JP5392063B2 - Lithium ion secondary battery, vehicle and battery-equipped equipment - Google Patents

Description

  The present invention relates to a lithium ion secondary battery comprising a power generation element formed by winding a current collector plate and an electrode plate (positive electrode plate, negative electrode plate) having an active material layer and a separator, and this lithium ion secondary battery. The present invention relates to mounted vehicles and battery-mounted devices.

In recent years, lithium ion secondary batteries have been used as power sources for driving portable electronic devices such as hybrid cars, notebook computers, and video camcorders.
Such a lithium ion secondary battery is a lithium ion secondary battery (hereinafter, referred to as a belt-shaped lithium ion secondary battery including a negative electrode plate, a positive electrode plate, and a separator interposed between them). Simply referred to as a battery).

  In relation to such a battery, in Patent Document 1, among strip-shaped current collectors (positive electrode current collector plate, negative electrode current collector plate) extending in the longitudinal direction, the battery is located at the center in the width direction orthogonal to the longitudinal direction. Lithium secondary in which a first region in which protrusions are regularly formed is formed on the surface, and a second region in which protrusions are randomly formed on the surface located on both side edges in the width direction. Battery electrodes (positive electrode plate, negative electrode plate) are disclosed.

JP 2008-103231 A

  In the second region of the current collector in the electrode for a lithium secondary battery described above, the adhesiveness to the active material (positive electrode active material layer, negative electrode active material layer) is higher than that in the first region. For this reason, the peeling between the positive electrode active material layer (or the negative electrode active material layer) and the positive electrode current collector plate (or the negative electrode current collector plate) that occurs in the second region located at both ends of the edge during charging and discharging is performed. It is possible to suppress the deterioration of the cycle characteristics of the battery.

  However, as described in Patent Document 1, the surface of the current collector (positive electrode current collector plate, negative electrode current collector plate) is modified to provide a first region and a second region having different characteristics, respectively, It is difficult to form a current collector having an active material (positive electrode active material layer, negative electrode active material layer) disposed thereon.

  Therefore, the inventors have improved the characteristics of the positive electrode active material layer and the negative electrode active material layer, not the current collector (positive electrode current collector plate, negative electrode current collector plate), and thereby improved the positive electrode active material layer and the positive electrode current collector plate. And improving at least any adhesion between the negative electrode active material layer and the negative electrode current collector plate. However, for example, when the amount of the binder in the active material layer is increased to increase the peel strength between the active material layer and the current collector plate over the entire surface, the discharge rate characteristics of the battery using this decrease. This is not preferable. Since the increase in the amount of the binder hinders the movement of lithium ions in the active material layer over the entire surface of the active material layer, it is considered that the binder material was particularly affected by the discharge at a high rate. The discharge rate characteristic is the ratio of the battery capacity when the battery is discharged with a large (high rate) discharge current value to the battery capacity when the battery is discharged with a small (low rate) discharge current value. It is a characteristic represented by (high rate capacity maintenance rate), and the larger the ratio (the battery capacity is less likely to decrease even at a high rate), the more preferable.

  The present invention has been made in view of such problems, and provides a lithium ion secondary battery that is easy to manufacture and has good battery characteristics, a vehicle equipped with the lithium ion secondary battery, and a battery-equipped device. With the goal.

  One embodiment of the present invention includes a strip-shaped positive electrode current collector plate having conductivity, and a positive electrode current collector plate which is disposed on the positive electrode current collector plate and includes positive electrode active material particles and a binder. A strip-shaped positive electrode plate having a strip-shaped positive electrode active material layer extending in the direction of the electrode, a conductive strip-shaped negative electrode current collector plate, and a negative electrode active material particle and a binder disposed on the negative electrode current collector plate. A negative electrode active material layer extending in the longitudinal direction of the negative electrode current collector plate, the negative electrode plate having a band shape facing the positive electrode plate, and between the positive electrode plate and the negative electrode plate A lithium ion secondary battery comprising a power generation element formed by winding a separator interposed between the positive electrode active material layer and the positive electrode current collector plate, and the negative electrode active material Orthogonal to the longitudinal direction for at least one of the peel strength between the layer and the negative electrode current collector plate For that the width direction, by varying the characteristics of the active material layer, a lithium ion secondary battery comprising a higher side edge portions than in the central portion in the width direction.

In the above-described battery, at least one of the peel strength between the positive electrode active material layer and the positive electrode current collector plate and the peel strength between the negative electrode active material layer and the negative electrode current collector plate is compared with the central portion in the width direction. The side edges are raised. Thereby, about the said active material layer, it can suppress that the width direction both-sides edge which is easy to peel from peeling from a current collecting plate.
On the other hand, by increasing the peel strength, compared to the side edges where the electrical characteristics such as the ease of movement of lithium ions tend to decrease, such a decrease in characteristics is less likely to occur at the center, Good characteristics can be obtained for the entire active material layer.
Thus, it is possible to obtain a battery having good battery characteristics while suppressing peeling of the active material layer.

  Examples of the peel strength measuring method include a cross-cut test and an immersion test in which the electrode plate is immersed in N-methyl-2-pyrrolidone (NMP) having a liquid temperature of 60 ° C. for 30 days. Among these, the cross-cut test is, for example, using a commercially available automatic cross-cut peel tester to cut the cut through the active material layer to reach the current collector plate and attach the adhesive tape. This is a test in which the state of the surface when peeled is observed and evaluated by a classification table for evaluating the peel strength from the surface state.

  In addition, as a method for making the characteristics of the active material layer different, for example, in the positive electrode active material layer (or the negative electrode active material layer), for example, the peel strength between the width direction center portion and the width direction both end edges is made different. Examples of the method include changing the amount according to the amount of the binder, the crystallinity of the binder, and the molecular weight of the binder.

  Furthermore, in the lithium ion secondary battery described above, in the positive electrode active material layer and the negative electrode active material layer, the both side edge portions are made higher than the central portion in the width direction with respect to the peel strength. The active material layer may be a lithium ion secondary battery in which the amount of the binder in the active material layer is increased at both side edges as compared to the central portion.

  When the amount of the binder in the active material layer is increased, the peel strength between the active material layer and the current collector plate can be increased. For this reason, in the battery described above, the peel strength between the active material layer and the current collector plate can be reliably increased at both side edges as compared to the central portion in the width direction, and the active material layer can be peeled off. It can be set as the battery which has favorable battery characteristics, suppressing it reliably.

  Or it is the above-mentioned lithium ion secondary battery, Comprising: About the said peeling strength among the said positive electrode active material layers and the said negative electrode active material layers, the said both edge part was made high compared with the said center part of the said width direction. The active material layer may be a lithium ion secondary battery in which the degree of crystallinity of the binder in the active material layer is higher at both side edges than at the center.

  When the crystallinity of the binder in the active material layer is increased, the viscosity of the binder is increased, and the peel strength between the active material layer and the current collector plate can be increased. For this reason, in the battery described above, the peel strength between the active material layer and the current collector plate can be reliably increased at both side edges as compared to the central portion in the width direction, and the active material layer can be peeled off. It can be set as the battery which has favorable battery characteristics, suppressing it reliably.

  In addition, as a measuring means which measures a crystallinity degree, the heat of fusion measurement using a differential scanning calorimeter (DSC) is mentioned, for example.

  Or it is the above-mentioned lithium ion secondary battery, Comprising: About the said peeling strength among the said positive electrode active material layers and the said negative electrode active material layers, the said both edge part was made high compared with the said center part of the said width direction. The active material layer may be a lithium ion secondary battery in which the molecular weight of the binder in the active material layer is increased at both side edge portions as compared to the central portion.

  When the molecular weight of the binder in the active material layer is increased, the viscosity of the binder is increased, and the peel strength between the active material layer and the current collector plate can be increased. For this reason, in the battery described above, the peel strength between the active material layer and the current collector plate can be reliably increased at both side edges as compared to the central portion in the width direction, and the active material layer can be peeled off. It can be set as the battery which has favorable battery characteristics, suppressing it reliably.

  Or the other aspect of this invention is a vehicle which mounts one of the above-mentioned lithium ion secondary batteries, and uses the electrical energy stored in this lithium ion secondary battery for all or one part of a motive power source.

  Since the above-mentioned vehicle is equipped with a battery having good battery characteristics, it can be a vehicle having a power source with stable performance.

  The vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source. For example, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, a forklift, an electric wheelchair, an electric vehicle Examples include assist bicycles and electric scooters.

  Alternatively, according to another aspect of the present invention, a battery-mounted device in which any one of the above-described lithium ion secondary batteries is mounted and the electric energy stored in the lithium ion secondary battery is used for all or part of the driving energy source. It is.

  Since the above-described battery-mounted device is equipped with a battery having good battery characteristics, it can be a battery-mounted device having a power source with stable performance.

  In addition, as a battery mounting apparatus, what is necessary is just an apparatus which mounts a battery and uses this for all or one part of an energy source, for example, a personal computer, a mobile telephone, a battery-powered electric tool, an uninterruptible power supply, etc. And various home appliances driven by batteries, office equipment, and industrial equipment.

3 is a perspective view of a battery according to Embodiment 1, Modification 1 and Modification 2. FIG. It is a perspective view of the positive electrode plate of Embodiment 1, Modification 1, and Modification 2. It is a perspective view of the negative electrode plate of Embodiment 1, modification 1, and modification 2. FIG. It is explanatory drawing of the positive electrode plate of a modification 1, and a negative electrode plate. It is explanatory drawing of the vehicle concerning Embodiment 2. FIG. It is explanatory drawing of the battery mounting apparatus concerning Embodiment 3. FIG.

(Embodiment 1)
Next, Embodiment 1 of the present invention will be described with reference to the drawings.
First, the battery 1 according to the first embodiment will be described with reference to FIG.
The battery 1 is formed by winding a strip-shaped positive electrode plate 20, a strip-shaped negative electrode plate 30, and a strip-shaped separator 50 interposed between the positive electrode plate 20 and the negative electrode plate 30. It is a lithium ion secondary battery provided with the electric power generation element 10 impregnated with the electrolyte solution 60 (refer FIG. 1). The battery 1 includes a power generation element 10 accommodated in a battery case 80.

  The battery case 80 has a battery case body 81 and a sealing lid 82 both made of aluminum. Among these, the battery case main body 81 has a bottomed rectangular box shape, and an insulating film (not shown) made of resin and bent into a box shape is interposed between the battery case 80 and the power generation element 10. The sealing lid 82 has a rectangular plate shape, closes the opening of the battery case body 81, and is welded to the battery case body 81. Of the positive electrode current collecting member 91 and the negative electrode current collecting member 92 connected to the power generation element 10, the positive electrode terminal portion 91 </ b> A and the negative electrode terminal portion 92 </ b> A located at the tips of the sealing lid 82 pass through, respectively. 1 protrudes from the lid surface 82a facing upward. Insulating members 95 made of insulating resin are interposed between the positive electrode terminal portion 91A and the negative electrode terminal portion 92A and the sealing lid 82 to insulate each other. Further, a rectangular plate-shaped safety valve 97 is also sealed on the sealing lid 82.

In addition, the electrolytic solution 60 was prepared by adding LiPF ₆ as a solute to a mixed organic solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were adjusted to EC: DMC = 3: 7 by volume ratio, and lithium ions were added. This is a non-aqueous electrolyte having a concentration of 1 mol / l.

The power generation element 10 has a wound-type configuration in which a strip-like positive electrode plate 20 and a negative electrode plate 30 are wound into a flat shape via a strip-like separator 50 (see FIG. 1). In the power generation element 10, the positive electrode plate 20 and the negative electrode plate 30 face each other. Further, the positive electrode plate 20 and the negative electrode plate 30 of the power generation element 10 are respectively joined to a plate-like negative electrode current collecting member 92 or a positive electrode current collecting member 91 bent in a crank shape (see FIG. 1).
Among these, the strip-shaped separator 50 made of porous polypropylene is interposed between the positive electrode plate 20 and the negative electrode plate 30 to separate them. The separator 50 is entirely impregnated with the electrolytic solution 60 described above.

  Further, as shown in FIG. 2, the positive electrode plate 20 has a strip shape extending in the longitudinal direction DA, and an aluminum foil 28 (foil thickness is 15 μm) made of conductive aluminum and on both main surfaces of the aluminum foil 28. And two strip-shaped positive electrode active material layers 21 and 21 extending in the longitudinal direction DL.

Among these, the positive electrode active material layer 21 has different characteristics of the positive electrode active material layer 21 in the width direction DW orthogonal to the longitudinal direction DL. Specifically, as shown in FIG. 2, the positive electrode active material layer 21 includes a belt-like central portion 21 </ b> C located at the center in the width direction DW, two belt-like edge portions 21 </ b> E located at both side edges in the width direction DW, 21E, and two belt-like intermediate portions 21M and 21M located between the central portion 21C and the edge portion 21E.
These central part 21C, edge part 21E and intermediate part 21M are all positive electrode active material particles 24 made of LiCoO ₂ , conductive material 25 made of carbon black, and polyvinylidene fluoride (PVDF) having a crystallization temperature of about 140 ° C. The binder 23 which consists of is included. However, in the central part 21C, the edge part 21E, and the intermediate part 21M, the weight ratios of the positive electrode active material particles 24, the conductive material 25, and the binder material 23 are different.
Specifically, the weight ratio of the positive electrode active material particles 24, the conductive material 25, and the binder 23 in the central portion 21C is determined as follows: positive electrode active material particles 24: conductive material 25: binder 23 = 88: 9: 3 It is as. Further, the weight ratio in the edge portion 21E is set as positive electrode active material particles 24: conductive material 25: binder 23 = 85: 6: 9. Furthermore, the weight ratio in the intermediate portion 21M is set as positive electrode active material particles 24: conductive material 25: binder 23 = 87: 8: 5. That is, the amount of the positive electrode active material particles 24 is increased in the order of the central portion 21C, the intermediate portion 21M, and the edge portion 21E, that is, the amount increases toward the edge portions 21E and 21E on both sides from the central portion 21C.

  On the other hand, as shown in FIG. 3, the negative electrode plate 30 has a strip shape extending in the longitudinal direction DA, a copper foil 38 made of conductive copper (foil thickness is 15 μm), and a main surface of the copper foil 38. It has two strip-shaped negative electrode active material layers 31 and 31 that are arranged and extend in the longitudinal direction DL.

Among these, the negative electrode active material layer 31 is different in the characteristics of the negative electrode active material layer 31 in the width direction DW, like the positive electrode active material layer 21. Specifically, as shown in FIG. 3, the negative electrode active material layer 31 includes a strip-shaped central portion 31C located at the center in the width direction DW, two strip-shaped edge portions 31E located at both side edges in the width direction DW, 31E and two strip-shaped intermediate portions 31M and 31M located between the central portion 31C and the edge portion 31E.
Each of the central part 31C, the edge part 31E and the intermediate part 31M includes a negative electrode active material particle 34 made of graphite powder and a binder 33 made of PVDF having a crystallization temperature of about 140 ° C. However, the weight ratios of the negative electrode active material particles 34 and the binder 33 are different in the central portion 31C, the edge portion 31E, and the intermediate portion 31M.
Specifically, the weight ratio of the negative electrode active material particles 34 and the binder 33 in the central portion 31C is set as the negative electrode active material particles 34: binder 33 = 965: 35. Moreover, the weight ratio in the edge part 31E is set as the negative electrode active material particle 34: binder 33 = 905: 95. Furthermore, the weight ratio in the intermediate portion 31M is set as negative electrode active material particles 34: binder 33 = 935: 65. That is, the amount of the negative electrode active material particles 34 is increased in the order of the central portion 31C, the intermediate portion 31M, and the edge portion 31E, that is, increases toward the edge portions 31E and 31E on both sides from the central portion 31C.

By the way, in order to evaluate the discharge rate characteristics, cycle characteristics, and presence / absence of delamination in the active material layer of the battery 1, the present inventors have the same positive electrode active material layer, negative electrode active material layer, separator as in the battery 1. A cylindrical sample battery T1 using the electrolyte solution was prepared.
Specifically, first, 88 g of the positive electrode active material particles 24 and 9 g of the conductive material 25 are put into 125 ml of N-methyl-2-pyrrolidone (NMP) in which 3 g of the binder 23 is dissolved. The first positive electrode paste (not shown) was prepared by kneading so as to be uniform (the binder 23 in the first positive electrode paste is 3 wt%).
Similarly, 87 g of the positive electrode active material particles 24 and 8 g of the conductive material 25 are respectively added to 125 ml of NMP in which 5 g of the binder 23 is dissolved, and kneaded uniformly to obtain a second positive electrode paste (not shown). (The binder 23 in the second positive electrode paste is 5 wt%). Also, 85 g of the positive electrode active material particles 24 and 6 g of the conductive material 25 are respectively added to 125 ml of NMP in which 9 g of the binder 23 is dissolved, and they are kneaded uniformly to obtain a third positive electrode paste (not shown). This was produced (the binder 23 in the second positive electrode paste was 9 wt%).

These first, second and third positive electrode pastes were applied to a strip-shaped aluminum aluminum foil (foil thickness: 15 μm) extending in the longitudinal direction and dried.
Specifically, first, the first positive electrode paste was applied in a band shape with a width of 30.0 mm to the center position in the width direction orthogonal to the longitudinal direction of both main surfaces of the aluminum foil. After the application, the first positive electrode paste on the aluminum foil was dried at 120 ° C.
Next, the second positive electrode paste was applied to the main surface on one side in a strip shape with a width of 7.5 mm so as to be adjacent to both edges in the width direction of the dried first positive electrode paste, and dried. . Further, the third positive electrode paste is applied to both side edges of the aluminum foil in the width direction so as to be adjacent to the edge of the second positive electrode paste in strips with a width of 1.5 mm and two strips on one main surface. , Dried. Thus, when the first, second, and third positive electrode pastes are viewed in the width direction, the aluminum foil is arranged in the order of the third positive electrode paste, the second positive electrode paste, the first positive electrode paste, the second positive electrode paste, and the third positive electrode paste. Lined up on both main faces.

Each dried positive electrode paste is compressed by a roll press (not shown) to be densified, and the positive electrode active material having a central part, an edge part, and an intermediate part on the aluminum foil, which is the same as the positive electrode active material layer 21 according to the battery 1 described above. A material layer (not shown) was prepared. In this positive electrode active material layer, the center, edge, and intermediate portions in the width direction are 30.0, 7.5, and 3.5 mm, respectively, the positive electrode active material layer has a thickness of 90 μm, and a density of 1.6 g / cm ³ .
The produced positive electrode active material layer was cut into a shape of 52 mm × 720 mm together with the aluminum foil (among these, the size of the portion carrying the positive electrode active material layer was 52 mm × 680 mm) to obtain a positive electrode plate (not shown).

On the other hand, 96.5 g of the negative electrode active material particles 34 described above was added to 125 ml of NMP in which 3.5 g of the binder 33 was dissolved, and kneaded to prepare a first negative electrode paste (not shown) (this) The binder 33 in the first negative electrode paste is 3.5 wt%).
Similarly, 93.5 g of the negative electrode active material particles 34 are added to 125 ml of NMP in which 6.5 g of the binder 33 is dissolved, and the second negative electrode paste (not shown) is added, and 9.5 g of the binder 33 is added. 90.5 g of negative electrode active material particles 34 were added to 125 ml of dissolved NMP to prepare third negative electrode pastes (not shown), respectively (the binder 33 in the second and third negative electrode pastes was 6.5, respectively). 9.5 wt%).

These first, second and third negative electrode pastes were applied to a strip-like copper copper foil CF (foil thickness of 15 μm) extending in the longitudinal direction.
Specifically, the 1st negative electrode paste was apply | coated to the center position of the width direction orthogonal to a longitudinal direction of both the main surfaces of copper foil, respectively with the width | variety of 30.0 mm at strip | belt shape. After the application, the first negative electrode paste on the copper foil was dried at 120 ° C.
Next, the second negative electrode paste was applied in strips with a width of 7.5 mm and two strips on one main surface so as to be adjacent to both edges in the width direction of the dried first negative electrode paste, and dried. . Further, the third negative electrode paste was applied in strips with a width of 1.5 mm and two strips on one side of the main surface on both sides of the copper foil in the width direction so as to be adjacent to the edge of the second negative electrode paste. , Dried. Thus, when the first, second, and third negative electrode pastes are viewed in the width direction, the copper foil in the order of the third negative electrode paste, the second negative electrode paste, the first negative electrode paste, the second negative electrode paste, and the third negative electrode paste. Lined up on both main faces.

Each of the dried negative electrode pastes is compressed by a roll press (not shown) to increase the density, and the negative electrode active material having the central part, the edge part, and the intermediate part on the copper foil, which is the same as the negative electrode active material layer 31 of the battery 1 described above. A material layer (not shown) was prepared. In this negative electrode active material layer, the center, edge, and intermediate portions in the width direction are 30.0, 7.5, and 5.0 mm, respectively, the negative electrode active material layer has a thickness of 40 μm, and a density of 1.2 g / cm ³ .
The produced negative electrode active material layer was cut into a shape of 55 mm × 740 mm together with the copper foil (among these, the size of the portion carrying the negative electrode active material layer was 55 mm × 720 mm) to obtain a negative electrode plate (not shown).

  The positive electrode plate and the negative electrode plate are laminated with a polyethylene separator (not shown) having a thickness of 30 μm interposed therebetween, and the positive electrode plate, the negative electrode plate and the separator are wound to form a wound type. A power generation element (not shown) was prepared. This power generation element was inserted into a 18650 type cylindrical case, and the above-described electrolytic solution 60 was injected therein, followed by sealing to manufacture a sample battery T1 (not shown).

Among the sample batteries T1, the battery capacity of a new (initial) battery that was just manufactured was measured. Specifically, first, a constant current charge and a constant current discharge (both 0.1 C) are performed in a voltage range of 3.0 to 4.1 V for a sample battery T1 in a temperature environment of 25 ° C. The discharge was repeated for 3 cycles (conditioning).
Subsequently, the battery was charged to 4.1 V at a current value of 1.0 C, and then maintained for 2.5 hours while gradually decreasing the current value while maintaining the voltage in a temperature environment of 25 ° C. (constant current). -Constant voltage charging). Further, under a temperature environment of 25 ° C., constant current discharge was performed until the current value of 1 / 3C became 3.0 V, and the discharged battery capacity was measured. The battery capacity at this time is referred to as “1 / 3C battery capacity”.
Subsequently, after performing the above-described constant current-low voltage charging again, the current value was changed to 20 C, constant current discharging was performed, and the battery capacity was measured.
And from each measured battery capacity, the high rate capacity maintenance rate in case discharge current value is 20C was computed. This high rate capacity maintenance ratio is obtained by dividing the battery capacity of each discharge current value by the 1 / 3C battery capacity (percentage).

Furthermore, a cycle test in which constant current charging (current value is 2 C) and constant current discharging (current value is 2 C) was repeated in the voltage range of 3.0 to 4.1 V for the sample battery T1 subjected to the above test. . Specifically, in a temperature environment of 60 ° C., 500 cycles were repeated continuously, with one set of charging / discharging as one cycle.
Thereafter, the battery capacity of the sample battery T1 was measured in the same manner as described above. And the cycle capacity maintenance factor of sample battery T1 after a cycle test was computed. This cycle capacity maintenance ratio is obtained by dividing the battery capacity after the cycle test by the battery capacity before the cycle test (percentage).

  After the cycle test, the presence or absence of peeling near the edge of the positive electrode active material layer and the negative electrode active material layer was confirmed. Specifically, using a commercially available automatic crosscut peel tester, when the cuts reaching the current collector plate through each active material layer were made in a grid pattern, the adhesive tape was attached and peeled off The state of the surface was observed, and the peel strength of each active material layer was determined according to the classification table. In addition, when peeling was not seen in any of the positive electrode active material layer and the negative electrode active material layer, “no peeling” was determined, and “other than that” was determined otherwise.

In the same manner as this sample battery T1, comparative batteries C1 and C2 as comparative examples were also manufactured, and the battery characteristics (high rate capacity maintenance rate and cycle capacity maintenance rate) of these batteries were measured in the same manner as the sample battery T1. did.
However, the comparative battery C1 has a positive electrode active material layer using the first positive electrode paste including 9.0 wt% of the binder 23 as a whole, and the first negative electrode paste including 9.5 wt% of the binder 33. Is different from the sample battery T1 in that it has a negative electrode active material layer.
Further, the comparative battery C2 has a positive electrode active material layer using a third positive electrode paste containing 3.0 wt% of the binder 23 as a whole, and a third negative electrode paste containing 3.5 wt% of the binder 33. Is different from the sample battery T1 in that it has a negative electrode active material layer.
The weight ratio of the binder in the positive electrode active material layer and the negative electrode active material layer of the sample battery T1 and the comparative batteries C1 and C2, presence or absence of peeling near the edge of the positive electrode active material layer and the negative electrode active material layer, cycle capacity Table 1 shows the maintenance rate and the high rate capacity maintenance rate.

According to Table 1, regarding the presence / absence of peeling, the sample battery T1 and the comparative battery C1 were judged as “no peeling”. On the other hand, the comparison battery C2 was judged as “with peeling”. In addition, the cycle capacity maintenance rates (84% and 75%) of the sample battery T1 and the comparative battery C1 are clearly higher than the cycle capacity maintenance rates (37%) of the comparative battery C2.
In the sample battery T1 and the comparative battery C1, the weight ratio of the binder at the edges of the positive electrode active material layer and the negative electrode active material layer is increased (9.0 wt% and 9.5 wt%), respectively. Thus, by increasing the amount of the binder, the peel strength between the positive electrode active material layer and the aluminum foil and between the negative electrode active material layer and the copper foil can be increased, and between them It is considered that peeling of the film could be suppressed. For this reason, it is considered that the sample battery T1 and the comparative battery C1 were able to suppress the deterioration of the cycle characteristics.

Furthermore, when comparing the sample battery T1 and the comparative battery C1, the high rate capacity retention rate (72%) of the sample battery T1 is higher than that (45%) of the comparative battery C1. From this, the battery in which the weight ratio of the binder of the whole positive electrode active material layer and the whole negative electrode active material layer is uniformly high (9.0 wt% and 9.5 wt%) is higher in the central portion in the width direction. When the weight ratio of the binder is lower than that of the edge (3.0 wt% and 3.5 wt%), the high rate capacity retention rate can be increased, that is, the deterioration of the discharge rate characteristics can be suppressed. I understand.
This is because when the weight ratio of the binder is increased throughout the active material layer, the movement of lithium ions in the positive electrode active material layer and the negative electrode active material layer is hindered over the entire surface of the active material layer. It is affected by that. On the other hand, when the weight ratio of the binder is increased only in the edge portion (and the intermediate portion) of the active material layer as in the sample battery T1, the influence is limited. .

From the above, in the battery 1 using the above-described sample battery T1, and further the positive electrode active material layer and the negative electrode active material layer having the same configuration as the sample battery T1, both the positive electrode active material layer and the negative electrode active material layer were peeled off. It can suppress that the edge part of the width direction which is easy peels from aluminum foil and copper foil.
On the other hand, by increasing the peel strength between the positive electrode active material layer and the aluminum foil and between the negative electrode active material layer and the copper foil, electrical characteristics such as ease of movement of lithium ions Such a decrease in characteristics is less likely to occur in the central portion than in the edge portion, which tends to decrease, so that favorable characteristics can be obtained for the positive electrode active material layer and the negative electrode active material layer as a whole.
Thus, the sample battery T1 and the battery 1 can be batteries having good battery characteristics (cycle characteristics, discharge rate characteristics) while suppressing the peeling of the active material layer.

  Further, in the sample battery T1 and the battery 1 described above, since the amount of the binder at the edge of the positive electrode active material layer and the negative electrode active material layer is larger than that in the central portion, the active material layer and the current collector plate Can be reliably increased at the edge compared to the central portion in the width direction. Therefore, it is possible to obtain a battery having good battery characteristics while reliably suppressing peeling of the active material layer.

Next, a method for manufacturing the battery 1 according to the first embodiment will be described.
First, the power generation element 10 is manufactured in substantially the same manner as the sample battery T1. Specifically, first, the first positive electrode paste, the second positive electrode paste, and the third positive electrode paste described above are respectively applied to both main surfaces of the aluminum foil 28 and dried, and these are applied in the width direction of the aluminum foil 28. As viewed from DW, the third positive electrode paste, the second positive electrode paste, the first positive electrode paste, the second positive electrode paste, and the third positive electrode paste were arranged on both main surfaces of the aluminum foil 28 in the order. These are compressed by a roll press (not shown) and densified to produce a positive electrode active material layer 21, and a belt-like positive electrode plate 20 is completed (see FIG. 2).

On the other hand, the first negative electrode paste, the second negative electrode paste, and the third negative electrode paste described above are respectively applied to both main surfaces of the copper foil 38 and dried, and these are seen in the width direction DW of the copper foil 38. The third negative electrode paste, the second negative electrode paste, the first negative electrode paste, the second negative electrode paste, and the third negative electrode paste were arranged on both main surfaces of the copper foil 38 in this order. These are compressed by a roll press (not shown) and densified to produce a negative electrode active material layer 31, and a strip-like negative electrode plate 30 is completed (see FIG. 3).
A power generation element 10 is obtained by winding the separator 50 between the positive electrode plate 20 and the negative electrode plate 30 manufactured as described above.

  Thereafter, the positive electrode current collecting member 91 and the negative electrode current collecting member 92 are respectively welded to the positive electrode plate 20 (aluminum foil 28) and the negative electrode plate 30 (copper foil 38), inserted into the battery case body 81, and the above-described electrolysis. After injecting the liquid 60, the battery case body 81 is sealed with a sealing lid 82 by welding. Thus, the battery 1 is completed (see FIG. 1).

(Modification 1)
Next, the battery 101 according to the first modification of the present invention will be described with reference to FIGS.
This modification 1 is different from the battery 1 of the first embodiment described above in that the crystallinity of the binder in the positive electrode active material layer and the negative electrode active material layer is increased in the order of the central part, the intermediate part, and the edge part. The others are the same.
Therefore, differences from the first embodiment will be mainly described, and description of similar parts will be omitted or simplified. In addition, about the same part, the same effect is produced. In addition, the same contents are described with the same numbers.

  The battery 101 according to the first modification is formed by winding a strip-shaped positive electrode plate 120, a strip-shaped negative electrode plate 130, and a strip-shaped separator 50 interposed between the positive electrode plate 120 and the negative electrode plate 130. The lithium ion secondary battery includes a power generation element 110 in which the separator 50 is impregnated with the electrolytic solution 60 (see FIG. 1).

  The power generation element 110 has a wound type configuration in which the belt-like positive electrode plate 120 and the negative electrode plate 130 are wound into a flat shape via the belt-like separator 50, as in the battery 1 of the first embodiment ( (See FIG. 1). Among these, as shown in FIG. 2, the positive electrode plate 120 includes two aluminum foils 28 that are the same as those of the battery 1 and two strip-shaped positive electrode active members that are disposed on both main surfaces of the aluminum foil 28 and extend in the longitudinal direction DL. Material layers 121 and 121.

As in the first embodiment, the positive electrode active material layer 121 has different characteristics of the positive electrode active material layer 121 in the width direction DW perpendicular to the longitudinal direction DL. Specifically, as shown in FIG. 2, the width direction DW includes one central part 121C, two edge parts 121E and 121E, and two intermediate parts 121M and 121M.
The central part 121C, the edge part 121E and the intermediate part 121M are all positive electrode active material particles 24 made of LiCoO ₂ , a conductive material 25 made of carbon black, and a binder made of PVDF having a crystallization temperature of about 140 ° C. (The center binder 123C, the edge binder 123E, and the intermediate binder 123M described below). However, in the central part 121C, the edge part 121E, and the intermediate part 121M, the crystallinity of the binders (the central part binder 123C, the edge part binder 123E, and the intermediate part binder 123M) included therein is set. It is different.

  Specifically, in the central part 121C, the edge part 121E, and the intermediate part 121M, the central part binder 123C having a crystallinity of 20 to 30%, the edge part binder 123E having 40 to 50%, and 30 to 30%. 40% of the intermediate portion binder 123M is included. That is, the degree of crystallinity of the binders 123C, 123M, and 123E is increased in the order of the central portion 121C, the intermediate portion 121M, and the edge portion 121E, that is, the higher the direction from the central portion 121C to the edge portions 121E and 121E on both sides. . The higher the degree of crystallinity of the binder, the higher the viscosity of the binder. Therefore, the peel strength of the positive electrode active material layer 121 increases from the center 121C toward the edge 121E.

In addition, the negative electrode active material layer 131 has different characteristics of the negative electrode active material layer 131 in the width direction DW perpendicular to the longitudinal direction DL, as in the first embodiment. Specifically, as shown in FIG. 3, the width direction DW includes one central portion 131C, two edge portions 131E and 131E, and two intermediate portions 131M and 131M.
The central part 131C, the edge part 121E, and the intermediate part 131M are all composed of negative electrode active material particles 34 of graphite powder and a binder made of PVDF having a crystallization temperature of about 140 ° C. (the central part binder described below) 133C, edge binder 133E, intermediate binder 133M). However, in the central part 131C, the edge part 131E, and the intermediate part 131M, the crystallinity of the binding materials (the central part binding material 133C, the edge part binding material 133E, and the intermediate part binding material 133M) included therein is set. It is different.

  Specifically, in the central portion 131C, the edge portion 131E, and the intermediate portion 131M, the central portion binding material 133C having a crystallinity of 20 to 30%, the edge portion binding material 133E having 40 to 50%, and 30 to 30%. 40% of the intermediate binder 133M is included. That is, the degree of crystallinity of the binders 133C, 133M, and 133E increases in the order of the central portion 131C, the intermediate portion 131M, and the edge portion 131E, that is, increases toward the edge portions 131E and 131E on both sides from the central portion 131C. . The higher the degree of crystallinity of the binder, the higher the viscosity of the binder. Therefore, the peel strength of the negative electrode active material layer 131 is increased from the center portion 131C toward the edge portion 131E.

In the first modification, the crystallinity of the binder is changed depending on the difference in the maximum temperature at which the binder is exposed.
Since the crystallization temperature of PVDF used for the above-mentioned binder is about 140 ° C., when the paste is heated and dried to form an active material layer, for example, the binder is heated to a temperature higher than its crystallization temperature. (For example, 160 degreeC) can be made to crystallize, ie, it can be set as the binder which has a comparatively high crystallinity degree. Conversely, by increasing the binder only to a temperature below its crystallization temperature (for example, 120 ° C.), it is not crystallized (or slightly crystallized), that is, relatively low crystals. A binding material having a degree of conversion can be obtained.

By the way, in order to evaluate the discharge rate characteristics, cycle characteristics, and presence / absence of delamination in the active material layer of the battery 1 described above, the present inventors have the same positive electrode active material as that of the battery 101 in the same manner as in the first embodiment. A cylindrical sample battery T2 using a layer, a negative electrode active material layer, a separator, and an electrolytic solution was prepared.
Specifically, first, 85 g of the positive electrode active material particles 24 and 10 g of the conductive material 25 are respectively added to 125 ml of NMP in which 5 g of the above-described binder (PVDF) is dissolved, and kneaded to be uniform. A positive electrode paste 121P was produced.

This positive electrode paste 121P was applied to a strip-shaped aluminum aluminum foil AF (foil thickness of 15 μm) extending in the longitudinal direction and dried.
Specifically, first, as shown in FIG. 4A, the positive electrode paste 121P is spaced apart by a width dimension of 45 mm including the center in the width direction DW on both main surfaces of the aluminum foil AF. Two strips were applied in a band shape with a width of 5 mm. After the application, this positive electrode paste 121P was dried at 160 ° C. Since the drying temperature is higher than the crystallization temperature of the binder (about 140 ° C.), the drying of the positive electrode paste 121P proceeds and the crystallization of the binder in the positive electrode paste 121P proceeds. As a result, the positive electrode paste 121P becomes an edge portion of the uncompressed positive electrode active material layer including the edge portion binder 123E having a crystallinity of 40 to 50%.

Next, as shown in FIG. 4B, the dried positive electrode paste 121P including the edge binder 123E with an interval of a width of 30 mm including the center in the width direction DW, as shown in FIG. 4B. Two strips with a width of 7.5 mm were applied adjacent to the inside of the paste. After the application, this positive electrode paste 121P was dried at 140 ° C. Since the drying temperature is almost the same as the crystallization temperature of the binder, the drying of the positive electrode paste 121P proceeds and the crystallization of the binder in the positive electrode paste 121P proceeds (however, the edge binder described above) Crystallization does not progress as much as 123E). Thereby, this positive electrode paste 121P becomes an intermediate part of the uncompressed positive electrode active material layer including the intermediate part binder 123M having a crystallinity of 30 to 40%.
Further, the positive electrode paste 121P was applied in a strip shape with a width of 30 mm including the center in the width direction DW, adjacent to the inside sandwiched by two dried positive electrode pastes including the intermediate binder 123M. . After the application, this positive electrode paste 121P was dried at 120 ° C. Since the drying temperature is lower than the crystallization temperature of the binder, the drying of the positive electrode paste 121P proceeds, but the crystallization of the binder in the positive electrode paste 121P does not progress much. Thereby, this positive electrode paste 121P becomes a central portion of the uncompressed positive electrode active material layer including the central portion binder 123C having a crystallinity of 20 to 30%.
Thus, when the uncompressed positive electrode active material layer is viewed in the width direction DW, it includes the edge binder 123E, the intermediate binder 123M, the central binder 123C, and the intermediate portion. They were arranged on both main surfaces of the aluminum foil AF in the order of the binder material 123M and the edge binder material 123E.

This uncompressed positive electrode active material layer is compressed and densified by a roll press (not shown), and is the same as the positive electrode active material layer 121 applied to the battery 101 described above, on the aluminum foil AF, at the center, the edge, and the intermediate portion. A positive electrode active material layer (not shown) was prepared. In this positive electrode active material layer, the center, edge, and intermediate portions in the width direction are 30.0, 7.5, and 3.5 mm, respectively, the positive electrode active material layer has a thickness of 90 μm, and a density of 1.6 g / cm ³ .
The produced positive electrode active material layer was cut into a shape of 52 mm × 720 mm together with the aluminum foil (among these, the size of the portion carrying the positive electrode active material layer was 52 mm × 680 mm) to obtain a positive electrode plate (not shown).

On the other hand, 92.5 g of the negative electrode active material particles 34 described above was added to 125 ml of NMP in which 7.5 g of the above-described binder 33 was dissolved, and kneaded to prepare a negative electrode paste 131P.
This negative electrode paste was applied to a strip-like copper copper foil CF (foil thickness of 15 μm) extending in the longitudinal direction and dried.

  Specifically, first, as shown in FIG. 4A, the negative electrode paste 131P is spaced apart by a width dimension of 45 mm including the center in the width direction DW on both main surfaces of the copper foil CF. Two strips were applied in a band shape with a width of 5 mm. After application, the negative electrode paste 131P was dried at 160 ° C. As a result, the negative electrode paste 131P becomes an edge of the uncompressed negative electrode active material layer including the edge binder 133E having a crystallinity of 40 to 50%.

Next, as shown in FIG. 4B, the dried negative electrode of the two strips of the negative electrode paste 131P including the edge binder 133E while being spaced by a width of 30 mm including the center in the width direction DW. Two strips with a width of 7.5 mm were applied adjacent to the inside of the paste. After the application, this negative electrode paste 131P was dried at 140 ° C. Thereby, this negative electrode paste 131P becomes an intermediate part of the uncompressed negative electrode active material layer including the intermediate part binder 133M having a crystallinity of 30 to 40%.
Further, the negative electrode paste 131P was applied in a strip shape with a width of 30 mm including the center in the width direction DW, adjacent to the inside sandwiched by two dried negative electrode pastes including the intermediate binder 133M. . After the application, this negative electrode paste 131P was dried at 120 ° C. As a result, the negative electrode paste 131P becomes the central portion of the uncompressed negative electrode active material layer including the central binder 133C having a crystallinity of 20 to 30%.

Further, the uncompressed negative electrode active material layer (edge portion, intermediate portion, center portion) is compressed by a roll press (not shown) to increase the density, and the copper foil CF is the same as the negative electrode active material layer 131 applied to the battery 101 described above. A negative electrode active material layer (not shown) having a central portion, an edge portion, and an intermediate portion was formed thereon. In this negative electrode active material layer, the center, edge, and intermediate portions in the width direction are 30.0, 7.5, and 5.0 mm, respectively, the negative electrode active material layer has a thickness of 40 μm, and a density of 1.2 g / cm ³ .
The produced negative electrode active material layer was cut into a shape of 55 mm × 740 mm together with the copper foil (among these, the size of the portion carrying the negative electrode active material layer was 55 mm × 720 mm) to obtain a negative electrode plate (not shown).

  The positive electrode plate and the negative electrode plate are laminated with a polyethylene separator (not shown) having a thickness of 30 μm interposed therebetween, and the positive electrode plate, the negative electrode plate and the separator are wound to form a wound type. A power generation element (not shown) was prepared. This power generation element was inserted into a 18650 type cylindrical case, and the above-described electrolytic solution 60 was injected therein, followed by sealing to manufacture a sample battery T2 (not shown).

For the sample battery T2, the same measurement as in the first embodiment was performed.
That is, of the sample battery T2, the battery capacity of a new (initial) battery that was just manufactured was measured. Specifically, after conditioning, constant current discharge was performed until the current value of 1 / 3C became 3.0 V, and the discharged battery capacity (“1 / 3C battery capacity”) was measured.
Subsequently, the battery capacity was measured by changing the current value to 20 C and performing constant current discharge. The high rate capacity retention rate was calculated from this battery capacity.

Further, a cycle test similar to that of the first embodiment was performed on the sample battery T2 on which the above test was performed.
Thereafter, the battery capacity of the sample battery T2 was measured in the same manner as described above. And the cycle capacity maintenance factor of sample battery T2 after a cycle test was computed.
Furthermore, the presence or absence of peeling in the vicinity of the edge portion of the subsequent positive electrode active material layer and negative electrode active material layer was confirmed in the same manner as in Embodiment 1.

Similarly to this sample battery T2, comparative batteries C3 and C4, which are comparative examples, were also manufactured, and the battery characteristics (high rate capacity maintenance rate and cycle capacity maintenance rate) of these batteries were measured in the same manner as the sample battery T2. did.
However, the comparative battery C3 includes a positive electrode active material layer containing a binder with a crystallinity of 40 to 50% and a negative electrode active material layer containing a binder with a crystallinity of 40 to 50%. And different from the sample battery T2.
Further, the comparative battery C4 includes a positive electrode active material layer containing a binder with a crystallinity of 20 to 30% and a negative electrode active material layer containing a binder with a crystallinity of 20 to 30%. And different from the sample battery T2.
In these sample battery T2 and comparative batteries C3 and C4, the weight ratio of the binder in the positive electrode active material layer and the negative electrode active material layer, the presence or absence of peeling near the edge of the positive electrode active material layer and the negative electrode active material layer, cycle capacity Table 2 shows the maintenance rate and the high rate capacity maintenance rate.

According to Table 2, regarding the presence / absence of peeling, the sample battery T2 and the comparative battery C3 were judged as “no peeling”. On the other hand, the comparison battery C4 was judged as “with peeling”. Further, the cycle capacity maintenance rates (88% and 78%) of the sample battery T2 and the comparative battery C3 are higher than the cycle capacity maintenance rates (62%) of the comparative battery C4.
In the sample battery T2 and the comparative battery C3, the crystallinity of the binders (edge binders 123E and 133E) at the edges of the positive electrode active material layer and the negative electrode active material layer is increased (40 to 50). %). By increasing the crystallinity of the edge binders 123E and 133E in this way, the viscosity of the edge binders 123E and 133E can be increased. Therefore, it is considered that the peel strength between the positive electrode active material layer and the aluminum foil and between the negative electrode active material layer and the copper foil can be increased, and the peel between them can be suppressed. For this reason, it is considered that in the sample battery T2 and the comparative battery C3, it was possible to suppress a decrease in cycle characteristics.

Furthermore, when comparing the sample battery T2 and the comparative battery C3, the high rate capacity maintenance rate (76%) of the sample battery T2 is higher than that of the comparative battery C3 (58%). From this, the drying temperature of the binder in the central portion in the width direction is higher than that of the battery in which the drying temperature of the entire positive electrode active material layer and the entire negative electrode active material layer is uniformly high (160 ° C.). It can be seen that the lower rate (120 ° C.) compared to the edge portion can increase the high rate capacity retention rate, that is, suppress the deterioration of the discharge rate characteristics.
This is because when the crystallinity of the binder is increased over the entire active material layer, and the viscosity of the binder is increased, lithium ions in the positive electrode active material layer and the negative electrode active material layer are spread over the entire surface of the active material layer. Movement is hindered, particularly affected by high rate discharges. On the other hand, it is considered that the influence is limited when the crystallinity of the binder is increased only in the edge portion (and the intermediate portion) of the active material layer as in the sample battery T2. .

  As described above, in the battery 101 using the above-described sample battery T2 and further the positive electrode active material layer and the negative electrode active material layer having the same configuration as the sample battery T2, the binder at the edge of the positive electrode active material layer and the negative electrode active material layer. Since the crystallinity of the layer is higher than that of the central portion, the peel strength between the active material layer and the current collector plate can be reliably increased at the edge portion compared to the central portion in the width direction. it can. Therefore, it is possible to obtain a battery having good battery characteristics while reliably suppressing peeling of the active material layer.

Next, a method for manufacturing the battery 101 according to the first modification will be described.
First, the power generation element 110 is manufactured in substantially the same manner as the sample battery T2. Specifically, first, the above-described positive electrode paste 121P was applied in two strips at intervals of a predetermined width dimension including the center in the width direction DW of both main surfaces of the aluminum foil 28. After the application, the positive electrode paste 121P on the aluminum foil 28 was dried at 160 ° C.
Next, the positive electrode paste 121P is adjacent to the inside sandwiched by the two dried positive electrode pastes including the edge binder 123E, and in a band shape with a predetermined width dimension including the center in the width direction DW. Two strips were applied. After the application, the positive electrode paste 121P on the aluminum foil 28 was dried at 140 ° C.
Further, a single strip of the positive electrode paste 121P was applied adjacent to the inner side sandwiched by two dried positive electrode pastes including the intermediate binder 123M. After the application, the positive electrode paste 121P on the aluminum foil 28 was dried at 120 ° C.
Thus, when the uncompressed positive electrode active material layer is viewed in the width direction DW, it includes the edge binder 123E, the intermediate binder 123M, the central binder 123C, and the intermediate portion. They were arranged on both main surfaces of the aluminum foil 28 in the order of the binder material 123M and the edge binder material 123E.
Such an uncompressed positive electrode active material layer is compressed by a roll press (not shown) to be densified to produce a positive electrode active material layer 121, and a belt-like positive electrode plate 120 is completed (see FIG. 2).

On the other hand, the negative electrode paste 131P described above was first applied in two strips at intervals of a predetermined width dimension including the center in the width direction DW of both main surfaces of the copper foil 38. After application, the negative electrode paste 131P on the copper foil 38 was dried at 160 ° C.
Next, the negative electrode paste 131P is adjacent to the inner side sandwiched by the two dried negative electrode pastes including the edge binder 133E, and in the form of a band with a predetermined width dimension including the center in the width direction DW. Two strips were applied. After the application, the negative electrode paste 131P on the copper foil 38 was dried at 140 ° C.
Further, a single strip of the negative electrode paste 131P was applied adjacent to the inner side sandwiched by two dried negative electrode pastes including the intermediate binder 133M. After application, the negative electrode paste 131P on the copper foil 38 was dried at 120 ° C.
Thus, the uncompressed negative electrode active material layer as viewed in the width direction DW includes the edge binder 133E, the intermediate binder 133M, the central binder 133C, the intermediate portion They were arranged on both main surfaces of the copper foil 38 in the order of those including the binder 133M and those including the edge binder 133E.
Such an uncompressed negative electrode active material layer is compressed and densified by a roll press (not shown) to produce a negative electrode active material layer 131, and a strip-shaped negative electrode plate 130 is completed (see FIG. 3).
A power generation element 110 is obtained by winding the separator 50 between the positive electrode plate 120 and the negative electrode plate 130 manufactured as described above.

  Thereafter, the positive electrode current collecting member 91 and the negative electrode current collecting member 92 are welded to the positive electrode plate 120 (aluminum foil 28) and the negative electrode plate 130 (copper foil 38), respectively, inserted into the battery case body 81, and the above-described electrolysis. After injecting the liquid 60, the battery case body 81 is sealed with a sealing lid 82 by welding. Thus, the battery 101 is completed (see FIG. 1).

(Modification 2)
Next, a battery 201 according to the second modification of the present invention will be described with reference to FIGS.
This modification 2 is different from the battery 1 of the first embodiment described above in that the molecular weight of the binder in the positive electrode active material layer and the negative electrode active material layer is increased in the order of the central part, the intermediate part, and the edge part. Other than that, the same applies.
Therefore, differences from the first embodiment will be mainly described, and description of similar parts will be omitted or simplified. In addition, about the same part, the same effect is produced. In addition, the same contents are described with the same numbers.

  A battery 201 according to the second modification is formed by winding a strip-shaped positive electrode plate 220, a strip-shaped negative electrode plate 230, and a strip-shaped separator 50 interposed between the positive electrode plate 220 and the negative electrode plate 230. The lithium ion secondary battery includes a power generation element 210 in which the separator 50 is impregnated with the electrolytic solution 60 (see FIG. 1).

  The power generation element 210 has a wound-type configuration in which the strip-like positive electrode plate 220 and the negative electrode plate 230 are wound into a flat shape via the strip-like separator 50, as in the battery 1 of the first embodiment ( (See FIG. 1). Among these, as shown in FIG. 2, the positive electrode plate 220 includes two aluminum foils 28 that are the same as those of the battery 1 and two strip-shaped positive electrode active members that are disposed on both main surfaces of the aluminum foil 28 and extend in the longitudinal direction DL. Material layers 221 and 221.

As in the first embodiment, the positive electrode active material layer 221 has different characteristics of the positive electrode active material layer 221 in the width direction DW perpendicular to the longitudinal direction DL. Specifically, as shown in FIG. 2, the width direction DW includes one central portion 221C, two edge portions 221E and 221E, and two intermediate portions 221M and 221M.
The central part 221C, the edge part 221E and the intermediate part 221M are all positive electrode active material particles 24 made of LiCoO ₂ , conductive material 25 made of carbon black, and a binder made of PVDF (the central part binder described below). Material 223C, edge binder 223E, intermediate binder 223M). However, in the central part 121C, the edge part 121E, and the intermediate part 121M, the size of the molecular weight of the binder (the central part binder 223C, the edge part binder 223E, and the middle part binder 223M) included therein is set. Each is different.

  Specifically, the central part 221C, the edge part 221E, and the intermediate part 221M include a central part binder 223C having a molecular weight of 280,000, an edge binder 223E having a molecular weight of 1,000,000, and an intermediate part having a molecular weight of 500,000. Each part binding material 223M is included. That is, the molecular weights of the binding materials 223C, 223M, and 223E are increased in the order of the center portion 221C, the intermediate portion 221M, and the edge portion 221E, that is, the binding materials 223C, 223M, and 223E are increased toward the edge portions 221E and 221E on both sides from the center portion 221C. is there. The greater the molecular weight of the binder, the higher the viscosity of the binder, so that the peel strength of the positive electrode active material layer 221 increases from the central portion 221C toward the edge portion 221E.

In addition, the negative electrode active material layer 231 has different characteristics of the negative electrode active material layer 231 in the width direction DW orthogonal to the longitudinal direction DL, as in the first embodiment. Specifically, as shown in FIG. 3, the width direction DW includes one central portion 231C, two edge portions 231E and 231E, and two intermediate portions 231M and 231M.
The central portion 231C, the edge portion 221E, and the intermediate portion 231M are all composed of negative electrode active material particles 34 of graphite powder and a binder made of PVDF (a central binder 233C and an edge binder 233E described below). , Intermediate binder 233M). However, in the central portion 231C, the edge portion 231E, and the intermediate portion 231M, the molecular weights of the binding materials (the central binding material 233C, the edge binding material 233E, and the intermediate binding material 233M) included therein are set. Each is different.

  Specifically, the central part 231C, the edge part 231E, and the intermediate part 231M include a central part binder 233C having a molecular weight of 280,000, an edge binder 233E having a molecular weight of 1,000,000, and an intermediate part having a molecular weight of 500,000. Each part binding material 233M is included. That is, like the positive electrode side, the molecular weight of the binders 233C, 233M, and 233E increases in the order of the central portion 231C, the intermediate portion 231M, and the edge portion 231E, that is, from the central portion 231C to the edge portions 231E and 231E on both sides. It gets bigger as you go. For this reason, the peel strength of the negative electrode active material layer 231 increases as it goes from the central portion 231C to the edge portion 231E, similarly to the positive electrode active material layer 221.

By the way, in order to evaluate the discharge rate characteristics, cycle characteristics, and presence / absence of delamination in the active material layer of the battery 201 as described in the first embodiment, the present inventors have the same positive electrode active material as that of the battery 201. A cylindrical sample battery T3 using a layer, a negative electrode active material layer, a separator, and an electrolytic solution was prepared.
Specifically, first, 85 g of the positive electrode active material particles 24 and 10 g of the conductive material 25 are charged into 125 ml of NMP in which 5 g of the above-described central binder 223C (molecular weight is 280,000) is dissolved. And knead | mixed so that it might become uniform, The 1st positive electrode paste (not shown) was produced.
Similarly, 85 g of the positive electrode active material particles 24 and 10 g of the conductive material 25 are respectively added to 125 ml of NMP in which 5 g of the above-described intermediate binder 223M (molecular weight is 500,000) is dissolved. The mixture was kneaded to produce a second positive electrode paste (not shown). Moreover, 85 g of the positive electrode active material particles 24 and 10 g of the conductive material 25 are respectively added to 125 ml of NMP in which 5 g of the edge binder 223E (molecular weight is 1,000,000) is dissolved, so that it becomes uniform. The mixture was kneaded to prepare a third positive electrode paste (not shown).

Using these first, second, and third positive electrode pastes, in the same manner as the sample battery T1 of the first embodiment, the same as the positive electrode active material layer 221 according to the battery 201 described above, on the aluminum foil, the center portion, the edge A positive electrode active material layer (not shown) having a part and an intermediate part was produced. In this positive electrode active material layer, the center, edge, and intermediate portions in the width direction are 30.0, 7.5, and 3.5 mm, respectively, the positive electrode active material layer has a thickness of 90 μm, and a density of 1.6 g / cm ³ .
Further, the produced positive electrode active material layer was cut into a shape of 52 mm × 720 mm together with the aluminum foil (of which the size of the portion carrying the positive electrode active material layer was 52 mm × 680 mm), and a positive electrode plate (not shown) did.

On the other hand, 92.5 g of the negative electrode active material particles 34 described above is added to 125 ml of NMP in which 5.5 g of the above-mentioned central binder 233C (molecular weight is 280,000) is dissolved, and the first kneaded. A negative electrode paste (not shown) was prepared.
Similarly, 92.5 g of the negative electrode active material particles 34 is put into 125 ml of NMP in which 5.5 g of the above-mentioned intermediate binder 233M (molecular weight is 500,000) is dissolved, and kneaded to obtain the second negative electrode paste. (Not shown) was prepared. Further, 92.5 g of the negative electrode active material particles 34 was put into 125 ml of NMP in which 5.5 g of the edge binder 233E (molecular weight is 1,000,000) was dissolved, and kneaded to obtain a third negative electrode paste (illustrated). Not).

Using these first, second, and third negative electrode pastes, the same as the negative electrode active material layer 231 according to the battery 201 described above, on the copper foil, in the same manner as the sample battery T1 of the first embodiment, the center portion, the edge A negative electrode active material layer (not shown) having a part and an intermediate part was produced. In this negative electrode active material layer, the center, edge, and intermediate portions in the width direction are 30.0, 7.5, and 5.0 mm, respectively, the negative electrode active material layer has a thickness of 40 μm, and a density of 1.2 g / cm ³ .
Further, the produced negative electrode active material layer was cut into a 55 mm × 740 mm shape together with the copper foil (of which the size of the portion carrying the negative electrode active material layer was 55 mm × 720 mm), and a negative electrode plate (not shown) did.

  The positive electrode plate and the negative electrode plate are laminated with a polyethylene separator (not shown) having a thickness of 30 μm interposed therebetween, and the positive electrode plate, the negative electrode plate and the separator are wound to form a wound type. A power generation element (not shown) was prepared. This power generation element was inserted into a 18650 type cylindrical case, and the above-described electrolytic solution 60 was injected therein, followed by sealing to manufacture a sample battery T3 (not shown).

For the sample battery T3, the same measurement as in the first embodiment was performed.
That is, of the sample battery T3, the battery capacity of a new (initial) battery that was just manufactured was measured. Specifically, after conditioning, constant current discharge was performed until the current value of 1 / 3C became 3.0 V, and the discharged battery capacity (“1 / 3C battery capacity”) was measured.
Subsequently, the battery capacity was measured by changing the current value to 20 C and performing constant current discharge. The high rate capacity retention rate was calculated from this battery capacity.

Further, a cycle test similar to that of the first embodiment was performed on the sample battery T3 subjected to the above-described test.
Thereafter, the battery capacity of the sample battery T3 was measured in the same manner as described above. And the cycle capacity maintenance factor of sample battery T3 after a cycle test was computed.
Furthermore, the presence or absence of peeling in the vicinity of the edge portion of the subsequent positive electrode active material layer and negative electrode active material layer was confirmed in the same manner as in Embodiment 1.

A comparative battery C5, which is a comparative example, was also manufactured in the same manner as the sample battery T3, and the battery characteristics (high rate capacity retention ratio and cycle capacity retention ratio) of these batteries were measured in the same manner as the sample battery T3.
However, the comparative battery C5 is different from the sample battery T3 in that the whole positive electrode active material layer and the whole negative electrode active material layer contain a binder having a molecular weight of 1,000,000.
In these sample battery T3 and comparative battery C5, the weight ratio of the binder in the positive electrode active material layer and the negative electrode active material layer, presence or absence of peeling near the edge of the positive electrode active material layer and the negative electrode active material layer, cycle capacity maintenance rate Table 3 shows the high rate capacity maintenance rate. In addition, the data of the comparative battery C4 is listed again in Table 3.

According to Table 3, regarding the presence / absence of peeling, the sample battery T3 and the comparative battery C5 were judged as “no peeling”. On the other hand, the comparison battery C4 was judged as “with peeling”. Further, the cycle capacity maintenance rates (86% and 77%) of the sample battery T3 and the comparative battery C5 are higher than the cycle capacity maintenance rates (62%) of the comparative battery C4.
In the sample battery T3 and the comparative battery C5, the molecular weights of the binders at the edges of the positive electrode active material layer and the negative electrode active material layer are each increased (one million). Thus, by increasing the molecular weight of the binder, the viscosity of the binder at the edge can be increased. Therefore, it is considered that the peel strength between the positive electrode active material layer and the aluminum foil and between the negative electrode active material layer and the copper foil can be increased, and the peel between them can be suppressed. For this reason, it is considered that in the sample battery T3 and the comparative battery C5, it was possible to suppress a decrease in cycle characteristics.

Furthermore, when comparing the sample battery T3 and the comparative battery C5, the high rate capacity retention rate (74%) of the sample battery T3 is higher than that of the comparative battery C5 (52%). From this, the molecular weight of the binder in the central portion in the width direction is less than that of the battery in which the molecular weight of the binder in the whole positive electrode active material layer and the whole negative electrode active material layer is uniformly large (1 million). It can be seen that a smaller (280,000) portion than the portion can increase the high rate capacity retention rate, that is, can suppress a decrease in discharge rate characteristics.
This is because when the molecular weight of the binder is increased over the entire active material layer to increase the viscosity of the binder, lithium ions in the positive electrode active material layer and the negative electrode active material layer are spread over the entire surface of the active material layer. Movement is hindered, particularly affected by high rate discharges. On the other hand, it is considered that the influence is limited when the molecular weight of the binder is increased only in the edge portion (and the intermediate portion) of the active material layer as in the sample battery T3.

  As described above, in the battery 201 using the above-described sample battery T3 and the positive electrode active material layer and the negative electrode active material layer having the same configuration as the sample battery T3, the binder at the edge of the positive electrode active material layer and the negative electrode active material layer. Therefore, the peel strength between the active material layer and the current collector plate can be reliably increased at the edge as compared with the central portion in the width direction. Therefore, it is possible to obtain a battery having good battery characteristics while reliably suppressing peeling of the active material layer.

  Note that the manufacturing method of the battery 201 is substantially the same as that of the battery 1 of the first embodiment, and a description thereof will be omitted.

(Embodiment 2)
A vehicle 300 according to the second embodiment is equipped with a battery pack 310 including a plurality of the above-described batteries 1, 101, 201. Specifically, as shown in FIG. 5, vehicle 300 is a hybrid vehicle that is driven by using engine 340, front motor 320, and rear motor 330 in combination. The vehicle 300 includes a vehicle body 390, an engine 340, a front motor 320, a rear motor 330, a cable 350, an inverter 360, and a battery pack 310 having a rectangular box shape. Among these, the battery pack 310 contains a plurality of the above-described batteries 1, 101, 201.

  Since the vehicle 300 according to the second embodiment is equipped with the batteries 1, 101, and 201 having good battery characteristics, the vehicle 200 having a power source with stable performance can be obtained.

(Embodiment 3)
Further, the hammer drill 400 of the third embodiment is equipped with the battery pack 410 including the batteries 1, 101, 201 described above, and the battery-equipped device having the battery pack 410 and the main body 420 as shown in FIG. It is. Note that the battery pack 410 is accommodated in the bottom portion 421 of the main body 420 of the hammer drill 400.

  Since the hammer drill 400 according to the third embodiment is equipped with the batteries 1, 101, 201 having good battery characteristics, it can be a battery-equipped device having a power source with stable performance.

In the above, the present invention has been described with reference to the first to third embodiments and the first and second modifications. However, the present invention is not limited to the above-described embodiments, and may be appropriately changed without departing from the gist thereof. Needless to say, this is applicable.
For example, in Embodiment 1, Variations 1 and 2, for both the peel strength between the positive electrode active material layer and the positive electrode current collector plate, and the peel strength between the negative electrode active material layer and the negative electrode current collector plate, A battery is shown in which both side edges are made higher than the central part in the width direction by making the characteristics of the active material layer different. However, the width direction can be changed by changing the characteristics of the active material layer with respect to the peel strength between the positive electrode active material layer and the positive electrode current collector plate or the peel strength between the negative electrode active material layer and the negative electrode current collector plate. It is good also as a battery which makes a both-sides edge part high compared with the center part. In such a battery, both the positive electrode side peel strength and the negative electrode side peel strength are superior to those of the battery in which both side edges are not higher than the central portion in the width direction ( It has been found that a battery having cycle characteristics and discharge rate characteristics can be obtained.

1,101,201 battery (lithium ion secondary battery)
10, 110, 210 Power generation element 20, 120, 220 Positive electrode plate 21, 121, 221 Positive electrode active material layer 21C, 121C, 221C Central portion 21E, 121E, 221E Edge portion (both side edge portions)
23, 33 Binder 24 Positive electrode active material particles 28 Aluminum foil (positive electrode current collector plate)
30, 130, 230 Negative electrode plates 31, 131, 231 Negative electrode active material layers 31C, 131C, 231C Central portions 31E, 131E, 231E Edge portions (both side edge portions)
34 Negative electrode active material particles 38 Copper foil (negative electrode current collector plate)
50 Separator 123C, 133C, 223C, 233C Central binder (binder)
123E, 133E, 223E, 233E Edge binder (binder)
123M, 133M, 223M, 233M Intermediate binder (binder)
300 Vehicle 400 Hammer drill (battery mounted equipment)
DL Longitudinal direction DW Width direction

Claims (6)

Conductive strip-shaped positive electrode current collector plate, and a strip-shaped positive electrode active material disposed on the positive electrode current collector plate, including positive electrode active material particles and a binder, and extending in the longitudinal direction of the positive electrode current collector plate A belt-like positive electrode plate having a layer;
Conductive strip-shaped negative electrode current collector plate, and strip-shaped negative electrode active material disposed on the negative electrode current collector plate, including negative electrode active material particles and a binder, and extending in the longitudinal direction of the negative electrode current collector plate A strip-shaped negative electrode plate having a layer and facing the positive electrode plate;
A lithium ion secondary battery comprising a power generation element formed by winding a separator interposed between the positive electrode plate and the negative electrode plate,
The width orthogonal to the longitudinal direction of at least one of the peel strength between the positive electrode active material layer and the positive electrode current collector plate and the peel strength between the negative electrode active material layer and the negative electrode current collector plate A lithium ion secondary battery in which both side edges are made higher than the center in the width direction by making the characteristics of the active material layer different in the direction. The lithium ion secondary battery according to claim 1,
Among the positive electrode active material layer and the negative electrode active material layer, for the peel strength, the active material layer having the side edges higher than the central portion in the width direction,
A lithium ion secondary battery in which the amount of the binder in the active material layer is increased at both side edges as compared to the central portion. The lithium ion secondary battery according to claim 1,
Among the positive electrode active material layer and the negative electrode active material layer, for the peel strength, the active material layer having the side edges higher than the central portion in the width direction,
The lithium ion secondary battery which makes the crystallinity of the said binder in the said active material layer high in the said both edge part compared with the said center part. The lithium ion secondary battery according to claim 1,
Among the positive electrode active material layer and the negative electrode active material layer, for the peel strength, the active material layer having the side edges higher than the central portion in the width direction,
The lithium ion secondary battery which makes the molecular weight of the said binder in the said active material layer large at the said both edge part compared with the said center part. A vehicle on which the lithium ion secondary battery according to any one of claims 1 to 4 is mounted and the electric energy stored in the lithium ion secondary battery is used for all or part of a power source. A battery-equipped device in which the lithium ion secondary battery according to any one of claims 1 to 4 is mounted and the electric energy stored in the lithium ion secondary battery is used for all or a part of a drive energy source. .

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