Negative electrode active material layer

Abstract

To provide a negative electrode active material layer including a resistance to be improved.SOLUTION: A negative electrode active material layer of the present disclosure, contains a carbonaceous negative electrode, and an orientation degree I004 / I110 measured by an X-ray diffraction of the negative electrode active material layer is 1.00 or more and 2.00 or less. In a frequency distribution of D / G of the carbonaceous negative electrode that is a ratio to a peak strength of a G band of a peak strength of a D band obtained by Raman mapping measurement obtained by the Raman mapping measurement, a mode value is 0.5 or more and 0.8 or less, and a half value width of the peak having the mode value is 0.3 or more and 0.6 or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a negative electrode active material layer.

Background Art

[0002] As a negative electrode active material of a secondary battery, particularly a lithium ion secondary battery, a carbon material such as graphite is generally used. Among them, graphite has a structure in which hexagonal network planes of carbon atoms are regularly stacked. Charge and discharge are performed by the insertion and desorption reaction of lithium ions from the ends of the stacked network planes. In particular, in order to confirm the performance of graphite as an active material, in Raman mapping, the ratio of the values of the "G band" and the "D band" is evaluated. The "G band" indicates the peak intensity at a wavelength of 1580 cm -1 and the "D band" indicates the peak intensity at a wavelength of 1360 cm -1 .

[0003] Patent Document 1 discloses carbonaceous particles for a negative electrode material in which the mode value of G / D is 0.87 to 0.96 and the R value when the cumulative frequency from the smaller side of G / D is 50% is 0.88 to 0.92.

[0004] Patent Document 2 describes a negative electrode active material having a G / D ratio of 0.21 or more.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present disclosure provides a negative electrode active material layer having improved resistance.

Means for Solving the Problem

[0007] As a result of intensive studies, the present inventors have found that the above problems can be solved by the following means, and have completed the present disclosure. That is, the present disclosure is as follows: <Aspect 1> A negative electrode active material layer containing a carbonaceous negative electrode active material, The orientation degree I measured by X-ray diffraction of the carbonaceous negative electrode active material layer 004 / I 110 is 1.00 or more and 2.00 or less, and In the D / G frequency distribution of the carbonaceous negative electrode active material, which is the ratio of the peak intensity of the D band to the peak intensity of the G band obtained by Raman mapping measurement, the mode value is 0.50 or more and 0.80 or less, and the half-width of the peak having the mode value is 0.3 or more and 0.6 or less, Negative electrode active material layer. <Aspect 2> The negative electrode active material layer according to Aspect 1, wherein the D50 particle diameter of the carbonaceous negative electrode active material measured by the laser diffraction method is 17.0 μm or less. <Aspect 3> The negative electrode active material layer according to Aspect 1 or 2, wherein the carbonaceous negative electrode active material is graphite. <Aspect 4> The negative electrode active material layer according to any one of Aspects 1 to 3, having a density of 1.2 g / cc or more and 1.6 g / cc or less. <Aspect 5> A secondary battery having at least the negative electrode active material layer, a separator, and a positive electrode active material layer according to any one of Aspects 1 to 4.

Advantages of the Invention

[0008] According to the present disclosure, a negative electrode active material layer having improved resistance can be provided.

Brief Description of the Drawings

[0009]

Figure 1

Modes for Carrying Out the Invention

[0010] 《Negative electrode active material layer》 The negative electrode active material layer of the present disclosure contains a carbonaceous negative electrode active material, The orientation degree I measured by X-ray diffraction of the negative electrode active material layer 004 / I 110 is 1.00 or more and 2.00 or less, and In the frequency distribution of D / G of the carbonaceous negative electrode active material, which is the ratio of the peak intensity of the D band to the peak intensity of the G band obtained by Raman mapping measurement, the mode value is 0.5 or more and 0.8 or less, and the half-width of the peak having the mode value is 0.3 or more and 0.6 or less.

[0011] According to the negative electrode active material layer of the present disclosure, the negative electrode active material layer has an appropriate orientation degree, and the reaction surface of the carbonaceous negative electrode active material optimally matches the diffusion direction of lithium ions. In addition, the carbonaceous negative electrode active material has a frequency distribution (mode value and half-width) of an appropriate D / G value, thereby providing an appropriate lithium ion insertion site. As a result of these, it is considered that the resistance is reduced when used in a lithium ion battery.

[0012] The orientation degree I measured by X-ray diffraction (XRD) of the negative electrode active material layer 004 / I 110 may be 1.00 or more, 1.10 or more, or 1.20 or more, and may also be 2.00 or less, 1.90 or less, 1.80 or less, 1.70 or less, 1.60 or less, 1.50 or less, or 1.40 or less. The larger this value is, the higher the orientation degree is shown. By increasing the density of the negative electrode active material layer, the above orientation degree can be increased. Here, in the present disclosure, the orientation degree is the ratio of the peak intensity I of the (004) plane of the crystal constituting the negative electrode active material layer measured by X-ray diffraction (XRD) 004 to the peak intensity I of the (110) plane 110 and means the ratio.

[0013] From the perspective of obtaining the above-mentioned degree of orientation, the density of the negative electrode active material layer is preferably 1.1 g / cc or more, 1.2 g / cc or more, or 1.3 g / cc or more, and 1.7 g / cc or less, 1.6 g / cc or less, or 1.5 g / cc or less.

[0014] The negative electrode active material layer may contain any other components. Examples of other components include a conductive assistant, a binder, and the like.

[0015] Hereinafter, each component of the present disclosure will be described.

[0016] 〈Carbonaceous negative electrode active material〉 In the D / G frequency distribution of the carbonaceous negative electrode active material of the present disclosure, which is the ratio of the peak intensity of the D band to the peak intensity of the G band obtained by Raman mapping measurement, the mode value is 0.5 or more and 0.8 or less, and the half-width at half maximum of the peak having the mode value is 0.3 or more and 0.6 or less.

[0017] Here, in this specification, the "D band" indicates the peak intensity at a wavelength of 1360 cm -1 and the "G band" indicates the peak intensity at a wavelength of 1580 cm -1 .

[0018] In addition, the Raman mapping measurement can be performed under the following conditions. Magnification of the objective lens: 50 times Exposure time: 2 seconds Number of integrations: 4 times Sampling range: 100 μm × 100 μm Measurement interval: 2 μm

[0019] The above-mentioned most frequent value of D / G may be 0.50 or more, 0.55 or more, 0.60 or more, 0.65 or more, or 0.70 or more, and may also be 0.80 or less, or 0.75 or less. When the crystallinity of the carbonaceous negative electrode active material is increased, the most frequent value of D / G decreases. By performing a pulverization treatment on the carbonaceous negative electrode active material, that is, reducing the particle size, or by coating the carbonaceous negative electrode active material, the crystallinity of the carbonaceous negative electrode active material can be increased, thereby reducing the most frequent value of D / G.

[0020] When this most frequent value is converted to G / D, it is 2.00 or less, 1.82 or less, 1.67 or less, 1.54 or less, or 1.43 or less, and corresponds to 1.25 or more, or 1.33 or more.

[0021] The above-mentioned half-value width may be 0.30 or more, 0.35 or more, 0.40 or more, or 0.45 or more, and may also be 0.60 or less, 0.55 or less, or 0.50 or less.

[0022] In addition, in the Raman mapping of the carbonaceous negative electrode active material of the present disclosure, the region A where the value of D / G is 0.5 or more and 0.8 or less can be uniformly distributed. When there is a region B where the value of D / G is outside this range, the positional relationship between region A and region B can be a positional relationship such as an island-in-sea structure with region A as the sea and region B as the island.

[0023] As the carbonaceous negative electrode active material having the above-mentioned frequency distribution characteristics, various substances whose potential for occluding and releasing ions (charge-discharge potential) is lower than that of the above-mentioned positive electrode active material can be used. For example, carbon-based active materials such as graphite, graphite, and hard carbon can be used. The carbonaceous negative electrode active material may be used alone as only one type, or two or more types may be combined and used.

[0024] In particular, when the carbonaceous negative electrode active material is graphite, the D50 particle size of the graphite may be 20.0 μm or less, 18.0 μm or less, 17.0 μm or less, 16.5 μm or less, 16.0 μm or less, or 15.7 μm or less, and may also be 5.0 μm or more, 6.0 μm or more, 7.0 μm or more, 8.0 μm or more, 9.0 μm or more, 10.0 μm or more, 11.0 μm or more, 12.0 μm or more, 13.0 μm or more, or 14.0 μm or more. Here, in the present disclosure, the D50 particle size means the value of the median diameter (D50) calculated on a volume basis by the laser diffraction method.

[0025] 〈Binder〉 As the binder optionally contained in the negative electrode active material layer, those known as binders used in secondary batteries may be used. For example, styrene-butadiene rubber (SBR)-based binders, carboxymethyl cellulose (CMC)-based binders, acrylonitrile-butadiene rubber (ABR)-based binders, butadiene rubber (BR)-based binders, polyvinylidene fluoride (PVDF)-based binders, polytetrafluoroethylene (PTFE)-based binders, etc. may be used. Only one type of binder may be used alone, or a combination of two or more types may be used. The amount of the binder contained in the negative electrode active material layer is not particularly limited.

[0026] 〈Conductive aid〉 As the conductive aid optionally contained in the negative electrode active material layer, those known as conductive aids used in secondary batteries may be used. Specifically, carbon materials such as ketjen black (KB), vapor-grown carbon fiber (VGCF), acetylene black (AB), carbon nanotube (CNT), carbon nanofiber (CNF), carbon black, coke, graphite, etc. may be used. Alternatively, a metal material capable of withstanding the environment during battery use may also be used. As the conductive aid, only one type may be used alone, or a combination of two or more types may be used. The shape of the conductive aid may be various shapes such as powdery or fibrous. The amount of the conductive aid contained in the negative electrode active material layer is not particularly limited.

[0027] "Secondary Battery" The secondary battery of the present disclosure has at least the above-mentioned negative electrode active material layer, separator, and positive electrode active material layer.

[0028] Figure 1 schematically shows the configuration of a secondary battery 100 according to the first embodiment of the present disclosure. As shown in Figure 1, the secondary battery 100 may include a positive electrode 10, a separator 20, and a negative electrode 30. Also, the positive electrode 10 may include a positive electrode active material layer 11 and a positive electrode current collector layer 12, and the negative electrode 30 may include a negative electrode active material layer 31 and a negative electrode current collector layer 32. In this case, the positive electrode active material layer 11 may contain the above-mentioned positive electrode active material. Further, although not shown, the electrolyte may be contained in the positive electrode active material layer 11 and the negative electrode active material layer 31, for example, in the form of an electrolytic solution.

[0029] 〈Negative Electrode Current Collector Layer〉 The negative electrode current collector layer may be composed of a known metal or the like that can be used as the negative electrode current collector of the secondary battery. Such a metal may be, for example, a metal material containing at least one element selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Pb, Co, Cr, Zn, Ge, In, Sn, Zr. The form of the negative electrode current collector layer is not particularly limited and may be various forms such as foil-like, mesh-like, porous-like, etc. The negative electrode current collector layer may be formed by plating or vapor depositing the above-mentioned metal on the surface of a substrate made of an arbitrary material. Also, the surface of the negative electrode current collector layer may be coated with a carbon material or the like.

[0030] 〈Separator〉 As the separator, those known as separators used in secondary batteries may be used. For example, the separator may be made of resins such as polyethylene (PE), polypropylene (PP), polyester, and polyamide. The separator may have a single-layer structure or a multi-layer structure. As the multi-layer structure separator, for example, a multi-layer structure separator composed of the above resins, such as a two-layer structure separator of PE / PP, or a three-layer structure separator of PP / PE / PP or PE / PP / PE, etc. can be used. The separator may be made of non-woven fabrics such as cellulose non-woven fabric, resin non-woven fabric, and glass fiber non-woven fabric. The thickness of the separator is not particularly limited, and for example, it may be 5 μm or more and 1 mm or less.

[0031] 〈Positive electrode active material layer〉 The positive electrode active material layer contains a positive electrode active material. Further, the positive electrode active material layer may contain optional other components. Examples of other components include a conductive assistant and a binder.

[0032] (Positive electrode active material) As the positive electrode active material, any positive electrode active material can be used according to the form of the secondary battery, and it is not particularly limited. For example, when the secondary battery is a lithium ion secondary battery, as the positive electrode active material, for example, a lithium-containing oxide can be used.

[0033] The lithium-containing oxide as the positive electrode active material is not particularly limited, and for example, it may contain at least Li, at least one transition metal element selected from Co, Ni, and Mn, and O. As such a lithium-containing oxide, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganate (LiMn2O4), or nickel-cobalt-manganese-based oxides (NCM) in which some of these elements are substituted with other elements can be used. NCM generally contains Li a Mn x Ni y Co z O 2±δIt is represented by the general formula (0 < a ≤ 1.5, 0 ≤ x ≤ 1.5, 0 ≤ y ≤ 1.5, 0 ≤ z ≤ 1.5, 0 < δ(=x + y + z) < 1.5). The lithium-containing oxide as the positive electrode active material may have, for example, an O2-type structure, an O3-type structure, or a crystal structure other than these. As the positive electrode active material, only one kind may be used alone, or two or more kinds may be used in combination.

[0034] 〈Positive Electrode Current Collector Layer〉 The positive electrode current collector layer may be composed of a known metal or the like that can be used as the positive electrode current collector of the secondary battery. Such a metal may be a metal material containing at least one element selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Pb, Co, Cr, Zn, Ge, In, Sn, and Zr. The form of the positive electrode current collector layer is not particularly limited, and may be various forms such as foil, mesh, and porous. The negative electrode current collector layer may be obtained by plating or vapor-depositing the above metal on the surface of a substrate composed of an arbitrary material.

[0035] 〈Electrolyte〉 The electrolyte contains a solvent and an electrolyte. The electrolyte may contain an alkali metal ion, for example, a lithium ion, as a carrier ion.

[0036] (Solvent) As the solvent, water and organic solvents can be used.

[0037] As the organic solvent, for example, carbonate solvents such as ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) can be used. These organic solvents may be used alone or in combination.

[0038] (Electrolyte) The electrolyte is selected according to the form of the secondary battery. For example, when the secondary battery is a lithium-ion secondary battery, it may be a lithium salt, for example. As the lithium salt, LiPF6 or the like can be used, for example.

Examples

[0039] The present disclosure will be specifically described by way of examples and comparative examples, but the present disclosure is not limited thereto.

[0040] 《Fabrication of secondary battery》 〈Example 1〉 92 parts by mass of LiNiCoMnO2 as a positive electrode active material, 5 parts by mass of acetylene black as a conductive assistant, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a slurry for a positive electrode active material layer.

[0041] Next, the obtained slurry for the positive electrode active material layer was applied to an Al foil having a thickness of 15 μm as a positive electrode current collector layer, and this was pressed to a predetermined thickness to obtain a positive electrode.

[0042] 98 parts by mass of graphite (carbonaceous negative electrode active material C, D50 particle diameter 16.5 μm) as a carbonaceous negative electrode active material, 1 part by mass of carboxymethyl cellulose and 1 part by mass of styrene-butadiene rubber as a binder were mixed to prepare a slurry for a negative electrode active material layer.

[0043] Next, the obtained slurry for the negative electrode active material layer was applied to a Cu foil having a thickness of 10 μm as a negative electrode current collector layer, and the applied slurry for the negative electrode active material layer was pressed so that the density of the negative electrode active material layer became 1.4 g / cc to obtain a negative electrode.

[0044] The orientation degree I 004 / I 110 of the obtained negative electrode active material layer was measured by X-ray diffraction.

[0045] The obtained positive electrode and negative electrode were wound through a polypropylene / polyethylene / polypropylene three-layer sheet having a thickness of 24 μm as a separator to prepare an electrode group.

[0046] Current collector plates with lids were welded to both ends of the electrode group, inserted into the case, and the lid plate and the case were welded. Next, a predetermined amount of electrolyte was injected through the injection hole, a sealing screw was tightened on the injection hole, and after injection, it was left for an appropriate time to be impregnated with the electrolyte. After charging, aging was carried out at 60 °C to obtain the secondary battery of Example 1. As the solvent of the electrolyte, 3 parts by mass of ethylene carbonate, 3 parts by mass of dimethyl carbonate, and 4 parts by mass of ethyl methyl carbonate were used. As the electrolyte, LiPF6 was used at a concentration of 1 mol / L.

[0047] In addition, Raman mapping of the carbonaceous negative electrode active material used was measured under the following conditions, and thereby, the mode value of D / G and the half-width of the peak having the mode value were obtained. Magnification of the objective lens: 50 times Exposure time: 2 seconds Number of integrations: 4 times Sampling range: 100 μm × 100 μm Measurement interval: 2 μm

[0048] 〈Examples 2 to 6 and Comparative Examples 1 to 7〉 Secondary batteries of Examples 2 to 6 and Comparative Examples 1 to 7 were produced in the same manner as in Example 1, except that carbonaceous negative electrode active materials of the types shown in Table 1 were used as the carbonaceous negative electrode active material and the density of the negative electrode active material layer was adjusted as shown in Table 1.

[0049] The details of the carbonaceous negative electrode active materials shown in Table 1 are as follows. Carbonaceous negative electrode active material A: Graphite with a D50 particle size of 15.5 μm Carbonaceous negative electrode active material B: Graphite with a D50 particle size of 15.8 μm Carbonaceous negative electrode active material D: Graphite with a D50 particle size of 14.7 μm Carbonaceous negative electrode active material E: Graphite with a D50 particle size of 15.5 μm Carbonaceous negative electrode active material F: Graphite with a D50 particle size of 15.6 μm Carbonaceous negative electrode active material G: Graphite with a D50 particle size of 16.9 μm Carbonaceous negative electrode active material H: Graphite with a D50 particle size of 16.7 μm Carbonaceous negative electrode active material I: Graphite with a D50 particle diameter of 15.8 μm

[0050] "Measurement of Resistance" In an atmosphere controlled at -10°C, from a state of SOC 60%, it was energized at 2C for 10 minutes. The resistance was measured from the difference between the voltage after charging and the voltage before charging and the current value.

[0051] The configurations and evaluation results of the examples and comparative examples are shown in Table 1.

[0052]

Table 1

[0053] From Table 1, it can be understood that in the frequency distribution of D / G of the carbonaceous negative electrode active material, where the orientation degree I 004 / I 110 is 1.00 or more and 2.00 or less, and is the ratio of the peak intensity of the D band to the peak intensity of the G band obtained by Raman mapping measurement, the mode value is 0.50 or more and 0.80 or less, and the half-width of the peak having the mode value is 0.3 or more and 0.6 or less, a secondary battery having a negative electrode active material layer of the example can achieve a low resistance.

[0054] Also, although not shown in the figure, in the Raman mapping of the carbonaceous negative electrode active material of Example 3, the positional relationship between region A where the D / G value was uniformly distributed in the range of 0.5 or more and 0.8 or less and region B where the D / G value was outside this range was a positional relationship like a sea-island structure with region A as the sea and region B as the island.

Explanation of Signs

[0055] 10 Positive electrode 11 Positive electrode active material layer 12 Positive electrode current collector 20 Separator 30 Negative electrode 31 Negative electrode active material layer 32 Negative electrode current collector 100 Secondary battery

Claims

1. A negative electrode active material layer containing a carbonaceous negative electrode active material, The orientation degree I measured by X-ray diffraction of the carbonaceous negative electrode active material layer ００４ / I １１０ is 1.00 or more and 2.00 or less, and In the D / G frequency distribution of the carbonaceous negative electrode active material, which is the ratio of the peak intensity of the D band to the peak intensity of the G band obtained by Raman mapping measurement, the mode value is 0.50 or more and 0.80 or less, and the half-width of the peak having the mode value is 0.3 or more and 0.6 or less. Negative electrode active material layer.

2. The negative electrode active material layer according to claim 1, wherein the D50 particle size of the carbonaceous negative electrode active material measured by the laser diffraction method is 17.0 μm or less.

3. The negative electrode active material layer according to claim 1 or 2, wherein the carbonaceous negative electrode active material is graphite.

4. The negative electrode active material layer according to claim 1 or 2, having a density of 1.2 g / cc or more and 1.6 g / cc or less.

5. A secondary battery comprising at least the negative electrode active material layer according to claim 1 or 2, a separator, and a positive electrode active material layer.

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