Lithium metal secondary battery, method for manufacturing negative electrode, and method for charging and discharging lithium metal secondary battery

Abstract

To reduce swelling of cells due to Li metal precipitation.SOLUTION: A lithium metal secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative electrode current collector and a pillar layer. The pillar layer is arranged on a surface of the negative electrode current collector. The pillar layer includes a plurality of insulating pillars. Each of the insulating pillars extends in a direction from the surface of the negative electrode current collector toward the positive electrode. Lithium ions are dissolved in the electrolyte. A negative electrode charge reaction is a lithium metal precipitation reaction in a gap between the insulating pillars. A negative electrode discharge reaction is a lithium metal dissolution reaction in the gap.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a lithium metal secondary battery, a method for producing a negative electrode, and a method for charging and discharging a lithium metal secondary battery. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 2001-250559 discloses a lithium metal secondary battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-250559 Summary of the Invention [Problem to be solved by the invention]

[0004] In a lithium metal secondary battery (hereinafter also referred to as a "cell"), the charging reaction of the negative electrode is a deposition reaction of Li metal. As Li metal deposits, the thickness of the negative electrode increases. This increase in the thickness of the negative electrode can cause the cell to swell. Therefore, an object of the present disclosure is to reduce the cell swelling that accompanies the deposition of Li metal. [Means for solving the problem]

[0005] The technical configuration and effects of the present disclosure will be described below. However, the mechanism of action in this specification includes speculation. The mechanism of action does not limit the technical scope of the present disclosure.

[0006] 1. A lithium metal secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative electrode current collector and a pillar layer. The pillar layer is disposed on the surface of the negative electrode current collector. The pillar layer includes a plurality of insulating pillars. Each of the plurality of insulating pillars extends from the surface of the negative electrode current collector toward the positive electrode. Lithium ions are dissolved in the electrolyte. The charging reaction of the negative electrode is a deposition reaction of lithium metal in the gaps between the insulating pillars. The discharging reaction of the negative electrode is a dissolution reaction of lithium metal in the gaps.

[0007] In the cell described in "1" above, the negative electrode includes a pillar layer. The pillar layer includes a plurality of insulating pillars. The plurality of insulating pillars can form a frame (framework). Li metal can be deposited in the gaps between the insulating pillars. Even if Li metal is deposited, it is thought that the external dimensions of the pillar layer (frame) are unlikely to change. By depositing Li metal so that the Li metal fits within the frame, an increase in the thickness of the negative electrode can be reduced. In other words, swelling of the cell due to the deposition of Li metal can be reduced.

[0008] However, each pillar is insulating. If the pillars were conductive, it may not be possible to reduce cell swelling. That is, if the pillars were conductive, electrons could be supplied to the pillars. Therefore, at the tip of the pillar (the point closest to the positive electrode), Li ions could receive electrons and precipitate as Li metal. During charging, the Li metal could grow toward the positive electrode. That is, the Li metal could progress in a direction away from the pillar layer. Therefore, it is thought to be difficult to fit the Li metal inside the pillar layer (frame).

[0009] Because the pillars are insulating, Li ions can receive electrons on the surface of the negative electrode current collector at the start of charging, causing Li metal to deposit. Since Li metal deposition begins on the surface of the negative electrode current collector, Li metal can progress inside the pillar layer during charging.

[0010] 2. In the lithium metal secondary battery described in the above item "1," each of the insulating pillars may include, for example, a resist material.

[0011] For example, a plurality of insulating pillars may be formed by photolithography.

[0012] 3. In the lithium metal secondary battery described in the above item "1" or "2," each of the insulating pillars may have an aspect ratio of, for example, 1 or less. The "aspect ratio" is calculated by the following formula (F-1). A R =H / D …(F-1) In the formula, A R indicates the aspect ratio. H indicates the height of the insulating pillar. D indicates the diameter of the insulating pillar.

[0013] It is expected that the insulating pillars will be less likely to fall off from the surface of the negative electrode current collector when the aspect ratio of the insulating pillars is 1 or less. Note that the aspect ratio is a dimensionless quantity.

[0014] 4. In the lithium metal secondary battery according to any one of the above items "1" to "3," each of the insulating pillars may have, for example, a diameter of 100 to 300 μm and a height of 1 to 100 μm.

[0015] 5. In the lithium metal secondary battery according to any one of the above items 1 to 4, the electrolyte may contain a solvent and a solute. The solvent may contain, for example, hydrofluoroether (HFE). The solute may contain, for example, an imide salt.

[0016] When the electrolyte contains HFE and an imide salt, for example, an improvement in output is expected.

[0017] 6. In the lithium metal secondary battery according to any one of the above items "1" to "5," the pillar layer may have a porosity of, for example, 50 to 95%. The "porosity" is calculated by the following formula (F-2). P O ={(S0-S1) / S0}×100 …(F-2) In the formula, P O indicates the porosity. The porosity is expressed as a percentage. S0 indicates the area of the negative electrode current collector where the pillar layer is arranged. S1 indicates the total adhesion area of multiple insulating pillars.

[0018] The higher the porosity, the more Li metal can be stored in the pillar layer. This means that an improvement in energy density is expected. For example, pressure may be applied in the thickness direction of the pillar layer (the height direction of the insulating pillars). For example, pressure (confining pressure) may be generated when a restraining member restrains the periphery of the cell. If the confining pressure is concentrated in some insulating pillars, uneven deposition of Li metal may occur. For example, the lower the porosity (the higher the density of the insulating pillars), the more the confining pressure is expected to be dispersed throughout multiple insulating pillars. A porosity of 50 to 95% tends to provide a good balance between energy density and the dispersibility of the confining pressure. Note that porosity is a dimensionless quantity. In the above formula (F-2), S0 can be considered as the area of the region (figure) enclosed by the outline of the pillar layer in a planar view.

[0019] 7. The method for producing a negative electrode for a lithium metal secondary battery according to any one of the above items "1" to "6" may include, for example, the following steps (a) to (c): (a) Prepare a negative electrode current collector. (b) A resist material is disposed on the surface of the negative electrode current collector to form a resist layer. (c) A pillar layer is formed by selectively removing a portion of the resist layer.

[0020] By photolithography, the arrangement of the insulating pillars can be arbitrarily patterned.

[0021] 8. The method for charging and discharging a lithium metal secondary battery includes the following (d) and (f): (d) Charging a lithium metal secondary battery. (f) Discharging the lithium metal secondary battery. The lithium metal secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative electrode current collector and a pillar layer. The pillar layer is disposed on the surface of the negative electrode current collector. The pillar layer includes a plurality of insulating pillars. Each of the plurality of insulating pillars extends from the surface of the negative electrode current collector toward the positive electrode. Lithium ions are dissolved in the electrolyte. The above step (d) includes depositing lithium metal in the gaps between the insulating pillars. The step (f) involves dissolving lithium metal in the gap.

[0022] 9. In the method for charging and discharging a lithium metal secondary battery described in the above item "8," the lithium metal may be deposited so as to extend in a net-like pattern in plan view.

[0023] In a plan view, the insulating pillars may be dispersed in a dot pattern. Therefore, in a plan view, the gaps between the insulating pillars spread in a network pattern. Therefore, the Li metal may form a network-like continuous phase in the gaps. The formation of a continuous phase of the Li metal may reduce the occurrence of isolated Li metal. The occurrence of isolated Li metal may result in unevenness in the amount of Li metal precipitated.

[0024] 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 example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure. The present embodiment and the example are illustrative in all respects. The present embodiment and the example are non-restrictive. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is originally intended that any configuration may be extracted from the present embodiment and the example and that they may be arbitrarily combined. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a conceptual diagram showing an example of a lithium metal secondary battery according to this embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view showing an insulating pillar in this embodiment. [Figure 3] FIG. 3 is a schematic plan view showing an example of an arrangement pattern of insulating pillars. [Figure 4] FIG. 4 is a table showing the first cell configuration. [Figure 5] FIG. 5 is a table showing the second cell configuration. [Figure 6] FIG. 6 is a table showing the third cell configuration. [Figure 7] FIG. 7 is a schematic flowchart of the method for producing a negative electrode in this embodiment. [Figure 8] FIG. 8 is a schematic flowchart of the charge / discharge method according to this embodiment. [Figure 9] FIG. 9 is a conceptual diagram showing a battery system in this embodiment. [Figure 10] FIG. 10 is a table showing cell configurations and evaluation results. [Figure 11] FIG. 11 is a schematic plan view showing the No. 4 frame. [Figure 12] FIG. 12 is a conceptual diagram showing the precipitation behavior of No. 1. [Figure 13] FIG. 13 is a conceptual diagram showing the deposition behavior of No. 2. [Figure 14] FIG. 14 is a conceptual diagram showing the deposition behavior of No. 3. DETAILED DESCRIPTION OF THE INVENTION

[0026] <Terms and definitions> The terms "comprise," "include," "have," and variations thereof (e.g., "consisting of") are open-ended. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is closed-ended. However, even closed-ended terms do not exclude additional elements that are normally incidental impurities or unrelated to the disclosed technology. The term "consisting essentially of..." is semi-closed. Semi-closed terms allow for the addition of elements that do not substantially affect the basic and novel characteristics of the disclosed technology.

[0027] 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."

[0028] Unless otherwise specified, the order of execution of multiple steps, actions, operations, etc. included in various methods is not limited to the order described. For example, multiple steps may proceed simultaneously. For example, multiple steps may occur one after the other.

[0029] Elements expressed in the singular include the plural unless otherwise specified. For example, "particle" includes not only "one particle" but also "multiple particles (particle group)" and "aggregates of particles (powder, powder)."

[0030] Geometric terms (such as "parallel," "perpendicular," and the like) should not be interpreted in a strict sense. For example, "parallel" may deviate slightly from the strict meaning of "parallel." Geometric terms may include, for example, tolerances, errors, and the like in design, work, and manufacturing. The dimensional relationships in each drawing may not match the actual dimensional relationships. To aid the reader's understanding, the dimensional relationships (length, width, thickness, and the like) in each drawing may be changed. Furthermore, some components may be omitted.

[0031] "Planar view" means that an object is viewed from a line of sight parallel to the thickness direction of the object. The planar view may correspond to the XY plane in each drawing. "Cross-sectional view" means that an object is viewed from a line of sight perpendicular to the thickness direction of the object. The cross-sectional view may correspond to the XZ plane or YZ plane in each drawing.

[0032] A "pillar" refers to a solid body having two bases (first base, second base) and a side surface. The two bases may be parallel to each other. The height (H) of the pillar is the distance between the first base and the second base. The direction parallel to the height is the height direction (which may also be referred to as the "axial direction"). The diameter (D) of the pillar refers to the diameter of the first or second base. If the diameter of the first base is different from the diameter of the second base, the larger diameter is considered to be the diameter of the pillar. If each base is not circular, the diameter refers to the maximum Feret diameter.

[0033] Unless otherwise specified, a numerical range such as "m to n%" includes both the upper and lower limits. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% and less than n%." Furthermore, 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 elsewhere in this specification, in a table, a figure, or the like.

[0034] 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 depending on the application of the disclosed technology. All numerical values may be expressed with significant figures. Unless otherwise specified, measured values may be average values of multiple measurements. 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. Measured values may be rounded to the nearest significant figure. Measured values may include errors, such as those associated with the detection limits of the measuring device.

[0035] The stoichiometric composition formula indicates a representative example of a compound. The compound may have a non-stoichiometric composition. For example, "Al2O3" is not limited to a compound having a substance ratio (molar ratio) of "Al / O = 2 / 3." Unless otherwise specified, "Al2O3" indicates a compound containing Al and O in any composition ratio. Furthermore, for example, the compound may be doped with a trace element, or a portion of Al and O may be substituted with another element.

[0036] 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 the introduction of a functional group, atomic substitution, 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, alkyl groups, alkenyl groups, alkynyl groups, cycloalkyl groups, unsaturated cycloalkyl groups, aromatic groups, heterocyclic groups, halogen atoms (such as F, Cl, Br, and I), OH groups, SH groups, CN groups, SCN groups, OCN groups, nitro groups, alkoxy groups, unsaturated alkoxy groups, amino groups, alkylamino groups, dialkylamino groups, aryloxy groups, acyl groups, alkoxycarbonyl groups, acyloxy groups, aryloxycarbonyl groups, acylamino groups, alkoxycarbonylamino groups, aryloxycarbonylamino groups, sulfonylamino groups, sulfamoyl groups, carbamoyl groups, alkylthio groups, arylthio groups, sulfonyl groups, sulfinyl groups, ureido groups, phosphoric acid amide groups, sulfo groups, carboxy groups, hydroxamic acid groups, sulfino groups, hydrazino groups, imino groups, and silyl groups. These substituents may be further substituted. When there are two or more substituents, the substituents may be the same or different, and multiple substituents may be bonded to each other to form a ring.

[0037] <<Lithium metal secondary battery>> 1 is a conceptual diagram showing an example of a lithium metal secondary battery according to this embodiment. A cell 100 includes a power generating element 50 and an electrolyte (not shown).

[0038] <Exterior body> The cell 100 may include an exterior body (not shown). The exterior body may house the power generating element 50 and the electrolyte. The exterior body may have any shape. For example, the exterior body may be a metal case or a pouch made of a metal foil laminated film. The case may have any shape. For example, the case may be cylindrical, rectangular, flat, coin-shaped, or the like. The exterior body may contain, for example, Al. The exterior body may house, for example, one power generating element 50, or may house multiple power generating elements 50. The multiple power generating elements 50 may form, for example, a series circuit or a parallel circuit. Within the exterior body, the multiple power generating elements 50 may be stacked in the thickness direction of the cell 100.

[0039] <Power generation elements> The power generating element 50 includes a positive electrode 10 and a negative electrode 20. The power generating element 50 may further include 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 configuration. The power generating element 50 may be, for example, a laminated type. For example, the power generating element 50 may be formed by alternately stacking the positive electrodes 10 and the negative electrodes 20 with the separator 30 sandwiched between them. The power generating element 50 may be, for example, a wound type. For example, a laminate may be formed by stacking a strip-shaped positive electrode 10, a strip-shaped separator 30, and a strip-shaped negative electrode 20. 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.

[0040] The power generating element 50 may have, for example, an anode-free structure. An "anode-free structure" refers to a structure in which no solid negative electrode active material is present before the first charge. Of course, the power generating element 50 does not have to have an anode-free structure.

[0041] <Negative electrode> The negative electrode 20 may be, for example, in the form of a sheet. The negative electrode 20 includes a negative electrode current collector 21 and a pillar layer 22.

[0042] 《Negative electrode current collector》 The negative electrode current collector 21 is conductive. The negative electrode current collector 21 supports the pillar layer 22 (plurality of insulating pillars 1). The negative electrode current collector 21 may be, for example, sheet-shaped. The negative electrode current collector 21 may have a thickness of, for example, 5 to 50 μm. The negative electrode current collector 21 may include, for example, a metal foil or the like. The negative electrode current collector 21 may include, for example, at least one selected from the group consisting of Cu, Ni, Fe, Zn, Pb, Ag, and Au. The negative electrode current collector 21 may include, for example, a Cu foil, a Cu alloy foil, or the like.

[0043] Pillar Layer The pillar layer 22 is disposed on the surface of the negative electrode current collector 21. The pillar layer 22 may be disposed on only one surface of the negative electrode current collector 21. The pillar layer 22 may be disposed on both the front and back surfaces of the negative electrode current collector 21. The pillar layer 22 includes a plurality of insulating pillars 1. The plurality of insulating pillars 1 may be fixed to the surface of the negative electrode current collector 21, for example. The plurality of insulating pillars 1 may be attached to the surface of the negative electrode current collector 21, for example.

[0044] The plurality of insulating pillars 1 standing in a forest form gaps 2 between the insulating pillars 1. In the gaps 2, charge / discharge reactions (dissolution and precipitation reactions of Li metal 2a) can proceed.

[0045] FIG. 2 is a schematic cross-sectional view showing an insulating pillar in this embodiment. The insulating pillar 1 includes a first bottom surface 1a, a second bottom surface 1b, and a side surface 1c. The side surface 1c connects the first bottom surface 1a and the second bottom surface 1b. The insulating pillar 1 may be, for example, cylindrical or rectangular. That is, the side surface 1c may be a curved surface or may include multiple flat surfaces. The first bottom surface 1a is attached to the surface of the negative electrode current collector 21. The second bottom surface 1b may be in contact with, for example, the separator 30. The second bottom surface 1b may be in contact with, for example, the positive electrode 10.

[0046] As long as the first bottom surface 1a is fixed to the negative electrode current collector 21, for example, the first bottom surface 1a and the second bottom surface 1b do not have to be flat. For example, the second bottom surface 1b may be curved. For example, the second bottom surface 1b may be raised in a hemispherical shape. In other words, the insulating pillar 1 may form a pillar bump.

[0047] Each of the insulating pillars 1 extends from the surface of the negative electrode current collector 21 toward the positive electrode 10. That is, the height direction of the insulating pillar 1 is aligned with the thickness direction of the negative electrode 20 (pillar layer 22). The height direction of the insulating pillar 1 may be parallel to the thickness direction of the pillar layer 22. The insulating pillar 1 may be, for example, a rectangular pillar or an oblique pillar. The angle formed between the first bottom surface 1a (second bottom surface 1b) and the side surface 1c may be, for example, 15 to 90°, 30 to 90°, 45 to 90°, 60 to 90°, or 75 to 90°. It is considered that the closer this angle is to 90° (the closer the insulating pillar 1 is to a rectangular pillar), the smaller the tortuosity. The "tortuosity" refers to the path length divided by the thickness of the pillar layer 22. The "path length" refers to the length of the path of Li ions when they permeate the pillar layer 22 in the thickness direction. The minimum value of the tortuosity is 1. The lower the tortuosity, the more improved the output can be expected. The pillar layer 22 may have a tortuosity of, for example, 1 to 1.5, 1 to 1.2, 1 to 1.1, or 1 to 1.05.

[0048] The insulating pillar 1 may have a height (H) of, for example, 1 to 1000 μm. That is, the pillar layer 22 may have a thickness of 1 to 1000 μm. The height of the insulating pillar 1 may be, for example, 1 to 500 μm, 1 to 300 μm, 1 to 100 μm, 10 to 100 μm, 50 to 100 μm, or 50 to 70 μm.

[0049] The insulating pillar 1 may have a diameter (D) of, for example, 1 to 1000 μm. The diameter of the insulating pillar 1 may be, for example, 5 to 500 μm, 100 to 300 μm, or 140 to 240 μm. The diameter of the insulating pillar 1 may be larger than the average pore size of the separator 30. The diameter of the insulating pillar 1 may be constant or may vary in the height direction of the insulating pillar 1. A constant diameter may reduce the tortuosity.

[0050] The insulating pillar 1 has, for example, an aspect ratio (A R =H / D). When the aspect ratio of the insulating pillar 1 is 1 or less, it is expected that the insulating pillar 1 will be less likely to fall off from the surface of the negative electrode current collector 21. The insulating pillar 1 may have an aspect ratio of, for example, 0.1 to 0.99, 0.1 to 0.8, 0.2 to 0.6, or 0.27 to 0.45.

[0051] The pillar layer 22 is an aggregate of the insulating pillars 1. The pillar layer 22 can be referred to as, for example, a "pillar array." The insulating pillars 1 may be arranged in any pattern. The arrangement pattern may be regular or irregular.

[0052] 3 is a schematic plan view showing an example of an arrangement pattern of insulating pillars. The insulating pillars 1 may be dispersed in a dot pattern, for example. The insulating pillars 1 may be arranged in a lattice pattern, for example. The insulating pillars 1 may be arranged in a triangular lattice pattern, an isosceles triangular lattice pattern, a regular triangular lattice pattern, a rectangular lattice pattern, a square lattice pattern, or the like. In FIG. 3, the insulating pillars 1 are arranged in a triangular lattice pattern, for example.

[0053] The first bottom surface 1a and the second bottom surface 1b may have any planar shape. The first bottom surface 1a may have the same planar shape as the second bottom surface 1b, or may have a different planar shape. The first bottom surface 1a and the second bottom surface 1b may each independently have a planar shape such as a circle, an ellipse, a triangle, a rectangle, a square, or a hexagon. In FIG. 3, a circular second bottom surface 1b is depicted as an example.

[0054] The term "multiple insulating pillars 1" refers to two or more insulating pillars 1. The upper limit of the number is arbitrary. The number density of the insulating pillars 1 in a plan view is also arbitrary. The number density is, for example, 1 to 1000 pieces / mm 2 , 5~500 pieces / mm 2 , 10~100 pieces / mm 2 , or 10 to 30 pieces / mm 2 may be.

[0055] In a plan view, the insulating pillars 1 may be arranged, for example, at equal intervals. The interval between the insulating pillars 1 ("pitch (p)") may be, for example, 1 to 1000 μm, 5 to 500 μm, 10 to 300 μm, or 50 to 500 μm. The pitch may be larger than the average pore size of the separator 30, for example.

[0056] The gaps 2 may be continuous in a network form. The pillar layer 22 may have a porosity of, for example, 1 to 99%, 5 to 95%, 10 to 95%, 30 to 95%, or 50 to 95%. When the porosity is 50 to 95%, a good balance between energy density and dispersibility of confining pressure tends to be achieved. The porosity may be, for example, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more. The porosity may be, for example, 90% or less, 80% or less, 70% or less, or 60% or less.

[0057] The insulating pillar 1 exhibits electrical insulation. 5 The insulating pillar 1 may have a volume resistivity of 1×10 Ω·cm or more. 10 Ω·cm or more, or 1×10 15It may have a volume resistivity of Ω·cm or more.

[0058] The insulating pillar 1 can be formed of any material as long as it is electrically insulating. The insulating pillar 1 may be insoluble in an electrolyte. The insulating pillar 1 may contain, for example, a ceramic material, a glass material, or the like. The insulating pillar 1 may contain, for example, at least one selected from the group consisting of SiO2, GeO2, BO3, PO5, As2O5, Li2O, Na2O, KO, MgO, CaO, BaO, Al2O3, TiO2, and ZrO2.

[0059] The insulating pillar 1 may contain, for example, a resin material. The insulating pillar 1 may contain, for example, engineering plastic, super engineering plastic, etc. The insulating pillar 1 may contain, for example, at least one selected from the group consisting of polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide (PA), and polyamideimide (PAI).

[0060] The insulating pillar 1 may include, for example, a resist material. When the insulating pillar 1 includes a resist material, multiple insulating pillars 1 can be formed by photolithography. The resist material may be, for example, a positive type or a negative type. The resist material may include, for example, at least one type selected from the group consisting of a phenolic resin (e.g., novolac resin), an acrylic resin, and a methacrylic resin.

[0061] Seed particles The negative electrode 20 may further include, for example, seed particles (not shown). The seed particles can serve as seeds for Li nucleation during charging. The seed particles may be disposed, for example, on the surface of the negative electrode current collector 21. The seed particles may be disposed in the gaps 2. The seed particles may include, for example, at least one selected from the group consisting of Li, Mg, Al, Zn, Ag, Pt, and Au. The seed particles may be, for example, nanoparticles. The seed particles may have a D50 of, for example, 1 to 200 nm.

[0062] 《Second negative electrode active material》 The negative electrode 20 may further include, for example, a negative electrode active material other than Li (hereinafter also referred to as "second negative electrode active material"). The second negative electrode active material may include, for example, an insertion-type active material, an alloy-type active material, etc. For example, a combination of Li metal and an insertion-type active material may improve cycle durability, etc. The second negative electrode active material may be, for example, particulate. The second negative electrode active material may be, for example, disposed in the gaps 2. The second negative electrode active material may be, for example, disposed on the surface of the negative electrode current collector 21.

[0063] The second negative electrode active material may be, for example, natural graphite, artificial graphite, soft carbon, hard carbon, silicon (Si), SiO, Li silicate, Si-based alloy, tin (Sn), SnO, Sn-based alloy, and Li4Ti5O 12 It may contain at least one selected from the group consisting of:

[0064] <Carbon-based active material> "Graphite" is a general term for natural graphite and artificial graphite. Graphite may be a mixture of natural graphite and artificial graphite. The mixing ratio (mass ratio) may be, for example, "natural graphite / artificial graphite = 1 / 9 to 9 / 1," "natural graphite / artificial graphite = 2 / 8 to 8 / 2," or "natural graphite / artificial graphite = 3 / 7 to 7 / 3."

[0065] Graphite may contain a dopant. The dopant may contain, for example, at least one selected from the group consisting of B, N, P, Li, and Ca. The addition amount may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1% in mole fraction.

[0066] The surface of the graphite may be coated with, for example, amorphous carbon. The surface of the graphite may be coated with, for example, a different material. The different material may contain, for example, at least one selected from the group consisting of P, W, Al, and O. The different material may contain, for example, at least one selected from the group consisting of Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO 3、 and Li3PO4.

[0067] 〈Alloy-based active material〉 SiO may be represented by, for example, the following formula (A-1).

[0068] SiO x …(A-1) In the formula, the relationship of 0 < x < 2 is satisfied.

[0069] In the above formula (A-1), x may satisfy, for example, 0.5 ≦ x ≦ 1.5, or 0.8 ≦ x ≦ 1.2.

[0070] The Li silicate may contain, for example, at least one selected from the group consisting of Li4SiO4, Li2SiO3, Li2Si2O5, and Li8SiO6. The second negative electrode active material may contain, for example, a mixture of Si and Li silicate. The mixing ratio (mass ratio) may be, for example, "Si / Li silicate = 1 / 9 to 9 / 1", "Si / Li silicate = 2 / 8 to 8 / 2", "Si / Li silicate = 3 / 7 to 7 / 3", or "Si / Li silicate = 4 / 6 to 6 / 4".

[0071] The alloy-based active material (e.g., Si, SiO) may contain an additive. The additive may be, for example, a substitutional solute atom or an interstitial solute atom. The additive may be a deposit attached to the surface of the alloy-based active material. The deposit may be, for example, an element, an oxide, a carbide, a nitride, a halide, or the like. The amount added may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1% in terms of mole fraction. The additive may contain, for example, at least one selected from the group consisting of Li, Na, K, Rb, Be, Mg, Ca, Sr, Fe, Ba, B, Al, Ga, In, C, Ge, Sn, Pb, N, P, As, Y, Sb, and S. That is, SiO may be doped with Mg or Na. For example, Mg silicate, Na silicate, etc. may be formed. For example, boron oxide (for example, B2O3), yttrium oxide (for example, Y2O3, etc.), etc. may be added to SiO.

[0072] <Si-C composite material> The second negative electrode active material may include, for example, a composite material of a carbon-based active material (such as graphite) and an alloy-based active material (such as Si). A composite material containing Si and carbon may also be called a "Si-C composite material." For example, Si fine particles may be dispersed in carbon particles. For example, Si fine particles may be dispersed in graphite particles. For example, Li silicate particles may be coated with a carbon material (such as amorphous carbon). A Si-C composite material and graphite may be mixed and used.

[0073] <Multi-component system> The second negative electrode active material may contain two or more components. The second negative electrode active material may contain a carbon-based active material (such as graphite) and an alloy-based active material (such as Si or SiO). The mixing ratio (mass ratio) of the carbon-based active material to the alloy-based active material may be, for example, "carbon-based active material / alloy-based active material=1 / 9 to 9 / 1," "carbon-based active material / alloy-based active material=2 / 8 to 8 / 2," "carbon-based active material / alloy-based active material=3 / 7 to 7 / 3," or "carbon-based active material / alloy-based active material=4 / 6 to 6 / 4."

[0074] <Binder> The second negative electrode active material may be fixed to the negative electrode current collector 21 or the like by, for example, a binder. The binder may contain any component. For example, the binder may contain at least one selected from the group consisting of polyacrylic acid (PAA), carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), acrylate butadiene rubber (ABR), polyacrylonitrile (PAN), and derivatives thereof.

[0075] <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 current collector 11 and a positive electrode active material layer 12. The positive electrode current collector 11 is conductive. The positive electrode current collector 11 supports the positive electrode active material layer 12. The positive electrode current collector 11 may be, for example, in the form of a sheet. The positive electrode current collector 11 may have a thickness of, for example, 5 to 50 μm. The positive electrode current collector 11 may include, for example, a metal foil. The positive electrode current collector 11 may include, for example, at least one selected from the group consisting of Al, Mn, Ti, Fe, and Cr. The positive electrode current collector 11 may include, for example, an Al foil, an Al alloy foil, a Ti foil, a stainless steel (SUS) foil, or the like.

[0076] An intermediate layer (not shown) may be formed between the positive electrode current collector 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.

[0077] The positive electrode active material layer 12 is disposed on the surface of the positive electrode current collector 11. The positive electrode active material layer 12 may be disposed on only one surface of the positive electrode current collector 11. The positive electrode active material layer 12 may be disposed on both the front and back surfaces of the positive electrode current collector 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.

[0078] Conductive materials The conductive material can form an electron conduction path within 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. For example, the conductive material may contain at least one material selected from the group consisting of graphite, acetylene black (AB), Ketjen Black (registered trademark), vapor grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes (GF).

[0079] Binder The binder can fix the positive electrode active material layer 12 to the positive electrode current collector 11. The amount of binder may be, for example, 0.1 to 10 parts by mass per 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 polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), tetrafluoroethylene (PTFE), CMC, PAA, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ether, and derivatives thereof.

[0080] Other ingredients 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 contain, for example, polyoxyethylene allyl phenyl ether phosphate, zeolite, silane coupling agent, MoS2, WO3, etc.

[0081] 《Positive Electrode Active Material》 The positive electrode active material may be, for example, particulate. The positive electrode active material may contain any components. The positive electrode active material may contain, for example, a transition metal oxide, a polyanion compound, etc. Within 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).

[0082] 〈Transition Metal Oxide: Space Group R-3m〉 The transition metal oxide may have any crystal structure. The transition metal oxide may contain, for example, a crystal structure belonging to the space group R-3m, etc. For example, a compound represented by the general formula "LiMO2" 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 (C-1).

[0083] Li 1-a Ni x M 1-x O2…(C-1) In the formula, the relationship of -0.5 ≦ a ≦ 0.5, 0 < x ≦ 1 is satisfied. M may contain at least one selected from the group consisting of Co, Mn, and Al, for example.

[0084] In the above formula (C-1), x may satisfy a relationship such as 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. a may satisfy a relationship such as -0.4 ≤ a ≤ 0.4, -0.3 ≤ a ≤ 0.3, -0.2 ≤ a ≤ 0.2, or -0.1 ≤ a ≤ 0.1.

[0085] The transition metal oxide may include, for example, at least one selected from the group consisting of LiCoO2, LiMnO2, LiNi 0.9 Co 0.1 O2, LiNi 0.9 Mn 0.1 O2, and LiNiO2.

[0086] 〈NCM〉 The transition metal oxide may be represented, for example, by the following formula (C-2). The compound represented by the following formula (C-2) may also be referred to as "NCM".

[0087] Li 1-a Ni x Co y Mn z O2…(C-2) In the formula, the relationships of -0.5 ≤ a ≤ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied.

[0088] In the above formula (C-2), x may satisfy a relationship such as 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.

[0089] In the above formula (C-2), y may satisfy a relationship such as 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.

[0090] In the above formula (C-2), z may satisfy a relationship such as 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.

[0091] NCM is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2, LiNi 0.3 Co 0.4 Mn 0.3 O2, LiNi 0.3 Co 0.3 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn ) 0.1 O2, LiNi 0.5 Co 0.1 Mn 0.4 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.3 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, and LiNi 0.9 Co 0.05 Mn 0.05 may contain at least one selected from the group consisting of O2.

[0092] 〈NCA〉 The transition metal oxide may be represented, for example, by the following formula (C-3). The compound represented by the following formula (C-3) may also be referred to as "NCA".

[0093] Li 1-a Ni x Co y Al z O2…(C-3) In the formula, the relationships of -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied.

[0094] In the above formula (C-3), x may satisfy, 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.

[0095] In the above formula (C-3), y may satisfy, 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.

[0096] In the above formula (C-3), z may satisfy, 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.

[0097] NCA is, for example, LiNi 0.7 Co 0.1 Al 0.2 O2, LiNi 0.7 Co 0.2 Al 0.1 O2, LiNi 0.8 Co 0.1 Al 0.1 O2, LiNi0.8 Co 0.17 Al 0.03 O2, LiNi 0.8 Co 0.15 Al 0.05 O2 and LiNi 0.9 Co 0.05 Al 0.05 O2.

[0098] <Multi-component system> The positive electrode active material may contain, for example, two or more types of NCM. 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) in the above formula (C-2) is 0.6 or more. NCM (0.6≦x) may also be referred to as, for example, a "high nickel material." NCM (0.6≦x) is, for example, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc. "NCM (x<0.6)" refers to a compound in which x (Ni ratio) is less than 0.6 in the above formula (C-2). NCM (x<0.6) is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc. 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."

[0099] 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.

[0100] <Transition metal oxides: space group C2 / m> 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 (C-4).

[0101] Li2MO3…(C-4) In the formula, M may include, for example, at least one selected from the group consisting of Ni, Co, Mn, and Fe.

[0102] The positive electrode active material may include, for example, a mixture of LiMO2 (space group R-3m) and Li2MO3 (space group C2 / m), or a solid solution of LiMO2 and Li2MO3 (Li2MO3-LiMO2).

[0103] <Transition metal oxides: space group Fd-3m> 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 (C-5). LiMn 2-x M x O4…(C-5) In the formula, the relationship 0≦x≦2 is satisfied. M may include, for example, at least one selected from the group consisting of Ni, Fe, and Zn.

[0104] LiM2O4 (space group Fd-3m) is, for example, LiMn2O4 and LiMn 1.5 Ni 0.5 The positive electrode active material may contain at least one selected from the group consisting of LiMO2 (space group R-3m) and LiM2O4 (space group Fd-3m). The positive electrode active material may contain, for example, a mixture of LiMO2 (space group R-3m) and LiM2O4 (space group Fd-3m). The mixing ratio (mass ratio) of LiMO2 (space group R-3m) and LiM2O4 (space group Fd-3m) may be, for example, "LiMO2 / LiM2O4 = 9 / 1 to 9 / 1," "LiMO2 / LiM2O4 = 9 / 1 to 5 / 5," or "LiMO2 / LiM2O4 = 9 / 1 to 7 / 3."

[0105] <Polyanion Compounds> The polyanion compound may contain, for example, a phosphate (such as LiFePO4), a silicate, a borate, etc. The polyanion compound may be represented, for example, by the following formulas (C-6) to (C-9).

[0106] LiMPO4…(C-6) Li 2-x MPO4F...(C-7) Li2MSiO4…(C-8) LiMBO3…(C-9) In the above formulas (C-6) to (C-9), M may include, for example, at least one selected from the group consisting of Fe, Mn, and Co. In the above formula (C-7), for example, the relationship 0≦x≦2 may be satisfied.

[0107] The positive electrode active material may contain, for example, a mixture of LiMO2 (space group R-3m) and a polyanionic compound. The mixing ratio (mass ratio) of LiMO2 (space group R-3m) and the polyanionic compound may be, for example, "LiMO2 / polyanionic compound = 9 / 1 to 9 / 1," "LiMO2 / polyanionic compound = 9 / 1 to 5 / 5," or "LiMO2 / polyanionic compound = 9 / 1 to 7 / 3."

[0108] Dopant 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 composite.

[0109] The dopant may include at least one selected from the group consisting of, for example, 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.

[0110] For example, the set "Zr, Mg, W, Sm", the set "Ti, Mn, Nb, Si, Mo", or the set "Er, Mg" may be added to the NCA.

[0111] For example, Ti may be added to the NCM. For example, a combination of "Zr, W", a combination of "Si, W", or a combination of "Zr, W, Al, Ti, Co" may be added to the NCM.

[0112] <Surface coating> The positive electrode 10 may include composite particles. The composite particles include a core particle and a coating layer. The core particle includes a positive electrode active material. The coating layer covers at least a portion of the surface of the core particle. The coating layer may have a thickness of, for example, 1 to 3,000 nm, 5 to 2,000 nm, 10 to 1,000 nm, 10 to 100 nm, or 10 to 50 nm. The thickness of the coating layer can be measured, for example, from a scanning electron microscope (SEM) image of the particle cross section. That is, a sample is prepared by embedding the composite particles in a resin material. The sample is subjected to cross-section processing using an ion milling device. For example, an ion milling device manufactured by Hitachi High-Technologies Corporation, product name: ArBlade (registered trademark) 5000 (or equivalent), may be used. The cross section of the sample is observed using an SEM. For example, an SEM device manufactured by Hitachi High-Technologies Corporation, product name: SU8030 (or equivalent), may be used. The thickness of the coating layer is measured in 20 fields for each of 10 composite particles, and the arithmetic mean of the thicknesses of 200 points in total is used.

[0113] The proportion of the surface of the core particle that is covered with the coating 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.

[0114] 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 consisting of composite particles is placed 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. Multiple elements are detected by analyzing the measurement data. The ratio of each detected element is calculated from the area of each peak. The coverage can be calculated using the following formula (F-3).

[0115] θ={I1 / (I0+I1)}×100 …(F-3) θ: Coverage rate [%] I0: Ratio of elements originating from the core particle I1: Ratio of elements derived from the coating layer For example, if the core particle contains NCM, I0 indicates the total element ratio of "Ni, Co, Mn." For example, if the core particle contains NCA, I0 indicates the total element ratio of "Ni, Co, Al." For example, if the coating layer contains P and B, I1 indicates the total element ratio of "P, B."

[0116] The coating layer may contain any component. The coating layer may contain, for example, an element, 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. The coating layer may contain, for example, B, Al, W, Zr, Ti, Co, F, lithium compounds (e.g., Li2CO3, LiHCO3, LiOH, Li2O, etc.), tungsten oxide (e.g., WO3, etc.), titanium oxide (e.g., TiO2, etc.), zirconium oxide (e.g., ZrO2), boron oxide, boron phosphate (e.g., BPO4, etc.), aluminum oxide (e.g., Al2O3, etc.), boehmite, aluminum hydroxide, phosphate (e.g., Li3PO 4、 (NH4)3PO4, AlPO4), borates (e.g., Li2B4O7, LiBO3, etc.), polyacrylates (Li salts, Na salts, NH4 salts, etc.), acetates (e.g., Li salts, etc.), CMC (Na salts, Li salts, NH4 salts, etc.), LiNbO 3、 It may contain at least one selected from the group consisting of Li2TiO3 and Li-containing halides (for example, LiAlCl4, LiTiAlF6, LiYBr6, LiYCl6, etc.).

[0117] <Hollow particles / solid particles> "Hollow particles" refer to secondary particles in which, in a cross-sectional image, the area of the cavity in the center is 30% or more of the cross-sectional area of the entire particle. The proportion of the cavity in a hollow particle may be, for example, 40% or more, 50% or more, or 60% or more. "Solid particles" refer to secondary particles in which, in a cross-sectional image of the particle, the area of the cavity in the center is less than 30% of the cross-sectional area of the entire particle. The proportion 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 either 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."

[0118] <Large particles / Small particles> "Electrode active material" is a general term for positive electrode active material and negative electrode active material. The electrode active material may have, for example, a unimodal particle size distribution (number basis). The electrode active material may have, for example, a multimodal particle size distribution. The electrode active material may have, for example, a bimodal particle size distribution. That is, the electrode active material may contain large particles and small particles. When the particle size distribution is bimodal, the particle diameter corresponding to the peak top of the larger particle diameter is the particle diameter of the large particles (d L The particle size corresponding to the peak top of 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.

[0119] 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 / S S =1 / 9~9 / 1", "S L / S S =5 / 5~9 / 1" or "S L / S S =7 / 3~9 / 1" is also acceptable.

[0120] The number-based particle size distribution is measured by microscopy. Multiple cross-sectional samples are taken from the electrode active material layer. The cross-sectional samples may include, for example, cross sections perpendicular to the surface of the electrode active material layer. For example, the surface to be observed is cleaned by ion milling or the like. The cross-sectional samples are observed using an SEM. The observation magnification is adjusted so that 10 to 100 particles fit within the observation field. The Feret diameters of all particles in the image are measured. The "Feret diameter" refers to the distance between the two most distant points on the particle's contour. By observing multiple cross-sectional samples, a total of 1,000 or more Feret diameters are obtained. A number-based particle size distribution is created from the 1,000 or more Feret diameters.

[0121] A bimodal particle size distribution can be formed by mixing two types of particles. The two types of particles have different particle size distributions. For example, the two types of particles may have different D50s. "D50" refers to the particle size at which the cumulative frequency from the smaller particle size reaches 50% in a volume-based particle size distribution. D50 can be measured by laser diffraction. The measurement sample is a powder. 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 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."

[0122] The large particles and the small particles may have the same composition or 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).

[0123] <Electrolytes> The electrolyte dissolves Li ions. The electrolyte may be a liquid electrolyte or a gel electrolyte. The liquid electrolyte may include, for example, an electrolytic solution. The electrolytic solution includes a solvent and a solute.

[0124] 《Solute》 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 oxalate complex, a halide, or the like. The solute may include, for example, at least one selected from the group consisting of LiPF6, LiBF4, LiClO4, LiAsF6, LiSbF6, LiN(SO2F)2 "LiFSI", LiN(SO2CF3)2 "LiTFSI", LiB(C2O4)2 "LiBOB", LiBF2(C2O4) "LiDFOB", LiPF2(C2O4)2 "LiDFOP", LiPO2F2, FSO3Li, LiI, LiBr, and derivatives thereof.

[0125] "solvent" <Ether solvents> The electrolytic solution may contain an ether-based solvent. The solvent may contain, for example, HFE. The HFE may contain 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.

[0126] The HFE may contain, for example, at least one selected from the group consisting of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), 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.

[0127] The solvent may also contain an ether other than HFE (hereinafter also referred to as "second ether"). The second ether may contain, for example, 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, and derivatives thereof. The solvent may contain, for example, 1 to 50% by volume of the second ether (DME, etc.), with the balance being HFE. The solvent may contain, for example, 10 to 40% by volume of the second ether, with the balance being HFE.

[0128] <Carbonate solvent> 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.

[0129] 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."

[0130] 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 to 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".

[0131] 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 (E-1).

[0132] V EC +V FEC +V EMC +V DMC +V DEC =10 ...(E-1) In the formula, V EC , V FEC , V EMC , V DMC , V DEC indicates the volume ratio of EC, FEC, EMC, DMC, and DEC, respectively. 1≦V EC ≦4, 0≦V FEC ≦3, V EC +V FEC ≦4, 0≦V EMC ≦9, 0≦V DMC ≦9, 0≦VDEC ≦9, 6≦V EMC +V DMC +V DEC ≦9 The relationship is satisfied.

[0133] In the above formula (E-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.

[0134] The solvent may have a composition, for example, in volume ratios 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," or "EC / FEC / DMC / EMC=1 / 2 / 3 / 4."

[0135] <Additives> The electrolyte may contain any additive. The amount of additive (mass fraction relative to the total amount of the 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 accelerator, an SEI formation inhibitor, a gas generator, an overcharge inhibitor, a flame retardant, an antioxidant, an electrode protectant, a surfactant, etc.

[0136] 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-methylbenzotrifluoride, The solvent may contain at least one selected from the group consisting of solvents such as benzothiazole, tetrathiafulvane, etc., nitrile compounds (e.g., adiponitrile, succinonitrile, etc.), phosphate esters (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.

[0137] The components described above as solutes and solvents may be used as minor components (additives). The additives may include, for example, at least one selected from the group consisting of LiBF, LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPOF, FSOLi, LiI, LiBr, HFE, DOX, PC, FEC, and derivatives thereof.

[0138] Ionic liquids The liquid electrolyte may contain an ionic liquid. The liquid electrolyte may contain, for example, at least one selected from the group consisting of sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidinium salts, morpholinium salts, phosphonium salts, imidazolium salts, and derivatives thereof.

[0139] Gel electrolyte The gel electrolyte may include a liquid 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 the group consisting of PVdF, PVdF-HFP, PAN, PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0140] <Separator> The separator 30 can separate the positive electrode 10 from the negative electrode 20. 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.

[0141] Resin film 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 in the resin skeleton. The resin film can allow electrolytes to pass through. The resin film may have, for example, an average pore size of 1 μm or less. The resin film may have, for example, an average pore size of 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, for example, a pore size of 50 to 250 s / 100 cm. 3 The "Gurley value" can be measured by the Gurley test method.

[0142] The resin film may contain at least one selected from the group consisting of, for example, olefin-based resins, polyurethane-based resins, polyamide-based resins, cellulose-based resins, polyether-based resins, acrylic-based resins, and polyester-based resins. 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.

[0143] The resin film may have, for example, a single-layer structure. The resin film may be made 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.

[0144] 《Inorganic particle layer》 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 the front and back 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. The inorganic particle layer may be formed on the surface of the positive electrode 10, or on the surface of the negative electrode 20.

[0145] The inorganic particle layer is porous. The inorganic particle layer contains inorganic particles. The inorganic particles may also be referred to as "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 contain, for example, a heat-resistant material. An inorganic particle layer containing a heat-resistant material is also referred to as an "HRL (Heat Resistance Layer)." The inorganic particles may contain at least one type 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, or 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 contain a binder. The binder may contain, for example, at least one selected from the group consisting of acrylic resins, polyamide resins, fluorine resins, aromatic polyether resins, and liquid crystal polyester resins.

[0146] 《Organic particle layer》 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.

[0147] 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 contains organic particles. The organic particles may also be referred to as "organic filler." The organic particles may contain a heat-resistant material. The organic particles may contain 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.

[0148] Separator 30 may include, for example, a mixed layer, which includes both inorganic and organic particles.

[0149] <Cell configuration> FIG. 4 is a table showing the first cell configuration. FIG. 5 is a table showing the second cell configuration. FIG. 6 is a table showing the third cell configuration. In each table, when multiple materials are listed in a box, the listing includes each material alone and combinations thereof. For example, when materials "α, β, γ" are listed in a box, the listing indicates "at least one selected from the group consisting of α, β, and γ." Any element may be extracted from the first to third cell configurations and combined in any desired manner.

[0150] This embodiment may be incorporated into, for example, the first to third cell configurations. This embodiment may be combined with, for example, the first to third cell configurations. This embodiment may replace, for example, part of the first to third cell configurations. For example, the negative electrode in the first cell configuration may be replaced with the negative electrode in this embodiment (negative electrode current collector 21, pillar layer 22). For example, the negative electrode in the first cell configuration may be used in combination with the negative electrode in this embodiment. Combining the first to third cell configurations with this embodiment may improve cell performance.

[0151] <<Negative electrode manufacturing method>> The negative electrode 20 can be manufactured by any method. For example, the insulating pillars 1 may be formed by CVD (Chemical Vapor Deposition), ALD (Atomic Layer Deposition), PVD (Physical Vapor Deposition), EPD (Electrophoretic Deposition), selective dry etching, laser processing, additive manufacturing, or the like. For example, the insulating pillars 1 may be formed by photolithography. Hereinafter, as an example, a method of manufacturing the negative electrode 20 by photolithography will be described.

[0152] 7 is a schematic flowchart of a method for manufacturing a negative electrode according to this embodiment. Hereinafter, the "method for manufacturing a negative electrode according to this embodiment" may be abbreviated as "this manufacturing method." This manufacturing method includes "(a) preparation of a negative electrode current collector," "(b) formation of a resist layer," and "(c) formation of a pillar layer."

[0153] <(a) Preparation of negative electrode current collector> This manufacturing method includes preparing a negative electrode current collector 21. Details of the negative electrode current collector 21 are as described above. The negative electrode current collector 21 may be manufactured or may be commercially available. For example, electrolytic copper foil, rolled copper foil, or the like may be prepared as the negative electrode current collector 21.

[0154] <(b) Formation of resist layer> This manufacturing method includes forming a resist layer (not shown) by disposing a resist material on the surface of the negative electrode current collector 21. The resist material may be, for example, a liquid type or a dry film type. For example, if the resist material is a liquid type, the resist layer can be formed by applying the resist material to the surface of the negative electrode current collector 21. For example, the resist material may be applied using a spin coater or the like. If the resist material is a dry film type, the resist layer can be formed by laminating a dry film on the surface of the negative electrode current collector 21. The thickness of the resist layer can correspond to the height of the insulating pillar 1. The thickness of the resist layer may be adjusted to match the desired height of the insulating pillar 1.

[0155] <(c) Formation of pillar layer> This manufacturing method includes forming a pillar layer 22 by selectively removing a portion of a resist layer. An example will be described in which the resist material is negative. The resist layer is covered with a photomask. The bottom shape and arrangement of the insulating pillars 1 can be adjusted by a pattern drawn on the photomask. For example, light is irradiated onto the resist layer through the photomask. The wavelength of light is selected depending on the resist material. For example, ultraviolet (UV) light may be irradiated. The light irradiation (exposure) forms a photosensitive portion and a non-photosensitive portion. The photosensitive portion is the portion irradiated with light. The photosensitive portion may be hardened. The non-photosensitive portion is the portion not irradiated with light. The non-photosensitive portion can be dissolved by a developer. The developer is selected depending on the resist material. The developer may contain, for example, caustic soda. The insulating pillars 1 (photosensitive portions) can be formed by removing the non-photosensitive portions. That is, the pillar layer 22 can be formed by selectively removing a portion of the resist layer.

[0156] <<Charge / discharge method>> FIG. 8 is a schematic flowchart of the charge / discharge method of this embodiment. Hereinafter, the "charge / discharge method of this embodiment" may be abbreviated as "the present charge / discharge method." The present charge / discharge method includes "(d) charging" and "(f) discharging." The order in FIG. 8 is an example. The present charge / discharge method includes "(d) charging" and "(f) discharging" in any order, as long as "(d) charging" and "(f) discharging" are each included at least once. For example, charging may be performed twice in succession, followed by discharging. For example, a rest period may be provided between "(d) charging" and "(f) discharging."

[0157] <(d) Charging> This charge / discharge method includes charging the cell 100. The charging includes depositing Li metal 2a in the gap 2. During charging, deposition of Li metal 2a may begin from the surface of the negative electrode current collector 21 (see FIG. 1). Deposition of Li metal 2a may progress along the thickness direction (Z-axis direction) of the pillar layer 22. Charging is terminated before Li metal 2a is exposed from the pillar layer 22. By charging so that Li metal 2a is contained within the pillar layer 22, swelling of the cell 100 can be reduced.

[0158] In a plan view (XY plane), the Li metal 2a can be precipitated so as to extend in a network pattern (see FIG. 3). This is because the insulating pillars 1 form a dispersed phase. By forming a continuous phase of the Li metal 2a within the pillar layer 22, it is expected that the amount of Li metal 2a precipitated in the in-plane direction will be uniform. The in-plane direction refers to any direction perpendicular to the thickness direction (Z-axis direction). By making the amount of Li metal 2a precipitated in the in-plane direction uniform, it is expected that swelling of the cell 100 will be further reduced.

[0159] <(f) Discharge> This charge / discharge method includes discharging the cell 100. Discharging includes dissolving the Li metal 2a in the gap 2 into the electrolyte. During discharge, dissolution of the Li metal 2a may begin from the side closer to the positive electrode 10. The dissolution of the Li metal 2a may proceed along the thickness direction of the pillar layer 22. All or part of the Li metal 2a may dissolve. Even if the Li metal 2a dissolves, it is believed that the external dimensions of the pillar layer 22 (frame) are unlikely to change. The dissolution of the Li metal 2a in the pillar layer 22 can reduce the volumetric change (shrinkage) of the cell 100.

[0160] <<Battery system>> 9 is a conceptual diagram showing a battery system according to this embodiment. The battery system 1000 may be mounted on, for example, an electric vehicle. The battery system 1000 may include, for example, a cell 100, a charge / discharge device 200, and a control device 300.

[0161] The battery system 1000 may include one cell 100 or multiple cells 100. The multiple cells 100 may form a module or a battery pack. The charging / discharging device 200 and the control device 300 may execute the above-mentioned charging / discharging method (FIG. 8). The charging / discharging device 200 charges or discharges the cell 100. The control device 300 may include various sensors (current sensor, voltage sensor, temperature sensor, etc.). The control device 300 may control, for example, the magnitude of the current amount based on various information acquired by the sensors. The charging / discharging device 200 and the control device 300 may be integrated, for example. For example, the control device 300 may include the charging / discharging device 200. [Example]

[0162] <<Evaluation>> 10 is a table showing the cell configurations and evaluation results. Cells No. 1 to 6 were fabricated as follows. Hereinafter, for example, "cell No. 1" may be simply referred to as "No. 1."

[0163] <Cell manufacturing> No. 1 Cathode active material (LiNi 0.5 Co 0.2 Mn 0.3 A slurry was formed by mixing O2), a conductive material (AB), a binder (PVdF), and a dispersion medium (N-methyl-2-pyrrolidone). The mixture ratio was "positive electrode active material / conductive material / binder = 90 / 5 / 5 (mass ratio)". Al foil (thickness 15 μm) was prepared as a positive electrode current collector. The slurry was applied to the surface of the positive electrode current collector to form a coating film. The coating film was dried to form a positive electrode active material layer. The positive electrode active material layer was pressed to fabricate a positive electrode.

[0164] A Cu foil (thickness 10 μm) was prepared as the negative electrode current collector. A resin film (thickness 20 μm) was prepared as the separator. The resin film had a three-layer structure (PP layer / PE layer / PP layer). A power generating element was formed by laminating the positive electrode, separator, and negative electrode current collector. A pouch made of Al laminate film was prepared as the exterior body. The power generating element and liquid electrolyte were sealed in the exterior body to produce a cell.

[0165] The liquid electrolyte contained the following components: Solvent: DME / TTE = 1 / 2 (volume ratio) Solute: LiFSI (1.8mol / L)

[0166] No.2 A porous metal body was prepared as a frame. The porous metal body included a conductive skeleton. The porous metal body was laminated on a negative electrode current collector to produce a negative electrode. A power generating element was formed by laminating a positive electrode, a separator, and a negative electrode. Except for these, a cell was manufactured in the same manner as No. 1. The porous metal body had a porosity of 70%. For convenience, the porosity of the porous metal body is indicated in the porosity box in the table of FIG. 10.

[0167] No.3 A nonwoven fabric was prepared as a frame. The nonwoven fabric was made of cellulose fiber. The cellulose fiber had insulating properties. The negative electrode was fabricated by laminating the nonwoven fabric on a negative electrode current collector. Except for this, a cell was fabricated in the same manner as No. 2. The nonwoven fabric had a porosity of 70%. For convenience, the porosity of the nonwoven fabric is indicated in the porosity box in the table in Figure 10.

[0168] No.4 A dry film resist (hereinafter referred to as "dry film") was prepared. The dry film was laminated on a negative electrode current collector to form a resist layer. The resist layer was covered with a photomask. Part of the resist layer was removed by photolithography.

[0169] Figure 11 is a schematic plan view showing the frame of No. 4. The resist layer 3 remains in a mesh (two-dimensional network) shape. Through-holes (gaps 2) are formed in a dot pattern. Apart from this, the cell was manufactured in the same way as No. 2.

[0170] No.5 By changing the photomask pattern, the resist layer was left in a dotted pattern, i.e., multiple insulating pillars 1 (pillar layers 22) were formed (see Figure 3). Except for this, a cell was manufactured in the same way as No. 4.

[0171] No.6 A cell was fabricated similar to No. 5 except that the diameter of the insulating pillar was changed (see Figure 10).

[0172] <Evaluation> A restraining jig is attached to the cell. The restraining jig restrains the periphery of the cell. The restraining jig has a fixed dimension. The restraining jig limits the expansion of the cell. This restraining method may also be called "fixed size restraint" or "fixed size." The restraining jig is equipped with a load cell. The load cell measures the restraining load. During charging, the cell tries to expand, exerting a force on the restraining jig and increasing the restraining load (the thickness of the cell does not substantially change).

[0173] The cell was set in the charge / discharge device. 1mA / cm 2 Constant current charging was carried out at a current density of 1 / 2 V until the cell voltage reached 4.2 V. The load increase rate was calculated using the following formula (F-4).

[0174] ΔL={(L1-L0) / L0}×100 …(F-4) ΔL: Load increase rate [%] L1: Restraint load after charging L0: Restraint load before charging (In this evaluation, L0 = 1.3 MPa)

[0175] In the table of FIG. 10, under the heading "Load increase rate," "A" indicates that the load increase rate was less than 10%. "B" indicates that the load increase rate was 10% or more but less than 20%. "C" indicates that the load increase rate was 20% or more. It is believed that the lower the load increase rate, the less swelling of the cell due to the precipitation of Li metal.

[0176] <Result> No. 1 has a high load increase rate. Figure 12 is a conceptual diagram showing the deposition behavior of No. 1. No. 1 does not include a frame. Upon charging, Li metal 2a is deposited on the surface of the negative electrode current collector 21. It is believed that the deposited Li metal 2a pushes away surrounding components, causing the cell to swell.

[0177] No. 2 has a high load increase rate. Figure 13 is a conceptual diagram showing the deposition behavior of No. 2. In No. 2, the frame includes a conductive skeleton 4. Deposition of Li metal 2a begins at the tip of the frame. Li metal 2a grows toward the positive electrode 10. It is believed that the deposited Li metal 2a pushes aside surrounding components, causing the cell to expand.

[0178] No. 3 has a high load increase rate. Figure 14 is a conceptual diagram showing the deposition behavior of No. 3. The frame of No. 3 is nonwoven fabric 5. Upon charging, Li metal 2a is deposited on the surface of negative electrode current collector 21. The deposited Li metal 2a cannot penetrate into the interior of nonwoven fabric 5 and accumulates, pushing nonwoven fabric 5 aside. This is thought to be because it is difficult for Li metal 2a to penetrate into the gaps between the intricately entangled fibers.

[0179] Nos. 5 and 6 have a low load increase rate. The frame of Nos. 5 and 6 is a pillar layer 22 (plurality of insulating pillars 1). Upon charging, Li metal 2a is deposited on the surface of the negative electrode current collector 21 (see FIG. 1). The Li metal 2a is deposited in the gaps 2 between the insulating pillars 1. The Li metal 2a grows within the gaps 2. Even if the amount of deposited Li metal 2a increases, it is thought that the external dimensions of the pillar layer 22 are unlikely to change. Therefore, it is thought that cell swelling can be reduced.

[0180] No. 4 has a higher load increase rate than Nos. 5 and 6. In No. 4, the resist is the continuous phase, and the Li metal is the dispersed phase. It is thought that the isolation of the Li metal makes it easier for the amount of Li metal precipitation to become non-uniform in the in-plane direction. On the other hand, in Nos. 5 and 6, the resist (insulating pillars) is the dispersed phase, and the Li metal is the continuous phase. It is thought that the Li metal being the continuous phase makes it easier for the amount of Li metal precipitation to become uniform in the in-plane direction. It is thought that the uniformity of the amount of Li metal precipitation in the in-plane direction reduces cell swelling. [Explanation of symbols]

[0181] 1 insulating pillar, 1a first bottom surface, 1b second bottom surface, 1c side surface, 2 gap, 2a Li metal, 3 resist layer, 4 conductive framework, 5 nonwoven fabric, 10 positive electrode, 11 positive electrode current collector, 12 positive electrode active material layer, 20 negative electrode, 21 negative electrode current collector, 22 pillar layer, 30 separator, 50 power generation element, 100 cell (Li metal secondary battery), 200 charge / discharge device, 300 control device, 1000 battery system.

Claims

1. a positive electrode, a negative electrode, and an electrolyte; the negative electrode includes a negative electrode current collector and a pillar layer, the pillar layer is disposed on a surface of the negative electrode current collector, the pillar layer is composed of a plurality of insulating pillars, The insulating pillars are arranged in a forest, so that, in a plan view, a continuous network of gaps is formed between the insulating pillars, each of the insulating pillars extends from the surface of the negative electrode current collector toward the positive electrode; each of the plurality of insulating pillars is entirely formed of an electrically insulating material; each of the plurality of insulating pillars has an aspect ratio of 0.1 or more and 1 or less; The aspect ratio is expressed by the formula (F-1): A R =H / D...(F-1) It is found by In the formula (F-1), A R represents the aspect ratio, H represents the height of the insulating pillar, and D represents the diameter of the insulating pillar. Lithium ions are dissolved in the electrolyte, The charging reaction of the negative electrode is a deposition reaction of lithium metal in the gaps between the insulating pillars; and The discharge reaction of the negative electrode is a dissolution reaction of the lithium metal in the gap. Lithium metal secondary battery.

2. each of the plurality of insulating pillars includes a resist material; The lithium metal secondary battery according to claim 1 .

3. Each of the plurality of insulating pillars has a diameter of 100 to 300 μm and a height of 1 to 100 μm. The lithium metal secondary battery according to claim 1 .

4. the electrolyte includes a solvent and a solute; the solvent comprises a hydrofluoroether; The solute comprises an imide salt. The lithium metal secondary battery according to claim 1 .

5. the pillar layer has a porosity of 50 to 95%; The porosity is calculated by the formula (F-2): P O ={(S 0 -S 1 ) / S 0 }×100 …(F-2) It is found by In the formula (F-2), P O indicates the porosity, and S 0 represents the area of the region in which the pillar layer is disposed out of the area of the negative electrode current collector, and S 1 represents the total adhesion area of the insulating pillars; The lithium metal secondary battery according to any one of claims 1 to 4.

6. The diameter of the insulating pillar varies in a height direction of the insulating pillar. The lithium metal secondary battery according to any one of claims 1 to 4.

7. In the plan view, the arrangement pattern of the insulating pillars is irregular. The lithium metal secondary battery according to any one of claims 1 to 4.

8. 2. A method for producing a negative electrode for a lithium metal secondary battery according to claim 1, comprising: (a) providing the negative electrode current collector; (b) forming a resist layer by disposing a resist material on the surface of the negative electrode current collector; and (c) selectively removing a portion of the resist layer to form the pillar layer; Including, A method for manufacturing a negative electrode.

9. (d) charging the lithium metal secondary battery; and (f) discharging the lithium metal secondary battery; Including, The lithium metal secondary battery includes a positive electrode, a negative electrode, and an electrolyte; the negative electrode includes a negative electrode current collector and a pillar layer, the pillar layer is disposed on a surface of the negative electrode current collector, the pillar layer is composed of a plurality of insulating pillars, The insulating pillars are arranged in a forest, so that gaps extending in a network pattern are formed between the insulating pillars in a plan view, each of the insulating pillars extends from the surface of the negative electrode current collector toward the positive electrode; each of the plurality of insulating pillars is entirely formed of an electrically insulating material; each of the plurality of insulating pillars has an aspect ratio of 0.1 or more and 1 or less; The aspect ratio is expressed by the formula (F-1): A R =H / D...(F-1) It is found by In the formula (F-1), A R represents the aspect ratio, H represents the height of the insulating pillar, and D represents the diameter of the insulating pillar. Lithium ions are dissolved in the electrolyte, (d) includes depositing lithium metal in the gaps between the insulating pillars; and (f) includes dissolving the lithium metal in the gap; In the plan view, the lithium metal is precipitated so as to extend in a network shape. A method for charging and discharging a lithium metal secondary battery.

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