JP7517480B2 - Secondary battery - Google Patents

Description

This technology relates to secondary batteries.

As various electronic devices such as mobile phones become widespread, secondary batteries are being developed as power sources that are small, lightweight, and have high energy density. These secondary batteries have a positive electrode and a negative electrode as well as an electrolyte layer, and the electrolyte layer contains an electrolyte solution and a polymer compound.

Various studies have been conducted on the configuration of secondary batteries with electrolyte layers. Specifically, in order to improve high-temperature reliability, a gel electrolyte membrane is provided between the positive electrode and the separator, and a gel electrolyte membrane is provided between the negative electrode and the separator (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 11-283674

Various studies have been conducted on the battery characteristics of secondary batteries, but the cycle characteristics of these batteries are still insufficient and there is room for improvement.

Therefore, there is a demand for secondary batteries that can achieve excellent cycle characteristics.

A secondary battery according to an embodiment of the present technology includes a first electrolyte layer containing a first electrolytic solution and a first polymer compound, an electrode and a separator that face each other via the first electrolyte layer, and a second electrolyte layer that is adjacent to the first electrolyte layer in a direction intersecting the direction in which the electrode and the separator face each other via the first electrolyte layer and contains a second electrolytic solution and a second polymer compound. The ratio of the weight of the second electrolytic solution to the weight of the second polymer compound is greater than the ratio of the weight of the first electrolytic solution to the weight of the first polymer compound.

In a secondary battery according to one embodiment of the present technology, the electrode and the separator face each other via a first electrolyte layer (first electrolytic solution and first polymer compound), and a second electrolyte layer (second electrolytic solution and second polymer compound) is adjacent to the first electrolyte layer in a direction intersecting the direction in which the electrode and the separator face each other via the first electrolyte layer, and the ratio of the weight of the second electrolytic solution to the weight of the second polymer compound is greater than the ratio of the weight of the first electrolytic solution to the weight of the first polymer compound, thereby achieving excellent cycle characteristics.

Note that the effects of this technology are not necessarily limited to the effects described here, but may be any of a series of effects related to this technology described below.

1 is a perspective view illustrating a configuration of a secondary battery according to an embodiment of the present technology. 2 is an enlarged cross-sectional view showing the configuration of the battery element (wound electrode body) shown in FIG. 1. FIG. 13 is a cross-sectional view illustrating a configuration of a secondary battery according to Modification 5. 4 is an enlarged cross-sectional view showing the configuration of the battery element (laminated electrode body) shown in FIG. 3. FIG. 1 is a block diagram showing a configuration of an application example of a secondary battery.

Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The description will be given in the following order.

1. Secondary battery 1-1. Configuration 1-2. Operation 1-3. Manufacturing method 1-4. Actions and effects 2. Modifications 3. Uses of secondary batteries

<1. Secondary battery>
First, a secondary battery according to an embodiment of the present technology will be described.

The secondary battery described here is a secondary battery in which battery capacity is obtained by utilizing the absorption and release of electrode reactants, and is equipped with a positive electrode, a negative electrode, and an electrolyte solution, which is a liquid electrolyte.

In this secondary battery, the charge capacity of the negative electrode is greater than the discharge capacity of the positive electrode. In other words, the electrochemical capacity per unit area of the negative electrode is set to be greater than the electrochemical capacity per unit area of the positive electrode. This is to prevent electrode reactants from depositing on the surface of the negative electrode during charging.

The type of electrode reactant is not particularly limited, but specifically, it is a light metal such as an alkali metal or an alkaline earth metal. The alkali metals are lithium, sodium, potassium, etc., and the alkaline earth metals are beryllium, magnesium, calcium, etc.

In the following, we will use an example in which the electrode reactant is lithium. A secondary battery that obtains battery capacity by utilizing the absorption and release of lithium is known as a lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is absorbed and released in an ionic state.

<1-1. Configuration>
Fig. 1 shows a perspective view of a secondary battery, and Fig. 2 shows an enlarged cross-sectional view of the battery element 20 shown in Fig. 1. However, Fig. 1 shows a state in which the exterior film 10 and the battery element 20 are separated from each other, and shows a cross section of the battery element 20 along the XZ plane by a broken line. Fig. 2 shows a cross section of the battery element 20 along the YZ plane.

As shown in Figures 1 and 2, this secondary battery includes an exterior film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42. The secondary battery described here is a laminate film type secondary battery that uses a flexible exterior film 10.

Note that the "thickness" described below is the dimension in the vertical direction (Z-axis direction) in Figure 2, and the "width" described below is the dimension in the horizontal direction (Y-axis direction) in Figure 2.

[Exterior film and sealing film]
As shown in FIG. 1, the exterior film 10 is a flexible exterior member that houses the battery element 20, and has a bag-like structure that is sealed with the battery element 20 housed therein.

Here, the exterior film 10 is a single film-like member that is folded in a folding direction F. This exterior film 10 is provided with a recessed portion 10U (a so-called deep drawn portion) for accommodating the battery element 20.

Specifically, the exterior film 10 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside, and when the exterior film 10 is folded, the outer peripheral edges of the opposing fusion layers are fused to each other. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

However, the configuration (number of layers) of the exterior film 10 is not particularly limited and may be one or two layers, or four or more layers.

The sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

The sealing film 41 is a sealing member that prevents outside air from entering the inside of the exterior film 10. The sealing film 41 also contains a polymer compound such as polyolefin that has adhesion to the positive electrode lead 31, and the polyolefin is polypropylene or the like.

The configuration of the sealing film 42 is the same as that of the sealing film 41, except that the sealing film 42 is a sealing member that has adhesion to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as polyolefin that has adhesion to the negative electrode lead 32.

[Battery element]
As shown in FIGS. 1 and 2 , the battery element 20 is a power generating element including a positive electrode 21, a negative electrode 22, a separator 23, a positive electrode electrolyte layer 24, a negative electrode electrolyte layer 25, a positive electrode liquid retaining layer 26, and a negative electrode liquid retaining layer 27, and is housed inside the exterior film 10.

This battery element 20 is a so-called wound electrode body. That is, in the battery element 20, the positive electrode 21 and the negative electrode 22 are mainly stacked on each other via the separator 23, the positive electrode electrolyte layer 24, and the negative electrode electrolyte layer 25, and the positive electrode 21, the negative electrode 22, the separator 23, the positive electrode electrolyte layer 24, and the negative electrode electrolyte layer 25 are wound around the winding axis P, which is a virtual axis extending in the Y-axis direction. The positive electrode electrolyte layer 26 is disposed next to the positive electrode electrolyte layer 24, and is adjacent to the positive electrode electrolyte layer 24, and the negative electrode electrolyte layer 27 is disposed next to the negative electrode electrolyte layer 25, and is adjacent to the negative electrode electrolyte layer 25. As a result, the positive electrode 21 and the negative electrode 22 are wound while facing each other via the separator 23, the positive electrode electrolyte layer 24, and the negative electrode electrolyte layer 25.

The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the battery element 20 is flat, the cross section (cross section along the XZ plane) of the battery element 20 intersecting with the winding axis P has a flat shape defined by the long axis J1 and the short axis J2. The long axis J1 is an imaginary axis that extends in the X-axis direction and has a length greater than the short axis J2, and the short axis J2 is an imaginary axis that extends in the Z-axis direction intersecting with the X-axis direction and has a length smaller than the long axis J1. Here, since the three-dimensional shape of the battery element 20 is a flat cylindrical shape, the cross section of the battery element 20 has a flattened, approximately elliptical shape.

(Positive electrode)
The positive electrode 21 is an electrode for promoting charge/discharge reactions. As shown in FIG. 2, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B.

The positive electrode collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. The positive electrode collector 21A contains a conductive material such as a metal material, and the metal material is aluminum or the like. The width of the positive electrode collector 21A is set so as not to be larger than the width of the positive electrode active material layer 21B, and more specifically, is the same as the width of the positive electrode active material layer 21B. This is because the energy density per volume of the battery element 20 increases since the volume of the positive electrode collector 21A is prevented from increasing.

Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode collector 21A and contains one or more types of positive electrode active materials capable of absorbing and releasing lithium. However, the positive electrode active material layer 21B may be provided only on one side of the positive electrode collector 21A on the side where the positive electrode 21 faces the negative electrode 22. The positive electrode active material layer 21B may further contain one or more types of other materials such as a positive electrode binder and a positive electrode conductor. The method of forming the positive electrode active material layer 21B is not particularly limited, but specifically, it is one or more types of coating methods.

The type of the positive electrode active material is not particularly limited, but specifically, it is a lithium-containing compound. The lithium-containing compound is a compound containing one or more transition metal elements as constituent elements together with lithium, and may further contain one or more other elements as constituent elements. The type of the other element is not particularly limited as long as it is an element other than lithium and transition metal elements, but specifically, it is an element belonging to Groups 2 to 15 in the long periodic table. The type of the lithium-containing compound is not particularly limited, but specifically, it is an oxide, a phosphate compound, a silicate compound, a borate compound, etc. Specific examples of oxides are LiNiO ₂ , LiCoO ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiNi _0.33 Co _0.33 Mn _0.33 O ₂ and LiMn ₂ O ₄ . Specific examples of phosphate compounds include _LiFePO4 and _LiMnPO4 .

The positive electrode binder contains one or more of synthetic rubbers and polymeric compounds. Synthetic rubbers include styrene-butadiene rubbers, fluororubbers, and ethylene-propylene-diene. Polymeric compounds include polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

The positive electrode conductive agent contains one or more conductive materials such as carbon materials, and the carbon materials include graphite, carbon black, acetylene black, and ketjen black. However, the conductive material may also be a metal material or a polymer compound.

(Negative electrode)
The negative electrode 22 is another electrode for promoting charge/discharge reactions. As shown in FIG. 2, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B.

The negative electrode collector 22A has a pair of surfaces on which the negative electrode active material layer 22B is provided. The negative electrode collector 22A contains a conductive material such as a metal material, and the metal material is copper or the like. The width of the negative electrode collector 22A is set so as not to be larger than the width of the negative electrode active material layer 22B, and more specifically, is the same as the width of the negative electrode active material layer 22B. This is because the energy density per volume of the battery element 20 increases since the volume of the negative electrode collector 22A is prevented from increasing.

Here, the negative electrode active material layer 22B is provided on both sides of the negative electrode collector 22A and contains one or more types of negative electrode active materials capable of absorbing and releasing lithium. However, the negative electrode active material layer 22B may be provided only on one side of the negative electrode collector 22A on the side where the negative electrode 22 faces the positive electrode 21. The negative electrode active material layer 22B may further contain one or more types of other materials such as a negative electrode binder and a negative electrode conductive agent. The method of forming the negative electrode active material layer 22B is not particularly limited, but specifically, it is one or more types of a coating method, a gas phase method, a liquid phase method, a thermal spraying method, and a sintering method (sintering method).

The type of the negative electrode active material is not particularly limited, but specifically, one or both of a carbon material and a metal-based material. This is because a high energy density can be obtained. The carbon material is graphitizable carbon, non-graphitizable carbon, graphite (natural graphite and artificial graphite), etc. The metal-based material is a material containing one or more of metal elements and metalloid elements that can form an alloy with lithium as a constituent element, and specific examples of the metal element and metalloid element are one or both of silicon and tin. This metal-based material may be a single substance, an alloy, a compound, a mixture of two or more of them, or a material containing two or more phases of them. Specific examples of the metal-based material are TiSi ₂ and SiO _x (0<x≦2, or 0.2<x<1.4), etc.

The details regarding the negative electrode binder and the negative electrode conductor are the same as the details regarding the positive electrode binder and the positive electrode conductor, respectively.

Here, the width of the negative electrode active material layer 22B is greater than the width of the positive electrode active material layer 21B. This is to prevent lithium released from the positive electrode 21 from being unintentionally precipitated in the negative electrode 22.

(Separator)
2, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and allows lithium ions to pass through while preventing contact (short circuit) between the positive electrode 21 and the negative electrode 22. This separator 23 contains a polymer compound such as polyethylene.

(Positive Electrolyte Layer)
The positive electrode electrolyte layer 24 is a first electrolyte layer that functions as an intermediary for lithium stored and released in the positive electrode 21, and is disposed between the positive electrode 21 and the separator 23 as shown in Fig. 2. That is, the positive electrode 21 and the separator 23 face each other via the positive electrode electrolyte layer 24. Here, the positive electrode electrolyte layer 24 is sandwiched between the positive electrode 21 and the separator 23, and is adjacent to both the positive electrode 21 and the separator 23.

Specifically, the positive electrode electrolyte layer 24 is a gel electrolyte containing an electrolyte solution and a polymer compound, and the electrolyte solution is held by the polymer compound. By using the positive electrode electrolyte layer 24, which is an electrolyte in a gel state, leakage of the electrolyte solution is prevented, unlike when the electrolyte solution, which is a liquid electrolyte, is used as is.

The electrolyte solution described here is the first electrolyte solution contained in the positive electrode electrolyte layer 24. There may be only one type of electrolyte solution, or two or more types. Specifically, the electrolyte solution contains a solvent and an electrolyte salt.

The solvent contains one or more of non-aqueous solvents (organic solvents), and an electrolyte containing the non-aqueous solvent is a so-called non-aqueous electrolyte. The non-aqueous solvent is an ester or ether, and more specifically, a carbonate ester compound, a carboxylate ester compound, and a lactone compound. Specific examples of carbonate ester compounds are ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Specific examples of carboxylate compounds are ethyl acetate, ethyl propionate, and propyl propionate. Specific examples of lactone compounds are gamma-butyrolactone and gamma-valerolactone.

The electrolyte salt contains one or more of light metal salts such as lithium salts. Specific examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bis(fluorosulfonyl)imide (LiN(FSO ₂ ) ₂ ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF ₃ SO ₂ ) ₂ ), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF ₃ SO ₂ ) ₃ ), and lithium bis(oxalato)borate (LiB(C ₂ O ₄ ) ₂ ). The content of the electrolyte salt is not particularly limited, but is specifically 0.3 mol/kg to 3.0 mol/kg relative to the solvent. This is because high ionic conductivity can be obtained.

The electrolyte may further contain one or more of the additives. Specifically, the additives include unsaturated cyclic carbonates, halogenated cyclic carbonates, sulfonates, phosphates, acid anhydrides, nitrile compounds, and isocyanate compounds.

Specific examples of unsaturated cyclic carbonates include vinylene carbonate, vinylethylene carbonate, and methyleneethylene carbonate. Specific examples of halogenated cyclic carbonates include monofluoroethylene carbonate and difluoroethylene carbonate. Specific examples of sulfonic acid esters include propane sultone and propene sultone. Specific examples of phosphate esters include trimethyl phosphate and triethyl phosphate. Specific examples of acid anhydrides include succinic anhydride, 1,2-ethane disulfonic anhydride, and 2-sulfobenzoic anhydride. Specific examples of nitrile compounds include succinonitrile. Specific examples of isocyanate compounds include hexamethylene diisocyanate.

The polymer compound described here is the first polymer compound contained in the positive electrode electrolyte layer 24. There may be only one type of polymer compound, or two or more types.

Specifically, the polymer compound contains one or both of a vinylidene fluoride homopolymer and a vinylidene fluoride copolymer. This is because excellent physical strength and excellent electrochemical stability can be obtained in the positive electrode electrolyte layer 24. The vinylidene fluoride homopolymer is so-called polyvinylidene fluoride. The vinylidene fluoride copolymer is a copolymer of vinylidene fluoride and one or more types of polymerization components (monomers), and the types of the polymerization components are not particularly limited.

In particular, it is preferable that the copolymer of vinylidene fluoride contains hexafluoropropylene as a polymerization component. In other words, it is preferable that the polymer compound is a copolymer of vinylidene fluoride and hexafluoropropylene. This is because the amount of electrolyte held by the positive electrode electrolyte layer 24 increases.

In this case, it is preferable that the copolymer of vinylidene fluoride further contains one or both of an unsaturated dibasic acid and an unsaturated dibasic acid monoester as a polymerizable component. That is, it is preferable that the polymer compound is a copolymer of vinylidene fluoride, hexafluoropropylene, and an unsaturated dibasic acid, a copolymer of vinylidene fluoride, hexafluoropropylene, and an unsaturated dibasic acid monoester, or a copolymer of vinylidene fluoride, hexafluoropropylene, an unsaturated dibasic acid, and an unsaturated dibasic acid monoester. This is because the amount of electrolyte held by the positive electrode electrolyte layer 24 is further increased.

Specific examples of unsaturated dibasic acids are maleic acid, fumaric acid, itaconic acid, citraconic acid, etc. Specific examples of unsaturated dibasic acid monoesters are maleic acid monomethyl ester, maleic acid monoethyl ester, fumaric acid monomethyl ester, fumaric acid monoethyl ester, itaconic acid monomethyl ester, itaconic acid monoethyl ester, citraconic acid monomethyl ester, citraconic acid monoethyl ester, etc.

It is preferable that the positive electrode electrolyte layer 24 further contains a plurality of insulating particles, because this increases the amount of electrolyte held by the positive electrode electrolyte layer 24.

The insulating particles contain one or both of an inorganic material and a polymer compound. Specific examples of inorganic materials include aluminum oxide, zirconium oxide, titanium oxide, and magnesium oxide. Specific examples of polymer compounds include acrylic resin and styrene resin.

(Negative Electrolyte Layer)
The negative electrode electrolyte layer 25 is another first electrolyte layer that functions as an intermediary for lithium stored and released in the negative electrode 22, and is disposed between the negative electrode 22 and the separator 23 as shown in Fig. 2. That is, the negative electrode 22 and the separator 23 face each other via the negative electrode electrolyte layer 25. Here, the negative electrode electrolyte layer 25 is sandwiched between the negative electrode 22 and the separator 23, and is adjacent to both the negative electrode 22 and the separator 23.

Specifically, the negative electrode electrolyte layer 25 has a configuration similar to that of the positive electrode electrolyte layer 24. That is, the negative electrode electrolyte layer 25 is a gel electrolyte containing an electrolyte solution and a polymer compound, and the electrolyte solution is held by the polymer compound. By using the negative electrode electrolyte layer 25, leakage of the electrolyte solution is prevented.

The electrolyte solution described here is another first electrolyte solution contained in the anode electrolyte layer 25, and the polymer compound described here is another first polymer compound contained in the anode electrolyte layer 25. Details regarding the electrolyte solution and polymer compound contained in the anode electrolyte layer 25 are similar to the details regarding the electrolyte solution and polymer compound contained in the cathode electrolyte layer 24. Of course, the anode electrolyte layer 25 may contain a plurality of insulating particles.

However, the type of electrolyte contained in the negative electrode electrolyte layer 25 and the type of electrolyte contained in the positive electrode electrolyte layer 24 may be the same or different. Similarly, the type of polymer compound contained in the negative electrode electrolyte layer 25 and the type of polymer compound contained in the positive electrode electrolyte layer 24 may be the same or different.

(Positive electrode electrolyte layer)
The positive electrode liquid retaining layer 26 is a second electrolyte layer that supplies an electrolytic solution to the positive electrode electrolyte layer 24, and is adjacent to the positive electrode electrolyte layer 24 as shown in Fig. 2. More specifically, the positive electrode liquid retaining layer 26 is adjacent to the positive electrode electrolyte layer 24 in a direction (Y-axis direction) that intersects with the direction (Z-axis direction) in which the positive electrode 21 and the separator 23 face each other via the positive electrode electrolyte layer 24. Here, the positive electrode liquid retaining layer 26 is not sandwiched between the positive electrode 21 and the separator 23, but is in contact with a side surface of the positive electrode electrolyte layer 24.

Here, the positive electrode liquid retaining layers 26 are disposed on both sides of the positive electrode electrolyte layer 24, so that the battery element 20 includes two positive electrode liquid retaining layers 26. That is, the first positive electrode liquid retaining layer 26 is disposed to the right of the positive electrode electrolyte layer 24, so that it is adjacent to the right side surface of the positive electrode electrolyte layer 24. The second positive electrode liquid retaining layer 26 is disposed to the left of the positive electrode electrolyte layer 24, so that it is adjacent to the left side surface of the positive electrode electrolyte layer 24.

The positive electrode liquid retaining layer 26 is disposed on one side of the separator 23 and is therefore supported by the separator 23.

Specifically, the positive electrode liquid retaining layer 26 has a configuration similar to that of the positive electrode electrolyte layer 24. That is, the positive electrode liquid retaining layer 26 is a gel electrolyte containing an electrolyte solution and a polymer compound, and the electrolyte solution is retained by the polymer compound. This is because the positive electrode liquid retaining layer 26 is capable of retaining the electrolyte solution and is also capable of supplying the electrolyte solution to the positive electrode electrolyte layer 24.

The electrolyte solution described here is the second electrolyte solution contained in the positive electrode liquid retaining layer 26, and the polymer compound described here is the second polymer compound contained in the positive electrode liquid retaining layer 26. Details regarding the electrolyte solution and polymer compound contained in the positive electrode liquid retaining layer 26 are similar to the details regarding the electrolyte solution and polymer compound contained in the positive electrode electrolyte layer 24. Of course, the positive electrode liquid retaining layer 26 may contain a plurality of insulating particles.

However, the type of electrolyte contained in the positive electrode liquid retaining layer 26 and the type of electrolyte contained in the positive electrode electrolyte layer 24 may be the same or different. Similarly, the type of polymer compound contained in the positive electrode liquid retaining layer 26 and the type of polymer compound contained in the positive electrode electrolyte layer 24 may be the same or different.

Here, the ratio of the weight of the electrolyte to the weight of the polymer compound in the positive electrode liquid retaining layer 26 (weight ratio R2 = weight of electrolyte / weight of polymer compound) is greater than the ratio of the weight of the electrolyte to the weight of the polymer compound in the positive electrode electrolyte layer 24 (weight ratio R1 = weight of electrolyte / weight of polymer compound). This is because a sufficient amount of electrolyte is supplied from the positive electrode liquid retaining layer 26 to the positive electrode electrolyte layer 24, so that the decrease in discharge capacity is suppressed even when charging and discharging are repeated. As a result, the thickness T1 of the positive electrode electrolyte layer 24 can be thin, and the energy density per volume of the battery element 20 is increased. The weight ratio R1 is a parameter that represents the content of the electrolyte in the positive electrode electrolyte layer 24, and the weight ratio R2 is a parameter that represents the content of the electrolyte in the positive electrode liquid retaining layer 26.

To determine the weight ratio R1, the secondary battery is disassembled to recover the positive electrode electrolyte layer 24, and then the positive electrode electrolyte layer 24 is analyzed using thermogravimetric differential thermal analysis (TG-DTA). This allows the weight of the electrolyte and the weight of the polymer compound to be measured, and the weight ratio R1 can be calculated based on the measurement results.

The procedure for determining weight ratio R2 is similar to that for determining weight ratio R1, except that the positive electrode liquid retaining layer 26 is recovered and analyzed instead of the positive electrode electrolyte layer 24.

The thickness T2 of the positive electrode liquid retaining layer 26 is not particularly limited and can be set arbitrarily. In particular, it is preferable that the thickness T2 of the positive electrode liquid retaining layer 26 is greater than the thickness T1 of the positive electrode electrolyte layer 24. This is because the amount of electrolyte held by the positive electrode liquid retaining layer 26 increases, and therefore the amount of electrolyte supplied from the positive electrode liquid retaining layer 26 to the positive electrode electrolyte layer 24 increases.

To obtain the thickness T1, first, the secondary battery is disassembled to recover the battery element 20. Next, the battery element 20 is cut along the YZ plane to expose the cross section of the battery element 20 (see FIG. 2). In this case, it is preferable to cut the battery element 20 at a flat portion of the battery element 20 having a flat three-dimensional shape. Next, the thickness of the positive electrode electrolyte layer 24 is measured by observing the cross section of the battery element 20 using a microscope such as a scanning electron microscope (SEM). In this case, the distance between the positive electrode active material layer 21B and the separator 23 is measured, and the distance is taken as the thickness of the positive electrode electrolyte layer 24. The observation magnification can be set arbitrarily. Finally, the thickness of the positive electrode electrolyte layer 24 is measured at 30 different locations, and the average value of the 30 thicknesses is calculated to obtain the thickness T1.

The procedure for determining thickness T2 is similar to the procedure for determining thickness T1, except that the thickness of the positive electrode liquid retaining layer 26 is measured based on the observation of the cross section of the battery element 20.

Here, as described above, the width of the positive electrode current collector 21A is the same as the width of the positive electrode active material layer 21B. Also, as shown in FIG. 2, the positive electrode liquid retaining layer 26 is adjacent not only to the side surface of the positive electrode electrolyte layer 24 but also to a part of the side surface of the positive electrode active material layer 21B. As a result, the positive electrode liquid retaining layer 26 is not adjacent to the positive electrode current collector 21A, but is separated from the positive electrode current collector 21A.

(Negative electrode electrolyte layer)
The negative electrode liquid retaining layer 27 is another second electrolyte layer that supplies an electrolytic solution to the negative electrode electrolyte layer 25, and is adjacent to the negative electrode electrolyte layer 25 as shown in Fig. 2. More specifically, the negative electrode liquid retaining layer 27 is adjacent to the negative electrode electrolyte layer 25 in a direction (Y-axis direction) intersecting with a direction (Z-axis direction) in which the negative electrode 22 and the separator 23 face each other via the negative electrode electrolyte layer 25. Here, the negative electrode liquid retaining layer 27 is not sandwiched between the negative electrode 22 and the separator 23, but is in contact with a side surface of the negative electrode electrolyte layer 25.

Here, the negative electrode liquid retaining layers 27 are disposed on both sides of the negative electrode electrolyte layer 25, so that the battery element 20 includes two negative electrode liquid retaining layers 27. That is, the first negative electrode liquid retaining layer 27 is disposed to the right of the negative electrode electrolyte layer 25, so that it is adjacent to the right side surface of the negative electrode electrolyte layer 25. The second negative electrode liquid retaining layer 27 is disposed to the left of the negative electrode electrolyte layer 25, so that it is adjacent to the left side surface of the negative electrode electrolyte layer 25.

The negative electrode liquid retaining layer 27 is disposed on one side of the separator 23 (the side opposite to the side on which the positive electrode liquid retaining layer 26 is formed) and is therefore supported by the separator 23.

Specifically, the negative electrode liquid retaining layer 27 has a configuration similar to that of the negative electrode electrolyte layer 25. That is, the negative electrode liquid retaining layer 27 is a gel electrolyte containing an electrolyte solution and a polymer compound, and the electrolyte solution is retained by the polymer compound. This is because the negative electrode liquid retaining layer 27 is capable of retaining the electrolyte solution and is also capable of supplying the electrolyte solution to the negative electrode electrolyte layer 25.

The electrolyte solution described here is another second electrolyte solution contained in the negative electrode liquid-retaining layer 27, and the polymer compound described here is another second polymer compound contained in the negative electrode liquid-retaining layer 27. Details regarding the electrolyte solution and polymer compound contained in the negative electrode liquid-retaining layer 27 are similar to the details regarding the electrolyte solution and polymer compound contained in the negative electrode electrolyte layer 25. Of course, the negative electrode liquid-retaining layer 27 may contain multiple insulating particles.

However, the type of electrolyte contained in the negative electrode liquid retaining layer 27 and the type of electrolyte contained in the negative electrode electrolyte layer 25 may be the same or different. Similarly, the type of polymer compound contained in the negative electrode liquid retaining layer 27 and the type of polymer compound contained in the negative electrode electrolyte layer 25 may be the same or different.

Here, the ratio of the weight of the electrolyte to the weight of the polymer compound in the negative electrode electrolyte layer 27 (weight ratio R4 = weight of electrolyte / weight of polymer compound) is greater than the ratio of the weight of the electrolyte to the weight of the polymer compound in the negative electrode electrolyte layer 25 (weight ratio R3 = weight of electrolyte / weight of polymer compound). This is because a sufficient amount of electrolyte is supplied from the negative electrode electrolyte layer 27 to the negative electrode electrolyte layer 25, so that the decrease in discharge capacity is suppressed even when charging and discharging are repeated. As a result, the thickness T3 of the negative electrode electrolyte layer 25 can be thin, and the energy density per volume of the battery element 20 is increased. The weight ratio R3 is a parameter that represents the content of the electrolyte in the negative electrode electrolyte layer 25, and the weight ratio R4 is a parameter that represents the content of the electrolyte in the negative electrode electrolyte layer 27.

The procedure for determining weight ratio R3 is similar to that for determining weight ratio R1, except that the negative electrode electrolyte layer 25 is collected and analyzed instead of the positive electrode electrolyte layer 24. The procedure for determining weight ratio R4 is similar to that for determining weight ratio R1, except that the negative electrode electrolyte layer 27 is collected and analyzed instead of the positive electrode electrolyte layer 24.

The thickness T4 of the negative electrode liquid retaining layer 27 is not particularly limited and can be set arbitrarily. In particular, it is preferable that the thickness T4 of the negative electrode liquid retaining layer 27 is greater than the thickness T3 of the negative electrode electrolyte layer 25. This is because the amount of electrolyte held by the negative electrode liquid retaining layer 27 increases, and therefore the amount of electrolyte supplied from the negative electrode liquid retaining layer 27 to the negative electrode electrolyte layer 25 increases.

The procedure for determining thickness T3 is similar to that for determining thickness T1, except that the thickness of the negative electrode electrolyte layer 25 (the distance between the negative electrode active material layer 22B and the separator 23) is measured based on the observation of the cross section of the battery element 20. The procedure for determining thickness T4 is similar to that for determining thickness T1, except that the thickness of the negative electrode liquid retaining layer 27 is measured based on the observation of the cross section of the battery element 20.

Here, as described above, the width of the negative electrode current collector 22A is the same as the width of the negative electrode active material layer 22B. Also, as shown in FIG. 2, the negative electrode liquid retaining layer 27 is adjacent not only to the side surface of the negative electrode electrolyte layer 25 but also to a part of the side surface of the negative electrode active material layer 22B. As a result, the negative electrode liquid retaining layer 27 is not adjacent to the negative electrode current collector 22A and is separated from the negative electrode current collector 22A.

[Positive and negative electrode leads]
1, the positive electrode lead 31 is a positive electrode terminal connected to the positive electrode 21, and more specifically, is connected to the positive electrode current collector 21A. The positive electrode lead 31 is led out from the inside to the outside of the exterior film 10, and contains a conductive material such as aluminum. The shape of the positive electrode lead 31 is not particularly limited, and specifically, it is either a thin plate shape, a mesh shape, or the like.

As shown in FIG. 1, the negative electrode lead 32 is a negative electrode terminal connected to the negative electrode 22, and more specifically, is connected to the negative electrode current collector 22A. This negative electrode lead 32 is led out from the inside of the exterior film 10 to the outside, and contains a conductive material such as copper. Here, the lead-out direction of the negative electrode lead 32 is the same as the lead-out direction of the positive electrode lead 31. The details of the shape of the negative electrode lead 32 are the same as the details of the shape of the positive electrode lead 31.

<1-2. Operation>
When the secondary battery is charged, in the battery element 20, lithium is released from the positive electrode 21 and is absorbed in the negative electrode 22 through the positive electrode electrolyte layer 24 and the negative electrode electrolyte layer 25. On the other hand, when the secondary battery is discharged, in the battery element 20, lithium is released from the negative electrode 22 and is absorbed in the positive electrode 21 through the positive electrode electrolyte layer 24 and the negative electrode electrolyte layer 25. During these charging and discharging times, lithium is absorbed and released in an ionic state.

When the secondary battery is charged and discharged, the electrolyte in the positive electrode electrolyte layer 24 is consumed, and when the electrolyte in the negative electrode electrolyte layer 25 is consumed, electrolyte is supplied from the positive electrode electrolyte layer 26 to the positive electrode electrolyte layer 24, and electrolyte is supplied from the negative electrode electrolyte layer 27 to the negative electrode electrolyte layer 25.

<1-3. Manufacturing method＞
In the case of manufacturing a secondary battery, the positive electrode 21, the negative electrode 22, the positive electrode electrolyte layer 24, the negative electrode electrolyte layer 25, the positive electrode electrolyte layer 26, and the negative electrode electrolyte layer 27 are each produced by the procedure described below. Then, a secondary battery is produced using these.

[Preparation of Positive Electrode]
First, a mixture (cathode mixture) in which a cathode active material, a cathode binder, and a cathode conductive agent are mixed together is put into a solvent to prepare a paste-like cathode mixture slurry. This solvent may be an aqueous solvent or an organic solvent. Next, the cathode mixture slurry is applied to both sides of the cathode current collector 21A to form the cathode active material layer 21B. After this, the cathode active material layer 21B may be compression molded using a roll press or the like. In this case, the cathode active material layer 21B may be heated, or the compression molding may be repeated multiple times. As a result, the cathode active material layer 21B is formed on both sides of the cathode current collector 21A, and thus the cathode 21 is produced.

[Preparation of negative electrode]
The negative electrode 22 is formed by the same procedure as the procedure for producing the positive electrode 21 described above. Specifically, first, a mixture (negative electrode mixture) in which a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent are mixed together is poured into a solvent to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is applied to both sides of the negative electrode current collector 22A to form the negative electrode active material layer 22B. After this, the negative electrode active material layer 22B may be compression molded. As a result, the negative electrode active material layer 22B is formed on both sides of the negative electrode current collector 22A, and the negative electrode 22 is produced.

[Formation of Positive Electrolyte Layer and Formation of Negative Electrolyte Layer]
First, an electrolyte salt is added to a solvent. This dissolves or disperses the electrolyte salt in the solvent, thereby preparing an electrolyte solution. Next, a precursor solution is prepared by mixing the electrolyte solution, a polymer compound, and, if necessary, an additional solvent. Finally, the precursor solution is applied to the surface of the positive electrode 21 to form the positive electrode electrolyte layer 24.

The negative electrode electrolyte layer 25 is formed by a procedure similar to that for forming the positive electrode electrolyte layer 24 described above. Specifically, an electrolyte solution is prepared, and a precursor solution is prepared using the electrolyte solution and a polymer compound. The precursor solution is then applied to the surface of the negative electrode 22 to form the negative electrode electrolyte layer 25.

[Formation of Positive Electrode Liquid Retaining Layer and Formation of Negative Electrode Liquid Retaining Layer]
First, an electrolyte solution is prepared by adding an electrolyte salt to a solvent. Next, a precursor solution is prepared by mixing the electrolyte solution, a polymer compound, and an additional solvent, if necessary, with each other, and then the precursor solution is applied to one surface of the separator 23 to form the positive electrode liquid retaining layer 26. In this case, the surface of the separator 23 may be masked using a polymer film such as a polypropylene film.

The negative electrode liquid retaining layer 27 is formed by the same procedure as that for forming the positive electrode liquid retaining layer 26 described above. Specifically, an electrolyte is prepared, and a precursor solution is prepared using the electrolyte and a polymer compound. The precursor solution is then applied to one side of the separator 23 (the side opposite to the side on which the positive electrode liquid retaining layer 26 is formed), thereby forming the negative electrode liquid retaining layer 27.

[Assembly of secondary battery]
First, the positive electrode lead 31 is connected to the positive electrode current collector 21A of the positive electrode 21 by welding or the like, and the negative electrode lead 32 is connected to the negative electrode current collector 22A of the negative electrode 22 by welding or the like.

Next, the positive electrode 21 on which the positive electrode electrolyte layer 24 is formed and the negative electrode 22 on which the negative electrode electrolyte layer 25 is formed are laminated with each other through the separator 23 on which the positive electrode electrolyte layer 26 and the negative electrode electrolyte layer 27 are formed. As a result, the positive electrode electrolyte layer 26 is adjacent to the positive electrode electrolyte layer 24, and the negative electrode electrolyte layer 27 is adjacent to the negative electrode electrolyte layer 25. Next, the positive electrode 21, the negative electrode 22, the separator 23, the positive electrode electrolyte layer 24, the negative electrode electrolyte layer 25, the positive electrode electrolyte layer 26, and the negative electrode electrolyte layer 27 are wound to prepare the battery element 20. Next, the battery element 20 is pressed using a press or the like to mold the battery element 20 into a flat shape.

Next, after the battery element 20 is accommodated inside the recessed portion 10U, the exterior film 10 (adhesive layer/metal layer/surface protection layer) is folded to make the exterior films 10 face each other. Finally, the outer peripheral edges of the three sides of the exterior films 10 (adhesive layer) facing each other are joined to each other using a heat fusion method or the like. In this case, a sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32. As a result, the battery element 20 is enclosed inside the bag-shaped exterior film 10, and a secondary battery is assembled.

[Stabilization of secondary battery]
The assembled secondary battery is charged and discharged. Various conditions such as the environmental temperature, the number of charge/discharge cycles, and the charge/discharge conditions can be set arbitrarily. As a result, a coating is formed on each surface of the positive electrode 21 and the negative electrode 22, and the state of the secondary battery is electrochemically stabilized. Thus, a laminate film type secondary battery using the exterior film 10 is completed.

<1-4. Actions and Effects>
In this secondary battery, positive electrode 21 and separator 23 face each other with positive electrode electrolyte layer 24 interposed therebetween, and positive electrode liquid retaining layer 26 is adjacent to positive electrode electrolyte layer 24 in a direction (Y-axis direction) intersecting with the direction (Z-axis direction) in which positive electrode 21 and separator 23 face each other with positive electrode electrolyte layer 24 interposed therebetween, and weight ratio R2 of positive electrode liquid retaining layer 26 is greater than weight ratio R1 of positive electrode electrolyte layer 24.

As a result, as described above, when the electrolyte in the positive electrode electrolyte layer 24 is consumed during charging and discharging, the electrolyte is supplied from the positive electrode electrolyte holding layer 26 to the positive electrode electrolyte layer 24, so that the amount of electrolyte in the positive electrode electrolyte layer 24 is less likely to decrease. In this case, in particular, since the weight ratio R2 of the positive electrode electrolyte holding layer 26 is greater than the weight ratio R1 of the positive electrode electrolyte layer 24, a sufficient amount of electrolyte is supplied from the positive electrode electrolyte holding layer 26 to the positive electrode electrolyte layer 24. Therefore, even if charging and discharging are repeated, the decrease in discharge capacity is suppressed, and excellent cycle characteristics can be obtained.

The effects obtained based on the positive electrode electrolyte layer 24 and the positive electrode liquid retaining layer 26 described above can also be obtained based on the negative electrode electrolyte layer 25 and the negative electrode liquid retaining layer 27. That is, the negative electrode 22 and the separator 23 face each other through the negative electrode electrolyte layer 25, and the negative electrode liquid retaining layer 27 is adjacent to the negative electrode electrolyte layer 25 in a direction (Y-axis direction) intersecting with the direction (Z-axis direction) in which the negative electrode 22 and the separator 23 face each other through the negative electrode electrolyte layer 25, and the weight ratio R4 of the negative electrode liquid retaining layer 27 is greater than the weight ratio R3 of the negative electrode electrolyte layer 25. As a result, a sufficient amount of electrolyte is supplied from the negative electrode liquid retaining layer 27 to the negative electrode electrolyte layer 25, so that the amount of electrolyte in the negative electrode electrolyte layer 25 is less likely to decrease. Therefore, even if charging and discharging are repeated, the decrease in discharge capacity is suppressed, and excellent cycle characteristics can be obtained.

In particular, if the thickness T2 of the positive electrode liquid retaining layer 26 is greater than the thickness T1 of the positive electrode electrolyte layer 24, the amount of electrolyte held by the positive electrode liquid retaining layer 26 increases. This increases the amount of electrolyte supplied from the positive electrode liquid retaining layer 26 to the positive electrode electrolyte layer 24, resulting in a higher effect.

The effects obtained based on the thickness T1 of the positive electrode electrolyte layer 24 and the thickness T2 of the positive electrode liquid retention layer 26 described above can also be obtained based on the thickness T3 of the negative electrode electrolyte layer 25 and the thickness T4 of the negative electrode liquid retention layer 27. That is, if the thickness T4 of the negative electrode liquid retention layer 27 is greater than the thickness T3 of the negative electrode electrolyte layer 25, the amount of electrolyte held by the negative electrode liquid retention layer 27 increases. Therefore, the amount of electrolyte supplied from the negative electrode liquid retention layer 27 to the negative electrode electrolyte layer 25 increases, and a higher effect can be obtained.

Furthermore, if the polymer compound contained in the positive electrode electrolyte layer 24 contains one or both of a homopolymer of vinylidene fluoride and a copolymer of vinylidene fluoride, the positive electrode electrolyte layer 24 can have excellent physical strength and excellent electrochemical stability, thereby achieving even greater effects.

In this case, if the vinylidene fluoride copolymer contains hexafluoropropylene as a polymerization component, the amount of electrolyte held by the positive electrode electrolyte layer 24 increases, and a higher effect can be obtained. If the vinylidene fluoride copolymer further contains one or both of an unsaturated dibasic acid and an unsaturated dibasic acid monoester as a polymerization component, the amount of electrolyte held by the positive electrode electrolyte layer 24 increases, and a higher effect can be obtained.

Furthermore, if the positive electrode electrolyte layer 24 contains a plurality of insulating particles, the amount of electrolyte held by the positive electrode electrolyte layer 24 increases, thereby achieving a greater effect.

The effects obtained based on the configuration of the positive electrode electrolyte layer 24 described above (type of polymer compound and the presence or absence of multiple insulating particles) can also be obtained based on the respective configurations of the negative electrode electrolyte layer 25, the positive electrode liquid retention layer 26 and the negative electrode liquid retention layer 27.

Furthermore, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the absorption and release of lithium, resulting in even greater effects.

2. Modified Examples
The configuration of the secondary battery described above can be modified as appropriate, as described below, although any two or more of the series of modifications described below may be combined with each other.

[Modification 1]
2, the positive electrode liquid retaining layer 26 is disposed on both sides of the positive electrode electrolyte layer 24, so that the battery element 20 includes two positive electrode liquid retaining layers 26. However, since the positive electrode liquid retaining layer 26 is disposed on only one side of the positive electrode electrolyte layer 24, the battery element 20 may include only one positive electrode liquid retaining layer 26. Even in this case, the decrease in discharge capacity is suppressed even when charging and discharging are repeated, as compared with the case where the battery element 20 does not include the positive electrode liquid retaining layer 26, so that the same effect can be obtained.

The above-mentioned modification of the location of the positive electrode liquid retaining layer 26 is also applicable to the location of the negative electrode liquid retaining layer 27. That is, since the negative electrode liquid retaining layer 27 is arranged on both sides of the negative electrode electrolyte layer 25, the battery element 20 includes two negative electrode liquid retaining layers 27, but since the negative electrode liquid retaining layer 27 is arranged on only one side of the negative electrode electrolyte layer 25, the battery element 20 may include only one negative electrode liquid retaining layer 27. Even in this case, the decrease in discharge capacity is suppressed even when charging and discharging are repeated, compared to when the battery element 20 does not include the negative electrode liquid retaining layer 27, so the same effect can be obtained.

[Modification 2]
In Fig. 2, the positive electrode liquid retaining layer 26 is adjacent to the positive electrode electrolyte layer 24, and the negative electrode liquid retaining layer 27 is adjacent to the negative electrode electrolyte layer 25. However, the positive electrode liquid retaining layer 26 may be adjacent to the positive electrode electrolyte layer 24, while the negative electrode liquid retaining layer 27 may not be adjacent to the negative electrode electrolyte layer 25. Alternatively, the positive electrode liquid retaining layer 26 may not be adjacent to the positive electrode electrolyte layer 24, while the negative electrode liquid retaining layer 27 may be adjacent to the negative electrode electrolyte layer 25. Even in this case, the decrease in discharge capacity is suppressed even when charging and discharging are repeated, compared with the case where the positive electrode liquid retaining layer 26 is not adjacent to the positive electrode electrolyte layer 24 and the negative electrode liquid retaining layer 27 is not adjacent to the negative electrode electrolyte layer 25, so that the same effect can be obtained.

[Modification 3]
2, in the process of producing the battery element 20, the positive electrode liquid retaining layer 26 is formed on one surface of the separator 23, and then the separator 23 on which the positive electrode liquid retaining layer 26 has been formed is wound. However, the positive electrode liquid retaining layer 26 may be formed on one surface of the separator 23 after the separator 23 is wound. Even in this case, the battery element 20 including the positive electrode liquid retaining layer 26 can be produced, and therefore the same effect can be obtained.

The above-mentioned variations in the method of producing the battery element 20 including the positive electrode liquid retaining layer 26 are also applicable to the method of producing the battery element 20 including the negative electrode liquid retaining layer 27. That is, the negative electrode liquid retaining layer 27 is formed on one side of the separator 23, and then the separator 23 on which the negative electrode liquid retaining layer 27 is formed is wound. However, the separator 23 may be wound, and then the negative electrode liquid retaining layer 27 may be formed on one side of the separator 23. In this case, the battery element 20 including the negative electrode liquid retaining layer 27 can be produced, and the same effect can be obtained.

[Modification 4]
A porous membrane separator 23 was used. However, although not specifically shown here, a laminated separator including a polymer compound layer may also be used.

Specifically, the laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer disposed on one or both surfaces of the porous membrane. This is because the adhesion of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, thereby suppressing misalignment (winding misalignment) of the battery element 20. This suppresses swelling of the secondary battery even if a decomposition reaction of the electrolyte occurs. The polymer compound layer includes a polymer compound such as polyvinylidene fluoride. This is because polyvinylidene fluoride and the like have excellent physical strength and are electrochemically stable.

In addition, one or both of the porous film and the polymer compound layer may contain one or more types of the multiple insulating particles. This is because the multiple insulating particles dissipate heat when the secondary battery generates heat, improving the safety (heat resistance) of the secondary battery. Details regarding the multiple insulating particles are as described above.

When making a laminated separator, a precursor solution containing a polymer compound and a solvent is prepared, and then the precursor solution is applied to one or both sides of a porous membrane. In this case, multiple insulating particles may be added to the precursor solution, if necessary.

Even when this laminated separator is used, the same effect can be obtained because lithium ions can move between the positive electrode 21 and the negative electrode 22. In this case, as described above, the winding misalignment of the battery element 20 is suppressed, and therefore a higher effect can be obtained.

[Modification 5]
In Fig. 1 and Fig. 2, a battery element 20 which is a wound electrode body is used. However, as shown in Fig. 3 which corresponds to Fig. 1 and Fig. 4 which corresponds to Fig. 2, a battery element 50 which is a laminated electrode body may be used. In the following, reference will be made to Fig. 1 and Fig. 2 which have already been described.

The laminate film type secondary battery shown in Figures 3 and 4 has a configuration similar to that of the laminate film type secondary battery shown in Figures 1 and 2, except that it has a battery element 50 (positive electrode 51, negative electrode 52, separator 53, positive electrode electrolyte layer 54, negative electrode electrolyte layer 55, positive electrode electrolyte layer 56, and negative electrode electrolyte layer 57) and a positive electrode lead 58 and a negative electrode lead 59 instead of the battery element 20 (positive electrode 21, negative electrode 22, separator 23, positive electrode electrolyte layer 24, negative electrode electrolyte layer 25, positive electrode electrolyte layer 26, and negative electrode electrolyte layer 27) and positive electrode lead 31 and negative electrode lead 32.

The respective configurations of the positive electrode 51, negative electrode 52, separator 53, positive electrode electrolyte layer 54, negative electrode electrolyte layer 55, positive electrode liquid retention layer 56, negative electrode liquid retention layer 57, positive electrode lead 58 and negative electrode lead 59 are similar to the respective configurations of the positive electrode 21, negative electrode 22, separator 23, positive electrode electrolyte layer 24, negative electrode electrolyte layer 25, positive electrode liquid retention layer 26, negative electrode liquid retention layer 27, positive electrode lead 31 and negative electrode lead 32, except as described below.

That is, the relationship between the weight ratio R1 of the positive electrolyte layer 54 and the weight ratio R2 of the positive electrolyte layer 56, and the relationship between the weight ratio R3 of the negative electrolyte layer 55 and the weight ratio R4 of the negative electrolyte layer 57 are as described above. Also, the relationship between the thickness T1 of the positive electrolyte layer 54 and the thickness T2 of the positive electrolyte layer 56, and the relationship between the thickness T3 of the negative electrolyte layer 55 and the thickness T of the negative electrolyte layer 57 are as described above.

In the battery element 50, the positive electrode 51 and the negative electrode 52 are alternately stacked with the separator 53, the positive electrode electrolyte layer 54, and the negative electrode electrolyte layer 55 interposed therebetween. The positive electrode electrolyte layer 56 is adjacent to the positive electrode electrolyte layer 54, and the negative electrode electrolyte layer 57 is adjacent to the negative electrode electrolyte layer 55. The number of layers of the positive electrode 51, the negative electrode 52, the separator 53, the positive electrode electrolyte layer 54, and the negative electrode electrolyte layer 55 is not particularly limited and can be set arbitrarily. The positive electrode 51 includes a positive electrode collector 51A and a positive electrode active material layer 51B corresponding to the positive electrode collector 21A and the positive electrode active material layer 21B, and the negative electrode 52 includes a negative electrode collector 52A and a negative electrode active material layer 52B corresponding to the negative electrode collector 22A and the negative electrode active material layer 22B.

However, as shown in Figures 3 and 4, the positive electrode collector 51A includes a protrusion 51AT where the positive electrode active material layer 51B is not formed, and the negative electrode collector 52A includes a protrusion 52AT where the negative electrode active material layer 52B is not formed. This protrusion 52AT is arranged at a position where it does not overlap with the protrusion 51AT. The multiple protrusions 51AT are joined to each other to form a single lead-like joint 51Z, and the multiple protrusions 52AT are joined to each other to form a single lead-like joint 52Z. The positive electrode lead 58 is connected to the joint 51Z, and the negative electrode lead 59 is connected to the joint 52Z.

The manufacturing method of the secondary battery shown in Figures 3 and 4 is similar to the manufacturing method of the secondary battery shown in Figures 1 and 2, except that a battery element 50 is prepared instead of the battery element 20, and a secondary battery is assembled using a positive electrode lead 58 and a negative electrode lead 59 instead of a positive electrode lead 31 and a negative electrode lead 32.

Specifically, first, a positive electrode 51 having a positive electrode active material layer 51B formed on both sides of a positive electrode collector 51A (excluding the protruding portion 51AT), and a negative electrode 52 having a negative electrode active material layer 52B formed on both sides of a negative electrode collector 52A (excluding the protruding portion 52AT) are prepared. Next, a positive electrode electrolyte layer 54 is formed on the surface of the positive electrode 51, and a negative electrode electrolyte layer 55 is formed on the surface of the negative electrode 52. In addition, a positive electrode liquid retention layer 56 and a negative electrode liquid retention layer 57 are formed on both sides of a separator 53. Next, a battery element 50 is prepared by alternately stacking a positive electrode 51 having a positive electrode electrolyte layer 54 formed thereon and a negative electrode 52 having a negative electrode electrolyte layer 55 formed thereon through a separator 53 having a positive electrode liquid retention layer 56 and a negative electrode liquid retention layer 57 formed thereon.

Next, the plurality of protrusions 51AT are joined together by welding or the like to form joint 51Z, and the plurality of protrusions 52AT are joined together by welding or the like to form joint 52Z. Finally, the positive electrode lead 58 is connected to the protrusion 51AT by welding or the like, and the negative electrode lead 59 is connected to the protrusion 52AT by welding or the like.

When using this laminated electrode battery element 50, the same effect can be obtained as when using the wound electrode battery element 20, because the decrease in discharge capacity is suppressed even with repeated charging and discharging.

In addition, each of the above-mentioned modified examples 1 to 4 may be applied to battery element 50 instead of battery element 20.

<3. Uses of secondary batteries>
The use (application example) of the secondary battery is not particularly limited. The secondary battery used as a power source may be a main power source for electronic devices and electric vehicles, or may be an auxiliary power source. The main power source is a power source that is used preferentially regardless of the presence or absence of other power sources. The auxiliary power source is a power source that is used instead of the main power source, or a power source that is switched from the main power source.

Specific examples of uses for secondary batteries are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals. Storage devices such as backup power sources and memory cards. Power tools such as electric drills and power saws. Battery packs installed in electronic devices, etc. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid cars). Power storage systems such as home or industrial battery systems that store power in preparation for emergencies, etc. In these applications, one secondary battery may be used, or multiple secondary batteries may be used.

The battery pack may use a single cell or a battery pack. An electric vehicle is a vehicle that operates (runs) using a secondary battery as a driving power source, and may be a hybrid vehicle that also has a driving source other than the secondary battery. In a home power storage system, it is possible to use household electrical appliances, etc., by utilizing the power stored in the secondary battery, which is a power storage source.

Here, we will specifically explain an example of an application of a secondary battery. The configuration of the application example described below is merely an example and can be modified as appropriate.

Figure 5 shows the block diagram of a battery pack. The battery pack described here is a battery pack (a so-called soft pack) that uses one secondary battery, and is installed in electronic devices such as smartphones.

As shown in Figure 5, the battery pack includes a power source 61 and a circuit board 62. The circuit board 62 is connected to the power source 61 and includes a positive terminal 63, a negative terminal 64, and a temperature detection terminal 65.

The power source 61 includes one secondary battery. In this secondary battery, the positive electrode lead is connected to the positive electrode terminal 63, and the negative electrode lead is connected to the negative electrode terminal 64. This power source 61 can be connected to the outside via the positive electrode terminal 63 and the negative electrode terminal 64, and therefore can be charged and discharged. The circuit board 62 includes a control unit 66, a switch 67, a thermosensitive resistor (PTC element) 68, and a temperature detection unit 69. However, the PTC element 68 may be omitted.

The control unit 66 includes a central processing unit (CPU) and memory, and controls the operation of the entire battery pack. This control unit 66 detects and controls the usage state of the power source 61 as necessary.

When the voltage of the power source 61 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, the control unit 66 turns off the switch 67 to prevent the charging current from flowing through the current path of the power source 61. The overcharge detection voltage is not particularly limited, but is specifically 4.2V±0.05V, and the overdischarge detection voltage is not particularly limited, but is specifically 2.4V±0.1V.

The switch 67 includes a charge control switch, a discharge control switch, a charge diode, and a discharge diode, and switches between the presence and absence of a connection between the power source 61 and an external device in response to an instruction from the control unit 66. The switch 67 includes a field effect transistor (MOSFET) using a metal oxide semiconductor, and the charge/discharge current is detected based on the ON resistance of the switch 67.

The temperature detection unit 69 includes a temperature detection element such as a thermistor, measures the temperature of the power supply 61 using the temperature detection terminal 65, and outputs the temperature measurement result to the control unit 66. The temperature measurement result measured by the temperature detection unit 69 is used when the control unit 66 performs charge/discharge control in the event of abnormal heat generation, and when the control unit 66 performs correction processing when calculating the remaining capacity.

An example of this technology is described below.

<Examples 1 to 11 and Comparative Examples 1 to 3>
As described below, after the secondary battery was fabricated, the battery characteristics of the secondary battery were evaluated.

[Preparation of secondary battery]
A laminate film type lithium ion secondary battery including the battery element 20 (wound electrode body) shown in Figs. 1 and 2 was fabricated by the following procedure.

(Preparation of Positive Electrode)
First, 96 parts by mass of a positive electrode active material (LiNi _0.80 Co _0.15 Al _0.05 O ₂ which is a lithium-containing compound (oxide), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 1 part by mass of a positive electrode conductive agent (carbon black) were mixed together to prepare a positive electrode mixture. Next, the positive electrode mixture was added to a solvent (N-methyl-2-pyrrolidone which is an organic solvent), and the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector 21A (aluminum foil having a thickness of 15 μm) using a coating device, and then the positive electrode mixture slurry was dried to form a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B was compression molded using a roll press, and then the positive electrode current collector 21A on which the positive electrode active material layer 21B was formed was cut into a strip shape (48 mm × 300 mm). In this way, the positive electrode 21 was produced.

(Preparation of negative electrode)
First, 90 parts by mass of the negative electrode active material (artificial graphite, which is a carbon material) and 10 parts by mass of the negative electrode binder (polyvinylidene fluoride) were mixed together to prepare a negative electrode mixture. Next, the negative electrode mixture was added to a solvent (N-methyl-2-pyrrolidone, which is an organic solvent), and then the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of the negative electrode current collector 22A (copper foil with a thickness of 15 μm) using a coating device, and then the negative electrode mixture slurry was dried to form the negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B was compression-molded using a roll press machine, and then the negative electrode current collector 22A on which the negative electrode active material layer 22B was formed was cut into a strip (50 mm x 310 mm). This produced the negative electrode 22.

(Formation of Positive Electrolyte Layer)
First, electrolyte salt (lithium salt _LiPF6 ) was added to a solvent (carbonate ester compounds ethylene carbonate (EC) and propylene carbonate (PC)), and the solvent was then stirred. In this case, the mixing ratio (weight ratio) of the solvent was ethylene carbonate:propylene carbonate = 50:50, and the content of the electrolyte salt was 1 mol/kg relative to the solvent.

The polymer compounds used were polyvinylidene fluoride (PVDF), a homopolymer of vinylidene fluoride, and a copolymer of six types of vinylidene fluoride. The six types of vinylidene fluoride copolymers used were a copolymer of vinylidene fluoride and hexafluoropropylene (VH), a copolymer of vinylidene fluoride, hexafluoropropylene, and an unsaturated dibasic acid (maleic acid) (VHMA), a copolymer of vinylidene fluoride, hexafluoropropylene, and an unsaturated dibasic acid monoester (maleic acid monomethyl ester) (VHMMM), a copolymer of vinylidene fluoride, hexafluoropropylene, and an unsaturated dibasic acid monoester (maleic acid monoethyl ester) (VHMME), a copolymer of vinylidene fluoride, hexafluoropropylene, and an unsaturated dibasic acid monoester (citraconate monomethyl ester) (VHCMM), and a copolymer of vinylidene fluoride, hexafluoropropylene, and an unsaturated dibasic acid monoester (citraconate monoethyl ester) (VHCME). In this way, the electrolyte was prepared.

Next, the electrolyte, the polymer compound, and the additional solvent (dimethyl carbonate) were mixed together to prepare a mixed solution. Next, the mixed solution was heated and stirred using a homogenizer (heating temperature = 80 ° C, stirring time = 30 minutes to 1 hour) to prepare a sol-like precursor solution. Finally, the precursor solution was applied to the surface of the positive electrode 21, and then the precursor solution was dried to form the positive electrode electrolyte layer 24. When forming this positive electrode electrolyte layer 24, the weight ratio R1 was controlled by adjusting the mixing ratio of the electrolyte and the polymer compound, and the thickness T1 (μm) was controlled by adjusting the amount of the precursor solution applied. Details regarding the weight ratio R1 and the thickness T1 are as shown in Table 1.

(Formation of negative electrode electrolyte layer)
The negative electrode electrolyte layer 25 was formed by the same procedure as that for forming the positive electrode electrolyte layer 24, except that the precursor solution was applied to the surface of the negative electrode 22. Details regarding the weight ratio R3 and the thickness T3 are as shown in Table 1.

(Formation of Positive Electrode Liquid Retaining Layer)
Except for applying the precursor solution to one surface of separator 23 (a microporous polypropylene film having a thickness of 11 μm), positive electrode liquid retaining layer 26 was formed in the same manner as in the formation of positive electrode electrolyte layer 24. In this case, the mixing ratio of the electrolyte and the polymer compound was adjusted so that weight ratio R2 of positive electrode liquid retaining layer 26 was greater than weight ratio R1 of positive electrode electrolyte layer 24. Details regarding weight ratio R2 and thickness T2 are as shown in Table 1.

(Formation of negative electrode electrolyte layer)
Except for applying the precursor solution to one surface of the separator 23 (the surface opposite to the surface on which the positive electrode liquid retaining layer 26 is formed), the negative electrode liquid retaining layer 27 was formed in the same manner as in the formation of the positive electrode electrolyte layer 24. In this case, the mixing ratio of the electrolyte and the polymer compound was adjusted so that the weight ratio R4 of the negative electrode liquid retaining layer 27 was larger than the weight ratio R3 of the negative electrode electrolyte layer 25. Details of the weight ratio R4 and the thickness T4 are as shown in Table 1.

In Examples 1 to 10 and Comparative Examples 1 to 3, electrolytes having a common composition and a common type of polymer compound were used to form the positive electrode electrolyte layer 24, the negative electrode electrolyte layer 25, the positive electrode liquid retention layer 26, and the negative electrode liquid retention layer 27. Table 1 shows only one "Polymer compound" column, which indicates that a common type of polymer compound was used in the positive electrode electrolyte layer 24, the negative electrode electrolyte layer 25, the positive electrode liquid retention layer 26, and the negative electrode liquid retention layer 27, as described above.

In Example 11, the types of polymer compounds used to form the positive electrode electrolyte layer 24 and the negative electrode electrolyte layer 25 were different from the types of polymer compounds used to form the positive electrode liquid retaining layer 26 and the negative electrode liquid retaining layer 27. Specifically, PVDF was used to form the positive electrode electrolyte layer 24 and the negative electrode electrolyte layer 25, and VHMMM was used to form the positive electrode liquid retaining layer 26 and the negative electrode liquid retaining layer 27.

For comparison, neither the positive electrode liquid retaining layer 26 nor the negative electrode liquid retaining layer 27 was formed. For comparison, the positive electrode liquid retaining layer 26 was formed so that the weight ratio R2 was equal to or less than the weight ratio R1, and the negative electrode liquid retaining layer 27 was formed so that the weight ratio R4 was equal to or less than the weight ratio R3.

(Assembly of secondary batteries)
First, the aluminum positive electrode lead 31 was welded to the positive electrode current collector 21 A of the positive electrode 21 , and the copper negative electrode lead 32 was welded to the negative electrode current collector 22 A of the negative electrode 22 .

Next, the positive electrode 21 on which the positive electrode electrolyte layer 24 is formed and the negative electrode 22 on which the negative electrode electrolyte layer 25 is formed were laminated together via the separator 23 on which the positive electrode electrolyte layer 26 and the negative electrode electrolyte layer 27 are formed. Next, the positive electrode 21, the negative electrode 22, the separator 23, the positive electrode electrolyte layer 24, the negative electrode electrolyte layer 25, the positive electrode electrolyte layer 26, and the negative electrode electrolyte layer 27 were wound together to produce the battery element 20. Next, the battery element 20 was pressed using a press machine to mold the battery element 20 into a flat shape.

Next, the battery element 20 was placed inside the recess 10U, and the exterior film 10 (adhesive layer/metal layer/surface protection layer) was folded so that the exterior films 10 faced each other. The exterior film 10 was an aluminum laminate film in which the adhesive layer (polypropylene film with a thickness of 30 μm), the metal layer (aluminum foil with a thickness of 40 μm), and the surface protection layer (nylon film with a thickness of 25 μm) were laminated in this order from the inside.

Finally, the outer peripheral edges of three sides of the opposing exterior films 10 (fusing layers) were heat-sealed to each other. In this case, a sealing film 41 (a polypropylene film having a thickness of 5 μm) was inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 (a polypropylene film having a thickness of 5 μm) was inserted between the exterior film 10 and the negative electrode lead 32. As a result, the battery element 20 was enclosed inside the bag-shaped exterior film 10, and a secondary battery was assembled.

(Stabilization of secondary batteries)
The secondary battery was charged and discharged for one cycle in a room temperature environment (temperature = 23 ° C.). During charging, the battery was charged at a constant current of 0.1 C until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 0.05 C. During discharging, the battery was discharged at a constant current of 0.1 C until the voltage reached 3.0 V. 0.1 C is the current value at which the battery capacity (theoretical capacity) is fully discharged in 10 hours, and 0.05 C is the current value at which the battery capacity is fully discharged in 20 hours. This completed a laminate film type secondary battery.

[Evaluation of Battery Characteristics]
When the battery characteristics (cycle characteristics) of the secondary battery were evaluated, the results shown in Table 1 were obtained.

When investigating cycle characteristics, first, the discharge capacity (discharge capacity at the first cycle) was measured by charging and discharging the secondary battery in a room temperature environment (temperature = 23°C). Next, the discharge capacity (discharge capacity at the 300th cycle) was measured by repeatedly charging and discharging the secondary battery in the same environment until the number of cycles reached 300. Finally, the capacity retention rate, which is an index for evaluating cycle characteristics, was calculated based on the formula: capacity retention rate (%) = (discharge capacity at the 300th cycle / discharge capacity at the first cycle) x 100.

The charging and discharging conditions were the same as those for stabilizing the secondary battery, except that the charging current and discharging current were both changed to 0.5 C. 0.5 C is the current value that fully discharges the battery capacity in 2 hours.

[Discussion]
As shown in Table 1, the capacity retention rate varied greatly depending on the configuration of the secondary battery.

Specifically, when neither the positive electrode liquid retention layer 26 nor the negative electrode liquid retention layer 27 was used (Comparative Example 1), the capacity retention rate decreased significantly.

In contrast, when both the positive electrode liquid retaining layer 26 and the negative electrode liquid retaining layer 27 were used (Examples 1 to 11 and Comparative Examples 2 and 3), large differences in capacity retention rates occurred depending on the weight ratios R1 to R4.

That is, when the weight ratio R2 was equal to or less than the weight ratio R1 and the weight ratio R4 was equal to or less than the weight ratio R3 (Comparative Examples 2 and 3), the capacity retention rate increased very slightly compared to the case where neither the positive electrode liquid retaining layer 26 nor the negative electrode liquid retaining layer 27 was used (Comparative Example 1). However, the capacity retention rate was almost maintained, and therefore still significantly decreased.

When weight ratio R2 was greater than weight ratio R1 and weight ratio R4 was greater than weight ratio R3 (Examples 1 to 11), the capacity retention rate increased significantly compared to the case where neither the positive electrode liquid retention layer 26 nor the negative electrode liquid retention layer 27 was used (Comparative Example 1). In this case, the capacity retention rate increased by more than double, resulting in a dramatic increase in the capacity retention rate.

In particular, when weight ratio R2 was greater than weight ratio R1 and weight ratio R4 was greater than weight ratio R3, a series of trends was obtained, as described below.

First, when thickness T2 was greater than thickness T1 and thickness T4 was greater than thickness T3, the capacity retention rate was increased more.

Secondly, when a vinylidene fluoride copolymer was used as the polymer compound, more specifically when the vinylidene fluoride copolymer contained hexafluoropropylene as a polymerization component, the capacity retention rate was further increased. In this case, when the vinylidene fluoride copolymer further contained either an unsaturated dibasic acid or an unsaturated dibasic acid monoester as a polymerization component, the capacity retention rate was further increased.

<Examples 12 to 20>
As shown in Table 2, a secondary battery was produced and its battery characteristics were evaluated in the same manner as in Example 2, except that a plurality of insulating particles were contained in each of the positive electrode electrolyte layer 24, the negative electrode electrolyte layer 25, the positive electrode liquid retaining layer 26, and the negative electrode liquid retaining layer 27.

The positive electrode electrolyte layer 24, the negative electrode electrolyte layer 25, the positive electrode liquid retaining layer 26, and the negative electrode liquid retaining layer 27 were formed in the same manner, except that a plurality of insulating particles were added to the electrolyte, the polymer compound, and the additional solvent (dimethyl carbonate). As the material (insulating material) of the plurality of insulating particles, aluminum oxide (Al ₂ O ₃ , median diameter D50 = 0.4 μm) and titanium oxide (TiO ₂ , median diameter D50 = 0.4 μm), which are powdered inorganic materials, and acrylic resin (median diameter D50 = 0.4 μm), which is a powdered polymer compound, were used. The amount of the plurality of insulating particles added was 2.5 wt % of the sum of the weight of the electrolyte and the weight of the polymer compound.

As shown in Table 2, when each of the positive electrode electrolyte layer 24, the negative electrode electrolyte layer 25, the positive electrode liquid retention layer 26 and the negative electrode liquid retention layer 27 contained a plurality of insulating particles (Examples 12 to 20), the capacity retention rate was further increased.

<Examples 21 to 27 and Comparative Examples 4 to 6>
As shown in Table 3, secondary batteries were produced and their battery characteristics were evaluated in the same manner as in Examples 1 to 20 and Comparative Examples 1 to 3, except that a laminate film type lithium ion secondary battery having a battery element 50 (laminated electrode body) shown in FIGS. 3 and 4 was produced instead of a laminate film type lithium ion secondary battery having a battery element 20 (wound electrode body) shown in FIGS. 1 and 2.

The manufacturing procedure for a secondary battery having battery element 50 is similar to the manufacturing procedure for a secondary battery having battery element 20, except as described below.

A battery element 50 was produced by alternately stacking a positive electrode 51 on which a positive electrode electrolyte layer 54 was formed and a negative electrode 52 on which a negative electrode electrolyte layer 55 was formed, via a separator 53 on which a positive electrode electrolyte layer 56 and a negative electrode electrolyte layer 57 were formed. Next, a joint 51Z was formed by welding a plurality of protrusions 51AT to each other, and a joint 52Z was formed by welding a plurality of protrusions 52AT to each other. Next, a positive electrode lead 58 was welded to the protrusion 51AT, and a negative electrode lead 59 was welded to the protrusion 52AT.

As shown in Table 3, when battery element 50 (laminated electrode body) was used (Examples 21 to 27 and Comparative Examples 4 to 6), similar results were obtained as when battery element 20 (wound electrode body) was used (Examples 1 to 20 and Comparative Examples 1 to 3).

That is, when neither the positive electrode liquid retaining layer 56 nor the negative electrode liquid retaining layer 57 was used (Comparative Example 4), the capacity retention rate was significantly reduced. Even when both the positive electrode liquid retaining layer 56 and the negative electrode liquid retaining layer 57 were used, when the weight ratio R2 was equal to or less than the weight ratio R1 and the weight ratio R4 was equal to or less than the weight ratio R3 (Comparative Examples 5 and 6), the capacity retention rate was still significantly reduced.

In contrast, when both the positive electrode liquid retaining layer 56 and the negative electrode liquid retaining layer 57 were used, and the weight ratio R2 was greater than the weight ratio R1 and the weight ratio R4 was greater than the weight ratio R3 (Examples 21 to 27), the capacity retention rate increased significantly. In addition, the series of trends described in Table 1 were also obtained.

[summary]
From the results shown in Tables 1 to 3, when the positive electrode electrolyte layer 24 was disposed between the positive electrode 21 and the separator 23, the positive electrode liquid retaining layer 26 was adjacent to the positive electrode electrolyte layer 24, and the weight ratio R2 of the positive electrode liquid retaining layer 26 was larger than the weight ratio R1 of the positive electrode electrolyte layer 24, the capacity retention rate was significantly improved. Therefore, excellent cycle characteristics were obtained in the secondary battery.

In addition, even when a negative electrode electrolyte layer 25 is disposed between the negative electrode 22 and the separator 23, a negative electrode liquid retaining layer 27 is adjacent to the negative electrode electrolyte layer 25, and the weight ratio R4 of the negative electrode liquid retaining layer 27 is greater than the weight ratio R3 of the negative electrode electrolyte layer 25, the capacity retention rate is significantly improved, and therefore excellent cycle characteristics are obtained in the secondary battery.

The present technology has been described above with reference to one embodiment and an example, but the configuration of the present technology is not limited to the configuration described in the embodiment and example and can be modified in various ways.

Although the battery structure of the secondary battery has been described as being of a laminate film type, the type of battery structure is not particularly limited. Specifically, the battery structure may be of a cylindrical type, a square type, a coin type, a button type, etc.

Although the battery element configuration has been described as being wound and stacked, the configuration of the battery element is not particularly limited. Specifically, the battery element may be configured as a zigzag fold type in which the positive and negative electrodes are folded in a zigzag pattern.

Furthermore, although the electrode reactant is described as being lithium, the type of the electrode reactant is not particularly limited. Specifically, as described above, the electrode reactant may be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be other light metals such as aluminum.

The effects described in this specification are merely examples, and the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present technology.

Claims (7)

a first electrolyte layer including a first electrolytic solution and a first polymer compound;
an electrode and a separator facing each other with the first electrolyte layer interposed therebetween;
a second electrolyte layer adjacent to the first electrolyte layer in a direction intersecting a direction in which the electrodes and the separator face each other with the first electrolyte layer interposed therebetween, the second electrolyte layer including a second electrolytic solution and a second polymer compound;
a ratio of the weight of the second electrolytic solution to the weight of the second polymer compound is greater than a ratio of the weight of the first electrolytic solution to the weight of the first polymer compound;
Secondary battery. The thickness of the second electrolyte layer is greater than the thickness of the first electrolyte layer.
The secondary battery according to claim 1 . At least one of the first polymer compound and the second polymer compound includes at least one of a homopolymer of vinylidene fluoride and a copolymer of vinylidene fluoride.
The secondary battery according to claim 1 or 2. The vinylidene fluoride copolymer contains hexafluoropropylene as a polymerization component.
The secondary battery according to claim 3. The vinylidene fluoride copolymer further contains at least one of an unsaturated dibasic acid and an unsaturated dibasic acid monoester as a polymerization component.
The secondary battery according to claim 4. At least one of the first electrolyte layer and the second electrolyte layer further includes a plurality of insulating particles.
The secondary battery according to claim 1 . It is a lithium-ion secondary battery.
The secondary battery according to claim 1 .

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