Lithium secondary cell

Abstract

A lithium secondary cell (1) comprises: a positive electrode current collector (10); a positive electrode layer (40) formed on the positive electrode current collector; a negative electrode current collector (20); a negative electrode layer (50) formed on the negative electrode current collector; an electrolyte layer (60) provided between the positive electrode layer and the negative electrode layer and containing a solid electrolyte; and an insulator (70) having a frame shape surrounding the periphery of the positive electrode layer. The positive electrode layer includes a first surface (40a) in contact with the positive electrode current collector, a second surface (40c) on the opposite side from the first surface, and a lateral surface (40b) surrounded by the insulator. The insulator has an interposed part (71) interposed between the second surface and the negative electrode layer.

Description

Lithium secondary battery

[0001] The present invention relates to a lithium secondary battery containing a solid electrolyte in an electrolyte layer.

[0002] An all-solid-state lithium-ion secondary battery is known that includes a positive electrode layer, a positive electrode current collector, a negative electrode layer, a negative electrode current collector, a solid electrolyte layer, and an insulating film provided on the outer periphery of the positive electrode layer (Patent Document 1).

[0003] JP 2013-182842 A

[0004] In the above-mentioned lithium secondary battery, lithium ions (Li ＋ ) causes metallic lithium to deposit outside the negative electrode layer. As a result, if the deposited metallic lithium grows, it may come into contact with the positive electrode current collector, causing a short circuit.

[0005] The problem to be solved by the present invention is to provide a lithium secondary battery capable of suppressing the occurrence of short circuits by suppressing the deposition of metallic lithium.

[0006] The present invention solves the above problem by providing an insulator having a frame shape that surrounds the positive electrode layer, and by having this insulator have an intervening portion that is interposed between the negative electrode layer and a second surface that is located on the opposite side of the first surface that contacts the positive electrode current collector.

[0007] According to the present invention, the interposed portion can restrict the conduction path of lithium ions, thereby suppressing the deposition of metallic lithium in the portion outside the negative electrode layer, thereby suppressing the occurrence of short circuits due to the deposited metallic lithium.

[0008] Fig. 1 is a plan view showing a lithium secondary battery according to an embodiment of the present invention. Fig. 2 is a plan view showing a positive electrode current collector, a positive electrode tab, a power generating element, and an insulator according to an embodiment of the present invention. Fig. 3 is a cross-sectional view showing a power generating element, positive and negative electrode current collectors, and positive and negative electrode tabs in a cross section taken along line II-II in Fig. 1. Fig. 4 is a cross-sectional view showing a first modified example of a lithium secondary battery according to an embodiment of the present invention. Fig. 5 is a cross-sectional view showing a second modified example of a lithium secondary battery according to an embodiment of the present invention.

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

[0010] FIG. 1 is a plan view showing a lithium secondary battery 1 according to this embodiment. FIG. 2 is a plan view showing a positive electrode current collector 10, a positive electrode tab 15, a power generating element 30, and an insulator 70 according to this embodiment. FIG. 3 is a cross-sectional view showing the power generating element 30, the positive and negative electrode current collectors 10 and 20, and the positive and negative electrode tabs 15 and 25 in a cross section taken along line II-II in FIG. 1 . Note that FIG. 2 omits the illustration of the negative electrode current collector 20, the negative electrode tab 25, and the exterior body 80. Furthermore, for convenience, this embodiment describes a lithium secondary battery 1 having one power generating element 30, one positive and negative electrode current collector 10 and 20, and one positive and negative electrode tab 15 and 25, but this is not limited thereto, and the lithium secondary battery 1 may have a plurality of these.

[0011] As shown in FIG. 1 , the lithium secondary battery 1 in this embodiment includes a positive electrode current collector 10, a positive electrode tab 15, a negative electrode current collector 20, a negative electrode tab 25, a power generating element 30, an insulator 70, and an exterior body 80.

[0012] As shown in Fig. 2, 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 also be used. Examples of conductive resins include resins in which a conductive filler is added to a non-conductive polymer material.

[0013] The positive electrode current collector 10 in this embodiment has a main body portion 11 and an extension portion 12. The main body portion 11 is rectangular in plan view (when the positive electrode current collector 10 is viewed along the Z direction in the figure). The main body portion 11 has an outer shape composed of a first side 101, a second side 102, a third side 103, and a fourth side 104.

[0014] The extension portion 12 is a portion that extends from the first side 101 of the main body portion 11 so as to protrude in the −X direction in the figure. The width of this extension portion 12 in the Y direction is smaller than the width of the main body portion 11, and the extension portion 12 has a smaller rectangular shape than the main body portion 11. This extension portion 12 is joined to the positive electrode tab 15. Note that the positive electrode current collector 10 does not necessarily have to have such an extension portion 12. In that case, the positive electrode current collector 10 is joined to the positive electrode tab 15 in the vicinity of the first side 101.

[0015] The positive electrode tab 15 is a plate-like (or foil-like) member having electrical conductivity. The material constituting the positive electrode tab 15 and the material constituting the positive electrode current collector 10 may be the same or different. The positive electrode tab 15 is joined to the extension portion 12 of the positive electrode current collector 10. As shown in FIG. 1 , the positive electrode tab 15 extends from the inside to the outside of the exterior body 80.

[0016] The negative electrode current collector 20 is a conductive plate-like (or foil-like) member, similar to the positive electrode current collector 10, and has a shape obtained by inverting the shape of the positive electrode current collector 10 in the left-right direction in the drawing, although it is not particularly limited thereto. The material constituting this negative electrode current collector 20 can be the same as the material constituting the above-mentioned positive electrode current collector 10. Note that the material constituting the positive electrode current collector 10 and the material constituting the negative electrode current collector 20 may be different.

[0017] The negative electrode tab 25 is a plate-like (or foil-like) member having electrical conductivity. The material constituting the negative electrode tab 25 and the material constituting the negative electrode current collector 20 may be the same as or different from each other. The negative electrode tab 25 is joined to the negative electrode current collector 20. The negative electrode tab 25 extends from the inside to the outside of the exterior body 80.

[0018] 3 , the power generating element 30 is sandwiched between a positive electrode current collector 10 and a negative electrode current collector 20. The power generating element 30 is an element that contributes to the charging and discharging of the lithium secondary battery 1. The power generating element 30 includes a positive electrode layer 40, a negative electrode layer 50, and an electrolyte layer 60.

[0019] The positive electrode layer 40 is formed on the main surface 105 of the positive electrode current collector 10. The positive electrode layer 40 has a tapered shape that narrows from the positive electrode current collector 10 toward the negative electrode current collector 20, and as a result, the positive electrode layer 40 has a trapezoidal cross section. The positive electrode layer 40 can be formed by, but is not particularly limited to, applying a paste containing a positive electrode active material and a binder to the main surface 105 of the positive electrode current collector 10 and drying the paste.

[0020] The positive electrode layer 40 includes a first end face 40a, a side face 40b, and a second end face 40c. The first end face 40a is in contact with the main surface 105 of the positive electrode current collector 10 and is a surface that is approximately parallel to the main surface 105 of the positive electrode current collector 10. The first end face 40a in this embodiment corresponds to an example of the "first surface" in the present invention, and the second end face 40c in this embodiment corresponds to an example of the "second surface" in the present invention.

[0021] The side surface 40b is covered with an insulator 70. The side surface 40b is formed so as to surround the first end surface 40a and the second end surface 40c. The side surface 40b is a flat surface that slopes toward the center of the positive electrode layer 40 as it approaches the negative electrode current collector 20 from the positive electrode current collector 10. The side surface 40b is not perpendicular to the main surface of the positive electrode current collector 10. Note that the side surface 40b does not have to be sloped. In other words, the side surface 40b may be perpendicular to the main surface 105 of the positive electrode current collector 10.

[0022] The second end face 40c is the end face opposite to the first end face 40a. The second end face 40c is covered with the electrolyte layer 60 and the insulator 70. The second end face 40c is a flat surface that is approximately parallel to the main surface 105 of the positive electrode current collector 10.

[0023] The negative electrode layer 50 is formed on the main surface 205 of the negative electrode current collector 20. The negative electrode layer 50 in this embodiment has a rectangular cross section, but is not limited thereto, and may have a trapezoidal cross section like the positive electrode layer 40.

[0024] In this embodiment, the negative electrode layer 50 is shown in a fully discharged state. The negative electrode layer 50 includes an intermediate layer 51. The intermediate layer 51 is a layer for assisting the deposition of a lithium metal layer, and contains a material capable of absorbing and releasing lithium ions.

[0025] The lithium metal layer is composed of lithium metal deposited on the main surface 205 of the negative electrode current collector 20. The volume of this lithium metal layer increases as lithium metal is deposited during charging of the lithium secondary battery 1, and decreases as lithium metal is lost (moves toward the positive electrode layer 40) during discharging. The lithium metal layer may be deposited between the intermediate layer 51 and the negative electrode current collector 20, or between the intermediate layer 51 and the electrolyte layer 60.

[0026] The electrolyte layer 60 is interposed between the positive electrode layer 40 and the negative electrode layer 50. The electrolyte layer 60 may include a solid electrolyte made of a material with low electronic conductivity. As the solid electrolyte, for example, a sulfide solid electrolyte or an oxide solid electrolyte can be used, but it is preferable to use a sulfide solid electrolyte.

[0027] Examples of sulfide solid electrolytes include LiI-Li ２ S-SiS ２ , LiI-Li ２ S-P ２ O ５ , LiI-Li ３ P.O. ４ -P ２ S ５ , Li ２ S-P ２ S ５ , LiI-Li ３ P.S. ４ , LiI-LiBr-Li ３ P.S. ４ , Li ３ P.S. ４ , Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -Li ２ O, Li２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-SiS ２ , Li ２ S-SiS ２ - LiI, Li ２ S-SiS ２ - LiBr, Li ２ S-SiS ２ -LiCl, Li ２ S-SiS ２ -B ２ S ３ - LiI, Li ２ S-SiS ２ -P ２ S ５ - LiI, Li ２ S-B ２ S ３ , Li ２ S-P ２ S ５ -Z ｍ S ｎ (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li ２ S-GeS ２ , Li ２ S-SiS ２ -Li ３ P.O. ４ , Li ２ S-SiS ２ -Li ｘ MO ｙ (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In). ２ S-P ２ S ５ " The statement Li ２ S and P ２ S ５ The same applies to the other descriptions above. Alternatively, sulfide glass or the like may be used as the sulfide solid electrolyte.

[0028] As the oxide solid electrolyte, for example, a compound having a NASICON structure can be used. Examples of the compound having a NASICON structure include compounds represented by the general formula Li １＋ｘ Al ｘ Ge ２－ｘ (P.O. ４ ) ３ (0≦x≦2) (LAGP), a compound represented by the general formula Li １＋ｘ Al ｘ Ti ２－ｘ (P.O. ４ ) ３ (0≦x≦2) (LATP) and the like can be used. In addition, other oxide solid electrolytes include LiLaTiO (for example, Li ０．３４ La ０．５１ TiO ３ ), LiPON (e.g., Li ２．９ P.O. ３．３ N ０．４６ ), LiLaZrO (e.g., Li ７ La ３ Zr ２ O １２ ) etc. can be used.

[0029] Although not particularly limited, this electrolyte layer 60 is formed by transferring the positive electrode layer 40 and the insulator 70 while applying pressure. The electrolyte layer 60 may contain a non-solid electrolyte, and may contain, for example, a polymer electrolyte or a liquid electrolyte in addition to a solid electrolyte.

[0030] 1 to 3, the insulator 70 has a rectangular frame shape that surrounds the periphery of the positive electrode layer 40. The insulator 70 in this embodiment has electrical insulating properties. Furthermore, the insulator 70 is non-Li ion conductive and does not conduct lithium ions or suppresses the conduction of lithium ions.

[0031] The material for constituting the insulator 70 is not particularly limited, but may be, for example, metal oxide particles such as alumina or zirconia, a resin material, etc. Although not particularly limited, the insulator 70 can be formed by applying a paste containing a mixture of the above-mentioned metal oxide particles, a binder, etc. to the positive electrode current collector 10 so as to cover the positive electrode layer 40, and then drying the paste.

[0032] 3, the insulator 70 has an intervening portion 71 and a peripheral portion 72. The intervening portion 71 is interposed between the second end face 40c of the positive electrode layer 40 and the negative electrode layer 50, and is sandwiched between the second end face 40c and the electrolyte layer 60. The intervening portion 71 also directly contacts and covers the peripheral region of the second end face 40c.

[0033] The intervening portion 71 does not have to be in direct contact with the outer peripheral region of the second end face 40c; for example, a portion of the electrolyte layer 60 may be disposed between the intervening portion 71 and the outer peripheral region of the second end face 40c.

[0034] 2 and 3 , the interposition portion 71 includes a first portion 711 and a second portion 712. As shown in Fig. 2 , the first portion 711 constitutes one side of the rectangular frame-shaped interposition portion 71. The first portion 711 is located on the side of the positive electrode tab 15 and the extension portion 12 in the lithium secondary battery 1. On the other hand, the second portion 712 constitutes the other three sides of the interposition portion 71.

[0035] As shown in FIG. 3, the thickness T １ is the thickness T of the second portion 712 ２ It is thicker than １ >T ２ ). Such a thickness relationship can limit the lithium ion conduction path in the electrolyte layer 60 on the positive electrode tab 15 side, and can suppress the deposition of lithium metal in the portion outside the negative electrode layer 50 where no restraining pressure is applied. This can suppress the deposited lithium metal from going around from the negative electrode layer 50 to the positive electrode current collector 10 and contacting it, causing a short circuit. Furthermore, the thickness T ２By making the insulator 70 relatively thin, the volume of the insulator 70 that does not contribute to charging and discharging can be reduced, and the energy density of the lithium secondary battery 1 can be improved.

[0036] In addition, the thickness T of the first portion 711 １ is the thickness T of the electrolyte layer 60 ３ It is more than half the size of (T １ ≧½×T ３ ), the thickness T of the second portion 712 ２ is the thickness T of the electrolyte layer 60 ３ It is more than half the ２ ≧½×T ３ ) Such a thickness relationship can limit the lithium ion conduction paths in the electrolyte layer 60, and can suppress deposition of lithium metal in a portion outside the negative electrode layer 50 that is not subjected to a restraining pressure. This can suppress a short circuit between the deposited lithium metal and the positive electrode current collector 10.

[0037] Furthermore, the width W of this first portion 711 １ is the width W of the second portion 712 ２ is larger than (W １ >W ２ ) Such a width relationship can limit the lithium ion conduction path in the electrolyte layer 60 on the positive electrode tab 15 side, and can suppress the deposition of lithium metal in the portion outside the negative electrode layer 50 where no restraining pressure is applied. This can suppress the deposited lithium metal from wrapping around from the negative electrode layer 50 to the positive electrode current collector 10 and contacting it, causing a short circuit. Furthermore, the width W ２ By making the volume of the insulator 70 that does not contribute to charging and discharging small, the energy density of the lithium secondary battery 1 can be improved.

[0038] In addition, the width W of the first portion 711 １ is the thickness T of the electrolyte layer 60 ３ and is between 1 / 2 and 1 times (1≧W １ ≧½×T ３ ), the width W of the second portion 712 ２ is the thickness T of the electrolyte layer 60 ３is between 1 / 2 and 1 (1 ≧ W ２ ≧½×T ３ ) The interposed portion 71 having such a thickness can restrict the lithium ion conduction path in the electrolyte layer 60, and can suppress the deposition of lithium metal in a portion outside the negative electrode layer 50 that is not subjected to the restraining pressure. This can suppress a short circuit between the deposited lithium metal and the positive electrode current collector 10.

[0039] Furthermore, the interposition portion 71 in this embodiment has an upper surface 71 a and an inner peripheral surface 71 b, and includes a chamfered portion 713 between the upper surface 71 a and the inner peripheral surface 71 b. The chamfered portion 713 is formed in a rectangular ring shape. The formation of such a chamfered portion 713 can suppress the occurrence of cracks in the electrolyte layer 60 that comes into contact with the corners of the interposition portion 71 of the insulator 70 when the electrolyte layer 60 is transferred to the positive electrode layer 40 and the insulator 70.

[0040] The outer peripheral portion 72 has a rectangular frame shape and is formed integrally with the intermediate portion 71. The outer peripheral portion 72 is formed outside the intermediate portion 71 and surrounds the periphery of the intermediate portion 71. The outer peripheral portion 72 includes a portion sandwiched between the electrolyte layer 60 and the side surface 40b of the positive electrode layer 40, and a portion sandwiched between the electrolyte layer 60 and the positive electrode current collector 10.

[0041] The outer peripheral surface 72a of the outer peripheral portion 72 is the outermost end of the insulator 70 and is located outside the outermost end of the positive electrode layer 40, the outermost end of the electrolyte layer 60, and the outermost end of the negative electrode layer 50. That is, the outer diameter of the insulator 70 is larger than the outer diameter of the positive electrode layer 40, the outer diameter of the electrolyte layer 60, and the outer diameter of the negative electrode layer 50. In other words, a portion of the upper surface 70a of the insulator 70 is exposed without being covered by the electrolyte layer 60. This increases the creepage distance required for the deposited lithium metal to travel from the negative electrode layer 50 to the positive electrode current collector 10, thereby suppressing the occurrence of a short circuit.

[0042] The outer periphery 72 includes a third portion 721 and a fourth portion 722 as portions sandwiched between the electrolyte layer 60 and the positive electrode current collector 10. As shown in Fig. 2 , the third portion 721 constitutes one side of the rectangular frame-shaped outer periphery 72. The third portion 721 is located on the side of the positive electrode tab 15 and the extension portion 12 in the lithium secondary battery 1. On the other hand, the fourth portion 722 constitutes the other three sides of the outer periphery 72.

[0043] The width W of the third portion 721 ３ is the width W of the fourth portion 722 ４ is larger than (W ３ >W ４ ). This width relationship can limit the lithium ion conduction path in the electrolyte layer 60 on the positive electrode tab 15 side, and can suppress the deposition of lithium metal in the portion outside the negative electrode layer 50 where no restraining pressure is applied. This prevents the deposited lithium metal from wrapping around from the negative electrode layer 50 to the positive electrode current collector 10 and contacting it, causing a short circuit. Furthermore, the width W ４ By making the volume of the insulator 70 that does not contribute to charging and discharging small, the energy density of the lithium secondary battery 1 can be improved.

[0044] 1 , the exterior body 80 houses a positive electrode current collector 10, a positive electrode tab 15, a negative electrode current collector 20, a negative electrode tab 25, a power generating element 30, and an insulator 70. The pair of positive and negative electrode tabs 15, 25 extend from the inside of the exterior body 80 to the outside of the exterior body 80. Although not particularly limited, the exterior body 80 can be produced by bonding the outer peripheries of two laminate films together by thermocompression bonding or the like.

[0045] In the lithium secondary battery 1 as described above, by covering the outer peripheral region of the second end face 40c of the positive electrode layer 40 with the interposition portion 71, it is possible to restrict the conductive path of lithium ions and suppress the deposition of metallic lithium in the portion outside the negative electrode layer 50. This also makes it possible to suppress the occurrence of short circuits due to the deposited metallic lithium.

[0046] In the above embodiment, the upper surface of the insulator 70 is a plane that is substantially parallel to the main surface 105 of the positive electrode current collector 10, but this is not limiting. The upper surface of the insulator 70 may be inclined with respect to the main surface 105 of the positive electrode current collector 10.

[0047] Alternatively, as shown in the following first modified example, the upper surface 70a of the insulator 70 may be curved. FIG. 4 is a cross-sectional view showing a first modified example of the lithium secondary battery 1 according to the present embodiment. In this first modified example, the upper surface 70a of the insulator 70 has an arched shape that protrudes toward the negative electrode layer 50. Also in this modified example, the upper surface 70a is in direct contact with the electrolyte layer 60. Such an arched upper surface 70a can prevent cracks from occurring in the electrolyte layer 60 that contacts the corners of the interposed portion 71 of the insulator 70 when the electrolyte layer 60 is transferred to the positive electrode layer 40 and the insulator 70.

[0048] In the above embodiment, the insulator 70 surrounds the positive electrode layer 40, but this is not limiting. As shown in the following second modified example, the insulator 70 may surround the electrolyte layer 60 and the negative electrode layer 50.

[0049] 5 is a cross-sectional view showing a second modified example of the lithium secondary battery 1 according to the present embodiment. In this first modified example, the outer peripheral portion 72 of the insulator 70 further includes a fifth portion 73. The fifth portion 73 in this modified example is in direct contact with the side surface 60 a of the electrolyte layer 60 and the side surface 50 a of the anode layer 50, and surrounds the periphery of the electrolyte layer 60 and the anode layer 50. This prevents the deposited lithium metal from moving around from the anode layer 50 to the cathode current collector 10 and coming into contact with them, causing a short circuit.

[0050] In this modification, the fifth portion 73 surrounds the electrolyte layer 60 and the anode layer 50, but may surround only the electrolyte layer 60. Even in this case, the creepage distance required for the deposited lithium metal to travel from the anode layer 50 to the cathode current collector 10 can be increased, thereby suppressing the occurrence of a short circuit.

[0051] DESCRIPTION OF SYMBOLS 1... Lithium secondary battery 10... Positive electrode current collector 15... Positive electrode tab 20... Negative electrode current collector 25... Negative electrode tab 30... Power generating element 40... Positive electrode layer 50... Negative electrode layer 60... Electrolyte layer 70... Insulator 80... Exterior body

Claims

1. A lithium secondary battery comprising: a positive electrode current collector; a positive electrode layer formed on the positive electrode current collector; a negative electrode current collector; a negative electrode layer formed on the negative electrode current collector; an electrolyte layer provided between the positive electrode layer and the negative electrode layer and containing a solid electrolyte; and an insulator having a frame shape surrounding the positive electrode layer, wherein the positive electrode layer includes a first surface in contact with the positive electrode current collector, a second surface opposite to the first surface, and a side surface located between the first surface and the second surface and surrounded by the insulator, and the insulator has an intermediate portion interposed between the second surface and the negative electrode layer.

2. A lithium secondary battery according to claim 1, wherein the interposition portion includes a chamfered portion.

3. A lithium secondary battery according to claim 1 or 2, wherein the insulator has an arch shape that protrudes toward the negative electrode layer and includes a contact surface, at least a portion of which is in direct contact with the electrolyte layer.

4. A lithium secondary battery according to any one of claims 1 to 3, wherein the interposition portion is in direct contact with the second surface.

5. A lithium secondary battery according to any one of claims 1 to 4, wherein the thickness of the interposed portion is at least half the thickness of the electrolyte layer.

6. A lithium secondary battery according to any one of claims 1 to 5, wherein the width of the interposed portion is between 1 / 2 and 1 times the thickness of the electrolyte layer.

7. A lithium secondary battery according to any one of claims 1 to 6, further comprising a positive electrode tab joined to the positive electrode current collector, wherein the interposition portion includes a first portion located on the positive electrode tab side and a second portion other than the first portion, and the thickness of the first portion is greater than the thickness of the second portion.

8. A lithium secondary battery according to any one of claims 1 to 7, further comprising a positive electrode tab joined to the positive electrode current collector, wherein the interposition portion includes a first portion located on the positive electrode tab side and a second portion other than the first portion, and the width of the first portion is greater than the width of the second portion.

9. A lithium secondary battery according to any one of claims 1 to 8, further comprising a positive electrode tab joined to the positive electrode current collector, wherein the insulator includes a third portion in contact with the positive electrode current collector and located on the positive electrode tab side, and a fourth portion other than the third portion and in contact with the positive electrode current collector, wherein the width of the third portion is greater than the width of the fourth portion.

10. A lithium secondary battery according to any one of claims 1 to 9, wherein the insulator surrounds the side surface of the electrolyte layer.

11. A lithium secondary battery according to claim 10, wherein the insulator surrounds the side surface of the negative electrode layer.

12. A lithium secondary battery according to any one of claims 1 to 11, wherein the outer diameter of the insulator is larger than the outer diameter of the positive electrode layer, the outer diameter of the electrolyte layer, and the outer diameter of the negative electrode layer.

Images