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  • H01M2004/027—Negative electrodes
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  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to a negative electrode material for lithium ion secondary batteries, a negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery.
• Lithium ion secondary batteries have been widely used in electronic devices such as notebook personal computers (PCs), mobile phones, smart phones, and tablet PCs, taking advantage of their characteristics of small size, light weight, and high energy density.
• PCs notebook personal computers
• HEV hybrid electric vehicles
• plug-in hybrid electric vehicles have become popular.
• Electric vehicles such as (PHEV) are becoming popular, and the development of lithium ion secondary batteries (vehicle lithium ion secondary batteries) as batteries mounted in these vehicles is underway.
• Carbon materials are widely used as materials for negative electrode materials for lithium ion secondary batteries. Carbon materials used for negative electrode materials are roughly classified into graphite and carbon materials having a lower crystallinity than graphite (such as amorphous carbon). Graphite has a structure in which hexagonal mesh planes of carbon atoms are regularly stacked, and when used as a negative electrode material for lithium-ion secondary batteries, lithium ion insertion and desorption reactions proceed from the ends of the hexagonal mesh planes, and charging occurs. Discharge occurs.
• Amorphous carbon has irregular lamination of hexagonal mesh planes or no hexagonal mesh planes. Therefore, in the negative electrode material using amorphous carbon, the intercalation and deintercalation reactions of lithium ions proceed over the entire surface of the negative electrode material. Therefore, it is easier to obtain a lithium ion battery with better input/output characteristics than when graphite is used as the negative electrode material (see, for example, Patent Documents 1 and 2). On the other hand, since amorphous carbon has lower crystallinity than graphite, its energy density is lower than that of graphite.
• amorphous carbon and graphite are combined to improve input/output characteristics while maintaining high energy density, and graphite is coated with amorphous carbon.
• a negative electrode material has also been proposed in which the reactivity of the surface is reduced and the input/output characteristics are improved while maintaining good initial charge/discharge efficiency (see, for example, Patent Document 3).
• Lithium ion secondary batteries with high energy density are required to shorten the charging time.
• the current density is increased in order to fill the lithium ion secondary battery in a short period of time, lithium deposition tends to occur at the negative electrode, and the input characteristics, cycle characteristics, etc. tend to deteriorate.
• An object of one aspect of the present invention is to provide a negative electrode material for a lithium ion secondary battery and a negative electrode for a lithium ion secondary battery that can produce a lithium ion secondary battery having excellent input/output characteristics and cycle characteristics.
• Another object of one embodiment of the present invention is to provide a lithium-ion secondary battery with excellent input/output characteristics and cycle characteristics.
• a negative electrode material for a lithium ion secondary battery containing a carbon material that satisfies the following (1) and (2).
• the D90/D10 of the particle diameter on a volume basis is greater than 2.0 and less than 4.3.
• (2) N/S which is the value obtained by dividing the number N of particles having an equivalent circle diameter of 5 ⁇ m or less based on the number standard in the total number of measured particles of 10,000 by the specific surface area S obtained by nitrogen adsorption measurement at 77 K, is 750 (pieces/ g/cm 2 ) or more.
• ⁇ 2> The negative electrode material for a lithium ion secondary battery according to ⁇ 1>, wherein the carbon material satisfies the following (3).
• ⁇ 3> The negative electrode material for a lithium ion secondary battery according to ⁇ 1> or ⁇ 2>, wherein the carbon material satisfies the following (4).
• ⁇ 6> The lithium ion secondary according to any one of ⁇ 1> to ⁇ 5>, wherein the carbon material has an average interplanar spacing d 002 of 3.34 ⁇ to 3.38 ⁇ obtained by an X-ray diffraction method.
• ⁇ 7> The negative electrode material for a lithium ion secondary battery according to any one of ⁇ 1> to ⁇ 6>, wherein the carbon material has an R value of 0.1 to 0.4 in Raman spectroscopy.
• ⁇ 8> The negative electrode for a lithium ion secondary battery according to any one of ⁇ 1> to ⁇ 7>, wherein the carbon material has a specific surface area of 14 m 2 /g or less as determined by nitrogen adsorption measurement at 77K. material. ⁇ 9> The carbon material has no two or more exothermic peaks in the temperature range of 300° C. to 1000° C. in differential thermal analysis in an air stream, and any one of ⁇ 1> to ⁇ 8> A negative electrode material for a lithium ion secondary battery as described.
• a negative electrode for a lithium ion secondary battery comprising a negative electrode material layer containing the negative electrode material for a lithium ion secondary battery according to any one of ⁇ 1> to ⁇ 9>, and a current collector.
• a lithium ion secondary battery comprising the lithium ion secondary battery negative electrode according to ⁇ 10>, a positive electrode, and an electrolytic solution.
• An aspect of the present invention can provide a negative electrode material for a lithium ion secondary battery and a negative electrode for a lithium ion secondary battery that can produce a lithium ion secondary battery having excellent input/output characteristics and cycle characteristics. Furthermore, one embodiment of the present invention can provide a lithium ion secondary battery with excellent input/output characteristics and cycle characteristics.
• each component may contain multiple types of applicable substances.
• the content rate or content of each component is the total content rate or content of the multiple types of substances present in the composition unless otherwise specified. means quantity.
• Particles corresponding to each component in the present disclosure may include a plurality of types.
• the particle size of each component means a value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.
• the term “layer” includes not only the case where the layer is formed in the entire region when observing the region where the layer exists, but also the case where it is formed only in part of the region. included.
• the term “laminate” indicates stacking layers, and two or more layers may be bonded, or two or more layers may be detachable.
• a negative electrode material for a lithium ion secondary battery containing a carbon material satisfying the following (1) and (2).
• the D90/D10 of the particle diameter on a volume basis is greater than 2.0 and less than 4.3.
• N/S which is the value obtained by dividing the number N of particles having an equivalent circle diameter of 5 ⁇ m or less based on the number standard in the total number of measured particles of 10,000 by the specific surface area S obtained by nitrogen adsorption measurement at 77 K, is 750 (pieces/ g/cm 2 ) or more.
• spheroidized graphite obtained by spheronizing natural graphite tends to produce hollow particles during the spheronization process, and these hollow particles are likely to be deformed by press pressure and oriented in the horizontal direction.
• the pressing pressure required to obtain the desired electrode density can be reduced, so when the carbon material contained in the negative electrode material is spherical graphite, Even so, it is possible to suppress an increase in the lateral orientation of the carbon material.
• the fact that the number of particles N having a circle-equivalent diameter of 5 ⁇ m or less on a number basis in the total number of measured particles of 10,000 is large indicates that more carbon materials have small particle diameters.
• the diffusion distance of lithium ions in the solid tends to be short and the output characteristics tend to be good.
• the specific surface area S increases in (2) above, and the input/output characteristics of the lithium ion secondary battery tend to be further improved.
• an electrolysis reaction is likely to occur at the interface between the carbon material having a large specific surface area and the electrolytic solution, and current concentration is likely to be induced due to the drying up of the electrolytic solution. As a result, lithium deposition tends to occur, and the cycle characteristics tend to deteriorate.
• N/S which is the ratio of the particle number N and the specific surface area S
• the particle number N and the ratio The surface area S is the preferred balance. This makes it possible to improve the input/output characteristics of the lithium ion secondary battery while suppressing deterioration of the cycle characteristics of the lithium ion secondary battery.
• the carbon material expands and contracts repeatedly due to charging and discharging, so it is easy for the conductive path to break due to interfacial peeling between the carbon material and the current collector, peeling between the carbon materials, etc. Furthermore, the cycle characteristics of the lithium ion secondary battery may deteriorate due to a decrease in charge/discharge capacity due to the deactivated negative electrode active material and an increase in current density due to the effective negative electrode active material.
• the negative electrode material for a lithium ion secondary battery of the present disclosure by satisfying the above (1) and (2), the contact between the carbon material, which is the negative electrode active material, and the current collector, and between the carbon materials tend to increase.
• the negative electrode material for a lithium ion secondary battery of the present disclosure even when the carbon material repeatedly expands and contracts due to charging and discharging, a conductive path between the carbon material and the current collector and a conductive path between the carbon materials etc. can be manufactured. Due to the above, there is a tendency to be able to manufacture a lithium ion secondary battery that is excellent in life characteristics such as cycle characteristics, input/output characteristics, and the like.
• the negative electrode material for lithium ion secondary batteries of the present disclosure (hereinafter also simply referred to as “negative electrode material”) is a carbon material (hereinafter also referred to as “specific carbon material”) that satisfies the above (1) and (2). including.
• the content of the specific carbon material in the negative electrode material is not particularly limited. For example, it is preferably 50% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more. Preferably, 100% by mass is particularly preferred.
• the negative electrode material may contain carbon materials other than specific carbon materials.
• Other carbon materials are not particularly limited, and include scale-like, earth-like, and spherical natural graphite, graphite such as artificial graphite, amorphous carbon, carbon black, fibrous carbon, and nanocarbon. Other carbon materials may be used singly or in combination of two or more.
• the negative electrode material may contain particles containing an element capable of intercalating and deintercalating lithium ions.
• Elements capable of intercalating and deintercalating lithium ions are not particularly limited, and examples thereof include Si, Sn, Ge, and In.
• the specific carbon material has a volume-based particle size D90/D10 of greater than 2.0 and less than 4.3. It becomes easier to secure a conductive path between the carbon material and the current collector, a conductive path between the carbon materials, etc., so that a lithium-ion secondary battery with a high capacity retention rate and excellent cycle characteristics can be obtained, and the tap density is improved. From the viewpoint of facilitating the formation of a sintered body, D90/D10 is preferably greater than 2.2, more preferably greater than 2.5, and even more preferably greater than 3.0.
• D90/D10 may be changed within the above range in consideration of the amount of the negative electrode material composition applied to the current collector, the thickness of the negative electrode, and the like.
• the particle diameter (D10) of the carbon material is the particle diameter when the volume cumulative distribution curve is drawn from the small diameter side in the particle diameter distribution of the carbon material and the cumulative 10%.
• the particle size (D90) of the carbon material is the particle size at which the volume cumulative distribution curve is drawn from the small size side in the particle size distribution of the carbon material and the cumulative 90% is obtained.
• the particle size (D10) and particle size (D90) are determined by dispersing the carbon material in purified water containing a surfactant and using a laser diffraction particle size distribution analyzer (eg, SALD-3100 manufactured by Shimadzu Corporation). can be measured by a laser diffraction particle size distribution analyzer (eg, SALD-3100 manufactured by Shimadzu Corporation). can be measured by
• the average particle size (D50) of the specific carbon material is preferably 22 ⁇ m or less.
• the average particle diameter (D50) of the specific carbon material is 21 ⁇ m from the viewpoint of suppressing the diffusion distance of lithium from the surface to the inside of the negative electrode material and further improving the input/output characteristics of the lithium ion secondary battery. It is more preferably 20 ⁇ m or less, more preferably 20 ⁇ m or less.
• the average particle size (D50) of the specific carbon material is preferably 10 ⁇ m or more, more preferably 12 ⁇ m or more, from the viewpoint of suppressing deterioration in high-temperature storage characteristics of lithium-ion secondary batteries due to an increase in specific surface area. is more preferable, 15 ⁇ m or more is further preferable, and 17 ⁇ m or more is particularly preferable.
• the average particle size (D50) of the carbon material is the particle size when the volume cumulative distribution curve is drawn from the small size side in the particle size distribution of the carbon material and the cumulative 50%.
• the average particle size (D50) can be measured by dispersing the carbon material in purified water containing a surfactant and using a laser diffraction particle size distribution analyzer (eg, SALD-3100 manufactured by Shimadzu Corporation). can.
• the specific carbon material has an N/S value of 750, which is the value obtained by dividing the number N of particles with an equivalent circle diameter of 5 ⁇ m or less based on the number of 10,000 total measured particles by the specific surface area S obtained from nitrogen adsorption measurement at 77 K. (pieces ⁇ g/cm 2 ) or more.
• N/S is preferably 900 or more, more preferably 1200 or more, from the viewpoint of the input/output characteristics of the lithium ion secondary battery.
• N/S may be 2000 or less, or 1800 or less.
• the number of particles with an equivalent circle diameter of 5 ⁇ m or less based on the number of carbon materials and the ratio thereof are measured using a wet flow particle size and shape analyzer (FPIA-3000 manufactured by Malvern), and the average circularity is measured as described later. It can be measured in the same manner as the conditions.
• the specific surface area of the carbon material obtained from the nitrogen adsorption measurement at 77K can be obtained from the adsorption isotherm obtained from the nitrogen adsorption measurement at 77K using the BET method.
• the specific carbon material preferably satisfies (3) below.
• (3) The ratio of the number of particles having an equivalent circle diameter of 5 ⁇ m or less on a number basis to the total number of measured particles of 10,000 is 45% or more.
• the specific carbon material preferably has a particle number ratio of 45% or more, more preferably 53% or more, and 60% or more, from the viewpoint of better input/output characteristics of the lithium ion secondary battery. is more preferred.
• the upper limit of the particle number ratio is not particularly limited, and from the viewpoint of making it easier for the carbon material to satisfy the conditions (1) and (2) above and (5) described later, it is preferably 95% or less, and 90%. The following are more preferable.
• the specific surface area of the specific carbon material determined by nitrogen adsorption measurement at 77K is preferably 2 m 2 /g to 14 m 2 /g, more preferably 3 m 2 /g to 8 m 2 /g, and 4 m 2 /g to 6 m 2 /g is more preferred. If the aforementioned specific surface area is within the above range, there is a tendency to obtain a good balance between the input/output characteristics and the initial charge/discharge efficiency in the lithium ion secondary battery.
• the specific carbon material preferably satisfies the following (4) from the viewpoint of superior input/output characteristics and cycle characteristics of the lithium ion secondary battery.
• (4) Number-based equivalent circle diameter at 99% cumulative particle size distribution with X limited to particle sizes of 5 ⁇ m or more, circularity at cumulative 1% of circularity distribution with Y limited to particle sizes of 5 ⁇ m or more satisfies the following equation (a). Y ⁇ 0.3 ⁇ log 10 (X)+(0.5 ⁇ 0.3 ⁇ log 10 6) (a)
• the right side of the above formula (a) is a line segment passing through two points where (particle diameter ( ⁇ m), circularity) are (6 ⁇ m, 0.5) and (50, 0.8) (the particle diameter is logarithmic scale). Satisfying the above (4) means that the specific carbon material does not contain particles with a small degree of circularity (for example, a flat shape) and a large particle size, or contains a very small amount of particles.
• Y ⁇ [0.3 ⁇ log 10 (X)+(0.5 ⁇ 0.3 ⁇ log 10 6)] is preferably 0 or more, and the input of a lithium ion secondary battery is From the viewpoint of better output characteristics and cycle characteristics, it may be 0 or more and 0.15 or less, or 0 or more and 0.10 or less.
• a plane of a particle having a small circularity (e.g., flattened shape) and a large particle diameter is likely to be coordinated parallel to the plane of the current collector, and this parallel plane is perpendicular to the movement axis of lithium ions.
• the path length of lithium ions, electrolytic solution, etc. that move with charging and discharging is extended, and the overall charging and discharging characteristics are deteriorated.
• the movement of lithium ions and the electrolytic solution in the interparticle voids becomes smooth, and the input/output characteristics and cycle characteristics of the lithium ion secondary battery tend to be improved.
• the average circularity is the average value of the circularity of individual particles and can indicate the bulk powder shape, it is effective to study it from the perspective of improving the input/output characteristics and cycle characteristics of lithium-ion secondary batteries. Therefore, by using a specific carbon material that satisfies (4) above and (6) below, it becomes easier to obtain a lithium ion secondary battery that is particularly excellent in input/output characteristics and cycle characteristics.
• the number-based equivalent circle diameter at 99% of the cumulative distribution limited to particle diameters of 5 ⁇ m or more and the circularity at 1% of the cumulative circularity distribution limited to particle diameters of 5 ⁇ m or more are wet It can be measured with a flow type particle size/shape analyzer.
• the specific carbon material preferably satisfies (5) below.
• Tap density is 0.80 g/cm 3 to 0.95 g/cm 3 .
• the tap density of the specific carbon material is preferably 0.80 g/cm 3 or more, more preferably 0.85/cm 3 or more, from the viewpoint of better input/output characteristics and energy density in lithium ion secondary batteries. More preferably, it is 0.90/cm 3 or more.
• the tap density of the specific carbon material is preferably 0.95/cm 3 or less from the viewpoint of better yield of the negative electrode material and better cycle characteristics of the lithium ion secondary battery.
• the tap density of the carbon material tends to increase by increasing the average particle diameter (D50) of the carbon material, the average circularity of the carbon material, etc., and removing the carbon material that has a large particle diameter and is flat.
• the tap density of the carbon material is determined by putting 100 cm of the sample powder into a graduated flat - bottom test tube with a capacity of 150 cm (KRS-406, manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd.), and plugging the graduated flat-bottom test tube with a stopper. and the value obtained from the mass and volume of the sample powder after dropping this graduated flat-bottomed test tube from a height of 5 cm 250 times.
• the specific carbon material preferably satisfies the following (6) from the viewpoint of superior input/output characteristics and cycle characteristics in a lithium ion secondary battery.
• (6) The average circularity is 0.90 to 0.93.
• the average circularity of 0.90 or more suppresses the coordination of the specific carbon material parallel to the plane of the current collector.
• the path length of lithium ions, electrolyte, etc., that move with charging and discharging is shortened, and the movement of lithium ions and electrolyte that moves through the interparticle voids becomes smoother. Cycle characteristics tend to be good.
• the cycle characteristics of lithium ion secondary batteries tend to be improved.
• the first carbon material which is the raw material of a specific carbon material, is obtained by a spheronization treatment, it is possible to reduce the roughening of the first carbon material, so the high-temperature storage characteristics of the lithium ion secondary battery tend to be good.
• the yield of the spheronization process tends to be improved.
• the average circularity of the specific carbon material is preferably 0.90 to 0.93, more preferably 0.905 to 0.925.
• the circularity of the carbon material can be measured with a wet flow particle size/shape analyzer.
• the average interplanar spacing d 002 of the specific carbon material determined by the X-ray diffraction method is preferably 3.34 ⁇ to 3.38 ⁇ .
• the value of the average interplanar spacing d002 is 3.354 ⁇ , which is the theoretical value for graphite crystals, and the closer to this value, the higher the energy density tends to be.
• the value of the average interplanar spacing d 002 of the carbon material tends to decrease, for example, by increasing the temperature of the heat treatment when producing the negative electrode material. Therefore, there is a tendency that the average interplanar spacing d 002 of the carbon material can be controlled by adjusting the temperature of the heat treatment when producing the negative electrode material.
• the R value of Raman spectroscopic measurement with a specific carbon material is preferably 0.1 to 0.4, and from the viewpoint of excellent high temperature storage characteristics of lithium ion secondary batteries, it is 0.1 to 0.33. is more preferably 0.1 to 0.3, and particularly preferably 0.1 to 0.25.
• the R value is 0.1 or more, sufficient graphite lattice defects are present for lithium ions to be put in and taken out, and the deterioration of the input/output characteristics of the lithium ion secondary battery tends to be suppressed.
• the R value is 0.4 or less, the decomposition reaction of the electrolytic solution is sufficiently suppressed, and the decrease in the initial efficiency of the lithium ion secondary battery tends to be suppressed.
• the R value is defined as the intensity ratio (Id/Ig) of the maximum peak intensity Ig near 1580 cm -1 and the maximum peak intensity Id near 1360 cm -1 in the Raman spectroscopic spectrum obtained in Raman spectroscopic measurement.
• the peak appearing around 1580 cm ⁇ 1 is usually a peak identified as corresponding to the graphite crystal structure, and means a peak observed at, for example, 1530 cm ⁇ 1 to 1630 cm ⁇ 1 .
• the peak appearing around 1360 cm ⁇ 1 is usually identified as corresponding to the amorphous structure of carbon, and means, for example, the peak observed at 1300 cm ⁇ 1 to 1400 cm ⁇ 1 .
• the R value is measured using a Raman spectrometer (eg, Horiba, Ltd., XploRA PLUS), and the obtained spectrum is measured under the following conditions with the following range as a baseline.
• ⁇ Laser wavelength 532 nm
• Laser intensity 100 mW or more
• Neutral density filter 1%
• ⁇ Irradiation intensity 1mW
• ⁇ Measurement range 1000 cm -1 to 1800 cm -1
• Irradiation time 30 seconds
• ⁇ Irradiation area 1 ⁇ m 2 ⁇
• the specific carbon material preferably does not have two or more exothermic peaks in the temperature range of 300°C to 1000°C in differential thermal analysis (DTA analysis) in an air current. This tends to further improve the input/output characteristics and high-temperature storage characteristics of the lithium ion secondary battery.
• DTA analysis differential thermal analysis
• the carbon material does not have two or more exothermic peaks means that it does not have a plurality of identifiable exothermic peaks in the temperature range of 300 ° C. to 1000 ° C., that is, it does not have identifiable exothermic peaks. , or one.
• having a plurality of identifiable exothermic peaks means having a plurality of exothermic peaks whose peak values are separated by at least 5°C.
• differential thermal analysis can be measured using a simultaneous differential thermogravimetric analyzer (for example, EXSTAR TG/DTA6200 manufactured by Seiko Instruments Inc.). Specifically, using ⁇ -alumina as a reference, measurement is performed at a heating rate of 2.5 ° C./min under a flow of dry air of 300 mL/min, and the presence or absence of an exothermic peak of DTA at 300 ° C. to 1000 ° C. is confirmed. do.
• a simultaneous differential thermogravimetric analyzer for example, EXSTAR TG/DTA6200 manufactured by Seiko Instruments Inc.
• Specific carbon materials and other carbon materials are not particularly limited, and examples thereof include graphite, low-crystalline carbon, amorphous carbon, mesophase carbon, and the like.
• Examples of graphite include artificial graphite, natural graphite, graphitized mesophase carbon, and graphitized carbon fiber.
• As the carbon material spherical graphite particles are preferable, and spherical artificial graphite, spherical natural graphite, and the like are more preferable from the viewpoint of excellent charge/discharge capacity in lithium ion secondary batteries and excellent tap density.
• the graphite particles are preferably coated. can do.
• a negative electrode material composition is produced using a carbon material that has aggregated during coating, when the aggregation of the carbon material is loosened by agitation, the above-described region not coated with the carbon material is suppressed from being exposed. .
• the carbon material contained in the negative electrode material may be of one type alone or two or more types.
• the carbon material includes a first carbon material as a core and a second carbon material present on at least a part of the surface of the first carbon material and having a lower crystallinity than the first carbon material. good.
• the first carbon material and the second carbon material are not particularly limited as long as they satisfy the condition that the crystallinity of the second carbon material is lower than that of the first carbon material. is appropriately selected from.
• Each of the first carbon material and the second carbon material may be of one type alone or two or more types. The presence of the second carbon material on the surface of the first carbon material can be confirmed by observation with a transmission electron microscope.
• the second carbon material preferably contains at least one of crystalline carbon and amorphous carbon. Specifically, at least one selected from the group consisting of a carbonaceous substance and carbonaceous particles obtained from an organic compound that can be converted to carbonaceous by heat treatment (hereinafter also referred to as a precursor of the second carbonaceous material). Preferably.
• the precursor of the secondary carbon material is not particularly limited, and includes pitch, organic polymer compounds, and the like.
• the pitch for example, ethylene heavy end pitch, crude oil pitch, coal tar pitch, asphalt cracked pitch, pitch produced by pyrolyzing polyvinyl chloride, etc., and naphthalene produced by polymerizing in the presence of a super strong acid.
• organic polymer compounds include thermoplastic resins such as polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate and polyvinyl butyral, and natural substances such as starch and cellulose.
• the carbonaceous particles used as the second carbon material are not particularly limited, and include particles such as acetylene black, oil furnace black, ketjen black, channel black, thermal black, and soil graphite.
• the ratio of the amount of the first carbon material and the second carbon material in the carbon material is not particularly limited. From the viewpoint of improving the input/output characteristics of the lithium ion secondary battery, the ratio of the amount of the second carbon material to the total mass of the carbon material is preferably 0.1% by mass to 15% by mass, and 1% by mass to It is more preferably 10% by mass, and even more preferably 1% to 5% by mass.
• the amount of the second carbon material in the carbon material When calculating the amount of the second carbon material in the carbon material from the amount of the precursor of the second carbon material, it can be calculated by multiplying the amount of the precursor of the second carbon material by the residual carbon rate (% by mass). .
• the residual carbon ratio of the precursor of the second carbon material is obtained by using the precursor of the second carbon material alone (or in the state of a mixture of the precursor of the second carbon material and the first carbon material in a predetermined ratio). is heat-treated at a temperature at which the precursor of is changed to carbonaceous, and from the mass of the precursor of the second carbonaceous material before the heat treatment and the mass of the carbonaceous substance derived from the precursor of the second carbonaceous material after the heat treatment , thermogravimetric analysis, etc.
• the manufacturing method of the negative electrode material of the present disclosure is not particularly limited. From the viewpoint of efficiently producing a negative electrode material that satisfies the above conditions, when producing a carbon material using the precursors of the first carbon material and the second carbon material, it is preferable to produce the negative electrode material by the following method for producing the negative electrode material. .
• a method for producing a negative electrode material for a lithium ion secondary battery in one embodiment of the present invention includes a first carbon material serving as a core and a precursor of a second carbon material having a lower crystallinity than the first carbon material. A step of heat-treating the mixture to produce a specific carbon material may be included.
• the negative electrode material described above can be produced efficiently.
• the details and preferred embodiments of the first carbon material, the precursor of the second carbon material, and the specific carbon material are the same as those described in the item of the negative electrode material for the lithium ion secondary battery.
• the first carbon material is preferably spherical graphite particles, more preferably spherical artificial graphite, spherical natural graphite, or the like.
• Spherical graphite obtained by subjecting non-spherical graphite particles such as scaly graphite particles (for example, scaly natural graphite particles) to a spheroidizing treatment may be used as the first carbon material.
• spheroidized graphite can be obtained by applying a spheroidizing treatment to non-spherical graphite particles such as flake graphite particles under specific processing conditions. If necessary, non-spherical graphite particles such as flake graphite particles may be pulverized and then spheroidized, and the spheroidization may also serve as pulverization.
• the lower limit of the rotor peripheral speed during the spheronization process is preferably 65 m/min or more, more preferably 70 m/min or more, from the viewpoint that the D90/D10 of the specific carbon material easily satisfies the above (1).
• the upper limit of the rotor peripheral speed during the spheronization treatment is preferably 100 m/min or less from the viewpoint of easily satisfying the above (2) by adjusting the specific surface area obtained by nitrogen adsorption measurement of a specific carbon material at 77 K. , 90 m/min or less.
• the treatment time of the spheronization treatment is preferably 2.0 minutes to 7.0 minutes, and 2.5 minutes, from the viewpoint of making it easier for the D90/D10 of the specific carbon material to satisfy the above (1) and the above (2). ⁇ 6.0 minutes is more preferred.
• the product of the rotor peripheral speed and the treatment time is preferably 130 to 500, and 150 to 150, from the viewpoint that the D90/D10 of the specific carbon material easily satisfies the above (1) and the above (2). 450 is more preferred.
• the specific surface area of the specific carbon material From the viewpoint of suppressing electrolysis of the electrolyte in the lithium-ion secondary battery and maintaining high-temperature storage characteristics, it is preferable to prevent the specific surface area of the specific carbon material from becoming too high. From the viewpoint of suppressing an increase in the specific surface area that does not depend on the particle size of a specific carbon material, it is preferable to suppress the occurrence of cracks and surface irregularities caused by pulverization of graphite particles, spheroidizing treatment, and the like. Specifically, it is preferable to adjust the particle size, thickness, etc. of the graphite particles, or subject the graphite particles to spheroidizing treatment under the conditions of the rotor peripheral speed and treatment time as described above.
• the spheroidized graphite obtained by the spheronization treatment may be classified, and the spheroidized graphite obtained by removing the fine powder may be used as the first carbon material.
• the classification method is not particularly limited, and includes classification by cyclone, classification by sieving, and the like.
• the classification point is not particularly limited, and may be 1 ⁇ m to 10 ⁇ m, 1 ⁇ m to 5 ⁇ m, or 1 ⁇ m to 3 ⁇ m.
• the classification point may be decreased (for example, , may be 1 ⁇ m to 3 ⁇ m), the fine powder removed by classification (for example, classification by cyclone) is further sieved to remove fine powder smaller than 1 ⁇ m, etc., and the by-product particles are converted into spherical graphite from which fine powder has been removed. may be used as the first carbon material.
• the graphite particles to be spheroidized are preferably natural graphite, which is a cheaper material that does not require graphitization power.
• natural graphite which is a cheaper material that does not require graphitization power.
• the material yield is around 30%, and since around 70% has been removed, there has been a problem that the yield is extremely low.
• the removed by-product graphite is mixed with resin, for example, and used as a core material for pencils, etc.
• the recent spread of EVs has led to a rapid increase in the amount of by-product graphite, resulting in an oversupply of by-product graphite to meet demand. there is Therefore, it is desirable to improve the material yield in the step of spheroidizing natural graphite.
• natural graphite is contained in ore at about 10% by mass in, for example, the Heilongjiang region of the People's Republic of China, and ore by-products are also extremely abundant, so it is desirable to improve the yield in the process of spheroidizing natural graphite.
• the classification point is reduced (for example, 1 ⁇ m to 3 ⁇ m), or by-product particles from which fine powder smaller than 1 ⁇ m is removed are added to the first carbon material. You may use it. This makes it possible to improve the yield during the spheroidizing process. Furthermore, the conditions (2) and (3) are easily satisfied with the specific carbon material, and as a result, it becomes easy to manufacture a lithium-ion secondary battery having excellent input/output characteristics and high-temperature storage characteristics.
• the temperature at which the mixture is heat treated is preferably 950° C. to 1500° C., more preferably 1000° C. to 1300° C., more preferably 1050° C. to 1050° C., from the viewpoint of improving the input/output characteristics of the lithium ion secondary battery. It is more preferably 1250°C.
• the temperature at which the mixture is heat treated may be constant or may vary from the beginning to the end of the heat treatment.
• the content of the precursors of the first carbon material and the second carbon material in the mixture before heat treatment is not particularly limited.
• the content of the first carbon material is preferably 85% by mass to 99.9% by mass, preferably 90% by mass, with respect to the total mass of the mixture. It is more preferably up to 99% by mass, and even more preferably 95% by mass to 99% by mass.
• the content of the precursor of the second carbon material is preferably 0.1% by mass to 15% by mass with respect to the total mass of the mixture from the viewpoint of improving the input/output characteristics of the lithium ion secondary battery. It is preferably from 1% by mass to 10% by mass, and even more preferably from 1% by mass to 5% by mass.
• a negative electrode for a lithium ion secondary battery of the present disclosure includes a negative electrode material layer containing the above negative electrode material for a lithium ion secondary battery of the present disclosure, and a current collector.
• the negative electrode for a lithium ion secondary battery may contain other constituent elements, if necessary, in addition to the negative electrode material layer and current collector containing the negative electrode material described above.
• a negative electrode material and a binder are kneaded together with a solvent to prepare a slurry negative electrode material composition, which is applied onto a current collector to form a negative electrode material layer.
• the negative electrode material composition can be formed into a sheet-like or pellet-like shape and integrated with a current collector. Kneading can be performed using a dispersing device such as a stirrer, ball mill, super sand mill, pressure kneader, or the like.
• Binders include ethylenically unsaturated compounds such as styrene-butadiene copolymers, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, acrylonitrile, methacrylonitrile, hydroxyethyl acrylate and hydroxyethyl methacrylate.
• the negative electrode material composition contains a binder, the amount is not particularly limited.
• the content of the binder may be, for example, 0.5 parts by mass to 20 parts by mass with respect to 100 parts by mass in total of the negative electrode material and the binder.
• the solvent is not particularly limited as long as it can dissolve or disperse the binder.
• Specific examples include organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide and ⁇ -butyrolactone.
• the amount of the solvent used is not particularly limited as long as the negative electrode material composition can be made into a desired state such as a paste.
• the amount of the solvent used is preferably 60 parts by mass or more and less than 150 parts by mass with respect to 100 parts by mass of the negative electrode material, for example.
• the negative electrode material composition may contain a thickener.
• thickening agents include carboxymethylcellulose or its salts, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, ethylcellulose, polyvinyl alcohol, polyacrylic acid or its salts, alginic acid or its salts, oxidized starch, phosphorylated starch, casein and the like.
• the content of the thickening agent may be, for example, 0.1 to 5 parts by mass with respect to 100 parts by mass of the negative electrode material.
• the negative electrode material composition may contain a conductive auxiliary material.
• conductive auxiliary materials include carbon materials such as natural graphite, artificial graphite, carbon black (acetylene black, thermal black, furnace black, etc.), conductive oxides, and conductive nitrides.
• the amount is not particularly limited.
• the content of the conductive auxiliary material may be, for example, 0.5 parts by mass to 15 parts by mass with respect to 100 parts by mass of the negative electrode material.
• the material of the current collector is not particularly limited, and can be selected from aluminum, copper, nickel, titanium, stainless steel, and the like.
• the state of the current collector is not particularly limited, and can be selected from foil, perforated foil, mesh, and the like.
• porous materials such as porous metal (foamed metal) and carbon paper can also be used as current collectors.
• the method is not particularly limited, and metal mask printing method, electrostatic coating method, dip coating method, spray coating method, roll coating method, Known methods such as a doctor blade method, a comma coating method, a gravure coating method, and a screen printing method can be employed.
• the solvent contained in the negative electrode material composition is removed by drying. Drying can be performed using, for example, a hot air dryer, an infrared dryer, or a combination of these devices.
• Rolling treatment may be performed as necessary. The rolling treatment can be performed by a method such as a flat plate press or a calendar roll.
• the integration method is not particularly limited. For example, it can be carried out by a roll, flat plate press, or a combination of these means.
• the pressure during integration is preferably, for example, 1 MPa to 200 MPa.
• the lithium ion secondary battery of the present disclosure includes the above-described negative electrode for lithium ion secondary battery of the present disclosure (hereinafter also simply referred to as “negative electrode”), a positive electrode, and an electrolytic solution.
• the positive electrode can be obtained by forming a positive electrode material layer on the current collector in the same manner as the negative electrode manufacturing method described above.
• As the current collector it is possible to use a metal or alloy such as aluminum, titanium, or stainless steel in the form of a foil, a perforated foil, or a mesh.
• the electrolytic solution is not particularly limited, and for example, a solution obtained by dissolving a lithium salt as an electrolyte in a non-aqueous solvent (so-called organic electrolytic solution) can be used.
• Lithium salts include LiClO 4 , LiPF 6 , LiAsF 6 , LiBF 4 , LiSO 3 CF 3 and the like. Lithium salts may be used singly or in combination of two or more.
• Non-aqueous solvents include ethylene carbonate, fluoroethylene carbonate, chloroethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, cyclohexylbenzene, sulfolane, propanesultone, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidin-2-one, ⁇ -butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1, 2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, trimethyl phosphate, triethyl phosphate and
• the states of the positive electrode and the negative electrode in the lithium ion secondary battery are not particularly limited.
• the positive electrode, the negative electrode, and, if necessary, the separator disposed between the positive electrode and the negative electrode may be spirally wound, or may be stacked in a plate shape.
• the separator is not particularly limited, and for example, resin nonwoven fabric, cloth, microporous film, or a combination thereof can be used.
• resins include resins containing polyolefins such as polyethylene and polypropylene as main components. If the positive electrode and the negative electrode do not come into direct contact due to the structure of the lithium ion secondary battery, the separator may not be used.
• the shape of the lithium-ion secondary battery is not particularly limited.
• laminate-type batteries, paper-type batteries, button-type batteries, coin-type batteries, laminated-type batteries, cylindrical-type batteries, and square-type batteries can be used.
• the lithium-ion secondary battery of the present disclosure is suitable as a large-capacity lithium-ion secondary battery used in electric vehicles, power tools, power storage devices, and the like.
• EV electric vehicles
• HEV hybrid electric vehicles
• PHEV plug-in hybrid electric vehicles
• It is suitable as a lithium ion secondary battery.
• Example 1 (Preparation of spherical natural graphite) Scaly natural graphite (produced in Heilongjiangzhou, China) with an average particle size of 50 ⁇ m is spheroidized using a spheroidizing device (Nara Machinery Co., Ltd., Hybridization NHS-0), a rotor peripheral speed of 75.0 m / min, 2.5 minutes. A spheroidizing treatment was performed under the conditions of to produce spherical natural graphite. The produced spheroidized natural graphite was subjected to cyclone classification using a cyclone classifier, setting the classification point to 1 ⁇ m.
• a spheroidizing device Nara Machinery Co., Ltd., Hybridization NHS-0
• a spheroidizing treatment was performed under the conditions of to produce spherical natural graphite.
• the produced spheroidized natural graphite was subjected to cyclone classification using a cyclone classifier, setting the
• Example 2 Using a spheroidizing device (manufactured by Nara Machinery, Hybridization NHS-0), scaly natural graphite with an average particle size of 50 ⁇ m (produced in Heilongjiangzhou, China) was processed at a rotor peripheral speed of 85.0 m/min for 3.0 minutes. A spheroidizing treatment was performed to produce spherical natural graphite. The produced spheroidized natural graphite was subjected to cyclone classification using a cyclone classifier, setting the classification point to 10 ⁇ m. By-product particles were obtained by further removing particles of 1 ⁇ m or less by sieving the particles removed by the cyclone classification. 30 parts by mass of the obtained by-product particles were mixed with 70 parts by mass of spherical natural graphite (main particles in Table 1) obtained by cyclone classification to obtain spherical natural graphite used for producing a negative electrode material. .
• a spheroidizing device manufactured by Nara
• Example 2 (Preparation of negative electrode material) A negative electrode material was produced in the same manner as in Example 1, except that the spherical natural graphite obtained in Example 1 was replaced with the spherical natural graphite obtained in Example 2.
• Examples 3, 4, 7, 8 Spherical natural graphite was produced in the same manner as in Example 1, except that the scale-like natural graphite used in Example 1 was changed to one shown in Table 1, or the conditions for the spheroidizing treatment were changed as shown in Table 1. Graphite was obtained.
• a negative electrode material was produced in the same manner as in Example 1, except that the spherical natural graphite obtained in Example 3, 4, 7 or 8 was used instead of the spherical natural graphite obtained in Example 1. .
• Examples 5, 6, 9 Cyclone classification was carried out in the same manner as in Example 2, except that the scale-like natural graphite used in Example 2 was changed to that shown in Table 1, or the conditions for the spheroidizing treatment were changed as shown in Table 1. to obtain by-product particles.
• the obtained by-product particles and the spherical natural graphite obtained by the cyclone classification were mixed at the ratio shown in Table 1 to obtain the spherical natural graphite used for producing the negative electrode material.
• a negative electrode material was produced in the same manner as in Example 2, except that the spherical natural graphite obtained in Example 5, 6 or 9 was used instead of the spherical natural graphite obtained in Example 2.
• a negative electrode material was produced in the same manner as in Example 1, except that the spherical natural graphite obtained in Comparative Example 1, 2 or 4 was used instead of the spherical natural graphite obtained in Example 1.
• Table 1 shows the spheroidization conditions, cyclone classification conditions, and by-product particle addition conditions in each example and comparative example.
• the following methods were used to measure tap density, D90/D10, average particle size (50% D), average circularity, N 2 Measurement of specific surface area, average interplanar spacing, R value, exothermic peak, measurement of the number of particles with equivalent circle diameter of 5 ⁇ m or less and their ratio, number-based circles at cumulative 99% of particle diameter distribution limited to particle diameters of 5 ⁇ m or more Measurement of the equivalent diameter and measurement of the circularity at cumulative 1% of the circularity distribution limited to particle diameters of 5 ⁇ m or more were performed.
• Tables 2 and 3 "the measured value of the equivalent circle diameter and the boundary value of the circularity obtained from the formula (a)" is obtained by substituting the number-based equivalent circle diameter at 99% of the accumulation in the formula (a). means the value on the right side of .
• the liquid is circulated with a pump while applying ultrasonic waves (pump flow rate is 65% from the maximum value), the amount of water is adjusted so that the absorbance is 0.10 to 0.15, and the volume accumulation of the obtained particle size distribution
• the 50% particle size (D50) was defined as the average particle size.
• D90/D10 was obtained from the volume cumulative 10% particle diameter (D10) of the obtained particle size distribution and the volume cumulative 90% particle diameter (D90) of the obtained particle size distribution. Table 2 shows the results.
• the circularity of the negative electrode material was measured using a wet flow particle size/shape analyzer (FPIA-3000 manufactured by Malvern).
• the average circularity which is the number-based circularity at cumulative 50%, and the circularity at cumulative 1% of the circularity distribution limited to particle diameters of 5 ⁇ m or more were obtained.
• the measurement temperature was 25° C.
• the concentration of the measurement sample was 10 mass %
• the number of particles to be counted was 10,000.
• water was used as a dispersing solvent.
• the N 2 specific surface area was calculated by the BET method by measuring nitrogen adsorption at liquid nitrogen temperature (77 K) by the one-point method using a high-speed specific surface area/pore size distribution analyzer (FlowSorbIII, manufactured by Shimadzu Corporation). Table 2 shows the results.
• lithium ion secondary batteries for evaluating input/output characteristics were produced according to the following procedure. First, for 98 parts by mass of the negative electrode material, an aqueous solution (CMC concentration: 2% by mass) of CMC (carboxymethyl cellulose, manufactured by Daicel Finechem Co., Ltd., product number 2200) as a thickener is added so that the solid content of CMC becomes 1 part by mass. and kneaded for 10 minutes. Then, purified water was added so that the total solid content concentration of the negative electrode material and CMC was 40% by mass to 50% by mass, and the mixture was kneaded for 10 minutes.
• CMC concentration carboxymethyl cellulose, manufactured by Daicel Finechem Co., Ltd., product number 2200
• the negative electrode material composition is applied to an electrolytic copper foil having a thickness of 11 ⁇ m with a comma coater whose clearance is adjusted so that the coating amount per unit area is 10.0 mg/cm 2 to form a negative electrode material layer. did.
• the electrode density was adjusted to 1.65 g/cm 3 with a hand press.
• the electrodeposited copper foil on which the negative electrode material layer was formed was punched out into a disk shape with a diameter of 14 mm to prepare a sample electrode (negative electrode).
• the prepared sample electrode (negative electrode), separator, and counter electrode (positive electrode) were placed in a coin-shaped battery container in this order, and an electrolytic solution was injected to produce a coin-shaped lithium ion secondary battery.
• an electrolytic solution a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (the volume ratio of EC and EMC is 3:7) was mixed with 0.5 of vinylene carbonate (VC) with respect to the total amount of the mixed solution. % by mass and LiPF 6 dissolved to a concentration of 1 mol/L was used.
• Metallic lithium was used as the counter electrode (positive electrode).
• a polyethylene microporous membrane having a thickness of 20 ⁇ m was used as the separator.
• the DC resistance (DCR) of the lithium ion secondary battery was measured to obtain the power density of the battery. Specifically, it is as follows. In addition, Table 4 shows the results.
• lithium ion secondary batteries for cycle characteristic evaluation were produced in the following procedure. First, as a negative electrode material, 7 mass of SiO (heat treatment temperature: 1000 ° C., carbon coating amount: 5 mass%) subjected to carbon coating treatment is applied to 93 parts by mass of the negative electrode material prepared in each example and each comparative example. After the addition, they were mixed for 10 minutes to obtain a negative electrode active material.
• SiO heat treatment temperature: 1000 ° C., carbon coating amount: 5 mass
• CMC concentration 2% by mass
• CMC carboxymethyl cellulose, Daiichi Kogyo Seiyaku Co., Ltd., Cellogen WS-C
• purified water was added so that the total solid content concentration of the negative electrode material and CMC was 40% by mass to 50% by mass, and the mixture was kneaded for 10 minutes.
• an aqueous dispersion of SBR (BM400-B, Nippon Zeon Co., Ltd.) as a binder (SBR concentration: 40% by mass) was added so that the solid content of SBR was 1 part by mass, and mixed for 10 minutes.
• a paste-like negative electrode material composition was prepared.
• the negative electrode material composition is applied to an electrolytic copper foil having a thickness of 11 ⁇ m with a comma coater whose clearance is adjusted so that the coating amount per unit area is 10.0 mg/cm 2 to form a negative electrode material layer. did. After that, the electrode density was adjusted to 1.65 g/cm 3 by a roll press.
• a sample electrode (negative electrode) was produced by punching out the electrolytic copper foil on which the negative electrode material layer was formed so as to have a size of 4.0 cm ⁇ 3.0 cm.
• a positive electrode a positive electrode made of NMC was cut out in the same area, and a separator (made of a porous polyethylene film) was placed between the negative electrode and the positive electrode and combined.
• a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (the volume ratio of EC and EMC is 3:7) was mixed with 0.5 of vinylene carbonate (VC) with respect to the total amount of the mixed solution.
• % by mass 1.0% by mass of fluoroethylene carbonate (FEC) was added, and LiPF 6 was dissolved to a concentration of 1 mol/L.
• a negative electrode for the cycle characteristic evaluation was prepared, and the electrode density was adjusted to 1.65 g/cm 3 by a roll press.
• the pressed negative electrode was punched into a circle of 16 ⁇ , which was attached to a glass substrate with a double-faced tape to form a planar electrode surface without distortion.
• 3 ⁇ L of PC polycarbonate: manufactured by Kishida Chemical Co., Ltd.
• PC polycarbonate: manufactured by Kishida Chemical Co., Ltd.
• the pressed negative electrode is placed in a cell for X-ray diffraction measurement, and an X-ray diffraction measurement device (X-ray diffraction measurement device X-RAY DIFFRACTIOMETER MultiFlex manufactured by Rigaku Corporation) is used, a scanning speed of 0.25 ° / min, a tube voltage
• X-ray diffraction measurement device X-ray diffraction measurement device X-RAY DIFFRACTIOMETER MultiFlex manufactured by Rigaku Corporation
• a scanning speed 0.25 ° / min
• I 002 /I 110 which is the ratio of the obtained peak intensity of the 002 diffraction line (I 002 ) and the peak intensity of the 110 diffraction line (I 110 ), was obtained, and this value was taken as the electrode orientation.
• Table 4 shows the results.
• step 1 the lithium ion secondary battery produced in the same manner as in (Production of lithium ion secondary battery for input/output characteristic evaluation) described above is placed in a thermostat set at 25 ° C., and the current value is 0.2C. was charged at a constant current to a voltage of 0 V (V vs. Li/Li + ), and then charged at a constant voltage at 0 V until the current value reached 0.02C. After resting for 30 minutes, constant current discharge was performed at a current value of 0.2 C to a voltage of 1.5 V (V vs. Li/Li + ).
• step 1 (1st discharge capacity at 25°C after storage at 60°C for 21 days)/(2nd discharge capacity at 25°C before storage at 60°C) x 100
• Example 2 Comparing Example 2 and Comparative Example 3, the D50 was about 18 ⁇ m and the N 2 specific surface area was about the same as about 6 m 2 /g, but in Example 2 the DCR during charging was low and improved. Since Example 2 has a higher average circularity than Comparative Example 3, it is considered that the effect of the average circularity improves the DCR results. However, when comparing Comparative Example 2, which has a higher average circularity and a smaller D50, the input characteristics cannot be sufficiently improved only with a small D50, a large N2 specific surface area, and a high average circularity. was shown.
• an increase in the number of particles with an equivalent circle diameter of 5 ⁇ m or less/ N2 specific surface area which is the number of particles with an equivalent circle diameter of 5 ⁇ m or less per unit N2 specific surface area, increases the reaction area of the negative electrode material with the electrolyte solution. It means to improve the conductivity, shorten the distance of diffusion in the solid, and the like.
• consumption of the electrolytic solution is reduced, so it is thought that better cycle characteristics were obtained. .
• the curved path length which is the distance from one surface in the thickness direction to the other surface through the voids inside the negative electrode material layer, does not become too long, and the liquid Turns tend to be good. As a result, regions where the electrolytic solution and the negative electrode material cannot contact each other are less likely to occur, and favorable cycle characteristics are more likely to be maintained.
• D90/D10 is larger than a specific value, particles having a large particle diameter lengthen the tortuous path length and deteriorate the circulation of liquid.
• Comparative Example 3 has the longest liquid injection time and the highest electrode orientation compared to each of Examples and Comparative Examples, so it is considered that the curved path length is longer. As a result, in Comparative Example 3, the number of particles with an equivalent circle diameter of 5 ⁇ m or less that contributes to the cycle characteristics/ N2 specific surface area is larger than in Example 9, but because the injection time is longer, It is considered that the cycle characteristics are inferior.

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• 2021
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