JPWO2019221141A1 - Coin-type lithium secondary battery and IoT device - Google Patents

Abstract

Provided is a coin-type lithium secondary battery for which the battery resistance does not easily increase even when repeatedly operated under usage conditions (constant voltage charging or pulse charging / discharging) for IoT devices. This coin-shaped lithium secondary battery includes a positive electrode plate made of a lithium composite oxide sintered body plate, a negative electrode plate made of a titanium-containing sintered body plate, and a separator interposed between the positive electrode plate and the negative electrode plate. A positive electrode current collector provided on the surface of the positive electrode plate away from the separator, a negative electrode current collector provided on the surface of the negative electrode plate away from the separator, an electrolytic solution, a positive electrode can, and a negative electrode can. And an exterior body provided with a gasket, the positive electrode current collector further includes a positive electrode side carbon layer on the surface on the positive electrode plate side, and the positive electrode side carbon layer between the positive electrode current collector and the positive electrode plate is provided. The contact through is not maintained by the adhesion between the positive electrode current collector and the positive electrode plate, but by the pressure due to the caulking of the positive electrode can and the negative electrode can.

Description

The present invention relates to a coin-type lithium secondary battery and an IoT device.

Coin-type lithium secondary batteries are widely used in various devices that require charging, and various coin-type lithium secondary batteries have been proposed. For example, in Patent Document 1 (Japanese Unexamined Patent Publication No. 2004-335185), a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution are housed in a closed space formed by a positive electrode can, a negative electrode can, and an annular insulating gasket. A coin-shaped lithium secondary battery is disclosed in which the positive electrode is a pellet-shaped molded body of a positive electrode mixture having a thickness of 500 μm or more and has a conductive layer on the side surface of the positive electrode. In the secondary battery as described above, a powder dispersion type positive electrode (so-called coating electrode) manufactured by applying and drying a positive electrode mixture containing a positive electrode active material, a conductive auxiliary agent, a binder and the like is adopted. ..

By the way, in general, the powder dispersion type positive electrode contains a relatively large amount (for example, about 10% by weight) of components (binder and conductive auxiliary agent) that do not contribute to the volume, and therefore lithium composite oxidation as a positive electrode active material. The packing density of the object becomes low. Therefore, there is much room for improvement in the powder dispersion type positive electrode in terms of capacity and charge / discharge efficiency. Therefore, attempts have been made to improve the capacity and charge / discharge efficiency by forming the positive electrode or the positive electrode active material layer with a lithium composite oxide sintered body 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, it is expected that a high capacity and good charge / discharge efficiency can be obtained by increasing the packing density of the lithium composite oxide. To. For example, Patent Document 2 (Patent No. 5587052) describes 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 a conductive bonding layer. The positive electrode is disclosed. The positive electrode active material layer is said to be made of a lithium composite oxide sintered body plate having a thickness of 30 μm or more, a porosity of 3 to 30%, and an open pore ratio of 70% or more. Further, in Patent Document 3 (International Publication No. 2017/146808), a plurality of primary particles composed of a lithium composite oxide such as lithium cobalt oxide (LiCoO ₂ ) as a positive electrode of a lithium secondary battery provided with a solid electrolyte. It is disclosed to use an oriented sintered plate in which a plurality of primary particles are oriented with an average orientation angle of more than 0 ° and not more than 30 ° with respect to the plate surface of the positive electrode plate.

On the other hand, it has also been proposed to use a titanium-containing sintered plate as the negative electrode. For example, Patent Document 4 (Japanese Unexamined Patent Publication No. 2015-185337) discloses a lithium secondary battery using a lithium titanate (Li ₄ Ti ₅ O ₁₂ ) sintered body for the positive electrode or the negative electrode. However, this lithium secondary battery is an all-solid-state battery having a solid electrolyte layer between the positive electrode and the negative electrode, and is not a secondary battery using a non-aqueous electrolyte solution.

Japanese Unexamined Patent Publication No. 2004-335185 Japanese Patent No. 5587052 International Publication No. 2017/146808 Japanese Unexamined Patent Publication No. 2015-185337

In recent years, with the spread of IoT devices, a coin-type lithium secondary battery that is compact and thin, yet has high capacity and high output, and can be recharged at a constant voltage (CV) is desired. A secondary battery capable of constant voltage charging is advantageous in terms of miniaturization and cost reduction because it is not necessary to provide a current control IC. Therefore, it is conceivable to use a lithium composite oxide sintered body plate for the positive electrode in anticipation of high capacity and good charge / discharge efficiency. However, when a coin-shaped battery having a lithium composite oxide sintered body plate such as lithium cobalt oxide as a positive electrode plate is repeatedly operated under the usage conditions for IoT devices (constant voltage charging or pulse charging / discharging), the resistance of the battery Rise unexpectedly. In particular, since the electrode area of the coin-type battery is small, there is a disadvantage that even a slight increase in resistance has a large effect on the voltage drop.

The present inventors have now used predetermined sintered body plates as the positive electrode and the negative electrode, respectively, and made contact between the positive electrode sintered body plate and the positive electrode current collector with a carbon layer interposed therebetween. We provide a coin-type lithium secondary battery whose battery resistance does not easily increase even if it is repeatedly operated under the usage conditions (constant voltage charging or pulse charging / discharging) for IoT devices by holding it by the pressure of the positive electrode can and the negative electrode can. I got the finding that it can be done.

Therefore, an object of the present invention is to provide a coin-type lithium secondary battery for which the battery resistance does not easily increase even when repeatedly operated under usage conditions (constant voltage charging or pulse charging / discharging) for IoT devices.

According to one aspect of the invention
A positive electrode plate made of a lithium composite oxide sintered body plate and
A negative electrode plate made of a titanium-containing sintered body plate and
A separator interposed between the positive electrode plate and the negative electrode plate,
A positive electrode current collector provided on the surface of the positive electrode plate on the side away from the separator, and a positive electrode current collector.
A negative electrode current collector provided on the surface of the negative electrode plate on the side away from the separator, and
The positive electrode plate, the negative electrode plate, and the electrolytic solution impregnated in the separator,
An exterior body including a positive electrode can, a negative electrode can, and a gasket, wherein the positive electrode can and the negative electrode can are crimped via the gasket to form a closed space, and the positive electrode plate and the positive electrode collection are formed in the closed space. An electric body, the negative electrode plate, the negative electrode current collector, the separator, and an exterior body containing the electrolytic solution,
The positive electrode current collector further includes a positive electrode side carbon layer on the surface on the positive electrode plate side, and the contact between the positive electrode current collector and the positive electrode plate via the positive electrode side carbon layer is the positive electrode. Provided is a coin-shaped lithium secondary battery that is held by the pressure of the positive electrode can and the negative electrode can by caulking instead of bonding the current collector and the positive electrode plate.

According to another aspect of the present invention, an IoT device including the coin-shaped lithium secondary battery is provided.

It is a schematic sectional view of an example of the coin-type lithium secondary battery of this invention. It is an SEM image which shows an example of the cross section perpendicular to the plate surface of the oriented positive electrode plate. It is an EBSD image in the cross section of the oriented positive electrode plate shown in FIG. 6 is a histogram showing the distribution of the orientation angles of the primary particles in the EBSD image of FIG. 3 on an area basis.

Coin-type lithium secondary battery FIG. 1 schematically shows an example of the coin-type lithium secondary battery of the present invention. The lithium secondary battery 10 shown in FIG. 1 includes a positive electrode plate 12, a positive electrode current collector 14, a negative electrode plate 16, a negative electrode current collector 18, a separator 20, an electrolytic solution 22, and an exterior body 24. Be prepared. The positive electrode plate 12 is made of a lithium composite oxide sintered body plate. The negative electrode plate 16 is made of a titanium-containing sintered body plate. The separator 20 is interposed between the positive electrode plate 12 and the negative electrode plate 16. The positive electrode current collector 14 is provided on the surface of the positive electrode plate 12 on the side away from the separator 20 without adhesion. The negative electrode current collector 18 is provided on the surface of the negative electrode plate 16 on the side away from the separator 20. The electrolytic solution 22 is impregnated into the positive electrode plate 12, the negative electrode plate 16, and the separator 20. The exterior body 24 is an exterior body including a positive electrode can 24a, a negative electrode can 24b, and a gasket 24c, and the positive electrode can 24a and the negative electrode can 24b are crimped via the gasket 24c to form a closed space, and the inside of the closed space. A positive electrode plate 12, a positive electrode current collector 14, a negative electrode plate 16, a negative electrode current collector 18, a separator 20, and an electrolytic solution 22 are housed therein. The positive electrode current collector 14 further includes a positive electrode side carbon layer 13 on the surface on the positive electrode plate 12 side. Then, the contact between the positive electrode current collector 14 and the positive electrode plate 12 via the positive electrode side carbon layer 13 is not the adhesion between the positive electrode current collector 14 and the positive electrode plate 12, but the pressure due to the caulking of the positive electrode can 24a and the negative electrode can 24b. Held by. In addition, in this specification, "adhesion" means that one object and another object that comes into direct or indirect contact with it remain attached to each other even when an external force such as pressure is not applied. It means, and is typically realized by the application of an adhesive or an adhesive substance. In this way, predetermined sintered body plates are used as the positive electrode and the negative electrode, respectively, and the positive electrode plate 12 and the positive electrode current collector 14 are brought into contact with each other with the positive electrode side carbon layer 13 interposed therebetween, and the positive electrode is not bonded. Provided is a coin-type lithium secondary battery in which the battery resistance does not easily increase even if it is repeatedly operated under the usage conditions (constant voltage charging or pulse charging / discharging) for IoT devices by holding the can 24a and the negative electrode can 24b by the pressure of caulking. can do.

That is, as described above, a coin-type lithium secondary battery for IoT devices is desired. However, when a coin-shaped battery having a lithium composite oxide sintered body plate such as lithium cobalt oxide as a positive electrode plate is repeatedly operated under the usage conditions for IoT devices (constant voltage charging or pulse charging / discharging), the resistance of the battery Rise unexpectedly. In particular, since the electrode area of the coin-type battery is small, there is a disadvantage that even a slight increase in resistance has a large effect on the voltage drop. The reason why this phenomenon occurs is considered to be as follows. That is, in a coin-shaped battery, if the positive electrode sintered plate is attached (that is, adhered) to the positive electrode current collector with a conductive adhesive, it will be charged and discharged when repeatedly operated under the conditions of use for IoT. Due to the stress generated by the expansion and contraction of the lithium composite oxide sintered body plate, the positive electrode plate and the positive electrode current collector are gradually peeled off. That is, the lithium composite oxide sintered body plate expands during charging and contracts during discharging. Then, since the surface of the peeled portion becomes rough and the contact becomes poor, it is considered that the contact resistance increases, and as a result, the resistance of the battery increases. In this respect, in the lithium secondary battery 10 of the present invention, the positive electrode plate 12 is not attached (that is, adhered) to the positive electrode current collector 14 with a conductive adhesive, but is caulked by the positive electrode can 24a and the negative electrode can 24b. The pressure keeps the positive electrode plate 12 in contact with the positive electrode current collector 14. By doing so, the stress due to expansion and contraction of the positive electrode plate 12 can be efficiently released or relaxed at the non-adhesive interface while avoiding peeling between the positive electrode plate 12 and the positive electrode current collector 14, and as a result, the positive electrode It is possible to effectively suppress an increase in contact resistance due to expansion and contraction of the plate 12. Moreover, the contact resistance is further reduced by interposing the positive electrode side carbon layer 13 between the positive electrode plate 12 and the positive electrode current collector 14.

In particular, with the spread of IoT devices, a coin-type lithium secondary battery that is compact and thin, yet has high capacity and high output, and can be recharged at a constant voltage (CV) is desired. In this respect, according to the lithium secondary battery 10 according to the preferred embodiment of the present invention, such a requirement can be fully satisfied. In particular, by adopting predetermined sintered body plates as the positive electrode and the negative electrode, it is possible to realize not only heat resistance but also high capacity and high output, particularly constant voltage charging and high-speed charging. Therefore, the lithium secondary battery 10 of the present invention is preferably a battery for IoT devices. That is, according to another preferred embodiment of the present invention, an IoT device including a coin-type lithium secondary battery is provided. In addition, in this specification, "IoT" is an abbreviation for the Internet of Things (Internet of Things), and "IoT device" means any device connected to the Internet and exhibiting a specific function.

As described above, the lithium secondary battery 10 is preferably a coin-type lithium secondary battery having a high capacity, that is, a high energy density, while being small and thin. Specifically, the thickness of the lithium secondary battery 10 is 0.7 to 1.6 mm, preferably 0.8 to 1.6 mm, more preferably 0.9 to 1.4 mm, and even more preferably 1. It is 0 to 1.2 mm. The diameter of the lithium secondary battery 10 is 10 to 20 mm, preferably 10 to 18 mm, more preferably 11 to 16 mm, and even more preferably 12 to 14 mm. Energy density of the lithium secondary battery 10 is preferably a 35~200mWh / cm ^3, more preferably 40~200mWh / cm ^3, more preferably from 50~200mWh / cm ^3. The battery capacity of the lithium secondary battery 10 is preferably 1.8 to 45 mAh, more preferably 2.3 to 45 mAh, and even more preferably 4.5 to 20 mAh. The value obtained by dividing the battery capacity of the lithium secondary battery 10 by the thickness of the positive electrode plate 12 is preferably 1.8 to 28.1 mAh / mm, more preferably 3.5 to 17 mAh / mm, still more preferably. It is 5 to 8 mAh / mm. If the specifications are within the above range, it is extremely advantageous to incorporate the specifications into a device that can be relatively small, such as an IoT device.

The positive electrode plate 12 is a lithium composite oxide sintered body plate. The fact that the positive electrode plate 12 is a sintered body plate means that the positive electrode plate 12 does not contain a binder or a conductive auxiliary agent. This is because even if the green sheet contains a binder, the binder disappears or burns out during firing. Since the positive electrode plate 12 does not contain a binder, there is an advantage that deterioration of the positive electrode due to the electrolytic solution 22 can be avoided. The lithium composite oxide constituting the sintered body plate is particularly preferably lithium cobalt oxide (typically LiCoO ₂ (hereinafter, may be abbreviated as LCO)). Various lithium composite oxide sintered plates or LCO sintered plates are known, and are disclosed in, for example, Patent Document 2 (Patent No. 5587052) and Patent Document 3 (International Publication No. 2017/146808). You can use things.

According to a preferred embodiment of the present invention, the positive electrode plate 12, that is, the lithium composite oxide sintered body plate contains a plurality of primary particles composed of the lithium composite oxide, and the plurality of primary particles are formed on the plate surface of the positive electrode plate. On the other hand, the oriented positive electrode plate is oriented at an average orientation angle of more than 0 ° and 30 ° or less. FIG. 2 shows an example of a cross-sectional SEM image perpendicular to the plate surface of the oriented positive electrode plate 12, while FIG. 3 shows an electron backscatter diffraction (EBSD) image in a cross section perpendicular to the plate surface of the oriented positive electrode plate 12. Is shown. Further, FIG. 4 shows a histogram showing the distribution of the orientation angles of the primary particles 11 in the EBSD image of FIG. 3 on an area basis. In the EBSD image shown in FIG. 3, the discontinuity of the crystal orientation can be observed. In FIG. 3, the orientation angle of each primary particle 11 is shown by the shade of color, and the darker the color, the smaller the orientation angle. The orientation angle is an inclination angle formed by the (003) plane of each primary particle 11 with respect to the plate surface direction. In addition, in FIGS. 2 and 3, the portion shown in black inside the oriented positive electrode plate 12 is a pore.

The oriented positive electrode plate 12 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 those formed in a rectangular parallelepiped shape, a cube 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 complicated shape other than these.

Each primary particle 11 is composed of a lithium composite oxide. The lithium composite oxide is Li _x MO ₂ (0.05 <x <1.10, M is at least one transition metal, and M is typically one or more of Co, Ni and Mn. It is an oxide represented by). Lithium composite oxide has a layered rock salt structure. The layered rock salt structure is a crystal structure in which a lithium layer and a transition metal layer other than lithium are alternately laminated with an oxygen layer in between, that is, a transition metal ion layer and a lithium single layer are alternately laminated via oxide ions. It refers to a laminated crystal structure (typically, an α-NaFeO type ₂ structure, that is, a structure in which transition metals and lithium are regularly arranged in the [111] axis direction of a cubic rock salt type structure). Examples of lithium composite oxides are Li _x CoO ₂ (lithium cobaltate), Li _x NiO ₂ (lithium nickelate), Li _x MnO ₂ (lithium manganate), Li _x NimnO ₂ (lithium nickel manganate). , Li _x NiCoO ₂ (lithium nickel cobaltate), Li _x CoNiMnO ₂ (cobalt, nickel, lithium manganate), Li _x ComnO ₂ (lithium cobalt manganate), and the like, and Li _x CoO ₂ is particularly preferable. (Lithium cobaltate, typically LiCoO ₂ ). Lithium composite oxides include 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 may contain one or more elements selected from.

As shown in FIGS. 3 and 4, the average value of the orientation angles of each primary particle 11, that is, the average orientation angle is more than 0 ° and 30 ° or less. This brings the following various advantages: First, since each of the primary particles 11 is laid in a direction inclined with respect to the thickness direction, the adhesion between the primary particles can be improved. As a result, the lithium ion conductivity between a certain primary particle 11 and the other primary particles 11 adjacent to both sides in the longitudinal direction of the primary particle 11 can be improved, so that the rate characteristic can be improved. Secondly, the rate characteristics can be further improved. This is because, as described above, when lithium ions enter and exit, the oriented positive electrode plate 12 is dominated by expansion and contraction in the thickness direction rather than the plate surface direction, so that the expansion and contraction of the oriented positive electrode plate 12 becomes smooth. This is because the lithium ions can enter and exit smoothly.

The average orientation angle of the primary particles 11 is obtained by the following method. First, in an EBSD image in which a rectangular region of 95 μm × 125 μm is observed at a magnification of 1000 as shown in FIG. 3, three horizontal lines that divide the oriented positive electrode plate 12 into four equal parts in the thickness direction and the oriented positive electrode plate 12 Draw three vertical lines that divide the plate into four equal parts in the direction of the plate surface. Next, the average orientation angle of the primary particles 11 is obtained by arithmetically averaging the orientation angles of all the primary particles 11 intersecting at least one of the three horizontal lines and the three vertical lines. The average orientation angle of the primary particles 11 is preferably 30 ° or less, more preferably 25 ° or less, from the viewpoint of further improving the rate characteristics. The average orientation angle of the primary particles 11 is preferably 2 ° or more, more preferably 5 ° or more, from the viewpoint of further improving the rate characteristics.

As shown in FIG. 4, the orientation angle of each primary particle 11 may be widely distributed from 0 ° to 90 °, but most of them are distributed in a region of more than 0 ° and 30 ° or less. Is preferable. That is, when the cross section of the oriented sintered body constituting the oriented positive electrode plate 12 is analyzed by EBSD, the orientation angle of the oriented positive electrode plate 12 with respect to the plate surface of the primary particles 11 included in the analyzed cross section is 0 °. The total area of the primary particles 11 (hereinafter referred to as low-angle primary particles) having an ultra-30 ° or less is the primary particles 11 included in the cross section (specifically, the 30 primary particles 11 used to calculate the average orientation angle). It is preferably 70% or more, more preferably 80% or more, based on the total area of the particles. As a result, the proportion of the primary particles 11 having high mutual adhesion can be increased, so that the rate characteristics can be further improved. Further, it is more preferable that the total area of the low-angle primary particles having an orientation angle of 20 ° or less 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 low-angle primary particles having an orientation angle of 10 ° or less 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, as shown in FIGS. 2 and 3, the cross section of each primary particle 11 extends in a predetermined direction, and typically has a substantially rectangular shape. 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 among the primary particles 11 included in the analyzed cross section is included in the cross section. It is preferably 70% or more, more preferably 80% or more, based on the total area of the particles 11 (specifically, the 30 primary particles 11 used for calculating the average orientation angle). Specifically, in the EBSD image as shown in FIG. 3, the mutual adhesion between the primary particles 11 can be further improved, and as a result, the rate characteristics can be further improved. The aspect ratio of the primary particle 11 is a value obtained by dividing the maximum ferret diameter of the primary particle 11 by the minimum ferret diameter. The maximum ferret diameter is the maximum distance between the straight lines when the primary particles 11 are sandwiched between two parallel straight lines on the EBSD image when the cross section is observed. The minimum ferret diameter is the minimum distance between the straight lines when the primary particles 11 are sandwiched between two parallel straight lines on the EBSD image.

The average particle size of the plurality of primary particles constituting the oriented sintered body is preferably 5 μm or more. Specifically, the average particle size of the 30 primary particles 11 used in the calculation of the average orientation angle is preferably 5 μm or more, more preferably 7 μm or more, still more preferably 12 μm or more. As a result, the number of grain boundaries between the primary particles 11 in the direction in which the lithium ions are conducted is reduced, and the lithium ion conductivity as a whole is improved, so that the rate characteristics can be further improved. The average particle size 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 positive electrode plate 12 preferably contains pores. The inclusion of pores, especially open pores, in the sintered body allows the electrolyte to penetrate into the sintered body when incorporated into the battery as a positive electrode plate, resulting in improved lithium ion conductivity. be able to. This is because there are two types of conduction of lithium ions in the sintered body: conduction through the constituent particles of the sintered body and conduction through the electrolytic solution in the pores, but conduction through the electrolytic solution in the pores is better. This is because it is overwhelmingly fast.

The positive electrode plate 12, that is, the lithium composite oxide sintered body plate, preferably has a porosity of 20 to 60%, more preferably 25 to 55%, still more preferably 30 to 50%, and particularly preferably 30 to 45%. Is. The stress release effect due to the pores and the increase in capacity can be expected, and the mutual adhesion between the primary particles 11 can be further improved, so that the rate characteristics can be further improved. The porosity of the sintered body is calculated by polishing the cross section of the positive electrode plate by CP (cross section polisher) polishing, observing the SEM at a magnification of 1000, and binarizing the obtained SEM image. The average circle-equivalent diameter of each pore formed inside the oriented sintered body is not particularly limited, but is preferably 8 μm or less. The smaller the average circle equivalent diameter of each pore, the more the mutual adhesion between the primary particles 11 can be further improved, and as a result, the rate characteristics can be further improved. The average circle-equivalent diameter of the pores is a value obtained by arithmetically averaging the circle-equivalent diameters of 10 pores on the EBSD image. The equivalent circle diameter is the diameter of a circle having the same area as each pore on the EBSD image. It is preferable that each pore formed inside the oriented sintered body is an open pore connected to the outside of the positive electrode plate 12.

The positive electrode plate 12, that is, the lithium composite oxide sintered body plate, preferably has an average pore diameter of 0.1 to 10.0 μm, more preferably 0.2 to 5.0 μm, and further preferably 0.3 to 3. It is 0.0 μm. Within the above range, the occurrence of local stress concentration in large pores is suppressed, and the stress in the sintered body is easily released uniformly.

The thickness of the positive electrode plate 12 is preferably 60 to 450 μm, more preferably 70 to 350 μm, and even more preferably 90 to 300 μm. Within such a range, the active material capacity per unit area is increased to improve the energy density of the lithium secondary battery 10, and the deterioration of battery characteristics (particularly the increase in resistance value) due to repeated charging and discharging is caused. Can be suppressed.

The positive electrode current collector 14 is not particularly limited, but is preferably a metal foil such as a copper foil or an aluminum foil. The positive electrode current collector 14 is arranged between the positive electrode plate 12 and the positive electrode can 24a. Further, the positive electrode current collector 14 further includes a positive electrode side carbon layer 13 on the surface on the positive electrode plate 12 side. The positive electrode side carbon 13 is preferably adhered to the positive electrode current collector 14, but is not adhered to the positive electrode plate 12. The positive electrode side carbon layer 13 contributes to the reduction of the contact resistance between the positive electrode plate 12 and the positive electrode current collector 14. The positive electrode side carbon layer 13 is preferably composed of conductive carbon, and may be formed by, for example, applying a conductive carbon paste to the positive electrode current collector 14 by screen printing or the like and drying it.

The flatness of the positive electrode plate 12 is preferably 200 μm or less, more preferably 150 μm or less, and further preferably 100 μm or less. The flatness of the positive electrode plate 12 means "the magnitude of deviation from the geometrically correct plane of the planar shape" (JIS). For example, the positive electrode current collector 14 side of the positive electrode plate 12 is a three-dimensional shape measuring machine. It can be obtained by measuring the difference between the highest portion and the lowest portion in the plane when the shape is measured by (for example, VR-3200 manufactured by Keyence Co., Ltd.). By lowering the flatness of the positive electrode plate 12 in this way, the contact area between the positive electrode plate 12 and the positive electrode current collector 14 due to the pressure generated by caulking the positive electrode can 24a and the negative electrode can 24b is sufficiently secured, and the positive electrode plate 12 is sufficiently flat. The contact resistance between the 12 and the positive electrode current collector 14 can be reduced more effectively.

The negative electrode plate 16 is a titanium-containing sintered body plate. The titanium-containing sintered plate preferably contains lithium titanate Li ₄ Ti ₅ O ₁₂ (hereinafter, LTO) or niobium-titanium composite oxide Nb ₂ TiO ₇ , and more preferably contains LTO. Although LTO is typically known to have a spinel-type structure, other structures may be adopted during charging / discharging. For example, LTO reacts in a two-phase coexistence of Li ₄ Ti ₅ O ₁₂ (spinel structure) and Li ₇ Ti ₅ O ₁₂ (rock salt structure) during charging and discharging. Therefore, LTO is not limited to the spinel structure.

The fact that the negative electrode plate 16 is a sintered body plate means that the negative electrode plate 16 does not contain a binder or a conductive auxiliary agent. This is because even if the green sheet contains a binder, the binder disappears or burns out during firing. Since the negative electrode plate does not contain a binder, a high capacity and good charge / discharge efficiency can be obtained by increasing the packing density of the negative electrode active material (for example, LTO or Nb ₂ TiO ₇ ). The LTO sintered body plate can be produced according to the method described in Patent Document 4 (Japanese Unexamined Patent Publication No. 2015-185337).

The negative electrode plate 16, that is, the titanium-containing sintered body plate, has a structure in which a plurality of (that is, a large number) primary particles are bonded. Therefore, it is preferable that these primary particles are composed of LTO or Nb ₂ TiO ₇ .

The thickness of the negative electrode plate 16 is preferably 70 to 500 μm, preferably 85 to 400 μm, and more preferably 95 to 350 μm. The thicker the LTO sintered body plate, the easier it is to realize a battery with a high capacity and a high energy density. The thickness of the negative electrode plate 16 can be obtained, for example, by measuring the distance between the plate surfaces observed substantially in parallel when the cross section of the negative electrode plate 16 is observed by an SEM (scanning electron microscope).

The primary particle size, which is the average particle size of the plurality of primary particles constituting the negative electrode plate 16, is preferably 1.2 μm or less, more preferably 0.02 to 1.2 μm, and further preferably 0.05 to 0.7 μm. .. Within such a range, both lithium ion conductivity and electron conductivity are likely to be compatible, which contributes to the improvement of rate performance.

The negative electrode plate 16 preferably contains pores. By including pores, especially open pores, in the sintered body plate, when incorporated into a battery as a negative electrode plate, the electrolytic solution can permeate the inside of the sintered body plate, and as a result, lithium ion conductivity is improved. Can be improved. This is because there are two types of conduction of lithium ions in the sintered body: conduction through the constituent particles of the sintered body and conduction through the electrolytic solution in the pores, but conduction through the electrolytic solution in the pores is better. This is because it is overwhelmingly fast.

The porosity of the negative electrode plate 16 is preferably 20 to 60%, more preferably 30 to 55%, and even more preferably 35 to 50%. Within such a range, both lithium ion conductivity and electron conductivity are likely to be compatible, which contributes to the improvement of rate performance.

The average pore diameter of the negative electrode plate 16 is 0.08 to 5.0 μm, preferably 0.1 to 3.0 μm, and more preferably 0.12 to 1.5 μm. Within such a range, both lithium ion conductivity and electron conductivity are likely to be compatible, which contributes to the improvement of rate performance.

The negative electrode current collector 18 is not particularly limited, but is preferably a metal foil such as a copper foil or an aluminum foil. The negative electrode current collector 18 is arranged between the negative electrode plate 16 and the negative electrode can 24b. The negative electrode current collector 18 preferably further includes a negative electrode side carbon layer 17 on the surface on the negative electrode plate 16 side. Alternatively, the negative electrode plate 16 may further include a negative electrode side carbon layer 17 on the surface on the negative electrode current collector 18 side. In any case, it is preferable that the negative electrode side carbon layer 17 is interposed between the negative electrode current collector 18 and the negative electrode plate 16, so that the negative electrode side carbon layer 17 is between the negative electrode plate 16 and the negative electrode current collector 18. Contributes to the reduction of contact resistance. The negative electrode side carbon layer 17 is preferably composed of conductive carbon, and may be formed by, for example, applying a conductive carbon paste by screen printing or the like. The direct or indirect contact between the negative electrode current collector 18 and the negative electrode plate 16 (the negative electrode side carbon layer 17 may be interposed between them) is performed by bonding with a conductive adhesive such as a conductive carbon paste. It may be held by pressure due to caulking of the positive electrode can 24a and the negative electrode can 24b instead of bonding.

The separator 20 is preferably a separator made of cellulose, polyolefin, polyimide, polyester (for example, polyethylene terephthalate (PET)) or ceramic. Cellulose separators are advantageous in that they are inexpensive and have excellent heat resistance. Further, the polyimide, polyester (for example, polyethylene terephthalate (PET)) or cellulose separator is different from the widely used polyolefin separator, which is inferior in heat resistance, and not only has excellent heat resistance in itself, but also. It also has excellent wettability to γ-butyrolactone (GBL), which is an electrolyte component having excellent heat resistance. Therefore, when an electrolytic solution containing GBL is used, the electrolytic solution can be sufficiently permeated into the separator (without repelling). On the other hand, the ceramic separator has an advantage that it is excellent in heat resistance and can be manufactured together with the positive electrode plate 12 and the negative electrode plate 16 as one integrally sintered body as a whole. In the case of a ceramic separator, the ceramic constituting the separator is preferably at least one selected from MgO, Al ₂ O ₃ , ZrO ₂ , SiC, Si ₃ N ₄ , Al N, and cordierite, and more preferably. At least one selected from MgO, Al ₂ O ₃ , and ZrO ₂ .

The electrolytic solution 22 is not particularly limited, and a commercially available electrolytic solution for a lithium battery, such as a solution in which a lithium salt is dissolved in a non-aqueous solvent such as an organic solvent, may be used. In particular, an electrolytic solution having excellent heat resistance is preferable, and such an electrolytic solution preferably contains lithium borofluoride (LiBF ₄ ) in a non-aqueous solvent. In this case, the preferred non-aqueous solvent is at least one selected from the group consisting of γ-butyrolactone (GBL), ethylene carbonate (EC) and propylene carbonate (PC), and more preferably a mixed solvent composed of EC and GBL. , A single solvent composed of PC, a mixed solvent composed of PC and GBL, or a single solvent composed of GBL, and particularly preferably a mixed solvent composed of EC and GBL or a single solvent composed of GBL. The non-aqueous solvent contains γ-butyrolactone (GBL) to raise the boiling point, resulting in a significant improvement in heat resistance. From this point of view, the volume ratio of EC: GBL in the EC and / or GBL-containing non-aqueous solvent is preferably 0: 1 to 1: 1 (GBL ratio 50 to 100% by volume), more preferably 0: 1 to 1. 1: 1.5 (GBL ratio 60 to 100% by volume), more preferably 0: 1 to 1: 2 (GBL ratio 66.6 to 100% by volume), particularly preferably 0: 1 to 1: 3 (GBL ratio). 75 to 100% by volume). Lithium borofluoride (LiBF ₄ ) dissolved in a non-aqueous solvent is an electrolyte having a high decomposition temperature, which also brings about a significant improvement in heat resistance. The concentration of LiBF ₄ in the electrolytic solution 22 is preferably 0.5 to 2 mol / L, more preferably 0.6 to 1.9 mol / L, still more preferably 0.7 to 1.7 mol / L, and particularly preferably 0.7 to 1.7 mol / L. It is 0.8 to 1.5 mol / L.

The electrolytic solution 22 may further contain vinylene carbonate (VC) and / or fluoroethylene carbonate (FEC) and / or vinylethylene carbonate (VEC) as additives. Both VC and FEC have excellent heat resistance. Therefore, when the electrolytic solution 22 contains such an additive, an SEI film having excellent heat resistance can be formed on the surface of the negative electrode plate 16.

The exterior body 24 includes a closed space, in which the positive electrode plate 12, the positive electrode current collector 14, the negative electrode plate 16, the negative electrode current collector 18, the separator 20, and the electrolytic solution 22 are housed. The exterior body 24 may adopt a structure generally adopted for coin-type batteries (see, for example, Patent Document 1), and is not particularly limited. Typically, the exterior body 24 includes a positive electrode can 24a, a negative electrode can 24b, and a gasket 24c, and the positive electrode can 24a and the negative electrode can 24b are crimped via the gasket 24c to form a closed space. Further, as described above, the pressure due to the caulking of the positive electrode can 24a and the negative electrode can 24b maintains the contact between the positive electrode plate 12 and the positive electrode current collector 14 via the positive electrode side carbon layer 13. The positive electrode can 24a and the negative electrode can 24b can be made of a metal such as stainless steel, and are not particularly limited. The gasket 24c can be an annular member made of an insulating resin such as polypropylene, polytetrafluoroethylene, or PFA resin, and is not particularly limited.

Method for Producing Positive Positive Plate The positive electrode plate 12, that is, the lithium composite oxide sintered body plate may be manufactured by any method, but preferably (a) preparation of a lithium composite oxide-containing green sheet, (a) b) It is produced through the production of an excess lithium source-containing green sheet, which is carried out as desired, and (c) laminating and firing of the green sheet.

(A) Preparation of Lithium Composite Oxide-Containing Green Sheet First, a raw material powder composed of lithium composite oxide is prepared. The powder preferably contains precomposed plate particles (eg, LiCoO ₂ plate particles) having a composition of LiMO ₂ (M is as described above). The volume-based D50 particle size of the raw material powder is preferably 0.3 to 30 μm. For example, the method for producing LiCoO _2- plate particles can be carried out as follows. First, the LiCoO ₂ powder is synthesized by mixing the Co ₃ O ₄ raw material powder and the Li ₂ CO ₃ raw material powder and firing them (500 to 900 ° C., 1 to 20 hours). By pulverizing the obtained LiCoO ₂ powder to a volume-based D50 particle size of 0.2 μm to 10 μm with a pot mill, plate-shaped LiCoO ₂ particles capable of conducting lithium ions parallel to the plate surface can be obtained. Such LiCoO ₂ particles are plate-shaped, such as a method of growing a green sheet using LiCoO ₂ powder slurry and then crushing it, a flux method, hydrothermal synthesis, single crystal growth using a melt, and a sol-gel method. It can also be obtained by a method of synthesizing crystals. The obtained LiCoO ₂ particles are in a state of being easily cleaved along the cleavage plane. By cleaving the LiCoO ₂ particles by crushing, LiCoO ₂ plate-like particles can be produced.

The plate-shaped particles may be used alone as a raw material powder, or a mixed powder of the plate-shaped powder and another raw material powder (for example, Co ₃ O ₄ particles) may be used as a raw material powder. In the latter case, it is preferable that the plate-like powder functions as template particles for imparting orientation, and other raw material powders (for example, Co ₃ O ₄ particles) function as matrix particles that can grow along the template particles. In this case, it is preferable to use a powder obtained by mixing template particles and matrix particles in a ratio of 100: 0 to 3:97 as a raw material powder. When the Co ₃ O ₄ raw material powder is used as the matrix particles, the volume-based D50 particle size of the Co ₃ O ₄ raw material powder is not particularly limited and can be, for example, 0.1 to 1.0 μm, but the LiCo O ₂ template particles. It is preferable that the particle size is smaller than the volume standard D50 particle size of. The matrix particles can also be obtained by heat-treating the Co (OH) ₂ raw material at 500 ° C. to 800 ° C. for 1 to 10 hours. Further, as the matrix particles, in addition to Co ₃ O ₄ , Co (OH) ₂ particles may be used, or LiCo O ₂ particles may be used.

When the raw material powder is composed of 100% LiCoO ₂ template particles, or when LiCoO ₂ particles are used as matrix particles, a large-sized (for example, 90 mm × 90 mm square) and flat LiCoO ₂ sintered plate is obtained by firing. Can be done. Although the mechanism is not clear, it is expected that volume change during firing is unlikely to occur or local unevenness is unlikely to occur because synthesis to LiCoO ₂ is not performed during the firing process.

The raw material powder is mixed with a dispersion medium and various additives (binder, plasticizer, dispersant, etc.) to form a slurry. A lithium compound other than LiMO ₂ (for example, lithium carbonate) may be excessively added to the slurry by about 0.5 to 30 mol% for the purpose of promoting grain growth or compensating for volatile matter in the firing step described later. It is desirable not to add a pore-forming material to the slurry. It is preferable that the slurry is stirred under reduced pressure to defoam and the viscosity is adjusted to 4000 to 10000 cP. The obtained slurry is molded into a sheet to obtain a lithium composite oxide-containing green sheet. The green sheet thus obtained is an independent sheet-shaped molded product. An independent sheet (sometimes referred to as a "self-supporting film") is a sheet that can be handled independently of other supports (including flakes with an aspect ratio of 5 or more). That is, the independent sheet does not include a sheet that is fixed to another support (such as a substrate) and integrated with the support (inseparable or difficult to separate). Sheet molding is preferably performed using a molding method capable of applying a shearing force to plate-shaped particles (for example, template particles) in the raw material powder. By doing so, the average inclination angle of the primary particles can be set to more than 0 ° and 30 ° or less with respect to the plate surface. The doctor blade method is suitable as a molding method capable of applying a shearing force to the plate-shaped particles. The thickness of the lithium composite oxide-containing green sheet may be appropriately set so as to be the desired thickness as described above after firing.

(B) Preparation of green sheet containing excess lithium source (arbitrary step)
If desired, an excess lithium source-containing green sheet is prepared separately from the lithium composite oxide-containing green sheet. The excess lithium source is preferably a lithium compound other than LiMO ₂ in which components other than Li disappear by firing. A preferred example of such a lithium compound (excess lithium source) is lithium carbonate. The excess lithium source is preferably in the form of powder, and the volume-based D50 particle size of the excess lithium source powder is preferably 0.1 to 20 μm, more preferably 0.3 to 10 μm. Then, the lithium source powder is mixed with a dispersion medium and various additives (binder, plasticizer, dispersant, etc.) to form a slurry. It is preferable that the obtained slurry is stirred under reduced pressure to defoam and the viscosity is adjusted to 1000 to 20000 cP. The obtained slurry is molded into a sheet to obtain a green sheet containing an excess lithium source. The green sheet thus obtained is also an independent sheet-shaped molded product. Sheet molding can be performed by various well-known methods, but it is preferably performed by the doctor blade method. As for the thickness of the green sheet containing an excess lithium source, the molar ratio (Li / Co ratio) of the Li content in the green sheet containing an excess lithium source to the Co content in the lithium composite oxide-containing green sheet is preferably 0.1 or more. , More preferably, the thickness is set so that it can be 0.1 to 1.1.

(C) Lamination and firing of green sheets A lithium composite oxide-containing green sheet (for example, LiCoO ₂ green sheet) and, if desired, an excess lithium source-containing green sheet (for example, Li ₂ CO ₃ green sheet) are placed in this order on the lower setter. Then place the upper setter on it. The upper setter and lower setter are made of ceramics, preferably zirconia or magnesia. If the setter is made of magnesia, the pores tend to be smaller. The upper setter may have a porous structure or a honeycomb structure, or may have a dense structure. If the upper setter is dense, the pores in the sintered plate tend to be small and the number of pores tends to be large. If necessary, the excess lithium source-containing green sheet preferably has a molar ratio (Li / Co ratio) of Li content in the excess lithium source-containing green sheet to Co content in the lithium composite oxide-containing green sheet. It is preferably used by cutting out to a size of 1 or more, more preferably 0.1 to 1.1.

When a lithium composite oxide-containing green sheet (for example, LiCoO ₂ green sheet) is placed on the lower setter, the green sheet may be degreased as desired and then pre-baked at 600 to 850 ° C. for 1 to 10 hours. .. In this case, the excess lithium source-containing green sheet (for example, Li ₂ CO ₃ green sheet) and the upper setter may be placed in order on the obtained temporary baking plate.

Then, the green sheet and / or the calcined plate is sandwiched between setters, degreased as desired, and then heat-treated (fired) at a firing temperature in a medium temperature range (for example, 700 to 1000 ° C.) to obtain a lithium composite oxide. A sintered plate is obtained. This firing step may be performed in two steps or in one step. When firing in two degrees, it is preferable that the firing temperature of the first firing is lower than the firing temperature of the second firing. The sintered body plate thus obtained is also in the form of an independent sheet.

Method for manufacturing the negative electrode plate The negative electrode plate 16, that is, the titanium-containing sintered body plate may be manufactured by any method. For example, the LTO sintered body plate is preferably manufactured through (a) preparation of an LTO-containing green sheet and (b) firing of the LTO-containing green sheet.

(A) Preparation of LTO-containing green sheet First, a raw material powder (LTO powder) composed of lithium titanate Li ₄ Ti ₅ O ₁₂ is prepared. As the raw material powder, a commercially available LTO powder may be used, or may be newly synthesized. For example, a powder obtained by hydrolyzing a mixture of titanium tetraisopropoxyalcohol and isopropoxylithium may be used, or a mixture containing lithium carbonate, titania and the like may be calcined. The volume-based D50 particle size of the raw material powder is preferably 0.05 to 5.0 μm, more preferably 0.1 to 2.0 μm. When the particle size of the raw material powder is large, the pores tend to be large. When the raw material particle size is large, pulverization treatment (for example, pot mill pulverization, bead mill pulverization, jet mill pulverization, etc.) may be performed so as to have a desired particle size. Then, the raw material powder is mixed with a dispersion medium and various additives (binder, plasticizer, dispersant, etc.) to form a slurry. A lithium compound other than LiMO ₂ (for example, lithium carbonate) may be excessively added to the slurry by about 0.5 to 30 mol% for the purpose of promoting grain growth or compensating for volatile matter during the firing step described later. It is desirable not to add a pore-forming material to the slurry. It is preferable that the slurry is stirred under reduced pressure to defoam and the viscosity is adjusted to 4000 to 10000 cP. The obtained slurry is formed into a sheet to obtain an LTO-containing green sheet. The green sheet thus obtained is an independent sheet-shaped molded product. An independent sheet (sometimes referred to as a "self-supporting film") is a sheet that can be handled independently of other supports (including flakes with an aspect ratio of 5 or more). That is, the independent sheet does not include a sheet that is fixed to another support (such as a substrate) and integrated with the support (inseparable or difficult to separate). Sheet molding can be performed by various well-known methods, but it is preferably performed by the doctor blade method. The thickness of the LTO-containing green sheet may be appropriately set so as to be the desired thickness as described above after firing.

(B) Firing of LTO-containing green sheet Place the LTO-containing green sheet on the setter. The setter is made of ceramics, preferably zirconia or magnesia. The setter is preferably embossed. The green sheet placed on the setter in this way is put into the sheath. The sheath is also made of ceramics, preferably alumina. Then, in this state, after degreasing as desired, the LTO sintered body plate is obtained by firing. This firing is preferably performed at 600 to 900 ° C. for 1 to 50 hours, more preferably 700 to 800 ° C. for 3 to 20 hours. The sintered body plate thus obtained is also in the form of an independent sheet. The rate of temperature rise during firing is preferably 100 to 1000 ° C./h, more preferably 100 to 600 ° C./h. In particular, this heating rate is preferably adopted in the heating process of 300 ° C. to 800 ° C., and more preferably adopted in the heating process of 400 ° C. to 800 ° C.

(C) Summary The LTO sintered body plate can be preferably manufactured as described above. In this preferred production method, it is effective to 1) adjust the particle size distribution of the LTO powder and / or 2) change the rate of temperature rise during firing, and these realize various characteristics of the LTO sintered body plate. It is thought that it contributes to.

The present invention will be described in more detail with reference to the following examples. In the following examples, LiCoO ₂ will be abbreviated as "LCO" and Li ₄ Ti ₅ O ₁₂ will be abbreviated as "LTO".

Example A1
(1) Preparation of positive electrode plate (1a) Preparation of LCO green sheet First, Co ₃ O ₄ powder (manufactured by Shodo Chemical Industry Co., Ltd.) and Li weighed so that the molar ratio of Li / Co is 1.01. ₂ CO ₃ powder (manufactured by Honjo Chemical Co., Ltd.) was mixed and then kept at 780 ° C. for 5 hours. The obtained powder was pulverized with a pot mill so that the volume reference D50 was 0.4 μm to obtain a powder composed of LCO plate-like particles. 100 parts by weight of the obtained LCO powder, 100 parts by weight of a dispersion medium (toluene: isopropanol = 1: 1), 10 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Industry Co., Ltd.), and a plasticizer. 4 parts by weight (DOP: Di (2-ethylhexyl) phthalate, manufactured by Kurokin Kasei Co., Ltd.) and 2 parts by weight of a dispersant (product name: Leodor SP-O30, manufactured by Kao Corporation) were mixed. The resulting mixture was stirred under reduced pressure to defoam and the viscosity was adjusted to 4000 cP to prepare an LCO slurry. The viscosity was measured with a Brookfield LVT viscometer. The slurry thus prepared was formed into a sheet on a PET film by a doctor blade method to form an LCO green sheet. The thickness of the LCO green sheet after drying was 240 μm.

(1b) Preparation of LCO Sintered Plate The LCO green sheet peeled off from the PET film was cut into a 50 mm square with a cutter and placed in the center of a magnesia setter (dimensions 90 mm square, height 1 mm) as a lower setter. A porous magnesia setter as an upper setter was placed on the LCO green sheet. The LCO green sheet was placed in a 120 mm square alumina sheath (manufactured by Nikkato Corporation) with the LCO green sheet sandwiched between setters. At this time, the alumina sheath was not sealed, and the lid was closed with a gap of 0.5 mm. The obtained laminate was heated to 600 ° C. at a heating rate of 200 ° C./h and degreased for 3 hours, then heated to 870 ° C. at 200 ° C./h and held for 20 hours for firing. After firing, the temperature was lowered to room temperature, and then the fired body was taken out from the alumina sheath. In this way, an LCO sintered plate was obtained as a positive electrode plate. The obtained positive electrode plate was laser-processed into a shape of 9 mm × 9 mm square. The obtained positive electrode plate was cut into a circular shape having a diameter of 10 mm with a laser processing machine to obtain a positive electrode plate.

(2) Preparation of negative electrode plate (2a) Preparation of LTO green sheet First, 100 parts by weight of LTO powder (volume standard D50 particle size 0.06 μm, manufactured by Sigma-Aldrich Japan GK) and dispersion medium (toluene: isopropanol = 1: 1) 1) 100 parts by weight, binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), 20 parts by weight, plasticizer (DOP: Di (2-ethylhexyl) phosphorate, manufactured by Kurokin Kasei Co., Ltd.) 4 A parts by weight and 2 parts by weight of a dispersant (product name: Leodor SP-O30, manufactured by Kao Corporation) were mixed. The LTO slurry was prepared by stirring the obtained negative electrode raw material mixture under reduced pressure to defoam and adjusting the viscosity to 4000 cP. The viscosity was measured with a Brookfield LVT viscometer. The slurry thus prepared was formed into a sheet on a PET film by a doctor blade method to form an LTO green sheet. The thickness of the LTO green sheet after drying was set to a value such that the thickness after firing was 250 μm.

(2b) Firing of LTO Green Sheet The obtained green sheet was cut into 25 mm square pieces with a cutter knife and placed on an embossed zirconia setter. The green sheet on the setter was placed in an alumina sheath and held at 500 ° C. for 5 hours, then the temperature was raised at a heating rate of 200 ° C./h, and firing was performed at 800 ° C. for 5 hours. The obtained LTO sintered body plate was cut into a circular shape having a diameter of 10 mm with a laser processing machine to obtain a negative electrode plate.

(3) Preparation of Coin-Type Lithium Secondary Battery A coin-type lithium secondary battery 10 as schematically shown in FIG. 1 was produced as follows.

(3a) Adhesion of negative electrode plate and negative electrode current collector with conductive carbon paste Weigh acetylene black and polyimideamide in a mass ratio of 3: 1 and use an appropriate amount of NMP (N-methyl-2-) as a solvent. It was mixed with pyrrolidone) to prepare a conductive carbon paste as a conductive adhesive. A conductive carbon paste was screen-printed on an aluminum foil as a negative electrode current collector. The negative electrode plate prepared in (2) above is placed so as to fit within the undried print pattern (that is, the region coated with the conductive carbon paste), and vacuum dried at 60 ° C. for 30 minutes to form the negative electrode plate. A negative electrode structure in which the negative electrode current collector was bonded to the negative electrode current collector via a carbon layer was produced. The thickness of the carbon layer was 10 μm.

(3b) Preparation of positive electrode current collector with carbon layer Weigh acetylene black and polyimideamide in a mass ratio of 3: 1 and mix them together with an appropriate amount of NMP (N-methyl-2-pyrrolidone) as a solvent. To prepare a conductive carbon paste. A conductive carbon paste was screen-printed on an aluminum foil as a positive electrode current collector and then vacuum dried at 60 ° C. for 30 minutes to prepare a positive electrode current collector having a carbon layer formed on its surface. The thickness of the carbon layer was 5 μm.

(3c) Assembly of coin-shaped battery Between the positive electrode can and the negative electrode can, which form the battery case, from the positive electrode can to the negative electrode can, the positive electrode current collector, the positive electrode side carbon layer, the LCO positive electrode plate, and cellulose The separator, the LTO negative electrode plate, the negative electrode side carbon layer, and the negative electrode current collector are housed in this order, filled with an electrolytic solution, and then sealed by caulking the positive electrode can and the negative electrode can via a gasket. did. In this way, a coin cell type lithium secondary battery 10 having a diameter of 12 mm and a thickness of 1.0 mm was produced. At this time, as the electrolytic solution, LiBF ₄ was dissolved in an organic solvent in which ethylene carbonate (EC) and γ-butyrolactone (GBL) were mixed at a volume ratio of 1: 3 so as to have a concentration of 1.5 mol / L. The solution was used.

(4) Evaluation The initial characteristics and pulse discharge characteristics of the coin-type lithium secondary battery manufactured in (3) above were evaluated as shown below.

(Initial characteristic evaluation)
Using the produced coin-shaped battery, the discharge capacity was measured by performing the charge / discharge operation as follows. Specifically, the battery was charged with a constant current at a current value of 0.2 C rate under the condition of 25 ° C. until the battery voltage became 2.7 V. Then, under the current condition of maintaining the battery voltage at 2.7 V, the battery was charged at a constant voltage until the current value decreased to 1/10. After resting for 10 minutes, a constant current was discharged until the battery voltage reached 1.5 V at a current value of 0.2 C rate, and then rested for 10 minutes. These series of charge / discharge operations were regarded as one cycle, and were repeated for a total of two cycles under the condition of 25 ° C.

(Pulse discharge test)
The battery was charged to 50% (SOC 50%) when the discharge capacity in the second cycle was set to 100%, discharged at a current value of 0.5 C rate for 1 second, and the voltage drop at that time was read. After resting for 1 minute, the battery was charged at a current value of 0.5 C rate for 1 second, and then rested for 1 minute. A series of these charge / discharge operations was regarded as one cycle, and a total of 100 cycles were repeated under the condition of 25 ° C., and the voltage drop at the time of the 100th discharge was read. Using the first voltage drop (V) and the 100th voltage drop (V), the resistance increase rate (%) in the pulse discharge test, that is, the 100th resistance increase rate with respect to the first pulse discharge test is calculated as follows. Calculated based on the formula.
-Resistance increase rate = ([100th resistance value (Ω)] / [1st resistance value (Ω)] -1) x 100
= {([100th voltage drop (V)] x [0.5C rate current value (A)])
/ ([First voltage drop (V)] x [0.5C rate current value (A)])-1} x 100
= ([100th voltage drop (V)] / [1st voltage drop (V)]-1) × 100

Example A2
Instead of adhering the negative electrode plate of (3a) and the negative electrode current collector with the conductive carbon paste, a negative electrode current collector with a carbon layer is prepared according to the procedure of (3b) above, and together with a single negative electrode plate, the above ( A positive electrode plate, a negative electrode plate, and a battery were produced and evaluated in the same manner as in Example A1 except that they were used for assembling the coin-shaped battery of 3c).

Example A3 (comparison)
Instead of preparing the positive electrode current collector with a carbon layer of (3b) above, the positive electrode plate and the positive electrode current collector are bonded with a conductive carbon paste according to the procedure of (3a) above to perform the coin of (3c) above. A positive electrode plate, a negative electrode plate, and a battery were produced and evaluated in the same manner as in Example A1 except that they were used for assembling the shape battery.

Example A4 (comparison)
The positive electrode plate, as in Example A1, except that the conductive carbon paste was not applied to the positive electrode current collector and the negative electrode current collector (that is, the positive electrode side carbon layer and the negative electrode side carbon layer were not formed). A negative electrode plate and a battery were prepared and evaluated.

Example B1
(1) Preparation of positive electrode plate (1a) Preparation of LCO green sheet First, LCO raw material powder was prepared as shown in Table 2 to prepare powder A. 100 parts by weight of the obtained LCO powder (that is, powder A), 100 parts by weight of the dispersion medium (toluene: isopropanol = 1: 1), and 10 parts by weight of the binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Industry Co., Ltd.). 4 parts by weight of a plasticizer (DOP: Di (2-ethylhexyl) phthalate, manufactured by Kurokin Kasei Co., Ltd.) and 2 parts by weight of a dispersant (product name: Leodor SP-O30, manufactured by Kao Corporation) were mixed. .. The resulting mixture was stirred under reduced pressure to defoam and the viscosity was adjusted to 4000 cP to prepare an LCO slurry. The viscosity was measured with a Brookfield LVT viscometer. The slurry thus prepared was formed into a sheet on a PET film by a doctor blade method to form an LCO green sheet. The thickness of the LCO green sheet after drying was 240 μm.

(1b) Preparation of LCO sintered body plate The LCO green sheet peeled off from the PET film was cut into a 50 mm square with a cutter and placed in the center of a magnesia setter (dimensions 90 mm square, height 1 mm) as a lower setter. A porous magnesia setter as an upper setter was placed on the LCO sheet. The LCO sheet was placed in a 120 mm square alumina sheath (manufactured by Nikkato Corporation) with the LCO sheet sandwiched between setters. At this time, the alumina sheath was not sealed, and the lid was closed with a gap of 0.5 mm. The obtained laminate was heated to 600 ° C. at a heating rate of 200 ° C./h and degreased for 3 hours, and then heated to 820 ° C./h at 200 ° C./h and held for 20 hours for firing. After firing, the temperature was lowered to room temperature, and then the fired body was taken out from the alumina sheath. In this way, an LCO sintered body plate having a thickness of 220 μm was obtained as a positive electrode plate. The obtained positive electrode plate was cut into a circular shape having a diameter of 10 mm with a laser processing machine to obtain a positive electrode plate 12.

(2) Preparation of negative electrode plate (2a) Preparation of LTO green sheet First, 100 parts by weight of LTO powder (volume standard D50 particle size 0.06 μm, manufactured by Sigma-Aldrich Japan GK) and dispersion medium (toluene: isopropanol = 1: 1) 1) 100 parts by weight, binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), 20 parts by weight, plasticizer (DOP: Di (2-ethylhexyl) phosphorate, manufactured by Kurokin Kasei Co., Ltd.) 4 A parts by weight and 2 parts by weight of a dispersant (product name: Leodor SP-O30, manufactured by Kao Corporation) were mixed. The LTO slurry was prepared by stirring the obtained negative electrode raw material mixture under reduced pressure to defoam and adjusting the viscosity to 4000 cP. The viscosity was measured with a Brookfield LVT viscometer. The slurry thus prepared was formed into a sheet on a PET film by a doctor blade method to form an LTO green sheet. The thickness of the LTO green sheet after drying was set to a value such that the thickness after firing was 250 μm.

(2b) Firing of LTO Green Sheet The obtained green sheet was cut into 25 mm square pieces with a cutter knife and placed on an embossed zirconia setter. The green sheet on the setter was placed in an alumina sheath and held at 500 ° C. for 5 hours, then the temperature was raised at a heating rate of 200 ° C./h, and firing was performed at 765 ° C. for 5 hours. The obtained LTO sintered body plate was cut into a circular shape having a diameter of 10.5 mm with a laser processing machine to obtain a negative electrode plate.

(3) Preparation of Coin-Type Lithium Secondary Battery The coin-type lithium secondary battery 10 schematically shown in FIG. 1 was produced in the same manner as in Example A1.

(4) Evaluation The LCO sintered body plate (positive electrode plate) synthesized in (1b) above, the LTO sintered body plate (negative electrode plate) synthesized in (2b) above, and the coin produced in (3) above. Various evaluations were carried out on the lithium secondary battery as shown below.

<Average orientation angle of primary particles>
The LCO sintered body plate is polished with a cross section polisher (CP) (IB-15000CP, manufactured by JEOL Ltd.), and the obtained positive electrode plate cross section (cross section perpendicular to the plate surface of the positive electrode plate) is 1000 times as wide as the field view (cross section perpendicular to the plate surface of the positive electrode plate). EBSD measurement was performed at 125 μm × 125 μm) to obtain an EBSD image. This EBSD measurement was performed using a Schottky field emission scanning electron microscope (manufactured by JEOL Ltd., model JSM-7800F). For all the particles specified in the obtained EBSD image, the angle formed by the (003) plane of the primary particles and the plate surface of the positive electrode plate (that is, the inclination of the crystal orientation from (003)) is obtained as the tilt angle, and these are obtained. The average value of the angles was taken as the average orientation angle of the primary particles.

<Plate thickness>
The LCO or LTO sintered body plate is polished by a cross section polisher (CP) (manufactured by JEOL Ltd., IB-15000CP), and the cross section of the obtained positive electrode plate is observed by SEM (manufactured by JEOL Ltd., JSM6390LA) to obtain the positive electrode plate. The thickness was measured. The thickness of the LCO or LTO green sheet after drying described above with respect to the steps (1a) and (2a) was also measured in the same manner as described above.

<Porosity>
The LCO or LTO sintered body plate is polished with a cross section polisher (CP) (IB-15000CP, manufactured by JEOL Ltd.), and the cross section of the obtained positive electrode plate is observed by SEM with a field view (125 μm × 125 μm) of 1000 times (Japan). Electronic, JSM6390LA). The obtained SEM image was image-analyzed, the area of all pores was divided by the area of the positive electrode, and the obtained value was multiplied by 100 to calculate the porosity (%).

<Average pore size>
The average pore diameter of the LCO or LTO sintered body plate was measured by the mercury intrusion method using a mercury porosimeter (manufactured by Shimadzu Corporation, Autopore IV9510).

<Battery capacity>
The battery capacity was measured by the following procedure. That is, the initial capacity was measured by charging at a constant voltage of 2.7 V and then discharging at a discharge rate of 0.2 C, and the obtained initial capacity was adopted as the battery capacity.

<Energy density>
The energy density was calculated by multiplying the above battery capacity by the average voltage and dividing by the battery volume. At that time, the average value of the voltages at SOC 0%, 20%, 40%, 60%, 80%, and 100% was used as the average voltage.

<Battery capacity / thickness ratio>
The battery capacity / thickness ratio (mAh / mm) was calculated by dividing the battery capacity (mAh) by the battery thickness (mm).

<Constant voltage charge cycle performance>
The constant voltage charge cycle performance (discharge capacity retention rate) of the battery was measured by the following procedure. First, the initial capacitance was measured by charging at a constant voltage of 2.7 V and then discharging at a discharge rate of 0.2 C. Next, a total of 100 charge / discharge cycles including constant voltage charging at 2.7 V and discharge in which a current of 20 mA was passed for 0.5 seconds were carried out. Finally, the post-cycle capacitance was measured by charging at a constant voltage of 2.7 V and then discharging at 0.2 C. By dividing the measured post-cycle capacity by the initial capacity and multiplying by 100, the constant voltage charge cycle performance (%) was obtained as the discharge capacity retention rate.

<Rate of resistance increase after reflow>
The battery was charged at a constant voltage of 2.7 V, and the DC resistance was measured in the charged state. Then, discharge was performed at 0.2 C. The battery thus obtained was subjected to a solder reflow treatment accompanied by heating at 260 ° C. for 30 seconds. The battery after the solder reflow treatment was charged at a constant voltage of 2.7 V, and the DC resistance was measured. The resistance increase rate (%) after reflow was calculated by dividing the resistance value after reflow by the resistance value before reflow and multiplying by 100.

Example B2
A positive electrode plate, a negative electrode plate and a battery were produced in the same manner as in Example B1 except that powder B composed of LCO particles produced as shown in Table 2 was used instead of powder A, and various evaluations were performed. went.

Example B3
Similar to Example B1 except that 1) the LCO green sheet was thinned so that the thickness of the positive electrode plate was 60 μm, and 2) the LTO green sheet was thinned so that the thickness of the negative electrode layer was 70 μm. , Positive electrode plate, negative electrode plate and battery were prepared and various evaluations were performed.

Example B4
Similar to Example B1 except that 1) the LCO green sheet was thickened so that the thickness of the positive electrode plate was 330 μm, and 2) the LTO green sheet was thickened so that the thickness of the negative electrode layer was 400 μm. , Positive electrode plate, negative electrode plate and battery were prepared and various evaluations were performed.

Example B5
A positive electrode plate, a negative electrode plate, and a battery were produced in the same manner as in Example B1 except that powder C composed of LCO plate-like particles produced as shown in Table 2 was used instead of powder A. Evaluation was performed.

Example B6
1) The LCO green sheet was thinned so that the thickness of the positive electrode plate was 205 μm, and 2) the Li ₂ CO ₃ green sheet piece prepared by the following procedure was placed on the LCO green sheet prior to the placement of the upper setter. Positive electrode in the same manner as in Example B1 except that it was placed as an excess lithium source and 3) the LCO green sheet was calcined at 800 ° C. for 5 hours and then at 840 ° C. for 20 hours. A plate, a negative electrode plate, and a battery were prepared and evaluated in various ways.

(Preparation of Li ₂ CO ₃ green sheet (excess lithium source))
100 parts by weight of Li ₂ CO ₃ raw material powder (volume standard D50 particle size 2.5 μm, manufactured by Honjo Chemical Co., Ltd.), 5 parts by weight of binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), and plastic 2 parts by weight of the agent (DOP: di (2-ethylhexyl) phthalate, manufactured by Kurokin Kasei Co., Ltd.) and 2 parts by weight of the dispersant (Leodor SP-O30, manufactured by Kao Corporation) were mixed. The obtained mixture was stirred under reduced pressure to defoam and the viscosity was adjusted to 4000 cP to prepare a Li ₂ CO ₃ slurry. The viscosity was measured with a Brookfield LVT viscometer. The Li ₂ CO ₃ slurry thus prepared was formed into a sheet on a PET film by the doctor blade method to form a Li ₂ CO ₃ green sheet. For the thickness of the Li ₂ CO ₃ green sheet after drying, the Li / Co ratio, which is the molar ratio of the Li content in the Li ₂ CO ₃ green sheet to the Co content in the LCO green sheet, shall be a predetermined value. Was set so that To Co content in the resultant LCO calcined plate, the molar ratio of Li content in _Li 2 CO ₃ green sheet, sized to Li / Co ratio is 0.4, dried _Li 2 CO _{3 A} piece of green sheet was cut out.

Example B7
1) Further add Li ₂ CO ₃ raw material powder (volume standard D50 particle size 2.5 μm, manufactured by Honjo Chemical Co., Ltd.) to the LCO slurry so that the excess Li / Co ratio in the LCO green sheet becomes 0.2. 2) The LCO green sheet was thickened so that the thickness of the positive electrode plate was 320 μm, and 3) The firing of the LCO green sheet was held at 800 ° C. for 5 hours and then at 800 ° C. for 20 hours. A positive electrode plate, a negative electrode plate, and a battery were produced in the same manner as in Example B1 except that the above was performed, and various evaluations were performed. The excess Li / Co ratio is the molar ratio of the excess Li content derived from Li ₂ CO ₃ in the LCO green sheet to the Co content in the LCO green sheet.

Example B8
1) The amount of Li ₂ CO ₃ green sheet pieces placed was set to 0.6 in the Li / Co ratio. 2) The LCO green sheet was temporarily held at 700 ° C. for 3 hours after degreasing and before firing. The positive electrode plate and the battery were fired in the same manner as in Example B6, except that the firing was performed and 3) the two-step firing of the LCO green sheet was performed by holding at 800 ° C. for 5 hours and then at 820 ° C. for 20 hours. It was prepared and evaluated in various ways.

Example B9
1) Temporary firing in which the LCO green sheet was held at 900 ° C for 3 hours after degreasing and before firing, and 2) 1-step firing in which the LCO green sheet was held at 820 ° C for 10 hours instead of 2-step firing. A positive electrode plate, a negative electrode plate, and a battery were produced in the same manner as in Example B6 except that the above was performed, and various evaluations were performed.

Example B10
Similar to Example B1, except that 1) the firing temperature of the LTO green sheet was set to 830 ° C instead of 765 ° C, and 2) the LTO green sheet was thinned so that the thickness of the negative electrode layer was 180 μm. A positive electrode plate, a negative electrode plate and a battery were prepared and evaluated in various ways.

Example B11
Similar to Example B1, except that 1) the firing temperature of the LTO green sheet was 700 ° C. instead of 765 ° C., and 2) the LTO green sheet was thickened so that the thickness of the negative electrode layer was 350 μm. A positive electrode plate, a negative electrode plate and a battery were prepared and evaluated in various ways.

Example B12
1) The LTO green sheet was roll-pressed before firing, and 2) the Li ₂ CO ₃ sheet was placed on the LTO green sheet at the time of firing so as to be 5 mol% with respect to the Li amount of the LTO green sheet. A positive electrode plate, a negative electrode plate, and a battery were produced in the same manner as in Example B1 except for the above, and various evaluations were performed.

Example B13
As the LTO powder, an LTO powder obtained by spray-drying an LTO powder (volume standard D50 particle size 0.06 μm, manufactured by Sigma-Aldrich Japan LLC) and subjecting a powder having a D50 of 10 μm to a heat treatment at 600 ° C. was used. A positive electrode plate, a negative electrode plate, and a battery were produced in the same manner as in Example B1 except for the above, and various evaluations were performed.

Example B14
A positive electrode plate, a negative electrode plate, and a battery were produced in the same manner as in Example B1 except that the size of each component was changed so that the outer shape of the battery was a coin shape with a diameter of 20 mm and a thickness of 1.0 mm, and various evaluations were performed. went.

Example B15
1) The size of each component was changed so that the outer shape of the battery was 20 mm in diameter and 1.6 mm in thickness, and 2) the LCO green sheet was thickened so that the thickness of the positive electrode plate was 450 μm. And 3) A positive electrode plate, a negative electrode plate and a battery were produced in the same manner as in Example B1 except that the LTO green sheet was thickened so that the thickness of the negative electrode layer was 500 μm, and various evaluations were performed.

Example B16
A positive electrode plate, a negative electrode plate, and a battery were produced in the same manner as in Example 1 except that the size of each component was changed so that the outer shape of the battery was a coin shape with a diameter of 10 mm and a thickness of 0.7 mm, and various evaluations were performed. went.

Manufacturing conditions and evaluation results Table 3 shows the manufacturing conditions and the like of Examples B1 to 16, while Tables 4 and 5 show the evaluation results of Examples B1 to 16. Table 2 also shows details of the powders A to C referred to in Table 3.

Claims (15)

A positive electrode plate made of a lithium composite oxide sintered body plate and
A negative electrode plate made of a titanium-containing sintered body plate and
A separator interposed between the positive electrode plate and the negative electrode plate,
A positive electrode current collector provided on the surface of the positive electrode plate on the side away from the separator, and a positive electrode current collector.
A negative electrode current collector provided on the surface of the negative electrode plate on the side away from the separator, and
The positive electrode plate, the negative electrode plate, and the electrolytic solution impregnated in the separator,
An exterior body including a positive electrode can, a negative electrode can, and a gasket, wherein the positive electrode can and the negative electrode can are crimped via the gasket to form a closed space, and the positive electrode plate and the positive electrode collection are formed in the closed space. An electric body, the negative electrode plate, the negative electrode current collector, the separator, and an exterior body containing the electrolytic solution,
The positive electrode current collector further includes a positive electrode side carbon layer on the surface on the positive electrode plate side, and the contact between the positive electrode current collector and the positive electrode plate via the positive electrode side carbon layer is the positive electrode. A coin-shaped lithium secondary battery that is held not by bonding the current collector and the positive electrode plate but by the pressure of the positive electrode can and the negative electrode can by caulking. The coin type according to claim 1, wherein the negative electrode current collector further includes a negative electrode side carbon layer on the surface on the negative electrode plate side, or the negative electrode plate further includes a negative electrode side carbon layer on the surface on the negative electrode current collector side. Lithium secondary battery. The coin-shaped lithium secondary battery according to claim 1 or 2, wherein the thickness of the lithium secondary battery is 0.7 to 1.6 mm, and the diameter of the lithium secondary battery is 10 to 20 mm. The coin-type lithium secondary battery according to any one of claims 1 to 3, wherein the positive electrode plate has a thickness of 60 to 450 μm. The coin-type lithium secondary battery according to any one of claims 1 to 4, wherein the lithium composite oxide is lithium cobalt oxide. The coin-shaped lithium secondary battery according to any one of claims 1 to 5, wherein the positive electrode plate has a porosity of 20 to 60%. The coin-shaped lithium secondary battery according to any one of claims 1 to 6, wherein the positive electrode plate has an average pore diameter of 0.1 to 10.0 μm. The positive electrode plate contains a plurality of primary particles composed of a lithium composite oxide, and the plurality of primary particles are oriented at an average orientation angle of more than 0 ° and not more than 30 ° with respect to the plate surface of the positive electrode plate. The coin-shaped lithium secondary battery according to any one of claims 1 to 7, which is an oriented positive electrode plate. The coin-shaped lithium secondary battery according to any one of claims 1 to 8, wherein the negative electrode plate has a thickness of 70 to 500 μm. The coin-shaped lithium secondary battery according to any one of claims 1 to 9, wherein the titanium-containing sintered body contains lithium titanate or a niobium-titanium composite oxide. The coin-type lithium secondary battery according to any one of claims 1 to 10, wherein the negative electrode plate has a porosity of 20 to 60%. The coin-type lithium secondary battery according to any one of claims 1 to 11, wherein the negative electrode plate has an average pore diameter of 0.08 to 5.0 μm. Claim that the separator is made of cellulose, polyimide, polyester, or a ceramic selected from the group consisting of MgO, Al ₂ O ₃ , ZrO ₂ , SiC, Si ₃ N ₄ , Al N, and cordierite. The coin-type lithium secondary battery according to any one of 1 to 12. The electrolytic solution contains lithium borofluoride (LiBF ₄ ) in a non-aqueous solvent consisting of at least one selected from the group consisting of γ-butyrolactone (GBL), ethylene carbonate (EC) and propylene carbonate (PC). The coin-type lithium secondary battery according to any one of claims 1 to 13. An IoT device comprising the coin-type lithium secondary battery according to any one of claims 1 to 14.