JP2015002008A - Electrode including protective layer formed on active material layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode reducing resistance variation for each battery.SOLUTION: An electrode includes: a collector; an active material layer formed on the collector; and a protective layer formed on the active material layer and containing an inorganic compound and a binder at a mass ratio of 5:1-200:1. A surface roughness Raof the active material layer and a surface roughness Raof the protective layer satisfy a relation of Ra>Ra.

Description

  The present invention relates to an electrode including a protective layer formed on an active material layer.

  Generally, a battery has a positive electrode and a negative electrode. Each electrode of the battery includes a current collector for passing a current through the electrode, and an active material layer including an active material formed on the current collector. In recent years, with the expansion of battery applications, research on current collectors, active material layers, and the like constituting batteries has been actively conducted. Moreover, in order to increase the voltage, capacity, life, etc. of a battery, a battery having a pair of a positive electrode and a negative electrode is used as a unit, and a plurality of batteries are arranged in series or in parallel to form a battery of a plurality of units. .

  Here, even if the battery is designed to have a desired standard, if a large resistance variation occurs between the batteries, a battery that deviates from the standard may be manufactured. In addition, when a battery of a plurality of units is used, a battery that greatly deviates from the standard may be manufactured. That is, it is not preferable that a large resistance variation occurs between the batteries.

  In recent years, research on batteries has been reported focusing on reducing resistance variation. For example, Patent Document 1 discloses that a battery with small resistance variation is manufactured by devising a method of manufacturing a current collector terminal. Patent Document 2 discloses a battery having a small resistance variation in which the shape of the current collector terminal is devised.

JP 2011-170972 A JP 2011-159518 A

  The techniques disclosed in Patent Document 1 and Patent Document 2 are one method for reducing the resistance variation of the battery. However, it is assumed that there are various causes other than the current collector terminal in the resistance variation of the battery, and there is room for further resistance variation reduction.

  In view of such circumstances, the present invention has been made paying attention to an electrode constituting a battery, and an object of the present invention is to provide an electrode that reduces resistance variation for each battery.

The present inventor has intensively studied through many trials and errors. Unexpectedly, the present inventor has found that a battery using an electrode in which a protective layer having a surface roughness Ra ₂ smaller than Ra ₁ is provided on an active material layer having a surface roughness Ra ₁ causes resistance variation for each battery. As a result, the present invention has been completed.

The electrode of the present invention is formed on a current collector, an active material layer formed on the current collector, and the active material layer, and an inorganic compound and a binder are mixed in a mass ratio of 5: 1 to 200: 1. The surface roughness Ra ₁ of the active material layer and the surface roughness Ra _{2 of the} protective layer are Ra ₁ > Ra ₂ .

  About the battery using the electrode of this invention, the resistance variation for every battery is reduced.

It is a scanning electron micrograph of the electrode surface (protective layer surface) of Example 1 of this invention. 2 is a scanning electron micrograph of the electrode surface (active material layer surface) of Comparative Example 1. FIG.

  Below, the form for implementing this invention is demonstrated. Unless otherwise specified, the numerical range “ab” described herein includes the lower limit “a” and the upper limit “b”. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.

The electrode of the present invention is formed on a current collector, an active material layer formed on the current collector, and the active material layer, and an inorganic compound and a binder are mixed in a mass ratio of 5: 1 to 200: 1. The surface roughness Ra ₁ of the active material layer and the surface roughness Ra _{2 of the} protective layer are Ra ₁ > Ra ₂ .

  The electrode of the present invention can be used for various batteries. With respect to the type of battery, the type of battery is not limited as long as the battery includes a current collector and an active material layer. The electrode of the present invention may be used as an electrode of a primary battery such as a manganese battery, an alkaline manganese battery, a nickel battery, a silver oxide battery, a mercury battery, or a lithium battery, or a lithium ion secondary battery, a nickel metal hydride battery, nickel You may use as an electrode of secondary batteries, such as a cadmium storage battery.

  Hereinafter, although the case where the kind of battery in which the electrode of the present invention is used is a lithium ion secondary battery will be mainly described, the electrode of the present invention is not limited to being used for a lithium ion secondary battery.

  A current collector refers to a chemically inert electronic high conductor that continues to pass current through an electrode during battery discharge or charge. As a material of the current collector, at least one selected from silver, copper, gold, aluminum, magnesium, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, or Examples thereof include metal materials such as stainless steel and carbon materials such as graphite. In particular, aluminum or copper is preferable as the current collector material from the viewpoints of electrical conductivity, workability, and cost. The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 10 μm to 100 μm.

  The active material layer is a layer formed on the current collector and containing the active material.

  The active material is a substance that performs an oxidation reaction for sending electrons and / or a reduction reaction for receiving electrons. In addition, it can be said that the active material is a substance that releases ions to the electrolytic solution or a substance that receives ions from the electrolytic solution in accordance with the oxidation-reduction reaction. For example, the active material of a lithium ion secondary battery is a substance that can occlude and release lithium ions. An active material used in the positive electrode is referred to as a positive electrode active material, and an active material used in the negative electrode is referred to as a negative electrode active material.

As the positive electrode active material, a known material employed in each battery may be used. For example, as the positive electrode active material of a lithium ion secondary _{battery, Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 1, b + c + d + e = 1,0 ≦ e <1, D is Li, Fe , Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, 1.7 ≦ f ≦ 2.1), Li ₂ MnO ₂ , Li ₂ MnO ₃ , LiFePO ₄ , and lithium-containing metal oxides such as Li ₂ FeSO ₄ . In addition, the positive electrode active material of the lithium ion secondary battery is represented by LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (wherein M is selected from at least one of Co, Ni, Mn, and Fe). A polyanionic compound can be mentioned.

As the positive electrode active material of the lithium ion secondary batteries, from the viewpoint of high _{capacity, Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 1, b + c + d + e = 1,0 of the layered rock-salt structure < b <1, 0 <c <1, 0 <d <1, 0 ≦ e <1, D is selected from Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al Preferably at least one element, 1.7 ≦ f ≦ 2.1), of which 0 <b <70/100, 0 <c <50/100, 10/100 <d <1 Preferably, those within the ranges of 1/3 ≦ b ≦ 50/100, 20/100 ≦ c ≦ 1/3, 1/3 ≦ d <1, more preferably b = 1/3, c = 1/3, Particularly preferred are those where d = 1/3, or b = 50/100, c = 20/100, and d = 30/100.

As the negative electrode active material, a known material employed in each battery may be used. For example, as a negative electrode active material of a lithium ion secondary battery, a carbon-based material that can occlude and release lithium, an element that can be alloyed with lithium, a compound that has an element that can be alloyed with lithium, or a polymer material is exemplified. can do. Examples of the carbon-based material include non-graphitizable carbon, artificial graphite, natural graphite, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and carbon blacks. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature. Specific elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si. , Ge, Sn, Pb, Sb, Bi can be exemplified, and Si or Sn is particularly preferable. Specific examples of compounds having elements that can be alloyed with lithium include ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , _{CaSi 2, CrSi 2, Cu 5} Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO 2 or LiSnO, and SiO _x (0.5 ≦ x ≦ 1.5) is particularly preferable. Moreover, tin compounds (Cu-Sn alloy, Co-Sn alloy, etc.) can be illustrated as a compound which has an element which can be alloyed with lithium. Specific examples of the polymer material include polyacetylene and polypyrrole.

  There is no restriction | limiting in particular in the shape of an active material. The average particle diameter of the active material aggregate is preferably in the range of 1 to 100 μm, more preferably in the range of 2 to 50 μm, and particularly preferably in the range of 5 to 30 μm. In addition, what is necessary is just to measure an average particle diameter with general particle size distribution measuring apparatuses, such as a laser diffraction type particle size distribution measuring apparatus.

  The active material layer includes a binder and / or a conductive aid as necessary.

  The binder plays a role of binding the active material to the surface of the current collector. As binders, fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, carboxymethylcellulose, methylcellulose and styrene-butadiene rubber Well-known materials such as alkoxysilyl group-containing resins can be used. These binders can be added to the active material layer alone or in combination of two or more. Although there is no restriction | limiting in particular about the usage-amount of a binder, The range of 1-50 mass parts of binders with respect to 100 mass parts of active materials is preferable. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  A conductive additive is added to increase conductivity. Examples of the conductive assistant include carbon black, graphite, acetylene black, ketjen black (registered trademark), and vapor grown carbon fiber (Vapor Grown Carbon Fiber) which are carbonaceous fine particles. These conductive assistants can be added to the active material layer alone or in combination of two or more. Although there is no restriction | limiting in particular about the usage-amount of a conductive support agent, For example, it can be set as 1-30 mass parts of conductive support agents with respect to 100 mass parts of active materials.

  In order to form an active material layer on the surface of the current collector, the surface of the current collector can be formed using a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method. The active material may be directly applied to the surface. Specifically, a composition for forming an active material layer containing an active material and, if necessary, a binder and / or a conductive aid is prepared, and an appropriate solvent is added to the composition to obtain a paste-like liquid. To do. A solution in which a binder is dissolved in a solvent in advance or a dispersed suspension may be used. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, ethanol, methyl isobutyl ketone, and water. The paste-like liquid is applied to the surface of the current collector and then dried. Drying may be performed under normal pressure conditions or under reduced pressure conditions using a vacuum dryer. What is necessary is just to set drying temperature suitably, and the temperature beyond the boiling point of the said solvent is preferable. What is necessary is just to set drying time suitably according to an application quantity and drying temperature. In order to increase the density of the active material layer, a compression step may be added to the dried current collector on which the active material layer is formed.

  The protective layer is a layer formed on the active material layer and containing an inorganic compound and a binder at a mass ratio of 5: 1 to 200: 1. The protective layer protects the active material layer by reducing direct contact between the active material layer and the electrolytic solution or between the active material layer and the separator when a battery is formed using the electrode of the present invention. The protective layer may be formed on the positive electrode active material layer or may be formed on the negative electrode active material layer. The protective layer may be formed on the positive and negative bipolar active material layers.

Inorganic compounds include Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , MgO, SiC, AlN, BN, CaCO ₃ , MgCO ₃ , BaCO ₃ , talc, mica, kaolinite, CaSO ₄ , MgSO ₄ , BaSO ₄ , CaO, ZnO and zeolite can be exemplified. In the protective layer, one or more selected from these inorganic compounds can be used.

In the electrode of the present invention, since the surface roughness Ra ₂ of the surface roughness Ra ₁ and the protective layer of the active material layer has a relation of Ra _1> Ra _2, the average particle diameter of the inorganic compound, the active material layer Is required to be smaller than the average particle size of the active material used. When it shows about the preferable average particle diameter of an inorganic compound, a 0.1-10 micrometers thing is preferable, a 0.2-5 micrometers thing is more preferable, and a 0.4-3 micrometers thing is especially preferable. When the average particle diameter is too small, a case where the protective layer becomes too dense is assumed. As a result, the distance of the ion movement path between the positive electrode and the negative electrode is increased, and the movement path is blocked to decrease the number of movement paths themselves, which may increase the resistance of the battery. As described above, the average particle size may be measured with a general particle size distribution measuring device such as a laser diffraction particle size distribution measuring device.

  As the binder used for the protective layer, the binder described in the description of the active material layer may be employed alone or in combination. As the binder used for the protective layer, polyvinylidene fluoride is particularly preferable from the viewpoint of electrochemical stability.

  The protective layer of the present invention contains an inorganic compound and a binder at a mass ratio of 5: 1 to 200: 1. The mass ratio of the inorganic compound and the binder is more preferably within the range of 10: 1 to 100: 1, more preferably within the range of 15: 1 to 50: 1, and within the range of 20: 1 to 30: 1. Particularly preferred. If the blending amount of the binder in the protective layer is too small, the protective layer may lose its binding force to the active material layer, or the protective layer may collapse due to a decrease in the binding force between inorganic compounds in the protective layer. It is not preferable. Further, if the amount of the binder in the protective layer is too small, the flexibility of the entire protective layer is lost, and the protective layer may be broken by the pressure applied to the electrode, which is not preferable. If the compounding amount of the binder in the protective layer is too large, there is a concern that the hardness of the protective layer itself is lowered, the distance of the ion movement path between the positive electrode and the negative electrode is increased, and the movement path is blocked. This is not preferable because there is a concern that the number of movement paths themselves may decrease.

  Although there is no restriction | limiting in particular in the thickness of a protective layer, 0.1-10 micrometers is preferable, 0.5-8 micrometers is more preferable, and 1-7 micrometers is especially preferable.

The electrode of the present invention, the surface roughness Ra ₂ of the surface roughness Ra ₁ and the protective layer of the active material layer is characterized by a _Ra 1> Ra _2. Here, each surface roughness Ra is obtained by measuring the roughness on a straight line of a length l (el) in a sample by a non-contact method with a laser microscope in accordance with JIS B 0601. Specifically, the surface roughness Ra is obtained by measuring a height Z (x) at an arbitrary position x on a straight line having a length l in a sample with a laser microscope, and calculating an absolute value of Z (x) at a reference length. The average is calculated and can be expressed by the following equation.

  In order to provide a protective layer on an active material layer in the method for producing an electrode of the present invention, for example, a step of preparing a protective layer forming composition by dispersing constituent components of the protective layer in a solvent, and the protective layer What is necessary is just to implement a drying process, after implementing the process of apply | coating the composition for formation on an active material layer. The blending amount of the constituent components of the protective layer in the protective layer forming composition is preferably within the range of 10 to 50% by mass. The solvent used for the preparation of the composition for forming a protective layer is preferably a solvent that does not dissolve the inorganic compound, and may be appropriately selected from, for example, N-methyl-2-pyrrolidone, methanol, ethanol, methyl isobutyl ketone, and water. In the coating process, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method may be used. The drying step may be performed under normal pressure conditions or under reduced pressure conditions using a vacuum dryer. The drying temperature may be appropriately set within a range where the binder does not decompose, and a temperature equal to or higher than the boiling point of the solvent is preferable. What is necessary is just to set drying time suitably according to an application quantity and drying temperature.

  The electrode of the present invention can constitute a lithium ion secondary battery. The lithium ion secondary battery of this invention has a separator and electrolyte solution in addition to an electrode.

  The separator separates the positive electrode and the negative electrode, and allows ions to pass through while preventing a short circuit of current due to contact between the two electrodes. As the separator, a known one used in each battery may be used. For example, a porous film using one or more synthetic resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyester, and polyamide can be exemplified. The separator may have a single-layer structure using a single material or a stacked structure in which layers of a plurality of materials are stacked. The thickness of the separator is not particularly limited, but is preferably in the range of 5 μm to 100 μm, more preferably in the range of 10 μm to 50 μm, and particularly preferably in the range of 20 μm to 30 μm.

  The electrolytic solution is a solution containing a solvent and an electrolyte dissolved in the solvent. As the electrolytic solution, a known one used in each battery may be used.

  Examples of the solvent used for the electrolyte solution of the lithium ion secondary battery include non-aqueous solvents such as cyclic esters, chain esters, and ethers. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. A plurality of the above-described solvents may be used in combination as the solvent for the electrolytic solution. In particular, it is preferable to use three types of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate in combination.

Examples of the electrolyte of the lithium ion secondary battery include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ . The concentration of the electrolyte in the electrolytic solution is preferably in the range of 0.5 to 1.7 mol / L.

  The shape of the lithium ion secondary battery is not particularly limited, and various shapes such as a cylindrical shape, a laminated shape, a coin shape, and a laminated shape can be employed.

  The lithium ion secondary battery may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a lithium ion secondary battery for all or a part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form an assembled battery. Examples of the lithium ion secondary battery include various home electric appliances, office equipment, industrial equipment, and the like driven by batteries, such as personal computers and portable communication devices, in addition to vehicles.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to a following example.

Example 1
The electrode of the present invention was manufactured as follows.

96 parts by mass of Al ₂ O _{3 having} an average particle diameter of 0.5 μm and 4 parts by mass of polyvinylidene fluoride were mixed to prepare a mixture. N-methyl-2-pyrrolidone was added to the mixture to prepare a protective layer forming composition containing 32% by mass of the mixture.

  98 parts by mass of natural graphite having an average particle diameter of 20 μm, which is a negative electrode active material, and 1 part by mass of styrene butadiene rubber, which is a binder, were mixed with 1 part by mass of carboxymethyl cellulose. This mixture was dispersed in an appropriate amount of ion-exchanged water to prepare a slurry. A copper foil having a thickness of 20 μm was prepared as a negative electrode current collector. The slurry was applied in a film form on the surface of the copper foil using a doctor blade. The copper foil coated with the slurry was dried to remove water, and then the copper foil was pressed to obtain a bonded product. The obtained joined product was heat-dried at 120 ° C. for 6 hours with a vacuum dryer to obtain a copper foil on which a negative electrode active material layer was formed. The said protective layer formation composition was apply | coated to the film form on the negative electrode active material layer of copper foil using the doctor blade. This was dried at 120 ° C. for 6 hours to obtain a copper foil in which a protective layer having a thickness of 4 μm was formed on the negative electrode active material layer. This was used as the negative electrode of Example 1.

(Comparative Example 1)
A negative electrode of Comparative Example 1 was obtained in the same manner as in Example 1 except that the protective layer was not formed on the negative electrode active material layer.

<Evaluation of electrode>
The surface roughness Ra of the electrodes of Example 1 and Comparative Example 1 was measured using a laser microscope. The surface roughness Ra ₂ (surface roughness of the protective layer) of the electrode of Example 1 was Ra ₂ = 581 nm. Comparative Example 1 the surface of the electrode roughness Ra ₁ (the surface roughness of the negative electrode active material layer) was _Ra 1 = _888nm. A scanning electron micrograph of the electrode surface (protective layer surface) of Example 1 is shown in FIG. Moreover, the scanning electron micrograph of the electrode surface (active material layer surface) of the comparative example 1 is shown in FIG.

From the measurement results and scanning electron microscope photograph of observation of a laser microscope, the relationship between the surface roughness Ra ₂ of the surface roughness Ra ₁ and the protective layer of the active material layer, Ra _1> Ra is it clear ₂ is there.

(Application examples)
Using the negative electrode of Example 1, a lithium ion secondary battery was produced as follows.

94 parts by mass of a lithium-containing metal oxide having a layered rock salt structure represented by LiNi _5/10 Co _2/10 Mn _3/10 O ₂ having an average particle diameter of 10 μm as a positive electrode active material, and 3 parts by mass of acetylene black as a conductive auxiliary agent Part and 3 parts by mass of polyvinylidene fluoride as a binder were mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. An aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector. The slurry was applied to the surface of the aluminum foil using a doctor blade so as to form a film. The aluminum foil coated with the slurry was dried at 80 ° C. for 20 minutes to remove N-methyl-2-pyrrolidone by volatilization to obtain an aluminum foil on which a positive electrode active material layer was formed. The aluminum foil on which this positive electrode active material layer was formed was used as the positive electrode.

  A rectangular sheet (27 × 32 mm, thickness 25 μm) made of a polyethylene resin film was prepared as a separator.

A separator was installed on the protective layer of the negative electrode, and then a positive electrode was installed to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film. As an electrolytic solution, a solution in which LiPF ₆ was dissolved to 1 mol / L in a solvent obtained by mixing 30 parts by volume of ethylene carbonate, 30 parts by volume of methyl ethyl carbonate, and 40 parts by volume of dimethyl carbonate was used. Thereafter, the remaining one side was sealed to obtain a lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. In addition, the positive electrode and negative electrode of this lithium ion secondary battery are provided with a tab that can be electrically connected to the outside, and a part of this tab extends outside the lithium ion secondary battery. In the same manner, a total of ten lithium ion secondary batteries using the negative electrode of Example 1 were manufactured.

  Furthermore, ten lithium ion secondary batteries using the negative electrode of Comparative Example 1 were manufactured in the same manner.

<Battery evaluation>
For each of the 10 batteries using the electrode of Example 1 or Comparative Example 1, the following test was performed to measure the discharge resistance and the charge resistance. The results of the discharge resistance (Ω) are shown in Table 1, and the results of the charge resistance (Ω) are shown in Table 2, respectively.

<Discharge resistance>
A battery having a charging rate of 20% is discharged at a 2.5C rate for 10 seconds. The discharge resistance (Ω) is obtained by the following formula.
Discharge resistance (Ω) = | Voltage before discharge−Voltage after discharge | / Current value <Charge resistance>
A battery with a charging rate of 80% is charged for 10 seconds at a 2.5C rate. The charging resistance (Ω) is obtained by the following formula.
Charging resistance (Ω) = | Voltage before charging−Voltage after charging | / Current value

From the results of Table 1 and Table 2, the relationship between the surface roughness Ra ₂ of the surface roughness Ra ₁ and the protective layer of the active material layer, the battery using the electrode is Ra _1> Ra _2, the discharge resistance and charge It can be seen that the variation in both the resistance is remarkably reduced.

  This result is considered as follows.

  At the time of manufacturing the battery, a certain pressure is applied to the plate group in which the negative electrode, the separator, and the positive electrode are stacked in the direction of the layer thickness. Due to this pressure, the surfaces of the active material layers of both electrodes compress the separator. Here, the separator is deformed according to the surface shape of the active material layer. Large convex portions and large concave portions exist on the surface of the active material layer having a large surface roughness Ra. Here, for example, when a large convex portion on the surface of the positive electrode active material layer and a large convex portion on the surface of the negative electrode active material layer face each other through the separator, the pressure is concentrated on both the convex portions, and the deformation of the separator accompanying it. (The phenomenon is hereinafter referred to as “localization of deformation of the separator”). At locations where the deformation of the separator has been localized, the distance between the positive electrode active material layer and the negative electrode active material layer is remarkably shortened, and the resistance of ions flowing through this distance is compared with the resistance of ions flowing through other intervals. Become significantly smaller. And the resistance of the battery in which the localization of the deformation of the separator has occurred is lower than the resistance of other batteries. As a result, the resistance variation among the batteries increases.

However, in the electrode of the present invention the relationship between the surface roughness Ra ₂ of the surface roughness Ra ₁ and the protective layer of the active material layer is Ra _1> Ra ₂ protective layer is formed, the convex portion of the surface of the protective layer Therefore, pressure concentration is less likely to occur, and localization of deformation of the separator is suppressed to a certain extent. If it does so, in the battery using the electrode of this invention, the location where the space | interval of a positive electrode active material layer and a negative electrode active material layer becomes remarkably short does not exist, and the resistance variation for every battery is reduced.

Conversely, in the batteries relationship using an electrode protective layer is formed is Ra ₁ ≦ Ra ₂ between the surface roughness Ra ₂ of the surface roughness Ra ₁ and the protective layer of the active material layer, the deformation of the separator Localization is not suppressed, and it is considered that the variation in resistance between batteries increases.

Claims (7)

A current collector,
An active material layer formed on the current collector;
A protective layer formed on the active material layer and containing an inorganic compound and a binder in a mass ratio of 5: 1 to 200: 1;
An electrode characterized in that the surface roughness Ra ₁ of the active material layer and the surface roughness Ra ₂ of the protective layer satisfy Ra ₁ > Ra ₂ . The inorganic compound is Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , MgO, SiC, AlN, BN, CaCO ₃ , MgCO ₃ , BaCO ₃ , talc, mica, kaolinite, CaSO ₄ , MgSO ₄ , BaSO _4. The electrode according to claim 1, selected from CaO, ZnO, and zeolite.   The electrode according to claim 1, wherein the binder contains polyvinylidene fluoride.   The electrode according to claim 1, wherein the electrode is a negative electrode.   A battery comprising the electrode according to claim 1.   The battery according to claim 5, wherein the battery is a secondary battery.   The battery according to claim 5 or 6, wherein the battery is a lithium ion secondary battery.