JP2011076822A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance safety of a lithium ion secondary battery. <P>SOLUTION: A negative electrode of the lithium ion secondary battery is made of a negative active material layer and a current collector. The negative active material layer contains, as the main component, carbon in which a spacing of (002) planes d<SB>002</SB>measured with an X-ray diffraction device (XRD) is 0.340-0.390 nm, and the volume resistivity of the negative active material layer is 1×10<SP>-1</SP>to 1×10<SP>2</SP>Ωcm. Alternatively, carbon in which a spacing of (002) planes d<SB>002</SB>measured with the X-ray diffraction device (XRD) is not less than 0.3348 nm and less than 0.340 nm is contained as the main component, and the volume resistivity of the negative active material layer is 1×10<SP>-2</SP>to 1×10<SP>2</SP>Ωcm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery.

  With the development of mobile phones and notebook PCs in the 1980s and 1990s, secondary batteries have been improved in performance as power sources for them. As the secondary battery, a lithium ion secondary battery having a higher energy density is mainly used than a lead storage battery or a nickel cadmium battery.

  A non-aqueous solvent is mainly used for the electrolytic solution of the lithium ion secondary battery. Therefore, it is important to ensure safety so that the battery does not run out of heat even if overcharge, heating, short circuit, etc. occur, and the battery does not burst and ignite. As a technique for preventing an internal short circuit and improving reliability, in Japanese Patent Application Laid-Open No. 2004-39558 (Patent Document 1), a volume resistivity at −20 ° C. or more and −20 ° C. to 60 ° C. is applied to the positive and negative electrodes. It is disclosed to provide a conductive material that is at least 2.5 times the rate. As a result, a rapid temperature rise due to a short circuit current is suppressed.

  Japanese Patent Laying-Open No. 2005-011043 (Patent Document 2) discloses that a porous film made of a filler and a resin binder is bonded to at least one surface of a positive electrode and a negative electrode.

JP 2004-39558 A JP 2005-011043 A

  As in the cited document 1, the shutdown mechanism in which the short-circuit current cannot be suppressed unless the temperature becomes high has no effect of mildly generating heat at room temperature. Therefore, even if the current can hardly flow at 100 to 200 ° C. or less, sudden heat generation causes continuous heat generation when the positive electrode, the negative electrode, or the electrolyte reaches a temperature at which it self-heats, and thermal runaway occurs. There is a risk of it.

  As in Patent Document 2, the technique of providing an insulating layer on the negative electrode surface has no effect in the case of a short circuit caused by a foreign matter that breaks through the portion of the insulating layer. In addition, the insulating layer becomes a capacity loss.

  Accordingly, an object of the present invention is to study other methods for preventing thermal runaway and to improve the safety of lithium ion secondary batteries.

  A lithium ion secondary battery includes a positive electrode that occludes and releases lithium ions, a negative electrode that occludes and releases lithium ions, and an organic electrolyte solution in which an electrolyte containing lithium ions is dissolved. Has been placed. The negative electrode of the lithium ion secondary battery includes a negative electrode active material layer and a current collector. The lithium ion secondary battery of the present invention that solves the above problems is to apply a substance that increases resistance to the negative electrode active material, or to mix a substance that increases resistance to the negative electrode active material layer.

The volume resistivity of the negative electrode active material layer is 1 × 10 ⁻¹ to 1 × in the case of a carbon material (amorphous carbon) in which the interplanar spacing d ₀₀₂ of the carbon (002) plane is 0.340 to 0.390 nm. 10 ² Ω · cm, the surface spacing d ₀₀₂ of carbon (002) plane in the case of carbon material (graphite) is less than 0.3348 or more 0.340nm to ^{1 × 10 -2 ~1 × 10 2} Ω · cm It is preferable. By using the negative electrode active material layer in such a range, even when an internal short circuit occurs, the short circuit current can be suppressed, which contributes to the improvement of reliability.

  According to said structure, the reliability of a lithium ion secondary battery can be improved and it can be used conveniently for electronic devices, such as a mobile telephone and a notebook PC, a hybrid vehicle, and an electric vehicle.

Sectional drawing of a lithium ion secondary battery.

  A lithium ion secondary battery has a positive electrode and a negative electrode that reversibly occlude and release lithium ions, and the positive electrode and the negative electrode are arranged to face each other with a separator interposed therebetween. The positive and negative electrodes are each composed of an active material layer and a current collector for each of the positive and negative electrodes. Further, the battery includes an electrolytic solution that is inserted into a container such as a battery can and in which an electrolyte containing lithium is dissolved in a non-aqueous solvent.

  When the battery is crushed or foreign matter is mixed between the positive and negative electrodes, the positive electrode and the negative electrode may break through the separator and contact each other in the battery, causing an internal short circuit. When an internal short circuit occurs, a large current flows and the battery may burst or generate heat. In addition, in the case of overcharge, heating, short circuit, etc., there is a risk of battery heat generation or explosion.

As negative electrode active materials for lithium ion secondary batteries, lithium metal, alloys, and carbon materials are known. In lithium metals and alloys, dendrites are deposited as the charge and discharge cycles are repeated, but carbon materials do not have this problem and have good cycle characteristics and high safety. As the negative electrode active material, a carbon material (amorphous carbon) having an interplanar spacing d ₀₀₂ of 0.340 to 0.390 nm determined by X-ray diffractometer (XRD) measurement, or carbon ( 002) surface plane spacing d ₀₀₂ of used carbon material (graphite) is less than 0.3348 or more 0.340 nm. In the d ₀₀₂ is more than 0.390 nm, the irreversible capacity of the first increases, unfavorably the battery capacity decreases.

  A flammable non-aqueous solvent is mainly used for the electrolyte of the lithium ion secondary battery. Therefore, when a non-aqueous solvent is used, it is necessary to take measures to improve safety even if the negative electrode active material is a carbon material.

  The inventors of the present application have found that it is important to increase the volume resistivity of the negative electrode and suppress current at room temperature when an internal short circuit occurs in order to improve safety. This is because the carbon material used for the negative electrode has higher electron conductivity than the positive electrode material, and a large current flows when contact between the negative electrode and the can or the positive electrode occurs.

Therefore, the volume resistivity of the negative electrode active material layer is increased. A carbon material (amorphous carbon) having an interplanar spacing d ₀₀₂ of 0.340 to 0.390 nm obtained by X-ray diffractometer (XRD) measurement as a negative electrode active material, or carbon (002) Carbon having a surface spacing d ₀₀₂ of 0.3348 or more and less than 0.340 nm is used. In the former case, the resistance value of the negative electrode active material layer is 1 × 10 ⁻¹ or more, and in the latter case, 1 × 10 ^−2. By setting it as the above, the effect of sufficient short circuit current suppression is acquired. On the other hand, if the resistance value exceeds 1 × 10 ² Ω · cm, the electronic resistance becomes too high and the battery resistance increases, so it is preferable to adjust within the above range.
In particular, the volume resistivity of the negative electrode active material layer is preferably 1 × 10 ^{−1 to} 1 × 10 ¹ Ω · cm, more preferably 5 × 10 ^{−0 to} 1 × 10 ¹ Ω · cm. By setting it as such a volume resistivity, the short circuit current at the time of an internal short circuit can be suppressed.

  Examples of means for increasing the volume resistivity of the negative electrode include a method of coating the surface of the carbon active material and a method of adding a resistor to the negative electrode active material layer. The material to be coated and added is preferably a material that does not alloy with lithium ions. A material that is alloyed with lithium ions easily expands when alloyed, and when such a material is used, the cycle characteristics may deteriorate.

It is preferable to coat the surface of the main carbon material using a material having a high volume resistivity and not alloyed with lithium ions. The main material in which the volume resistivity of the carbon of the negative electrode active material d ₀₀₂ is 1 × 10 ^-1 or more 1 × 10 ² Ω · cm or less in the case of carbon 0.390nm than 0.340, d ₀₀₂ is 0.3348 In the case of carbon that is greater than or equal to 0.340 nm and greater than or equal to 1 × 10 ⁻² and less than or equal to 1 × 10 ² Ω · cm By setting it as this range, it is easy to adjust the volume low efficiency of the negative electrode active material layer to the above range. If the volume resistivity of the negative electrode active material layer is smaller than the above range, the effect of suppressing the short circuit current is small, and if the resistivity is large, the battery resistance is undesirably increased.

The material covering the carbon surface is preferably a material having a volume resistivity of 5 × 10 ⁴ Ω · cm to 10 ⁻¹ Ω · cm. When a carbon material is coated, it is suitable for adjusting to a resistance value in the above range, and the cost for performing the coating process is less likely to be required. It is preferable that the film thickness of the surface coating layer is 0.1% or more and 1% or less with respect to the cumulative 50% particle size (50% D) of the negative electrode active material. When it is less than 0.1%, it is difficult to uniformly cover the surface. Moreover, in the range exceeding 1%, the thickness of the resistance becomes too thick, and the resistance value may increase too much.

Examples of the raw material for coating the carbon surface include oxides such as CaO, Sc ₂ O ₃ , SrO ₂ , SnO ₂ , BaO, La ₂ O ₃ , Nd ₂ O ₃ , WO ₃ , Al ₂ O ₃ , and SiO ₂ . Alternatively, a nitride such as AlN, GaN, SiN, or a mixture thereof can be used. As a method for coating the carbon surface, for example, a coating method from a solution, a vapor deposition method, a Langmuir Blodget (LB) method, an electrolytic polymerization method, a plasma polymerization method, a CVD (chemical vapor deposition) method, a sputtering method, or the like is used. Can do.

Another method for increasing the volume resistivity of the negative electrode includes adding (mixing) a resistor to the negative electrode active material layer in place of or in addition to the coating material. As the resistor, a material having a high volume resistivity and not alloyed with lithium ions is used as in the case of the coating layer, and particles are preferable. For example, resin beads made of acrylic resin, polycarbonate resin, urethane resin, melamine resin, etc., glass beads made of glass such as soda glass, potassium glass, borosilicate glass, or CaO, Sc ₂ O ₃ , SrO ₂ , SnO ₂ , Examples thereof include oxides such as BaO, La ₂ O ₃ , Nd ₂ O ₃ , WO ₃ , Al ₂ O ₃ and SiO ₂ , nitrides such as AlN, GaN and SiN, and mixtures thereof. Both coating of the carbon material and mixing of the carbon material and resistor particles may be performed.

  The addition amount of the resistor is preferably 30 parts by weight or more and 50 parts by weight or less with respect to the negative electrode active material. If it is less than 30 parts by weight, there is a possibility that a conductive path is formed depending on the mixed state and the resistance becomes low, and if it exceeds 50 parts by weight, the battery capacity becomes too low.

  As a method of mixing the resistors, in addition to being uniformly dispersed in the negative electrode active material layer, a difference in content may be provided in the layer. It is not necessary to make the addition amount of the resistor uniform in the negative electrode active material layer. In particular, it is preferable to reduce the content of the resistor on the side in contact with the current collector as compared with the negative electrode surface side of the negative electrode active material layer. The effect of suppressing the short circuit current can be enhanced by adopting a configuration in which the amount of the resistor added is smaller on the interface side in contact with the current collector than on the negative electrode surface side. In addition, it is possible to increase the battery capacity by providing an active material layer in which no resistor is added to the active material layer without dispersing the resistor in the entire active material layer. The negative electrode active material layer can be realized by a multilayer structure composed of a plurality of layers in which the mixing ratio of the active material and the resistor is changed, or by changing the resistor dispersion method by heat treatment or the like. For example, the active material layer on the side in contact with the current collector is preferably provided with a layer that does not include the resistor. It is preferable that the negative electrode active material layer includes at least two layers, the current collector side layer does not include a resistor, and the resistor is mixed with the negative electrode surface side layer. Moreover, a high effect can be obtained by reducing the amount on the interface side in contact with the current collector with respect to the negative electrode surface side.

  The volume resistivity of the active material layer is measured by, for example, a method in which a metal electrode is formed between the active material layers and evaluated by a direct current four-terminal method, or a four-probe method using a resistivity measuring device. In addition, the volume resistivity of the carbon material is measured using, for example, a powder resistance measuring device with appropriate pressure applied.

(Negative electrode)
The method for producing the negative electrode carbon material for a lithium ion secondary battery of the present invention is not particularly limited. For example, an easily carbonized material obtained from natural carbon, petroleum coke, coal pitch coke, or the like is heat-treated at a high temperature of 1000 to 3000 ° C. And those that have been pulverized by heat-treating the thermoplastic resin, naphthalene, anthracene, phenanthrolen, coal tar, tar pitch, etc. in advance using an autoclave or other equipment and then calcining in an inert atmosphere at 800 ° C or higher. It is done. Any material can be pulverized to adjust the particle size, and then pulverized and classified to further adjust the particle size, thereby producing a carbon material.

  The negative electrode carbon material of the present invention preferably has a cumulative 50% particle size (50% D) determined by a laser diffraction / scattering particle size distribution analyzer of 3 μm to 30 μm, particularly preferably 3 μm to 25 μm. Particularly, it is preferably 5 μm or more and 20 μm or less. When the average particle size exceeds 30 μm, the electrodes are likely to be uneven, so that the battery characteristics are deteriorated and the ion diffusion length into the active material is long, so that there is a problem in the charge / discharge characteristics, less than 3 μm In the case of, there is a problem that it is difficult to increase the density because it is difficult to be crushed. The particle size distribution can be measured with a laser diffraction particle size distribution analyzer by dispersing a sample in purified water containing a surfactant, and the average particle size is calculated as 50% D.

Further, the negative electrode carbon material of the present invention has a specific surface area of 1 m ² / g or more and 10 m ² / g or less obtained from an adsorption isotherm obtained by 77K nitrogen adsorption measurement using the BET (Brunauer-Emmet-Teller) method. Is preferred. If it is less than 1 m ² / g, the reaction area between the active material and lithium ions decreases, so the charge / discharge characteristics deteriorate, and if it exceeds 10 m ² / g, reaction with the electrolyte tends to occur. The irreversible capacity increases and the life characteristics deteriorate.

  The method for producing the negative electrode is not particularly limited. For example, a solvent in which a binder is further dissolved or dispersed in the coated negative electrode active material, using a general kneading dispersion method such as a ball mill or a planetary mixer, Thoroughly knead and disperse, or use a common kneading and dispersing method such as ball mill, planetary mixer, etc. to dissolve or disperse the resistor and binder in the negative electrode carbon, and then mix and disperse the negative electrode mixture slurry. Create After that, the negative electrode mixture slurry is coated on a metal foil such as copper using a coating machine, and then vacuum-dried at an appropriate temperature of, for example, about 120 ° C. After compression molding using a press machine to a desired size. It can be cut or punched into a negative electrode.

  Although it does not specifically limit as a solvent at the time of producing a coating material, For example, N-methyl- 2-pyrrolidone (NMP), ethylene glycol, toluene, xylene etc. are mention | raise | lifted.

  The above-mentioned organic binder is not particularly limited as the above-mentioned binder. For example, styrene-butadiene copolymer, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meta ) Ethylenically unsaturated carboxylic acid esters such as acrylonitrile, hydroxyethyl (meth) acrylate, ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, polyvinylidene fluoride, polyethylene oxide, Examples thereof include high molecular compounds having high ionic conductivity such as polyepichlorohydrin, polyphosphazene, and polyacrylonitrile. The content of the organic binder is preferably 1 part by weight or more and 15 parts by weight or less with respect to 100 parts by weight in total of the negative electrode material for a lithium ion secondary battery of the present invention and the organic binder. If it is less than 1 part by weight, the electrode may be peeled off, and if it is above 15 parts by weight, the direct current resistance (DCR) may increase.

As will be described later, the above-described coating material and resistor are mixed, and the volume resistivity of the negative electrode active material layer is set to be a carbon (002) plane spacing d _{002 of} not less than 0.340 and not more than 0.390 nm. In the case of a material (amorphous carbon), a carbon material (graphite) having 1 × 10 ⁻¹ to 1 × 10 ² Ω · cm and a carbon (002) plane spacing d ₀₀₂ of 0.3348 or more and less than 0.340 nm In this case, it is preferably 1 × 10 ⁻² to 1 × 10 ² Ω · cm. By using the negative electrode active material layer in such a range, even when an internal short circuit occurs, the short circuit current can be suppressed, which contributes to the improvement of reliability.

(Positive electrode)
In preparing the positive electrode, a binder dissolved or dispersed in an appropriate solvent is added to the positive electrode active material and kneaded and dispersed using a general kneading and dispersing method such as a ball mill or a planetary mixer. An agent slurry is prepared. Thereafter, this positive electrode mixture slurry can be vacuum-dried at 120 ° C. after being applied onto a metal foil such as aluminum using a coating machine, and then cut or punched into a desired size after compression molding to obtain a positive electrode. .

In preparing the positive electrode, it is preferable to add a conductive aid if necessary for reducing DCR. Although it does not specifically limit as a conductive support agent, For example, amorphous carbon, such as powder carbon, scale-like carbon, or carbon black which has high electroconductivity, may be used. The content of the conductive assistant is preferably 0 to 15 parts by weight with respect to a total of 100 parts by weight of the negative electrode material for a lithium ion secondary battery and the conductive auxiliary of the present invention.
When it exceeds 15 parts by weight, the DCR reduction effect is small and only the capacity is significantly reduced.

As the positive electrode active material, a composite compound of lithium and a transition metal having a crystal structure such as spinel cubic, layered hexagonal, olivine orthorhombic or triclinic is used. From the viewpoint of high output and long life, a layered hexagonal crystal containing at least lithium, nickel, manganese, and cobalt is preferable, and LiMn _a Ni _b Co _cmd O ₂ is particularly preferable. (However, M is at least one selected from the group consisting of Fe, V, Ti, Cu, Al, Sn, Zn, Mg, and B, preferably Al, B, Mg). 0 ≦ a ≦ 0.6 , 0.3 ≦ b ≦ 0.7, 0 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.1. The positive electrode active material preferably has an average particle size of 10 μm or less.

(Electrolyte)
The electrolytic solution preferably has a linear or cyclic carbonate as a main component as a solvent, and can be mixed with esters, ethyls, and the like. Examples of carbonates include ethylene carbonate (EC), propylene carbonate, butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate, diethyl carbonate, and the like. These are used alone or in a mixed solvent.

The lithium salt of the electrolytic solution supplies lithium ions that move through the electrolytic solution by charging / discharging the battery. LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF _6, etc. are used alone or in combination. Can be used. The electrolyte concentration is preferably 0.7 or more and 1.5M, and if it is out of the above range, the DCR tends to increase.

  You may add the cyclic carbonate containing an unsaturated group to electrolyte solution. Examples of the cyclic carbonate containing an unsaturated group include vinylene carbonate and vinyl ethylene carbonate. The amount added is preferably 0.1 parts by weight or more and 5 parts by weight or less, assuming that the total weight of the electrolytic solution is 100 parts by weight. If the amount is less than the above range, the effect cannot be seen. If the amount is more than the above range, the DCR tends to increase.

  The separator is not particularly limited as long as it can prevent a short circuit between the positive electrode and the negative electrode. For example, a nonwoven fabric mainly composed of polyolefin such as polyethylene and polypropylene, cloth, microporous film, or a combination thereof may be used. Can do.

(battery)
The above configuration can be applied to various lithium ion secondary batteries, and the structure is not particularly limited. In a lithium ion secondary battery, a wound electrode group in which a positive electrode, a negative electrode, and a separator for separating them are stacked and wound, and a stacked electrode group in which a positive electrode, a negative electrode, and a separator are stacked are used.

  With the configuration as described above, the current that flows when an internal short circuit occurs can be suppressed. As a result, a lithium ion secondary battery with improved safety can be provided.

〔Example〕
Hereinafter, embodiments of the present invention will be described using examples. In addition, an Example is an example and all are not restricted to this. First, an example in which the resistance of the negative electrode active material layer is increased using a carbon active material that has been coated to increase the resistance will be described.

Example 1
In Example 1, an example in which a carbon active material in which a coating layer is provided to increase resistance as a negative electrode active material will be described.

The synthesis procedure of the negative electrode active material is shown. First, using an autoclave, coal-based coal tar was heat-treated at 400 ° C. to obtain raw coke. After pulverizing this raw coke, calcination was performed at 1500 ° C. in an inert atmosphere to obtain a carbon material having a carbon interlayer distance (d ₀₀₂ ) of 0.345 nm. Plane spacing d ₀₀₂ of the carbon 002 plane of the carbon material of the present embodiment is an X-ray diffractometer (Rigaku: RU200B) was used for the measurement. As the X-ray source, Cu was used and diffraction accuracy was corrected using Si. By performing profile fitting on the peak obtained by measurement, it can be calculated using the Bragg equation.

This carbon material was pulverized using an impact crusher equipped with a classifier, and coarse particles were removed with a 300 mesh sieve to obtain carbon particles. At that time, the average particle size was 16.6 μm and the specific surface area was 1.8 m ² / g. In addition, the particle diameter (50% D) of the material in an Example was investigated using the laser diffraction / scattering type particle size distribution measuring apparatus (Horiba Ltd. make: LA-920). A He—Ne laser 1 mW was used as a light source, and a dispersion medium of carbon particles was obtained by adding two drops of a surfactant to ion exchange water. The ultrasonic treatment was performed for 5 minutes or more in advance, and the ultrasonic treatment was also performed during the measurement, and the measurement was performed while preventing aggregation. The cumulative 50% particle size (50% D) of the measurement results was taken as the average particle size. In addition, the specific surface area of the carbon material is an adsorption isotherm measured by vacuum drying the carbon material at 120 ° C. for 3 hours, and then using BELSORP-mini manufactured by Nippon Bell Co., Ltd. and using nitrogen adsorption at 77K with an equilibrium time of 300 seconds. The line was analyzed by BET method.

The carbon particles were uniformly coated with CaO using a CVD method to a thickness of 20 nm to obtain a negative electrode active material. At this time, the volume resistivity of the negative electrode active material layer was 4.5 × 10 ⁻¹ Ω · cm, and the volume resistivity of the coated carbon was 4.6 × 10 ⁻¹ Ω · cm. The volume resistivity in the present example was measured using Lorester GP, MCP-T610 manufactured by Mitsubishi Chemical. The former is the result of measuring the coated active material layer itself, and the latter is the result of measuring the coated carbon. For the carbon material, the electrode was measured by a four-probe method based on the powder resistance applied with a pressure of 40 MPa.

(Example 2)
The same procedure as in Example 1 was performed except that the thickness coated using the CVD method was changed to 50 nm. The volume resistivity of the negative electrode active material layer was 1.4 × 10 ⁻⁰ Ω · cm, and the volume resistivity of the coated carbon was 1.3 × 10 ⁻⁰ Ω · cm.

(Example 3)
The same operation as in Example 1 was performed except that the thickness covered by the CVD method was changed to 100 nm. The volume resistivity of the negative electrode active material layer was 6.0 × 10 ⁻⁰ Ω · cm, and the volume resistivity of the coated carbon was 5.9 × 10 ⁻⁰ Ω · cm.

Example 4
The same procedure as in Example 1 was performed except that the thickness coated using the CVD method was changed to 150 nm. The negative electrode active material layer had a volume resistivity of 3.5 × 10 ¹ Ω · cm, and the coated carbon had a volume resistivity of 3.5 × 10 ¹ Ω · cm.

(Example 5)
The same procedure as in Example 1 was performed except that the calcination temperature was 2800 ° C.

The distance between carbon layers (d ₀₀₂ ) at this time was 0.336 nm, the average particle diameter was 15.8 μm, and the specific surface area was 1.9 m ² / g. At this time, the volume resistivity of the negative electrode active material layer was 7.5 × 10 ⁻² Ω · cm, and the volume resistivity of the coated carbon was 7.4 × 10 ⁻² Ω · cm.

(Example 6)
The same procedure as in Example 5 was performed, except that the thickness covered by the CVD method was changed to 50 nm. The negative electrode active material layer had a volume resistivity of 2.5 × 10 ⁻⁰ Ω · cm, and the coated carbon had a volume resistivity of 2.5 × 10 ⁻⁰ Ω · cm.

(Example 7)
The same procedure as in Example 5 was performed except that the thickness coated using the CVD method was changed to 100 nm. The negative electrode active material layer had a volume resistivity of 5.5 × 10 ⁻⁰ Ω · cm, and the coated carbon had a volume resistivity of 5.5 × 10 ⁻⁰ Ω · cm.

(Example 8)
The same procedure as in Example 5 was performed except that the thickness coated using the CVD method was changed to 150 nm. The volume resistivity of the negative electrode active material layer was 3.1 × 10 ¹ Ω · cm, and the volume resistivity of the coated carbon was 3.1 × 10 ¹ Ω · cm.

(Comparative Example 1)
The same procedure as in Example 1 was performed except that carbon was not coated. The negative electrode active material layer had a volume resistivity of 4.8 × 10 ⁻² Ω · cm, and the coated carbon had a volume resistivity of 4.8 × 10 ⁻² Ω · cm.

(Comparative Example 2)
The same procedure as in Example 1 was performed except that the thickness coated using the CVD method was changed to 3 nm.
The negative electrode active material layer had a volume resistivity of 1.5 × 10 ⁻² Ω · cm, and the coated carbon had a volume resistivity of 1.5 × 10 ⁻² Ω · cm.

(Comparative Example 3)
The same procedure as in Example 1 was performed except that the thickness coated using the CVD method was changed to 500 nm. The volume resistivity of the negative electrode active material layer was 5.8 × 10 ² Ω · cm, and the volume resistivity of the coated carbon was 5.8 × 10 ² Ω · cm.

(Comparative Example 4)
The same procedure as in Example 1 was performed except that the material coated using the CVD method was changed from CaO to Si alloyed with lithium. The negative electrode active material layer had a volume resistivity of 4.3 × 10 ⁻⁰ Ω · cm, and the coated carbon had a volume resistivity of 4.2 × 10 ⁻⁰ Ω · cm.

(Comparative Example 5)
The same procedure as in Example 5 was performed except that the coating on carbon was not performed. The negative electrode active material layer had a volume resistivity of 7.5 × 10 ⁻³ Ω · cm, and the coated carbon had a volume resistivity of 7.5 × 10 ⁻³ Ω · cm.

(Production of lithium ion secondary battery)
Next, a procedure for synthesizing the positive electrode active material will be described. Nickel oxide, manganese oxide, and cobalt oxide were used as raw materials, and weighed so that the atomic ratio of Ni: Mn: Co was 1: 1: 1, and pulverized and mixed with a wet pulverizer. Next, the pulverized mixed powder to which polyvinyl alcohol (PVA) was added as a binder was granulated with a spray dryer. The obtained granulated powder was put in a high-purity alumina container, pre-baked at 600 ° C. for 12 hours to evaporate PVA, crushed after air cooling. Further, lithium hydroxide monohydrate was added to the pulverized powder so that the atomic ratio of Li: transition metal (Ni, Mn, Co) was 1: 1: 1 and mixed well. This mixed powder was put into a high-purity alumina container and subjected to main firing at 900 ° C. for 6 hours. The obtained positive electrode active material was pulverized and classified with a ball mill. The average particle diameter of this positive electrode active material was 6 μm.

  Next, a lithium ion secondary battery was produced using the above positive electrode and negative electrode active materials.

  FIG. 1 is a diagram showing a cross-sectional view of a lithium ion secondary battery of the present invention. In FIG. 1, 10 is a positive electrode, 11 is a separator, 12 is a negative electrode, 13 is a battery can, 14 is a positive electrode tab, 15 is a negative electrode tab, 16 is an inner lid, 17 is an internal pressure release valve, 18 is a gasket, and 19 is a PTC element. , 20 is a battery lid.

First, a positive electrode was produced. 7.0 parts by weight and 2.0 parts by weight of powdered carbon and acetylene black as conductive materials were added to 85.0 parts by weight of the positive electrode active material, respectively, and 6.0 parts by weight of PVDF was previously added as a binder to N-methyl- A solution dissolved in 2-pyrrolidone (NMP) was added and further mixed with a planetary mixer to obtain a positive electrode mixture slurry. This slurry was uniformly and evenly applied to both surfaces of an aluminum foil having a thickness of 20 μm with an applicator. After the application, it was compression-molded so as to have an electrode density of 2.55 g / cc with a roll press machine to obtain a positive electrode.

  Next, a negative electrode was produced. As a negative electrode active material, a solution in which 91.6 parts by weight of the coated carbon material is used as a conductive material and 8.4 parts by weight of polyvinylidene fluoride (PVDF) is dissolved in NMP as a binder is added, and a planetary mixer is further added. To make a negative electrode mixture slurry. This slurry was applied uniformly and evenly on both sides of a rolled copper foil having a thickness of 10 μm with a coating machine. After the application, it was compression molded by a roll press machine so that the electrode density was 1.25 g / cc to obtain a negative electrode.

First, the positive electrode and the negative electrode were cut into desired sizes, and current collecting tabs were ultrasonically welded to the uncoated portions. Each of the current collecting tabs used an aluminum lead piece for the positive electrode and a nickel lead piece for the negative electrode. Thereafter, a separator having a thickness of 30 μm was wound while being sandwiched between a positive electrode and a negative electrode by a porous polyethylene film. The wound body was inserted into the battery can, the negative electrode tab was connected to the bottom of the battery can by resistance welding, and the positive electrode lid was connected to the positive electrode tab by ultrasonic welding. An electrolyte solution in which 1 mol / liter of LiPF ₆ was dissolved in a mixed solvent with a volume ratio of 1: 1: 1 of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) was poured, Thereafter, the positive electrode lid was caulked and sealed in a battery can to obtain a lithium ion battery.
The performance of the produced battery was confirmed by the following method.

(DCR measurement)
The DCR was measured to determine the battery power density. The produced battery was charged to 4.1 V at a current equivalent to 0.3 C around room temperature (25 ° C.), and then charged at a constant voltage at 4.1 V until the current reached 0.03 C. After a 30-minute pause, constant current discharge was performed up to 2.7 V with a constant current corresponding to 0.3 C.
This was repeated for 4 cycles to initialize, and the capacity density [mAh / g] around the weight of the battery was determined from the discharge capacity at the 4th cycle. Furthermore, after carrying out constant current charge to 3.6V at 0.3C, it discharged for 10 second with the electric current value of 4CA, 8CA, 12CA, and 16CA. The voltage value at this time was obtained, and the output density was obtained from the limit current when this was extrapolated to 2.5V.

(Cycle characteristics)
The cycle characteristics were measured using the battery whose DCR was measured. After carrying out 5000 cycles of 4.1V-2.7V with a constant current of 1CA, and further carrying out a constant current charge to 3.6V at 0.3C, it discharges for 10 seconds with the current value of 4CA, 8CA, 12CA, and 16CA. did. The DC resistance was determined from the slope of the obtained straight line. Moreover, the output density was calculated | required from the limiting current when this was extrapolated to 2.5V. In Table 1, the rate of increase in resistance after 5000 cycles (the initial resistance was taken as 100).
)showed that.

(Safety test)
Next, a battery crush test was performed as a safety test. A constant voltage / constant current charge with a charging voltage of 4.1 V, a charging time of 2 hours and a limiting current of 800 mA was performed, and a battery crushing test was performed. 6mm in diameter
The round bar was pressed against the center of the battery from the direction perpendicular to the direction in which the outer dimension of the battery was the longest, and crushed until the thickness of the battery was halved. At this time, the results were classified as no change, valve operation only, valve operation + smoke, valve operation + smoke + ignition. Here, only the valve operation is a state in which the safety valve is open, valve operation + smoke is a state in which the safety valve is open and gas is simultaneously ejected, and valve operation + smoke + ignition is a state in which gas is ejected from the battery and ignited. In each table, “no change” indicates no change, “valve operation” indicates only valve operation, “smoke” indicates valve operation + smoke, and “fire” indicates valve operation + smoke + ignition.

  Similarly, a battery crushing test was performed after an overcharge test. The procedure was the same as the crushing test except that the charging voltage was changed to 4.3V. Table 1 shows the test results of the batteries manufactured using the negative electrodes of Examples 1 to 8 and Comparative Examples 1 to 5.

From Examples 1 to 8 and Comparative Examples 1, 2 and 5 in Table 1, when the volume low efficiency is increased, ignition occurs at 4.1 V and 4.3 V during the crush test as compared with the case where the volume resistivity is low. Safety was improved because it was not seen. Moreover, when Examples 1-8 are compared with the comparative example 3, when the volume resistivity is too high, it can be seen that the output density is lowered because the DCR is rapidly increased. Further, the upper limit and lower limit of the volume resistivity change depending on the value of _d002 . Therefore, when the carbon (002) plane distance d ₀₀₂ obtained by X-ray diffractometer (XRD) measurement is 0.340 to 0.390 nm, the volume resistivity is 1 × 10. ^-1 or more and 1 × 10 ² Ω · cm or less is preferable. Further, when carbon whose d ₀₀₂ is 0.3348 or more and less than 0.340 nm is used as a main material, the volume resistivity of carbon is preferably 1 × 10 ⁻² or more and 1 × 10 ² Ω · cm or less.

  Moreover, when Examples 1-8 and the comparative example 4 are seen, if the material alloyed with lithium ion is selected as a coating | covering material, it turns out that cycling characteristics deteriorate.

Example 9
Instead of coating carbon, the same procedure as in Example 1 was performed except that 30 parts by weight of CaO was added as a resistor when preparing the negative electrode slurry. The volume resistivity of the negative electrode active material layer was 1.9 × 10 ⁻⁰ Ω · cm.

(Example 10)
The same operation as in Example 9 was performed except that the amount of CaO added was changed to 50 parts by weight. The volume resistivity of the negative electrode active material layer was 2.9 × 10 ¹ Ω · cm.

(Example 11)
This was performed in the same manner as in Example 9 except that a carbon layer to which no CaO was added was applied in advance, and 30 parts by weight of CaO was added as a resistor during the preparation of the negative electrode slurry. The volume resistivity of the negative electrode active material layer was 7.8 × 10 ⁻¹ Ω · cm.

(Comparative Example 6)
The same operation as in Example 9 was performed except that the amount of CaO added was changed to 10 parts by weight. The volume resistivity of the negative electrode active material layer was 4.2 × 10 ⁻² Ω · cm.

(Comparative Example 7)
The same operation as in Example 9 was performed except that the amount of CaO added was changed to 80 parts by weight. The volume resistivity of the negative electrode active material layer was 2.9 × 10 ³ Ω · cm.

(Comparative Example 8)
The same operation as in Example 9 was performed except that the additive species was changed from CaO to Si alloying with lithium ions. The volume resistivity of the negative electrode active material layer was 6.8 × 10 ⁻⁰ Ω · cm.

  Table 2 shows the test results of the batteries manufactured using the negative electrodes of Examples 9 to 11 and Comparative Examples 6 to 8.

  From Examples 9 to 11 and Comparative Examples 1 and 6 in Table 2, 4.1 V and 4. V in the crushing test according to the increase in volume low efficiency compared to the case where the volume resistivity is low as in Table 1. Safety was improved because no ignition was seen at 3V. Further, from Examples 9 to 11 and Comparative Example 7, when the volume low efficiency is too high, the output density is lowered because the DCR rapidly increases. It can be seen from Comparative Example 8 that the cycle characteristics are deteriorated when a material alloyed with lithium ions is selected as the coating material.

  Further, from Example 11, the capacity can be increased by providing a layer not including a resistor to form a multilayer structure.

  It is possible to provide a lithium ion secondary battery with improved battery safety during an internal short circuit.

DESCRIPTION OF SYMBOLS 10 Positive electrode 11 Separator 12 Negative electrode 13 Battery can 14 Positive electrode tab 15 Negative electrode tab 16 Inner cover 17 Internal pressure release valve 18 Gasket 19 PTC element 20 Battery cover

Claims (16)

An organic electrolytic solution in which a positive electrode that reversibly stores and releases lithium ions, a negative electrode that reversibly stores and releases lithium ions, a separator disposed between the positive electrode and the negative electrode, and an electrolyte containing the lithium ions are dissolved. In a lithium ion secondary battery comprising:
The negative electrode comprises a negative electrode active material layer and a current collector,
The negative active material layer surface spacing d ₀₀₂ of carbon (002) face obtained by X-ray diffractometer (XRD) measurement as a main material of carbon is 0.390nm than 0.340,
The lithium ion secondary battery, wherein the volumetric efficiency of the negative electrode active material layer is 1 × 10 ⁻¹ or more and 1 × 10 ² Ω · cm or less. An organic electrolytic solution in which a positive electrode that reversibly stores and releases lithium ions, a negative electrode that reversibly stores and releases lithium ions, a separator disposed between the positive electrode and the negative electrode, and an electrolyte containing the lithium ions are dissolved. In a lithium ion secondary battery comprising:
The negative electrode comprises a negative electrode active material layer and a current collector,
The negative active material layer, carbon (002) face plane spacing d ₀₀₂ of which is determined by X-ray diffractometer (XRD) measurement as a main material of carbon is less than 0.3348 or more 0.340 nm,
The negative electrode active material layer has a volume resistivity of 1 × 10 ⁻² or more and 1 × 10 ² Ω · cm or less. In the lithium ion secondary battery according to claim 1,
The lithium ion secondary battery according to claim 1, wherein a volume resistivity of carbon of the main material is 1 × 10 ⁻¹ or more and 1 × 10 ² Ω · cm or less. In the lithium ion secondary battery according to claim 2,
The lithium ion secondary battery according to claim 1, wherein a volume resistivity of carbon of the main material is 1 × 10 ⁻² or more and 1 × 10 ² Ω · cm or less. The lithium ion secondary battery according to claim 1 or 2,
The main material carbon has a coating layer of a material having a volume resistivity of 5 × 10 ⁴ Ω · cm or more and 1 × 10 ⁻¹ Ω · cm or less on a surface thereof. The lithium ion secondary battery according to claim 1 or 2,
2. The lithium ion secondary battery according to claim 1, wherein the main material carbon has a coating layer including an oxide, a nitride, or a mixture of an oxide and a nitride on a surface thereof. In the lithium ion secondary battery according to claim 6,
The covering layer includes at least one of CaO, Sc ₂ O ₃ , SrO ₂ , SnO ₂ , BaO, La ₂ O ₃ , Nd ₂ O ₃ , WO ₃ , AlN, GaN, and SiN. Ion secondary battery. The lithium ion secondary battery according to claim 1 or 2,
The carbon of the main material has a coating layer, and the film thickness of the coating layer is 0.1% or more and 1% or less with respect to the cumulative 50% particle size (50% D) of the carbon provided with the coating layer. A lithium ion secondary battery characterized by being. The lithium ion secondary battery according to claim 1 or 2,
The said negative electrode active material layer contains a resistor particle | grain, The lithium ion secondary battery characterized by the above-mentioned. 10. The lithium ion secondary battery according to claim 9, wherein the resistor particles contain at least one of glass beads, resin beads, oxide particles, and nitride particles. 11. 10. The lithium ion secondary battery according to claim 9, wherein the resistor particles are acrylic resin, polycarbonate resin, urethane resin, melamine resin, soda glass, potassium glass, borosilicate glass, CaO, Sc ₂ O ₃ , SrO. ₂ , a lithium ion secondary battery containing any one of SnO ₂ , BaO, La ₂ O ₃ , Nd ₂ O ₃ , WO ₃ , Al ₂ O ₃ , SiO ₂ , AlN, GaN, and SiN.   10. The lithium ion secondary battery according to claim 9, wherein the additive amount of the resistor particles is 30 to 50 parts by weight with respect to carbon of the main material.   10. The lithium ion secondary battery according to claim 9, wherein the amount of the resistor particles added is greater on the surface side of the negative electrode active material layer than on the current collector side of the negative electrode active material layer. Secondary battery. In the lithium ion secondary battery according to claim 9,
The negative electrode active material layer is composed of a plurality of layers, and the resistor particles are contained in at least one layer. In the lithium ion secondary battery according to claim 9,
A lithium ion secondary battery comprising a negative electrode active material layer not including the resistor particles and a layer including the resistor particles on the current collector from the current collector side. In the lithium ion secondary battery according to claim 9,
The lithium ion secondary battery, wherein the resistor particles are a material that does not alloy with lithium ions.

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