JP6733338B2 - Secondary battery - Google Patents

Description

The present disclosure relates to secondary batteries.

Japanese Patent Laying-Open No. 2015-072828 (Patent Document 1) discloses a secondary battery in which short-circuiting tabs are arranged at both ends in the stacking direction of the stacked electrode group in the battery case. In Patent Document 1, the short-circuit tab is said to be thicker than the current collector foil of the electrode plate that constitutes the laminated electrode group.

JP, 2005-072828, A

Generally, a positive electrode plate and a negative electrode plate (hereinafter sometimes collectively referred to as “electrode plate”) of a secondary battery expands and contracts with charge and discharge. Therefore, when charging and discharging are repeated, undulation (waviness) occurs in the out-of-plane direction on the electrode plate. When undulations occur on the electrode plate, the distance between the electrodes varies. This results in a decrease in battery performance.

The "laminated electrode group" is an electrode group configured by alternately stacking positive electrode plates and negative electrode plates. In the laminated electrode group, it may be possible to restrain the laminated electrode group in order to suppress the undulation of the electrode plate. For example, the restraint member arranged outside the battery case presses the laminated electrode group via the side wall of the battery case. In the stacking direction of the stacked electrode group, the stacked electrode group is constrained by being pressed from both ends toward the center.

In order to restrain the laminated electrode group, a restraint member and a restraint structure are required inside and outside the battery case. By adding the restraint member and the restraint structure, the volume energy density (energy per unit volume) of the battery pack is lowered.

Therefore, an object of the present disclosure is to suppress the undulation of the electrode plate due to charge/discharge without constraining the laminated electrode group.

The secondary battery of the present disclosure includes a battery case, a stacked electrode group housed in the battery case, and an electrolyte housed in the battery case.
The laminated electrode group includes a plurality of positive electrode plates, a plurality of separators, and a plurality of negative electrode plates. In the laminated electrode group, the positive electrode plates and the negative electrode plates are alternately laminated. The separator is interposed between the positive electrode plate and the negative electrode plate. The positive electrode plate and the negative electrode plate each include a collector foil and an active material layer. The active material layer is formed on the surface of the current collector foil.
In the stacking direction of the stacked electrode group, the current collector foil included in the positive electrode plate or the negative electrode plate that is the outermost layer is thicker than the current collector foils included in the positive electrode plate and the negative electrode plate that are not the outermost layers.

According to the new finding of the present disclosure, in the laminated electrode group, the waviness of the electrode plate is likely to occur from the electrode plates (that is, the outermost electrode plates) arranged at both ends in the stacking direction. It is presumed that this is because the electrode plate that is not the outermost layer is constrained from both sides by the adjacent electrode plates, while the electrode plate that is the outermost layer is not constrained on one side. The undulations generated at both ends of the laminated electrode group propagate toward the inside of the laminated electrode group.

As described above, in the secondary battery of the present disclosure, the collector foil of the outermost electrode plate is thicker than the collector foil of the non-outermost electrode plate. By increasing the rigidity of the electrode plate that is the outermost layer, the generation of undulations is suppressed in the electrode plate that is the outermost layer. Thereby, the generation of undulations can be suppressed even in the electrode plate that is not the outermost layer.

Therefore, according to the secondary battery of the present disclosure, simplification or substantial elimination of the restraint member and restraint structure is expected. This is expected to improve the volumetric energy density of the battery pack.

Note that, for example, when a thick current collecting tab or the like is arranged on the outer side of the outermost layer of the laminated electrode group as in Patent Document 1, it is possible to reduce the degree of waviness but suppress the occurrence of waviness itself. Can not. Therefore, in this case, it is considered necessary to restrain the laminated electrode group to some extent.

1 is a schematic diagram showing an example of a configuration of a secondary battery according to an embodiment of the present disclosure. It is a schematic sectional drawing which shows an example of a structure of the laminated electrode group which concerns on embodiment of this indication.

Hereinafter, an embodiment of the present disclosure (hereinafter referred to as “the present embodiment”) will be described. However, the following description does not limit the invention of the present disclosure.

<Secondary battery>
FIG. 1 is a schematic diagram showing an example of the configuration of the secondary battery according to the present embodiment. The secondary battery 1000 is, for example, a vehicle-mounted battery. The secondary battery 1000 may be a lithium-ion secondary battery or a nickel-hydrogen secondary battery. Here, a lithium ion secondary battery will be described as an example.

<< battery case >>
The secondary battery 1000 includes a battery case 200. The shape of the battery case 200 is rectangular (flat rectangular parallelepiped). The material of the battery case 200 may be, for example, an aluminum (Al) alloy or the like. The battery case 200 includes a case body 210 and a lid 220. The lid 220 is provided with a positive electrode terminal 221 and a negative electrode terminal 222. The battery case 200 may be provided with a safety valve, a liquid injection hole, a current cutoff mechanism, and the like. The battery case 200 may be, for example, a bag-shaped case made of an aluminum laminate film as long as it can store the laminated electrode group 100 and an electrolyte (not shown).

<<Stacked electrode group>>
The secondary battery 1000 includes the stacked electrode group 100. The stacked electrode group 100 is housed in the battery case 200. The stacked electrode group 100 is electrically connected to the positive electrode terminal 221 and the negative electrode terminal 222. The stacked electrode group 100 is not pressed by the side wall of the battery case 200. That is, the laminated electrode group 100 is not constrained.

FIG. 2 is a schematic cross-sectional view showing an example of the configuration of the laminated electrode group according to this embodiment. In FIG. 2, a cross section parallel to the stacking direction is shown. The laminated electrode group 100 includes a plurality of positive electrode plates 10, separators (not shown), and negative electrode plates 20, respectively. In the laminated electrode group 100, the positive electrode plates 10 and the negative electrode plates 20 are alternately laminated. Although not shown, the separator is interposed between the positive electrode plate 10 and the negative electrode plate 20. The positive electrode plate 10, the separator, and the negative electrode plate 20 may be bonded to each other with, for example, polyethylene oxide (PEO), polyvinylidene fluoride (PVdF), or the like.

In the laminated electrode group 100, the number of laminated electrode plates is not particularly limited. In the laminated electrode group 100, the number of the positive electrode plates 10 or the negative electrode plates 20 may be, for example, 10 to 100, 30 to 80, or 65 to 72. Good.

(Separator)
The plane shape of the separator is, for example, a rectangular shape. The planar shape means a shape when the separator and the electrode plate are observed from the stacking direction. The separator is an insulating porous film. The separator has a thickness of 5 to 30 μm, for example. The separator may be made of polyolefin such as polyethylene (PE) or polypropylene (PP), for example. The separator may be a single porous membrane. For example, the separator may be a PE porous membrane. The separator may include a plurality of porous membranes. For example, the separator may be formed by stacking a PE porous film and a PP porous film. A heat resistant layer containing inorganic particles (e.g., alumina) may be formed on the surface of the separator.

(Positive electrode plate and negative electrode plate)
The planar shapes of the positive electrode plate 10 and the negative electrode plate 20 are, for example, rectangular shapes. The positive electrode plate 10 and the negative electrode plate 20 each include a collector foil and an active material layer.

The positive electrode plate 10 includes a positive electrode current collector foil 11 and a positive electrode active material layer 12. The positive electrode current collector foil 11 may be, for example, an Al foil or the like. The positive electrode current collector foil 11 (except for the one included in the outermost layer 30) has a thickness of, for example, about 5 to 15 μm. The positive electrode active material layer 12 is formed on the surface (both front and back surfaces) of the positive electrode current collector foil 11. The positive electrode active material layer 12 is not formed on the end portion in the width direction of the positive electrode plate 10, and the positive electrode current collector foil 11 is exposed. The exposed positive electrode current collector foil 11 is connected to the positive electrode terminal 221 (see FIG. 1).

The positive electrode active material layer 12 has a thickness of, for example, about 10 to 100 μm. The positive electrode active material layer 12 contains a positive electrode active material, a conductive material, a binder, and the like. The positive electrode active material may be, for example, a lithium-containing metal oxide such as LiCoO ₂ or Li(NiCoMn)O ₂ . The conductive material may be carbon black such as acetylene black (AB) and furnace black. The binder may be, for example, PVdF, polytetrafluoroethylene (PTFE), or the like.

The negative electrode plate 20 includes a negative electrode current collector foil 21 and a negative electrode active material layer 22. The negative electrode current collector foil 21 may be, for example, a copper (Cu) foil or the like. The negative electrode current collector foil 21 (except the one included in the outermost layer 30) has a thickness of, for example, about 5 to 15 μm. The negative electrode active material layer 22 is formed on the surface (both front and back surfaces) of the negative electrode current collector foil 21. The area of the negative electrode active material layer 22 is larger than the area of the positive electrode active material layer 12 and smaller than the area of the separator. The negative electrode active material layer 22 is not formed on the end portion in the width direction of the negative electrode plate 20, and the negative electrode current collector foil 21 is exposed. The exposed negative electrode current collector foil 21 is connected to the negative electrode terminal 222 (see FIG. 1).

The negative electrode active material layer 22 has a thickness of, for example, about 10 to 100 μm. The negative electrode active material layer 22 contains a negative electrode active material, a binder, and the like. The negative electrode active material may be, for example, graphite or silicon. The binder may be, for example, carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR).

(Outermost layer)
In the present embodiment, the electrode plates arranged at both ends of the stacked electrode group 100 in the stacking direction are referred to as “outermost electrode plates”, and the other electrode plates are referred to as “non-outermost electrode plates”. To be done. FIG. 2 shows, as an example, a mode in which the electrode plate that is the outermost layer 30 is a negative electrode plate. However, the outermost electrode plate may be a positive electrode plate. Further, in FIG. 2, the negative electrode plate which is the outermost layer 30 includes the active material layer 32 on only one surface. However, the electrode plate which is the outermost layer 30 may include the active material layers 32 on both sides.

In the present embodiment, the current collector foil 31 included in the electrode plate (the negative electrode plate in FIG. 2) that is the outermost layer 30 is thicker than the current collector foil included in the electrode plate that is not the outermost layer 30. As a result, the generation of waviness is suppressed in the electrode plate that is the outermost layer 30. Since the generation of undulations is suppressed in the electrode plate that is the outermost layer 30, the undulations of the electrode plate that is not the outermost layer can also be suppressed.

Here, for convenience, the thickness of the current collector foil included in the electrode plate that is not the outermost layer 30 is “first thickness”, and the thickness of the current collector foil 31 included in the electrode plate that is the outermost layer 30 is “second thickness”. "Thickness". For example, when the first thickness is 5 to 15 μm, the second thickness is preferably 20 μm or more (more preferably 50 μm or more, even more preferably 100 μm or more, most preferably 200 μm or more). The thicker the second thickness is, the higher the effect of suppressing the waviness is expected.

On the other hand, if the second thickness is excessively large, the volume energy density of the battery may be reduced. Therefore, for example, when the first thickness is 5 to 15 μm, the second thickness is, for example, 1 mm or less (preferably 500 μm or less).

"Electrolytes"
The secondary battery 1000 includes an electrolyte. The electrolyte is housed in the battery case 200. In the present embodiment, the electrolyte may be a liquid electrolyte (electrolyte solution) or a gel electrolyte. Here, a liquid electrolyte is described as an example.

The liquid electrolyte contains an aprotic solvent and a supporting salt. The aprotic solvent is, for example, a mixed solvent of cyclic carbonate and chain carbonate. Examples of the cyclic carbonate include ethylene carbonate (EC) and propylene carbonate (PC). Examples of chain carbonates include dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), and the like. The mixing ratio of the cyclic carbonate and the chain carbonate may be, for example, “cyclic carbonate:chain carbonate=1:9 to 5:5” in volume ratio.

The supporting salt is dissolved in an aprotic solvent. Examples of the supporting salt include lithium salts such as LiPF ₆ , LiBF ₄ , and Li[N(FSO ₂ ) ₂ ]. The concentration of the supporting salt is, for example, about 0.5 to 2 mol/L (typically 0.8 to 1.5 mol/L).

Hereinafter, embodiments of the present disclosure will be described. However, the following examples do not limit the invention of the present disclosure.

<Manufacture of secondary battery>
Secondary batteries (lithium ion secondary batteries) according to Examples and Comparative Examples were manufactured as follows.

<Comparative example>
1. Preparation of Positive Electrode Plate The following materials were prepared.
Positive electrode active material: ternary positive electrode active material [Li(NiCoMn)O ₂ ]
Conductive material: AB
Binder: PVdF
Solvent: N-methyl-2-pyrrolidone (NMP)
Positive electrode current collector foil: Al foil (thickness: 12 μm)

A positive electrode paste was prepared by kneading a positive electrode active material, a conductive material, a binder and a solvent in a predetermined composition. The positive electrode paste was applied to the surface of the positive electrode current collector foil and dried. As a result, a positive electrode active material layer was formed on the surface of the positive electrode current collector foil. The positive electrode active material layer and the positive electrode current collector foil were rolled. The positive electrode active material layer and the positive electrode current collector foil were cut into predetermined dimensions. In this way, a plurality of rectangular positive electrode plates were prepared.

2. Preparation of Negative Electrode Plate The following materials were prepared.
Negative electrode active material: Graphite binder: CMC and SBR
Solvent: Water Negative electrode current collector foil: Cu foil (thickness: 10 μm)

A negative electrode paste was prepared by kneading the negative electrode active material, the binder, and the solvent in a predetermined composition. The negative electrode paste was applied to the surface of the negative electrode current collector foil and dried. As a result, a negative electrode active material layer was formed on the surface of the negative electrode current collector foil. The negative electrode active material layer and the negative electrode current collector foil were rolled. The negative electrode active material layer and the negative electrode current collector foil were cut into predetermined dimensions. In this way, a plurality of rectangular negative electrode plates were prepared.

3. Preparation of Electrolyte EC, EMC and DMC were mixed in a volume ratio of “EC:EMC:DMC=30:40:30” to prepare a mixed solvent. LiPF ₆ (1.1 mol/L) was dissolved in the mixed solvent. Thereby, the liquid electrolyte was prepared.

4. Assembling A plurality of PE porous membranes were prepared as separators. The separator had a rectangular shape of 112 mm×82 mm. The positive electrode plate and the negative electrode plate were alternately laminated with the separator interposed therebetween. As a result, a laminated electrode group was produced. This laminated electrode group includes 69 negative electrode plates and 68 positive electrode plates.

A predetermined battery case was prepared. The laminated electrode group and a predetermined amount of electrolyte were housed in a battery case. The laminated electrode group was connected to the positive electrode terminal and the negative electrode terminal. The battery case is sealed. As described above, the secondary battery according to the comparative example was manufactured.

"Example"
As the current collector foil for the outermost layer, current collector foils (Cu foil, thickness: 20 μm, 50 μm, 100 μm, 200 μm, 500 μm) shown in Table 1 below were prepared. By using these thick collector foils, various outermost negative electrode plates were prepared. The secondary batteries according to Examples 1 to 5 were manufactured by the same procedure as in the above Comparative Example except that the outermost layer negative electrode plate was arranged in the outermost layers (both ends in the stacking direction) of the stacked electrode group. produced.

<Evaluation>
The secondary battery manufactured as described above was evaluated as follows.

1. Out-of-plane swell (waviness)
The initial charge of the secondary battery was performed with the secondary battery being unrestrained. An X-ray CT (Computed Tomography) apparatus was used to perform tomography of the secondary battery in a charged state. Thereby, the waviness in the out-of-plane direction of the electrode plates included in the laminated electrode group was measured. Specifically, the stacking direction of the stacked electrode group was the height direction, and the maximum height difference in the electrode plate was measured. The results are shown in the column "Out-of-plane waviness" in Table 1 below.

2. Discharge Resistance The SOC (Sate Of Charge) of the secondary battery was adjusted to 50%. The "SOC" here is defined with 3V as 0% and 4.1V as 100%. At room temperature, the secondary battery was discharged at a discharge current of 6 C for 10 seconds. Here, the current that fully discharges the rated capacity of the battery in 1 hour is defined as “1C”. The amount of voltage drop during discharge was measured. The discharge resistance was calculated from the relationship between the voltage drop amount and the discharge current. The results are shown in the "Discharge resistance" column of Table 1 below.

As shown in Table 1 above, since the current collector foil included in the outermost electrode plate (negative electrode plate in this example) is thicker than the current collector foil of the electrode plate that is not the outermost layer, the undulation of the electrode plate It has been demonstrated that is suppressed. By suppressing the undulation of the electrode plate, the discharge resistance is reduced. That is, the battery performance is improved. It is considered that the variation in the distance between the electrodes is reduced.

The embodiments and examples disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the invention of the present disclosure is shown not by the above-described embodiments and examples but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims. To be done.

10 positive electrode plate, 11 positive electrode current collector foil, 12 positive electrode active material layer, 20 negative electrode plate, 21 negative electrode current collector foil, 22 negative electrode active material layer, 30 outermost layer, 31 current collector foil, 32 active material layer, 100 laminated electrode Group, 200 battery case, 210 case body, 220 lid, 221 positive electrode terminal, 222 negative electrode terminal, 1000 secondary battery.

Claims (1)

Battery case,
A stacked electrode group housed in the battery case, and an electrolyte housed in the battery case,
The stacked electrode group includes a plurality of positive electrode plates, separators and negative electrode plates, respectively, the battery case includes a case body and a lid, the lid is provided with a positive electrode terminal and a negative electrode terminal,
In the laminated electrode group,
The positive electrode plate and the negative electrode plate are alternately laminated,
The separator is interposed between the positive electrode plate and the negative electrode plate,
The positive electrode plate and the negative electrode plate each include a collector foil and an active material layer,
The active material layer is formed on the surface of the current collector foil,
In the stacking direction of the stacked electrode group,
The collection included in the positive electrode plate or the negative electrode plate is the outermost layer foil, the rather thick than said collector foil included in the positive electrode plate and the negative electrode plate are not the outermost layer,
The current collector foils included in the positive electrode plate and the negative electrode plate are respectively connected to the positive electrode terminal and the negative electrode terminal at the end portions in the width direction,
Secondary battery.

Images