Negative electrode of lithium ion secondary battery, manufacturing method and manufacturing apparatus thereof, and lithium ion secondary battery

Abstract

To provide a negative electrode of a lithium-ion battery having sufficient gravimetric energy density while suppressing dendrite growth of lithium metal, a method and apparatus for manufacturing the same, and a lithium-ion secondary battery.SOLUTION: A negative electrode NE of the lithium-ion secondary battery LiB1 has a negative electrode current collector N1 having a first surface N1a. The negative electrode current collector N1 has a plurality of protrusions PR1 on the first face N1a. The protrusions PR1 have a surface from which lithium can be deposited. The area of the projection region of the projections PR1 projected onto the first surface N1a is between 10 nm2 and 10000 nm2. The density of the projection area PR1 is between 1 piece / μm2 and 1000 pieces / μm2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The technical field of the present specification relates to a negative electrode for a lithium ion secondary battery, a method and apparatus for producing the same, and a lithium ion secondary battery. [Background technology]

[0002] Examples of chargeable and dischargeable electricity storage devices include secondary batteries, electric double layer capacitors, etc. Furthermore, examples of electricity storage devices that utilize lithium ions include lithium ion secondary batteries, lithium ion primary batteries, and lithium ion capacitors.

[0003] For example, Patent Document 1 discloses a lithium-ion secondary battery having a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. It discloses a technology using lithium cobalt oxide or lithium nickel oxide as the positive electrode active material and carbon as the negative electrode active material (claims and examples of Patent Document 1). Graphite is often used as the carbon material. Graphite can absorb or release one lithium ion per six carbon atoms in a six-membered ring. Furthermore, Patent Documents 2 and 3 disclose a technology that suppresses the dendrite growth of lithium metal by using a separator with a structure that forms fine compartments. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 2668678 [Patent Document 2] Patent No. 5331627 [Patent Document 3] WO 2021 / 049609 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to increase the weight energy density of a lithium ion secondary battery, it is preferable that the negative electrode material of the lithium ion secondary battery is lightweight and capable of absorbing (or depositing) a large amount of lithium.

[0006] However, when lithium-ion secondary batteries containing graphite, the currently mainstream negative electrode material, are used in electric vehicles, their weight energy density is insufficient. On the other hand, when lithium-ion secondary batteries containing lithium metal as the negative electrode material are used in electric vehicles, the weight energy density can be met. However, in this case, there is a problem that the positive and negative electrodes are prone to short-circuiting due to dendrite growth of lithium metal.

[0007] The problem to be solved by the technology of this specification is to provide a negative electrode for a lithium ion secondary battery that suppresses dendrite growth of lithium metal and has a sufficient weight energy density, a method and apparatus for manufacturing the same, and a lithium ion secondary battery. [Means for solving the problem]

[0008] The first aspect is A gas containing hydrogen gas is converted into plasma and supplied to a current collector made of Cu, The method for manufacturing a negative electrode of a lithium ion secondary battery includes forming a plurality of protrusions made of the same material as the current collector on a first surface of the current collector.

[0009] The negative electrode of this lithium-ion secondary battery has protrusions. Lithium can be deposited on the surface of the protrusions. Furthermore, dendrite growth of lithium metal can be suppressed. Therefore, even if a large amount of lithium metal is deposited in the negative electrode of this lithium-ion secondary battery, the problem of lithium metal dendrite growth hardly occurs. In other words, the negative electrode of this lithium-ion secondary battery has both the effect of suppressing lithium metal dendrite growth and sufficient weight energy density. [Effects of the Invention]

[0010] This specification provides a negative electrode for a lithium ion secondary battery that suppresses dendrite growth of lithium metal and has a sufficient weight energy density, a method and apparatus for manufacturing the same, and a lithium ion secondary battery. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram of a lithium-ion secondary battery LiB1 of a first embodiment. [Figure 2] 2 is a diagram schematically showing a cross section of a negative electrode NE of a lithium ion secondary battery LiB1 of the first embodiment. FIG. [Figure 3] 1 is a schematic diagram showing the configuration of a manufacturing device for treating a negative electrode in a lithium ion secondary battery LiB1 according to a first embodiment. [Figure 4] This is a scanning electron microscope photograph (part 1) showing the surface of a copper foil after irradiating it with hydrogen radicals. [Figure 5] This is a scanning electron microscope photograph (part 2) showing the surface of a copper foil after irradiating it with hydrogen radicals. [Figure 6] 6 is a graph showing the measurement results of the unevenness on the line in FIG. 5. [Figure 7] 10 is a graph showing the relationship between the amount of hydrogen supplied and the number of protrusions having an area of 10 nm 2 or more and 100 nm 2 or less. [Figure 8] 10 is a graph showing the relationship between the amount of hydrogen supplied and the number of protrusions having an area of 100 nm 2 or more and 1000 nm 2 or less. [Figure 9] 10 is a graph showing the relationship between the amount of hydrogen supplied and the number of protrusions having an area of 1000 nm 2 or more and 10000 nm 2 or less. [Figure 10] 10 is a graph showing the relationship between the amount of hydrogen supplied and the number of protrusions. [Figure 11] 10 is a graph showing the relationship between the magnitude of the bias and the number of protrusions having an area of 10 nm 2 or more and 100 nm 2 or less. [Figure 12]10 is a graph showing the relationship between the magnitude of the bias and the number of protrusions having an area of 100 nm 2 or more and 1000 nm 2 or less. [Figure 13] 10 is a graph showing the relationship between the magnitude of the bias and the number of protrusions having an area of 1000 nm 2 or more and 10000 nm 2 or less. [Figure 14] 10 is a graph showing the relationship between the magnitude of bias and the number of protrusions. [Figure 15] 1 is a photomicrograph showing the surface of a copper foil before exposure to hydrogen plasma. [Figure 16] 1 is a photomicrograph showing the surface of a copper foil after hydrogen plasma exposure. [Figure 17] 1 is a graph showing the charge-discharge characteristics of a lithium ion secondary battery in which a copper foil having protrusions formed thereon is used as a negative electrode. [Figure 18] 1 is a graph showing the charge-discharge characteristics of a lithium ion secondary battery in which a copper foil on which no protrusions are formed is used as a negative electrode. [Figure 19] 1 is a scanning microscope photograph (part 1) showing a cross section of a negative electrode of a lithium ion secondary battery having protrusions after repeated charge and discharge. [Figure 20] 1 is a scanning microscope photograph (part 2) showing a cross section of a negative electrode of a lithium ion secondary battery having protrusions after repeated charge and discharge. [Figure 21] 1 is a scanning microscope photograph showing the surface of lithium deposited on a negative electrode of a lithium ion secondary battery having protrusions. [Figure 22] 1 is a photomicrograph showing the surface of a copper foil after oxygen plasma exposure. [Figure 23] 1 is a graph showing the charge-discharge characteristics of a lithium ion secondary battery in which a copper foil on which protrusions are formed by oxygen plasma is used as a negative electrode. [Figure 24] 1 is a graph showing the results of a component analysis of copper foil on which protrusions have been formed using oxygen plasma. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, specific embodiments will be described with reference to the drawings, taking as examples a negative electrode of a lithium ion secondary battery, a manufacturing method and apparatus therefor, and a lithium ion secondary battery.

[0013] (First embodiment) 1. Lithium-ion secondary battery 1 is a schematic configuration diagram of a lithium ion secondary battery LiB1 of Embodiment 1. The lithium ion secondary battery LiB1 has a positive electrode PE, a negative electrode NE, a separator Sp1, an electrolytic solution ES1, and a container V1.

[0014] The positive electrode PE is the positive electrode of the lithium-ion secondary battery LiB1. The positive electrode PE has a positive electrode current collector P1 and a positive electrode active material layer P2. The positive electrode active material layer P2 is formed on the first surface P1a and the second surface P1b of the positive electrode current collector P1.

[0015] The positive electrode current collector P1 is a metal substrate. The positive electrode current collector P1 is, for example, a metal foil. The positive electrode current collector P1 may have other shapes. The material of the positive electrode current collector P1 is, for example, Al or Ti. The material of the positive electrode current collector P1 may also be a conductor such as another metal.

[0016] The positive electrode active material layer P2 contains a positive electrode active material, a conductive additive, and a binder. The positive electrode active material layer P2 may also contain a thickener. Examples of positive electrode active materials include lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and ternary materials. Examples of conductive additives include carbon black. Examples of binders include SBR. Examples of thickeners include carboxymethyl cellulose. Thus, the positive electrode active material layer P2 contains lithium atoms.

[0017] The negative electrode NE is the negative electrode of the lithium-ion secondary battery LiB1. The negative electrode NE has a negative electrode current collector N1. As will be described later, lithium is deposited on the negative electrode NE.

[0018] The negative electrode current collector N1 is a metal substrate. The negative electrode current collector N1 is, for example, a metal foil. The negative electrode current collector N1 may have other shapes. The material of the negative electrode current collector N1 is, for example, Cu. The negative electrode current collector N1 is, for example, a copper plate or copper foil. The material of the negative electrode current collector N1 may also be a conductor such as another metal.

[0019] The separator Sp1 serves to electrically insulate the positive electrode PE from the negative electrode NE, and is permeable to lithium ions in the electrolyte solution ES1.

[0020] The electrolyte ES1 has the property of transferring lithium ions between the positive electrode PE and the negative electrode NE. The electrolyte ES1 fills the container V1. The electrolyte ES1 is a liquid obtained by dissolving a lithium salt such as lithium hexafluorophosphate (LiPF6) in dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), or the like.

[0021] The container V1 accommodates the positive electrode PE, the negative electrode NE, the separator Sp1, and the electrolyte solution ES1 inside. The container V1 is made of a material that is less reactive with the electrolyte solution ES1.

[0022] 2.Protrusion 2 is a diagram schematically illustrating a cross section of the negative electrode NE of the lithium-ion secondary battery LiB1 of the first embodiment. The negative electrode current collector N1 has a first surface N1a. The first surface N1a is one surface of the negative electrode current collector N1. A plurality of protrusions PR1 are formed on the first surface N1a of the negative electrode current collector N1. The protrusions PR1 have a surface on which lithium can be deposited.

[0023] The protrusion PR1 is a portion of the negative electrode current collector N1 that partially protrudes from the first surface N1a. The protrusion PR1 may be composed of a single particle GR1 or a plurality of particles GR1. In this case, the material of the particle GR1 is preferably the same as the material of the negative electrode current collector N1. The particle GR1 is preferably fused to the first surface N1a of the negative electrode current collector N1 and integrated with the negative electrode current collector N1. This is to increase the adhesion between the negative electrode current collector N1 and the particle GR1 and prevent the particle GR1 from peeling off from the negative electrode current collector N1.

[0024] The planar size of the protrusion PR1 is measured by observing the surface of the negative electrode current collector N1 using a scanning electron microscope from a direction perpendicular to the first surface N1a. The area of the projection region of the protrusion PR1 projected onto the first surface N1a is 10 nm 2 More than 10000nm 2 Preferably, it is 20 nm or less. 2 More than 5000nm 2 The average maximum length of the projection area of the protrusion PR1 projected onto the first surface N1a is, for example, 10 nm or more and 200 nm or less. Here, the maximum length of the projection area is the longest length of a line segment that crosses the interior of the projection area.

[0025] The protrusion PR1 is, for example, 10 μm from the first surface N1a of the negative electrode current collector N1. 2 That is, the density of the protrusions in the projection area of the protrusion PR1 projected onto the first surface N1a is 1 / μm 2 More than 1000 pieces / μm 2 Preferably, it is 2 particles / μm or less. 2 More than 800 pieces / μm 2 More preferably, it is 3 particles / μm or less. 2 More than 500 pieces / μm 2 The area occupied by the projection region of the protrusion PR1 projected onto the first surface N1a is, for example, 1 / 10 or more and 8 / 10 or less of the area of the first surface.

[0026] As will be described later, when the protrusions PR1 are formed by irradiation with hydrogen plasma, it is believed that the protrusions PR1 are formed as follows: Copper particles GR1 are knocked out from the first surface N1a of the negative electrode current collector N1, and the knocked-out particles GR1 re-adhere to the first surface N1a of the negative electrode current collector N1 and fuse with the first surface N1a of the negative electrode current collector N1, thereby forming the protrusions PR1. It is believed that the size and density of the protrusions PR1 are important factors for lithium deposition.

[0027] The protrusions PR1 serve as starting points for lithium deposition, and are thought to align the deposition direction of lithium metal and suppress dendrite growth of lithium metal by suppressing the movement of lithium ions in a direction parallel to the first surface N1a of the negative electrode current collector N1.

[0028] 3. Charge and discharge reactions involving lithium ions 3-1.Charge and discharge reaction The charge / discharge reaction is, for example, a chemical reaction represented by the following chemical reaction formula. Li + + e - ⇔ Li …(1) Li 1-x CoO2 + xLi + + xe - ⇔ LiCoO2…(2) Equation (1) is the reaction in the negative electrode NE. Equation (2) is the reaction in the positive electrode active material layer P2. Both reactions involve lithium ions and electrons. A charge / discharge reaction is a chemical reaction in the positive electrode PE or negative electrode NE in which lithium ions are involved and electrons are exchanged. This charge / discharge reaction can result in the absorption or release of lithium ions, as well as the precipitation, deposition, adsorption, or dissolution of lithium or lithium compounds. If lithium or lithium compounds are precipitated, the charge / discharge reaction can occur outside the positive electrode active material layer P2 or negative electrode NE. The type of charge / discharge reaction varies depending on the materials used for the positive electrode active material layer P2 and negative electrode NE.

[0029] 4. Manufacturing equipment A manufacturing device for forming the protrusions PR1 on the first surface N1a of the negative electrode current collector N1 will be described.

[0030] 3 is a schematic diagram showing the configuration of a manufacturing apparatus for processing the negative electrode of the lithium-ion secondary battery LiB1 of the first embodiment. The manufacturing apparatus 1 has a plasma generation chamber 46 and a reaction chamber 10. The plasma generation chamber 46 is used to generate plasma therein and also to generate radicals to be supplied to the reaction chamber 10. The reaction chamber 10 is used to form a protrusion PR1 on the negative electrode current collector N1 by utilizing the radicals generated in the plasma generation chamber 46.

[0031] The manufacturing apparatus 1 also has a waveguide 47, a quartz window 48, and a slot antenna 49. The waveguide 47 is for introducing the microwaves 39. The slot antenna 49 is for introducing the microwaves 39 from the quartz window 48 into the plasma generation chamber 46.

[0032] The plasma generation chamber 46 is for generating surface wave plasma (SWP) by microwaves 39. The plasma generation chamber 46 is provided with a radical source inlet 42. The radical source inlet 42 is for supplying a gas that serves as a radical source into the inside of the plasma 61 generated in the plasma generation chamber 46.

[0033] A partition wall 44 is provided between the plasma generation chamber 46 and the reaction chamber 10. The partition wall 44 separates the plasma generation chamber 46 from the reaction chamber 10. The partition wall 44 also serves as a first electrode 22 for applying a voltage. A through-hole 14 is formed in the partition wall 44. This is for supplying radicals generated in the plasma generation chamber 46 to the reaction chamber 10.

[0034] The reaction chamber 10 is used to generate capacitively coupled plasma (CCP). The reaction chamber 10 is also used to form protrusions PR1 on the negative electrode current collector N1. The reaction chamber 10 has a second electrode 24, a heater 25, a raw material inlet 12, and an exhaust port 16. The second electrode 24 is used to apply a voltage between the second electrode 24 and the first electrode 22. The heater 25 is used to heat the negative electrode current collector N1 and control the temperature of the negative electrode current collector N1. Note that the raw material inlet 12 may be omitted in the first embodiment because it does not supply anything. The exhaust port 16 is connected to a vacuum pump or the like. The vacuum pump is used to adjust the pressure inside the reaction chamber 10.

[0035] As described above, the partition wall 44 also serves as the first electrode 22 for applying a voltage between it and the second electrode 24. A power source and a circuit are connected to the first electrode 22 in order to control the potential of the first electrode 22 over time. The second electrode 24 is used to apply a voltage between it and the first electrode 22. The second electrode 24 also serves as a mounting base for placing the negative electrode current collector N1 thereon. The second electrode 24 is grounded. The distance between the first electrode 22 and the second electrode 24 is approximately 5 cm. Of course, this value is not limiting.

[0036] 5. Negative electrode manufacturing method 5-1.Protrusion formation process First, the negative electrode current collector N1, before the protrusions PR1 are formed, is placed inside the manufacturing apparatus 1. At this time, the first surface N1a of the negative electrode current collector N1 faces up, and the second surface N1b is in contact with the second electrode 24. Next, microwaves 39 are introduced into the waveguide 47. The microwaves 39 are introduced into the plasma generation chamber 46 through the quartz window 48 by the slot antenna 49. This generates high-density plasma 60.

[0037] This high-density plasma 60 then diffuses inside the plasma generation chamber 46 to become plasma 61. This plasma 61 contains ions of the radical source supplied from the radical source inlet 42. A gas containing hydrogen gas is used as the radical source. Most of the ions in the plasma 61 collide with the partition wall 44. The radicals 38 pass through the through-holes 14 in the partition wall 44 and enter the reaction chamber 10. Then, a voltage is applied between the first electrode 22 and the second electrode 24. This generates plasma 34 inside the reaction chamber 10.

[0038] Radicals 38 are present in the atmosphere of the plasma 34. Then, protrusions PR1 grow on the first surface N1a of the negative electrode current collector N1 in the atmosphere of this plasma 34. At that time, copper particles GR1 are scattered from the first surface N1a of the negative electrode current collector N1 and re-adhere to the first surface N1a of the negative electrode current collector N1.

[0039] The pressure inside the reaction chamber 10 is within a range of 5 to 2000 mTorr (0.65 Pa to 267 Pa). The temperature of the negative electrode current collector N1 is within a range of 0°C to 500°C, preferably 0°C to 400°C. Of course, these are merely examples and the temperature is not limited to these numerical ranges.

[0040] 6. Manufacturing method of lithium-ion secondary battery 6-1. Negative electrode manufacturing process The negative electrode NE is manufactured as described above. That is, a gas containing hydrogen is converted into plasma and supplied to the current collector, forming a plurality of protrusions made of the same material as the current collector on the first surface of the current collector.

[0041] 6-2. Positive electrode manufacturing process A positive electrode PE is manufactured by forming a positive electrode active material layer P2 on a positive electrode current collector P1. To this end, for example, a slurry containing the positive electrode active material is manufactured, and the slurry is applied to the positive electrode current collector P1 and dried.

[0042] 6-3. Electrode body manufacturing process The positive electrode PE and the negative electrode NE are wound together with the separator Sp1 positioned therebetween to form an electrode assembly.

[0043] 6-4. Sealing process The electrode assembly is inserted into the case, the case is filled with electrolyte, and the case is then sealed.

[0044] 6-5.Other Other steps such as an aging step may also be carried out.

[0045] 7. Effects of the First Embodiment The negative electrode NE of the lithium-ion secondary battery LiB1 of the first embodiment has a protrusion PR1. The protrusion PR1 is a single particle GR1 or an aggregate of multiple particles GR1 fused to the first surface N1a of the negative electrode current collector N1. Therefore, lithium is likely to deposit starting from the protrusion PR1. Therefore, the negative electrode NE does not have a negative electrode active material that absorbs lithium, such as a carbon material.

[0046] 8. Variations 8-1. Protrusion formation process Other treatments may be performed as the protrusion forming step. Examples of treatments in the protrusion forming step include pressure treatment such as pressing, chemical treatment, and sputtering using a metal target such as copper or aluminum.

[0047] 8-2. Plasma gas The plasma gas in the first embodiment is hydrogen gas, but other gases may be used as the plasma gas, such as oxygen gas.

[0048] 8-3.Plasma equipment A plasma device other than that in the first embodiment may be used, for example, an inductively coupled plasma (ICP). Of course, other plasma devices may also be used. [Example]

[0049] (Experiment 1) 1.Protrusion 1-1.Capacitively Coupled Plasma (CCP) A protrusion PR1 was formed on a copper foil (copper substrate) inside the manufacturing apparatus 1. The conditions are shown in Table 1. The flow rate of hydrogen gas was 50 sccm. The flow rate of Ar was 5 sccm. The microwave power (MW power) was 400 W. The power applied between the electrodes (CCP power) was 400 W. The temperature of the heater 25 was 560°C. The processing time was 10 minutes.

[0050] It should be noted that no gas is supplied from the raw material inlet 12 into the manufacturing apparatus 1. Therefore, hydrogen gas plasma is generated, and hydrogen radicals are supplied to the copper foil.

[0051] [Table 1] Conditions Protrusion formation process H2 (sccm) 50 Ar(sccm) 5 MW power (W) 400 CCP power (W) 400 Pressure (Pa) 2 Heater temperature (℃) 560 Processing time (min) 10

[0052] Figure 4 is a scanning electron microscope photograph (part 1) showing the surface of a copper foil after irradiating it with hydrogen radicals. Figure 4 shows that numerous copper particles have accumulated on the surface of the copper foil, forming protrusions. Judging from the shape of the particles observed, it is believed that the copper particles were knocked out of the copper foil by the irradiation of hydrogen radicals and reattached to the surface of the copper foil. Thus, the maximum length of the projected area of a single copper particle (Cu grain) projected onto the copper foil is approximately 40 nm. The maximum length of the projected area of a protrusion PR1, consisting of an aggregate of copper particles, projected onto the copper foil is between 100 nm and 200 nm. The projected area occupies more than 1 / 10 of the area of the first surface N1a of the negative electrode current collector N1.

[0053] 1-2. Inductively Coupled Plasma (ICP) In this experiment, the protrusion forming step was carried out using an ICP apparatus instead of the manufacturing apparatus 1. Table 2 shows the processing conditions in the ICP apparatus.

[0054] [Table 2] Conditions Protrusion formation process H2 (sccm) 100 Ar(sccm) 15 ICP power (W) 1000 Pressure (Pa) 3 Heater temperature (℃) 560 Processing time (min) 10

[0055] 1-2-1. Hydrogen gas supply amount and protrusions The number and size of the protrusions were investigated by changing the amount of hydrogen gas supplied. The bias applied to the substrate support was 0 V.

[0056] Figure 5 is a scanning electron microscope photograph (part 2) showing the surface of a copper foil after irradiating it with hydrogen radicals. The white areas are the protrusions.

[0057] Figure 6 is a graph showing the measurement results of the unevenness on the line in Figure 5. The horizontal axis in Figure 6 is position, and the vertical axis in Figure 6 is height from the reference plane. As shown in Figure 6, protrusions with a height of about 200 nm and a width of about 200 nm were observed. As can be inferred from Figure 4, the height and width of the protrusions are approximately the same.

[0058] The area of the white region in the scanning electron microscope was measured using the scanning electron microscope function. The area of the white region corresponds to the two-dimensional size of the protrusion.

[0059] Figure 7 shows the relationship between the amount of hydrogen supplied and the area of the protrusions when the protrusion area is 10 nm 2 More than 100nm 2 The horizontal axis of FIG. 7 is the hydrogen supply amount (sccm). The vertical axis of FIG. 7 is the 10 μm 2 When the hydrogen supply rate is 100 sccm, the area is 10 nm 2 More than 100nm 2 There tends to be a large number of small protrusions such as those shown below.

[0060] Figure 8 shows the relationship between the amount of hydrogen supplied and the area of the protrusions when the protrusion area is 100 nm 2 More than 1000nm 2 The horizontal axis of FIG. 8 is the hydrogen supply amount (sccm). The vertical axis of FIG. 8 is the 10 μm 2 When the hydrogen supply rate is 50 sccm, the area is 100 nm 2 More than 1000nm 2 There tends to be a high number of medium-sized protrusions below.

[0061] Figure 9 shows the relationship between the amount of hydrogen supplied and the area of the protrusions when the protrusion area is 1000 nm 2 More than 10000nm 2 9 is a graph showing the relationship between the number of protrusions and the amount of hydrogen supplied (sccm). The horizontal axis of FIG. 9 is the amount of hydrogen supplied (sccm). The vertical axis of FIG. 9 is the amount of hydrogen supplied (sccm). 2 When the hydrogen supply rate is 100 sccm, the area is 1000 nm 2 More than 10000nm 2 There tends to be a large number of large protrusions such as those below.

[0062] 10 is a graph showing the relationship between the amount of hydrogen supplied and the number of protrusions. The horizontal axis of FIG. 10 is the amount of hydrogen supplied (sccm). The vertical axis of FIG. 10 is 10 μm. 2 The number of protrusions tends to be higher when the hydrogen supply rate is 100 sccm.

[0063] As described above, when the hydrogen supply rate is 100 sccm, the number of protrusions tends to be large. In this case, the number of small protrusions and the number of large protrusions are large.

[0064] When the hydrogen supply rate is 50 sccm, the area is 100 nm 2 More than 1000nm 2 There tends to be a large number of medium-sized protrusions below this size. At this time, the number of large and small protrusions is not so large. Therefore, in this case, the protrusions are uniform in size to a medium level.

[0065] 1-2-2. Bias and protrusions The supply amount of hydrogen was set to 100 sccm, and the bias applied to the second electrode 24 was varied. The bias applied to the second electrode 24 was a DC bias.

[0066] Figure 11 shows the relationship between the bias size and the area of the protrusion, which is 10 nm. 2 More than 100nm 2 The horizontal axis of FIG. 11 is bias. The vertical axis of FIG. 11 is 10 μm. 2 As shown in Figure 11, by applying a negative bias, the area of the protrusions was reduced to 10 nm 2 More than 100nm 2 The number of protrusions below decreases.

[0067] Figure 12 shows the relationship between the bias size and the area of the protrusion, which is 100 nm 2 More than 1000nm 2 The horizontal axis of FIG. 12 is bias. The vertical axis of FIG. 12 is 10 μm. 2 As shown in Figure 12, when a bias of -25 V was applied, the area of the protrusions was 100 nm 2 More than 1000nm 2 The number of protrusions below 100 nm is the largest. 2 More than 1000nm 2 When forming a substrate having a large number of protrusions as described below, it is preferable to apply a bias of about -25V.

[0068] Figure 13 shows the relationship between the bias magnitude and the area of the protrusion, which is 1000 nm 2 More than 10000nm 2 The horizontal axis of FIG. 13 is bias. The vertical axis of FIG. 13 is 10 μm. 2 As shown in Figure 13, when a bias of -50 V was applied, the area of the protrusions was 1000 nm 2 More than 10000nm 2 The number of protrusions below this is the largest. 2 More than 10000nm2 When forming a substrate having a large number of protrusions as described below, it is preferable to apply a bias of about -50V.

[0069] Figure 14 is a graph showing the relationship between the magnitude of the bias and the number of protrusions. The horizontal axis of Figure 14 is the bias. The vertical axis of Figure 14 is 10 μm. 2 When a negative bias is applied, the number of protrusions tends to decrease as the absolute value of the bias increases.

[0070] When the bias is 0V, the area is 10nm 2 More than 100nm 2 When the bias is -25V, the number of small protrusions with an area of 100nm or less tends to be large. 2 More than 1000nm 2 When the bias is -50V, the number of medium-sized protrusions below 1000nm tends to be large. 2 More than 10000nm 2 There is a tendency for the number of large protrusions as follows to be large. When the bias is -100V, protrusions tend to be less likely to be formed regardless of their size.

[0071] The larger the absolute value of the negative bias, the more easily the hydrogen ions collide with the substrate, and the higher the kinetic energy of the hydrogen ions.

[0072] In this way, by selecting the amount of hydrogen supplied and the bias value, it is possible to control to some extent the size and number of protrusions formed on the substrate.

[0073] (Experiment 2) 2. Lithium-ion secondary battery 2-1.Protrusion A protrusion PR1 was formed on a copper foil (copper substrate) inside the manufacturing apparatus 1. The conditions are shown in Table 3. The flow rate of hydrogen gas was 100 sccm. The flow rate of Ar was 5 sccm. The microwave power (MW power) was 400 W. The power applied between the electrodes (CCP power) was 400 W. The temperature of the copper foil was 700°C. The processing time was 10 minutes.

[0074] Note that no raw material gas is supplied to the inside of the manufacturing apparatus 1. Therefore, hydrogen gas plasma is generated and hydrogen radicals are supplied to the copper foil.

[0075] [Table 3] Conditions Protrusion formation process H2 (sccm) 100 Ar(sccm) 5 MW power (W) 400 CCP power (W) 400 Pressure (Pa) 2 Heater temperature (℃) 700 Processing time (min) 10

[0076] FIG. 15 is a micrograph showing the surface of the copper foil before exposure to hydrogen plasma.

[0077] Fig. 16 is a micrograph showing the surface of the copper foil after hydrogen plasma exposure, and as shown in Fig. 16, many protrusions are formed on the surface of the copper foil.

[0078] 2-2.Charge and discharge characteristics of lithium-ion secondary batteries A lithium-ion secondary battery LiB1 of the first embodiment was manufactured. The positive electrode current collector P1 was aluminum, and the positive electrode active material was lithium cobalt oxide. The negative electrode current collector N1 was copper. The negative electrode was copper foil only, with no carbon material. The electrolyte was 1M LiPF6. The positive electrode active material layer had a diameter of 1.6 cm. The negative electrode active material layer had a diameter of 1.3 cm.

[0079] The positive electrode active material layer contained lithium cobalt oxide, a conductive additive, and a binder. The conductive additive was acetylene black. The binder was PVDF. The weight ratio of the lithium cobalt oxide, acetylene black, and PVDF was 100:5:3.

[0080] Figure 17 is a graph showing the charge / discharge characteristics of a lithium-ion secondary battery using copper foil with protrusions as the negative electrode. The horizontal axis of Figure 17 represents capacity. The vertical axis of Figure 17 represents voltage. The charge or discharge current was 0.5 mA. The capacity of this lithium-ion secondary battery was 12.6 mAh.

[0081] Figure 18 is a graph showing the charge / discharge characteristics of a lithium-ion secondary battery using copper foil without protrusions as the negative electrode. The horizontal axis of Figure 17 represents capacity. The vertical axis of Figure 17 represents voltage. The charge or discharge current was 0.5 mA. The capacity of this lithium-ion secondary battery was approximately 0.6 mAh.

[0082] In this way, the copper foil having no carbon material and having protrusions formed thereon functions as the negative electrode of a lithium ion secondary battery, whereas if no protrusions are present, the copper foil does not function as the negative electrode of a lithium ion secondary battery.

[0083] 2-3.Micrographs Figure 19 is a scanning electron microscope photograph (part 1) showing the cross section of the negative electrode of a lithium-ion secondary battery with protrusions after repeated charge and discharge. As shown in Figure 19, lithium is deposited on the copper foil. Furthermore, the surface of the lithium is flat, and no dendrite growth is observed. Because lithium is deposited in this way, the negative electrode does not need to contain a material that absorbs lithium, such as a carbon material.

[0084] Figure 20 is a scanning electron microscope photograph (part 2) showing the cross section of the negative electrode of a lithium ion secondary battery with protrusions after repeated charge and discharge. As shown in Figure 20, the lithium has a film thickness of about 40 μm. Also, as shown in Figure 20, the surface of the deposited lithium is very flat, and no dendrites have formed.

[0085] FIG. 21 is a scanning microscope photograph showing the surface of lithium deposited on the negative electrode of a lithium ion secondary battery having protrusions.

[0086] When protrusions are present on the copper foil in this manner, the protrusions have a surface onto which lithium can be deposited.

[0087] (Experiment 3) 3. Oxygen Plasma 3-1.Protrusion Oxygen gas was used instead of hydrogen gas. The plasma conditions are as shown in Table 4.

[0088] [Table 4] Conditions Protrusion formation process O2 (sccm) 150 MW power (W) 400 CCP power (W) 400 Pressure (Pa) 2 Heater temperature (℃) 20 Processing time (min) 10

[0089] FIG. 22 is a micrograph showing the surface of a copper foil after oxygen plasma exposure. 。

[0090] 3-2.Charge and discharge characteristics of lithium-ion secondary batteries As in Experiment 2, a lithium-ion secondary battery was fabricated.

[0091] Figure 23 is a graph showing the charge / discharge characteristics of a lithium-ion secondary battery when copper foil with protrusions formed by oxygen plasma was used as the negative electrode. The horizontal axis of Figure 23 is capacity. The vertical axis of Figure 23 is voltage. The charge or discharge current was 0.5 mA. The capacity of this lithium-ion secondary battery was 10.58 mAh.

[0092] Fig. 24 is a graph showing the results of a component analysis of copper foil on which protrusions were formed using oxygen plasma. As shown in Fig. 24, the copper foil after treatment with oxygen plasma contains a certain amount of oxygen atoms.

[0093] (Addendum) The negative electrode of the lithium ion secondary battery according to the first embodiment includes a current collector having a first surface, the current collector having a plurality of protrusions on the first surface, and the protrusions having a surface on which lithium can be deposited.

[0094] In the negative electrode of the lithium ion secondary battery in the second embodiment, the area of the projected region obtained by projecting the protrusion onto the first surface is 10 nm 2 More than 10000nm 2 The density of the protrusions is 1 / μm 2 More than 1000 pieces / μm 2 The following is the result.

[0095] In the negative electrode of the lithium ion secondary battery according to the third aspect, the average maximum length of the projected region of the protrusions projected onto the first surface is 10 nm or more and 200 nm or less, and the area occupied by the projected region is 1 / 10 or more of the area of the first surface.

[0096] In the negative electrode of the lithium ion secondary battery according to the fourth embodiment, the protrusions are made of the same material as the current collector, and are fused with the first surface of the current collector to be integrated with the current collector.

[0097] In the negative electrode of the lithium ion secondary battery according to the fifth embodiment, the current collector is made of copper.

[0098] The negative electrode of the lithium ion secondary battery in the sixth embodiment does not contain a carbon material.

[0099] A lithium ion secondary battery according to a seventh aspect includes a positive electrode and a negative electrode. The negative electrode includes a current collector having a first surface. The current collector includes a plurality of protrusions on the first surface. The protrusions have a surface on which lithium can be deposited.

[0100] In the eighth aspect of the method for manufacturing a negative electrode of a lithium ion secondary battery, a gas containing hydrogen gas is converted into plasma and supplied to a current collector, and a plurality of protrusions made of the same material as the current collector are formed on a first surface of the current collector.

[0101] In the ninth aspect of the method for producing a negative electrode for a lithium ion secondary battery, the protrusions are made of the same material as the current collector and are fused to the first surface of the current collector.

[0102] In a tenth aspect, an apparatus for manufacturing a negative electrode for a lithium ion secondary battery includes a plasma generation chamber that converts a gas containing hydrogen gas into plasma, and a reaction chamber that supplies the gas converted into plasma in the plasma generation chamber to a current collector and forms a plurality of protrusions made of the same material as the current collector on a first surface of the current collector.

[0103] In the eleventh aspect of the apparatus for manufacturing a negative electrode for a lithium ion secondary battery, the reaction chamber is made of the same material as the current collector, and forms a protrusion that is fused with the first surface of the current collector and is integrated with the current collector. [Explanation of symbols]

[0104] LiB1...Lithium-ion secondary battery PE: Positive electrode P1…Positive electrode current collector P2...Positive electrode active material layer NE...negative electrode N1…Negative electrode current collector N1a…Side 1 PR1…Protrusion GR1…particle Sp1...Separator ES1…Electrolyte V1…Container

Claims

1. A gas containing hydrogen gas is converted into plasma and supplied to a current collector made of copper, forming a plurality of protrusions made of the same material as the current collector on a first surface of the current collector;

2. 2. The method for producing a negative electrode of a lithium ion secondary battery according to claim 1, The protrusion is The material is the same as that of the current collector, The first surface of the current collector is fused to the first surface. A method for producing a negative electrode of a lithium ion secondary battery, comprising:

3. a plasma generation chamber for generating plasma from a gas containing hydrogen gas; a reaction chamber in which the gas plasmatized in the plasma generation chamber is supplied to a current collector made of copper, and a plurality of protrusions made of the same material as the current collector are formed on a first surface of the current collector; 2. A manufacturing apparatus for a negative electrode of a lithium ion secondary battery, comprising:

4. 4. The apparatus for manufacturing a negative electrode of a lithium ion secondary battery according to claim 3, The reaction chamber comprises: forming the protrusions, which are made of the same material as the current collector and which are fused with the first surface of the current collector to be integral with the current collector; 2. A manufacturing apparatus for a negative electrode of a lithium ion secondary battery, comprising:

Images