Lithium secondary battery

Abstract

To enhance cycle endurance of a lithium secondary battery.SOLUTION: A lithium secondary battery includes a positive electrode, a separator, a negative electrode, and an electrolytic solution. The negative electrode includes a current collector. The current collector has a thickness from 10 to 20 μm. The current collector has a plurality of through holes. The through holes satisfy relationships of expression (1) and expression (2): 1.50≤B / A≤3.0 (1) and 0.05≤A≤0.18 (2) where a diameter of each of the through holes at a surface of the current collector is defined as a (mm), a center-to-center distance between each of the through holes and another through hole closest thereto is defined as b (mm), an average value of the diameter a (mm) is defined as A (mm), and an average value of the center-to-center distance b (mm) is defined as B (mm).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to lithium secondary batteries. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2019-160776 (Patent Document 1) discloses providing a plurality of protrusions on each of a first surface and a second surface of a negative electrode current collector. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-160776 A Summary of the Invention [Problem to be solved by the invention]

[0004] As described in the above literature, in lithium secondary batteries that utilize the dissolution and precipitation reaction of lithium metal as the negative electrode reaction, lithium metal precipitates from the electrolyte during charging. During discharging, lithium metal dissolves into the electrolyte. By utilizing the dissolution and precipitation reaction, it is expected that the energy density will increase. However, there is room for improvement in the cycle durability of lithium secondary batteries.

[0005] An object of the present disclosure is to improve the cycle durability of lithium secondary batteries. [Means for solving the problem]

[0006] The technical configuration and effects of the present disclosure will be described below. However, the mechanism of action in this specification includes assumptions. The mechanism of action does not limit the technical scope of the present disclosure.

[0007] 1. A lithium secondary battery includes a positive electrode, a separator, a negative electrode, and an electrolyte. A lithium secondary battery is a battery that utilizes a dissolution and precipitation reaction of lithium metal as a reaction at the negative electrode. The negative electrode includes a current collector. The current collector has a thickness of 10 to 20 μm. The current collector has a plurality of through holes. Assuming that each of the through holes has a diameter at the surface of a (mm), a center-to-center distance between the through hole and the closest other through hole is b (mm), and further that the average value of the diameters a (mm) is A (mm) and the average value of the center-to-center distances b (mm) is B (mm), then Equation (1) and Equation (2): 1.50≦B / A≦3.0 (1) 0.05≦A≦0.18 (2) Satisfy the relationship.

[0008] In a lithium secondary battery that utilizes a dissolution and precipitation reaction of lithium metal as a reaction of the negative electrode, lithium metal may precipitate from multiple starting points on the negative electrode to form multiple precipitates during charging. Each precipitate may cause the negative electrode to expand, which may cause a decrease in the capacity retention rate. The expansion of the negative electrode refers to an increase in the total volume of the negative electrode and the volume of the precipitated lithium metal. In addition, as each precipitate grows and becomes larger, a part or all of it becomes more likely to fall off into the electrolyte. The fallen lithium metal may become an irreversible capacity. Due to the expansion of the negative electrode and the increase in the amount of lithium metal precipitates that fall off into the electrolyte, the capacity retention rate of the lithium secondary battery decreases and the cycle durability decreases.

[0009] For example, Patent Document 1 discloses that the deposition of lithium metal is controlled by providing multiple protrusions on each of the first and second surfaces of the negative electrode current collector. However, the process of providing multiple protrusions on each of the first and second surfaces of the negative electrode current collector is complicated. In addition, since the multiple protrusions are made of a resin material, the surfaces of the protrusions do not become the deposition starting points of lithium metal. In contrast, in the present disclosure, the deposition of lithium metal is controlled by using a current collector having multiple through holes. The inner walls of the multiple through holes become the deposition starting points, and the process of providing the multiple through holes is simple.

[0010] In the present disclosure, the cycle durability of a lithium secondary battery can be improved. This can be achieved by the current collector having a plurality of through holes, and the plurality of through holes being arranged to satisfy the above formula (1) and formula (2). That is, since the current collector has a plurality of through holes, lithium metal is also precipitated from the inner walls of the plurality of through holes, and the number of starting points of precipitation increases moderately. When the number of starting points of precipitation increases moderately, the current density of each precipitate decreases, and each precipitate precipitated from each starting point can be grown to a high density. And, when the density of each precipitate is high, the falling off is suppressed. In addition, each precipitate grows from a high density and moderately close starting point, so that the expansion of the negative electrode is suppressed even after the multiple precipitates become a continuous precipitate by subsequent growth. It is presumed that the growth of the precipitates from the moderately close starting points is possible when the multiple through holes satisfy the relationship of the above formula (1) and formula (2).

[0011] 2. The lithium secondary battery described in the above item "1" may include, for example, the following configuration: The current collector is a copper foil or a copper alloy foil.

[0012] 3. The lithium secondary battery according to the above item "1" or "2" may include, for example, the following configuration: The current collector has a surface opening ratio of 5.0 to 35.0%.

[0013] It is expected that a surface aperture ratio of 10.1% or more will increase the number of starting points from which lithium metal will deposit, and that the current density of the deposits from each starting point will decrease. Also, a surface aperture ratio of 35.0% or less will ensure that lithium metal will deposit from appropriately close starting points.

[0014] 4. The lithium secondary battery according to any one of the above items "1" to "3" may include, for example, the following configuration: 2 The exposed surface area is 0.86~0.99cm 2 It is.

[0015] 5. The lithium secondary battery according to the above item "1" is, for example, a copper foil or a copper alloy foil, the surface has an opening ratio of 5.0 to 35.0%, and the surface has an opening ratio of 1 cm 2 The exposed surface area is 0.86~0.99cm 2 It is.

[0016] 6. The method for producing a lithium secondary battery described in "1" above includes, for example, a step of preparing the current collector, a step of assembling a lithium secondary battery precursor including the positive electrode, the separator, the negative electrode, and the electrolyte, and a step of charging the lithium secondary battery precursor to deposit lithium metal on the negative electrode.

[0017] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present embodiment") will be described. However, the present embodiment and the present embodiment do not limit the technical scope of the present disclosure. The present embodiment and the present embodiment are illustrative in all respects. The present embodiment and the present embodiment are non-restrictive. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the description of the claims. For example, it is originally intended that any configuration may be extracted from the present embodiment and the present embodiment, and that they may be arbitrarily combined. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a conceptual diagram showing a lithium secondary battery according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a conceptual diagram illustrating an example of a current collector in the present embodiment. [Diagram 3] FIG. 4 is a conceptual diagram showing another example of the current collector in the present embodiment. [Figure 4] 3 is a conceptual diagram showing a charge / discharge process in the vicinity of a current collector of the lithium secondary battery according to the present embodiment. FIG. [Diagram 5] 1 shows a first configuration example of a lithium secondary battery in the present embodiment. [Figure 6] 4 shows a second configuration example of the lithium secondary battery in the present embodiment. [Figure 7] 3 shows a third configuration example of the lithium secondary battery in the present embodiment. [Figure 8] Table 1 shows the arrangement pattern of the through holes in the current collector and the evaluation results. [Figure 9] 1 is a graph showing cycle discharge capacity retention rates of Nos. 1 to 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] <Terminology explanation> The terms used in this specification are explained. Terms not explained here may be explained at each use in this specification.

[0020] The words "comprise," "include," "have," and variations thereof (e.g., "consisting of") are open-ended. The open-ended form may or may not include additional elements in addition to the required elements. The words "consisting of" are closed-ended. However, the closed form does not exclude additional elements that are normally associated with the technology or that are unrelated to the technology disclosed. The words "consisting essentially of..." are semi-closed. The semi-closed form allows for the addition of elements that do not substantially affect the basic and novel characteristics of the technology disclosed.

[0021] Expressions such as "may" and "may" are used in the permissive sense, meaning "to have the possibility," rather than in the obligatory sense, meaning "to have to."

[0022] Elements expressed in the singular form include the plural form unless otherwise specified. For example, "particle" includes not only "one particle" but also "multiple particles (particle group)" and "aggregate of particles (powder, powder)."

[0023] Numerical ranges such as "m to n%" include the upper and lower limits unless otherwise specified. That is, "m to n%" indicates a numerical range of "m% or more and n% or less". Also, "m% or more and n% or less" includes "more than m% and less than n%". "More than" and "less than" are represented by an inequality sign with an equal sign "≦". "More than" and "less than" are represented by an inequality sign without an equal sign "<". A numerical value arbitrarily selected from within the numerical range may be set as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value described in another part, table, figure, etc. of this specification.

[0024] All numerical values ​​are modified by the term "about". The term "about" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximations that may vary depending on the application of the disclosed technology. All numerical values ​​may be expressed in significant figures. Measurements may be average values ​​of multiple measurements unless otherwise specified. The number of measurements may be three or more, five or more, or ten or more. In general, the more measurements are made, the more reliable the average value is expected to be. Measurements may be rounded off based on the number of significant figures. Measurements may include errors associated with, for example, the detection limit of the measurement device.

[0025] The stoichiometric formulas are representative of the compounds. The compounds may have non-stoichiometric compositions. For example, "Al 2 O 3 " is not limited to a compound having a substance amount ratio (molar ratio) of "Al / O=2 / 3". 2 O 3 " indicates a compound containing Al and O in any composition ratio, unless otherwise specified. For example, the compound may be doped with a trace element. A part of Al and O may be substituted with another element.

[0026] The term "derivative" refers to a compound in which a part of a parent compound has been modified by at least one method selected from the group consisting of introduction of a substituent, substitution of an atom, oxidation, reduction, and other chemical reactions. The modification may be at one or more locations. The "substituent" may include at least one selected from the group consisting of, for example, an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an unsaturated cycloalkyl group, an aromatic group, a heterocyclic group, a halogen atom (F, Cl, Br, I, etc.), an OH group, an SH group, a CN group, an SCN group, an OCN group, a nitro group, an alkoxy group, an unsaturated alkoxy group, an amino group, an alkylamino group, a dialkylamino group, an aryloxy group, an acyl group, an alkoxycarbonyl group, an acyloxy group, an aryloxycarbonyl group, an acylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfonylamino group, a sulfamoyl group, a carbamoyl group, an alkylthio group, an arylthio group, a sulfonyl group, a sulfinyl group, a ureido group, a phosphoric acid amide group, a sulfo group, a carboxy group, a hydroxamic acid group, a sulfino group, a hydrazino group, an imino group, and a silyl group. These substituents may be further substituted. When there are two or more substituents, the substituents may be the same or different. A plurality of substituents may be bonded to each other to form a ring. The derivative of the polymer compound (resin material) may also be called a "modified product."

[0027] The "copolymer" includes at least one type selected from the group consisting of an unspecified type, a statistical type, a random type, an alternating type, a periodic type, a block type, and a graft type.

[0028] "SOC (State Of Charge)" indicates the percentage of the battery's charge capacity at that point in time relative to the battery's fully charged capacity.

[0029] The term "lithium secondary battery" refers to a battery in which the negative electrode reaction includes a dissolution and precipitation reaction of lithium metal. For example, the dissolution and precipitation reaction of lithium metal may account for 1 to 100%, 25 to 100%, 50 to 100%, or 75 to 100% of the negative electrode capacity. The negative electrode capacity indicates a reversible capacity. For example, lithium metal may be precipitated on the negative electrode at an SOC of 1 to 100%, 1 to 75%, 1 to 50%, or 1 to 25%. At an SOC of 0% (at full discharge), the lithium metal may be entirely dissolved in the electrolyte. At an SOC of 0%, a part of the lithium metal may remain on the negative electrode.

[0030] In addition, the precipitation of lithium metal in a lithium ion secondary battery can usually result in irreversible capacity. The precipitation of lithium metal in a lithium ion secondary battery is, for example, an unintended reaction. The precipitation of lithium metal in a lithium ion secondary battery can occur, for example, during abnormality or misuse.

[0031] In an "anode-free battery", lithium metal is not present in the negative electrode before the first charge (after assembly, before the first charge). The anode-free battery is assembled in a state in which the negative electrode does not contain lithium metal (negative electrode active material). In this disclosure, the lithium secondary battery assembled in this manner before the first charge is also referred to as a "lithium secondary battery precursor". During the first charge, lithium is supplied from the positive electrode to the negative electrode, and lithium metal is precipitated on the negative electrode for the first time. In an anode-free battery, the lithium metal may be completely dissolved during full discharge.

[0032] <Lithium secondary battery> 1 is a conceptual diagram showing a lithium secondary battery in this embodiment. A battery 100 includes a power generating element 50 and an electrolyte (not shown).

[0033] <Exterior body> The battery 100 may include an exterior body (not shown). The exterior body may house the power generating element 50 and an electrolyte. The exterior body may have any shape. The exterior body may be, for example, a metal case or a pouch made of a metal foil laminated film. The case may have any shape. The case may be, for example, cylindrical, rectangular, flat, coin-shaped, or the like. The exterior body may include, for example, Al, or the like. The exterior body may house, for example, one power generating element 50, or may house a plurality of power generating elements 50. The plurality of power generating elements 50 may form, for example, a series circuit or a parallel circuit. In the exterior body, the plurality of power generating elements 50 may be stacked in the thickness direction of the battery 100.

[0034] <Power generation elements> The power generating element 50 includes a positive electrode 10, a negative electrode 20, and a separator 30. The separator 30 is disposed between the positive electrode 10 and the negative electrode 20. The power generating element 50 may have any shape. The power generating element 50 may have a bipolar structure or a monopolar structure. The power generating element 50 may be, for example, a laminated type. For example, the power generating element 50 may be formed by alternately laminating the positive electrode 10 and the negative electrode 20 while sandwiching the separator 30 between them. For example, the strip-shaped separator 30 may be zigzag-folded, and the positive electrode 10 and the negative electrode 20 may be alternately disposed each time the separator 30 is folded. The power generating element 50 may be, for example, a wound type. For example, the positive electrode 10, the negative electrode 20, and the separator 30 may all be strip-shaped. For example, the positive electrode 10, the separator 30, and the negative electrode 20 may be laminated in this order to form a laminate. The laminate may be spirally wound to form the power generating element 50. The wound type power generating element 50 may be formed into a flat shape after winding.

[0035] <Negative electrode> Negative electrode 20 includes a current collector 21. At an SOC greater than 0%, negative electrode 20 further includes a Li metal layer 23 on current collector 21. As the SOC increases or decreases, the thickness of Li metal layer 23 also increases or decreases. Li metal layer 23 may be composed of a plurality of precipitates, or may be composed of a continuous, integrated precipitate.

[0036] The current collector 21 has electrical conductivity. The current collector 21 can function as a current collector, and examples of the current collector include foil and film. The current collector 21 may have a thickness of 10 to 20 μm, for example, 12 to 18 μm. The material of the current collector 21 may be a conductive material such as a metal or an alloy, other than lithium metal and lithium alloy. The conductive material is preferably a material that does not react with lithium. Such a conductive material may include at least one selected from the group consisting of copper (Cu), nickel (Ni), iron (Fe), zinc (Zn), lead (Pb), silver (Ag), and gold (Au). Examples of the alloy include copper alloy and stainless steel (SUS). The current collector 21 is, for example, a copper foil or a copper alloy foil.

[0037] The current collector 21 has a plurality of through holes. If the diameter of each through hole on the surface is a (mm), the center-to-center distance between the closest through hole and the diameter a (mm) is b (mm), and the average value of the diameter a (mm) is A (mm), and the average value of the center-to-center distance b (mm) is B (mm), then the following formulas (1) and (2): 1.50≦B / A≦3.0 (1) 0.05≦A≦0.18 (2) The above average value is the arithmetic average.

[0038] The arrangement pattern of the multiple through holes is not limited as long as it satisfies the above formula (1) and formula (2). The surface shape of the multiple through holes is not limited, and may be, for example, a circle, an ellipse, or a rectangle. The diameter of the through hole is the diameter of the circle when the shape of the through hole on the surface is a circle, and is the diameter of the smallest circle that encompasses the shape of the surface when the shape of the through hole is other than a circle. In addition, the center of the through hole is the center of the circle when the shape of the through hole on the surface is a circle, and is the center of the smallest circle that encompasses the shape of the surface when the shape of the through hole is other than a circle. The diameter a (mm) and center-to-center distance b (mm) of the through hole can be obtained from an image taken by SEM.

[0039] The current collector 21 is not limited as long as the arrangement pattern of the plurality of through holes in the target region satisfies the above formula (1) and formula (2). The target region may be the entire region of the surface of the current collector 21 or a part of the region.

[0040] The arrangement pattern of the multiple through holes can be, for example, represented by formula (1a) and formula (2a): 1.55≦B / A≦3.0 (1a) 0.08≦A≦0.14 (2a) The above relationship may be satisfied.

[0041] A negative electrode mixture layer may be formed on the surface of the current collector 21. The negative electrode mixture layer is formed, for example, by applying a paste containing a negative electrode active material such as a carbon material such as graphite or a Si material to at least a part of the surface of the negative electrode current collector. In addition, a metal coat may be applied to the surface of the current collector 21. The metal coat may contain at least one selected from the group consisting of magnesium (Mg), aluminum (Al), zinc (Zn), silver (Ag), gold (Au), platinum (Pt), and tin (Sn).

[0042] FIG. 2 is a conceptual diagram showing an example of a current collector in this embodiment. FIG. 2 is a schematic diagram showing the top surface (one surface) of the current collector 21. The current collector 21 has a plurality of through holes 211. In the arrangement pattern shown in FIG. 2, the through holes 211 have six closest through holes 211 other than the through holes 211 arranged on the outermost periphery. The through holes 211 have a circular shape on the top surface. The plurality of through holes 211 are arranged so that each has a constant diameter a1 (mm) and a center-to-center distance between the through holes 211 and the closest other through holes 211 is constant b1 (mm). In the arrangement pattern shown in FIG. 2, the average diameter A (mm) of the through holes 211 is a1 (mm), and the average center-to-center distance B (mm) is b1 (mm).

[0043] FIG. 3 is a conceptual diagram showing an example of the current collector in this embodiment different from FIG. 2. FIG. 3 is a schematic diagram showing the top surface (one surface) of the current collector 21. The current collector 21 has a plurality of through holes 212. In the arrangement pattern shown in FIG. 3, the through holes 212 have four closest through holes 212 other than the through holes 212 arranged on the outermost periphery. The through holes 212 have a circular shape on the top surface. The plurality of through holes 212 are arranged so that each has a constant diameter a2 (mm) and is arranged such that the center-to-center distance between each of the through holes 212 and the closest other through holes 212 is a constant b2 (mm). In the arrangement pattern shown in FIG. 3, the average diameter A (mm) of the through holes 212 is a2 (mm), and the average center-to-center distance B (mm) is b2 (mm).

[0044] The current collector 21 in this embodiment has an aperture ratio on one surface of, for example, 5.0 to 35.0%, or may be 6.0 to 32.0%, or may be 7.0 to 30.0%. The aperture ratio on the surface means the ratio of the total area of ​​the surface of a plurality of through holes to the area occupied by one surface of the current collector 21. For example, in the example shown in Fig. 2 and Fig. 3, it means the ratio of the total area of ​​the holes on the surface of the through holes 211 and 212 formed in the current collector 21 to the area occupied by the upper surface of the current collector 21.

[0045] In this embodiment, the current collector 21 is 2 The exposed surface area of ​​the permeable surface is, for example, 0.86 to 0.99 cm 2 0.87~0.98cm 2 The exposed area here means the area obtained by subtracting the total area of ​​the surfaces of the through holes from the area occupied by one surface of the current collector 21, and adding the area of ​​the inner walls of the through holes, and the value obtained by dividing the exposed area by the surface area of ​​the current collector 21 is the area per 1 cm of the surface. 2 The exposed surface here refers to a surface that is intended to become an interface with the Li metal layer 23 when the Li metal layer 23 is formed, and includes the surface of the current collector 21 that faces the positive electrode 30 via the separator 30 (excluding the surface of the through hole) and the inner wall of the through hole.

[0046] In the current collector 21 of this embodiment, the processing method for forming the plurality of through holes is not limited, and they can be formed by electric discharge processing, cutting processing, laser processing, or the like.

[0047] FIG. 4 is a conceptual diagram showing the charge / discharge process near the negative electrode of the lithium secondary battery in this embodiment. FIG. 4(a) shows an initial state. When the lithium secondary battery is charged from the initial state, lithium metal starts to precipitate from a plurality of starting points of the current collector 21 to form precipitates 23a, as shown in FIG. 4(b). The current collector 21 has a plurality of through holes 213, and the inner walls of the plurality of through holes 213 also become starting points for the formation of precipitates 23a. When charging is continued in this state, as shown in FIG. 4(c), the precipitates 23a precipitated and grown from different starting points are integrated to form a Li metal layer 23. Next, when the lithium secondary battery is discharged, the metallic lithium layer 23 is dissolved. The Li metal layer 23 may be formed by integrating precipitates, or may be composed of a plurality of precipitates.

[0048] <Positive electrode> The positive electrode 10 may be, for example, in the form of a sheet. The positive electrode 10 may include, for example, a positive electrode substrate 11 and a positive electrode active material layer 12. The positive electrode substrate 11 has electrical conductivity. The positive electrode substrate 11 can function as a current collector. The positive electrode substrate 11 supports the positive electrode active material layer 12. The positive electrode substrate 11 may be, for example, in the form of a sheet. The positive electrode substrate 11 may have a thickness of, for example, 5 to 50 μm. The positive electrode substrate 11 may include, for example, a metal foil. The positive electrode substrate 11 may include, for example, at least one selected from the group consisting of aluminum (Al), manganese (Mn), titanium (Ti), iron (Fe), and chromium (Cr). The positive electrode substrate 11 may include, for example, an Al foil, an Al alloy foil, a Ti foil, a SUS foil, or the like.

[0049] An intermediate layer (not shown) may be formed between the positive electrode substrate 11 and the positive electrode active material layer 12. The intermediate layer does not contain a positive electrode active material. The intermediate layer may have a thickness of, for example, 0.1 to 5 μm. The intermediate layer may contain, for example, a conductive material, an insulating material, a binder, etc. The conductive material and the binder will be described later. The insulating material may contain, for example, alumina, boehmite, aluminum hydroxide, etc.

[0050] The positive electrode active material layer 12 is disposed on the surface of the positive electrode substrate 11. The positive electrode active material layer 12 may be disposed on only one surface of the positive electrode substrate 11. The positive electrode active material layer 12 may be disposed on both the front and back surfaces of the positive electrode substrate 11. The positive electrode active material layer 12 may have a thickness of, for example, 10 to 1000 μm, 50 to 500 μm, or 100 to 300 μm. The positive electrode active material layer 12 contains a positive electrode active material. The positive electrode active material layer 12 may further contain, for example, a conductive material and a binder.

[0051] The conductive material can form an electronic conduction path in the positive electrode active material layer 12. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material. The conductive material may contain any component. The conductive material may contain, for example, at least one selected from the group consisting of graphite, acetylene black (AB), Ketjen Black (registered trademark), vapor grown carbon fiber (VGCF), carbon nanotube (CNT), and graphene flake (GF).

[0052] The binder can fix the positive electrode active material layer 12 to the positive electrode substrate 11. The amount of the binder may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material. The binder may contain any component. For example, the binder may contain at least one selected from the group consisting of PVDF, PVDF-HFP, PTFE, CMC, PAA, PVA, PVP, polyoxyethylene alkyl ether, and derivatives thereof.

[0053] The positive electrode active material layer 12 may further contain, for example, an inorganic filler, an organic filler, a solid electrolyte, a surface modifier, a lubricant, a flame retardant, a protective agent, a flux, a coupling agent, an adsorbent, etc. The positive electrode active material layer 12 may further contain, for example, polyoxyethylene allyl phenyl ether phosphate, zeolite, a silane coupling agent, MoS 2 , WO 3 etc. may be included.

[0054] The positive electrode active material may be, for example, in the form of particles. The positive electrode active material may contain any component. The positive electrode active material may contain, for example, a transition metal oxide, a polyanion compound, etc. The composition within one particle (positive electrode active material) may be uniform or non-uniform. For example, the composition may be graded from the surface to the center of the particle. The composition may change continuously or discontinuously (in steps).

[0055] The transition metal oxide may have any crystal structure. The transition metal oxide may include, for example, a crystal structure belonging to the space group R-3m. For example, a compound represented by the general formula "LiMO 2 " may have a crystal structure belonging to the space group R-3m. The transition metal oxide may be represented, for example, by the following formula (3-1). Li 1-a Ni x M 1-x O 2 …(3-1) In the above formula (3-1), M may include, for example, at least one selected from the group consisting of Co, Mn, and Al. For example, the relationship of -0.5 ≦ a ≦ 0.5, 0 < x ≦ 1 may be satisfied. For example, the relationship of -0.4 ≦ a ≦ 0.4, -0.3 ≦ a ≦ 0.3, -0.2 ≦ a ≦ 0.2, or -0.1 ≦ a ≦ 0.1 may be satisfied. For example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x ≦ 1 may be satisfied.

[0056] The transition metal oxide may include, for example, at least one selected from the group consisting of LiCoO 2 , LiMnO 2 , LiNi 0.9 Co 0.1 O 2 , LiNi 0.9 Mn 0.1 O 2 , and LiNiO 2 .

[0057] The transition metal oxide may be represented, for example, by the following formula (3-2). The compound represented by the following formula (3-2) may also be referred to as "NCM". Li 1-a Ni x Co y Mn z O 2 …(3-2) In the above formula (3-2), for example, the relationships of -0.5≦a≦0.5, 0<x<1, 0<y<1, 0<z<1, and x + y + z = 1 may be satisfied. For example, the relationship of 0<x≦0.1, 0.1≦x≦0.2, 0.2≦x≦0.3, 0.3≦x≦0.4, 0.4≦x≦0.5, 0.5≦x≦0.6, 0.6≦x≦0.7, 0.7≦x≦0.8, 0.8≦x≦0.9, or 0.9≦x<1 may be satisfied. For example, the relationship of 0<y≦0.1, 0.1≦y≦0.2, 0.2≦y≦0.3, 0.3≦y≦0.4, 0.4≦y≦0.5, 0.5≦y≦0.6, 0.6≦y≦0.7, 0.7≦y≦0.8, 0.8≦y≦0.9, or 0.9≦y<1 may be satisfied. For example, the relationship of 0<z≦0.1, 0.1≦z≦0.2, 0.2≦z≦0.3, 0.3≦z≦0.4, 0.4≦z≦0.5, 0.5≦z≦0.6, 0.6≦z≦0.7, 0.7≦z≦0.8, 0.8≦z≦0.9, or 0.9≦z<1 may be satisfied.

[0058] NCM is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 、LiNi 0.4 Co 0.3 Mn 0.3 O 2 、LiNi 0.3 Co 0.4 Mn 0.3 O 2 、LiNi 0.3 Co 0.3 Mn 0.4 O 2 、LiNi 0.5 Co 0.2 Mn 0.3 O 2 、LiNi 0.5 Co 0.3 Mn 0.2 O 2 、LiNi 0.5 Co 0.4 Mn 0.1 O 2 、LiNi 0.5 Co 0.1 Mn 0.4 O 2, LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.6 Co 0.3 Mn 0.1 O 2 , LiNi 0.6 Co 0.1 Mn 0.3 O 2 , LiNi 0.7 Co 0.1 Mn 0.2 O 2 , LiNi 0.7 Co 0.2 Mn 0.1 O 2 , LiNi 0.8 Co 0.1 Mn 0.1 O 2 , and may contain at least one selected from the group consisting of LiNi 0.9 Co 0.05 Mn 0.05 O 2 .

[0059] The transition metal oxide may be represented, for example, by the following formula (3-3). The compound represented by the following formula (3-3) may also be referred to as "NCA". Li 1-a Ni x Co y Al z O 2 …(3-3) In the above formula (3-3), for example, the relationship of -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 may be satisfied. For example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x < 1 may be satisfied. For example, the relationship of 0 < y ≤ 0.1, 0.1 ≤ y ≤ 0.2, 0.2 ≤ y ≤ 0.3, 0.3 ≤ y ≤ 0.4, 0.4 ≤ y ≤ 0.5, 0.5 ≤ y ≤ 0.6, 0.6 ≤ y ≤ 0.7, 0.7 ≤ y ≤ 0.8, 0.8 ≤ y ≤ 0.9, or 0.9 ≤ y < 1 may be satisfied. For example, the relationship of 0 < z ≤ 0.1, 0.1 ≤ z ≤ 0.2, 0.2 ≤ z ≤ 0.3, 0.3 ≤ z ≤ 0.4, 0.4 ≤ z ≤ 0.5, 0.5 ≤ z ≤ 0.6, 0.6 ≤ z ≤ 0.7, 0.7 ≤ z ≤ 0.8, 0.8 ≤ z ≤ 0.9, or 0.9 ≤ z < 1 may be satisfied.

[0060] NCA is, for example, LiNi 0.7 Co 0.1 Al 0.2 O 2 、LiNi 0.7 Co 0.2 Al 0.1 O 2 、LiNi 0.8 Co 0.1 Al 0.1 O 2 、LiNi 0.8 Co 0.17 Al 0.03 O 2 、LiNi 0.8 Co 0.15 Al 0.05 O 2 、and may contain at least one selected from the group consisting of LiNi 0.9 Co 0.05 Al 0.05 O 2

[0061] The positive electrode active material may contain, for example, two or more types of NCM or the like. The positive electrode active material may contain, for example, NCM(0.6 ≤ x) and NCM(x < 0.6). "NCM(0.6 ≤ x)" refers to a compound in which x (Ni ratio) is 0.6 or more in the above formula (2-2). NCM(0.6 ≤ x) may be referred to as, for example, "high nickel material". NCM(0.6 ≤ x) is, for example, LiNi 0.8 Co 0.1 Mn 0.1 O 2"NCM(x<0.6)" refers to a compound in which x (Ni ratio) is less than 0.6 in the above formula (2-2). NCM(x<0.6) is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 The mixing ratio (mass ratio) of NCM(0.6≦x) and NCM(x<0.6) may be, for example, "NCM(0.6≦x) / NCM(x<0.6)=9 / 1 to 1 / 9," "NCM(0.6≦x) / NCM(x<0.6)=9 / 1 to 4 / 6," or "NCM(0.6≦x) / NCM(x<0.6)=9 / 1 to 3 / 7."

[0062] The positive electrode active material may contain, for example, NCA and NCM. The mixing ratio (mass ratio) of NCA and NCM may be, for example, "NCA / NCM=9 / 1 to 1 / 9", "NCA / NCM=9 / 1 to 4 / 6", or "NCA / NCM=9 / 1 to 3 / 7". The Ni ratios of NCA and NCM may be the same or different. The Ni ratio of NCA may be higher than the Ni ratio of NCM. The Ni ratio of NCA may be lower than the Ni ratio of NCM.

[0063] The transition metal oxide may have, for example, a crystal structure belonging to the space group C2 / m. The transition metal oxide may be represented by, for example, the following formula (3-4). Li 2 MO 3 …(3-4) In the above formula (3-4), M may include, for example, at least one selected from the group consisting of Ni, Co, Mn, and Fe.

[0064] The positive electrode active material is, for example, LiMO 2 (space group R-3m) and Li 2 MO 3 (space group C2 / m). The positive electrode active material may include, for example, LiMO 2 and Li 2 MO 3 Solid solution with (Li 2 MO 3 -LiMO2 ) etc.

[0065] The transition metal oxide may have, for example, a crystal structure belonging to the space group Fd-3m. The transition metal oxide may be represented by, for example, the following formula (3-5). LiMn 2-x M x O 4 …(3-5) In the above formula (2-5), M may include, for example, at least one selected from the group consisting of Ni, Fe, and Zn. For example, the relationship 0≦x≦2 may be satisfied.

[0066] LiM 2 O 4 (Space group Fd-3m) is, for example, LiMn 2 O 4 , and LiMn 1.5 Ni 0.5 O 4 The positive electrode active material may contain at least one selected from the group consisting of LiMO 2 (space group R-3m) and LiM 2 O 4 (space group Fd-3m) may be included. 2 (space group R-3m) and LiM 2 O 4 The mixing ratio (mass ratio) with (space group Fd-3m) is, for example, "LiMO 2 / LiM 2 O 4 =9 / 1~9 / 1", "LiMO 2 / LiM 2 O 4 =9 / 1~5 / 5" or "LiMO 2 / LiM 2 O 4 =9 / 1~7 / 3".

[0067] The polyanionic compound may be, for example, a phosphate (e.g., LiFePO 4 The polyanion compound may contain, for example, any of the following formulas (3-6) to (3-9): LiMPO 4 …(3-6) Li 2-x MPO 4 F …(3-7) Li 2 MSiO 4 …(3-8) LiMBO 3 …(3-9) In the above formulas (3-6) to (3-9), M may, for example, include at least one selected from the group consisting of Fe, Mn, and Co. In the above formula (3-7), for example, the relationship 0≦x≦2 may be satisfied.

[0068] The positive electrode active material is, for example, LiMO 2 (space group R-3m) and a mixture of polyanionic compounds. 2 The mixing ratio (mass ratio) of the space group R-3m and the polyanion compound is, for example, 2 / Polyanion compound = 9 / 1 to 9 / 1", "LiMO 2 / Polyanion compound = 9 / 1 to 5 / 5" or "LiMO 2 / polyanion compound=9 / 1 to 7 / 3".

[0069] A dopant may be added to the positive electrode active material. The dopant may be diffused throughout the particle or distributed locally. For example, the dopant may be unevenly distributed on the particle surface. The dopant may be a substitutional solid solution atom or an interstitial solid solution atom. The amount of dopant added (molar fraction relative to the entire positive electrode active material) may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1%. One type of dopant may be added, or two or more types of dopants may be added. Two or more types of dopants may form a complex.

[0070] The dopant may include at least one selected from the group consisting of, for example, B, C, N, halogens, Si, Na, Mg, Al, Mn, Co, Cr, Sc, Ti, V, Cu, Zn, Ga, Ge, Se, Sr, Y, Zr, Nb, Mo, In, Pb, Bi, Sb, Sn, W, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and actinides.

[0071] For example, the set of "Zr, Mg, W, Sm", the set of "Ti, Mn, Nb, Si, Mo", or the set of "Er, Mg" may be added to the NCA. For example, Ti may be added to the NCM. For example, the set of "Zr, W", the set of "Si, W", or the set of "Zr, W, Al, Ti, Co" may be added to the NCM.

[0072] The positive electrode 10 may include a composite particle. The composite particle includes a core particle and a shell layer. The core particle includes a positive electrode active material. The shell layer covers at least a part of the surface of the core particle. The shell layer may have a thickness of, for example, 1 to 3000 nm, 5 to 2000 nm, 10 to 1000 nm, 10 to 100 nm, or 10 to 50 nm. The thickness of the shell layer can be measured, for example, in an SEM image of a particle cross section. That is, a sample is prepared by embedding the composite particle in a resin material. The sample is subjected to a cross-section processing by an ion milling device. For example, an ion milling device "Product name: ArBlade (registered trademark) 5000" (or an equivalent product) manufactured by Hitachi High-Technologies Corporation may be used. The cross section of the sample is observed by SEM. For example, an SEM device "Product name: SU8030" (or an equivalent product) manufactured by Hitachi High-Technologies Corporation may be used. The shell layer thickness is measured in 20 fields for each of 10 composite particles, and the arithmetic mean of the thicknesses of 200 points in total is taken.

[0073] The proportion of the surface of the core particle that is covered with the shell layer is also referred to as the "coverage." The coverage may be, for example, 1% or more, 10% or more, 30% or more, 50% or more, or 70% or more. The coverage may be, for example, 100% or less, 90% or less, or 80% or less.

[0074] The coverage can be measured, for example, by XPS (X-ray Photoelectron Spectroscopy). For example, an XPS device manufactured by ULVAC-PHI, Inc., product name: PHI X-tool (or equivalent) may be used. A sample (powder) is set in the XPS. Narrow scan analysis is performed. The measurement data is processed by analysis software. For example, analysis software manufactured by ULVAC-PHI, Inc., product name: MulTiPak (or equivalent) may be used. The measurement data is analyzed to detect multiple elements. The ratio of each detected element is calculated from the area of ​​each peak. The coverage is calculated by the following formula (2-10). θ={I 1 / (I 0 +I 1 )}×100 …(3-10) θ: Coverage rate [%] I 0 : Ratio of elements originating from core particles I 1 : Ratio of elements originating from the shell layer For example, if the core particle contains NCM, I 0 indicates the total element ratio of "Ni, Co, Mn". For example, when the core particle contains NCA, I 0 indicates the total element ratio of "Ni, Co, Al". For example, if the shell layer contains P and B, I 1 indicates the total element ratio of "P, B".

[0075] The shell layer may contain any component. For example, the shell layer may contain a simple substance, an organic substance, an inorganic acid salt, an organic acid salt, a hydroxide, an oxide, a carbide, a nitride, a sulfide, a halide, or the like. For example, the shell layer may contain B, Al, W, Zr, Ti, Co, F, a lithium compound (e.g., Li 2 CO3 , LiHCO 3 , LiOH, Li 2 O, etc.), tungsten oxide (e.g. WO 3 etc.), titanium oxide (e.g. TiO 2 etc.), zirconium oxide (e.g. ZrO 2 ), boron oxide, boron phosphate (e.g. BPO 4 etc.), aluminum oxide (e.g. Al 2 O 3 etc.), boehmite, aluminum hydroxide, phosphates [e.g. Li 3 PO 4、 (NH 4 ) 3 PO 4 , AlPO 4 〕, borates (e.g., Li 2 B 4 O 7 , LiBO 3 etc.), polyacrylates (Li salt, Na salt, NH 4 salts, etc.), acetate salts (e.g., Li salts, etc.), CMC (Na salts, Li salts, NH 4 Salt, etc.), LiNbO 3、 Li 2 TiO 3 , and Li-containing halides (e.g., LiAlCl 4 , LiTiAlF 6 , LiYBr 6 , LiYCl 6 The compound may contain at least one selected from the group consisting of:

[0076] The "hollow particles" and "solid particles" are secondary particles (aggregates of primary particles). In a cross-sectional image of a "hollow particle", the area ratio of the cavity in the center is 30% or more of the cross-sectional area of ​​the entire particle. The ratio of the cavity in a hollow particle may be, for example, 40% or more, 50% or more, or 60% or more. In a cross-sectional image of a "solid particle", the area ratio of the cavity in the center is less than 30% of the cross-sectional area of ​​the entire particle. The ratio of the cavity in a solid particle may be, for example, 20% or less, 10% or less, or 5% or less. The positive electrode active material may be hollow particles or solid particles. A mixture of hollow particles and solid particles may be used. The mixing ratio (mass ratio) of hollow particles to solid particles may be, for example, "hollow particles / solid particles=1 / 9 to 9 / 1," "hollow particles / solid particles=2 / 8 to 8 / 2," "hollow particles / solid particles=3 / 7 to 7 / 3," or "hollow particles / solid particles=4 / 6 to 6 / 4."

[0077] The positive electrode active material may have, for example, a unimodal particle size distribution (based on number). The positive electrode active material may have, for example, a multimodal particle size distribution. The positive electrode active material may have, for example, a bimodal particle size distribution. That is, the positive electrode active material may contain "large particles" and "small particles". When the particle size distribution is bimodal, the particle size corresponding to the peak top of the larger particle size is the particle size of the large particles (d L The particle size corresponding to the peak top with the smaller particle size is considered to be the particle size of the small particles (d S ) is considered as the particle size ratio (d L / d S ) may be, for example, 2 to 10, 2 to 5, or 2 to 4. L may be, for example, 8 to 20 μm, or 8 to 15 μm. S may be, for example, 1 to 10 μm or 1 to 5 μm.

[0078] For example, the particle size distribution may be subjected to peak separation processing using waveform analysis software. L ) and the peak area due to small particles (S S ) is expressed as, for example, "S L / SS =1 / 9~9 / 1", "S L / S S =5 / 5~9 / 1" or "S L / S S =7 / 3~9 / 1".

[0079] The particle size distribution based on the number is measured by a microscopy method. A plurality of cross-sectional samples are taken from the positive electrode active material layer 12. The cross-sectional samples may include, for example, a cross section perpendicular to the surface of the positive electrode active material layer 12. For example, a cleaning process is performed on the observation surface by ion milling or the like. The cross-sectional samples are observed by SEM. The observation magnification is adjusted so that 10 to 100 particles are contained within the observation field of view. The Feret diameters of all particles in the image are measured. The "Feret diameter" indicates the distance between the two most distant points on the contour line of a particle. By observing a plurality of cross-sectional samples, a total of 1000 or more Feret diameters are obtained. A particle size distribution based on the number is created from the 1000 or more Feret diameters.

[0080] A bimodal particle size distribution can be formed by mixing two kinds of particles. The two kinds of particles have different particle size distributions. For example, the two kinds of particles may have different D50s. For example, the large particles may have a D50 of 8 to 20 μm, or 8 to 15 μm. For example, the small particles may have a D50 of 1 to 10 μm, or 1 to 5 μm. The ratio of the D50 of the large particles to the D50 of the small particles may be, for example, 2 to 10, 2 to 5, or 2 to 4. The mixing ratio (mass ratio) of the large particles and the small particles may be, for example, "large particles / small particles=1 / 9 to 9 / 1", "large particles / small particles=5 / 5 to 9 / 1", or "large particles / small particles=7 / 3 to 9 / 1".

[0081] The large particles may have the same composition as the small particles, or may have different compositions. For example, the large particles may be NCA and the small particles may be NCM. For example, the large particles may be NCM (0.6≦x) and the small particles may be NCM (x<0.6).

[0082] <Electrolyte> The electrolyte is a liquid electrolyte. The electrolyte contains Li ions. The electrolyte may contain, for example, a solute and a solvent.

[0083] The concentration of the solute may be, for example, 0.5 to 1 mol / L, 1 to 1.5 mol / L, 1.5 to 2 mol / L, 2 to 2.5 mol / L, or 2.5 to 3 mol / L. The solute includes a supporting salt (Li salt). The solute may include, for example, an inorganic acid salt, an imide salt, an oxalato complex, a halide, or the like. The solute may include, for example, LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiSbF 6 , LiN(SO 2 F) 2 "Commonly known as LiFSI", LiN(SO 2 CF 3 ) 2 "Commonly known as: LiTFSI", LiB(C 2 O 4 ) 2 "Commonly known as: LiBOB", LiBF 2 (C 2 O 4 ) "Commonly known as LiDFOB", LiPF 2 (C 2 O 4 ) 2 "Commonly known as LiDFOP", LiPO 2 F 2 , FSO 3 It may contain at least one selected from the group consisting of Li, LiI, LiBr, and derivatives thereof.

[0084] The electrolyte may contain, for example, an ether-based solvent, which may include at least one selected from the group consisting of tetrahydrofuran (THF), 1,4-dioxane (DOX), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), ethylglyme, triglyme, tetraglyme, hydrofluoroether (HFE), and derivatives thereof.

[0085] The HFE may include at least one selected from the group consisting of, for example, a difluoromethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, a 2,2,3,3,3-pentafluoropropyl group, a 2,2,3,3-tetrafluoropropyl group, a 1,1,1,3,3,3-hexafluoroisopropyl group, a 1,1,2,3,3,3-hexafluoropropyl group, a 2,2,3,3,4,4,4-heptafluorobutyl group, a 2,2,3,3,4,4-hexafluorobutyl group, and a 2,2,3,3,4,4,5,5-octafluoropentyl group.

[0086] The HFE may include, for example, at least one selected from the group consisting of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, 2,2,3,3-tetrafluoropropyl 1,1,2,3,3,3-hexafluoropropyl ether, 2,2,3,3,4,4,5,5-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether, and derivatives thereof.

[0087] The electrolytic solution may contain, for example, a carbonate-based solvent (carbonate ester-based solvent). The solvent may contain, for example, a cyclic carbonate, a chain carbonate, a fluorinated carbonate, or the like. The solvent may contain, for example, at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (FEC), difluoroethylene carbonate, 4,4-difluoroethylene carbonate, trifluoroethylene carbonate, perfluoroethylene carbonate, fluoropropylene carbonate, difluoropropylene carbonate, and derivatives thereof.

[0088] The solvent may contain a cyclic carbonate (EC, PC, FEC, etc.) and a chain carbonate (EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate to the chain carbonate may be, for example, "cyclic carbonate / chain carbonate=1 / 9 to 4 / 6", "cyclic carbonate / chain carbonate=2 / 8 to 3 / 7", or "cyclic carbonate / chain carbonate=3 / 7 to 4 / 6".

[0089] The solvent may contain a cyclic carbonate (EC, PC, etc.) and a fluorinated cyclic carbonate (FEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate and the fluorinated cyclic carbonate may be, for example, "cyclic carbonate / fluorinated cyclic carbonate=99 / 1 to 90 / 10", "cyclic carbonate / fluorinated cyclic carbonate=9 / 1 to 1 / 9", "cyclic carbonate / fluorinated cyclic carbonate=9 / 1 to 7 / 3", or "cyclic carbonate / fluorinated cyclic carbonate=3 / 7 to 1 / 9".

[0090] The solvent may contain, for example, EC, FEC, EMC, DMC, and DEC. The volume ratio of each component may satisfy, for example, the relationship represented by the following formula (4-1). V EC +V FEC +V EMC +V DMC +V DEC =10 …(4-1) In the above formula (3-1), V EC , V FEC , V EMC , V DMC , V DEC indicates the volume ratio of EC, FEC, EMC, DMC, and DEC, respectively. For example, 1≦V EC ≦4, 0≦V FEC ≦3,V EC +V FEC ≦4, 0≦V EMC ≦9, 0≦V DMC ≦9, 0≦V DEC ≦9, 6≦V EMC +V DMC +V DEC≦9 The relationship may be satisfied.

[0091] In the above formula (4-1), For example, 1≦V EC ≦2 or 2≦V EC The relationship ≦3 may be satisfied. For example, 1≦V FEC ≦2 or 2≦V FEC The relationship ≦4 may be satisfied. For example, 3≦V EMC ≦4 or 6≦V EMC The relationship ≦8 may be satisfied. For example, 3≦V DMC ≦4 or 6≦V DMC The relationship ≦8 may be satisfied. For example, 3≦V DEC ≦4 or 6≦V DEC The relationship ≦8 may be satisfied.

[0092] The solvent may have a composition, for example, by volume, of "EC / EMC=3 / 7", "EC / DMC=3 / 7", "EC / FEC / DEC=1 / 2 / 7", "EC / DMC / EMC=3 / 4 / 3", "EC / DMC / EMC=3 / 3 / 4", "EC / FEC / DMC / EMC=2 / 1 / 4 / 3", "EC / FEC / DMC / EMC=1 / 2 / 4 / 3", "EC / FEC / DMC / EMC=2 / 1 / 3 / 4", "EC / FEC / DMC / EMC=1 / 2 / 3 / 4", or the like.

[0093] The electrolyte may contain any additive. The amount of additive (mass fraction relative to the total electrolyte) may be, for example, 0.01 to 5%, 0.05 to 3%, or 0.1 to 1%. The additive may include, for example, an SEI (Solid Electrolyte Interphase) formation promoter, an SEI formation inhibitor, a gas generating agent, an overcharge inhibitor, a flame retardant, an antioxidant, an electrode protector, a surfactant, and the like.

[0094] Examples of the additives include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3-propane sultone (PS), tert-amylbenzene, 1,4-di-tert-butylbenzene, biphenyl (BP), cyclohexylbenzene (CHB), ethylene sulfite (ES), propane sultone (PS), ethylene sulfate (DTD), γ-butyrolactone, phosphazene compounds, carboxylic acid esters (e.g., methyl formate (MF), methyl acetate (MA), methyl propionate (MP), diethyl malonate (DEM), etc.), fluorobenzenes (e.g., monofluorobenzene (FB), 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4,5-tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, etc.), fluorotoluenes (e.g., 2-fluorotoluene, 3-fluorotoluene, 4-fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,6-difluorotoluene, 3,4-difluorotoluene, octafluorotoluene, etc.), benzotrifluorides (e.g., benzotrifluoride, 2-fluorobenzotrifluoride, 3-fluorobenzotrifluoride, 4-fluorobenzotrifluoride, 2-methylbenzotrifluoride, 3-methylbenzotrifluoride, 4-methylbenzotrifluoride, etc.), fluoroxylenes (e.g., 3-fluoro-o-xylene, 4-fluoro-o-xylene, 2-fluoro-m-xylene, 5-fluoro-m-xylene, etc.), sulfur-containing heterocyclic compounds (e.g., benzothiazole, 2-methylbenzyl The solvent may contain at least one selected from the group consisting of anhydrides (e.g., benzothiazole, tetrathiafulvane, etc.), nitrile compounds (e.g., adiponitrile, succinonitrile, etc.), phosphates (e.g., trimethyl phosphate, triethyl phosphate, etc.), carboxylic acid anhydrides (e.g., acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride, etc.), alcohols (e.g., methanol, ethanol, n-propyl alcohol, ethylene glycol, diethylene glycol monomethyl ether, etc.), and derivatives thereof.

[0095] The components previously described as solutes and solvents may be used as additives (minor components). Additives include, for example, LiBF 4 , LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPO 2 F 2 , FSO 3 It may contain at least one selected from the group consisting of Li, LiI, LiBr, HFE, DOX, PC, FEC, and derivatives thereof.

[0096] The electrolyte may include an ionic liquid. The electrolyte may include at least one selected from the group consisting of a sulfonium salt, an ammonium salt, a pyridinium salt, a piperidinium salt, a pyrrolidinium salt, a morpholinium salt, a phosphonium salt, an imidazolium salt, and derivatives thereof.

[0097] The battery 100 may include a gel electrolyte. The gel electrolyte includes an electrolytic solution and a polymer material. The polymer material may form a polymer matrix. The polymer material may include at least one selected from the group consisting of, for example, PVDF, PVDF-HFP, PAN, PVDF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0098] <separator> The separator 30 has electrical insulation properties. The separator 30 may include, for example, at least one selected from the group consisting of a resin film, an inorganic particle layer, and an organic particle layer. The separator 30 may include, for example, a resin film and an inorganic particle layer.

[0099] The resin film is porous. The resin film may include, for example, a microporous film, a nonwoven fabric, etc. The resin film includes a resin skeleton. The resin skeleton may be continuous, for example, in a network form. Pores are formed in the gaps of the resin skeleton. The resin film can transmit an electrolytic solution. The resin film may have an average pore size of, for example, 1 μm or less. The resin film may have an average pore size of, for example, 0.01 to 1 μm, or 0.1 to 0.5 μm. The "average pore size" can be measured by mercury intrusion porosimetry. The resin film may have a pore size of, for example, 50 to 250 s / 100 cm. 3 The "Gurley value" may be measured by the Gurley test method.

[0100] The resin film may contain at least one selected from the group consisting of, for example, olefin resin, urethane resin, polyamide resin, cellulose resin, polyether resin, acrylic resin, and polyester resin. The resin film may contain at least one selected from the group consisting of, for example, polyethylene (PE), polypropylene (PP), polyamide (PA), polyamideimide (PAI), polyimide (PI), aromatic polyamide (aramid), polyphenylene ether (PPE), and derivatives thereof. The resin film may be formed by, for example, a stretching method, a phase separation method, or the like. The resin film may have a thickness of, for example, 5 to 50 μm, or 10 to 25 μm.

[0101] The resin film may have, for example, a single-layer structure. The resin film may be composed of, for example, a PE layer. The skeleton of the PE layer is formed of PE. The PE layer may have a shutdown function. The resin film may have, for example, a multi-layer structure. The resin film may include, for example, a PP layer and a PE layer. The skeleton of the PP layer is formed of PP. The resin film may have, for example, a three-layer structure. The resin film may be formed by laminating, for example, a PP layer, a PE layer, and a PP layer in this order. The thickness of the PE layer may be, for example, 5 to 20 μm. The thickness of the PP layer may be, for example, 3 to 10 μm.

[0102] An inorganic particle layer may be formed on the surface of the resin film. The inorganic particle layer may be formed on only one side of the resin film, or on both sides. The inorganic particle layer may be formed on the surface facing the positive electrode 10, or on the surface facing the negative electrode 20.

[0103] The inorganic particle layer is porous. The inorganic particle layer includes inorganic particles. The inorganic particles may also be called "inorganic filler". Pores are formed in the gaps between the inorganic particles. The inorganic particle layer may have a thickness of, for example, 0.5 to 10 μm, or 1 to 5 μm. The inorganic particles may include, for example, a heat-resistant material. The inorganic particle layer including a heat-resistant material is also called "HRL (Heat Resistance Layer)". The inorganic particles may include at least one selected from the group consisting of boehmite, alumina, zirconia, titania, magnesia, silica, and the like. The inorganic particles may have any shape. The inorganic particles may be, for example, spherical, rod-like, plate-like, fibrous, and the like. The inorganic particles may have a D50 of, for example, 0.1 to 10 μm, or 0.5 to 3 μm. The inorganic particle layer may further include a binder. The binder may contain at least one selected from the group consisting of, for example, acrylic resins, polyamide resins, fluorine resins, aromatic polyether resins, and liquid crystal polyester resins.

[0104] The separator 30 may include, for example, an organic particle layer. The separator 30 may include, for example, an organic particle layer instead of a resin film. The separator 30 may include, for example, an organic particle layer instead of an inorganic particle layer. The separator 30 may include both a resin film and an organic particle layer. The separator 30 may include both an inorganic particle layer and an organic particle layer. The separator 30 may include a resin film, an inorganic particle layer, and an organic particle layer.

[0105] The organic particle layer may have a thickness of, for example, 0.1 to 50 μm, 0.5 to 20 μm, 0.5 to 10 μm, or 1 to 5 μm. The organic particle layer includes organic particles. The organic particles may also be referred to as "organic filler". The organic particles may include a heat-resistant material. The organic particles may include at least one selected from the group consisting of, for example, PE, PP, PTFE, PI, PAI, PA, and aramid. The organic particles may be, for example, spherical, rod-like, plate-like, fibrous, or the like. The organic particles may have a D50 of, for example, 0.1 to 10 μm, or 0.5 to 3 μm.

[0106] Separator 30 may, for example, include a mixed layer that includes both inorganic and organic particles.

[0107] <Battery configuration example> FIG. 5 is a first configuration example. FIG. 6 is a second configuration example. FIG. 7 is a third configuration example. In the tables in each figure, when multiple types of materials are listed in a cell, the description includes each material alone and combinations thereof. For example, when materials "α, β, γ" are listed in a cell, the description indicates "at least one type selected from the group consisting of α, β, and γ."

[0108] In this embodiment, as long as the current collector 21 has a configuration having a plurality of through holes as shown in the above embodiment and the negative electrode 20 utilizes the dissolution and precipitation reaction of lithium metal, other configurations (such as the combination of the positive electrode, separator, and electrolyte) are arbitrary. For example, any element may be extracted from the first, second, and third configuration examples and combined in any combination.

[0109] <Battery manufacturing example> In this embodiment, as long as the current collector 21 has a configuration shown in the above embodiment having a plurality of through holes and the negative electrode 20 utilizes a dissolution and precipitation reaction of lithium metal, any method for manufacturing a lithium secondary battery may be used. For example, a manufacturing method including a step of preparing the current collector 21, a step of assembling a lithium secondary battery precursor including a positive electrode, a separator, a negative electrode, and an electrolyte, and a step of charging the lithium secondary battery precursor to precipitate lithium metal on the negative electrode may be used. The step of precipitating lithium metal allows the Li metal layer 23 to be formed. EXAMPLES

[0110] <Production of test batteries> Test batteries (anode-free batteries) according to No. 1 to No. 5 were manufactured according to the following procedure. Hereinafter, for example, "test battery according to No. 1" may be simply referred to as "No. 1".

[0111] No.1 NCM was mixed as an active material, PVdF as a binder, and a conductive additive, and the resulting mixture was transferred to a container and stirred (2000 rpm, 1 minute) with a THINKY masher 3 to 4 times. After that, N-methylpyrrolidone (NMP) was added while checking the viscosity, and the mixture was stirred until it became uniform (2000 rpm, 5 minutes). If necessary, additional NMP was added and stirred (2000 rpm, 2 minutes). In this way, a slurry was obtained.

[0112] An aluminum foil (thickness: 16 μm) was prepared as a positive electrode substrate. The slurry obtained above was applied onto the aluminum foil (thickness: 16 μm) using a doctor blade. Doctor blades with gaps of 350, 375, and 400 μm were used. The coating weight after the solvent was dried was taken as the basis weight, and the basis weight was about 23 mg / cm. 2 The density was then adjusted to 2.4 to 2.9 g / cc using a roll press. 2 ) or Lamicelle (approx. 27 cm 2 ) to prepare the positive electrode.

[0113] A resin film (thickness: 20 μm) was prepared as a separator. The resin film contained PP / PE.

[0114] Copper foil (thickness: 15 μm) was prepared as a negative electrode. The copper foil was coated with a metal without being processed to form through holes, and used as a current collector.

[0115] The positive electrode, the separator, and the negative electrode were laminated in this order to form a power generating element. The power generating element was housed in an exterior body. An electrolyte was injected into the exterior body. The composition of the electrolyte was as follows.

[0116] Electrolyte composition Solute: LiTFSI (1mol / L) Solvent: PC / FEC=7 / 3 (volume ratio)

[0117] After the electrolyte was injected, the exterior was sealed, and thus a test battery was produced.

[0118] No.2~5 Copper foil (thickness: 15 μm) was prepared as the negative electrode. A plurality of through holes were formed in the copper foil by laser processing in the arrangement pattern shown in FIG. 2, and this was used as a current collector. Table 1 in FIG. 8 shows the arrangement pattern of the plurality of through holes in the current collector, the measured values ​​for the shape of the through holes, and the values ​​calculated from the measured values ​​for the shape of the through holes. The measured values ​​for the shape of the through holes are the average value A (mm) of the diameter a (mm) and the average value B (mm) of the center-to-center distance b (mm). The measured values ​​shown in Table 1 in FIG. 8 were calculated by measuring an SEM image of one surface of the current collector. The values ​​calculated from the measured values ​​are the value of B / A, the opening ratio (%), and the area per 1 cm of the surface. 2 Exposed area per unit (cm 2 A test battery was fabricated similarly to No. 1, except that a copper foil having a plurality of through holes was used as the current collector.

[0119] <Evaluation> A cycle test was carried out under the following conditions: 1. Rest: 60 min 2.CCCV charging: (1 / 4)C (ending current (1 / 100)C) 3. Rest: 5 minutes 4.CC discharge: (1 / 4)C 3.0V 5. Rest: 5 min Number of cycles from 2. to 5. above: 20

[0120] The discharge capacity retention rate for each cycle was calculated by dividing the discharge capacity for each cycle by the discharge capacity for the first cycle, and is expressed as a percentage.

[0121] <Result> Table 1 (FIG. 8) shows the discharge capacity retention rate at the 20th cycle. FIG. 9 shows the number of cycles on the horizontal axis and the discharge capacity retention rate corresponding to the number of cycles on the vertical axis. It is considered that the higher the discharge capacity retention rate, the better the cycle durability. No. 2, No. 3, and No. 4 had improved cycle durability compared to No. 1 (no through holes) and No. 5 (multiple through holes not satisfying the condition of formula (1)). It can be seen from FIG. 8 and FIG. 9 that when B / A is in the range of 1.5 to 3.0, the discharge capacity retention rate tends to improve.

[0122] From the discharge capacity retention rate at the 20th cycle shown in Table 1 (FIG. 8), it can be seen that when the aperture ratio of the current collector is 5.0 to 35.0%, the discharge capacity retention rate at the 20th cycle tends to be improved. 2 The exposed surface area is 0.86~0.99cm 2 It can be seen that when the discharge capacity retention rate at the 20th cycle is 100%, the discharge capacity retention rate at the 20th cycle tends to be improved. [Explanation of symbols]

[0123] 11 positive electrode substrate, 12 positive electrode active material layer, 20 negative electrode, 21 current collector, 23 Li metal layer, 23a deposit, 30 separator, 50 power generating element, 100 lithium secondary battery, 211, 212, 213 through holes.

Claims

1. A lithium secondary battery comprising a positive electrode, a separator, a negative electrode, and an electrolyte, the battery utilizing a dissolution and precipitation reaction of lithium metal as a reaction at the negative electrode, The negative electrode includes a current collector, The current collector is The thickness is 10 to 20 μm, A plurality of through holes are provided. Assuming that each of the through holes has a diameter on the surface as a (mm), a center-to-center distance between the closest through hole and the diameter a (mm) is b (mm), and furthermore that the average value of the diameter a (mm) is A (mm), and the average value of the center-to-center distance b (mm) is B (mm), then Equation (1) and Equation (2): 1.50≦B / A≦3.0 (1) 0.05≦A≦0.18 (2) Satisfy the relationship Lithium secondary battery.

2. 2. The lithium secondary battery according to claim 1, wherein the current collector is made of copper or a copper alloy.

3. 3. The lithium secondary battery according to claim 1, wherein the surface of the current collector has an opening ratio of 5.0 to 35.0%.

4. The current collector has a surface area of ​​1 cm ２ The exposed surface area is 0.86 to 0.99 cm ２ 3. The lithium secondary battery according to claim 1 or 2,

5. The current collector is a copper foil or a copper alloy foil, the opening ratio of the surface is 5.0 to 35.0%, and the surface is ２ The exposed surface area is 0.86 to 0.99 cm ２ The lithium secondary battery according to claim 1 ,

6. A method for producing the lithium secondary battery according to claim 1, comprising the steps of: providing the current collector; assembling a lithium secondary battery precursor including the positive electrode, the separator, the negative electrode, and the electrolyte; and charging the lithium secondary battery precursor to deposit lithium metal on the negative electrode.

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