Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein: the negative electrode has a negative electrode core body and a negative electrode mixture layer disposed on the surface of the negative electrode core body; the negative electrode mixture layer contains an Si-containing material; the positive electrode has a positive electrode core body and a positive electrode mixture layer disposed on the surface of the positive electrode core body; the positive electrode mixture layer contains a positive electrode active material, porous carbon, and carbon nanotubes; the density of the positive electrode mixture layer is 3.30 g / cm3 or higher; the porous carbon has a plurality of through-holes; and the particle fracture strength Fa of the positive electrode active material and the particle fracture strength Fc of the porous carbon satisfy Fa≤Fc.

Description

Nonaqueous electrolyte secondary battery Cross-reference to Related Application

[0001] The present application claims the benefit of priority from Japanese Patent Application No. 2025-045845 filed with the Japan Patent Office on March 19, 2025, and the entire content of the above patent application is incorporated herein by reference.

[0002] The present disclosure relates to a nonaqueous electrolyte secondary battery.

[0003] Patent Document 1 discloses "porous carbon particles in which a pore diameter peak on the adsorption side measured by the BJH method exists between 2.6 nm and 200 nm, the specific surface area is 100 to 600 m ２ / g, and the pore volume in the range of 2.6 nm to 200 nm on the adsorption side measured by the BJH method is 0.4 ml / g or more".

[0004] Patent Document 2 discloses "a secondary battery comprising a battery case, an electrode assembly accommodated in the battery case, and a current interrupting mechanism that interrupts electrical connection between the electrode assembly and an external terminal, wherein the electrode assembly includes a positive electrode current collector and a positive electrode active material layer held by the positive electrode current collector, the positive electrode active material layer includes a plurality of hollow positive electrode active material particles, a plurality of void support particles that are distinct from the hollow positive electrode active material particles and secure predetermined voids in the positive electrode active material layer, and a plurality of conductive material particles that are distinct from the void support particles and secure electrical conduction of the positive electrode active material layer, the positive electrode active material layer has voids with an electrode plate pore diameter of 0.5 μm or more, an average particle diameter B of the void support particles satisfies 1 / 3 ≤ (B / A) ≤ 2 relative to an average particle diameter A of the hollow positive electrode active material particles, and a crushing strength of the void support particles is higher than a crushing strength of the conductive material particles".

[0005] JP 2019-151525 A, JP 2014-82116 A

[0006] Along with the increase in capacity of nonaqueous electrolyte secondary batteries, higher density of electrodes and thicker electrode mixture layers have been progressing. Accordingly, development of a positive electrode having high liquid retention capability for nonaqueous electrolyte is desired. Suppressing liquid depletion of the nonaqueous electrolyte in the positive electrode and reducing reaction resistance are important issues.

[0007] It is thought that electrolyte depletion can be suppressed by including porous carbon with pores capable of holding non-aqueous electrolytes in the positive electrode mixture layer. However, when the positive electrode mixture layer is made denser, much of the porous carbon is crushed, and the pores of the porous carbon are not effectively utilized to hold non-aqueous electrolytes, making it difficult to reduce reaction resistance.

[0008] One aspect of this disclosure comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode comprises a negative electrode core and a negative electrode mixture layer disposed on the surface of the negative electrode core, the negative electrode mixture layer comprises a Si-containing material, the positive electrode comprises a positive electrode core and a positive electrode mixture layer disposed on the surface of the positive electrode core, the positive electrode mixture layer comprises a positive electrode active material, porous carbon, and carbon nanotubes, and the active material density of the positive electrode mixture layer is 3.3 g / cm³. ３ The present invention relates to a non-aqueous electrolyte secondary battery in which the porous carbon has a plurality of through-holes, and the particle fracture strength Fa of the positive electrode active material and the particle fracture strength Fc of the porous carbon satisfy Fa ≤ Fc.

[0009] According to this disclosure, the liquid retention capacity of the non-aqueous electrolyte in the positive electrode can be increased, thereby reducing the reaction resistance of the non-aqueous electrolyte secondary battery. Novel features of the present invention are described in the appended claims, but the present invention, both in terms of structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings.

[0010] This is a schematic longitudinal cross-sectional view showing a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure.

[0011] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties or conditions are given as examples, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit is not greater than or equal to the upper limit. When multiple materials are given as examples, one of them may be selected and used alone, or two or more may be used in combination.

[0012] This disclosure encompasses any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims. In other words, any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims, is possible, provided that no technical inconsistency arises.

[0013] [Positive Electrode] Hereinafter, the positive electrode relating to this disclosure will also be referred to as "positive electrode (P)". Non-aqueous electrolyte secondary batteries include lithium-ion secondary batteries using a liquid non-aqueous electrolyte (electrolyte), solid-state batteries containing a gel electrolyte, and the like. A non-aqueous electrolyte secondary battery comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte. A separator is usually placed between the positive electrode and the negative electrode.

[0014] The positive electrode (P) comprises a positive electrode core (positive electrode current collector) and a positive electrode mixture layer disposed on the surface of the positive electrode core. The positive electrode mixture layer is composed of a positive electrode mixture and is in the form of a layer or film. The positive electrode mixture contains at least a positive electrode active material and porous carbon. The positive electrode mixture usually further contains a binder. The porous carbon retains a non-aqueous electrolyte, thereby enhancing the electrolyte retention of the positive electrode, and also acts as a conductive agent.

[0015] The positive electrode mixture layer can be formed by applying a positive electrode slurry, which is obtained by dispersing a positive electrode mixture in a dispersion medium, onto the surface of a positive electrode current collector and drying the applied slurry. The dried coating film may be rolled as necessary. The positive electrode mixture layer may be formed on one surface of the positive electrode core, or may be formed on both surfaces of the positive electrode core. The dispersion medium is not particularly limited, and for example, water, alcohol, N-methyl-2-pyrrolidone (NMP) or the like can be used.

[0016] The positive electrode core is composed of a sheet-shaped conductive material. As the positive electrode core, a non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh, a net, or a punched sheet) is used. The positive electrode mixture layer is supported on one or both surfaces of the positive electrode core. The material of the positive electrode core is not particularly limited, and stainless steel, aluminum, aluminum alloy, titanium or the like can be used.

[0017] 1 m of one side of the positive electrode core ２ The mass of the positive electrode mixture layer formed per unit area may be, for example, 200 g or more, and is preferably 250 g or more. This enables an increase in the capacity of a non-aqueous electrolyte secondary battery. Specifically, increasing the thickness of the positive electrode mixture layer or increasing the density of the positive electrode mixture layer can increase the capacity of the non-aqueous electrolyte secondary battery.

[0018] The thickness of the positive electrode mixture layer is not particularly limited, and for example, it may be in the range of 50 µm to 250 µm per side of the core. In the positive electrode according to the present disclosure, an increase in internal resistance is suppressed even when the positive electrode mixture layer is thickened. One positive electrode mixture layer may be formed of a plurality of layers having mutually different compositions.

[0019] The active material density of the positive electrode mixture layer is, for example, 3.3 g / cm ３ or more, and may be 3.3 g / cm ３ to 3.8 g / cm ３ or may be 3.5 g / cm ３ to 3.8 g / cm ３ or may be 3.6 g / cm ３ to 3.8 g / cm ３This may also be the case. The positive electrode according to this disclosure suppresses an increase in internal resistance even when the density of the positive electrode mixture layer is significantly increased. By increasing the density of the positive electrode mixture layer in this way, it is possible to increase the capacity of non-aqueous electrolyte secondary batteries. The density of the positive electrode mixture layer can be increased by increasing the mass content of the positive electrode active material in the positive electrode mixture or by rolling the positive electrode mixture at high pressure on the positive electrode core to form the positive electrode mixture layer. Note that the active material density of the positive electrode mixture layer may be rephrased as the packing density of the positive electrode active material contained in the positive electrode mixture layer.

[0020] (Porous Carbon (C)) The porous carbon used in this disclosure has a structure different from carbon black, which contains almost no pores, and activated carbon, which mainly contains only fine pores, because the pore volume occupied by pores of a desired pore size can be arbitrarily designed. Hereinafter, the porous carbon used in this disclosure will also be referred to as "porous carbon (C)". The porous carbon particles used in this disclosure will also be referred to as "carbon particles (C)".

[0021] Porous carbon (C) has multiple through-pores. In other words, porous carbon (C) particles (carbon particles (C)) have a three-dimensional structure with multiple through-pores. Through-pores are voids that continuously connect one part of the surface of a carbon particle (C) to another part of the surface. The multiple through-pores serve to hold the electrolyte. The electrolyte can be absorbed into the through-pores. The presence of through-pores can be confirmed by observing carbon particles (C) with a scanning electron microscope (SEM) or chromatograph (TEM).

[0022] By binarizing and processing SEM or TEM images of carbon particles (C), the ratio of the area of ​​observable through-holes to the area enclosed by the contour of the carbon particle (C) (hereinafter also referred to as the "pore area ratio") can be calculated. The pore area ratio is, for example, 10% to 90%, and preferably 20% to 60%. The pore area ratio may also be determined as the average value of the pore area ratios of 100 arbitrarily selected particles.

[0023] Here, it is preferable that the particle fracture strength Fa of the positive electrode active material and the particle fracture strength Fc of the porous carbon (C) (i.e., carbon particles (C)) satisfy the relationship Fa ≤ Fc, and more preferably Fa < Fc. When the relationship Fa ≤ Fc is satisfied, when the particles of the positive electrode active material and the carbon particles (C) exert pressure on each other in the positive electrode mixture layer, the crushing of the carbon particles (C) is suppressed. In particular, when the positive electrode mixture layer is made denser, the carbon particles (C) are subjected to strong pressure from the particles of the positive electrode active material. In this case, by satisfying the relationship Fa ≤ Fc, the carbon particles (C) become less susceptible to damage, and many of the pores of the carbon particles (C) are maintained. As a result, many of the pores of the carbon particles (C) can act as reservoirs that hold non-aqueous electrolytes. That is, the liquid retention capacity of the positive electrode is improved, and it becomes easier to suppress the increase in reaction resistance associated with liquid depletion.

[0024] From the viewpoint of highly suppressing the crushing or damage of carbon particles (C), the ratio of the particle fracture strength Fc of porous carbon (C) to the particle fracture strength Fa of the positive electrode active material (Fc / Fa ratio) is preferably 1.05 ≤ Fc / Fa, more preferably 1.1 ≤ Fc / Fa, may also be 1.15 ≤ Fc / Fa, or 1.2 ≤ Fc / Fa. On the other hand, from the viewpoint of preventing damage to the particles of the positive electrode active material, the Fc / Fa ratio may be Fc / Fa ≤ 1.5. For example, the Fc / Fa ratio may be 1.05 ≤ Fc / Fa ≤ 1.5, 1.1 ≤ Fc / Fa ≤ 1.5, 1.15 ≤ Fc / Fa ≤ 1.5, or 1.2 ≤ Fc / Fa ≤ 1.5.

[0025] From a similar viewpoint, the difference (Fc-Fa) between the particle fracture strength Fa of the positive electrode active material and the particle fracture strength Fc of porous carbon (C) is preferably 10 MPa or more, may be 20 MPa or more, or may be 30 MPa or more. On the other hand, from the viewpoint of preventing damage to the particles of the positive electrode active material, the difference (Fc-Fa) may be, for example, 40 MPa or less. The difference (Fc-Fa) may be, for example, 10 MPa ≤ (Fc-Fa) ≤ 40 MPa, 20 MPa ≤ (Fc-Fa) ≤ 40 MPa, or 30 MPa ≤ (Fc-Fa) ≤ 40 MPa.

[0026] The particle fracture strength Fa of the positive electrode active material is, for example, 100 MPa or more, but may also be 110 MPa or more, 130 MPa or more, 150 MPa or more, or 160 MPa or more. When the positive electrode mixture layer is made denser, the particles of the positive electrode active material are subjected to strong pressure from the carbon particles (C). A positive electrode active material having such a particle fracture strength Fa is less susceptible to crushing or damage, and therefore its degradation is less likely to progress. Alternatively, the particle fracture strength Fa of the positive electrode active material may also be, for example, 220 MPa or less, but may also be 210 MPa or less, 200 MPa or less, 190 MPa or less, or 180 MPa or less. A positive electrode active material having such a particle fracture strength Fa has high packing properties in the positive electrode and is suitable for high density and thick film formation of the positive electrode mixture layer. The particle fracture strength Fa of the positive electrode active material may be, for example, 100 MPa ≤ Fa ≤ 220 MPa, 110 MPa ≤ Fa ≤ 200 MPa, 110 MPa ≤ Fa ≤ 180 MPa, or 130 MPa ≤ Fa ≤ 180 MPa.

[0027] The particle fracture strength Fc of porous carbon (C) is, for example, 100 MPa or more, but may also be 110 MPa or more, 120 MPa or more, 130 MPa or more, 140 MPa or more, 150 MPa or more, 160 MPa or more, 170 MPa or more, or 180 MPa or more. Porous carbon having such a particle fracture strength Fc is less susceptible to crushing or damage, making it easier to maintain the liquid retention properties of the positive electrode. Alternatively, the particle fracture strength Fc of porous carbon may also be, for example, 220 MPa or less, but may also be 210 MPa or less, 200 MPa or less, 190 MPa or less, or 180 MPa or less. Porous carbon (C) having such a particle fracture strength Fc has high packing properties in the positive electrode and is suitable for increasing the density and thickness of the positive electrode mixture layer. The particle fracture strength Fc of porous carbon (C) may be, for example, 120 MPa ≤ Fa ≤ 220 MPa, 120 MPa ≤ Fa ≤ 200 MPa, or 130 MPa ≤ Fa ≤ 200 MPa.

[0028] In particular, the particle fracture strength Fc of porous carbon (C) is preferably 150 MPa or higher. By setting 150 MPa ≤ Fc, it becomes possible to select a positive electrode active material that satisfies the relationship Fa < Fc and has the largest possible particle fracture strength Fa. In that case, when the degree of density and thickness of the positive electrode mixture layer is increased, crushing or damage to both the porous carbon (C) and the positive electrode active material becomes much less likely, and the degradation of the positive electrode is significantly suppressed. The particle fracture strength Fc of porous carbon (C) may be, for example, 150 MPa ≤ Fa ≤ 220 MPa, 170 MPa ≤ Fa ≤ 220 MPa, or 180 MPa ≤ Fa ≤ 200 MPa.

[0029] (Measurement of Particle Breaking Strength) The method for controlling the particle breaking strength (Fa, Fc) is not particularly limited. For example, it can be controlled to achieve the desired particle breaking strength by the manufacturing method of the positive electrode active material and porous carbon (C). In the case of the positive electrode active material, it may be controlled by, for example, the heating temperature of the raw materials during synthesis of the positive electrode active material, the composition of the raw materials, etc. In the case of porous carbon (C), it may be controlled by, for example, the type of raw materials used during the production of porous carbon (C), the processing conditions of the raw materials, etc.

[0030] The particle fracture strength (Fa, Fc) can be measured using a commercially available measuring device (for example, the micro-compression tester (MCT-201) manufactured by Shimadzu Corporation) by following the procedure below.

[0031] (1) The positive electrode active material and porous carbon (C) are scattered on the lower pressure plate (SKS flat plate) of the measuring device. Here, the median of the particle size distribution of porous carbon (C) (carbon particles (C)) is defined as D50(c), and the median of the particle size distribution of the positive electrode active material is defined as D50(a).

[0032] (2) For porous carbon (C), carbon particles (C) close in size to D50(c) are selected as samples while observing with an optical microscope. For positive electrode active material, particles of positive electrode active material close in size to D50(a) are selected as samples while observing with an optical microscope.

[0033] (3) A diamond flat indenter with a diameter of 50 μm is used as the upper indenter, and only one particle selected as the sample is placed between this upper indenter and the lower pressure plate.

[0034] (4) The upper pressure bar is slowly lowered, and from the moment it comes into contact with the sample (when the descent speed changes), a load is applied at a constant acceleration (specifically, a displacement speed of 2.7 mN / sec).

[0035] (5) Measure the relationship between the load and the deformation of the sample. The point at which the deformation of the sample changes abruptly (the inflection point of the load-deformation profile) is defined as the fracture point. The fracture strength is calculated from the load and particle size of the sample at that time based on the following formula. The fracture strength is calculated by taking five measurements and taking the average value.

[0036] St = 2.8P / πd ２ St: Breaking strength [MPa or N / mm] ２ ] P: Load [N] d: Particle diameter [mm]

[0037] The particle size of the sample should preferably be within ±5% of the median D50 of the particle size distribution. The sphericity of the sample should preferably be 85% or higher. The particle size of the sample can be determined as the average value of the maximum particle size observed under a microscope and the diameter perpendicular to that maximum diameter.

[0038] The sample to be measured can be prepared by disassembling a secondary battery, removing the positive electrode, peeling off the positive electrode mixture layer from the positive electrode core, washing it with anhydrous ethyl methyl carbonate or dimethyl carbonate, and then separating the positive electrode mixture, which has been lightly ground in a mortar, using methods such as centrifugation as needed.

[0039] The sample of the positive electrode active material may be prepared by drying the pulverized positive electrode mixture in a dry atmosphere for 1 hour, immersing it in weakly boiled 6M hydrochloric acid for 10 minutes, washing it with deionized water, drying it at 200°C for 1 hour, and then centrifuging it.

[0040] Porous carbon (C) may be separated by dissolving organic matter such as the cathode binder in an organic solvent such as NMP by placing the pulverized cathode mixture into the solvent, and then dissolving the cathode active material in aqua regia. This separates only the carbonaceous material. If the carbonaceous material contains materials other than porous carbon (C) (e.g., carbon nanotubes), the porous carbon (C) and carbon nanotubes can be separated, for example, by sieving the separated carbonaceous material.

[0041] The specific surface area of ​​porous carbon (C) is not particularly limited, but for example, 100 m ２ It may be less than / g. Specific surface area of ​​100 m² ２ By controlling the amount to less than 1g, not only is the liquid retention of the cathode improved by porous carbon (C), but the electronic conductivity is also improved. The specific surface area is 80 m². ２ Less than / g is also acceptable, 60m ２ It may be less than / g. As the specific surface area decreases, the diameter of the through-holes increases, and the movement of lithium ions within the through-holes tends to become easier. Also, as the specific surface area decreases, it is easier to ensure high electronic conductivity in porous carbon (C).

[0042] The specific surface area of ​​porous carbon (C) is the BET specific surface area measured by the BET method. The BET specific surface area is measured by the gas adsorption method. Nitrogen gas is used as the gas. Details of the BET method should be in accordance with JIS Z8830:2013. Specifically, the amount of nitrogen adsorbed onto porous carbon (C) at liquid nitrogen temperature is measured. The porous carbon (C) sample is filled into a sample tube of a measuring device (for example, the Shimadzu Corporation's automatic specific surface area / pore distribution analyzer "Tristar II 3020"), the sample tube is cooled to -196°C, the pressure is reduced, and then nitrogen (99.999% purity) is adsorbed onto the sample at the desired relative pressure, and the adsorption isotherm is measured. From the obtained adsorption isotherm, the BET specific surface area is determined by a multi-point method (for example, 3 points) in the relative pressure range of 0.05 to 0.1.

[0043] Porous carbon (C) has a pore size distribution suitable for maintaining electrolytes. The mode diameter of the pore size distribution of carbon particles (C) may be, for example, between 2 nm and 200 nm, or between 2 nm and 50 nm. When the mode diameter of porous carbon (C) is within such a range, it is thought that the movement of lithium ions in the through-pores of porous carbon (C) becomes easier.

[0044] The total pore volume of porous carbon (C) is not particularly limited, but for example, 0.04 cm³. ３ / g or more 0.40cm ３ It is less than / g and 0.04 cm ３ / g or more 0.40cm ３ It can be less than 0.04 cm / g. ３ / g or more 0.25cm ３ It may be less than / g. When the total pore volume of porous carbon (C) is within this range, the ability of porous carbon (C) to hold non-aqueous electrolytes is increased, and the liquid retention of the positive electrode is further improved. Note that the total pore volume of porous carbon (C) is the cumulative pore volume in the range of 1 nm to 200 nm.

[0045] The pore size distribution, integrated pore volume, and total pore volume of porous carbon (C) can be determined by analyzing the adsorption isotherms of porous carbon (C), which are measured when determining the BET specific surface area, using the BJH (Barrett Joyner Hallenda) method and the DTF (Density Functional Theory) method. The QS-DTF method (Slitpore, Equilibrium Model) may be used as the DTF method.

[0046] The median particle size distribution (D50) of the porous carbon (C) is not particularly limited, but for example, it may be between 0.1 μm and 7.0 μm, or between 0.5 μm and 7.0 μm. When the median particle size distribution (D50) of the porous carbon (C) is within this range, the dispersibility of the porous carbon (C) in the positive electrode mixture layer can be improved. By improving the dispersibility of the porous carbon (C), it becomes easier for it to contribute to improving the liquid retention and conductivity of the positive electrode mixture layer. It is preferable that the porous carbon (C) has multiple through-holes (for example, three or more) with a maximum diameter of 1% or more of the median particle size distribution (D50) of the porous carbon (C). For example, when counting the number of through-holes having a maximum diameter of 1% or more of D50 for 100 particles arbitrarily selected from porous carbon (C), it is preferable that the 100 particles have, on average, 3 or more (e.g., 5 or more, 10 or more, or 20 or more) through-holes having a maximum diameter of 1% or more of D50. Porous carbon (C) may have 5 or more, 10 or more, or 20 or more through-holes having a maximum diameter of 1% or more of the median (D50) of the particle size distribution of porous carbon (C).

[0047] The median (D50) particle size distribution of porous carbon (C) is the median particle size (median diameter) in the particle size distribution measured, for example, by laser diffraction scattering. A measuring device such as the "LA-750" manufactured by HORIBA, Ltd. can be used.

[0048] The porosity of porous carbon (C) may be less than 50 volume%. By setting the porosity to less than 50 volume%, the strength of porous carbon (C) is further increased, and its breakdown within the cathode mixture layer is further suppressed. As a result, liquid retention is maintained over a long period of time. The porosity may be between 10 volume% and 60 volume%, or between 15 volume% and 35 volume%.

[0049] The porosity of porous carbon is measured by the mercury intrusion method. Details of the mercury intrusion method should be followed in accordance with JIS R1655:2003. Since mercury exhibits a contact angle of 90° or more with almost all solids, mercury does not enter the voids even when it comes into contact with the sample. Therefore, the porosity can be calculated from the volume of mercury when no pressure is applied (apparent volume) and the amount of mercury intruded into the voids by applying external pressure to the mercury (volume of the voids).

[0050] The porous carbon (C), which is the sample used to measure each physical property, may be prepared as described above by disassembling the battery, removing the positive electrode, peeling off the positive electrode mixture layer, and separating it from the positive electrode mixture. That is, after removing non-aqueous electrolytes and other materials by washing, the positive electrode mixture layer is peeled off from the positive electrode core and the positive electrode mixture is pulverized. Organic materials such as the positive electrode binder are separated by dissolving them in an organic solvent. The positive electrode active material is separated by dissolving it in aqua regia. In this way, porous carbon (C), which is a carbonaceous material, is separated. Subsequently, by classifying the carbonaceous material, it is possible to separate porous carbon (C) from carbon nanotubes with long average lengths. Alternatively, porous carbon (C), which is the raw material for the positive electrode mixture layer, may be obtained and prepared. Furthermore, physical properties such as the porous carbon (C) content, specific surface area, total pore volume, average pore diameter, median particle size distribution, and porosity may be analyzed by observing the morphology of a cross-section parallel to the thickness direction of the positive electrode mixture layer.

[0051] The content of porous carbon (C) in the positive electrode mixture layer may be, for example, less than 10% by mass. Because porous carbon (C) is bulky, it can exhibit sufficient liquid retention even in small amounts. From the viewpoint of increasing the density of the positive electrode active material in the positive electrode mixture layer, it is preferable that the content of porous carbon (C) be less than 10% by mass. The content of porous carbon (C) may be less than 5% by mass, less than 3% by mass, or less than 1% by mass. However, from the viewpoint of obtaining a significant effect of improving the liquid retention of the positive electrode by porous carbon (C), it is preferable that the content of porous carbon (C) in the positive electrode mixture layer be 0.1% by mass or more.

[0052] (Carbon Nanotubes) The cathode composite layer can have its resistance further significantly reduced by including carbon nanotubes (hereinafter also referred to as "CNTs"). CNTs also have the effect of suppressing variations in potential within the cathode.

[0053] It is believed that CNTs form main conductive pathways, while porous carbon (C) can form fine conductive pathways. As a result, conductive pathways extend throughout the entire positive electrode mixture layer, significantly improving current collection from the positive electrode mixture layer.

[0054] The CNTs may be single-walled CNTs (SWCNTs) or multi-walled CNTs (MWCNTs). Examples of multi-walled CNTs include two-walled CNTs, three-walled CNTs, and CNTs with four or more layers. The positive electrode mixture layer preferably contains single-walled CNTs and / or multi-walled CNTs. The multi-walled CNTs contained in the positive electrode mixture layer may be one type of multi-walled CNT or multiple types of multi-walled CNTs with different numbers of layers.

[0055] The CNTs preferably have a slender and elongated shape. The average diameter Da of the CNTs is preferably, for example, 10 nm or less, more preferably 6 nm or less, and even more preferably 2 nm or less. The average length La of the CNTs is preferably, for example, 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.

[0056] Here, the average length La of the CNTs is the average length of bundled CNTs formed by two or more CNTs joining together. The aspect ratio expressed as La / Da is, for example, 1000 or more, and preferably 10000 or more. Note that the positive electrode mixture layer may also contain CNTs in an isolated state without forming bundles.

[0057] The average diameter Da of a carbon nanotube (CNT) is determined by image analysis using a transmission electron microscope (TEM). The average diameter Da of a CNT can be measured by the following method: First, 100 CNTs are arbitrarily selected, and the diameter (outer diameter) of one arbitrary point on each is measured. Then, the average diameter Da is obtained by taking the arithmetic mean of the measured diameters.

[0058] The average length La of a carbon nanotube (CNT) is determined by image analysis using a scanning electron microscope (SEM). The average length La is calculated by selecting 100 arbitrary bundles of CNTs, measuring their lengths (the length when the bundled CNTs are straightened out), and taking the arithmetic mean of these lengths.

[0059] The amount of CNTs contained in the positive electrode mixture layer may be trace. Combined with the presence of porous carbon (C), even a trace amount of CNTs can exert a sufficient effect in improving conductivity. The CNT content in the positive electrode mixture layer may be, for example, 1% by mass or less, less than 1% by mass, 0.9% by mass or less, or 0.5% by mass or less. Preferably, the CNT content in the positive electrode mixture layer is, for example, 0.001% by mass to 0.9% by mass.

[0060] The CNTs used as measurement samples for each physical property can be prepared as described above by disassembling a battery, removing the positive electrode, peeling off the positive electrode mixture layer, and separating it from the positive electrode mixture. Alternatively, the CNTs used as raw materials for the positive electrode mixture layer can be obtained and prepared.

[0061] (Positive electrode active material) The positive electrode active material includes a material that electrochemically intercepts and releases lithium ions. The material that electrochemically intercepts and releases lithium ions may be a lithium transition metal composite oxide. Examples of lithium transition metal composite oxides include layered compounds with a rock salt crystal structure, spinel compounds, and polyanionic compounds. Among lithium transition metal composite oxides, composite oxides that contain at least Ni and in which the proportion of Ni to all metal elements other than Li is 50 mol% or more (hereinafter also referred to as "composite oxide (HN)") are preferred in that they exhibit high capacity.

[0062] In a composite oxide (HN), the proportion of Ni among the metal elements other than Li may be 50 atomic% or more, 80 atomic% or more, or 90 atomic% or more. In a composite oxide (HN), the proportion of Ni among the metal elements other than Li may be less than 100 atomic%, 99 atomic% or less, or 98 atomic% or less.

[0063] Examples of preferred composite oxides (HN) include rock salt-type layered compounds. For example, a compound with the composition of formula (C): Liα Ni(1-x1-x2-x3-y)Co ｘ１ Mn ｘ２ Al ｘ３ M ｙ O ２＋β A lithium transition metal composite oxide represented by is preferred. However, formula (C) satisfies 0.95 ≤ α ≤ 1.05, 0.5 ≤ 1-x1-x2-x3-y ≤ 0.99, 0 ≤ x1 ≤ 0.1, 0 ≤ x2 ≤ 0.5, 0 ≤ x3 ≤ 0.1, 0 ≤ y ≤ 0.1, and -0.05 ≤ β ≤ 0.05. M is at least one selected from the group consisting of Ti, Zr, Nb, Mo, W, Fe, Zn, B, Si, Mg, Ca, Sr, and Y.

[0064] Composite oxides (HN) with a high Ni content tend to have unstable crystal structures, and side reactions can cause metals such as Ni to leach out of the composite oxide (HN). The leached Ni forms a film on the particle surface of the composite oxide (HN) with a structure that hinders the absorption and release of Li ions, leading to an increase in internal resistance. On the other hand, when the positive electrode mixture layer contains porous carbon (C), the liquid retention capacity of the positive electrode mixture layer is improved, reducing the reaction resistance of the composite oxide (HN), suppressing side reactions, and preventing an increase in internal resistance.

[0065] At least one element selected from the group consisting of B, N, P, Mg, Ca, Sr, Ba, Ti, W, Zr, and Al may be unevenly distributed on the surface of the lithium transition metal composite oxide. The element unevenly distributed on the surface has the effect of suppressing the formation of a high-resistance film on the particle surface of the composite oxide (HN).

[0066] (Positive electrode binder) Examples of binders for the positive electrode mixture include resin materials such as fluororesins like polytetrafluoroethylene and polyvinylidene fluoride (PVDF); polyolefin resins like polyethylene and polypropylene; polyamide resins like aramid resin; and polyimide resins like polyimide and polyamideimide. These may be used individually or in combination of two or more.

[0067] [Negative electrode] The negative electrode includes at least a negative electrode core (negative electrode current collector) and may comprise a negative electrode mixture layer formed on the surface of the negative electrode current collector and containing a negative electrode active material. The negative electrode mixture layer is composed of a negative electrode mixture and is in the form of layers or a film. The negative electrode mixture includes at least a negative electrode active material and usually further includes a conductive agent and a binder.

[0068] Lithium metal secondary batteries do not necessarily have a negative electrode mixture layer. Lithium ion secondary batteries do have a negative electrode mixture layer.

[0069] The negative electrode mixture layer can be formed by coating the surface of the negative electrode core with a negative electrode slurry, which is obtained by dispersing the negative electrode mixture in a dispersion medium, and drying it. The dried coating may be rolled if necessary. The negative electrode mixture layer may be formed on one surface of the negative electrode current collector, or on both surfaces.

[0070] The negative electrode core is composed of a sheet-like conductive material. Non-porous conductive substrates (such as metal foil) and porous conductive substrates (such as mesh, net, or perforated sheet) can be used as the negative electrode core. The material of the negative electrode core is not particularly limited, but stainless steel, nickel, nickel alloys, copper, copper alloys, etc., can be used.

[0071] One side of the negative electrode core, 1m ２ The mass of the negative electrode mixture layer formed around the core may be, for example, 50 g or more, and preferably 100 g or more. By increasing this mass to 100 g or more, the amount of the positive electrode mixture layer applied can be increased from the viewpoint of maintaining an appropriate negative electrode / positive electrode capacity ratio, thereby enabling higher capacity non-aqueous electrolyte secondary batteries. This mass can be increased by making the negative electrode mixture layer thicker or by increasing the density of the negative electrode active material in the negative electrode mixture layer. There are no particular limitations on the thickness of the negative electrode mixture layer, but for example, it may be in the range of 60 μm to 240 μm per side of the core. By using the positive electrode (P) according to this disclosure, even if the negative electrode mixture layer is thickened, an increase in internal resistance can be suppressed. The density of the negative electrode mixture layer is, for example, 1.0 g / cm³. ３ ~2.0 g / cm ３ It may be within the range.

[0072] The volumes of the positive and negative electrodes increase and decrease with charging and discharging. The volume change of the negative electrode is particularly large. When the negative electrode expands during charging, the internal pressure of the electrode group increases, pushing the non-aqueous electrolyte out from the positive electrode. Therefore, the liquid retention properties of porous carbon (C) are more effective when the expansion rate of the negative electrode during charging is large.

[0073] The volume Vc of the negative electrode in a fully charged battery may be 125% or more of the volume Vdc of the negative electrode in a completely discharged battery. Even with such a large expansion rate of the negative electrode, excellent charge-discharge cycle characteristics can be maintained by using a positive electrode (P).

[0074] A fully charged state refers to a state where the battery has been charged to a charge level of, for example, 0.98 × C or higher (SOC = 98% or higher), where C is the rated capacity of the battery. A completely discharged state refers to a state where the battery has been discharged to a charge level of, for example, 0.05 × C or lower (SOC = 5% or lower). Note that the amount of charge required to charge a completely discharged battery (SOC = 0%) to a fully charged state (SOC = 100%) corresponds to the rated capacity. The voltage of a fully charged battery corresponds to the charge termination voltage. The voltage of a completely discharged battery corresponds to the discharge termination voltage.

[0075] (Negative electrode active material) The negative electrode active material includes a material that electrochemically intercepts and releases lithium ions. As the material that electrochemically intercepts and releases lithium ions, carbonaceous materials, Si-containing materials, etc., can be used. The negative electrode active material may be used alone or in combination of two or more types. The negative electrode active material may include a carbonaceous material. The negative electrode active material may include a Si-containing material. It is preferable that the negative electrode active material includes a carbon material and a Si-containing material.

[0076] (Carbonaceous materials) Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon). Carbonaceous materials may be used individually or in combination of two or more types.

[0077] Among carbonaceous materials, graphite is preferred due to its excellent charge-discharge stability and low irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles. The graphite particles may partially contain amorphous carbon, easily graphitizable carbon, and difficult-to-graphitize carbon.

[0078] Graphite is a carbonaceous material in which a graphite-type crystal structure is well-developed. The average interplanar spacing d002 of the (002) planes of graphite, as measured by X-ray diffraction, may be, for example, 0.340 nm or less, or 0.3354 nm or more and 0.340 nm or less.

[0079] (Si-containing material) The Si-containing material may be, for example, a carbon composite particle containing a carbon phase and a Si phase dispersed within the carbon phase. The carbon phase may consist of, for example, amorphous carbon (i.e., amorphous carbon) or crystalline carbon. Amorphous carbon may be, for example, hard carbon, soft carbon, or something else. Amorphous carbon generally refers to a carbonaceous material in which the average interplanar spacing d002 of (002) planes, measured by X-ray diffraction, exceeds 0.340 nm. Examples of crystalline carbon include carbon having a graphite-type crystal structure, such as graphite. Crystalline carbon such as graphite refers to a carbonaceous material in which d002 is 0.340 nm or less (for example, 0.3354 nm or more and 0.340 nm or less).

[0080] The Si phase content in the carbon composite particles is, for example, 30% to 80% by mass, and may also be 40% to 70% by mass. In this range, a higher initial volume can be obtained.

[0081] The Si-containing material may be a compound containing Si, or it may be a composite particle in which a Si phase (fine Si phase) is dispersed within a lithium ion conducting phase (matrix). Examples of Si-containing compounds include silicon dioxide (SiO₂). ｘ ) are examples. The lithium ion conducting phase is SiO ２ Preferably, it contains at least one selected from the group consisting of phases and silicate phases. Specific examples of composite particles include SiO ２ Phase and SiO ２Examples include composite particles containing a Si phase dispersed within the phase, and composite particles containing a silicate phase and a Si phase dispersed within the silicate phase (silicate composite particles).

[0082] SiO ２ The phase is an amorphous phase containing 95% or more by mass of silicon dioxide. SiO ２ Composite particles in which the Si phase is dispersed within the phase are SiO ｘ It is expressed as follows: x may be, for example, 0.5 ≤ x < 2, and 0.8 ≤ x ≤ 1.6. SiO ｘ For example, silicon monoxide is heat-treated and undergoes a disproportionation reaction to produce SiO ２ It is obtained by separating the phase from the fine Si phase.

[0083] The silicate phase preferably contains at least one of alkali metal elements (Group 1 elements other than hydrogen in the long-period periodic table) and Group 2 elements in the long-period periodic table. Alkali metal elements include lithium (Li), potassium (K), sodium (Na), etc. Group 2 elements include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), etc. The lithium silicate phase has the formula: Li ２ｙ SiO ２＋ｙ The composition may be represented by (0 < y < 2), where y may be 1 / 2 or 1. Silicate composite particles in which the Si phase is dispersed within the silicate phase can be obtained, for example, by grinding a mixture of silicate and raw silicon while stirring in a ball mill or the like to produce fine particles, and then heat-treating the mixture in an inert atmosphere.

[0084] The Si phase content dispersed within the silicate phase may be 30% to 95% by mass, or 35% to 75% by mass, relative to the total silicate composite particles.

[0085] When the negative electrode mixture layer contains a Si-containing material, the Si-containing material content in the negative electrode mixture layer may be, for example, 3% by mass or more, and may be 5% by mass or more. The Si-containing material content may be, for example, 15% by mass or less, and may be 10% by mass or less. A negative electrode mixture layer containing Si-containing material at such a content is prone to large expansion and contraction, so it is desirable to use it in combination with a positive electrode (P). The Si-containing material content in the negative electrode mixture layer may be, for example, 3% by mass to 15% by mass, and may be 5% by mass to 10% by mass. In this case, the Si phase content in the negative electrode mixture layer may be, for example, 1% by mass to 15% by mass, and may be 1% by mass to 10% by mass, 1.5% by mass to 10% by mass, or 2% by mass to 10% by mass.

[0086] (Negative electrode binder) Examples of binders for negative electrode mixtures include resin materials such as fluororesins (e.g., polytetrafluoroethylene, polyvinylidene fluoride), polyolefin resins (e.g., polyethylene, polypropylene), polyamide resins (e.g., aramid resin), polyimide resins (e.g., polyimide, polyamideimide), acrylic resins (e.g., polyacrylic acid, polymethacrylic acid, acrylic acid-methacrylic acid copolymer, ethylene-acrylic acid copolymer, or salts thereof), vinyl resins (e.g., polyvinyl acetate), and rubber-like materials (e.g., styrene-butadiene copolymer rubber (SBR)). A single binder may be used, or two or more may be used in combination.

[0087] (Thickener) The negative electrode mixture may contain a thickener to thicken the negative electrode slurry. Examples of thickeners include cellulose derivatives such as cellulose ether. Examples of cellulose derivatives include CMC and its modified forms, and methylcellulose. Modified forms of CMC also include salts of CMC. Examples of salts include alkali metal salts (e.g., sodium salts) and ammonium salts. A single thickener may be used, or two or more may be used in combination.

[0088] (Negative electrode conductive agent) Examples of conductive agents for negative electrode mixtures include carbon blacks such as acetylene black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and organic conductive materials such as phenylene derivatives. These may be used individually or in combination of two or more types.

[0089] [Separator] Typically, a separator is interposed between the positive and negative electrodes. The separator has high ion permeability and possesses appropriate mechanical strength and insulating properties. As the separator, microporous thin films, woven fabrics, nonwoven fabrics, etc., can be used. Polyolefins such as polypropylene and polyethylene are preferred as the material of the separator.

[0090] One example of a secondary battery structure is a structure in which an electrode group, in which a positive electrode and a negative electrode are wound around each other with a separator, and an electrolyte are housed in an outer casing. Alternatively, other forms of electrode groups may be used instead of wound electrode groups, such as a laminated electrode group in which the positive electrode and negative electrode are stacked with a separator. Secondary batteries may take any form, such as cylindrical, prismatic, coin-type, button-type, or laminated type.

[0091] [Non-aqueous electrolytes] Non-aqueous electrolytes are ionic conductive (e.g., lithium ion conductive). Non-aqueous electrolytes may be liquid non-aqueous electrolytes (electrolytes). An electrolyte contains a non-aqueous solvent and a solute dissolved in the non-aqueous solvent. An example of a solute is a lithium salt. Various additives may be added to non-aqueous electrolytes.

[0092] Various known organic solvents can be used as non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonate esters, linear carbonate esters, cyclic carboxylic acid esters, linear carboxylic acid esters, linear ethers, cyclic ethers, fluorinated linear ethers, and fluorinated cyclic ethers.

[0093] Examples of cyclic carbonate esters include propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC).

[0094] Examples of linear carbonate esters include diethylene carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0095] Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL).

[0096] Examples of linear carboxylic acid esters include non-aqueous solvents such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0097] Examples of linear ethers include dimethyl ether, ethyl methyl ether, diethyl ether, ethyl propyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, and o-dimethoxybenzene.

[0098] Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, and crown ethers.

[0099] Fluorinated linear ethers have a structure in which one or more hydrogen atoms of the above-mentioned linear ether are replaced with fluorine. Examples of fluorinated linear ethers include bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. An example of a fluorinated cyclic ether is 3,3,4,4-tetrafluorotetrahydrofuran.

[0100] The non-aqueous solvent may be used alone or in combination of two or more types.

[0101] Examples of lithium salts include lithium salts of chlorine-containing acids, lithium salts of fluorine-containing acids, lithium salts of fluorine-containing acidimides, lithium halides, and lithium salts containing oxalate complexes. An example of a lithium salt of a chlorine-containing acid is LiClO2. ４ LiAlCl ４ LiB １０ Cl １０ Examples include LiPFA. ６ LiPF ２ O ２ LiBF ４ LiSbF ６ LiAsF ６ LiCF ３ SO ３ LiCF ３ CO ２ Examples include LiN(FSO). ２ ) ２ (Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(CF ３ SO ２ ) ２ ,LiN(CF ３ SO ２ ) (FSO ２ ), LiN (CF ３ SO ２ ) (C ４ F ９ SO ２ ), LiN(C ２ F ５SO ２ ) ２ Examples include LiCl, LiBr, and LiI. An example of an oxalate complex-containing lithium salt is LiB(C). ２ O ４ ) ２ LiBF ２ (C ２ O ４ ), LiPF ４ (C ２ O ４ ), LIPF ２ (C ２ O ４ ) ２ These are some examples. The lithium salts described above may be used individually or in combination of two or more types.

[0102] The non-aqueous electrolyte preferably contains fluoroethylene carbonate (FEC) as a solvent. Furthermore, the non-aqueous electrolyte preferably contains lithium bis(fluorosulfonyl)imide (LiFSI) as a lithium salt. That is, the non-aqueous electrolyte preferably contains at least one selected from the group consisting of fluoroethylene carbonate (FEC) and lithium bis(fluorosulfonyl)imide (LiFSI). The inclusion of fluoroethylene carbonate (FEC) facilitates the formation of a stable fixed electrolyte film (SEI) on the surface of the positive or negative electrode, particularly reducing reaction resistance. Additionally, lithium bis(fluorosulfonyl)imide exhibits excellent ion dissociation in the solvent and provides a low-viscosity non-aqueous electrolyte, thereby enhancing the conductivity of the non-aqueous electrolyte.

[0103] The concentration of lithium salt in the non-aqueous electrolyte may be 1 mol / L or more and 5 mol / L or less, or 1 mol / L or more and 3 mol / L or less. By setting the lithium salt concentration within the above range, a liquid non-aqueous electrolyte (non-aqueous electrolyte solution) with excellent ionic conductivity and appropriate viscosity can be obtained.

[0104] Non-aqueous electrolytes may contain various known additives. Examples of such additives include 1,3-propanesalton, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, fluorobenzene, and ethylene sulfite (ES).

[0105] The structure of the secondary battery will be described below with reference to Figure 1. Figure 1 is a longitudinal cross-sectional view of a cylindrical non-aqueous electrolyte secondary battery 10, which is an example of this embodiment. However, this disclosure is not limited to the following configuration.

[0106] The secondary battery 10 comprises an electrode group 18, a non-aqueous electrolyte (not shown), and a bottomed cylindrical battery case 22 that houses these components. A sealing body 11 is crimped and fixed to the opening of the battery case 22 via a gasket 21. This seals the inside of the battery. The sealing body 11 comprises a valve body 12, a metal plate 13, and an annular insulating member 14 interposed between the valve body 12 and the metal plate 13. The valve body 12 and the metal plate 13 are connected to each other at their respective centers. A positive electrode lead 15a, which extends from the positive electrode plate 15, is connected to the metal plate 13. Therefore, the valve body 12 functions as an external terminal for the positive electrode. A negative electrode lead 16a, which extends from the negative electrode plate 16, is connected to the inner surface of the bottom of the battery case 22. An annular groove 22a is formed near the open end of the battery case 22. A first insulating plate 23 is positioned between one end face of the electrode group 18 and the annular groove 22a. A second insulating plate 24 is positioned between the other end face of the electrode group 18 and the bottom of the battery can 22. The electrode group 18 is formed by winding a positive electrode plate 15 and a negative electrode plate 16 with a separator 17 in between.

[0107] (Note) The following technologies are disclosed in accordance with the above description. (Technology 1) A positive electrode comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the negative electrode comprises a negative electrode core and a negative electrode mixture layer disposed on the surface of the negative electrode core, the negative electrode mixture layer comprises a Si-containing material, the positive electrode comprises a positive electrode core and a positive electrode mixture layer disposed on the surface of the positive electrode core, the positive electrode mixture layer comprises a positive electrode active material, porous carbon and carbon nanotubes, and the active material density of the positive electrode mixture layer is 3.30 g / cm³ ３(Technology 2) The non-aqueous electrolyte secondary battery according to Technology 1, wherein the porous carbon has a plurality of through-holes, and the particle fracture strength Fa of the positive electrode active material and the particle fracture strength Fc of the porous carbon satisfy Fa ≤ Fc. (Technology 3) The non-aqueous electrolyte secondary battery according to Technology 1 or 2, wherein the diameter of the carbon nanotube is 6 nm or less. (Technology 4) The non-aqueous electrolyte secondary battery according to Technology 1 or 2, wherein the median value (D50) of the particle size distribution of the porous carbon is 0.5 μm or more and 7.0 μm or less. ３ / g or more 0.40cm ３ (Technology 5) A non-aqueous electrolyte secondary battery according to any one of Technology 1 to 3, wherein the amount is less than or equal to / g. (Technology 5) A non-aqueous electrolyte secondary battery according to any one of Technology 1 to 4, wherein the mode diameter of the pore size distribution of the porous carbon is 2 nm or more and 50 nm or less. (Technology 6) A non-aqueous electrolyte secondary battery according to any one of Technology 1 to 5, wherein the particle fracture strength of the porous carbon is 150 MPa or more. (Technology 7) A non-aqueous electrolyte secondary battery according to any one of Technology 1 to 6, wherein the content of the Si-containing material in the negative electrode mixture layer is 5% by mass or more. (Technology 8) A non-aqueous electrolyte secondary battery according to any one of Technology 1 to 7, wherein the non-aqueous electrolyte comprises at least one selected from the group consisting of fluoroethylene carbonate (FEC) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0108] [Examples] The present disclosure will be described in detail below based on examples and comparative examples relating to lithium-ion secondary batteries. The present disclosure is not limited to the following examples.

[0109] Examples 1-5, Comparative Examples 1-4: Lithium-ion secondary batteries (batteries A1-A5 in Examples 1-5, batteries B1-B4 in Comparative Examples 1-4) were fabricated and evaluated according to the following procedure.

[0110] (1) Production of negative electrode 92 parts by mass of graphite powder as a negative electrode active material, a predetermined amount of SiO powder, 0.8 parts by mass of carboxymethyl cellulose (CMC), 1.2 parts by mass of styrene butadiene rubber (SBR), and an appropriate amount of water were mixed to obtain a negative electrode slurry. Next, the negative electrode slurry was applied onto the surface of a copper foil so as to obtain an appropriate positive / negative electrode capacity ratio, the coating film was dried, and then rolled to form a negative electrode mixture layer with a thickness of 100 μm on each side of the copper foil. The active material density of the negative electrode mixture layer was set to 1.6 g / cm ３ . The content of SiO powder in the negative electrode mixture layer is as shown in Table 1.

[0111] (2) Production of positive electrode A lithium-containing composite oxide (LiNi ０．８８ Co ０．０７ Mn ０．０５ O ２ ) having a median particle size distribution (D50) of 10 μm and the particle fracture strength Fa shown in Table 1, 100 parts by mass of said composite oxide, 1 part by mass of polyvinylidene fluoride, 0.4 parts by mass of porous carbon (C) having the physical properties shown in Table 1, 0.8 parts by mass of CNTs having the average diameter shown in Table 1, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were mixed to obtain a positive electrode slurry. Next, the positive electrode slurry was applied onto the surface of an aluminum foil, the coating film was dried, and then rolled to form a positive electrode mixture layer with a thickness of 95 μm (the active material density is the value shown in Table 1) on each side of the aluminum foil, thereby obtaining a positive electrode.

[0112] Here, CNTs with an average length La = 20 μm were used.

[0113] The mode diameter of the pore size distribution of the porous carbon (C) was within the range of 2 nm to 50 nm.

[0114] 100 pieces of each porous carbon (C) were arbitrarily selected, and cross-sectional SEM images and TEM images of all particles were subjected to image processing to calculate the pore area ratio of the porous carbon (C). The pore area ratio of all particles was within the range of 20% to 60%. The porosity of the porous carbon (C) was 15 vol% to 60 vol%.

[0115] (3) Preparation of non-aqueous electrolyte A mixed solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC = 4:1:15, to which lithium hexafluoride phosphate (LiPF) ６ A non-aqueous electrolyte was prepared by adding 0.8 mol / liter of ) and 0.5 mol / liter of LiFSI, and containing 0.2% by mass of FEC.

[0116] (4) Preparation of Non-Aqueous Electrolyte Secondary Battery An Al positive electrode lead was attached to the positive electrode obtained above, and a Ni negative electrode lead was attached to the negative electrode obtained above. In an inert gas atmosphere, the positive electrode and negative electrode were wound in a spiral shape via a polyethylene thin film (separator) to prepare a wound electrode group. The electrode group was housed in a cylindrical outer casing, the non-aqueous electrolyte was injected, and the outer casing was sealed to prepare cylindrical 2170 batteries A1 to A5 (Examples) and B1 to B4 (Comparative Examples).

[0117]

[0118] [Evaluation] [DCIR] In a temperature environment of 25°C, the batteries for each example were charged with a constant current of 0.2 It until the voltage reached 4.2V, and then charged with a constant voltage of 4.2V until the current reached 0.02 It. After that, they were left to rest for 20 minutes. In this way, batteries with a state of charge (SOC) of 100% were obtained. The obtained SOC 100% batteries were discharged with a constant current of 0.3 It until the state of charge (SOC) reached 10%. For the SOC 10% batteries, the voltage values ​​were measured when they were discharged for 10 seconds at current values ​​of 0A, 0.1A, 0.5A, and 1.0A. The DCIR was calculated from the absolute value of the slope when the relationship between the discharge current value and the voltage value after 10 seconds was approximated by the least squares method as a straight line.

[0119] Table 1 shows the evaluation results for batteries A1-A5 and B1-B4. In Table 1, DCIR is a relative value with the result for battery B1 in Comparative Example 1 set to 100. The higher the liquid retention capacity of the non-aqueous electrolyte in the positive electrode and the lower the reaction resistance, the smaller the DCIR. Batteries with smaller DCIR values ​​can be said to have lower internal resistance and be superior.

[0120] Table 1 shows that when a cathode containing porous carbon (C) satisfying Fa ≤ Fc is used, the DCIR is significantly reduced.

[0121] The non-aqueous electrolyte secondary battery having a positive electrode according to this disclosure is useful for a variety of applications, including electronic devices such as mobile phones, smartphones, and tablet devices, as well as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles.

[0122] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0123] 10: Secondary battery, 11: Sealing body, 12: Valve body, 13: Metal plate, 14: Insulating member, 15: Positive electrode plate, 15a: Positive electrode lead, 16: Negative electrode plate, 16a: Negative electrode lead, 17: Separator, 18: Electrode group, 21: Gasket, 22: Battery can, 22a: Groove, 23: First insulating plate, 24: Second insulating plate

Claims

1. The electrode comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode core and a negative electrode mixture layer disposed on the surface of the negative electrode core, the negative electrode mixture layer contains a Si-containing material, the positive electrode has a positive electrode core and a positive electrode mixture layer disposed on the surface of the positive electrode core, the positive electrode mixture layer contains a positive electrode active material, porous carbon, and carbon nanotubes, and the active material density of the positive electrode mixture layer is 3.3 g / cm³. ３ The above describes a non-aqueous electrolyte secondary battery in which the porous carbon has a plurality of through holes, and the particle fracture strength Fa of the positive electrode active material and the particle fracture strength Fc of the porous carbon satisfy Fa ≤ Fc.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the diameter of the carbon nanotube is 6 nm or less.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the median (D50) of the particle size distribution of the porous carbon is 0.5 μm or more and 7.0 μm or less.

4. The total pore volume of the porous carbon is 0.04 cm³. ３ / g or more 0.40cm ３ A non-aqueous electrolyte secondary battery according to claim 1, wherein the amount is less than or equal to / g.

5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the mode diameter of the pore size distribution of the porous carbon is 2 nm or more and 50 nm or less.

6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the particle fracture strength of the porous carbon is 150 MPa or more.

7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of Si-containing material in the negative electrode mixture layer is 5% by mass or more.

8. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte comprises at least one selected from the group consisting of fluoroethylene carbonate (FEC) and lithium bis(fluorosulfonyl)imide (LiFSI).

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