JP2023021654A - Positive electrode, secondary battery, battery pack, and vehicle - Google Patents

Abstract

To provide a positive electrode having low resistance and capable of achieving a high capacity retention rate.SOLUTION: According to one embodiment, a positive electrode is provided. The positive electrode includes a positive electrode active material-containing layer containing positive electrode active material particles and a water-soluble polymer. The positive electrode active material particles include lithium composite oxide particles exhibiting an operating potential of 4.4 V or higher on the basis of metallic lithium, and a conductive polymer covering at least part of surfaces of the lithium composite oxide particles. A ratio of the mass of the conductive polymer to the mass of the lithium composite oxide particles is in a range of 0.5% by mass to 5.0% by mass.SELECTED DRAWING: Figure 1

Description

Embodiments of the present invention relate to positive electrodes, secondary batteries, battery packs, and vehicles.

Non-aqueous electrolyte batteries, typified by lithium-ion batteries in which lithium ions are the carrier of electric charge, have the advantages of high energy density and high output. Widely applied to large-scale applications. Lithium transition metal composite oxides such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), and lithium manganate (LiMn ₂ O ₄ ) have been used as positive electrode active materials for non-aqueous electrolyte batteries. It is In addition, products using a carbon material as a negative electrode active material have been put on the market.

As a negative electrode active material, instead of a carbon material, a non-aqueous electrolyte battery using a lithium-titanium composite oxide having a high lithium absorption/desorption potential of about 1.55 V relative to metallic lithium has been put to practical use. Lithium-titanium composite oxides are excellent in cycle characteristics because their volume changes little during charging and discharging. In addition, a negative electrode containing a lithium-titanium composite oxide does not deposit lithium metal during lithium absorption/desorption, so a secondary battery equipped with this negative electrode can be charged with a large current.

As for the positive electrode active material, lithium manganate (LiMn ₂ O ₄ ) has the advantages of abundant resources, low cost, low environmental impact, and high safety in an overcharged state. Therefore, lithium manganate is being studied as a substitute material for lithium cobaltate (LiCoO ₂ ). On the other hand, the average operating potential of lithium manganate is about 4.0 V based on metallic lithium. Therefore, there is a problem that it is difficult to achieve a high battery voltage.

Therefore, attempts have been made to increase the battery voltage by using a positive electrode material that exhibits a high positive electrode potential of about 4.5 V to 5.0 V relative to metallic lithium. However, in a positive electrode exhibiting a high positive electrode potential, there is a problem of elution of metal accompanying gas generation and hydrofluoric acid generation.

JP-A-7-263026

Hongyu Dong et al. "Improved High Temperature Performance of a Spinel LiNi0.5Mn1.5O4 Cathode for High-Voltage Lithium-Ion Batteries by Surface Modification of a Flexible Conductive Nanolayer" ACS Omega 2019, 4, 185-194

The present invention provides a positive electrode having a low resistance and capable of achieving a high capacity retention rate, a secondary battery comprising the positive electrode, a battery pack comprising the secondary battery, and a vehicle comprising the battery pack. With the goal.

According to embodiments, a positive electrode is provided. The positive electrode includes a positive electrode active material-containing layer containing positive electrode active material particles and a water-soluble polymer. The positive electrode active material particles include lithium composite oxide particles exhibiting an operating potential of 4.4 V or higher relative to metallic lithium, and a conductive polymer covering at least a portion of the lithium composite oxide particle surfaces. The ratio of the mass of the conductive polymer to the mass of the lithium composite oxide particles is in the range of 0.5% by mass to 5.0% by mass.

According to another embodiment, a secondary battery is provided. A secondary battery includes a positive electrode, a negative electrode, and an electrolyte according to the embodiment.

According to another embodiment, a battery pack is provided. A battery pack includes a secondary battery according to an embodiment.

According to another embodiment, a vehicle is provided. A vehicle includes the battery pack according to the embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing which shows schematically an example of the positive electrode which concerns on embodiment. BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing which shows schematically an example of the secondary battery which concerns on embodiment. FIG. 3 is an enlarged sectional view of part A of the secondary battery shown in FIG. 2 ; FIG. 3 is a partially cutaway perspective view schematically showing another example of the secondary battery according to the embodiment; FIG. 5 is an enlarged cross-sectional view of the B portion of the secondary battery shown in FIG. 4 ; The perspective view which shows roughly an example of the assembled battery which concerns on embodiment. 1 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment; FIG. FIG. 8 is a block diagram showing an example of an electric circuit of the battery pack shown in FIG. 7; 1 is a partially transparent view schematically showing an example of a vehicle according to an embodiment; FIG. The figure which showed roughly an example of the control system regarding the electric system in the vehicle which concerns on embodiment.

Hereinafter, embodiments will be described with reference to the drawings as appropriate. In addition, the same code|symbol shall be attached|subjected to the common structure through embodiment, and the overlapping description is abbreviate|omitted. In addition, each drawing is a schematic diagram for explaining the embodiments and promoting understanding thereof, and there are places where the shapes, dimensions, ratios, etc. are different from the actual device, but these are the following explanations and known techniques. Consideration can be taken into consideration and the design can be changed as appropriate.

In a secondary battery, when a lithium composite oxide having an operating potential of 4.4 V (vs. Li/Li ⁺ ) or more is used as a positive electrode active material, gas mainly composed of hydrogen gas is generated. Alternatively, if the binder and electrolyte salt contain fluorine atoms, hydrofluoric acid is generated. In the positive electrode active material, since metals are eluted with the generation of hydrogen gas and hydrofluoric acid, there is a problem that the discharge capacity decreases due to repeated charge-discharge cycles.

It has been reported that metal elution from the positive electrode active material can be suppressed by coating the positive electrode active material particles with a conductive polymer such as polyaniline. However, since the conductive polymer itself as a polymer is difficult to dissolve in water or an organic solvent, it is difficult to directly coat the positive electrode active material particles with the conductive polymer itself. Also, a method of covering the surface of active material particles while polymerizing a monomer constituting a conductive polymer using a polymerization initiator has been reported. However, in this case, it is difficult to coat the surface of the active material particles with a sufficient amount of conductive polymer.

The present inventors have found that when a conductive polymer is coated on the surface of lithium composite oxide particles having a high operating potential of 4.4 V (vs. Li/Li ⁺ ) or higher, water-soluble polymers are present between the particles. It has been found that the conductive polymer is easily retained on the surface of the active material particles.

(First embodiment)
According to a first embodiment, a positive electrode is provided. The positive electrode includes a positive electrode active material-containing layer containing positive electrode active material particles and a water-soluble polymer. The positive electrode active material particles include lithium composite oxide particles exhibiting an operating potential of 4.4 V or higher relative to metallic lithium, and a conductive polymer covering at least a portion of the lithium composite oxide particle surfaces. The ratio of the mass of the conductive polymer to the mass of the lithium composite oxide particles is in the range of 0.5% by mass to 5.0% by mass.

The lithium composite oxide particles contained in the positive electrode according to the embodiment are coated with a conductive polymer in an amount of 0.5% by mass to 5.0% by mass. The conductive polymer coats the lithium composite oxide particles, for example, in the form of a film. Since the above ratio is 0.5% by mass or more, metal elution can be suppressed even in lithium composite oxide particles exhibiting a high action potential. One reason for this is thought to be that the lithium composite oxide particles and the electrolyte are less likely to come into direct contact with each other. On the other hand, if this ratio exceeds 5.0% by mass, the battery resistance is excessively increased, and the weight energy density and/or the volume energy density are lowered, which is not preferable. The ratio of the mass of the conductive polymer to the mass of the lithium composite oxide particles is preferably in the range of 1.0% by mass to 4.0% by mass.

The electrical conductivity of the conductive polymer is, for example, in the range of 1 S/cm to 200 S/cm, preferably in the range of 10 S/cm to 200 S/cm. In order to suppress an increase in electrical resistance caused by coating the surface of the active material particles with the conductive polymer, the electrical conductivity of the conductive polymer is preferably high. Conductive polymers, for example, are water-insoluble.

The conductive polymer is not particularly limited as long as it has electronic conductivity, but is preferably at least one selected from the group consisting of polyanilines, polypyrroles and polythiophenes, for example. The electrical conductivity of polyanilines is, for example, in the range of 10 S/cm to 50 S/cm. The electrical conductivity of polypyrroles is, for example, in the range of 50 S/cm to 100 S/cm. The electrical conductivity of polythiophenes is, for example, in the range of 50 S/cm to 150 S/cm.

Examples of polyanilines include polyaniline, poly(2-methylaniline), poly(3-isobutylaniline), poly(2-anilinesulfonic acid), and poly(3-anilinesulfonic acid).

Examples of polypyrroles include polypyrrole, poly(N-methylpyrrole), poly(3-methylpyrrole), poly(3-ethylpyrrole), poly(3-n-propylpyrrole), poly(3-butylpyrrole), Poly(3-octylpyrrole), Poly(3-decylpyrrole), Poly(3-dodecylpyrrole), Poly(3,4-dimethylpyrrole), Poly(3,4-dibutylpyrrole), Poly(3-carboxypyrrole) ), poly (3-methyl-4-carboxypyrrole), poly (3-methyl-4-carboxyethylpyrrole), poly (3-methyl-4-carboxybutylpyrrole), poly (3-hydroxypyrrole), poly ( 3-methoxypyrrole), poly(3-ethoxypyrrole), poly(3-butoxypyrrole), poly(3-hexyloxypyrrole), and poly(3-methyl-4-hexyloxypyrrole).

Examples of polythiophenes include polythiophene, poly(3-methylthiophene), poly(3-ethylthiophene, poly(3-propylthiophene), poly(3-butylthiophene), poly(3-hexylthiophene), poly(3 -heptylthiophene), poly(3-octylthiophene), poly(3-decylthiophene), poly(3-dodecylthiophene), poly(3-octadecylthiophene), poly(3-bromothiophene), poly(3-chloro thiophene), poly(3-iodothiophene), poly(3-cyanothiophene), poly(3-phenylthiophene), poly(3,4-dimethylthiophene), poly(3,4-dibutylthiophene), poly(3 -hydroxythiophene), poly(3-methoxythiophene), poly(3-ethoxythiophene), poly(3-butoxythiophene), poly(3-hexyloxythiophene), poly(3-heptyloxythiophene), poly(3 -octyloxythiophene), poly(3-decyloxythiophene), poly(3-dodecyloxythiophene), poly(3-octadecyloxythiophene), poly(3,4-dihydroxythiophene), poly(3,4-dimethoxy thiophene), poly(3,4-diethoxythiophene), poly(3,4-dipropoxythiophene), poly(3,4-dibutoxythiophene), poly(3,4-dihexyloxythiophene), poly(3 ,4-diheptyloxythiophene), poly(3,4-dioctyloxythiophene), poly(3,4-didecyloxythiophene), poly(3,4-didodecyloxythiophene), poly(3,4- ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), poly(3,4-butylenedioxythiophene), poly(3-methyl-4-methoxythiophene), poly(3-methyl-4- ethoxythiophene), poly(3-carboxythiophene), poly(3-methyl-4-carboxythiophene), poly(3-methyl-4-carboxyethylthiophene), poly(3-methyl-4-carboxybutylthiophene), Poly(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-propanesulfonate), poly(3-[(2,3-dihydrothieno[3,4 Potassium b]-[1,4]dioxepin-3-yloxy]-1-propanesulfonate mu), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-methyl-1-propanesulfonate), poly(3- [(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-ethyl-1-propanesulfonate sodium), poly(3-[(2,3-dihydrothieno Sodium [3,4-b]-[1,4]dioxepin-3-yloxy]-1-propyl-1-propanesulfonate), poly(3-[(2,3-dihydrothieno[3,4-b] -[1,4]dioxepin-3-yloxy]-1-butyl-1-propanesulfonate), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin -3-yloxy]-1-pentyl-1-propanesulfonate), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1 -sodium hexyl-1-propanesulfonate), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-isopropyl-1-propanesulfone sodium acid), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-isobutyl-1-propanesulfonate), poly(3 -[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-isopentyl-1-propanesulfonate sodium), poly(3-[(2,3- Sodium dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-fluoro-1-propanesulfonate), poly(3-[(2,3-dihydrothieno[3,4-b) ]-[1,4]dioxepin-yloxy]-1-methyl-1-propanesulfonic acid potassium), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin- 3-yloxy]-1-methyl-1-propanesulfonic acid), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-methyl -1-ammonium propanesulfonate), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-methyl-1-propanesulfonate triethyl ammonium), poly(4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-butanesulfonate), poly(4-[(2, 3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-butanesulfonic acid potassium), poly(4-[(2,3-dihydrothieno[3,4-b]- [1,4]dioxepin-3-yloxy]-1-methyl-1-butanesulfonate sodium), poly(4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin- 3-yloxy]-1-methyl-1-butanesulfonic acid potassium), poly(4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1- Sodium fluoro-1-butanesulfonate) and poly(4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-fluoro-1-butane potassium sulfonate).

The water-soluble polymer contained in the positive electrode active material-containing layer is highly insoluble in the non-aqueous electrolyte. Therefore, even when the positive electrode is impregnated with the non-aqueous electrolyte, the structure of the positive electrode active material-containing layer can be stably maintained. As a result, the active material particles coated with the conductive polymer are less likely to fall off from the positive electrode active material-containing layer even when charge-discharge cycles are repeated. In addition, since it is possible to prevent the coated lithium composite oxide particle surface or the conductive polymer coated surface from being excessively exposed to the non-aqueous electrolyte, it suppresses metal elution and gas generation, resulting in excellent capacity. Retention rate can be achieved.

The HLB (Hydrophilic-Lipophilic Balance) value of the water-soluble polymer is, for example, in the range of 8 or more and 20 or less, preferably 10 or more and 20 or less. The HLB value of the water-soluble polymer can be in the range of 15-19. The HLB value is an index representing the ratio of hydrophilicity and hydrophobicity of surfactants. The HLB value takes a value between 0 and 20, and the closer to 0, the more hydrophobic it is, and the closer to 20, the more hydrophilic it is.

Polymers that dissolve in water are referred to herein as water-soluble polymers. Whether or not the positive electrode contains a water-soluble polymer is examined by the following procedure. First, the positive electrode is exposed to water to examine whether or not the layer containing the positive electrode active material dissolves. Next, when the positive electrode active material-containing layer is dissolved in water, the solution is subjected to GC-MS (Gas Chromatography-Mass Spectrometry), LC-MS (Liquid Chromatography-Mass Spectrometry). chromatography mass spectrometry), FT-IR (Fourier Transform - Infrared Spectroscopy), NMR (Nuclear Magnetic Resonance), etc. to identify the type of water-soluble polymer be able to.

The HLB value of the water-soluble polymer is, for example, within the range of 8 or more and 20 or less. The water-soluble polymer is a material used as a water-based binder when manufacturing the positive electrode, which will be described later. A method for measuring the HLB value of the water-soluble polymer contained in the positive electrode active material-containing layer will be described later. The HLB value of the water-soluble polymer is preferably 10 or more. In this case, even when the positive electrode active material-containing layer is impregnated with the non-aqueous electrolyte, the electrode material constituting the positive electrode active material-containing layer tends to exist stably without being decomposed.

The water-soluble polymer is, for example, at least one selected from the group consisting of acrylic polymer, urethane polymer, carboxymethylcellulose (CMC), alginic acid polymer, polyether, polyvinyl alcohol, water-soluble polyester, and dicarboxylated polysaccharide. be. Among them, at least one selected from the group consisting of acrylic polymer, CMC and alginic acid polymer is preferable from the viewpoint of maintaining high peel strength so that the positive electrode active material-containing layer does not peel off from the current collector.

The mass ratio of the water-soluble polymer in the positive electrode active material-containing layer is, for example, within the range of 1% by mass to 10% by mass, preferably within the range of 2% by mass to 8% by mass. When the mass of the water-soluble polymer contained in the positive electrode active material-containing layer is excessively small, the bonding strength between the electrode materials constituting the layer may be insufficient, resulting in insufficient electrode strength. As a result, the positive electrode active material-containing layer may peel off from the current collector during charging and discharging, resulting in a decrease in capacity. On the other hand, when the mass of the water-soluble polymer contained in the positive electrode active material-containing layer is excessively large, the internal resistance increases, which is not preferable.

Hereinafter, positive electrodes according to embodiments will be described in detail.

The positive electrode can include a positive electrode current collector and a positive electrode active material-containing layer. The positive electrode active material-containing layer may be formed on one side or both sides of the positive electrode current collector. The positive electrode active material-containing layer contains at least the water-soluble polymer as a binder. The positive electrode active material-containing layer can optionally contain a conductive material.

The positive electrode according to the embodiment is, for example, a battery positive electrode, a secondary battery positive electrode, a non-aqueous electrolyte secondary battery positive electrode, or a lithium secondary battery positive electrode.

The positive electrode active material particles contain, as an active material, lithium composite oxide particles exhibiting an operating potential of 4.4 V or higher relative to metallic lithium. The number of lithium composite oxide particles may be one or more. The positive electrode active material particles may be composed only of lithium composite oxide particles exhibiting an operating potential of 4.4 V or higher relative to metallic lithium. However, at least part of the surface of one or more lithium composite oxide particles is coated with a conductive polymer. The positive electrode active material particles may contain only one type or plural types of lithium composite oxide particles exhibiting an operating potential of 4.4 V or higher relative to metallic lithium.

An example of a lithium composite oxide exhibiting an operating potential of 4.4 V or more based on metallic lithium is an oxide represented by the following general formula (A).
_{LiuM1xMn2 - xO4 (} A)
In general formula (A), M1 is at least one selected from the group consisting of Mn, Ni, Fe, Co, Cr, Mg, Zn, Al and Cu, u satisfies 0<u≦1, x satisfies 0<x≦1.

Specific examples of the lithium composite oxide represented by formula (A) include LiNi _0.5 Mn _1.5 O ₄ and LiCu _0.5 Mn _1.5 O ₄ .

The lithium composite oxide exhibiting an operating potential of 4.4 V or more based on metallic lithium includes, for example, at least one selected from the group consisting of lithium nickel manganese oxide and lithium phosphate compound. Among the above lithium composite oxides, the positive electrode active material particles preferably contain lithium nickel manganese oxide because of its high electron conductivity and stable structure even when the voltage is increased to around 5V. Lithium nickel manganese oxide has, for example, a spinel crystal structure.

Lithium nickel manganese oxide is represented, for example, by the following general formula (I). In this case, as described above, the structure is stable even if the voltage is increased, so it is easy to obtain excellent cycle life characteristics while maintaining a high operating voltage.
_{LiuNixMn2 - xO4 (} I)
In general formula (I), u satisfies 0<u≦1, and x satisfies 0<x≦1.

A lithium phosphate compound is represented, for example, by the following general formula (II).

_{LiwM2yCo1 - yPO4 (} II)
In general formula (II), M2 is at least one selected from the group consisting of Ni and Cu, w satisfies 0<w≦1, and y satisfies 0≦y≦1. A lithium phosphate compound has, for example, an olivine crystal structure.

Specific examples of the lithium phosphate compound represented by formula (II) include LiNiPO ₄ and LiCoPO ₄ .

Positive electrode active material particles according to embodiments may include other active materials that exhibit an operating potential of less than 4.4 V relative to lithium metal. The ratio of the other active material to the entire positive electrode active material particles may be 20% by mass or less, 10% by mass or less, or 0% by mass.

Other active materials include oxides or sulfides, for example. Examples of such compounds include manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (e.g. Li _x Mn ₂ O ₄ or Li _x MnO ₂ ; 0<x≦1), lithium nickel Composite oxides (e.g. Li _x NiO ₂ ; 0<x≤1), lithium cobalt composite oxides (e.g. Li _x CoO ₂ ; 0 < x ≤ 1), lithium nickel cobalt composite oxides (e.g. Li _x Ni _1-y Co _y O ₂ ; 0<x≦1, 0<y<1), lithium-manganese-cobalt composite oxide (for example, Li _{x Mny} Co _1-y O ₂ ; 0<x≦1, 0<y<1), iron sulfate (Fe ₂ (SO ₄ ) ₃ ), vanadium oxide (eg V ₂ O ₅ ), and lithium nickel cobalt manganese composite oxide (Li _x Ni _1-yz Co _y Mn _z O ₂ ; 0<x≦ 1, 0<y<1, 0<z<1, y+z<1).

The primary particle size of the positive electrode active material is preferably 100 nm or more and 10 μm or less. A positive electrode active material having a primary particle size of 100 nm or more is easy to handle in industrial production. A positive electrode active material having a primary particle size of 10 μm or less can facilitate diffusion of lithium ions in a solid.

The specific surface area of the positive electrode active material is preferably 0.1 m ² /g or more and 10 m ² /g or less. A positive electrode active material having a specific surface area of 0.1 m ² /g or more can sufficiently secure Li ion intercalation/deintercalation sites. A positive electrode active material having a specific surface area of 10 m ² /g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

The aforementioned water-soluble polymer is contained in the positive electrode active material-containing layer as a binder. The binder can fill the gaps between the dispersed positive electrode active materials and bind the positive electrode active material and the positive electrode current collector. As the positive electrode binder, any type of water-soluble polymer can be used without limitation. The positive electrode active material-containing layer may contain only a water-soluble polymer as a binder, or may further contain another binder. Examples of other binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, and imide compounds. The amount of the water-soluble polymer contained in the positive electrode binder may be 80% by mass or more, 90% by mass or more, or 100% by mass.

The conductive material is blended in order to improve the current collection performance and to suppress the contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive materials include vapor grown carbon fibers (VGCF), carbon blacks such as acetylene black, graphite, carbonaceous materials such as carbon nanofibers and carbon nanotubes. One of these may be used as the conductive material, or two or more may be combined and used as the conductive material. Also, the conductive material can be omitted.

In the positive electrode active material containing layer, the positive electrode active material particles and the positive electrode binder are preferably blended at a ratio of 80% by mass or more and 98% by mass or less and 1% by mass or more and 20% by mass or less.

Sufficient electrode strength can be obtained by setting the amount of the binder to 1% by mass or more. Also, the binder can function as an insulator. Therefore, if the amount of the binder is 20% by mass or less, the amount of the insulator contained in the electrode is reduced, so the internal resistance can be reduced.

When a conductive material is added, the positive electrode active material, the binder, and the conductive material each contain 77% by mass or more and 95% by mass or less, 1% by mass or more and 20% by mass or less, and 3% by mass or more and 15% by mass or less. It is preferable to blend them in proportions.

By setting the amount of the conductive material to 3% by mass or more, the above effects can be exhibited. Also, by setting the amount of the conductive material to 15% by mass or less, the proportion of the conductive material in contact with the electrolyte can be reduced. When this ratio is low, decomposition of the electrolyte can be reduced under high-temperature storage.

The positive electrode current collector is preferably an aluminum foil or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu and Si.

The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

In addition, the positive electrode current collector can include a portion where the positive electrode active material-containing layer is not formed on the surface thereof. This portion can serve as a positive current collecting tab.

The electrode density of the positive electrode (not including the current collector) is preferably 2.0 g/cm ³ or more and 4.0 g/cm ³ or less. A positive electrode in which the density of the positive electrode active material-containing layer is within this range is excellent in energy density and electrolyte retention. More preferably, the electrode density of the positive electrode is 2.5 g/cm ³ or more and 3.5 g/cm ³ or less.

An example of the positive electrode according to the embodiment will be described with reference to the drawings.

FIG. 1 is a cross-sectional view schematically showing a positive electrode according to one example. The positive electrode 5 includes a positive electrode current collector 5a and a positive electrode active material-containing layer 5b provided on the positive electrode current collector 5a. Here, an example in which the positive electrode active material-containing layer 5b is provided on one side of the positive electrode current collector 5a is shown, but the positive electrode active material-containing layer 5b is provided on both sides of the positive electrode current collector 5a. good too. Although the thickness of the positive electrode active material containing layer 5b is not particularly limited, it is, for example, within the range of 10 μm to 100 μm.

Positive electrode active material-containing layer 5b includes one or more positive electrode active material particles 5c and water-soluble polymer 5d. The positive electrode active material particles 5c include lithium composite oxide particles 51 exhibiting an operating potential of 4.4 V (vs. Li/Li ⁺ ) or higher, and a conductive polymer 52 covering at least a portion of the surface of the lithium composite oxide particles 51. and FIG. 1 shows the case where the positive electrode active material containing layer 5b contains the positive electrode conductive material 5e, but the positive electrode conductive material 5e does not necessarily need to be added.

The entire positive electrode active material containing layer 5b is bound with a water-soluble polymer 5d that functions as a binder. Therefore, direct contact of the lithium composite oxide particles 51 with a non-aqueous electrolyte (not shown) is suppressed, and metal elution and/or gas generation from the lithium composite oxide particles 51 is suppressed. As a result, deterioration of the positive electrode due to charge-discharge cycles can be suppressed. Also, the ratio of the mass of the conductive polymer 52 to the mass of the lithium composite oxide particles 51 is within the range of 0.5% by mass to 5.0% by mass. Therefore, the secondary battery including the positive electrode according to the embodiment has low resistance and can achieve a high capacity retention rate.

<Measurement of coating amount of conductive polymer>
The ratio of the mass of the conductive polymer to the mass of the lithium composite oxide particles exhibiting an operating potential of 4.4 V or more based on metallic lithium can be measured as follows.

The positive electrode is washed with propylene carbonate, dried, and then the positive electrode active material-containing layer is peeled off from the current collector. The removed positive electrode active material-containing layer is sufficiently washed with pure water to remove the water-soluble polymer. The residue after washing is centrifuged to remove the conductive material, and then dried in a vacuum. The mass of the solid obtained is then determined. The solid is, for example, a positive electrode active material particle containing lithium composite oxide particles exhibiting an operating potential of 4.4 V or higher relative to metallic lithium and a conductive polymer covering at least part of the particle surface. Next, the obtained solid is subjected to combustion treatment at a temperature of 800° C. for 10 hours or longer. The combustion decomposes the conductive polymer to obtain only lithium composite oxide particles. The mass of the resulting particles is then measured and the mass of the conductive polymer is found by subtracting the mass of the particles from the mass of the solid. Also, the ratio of the mass of the conductive polymer to the mass of the lithium composite oxide particles can be calculated.

<Electrical conductivity measurement of conductive polymer>
The positive electrode active material-containing layer is thoroughly washed with pure water, and the conductive material is removed by centrifugal separation to obtain particles in the same manner as described in the measurement of the coat amount. The obtained particles are treated with an acid to dissolve and remove the active material. By measuring the polymer component thus obtained by the AC impedance method, the electrical conductivity of the conductive polymer covering at least part of the surface of the active material particles can be obtained.

<Measurement of HLB value of water-soluble polymer>
The HLB value of the water-soluble polymer can be determined by the Davis method. First, as described below, it is necessary to identify the type of water-soluble polymer contained in the positive electrode and specify the hydrophilic group and the hydrophobic group.

The water-soluble polymer is dissolved and extracted from the positive electrode active material-containing layer with a solvent that dissolves only the water-soluble polymer, and filtered to remove the active material, the conductive agent, and the like. Pure water, for example, is an example of the solvent that dissolves only the water-soluble polymer. After that, the filtrate is subjected to GC-MS (Gas Chromatography-Mass Spectrometry), LC-MS (Liquid Chromatography-Mass Spectrometry) or FT-IR (Fourier Transform-Infrared Spectroscopy: The type of water-soluble polymer can be identified by analysis such as Fourier transform infrared spectroscopy. Alternatively, the type of water-soluble polymer may be identified by analyzing the surface of the positive electrode with infrared spectroscopy (ATR: Attenuated Total Reflectance).

In the Davis method, a predetermined base number is determined according to the hydrophilic group and hydrophobic group contained in the compound. For example, a hydroxyl group is a hydrophilic group and its base number is 1.9. Further, for example, a methyl group and a methylene group are hydrophobic groups, and their base number is -0.475. The HLB value of the target water-soluble polymer is calculated from the following formula (1).
Formula (1): [HLB value] = 7 + SUM ₁ - SUM ₂
In formula (1), SUM ₁ represents the total number of hydrophilic groups, and SUM ₂ represents the total number of hydrophobic groups.

<Measurement of amount of water-soluble polymer>
An active material-containing layer to be measured is prepared. For example, a certain amount of active material-containing layer is obtained from the positive electrode using a spatula or the like. The mass of the obtained active material-containing layer is measured. After that, the water-soluble polymer is dissolved, extracted, and filtered with pure water or the like in the same manner as the pretreatment in the HLB value measurement described above. By evaporating the solvent in the resulting solution, a solidified water-soluble polymer is obtained. Measure the mass of this water-soluble polymer. Then, the mass ratio of the water-soluble polymer in the positive electrode active material-containing layer is calculated by dividing the mass of the water-soluble polymer by the previously measured mass of the active material-containing layer and multiplying by 100.

The crystal structure and elemental composition of the positive electrode active material can be confirmed, for example, by powder X-ray diffraction (XRD) measurement and inductively coupled plasma (ICP) emission spectroscopy described below. . In addition, the crystal structure and elemental composition of the negative electrode active material, which will be described later, can also be analyzed by the methods described below.

<Powder X-ray diffraction measurement of active material>
Powder X-ray diffraction measurement of the active material can be performed, for example, as follows.
First, the target sample is pulverized until the average particle size becomes about 5 μm. The pulverized sample is packed into a holder portion with a depth of 0.2 mm formed on a glass sample plate. At this time, care should be taken so that the sample is sufficiently filled in the holder portion. Also, be careful to fill the sample in just the right amount so that cracks, voids, etc. do not occur. Next, another glass plate is pressed from the outside to flatten the surface of the sample filled in the holder portion. Be careful not to cause unevenness from the reference surface of the holder due to excessive or insufficient filling.

Next, the glass plate filled with the sample is placed in a powder X-ray diffractometer, and a diffraction pattern (X-Ray Diffraction pattern) is obtained using Cu-Kα rays.

Note that the orientation of the particles may become large depending on the particle shape of the sample. If the orientation of the sample is high, there is a possibility that the position of the peak will shift or the intensity ratio will change depending on how the sample is packed. Such highly oriented samples are measured using a glass capillary. Specifically, a sample is inserted into a capillary, and the capillary is placed on a rotating sample stage for measurement. Such a measurement method can relax the orientation. As the glass capillary, it is preferable to use a Lindemann glass capillary having a diameter of 1 mm to 6 mmφ.

When powder X-ray diffraction measurement is performed on the active material contained in the secondary battery or electrode, it can be performed, for example, as follows.
First, in order to grasp the crystal state of the active material, the active material is brought into a state in which lithium ions are completely detached. For example, if an active material is used in the negative electrode, the battery is fully discharged. For example, the battery is repeatedly discharged at 0.1 C current at 25° C. until the rated final voltage or battery voltage reaches 1.0 V, and the current value during discharge is 1/100 or less of the rated capacity. By doing so, the battery can be discharged. Remaining lithium ions may be present even in the discharged state.

The cell is then disassembled in an argon-filled glovebox and the electrodes are removed and washed with a suitable solvent. As a suitable solvent eg ethyl methyl carbonate can be used. Insufficient cleaning of the electrode may result in contamination with an impurity phase such as lithium carbonate or lithium fluoride due to the influence of lithium ions remaining in the electrode. In that case, it is preferable to use an airtight container in which the measurement atmosphere can be an inert gas. At this time, the peaks derived from the metal foil, which is the current collector, the conductive agent, the binder, and the like are measured in advance using EDX and grasped. Of course, if these are known in advance, this operation can be omitted. When the peak of the current collector and the peak of the active material overlap, it is desirable to peel the active material-containing layer from the current collector for measurement. This is to separate overlapping peaks when quantitatively measuring peak intensities. The active material-containing layer may be physically peeled off. The active material-containing layer is easily exfoliated by applying ultrasonic waves in an appropriate solvent. When ultrasonic treatment is performed to peel the active material-containing layer from the current collector, the electrode body powder (including the active material, the conductive agent, and the binder) can be recovered by volatilizing the solvent. Powder X-ray diffraction measurement of the active material can be performed by filling the recovered electrode body powder in, for example, a Lindemann glass capillary or the like and performing measurement. The electrode body powder collected by ultrasonic treatment can be subjected to various analyzes other than the powder X-ray diffraction measurement.

<ICP emission spectroscopy>
The composition of the active material can be analyzed using, for example, inductively coupled plasma (ICP) emission spectroscopy. At this time, the abundance ratio (molar ratio) of each element depends on the sensitivity of the analyzer used. Therefore, the measured molar ratio may deviate from the actual molar ratio by the error of the measuring device. However, even if the numerical value deviates within the error range of the analyzer, the performance of the active material according to the embodiment can be sufficiently exhibited.

In order to measure the composition of the active material incorporated in the battery by ICP emission spectroscopy, specifically, the following procedure is performed.

First, the electrode containing the active material to be measured is taken out from the secondary battery and washed according to the procedure described in the section of powder X-ray diffraction measurement. A portion containing an electrode active material such as an active material containing layer is peeled off from the washed electrode. For example, the portion containing the electrode active material can be peeled off by irradiating ultrasonic waves. As a specific example, for example, an electrode can be placed in ethyl methyl carbonate placed in a glass beaker, and vibrated in an ultrasonic cleaner to separate the active material-containing layer containing the electrode active material from the electrode current collector. can.

Next, the peeled portion is heated in the air for a short period of time (for example, at 500° C. for about 1 hour) to burn off unnecessary components such as the binder component and carbon. By dissolving this residue with an acid, a liquid sample containing an active material can be prepared. At this time, hydrochloric acid, nitric acid, sulfuric acid, hydrogen fluoride, etc. can be used as the acid. By subjecting this liquid sample to ICP analysis, the composition in the active material can be known.

<Manufacturing method of positive electrode>
The positive electrode according to the embodiment can be produced, for example, by the following method.

The manufacturing method of the positive electrode is
dissolving an electropolymerizable monomer of a conductive polymer in a solvent to prepare a monomer-containing solution;
a step of adding lithium composite oxide particles exhibiting an operating potential of 4.4 V or more based on metallic lithium to the monomer-containing solution, followed by drying to obtain the lithium composite oxide particles coated with the monomer;
a step of mixing the lithium composite oxide particles coated with the monomer and an aqueous binder containing water to obtain a slurry;
a step of applying the slurry to one or both sides of a current collector, followed by drying and pressing to obtain a positive electrode in a non-initial charged state;
preparing a negative electrode and an electrolyte;
and performing initial charging so that the positive electrode potential of the positive electrode in the non-initial charged state is 4.4 V or more based on metallic lithium.

Lithium composite oxide particles exhibiting an operating potential of 4.4 V (vs. Li/Li ⁺ ) or more are coated in advance with a conductive polymer monomer that can be electropolymerized prior to preparing a slurry for producing a positive electrode. do. The electropolymerizable monomer of the conductive polymer is a monomer that forms the conductive polymer by polymerizing. Examples of electropolymerizable monomers for conductive polymers include, for example, anilines, pyrroles and thiophenes. As anilines, a monomer that constitutes at least one of the polyanilines described above can be used. As pyrroles, a monomer that constitutes at least one of the polypyrroles described above can be used. As thiophenes, a monomer that constitutes at least one of the polythiophenes described above can be used.

The type of solvent contained in the monomer-containing solution is not particularly limited as long as the solvent can dissolve the monomers used. However, from the viewpoint of evaporating the solvent after coating the surface of the lithium composite oxide particles with the monomer-containing solution, the solvent is preferably an organic solvent. Acetone, for example, can be used as a solvent in the monomer-containing solution.

By adjusting the mass of the electrolytically polymerizable monomer contained in the monomer-containing solution, it is possible to adjust the mass of the monomer that coats the lithium composite oxide particles. The mass of the monomer in the monomer-containing solution can be appropriately changed according to the desired coating amount, and is, for example, within the range of 0.5 mass % to 5.0 mass %. All or almost all of the monomers contained in the monomer-containing solution are coated on the surfaces of the lithium composite oxide particles. In other words, the amount of the monomer charged can be regarded as the amount of conductive polymer coating on the surface of the lithium composite oxide particles in the positive electrode active material to be produced.

The lithium composite oxide particles coated with the monomer-containing solution are dried, for example, on a hot plate. This drying is performed, for example, on a hot plate set at a temperature of 80.degree. C. to 120.degree. C. for 5 to 60 minutes. By drying the lithium composite oxide particles coated with the monomer-containing solution, the solvent is evaporated to obtain composite particles coated with the monomer. The drying method is not limited to heating, and for example, vacuum drying may be performed.

Next, a water-based binder is prepared. The water-based binder contains water as a solvent and a water-soluble polymer. Since the water-soluble polymer is dissolved in water, the water-based binder may be in the state of emulsion, for example.

The previously prepared lithium composite oxide particles coated with a monomer are added to an aqueous binder to obtain a positive electrode preparation slurry. A conductive material may be further dispersed in the slurry. The electrolytically polymerizable monomer is difficult to dissolve in the water constituting the water-based binder. Therefore, the lithium composite oxide particles provided with a monomer coat can exist in the slurry as they are coated. In other words, the water-based binder is excellent in retaining the monomer coat of the lithium composite oxide particles provided with the monomer coat while appropriately binding the material constituting the positive electrode active material-containing layer. If an organic solvent-based binder were used instead of the water-based binder, the monomer coat would be eluted into the organic solvent. In that case, it is difficult to manufacture the positive electrode while retaining the monomer coat of the lithium composite oxide particles.

The amounts of the lithium composite oxide particles, the conductive material, and the water-based binder (water-soluble polymer) contained in the positive electrode preparation slurry are within the numerical ranges described above, for example, for each material contained in the positive electrode active material-containing layer to be produced. Adjust accordingly.

The prepared slurry is applied to one side or both sides of the current collector. Next, the applied slurry is dried to obtain a laminate of the positive electrode active material-containing layer and the current collector. After that, the laminate is pressed. Thus, a positive electrode in a non-initial charged state is produced. Separately, a negative electrode and an electrolyte are prepared, for example, according to the method described later.

A battery is assembled using at least the positive electrode, the negative electrode, and the electrolyte in the uninitially charged state described above. After that, initial charging is performed so that the positive electrode potential of the positive electrode in the non-initial charged state becomes 4.4 V or more based on metallic lithium. By this initial charge, the monomers coated on the surfaces of the lithium composite oxide particles are electrolytically polymerized to form a conductive polymer. Thus, the positive electrode according to the embodiment can be manufactured.

In order to appropriately polymerize the electrolytically polymerizable monomers to produce a conductive polymer coat, the positive electrode is desirably at least 4.0 V (vs. Li/Li ⁺ ) or more during the initial charge of the secondary battery. should operate at a working potential of 4.4 V (vs. Li/Li ⁺ ) or higher. If the positive electrode operating potential at the time of initial charge is less than 4.4 V (vs. Li/Li ⁺ ), it may not be possible to form a uniform conductive polymer coat. Here, if the lithium composite oxide particles contained in the positive electrode active material have an average operating potential of less than 4.4 V (vs. Li/Li ⁺ ), the battery voltage for polymerizing the monomer will be the lithium composite oxide. The particles can't withstand it, and their crystal structure breaks down, changing to a structure that can't be charged or discharged.

The conditions for the initial charge are not particularly limited as long as the working potential of the positive electrode is 4.4 V (vs. Li/Li ⁺ ) or more, but for example, the conditions are as follows. The secondary battery is charged at 25° C. with a current value of 0.1C to 2.0C until the battery voltage reaches 2.5V to 4.0V. Note that the current value during charging is shown in units of 1C, which represents the current value at which the SOC becomes 0% in 1 hour when the secondary battery is discharged from a 100% SOC state.

According to a first embodiment, a positive electrode is provided. The positive electrode includes a positive electrode active material-containing layer containing positive electrode active material particles and a water-soluble polymer. The positive electrode active material particles include lithium composite oxide particles exhibiting an operating potential of 4.4 V or higher relative to metallic lithium, and a conductive polymer covering at least a portion of the lithium composite oxide particle surfaces. The ratio of the mass of the conductive polymer to the mass of the lithium composite oxide particles is in the range of 0.5% by mass to 5.0% by mass. This positive electrode has a low resistance and can achieve a high capacity retention rate.

(Second embodiment)
According to a second embodiment, a secondary battery is provided that includes the positive electrode, negative electrode, and electrolyte according to the first embodiment. The secondary battery can be, for example, a lithium secondary battery. Also, the secondary battery may be a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

A secondary battery can further comprise a separator disposed between the positive electrode and the negative electrode. The negative electrode, positive electrode and separator can constitute an electrode group. An electrolyte may be retained on the electrodes.

In addition, the secondary battery can further include an exterior member that accommodates the electrode group and the electrolyte.

Furthermore, the secondary battery may further comprise a negative terminal electrically connected to the negative electrode and a positive terminal electrically connected to the positive electrode.

The positive electrode, negative electrode, electrolyte, separator, exterior member, negative electrode terminal, and positive electrode terminal will be described in detail below.

(1) Positive Electrode The positive electrode according to the first embodiment can be used as the positive electrode provided in the secondary battery according to the second embodiment.

(2) Negative Electrode The negative electrode can include a negative electrode current collector and a negative electrode active material-containing layer. The negative electrode active material-containing layer may be formed on one side or both sides of the negative electrode current collector. The negative electrode active material-containing layer may contain a negative electrode active material, and optionally a conductive material and a binder.

The negative electrode active material includes, for example, at least one titanium-containing oxide selected from the group consisting of titanium oxides, lithium-titanium composite oxides, niobium-titanium composite oxides, and sodium-niobium-titanium composite oxides. Specific examples of titanium-containing oxides include lithium titanate having a ramsdellite structure (e.g., Li _2+y Ti ₃ O ₇ , 0≦y≦3) and lithium titanate having a spinel structure (e.g., Li _{4 +x} Ti ₅ O ₁₂ , 0≦x≦3), monoclinic titanium dioxide (TiO ₂ ), anatase titanium dioxide, rutile titanium dioxide, hollandite titanium composite oxide, monoclinic niobium titanium composite oxide , and orthorhombic titanium-containing composite oxides. Above all, from the viewpoint of achieving both high capacity and high rate performance, the negative electrode active material preferably contains at least one selected from the group consisting of lithium-titanium composite oxides and niobium-titanium composite oxides. The lithium-titanium composite oxide can have a spinel-type crystal structure. The niobium-titanium composite oxide can have a monoclinic crystal structure.

Examples of the monoclinic niobium-titanium composite oxide include compounds represented by Li _x Ti _1-y M1 _y Nb _2-z M2 _z O _7+δ . 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. A specific example of the monoclinic niobium-titanium composite oxide is Li _x Nb ₂ TiO ₇ (0≦x≦5).

Another example of the monoclinic niobium-titanium composite oxide is a compound represented by Ti1 _{-yM3y + zNb2- zO7-[delta]} . Here, M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. Each subscript in the composition formula is 0≦y<1, 0≦z≦2, −0.3≦δ≦0.3.

An example of the orthogonal titanium-containing composite oxide is a compound represented by Li _2+a M(I) _2-b Ti _6-c M(II) _d O _14+σ . Here, M(I) is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb and K; M(II) is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. Each subscript in the composition formula is 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, −0.5≦σ≦0.5. A specific example of the orthogonal titanium-containing composite oxide is Li _2+a Na ₂ Ti ₆ O ₁₄ (0≦a≦6).

The conductive material is blended in order to improve the current collection performance and suppress the contact resistance between the active material and the current collector. Examples of conductive materials include vapor grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as the conductive material, or two or more may be combined and used as the conductive material. Alternatively, instead of using a conductive material, the surface of the active material particles may be coated with a carbon coating or an electronically conductive inorganic material.

The binder is blended to fill the gaps between the dispersed active materials and to bind the active material and the negative electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose. ; CMC), and salts of CMC. One of these may be used as the binding material, or two or more may be combined and used as the binding material.

The mixing ratio of the negative electrode active material, the conductive material, and the binder in the negative electrode active material-containing layer can be appropriately changed depending on the application of the negative electrode. For example, it is preferable to mix the negative electrode active material, the conductive material, and the binder at a ratio of 70% by mass or more and 96% by mass or less, 2% by mass or more and 28% by mass or less, and 2% by mass or more and 28% by mass or less. . By setting the amount of the conductive material to 2% by mass or more, the current collection performance of the negative electrode active material-containing layer can be improved. Moreover, by setting the amount of the binder to 2% by mass or more, the binding between the negative electrode active material-containing layer and the current collector becomes sufficient, and excellent cycle performance can be expected. On the other hand, it is preferable that the conductive material and the binder each be 28% by mass or less in order to increase the capacity.

The negative electrode current collector is a material that is electrochemically stable at a potential at which lithium (Li) is inserted into and extracted from the active material, for example, a potential nobler than 1.0 V (vs. Li/Li ⁺ ). is used. For example, the current collector is preferably made of copper, nickel, stainless steel or aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu and Si. The thickness of the current collector is preferably 5 μm or more and 20 μm or less. A current collector having such a thickness can balance the strength and lightness of the electrode.

In addition, the negative electrode current collector can include a portion where the negative electrode active material-containing layer is not formed on the surface thereof. This portion can serve as a negative electrode current collecting tab.

The density of the negative electrode active material-containing layer (not including the current collector) is preferably 1.8 g/cm ³ or more and 2.8 g/cm ³ or less. A negative electrode in which the density of the negative electrode active material-containing layer is within this range is excellent in energy density and electrolyte retention. More preferably, the density of the negative electrode active material-containing layer is 2.1 g/cm ³ or more and 2.6 g/cm ³ or less.

A negative electrode can be produced, for example, by the following method. First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. This slurry is applied to one side or both sides of the current collector. Next, the applied slurry is dried to obtain a laminate of the active material-containing layer and the current collector. After that, the laminate is pressed. Thus, a negative electrode is produced.

Alternatively, the negative electrode may be produced by the following method. First, an active material, a conductive agent and a binder are mixed to obtain a mixture. The mixture is then formed into pellets. A negative electrode can then be obtained by placing these pellets on a current collector.

(3) Electrolyte As the electrolyte, for example, a liquid nonaqueous electrolyte or a gelled nonaqueous electrolyte can be used. A liquid non-aqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol/L or more and 2.5 mol/L or less.

Examples of electrolyte salts include lithium perchlorate ( _LiClO4 ), lithium hexafluorophosphate ( _LiPF6 ), lithium tetrafluoroborate ( _LiBF4 ), lithium arsenic hexafluoride ( _LiAsF6 ), trifluoromethane Included are lithium salts such as lithium sulfonate (LiCF ₃ SO ₃ ) and lithium bistrifluoromethylsulfonylimide (LiN(CF ₃ SO ₂ ) ₂ ), and mixtures thereof. The electrolyte salt is preferably one that is difficult to oxidize even at high potentials, and most preferably LiPF ₆ .

Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), vinylene carbonate (VC); diethyl carbonate (DEC), dimethyl carbonate; Chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC); tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), dioxolane (DOX) linear ethers such as dimethoxy ethane (DME), diethoxy ethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (sulfolane; SL). These organic solvents can be used alone or as a mixed solvent.

A gel nonaqueous electrolyte is prepared by combining a liquid nonaqueous electrolyte and a polymer material. As the polymeric material, for example, at least one selected from the group consisting of polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, acrylic polymer, polyamide and polyvinyl alcohol can be used. By using a gel electrolyte as the electrolyte, it is possible to suppress metal elution from the positive electrode and suppress generation of gas such as hydrogen. As a result, excellent cycle life characteristics are obtained.

Alternatively, as the non-aqueous electrolyte, in addition to a liquid non-aqueous electrolyte and a gel non-aqueous electrolyte, a room temperature molten salt (ionic melt) containing lithium ions, a polymer solid electrolyte, an inorganic solid electrolyte, etc. good too.

Room-temperature molten salt (ionic melt) refers to a compound that can exist as a liquid at room temperature (15° C. or higher and 25° C. or lower) among organic salts composed of a combination of organic cations and anions. The room-temperature molten salt includes a room-temperature molten salt that exists as a liquid by itself, a room-temperature molten salt that becomes liquid when mixed with an electrolyte salt, a room-temperature molten salt that becomes liquid when dissolved in an organic solvent, or a mixture thereof. be In general, the melting point of room-temperature molten salt used in secondary batteries is 25° C. or less. Also, organic cations generally have a quaternary ammonium skeleton.

A polymer solid electrolyte is prepared by dissolving an electrolyte salt in a polymer material and solidifying it.

An inorganic solid electrolyte is a solid substance having Li ion conductivity.

(4) Separator The separator is formed of, for example, a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. . From the viewpoint of safety, it is preferable to use a porous film made of polyethylene or polypropylene. This is because these porous films can melt at a certain temperature and cut off the electric current.

A solid electrolyte layer containing solid electrolyte particles can also be used as a separator. The solid electrolyte layer may contain one type of solid electrolyte particles, or may contain a plurality of types of solid electrolyte particles. The solid electrolyte layer may be a solid electrolyte composite membrane containing solid electrolyte particles. A solid electrolyte composite membrane is, for example, formed by molding solid electrolyte particles into a membrane using a polymer material. The solid electrolyte layer may contain at least one selected from the group consisting of a plasticizer and an electrolyte salt. If the solid electrolyte layer contains an electrolyte salt, for example, the alkali metal ion conductivity of the solid electrolyte layer can be further enhanced.

Examples of polymeric materials include polyethers, polyesters, polyamines, polyethylenes, silicones and polysulfides.

The lithium ion conductivity of the solid electrolyte is preferably 1×10 ⁻¹⁰ S/cm or more at 25° C. When the solid electrolyte has a lithium ion conductivity of 1×10 ⁻¹⁰ S/cm or more at 25° C., the lithium ion concentration in the vicinity of the surface of the solid electrolyte tends to increase, so that rate performance and life characteristics can be improved. More preferably, the lithium ion conductivity of the solid electrolyte at 25° C. is 1×10 ⁻⁶ S/cm or more. The upper limit of the lithium ion conductivity of the solid electrolyte is, according to one example, 2×10 ⁻² S/cm.

Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and polymer solid electrolytes. Specifically, the solid electrolyte is a sulfide-based Li ₂ SeP ₂ S ₅ -based glass ceramics, or a lithium-lanthanum-titanium composite oxide (for example, Li _0.5 La _0.5 TiO) which is an inorganic compound having a perovskite structure. ₃ ), _an inorganic compound having a LISICON-type _structure (e.g., _{Li3.6Si0.6P0.4O4} ) _, an inorganic compound having _a NASICON-type skeleton, an amorphous LIPON ( _Li2.9PO3.3 N _0.46 ), lithium calcium zirconium oxide (Li _1.2 Zr _1.9 Ca _0.1 (PO ₄ ) ₃ ), and at least one selected from the group consisting of inorganic compounds having a garnet structure include. The coating layer may contain one type of solid electrolyte, or may contain two or more types of solid electrolytes.

The inorganic compound having a NASICON-type skeleton is an inorganic compound represented by the general formula LiM ₂ (PO ₄ ) ₃ (M is one or more selected from Ti, Ge, Sr, Zr, Sn and Al). is preferred. Among them, Li _1+x Al _x Ge _2-x (PO ₄ ) ₃ , Li _1+x Al _x Zr _2-x (PO ₄ ) ₃ , and Li _1+x Al _x Ti _2-x (PO ₄ ) ₃ (LATP) are ion-conducting It is preferable because it has high resistance and high electrochemical stability against water. In the above, x preferably satisfies 0≦x≦0.5.

Examples of inorganic compounds having a garnet _structure include _{Li5+ xAyLa3 - yM2O12} (A is at least one selected from the group consisting of Ca, Sr and Ba, M is Nb and Ta), _{Li3M2 - xZr2O12} ( _{M is} at least one selected from the group consisting of Ta and Nb), _{Li7-3xAlxLa 3Zr3O12 , and Li7La3Zr2O12 . _ _} In the above, x is, for example, 0≤x<0.8, preferably 0≤x≤0.5. y is, for example, 0≦y<2. The oxide having a garnet-type structure may consist of one of these compounds, or may contain a mixture of two or more of these compounds. Among these, Li _6.25 Al _0.25 La ₃ Zr ₃ O ₁₂ and Li ₇ La ₃ Zr ₂ O ₁₂ have high ionic conductivity and are electrochemically stable, and are excellent in discharge performance and cycle life performance.

If the solid electrolyte contains elemental sulfur, the sulfur component will dissolve in the organic electrolyte, which will be described later, which is not preferable. The solid electrolyte preferably does not contain elemental sulfur.

Preferred solid electrolytes are LATP (Li _1+x Al _x Ti _2-x (PO ₄ ) ₃ ) having a NASICON-type skeleton, amorphous LIPON, garnet-type lithium-lanthanum-zirconium-containing oxides (eg, Li ₇ La ₃ Zr ₂ O ₁₂ :LLZ) and other oxides.

The lithium ion conductivity at 25° C. of the inorganic compound represented by LiM ₂ (PO ₄ ) ₃ having a NASICON skeleton is, for example, within the range of 1×10 ⁻³ S/cm to 1×10 ⁻⁵ S/cm. be. The lithium ion conductivity of LIPON (Li _2.9 PO _3.3 N _0.46 ) at 25° C. is 3×10 ⁻⁶ S/cm. Garnet-type LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) has a lithium ion conductivity at 25° C. of 3×10 ⁻⁴ S/cm.

Among these, the solid electrolyte is preferably LATP having a NASICON-type skeleton. LATP has high lithium ion conductivity and is not decomposed by water, so it can exist stably even in the air.

(5) Exterior Member As the exterior member, for example, a container made of a laminate film or a metal container can be used.

The thickness of the laminate film is, for example, 0.5 mm or less, preferably 0.2 mm or less.

A multilayer film including a plurality of resin layers and metal layers interposed between the resin layers is used as the laminate film. The resin layer contains polymer materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layer is preferably made of aluminum foil or aluminum alloy foil for weight reduction. The laminate film can be formed into the shape of the exterior member by performing sealing by heat sealing.

The wall thickness of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and still more preferably 0.2 mm or less.

A metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc and silicon. When the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content is preferably 100 ppm by mass or less.

The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), rectangular, cylindrical, coin-shaped, button-shaped, or the like. The exterior member can be appropriately selected according to the size of the battery and the application of the battery.

(6) Negative Electrode Terminal The negative electrode terminal can be made of a material that is electrochemically stable at the Li absorption/desorption potential of the negative electrode active material and has conductivity. Specifically, the material of the negative electrode terminal includes copper, nickel, stainless steel, aluminum, or at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. An aluminum alloy is mentioned. As a material for the negative terminal, it is preferable to use aluminum or an aluminum alloy. In order to reduce contact resistance with the negative electrode current collector, the negative electrode terminal is preferably made of the same material as the negative electrode current collector.

(7) Positive electrode terminal The positive electrode terminal can be made of a material that is electrically stable and conductive in a potential range of 3 V to 5 V (vs. Li/Li ⁺ ) with respect to the oxidation-reduction potential of lithium. can. Materials for the positive electrode terminal include aluminum or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu and Si. In order to reduce contact resistance with the positive electrode current collector, the positive electrode terminal is preferably made of the same material as the positive electrode current collector.

Next, the secondary battery according to the second embodiment will be described more specifically with reference to the drawings.

FIG. 2 is a cross-sectional view schematically showing an example of a secondary battery according to the second embodiment. FIG. 3 is an enlarged cross-sectional view of the A portion of the secondary battery shown in FIG.

The secondary battery 100 shown in FIGS. 2 and 3 includes the bag-shaped exterior member 2 shown in FIGS. 2 and 3, the electrode group 1 shown in FIG. 3, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the bag-shaped exterior member 2 . An electrolyte (not shown) is held in the electrode group 1 .

The bag-shaped exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed therebetween.

As shown in FIG. 2, the electrode group 1 is a flat wound electrode group. The flat wound electrode group 1 includes a negative electrode 3, a separator 4, and a positive electrode 5, as shown in FIG. A separator 4 is interposed between the negative electrode 3 and the positive electrode 5 .

The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b. In the portion of the negative electrode 3 positioned at the outermost shell of the wound electrode group 1, the negative electrode active material containing layer 3b is formed only on the inner surface side of the negative electrode current collector 3a as shown in FIG. In other parts of the negative electrode 3, negative electrode active material-containing layers 3b are formed on both surfaces of the negative electrode current collector 3a.

The positive electrode 5 includes a positive electrode current collector 5a and positive electrode active material-containing layers 5b formed on both sides thereof.

As shown in FIG. 2 , the negative electrode terminal 6 and the positive electrode terminal 7 are located near the outer peripheral edge of the wound electrode group 1 . The negative electrode terminal 6 is connected to the outermost shell portion of the negative electrode current collector 3a. The positive electrode terminal 7 is connected to the outermost shell portion of the positive electrode current collector 5a. These negative terminal 6 and positive terminal 7 are extended outside from the opening of the bag-like exterior member 2 . A thermoplastic resin layer is provided on the inner surface of the bag-shaped exterior member 2, and is heat-sealed to close the opening.

The secondary battery according to the second embodiment is not limited to the secondary battery having the configuration shown in FIGS. 2 and 3, and may be the battery having the configuration shown in FIGS. 4 and 5, for example.

FIG. 4 is a partially cutaway perspective view schematically showing another example of the secondary battery according to the second embodiment. FIG. 5 is an enlarged cross-sectional view of the B portion of the secondary battery shown in FIG.

A secondary battery 100 shown in FIGS. 4 and 5 includes an electrode group 1 shown in FIGS. 4 and 5, an exterior member 2 shown in FIG. 4, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed inside the exterior member 2 . An electrolyte is held in the electrode group 1 .

The exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed therebetween.

The electrode group 1 is a laminated electrode group, as shown in FIG. The laminated electrode group 1 has a structure in which a negative electrode 3 and a positive electrode 5 are alternately laminated with a separator 4 interposed therebetween.

Electrode group 1 includes a plurality of negative electrodes 3 . Each of the plurality of negative electrodes 3 includes a negative electrode current collector 3a and negative electrode active material-containing layers 3b carried on both sides of the negative electrode current collector 3a. Moreover, the electrode group 1 includes a plurality of positive electrodes 5 . Each of the plurality of positive electrodes 5 includes a positive electrode current collector 5a and positive electrode active material-containing layers 5b supported on both sides of the positive electrode current collector 5a.

The negative electrode current collector 3a of each negative electrode 3 includes, on one side thereof, a portion 3c on which no negative electrode active material-containing layer 3b is supported. This portion 3c serves as a negative electrode current collecting tab. As shown in FIG. 5 , the portion 3 c functioning as a negative electrode current collecting tab does not overlap the positive electrode 5 . A plurality of negative electrode current collecting tabs (part 3 c ) are electrically connected to strip-shaped negative electrode terminals 6 . The tip of the strip-shaped negative electrode terminal 6 is drawn out of the exterior member 2 .

Although not shown, 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 serves as the positive current collecting tab. The positive electrode current collecting tab does not overlap with the negative electrode 3, like the negative electrode current collecting tab (portion 3c). Also, the positive electrode current collecting tab is located on the opposite side of the electrode group 1 to the negative electrode current collecting tab (portion 3c). The positive electrode current collecting 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 of the negative electrode terminal 6 and is drawn out of the exterior member 2 .

A secondary battery according to the second embodiment includes the positive electrode according to the first embodiment. Therefore, this secondary battery has a low resistance and can achieve a high capacity retention rate.

(Third Embodiment)
According to a third embodiment, an assembled battery is provided. The assembled battery according to the third embodiment includes a plurality of secondary batteries according to the second embodiment.

In the assembled battery according to the third embodiment, the cells may be electrically connected in series or in parallel and arranged, or may be arranged by combining series connection and parallel connection.

Next, an example of the assembled battery according to the third embodiment will be described with reference to the drawings.

FIG. 6 is a perspective view schematically showing an example of an assembled battery according to the third embodiment. The assembled battery 200 shown in FIG. 6 includes five single cells 100a to 100e, four bus bars 21, a positive electrode lead 22, and a negative electrode lead . Each of the five cells 100a to 100e is a secondary battery according to the second embodiment.

The bus bar 21 connects, for example, the negative terminal 6 of one cell 100a and the positive terminal 7 of the adjacent cell 100b. In this manner, five cells 100 are connected in series by four busbars 21 . That is, the assembled battery 200 in FIG. 6 is a five-series assembled battery. Although an example is not shown, in an assembled battery including a plurality of cells electrically connected in parallel, for example, a plurality of negative terminals are connected to each other by a bus bar and a plurality of positive terminals are connected to each other by a bus bar. Thus, a plurality of cells can be electrically connected.

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

An assembled battery according to the third embodiment includes the secondary battery according to the second embodiment. Therefore, this assembled battery can achieve a low resistance and a high capacity retention rate.

(Fourth embodiment)
According to a fourth embodiment, a battery pack is provided. This battery pack includes an assembled battery according to the third embodiment. The battery pack may include a single secondary battery according to the second embodiment instead of the assembled battery according to the third embodiment.

The battery pack according to the fourth embodiment can further include a protection circuit. The protection circuit has a function of controlling charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses a battery pack as a power source (for example, an electronic device, an automobile, etc.) may be used as a protection circuit for the battery pack.

Moreover, the battery pack according to the fourth embodiment can further include an external terminal for power supply. The external terminal for energization is for outputting current from the secondary battery to the outside and/or for inputting current from the 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 for power supply. Also, when charging the battery pack, a charging current (including regenerated energy from the power of an automobile or the like) is supplied to the battery pack through an external terminal for power supply.

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

FIG. 7 is an exploded perspective view schematically showing an example of a battery pack according to the fourth embodiment. 8 is a block diagram showing an example of an electric circuit of the battery pack shown in FIG. 7. FIG.

A battery pack 300 shown in FIGS. 7 and 8 includes a container 31, a lid 32, a protective sheet 33, an assembled battery 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown). .

A storage container 31 shown in FIG. 7 is a bottomed rectangular container having a rectangular bottom surface. The storage container 31 is configured to be able to store the protective sheet 33 , the assembled battery 200 , the printed wiring board 34 , and the wiring 35 . Lid 32 has a rectangular shape. The lid 32 accommodates the assembled battery 200 and the like by covering the container 31 . Although not shown, the storage container 31 and the lid 32 are provided with openings, connection terminals, or the like for connection to an external device or the like.

The assembled battery 200 includes a plurality of single cells 100 , a positive lead 22 , a negative lead 23 , and an adhesive tape 24 .

At least one of the plurality of cells 100 is the secondary battery according to the second embodiment. Each of the plurality of cells 100 is electrically connected in series as shown in FIG. The plurality of single cells 100 may be electrically connected in parallel, or may be connected in a combination of series connection and parallel connection. When a plurality of unit cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

The adhesive tape 24 fastens the plurality of unit cells 100 . Instead of the adhesive tape 24, heat-shrinkable tape may be used to fix the plurality of unit cells 100. FIG. In this case, the protection sheets 33 are placed on both sides of the assembled battery 200 , the heat-shrinkable tape is wrapped around, and then the heat-shrinkable tape is heat-shrunk to bind the plurality of unit cells 100 together.

One end of the positive lead 22 is connected to the assembled battery 200 . One end of the positive electrode lead 22 is electrically connected to the positive electrode of one or more cells 100 . One end of the negative lead 23 is connected to the assembled battery 200 . One end of the negative electrode lead 23 is electrically connected to the negative electrode of one or more cells 100 .

The printed wiring board 34 is installed along one short-side surface of the inner surface of the container 31 . The printed wiring board 34 includes a positive connector 342, a negative connector 343, a thermistor 345, a protection circuit 346, wirings 342a and 343a, an external terminal 350 for conducting electricity, and a positive wiring (positive wiring) 348a. and a negative wiring (negative wiring) 348b. One main surface of the printed wiring board 34 faces one side surface of the assembled battery 200 . An insulating plate (not shown) is interposed between the printed wiring board 34 and the assembled battery 200 .

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

The thermistor 345 is fixed to one main surface of the printed wiring board 34 . The thermistor 345 detects the temperature of each cell 100 and transmits the detection signal to the protection circuit 346 .

An external terminal 350 for conducting electricity is fixed to the other main surface of the printed wiring board 34 . External terminal 350 for power supply is electrically connected to a device outside battery pack 300 . The external terminal 350 for energization includes a positive terminal 352 and a negative terminal 353 .

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

The protective sheets 33 are arranged on both inner side surfaces in the long side direction of the container 31 and on the inner side surface in the short side direction facing the printed wiring board 34 with the assembled battery 200 interposed therebetween. The protective sheet 33 is made of resin or rubber, for example.

The protection circuit 346 controls charging and discharging of the plurality of cells 100 . In addition, based on the detection signal transmitted from the thermistor 345 or the detection signal transmitted from each unit cell 100 or the assembled battery 200, the protection circuit 346 and the external terminal for energizing the external device. 350 (positive terminal 352, negative terminal 353) is cut off.

Examples of the detection signal transmitted from the thermistor 345 include a signal that detects that the temperature of the unit cell 100 is equal to or higher than a predetermined temperature. Examples of detection signals transmitted from the individual cells 100 or the assembled battery 200 include signals that detect overcharge, overdischarge, and overcurrent of the cells 100 . When detecting overcharge or the like for each unit 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 .

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.

The battery pack 300 also has the external terminals 350 for power supply as described above. Therefore, the battery pack 300 can output current from the assembled battery 200 to an external device and input current from the external device to the assembled battery 200 via the external terminal 350 for power supply. In other words, when the battery pack 300 is used as a power source, current from the assembled battery 200 is supplied to the external device through the external terminals 350 for power supply. Also, when charging the battery pack 300 , a charging current from an external device is supplied to the battery pack 300 through the external terminal 350 for power supply. When this battery pack 300 is used as an on-vehicle battery, the regenerated energy of the motive power of the vehicle can be used as the charging current from the external device.

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, may be connected in parallel, or may be connected in a combination of series connection and parallel connection. Also, the printed wiring board 34 and the wiring 35 may be omitted. In this case, the positive-side lead 22 and the negative-side lead 23 may be used as the positive-side terminal and the negative-side terminal, respectively, of the external terminals for electricity supply.

Such battery packs are used in applications that require excellent cycle performance when drawing a large current, for example. Specifically, this battery pack is used, for example, as a power supply for electronic equipment, a stationary battery, and a vehicle battery for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly suitable for use as a vehicle battery.

A battery pack according to the fourth embodiment includes the secondary battery according to the second embodiment or the assembled battery according to the third embodiment. Therefore, this battery pack has a low resistance and can achieve a high capacity retention rate.

(Fifth embodiment)
According to a fifth embodiment, a vehicle is provided. This vehicle is equipped with the battery pack according to the fourth embodiment.

In the vehicle according to the fifth embodiment, the battery pack recovers, for example, regenerative energy of power of the vehicle. The vehicle may include a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

Examples of vehicles according to the fifth embodiment include two- to four-wheeled hybrid electric vehicles, two- to four-wheeled electric vehicles, assisted bicycles, and railway vehicles.

The mounting position of the battery pack in the vehicle is not particularly limited. For example, when the battery pack is installed in an automobile, the battery pack can be installed in the engine compartment of the vehicle, behind the vehicle body, or under the seat.

A vehicle may be equipped with a plurality of battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, may be electrically connected in parallel, or may be electrically connected by combining series connection and parallel connection. good too. For example, when each battery pack includes an assembled battery, the assembled batteries may be electrically connected in series or may be electrically connected in parallel. may be connected to Alternatively, if each battery pack contains a single battery, the respective batteries may be electrically connected in series, electrically in parallel, or a combination of series and parallel connections. may be electrically connected.

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

FIG. 9 is a partially transparent view schematically showing an example of the vehicle according to the embodiment.

A vehicle 400 shown in FIG. 9 includes a vehicle body 40 and a battery pack 300 according to the embodiment. In the example shown in FIG. 9, the vehicle 400 is a four-wheeled automobile.

This vehicle 400 may be equipped with a plurality of battery packs 300 . In this case, the batteries (eg, cells or assembled batteries) included in the battery pack 300 may be connected in series, connected in parallel, or connected in a combination of series connection and parallel connection.

FIG. 9 shows an example in which the battery pack 300 is installed in the engine room located in front of the vehicle body 40 . As described above, battery pack 300 may be mounted, for example, in the rear of vehicle body 40 or under the seat. This battery pack 300 can be used as a power source for vehicle 400 . Also, this battery pack 300 can recover the regenerated energy of the power of the vehicle 400 .

Next, an embodiment of the vehicle according to the fifth embodiment will be described with reference to FIG.

FIG. 10 is a diagram schematically showing an example of a control system for an electrical system in a vehicle according to the fifth embodiment. A vehicle 400 shown in FIG. 10 is an electric vehicle.

A vehicle 400 shown in FIG. 10 includes a vehicle body 40, a vehicle power source 41, a vehicle ECU (ECU: Electric Control Unit) 42 that is a control device higher than the vehicle power source 41, and external terminals (external A terminal 43 for connecting to a power supply, an inverter 44 and a drive motor 45 are provided.

A vehicle 400 is equipped with a vehicle power source 41, for example, in an engine room, in the rear of a vehicle body, or under a seat. In the vehicle 400 shown in FIG. 10, the locations where the vehicle power source 41 is mounted are schematically shown.

The vehicle power supply 41 includes a plurality (eg, three) of battery packs 300 a , 300 b and 300 c , a battery management unit (BMU) 411 , and a communication bus 412 .

The battery pack 300a includes an assembled battery 200a and an assembled battery monitoring device 301a (for example, VTM: Voltage Temperature Monitoring). The battery pack 300b includes an assembled battery 200b and an assembled battery monitoring device 301b. The battery pack 300c includes an assembled battery 200c and an assembled battery monitoring device 301c. Battery packs 300a-300c are battery packs similar to battery pack 300 described above, and assembled batteries 200a-200c are assembled batteries similar to assembled battery 200 described above. The assembled batteries 200a-200c are electrically connected in series. Battery packs 300 a , 300 b , and 300 c can be independently removed and replaced with another battery pack 300 .

Each of the assembled batteries 200a-200c includes a plurality of cells connected in series. At least one of the plurality of cells is the secondary battery according to the second embodiment. The assembled batteries 200a-200c charge and discharge through the positive terminal 413 and the negative terminal 414, respectively.

The battery management device 411 communicates with the assembled battery monitoring devices 301a to 301c and collects information on the voltage, temperature, etc. of each of the cells 100 included in the assembled batteries 200a to 200c included in the vehicle power source 41. do. Thereby, the battery management device 411 collects information on maintenance of the vehicle power source 41 .

The battery management device 411 and the assembled battery monitoring devices 301 a to 301 c are connected via a communication bus 412 . In communication bus 412, one set of communication lines is shared by a plurality of nodes (battery management device 411 and one or more assembled battery monitoring devices 301a-301c). The communication bus 412 is, for example, a communication bus configured based on the CAN (Control Area Network) standard.

The assembled battery monitoring devices 301a to 301c measure the voltage and temperature of the individual single cells that make up the assembled batteries 200a to 200c based on commands by communication from the battery management device 411. FIG. However, the temperature can be measured at only a few points per assembled battery, and it is not necessary to measure the temperature of all the single cells.

The vehicle power source 41 can also have an electromagnetic contactor (for example, a switch device 415 shown in FIG. 10) that switches between the presence or absence of electrical connection between the positive terminal 413 and the negative terminal 414 . The switch device 415 includes a precharge switch (not shown) that is turned on when the battery packs 200a-200c are charged, and a switch that is turned on when the output from the battery packs 200a-200c is supplied to the load. and a main switch (not shown). Each of the precharge switch and the main switch has a relay circuit (not shown) that is switched on or off by a signal supplied to a coil arranged near the switch element. Electromagnetic contactors such as the switch device 415 are controlled based on control signals from the battery management device 411 or the vehicle ECU 42 that controls the operation of the vehicle 400 as a whole.

The inverter 44 converts the input DC voltage into a three-phase alternating current (AC) high voltage for driving the motor. Three-phase output terminals of the inverter 44 are connected to respective three-phase input terminals of the driving motor 45 . The inverter 44 is controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 for controlling the operation of the entire vehicle. By controlling the inverter 44, the output voltage from the inverter 44 is adjusted.

The drive motor 45 is rotated by power supplied from the inverter 44 . A driving force generated by the rotation of the driving motor 45 is transmitted to the axle and the driving wheels W via, for example, a differential gear unit.

Although not shown, vehicle 400 includes a regenerative braking mechanism (regenerator). The regenerative braking mechanism rotates the drive motor 45 when the vehicle 400 is braked, and converts kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative brake mechanism is input to the inverter 44 and converted into direct current. The converted DC current is input to vehicle power source 41 .

One terminal of the connection line L<b>1 is connected to the negative terminal 414 of the vehicle power supply 41 . The other terminal of the connection line L1 is connected to the negative input terminal 417 of the inverter 44 . A current detection unit (current detection circuit) 416 in the battery management device 411 is provided between the negative terminal 414 and the negative input terminal 417 on the connection line L1.

One terminal of the connection line L2 is connected to the positive terminal 413 of the vehicle power source 41 . The other terminal of the connection line L2 is connected to the positive input terminal 418 of the inverter 44 . A switch device 415 is provided between the positive terminal 413 and the positive input terminal 418 on the connection line L2.

The external terminal 43 is connected to the battery management device 411 . The external terminal 43 can be connected to, for example, an external power supply.

The vehicle ECU 42 cooperatively controls the vehicle power source 41, the switch device 415, the inverter 44, and the like together with other management devices and control devices including the battery management device 411 in response to operation input by the driver or the like. The cooperative control of the vehicle ECU 42 and the like controls the output of electric power from the vehicle power source 41, the charging of the vehicle power source 41, and the like, and manages the vehicle 400 as a whole. Between the battery management device 411 and the vehicle ECU 42, data transfer related to the maintenance of the vehicle power source 41, such as the remaining capacity of the vehicle power source 41, is performed via a communication line.

A vehicle according to the fifth embodiment includes the battery pack according to the fourth embodiment. Therefore, according to this embodiment, it is possible to provide a vehicle equipped with a battery pack that is low in resistance and capable of achieving a high capacity retention rate.

[Example]
Examples are described below, but embodiments are not limited to the examples described below.

(Example 1)
A secondary battery was produced in the following procedure.

<Preparation of positive electrode>
A spinel-type lithium-nickel composite oxide (LiNi _0.5 Mn _1.5 O ₄ :LNMO) powder was prepared as a positive electrode active material. Aniline monomer was dissolved in acetone in an amount of 1% by weight relative to the weight of LNMO to prepare a monomer-containing solution. LNMO powder was added to the resulting monomer-containing solution to prepare a dispersion, and the dispersion was stirred for 10 minutes and then dried by heating to remove the solvent. Thus, an LNMO powder coated with aniline monomer was produced.

100 parts by mass of the obtained powder, 5 parts by mass of acetylene black as a conductive material, and 5 parts by mass of an alginic acid binder as a water-based binder were added to pure water and mixed to prepare a slurry. This slurry was applied to both sides of a current collector made of aluminum foil with a thickness of 12 μm to obtain a laminate, which was dried in a constant temperature bath at 120° C. and then pressed to obtain a positive electrode. .

<Production of negative electrode>
100 parts by mass of niobium titanium composite oxide (Nb ₂ TiO ₇ :NTO) powder as a negative electrode active material, 4 parts by mass of acetylene black as a conductive material, 2 parts by mass of carboxymethyl cellulose (CMC) as a binder, and styrene 2 parts by mass of butadiene copolymer (SBR) was added to pure water and mixed to prepare a slurry. This slurry was applied to both sides of a current collector made of aluminum foil having a thickness of 12 μm to obtain a laminate, which was dried in a constant temperature bath at 120° C. and then pressed to obtain a negative electrode. .

<Production of electrode group>
A positive electrode, a separator, a negative electrode, and a separator were laminated in this order to obtain a laminate. This laminate was then spirally wound. A flat electrode group was produced by hot-pressing this at 80°C. The obtained electrode group was housed in a pack made of a laminate film having a three-layer structure of nylon layer/aluminum layer/polyethylene layer and having a thickness of 0.1 mm, and was placed in a vacuum at 120° C. for 16 hours. Dried.

<Preparation of non-aqueous electrolyte>
A non-aqueous electrolyte was obtained by dissolving 1 mol/L of LiPF ₆ as an electrolyte in a mixed solvent of propylene carbonate (PC) and diethyl carbonate (DEC) (volume ratio 1:2). Electrolyte adjustments were performed in an argon box.

<Production of secondary battery, initial charge and charge-discharge cycle test>
After the non-aqueous electrolyte was injected into the laminated film pack containing the electrode group, the pack was completely sealed by heat sealing to obtain a secondary battery in a non-initial charged state.

The produced secondary battery was subjected to a charge-discharge cycle test in a 25° C. environment. In charging and discharging, the battery was first charged to 3.6 V at 20 mA, and then discharged to 2.3 V at 20 mA. The average operating potential of the positive electrode during initial charge was 4.7 V (vs. Li/Li ⁺ ). Then, after charging and discharging at 100 mA, the upper part of the laminate pack was opened in an Ar atmosphere, and the internal gas was discharged under vacuum. After that, the upper portion of the laminate pack was completely sealed again by heat sealing. Further, charging and discharging were performed at 20 mA up to 3.6 V, and after confirming the capacity of the battery, 100 cycles of charging and discharging were repeated at 100 mA. Then, the capacity retention rate was calculated from the initial discharge capacity and the discharge capacity at the 100th cycle. After 100 cycles, the secondary battery was sealed in a container whose interior was in a vacuum state.

(Example 2-5)
A secondary battery was produced in the same manner as in Example 1, except that the amount of monomer contained in the monomer-containing solution was changed according to the column of "Conductive polymer coat amount (% by mass)" in Table 1. .

(Example 6)
A secondary battery was produced in the same manner as in Example 2, except that pyrrole was used as the electropolymerizable monomer.

(Example 7)
A secondary battery was produced in the same manner as in Example 2, except that thiophene was used as the electrolytically polymerizable monomer.

(Example 8)
A secondary battery was fabricated in the same manner as in Example 2, except that lithium phosphate compound (LiCoPO ₄ :LCP) powder was used as the positive electrode active material.

(Example 9)
A secondary battery was produced in the same manner as in Example 6, except that LCP powder was used as the positive electrode active material.

(Example 10)
A secondary battery was produced in the same manner as in Example 7, except that LCP powder was used as the positive electrode active material.

(Example 11)
A secondary battery was produced in the same manner as in Example 2, except that the amount of the alginic acid binder added was changed to 2 parts by mass when preparing the positive electrode slurry.

(Example 12)
A secondary battery was produced in the same manner as in Example 2, except that the amount of the alginic acid binder added was changed to 8 parts by mass when preparing the positive electrode slurry.

(Example 13)
A secondary battery was produced in the same manner as in Example 11, except that the type of aqueous binder was changed to carboxymethyl cellulose (CMC).

(Example 14)
A secondary battery was produced in the same manner as in Example 2, except that the type of aqueous binder was changed to carboxymethyl cellulose (CMC).

(Example 15)
A secondary battery was produced in the same manner as in Example 2, except that the type of the negative electrode active material was changed from niobium-titanium composite oxide (NTO) to lithium-titanium composite oxide (Li ₄ Ti ₅ O ₁₂ : LTO). bottom.

(Comparative example 1)
A secondary battery was produced in the same manner as in Example 1, except that no electrolytically polymerizable monomer was used. That is, the positive electrode active material in Comparative Example 1 was LNMO powder without a conductive polymer coat.

(Comparative example 2)
A secondary battery was produced in the same manner as in Example 1, except that the amount of monomer contained in the monomer-containing solution was changed to 10% by mass with respect to the mass of the LNMO powder used.

(Comparative Example 3)
The same procedure as in Example 2 except that PVDF was used as an organic solvent-based binder instead of the water-based binder, and the amount added was changed to 3 parts by mass with respect to 100 parts by mass of the positive electrode active material. A secondary battery was produced by the method. PVDF, which is added as a binder when preparing the positive electrode slurry, is added in a state of being dissolved in an N-methyl-2-pyrrolidone (NMP) solvent. Therefore, when the positive electrode active material coated with the aniline monomer is added to the slurry, at least part of the aniline monomer coat is eluted into the slurry. The aniline monomer eluted into the slurry dissolves in the electrolytic solution, becomes a side reaction component, and generates a large amount of gas.

(Comparative Example 4)
In the same manner as in Example 2, except that LiMn ₂ O ₄ (LMO) powder having an average operating potential of 4.0 V (vs. Li/Li ⁺ ) was used as the positive electrode active material instead of LNMO. A secondary battery was produced.

<DC (Direct Current) resistance measurement>
DC resistance was measured as follows for the secondary battery produced in each example.
The secondary battery was discharged at a constant current (CC) of 0.2C until the voltage reached 2.5V. After that, the secondary battery was charged at a constant current (CC) of 0.2C until the voltage reached 3.6V. Next, the secondary battery was charged at a constant voltage (CV) of 3.11 V until the current value became 1/20C, thereby setting the state of charge of the secondary battery to 50% SOC. A secondary battery adjusted to an SOC of 50% was discharged at a constant current (CC) of 1 C and 10 C for 200 ms, respectively, and the DC resistance [mΩ] was obtained from the difference between the voltage value and the current value at this time.

The above results are summarized in Table 1 below. In Table 1, the column "Conductive polymer coating amount (% by mass)" shows the ratio of the mass of the conductive polymer to the mass of the lithium composite oxide particles contained in the active material-containing layer as the positive electrode active material. ing. The column of "amount of water-soluble polymer (% by mass)" shows the mass ratio of the water-soluble polymer in the positive electrode active material-containing layer.

Table 1 reveals the following.
The positive electrode active material-containing layer included in the positive electrode in each of Examples 1 to 15 contains one or more lithium composite oxide particles exhibiting an operating potential of 4.4 V or higher relative to metallic lithium. At least part of the surface of these lithium composite oxide particles is coated with a conductive polymer. The ratio of the mass of the conductive polymer to the mass of the one or more lithium composite oxide particles is in the range of 0.5 wt% to 5.0 wt%. In addition, the positive electrode active material-containing layer contains a water-soluble polymer. Therefore, all of Examples 1 to 15 achieved excellent capacity retention, low DC resistance, and low gas generation.

When comparing Examples 1-7 and 11-15 using lithium nickel manganese oxide (LNMO) as the positive electrode active material with Comparative Example 1-3 using LNMO, Examples 1-7 and 11-15 It can be seen that both a high capacity retention rate and a low resistance can be achieved with respect to In Examples 8 to 10 using LiCoPO ₄ (LCP), which is a lithium phosphate compound, both high capacity retention and low resistance were achieved.

In Comparative Example 1, since the LNMO particles were not coated with a conductive polymer, contact between the LNMO particles and the non-aqueous electrolyte could not be suppressed, and gas generation increased. As a result, the capacity retention rate was inferior. Comparative Example 2 had a significant increase in DC resistance because the LNMO particles as the active material were coated with an excessive amount of conductive polymer. Comparative Example 3 is an example using PVDF as an organic solvent-based binder as a positive electrode binder. In this case, the aniline monomer covering the surfaces of the positive electrode active material particles is eluted into the organic solvent during preparation of the positive electrode slurry. Therefore, it is considered that the surface of the active material was not coated with the conductive polymer even after the initial charging. As a result, it is considered that the side reaction on the surface of the LNMO particles as the positive electrode active material could not be suppressed, resulting in an increase in gas generation and a decrease in the capacity retention rate.

Comparative Example 4 is an example of using lithium manganese oxide (LiMn ₂ O ₄ : LMO) with an average operating potential of 4.0 V (vs. Li/Li ⁺ ) as the positive electrode active material (lithium composite oxide). . On the other hand, in order to sufficiently electropolymerize the aniline monomer, it is necessary to raise the positive electrode potential to, for example, 4.4 V or higher. In Comparative Example 4, as a result of raising the positive electrode potential to 4.4 V or more to polymerize the aniline monomer, the LMO could not withstand such a working voltage, and its crystal structure collapsed. As a result, intercalation and deintercalation of lithium ions ceased.

As shown in Examples 2 to 4, when the ratio of the mass of the conductive polymer to the mass of the lithium composite oxide particles as the positive electrode active material is in the range of 1.0% to 4.0% by mass, It can be seen that the capacity retention rate and the DC resistance are well balanced and excellent compared to the case outside the range. In Examples 1-15, since the water-soluble polymer used had an HLB value within the range of 15 to 19, the positive electrode active material-containing layer was stable against the non-aqueous electrolyte.

According to at least one embodiment and example described above, a positive electrode is provided. The positive electrode includes a positive electrode active material-containing layer containing positive electrode active material particles and a water-soluble polymer. The positive electrode active material particles include lithium composite oxide particles exhibiting an operating potential of 4.4 V or higher relative to metallic lithium, and a conductive polymer covering at least a portion of the lithium composite oxide particle surfaces. The ratio of the mass of the conductive polymer to the mass of the lithium composite oxide particles is in the range of 0.5% by mass to 5.0% by mass. This positive electrode has a low resistance and can achieve a high capacity retention rate.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 1... Electrode group, 2... Exterior member, 3... Negative electrode, 3a... Negative electrode collector, 3b, 3c... Negative electrode collector tab, 4... Separator, 5... Positive electrode, 5a... Positive electrode collector, 5b... Positive electrode active material Content layer 5c Positive electrode active material particles 5d Water-soluble polymer 5e Positive electrode conductive material 6 Negative electrode terminal 7 Positive electrode terminal 21 Bus bar 22 Lead on positive electrode side 22a Other end 23 Negative electrode Side lead 23a Other end 24 Adhesive tape 31 Container 32 Lid 33 Protection sheet 34 Printed wiring board 35 Wiring 40 Vehicle body 41 Vehicle power source 42 Electrical control device 43 External terminal 44 Inverter 45 Drive motor 51 Lithium composite oxide particles 52 Conductive polymer 100 Secondary battery 200 Assembled battery 200a Assembled battery 200b Assembled battery 200c... Assembled battery 300... Battery pack 300a... Battery pack 300b... Battery pack 300c... Battery pack 301a... Assembled battery monitoring device 301b... Assembled battery monitoring device 301c... Assembled battery monitoring device 342 Positive side connector 343 Negative side connector 345 Thermistor 346 Protection circuit 342a Wiring 343a Wiring 350 External terminal for energization 352 Positive terminal 353 Negative terminal 348a Positive wiring 348b Negative wiring 400 Vehicle 411 Battery management device 412 Communication bus 413 Positive terminal 414 Negative terminal 415 Switch device 416 Current detector 417 Negative input Terminals 418... positive input terminal, L1... connection line, L2... connection line, W... drive wheel.

Claims (14)

A positive electrode active material-containing layer containing positive electrode active material particles and a water-soluble polymer,
The positive electrode active material particles are
Lithium composite oxide particles exhibiting an operating potential of 4.4 V or more based on metallic lithium;
and a conductive polymer covering at least part of the surface of the lithium composite oxide particles,
The positive electrode, wherein the ratio of the mass of the conductive polymer to the mass of the lithium composite oxide particles is in the range of 0.5% by mass to 5.0% by mass. 2. The positive electrode according to claim 1, wherein said conductive polymer is at least one selected from the group consisting of polyanilines, polypyrroles and polythiophenes. 3. The positive electrode according to claim 1, wherein the ratio of the mass of said conductive polymer to the mass of said lithium composite oxide particles is in the range of 1.0% by mass to 4.0% by mass. 4. The positive electrode according to claim 1, wherein the water-soluble polymer has an HLB (Hydrophilic-Lipophilic Balance) value in the range of 8 or more and 20 or less. 5. The positive electrode according to claim 1, wherein the weight ratio of the water-soluble polymer in the positive electrode active material-containing layer is in the range of 1% by mass to 10% by mass. The water-soluble polymer is at least one selected from the group consisting of acrylic polymer, urethane polymer, carboxymethylcellulose (CMC), alginic acid polymer, polyether, polyvinyl alcohol, water-soluble polyester, and dicarboxylated polysaccharide. The positive electrode according to any one of claims 1 to 5. The positive electrode according to any one of claims 1 to 6, wherein the lithium composite oxide contains at least one selected from the group consisting of lithium nickel manganese oxide and lithium phosphate compound. The positive electrode according to any one of claims 1 to 7,
a negative electrode;
A secondary battery comprising an electrolyte. The negative electrode includes a negative electrode active material-containing layer containing a negative electrode active material,
9. The second method according to claim 8, wherein the negative electrode active material contains at least one titanium-containing oxide selected from the group consisting of titanium oxides, lithium-titanium composite oxides, niobium-titanium composite oxides, and sodium-niobium-titanium composite oxides. next battery. A battery pack comprising the secondary battery according to claim 9 . an external terminal for energization;
11. The battery pack of claim 10, further comprising a protection circuit. The battery pack according to claim 10 or 11, comprising a plurality of said secondary batteries, wherein said secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. A vehicle equipped with the battery pack according to any one of claims 10 to 12. 14. The vehicle of claim 13, including a mechanism for converting kinetic energy of the vehicle into regenerative energy.

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