JP4025094B2 - Positive electrode for lithium ion secondary battery and lithium ion secondary battery using the positive electrode - Google Patents

Positive electrode for lithium ion secondary battery and lithium ion secondary battery using the positive electrode Download PDF

Info

Publication number
JP4025094B2
JP4025094B2 JP2002057076A JP2002057076A JP4025094B2 JP 4025094 B2 JP4025094 B2 JP 4025094B2 JP 2002057076 A JP2002057076 A JP 2002057076A JP 2002057076 A JP2002057076 A JP 2002057076A JP 4025094 B2 JP4025094 B2 JP 4025094B2
Authority
JP
Japan
Prior art keywords
positive electrode
μm
average particle
active material
particle size
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
JP2002057076A
Other languages
Japanese (ja)
Other versions
JP2003257416A (en
Inventor
敏博 厨子
聖司 岡田
賢一 木津
健 森内
Original Assignee
三菱電線工業株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 三菱電線工業株式会社 filed Critical 三菱電線工業株式会社
Priority to JP2002057076A priority Critical patent/JP4025094B2/en
Publication of JP2003257416A publication Critical patent/JP2003257416A/en
Application granted granted Critical
Publication of JP4025094B2 publication Critical patent/JP4025094B2/en
Expired - Fee Related legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage
    • Y02E60/12Battery technologies with an indirect contribution to GHG emissions mitigation
    • Y02E60/122Lithium-ion batteries

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery.
[0002]
[Prior art]
Lithium ion secondary batteries can achieve higher energy density and higher voltage than nickel-cadmium batteries and the like, and in recent years, they have been rapidly adopted as driving sources for portable devices such as mobile phones and notebook computers.
[0003]
A positive electrode of a lithium ion secondary battery is generally configured by forming a layer of a mixture containing an active material, a conductive material, and a binder on a current collector made of a metal foil such as an Al foil. Such a composite layer is usually formed by applying and drying a slurry containing an active material, a conductive material and a binder on a current collector, and subjecting the resulting coating film to a rolling treatment. Here, as the active material, LiCoO2Li-Co based composite oxides (granular materials) such as graphite are used, and carbon materials such as graphite and carbon black are used as the conductive material.
[0004]
It is known that the larger the particle size of the Li—Co-based composite oxide that is the active material, the less likely to cause an abnormal reaction, and a larger particle size is preferable from the viewpoint of battery safety. However, as the particle size increases, the electrical resistance of the positive electrode increases and the battery characteristics (particularly the discharge load characteristics) tend to decrease. The inventors use a Li—Co based composite oxide (average particle size of 17 μm or more) having a large particle size as an active material, and the surface of the Li—Co based composite oxide (particle) is used as a conductive material. A gap between particles of the carbon material (first conductive material) having a fine particle size (average particle size of 1 μm or less) that increases the conductivity of the surface by coating and the Li—Co-based composite oxide (particles) The conductivity of the positive electrode has been increased by using a carbon material (second conductive material) having an average particle size of about 5 μm or more, which increases the conductivity between the particles.
[0005]
On the other hand, in order to increase the capacity of the battery, the amount of the active material in the positive electrode is increased. However, in order to obtain a battery of a prescribed size, the thickness of the positive electrode is limited to a predetermined thickness or less, so It is necessary to adjust the positive electrode to a predetermined thickness or less by rolling (compressing) a layer of the composite material containing the material and the binder (hereinafter also referred to as “composite material layer” or “positive electrode composite material layer”).
[0006]
The recent demand for higher battery capacity has not stopped, and the amount of active material has been increased more than before, and the composite layer has been compressed (rolled) more strongly. In the battery using the positive electrode manufactured in this way, there is a problem that the incidence of internal shorts (the positive electrode breaks through the separator and comes into contact with the negative electrode) increases, and the low temperature characteristics deteriorate.
[0007]
[Problems to be solved by the invention]
In view of the above circumstances, the present invention provides a positive electrode for a lithium ion secondary battery capable of achieving a lithium ion secondary battery that exhibits high capacity, good low-temperature characteristics, and is less susceptible to internal short-circuits and abnormal reactions, and the An object is to provide a lithium ion secondary battery using a positive electrode.
[0008]
[Means for Solving the Problems]
As a result of the study by the present inventors, the problem of the above internal short circuit is caused by irregularities on the surface of the composite material layer that appears when the composite material layer is highly compressed (rolled). It was found that the difference in unevenness on the surface of the composite material layer was reduced (the packing density of the composite material was improved) by using the scale-like graphitized carbon of ˜6 μm as the conductive material. Therefore, the use of scaly graphitized carbon having such a specific particle size range as a conductive material was investigated to reduce the particle size of the active material (Li-Co composite oxide) in order to increase the capacity of the battery. However, planarization of the surface of the composite layer is not yet sufficient, and as a result of further research, a group of particles of Li—Co based composite oxide having a relatively large particle size (average particle size as an active material) 7 to 13 μm) and a group of particles of Li—Co based composite oxide having a relatively small particle size (average particle size of 1 to 6 μm) are used at a specific ratio, and the specific particle size range (average particle size) By using carbon black with a small particle diameter (average particle diameter of 0.5 μm or less) as a conductive material together with flaky graphitized carbon having a diameter of 1 to 6 μm, the surface of the composite layer can be sufficiently flattened (internal Both short-circuit prevention and battery capacity increase, and the battery reacts abnormally. Without causing, it found that low temperature characteristics are significantly improved, in which the present invention has been completed.
That is, the present invention is characterized by the following configuration.
[0009]
(1) A positive electrode for a lithium ion secondary battery, which is formed by forming a mixture layer containing an active material, a conductive material and a binder on a current collector,
The active material is composed of a Li-Co composite oxide having an average particle diameter of 7 to 13 µm and a Li-Co composite oxide having an average particle diameter of 1 to 6 µm in a ratio of 1: 0.1 to 1.5 (weight). Ratio)
The conductive material is a mixture containing scaly graphitized carbon having an average particle diameter of 1 to 6 μm and carbon black having an average particle diameter of 0.5 μm or less in a ratio (weight ratio) of 1: 0.01 to 1,
A positive electrode for a lithium secondary battery, wherein a ratio (weight ratio) between an active material and a conductive material is 1: 0.01 to 0.1.
(2) A lithium ion secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution, wherein the positive electrode is composed of the positive electrode described in (1) above. Lithium ion secondary battery.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The positive electrode for a lithium ion secondary battery of the present invention (hereinafter also simply referred to as a positive electrode) is formed by forming a layer of a mixture containing an active material, a conductive material and a binder on a current collector,
An active material includes an Li—Co based composite oxide (first active material) having an average particle size of 7 to 13 μm and an Li—Co based composite oxide (second active material) having an average particle size of 1 to 6 μm. In a ratio (weight ratio) of 1: 0.1 to 1.5 (first active material: second active material),
As a conductive material, a weight ratio of 1: 0.01 to 1 (scalar graphitized carbon: carbon black) between flaky graphitized carbon having an average particle size of 1 to 6 μm and carbon black having an average particle size of 0.5 μm or less. Use the mixture containing in
The ratio (weight ratio) between the active material and the conductive material is 1: 0.01 to 0.1.
[0011]
That is, in the positive electrode of the present invention, it is important to use scale-like graphitized carbon having an average particle size of 1 to 6 μm as the conductive material. In scale-like graphitized carbon having an average particle size of less than 1 μm, The surface of the layer is not sufficiently flattened, and it becomes difficult to obtain conductivity between the active material particles. In addition, in the scale-like graphitized carbon having an average particle size exceeding 6 μm, filling inhibition of the active material having a small particle size occurs. In the present invention, the average particle size of the scale-like graphitized carbon is preferably 2 to 4 μm, particularly preferably 2 to 3 μm.
[0012]
In addition, the active material includes a group of Li—Co composite oxide particles having a relatively large particle size (first active material, average particle size: 7 to 13 μm) and a Li—Co composite oxide having a relatively small particle size. And a mixture ratio (first active material: second active material) of 1: 0.1-1 with a mixture of particles (second active material, average particle size: 1-6 μm). .5 (weight ratio) is important. When the ratio of the first active material is increased away from the mixing ratio, the surface of the composite material layer is not sufficiently flattened, and the low-temperature characteristics tend to deteriorate. On the other hand, when the ratio of the second active material increases, the reaction area of the active material becomes too large, and the safety of the battery tends to decrease.
[0013]
In the present invention, the average particle size of the first active material is preferably 8 to 11 μm, particularly preferably 8 to 10 μm, and the average particle size of the second active material is preferably 2 to 5 μm, particularly preferably 3 to 3 μm. 5 μm. The mixing ratio of the first active material and the second active material is preferably 1: 0.2 to 1.0, and particularly preferably 1: 0.2 to 0.6.
[0014]
In the positive electrode of the present invention, it is important to use carbon black having an average particle diameter of 0.5 μm or less together with the scale-like graphitized carbon having an average particle diameter of 1 to 6 μm as the conductive material. By using carbon black having a particle size of 0.5 μm or less, the flatness of the surface of the positive electrode mixture layer is further improved, and excellent low temperature characteristics can be obtained.
[0015]
In the present invention, the carbon black having an average particle diameter of 0.5 μm or less preferably has an average particle diameter of 80 nm (0.08 μm) or less, and the lower limit of the average particle diameter is 5 nm (0.005 μm) or more. is there. This is because those having an average particle size of less than 5 nm (0.005 μm) are flocculated in the preparation of the slurry for forming the composite material layer, and a homogeneous slurry cannot be prepared.
[0016]
In the positive electrode of the present invention, the ratio of the active material to the conductive material (active material: conductive material) is usually 1: 0.01 to 0.1 (weight ratio), preferably 1: 0.02 to 0.00. 07. When the ratio of the conductive material is small outside this range, the mixture layer is not sufficiently flattened, and problems such as a decrease in the discharge load characteristics of the battery due to an increase in the electrical resistance of the positive electrode are caused. If the ratio of the conductive material increases away from the above, the occupation ratio of the active material in the composite layer becomes too small, and the battery capacity cannot be increased.
[0017]
Moreover, it is important to set the ratio (weight ratio) between the scale-like graphitized carbon and the carbon black in the conductive material within a range of 1: 0.01 to 1 (scale-like graphitized carbon: carbon black), Preferably it is 1: 0.2-0.5. If the ratio of scale-like graphitized carbon decreases outside this range, the surface of the composite layer will not be sufficiently flattened (it tends to cause internal short circuit), and if the ratio of carbon black is small, good low temperature The characteristics cannot be obtained, and the flatness of the surface of the composite material layer is also lowered.
[0018]
In the present invention, as a specific example of the Li—Co-based composite oxide used for the active material (the first active material and the second active material), LiCoO2Or LiACo1-XMeXO2The thing shown by is mentioned. The latter LiACo1-XMeXO2In the formula, A is preferably 0.05 to 1.5, particularly preferably 0.1 to 1.1. X is preferably from 0.01 to 0.5, particularly preferably from 0.02 to 0.2. Examples of the element Me include group 3-10 elements of the periodic table such as Zr, V, Cr, Mo, Mn, Fe, Ni, and group 13-15 elements such as B, Al, Ge, Pb, Sn, Sb. Can be mentioned.
[0019]
In the present invention, a first active material (Li—Co based composite oxide having an average particle size of 7 to 13 μm) and a second active material (Li—Co based composite oxide having an average particle size of 1 to 6 μm) May have the same composition (the same constituent element and the same constituent element quantity ratio) or a different composition ((1) same constituent element, different constituent element quantity ratio, (2) different constituent elements) However, the same composition is preferable and both are LiCoO.2Is particularly preferred.
[0020]
In the Li—Co based composite oxide used in the present invention, for example, a lithium compound and a cobalt compound as starting materials are mixed so that an atomic ratio of cobalt to lithium is 1: 1 to 0.8: 1. Then, the mixture is reacted in an air atmosphere at a temperature of 700 ° C. to 1200 ° C. by heating for 3 hours to 50 hours, etc., and the reaction product is further pulverized into a granular material, or the granular material The product is further classified and used. The pulverized granular material is subjected to a heat treatment at a temperature of about 400 ° C. to 750 ° C. (preferably 450 ° C. to 700 ° C.) for about 0.5 hours to 50 hours (preferably 1 hour to 20 hours). Also good. By such heat treatment, the specific surface area can be reduced with almost no change in the average particle diameter of the granular material, which gives favorable results in the low temperature characteristics and charge / discharge cycle characteristics of the battery. The heat treatment can be performed, for example, in an air atmosphere or an inert gas atmosphere such as nitrogen or argon. However, if carbon dioxide gas is present in the atmosphere, lithium carbonate is generated and the content of impurities may increase. Therefore, it is preferable to carry out in an atmosphere where the partial pressure of carbon dioxide gas is about 10 mmHg or less.
[0021]
Examples of the lithium compound used as the starting material include lithium oxide, lithium hydroxide, lithium halide, lithium nitrate, lithium oxalate, and lithium carbonate, and mixtures thereof. Examples of the cobalt compound include cobalt oxide, cobalt hydroxide, cobalt halide, cobalt nitrate, cobalt oxalate, and cobalt carbonate, and mixtures thereof. LiACo1-XMeXO2When a Li—Co based composite oxide represented by the formula (1) is produced, a necessary amount of a substitution element compound may be added to a mixture of a lithium compound and a cobalt compound.
[0022]
In the present invention, in the first active material (Li—Co composite oxide having an average particle diameter of 7 to 13 μm) and the second active material (Li—Co composite oxide having an average particle diameter of 1 to 6 μm). The value of the average particle diameter is a volume average diameter in a number-based distribution, and is a value measured by the following measurement method.
[0023]
First, a granular material to be measured is put into an organic liquid such as water or ethanol, and an ultrasonic wave of about 35 kHz to 40 kHz is applied to perform dispersion processing for about 2 minutes. Here, the amount of the particulate matter to be measured is such that the laser transmittance (ratio of the output light amount to the incident light amount) of the dispersion liquid after the dispersion treatment is 70% to 95%. Next, this dispersion is applied to a microtrack particle size analyzer, and the particle diameters (D1, D2, D3,...) Of individual particles and the number of particles (N1, N2, N3) for each particle diameter are scattered by laser light scattering.・ ・ ・) Is measured. This particle size distribution measurement is calculated as the particle size distribution of a spherical particle group that has the theoretical intensity closest to the observed scattering intensity distribution (the particle is a cross-section with the same area as the projected image obtained by laser light irradiation). (It is assumed that the sphere has a circle, and the diameter (sphere equivalent diameter) of this cross-sectional circle is measured as the particle size).
The average particle size (μm) is calculated by the following formula from the particle size (D) of each particle and the number (N) of each particle size.
[0024]
Average particle diameter (μm) = (ΣNDThree/ ΣN)13
[0025]
In the present invention, the entire active material, that is, the mixture of the first Li—Co based composite oxide and the second Li—Co based composite oxide usually has an average particle size of 5 to 5 as defined by the above formula. In the range of 13 μm (preferably 7 to 11 μm), 10% volume diameter (D10) (particle size value in which the sum of volume ratios below a certain particle diameter is 10% with respect to the total volume ratio of all measured particles ) Is 2 to 6 μm, 90% volume diameter (D90) (the particle diameter value at which the sum of volume ratios below a certain particle diameter is 90% relative to the total volume ratio of all measured particles) is 15 to 25 μm Form a particle size distribution.
[0026]
In the present invention, the scale-like graphitized carbon having an average particle diameter of 1 to 6 μm can be either artificial or natural, but is preferably artificial because it has less impurities and gives more preferable results.
[0027]
In addition, the particle size of the flaky graphitized carbon means the diameter of a cross-sectional circle (a sphere equivalent diameter) when the flaky graphitized carbon is assumed to be a sphere, and the average particle size is the above-described Li-Co composite oxidation. It is a volume average diameter in a number-based distribution measured by a method similar to that for a product (method using a microtrack particle size analyzer).
[0028]
In addition, the particle size of carbon black having a flat particle size of 0.5 μm or less used together with scaly graphitized carbon is the diameter of a cross-sectional circle (sphere equivalent diameter) when the carbon black particles are assumed to be spheres, The average particle diameter is measured using an electron microscope. That is, first take an electron micrograph by setting the magnification so that 20 or more particles are in the field of view, then calculate the area of each particle image shown in the photograph, and then calculate the same from this calculated area. The diameter of a circle having an area is calculated, and this diameter is used as the particle diameter (assuming a particle made of a sphere having a cross-sectional circle of this diameter, and the diameter of the sphere is used as the particle diameter). ) To obtain the average particle size.
[0029]
Carbon black having an average particle size of 0.5 μm or less can be used as it is, but even if the average particle size exceeds 0.5 μm (commercial product), a known grinder (for example, wet type) It can also be used after being pulverized (further classified as required) by an ultrafine particle dispersion pulverizer or the like, and having a mean particle size of 0.5 μm or less. Preferable examples include acetylene black, oil furnace black, and Ixtra conductive furnace black. Oil furnace black is particularly preferable.
[0030]
In the positive electrode of the present invention, a slurry is prepared by mixing the specific active material and the specific conductive material, a polymer binder, and a solvent, and the slurry is applied on a current collector (one side or both sides). Then, it is produced by drying to form a composite layer, and further rolling the composite layer.
[0031]
As the polymer binder, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, ethylene-propylene-diene polymer and the like are suitable, and among these, polyvinylidene fluoride is preferred.
[0032]
The amount of the polymer binder in the composite material layer (slurry) is generally 1 to 10 parts by weight, preferably 2 to 5 parts by weight with respect to 100 parts by weight of the active material. When the polymer binder is less than 1 part by weight, the bonding between the materials constituting the composite material layer becomes insufficient, the composite material layer is lost from the current collector, and the charge / discharge characteristics are deteriorated. On the other hand, if the polymer binder exceeds 10 parts by weight, the electrical resistance value of the composite material layer (positive electrode) is increased, and the low temperature characteristics tend to be lowered, which is not preferable.
[0033]
The slurry is usually prepared by kneading an active material, a conductive material and a polymer binder together with an appropriate solvent. The solvent is not particularly limited, but N-methylpyrrolidone is preferable. Moreover, kneading | mixing is performed by conventionally well-known kneading apparatuses, such as a planetary dispa kneading apparatus (made by Asada Iron Works), for example.
[0034]
Coating of the slurry on the current collector is performed by a conventionally known coating machine of a comma roll type or a die coat type, and the slurry is dried together with the current collector with the slurry coated on the current collector. Using a drying device such as a warm air drying oven, the drying is performed at a temperature of 80 to 200 ° C., preferably 100 to 180 ° C. for 2 to 5 minutes.
[0035]
In addition, although the coating amount of the slurry varies depending on the target battery capacity, it is generally 30 to 100 mg / cm as indicated by the adhesion amount after drying per unit area of the current collector (adhesion amount of the mixture).2Degree.
[0036]
The rolling (compression) treatment of the mixed material layer after drying is performed by rolling the entire positive electrode (current collector + composite material layer) using a rolling press or the like. The rolling conditions are generally set so that the rolling temperature is 20 to 100 ° C. and the rolling rate is 10 to 60% (preferably 20 to 50%). Here, the rolling temperature is the temperature of the composite material layer, and the rolling rate is a scale representing the degree of rolling called the rolling reduction, and the thickness of the positive electrode plate (current collector + composite material layer) before rolling. Where h1 is the thickness of the positive electrode plate (current collector + mixture layer) after rolling, and h3 is the thickness of the current collector.
Rolling ratio (%) = (h1-h2) × 100 / (h1-h3) (II)
[0037]
In addition, when the temperature in a rolling process is lower than said range, it is easy to produce a crack (crack) in a compound material layer by rolling, and it is not preferable. On the other hand, when it is high, the impregnation with the electrolytic solution does not proceed sufficiently, resulting in an increase in resistance, which is not preferable. Moreover, since the positive electrode (electrode) thickness cannot be made sufficiently small when the rolling rate in the rolling process is smaller than the above range, it becomes difficult to store in a battery can of a predetermined size.
[0038]
In the positive electrode of the present invention thus obtained, the composite layer has excellent flatness in which the difference in thickness between the maximum thickness portion and the minimum thickness portion is 10 μm or less. Here, the difference in thickness between the maximum thickness portion and the minimum thickness portion means that the cross section of the positive electrode (electrode) is observed with an SEM, and a photograph is taken. The maximum thickness portion and the minimum thickness portion of the composite material layer reflected in the photograph are taken. The thickness is measured with calipers, and the difference is obtained. The photograph is taken with respect to arbitrary five cross sections of the positive electrode (electrode), and the average value of the difference in thickness between the maximum thickness portion and the minimum thickness portion at the five points is calculated.
[0039]
As the current collector used for the positive electrode of the present invention, for example, a conventional one such as a foil or an expanded metal formed of aluminum, an aluminum alloy, titanium or the like can be used. When the current collector is a foil or a perforated foil, the thickness is usually about 5 to 100 μm, preferably about 10 to 50 μm. When the current collector is an expanded metal, the thickness is usually about 25 to 300 μm, preferably about 30 to 150 μm.
[0040]
The lithium ion secondary battery of this invention is comprised using the positive electrode of this invention demonstrated above. The constituent elements of the battery other than the positive electrode such as the negative electrode, the electrolytic solution, and the separator are not particularly limited, and known ones can be used according to a conventional method.
[0041]
The negative electrode is formed by forming a layer of a composite material containing an active material and a binder on a current collector. Examples of the active material include graphites (natural and artificial), carbon black, and amorphous carbon materials. The granular carbon material currently used as an active material for negative electrodes of well-known lithium secondary batteries, such as (hard carbon, soft carbon), activated carbon, can be used. Among these, graphite is preferable, and artificial graphite (graphitized carbon) is particularly preferable. Moreover, in graphite, fibrous things other than a granular material can be used, and this fibrous graphite carbon may be linear or curled, and the size is not particularly limited, but the average fiber length is 1 to 100 μm. And those having an average fiber length of 3 to 50 μm are particularly preferred. The aspect ratio (average fiber length / average fiber diameter) of the fibrous graphitized carbon is preferably 1 to 5, particularly preferably 3 to 5.
[0042]
The size (fiber diameter, fiber length) of the fibrous graphitized carbon can be measured using an electron microscope. That is, the magnification can be set so that 20 or more fibers are in the field of view, an electron micrograph is taken, and the fiber diameter and fiber length of each fiber in the photograph are measured with a caliper or the like. The fiber length may be measured by measuring the shortest distance between one end and the other end if the fiber is linear. However, if the fiber is curled or the like, any two points on the fiber that are most distant from each other are taken, the distance between the two points is measured, and this is taken as the fiber length. The average fiber diameter and the average fiber length are the number average values of the measured numbers.
[0043]
Examples of the binder include binders conventionally used for the active material layer of the negative electrode of a lithium secondary battery, for example, fluorine resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), ethylene- Polymer materials such as propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) are used.
[0044]
The amount of active material in the negative electrode mixture layer (the amount of active material present per unit area of the current collector) is usually 3 to 30 mg / cm.2Degree, preferably 5-20 mg / cm2Degree. Moreover, the ratio of the active material and the binder in the composite layer is generally 80:20 to 98: 2 in weight ratio (active material: binder).
[0045]
The electrolyte preferably has a viscosity adjusted to 3 cps or less, and the electrolyte having a viscosity of 3 cps or less includes at least one selected from diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), ethylene carbonate (EC), It is preferably achieved by a mixed solvent of propylene carbonate (PC) and dimethyl carbonate (DMC).
[0046]
At this time, the total amount of ethylene carbonate (EC) and propylene carbonate (PC) is preferably 25% by volume or less, and the specific composition is, for example, at least one selected from diethyl carbonate and ethyl methyl carbonate. 25 vol% to 50 vol% (preferably 30 vol% to 35 vol%), ethylene carbonate 4 vol% to 20 vol% (preferably 6 vol% to 18 vol%), propylene carbonate 3 vol% to 17 vol% % (Preferably 5% by volume to 15% by volume) and dimethyl carbonate by 40% to 60% by volume (preferably 45% by volume to 55% by volume).
[0047]
In at least one selected from diethyl carbonate and ethyl methyl carbonate, if the mixing ratio is less than 25% by volume, the freezing point of the electrolyte rises, and the internal resistance of the battery is reduced particularly at a low temperature of −20 ° C. or lower. This may increase the charge / discharge cycle characteristics and low temperature characteristics, which is not preferable. On the other hand, when the mixing ratio exceeds 50% by volume, the viscosity of the electrolytic solution is increased to increase the internal resistance of the battery, and the charge / discharge cycle characteristics are deteriorated.
[0048]
In ethylene carbonate, if the mixing ratio is less than 4% by volume, it is difficult to form a stable film on the surface of the negative electrode plate, and cycle characteristics may be deteriorated. Moreover, when the said mixing ratio exceeds 20 volume%, the viscosity of electrolyte solution rises, the internal resistance of a battery is increased, and a charge / discharge cycle characteristic may fall, and it is unpreferable.
[0049]
In the case of propylene carbonate, if the mixing ratio is less than 3% by volume, the effect of suppressing an increase in impedance associated with the charge / discharge cycle is reduced, and cycle characteristics may be deteriorated. If the mixing ratio exceeds 17% by volume, the viscosity of the electrolytic solution is increased, the internal resistance of the battery is increased, and charge / discharge cycle characteristics are deteriorated.
[0050]
In dimethyl carbonate, if the mixing ratio is less than 40% by volume, the viscosity of the electrolytic solution increases, the internal resistance of the battery is increased, and charge / discharge cycle characteristics are deteriorated. When the mixing ratio exceeds 60% by volume, the volatilization of the electrolytic solution easily proceeds and the high temperature characteristics tend to deteriorate, which is not preferable.
[0051]
Examples of the lithium salt dissolved in the electrolyte include LiClO.Four, LiBFFour, LiPF6, LiAsF6LiAlClFour, Li (CFThreeSO2)2N etc. are mentioned. Among these, only 1 type may be used and 2 or more types may be used. Of these, LiPF has a large dissociation constant, high thermal stability, and low toxicity.6Is preferably used.
[0052]
It can be said that increasing the lithium salt dissolved in the electrolytic solution is effective in terms of increasing the limit current density at room temperature or higher. However, salt dissociation is limited at low temperatures. Therefore, even if the amount of lithium salt is increased, it is not possible to expect an increase in the amount of lithium salt that is effective for carrying the charge. Conversely, the viscosity of the electrolyte is increased and the diffusion rate of lithium ions is decreased, resulting in low temperature characteristics. Will be reduced. Therefore, the electrolyte solution should be prepared so that the concentration of the lithium salt is 0.5 mol / L to 1.5 mol / L, preferably 0.7 mol / L to 1.2 mol / L.
[0053]
As the separator, a known separator conventionally used in lithium secondary batteries such as a polyolefin separator is used. Here, the separator may be a porous one or a separator (solid separator) in which pores are not substantially formed. The polyolefin separator may be a single polyethylene (PE) layer or a single polypropylene (PP) layer, but a type in which a polyethylene layer and a polypropylene layer are laminated is preferable. In the case of the laminated type, the number of laminated layers and the laminated pattern are not particularly limited, but a three-layer type such as PP / PE / PP is preferable from the viewpoint of preventing internal short circuit at a higher level. Although the thickness of a separator changes also with the form of a battery, generally it is about 10-50 micrometers. In the present invention, even when a separator having a relatively thin thickness of about 15 to 30 μm is used to reduce the size (thinner) of the battery, the occurrence of an internal short circuit can be sufficiently prevented.
[0054]
The form of the battery is not particularly limited. Conventionally used lithium secondary batteries can be used, for example, cylindrical cans, rectangular cans, button-like cans made of metal such as Fe, Fe (Ni plating), SUS, aluminum, aluminum alloy, etc. Alternatively, a sheet-like exterior material such as a laminate film is used. The laminate film is preferably one in which a thermoplastic resin laminate layer such as polyester or polypropylene is formed on at least one surface of a metal foil such as copper or aluminum.
[0055]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
[Positive electrode]
LiCoO with an average particle size of 10 μm2(First active material) 65 parts by weight of LiCoO having an average particle size of 5 μm2(Second active material) 28 parts by weight, 3 parts by weight of scaly graphitized carbon (first conductive material) having an average particle diameter of 2 μm, and oil furnace black (second conductive material) having an average particle diameter of 40 nm (0.04 μm) Material) 1 part by weight and 3 parts by weight of polyvinylidene fluoride (binder) are kneaded (mixed) with N-methyl-2-pyrrolidone as a dispersion solvent to prepare a slurry, and the slurry is a current collector It is applied onto both sides of an aluminum foil (width 55 mm, length 600 mm), dried to form a composite layer, and further subjected to a rolling treatment (rolling temperature: 30 ° C., rolling rate: 40%), so that the total thickness is A 150 μm positive electrode was completed.
[0056]
[Negative electrode]
100 parts by weight of graphitized carbon fiber (average fiber diameter 8 μm) as an active material and 5 parts by weight of polyvinylidene fluoride as a binder are mixed with N-methyl-2-pyrrolidone as a dispersion solvent to form a slurry, This slurry was applied to both sides of a copper foil having a width of 57 mm and a length of 600 mm to be a current collector, dried to form a composite layer, and further subjected to a rolling treatment to complete a negative electrode having a total thickness of 150 μm. .
[0057]
[Assembly of lithium secondary battery]
LiPF was added to a mixed solvent composed of 4% by volume of diethyl carbonate, 29% by volume of ethyl methyl carbonate, 9% by volume of propylene carbonate, 11% by volume of ethylene carbonate, and 47% by volume of dimethyl carbonate.6Was dissolved at 1 mol / L to prepare an electrolytic solution. Then, the prepared positive electrode and negative electrode are wound through a polypropylene-polyethylene composite separator (overall thickness 20 μm, laminated configuration PP / PE / PP), and this is wound into a cylindrical battery can (outer diameter 18 mm, inner diameter 17. 5 mm, height 65 mm), and thereafter, an electrolyte was impregnated between the positive electrode and the negative electrode to complete a lithium secondary battery.
[0058]
Example 2
The first active material is LiCoO having an average particle size of 8 μm.2In 65 parts by weight, the second active material is LiCoO having an average particle diameter of 3 μm.2A positive electrode having an overall thickness of 150 μm was produced in accordance with Example 1 except that the content was changed to 28 parts by weight. A battery was fabricated in the same manner as in Example 1 except for this positive electrode.
[0059]
Example 3
First active material (LiCoO having an average particle size of 10 μm2) Was changed to 79 parts by weight, and the second active material (LiCoO having an average particle size of 5 μm) was changed.2) Was changed to 14 parts by weight, and a positive electrode having an overall thickness of 150 μm was produced in accordance with Example 1. A battery was fabricated in the same manner as in Example 1 except for this positive electrode.
[0060]
Example 4
First active material (LiCoO having an average particle size of 10 μm2) Was changed to 43 parts by weight, and the second active material (LiCoO having an average particle size of 5 μm)2) Was changed to 50 parts by weight, respectively, and a positive electrode having an overall thickness of 150 μm was produced in accordance with Example 1. A battery was fabricated in the same manner as in Example 1 except for this positive electrode.
[0061]
Comparative Example 1
LiCoO with an average particle size of 20 μm as the active material291 parts by weight, 5 parts by weight of spherical graphitized carbon (first conductive material) having an average particle diameter of 6 μm and oil furnace black (second conductive material) having an average particle diameter of 40 nm (0.04 μm) as the conductive material A positive electrode having an overall thickness of 150 μm was prepared in the same manner as in Example 1 except that 1 part by weight was used. A battery was fabricated in the same manner as in Example 1 except for this positive electrode.
[0062]
Comparative Example 2
A positive electrode having an overall thickness of 150 μm was prepared in accordance with Example 1 except that the first conductive material was changed to 3 parts by weight of spherical graphitized carbon having an average particle diameter of 6 μm. A battery was fabricated in the same manner as in Example 1 except for this positive electrode.
[0063]
Comparative Example 3
A positive electrode having an overall thickness of 150 μm was prepared in accordance with Example 1, except that the first conductive material was changed to 3 parts by weight of massive graphitized carbon having an average particle diameter of 5 μm. A battery was fabricated in the same manner as in Example 1 except for this positive electrode. Here, the “bulky” of massive graphitized carbon means a massive having irregularities on the surface such as rocks.
[0064]
Comparative Example 4
Instead of using oil furnace black (second conductive material) having an average particle size of 40 nm (0.04 μm), the amount of scaly graphitized carbon (first conductive material) having an average particle size of 2 μm is 4 parts by weight. A positive electrode having an overall thickness of 150 μm was produced in accordance with Example 1 except that the thickness was changed to. A battery was fabricated in the same manner as in Example 1 except for this positive electrode.
[0065]
An evaluation test was conducted on the lithium ion secondary batteries produced in the above examples and comparative examples. The results are shown in Table 1. The rolling load (t / cm) in Table 1 is a value obtained by dividing the load (T) applied to the electrode (positive electrode) during rolling by the electrode width (W), and the rolling load is attached to the rolling device. It was obtained from a rolling load meter. The electrode width (W) is a width in a direction orthogonal to the traveling direction of the electrode (axial direction of the rolling roll). It means that the smaller the rolling load, the smaller the load applied to the positive electrode (electrode) during rolling and the better the workability.
[0066]
[Battery initial capacity]
Under an environment of 20 ° C., after constant current-constant voltage charge (2000 mA, 4.2 V), constant current discharge (400 mA, cut-off voltage: 3 V) is performed, and capacity [mA · H] is obtained from discharge time × current. .
[0067]
[Low temperature characteristics test]
After charging at room temperature, this is left in an atmosphere of −20 ° C. for 6 hours. The charging here is the same as that in the measurement of the initial capacity. Next, discharge is performed in this air atmosphere at −20 ° C. with a 1 C (2000 mAh) / 3 V cut-off, and the discharge capacity [mA · H] is obtained from the discharge time × current at that time.
[0068]
[Internal short test]
100 batteries are fully charged to 4.2 V and left for 2 weeks, and the voltage after being left is measured. The number of such batteries is defined as n1 as a cut-off reference (the voltage after being left is 4 V or less). Then, assuming that the average voltage of (100−n1) batteries is Vn, the number n2 of batteries having a voltage 10mV lower than Vn is used, and the defect rate (= internal short circuit occurrence rate) is calculated by the following formula.
Defective rate (%) = [(n1 + n2) / 100] × 100
[0069]
[Nail penetration test (safety test)]
The battery is charged at 1.5 A until the voltage reaches 4.3 V. Immediately after charging, a nail with an outer diameter of 3 mm is moved at a speed of 4 cm / second around the center between the positive electrode terminal and the negative electrode terminal of each lithium ion secondary battery. A safety test was conducted to penetrate through the battery and examine the number of fires in ten. Of the 10 samples, one that ignited was rejected (x), and one that did not ignite 10 was determined to be acceptable (O).
[0070]
The above test results are shown in Table 1 below.
[0071]
[Table 1]
[0072]
In the table, (foil breakage) in the rolling load of Comparative Examples 1 and 2 means that the foil was cut or damaged during the rolling process.
[0073]
【The invention's effect】
As is clear from the above description, by using the positive electrode for the lithium ion secondary battery of the present invention, it exhibits high capacity and excellent low temperature characteristics, and is also highly efficient and has an internal short circuit and an abnormal reaction. A highly reliable lithium secondary battery can be realized.

Claims (2)

  1. A positive electrode for a lithium ion secondary battery, which is formed by forming a mixture layer containing an active material, a conductive material and a binder on a current collector,
    Active material has an average particle size of the L iC o O 2 of 7~13μm and an average particle size of 1~6μm L iC o O 2 1: in a proportion of 0.1 to 1.5 (weight ratio) A mixture of
    The conductive material is a mixture containing scaly graphitized carbon having an average particle diameter of 2 to 3 μm and carbon black having an average particle diameter of 0.5 μm or less in a ratio (weight ratio) of 100 : 1 to 3: 1 . ,
    A positive electrode for a lithium secondary battery, wherein a ratio (weight ratio) between an active material and a conductive material is 1: 0.01 to 0.1.
  2.   A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution, wherein the positive electrode comprises the positive electrode according to claim 1. .
JP2002057076A 2002-03-04 2002-03-04 Positive electrode for lithium ion secondary battery and lithium ion secondary battery using the positive electrode Expired - Fee Related JP4025094B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2002057076A JP4025094B2 (en) 2002-03-04 2002-03-04 Positive electrode for lithium ion secondary battery and lithium ion secondary battery using the positive electrode

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2002057076A JP4025094B2 (en) 2002-03-04 2002-03-04 Positive electrode for lithium ion secondary battery and lithium ion secondary battery using the positive electrode

Publications (2)

Publication Number Publication Date
JP2003257416A JP2003257416A (en) 2003-09-12
JP4025094B2 true JP4025094B2 (en) 2007-12-19

Family

ID=28667432

Family Applications (1)

Application Number Title Priority Date Filing Date
JP2002057076A Expired - Fee Related JP4025094B2 (en) 2002-03-04 2002-03-04 Positive electrode for lithium ion secondary battery and lithium ion secondary battery using the positive electrode

Country Status (1)

Country Link
JP (1) JP4025094B2 (en)

Families Citing this family (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU2003266620A1 (en) 2002-09-26 2004-04-19 Seimi Chemical Co., Ltd. Positive electrode active substance for lithium secondary battery and process for producing the same
KR100548988B1 (en) * 2003-11-26 2006-02-02 학교법인 한양학원 Manufacturing process of cathodes materials of lithium second battery, the reactor used therein and cathodes materials of lithium second battery manufactured thereby
JP4639775B2 (en) * 2004-11-26 2011-02-23 パナソニック株式会社 Nonaqueous electrolyte secondary battery
KR20060091486A (en) 2005-02-15 2006-08-21 삼성에스디아이 주식회사 Cathode active material, method of preparing the same, and cathode and lithium battery containing the material
JP5176356B2 (en) * 2006-04-21 2013-04-03 住友化学株式会社 Positive electrode powder and positive electrode mixture
US20090104526A1 (en) * 2006-04-21 2009-04-23 Kazuyuki Tanino Powder for positive electrode and positive electrode mix
KR100907621B1 (en) * 2006-08-28 2009-07-15 주식회사 엘지화학 A positive electrode mixture containing a conductive material of two components and a lithium secondary battery composed of it
KR100834053B1 (en) 2006-09-29 2008-06-02 한양대학교 산학협력단 Cathode, and lithium secondary battery and hybrid capacitor comprising same
JP2008159410A (en) * 2006-12-25 2008-07-10 Matsushita Electric Ind Co Ltd Cathode plate for nonaqueous secondary battery, and nonaqueous secondary battery using this
KR101123060B1 (en) 2007-07-23 2012-03-15 주식회사 엘지화학 High Power Secondary Battery
JP5205090B2 (en) * 2008-03-19 2013-06-05 日立ビークルエナジー株式会社 Positive electrode for lithium secondary battery and lithium secondary battery using the same
JP5254722B2 (en) * 2008-09-25 2013-08-07 日立ビークルエナジー株式会社 lithium secondary battery
CN102447107A (en) * 2011-10-17 2012-05-09 江苏科捷锂电池有限公司 High density lithium ion battery cathode material lithium cobalt oxide and preparation method thereof
CN102683743A (en) * 2012-06-28 2012-09-19 上海广为美线电源电器有限公司 High-power lithium oil battery
JP6105224B2 (en) * 2012-08-09 2017-03-29 東洋インキScホールディングス株式会社 Primer composition, nickel metal hydride secondary battery positive electrode and method for producing the same
JP2014123529A (en) * 2012-12-21 2014-07-03 Jfe Mineral Co Ltd Positive electrode material for lithium secondary battery
CN103904310A (en) * 2012-12-28 2014-07-02 北京当升材料科技股份有限公司 Preparation method for mixed nickel-cobalt-lithium manganate material
CN105474435A (en) * 2013-06-21 2016-04-06 卡博特公司 Active materials for lithium ion batteries
JP6456630B2 (en) * 2013-09-18 2019-01-23 株式会社東芝 Non-aqueous electrolyte battery
KR20160017364A (en) 2014-08-05 2016-02-16 삼성에스디아이 주식회사 Positive electrode composition for rechargeable lithium battery, and positive electrode for rechargeable lithium battery and rechargeable lithium battery including the same
KR20170009097A (en) * 2015-07-15 2017-01-25 주식회사 엘지화학 Cathode improved conductivity and electrochemical device including the same
US10128508B2 (en) 2015-12-09 2018-11-13 Lg Chem, Ltd. Positive electrode material slurry for lithium secondary battery including at least two conductive materials and lithium secondary battery using the same

Also Published As

Publication number Publication date
JP2003257416A (en) 2003-09-12

Similar Documents

Publication Publication Date Title
JP6465538B2 (en) Method for producing solid solution lithium-containing transition metal oxide, method for producing positive electrode for nonaqueous electrolyte secondary battery, and method for producing nonaqueous electrolyte secondary battery
EP2648249B1 (en) Negative active material, lithium battery including the material, and method for manufacturing the material
EP3096379B1 (en) Negative electrode material for nonaqueous electrolyte secondary batteries and method for producing negative electrode active material particles
JP5861208B2 (en) Positive electrode active material for improving output and lithium secondary battery including the same
KR101668974B1 (en) Active material particles and use of same
JP5300502B2 (en) Battery active material, non-aqueous electrolyte battery and battery pack
US8748036B2 (en) Non-aqueous secondary battery
JP5162825B2 (en) Negative electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery using the same
JP4717847B2 (en) Positive electrode active material and lithium secondary battery including the same
JP4626105B2 (en) Lithium ion secondary battery
JP5737596B2 (en) Secondary battery
JP5348706B2 (en) Negative electrode for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery using the same, and method for producing negative electrode for nonaqueous electrolyte secondary battery
JP5812357B2 (en) secondary battery
JP4274090B2 (en) Graphite powder and non-aqueous electrolyte secondary battery
KR101215416B1 (en) Cathode materials for lithium batteries
JP3585122B2 (en) Non-aqueous secondary battery and its manufacturing method
RU2315395C1 (en) High-capacity secondary lithium battery
KR101730956B1 (en) Negative active material, manufacturing method thereof, and lithium battery containing the material
US9673436B2 (en) Nonaqueous electrolyte secondary battery
JPWO2012001840A1 (en) Negative electrode for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery
EP2819226A1 (en) Positive-electrode material for nonaqueous-electrolyte secondary battery, manufacturing method therefor, and nonaqueous-electrolyte secondary battery using said positive-electrode material
KR100783293B1 (en) Cathode Active Material and Lithium Secondary Battery Containing the Same
KR20100071941A (en) Lithium secondary battery having high power
EP2579363A1 (en) Negative electrode for secondary battery, and process for production thereof
KR101471795B1 (en) Nonaqueous electrolyte lithium secondary battery

Legal Events

Date Code Title Description
A621 Written request for application examination

Free format text: JAPANESE INTERMEDIATE CODE: A621

Effective date: 20050222

A977 Report on retrieval

Free format text: JAPANESE INTERMEDIATE CODE: A971007

Effective date: 20070413

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20070522

A521 Written amendment

Free format text: JAPANESE INTERMEDIATE CODE: A523

Effective date: 20070720

TRDD Decision of grant or rejection written
A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

Effective date: 20070904

A61 First payment of annual fees (during grant procedure)

Free format text: JAPANESE INTERMEDIATE CODE: A61

Effective date: 20071004

R150 Certificate of patent or registration of utility model

Free format text: JAPANESE INTERMEDIATE CODE: R150

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20101012

Year of fee payment: 3

LAPS Cancellation because of no payment of annual fees