阅读说明：本技术 锂二次电池
(Lithium secondary battery
) 是由 大塚春男
藤田雄树 于 2019-02-27 设计创作，主要内容包括：提供一种锂二次电池(1),锂二次电池的正极(2)具备：具有导电性的片状的正极集电体(21)以及为包含锂复合氧化物的板状陶瓷烧结体的正极活性物质板(22)。正极活性物质板(22)与正极集电体(21)接合而与隔板(4)对置。负极(3)具备：具有导电性的片状的负极集电体(31)以及包含碳质材料或锂吸储物质的负极活性物质层(32)。负极活性物质层(32)涂敷于负极集电体(31)而与隔板(4)对置。外装体(6)经由正极接合层(63)而与正极集电体(21)接合,且经由负极接合层(64)而与负极集电体(31)接合。负极集电体(31)与外装体(6)之间的接合强度亦即负极接合强度小于正极集电体(21)与外装体(6)之间的接合强度亦即正极接合强度。据此,能够抑制外装体(6)产生褶皱。(Provided is a lithium secondary battery (1), wherein a positive electrode (2) of the lithium secondary battery is provided with: a sheet-like positive electrode collector (21) having conductivity, and a positive electrode active material plate (22) which is a plate-like ceramic sintered body containing a lithium composite oxide. The positive electrode active material plate (22) is joined to the positive electrode current collector (21) and faces the separator (4). The negative electrode (3) is provided with: a sheet-like negative electrode current collector (31) having conductivity, and a negative electrode active material layer (32) containing a carbonaceous material or a lithium-absorbing material. The negative electrode active material layer (32) is applied to the negative electrode current collector (31) so as to face the separator (4). The outer package (6) is joined to the positive electrode current collector (21) via a positive electrode joining layer (63) and is joined to the negative electrode current collector (31) via a negative electrode joining layer (64). The bonding strength between the negative electrode current collector (31) and the outer package (6), that is, the negative electrode bonding strength, is smaller than the bonding strength between the positive electrode current collector (21) and the outer package (6), that is, the positive electrode bonding strength. This can prevent the outer package (6) from being wrinkled.)
1. A thin lithium secondary battery is provided with:
a positive electrode;
a separator laminated on the positive electrode in a predetermined lamination direction;
a negative electrode stacked on a side of the separator opposite to the positive electrode in the stacking direction;
an electrolyte solution impregnated in the positive electrode, the negative electrode, and the separator; and
a sheet-like casing that covers the positive electrode and the negative electrode from both sides in the stacking direction and accommodates the positive electrode, the separator, the negative electrode, and the electrolyte solution therein,
the positive electrode includes:
a sheet-shaped positive electrode current collector having conductivity; and
a positive electrode active material plate which is a plate-like sintered ceramic body containing a lithium composite oxide, is joined to the positive electrode current collector, and faces the separator,
the negative electrode includes:
a sheet-shaped negative electrode current collector having conductivity; and
a negative electrode active material layer that includes a carbonaceous material or a lithium occlusion material and is applied to the negative electrode current collector so as to face the separator,
the outer package is bonded to the positive electrode current collector via a positive electrode bonding layer and bonded to the negative electrode current collector via a negative electrode bonding layer,
the bonding strength between the negative electrode current collector and the outer package, that is, the negative electrode bonding strength, is smaller than the bonding strength between the positive electrode current collector and the outer package, that is, the positive electrode bonding strength.
2. The lithium secondary battery according to claim 1,
the positive electrode bonding strength and the negative electrode bonding strength are both 1N/15mm or more,
the difference between the positive electrode bonding strength and the negative electrode bonding strength is 0.8N/15mm or more.
3. The lithium secondary battery according to claim 1 or 2,
the thickness of the positive electrode bonding layer is 0.5 [ mu ] m or more and 10 [ mu ] m or less,
the thickness of the negative electrode bonding layer is 0.5 [ mu ] m or more and 10 [ mu ] m or less.
4. The lithium secondary battery according to any one of claims 1 to 3,
the lithium secondary battery is used as a power supply source in a sheet-like device or a device having flexibility.
5. The lithium secondary battery according to claim 4,
the lithium secondary battery is used as a power supply source in the smart card as the device having flexibility.
Technical Field
The present invention relates to a thin lithium secondary battery.
Background
Conventionally, as a positive electrode active material layer in a lithium secondary battery (also referred to as a lithium ion secondary battery), there are known: a powder-dispersed positive electrode active material layer formed by molding a kneaded product of a powder of a lithium composite oxide (i.e., a lithium transition metal oxide), a binder, a conductive agent, and the like (jp 2017-79192 a (document 1)). On the other hand, japanese patent No. 5587052 (document 2) proposes a technique for increasing the capacity of a positive electrode by using a lithium composite oxide sintered plate as a positive electrode active material layer joined to a positive electrode current collector.
In the lithium primary battery disclosed in jp 2013-97931 a (document 3), a positive electrode active material layer formed by molding a kneaded product of manganese dioxide, a binder, a conductive agent, and the like is supported by a positive electrode current collector. Further, a lithium foil as a negative electrode active material layer is pressure-bonded to a negative electrode current collector. In this lithium primary battery, a technique is disclosed in which the positive electrode current collector and the negative electrode current collector are joined to the outer casing via a thermoplastic resin so as to suppress the occurrence of wrinkles or fractures in the outer casing when a bending load is applied thereto.
However, in a thin lithium secondary battery mounted in a smart card or the like, if a sintered plate is used as the positive electrode active material layer, the outer package may be wrinkled during a twisting test of the smart card or the like. It can be considered that: the occurrence of wrinkles is caused by stress or the like generated between the outer package which is relatively easily deformed and the sintered plate (i.e., the positive electrode active material layer) which is relatively hardly deformed. Even when applied to the joining of the positive electrode current collector and the negative electrode current collector described in document 3 to the outer casing, the occurrence of wrinkles cannot be sufficiently prevented.
Disclosure of Invention
The present invention is directed to a thin lithium secondary battery, and an object of the present invention is to suppress the occurrence of wrinkles in an outer package.
A thin lithium secondary battery according to a preferred aspect of the present invention includes: a positive electrode; a separator laminated on the positive electrode in a predetermined lamination direction; a negative electrode stacked on a side of the separator opposite to the positive electrode in the stacking direction; an electrolyte solution impregnated in the positive electrode, the negative electrode, and the separator; and a sheet-like outer covering that covers the positive electrode and the negative electrode from both sides in the stacking direction and accommodates the positive electrode, the separator, the negative electrode, and the electrolyte solution therein. The positive electrode includes: a sheet-shaped positive electrode current collector having conductivity; and a positive electrode active material plate which is a plate-like ceramic sintered body containing a lithium composite oxide, is joined to the positive electrode current collector, and faces the separator. The negative electrode includes: a sheet-shaped negative electrode current collector having conductivity; and a negative electrode active material layer that contains a carbonaceous material or a lithium occlusion material, is applied to the negative electrode current collector, and faces the separator. The outer package is bonded to the positive electrode current collector via a positive electrode bonding layer, and is bonded to the negative electrode current collector via a negative electrode bonding layer. The bonding strength between the negative electrode current collector and the outer package, that is, the negative electrode bonding strength, is smaller than the bonding strength between the positive electrode current collector and the outer package, that is, the positive electrode bonding strength. According to the present invention, wrinkles can be suppressed from occurring in the outer package.
Preferably, the positive electrode bonding strength and the negative electrode bonding strength are both 1N/15mm or more, and the difference between the positive electrode bonding strength and the negative electrode bonding strength is 0.8N/15mm or more.
Preferably, the positive electrode bonding layer has a thickness of 0.5 μm or more and 10 μm or less, and the negative electrode bonding layer has a thickness of 0.5 μm or more and 10 μm or less.
Preferably, the lithium secondary battery is used as a power supply source in a sheet-like device or a device having flexibility. More preferably, the lithium secondary battery is used as a power supply source in a smart card as a device having the flexibility.
The above objects, and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the present invention with reference to the accompanying drawings.
Drawings
Fig. 1 is a sectional view of a lithium secondary battery according to an embodiment.
Fig. 2 is a plan view of the positive electrode.
Detailed Description
Fig. 1 is a sectional view showing a structure of a lithium secondary battery 1 according to an embodiment of the present invention. In fig. 1, the lithium secondary battery 1 and its structure are depicted thicker than actual ones in order to facilitate understanding of the drawing. In fig. 1, the structures of a part of the front side and the back side of the cross section are collectively shown.
The lithium secondary battery 1 is used as a power supply source in, for example, a sheet-like device or a device having flexibility. A pellet device is a thin device that is easily deformed by a relatively small force, and is also called a film-like device. In the present embodiment, the lithium secondary battery 1 is used as a power supply source in, for example, a smart card having an arithmetic processing function. Smart cards are flexible devices of the card type.
The lithium secondary battery 1 is a small and thin battery. The shape of the lithium secondary battery 1 in plan view is, for example, substantially rectangular. For example, the lithium secondary battery 1 has a longitudinal length of 27mm to 46mm and a lateral length of 38mm to 46mm in a plan view. The thickness of the lithium secondary battery 1 (i.e., the thickness in the vertical direction in fig. 1) is, for example, 0.30mm to 0.45 mm. The lithium secondary battery 1 is a sheet-like or thin plate-like member having flexibility. The sheet-like member is a thin member that is easily deformed by a relatively small force, and is also called a film-like member. The same applies to the following description.
The lithium secondary battery 1 includes: positive electrode 2, negative electrode 3, separator 4, electrolyte 5, casing 6, and 2 terminals 7. In the example shown in fig. 1, the positive electrode 2, the separator 4, and the negative electrode 3 are stacked in the vertical direction in the drawing. In the following description, the upper side and the lower side in fig. 1 are simply referred to as "upper side" and "lower side". The vertical direction in fig. 1 is simply referred to as the "vertical direction" and also as the "stacking direction". The vertical direction in fig. 1 does not necessarily have to coincide with the actual vertical direction when the lithium secondary battery 1 is mounted on a device such as a smart card.
In the example shown in fig. 1, the separator 4 is laminated on the upper surface of the positive electrode 2 in the lamination direction. The negative electrode 3 is stacked on the upper surface of the separator 4 in the stacking direction. In other words, the negative electrode 3 is stacked on the side of the separator 4 opposite to the positive electrode 2 in the stacking direction. For example, each of the positive electrode 2, the separator 4, and the negative electrode 3 is substantially rectangular in plan view. The positive electrode 2, the separator 4, and the negative electrode 3 have substantially the same shape (i.e., substantially the same shape and substantially the same size) in a plan view.
The exterior body 6 is a sheet-like member. The package 6 is formed of a laminate film in which a metal foil 61 made of a metal such as aluminum (Al) and an insulating resin layer 62 are laminated. The package 6 is a bag-shaped member in which the resin layer 62 is located inside the metal foil 61.
The outer package 6 covers the positive electrode 2 and the negative electrode 3 from both sides in the stacking direction. The casing 6 accommodates the positive electrode 2, the separator 4, the negative electrode 3, and the electrolyte 5 therein. The electrolyte 5 is continuously present around the positive electrode 2, the separator 4, and the negative electrode 3. In other words, the electrolyte 5 is interposed between the positive electrode 2 and the negative electrode 3. The electrolyte 5 is a liquid electrolyte solution, and is impregnated into the positive electrode 2, the separator 4, and the negative electrode 3. In fig. 1, the electrolyte 5 is not given parallel oblique lines. The 2 terminals 7 protrude from the inside of the package 6 to the outside. Inside the outer package 6, one terminal 7 is electrically connected to the positive electrode 2, and the other terminal 7 is electrically connected to the negative electrode 3.
The positive electrode 2 includes: a positive electrode current collector 21, a positive electrode active material plate 22, and a conductive bonding layer 23. The positive electrode current collector 21 is a sheet-like member having conductivity. The lower surface of the positive electrode current collector 21 is bonded to the resin layer 62 of the package 6 via the positive electrode bonding layer 63. The positive electrode active material plate 22 is a relatively thin plate-like ceramic sintered body containing a lithium composite oxide. The positive electrode active material plate 22 is bonded to the upper surface of the positive electrode current collector 21 via the conductive bonding layer 23. The positive electrode active material plate 22 faces the separator 4 in the vertical direction.
The positive electrode current collector 21 includes: for example, a metal foil made of a metal such as aluminum, and a conductive carbon layer laminated on the upper surface of the metal foil. In other words, the main surface of the positive electrode current collector 21 facing the positive electrode active material plate 22 is coated with a conductive carbon layer. The metal foil may be formed of various metals other than aluminum (e.g., stainless steel). The conductive carbon layer may be omitted from the positive electrode current collector 21.
The positive electrode bonding layer 63 is formed of, for example, a mixed resin of an acid-modified polyolefin resin and an epoxy resin. The positive electrode bonding layer 63 may be formed of other various materials. The thickness of the positive electrode bonding layer 63 is, for example, 0.5 to 10 μm, preferably 0.5 to 5 μm, and more preferably 0.5 to 3 μm. The bonding strength between the positive electrode current collector 21 and the outer package 6 by the positive electrode bonding layer 63 (hereinafter referred to as "positive electrode bonding strength") is, for example, 1N/15mm or more, preferably 1.5N/15mm or more, and more preferably 2.0N/15mm or more. The upper limit of the positive electrode bonding strength is not particularly limited, and the positive electrode bonding strength is typically 12N/15mm or less.
The positive electrode active material plate 22 has: a plurality (i.e., a large number) of primary particles are combined to obtain a structure. The primary particles are composed of a lithium composite oxide having a layered rock salt structure. The lithium composite oxide is typically represented by the general formula: lipMO2(wherein 0.05 < p < 1.10). M is at least 1 transition metal, and includes, for example, 1 or more selected from cobalt (Co), nickel (Ni), and manganese (Mn). The layered rock salt structure is: and a crystal structure in which lithium layers and transition metal layers other than lithium are alternately stacked with oxygen layers interposed therebetween. That is, the layered rock salt structure is: crystal structure in which transition metal ion layers and lithium individual layers are alternately stacked via oxide ions (typically α -NaFeO)2The structure is as follows: transition metal and lithium in cubic rock salt type structure [111 ]]A structure regularly arranged in the axial direction).
The conductive bonding layer 23 contains a conductive powder and a binder. The conductive powder is: such as acetylene black or ketjen black. The conductive bonding layer 23 is formed by applying the above-described conductive powder, a binder, and a liquid or paste binder containing a solvent to the positive electrode current collector 21 or the positive electrode active material plate 22, and evaporating and solidifying the solvent between the positive electrode current collector 21 and the positive electrode active material plate 22.
Fig. 2 is a plan view showing the positive electrode 2. The positive electrode active material plate 22 includes a plurality of active material plate elements 24. The plurality of active material plate elements 24 are bonded to the positive electrode current collector 21 via the conductive bonding layer 23. The plurality of active material plate elements 24 are arranged in a matrix (i.e., lattice shape) on the positive electrode current collector 21. The shape of each active material plate element 24 in a plan view is, for example, substantially rectangular. The plurality of active material plate elements 24 have substantially the same shape (i.e., substantially the same shape and substantially the same size) in a plan view. The plurality of active material plate elements 24 are separated from each other in a plan view.
In the example shown in fig. 2, 6 active material plate elements 24 each having a substantially square shape in plan view are arranged in a matrix of 2 pieces in the vertical direction × 3 pieces in the horizontal direction. The length of one side of each active material plate element 24 in a plan view is, for example, 9.5mm to 10.5 mm. The number and arrangement of the plurality of active material plate elements 24 may be variously changed. The shape of each active material plate element 24 may be variously modified.
In the lithium secondary battery 1, the bonding strength between the positive electrode current collector 21 and the outer package 6 in the region overlapping each active material plate element 24 in the stacking direction is greater than the bonding strength between the positive electrode current collector 21 and the outer package 6 in the region overlapping the gap between the plurality of active material plate elements 24 in the stacking direction.
The thickness of the positive electrode current collector 21 is, for example, 9 to 50 μm, preferably 9 to 20 μm, and more preferably 9 to 15 μm. The thickness of the positive electrode active material plate 22 (i.e., the thickness of each active material plate element 24) is, for example, 15 to 200 μm, preferably 30 to 150 μm, and more preferably 50 to 100 μm. The thickness of the conductive bonding layer 23 (i.e., the thickness of each bonding layer element 25) is, for example, 3 to 28 μm, preferably 3 to 15 μm, and more preferably 3 to 10 μm.
The negative electrode 3 includes: a negative electrode collector 31 and a negative electrode active material plate 32. The negative electrode current collector 31 is a sheet-like member having conductivity. The upper surface of the negative electrode current collector 31 is bonded to the resin layer 62 of the package 6 via the negative electrode bonding layer 64. The negative electrode active material plate 32 contains a carbonaceous material or a lithium occluding material. The negative electrode active material layer 32 is applied on the lower surface of the negative electrode current collector 31. The negative electrode active material layer 32 faces the separator 4 in the vertical direction.
The negative electrode current collector 31 is: for example, a metal foil made of a metal such as copper (Cu). The metal foil may be formed of various metals other than copper (e.g., nickel, etc.). The rigidity with respect to bending of the negative electrode current collector 31 in the lamination direction is higher than, for example: rigidity with respect to bending of the positive electrode current collector 21 in the stacking direction. In the negative electrode active material layer 32, the carbonaceous material is, for example, graphite, and the lithium occluding material is, for example, silicon.
The negative electrode bonding layer 64 is formed of, for example, a mixed resin of an acid-modified polyolefin resin and an epoxy resin. The negative electrode bonding layer 64 may be formed of other various materials. The negative electrode bonding layer 64 is formed of substantially the same material as the positive electrode bonding layer 63 (i.e., a material having substantially the same composition and substantially the same content of each component). The thickness of the negative electrode bonding layer 64 is, for example, 0.5 to 10 μm, preferably 0.5 to 5 μm, and more preferably 0.5 to 3 μm. The bonding strength between the negative electrode current collector 31 and the outer package 6 by the negative electrode bonding layer 64 (hereinafter referred to as "negative electrode bonding strength") is, for example, 0.8N/15mm or more, preferably 1.2N/15mm or more, and more preferably 2.0N/15mm or more. The upper limit of the negative electrode bonding strength is not particularly limited, and the negative electrode bonding strength is typically 12N/15mm or less.
The negative electrode bonding strength is less than the positive electrode bonding strength. The difference between the positive electrode bonding strength and the negative electrode bonding strength is, for example, 0.8N/15mm or more, preferably 1N/15mm or more, and more preferably 2N/15mm or more. The upper limit of the difference between the positive electrode bonding strength and the negative electrode bonding strength is not particularly limited, and the difference is typically 6N/15mm or less, more typically 5N/15mm or less.
The thickness of the negative electrode current collector 31 is, for example, 8 to 25 μm, preferably 8 to 20 μm, and more preferably 8 to 15 μm. The thickness of the negative electrode active material layer 32 is, for example, 50 to 200. mu.m, preferably 70 to 180 μm, and more preferably 80 to 150 μm.
As described above, the lithium secondary battery 1 includes: positive electrode 2, separator 4, negative electrode 3, electrolyte 5, and outer package 6. The separator 4 is stacked on the positive electrode 2 in a predetermined stacking direction. The negative electrode 3 is stacked on the opposite side of the separator 4 from the positive electrode 2 in the stacking direction. The electrolyte 5 is: an electrolyte solution impregnated in the positive electrode 2, the negative electrode 3, and the separator 4. The outer package 6 is: a sheet-like member in which the positive electrode 2 and the negative electrode 3 are coated from both sides in the stacking direction. The casing 6 accommodates the positive electrode 2, the separator 4, the negative electrode 3, and the electrolyte 5 therein.
The positive electrode 2 includes: a sheet-shaped positive electrode current collector 21 having conductivity; and a positive electrode active material plate 22 which is a plate-like ceramic sintered body containing a lithium composite oxide. The positive electrode active material plate 22 is joined to the positive electrode current collector 21 so as to face the separator 4. The negative electrode 3 includes: a sheet-like negative electrode current collector 31 having conductivity; and a negative electrode active material plate 32 containing a carbonaceous material or a lithium occluding material. The negative electrode active material layer 32 is applied to the negative electrode current collector 31 so as to face the separator 4. The package 6 is bonded to the positive electrode current collector 21 via the positive electrode bonding layer 63, and is bonded to the negative electrode current collector 31 via the negative electrode bonding layer 64. The bonding strength between the negative electrode current collector 31 and the outer package 6, that is, the negative electrode bonding strength is smaller than the bonding strength between the positive electrode current collector 21 and the outer package 6, that is, the positive electrode bonding strength.
As described above, in the lithium secondary battery 1, the joint strength (i.e., the positive electrode joint strength) between the positive electrode 2 provided with the positive electrode active material plate 22 having relatively high rigidity and the outer package 6 is large, and the joint strength (i.e., the negative electrode joint strength) between the negative electrode 3 provided with the negative electrode active material layer 32 having relatively low rigidity and the outer package 6 is small. In other words, the positive electrode 2, which is relatively less likely to deform, is strongly bonded to the casing 6, and the negative electrode 3, which is relatively more likely to deform, is weakly bonded to the casing 6. Accordingly, when the lithium secondary battery 1 is twisted (for example, when both left and right end portions of the lithium secondary battery 1 are twisted in opposite directions), the difference between the stress generated between the positive electrode 2 and the casing 6 and the stress generated between the negative electrode 3 and the casing 6 can be reduced. As a result, it is possible to suppress: the casing 6 is wrinkled due to a difference in bending rigidity between the positive electrode 2 and the negative electrode 3, or the like.
As described above, in the lithium secondary battery 1, it is possible to suppress: the outer package 6 is wrinkled when the lithium secondary battery 1 is deformed. Therefore, the lithium secondary battery 1 is particularly suitable for: a sheet-like device, which is a device that is relatively easily deformed and easily applies a bending load, or a power supply source in a device having flexibility. In the case where the lithium secondary battery 1 is used as a power supply source in a smart card, which is one of the devices having flexibility, it is possible to favorably realize both: the reduction in thickness of the smart card and the suppression of the bulging of the card surface due to the wrinkles of the outer case 6 when the smart card is deformed.
Tables 1 and 2 show the relationship between the positive electrode bonding strength and the negative electrode bonding strength of the lithium secondary battery 1 and the protrusion of the card surface when the smart card is deformed, for the smart card on which the lithium secondary battery 1 is mounted. In examples 1 to 5, the positive electrode bonding strength was higher than the negative electrode bonding strength, and in comparative examples 1 and 2, the positive electrode bonding strength was lower than the negative electrode bonding strength. In examples 1 to 5, the positive electrode bonding strength was 1.1 times or more and 2.5 times or less the negative electrode bonding strength. The positive electrode bonding strength is changed by changing the bonding temperature at which the positive electrode collector 21 and the positive electrode 2 are bonded and the pressure applied during bonding. The same applies to the negative electrode bonding strength.
[ Table 1]
[ Table 2]
The positive electrode bonding strength and the negative electrode bonding strength in table 2 were obtained by a peel test. The peel test was performed using a peel tester in the following order. As the peel tester, a force gauge "ZTA-20N", a vertical electric measuring rack "MX 2-500N" and a membrane cartridge "FC-21" manufactured by Imada were used.
In this peeling test, first, the lithium secondary battery 1 was disassembled to obtain: a structure in which the positive electrode 2 and the casing 6 are joined together via the positive electrode joining layer 63 (hereinafter referred to as "positive electrode-casing assembly"), and a structure in which the negative electrode 3 and the casing 6 are joined together via the negative electrode joining layer 64 (hereinafter referred to as "negative electrode-casing assembly").
When the positive electrode bonding strength was obtained, the positive electrode active material plate 22 was removed from the positive electrode-exterior assembly, and a square test piece having a width of 15mm × a length of 25mm was cut from the portion where the positive electrode current collector 21 and the exterior assembly 6 were bonded. Next, the positive electrode current collector 21 and the outer package 6 were peeled off at one end in the longitudinal direction of the test piece to a length of 5 mm. Next, the peeled portion of the test piece (i.e., the end portion of the positive electrode current collector 21 and the end portion of the exterior body 6) was held by a film chuck of a peeling tester. Then, a T-shaped peeling test was performed at a drawing speed of 300mm/min to obtain: the maximum value of the tensile strength when the positive electrode current collector 21 is peeled from the outer package 6 is referred to as "positive electrode bonding strength".
When the negative electrode bonding strength was obtained, a square test piece having a width of 15mm × a length of 25mm was cut out from the portion where the negative electrode current collector 31 and the outer package 6 were bonded in the negative electrode-outer package assembly. Next, the negative electrode current collector 31 and the outer package 6 were peeled off by a length of 5mm from one end portion of the test piece in the longitudinal direction. Next, the peeled portion of the test piece (i.e., the end portion of the negative electrode current collector 31 and the end portion of the outer package 6) was held by a film chuck of a peeling tester. Then, a T-shaped peeling test was performed at a drawing speed of 300mm/min to obtain: the maximum value of the tensile strength when the negative electrode current collector 31 is peeled from the outer package 6 is referred to as "negative electrode bonding strength".
The maximum protrusion of the card surface in table 2 indicates: maximum height of the protrusion of the card surface after the smart card was subjected to the torsion test in accordance with "JIS X6305-1 (ISO/IEC 10373-1)". In examples 1 to 5, the maximum protrusion of the card surface was suppressed to 45 μm or less, and the results of the warpage test were good. On the other hand, in comparative examples 1 and 2, the maximum protrusion of the card surface was larger than 45 μm.
As described above, both the positive electrode bonding strength and the negative electrode bonding strength are preferably 1N/15mm or more. Further, the difference between the positive electrode bonding strength and the negative electrode bonding strength is preferably 0.8N/15mm or more. Accordingly, as shown in examples 1 to 4, the maximum protrusion of the card surface was suppressed to less than 40 μm. That is, it is possible to suppress more favorably: the outer package 6 is wrinkled when the lithium secondary battery 1 is deformed.
As described above, the thickness of the positive electrode bonding layer 63 is preferably 0.5 μm or more and 10 μm or less. The thickness of the negative electrode bonding layer 64 is also preferably 0.5 μm or more and 10 μm or less. This makes it possible to reduce the thickness of the lithium secondary battery 1 and to achieve good bonding between the positive electrode 2 and the negative electrode 3 and the outer package 6.
In the lithium secondary battery 1, the positive electrode bonding layer 63 and the negative electrode bonding layer 64 are formed of the same material. This can simplify the production of the lithium secondary battery 1.
Various modifications can be made to the lithium secondary battery 1 described above.
For example, the positive electrode active material plate 22 does not necessarily need to be divided into a plurality of active material plate elements 24, and may be 1 plate-shaped ceramic sintered body.
The positive electrode bonding layer 63 and the negative electrode bonding layer 64 may be formed of different materials (e.g., different kinds of resins).
The thickness of the positive electrode bonding layer 63 may be less than 0.5 μm or more than 10 μm. Similarly, the thickness of the negative electrode bonding layer 64 may be smaller than 0.5 μm or larger than 10 μm.
The positive electrode bonding strength may be less than 1N/15 mm. The negative electrode bonding strength may be less than 1N/15 mm. In addition, the difference between the positive electrode bonding strength and the negative electrode bonding strength may be less than 0.8N/15 mm.
The rigidity with respect to bending of the negative electrode current collector 31 in the stacking direction may be lower than or substantially the same as the rigidity with respect to bending of the positive electrode current collector 21 in the stacking direction.
The lithium secondary battery 1 can be used as a power supply source in a device having flexibility (for example, a card-type device) other than a smart card or a sheet-type device (for example, a wearable device or a body-fitted device provided in clothing or the like). The lithium secondary battery 1 can be used as a power supply source for various objects (for example, IoT modules) other than the above-described devices.
The configurations in the above embodiments and modifications may be appropriately combined as long as they are not contradictory to each other.
Although the present invention has been described in detail, the above description is illustrative and not restrictive. Therefore, it can be said that various modifications and variations can be adopted without departing from the scope of the present invention.
Industrial applicability
The lithium secondary battery of the present invention can be used in various fields in which lithium secondary batteries are used, for example, as a power supply source in a smart card having an arithmetic processing function.
Description of the symbols
1 lithium secondary battery 2 positive electrode
3 negative electrode 4 separator
5 electrolyte 6 outer package
21 positive electrode collector 22 positive electrode active material plate
31 negative electrode collector 32 negative electrode active material layer
63 positive electrode bonding layer 64 negative electrode bonding layer
