Lithium secondary battery

Abstract

The present disclosure relates to a lithium secondary battery. The lithium secondary battery includes a positive electrode, a separator, a negative electrode, and an electrolyte solution. The negative electrode includes a current collector. The current collector has a thickness of 10-20 [mu] m. The current collector has a plurality of through-holes. For each through hole, when the diameter of the surface is a (mm), the center-to-center distance from another through hole closest to the surface is b (mm), the average value of the diameters a (mm) is A (mm), and the average value of the center-to-center distance b (mm) is B (mm), the relationship of formula (1) and formula (2) is satisfied: 1.50 < = B / A < = 3.0 (1) 0.05 < = A < = 0.18 (2).

Description

Technical Field

[0001] The present disclosure relates to a lithium secondary battery. Background Art

[0002] Japanese Patent Application Publication No. 2019-160776 discloses that a plurality of protrusions are provided on each of the first surface and the second surface of a negative electrode current collector. Summary of the invention

[0003] As described in the above-mentioned literature, in a lithium secondary battery that utilizes the dissolution and precipitation reaction of lithium metal as the reaction of the negative electrode, lithium metal is precipitated from the electrolyte during charging. During discharge, lithium metal dissolves in 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.

[0004] An object of the present disclosure is to improve the cycle durability of a lithium secondary battery.

[0005] The following describes the structure and effects of the technology disclosed in the present invention. However, the mechanism of action in this specification includes assumptions. The mechanism of action does not limit the scope of the technology disclosed in the present invention.

[0006] 1. A lithium secondary battery comprises a positive electrode, a separator, a negative electrode and an electrolyte. A lithium secondary battery is a battery that utilizes the dissolution reaction of lithium metal as the reaction of the negative electrode. The negative electrode comprises a current collector. The thickness of the current collector is 10 to 20 μm. The current collector has a plurality of through holes. For each of the through holes, the diameter at the surface is set to a (mm), the center-to-center distance to the closest through hole is set to b (mm), and the average value of the diameter a (mm) is set to A (mm), and the average value of the center-to-center distance b (mm) is set to B (mm), and the relationship between equations (1) and (2) is satisfied:

[0007] 1.50≤B / A≤3.0 (1)

[0008] 0.05≤A≤0.18 (2).

[0009] In a lithium secondary battery that utilizes the dissolution and precipitation reaction of lithium metal as the reaction of the negative electrode, when charging, lithium metal sometimes precipitates from multiple starting points on the negative electrode to form multiple precipitates. Each precipitate causes the expansion of the negative electrode, which can be the reason for the reduction of the capacity retention rate. The so-called expansion of the negative electrode refers to the increase in the combined volume of the volume of the negative electrode and the volume of the precipitated lithium metal. In addition, as each precipitate grows larger, part or all of it is easy to fall off in the electrolyte. The detached lithium metal can become irreversible capacity. Due to the expansion of the negative electrode and the increase in the precipitates of lithium metal that fall off in the electrolyte, the capacity retention rate of the lithium secondary battery is reduced and the cycle durability is reduced.

[0010] For example, Patent Document 1 discloses that a plurality of protrusions are provided on the first surface and the second surface of the negative electrode current collector to control the precipitation of lithium metal. However, the processing of providing a plurality of protrusions on the first surface and the second surface of the negative electrode current collector is complicated. In addition, the plurality of protrusions are made of resin material, so the surface of the protrusions will not become the precipitation starting point of lithium metal. In the present disclosure, a current collector having a plurality of through holes is used to control the precipitation of lithium metal. The inner walls of the plurality of through holes become the precipitation starting point, and the processing of providing a plurality of through holes is simple.

[0011] In the present disclosure, the cycle durability of lithium secondary batteries can be improved. This can be achieved by having a plurality of through holes in the current collector and arranging the plurality of through holes in a manner satisfying the above-mentioned 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 wall of the plurality of through holes, and the number of starting points for precipitation is moderately increased. If the number of starting points for precipitation is moderately increased, the current density of each precipitate is reduced, and each precipitate precipitated from each starting point can be grown at a high density. Moreover, if the density of each precipitate is high, the shedding is suppressed. In addition, each precipitate grows at a high density and from a starting point that is moderately close, so that after the subsequent growth, the plurality of precipitates become continuous precipitates, the expansion of the negative electrode is also suppressed. It is inferred that the growth of the precipitate from the moderately close starting point satisfies the relationship between the above-mentioned formula (1) and formula (2) through a plurality of through holes, thereby being able to be achieved.

[0012] 2. The lithium secondary battery described in the above “1” may include the following configurations, for example: The current collector is copper foil or copper alloy foil.

[0013] 3. The lithium secondary battery described in the above “1” or “2” may include, for example, the following configuration: The surface opening ratio of the current collector is 5.0 to 35.0%.

[0014] When the surface opening ratio is 5.0% or more, the number of starting points for lithium metal precipitation is expected to increase, and the current density of the precipitate precipitated from each starting point is expected to decrease. In addition, when the surface opening ratio is 35.0% or less, lithium metal is expected to precipitate from starting points that are appropriately close.

[0015] 4. The lithium secondary battery described in any one of "1" to "3" above may include, for example, the following configuration. 2 The exposed area is 0.86~0.99cm 2 .

[0016] 5. The lithium secondary battery described in the above “1”, for example, the current collector is copper foil or copper alloy foil, the surface opening ratio is 5.0 to 35.0%, and the surface is per 1 cm 2 The exposed area is 0.86~0.99cm 2 .

[0017] 6. The method for manufacturing a lithium secondary battery described in the above “1”, for example, comprises: a process of preparing the collector; a process of assembling a lithium secondary battery precursor, which comprises the positive electrode, the separator, the negative electrode and the electrolyte; and a process of charging the lithium secondary battery precursor so that lithium metal is precipitated at the negative electrode.

[0018] The following describes 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 example") . However, the present embodiment and the present example do not limit the scope of the technology of the present disclosure. The present embodiment and the present example are illustrative in all aspects. The present embodiment and the present example are non-restrictive. The scope of the technology of the present disclosure includes all changes within the meaning and scope equivalent to the description of the claims. For example, it was originally intended to extract arbitrary structures from the present embodiment and the present example and to combine them arbitrarily.

[0019] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a conceptual diagram showing a lithium secondary battery in this embodiment.

[0021] Figure 2 This is a conceptual diagram showing an example of a current collector in this embodiment.

[0022] Figure 3 This is a conceptual diagram showing another example of the current collector in this embodiment.

[0023] Figure 4 This is a conceptual diagram showing the charge and discharge process near the current collector of the lithium secondary battery in this embodiment.

[0024] Figure 5 This is a first configuration example of the lithium secondary battery in this embodiment.

[0025] Figure 6 This is a second configuration example of the lithium secondary battery in this embodiment.

[0026] Figure 7 This is a third configuration example of the lithium secondary battery in this embodiment.

[0027] Figure 8 Table 1 shows the arrangement pattern of the through holes of the current collector and the evaluation results.

[0028] Fig. 9 It is a graph which shows the cycle discharge capacity maintenance rate of No.1-5. DETAILED DESCRIPTION

[0029] <Explanation of terms>

[0030] The terms used in this specification are explained below. Terms that are not explained here will be explained each time they are used in this specification.

[0031] The description of "includes", "comprising", "having" and their variations (such as "consisting of...", etc.) is an open form. In addition to the necessary elements, the open form may or may not further include additional elements. The description of "consisting of..." is a closed form. However, even in a closed form, usually incidental impurities and additional elements unrelated to the technology disclosed in this disclosure are not excluded. The description of "essentially consisting of..." is a semi-closed form. In the semi-closed form, it is allowed to add elements that have basically no effect on the basic and novel characteristics of the technology disclosed in this disclosure.

[0032] Expressions such as “may” and “could” are not used in an obligatory sense, such as “must have”, but in a permissive sense, such as “having the possibility of…”.

[0033] Elements expressed in the singular form also include the plural form unless otherwise specified. For example, "particle" includes not only "one particle" but also "a plurality of particles (a group of particles)" and "an aggregate of particles (powder, powder)".

[0034] Unless otherwise specified, numerical ranges such as "m to n%" include upper limits and lower limits. That is, "m to n%" represents a numerical range of "above m% and below n%. In addition, "above m% and below n%" includes "greater than m% and less than n%. "Above" and "below" are represented by an inequality sign "≤" with an equal sign. "Greater than" and "less than" are represented by an inequality sign "<" without an equal sign. A numerical value arbitrarily selected from the numerical range can be used as a new upper limit or lower limit. For example, a new numerical range can be set by arbitrarily combining a numerical value within the numerical range with a numerical value recorded in other parts, tables, figures, etc. in this specification.

[0035] 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 approximate values ​​that may vary according to the utilization form of the disclosed technology. All numerical values ​​may be represented by significant figures. Unless otherwise specified, the measured value may be an average value from multiple measurements. The number of measurements may be more than 3 times, more than 5 times, or more than 10 times. In general, the more measurements are made, the higher the reliability of the average value is expected to be. The measured value may be rounded off based on the number of significant figures. The measured value may include errors such as those associated with the detection limit of the measuring device.

[0036] Stoichiometric composition formulas represent representative examples of compounds. Compounds may have non-stoichiometric compositions. For example, "Al 2 O 3 " is not limited to compounds having an amount ratio (molar ratio) of "Al / O = 2 / 3". 2 O 3 " " refers to a compound containing Al and O in an arbitrary composition ratio unless otherwise specified. For example, the compound may be doped with a trace element. A portion of Al and O may be replaced by another element.

[0037] "Derivative" means a compound obtained by changing a part of a compound that becomes a parent body by at least one selected from the introduction of a substituent, replacement of atoms, oxidation, reduction and other chemical reactions. The change site may be one or more. "Substituent" may include, for example, at least one selected from the following: alkyl, alkenyl, alkynyl, cycloalkyl, unsaturated cycloalkyl, aromatic group, heterocyclic group, halogen atom (F, Cl, Br, I, etc.), OH group, SH group, CN group, SCN group, OCN group, nitro group, alkoxy group, unsaturated alkoxy group, amino group, alkylamino, dialkylamino, aryloxy group, acyl group, alkoxycarbonyl group, acyloxy group, aryloxycarbonyl group, acylamino, alkoxycarbonylamino, aryloxycarbonylamino, sulfonylamino, sulfamoyl, carbamoyl, alkylthio, arylthio, sulfonyl, sulfinyl, urea group, phosphoramido, sulfo, carboxyl, hydroxamic acid group, sulfinyl, hydrazine group, imino, and silyl group. These substituents may be further substituted. When there are two or more substituents, the substituents may be the same or different. Multiple substituents may be bonded to each other to form a ring. It should be noted that the derivative of the polymer compound (resin material) may also be referred to as a "modified body".

[0038] The "copolymer" includes at least one 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.

[0039] “SOC (State Of Charge)” indicates the percentage of the charge capacity of the battery at that moment relative to the full charge capacity of the battery.

[0040] "Lithium secondary battery" refers to a battery in which the negative electrode reaction includes the dissolution and precipitation reaction of lithium metal. For example, the dissolution and precipitation reaction of lithium metal may account for 1-100%, 25-100%, 50-100%, or 75-100% of the negative electrode capacity. The negative electrode capacity represents the reversible capacity. For example, at an SOC of 1-100%, 1-75%, 1-50%, or 1-25%, lithium metal may be precipitated at the negative electrode. At an SOC of 0% (when fully discharged), the lithium metal may be completely dissolved in the electrolyte. At an SOC of 0%, a portion of the lithium metal may remain at the negative electrode.

[0041] It should be noted that, generally, the deposition of lithium metal in a lithium ion secondary battery may become irreversible capacity. The deposition of lithium metal in a lithium ion secondary battery is, for example, an unintentional reaction. The deposition of lithium metal in a lithium ion secondary battery may occur, for example, in abnormal conditions or when used improperly.

[0042] In an "anode-free battery", there is no lithium metal at the negative electrode before the initial charge (after assembly and before the initial charge). The anode-free battery is assembled in a state where the negative electrode does not contain lithium metal (negative electrode active material). The lithium secondary battery assembled in this way before the initial charge is also referred to as a "lithium secondary battery precursor" in the present disclosure. During the initial charge, lithium metal is first precipitated at the negative electrode by supplying lithium from the positive electrode to the negative electrode. In an anode-free battery, all the lithium metal can be dissolved when fully discharged.

[0043] <Lithium secondary battery>

[0044] Figure 1 This is a conceptual diagram showing a lithium secondary battery in this embodiment. The battery 100 includes a power generation element 50 and an electrolyte solution (not shown).

[0045] <Exterior body>

[0046] The battery 100 may include an outer casing (not shown). The outer casing may contain a power generation element 50 and an electrolyte. The outer casing may have any form. The outer casing may be, for example, a metal shell, or a bag made of a metal foil laminate film. The shell may have any shape. The shell may be, for example, cylindrical, square, flat, coin-shaped, etc. The outer casing may contain, for example, Al, etc. The outer casing may contain, for example, one power generation element 50, or a plurality of power generation elements 50. The plurality of power generation elements 50 may form, for example, a series circuit or a parallel circuit. In the outer casing, a plurality of power generation elements 50 may be stacked in the thickness direction of the battery 100.

[0047] <Power generation element>

[0048] The power generation 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 generation element 50 can have any form. The power generation element 50 can be a bipolar structure or a monopolar structure. For example, the power generation element 50 can be a stacked type. For example, by sandwiching the separator 30 between the positive electrode 10 and the negative electrode 20 and alternately stacking the positive electrode 10 and the negative electrode 20, the power generation element 50 can be formed. For example, the belt-shaped separator 30 can be zigzagged (つづら折り), and each time the separator 30 turns back, the positive electrode 10 and the negative electrode 20 are alternately arranged. For example, the power generation element 50 can be a wound type. For example, the positive electrode 10, the negative electrode 20, and the separator 30 can all be belt-shaped. For example, by sequentially stacking the positive electrode 10, the separator 30, and the negative electrode 20, a laminate can be formed. By winding the laminate into a spiral shape, the power generation element 50 can be formed. The wound power generation element 50 can be formed into a flat shape after winding.

[0049] <Negative electrode>

[0050] The negative electrode 20 includes a current collector 21. At an SOC greater than 0%, the negative electrode 20 further includes a Li metal layer 23 on the current collector 21. With the increase or decrease of the SOC, the thickness of the Li metal layer 23 also increases or decreases. The Li metal layer 23 can be composed of a plurality of precipitates, or can also be a structure in which the precipitates are continuously integrated.

[0051] The current collector 21 has conductivity. The current collector 21 can function as a current collector, and examples include foils, films, etc. The thickness of the current collector 21 is 10 to 20 μm, and for example, it can be 12 to 18 μm. The material of the current collector 21 can be any conductive material such as metal, alloy, etc., as long as it is other than lithium metal and lithium alloy. The conductive material is preferably a material that does not react with lithium. Such a conductive material can include, for example, at least one selected from copper (Cu), nickel (Ni), iron (Fe), zinc (Zn), lead (Pb), silver (Ag), and gold (Au). As alloys, copper alloys, stainless steel (SUS), etc. can be cited. The current collector 21 is, for example, a copper foil or a copper alloy foil.

[0052] The current collector 21 has a plurality of through holes. For each through hole, if the diameter of the surface is set to a (mm), the distance between the center and the center of the other through hole closest to it is set to b (mm), and further, the average value of the diameter a (mm) is set to A (mm), and the average value of the center distance b (mm) is set to B (mm), then the relationship of formula (1) and formula (2) is satisfied:

[0053] 1.50 ≤ B / A ≤ 3.0 (1)

[0054] 0.05 ≤ A ≤ 0.18 (2).

[0055] In the above, the average value is the arithmetic mean.

[0056] The arrangement pattern of the plurality of through holes is not limited as long as it satisfies the above-mentioned formula (1) and the above-mentioned formula (2). The shape of the surface of the plurality of through holes is not limited, and may be, for example, circular, elliptical, or rectangular. As for the diameter of the through hole, when the shape of the through hole on the surface is circular, it is set to the diameter of the circle, and when it is a shape other than a circle, it is set to the diameter of the smallest circle that includes the shape of the surface. In addition, as for the center of the through hole, when the shape of the through hole on the surface is circular, it is set to the center of the circle, and when it is a shape other than a circle, it is set to the center of the smallest circle that includes the shape of the surface. For the through hole, the diameter a (mm) and the center-to-center distance b (mm) can be obtained from an image taken using an SEM.

[0057] 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 equations (1) and (2). The target region may be the entire surface of the current collector 21 or a portion thereof.

[0058] The arrangement pattern of the plurality of through holes may, for example, satisfy the relationship between equation (1a) and equation (2a):

[0059] 1.55≤B / A≤3.0(1a)

[0060] 0.08≤A≤0.14(2a).

[0061] A negative electrode composite layer may be formed on the surface of the current collector 21. The negative electrode composite layer is formed, for example, by applying a paste containing a carbon material such as graphite, a negative electrode active material such as a Si material, to at least a portion of the surface of the negative electrode current collector. In addition, a metal coating may be applied to the surface of the current collector 21. The metal coating may include at least one selected from magnesium (Mg), aluminum (Al), zinc (Zn), silver (Ag), gold (Au), platinum (Pt) and tin (Sn).

[0062] Figure 2 This is a conceptual diagram showing an example of a current collector in this embodiment. Figure 2 The upper surface (one surface) of the current collector 21 is schematically shown. The current collector 21 has a plurality of through holes 211. Figure 2 In the arrangement pattern shown, in addition to the through-holes 211 arranged at the outermost periphery, there are 6 other through-holes 211 closest to each other. The through-holes 211 are circular in shape. The through-holes 211 are arranged so that each has a constant diameter a1 (mm) and a constant center distance b1 (mm) from the other through-holes 211 closest to it. Figure 2In the arrangement pattern shown, the average value A (mm) of the diameter of the through holes 211 is a1 (mm), and the average value B (mm) of the center-to-center distance is b1 (mm).

[0063] Figure 3 To illustrate the difference between the current collector and the current collector in this embodiment Figure 2 Concept image of a different example. Figure 3 The upper surface (one surface) of the current collector 21 is schematically shown. The current collector 21 has a plurality of through holes 212. Figure 3 In the arrangement pattern shown, in addition to the through holes 212 arranged at the outermost periphery, there are four other through holes 212 closest to each other. The through holes 212 are circular in shape. The through holes 212 are arranged so that each has a constant diameter a2 (mm) and a constant center distance b2 (mm) from the other through holes 212 closest to it. Figure 3 In the arrangement pattern shown, the average value A (mm) of the diameter of the through holes 212 is a2 (mm), and the average value B (mm) of the center-to-center distance is b2 (mm).

[0064] The aperture ratio of one surface of the current collector 21 in this embodiment is, for example, 5.0 to 35.0%, 6.0 to 32.0%, or 7.0 to 30.0%. The aperture ratio of the surface means the ratio of the total area of ​​the plurality of through holes on the surface to the area occupied by one surface of the current collector 21. Figure 2 and Figure 3 In the example shown, it means the ratio of the total area of ​​the sizes of the through holes 211 and 212 formed in the current collector 21 on the surface to the area occupied by the upper surface of the current collector 21 .

[0065] In this embodiment, the surface of the current collector 21 is 1 cm 2 The exposed surface area of ​​the exposed surface is, for example, 0.86 to 0.99 cm 2 , can be 0.87~0.98cm 2 The exposed area here refers to the area obtained by subtracting the total area of ​​multiple through holes on the surface from the area occupied by one surface of the collector 21, and then adding the area of ​​the inner wall of the through hole. The value obtained by dividing the exposed area by the surface area of ​​the collector 21 is the value per 1 cm of the surface. 2 The exposed surface is a surface intended to be an interface with the Li metal layer 23 when the Li metal layer 23 is formed, and is composed of the surface of the collector 21 that is opposite to the positive electrode 10 via the separator 30 (excluding the surface of the through hole) and the inner wall of the through hole.

[0066] In the current collector 21 of the present embodiment, the processing method for forming the plurality of through holes is not limited, and the through holes can be formed by electrical discharge machining, cutting machining, laser machining, or the like.

[0067] Figure 4 This is a conceptual diagram showing the charge and discharge process near the negative electrode of the lithium secondary battery in this embodiment. Figure 4 (a) shows the initial state. If the lithium secondary battery is charged from the initial state, Figure 4 As shown in (b), lithium metal begins to precipitate from multiple starting points of the current collector 21 to form precipitates 23a. The current collector 21 has multiple through holes 213, and the inner walls of the multiple through holes 213 also become starting points for the formation of precipitates 23a. If charging is continued in this way, Figure 4 As shown in (c), the precipitates 23a precipitated and grown from different starting points form an integrated Li metal layer 23. Next, when the lithium secondary battery is discharged, the metal lithium layer 23 is dissolved. The Li metal layer 23 may be a layer formed by integrating the precipitates, or may be composed of a plurality of precipitates.

[0068] <Positive electrode>

[0069] The positive electrode 10 may be, for example, in a sheet shape. 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 conductivity. The positive electrode substrate 11 may 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 a sheet shape. The positive electrode substrate 11 may have, for example, a thickness of 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 aluminum (Al), manganese (Mn), titanium (Ti), iron (Fe) and chromium (Cr). The positive electrode substrate 11 may include, for example, Al foil, Al alloy foil, Ti foil, SUS foil, and the like.

[0070] 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 include, for example, a conductive material, an insulating material, an adhesive, and the like. The conductive material and the adhesive will be described later. The insulating material may include, for example, aluminum oxide, boehmite, aluminum hydroxide, and the like.

[0071] The positive electrode active material layer 12 is arranged on the surface of the positive electrode substrate 11. The positive electrode active material layer 12 may be arranged only on one side of the positive electrode substrate 11. The positive electrode active material layer 12 may also be arranged on both the front and back sides 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.

[0072] The conductive material can form an electron 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 relative to 100 parts by mass of the positive electrode active material. The conductive material may include optional components. The conductive material may include, for example, at least one selected from graphite, acetylene black (AB), Ketjen black (registered trademark), vapor grown carbon fiber (VGCF), carbon nanotube (CNT), and graphene sheet (GF).

[0073] The binder can fix the positive electrode active material layer 12 to the positive electrode substrate 11. The amount of the binder can be, for example, 0.1 to 10 parts by mass relative to 100 parts by mass of the positive electrode active material. The binder can include optional components. For example, the binder can include at least one selected from PVDF, PVDF-HFP, PTFE, CMC, PAA, PVA, PVP, polyoxyethylene alkyl ether, and derivatives thereof.

[0074] The positive electrode active material layer 12 may further include, for example, inorganic fillers, organic fillers, solid electrolytes, surface modifiers, lubricants, flame retardants, protective agents, fluxes, coupling agents, adsorbents, etc. The positive electrode active material layer 12 may include, for example, polyoxyethylene allylphenyl ether phosphate, zeolite, silane coupling agents, MoS 2 , WO 3 wait.

[0075] The positive electrode active material may be, for example, in the form of particles. The positive electrode active material may contain optional components. The positive electrode active material may contain, for example, transition metal oxides, polyanionic compounds, etc. In one particle (positive electrode active material), the composition may be uniform or non-uniform. For example, the composition may be inclined from the surface to the center of the particle. The composition may change continuously or discontinuously (stepwise).

[0076] The transition metal oxide may have any crystal structure. For example, the transition metal oxide may include a crystal structure belonging to the space group R-3m. For example, the general formula "LiMO 2 The compound represented by " may have a crystal structure belonging to the space group R-3m. The transition metal oxide may be represented by the following formula (3-1), for example.

[0077] Li 1-a Ni x M 1-x O 2 …(3-1)

[0078] In the above formula (3-1), M may include, for example, at least one selected from Co, Mn, and Al. For example, the relationship of -0.5≤a≤0.5 and 0<x≤1 may be satisfied.

[0079] 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.

[0080] 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.

[0081] The transition metal oxide may include, for example, LiCoO 2 、LiMnO 2 、LiNi 0.9 Co 0.1 O 2 、LiNi 0.9 Mn 0.1 O 2 and LiNiO 2 At least one of .

[0082] The transition metal oxide can be represented by, for example, the following formula (3-2). The compound represented by the following formula (3-2) may also be referred to as "NCM".

[0083] Li 1-a Ni x Co y Mn z O 2 …(3-2)

[0084] In the above formula (3-2), for example, the following relationships may be satisfied: -0.5≤a≤0.5, 0<x<1, 0<y<1, 0<z<1, and x+y+z=1.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] The NCM may include, for example, a 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 O2 and LiNi 0.9 Co 0.05 Mn 0.05 O 2 At least one of .

[0089] The transition metal oxide can be represented by, for example, the following formula (3-3). The compound represented by the following formula (3-3) may also be referred to as "NCA".

[0090] Li 1-a Ni x Co y Al z O 2 …(3-3)

[0091] In the above formula (3-3), for example, the following relationships may be satisfied: -0.5≤a≤0.5, 0<x<1, 0<y<1, 0<z<1, and x+y+z=1.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] NCA may include, for example, a 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 Al0.03 O 2 、LiNi 0.8 Co 0.15 Al 0.05 O 2 , and LiNi 0.9 Co 0.05 Al 0.05 O 2 At least one of .

[0096] The positive electrode active material may include, for example, two or more NCMs. The positive electrode active material may include, for example, NCM (0.6 ≤ x) and NCM (x < 0.6). "NCM (0.6 ≤ x)" means a compound in which x (Ni ratio) is greater than 0.6 in the above formula (3-2). NCM (0.6 ≤ x) may also be referred to as "high nickel material". NCM (0.6 ≤ x) may include, for example, LiNi 0.8 Co 0.1 Mn 0.1 O 2 "NCM (x < 0.6)" means a compound in which x (Ni ratio) is less than 0.6 in the above formula (3-2). NCM (x < 0.6) contains, 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) can be, for example, "NCM (0.6≤x) / NCM (x<0.6)=9 / 1~1 / 9", "NCM (0.6≤x) / NCM (x<0.6)=9 / 1~4 / 6", or "NCM (0.6≤x) / NCM (x<0.6)=9 / 1~3 / 7".

[0097] The positive electrode active material may include, 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 ratio between 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 also be lower than the Ni ratio of NCM.

[0098] The transition metal oxide may include, for example, a crystal structure belonging to the space group C2 / m, etc. The transition metal oxide may be represented by, for example, the following formula (3-4).

[0099] Li 2 MO 3 …(3-4)

[0100] In the above formula (3-4), M may include at least one selected from Ni, Co, Mn, and Fe, for example.

[0101] The positive electrode active material may include, 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 With Li 2 MO 3 Solid solution (Li 2 MO 3 -LiMO 2 )wait.

[0102] The transition metal oxide may include, for example, a crystal structure belonging to the space group Fd-3m, etc. The transition metal oxide may be represented by, for example, the following formula (3-5).

[0103] LiMn 2-x M x O 4 …(3-5)

[0104] In the above formula (3-5), M may include, for example, at least one selected from Ni, Fe, and Zn. For example, the relationship of 0≤x≤2 may be satisfied.

[0105] LiM 2 O 4 (space group Fd-3m) may include, for example, LiMn 2 O 4 and LiMn 1.5 Ni 0.5 O 4 At least one of the following. The positive electrode active material may include, for example, LiMO 2 (space group R-3m) and LiM 2 O 4 (space group Fd-3m). LiMO 2 (space group R-3m) and LiM 2 O 4 The mixing ratio (mass ratio) of (space group Fd-3m) can be, 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”.

[0106] The polyanionic compound may, for example, comprise a phosphate (e.g., LiFePO 4 The polyanion compound can be represented by the following formulae (3-6) to (3-9), for example.

[0107] LiMPO 4 …(3-6)

[0108] Li 2-x MPO 4 F…(3-7)

[0109] Li 2 MSiO 4 …(3-8)

[0110] LiMBO 3 …(3-9)

[0111] In the above formulae (3-6) to (3-9), M may include, for example, at least one selected from Fe, Mn, and Co. In the above formula (3-7), for example, the relationship of 0≤x≤2 may be satisfied.

[0112] The positive electrode active material may include, for example, LiMO 2 A mixture of (space group R-3m) and polyanionic compounds. LiMO 2 The mixing ratio (mass ratio) of (space group R-3m) and the polyanion compound can be, for example, "LiMO 2 / polyanion compound = 9 / 1 to 9 / 1", "LiMO 2 / polyanionic compound = 9 / 1 to 5 / 5", or "LiMO 2 / polyanionic compound = 9 / 1 to 7 / 3".

[0113] Dopants may be added to the positive electrode active material. The dopant may diffuse throughout the particle or be locally distributed. For example, the dopant may be localized on the particle surface. The dopant may be a substitutional solid solution atom or an intrusive solid solution atom. The amount of dopant added (molar fraction relative to the total positive electrode active material) may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1%. One dopant may be added, or two or more dopants may be added. Two or more dopants may form a composite.

[0114] The dopant may, for example, include at least one selected from B, C, N, halogen, 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.

[0115] For example, the group of "Zr, Mg, W, Sm", the group of "Ti, Mn, Nb, Si, Mo", or the group of "Er, Mg" may be added to NCA. For example, Ti may be added to NCM. For example, the group of "Zr, W", the group of "Si, W", or the group of "Zr, W, Al, Ti, Co" may be added to NCM.

[0116] The positive electrode 10 may include composite particles. The composite particles include core particles and shell layers. The core particles include a positive electrode active material. The shell layer covers at least a portion 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, based on an SEM image of a particle cross section. That is, a sample is prepared by embedding the composite particles in a resin material. An ion milling device is used to expose the sample in a cross section. For example, an ion milling device "Product Name: ArBlade (registered trademark) 5000" (or its equivalent) manufactured by Hitachi High-Technologies Corporation can be used. The cross section of the sample is observed using SEM. For example, an SEM device "Product Name: SU8030" (or its equivalent) manufactured by Hitachi High-Technologies Corporation can be used. For 10 composite particles, the thickness of the shell layer is measured in 20 fields of view respectively. The arithmetic average of the thickness at a total of 200 locations is used.

[0117] The ratio of the portion of the surface of the core particle covered by the shell layer is also referred to as "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.

[0118] The coverage rate can be measured, for example, by XPS (X-ray Photoelectron Spectroscopy). For example, the XPS device "Product Name: PHI X-tool" (or its equivalent) manufactured by ULVAC-PHI can be used. The sample (powder) is placed on the XPS. A narrow scan analysis is performed. The measurement data is processed using analytical software. For example, the analytical software "Product Name: MulTiPak" (or its equivalent) manufactured by ULVAC-PHI can be used. By analyzing the measurement data, a variety of elements are detected. The ratio of each detected element is calculated from the area of ​​each peak. The coverage rate is calculated according to the following formula (3-10).

[0119] θ={I 1 / (I 0 +I 1 )}×100…(3-10)

[0120] θ: Coverage rate [%]

[0121] I 0 : Ratio of elements from nuclear particles

[0122] I 1 : Ratio of elements from the shell

[0123] For example, in the case where the core particle comprises an 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, when the shell layer contains P and B, I 1 Indicates the total element ratio of "P, B".

[0124] 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, etc. The shell layer may contain, for example, a compound selected from B, Al, W, Zr, Ti, Co, F, a lithium compound (e.g., Li 2 CO 3 、LiHCO 3 、LiOH、Li 2 O, etc.), tungsten oxide (such as WO 3 etc.), titanium oxide (such as TiO 2 etc.), zirconium oxide (such as ZrO 2 ), boron oxide, boron phosphate (such as BPO 4 etc.), aluminum oxide (such as Al 2 O 3 etc.), boehmite, aluminum hydroxide, phosphates [such as Li 3 PO4、 (NH 4 ) 3 PO 4 、AlPO 4 ], borates (such as Li 2 B 4 O 7 、LiBO 3 etc.), polyacrylates (Li salts, Na salts, NH 4 salts, etc.), acetates (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 At least one of the above.

[0125] "Hollow particles" and "solid particles" are secondary particles (agglomerates of primary particles). In the cross-sectional image of "hollow particles", the proportion of the area of ​​the hollow in the center is more than 30% of the cross-sectional area of ​​the entire particle. The proportion of the hollow in the hollow particles may be, for example, more than 40%, more than 50%, or more than 60%. In the cross-sectional image of "solid particles", the proportion of the area of ​​the hollow in the center is less than 30% of the cross-sectional area of ​​the entire particle. The proportion of the hollow in the solid particles may be, for example, less than 20%, less than 10%, or less than 5%. The positive electrode active material may be a hollow particle or a solid particle. A mixture of hollow particles and solid particles may be used. The mixing ratio (mass ratio) of hollow particles and solid particles can 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".

[0126] The positive electrode active material may have, for example, a unimodal particle size distribution (number basis). 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 regarded as the particle size of the large particle (d L The particle size corresponding to the peak top of the smaller particle size is regarded as the particle size of the smaller particle (d S ). Particle size ratio (d L / d S ) may be, for example, 2 to 10, 2 to 5, or 2 to 4. LFor example, it may be 8 to 20 μm, or 8 to 15 μm. S For example, it may be 1 to 10 μm, or 1 to 5 μm.

[0127] For example, waveform analysis software can be used to perform peak separation on the particle size distribution. The peak area (S L ) and the peak area from small particles (S S ) can be, for example, "S L / S S =1 / 9~9 / 1", "S L / S S =5 / 5~9 / 1”, or “S L / S S =7 / 3~9 / 1”.

[0128] The particle size distribution based on the number of particles is measured by microscopy. Multiple cross-sectional samples are collected from the positive electrode active material layer 12. The cross-sectional sample may include, for example, a cross-sectional surface perpendicular to the surface of the positive electrode active material layer 12. For example, the observation object surface is cleaned by ion milling or the like. The cross-sectional sample is observed by SEM. The observation magnification is adjusted in such a way that 10 to 100 particles are included in the observation field of view. The Feret diameter of all particles in the image is measured. "Ferret diameter" indicates the distance between the two farthest points on the contour line of the particle. By observing multiple cross-sectional samples, a total of more than 1000 Feret diameters are obtained. The particle size distribution based on the number of particles is made from more than 1000 Feret diameters.

[0129] 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, large particles may have a D50 of 8 to 20 μm, or 8 to 15 μm. For example, small particles may have a D50 of 1 to 10 μm, or 1 to 5 μm. The ratio of the D50 of large particles to the D50 of small particles may be, for example, 2 to 10, 2 to 5, or 2 to 4. The mixing ratio (mass ratio) of large particles to 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".

[0130] It should be noted that 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).

[0131] <Electrolyte>

[0132] The electrolyte is a liquid electrolyte. The electrolyte contains Li ions. The electrolyte may contain a solute and a solvent, for example.

[0133] 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 oxalic acid complex, a halide, etc. The solute may include, for example, a compound selected from LiPF 6 , LiBF 4 、LiClO 4 、LiAsF 6 、LiSbF 6 、LiN(SO 2 F) 2 "Common name: LiFSI", LiN(SO 2 CF 3 ) 2 "Common name: LiTFSI", LiB(C 2 O 4 ) 2 "Common name: LiBOB", LiBF 2 (C 2 O 4 ) "Common name: LiDFOB", LiPF 2 (C 2 O 4 ) 2 "Common name: LiDFOP", LiPO 2 F 2 、FSO 3 At least one of Li, LiI, LiBr, and derivatives thereof.

[0134] The electrolyte may include, for example, an ether solvent. The solvent may include, for example, at least one selected from tetrahydrofuran (THF), 1,4-dioxane (DOX), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), ethyl glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, hydrofluoroether (HFE), and derivatives thereof.

[0135] For example, HFE may include at least one selected from the group consisting of 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.

[0136] For example, HFE may include at least one selected from 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.

[0137] The electrolyte may include, for example, a carbonate-based solvent (carbonate-based solvent). The solvent may include, for example, a cyclic carbonate, a chain carbonate, a fluorinated carbonate, etc. The solvent may include, for example, at least one selected from 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 their derivatives.

[0138] The solvent may include cyclic carbonates (EC, PC, FEC, etc.) and linear carbonates (EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of cyclic carbonates and linear carbonates may be, for example, "cyclic carbonate / linear carbonate = 1 / 9 to 4 / 6", "cyclic carbonate / linear carbonate = 2 / 8 to 3 / 7", or "cyclic carbonate / linear carbonate = 3 / 7 to 4 / 6".

[0139] The solvent may include cyclic carbonate (EC, PC, etc.) and fluorinated cyclic carbonate (FEC, etc.). The mixing ratio (volume ratio) of cyclic carbonate and 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".

[0140] The solvent may contain, for example, EC, FEC, EMC, DMC, and DEC. The volume ratio of each component may satisfy the relationship represented by, for example, the following formula (4-1).

[0141] V EC +V FEC +V EMC +V DMC +V DEC =10…(4-1)

[0142] In the above formula (4-1), V EC 、V FEC 、V EMC 、VDMC 、V DEC They represent the volume ratios of EC, FEC, EMC, DMC and DEC respectively.

[0143] 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 The relationship is ≤9.

[0144] In the above formula (4-1), for example, 1≤V EC ≤2, or 2≤V EC The relationship is ≤3.

[0145] For example, 1≤V FEC ≤2, or 2≤V FEC The relationship is ≤4.

[0146] For example, 3≤V EMC ≤4, or 6≤V EMC The relationship is ≤8.

[0147] For example, 3≤V DMC ≤4, or 6≤V DMC The relationship is ≤8.

[0148] For example, 3≤V DEC ≤4, or 6≤V DEC The relationship is ≤8.

[0149] The solvent can be expressed by volume ratio, for example, and may have a composition 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", etc.

[0150] The electrolyte may contain optional additives. The amount of addition (relative to the mass fraction of the entire electrolyte) may be, for example, 0.01 to 5%, 0.05 to 3%, or 0.1 to 1%. The additives may include, for example, SEI (Sol id Electrolyte Interphase) formation promoters, SEI formation inhibitors, gas generators, overcharge preventers, flame retardants, antioxidants, electrode protectants, surfactants, etc.

[0151] The additive may include, for example, at least one selected from the following: 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, carboxylates [such as methyl formate (MF), methyl acetate (MA), methyl propionate (MP), diethyl malonate (DEM), etc.], fluorobenzenes [such as monofluorobenzene (F B), 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.), fluorotoluene (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.), trifluoromethylbenzene (benzotr

[0043] The invention also includes trifluoromethylbenzene, 2-fluorotrifluoromethylbenzene, 3-fluorotrifluoromethylbenzene, 4-fluorotrifluoromethylbenzene, 2-methyltrifluoromethylbenzene, 3-methyltrifluoromethylbenzene, 4-methyltrifluoromethylbenzene, 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-methylbenzothiazole, tetrathiafulvalene, etc.), nitrile compounds (e.g. adiponitrile, succinonitrile, etc.), phosphates (e.g. trimethyl phosphate, triethyl phosphate, etc.), carboxylic anhydrides (e.g. acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride, etc.), alcohols (e.g. methanol, ethanol, n-propanol, ethylene glycol, diethylene glycol monomethyl ether, etc.), and derivatives thereof.

[0152] The components described as solute and solvent may be used as additives (trace components). The additives may include, for example, LiBF 4 , LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPO 2 F 2 、FSO 3At least one of Li, Li I, LiBr, HFE, DOX, PC, FEC, and derivatives thereof.

[0153] The electrolyte may contain an ionic liquid. For example, the electrolyte may contain at least one selected from sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidinium salts, morpholinium salts, phosphonium salts, imidazolium salts, and derivatives thereof.

[0154] The battery 100 may include a gel electrolyte. The gel electrolyte includes an electrolyte and a polymer material. The polymer material may form a polymer matrix. The polymer material may include, for example, at least one selected from PVDF, PVDF-HFP, PAN, PVDF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0155] <Separator>

[0156] The separator 30 has electrical insulation. The separator 30 may include, for example, at least one selected from 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.

[0157] 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 in a network, for example. Pores are formed in the gaps of the resin skeleton. The resin film allows the electrolyte to pass through. The resin film may have, for example, an average pore diameter of less than 1 μm. The resin film may have, for example, an average pore diameter of 0.01 to 1 μm, or 0.1 to 0.5 μm. The "average pore diameter" can be measured by mercury intrusion. The resin film may have, for example, a pore diameter of 50 to 250 s / 100 cm 3 Gurley value. The "Gurley value" can be measured by the Gurley test method.

[0158] The resin film may include, for example, at least one selected from olefin resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, acrylic resins, and polyester resins. The resin film may include, for example, at least one selected from polyethylene (PE), polypropylene (PP), polyamide (PA), polyamideimide (PAI), polyimide (PI), aromatic polyamide (aramid), polyphenylene ether (PPE), and their derivatives. The resin film may be formed, for example, by a stretching method, a phase separation method, etc. The resin film may have a thickness of, for example, 5 to 50 μm, or 10 to 25 μm.

[0159] The resin film may have a single-layer structure, for example. The resin film may be composed of a PE layer, for example. The skeleton of the PE layer is formed of PE. The PE layer may have a shutdown function. The resin film may have a multi-layer structure, for example. The resin film may include a PP layer and a PE layer. The skeleton of the PP layer is formed of PP. The resin film may have a three-layer structure, for example. The resin film may be formed by stacking a PP layer, a PE layer, and a PP layer in sequence. 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.

[0160] The 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 side opposite to the positive electrode 10, or on the side opposite to the negative electrode 20.

[0161] The inorganic particle layer is porous. The inorganic particle layer contains inorganic particles. The inorganic particles can also be called "inorganic fillers". Pores are formed in the gaps between the inorganic particles. The inorganic particle layer can have a thickness of, for example, 0.5 to 10 μm, or 1 to 5 μm. The inorganic particles can contain, for example, heat-resistant materials. The inorganic particle layer containing heat-resistant materials is also called "HRL (Heat Res istance Layer)". The inorganic particles can contain at least one selected from boehmite, alumina, zirconium oxide, titanium dioxide, magnesium oxide and silicon dioxide. The inorganic particles can have any shape. The inorganic particles can be, for example, spherical, rod-shaped, plate-shaped, fibrous, etc. The inorganic particles can have a D50 of, for example, 0.1 to 10 μm, or 0.5 to 3 μm. The inorganic particle layer can further contain a binder. The binder can contain, for example, at least one selected from acrylic resins, polyamide resins, fluorine resins, aromatic polyether resins, and liquid crystal polyester resins.

[0162] 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.

[0163] 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 fillers". The organic particles may include heat-resistant materials. The organic particles may include, for example, at least one selected from PE, PP, PTFE, PI, PAI, PA, and aromatic polyamide. The organic particles may be, for example, spherical, rod-shaped, plate-shaped, fibrous, and the like. The organic particles may have a D50 of, for example, 0.1 to 10 μm, or 0.5 to 3 μm.

[0164] The separator 30 may include, for example, a mixed layer. The mixed layer includes both inorganic particles and organic particles.

[0165] <Battery Configuration Example>

[0166] Figure 5 This is the first configuration example. Figure 6 This is the second configuration example. Figure 7 This is a third configuration example. In the tables in the figures, when multiple materials are recorded in the grid, the record includes each material alone and their combination. For example, when the material "α, β, γ" is recorded in the grid, the record means "at least one selected from α, β and γ".

[0167] In this embodiment, as long as the current collector 21 has a plurality of through holes as shown in the above embodiment and the negative electrode 20 utilizes the dissolution reaction of lithium metal, other configurations (combination of positive electrode, separator and electrolyte, etc.) are arbitrary. For example, any elements can be extracted from the first configuration example, the second configuration example and the third configuration example and combined arbitrarily.

[0168] <Battery Manufacturing Example>

[0169] In this embodiment, as long as the current collector 21 is a structure shown in the above embodiment with a plurality of through holes and the negative electrode 20 utilizes the dissolution and precipitation reaction of lithium metal, the manufacturing method of the lithium secondary battery is arbitrary. For example, a manufacturing method having the following steps can be illustrated: 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 at the negative electrode. By the step of precipitating lithium metal, the Li metal layer 23 can be formed.

[0170] Example

[0171] <Manufacturing of test batteries>

[0172] The test cells (anode-free cells) of Nos. 1 to 5 were manufactured by the following procedure. Hereinafter, for example, "test cell of No. 1" may be simply referred to as "No. 1" or the like.

[0173] No.1

[0174] Mix NCM as an active material, PVdF as a binder, and a conductive additive, transfer the resulting mixture to a container, and stir it 3 to 4 times using Awatori Rentaro (THINKY) (2000 rpm, 1 minute). Then, add N-methylpyrrolidone (NMP) while confirming the viscosity, and stir until it becomes uniform (2000 rpm for 5 minutes). If necessary, add additional NMP and stir (2000 rpm for 2 minutes). In this way, a slurry is obtained.

[0175] As a positive electrode substrate, prepare aluminum foil (thickness: 16 μm). Use a scraper to apply the above-obtained slurry on aluminum foil (thickness: 16 μm). As scrapers, scrapers with gaps of 350, 375, and 400 μm were used. The coating weight after the solvent was dried was set as the unit area weight, and the unit area weight was set to about 23 mg / cm 2 Then, the density was adjusted to 2.4 to 2.9 g / cc using a roller press. Then, the cells were cut into coin cells (approximately 1.5 cm 2 ) or laminated battery (about 27cm 2 ) size, prepare the positive electrode.

[0176] As a separator, a resin film (thickness: 20 μm) was prepared. The resin film contained PP / PE.

[0177] As a negative electrode, a copper foil (thickness: 15 μm) was prepared. The copper foil was not processed to form through holes, but was coated with a metal and used as a current collector.

[0178] The positive electrode, separator and negative electrode are stacked in order to form a power generating element. The power generating element is housed in an outer casing. An electrolyte is injected into the outer casing. The composition of the electrolyte is as follows.

[0179] Electrolyte composition

[0180] Solute: LiTFSI (1 mol / L)

[0181] Solvent: PC / FEC=7 / 3 (volume ratio)

[0182] After the electrolyte solution was injected, the outer casing was sealed. Through the above operation, a test battery was manufactured.

[0183] No.2~5

[0184] As the negative electrode, a copper foil (thickness: 15 μm) was prepared. The copper foil was processed by laser. Figure 2 The arrangement pattern shown forms a plurality of through holes, which serve as current collectors. Figure 8Table 1 shows the arrangement pattern of multiple through holes in the collector, measured values ​​related to the shape of the through holes, and values ​​calculated from the measured values ​​related to the shape of the through holes. As measured values ​​related to the shape of the through holes, the average value A (mm) of the diameter a (mm) and the average value B (mm) of the center-to-center distance b (mm) are shown. Figure 8 The measured values ​​shown in Table 1 are values ​​calculated by measuring the SEM image of one surface of the current collector. The values ​​calculated from the measured values ​​are shown as B / A values, opening ratio (%), and surface area per 1 cm 2 Exposure area (cm 2 ) A test cell was produced in the same manner as in No. 1 except that a copper foil having a plurality of through holes was used as the current collector.

[0185] <Evaluation>

[0186] The cycle test was carried out under the following conditions.

[0187] 1. Rest: 60 minutes

[0188] 2.CCCV charging: (1 / 4)C (termination current (1 / 100)C)

[0189] 3. Rest: 5 minutes

[0190] 4.CC discharge: (1 / 4)C 3.0V

[0191] 5. Rest: 5 minutes

[0192] Number of cycles of 2. to 5. above: 20

[0193] The discharge capacity at each cycle was divided by the discharge capacity at the first cycle to determine the discharge capacity retention rate at each cycle. The discharge capacity retention rate at each cycle was expressed as a percentage.

[0194] <Results>

[0195] In Table 1 ( Figure 8 ) shows the discharge capacity retention rate at the 20th cycle. Fig. 9 In the figure, the horizontal axis shows the number of cycles, and the vertical axis shows the discharge capacity retention rate corresponding to the number of cycles. It is believed that the higher the discharge capacity retention rate, the better the cycle durability. No.2, No.3, and No.4 have improved cycle durability compared to No.1 (no through holes) and No.5 (multiple through holes do not satisfy the condition of formula (1)). Figure 8 and Fig. 9 It is found that when B / A is in the range of 1.5 to 3.0, the discharge capacity retention rate tends to improve.

[0196] From Table 1( Figure 8) shows that the discharge capacity retention rate at the 20th cycle tends to increase when the aperture ratio of the current collector is 5.0 to 35.0%. Figure 8 ) shows that the discharge capacity retention rate at the 20th cycle is 2 The exposed area is 0.86~0.99cm 2 When , there is a tendency that the discharge capacity retention rate at the 20th cycle is improved.

Claims

1. A lithium secondary battery comprising a positive electrode, a separator, a negative electrode and an electrolyte, wherein the reaction of the negative electrode utilizes a dissolution reaction of lithium metal, wherein: The negative electrode includes a current collector, the current collector has a thickness of 10 to 20 μm, and the current collector has a plurality of through holes. For each of the through holes, the diameter of the surface is set to a (mm), the center-to-center distance to another through hole closest to the through hole is set to b (mm), and the average value of the diameter a (mm) is set to A (mm), and the average value of the center-to-center distance b (mm) is set to B (mm), and the relationship between equations (1) and (2) is satisfied: 1.50≤B / A≤3.0 (1) 0.05≤A≤0.18 (2)。 2. The lithium secondary battery according to claim 1, wherein The current collector is copper or a copper alloy.

3. The lithium secondary battery according to claim 1 or claim 2, wherein: The surface of the current collector has an opening ratio of 5.0 to 35.0%.

4. The lithium secondary battery according to claim 1 or claim 2, wherein: The surface of the current collector is per 1 cm 2 The exposed area is 0.86~0.99cm 2 .

5. The lithium secondary battery according to claim 1, wherein The collector is copper foil or copper alloy foil, the surface opening rate is 5.0-35.0%, and the surface per 1 cm 2 The exposed area is 0.86~0.99cm 2 .

6. The method for manufacturing a lithium secondary battery according to claim 1 comprises: a process of preparing the current collector; a process of assembling a lithium secondary battery precursor comprising the positive electrode, the separator, the negative electrode and the electrolyte; and a process of charging the lithium secondary battery precursor so that lithium metal is precipitated at the negative electrode.

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