Cell

Abstract

To increase contact between a negative active material and a collector in a lithium ion secondary battery.SOLUTION: A cell 1 includes a negative electrode current collector 50, and a negative active material 40 disposed in the negative electrode current collector 50. The negative electrode current collector 50 includes: a metal layer 51 containing molybdenum and overlapping the negative active material 40; an oxide film layer 52 partially covering a surface of the metal layer 51 between the negative active material 40 and the metal layer 51; a plurality of first protrusions 53 containing silicon and located on a surface of the metal layer 51 that is not covered by the oxide film layer 52 between the negative active material 40 and the metal layer 51; and a plurality of second protrusions 54 containing silicon and located on a surface of the oxide film layer 52. The height of the plurality of first protrusions 53 is greater than the height of the plurality of second protrusions 54. Neighboring two first protrusions 53 of the plurality of first protrusions 53 have different heights.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to batteries. [Background technology]

[0002] Patent Document 1 discloses an electrode for a lithium secondary battery in which an intermediate layer containing Mo (molybdenum) is formed on a current collector, and a thin film is deposited on the intermediate layer. The thin film is formed of an active material (e.g., silicon) that absorbs and releases lithium ions. The material of the current collector is, for example, copper. The intermediate layer prevents copper from diffusing excessively into the thin film. This makes it possible to prevent a decrease in charge-discharge cycle life characteristics. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2002-373644 A Summary of the Invention [Problem to be solved by the invention]

[0004] Silicon, which is used as the material of the thin film in Patent Document 1, is sometimes used as a negative electrode active material to improve battery capacity. However, when silicon is used as the negative electrode active material, the volume change of the thin film during charging and discharging is relatively large, and the adhesion between the negative electrode active material and the current collector may decrease.

[0005] The present disclosure has been made in view of the above, and has an object to provide a battery capable of improving the adhesion between a negative electrode active material and a current collector. [Means for solving the problem]

[0006] The battery disclosed herein comprises a current collector and a negative electrode active material disposed on the current collector, the current collector comprising a metal layer containing molybdenum and overlapping the negative electrode active material, an oxide film layer between the negative electrode active material and the metal layer and partially covering a surface of the metal layer, and a plurality of first protrusions containing silicon and located on a surface of the metal layer not covered by the oxide film layer between the negative electrode active material and the metal layer, and a plurality of second protrusions containing silicon and located on the surface of the oxide film layer, wherein a height of the plurality of first protrusions is greater than a height of the plurality of second protrusions, and heights of two adjacent first protrusions in the plurality of first protrusions are different from each other. Effect of the Invention

[0007] According to the present disclosure, in a battery, the adhesion between the negative electrode active material and the current collector can be improved. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a battery according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a schematic diagram showing the configuration of the negative electrode current collector. [Diagram 3] FIG. 3 is a partially enlarged view of the negative electrode current collector shown in FIG. [Figure 4] FIG. 4 is a diagram showing a state in which two adjacent first protrusions have the same height. [Diagram 5] FIG. 5 is an enlarged view of the surface of a current collector having a desired anchoring effect. [Figure 6] FIG. 6 is a diagram showing a cross-sectional shape of the current collector shown in FIG. [Figure 7] FIG. 7 is a diagram showing a set of first protrusions formed by two first protrusions adjacent to each other. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments will be described in detail with reference to the drawings. Note that the present disclosure is not limited to these embodiments. It goes without saying that each embodiment is an example, and partial replacement or combination of the configurations shown in different embodiments is possible.

[0010] FIG. 1 is a schematic diagram showing a configuration of a battery 1 according to an embodiment of the present disclosure. The battery 1 is a secondary battery. Specifically, the battery 1 is a lithium battery. The battery 1 is an all-solid-state battery. The battery 1 includes a positive electrode current collector 10, a positive electrode active material 20, a solid electrolyte 30, a negative electrode active material 40, and a negative electrode current collector 50. The negative electrode current collector 50 corresponds to a "current collector."

[0011] The positive electrode current collector 10 is a conductive layer, and is, for example, a metal. Specifically, aluminum foil or the like can be used as the material of the positive electrode current collector 10. On the positive electrode current collector 10, a positive electrode active material 20 is disposed.

[0012] A metal oxide containing lithium ions is used for the positive electrode active material 20. The positive electrode active material 20 is, for example, lithium cobalt oxide or lithium nickel oxide.

[0013] The solid electrolyte 30 is sandwiched between the positive electrode active material 20 and the negative electrode active material 40. The solid electrolyte 30 is a sintered body. The material of the solid electrolyte is not particularly limited as long as it is a material that allows ions to move between the positive electrode active material 20 and the negative electrode active material 40. The material of the solid electrolyte is, for example, a sulfide, and Li6PS5Cl, Li3PS4, Li4SnS4, etc. are used. In other words, the solid electrolyte 30 is a sulfide-based solid electrolyte. The solid electrolyte 30 formed of a sulfide has excellent thermoformability, so that a good bonding interface with the active material of the positive electrode active material 20 can be formed.

[0014] Silicon is used for the negative electrode active material 40. When the negative electrode active material 40 is silicon, the volume change of the negative electrode active material 40 is relatively large when the battery 1 is charged and discharged. The negative electrode active material 40 is disposed on the negative electrode current collector 50.

[0015] 2 is a schematic diagram showing the configuration of the negative electrode current collector 50. The negative electrode current collector 50 includes a metal layer 51, an oxide film layer 52, a plurality of first protrusions 53, and a plurality of second protrusions .

[0016] The metal layer 51 contains molybdenum. In this embodiment, the metal layer 51 is formed only of molybdenum. Molybdenum has a relatively high sulfur resistance. That is, the metal layer 51 has a relatively high resistance to the solid electrolyte 30. The metal layer 51 overlaps the negative electrode active material 40. A surface of the metal layer 51 facing the negative electrode active material 40 (hereinafter referred to as the facing surface 51a) is partially covered with an oxide film layer 52. In other words, the facing surface 51a of the metal layer 51 has a covered portion 51b covered with the oxide film layer 52 and an exposed portion 51c not covered with the oxide film layer 52. The oxide film layer 52 partially covers the surface (facing surface 51a) of the metal layer 51 between the negative electrode active material 40 and the metal layer 51.

[0017] In this manner, the state in which the opposing surface 51a of the metal layer 51 is partially covered with the oxide film layer 52 is formed by partially removing the natural oxide film by, for example, sandblasting, from the state in which the entire opposing surface 51a of the metal layer 51 is covered with the natural oxide film. In other words, the oxide film layer 52 is a part of the natural oxide film formed on the opposing surface 51a of the metal layer 51.

[0018] The multiple first protrusions 53 are located in the exposed portion 51c. In other words, the multiple first protrusions 53 are located on the surface (opposing surface 51a) of the metal layer 51 that is not covered with the oxide film layer 52, between the negative electrode active material 40 and the metal layer 51. The multiple second protrusions 54 are located on the surface of the oxide film layer 52. The first protrusions 53 and the second protrusions 54 contain silicon. The linear expansion coefficient of silicon (approximately 2.6×10 -6 (1 / K) and the linear expansion coefficient of molybdenum (approximately 5.2×10 -6 (1 / K)) is extremely small. Therefore, separation between the first protrusion 53 and the opposing surface 51a due to temperature change is suppressed.

[0019] The silicon of the first protrusion 53 and the second protrusion 54 is amorphous. The spectrum peak observed by Raman spectroscopy for the silicon (amorphous silicon) of the first protrusion 53 and the second protrusion 54 is 480 cm -1 More than 490cm -1 The density of amorphous silicon is lower than that of silicon having a crystalline structure. Therefore, when the first protrusion 53 and the second protrusion 54 absorb lithium ions, the expansion of the first protrusion 53 and the second protrusion 54 is suppressed. The silicon of the first protrusion 53 and the second protrusion 54 may be silicon having a crystalline structure.

[0020] The first protrusion 53 and the second protrusion 54 are formed by depositing silicon by, for example, vapor deposition on the metal layer 51 from which the native oxide film has been partially removed as described above.

[0021] Specifically, silicon deposited on the exposed portion 51c of the facing surface 51a and the surface of the oxide film layer 52 grows while forming a crystal nucleus, thereby forming the first protrusion portion 53 and the second protrusion portion 54. The exposed portion 51c of the facing surface 51a is active, and silicon forms a crystal nucleus at the exposed portion 51c without migrating. On the other hand, the surface of the oxide film layer 52 is chemically more stable than the exposed portion 51c, and silicon forms a crystal nucleus while migrating at the surface of the oxide film layer 52. Therefore, the growth of silicon at the exposed portion 51c is faster than the growth of silicon at the surface of the oxide film layer 52. Therefore, the height of the multiple first protrusion portions 53 is higher than the height of the multiple second protrusion portions 54. The height of the first protrusion portion 53 and the height of the multiple second protrusion portions 54 are approximately 3 μm or more and 6 μm or less.

[0022] In a state in which the negative electrode active material 40 is disposed on the negative electrode current collector 50, the multiple first protrusions 53 bite into the negative electrode active material 40 to exert an anchor effect. Therefore, even if the volume of the negative electrode active material 40 changes during charging and discharging, the negative electrode current collector 50 is prevented from peeling off from the negative electrode active material 40. This can improve the adhesion between the negative electrode current collector 50 and the negative electrode active material 40. This can improve the charge / discharge cycle life characteristics.

[0023] Fig. 3 is a partially enlarged view of the negative electrode current collector 50 shown in Fig. 2. The heights of two adjacent first protrusions 53 in the plurality of first protrusions 53 are different from each other. When the heights of two adjacent first protrusions 53 are different from each other, peeling of the first protrusions 53 from the exposed portion 51c is suppressed as described below, compared to when the heights of the two first protrusions 53 are equal.

[0024] 4 is a diagram showing a state in which two adjacent first protrusions 53 have the same height. Two adjacent first protrusions 53 are connected to each other. As shown in FIG. 4, the upper end of the portion where the two adjacent first protrusions 53 are connected is defined as a connection point S. When the volume of the negative electrode active material 40 changes during charging and discharging, a force acts on each of the two first protrusions 53 from the negative electrode active material 40.

[0025] The moment generated at the connection point S by the force acting from the negative electrode active material 40 is higher when the heights of the two first protrusions 53 are equal to each other than when the heights of the two first protrusions 53 are different from each other. In other words, when the heights of the two first protrusions 53 are equal to each other, a crack is more likely to occur at the connection point S due to a change in volume of the negative electrode active material 40 than when the heights of the two first protrusions 53 are different from each other. If a so-called leak path is formed by this crack, the battery capacity decreases.

[0026] In this manner, the heights of two adjacent first protrusions 53 among the plurality of first protrusions 53 are different, thereby suppressing the formation of leak paths and the decrease in battery capacity. That is, the ratio Rh of the heights of the two first protrusions 53 is less than 1 (ratio Rh<1). The ratio Rh is a value obtained by dividing the height (HL: see FIG. 3) of the shorter first protrusion 53 of the two first protrusions 53 by the height (HH: see FIG. 3) of the taller first protrusion 53 (ratio Rh=HL / HH).

[0027] Furthermore, the height of the first protrusions 53 may increase due to stress (hereinafter referred to as residual stress) remaining in the manufacturing process (e.g., vapor deposition) of the first protrusions 53. When the height of the shorter first protrusion 53 of two adjacent first protrusions 53 increases, the heights of the two adjacent first protrusions 53 may become equal. Therefore, regarding the relationship in height between the two first protrusions 53, it is preferable that the heights of the two first protrusions 53 are different even if the height of the shorter first protrusion 53 of the two first protrusions 53 increases.

[0028] Assuming that all of the residual stress acts in a direction along the opposing surface 51a, the height of the first protrusion 53 increases based on the Poisson's ratio of silicon (0.26). If the height (HH) of the first protrusion 53 that is the taller of the two first protrusions 53 is set to "1", then if the height (HL) of the first protrusion 53 that is the shorter of the two first protrusions 53 is set to be smaller than "0.74 (=1-0.26)" (HL<0.74), the height (HL) of the shorter first protrusion 53 is smaller than "1" (i.e., HL+0.26<1) even if it is increased by the residual stress. In other words, even if the height of the shorter first protrusion 53 is increased by the residual stress, the heights of the two first protrusions 53 are different from each other. Therefore, the ratio Rh of the heights of the two first protrusions 53 is less than 0.74 (ratio Rh (=HL / HH)<0.74).

[0029] In order for the first protrusions 53 to exert the desired anchoring effect, it is desirable that the height ratio Rh of the two first protrusions 53 is 0.04 or more. This is derived by observing the surface of current collector B having the desired anchoring effect and the surface of a current collector not having the desired anchoring effect.

[0030] Fig. 5 is an enlarged view of the surface of current collector B having the desired anchor effect. Fig. 6 is a view showing the cross-sectional shape of current collector B shown in Fig. 5. The material of current collector B shown in Figs. 5 and 6 is copper. The anchor effect is determined by the shape of the surface of current collector B, regardless of the material of current collector B. Therefore, even if the material of first protrusion portion 53 of this embodiment is silicon, the observation results of the surface of current collector B in Figs. 5 and 6 are applicable.

[0031] In the current collector B shown in FIGS. 5 and 6, the surface of the current collector B is uneven, and the height ratio of two adjacent protrusions T is 0.04 or more. On the other hand, in a current collector (not shown) that does not have the desired anchor effect, the surface of the current collector is uneven, and the height ratio of two adjacent protrusions is 0.025 or more. Therefore, when the height ratio of two adjacent protrusions T is 0.04 or more, the desired anchor effect is exerted. Therefore, in the negative electrode current collector 50, the height ratio Rh of the two first protrusions 53 is 0.04 or more (Rh≧0.04).

[0032] Fig. 7 is a diagram showing a set of first protrusions C formed by two adjacent first protrusions 53. Fig. 7 shows a state in which the number of the set of first protrusions C per unit area is one. The opposing surface 51a shown in Fig. 7 is rectangular with the length of one side being unit length a. In other words, the area of ​​the opposing surface 51a shown in Fig. 7 corresponds to the unit area.

[0033] The number of first protrusions C per unit area, which is a set of two adjacent first protrusions 53, is 0.4×10 5 (pcs / mm 2 ) or more than 1.1×10 5 (pcs / mm 2) or less. This is derived by observing the surface of current collector B having the desired anchor effect and the surface of current collector B not having the desired anchor effect.

[0034] Specifically, in the current collector B having the anchor effect shown in FIG. 6, the pitch P in one direction of one set of protrusions Ct composed of two protrusions T is 3 to 5 μm. In other words, in a plan view of the current collector B, one set of protrusions Ct is present in a rectangular region with one side having a length of 3 to 5 μm. In other words, the number of one set of protrusions Ct per unit area is 0.4×10 5 (pcs / mm 2 ) or more than 1.1×10 5 (pcs / mm 2 ) or less.

[0035] On the other hand, in a current collector that does not have an anchor effect, the pitch of one pair of protrusions in one direction is 1 to 5 μm. In other words, the number of one pair of protrusions per unit area is 0.4×10 5 (pcs / mm 2 ) in some cases. Therefore, the number of protrusions Ct per unit area is less than 0.4 × 10 5 (pcs / mm 2 ) or more than 1.1×10 5 (pcs / mm 2 ) or less, the desired anchor effect is exerted. Therefore, in the negative electrode current collector 50, the number of the set of first protrusions C per unit area is 0.4×10 5 (pcs / mm 2 ) or more than 1.1×10 5 (pcs / mm 2 ) or less.

[0036] As described above, by determining the ratio Rh and the number per unit area of ​​one set of first protrusions C, the negative electrode current collector 50 reliably has a desired anchor effect. Therefore, peeling of the first protrusions 53 from the metal layer 51 is reliably suppressed, and the adhesion between the negative electrode current collector 50 and the negative electrode active material 40 can be reliably improved.

[0037] Lithium ions are also absorbed in the areas of the surface of the oxide film layer 52 where the second protrusions 54 are not formed. Therefore, the oxide film layer 52 contributes to improving the battery capacity.

[0038] 2, the oxide film layer 52 is present around the first protrusion 53. The oxide film layer 52 expands when it absorbs lithium ions. When the oxide film layer 52 expands, the first protrusion 53 is pressed in a direction along the opposing surface 51a and extends in the height direction. This further improves the anchor effect.

[0039] The above-described embodiments and modifications are intended to facilitate understanding of the present disclosure, and are not intended to limit the present disclosure. The present disclosure may be modified or improved without departing from the spirit of the present disclosure, and equivalents thereof are also included in the present disclosure.

[0040] For example, the solid electrolyte 30 may be an oxide-based solid electrolyte. Alternatively, the battery 1 may include a liquid electrolyte instead of the solid electrolyte 30.

[0041] The negative electrode active material 40 may be a carbon-based material and lithium titanate. The metal layer 51 may contain a metal other than molybdenum (e.g., tungsten, magnesium, etc.). The metal layer 51 may be laminated on the surface of another metal layer formed of another metal (e.g., stainless steel).

[0042] The battery 1 may be a secondary battery other than a lithium battery, or may be a primary battery.

[0043] The present disclosure may also be implemented in the following combinations:

[0044] (1) A current collector; a negative electrode active material disposed on the current collector; The current collector is a metal layer containing molybdenum and overlapping the negative electrode active material; an oxide film layer between the negative electrode active material and the metal layer, the oxide film layer partially covering a surface of the metal layer; a plurality of first protrusions containing silicon, the first protrusions being located on a surface of the metal layer that is not covered with the oxide film layer between the negative electrode active material and the metal layer; a plurality of second protrusions on a surface of the oxide film layer, the second protrusions containing silicon; The height of the plurality of first protrusions is greater than the height of the plurality of second protrusions, The heights of two adjacent first protrusions in the plurality of first protrusions are different from each other. battery.

[0045] (2) The ratio of the heights of the two first protrusions is less than 0.74; (1) The battery according to (1).

[0046] (3) The ratio of the heights of the two first protrusions is 0.04 or more; The battery according to (1) or (2).

[0047] (4) The number of first protrusions per unit area in one set of the two first protrusions is 0.4×10 5 (pcs / mm 2 ) or more than 1.1×10 5 (pcs / mm 2 ) or less, A battery according to any one of (1) to (3).

[0048] (5) The silicon of the first protrusion and the second protrusion is amorphous. A battery described in any one of (1) to (4).

[0049] (6) The metal layer is formed only of molybdenum. A battery described in any one of (1) to (5).

[0050] (7) Silicon is used as the negative electrode active material. A battery according to any one of (1) to (6).

[0051] (8) Further comprising a sulfide-based solid electrolyte; A battery according to any one of (1) to (7). [Explanation of symbols]

[0052] 1 battery 40 Negative electrode active material 50 Negative electrode current collector (current collector) 51 Metal layer 51a Opposite side 51c Exposed part 52 Oxide layer 53 1st protrusion 54 2nd protrusion C 1st protrusion of set Rh ratio

Claims

1. A current collector; a negative electrode active material disposed on the current collector; The current collector is a metal layer containing molybdenum and overlapping the negative electrode active material; an oxide film layer between the negative electrode active material and the metal layer, the oxide film layer partially covering a surface of the metal layer; a plurality of first protrusions, each of which contains silicon and is located on a surface of the metal layer that is not covered with the oxide film layer, between the negative electrode active material and the metal layer; a plurality of second protrusions on a surface of the oxide film layer, the second protrusions containing silicon; The height of the first protrusions is greater than the height of the second protrusions, The heights of two adjacent first protrusions in the plurality of first protrusions are different from each other. battery.

2. The ratio of the heights of the two first protrusions is less than 0.74; 10. The battery of claim 1.

3. The ratio of the heights of the two first protrusions is 0.04 or more.

10. The battery of claim 1.

4. The number of the first protrusions per unit area of ​​one set of the two first protrusions is 0.4×10 ５ (pcs / mm ２ ) or more 1.1 x 10 ５ (pcs / mm ２ ) is less than or equal to 10. The battery of claim 1.

5. The silicon of the first protrusion and the second protrusion is amorphous.

10. The battery of claim 1.

6. The metal layer is formed only of molybdenum.

10. The battery of claim 1.

7. Silicon is used as the negative electrode active material.

10. The battery of claim 1.

8. Further comprising a sulfide-based solid electrolyte; 10. The battery of claim 1.

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