Secondary batteries, battery packs, vehicles, and stationary power supplies

Abstract

To provide a secondary battery and a battery pack that exhibit high charge / discharge efficiency and long life performance, and a vehicle and a stationary power source that are equipped with the battery pack.SOLUTION: A secondary battery includes a negative electrode including a negative electrode active material-containing layer, a positive electrode including a positive electrode active material-containing layer, a separator located between the negative electrode and the positive electrode, and an aqueous electrolyte. The separator includes a composite layer including inorganic solid particles and a polymer material. The particle size distribution of the inorganic solid particles in the composite layer includes at least two peaks. The frequency FPS of the peak top PS of the smallest particle size peak in the particle size distribution and the frequency FPL of the peak top PL of the largest particle size peak satisfy the relationship 0.9≤FPS / FPL≤5. The porosity of the composite layer is smaller than both the porosity of the negative electrode active material-containing layer and the porosity of the positive electrode active material-containing layer, and is 1% or more and less than 15%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Embodiments of the present invention relate to secondary batteries, battery packs, vehicles, and stationary power supplies. [Background technology]

[0002] Non-aqueous electrolyte batteries, such as lithium-ion batteries, are used as power sources in a wide range of fields. Non-aqueous electrolyte batteries come in various forms, from small ones for electronic devices to large ones for electric vehicles. Because non-aqueous electrolyte batteries use non-aqueous electrolytes containing flammable substances such as ethylene carbonate, safety measures are required.

[0003] Development is underway on aqueous electrolyte batteries that use aqueous electrolytes containing non-flammable aqueous solvents instead of non-aqueous electrolytes. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2010-56027 [Patent Document 2] Japanese Patent Publication No. 2018-160443 [Patent Document 3] Japanese Patent Publication No. 2018-163893 [Patent Document 4] Japanese Patent Publication No. 2019-57373 [Non-patent literature]

[0005] [Non-Patent Document 1] Appl. Mater. Interfaces 2014, 6, 526-531 [Non-Patent Document 2] Materials Sciences and Applications, 2014, 5, 81-85 [Non-Patent Document 3] Appl. Mater. Interfaces 2016, 8, 23688-23695 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The objective is to provide secondary batteries and battery packs that exhibit high charge / discharge efficiency and long lifespan, as well as vehicles and stationary power supplies equipped with such battery packs. [Means for solving the problem]

[0007] According to the embodiment, a secondary battery is provided comprising a negative electrode containing a negative electrode active material layer, a positive electrode containing a positive electrode active material layer, a separator located between the negative electrode and the positive electrode, and an aqueous electrolyte. The separator includes a composite layer containing electrically insulating inorganic solid particles and a polymer material. The particle size distribution of the inorganic solid particles in the composite layer includes at least two peaks. The peak top P of the smallest particle size in the particle size distribution is S Frequency FP S and the peak top P of the peak on the side with the largest particle size L Frequency FP L This means that 0.9 ≤ FP S / FP L The relationship is ≤5. The porosity of the composite layer is less than the porosity of the negative electrode active material-containing layer and the positive electrode active material-containing layer, and is between 1% and 15%.

[0008] According to another embodiment, a battery pack comprising a secondary battery according to the above embodiment is provided.

[0009] Furthermore, according to another embodiment, a vehicle is provided that is equipped with the battery pack according to the above embodiment.

[0010] Furthermore, according to another embodiment, a stationary power supply comprising a battery pack according to the above embodiment is provided. [Brief explanation of the drawing]

[0011] [Figure 1] A graph showing an example of the particle size distribution of a composite layer that may be included in a secondary battery according to this embodiment. [Figure 2] A schematic cross-sectional view showing an example of a composite layer that may be included in the secondary battery according to this embodiment. [Figure 3] A schematic cross-sectional view showing an example of a conventional composite layer. [Figure 4] A schematic cross-sectional view showing an example of an electrode group that may be included in a secondary battery according to this embodiment. [Figure 5] A schematic cross-sectional view showing an example of a secondary battery according to this embodiment. [Figure 6] Figure 5 shows a cross-sectional view of a secondary battery along the line VI-VI. [Figure 7] A partially cutaway perspective view schematically showing another example of a secondary battery according to the embodiment. [Figure 8] Figure 7 shows an enlarged cross-sectional view of section E of the secondary battery. [Figure 9] A schematic perspective view showing an example of a battery pack according to this embodiment. [Figure 10] A schematic perspective view showing an example of a battery pack according to the embodiment. [Figure 11] An exploded perspective view schematically showing another example of a battery pack according to the embodiment. [Figure 12] A block diagram showing an example of the electrical circuit of the battery pack shown in Figure 11. [Figure 13] A partially transparent view schematically showing an example of a vehicle according to the embodiment. [Figure 14] A block diagram showing an example of a system including a stationary power supply according to the embodiment. [Modes for carrying out the invention]

[0012] Generally, the potential window of aqueous electrolytes is narrower than that of non-aqueous electrolytes. Therefore, in aqueous electrolyte batteries, depending on the combination of positive and negative electrodes, the water in the aqueous electrolyte may undergo electrolysis during the initial charging. For example, lithium titanate (Li4Ti5O), which has a spinel structure... 12In aqueous electrolyte batteries that use materials that operate at relatively low potentials, such as ), as the negative electrode active material, when the battery is operated, electrolysis of water occurs on the negative electrode surface, which can reduce charge / discharge efficiency or cause self-discharge. Furthermore, the electrolysis of water generates protons (hydrogen cations; H2) which produce hydrogen (H2). + Because this involves a reduction reaction, safety may be compromised. Therefore, separators used in aqueous electrolyte batteries require a dense structure that suppresses contact with the water electrode, that is, to provide high water-blocking properties.

[0013] Furthermore, in secondary batteries using lithium metal or zinc metal as electrodes, and in secondary batteries using electrolytes containing lithium ions or zinc ions, deposits such as lithium dendrites and zinc dendrites may form on the electrodes during charging and discharging. If these dendrites penetrate the separator, an internal short circuit may occur. Therefore, the separator needs to be dense in order to prevent these dendrites from penetrating it.

[0014] One example of a separator with particularly high density is a solid electrolyte membrane. A solid electrolyte membrane is a membrane composed solely of ion-conducting solid electrolyte particles. Because a solid electrolyte membrane does not allow solvents to pass through but selectively allows specific ions to pass through, it has complete water-impermeable properties. However, solid electrolyte membranes have low flexibility and therefore lack sufficient durability. Furthermore, using a solid electrolyte membrane as a separator requires a certain thickness, making it difficult to increase the energy density of the battery.

[0015] To address this problem, polymer composite films have been proposed in which solid electrolyte particles are bonded together with polymer materials. Although polymer composite films do not exhibit the same level of water-impermeability as solid electrolyte films, they possess high density and can be impregnated with small amounts of aqueous electrolytes. Furthermore, polymer composite films are more flexible than solid electrolyte films and can be made into thin films.

[0016] (First Embodiment) According to the first embodiment, a secondary battery is provided. The secondary battery includes a negative electrode, a positive electrode, a separator, and an aqueous electrolyte. The separator is positioned between the negative electrode and the positive electrode. The separator is composed of a composite layer containing inorganic solid particles and a polymer material. The particle size distribution of the inorganic solid particles in the composite layer includes at least two peaks. The peak top P S of the peak on the side with the smallest particle size in the particle size distribution S and the peak top P L of the peak on the side with the largest particle size L satisfy the relationship of 0.9 ≦ FP S / FP L ≦ 5. The negative electrode includes a negative electrode active material-containing layer, and the positive electrode includes a positive electrode active material-containing layer. The porosity of the composite layer is less than the porosity of both the negative electrode active material-containing layer and the positive electrode active material-containing layer. Also, the porosity of the composite layer is 1% or more and less than 15%.

[0017] FIG. 1 shows an example of the particle size distribution as described above. FIG. 1 is a graph showing an example of the particle size distribution of the composite layer that may be included in the secondary battery according to the embodiment. The particle size distribution can be obtained by the laser diffraction scattering method and represents the volume frequency (%) for each particle diameter in the inorganic solid particles included in the composite layer. The exemplified particle size distribution curve includes two peaks. The position in the horizontal axis direction of the peak top P S of the peak on the small particle size side is 0.7 μm, and the position in the horizontal axis direction of the peak top P L of the peak on the large particle size side is 3 μm. The ratio FP S of the volume frequency FP L of the inorganic solid particles having a particle diameter (3 μm) corresponding to the peak top P S to the volume frequency FP S of the inorganic solid particles having a particle diameter (0.7 μm) corresponding to the peak top P S / FP L is 1.8.

[0018] In the secondary battery with the above configuration, a composite layer is provided between the negative electrode and the positive electrode, functioning as a separator between them. The composite layer contains inorganic solid particles and polymer materials, and may be, for example, a polymer composite film. The particle size distribution of the inorganic solid particles contained in the composite layer is bimodal or has more modalities, that is, it contains two or more modes (peaks). The ratio of the volume-based frequency maxima (FP) between the mode located on the smallest particle diameter side and the mode located on the largest particle diameter side among the multiple modes (peaks) is... S / FP L The ratio is between 0.9 and 5. In a composite layer containing small and large particles in a ratio that yields such a particle size distribution, the curvature of the channels formed in the gaps between particles is high. That is, there are many twists and turns in the paths through which water molecules and protons can move within the composite layer. As a result, the amount of water molecules and protons that move can be suppressed, and thus the supply of these reactants to the negative electrode in the electrolysis reaction can be reduced, thereby suppressing water splitting at the negative electrode. Therefore, this secondary battery can exhibit high charge and discharge efficiency. Furthermore, the secondary battery can exhibit high lifespan performance.

[0019] The explanation will be given with reference to the drawings. Figure 2 is a schematic cross-sectional view showing an example of a composite layer that may be included in a secondary battery according to this embodiment. The composite layer 4 includes small-particle inorganic solid particles 47, large-particle inorganic solid particles 48, and a polymer material (not shown) as a binder. In such a composite layer 4 where the particle size distribution of inorganic solid particles 47, 48 is bimodal, the degree of curvature of the channels, which are composed of continuous vacancies formed in the gaps between the inorganic solid particles 47, 48 bound together by the polymer material, is high. Therefore, the distance of the path 44 through which water molecules and protons pass through the composite layer 4 becomes longer, and the movement speed of water molecules and protons within the composite layer 4 is suppressed. Although omitted in Figure 2, some of the gaps between the inorganic solid particles 47, 48 are filled with the polymer material, so not all of the gaps between the particles become channels.

[0020] For comparison, an example of a conventional composite layer is schematically shown in Figure 3. In a conventional composite layer 40 with a monomodal particle size distribution, although there is some variation in particle size, the particle size of the inorganic solid particles 49 in the composite layer 40 remains roughly the same. Therefore, although the density can be increased by using fine particles, the curvature of the channels formed between the particles does not increase. Consequently, the distance of the paths 44 for water molecules and protons moving within the composite layer 40 cannot be increased.

[0021] A negative electrode, a positive electrode, and a separator can constitute an electrode group. A water-based electrolyte can be held within the electrode group.

[0022] The secondary battery according to this embodiment may be, for example, a lithium-ion secondary battery or a sodium-ion secondary battery. The secondary battery also includes an aqueous electrolyte secondary battery containing an aqueous electrolyte.

[0023] Furthermore, the secondary battery may further comprise an outer casing that houses the electrode group and the aqueous electrolyte.

[0024] Furthermore, the secondary battery may further include a negative terminal electrically connected to the negative electrode and a positive terminal electrically connected to the positive electrode.

[0025] The composite layer can be bonded to at least one of the negative electrode and the positive electrode. For example, a composite layer may be formed on the surface of the negative electrode to constitute a separator, or a composite layer may be formed on the surface of the positive electrode to constitute a separator. A composite layer may be formed on the respective surfaces of the negative electrode and the positive electrode. Alternatively, a single composite layer may be bonded to both the negative electrode and the positive electrode.

[0026] The secondary battery may further include other separators independent of the separator made of the composite layer. These other separators may be placed, for example, between the composite layer and the negative electrode, or between the composite layer and the positive electrode. Furthermore, the secondary battery may include multiple composite layers; for example, one composite layer, another separator, and yet another composite layer may be arranged between the negative and positive electrodes in this order. The other separators may be impregnated with an aqueous electrolyte.

[0027] The following describes in detail the negative electrode, positive electrode, separator (composite layer and optionally other separator), aqueous electrolyte, outer casing, negative electrode terminal, and positive electrode terminal.

[0028] (Negative electrode) The negative electrode includes a negative electrode active material-containing layer. The negative electrode active material-containing layer includes the negative electrode active material and optionally a conductive agent and a binder.

[0029] The negative electrode may further include a negative electrode current collector. The negative electrode active material-containing layer is provided, for example, on at least one surface of the negative electrode current collector. The negative electrode active material-containing layer may be provided on one main surface of the negative electrode current collector, or the negative electrode active material-containing layer may be provided on one main surface of the negative electrode current collector and the main surface on the opposite side of it.

[0030] The negative electrode active material-containing layer contains a lithium ion insertion-desorption potential of 1V to 3V relative to the oxidation-reduction potential of lithium (vs. Li / Li). + It is desirable that the negative electrode active material contains a compound that is )

[0031] In an aqueous electrolyte battery equipped with a negative electrode containing a compound whose lithium-ion insertion-desorption potential falls within the above range, during the initial charge, the water contained in the solvent of the aqueous electrolyte can be electrolyzed inside and near the negative electrode. This is because, during the initial charge, lithium ions are inserted into the negative electrode active material, causing the potential of the negative electrode to decrease. When the negative electrode potential falls below the hydrogen generation potential, some of the water inside and near the negative electrode is converted into hydrogen (H2) and hydroxide ions (OH). - ) is decomposed into this. As a result, the pH of the aqueous electrolyte present inside and near the negative electrode increases.

[0032] The hydrogen evolution potential at the negative electrode depends on the pH of the aqueous electrolyte. That is, as the pH of the aqueous electrolyte in contact with the negative electrode increases, the hydrogen evolution potential at the negative electrode decreases. The lower limit of the lithium ion insertion-desorption potential is 1V or higher (vs. Li / Li +In a battery using a negative electrode active material that is , although the potential of the negative electrode is lower than the hydrogen generation potential during the first charge, after the first charge, the potential of the negative electrode tends to be higher than the hydrogen generation potential, so that the decomposition of water at the negative electrode is less likely to occur.

[0033] The lithium ion insertion - desorption potential is a potential based on the oxidation - reduction potential of lithium, and is 1 V or more and 3 V or less (vs. Li / Li + ) Examples of the compound include titanium oxide and titanium - containing oxide. Examples of the titanium - containing oxide include lithium titanium composite oxide, niobium titanium - based oxide, sodium niobium titanium - based oxide, etc. The negative electrode active material can contain one or more of titanium oxide and titanium - containing oxide.

[0034] The titanium oxide includes, for example, titanium oxide with a monoclinic structure, rutile - structured titanium oxide, and anatase - structured titanium oxide. The titanium oxide of each crystal structure can have a composition before charging represented by TiO2 and a composition after charging represented by Li x TiO2 (where the subscript x satisfies 0 ≤ x ≤ 1). Also, the structure of the titanium oxide with a monoclinic structure before charging can be represented as TiO2(B).

[0035] Examples of the lithium titanium oxide include lithium titanium oxide with a spinel structure (for example, a compound represented by the general formula Li 4+x Ti5O 12 and - 1 ≤ x ≤ 3) and lithium titanium oxide with a lamellar structure (for example, a compound represented by Li 2+x Ti3O7 and - 1 ≤ x ≤ 3, a compound represented by Li 1+x Ti2O4 and 0 ≤ x ≤ 1, a compound represented by Li 1.1+x Ti 1.8 O4 and 0 ≤ x ≤ 1, a compound represented by Li 1.07+x Ti 1.86 O4 and 0 ≤ x ≤ 1, a compound represented by Li x TiO2 and 0 < x ≤ 1), etc. Further, the lithium titanium oxide may be a lithium titanium composite oxide into which a different element has been introduced.

[0036] Examples of monoclinic niobium titanate-based oxides include Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ compounds represented by. Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. Each subscript in the composition formula is 0≦x≦5, 0≦y<1, 0≦z<2, -0.3≦δ≦0.3. Specific examples of monoclinic niobium titanate-based oxides include Li x Nb2TiO7(0≦x≦5).

[0037] Other examples of monoclinic niobium titanate-based oxides include Li x Ti 1-y M3 y+z Nb 2-z O 7-δ compounds represented by. Here, M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo. Each subscript in the composition formula is 0≦x≦5, 0≦y<1, 0≦z<2, -0.3≦δ≦0.3.

[0038] Sodium niobium titanate-based oxides are, for example, of the general formula Li 2+x Na 2-a M4 b Ti 6-c-d Nb c M5 d O 14+δ represented by, where 0≦x≦4, 0≦a<2, 0≦b<2, 0<c<6, 0≦d<3, c + d<6, -0.5≦δ≦0.5, M4 includes one or more selected from the group consisting of Cs, K, Sr, Ba, Ca, and M5 includes one or more selected from the group consisting of Zr, Sn, V, Ta, Mo, W, Fe, Co, Mn, Al, including orthorhombic Na-containing niobium titanate composite oxides.

[0039] It is preferable to use anatase-structured titanium oxide, monoclinic-structured titanium oxide, spinel-structured lithium titanium oxide, niobium-titanium oxide, or a mixture thereof as the negative electrode active material. On the one hand, when anatase-structured titanium oxide, monoclinic-structured titanium oxide, or spinel-structured lithium titanium oxide is used as the negative electrode active material, a high electromotive force can be obtained by combining it with a positive electrode using, for example, a lithium manganese composite oxide as the positive electrode active material. On the other hand, high capacity can be achieved by using niobium-titanium oxide.

[0040] The negative electrode active material may be contained in the active material-containing layer, for example, in the form of particles. The negative electrode active material particles may be primary particles, secondary particles which are aggregates of primary particles, or mixtures of individual primary and secondary particles. The shape of the particles is not particularly limited and may be spherical, elliptical, flattened, or fibrous, for example.

[0041] The average particle size (diameter) of the secondary particles of the negative electrode active material is preferably 3 μm or larger, and more preferably 5 μm to 20 μm. Within this range, the surface area of ​​the active material is small, which further suppresses the decomposition of water.

[0042] It is desirable that the average particle diameter of the primary particles of the negative electrode active material be 1 μm or less. This shortens the diffusion distance of Li ions within the active material and increases the specific surface area. As a result, excellent high input performance (rapid charging) can be obtained. Furthermore, it is preferable that the average particle diameter of the primary particles of the negative electrode active material be 0.001 μm or more. It is more preferable that the average particle diameter of the primary particles of the negative electrode active material be between 0.1 μm and 0.8 μm.

[0043] These primary and secondary particle diameters refer to the particle size at which the integrated volume value in the particle size distribution determined by a laser diffraction particle size distribution analyzer becomes 50%. Details of particle size distribution measurement using the laser diffraction method will be described later.

[0044] The porosity of the negative electrode active material-containing layer is preferably between 5% and 50%. This allows for the creation of a high-density negative electrode with excellent affinity to aqueous electrolytes. More preferably, the porosity of the negative electrode active material-containing layer is between 8% and 40%. The method for measuring the porosity of the active material-containing layer will be described later.

[0045] Conductive agents are added to enhance current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include carbonaceous materials such as vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and graphite. In addition, fibrous carbon materials such as carbon nanotubes and carbon nanofibers can be used as conductive agents. One of these may be used as a conductive agent, or two or more may be used in combination. Alternatively, instead of using a conductive agent, a carbon coating or an electronically conductive inorganic material coating may be applied to the surface of the active material particles.

[0046] The binder has the function of binding the negative electrode active material and the conductive agent. Examples of binders include, but are not limited to, at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), carboxymethylcellulose (CMC), fluororubber, styrene-butadiene rubber, acrylic resin or its copolymer, polyacrylic acid, and polyacrylonitrile. For example, the polymer material contained in the composite layer can be used as the binder. By using the same polymer material as used in the composite layer as the binder for the negative electrode active material-containing layer, the degree of bonding between the two can be improved. Details of the polymer material in the composite layer will be described later. The binder may be of one type, or two or more types may be mixed and used.

[0047] Preferably, the proportions of the negative electrode active material, conductive agent, and binder in the negative electrode active material-containing layer are within the ranges of 70% to 95% by mass for the negative electrode active material, 3% to 20% by mass for the conductive agent, and 2% to 10% by mass for the binder. A conductive agent content of 3% by mass or more improves the current collection performance of the negative electrode active material-containing layer. A binder content of 2% by mass or more provides sufficient electrode strength. The binder can function as an insulator. Therefore, a binder content of 10% by mass or less reduces the insulating portion within the electrode.

[0048] The material used for the negative electrode current collector is a substance that is electrochemically stable in the electrode potential range when alkali metal ions are inserted or removed. The negative electrode current collector is preferably made of zinc foil, aluminum foil, or aluminum alloy foil containing one or more elements selected from magnesium (Mg), titanium (Ti), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), and silicon (Si), and is surface-coated with a metal with a high hydrogen overpotential, such as Zn or Sn. Besides foil, other forms of negative electrode current collectors include porous bodies or meshes. For improved energy density and output, a foil form with a small volume and large surface area is desirable.

[0049] The thickness of the negative electrode current collector is preferably between 5 μm and 20 μm. A negative electrode current collector with such a thickness can balance electrode strength and weight reduction.

[0050] Furthermore, the current collector may include portions on its surface where the negative electrode active material-containing layer is not formed. These portions can function as negative electrode current collector tabs. Alternatively, a separate negative electrode current collector tab may be electrically connected to the negative electrode.

[0051] (positive electrode) The positive electrode includes a positive electrode active material-containing layer. The positive electrode may further include a positive electrode current collector. The positive electrode active material-containing layer may be formed on one or both sides of the positive electrode current collector. The positive electrode active material-containing layer may contain the positive electrode active material and optionally a conductive agent and a binder.

[0052] As the positive electrode active material, for example, an oxide or a sulfide can be used. The positive electrode may contain, as the positive electrode active material, one kind of compound alone, or may contain a combination of two or more kinds of compounds. Examples of the oxide and the sulfide include compounds into which Li or Li ions can be inserted and desorbed.

[0053] Examples of such compounds include manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (e.g., Li x Mn2O4 or Li x MnO2; 0 < x ≦ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≦ 1, 0 < y < 2), lithium phosphate having an olivine structure (e.g., Li x FePO4; 0 < x ≦ 1, Li x Fe 1-y Mn y PO4; 0 < x ≦ 1, 0 < y ≦ 1, Li x CoPO4; 0 < x ≦ 1), iron sulfate (Fe2(SO4)3), vanadium oxide (e.g., V2O5), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≦ 1, 0 < y < t, 0 < z < 1, y + z < 1) are included.

[0054] Among the above, examples of more preferable compounds as the positive electrode active material include lithium manganese composite oxides having a spinel structure (for example, Li x Mn2O4; 0 < x ≦ 1), lithium nickel composite oxides (for example, Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxides (for example, Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxides (for example, Li x Ni 1-y Co y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese nickel composite oxides having a spinel structure (for example, Li x Mn 2-y Ni y O4; 0 < x ≦ 1, 0 < y < 2), lithium manganese cobalt composite oxides (for example, Li x Mn y Co 1-y O2; 0 < x ≦ 1, 0 < y < 1), lithium iron phosphate (for example, Li x FePO4; 0 < x ≦ 1), and lithium nickel cobalt manganese composite oxides (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≦ 1, 0 < y < 1, 0 < z < 1, y + z < 1) are included. When these compounds are used as the positive electrode active material, the positive electrode potential can be increased.

[0055] When a room-temperature molten salt is used as the electrolyte of the battery, it is preferable to use a positive electrode active material containing lithium iron phosphate, Li x VPO4F (0 ≦ x ≦ 1), a lithium manganese composite oxide, a lithium nickel composite oxide, a lithium nickel cobalt composite oxide, or a mixture thereof. Since these compounds have low reactivity with the room-temperature molten salt, the cycle life can be improved. Details of the room-temperature molten salt will be described later.

[0056] The primary particle size of the positive electrode active material is preferably between 100 nm and 1 μm. Positive electrode active material with a primary particle size of 100 nm or more is easy to handle in industrial production. Positive electrode active material with a primary particle size of 1 μm or less allows for smooth diffusion of lithium ions within the solid.

[0057] The specific surface area of ​​the positive electrode active material is 0.1 m². 2 / g or more 10m 2 It is preferable that it is less than or equal to / g. 0.1m 2 A positive electrode active material with a specific surface area of ​​10m or more can adequately secure sites for Li ion intercalation and release. 2 Positive electrode active materials with a specific surface area of ​​less than / g are easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0058] The binder has the function of binding the positive electrode active material and the conductive agent. Examples of binders include, but are not limited to, at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, ethylene-butadiene rubber, polypropylene (PP), polyethylene (PE), carboxymethylcellulose (CMC), polyimide (PI), and polyacrylimide (PAI). For example, the polymer material contained in the composite layer can be used as the binder. By using the same polymer material as used in the composite layer as the binder for the positive electrode active material-containing layer, the degree of bonding between the two can be improved. The binder may be of one type, or two or more types may be mixed and used.

[0059] In the positive electrode active material-containing layer, it is preferable that the positive electrode active material and the binder are blended in proportions of 80% to 98% by mass and 2% to 20% by mass, respectively.

[0060] Sufficient electrode strength can be obtained by using a binder amount of 2% by mass or more. Furthermore, the binder can function as an insulator. Therefore, by reducing the binder amount to 20% by mass or less, the amount of insulator contained in the electrode decreases, thus reducing internal resistance.

[0061] When a conductive agent is added, it is preferable that the positive electrode active material, binder, and conductive agent are blended in proportions of 77% to 95% by mass, 2% to 20% by mass, and 3% to 15% by mass, respectively.

[0062] The above-mentioned effects can be achieved by increasing the amount of conductive agent to 3% by mass or more. Furthermore, by reducing the amount of conductive agent to 15% by mass or less, the proportion of conductive agent in contact with the electrolyte can be reduced. This lower proportion reduces the decomposition of the electrolyte under high-temperature storage conditions.

[0063] The positive electrode current collector may be made of metals such as stainless steel, aluminum (Al), and titanium (Ti), or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si. The positive electrode current collector may have the shape of foil, porous body, or mesh. To prevent corrosion due to reaction between the positive electrode current collector and the aqueous electrolyte, the surface of the positive electrode current collector may be coated with a different element. The positive electrode current collector is preferably made of a material with excellent corrosion resistance and oxidation resistance, such as Ti foil. If an aqueous solution of Li2SO4 is used as the aqueous electrolyte, Al may be used as the positive electrode current collector because corrosion does not progress.

[0064] Furthermore, the positive electrode current collector may include portions on its surface where the positive electrode active material-containing layer is not formed. These portions can function as positive electrode current collector tabs. Alternatively, a separate positive electrode current collector tab may be electrically connected to the positive electrode.

[0065] (Separator) The separator is located between the negative and positive electrodes. The separator includes a composite layer. The separator may consist of a composite layer, or a composite layer and other separators. Therefore, the separator may be a laminate of a composite layer and other separators, or the composite layer may be sandwiched between other separators. The composite layer and other separators that the separator may include are described below.

[0066] ((composite layer)) The composite layer is located between the negative electrode and the positive electrode. The composite layer may be provided, for example, on the negative electrode active material-containing layer. Alternatively, the composite layer may be provided, for example, on the positive electrode active material-containing layer. The composite layer may be provided on both the negative electrode active material-containing layer and the positive electrode active material-containing layer, respectively. For example, in electrodes where active material-containing layers are supported on both sides of the current collector, the composite layer may be provided on the main surface of one of the active material-containing layers, or on the main surfaces of both active material-containing layers.

[0067] The composite layer comprises inorganic solid particles and polymer material. The inorganic solid particles can be materials exhibiting electrical insulation properties. When materials exhibiting electrical insulation properties are used for the inorganic solid particles, the composite layer can also function as a separator that electrically insulates the negative and positive electrodes.

[0068] The composite layer may be bonded to at least one of the positive electrode and the negative electrode. A composite layer may be bonded individually to both the positive and negative electrodes. Alternatively, a single composite layer may be bonded to both the positive and negative electrodes. Preferably, the peel strength at the interface between the composite layer and the electrode is greater than 0.3 N / mm. That is, the peel strength σ represents the degree of bonding between the negative electrode and the composite layer. n It is preferable that the value is greater than 0.3 N / mm. Similarly, the peel strength σ, which represents the degree of bonding between the positive electrode and the composite layer, is also important. p It is preferable that the peel strength is greater than 0.3 N / mm. When a composite layer is bonded to both the positive and negative electrodes, the peel strength σ n and peel strength σ p It is preferable that both are greater than 0.3 N / mm. Peel strength σ n and peel strength σ pThis is measured by the surface and interface cutting method described later.

[0069] The composite layer has a porosity of 1% or more and less than 15%. In addition, the porosity of the composite layer is less than that of either the negative electrode active material-containing layer or the positive electrode active material-containing layer. By providing such a dense composite layer in between, the amount of water molecules and protons moving between the positive and negative electrodes can be suppressed. As a result, side reactions such as continuous water decomposition can be suppressed, and battery performance is improved. In such secondary batteries, a water-based electrolyte with good conductivity is used, so even if the composite layer is dense, the increase in electrical resistance is not a concern. In contrast, in non-aqueous electrolyte batteries, the conductivity of the non-aqueous solvent is not high, so the electrical resistance may increase when a dense composite layer or separator is used. It is preferable that the porosity of the composite layer is 2.5% or more.

[0070] The inorganic solid particles contained in the composite layer are electrically insulating. Examples of inorganic solid particles include oxide ceramics such as alumina, silica, zirconia, yttria, magnesium oxide, calcium oxide, barium oxide, strontium oxide, and vanadium oxide; carbonates and sulfates such as sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lanthanum carbonate, cerium carbonate, calcium sulfate, magnesium sulfate, aluminum sulfate, gypsum, and barium sulfate; phosphates such as hydroxyapatite, lithium phosphate, zirconium phosphate, and titanium phosphate; and nitride ceramics such as silicon nitride, titanium nitride, and boron nitride. The inorganic particles listed above may also be in the form of hydrates.

[0071] Other examples of inorganic solid particles include solid electrolyte particles that have ionic conductivity for alkali metal ions. Inorganic solid particles that have ionic conductivity for lithium ions and sodium ions are more preferred. Here, lithium ion conductivity means 1 × 10⁻⁶ at 25°C. -6This refers to exhibiting a lithium-ion conductivity of S / cm or higher. Lithium-ion conductivity can be measured, for example, by the AC impedance method. By using such inorganic solid particles, a composite layer having lithium-ion conductivity or sodium-ion conductivity can be obtained.

[0072] Examples of inorganic solid particles having lithium ion conductivity include oxide-based solid electrolytes and sulfide-based solid electrolytes. Oxide-based solid electrolytes have a NASICON (Sodium (Na) Super Ionic Conductor) type structure and the general formula Li 1+x Mα 2( It is preferable to use a lithium phosphate solid electrolyte represented by PO4)3. In the above general formula, Mα is one or more selected from the group consisting of, for example, titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The subscript x is in the range of 0 ≤ x ≤ 2.

[0073] A specific example of a lithium phosphate solid electrolyte having a NASICON-type structure is Li 1+x Al x Ti 2-x LATP compounds represented as (PO4)3 where 0.1 ≤ x ≤ 0.5; Li 1+x Al y Mβ 2-y A compound represented as (PO4)3 where Mβ is 1 or more selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca, and 0≦x≦1 and 0≦y≦1; Li 1+x Al x Ge 2-x Compounds represented as (PO4)3 such that 0 ≤ x ≤ 2; and Li 1+x Al x Zr 2-x Compounds represented as (PO4)3 where 0 ≤ x ≤ 2; Li 1+x+y Al x Mγ 2-x Si y P 3-y O 12A compound represented by [compound formula] where Mγ is one or more selected from the group consisting of Ti and Ge, 0 < x ≦ 2, and 0 ≦ y < 3; Li 1+2x Zr 1-x Ca x Compounds represented by [compound formula] where 0 ≦ x < 1 can be mentioned. Li 1+2x Zr 1-x Ca x (PO4)3 has high water resistance, low reducibility and low cost, and is preferably used as inorganic solid electrolyte particles.

[0074] In addition to the above lithium phosphate solid electrolyte, as the oxide-based solid electrolyte, there are also Li x PO y N z An amorphous LIPON compound represented by [compound formula] where 2.6 ≦ x ≦ 3.5, 1.9 ≦ y ≦ 3.8, and 0.1 ≦ z ≦ 1.3 (for example, Li 2.9 PO 3.3 N 0.46 ); A garnet-type structure La 5+x A x La 3-x Mδ2O 12 represented by [compound formula] where A is one or more selected from the group consisting of Ca, Sr, and Ba, Mδ is one or more selected from the group consisting of Nb and Ta, and 0 ≦ x ≦ 0.5; Li3Mδ 2-x L2O 12 represented by [compound formula] where Mδ is one or more selected from the group consisting of Ta and Nb, L may contain Zr, and 0 ≦ x ≦ 0.5; Li 7-3x Al x La3Zr3O 12 represented by [compound formula] where 0 ≦ x ≦ 0.5; Li 5+x La3Mδ 2-x Zr x O 12 represented by [compound formula] where Mδ is one or more selected from the group consisting of Nb and Ta, and 0 ≦ x ≦ 2, LLZ compound (for example, Li7La3Zr2O 12 ); And compounds represented by [compound formula] having a perovskite-type structure La 2 / 3-x Li x TiO3 where 0.3 ≦ x ≦ 0.7 can be mentioned. The solid electrolyte may be one type, or two or more types may be mixed and used.

[0075] Furthermore, a sodium-containing solid electrolyte may be used as the inorganic solid particles having ionic conductivity for sodium ions. Sodium-containing solid electrolytes have excellent ionic conductivity for sodium ions. Examples of sodium-containing solid electrolytes include β-alumina, sodium phosphorus sulfide, and sodium phosphorus oxide. The sodium ion-containing solid electrolyte is preferably in the form of glass ceramics.

[0076] The shape of inorganic solid particles is not particularly limited, but can be spherical, elliptical, flattened, or fibrous, for example.

[0077] The particle size distribution of inorganic solid particles in the composite layer is at least bimodal. Of the at least two peaks included in the particle size distribution, the peak P on the side with the smallest particle size is the peak top. S The particle diameter corresponding to the position is defined as the first particle diameter. Of at least two peaks, the peak top P on the side with the largest particle size is selected. L The particle diameter corresponding to the position is defined as the second particle diameter. In the particle size distribution, the frequency FP of the first particle diameter is determined based on volume. S and frequency FP of the second particle size S This means that 0.9 ≤ FP S / FP L The relationship is ≤5. Preferably, the first particle diameter is in the range of 0.3 μm to 0.8 μm, and the second particle diameter is in the range of 1 μm to 4 μm. For example, the composite layer may contain inorganic solid particles that are a mixture of at least first particles with a small particle diameter having a mode diameter of 0.3 μm to 0.8 μm and second particles with a large particle diameter having a mode diameter of 1 μm to 4 μm. The particle size distribution of the inorganic solid particles in the composite layer can be measured by the laser diffraction method described later.

[0078] In the composite layer, inorganic solid particles may be of a single type or a mixture of multiple types.

[0079] The polymer material contained in the composite layer enhances the binding properties between inorganic solid particles. The weight-average molecular weight of the polymer material is, for example, 3000 or more. When the weight-average molecular weight of the polymer material is 3000 or more, the binding properties of the inorganic solid particles can be further enhanced. The weight-average molecular weight of the polymer material is preferably 3000 to 5,000,000, more preferably 5000 to 2,000,000, and even more preferably 10,000 to 1,000,000. The weight-average molecular weight of the polymer material can be determined by gel permeation chromatography (GPC).

[0080] Polymeric materials may be polymers consisting of a single monomer unit, copolymers consisting of multiple monomer units, or mixtures thereof. Preferably, polymeric materials contain monomer units composed of hydrocarbons having a functional group containing one or more selected from the group consisting of oxygen (O), sulfur (S), nitrogen (N), and fluorine (F). Preferably, the proportion of the polymeric material composed of monomer units is 70 mol% or more. Hereinafter, these monomer units will be referred to as first monomer units. Furthermore, in copolymers, components other than the first monomer units will be referred to as second monomer units. The copolymer of the first monomer unit and the second monomer unit may be an alternating copolymer, a random copolymer, or a block copolymer.

[0081] In polymer materials, if the proportion of the portion composed of first monomer units is less than 70 mol%, the water-impermeable properties of the composite layer may decrease. In polymer materials, it is preferable that the proportion of the portion composed of first monomer units is 90 mol% or more. Most preferably, the polymer material is a polymer composed of 100 mol% first monomer units, that is, a polymer consisting only of first monomer units.

[0082] The first monomer unit may be a compound having a functional group in its side chain containing one or more elements selected from the group consisting of oxygen (O), sulfur (S), nitrogen (N), and fluorine (F), and whose main chain is composed of carbon-carbon bonds. The hydrocarbon may have one or more functional groups containing one or more elements selected from the group consisting of oxygen (O), sulfur (S), nitrogen (N), and fluorine (F). The functional groups in the first monomer unit enhance the conductivity of alkali metal ions passing through the composite layer.

[0083] Examples of the first monomer unit include one or more selected from the group consisting of vinyl formal, vinyl alcohol, vinyl acetate, vinyl acetal, vinyl butyral, acrylic acid and its derivatives, methacrylic acid and its derivatives, acrylonitrile, acrylamide and its derivatives, styrene sulfonic acid, polyvinylidene fluoride, and tetrafluoroethylene.

[0084] The polymer material preferably contains one or more selected from the group consisting of polyvinyl formal, polyvinyl alcohol (PVA), polyvinyl acetal, polyvinyl butyral (PVB), polymethyl methacrylate, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), fluororubber, styrene butadiene rubber, polyacrylic acid compounds, imide compounds, and carboxymethylcellulose (CMC).

[0085] A second monomer unit is a compound other than the first monomer unit, that is, a compound that does not have a functional group containing one or more selected from the group consisting of oxygen (O), sulfur (S), nitrogen (N), and fluorine (F), or a compound that has such a functional group but is not a hydrocarbon. Examples of second monomer units include ethylene oxide and styrene. Examples of polymers consisting of second monomer units include polyethylene oxide (PEO) and polystyrene (PS).

[0086] The types of functional groups contained in the first and second monomer units can be identified by Fourier Transform Infrared Spectroscopy (FT-IR). Furthermore, the fact that the first monomer unit consists of hydrocarbons can be determined by nuclear magnetic resonance (NMR). In addition, the proportion of the copolymer of the first and second monomer units that is composed of the first monomer unit can be calculated by NMR.

[0087] The polymer material content in the composite layer is preferably 10% by volume or more, and more preferably 20% by volume or more. From the viewpoint of increasing the flexibility of the composite layer, a higher polymer material content is preferable. Also, a higher polymer material content tends to result in a higher density of the composite layer. From the viewpoint of increasing the ionic conductivity of the composite layer, the polymer material content is preferably 50% by volume or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. The polymer material content in the composite layer can be calculated by thermogravimetric (TG) analysis.

[0088] The polymer material included in the composite layer may be a single type or a mixture of multiple types.

[0089] The composite layer may contain plasticizers and electrolyte salts in addition to inorganic solid particles and polymer materials. For example, if the composite layer contains electrolyte salts, the alkali metal ion conductivity of the composite layer can be further enhanced.

[0090] From the viewpoint of minimizing internal short circuits, the thickness of the composite layer is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 10 μm or more. Furthermore, from the viewpoint of increasing ionic conductivity and energy density, the thickness of the composite layer is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. If multiple composite layers are included, their thicknesses may be the same or different.

[0091] ((other separators)) Other separators that can be used include, for example, nonwoven fabrics or self-supporting porous membranes. Examples of materials used for nonwoven fabrics or self-supporting porous membranes include polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF). The other separator is preferably a cellulose nonwoven fabric.

[0092] The thickness of the other separators is, for example, 1 μm or more, preferably 3 μm or more. A thicker other separator makes it less likely for internal short circuits to occur in the secondary battery. The thickness of the other separators is, for example, 30 μm or less, preferably 10 μm or less. A thinner other separator tends to result in lower internal resistance of the secondary battery and a higher volumetric energy density of the secondary battery.

[0093] (aqueous electrolyte) Aqueous electrolytes contain an aqueous solvent and an electrolyte salt. Aqueous electrolytes are, for example, liquid. A liquid aqueous electrolyte is an aqueous solution prepared by dissolving an electrolyte salt as a solute in an aqueous solvent. In an aqueous solution, the amount of aqueous solvent is preferably 1 mole or more, and more preferably 3.5 moles or more, per 1 mole of salt (the solute).

[0094] As the aqueous solvent, a solution containing water can be used. Here, the solution containing water may be pure water or a mixed solvent of water and an organic solvent. The proportion of water in the aqueous solvent is, for example, 50% by volume or more, and preferably 90% by volume or more.

[0095] The aqueous electrolyte may also be a gel electrolyte. The gel electrolyte is prepared by mixing and compounding the above-mentioned liquid aqueous electrolyte with a polymer compound. Examples of polymer compounds include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

[0096] The presence of water in an aqueous electrolyte can be confirmed by GC-MS (Gas Chromatography - Mass Spectrometry) measurement. Furthermore, the salt concentration and water content in the aqueous electrolyte can be measured, for example, by ICP (Inductively Coupled Plasma) emission spectrometry. By weighing a specified amount of the aqueous electrolyte and calculating the salt concentration, the molar concentration (mol / L) can be calculated. Additionally, by measuring the specific gravity of the aqueous electrolyte, the number of moles of solute and solvent can be calculated.

[0097] As the electrolyte salt, for example, lithium salts, sodium salts, or mixtures thereof can be used. One or more types of electrolyte salts can be used.

[0098] Examples of lithium salts that can be used include lithium chloride (LiCl), lithium bromide (LiBr), lithium hydroxide (LiOH), lithium sulfate (Li2SO4), lithium nitrate (LiNO3), lithium acetate (CH3COOLi), lithium oxalate (Li2C2O4), lithium carbonate (Li2CO3), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI; LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiFSI; LiN(SO2F)2), and lithium bisoxalate borate (LiBOB; LiB[(OCO)2]2).

[0099] Examples of sodium salts that can be used include sodium chloride (NaCl), sodium sulfate (Na2SO4), sodium hydroxide (NaOH), sodium nitrate (NaNO3), and sodium trifluoromethanesulfonylamide (NaTFSA).

[0100] The lithium salt preferably contains LiCl. Using LiCl can increase the lithium ion concentration of the aqueous electrolyte. Furthermore, the lithium salt preferably contains at least one of LiSO4 and LiOH in addition to LiCl.

[0101] In addition to lithium salts, zinc salts such as zinc chloride and zinc sulfate may also be added to the electrolyte. By adding such compounds to the electrolyte, a zinc-containing coating layer and / or zinc oxide-containing region can be formed at the negative electrode. These zinc-containing components have the effect of suppressing hydrogen generation at the electrode on which they are formed.

[0102] The molar concentration of lithium ions or sodium ions in the aqueous electrolyte is preferably 3 mol / L or higher, preferably 6 mol / L or higher, and preferably 12 mol / L or higher. When the concentration of lithium ions or sodium ions in the aqueous electrolyte is high, the electrolysis of the aqueous solvent at the electrode is easily suppressed, and hydrogen generation from the electrode tends to be low.

[0103] The pH of the aqueous electrolyte is preferably between 3 and 14, and more preferably between 4 and 13. The pH values ​​were measured at 25±2℃.

[0104] (Exterior components) The outer casing containing the electrode group and aqueous electrolyte can be a metal container, a laminated film container, or a resin container.

[0105] Metal containers made of nickel, iron, and stainless steel, in square or cylindrical shapes, can be used. Resin containers made of polyethylene or polypropylene can be used.

[0106] The thickness of the resin container and the metal container is preferably within the range of 0.05 mm to 1 mm. More preferably, the thickness is 0.5 mm or less, and even more preferably 0.3 mm or less.

[0107] Examples of laminate films include multilayer films in which a metal layer is coated with a resin layer. Examples of metal layers include stainless steel foil, aluminum foil, and aluminum alloy foil. Polymers such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET) can be used for the resin layer. The thickness of the laminate film is preferably in the range of 0.01 mm to 0.5 mm. More preferably, the thickness of the laminate film is 0.2 mm or less.

[0108] (Negative terminal) The negative terminal has a potential range of 1V to 3V relative to the oxidation-reduction potential of lithium (vs. Li / Li +The negative electrode terminal can be formed from a material that is electrochemically stable and conductive. Specifically, the negative electrode terminal material can be zinc, copper, nickel, stainless steel or aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable to use zinc or a zinc alloy as the material for the negative electrode terminal. It is preferable that the negative electrode terminal be made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0109] (Positive terminal) The positive terminal has a potential range of 2.5V to 4.5V relative to the oxidation-reduction potential of lithium (vs. Li / Li + The positive electrode terminal can be formed from a material that is electrically stable and conductive. Examples of materials for the positive electrode terminal include titanium, aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable that the positive electrode terminal be formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0110] Such secondary batteries can be used in various forms, such as prismatic, cylindrical, flat, thin, and coin-type. Furthermore, the secondary battery may have a bipolar structure. A secondary battery with a bipolar structure has the advantage of being able to produce multiple series-connected cells in a single cell.

[0111] Figure 4 shows an example of the electrode group described above. Figure 4 is a schematic cross-sectional view showing an example of an electrode group that can be included in the secondary battery according to this embodiment.

[0112] Electrode group 1 includes a negative electrode 3, a composite layer 41, another composite layer 42, and a positive electrode 5. The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material containing layer 3b. The positive electrode 5 includes a positive electrode current collector 5a and a positive electrode active material containing layer 5b. The composite layers 41 and 42 are arranged between the negative electrode 3 and the positive electrode 5. It is desirable that the composite layer 41 is in contact with the main surface of the negative electrode active material containing layer 3b at least in a position opposite to the negative electrode current collector 3a, as shown in the figure. More preferably, the composite layer 41 is bonded to the negative electrode active material containing layer 3b. It is desirable that the composite layer 42 is in contact with the main surface of the positive electrode active material containing layer 5b at least in a position opposite to the positive electrode current collector 5a, as shown in the figure. More preferably, the composite layer 42 is bonded to the positive electrode active material containing layer 5b. One of the composite layer 41 and composite layer 42 may be omitted.

[0113] Hereinafter, an example of a secondary battery according to the embodiment will be described with reference to the drawings. Figure 5 is a schematic cross-sectional view showing an example of a secondary battery according to the embodiment. Figure 6 is a cross-sectional view of the secondary battery shown in Figure 5 along the line VI-VI.

[0114] The electrode group 1 is housed within an outer casing member 2, which is a rectangular cylindrical metal container. The electrode group 1 includes a negative electrode 3, a positive electrode 5, a composite layer 41, and a composite layer 42. The composite layers 41 and 42 function as separators and are provided, for example, on the main surfaces of the negative electrode 3 and the positive electrode 5, respectively. The electrode group 1 has a structure in which the positive electrode 5 and the negative electrode 3 are spirally wound with the composite layers 41 and 42 acting as separators interposed between them to form a flattened shape. An aqueous electrolyte (not shown) is held in the electrode group 1. As shown in Figure 5, multiple strip-shaped negative electrode leads 16 are electrically connected to each of the multiple ends of the negative electrode 3 located on the end face of the electrode group 1. Similarly, multiple strip-shaped positive electrode leads 17 are electrically connected to each of the multiple ends of the positive electrode 5 located on the same end face. These multiple negative electrode leads 16 are bundled together and connected to the negative electrode terminal 6, as shown in Figure 6. Also, although not shown in the diagram, the positive lead 17 is similarly bundled together and electrically connected to the positive terminal 7.

[0115] The metal sealing plate 10 is fixed to the opening of the metal exterior member 2 by welding or the like. The negative terminal 6 and positive terminal 7 are each led out to the outside through outlet holes provided in the sealing plate 10. A negative terminal gasket 8 and a positive terminal gasket 9 are placed on the inner circumferential surface of each outlet hole in the sealing plate 10 to prevent short circuits caused by contact with the negative terminal 6 and positive terminal 7. By placing the negative terminal gasket 8 and the positive terminal gasket 9, the airtightness of the secondary battery 100 can be maintained.

[0116] A control valve 11 (safety valve) is positioned on the sealing plate 10. If the internal pressure in the battery cell increases due to gas generated by the electrolysis of an aqueous solvent, the generated gas can be released to the outside through the control valve 11. As the control valve 11, for example, a resettable type can be used that operates when the internal pressure exceeds a set value and functions as a sealing plug when the internal pressure decreases. Alternatively, a non-resettable type control valve that does not recover its function as a sealing plug once activated may be used. In Figure 5, the control valve 11 is positioned in the center of the sealing plate 10, but the position of the control valve 11 may also be at the edge of the sealing plate 10. The control valve 11 may be omitted.

[0117] Furthermore, the sealing plate 10 is provided with an injection port 12. The aqueous electrolyte can be injected through this injection port 12. After the aqueous electrolyte has been injected, the injection port 12 can be sealed with a sealing plug 13. The injection port 12 and the sealing plug 13 may be omitted.

[0118] Figure 7 is a schematic partially cutaway perspective view showing another example of a secondary battery according to the embodiment. Figure 8 is an enlarged cross-sectional view of section E of the secondary battery shown in Figure 7. Figures 7 and 8 show an example of a secondary battery 100 using a laminate film exterior member as the exterior member.

[0119] The secondary battery 100 shown in Figures 7 and 8 comprises an electrode group 1 shown in Figures 7 and 8, an outer casing member 2 shown in Figure 7, and an aqueous electrolyte (not shown). The electrode group 1 and the aqueous electrolyte are housed within the outer casing member 2. The aqueous electrolyte is held by the electrode group 1.

[0120] The exterior component 2 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0121] As shown in Figure 8, electrode group 1 is a stacked electrode group. The stacked electrode group 1 has a structure in which negative electrode 3 and positive electrode 5 are alternately stacked with composite layers 41 and 42 interposed between them.

[0122] The electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 comprises a negative electrode current collector 3a and a negative electrode active material-containing layer 3b supported on both sides of the negative electrode current collector 3a. A composite layer 41 is in contact with the negative electrode active material-containing layer 3b on each side. The electrode group 1 also includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 comprises a positive electrode current collector 5a and a positive electrode active material-containing layer 5b supported on both sides of the positive electrode current collector 5a. A composite layer 42 is in contact with the positive electrode active material-containing layer 5b on each side.

[0123] Each negative electrode 3's negative electrode current collector 3a includes a portion on one side where the negative electrode active material-containing layer 3b is not provided on any surface. This portion functions as a negative electrode current collector tab 3c. As shown in Figure 8, the negative electrode current collector tab 3c does not overlap with the positive electrode 5. Furthermore, multiple negative electrode current collector tabs 3c are electrically connected to a strip-shaped negative electrode terminal 6. The tip of the strip-shaped negative electrode terminal 6 is extended to the outside of the outer casing member 2.

[0124] Although not shown in the diagram, the positive electrode current collector 5a of each positive electrode 5 includes a portion on one side where the positive electrode active material-containing layer 5b is not supported on any surface. This portion functions as a positive electrode current collector tab. The positive electrode current collector tab, like the negative electrode current collector tab 3c, does not overlap with the negative electrode 3. Furthermore, the positive electrode current collector tab is located on the opposite side of the electrode group 1 from the negative electrode current collector tab 3c. The positive electrode current collector tab is electrically connected to a strip-shaped positive electrode terminal 7. The tip of the strip-shaped positive electrode terminal 7 is located on the opposite side from the negative electrode terminal 6 and is extended to the outside of the outer casing member 2.

[0125] In the secondary battery 100 illustrated in the above figures, composite layers 41 and 42 were interposed as separators between the negative electrode 3 and the positive electrode 5. Either composite layer 41 or composite layer 42 may be omitted.

[0126] <Manufacturing method> Next, an example of a method for manufacturing the electrode group included in the secondary battery according to the embodiment will be described.

[0127] The negative electrode can be obtained, for example, by the following method. First, a slurry is prepared by suspending the negative electrode active material, conductive agent, and binder in a suitable solvent. This slurry is applied to one or both sides of the negative electrode current collector. The coating on the negative electrode current collector is dried to form a negative electrode active material-containing layer. Then, the negative electrode current collector and the negative electrode active material-containing layer formed thereon are pressed. When forming a composite layer on the negative electrode, pressing may be performed after the composite layer is formed, or both before and after the composite layer is formed, in order to control the density of the negative electrode active material-containing layer and the composite layer to desired values.

[0128] The positive electrode can be obtained, for example, by the following method. First, a slurry is prepared by suspending the positive electrode active material, conductive agent, and binder in a suitable solvent. This slurry is applied to one or both sides of the positive electrode current collector. The coating on the positive electrode current collector is dried to form a positive electrode active material-containing layer. Then, the positive electrode current collector and the positive electrode active material-containing layer formed thereon are pressed. When forming a composite layer on the positive electrode, pressing may be performed after the composite layer is formed, or both before and after the composite layer is formed, in order to control the density of the positive electrode active material-containing layer and the composite layer to desired values.

[0129] The composite layer can be formed on the positive and / or negative electrodes, for example, as follows:

[0130] A slurry for forming a composite layer is prepared. The slurry for forming the composite layer is obtained by mixing inorganic solid particles, polymer material, and a solvent, and then stirring the resulting mixture.

[0131] As a solvent, it is preferable to use one that can dissolve polymer materials. Examples of solvents include alcohols such as ethanol, methanol, isopropyl alcohol, n-propyl alcohol, and benzyl alcohol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and diacetone alcohol; esters such as ethyl acetate, methyl acetate, butyl acetate, ethyl lactate, methyl lactate, and butyl lactate; ethers such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, 1,4-dioxane, and tetrahydrofuran; glycols such as ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, butyl carbitol acetate, and ethyl carbitol acetate; and Glycol ethers such as ethyl carbitol, ethyl carbitol, and butyl carbitol; aprotic polar solvents such as dimethylformamide, dimethylacetamide, acetonitrile, valeronitrile, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and γ-butyrolactam; cyclic carboxylic acid esters such as gamma-butyrolactone, gamma-valerolactone, gamma-macarolactone, and epsilon-caprolactone; and chain-like carbonate compounds such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propylisopropyl carbonate, ethyl methyl carbonate, and methyl-n-propyl carbonate are used.

[0132] A composite layer forming slurry is applied to the active material-containing layer on one main surface of the negative or positive electrode, for example, by a doctor blade method, to obtain a coating film. Alternatively, the composite layer forming slurry may be applied to the active material-containing layer on both the front and back main surfaces of the negative or positive electrode to obtain a coating film on each main surface. The composite layer forming slurry applied to each main surface may have the same composition or different compositions. Furthermore, the slurry applied to the negative electrode and the slurry applied to the positive electrode may have the same composition or different compositions. This coating film is dried at a temperature of 50°C to 150°C. In this way, a laminate is obtained in which the dried coating film is provided on the active material-containing layer on one or both sides of the electrode.

[0133] Next, this laminate is subjected to a roll press treatment. For the roll press treatment, for example, a press device equipped with two rollers, one above and one below, is used. By using such a press device, if coatings are applied to both sides of the electrode, both coatings can be pressed simultaneously. In this case, the heating temperature of the rollers can be appropriately changed according to the desired structure. For example, the heating temperature of the rollers is set to a temperature within ±20°C of the softening point of the polymer material in the coating. Alternatively, the coating can be roll-pressed at room temperature of 25°C. It is preferable that the heating temperature of the rollers is lower than the melting point of the polymer material. If the heating temperature is raised above the melting point of the polymer material, the polymer material on the surface side of the coating may melt, and the voids may be completely lost. The complete loss of voids is undesirable because it reduces the ionic conductivity of the composite layer.

[0134] The softening and melting points of polymer materials can vary depending on the molecular weight and monomer unit ratio. For example, PVdF has a softening point of 135°C to 145°C and a melting point of 170°C to 180°C. Polyvinyl formal has a softening point of 120°C to 130°C and a melting point of 190°C to 200°C. Polyvinyl butyral has a softening point of 120°C to 130°C and a melting point of 190°C to 200°C.

[0135] Alternatively, a composite layer with a laminated structure may be provided by coating two types of slurry in a two-layer structure.

[0136] Furthermore, as described above, for each electrode, in order to control the density of the active material-containing layer and the composite layer, pressing may be performed prior to the application of the slurry for forming the composite layer, and then pressing may be performed again after the slurry coating has dried.

[0137] In this way, a negative electrode and / or a positive electrode supporting the composite layer can be obtained. While the above-described press device allows for simultaneous roll-press processing of the coatings on both sides of the electrode, the roll-press processing may be performed on one side at a time. Even when the coating is applied to only one side of the electrode, the above-described press device with two rollers (one above and one below) can be used.

[0138] Here, the peel strength σ at the joint surface between the composite layer and the negative electrode is determined by the press pressure applied after the slurry coating for forming the composite layer has dried. n and the peel strength σ at the junction between the composite layer and the positive electrode p The peel strength σ can change. For example, if the press pressure is reduced, the peel strength σ may change. n and σ p The peel strength σ may decrease. Also, the composition of the slurry for forming the composite layer can affect the peel strength σ. n and σ p The peel strength σ can change. For example, if the proportion of polymer material is increased, the peel strength σ may change. n and σ p This could increase.

[0139] The porosity of the resulting composite layer can also vary depending on the slurry composition. For example, increasing the proportion of polymer material may result in increased porosity.

[0140] In addition, the thickness of the composite layer can change depending on the coating speed of the slurry used to form the composite layer. For example, reducing the coating speed may increase the thickness of the composite layer.

[0141] A negative electrode and a positive electrode, each bearing a composite layer, are laminated such that the main surfaces of the negative electrode active material-containing layer and the positive electrode active material-containing layer face each other via the composite layer. In addition to the composite layer, other separators such as nonwoven fabric may be sandwiched between the negative electrode and the positive electrode. For example, when manufacturing a laminated electrode group, multiple negative electrodes and positive electrodes may be laminated alternately with at least one composite layer interposed between them as a separator. Alternatively, when manufacturing a wound electrode group, one or more negative electrodes and positive electrodes may be laminated with a separator (at least one composite layer) in between, and then the resulting laminate may be wound in a spiral shape. After lamination, or after lamination and further winding, the resulting structure is pressed. An electrode group can be manufactured in this way.

[0142] By following the above procedure, an electrode group according to the embodiment can be obtained. Using the obtained electrode group and a separately prepared aqueous electrolyte, a secondary battery according to the embodiment can be assembled.

[0143] <Measurement method> This section describes various measurement methods. Specifically, it explains how to measure particle size distribution using laser diffraction, peel strength between the electrode and the composite layer, porosity of the composite layer and the active material-containing layer, and pH of aqueous electrolytes.

[0144] (Method for measuring particle size distribution) The particle size distribution of inorganic solid particles contained in the composite layer, and the particle size distribution of the active material contained in the electrodes, can be determined using a laser diffraction particle size distribution analyzer. For example, the Shimadzu SALD-300 is used as a laser diffraction particle size distribution analyzer. During the measurement, the photometric distribution is measured 64 times at 2-second intervals. As the sample for measuring the particle size distribution of inorganic solid particles in the composite layer, a dispersion diluted with ethanol to a concentration of inorganic solid particles of 0.01% to 5% by mass is used. As the sample for measuring the particle size distribution of the electrode active material, a dispersion diluted with N-methyl-2-pyrrolidone to a concentration of active material particles of 0.1% to 1% by mass is used. Alternatively, 0.1 g of active material is dispersed in 1 ml to 2 ml of distilled water containing a surfactant and used as the measurement sample.

[0145] (Method for measuring peel strength) Delamination strength σ at the interface between the negative electrode and the composite layer n and the peel strength σ at the interface between the positive electrode and the composite layer p This can be measured by surface and interface cutting. Details are as follows:

[0146] The secondary battery is discharged, then the battery is disassembled and the electrode group is removed. Before measurement, the outer surface of the electrode group is washed with pure water, and then it is immersed in pure water and left for more than 48 hours. After that, it is washed again with pure water and dried in a 100°C vacuum drying oven for more than 48 hours to prepare the electrode group as a measurement sample.

[0147] The peel strength of the surface and interfacial cutting method can be measured using a cutting strength measuring device such as SAICAS (Surface And Interfacial Cutting Analysis System; registered trademark). The surface and interfacial cutting method is sometimes referred to as the SAICAS method. For example, the DN-GS manufactured by Daipla Wintes Co., Ltd. can be used as the measuring device. For the cutting edge, for example, a ceramic blade made of borazon material with a blade width of 1.0 mm is used. For measurement conditions, for example, the blade angle is set to a rake angle of 20 degrees and a relief angle of 10 degrees.

[0148] First, a vertical cutting is performed on one of the members forming the interface to be measured in the sample, with a pressing load of 1N (constant load mode). Here, the peel strength σ between the composite layer and the negative electrode is measured. n When measuring, for example, the cutting symmetrical component may be either the composite layer or the negative electrode active material-containing layer. The peel strength σ between the composite layer and the positive electrode. p When measuring, for example, the cutting symmetrical component may be either a composite layer or a positive electrode active material-containing layer.

[0149] Cutting is performed at a constant speed of 2 μm / sec horizontally and 0.2 μm / sec vertically, with a shear angle of 45°. When the blade reaches the interface to be measured, the material being cut delaminates at the interface, reducing the horizontal load (horizontal force) on the blade. At this stage, the vertical load is controlled to 0.5 N to maintain a constant vertical blade position. Subsequently, the horizontal force (horizontal load) is measured at a horizontal speed of 2 μm / sec. After the horizontal force due to delamination becomes constant, measurements are continued over a 0.5 mm length, and the average strength of the horizontal force measured in this length range is taken as the delamination strength at that interface.

[0150] The delamination strength between each component in the electrode group is measured using the method described above, and the delamination strength σ between the composite layer and the negative electrode is measured. n and the peel strength σ between the composite layer and the positive electrode p Find each of them.

[0151] Due to the characteristics of surface and interface cutting methods, values ​​exceeding zero may be observed even at interfaces where there is no bonding or adhesion between surfaces. Even if the measured value is not zero, if the peel strength value is 0.1 N / mm or less, it is determined that the surfaces forming that interface are not bonded or adhered to each other.

[0152] (Method for measuring the porosity of composite layers and active material-containing layers) The porosity of the composite layer can be measured through cross-sectional observation using a scanning electron microscope (SEM). Similarly, the porosity of the active material-containing layers of the negative and positive electrodes can also be measured by the same SEM observation method. Further details are as follows.

[0153] The secondary battery is discharged, then the battery is disassembled and the electrode group is removed. Before measurement, each surface of the electrode group is washed with pure water, and then immersed in pure water for more than 48 hours. After that, each surface is washed again with pure water, and it is dried in a vacuum drying oven at 100°C for more than 48 hours. Next, the cross-section is polished by ion milling to obtain the cross-section of the composite layer to be measured. The polished cross-section is observed with an SEM at 5000x magnification, and an SEM image with a resolution of 1280 x 960 pixels is obtained. The SEM image is converted to monochrome 256 grayscale, and binarized with a threshold set so that solid particles and binders are displayed in white and voids in black. The porosity is determined as the area of ​​the black pixels indicating voids relative to the area of ​​all pixels in the binarized cross-sectional image.

[0154] This operation is performed five times in an arbitrary region of the cross-section of the composite layer (five SEM images), and the porosity is calculated by taking the average.

[0155] Similarly, for the active material-containing layer of each electrode, a binarized SEM image is used to measure the porosity five times in an arbitrary region of the cross-section of the active material-containing layer (five SEM images), and the average of these measurements is taken to calculate the porosity.

[0156] (Method for measuring the pH of aqueous electrolytes) The method for measuring the pH of aqueous electrolytes is as follows:

[0157] The electrolyte is extracted from a discharged secondary battery by opening its casing, or by disassembling the secondary battery and extracting the electrolyte from the electrode group. After measuring the volume of the extracted electrolyte, the pH value is measured using a pH meter. The pH value is measured as follows, for example. For this measurement, a Horiba F-74 manufactured by Horiba Ltd. is used, and the measurement is performed in an environment of 25±2℃. First, standard solutions of pH 4.0, 7.0, and 9.0 are prepared. Next, the F-74 is calibrated using these standard solutions. An appropriate amount of the electrolyte (electrolyte solution) to be measured is prepared and placed in a container, and the pH is measured. After measuring the pH, the sensor part of the F-74 is cleaned. When measuring a different target, the above procedure, i.e., calibration, measurement, and cleaning, is performed each time.

[0158] The secondary battery according to the first embodiment includes a composite layer as a separator between the negative electrode and the positive electrode, and contains an aqueous electrolyte. The particle size distribution of the inorganic solid particles contained in the composite layer includes at least two peaks, and the frequency FP of the peak located on the smallest diameter side S and the frequency FP of the peak located on the maximum diameter side L This means 0.9 ≤ FP S / FP L The relationship is ≤5. The porosity of the composite layer is less than that of either the negative electrode active material-containing layer or the positive electrode active material-containing layer. The porosity of the composite layer is within the range of 1% to less than 15%. This secondary battery can exhibit high charge / discharge efficiency and high lifespan performance.

[0159] (Second Embodiment) According to the second embodiment, a battery pack is provided. The battery pack comprises a plurality of secondary batteries according to the first embodiment.

[0160] In the battery pack according to this embodiment, each individual cell may be arranged in series or parallel connections, or a combination of series and parallel connections may be used.

[0161] Next, we will explain an example of a battery pack, referring to the diagram.

[0162] Figure 9 is a schematic perspective view showing an example of a battery pack according to the embodiment. The battery pack 200 shown in Figure 9 comprises five single cells 100a to 100e, four busbars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five single cells 100a to 100e is a secondary battery according to the first embodiment.

[0163] The busbar 21 connects, for example, the negative terminal 6 of one cell 100a to the positive terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by four busbars 21. That is, the battery pack 200 in Figure 9 is a battery pack with five cells in series. Although not illustrated, in a battery pack containing multiple cells that are electrically connected in parallel, the multiple cells can be electrically connected, for example, by connecting multiple negative terminals to each other and multiple positive terminals to each other by busbars.

[0164] The positive terminal 7 of at least one of the five single cells 100a to 100e is electrically connected to the positive lead 22 for external connection. In addition, the negative terminal 6 of at least one of the five single cells 100a to 100e is electrically connected to the negative lead 23 for external connection.

[0165] The battery pack according to the second embodiment comprises the secondary battery according to the first embodiment. Therefore, the battery pack can exhibit high charge / discharge efficiency and long lifespan.

[0166] (Third embodiment) According to the third embodiment, a battery pack including a secondary battery according to the first embodiment is provided. This battery pack may comprise a battery pack according to the second embodiment. This battery pack may comprise a single secondary battery according to the first embodiment instead of the battery pack according to the second embodiment.

[0167] The battery pack may further include a protection circuit. The protection circuit has the function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobile, etc.) may be used as the protection circuit for the battery pack.

[0168] Furthermore, the battery pack may also be equipped with external terminals for power supply. These external terminals are for outputting current from the secondary battery to the outside and / or for inputting current from an outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals. Also, when charging the battery pack, the charging current (including regenerative energy from the power of an automobile, etc.) is supplied to the battery pack through the external terminals.

[0169] Next, an example of a battery pack according to the embodiment will be described with reference to the drawings.

[0170] Figure 10 is a schematic perspective view showing an example of a battery pack according to this embodiment.

[0171] The battery pack 300 includes, for example, a battery pack consisting of secondary batteries as shown in Figures 7 and 8. The battery pack 300 includes a housing 310 and a battery pack 200 housed within the housing 310. The battery pack 200 consists of a plurality (e.g., five) of secondary batteries 100 connected electrically in series. The secondary batteries 100 are stacked in the thickness direction. The housing 310 has openings 320 on the top and on each of its four sides. The sides from which the negative terminal 6 and positive terminal 7 of the secondary battery 100 protrude are exposed to the openings 320 of the housing 310. The output positive terminal 332 of the battery pack 200 is strip-shaped, with one end electrically connected to one of the positive terminals 7 of the secondary battery 100, and the other end protruding from the opening 320 of the housing 310 and extending from the top of the housing 310. On the other hand, the output negative terminal 333 of the battery pack 200 is strip-shaped, with one end electrically connected to one of the negative terminals 6 of the secondary battery 100, and the other end protruding from the opening 320 of the housing 310 and extending out from the top of the housing 310.

[0172] Another example of the battery pack will be described in detail with reference to Figures 11 and 12. Figure 11 is an exploded perspective view schematically showing another example of a battery pack according to the embodiment. Figure 12 is a block diagram showing an example of the electrical circuit of the battery pack shown in Figure 11.

[0173] The battery pack 300 shown in Figures 11 and 12 comprises a housing 31, a lid 32, a protective sheet 33, a battery pack 200, a printed circuit board 34, wiring 35, and an insulating plate (not shown).

[0174] The container 31 shown in Figure 11 is a rectangular-bottomed rectangular container. The container 31 is configured to accommodate a protective sheet 33, a battery pack 200, a printed circuit board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the container 31, thereby housing the battery pack 200 and the other components. The container 31 and the lid 32 are provided with openings or connection terminals for connecting to external devices, etc., although these are not shown in the figures.

[0175] The battery pack 200 comprises multiple individual cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0176] At least one of the multiple single cells 100 is a secondary battery according to the embodiment. Each of the multiple single cells 100 is electrically connected in series as shown in Figure 12. The multiple single cells 100 may also be electrically connected in parallel, or they may be connected in a combination of series and parallel connections. When the multiple single cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0177] The adhesive tape 24 fastens multiple single cells 100 together. Alternatively, heat-shrinkable tape may be used to secure the multiple single cells 100 instead of the adhesive tape 24. In this case, protective sheets 33 are placed on both sides of the battery pack 200, the heat-shrinkable tape is wrapped around it, and then the heat-shrinkable tape is heat-shrinked to bundle the multiple single cells 100 together.

[0178] One end of the positive lead 22 is connected to the battery pack 200. One end of the positive lead 22 is electrically connected to the positive terminal of one or more single cells 100. One end of the negative lead 23 is connected to the battery pack 200. One end of the negative lead 23 is electrically connected to the negative terminal of one or more single cells 100.

[0179] The printed circuit board 34 is installed along one of the shorter sides of the inner surface of the housing container 31. The printed circuit board 34 includes a positive terminal connector 342, a negative terminal connector 343, a thermistor 345, a protection circuit 346, wiring 342a and 343a, an external terminal 350 for energization, a positive side wiring (positive wiring) 348a, and a negative side wiring (negative wiring) 348b. One main surface of the printed circuit board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed circuit board 34 and the battery pack 200.

[0180] The other end 22a of the positive lead 22 is electrically connected to the positive connector 342. The other end 23a of the negative lead 23 is electrically connected to the negative connector 343.

[0181] The thermistor 345 is fixed to one main surface of the printed circuit board 34. The thermistor 345 detects the temperature of each of the single cells 100 and transmits the detection signal to the protection circuit 346.

[0182] The external power supply terminal 350 is fixed to the other main surface of the printed circuit board 34. The external power supply terminal 350 is electrically connected to equipment located outside the battery pack 300. The external power supply terminal 350 includes a positive terminal 352 and a negative terminal 353.

[0183] The protection circuit 346 is fixed to the other main surface of the printed circuit board 34. The protection circuit 346 is connected to the positive terminal 352 via the positive side wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative side wiring 348b. The protection circuit 346 is also electrically connected to the positive side connector 342 via wiring 342a. The protection circuit 346 is also electrically connected to the negative side connector 343 via wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the multiple single cells 100 via wiring 35.

[0184] The protective sheet 33 is disposed on the inner surfaces of both long sides of the storage container 31 and on the inner surface in the short side direction facing the printed wiring board 34 via the assembled battery 200. The protective sheet 33 is made of, for example, resin or rubber.

[0185] The protection circuit 346 controls the charging and discharging of the plurality of single cells 100. Further, the protection circuit 346 interrupts the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352, negative terminal 353) for energizing the external device based on the detection signal transmitted from the thermistor 345 or the detection signal transmitted from each single cell 100 or the assembled battery 200.

[0186] Examples of the detection signal transmitted from the thermistor 345 include a signal that detects that the temperature of the single cell 100 is equal to or higher than a predetermined temperature. Examples of the detection signal transmitted from each single cell 100 or the assembled battery 200 include a signal that detects overcharge, overdischarge, and overcurrent of the single cell 100. When detecting overcharge or the like for each single cell 100, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each single cell 100.

[0187] Note that, as the protection circuit 346, a circuit included in a device (for example, an electronic device, an automobile, etc.) that uses the battery pack 300 as a power source may be used.

[0188] In addition, as described above, this battery pack 300 includes an external terminal 350 for energization. Therefore, this battery pack 300 can output the current from the assembled battery 200 to an external device via the external terminal 350 for energization, and can also input the current from the external device to the assembled battery 200. In other words, when using the battery pack 300 as a power source, the current from the assembled battery 200 is supplied to the external device through the external terminal 350 for energization. Also, when charging the battery pack 300, the charging current from the external device is supplied to the battery pack 300 through the external terminal 350 for energization. When this battery pack 300 is used as an in-vehicle battery, the regenerative energy of the vehicle's power can be used as the charging current from the external device.

[0189] Note that the battery pack 300 may include a plurality of assembled batteries 200. In this case, the plurality of assembled batteries 200 may be connected in series, in parallel, or in a combination of series and parallel connections. Also, the printed wiring board 34 and the wiring 35 may be omitted. In this case, the positive electrode side lead 22 and the negative electrode side lead 23 may be used as the positive side terminal and the negative side terminal of the external terminal for energization, respectively.

[0190] Such a battery pack is used in applications that require excellent cycle performance, for example, when drawing a large current. Specifically, this battery pack is used, for example, as the power source of electronic devices, a stationary battery, and an in-vehicle battery for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly preferably used as an in-vehicle battery.

[0191] The battery pack according to the third embodiment includes the secondary battery according to the first embodiment or the assembled battery according to the second embodiment. Therefore, the battery pack can exhibit high charge-discharge efficiency and high life performance.

[0192] (Fourth Embodiment) According to the fourth embodiment, a vehicle is provided. This vehicle is equipped with the battery pack according to the third embodiment.

[0193] In such a vehicle, the battery pack, for example, recovers regenerative energy from the vehicle's power. The vehicle may also include a mechanism (regenerator) that converts the vehicle's kinetic energy into regenerative energy.

[0194] Examples of vehicles include, for example, two-wheeled or four-wheeled hybrid electric vehicles, two-wheeled or four-wheeled electric vehicles, electric assist bicycles, and railway vehicles.

[0195] The mounting location of the battery pack in a vehicle is not particularly limited. For example, when a battery pack is installed in an automobile, it can be mounted in the engine compartment, at the rear of the vehicle, or under the seats.

[0196] A vehicle may be equipped with multiple battery packs. In this case, the batteries contained in each battery pack may be electrically connected in series, in parallel, or a combination of series and parallel connections. For example, if each battery pack contains a battery pack, the battery packs may be electrically connected in series, in parallel, or a combination of series and parallel connections. Alternatively, if each battery pack contains a single battery, the batteries may be electrically connected in series, in parallel, or a combination of series and parallel connections.

[0197] Next, an example of a vehicle according to the embodiment will be described with reference to the drawings.

[0198] Figure 13 is a schematic partial transparency drawing showing an example of a vehicle.

[0199] The vehicle 400 shown in Figure 13 includes a vehicle body 401 and a battery pack 300 according to the third embodiment. In the example shown in Figure 13, the vehicle 400 is a four-wheeled automobile.

[0200] This vehicle 400 may be equipped with multiple battery packs 300. In this case, the batteries contained in the battery pack 300 (for example, single cells or battery packs) may be connected in series, in parallel, or in a combination of series and parallel connections.

[0201] Figure 13 illustrates an example in which the battery pack 300 is mounted in the engine compartment located in front of the vehicle body 401. As described above, the battery pack 300 may also be mounted, for example, in the rear of the vehicle body 401 or under the seats. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy from the vehicle 400's power.

[0202] The vehicle according to the fourth embodiment is equipped with the battery pack according to the third embodiment. Therefore, the vehicle has excellent driving performance and reliability.

[0203] (Fifth embodiment) According to the fifth embodiment, a stationary power supply including a battery pack according to the third embodiment is provided.

[0204] The stationary power supply may be equipped with a battery pack according to the second embodiment or a secondary battery according to the first embodiment instead of the battery pack according to the third embodiment. The stationary power supply can exhibit high efficiency and long lifespan.

[0205] Figure 14 is a block diagram showing an example of a system including a stationary power supply according to an embodiment. Figure 14 is a diagram showing an example of the application of battery packs 300A and 300B according to the third embodiment to stationary power supplies 112 and 123. In the illustrated example, a system 110 is shown in which stationary power supplies 112 and 123 are used. System 110 comprises a power plant 111, a stationary power supply 112, a consumer-side power grid 113, and an energy management system (EMS) 115. A power grid 116 and a communication network 117 are also formed in system 110, and the power plant 111, stationary power supply 112, consumer-side power grid 113, and EMS 115 are connected via the power grid 116 and the communication network 117. EMS 115 utilizes the power grid 116 and the communication network 117 to perform control to stabilize the entire system 110.

[0206] Power plant 111 generates a large amount of electricity using fuel sources such as thermal and nuclear power. Electricity is supplied from power plant 111 through the power grid 116, etc. A battery pack 300A is installed in stationary power supply 112. The battery pack 300A can store electricity supplied from power plant 111, etc. The stationary power supply 112 can also supply the electricity stored in the battery pack 300A through the power grid 116, etc. System 110 is equipped with a power converter 118. The power converter 118 includes a converter, inverter, and transformer, etc. Therefore, the power converter 118 can perform conversion between DC and AC, conversion between ACs with different frequencies relative to each other, and voltage transformation (boost and step down). For this reason, the power converter 118 can convert the electricity from power plant 111 into electricity that can be stored in the battery pack 300A.

[0207] The consumer-side power system 113 includes power systems for factories, buildings, and households. The consumer-side power system 113 is equipped with a consumer-side EMS 121, a power converter 122, and a stationary power supply 123. The stationary power supply 123 is fitted with a battery pack 300B. The consumer-side EMS 121 performs control to stabilize the consumer-side power system 113.

[0208] Power from the power plant 111 and power from the battery pack 300A are supplied to the customer-side power system 113 through the power grid 116. The battery pack 300B can store the power supplied to the customer-side power system 113. Also, similar to the power conversion device 118, the power conversion device 122 includes a converter, an inverter, a transformer, and the like. Therefore, the power conversion device 122 can perform conversion between DC and AC, conversion between ACs with different frequencies from each other, and voltage conversion (boosting and bucking), etc. For this reason, the power conversion device 122 can convert the power supplied to the customer-side power system 113 into power that can be stored in the battery pack 300B.

[0209] Note that the power stored in the battery pack 300B can be used, for example, for charging a vehicle such as an electric vehicle. Also, a natural energy source may be provided in the system 110. In this case, the natural energy source generates power by natural energy such as wind power and sunlight. And in addition to the power plant 111, power is also supplied from the natural energy source through the power grid 116.

Example

[0210] Hereinafter, the examples will be described in detail.

[0211] (Example 1) <Fabrication of the negative electrode> The negative electrode was fabricated as follows. The negative electrode active material, the conductive agent, and the binder were dispersed in an N-methyl-2-pyrrolidone (NMP) solvent to prepare a negative electrode active material-containing slurry. The ratios of the conductive agent and the binder in the negative electrode active material-containing layer were 5 parts by mass and 1 part by mass, respectively, with respect to 100 parts by mass of the negative electrode active material. As the negative electrode active material, lithium titanate Li4Ti5O 12 powder (TLO) was used. As the conductive agent, graphite powder was used. As the binder, polyvinylidene fluoride (PVdF) resin was used.

[0212] Next, the prepared slurry was applied to both sides of the negative electrode current collector, and the coating film was dried to form a negative electrode active material-containing layer. A 50 μm thick Zn foil was used as the negative electrode current collector. When applying the slurry to the Zn foil, for the outermost layer of the electrode group of the negative electrode to be fabricated, the slurry containing the negative electrode active material was applied to only one side of the Zn foil, while for the remaining parts, the slurry containing the negative electrode active material was applied to both sides of the Zn foil. At this time, the drying temperature of the slurry containing the negative electrode active material was 130°C, and the slurry coating speed was 10 m / min.

[0213] <Fabrication of composite layers> Next, inorganic solid particles and polymer material were mixed with N-methyl-2-pyrrolidone (NMP) to obtain a slurry for composite layer formation. Alumina powder was used as the inorganic solid particles. In this study, inorganic solid particles exhibiting a particle size distribution with at least two peaks were used. The peak top P was the peak on the smallest particle size side. S The particle diameter corresponding to the position (first particle diameter), and the peak top P on the side with the largest particle size. L The particle sizes corresponding to the positions (second particle size) were 0.7 μm and 3 μm, respectively. Polyvinylidene fluoride (PVdF) resin was used as the polymer material. The volume ratio of inorganic solid particles to polymer material was 64.6:35.4. The above components were added to NMP and mixed to prepare a slurry. This slurry was coated onto the surface of the negative electrode active material-containing layer on each side of the negative electrode at a coating speed of 10 m / min, and the resulting coating film was dried at a temperature of 130°C. Subsequently, the coating film was pressed to obtain a negative electrode supporting a composite layer (separator layer). The thickness of the composite layer at this time was 10 μm.

[0214] <Fabrication of the positive electrode> A slurry for preparing a positive electrode was prepared by mixing a positive electrode active material, a conductive agent, a binder, and a solvent. Lithium manganese oxide (LiMn2O4, LMO) was used as the positive electrode active material. Graphite powder was used as the conductive agent. Polyvinylidene fluoride (PVdF) was used as the binder. N-methyl-2-pyrrolidone (NMP) was used as the solvent. The mass ratio of the positive electrode active material, conductive agent, and binder in the slurry was 100:5:5. This slurry for preparing a positive electrode was applied to both sides of a 12 μm Ti foil used as the positive electrode current collector and dried. At this time, the drying temperature of the slurry containing the positive electrode active material was 130°C, and the slurry coating speed was 10 m / min. The positive electrode was obtained by pressing this laminate.

[0215] <Fabrication of electrode groups> A laminate was obtained by stacking a negative electrode supporting a composite layer with a positive electrode. These electrodes were stacked so that the composite layer, acting as a separator layer, was located between the negative electrode active material-containing layer and the positive electrode active material-containing layer. The laminate was then wound in a spiral shape with the negative electrode side at the outermost periphery, and then pressed with 5kN to produce a group of flattened electrodes.

[0216] <Battery assembly> The obtained electrode group was placed inside a polypropylene resin container. Next, a 12M LiCl aqueous solution prepared as an aqueous electrolyte was poured into the container to fabricate a secondary battery.

[0217] (Example 2) A secondary battery was fabricated in the same manner as in Example 1, except that the surface on which the composite layer is formed was changed from the negative electrode surface to the positive electrode surface (the surface of the positive electrode active material-containing layer on both sides).

[0218] (Example 3) A secondary battery was fabricated in the same manner as in Example 1, except that a composite layer was formed on the positive electrode surface in addition to the negative electrode surface.

[0219] (Examples 4 to 13) The inorganic solid particles (alumina) used for the composite layer formed on the negative electrode surface have a first particle diameter and a second particle diameter in their particle size distribution, as shown in Table 3 below (peak top P). S and P L As shown in the position, the frequency ratio FP corresponding to them S / FP L A secondary battery was fabricated in the same manner as in Example 1, except that the components were changed as shown in Table 3.

[0220] (Examples 14 to 16) A secondary battery was fabricated in the same manner as in Example 1, except that the component ratio (volume ratio) of inorganic solid particles (alumina) and polymer material (PVdF) used in the composite layer formed on the negative electrode surface was changed as shown in Table 1 below.

[0221] (Examples 17 to 20) The inorganic solid particles used in the composite layer formed on the negative electrode surface are changed to the materials shown in Table 1, and the first and second particle sizes in their particle size distribution are the peak top P shown in Table 3. S and P L As shown in the position, the frequency ratio FP corresponding to them S / FP L The following changes were made as shown in Table 3. In the table, LATP is Li 1.5 Al 0.5 Ti 1.5 (PO4)3 is the reference, and LLZ is Li7La3Zr2O 12 This refers to [the specified element]. In addition, the component ratio (volume ratio) of inorganic solid particles and polymer material was changed as shown in Table 1 below. Aside from these changes, the secondary battery was fabricated in the same manner as in Example 1.

[0222] (Example 21) A secondary battery was fabricated using the same method as in Example 1, except that the active material used in the negative electrode was changed to Nb2TiO7(TNO).

[0223] (Example 22) The active material used in the positive electrode is LiNi 0.5 Co 0.2 Mn 0.3The secondary battery was fabricated using the same method as in Example 1, except that O2(NCM) was used instead.

[0224] (Comparative Examples 1 and 2) A secondary battery was fabricated in the same manner as in Example 1, except that the inorganic solid particles (alumina) used in the composite layer formed on the negative electrode surface were changed to those showing a single peak in their particle size distribution as shown in Table 3.

[0225] (Comparative Example 3) A secondary battery was fabricated in the same manner as in Example 1, except that the formation of a composite layer on the negative electrode surface was omitted and a cellulose nonwoven fabric was used as the separator.

[0226] (Comparative Examples 4 and 5) The inorganic solid particles used for the composite layer formed on the negative electrode surface are defined by the peak top P of the first and second particle sizes in their particle size distribution. S and P L Frequency ratio corresponding to FP S / FP L A secondary battery was manufactured in the same manner as in Example 1, except that the components were changed as shown in Table 3.

[0227] (Comparative Examples 6 and 7) A secondary battery was fabricated in the same manner as in Example 1, except that the component ratio (volume ratio) of inorganic solid particles (alumina) and polymer material (PVdF) used in the composite layer formed on the negative electrode surface was changed as shown in Table 2 below.

[0228] <Performance evaluation of secondary batteries> The charge-discharge efficiency of the secondary batteries according to Examples 1 to 22 and Comparative Examples 1 to 7 was measured. Specifically, first, each secondary battery was charged at a constant current corresponding to the 1-hour rate and 10-hour rate (1C and 0.1C), respectively, in an environment of 25°C until the battery voltage reached 2.7V. This state was maintained for 30 minutes. Then, the battery was discharged at the same constant current as during charging until the battery voltage reached 2.1V. This state was maintained for 30 minutes. This series of operations constituted one charge-discharge cycle, and this was repeated 100 times. For each case where the cycle was performed at each rate, the discharge capacity and charge capacity at the 100th cycle were measured, and the charge-discharge efficiency (discharge capacity / charge capacity) was calculated using the measured values. In addition, the capacity at the 100th cycle relative to the initial capacity measured during the first charge-discharge, i.e., the capacity retention rate at 100 cycles (discharge capacity at 100th cycle / discharge capacity at 1st cycle), was calculated to determine the life performance.

[0229] <Peel strength evaluation> After measuring the charge / discharge efficiency and life performance as described above, the secondary batteries were discharged and disassembled using the previously described method, the electrode groups were removed and cleaned, and the peel strength between each component was measured by surface / interface cutting. Specifically, for each secondary battery, the peel strength σ between the negative electrode and the composite layer formed on the negative electrode was measured. n and / or peel strength σ between the positive electrode and the composite layer formed on the positive electrode p Each of these measurements was performed. However, in Comparative Example 3, a cellulose nonwoven fabric was sandwiched between the positive and negative electrodes as a separator, and there was no composite layer, so the peel strength was considered zero without measurement.

[0230] The measuring device used was the DN-GS manufactured by Daipla Wintes Co., Ltd. A ceramic blade made of borazon material with a blade width of 1.0 mm was used for the cutting edge. The measurement conditions were a rake angle of 20 degrees and a relief angle of 10 degrees.

[0231] <Measurement of porosity> The negative and positive electrodes were separated from the electrode group extracted from the secondary battery, while retaining the composite layer (if present) on each surface. The porosity of each composite layer and active material-containing layer was measured using the method described above, with the samples obtained after washing and drying the separated electrodes.

[0232] Tables 1-5 summarize the manufacturing conditions and various evaluation results for secondary batteries related to Examples 1-22 and Comparative Examples 1-7.

[0233] Table 1 shows the details of the materials used for the negative electrode, positive electrode, and composite layer in Examples 1 to 22, and Table 2 shows the details in Comparative Examples 1 to 7. Specifically, the composition of the electrode active material and the composition of each composite layer are shown. Regarding the composition of the active material, Li4Ti5O 12 TLO, Nb2TiO7 is TNO, LiMn2O4 is LMO, and LiNi 0.5 Co 0.2 Mn 0.3 O2 is abbreviated as "NCM". The composition of the composite layer is shown as the inorganic solid particle material, polymer material, and their volume ratio. For the inorganic solid particle material, Li 1.5 Al 0.5 Ti 1.5 (PO4)3 is "LATP", alumina is "Al2O3", and Li7La3Zr2O 12 These are denoted as "LLZ". For polymer materials, polyvinylidene fluoride is denoted as "PVdF". In addition, if there is no applicable item in each table, it is indicated as "Not applicable" with "-".

[0234] Tables 3 and 4 show further details regarding the negative electrode and positive electrode, respectively. Specifically, details of the peaks in the particle size distribution of inorganic solid particles for each composite layer formed on each electrode, thickness and porosity, porosity of the active material-containing layer, and the peel strength σ of the composite layer relative to the electrode. n and σ p This shows the details of the particle size distribution, specifically the peak top P on the smallest particle diameter side. S The position of the peak top P on the side with the largest particle diameter. LThe position and the frequency ratio FP corresponding to them S / FP L This indicates.

[0235] Table 5 shows the results of performance evaluations of secondary batteries cycled at each rate. The performance evaluation of secondary batteries is shown as follows: the charge-discharge efficiency at the 100th charge-discharge cycle calculated as described above, the discharge capacity at the 100th cycle, and the life performance evaluated by the capacity retention rate at the 100th cycle.

[0236] [Table 1]

[0237] [Table 2]

[0238] [Table 3]

[0239] [Table 4]

[0240] [Table 5]

[0241] In Comparative Example 3, an electrode group was used in which electrodes without a composite layer were laminated with a cellulose nonwoven fabric as a separator. Therefore, in Comparative Example 3, all items representing the composite layer are indicated with "-". Comparing Comparative Example 3, which does not have a composite layer on the electrode, with Comparative Examples 1 and 2, which have a composite layer on the electrode, it can be seen that the formation of a composite layer is more effective in terms of both charge / discharge efficiency and lifespan performance. In Comparative Example 3, both efficiency and lifespan performance are degraded compared to Comparative Examples 1 and 2, suggesting that many side reactions due to the electrolysis of water during charge / discharge occur, and it can be seen that these are suppressed by forming a composite layer on the electrode surface.

[0242] Comparing Comparative Examples 1 and 2 with Comparative Examples 4 and 5, it can be seen that by at least bimodalizing the peak particle size of the insulating inorganic solid particles used in the composite layer, the lifespan performance is improved while maintaining the charge-discharge efficiency.

[0243] Table 5 shows the battery performance evaluation results, indicating that the secondary batteries produced in Examples 1 to 22 showed significantly improved efficiency and lifespan performance during low-rate charge and discharge compared to the secondary batteries produced in Comparative Examples 1 to 7.

[0244] In Examples 1 to 22, except for Examples 2 and 3, a composite layer was formed on the negative electrode and not on the positive electrode, so the peel strength σ between the positive electrode and the composite layer was... p The values ​​were 0.1 N / mm or less. In addition, in those embodiments, the peel strength σ between the negative electrode and the composite layer was n It showed a value of 0.3 N / mm or higher. In contrast, in Example 2, where the composite layer was formed on the positive electrode instead of the negative electrode, σ p The value is 0.3 N / mm or higher, σ n The value was less than 0.1 N / mm. Furthermore, in Example 3, in which a composite layer was formed on both the positive and negative electrodes, σ n and σ p All values ​​were 0.3 N / mm or higher. In other words, in electrodes with a composite layer, the interface between the composite layer and the electrode showed a peel strength of 0.3 N / mm or higher, while in electrodes with only simple lamination, the interfacial peel strength was 0.1 N / mm or lower, indicating that bonding was not achieved.

[0245] Comparing Example 1 and Example 2, the formation of a composite layer on the negative electrode resulted in higher efficiency and lifespan, suggesting that the negative electrode is more prone to side reactions. Nevertheless, even in Example 2, the formation of the composite layer significantly improved both efficiency and lifespan compared to Comparative Example 3.

[0246] As can be seen from the comparison between Examples 1 to 22 and Comparative Examples 1 and 2, the particle size distribution of the insulating inorganic solid particles forming the composite layer is at least bimodal, and the smallest particle size peak top P S and the peak top P with the largest particle size L Frequency FP S and FP L The ratio of FP S / FP L Setting it to ≥0.9 further improved efficiency during low-rate cycles.

[0247] In a comparison between Example 1 and Examples 4 through 11, the peak top P on the small particle size side was S Either shift the position to a smaller particle size, or increase the peak top P on the larger particle size side. L Shifting the position to a larger particle size resulted in a slight decrease in efficiency at low rates. On the one hand, as the particle size of the small-particle inorganic solid particles decreased, the curvature of the flow path within the composite layer decreased, making liquid flow within the composite layer easier, and as a result, the side reaction between water and the electrode was not suppressed to a great extent. On the other hand, as the particle size of the large-particle inorganic solid particles increased, an increase in porosity was observed, and as a result, the amount of liquid contained in the pores increased, and in this case too, the side reaction between water and the electrode was not suppressed to a great extent. Nevertheless, in Examples 4 to 11, significantly higher efficiency and lifetime performance were obtained compared to Comparative Examples 1 and 2, especially at low rates, indicating that the formation of composite layers on both the negative and positive electrodes is effective in improving lifetime performance.

[0248] Furthermore, regarding the comparison between Example 1 and Examples 12 and 13, on the one hand, FP S / FP LWhen the size decreases, the proportion of large particle sizes increases, leading to an increase in porosity, and in other ways, FP S / FP L When the particle size becomes extremely large, the particle size distribution approaches monomodal, which reduces the curvature of the flow path within the composite layer, leading to an increase in liquid flow and a slight decrease in performance. Nevertheless, in Examples 12 and 13, a significant improvement in performance is observed compared to Comparative Examples 1 and 2.

[0249] In Examples 14 to 16, the ratio of polymer material (binder) in the composite layer was varied. As the binder ratio decreased, the porosity increased. On the one hand, with a binder ratio of 20.4 volume%, a composite layer with a porosity of 14.5% was obtained. Although there was a decrease in performance compared to Example 1, it was a significant improvement compared to Comparative Examples 1 and 2 (Example 15). On the other hand, with a binder ratio of 42.2 volume%, the proportion of binder penetrating into the voids in the composite layer increased, resulting in a decrease in porosity and a reduction in capacity (Example 16). This is thought to be due to an increase in battery resistance, but it showed good performance in terms of efficiency and lifespan. However, as shown in Comparative Examples 6 and 7, if the amount of binder is extremely small or large, the porosity also becomes extremely large. On the one hand, with a binder ratio of 6.4 volume%, the porosity was 15.9%, and the composite layer could not exert its effect of suppressing liquid flow, resulting in a significant deterioration in performance (Comparative Example 6). On the other hand, at a binder ratio of 50.8% by volume, the porosity was 0.4%, resulting in a significant increase in battery resistance and a deterioration in capacity and lifespan (Comparative Example 7).

[0250] A comparison of Examples 1 to 13 and Examples 17 to 20 shows that the above effects can be obtained even if the inorganic solid particles used in the composite layer are not alumina. Similarly, the effects can be obtained even when the electrode active material is different, as in Examples 21 and 22.

[0251] As shown above, a comparison between Examples 1 to 22 and Comparative Examples 1 to 7 reveals that by having at least two peaks in the particle size distribution of the insulating particles forming the composite layer, and by setting the ratio of the size of the smallest particle size peak to the size of the largest particle size peak to be between 0.9 and 5, a secondary battery with good charge / discharge efficiency and lifespan performance can be provided.

[0252] According to one or more embodiments and examples described above, a secondary battery is provided comprising a negative electrode, a positive electrode, a separator, and an aqueous electrolyte. The negative electrode includes a negative electrode active material-containing layer. The positive electrode includes a positive electrode active material-containing layer. The separator is located between the negative electrode and the positive electrode and includes a composite layer comprising inorganic solid particles and a polymer material. The particle size distribution of the inorganic solid particles in the composite layer includes at least two peaks, with the peak top P being the minimum particle size peak. S Frequency FP S and the peak top P of the maximum particle size peak L Frequency FP L This means 0.9 ≤ FP S / FP L The relationship is ≤5. The porosity of the composite layer is less than the porosity of either the negative electrode active material-containing layer or the positive electrode active material-containing layer, and is between 1% and 15%. With the above configuration, it is possible to provide a secondary battery and battery pack that exhibit high charge / discharge efficiency and high lifespan performance, as well as a vehicle and stationary power supply equipped with the battery pack.

[0253] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0254] Several embodiments of the present invention are described below. [1] A negative electrode comprising a negative electrode containing a negative electrode active material layer, a positive electrode containing a positive electrode active material layer, a separator located between the negative electrode and the positive electrode and comprising a composite layer containing inorganic solid particles and a polymer material, and an aqueous electrolyte, wherein the particle size distribution of the inorganic solid particles in the composite layer includes at least two peaks, and the peak top P of the smallest particle size in the particle size distribution is S Frequency FP S and the peak top P of the peak on the side with the largest particle size L Frequency FP L This means 0.9 ≤ FP S / FP L A secondary battery in which the relationship is ≤ 5, the porosity of the composite layer is less than the porosity of the negative electrode active material-containing layer and the porosity of the positive electrode active material-containing layer, and is between 1% and 15%. [2] The composite layer is bonded to at least one of the negative electrode and the positive electrode, and the peel strength between the negative electrode and the composite layer σ n The peel strength σ between the positive electrode and the composite layer is greater than 0.3 N / mm. p The peel strength σ is greater than 0.3 N / mm. n and the peel strength σ p A secondary battery as described in [1], where both of the following are greater than 0.3 N / mm. [3] The aforementioned peak top P S The position of is within the range of 0.3 μm to 0.8 μm, and the peak top P L The secondary battery described in [1] or [2], wherein the position of is within the range of 1 μm to 4 μm. [4] The secondary battery according to any one of [1] to [3], wherein the content of the polymer material in the composite layer is 20% by volume or more. [5] The negative electrode has a lithium ion insertion-decompression potential of 1V to 3V relative to the oxidation-reduction potential of lithium (vs. Li / Li + A secondary battery according to any one of [1] to [4], comprising a negative electrode active material containing a compound that is ). [6] A battery pack comprising a rechargeable battery as described in any one of [1] through [5]. [7] The battery pack described in [6], further comprising an external terminal for power supply and a protection circuit. [8] The battery pack according to [6] or [7], comprising a plurality of the secondary batteries, wherein the plurality of secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. A vehicle equipped with a battery pack as described in any one of [9] [6] through [8].

[10] The vehicle according to [9], which includes a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

[11] A stationary power supply comprising a battery pack as described in any one of [6] through [8]. [Explanation of Symbols]

[0255] 1…Electrode group, 2…Outer casing, 3…Negative electrode, 3a…Negative electrode current collector, 3b…Negative electrode active material containing layer, 3c…Negative electrode current collector tab, 4…Composite layer, 5…Positive electrode, 5a…Positive electrode current collector, 5b…Positive electrode active material containing layer, 6…Negative electrode terminal, 7…Positive electrode terminal, 8…Negative electrode gasket, 9…Positive electrode gasket, 10…Sealing plate, 11…Control valve, 12…Injection port, 13…Sealing plug, 16…Negative electrode lead, 17…Positive electrode Lead, 21...Busbar, 22...Positive lead, 23...Negative lead, 24...Adhesive tape, 31...Container, 32...Lid, 33...Protective sheet, 34...Printed circuit board, 35...Wiring, 40...Composite layer, 41...Composite layer, 42...Composite layer, 44...Path, 47...Inorganic solid particles, 48...Inorganic solid particles, 49...Inorganic solid particles, 100...Secondary battery, 110...System, 11 1...Power plant, 112...Stationary power supply, 113...Customer-side power system, 115...Energy management system, 116...Power grid, 117...Communication network, 118...Power converter, 121...Customer-side EMS, 122...Power converter, 123...Stationary power supply, 200...Battery pack, 300...Battery pack, 300A...Battery pack, 300B...Battery pack, 310...Housing, 320...Opening, 332...Output positive terminal, 333...Output negative terminal, 342...Positive side connector, 343...Negative side connector, 345...Thermistor, 346...Protection circuit, 342a...Wiring, 343a...Wiring, 350...External terminal for energization, 352...Positive side terminal, 353...Negative side terminal, 348a...Positive side wiring, 348b...Negative side wiring, 400...Vehicle, 401...Vehicle body.

Claims

1. A negative electrode containing a negative electrode active material layer, A positive electrode containing a positive electrode active material layer, A separator located between the negative electrode and the positive electrode, comprising a composite layer containing inorganic solid particles and a polymer material, Water-based electrolytes and It is equipped with, The particle size distribution of the inorganic solid particles in the composite layer includes at least two peaks, and the peak top P of the smallest particle size in the particle size distribution is... S Frequency FP S and the peak top P of the peak on the side with the largest particle size L Frequency FP L This means 0.9 ≤ FP S / FP L The relationship is ≤ 5, A secondary battery in which the porosity of the composite layer is less than that of the negative electrode active material-containing layer and the positive electrode active material-containing layer, and is between 1% and 15%.

2. The composite layer is joined to at least one of the negative electrode and the positive electrode, and the peel strength σ between the negative electrode and the composite layer ｎ is greater than 0.3 N / mm and not more than 0.76 N / mm, or the peel strength σ between the positive electrode and the composite layer ｐ is greater than 0.3 N / mm and not more than 0.76 N / mm, or both the peel strength σ ｎ and the peel strength σ ｐ are greater than 0.3 N / mm and not more than 0.76 N / mm. The secondary battery according to claim 1

3. The aforementioned peak top P S The position is within the range of 0.3 μm to 0.8 μm, and the peak top P L The secondary battery according to claim 1 or 2, wherein the position is within the range of 1 μm to 4 μm.

4. The secondary battery according to claim 1 or 2, wherein the content of the polymer material in the composite layer is 20% by volume or more.

5. The negative electrode has a lithium ion insertion-desorption potential of 1V to 3V relative to the lithium oxidation-reduction potential (vs. Li / Li). ＋ A secondary battery according to claim 1 or 2, comprising a negative electrode active material containing a compound that is ).

6. A secondary battery comprising the secondary battery described in claim 1 or 2, A battery pack that further includes external terminals for power supply and a protection circuit.

7. The battery pack according to claim 6, comprising a plurality of the secondary batteries, wherein the plurality of secondary batteries are electrically connected in series, parallel, or a combination of series and parallel.

8. A vehicle comprising the battery pack described in claim 6.

9. The vehicle according to claim 8, further comprising a mechanism for converting the kinetic energy of the vehicle into regenerative energy and supplying it to the battery pack as a charging current through the external terminal for energization.

10. A stationary power supply comprising the battery pack described in claim 6.

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