Negative electrode body and method for manufacturing the same

Abstract

The objective of this invention is to suppress electrode expansion in a negative electrode material layer comprising a silicon-based material. The negative electrode body comprises: a current collector; and a negative electrode material layer disposed on the current collector, the negative electrode material layer having: first active material particles; second active material particles dispersed between the first active material particles and composed of a silicon-based material; and a coating layer covering the surface of the second active material particles and composed of carbon nanotubes. The first active material particles are composed of a different type of carbon material than the carbon nanotubes, and the coating layer has a porosity of 50% or more.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a negative electrode body of a battery (typically a non-aqueous secondary battery) and a method for manufacturing the same. Background Technology

[0002] Patent Document 1 describes a negative electrode body. The negative electrode body includes a negative electrode material layer disposed on a current collector. The negative electrode material layer comprises a negative electrode active material and a layer composed of carbon coating the surface of the negative electrode active material. The negative electrode active material is silicon alloy particles.

[0003] Patent Document 1: Japanese Patent Application Publication No. 10-321226 Summary of the Invention

[0004] Silicon-based materials (including silicon monomers) have higher capacity than carbon materials as negative electrode active materials in batteries. Therefore, silicon-based materials have attracted attention as negative electrode active materials, for example, in the field of lithium-ion batteries. However, silicon-based materials exhibit relatively large volume changes during charge and discharge. Therefore, electrode expansion during charging is considered a problem when silicon-based materials are included in the negative electrode material layer. This specification provides a novel technique for suppressing electrode expansion in a negative electrode material layer containing silicon-based materials.

[0005] The technology disclosed in this specification is embodied in a negative electrode body. This negative electrode body comprises: a current collector; and a negative electrode material layer disposed on the current collector, the negative electrode material layer having: first active material particles; second active material particles dispersed between the first active material particles and composed of a silicon-based material; and a coating layer covering the surface of the second active material particles and composed of carbon nanotubes. The first active material particles are composed of a different type of carbon material than the carbon nanotubes, and the coating layer has a porosity of 50% or more.

[0006] In the aforementioned negative electrode body, a second active material particle, composed of a silicon-based material, is dispersed between first active material particles composed of carbon material in the negative electrode material layer. Furthermore, a coating layer composed of carbon nanotubes is provided on the surface of the second active material particles. The porosity of the carbon nanotube coating layer is 50% or more, and it possesses flexibility capable of contracting with external force. According to this structure, a flexible coating layer is sandwiched between the first and second active material particles. Therefore, even if the second active material particles expand during charging, the expansion is absorbed by the contraction of the coating layer. This suppresses electrode expansion caused by the expansion of the second active material particles.

[0007] The technology disclosed in this specification is also embodied in the manufacturing method of the negative electrode body. The aforementioned negative electrode body is not particularly limited and can be manufactured by the following method. This manufacturing method includes: a step of producing a granulated body by forming a coating layer made of carbon nanotubes on the surface of a second active material particle made of a silicon-based material; a step of mixing the granulated body, a first active material particle made of a carbon material of a different type than the carbon nanotubes, a binder, and water to produce a negative electrode material slurry; a step of coating the negative electrode material slurry onto the surface of a current collector; and a step of drying the negative electrode material slurry coated on the surface of the current collector. The coating layer has a porosity of 50% or more. According to this structure, a negative electrode body with a flexible coating layer disposed in the gap between the first and second active material particles can be manufactured. In this structure, even if the second active material particle expands during charging, the expansion of the second active material is absorbed by the contraction of the coating layer. Therefore, the expansion of the electrode caused by the expansion of the second active material particle can be suppressed.

[0008] In the above-described negative electrode body and / or manufacturing method, the thickness of the coating layer can be 0.5 μm or more and 5 μm or less. Preferably, the thickness of the coating layer can be 1 μm or more and 3 μm or less. This structure helps to suppress electrode expansion caused by the expansion of the second active material particles.

[0009] In addition to or instead of the above, the carbon nanotubes constituting the coating layer may be multilayer carbon nanotubes. Compared with single-layer carbon nanotubes, using multilayer carbon nanotubes can disperse the carbon nanotubes to a high concentration, which is beneficial for the formation of the coating layer.

[0010] In addition to or instead of the above, the silicon-based material may include at least one selected from the group consisting of silicon, silicon carbide, silicon monoxide, and silicon alloys. Attached Figure Description

[0011] Figure 1 This is a cross-sectional view of the negative electrode.

[0012] Figure 2 This is a diagram used to illustrate the manufacturing method of the negative electrode.

[0013] Figure 3 This is a diagram used to illustrate the manufacturing method of the negative electrode.

[0014] Figure 4 This is a diagram used to illustrate the manufacturing method of the negative electrode.

[0015] Figure 5 This is a diagram used to illustrate the manufacturing method of the negative electrode.

[0016] Figure 6It is a flowchart illustrating a series of steps in the manufacturing process of the negative electrode. Detailed Implementation

[0017] (Structure of the negative electrode)

[0018] Referring to the accompanying drawings, a negative electrode body 10 according to one embodiment will be described. The negative electrode body 10 can be used as the negative electrode of a secondary battery such as a lithium-ion battery. In particular, the negative electrode body 10 is used in a non-aqueous secondary battery using a non-aqueous electrolyte. Figure 1 As shown, the negative electrode body 10 includes a current collector 12 and a negative electrode material layer 14. The negative electrode material layer 14 is disposed on the surface 12a of the current collector 12. In addition, the negative electrode material layer 14 can be disposed not only on the surface 12a of the current collector 12, but also on the back side.

[0019] The current collector 12 is a conductive sheet, such as copper foil or other metal foil. In this case, there are no particular limitations, and at least surface 12a of the current collector 12 can be made of copper. The thickness of the current collector 12 can be between about 5 μm and about 50 μm. The current collector 12 can be made of any conductive material, or it can be made of metals other than copper.

[0020] Figure 1 A cross-sectional view of the negative electrode body 10 is shown. Figure 1 The lower part) and a diagram schematically showing the internal structure of the negative electrode material layer 14 (the lower part) and (the lower part) Figure 1 (The upper part). For example, Figure 1 As shown, the negative electrode material layer 14 includes a first active material particle 16, a second active material particle 18, a coating layer 24, a binder 20, and a conductive additive 22.

[0021] The first active material particle 16 is the main component of the active material in the negative electrode material layer 14. The first active material particle 16 is composed of carbon material. Examples of carbon materials include graphite, hard carbon, and soft carbon. Typically, the first active material particle 16 can be graphite. The particle size of the first active material particle 16 can be about 5 μm or more and about 50 μm or less. Here, the term "particle size" as used in this specification refers to the average particle size, which is the particle size (D50) of the cumulative 50% of the particle size distribution on a volume basis as determined by laser diffraction / scattering.

[0022] The second active material particle 18, together with the first active material particle 16, serves as the active material of the negative electrode material layer 14. The content of the second active material particle 18 in the negative electrode material layer 14 is much less than the content of the first active material particle 16, and the second active material particle 18 is dispersed among the first active material particles 16. That is, in the negative electrode material layer 14, the second active material particle 18 is configured to be surrounded by the first active material particles 16. The second active material particle 18 is composed of a silicon-based material containing silicon. Examples of silicon-based materials include silicon oxides such as silicon (Si), silicon carbide (SiC), and silicon monoxide (SiO), as well as silicon alloys (alloys formed from silicon and other metals such as aluminum (Al), iron (Fe), and manganese (Mn). Typically, the second active material particle 18 can be silicon carbide. The silicon-based material can be composed of a single material or multiple materials. The particle size of the second active material particle 18 can be approximately 5 μm or more and approximately 50 μm or less.

[0023] The coating layer 24 coats the surface of the second active material particle 18. The coating layer 24 is composed of carbon nanotubes. Examples of carbon nanotubes constituting the coating layer 24 include multilayer carbon nanotubes and single-layer carbon nanotubes. Typically, the carbon nanotubes constituting the coating layer 24 can be multilayer carbon nanotubes. Compared with single-layer carbon nanotubes, using multilayer carbon nanotubes allows for the dispersion of carbon nanotubes at a high concentration, which is beneficial for the formation of the coating layer 24.

[0024] Adhesive 20 is present between the active material particles 16 and 18, and bonds the active material particles 16 and 18 together. Examples of adhesive 20 include polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyacrylonitrile (PAN). Typically, adhesive 20 can be polyacrylic acid. In addition, adhesive 20 can be composed of a single material or multiple materials.

[0025] The conductive additive 22 is dispersed in the negative electrode material layer 14 between the active material particles 16 and 18. Examples of conductive additives 22 include carbon nanotubes, carbon black (e.g., acetylene black, furnace black, Ketjen black, etc.), coke, graphite, and other carbon materials. Typically, the conductive additive 22 can be a single layer of carbon nanotubes. The conductive additive 22 can be composed of a single material or multiple materials. However, in a variation, the negative electrode material layer 14 may not contain the conductive additive 22.

[0026] (Manufacturing method of negative electrode)

[0027] refer to Figure 2-6 An example of a method for manufacturing the negative electrode body 10 will be described. The negative electrode body 10 can be manufactured according to... Figure 6 The process shown is used for manufacturing.

[0028] In step S2, the process of mixing the second active material particles 18 and carbon nanotubes 26 to produce granules 30 is carried out. Specifically, as... Figure 2 As shown, granules 30 are produced by forming a coating layer 24 composed of carbon nanotubes 26 on the surface of the second active material particles 18. Although this is just one example, a flow-layer granulation dryer 50 can be used in the production of granules 30 (hereinafter, the granulation method using this flow-layer granulation dryer will also be referred to as the "flow-layer method"). In this case, a dispersion containing carbon nanotubes 26 is sprayed onto the second active material particles 18 in the flow layer 54 using a spray device 52 and then dried, thereby producing granules 30. However, the production of granules 30 is not limited to the flow-layer granulation dryer 50, and other types of devices that can be used for particle coating can also be used. For example, in the production of granules 30, a mixer that performs stirring and drying under reduced pressure can be used (hereinafter, the granulation method using this mixer will also be referred to as the "reduced pressure stirring and drying method"). In this case, a slurry can be prepared from the second active material particles 18 and the carbon nanotube dispersion, and granules 30 can be produced by stirring and drying based on reduced pressure heating.

[0029] The porosity of the coating layer 24 is approximately 50% or more and approximately 80% or less. However, the porosity of the coating layer 24 only needs to be approximately 50% or more; for example, it can be less than 85% or less, or less than 90%. For example, the porosity of the coating layer 24 is adjusted by the amount of carbon nanotubes 26 applied in step S2. The porosity of the coating layer 24 is calculated from the thickness of the coating layer 24, the surface area of ​​the second active material particle 18, the mass of the added carbon nanotubes 26, and the true density of the carbon nanotubes 26. The surface area of ​​the second active material particle 18 can be the product of the mass of the added second active material particle 18 and the specific surface area of ​​the second active material particle 18. The thickness of the coating layer 24 is calculated from the particle size (D50) of the second active material particle 18 and the particle size (D50) of the granule 30. The thickness of the coating layer 24 can be the difference between the particle size (D50) of the second active material particle 18 and the particle size (D50) of the granulated body 30, divided by 2. In this embodiment, the particle size (D50) of the second active material particle 18 and the particle size (D50) of the granulated body 30 can be determined by wet laser diffraction / scattering in (N-methyl-2-pyrrolidone) NMP solvent.

[0030] In step S4, the process of mixing the granules 30 prepared in step S2, the first active material particles 16, the binder 20, and water to prepare the negative electrode material slurry 40 is carried out. Specifically, as follows... Figure 3As shown, firstly, for example, an aqueous solution of granules 30, first active material particles 16, binder 20, and water are mixed using a mixer 60. After further adding water and mixing the obtained mixture, a negative electrode material slurry 40 is prepared by further mixing a dispersion containing conductive additive 22. At this time, as... Figure 3 As shown, in the negative electrode material slurry 40, the granules 30 are dispersed among the first active material particles 16.

[0031] In step S6, as Figure 4 As shown, for example, the process of applying the negative electrode material slurry 40 prepared in step S4 onto the current collector 12 using an applicator 70 is carried out.

[0032] In step S8, a process is performed, for example, to dry the negative electrode material slurry 40 coated on the current collector 12 in step S6 in a drying oven 80. This produces a negative electrode material layer 14 with a coating layer 24 sandwiched between the first active material particles 16 and the second active material particles 18.

[0033] Through the above processes, a negative electrode body 10 is manufactured. In this negative electrode body 10, second active material particles 18, which are composed of silicon-based materials, are dispersed between first active material particles 16, which are composed of carbon materials, in the negative electrode material layer 14. Furthermore, a coating layer 24 composed of carbon nanotubes 26 is provided on the surface of the second active material particles 18. The porosity of the coating layer 24 is 50% or more, and it has the flexibility to contract relative to external forces. According to this structure, the flexible coating layer 24 is sandwiched between the first active material particles 16 and the second active material particles 18. Therefore, even if the second active material particles 18 expand during charging, the expansion of the second active material particles 18 will be absorbed by the contraction of the coating layer 24. As a result, the expansion of the electrode (i.e., the negative electrode body 10) caused by the expansion of the second active material particles 18 can be suppressed.

[0034] Although this is just one example, the thickness of the coating layer 24 is approximately 0.5 μm or more and approximately 5 μm or less. Preferably, the thickness of the coating layer 24 can be approximately 1.0 μm or more and approximately 3.0 μm or less. If the coating layer 24 is within this thickness range, it is beneficial to suppress electrode expansion caused by the expansion of the second active material particles 18 during charging. However, in a modified example, the thickness of the coating layer 24 can be 0.3 μm or more, or the thickness of the coating layer 24 can be 8 μm or less.

[0035] Next, with reference to Table 1, embodiments of the present invention will be described. However, the following description does not limit the structure involved in the present invention. First, negative electrode bodies 10 of Examples 1 to 9 and negative electrode bodies of comparative examples were fabricated.

[0036] (Negative electrode body of Example 1)

[0037] The negative electrode 10 of Example 1 was manufactured according to the aforementioned manufacturing method. Graphite was used in the first active material particle 16. Silicon carbide was used in the second active material particle 18. Multilayer carbon nanotubes (MWCNTs) were used in the carbon nanotubes (hereinafter referred to as CNTs) 26, and a 3% by mass aqueous dispersion of MWCNTs was used as the CNT dispersion. Polyacrylic acid (PAA) was used in the binder 20, and an aqueous PAA solution was used as the binder solution. Single-layer carbon nanotubes (SWCNTs) were used in the conductive additive 22, and a 0.4% by mass aqueous dispersion of SWCNTs was used as the conductive additive dispersion. The first active material particle 16 and the second active material particle 18 were combined in a mass ratio of 80 / 20.

[0038] In the process of making granules 30 ( Figure 6 In step S2), the second active material particles 18 and the CNT dispersion were mixed using a fluidized bed granulation dryer (i.e., by fluidized bed method). This produced granules 30. In this embodiment, the coating layer 24 in the granules 30 has a thickness of 0.3 μm and a porosity of 76%.

[0039] In the process of making negative electrode material slurry 40 ( Figure 6 In step S4), firstly, the first active material particles 16, binder solution, and water are added to the prepared granules 30, and then mixed using a mixer. After further adding water and mixing the resulting mixture, a conductive additive dispersion is added and mixed. Thus, a negative electrode material slurry 40 is prepared.

[0040] In the process of coating negative electrode material slurry 40 ( Figure 6 In step S6), the negative electrode material slurry 40 is applied to the current collector 12 using an applicator. The current collector 12 uses copper foil (thickness: 8 μm).

[0041] In the process of drying the negative electrode material slurry 40 ( Figure 6In step S8), the negative electrode material slurry 40 coated on the current collector 12 is dried using a drying oven at 100°C. This results in a flexible coating layer 24 sandwiched between the first active material particles 16 and the second active material particles 18 within the negative electrode material layer 14. In the negative electrode material layer 14, the mass ratio of negative electrode active material / conductive additive 22 / dispersant / binder is 97.75 / 0.10 / 0.15 / 2.00. Furthermore, the mass of the dispersant refers to the mass of the dispersant contained in the SWCNT dispersion of the conductive additive 22. The areal density of the current collector 12 on the negative electrode material layer 14 is 7.3 mg / cm³. 2 Finally, the negative electrode material layer 14 was compressed using a roller press, and its density was adjusted to 1.0 g / cm³. 3 .

[0042] (Negative electrode bodies of Examples 2-9)

[0043] In the process of producing the granules 30 of Examples 2 to 6, coating layers 24 with thicknesses of 0.5 μm, 1.0 μm, 3.3 μm, 5.1 μm, and 7.2 μm were formed instead of the 0.3 μm coating layer 24 of Example 1. In the process of producing the granules 30 of Examples 7 to 9, a reduced pressure stirring drying method was used instead of the flow layer granulation drying method of Examples 1 to 6. Furthermore, in the process of producing the granules 30 of Examples 7 to 9, coating layers 24 with porosities of 60%, 51%, and 38% were formed instead of the 72-78% porosity coating layers 24 of Examples 1 to 6. Regarding other processes, the negative electrode body 10 was produced by the same manufacturing method as in Example 1.

[0044] (The negative electrode of the comparative example)

[0045] In the comparative example, the steps for producing the granulated body 30 and the steps for producing the negative electrode material slurry 40 were changed compared to Example 1. Specifically, firstly, the first active material particles 16 and the second active material particles 18, the binder solution, and water were mixed using a mixer. Then, after further adding the binder solution to the obtained mixture, a conductive additive dispersion was mixed, thereby producing the negative electrode material slurry. That is, in the comparative example, the step of producing the granulated body 30 was omitted to produce the negative electrode material slurry, and the negative electrode body of the comparative example did not have the coating layer 24. The other steps were the same as the manufacturing method of Example 1.

[0046] (Positive electrode)

[0047] The positive electrode used in Examples 1-9 and the Comparative Examples was a common electrode. The positive electrode active material was lithium nickel cobalt manganese oxide (NCM, manufactured by Sumitomo Metal Mining Co., Ltd.). The conductive material was acetylene black (manufactured by Denka Company Limited, "Li-435"). The binder was polyvinylidene fluoride (PVdF), and the binder solution used was a 5% by mass N-methyl-2-pyrrolidone (NMP) solution of PVdF (manufactured by Kureha Battery Materials Japan (KBMJ), "#7305").

[0048] First, the positive electrode active material, conductive material, and binder solution were mixed using a mixer. The binder solution was then added to the resulting mixture to prepare a positive electrode material slurry. Next, the obtained positive electrode material slurry was coated onto a current collector using a coating applicator. The current collector used aluminum foil (thickness: 12 μm). The positive electrode material slurry coated onto the current collector was dried using a drying oven at 120°C. This produced a positive electrode body with a positive electrode material layer. Furthermore, in the positive electrode material layer, the mass ratio of positive electrode active material / conductive material / binder was 95 / 2.5 / 2.5. The areal density of the positive electrode material layer on the current collector was 19.5 mg / cm³. 2 Finally, the positive electrode material layer was compressed using a roller press, and its density was adjusted to 3.1 g / cm³. 3 .

[0049] (Battery cell fabrication)

[0050] A laminated battery cell was fabricated by stacking the negative electrode body 10 and the positive electrode body of Example 1 in a separator, and introducing a non-aqueous electrolyte into the resulting laminate. Battery cells were also fabricated in the same manner for the negative electrode bodies 10 of Examples 2-9 and the negative electrode bodies of the comparative examples.

[0051] (Evaluation of battery cells)

[0052] For each fabricated battery cell, the initial DC internal resistance (DCIR), capacity retention, and cycle expansion rate were evaluated. The evaluation results are shown in Table 1. Here, capacity retention represents the full-charge capacity of the battery after 100 charge-discharge cycles at 0.5C, as a percentage of the initial full-charge capacity. Furthermore, in the cycle expansion rate measurement, a contact displacement gauge was installed on the battery cell to measure the displacement of the battery cell thickness during multiple charge-discharge cycles (e.g., dozens of cycles). The cycle expansion rate represents the percentage of the battery cell thickness displacement over multiple cycles relative to the initial battery cell thickness.

[0053] The initial DCIR value, capacity retention rate, and cycle expansion rate measured in each battery cell are shown in Table 1. In Table 1, the test results are marked as "Good" (◎), "Acceptable" (〇), and "Unacceptable" (×) to indicate battery performance. Furthermore, for the initial DCIR value, a result below 2Ω is considered "Acceptable," and a result above 2Ω is considered "Unacceptable." For the capacity retention rate, a result above 90% is considered "Acceptable," and a result below 90% is considered "Unacceptable." For the cycle expansion rate, a lower result indicates higher battery performance: below 2.5% is considered "Good," above 2.5% but below 3% is considered "Acceptable," and above 3% is considered "Unacceptable."

[0054] [Table 1]

[0055]

[0056] (Examples 1-6)

[0057] As described above, in the negative electrode bodies 10 of Examples 1 to 6, granules 30 were fabricated using the flow layer method. In the negative electrode bodies 10 of Examples 1 to 6, a coating layer 24 with a porosity of around 75% and high (i.e., high flexibility) was successfully fabricated. Hereinafter, the evaluation results of battery cells using the negative electrode bodies 10 of Examples 1 to 6 are compared.

[0058] In the battery cells using the negative electrode bodies 10 of Examples 2 to 5, the initial DCIR value was 1.52 to 1.98 Ω, and the capacity retention rate was 90 to 92%, both of which were deemed "acceptable". Furthermore, in the battery cells using the negative electrode bodies 10 of Examples 2 to 5, the cycle expansion rate was also 2.2% to 2.9%, both of which were deemed "acceptable" or better, indicating good performance. Therefore, it was confirmed that if the thickness of the coating layer 24 is 0.5 μm or more and 5.0 μm or less, the expansion of the second active material particles 18 is absorbed by the contraction of the coating layer 24, thus suppressing the expansion of the electrode (i.e., the negative electrode body 10 when used as a battery electrode) caused by the expansion of the second active material particles 18. In particular, the cycle expansion rates of the battery cells using the negative electrode bodies 10 of Examples 3 and 4 were 2.3% and 2.2%, respectively, which were deemed "good". Therefore, it was confirmed that if the thickness of the coating layer 24 is 1.0 μm or more and 3.5 μm or less, it is relatively advantageous to suppress electrode expansion.

[0059] However, in the battery cell using the negative electrode body 10 of Example 1, the initial DCIR value (1.55Ω) and capacity retention rate (92%) were deemed "acceptable," which is good compared to Examples 1-5, but the cycle expansion rate (3.2%) was deemed "unacceptable." This is believed to be because if the thickness of the coating layer 24 is as small as 0.3 μm, the expansion of the second active material particles 18 during charging cannot be fully absorbed by the coating layer 24, thus failing to observe an effect on suppressing electrode expansion.

[0060] Furthermore, in the battery cell using the negative electrode 10 of Example 6, the cycle expansion rate (2.5%) was deemed "acceptable," but the initial DCIR value (2.81Ω) and capacity retention rate (86%) were both deemed "unacceptable." This is believed to be because if the thickness of the coating layer 24 is 7.2 μm, the insertion and extraction of lithium ions are hindered by the thick coating layer 24.

[0061] (Examples 7-9)

[0062] As described above, in the negative electrode bodies 10 of Examples 7-9, granules 30 were prepared using a reduced-pressure stirring and drying method. In the negative electrode bodies 10 of Examples 7-9, a coating layer 24 with a thickness of approximately 1.7 μm was formed. Furthermore, in the negative electrode bodies 10 of Examples 7-9, by adjusting the stirring speed during the preparation of the granules 30, coating layers 24 with varying porosities could be formed. On the other hand, compared to the negative electrode bodies 10 of Examples 1-6 prepared by the flow layer method, the porosity of the coating layer 24 in the negative electrode bodies 10 of Examples 7-9 is lower. The evaluation results of battery cells using the negative electrode bodies 10 of Examples 7-9 are compared below.

[0063] In the battery cells using the negative electrode 10 of Examples 7 and 8, the initial DCIR values ​​(1.79Ω, 1.91Ω), capacity retention (91%, 91%), and cycle expansion rates (2.6%, 2.8%) were all deemed "acceptable," indicating good results. On the other hand, in the battery cell using the negative electrode 10 of Example 9, the cycle expansion rate (2.9%) was deemed "acceptable," but the initial DCIR value (2.44Ω) and capacity retention rate (84%) were deemed "unacceptable." This is believed to be because if the porosity of the coating layer 24 is as low as 38%, the insertion and extraction of lithium ions are hindered by the relatively densely formed coating layer 24.

[0064] (Comparative example)

[0065] As described above, the negative electrode body of the comparative example does not have a coating layer 24. In the battery cell using the negative electrode body of the comparative example, the initial DCIR value (1.50Ω) and capacity retention rate (92%) were both determined to be "acceptable". On the other hand, the cycle expansion rate (3.2%) was determined to be "unacceptable". This is because there is no coating layer 24 to absorb the expansion of the second active material particles 18 during charging, so it is assumed that the electrode expansion is due to the expansion of the second active material particles 18.

[0066] Symbol Explanation

[0067] 10-Negative electrode body, 12-Current collector, 14-Negative electrode material layer, 16-First active material particle, 18-Second active material particle, 20-Binder, 24-Coating layer, 26-Carbon nanotube, 30-Particle, 40-Negative electrode material slurry.

Claims

1. A negative electrode body, characterized in that it comprises: Current collector; and A negative electrode material layer is disposed on the current collector. The negative electrode material layer has the following characteristics: First active substance particle; The second active material particles are dispersed among the first active material particles and are composed of a silicon-based material; and The coating layer, which covers the surface of the second active material particles, is composed of carbon nanotubes. The first active material particles are composed of a different type of carbon material than the carbon nanotubes. The coating layer has a porosity of more than 50%.

2. The negative electrode body according to claim 1, characterized in that, The thickness of the coating layer is greater than 0.5 μm and less than 5 μm.

3. The negative electrode body according to claim 1, characterized in that, The carbon nanotubes constituting the coating layer are multilayer carbon nanotubes.

4. The negative electrode body according to claim 1, characterized in that, The silicon-based material comprises at least one selected from the group consisting of silicon, silicon carbide, silicon monoxide, and silicon alloys.

5. A method for manufacturing a negative electrode body, characterized by include: A process for producing granules by forming a coating layer of carbon nanotubes on the surface of a second active material particle made of silicon-based material. The process of mixing the granules, first active material particles composed of carbon materials of a different type than the carbon nanotubes, binder and water to prepare a negative electrode material slurry; The process of coating the negative electrode material slurry onto the surface of the current collector; and The process of drying the negative electrode material slurry coated on the surface of the current collector. The coating layer has a porosity of more than 50%.

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