阅读说明：本技术 锂二次电池及内置电池的卡片
(Lithium secondary battery and card with built-in battery
) 是由 大塚春男
藤田雄树
小林伸行 于 2019-02-27 设计创作，主要内容包括：提供一种覆膜形态的锂二次电池,其尽管具备锂复合氧化物烧结体板作为正极板,但即使反复弯曲,也不容易在正极板端部附近产生褶皱。该锂二次电池具备：锂复合氧化物烧结体板亦即正极板、负极层、隔板、电解液和1对外包装膜,所述1对外包装膜的外周缘彼此密封而形成收纳电池元件的内部空间,负极层及隔板的相当于外延部的部分比负极层及隔板的相当于主体部的部分更偏向正极板侧。(Provided is a film-form lithium secondary battery which, despite having a lithium composite oxide sintered plate as a positive electrode plate, is less likely to have wrinkles in the vicinity of the end of the positive electrode plate even when repeatedly bent. The lithium secondary battery includes: the lithium composite oxide sintered plate includes a positive electrode plate, a negative electrode layer, a separator, an electrolyte, and 1 pair of outer films, wherein outer peripheral edges of the 1 pair of outer films are sealed with each other to form an internal space for housing a battery element, and portions of the negative electrode layer and the separator corresponding to the extension portions are shifted to the positive electrode plate side than portions of the negative electrode layer and the separator corresponding to the body portion.)
1. A lithium secondary battery is provided with:
a positive electrode plate which is a lithium composite oxide sintered plate;
a carbon-containing negative electrode layer having a size larger than that of the positive electrode plate;
a separator interposed between the positive electrode plate and the negative electrode layer, the separator having a size greater than the size of the positive electrode plate and the negative electrode layer;
an electrolyte impregnated into the positive electrode plate, the negative electrode layer, and the separator; and
1 pairs of outer packaging films, wherein the outer peripheries of the 1 pairs of outer packaging films are sealed with each other to form an inner space, and the positive electrode plate, the negative electrode layer, the separator and the electrolyte are accommodated in the inner space,
Wherein the content of the first and second substances,
an outer peripheral portion of the separator is in close contact with at least the outer peripheral edge of the outer film on the positive electrode plate side or a peripheral region in the vicinity thereof, and partitions a section for housing the positive electrode and a section for housing the negative electrode,
the lithium secondary battery includes:
a body portion having a multilayer structure including the positive electrode plate, the separator, the negative electrode layer, and the 1 pair of outer films over an entire region; and
an extension portion located further to the outside than the outer peripheral edge of the positive electrode plate and having the separator, the negative electrode layer, and the 1 pair of outer packaging films,
the portions of the negative electrode layer and the separator corresponding to the extended portions are closer to the positive electrode plate side than the portions of the negative electrode layer and the separator corresponding to the main body portion.
2. The lithium secondary battery according to claim 1,
the lithium secondary battery is a thin secondary battery that can be built in a card.
3. The lithium secondary battery according to claim 1 or 2,
the thickness of the lithium secondary battery is 350 to 500 [ mu ] m.
4. The lithium secondary battery according to any one of claims 1 to 3,
the thickness of the positive plate is 70-120 mu m.
5. The lithium secondary battery according to any one of claims 1 to 4,
the spacing distance between the end of the positive electrode plate and the end of the negative electrode layer is 50-2000 mu m on the whole periphery of the positive electrode plate and the negative electrode layer.
6. The lithium secondary battery according to any one of claims 1 to 5,
the thickness of the negative electrode layer is 70-160 mu m.
7. The lithium secondary battery according to any one of claims 1 to 6,
the thickness of each outer packaging film is 50-80 mu m.
8. The lithium secondary battery according to any one of claims 1 to 7,
the outer packaging film is a laminated film comprising a resin film and a metal foil.
9. The lithium secondary battery according to any one of claims 1 to 8,
the separator is made of polyolefin, polyimide or cellulose.
10. The lithium secondary battery according to any one of claims 1 to 9,
the lithium composite oxide is lithium cobaltate.
11. The lithium secondary battery according to any one of claims 1 to 10,
the lithium composite oxide sintered body plate is an oriented positive electrode plate that includes a plurality of primary particles made of a lithium composite oxide, and the plurality of primary particles are oriented at an average orientation angle of more than 0 DEG and 30 DEG or less with respect to a plate surface of the positive electrode plate.
12. The lithium secondary battery according to any one of claims 1 to 11,
the battery element further includes a positive electrode current collector and a negative electrode current collector.
13. A card with a built-in battery includes:
a resin base material; and
the lithium secondary battery according to any one of claims 1 to 12 embedded in the resin base.
Technical Field
The present invention relates to a lithium secondary battery and a card incorporating the battery.
Background
In recent years, smart cards incorporating a battery have been put to practical use. An example of a smart card with a built-in primary battery is a credit card with a one-time password display function. As an example of a smart card incorporating a secondary battery, a card with fingerprint authentication/wireless communication functions, which includes a wireless communication IC, an ASIC for fingerprint analysis, and a fingerprint sensor, can be given. Batteries for smart cards are generally required to have a thickness of less than 0.45mm, a high capacity, a low resistance, a bending resistance, and a process temperature resistance.
Secondary batteries for this purpose and cards carrying secondary batteries have been proposed. For example, patent document 1 (japanese patent application laid-open No. 2017-79192) discloses a secondary battery that is built in a plate-like member such as a card and has sufficient strength even when the plate-like member is bent. The secondary battery includes: an electrode body including a positive electrode and a negative electrode; a sheet-like laminate film exterior body whose outer peripheral side is welded in a state of covering the electrode body; and a positive electrode connection terminal and a negative electrode connection terminal, one end of which is connected to the electrode body and the other end of which extends from the laminate film exterior body to the outside. Further, patent document 2 (jp 2006-331838 a) discloses a thin battery in which large wrinkles are not easily generated on the surface and which has excellent buckling resistance. The thin battery includes: a battery body portion in which a separator, a positive electrode layer, and a negative electrode layer are housed between a positive electrode current collector and a negative electrode current collector; and a sealing part including a resin frame member for sealing the periphery of the battery body part, wherein D1 is 100 μm or more and 320 μm or less and D1/D2 is 0.85 or less, where D1 is the thickness of the sealing part and D2 is the maximum thickness of the battery center part. In the secondary batteries disclosed in patent documents 1 and 2, a powder dispersion type positive electrode is used, which is produced by applying a positive electrode mixture containing a positive electrode active material, a conductive auxiliary agent, a binder, and the like, and drying the positive electrode mixture.
However, in general, since the powder dispersion type positive electrode contains a large amount (for example, about 10% by weight) of components (binder and conductive assistant) that do not contribute to capacity, the packing density of the lithium composite oxide as the positive electrode active material is lowered. Therefore, the powder dispersion type positive electrode has a large room for improvement in capacity and charge/discharge efficiency. Therefore, attempts have been made to improve the capacity and the charge/discharge efficiency by forming the positive electrode or the positive electrode active material layer from a lithium composite oxide sintered plate. In this case, since the positive electrode or the positive electrode active material layer does not contain a binder or a conductive auxiliary agent, the packing density of the lithium composite oxide becomes high, and high capacity and good charge/discharge efficiency can be expected. For example, patent document 3 (japanese patent No. 5587052) discloses a positive electrode for a lithium secondary battery, including: a positive electrode current collector; and a positive electrode active material layer bonded to the positive electrode current collector via the conductive bonding layer. The positive electrode active material layer is composed of a lithium composite oxide sintered plate having a thickness of 30 [ mu ] m or more, a porosity of 3 to 30%, and an open pore ratio of 70% or more. Patent document 4 (international publication No. 2017/146088) discloses the use of an oriented sintered body plate containing lithium cobaltate (LiCoO) as a positive electrode of a lithium secondary battery having a solid electrolyte 2) And a plurality of primary particles made of the lithium composite oxide, wherein the plurality of primary particles are oriented at an average orientation angle of more than 0 DEG and not more than 30 DEG with respect to the plate surface of the positive electrode plate.
Disclosure of Invention
However, the card incorporating the film-covered battery including the sintered lithium composite oxide plate (positive electrode plate) as disclosed in patent documents 3 and 4 has the following problems: when a repeated bending test is performed up to several hundred times as required by JIS (japanese industrial standards), wrinkles are likely to occur on the surface of the card near the end of the positive electrode plate.
The inventors have now obtained the following insights: in a lithium secondary battery in the form of a film-coated battery provided with a positive electrode sintered body plate, the portions of the negative electrode layer and the separator corresponding to the extended portions are formed so as to be more on the positive electrode plate side than the portions of the negative electrode layer and the separator corresponding to the main body portion, and therefore, even if the lithium secondary battery is repeatedly bent, wrinkles are less likely to occur in the vicinity of the end portion of the positive electrode plate. The following insights have also been obtained: in particular, when the coated lithium secondary battery satisfying the above conditions is subjected to repeated bending tests of several hundred times as required by JIS standards in the form of a card of a built-in battery, wrinkles are not easily generated in the vicinity of the end of the positive electrode plate.
Accordingly, an object of the present invention is to provide a film-coated lithium secondary battery including a lithium composite oxide sintered plate as a positive electrode plate, which is less likely to cause wrinkles in the vicinity of the end of the positive electrode plate even when repeatedly bent (particularly, in the form of a card incorporating the battery).
According to one aspect of the present invention, there is provided a lithium secondary battery including:
a positive electrode plate which is a lithium composite oxide sintered plate;
a carbon-containing negative electrode layer having a size larger than that of the positive electrode plate;
a separator interposed between the positive electrode plate and the negative electrode layer, the separator having a size greater than the size of the positive electrode plate and the negative electrode layer;
an electrolyte impregnated into the positive electrode plate, the negative electrode layer, and the separator; and
1 pairs of outer packaging films, wherein the outer peripheries of the 1 pairs of outer packaging films are sealed with each other to form an inner space, and the positive electrode plate, the negative electrode layer, the separator and the electrolyte are accommodated in the inner space,
wherein the content of the first and second substances,
an outer peripheral portion of the separator is in close contact with at least the outer peripheral edge of the outer film on the positive electrode plate side or a peripheral region in the vicinity thereof, and partitions a section for housing the positive electrode and a section for housing the negative electrode,
The lithium secondary battery includes:
a body portion having a multilayer structure including the positive electrode plate, the separator, the negative electrode layer, and the 1 pair of outer films over an entire region; and
an extension portion located further to the outside than the outer peripheral edge of the positive electrode plate and having the separator, the negative electrode layer, and the 1 pair of outer packaging films,
the portions of the negative electrode layer and the separator corresponding to the extended portions are closer to the positive electrode plate side than the portions of the negative electrode layer and the separator corresponding to the main body portion.
According to another aspect of the present invention, there is provided a battery-embedded card including a resin base and the lithium secondary battery embedded in the resin base.
Drawings
Fig. 1A is a schematic cross-sectional view conceptually showing an example of a lithium secondary battery of the present invention.
Fig. 1B is a schematic cross-sectional view showing an enlarged structure of an epitaxial portion of the lithium secondary battery shown in fig. 1A.
Fig. 2A is a view showing a first half of an example of a manufacturing process of a lithium secondary battery.
Fig. 2B is a diagram illustrating a second half of an example of a process for manufacturing a lithium secondary battery, which is a process performed subsequent to the process illustrated in fig. 2A. The right end of fig. 2B includes a photograph of a film coated battery.
Fig. 3 is an SEM image showing an example of a cross section perpendicular to the plate surface of the oriented positive electrode plate.
Fig. 4 is an EBSD image at a cross-section of the oriented positive plate shown in fig. 3.
Fig. 5 is a histogram showing a distribution of orientation angles of primary particles in the EBSD image of fig. 4 on an area basis.
Fig. 6 is a laser microscope image obtained by imaging a cross section of the lithium secondary battery produced in example 1.
Fig. 7 is a schematic diagram for explaining a surface profile of the height H of the convex portion generated on the card surface by the repeated bending test.
Detailed Description
Lithium secondary battery
Fig. 1A and 1B schematically show an example of a lithium secondary battery of the present invention. The lithium secondary battery 10 shown in fig. 1A and 1B includes a positive electrode plate 16, a separator 18, a negative electrode layer 20, an electrolyte (not shown), and 1 pair of outer films 26. The positive electrode plate 16 is a lithium composite oxide sintered plate. Negative electrode layer 20 comprises carbon and is larger in size than positive electrode plate 16. The separator 18 is interposed between the positive electrode plate 16 and the negative electrode layer 20 and has a size larger than those of the positive electrode plate 16 and the negative electrode layer 20. The electrolyte permeates into positive electrode plate 16, negative electrode layer 20, and separator 18. In the case of 1 pair of outer films 26, the outer peripheries thereof are sealed to each other to form an internal space, and the positive electrode plate 16, the negative electrode layer 20, the separator 18, and the electrolyte are accommodated in the internal space. The outer peripheral portion of the separator 18 is in close contact with at least the outer peripheral edge of the outer film 26 on the positive electrode plate 16 side or its vicinity, and partitions the region accommodating the positive electrode plate 16 and the region accommodating the negative electrode layer 20. In addition, the lithium secondary battery 10 includes: a main body portion M having a multilayer structure including the positive electrode plate 16, the separator 18, the negative electrode layer 20, and 1 pair of outer films 26 over the entire area; and an extended portion E located outside the outer peripheral edge of the positive electrode plate 16, and having the separator 18, the negative electrode layer 20, and 1 pair of outer films 26. The portions of the negative electrode layer 20 and the separator 18 corresponding to the extended portions E are located closer to the positive electrode plate 16 than the portions of the negative electrode layer 20 and the separator 18 corresponding to the main body portion M. In the lithium secondary battery 10 of the film battery type including the positive electrode sintered body plate, the portions of the negative electrode layer 20 and the separator 18 corresponding to the extended portions E are formed in a shape shifted toward the positive electrode plate 16 side from the portions of the negative electrode layer 20 and the separator 18 corresponding to the body portion M, and therefore, wrinkles are less likely to occur in the vicinity of the end portion of the positive electrode plate even when the battery is repeatedly bent. In particular, even when the lithium secondary battery 10 satisfying the above conditions is subjected to repeated bending tests of several hundred times as required by JIS standards in the form of a card with a built-in battery, wrinkles are not easily generated in the vicinity of the end of the positive electrode plate.
That is, as described above, the card incorporating the film-covered battery including the lithium composite oxide sintered plate (positive electrode plate) as disclosed in patent documents 3 and 4 has the following problems: when a repeated bending test is performed up to several hundred times as required by JIS standard, wrinkles are likely to occur on the surface of the card near the end of the positive electrode plate. In this regard, according to the lithium secondary battery of the present invention, these wrinkles can be effectively suppressed. The reason is considered to be that, as specifically shown in fig. 1B, the outer shape of the outer film 26 following the shape of the positive electrode plate 16 and the negative electrode layer 20 is formed into a sectional shape converging in multiple stages toward the outer peripheral edge thereof by the shape of the negative electrode layer 20 and the separator 18 toward the positive electrode plate 16 side rather than the portion thereof corresponding to the main body portion M, and as a result, the end portion of the positive electrode plate 16 is less likely to push up the outer film 26. Therefore, the lithium secondary battery 10 of the present invention is preferably a thin secondary battery that can be incorporated in a card, and more preferably a thin secondary battery that is embedded in a resin substrate and used for card formation. That is, according to another preferred embodiment of the present invention, there is provided a battery-incorporated card including a resin base and a lithium secondary battery embedded in the resin base. A typical embodiment of the battery-equipped card includes 1 pair of resin films and a lithium secondary battery sandwiched between the 1 pair of resin films, and preferably, the resin films are bonded to each other with an adhesive or the resin films are thermally bonded to each other by hot pressing.
As described above, the portions of the negative electrode layer 20 and the separator 18 corresponding to the extended portions E are located closer to the positive electrode plate 16 than the portions of the negative electrode layer 20 and the separator 18 corresponding to the main body portion M. Here, "toward the positive electrode plate 16 side" means: when a center line passing through the center in the thickness direction of the negative electrode layer 20 or the separator 18 is drawn in the cross section of the lithium secondary battery 10, the center line at the extended portion E is offset toward the positive electrode plate 16 (i.e., toward the outer film 26 in contact with the positive electrode plate 16) from the center line at the main body portion M. In other words, it can be said that this means: the portions of negative electrode layer 20 and separator 18 corresponding to extended portion E enter (penetrate) the outer region around positive electrode plate 16.
The positive electrode plate 16 is a lithium composite oxide sintered plate. The positive electrode plate 16 being a sintered plate means that the positive electrode plate 16 does not contain a binder. This is because, even if the green sheet contains a binder, the binder disappears or burns off during firing. Further, since the positive electrode plate 16 does not contain a binder, there is an advantage that deterioration of the positive electrode due to the electrolyte can be avoided. The lithium composite oxide constituting the sintered body plate is preferably lithium cobaltate (typically LiCoO)2(hereinafter sometimes abbreviated as LCO)). Various lithium composite oxide sintered plates and LCO sintered plates are known, and for example, sintered plates disclosed in patent document 3 (japanese patent No. 5587052) and patent document 4 (international publication No. 2017/146088) can be used.
According to a preferred embodiment of the present invention, the positive electrode plate 16, i.e., the lithium composite oxide sintered plate, is an oriented positive electrode plate that includes a plurality of primary particles made of a lithium composite oxide and is oriented at an average orientation angle of more than 0 ° and 30 ° or less with respect to a plate surface of the positive electrode plate. Fig. 3 shows an example of an SEM image of a cross section perpendicular to the plate surface of the oriented positive electrode plate 16, and fig. 4 shows an Electron Back Scattering Diffraction (EBSD) image of a cross section perpendicular to the plate surface of the oriented positive electrode plate 16. Fig. 5 shows a histogram showing the distribution of the orientation angles of the primary particles 11 in the EBSD image of fig. 4 on an area basis. In the EBSD image shown in fig. 4, discontinuity of crystal orientation can be observed. In fig. 4, the orientation angle of each primary particle 11 is represented by the shade of the color, and the darker the color, the smaller the orientation angle. The orientation angle is an inclination angle of the (003) plane of each primary particle 11 with respect to the plate surface direction. In fig. 3 and 4, the portions indicated by black inside the oriented positive electrode plate 16 are air holes.
The oriented positive electrode plate 16 is an oriented sintered body composed of a plurality of primary particles 11 bonded to each other. Each primary particle 11 is mainly plate-shaped, but may include primary particles formed in a rectangular parallelepiped shape, a cubic shape, a spherical shape, or the like. The cross-sectional shape of each primary particle 11 is not particularly limited, and may be a rectangle, a polygon other than a rectangle, a circle, an ellipse, or a complex shape other than these.
Each primary particle 11 is made of a lithium composite oxide. The lithium composite oxide is made of LixMO2(0.05<x<1.10, M is at least one transition metal, M typically comprises one or more of Co, Ni and Mn). The lithium composite oxide has a layered rock salt structure. The layered rock salt structure refers to: 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, a crystal structure in which a transition metal ion layer and a lithium single layer are alternately stacked with an oxide ion interposed therebetween (typically, α -NaFeO2Type structure, i.e. transition metal and lithium along cubic rock salt type structure [111 ]]A structure in which the axial directions are regularly arranged). Examples of the lithium composite oxide include LixCoO2(lithium cobaltate), LixNiO2(lithium nickelate), LixMnO2(lithium manganate), LixNiMnO2(lithium nickel manganese oxide), LixNiCoO2(lithium nickel cobalt oxide), LixCoNiMnO2(lithium cobalt nickel manganese oxide), LixCoMnO2(lithium cobalt manganese) and the like, and Li is particularly preferablexCoO2(lithium cobaltate, typically LiCoO)2). The lithium composite oxide may contain one or more elements selected from Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ag, Sn, Sb, Te, Ba, Bi, and W.
As shown in fig. 4 and 5, the average value of the orientation angles of the primary particles 11, that is, the average orientation angle exceeds 0 ° and is 30 ° or less. Thereby bringing about the following various advantages. First, since the primary particles 11 are in a state of lying down in a direction inclined with respect to the thickness direction, the adhesion between the primary particles can be improved. As a result, lithium ion conductivity between a certain primary particle 11 and other primary particles 11 adjacent to each other on both sides in the longitudinal direction of the primary particle 11 can be improved, and thus rate characteristics can be improved. Second, the magnification characteristics can be further improved. This is because: as described above, since the oriented positive electrode plate 16 is more likely to expand and contract in the thickness direction than in the plate surface direction when lithium ions are taken in, the lithium ions can be smoothly taken in and out when the expansion and contraction of the oriented positive electrode plate 16 are smooth.
The average orientation angle of the primary particles 11 is obtained by the following method. First, in an EBSD image shown in fig. 4, which is obtained by observing a rectangular region of 95 × 125 μm at a magnification of 1000 times, 3 horizontal lines that quartet the oriented positive electrode plate 16 in the thickness direction and 3 vertical lines that quartet the oriented positive electrode plate 16 in the plate surface direction are drawn. Next, the orientation angles of all the primary particles 11 intersecting at least 1 line of the 3 horizontal lines and 3 vertical lines are arithmetically averaged, thereby obtaining an average orientation angle of the primary particles 11. From the viewpoint of further improving the magnification characteristics, the average orientation angle of the primary particles 11 is preferably 30 ° or less, and more preferably 25 ° or less. From the viewpoint of further improving the magnification characteristics, the average orientation angle of the primary particles 11 is preferably 2 ° or more, and more preferably 5 ° or more.
As shown in fig. 5, the orientation angle of each primary particle 11 may be widely distributed from 0 ° to 90 °, and preferably, the majority thereof is distributed in a region exceeding 0 ° and being 30 ° or less. That is, when the cross section of the orientation sintered body constituting the orientation positive electrode plate 16 is analyzed by EBSD, the total area of the primary particles 11 (hereinafter referred to as low-angle primary particles) having an orientation angle exceeding 0 ° and not more than 30 ° with respect to the plate surface of the orientation positive electrode plate 16 among the primary particles 11 included in the analyzed cross section is preferably 70% or more, and more preferably 80% or more, with respect to the total area of the primary particles 11 included in the cross section (specifically, 30 primary particles 11 for calculating the average orientation angle). This can increase the proportion of the primary particles 11 having high mutual adhesion, and thus can further improve the rate characteristics. More preferably, the total area of the primary particles having an orientation angle of 20 ° or less among the low-angle primary particles is 50% or more of the total area of the 30 primary particles 11 used for calculating the average orientation angle. Further, it is more preferable that the total area of the primary particles having an orientation angle of 10 ° or less among the low-angle primary particles is 15% or more with respect to the total area of the 30 primary particles 11 used for calculating the average orientation angle.
Since each primary particle 11 is mainly plate-shaped, the cross section of each primary particle 11 extends in a predetermined direction, typically, is substantially rectangular, as shown in fig. 3 and 4. That is, when the cross section of the oriented sintered body is analyzed by EBSD, the total area of the primary particles 11 having an aspect ratio of 4 or more in the primary particles 11 included in the analyzed cross section is preferably 70% or more, and more preferably 80% or more, with respect to the total area of the primary particles 11 included in the cross section (specifically, 30 primary particles 11 for calculating the average orientation angle). Specifically, in the EBSD image shown in fig. 4, the mutual adhesion between the primary particles 11 can be further improved, and as a result, the magnification characteristics can be further improved. The aspect ratio of the primary particles 11 is a value obtained by dividing the maximum feret diameter by the minimum feret diameter of the primary particles 11. The maximum feret diameter is: the maximum distance between the primary particles 11 in the EBSD image in the cross-sectional observation when the primary particles are sandwiched between 2 parallel straight lines. The minimum Ferrett diameter is: the minimum distance between the parallel 2 straight lines of the primary particle 11 on the EBSD image.
The average particle diameter of the plurality of primary particles constituting the oriented sintered body is preferably 5 μm or more. Specifically, the average particle diameter of the 30 primary particles 11 used for calculating the average orientation angle is preferably 5 μm or more, more preferably 7 μm or more, and still more preferably 12 μm or more. This reduces the number of grain boundaries between the primary particles 11 in the direction of lithium ion conduction, thereby improving the overall lithium ion conductivity, and thus further improving the rate characteristics. The average particle diameter of the primary particles 11 is a value obtained by arithmetically averaging the equivalent circle diameters of the primary particles 11. The equivalent circle diameter is: the diameter of a circle having the same area as each primary particle 11 on the EBSD image.
The density of the oriented sintered body constituting the oriented positive electrode plate 16 is preferably 70% or more, more preferably 80% or more, and still more preferably 90% or more. This can further improve the adhesiveness between the primary particles 11, and thus can further improve the rate characteristics. The density of the oriented sintered body was calculated as follows: the density was calculated by grinding the cross section of the positive electrode plate by CP (cross-sectional polishing) grinding, observing the cross section with SEM at 1000 magnifications, and binarizing the obtained SEM image. The average equivalent circle diameter of each pore formed in the oriented sintered body is not particularly limited, but is preferably 8 μm or less. As the average equivalent circle diameter of each pore is smaller, the adhesiveness between the primary particles 11 can be further improved, and as a result, the magnification characteristics can be further improved. The average equivalent circle diameter of the air holes is a value obtained by arithmetically averaging the equivalent circle diameters of 10 air holes on the EBSD image. The equivalent circle diameter is: the diameter of a circle on the EBSD image having the same area as each air hole. The pores formed in the oriented sintered body may be open pores connected to the outside of the oriented positive electrode plate 16, but preferably do not penetrate the oriented positive electrode plate 16. Each air hole may be a closed air hole.
The thickness of the positive electrode plate 16 is not particularly limited, but is preferably 70 to 120 μm, more preferably 80 to 100 μm, still more preferably 80 to 95 μm, and particularly preferably 85 to 95 μm. Within this range, the active material capacity per unit area can be increased, the energy density of the lithium secondary battery 10 can be increased, deterioration of battery characteristics (particularly, an increase in resistance value) due to repeated charge and discharge can be suppressed, and the occurrence of wrinkles in the vicinity of the end of the positive electrode plate 16 due to repeated bending can be more effectively suppressed. The size of the positive electrode plate 16 is preferably 5mm × 5mm square or more, and more preferably 10mm × 10mm to 200mm × 200mm square, more preferably 10mm × 10mm to 100mm × 100mm square; in other words, it is preferably 25mm2More preferably 100 to 40000mm2More preferably 100 to 10000mm2。
The negative electrode layer 20 contains carbon as a negative electrode active material. Examples of the carbon include graphite (graphite), pyrolytic carbon, coke, a resin fired body, mesophase spherule, mesophase pitch, and the like, and graphite is preferable. The graphite may be any one of natural graphite and artificial graphite. The negative electrode layer 20 preferably further includes a binder. Examples of the binder include styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), and the like, and styrene-butadiene rubber (SBR) or polyvinylidene fluoride (PVDF) is preferable. Particularly, when γ -butyrolactone (GBL) having excellent heat resistance is used as the electrolyte, styrene-butadiene rubber (SBR) is more preferably used as the binder, because it is difficult to dissolve in GBL and deterioration of the binder function due to heating can be avoided.
The thickness of the negative electrode layer 20 is not particularly limited, but is preferably 70 to 160 μm, more preferably 80 to 150 μm, still more preferably 90 to 140 μm, and particularly preferably 100 to 130 μm. Within this range, the active material capacity per unit area can be increased, the energy density of the lithium secondary battery 10 can be increased, and the occurrence of wrinkles in the vicinity of the end of the positive electrode plate 16 due to repeated bending can be more effectively suppressed.
The separator 18 is preferably a separator made of polyolefin, polyimide, polyester (e.g., polyethylene terephthalate (PET)), or cellulose. Examples of polyolefins include polypropylene (PP), Polyethylene (PE), and combinations thereof. From the viewpoint of low cost, a separator made of polyolefin or cellulose is preferable. In addition, the surface of the separator 18 may be made of aluminum oxide (Al)2O3) Magnesium oxide (MgO), silicon oxide (SiO)2) And the like. On the other hand, a separator made of polyimide or cellulose is preferable from the viewpoint of excellent heat resistance. Unlike separators made of widely used polyolefin having poor heat resistance, separators made of polyimide, polyester (for example, polyethylene terephthalate (PET)), or cellulose are made ofThe composition has excellent heat resistance, and also has excellent wettability to gamma-butyrolactone (GBL) which is an electrolyte component having excellent heat resistance. Therefore, in the case of using an electrolytic solution containing GBL, the electrolytic solution can be sufficiently permeated (without being repelled) into the separator. A particularly preferred separator is a polyimide separator from the viewpoint of heat resistance. Polyimide separators are commercially available, and have extremely complicated fine structures, and therefore have the following advantages: the extension of lithium dendrites precipitated upon overcharge and the short circuit caused thereby can be more effectively prevented or delayed.
The electrolyte (not shown) is not particularly limited, and a lithium salt (e.g., LiPF) may be used6) And a commercially available electrolyte for lithium batteries, such as a liquid obtained by dissolving the electrolyte in an organic solvent (for example, a mixed solvent of Ethylene Carbonate (EC) and ethyl methyl carbonate (MEC), a mixed solvent of Ethylene Carbonate (EC) and diethyl carbonate (DEC), or a mixed solvent of Ethylene Carbonate (EC) and Ethyl Methyl Carbonate (EMC)).
In the case of forming a lithium secondary battery having excellent heat resistance, it is preferable that the electrolyte solution contains lithium fluoroborate (LiBF) in a nonaqueous solvent4). In this case, the nonaqueous solvent may be a single solvent composed of γ -butyrolactone (GBL) or a mixed solvent composed of γ -butyrolactone (GBL) and Ethylene Carbonate (EC). When the nonaqueous solvent contains gamma-butyrolactone (GBL), the boiling point increases, resulting in a significant improvement in heat resistance. From such a viewpoint, EC in the nonaqueous solvent: the volume ratio of GBL is preferably 0: 1-1: 1(GBL ratio 50 to 100 vol%), more preferably 0: 1-1: 1.5(GBL ratio 60 to 100 vol%), preferably 0: 1-1: 2(GBL ratio of 66.6 to 100 vol%), preferably 0: 1-1: 3(GBL ratio 75 to 100 vol%). Lithium fluoroborate (LiBF) dissolved in non-aqueous solvent 4) This is an electrolyte having a high decomposition temperature, and this also leads to a significant improvement in heat resistance. LiBF in electrolyte4The concentration is preferably 0.5 to 2mol/L, more preferably 0.6 to 1.9mol/L, still more preferably 0.7 to 1.7mol/L, and particularly preferably 0.8 to 1.5 mol/L.
The electrolyte preferably also contains Vinylene Carbonate (VC) and/or fluoroethylene carbonate (FEC) and/or Vinyl Ethylene Carbonate (VEC) as additives. VC and FEC are excellent in heat resistance. Therefore, when the electrolyte solution contains the additive, a SEI film having excellent heat resistance can be formed on the surface of negative electrode layer 20.
The thickness of the lithium secondary battery 10 is preferably 350 to 500. mu.m, more preferably 380 to 450 μm, and still more preferably 400 to 430. mu.m. With a thickness within such a range, a thin lithium battery suitable for being incorporated in thin devices such as smart cards can be formed. In addition, the occurrence of wrinkles in the vicinity of the end of the positive electrode plate 16 due to repeated bending is also suppressed.
The outer peripheries of the 1 pair of outer films 26 are sealed to each other to form an internal space, and the battery element 12 and the electrolyte are accommodated in the internal space. That is, as shown in fig. 1A and 1B, the battery element 12 and the electrolyte solution, which are the contents of the lithium secondary battery 10, are wrapped and sealed with the exterior film 26 by 1, and as a result, the lithium secondary battery 10 is in a so-called film battery form. Here, the battery element 12 is defined as an element including the positive electrode plate 16, the separator 18, and the negative electrode layer 20, and typically further includes a positive electrode current collector (not shown) and a negative electrode current collector (not shown). The positive electrode current collector and the negative electrode current collector are not particularly limited, and preferably metal foils such as copper foil and aluminum foil. The positive electrode current collector is preferably interposed between the positive electrode plate 16 and the exterior film 26, and the negative electrode current collector is preferably interposed between the negative electrode layer 20 and the exterior film 26. Preferably, the positive electrode terminal is provided on the positive electrode current collector so as to extend from the positive electrode current collector, and the negative electrode terminal is provided on the negative electrode current collector so as to extend from the negative electrode current collector. Preferably, the outer edges of the lithium secondary battery 10 are sealed by thermally bonding the outer films 26 to each other. In the sealing by thermal bonding, it is preferable to perform the sealing by using a hot bar (also referred to as a heating bar) which is generally used for heat sealing. Typically, it is preferable that the outer peripheral edge of the quadrangular shape 1 of the lithium secondary battery 10 to the outer packaging film 26 is sealed over the entire outer periphery 4.
The outer film 26 may be a commercially available outer film. The thickness of the outer film 26 is preferably 50 to 80 μm, more preferably 55 to 70 μm, and still more preferably 55 to 65 μm per sheet. The outer packaging film 26 is preferably a laminated film comprising a resin film and a metal foil, and more preferably an aluminum laminated film comprising a resin film and an aluminum foil. The laminate film is preferably formed by providing a resin film on both sides of a metal foil such as an aluminum foil. In this case, it is preferable that the resin film on one side of the metal foil (hereinafter referred to as a surface protective film) is made of a material having excellent reinforcement properties such as nylon, polyamide, polyethylene terephthalate, polyimide, polytetrafluoroethylene, polychlorotrifluoroethylene, and the resin film on the other side of the metal foil is made of a heat sealing material such as polypropylene.
As described above, the size of the negative electrode layer 20 is larger than that of the positive electrode plate 16, and on the other hand, the size of the separator 18 is larger than that of the positive electrode plate 16 and the negative electrode layer 20. The outer peripheral portion of the separator 18 is in close contact with at least the outer peripheral edge of the outer film 26 on the positive electrode plate 16 side or a peripheral region in the vicinity thereof, and partitions the region accommodating the positive electrode plate 16 and the region accommodating the negative electrode layer 20. The outer peripheral portion of separator 18 may be in close contact with the outer peripheral edge of outer film 26 on the negative electrode layer 20 side or its vicinity.
The distance D between the end of the positive electrode plate 16 and the end of the negative electrode layer 20 is preferably 50 to 2000 μm, more preferably 200 to 1500 μm, even more preferably 200 to 1000 μm, particularly preferably 200 to 800 μm, more particularly preferably 450 to 600 μm, and most preferably 450 to 550 μm over the entire periphery of the positive electrode plate 16 and the negative electrode layer 20. Here, as shown in fig. 1A, the spacing distance D between the end of the positive electrode plate 16 and the end of the negative electrode layer 20 refers to a distance from the end of the positive electrode plate 16 to the end of the negative electrode layer 20 in the vicinity thereof; in other words, the negative electrode layer 20 may be said to have a width extending from the positive electrode plate 16.
Method for manufacturing lithium cobaltate oriented sintered plate
The oriented positive electrode plate or the oriented sintered plate preferably used in the lithium secondary battery of the present invention can be produced by any production method, but is preferably produced by (1) LiCoO as in the following examples2Production of template particles, (2) production of matrix particles, (3) production of green sheets, and (4) production of oriented sintered plates.
(1)LiCoO2Preparation of template particles
Mixing Co3O4Raw material powder and Li2CO3And (4) mixing the raw material powder. Firing the obtained mixed powder at 500-900 ℃ for 1-20 hours to synthesize LiCoO2And (3) powder. The obtained LiCoO was subjected to a pot ball mill2The powder is pulverized to a particle size of 0.1 to 10 [ mu ] m based on the volume of D50, and a plate-like LiCoO capable of conducting lithium ions parallel to the plate surface is obtained 2Particles. The resulting LiCoO2The particles are in a state of being easily cleaved along the cleavage plane. LiCoO by fragmentation2The particles are cleaved to produce LiCoO2A template particle. Such LiCoO2The particles can also be obtained by using LiCoO2A method of crushing a green sheet of powder slurry after crystal grain growth, a method of synthesizing a plate crystal such as a flux method, hydrothermal synthesis, single crystal growth using a melt, a sol-gel method, or the like.
In this step, as described below, the distribution of the primary particles 11 constituting the oriented positive electrode plate 16 can be controlled.
By adjusting LiCoO2At least one of the aspect ratio and the particle diameter of the template particles can control the total area ratio of the low-angle primary particles having an orientation angle of more than 0 ° and not more than 30 °. Specifically, the more LiCoO is increased2The aspect ratio of the template particles, and LiCoO increase2The larger the particle size of the template particles, the higher the ratio of the total area of the low-angle primary particles. LiCoO2The aspect ratio and the particle size of the template particles can be respectively adjusted by Co3O4Raw material powder and Li2CO3The particle size of the raw material powder, the pulverization conditions (pulverization time, pulverization energy, pulverization method, etc.) during pulverization, and/or the classification after pulverization are controlled.
By adjusting LiCoO2The aspect ratio of the template particles can be controlled to a total area ratio of the primary particles 11 having an aspect ratio of 4 or more. Specifically, the more LiCoO is increased2The aspect ratio of the template particles can be increased by increasing the total area ratio of the primary particles 11 having an aspect ratio of 4 or more. LiCoO2The method of adjusting the aspect ratio of the template particles is as described above.
'Tong' for clearing away heat and toxic materialsOver-conditioned LiCoO2The average particle diameter of the primary particles 11 can be controlled by the particle diameter of the template particles.
By adjusting LiCoO2The particle size of the template particles can control the compactness of the oriented positive electrode plate 16. Specifically, the more LiCoO is reduced2The greater the particle size of the template particles, the greater the compactness of the oriented positive electrode plate 16.
(2) Preparation of matrix particles
Mixing Co3O4The raw material powder is used as matrix particles. Co3O4The volume-based D50 particle size of the raw material powder is not particularly limited, and may be, for example, 0.1 to 1.0. mu.m, but is preferably smaller than LiCoO2The volume basis D50 particle size of the template particles. The matrix particles may be prepared by reacting Co (OH) at 500 to 800 DEG C2The raw material is heat-treated for 1 to 10 hours. In addition, in the matrix particles, Co is removed3O4In addition, Co (OH) may be used2Particles, LiCoO can also be used 2Particles.
In this step, as described below, the distribution of the primary particles 11 constituting the oriented positive electrode plate 16 can be controlled.
By adjusting the particle size of the matrix particles relative to LiCoO2The ratio of the particle diameters of the template particles (hereinafter referred to as "matrix/template particle diameter ratio") can control the total area ratio of the low-angle primary particles having an orientation angle of more than 0 ° and not more than 30 °. Specifically, as the particle size ratio of the matrix/template is decreased, that is, as the particle size of the matrix particles is decreased, the matrix particles are more likely to enter LiCoO in the firing step described later2The more the template particles, the higher the total area ratio of the low-angle primary particles can be.
By adjusting the matrix/template particle diameter ratio, the total area ratio of the primary particles 11 having an aspect ratio of 4 or more can be controlled. Specifically, the smaller the matrix/template particle diameter ratio, that is, the smaller the particle diameter of the matrix particles, the higher the total area ratio of the primary particles 11 having an aspect ratio of 4 or more can be.
The density of the oriented positive plates 16 can be controlled by adjusting the matrix/template particle size ratio. Specifically, the density of the oriented positive electrode plate 16 can be increased as the matrix/template particle diameter ratio, that is, the particle diameter of the matrix particles is decreased.
(3) Production of Green sheet
Subjecting LiCoO to condensation2The template particles and the matrix particles are mixed at a ratio of 100: 0 to 3: 97 to obtain a mixed powder. The mixed powder, the dispersion medium, the binder, the plasticizer, and the dispersant are mixed, stirred under reduced pressure to defoam the mixture, and adjusted to a desired viscosity to prepare a slurry. Next, LiCoO was used as a coupling agent2And a molding method in which shear force is applied to the template particles, and the prepared slurry is molded to form a molded body. In this way, the average orientation angle of each primary particle 11 can be made to exceed 0 ° and be 30 ° or less. As being capable of reacting with LiCoO2The molding method in which shear force is applied to the template particles is preferably a doctor blade method. In the case of using the doctor blade method, the prepared slurry was molded on a PET film to form a green sheet as a molded body.
In this step, as described below, the distribution of the primary particles 11 constituting the oriented positive electrode plate 16 can be controlled.
By adjusting the molding speed, the total area ratio of the low-angle primary particles having an orientation angle of more than 0 ° and 30 ° or less can be controlled. Specifically, the higher the molding speed, the higher the ratio of the total area of the low-angle primary particles can be.
The average particle diameter of the primary particles 11 can be controlled by adjusting the density of the molded body. Specifically, the average particle diameter of the primary particles 11 can be increased as the density of the molded article is increased.
By adjusting LiCoO2The mixing ratio of the template particles to the matrix particles also allows the density of the oriented positive electrode plate 16 to be controlled. Specifically, the more LiCoO2The more the template particles, the less dense the oriented positive electrode plate 16 can be.
(4) Production of oriented sintered plate
The molded body of the slurry is placed on a zirconia setter plate, and heat treatment (primary firing) is performed at 500 to 900 ℃ for 1 to 10 hours to obtain a sintered plate as an intermediate. With lithium plates (e.g. of the typeContaining Li2CO3Sheet of (2) was placed on a zirconia setter plate in this state while sandwiching the sintered plate vertically, and secondary firing was carried out to obtain LiCoO2And (5) sintering the plate. Specifically, a sintering plate carrying a sintering plate clamped by lithium sheets is placed in an alumina sagger, is sintered for 1 to 20 hours at 700 to 850 ℃ in the atmosphere, then is clamped by the lithium sheets up and down, and is sintered for 1 to 40 hours at 750 to 900 ℃ to obtain LiCoO2And (5) sintering the plate. The firing step may be performed in two or one step. When the firing is performed in two stages, the firing temperature at the first stage is preferably lower than the firing temperature at the second stage. The total amount of lithium pieces used in the secondary firing may be set so that the Li/Co ratio, which is the molar ratio of the amount of Li in the green sheet and the lithium pieces to the amount of Co in the green sheet, is 1.0.
In this step, as described below, the distribution of the primary particles 11 constituting the oriented positive electrode plate 16 can be controlled.
By adjusting the temperature rise rate during firing, the total area ratio of the low-angle primary particles having an orientation angle of more than 0 ° and 30 ° or less can be controlled. Specifically, as the temperature increase rate is higher, sintering of the matrix particles is suppressed, and the total area ratio of the low-angle primary particles can be increased.
By adjusting the heat treatment temperature of the intermediate, the total area ratio of the low-angle primary particles having an orientation angle of more than 0 ° and not more than 30 ° can be controlled. Specifically, as the heat treatment temperature of the intermediate is lowered, sintering of the matrix particles is suppressed, and the total area ratio of the low-angle primary particles can be increased.
The average particle diameter of the primary particles 11 can be controlled by adjusting at least one of the temperature increase rate during firing and the heat treatment temperature of the intermediate. Specifically, the average particle size of the primary particles 11 can be increased as the temperature increase rate is increased and the heat treatment temperature of the intermediate is decreased.
By adjusting Li (e.g. Li) at firing2CO3) At least one of the amount of the sintering aid (e.g., boric acid and bismuth oxide) and the amount of the primary particles can be controlled 11 average particle diameter. Specifically, the average particle diameter of the primary particles 11 can be increased as the amount of Li is increased and the amount of sintering aid is increased.
The density of the oriented positive electrode plate 16 can be controlled by adjusting the distribution at the time of firing. Specifically, the density of the oriented positive electrode plate 16 can be increased as the firing temperature is lowered and the firing time is increased.
