first element and the second element are evaporated sequentially or alternately.