JP5437536B2 - Current collector for electrode, negative electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a chargeable / dischargeable nonaqueous electrolyte secondary battery such as a lithium ion secondary battery, an electrode used in the secondary battery, and a current collector as a component of the electrode.

  The lithium ion secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. The negative electrode is formed by applying carbon particles as a negative electrode active material layer to the surface of a negative electrode current collector made of a copper foil having a smooth surface, and further pressing it. Lithium ion secondary batteries are currently used in mobile phones, notebook computers and the like. An aluminum foil is used for the positive electrode current collector of this lithium ion secondary battery, and a copper foil subjected to rust prevention treatment is mainly used for the negative electrode current collector.

  As the negative electrode current collector for a lithium ion secondary battery, an electrolytic copper foil in which the difference in surface roughness between the glossy surface and the rough surface (both surfaces of the copper foil) is reduced is used. Thereby, the fall of the charging / discharging efficiency of a battery is suppressed. (See Patent Document 1)

  The electrolytic copper foil having a small difference in surface roughness between the glossy surface and the rough surface as described above is produced by adding an organic or inorganic compound or an ionic species to an electrolytic solution for depositing copper. For example, a method for producing an electrolytic copper foil using an electrolytic solution to which an organic compound, chloride ion, low molecular weight glue and high molecular polysaccharide are added is disclosed (see Patent Document 2). The electrolytic copper foil manufactured by such a manufacturing method is coated with a slurry containing carbon-based active material particles and the like on the surface of the copper foil, and after drying, is further pressed into a negative electrode.

  Recently, lithium ion secondary batteries using germanium, silicon, tin, etc., which are electrochemically alloyed with lithium during charging, have been proposed for the purpose of increasing the capacity of lithium ion secondary batteries. (See Patent Document 3).

  An electrode (negative electrode) for a lithium ion secondary battery for the purpose of increasing the capacity is obtained by depositing, for example, silicon on an amorphous silicon thin film or microcrystalline silicon thin film on a current collector such as a copper foil by CVD or sputtering. As it is deposited and formed. Since the thin film layer of the active material prepared by such a method is in close contact with the current collector, it has been found that it exhibits good charge / discharge cycle characteristics (see Patent Document 4).

  Recently, a forming method has been developed in which powdered silicon together with an imide binder is slurried with an organic solvent, applied onto a copper foil, dried and pressed to form an electrode.

Japanese Patent No. 3742144 Japanese Patent No. 3313277 Japanese Patent Laid-Open No. 10-255768 Japanese Patent Laid-Open No. 2002-083594

  However, for example, in a silicon active material having a high theoretical specific capacity, the volume of the active material layer expands and contracts during charging and discharging. That is, when the lithium ions are occluded during charging, the volume expands by about 4 times at the maximum, and the lithium ions are released and contracted during discharging. Thereby, the phenomenon in which the active material is pulverized and peeled from the current collector is observed. Further, since the active material layer is in close contact with the current collector, there is a problem that a large stress is applied to the current collector when the volume of the active material layer expands and contracts due to repeated charge and discharge.

  When such an electrode with large expansion and contraction is accommodated in the battery and repeated charging and discharging a number of times, the current collector also expands and contracts, and thus the current collector is wrinkled. In order to allow wrinkles, it is necessary to make room for the volume occupied by the electrode in the battery, but this causes a problem that the energy density (or charge / discharge capacity) per volume decreases.

  In addition, if the energy density per volume (or charge / discharge capacity) is increased, there is no room for the expansion and contraction of the current collector, so that the current collector is broken and stable battery performance can be maintained. The problem of disappearing.

  Further, not only wrinkles due to stress on the current collector, but also peeling between the current collector and the active material layer causes a problem that the cycle characteristics of the battery deteriorate.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide lithium ion secondary batteries using a negative electrode in which an active material having a high specific capacity such as silicon or tin is deposited on a current collector. In secondary batteries, generation of wrinkles on the current collector, breakage of the current collector, or peeling between the current collector and the active material layer is suppressed, and the adhesion between the active material and the current collector is high, and the performance is stable for a long time. It is to provide a lithium ion secondary battery capable of maintaining the above.

In order to achieve the above-mentioned object, the following invention is provided.
(1) An electrode current collector for forming an active material-containing layer using a slurry containing an electrode active material and an aqueous binder, wherein the surface on which the active material-containing layer is formed has a roughness (Z axis ) A negative electrode for a non-aqueous electrolyte secondary battery, wherein a surface area ratio obtained by dividing an actual surface area by a unit plane area when the resolution in the direction is 0.05 μm is 1.13 to 3.95 Current collector for electrodes for use in
(2) The current collector for an electrode according to (1), wherein the surface area ratio is 1.11 to 2.36.
(3) The electrode current collector according to (1), wherein the surface area ratio is 1.11 to 1.98.
(4) The electrode current collector according to (1), wherein the surface area ratio is 1.11 to 1.46.
(5) The electrode current collector according to any one of (1) to (4), wherein the electrode current collector is a copper foil.
(6) The electrode current collector according to (5) , wherein the electrode current collector is a roughened copper foil.
(7) The surface of the current collector for electrodes has any one or more of a chromate treatment layer, a benzotriazole treatment layer, a silane coupling treatment layer, a nickel treatment layer, a zinc treatment layer, and a tin treatment layer. The current collector for an electrode according to any one of (1) to (6) .
(8) The electrode current collector has a tensile strength of 450 MPa or more, a breaking elongation of 3% or more, a breaking elongation of 3% or more after heating at 180 ° C. for 5 minutes, and after heating at 300 ° C. for 1 hour. The electrode current collector according to any one of (1) to (7) , which has a tensile strength of 300 MPa or more.
(9) An active material-containing layer is formed on a current collector for an electrode according to claim 1 using a slurry containing an electrode active material and an aqueous binder, for a non-aqueous electrolyte secondary battery Negative electrode .
(10) The negative electrode for a nonaqueous electrolyte secondary battery according to (9) , wherein the electrode active material contains silicon or tin .
(11) A nonaqueous electrolyte secondary battery using the negative electrode according to (9) or (10) .

  According to the present invention, in a lithium ion secondary battery using a negative electrode in which an active material having a high specific capacity such as silicon or tin is deposited on a current collector, wrinkles of the current collector, breakage of the current collector, or It is possible to provide a lithium ion secondary battery in which separation between the current collector and the active material layer is suppressed, the adhesion between the active material and the current collector is high, and stable performance can be maintained for a long time. In general, an electrode using a water-based binder is inferior in adhesion between a copper foil and an electrode coating film and has a shorter charge / discharge cycle life than an organic solvent-based binder. According to the present invention, swelling and peeling of the interface with the aqueous binder-using electrode can be prevented, and the cycle life is improved. For an electrode using an organic solvent binder, the adhesion is improved and the cycle life is extended by specifying a large interface real surface area.

(A) Electrode 3 according to the first or second embodiment, (b) Cross-sectional view showing the electrode 6 according to the first or second embodiment, (c) Electrode according to the first or second embodiment FIG. FIG. 3 is a cross-sectional view showing a nonaqueous electrolyte secondary battery 11. The plot which shows the capacity | capacitance maintenance factor in the Example of (a) the electrode using an aqueous binder, and (b) the electrode using an organic-solvent binder.

[First Embodiment]
(Configuration of current collector according to the first embodiment)
The current collectors for electrodes according to the first embodiment are current collectors 1, 4, and 7 shown in FIGS. 1 (a), 1 (b), and 1 (c). The current collectors 1, 4, and 7 form the active material-containing layers 2, 5, and 8 by applying a slurry containing an electrode active material or a conductive additive and an aqueous binder. When the surface of the current collectors 1, 4, 7 on which the active material containing layers 2, 5, 8 are formed is measured with a resolution in the roughness (Z-axis) direction of 0.05 μm, the actual surface area is the unit plane area The surface area ratio divided by is 1.1 to 4.0.

The actual surface area is a surface area including the surface area of minute irregularities on the surface. The actual surface area of the surface of the electrode current collector is measured by measuring the surface of the minute compartment and image analysis using an ultra-deep shape measurement laser microscope. For example, a laser microscope using a pinhole confocal optical scanning method is based on the following measurement analysis. Laser scanning measurement is performed on the position of a point having a number determined by the resolution of the apparatus in an XY plane having a specific vertical and horizontal screen width at a specified magnification at a certain height position in the Z-axis direction. This is moved in the Z-axis direction for each designated resolution, and XY in-plane measurement is repeatedly performed. After each plane data is captured, the three-dimensional representation is calculated. In the current apparatus, the observation magnification is several hundred times to 20,000 times, the planar laser scanning accuracy is from 1024 × 768 pixels to 2048 × 1536 pixels, and the Z-axis direction linear scale resolution is 10 nm (0.01 μm) to 0.5 nm. (0.0005 μm) is possible and these values depend on the device.
The unit plane area is a geometric area in the measured range ignoring surface irregularities. The surface area ratio is a value obtained by dividing the actual surface area by the unit plane area. The higher the surface smoothness is, the more the surface area ratio is closer to the minimum value of 1 as there are no surface irregularities. Higher surface area ratio means more uneven surface.

  In general, the higher the surface area ratio, the greater the area that is actually in close contact, so the adhesion is improved. On the other hand, in a surface shape with a high surface area ratio, problems such as uneven shapes, changes in actual thickness due to uneven shapes, changes in slurry application amount, electrode thickness, and the like are also derived. For example, in the convex portion, current concentration occurs at the time of charging / discharging, and the current density increases, so that a side reaction occurs at the interface. This may cause an obstacle such as a decomposition reaction of the electrolyte component. A particularly severe example is the combined effect of water and surface convexity. In a non-aqueous electrolyte secondary battery, the treatment is performed so as not to include the aqueous solvent in the electrolytic solution in principle, but water, hydrogen fluoride ions, and the like are often contained on the order of ppm. As charging / discharging is repeated, there is a high possibility that it gradually increases due to side reactions and the like. Also, water may remain in the aqueous binder electrode coating film depending on the drying conditions. When the surface convex shape is strong, these trace amounts of moisture and the like cause reductive decomposition due to high current density at the negative electrode surface or the copper foil interface. The hydrogen gas generated at this time causes swelling of the electrode coating film and peeling from the current collector. In order to prevent such a phenomenon, it is necessary to suppress a surface area ratio obtained by dividing an actual surface area by a unit plane area to 4.0 or less for a current collector used for electrode preparation with an aqueous binder. Thereby, since reductive decomposition of water is suppressed significantly, the adhesiveness fall of an electrode coating film and the fall of charging / discharging characteristic are suppressed. For the above reasons, the smaller the surface area ratio of the current collector of the electrode using the aqueous binder, the better, but the lower limit is about 1.1.

  For the same reason as described above, it is suitable that the surface roughness of the current collector in the electrode using the aqueous binder is also small. The ten-point average roughness Rz is desirably 2.0 μm or less. The lower limit is about Rz 1.0 μm. That is, the surface roughness Rz of the current collectors 1, 4, and 7 shown in FIGS. 1A, 1 </ b> B, and 1 </ b> C, which is the electrode current collector according to the first embodiment, is 1.0 to 1.0. It has a feature of 2.0 μm.

  In the present invention, the current collector is preferably thin, and therefore, it is preferably a metal foil such as a copper foil or an aluminum foil, particularly an electrolytic copper foil or a rolled copper foil in the case of a copper foil. The thickness of the current collector is preferably about 8 μm for the thin and about 20 μm for the thick depending on the battery application. This is because if the thickness is 8 μm or less, the strength of the foil cannot be maintained, and breakage occurs when the active material expands or contracts. On the other hand, when the thickness exceeds 20 μm, the battery characteristics can be satisfied, but the battery itself is large and heavy.

The active material-containing layer can be formed by being deposited on one side or both sides of the current collector. If it is not restricted to the said water-system binder, it is preferable that the surface roughness Rz of the surface of the collector which forms an active material content layer generally is 1.0-5 micrometers. When the active material-containing layer is formed on both surfaces of the current collector, the surface roughness Rz on both sides of the current collector is 1.0 to 5 μm, and the difference between the front and back surfaces is 3 μm or less. preferable.
Generally, when the value of Rz is lower than the lower limit, adhesion due to the anchor effect with the active material is poor. On the other hand, when the value of Rz exceeds the upper limit value, the active material does not uniformly enter the depth of the roughened surface, and the adhesion between the copper foil and the active material is deteriorated. On the other hand, when a side reaction occurs due to an electrode reaction, a large rough surface may promote the reaction. An appropriate region is recognized in the case of the water-based binder described above or depending on the binder used as described later. In addition, in the case of a cylindrical or square battery that is wound many times, using a current collector with too large irregularities or surface roughness limits the number of multiple windings, and that alone limits the capacity of the entire battery. It leads to that. In addition, if the difference between the front and back of the surface roughness is large, the thickness of the active material is different on both sides in the active material coating process, and the characteristics of the completed electrode are deteriorated.

  Further, when the current collector is a copper foil, a surface roughening treatment may be performed, and the surface roughening treatment has a particle diameter of 0.1 to 3 μm and copper or copper containing Cu as a main component. It is preferable that the fine particles of the alloy be applied to the surface. A roughening treatment layer in which the roughened particles are fixed to the surface of the copper foil by copper plating is formed using the alloy fine particles made of copper or a copper alloy containing Cu as a main component as the roughened particles. This is because the adhesion between the roughened particles and the untreated copper foil is improved, and the roughness can be easily adjusted by controlling the crystal grain size of the roughened particles. Thereby, the applicability | paintability and adhesiveness of an active material (or slurry) improve more. In addition, the main component means containing 50% by mass or more.

  Further, when the current collector is an aluminum foil, it is preferable to increase the actual surface area by performing fine surface roughening by an immersion treatment in an etching solution or an etching treatment such as alternating current electrolytic etching.

  It is preferable that any one or more of a chromate treatment layer, a benzotriazole treatment layer, a silane coupling treatment layer, a nickel treatment layer, a zinc treatment layer, and a tin treatment layer is provided on the surface of the current collector for electrodes. The chromate treatment layer is a passive layer obtained on the surface by immersing the current collector in an aqueous solution such as chromate or dichromate or by performing electrolytic treatment. The benzotriazole-treated layer is a layer generated on the current collector surface by immersing the current collector in a benzotriazole aqueous solution. The silane coupling treatment layer is a layer obtained by immersing the surface of the current collector with a silane coupling agent solution. The nickel treatment layer is a nickel layer obtained by performing nickel plating or the like on the current collector surface. The zinc treatment layer is a zinc layer obtained by galvanizing the surface of the current collector. The tin treatment layer is a tin layer obtained by performing tin plating or the like on the current collector surface. Any of the plating treatments can be performed according to a conventional method, and a thin layer of 1 μm or less that does not inhibit high conductivity is desirable.

(Mechanical characteristics of current collector)
Generally, when the mechanical properties such as the tensile strength and elongation at break of the current collector are lowered, the current collector is broken. The battery expands and contracts regardless of the roughening treatment, such as when mainly using high specific capacity negative electrode active materials such as germanium, silicon, and tin, or when mixed with carbon-based active materials. The electric body cannot absorb and breaks. In order to prevent breakage, it is preferable that the current collector has a tensile strength of 450 MPa or more and a break elongation of about 3% or more.

  Moreover, the negative electrode collector for lithium ion batteries has a drying process in the manufacturing process. If this drying is insufficient, the characteristics of the battery deteriorate. However, when the copper foil as the current collector is softened by heat in the drying process, distortion due to partial elongation occurs, the electrode manufacturing process does not meet the electrode design specifications, and in extreme cases, the foil breaks. Therefore, it is preferable that the elongation at break after heating at 180 ° C. for 5 minutes is also 3% or more. Furthermore, at the time of charging / discharging as described above, the battery can be obtained by using an organic solvent-based binder that has high heat resistance that brings a large volume change and stress strain due to expansion and contraction to the current collector foil and excellent mechanical strength such as elastic modulus. The characteristics may also be improved. In this case, in order to maintain the tensile strength of the current collector after drying and baking, a heat-resistant copper foil is used for the current collector foil, and a foil having a tensile strength of 300 MPa or more after heating at 300 ° C. for 1 hour is preferable.

  In the present invention, the tensile strength and the elongation rate are values measured by a method defined in Japanese Industrial Standard (JIS K 6251). Further, the surface roughness Rz is a ten-point average roughness defined in Japanese Industrial Standard (JIS B 0601-1994), for example, a value measured by a surface roughness meter.

  The electrode which formed the active material containing layers 2, 5, and 8 by apply | coating the slurry containing an electrode active material or a conductive support agent, and a water-system binder to the electrode collectors 1, 4, and 7 which concern on 1st Embodiment. 3, 6, and 9 are excellent in cycle characteristics and have a long life.

(Configuration of current collector according to the second embodiment)
The electrode current collectors according to the second embodiment are current collectors 1, 4, and 7 shown in FIGS. 1 (a), (b), and (c). A current collector used for an electrode 10 for forming an active material-containing layer 2, 5, 8 by applying a slurry containing an electrode active material or a conductive additive and an organic solvent-based binder, the active material-containing layer 2, 5, and 8, the surface area ratio obtained by dividing the actual surface area by the unit plane area is 1.0 to 7.0. In other words, a 50μm square planar micro surface of the current collector was measured with an ultra deep shape measuring microscope, or the roughening treatment after the current collector, it is preferable that each of the surface area is 2500~17500μm ² / 2500μm ^2.

  The second embodiment is the same as the first embodiment except that the surface area ratio obtained by dividing the actual surface area by the unit plane area is different and that the binder contained in the slurry used is an organic solvent-based binder. It has the composition of. Since the binder is organic solvent-based, there is less moisture film remaining than water-based binders, and there is less gas generation due to reductive decomposition like water-based binders, so there is a need to suppress the surface area ratio compared to water-based binders. Low. Therefore, the current collector surface can be set to an optimum surface area ratio excellent in electrode coating film adhesion and battery electrode characteristics.

  Active material containing layers 2, 5, 8 are formed by applying a slurry containing an electrode active material or a conductive additive and an organic solvent binder to the electrode current collectors 1, 4, 7 according to the second embodiment. The electrodes 3, 6, and 9 have excellent cycle characteristics and a long life.

(Method for producing current collector for electrode according to the present invention)
When the current collector for an electrode according to the present invention is made of a copper foil, it is produced by producing an untreated foil and then performing a functional surface treatment such as a roughening treatment or rust prevention. A current collector 1 shown in FIG. 1 (a) is a current collector in which the surface of an untreated copper foil is subjected to rust prevention treatment and smooth plating treatment. FIG.1 (b) is the electrical power collector which performed the roughening process by the etching by a chemical agent or alternating current etching on the surface of untreated copper foil. A current collector 7 shown in FIG. 1 (c) is a current collector that has been subjected to a roughening treatment for forming a bump-shaped copper layer containing copper alloy fine particles 10 on the surface.

(Production method of untreated copper foil)
Below, an example of the preparation methods of the untreated copper foil used for the collector for lithium ion secondary battery electrodes of this invention is demonstrated. An aqueous solution of sulfuric acid and copper as an electrolyte is provided between an insoluble anode (DSA) made of titanium coated with a white metal element or an oxide thereof and a titanium cathode drum provided to face the anode. Supply. Copper is deposited on the surface of the cathode drum by applying a direct current between the two electrodes while rotating the cathode drum at a constant speed. The deposited copper is peeled off from the surface of the cathode drum and continuously wound up to produce an electrolytic copper foil.

  The untreated copper foil used for the copper foil for a lithium ion secondary battery electrode of the present invention includes, for example, a compound having a mercapto group, a chloride ion, a low molecular weight glue having a molecular weight of 10,000 or less, and a high molecular weight in a sulfuric acid-copper electrolyte. It can be produced by adding saccharides. For example, MPS (3-mercapto 1-propanesulfonic acid sodium), HEC (hydroxyethyl cellulose), glue can be mentioned.

In the electrolytic copper foil, the surface in contact with the titanium cathode drum is generally a glossy surface (hereinafter referred to as S surface), and the surface in contact with the electrolytic solution is generally defined as a mat surface (hereinafter referred to as M surface). The electrolytic copper foil before the roughening treatment in the present invention is preferably a double-sided smooth or glossy foil, and the surface Rz of both surfaces is preferably as low as 2.5 μm or less, and a foil having a small difference in front and back is suitable. However, the electrolytic copper foil manufactured by the conventional printed circuit application technology has ridges and valleys on the M surface, and the surface roughness of the foil thickness of 18 μm or less is about 2.2 to 5.0 μm. Even if, for example, a roughening treatment is performed on the copper foil having a rough surface as described above, a sufficient effect cannot be obtained. That is, when a foil having a large surface roughness when not treated is used, the uneven shape is further increased, resulting in a non-uniform rough surface shape having a large surface roughness. Of the current collector after the surface roughening treatment, because the surface area 25000μm ² / 2500μm ² becomes larger than the surface area ratio not sufficiently pulled the effect of exceeding the present invention 10. A current collector surface shape that is uniformly finely roughened is desirable.

(Roughening treatment of untreated copper foil)
In order to obtain a current collector surface having a surface roughness Rz of about 1.0 to 2.0 μm or about 5 μm, the surface of some untreated electrolytic copper foils is roughened. As this roughening treatment, an electrolytic plating method can be suitably employed. The electrolytic plating method is a method of roughening the surface by forming a thin film layer having irregularities on the surface of the untreated electrolytic copper foil. Even if the untreated foil conforms to the above surface roughness, a part of which has been subjected to a functional surface treatment in addition to a rust prevention treatment such as a chromate treatment or a silane coupling treatment can be used. Moreover, in order to reduce surface roughness, unevenness, and surface area ratio, it is possible to perform smooth plating treatment.

  As the roughening treatment, for example, a roughening treatment layer which is a plating film mainly composed of copper such as copper or copper alloy is formed on the surface of the untreated electrolytic copper foil by an electrodeposition method. As the electrolytic plating method, the following method is preferable. First, an untreated electrolytic copper foil is immersed in a copper plating electrolytic solution having a particle diameter of 0.1 to 3 μm and added with copper or copper alloy fine particles containing Cu as a main component. Fine particles are imparted to the surface of the untreated electrolytic copper foil to form a coarse powdery copper plating layer. Next, capsule plating is performed on the grainy copper plating layer so as not to impair the uneven shape. Thereby, a substantially smooth plating layer is deposited, and the granular copper is used as a so-called bumpy copper layer. The surface on which the bumpy copper layer is formed becomes a rough surface.

  For example, you may use the roughening method by the plating currently disclosed by patent document (Japanese Patent Publication No.53-39376) used for the copper foil for printed circuits. That is, after a granular copper plating layer is formed by so-called “bake plating”, capsule plating is performed on the granular copper plating layer so as not to impair the uneven shape. As a result, a substantially smooth plating layer is deposited to make the powdered copper into a so-called bumpy copper layer. The surface on which the bumpy copper layer is formed becomes a rough surface.

  Further, etching with a chemical such as formic acid or hydrochloric acid or roughening treatment by alternating current etching may be used, and it is also applicable to aluminum foil and each alloy foil.

(Electrode using current collector for electrode according to the present invention)
As shown in FIGS. 1A, 1B, and 1C, the non-aqueous electrolyte secondary battery electrodes 3, 6, and 7 according to the first and second embodiments are arranged in the first and second embodiments. The active material containing layers 2, 5, 8 are formed by applying a slurry containing an electrode active material or a conductive additive and an aqueous binder to the electrode current collectors 1, 4, 7 according to the embodiment. And

  The active material in the present invention is a material that occludes and releases lithium, and includes an active material that occludes lithium by alloying. Examples of such an active material include carbon, silicon, germanium, tin, lead, zinc, magnesium, sodium, aluminum, potassium, indium, and antimony. Among these, silicon and tin are preferably used because of their high theoretical capacity. Therefore, the active material-containing layer used in the present invention is preferably a layer containing silicon or tin as a main component, and particularly preferably a layer containing silicon as a main component.

  Further, the active material in the present invention can be used regardless of crystal, amorphous or microcrystal. Further, it is possible to use a form in which a part of the active material is an alloy, a form in which an alloy is attached to a single substance, or a form in which both the simple substance and the alloy are mixed with a slurry and then mixed and mixed. For example, a single element of the above active material, cobalt, nickel, calcium, scandium, copper, silver, gold, iron, titanium, vanadium, chromium, manganese, strontium, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, barium , A mixture of a metal selected from hafnium, tantalum, tungsten, and iridium and an alloy of the active material, or a bonding form of a simple substance and the alloy. In particular, when silicon is used as an active material, manganese, chromium, strontium, cobalt, zirconium, niobium, molybdenum, titanium, vanadium, nickel, calcium, iron, gold, silver, copper, scandium, tungsten, iridium, hafnium, An alloy form with a metal selected from barium, rhodium, ruthenium and yttrium is desirable. These include a first phase of a single active material and a solid solution, and a second phase that is a compound of an active material element and other elements, in which both phases are joined.

  The form containing the active material element includes primary particles and secondary particles obtained by enlarging the primary particles by granulation, and those having a particle size of about 0.01 to 10 μm are used. Furthermore, a form in which the surface of these active materials is coated with a conductive material, or subjected to hydrophilicity, hydrophobicity treatment, non-aggregation dispersion treatment, or the like may be used. Preferable examples include an amorphous carbon coat that prevents a decrease in conductivity due to surface oxidation of silicon. From the electrochemical theoretical specific capacity, silicon or a silicon-silicon alloy or the above-described carbon-coated form is preferably used. For the purpose of extending the life of the charge / discharge cycle, a silicon-based active material form partially incorporating oxygen is also used. This is because the silicon oxide form having oxygen relaxes the volume expansion due to electrochemical alloying of lithium ions, so that the active material silicon can be prevented from being broken and pulverized. From the same reason and the further stability of charge / discharge characteristics, it is excellent as an electrode battery containing an active material in which a carbon-based active material is mixed with silicon or tin.

  The active material-containing layer in the present invention is formed by applying an active material or a conductive auxiliary agent into a slurry together with a binder and a solvent, and applying, drying and pressing the surface of the current collector (copper foil).

  As the binder, an aqueous binder or an organic solvent binder can be used. Further, when using an aqueous binder, an aqueous solvent can be used as a solvent, and when using an organic solvent binder, an organic solvent can be used as a solvent.

  As the water-based binder, a water-based binder in which a polymer represented by styrene-butadiene copolymer (SBR), latex, and polyacrylate is dispersed in water can be used.

  As the organic solvent binder, polyvinylidene fluoride, epoxy resin, polyamideimide, polybenzimidazole, and polyimide can be used. It is preferable that the coating film obtained by drying or baking and curing these organic solvent binders has a tensile strength of 150 MPa or more, a tensile elastic modulus of 2 GPa or more, and an elongation of 20% or more. In non-aqueous electrolyte secondary batteries using a metal-based active material having a high electrochemical specific capacity such as silicon, the volume expands greatly due to electrochemical alloying (charging) of lithium and the volume is increased by dealloying (discharging). Shrink. Therefore, a large stress acts on the current collector / electrode coating interface or around the active material between the coatings, and there is a possibility that interface peeling, cohesive failure, or coating failure occurs. This is because, in order to prevent or inhibit this, it is preferable that the binder or polymer forming the coating film matrix has a characteristic that is difficult to be plastically deformed by stress.

  In the active material-containing layer in the present invention, lithium may be occluded or added in advance. Lithium may be added when forming the active material-containing layer. That is, an active material-containing layer containing lithium is formed on the current collector surface in advance. Moreover, after forming an active material content layer, you may occlude or add lithium to an active material content layer. Examples of the method for inserting or adding lithium into the active material-containing layer include a method for electrochemically inserting or adding lithium.

(Configuration of lithium ion secondary battery)
A lithium ion secondary battery of the present invention comprises a negative electrode comprising the lithium ion secondary battery electrode of the present invention, a positive electrode using a material that absorbs and releases lithium as an active material, and a nonaqueous electrolyte. . For example, as shown in FIG. 2, the non-aqueous electrolyte secondary battery 11 which is a lithium ion secondary battery of the present invention includes a positive electrode 13 and a negative electrode 12, which are separator-negative electrode-separator-positive electrode through a separator 15. Laminated in order. At this time, the positive electrode 13 is wound so as to be on the inner side to constitute an electrode plate group, which is inserted into the battery can 19. The positive electrode 13 is connected to the positive electrode terminal 25 via the positive electrode lead 21, and the negative electrode 12 is connected to the battery can 19 via the negative electrode lead 23. Therefore, the chemical energy generated inside the nonaqueous electrolyte secondary battery 11 can be taken out as electric energy. Next, the battery 17 is filled with the electrolyte 17 so as to cover the electrode plate group. Then, it can manufacture by attaching the sealing body 27 to the upper end (opening part) of the battery can 19 via a cyclic | annular insulating gasket. At this time, the sealing body 27 is composed of a circular lid plate and the positive electrode terminal 25 on the upper portion thereof, and has a structure in which a safety valve mechanism is built therein.

  The non-aqueous electrolyte used in the lithium ion secondary battery of the present invention is an electrolyte in which a solute is dissolved in a solvent. The solvent for the nonaqueous electrolyte is not particularly limited as long as it is a solvent used in a lithium ion secondary battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate, dimethyl carbonate, and diethyl carbonate. And chain carbonates such as methyl ethyl carbonate. Preferably, a mixed solvent of a cyclic carbonate and a chain carbonate is used. Alternatively, a mixed solvent of the above cyclic carbonate and an ether solvent such as 1,2-dimethoxyethane or 1,2-diethoxyethane, or a chain ester such as γ-butyrolactone, sulfolane, or methyl acetate may be used. Good.

The solute of the nonaqueous electrolyte is not particularly limited as long as it is a solute used for a lithium ion secondary battery. For example, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , Examples thereof include LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , and Li ₂ B ₁₂ Cl ₁₂ . In particular, LiXFy (wherein X is P, As, Sb, B, Bi, Al, Ga, or In, y is 6 when X is P, As, or Sb, and X is B, Bi, Al) , Ga or the y when in is 4.), lithium perfluoroalkyl sulfonic acid imide _{LiN (C m F 2m + 1} SO 2) (C n F 2n + 1 SO 2) ( wherein,, m and n Are each independently an integer of 1 to 4.) or lithium perfluoroalkylsulfonic acid methide LiC (C _p F _{2p + 1} SO ₂ ) (C _q F _{2q + 1} SO ₂ ) (C _r F _{2r + 1} SO ₂ ) (wherein p, q and r are each independently an integer of 1 to 4), and mixed solutes are preferably used. Among these, a mixed solute of LiPF ₆ and LiN (C ₂ F ₅ SO ₂ ) ₂ is particularly preferably used.

As the non-aqueous electrolyte, a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride with an electrolytic solution, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used.

  The electrolyte of the lithium ion secondary battery of the present invention is limited as long as the Li compound as a solute that develops ionic conductivity and the solvent that dissolves and retains it are not decomposed by the voltage at the time of charging, discharging or storing the battery. Can be used without any problem.

Further, as the positive electrode active material used for the positive electrode, lithium-containing transition metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiCo _0.5 Ni _0.5 O ₂ , LiNi _0.7 Co _0.2 Mn _0.1 O ₂ , Examples include metal oxides such as MnO ₂ that do not contain lithium. In addition, any substance that can electrochemically alloy lithium can be used without limitation.

  According to the present invention, since it is possible to provide an optimum specification of the current collector according to the electrode binder, the interfacial adhesion and the like are not impaired even after repeated charge and discharge, and an electrode that can achieve a high cycle life. A secondary battery can be provided.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications within a range not changing the gist thereof. Is.

[Examples and Comparative Examples]
[Manufacture of untreated copper foil]
Under the electrolysis conditions shown in Table 1, three types of untreated copper foils (A, B, C) having a thickness of 10 μm were formed using a noble metal oxide-coated titanium electrode for the anode and a titanium rotating drum for the cathode. . The electrolysis conditions can be changed as appropriate, and are not limited to these concentrations and electrolysis conditions. Table 2 shows the performance of the copper foil produced.

  The thickness is a value measured with a micrometer, and the tensile strength and elongation at break are values measured using a tensile tester (Model 1122 manufactured by Instron). The surface roughness Rz was measured with a stylus type surface roughness meter (SE-3C type, manufactured by Kosaka Laboratory).

[Roughening treatment of untreated copper foil]
The both surfaces of the copper foils made under the above conditions are subjected to copper burn plating by electrolytic plating under the following conditions to form a uniform fine-grained copper plating layer. Furthermore, smooth copper plating (capsule plating) is performed on the granular powder copper plating layer so as not to impair the uneven shape. Through these steps, the adhesion between the granular copper and the electrolytic copper foil was improved. Then, it immersed in the chromium trioxide aqueous solution, and various roughened electrolytic copper foils shown in Tables 3 and 4 were created. A part of the untreated foil A was subjected only to rust prevention treatment or smooth plating, and a foil having a smaller surface roughness and area ratio than the untreated foil was produced.

Granular plating conditions:
Copper sulfate 80g / L
Sulfuric acid 110-160g / L
Additive * Appropriate amount Liquid temperature 30-60 ° C
Current density 10-50A / dm ²
Treatment time 2 to 20 seconds * Additive: Fine particles of copper alloy having a particle size of 0.1 to 3 μm.

Dense copper plating (capsule plating) conditions:
Copper sulfate 200g / L
Sulfuric acid 90 ~ 130g / L
Liquid temperature 30-60 ° C
Current density 10-30A / dm ²
Processing time 2 to 20 seconds

The surface roughness Rz, actual surface area, and surface area ratio of the copper foil after the roughening treatment were measured. The surface roughness Rz was measured by the method described above. Moreover, the actual surface area was measured using the ultra deep shape measuring laser microscope VK-8500 made by KEYENCE. The surface area ratio was obtained by dividing the actual surface area by the unit plane area. The measurement was performed at an observation magnification of 2,000 and a 50 μm square micro-plane (area 2500 μm ² ) was measured. The planar laser scanning was performed at 1024 × 768 pixels (800,000 points) and the resolution in the roughness (Z-axis) direction was 0.05 μm. Each in-plane data was three-dimensionally aggregated for each Z-axis position, and the actual surface area was calculated by image analysis processing. However, the actual surface area and the surface area ratio in the example table are described with respect to a value (100 μm square, 10000 μm ² ) multiplied by 4 for easy understanding.

[Creation of working electrode (negative electrode)]
Working electrodes were prepared using the prepared roughened electrolytic copper foil as a current collector, and the electrode characteristics were evaluated. In the case of using an aqueous binder, the silicon electrode is applied on a current collector by applying a silicon powder and acetylene black, an aqueous sodium carboxymethylcellulose solution and an aqueous dispersion SBR, which are kneaded and adjusted in a conventional manner, and dried. It was produced by pressing. In the case of using an organic solvent binder, the silicon electrode is formed on a current collector on a silicon powder and acetylene black, a polyimide precursor (polyamic acid as an organic solvent binder), NMP (N-methyl-2-pyrrolidone, It was prepared by applying a kneaded and adjusted slurry as an organic solvent, drying and pressing. Three types of polyimides (1), (2), and (3) are used as the polyimide, and the tensile strength as a coating film is (1) 400 MPa, (2) 170 MPa, (3) 125 MPa, and the coating film elastic modulus is Three types were used: (1) 8 GPa, (2) 3 GPa, (3) 1 GPa, and coating elongation percentages of (1) 50%, (2) 22%, and (3) 11%. Polyimide (1) was used except that polyimide (2) was used in Example 32 and (3) was used in Example 33.

[Create beaker cell]
Using the above working electrode (negative electrode), a three-electrode cell comprising a counter electrode, a test electrode, and a reference electrode was produced in a glove box under an argon gas atmosphere. The cell was configured by hermetically assembling in a SUS container and injecting an electrolyte between the test electrode and the reference electrode. As the electrolytic solution, an electrolytic solution in which at least 1 mol / liter of LiPF ₆ was dissolved in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 was used. Lithium metal was used as the counter electrode and the reference electrode.

[Evaluation of charge / discharge cycle characteristics]
The cell prepared as described above is charged at a constant current corresponding to a 0.1 C rate (1 hour rate) at 25 ° C. until the potential of the working electrode reaches 0.02 V (vs. Li / Li ⁺ ). did. Thereafter, when the current was reduced to 0.05 C, the cut-off was performed. After standing for 10 minutes, discharging was performed at a constant current corresponding to a 0.1 C rate until the potential of the working electrode reached 1.5 V (vs. Li ^/ Li ⁺ ). Similarly, four cycles from the second to the fifth cycle were tested with a current corresponding to a 0.2 C rate. Next, 50 cycles of charge and discharge were performed at a current corresponding to a 0.5 C rate from the sixth time. The discharge capacity retention after 50 cycles was evaluated. The evaluation results are shown in Tables 3 and 4. Tables 3 and 4 also show the presence or absence of wrinkles on the electrode copper foil after 50 cycles of charge and discharge.

  As shown in Table 3 and FIG. 3A, in the electrode using the water-based binder, the capacity retention ratio is decreased as the surface area ratio is increased. Such a relationship was first detected by the high-resolution area measurement method as in the present case. The current collector of Example 8 had a surface area ratio of 2.36 and was smaller than 4.0. Therefore, the capacity retention rate of the cycle test was as good as 44%. In the electrode using the current collector with a surface area ratio of 3.95 in Example 13, the capacity retention rate decreased to 33%. On the other hand, Comparative Example 1 having a surface area ratio of 4.21 had a capacity retention rate of 29%. That is, since the surface area ratio of 4.0 or more was not satisfied, the capacity retention ratio was 30%, which was greatly reduced. In Examples 1 to 13 using an aqueous binder, the 10-point average surface roughness Rz was adjusted to be within a certain range (1.0 to 2.0 μm) on the surface on which the active material-containing layer was formed. .

  This is because, in an electrode using a water-based binder, an electrode side reaction between the electrode and the electrolytic solution occurs, so that it is considered that a lower surface area ratio has a longer life so that expansion and contraction of the active material can be suppressed. . On the other hand, if the surface area ratio is too large, the expansion / contraction is too large, and it is considered that the active material-containing layer is peeled off or pulverized.

  As shown in Table 4 and FIG. 3, in the electrode using the organic solvent binder of the polyimide binder, the current collectors of Examples 14 to 33 have a surface area ratio of 1.0 to 7.0. Therefore, the capacity retention rate of the cycle test was 60% or more, which was better than that of the aqueous binder. Furthermore, the capacity retention ratio in the case of the electrode using the surface area ratio of the current collectors of Examples 19 to 29 in the range of 1.4 to 6.5 is 70% or more. According to the current collector electrode having a surface area ratio of 2.0 to 4.0 in Examples 21 to 26, a maintenance ratio of 75% or more is obtained, and each is good.

  Moreover, Examples 31-33 differ in the kind of polyimide used for a binder. The polyimide used in Example 31 has the highest coating film strength (and elastic modulus or elongation). The polyimide used in Example 32 has the next highest strength (supra). On the other hand, since the polyimide used in Example 33 has the properties of the coating film, the tensile strength is less than 150 MPa, the tensile elastic modulus is less than 2 GPa, and the elongation at break is less than 20%. Compared to the capacity maintenance rate. It has been found that the polyimide used for the binder is more effective for large volume changes accompanying high capacity charge / discharge of silicon or the like and has a higher capacity retention ratio as the strength and elastic modulus are higher.

  The following can be considered as the reason why an organic solvent binder such as a polyimide binder has a high capacity retention rate. In an electrode using an organic solvent-based binder, the coating film does not easily contain moisture, so electrode side reactions between the electrode and the electrolyte solution are unlikely to occur, and gas generation is unlikely to occur. Even when the surface area ratio is large, a high capacity retention rate can be maintained. On the other hand, when the surface area ratio is too small, the adhesion between the current collector and the active material-containing layer that is a coating film is deteriorated, and the active material-containing layer is peeled off during repeated charging and discharging. Furthermore, since the adhesiveness is poor, it is difficult to secure a conductive path. Further, if the surface area ratio is too large, the expansion / contraction is too large, and it is considered that the active material-containing layer is peeled off or pulverized.

  On the other hand, among the mechanical properties of the current collector copper foil, the capacity retention rate of Comparative Example 5 using untreated copper foil C (Table 2) having the smallest tensile strength after heating at 300 ° C. is less than 30%. Deteriorated. Since Example 29 using untreated foil A and Example 31 using untreated foil B have substantially the same Rz and the same polyimide used, they are suitable for comparison due to differences in untreated copper foil. The result of the capacity retention rate in the charge / discharge test is 71% of the untreated foil A (Example 29) as compared to 90% of the untreated foil B (Example 31). When using an organic solvent-based binder, the difference in the capacity retention ratio between Example 31 and Example 29 is not due to the effect of the surface area ratio on the capacity retention ratio. The difference is greatly affected. First, C foil which is inferior in heat resistance was softened by high-temperature heat baking treatment (imidization) from the polyimide binder precursor after slurry application. As a result, the current collector and the electrode could not follow the volume change during large charge / discharge, and wrinkles were generated. At the same time, there was a lack of lithium ion conduction and electronic conduction paths due to detachment and partial peeling of the coating film. As a result, it is considered that the capacity was greatly reduced. The comparison between the two examples using the untreated foil A and the untreated foil B also seems to have caused a difference in heat resistance in a difference in capacity retention rate.

  According to the present invention, since it is possible to provide an optimum specification of the current collector according to the electrode binder, the interfacial adhesion and the like are not impaired even after repeated charge and discharge, and an electrode that can achieve a high cycle life. A secondary battery can be provided.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the technical idea disclosed in the present application. Of course, it is understood that they belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ......... Current collector 2 ......... Active material containing layer 3 ......... Electrode 4 ......... Current collector 5 ......... Active material containing layer 6 ......... Electrode 7 ......... Current collector 8 ... ... Active material-containing layer 9 ......... Electrode 10 ......... Particulate 11 ......... Non-aqueous electrolyte secondary battery 12 ......... Negative electrode 13 ......... Positive electrode 15 ......... Separator 17 ... …… Electrolyte 19 ......... Battery Can 21 ......... Positive lead 23 ......... Negative lead 25 ......... Positive terminal 27 ......... Sealing body

Claims (11)

An electrode current collector for forming an active material-containing layer using a slurry containing an electrode active material and an aqueous binder, wherein the active material-containing layer is formed in a direction of roughness (Z-axis). The surface area ratio obtained by dividing the actual surface area when the resolution is measured at 0.05 μm by the unit plane area is 1.11 to 3.95 ,
An electrode current collector for use in a negative electrode for a non-aqueous electrolyte secondary battery .   The current collector for an electrode according to claim 1, wherein the surface area ratio is 1.11 to 2.36.   The current collector for an electrode according to claim 1, wherein the surface area ratio is 1.11 to 1.98.   The current collector for an electrode according to claim 1, wherein the surface area ratio is 1.11 to 1.46. The current collector for an electrode according to any one of claims 1 to 4, wherein the current collector for an electrode is a copper foil. The current collector for an electrode according to claim 5 , wherein the current collector for an electrode is a roughened copper foil. The surface of the current collector for an electrode has one or more of a chromate treatment layer, a benzotriazole treatment layer, a silane coupling treatment layer, a nickel treatment layer, a zinc treatment layer, and a tin treatment layer. The current collector for an electrode according to any one of 1 to 6 . The electrode current collector has a tensile strength of 450 MPa or more, a breaking elongation of 3% or more, a breaking elongation of 3% or more after heating at 180 ° C. for 5 minutes, and a tensile strength of 300 MPa after heating at 300 ° C. for 1 hour. electrode current collector according to any one of claims 1 to 7, characterized in that at least. A negative electrode for a nonaqueous electrolyte secondary battery, wherein an active material-containing layer is formed using a slurry containing an electrode active material and an aqueous binder on the electrode current collector according to claim 1. The negative electrode for a nonaqueous electrolyte secondary battery according to claim 9 , wherein the electrode active material contains silicon or tin . A non-aqueous electrolyte secondary battery using the negative electrode according to claim 9 or 10 .

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