Lithium metal negative electrode secondary battery

Abstract

To improve cycle durability of a lithium metal negative electrode secondary battery.SOLUTION: A lithium metal negative electrode secondary battery includes a positive electrode, a separator, a negative electrode, and an electrolyte. The electrolyte contains Li ions. The separator is interposed between the positive electrode and the negative electrode. The negative electrode includes a negative electrode substrate and a Li metal layer. The Li metal layer contains a continuous phase and a dispersed phase. The continuous phase contains Li metal. The dispersed phase contains a Li ion conductor. The Li ion conductor has a Li ion conductivity of 1.0×10-13-2.0×10-9 S / cm.SELECTED DRAWING: Figure 11

Description

[Technical Field]

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

[0002] Japanese Patent Application Laid-Open No. 2021-166195 (Patent Document 1) discloses forming a layer containing lithium phosphate on the surface of a negative electrode current collector. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-166195 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, the negative electrode of a lithium (Li) ion secondary battery utilizes an insertion reaction, which is a reaction in which Li ions enter and exit the crystals of a host material (such as graphite).

[0005] The negative electrode of a Li metal negative electrode secondary battery utilizes a dissolution-precipitation reaction. That is, during charging, Li metal precipitates from the electrolyte. During discharging, Li metal dissolves into the electrolyte. By utilizing the dissolution-precipitation reaction, an increase in energy density is expected. However, Li metal negative electrode secondary batteries still have room for improvement in cycle durability.

[0006] An object of the present disclosure is to improve the cycling durability of Li metal negative electrode secondary batteries. [Means for solving the problem]

[0007] 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.

[0008] 1. A lithium metal negative electrode secondary battery includes a positive electrode, a separator, a negative electrode, and an electrolyte. The electrolyte contains lithium ions. The separator is interposed between the positive electrode and the negative electrode. The negative electrode includes a negative electrode substrate and a lithium metal layer. The lithium metal layer includes a continuous phase and a dispersed phase. The continuous phase contains lithium metal. The dispersed phase contains a lithium ion conductor. The lithium ion conductor has a 1.0×10 -13 ~2.0×10 -9 It has a lithium ion conductivity of 100 S / cm.

[0009] Conventionally, in Li metal negative electrode secondary batteries, Li metal can be deposited non-uniformly during charging. Repeated charge and discharge (repeated dissolution and precipitation) can amplify the non-uniformity of Li metal. For example, Patent Document 1 proposes forming a protective layer on the surface of the negative electrode substrate. The protective layer contains lithium phosphate (Li3PO4). Patent Document 1 states that the presence of the protective layer results in uniform deposition of Li metal.

[0010] However, the presence of the protective layer may actually accelerate capacity degradation. Li ions conduct through the protective layer and reach the surface of the negative electrode substrate. Li ions accept electrons on the surface of the negative electrode substrate, resulting in the deposition of Li metal. The Li metal can form a Li metal layer. As Li metal deposits (charges), the thickness of the Li metal layer can increase. The Li metal layer grows, pushing up against the protective layer, forming a three-layer structure. The three-layer structure includes the negative electrode substrate, the Li metal layer, and the protective layer, in that order. In a three-layer structure (negative electrode substrate / Li metal layer / protective layer), the protective layer can inhibit contact between the Li metal layer and the electrolyte. As a result, poor electrolyte impregnation into the Li metal layer can occur. Poor electrolyte impregnation makes it difficult to transport charge carriers (Li ions) to the interface between the negative electrode substrate and the Li metal layer. A lack of Li ion supply reduces the size of the Li metal deposits. The miniaturization of the Li metal precipitate size can accelerate a side reaction between the Li metal and the electrolyte at the interface between the Li metal layer and the negative electrode substrate. As a result, the peel strength between the Li metal layer and the negative electrode substrate can decrease. The peeling at the interface between the Li metal layer and the negative electrode substrate can rapidly deteriorate the capacity.

[0011] The Li3PO4 contained in the protective layer of Patent Document 1 is usually 1.0 × 10 -7 In contrast, in the present disclosure, a Li-ion conductor having a significantly lower Li-ion conductivity is used. That is, the Li-ion conductor has a Li-ion conductivity of 2.0 × 10 -9 It has a Li-ion conductivity of less than 5 S / cm.

[0012] Based on conventional knowledge, it is presumed that the placement of a Li-ion conductor with low Li-ion conductivity on the surface of the negative electrode substrate inhibits the movement of Li ions and promotes capacity degradation. However, according to the new knowledge of the present disclosure, -9A density of 0.5 S / cm or less can change the morphology of Li metal deposition, reducing capacity degradation. That is, the Li metal layer can grow in a form incorporating the Li-ion conductor. In the Li metal layer, Li metal forms a continuous phase, and the Li-ion conductor forms a dispersed phase. Within the Li metal layer, the mobility of Li ions can increase at the three-phase interface between Li metal, Li-ion conductor, and electrolyte. This can promote the supply of Li ions to the interface between the Li metal layer and the negative electrode substrate. As a result, the frequency of side reactions between Li metal and the electrolyte at the interface between the Li metal layer and the negative electrode substrate can be reduced. Maintaining the peel strength between the Li metal layer and the negative electrode substrate is thought to reduce capacity degradation. This means that improved cycle durability is expected.

[0013] However, the Li ion conductivity is 1.0 × 10 -13 If the Li-ion conductivity is less than 1.0 × 10 S / cm, the mobility of Li ions is excessively hindered, which may accelerate the deterioration of capacity. -13 S / cm or more.

[0014] 2. The lithium metal negative electrode secondary battery described in the above item "1" may have, for example, the following configuration: The lithium ion conductor includes a first component, a second component, and a third component. The first component is Li. The second component is at least one selected from the group consisting of Mg, Al, Ti, Zn, Zr, Nb, Mo, Ta, W and rare earth elements. The third component is at least one selected from the group consisting of B, N, O, Si, P, S, Ge and a halogen.

[0015] 3. The lithium metal negative electrode secondary battery according to the above item "1" or "2" may have, for example, the following configuration: The dispersed phase further includes a binder, and the volume fraction of the binder relative to the total volume of the lithium ion conductor and the binder is less than 0.2.

[0016] When the volume fraction of the binder is less than 0.2, the Li ion conductor tends to be easily incorporated into the Li metal layer.

[0017] 4. The lithium metal negative electrode secondary battery according to any one of the above items "1" to "3" may have, for example, the following configuration: The lithium metal negative electrode secondary battery satisfies the relationship of the following formula (1-1). 0.1≦A1 / A0≦0.5 …(1-1) In the above formula (1-1), A0 and A1 are values ​​measured at 100% SOC. A0 represents the area occupied by lithium metal in the cross section of the lithium metal layer. A1 represents the area occupied by the lithium ion conductor in the cross section of the lithium metal layer.

[0018] Hereinafter, "A1 / A0" in the above formula (1-1) is also referred to as "the abundance ratio of the Li ion conductor." When the abundance ratio of the Li ion conductor is 0.1 to 0.5 (10 to 50%), improvement in cycle durability is expected.

[0019] 5. The lithium metal negative electrode secondary battery according to any one of the above items 1 to 4 may include, for example, the following configuration: The lithium ion conductor includes lithium phosphate.

[0020] As mentioned above, the Li ion conductivity of Li3PO4 is usually 1.0 × 10 -7 In the present disclosure, for example, Li3PO4 is subjected to a treatment that disrupts the crystallinity of the particle surface, thereby increasing the Li ion conductivity of Li3PO4 to 2.0 × 10 -9 It can be adjusted to S / cm or less.

[0021] 6. The lithium metal negative electrode secondary battery described in any one of the above items "1" to "5" may be, for example, an anode-free battery.

[0022] Since the lithium metal negative electrode secondary battery is an anode-free battery, for example, an improvement in energy density is expected.

[0023] 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]

[0024] [Figure 1] FIG. 1 is a conceptual diagram showing a method for measuring Li-ion conductivity. [Figure 2] FIG. 2 is a conceptual diagram showing a Li metal negative electrode secondary battery in this embodiment. [Figure 3] FIG. 3 is a conceptual diagram showing a Li-ion conductor in this embodiment. [Figure 4] FIG. 4 shows a first configuration example. [Figure 5] FIG. 5 shows a second configuration example. [Figure 6] FIG. 6 shows a third configuration example. [Figure 7] FIG. 7 is Table 1 showing the evaluation results. [Figure 8] FIG. 8 is Table 2 showing the evaluation results. [Figure 9] FIG. 9 is Table 3 showing the evaluation results. [Figure 10] FIG. 10 is Table 4 showing the evaluation results. [Figure 11] FIG. 11 is a graph showing the evaluation results of FIG. [Figure 12] FIG. 12 is a graph showing the evaluation results of FIG. [Figure 13] FIG. 13 is a conceptual diagram showing the deposition form of Li metal in No. 2. DETAILED DESCRIPTION OF THE INVENTION

[0025] <Terminology> Terms used in this specification are explained below. Terms not explained here may be explained whenever they are used in this specification.

[0026] 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] 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)."

[0029] Numerical ranges such as "m to n%" include the upper and lower limits unless otherwise specified. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% and less than n%." "Equal to or more" and "equal to or less" are represented by an inequality sign "≦." "More than" and "less than" are represented by an inequality sign "<" without an equality sign. A numerical value arbitrarily selected from within the numerical range may be used 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.

[0030] 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.

[0031] 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. For example, the compound may be doped with a trace element. A portion of Al and O may be substituted with another element.

[0032] The term "derivative" refers to a compound in which a part of a parent compound has been modified by at least one method selected from the group consisting of introduction of a substituent, substitution of an atom, oxidation, reduction, and other chemical reactions. The modification may be at one or more locations. The "substituent" may include at least one selected from the group consisting of, for example, 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. Multiple substituents may be bonded to each other to form a ring. Derivatives of polymer compounds (resin materials) may also be called "modified products."

[0033] The "copolymer" includes at least one selected from the group consisting of unspecified type, statistical type, random type, alternating type, periodic type, block type, and graft type.

[0034] "SOC (State Of Charge)" indicates the percentage of the battery's current charge capacity relative to the battery's fully charged capacity.

[0035] A "lithium metal negative electrode secondary battery" refers to a battery in which the negative electrode reaction includes a dissolution and precipitation reaction of Li metal. For example, the dissolution and precipitation reaction of Li metal may account for 1 to 100%, 25 to 100%, 50 to 100%, or 75 to 100% of the negative electrode capacity. The negative electrode capacity indicates a reversible capacity. For example, Li metal may be precipitated on the negative electrode at an SOC of 1 to 100%, 1 to 75%, 1 to 50%, or 1 to 25%. At an SOC of 0% (fully discharged), the Li metal may be completely dissolved in the electrolyte. At an SOC of 0%, some of the Li metal may remain in the negative electrode. Even if the Li metal is completely dissolved at an SOC of 0%, the negative electrode is considered to contain a Li metal layer as long as a Li metal layer can be formed at an SOC greater than 0%.

[0036] When the Li metal layer contains a dispersed phase (Li ion conductor) at 100% SOC, the Li metal layer is considered to contain a dispersed phase. The above description of "1" that "the lithium metal layer contains a continuous phase and a dispersed phase" may be rephrased as, for example, "the lithium metal negative electrode secondary battery is configured such that the lithium metal layer contains a continuous phase and a dispersed phase at 100% SOC."

[0037] Typically, the deposition of Li metal in a Li-ion secondary battery can result in irreversible capacity. The deposition of Li metal in a Li-ion secondary battery is, for example, an unintended reaction. The deposition of Li metal in a Li-ion secondary battery can occur, for example, during abnormalities or misuse.

[0038] In an "anode-free battery," no Li metal is present in the negative electrode before the first charge (after assembly, before the first charge). Anode-free batteries are assembled without the negative electrode containing any Li metal (negative electrode active material). During the first charge, Li is supplied from the positive electrode to the negative electrode, causing Li metal to precipitate on the negative electrode for the first time. In an anode-free battery, all of the Li metal may dissolve during full discharge.

[0039] "Li ion conductivity" is measured in the following procedure. Figure 1 is a conceptual diagram showing a method for measuring Li ion conductivity. A cylindrical jig 80 is prepared. The cylindrical jig 80 has a first open end face 81 and a second open end face 82. The inner wall of the cylindrical jig 80 is insulated. A first piston 91 and a second piston 92 are prepared. Both the first piston 91 and the second piston 92 are made of stainless steel (SUS). The first piston 91 is inserted from the first open end face 81. Inside the cylindrical jig 80, a sample 83 (powder of a Li ion conductor) is filled on the first piston 91. The second piston 92 is inserted from the second open end face 82. The sample 83 is charged with a Li ion conductivity of 5 tf / cm 2 The first piston 91 and the second piston 92 are pressed together so that a pressure of (490 MPa) is applied. By applying pressure, the sample 83 can be formed into a disk-shaped pellet. The sample 83 may also be formed into a cylindrical pellet. Current and voltage terminals are connected to the first piston 91 and the second piston 92, respectively. The AC impedance is measured using an impedance analyzer (for example, manufactured by Solartron). The measurement temperature is 25°C. In the Cole-Cole plot, the resistance is calculated from the intersection of the semicircle and the real axis (horizontal axis). The Li-ion conductivity is calculated using the following equation (1-2). σ=1 / {(R×A) / T)} …(1-2) σ: Li ion conductivity R: Resistance calculated from AC impedance A: Base area of ​​sample 83 (disk-shaped pellet) T: Thickness (height) of sample 83 (disc-shaped pellet)

[0040] The "proportion of lithium ion conductor present" is measured by the following procedure. The state of charge (SOC) of the lithium metal negative electrode secondary battery is adjusted to 100%. At 100% SOC, the lithium metal negative electrode secondary battery is disassembled to recover the negative electrode. The sample is prepared by performing a cross-sectioning process on the lithium metal layer. The sample includes a cross-section parallel to the thickness direction of the lithium metal layer. Element mapping analysis is performed on the cross-section of the lithium metal layer by SEM-EDS (Scanning Electron Microscope Energy Dispersive x-ray Spectroscopy). The analysis area is, for example, rectangular. The analysis area can be set to include, for example, the interface between the lithium metal layer and the negative electrode substrate and the surface of the lithium metal layer. In the element mapping image, the occupied area (A0) of the lithium metal is determined from the number of pixels derived from the lithium metal. In the element mapping image, the occupied area (A1) of the lithium ion conductor is determined from the number of pixels derived from the lithium ion conductor. By dividing A1 by A0, the proportion of the lithium ion conductor present (A1 / A0) is determined. The proportion is a dimensionless quantity. The proportion may be expressed as a percentage.

[0041] Note that the description "the lithium metal negative electrode secondary battery satisfies the relationship of formula (1-1)" in the above "4" may be rephrased, for example, as "the lithium metal negative electrode secondary battery is configured to satisfy the relationship of formula (1-1) at 100% SOC."

[0042] The "average particle size" indicates the particle size at which the integration becomes 50% in the volume-based particle size distribution (cumulative distribution). This particle size may also be referred to as "D50". The average particle size can be measured by the laser diffraction method.

[0043] <Lithium metal negative electrode secondary battery> Figure 2 is a conceptual diagram showing the lithium metal negative electrode secondary battery in this embodiment. The battery 100 includes a power generation element 50 and an electrolytic solution (not shown).

[0044] <Outer package> The battery 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 battery 100.

[0045] <Power generation elements> The power generating element 50 includes a positive electrode 10, a negative electrode 20, and a separator 30. The separator 30 is disposed between the positive electrode 10 and the negative electrode 20. The power generating element 50 may have any 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. For example, a strip-shaped separator 30 may be folded zigzag, with the positive electrodes 10 and the negative electrodes 20 arranged alternately each time the separator 30 is folded. The power generating element 50 may be, for example, a wound type. For example, the positive electrode 10, the negative electrode 20, and the separator 30 may all be strip-shaped. For example, a laminate may be formed by stacking the positive electrode 10, the separator 30, and the negative electrode 20 in this order. The power generating element 50 may be formed by spirally winding the laminate. The wound type power generating element 50 may be formed into a flat shape after being wound.

[0046] <Negative electrode> The negative electrode 20 includes a negative electrode substrate 21 and a Li metal layer 22. The negative electrode substrate 21 can provide a deposition site for Li metal. The negative electrode substrate 21 has conductivity. The negative electrode substrate 21 can function as a current collector. The negative electrode substrate 21 may have a thickness of, for example, 5 to 50 μm. The negative electrode substrate 21 may include, for example, a metal foil, a metal porous body, etc. The negative electrode substrate 21 may include at least one selected from the group consisting of Cu, Ni, Fe, Zn, Pb, Ag, and Au. The negative electrode substrate 21 may include, for example, a Cu foil, a Cu alloy foil, etc.

[0047] With the increase or decrease of SOC, the thickness of the Li metal layer 22 also increases or decreases. The Li metal layer 22 includes a continuous phase 22a and a dispersed phase 22b. The continuous phase 22a contains Li metal. The dispersed phase 22b contains a Li ion conductor. By including a Li ion conductor in the dispersed phase 22b, an improvement in cycle durability is expected.

[0048] The dispersed phase 22b is dispersed in the continuous phase 22a. The average distance between the dispersed phases 22b may be, for example, 1 to 10 μm. The average distance between the dispersed phases 22b can be measured, for example, in a cross-sectional image of the Li metal layer 22. The dispersed phase 22b may consist of a single particle or may include a particle aggregate (a plurality of particles). The Feret diameter of the dispersed phase 22b may be, for example, 0.1 to 5 μm, 0.5 to 3 μm, or 1 to 3 μm. The Feret diameter of the dispersed phase 22b indicates the distance between the two farthest points on the contour line of the dispersed phase 22b in a cross-sectional image of the Li metal layer 22.

[0049] As long as the dispersed phase 22b is distributed inside the Li metal layer 22, a part of the Li ion conductor may be distributed outside the Li metal layer 22. For example, a part of the Li ion conductor may be distributed between the Li metal layer 22 and the negative electrode substrate 21.

[0050] <The proportion of the Li ion conductor present> The abundance ratio of the Li ion conductor may be, for example, 0.05 to 0.6 (5 to 60%), or 0.1 to 0.5 (10 to 50%). When the abundance ratio of the Li ion conductor is 0.1 to 0.5, improvement in cycle durability is expected. The abundance ratio of the Li ion conductor may be, for example, 0.2 or more, 0.3 or more, or 0.4 or more. The abundance ratio of the Li ion conductor may be, for example, 0.4 or less, 0.3 or less, or 0.2 or less.

[0051] <Binder> The dispersed phase 22b may further contain a binder. The volume fraction of the binder with respect to the total of the Li-ion conductor and the binder may be, for example, less than 0.2 (less than 20%). That is, the dispersed phase 22b may contain less than 20% by volume of the binder, with the remainder being the Li-ion conductor. When the volume fraction of the binder is less than 0.2, the dispersed phase 22b tends to be easily formed. The volume fraction of the binder may be expressed as a percentage. The volume fraction of the binder may be, for example, 0.19 or less, 0.15 or less, 0.1 or less, 0.05 or less, 0.03 or less, or 0.01 or less. The volume fraction of the binder may be, for example, 0.001 or more, 0.005 or more, 0.01 or more, 0.03 or more, 0.05 or more, 0.1 or more, 0.15 or more, or 0.19 or more.

[0052] The binder may include any component. For example, the binder may include a material that can swell with the electrolyte. Swelling of the binder may promote the formation of the dispersed phase 22b. For example, the binder may include at least one selected from the group consisting of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ether, styrene butadiene rubber (SBR), acrylate butadiene rubber (ABR), polyacrylonitrile (PAN), and derivatives thereof.

[0053] <Lithium ion conductor> The lithium ion conductor has a lithium ion conductivity of 1.0×10 -13 ~2.0×10 -9 S / cm. With a lithium ion conductivity of 1.0×10 -13 ~2.0×10 -9 S / cm, an improvement in cycle durability is expected. The lithium ion conductivity may be, for example, 1.0×10 -12 S / cm or more, 1.0×10 -11 S / cm or more, or 1.0×10 -10 S / cm or more. The lithium ion conductivity may be, for example, 1.0×10 -10 S / cm or less, 1.0×10 -11 S / cm or less, or 1.0×10 -12 S / cm or less.

[0054] The lithium ion conductor is solid. The lithium ion conductor may be a group of particles. The lithium ion conductor may have an average particle size of, for example, 100~3000nm (0.1~3μm), 200~2000nm, or 300~1500nm. The average particle size of the lithium ion conductor may be, for example, 500nm or more, 1000nm or more, or 1300nm or more. The average particle size of the lithium ion conductor may be, for example, 1300nm or less, 1000nm or less, or 500nm or less.

[0055] As long as the lithium ion conductor has a lithium ion conductivity of 1.0×10 -13 ~2.0×10 -9 S / cm, it can have any composition. The lithium ion conductor may include, for example, a first component, a second component, and a third component. The first component is Li.

[0056] The second component is at least one selected from the group consisting of Mg, Al, Ti, Zn, Zr, Nb, Mo, Ta, W, and rare earth elements. The "rare earth elements" may include, for example, lanthanoids. The rare earth elements may include, for example, at least one selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0057] The third component is at least one selected from the group consisting of B, N, O, Si, P, S, Ge, and halogen. The "halogen" may include, for example, at least one selected from the group consisting of F, Cl, Br, and I.

[0058] The Li ion conductor may include, for example, a phosphate compound. The Li ion conductor may include, for example, Li3PO4.

[0059] The Li ion conductor may include, for example, a lithium nitride phosphate compound (LIPON). The Li ion conductor may have, for example, the composition of the following formula (1-3). Li x PO y N z …(1-3) In the above formula (1-3), x may satisfy, for example, the relationship of 2 ≦ x < 3. y may satisfy, for example, the relationship of 3 ≦ y < 4. z may satisfy, for example, the relationship of 0.1 < z < 0.5.

[0060] The Li ion conductor may be, for example, of the NASICON type. The Li ion conductor may have, for example, the composition of the following formula (1-4). Li 1+x Al x M 2-x (PO4)3…(1-4) In the above formula (1-4), M is at least one selected from the group consisting of Ti and Ge. x satisfies the relationship of 0 ≦ x ≦ 2.

[0061] The lithium ion conductor may, for example, have a composition represented by the following formula (1-5). Li 1-x Al x M 2-x (PO4)3…(1-5) In the above formula (1-5), M is at least one selected from the group consisting of Ti and Ge. x satisfies the relationship of 0.3 ≦ x ≦ 0.4.

[0062] The lithium ion conductor may, for example, contain a composite oxide. The lithium ion conductor may, for example, contain at least one selected from the group consisting of LiNbO3, Li2WO4, Li3BO3, LiBO2, Li2SO4, Li2SO3, Li2TiO3, Li2Ti2O5, Li2MoO4, Li2ZrO3, and LiAlO2.

[0063] The lithium ion conductor may, for example, contain a garnet-type oxide. The lithium ion conductor may, for example, have a composition represented by the following formula (1-6). Li 7-x M 1 Zr 2-x M 2 y O 12 …(1-6) In the above formula (1-6), M 1 is a rare earth element. M 1 may be, for example, La. M 2 is, for example, at least one selected from the group consisting of Mg, Nb, and Ta. x may, for example, satisfy the relationship of 0 ≦ x ≦ 1. y may, for example, satisfy the relationship of 0 ≦ y ≦ 1.

[0064] The lithium ion conductor may, for example, contain a perovskite-type oxide. The lithium ion conductor may, for example, have a composition represented by the following formula (1-7). Li 3x La 0.66-x TiO3…(1-7) In the above formula (1-7), x may, for example, satisfy the relationship of 0 < x < 0.66.

[0065] The lithium ion conductor may have, for example, a composition represented by the following formula (1-8). Li 3x La 0.33-x NbO3…(1-8) In the above formula (1-8), x may satisfy, for example, the relationship of 0 < x < 0.33.

[0066] <; The lithium ion conductor may contain, for example, an inverse perovskite type compound. The lithium ion conductor may have, for example, a composition represented by the following formula (1-9). Li 3-x (OH x )Cl …(1-9) In the above formula (1-9), x may satisfy, for example, the relationship of 0 ≦ x ≦ 1.

[0067] The lithium ion conductor may be, for example, of the LISICON type. The lithium ion conductor may have, for example, a composition represented by the following formula (1-10). Li 2+2x Zn 1-x GeO4…(1-10) In the above formula (1-10), x may satisfy, for example, the relationship of -0.36 < x < 0.87.

[0068] The Li-ion conductor may include, for example, an oxide glass. The oxide glass may be a glass ceramic (partially crystallized glass). The glass may be a solid solution. The composition of the glass may be expressed, for example, by the raw material composition. For example, "Li2O-Al2O3-SiO2-P2O5-TiO2" indicates a material produced by mixing Li2O, Al2O3, SiO2, P2O5, and TiO2 in an arbitrary molar ratio. The mixing ratio may be expressed by adding a number before each raw material. For example, "50Li4SiO4-50Li3BO3" indicates a mixing ratio of "Li4SiO4 / Li3BO3 = 50 / 50 (molar ratio)." The raw materials of the glass may include, for example, at least one selected from the group consisting of Li2O, Al2O3, SiO2, P2O5, TiO2, Li2SO4, Li3BO3, Li3BO4, Li4SiO4, and Li3PO4. The Li-ion conductor may include, for example, at least one selected from the group consisting of Li2O-Al2O3-SiO2-P2O5-TiO2, Li2SO4-Li3BO3, Li3BO4-Li4SiO4, and Li3PO4-Li3BO3.

[0069] The Li ion conductor may include, for example, a sulfide, a halide, etc. The sulfide may be, for example, a glass, a glass ceramic, an argyrodite, etc. The Li ion conductor may include, for example, Li 10 GeP2S 12 , Li7P3S 11 , Li 3.25 Ge 0.25 P 0.75 S4, Li 3.25 P 0.95 The Li-ion conductor may contain at least one selected from the group consisting of Li2S—B2S3—LiI, Li2S—Si2S2—LiI, and Li2S—Si2S2—Li4SiO4.

[0070] The lithium ion conductor may contain at least one selected from the group of materials described in FIGS. 7 to 10, for example.

[0071] <Method for adjusting lithium ion conductivity> Generally, the lithium ion conductor having the above composition has a lithium ion conductivity of 10 -5 S / cm or more. Therefore, the lithium ion conductivity is reduced so as to be 1.0×10 -13 ~2.0×10 -9 S / cm. For example, the pulverization treatment and the sintering treatment may be alternately repeated for the lithium ion conductor. The pulverization treatment can be carried out by, for example, a mechanochemical device or the like. The sintering treatment can be carried out at a low temperature. The sintering temperature may be, for example, about 200°C.

[0072] [[ID=B]]

[0073] <Positive electrode> The positive electrode 10 may be, for example, in the form of a sheet. The positive electrode 10 may include, for example, a positive electrode substrate 11 and a positive electrode active material layer 12. The positive electrode substrate 11 is conductive. The positive electrode substrate 11 can function as a current collector. The positive electrode substrate 11 supports the positive electrode active material layer 12. The positive electrode substrate 11 may be, for example, in the form of a sheet. The positive electrode substrate 11 may have a thickness of, for example, 5 to 50 μm. The positive electrode substrate 11 may include, for example, a metal foil. The positive electrode substrate 11 may include, for example, at least one selected from the group consisting of Al, Mn, Ti, Fe, and Cr. The positive electrode substrate 11 may include, for example, an Al foil, an Al alloy foil, a Ti foil, a SUS foil, or the like.

[0074] An intermediate layer (not shown) may be formed between the positive electrode substrate 11 and the positive electrode active material layer 12. The intermediate layer does not contain a positive electrode active material. The intermediate layer may have a thickness of, for example, 0.1 to 5 μm. The intermediate layer may contain, for example, a conductive material, an insulating material, a binder, etc. The conductive material and the binder will be described later. The insulating material may contain, for example, alumina, boehmite, aluminum hydroxide, etc.

[0075] The positive electrode active material layer 12 is disposed on the surface of the positive electrode substrate 11. The positive electrode active material layer 12 may be disposed on only one surface of the positive electrode substrate 11. The positive electrode active material layer 12 may be disposed on both the front and back surfaces of the positive electrode substrate 11. The positive electrode active material layer 12 may have a thickness of, for example, 10 to 1000 μm, 50 to 500 μm, or 100 to 300 μm. The positive electrode active material layer 12 contains a positive electrode active material. The positive electrode active material layer 12 may further contain, for example, a conductive material and a binder.

[0076] 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).

[0077] The binder can fix the positive electrode active material layer 12 to the positive electrode substrate 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 PVDF, PVDF-HFP, PTFE, CMC, PAA, PVA, PVP, polyoxyethylene alkyl ether, and derivatives thereof.

[0078] 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 also contain, for example, polyoxyethylene allyl phenyl ether phosphate, zeolite, a silane coupling agent, MoS2, WO3, etc.

[0079] The positive electrode active material may be, for example, in the form of particles. The positive electrode active material may contain any component. The positive electrode active material may contain, for example, a transition metal oxide, a polyanion compound, etc. The composition within one particle (positive electrode active material) may be uniform or non-uniform. For example, the composition may be graded from the surface toward the center of the particle. The composition may change continuously or discontinuously (in steps).

[0080] The transition metal oxide may have any crystal structure. The transition metal oxide may include, for example, a crystal structure belonging to the space group R-3m. For example, a compound represented by the general formula "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 (2-1). Li 1-a Ni x M 1-x O2…(2-1) In the above formula (2-1), M may include, for example, at least one selected from the group consisting of Co, Mn, and Al. For example, the relationship of -0.5 ≦ a ≦ 0.5, 0 < x ≦ 1 may be satisfied. For example, the relationship of -0.4 ≦ a ≦ 0.4, -0.3 ≦ a ≦ 0.3, -0.2 ≦ a ≦ 0.2, or -0.1 ≦ a ≦ 0.1 may be satisfied. For example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x ≦ 1 may be satisfied.

[0081] 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.

[0082] The transition metal oxide may be represented, for example, by the following formula (2-2). The compound represented by the following formula (2-2) may also be referred to as "NCM". Li 1-a Ni x Co y Mn z O2…(2-2) In the above formula (2-2), for example, the relationship of -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1 may be satisfied. For example, the relationship of 0 < x ≤ 0.1, 0.1 ≤ x ≤ 0.2, 0.2 ≤ x ≤ 0.3, 0.3 ≤ x ≤ 0.4, 0.4 ≤ x ≤ 0.5, 0.5 ≤ x ≤ 0.6, 0.6 ≤ x ≤ 0.7, 0.7 ≤ x ≤ 0.8, 0.8 ≤ x ≤ 0.9, or 0.9 ≤ x < 1 may be satisfied. For example, the relationship of 0 < y ≤ 0.1, 0.1 ≤ y ≤ 0.2, 0.2 ≤ y ≤ 0.3, 0.3 ≤ y ≤ 0.4, 0.4 ≤ y ≤ 0.5, 0.5 ≤ y ≤ 0.6, 0.6 ≤ y ≤ 0.7, 0.7 ≤ y ≤ 0.8, 0.8 ≤ y ≤ 0.9, or 0.9 ≤ y < 1 may be satisfied. For example, the relationship of 0 < z ≤ 0.1, 0.1 ≤ z ≤ 0.2, 0.2 ≤ z ≤ 0.3, 0.3 ≤ z ≤ 0.4, 0.4 ≤ z ≤ 0.5, 0.5 ≤ z ≤ 0.6, 0.6 ≤ z ≤ 0.7, 0.7 ≤ z ≤ 0.8, 0.8 ≤ z ≤ 0.9, or 0.9 ≤ z < 1 may be satisfied.

[0083] 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 Co0.1 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 It may contain at least one selected from the group consisting of O2.

[0084] The transition metal oxide may be represented, for example, by the following formula (2-3). The compound represented by the following formula (2-3) may also be referred to as "NCA". Li 1-a Ni x Co y Al z O2…(2-3) In the above formula (2-3), for example, the relationship of -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 may be satisfied. For example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x < 1 may be satisfied. For example, the relationship of 0 < y ≦ 0.1, 0.1 ≦ y ≦ 0.2, 0.2 ≦ y ≦ 0.3, 0.3 ≦ y ≦ 0.4, 0.4 ≦ y ≦ 0.5, 0.5 ≦ y ≦ 0.6, 0.6 ≦ y ≦ 0.7, 0.7 ≦ y ≦ 0.8, 0.8 ≦ y ≦ 0.9, or 0.9 ≦ y < 1 may be satisfied. For example, the relationship of 0 < z ≦ 0.1, 0.1 ≦ z ≦ 0.2, 0.2 ≦ z ≦ 0.3, 0.3 ≦ z ≦ 0.4, 高.4 ≦ z ≦ 0.5, 0.5 ≦ z ≦ 0.6, 0.6 ≦ z ≦ 0.7, 0.7 ≦ z ≦ 0.8, 0.8 ≦ z ≦ 0.9, or 0.9 ≦ z < 1 may be satisfied.

[0085] NCA is, for example, LiNi 0.7 Co 0.1 Al 0.2 O2, LiNi 0.7 Co 0.2 Al0.1 O2, LiNi 0.8 Co 0.1 Al 0.1 O2, LiNi 0.8 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.

[0086] 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 (2-2) 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 (2-2). 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."

[0087] 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.

[0088] 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 (2-4). Li2MO3…(2-4) In the above formula (2-4), M may include, for example, at least one selected from the group consisting of Ni, Co, Mn, and Fe.

[0089] 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).

[0090] 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 (2-5). LiMn 2-x M x O4…(2-5) In the above formula (2-5), M may include, for example, at least one selected from the group consisting of Ni, Fe, and Zn. For example, the relationship 0≦x≦2 may be satisfied.

[0091] LiM2O4 (space group Fd-3m) is, for example, LiMn2O4 and LiMn 1.5 Ni 0.5The 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."

[0092] The polyanion compound may include, for example, a phosphate (such as LiFePO4), a silicate, a borate, etc. The polyanion compound may be represented by, for example, the following formulas (2-6) to (2-9). LiMPO4…(2-6) Li 2-x MPO4F...(2-7) Li2MSiO4…(2-8) LiMBO3…(2-9) In the above formulas (2-6) to (2-9), M may include, for example, at least one selected from the group consisting of Fe, Mn, and Co. In the above formula (2-7), for example, the relationship 0≦x≦2 may be satisfied.

[0093] 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) to 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."

[0094] 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.

[0095] 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.

[0096] For example, the set of "Zr, Mg, W, Sm", the set of "Ti, Mn, Nb, Si, Mo", or the set of "Er, Mg" may be added to the NCA. For example, Ti may be added to the NCM. For example, the set of "Zr, W", the set of "Si, W", or the set of "Zr, W, Al, Ti, Co" may be added to the NCM.

[0097] The positive electrode 10 may include composite particles. The composite particles include a core particle and a shell layer. The core particle includes a positive electrode active material. The shell layer covers at least a portion of the surface of the core particle. The shell layer may have a thickness of, for example, 1 to 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 shell layer can be measured, for example, from an 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 cross-sectioned 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 shell thickness is measured in 20 fields for each of 10 composite particles, and the arithmetic mean of the thicknesses of 200 points in total is used.

[0098] The proportion of the surface of the core particle that is covered with the shell layer is also referred to as the "coverage." The coverage may be, for example, 1% or more, 10% or more, 30% or more, 50% or more, or 70% or more. The coverage may be, for example, 100% or less, 90% or less, or 80% or less.

[0099] 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. The sample (powder) 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. By analyzing the measurement data, multiple elements are detected. The ratio of each detected element is calculated from the area of ​​each peak. The coverage can be calculated using the following formula (2-10). θ={I1 / (I0+I1)}×100 …(2-10) θ: Coverage rate [%] I0: Ratio of elements originating from the core particle I1: Ratio of elements derived from the shell 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 shell layer contains P and B, I1 indicates the total element ratio of "P and B."

[0100] The shell layer may contain any component. The shell 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 shell layer may contain, for example, B, Al, W, Zr, Ti, Co, F, a lithium compound (e.g., Li2CO3, LiHCO3, LiOH, Li2O, etc.), a tungsten oxide (e.g., WO3, etc.), a titanium oxide (e.g., TiO2, etc.), a zirconium oxide (e.g., ZrO2), a boron oxide, a boron phosphate (e.g., BPO4, etc.), an aluminum oxide (e.g., Al2O3, etc.), boehmite, an aluminum hydroxide, a 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.).

[0101] "Hollow particles" and "solid particles" are secondary particles (aggregates of primary particles). In a cross-sectional image of a "hollow particle," the area ratio of the cavity in the center is 30% or more of the cross-sectional area of ​​the entire particle. The ratio of the cavity in a hollow particle may be, for example, 40% or more, 50% or more, or 60% or more. In a cross-sectional image of a "solid particle," the area ratio of the cavity in the center is less than 30% of the cross-sectional area of ​​the entire particle. The ratio of the cavity in a solid particle may be, for example, 20% or less, 10% or less, or 5% or less. The positive electrode active material may be hollow particles or solid particles. A mixture of hollow particles and solid particles may be used. The mixing ratio (mass ratio) of hollow particles to solid particles may be, for example, "hollow particles / solid particles = 1 / 9 to 9 / 1," "hollow particles / solid particles = 2 / 8 to 8 / 2," "hollow particles / solid particles = 3 / 7 to 7 / 3," or "hollow particles / solid particles = 4 / 6 to 6 / 4."

[0102] The positive electrode active material may have, for example, a unimodal particle size distribution (based on the number of particles). The positive electrode active material may have, for example, a multimodal particle size distribution. The positive electrode active material may have, for example, a bimodal particle size distribution. That is, the positive electrode active material may contain "large particles" and "small particles". When the particle size distribution is bimodal, the particle 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.

[0103] For example, the particle size distribution may be subjected to peak separation processing using waveform analysis software. L ) and the peak area due to small particles (S S ) is expressed as, for example, "S L / SS =1 / 9~9 / 1", "S L / S S =5 / 5~9 / 1" or "S L / S S =7 / 3~9 / 1" is also acceptable.

[0104] The number-based particle size distribution is measured by microscopy. Multiple cross-sectional samples are taken from the positive electrode active material layer 12. The cross-sectional samples may include, for example, cross sections perpendicular to the surface of the positive electrode active material layer 12. 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 outline of a particle. 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.

[0105] 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. For example, the large particles may have a D50 of 8 to 20 μm or 8 to 15 μm. For example, the small particles may have a D50 of 1 to 10 μm or 1 to 5 μm. The ratio of the D50 of the large particles to the D50 of the small particles may be, for example, 2 to 10, 2 to 5, or 2 to 4. The mixing ratio (mass ratio) of the large particles to the small particles may be, for example, "large particles / small particles = 1 / 9 to 9 / 1," "large particles / small particles = 5 / 5 to 9 / 1," or "large particles / small particles = 7 / 3 to 9 / 1."

[0106] The large particles may have the same composition as the small particles, or may have different compositions. For example, the large particles may be NCA and the small particles may be NCM. For example, the large particles may be NCM (0.6≦x) and the small particles may be NCM (x<0.6).

[0107] <Electrolyte> The electrolyte is a liquid electrolyte. The electrolyte contains Li ions. The electrolyte may contain, for example, a solute and a solvent.

[0108] 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, etc. The solute may include at least one selected from the group consisting of, for example, LiPF6, LiBF4, LiClO4, LiAsF6, LiSbF6, LiN(SO2F)2 (commonly known as LiFSI), LiN(SO2CF3)2 (commonly known as LiTFSI), LiB(C2O4)2 (commonly known as LiBOB), LiBF2(C2O4) (commonly known as LiDFOB), LiPF2(C2O4)2 (commonly known as LiDFOP), LiPO2F2, FSO3Li, LiI, LiBr, and derivatives thereof.

[0109] The electrolyte may contain, for example, an ether-based solvent, such as at least one selected from the group consisting of tetrahydrofuran (THF), 1,4-dioxane (DOX), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), ethylglyme, triglyme, tetraglyme, hydrofluoroether (HFE), and derivatives thereof.

[0110] The HFE may include at least one selected from the group consisting of, for example, a difluoromethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, a 2,2,3,3,3-pentafluoropropyl group, a 2,2,3,3-tetrafluoropropyl group, a 1,1,1,3,3,3-hexafluoroisopropyl group, a 1,1,2,3,3,3-hexafluoropropyl group, a 2,2,3,3,4,4,4-heptafluorobutyl group, a 2,2,3,3,4,4-hexafluorobutyl group, and a 2,2,3,3,4,4,5,5-octafluoropentyl group.

[0111] 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, 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.

[0112] 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.

[0113] 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."

[0114] 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".

[0115] 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 (3-1). V EC +V FEC +V EMC +V DMC +V DEC =10 …(3-1) In the above formula (3-1), V EC , V FEC , V EMC , V DMC , V DEC indicates the volume ratio of EC, FEC, EMC, DMC, and DEC, respectively. For example, 1 ≤ V EC ≦4, 0≦V FEC ≦3, V EC +V FEC ≦4, 0≦V EMC ≦9, 0≦V DMC ≦9, 0≦V DEC ≦9, 6≦V EMC +V DMC +V DEC ≦9 The relationship may be satisfied.

[0116] In the above formula (3-1), 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 FECThe 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.

[0117] 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."

[0118] 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.

[0119] 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.

[0120] The components described above as solutes and solvents may be used as additives (trace components). 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.

[0121] The electrolytic solution may contain an ionic liquid, 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.

[0122] The battery 100 may include a gel electrolyte. The gel electrolyte includes an electrolytic solution and a polymer material. The polymer material may form a polymer matrix. The polymer material may include, 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.

[0123] <Separator> The separator 30 has electrical insulation properties. The separator 30 may include, for example, at least one selected from the group consisting of a resin film, an inorganic particle layer, and an organic particle layer. The separator 30 may include, for example, a resin film and an inorganic particle layer.

[0124] 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 is permeable to an electrolytic solution. 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.

[0125] The resin film may contain at least one selected from the group consisting of, for example, olefin-based resins, urethane-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.

[0126] The resin film may have, for example, a single-layer structure. The resin film may be composed of, for example, a PE layer. The skeleton of the PE layer is formed of PE. The PE layer may have a shutdown function. The resin film may have, for example, a multi-layer structure. The resin film may include, for example, a PP layer and a PE layer. The skeleton of the PP layer is formed of PP. The resin film may have, for example, a three-layer structure. The resin film may be formed by laminating, for example, a PP layer, a PE layer, and a PP layer in this order. The thickness of the PE layer may be, for example, 5 to 20 μm. The thickness of the PP layer may be, for example, 3 to 10 μm.

[0127] An inorganic particle layer may be formed on the surface of the resin film. The inorganic particle layer may be formed on only one side of the resin film, or on both 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] Separator 30 may include, for example, a mixed layer, which includes both inorganic and organic particles.

[0132] <Battery configuration example> FIG. 4 is a first configuration example. FIG. 5 is a second configuration example. FIG. 6 is a third configuration example. In the tables in each figure, when multiple types of 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."

[0133] In this embodiment, as long as the dispersed phase 22b (Li ion conductor) is disposed in the Li metal layer 22 and the negative electrode 20 utilizes the dissolution and precipitation reaction of Li metal, other configurations (such as the combination of the positive electrode, separator, and electrolyte) are arbitrary. For example, any elements may be extracted from the first, second, and third configuration examples and combined in any combination. [Example]

[0134] <Test Battery Manufacturing> Test batteries (anode-free batteries) according to Nos. 1 to 55 were manufactured according to the following procedure. Hereinafter, for example, "test battery according to No. 1" may be simply referred to as "No. 1."

[0135] No.1 An Al foil was prepared as a positive electrode substrate. A positive electrode paint was applied to the surface of the Al foil using a die coater and dried. This formed a positive electrode active material layer. The positive electrode active material layer was compressed using a rolling mill. A positive electrode blank was produced in this manner. The positive electrode blank was cut into a predetermined shape to prepare a positive electrode. The positive electrode active material was LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 It was O2.

[0136] A resin film (thickness: 20 μm) was prepared as a separator. The resin film contained an olefin-based resin.

[0137] A Cu foil was prepared as a negative electrode substrate, and the Cu foil was cut into a predetermined shape to prepare a negative electrode.

[0138] A power generating element was formed by stacking a positive electrode, a separator, and a negative electrode in this order. The power generating element was then housed in an outer casing. An electrolyte solution was poured into the outer casing. The composition of the electrolyte solution was as follows:

[0139] Electrolyte composition Solute: LiPF6 (1mol / L) Solvent: EC / DMC = 1 / 1 (volume ratio)

[0140] After the electrolyte was injected, the exterior was sealed. The test battery was assembled in this manner. The test battery was charged using a constant current method, and a Li metal layer was formed on the surface of the negative electrode substrate. The test battery was manufactured in this manner.

[0141] No.2 Commercially available Li3PO4 powder (Li ion conductivity: 1 × 10) was prepared using a mechanochemical device. -7 S / cm) was crushed. The crushed material was sintered at low temperature. Crushing and low-temperature sintering were repeated alternately. This resulted in the Li-ion conductivity of Li3PO4 reaching 2×10 -9 It was adjusted to S / cm.

[0142] A PVDF solution was prepared. Li3PO4 powder (Li ion conductivity: 2 × 10 -9 A coating material was prepared by mixing a Li-ion conductor (Li-ion conductor / PVDF solution) and a PVDF solution. The mixing ratio was 80 / 20 (mass ratio). The coating material was applied to the surface of the negative electrode substrate by gravure coating and then dried. This prepared the negative electrode. Except for these steps, a test battery was assembled in the same manner as No. 1. The test battery was charged using a constant current method, and a Li metal layer was formed on the surface of the negative electrode substrate. This is how the test battery was manufactured.

[0143] No.3 Li3PO4 powder (Li ion conductivity: 1×10 -7 A coating material was prepared by mixing a Li-ion conductor (Li-ion conductor / PVDF solution) and a PVDF solution. The mixing ratio was "Li-ion conductor / PVDF solution = 99 / 1 (mass ratio)." The coating material was applied to the surface of the negative electrode substrate by gravure coating and dried. This prepared the negative electrode. Except for these steps, a test battery was assembled in the same way as No. 1. The test battery was charged by a constant current method, and a Li metal layer was formed on the surface of the negative electrode substrate. This is how the test battery was manufactured.

[0144] No.4 Li3PO4 powder (Li ion conductivity: 2×10 -9 A test cell was fabricated in the same manner as No. 3, except that a paint was prepared by mixing a PVDF solution with a PVDF solution.

[0145] No.5~No.9 FIG. 7 is Table 1 showing the evaluation results. As shown in Table 1, test batteries were manufactured in the same manner as No. 4, except that the Li ion conductivity of Li3PO4 was adjusted. In FIG. 7 etc., for example, the description "2E-09" means "2 x 10 -9 " indicates.

[0146] No.10~No.15 Figure 8 shows the evaluation results in Table 2. Test batteries were fabricated in the same manner as No. 4, except that the amount of coating containing Li3PO4 on the negative electrode was changed. It is believed that the proportion of the Li-ion conductor present changes depending on the amount of coating.

[0147] No.16~No.39 9 shows Table 3 showing the evaluation results. Test batteries were fabricated in the same manner as No. 4, except that the Li-ion conductors listed in Table 3 were used instead of Li3PO4.

[0148] No.40~No.55 10 is Table 4 showing the evaluation results. Test batteries were fabricated in the same manner as No. 4, except that the Li-ion conductors listed in Table 4 were used instead of Li3PO4.

[0149] <Evaluation> Constant temperature performance The OCV (Open Circuit Voltage) of the test battery was adjusted to 3.7 V. The battery was discharged at a current of 5 C for 8 seconds in a temperature environment of -10°C. The battery resistance was calculated using the following formula (5-1). R=ΔV / I…(5-1) R: Battery resistance ΔV: Voltage drop during 8 seconds of discharge I: Current equivalent to 5C

[0150] The battery resistances are shown in Tables 1 to 4 (Figs. 7 to 10). Each battery resistance is a normalized value, with the resistance of battery No. 1 set to "1." The smaller the value, the better the low-temperature performance. "C" is the symbol that indicates the time rate of the current. A current of 1C discharges the rated capacity of the battery in 1 hour.

[0151] Cycle durability A cycle test was carried out under the following conditions: Ambient temperature: 70°C Charge / discharge method: constant current method Current rate: 1C Voltage range: 3.3~4.2V Number of cycles: 200

[0152] The cycle capacity retention rate was calculated by dividing the discharge capacity at the 200th cycle by the discharge capacity at the 1st cycle. The cycle capacity retention rate is expressed as a percentage. The cycle capacity retention rates are shown in Tables 1 to 4 (FIGS. 7 to 10). A higher cycle capacity retention rate is considered to indicate better cycle durability.

[0153] Distribution and abundance of Li-ion conductors At 100% SOC, the test battery was disassembled and the anode was recovered. The distribution of Li-ion conductors was confirmed in the cross section of the Li metal layer. Furthermore, the proportion of Li-ion conductors present was measured using the procedure described above.

[0154] <Result> 13 is a conceptual diagram showing the deposition form of Li metal in No. 2. In No. 2, the Li ion conductor was distributed outside the Li metal layer 22. A Li ion conductor layer 22c was formed between the Li metal layer 22 and the separator 30. That is, a three-layer structure (negative electrode substrate 21 / Li metal layer 22 / Li ion conductor layer 22c) was formed. No. 2 had a lower cycle durability than No. 1 (without a Li ion conductor).

[0155] No. 3 differs from No. 2 in the volume fraction of the binder. In No. 3, the Li-ion conductor was distributed inside the Li metal layer (see Figure 2). No. 3 had improved cycle durability compared to Nos. 1 and 2. However, the improvement was small.

[0156] No. 4 differs from No. 3 in the Li-ion conductivity of the Li-ion conductor. In No. 4, the Li-ion conductor is distributed inside the Li metal layer. No. 4 has significantly improved cycle durability compared to No. 3.

[0157] FIG. 11 is a graph showing the evaluation results of FIG. 7. The graph of FIG. 7 is a semi-logarithmic graph, with the horizontal axis being the logarithmic axis. The Li-ion conductor is distributed inside the Li metal layer, and the Li-ion conductivity of the Li-ion conductor is 1.0×10 -13 ~2.0×10 -9 When the dielectric constant is 0.05 S / cm, the cycle durability tends to be significantly improved.

[0158] In Figure 7 (Table 1), it can be seen that when cycle durability is good, low-temperature performance also tends to be good. It is possible that the mobility of Li ions in low-temperature environments is significantly improved by the formation of a dispersed phase of Li ion conductors in the Li metal layer.

[0159] Fig. 12 is a graph showing the evaluation results of Fig. 8. When the abundance ratio of the Li ion conductor is 0.1 to 0.5, there is a tendency for the cycle durability to improve significantly.

[0160] In Li-ion conductors with various compositions, the Li-ion conductivity is 1.0×10 -13 ~2.0×10 -9 When the dielectric constant is 0.05 S / cm, the cycle durability tends to improve (see FIGS. 9 and 10). [Explanation of symbols]

[0161] 1 center portion, 2 surface layer portion, 5 particle, 10 positive electrode, 11 positive electrode substrate, 12 positive electrode active material layer, 20 negative electrode, 21 negative electrode substrate, 22 Li metal layer, 22a continuous phase, 22b dispersed phase, 22c Li ion conductor layer, 30 separator, 50 power generating element, 80 cylindrical jig, 81 first opening end surface, 82 second opening end surface, 83 sample, 91 first piston, 92 second piston, 100 battery (Li metal negative electrode secondary battery).

Claims

1. a positive electrode, a separator, a negative electrode, and an electrolyte; the electrolyte solution contains lithium ions, the separator is interposed between the positive electrode and the negative electrode, the negative electrode includes a negative electrode substrate and a lithium metal layer; the lithium metal layer comprises a continuous phase and a dispersed phase; the continuous phase comprises lithium metal; the dispersed phase comprises a lithium ion conductor; and The lithium ion conductor is 1.0×10 -13 ~2.0 x 10 -9 S / cm lithium ion conductivity, Lithium metal negative electrode secondary battery.

2. the lithium ion conductor includes a first component, a second component, and a third component; the first component is Li; The second component is at least one selected from the group consisting of Mg, Al, Ti, Zn, Zr, Nb, Mo, Ta, W, and rare earth elements; and the third component is at least one selected from the group consisting of B, N, O, Si, P, S, Ge, and a halogen; 2. The lithium metal negative electrode secondary battery according to claim 1.

3. the dispersed phase further comprises a binder; and The volume fraction of the binder relative to the total volume of the lithium ion conductor and the binder is less than 0.

2.

3. The lithium metal negative electrode secondary battery according to claim 1 or claim 2.

4. Formula (1-1): 0.1≦A 1 / A 0 ≦0.5 …(1-1) Fulfilling the relationship, In the formula (1-1), A 0 and A 1 is the value measured at 100% SOC, A 0 indicates the area occupied by the lithium metal in the cross section of the lithium metal layer, and A 1 indicates the area occupied by the lithium ion conductor in the cross section of the lithium metal layer, 3. The lithium metal negative electrode secondary battery according to claim 1 or claim 2.

5. The lithium ion conductor includes lithium phosphate.

3. The lithium metal negative electrode secondary battery according to claim 1 or claim 2.

6. It is an anode-free battery.

3. The lithium metal negative electrode secondary battery according to claim 1 or claim 2.

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