JP2019175604A - Lithium secondary battery - Google Patents

Abstract

To suppress the decrease of the connection strength of an active material plate and a current collector.SOLUTION: A lithium secondary battery 1 comprises a positive electrode 2, a negative electrode 3, and an electrolyte 5. The electrolyte 5 is interposed between the positive electrode 2 and the negative electrode 3. The positive electrode 2 has a conductive sheet-like positive electrode current collector 21, and a positive electrode active material plate 22 composed of a plate-like ceramic sintered compact containing a lithium composite oxide. The positive electrode active material plate 22 is joined to the positive electrode current collector 21 through a conductive junction layer 23. The conductive junction layer 23 contains conductive powder, and a binder containing a polyimideamide resin. The positive electrode active material plate 22 has a structure in which a plurality of primary particles having a lamellar rock-salt structure are coupled. The plurality of primary particles have an average tilt angle of over 0° up to 30°. The average tilt angle is an average value of angles that (003) planes of the plurality of primary particles form with respect to a main face of the positive electrode active material plate 22. Thus, the decrease in the connection strength of the positive electrode active material plate 22 and the positive electrode current collector 21 can be suppressed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a thin lithium secondary battery.

  Conventionally, as a positive electrode active material layer in a lithium secondary battery (also called a lithium ion secondary battery), a kneaded material such as a powder of a lithium composite oxide (that is, a lithium transition metal oxide), a binder, and a conductive agent is formed. A powder-dispersed positive electrode active material layer formed in this manner is known. On the other hand, Patent Document 1 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 bonded to a positive electrode current collector.

Japanese Patent No. 5587052

  By the way, in a thin lithium secondary battery mounted on a smart card or the like, a bending load is repeatedly applied in a bending test or the like of the smart card. When a sintered plate is used as the positive electrode active material layer of the lithium secondary battery, the bonding strength between the sintered plate (that is, the active material plate) and the current collector may be reduced by the bending test or the like. In addition, when the processing temperature when mounting a lithium secondary battery on a smart card or the like (for example, the temperature during lamination processing) is high, the conductive bonding layer that bonds the active material plate and the current collector reacts with the electrolyte. Then, it may gel and the bonding strength between the active material plate and the current collector may be reduced. If the bonding strength between the active material plate and the current collector is reduced, the voltage may become unstable when the lithium secondary battery is discharged.

  This invention is made | formed in view of the said subject, and aims at suppressing the fall of the joining strength of an active material board and a collector.

  A thin lithium secondary battery according to a preferred embodiment of the present invention includes a positive electrode, a negative electrode, and an electrolyte interposed between the positive electrode and the negative electrode. The positive electrode is a sheet-shaped current collector having conductivity, and a plate-like ceramic sintered body containing a lithium composite oxide, and an active material plate bonded to the current collector through a conductive bonding layer; . The conductive bonding layer includes conductive powder and a binder including a polyimide amide resin. The active material plate has a structure in which a plurality of primary particles having a layered rock salt structure are combined. The average inclination angle of the plurality of primary particles is larger than 0 ° and not larger than 30 °. The average inclination angle is an average value of angles formed by the (003) planes of the plurality of primary particles and the main surface of the active material plate.

  Preferably, the weight of the conductive powder in the conductive bonding layer is 50% or more and 1000% or less of the weight of the binder.

  Preferably, the thickness of the conductive bonding layer is 3 μm or more and 28 μm or less.

  Preferably, the active material plate has a porosity of 25% or more and 45% or less.

  Preferably, the main surface of the current collector facing the active material plate is covered with a conductive carbon layer.

  Preferably, the lithium secondary battery is used as a power supply source in a sheet-like device or a flexible device. More preferably, the lithium secondary battery is used as a power supply source in a smart card which is the flexible device.

  In the present invention, it is possible to suppress a decrease in bonding strength between the active material plate and the current collector.

It is sectional drawing of the lithium secondary battery which concerns on one embodiment. It is a top view of a positive electrode. It is a bottom view of an active material board element.

  FIG. 1 is a cross-sectional view showing a configuration of a lithium secondary battery 1 according to an embodiment of the present invention. In FIG. 1, in order to facilitate understanding of the drawing, the lithium secondary battery 1 and its configuration are drawn thicker than actual. FIG. 1 also shows a part of the structure on the near side and the far side from the cross section.

  The lithium secondary battery 1 is used as a power supply source in, for example, a sheet-like device or a flexible device. A sheet-like 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 a smart card having an arithmetic processing function, for example. A smart card is a card-type flexible device.

  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, a substantially rectangular shape. For example, the length in the vertical direction in the plan view of the lithium secondary battery 1 is 10 mm to 46 mm, and the length in the horizontal direction is 10 mm to 46 mm. The thickness of the lithium secondary battery 1 (that is, the thickness in the vertical direction in FIG. 1) is, for example, 0.30 mm to 0.45 mm. The lithium secondary battery 1 is a sheet-like or flexible thin plate-like member. A 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 a positive electrode 2, a negative electrode 3, a separator 4, an electrolyte 5, an exterior body 6, and two terminals 7. In the example illustrated 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”. Further, the vertical direction in FIG. 1 is simply referred to as “vertical direction” and is also referred to as “stacking direction”. The vertical direction in FIG. 1 does not 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 illustrated in FIG. 1, the separator 4 is stacked on the upper surface of the positive electrode 2 in the stacking direction. The negative electrode 3 is laminated on the upper surface of the separator 4 in the lamination direction. In other words, the negative electrode 3 is stacked on the opposite side of the separator 4 from the positive electrode 2 in the stacking direction. For example, each of the positive electrode 2, the separator 4, and the negative electrode 3 has a substantially rectangular shape in plan view. The positive electrode 2, the separator 4, and the negative electrode 3 have substantially the same shape (that is, approximately the same shape and approximately the same size) in plan view.

  The exterior body 6 is a sheet-like member. The exterior body 6 is formed of a laminated film in which a metal foil 61 formed of a metal such as aluminum (Al) and an insulating resin layer 62 are laminated. The exterior body 6 is a bag-shaped member in which the resin layer 62 is located inside the metal foil 61.

  The exterior body 6 covers the positive electrode 2 and the negative electrode 3 from both sides in the stacking direction. The exterior body 6 accommodates the positive electrode 2, the separator 4, the negative electrode 3, and the electrolyte 5 inside. 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 and impregnates the positive electrode 2, the separator 4, and the negative electrode 3. In FIG. 1, the application of parallel diagonal lines to the electrolyte 5 is omitted. The two terminals 7 protrude from the inside of the exterior body 6 to the outside. In the exterior body 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 exterior body 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 onto 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 formed 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 covered with the conductive carbon layer. The above-mentioned metal foil is formed of various metals other than aluminum (for example, copper, nickel, silver, gold, chromium, iron, tin, lead, tungsten, molybdenum, titanium, zinc, or alloys containing these). May be. Further, 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 various other materials.

The positive electrode active material plate 22 has a structure in which a plurality of (that is, a large number) primary particles are bonded. The primary particles are composed of a lithium composite oxide having a layered rock salt structure. The lithium composite oxide is typically an oxide represented by a general formula: Li _p MO ₂ (wherein 0.05 <p <1.10). M is at least one kind of transition metal, and includes, for example, one or more selected from cobalt (Co), nickel (Ni), and manganese (Mn). The layered rock salt structure is a crystal structure in which lithium layers and transition metal layers other than lithium are alternately stacked with an oxygen layer interposed therebetween. That is, the layered rock salt structure has a crystal structure in which transition metal ion layers and lithium single layers are alternately stacked via oxide ions (typically, α-NaFeO ₂ type structure: cubic rock salt type structure [111 ] A structure in which transition metals and lithium are regularly arranged in the axial direction.

Preferable examples of the lithium composite oxide having a layered rock salt structure include lithium cobaltate (Li _p CoO ₂ (where 1 ≦ p ≦ 1.1), lithium nickelate (LiNiO ₂ ), lithium manganate (Li _2). MnO _3), lithium nickel manganese oxide _{(Li p (Ni 0.5, Mn} 0.5) O 2), the general _{formula: Li p (Co x, Ni} y, in Mn z) _{O 2} (wherein 0.97 ≦ p ≦ 1.07, x + y + z = 1 solid solution represented _{by), Li p (Co x,} Ni y, in Al z) O2 (wherein, 0.97 ≦ p ≦ 1.07, x + y + z = 1,0 < x ≦ 0.25, 0.6 ≦ y ≦ 0.9 and 0 <z ≦ 0.1), or Li ₂ MnO ₃ and LiMO ₂ (wherein M is Co, Ni, etc.) Transition metal), particularly preferably. , Lithium composite oxide is lithium cobaltate _Li p CoO ₂ (wherein, 1 ≦ p ≦ 1.1), for example, LiCoO _2.

  The positive electrode active material plate 22 is made of magnesium (Mg), Al, silicon (Si), calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu). , Zinc (Zn), gallium (Ga), germanium (Ge), strontium (Sr), yttrium (Y), zirconia (Zr), niobium (Nb), molybdenum (Mo), silver (Ag), tin (Sn) , Antimony (Sb), tellurium (Te), barium (Ba), bismuth (Bi) and other elements may be further included. The positive electrode active material plate 22 may be sputtered with gold (Au) or the like as a current collecting aid.

  In the positive electrode active material plate 22, the primary particle size which is the average particle size of the plurality of primary particles is, for example, 20 μm or less, and preferably 15 μm or less. Moreover, the said primary particle size is 0.2 micrometer or more, for example, Preferably it is 0.4 micrometer or more. The primary particle size can be measured by analyzing an SEM (scanning electron microscope) image of the cross section of the positive electrode active material plate 22. Specifically, for example, the positive electrode active material plate 22 is processed with a cross section polisher (CP) to expose a polished cross section, and the polished cross section is exposed to a predetermined magnification (for example, 1000 times) and a predetermined field of view (for example, 125 μm × 125 μm). ). At this time, the visual field is set so that 20 or more primary particles exist in the visual field. The diameter of the circumscribed circle when the circumscribed circle is drawn for all the primary particles in the obtained SEM image is obtained, and the average value of these is used as the primary particle diameter.

  In the positive electrode active material plate 22, the average inclination angle of the plurality of primary particles is greater than 0 ° and 30 ° or less. The average inclination angle is preferably 5 ° or more and 28 ° or less, and more preferably 10 ° or more and 25 ° or less. The average inclination angle is an average value of angles formed by the (003) planes of the plurality of primary particles and the main surface of the positive electrode active material plate 22 (for example, the lower surface of the positive electrode active material plate 22).

  The inclination angle of the primary particles (that is, the angle formed between the (003) plane of the primary particles and the main surface of the positive electrode active material plate 22) is obtained by analyzing the cross section of the positive electrode active material plate 22 by electron beam backscatter diffraction (EBSD). Can be measured. Specifically, for example, the positive electrode active material plate 22 is processed with a cross section polisher to expose a polished cross section, and the polished cross section is EBSD at a predetermined magnification (for example, 1000 times) and a predetermined field of view (for example, 125 μm × 125 μm). Analyze by In the obtained EBSD image, the inclination angle of each primary particle is expressed by color shading, and the darker the color, the smaller the orientation angle. And the average value of the inclination angle of the several primary particle calculated | required from the EBSD image is made into the above-mentioned average inclination angle.

  In the primary particles constituting the positive electrode active material plate 22, the proportion of the primary particles having an inclination angle of 0 ° or more and 30 ° or less is preferably 60% or more, more preferably 80% or more, and still more preferably. Is 90% or more. The upper limit of the ratio is not particularly limited, and may be 100%. The said ratio can be calculated | required by calculating | requiring the total area of the primary particle whose inclination | tilt angle is 0 degree or more and 30 degrees or less in the above-mentioned EBSD image, and dividing the total area of the said primary particle by the total particle area.

  The porosity of the positive electrode active material plate 22 is, for example, 25% to 45%. In the present specification, the “porosity” is a volume ratio of pores (including open pores and closed pores) in the positive electrode active material plate 22. The porosity can be measured by image analysis of a cross-sectional SEM (scanning electron microscope) image of the positive electrode active material plate 22. For example, the positive electrode active material plate 22 is processed with a cross section polisher (CP) to expose the polished cross section. The polished cross section is observed by SEM at a predetermined magnification (for example, 1000 times) and a predetermined field of view (for example, 125 μm × 125 μm). The obtained SEM image is subjected to image analysis, the area of all the pores in the field of view is divided by the area (cross-sectional area) of the positive electrode active material plate 22 in the field of view, and the obtained value is multiplied by 100 to obtain the porosity. Get (%).

  The average pore diameter that is the average value of the diameters of the pores contained in the positive electrode active material plate 22 is, for example, 15 μm or less, preferably 12 μm or less, and more preferably 10 μm or less. Moreover, the said average pore diameter is 0.1 micrometer or more, for example, Preferably it is 0.3 micrometer or more. The above-mentioned pore diameter is typically the diameter of the sphere when the pore is assumed to be a sphere having the same volume or the same cross-sectional area. The average pore diameter is an average value of the diameters of a plurality of pores calculated on the basis of the number. The average pore diameter can be obtained by a well-known method such as analysis of a cross-sectional SEM image or a mercury intrusion method. Preferably, the average pore diameter is measured by a mercury intrusion method using a mercury porosimeter.

  The conductive bonding layer 23 includes conductive powder and a binder. The conductive powder is, for example, a powder of acetylene black, scaly natural graphite, carbon nanotube, carbon nanofiber, carbon nanotube derivative, or carbon nanofiber derivative. The binder includes, for example, a polyimide amide resin. The polyimide amide resin contained in the binder may be one type or two or more types. The binder may contain a resin other than the polyimide amide resin. The conductive bonding layer 23 is formed by applying the above-described conductive powder and binder, and a liquid or paste-like adhesive containing a solvent to the positive electrode current collector 21 or the positive electrode active material plate 22, and thereby the positive electrode current collector 21. And the positive electrode active material plate 22 is formed by evaporation and solidification of the solvent.

  Preferably, the conductive bonding layer 23 does not substantially contain substances other than the conductive powder and the binder. In other words, the total ratio of the conductive powder and the binder in the conductive bonding layer 23 is substantially 100% by weight. The weight of the conductive powder in the conductive bonding layer 23 is, for example, 50% to 1000% of the weight of the binder, preferably 100% to 750%, and more preferably 250% to 750%. The volume ratio of the conductive powder in the conductive bonding layer 23 is, for example, 50% to 90%.

  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 arranged in a matrix (that is, a lattice) on the positive electrode current collector 21. The shape of each active material plate element 24 in plan view is, for example, a substantially rectangular shape. The plurality of active material plate elements 24 have substantially the same shape (that is, substantially the same shape and substantially the same size) in plan view. The plurality of active material plate elements 24 are separated from each other in plan view.

  In the example shown in FIG. 2, six active material plate elements 24 that are substantially square in a plan view are arranged in a matrix of 2 × 3. The length of one side in the plan view of each active material plate element 24 is, for example, 5 mm to 40 mm. The number and arrangement of the plurality of active material plate elements 24 may be variously changed. Further, the shape of each active material plate element 24 may be variously changed.

  The conductive bonding layer 23 includes a plurality of bonding layer elements 25 corresponding to the plurality of active material plate elements 24. In FIG. 2, the outline (that is, the outer edge) of each bonding layer element 25 of the conductive bonding layer 23 is indicated by a broken line. The number of the bonding layer elements 25 is the same as the number of the active material plate elements 24, for example. Each of the plurality of bonding layer elements 25 is disposed between the positive electrode current collector 21 and the plurality of active material plate elements 24 in the vertical direction. In the positive electrode 2, a plurality of active material plate elements 24 are respectively bonded to the positive electrode current collector 21 by a plurality of bonding layer elements 25. In the positive electrode 2, one bonding layer element 25 may be bonded to the positive electrode current collector 21 by two or more bonding layer elements 25.

  The shape of each bonding layer element 25 in plan view is, for example, a substantially circular shape. In the plan view, each bonding layer element 25 is smaller than the active material plate element 24, and the entire bonding layer element 25 is covered with the active material plate element 24. In other words, the entire outer edge of the bonding layer element 25 is located inside the outer edge of the active material plate element 24 in plan view. In other words, each bonding layer element 25 does not protrude around the active material plate element 24. The shape of the bonding layer element 25 in plan view is not limited to a substantially circular shape, and may be variously changed such as a substantially oval shape or a substantially elliptical shape.

  The thickness of the positive electrode current collector 21 is, for example, 9 μm to 50 μm, preferably 9 μm to 20 μm, and more preferably 9 μm to 15 μm. The thickness of the positive electrode active material plate 22 (that is, the thickness of each active material plate element 24) is, for example, 15 μm to 200 μm, preferably 30 μm to 150 μm, and more preferably 50 μm to 100 μm. The thickness of the conductive bonding layer 23 (that is, the thickness of each bonding layer element 25) is, for example, 3 μm to 28 μm, and preferably 5 μm to 25 μm.

  FIG. 3 is a bottom view showing a main surface of one active material plate element 24 facing the positive electrode current collector 21. The main surface is the lower surface in FIG. 1 and is referred to as a “joining surface 26” in the following description. In the example shown in FIG. 3, the joint surface 26 has a substantially square shape. The joint surfaces 26 of the other five active material plate elements 24 are the same as those shown in FIG. In FIG. 3, the outer edge of the bonding layer element 25 of the conductive bonding layer 23 located between the bonding surface 26 of the active material plate element 24 and the positive electrode current collector 21 is also shown by a two-dot chain line.

  The joining surface 26 of the active material plate element 24 includes a joining region 261 and a non-joining region 262. . In FIG. 3, in order to facilitate understanding of the drawing, parallel oblique lines are given to the joint regions 261 and 262. The bonding region 261 is a region where the bonding layer element 25 of the conductive bonding layer 23 exists between the active material plate element 24 and the positive electrode current collector 21. Therefore, in the joining region 261, the active material plate element 24 and the positive electrode current collector 21 are joined by the joining layer element 25. The non-joining region 262 is a region disposed around the joining region 261. In the non-bonding region 262, the conductive bonding layer 23 does not exist between the active material plate element 24 and the positive electrode current collector 21. Therefore, the active material plate element 24 and the positive electrode current collector 21 are not bonded in the non-bonded region 262.

  The bonding region 261 is located at the center of the bonding surface 26. In the example illustrated in FIG. 3, the bonding region 261 is a substantially circular region. The non-bonding region 262 preferably surrounds the entire periphery of the bonding region 261. In each bonding surface 26, the area of the non-bonding region 262 is, for example, 64% to 570%, preferably 64% to 400%, more preferably 64% to 200% of the area of the bonding region 261. . In other words, the area of the bonding region 261 is, for example, 15% to 61%, preferably 20% to 61% of the total area of the bonding region 261 and the non-bonding region 262 (that is, the total area of the bonding surface 26). More preferably, it is 30% to 61%.

  The negative electrode 3 includes a negative electrode current collector 31 and a negative electrode active material layer 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 exterior body 6 via the negative electrode bonding layer 64. The negative electrode active material layer 32 includes a carbonaceous material or a lithium storage 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 a metal foil formed of a metal such as copper, for example. The metal foil is made of various metals other than copper (for example, copper, stainless steel, nickel, aluminum, silver, gold, chromium, iron, tin, lead, tungsten, molybdenum, titanium, zinc, or alloys containing them) ). 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 various other materials. In the negative electrode active material layer 32, the carbonaceous material is, for example, natural graphite, artificial graphite, non-graphitizable carbon having amorphous, or graphitizable carbon, and the lithium storage material is, for example, silicon, Aluminum, tin, iron, iridium, or an alloy, oxide, fluoride, or the like containing these.

  The thickness of the negative electrode current collector 31 is, for example, 5 μm to 25 μm, preferably 8 μm to 20 μm, and more preferably 8 μm to 15 μm. The thickness of the negative electrode active material layer 32 is, for example, 20 μm to 300 μm, preferably 30 μm to 250 μm, and more preferably 30 μm to 150 μm.

  As described above, the lithium secondary battery 1 includes the positive electrode 2, the negative electrode 3, and the electrolyte 5. The electrolyte 5 is interposed between the positive electrode 2 and the negative electrode 3. The positive electrode 2 includes a sheet-shaped current collector having conductivity (that is, the positive electrode current collector 21) and an active material plate (that is, a positive electrode active material plate 22) that is a plate-shaped ceramic sintered body containing a lithium composite oxide. ). The positive electrode active material plate 22 is bonded to the positive electrode current collector 21 via the conductive bonding layer 23. The conductive bonding layer 23 includes conductive powder and a binder containing a polyimide amide resin. Thereby, the gelatinization of the conductive bonding layer 23 due to the reaction with the electrolyte 5 at a high temperature or the like can be suppressed.

  The positive electrode active material plate 22 has a structure in which a plurality of primary particles having a layered rock salt structure are combined. The average inclination angle of the plurality of primary particles is greater than 0 ° and 30 ° or less. The average inclination angle is an average value of angles formed by the (003) planes of the plurality of primary particles and the main surface of the positive electrode active material plate 22. Thereby, the internal stress of the positive electrode active material plate 22 generated when the crystal lattice expands and contracts due to the charge / discharge cycle is applied to the main surface of the positive electrode active material plate 22 facing the conductive bonding layer 23 and the positive electrode current collector 21. It can suppress adding.

  As described above, the main surface of the positive electrode active material plate 22 in contact with the conductive bonding layer 23 is a main surface to which internal stress generated during expansion and contraction of the crystal lattice is difficult to be applied, and conductivity due to reaction with the electrolyte 5 or the like. By suppressing the gelation of the conductive bonding layer 23, it is possible to suppress a decrease in bonding strength between the positive electrode active material plate 22 and the positive electrode current collector 21. As a result, the voltage stability during charging and discharging of the lithium secondary battery 1 can be improved.

  As described above, in the lithium secondary battery 1, it is possible to suppress a decrease in the bonding strength between the positive electrode active material plate 22 and the positive electrode current collector 21, so that the positive electrode active material plate 22 is deformed when the lithium secondary battery 1 is deformed. Can be prevented from being detached from the positive electrode current collector 21. Therefore, the lithium secondary battery 1 is particularly suitable for a power supply source in a device that is relatively easily deformed and is easily subjected to a bending load, that is, a sheet-like device or a flexible device.

  When the lithium secondary battery 1 is used as a power supply source in a smart card which is one of the flexible devices, the processing temperature is increased during the manufacture of the smart card, and the positive electrode active material plate 22 It is possible to preferably achieve both suppression of desorption from the positive electrode current collector 21. The processing at the time of manufacturing the smart card is, for example, lamination processing of a smart card. In the lithium secondary battery 1, for example, even in hot lamination processing at a processing temperature of 100 ° C. to 150 ° C., a decrease in bonding strength between the positive electrode active material plate 22 and the positive electrode current collector 21 can be suppressed.

  In Tables 1 and 2, the weight ratio of the conductive powder and the binder in the conductive bonding layer 23, the value obtained by dividing the weight of the conductive powder in the conductive bonding layer 23 by the weight of the binder, the thickness of the conductive bonding layer 23 , The porosity of the active material plate element 24, the bonding strength of the active material plate element 24 and the positive electrode current collector 21 when the presence or absence of the conductive carbon layer in the positive electrode current collector 21 is changed, and the lithium secondary The battery characteristic of the battery 1 is shown.

  In Examples 1 to 5 and 9 to 11, the peel strength measured in the peel test was 0.25 N or more, and the active material plate element 24 and the positive electrode current collector 21 were mechanically suitably bonded. Moreover, in Examples 1-5 and 9-11, 1C / 0.5C which shows a battery characteristic is 75% or more, and the active material board element 24 and the positive electrode collector 21 are electrically connected suitably. It was.

  In Example 6, since the weight ratio of the conductive powder was relatively small, the electrical characteristics were slightly low, but the active material plate element 24 and the positive electrode current collector 21 were mechanically suitably joined. In Example 7, since the binder weight ratio was relatively small, the peel strength was slightly small, but the active material plate element 24 and the positive electrode current collector 21 were electrically connected appropriately. In Example 8, since the conductive bonding layer 23 was relatively thick, the electrical characteristics were slightly low, but the active material plate element 24 and the positive electrode current collector 21 were mechanically suitably bonded.

  The peel test was performed in the following procedure using a peel tester. As a peel tester, a force gauge “ZTA-20N” manufactured by Imada Co., Ltd. and a vertical electric measurement stand “MX2-500N” were used.

  In the peeling test, first, an active material plate element 24 was bonded onto a current collector test piece corresponding to the positive electrode current collector 21 via a conductive bonding layer 23 to prepare a test piece. The active material plate element 24 is a square plate having a side of 10 mm in plan view. The current collector test piece is an aluminum foil having a thickness of 9 μm manufactured by Fukuda Metal Foil Powder Co., Ltd., and has a rectangular shape of 10 mm × 30 mm in plan view. The conductive bonding layer 23 was applied in a substantially circular shape to the central portion of the bonding surface 26 of the active material plate element 24. The active material plate element 24 was bonded to one end in the longitudinal direction of the current collector test piece via the conductive bonding layer 23.

  Subsequently, the test piece was fixed on a metal plate, and the metal plate was set in a peel tester. The test piece is fixed to the metal plate by attaching the main surface of the active material plate element 24 of the test piece (that is, the main surface opposite to the main surface facing the current collector test piece) via a carbon tape or the like. This was done by bonding to a metal plate. Next, the other end in the longitudinal direction of the current collector test piece (that is, the end opposite to the end where the active material plate element 24 is joined) is perpendicular to the metal plate by a peel tester. Pulled in the right direction. And the maximum value of the tensile strength at the time of a collector test piece peeling from the active material board element 24 was acquired as "peeling strength."

  As can be seen from Examples 1 to 3 and Examples 6 and 7, in the lithium secondary battery 1, the weight of the conductive powder in the conductive bonding layer 23 is 50% or more and 1000% or less of the weight of the binder. It is preferable that Thereby, in the lithium secondary battery 1, the increase in conduction between the positive electrode active material plate 22 and the positive electrode current collector 21 and the suppression of the decrease in bonding strength can be suitably achieved. Specifically, by setting the weight of the conductive powder to 50% or more of the weight of the binder, conduction between the positive electrode active material plate 22 and the positive electrode current collector 21 can be increased, and the positive electrode active material plate 22 and the positive electrode current collector 21 can be electrically connected suitably. Further, by setting the weight of the conductive powder to 1000% or less of the weight of the binder, the bonding strength between the positive electrode active material plate 22 and the positive electrode current collector 21 can be increased, and the positive electrode active material plate 22 and the positive electrode current collector can be increased. The electric body 21 can be mechanically suitably connected.

  As can be seen from Examples 1, 4, and 8 described above, the thickness of the conductive bonding layer 23 is preferably 3 μm or more and 28 μm or less. By setting the thickness of the conductive bonding layer 23 to 3 μm or more, the bonding strength between the positive electrode active material plate 22 and the positive electrode current collector 21 can be increased. Moreover, the positive electrode 2 and the lithium secondary battery 1 can be thinned by setting the thickness of the conductive bonding layer 23 to 28 μm or less.

  As can be seen from Examples 1, 5, 9, and 10 described above, in the lithium secondary battery 1, the porosity of the positive electrode active material plate 22 is preferably 25% or more and 45% or less. As described above, the pores include both open pores and closed pores, and the number of open pores is increased by setting the porosity of the positive electrode active material plate 22 to 25% or more. As a result, a part of the conductive bonding layer 23 suitably enters the open pores of the positive electrode active material plate 22. Then, the bonding strength between the positive electrode active material plate 22 and the positive electrode current collector 21 can be increased by the anchor effect of the conductive bonding layer 23 that has entered the open pores of the positive electrode active material plate 22. In particular, when the weight of the conductive powder in the conductive bonding layer 23 is 50% or more and 1000% or less of the weight of the binder, the conductive bonding layer 23 more appropriately enters the open pores. Can be increased. Moreover, the capacity | capacitance of the lithium secondary battery 1 can be enlarged by making the porosity of the positive electrode active material board 22 into 45% or less.

  As can be seen from Examples 1 and 11, the main surface of the positive electrode current collector 21 facing the positive electrode active material plate 22 is preferably covered with a conductive conductive carbon layer. Thereby, the electrical connection between the positive electrode current collector 21 and the positive electrode active material plate 22 can be increased. As a result, the output of the lithium secondary battery 1 can be increased (that is, the battery characteristics can be improved).

  Various modifications can be made in the above-described lithium secondary battery 1.

  For example, the thickness of the conductive bonding layer 23 may be less than 3 μm or greater than 28 μm.

  The components of the conductive bonding layers 23 and 33a may be variously changed. For example, the weight of the conductive powder may be less than 50% of the weight of the binder and may be greater than 1000%.

  The porosity of the positive electrode active material plate 22 may be less than 25% or greater than 45%.

  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 a single plate-like ceramic sintered body.

  The lithium secondary battery 1 is a flexible device (for example, a card-type device) other than a smart card, or a sheet-like device (for example, a wearable device provided on clothes or a body-attached device). It may be used as a power supply source. Further, the lithium secondary battery 1 may be used as a power supply source for various objects (for example, an IoT module) other than the above-described devices.

  The configurations in the above-described embodiments and modifications may be combined as appropriate as long as they do not contradict each other.

  The lithium secondary battery of the present invention can be used in various fields where a lithium secondary battery is used, for example, as a power supply source in a smart card having an arithmetic processing function.

DESCRIPTION OF SYMBOLS 1 Lithium secondary battery 2 Positive electrode 3 Negative electrode 5 Electrolyte 21 Positive electrode collector 22 Positive electrode active material board 23 Conductive joining layer

Claims (7)

A thin lithium secondary battery,
A positive electrode;
A negative electrode,
An electrolyte interposed between the positive electrode and the negative electrode;
With
The positive electrode is
A sheet-like current collector having conductivity;
A plate-like ceramic sintered body containing a lithium composite oxide, an active material plate joined to the current collector through a conductive joining layer;
With
The conductive bonding layer is
Conductive powder;
A binder containing a polyimide amide resin;
Including
The active material plate has a structure in which a plurality of primary particles having a layered rock salt structure are combined,
The average inclination angle of the plurality of primary particles is greater than 0 ° and 30 ° or less,
The average inclination angle is an average value of an angle formed by a (003) plane of the plurality of primary particles and a main surface of the active material plate. The lithium secondary battery according to claim 1,
The lithium secondary battery according to claim 1, wherein the weight of the conductive powder in the conductive bonding layer is 50% or more and 1000% or less of the weight of the binder. The lithium secondary battery according to claim 1 or 2,
The lithium secondary battery, wherein the conductive bonding layer has a thickness of 3 μm or more and 28 μm or less. A lithium secondary battery according to any one of claims 1 to 3,
The lithium secondary battery, wherein the active material plate has a porosity of 25% or more and 45% or less. A lithium secondary battery according to any one of claims 1 to 4,
A lithium secondary battery, wherein a main surface of the current collector facing the active material plate is covered with a conductive carbon layer. A lithium secondary battery according to any one of claims 1 to 5,
A lithium secondary battery, which is used as a power supply source in a sheet-like device or a flexible device. The lithium secondary battery according to claim 6,
A lithium secondary battery, which is used as a power supply source in a smart card which is the flexible device.

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