Active material for non-aqueous electrolyte secondary batteries, non-aqueous electrolyte secondary batteries, and manufacturing method of active material for non-aqueous electrolyte secondary batteries.

Abstract

To reduce the internal resistance of a non-aqueous electrolyte secondary battery.SOLUTION: A method for manufacturing a negative electrode active material for a lithium ion secondary battery includes a pore-forming step (S1) of forming pores in a carbon material, a nitrogen-containing compound mixing step (S2) of mixing a nitrogen-containing compound into the carbon material in which pores are formed, a nitrogen-doping step (S5) for vaporizing or liquefying the nitrogen-containing compound by a heat treatment (S3) to introduce it into the pores (S4), and introducing and replacing a nitrogen element, and then a residue removal step (S6) of removing the residue of the nitrogen-containing compound. Therefore, a nitrogen-doped layer can be formed in a carbon material whose surface area has been expanded by pores.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to an active material for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a method for manufacturing an active material for a non-aqueous electrolyte secondary battery, and more particularly to an active material for a non-aqueous electrolyte secondary battery, which reduces the internal resistance of the non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a method for manufacturing an active material for a non-aqueous electrolyte secondary battery. [Background technology]

[0002] BACKGROUND ART Non-aqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, have high energy density and high capacity, and are therefore used as power sources for driving electric vehicles (EVs), hybrid vehicles (HVs), and the like.

[0003] A nonaqueous electrolyte secondary battery, such as a lithium ion secondary battery, is constructed by stacking a positive electrode plate and a negative electrode plate with a separator interposed therebetween to form an electrode assembly, which is housed in a battery case filled with an electrolyte. The negative electrode plate is provided with a negative electrode active material made of a carbon material.

[0004] In order to achieve a longer life for such secondary batteries, carbon materials doped with nitrogen (nitrogen doping, N-doping) have been proposed. For example, Patent Document 1 discloses the following invention of an electric double layer capacitor. The electric double layer capacitor is a porous carbon material that has an ordered structure reflecting the structural characteristics of the porous material used as a template, has internal pores, and is nitrogen-doped to provide functionality. This porous carbon material is produced by introducing an organic substance into the surface and pores of the porous material and carbonizing the organic substance by heating it. A gaseous nitrogen-containing compound is then introduced to deposit nitrogen within the carbon skeleton by chemical vapor deposition. The porous material used as a template is then removed to produce the electric double layer capacitor.

[0005] When used as an electrode material to construct an electric double layer capacitor, the nitrogen-doped porous carbon material, which has nitrogen doped into the carbon skeleton, exhibits properties that enable high power density and rapid charging and discharging.Furthermore, it has excellent properties that contribute to a long lifespan.

[0006] Patent Document 2 also discloses the following nonaqueous electrolyte storage element. It comprises a positive electrode containing a positive electrode active material capable of inserting and desorbing anions, a negative electrode containing a negative electrode active material, and a nonaqueous electrolyte. The positive electrode active material has a plurality of mesopores forming a three-dimensional network structure, and contains a carbon material containing at least one of nitrogen and a nitrogen compound on the surface of the carbon material or inside the mesopores formed therein. Such a nonaqueous electrolyte storage element has the advantages of having a high discharge capacity and generating little gas during charging and discharging. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-310514 [Patent Document 2] Japanese Patent Application Publication No. 2017-228514 Summary of the Invention [Problem to be solved by the invention]

[0008] In the inventions described in Patent Documents 1 and 2, it is assumed that the drag reduction effect can be obtained by doping graphite with nitrogen. However, according to the analysis by the present inventors, the reaction with Li ions occurs on the graphite surface, so that nitrogen doping into the interior of the graphite has almost no effect, and it was found that in order to maximize the nitrogen doping effect, it is necessary to concentrate the distribution of N element in the surface layer of the graphite.

[0009] Furthermore, it was found that even if it were possible to concentrate N element in the surface layer of graphite, the number of places where nitrogen could be introduced is limited due to the specific surface area of ​​graphite, and therefore the enhancement of the nitrogen doping effect on graphite is limited.

[0010] The problem to be solved by the active material for a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery, and the method for producing an active material for a non-aqueous electrolyte secondary battery of the present invention is to reduce the internal resistance of a non-aqueous electrolyte secondary battery. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, the active material for a non-aqueous electrolyte secondary battery of the present invention is characterized by comprising: a carbon material serving as an active material for a non-aqueous electrolyte secondary battery, the carbon material having pores formed on its surface; and a nitrogen-doped layer provided on the surface of the carbon material and on the inner walls of the peripheries of the openings of the pores.

[0012] It is desirable that a nitrogen-doped layer be formed on the inner wall of the pore opening periphery in a range inside the carbon material that can come into contact with the electrolyte of the nonaqueous electrolyte solution. It is desirable that the N / C intensity ratio is 1.6 or more and 2.7 or less at a depth of more than 0 [nm] and not more than 5 [nm] from the surface of the carbon material, and that the N / C intensity ratio is 1.6 or less at a depth of more than 5 [nm] and not more than 50 [nm].

[0013] The carbon material in which the pores are formed has a specific surface area of ​​7.5 [m 2 / g] or more, 9.7[m 2 / g or less is desirable. The pores in the carbon material preferably have an average pore diameter of 13.4 nm or more and 15.8 nm or less.

[0014] The carbon material in which the pores are formed has a total pore volume V of 0.0316 [cm 3 / g] or more, 0.0326[cm 3 / g or less is desirable. The non-aqueous electrolyte secondary battery of the present invention is characterized in that the above-mentioned active material for non-aqueous electrolyte secondary batteries is used as a negative electrode active material.

[0015] The method for producing an active material for a non-aqueous electrolyte secondary battery of the present invention is characterized by comprising: a pore-forming step of forming pores in a carbon material that will serve as an active material for a non-aqueous electrolyte secondary battery; a nitrogen-containing compound-mixing step of mixing a nitrogen-containing compound with the carbon material in which the pores have been formed; a nitrogen-doping step of vaporizing or liquefying the nitrogen-containing compound by heat treatment, introducing the nitrogen-containing compound into the pores, and introducing and substituting nitrogen element onto the surface of the carbon material; and a residue-removing step of removing residue of the nitrogen-containing compound.

[0016] It is desirable that the molecular diameter of the nitrogen-containing compound is larger than the average opening diameter of the pores. The inner walls of the pores around the openings are preferably doped with nitrogen in the area inside the carbon material that can come into contact with the electrolyte of the nonaqueous electrolyte.

[0017] The carbon material before the pores are formed has a specific surface area of ​​4.3 [m 2 / g] or more, 7.6[m 2 / g or less is desirable. The carbon material before the pores are formed preferably has an average pore diameter of 13.7 nm or more and 20.1 nm or less.

[0018] The carbon material before the pores are formed has a total pore volume V of 0.0227 cm 3 / g] or more, 0.0331[cm 3 / g or less is desirable. In the pore formation step, the pores can be formed by gas activation or chemical activation. The pore formation is performed by irradiating microwaves with gas activation, and the microwaves to be irradiated are preferably 500 W or more and 1200 W or less, and the irradiation time is preferably 5 min or more and 15 min or less.

[0019] The nitrogen-containing compound is preferably melamine, an amino acid, or urea. The nitrogen doping step is preferably carried out in an inert gas atmosphere.

[0020] The nitrogen doping step is preferably carried out at a temperature of 200° C. or higher and 1000° C. or lower for a period of 0.5 hours or higher and 2 hours or lower. The nitrogen doping step desirably sets the N / C intensity ratio to 1.6 or more and 2.7 or less at a depth of more than 0 [nm] and less than 5 [nm] from the surface of the carbon material, and sets the N / C intensity ratio to 1.6 or less at a depth of more than 5 [nm] and less than 50 [nm].

[0021] The specific surface area of ​​the carbon material in which the pores are formed is 7.5 [m 2 / g] or more, 9.7[m 2 / g or less is desirable. The average pore diameter of the carbon material in which the pores are formed is preferably 13.4 nm or more and 15.8 nm or less.

[0022] The total pore volume V of the carbon material in which the pores are formed is 0.0316 [cm 3 / g] or more, 0.0326[cm 3 / g] is desirable. [Effects of the Invention]

[0023] According to the active material for a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery, and the method for producing the active material for a non-aqueous electrolyte secondary battery of the present invention, the internal resistance of the non-aqueous electrolyte secondary battery can be reduced. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a graph comparing the internal resistance of a lithium ion secondary battery according to the prior art with that of the lithium ion secondary battery of the present embodiment. [Figure 2] 1 is a schematic diagram illustrating the invention in which a carbon material having pores according to an embodiment of the present invention is doped with nitrogen. [Figure 3] 1 is a schematic diagram illustrating the invention in which a carbon material having pores according to an embodiment of the present invention is doped with nitrogen. [Figure 4]1 is a schematic diagram illustrating the invention in which a carbon material having pores according to an embodiment of the present invention is doped with nitrogen. [Figure 5] 1 shows a lithium ion secondary battery manufactured using the negative electrode active material 1 for lithium ion secondary batteries of the present embodiment. [Figure 6] 1 is a perspective view showing the appearance of a lithium ion secondary battery according to an embodiment of the present invention; [Figure 7] FIG. 2 is a perspective view showing a part of the electrode body 20 in an expanded state. [Figure 8] 1 is a flowchart showing the steps of a method for producing an active material for a lithium ion secondary battery according to the present embodiment. [Figure 9] FIG. 2 is a schematic diagram of graphite in which pores 23 are not formed. [Figure 10] FIG. 2 is a schematic diagram showing a carbon material 2 in which pores 23 are formed. [Figure 11] FIG. 2 is a schematic diagram showing a state in which a nitrogen-containing compound 44 is mixed into a carbon material 2 in which pores 23 are formed. [Figure 12] 1 is a schematic diagram showing a state in which a nitrogen-containing compound 44 is mixed into a carbon material 2 in which pores 23 are formed. [Figure 13] 2 is a schematic diagram showing a state in which a nitrogen-containing compound 4 is introduced into pores 23 formed in a carbon material 2. FIG. [Figure 14] FIG. 2 is a schematic diagram showing a state in which nitrogen atoms from a nitrogen-containing compound 4 introduced into pores 23 formed in a carbon material 2 are substituted for graphite, resulting in nitrogen doping. [Figure 15] FIG. 2 is a schematic diagram showing a negative electrode active material 1 in which a nitrogen-doped layer 41 is formed by burning off the residue of the nitrogen-containing compound after the nitrogen present in pores 23 has been substituted. [Figure 16] 1 is a graph showing the depth [nm] from the surface 22 of the carbon material 2 and the N / C intensity ratio (the ratio of doped nitrogen atoms N to carbon atoms C). [Figure 17] FIG. 1 is a schematic diagram illustrating an invention in which nitrogen is doped into a conventional carbon material having micropores. [Figure 18] FIG. 1 is a schematic diagram illustrating an invention in which nitrogen is doped into a conventional carbon material having micropores. [Figure 19] FIG. 1 is a schematic diagram illustrating an invention in which nitrogen is doped into a conventional carbon material having micropores. [Figure 20] FIG. 1 is a schematic diagram illustrating an invention in which nitrogen is doped into a conventional carbon material having micropores. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, the active material for a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery, and the method for manufacturing the active material for a non-aqueous electrolyte secondary battery of the present invention will be described in terms of an active material for a lithium ion secondary battery and a method for manufacturing the same with reference to Figures 1 to 16. Note that this embodiment is merely an example of the present invention, and the present invention is not limited to this embodiment.

[0026] <About each value> In the present application, the "average pore diameter Dp [nm]" is measured by gas adsorption or mercury porosimetry. Since the pore distribution in this embodiment has an average pore diameter of 13.7 to 20.1 [nm], either method can be used, but in this embodiment, the measurement was performed using mercury porosimetry. Here, in this application, the "average pore diameter Dp [nm]" refers to the median diameter (d50) in the pore distribution of pores.

[0027] In addition, in this application, "particle size" or "average particle size" refers to the median diameter (d50) in a frequency distribution measured by a laser diffraction method unless otherwise specified. Similarly, other average values ​​also refer to the median value (d50) unless otherwise specified.

[0028] <Principle of this embodiment> 2 to 5 are schematic diagrams illustrating the invention in which a carbon material having micropores is doped with nitrogen according to this embodiment. The active material for a non-aqueous electrolyte secondary battery according to this embodiment will be described with reference to FIGS. 2 to 5. Note that the schematic diagrams in this embodiment are intended to explain the principles of the invention and do not accurately represent the shape or dimensions.

[0029] As described in the prior art, there have been conventional lithium ion secondary batteries in which nitrogen is doped into a carbon material. The active material for lithium ion secondary batteries of the present embodiment has a different configuration and effect from the prior art in the following respects, and its technical concept is different.

[0030] According to the analysis by the present inventors, lithium ion L + It was found that the reaction with N occurs on the surface of graphite, so doping the interior of graphite with N is meaningless, and that to maximize the nitrogen doping effect, it is necessary to concentrate the distribution of nitrogen atoms N on the surface of graphite.

[0031] In this embodiment, pores 23 were formed in the manufacturing process as shown in Fig. 2. Then, when nitrogen doping was performed as shown in Fig. 3, the average molecular diameter Dn of the nitrogen-containing compound 4 was set to be larger than the average opening diameter Dp of the pores 23. Therefore, the nitrogen-containing compound 4 remained in contact with the inner walls 23a around the openings of the pores 23, and did not nitrogen-dope the interior 21 of the carbon material deeper than the openings 23c of the pores 23. As a result, as shown in Fig. 4, a nitrogen-doped layer 41 was formed on the surface 22 of the carbon material 2 and on the inner walls 23b around the openings of the pores 23, but no nitrogen-doped layer 41 was present in the interior 21 of the carbon material deeper than the openings 23c.

[0032] Therefore, in this embodiment, the nitrogen-containing compound 4 mixed with the carbon material 2 intensively dopes the surface 22 of the carbon material 2 and the inner wall 23b around the opening of the pore 23 with nitrogen, so that the nitrogen-containing compound 4 can be efficiently used for nitrogen doping.

[0033] 5, the area of ​​the inside 21 of the carbon material deeper than the opening 23c of the pore 23 is not doped with nitrogen. Therefore, the pore 23 is not blocked by the nitrogen-doped layer 41, and lithium ions L with small diameters can be easily doped. + can freely enter the range of the interior 21 of the carbon material deeper than the openings 23c of the pores 23.

[0034] On the other hand, the electrolyte 3, which has a larger average diameter De than the pores 23, cannot penetrate into the area of ​​the carbon material interior 21 deeper than the pore openings 23c. Therefore, no high-resistance SEI (solid electrolyte interphase, an interfacial film that suppresses decomposition of the electrolyte) coating is formed in the area of ​​the carbon material interior 21 deeper than the pore openings 23c, and therefore nitrogen doping is not required.

[0035] Therefore, in the range of the interior 21 of the carbon material deeper than the opening 23c of the pore 23, lithium ions L + Therefore, the surface area of ​​the pores 23 is increased, which contributes to the effect of reducing the internal resistance.

[0036] <Examples and Comparative Examples> FIG. 1 is a graph comparing the cell resistance (internal resistance) of Comparative Examples 1 to 3 of conventional lithium ion secondary batteries with Example 1 of the lithium ion secondary battery of this embodiment.

[0037] <Comparative Example 1> In the negative electrode using conventional graphite shown in Comparative Example 1, neither nitrogen doping nor pore formation was performed, and the cell resistance in this case was used as the standard for comparison.

[0038] <Comparative Example 2> Comparative Example 2 is a nitrogen-doped version of Comparative Example 1, and the cell resistance is lower than that of Comparative Example 1. This is thought to be due to the effect of nitrogen doping near the surface of the graphite, which reduces the surface reaction activation energy for Li-ion insertion.

[0039] <Comparative Example 3> In Comparative Example 3, the same pores as in Example 1 were formed in the conventional graphite shown in Comparative Example 1, but Comparative Example 3 was not doped with nitrogen.

[0040] Increasing the surface area of ​​graphite, which is an active material, is considered to increase the main reaction at the negative electrode. Therefore, in Comparative Example 3, the same pores as in Example 1 were formed in the graphite to increase the surface area. As a result, Comparative Example 3 showed a higher cell resistance than Comparative Example 1.

[0041] This is presumably because the main reaction at the negative electrode increased due to the increased surface area of ​​the graphite, initially reducing the cell resistance. However, the formation of pores creates numerous irregularities on the surface of the active material, causing current unevenness on the graphite surface and creating areas of high current density. In this process, side reactions become more severe in areas of high current density, making it easier for SEI to form. Subsequently, an SEI with high resistance was formed over time. As a result, it is presumed that the cell resistance ultimately increased compared to Comparative Example 1.

[0042] Example 1 Example 1 is a lithium ion secondary battery according to the present embodiment, in which pores were formed in conventional graphite and then nitrogen doped. The pores were formed under the same conditions as in Comparative Example 3. The nitrogen doping was also carried out under the same conditions as in Comparative Example 2.

[0043] As a result, Example 1 exhibited a lower cell resistance than any of Comparative Examples 1, 2, and 3. That is, by adding the configuration of Comparative Example 2, which had a higher resistance than Comparative Example 3, to the configuration of Comparative Example 3, the cell resistance was actually reduced to be smaller than the average resistance, and further reduced than Comparative Example 2. The reason for this will be explained.

[0044] <Principle of Cell Resistance Reduction in This Embodiment> FIG. 2 is a schematic diagram showing a state in which pores 23 are formed on a surface 22 of graphite, which is a carbon material 2, to increase the surface area.

[0045] First, the inventors formed pores 23 on the surface 22 of graphite, which is the carbon material 2. This was done to expand the surface area of ​​the surface 22 of the carbon material 2 in order to increase the area for accepting Li ions. If this was left as it was, the cell resistance would increase, as in Comparative Example 3.

[0046] Therefore, the inventors hypothesized that by doping the surface 22 of the graphite on which the pores 23 are formed with nitrogen, it is possible to inactivate the side reaction sites that are generated when the pores 23 are formed. They then decided to verify this hypothesis. With such a configuration, it was predicted that the activation energy reduction effect of the nitrogen element would further reduce the resistance to the Li ion insertion reaction. The inventors arrived at the invention of this embodiment through verification of this hypothesis.

[0047] <Nitrogen doping in the prior art> 17 to 20 are schematic diagrams illustrating a conventional invention in which nitrogen is doped into a carbon material 2 having pores 23. As described above, Patent Documents 1 and 2 also disclose inventions in which nitrogen is doped into a carbon material having pores.

[0048] In conventional methods, as shown in FIG. 17, pores 23 are formed on a surface 22 of a carbon material 2 made of graphite by using a template or forming a three-dimensional network structure. 18, a nitrogen-containing compound 4 having a small molecular diameter, such as ammonia, is allowed to penetrate into the pores 23 and into the interior 21 of the carbon material 2 to perform nitrogen doping. At this time, the nitrogen-containing compound 4 reaches the interior 21 of the carbon material 2 through the pores 23.

[0049] 19 , nitrogen doping is performed by the nitrogen-containing compound 4 that has penetrated into the interior 21 of the carbon material 2, forming a nitrogen-doped layer 41. This nitrogen-doped layer 41 is formed not only on the surface of the carbon material 2, but also so as to cover the inner walls 23a of the pores 23 in the interior 21 of the carbon material 2.

[0050] FIG. 20 shows a lithium ion secondary battery manufactured using the negative electrode active material 1 for lithium ion secondary batteries of this embodiment. As shown in FIG. 19, the nitrogen-doped layer 41 formed on the surface of the carbon material 2 and covering the inner walls 23a of the pores 23 in the interior 21 of the carbon material 2 blocks the penetration of the electrolyte 3 of the non-aqueous electrolyte. Therefore, not only the electrolyte but also lithium ions L + Therefore, the main reaction on the inner wall 23a of the pore 23 is also unlikely to occur.

[0051] As described above, even if the surface area is increased by the presence of pores 23, the inner walls 23a of pores 23 do not actually contribute to the main reaction at the negative electrode. <Nitrogen doping in this embodiment> Hereinafter, the invention of the active material in which the carbon material 2 having pores 23 of this embodiment is doped with nitrogen will be described in detail with reference to FIGS.

[0052] <Formation of pores 23> In this embodiment, as shown in Fig. 2, microwaves are irradiated onto the surface 22 of a carbon material 2 made of graphite to form pores 23. By adjusting the microwave output [W] and irradiation time, a predetermined pore diameter [nm] and pore volume V [cm 3 / g] of pores 23 are formed.

[0053] The pores 23 may be formed by gas activation using carbon dioxide, water vapor, air, or the like, or by chemical activation using zinc chloride, sulfate, phosphoric acid, or the like. For gas activation, a method using air as the gas and irradiating with microwaves is preferred.

[0054] In the field of catalysis, the International Union of Pure and Applied Chemistry (IUPAC) defines pores with a diameter of 2 nm or less as micropores, pores with a diameter of more than 2 nm but not more than 50 nm as mesopores, and pores with a diameter of more than 50 nm as macropores. In this embodiment, the pores 23 shown have an average pore diameter Dp (d50) of 13.7 to 20.1 nm, which corresponds to mesopores according to the IUPAC definition.

[0055] <Nitrogen-containing compound mixture> Next, as shown in FIG. 3, a nitrogen-containing compound 4 with a large molecular diameter, such as melamine, amino acid, or urea, is mixed with the carbon material 2 with the pores 23 formed therein. As shown in FIG. 3, the nitrogen-containing compound 4 with a large molecular diameter, such as melamine, amino acid, or urea, cannot penetrate into the interior 21 of the carbon material 2 with the relatively small pores 23. In this state, the carbon material 2 is doped with nitrogen. The nitrogen-containing compound 4 can only reach the inner wall 23b around the opening 23c of the pore 23. Therefore, unlike the prior art shown in FIG. 18, the nitrogen-containing compound 4 does not reach the interior 21 of the carbon material 2 with the pores 23.

[0056] <Nitrogen-doped carbon material 2> 4, after nitrogen doping, a nitrogen-doped layer 41 is formed only on the surface 22 of the carbon material 2 and on the inner wall 23b around the opening of the pore 23. Therefore, the nitrogen-doped layer 41 is not formed on the inner wall 23a of the inside 21 of the carbon material 2 in the pore 23. On the inner wall 23a of the inside 21 of the carbon material 2 in the pore 23, the carbon material 2 is exposed.

[0057] <Effects in lithium-ion secondary batteries> 5 shows a lithium ion secondary battery manufactured using the negative electrode active material 1 for lithium ion secondary batteries of this embodiment. As shown in Fig. 5, a nitrogen-doped layer 41 is formed on the surface 22 of the carbon material 2 and on the inner wall 23b around the opening of the pore 23.

[0058] The inner diameter of the pores 23 in the interior 21 of the carbon material 2 is smaller than that of the electrolyte 3 of the non-aqueous electrolyte solution, and the electrolyte 3 of the non-aqueous electrolyte solution does not reach the inner walls 23a of the pores 23 in the interior 21 of the carbon material 2. Therefore, the electrolyte 3 of the non-aqueous electrolyte solution does not form an SEI. On the other hand, the lithium ions L + has a small diameter, and lithium-ion L + can reach the inner wall 23a of the inside 21 of the carbon material 2 of the pore 23, contributing to the main reaction and lowering the resistance.

[0059] In this state, Li ions L + The reduction in the surface reaction activation energy for intercalation suppresses side reactions, thereby suppressing an increase in cell resistance due to the formation of SEI on the surface 22 of the carbon material 2 and on the inner wall 23b around the opening of the pore 23.

[0060] On the other hand, the electrolyte 3 cannot penetrate the inner wall 23a of the inside 21 of the carbon material 2 of the pore 23. Therefore, even if there is an uneven current density, the formation of SEI is suppressed in the inside 21 of the pore 23. As a result, an increase in cell resistance due to side reactions is suppressed. In addition, lithium ions L + reaches the inner walls 23a of the interior 21 of the carbon material 2 in the pores 23, contributes to the main reaction, and reduces the cell resistance.

[0061] <Lithium-ion secondary battery> Fig. 6 is a perspective view showing the appearance of a lithium-ion secondary battery of this embodiment. As shown in Fig. 6, a lithium-ion secondary battery 10, which is an example of a non-aqueous secondary battery, is configured as a cell battery. A plurality of lithium-ion secondary batteries 10 are stacked and sealed in a resin case or the like, and then equipped with a control device, measuring instrument, etc., to be used as an in-vehicle battery pack. A battery pack including the lithium-ion secondary battery 10 is used in hybrid vehicles and electric vehicles.

[0062] The lithium-ion secondary battery 10 includes a battery case 11 and a lid 12. The battery case 11 has a rectangular parallelepiped shape with an opening on the upper side. The lid 12 seals the opening of the battery case 11. The battery case 11 and the lid 12 are made of a metal such as an aluminum alloy. The lithium-ion secondary battery 10 forms a sealed battery container by attaching the lid 12 to the battery case 11.

[0063] The lid 12 is provided with two external terminals 13a, 13b. The external terminals 13a, 13b are used for charging and discharging power. An electrode assembly 15 is housed inside the battery case 11. A positive electrode side current collector 15a, which is the positive electrode side end of the electrode assembly 15, is electrically connected to the positive electrode external terminal 13a via a positive electrode side current collector 14a. A negative electrode side current collector 15b, which is the negative electrode side end of the electrode assembly 15, is electrically connected to the negative electrode external terminal 13b via a negative electrode side current collector 14b. A nonaqueous electrolyte is injected into the battery case 11 through an inlet (not shown).

[0064] Fig. 7 is a perspective view showing a portion of the electrode assembly 15 in an expanded state. As shown in Fig. 7, the electrode assembly 15 is a flat wound body obtained by winding a laminate in which long positive electrode plates 16 and negative electrode plates 17 are stacked with separators 18 interposed therebetween. In the laminate before winding, the positive electrode plates 16, separator 18, negative electrode plates 17, and separator 18 are stacked in this order so that the longitudinal directions of the positive electrode plates 16 and negative electrode plates 17 are aligned.

[0065] <Positive electrode> The positive electrode plate 16 includes a sheet-like positive electrode substrate 16a formed in a long shape and a positive electrode mixture layer 16b provided on both sides of the positive electrode substrate 16a. The positive electrode plate 16 is produced by kneading the materials that make up the positive electrode mixture layer 16b to prepare a positive electrode mixture paste, and then applying the positive electrode mixture paste to the positive electrode substrate 16a and drying it. The positive electrode substrate 16a functions as a current collector for the positive electrode. The positive electrode substrate 16a is a thin film made of aluminum or an alloy mainly composed of aluminum.

[0066] A connection part 16c where the positive electrode base material 16a is exposed without the positive electrode mixture layer 16b formed is provided at one end in the short direction of the positive electrode plate 16. In the wound body state, the facing surfaces of the connection part 16c are pressed against each other to form the positive electrode side current collecting part 15a.

[0067] The positive electrode mixture paste, which is the material of the positive electrode mixture layer 16b, includes a positive electrode active material, a positive electrode conductive material, a positive electrode solvent, and a positive electrode binder. The positive electrode active material is a material capable of absorbing and releasing lithium ions, and examples of such materials include lithium cobalt oxide (LiCoO), lithium manganese oxide (LiMnO), and lithium nickel oxide (LiNiO). Alternatively, a material in which LiCoO, LiMnO, and LiNiO are mixed in any ratio may be used.

[0068] Examples of the positive electrode conductive material include carbon black such as acetylene black and ketjen black, and graphite. Examples of the positive electrode solvent include NMP (N-methyl-2-pyrrolidone) solution. Examples of the positive electrode binder include polyvinylidene fluoride, polytetrafluoroethylene, and carboxymethyl cellulose (CMC).

[0069] <Negative electrode> The negative electrode plate 17 includes a sheet-like negative electrode substrate 17a formed in a long shape, and a negative electrode mixture layer 17b provided on both sides of the negative electrode substrate 17a. The negative electrode plate 17 is produced by kneading materials constituting the negative electrode mixture layer 17b to prepare a negative electrode mixture paste, and then applying the negative electrode mixture paste to the negative electrode substrate 17a and drying it. The negative electrode substrate 17a functions as a current collector for the negative electrode. The negative electrode substrate 17a can be a thin film made of copper or an alloy mainly composed of copper.

[0070] A connection part 17c where the negative electrode base material 17a is exposed without the negative electrode mixture layer 17b formed is provided at one end in the short direction of the negative electrode plate 17. In the wound body state, the opposing surfaces of the connection part 17c are pressed against each other to form the negative electrode side current collecting part 15b.

[0071] The negative electrode mixture layer 17b is provided on the surface of the negative electrode substrate 17a. The material of the negative electrode mixture layer 17b, a negative electrode mixture paste, contains a negative electrode active material, a negative electrode dispersant, a negative electrode solvent, a negative electrode binder, etc. In this embodiment, water is used as the negative electrode solvent.

[0072] The negative electrode active material is a material capable of absorbing and releasing lithium ions, such as graphite, such as natural graphite or artificial graphite. In this embodiment, powdered graphite is used as the negative electrode active material. Typical graphite has hydrophilic groups, such as carboxyl groups and hydroxyl groups, as functional groups present on the particle surface. Near the functional groups on the graphite particle surface, hydrophobicity decreases, thereby reducing the adsorption of the negative electrode dispersant to the graphite particle surface. In this embodiment, graphite from which the surface functional groups have been removed by surface treatment is used as the negative electrode active material in order to increase the adsorption of the negative electrode dispersant to the graphite particle surface. Specifically, the graphite used in this embodiment is one in which the functional groups present on the graphite particle surface have been removed by heat treatment in a high-temperature environment in an inert gas atmosphere, such as argon.

[0073] The negative electrode dispersant coats the surface of the negative electrode active material and forms an interface with the negative electrode solvent, thereby enhancing the dispersibility of the negative electrode active material in the negative electrode solvent. The negative electrode dispersant is a water-soluble polymer material that has adsorptivity for graphite, which is the negative electrode active material. An example of the negative electrode dispersant is carboxymethyl cellulose (CMC). CMC has hydrophilic and hydrophobic functional groups, so it has adsorptivity for graphite, which is the negative electrode active material, and affinity for water, which is the negative electrode solvent.

[0074] The negative electrode binder enhances the binding force between particles of the negative electrode active material. The negative electrode binder is a water-soluble polymer material, such as styrene butadiene rubber (SBR). SBR is a non-polar polymer material.

[0075] <separator> The separator 18 prevents contact between the positive electrode plate 16 and the negative electrode plate 17, and also holds the non-aqueous electrolyte between the positive electrode plate 16 and the negative electrode plate 17. When the electrode assembly 15 is immersed in the non-aqueous electrolyte, the non-aqueous electrolyte permeates from the ends of the separator 18 toward the center.

[0076] The separator 18 is a nonwoven fabric made of polypropylene or the like. As the separator 18, for example, a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, or a porous polyvinyl chloride membrane, an ion-conductive polymer electrolyte membrane, or the like can be used.

[0077] <Nonaqueous electrolyte> The non-aqueous electrolyte is a composition in which a supporting salt is contained in a non-aqueous solvent. The non-aqueous solvent can be one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, etc. The supporting salt can be one or more lithium compounds (lithium salts) selected from LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc.

[0078] In this embodiment, ethylene carbonate is used as the non-aqueous solvent. Lithium bis(oxalato)borate (LiBOB) is added as a lithium salt to the non-aqueous electrolyte solution as an additive. For example, LiBOB is added to the non-aqueous electrolyte solution so that the concentration of LiBOB in the non-aqueous electrolyte solution is 0.001 to 0.1 mol / L.

[0079] <Method for producing active material for non-aqueous electrolyte secondary batteries> FIG. 8 is a flowchart showing the steps of the method for producing an active material for a lithium ion secondary battery according to this embodiment.

[0080] When the manufacturing method for the active material for a lithium ion secondary battery of this embodiment is started (start), the procedure of "pore formation (S1)" is performed. Then, the procedure of "mixing nitrogen-containing compound (S2)" is performed, followed by heating. Depending on the stage, the process progresses to "evaporating or liquefying the nitrogen-containing compound by heat treatment (S3)," "introducing the nitrogen-containing compound into the pores (S4)," and "introducing and substituting nitrogen element on the graphite pore surface (S5)." Then, the process progresses to "burning off the residue of the nitrogen-containing compound (S6)." When these procedures are completed, the active material for a lithium ion secondary battery is "completed." Each of these procedures will be described in detail below with reference to FIGS. 9 to 15.

[0081] <Preparation process> First, Fig. 9 is a schematic diagram of graphite in which pores 23 are not formed. As shown in Fig. 9, graphite to be used as carbon material 2 is prepared prior to the start. Even in a natural state, graphite has pores 23 formed in the following state to some extent. The graphite used in this embodiment has a specific surface area S = 4.3 [m 2 / g] or more, 7.6[m 2 / g] or less. The average pore diameter Dc is 13.7 [nm] or more and 20.1 [nm] or less. The total pore volume V is 0.0227 [cm] 3 / g] or more, 0.0331[cm 3 / g] or less. When the method for producing an active material for a lithium ion secondary battery is started (start), first, pores 23 are formed.

[0082] <Pore formation (S1)> FIG. 10 is a schematic diagram showing a carbon material 2 in which pores 23 are formed. As shown in FIG. 10, in the pore formation step (S1), the microwave output is set to a range of 500 [W] or more and 1200 [W] or less. The irradiation time is adjusted to 5 [min] or more and 15 [min] or less. The output [W] and time [min] are determined based on the specific surface area S [m 2 / g], average pore diameter Dp [nm], total pore volume V [cm 3 / g] is adjusted as appropriate.

[0083] Specifically, microwaves are irradiated so that the graphite after pore formation after microwave irradiation falls within the following range: specific surface area S is 7.5 [m 2 / g] or more, 9.7[m 2 / g] or less. The average pore diameter Dp is 13.4 [nm] or more and 15.8 [nm] or less. The total pore volume V is 0.0316 [cm 3 / g] or more, 0.0326[cm 3 / g] or less.

[0084] In Example 1, the specific surface area is 4.32 [m 2 / g] of graphite was irradiated with microwaves at 1200 W for 5 min to form pores on the graphite surface. <Nitrogen-containing compound mixture (S2)> 11 is a schematic diagram showing a state in which a nitrogen-containing compound 44 is mixed into a carbon material 2 having pores 23 formed therein. Next, as shown in FIG. 11, nitrogen-containing compounds 44 such as nitrogen-containing cyclic compounds such as melamine, N-methylpyrrolidone, pyridine, and pyrrole, compounds having an amino group such as amino acid, urea, and aniline, compounds having an amide bond such as formamide, acetamide, and acetanilide, and compounds having a cyano group such as acetonitrile and acrylonitrile are mixed into the carbon material 2 having pores 23 formed therein. These nitrogen-containing compounds have larger molecular diameters than ammonia and the like, and are larger than the average pore diameter Dp [nm] of the pores 23.

[0085] In Example 1, 10 wt % of melamine, which is a nitrogen-containing compound, was mixed into the carbon material 2 in which the pores 23 were formed. <Vaporizing or liquefying nitrogen-containing compounds through heat treatment (S3)> FIG. 12 is a schematic diagram showing a state in which a nitrogen-containing compound 44 is mixed with a carbon material 2 having pores 23 formed therein. In the state shown in FIG. 12, when the carbon material 2 and the nitrogen-containing compound 4 are melamine, the mixed powder is heated in an inert gas atmosphere, such as nitrogen gas (N), at a temperature of 750°C to 800°C. The heating time is 0.5 hours to 2 hours, preferably 1 hour. As a result, the melamine vaporizes or liquefies as an initial phenomenon during heating.

[0086] When using other nitrogen-containing compounds, the treatment is carried out at a temperature 50 to 100°C higher than the decomposition temperature of the nitrogen-containing compound. Specifically, the temperature may be appropriately set within the range of 200 to 1000°C depending on the type of nitrogen-containing compound. The heating time may also be selected so that the nitrogen-containing compound is sufficiently decomposed.

[0087] In Example 1, the heat treatment was carried out in a nitrogen gas atmosphere at a temperature of 800° C. for a heating time of 1 hour. <Introduction of nitrogen-containing compounds into pores (S4)> Fig. 13 is a schematic diagram showing a state in which a nitrogen-containing compound 4 is introduced into pores 23 formed in a carbon material 2. As shown in Fig. 13, melamine vaporized or liquefied in the first stage of the heat treatment is introduced into pores 23 on the graphite surface in the next stage.

[0088] <Substitution of nitrogen atoms on the graphite pore surface (S5)> FIG. 14 is a schematic diagram showing a state in which nitrogen atoms from the nitrogen-containing compound 4 introduced into the pores 23 formed in the carbon material 2 are substituted for graphite, resulting in nitrogen doping.

[0089] During the latter half of the heating process, nitrogen atoms are substituted for carbon atoms of graphite at the contact points between the graphite pore surface and melamine, completing the nitrogen doping. Here, the ratio of doped nitrogen atoms N to carbon atoms C is defined as the N / C intensity ratio. The carbon material 2 after nitrogen doping has an N / C intensity ratio of 1.6 or more and 2.7 or less at a depth of 0 to 5 nm from the surface 22, and an N / C intensity ratio of 1.6 or less at a depth of more than 5 nm to 50 nm.

[0090] <Burning of residues of nitrogen-containing compounds (S6)> 15 is a schematic diagram showing the negative electrode active material 1 in which the nitrogen-doped layer 41 is formed by burning off the residue of the nitrogen-containing compound after the nitrogen present in the pores 23 has been substituted. As shown in FIG. 15, the melamine residue is burned off at the end of the heating.

[0091] <Complete> Through the above-described procedure, nitrogen is doped into the pores 23, and the negative electrode active material 1 having the nitrogen-doped layer 41 formed thereon is completed.

[0092] <Operation of this embodiment> FIG. 16 is a graph showing the N / C intensity ratio (the ratio of doped nitrogen atoms N to carbon atoms C) versus the depth [nm] from the surface 22 of the carbon material 2. As shown in FIG. 16, the N / C intensity ratio at the surface 22 (depth 0 [nm]) of the carbon material 2 is approximately 2.8, indicating a high ratio of nitrogen atoms. On the other hand, at a depth of 5 [nm], the N / C intensity ratio drops sharply to approximately 1.6. Furthermore, at a depth of 10 [nm], it drops further to approximately 1.2, at a depth of 25 [nm], it drops further to approximately 1.0, and at a depth of 50 [nm], it drops further to 0.5. From this result, nitrogen atoms are present in large numbers at the surface 22 of the carbon material 2, but rapidly decrease in the interior. In other words, it can be seen that the nitrogen-doped layer 41 is concentrated at the surface 22 and does not penetrate into the interior.

[0093] As can be seen from the above results, in this embodiment, the nitrogen-containing compound 4 mixed with the carbon material 2 is intensively doped with nitrogen on the surface 22 of the carbon material 2 and the inner wall 23b around the opening of the pore 23. Therefore, the nitrogen-containing compound 4 can be efficiently used for nitrogen doping.

[0094] The above results also reveal that the area of ​​the carbon material interior 21 deeper than the opening 23c of the pore 23 is not doped with nitrogen. Therefore, the pore 23 is not blocked by the nitrogen-doped layer 41, and lithium ions L with small diameters can be easily absorbed. + can freely enter the range of the interior 21 of the carbon material deeper than the openings 23c of the pores 23.

[0095] On the other hand, the electrolyte 3, which has an average diameter De larger than that of the pores 23, cannot penetrate into the area of ​​the carbon material interior 21 deeper than the openings 23c of the pores 23. Therefore, no SEI film is formed in the area of ​​the carbon material interior 21 deeper than the openings 23c of the pores 23, and therefore nitrogen doping is not required.

[0096] Therefore, in the range of the interior 21 of the carbon material deeper than the opening 23c of the pore 23, lithium ions L + Therefore, the surface area of ​​the pores 23 is increased, which contributes to the effect of reducing the internal resistance.

[0097] (Effects of this embodiment) (1) The active material for a lithium ion secondary battery of this embodiment has the effect of reducing the internal resistance of a non-aqueous electrolyte secondary battery.

[0098] (2) The active material for a non-aqueous electrolyte secondary battery of this embodiment includes a carbon material 2 serving as an active material for a non-aqueous electrolyte secondary battery, having pores 23 formed on its surface 22, and a nitrogen-doped layer 41 provided on the surface 22 of the carbon material 2 and on the inner walls 23b around the openings 23c of the pores 23. Therefore, the cell resistance of a lithium-ion secondary battery can be effectively reduced by the synergistic effect of the expansion of the surface area due to the pores 23 and the suppression of side reactions due to the nitrogen doping.

[0099] (3) In particular, the nitrogen-doped layer 41 is formed on the inner wall 23b around the opening of the pore 23 in the range of the carbon material 2 that can come into contact with the electrolyte 3 of the non-aqueous electrolyte solution. This has the effect of effectively suppressing the formation of an SEI coating by the electrolyte 3, which has high resistance due to side reactions. In addition, since the nitrogen-doped layer 41 is not formed on the inner wall 23a of the inside 21 of the carbon material 2 other than the inner wall 23b around the opening of the pore 23, the negative electrode active material 1 can absorb lithium ions L + This has the effect of allowing the main reaction to occur effectively.

[0100] (4) The negative electrode active material 1 of this embodiment has an N / C intensity ratio of 1.6 to 2.7 at a depth of more than 0 nm and not more than 5 nm from the surface 22 of the carbon material 2, and an N / C intensity ratio of 1.6 or less at a depth of more than 5 nm and not more than 50 nm. Therefore, the nitrogen-doped layer 41 is configured to be concentrated on the surface 22 where side reactions are likely to occur. This has the effect of preventing the formation of unnecessary nitrogen-doped layer 41.

[0101] (5) The carbon material 2 in which the pores 23 are formed has a specific surface area of ​​7.5 [m 2 / g] or more, 9.7[m 2 / g] or less, there is an effect that the surface area that is responsible for the main reaction of the active material can be increased.

[0102] (6) The pores 23 of the carbon material 2 have an average pore diameter Dp [nm] (d50) of 13.4 [nm] or more and 15.8 [nm] or less, which has the effect of preventing the electrolyte 3, which has a large diameter, from entering the pores 23 and forming an SEI.

[0103] (7) The carbon material 2 in which the pores 23 are formed has a total pore volume V of 0.0316 cm 3 / g] or more, 0.0326[cm 3 / g] or less. Therefore, the surface area of ​​the pores 23 responsible for the main reaction is large, and side reactions are suppressed inside the pores, so that the cell resistance can be effectively suppressed.

[0104] (8) The method for producing the negative electrode active material 1 for the lithium-ion secondary battery 10 of this embodiment also includes a pore-forming step (S1) for forming pores 23 in the carbon material 2. It also includes a nitrogen-containing compound mixing step (S2) for mixing the nitrogen-containing compound 4 with the carbon material 2 in which the pores 23 have been formed. It also includes a nitrogen-doping step (S5) for vaporizing or liquefying the nitrogen-containing compound 4 by heat treatment (S3), introducing the nitrogen-containing compound 4 into the pores 23 (S4), and introducing and substituting the nitrogen element. It also includes a residue removal step (S6) for removing residues of the nitrogen-containing compound 4. This has the effect of allowing a nitrogen-doped layer 41 to be formed on the carbon material 2 whose surface area has been increased by the pores 23.

[0105] (9) The molecular diameter of the nitrogen-containing compound 4 is set to be larger than the average opening diameter Dp of the pores 23. This has the effect of allowing the nitrogen-doped layer 41 to be formed only on the surfaces 22 of the pores 23 and on the inner walls 23b around the openings 23c of the pores 23. This has the effect of preventing unnecessary nitrogen-doped layer 41 from being formed on the inner walls 23b of the interiors 21 of the carbon material 2 in the pores 23.

[0106] (10) Before the pores 23 are formed, the carbon material 2 has a specific surface area of ​​4.3 m 2 / g] or more, 7.6[m 2 / g] or less. This has the effect of making it possible to form the necessary pores 23 in the step of forming pores by microwaves (S1).

[0107] (11) Furthermore, the carbon material 2 before the formation of the pores 23 has an average pore diameter Dp [nm] of 13.7 [nm] or more and 20.1 [nm] or less. This has the effect of enabling the necessary pores 23 to be formed in the step of pore formation (S1) using microwaves.

[0108] (12) The carbon material 2 before the pores 23 are formed has a total pore volume V of 0.0227 cm 3 / g] or more, 0.0331[cm 3 / g] or less. Therefore, there is an effect that the necessary pores 23 can be formed in the step of forming pores by microwaves (S1).

[0109] (13) In the pore forming step (S1), pores are formed by irradiating microwaves. The microwaves irradiated are 500 W or more and 1200 W or less, and the irradiation time is 5 min or more and 15 min or less. This has the effect of easily forming pores 23 according to the desired conditions.

[0110] (14) Melamine, amino acid, urea, or the like is used as the nitrogen-containing compound 4. Therefore, the molecular diameter of the nitrogen-containing compound 4 is large and it cannot penetrate into the pores 23. Therefore, there is an effect that the nitrogen-doped layer 41 can be formed only on the surfaces 22 of the pores 23 and on the inner walls 23b around the openings 23c of the pores 23.

[0111] (15) The nitrogen doping step (S5) is performed in an inert gas atmosphere. In particular, nitrogen gas (N2) is used. The nitrogen doping step is performed at a temperature of 750°C to 800°C for 0.5 hours to 2 hours. This has the effect of forming a good nitrogen-doped layer 41.

[0112] (16) In the nitrogen doping step (S6), the N / C intensity ratio is set to 1.6 or more and 2.7 or less at a depth of more than 0 [nm] and not more than 5 [nm] from the surface 22 of the carbon material 2. Also, the N / C intensity ratio is set to 1.6 or less at a depth of more than 5 [nm] and not more than 50 [nm]. Therefore, the nitrogen-doped layer 41 can be formed so as to be concentrated on the surface 22 where side reactions are likely to occur, and there is an effect that unnecessary nitrogen-doped layer 41 is not formed.

[0113] (17) The specific surface area of ​​the carbon material 2 in which the pores 23 are formed is 7.5 [m 2 / g] or more, 9.7[m 2 / g] or less. Therefore, the surface area of ​​the pores 23 responsible for the main reaction is increased. As a result, side reactions are suppressed inside the pores, and the cell resistance can be effectively suppressed.

[0114] (18) The average pore diameter Dp [nm] of the carbon material 2 in which the pores 23 are formed is set to be 13.4 [nm] or more and 15.8 [nm] or less. This prevents the electrolyte 3 of the nonaqueous electrolytic solution from penetrating into the interior 21 of the carbon material 2 in the pores 23. As a result, there is an effect that the formation of an SEI is suppressed on the inner walls 23a inside the pores 23.

[0115] (19) The total pore volume V of the carbon material 2 in which the pores 23 are formed is 0.0316 [cm 3 / g] or more, 0.0326[cm 3 / g]. This allows the surface area with which the positive electrode active material 1 reacts to be increased.

[0116] (20) The active material for lithium ion secondary batteries of this embodiment exhibits its effects due to the synergistic effect of the combination of the pore formation step (S1) and the nitrogen doping step (S5). Therefore, those skilled in the art can implement the active material for lithium ion secondary batteries using conventional raw materials and conventional manufacturing processes.

[0117] (Another example) This embodiment shows an example of how the present invention is implemented, and the present invention is not limited to this embodiment.

[0118] The numerical values ​​and ranges in this embodiment are merely examples and can be optimized and implemented by those skilled in the art. The illustrated schematic diagrams are simplified or exaggerated in order to explain the principles of the invention, and the shapes, dimensions, numbers, etc. thereof do not limit the present invention.

[0119] While this embodiment illustrates an in-vehicle lithium-ion secondary battery 10, the present invention is not limited to this and can be widely applied to non-aqueous electrolyte secondary batteries. For example, the battery can be used in aircraft and ships. Alternatively, the battery can be used as a stationary battery in home or factory facilities. Furthermore, the present invention can be applied to cylindrical non-aqueous electrolyte secondary batteries, regardless of their rectangular plate shape.

[0120] The flowchart shown in FIG. 8 is an example, and steps can be added, deleted, or changed, or the order can be changed. The present invention may be implemented by those skilled in the art by adding, deleting, or modifying its components within the scope of the claims. [Explanation of symbols]

[0121] 1...Negative electrode active material 2...Carbon materials 3...Non-aqueous electrolyte 4...Nitrogen-containing compounds 10...Lithium ion secondary battery (non-aqueous electrolyte secondary battery) 11...Battery case 12...lid body 13a,13b...External terminal 14a...positive electrode side current collecting member 14b...Negative electrode side current collecting member 15...Electrode body 15a…Positive side current collector 15b...Negative electrode side current collecting part 16...Positive electrode plate 16a...Cathode base material 16b...Positive electrode mixture layer 16c...Connection 17...Negative electrode plate 17a...Negative electrode base material 17b...negative electrode mixture layer 17c connection 18...Separator 21...(carbon material) inside 22...(carbon material) surface 23...pore 23a...(pore) inner wall 23b...Inner wall (around the opening) 23c...(pore) opening 41...Nitrogen-doped layer Dc[nm]…Carbon material average particle diameter (d50) V [cm 3 / g]...total pore volume Dp [nm]...Average pore opening diameter (d50) L + …Lithium-ion Dn [nm]...Average diameter of nitrogen-containing compounds (d50) S[m 2 / g]…Specific surface area ...Molecular diameter of nitrogen-containing compounds

Claims

1. a carbon material having pores formed on its surface and serving as an active material for a non-aqueous electrolyte secondary battery; a nitrogen-doped layer provided on the surface of the carbon material and on the inner wall of the periphery of the opening of the pore; Equipped with The carbon material in which the pores are formed is The specific surface area is 7.5 [m 2 / g] or more and 9.7 [m 2 / g] or less. The active material for a non-aqueous electrolyte secondary battery is characterized by the above.

2. a carbon material having pores formed on its surface and serving as an active material for a non-aqueous electrolyte secondary battery; a nitrogen-doped layer provided on the surface of the carbon material and on the inner wall of the periphery of the opening of the pore; Equipped with The pores of the carbon material are The average pore diameter is 13.4 nm or more and 15.8 nm or less. The active material for a non-aqueous electrolyte secondary battery is characterized by the above.

3. a carbon material having pores formed on its surface and serving as an active material for a non-aqueous electrolyte secondary battery; a nitrogen-doped layer provided on the surface of the carbon material and on the inner wall of the periphery of the opening of the pore; Equipped with The carbon material in which the pores are formed is An active material for a non-aqueous electrolyte secondary battery, characterized in that the total pore volume V is 0.0316 [cm 3 / g] or more and 0.0326 [cm 3 / g] or less.

4. 4. The active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein a nitrogen-doped layer is formed on the inner wall of the pore at the periphery of the opening of the pore in a range inside the carbon material that can come into contact with an electrolyte of the non-aqueous electrolyte.

5. 4. The active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the N / C intensity ratio is 1.6 or more and 2.7 or less at a depth of more than 0 [nm] and not more than 5 [nm] from the surface of the carbon material, and the N / C intensity ratio is 1.6 or less at a depth of more than 5 [nm] and not more than 50 [nm].

6. A non-aqueous electrolyte secondary battery, characterized in that the active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3 is used as a negative electrode active material.

7. a pore formation step of forming pores in a carbon material that will be an active material for a non-aqueous electrolyte secondary battery; a nitrogen-containing compound mixing step of mixing a nitrogen-containing compound with the carbon material in which the pores have been formed; a nitrogen doping step of vaporizing or liquefying the nitrogen-containing compound by heat treatment, introducing the nitrogen-containing compound into the pores, and introducing and substituting nitrogen element onto the surface of the carbon material; a residue removal step of removing residues of the nitrogen-containing compound; Equipped with In the pore forming step, The pores are formed by gas activation or chemical activation, The method for producing an active material for a non-aqueous electrolyte secondary battery is characterized in that the formation of the pores is carried out by irradiating gas activation with microwaves, the microwaves to be irradiated are 500 [W] or more and 1200 [W] or less, and the irradiation time is 5 [min] or more and 15 [min] or less.

8. a pore formation step of forming pores in a carbon material that will be an active material for a non-aqueous electrolyte secondary battery; a nitrogen-containing compound mixing step of mixing a nitrogen-containing compound with the carbon material in which the pores have been formed; a nitrogen doping step of vaporizing or liquefying the nitrogen-containing compound by heat treatment, introducing the nitrogen-containing compound into the pores, and introducing and substituting nitrogen element onto the surface of the carbon material; a residue removal step of removing residues of the nitrogen-containing compound; Equipped with A method for producing an active material for a non-aqueous electrolyte secondary battery, wherein the specific surface area of ​​the carbon material having the pores formed therein is 7.5 [m 2 / g] or more and 9.7 [m 2 / g] or less.

9. a pore formation step of forming pores in a carbon material that will be an active material for a non-aqueous electrolyte secondary battery; a nitrogen-containing compound mixing step of mixing a nitrogen-containing compound with the carbon material in which the pores have been formed; a nitrogen doping step of vaporizing or liquefying the nitrogen-containing compound by heat treatment, introducing the nitrogen-containing compound into the pores, and introducing and substituting nitrogen element onto the surface of the carbon material; a residue removal step of removing residues of the nitrogen-containing compound; Equipped with The method for producing an active material for a non-aqueous electrolyte secondary battery, wherein the average pore diameter of the carbon material having the pores formed therein is 13.4 nm or more and 15.8 nm or less.

10. a pore formation step of forming pores in a carbon material that will be an active material for a non-aqueous electrolyte secondary battery; a nitrogen-containing compound mixing step of mixing a nitrogen-containing compound with the carbon material in which the pores have been formed; a nitrogen doping step of vaporizing or liquefying the nitrogen-containing compound by heat treatment, introducing the nitrogen-containing compound into the pores, and introducing and substituting nitrogen element onto the surface of the carbon material; a residue removal step of removing residues of the nitrogen-containing compound; Equipped with A method for producing an active material for a non-aqueous electrolyte secondary battery, wherein the total pore volume V of the carbon material having the pores formed therein is set to 0.0316 cm 3 / g or more and 0.0326 cm 3 / g or less.

11. 11. The method for producing an active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein the molecular diameter of the nitrogen-containing compound is larger than the average opening diameter of the pores.

12. The method for producing an active material for a non-aqueous electrolyte secondary battery according to any one of claims 7 to 10, wherein the nitrogen doping is performed on an inner wall of the periphery of the opening of the pore in an area inside the carbon material that can come into contact with an electrolyte of a non-aqueous electrolyte.

13. The carbon material before the pores are formed is Specific surface area 4.3 [m ２ / g] or more, 7.6[m ２ / g or less The method for producing an active material for a non-aqueous electrolyte secondary battery according to any one of claims 7 to 10,

14. The carbon material before the pores are formed is The average pore diameter is 13.7 nm or more and 20.1 nm or less. The method for producing an active material for a non-aqueous electrolyte secondary battery according to any one of claims 7 to 10,

15. The carbon material before the pores are formed is The total pore volume V is 0.0227 [cm ３ / g] or more, 0.0331[cm ３ 11. The method for producing an active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein the surface area of ​​the active material is 0.05 μm or less.

16. 11. The method for producing an active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein the nitrogen-containing compound is melamine, an amino acid, or urea.

17. 11. The method for producing an active material for a non-aqueous electrolyte secondary battery according to claim 7, further comprising a step of removing a residue of the nitrogen-containing compound.

18. The nitrogen doping step is performed in an inert gas atmosphere, 11. The method for producing an active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein the nitrogen doping step is carried out at a temperature of 200°C or more and 1000°C or less for 0.5 hours or more and 2 hours or less.

19. 11. The method for producing an active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein the nitrogen doping step sets an N / C intensity ratio of 1.6 to 2.7 at a depth of more than 0 nm and not more than 5 nm from the surface of the carbon material, and sets an N / C intensity ratio of 1.6 or less at a depth of more than 5 nm and not more than 50 nm from the surface of the carbon material.

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