JP6658182B2 - Electrode structure and lithium secondary battery - Google Patents

Description

  The present invention relates to an electrode structure and a lithium secondary battery.

  Conventionally, as a lithium secondary battery, the value A obtained by dividing the DBP oil absorption of the positive electrode active material particles by the porosity of the positive electrode active material layer and the thickness of the positive electrode active material layer, and the oil absorption of linseed oil of the negative electrode active material particles A battery is proposed in which the ratio A / B of a value obtained by dividing the amount by the porosity of the negative electrode active material layer and the thickness B of the negative electrode active material layer is 0.78 ≦ (A / B) ≦ 1.22. (See Patent Document 1). In this battery, the characteristics of the holding power of the electrolytic solution are adjusted in a generally well-balanced manner between the positive electrode active material layer and the negative electrode active material layer. For this reason, in applications where charging and discharging are repeated at a high rate (high current), even when electrolyte flows in and out of the positive electrode and the negative electrode of the battery are severely repeated, the increase in resistance of the battery can be suppressed.

JP 2013-109929 A

  However, in the battery of Patent Literature 1, by adjusting the characteristics of the holding power of the electrolytic solution between the positive electrode active material layer and the negative electrode active material layer, it is possible to suppress a rise in resistance and increase the durability against high-rate charging and discharging. However, it is not yet sufficient, and it has been desired to further improve the durability against high-rate charge / discharge.

  The present invention has been made in view of such problems, and has as its main object to provide an electrode structure and a lithium secondary battery that can further suppress an increase in internal resistance.

  After extensive research to achieve the above-mentioned object, the present inventors have determined that the liquid absorption height measured according to the Bilek method has a predetermined relationship, a positive electrode, a negative electrode, a layer on the positive electrode side of the separator and When a layer on the negative electrode side of the separator was prepared and an electrode structure was produced using these, it was found that an increase in internal resistance could be further suppressed, and the present invention was completed.

That is, the electrode structure of the present invention,
A positive electrode, a negative electrode, and two or more separators interposed between the positive electrode and the negative electrode,
The liquid absorption height of the positive electrode was A (mm), the liquid absorption height of the negative electrode was B (mm), and the liquid absorption of the layer on the positive electrode side of the separator was measured by absorbing a test solution for 10 minutes by a birec method. When the height is C (mm) and the liquid absorption height of the layer on the negative electrode side of the separator is D (mm), (DC) / (AB)> 0 is satisfied.

The lithium secondary battery of the present invention,
The electrode structure described above,
A non-aqueous electrolyte interposed between the positive electrode and the negative electrode and conducting lithium ions,
It is provided with.

  In the electrode structure and the lithium secondary battery of the present invention, an increase in internal resistance can be further suppressed. The reason why such an effect is obtained is presumed as follows. For example, when a separator having a one-layer structure is used, a difference in the ease of circulation of the electrolyte between the positive electrode and the negative electrode, the retention of the electrolyte, and the like, particularly when the battery is charged and discharged at a high rate. The bias in the concentration increases, and the resistance tends to increase. However, two or more layers of separators are provided, and (DC) / (AB)> 0 is satisfied. That is, a separator having a high liquid absorption height is arranged on the electrode side having a low liquid absorption height, It is considered that the bias of the salt concentration can be reduced by disposing a separator having a low liquid absorption height on the electrode side having a high liquid absorption height. Thus, it is presumed that the increase in resistance can be further suppressed. Here, the “birec method” is a liquid absorption method according to JIS L 1907: 2010.

FIG. 2 is a schematic diagram illustrating an example of a lithium secondary battery 10. Sectional drawing which shows an example of the electrode structure 11. FIG. Explanatory drawing which shows the measuring method of a liquid absorption height. FIG. 2 is a schematic diagram showing an example of a lithium secondary battery 30.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram illustrating an example of the lithium secondary battery 10 of the present invention. FIG. 2 is a cross-sectional view illustrating an example of the electrode structure 11. As shown in FIGS. 1 and 2, the lithium secondary battery 10 of the present embodiment includes, for example, a positive electrode sheet 15 in which a positive electrode mixture layer 14 is formed on a current collector 13, and a negative electrode mixture A negative electrode sheet 18 having the layer 17 formed thereon, a separator 21 provided between the positive electrode sheet 15 and the negative electrode sheet 18 and having a positive electrode side layer 20 and a negative electrode side layer 19, and a separator 21 between the positive electrode sheet 15 and the negative electrode sheet 18. And a non-aqueous electrolyte solution 22 that satisfies the following conditions. In this lithium secondary battery 10, a separator 21 is sandwiched between a positive electrode sheet 15 and a negative electrode sheet 18, these are wound and inserted into a cylindrical case 23, and the positive electrode terminal 24 and the negative electrode sheet 18 connected to the positive electrode sheet 15 are connected. And a negative electrode terminal 26 connected to the negative electrode terminal 26.

  The lithium secondary battery 10 includes a positive electrode sheet 15 including a positive electrode active material and a current collector 13, a negative electrode sheet 18 including a negative electrode active material and a current collector 16, and a positive electrode sheet 15 and a negative electrode sheet 18. And a separator 21 having a layer 20 on the positive electrode side and a layer 19 on the negative electrode side interposed therebetween. In this electrode structure 11, the liquid absorption height of the positive electrode mixture layer 14 was measured as A (mm), and the liquid absorption height of the negative electrode mixture layer 17 was measured as B ( mm), the liquid absorption height of the layer 20 on the positive electrode side of the separator 21 is C (mm), and the liquid absorption height of the layer 19 on the negative electrode side of the separator 21 is D (mm). / (AB)> 0 is satisfied.

  Here, a method of measuring the liquid absorption height will be described. The method of measuring the liquid absorption height shall be performed in accordance with the birec method of JIS L 1907: 2010. The method of measuring the liquid absorption height is such that the sample solution is not limited to water, the size of the test piece is about 100 cm × 2.5 cm, and the direction in which the sample is collected corresponds to the axial direction of the battery. The method is the same as the birec method of JIS L 1907: 2010, except that a direction (only one direction) is satisfied and a weight is attached to the end of the test piece on the side to be immersed as necessary.

  FIG. 3 is an explanatory diagram showing a method of measuring the liquid absorption height. As shown in FIG. 3, after fixing the test piece 60 on a horizontal bar 60 supported on the liquid surface of the container 52 containing the test solution 66 with a pin or the like, the lower end portion 62 of the test piece 60 (from the lower end end). (20 mm ± 2 mm) so as to be immersed in the test solution 66, and left as it is for 10 minutes. After the standing, the height T (hereinafter also referred to as the liquid absorption height) at which the test solution 66 has risen due to the capillary phenomenon is measured in units of 1 mm on a scale.

  As the test piece 60, each of the positive electrode sheet 15, the negative electrode sheet 18, the positive electrode side layer 20 of the separator 21, and the negative electrode side layer 19 of the separator 21 (or from a sheet of the same material), each having a size of 100 cm × 2.5 cm Use the one cut out to the size. The longitudinal direction of the test piece 60 is made to coincide with the winding axis direction (hereinafter, referred to as the axial direction) when each member is wound and assembled into the lithium secondary battery 10. In FIG. 3, a weight 64 is attached to the end of the test piece 60 on the lower end 62 side, and the floating of the lower end 62 is suppressed. When the positive electrode mixture layer 14 and the negative electrode mixture layer 17 can maintain the shape alone, the positive electrode mixture layer 14 and the negative electrode mixture layer 17 (or the same The test piece 60 may be cut out from a material sheet) and used.

  The type of the test solution 66 is not particularly limited. This is because the values of A, B, C, and D may change depending on the type of the test solution 66, but the ratio of (D−C) / (A−B) is considered to have no significant difference. It is preferable that the test solution 66 has low volatility from the viewpoint of easy evaluation. The test solution 66 may be a solvent or the like exemplified later as the nonaqueous electrolyte solution 22 of the lithium secondary battery 10, and may be, for example, propylene carbonate. Propylene carbonate has low volatility and is suitable for evaluation. In addition, the test solution 66 may be water. The type of the test solution 66 may be the same as or different from the solvent used for the non-aqueous electrolyte 22 of the lithium secondary battery 10. The temperature of the test solution is 20 ° C ± 2 ° C.

  The value of (DC) / (AB) may be larger than 0, but is preferably 1 or more, and more preferably 2 or more. In such a case, it is considered that the bias of the salt concentration can be further reduced and the increase in resistance can be further suppressed. The upper limit of the value of (DC) / (AB) is not particularly limited, but may be 100 or less, 75 or less, 50 or less.

  The value of | AB | may be greater than 0, but may be 1 or more, 3 or more, or 5 or more. When the value of | AB | is large, the bias of the salt concentration tends to increase when a single-layer separator or the like is used, so that the application of the present invention is significant. It should be noted that the values of A and B may be appropriately set so that the charge / discharge characteristics are good, and A may be larger than B or B may be larger than A.

  As shown in FIG. 2, a positive electrode mixture layer 14 containing a positive electrode active material is formed on both surfaces of the positive electrode sheet 15. The positive electrode mixture layer 14 may be formed on one surface of the positive electrode sheet 15 depending on the structure to be adopted. The thickness a per one surface of the positive electrode mixture layer 14 may be, for example, 10 μm or more and 500 μm or less, or may be 20 μm or more and 200 μm or less.

  The positive electrode sheet 15 is prepared, for example, by mixing a positive electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like positive electrode mixture, applying it to the surface of the current collector 13 and drying it. In order to increase the electrode density, it may be formed by compression. The liquid absorption height A of the positive electrode sheet 15 can be adjusted by, for example, adjusting the types and amounts of the positive electrode active material, the conductive material, and the binder used, or adjusting the electrode density. The liquid absorption height A may be, for example, 1 mm or more, 2 mm or more, 5 mm or more, or the like. Moreover, it is good also as 50 mm or less, 30 mm or less, 20 mm or less.

As the positive electrode active material, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, or the like can be used. Specifically, transition metal sulfides such as TiS ₂ , TiS ₃ , MoS ₃ , and FeS _2, and a basic composition formula of Li _(1-x) MnO ₂ (0 <x <1, the same applies hereinafter) and Li _{(1 -x)} Lithium manganese composite oxide such as Mn ₂ O _4, lithium cobalt composite oxide whose basic composition formula is Li _(1-x) CoO _2, etc., basic composition formula of Li _(1-x) NiO ₂ etc. lithium nickel composite oxide, the basic compositional formula _{Li (1-x) Ni a} Co b Mn c O 2 ( where 0 <a <1,0 <b < 1,0 <c <1, a + b + c = 1 ), A lithium vanadium composite oxide having a basic composition formula such as LiV ₂ O _3, and a transition metal oxide having a basic composition formula such as V ₂ O _5. it can. Of these, lithium transition metal composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ are preferred. Note that the “basic composition formula” means that the composition of each element may be different or other elements may be included.

  The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode. For example, graphite such as natural graphite (scale graphite, flake graphite) or artificial graphite, acetylene black, carbon black, Ketjen black, carbon whiskers, needle coke, carbon fiber, and one or a mixture of two or more of metals (copper, nickel, aluminum, silver, gold, and the like) can be used. Among these, carbon black and acetylene black are preferable as the conductive material from the viewpoints of electron conductivity and coatability.

  The binder plays a role of binding the active material particles and the conductive material particles. For example, a binder resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a fluorine-containing resin such as fluororubber, or polypropylene, Thermoplastic resins such as polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. Further, an aqueous dispersion of a cellulose-based or styrene-butadiene rubber (SBR) as an aqueous binder can also be used.

  Examples of the solvent in which the positive electrode active material, the conductive material, and the binder are dispersed include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylene triamine, N, N-dimethylaminopropylamine And organic solvents such as ethylene oxide and tetrahydrofuran. Further, a dispersant, a thickener, and the like may be added to water, and the active material may be slurried with a latex such as SBR. As the thickener, for example, polysaccharides such as carboxymethylcellulose and methylcellulose can be used alone or as a mixture of two or more.

  Examples of the application method include roller coating such as an applicator roll, screen coating, a doctor blade method, spin coating, and a bar coater, and any of these can be used to obtain an arbitrary thickness and shape.

  The current collector 13 includes aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, and the like, and aluminum or copper for the purpose of improving adhesiveness, conductivity, and oxidation resistance. The surface of which has been treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. Examples of the shape of the current collector 13 include a foil shape, a film shape, a sheet shape, a net shape, a punched or expanded material, a lath body, a porous body, a foamed body, and a formed body of a fiber group. The thickness of the current collector 13 is, for example, 1 to 500 μm.

  On the negative electrode sheet 18, a negative electrode mixture layer 17 containing a negative electrode active material is formed on both surfaces thereof. The negative electrode mixture layer 17 may be formed on one side of the negative electrode sheet 18 according to the structure to be adopted. The thickness b per one surface of the negative electrode mixture layer 17 may be, for example, 10 μm or more and 500 μm or less, or 20 μm or more and 200 μm or less.

  The negative electrode sheet 18 is prepared, for example, by mixing a negative electrode active material, a conductive material, and a binder, adding an appropriate solvent, and forming a paste-like negative electrode mixture on the surface of the current collector 16 by drying. In order to increase the electrode density, it may be formed by compression. The liquid absorption height B of the negative electrode sheet 18 can be adjusted by, for example, adjusting the types and amounts of the negative electrode active material, the conductive material, and the binder used, or adjusting the electrode density. The liquid absorption height B may be, for example, 1 mm or more, 2 mm or more, 5 mm or more, or the like. Moreover, it is good also as 50 mm or less, 30 mm or less, 20 mm or less.

  Examples of the negative electrode active material include a carbonaceous material capable of inserting and extracting lithium ions, a composite oxide containing a plurality of elements, and a conductive polymer. Examples of the carbonaceous material include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Among these, graphites such as artificial graphite and natural graphite have an operating potential close to metallic lithium, can be charged and discharged at a high operating voltage, and suppresses self-discharge when a lithium salt is used as a supporting salt, This is preferable because the irreversible capacity at the time of charging can be reduced. Examples of the composite oxide include a lithium titanium composite oxide and a lithium vanadium composite oxide. Among them, a carbonaceous material is preferable as the negative electrode active material from the viewpoint of safety. As the conductive material, the binder, the solvent, and the like used for the negative electrode sheet 18, those exemplified for the positive electrode sheet 15 can be used. The current collector 16 of the negative electrode sheet 18 includes copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al—Cd alloy, etc., as well as adhesiveness, conductivity, and reduction resistance. For the purpose of improving the properties, for example, those obtained by treating the surface of copper or the like with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. The shape of the current collector 16 can be the same as that of the positive electrode.

  The separator 21 includes a layer 20 on the positive electrode side and a layer 19 on the negative electrode side. The separator 21 may be composed of two layers, that is, a layer 20 on the positive electrode side and a layer 19 on the negative electrode side, or may include one or more layers between the layer 20 on the positive electrode side and the layer 19 on the negative electrode side. May be configured. The layers may be joined by welding or the like, or may not be joined. The material of each layer is not particularly limited as long as it has a composition that can withstand the use range of the lithium secondary battery 10. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or an olefin resin such as polyethylene or polypropylene is used. A thin microporous membrane is exemplified.

  In the separator 21, the liquid-absorbing height C of the layer 20 on the positive electrode side and the liquid-absorbing height D of the layer 19 on the negative electrode side are adjusted, for example, by adjusting the material, density, and hole shape of the material constituting the layer. Can be adjusted. The liquid absorption heights C and D may be, for example, 1 mm or more, 2 mm or more, and 10 mm or more. Further, it may be 500 mm or less, 300 mm or less, 200 mm or less, or the like.

  In the separator 21, the thickness c of the layer 20 on the positive electrode side and the thickness d of the layer 19 on the negative electrode side are preferably 5 μm or more, more preferably 15 μm or more, and even more preferably 25 μm or more. When a thick separator is used, the difference in the ease of circulation of the electrolyte between the positive electrode and the negative electrode and the difference in the holding power of the electrolyte are more affected by the supply and holding power of the electrolyte in each layer of the separator. It can be eased. The upper limits of the thicknesses c and d are not particularly limited, but may be, for example, 500 μm or less, 200 μm or less. Here, the thickness c of the layer 20 on the positive electrode side and the layer thickness d on the negative electrode side preferably satisfy, for example, a value of c / d of 0.05 or more and 15 or less, and more preferably 0.5 or more and 10 or less. Is more preferred. Further, the thickness c of the layer 20 on the positive electrode side is preferably such that the value of c / a satisfies 0.1 or more and 5 or less, and 0.2 or more and 1.5 or less, with respect to the thickness a of the positive electrode mixture layer 14. It is more preferable to satisfy the following. The thickness d of the layer 19 on the negative electrode side is preferably such that the value of d / b satisfies 0.1 or more and 5 or less with respect to the thickness b of the negative electrode mixture layer 17; It is more preferable to satisfy the following. In the case where an extremely thin layer such as 1 μm or less or 3 μm or less or a layer only responsible for mechanical strength is present on the outermost layer on the positive electrode side or the negative electrode side of the separator 21, if such a layer alone is used, It is not treated as the layer 20 or the layer 19 on the negative electrode side. In this case, the layer on the positive electrode side including an extremely thin layer is treated as the layer 20 on the positive electrode side, and the layer on the negative electrode side including the extremely thin layer is treated as the layer 19 on the negative electrode side.

  As the non-aqueous electrolyte 22 of the lithium secondary battery 10, a non-aqueous electrolyte or a non-aqueous gel electrolyte in which a supporting salt is dissolved in a solvent can be used. Examples of the solvent include carbonates, esters, ethers, nitriles, furans, sulfolane, dioxolane and the like, and these can be used alone or as a mixture. Specifically, cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, chloroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t are used as carbonates. -Butyl carbonate, di-i-propyl carbonate, chain carbonates such as t-butyl-i-propyl carbonate, γ-butyl lactone, cyclic esters such as γ-valerolactone, methyl formate, methyl acetate, ethyl acetate, Chain esters such as methyl butyrate, ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane; nitriles such as acetonitrile and benzonitrile; tetrahydrofuran Examples thereof include furans such as orchid and methyltetrahydrofuran, sulfolane such as sulfolane and tetramethylsulfolane, and dioxolanes such as 1,3-dioxolan and methyldioxolan. Among them, a combination of a cyclic carbonate and a chain carbonate is preferable. According to this combination, not only the cycle characteristics representing the battery characteristics in repeated charging and discharging are excellent, but also the viscosity of the electrolyte, the obtained battery electric capacity, the battery output, and the like can be balanced. it can. Note that cyclic carbonates are considered to have a relatively high relative dielectric constant and increase the dielectric constant of the electrolytic solution, and chain carbonates are considered to suppress the viscosity of the electrolytic solution.

The supporting salt is, for example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiSbF ₆ , LiSiF ₆ , LiAlF ₄ , LiSCN, LiClO. ₄ , LiCl, LiF, LiBr, LiI, LiAlCl _{4 and the} like. Among them, inorganic salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ and LiClO ₄ , and organic salts such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and LiC (CF ₃ SO ₂ ) ₃ It is preferable to use one or more selected salts in combination from the viewpoint of electrical characteristics. The concentration of the supporting salt in the non-aqueous electrolyte is preferably from 0.1 mol / L to 5 mol / L, more preferably from 0.5 mol / L to 2 mol / L. When the concentration for dissolving the supporting salt is 0.1 mol / L or more, a sufficient current density can be obtained, and when the concentration is 5 mol / L or less, the electrolytic solution can be further stabilized. Further, a flame retardant such as phosphorus-based or halogen-based may be added to the non-aqueous electrolyte.

  In the lithium secondary battery 10 of the present embodiment described in detail above, a separator having two or more layers, a separator having a high liquid absorption height is disposed on the electrode side having a low liquid absorption height, and an electrode having a high liquid absorption height is provided. A separator having a low liquid absorption height is arranged on the side. For this reason, it is considered that the bias of the salt concentration, which may be caused by the difference in the ease of circulation of the electrolyte and the retention of the electrolyte between the inside of the positive electrode and the inside of the negative electrode, can be further suppressed. Specifically, the difference in the ease of circulation of the electrolyte and the retention of the electrolyte between the inside of the positive electrode and the inside of the negative electrode is reduced by the supply and retention of the electrolyte in each layer of the separator, and the lithium ion concentration is reduced. It is considered that the bias can be suppressed. Therefore, it is considered that an increase in resistance during high-rate charging and discharging can be further suppressed.

  It should be noted that the present invention is not limited to the above-described embodiment at all, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  For example, in the above-described embodiment, the positive electrode sheet 15, the negative electrode sheet 18, and the separator 21 are described as the electrode structure 11 which is stacked and wound. However, the present invention is not particularly limited thereto. Good. Further, in the above-described embodiment, the shape of the lithium secondary battery is cylindrical, but is not particularly limited thereto, and examples thereof include a coin type, a button type, a sheet type, a stacked type, a flat type, and a square type. . Further, the present invention may be applied to a large vehicle used for an electric vehicle or the like.

  FIG. 4 is a schematic diagram showing an example of another lithium secondary battery 30 of the present invention. As shown in FIG. 4, the coin-type lithium secondary battery 30 includes a cup-shaped battery case 33, a positive electrode mixture layer 34 having a positive electrode active material, provided inside the battery case 33, and a negative electrode active material layer. A negative electrode mixture layer 37 provided at a position facing the positive electrode mixture layer 34 with a separator 41 interposed therebetween, a gasket 43 formed of an insulating material, and an opening in the battery case 33. And a sealing plate 36 for sealing the battery case 33 via a gasket 43. The lithium secondary battery 30 contains a non-aqueous electrolyte 42 that conducts lithium ions in a battery case 33. The electrode structure 31 includes a positive electrode 35 including a battery case 33 and a positive electrode mixture layer 34, a negative electrode 38 including a sealing plate 36 and a negative electrode mixture layer 37, and a separator 41 interposed between the positive electrode 35 and the negative electrode 38. It has. In the lithium secondary battery 30 and the electrode structure 31, the separator 41 includes a layer 40 on the positive electrode side and a layer 39 on the negative electrode side. The liquid absorption heights A to D of the positive electrode 35 (the positive electrode mixture layer 34), the negative electrode 38 (the negative electrode mixture layer 37), the positive electrode side layer 40, and the negative electrode side layer 39 are (D− C) / (AB)> 0 is satisfied. In a battery that is not a wound type, such as a coin-type lithium secondary battery 30, the direction in which the test piece used for measuring the liquid absorption height is not particularly limited. Since general electrode materials and separator materials are considered to have very small in-plane anisotropy, the influence of the direction of sample collection on the value of (DC) / (AB) is very small. It is considered small. The electrode structure 31 has a structure having one positive electrode mixture layer 34 and one negative electrode mixture layer 37, but may have a multilayer structure. In this case, among the separators between the positive electrode mixture layer and the negative electrode mixture layer, one or more separators, preferably all the separators, are two or more separators, a positive electrode mixture layer, a negative electrode mixture layer, The liquid absorption heights A to D of the layer on the positive electrode side of the separator and the layer on the negative electrode side of the separator may satisfy (DC) / (AB)> 0.

  In the above-described embodiment, the lithium secondary batteries 10 and 30 including the electrode structures 11 and 31 have been described. However, the electrode structures 11 and 31 used in the lithium secondary battery may be used. Even in this case, when used for a lithium secondary battery, the same effect as that of the lithium secondary battery can be obtained.

  In the embodiment described above, the electrode structures 11, 31 are used for the lithium secondary batteries 10, 30, but may be used for other than the lithium secondary batteries. For example, the positive electrode and the negative electrode may be used for batteries (alkali metal secondary batteries, alkaline earth metal secondary batteries, onium batteries, etc.) that occlude and release alkali metals, alkaline earth metals, and onium instead of lithium. Good. The invention is not limited to batteries, and may be used for capacitors, hybrid capacitors combining a battery and a capacitor, and the like.

  Hereinafter, examples in which the battery of the present invention is specifically manufactured will be described as examples. Here, a lithium-ion secondary battery using a nickel-cobalt-manganese (NCM) -based material as a positive electrode active material, graphite as a negative electrode active material, and a non-aqueous electrolyte as an electrolyte was manufactured.

[Example 1]
(Production of battery)
91% by mass of an NCM-based material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) as a positive electrode active material, 6% by mass of acetylene black (Denki Kagaku Kogyo HS100) as a conductive material, and polyfluorinated as a binder A mixture of 3% by mass of vinylidene chloride (KF polymer manufactured by Kureha Chemical Industry) was mixed to prepare a positive electrode mixture. The obtained positive electrode mixture is dispersed in N-methyl-2-pyrrolidone (NMP) to form a paste. This paste is applied to both sides of an aluminum foil having a thickness of 15 μm, dried, and roll-pressed to obtain a positive electrode sheet electrode. I got The thickness of the positive electrode mixture layer was 65 μm per side. The size of the positive electrode was 54 mm × 450 mm.

  98% by mass of graphite as a negative electrode active material, 1% by mass of carboxymethyl cellulose (CMC) as a thickener, and 1% by mass of styrene butadiene rubber (SBR) as a binder were mixed to prepare a negative electrode mixture. The obtained negative electrode mixture was dispersed in water to form a paste. This paste was applied to both sides of a 10-μm-thick copper foil, dried, and roll-pressed to obtain a negative electrode sheet electrode. The thickness of the negative electrode mixture layer was 68 μm per side. The negative electrode sheet electrode was 56 mm × 500 mm.

  Phosphorus hexafluoride was added to a nonaqueous solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of EC: DMC: EMC = 30: 40: 30. Lithium oxide was added to 1 mol / L to obtain an electrolyte solution.

  The above positive / negative electrode sheet electrode was wound into a roll via a separator 1 (58 mm × 500 mm) in which a 15 μm-thick layer on the positive electrode side and a 15 μm-thick negative electrode layer were welded, and a 18650-type battery for testing was obtained. After inserting into a can and injecting the above electrolyte, the top cap was caulked and sealed.

(Derivation of (DC) / (AB))
With respect to the separator and the electrode, the following evaluation was performed according to the Bilek method of JIS L 1907: 2010. A test piece for evaluation was prepared by cutting the separator into two layers, and cutting each of the positive electrode and the negative electrode into 2.5 cm × 20 cm. At that time, the test piece was prepared such that the axial direction of the battery was the longitudinal direction of the test piece. Next, one end in the longitudinal direction of each test piece was sandwiched between clips fixed at an appropriate height, and a weight was attached to the other end in the longitudinal direction and suspended. A part (about 2 cm at the lower end) of the test piece on the side to which the weight was attached was immersed in a container containing propylene carbonate (PC). The time at which the immersion was started was set to 0 minute, and the height at which the test piece absorbed the liquid over 10 minutes was measured from the position of the liquid surface of propylene carbonate. The liquid absorption height A (mm) of the positive electrode, the liquid absorption height B (mm) of the negative electrode, the liquid absorption height C (mm) of the separator layer facing the positive electrode, and the liquid absorption height of the separator layer facing the negative electrode The value D (mm) was measured, and the value of (DC) / (AB) was obtained.

(Charging / discharging test)
The prepared battery was first subjected to a charge / discharge cycle for activation (conditioning), and then subjected to a high-rate deterioration endurance test to evaluate the high-rate deterioration endurance performance. The test conditions for the high-rate degradation endurance test are as follows. All evaluations were performed in a 20 ° C. environment. First, the battery was adjusted to SOC 60%. Then, the battery was discharged at a rate of 10 C for 10 seconds and stopped for 5 seconds. Subsequently, the SOC was returned to 60% by charging at a rate of 2.5 C for 40 seconds, followed by a 5 second pause. This charge / discharge cycle was performed 8000 times.

(Resistance measurement)
Resistance was evaluated by IV resistance. In the measurement of IV resistance, the evaluation cell was adjusted to SOC 60% in a temperature environment of 20 ° C., and after a pause of 10 minutes, the cell was discharged at a constant current of 30 C for 10 seconds (CC discharge). Here, the lower limit voltage during discharging was 3.0 V. From this, the slope of V = IR (R = V / I) was defined as IV resistance. This resistance measurement is performed before and after the above-described high-rate degradation durability test, and the internal resistance R ₀ [V] before the high-rate degradation durability test and the internal resistance R [V] after the high-rate degradation durability test are derived, and R × 100 / R ₀ The internal resistance increase rate expressed by

[Example 2]
Evaluation was performed in the same manner as in Example 1 except that the separator 1 was replaced with a separator 2 (58 mm × 500 mm) in which a layer on the positive electrode side having a thickness of 25 μm and a layer on the negative electrode side having a thickness of 15 μm were used.

[Example 3]
Evaluation was performed in the same manner as in Example 1 except that the separator 1 was replaced with a separator 3 (58 mm × 500 mm) in which a layer on the positive electrode side having a thickness of 50 μm and a layer on the negative electrode side having a thickness of 15 μm were welded.

[Example 4]
Instead of the separator 1, a separator 4 (58 mm × 500 mm) in which a 15 μm-thick layer on the positive electrode side and a 15 μm-thick negative electrode layer were welded, and the thickness of the positive electrode mixture layer was 112 μm per side was used. Evaluation was performed in the same manner as in Example 1.

[Example 5]
Instead of the separator 1, a separator 5 (58 mm × 500 mm) in which a 25 μm-thick layer on the positive electrode side and a 15 μm-thick layer on the negative electrode side were used, and the thickness of the positive electrode mixture layer was 112 μm per side was used. Evaluation was performed in the same manner as in Example 1.

[Example 6]
A separator 6 (58 mm × 500 mm) in which a 50 μm-thick positive electrode layer and a 15 μm-thick negative electrode layer were welded in place of the separator 1, and the thickness of the positive electrode mixture layer was 112 μm per side was used. Evaluation was performed in the same manner as in Example 1.

[Comparative Example 1]
Evaluation was performed in the same manner as in Example 1 except that the separator 1 was replaced with a single-layer separator 7 (58 mm × 500 mm) made of polyethylene and having a thickness of 25 μm manufactured by a wet method.

[Comparative Example 2]
Evaluation was performed in the same manner as in Example 1 except that the separator 1 was replaced with a separator 8 (58 mm × 500 mm) in which a 15 μm-thick layer on the positive electrode side and a 25 μm-thick layer on the negative electrode side were welded.

[Experimental result]
Table 1 shows the values of A, B, C, and D, the value of (DC) / (AB), and the rate of increase in resistance. As shown in Table 1, in Examples 1 to 6 satisfying (DC) / (AB)> 0, the resistance increase rate was lower than Comparative Examples 1 and 2 not satisfying this. From this, it was found that in the present invention, an increase in internal resistance can be further suppressed. Among the examples, in Example 6, in which the value of (DC) / (AB) was the largest, at 41.5, the rate of increase in resistance was larger than that of the others, so that (DC) It was presumed that the value of / (AB) may not be too large, and it was presumed that, for example, 100 or less was preferable. In Example 6, in which the value of | AB | was the smallest at 4, the rate of increase in resistance was larger than the others, and it is inferred that the value of | AB | For example, it was presumed that | AB | ≧ 1 was more preferable.

  Further, in the present embodiment, a relationship was found between the value of (DC) / (AB) and the rate of increase in resistance, and therefore, the bireck method according to JIS L 1907: 2010 was used. It was found that the electrolytic solution holding power and the like could be evaluated by a simple method.

  It is to be noted that the present invention is not limited to the above-described embodiment at all, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  INDUSTRIAL APPLICABILITY The present invention can be used in the field of the battery industry and the like.

  Reference Signs List 10 lithium secondary battery, 11 electrode structure, 13 current collector, 14 positive electrode mixture layer, 15 positive electrode sheet, 16 current collector, 17 negative electrode mixture layer, 18 negative electrode sheet, 19 negative electrode side layer, 20 positive electrode side Layer, 21 separator, 22 non-aqueous electrolyte, 23 cylindrical case, 24 positive electrode terminal, 26 negative electrode terminal, 30 lithium secondary battery, 31 electrode structure, 33 battery case, 34 positive electrode mixture layer, 35 positive electrode, 36 sealing Plate, 37 negative electrode mixture layer, 38 negative electrode, 39 negative electrode side layer, 40 positive electrode side layer, 41 separator, 42 non-aqueous electrolyte, 43 gasket, 50 horizontal bar, 52 container, 60 test piece, 62 lower end, 64 weights, 66 reagents.

Claims (6)

A positive electrode, a negative electrode, and two or more separators interposed between the positive electrode and the negative electrode,
The liquid absorption height of the positive electrode was A (mm), the liquid absorption height of the negative electrode was B (mm), and the liquid absorption of the layer on the positive electrode side of the separator was measured by absorbing a test solution for 10 minutes by a birec method. When the height is C (mm) and the liquid absorption height of the layer on the negative electrode side of the separator is D (mm), 0 <(DC) / (AB) ≦ 100 is satisfied.
Electrode structure. A positive electrode, a negative electrode, and two or more separators interposed between the positive electrode and the negative electrode,
The liquid absorption height of the positive electrode was A (mm), the liquid absorption height of the negative electrode was B (mm), and the liquid absorption of the layer on the positive electrode side of the separator was measured by absorbing a test solution for 10 minutes by a birec method. When the height is C (mm) and the liquid absorption height of the layer on the negative electrode side of the separator is D (mm), (DC) / (AB)> 0 and | AB | ≧ Satisfy 1
Electrode structure. The electrode structure according to claim 2 , wherein 0 <(DC) / (AB) ≦ 100 is satisfied.   The electrode structure according to any one of claims 1 to 3, wherein the reagent is propylene carbonate. The electrode structure is a wound electrode structure,
The electrode structure according to claim 1, wherein the liquid absorption height is an axial liquid absorption height. An electrode structure according to any one of claims 1 to 5,
A non-aqueous electrolyte interposed between the positive electrode and the negative electrode and conducting lithium ions,
Rechargeable lithium battery.

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