Lithium secondary battery

Abstract

To provide a lithium secondary battery that can suppress powder falling from an electrode layer.SOLUTION: An all-solid-state battery 1 includes a power generating element 30 in which a positive electrode layer 40, a solid electrolyte layer 50, and a negative electrode layer 60 are stacked in this order, a positive electrode current collector 10 in contact with the positive electrode layer 40, a negative electrode current collector 20 in contact with the negative electrode layer 60, and a covering portion 70 that covers outer peripheral surfaces 41, 61 of the positive and negative electrode layers 40, 60 and is in contact with the positive and negative electrode current collectors 10, 20, and the covering portion 70 is in contact with the outer peripheral surfaces 41, 61 of the positive and negative electrode layers 40, 60 and includes a first contact portion 72 that has a first recess 721a and a first protrusion 722a.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a lithium secondary battery. [Background technology]

[0002] An all-solid-state battery is known in which the first current collector layer, the first active material layer, the second active material layer, the first solid electrolyte layer, and the second solid electrolyte layer extend outward beyond the third active material layer and the fourth active material layer to form an extension portion (see Patent Document 1). An insulating resin layer is also provided continuously over one surface of the first solid electrolyte layer, the side surface of the extension portion, and the other surface of the second solid electrolyte layer (see paragraph

[0043] and Figures 2 and 4 of Patent Document 1). This insulating resin layer prevents the battery from sliding off at its ends. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-4697 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-described conventional technology, the insulating resin layer has insufficient adhesion, and the insulating resin layer may peel off from the active material layer due to vibration or impact. In this case, further vibration or impact may cause friction between the peeled insulating resin layer and the active material layer, resulting in an increase in powder falling off from the active material layer.

[0005] The problem to be solved by the present invention is to provide a lithium secondary battery capable of suppressing powder falling off from the electrode layer. [Means for solving the problem]

[0006] The present invention solves the above problem by providing a first contact portion, which contacts the outer peripheral surface of the first electrode layer and has a first recess and a first protrusion, in a covering portion that covers the outer peripheral surface of the first electrode layer and contacts a first current collector. [Effects of the Invention]

[0007] According to the present invention, powder falling from the first electrode layer can be suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing an example of an all-solid-state battery according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing a modification of the power generating element and the first covering portion in the embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view showing a modified example of the positive electrode layer in the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] 1 is a cross-sectional view showing an all-solid-state battery 1 according to this embodiment. The all-solid-state battery 1 according to this embodiment corresponds to an example of the "lithium secondary battery" according to the present invention.

[0011] 1, the all-solid-state battery 1 includes a positive electrode current collector 10, a negative electrode current collector 20, a power generating element 30 interposed therebetween, and a covering portion 70. Note that, although Fig. 1 illustrates only a pair of the positive and negative electrode current collectors 10, 20 and a portion of the power generating element 30, the all-solid-state battery 1 may include a plurality of positive and negative electrode current collectors 10, 20 sandwiching the power generating element 30 therebetween, or may include a plurality of covering portions 70 covering the power generating element 30.

[0012] The positive electrode current collector 10 is a conductive plate-like (or foil-like) member and is made of, for example, a metal or a conductive resin, although it is not particularly limited thereto. Examples of metals that can be used include aluminum, nickel, iron, stainless steel, titanium, and copper. Alternatively, a clad material of nickel and aluminum, or a clad material of copper and aluminum may be used. Examples of conductive resins include resins in which a conductive filler is added to a non-conductive polymer material.

[0013] The negative electrode current collector 20, like the positive electrode current collector 10, is a conductive plate-like (or foil-like) member and is not particularly limited, and is made of, for example, a metal or a conductive resin. The metal and conductive resin may be the same materials as those used to make the positive electrode current collector 10. The material used to make the positive electrode current collector 10 and the material used to make the negative electrode current collector 20 may be the same or different.

[0014] A power generating element 30 is interposed between the positive and negative electrode current collectors 10, 20. This power generating element 30 has a positive electrode layer 40, a solid electrolyte layer 50, and a negative electrode layer 60. In this power generating element 30, the positive electrode layer 40, the solid electrolyte layer 50, and the negative electrode layer 60 are stacked in this order along the Z direction. Hereinafter, the Z direction in this embodiment may also be referred to as the stacking direction.

[0015] The positive electrode layer 40 is formed on the main surface of the positive electrode current collector 10. In this embodiment, the positive electrode layer 40 is a prismatic or cylindrical layer, and therefore the positive electrode layer 40 has a substantially rectangular cross section. Although not particularly limited, the positive electrode layer 40 can be formed by applying a paste containing a positive electrode active material and a binder to the main surface of the positive electrode current collector 10 and drying the paste.

[0016] The solid electrolyte layer 50 is provided on the positive electrode layer 40 and is interposed between the positive electrode layer 40 and the negative electrode layer 60. A solid electrolyte made of a material with low electronic conductivity can be used as the material for this solid electrolyte layer. For example, a sulfide solid electrolyte or an oxide solid electrolyte can be used, but a sulfide solid electrolyte is preferably used. The solid electrolyte layer 50 can be formed by, but is not limited to, applying a paste containing a solid electrolyte and a binder onto the positive electrode layer 40 and the covering portion 70 and drying the paste.

[0017] In this embodiment, a completely solid electrolyte layer composed only of a solid electrolyte is exemplified as the solid electrolyte layer 50 included in the all-solid-state battery 1, but the electrolyte layer is not limited to this. Instead of such a solid electrolyte layer 50, an electrolyte layer containing an electrolyte that is not solid in at least a portion thereof may be used. For example, the electrolyte layer may contain a polymer electrolyte or a liquid electrolyte in addition to a solid electrolyte.

[0018] The solid electrolyte layer 50 has an intervening portion 51 and a protruding portion 52. The intervening portion 51 is in direct contact with the positive electrode layer 40 and the negative electrode layer 60, and is interposed between the positive electrode layer 40 and the negative electrode layer 60. The protruding portion 52 protrudes outward from the intervening portion 51. The protruding portion 52 is not in direct contact with the positive electrode layer 40 or the negative electrode layer 60, and is sandwiched between the covering portions 70.

[0019] The anode layer 60 is formed on the solid electrolyte layer 50. In this embodiment, the anode layer 60 is a prismatic or cylindrical layer, and therefore the anode layer 60 has a substantially rectangular cross section. Although not particularly limited, the anode layer 60 can be formed by applying a paste containing a positive electrode active material and a binder to the main surface of the anode current collector 20 and drying the paste.

[0020] The covering portion 70 in this embodiment is disposed outside the positive electrode layer 40 and the negative electrode layer 60, and directly contacts and covers the outer peripheral surfaces 41, 61 of the positive electrode layer 40 and the negative electrode layer 60. In this way, the covering portion 70 fastens the positive electrode layer 40 and the negative electrode layer 60. The covering portion 70 can prevent the active material from sliding off from the positive electrode layer 40 and the negative electrode layer 60. In other words, powder falling off of the positive electrode layer 40 and the negative electrode layer 60 can be prevented.

[0021] The coating portion 70 is non-Li ion conductive and does not conduct lithium ions. The coating portion 70 also has electrical insulation properties. Because the coating portion 70 is non-Li ion conductive, lithium metal is less likely to deposit in the coating portion 70, which makes it possible to suppress the occurrence of a short circuit between the lithium metal and the positive electrode layer 40 or the positive electrode current collector 10.

[0022] The material for forming such a covering portion 70 is not particularly limited, and may be, for example, particles of a non-Li-ion conductive metal oxide such as alumina or zirconia. Alternatively, a resin material such as polyimide may be used as the material for forming the covering portion 70. However, since metal oxide particles are unlikely to retain Li-ion conductivity even after long-term use, it is preferable to use metal oxide particles as the material for forming the covering portion 70. The covering portion 70 may be formed by, but is not particularly limited to, curing a paste containing metal oxide particles and a binder.

[0023] The covering portion 70 in this embodiment includes a first covering portion 71 and a second covering portion 75. The first covering portion 71 is interposed between the protruding portion 52 of the solid electrolyte layer 50 and the positive electrode current collector 10, and is in direct contact with and covers the outer peripheral surface 41 of the positive electrode layer 40. The first covering portion 71 has a hollow ring shape, and the positive electrode layer 40 is located inside this first covering portion 71.

[0024] The first covering portion 71 includes a first contact portion 72 and a second contact portion 73. The first contact portion 72 is in direct contact with the outer peripheral surface 41 of the positive electrode layer 40 and covers the outer peripheral surface 41. The first contact portion 72 includes a plurality of (three in this example) first recesses 721a and a plurality of (two in this example) first protrusions 722a. In the first contact portion 72 of this embodiment, the first recesses 721a and the first protrusions 722a are arranged alternately adjacent to each other along the stacking direction. Therefore, the outer peripheral surface 41 of the positive electrode layer 40 has an uneven surface that complements the uneven surface of the first contact portion 72.

[0025] Although not particularly limited, the width of the first recess 721a in the Z direction can be 1 / 50 or more of the height of the first covering portion 71 in the Z direction. Similarly, the width of the first protrusion 722a in the Z direction can be 1 / 50 or more of the height of the first covering portion 71 in the Z direction. Furthermore, the depth of the first recess 721a in the X direction can be 1 / 50 or more of the height of the first covering portion 71 in the Z direction. Similarly, the height of the first protrusion 722a in the X direction can be 1 / 50 or more of the height of the first covering portion 71 in the Z direction.

[0026] Such a first contact portion 72 improves the adhesion at the interface between the first covering portion 71 and the positive electrode layer 40, thereby further suppressing peeling of the first contact portion 72. This makes it possible to suppress powder falling off from the positive electrode layer 40 and prevent the occurrence of a short circuit.

[0027] The first recess 721a is recessed in a direction away from the center of the power generating element 30 (-X direction in the figure), and the first protrusion 722a protrudes in a direction toward the center of the power generating element 30 (+X direction in the figure).

[0028] In this embodiment, the first recess 721a constitutes the lower end 72a of the first contact portion 72, and also constitutes the upper end 72b of the first contact portion 72. The lower end 72a in this embodiment corresponds to an example of the "first end" in the present invention, and the upper end 72b in this embodiment corresponds to an example of the "second end" in the present invention.

[0029] By forming the lower end 72a as the first recess 721a in this manner, the shape of the lower end of the positive electrode layer 40 can be made into a convex shape corresponding to the first recess 721a. This increases the contact area between the positive electrode layer 40 and the positive electrode current collector 10, thereby suppressing peeling between the positive electrode layer 40 and the positive electrode current collector 10. This suppresses powder falling from the positive electrode layer 40 and prevents short circuits. Furthermore, this increases the number of electron conduction paths between the positive electrode layer 40 and the positive electrode current collector 10, thereby suppressing current concentration.

[0030] Furthermore, by forming the upper end 72b as the first recess 721a, the shape of the upper end of the positive electrode layer 40 can be made into a convex shape corresponding to the first recess 721a. This increases the contact area between the positive electrode layer 40 and the solid electrolyte layer 50, thereby preventing peeling between the positive electrode layer 40 and the solid electrolyte layer 50. Furthermore, this increases the number of ion conduction paths between the positive electrode layer 40 and the solid electrolyte layer 50, thereby preventing current concentration.

[0031] In this embodiment, the lower end 72a and the upper end 72b are the first recessed portion 721a, but are not limited to this and may be the first protruding portion 722a. However, if the upper end 72b is the first protruding portion 722a, it is preferable to use the form shown in the following modified example.

[0032] 2 is an enlarged cross-sectional view showing a modified example of the power generating element 30 and the first covering portion 71 in this embodiment. As shown in FIG. 2, the upper end portion 72b of the first covering portion 71 in this modified example is a first convex portion 722a. The first convex portion 722a in this modified example corresponds to an example of the "third convex portion" in the present invention.

[0033] In this modified example, the outer peripheral surface 61 of the negative electrode layer 60 is located between the top 722b of the first convex portion 722a and the bottom 721b of the first concave portion 721a adjacent to the first convex portion 722a when viewed from the stacking direction (when viewed from the Z direction).

[0034] With such a position of the outer peripheral surface 61, the current concentrated at the upper end of the positive electrode layer 40 can be diffused near the outer peripheral surface 61, thereby suppressing current concentration (concentration of lithium ions). Furthermore, if the outer peripheral surface 61 is positioned outside the bottom 721b (on the −X direction side in the drawing) when viewed from the stacking direction, some lithium ions may have difficulty returning to the positive electrode layer 40. On the other hand, if the outer peripheral surface 61 is positioned inside the top 722b (on the +X direction side in the drawing) when viewed from the stacking direction, current concentration may be more likely to occur compared to this modified example.

[0035] Returning to FIG. 1 , the second contact portion 73 is in direct contact with the lower surface of the protruding portion 52 of the solid electrolyte layer 50. This second contact portion 73 includes a plurality of (three in this example) second recesses 731a and a plurality of (two in this example) second protruding portions 732a. In the second contact portion 73 of this embodiment, these second recesses 731a and second protruding portions 732a are arranged alternately adjacent to each other along the X direction in the figure. Therefore, the lower surface of the protruding portion 52 has an uneven surface that complements the uneven surface of the second contact portion 73.

[0036] Such second contact portion 73 improves the adhesion at the interface between the first covering portion 71 and the solid electrolyte layer 50, thereby further suppressing peeling of the second contact portion 73. This makes it possible to suppress powder falling off from the positive electrode layer 40 and prevent the occurrence of short circuits.

[0037] The second covering portion 75 is interposed between the protruding portion 52 of the solid electrolyte layer 50 and the negative electrode current collector 20, and is in direct contact with and covers the outer peripheral surface 61 of the negative electrode layer 60. Similar to the first covering portion 71, the second covering portion 75 has a hollow ring shape, and the negative electrode layer 60 is located inside this second covering portion 75.

[0038] The second covering portion 75 has a configuration basically similar to that of the first covering portion 71, and therefore a detailed description thereof will be omitted. That is, like the first covering portion 71, the second covering portion 75 includes a first contact portion having an uneven shape that directly contacts the outer peripheral surface 61 of the negative electrode layer 60, and a second contact portion having an uneven shape that contacts the upper surface of the protrusion 52 of the solid electrolyte layer 50. This makes it possible to suppress peeling at the interface between the second covering portion 75 and the negative electrode layer 60, and also to suppress peeling at the interface between the second covering portion 75 and the solid electrolyte layer 50. This makes it possible to suppress powder falling from the negative electrode layer 60, and to prevent the occurrence of a short circuit.

[0039] The all-solid-state battery 1 as described above can prevent peeling at the interface between the covering portion 70 and the power generating element 30, thereby preventing powder falling and the occurrence of short circuits.

[0040] Although the positive electrode layer 40 in the above embodiment is configured from a single layer, the present invention is not limited to this. The positive electrode layer 40 may be configured from multiple layers, as in the following modified examples.

[0041] 3 is a cross-sectional view showing a modification of the positive electrode layer 40 in this embodiment. As shown in FIG. 3, in this modification, a positive electrode stack 40A composed of a plurality of positive electrode layers 40a to 40c is provided instead of the positive electrode layer 40.

[0042] Each of the positive electrode layers 40a to 40b has a contact surface 42 that comes into contact with the other positive electrode layers, and these contact surfaces are provided at positions corresponding to the first protrusions 722a. In this embodiment, the contact surfaces are provided at positions adjacent to the tops 722b of the first protrusions 722a.

[0043] Such a positive electrode laminate 40A can be formed by, but is not limited to, the following method. First, a first coating portion 71 is formed on a positive electrode current collector 10. Next, a positive electrode paste containing a positive electrode active material and a binder is applied to the positive electrode current collector 10. At this time, the thickness of the applied positive electrode paste is set to a thickness such that the positive electrode paste overlaps with the tops 722b of the lower first protrusions 722a. Next, the applied positive electrode paste is dried to form the positive electrode layer 40a.

[0044] Next, positive electrode paste is applied onto the positive electrode layer 40a. At this time, the thickness of the applied positive electrode paste is set to a thickness that overlaps the top 722b of the upper first convex portion 722a. Next, the applied positive electrode paste is dried to form the positive electrode layer 40b.

[0045] Next, a positive electrode paste is applied onto the positive electrode layer 40b. At this time, the thickness of the applied positive electrode paste is set to a thickness that overlaps the upper end portion 72b of the first coating portion. Next, the applied positive electrode paste is dried to form the positive electrode layer 40c.

[0046] Since the positive electrode laminate 40A according to this modified example is formed as described above, gaps are unlikely to occur between the first covering portion 71 and the positive electrode laminate 40A, and peeling at the interface between the first covering portion 71 and the positive electrode laminate 40A can be suppressed, thereby suppressing powder falling and the occurrence of short circuits.

[0047] In the positive electrode laminate 40A of this modification, each of the positive electrode layers 40a to 40c has a contact portion 43 including a contact surface 42 and a non-contact portion 44 other than the contact portion 43. The binder concentration in the contact portion 43 can be made higher than the binder concentration in the non-contact portion 44.

[0048] This improves the adhesion between the positive electrode layers 40a to 40c in the positive electrode stack 40A, making the positive electrode layers 40a to 40c less likely to peel off from one another, further reducing the risk of short circuits due to powder falling off.

[0049] Although the above example illustrates a case where the covering portion 70 is formed before the positive electrode layer 40, the covering portion 70 may be formed by applying and drying a paste constituting the covering portion 70 onto the positive electrode layer 40 after the positive electrode layer 40 is formed. In this case, by making the outer peripheral surface 41 of the positive electrode layer 40 an uneven surface, a contact portion that corresponds complementarily to the uneven surface can be formed in the covering portion 70.

[0050] Moreover, such a positive electrode laminate 40A can be formed by a method of using a positive electrode paste with a high binder concentration near the top 722b of the first convex portion 722a, or by a method of providing a distribution in the binder concentration by utilizing the difference in specific gravity between the positive electrode active material and the binder.

[0051] Furthermore, although not particularly limited, the positive electrode layer 40 may have a tapered shape that narrows from the positive electrode current collector 10 toward the negative electrode current collector 20. In this case, the positive electrode layer 40 has a trapezoidal cross section.

[0052] In addition, in the above embodiment, the covering portion 70 covers both the positive electrode layer 40 and the negative electrode layer 60, but this is not limited to this, and the covering portion 70 may cover only one of the positive electrode layer 40 or the negative electrode layer 60. [Explanation of symbols]

[0053] 1…All-solid-state battery 10...Positive electrode current collector 20...Negative electrode current collector 30...Power generation element 40...Positive electrode layer 50...Solid electrolyte layer 60...Negative electrode layer 70...Covering part

Claims

1. a power generating element in which a first electrode layer, an electrolyte layer containing a solid electrolyte, and a second electrode layer are stacked in this order; a first current collector in contact with the first electrode layer; a second current collector in contact with the second electrode layer; a covering portion that covers an outer peripheral surface of the first electrode layer and is in contact with the first current collector, The covering portion is in contact with the outer peripheral surface of the first electrode layer and includes a first contact portion having a first recess and a first protrusion.

2. 2. The lithium secondary battery according to claim 1, a first end of the first contact portion contacting the first current collector; The first end portion of the lithium secondary battery is the first recess portion.

3. 2. The lithium secondary battery according to claim 1, a second end of the first contact contacting the electrolyte layer; The second end of the lithium secondary battery is the first recess.

4. 2. The lithium secondary battery according to claim 1, The covering portion is in contact with the electrolyte layer and includes a second contact portion having a second recess and a second protrusion.

5. The lithium secondary battery according to any one of claims 1 to 4, the first electrode layer is a positive electrode layer, the second electrode layer is a negative electrode layer, the covering portion is interposed between the first current collector and the electrolyte layer, the first recessed portion and the first protruding portion are aligned along the stacking direction of the power generating element, the first protrusion includes a third protrusion in contact with the electrolyte layer, A lithium secondary battery in which the outer surface of the second electrode layer is located between the top of the third convex portion and the bottom of the first concave portion adjacent to the third convex portion when viewed from the stacking direction.

6. 2. The lithium secondary battery according to claim 1, the first electrode layer is a positive electrode laminate composed of a plurality of positive electrode layers stacked on top of each other, the positive electrode layer includes a contact surface that contacts another positive electrode layer; The contact surface is provided at a position corresponding to the first protrusion.

7. 7. The lithium secondary battery according to claim 6, the positive electrode layer includes a positive electrode active material and a binder, The positive electrode layer is a contact portion including the contact surface; a non-contact portion other than the contact portion, A lithium secondary battery, wherein the concentration of the binder in the contact portion is higher than the concentration of the binder in the non-contact portion.

Images