Metal negative electrode of secondary battery and method for manufacturing the same

Abstract

To provide a metal negative electrode of a secondary battery which can make a manufacturing process easier and can suppress dendrite which grows to a positive electrode, and a method for manufacturing the metal electrode.SOLUTION: In a metal negative electrode 3 of a chargeable and dischargeable secondary battery 1, a small protruding shape 3a in the shape of a weight of which diameter becomes smaller in a position closer to a protrusion end 3aa is formed integrally with a surface H, the protrusion end 3aa of the small protruding shape 3a is formed of an acute angle, a bending circular cone, or an angular cone, and at least 50% of the whole small protrusion shapes 3a are small protrusion shapes in which a ratio of a size a of the bottom surface and a size b of the height direction is at least 1:3.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a metallic negative electrode for a rechargeable and dischargeable secondary battery and a method for producing the same. [Background technology]

[0002] For electric vehicles (EVs) such as electric cars and electric motorcycles, extending the driving range is considered an important issue, and in order to solve this issue, it is necessary to increase the capacity and voltage of the secondary batteries installed in the vehicles. There are various problems in increasing the capacity and voltage of such secondary batteries, one of which is the problem of dendrites that occur in the metal negative electrodes of secondary batteries.

[0003] Such dendrites are needle-like protrusions that occur on the metal negative electrode when the secondary battery is charged and discharged, and grow with repeated charging and discharging. When such dendrites grow, they may penetrate the separator and their tips may come into contact with the positive electrode, causing a short circuit. Therefore, as disclosed in Patent Document 1, for example, a technique has been disclosed for suppressing the growth of dendrites by fusing particles on the surface of the metal negative electrode to form protrusions in advance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-187895 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above-mentioned conventional technology, protrusions are formed by fusing particles onto the surface of the metal negative electrode of a lithium-ion secondary battery, which requires particles separate from the base material, complicates the manufacturing process and increases manufacturing costs, and is considered insufficient to suppress dendrites growing toward the positive electrode. As a result, when the secondary battery is repeatedly charged and discharged over a long period of time, the tips of the grown dendrites may come into contact with the positive electrode, causing a short circuit.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a metal negative electrode for a secondary battery that can simplify the manufacturing process and suppress dendrites growing toward the positive electrode, and a manufacturing method thereof. [Means for solving the problem]

[0007] The invention described in claim 1 is characterized in that in a metal negative electrode of a chargeable and dischargeable secondary battery, minute pyramidal protrusions whose diameter continuously decreases toward their tips are integrally formed on the surface.

[0008] A second aspect of the present invention is the metallic negative electrode of the secondary battery of the first aspect, wherein the minute protrusions have a shape of a cone or pyramid with an acute or curved tip.

[0009] The invention described in claim 3 is characterized in that, in the metal negative electrode of the secondary battery described in claim 2, the microprotrusion shapes have a ratio of bottom dimension to height dimension of 1:3 or more, accounting for 50% or more of the entire microprotrusion shapes.

[0010] The invention described in claim 4 is characterized in that, in the metal negative electrode of the secondary battery described in claim 1, the surface including the microprotrusion shape has a surface area at least twice as large as a flat surface on which the microprotrusion shape is not formed.

[0011] The invention described in claim 5 is characterized in that the metal negative electrode of the secondary battery described in claim 1 is made of a material selected from the group consisting of zinc, copper, lithium, magnesium, sodium, potassium, and calcium, as well as any of those containing these metals as components or alloys.

[0012] The invention described in claim 6 is a manufacturing method for a metal negative electrode of a rechargeable and dischargeable secondary battery, characterized in that a cone-shaped micro-protrusion shape whose diameter continuously decreases toward the tip is integrally formed on the surface by surface processing including dry surface processing in which the surface is irradiated with particle beams such as neutral atoms or neutral molecules, or quantum beams such as laser light or ion beams, or plasma, wet surface processing including chemical etching using a solution, and dry and wet film formation methods. Effect of the Invention

[0013] According to the present invention, minute pyramidal protrusions with a diameter that continuously decreases toward the tip are integrally formed on the surface, thereby simplifying the manufacturing process and suppressing dendrites growing toward the positive electrode. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing a secondary battery to which a metal negative electrode according to an embodiment of the present invention is applied; [Diagram 2] Schematic diagram showing the metal negative electrode of the secondary battery [Diagram 3] Schematic diagram showing the shape of microprojections formed on the metal negative electrode (before dendrite formation) [Figure 4] A schematic diagram showing the state in which dendrites are formed in the same microprojection shape. [Diagram 5] Micrograph showing the shape of the same microprojections (before dendrite formation) [Figure 6] A magnified micrograph showing the shape of the same microprojections (before dendrite formation) [Figure 7] Micrograph showing the shape of the same microprojections (after dendrite formation) [Figure 8]Magnified micrograph showing the shape of the same microprojections (after dendrite formation) [Figure 9] A graph showing the relationship between capacity and potential, comparing a metal negative electrode (roughened) on which a microprojection shape according to the present invention is formed and a metal negative electrode (untreated) on which a microprojection shape is not formed. [Figure 10] Graph showing experimental results when charging and discharging a metal negative electrode (with unevenness treatment) on which a microprojection shape according to the present invention is formed. [Figure 11] A graph showing the experimental results of repeated charging and discharging of a metal negative electrode (untreated) on which no microprojections were formed. [Figure 12] FIG. 13 is a schematic diagram showing the shape of a microprojection (a cone shape with a curved tip) according to another embodiment of the present invention. [Figure 13] FIG. 13 is a schematic diagram showing the shape of a minute protrusion (a pyramidal shape with an acute tip) according to another embodiment of the present invention; [Figure 14] FIG. 13 is a schematic diagram showing the shape of a microprojection (a pyramidal shape with a curved tip) according to another embodiment of the present invention. [Figure 15] FIG. 13 is a schematic diagram showing the shape of a microprojection (a cone shape with a truncated tip) according to another embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The metal negative electrode of this embodiment is composed of a metal plate-shaped member applied to a chargeable and dischargeable secondary battery, and the applicable secondary battery 1 is composed of a metal positive electrode 2, a metal negative electrode 3, a separator 4, a positive electrode side current collector 5, a negative electrode side current collector 6, and a case C containing an alkaline electrolyte (alkaline electrolyte E), as shown in Figure 1.

[0016] The metal positive electrode 2 is made of a sheet-like member (nickel foil) made of nickel (Ni) and is attached to the surface of the positive electrode side current collector 5, and is configured to be attached to the case C in a state facing the metal negative electrode 3 and the separator 4. The separator 4 is made of, for example, a nonwoven fabric, and is configured to be attached to a position between the metal positive electrode 2 and the metal negative electrode 3 in the case C.

[0017] The metal negative electrode 3 is made of a sheet-like member (zinc foil) made of zinc (Zn), and is attached to the surface of the negative electrode side current collector 6, and is configured to be attached to the case C in a state facing the metal positive electrode 2 and the separator 4. The metal negative electrode 3 may be made of a material selected from the group consisting of zinc, copper (Cu), lithium (Li), magnesium (Mg), sodium (Na), potassium (K), calcium (Ca), and metals containing these metals as components or alloys.

[0018] The secondary battery 1 can be charged or discharged by connecting a power source such as a battery or a load such as a motor between the positive electrode side current collector 5 in contact with the metal positive electrode 2 and the negative electrode side current collector 6 in contact with the metal negative electrode 3. In other words, the secondary battery 1 can convert electrical energy into chemical energy and store (charge) it by passing a current in the opposite direction to that during discharging.

[0019] 2 and 3, the metal negative electrode 3 according to this embodiment has a cone-shaped microprojection shape 3a whose diameter continuously decreases toward the tip 3aa integrally formed on the surface H. Specifically, the metal negative electrode 3 according to this embodiment has a plurality of microprojection shapes 3a whose tip 3aa is an acute-angled cone formed on its surface H, and those having a ratio of the dimension a (diameter dimension) of the bottom surface 3ab to the height dimension b (dimension from the tip 3aa to the bottom surface 3ab) of 1:3 account for 50% or more of the entire microprojection shapes 3a.

[0020] Such microprojection shapes 3a can be obtained, for example, by dry surface processing (sputtering processing) in which surface H is irradiated with particle beams such as neutral atoms or neutral molecules or quantum beams such as laser light, and a large number of microprojection shapes 3a are formed in groups as shown in the micrographs of Figures 5 and 6. Moreover, surface H including the microprojection shapes 3a of the metal negative electrode 3 according to this embodiment has a surface area at least twice as large as that of a plane on which the microprojection shapes 3a are not formed.

[0021] When the secondary battery 1 according to this embodiment is charged or discharged, dendrites D are generated on the side surfaces 3ac of the minute protrusion shapes 3a, as shown in Fig. 4. Specifically, zinc (Zn) which is the metal negative electrode dissolves in the electrolyte (such as alkaline electrolyte E) and becomes Zn+4OH - →Zn(OH)4 2- +2e - When the secondary battery 1 is charged, the electrical energy used during charging further converts the Zn(OH)4 2- →ZnO+H2O+2OH - This chemical reaction occurs, resulting in the precipitation of ZnO, known as dendritic seeds (see Figures 7 and 8).

[0022] When the secondary battery 1 is discharged, the dendrite D is composed of ZnO+H2O+2OH - →Zn(OH)4 2- The ZnO formed on the surface of the metal negative electrode dissolves due to a chemical reaction (see Figures 5 and 6), but as the secondary battery 1 is repeatedly charged and discharged, the ZnO continues to precipitate and gradually grows locally.

[0023] As dendrite D grows in this way, there is a possibility that its tip will break through separator 4 and reach metal positive electrode 2, and if the tip of dendrite D comes into contact with metal positive electrode 2, it will short circuit and cause loss of function of secondary battery 1. Furthermore, dendrite D precipitated in this embodiment contains insulating oxide (ZnO), and therefore may adversely affect the conductivity of metal negative electrode 3 compared to the initial surface state (Zn) which has excellent conductivity, and may deteriorate battery performance.

[0024] In contrast, the metal negative electrode 3 according to this embodiment has microprojection shapes 3a formed on its surface H, and the microprojection shapes 3a are pyramidal (conical) extending in a direction α perpendicular to the surface H as shown in Fig. 4, so that the dendrites D generated on the side surfaces 3ac grow in a direction shifted by a predetermined angle from the perpendicular direction α. ​​On the other hand, the separator 4 and metal positive electrode 2 of the secondary battery 1 are attached in the direction α perpendicular to the surface H of the metal negative electrode 3, so that it is difficult for the tip of the grown dendrite D to reach the separator 4 and the metal positive electrode 2, and therefore a short circuit of the secondary battery 1 can be suppressed.

[0025] However, since the metal negative electrode 3 has a plurality of microprojection shapes 3a formed on its surface H, the surface area is increased, and even if dendrites D containing insulating oxide (ZnO) are generated, deterioration of the electrical conductivity of the metal negative electrode 3 can be relatively suppressed. Furthermore, since the microprojection shapes 3a according to this embodiment are formed on the surface H of the metal negative electrode 3 by surface processing (ion beam irradiation processing (also called sputtering processing)), the surface is formed more directly, making it possible to eliminate the need for materials separate from the base material or particles resulting from processing, and simplifying the manufacturing process and materials.

[0026] Although the microprotrusion shape 3a according to this embodiment has a conical shape with an acute-angled tip 3aa as shown in Fig. 3, it may have a conical shape with a curved tip 3aa as shown in Fig. 12, a pyramidal shape with an acute-angled tip 3aa as shown in Fig. 13, or a pyramidal shape with a curved tip 3aa as shown in Fig. 14. Also, it may have a cut-shaped microprotrusion shape 3a in which the conical tip 3aa is cut out to form a plane (pointed tip surface) as shown in Fig. 15.

[0027] The microprotrusion shape 3a of the metal negative electrode 3 in this embodiment is formed by dry surface processing in which the surface is irradiated with particle beams such as neutral atoms or neutral molecules, or quantum beams such as laser light or ion beams, or plasma, but is not limited to this, and the cone-shaped microprotrusion shape 3a, whose diameter continuously decreases toward the tip 3aa, may be integrally formed on the surface H by wet surface processing including chemical etching using a solution, and surface processing including dry and wet film formation methods.

[0028] Next, experimental results showing the technical advantages of the metal negative electrode 3 according to this embodiment will be described. An example (unevenness treatment) was prepared in which the surface of a zinc foil (Zn) of 1 cm in length, 1 cm in width, and 50 μm in thickness was subjected to sputtering to form minute protrusions 3a, and a comparative example (untreated) in which the surface of a zinc foil (Zn) of 1 cm in length, 1 cm in width, and 50 μm in thickness was left flat without any treatment. 2 The chemical reaction that occurs when charging the secondary battery 1 with a current of Zn(OH)4 2- →ZnO+H2O+2OH - The relationship between the input current and the voltage was observed.

[0029] As a result, as shown in FIG. 9, the voltage required for the chemical reaction is larger in the Example than in the Comparative Example. In other words, the overvoltage for the generation of ZnO, which is a dendrite species, is smaller in the Example. This is thought to be because the Example has a larger surface area due to the formation of the unevenness treatment compared to the Comparative Example, which results in a smaller overvoltage per unit area. Therefore, it was found that the Example has a lower resistance on the electrode surface than the Comparative Example, and that the load applied when a current is passed through the metal negative electrode 3 can be reduced.

[0030] Next, an experiment was conducted in which the Example and Comparative Example were repeatedly discharged and charged, and the voltage was measured each time. As a result, the Example was able to measure a predetermined voltage even after about 200 discharge and charge cycles, as shown in Figure 10, whereas the Comparative Example was unable to measure a predetermined voltage after about 10 discharge and charge cycles, as shown in Figure 11. This shows that the Example has a significantly improved battery life compared to the Comparative Example.

[0031] According to this embodiment, the pyramidal microprojection shape 3a whose diameter continuously decreases toward the tip 3aa is integrally formed on the surface H, so that separate particles and the like are not required in the manufacturing process, the manufacturing process can be simplified, and dendrites D growing toward the metal positive electrode 2 can be suppressed. In particular, the microprojection shape 3a is formed of a cone or pyramid whose tip 3aa is acute-angled or curved, so that dendrites D growing toward the metal positive electrode 2 can be reliably suppressed.

[0032] Moreover, in the microprojection shapes 3a according to this embodiment, those having a ratio of the dimension a of the bottom surface 3ab to the dimension b in the height direction of 1:3 or more account for 50% or more of the entire microprojection shapes 3a, so that it is possible to reliably suppress dendrites D growing toward the metal positive electrode 2 while improving the surface area. Furthermore, as in this embodiment, the surface H including the microprojection shapes 3a has a surface area at least twice that of a plane on which the microprojection shapes 3a are not formed, thereby making it possible to further improve the surface area.

[0033] Furthermore, the metal negative electrode 3 according to this embodiment is made of a material selected from the group consisting of zinc, copper, lithium, magnesium, sodium, potassium, and calcium, and those metals contained in the components or alloys, and can be applied to a general-purpose secondary battery 1. In addition, the surface H is subjected to dry surface processing in which a particle beam such as a neutral atom or neutral molecule or a quantum beam such as a laser beam is irradiated, wet surface processing including chemical etching with a solution, and surface processing including dry and wet film formation methods, so that the cone-shaped microprojection shape 3a, the diameter of which is continuously reduced toward the tip 3aa, is integrally formed on the surface, and the surface of the base material can be deformed to form the microprojection shape 3a, and separate particles and the like are not required in the manufacturing process.

[0034] Although the present embodiment has been described above, the present invention is not limited to this, and for example, the applicable secondary battery 1 is not limited to rocking chair type secondary batteries such as zinc-air secondary batteries, zinc-nickel secondary batteries, zinc-silver secondary batteries, lithium-air secondary batteries, lithium-sulfur secondary batteries, magnesium-air secondary batteries, sodium-sulfur secondary batteries, potassium secondary batteries, calcium secondary batteries, and polyvalent ion secondary batteries, but may also be any one of systems that do not utilize a redox reaction in the positive electrode, such as a lithium ion capacitor. [Industrial Applicability]

[0035] The present invention can also be applied to devices with different external shapes or devices with added functions, etc., so long as they have the same gist as the present invention. [Explanation of symbols]

[0036] 1 Secondary battery 2 Metallic positive electrode 3 Metal anode 3a Micro protrusion shape 3aa tip 3ab bottom 3ac side 4. Separator 5 Positive electrode collector 6 Negative electrode collector C Case H surface D Dendrite E Electrolyte

Claims

1. In a metallic negative electrode of a rechargeable and dischargeable secondary battery, A metal negative electrode for a secondary battery, characterized in that minute pyramidal protrusions, the diameter of which decreases continuously toward the tip, are integrally formed on the surface.

2. 2. The metallic negative electrode of a secondary battery according to claim 1, wherein the minute protrusions have a shape of a cone or pyramid with an acute or curved tip.

3. 3. The metal negative electrode of a secondary battery according to claim 2, characterized in that the ratio of the bottom dimension to the height direction dimension of the microprotrusion shapes is 1:3 or more in 50% or more of the total microprotrusion shapes.

4. 2. The metallic negative electrode of a secondary battery according to claim 1, wherein the surface including said minute protrusions has a surface area at least twice as large as a flat surface on which said minute protrusions are not formed.

5. 2. The metallic negative electrode of the secondary battery according to claim 1, characterized in that it is made of a material selected from the group consisting of zinc, copper, lithium, magnesium, sodium, potassium and calcium, and alloys containing these metals as components.

6. A method for producing a metal negative electrode of a chargeable and dischargeable secondary battery, comprising: A method for manufacturing a metal negative electrode for a secondary battery, characterized in that a cone-shaped micro-protrusion shape that continuously reduces in diameter toward its tip is integrally formed on the surface by surface processing including dry surface processing in which the surface is irradiated with particle beams such as neutral atoms or neutral molecules, or quantum beams such as laser light or ion beams, or plasma, wet surface processing including chemical etching using a solution, and dry and wet film formation methods.

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