WO2020012586A1 - Lithium-ion secondary battery and lithium-ion secondary battery production method - Google Patents

Abstract

This lithium-ion secondary battery includes: a negative electrode containing graphite particles which exhibit a roundness standard deviation of 0.05-0.10 in the cumulative frequency range of 10-90% by number of particles starting from the low-roundness side thereof in a cumulative frequency distribution of roundness obtained by a particle analyzer of the flow type; a positive electrode which contains one or more lithium compound types selected from the group consisting of LiCoO₂, LiNi_xMn_yCo_1-x-yO₂ (0<x<1, 0<y<1, x+y<1), LiNi_2-xMn_xO₄(0<x≤2), and LiFePO₄; and an electrolyte.

Description

Lithium ion secondary battery and method of manufacturing lithium ion secondary battery

The present disclosure relates to a lithium ion secondary battery and a method for manufacturing a lithium ion secondary battery.

Lithium-ion batteries (lithium-ion secondary batteries) are lightweight, high-energy-density secondary batteries that are used as power sources for portable devices such as notebook computers and mobile phones by utilizing their characteristics.
In recent years, lithium ion secondary batteries have been developed not only for consumer applications such as portable devices, but also for large-scale power storage systems for renewable energy such as in-vehicle applications, solar power generation, and wind power generation. In particular, in applications to the automotive field, lithium-ion secondary batteries are required to have excellent input characteristics in order to improve the efficiency of energy use by regeneration. In addition, lithium ion secondary batteries are also required to have excellent long-term life characteristics.
For example, Patent Literature 1 includes two types of graphitic particles having different optimum Raman R values (crystallinity), and one of them has an average circularity determined by a flow type particle analyzer of 0.9 or more. Accordingly, a negative electrode material for a non-aqueous secondary battery exhibiting high capacity, rapid charge / discharge characteristics, and high cycle characteristics has been proposed.
Further, in Patent Document 2, non-aqueous secondary particles exhibiting excellent characteristics of charge / discharge efficiency with low irreversible capacity by mixing graphite particles having an average circularity of 0.9 or more with graphite particles having a high aspect ratio. A negative electrode material for a battery has been proposed.

JP 2010-251315 A JP-A-2015-164143

However, in Patent Document 1, the two types of graphite are simply mixed, and although the continuous rapid input characteristic is superior to the conventional technology, the effect on the pulse charging characteristic is weak. It became clear from the examination of the people. In Patent Document 2, irreversible capacity is suppressed by mixing two types of graphite, and one type of graphite has a high aspect ratio, but no attention is paid to charging with a pulse. . Further, the inventors have found that the graphitic particles having a high aspect ratio have little effect on the charging characteristics by pulse.
In view of the above conventional circumstances, an object of the present disclosure is to provide a lithium ion secondary battery having a small irreversible capacity and excellent pulse charging characteristics, and a method for manufacturing the same.

Specific means for solving the above problems are as follows.
<1> In the cumulative frequency distribution with respect to the circularity obtained by the flow type particle analyzer, the standard deviation of the circularity is 0.1 to 90% by number in the range where the cumulative frequency from the lower circularity is 10% to 90%. A negative electrode comprising graphite particles of from 0.05 to 0.10.
_{LiCoO 2, LiNi x Mn y Co} 1-x-y O 2 (0 <x <1,0 <y <1, x + y <1), LiNi 2-x Mn x O 4 (0 <x ≦ 2) and LiFePO a positive electrode comprising at least one lithium compound selected from the group consisting of _4,
An electrolyte;
Lithium ion secondary batteries including.
<2> The lithium ion secondary battery according to <1>, wherein the circularity of the graphite particles when the cumulative frequency is 10% by number is 0.70 to 0.91.
<3> The lithium ion secondary battery according to <1> or <2>, wherein the graphite particles have a volume average particle diameter of 2 μm to 30 μm.
<4> peak in the Raman spectrum when irradiated with a laser beam of 532nm to the graphite ^particles, in the range of ^{1300 cm} -1 ~ 1400 cm ^-1 to the peak intensity IG in the range of 1580 cm -1 ~ 1620 cm ^-1 The lithium ion secondary battery according to any one of <1> to <3>, wherein a Raman R value (ID / IG), which is a ratio of the intensity ID, is 0.10 to 0.60.
<5> The lithium ion secondary according to any one of <1> to <4>, wherein the negative electrode further includes carbon particles having an average circularity determined by a flow type particle analyzer of 0.94 or less. battery.
<6> In the cumulative frequency distribution with respect to the circularity determined by the flow type particle analyzer, the standard deviation of the circularity is 0.1% to 90% by number in the range where the cumulative frequency from the low circularity side is 10% to 90%. Disposing a negative electrode mixture containing graphite particles having a particle size of 0.05 to 0.10 on the surface of the negative electrode current collector to produce a negative electrode;
_{LiCoO 2, LiNi x Mn y Co} 1-x-y O 2 (0 <x <1,0 <y <1, x + y <1), LiNi 2-x Mn x O 4 (0 <x ≦ 2) and LiFePO A step of disposing a positive electrode mixture containing at least one lithium compound selected from the group consisting of _{4 on} the surface of a positive electrode current collector to produce a positive electrode;
A method for producing a lithium ion secondary battery comprising:

According to the present disclosure, it is possible to provide a lithium ion secondary battery having a small irreversible capacity and excellent pulse charging characteristics, and a method for manufacturing the same.

1 is a cross-sectional view of a lithium ion secondary battery according to an embodiment of the present disclosure.

Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and ranges thereof, and does not limit the present invention. Further, various changes and modifications by those skilled in the art are possible within the scope of the technical idea of the present disclosure.
In the present disclosure, the term "step" includes, in addition to a step independent of other steps, even if the purpose of the step is achieved even if it cannot be clearly distinguished from other steps, the step is also included. .
In the present disclosure, the numerical ranges indicated by using “to” include the numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In the numerical ranges described in stages in the present disclosure, the upper limit or lower limit described in one numerical range may be replaced with the upper limit or lower limit of the numerical range described in other stages. . Further, in the numerical range described in the present disclosure, the upper limit or the lower limit of the numerical range may be replaced with the value shown in the embodiment.
In the present disclosure, each component may include a plurality of corresponding substances. When there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, the content or content of each component is the total content or content of the plurality of substances present in the composition. Means the amount.
In the present disclosure, a plurality of types of particles corresponding to each component may be included. When a plurality of types of particles corresponding to each component are present in the composition, the particle size of each component means a value of a mixture of the plurality of types of particles present in the composition unless otherwise specified.
In the present disclosure, the term “layer” or “film” means that when a region where the layer or film exists is observed, in addition to the case where the layer or film is formed over the entire region, only a part of the region is used. The case where it is formed is also included.
In the present disclosure, the “solid content” of the positive electrode mixture or the negative electrode mixture means a remaining component obtained by removing a volatile component such as an organic solvent from the positive electrode mixture slurry or the negative electrode mixture slurry.
When an embodiment is described with reference to the drawings in the present disclosure, the configuration of the embodiment is not limited to the configuration illustrated in the drawings. Also, the size of the members in each drawing is conceptual, and the relative relationship of the sizes between the members is not limited to this.

≪Lithium ion secondary battery≫
According to the lithium ion secondary battery of the present disclosure, in the cumulative frequency distribution with respect to the circularity obtained by the flow-type particle analyzer, the circular frequency is in a range where the cumulative frequency from the lower circularity side is 10% to 90% by number. every time a negative electrode containing a graphite particles standard deviation is 0.05 to _{0.10, LiCoO 2, LiNi x Mn y} Co 1-x-y O 2 (0 <x <1,0 <y <1, x + y <1), a positive electrode containing at least one lithium compound selected from the group consisting of LiNi _2-x Mn _x O ₄ (0 <x ≦ 2) and LiFePO _4, and an electrolyte.
The lithium ion secondary battery of the present disclosure has a small irreversible capacity and is excellent in pulse charging characteristics. Although the reason is not necessarily clear, it is considered that a lithium ion secondary battery excellent in the above characteristics can be obtained by using a negative electrode containing a specific negative electrode active material and a positive electrode containing a specific lithium compound in combination.

First, the outline of the lithium ion secondary battery will be briefly described. The lithium ion secondary battery includes the above-described negative electrode, positive electrode, and electrolyte.

In one embodiment, the lithium ion secondary battery may have a configuration in which a nonaqueous electrolyte including a positive electrode, a negative electrode, a separator, and an electrolyte is provided in a battery container. At this time, the separator is arranged between the positive electrode and the negative electrode.
In this embodiment, when charging the lithium ion secondary battery, a charger is connected between the positive electrode and the negative electrode. During charging, lithium ions inserted into the positive electrode active material are desorbed and released into the non-aqueous electrolyte. The lithium ions released into the non-aqueous electrolyte move in the non-aqueous electrolyte, pass through the separator, and reach the negative electrode. The lithium ions reaching the negative electrode are inserted into a negative electrode active material constituting the negative electrode.
In this embodiment, at the time of discharging, an external load is connected between the positive electrode and the negative electrode. At the time of discharging, lithium ions inserted in the negative electrode active material are desorbed and released into the non-aqueous electrolyte. At this time, electrons are emitted from the negative electrode. Then, the lithium ions released into the non-aqueous electrolyte move in the non-aqueous electrolyte, pass through the separator, and reach the positive electrode. The lithium ions reaching the positive electrode are inserted into the positive electrode active material constituting the positive electrode. When lithium ions are inserted into the positive electrode active material, electrons flow into the positive electrode. In this manner, discharge is performed by the transfer of electrons from the negative electrode to the positive electrode.

As described above, the lithium ion secondary battery can be charged and discharged by inserting and removing lithium ions between the positive electrode active material and the negative electrode active material. A configuration example of an actual lithium ion secondary battery will be described later (for example, see FIG. 1).
Next, a negative electrode, a positive electrode, an electrolyte, and other components provided as needed, which are components of the lithium ion secondary battery of the present disclosure, will be sequentially described.

<Negative electrode>
In the negative electrode used in the lithium ion secondary battery according to the present disclosure, the cumulative frequency distribution with respect to the circularity determined by the flow type particle analyzer has a range in which the cumulative frequency from the lower circularity is 10% to 90% by number. The graphite particles include a standard deviation of circularity (hereinafter, sometimes referred to as “standard deviation of circularity in a specific range”) of 0.05 to 0.10. Graphitic particles can function as a negative electrode active material. Hereinafter, the negative electrode material containing the graphite particles as the negative electrode active material is also referred to as “negative electrode material”.

(Graphitic particles)
The standard deviation of the circularity in a specific range of the graphite particles is preferably 0.06 to 0.10, more preferably 0.06 to 0.09, and more preferably 0.06 to 0.08. Is more preferred.
The circularity of the graphitic particles can be measured using a flow type particle analyzer (for example, a wet flow type particle size / shape analyzer FPIA-3000 manufactured by Malvern Co.). For analysis of the cumulative frequency distribution, the average circularity, and the standard deviation of circularity in a specific range based on the circularity measurement results, refer to the FPIA-3000 academic materials (published second edition on August 31, 2006). Can be carried out on the basis.
The measurement temperature is 25 ° C., the concentration of the measurement sample is 10% by mass, and the number of particles to be counted is 10,000. Water is used as a solvent for dispersion.
When measuring the circularity of the graphite particles, it is preferable to disperse the graphite particles in advance. For example, it is possible to disperse the graphite particles using an ultrasonic dispersion, a vortex mixer, or the like. In order to suppress the influence of the collapse or breakage of the graphite particles, the intensity and time of stirring may be appropriately adjusted in consideration of the strength of the graphite particles to be measured.
As the ultrasonic treatment, for example, after storing an arbitrary amount of water in a tank of an ultrasonic cleaner (for example, ASU-10D, manufactured by As One Corporation), a test tube containing a dispersion liquid of the graphitic particles is placed. It is preferable to perform ultrasonic treatment for 1 to 10 minutes together with the holder. Within this time, it is easy to disperse the graphite particles while suppressing particle collapse, particle destruction, increase in sample temperature, and the like.

If the standard deviation of the circularity in the specific range is in the range of 0.05 to 0.10. The average circularity of the graphite particles is not particularly limited. For example, the average circularity of the graphite particles is preferably 0.70 or more, more preferably 0.80 or more, and even more preferably 0.85 or more. The average circularity of the graphitic particles may be greater than 0.90, greater than 0.92, or greater than 0.94. When the average circularity of the graphite particles is 0.70 or more, continuous charge acceptability tends to be improved.
In one embodiment, the average circularity of the graphitic particles may be larger than the average circularity of the carbon particles described below.

Further, when the cumulative frequency of the graphite particles (accumulated frequency from the lower circularity in the cumulative frequency distribution with respect to the circularity determined by the flow type particle analyzer) is 10% by number, the circularity is 0.1%. It is preferably from 70 to 0.91, may be from 0.80 to 0.91, and may be from 0.85 to 0.91.

The volume average particle size of the graphite particles is not particularly limited, but is preferably 2 μm to 30 μm, more preferably 2.5 μm to 25 μm, further preferably 3 μm to 20 μm, and more preferably 5 μm to 20 μm. Is particularly preferred. When the volume average particle diameter of the graphite particles is 30 μm or less, the discharge capacity and discharge characteristics tend to be improved. When the volume average particle diameter of the graphite particles is 2 μm or more, the initial charge / discharge efficiency tends to be improved.
The volume average particle size is determined by measuring the volume-based particle size distribution using a particle size distribution measuring device (for example, SALD-3000 manufactured by Shimadzu Corporation) using a laser light scattering method, and calculating d50 (median diameter). Can be sought.

BET specific surface area of the graphite particles is not particularly ^limited, is preferably from 0.8m ² /g~8.0m 2 / ^g, more to be 1.0m ² /g~7.0m 2 / g ^preferably, it is more preferably 1.5m ² /g~6.0m 2 / g. When the BET specific surface area of the graphite particles is 0.8 m ² / g or more, excellent battery performance tends to be obtained. When the BET specific surface area of the graphite particles is 8.0 m ² / g or less, the tap density tends to increase, and the mixing property with other materials such as a binder and a conductive material tends to be improved.
The BET specific surface area can be measured from the nitrogen adsorption capacity according to JIS Z 8830: 2013. As the evaluation device, for example, AUTOSARB-1 (trade name) manufactured by QUANTACHROME can be used. When measuring the BET specific surface area, since it is considered that the moisture adsorbed on the sample surface and the structure may affect the gas adsorption capacity, it is preferable to first perform a pretreatment for removing moisture by heating. .
In the pre-treatment, the measurement cell into which 0.05 g of the measurement sample was charged was evacuated to 10 Pa or less by a vacuum pump, heated at 110 ° C., and maintained for 3 hours or more. (25 ° C). After performing this pretreatment, the evaluation temperature is set to 77 K, and the evaluation pressure range is measured as a relative pressure (equilibrium pressure with respect to the saturated vapor pressure) of less than 1.

The graphite particles in the present disclosure are those containing graphite as a component and having an average plane spacing (d ₀₀₂ ) of less than 0.3400 nm in X-ray wide-angle diffraction. Note that the theoretical value of the average interplanar spacing (d ₀₀₂ ) of graphite crystals is 0.3354 nm, and the energy density tends to increase as the value approaches this value.
The average plane spacing (d ₀₀₂ ) appears near the point where the diffraction angle 2θ is 24 ° to 27 ° in a diffraction profile obtained by irradiating a sample with X-rays (CuKα rays) and measuring the diffraction lines with a goniometer. , Based on the diffraction peak corresponding to the carbon 002 plane.
The average plane distance (d ₀₀₂ ) can be measured under the following conditions.
Source: CuKα ray (wavelength = 0.15418 nm)
Output: 40kV, 20mA
Sampling width: 0.010 °
Scanning range: 10 ° to 35 °
Scan speed: 0.5 ° / min

Bragg's equation: 2dsinθ = nλ
Here, d is the length of one cycle, θ is the diffraction angle, n is the reflection order, and λ is the X-ray wavelength.

As the graphite particles, particles obtained by pulverizing massive natural graphite may be used. Since the graphite particles obtained by pulverizing massive natural graphite may contain impurities, it is preferable to purify the natural graphite by a purification treatment.
The method for refining natural graphite is not particularly limited and can be appropriately selected from commonly used refining methods. For example, flotation, electrochemical treatment, chemical treatment and the like can be mentioned.

The purity of the natural graphite is preferably 99.8% or more (ash content 0.2% or less), more preferably 99.9% or more (ash content 0.1% or less) on a mass basis. When the purity is 99.8% or more, the safety of the battery is further improved, and the battery performance tends to be further improved.
The purity of natural graphite can be calculated, for example, by allowing 100 g of graphite to stand in a furnace at 800 ° C. for 48 hours or more in an air atmosphere, and then measuring the remaining amount derived from ash.

As the graphite particles, artificial graphite obtained by firing a resin material such as an epoxy resin or a phenol resin, or a pitch material obtained from petroleum, coal or the like may be used.

The method for obtaining the artificial graphite is not particularly limited, for example, a thermoplastic resin, naphthalene, anthracene, phenanthroline, coal tar, tar pitch and the like are calcined in an inert atmosphere at 800 ° C or higher, There is a method of obtaining artificial graphite as a fired product. Next, the obtained fired product is pulverized by a known method such as a jet mill, a vibration mill, a pin mill, a hammer mill and the like, and the graphite particles derived from artificial graphite are prepared by adjusting the volume average particle diameter to about 2 to 40 μm. can do. Before calcining, the raw material may be subjected to heat treatment in advance. In the case where the raw material is subjected to heat treatment, for example, a heat treatment is performed in advance by a device such as an autoclave, and after coarsely pulverized by a known method, the raw material that has been heat-treated in an inert atmosphere of 800 ° C. or higher is calcined in the same manner as described above. Then, the graphite particles derived from the artificial graphite can be obtained by pulverizing the obtained fired product artificial graphite and adjusting the volume average particle diameter to about 2 μm to 40 μm.

Graphitic particles may be modified by other materials than graphite. The graphite particles may have, for example, a low-crystalline carbon layer on the surface of graphite serving as a nucleus. When the graphite particles have a low-crystalline carbon layer on the surface of graphite, the ratio (mass ratio) of the low-crystalline carbon layer to 1 part by mass of graphite is preferably 0.005 to 10, more preferably 0.005 to 5. More preferably, it is more preferably 0.005 to 0.08. When the ratio (mass ratio) of the low crystalline carbon layer to graphite is 0.005 or more, the initial charge / discharge efficiency and the life characteristics tend to be excellent. If it is less than 10, the output characteristics tend to be excellent.
When the graphite particles are modified with a material other than graphite, the content of graphite and other materials other than graphite contained in the graphite particles may be, for example, TG-DTA (Thermogravimetry-Differential Thermal Analysis, differential). Thermo-thermogravimetric measurement) is used to measure the weight change in an air stream, and can be calculated based on the weight loss ratio when the temperature is raised from 500 ° C. to 600 ° C. At this time, a weight change in a temperature range from 500 ° C. to 600 ° C. can be attributed to a weight change derived from a material other than graphite. On the other hand, the balance after the completion of the heat treatment can be attributed to the amount of graphite.

The ratio of the Raman spectrum when irradiated with a laser beam of 532nm relative to graphite ^particles, the peak intensity ID in the range of ^{1300 cm} -1 ~ 1400 cm ^-1 to the peak intensity IG in the range of 1580 cm -1 ~ 1620 cm ^-1 The Raman R value (ID / IG) is not particularly limited. For example, the Raman R value is preferably 0.10 to 0.60, more preferably 0.15 to 0.55, and even more preferably 0.20 to 0.50.
The Raman spectrum can be measured using a Raman spectrometer (for example, DXR manufactured by Thermo Fisher Scientific).

-Carbon particles having an average circularity of 0.94 or less-
In one embodiment, the negative electrode may include carbon particles having an average circularity determined by a flow type particle analyzer of 0.94 or less (hereinafter, also simply referred to as “carbon particles”). In the present disclosure, the “carbon particles” are carbon particles having at least one of a particle size distribution and a circularity distribution (average circularity, standard deviation of circularity in a specific range, and the like) of the aforementioned “graphitic particles”. Represents a different set inclusively. The material of the carbon particles may be the same as or different from the graphite particles.
Examples of the carbon particles include natural graphite such as flaky natural graphite, spherical natural graphite obtained by spheroidizing flaky natural graphite, artificial graphite, and amorphous carbon. From the viewpoint of input characteristics, the carbon particles preferably include natural graphite.

The average circularity of the carbon particles is 0.94 or less, preferably 0.81 to 0.94, and more preferably 0.85 to 0.92. When the average circularity is 0.94 or less, the input characteristics and the cycle characteristics tend to be improved. Although the reason for this is not necessarily clear, it is presumed that one of the reasons is that the inclusion of carbon particles having an average circularity of 0.94 or less makes it easy to obtain an efficient conductive path.
The average circularity of carbon particles can be measured in the same manner as the average circularity of graphite particles.

Regarding the carbon particles, in the cumulative frequency distribution with respect to the circularity obtained by the flow type particle analyzer, the standard deviation of the circularity in a range where the cumulative frequency from the lower circularity is 10% to 90% is There is no particular limitation. For example, the standard deviation may be 0.06 to 0.65, 0.10 to 0.60, or more than 0.10 and 0.60 or less.

Regarding the carbon particles, in the cumulative frequency distribution with respect to the circularity obtained by the flow type particle analyzer, the circularity when the cumulative frequency from the lower circularity side is 10% by number is not particularly limited. For example, the circularity may be 0.40 to 0.85, may be 0.40 or more and less than 0.85, may be 0.45 to 0.80, and may be 0.45 or more. It may be less than 0.80, 0.45 to 0.69, or 0.45 to 0.65.

体積 The volume average particle diameter of the carbon particles is not particularly limited, but is preferably 0.5 μm to 15 μm, more preferably 1 μm to 10 μm, and still more preferably 1 μm to 7 μm. When the volume average particle size of the carbon particles is in the range of 0.5 μm to 15 μm, excessive decomposition of the electrolytic solution is suppressed, and the cycle characteristics tend to be improved. The volume average particle size of the carbon particles can be measured by the same method as the volume average particle size of the graphite particles.

The BET specific surface area of the carbon particles is not particularly limited, but is preferably ² m ² / g to 50 m ² / g, more preferably 2 m ² / g to 40 m ² / g, and more preferably 3 m ² / g to 30 m ^2. / G is more preferable. When the BET specific surface area of the carbon particles is in the range of ² m ² / g to 50 m ² / g, excessive decomposition of the electrolytic solution is suppressed, and input characteristics tend to be improved. The BET specific surface area of the carbon particles can be measured by the same method as the BET specific surface area of the graphite particles.

The average interplanar spacing (d ₀₀₂ ) of the carbon particles determined by the X-ray diffraction method is preferably from 0.3354 nm to 0.3400 nm, more preferably from 0.3354 nm to 0.3380 nm. When the average plane distance (d ₀₀₂ ) of the carbon particles is 0.3400 nm or less, both the initial charge / discharge efficiency and the energy density of the lithium ion secondary battery tend to be excellent.

The value of the average interplanar spacing (d ₀₀₂ ) of the carbon particles tends to be reduced, for example, by increasing the temperature of the heat treatment when producing the negative electrode material. Therefore, by adjusting the temperature of the heat treatment at the time of manufacturing the negative electrode material, the average surface spacing (d ₀₀₂ ) of the negative electrode material can be controlled.

(4) The carbon particles may have a carbonaceous substance different from the carbon particles on at least a part of the surface thereof, if necessary.

Is the ratio of the peak intensity ID in the range of ^{1300 cm} -1 ~ 1400 cm ^-1 to the peak intensity IG in the range of ^{1580 cm} -1 ~ 1620 cm ^-1 in the Raman spectrum when irradiated with a laser beam of 532nm to the carbon particles The Raman R value (ID / IG) is not particularly limited. For example, the Raman R value is preferably from 0.10 to 1.00, more preferably from 0.20 to 0.80, and even more preferably from 0.20 to 0.70. When the Raman R value is 0.10 or more, there are sufficient lattice defects used for insertion and desorption of lithium ions, and a decrease in input / output characteristics tends to be suppressed. When the R value is 1.00 or less, the decomposition reaction of the electrolytic solution is sufficiently suppressed, and a decrease in the initial efficiency tends to be suppressed.

When the negative electrode contains graphite particles and carbon particles, the mass ratio of the graphite particles to the carbon particles (graphite particles: carbon particles) in the negative electrode material is preferably 51:49 to 99: 1, and 65:99 to 99: 1. The ratio is more preferably from 35 to 98: 2, even more preferably from 80:20 to 95: 5.

When the negative electrode contains graphite particles and carbon particles, the carbon particles preferably have a smaller volume average particle diameter than the graphite particles. Thereby, the cycle characteristics tend to be improved.
When the negative electrode contains graphite particles and carbon particles, the ratio of the volume average particle diameter of the graphite particles to the carbon particles (graphite particles: carbon particles) may be from 10: 0.1 to 10: 9. Preferably, it is 10: 0.3 to 10: 8, more preferably 10: 0.5 to 10: 5. When the ratio of the volume average particle diameter of the graphite particles to the carbon particles is 10: 0.1 to 10: 9, excellent pulse charging characteristics, cycle characteristics, and storage characteristics tend to be easily obtained.

When the negative electrode contains graphite particles and carbon particles, the negative electrode has graphite particles having a standard deviation of circularity in a specific range of 0.05 to 0.10 and an average circularity of 0.94 or less. It can be confirmed that carbon particles are contained as follows. The negative electrode material used for the negative electrode is separated into graphitic particles and carbon particles by an ultrasonic separator (eg, As One Corporation, ASU-6D). With respect to the obtained graphitic particles and carbon particles, the standard deviation and average circularity of the circularity in a specific range are determined as described above.

(Other particles)
The negative electrode may contain, as the negative electrode active material, graphite particles and, if necessary, particles other than the above-described carbon particles. For example, particles such as metal oxides such as tin oxide and silicon oxide, metal composite oxides, lithium alone, lithium alloys such as lithium aluminum alloys, and materials such as materials capable of forming alloys with lithium such as Sn and Si may be used in combination. . One type of these particles may be used alone, or two or more types may be used in combination.

In one embodiment, the negative electrode may include particles containing silicon atoms as the negative electrode active material. The particles containing silicon atoms can be selected from silicon (Si) and other silicon-containing compounds, and are preferably silicon oxides from the viewpoint of capacity, cycle characteristics, and the like. The silicon oxide may be any oxide containing silicon, and examples include silicon monoxide (also referred to as silicon oxide), silicon dioxide, and silicon suboxide. These may be used alone or in combination of two or more.
Among silicon oxides, silicon oxide and silicon dioxide are generally represented as silicon monoxide (SiO) and silicon dioxide (SiO ₂ ), respectively, but the surface state (for example, the presence of an oxide film), Depending on the state of formation of the compound, the compositional formula SiOx (x is 0 <x ≦ 2) may be used as the measured value (or converted value) of the contained element in some cases. In this case, silicon oxide is used. The value of x can be calculated, for example, by quantifying oxygen contained in silicon oxide by an inert gas melting-non-dispersive infrared absorption method. Further, when a disproportionation reaction of silicon oxide (2SiO → Si + SiO ₂ ) is involved in the production process of the particle A, it is expressed in a state containing silicon and silicon dioxide (in some cases, silicon oxide) due to a chemical reaction. In some cases, silicon oxide is used.

When producing silicon oxide particles by the disproportionation reaction of silicon oxide, silicon oxide as a raw material, for example, cooling a gas of silicon monoxide generated by heating a mixture of silicon dioxide and metal silicon and It can be obtained by a known sublimation method for precipitation. Further, it can be obtained from the market as silicon oxide, silicon monoxide, Silicon @ Monoxide, or the like.

粒子 The particles containing silicon atoms may have a structure in which silicon crystallites are dispersed in silicon oxide particles. Whether or not silicon crystallites are present in the silicon oxide particles can be confirmed, for example, by powder X-ray diffraction (XRD) measurement. When silicon crystallites are present in the silicon oxide particles, when powder X-ray diffraction (XRD) measurement is performed using CuKα radiation having a wavelength of 0.15418 nm as a source, 2θ is around 28.4 °. A diffraction peak derived from Si (111) is observed. When silicon crystallites are present in the silicon oxide, it is easy to obtain a high initial discharge capacity and good initial charge / discharge efficiency.

The metal composite oxide is not particularly limited as long as it can occlude and release lithium, and those containing Ti, Li or both Ti and Li are preferable from the viewpoint of discharge characteristics.

When the negative electrode material contains graphite particles as the negative electrode active material and particles other than the carbon particles included as necessary, the ratio of the particles other than the graphite particles and the carbon particles in the negative electrode material is 0.5 mass % To 20% by mass, more preferably 1% to 15% by mass.

[Specific configuration of negative electrode]
Hereinafter, a specific configuration of the negative electrode according to one embodiment will be described. In addition, the negative electrode used for the lithium ion secondary battery of the present disclosure is not limited to the following specific configuration.

に お い て In one embodiment, the negative electrode (negative electrode plate) has a current collector (negative electrode current collector) and a negative electrode mixture layer disposed on the surface thereof. The negative electrode mixture layer is a layer of a negative electrode mixture containing a negative electrode active material disposed on the surface of the current collector. In the present disclosure, in the cumulative frequency distribution with respect to the circularity determined by the flow type particle analyzer, the negative electrode mixture has a circularity within a range where the cumulative frequency from the low circularity side is 10% to 90% by number. Contains graphitic particles having a standard deviation of 0.05 to 0.10.

Next, the negative electrode mixture layer and the current collector will be described in detail. The negative electrode mixture layer contains a negative electrode active material, a binder used as necessary, and the like, and is disposed on the current collector. The method for forming the negative electrode mixture layer is not limited, and for example, is formed as follows. A negative electrode active material, a binder and a conductive material used as necessary, and other materials such as a thickener are dissolved or dispersed in a dispersion solvent to form a slurry of a negative electrode mixture, which is applied to a current collector, By drying (wet method), a negative electrode mixture layer can be formed.

The content of the negative electrode material in the negative electrode mixture layer is preferably 80% by mass or more, more preferably 85% by mass or more based on the total amount of the negative electrode mixture layer, from the viewpoint of increasing the capacity of the battery. , 90% by mass or more. Here, in the cumulative frequency distribution with respect to the circularity obtained by the flow-type particle analyzer, the negative electrode material is defined as a circularity of the circularity within a range where the cumulative frequency from the lower circularity is 10% to 90% by number. A negative electrode material is obtained by combining graphite particles having a standard deviation of 0.05 to 0.10. And other negative electrode active materials included as necessary.

Examples of the conductive material for the negative electrode include natural graphite other than the graphite particles according to the negative electrode material for a lithium ion secondary battery of the present disclosure, graphite (graphite) such as artificial graphite, carbon black such as acetylene black, and needle coke or the like. Regular carbon or the like can be used. As the conductive material for the negative electrode, one type may be used alone, or two or more types may be used in combination. As described above, by adding the conductive material, there is a tendency that effects such as reduction of the resistance of the electrode are exerted.

The content of the conductive material with respect to the mass of the negative electrode mixture layer is preferably from 1% by mass to 45% by mass, and more preferably from 2% by mass to 42% by mass from the viewpoint of improving conductivity and reducing the initial irreversible capacity. More preferably, it is more preferably from 3% by mass to 40% by mass. When the content of the conductive material is 1% by mass or more, sufficient conductivity tends to be easily obtained. When the content of the conductive material is 45% by mass or less, a decrease in battery capacity tends to be suppressed.

The binder for the negative electrode is not particularly limited as long as it is a material that is stable with respect to the nonaqueous electrolyte or the dispersion solvent used in forming the electrode. Specifically, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polyimide, cellulose, and nitrocellulose; rubber-like polymers such as SBR (styrene-butadiene rubber) and NBR (acrylonitrile-butadiene rubber); polyvinylidene fluoride Fluorinated polymers such as (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-vinylidene fluoride copolymer; polymer compositions having ion conductivity of alkali metal ions (particularly lithium ions) Things. In addition, as the binder for the negative electrode, one type may be used alone, or two or more types may be used in combination.
Among them, it is preferable to use a fluorine-based polymer represented by SBR or polyvinylidene fluoride.

The content of the binder relative to the mass of the negative electrode mixture layer is preferably 0.1% by mass to 20% by mass, more preferably 0.5% by mass to 15% by mass, and more preferably 0.6% by mass. % To 10% by mass.
When the content of the binder is 0.1% by mass or more, the negative electrode active material can be sufficiently bound, and sufficient mechanical strength of the negative electrode mixture layer tends to be obtained. When the content of the binder is 20% by mass or less, sufficient battery capacity and conductivity tend to be obtained.

When a fluorine-based polymer typified by polyvinylidene fluoride is used as the main component, the content of the binder with respect to the mass of the negative electrode mixture layer is 1% by mass to 15% by mass. Is preferably 2% by mass to 10% by mass, and more preferably 3% by mass to 8% by mass.

Thickeners are used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specific examples include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. As the thickener, one type may be used alone, or two or more types may be used in combination.

When a thickener is used, the content of the thickener with respect to the mass of the negative electrode mixture layer is preferably 0.1% by mass to 5% by mass from the viewpoint of input / output characteristics and battery capacity. It is more preferably from 3% by mass to 3% by mass, and further preferably from 0.6% by mass to 2% by mass.

As the dispersion solvent for forming the slurry, as long as the solvent can dissolve or disperse the negative electrode active material, and a binder, a conductive material or a thickener used as necessary, There is no limitation, and either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water, alcohol, and a mixed solvent of water and alcohol. Examples of organic solvents include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethyl sulfoxide , Benzene, xylene, hexane and the like. In particular, when an aqueous solvent is used, it is preferable to use a thickener.

The negative electrode mixture layer formed on the current collector is preferably compacted by a hand press, a roller press, or the like in order to improve the packing density of the negative electrode active material.
The density of the consolidated negative electrode mixture layer is preferably from 0.7 g / cm ³ to 2 g / cm ³ , more preferably from 0.8 g / cm ³ to 1.9 g / cm ³ , and more preferably from 0.1 g / cm ³ to 1.9 g / cm ³ . More preferably, it is 9 g / cm ³ to 1.8 g / cm ³ .
When the density of the negative electrode mixture layer is 0.7 g / cm ³ or more, the conductivity between the negative electrode active materials is improved, the increase in battery resistance can be suppressed, and the capacity per unit volume tends to be improved. . When the density of the negative electrode mixture layer is 2 g / cm ³ or less, deterioration of the discharge characteristics due to an increase in the initial irreversible capacity and a decrease in the permeability of the nonaqueous electrolyte near the interface between the current collector and the negative electrode active material are prevented. There is a tendency that the risk of inviting them is reduced.
In addition, the amount of one-sided application of the slurry of the negative electrode mixture to the current collector when forming the negative electrode mixture layer is from 30 g / m ² to 30 g / m ² as a solid content of the negative electrode mixture from the viewpoint of energy density and input / output characteristics. It is preferably 150 g / m ² , more preferably 40 g / m ² to 140 g / m ² , and further preferably 45 g / m ² to 130 g / m ² .
In consideration of the amount of the negative electrode mixture slurry applied to the current collector on one side and the density of the negative electrode mixture layer, the average thickness of the negative electrode mixture layer is preferably 10 μm to 150 μm, and more preferably 15 μm to 140 μm. More preferably, the thickness is 15 μm to 120 μm.

材質 The material of the current collector for the negative electrode is not particularly limited, and specific examples include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Among them, copper is preferred from the viewpoint of ease of processing and cost.

形状 The shape of the current collector is not particularly limited, and materials processed into various shapes can be used. Specific examples include a metal foil, a metal plate, a metal thin film, and an expanded metal. Among them, a metal thin film is preferable, and a copper foil is more preferable. The copper foil includes a rolled copper foil formed by a rolling method and an electrolytic copper foil formed by an electrolytic method, and both are suitable as current collectors.

The average thickness of the current collector is not particularly limited. For example, the thickness is preferably 5 μm to 50 μm, more preferably 8 μm to 40 μm, and still more preferably 9 μm to 30 μm.
When the average thickness of the current collector is less than 25 μm, the strength can be improved by using a stronger copper alloy (such as phosphor bronze, titanium copper, Corson alloy, or Cu—Cr—Zr alloy) than pure copper. .

<Positive electrode>
The positive electrode used in a lithium ion secondary battery of the present disclosure (hereinafter, simply referred to as "positive electrode") _{is, LiCoO 2, LiNi x Mn y} Co 1-x-y O 2 (0 <x <1,0 < y <1, x + y <1), and at least one lithium compound selected from the group consisting of LiNi _2-x Mn _x O ₄ (0 <x ≦ 2) and LiFePO ₄ . The lithium compound can function as a positive electrode active material.
By using these lithium compounds as the positive electrode, the performance provided by the above-described negative electrode can be effectively exhibited. For example, by combining the positive electrode with the above-described negative electrode, a lithium ion secondary battery having a small irreversible capacity and excellent pulse charging characteristics can be obtained. Further, the lithium ion secondary battery tends to have excellent storage characteristics.

Although not shown in the above chemical formula of the lithium compound, the molar ratio of lithium is not limited to 1, and is a value that increases or decreases due to charge and discharge. For example, the molar ratio of lithium in the chemical formula of the lithium compound may be more than 0 and 1.2 or less.

_Further, in _{LiNi x Mn y Co 1-x} -y O 2 (0 <x <1,0 <y <1, x + y <1) the lithium compound represented by, from the viewpoint of energy density, 0.2 <x < It is preferably 1, and more preferably 0.2 <x <0.9. In addition, from the viewpoint of availability and the like, it is preferable that 0 <y <0.8, more preferably 0 <y <0.5, and 0.1 <y <0.5. Is more preferred. In particular, it is preferable that 0.2 <x <1 and 0 <y <0.5.

_{LiNi x Mn y Co 1-x} -y As O 2 (0 <x <1,0 <y <1, x + y <1) the lithium compound represented _by, LiNi _1/3 Mn _{1/3 Co 1/3} O ₂ , LiNi _5/10 Mn _3/10 Co _2/10 O ₂ , LiNi _6/10 Mn _2/10 Co _2/10 O ₂ , LiNi _8/10 Mn _1/10 Co _1/10 O _{2 and the} like. .

In the lithium compound represented by LiNi _2-x Mn _x O ₄ (0 <x ≦ 2), it is preferable that 0.4 <x ≦ 2, and it may be 0.4 <x <2.

Examples of the lithium compound represented by LiNi _2-x Mn _x O ₄ (0 <x ≦ 2) include LiNi _0.5 Mn _1.5 O ₄ , LiMn ₂ O _{4 and the} like.

Among these lithium compounds, from the viewpoint of cycle characteristics and thermal stability, at least one selected from the group consisting of LiNi _2-x Mn _x O ₄ (0 <x ≦ 2) and LiFePO ₄ is preferable, and LiFePO 4 ₄ is more preferred. Energy density, the initial charge-discharge efficiency, the pulse charging characteristics, from the viewpoint of a balance of such storage _{characteristics, LiNi x Mn y Co 1-} x-y O 2 is preferred.

The lithium compound may be further modified with a different metal, ceramic, or the like.
The modification method and modification state in this case are not particularly limited. For example, a part of the lithium compound used for the positive electrode may be replaced with a different metal, ceramic, or the like. Further, the surface of the particles of the lithium compound may be adhered or coated with a dissimilar metal, ceramic, or the like.
The substance used for the modification is not particularly limited, and metals such as Al and Mg, and oxides such as MgO, ZnO ₂ , CeO ₂ , and Li ₄ Ti ₅ O ₁₂ can be used.

The lithium compound is used as a positive electrode active material in the form of particles. The particle shape is not particularly limited, and may be a lump, a polyhedron, a sphere, an oval sphere, a plate, a needle, a column, or the like.

The volume average particle diameter (d50) of the particles of the positive electrode active material (the volume average particle diameter (d50) of the secondary particles when the primary particles are aggregated to form secondary particles) is determined by the tap density (fillability). ), From the viewpoint of mixing with other materials when forming the electrode, the thickness is preferably 1 μm to 30 μm, more preferably 3 μm to 25 μm, and still more preferably 5 μm to 15 μm. The volume average particle diameter (d50) of the particles of the positive electrode active material can be measured in the same manner as in the case of the graphite particles.

Range of BET specific surface area of particles of the positive electrode active material is ^preferably 0.2m ² /g~4.0m 2 / ^g, more to be 0.3m ² /g~2.5m 2 / g ^preferably, it is more preferably 0.4m ² /g~1.5m 2 / g.
When the BET specific surface area of the particles of the positive electrode active material is 0.2 m ² / g or more, excellent battery performance tends to be obtained. Further, when the BET specific surface area of the particles of the positive electrode active material is 4.0 m ² / g or less, the tap density tends to increase, and the mixing property with other materials such as a binder and a conductive material tends to be good. is there. The BET specific surface area can be measured in the same manner as in the case of the graphite particles.

The positive electrode may contain other positive electrode active materials in addition to the lithium compound. As the positive electrode active material other than the lithium compound, those commonly used in this field may be used. For example, lithium-containing composite metal oxides other than the above-mentioned lithium compounds, chalcogen compounds, manganese dioxide and the like can be mentioned.

The lithium-containing composite metal oxide is a metal oxide containing lithium and a transition metal or a metal oxide in which a part of the transition metal in the metal oxide is replaced by a different element. Here, examples of the different elements include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V and B, and Mn, Al, Co , Ni and Mg are preferred. One kind of the different kinds of elements may be used alone, or two or more kinds may be used in combination.
The combination may lithium-containing composite metal oxide _{be, Li x NiO 2, Li x} Co y Ni 1-y O 2, Li x Co y M 1 1-y O z (Li x Co y M 1 1- _{In y Oz} , M ¹ represents at least one element selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Ni, Cu, Zn, Al, Cr, Pb, Sb, V and B. ), Li _x Ni _1-y M ² _y O _z (in Li _x Ni _1-y M ² _y O _z , M ² is Na, Mg, Sc, Y, Mn, Fe, Co, Cu, Zn, Al, And at least one element selected from the group consisting of Cr, Pb, Sb, V and B). Here, x is in the range of 0 <x ≦ 1.2, y is in the range of 0 to 0.9, and z is in the range of 2.0 to 2.3. Further, the x value indicating the molar ratio of lithium increases or decreases due to charge and discharge.
Examples of the chalcogen compound include titanium disulfide and molybdenum disulfide. One of these positive electrode active materials may be used alone, or two or more thereof may be used in combination.

_{LiCoO 2, LiNi x Mn y Co} 1-x-y O 2 (0 <x <1,0 <y <1, x + y <1), LiNi 2-x Mn x O 4 (0 <x ≦ 2) and LiFePO The total content of at least one lithium compound selected from the group consisting of No. ₄ is preferably 65% by mass or more, more preferably 70% by mass or more based on the total amount of the positive electrode mixture layer, from the viewpoint of energy density. More preferably, it is still more preferably 80% by mass or more.

[Specific configuration of positive electrode]
Hereinafter, a specific configuration of the positive electrode in one embodiment will be described. In addition, the positive electrode used for the lithium ion secondary battery of the present disclosure is not limited to the following embodiments.

In one embodiment, the positive electrode (positive electrode plate) has a current collector (positive electrode current collector) and a positive electrode mixture layer disposed on the surface thereof. The positive electrode mixture layer is a layer including at least a positive electrode active material disposed on the surface of the current collector. Positive electrode _{mixture, LiCoO 2, LiNi x Mn y} Co 1-x-y O 2 (0 <x <1,0 <y <1, x + y <1), LiNi 2-x Mn x O 4 (0 <x ≦ 2) and at least one lithium compound selected from the group consisting of LiFePO ₄ .

Next, the positive electrode mixture layer and the current collector will be described in detail. The positive electrode mixture layer contains a positive electrode active material, a binder used as needed, and the like, and is disposed on the current collector. The method for forming the positive electrode mixture layer is not limited, and is formed, for example, as follows. The positive electrode active material and, if necessary, materials such as a binder, a conductive material, and a thickener are dry-mixed to form a sheet, which is pressed to a current collector (dry method) to form a positive electrode. An agent layer can be formed. Alternatively, a positive electrode active material, and a binder, a conductive material, and a material such as a thickener used as necessary are dissolved or dispersed in a dispersion solvent to form a slurry of the positive electrode mixture, which is applied to a current collector. By drying (wet method), a positive electrode mixture layer can be formed.
Mixing of the positive electrode active material and materials such as a binder, a conductive material, and a thickener used as necessary can be performed using a dispersing device such as a stirrer, a ball mill, a super sand mill, and a pressure kneader. .

Examples of the conductive material for the positive electrode include metal materials such as copper and nickel; graphite (graphite) such as natural graphite and artificial graphite; carbon black such as acetylene black; and carbonaceous materials such as amorphous carbon such as needle coke. Can be In addition, as the conductive material for the positive electrode, one type may be used alone, or two or more types may be used in combination.

The content of the conductive material with respect to the mass of the positive electrode mixture layer is preferably 0.01% by mass to 50% by mass, more preferably 0.1% by mass to 30% by mass, and more preferably 1% by mass to 15% by mass. More preferably, it is mass%. When the content of the conductive material is 0.01% by mass or more, sufficient conductivity tends to be easily obtained. When the content of the conductive material is 50% by mass or less, a decrease in battery capacity tends to be suppressed.

The binder for the positive electrode is not particularly limited, and when the positive electrode mixture layer is formed by a wet method, a material having good solubility or dispersibility in a dispersion solvent is selected. Specifically, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polyimide, and cellulose; rubbery polymers such as SBR (styrene-butadiene rubber) and NBR (acrylonitrile-butadiene rubber); and polyvinylidene fluoride (PVdF) Fluoropolymers such as polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-vinylidene fluoride copolymer; and polymer compositions having ion conductivity of alkali metal ions (particularly lithium ions). No. In addition, the binder for the positive electrode may be used alone or in combination of two or more.
From the viewpoint of the stability of the positive electrode, it is preferable to use a fluorine-based polymer such as polyvinylidene fluoride (PVdF) or a polytetrafluoroethylene-vinylidene fluoride copolymer as the binder.

The content of the binder with respect to the mass of the positive electrode mixture layer is preferably 0.1% by mass to 60% by mass, more preferably 1% by mass to 40% by mass, and more preferably 3% by mass to 10% by mass. % Is more preferable.
When the content of the binder is 0.1% by mass or more, the positive electrode active material can be sufficiently bound, sufficient mechanical strength of the positive electrode mixture layer can be obtained, and battery performance such as cycle characteristics can be improved. There is a tendency. When the content of the binder is 60% by mass or less, sufficient battery capacity and conductivity tend to be obtained.

Thickeners are used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specific examples include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. As the thickener, one type may be used alone, or two or more types may be used in combination.

When a thickener is used, the content of the thickener with respect to the weight of the positive electrode mixture layer is preferably 0.1% by mass to 20% by mass from the viewpoint of input / output characteristics and battery capacity. It is more preferably from 15% by mass to 15% by mass, and still more preferably from 1% by mass to 10% by mass.

As the dispersion solvent for forming the slurry, as long as the solvent is capable of dissolving or dispersing the positive electrode active material, and a binder, a conductive material or a thickener used as needed, There is no limitation, and either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water, alcohol, and a mixed solvent of water and alcohol. Examples of organic solvents include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethyl sulfoxide , Benzene, xylene, hexane and the like. In particular, when an aqueous solvent is used, it is preferable to use a thickener.

The positive electrode mixture layer formed on the current collector by a wet method or a dry method is preferably compacted by a hand press, a roller press, or the like in order to improve the packing density of the positive electrode active material.
The density of the consolidated positive electrode mixture layer is preferably in the range of 2.5 g / cm ³ to 3.5 g / cm ³ from the viewpoint of further improving input / output characteristics and safety, and is preferably 2.55 g / cm ³ . more preferably ³ to a range of 3.15 g / cm ^3, more preferably in the range of 2.6g / cm 3 ~ 3.0g / cm 3.
Further, the amount of one-sided slurry of the positive electrode mixture applied to the current collector when forming the positive electrode mixture layer is from 30 g / m ² to 30 g / m ² as a solid content of the positive electrode mixture from the viewpoint of energy density and input / output characteristics. It is preferably 170 g / m ² , more preferably 40 g / m ² to 160 g / m ² , even more preferably 40 g / m ² to 150 g / m ² .
In consideration of the amount of the positive electrode mixture slurry applied to the current collector on one side and the density of the positive electrode mixture layer, the average thickness of the positive electrode mixture layer is preferably 19 μm to 68 μm, and more preferably 23 μm to 64 μm. More preferably, it is more preferably from 36 μm to 60 μm. In the present disclosure, the average thickness of the mixture layer is an average value of the thickness at any 10 positions.

材質 The material of the current collector for the positive electrode is not particularly limited, and a metal material is particularly preferable. Examples of the metal material include metals or alloys such as aluminum, titanium, and stainless steel. Among them, aluminum is preferable as the current collector.

形状 The shape of the current collector is not particularly limited, and materials processed into various shapes such as a foil shape, a perforated foil shape, and a mesh shape can be used. Examples of the metal material include those having a shape such as a metal foil, a metal plate, a metal thin film, and an expanded metal. Among them, a metal thin film is preferably used. Note that the thin film may be appropriately formed in a mesh shape.

The average thickness of the current collector is not particularly limited, and is preferably 1 μm to 1 mm, and more preferably 3 μm to 100 μm, from the viewpoint of obtaining the necessary strength and good flexibility as the current collector. More preferably, it is more preferably 5 μm to 100 μm.

For the positive electrode, a positive electrode material slurry is prepared by kneading a positive electrode material for a lithium ion secondary battery and an organic binder together with a solvent with a dispersing device such as a stirrer, a ball mill, a super sand mill, and a pressure kneader in the same manner as the negative electrode. This is applied to a current collector to form a positive electrode mixture layer, or a paste-like positive electrode material slurry is formed into a sheet shape, a pellet shape, or the like, and this is integrated with the current collector. Obtainable. In this case, the current collector may be a band-shaped metal, alloy, such as aluminum, titanium, or stainless steel, in a foil shape, a perforated foil shape, a mesh shape, or the like.

負極 The negative electrode and the positive electrode used in the lithium ion secondary battery of the present disclosure can be used in combination without any particular limitation as long as they are within the above-described range of the negative electrode and the positive electrode.

In the case where particles containing silicon atoms are used as the negative electrode active material, it is preferable to use a positive electrode containing iron or nickel from the viewpoint of capacity. For example, when the negative electrode contains particles containing SiO, from the viewpoint of capacity and _{efficiency, LiNi x Mn y Co 1-} x-y O 2 (0 <x <1,0 <y <1, x + y <1 ) Is preferable. When the negative electrode contains particles containing Si, it is preferable to combine the negative electrode with a positive electrode containing LiCoO ₂ from the viewpoint of efficiency. From the viewpoint of cycleability, it is preferable to combine with the positive electrode containing LiFePO ₄ regardless of whether the negative electrode contains SiO or the negative electrode contains Si.

<Electrolyte>
A lithium ion secondary battery contains a lithium salt as an electrolyte.
The lithium salt is not particularly limited as long as it is a lithium salt that can be used as an electrolyte of a non-aqueous electrolyte for a lithium ion secondary battery, and inorganic lithium salts, fluorine-containing organic lithium salts, oxalatoborate salts, and the like shown below. Is mentioned.
Examples of the inorganic lithium _{salt, LiPF 6, LiBF 4, LiAsF} 6, LiSbF 6 inorganic fluoride salts, such _as, LiClO _4, Libro 4, perhalogenate of LiIO _4, etc., and the like inorganic chloride salts such as LiAlCl ₄ Can be
Examples of the fluorinated organic lithium salt include perfluoroalkane sulfonates such as LiCF ₃ SO ₃ ; LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ perfluoroalkanesulfonyl imide salts of F ₉ SO ₂₎ and the like; _LiC (CF 3 _{SO 2)} perfluoroalkanesulfonyl methide salts of _{3 such; Li [PF 5 (CF 2} CF 2 CF 3)], Li [PF _{4 (CF 2 CF 2 CF 3} ) 2], Li [PF 3 (CF 2 CF 2 CF 3) 3], Li [PF 5 (CF 2 CF 2 CF 2 CF 3)], Li [PF 4 (CF 2 _{CF 2 CF 2 CF 3) 2} ], etc. fluoroalkyl fluorophosphate such _{Li [PF 3 (CF 2 CF} 2 CF 2 CF 3) 3] and the like.
Examples of the oxalatoborate salt include lithium bis (oxalato) borate and lithium difluorooxalatoborate.
One lithium salt may be used alone, or two or more lithium salts may be used in combination. Among them, lithium hexafluorophosphate (LiPF ₆ ) is preferable in terms of comprehensively determining solubility in a solvent, charge / discharge characteristics, output characteristics, and cycle characteristics of a lithium ion secondary battery.

The electrolyte may be present in the non-aqueous electrolyte. The non-aqueous electrolyte generally includes a non-aqueous solvent and a lithium salt (electrolyte).
Examples of the non-aqueous solvent include cyclic carbonate, chain carbonate, and cyclic sulfonic acid ester.
As the cyclic carbonate, those having 2 to 6 carbon atoms in an alkylene group constituting the cyclic carbonate are preferable, and those having 2 to 4 are more preferable. Examples include ethylene carbonate, propylene carbonate, and butylene carbonate. Among them, ethylene carbonate and propylene carbonate are preferred.
As the chain carbonate, a dialkyl carbonate is preferable, two alkyl groups each having 1 to 5 carbon atoms are preferable, and those having 1 to 4 carbon atoms are more preferable. Symmetrical chain carbonates such as dimethyl carbonate, diethyl carbonate and di-n-propyl carbonate; asymmetric chain carbonates such as ethyl methyl carbonate, methyl-n-propyl carbonate and ethyl-n-propyl carbonate. Among them, dimethyl carbonate and ethyl methyl carbonate are preferred. Dimethyl carbonate is more excellent in oxidation resistance and reduction resistance than diethyl carbonate, and thus tends to improve cycle characteristics. Ethyl methyl carbonate has an asymmetric molecular structure and a low melting point, so that it tends to be able to improve low-temperature characteristics. A mixed solvent in which ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are combined is particularly preferable because battery characteristics can be secured in a wide temperature range.
From the viewpoint of battery characteristics, the content of the cyclic carbonate and the chain carbonate is preferably 85% by mass or more, more preferably 90% by mass or more, and preferably 95% by mass or more based on the total amount of the nonaqueous solvent. Is more preferable.
When the cyclic carbonate and the chain carbonate are used in combination, the mixing ratio of the cyclic carbonate and the chain carbonate is such that the cyclic carbonate / chain carbonate (volume ratio) is 1/9 to 6/4 from the viewpoint of battery characteristics. Preferably, the ratio is 2/8 to 5/5.
Examples of the cyclic sulfonic acid ester include 1,3-propane sultone, 1-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, and , 4-butene sultone and the like. Among them, 1,3-propane sultone and 1,4-butane sultone are particularly preferable from the viewpoint of further reducing the DC resistance.
The non-aqueous electrolyte may further contain a chain ester, a cyclic ether, a chain ether, a cyclic sulfone, or the like.
Examples of the chain ester include methyl acetate, ethyl acetate, propyl acetate, methyl propionate and the like. Among them, it is preferable to use methyl acetate from the viewpoint of improving low-temperature characteristics.
Examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and the like.
Examples of the chain ether include dimethoxyethane and dimethoxymethane.
Examples of the cyclic sulfone include sulfolane and 3-methylsulfolane.

The non-aqueous electrolyte may contain a silyl phosphate compound.
Specific examples of the silyl phosphate compound include tris (trimethylsilyl) phosphate, dimethyltrimethylsilyl phosphate, methylbis (trimethylsilyl) phosphate, diethyltrimethylsilyl phosphate, ethylbis (trimethylsilyl) phosphate, dipropyltrimethylsilyl phosphate and phosphoric acid Propylbis (trimethylsilyl), dibutyltrimethylsilyl phosphate, butylbis (trimethylsilyl) phosphate, dioctyltrimethylsilyl phosphate, octylbis (trimethylsilyl) phosphate, diphenyltrimethylsilyl phosphate, phenylbis (trimethylsilyl) phosphate, di (trifluoroethyl phosphate) ) (Trimethylsilyl), trifluoroethyl bis (trimethylsilyl) phosphate and trimethylsilyl group Compounds substituted with a lucylyl group, triphenylsilyl group, t-butyldimethylsilyl group, etc., and compounds having a so-called condensed phosphate ester structure in which phosphate esters are condensed and a phosphorus atom is bonded via oxygen. No.
Among these, it is preferable to use tris (trimethylsilyl) phosphate (TMSP). Tris (trimethylsilyl) phosphate can suppress an increase in resistance with a smaller amount of addition than other silyl phosphate compounds.
One of these silyl phosphates may be used alone, or two or more thereof may be used in combination.
When the nonaqueous electrolyte contains a silyl phosphate compound, the content of the silyl phosphate compound is preferably from 0.1% by mass to 5% by mass relative to the total amount of the nonaqueous electrolyte. It is more preferably from 0.3% by mass to 3% by mass, even more preferably from 0.4% by mass to 2% by mass.
In particular, when the non-aqueous electrolyte contains tris (trimethylsilyl) phosphate (TMSP), the content of tris (trimethylsilyl) phosphate (TMSP) is 0.1% by mass to the total amount of the non-aqueous electrolyte. It is preferably 0.5% by mass, more preferably 0.1% by mass to 0.4% by mass, even more preferably 0.2% by mass to 0.4% by mass. When the content of TMSP is in the above range, the life characteristics tend to be improved by the action of thin SEI (Solid Electrolyte Interphase) and the like.

Further, the non-aqueous electrolyte may contain vinylene carbonate (VC). By using VC, a stable film is formed on the surface of the negative electrode during charging of the lithium ion secondary battery. This coating has the effect of suppressing the decomposition of the non-aqueous electrolyte on the negative electrode surface.
The content of vinylene carbonate is preferably from 0.3% by mass to 1.6% by mass, more preferably from 0.3% by mass to 1.5% by mass, based on the total amount of the nonaqueous electrolyte. More preferably, the content is 0.3% by mass to 1.3% by mass. When the content of vinylene carbonate is in the above range, the life characteristics can be improved, and the effect of excessive VC being decomposed at the time of charging and discharging of the lithium ion secondary battery and lowering the charging and discharging efficiency can be prevented. Tend to be able to.

濃度 There is no particular limitation on the concentration of the electrolyte in the non-aqueous electrolyte. The concentration of the electrolyte is preferably at least 0.5 mol / L, more preferably at least 0.6 mol / L, even more preferably at least 0.7 mol / L. Further, the concentration of the electrolyte is preferably 2 mol / L or less, more preferably 1.8 mol / L or less, even more preferably 1.7 mol / L or less. When the concentration of the electrolyte is 0.5 mol / L or more, the electric conductivity of the non-aqueous electrolyte tends to be sufficient. When the concentration of the electrolyte is 2 mol / L or less, an increase in the viscosity of the non-aqueous electrolyte is suppressed, and the electric conductivity tends to increase. When the electric conductivity of the non-aqueous electrolyte increases, the performance of the lithium ion secondary battery tends to improve.

<Separator>
The lithium ion secondary battery may have a separator.
The separator is not particularly limited as long as it has ion permeability while electrically insulating the positive electrode and the negative electrode, and has resistance to oxidizing property on the positive electrode side and reducing property on the negative electrode side. As a material (material) of the separator satisfying such characteristics, a resin, an inorganic substance, or the like is used.
As the resin, an olefin-based polymer, a fluorine-based polymer, a cellulose-based polymer, polyimide, nylon, or the like is used. It is preferable to select from materials that are stable with respect to the nonaqueous electrolyte and have excellent liquid retention properties, and it is preferable to use a porous sheet or nonwoven fabric made of a polyolefin such as polyethylene or polypropylene as a raw material.
As the inorganic substance, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and glass are used. For example, a non-woven fabric, a woven fabric, or a thin film-shaped substrate such as a microporous film made of the above-mentioned inorganic substance in the form of fibers or particles can be used as the separator. As the thin film-shaped substrate, those having a pore size of 0.01 μm to 1 μm and an average thickness of 5 μm to 50 μm are preferably used. In addition, the above-mentioned fiber-shaped or particle-shaped inorganic substance formed into a composite porous layer using a binder such as a resin can be used as a separator. The composite porous layer may be formed on the surface of another separator to form a multilayer separator. Further, this composite porous layer may be formed on the surface of the positive electrode or the negative electrode to serve as a separator.

<Other components>
The lithium ion secondary battery may have other components. For example, a lithium ion secondary battery may be provided with a cleavage valve. By opening the cleavage valve, a pressure increase inside the battery can be suppressed, and safety can be improved.
Further, a component that releases an inert gas (for example, carbon dioxide) as the temperature rises may be provided. By providing such a component, when the temperature inside the battery rises, the cleavage valve can be quickly opened due to generation of an inert gas, and safety can be improved. As a material used for the constituent members, lithium carbonate, polyethylene carbonate, polypropylene carbonate, and the like are preferable.

[Specific embodiment of lithium ion secondary battery]
Next, an embodiment in which the present disclosure is applied to a 18650-type cylindrical lithium ion secondary battery will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a lithium ion secondary battery according to an embodiment of the present disclosure.
As shown in FIG. 1, the lithium ion secondary battery 1 of the present disclosure includes a nickel-plated steel bottomed cylindrical battery container 6. The battery container 6 accommodates an electrode winding group 5 in which a belt-like positive electrode plate 2 and a negative electrode plate 3 are spirally wound in cross section via a polyethylene porous sheet separator 4. For example, the separator 4 is set to have a width of 58 mm and an average thickness of 30 μm. At the upper end face of the electrode winding group 5, a ribbon-shaped positive electrode tab terminal having one end fixed to the positive electrode plate 2 is drawn out. The other end of the positive electrode tab terminal is disposed above the electrode winding group 5 and is joined to the lower surface of a disk-shaped battery lid serving as a positive electrode external terminal by ultrasonic welding. On the other hand, from the lower end surface of the electrode winding group 5, a copper ribbon-shaped negative electrode tab terminal having one end fixed to the negative electrode plate 3 is led out. The other end of the negative electrode tab terminal is joined to the inner bottom of the battery container 6 by resistance welding. Therefore, the positive electrode tab terminal and the negative electrode tab terminal are respectively led out on opposite sides of both end surfaces of the electrode winding group 5. Note that an insulating coating (not shown) is provided on the entire outer peripheral surface of the electrode winding group 5. The battery cover is caulked and fixed to the upper part of the battery container 6 via an insulating resin gasket. For this reason, the inside of the lithium ion secondary battery 1 is sealed. A non-aqueous electrolyte (not shown) is injected into the battery container 6.

<Production method of lithium ion secondary battery>
The method for manufacturing a lithium ion secondary battery according to the present disclosure includes:
In the cumulative frequency distribution for the circularity determined by the flow type particle analyzer, the standard deviation of the circularity is 0.05 to 0 in a range where the cumulative frequency from the lower circularity is 10% to 90% by number. Placing a negative electrode mixture containing the graphite particles that is .10 on the surface of the negative electrode current collector to produce a negative electrode;
_{LiCoO 2, LiNi x Mn y Co} 1-x-y O 2 (0 <x <1,0 <y <1, x + y <1), LiNi 2-x Mn x O 4 (0 <x ≦ 2) and LiFePO A step of disposing a positive electrode mixture containing at least one lithium compound selected from the group consisting of _{4 on} the surface of a positive electrode current collector to produce a positive electrode;
including.
The details of the graphite particles, the negative electrode mixture, the negative electrode current collector, the negative electrode, the lithium compound, the positive electrode mixture, the positive electrode current collector, and the positive electrode are as described above.

Hereinafter, embodiments of the present disclosure will be specifically described with reference to examples, but embodiments of the present disclosure are not limited to the following examples.

<Example 1>
[Preparation of positive electrode plate]
The production of the positive electrode plate was performed as follows. (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ) (BET specific surface area: 0.4 m ² / g, volume average particle diameter (d50): 6.5 μm) was used as the positive electrode active material. To this positive electrode active material, acetylene black (trade name: HS-100, volume average particle diameter 48 nm (catalog of Denka Corporation), manufactured by Denka Corporation) as a conductive material and polyvinylidene fluoride as a binder are sequentially added. Then, a mixture of the positive electrode materials was obtained by mixing. The mass ratio was positive electrode active material: conductive material: binder = 80: 13: 7. Further, N-methyl-2-pyrrolidone (NMP) as a dispersion solvent was added to the above mixture, and the mixture was kneaded to form a slurry. This slurry was applied substantially evenly and uniformly to both surfaces of an aluminum foil having an average thickness of 20 μm as a current collector for the positive electrode. Thereafter, a drying treatment was performed, and the mixture was pressed to a density of 2.7 g / cm ³ by pressing.

[Preparation of negative electrode plate]
The production of the negative electrode plate was performed as follows.
When the volume average particle diameter (d50) shown in Table 1 as a negative electrode active material, the standard deviation of circularity in a specific range (standard deviation of circularity), and the cumulative frequency from the lower circularity side is 10% by number Graphitic particles exhibiting a circularity (10 number% circularity), a Raman R value (R value), and a BET specific surface area (BET) (plane spacing d ₀₀₂ = 0.336 nm in the C-axis direction) were used.
To this negative electrode active material, carboxymethyl cellulose (CMC) as a thickener and styrene-butadiene rubber (SBR) as a binder were added. The mass ratio of these was set to negative electrode active material: CMC: SBR = 98: 1: 1. Purified water, which is a dispersion solvent, was added thereto and kneaded to form slurries of Examples and Comparative Examples. This slurry was substantially uniformly and uniformly applied to both surfaces of a rolled copper foil having an average thickness of 10 μm as a current collector for a negative electrode. The density of the negative electrode mixture layer was 1.3 g / cm ³ .

[Production of lithium ion secondary battery]
The positive electrode plate and the negative electrode plate are cut into predetermined sizes, and a single-layer separator of polyethylene having an average thickness of 30 μm (trade name: Hypore, manufactured by Asahi Kasei Corporation, “Hipore” is a registered trademark) ) Was sandwiched between them to form a roll-shaped electrode body. At this time, the lengths of the positive electrode, the negative electrode, and the separator were adjusted so that the diameter of the electrode body was 17.15 mm. A current collecting lead was attached to the electrode body, inserted into a 18650 type battery case, and then a non-aqueous electrolyte was injected into the battery case. In the non-aqueous electrolyte, ethylene carbonate (EC), which is a cyclic carbonate, and dimethyl carbonate (DMC), which is a chain carbonate, and ethyl methyl carbonate (EMC) are mixed so that their volume ratios are 2: 3: 2. In which lithium hexafluorophosphate (LiPF ₆ ) as a lithium salt (electrolyte) is dissolved at a concentration of 1.2 mol / L, and 1.0 mass% of vinylene carbonate (VC) is added. Was used. Finally, the battery case was sealed to complete a lithium ion secondary battery.

[Evaluation of battery characteristics (initial charge / discharge efficiency)]
The prepared lithium ion secondary battery was charged at a constant current of 0.5 C to 4.2 V in an environment of 25 ° C., and when the voltage reached 4.2 V, the current was maintained at that voltage until the current value reached 0.01 C. Voltage was charged (Charge 1). Thereafter, the battery was discharged to 2.7 V at a constant current of 0.5 C (discharge 1). This was performed for three cycles. In addition, a pause of 30 minutes was provided between each charge and discharge. The lithium ion secondary battery after the execution of three cycles is referred to as an initial state. The discharge capacity after three cycles is defined as discharge capacity 1.
The initial charge / discharge efficiency was calculated from the following equation. Table 1 shows the results.
Initial charge / discharge efficiency = (capacity of discharge 1 (mAh)) / (capacity of charge 1 (mAh)) × 100

[Evaluation of pulse charging characteristics]
The pulse charging characteristics were determined from the Li deposition state. After leaving the battery in the initial state in a -30 ° C. constant temperature bath for 5 hours so that the inside of the battery becomes close to the environmental temperature, the battery is charged at 20 A corresponding to a current value of 20 C for 5 seconds, and then the battery is disassembled. Then, the deposited state of Li was confirmed by SEM (Scanning electron microscope, manufactured by Keyence Corporation, SU3500). Table 1 shows the obtained results. When no precipitation of Li was observed, it was determined that the pulse charging characteristics were excellent.

[Evaluation of high-temperature characteristics (storage characteristics)]
The battery in the initial state was charged at a constant current of 0.5 V to 4.2 V at an environment of 25 ° C., and was charged at a constant voltage until the current value reached 0.01 C at 4.2 V from when the voltage reached 4.2 V. Then, it left still for 90 days in the environment of 60 ° C. The stationary battery was placed in an environment of 25 ° C. for 6 hours, and was discharged to 2.7 V at a constant current of 0.5 C. Subsequently, the battery was charged at a constant current of 0.5 V to 4.2 V, and was charged at a constant voltage until the current value reached 0.01 C at the voltage when the voltage reached 4.2 V. After a rest of 30 minutes, the battery was discharged to 2.7 V at a constant current discharge of 0.5 C (discharge 2). The storage characteristics were evaluated as follows.
Storage characteristics (%) = (discharge capacity 2 (mAh)) / (discharge capacity 1 (mAh)) × 100

<Examples 2, 8, 9 and Comparative Example 3>
(LiNi _5/10 Mn _3/10 Co _2/10 O ₂ ) having a BET specific surface area of 0.4 m ² / g and a volume average particle diameter (d50) of 6.5 μm was used as the positive electrode active material. Example 1 was the same as Example 1 except that the graphite particles shown in Table 1 were used.

<Example 3>
Performed except that (LiNi _6/10 Mn _2/10 Co _2/10 O ₂ ) (BET specific surface area was 0.4 m ² / g, volume average particle diameter (d50) was 6.5 μm) as the positive electrode active material. Same as Example 1.

<Example 4>
Except that (LiNi _8/10 Mn _1/10 Co _1/10 O ₂ ) (BET specific surface area was 0.4 m ² / g, volume average particle diameter (d50) was 6.5 μm) was used as the positive electrode active material. Same as Example 1.

<Examples 5, 10, 11>
(LiCoO ₂ ) (BET specific surface area: 0.4 m ² / g, volume average particle diameter (d50): 7.0 μm) was used as the positive electrode active material, and the graphite particles shown in Table 1 were used as the negative electrode active material. Other than the above, it is the same as the first embodiment.

<Examples 6, 12, 13>
Initial charge / discharge was performed using (LiFePO ₄ ) (BET specific surface area: 0.4 m ² / g, average particle diameter (d50): 10 μm) as the positive electrode active material, and the graphite particles shown in Table 1 as the negative electrode active material. It is the same as Example 1 except that the charging voltage in the evaluation of the efficiency and the storage characteristics was 3.6 V.

<Examples 7, 14, 15>
Spinel type (LiMn ₂ O ₄ ) (BET specific surface area 0.4 m ² / g, volume average particle diameter (d50) 11 μm) was used as the positive electrode active material, and the graphite particles shown in Table 1 were used as the negative electrode active material. It is the same as Example 1 except that it was used.

<Comparative Examples 1 and 4>
(LiMn ₂ PO ₄ ) (BET specific surface area 0.4 m ² / g, volume average particle diameter (d50) 10 μm) was used as the positive electrode active material, and the graphite particles shown in Table 1 were used as the negative electrode active material. Other than the above, it is the same as the first embodiment.

<Comparative Example 2>
The same as Example 1 except that (LiNiO ₂ ) (BET specific surface area: 0.4 m ² / g, volume average particle diameter (d50): 10 μm) was used as the positive electrode active material.

明 ら か As is clear from Table 1, it can be seen that the lithium ion secondary battery using the negative electrode material for a lithium ion secondary battery of the present disclosure has excellent initial charge / discharge efficiency and pulse charge characteristics.

All documents, patent applications, and technical standards mentioned herein are to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated by reference. Incorporated herein by reference.

DESCRIPTION OF SYMBOLS 1 ... Lithium ion secondary battery, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5 ... Electrode winding group, 6 ... Battery container

Claims (6)

1. In the cumulative frequency distribution for the circularity determined by the flow type particle analyzer, the standard deviation of the circularity is 0.05 to 0 in a range where the cumulative frequency from the lower circularity is 10% to 90% by number. A negative electrode comprising graphitic particles that is .10;
   _{LiCoO 2, LiNi x Mn y Co} 1-x-y O 2 (0 <x <1,0 <y <1, x + y <1), LiNi 2-x Mn x O 4 (0 <x ≦ 2) and LiFePO a positive electrode comprising at least one lithium compound selected from the group consisting of _4,
   An electrolyte;
   Lithium ion secondary batteries including.
2. The lithium ion secondary battery according to claim 1, wherein the circularity of the graphite particles when the cumulative frequency is 10% by number is 0.70 to 0.91.
3. (4) The lithium ion secondary battery according to (1) or (2), wherein the volume average particle diameter of the graphite particles is 2 μm to 30 μm.
4. In the Raman spectrum when irradiated with a laser beam of 532nm to the graphite ^particles, the peak intensity ID in the range of ^{1300 cm} -1 ~ 1400 cm ^-1 to the peak intensity IG in the range of 1580 cm -1 ~ 1620 cm ^-1 The lithium ion secondary battery according to any one of claims 1 to 3, wherein a Raman R value (ID / IG) as a ratio is 0.10 to 0.60.
5. The lithium ion secondary battery according to any one of claims 1 to 4, wherein the negative electrode further includes carbon particles having an average circularity determined by a flow type particle analyzer of 0.94 or less.
6. In the cumulative frequency distribution for the circularity determined by the flow type particle analyzer, the standard deviation of the circularity is 0.05 to 0 in a range where the cumulative frequency from the lower circularity is 10% to 90% by number. Placing a negative electrode mixture containing the graphite particles that is .10 on the surface of the negative electrode current collector to produce a negative electrode;
   _{LiCoO 2, LiNi x Mn y Co} 1-x-y O 2 (0 <x <1,0 <y <1, x + y <1), LiNi 2-x Mn x O 4 (0 <x ≦ 2) and LiFePO A step of disposing a positive electrode mixture containing at least one lithium compound selected from the group consisting of _{4 on} the surface of a positive electrode current collector to produce a positive electrode;
   A method for producing a lithium ion secondary battery comprising:

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