JP7809673B2 - Electrode manufacturing method and battery manufacturing method - Google Patents

Description

Embodiments relate to methods for manufacturing electrodes and methods for manufacturing batteries.

To improve the lifespan of electrodes using niobium-titanium oxide, hydrophilic binders such as carboxymethyl cellulose (CMC) are added to the electrodes. However, these electrodes tend to bend easily when made large, making them difficult to handle during manufacturing.

JP 2019-53944 A

The embodiments aim to provide an electrode manufacturing method and a battery manufacturing method that can reduce the occurrence of defects during manufacturing.

According to an embodiment, the method includes: applying a slurry containing water and at least one of a niobium-containing oxide and a titanium-containing oxide to a current collector to obtain a structure;
a step of drying the slurry to form an active material-containing layer;
pressing the structure;
and laminating a plurality of structures and drying both outermost layers of the resulting laminate under pressure, thereby reducing the moisture content of the active material-containing layer to 600 ppm by mass or less as determined by the Karl Fischer method.

According to the embodiment, a method for manufacturing an electrode assembly includes a step of using the electrode obtained by the method of the embodiment as a first electrode and disposing a separator between the first electrode and a second electrode;
a step of housing the electrode group in an exterior member;
and retaining a non-aqueous electrolyte in the electrode group housed in the exterior member.

FIG. 1 is a flow diagram illustrating an example of a method according to an embodiment. 3A and 3B are schematic diagrams showing an example of coating and drying in the method of the embodiment. FIG. 1 is a plan view showing an example of a structure. 4 is a cross-sectional view of the structure shown in FIG. 3 taken along line IV-IV. 4 is a cross-sectional view of the structure shown in FIG. 3 taken along line VV. FIG. 10 is a side view showing a state in which a portion of the structure without an active material-containing layer is sandwiched between a pair of rollers. FIG. 2 is a cross-sectional view of a structure in which a portion without an active material layer is sandwiched between a pair of rollers, taken along a direction perpendicular to the conveying direction. FIG. 1 is a schematic perspective view showing an example of a roll of a structure. FIG. 2 is a schematic diagram showing an example of pressing and winding in the method of the embodiment. FIG. 10 is an enlarged cross-sectional view showing the pressing step shown in FIG. 9 . FIG. 4 is a schematic plan view showing an example of cutting in the method of the embodiment. FIG. 2 is a plan view showing an electrode manufactured by the method of the embodiment. FIG. 10 is a plan view showing an electrode having a wrinkled tab. FIG. 10 is a plan view showing a housing used in the second drying step of the method of the embodiment. 15 is a cross-sectional view of the housing shown in FIG. 14 taken along line XV-XV. FIG. 2 is a partially cutaway perspective view of a battery manufactured by a method according to an embodiment. FIG. 17 is an enlarged cross-sectional view of a portion indicated by B in FIG. 16 . FIG. 10 is a perspective view showing another example of a stacked electrode group manufactured by the method of the embodiment. 3 is a cross-sectional view of a battery manufactured by a method according to an embodiment, taken in a direction perpendicular to the terminal extending direction. FIG. FIG. 20 is an enlarged cross-sectional view of a portion indicated by A in FIG. 19 .

(First embodiment)
The first embodiment relates to a method for manufacturing an electrode.

Electrodes made by applying a slurry containing water and at least one of niobium-containing oxide and titanium-containing oxide to a current collector, drying, pressing, and cutting the resulting material, tend to bend easily when the electrode area is increased. This can lead to defects such as the electrode bending and deforming when transported by a transport device such as a vacuum, or falling off the transport device.

The method of the embodiment includes a step of applying a slurry containing water and at least one of a niobium-containing oxide and a titanium-containing oxide to a current collector to obtain a structure;
drying the slurry to form an active material-containing layer;
pressing the structure;
and laminating a plurality of the structures and drying both outermost layers of the resulting laminate under pressure, thereby reducing the moisture content of the active material-containing layer to 600 ppm by mass or less as determined by the Karl Fischer method.

According to the method of the embodiment, when an electrode or battery is manufactured, the electrode has a moderate hardness, so it is less likely to bend even when the electrode area is large when the electrode is transported to the next process or a predetermined position. As a result, it is possible to prevent the electrode from bending and falling from the transport device during transport, preventing defects such as electrode damage (chipping, cracking, peeling, etc.) due to dropping, or the electrode not being transported to the predetermined position. Furthermore, it becomes easier to automate the process of manufacturing a stacked electrode group by placing a separator between this electrode and counter electrode.

The method of this embodiment will be described below with reference to Figures 1 to 15.

The electrode manufacturing method of this embodiment can include steps S1 to S5 shown in Figure 1.

First, we will explain the slurry coating S1 and first drying S2.

Figure 2 shows an example of an apparatus used in slurry coating S1 and first drying S2. This apparatus includes a slurry coating device 20, a drying furnace 21, and a curvature correction unit 22. The slurry coating device 20 includes a slurry storage unit 23, a first die coater 24, and a second die coater 25. A current collector roll 26, on which a current collector 3a (e.g., a negative electrode current collector 3a) to be processed is wound into a roll, is disposed upstream of the transport path F1. A take-up roller 27 is disposed downstream of the transport path F1. The current collector 3a sent from the current collector roll 26 moves along the transport path F1 and is taken up by the take-up roller 27.

The first die coater 24 is located above the current collector 3a moving along the transport path F1. The second die coater 25 is located below the current collector 3a moving along the transport path F1. The second die coater 25 is located downstream of the first die coater 24. The slurry storage unit 23 supplies slurry to the first die coater 24 via a slurry supply flow path 23a. The slurry storage unit 23 also supplies slurry to the second die coater 25 via another slurry supply flow path (not shown). The slurry storage unit 23 includes, for example, a slurry storage container and a liquid feed pump (not shown).

The drying furnace 21 is located downstream of the slurry applicator 20 on the transport path F1. The drying furnace 21 has an inlet (not shown) through which the current collector 3a (hereinafter referred to as the structure) coated with the slurry is inserted into the drying furnace 21, and an outlet (not shown) through which the structure is discharged after moving within the drying furnace 21 along the transport path F1.

The curvature correction unit 22 is located downstream of the first die coater 24 and the second die coater 25, at one or more locations within the drying oven 21, or between the drying oven 21 and the take-up roller 27. By locating the curvature correction unit 22 downstream of the first die coater 24 and the second die coater 25, the surface coated by the first die coater 24 and the second die coater 25 is less susceptible to the influence of the curvature correction unit 22, thereby maintaining the flatness of the coated surface. As shown in Figures 6 and 7, the curvature correction unit 22 can be composed of a pair of rollers. The curvature correction unit 22 is composed of a guide roller 28 located above the structure moving along the transport path F1, and a conveying roller 29 located below the structure moving along the transport path F1. The guide roller 28 and the conveying roller 29 are each made of a metal such as iron or stainless steel.

Next, we will explain the details of each of the slurry coating S1 and first drying S2 processes.

First, a slurry containing at least one of a niobium-containing oxide and a titanium-containing oxide, and water is supplied to the slurry storage unit 23. The slurry is prepared, for example, by dispersing at least one of a niobium-containing oxide and a titanium-containing oxide, a conductive agent, and a binder in a solvent containing water. The active material, conductive agent, binder, and solvent are described below. The slurry supplied to the slurry storage unit 23 is supplied to the first die coater 24 and the second die coater 25 via the slurry supply flow path. The current collector 3a sent out from the current collector roll 26 moves along the conveying path F1, and in the first die coater 24, the slurry is coated (applied) on one side of the current collector 3a, except for both end portions perpendicular to the conveying direction (longitudinal direction). The current collector (structure) with the slurry coated on one side moves along the transport path F1, is introduced into the drying furnace 21 from its entrance, undergoes first drying S2 in the drying furnace 21, and is then discharged from the exit of the drying furnace 21 and taken up by the take-up roller 27. This winds up the structure into a roll.

Then, the other uncoated side of the current collector 3a is sent from the rolled structure to the second die coater 25. The other uncoated side of the current collector 3a is coated with slurry, except for both ends perpendicular to the conveying direction (longitudinal direction). This completes the slurry coating S1. The current collector (structure) with the slurry coated on the other side moves along the conveying path F1 and is introduced into the drying furnace 21 from its entrance. After undergoing the first drying S2 in the drying furnace 21, it is discharged from the exit of the drying furnace 21 and taken up by the take-up roller 27. This completes the first drying S2.

In the structure 10 shown in Figures 3 to 5, the region where the slurry is applied to form an active material-containing layer is indicated by 3b, and the region where the slurry is not applied and no active material-containing layer exists is indicated by 3a. The region 3b of the structure where the slurry is applied shrinks in the short side direction due to drying in the drying furnace 21. On the other hand, both end portions 3a perpendicular to the transport direction (longitudinal direction) of the structure do not have slurry applied, and therefore hardly shrink due to drying. The stress difference caused by this phenomenon causes the end portions where the active material-containing layer is not formed to tend to bend. The direction of the force tending to bend is indicated by the symbol 30 in Figure 2.

After the slurry is applied, the active material-containing layer-free portions located at both ends of the short side of the structure are sandwiched between guide roller 28 and conveying roller 29 and moved along conveying path F1 to take-up roller 27, as shown in Figures 6 and 7. This allows the structure to be stretched in the direction (short direction) perpendicular to the conveying direction (longitudinal direction) while moving along conveying path F1, thereby suppressing curvature due to drying of the slurry. Note that Figure 7 shows an example in which active material-containing layers 3b are formed on both sides of current collector 3a. However, it is also possible to perform curvature correction using guide roller 28 and conveying roller 29 when forming active material-containing layer 3b on one side of current collector 3a, and then perform curvature correction using guide roller 28 and conveying roller 29 when forming active material-containing layer 3b on the other side of current collector 3a. Figure 8 shows an example of a roll 31 of the structure wound by take-up roller 27. The winding core located at the winding center of roll 31 of the structure is omitted in Figure 8.

The first drying step may be performed so that the moisture content of the active material-containing layer measured by the Karl Fischer method is greater than the moisture content of the active material-containing layer measured by the Karl Fischer method after the second drying step S5. The first drying step may be performed, for example, so that the active material-containing layer has a moisture content of 1,000 to 10,000 ppm by mass measured by the Karl Fischer method. This prevents breakage and chipping of the structure during pressing and cutting, at least during pressing and cutting. The method for measuring the moisture content by the Karl Fischer method is described below. Two samples (including the current collector) measuring 3 mm x 2 cm are cut from the short side at the beginning and the short side at the end of the roll 31 of the structure. The two prepared samples are prevented from drying out before measuring the moisture content. Specifically, for example, after preparing the samples, they are placed in a sealed container and taken to the measuring instrument. Alternatively, the samples are prepared at the measuring instrument's location and immediately measured on the spot.

For each of the two samples prepared as described above, the moisture content is measured by coulometric titration using a Karl Fischer moisture meter (VA-06, manufactured by Mitsubishi Chemical Analytech Co., Ltd.). Specifically, the sample is heated to 140°C and nitrogen gas is introduced at a flow rate of 200 ml/min. The moisture content is calculated from the amount of electricity consumed in the reaction between water and iodine. The average of the two moisture contents obtained is taken as the moisture content of the slurry as determined by the Karl Fischer method.

The short side of the structure where winding begins may be, for example, the short side where the structure emerges from the exit after passing through a drying oven. On the other hand, the short side of the structure where winding ends may be, for example, the position where the head is released after coating is completed.

By setting the moisture content of the active material-containing layer to 1,000 ppm by mass or more as measured by the Karl Fischer method, it is possible to prevent the structure from breaking or chipping during pressing after drying. By setting the moisture content to 10,000 ppm by mass or less, it is possible to avoid defects during pressing, such as the slurry adhering to the press roller. A more preferable range for the moisture content is 1,500 ppm by mass or more and 5,000 ppm by mass or less.

The drying temperature for the slurry can be in the range of 25°C or higher and 100°C or lower, and more preferably 25°C or higher and lower than 80°C. By setting the drying temperature in the range of 25°C or higher and 100°C or lower, it is possible to remove moisture from the materials that make up the active material-containing layer while leaving a predetermined amount of moisture remaining. When the drying temperature is in the range of 25°C or higher and lower than 80°C, the drying time can be in the range of 10 seconds or higher and 600 seconds or lower, for example. More preferably, it is in the range of 60 seconds or higher and 240 seconds or lower. Here, the drying temperature is, for example, the temperature inside the drying furnace 21.

The moisture content of the active material-containing layer as determined by the Karl Fischer method can be adjusted, for example, by the drying temperature, drying time, and composition of the active material-containing layer.

The structure 10 that has undergone the first drying step S2 is wound up by the winding roller 27. Moisture-containing structures may come into contact with each other and transfer unevenness to each other. By adjusting the winding tension according to the moisture content of the active material-containing layer of the structure 10, it is possible to avoid the phenomenon of transfer, in which the active material-containing layer is compressed and unevenness occurs on the surface. The winding tension can be set, for example, in the range of 5 N to 30 N.

The coating S1 and first drying S2 may be performed on one side of the current collector at a time, or on both sides of the current collector simultaneously. For example, after applying the slurry to one side of the current collector, the drying conditions for the slurry are adjusted to form an active material-containing layer with a moisture content of 1,000 ppm by mass or more and 10,000 ppm by mass or less, as measured by the Karl Fischer method. Next, the slurry may be applied to the other side of the current collector, and the slurry may be dried using a similar drying method, thereby obtaining a current collector (structure) with an active material-containing layer with a moisture content of 1,000 ppm by mass or more and 10,000 ppm by mass or less, as measured by the Karl Fischer method. Furthermore, applying and drying the slurry to the other side of the current collector may be omitted.

Next, we will explain press S3. An example of the device used in press S3 is shown in Figures 9 and 10.

The example manufacturing apparatus 32 in FIG. 9 includes a rolling section and a winding section 40. In the manufacturing apparatus 32, the structure 10, after the active material-containing layer 3b has been dried, is transported into the rolling section. The structure 10 then passes through guide rollers 35-39 in this order from the rolling section and is transported to the winding section 40. The winding section 40 winds up the transported structure 10. In the example in FIG. 9, the winding section 40 includes a winding reel, and the structure 10 is wound into a roll on the winding reel. In addition, in the example in FIG. 9, between the rolling section and the winding section 40, the structure 10 is guided from the upstream side to the downstream side by five guide rollers 35, 36, 37, 38, and 39. Each of the guide rollers 35-39 is formed of a metal such as iron or stainless steel.

The rolling unit rolls the active material-containing layer 3b of the transported structure 10 using a roll press or the like. As shown in FIG. 10 , the rolling unit includes a pair of press rollers 33, 34, each made of a metal such as iron or stainless steel. The press roller 33 presses the active material-containing layer 3b from one side of the thickness of the structure 10, while the press roller 34 presses the active material-containing layer 3b from the opposite side of the thickness of the structure 10. As a result, the active material-containing layer 3b is sandwiched between the press rollers 33, 34 in the thickness direction of the structure 10, and pressure (pressing pressure) is applied to the active material-containing layer 3b in the thickness direction of the structure 10. When the active material-containing layer 3b is coated on both sides of the current collector 3a, the active material-containing layer 3b is pressed with the press rollers 33, 34 each in contact with the active material-containing layer 3b. Furthermore, when the active material-containing layer 3b is coated on only one side of the current collector 3a, the active material-containing layer 3b is pressed with one of the press rollers 33, 34 in contact with the active material-containing layer 3b and the other press roller 33, 34 in contact with the coated area of the current collector 3a. The pressure from the press rollers 33, 34 compresses the active material-containing layer 3b in the thickness direction of the structure 10 and stretches it in the longitudinal direction of the structure 10.

After rolling, the structure is wound up in the winding section 40. At this time, winding tension is applied to the structure 10. Because the surface of the structure after rolling is smooth, even if the winding tension is increased, a flat electrode can be formed without transferring unevenness between the two surfaces. Furthermore, if the moisture content of the structure is low, it is desirable to reduce the tensile stress to avoid breakage. The winding tension can be adjusted in the range of 10 N or more and 100 N or less. To suppress wrinkles during pressing, it is preferable to apply a winding tension of 30 N or more.

Next, we will explain cutting S4.

The structure wound into a roll in the previous process is sent out and cut into a predetermined shape by punching using a punching die, as shown in Figure 11. In Figure 11, the cut edges are indicated by dotted lines. This results in an electrode 3 having the structure shown in Figure 12, for example. As shown in Figure 12, the electrode 3 comprises a rectangular current collector 3a, active material-containing layers 3b provided on both main surfaces of the current collector 3a, and a current collector tab 3c protruding in a strip shape from one end of the current collector 3a. The current collector tab 3c is formed by punching out a predetermined shape from a portion of the current collector 3a where the active material-containing layer is not formed.

An example of cutting using a punching die is cutting (punching) using a Thomson blade.

Figure 13 shows an example of an electrode for a comparative example in which wrinkles 41 occurred in the current collecting tab 3c near the active material-containing layer 3b during pressing. According to the method of the embodiment, the electrode is less likely to break even when a large tension is applied during pressing, so wrinkles can be avoided in the tab portion.

Note that cutting S4 is performed to obtain the desired shape, so it can be omitted if the desired shape can be obtained through steps up to S3.

Next, we will explain the second drying step S5.

The second drying step S5 involves stacking multiple structures (or electrodes) after pressing S3 or cutting S4 in the thickness direction, and drying the resulting laminate while applying pressure to both sides of the laminate that intersect with the stacking direction, thereby reducing the moisture content of the active material-containing layer to 600 ppm by mass or less as measured by the Karl Fischer method. The second drying step is described with reference to Figures 14 and 15.

Figures 14 and 15 show a jig used for the second drying. The housing 50 shown in Figures 14 and 15 includes a container 51, a cover plate 52, a bottom plate 53, and a spring member 54. In Figures 14 and 15, the long side direction of the container 51 is indicated as the y-axis direction, the short side direction of the container 51 is indicated as the x-axis direction, and the depth direction of the container 51 is indicated as the z-axis direction. The container 51 has a bottomed rectangular cylindrical shape. The bottom plate 53 has the same or approximately the same planar dimensions as a plane along the x- and y-axes enclosed by the inner wall of the container 51. The bottom plate 53 is positioned at a predetermined height in the z-axis direction from the inner bottom surface of the container 51. The spring member 54 is, for example, a coil spring. The spring member 54 is positioned between the inner bottom surface of the container 51 and the bottom plate 53. When the spring member 54 contracts, the position of the bottom plate 53 within the container 51 moves downward along the z-axis direction. Furthermore, when the spring member 54 expands, the position within the container 51 moves upward along the z-axis direction. Multiple objects (e.g., electrodes 3) are prepared for the second drying step S5. The use of multiple electrodes 3 increases production efficiency. The multiple electrodes 3 are stacked on the bottom plate 53 within the container 51 so that the thickness direction of the electrodes 3 is parallel to the depth direction (z-axis direction) of the container 51. The cover plate 52 is placed at the opening of the container 51. The upper end of the long side (y-axis direction) of the opening of the container 51 is bent inward to fix the cover plate 52 to the opening of the container 51. The stack of electrodes 3 is sandwiched between the cover plate 52 and the bottom plate 53. Furthermore, the stack of electrodes 3 receives an upward force along the z-axis direction due to the elastic force of the spring member 54 via the bottom plate 53. Therefore, the stack of electrodes 3 is sandwiched between the cover plate 52 and the bottom plate 53, with both sides pressurized. This prevents the electrode 3 from warping, curving, or other deformation during the second drying step. The container 51, cover plate 52, and bottom plate 53 can be made of a metal such as Al or an Al alloy.

The housing 50 containing the electrode 3 stack described above is placed in a drying oven and subjected to second drying S5. Second drying S5 is performed so that the moisture content of the electrode 3, as measured by the Karl Fischer method, is 600 ppm by mass or less. By reducing the moisture content to 600 ppm by mass or less, the hardness of the electrode 3 can be increased. This prevents manufacturing defects, such as electrode drop, electrode deformation, or inability to transport the electrode to the designated position, when transporting the electrode to a subsequent process. Furthermore, when an electrode group is produced by using the electrode 3 as the first electrode and placing a separator between the first and second electrodes, these electrodes must be held in the designated position by a transport device such as a vacuum. However, because the electrode does not fall from the transport device, misalignment of the electrode can be avoided and chipping, cracking, and other problems can be prevented. As a result, insulation defects in the electrode group can be suppressed.

This reduces defects during transportation and insulation failure in the electrode group, thereby improving production yield. Furthermore, keeping the moisture content at 600 ppm by mass or less is useful for improving the performance of batteries equipped with non-aqueous electrolytes. The lower limit of the moisture content can be set at 50 ppm by mass. By keeping the moisture content at 50 ppm by mass or more, moisture can be left in the pores of the electrode, thereby preventing thermal degradation of electrode components (e.g., binders) and preventing the electrode from becoming unnecessarily hard and brittle.

The drying temperature in the second drying step can be in the range of 80°C to 160°C, and more preferably 100°C to 140°C. This allows the electrode to be dried to an appropriate hardness, thereby suppressing bending deformation when the electrode area is increased. The drying time can be, for example, in the range of 1 hour to 48 hours, and more preferably 6 hours to 24 hours. Here, the drying temperature is, for example, the temperature inside the drying oven.

The moisture content of the active material-containing layer as determined by the Karl Fischer method can be adjusted, for example, by the drying temperature, drying time, and composition of the active material-containing layer.

The second drying can be, for example, vacuum drying or reduced pressure drying.

The method for measuring the moisture content of electrode 3 using the Karl Fischer method is described below. After the second drying S5, the moisture content of each of the three electrodes 3 in the electrode 3 stack in container 51, including the electrode 3 located on each of the outermost layers and the electrode 3 located in the center of the stack, is measured using the Karl Fischer method in the same manner as described for the first drying S2. The average of the three measured values obtained is used as the desired value.

Electrodes can be manufactured using a method including the steps described above.

Details of the electrodes manufactured using the method of this embodiment are provided below.

The electrode may include a current collector and an active material-containing layer. The active material-containing layer may be laminated or formed on one or both sides of the current collector. The active material-containing layer may include an active material and, optionally, a conductive agent and a binder.

The electrode can be used as a positive or negative electrode.

The active material includes at least one of a niobium-containing oxide and a titanium-containing oxide. Examples of niobium-containing oxides include monoclinic niobium-containing oxides and niobium-titanium-containing oxides. Examples of monoclinic niobium-containing oxides include _monoclinic niobium-titanium _- containing oxides such as _Nb2TiO7 , _Nb2Ti2O9 , _Nb10Ti2O29 , _Nb14TiO37 , _{and Nb24TiO62 .} The niobium _- titanium-containing oxide may be _a substituted niobium-titanium composite oxide in which at least a portion of the _Nb and/or Ti is substituted with a different element. Examples of the substituting element include Na, K, Ca, Co, Ni, Si, P, V, Cr, Mo, Ta, Zr, Mn, Fe, Mg, B, Pb, and Al. The substituted niobium titanium composite oxide may contain one type of substitution element or two or more types of substitution elements. The active material particles may contain one type of niobium-containing oxide or multiple types of niobium-containing oxides. The niobium-containing oxide preferably contains _Nb2TiO7 with a monoclinic structure. In this case, _an electrode with excellent capacity and rate performance can be obtained.

An example of a monoclinic niobium titanium-containing oxide is a compound represented by Li _x Ti _1-y M1 _y Nb _2-z M2 _z O _7+δ , where M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3.

Another example of the monoclinic structure niobium titanium-containing oxide is a compound represented by Ti1 _{-yM3y +zNb2 -zO7 -δ} , where M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3.

Another example of the monoclinic structure niobium titanium-containing oxide is one represented by Li _a TiM _b Nb _2±β O _7±σ (0≦a≦5, 0≦b≦0.3, 0≦β≦0.3, 0≦σ≦0.3, M is at least one element selected from the group consisting of Fe, V, Mo, and Ta).

The niobium-containing oxide may contain unavoidable impurities. Examples of unavoidable impurities include K, Na, Si, and P.

The niobium-containing oxide may contain lithium ions upon charging. Alternatively, the niobium-containing oxide may be synthesized as a lithium-containing niobium-containing oxide by using a lithium-containing compound such as lithium carbonate as the starting material for the niobium-containing oxide.

Titanium-containing oxides include, for example, titanium dioxide with a monoclinic structure, titanium dioxide with a rutile structure, and titanium dioxide with an anatase structure. The composition of titanium dioxide with each crystal structure before charging can be expressed as _TiO2 , and the composition after charging can be expressed as _LixTiO2 (x is 0≦x≦1). The structure of monoclinic titanium dioxide before charging can be expressed as _{TiO2 (} B).

The titanium-containing oxide may contain unavoidable impurities. Examples of unavoidable impurities include K, Na, Cs, Ba, Ca, Si, and P.

When the niobium-containing oxide and titanium-containing oxide are mixed with a water-containing solvent (described below) and contained in a slurry, they preferably do not contain lithium. This prevents the slurry from becoming alkaline, thereby preventing deterioration of the current collector.

The active material may be one or more types. The active material may also contain a second active material other than the niobium-containing oxide and the titanium-containing oxide. Examples of the second active material include lithium titanate having a ramsdellite structure (e.g., Li _2+y Ti ₃ O ₇ , 0≦y≦3), lithium titanate having a spinel structure (e.g., Li _4+x Ti ₅ O ₁₂ , 0≦x≦3), hollandite-type titanium composite oxide, and orthorhombic titanium composite oxide.

The active material may be in the form of particles. The active material particles may be, for example, primary particles alone, secondary particles formed by aggregation of primary particles, or a mixture of primary and secondary particles.

Conductive agents are added to improve current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon nanotubes, carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as the conductive agent, or two or more may be used in combination. Alternatively, instead of using a conductive agent, the surface of the active material particles may be coated with carbon or an electronically conductive inorganic material.

The binder fills the gaps between the active material and can bind the active material and the current collector. The binder has affinity for water-containing solvents and can be dispersed or dissolved in water-containing solvents. Examples of binders include carboxymethyl cellulose (CMC) and CMC salts. Examples of CMC salts include sodium CMC salt and potassium CMC salt. One of these may be used as the binder, or two or more may be used in combination as the binder. Binders containing CMC and/or CMC salts can coat the surfaces of niobium-containing oxide particles, thereby suppressing reaction between the niobium-containing oxide particles and the electrolyte.

Styrene-butadiene rubber may be added to the binder containing CMC and/or a salt of CMC. This can improve the bonding strength between the active material-containing layer and the current collector.

The water-containing solvent may be water alone or a polar solvent containing water.

The active material-containing layer may contain a solid electrolyte. The lithium ion conductivity of the solid electrolyte may be, for example, 1 x ^10-6 Scm ^-1 or more at 25°C. Examples of lithium ion conductive solid electrolytes include lithium ion conductive oxide-based solid electrolytes and lithium ion conductive sulfide-based solid electrolytes. Examples of lithium _ion conductive oxide-based solid electrolytes include a lithium phosphate solid electrolyte with a NASICON structure _{, amorphous} LIPON ( _{Li2.9PO3.3N0.46} ), or LLZ _{( Li7La3Zr2O12} ) with a _garnet structure.

As an example, the active material, conductive agent, and binder in the active material-containing layer are preferably blended in proportions of 68% by mass or more and 96% by mass or less, 2% by mass or more and 30% by mass or less, and 2% by mass or more and 30% by mass or less, respectively. By using 2% or more of conductive agent, the current collection performance of the active material-containing layer can be improved. Furthermore, by using 2% or more of binder, sufficient adhesion between the active material-containing layer and the current collector can be achieved, and excellent cycle performance can be expected. On the other hand, it is preferable to use 30% or less of conductive agent and binder, respectively, in order to achieve high capacity.

The current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted into and extracted from the active material. Examples of current collectors include copper, nickel, stainless steel, aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm or more and 20 μm or less. A current collector with this thickness can balance the strength and weight of the electrode.

The current collector may also include a portion on its surface where the active material-containing layer is not formed. This portion can function as a current collecting tab.

According to the method of the first embodiment described above, the second drying step includes stacking a plurality of structures along their thickness direction, and drying the resulting laminate while applying pressure to both surfaces of the laminate intersecting the stacking direction, thereby reducing the moisture content of the active material-containing layer to 600 ppm by mass or less as measured by the Karl Fischer method. As a result, it is possible to reduce the occurrence of defects during transportation and insulation defects in the electrode group, thereby improving the production yield.
Second Embodiment
The second embodiment relates to a method for manufacturing a battery.

The second embodiment includes a step of preparing an electrode group by using the electrode obtained by the method of the first embodiment as a first electrode and disposing a separator between the first electrode and a second electrode;
a step of housing the electrode group in an exterior member;
and retaining a non-aqueous electrolyte in the electrode group housed in the exterior member.

The method of the second embodiment includes steps S6 to S9 shown in Figure 1.

We will now explain electrode group preparation S6.

The electrode group is produced, for example, by placing a separator between a first electrode and a second electrode. The shape of the electrode group is not particularly limited, and examples include a stack of a first electrode, a separator, and a second electrode; a first electrode, a separator, and a second electrode wound into a flat or cylindrical shape; and a first electrode, a separator, and a second electrode folded in a zigzag pattern.

Explain the second electrode and separator.

The second electrode may include a second current collector and a second active material-containing layer. The second active material-containing layer may be formed on one or both sides of the second current collector. The second active material-containing layer may include a second active material and, optionally, a conductive agent and a binder. The second electrode may be either a positive electrode or a negative electrode, but if the first electrode is a negative electrode, it may be a positive electrode.

The second active material may be, for example, an oxide or sulfide. The second electrode may contain one type of compound alone as the active material, or a combination of two or more types of compounds. Examples of oxides and sulfides include compounds that can insert and extract Li or Li ions.

Examples of such compounds include manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxides (e.g., Li _x Mn ₂ O ₄ or Li _x MnO ₂ ; 0<x≦1), lithium nickel composite oxides (e.g., Li _x NiO ₂ ; 0<x≦1), lithium cobalt composite oxides (e.g., Li _x CoO ₂ ; 0<x≦1), lithium nickel cobalt composite oxides (e.g., Li _x Ni _1-y Co _y O ₂ ; 0<x≦1, 0<y<1), lithium manganese cobalt composite oxides (e.g., Li _x Mn _y Co _1-y O ₂ ; 0<x≦1, 0<y<1), and lithium manganese nickel composite oxides having a spinel structure (e.g., Li _x Mn _2-y Ni _y O _{4 ;} 0<x≦1, 0<y<2), lithium phosphate oxides having an olivine _structure (e.g., _LixFePO4 ; 0<x≦1, _{LixFe1 - yMnyPO4} ; 0<x≦1, 0<y≦ ₁ , _LixCoPO4 ; 0<x≦1), iron sulfate ( _Fe2 ( _SO4 ) ₃ ), vanadium oxides (e.g. _{, V2O5} ), _LiNixCoyMzO2 (x+ _y + _z = ₁ , x≧0.8, M consists of Mn and Al), and lithium nickel cobalt _manganese composite oxides ( _{LixNi1 -yzCoyMnzO2 ;} 0<x≦1 _, 0<y<1, 0<z<1, y+z<1).

The primary particle size of the second active material is preferably 100 nm or more and 1 μm or less. A second active material with a primary particle size of 100 nm or more is easy to handle in industrial production. A second active material with a primary particle size of 1 μm or less allows lithium ions to diffuse smoothly within the solid.

The specific surface area of the second active material is preferably 0.1 ^m /g or more and 10 ^m /g or less. A second active material having a specific surface area of ^{0.1 m} /g or more can ensure sufficient sites for absorbing and releasing Li ions. A second active material having a specific surface area of ^{10 m} /g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

The binder is added to fill the gaps between the dispersed second active material particles and to bind the second active material to the second current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as the binder, or two or more may be used in combination.

The conductive agent is blended to improve current collection performance and reduce contact resistance between the second active material and the second current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as the conductive agent, or two or more may be used in combination. The conductive agent may also be omitted.

In the second active material-containing layer, the second active material and binder are preferably blended in proportions of 80% by mass or more and 98% by mass or less, and 2% by mass or more and 20% by mass or less, respectively.

By using a binder amount of 2% by mass or more, sufficient electrode strength can be achieved. The binder can also function as an insulator. Therefore, by using a binder amount of 20% by mass or less, the amount of insulator contained in the electrode is reduced, thereby reducing internal resistance.

When a conductive agent is added, the second active material, binder, and conductive agent are preferably blended in proportions of 77% by mass or more and 95% by mass or less, 2% by mass or more and 20% by mass or less, and 3% by mass or more and 15% by mass or less, respectively.

By setting the amount of conductive agent to 3% by mass or more, the above-mentioned effects can be achieved. Furthermore, by setting the amount of conductive agent to 15% by mass or less, the proportion of conductive agent that comes into contact with the electrolyte can be reduced. This low proportion can reduce electrolyte decomposition during high-temperature storage.

The second current collector is preferably aluminum foil or aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, and more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

The second current collector may also include a portion on its surface where the second active material-containing layer is not formed. This portion can function as a second current collecting tab.

The second electrode is prepared, for example, by suspending the second active material, conductive agent, and binder in a solvent to prepare a slurry. This slurry is then applied to one or both sides of a current collector. The applied slurry is then dried to obtain a laminate of an active material-containing layer and a current collector. This laminate is then pressed. In this manner, the second electrode is produced. Alternatively, the second electrode may be produced by the following method. First, the active material, conductive agent, and binder are mixed to obtain a mixture. Next, this mixture is formed into pellets. Next, these pellets are placed on a current collector to obtain the second electrode.

The separator is formed, for example, from a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. From a safety standpoint, it is preferable to use a porous film formed from polyethylene or polypropylene. This is because these porous films melt at a certain temperature and are able to interrupt electrical current.

An electrolyte layer containing a solid electrolyte may be used as the separator. The lithium ion conductivity of the solid electrolyte may be, for example, 1 x ^10-6 Scm ^-1 or more at 25°C. Examples of lithium ion conductive solid electrolytes include lithium ion conductive oxide-based solid electrolytes and lithium ion conductive sulfide-based solid electrolytes. Examples of lithium ion conductive oxide-based solid electrolytes include a lithium phosphate solid electrolyte with a NASICON structure _{, amorphous LIPON} ( _{Li2.9PO3.3N0.46} ), or LLZ _{( Li7La3Zr2O12} ) with a _garnet structure.

Next, we will explain step S7, which involves storing the electrode group in the exterior member.

The electrode group is housed in an outer casing. The outer casing is not sealed and is left open. Before housing, current collecting leads may be electrically connected to each of the first and second electrodes of the electrode group.

The exterior member can be, for example, a container made of laminated film or a metal container.

The thickness of the laminate film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

The laminate film used is a multilayer film containing multiple resin layers and metal layers sandwiched between these resin layers. The resin layers contain polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layers are preferably made of aluminum foil or aluminum alloy foil to reduce weight. The laminate film can be molded into the shape of the exterior component by sealing it with heat.

The wall thickness of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

The metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. If the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content thereof is preferably 100 ppm by mass or less.

The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior member can be selected appropriately depending on the battery dimensions and intended use.

The current collecting lead can be formed, for example, from a conductive material. Examples of conductive materials include the same type of material as the current collector of the electrode or the current collector of the second electrode.

The electrode group housed in the exterior member may be dried at a temperature of 80°C or higher and 150°C or lower. The drying process is carried out while the exterior member is still unsealed.

By setting the drying temperature in the range of 80° C. to 150° C., it is possible to remove moisture contained in the electrode assembly without thermally deteriorating the materials contained in the electrode assembly. When the drying temperature is 80° C. to 150° C., the drying time can be, for example, 1 hour to 72 hours.
If the electrode group has reached an appropriate moisture content through the second drying step S5, the drying step in which the electrode group is housed in the exterior member may be omitted, thereby enabling shortening of the tact time.

Next, we will explain step S8, which involves storing the electrolyte in the exterior member.

The electrolyte is retained in the electrode group while the exterior member is left open. The retention process is carried out, for example, in a dehumidified atmosphere or dry air.

Examples of the electrolyte include non-aqueous electrolytes and aqueous electrolytes. Examples of non-aqueous electrolytes that can be used include liquid non-aqueous electrolytes and gel-type non-aqueous electrolytes. Liquid non-aqueous electrolytes are prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol/L or more and 2.5 mol/L or less.

Examples of electrolyte salts include lithium salts such as lithium perchlorate ( _LiClO4 ), lithium hexafluorophosphate ( _LiPF6 ), lithium tetrafluoroborate ( _LiBF4 ), lithium hexafluoride ( _LiAsF6 ), lithium trifluoromethanesulfonate ( _LiCF3SO3 ), and lithium bistrifluoromethylsulfonylimide (LiN( _CF3SO2 ) _{2 )} , and mixtures thereof. The electrolyte salt is preferably one that is difficult to oxidize even at high potentials, and _{LiPF6 is} most preferred.

Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or as a mixed solvent.

Gel-type non-aqueous electrolytes are prepared by combining a liquid non-aqueous electrolyte with a polymer material. Examples of polymer materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

Alternatively, in addition to liquid nonaqueous electrolytes and gel nonaqueous electrolytes, room-temperature molten salts containing lithium ions (ionic melts), polymer solid electrolytes, inorganic solid electrolytes, etc. may also be used as nonaqueous electrolytes.

A room-temperature molten salt (ionic melt) refers to an organic salt composed of a combination of organic cations and anions that can exist as a liquid at room temperature (15°C or higher and 25°C or lower). Room-temperature molten salts include room-temperature molten salts that exist as a liquid on their own, room-temperature molten salts that become liquid when mixed with an electrolyte salt, room-temperature molten salts that become liquid when dissolved in an organic solvent, and mixtures of these. Generally, the melting point of room-temperature molten salts used in secondary batteries is 25°C or lower. Furthermore, organic cations generally have a quaternary ammonium skeleton.

Polymer solid electrolytes are prepared by dissolving an electrolyte salt in a polymer material and solidifying it.

The inorganic solid electrolyte is a solid material having Li ion conductivity. The lithium ion conductivity of the solid electrolyte may be, for example, 1×10 ⁻⁶ Scm ⁻¹ or more at 25° C. Examples of lithium ion conductive solid electrolytes are as described above.

Next, sealing S9 will be explained.

A battery is obtained by sealing the exterior material. The sealing method varies depending on the type of exterior material. For example, heat sealing can be used for containers made of laminated film. Laser welding can be used for containers made of metal.

Examples of batteries that can be manufactured using the method of the embodiment are shown in Figures 16 to 20.

Figures 16 and 17 show examples of batteries equipped with stacked electrode groups.

The secondary battery 100 shown in Figures 16 and 17 includes an electrode group 1 shown in Figures 16 and 17, an exterior member 2 shown in Figure 16, and a non-aqueous electrolyte (not shown). The electrode group 1 and non-aqueous electrolyte are housed within the exterior member 2. The non-aqueous electrolyte is held in the electrode group 1.

The exterior member 2 consists of a laminate film containing two resin layers and a metal layer sandwiched between them.

As shown in Figure 17, the electrode group 1 is a laminated electrode group. The laminated electrode group 1 has a structure in which negative electrodes 3 and positive electrodes 5 are alternately stacked with separators 4 interposed between them.

The electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b supported on both sides of the negative electrode current collector 3a. The electrode group 1 also includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 includes a positive electrode current collector 5a and a positive electrode active material-containing layer 5b supported on both sides of the positive electrode current collector 5a.

The negative electrode current collector 3a of each negative electrode 3 includes a portion 3c on one side where no negative electrode active material-containing layer 3b is supported on any surface. This portion 3c serves as a negative electrode current collector tab. The portion 3c serving as the negative electrode current collector tab does not overlap with the positive electrode 5. Furthermore, the multiple negative electrode current collector tabs (portions 3c) are electrically connected to a strip-shaped negative electrode terminal 6. The tip of the strip-shaped negative electrode terminal 6 extends outside the exterior member 2.

Although not shown, the positive electrode current collector 5a of each positive electrode 5 includes a portion on one side where the positive electrode active material-containing layer 5b is not supported on any surface. This portion functions as a positive electrode current collector tab. Like the negative electrode current collector tab (portion 3c), the positive electrode current collector tab does not overlap with the negative electrode 3. The positive electrode current collector tab is located on the opposite side of the electrode group 1 from the negative electrode current collector tab (portion 3c). The positive electrode current collector tab is electrically connected to a strip-shaped positive electrode terminal 7. The tip of the strip-shaped positive electrode terminal 7 is located opposite the negative electrode terminal 6 and is extended to the outside of the exterior member 2.

The stacked electrode group is not limited to the structure shown in Figure 17. Another example of a stacked electrode group 1 is shown in Figure 18. A positive electrode 5, a negative electrode 3, a positive electrode 5, and a negative electrode 3 are arranged in this order, sandwiched between separators 4 folded diagonally. A positive electrode current collecting tab 5c protrudes from one long side of the separator 4 folded diagonally. A negative electrode current collecting tab (not shown) protrudes from the other long side of the separator 4 folded diagonally. The order of the positive electrode 5 and negative electrode 3 is not limited to that shown in Figure 18, and the order may be negative electrode 3, positive electrode 5.

Figures 19 and 20 show examples of batteries equipped with wound electrode groups.

The secondary battery 100 shown in Figures 19 and 20 includes a bag-shaped exterior member 2 shown in Figures 19 and 20, an electrode group 1 shown in Figure 19, and an electrolyte (not shown). The electrode group 1 and non-aqueous electrolyte are housed within the bag-shaped exterior member 2. The non-aqueous electrolyte (not shown) is held in the electrode group 1.

The bag-shaped exterior member 2 is made of a laminate film containing two resin layers and a metal layer sandwiched between them.

As shown in Figure 19, the electrode group 1 is a flat, wound electrode group. As shown in Figure 20, the flat, wound electrode group 1 includes a negative electrode 3, a separator 4, and a positive electrode 5. The separator 4 is interposed between the negative electrode 3 and the positive electrode 5.

The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b. In the portion of the negative electrode 3 located at the outermost shell of the wound electrode group 1, the negative electrode active material-containing layer 3b is formed only on the inner surface of the negative electrode current collector 3a, as shown in Figure 20. In other portions of the negative electrode 3, the negative electrode active material-containing layer 3b is formed on both sides of the negative electrode current collector 3a.

The positive electrode 5 includes a positive electrode current collector 5a and a positive electrode active material-containing layer 5b formed on both sides of the positive electrode current collector 5a.

As shown in Figure 19, the negative electrode terminal 6 and positive electrode terminal 7 are located near the outer peripheral edge of the wound electrode group 1. The negative electrode terminal 6 is connected to the outermost portion of the negative electrode current collector 3a. The positive electrode terminal 7 is connected to the outermost portion of the positive electrode current collector 5a. The negative electrode terminal 6 and positive electrode terminal 7 extend outward from the opening of the bag-shaped exterior member 2. A thermoplastic resin layer is provided on the inner surface of the bag-shaped exterior member 2, and the opening is closed by heat sealing this.

The battery manufactured by the method of the second embodiment may be used as a battery assembly or incorporated into a battery pack. The battery according to this embodiment is suitable for use in applications requiring excellent cycle performance when drawing large current. Specifically, it is used as a power source for digital cameras, or as a vehicle battery for, for example, two- to four-wheeled hybrid electric vehicles, two- to four-wheeled electric vehicles, power-assisted bicycles, or railway vehicles (e.g., electric trains), or as a stationary battery. In particular, it is suitable for use as an on-board battery installed in a vehicle.

According to the second embodiment described above, batteries are manufactured using electrodes manufactured using the method of the first embodiment. As a result, defects during electrode manufacturing can be reduced, thereby improving the yield of battery manufacturing.

Examples will be described below.
Example 1
Particles of monoclinic niobium titanium-containing oxide having a composition represented _by the formula _TiNb2O7 were prepared as the active material. Acetylene black was also prepared as a conductive agent, and carboxymethyl cellulose and styrene-butadiene rubber were prepared as binders. These were mixed in pure water so that the mass ratio of active material:acetylene black:carboxymethyl cellulose:styrene-butadiene rubber was 90:5:2.5:2.5 to obtain a slurry. This slurry was applied to one side of a strip-shaped current collector made of 12 μm-thick aluminum foil, excluding both ends in the short side direction, and the coating was dried for 240 seconds in a drying oven set at 60°C. During this primary drying, the active material-containing layer-free portions located at both ends in the short side direction of the current collector were sandwiched between guide roller 28 and conveyor roller 29 shown in FIG. 6 .

In addition, the winding tension of the structure after single-side coating was adjusted to 10 N relative to the aluminum current collector. This prevented the semi-dried structures from transferring to each other. After single-side coating was completed, the slurry was applied to the uncoated side of the strip-shaped current collector in the same manner. Thus, a 400-m-long structure was obtained in which active material-containing layers were formed on both sides of the strip-shaped current collector, excluding both ends in the short side direction. The structure was wound into a roll. The moisture content of the active material-containing layer of the structure was measured by the Karl Fischer method as described above, and the results are shown in Table 1. The resulting structure was then subjected to roll pressing so that the density of the active material-containing layer was 2.65 g/ ^cm3 . During roll pressing, the initial tensile tension was set to 100 N, and pressing was performed at a speed of 1 m per minute. If breakage occurred during pressing, the tensile tension was reduced by 10 N increments, and the tension at which the electrode no longer broke per 100 m of rolling distance was determined. The electrode pressed at that tension was then subjected to the next process. The tension during pressing was 80N.

The resulting electrode was punched out into 50 electrode shapes as shown in Figure 12 using a punching machine with a Thomson blade, producing the electrodes of Example 1. The electrode of Example 1 had a long side length of 150 mm and a short side length of 60 mm of the active material-containing layer. The width of the current collecting tab (width parallel to the short side of the active material-containing layer) was 30 mm. The length of the current collecting tab (width parallel to the long side of the active material-containing layer) was 10 mm. The outer periphery of the electrode of Example 1 was observed with a stereomicroscope, and electrodes with observed cracks in the active material-containing layer, cracks in the current collector, peeling of the active material-containing layer, or deformation or peeling due to wrinkles in the current collecting tab were deemed to have been cut poorly. There were zero cutting defects.

One hundred electrodes prepared using the method of Example 1 were used as negative electrodes. These negative electrodes were inserted into the container 51 of the housing 50 shown in Figures 14 and 15, sandwiched between the cover plate 52 and the bottom plate 53, and vacuum dried at 140°C for 12 hours. After drying, the moisture content of the negative electrodes located on the top and bottom outermost layers of the electrode stack and the three negative electrodes located in the center was measured using the Karl Fischer method described above, and the average value was calculated and shown in Table 1.

Next, lithium cobalt oxide (LiCoO ₂ ) particles were prepared as the positive electrode active material. Acetylene black was also prepared as a conductive agent, and PVdF was prepared as a binder. These were dispersed in N-methyl-2-pyrrolidone (NMP) so that the mass ratio of active material:acetylene black:PVdF was 90:5:5 to obtain a slurry. This slurry was applied to both sides of a current collector made of 12 μm aluminum foil, and the coating was dried at 100°C for 240 seconds. Thus, a laminate was obtained in which an active material-containing layer was formed on both sides of the current collector. The resulting laminate was then subjected to a roll press so that the density of the active material-containing layer was 2.2 g/cm ³ , obtaining a positive electrode roll. Ninety positive electrodes were fabricated by punching out a 58 mm x 148 mm shape from the obtained positive electrode roll.

A laminated electrode assembly was fabricated using the positive and negative electrodes and polyethylene separators fabricated as described above. The positive and negative electrodes were set in an electrode laminate manufacturing device. The positive and negative electrodes were transported by a vacuum chuck of the laminate manufacturing device, and the polyethylene separator was sandwiched between the positive and negative electrodes in a zigzag pattern to obtain a flat laminated electrode assembly. Ten sets of electrode laminates each consisting of nine positive electrodes and ten negative electrodes were thus fabricated. Positive and negative terminals were connected to the electrode assembly. To confirm the insulation properties of the laminated electrode assembly, an insulation resistance test was performed using an insulation resistance tester. A DC voltage of 600 V was applied, and a resistance of 5 MΩ or higher was deemed pass. All ten sets passed. Therefore, no internal short circuits were observed in the fabricated electrode assembly. The number of internal short circuits that occurred is shown in Table 1.
Example 2
The drying temperature of the slurry (temperature of the drying oven in the first drying) and drying time were changed as shown in Table 1 below, and the moisture content of the active material-containing layer measured by the Karl Fischer method was changed as shown in Table 1 below. Except for this, 100 negative electrodes were produced in the same manner as in Example 1. When the number of cutting defects occurred for the obtained negative electrode of Example 2 was measured in the same manner as in Example 1, it was found to be zero.

These negative electrodes were inserted into container 51 of housing 50, sandwiched between cover plate 52 and bottom plate 53, and vacuum dried at 140°C for 48 hours. After drying, the moisture content of the negative electrodes located on the top and bottom outermost layers of the electrode stack and the three negative electrodes located in the center was measured using the Karl Fischer method described above, and the average value was calculated and shown in Table 1.

Next, 90 positive electrodes were produced in the same manner as in Example 1.

A laminated electrode assembly was fabricated using the positive and negative electrodes and polyethylene separators fabricated as described above. The positive and negative electrodes were set in an electrode laminate manufacturing device. The positive and negative electrodes were transported by a vacuum chuck of the laminate manufacturing device, and the polyethylene separator was sandwiched between the positive and negative electrodes in a zigzag pattern to obtain a flat laminated electrode assembly. Ten sets of electrode laminates each consisting of nine positive electrodes and ten negative electrodes were thus fabricated. Positive and negative terminals were connected to the electrode assembly. To confirm the insulation properties of the laminated electrode assembly, an insulation resistance test was performed using an insulation resistance tester. A DC voltage of 600 V was applied, and a resistance of 5 MΩ or higher was deemed pass. All ten sets passed. Therefore, no internal short circuits were observed in the fabricated electrode assembly. The number of internal short circuits that occurred is shown in Table 1.
Example 3
The drying temperature of the slurry (temperature of the drying oven in the first drying) and drying time were changed as shown in Table 1 below, and the moisture content of the active material-containing layer measured by the Karl Fischer method was changed as shown in Table 1 below. Except for this, 100 negative electrodes were produced in the same manner as in Example 1. When the number of cutting defects occurred for the obtained negative electrode of Example 3 was measured in the same manner as in Example 1, it was found to be zero.

These negative electrodes were inserted into container 51 of housing 50, sandwiched between cover plate 52 and bottom plate 53, and vacuum dried at 140°C for 24 hours. After drying, the moisture content of the negative electrodes located on the top and bottom outermost layers of the electrode stack and the three negative electrodes located in the center was measured using the Karl Fischer method described above, and the average value was calculated and shown in Table 1.

Next, 90 positive electrodes were produced in the same manner as in Example 1.

A laminated electrode assembly was fabricated using the positive and negative electrodes and polyethylene separators fabricated as described above. The positive and negative electrodes were set in an electrode laminate manufacturing device. The positive and negative electrodes were transported by a vacuum chuck of the laminate manufacturing device, and the polyethylene separator was sandwiched between the positive and negative electrodes in a zigzag pattern to obtain a flat laminated electrode assembly. Ten sets of electrode laminates each consisting of nine positive electrodes and ten negative electrodes were thus fabricated. Positive and negative terminals were connected to the electrode assembly. To confirm the insulation properties of the laminated electrode assembly, an insulation resistance test was performed using an insulation resistance tester. A DC voltage of 600 V was applied, and a resistance of 5 MΩ or higher was deemed pass. All ten sets passed. Therefore, no internal short circuits were observed in the fabricated electrode assembly. The number of internal short circuits that occurred is shown in Table 1.
<Comparative Example 1>
The drying temperature of the slurry (temperature of the drying oven in the first drying) and drying time were changed as shown in Table 1 below, and the moisture content of the active material-containing layer measured by the Karl Fischer method was changed as shown in Table 1 below. Except for this, 100 negative electrodes were produced in the same manner as in Example 1. When the number of cutting defects occurred for the obtained negative electrode of Comparative Example 1 was measured in the same manner as in Example 1, it was found to be zero.

These negative electrodes were inserted into the container 51 of the housing 50, sandwiched between the cover plate 52 and the bottom plate 53, and vacuum dried at 140°C for 20 hours. After drying, the moisture content of the negative electrodes located on the top and bottom outermost layers of the electrode stack and the three negative electrodes located in the center was measured using the Karl Fischer method described above, and the average value was calculated and shown in Table 1.

Next, 90 positive electrodes were produced in the same manner as in Example 1.

A laminated electrode assembly was produced using the positive and negative electrodes and polyethylene separators prepared as described above. The positive and negative electrodes, along with the separator, were placed in an electrode laminate manufacturing device. The positive and negative electrodes were transported by a vacuum chuck of the laminate manufacturing device, and the polyethylene separator was sandwiched between the positive and negative electrodes in a zigzag pattern to obtain a flat laminated electrode assembly. Ten sets of electrode laminates each consisting of nine positive electrodes and ten negative electrodes were thus produced. Positive and negative terminals were connected to the electrode assembly. An insulation resistance test was performed using an insulation resistance tester to confirm the insulation of the laminated electrode assembly. A DC voltage of 600 V was applied, and a test result of 5 MΩ or higher was deemed pass. Seven of the ten sets passed. The number of internal short circuits is shown in Table 1.
<Comparative Example 2>
A battery of Comparative Example 2 was manufactured without carrying out the first drying and the second drying.

A slurry having the same composition as in Example 1 was applied to both sides of a strip-shaped current collector made of 12 μm-thick aluminum foil, excluding both ends in the short side direction, and the slurry was dried at 100°C. The resulting structure was subjected to a roll press so that the density of the active material-containing layer was 2.65 g/ ^cm3 . After pressing, the active material-containing layer was humidified for 120 hours in an environment with a dew point of 40°C, thereby setting the moisture content of the active material-containing layer to 2000 ppm by mass as determined by the Karl Fischer method. The resulting electrode was punched out into 100 electrodes with the same electrode shape as in Example 1 using a punching tool with a Thomson blade, to prepare a negative electrode of Comparative Example 2.

Next, 90 positive electrodes were produced in the same manner as in Example 1.

A stacked electrode assembly was produced using the positive and negative electrodes and polyethylene separators prepared as described above. The positive and negative electrodes, along with the separator, were placed in an electrode stack manufacturing device. The positive and negative electrodes were transported by the vacuum chuck of the stack manufacturing device, and the positive and negative electrodes were stacked with the polyethylene separator sandwiched between them in a zigzag pattern, resulting in a flat stacked electrode assembly. Ten sets of electrode stacks, each consisting of nine positive electrodes and ten negative electrodes, were thus produced. Positive and negative terminals were connected to these electrode assemblies. To confirm the insulation properties of this stacked electrode assembly, an insulation resistance test was conducted using an insulation resistance meter. A DC voltage of 600 V was applied, and a resistance of 5 MΩ or higher was deemed pass. Eight of the ten sets passed. The number of internal short circuits that occurred is shown in Table 1.

As shown in Table 1, the methods of Examples 1 to 3 produce negative electrodes with appropriate hardness, preventing insulation defects from occurring in the stacked electrode assembly. Furthermore, the methods of Examples 1 to 3 press the active material-containing layer in a hydrated state, making it less likely to break even when a large tension is applied during pressing. The tension press can prevent the electrode from curving after pressing, thereby reducing distortion of the coated and uncoated areas, thereby reducing cutting defects in the electrode. Furthermore, correcting the curvature during drying of the slurry (first drying), as in Examples 1 to 3, can further enhance the effect of preventing cutting defects.

On the other hand, when using the method of Comparative Example 1, the moisture content after the second drying was greater than 600 ppm, causing the negative electrode to sag during stacking and resulting in stack misalignment, resulting in an internal short circuit due to poor insulation.

Furthermore, with the method of Comparative Example 2, the negative electrode was humidified after pressing, which caused the resulting negative electrode to warp during stacking and resulted in stack misalignment, resulting in an internal short circuit due to poor insulation. Furthermore, in Comparative Example 2, the electrode was exposed to a dew-point environment after pressing to soak up water, which made cutting defects less likely, but because time was required for soaking up water and tension could not be applied during pressing, wrinkles occurred in the electrode tab area, and a non-defective product could not be obtained.

Therefore, the method of the embodiment can improve tact time (production efficiency) and yield.

The electrode manufacturing method of at least one of these embodiments or examples includes the steps of: applying a slurry containing at least one of a niobium-containing oxide and a titanium-containing oxide and water to a current collector to obtain a structure; drying the slurry to form an active material-containing layer; pressing the structure; and stacking multiple structures and drying the outermost layers of both of the resulting stacks under pressure, thereby reducing the moisture content of the active material-containing layer to 600 ppm by mass or less as measured by the Karl Fischer method. This reduces the occurrence of defects during transportation and insulation defects in the electrode group, thereby improving manufacturing yield.

While several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in a variety of other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their variations are within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

The invention according to the embodiment will be described below.
<1>
a step of applying a slurry containing water and at least one of a niobium-containing oxide and a titanium-containing oxide to a current collector to obtain a structure;
drying the slurry to form an active material-containing layer;
pressing the structure;
and laminating a plurality of the structures and drying both outermost layers of the resulting laminate under pressure, thereby reducing the water content of the active material-containing layer to 600 ppm by mass or less as determined by the Karl Fischer method.
<2>
The method for manufacturing an electrode according to <1>, wherein the drying of the slurry is carried out so that the water content of the active material-containing layer measured by Karl Fischer method is 1,000 ppm by mass or more and 10,000 ppm by mass or less.
<3>
the coating is performed while the current collector is being moved in a transport direction, excluding at least an end portion of the current collector parallel to the transport direction,
The method for manufacturing an electrode according to <1> or <2>, wherein the drying of the slurry is performed while moving the structure in the transport direction and pulling the end of the structure in a direction intersecting the transport direction.
＜4＞
The method for manufacturing an electrode according to any one of <1> to <3>, further comprising a step of adjusting tension applied to the structure in a transport direction according to the moisture content.
<5>
The method for manufacturing an electrode according to any one of <1> to <4>, further comprising, after the pressing, cutting the structure after the pressing.
<6>
The niobium-containing oxide includes at least one selected from the group consisting of niobium-containing oxides represented by the general formula Li _x Ti _{1 -y} M1 _y Nb _2-z M2 _z O _7+δ and niobium-containing oxides represented by the general formula Li _x Ti 1-y _{M3 y+z} Nb _2-z O _7-δ ,
The method for producing an electrode according to any one of <1> to <5>, wherein M1 is at least one selected from the group consisting of Zr, Si, and Sn, M2 is at least one selected from the group consisting of V, Ta, and Bi, M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo, x satisfies 0≦x≦5, y satisfies 0≦y<1, z satisfies 0≦z<2, and δ satisfies −0.3≦δ≦0.3.
＜７＞
The method for producing an electrode according to any one of <1> to <6>, wherein the titanium-containing oxide includes at least one selected from the group consisting of monoclinic titanium dioxide, anatase titanium dioxide, rutile titanium dioxide, and bronze titanium dioxide.
＜8＞
a step of preparing an electrode group by using the electrode obtained by the method according to any one of <1> to <7> as a first electrode and disposing a separator between the first electrode and a second electrode;
a step of housing the electrode group in an exterior member;
and causing the electrode group housed in the exterior member to retain a non-aqueous electrolyte.

REFERENCE SIGNS LIST 1...electrode group, 2...exterior member, 3...negative electrode, 3a...negative electrode current collector, 3b...negative electrode active material-containing layer, 3c...negative electrode current collector tab, 4...separator, 5...positive electrode, 5a...positive electrode current collector, 5b...positive electrode active material-containing layer, 5c...positive electrode current collector tab, 6...negative electrode terminal, 7...positive electrode terminal, 10...structure, 20...slurry coating device, 21...drying furnace, 22...curvature correction section, 23...slurry storage section, 24...first die coater, 25...second die coater, 26...current collector roll, 27...winding roller, F1...conveyor Feed path, 28...guide roller, 29...conveyor roller, 31...structural roll, 32...manufacturing apparatus, 33, 34...press rollers, 35-39...guide rollers, 40...winding section, 50...casing, 51...container, 52...cover plate, 53...bottom plate, 54...spring member, 100...secondary battery, S1...slurry coating, S2...first drying, S3...pressing, S4...cutting, S5...second drying, S6...electrode group production, S7...electrode group stored in exterior member, S8...electrolyte stored in exterior member, S9...sealing.

Claims (8)

a step of applying a slurry containing water and at least one of a niobium-containing oxide and a titanium-containing oxide to a current collector to obtain a structure;
drying the slurry to form an active material-containing layer;
pressing the structure;
and laminating a plurality of the structures and drying both outermost layers of the resulting laminate under pressure, thereby reducing the water content of the active material-containing layer to 600 ppm by mass or less as determined by the Karl Fischer method. The electrode manufacturing method described in claim 1, wherein the slurry is dried so that the moisture content of the active material-containing layer, as measured by the Karl Fischer method, is 1,000 ppm by mass or more and 10,000 ppm by mass or less. the coating is performed while the current collector is being moved in a transport direction, excluding at least an end portion of the current collector parallel to the transport direction,
The method for manufacturing an electrode according to claim 2 , wherein the drying of the slurry is performed while the structure is being moved in the transport direction and while the end portion of the structure is being pulled in a direction intersecting the transport direction. The electrode manufacturing method described in claim 3 further includes a step of adjusting the tension applied to the structure in the transport direction according to the moisture content. The electrode manufacturing method described in claim 1 further comprises a step of cutting the pressed structure after the pressing. The niobium-containing oxide includes at least one selected from the group consisting of niobium-containing oxides represented by the general formula Li _x Ti _{1 -y} M1 _y Nb _2-z M2 _z O _7+δ and niobium-containing oxides represented by the general formula Li _x Ti 1-y _{M3 y+z} Nb _2-z O _7-δ ,
2. The method for producing an electrode according to claim 1, wherein M1 is at least one selected from the group consisting of Zr, Si, and Sn, M2 is at least one selected from the group consisting of V, Ta, and Bi, M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo, x satisfies 0≦x≦5, y satisfies 0≦y<1, z satisfies 0≦z<2, and δ satisfies −0.3≦δ≦0.3. The method for manufacturing an electrode according to claim 1, wherein the titanium-containing oxide includes at least one selected from the group consisting of monoclinic titanium dioxide, anatase titanium dioxide, rutile titanium dioxide, and bronze titanium dioxide. a step of preparing an electrode group by using the electrode obtained by the method according to any one of claims 1 to 7 as a first electrode and disposing a separator between the first electrode and a second electrode;
a step of housing the electrode group in an exterior member;
and causing the electrode group housed in the exterior member to retain a non-aqueous electrolyte.