WO2024058054A1

WO2024058054A1 - Secondary battery

Info

Publication number: WO2024058054A1
Application number: PCT/JP2023/032727
Authority: WO
Inventors: 慶若林
Original assignee: 株式会社村田製作所
Priority date: 2022-09-16
Filing date: 2023-09-07
Publication date: 2024-03-21

Abstract

Provided is a secondary battery in which charging and discharging reactions occur more favorably, thereby improving the volumetric energy density of an electrode. A secondary battery 100 according to the present disclosure comprises an electrode structure 10 composed of a positive electrode 1 and a negative electrode 2 having a larger area than the positive electrode 1, the positive and negative electrodes being disposed opposite to each other with a separator 3 interposed therebetween. The negative electrode 2 has an opposite part 21 opposite to the positive electrode 1 and a non-opposite part 22 that is not opposite to the positive electrode 1. The surface of the non-opposite part 22 is rougher than the surface of the opposite part 21.

Description

secondary battery

The present disclosure relates to secondary batteries.

Secondary batteries can be repeatedly charged and discharged, and are used for a variety of purposes. For example, secondary batteries are used in mobile devices such as mobile phones, smartphones, and notebook computers.

Patent Document 1 discloses a battery electrode in which the porosity of an upper layer of an electrode active material coated on the surface of a current collector is higher than that of a lower layer. According to the electrode described in Patent Document 1, it is disclosed that impregnation with an electrolytic solution is improved by making the electrode surface portion have a higher porosity than the inside of the electrode.

Japanese Patent Application Publication No. 2010-153403

The inventor of the present application has noticed that there are problems that need to be overcome with conventional secondary batteries, and has found it necessary to take measures to address them. Specifically, the inventor of the present application has found that there are the following problems.

Since the electrode described in Patent Document 1 has many pores formed on the surface of the electrode, there is a concern that the energy density per volume of the electrode may decrease. Further, the charging and discharging reaction of a battery occurs at the position where the positive electrode and the negative electrode face each other, but if a large number of pores are formed at the position where the electrodes face each other, there is a concern that the charging and discharging reaction will be adversely affected. As a result, the cycle characteristics of the battery deteriorated.

The present disclosure has been made in view of such problems. That is, the main objective of the present disclosure is to provide a secondary battery in which charging and discharging reactions occur more appropriately and cycle characteristics are further improved.

The secondary battery according to the present disclosure is
comprising an electrode structure in which a positive electrode and a negative electrode having a larger area than the positive electrode are arranged facing each other with a separator interposed therebetween;
The negative electrode has a facing portion facing the positive electrode and a non-facing portion not facing the positive electrode,
The surface of the non-opposing portion is rougher than the surface of the opposing portion.

According to the secondary battery according to the present disclosure, the surface of the opposing part of the negative electrode that faces the positive electrode is rougher than the surface of the non-facing part of the negative electrode that does not face the positive electrode, so that charging and discharging reactions can occur more favorably. Thus, the energy density per volume of the electrode can be improved.

FIG. 1A is a cross-sectional view of a positive electrode, a negative electrode, and a separator. FIG. 1B is a plan view of the positive electrode, negative electrode, and separator. FIG. 2 is an enlarged sectional view of main parts of a positive electrode, a negative electrode, and a separator. FIG. 3 is a perspective view of an electrode structure having a wound structure. FIG. 4 is a schematic cross-sectional view showing the electrode structure housed in the exterior member. FIG. 5 is a schematic cross-sectional view showing a state in which an electrolytic solution is supplied into the exterior member. FIG. 6 is a schematic cross-sectional view schematically showing an embodiment of the secondary battery of the present disclosure. FIG. 7A schematically shows an exemplary form of a secondary battery, and is a perspective view of a button-shaped/coin-shaped secondary battery. FIG. 7B schematically shows an example of a secondary battery, and is a perspective view of a square secondary battery. FIG. 8 is a schematic cross-sectional view schematically showing another embodiment of the secondary battery of the present disclosure.

Below, a secondary battery according to an embodiment of the present disclosure will be described in more detail. Although explanations will be made with reference to drawings as necessary, various elements in the drawings are merely shown schematically and illustratively for understanding the present disclosure, and the appearance and dimensional ratio may differ from the actual ones. .

The "up-down direction" and "left-right direction" described directly or indirectly in this specification correspond to the up-down direction and the left-right direction in the drawings. Unless otherwise specified, the same reference numerals or symbols indicate the same members/parts or the same meanings. In addition, "cross-sectional view" described directly or indirectly in this specification refers to a virtual view of a secondary battery cut along the "vertical direction" of the electrode assembly/electrode constituent layers that constitute the secondary battery. It is based on a cross section. Similarly, the direction of "thickness" described directly or indirectly in this specification is based on the "vertical direction" of the electrode material constituting the secondary battery. For example, in the case of a "thick plate-shaped secondary battery" such as a button type or coin type, the direction of "thickness" corresponds to the thickness direction of the secondary battery. The term "planar view" used in this specification is based on a sketch when the object is viewed from above or below along the thickness direction. Unless otherwise specified, the same reference numerals or symbols indicate the same members/parts or the same meanings.

In this specification, the "top surface" refers to the surface that is located above the battery in the vertical direction, and the "bottom surface" refers to the surface that is positioned above the battery in the vertical direction. It means the surface positioned on the lower side. Assuming a typical secondary battery with two opposing main surfaces, the "top surface" in this specification refers to one of the main surfaces, and the "bottom surface" refers to one of the main surfaces. Pointing to the other side.

[Description of the secondary battery of the present disclosure]
The term "secondary battery" used herein refers to a battery that can be repeatedly charged and discharged. Therefore, the secondary battery according to the present disclosure is not excessively limited by its name, and may also include, for example, power storage devices. The secondary battery 100 of the present disclosure may include an electrode structure 10, an exterior member 50 that accommodates the electrode structure 10, and an electrolyte 80. Each component constituting the secondary battery of the present disclosure will be described in detail below with reference to FIGS. 1 to 8.

[Electrode structure]
The electrode structure 10 is made by rolling a sheet or plate-like member (see FIGS. 1 and 2) in which a positive electrode 1 and a negative electrode 2 having a larger area than the positive electrode 1 are arranged facing each other with a separator 3 in between. (See FIG. 3). Note that the electrode structure 10 of the present disclosure is not limited to a wound structure, but may have a laminated structure in which the positive electrode 1, the separator 3, and the negative electrode 2 are stacked on a plane (see FIG. 8), or , a so-called stack-and-fold structure in which the positive electrode 1, separator 3, and negative electrode 2 are laminated on a long film and then folded may be used. Each component constituting the electrode structure 10 will be described in detail below.

[Positive electrode]
The positive electrode 1 may include at least a positive electrode current collector 1a and a positive electrode material 1b. In the example shown in FIG. 1A, the positive electrode material 1b is provided on both sides of the positive electrode current collector 1a, but the present invention is not limited to this example, and the positive electrode material 1b may be provided only on one side of the positive electrode current collector 1a. good.

The positive electrode current collector 1a is a member that helps collect and supply electrons generated in the active material due to battery reactions. For example, the positive electrode current collector 1a may be made into a rectangular shape by cutting a sheet-like metal member, and may have a porous or perforated form. Further, the current collector may be metal foil, punched metal, net, expanded metal, or the like.

As an example, the positive electrode current collector 1a may be made of a metal foil containing at least one selected from the group consisting of aluminum, stainless steel, nickel, etc., and for example, aluminum foil is preferable.

The positive electrode material 1b may contain a positive electrode active material as an electrode active material. When the positive electrode active material is composed of, for example, granules, a binder may be included in the positive electrode material 1b in order to ensure sufficient contact between the particles and shape retention. Furthermore, a conductive additive may be included in the positive electrode material 1b in order to facilitate the transmission of electrons that promote battery reactions. Since the positive electrode material 1b contains a plurality of components in this manner, the positive electrode material 1b can also be referred to as a "positive electrode composite material."

The positive electrode active material is preferably a material that contributes to intercalation and desorption of lithium ions. From this point of view, it is preferable that the positive electrode active material is, for example, a lithium-containing composite oxide. More specifically, the positive electrode active material is preferably a lithium transition metal composite oxide containing lithium and at least one transition metal selected from the group consisting of cobalt, nickel, manganese, and iron. That is, in the positive electrode material 1b of the secondary battery 100 according to the present disclosure, such a lithium transition metal composite oxide may preferably be included as a positive electrode active material. For example, the positive electrode active material may be lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium iron phosphate, or a material in which some of the transition metals thereof are replaced with another metal. Although such positive electrode active materials may be contained as a single species, they may be contained in a combination of two or more types.

Binders that may be included in the positive electrode material 1b include, but are not particularly limited to, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and polytetrafluoroethylene. At least one selected from the group consisting of: The conductive additive that can be included in the positive electrode material 1b is not particularly limited, but includes carbon black such as thermal black, furnace black, channel black, Ketjen black, and acetylene black, graphite, carbon nanotubes, and vapor-phase growth. Examples include at least one selected from carbon fibers such as carbon fibers, metal powders such as copper, nickel, aluminum and silver, and polyphenylene derivatives.

The thickness of the positive electrode material 1b is not particularly limited, but may be 1 μm or more and 300 μm or less, for example, 5 μm or more and 200 μm or less. The thickness dimension of the positive electrode material layer is the thickness inside the secondary battery, and the average value of the measured values at arbitrary 10 points may be adopted.

[Negative electrode]
The negative electrode 2 may include at least a negative electrode current collector 2a and a negative electrode material 2b. In the example shown in FIG. 1A, the negative electrode material 2b is provided on both sides of the negative electrode current collector 2a, but the invention is not limited to this example, and the negative electrode material 2b may be provided only on one side of the negative electrode current collector 2a. good.

The negative electrode current collector 2a is a member that helps collect and supply electrons generated in the active material due to battery reactions. The negative electrode current collector 2a is preferably made of a metal foil containing at least one member selected from the group consisting of nickel, copper, nickel-plated copper, stainless steel (SUS), etc., for example, copper foil. It's good to be there. Note that "stainless steel" in this specification refers to, for example, stainless steel specified in "JIS G 0203 Iron and Steel Terminology", and may be an alloy steel containing chromium or chromium and nickel. .

The negative electrode material 2b may contain a negative electrode active material as an electrode active material. When the negative electrode active material is composed of, for example, a granular material, a binder may be included in the negative electrode material 2b for more sufficient contact between the particles and shape retention. Furthermore, a conductive additive may be included in the negative electrode material 2b in order to facilitate the transmission of electrons that promote battery reactions. Since the negative electrode material 2b contains a plurality of components in this manner, it can also be referred to as a "negative electrode composite material."

The negative electrode active material is preferably a material that contributes to intercalation and desorption of lithium ions. From this point of view, the negative electrode active materials include C (carbon), Si (silicon), SiO _x (silicon oxide), Sn (tin), Bi (bismuth), Ti (titanium), Mn (manganese), Fe ( At least one selected from the group consisting of iron), Ni (nickel), Cu (copper), and the like can be mentioned.

The binder that may be included in the negative electrode material 2b is not particularly limited, but at least one selected from the group consisting of styrene-butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyimide resin, and polyamideimide resin. can be mentioned. The conductive additive that can be included in the negative electrode material 2b is not particularly limited, but includes carbon black such as thermal black, furnace black, channel black, Ketjen black, and acetylene black, graphite, carbon nanotubes, and vapor-phase growth. Examples include at least one selected from carbon fibers such as carbon fibers, metal powders such as copper, nickel, aluminum and silver, and polyphenylene derivatives. Note that the negative electrode material 2b may contain a component resulting from a thickener component (for example, carboxymethyl cellulose) used during battery manufacture.

The thickness of the negative electrode material 2b is not particularly limited, but may be 1 μm or more and 300 μm or less, for example, 5 μm or more and 200 μm or less. The thickness dimension of the negative electrode material 2b is the thickness inside the secondary battery, and the average value of the measured values at ten arbitrary locations may be adopted.

The negative electrode 2 in the secondary battery of the present disclosure is designed to have a larger area than the positive electrode 1 in plan view (see FIG. 1B). Here, in a typical secondary battery, when a battery reaction occurs between the positive electrode 1 and the negative electrode 2, dendrites tend to precipitate on the outer periphery of the negative electrode 2, and there is a possibility that this dendrite comes into contact with the positive electrode 1 and causes an internal short circuit. There is. In order to prevent this internal short circuit, the negative electrode 2 is designed to have a larger area than the positive electrode 1 in plan view. That is, the negative electrode 2 includes a facing portion 21 that faces the positive electrode 1 and a non-facing portion 22 that does not face the positive electrode 1 (see FIGS. 1A and 2). In other words, the area of the negative electrode 2 is designed to be larger than the area of the positive electrode 1 by the area of the non-facing portion 22 of the negative electrode 2 . Note that the length L (see FIG. 2) of the non-opposed portion 22 is preferably 0.2 mm or more.

The non-opposing portion 22 is rougher than the opposing portion 21. As used herein, the term "roughness" indicates that the judgment is made by comparing the "roughness index" of the non-opposed portion 22 and the opposing portion 21 through an external inspection. That is, the main aspect is that the determination is made by comparing the surface roughness of the non-opposing portion 22 and the surface roughness of the opposing portion 21. Furthermore, the term "becoming rough" refers to the roughness that inherently exists in the non-opposed portion 22 and the opposing portion 21, although there is little change in appearance. ” and “the surface of the particles constituting the opposing portion” may also be included in the judgment by comparing the “roughness index”. Regarding the "inherently existing roughness", the porosity must not differ greatly between the bulk region (region not on the surface) of the facing part 21 and the bulk region (region not on the surface) of the non-facing part 22. is preferred. Furthermore, examples of "roughness indicators" include surface roughness (arithmetic mean roughness (Ra or Sa), maximum height (Rz or Sz), root mean square roughness (Rq or Sq)), etc. . The verification test regarding the roughness will be described in detail in the examples below.

The process of changing the roughness of the non-opposed portion 22 may be performed by, for example, laser treatment to make the roughness of the “surface” and/or the “surface of the constituent particles” of the non-opposed portion 22 rougher than that of the opposing portion 21. Note that the roughness modification treatment is not limited to laser treatment, and may be, for example, plasma treatment, physical grinding treatment, surface modification treatment by heating, or the like.

By making the surface of the non-opposing portion 22 of the negative electrode 2 rougher than the surface of the opposing portion 21, the impregnating property of the electrolytic solution, which will be described later, is improved, and the electrolytic solution can be easily permeated into the electrode uniformly. Therefore, the charging/discharging reaction of the battery can be caused more suitably. In addition, since the facing part 21 that causes the charging/discharging reaction of the battery is not subjected to any treatment to roughen its surface and/or the surfaces of the constituent particles, the energy density per volume of the electrode can be improved.

As an example of a preferable aspect of the non-opposing portion 22, the non-opposing portion 22 may be provided outside the opposing portion 21. With such an embodiment, the electrolytic solution can be impregnated from the non-opposing part 22 toward the opposing part 21, so that the electrode can be more uniformly impregnated with the electrolytic solution. More preferably, the non-opposing portion 22 may be provided at the outer peripheral edge of the opposing portion 21. With such an embodiment, the electrolytic solution can be uniformly impregnated from the outer periphery of the facing portion 21 . As an example of a more preferable aspect of the non-opposed portions 22, the non-opposed portions 22 located on both sides of the opposing portion 21 may be provided symmetrically with respect to the opposing portion 21. With such an embodiment, it is possible to more uniformly impregnate the electrolytic solution.

[Separator]
The separator 3 is a member provided from the viewpoint of preventing short circuits due to contact between the positive electrode 1 and the negative electrode 2 and retaining electrolyte. In other words, the separator 3 can be said to be a member that allows ions to pass through while preventing electronic contact between the positive electrode 1 and the negative electrode 2. Preferably, the separator 3 is a porous or microporous insulating member and has a membrane form due to its small thickness. Although this is merely an example, a microporous membrane made of polyolefin may be used as the separator 3. In this regard, the microporous membrane used as the separator 3 may contain, for example, only polyethylene (PE) or only polypropylene (PP) as the polyolefin. Furthermore, the separator 3 may be a laminate composed of a "microporous membrane made of PE" and a "microporous membrane made of PP." The surface of the separator 3 may be covered with an inorganic particle coating layer, an adhesive layer, or the like. The surface of the separator 3 may have adhesive properties. In the present disclosure, the separator 3 is not particularly limited by its name, and may be a solid electrolyte, a gel electrolyte, an insulating inorganic particle, or the like having a similar function.

It is preferable that the separator 3 has a larger area than the positive electrode 1 and the negative electrode 2 in plan view (see FIG. 1B). By adopting such an aspect, short circuit due to contact between the positive electrode 1 and the negative electrode 2 can be more effectively prevented. Furthermore, the amount of protrusion of the separator 3 that protrudes from both sides of the positive electrode 1 and the negative electrode 2 in a cross-sectional view (FIG. 1A) may be symmetrical with respect to the positive electrode 1 and the negative electrode 2. In this embodiment, since the amount of protrusion of the separator 3 is the same on both sides of the positive electrode 1 and the negative electrode 2, short circuits due to contact between the positive electrode 1 and the negative electrode 2 can be more effectively prevented.

[Exterior parts]
The exterior member 50 may be a member that can house or enclose the electrode structure 10. Preferably, the exterior member 50 is a metal exterior body having a non-laminated configuration. The metal sheath may be a single member made of metal such as stainless steel (SUS) and/or aluminum. In a broad sense, the term "metal single member" here means that the exterior member 50 does not have a so-called laminate structure, and in a narrow sense, it means that the exterior member 50 is substantially made of only metal. It means that. When the exterior member 50 is made of substantially only metal, the surface of the metal exterior body may be subjected to an appropriate surface treatment.

From the viewpoint of easily storing the electrode structure 10 in the exterior member 50, the exterior member 50 may include a lid-shaped member 51 and a cup-shaped member 52. The lid-like member 51 and the cup-like member 52 may be joined by welding (see FIGS. 4 to 6).

The lid-like member 51 may have an opening 51a formed in the center (for example, see FIG. 6). A terminal member 60 may be provided to cover the opening 51a. An insulating member 70 may be arranged between the terminal member 60 and the lid-like member 51.

Since the insulating member 70 is provided to fill the gap between the lid-like member 51 and the terminal member 60, it can also be considered to contribute to "sealing". As shown in FIG. 6, the insulating member 70 may have a shape along the lid-like member 51 so as to extend to an area outside the terminal member 60. That is, the insulating member 70 may be provided on the exterior member 50 so as to protrude outward from the terminal member 60. The type of insulating member 70 is not particularly limited as long as it exhibits "insulating properties". Preferably, the insulating material has not only "insulating properties" but also "adhesive properties". For example, the insulating member 70 may include thermoplastic resin. By way of one specific example only, the insulation material may comprise polyolefins such as polyethylene and/or polypropylene.

The terminal member 60 means an output terminal for connection with external equipment in the secondary battery. The terminal member 60 may have a flat plate shape, for example. The flat terminal member 60 may be, for example, a metal plate. The material of the terminal member 60 is not particularly limited, and may include at least one metal selected from the group consisting of aluminum, nickel, and copper. As can be seen from the preferred embodiment shown in FIG. 6, the terminal member 60 may have a shape that follows the lid-like member 51. That is, in the illustrated cross-sectional view, the terminal member 60, the surface of the lid-like member 51 on which the terminal member 60 is provided, and the insulating member 70 may have a mutually parallel arrangement relationship. The shape of the terminal member 60 in plan view is not particularly limited, and may be, for example, circular (see FIG. 7A) or rectangular including a square (see FIG. 7B). The terminal member 60 may be electrically connected to a lead (not shown) drawn out from the positive electrode current collector 1a in the electrode structure 10. That is, since the terminal member 60 is electrically connected to the positive electrode 1, it may function as a positive electrode of the secondary battery.

The cup-shaped member 52 has a storage space for storing the electrode structure 10, and the electrode structure 10 may be stored in the storage space. More specifically, the electrode structure 10 may be housed so that the direction along the winding axis of the electrode structure 10 is parallel to the thickness direction of the secondary battery. By adopting such a storage configuration, the electrolytic solution 80, which will be described later, can be supplied along the winding axis of the electrode structure 10, so that the electrolytic solution 80 can be efficiently supplied.

The dimension of the cup-shaped member 52 in the thickness direction is preferably approximately equal to the dimension along the winding axis of the electrode structure 10. Note that the term "substantially equal" as used herein is intended to include allowing an error of approximately ±10%. By setting the dimension of the cup-shaped member 52 in the thickness direction as described above, the cup-shaped member 52 can have a reduced surplus void in the storage space. Even when the electrode structure 10 is housed in such a cup-shaped member 52, the electrolytic solution 80 can be efficiently impregnated because the non-opposing portion 22 is rough.

It is preferable that the width direction dimension 52a of the cup-shaped member 52 is longer than the thickness direction dimension 52b of the cup-shaped member 52 (see FIG. 5). With such dimensions of the cup-shaped member 52, the electrolytic solution 80 can be uniformly permeated in the thickness direction of the cup-shaped member 52.

The cup-shaped member 52 may be electrically connected to a lead (not shown) drawn out from the negative electrode current collector 2a in the electrode structure 10. That is, since the cup-shaped member 52 is electrically connected to the negative electrode, it may function as a negative electrode of the secondary battery.

[Electrolyte]
In the secondary battery of the present disclosure, the above-described electrode structure 10 may be enclosed in an exterior member 50, which will be described later, together with an electrolytic solution 80. When the positive electrode and the negative electrode have a layer capable of intercalating and deintercalating lithium ions, the electrolytic solution 80 is preferably a "non-aqueous" electrolyte such as an organic electrolyte or an organic solvent. That is, it is preferable that the electrolyte is a non-aqueous electrolyte. Metal ions released from the electrodes (positive and negative electrodes) are present in the electrolyte, and therefore the electrolyte assists in the movement of metal ions in battery reactions.

A non-aqueous electrolyte is an electrolyte containing a solvent and a solute. A specific nonaqueous electrolyte solvent may contain at least carbonate. Such carbonates may be cyclic carbonates and/or linear carbonates. Although not particularly limited, examples of the cyclic carbonates include at least one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC). be able to. Examples of chain carbonates include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), and dipropyl carbonate (DPC). By way of example only, a combination of cyclic carbonates and chain carbonates may be used as the non-aqueous electrolyte, for example a mixture of ethylene carbonate and diethyl carbonate may be used. Moreover, as a specific solute of the non-aqueous electrolyte, for example, Li salt such as LiPF ₆ and/or LiBF ₄ may be used.

As shown in FIG. 5, the electrolyte 80 may be supplied by the electrolyte supply device 80s with the electrode structure 10 housed in the cup-shaped member 52. By adopting such a supply mode, the electrode structure 10 can be impregnated with the electrolytic solution. More specifically, by suitably infiltrating the electrolytic solution 80 from the non-opposing portion 22 of the negative electrode 2, which has good impregnating properties, the electrolytic solution can be easily infiltrated into the electrode uniformly. For example, the electrolytic solution 80 may be uniformly infiltrated in the direction of gravity from the non-opposed portion located on the upper side shown in FIG. The electrolytic solution 80 can be uniformly permeated by, for example. Therefore, the charging/discharging reaction of the battery can be caused more suitably.

Examples related to the present disclosure will be described. Secondary batteries of Examples 1 to 5 and Comparative Example 1 below were created.

[Common configuration of secondary batteries of Examples 1 to 5 and Comparative Example 1]
As secondary batteries of Examples 1 to 5 and Comparative Example 1, secondary batteries having an electrode structure 10 configured by winding a positive electrode and a negative electrode with a separator in between, as shown in FIG. 6, were created. Note that the details of the electrode structure (positive electrode, negative electrode, separator), exterior member, and electrolyte that constitute the secondary battery are as described in [Description of the secondary battery of the present disclosure].

[Configuration unique to Example 1]
An IR laser (model number MD-X1000, Keyence) was irradiated to the non-opposed portion of the negative electrode to roughen the surface of the negative electrode. Note that the IR laser irradiation conditions were a frequency of 180 kHz, a scan speed of 4500 mm/sec, and one irradiation number, and the output of the IR laser was set to 5%.

[Configuration unique to Example 2]
An IR laser (model number MD-X1000, Keyence) was irradiated to the non-opposed portion of the negative electrode to roughen the surface of the negative electrode. Note that the IR laser irradiation conditions were a frequency of 180 kHz, a scan speed of 4500 mm/sec, and the number of irradiations was once, and the output of the IR laser was set to 25%.

[Configuration unique to Embodiment 3]
An IR laser (model number MD-X1000, Keyence) was irradiated to the non-opposed portion of the negative electrode to roughen the surface of the negative electrode. Note that the IR laser irradiation conditions were a frequency of 180 kHz, a scan speed of 4500 mm/sec, and one irradiation number, and the output of the IR laser was set to 50%.

[Configuration unique to Embodiment 4]
An IR laser (model number MD-X1000, Keyence) was irradiated to the non-opposed portion of the negative electrode to roughen the surface of the negative electrode. The IR laser irradiation conditions were a frequency of 180 kHz, a scan speed of 4500 mm/sec, and one irradiation frequency, and the output of the IR laser was set to 75%.

[Configuration unique to Example 5]
An IR laser (model number MD-X1000, Keyence) was irradiated to the non-opposed portion of the negative electrode to roughen the surface of the negative electrode. Note that the IR laser irradiation conditions were a frequency of 180 kHz, a scan speed of 4500 mm/sec, and a number of irradiation times, and the output of the IR laser was set to 100%.

[Configuration of Comparative Example 1]
The non-opposed portion of the negative electrode was not irradiated with the IR laser. In other words, the surface of the negative electrode is not roughened.

The created secondary battery was evaluated for [composite material surface roughness], [negative electrode active material surface roughness], [solvent penetration time], and [secondary battery cycle characteristics]. The specific evaluation method for each evaluation is as follows.

[Evaluation of composite material surface roughness]
The negative electrode (negative electrode composite material) was observed using a laser microscope (model number VR-3200, Keyence). The observation conditions were set to ×80 magnification and auto illumination. After the above observation, the surface roughness of the negative electrode composite material was measured. Note that the surface roughness was measured using n=3 per field of view (3.8 mm x 2.9 mm). Moreover, the surface roughness was calculated using the arithmetic mean height (Sa) of the surface roughness.

[Evaluation of surface roughness of negative electrode active material]
The negative electrode active material was observed using a laser microscope (model number VR-3200, Keyence). Specifically, particles constituting the negative electrode active material were observed. The observation conditions were set to ×50 magnification and auto illumination. After the above observation, the surface roughness of the particles constituting the negative electrode active material was measured. Note that the active material surface roughness is calculated by drawing a line with a length of 10 μm on the active material particle surface, measuring the average height on the line, and using the arithmetic mean height (Ra) of the line roughness. did.

[Evaluation of solvent penetration time]
The method for evaluating the time for solvent penetration into the negative electrode was to drop 5 μl of dimethyl carbonate (DMC) onto the negative electrode using a micropipette, and then visually evaluate the time until the solvent soaked into the negative electrode. The time it took for the color to penetrate was defined as the time when the color of DMC disappeared. The solvent penetration time was measured using a digital microscope (model number VHX-6000, Keyence). The observation conditions were magnification x20 and coaxial epi-illumination. Note that if an electrolytic solution containing Li salt and additives is used, it will deposit on the dropping surface, making it impossible to determine whether or not it has penetrated, so a DMC solvent was used in this evaluation.

[Cycle characteristic evaluation]
Charge/discharge cycle characteristics were evaluated based on a secondary battery having the above surface roughness. The charge/discharge cycle conditions were constant current charging at 2.0 C and 4.4 V on the charging side and constant current discharging at 0.5 C and 3.0 V on the discharging side, and 100 cycles were repeated at an environmental temperature of 23°C. In addition, when determining the cycle characteristics, if the discharge capacity retention rate at 100 cycles (the ratio of the discharge capacity at 100 cycles to the initial 1 cycle discharge capacity expressed as a percentage) is less than 95%, it is considered unsuitable (× ), 95% or more was considered good (〇).

The above evaluation results are shown in the table below.

According to the above evaluation results, focusing on the surface roughness of the composite material, the secondary batteries of Examples 1 to 5 have a larger surface roughness of the composite material than the secondary battery of Comparative Example 1. In other words, in the secondary batteries of Examples 1 to 5, the surface roughness of the composite material in the non-opposing part that was irradiated with the IR laser was greater than the surface roughness of the composite material in the facing part that was not irradiated with the IR laser. ing. Regarding the solvent DMC penetration time, the secondary batteries of Examples 1 to 5 are shorter than the secondary battery of Comparative Example 1. In other words, the secondary batteries of Examples 1 to 5 had improved electrolyte impregnation properties compared to the secondary battery of Comparative Example 1.

Furthermore, focusing on the surface roughness of the negative electrode active material, the secondary batteries of Examples 1 to 5 have larger surface roughness of the negative electrode active material than the secondary battery of Comparative Example 1. In other words, in the secondary batteries of Examples 1 to 5, the surface roughness of the negative electrode active material in the non-opposing part that was irradiated with the IR laser was greater than the surface roughness of the negative electrode active material in the facing part that was not irradiated with the IR laser. It's getting bigger. Regarding the solvent DMC penetration time, the secondary batteries of Examples 1 to 5 are shorter than the secondary battery of Comparative Example 1. In other words, the secondary batteries of Examples 1 to 5 had improved electrolyte impregnation properties compared to the secondary battery of Comparative Example 1.

Furthermore, focusing on the cycle characteristics, the cycle characteristics of the secondary batteries of Examples 1 to 5 were better than the cycle characteristics of the secondary battery of Comparative Example 1.

Aspects of the secondary battery of the present disclosure are as follows.
<1> An electrode structure in which a positive electrode and a negative electrode having a larger area than the positive electrode are arranged facing each other with a separator interposed therebetween;
The negative electrode has a facing portion facing the positive electrode and a non-facing portion not facing the positive electrode,
A secondary battery, wherein the surface of the non-opposing portion is rougher than the surface of the opposing portion.
<2> The secondary battery according to <1>, wherein the non-opposing portion is provided outside the opposing portion.
<3> The secondary battery according to <1> or <2>, wherein the electrode structure is configured by winding the positive electrode and the negative electrode with the separator interposed therebetween.
<4> The secondary battery according to <3>, wherein the direction along the winding axis of the winding is parallel to the thickness direction of the secondary battery.
<5> The secondary battery according to <3> or <4>, wherein a dimension of the electrode structure along the winding axis is approximately equal to a dimension in the thickness direction of an exterior member housing the electrode structure.
<6> The secondary battery according to <5>, wherein the dimension in the width direction of the exterior member perpendicular to the thickness direction is longer than the dimension in the thickness direction.
<7> The secondary battery according to any one of <1> to <6>, wherein the electrode structure is impregnated with an electrolyte.
<8> The negative electrode comprises a composite material containing a negative electrode active material,
The secondary battery according to any one of <1> to <7>, wherein the surface roughness of the composite material in the non-facing portion is greater than the surface roughness of the composite material in the opposing portion.
<9> The negative electrode comprises a composite material containing a negative electrode active material,
The secondary according to any one of <1> to <7>, wherein the surface roughness of the negative electrode active material in the non-facing portion is greater than the surface roughness of the negative electrode active material in the facing portion. battery.
<10> The negative electrode comprises a composite material containing a negative electrode active material,
Any one of <1> to <9>, wherein the negative electrode active material contains at least one selected from the group consisting of C, Si, SiO _x , Sn, Bi, Ti, Mn, Fe, Ni, and Cu. The secondary battery described in item 1.
<11> The secondary battery according to any one of <1> to <10>, wherein the positive electrode and the negative electrode are capable of intercalating and deintercalating lithium ions.

Note that the embodiments disclosed herein are illustrative in all respects, and are not the basis for a limited interpretation. Therefore, the technical scope of the present disclosure should not be interpreted only by the embodiments described above, but should be defined based on the claims. Further, the technical scope of the present disclosure includes all changes within the meaning and scope equivalent to the claims.

The secondary battery according to the present disclosure can be used in various fields where power storage is expected. Although this is just an example, the secondary battery of the present disclosure can be used in the electrical, information, and communication fields where mobile devices are used (e.g., mobile phones, smartphones, notebook computers, digital cameras, activity meters, arm computers, electronic Paper, RFID tags, card-type electronic money, electric/electronic equipment fields including small electronic devices such as smart watches, or mobile equipment fields), household/small industrial applications (e.g., power tools, golf carts, household/nursing use)・Industrial robots), large industrial applications (e.g. forklifts, elevators, harbor cranes), transportation systems (e.g. hybrid cars, electric cars, buses, trains, electrically assisted bicycles, electric motorcycles, etc.) ), power system applications (e.g. various power generation, road conditioners, smart grids, home-installed power storage systems, etc.), medical applications (medical equipment such as earphones and hearing aids), and pharmaceutical applications (medication management systems, etc.) The present disclosure can also be used in the field of IoT), space/deep sea applications (for example, fields of space probes, underwater research vessels, etc.), and the like.

1 Positive electrode 1a Positive electrode current collector 1b Positive electrode material 2 Negative electrode 2a Negative electrode current collector 2b Negative electrode material 21 Opposed portion 22 Non-opposed portion 3 Separator 10 Electrode structure 50 Exterior member 51 Lid-like member 51a Opening portion 52 Cup-shaped member 52a Cup-shaped Dimension in the width direction of the member 52b Dimension in the thickness direction of the cup-shaped member 60 Terminal member 70 Insulating member 80 Electrolyte 80s Electrolyte supply device 100 Secondary battery L Length of non-opposed portion

Claims

comprising an electrode structure in which a positive electrode and a negative electrode having a larger area than the positive electrode are arranged facing each other with a separator interposed therebetween;
The negative electrode has a facing portion facing the positive electrode and a non-facing portion not facing the positive electrode,
A secondary battery, wherein the surface of the non-opposing portion is rougher than the surface of the opposing portion.
The secondary battery according to claim 1, wherein the non-opposing portion is provided outside the opposing portion.
The secondary battery according to claim 1 or 2, wherein the electrode structure is configured by winding the positive electrode and the negative electrode with the separator interposed therebetween.
The secondary battery according to claim 3, wherein the direction along the winding axis of the winding is parallel to the thickness direction of the battery.
The secondary battery according to claim 3 or 4, wherein a dimension of the electrode structure along the winding axis is approximately equal to a dimension in the thickness direction of an exterior member that accommodates the electrode structure.
The secondary battery according to claim 5, wherein a dimension in the width direction of the exterior member perpendicular to the thickness direction is longer than a dimension in the thickness direction.
The secondary battery according to any one of claims 1 to 6, wherein the electrode structure is impregnated with an electrolyte.
The negative electrode comprises a composite material containing a negative electrode active material,
The secondary battery according to any one of claims 1 to 7, wherein the surface roughness of the composite material in the non-facing portion is greater than the surface roughness of the composite material in the opposing portion.
The negative electrode comprises a composite material containing a negative electrode active material,
The secondary battery according to any one of claims 1 to 7, wherein the surface roughness of the negative electrode active material in the non-facing portion is greater than the surface roughness of the negative electrode active material in the facing portion.
The negative electrode comprises a composite material containing a negative electrode active material,
10. The negative electrode active material comprises at least one selected from the group consisting of C, Si, SiO x , Sn, Bi, Ti, Mn, Fe, Ni, and Cu. The secondary battery described in .
The secondary battery according to any one of claims 1 to 10, wherein the positive electrode and the negative electrode are capable of inserting and extracting lithium ions.