JP7116890B2 - secondary battery - Google Patents

Description

The present invention relates to secondary batteries. Specifically, it relates to the configuration of the electrode body provided in the battery.

Secondary batteries such as lithium-ion secondary batteries, which can achieve relatively high output and high capacity, are important as power sources for vehicles that use electricity as a driving source, and power sources for electrical products such as personal computers and mobile terminals. is. In particular, lithium-ion secondary batteries, which are lightweight and provide high energy density, are preferable as high-output power sources for driving vehicles such as electric vehicles (EV), plug-in hybrid vehicles (PHV), and hybrid vehicles (HV). Demand is expected to grow further.

As one form of a typical secondary battery, a rectangular sheet-shaped positive electrode and a rectangular sheet-shaped negative electrode are laminated, and a so-called laminated electrode body is housed in an outer package such as a laminate film. A secondary battery with a closed structure can be mentioned.
In a secondary battery comprising a laminated electrode body having such a structure, various structures have been proposed as the structure of the positive electrode and the negative electrode of the laminated electrode body (hereinafter referred to as "electrodes" when the positive and negative are not particularly distinguished). In general, as a positive electrode, a positive electrode current collector such as aluminum (hereinafter simply referred to as a "current collector" when there is no particular distinction between positive and negative) is coated with a positive electrode active material layer (hereinafter, when there is no particular distinction between positive and negative, simply (referred to as an "active material layer"). Similarly, the negative electrode includes a negative electrode current collector such as copper provided with a negative electrode active material layer.
Then, the positive electrode active material layer and the negative electrode active material layer are overlapped with a separator layer interposed therebetween for preventing contact therebetween, and pressed in the stacking direction with a predetermined pressure. A laminated electrode assembly is thus constructed.

Japanese Patent Application Laid-Open No. 2001-15153

By the way, one of the problems of the secondary battery including the laminated electrode body having the structure described above is the expansion and contraction of the active material layer during charging and discharging.
With the expansion and contraction of the active material, a force (hereinafter referred to as "reaction force") acting to suppress the expansion and contraction, such as a frictional force between the active material layer and the current collector, is generated. It has been known. In particular, when the horizontal plane of the laminated electrode body is rectangular, the short side direction of the rectangle in the horizontal direction of the laminated electrode body (hereinafter simply referred to as the "horizontal direction") (hereinafter referred to as the "Y direction"). For example, see FIG. 2.) and the long side direction (hereinafter referred to as “X direction”; see FIG. 2, for example). Specifically, in the Y direction, the filling distance of the active material is short, and the reaction force can be smaller than in the X direction, in which the filling distance of the active material is longer.
At this time, the difference in magnitude of the reaction force as described above directly leads to the difference in expansion distance of the active material layer in the horizontal direction between the X direction and the Y direction. Due to the difference in the expansion distance, cracks are more likely to occur in the active material layer in the Y direction than in the X direction, in which the expansion distance of the active material is relatively large particularly during rapid charging. The active material may easily slide down from the edge of the The occurrence of the cracks and the sliding of the active material are not preferable because they form a region in which the ion path is blocked inside the laminated electrode body, and also become a factor in deteriorating the battery performance.

As a means for preventing cracks in the active material layer and slipping of the active material due to the expansion and contraction of the active material during charging and discharging, a plurality of battery elements consisting of the active material layer and the separator layer are provided with appropriate gaps. For example, they are spaced apart to reduce the difference in the magnitude of the reaction force depending on the direction (Patent Document 1). However, in the configuration disclosed in Patent Document 1, for example, when the secondary battery is used while restrained in the stacking direction, there is a risk that the voids inside the electrode body will be crushed to cause a short circuit. Moreover, the greater the number of battery elements placed between current collectors, the greater the risk of such short circuits.

Therefore, the present invention was created to solve the above-described problems related to the secondary battery, and suppresses the occurrence of a difference in expansion distance between the X direction and the Y direction of the active material layer in the horizontal direction of the laminated electrode body. An object of the present invention is to provide a secondary battery that can prevent deterioration of battery performance caused by the difference.

In order to achieve the above object, the secondary battery disclosed herein comprises a rectangular sheet-shaped positive electrode and a rectangular sheet-shaped negative electrode with a separator layer interposed between them to physically separate the positive and negative electrodes. It has an electrode body with an alternately laminated structure. The positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. In at least one of the positive electrode and the negative electrode, the active material layers are spaced apart from each other on the current collector and have an aspect ratio (long side length/short side length) of 1 or more and 1.5 or less. A plurality of rectangular active material layers are formed, and the current collector has an active material layer exposed portion where the rectangular active material layer does not exist. Here, the separator layer is present between the exposed portion between the active material layers and the other opposing electrode.

In the secondary battery having such a configuration, the difference in the magnitude of the reaction force generated in the X direction and the Y direction in the horizontal direction of the laminated electrode assembly can be reduced by arranging the plurality of active material layers in the at least one electrode. can be done. As a result, the difference in expansion distances in these directions can be reduced. Thereby, it is possible to prevent the deterioration of the battery performance due to the difference in the expansion distance.

1 is a cross-sectional view schematically illustrating the configuration of a secondary battery according to one embodiment; FIG. FIG. 3 is a plan view schematically illustrating a positive electrode that constitutes a laminated electrode body of a secondary battery according to one embodiment; 1 is a plan view schematically illustrating a positive electrode that constitutes a laminated electrode body of a secondary battery according to an embodiment, in which (A) is the positive electrode of Example 1, (B) is the positive electrode of Example 2, (C) shows the positive electrode of the comparative example.

Preferred embodiments of the secondary battery disclosed herein will be described below with appropriate reference to the drawings. Matters other than those specifically mentioned in this specification, which are necessary for carrying out the present invention, can be grasped as design matters by those skilled in the art based on the prior art in the field. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field. Further, in each drawing, the same reference numerals are given to the members and parts that have the same function. Also, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships.

As used herein, the term "secondary battery" generally refers to a power storage device that can be repeatedly charged and discharged, and includes so-called storage batteries such as lithium ion secondary batteries and power storage elements such as electric double layer capacitors. The term "lithium ion secondary battery" refers to a secondary battery that uses lithium ions as charge carriers and is charged and discharged by movement of lithium ions between positive and negative electrodes. Further, the term "all-solid battery" refers to a secondary battery having a solid electrolyte.
Hereinafter, the present invention will be described in detail by taking a flat prismatic lithium ion secondary battery as an example. It should be noted that the embodiments described below are not intended to limit the present invention to those described in such embodiments.

As shown in FIG. 1 , in a secondary battery 10 (here, a lithium-ion battery) according to the present embodiment, a flat-shaped laminated electrode body 20 is attached to a flat exterior body 60 corresponding to the shape of the laminated electrode body 20 . It is a secondary battery with a sealed structure that is housed. The laminated electrode body 20 includes a sheet-shaped positive electrode 30 and a sheet-shaped negative electrode 40, while interposing a separator layer (a solid electrolyte layer in the case of an all-solid battery) 50 that physically separates the positive and negative electrodes from each other. (arrow Z in FIG. 1).

As shown in FIG. 1, cathode 30 comprises cathode current collector 32 and cathode active material layer 34 . On the other hand, the negative electrode 40 includes a negative electrode current collector 42 and a negative electrode active material layer 44 .
Here, a plurality of positive electrode active material layers 34 are arranged on the positive electrode current collector 32 so as to be spaced apart from each other in the X direction. In addition, the positive electrode current collector 32 is formed with a positive electrode active material interlayer exposed portion 33 where the positive electrode active material layer 34 does not exist. In the Z direction, between the positive electrode active material layer exposed portion 33 and the negative electrode 40 (specifically, between the negative electrode active material layer 44) is a separator layer 50 that physically separates them. exists.

FIG. 2 shows a plan view of the configuration of the positive electrode 30 . The positive electrode current collector 32 is rectangular and has a positive electrode current collecting tab 36 at a predetermined position. Although it is particularly preferable that the positive electrode current collector 32 has a rectangular shape, the long side length Wa and the short side length Wb are not particularly limited.
The positive electrode active material layer 34 is rectangular. The positive electrode active material layer 34 may be rectangular, and the length a of the long side to the length b of the short side (i.e., a/b; hereinafter referred to as “aspect ratio”) is equal to From the viewpoint of securing the area occupied by the positive electrode active material layer 34, it is preferably 1.5, 1.4, or 1.3 or less. Also, the positive electrode active material layer 34 may be square, in which case the aspect ratio is 1.0. That is, the aspect ratio of the positive electrode active material layer 34 may be 1.0 or more and 1.5 or less, 1.0 or more and 1.4 or less, or 1.0 or more and 1.3 or less. The aspect ratio is not affected by the composition of the positive electrode active material layer 34, the material of the positive electrode current collector 30, and the like.

The number of positive electrode active material layers 34 arranged on the positive electrode current collector 32 is not limited as long as it satisfies the above aspect ratio. good.
In addition, the distance α of the positive electrode active material layer exposed portion 33 on the positive electrode current collector 32 is not particularly limited as long as the positive electrode active material layer 34 satisfies the above aspect ratio. can be appropriately set according to the size and number of the . For example, the length Wa of the long side of the positive electrode current collector 32 in the X direction is preferably 1% or more and 10% or less, more preferably 2% or more and 8% or less, and even more preferably 3% or more and 6% or less. This makes it possible to avoid the concentration of reaction force in the Y direction due to the expansion and contraction of the secondary battery due to charging and discharging, and reduce the difference in expansion distance between the direction and the X direction.

Although the thickness of the positive electrode active material layer 34 is not particularly limited, it is typically suitably 50 μm or more and 300 μm or less, more preferably 200 μm or less, and even more preferably 100 μm or less. On the other hand, the thickness of the negative electrode active material layer 44 is not particularly limited. Typically, 50 μm or more and 300 μm or less is suitable, 200 μm or less is more preferable, and 100 μm or less is even more preferable.

Materials and members that constitute the separator layer 50, the positive electrode 30, and the negative electrode 40 of the electrode body 20 may be the same as those used in conventional general secondary batteries without limitation.

The positive electrode current collector 32 is made of, for example, a metal material such as aluminum, nickel, titanium, or stainless steel.

Lithium transition metal oxides such as LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , and LiFePO as positive electrode active materials ₄ and the like, and lithium transition metal phosphate compounds.

For the negative electrode current collector 42, for example, copper (for example, copper foil) or an alloy mainly composed of copper can be used.

Examples of negative electrode active materials include carbon-based negative electrode active materials such as graphite, mesocarbon microbeads, and carbon black, graphite-based materials such as natural graphite (plumbago) and artificial graphite, silicon and tin, and compounds thereof. .

The positive electrode active material layer 34 and the negative electrode active material layer 44 may contain a conductive aid, a binder, or the like, if necessary.
Examples of conductive aids include acetylene black (AB), vapor growth carbon (VGC), and ketjen black. Examples of binders include polyvinylidene fluoride (PVDF), butyl rubber (BR), styrene-butadiene rubber (SBR), and acrylonitrile-butadiene rubber (ABR).

Note that when the secondary battery 10 according to the present embodiment is an all-solid battery, a solid electrolyte layer instead of the separator layer 50 provides insulation between the positive electrode 30 and the negative electrode 40 . As the solid electrolyte, it is preferable to use a sulfide-based solid electrolyte, which includes crystalline sulfide, glass, or glass-ceramics. Also, an oxide-based solid electrolyte may be used, and suitable examples thereof include various oxides having a NASICON structure, a garnet-type structure, or a perovskite-type structure. In addition, the positive electrode active material layer 34 and the negative electrode active material layer 44 can contain a solid electrolyte as needed.

The laminated electrode body 20 is produced using the materials and members described above, and the secondary battery 10 according to the present embodiment is constructed. In the secondary battery, the difference in the magnitude of the reaction force generated in the X direction and the Y direction can be reduced by the configuration of the positive electrode 30 described above. As a result, the difference in the expansion distance in the horizontal direction becomes small, and it is possible to prevent the active material layer from cracking and the active material from sliding down, particularly in the Y direction. Therefore, formation of a region in which an ion path may be blocked is prevented inside the laminated electrode body, and good battery performance of the battery can be maintained.

Further, in the secondary battery according to the present embodiment, the separator layer 50 exists between the positive electrode active material interlayer exposed portion 33 and the negative electrode active material 44 (see FIG. 1). As a result, even if the negative electrode active material expands during charging and discharging, the negative electrode active material is prevented from entering the positive electrode active material interlayer exposed portion 33, and the negative electrode active material and the positive electrode active material are in direct contact with each other. It is possible to prevent an internal short circuit from occurring. Furthermore, since the number of active material layers arranged between the current collectors is a predetermined number, it is possible to reduce the slippage of the active material inside the electrode body compared to the conventional technology, and reduce the risk of short circuit.

Hereinafter, test examples will be described with respect to the secondary battery disclosed herein using an all-solid-state lithium ion battery as an example, but the present invention is not intended to be limited to those shown in such test examples. In addition, the following compounding ratios are mass ratios.

[Test Example 1: Production of test secondary battery]
Test secondary batteries (Example 1, Example 2, Comparative Example) shown in FIGS. 3A to 3C were produced by the process described below.
<Example 1>
-Preparation of positive electrode-
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ powder (LNMC) having an average particle size of 1 to 10 μm was used as the positive electrode active material, and a sulfide solid electrolyte was used as the solid electrolyte. AB as an agent and PVdF as a binder, LNMC: solid electrolyte = 75:25, and 2 parts by mass of the conductive aid and 1.5 parts by mass of the binder were weighed with respect to 100 parts by mass of the active material. was dispersed in butyric acid using an ultrasonic homogenizer (manufactured by SMT, UH-50) to prepare a positive electrode paste having a solid content of 50% by mass. This paste was applied to one side of an aluminum foil as a positive electrode current collector 32 in the shape shown in FIG. Each positive electrode active material layer 34 was formed to have an aspect ratio of 1.0 and a distance α of the exposed portion 33 between the positive electrode active material layers of 2 mm.

-Preparation of negative electrode-
Natural graphite (C) as the negative electrode active material powder, sulfide solid electrolyte powder as the solid electrolyte, and SBR as the binder, active material: solid electrolyte = 58:42 (mass ratio), per 100 parts by mass of the active material These materials were kneaded with butyric acid using an ultrasonic homogenizer to prepare a negative electrode paste having a solid content of 50% by mass. This paste was applied to one side of a copper foil as a negative electrode current collector (see the shape shown in FIG. 3(C)) and dried to form a negative electrode active material layer with a predetermined thickness, which was used as a negative electrode.

-Preparation of separator layer (here, solid electrolyte layer)-
A sulfide solid electrolyte powder as a solid electrolyte and PVDF as a binder were used at a mass ratio of solid electrolyte:binder = 95:5. An electrolyte paste was prepared. This paste was applied to the surface of the negative electrode active material layer prepared above and dried to form a solid electrolyte layer. Then, the layers of the active material of each prepared electrode were stacked so as to be insulated by the solid electrolyte layer to produce a laminated electrode body.

-Fabrication of all-solid-state battery-
The positive electrode prepared above was punched out, then the negative electrode was punched out, and these were bonded together to prepare a laminated electrode body. The laminated electrode assembly was sandwiched between two laminate films, and the entire periphery was heat-sealed to fabricate a secondary battery for evaluation test of Example 1.

<Example 2>
In the fabrication of the positive electrode active material layer 30, except that the positive electrode active material layer 34 applied to the positive electrode current collector 32 and having an aspect ratio of 1.5 was applied in the shape shown in FIG. Using the same materials and steps as in Example 1, a secondary battery for evaluation test of Example 2 was produced.

<Comparative example>
In the fabrication of the positive electrode active material layer 30, except that the positive electrode active material layer 34 applied to the positive electrode current collector 32 and having an aspect ratio of 3.0 was applied in the shape shown in FIG. Using the same materials and processes as in Example 1, a secondary battery for evaluation test of Comparative Example was produced.

[Test Example 2: Determination of capacity retention rate by cycle test of secondary batteries for each evaluation test]
Each sample battery was constrained to a fixed size in the stacking direction of the electrode bodies at 10 MPa using a constraining jig consisting of two SUS steel end plates (constraining plates) and constraining members (bolts and nuts). Next, charge-discharge cycles were performed under the following conditions, and the capacity retention rate of the 100th cycle with respect to the capacity of the 1st cycle was measured. That is, in an environment of 60° C., one cycle of charging and discharging was defined as constant current charging to 4.1 V at 1/3 C and discharging to 3 V at 1/3 C. After the cycle test, the evaluation test secondary battery was dismantled, and the discharge capacity retention rate (%) was calculated as “(capacity after cycle test/initial capacity)×100”.
The results are shown in the corresponding columns of Table 1.

[Test Example 3: Determination of electrode elongation rate in Y direction by cycle test of secondary batteries for each evaluation test]
For each positive electrode sample, the short side length La of the positive electrode active material layer before hot pressing and the short side length Lb of the positive electrode active material layer after the cycle test were determined, and the electrode elongation rate was calculated by the following formula (1). was calculated.
Electrode elongation rate (%) = (Lb - La) / La x 100 (1)
The results are shown in the corresponding columns of Table 1.

As is clear from the results shown in Table 1, in Examples 1 and 2 in which two or three positive electrode active material layers having an aspect ratio of 1.0 or more and 1.5 or less were arranged, 90% after the cycle test A high discharge capacity retention ratio was shown. Moreover, in Examples 1 and 2, the electrode elongation rate in the Y direction was lower than 0.5%.
From the above results, the secondary battery according to the present embodiment has excellent cycle characteristics (that is, maintenance of good battery performance).

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. For example, in the above example, a plurality of active material layers are arranged on the positive electrode current collector, but a plurality of active material layers may be provided on the negative electrode current collector. Also, a plurality of active material layers may be provided on both the positive electrode current collector and the negative electrode current collector. From the viewpoint of improving the lithium ion deposition resistance of the negative electrode, the negative electrode active material layer is preferably larger than the positive electrode active material layer. Moreover, although the all-solid-state lithium-ion secondary battery was illustrated in the above embodiment, a secondary battery that does not contain a solid electrolyte and uses a non-aqueous electrolyte as an electrolyte may be produced. Also in these cases, the same effects as those exemplified above can be exhibited.

10: Secondary battery 20: Electrode body 30: Positive electrode 32: Positive electrode current collector 33: Positive electrode active material interlayer exposed portion 34: Positive electrode active material layer 36: Positive electrode current collecting tab 40: Negative electrode 42: Negative electrode current collector 44: Negative electrode active material layer 50: Separator layer 60: Armor X: Long side direction Y: Short side direction Z: Stacking direction α: Distance a: Length of long side of active material layer b: Length of short side of active material layer Wa: Length of long side of current collector Wb: Length of short side of current collector

Claims (1)

A secondary battery comprising an electrode body having a structure in which a rectangular sheet-shaped positive electrode and a rectangular sheet-shaped negative electrode are alternately laminated with a separator layer interposed therebetween for physically separating the positive and negative electrodes,
The secondary battery is an all-solid battery comprising a solid electrolyte layer as the separator layer,
The positive electrode isrectangular sheetA positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector,
The negative electrode isrectangular sheeta negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector;
At least one electrode of the positive electrode and the negative electrode,
two or three the active material layerbut,Rectangular shapes having an aspect ratio (long side length/short side length) of 1 or more and 1.5 or less are spaced apart from each other on the current collector.shaped likeand the current collector is formed with an exposed portion between the active material layers where the rectangular active material layer does not exist,
Here, the separator layer is present between the active material layer exposed portion and the other opposing electrode.and the length α of the active material layer exposed portion in the long side direction of the current collector is 3% or more and 6% or less of the length Wa of the long side of the current collector., secondary battery.

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