Negative electrode body and method for manufacturing the same

Abstract

The present application relates to a negative electrode body and a method for manufacturing the same. The negative electrode body includes a current collector and a negative electrode material layer provided on the current collector. The negative electrode material layer includes first active material particles composed of a carbon material, second active material particles composed of a silicon-based material and dispersed between the first active material particles, and a superabsorbent polymer attached to a surface of the second active material particles and forming a gap with the first active material particles.

Description

Technical Field

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

[0002] Japanese Patent Application Publication No. 2024-526507 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 porous carbon and a negative electrode active material filling the pore structure of the porous carbon. The negative electrode active material is silicon nanoparticles. Summary of the Invention

[0003] Silicon-based materials (including elemental silicon) have higher capacity than carbon materials as negative electrode active materials in batteries. Therefore, silicon-based materials have attracted considerable attention as negative electrode active materials, for example, in the field of lithium-ion batteries. On the other hand, silicon-based materials exhibit significant volume changes during charging and discharging. Therefore, electrode expansion during charging is considered a problem when the negative electrode material layer contains silicon-based materials. This specification provides a novel technique for suppressing electrode expansion in a negative electrode material layer containing silicon-based materials.

[0004] The technology disclosed in this specification is a method for manufacturing a negative electrode body. This manufacturing method includes: The process of making composite particles by attaching a superabsorbent polymer to the surface of a second active material particle made of a silicon-based material. The process of mixing the composite particles, the first active material particles made of carbon material, and water to make a negative electrode material slurry; The process of coating the negative electrode material slurry onto the surface of the current collector; and The process involves drying the negative electrode material slurry coated on the surface of the current collector, causing the superabsorbent polymer attached to the surface of the second active material particles to shrink, thereby forming a void between the superabsorbent polymer and the first active material particles.

[0005] According to the above configuration, in the negative electrode material slurry coated onto the surface of the current collector, second active material particles made of silicon-based material are dispersed among first active material particles made of carbon material. Furthermore, a highly absorbent polymer in a swollen state is attached to the surface of the second active material particles, and this highly absorbent polymer is positioned between the first and second active material particles. When the negative electrode material slurry with this structure is dried, the highly absorbent polymer shrinks, creating voids between the highly absorbent polymer attached to the second active material particles and the first active material particles. That is, voids are formed around the second active material particles. Therefore, in the manufactured negative electrode body, even if the second active material particles expand during charging, the resulting electrode expansion can be suppressed.

[0006] In the above manufacturing method, the composite particles can also be produced by mixing the second active material particles, the superabsorbent polymer, and water during the process of making the composite particles. With this configuration, the friction between the superabsorbent polymer and the second active material particles increases due to the swelling of the superabsorbent polymer, thereby promoting the formation of the composite particles.

[0007] The technology disclosed in this specification is also embodied in a negative electrode body. While there are no particular limitations on this negative electrode body, it can be manufactured using the methods described above. This negative electrode body includes a current collector and a negative electrode material layer disposed on the current collector.

[0008] The negative electrode material layer has the following characteristics: The first active material particles are composed of carbon materials; Second active material particles, dispersed between the first active material particles and composed of silicon-based materials; and A highly absorbent polymer that adheres to the surface of the second active material particles and forms gaps between itself and the first active material particles.

[0009] According to this configuration, since there are gaps around the second active material particles, even if the second active material particles expand during charging, the resulting electrode expansion can be suppressed.

[0010] In the above-described negative electrode body and / or manufacturing method, the superabsorbent polymer may comprise at least one selected from the group consisting of polyacrylic acid, polyvinyl alcohol, polyethylene glycol, and polyacrylonitrile.

[0011] Based on the above, or as an alternative, the silicon-based material may include at least one selected from the group consisting of silicon, silicon carbide, silicon monoxide, and silicon alloys.

[0012] As described above, in this technology, the superabsorbent polymer is pre-attached to the surface of the second active material particles. Therefore, the superabsorbent polymer is locally present around the second active material particles. In this case, within the negative electrode material layer, the content of the superabsorbent polymer in a unit region containing the second active material particles can be more than 10 times higher than the content of the superabsorbent polymer in a unit region not containing the second active material particles. Attached Figure Description

[0013] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like symbols denote like elements.

[0014] Figure 1 A cross-sectional view of the negative electrode is shown.

[0015] Figure 2 A diagram illustrating the manufacturing method of the negative electrode body is shown.

[0016] Figure 3 A diagram illustrating the manufacturing method of the negative electrode body is shown.

[0017] Figure 4 A diagram illustrating the manufacturing method of the negative electrode body is shown.

[0018] Figure 5 A diagram illustrating the manufacturing method of the negative electrode body is shown.

[0019] Figure 6 This is a flowchart illustrating a series of steps in the manufacturing method of the negative electrode. Detailed Implementation

[0020] Composition of negative electrode body

[0021] 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 that uses 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. It should be noted that the negative electrode material layer 14 can be disposed not only on the surface 12a of the current collector 12, but also on its back side.

[0022] The current collector 12 is a conductive sheet, such as copper foil or other metal foil. While not particularly limited, it is preferable that at least surface 12a of the current collector 12 is 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 a metal other than copper.

[0023] Figure 1 A cross-sectional view of the negative electrode body 10 is shown. Figure 1 (lower part) and a cross-sectional view of a portion of the anode material layer 14 enlarged ( Figure 1 (The upper part). For example, Figure 1 As shown, the negative electrode material layer 14 comprises a first active material particle 16, a second active material particle 18, a superabsorbent polymer 20, and a conductive additive 22.

[0024] The first active material particles 16 are the main component of the active material in the negative electrode material layer 14. The first active material particles 16 are composed of carbon materials. Examples of carbon materials include graphite, hard carbon, and soft carbon. Typically, the first active material particles 16 are graphite. The particle size of the first active material particles 16 can be approximately 5 μm or more and approximately 50 μm or less. Here, "particle size" as described in this specification refers to the average particle size, meaning the particle size (D50) at which the cumulative value of the volumetric particle size distribution measured by laser diffraction / scattering method reaches 50%.

[0025] The second active material particle 18 serves as the active material in the negative electrode material layer 14, and is used together with the first active material particle 16. The content of the second active material particle 18 in the negative electrode material layer 14 is significantly 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 with other metals such as aluminum (Al), iron (Fe), and manganese (Mn). Typically, the second active material particle 18 is silicon carbide. The silicon-based material can be composed of a single material or two or more materials. The particle size of the second active material particle 18 can be approximately 5 μm or more and approximately 50 μm or less.

[0026] The superabsorbent polymer 20 adheres to the surface of the second active material particles 18 and forms voids AG between it and the first active material particles 16. Examples of superabsorbent polymers 20 include polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyacrylonitrile (PAN). Typically, the superabsorbent polymer 20 is polyacrylic acid. It should be noted that the superabsorbent polymer 20 can be composed of a single material or two or more materials. As an example, the superabsorbent polymer 20 also functions as a binder for the negative electrode material layer 14. However, in modified examples, the negative electrode material layer 14 may contain other binders besides the superabsorbent polymer 20.

[0027] The conductive additive 22 is dispersed between the active material particles 16 and 18 in the negative electrode material layer 14. 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 is, for example, a single layer of carbon nanotubes. The conductive additive 22 can be composed of a single material or two or more materials. However, in variations, the negative electrode material layer 14 may not contain the conductive additive 22.

[0028] Manufacturing method of negative electrode body

[0029] Reference Figures 2-6 An example of the manufacturing method of 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.

[0030] In S2, a process is performed to mix the second active material particles 18 and the superabsorbent polymer 20 to produce composite particles 30. Specifically, as follows... Figure 2 As shown, composite particles 30 are produced by attaching a superabsorbent polymer 20 to the surface of the second active material particles 18. It should be noted that the superabsorbent polymer 20 used here can be granular. In this case, the particle size of the superabsorbent polymer 20 when it swells due to water absorption can be about 1 μm or more and about 2 μm or less. As an example, the composite particles 30 can be produced using a mixing system 50. However, the production of composite particles 30 is not limited to the mixing system 50, and other types of devices suitable for particle composite formation can also be used. Typically, a wet process in which the second active material particles 18 and the superabsorbent polymer 20 are mixed with water can also be used. When the composite particles 30 are produced using a wet process, the friction between the superabsorbent polymer 20 and the second active material particles 18 increases due to the swelling of the superabsorbent polymer 20, resulting in the formation of composite particles 30. It should be noted that when using a wet process, the composite particles 30 can be dried before proceeding to step S4. However, the composite particles 30 can also be produced using a dry process without mixing water, instead of a wet process.

[0031] In S4, a process is performed to mix the composite particles 30, the first active material particles 16, and water prepared in S2 to prepare the negative electrode material slurry 40. Specifically, as follows... Figure 3 As shown, firstly, for example, a mixer 60 is used to mix the composite particles 30, the first active material particles 16, and water. After further mixing with water, a dispersion containing the conductive additive 22 is mixed in to prepare the negative electrode material slurry 40. At this time, in the negative electrode material slurry 40, as... Figure 3As shown, the composite particles 30 are dispersed among the first active material particles 16. That is, the composite particles 30 are mixed with water, and the surface of the second active material particles 18 is coated with a superabsorbent polymer 20 in a swollen state. Furthermore, the swollen superabsorbent polymer 20 is located between the first active material particles 16 and the second active material particles 18.

[0032] In S6, such as Figure 4 As shown, a process is performed, for example, by coating the negative electrode material slurry 40 prepared in S4 onto the current collector 12 using a coating machine.

[0033] In S8, a process is performed to form a void AG between the superabsorbent polymer 20 and the first active material particles 16. Specifically, the negative electrode material slurry 40 coated onto the current collector 12 in S6 is dried, for example, in a drying oven 80. As a result, the superabsorbent polymer 20, which is in a swollen state and attached to the surface of the second active material particles 18, shrinks (i.e., dehydrates). Consequently, a void AG is formed between the superabsorbent polymer 20 and the first active material particles 16.

[0034] Through the above processes, the negative electrode body 10 is manufactured. As described above, when the negative electrode material layer 14 is still a negative electrode material slurry 40, a highly absorbent polymer 20 in a swollen state is attached to the surface of the second active material particles 18. Furthermore, the highly absorbent polymer 20 is located between the first active material particles 16 and the second active material particles 18. When the negative electrode material slurry 40 with this structure is dried, the highly absorbent polymer 20 shrinks, forming a void AG between the highly absorbent polymer 20 attached to the second active material particles 18 and the first active material particles 16. That is, a void is formed around the second active material particles 18. Therefore, in the manufactured negative electrode body 10, even if the second active material particles 18 expand during charging, 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.

[0035] It should be noted that in the manufacturing method of the negative electrode body 10, the superabsorbent polymer 20 is pre-attached to the surface of the second active material particles 18. Therefore, the superabsorbent polymer 20 is locally present around the second active material particles 18 of the negative electrode material layer 14. For example, as... Figure 5 As shown, within the negative electrode material layer 14, the first unit region ( Figure 5 The content of superabsorbent polymer 20 in A1 can reach the second unit region ( Figure 5The content of superabsorbent polymer 20 in A2) is more than 10 times higher. The first unit region contains second active substance particles 18. The second unit region does not contain second active substance particles 18. It should be noted that the superabsorbent polymer 20 is locally present around the second active substance particles 18, such as... Figure 1 As shown, the negative electrode material layer 14 can be observed using cross-sectional images obtained using a scanning electron microscope (SEM) or similar methods.

[0036] Next, referring to Table 1, embodiments related to this technology will be described. However, the following description is not intended to limit the configuration related to this technology. First, negative electrode bodies 10 of Examples 1 to 4 and negative electrode bodies of comparative examples were fabricated.

[0037] Negative electrode body of Example 1

[0038] The negative electrode body 10 of Example 1 was manufactured according to the aforementioned manufacturing method. The first active material particle 16 used was graphite. The second active material particle 18 used was silicon carbide. The binder used was polyacrylic acid (PAA) particles. The superabsorbent polymer 20 used polyacrylic acid (PAA) particles, the particle size of which was 1.0 μm when the PAA swelled due to water absorption (hereinafter referred to as the swelling particle size). The conductive additive 22 used was single-layer carbon nanotubes (SWCNTs), and a 0.4% mass percentage 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.

[0039] In the process of making composite particles 30 ( Figure 6 In step S2), the second active material particles 18 and the superabsorbent polymer 20 were mixed using a mixing system 50 (circumferential speed: 15 m / s, compounding time: 15 minutes) via a dry process. This produced composite particles 30.

[0040] In the process of making negative electrode material slurry 40 ( Figure 6 In step S4), firstly, first active material particles 16 and water are added to the prepared composite particles 30 and mixed using a mixer. Water is then added to the resulting mixture, followed by mixing, and then a solution of conductive additive 22 containing a dispersant is added and mixed. This produces the negative electrode material slurry 40.

[0041] In the process of coating negative electrode material slurry 40 ( Figure 6 In step S6), a coating machine is used to coat the negative electrode material slurry 40 onto the current collector 12. The current collector 12 uses copper foil (thickness: 8μm).

[0042] In the process of forming voids AG ( Figure 6 In step S8), the negative electrode material slurry 40 coated onto the current collector 12 was dried using a drying oven at 100°C. As a result, the superabsorbent polymer 20 dries and shrinks inside the negative electrode material layer 14, thus forming voids AG between the superabsorbent polymer 20 and the first active material particles 16. In the negative electrode material layer 14, the mass ratio of negative electrode active material / conductive additive 22 / dispersant / PAA is 97.75 / 0.10 / 0.15 / 2.00. It should be noted that the mass of PAA here refers to the sum of the mass of the binder and the mass of the superabsorbent polymer 20. The weight per unit area of ​​the negative electrode material layer 14 on the current collector 12 is 7.3 mg / cm². 2 Finally, the negative electrode material layer 14 is compressed using a roller press to adjust its density to 1.0 g / cm³. 3 .

[0043] Negative electrode bodies of Examples 2-4

[0044] In Examples 2-4, the steps for manufacturing the composite particles 30 were changed compared to Example 1 to manufacture the negative electrode body 10. In Example 2, a wet process was used instead of the dry process in Example 1 for manufacturing the composite particles 30. In Example 3, PAA particles with a swollen particle size of 1.4 μm were used instead of the PAA particles with a swollen particle size of 1.0 μm used in Example 1 as the superabsorbent polymer 20. In Example 4, the same wet process as in Example 2 was used for manufacturing the composite particles 30, and PAA particles with a swollen particle size of 1.4 μm, the same as in Example 3, were used as the superabsorbent polymer 20. Regarding the other steps, the negative electrode body 10 was manufactured using the same manufacturing method as in Example 1.

[0045] Negative electrode body of the comparative example

[0046] In the comparative example, the steps for preparing the composite particles 30 and the steps for preparing the negative electrode material slurry 40 were changed compared to Example 1. Additionally, the same PAA as in Example 1 was used as the binder. However, instead of the PAA particles of Example 1, an aqueous PAA solution was used as the binder solution. 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, the binder solution was further mixed into the resulting mixture, thereby preparing the negative electrode material slurry. That is, in the comparative example, the step of preparing the composite particles 30 was omitted when preparing the negative electrode material slurry. The other steps were the same as the manufacturing method of Example 1.

[0047] Positive electrode body

[0048] The positive electrode bodies of Examples 1-4 and the Comparative Examples used a common positive electrode body. The positive electrode active material used was lithium nickel cobalt manganese oxide (NCM, manufactured by Sumitomo Metal Mining). The conductive material used was acetylene black (manufactured by Denka, "Li-435"). The binder used was polyvinylidene fluoride (PVdF). As the binder solution, a 5% by mass N-methyl-2-pyrrolidone (NMP) solution of PVdF (manufactured by Kureha Battery Materials Japan (KBMJ), "#7305") was used.

[0049] 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 machine. 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. It should be noted that the mass ratio of positive electrode active material / conductive material / binder in the positive electrode material layer is 95 / 2.5 / 2.5. The weight per unit area of ​​the positive electrode material layer on one side of the current collector is 19.5 mg / cm². 2 Finally, the positive electrode material layer was compressed using a roller press to adjust its density to 3.1 g / cm³. 3 .

[0050] Evaluation of battery cells

[0051] The negative electrode body 10 of Example 1 and the positive electrode body were laminated together with a separator between them, and a non-aqueous electrolyte was introduced into the resulting laminate to fabricate a laminated battery cell. Battery cells were also fabricated in the same manner for the negative electrode bodies 10 of Examples 2 to 4 and the negative electrode bodies of the comparative examples.

[0052] Evaluation of battery cells

[0053] 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. Regarding capacity retention, the full-charge capacity of the battery was measured after 100 charge-discharge cycles at a rate of 0.5C, and expressed as the ratio of the full-charge capacity after 100 cycles to the initial full-charge capacity. Furthermore, in measuring the cycle expansion rate, a contact displacement gauge was installed on the battery cell to measure the displacement of the cell thickness during multiple charge-discharge cycles (e.g., dozens of cycles). The cycle expansion rate was expressed as the ratio of the displacement of the cell thickness over multiple cycles to the initial cell thickness.

[0054] The initial DCIR value, capacity retention rate, and cycle expansion rate measured for each battery cell are shown in Table 1. In Table 1, regarding the measurement results, as battery performance, "Good" is marked as "Good," "Acceptable" as "Acceptable," and "Unacceptable" as "Unacceptable." It should be noted that for the initial DCIR value, if the measured result is below 2Ω, it is judged as "Acceptable," and if the measured result is above 2Ω, it is judged as "Unacceptable." Regarding the capacity retention rate, if the measured result is above 90%, it is judged as "Acceptable," and if the measured result is below 90%, it is judged as "Unacceptable." Regarding the cycle expansion rate, the lower the measured result, the higher the battery performance. If it is less than 2.5%, it is judged as "Good," if it is above 2.5% and less than 3%, it is judged as "Acceptable," and if it is above 3%, it is judged as "Unacceptable."

[0055]

[0056] Initial DCIR value

[0057] The initial DCIR value of the battery cell using the negative electrode body of the comparative example was 1.50Ω, which was "acceptable". In contrast, the initial DCIR values ​​of the battery cells using the negative electrode body 10 of Examples 1 to 4 were 1.55Ω, 1.69Ω, 1.52Ω, and 1.64Ω, respectively. Although some of them were slightly increased compared to the comparative example, they were all within the acceptable range and were therefore determined to be "acceptable".

[0058] Capacity maintenance rate

[0059] The capacity retention rates of the battery cells using the negative electrode bodies 10 of Examples 1 to 4 and the negative electrode bodies of the comparative examples were all 91% to 92%, which were roughly equivalent, and were all judged to be "acceptable".

[0060] Cyclic expansion rate

[0061] The battery cell using the comparative example negative electrode body had a cycle expansion rate of 3.2%, which was deemed "unacceptable". On the other hand, the battery cell using the negative electrode bodies 10 of Examples 1 to 4 had cycle expansion rates of 2.2% to 2.6%, both of which were deemed "acceptable" or better, showing good performance. That is, it can be considered that since voids can be formed around the second active material particles 18 in the negative electrode material layer 14, 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 can be suppressed. In particular, the battery cells using the negative electrode bodies 10 of Examples 2 and 4, which were manufactured by a wet process, had cycle expansion rates of 2.3% and 2.2%, respectively, which were deemed "good". Therefore, it can be considered that the wet process promotes the formation of composite particles 30, and the composite particles 30 can be manufactured as expected, thus playing a more advantageous role in suppressing electrode expansion.

Claims

1. A negative electrode body, comprising a current collector and a negative electrode material layer disposed on the current collector, The negative electrode material layer has the following characteristics: The first active material particles are composed of carbon materials; Second active material particles, which are dispersed between the first active material particles and are composed of silicon-based materials; as well as A highly absorbent polymer that adheres to the surface of the second active material particles and forms gaps between itself and the first active material particles.

2. The negative electrode body according to claim 1, wherein The superabsorbent polymer comprises at least one selected from the group consisting of polyacrylic acid, polyvinyl alcohol, polyethylene glycol, and polyacrylonitrile.

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

4. The negative electrode body according to any one of claims 1 to 3, wherein Within the negative electrode material layer, the content of the superabsorbent polymer in a unit region containing the second active material particles is more than 10 times the content of the superabsorbent polymer in a unit region not containing the second active material particles.

5. A method for manufacturing a negative electrode body, comprising: The process of making composite particles by attaching a superabsorbent polymer to the surface of a second active material particle made of a silicon-based material. The process of mixing the composite particles, the first active material particles made of carbon material, and water to make a negative electrode material slurry; The process of coating the negative electrode material slurry onto the surface of the current collector; and The process involves drying the negative electrode material slurry coated on the surface of the current collector, causing the superabsorbent polymer attached to the surface of the second active material particles to shrink, thereby forming a void between the superabsorbent polymer and the first active material particles.

6. The manufacturing method according to claim 5, wherein, In the process of making the composite particles, the composite particles are made by mixing the second active material particles, the superabsorbent polymer, and water.

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