Patent Application
20210119263
The present disclosure relates to a nonaqueous electrolyte secondary battery.
PTL 1 has disclosed a battery in which in a cylindrical exterior package can made of iron or an iron alloy, an electrolyte solution and a winding electrode body formed by winding a positive electrode and a negative electrode with at least one separator interposed therebetween are received. It has been described that in this battery, two negative electrode leads are fitted to a winding start end and a winding finish end of the negative electrode located, respectively, at an inner circumference side and an outer circumference side of the electrode body, and those negative electrode leads are connected to a bottom portion of the exterior package can.
As is the winding electrode body described in PTL 1, when a negative electrode lead is disposed at an inner circumference side of an electrode body, since a positive electrode and a negative electrode are repeatedly wound at a radial-direction outer side, stress is generated in the electrode body due to an inner circumference-side negative electrode tab, and as a result, electrode plate deformation may occur in some cases.
Since the positive electrode is formed by cutting a long web having two surfaces on which positive electrode active material layers are formed, at a cut surface thereof, a core material of the positive electrode is exposed between the two active material layers provided on the front and the rear surfaces. Hence, when a winding start front end of the positive electrode is located at a portion at which the electrode plate deformation described above occurs, internal short circuit may occur between the core material of the positive electrode and the negative electrode in some cases. The internal short circuit described above may also occur by the electrode plate deformation generated due to a positive electrode lead.
An object of the present disclosure is to provide a nonaqueous electrolyte secondary battery which can suppress, in a winding type electrode body, the generation of internal short circuit between a negative electrode plate and a winding start front end of a positive electrode plate due to electrode plate deformation at positions corresponding to a positive electrode lead and a negative electrode lead.
A nonaqueous electrolyte secondary battery according to the present disclosure comprises: an electrode body in which a positive electrode plate having a positive electrode lead and a negative electrode plate having a negative electrode lead are wound in a spiral shape with at least one separator interposed therebetween. The positive electrode lead is connected to the positive electrode plate at a radial-direction intermediate position of the electrode body, and the negative electrode lead is connected to the negative electrode plate at a winding start end thereof. In a radial-direction cross-section of the electrode body, when a region defined by the outermost circumference of the negative electrode plate and two straight lines extending from a winding central axis of the electrode body through two points which are apart outside from two circumference-direction ends of the negative electrode lead by an angle of 10° with respect to the winding central axis is regarded as a first region, and when a region defined by two straight lines in contact with two circumference-direction ends of the positive electrode lead each drawn in parallel to a straight line between a circumference-direction center of the positive electrode lead and the winding central axis, the outermost circumference of the negative electrode plate, and the innermost circumference thereof is regarded as a second region, a winding start front end of the positive electrode plate is disposed in a region other than the first and the second regions.
According to the nonaqueous electrolyte secondary battery of the present disclosure, in the electrode body, in the region other than the first region in which the electrode plate deformation may occur due to the negative electrode lead and the second region in which the electrode plate deformation may occur due to the positive electrode lead, since the winding start front end of the positive electrode plate is disposed, the internal short circuit caused by the electrode plate deformation due to the positive electrode lead and the negative electrode lead can be effectively suppressed.
Hereinafter, an embodiment according to the present invention will be described in detail with reference to the attached drawings. In the following description, particular shapes, materials, numeral values, directions, and the like are described by way of example to facilitate the understanding of the present invention, and those may be appropriately changed in accordance with the application, the object, the specification, and the like. In addition, the following term “approximately” is used to indicate, for example, besides “exactly the same”, “substantially the same”. Furthermore, in the following description, when embodiments, modified examples, and the like are included, the use of characteristic portions thereof in appropriate combination has been taken into consideration from the beginning.
The positive electrode plate 11 includes a belt-shaped positive electrode collector 30 (see
The negative electrode plate 12 includes a belt-shaped negative electrode collector 35 (see
The positive electrode lead 19 and the negative electrode leads 20a and 20b are each a belt-shaped electrically conductive member having a thickness larger than that of the collector. The thickness of the lead is, for example, 3 to 30 times the thickness of the collector and is, in general, 50 to 500 μm. Although a material forming each lead is not particularly limited, the positive electrode lead 19 is preferably formed of a metal containing aluminum as a primary component, and the negative electrode leads 20a and 20b are each preferably formed of a metal containing nickel or copper as a primary component. In addition, the number of the leads, the arrangement thereof, and the like are not particularly limited. For example, the negative electrode lead may only be fitted to a winding start end of the negative electrode plate 12.
In the example shown in
As described above, the electrode body 14 has a winding structure in which the positive electrode plate 11 and the negative electrode plate 12 are wound in a spiral shape with the separators 13 interposed therebetween. The positive electrode plate 11, the negative electrode plate 12, and the separators 13 are each formed to have a belt shape and are spirally wound so as to be alternately laminated to each other in the radial direction β of the electrode body 14. In the electrode body 14, the longitudinal direction of each electrode is a winding direction γ, and the width direction of each electrode is an axial direction α. In this embodiment, in a winding core of the electrode body 14, a space 28 is formed. The electrode body 14 is wound in a spiral shape around a winding central axis 29 extending in the axis direction at the center of the space 28. In this case, the winding central axis 29 is a central axis extending in the axis direction at a radial-direction central position of the space 28 and is a winding central axis of the electrode body 14.
The case main body 15 is a metal-made bottom-closed cylindrical container. Between the case main body 15 and the sealing body 16, a gasket 27 is provided, so that the air-tightness in the battery case is secured. The case main body 15 has a protruding portion 21 which is formed, for example, by pressing a side surface portion from the outside and which supports the sealing body 16. The protruding portion 21 is preferably formed to have a ring shape along the circumference direction of the case main body 15, and the upper surface of the protruding portion 21 supports the sealing body 16.
The sealing body 16 includes the filter 22, a lower valve 23, an insulating member 24, an upper valve 25, and the cap 26, which are laminated sequentially from an electrode body 14 side. The individual members forming the sealing body 16 each have, for example, a circular shape or a ring shape and are electrically connected to each other except for the insulating member 24. The lower valve 23 and the upper valve 25 are connected to each other at central portions thereof, and between the peripheral portions thereof, the insulating member 24 is provided. When the internal pressure of the battery is increased by abnormal heat generation, for example, the lower valve 23 is fractured, and as a result, the upper valve 25 is swelled to a cap 26 side and is separated from the lower valve 23, so that the electrical connection between the above two valves is disconnected. When the internal pressure is further increased, the upper valve 25 is fractured, and gases are exhausted from an opening portion 26a of the cap 26.
Hereinafter, with reference to
As shown in
The positive electrode plate 11 includes the belt-shaped positive electrode collector 30 and the positive electrode active material layer 31 formed on the collector described above. In this embodiment, the positive electrode active material layers 31 are formed on two surfaces of the positive electrode collector 30. For the positive electrode collector 30, for example, foil of a metal, such as aluminum, or a film having a surface layer formed of the metal mentioned above may be used. A preferable positive electrode collector 30 is foil of a metal containing aluminum or an aluminum alloy as a primary component. The thickness of the positive electrode collector 30 is, for example, 10 to 30 μm.
The positive electrode active material layers 31 are preferably formed over the entire two surfaces of the positive electrode collector 30 except for an un-covered portion 32 which will be described later. The positive electrode active material layer 31 preferably contains a positive electrode active material, an electrically conductive agent, and a binder. The positive electrode plate 11 is formed by applying a positive electrode mixture slurry containing the positive electrode active material, the electrically conductive agent, the binder, and a solvent, such as N-methyl-2-pyrrolidone (NMP) on the two surfaces of the positive electrode collector 30, followed by drying and rolling.
As the positive electrode active material, for example, there may be mentioned a lithium transition metal oxide containing a transition metal element, such as Co, Mn, or Ni. Although the lithium transition metal oxide is not particularly limited, a composite oxide represented by a general formula of Li1+xMO2 (in the formula, −0.2<x≤0.2, and M includes at least one of Ni, Co, Mn, and Al) is preferable.
As an example of the electrically conductive agent described above, for example, there may be mentioned a carbon material, such as carbon black (CB), acetylene black (AB), Ketjen black, or graphite. As an example of the binder described above, for example, there may be mentioned a fluorine-based resin, such as a polytetrafluoroethylene (PTFE) or a poly(vinylidene fluoride) (PVdF), a polyacrylonitrile (PAN), a polyimide (PI), an acryl-based resin, or a polyolefin-based resin. In addition, those resins mentioned above each may be used together with a carboxymethyl cellulose (CMC) or its salt, a polyethylene oxide (PEO), or the like. Those resins may be used alone, or at least two types thereof may be used in combination.
The positive electrode plate 11 has at least one un-covered portion 32 at which the surface of the metal forming the positive electrode collector 30 is exposed. The un-covered portion 32 is a portion to which the positive electrode lead 19 is connected and is a portion at which the surface of the positive electrode collector 30 is not covered with the positive electrode active material layer 31. The un-covered portion 32 is formed to have a width larger than that of the positive electrode lead 19. The un-covered portion 32 is preferably provided at two surfaces of the positive electrode plate 11 so as to be overlapped with each other in the thickness direction of the positive electrode plate 11. The positive electrode lead 19 is bonded to the un-covered portion 32, for example, by ultrasonic wave welding.
In the example shown in
The negative electrode plate 12 includes the belt-shaped negative electrode collector 35 and the negative electrode active material layer 36 formed on the negative electrode collector described above. In this embodiment, the negative electrode active material layers 36 are formed on two surfaces of the negative electrode collector 35. For the negative electrode collector 35, for example, foil of a metal, such as copper, or a film having a surface layer formed of the metal mentioned above is used. The thickness of the negative electrode collector 35 is, for example, 5 to 30 μm.
The negative electrode active material layers 36 are preferably formed on the entire two surfaces of the negative electrode collector 35 except for un-covered portions 37a and 37b. The negative electrode active material layer 36 preferably contains a negative electrode active material and a binder. The negative electrode plate 12 is formed by applying a negative electrode mixture slurry containing the negative electrode active material, the binder, water, and the like on the two surfaces of the negative electrode collector 35, followed by drying and rolling.
The negative electrode active material is not particularly limited as long as being capable of reversibly occluding and releasing lithium ions, and for example, there may be used a carbon material, such as natural graphite or artificial graphite, a metal, such as Si or Sn, forming an alloy with lithium, or an alloy or a composite oxide, each of which contains the material mentioned above. For the binder contained in the negative electrode active material layer 36, for example, a resin similar to that used in the case of the positive electrode plate 11 may be used. When the negative electrode mixture slurry is prepared using an aqueous solvent, for example, a styrene-butadiene rubber (SBR), a CMC or its salt, a polyacrylic acid or its salt, or a poly(vinyl alcohol) may be used. Those compounds may be used alone, or at least two types thereof may be used in combination.
The negative electrode plate 12 has at least one un-covered portion 37a and at least one un-covered portion 37b at each of which the surface of the metal forming the negative electrode collector 35 is exposed. The un-covered portions 37a and 37b are portions to which the negative electrode leads 20a and 20b are connected, respectively, and are portions at each of which the surface of the negative electrode collector 35 is not covered with the negative electrode active material layer 36. The un-covered portions 37a and 37b each have an approximately rectangular shape in front view extending long in the width direction of the negative electrode plate 12 and are formed to have widths larger than those of the negative electrode leads 20a and 20b, respectively. The un-covered portions 37a are preferably formed at two surfaces of the negative electrode plate 12 so as to be overlapped with each other in the thickness direction of the negative electrode plate 12. The same configuration as described above may also be applied to the un-covered portion 37b.
In this embodiment, the negative electrode lead 20a is bonded to a surface of the negative electrode collector 35 facing an inner circumference side by ultrasonic wave welding or the like. One end portion (upper end) of the negative electrode lead 20a is disposed on the un-covered portion 37a, and the other end portion thereof is extended to a lower side from the lower end of the un-covered portion 37a.
In the example shown in
For the separator 13, a porous sheet having an ion permeability and an insulating property is used. As a concrete example of the porous sheet, for example, a fine pore thin film, a woven cloth, or a non-woven cloth may be mentioned. As a material of the separator 13, an olefin resin, such as a polyethylene or a polypropylene, is preferable. The thickness of the separator 13 is, for example, 10 to 50 μm. In accordance with the increase in capacity and power of the battery, the thickness of the separator 13 tends to be decreased. The separator 13 has, for example, a melting point of approximately 130° C. to 180° C.
The positive electrode plate 11, the negative electrode plate 12, and the separators 13, each of which has the structure described above, are wound in a spiral shape, so that the electrode body 14 is formed. The outermost circumference of the electrode body 14 is formed of the separator 13, and a winding finish end of the separator 13 is fixed by an insulating tape not shown. Accordingly, winding looseness of the electrode body 14 is not only prevented, but an outermost circumference side separator 13 or the like can also be prevented from being turned up when the electrode body 14 is inserted in the case main body 15. In addition, the insulating tape is preferably adhered to the outer circumference of the electrode body 14 by approximately one turn.
As shown in
The negative electrode lead 20a provided at the winding start end of the negative electrode plate 12 has a larger plate thickness and a higher rigidity than those of the negative electrode collector 35, the negative electrode lead 20a is relatively not easily bent into an arc shape. Hence, in the electrode body 14, by the influence of the negative electrode lead 20a which is not fully bent into an arc shape, in a region corresponding to the radial-direction outer side of the negative electrode lead 20a, the internal pressure (or internal stress) tends to be increased. As a result, when charge/discharge of the nonaqueous electrolyte secondary battery 10 is repeatedly performed, since the electrode body 14 is expanded and contracted, the electrode plate deformation may be generated in the positive electrode plate 11 and/or the negative electrode plate 12 in some cases.
Since the positive electrode plate 11 is formed by cutting a long web having a front and a rear surface on each of which the positive electrode active material layer 31 is formed, at a winding start front end 11a of the positive electrode plate 11, the metal-made positive electrode collector 30 forming the positive electrode plate 11 is exposed between the positive electrode active material layers 31 provided on the front and the rear surfaces of the positive electrode collector 30. Hence, when the winding start front end 11a of the positive electrode plate 11 is located at the portion at which the electrode plate deformation occurs as described above, the positive electrode collector exposed at the winding start front end 11a and the negative electrode plate 12 may break the separator 13, so that internal short circuit may occur in some cases. This internal short circuit may also occur by the electrode plate deformation generated due to the positive electrode lead 19. In order to prevent or suppress the internal short circuit due to the electrode plate deformation as described above, in the positional relationship between the negative electrode lead 20a and the positive electrode lead 19, the winding start front end 11a of the positive electrode plate 11 is preferably disposed at a position at which the electrode plate deformation is not likely to occur. Next, with reference to
As shown in
Next, the positive electrode lead 19 will be discussed. In this embodiment, a region defined by two straight lines 42a and 42b in contact with the two ends of the positive electrode lead 19 in the circumference direction each drawn in parallel to a straight line 41 between the center of the positive electrode lead 19 in the circumference direction and the winding central axis 29, the outermost circumference of the negative electrode plate 12, and the innermost circumference thereof is regarded as the second region B. In
As has thus been described, in the radial-direction cross-section of the electrode body 14, the winding start front end 11a of the positive electrode plate 11 is preferably disposed in the region other than the first region A and the second region B. Accordingly, the internal short circuit between the winding start front end 11a of the positive electrode plate 11 and the negative electrode plate 12 due to the positive electrode lead 19 or the negative electrode lead 20a can be effectively suppressed.
The present inventors of the present disclosure formed 12 types of electrode bodies shown in
[Formation of Positive Electrode Plate]
First, 100 parts by mass of a lithium transition metal oxide represented by LiNi0.88Co0.09Al0.03O2 as a positive electrode active material, 1 part by mass of acetylene black, and 0.9 parts by mass of poly(vinylidene fluoride) as a binder were mixed together, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was further added, so that a positive electrode mixture slurry was prepared. Next, this positive electrode mixture slurry was applied on two surfaces of a positive electrode collector formed from aluminum foil, and the coating films thus obtained were dried. After the collector on which the coating films were formed was rolled by rollers and was then cut into a predetermined electrode size, an aluminum-made positive electrode lead was ultrasonic welded to an un-covered portion provided at a longitudinal-direction central portion, so that a positive electrode plate was formed.
[Formation of Negative Electrode Plate]
First, 95 parts by mass of a graphite powder, 5 parts by mass of a silicon oxide, 1 part by mass of a carboxymethyl cellulose (CMC) as a thickening agent, and 1 part by mass of a styrene-butadiene rubber (SBR) as a binder were mixed together, and an appropriate amount of water was further added, so that a negative electrode mixture slurry was prepared. Next, this negative electrode mixture slurry was applied on two surfaces of a negative electrode collector formed from copper foil, and the coating films thus obtained were dried. After the collector on which the coating films were formed was rolled by rollers and was then cut into a predetermined electrode size, negative electrode leads were ultrasonic welded to un-covered portions provided at two longitudinal-direction ends, so that a negative electrode plate was prepared.
[Formation of Electrode Body]
The positive electrode plate and the negative electrode plate were wound with the separators each formed from a polyethylene-made porous film interposed therebetween, and an insulating tape was adhered to the outermost circumference portion, so that the electrode body of each of Experimental Examples 1 to 12 shown in
[Preparation of Nonaqueous Electrolyte]
To 100 parts by mass of a mixed solvent containing ethylene carbonate (EC) and dimethyl methyl carbonate (DMC) mixed at a volume ratio of 1:3, 5 parts by mass of vinylene carbonate (VC) was added, and LiPF6 was then dissolved to have a concentration of 1.5 mol/L, so that a nonaqueous electrolyte solution was prepared.
[Formation of Secondary Battery]
After insulating plates were disposed on the top and the bottom of the electrode body described above, the negative electrode leads of the electrode body were ultrasonic welded to a bottom portion of a case main body, and in addition, after the positive electrode lead of the electrode body was ultrasonic welded to a filter of a sealing body, the electrode body was received in the case main body. Subsequently, the nonaqueous electrolyte solution was charged in the case main body. Finally, an opening portion of the case main body was sealed by the sealing body, so that a nonaqueous electrolyte secondary battery was formed. The capacity of this secondary battery was 4,600 mAh.
[Charge/Discharge Conditions]
In an environment at 25° C., after a constant current charge at 1,380 mA (0.3 hour rate) was performed to a voltage of 4.2 V, a charge/discharge cycle in which a constant voltage charge at 4.2 V to a finish current of 92 mA, a rest for 20 minutes, a constant current discharge at a discharge current of 4,600 mA (one hour rare), and a rest for 20 minutes were performed in this order was repeatedly performed 500 cycles.
[Evaluation]
After the charge/discharge cycle test described above was performed, the position at which the electrode plate deformation of the electrode body occurred was investigated. As a result, in all Experimental Examples 1 to 12, it was confirmed that the electrode plate deformation occurred in at least one region of the first region A and the second region B. Hence, it could be confirmed that when the winding start front end of the positive electrode plate was disposed in a region other than the first and the second regions, the internal short circuit due to the electrode plate deformation could be suppressed.
In addition, the nonaqueous electrolyte secondary battery of the present disclosure is not limited to the above embodiment and the modified examples thereof and, of course, may be variously changed and/or improved within the content described in claims of the present disclosure and within the range equivalent thereto.
10 nonaqueous electrolyte secondary battery, 11 positive electrode plate, 11a winding start front end, 12 negative electrode plate, 12a electrode plate deformation portion, 13 separator, 14 electrode body, 15 case main body, 16 sealing body, 17 and 18 insulating plate, 19 positive electrode lead, 20a and 20b negative electrode lead, 21 protruding portion, 22 filter, 23 lower valve, 24 insulating member, 25 upper valve, 26 cap, 27 gasket, 28 space, 29 winding central axis, 30 positive electrode collector, 31 positive electrode active material layer, 32, 37a, and 37b un-covered portion, 35 negative electrode collector, 36 negative electrode active material layer, 40a, 40b, 41, 42a, and 42b straight line, A first region, B second region.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-058999 | Mar 2017 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/010114 | 3/15/2018 | WO | 00 |
