WO2021038922A1

WO2021038922A1 - Lithium ion secondary battery

Info

Publication number: WO2021038922A1
Application number: PCT/JP2020/007526
Authority: WO
Inventors: 俊介水上; 雄樹藤田; 浩一近藤; 拓明三橋
Original assignee: 日本碍子株式会社
Priority date: 2019-08-23
Filing date: 2020-02-25
Publication date: 2021-03-04
Also published as: TWI771657B; JP7126028B2; TW202109960A; JPWO2021038922A1

Abstract

The present invention provides a lithium ion secondary battery which has a configuration comprising a positive electrode plate that is composed of a lithium composite oxide sintered material plate and a negative electrode plate that is composed of a titanium-containing sintered material plate, and which still has both improved capacity and improved cycle characteristics. This lithium ion secondary battery is provided with a positive electrode plate that is composed of a lithium composite oxide sintered material plate, a negative electrode plate that is composed of a titanium-containing sintered material plate, a separator, a positive electrode collector, a negative electrode collector and an electrolyte solution; at least a part of the positive electrode collector-side surface of the positive electrode plate is bonded to the positive electrode collector, with a positive electrode-side electroconductive bonding layer being interposed therebetween; at least a part of the negative electrode collector-side surface of the negative electrode plate is bonded to the negative electrode collector, with a negative electrode-side electroconductive bonding layer being interposed therebetween; and the bonded area Sp, where the positive electrode collector and the positive electrode plate are bonded to each other with the positive electrode-side electroconductive bonding layer being interposed therebetween, and the bonded area Sn, where the negative electrode collector and the negative electrode plate are bonded to each other with the negative electrode-side electroconductive bonding layer being interposed therebetween, satisfy the relational expression 1.0 ≤ Sn/Sp ≤ 5.0.

Description

Lithium ion secondary battery

The present invention relates to a lithium ion secondary battery.

Lithium-ion secondary batteries are widely used in various devices that require charging. Many existing lithium-ion secondary batteries employ a powder-dispersed positive electrode (so-called coating electrode) produced by applying and drying a positive electrode mixture containing a positive electrode active material, a conductive auxiliary agent, a binder, and the like. ing.

In general, a powder-dispersed 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, a lithium composite oxide as a positive electrode active material. The packing density is 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 (for example, conductive carbon), a high packing density of the lithium composite oxide results in high capacity and good charge / discharge efficiency. Expected to be obtained. For example, Patent Document 1 (Japanese Patent No. 5587052) provides a lithium ion 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 of 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, Patent Document 2 (Patent No. 6374634) discloses a lithium composite oxide sintered body plate such as lithium _{cobalt oxide LiCoO 2} (hereinafter referred to as LCO) used for a positive electrode of a lithium ion secondary battery. ing. This lithium composite oxide sintered body plate has a structure in which a plurality of primary particles having a layered rock salt structure are bonded, has a porosity of 3 to 40%, and has an average pore diameter of 15 μm or less. It is said that the open porosity ratio is 70% or more, the thickness is 15 to 200 μm, and the primary particle size, which is the average particle size of the plurality of primary particles, is 20 μm or less. Further, in this lithium composite oxide sintered body plate, the average value of the angles formed by the (003) surface of the plurality of primary particles and the plate surface of the lithium composite oxide sintered body plate, that is, the average inclination angle is 0 °. It is said that it exceeds and is 30 ° or less.

On the other hand, it has also been proposed to use a titanium-containing sintered plate as the negative electrode. For example, Patent Document 3 (Japanese Unexamined Patent Publication No. 2015-185337) discloses a lithium ion secondary battery in which a lithium _{titanate (Li 4} Ti ₅ O _{12) sintered body is used for the positive electrode or the negative electrode.} _{Patent Document 4 (Patent No. 6392493) discloses a sintered plate of lithium titanate Li 4} Ti ₅ O ₁₂ (hereinafter referred to as LTO) used as a negative electrode of a lithium ion secondary battery. This LTO sintered body plate has a structure in which a plurality of primary particles are bonded, has a thickness of 10 to 290 μm, and has a primary particle size of 1.2 μm, which is the average particle size of the plurality of primary particles. It is said that the porosity is 21 to 45% and the open pore ratio is 60% or more.

Japanese Patent No. 5587052 Japanese Patent No. 6374634 Japanese Unexamined Patent Publication No. 2015-185337 Japanese Patent No. 6392493

In recent years, a lithium ion secondary battery having a high capacity and a high output while being compact and thin has been desired. Therefore, in anticipation of high capacity and good charge / discharge efficiency, a lithium composite oxide sintered body plate (for example, LCO sintered body plate) that does not contain conductive carbon is used as the positive electrode and does not contain conductive carbon. It has been proposed to use a titanium-containing sintered plate (for example, an LTO sintered plate) as a negative electrode (for example, Patent Document 4). However, it has been found that when a lithium ion secondary battery is actually manufactured using these sintered body plates, that is, a ceramic positive electrode plate and a ceramic negative electrode plate, the expected capacity cannot be obtained.

The present inventors have recently introduced a positive electrode current collector and a positive electrode plate in a lithium ion secondary battery including a positive electrode plate which is a lithium composite oxide sintered body plate and a negative electrode plate which is a titanium-containing sintered body plate. The area Sp where is bonded via the positive electrode side conductive bonding layer and the area Sn where the negative electrode current collector and the negative electrode plate are bonded via the negative electrode side conductive bonding layer are 1.0 ≦ Sn / Sp ≦. It was found that both capacitance and cycle characteristics can be improved by satisfying the relationship of 5.0.

Therefore, an object of the present invention is a configuration including a positive electrode plate which is a lithium composite oxide sintered body plate and a negative electrode plate which is a titanium-containing sintered body plate, but both capacity and cycle characteristics are improved. The purpose is to provide a lithium ion secondary battery.

According to one aspect of the invention
A positive electrode plate, which is a lithium composite oxide sintered body plate that does not contain conductive carbon,
A negative electrode plate that is a titanium-containing sintered body plate that does not contain conductive carbon,
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 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,
It is a lithium-ion secondary battery equipped with
At least a part of the surface of the positive electrode plate on the positive electrode current collector side is bonded to the positive electrode current collector via the positive electrode side conductive bonding layer.
At least a part of the surface of the negative electrode plate on the negative electrode current collector side is bonded to the negative electrode current collector via the negative electrode side conductive bonding layer.
The area Sp where the positive electrode current collector and the positive electrode plate are bonded via the positive electrode side conductive bonding layer, and the negative electrode current collector and the negative electrode plate are bonded via the negative electrode side conductive bonding layer. A lithium ion secondary battery is provided in which the area Sn satisfies the relationship of 1.0 ≦ Sn / Sp ≦ 5.0.

It is a schematic cross-sectional view of an example of the lithium ion 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.

FIG. 1 schematically shows an example of the lithium ion secondary battery of the present invention. The lithium ion secondary battery 10 shown in FIG. 1 includes a positive electrode plate 12, a negative electrode plate 14, a separator 16, a positive electrode current collector 18, a negative electrode current collector 20, and an electrolytic solution 22. The positive electrode plate 12 is a lithium composite oxide sintered body plate that does not contain conductive carbon. The negative electrode plate 14 is a titanium-containing sintered body plate that does not contain conductive carbon. The separator 16 is interposed between the positive electrode plate 12 and the negative electrode plate 14. The positive electrode current collector 18 is provided on the surface of the positive electrode plate 12 on the side away from the separator 16. The negative electrode current collector 20 is provided on the surface of the negative electrode plate 14 on the side away from the separator 16. The electrolytic solution 22 is impregnated into the positive electrode plate 12, the negative electrode plate 14, and the separator 16. At least a part of the surface of the positive electrode plate 12 on the positive electrode current collector 18 side is bonded to the positive electrode current collector 18 via the positive electrode side conductive bonding layer 24. At least a part of the surface of the negative electrode plate 14 on the negative electrode current collector 20 side is bonded to the negative electrode current collector 20 via the negative electrode side conductive bonding layer 26.

Then, the area Sp where the positive electrode current collector 18 and the positive electrode plate 12 are bonded via the positive electrode side conductive bonding layer 24, and the negative electrode current collector 20 and the negative electrode plate 14 are bonded via the negative electrode side conductive bonding layer 26. The area Sn to be formed satisfies the relationship of 1.0 ≦ Sn / Sp ≦ 5.0. The area Sp in which the positive electrode current collector 18 and the positive electrode plate 12 are bonded via the positive electrode side conductive bonding layer 24 is a positive electrode that contributes to the bonding between the positive electrode current collector 18 and the positive electrode plate 12. It means the occupied area of the side conductive bonding layer 24, and does not include the area of the region where the positive electrode current collector 18 and the positive electrode plate 12 are in contact with each other or facing each other without the positive electrode side conductive bonding layer 24 intervening. .. Similarly, the area Sn where the negative electrode current collector 20 and the negative electrode plate 14 are joined via the negative electrode side conductive bonding layer 26 contributes to these bonding between the negative electrode current collector 20 and the negative electrode plate 14. It means the occupied area of the negative electrode side conductive bonding layer 26, and does not include the area of the region where the negative electrode current collector 20 and the negative electrode plate 14 are in contact with or opposed to each other without the negative electrode side conductive bonding layer 26 intervening. To do. In the lithium ion secondary battery 10 including the positive electrode plate 12 which is a lithium composite oxide sintered body plate and the negative electrode plate 14 which is a titanium-containing sintered body plate, the positive electrode current collector 18 and the positive electrode plate 12 The area Sp where is bonded via the positive electrode side conductive bonding layer 24 and the area Sn where the negative electrode current collector 20 and the negative electrode plate 14 are bonded via the negative electrode side conductive bonding layer 26 are 1.0 ≦. By satisfying the relationship of Sn / Sp ≦ 5.0, both capacitance and cycle characteristics can be improved.

As described above, a lithium composite oxide sintered body plate containing no conductive carbon (for example, LCO sintered body plate) is used as the positive electrode, and a titanium-containing sintered body plate containing no conductive carbon (for example, LTO sintering) is used. When a lithium ion secondary battery was actually manufactured using the body plate as the negative electrode, it was found that the expected capacity could not be obtained. It is considered that this is because when the titanium-containing sintered plate is used to secure the function of electron conduction in the direction of the negative electrode surface, the capacity cannot be sufficiently taken out due to the lack of electron conductivity in the direction of the negative electrode surface. Then, by arranging the positive electrode side conductive bonding layer 24 and the negative electrode side conductive bonding layer 26 so as to satisfy the relationship of 1.0 ≦ Sn / Sp ≦ 5.0, the above problem can be conveniently solved. At the same time, the cycle characteristics can be improved.

This is considered to be as follows. That is, when Sn / Sp is 1.0 or more, the area Sn where the negative electrode current collector 20 and the negative electrode plate 14 are joined via the negative electrode side conductive bonding layer 26 is the positive electrode current collector 18 and the positive electrode. This means that the plate 12 has an area Sp equal to or larger than the area Sp joined via the positive electrode side conductive bonding layer 24. That is, by increasing the joint area Sn of the negative electrode current collector 20 and the negative electrode plate 14 to a size equal to or larger than the area Sp, the negative electrode current collector 20 and the negative electrode side conductive joint layer 26 conduct electron conduction in the negative electrode surface direction. It is thought that it will be possible to supplement the function and take out sufficient capacity. Further, the fact that Sn / Sp is 1.0 to 5.0 means that the joint area Sp of the positive electrode current collector 18 and the positive electrode plate 12 is reduced to a size equal to or smaller than the above area Sn, but is excessively small. By adjusting the joint area Sp of the positive electrode current collector 18 and the positive electrode plate 12 so as to be within such a selective range, it is possible to improve the cycle characteristics. In this respect, when the joint area Sp of the positive electrode current collector 18 and the positive electrode plate 12 is larger than the above area Sn (that is, Sn / Sp is less than 1.0), it faces the negative electrode plate 14 (that is, the negative electrode active material). The portion of the positive electrode plate 12 (positive electrode active material) bonded to the positive electrode current collector 18 also contributes significantly to charging and discharging, and a potential distribution is generated in the positive electrode plate 12 that contributes to charging and discharging, so that the electrolytic solution and the like are charged. It is considered that the cycle characteristics deteriorate due to the non-uniform growth of the film due to oxidative decomposition. Further, when the joint area Sp of the positive electrode current collector 18 and the positive electrode plate 12 is made too small to be less than one-fifth of the area Sn (that is, Sn / Sp exceeds 5.0), the positive electrode plate 12 is formed. Since the expansion and contraction of the lithium composite oxide (for example, LCO) due to occlusion / release of lithium is larger than that of the titanium-containing sintered body (for example, LTO) constituting the negative electrode plate 14, due to the expansion and contraction of the positive electrode plate 12 due to charge and discharge. It is considered that the positive electrode plate 12 and the positive electrode current collector 18 are separated from each other and the cycle characteristics are deteriorated. From the above viewpoint, the Sn / Sp ratio is 1.0 to 5.0, preferably 1.1 to 5.0, more preferably 1.5 to 5.0, and further preferably 2.5 to 5. It is 0.

As described above, at least a part of the surface of the negative electrode plate 14 on the negative electrode current collector 20 side is bonded to the negative electrode current collector 20 via the negative electrode side conductive bonding layer 26, and the negative electrode of the negative electrode plate 14 is preferable. At least 70%, more preferably at least 80%, even more preferably 90%, and most preferably all (100%) of the surface on the current collector 20 side is via the negative electrode current collector 20 and the negative electrode side conductive bonding layer 26. Are joined together. By increasing the ratio of the bonding area by the negative electrode side conductive bonding layer 26 in this way, the negative electrode current collector 20 and the negative electrode side conductive bonding layer 26 can more effectively supplement the electron conduction function in the negative electrode surface direction. , You will be able to take out more capacity.

The positive electrode plate 12 is a lithium composite oxide sintered body plate that does not contain conductive carbon. 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 those disclosed in, for example, Patent Document 1 (Patent No. 5587052) and Patent Document 2 (Patent No. 6374634) are known. Can be used.

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 a transition metal 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 (nickel cobalt _lithium), Li x CoNiMnO ₂ (cobalt-nickel-lithium _manganate), Li x CoMnO ₂ (cobalt-lithium manganate), and the like, particularly preferably _Li x CoO ₂ (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 can be 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 that intersect 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. ..

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 ion secondary battery 10, and the battery characteristics deteriorate (particularly, the resistance value increases) due to repeated charging and discharging. Can be suppressed.

The negative electrode plate 14 is a titanium-containing sintered body plate that does not contain conductive carbon. 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 14 is a sintered body plate means that the negative electrode plate 14 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 methods described in Patent Document 3 (Japanese Patent Laid-Open No. 2015-185337) and Patent Document 4 (Patent No. 6392493).

The negative electrode plate 14, that is, the titanium-containing sintered body plate, has a structure in which a plurality of (that is, a large number of) 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 14 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 14 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 14 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 14, 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 14 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 14 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 14 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 separator 16 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 electrolyte components. Therefore, 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 14 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 lithium batteries, such as a solution in which a lithium salt is dissolved in a non-aqueous solvent such as an organic solvent, may be used. Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), vinylethylene carbonate (VEC), and fluoroethylene carbonate (FEC), and dimethyl carbonate (DMC). , Diethyl carbonate (DEC), Ethylmethyl carbonate (EMC) and other chain carbonates, tetrahydrofuran (THF) and other cyclic ethers, dimethoxyethane (DME) and other chain ethers, γ-butyrolactone (GBL) and other lactones. , Nitrile such as acetonitrile (AN), cyclic sulfone such as sulfolane (SL), cyclic sulfonic acid ester such as propane sulton (PS) and the like. Such a non-aqueous solvent may be used alone or as a mixture of two or more kinds. Examples of lithium salts include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), and lithium. Examples thereof include bisfluorosulfonylimide (LiFSI) and lithium bis (oxalate) borate (LiBOB). Such lithium salts may be used alone or as a mixture of two or more kinds. The lithium salt concentration 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.

Preferably, the lithium ion secondary battery 10 further includes a pair of exterior films 28, and the outer peripheral edges of the exterior films 28 are sealed with each other to form an internal space, in which the positive electrode current collector 18 and the positive electrode side are formed. Containing the conductive bonding layer 24, the positive electrode plate 12, the separator 16, the negative electrode plate 14, the negative electrode side conductive bonding layer 26, the negative electrode current collector 20, and the electrolytic solution 22 (hereinafter collectively referred to as battery elements). That is, as shown in FIG. 1, the battery elements that are the contents of the lithium ion secondary battery 10 are packaged and sealed with a pair of exterior films 28, and as a result, the lithium ion secondary battery 10 is It is in the form of a so-called film exterior battery. The outer edge of the lithium ion secondary battery 10 is preferably sealed by heat-sealing the exterior films 28 to each other. Sealing by heat fusion is preferably performed using a heat bar (also referred to as a heating bar), which is generally used for heat sealing. Typically, it has a quadrilateral shape of the lithium ion secondary battery 10, and it is preferable that the outer peripheral edge of the pair of exterior films 28 is sealed over all four outer peripheral edges.

As the exterior film 28, a commercially available exterior film may be used. The thickness of the exterior film 28 is preferably 50 to 80 μm, more preferably 55 to 70 μm, and even more preferably 55 to 65 μm per sheet. The preferred exterior film 28 is a laminated film containing a resin film and a metal foil, and more preferably an aluminum laminated film containing a resin film and an aluminum foil. As the laminated film, it is preferable that resin films are provided on both sides of a metal foil such as an aluminum foil. In this case, the resin film on one side of the metal foil (hereinafter referred to as the surface protective film) is made of a material having excellent reinforcing properties such as nylon, polyamide, polyethylene terephthalate, polyimide, polytetrafluoroethylene, and polychlorotrifluoroethylene. The resin film on the other side of the metal foil is preferably made of a heat-sealing material such as polypropylene.

The positive electrode current collector 18 is provided on the surface of the positive electrode plate 12 on the side away from the separator 16, while the negative electrode current collector 20 is provided on the surface of the negative electrode plate 14 on the side away from the separator 16. Therefore, the positive electrode current collector 15 is interposed between the positive electrode plate 12 and the exterior film 28, while the negative electrode current collector 20 is interposed between the negative electrode plate 14 and the exterior film 28. Preferably, one of the positive electrode current collector 15 and the exterior film 28 is adhered, and the other of the negative electrode current collector 20 and the exterior film 28 is adhered. The positive electrode current collector 15 and the negative electrode current collector 20 are not particularly limited, but are preferably metal foils such as copper foil and aluminum foil.

The positive electrode tab terminal 19 is connected to the positive electrode current collector 18 and extends outward from the sealing portion of the pair of exterior films 28, while the negative electrode tab terminal (not shown) is connected to the negative electrode current collector 20. Then, it extends outward from the sealing portion of the pair of exterior films 28. In FIG. 1, the negative electrode tab terminal is not drawn because it is hidden behind the positive electrode tab terminal 19. More specifically, the positive electrode tab terminal 19 and the negative electrode tab terminal extend from different positions or different sides of a common one side of the sealing portion of the exterior film 28. The positive electrode tab terminal 19 and the negative electrode tab terminal are not particularly limited, but may be the same or different materials as the positive electrode current collector 15 and the negative electrode current collector 20, and are preferably metal foils such as copper foil and aluminum foil. .. Further, the connection between the positive electrode tab terminal 19 and the positive electrode current collector 15 and the connection between the negative electrode tab terminal and the negative electrode current collector 20 may be performed by a known connection method such as welding or adhesive, and are not particularly limited. Alternatively, the positive electrode tab terminal 19 and the positive electrode current collector 15, or the negative electrode tab terminal and the negative electrode current collector 20 may be an integral product made of the same material.

At least a part of the surface of the positive electrode plate 12 on the positive electrode current collector 18 side is bonded to the positive electrode current collector 18 via the positive electrode side conductive bonding layer 24. At least a part of the surface of the negative electrode plate 14 on the negative electrode current collector 20 side is bonded to the negative electrode current collector 20 via the negative electrode side conductive bonding layer 26. The positive electrode side conductive bonding layer 24 and the negative electrode side conductive bonding layer 26 are not particularly limited as long as a known or commercially available conductive adhesive is used, but for example, a conductive material, a binder, and, if desired, thickening. Examples thereof include those containing an agent in a predetermined compounding ratio. Examples of the conductive material include conductive carbon materials such as carbon black, acetylene black, graphite, carbon fiber, and carbon nanotubes. Examples of the binder include an acrylic binder, a styrene-butadiene rubber binder, and the like. Examples of thickeners include carboxymethyl cellulose and the like.

Method for Producing Positive Electrode Plate The positive electrode plate 12, that is, the lithium composite oxide sintered body plate may be produced by any method, but preferably (a) preparation of a lithium composite oxide-containing green sheet, (a) b) The green sheet containing an excess lithium source is produced as desired, and (c) the green sheet is laminated and fired.

(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 synthetic plate-like particles (eg, LiCoO ₂ plate-like 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. for 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 the 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 the matrix particles, a large format (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 in an amount of 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 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. Regarding 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 cut out to a size of 1 or more, more preferably 0.1 to 1.1, and used.

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 Negative Electrode Plate The negative electrode plate 14, 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 fired. 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 in an amount of 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 1
(1) Preparation of positive electrode plate (1a) Preparation of LCO green sheet First, 100 parts by weight of LCO (manufactured by Nippon Kagaku Kogyo Co., Ltd.) raw material powder and 100 parts by weight of dispersion medium (xylene: n-butanol = 1: 1). , Binder (Polyvinyl butyral: Part No. BM-2, manufactured by Sekisui Chemical Co., Ltd.), 10 parts by weight, Plasticizer (DOP: Di (2-ethylhexyl) phthalate, manufactured by Kurokin Kasei Co., Ltd.), 2 parts by weight, Dispersant (Product name Leodor SP-O30, manufactured by Kao Corporation) 4.5 parts by weight was mixed. A slurry was prepared by stirring the obtained 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 a green sheet. The thickness of the LCO green sheet after drying was 110 μm.

(1b) Preparation of LCO sintered body plate The LCO green sheet peeled off from the PET film was cut into a 35 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. As the upper setter, a porous alumina setter (dimensions 40 mm square, height 3 mm) was placed in the center on a green sheet. The green sheet on the setter was fired at 900 ° C. for 15 hours to obtain an LCO sintered body plate. In this way, the LCO sintered body plate was obtained as a positive electrode plate. The obtained positive electrode plate was laser-processed into a shape of 32 mm × 32 mm square.

(2) Preparation of negative electrode plate (2a) Preparation of LTO green sheet First, 100 parts by weight of LTO powder (manufactured by Sigma Aldrich Japan GK), 100 parts by weight of dispersion medium (xylene: n-butanol = 1: 1), and 100 parts by weight. 10 parts by weight of binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), 2 parts by weight of plasticizer (DOP: Di (2-ethylhexyl) phthalate, manufactured by Kurokin Kasei Co., Ltd.), and dispersant (dispersant) Product name Leodor SP-O30, manufactured by Kao Corporation) 1 part by weight was 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 110 μm.

(2b) Preparation of LTO sintered body plate The obtained green sheet was cut into a 35 mm square with a cutter knife and placed on a magnesia setter (dimensions 90 mm square, height 1 mm). As the upper setter, a porous alumina setter (dimensions 40 mm square, height 3 mm) was placed in the center on a green sheet. The green sheet on the setter was fired at 760 ° C. for 5 hours to obtain an LTO sintered plate. In this way, the LTO sintered body plate was obtained as a negative electrode plate. The obtained negative electrode plate was laser-machined into a shape of 30 mm × 30 mm square.

(3) Preparation of current collector A 20 μm aluminum foil was cut out to a size of 35 mm × 45 mm. A tab lead was arranged so as to protrude from the end on the short side of the cut out aluminum foil, and the aluminum foil and the tab lead were ultrasonically bonded to obtain a current collector.

(4) Preparation of conductive adhesive 30 parts by weight of conductive material (acetylene black), 60 parts by weight of binder (acrylic binder), and 10 parts by weight of thickener (carboxymethyl cellulose) are mixed, and pure water is added. A conductive adhesive was prepared.

(5) Preparation of Positive Electrode A conductive adhesive ^{was applied to the aluminum foil constituting the current collector in an area of 810 mm 2, and} a positive electrode plate was adhered so as to cover the entire portion coated with the conductive adhesive. This was dried at 100 ° C. for 12 hours to obtain a positive electrode.

(6) Preparation of Negative Electrode A conductive adhesive ^{was applied to an aluminum foil constituting another current collector with an area of 810 mm 2} , and a negative electrode plate was adhered so as to cover the entire portion coated with the conductive adhesive. .. This was dried at 100 ° C. for 12 hours to obtain a negative electrode.

(7) Preparation of Electrode Group The positive electrode and the negative electrode thus obtained were opposed to each other via a separator, and tape was wrapped around the outer circumference to fix them. At this time, the tab lead of the positive electrode and the tab lead of the negative electrode were arranged so as to extend in opposite directions from different sides facing each other. Further, the entire negative electrode plate constituting the negative electrode was made to face the positive electrode plate constituting the positive electrode.

(8) Preparation of Pre-Liquid Injection Battery Two laminated films were prepared and placed on the outer surfaces of the positive electrode and the negative electrode of the electrode group. Next, the laminated film arranged on the positive electrode side and the laminated film arranged on the negative electrode side were heat-sealed at the three peripheral edges of the electrode group. At this time, the positions of the two sides on which the tab leads are arranged are adjusted so that the portion where the insulating film provided on the tab leads and the laminate overlap is heat-sealed so that a part of the tab leads protrudes from the laminate film. .. This protruding tab lead was used as a terminal to be connected to the device during charging and discharging. Further, the other side on which the tab leads were not arranged was heat-sealed so as to be orthogonal to the two sealing sides on which the tab leads were arranged.

(9) Injection of non-aqueous electrolyte A non-aqueous electrolyte (electrolyte solution) was injected from the side where heat welding was not performed. As the non-aqueous electrolyte, a mixture of ethylene carbonate and ethyl methyl carbonate at a ratio of 1: 1 was used as the non-aqueous solvent, and 1 mol / l lithium hexafluoride phosphate was used as the electrolyte.

(10) Preparation of Battery After injection of the non-aqueous electrolyte, the remaining one side was heat-sealed to obtain a battery for charge / discharge cycle test.

(11) Evaluation of 0.2C discharge capacity before cycle The battery capacity was confirmed in an environment of 25 ° C. using the obtained battery. Charging was carried out by constant current constant voltage charging, specifically, constant current charging at 0.2 C until 2.7 V was reached, and then constant voltage charging at 2.7 V until the current value reached 0.02 C. .. The discharge was carried out at a constant current of 0.2 C until the voltage reached 1.5 V. The discharge capacity thus obtained was divided by the weight of the negative electrode plate measured in advance to obtain 0.2 C discharge capacity before the cycle.

(12) Cycle test Next, a charge / discharge cycle test was carried out. The charge / discharge cycle test was performed by repeating charging / discharging 1000 times in an environment of 25 ° C. Charging was carried out at a constant voltage of 2.7 V until the current value reached 0.2 C. The discharge was carried out by constant current discharge at 1C until the voltage reached 1.5V.

(13) Evaluation of capacity retention rate after 1000 cycles The battery capacity of a battery that was repeatedly charged and discharged for 1000 cycles was confirmed in an environment of 25 ° C. Charging was carried out by constant current constant voltage charging, specifically, constant current charging at 0.2 C until 2.7 V was reached, and then constant voltage charging at 2.7 V until the current value reached 0.02 C. .. The discharge was carried out at a constant current of 0.2 C until the voltage reached 1.5 V. The discharge capacity thus obtained was divided by the weight of the negative electrode plate measured in advance to obtain a 0.2C discharge capacity after 1000 cycles. Further, this value was divided by the 0.2C discharge capacity before the cycle and multiplied by 100 to obtain the capacity retention rate (%) after 1000 cycles.

Example 2
A battery was prepared and evaluated in the same manner as in Example 1 except that the conductive adhesive for the positive electrode ^{was applied in an area of 162 mm 2 in (5) above.}

Example 3
Same as in Example 1 except that the positive electrode conductive adhesive ^{was applied in an area of 630 mm 2} in (5) above and the negative electrode conductive adhesive was applied in an area of ^{630 mm 2 in (6) above.} The batteries were manufactured and evaluated.

Example 4
The same as in Example 1 except that the positive electrode conductive adhesive ^{was applied in an area of 126 mm 2} in (5) above and the negative electrode conductive adhesive was applied in an area of ^{630 mm 2 in (6) above.} Batteries were manufactured and evaluated.

Example 5
Same as in Example 1 except that the positive electrode conductive adhesive ^{was applied in an area of 900 mm 2} in (5) above and the negative electrode conductive adhesive was applied in an area of ^{900 mm 2 in (6) above.} The batteries were manufactured and evaluated.

Example 6
Same as in Example 1 except that the positive electrode conductive adhesive ^{was applied in an area of 818 mm 2} in (5) above and the negative electrode conductive adhesive was applied in an area of ^{900 mm 2 in (6) above.} The batteries were manufactured and evaluated.

Example 7
Same as in Example 1 except that the positive electrode conductive adhesive ^{was applied in an area of 360 mm 2} in (5) above and the negative electrode conductive adhesive was applied in an area of ^{900 mm 2 in (6) above.} The batteries were manufactured and evaluated.

Example 8
Same as in Example 1 except that the positive electrode conductive adhesive ^{was applied in an area of 180 mm 2} in (5) above and the negative electrode conductive adhesive was applied in an area of ^{900 mm 2 in (6) above.} The batteries were manufactured and evaluated.

Example 9 (comparison)
Same as in Example 1 except that the positive electrode conductive adhesive ^{was applied in an area of 1000 mm 2} in (5) above and the negative electrode conductive adhesive was applied in an area of ^{900 mm 2 in (6) above.} The batteries were manufactured and evaluated.

Example 10 (comparison)
Except that the positive electrode conductive adhesive ^{was applied in an area of 176.5 mm 2} in (5) above, and the negative electrode conductive adhesive was applied in an area of ^{900 mm 2 in (6) above.} The batteries were prepared and evaluated in the same manner.

Example 11 (comparison)
Same as in Example 1 except that the positive electrode conductive adhesive ^{was applied in an area of 700 mm 2} in (5) above and the negative electrode conductive adhesive was applied in an area of ^{630 mm 2 in (6) above.} The batteries were manufactured and evaluated.

Results Table 1 shows the evaluation results of the batteries produced in Examples 1 to 11. In Table 1, Sn / Sp is such that the negative electrode current collector and the negative electrode plate are conductive with respect to the area Sp where the positive electrode current collector and the positive electrode plate are bonded via the conductive adhesive (positive electrode side conductive bonding layer). It means the ratio of the area Sn bonded via the sex adhesive (negative electrode side conductive bonding layer).

As is clear from Table 1, in Examples 1 to 8 satisfying the relationship of 1.0 ≦ Sn / Sp ≦ 5.0, after 1000 cycles, which is significantly higher than in Examples 9 to 11 not satisfying the above relationship. Capacity retention rate has been achieved.

Claims

A positive electrode plate, which is a lithium composite oxide sintered body plate that does not contain conductive carbon,
A negative electrode plate that is a titanium-containing sintered body plate that does not contain conductive carbon,
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 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,
It is a lithium-ion secondary battery equipped with
At least a part of the surface of the positive electrode plate on the positive electrode current collector side is bonded to the positive electrode current collector via the positive electrode side conductive bonding layer.
At least a part of the surface of the negative electrode plate on the negative electrode current collector side is bonded to the negative electrode current collector via the negative electrode side conductive bonding layer.
The area Sp where the positive electrode current collector and the positive electrode plate are bonded via the positive electrode side conductive bonding layer, and the negative electrode current collector and the negative electrode plate are bonded via the negative electrode side conductive bonding layer. A lithium ion secondary battery in which the area Sn satisfies the relationship of 1.0 ≦ Sn / Sp ≦ 5.0.
The lithium ion secondary battery according to claim 1, wherein at least 70% of the surface of the negative electrode plate on the negative electrode current collector side is bonded to the negative electrode current collector via the negative electrode side conductive bonding layer.
The lithium ion secondary battery according to claim 1, wherein the entire surface of the negative electrode plate on the negative electrode current collector side is bonded to the negative electrode current collector via the negative electrode side conductive bonding layer.
The lithium ion 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 lithium ion secondary battery according to any one of claims 1 to 4, wherein the lithium composite oxide is lithium cobalt oxide.
The lithium ion secondary battery according to any one of claims 1 to 5, wherein the negative electrode plate has a thickness of 70 to 500 μm.
The lithium ion secondary battery according to any one of claims 1 to 6, wherein the titanium-containing sintered body contains lithium titanate or a niobium-titanium composite oxide.