JP2010177062A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium-ion secondary battery with improved safety of the battery without causing output fall due to DCR rise in comparison with conventional technology. <P>SOLUTION: In the lithium secondary battery having a cathode and an anode for reversibly occluding and releasing lithium ions, and an organic electrolyte solution with electrolyte containing the lithium ions dissolved, in which the cathode and the anode are arranged via a separator, an anode active material includes carbon, and the anode includes at least 0.5 to 1.5 wt.% phenolic antioxidant or 0.1 to 0.5 wt.% phosphorus antioxidant. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery.

  With the development of mobile phones and notebook PCs since around the 1990s and 1990s, secondary batteries have been required to have high performance for their power supplies. Under these demands, lithium batteries are mainly used for these batteries instead of lead-acid batteries and nickel-cadmium batteries because of their high energy density.

  Furthermore, in recent years, lithium secondary batteries have higher input / output characteristics than nickel-metal hydride batteries and lead-acid batteries, and thus have attracted attention as high-output power sources such as electric vehicles and hybrid electric vehicles. Among lithium secondary batteries for hybrid vehicles, a battery having a low direct current resistance (DCR) and a high output is particularly desired as compared with batteries for mobile phones and notebook PCs.

Japanese Patent Laid-Open No. 10-154531 JP 11-73964 A

  However, since lithium secondary batteries mainly use non-aqueous solvents, there is a risk of overheating, heating, short-circuiting, etc., resulting in a runaway runaway condition, leading to battery explosion and ignition. Safety is not guaranteed.

  As a method for improving the safety of lithium secondary batteries having such a risk, Patent Document 1 discloses a method of adding an antioxidant as a radical scavenger to the battery. In this patent, the added amount is 0.1 to 30% by weight, more preferably 1 to 20%, and it is described that the charge / discharge characteristics may be insufficient if it is more than this. Yes.

  On the other hand, Patent Document 2 discloses improvement of cycle characteristics and 2CA current characteristics by adding an antioxidant to the carbon negative electrode. In Patent Document 2, the addition amount is set to 0.1 to 5% by weight as an antioxidant, and it is described that a side effect occurs at more than this.

  However, since the above-mentioned patents are mainly specialized for mobile phones and notebook PCs, there is no description of DCR related to battery output. As a result of our study, when the amount of addition of the antioxidant is within the above range, there is a region where the DCR increases remarkably, and a high current pulse load with a large current such as 10 CA or 20 CA is required. It turned out that it was not suitable as a power supply. Furthermore, it was found that the increasing tendency of DCR with respect to the added amount differs depending on the kind of antioxidant to be added. However, Patent Documents 1 and 2 do not take that point into consideration, and for that reason, it has been necessary to study in order to use an antioxidant for a high-output power source.

  The lithium ion secondary battery of the present invention is a lithium ion secondary battery in which a positive electrode that occludes and releases lithium ions and a negative electrode that occludes and releases lithium ions are formed through a non-aqueous electrolyte and a separator. The negative electrode mixture contains a negative electrode active material, a conductive agent, and a binder, the negative electrode active material is a carbon material, and the negative electrode mixture contains a phenol group. It is characterized by containing 0.5 wt% or more and 1.5 wt% or less of a compound having 0.1 wt% or less and 0.1 wt% or less of a compound containing phosphorus.

  The present invention can provide a lithium secondary battery with improved safety without causing a decrease in output due to an increase in DCR.

Sectional drawing of the lithium ion battery used by this invention. The relationship diagram of antioxidant addition amount and power density.

  The technical features according to the embodiments of the present invention will be described below.

  The lithium ion secondary battery of the present invention is a lithium ion secondary battery in which a positive electrode that occludes and releases lithium ions and a negative electrode that occludes and releases lithium ions are formed through a non-aqueous electrolyte and a separator. The negative electrode mixture contains a negative electrode active material, a conductive agent, and a binder, the negative electrode active material is a carbon material, and the negative electrode mixture contains a phenol group. It is characterized by containing 0.5 wt% or more and 1.5 wt% or less of a compound having 0.1 wt% or less and 0.1 wt% or less of a compound containing phosphorus.

The specific surface area of the carbon material is 1 m ² / g or more and 6 m ² / g or less, and the average particle diameter of the carbon material is 10 μm or more and 20 μm or less.

  Further, the non-aqueous electrolyte contains a cyclic carbonate containing an unsaturated group. Further, when a compound having a phenol group is contained, the compound having a phenol group is 3,3 ', 3 ", 5,5', 5" -hexa-tert-butyl-a, a ', a "- (Mesitylene-2,4,6-triyl) tri-p-cresol, which contains a compound having phosphorus, the compound having phosphorus is tetrakis (2,4-di-tert-butyl) Phenyl) [1,1-biphenyl] -4,4'-diylphosphonite.

  The lithium ion secondary battery of the present invention is a lithium ion secondary battery in which a positive electrode that occludes and releases lithium ions and a negative electrode that occludes and releases lithium ions are formed via a non-aqueous electrolyte and a separator. The negative electrode has a current collector and a negative electrode mixture, the negative electrode mixture contains a negative electrode active material, a conductive agent, and a binder, the negative electrode active material is a carbon material, and the negative electrode mixture contains a phenol group. It is characterized by containing a compound having 0.5 to 1.5% by weight and a compound having phosphorus of 0.1 to 0.5% by weight.

  Furthermore, the ratio of the content A of the compound having phosphorus and the content B of the compound having a phenol group in the negative electrode mixture is 0.1 ≦ A / B ≦ 0.2. .

  Moreover, the present invention is a lithium ion secondary battery in which a positive electrode that occludes and releases lithium ions and a negative electrode that occludes and releases lithium ions are formed via a non-aqueous electrolyte and a separator, The negative electrode has a current collector and a negative electrode mixture, the negative electrode mixture contains a negative electrode active material, a conductive agent, and a binder, the negative electrode active material is a carbon material, and the negative electrode mixture contains an antioxidant. It is characterized by doing. Further, the antioxidant is characterized by containing an oxygen atom, and preferably has a hydroxyl group.

  Hereinafter, embodiments of the present invention will be described for each component.

  First, as a compound having a phenol group used in the present invention, that is, a phenolic antioxidant, 3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(Mesitylene-2,4,6-triyl) tri-p-cresol, 2,6-di-t-butyl-4-methylphenol, 2,4-dimethyl-6-tert-butylphenol, 2,2 ′ -Thiobis- (4-methyl-6-tert-butylphenol) and the like.

  Further, as a phosphorus-containing compound, that is, a phosphorus-based antioxidant, tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4′-diylphosphonite, tris ( Nonylphenyl) phosphite, distearyl pentaerythritol diphosphite, tristearyl phosphite, di (2-ethylhexyl) phosphate, etc., but depending on the effect of scavenging the radical that deactivates the generated radical or the generated radical The present invention is not limited to this as long as it has any of the peroxide effects that decompose the generated peroxide.

  Although the addition method of antioxidant is not specifically limited, It is preferable from the viewpoint of uniformly disperse | distributing antioxidant to contain in the negative electrode in the form added to the solvent at the time of creating a negative electrode coating material. By adding an antioxidant, it is possible to suppress the reaction between the radicals and peroxides generated from the electrolyte and the positive electrode during high temperature and overcharge, and the lithium in the negative electrode. Can be improved.

  The amount added in this case is the ratio of the total amount of the negative electrode mixture including the negative electrode active material, the conductive agent and the binder to the negative electrode mixture when the total weight is 100, and the phenolic antioxidant is 0.5% by weight or more. It is preferably 1.5% by weight or less.

  In the phosphorus-based antioxidant, the content is preferably 0.1% by weight or more and 0.5% by weight or less. When the addition amount of the phenolic antioxidant is less than 0.5% by weight or when the addition amount of the phosphorus antioxidant is less than 0.1% by weight, safety is not ensured and ignition or the like occurs. Further, when the addition amount of the phenolic antioxidant is more than 1.5% by weight or when the addition amount of the phosphorus antioxidant is more than 0.5% by weight, the DCR increases rapidly, and the battery This is not preferable because the power density when used in the above is lowered.

  The reason why the DCR suddenly increases with the addition amount of the antioxidant as a threshold value is assumed to be the following mechanism. When an antioxidant is added to the negative electrode, a certain amount of the antioxidant is decomposed, so that the SEI (solid electrolyte interface) on the negative electrode surface becomes thick. However, up to a certain SEI thickness, the rate-determining process of the charge / discharge reaction on the carbon surface is a process in which Li ions solvated in the electrolyte undergo a desolvation reaction. It hardly happens. However, when the SEI thickness exceeds a certain level, the rate-limiting process is derived from the movement of Li ions in the SEI, and as a result, the DCR increases rapidly with a certain addition amount as a threshold value.

  Also, the reason why the optimum range differs between phenolic antioxidants and phosphorus antioxidants is that phosphorous antioxidants are better at capturing peroxides than phenolic antioxidants, so even a small amount is effective. Instead, since the heat resistance and water resistance are inferior and the SEI tends to be thick with respect to the amount, a smaller addition amount range than the phenolic antioxidant is optimal.

  Moreover, the effect of a safety improvement can be heightened rather than single by adding both phosphorus antioxidant and phenolic antioxidant. In this case, the mixing ratio is particularly preferably in the range of 0.1 ≦ A / B ≦ 0.2 when the phosphorus antioxidant content is A and the phenolic antioxidant content is B. . Phenol-based antioxidants have a weaker peroxide capture than phosphorus-based antioxidants, but the weak points can be compensated for by adding a small amount of phosphorus-based antioxidants. However, if the phosphorus antioxidant is added excessively, the effect of the phenolic antioxidant is weakened, so the effect of adding both is lost.

  Moreover, since the antioxidant is present on the surface of the negative electrode active material, the effect can be increased by adjusting the shape of the negative electrode active material species. Specifically, the negative electrode carbon material in the present invention preferably has an average particle size (50% D) determined by a laser diffraction / scattering particle size distribution measuring apparatus of 5 μm or more and 20 μm or less. When the average particle diameter exceeds 20 μm, it becomes easy to form irregularities on the electrode, so that it becomes difficult to dispose the antioxidant evenly, and the effect of improving the safety of the antioxidant is reduced. Becomes too large, it becomes difficult to dispose the antioxidant uniformly, and the effect of improving the safety by the antioxidant is reduced. The particle size distribution can be measured with a laser diffraction particle size distribution analyzer by dispersing the sample in purified water containing a surfactant, and the average particle size is the particle size at which the cumulative volume of negative electrode carbon is 50%. Is calculated by

In addition, the negative electrode carbon material of the present invention has a specific surface area determined by using a BET (Brunauer-Emmet-Teller) method for an adsorption isotherm obtained from 77K nitrogen adsorption measurement, and an average particle size (50% D) is 10 μm or more and 20 μm. If it is less, or less than 1 m ² / g or more 6 m ² / g, or an average particle diameter (50% D) is 3m ² / g or more 10 m ² / g is the less the time of less than 10μm or 5μm Is preferred. When the average particle diameter (50% D) is 10 μm or more and 20 μm or less and exceeds 6 m ² / g, or 5 μm or more and less than 10 μm and exceeds 10 m ² / g, the carbon surface has fine irregularities, and thus the antioxidant. Is less likely to be evenly disposed, the effect of improving the safety by the antioxidant is reduced, and the average particle diameter (50% D) is 10 μm or more and 20 μm or less and less than 1 m ² / g, or the average particle diameter ( When the 50% D) is 5 μm or more and less than 10 μm and less than 3 m ² / g, the carbon material becomes a flat carbon material having a large aspect ratio, and therefore the electrodes are easily uneven and the antioxidant is not easily disposed evenly. Therefore, the effect of improving safety by the antioxidant is reduced.

  The method for producing a negative electrode carbon material for a lithium secondary battery of the present invention is not particularly limited as long as it is a carbon material having an average particle diameter (50% D) and a specific surface area. For example, natural graphite, petroleum coke, coal pitch coke, etc. After heat-treating the graphitizable material obtained from the above at a high temperature of 2500 ° C. or higher, or pulverizing thermoplastic resin, naphthalene, anthracene, phenanthrolene, coal tar, tar pitch, etc. by heat-treating them with an autoclave or other device in advance. And calcined in an inert atmosphere at 800 ° C. or higher. 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 method for producing the negative electrode is not particularly limited. For example, a general kneading dispersion method such as a ball mill or a planetary mixer is used for a solvent in which a negative electrode active material and an antioxidant are dissolved and a binder is further dissolved or dispersed. Use and knead and disperse well to prepare a negative electrode mixture slurry. 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 pressing machine, the desired size is obtained. It can be cut or punched into a negative electrode.

  Although it does not specifically limit as a solvent at the time of creating a coating material, It is preferable that an antioxidant can be dissolved. Examples thereof include N-methyl-2-pyrrolidone (NMP), ethylene glycol, toluene, xylene and the like.

  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% by weight or more and 15% by weight or less with respect to 100% 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% by weight, the electrode may peel off, and if it is more than 15% by weight, the DCR may increase.

  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 the preparation of the positive electrode mixture or the negative electrode mixture, it is preferable to add a conductive additive if necessary for reducing DCR. Although it does not specifically limit as a conductive support agent, For example, amorphous | non-crystalline carbon, such as powdered graphite with high electroconductivity, scale-like graphite, or carbon black, may be combined. The content of the conductive auxiliary is preferably 0 to 15% by weight when the total weight of the negative electrode active material and the conductive auxiliary of the present invention is 100% by weight. When it exceeds 15% by weight, the DCR reduction effect is reduced, 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 _c M _d O ₂ is particularly preferable (where M is Fe, V , Ti, Cu, Al, Sn, Zn, Mg, B, and preferably at least one selected from the group consisting of Al, B, Mg). Further, 0 ≦ a ≦ 0.6, 0.3 ≦ b ≦ 0.7, 0 ≦ c ≦ 0.4, and 0 ≦ d ≦ 0.1. The positive electrode active material preferably has an average particle size of 10 μm or less.

  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 desirably 0.7 M or more and 1.5 M or less, and DCR tends to increase when the electrolyte concentration is out of the above range.

  You may add the cyclic carbonate containing an unsaturated group to electrolyte solution. When added, the SEI becomes firm, so that the effect when the antioxidant is added can be enhanced. Examples of the cyclic carbonate containing an unsaturated group include vinylene carbonate and vinyl ethylene carbonate. The addition amount is preferably 0.1% by weight or more and 5% by weight or less, assuming that the total weight of the electrolytic solution is 100% 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 or polypropylene, cloth, microporous film, or a combination thereof may be used. Can do.

  The lithium ion secondary battery of the present invention can be obtained, for example, by arranging the negative electrode for a lithium ion secondary battery of the present invention and a positive electrode facing each other with a separator interposed therebetween and injecting an electrolytic solution.

  The structure of the lithium ion secondary battery of the present invention is not particularly limited. Usually, a positive electrode, a negative electrode, and a separator for separating them are wound to form a wound electrode group, or a laminated type to form a laminated type. It can be used as an electrode group.

  The lithium ion secondary battery of the present invention described above can provide a lithium secondary battery with improved safety without causing output reduction due to DCR increase.

  Hereinafter, embodiments of the present invention will be described in detail with reference to examples. The embodiment is an example, and is not necessarily limited thereto.

First, it shows from the examination result of the phenol antioxidant of Claim 1.
First, it was prepared from a positive electrode and a negative electrode active material.

(Example 1) Force A procedure for synthesizing a negative electrode active material will be described. First, using an autoclave, coal-based coal tar was heat-treated at 400 ° C. to obtain raw coke. After pulverizing this raw coke, it was calcined at 2800 ° C. in an inert atmosphere to obtain a carbon material. 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 15.6 μm and the specific surface area was 2.5 m ² / g.

  A procedure for synthesizing the positive electrode active material will be described. Nickel oxide, manganese oxide, and cobalt oxide were used as raw materials, weighed so that the Ni: Mn: Co ratio was 1: 1: 1 by atomic ratio, 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.

  The particle size (50% D) of the material in the examples was examined using a laser diffraction / scattering particle size distribution analyzer LA-920 manufactured by Horiba, Ltd. 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.

  The specific surface area of the carbon material is obtained by vacuum-drying the carbon material at 120 ° C. for 3 hours, and then using an adsorption isotherm measured using a BELSORP-mini manufactured by Nippon Bell Co., Ltd. using nitrogen adsorption at 77K and an equilibrium time of 300 seconds. Analyzed by the BET method.

Next, a lithium secondary battery was created.
FIG. 1 is a cross-sectional view of a lithium secondary battery according to 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% and 2.0% by weight of powdery graphite and acetylene black as conductive materials were added to 85.0% by weight of the positive electrode active material, respectively, and 6.0% by weight of PVDF was previously dissolved in NMP as a binder. The solution 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, carbon material is 85.0% by weight as a conductive material, 6.7% by weight of acetylene black, 8.3% by weight of PVDF as a binder and phenolic antioxidant as 0.0. 5% by weight of 3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol Was added to a NMP and mixed with a planetary mixer to form a negative electrode mixture slurry, which was uniformly and evenly applied to both sides of a rolled copper foil having a thickness of 10 μm by a coating machine. The negative electrode was compression-molded so as to have an electrode density of 1.15 g / cc by a press machine to obtain a negative electrode.

Thereafter, the positive electrode and the negative electrode were cut to a desired size, 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 is dissolved in a mixed solvent having a volume ratio of 1: 1, 1: 1 by volume ratio of EC, DMC, and DEC is injected, and then the positive electrode lid is caulked and sealed in a battery can. A lithium ion battery was obtained.

  Next, DCR was measured to determine the output density of the battery. 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 for initialization. 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.

  The results are shown in Table 1.

  The battery was then overcharged. After the DCR test was performed for 30 minutes, the battery was overcharged to a SOC of 200% at a charging current of 2 C, and the behavior was investigated. At this time, the results were classified into valve operation only, valve operation + smoke, and 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, only valve operation is described as “valve operation”, valve operation + smoke is “smoke”, and valve operation + smoke + ignition is described as “ignition”. The results are shown in Table 1.

(Example 2)
3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol negative electrode mixture A sample was prepared under the same conditions as in Example 1 except that the amount added was changed to 1.0% by weight, and an evaluation test was performed.

(Example 3)
3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol negative electrode mixture A sample was prepared under the same conditions as in Example 1 except that the amount added was changed to 1.5% by weight, and an evaluation test was performed.

(Comparative Example 1)
The same procedure as in Example 1 was performed except that the antioxidant was not added to the negative electrode mixture.

(Comparative Example 2)
3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol negative electrode mixture A sample was prepared under the same conditions as in Example 1 except that the amount added was changed to 0.2% by weight, and an evaluation test was performed.

(Comparative Example 3)
3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol negative electrode mixture A sample was prepared under the same conditions as in Example 1 except that the amount added was changed to 2.0% by weight, and an evaluation test was performed.

(Comparative Example 4)
3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol negative electrode mixture A sample was prepared under the same conditions as in Example 1 except that the amount added was changed to 3.0% by weight, and an evaluation test was performed.

  According to the comparison between Examples 1 to 3 and Comparative Examples 1 and 2 in Table 1, the lithium ion secondary batteries of Examples 1 to 3 did not cause a decrease in output due to DCR increase, and during the overcharge test. It is clear that safety has been improved because neither smoke nor ignition was seen. Further, comparing Examples 1 to 3 with Comparative Examples 3 and 4, it can be seen that by increasing the addition amount to 2.0% by weight or more, the DCR suddenly increased and the output density decreased.

Next, the examination result of phosphorus antioxidant is shown.
Example 4
Tetrakis instead of 3,3 ', 3 ", 5,5', 5" -hexa-tert-butyl-a, a ', a "-(mesitylene-2,4,6-triyl) tri-p-cresol The same conditions as in Example 1 except that 0.1% by weight of (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4'-diylphosphonite was added to the negative electrode mixture. Were prepared and evaluated.

(Example 5)
Tetrakis instead of 3,3 ', 3 ", 5,5', 5" -hexa-tert-butyl-a, a ', a "-(mesitylene-2,4,6-triyl) tri-p-cresol The same conditions as in Example 1 except that 0.3% by weight of (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4'-diylphosphonite was added to the negative electrode mixture. Were prepared and evaluated.

(Example 6)
Tetrakis instead of 3,3 ', 3 ", 5,5', 5" -hexa-tert-butyl-a, a ', a "-(mesitylene-2,4,6-triyl) tri-p-cresol The same conditions as in Example 1 except that 0.5% by weight of (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4'-diylphosphonite was added to the negative electrode mixture. Were prepared and evaluated.

(Comparative Example 5)
Tetrakis instead of 3,3 ', 3 ", 5,5', 5" -hexa-tert-butyl-a, a ', a "-(mesitylene-2,4,6-triyl) tri-p-cresol The same conditions as in Example 1, except that 0.05% by weight of (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4'-diylphosphonite was added to the negative electrode mixture. Were prepared and evaluated.

(Comparative Example 6)
Tetrakis instead of 3,3 ', 3 ", 5,5', 5" -hexa-tert-butyl-a, a ', a "-(mesitylene-2,4,6-triyl) tri-p-cresol Prepared under the same conditions as in Example 1 except that 1% by weight of (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4′-diylphosphonite was added to the negative electrode mixture. Then, an evaluation test was conducted.

(Comparative Example 7)
Tetrakis instead of 3,3 ', 3 ", 5,5', 5" -hexa-tert-butyl-a, a ', a "-(mesitylene-2,4,6-triyl) tri-p-cresol The same conditions as in Example 1 except that 2.0% by weight of (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4'-diylphosphonite was added to the negative electrode mixture. Were prepared and evaluated.

  By comparing Examples 4 to 6 and Comparative Examples 1 and 5 in Table 2, the lithium ion secondary batteries according to Examples 4 to 6 were subjected to an overcharge test without causing a decrease in output due to an increase in DCR. Since no smoke or ignition was observed, it is clear that safety has been improved. In addition, when Examples 4 to 6 and Comparative Examples 6 and 7 are compared, it can be seen that the DCR is rapidly increased and the output density is decreased by increasing the addition amount to 1.0% by weight or more.

  FIG. 2 shows the relationship between the phenol antioxidant addition amount, the phosphorus antioxidant addition amount, and the output density. It can be seen that the output density is remarkably lowered in the region exceeding 1.5% by weight in the case of phenol and in the region exceeding 0.5% by weight in the case of phosphorus.

  Next, the case where both a phosphorus antioxidant and a phenolic antioxidant are included will be described.

(Example 7)
3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol 0.5 wt. 0.1 wt% tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4′-diylphosphonite added to the negative electrode mixture, and An evaluation test was carried out under the same conditions as in Example 1 except that the current value was measured at 5C in addition to 2C during the overcharge test.

(Example 8)
3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol to the negative electrode Addition amount is 1.0% by weight and tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4′-diylphosphonite is 0.1% by weight in the negative electrode mixture. An evaluation test was performed under the same conditions as in Example 1 except that the current value was measured at 5C in addition to 2C during the overcharge test.

Example 9
3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol to the negative electrode The addition amount is 1.5% by weight, and tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4'-diylphosphonite is 0.3% by weight in the negative electrode mixture. An evaluation test was performed under the same conditions as in Example 1 except that the current value was measured at 5C in addition to 2C during the overcharge test.

(Example 10)
3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol 0.5 wt. And 0.3% by weight of tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4'-diylphosphonite added to the negative electrode and overcharge test In this case, a current value was also measured at 5C in addition to 2C.

(Example 11)
3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol to the negative electrode The addition amount is 1.0% by weight, and 0.5% by weight of tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4′-diylphosphonite as a negative electrode mixture. An evaluation test was performed under the same conditions as in Example 1 except that the current value was measured at 5C in addition to 2C during the overcharge test.

Example 12
3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol to the negative electrode The addition amount is 1.5% by weight, and 0.5% by weight of tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4'-diylphosphonite as a negative electrode mixture. An evaluation test was performed under the same conditions as in Example 1 except that the current value was measured at 5C in addition to 2C during the overcharge test.

(Example 13)
3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol to the negative electrode The addition amount is 1.5% by weight, and tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4'-diylphosphonite is 0.1% by weight in the negative electrode mixture. An evaluation test was performed under the same conditions as in Example 1 except that the current value was measured at 5C in addition to 2C during the overcharge test.

  From Examples 7 to 9 and 10 to 13 in Table 3, when the ratio A / B of the addition amount A of the phosphorus-based antioxidant and the addition amount B of the phenol-based antioxidant is 0.1 or more and 0.2 or less Then, it is clear that there is no smoke even at 5C and the safety is further improved.

  Next, the examination result of the average particle diameter and specific surface area of a negative electrode active material is shown.

(Example 14)
A carbon material was produced under the same conditions as in Example 1 except that the average particle size of the carbon material was 10.2 μm and the specific surface area was 5.5 m ² / g, and an evaluation test was performed.

(Example 15)
The crushing method was changed from an impact crusher to a jet mill, and the negative electrode active material was prepared under the same conditions as in Example 1 except that the average particle size was changed to 5.5 μm and the specific surface area was changed to 9.2 m ² / g. An evaluation test was conducted.

(Example 16)
The crushing method was changed from an impact crusher to a jet mill, and the negative electrode active material was produced under the same conditions as in Example 1 except that the average particle size of the negative electrode active material was changed to 8.7 μm and the specific surface area was changed to 4.2 m ² / g. An evaluation test was conducted.

(Example 17)
A negative electrode active material was produced under the same conditions as in Example 1 except that the average particle size was changed to 11.3 μm and the specific surface area was changed to 8.5 m ² / g, and an evaluation test was performed.

(Example 18)
The crushing method was changed from an impact crusher to a jet mill, and the negative electrode active material was produced under the same conditions as in Example 1 except that the average particle size was changed to 5.3 μm and the specific surface area was changed to 13.2 m ² / g. An evaluation test was conducted.

From Examples 1, 14 to 16 and Examples 17 and 18, when the specific surface area is 1 m ² / g or more and 6 m ² / g or less and the average particle size of the carbon material is 10 μm or more and 20 μm or less, otherwise It was clear that there was no smoke and safety was further improved compared to the case of.

  Next, the examination result at the time of adding vinylene carbonate is shown.

(Example 19)
An evaluation test was conducted under the same conditions as in Example 1 except that 2.0% by weight of vinylene carbonate was added to the electrolyte, and that the current value was measured at 5C in addition to 2C during the overcharge test. went.

(Example 20)
An evaluation test was carried out under the same conditions as in Example 1 except that the current value was measured at 5C in addition to 2C during the overcharge test.

  From Examples 19 and 20, it can be seen that by adding vinylene carbonate to the electrolyte, there is no smoke even at 5C, and the safety is further improved.

  Next, 3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-cresol and The examination result of tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4'-diylphosphonite is shown.

(Example 21)
An evaluation test was carried out under the same conditions as in Example 1 except that the phenolic antioxidant was changed to 2,6-di-t-butyl-4-methylphenol.

(Example 22)
An evaluation test was carried out under the same conditions as in Example 1 except that the phosphorus antioxidant was changed to tris (nonylphenyl) phosphite.

  From Examples 1 and 21, 3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri- It has been found that p-cresol is less smoking than 2,6-di-t-butyl-4-methylphenol, and the safety is further improved.

  From Examples 4 and 22, tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4′-diylphosphonite has less fuming than tris (nonylphenyl) phosphite. It was found that the safety was further improved.

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 (13)

A lithium ion secondary battery in which a positive electrode that occludes and releases lithium ions and a negative electrode that occludes and releases lithium ions are formed through a non-aqueous electrolyte and a separator,
The negative electrode has a current collector and a negative electrode mixture,
The negative electrode mixture contains a negative electrode active material, a conductive agent, and a binder,
The negative electrode active material is a carbon material,
The negative electrode mixture contains a phenol group-containing compound in an amount of 0.5 wt% to 1.5 wt%, or a phosphorus compound in an amount of 0.1 wt% to 0.5 wt%. Lithium ion secondary battery. ^2. The lithium ion secondary material according to claim 1, wherein the carbon material has a specific surface area of 1 m ² / g or more and 6 m ² / g or less, and the carbon material has an average particle diameter of 10 μm or more and 20 μm or less. Next battery.   The lithium ion secondary battery according to claim 1, wherein the nonaqueous electrolytic solution contains a cyclic carbonate containing an unsaturated group.   The compound having a phenol group is 3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-tert-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri The lithium ion secondary battery according to claim 1, wherein the lithium ion secondary battery is −p-cresol.   2. The compound according to claim 1, wherein the phosphorus-containing compound is tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4′-diylphosphonite. Lithium ion secondary battery. A lithium ion secondary battery in which a positive electrode that occludes and releases lithium ions and a negative electrode that occludes and releases lithium ions are formed through a non-aqueous electrolyte and a separator,
The negative electrode has a current collector and a negative electrode mixture,
The negative electrode mixture contains a negative electrode active material, a conductive agent, and a binder,
The negative electrode active material is a carbon material,
The negative electrode mixture contains a phenol group-containing compound in an amount of 0.5 wt% to 1.5 wt% and a phosphorus compound in an amount of 0.1 wt% to 0.5 wt%. Lithium ion secondary battery.   The ratio of the content A of the compound having phosphorus and the content B of the compound having phenol group is 0.1 ≦ A / B ≦ 0.2. Lithium ion secondary battery. The specific surface area of the carbon material is 1 m ² / g or more and 6 m ² / g or less, and the average particle diameter of the carbon material is 10 μm or more and 20 μm or less. Next battery.   The lithium ion secondary battery according to claim 6, wherein the nonaqueous electrolytic solution contains a cyclic carbonate containing an unsaturated group.   The lithium ion secondary battery according to claim 6, wherein the cyclic carbonate is vinylene carbonate. A lithium ion secondary battery in which a positive electrode that occludes and releases lithium ions and a negative electrode that occludes and releases lithium ions are formed through a non-aqueous electrolyte and a separator,
The negative electrode has a current collector and a negative electrode mixture,
The negative electrode mixture contains a negative electrode active material, a conductive agent, and a binder,
The negative electrode active material is a carbon material,
The lithium ion secondary battery, wherein the negative electrode mixture contains an antioxidant.   The lithium ion secondary battery according to claim 11, wherein the antioxidant contains an oxygen atom.   The lithium ion secondary battery according to claim 11, wherein the antioxidant has a hydroxyl group.

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