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 separator includes a porous substrate and a coating layer. The porous substrate has a first main surface and a second main surface. The first main surface faces the positive electrode. The second main surface faces the negative electrode. The coating layer covers the second main surface. The coating layer 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 12

Description

[Technical Field]

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

[0002] International Publication No. 2021 / 131533 (Patent Document 1) discloses a lithium metal negative electrode secondary battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 131533 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 separator includes a porous substrate and a coating layer. The porous substrate has a first main surface and a second main surface. The first main surface faces the positive electrode. The second main surface faces the negative electrode. The coating layer coats the second main surface. The coating layer 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] In conventional lithium metal negative electrode secondary batteries, lithium metal can be deposited non-uniformly in the in-plane direction of the negative electrode during charging. The "in-plane direction" refers to any direction perpendicular to the thickness direction. Repeated charge / discharge (repeated dissolution and precipitation) can amplify the non-uniformity of the lithium metal. As a result, the capacity retention rate can rapidly decrease.

[0010] In the present disclosure, the separator includes a coating layer. The coating layer faces the negative electrode. The coating layer includes a Li-ion conductor. In the present disclosure, the Li-ion conductor has a 1.0×10 -13 ~2.0×10 -9 It has a Li-ion conductivity of 2.0×10 S / cm. -9 Li-ion conductivity of 10 S / cm or less is significantly lower than general values. For example, the Li-ion conductivity of the electrolyte is 10 -2 The Li-ion conductivity of the solid electrolyte used in all-solid-state batteries can be as high as 10 -2 ~10 -4 It can be on the order of S / cm.

[0011] During charging, Li ions pass through the coating layer and reach the negative electrode. As mentioned above, the Li ion conductor contained in the coating layer has significantly low ionic conductivity. Therefore, it is thought that Li ions become congested at the interface between the Li ion conductor and the negative electrode (deposition field). This Li ion congestion can locally increase the Li ion concentration in the electrolyte. In other words, a Li ion-enriched layer can be formed. The Li ion-enriched layer can have a rectifying effect. By allowing Li ions to reach the negative electrode via the Li ion-enriched layer, the in-plane variation in the supply of Li ions can be reduced. Therefore, it is expected that Li metal will be deposited uniformly. Uniform Li metal deposition during charging is expected to improve cycle durability.

[0012] However, if the Li-ion conductivity of the Li-ion conductor is 1.0 × 10 -13 If the Li-ion conductivity is less than 1.0 × 10 S / cm, the Li-ions may become excessively stagnant, which may result in a decrease in cycle durability. -13 S / cm or more.

[0013] In Patent Document 1, a functional layer is laminated on a separator. The functional layer contains phosphate particles (specifically, lithium phosphate). Lithium phosphate (Li3PO4) is a Li-ion conductor. However, the Li-ion conductivity of Li3PO4 is usually 1.0 × 10 -7 S / cm. That is, the Li ion conductivity in Patent Document 1 may be 50 times or more higher than the Li ion conductivity in the present disclosure. The functional layer in Patent Document 1 is considered not to have a rectifying effect. Patent Document 1 states that the functional layer can suppress a temperature rise in the battery. The functional layer in Patent Document 1 is different from the coating layer in the present disclosure.

[0014] In the present disclosure, Li3PO4 is subjected to a treatment that disrupts the crystallinity of the particle surface, for example, so that the Li ion conductivity of Li3PO4 is increased to 2.0 × 10 -9 It can be adjusted to S / cm or less.

[0015] 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.

[0016] 3. The lithium metal negative electrode secondary battery described in the above item "1" or "2" may include, for example, the following configuration: The lithium ion conductor has an average particle size of, for example, 300 to 1500 nm.

[0017] When the average particle size of the Li-ion conductor is 300 to 1500 nm (0.3 to 1.5 μm), improvement in cycle durability is expected.

[0018] 4. The lithium metal negative electrode secondary battery according to any one of the above items "1" to "3" may include, for example, the following configuration: The coating layer has a thickness of 0.5 to 15 μm.

[0019] When the thickness of the coating layer is 0.5 to 15 μm, improvement in cycle durability is expected.

[0020] 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.

[0021] For example, the Li ion conductivity of Li3PO4 is 1.0×10 -13 ~2.0×10 -9 It may be adjusted to the range of S / cm.

[0022] 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.

[0023] Since the lithium metal negative electrode secondary battery is an anode-free battery, for example, an improvement in energy density is expected.

[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 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 Table 5 showing the evaluation results. [Figure 12] FIG. 12 is a graph showing the evaluation results of FIG. [Figure 13] FIG. 13 is a graph showing the evaluation results of FIG. [Figure 14] FIG. 14 is a graph showing the evaluation results of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0026] <Terminology> Terms used in this specification are explained below. Terms not explained here may be explained whenever they are used in this specification.

[0027] 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.

[0028] 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."

[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] 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.

[0031] 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.

[0032] 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.

[0033] 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."

[0034] 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.

[0035] "SOC (State Of Charge)" indicates the percentage of the battery's current charge capacity relative to the battery's fully charged capacity.

[0036] 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 entire amount of Li metal may be dissolved in the electrolyte. At an SOC of 0%, some Li metal may remain in the negative electrode.

[0037] Typically, Li metal deposition in a lithium ion secondary battery can result in irreversible capacity. Li metal deposition in a lithium ion secondary battery is, for example, an unintended reaction. Li metal deposition in a lithium 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 2The first piston 91 and the second piston 92 are pressed so that a pressure of (490 MPa) is applied. By pressurization, the sample 83 can be formed into a disk-shaped pellet. The sample 83 may be formed into a cylindrical pellet. Current-voltage terminals are connected to the first piston 91 and the second piston 92, respectively. An alternating current impedance is measured by an impedance analyzer (for example, manufactured by Solartron). The measurement temperature is 25 °C. In the Cole-Cole plot, the resistance is obtained from the intersection of the semi-circle and the real axis (horizontal axis). The Li-ion conductivity is obtained by the following formula (1-1). σ = 1 / {(R × A) / T)} …(1-1) σ: Li-ion conductivity R: Resistance obtained from the alternating current impedance A: Bottom area of the sample 83 (disk-shaped pellet) T: Thickness (height) of the sample 83 (disk-shaped pellet)

[0040] Incidentally, if necessary, the Li-ion conductivity may be measured by the following method. A separator including a porous base material and a coating layer is prepared. The coating layer contains a Li-ion conductor. An electrolytic solution is prepared. The Li-ion conductivity of the electrolytic solution is measured. The separator is impregnated with the electrolytic solution. The Li-ion conductivity of the separator impregnated with the electrolytic solution is measured. The Li conductivity of the Li-ion conductor is obtained by subtracting the Li-ion conductivity of the electrolytic solution from the measured value.

[0041] The "average particle size" indicates the particle size at which the integration becomes 50% in the volume-based particle size distribution (cumulative distribution). The particle size may also be referred to as "D50". The average particle size can be measured by the laser diffraction method.

[0042] Figure 2 is a conceptual diagram showing the Li metal negative electrode secondary battery in the present embodiment. The battery 100 includes a power generation element 50 and an electrolytic solution (not shown).

[0043] <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.

[0044] <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.

[0045] <Separator> Separator 30 includes a porous substrate 31 and a coating layer 32. The porous substrate 31 includes a first major surface 31a and a second major surface 31b. The first major surface 31a faces the positive electrode 10. The second major surface 31b faces the negative electrode 20. The coating layer 32 covers the second major surface 31b. The coating layer 32 faces the negative electrode 20. The coating layer 32 may cover the entire second major surface 31b. The coating layer 32 may cover a part of the second major surface 31b.

[0046] As long as the coating layer 32 is formed on the second major surface 31b, for example, a ceramic layer (not shown) or the like may be formed on the first major surface 31a. The ceramic material included in the ceramic layer may have Li ion conductivity or may not have Li ion conductivity. The ceramic layer may include, for example, alumina, boehmite, or the like.

[0047] In a cross section parallel to the thickness direction (Z-axis direction), the width of the coating layer 32 may be equal to or greater than the width of the positive electrode 10 (positive electrode active material layer 12). The width indicates the dimension in the X-axis direction or the Y-axis direction. In the negative electrode substrate 21, Li metal may be deposited in the region facing the positive electrode active material layer 12. By the deposition of Li metal, a Li metal layer 22 may be formed. The width of the negative electrode substrate 21 may be equal to or greater than the width of the coating layer 32.

[0048] <Thickness of the coating layer> The coating layer 32 may have a thickness of, for example, 0.1 to 20 μm, 0.4 to 16 μm, or 0.5 to 15 μm. When the thickness of the coating layer 32 is 0.5 to 15 μm, an improvement in cycle durability is expected. The thickness of the coating layer 32 may be, for example, 3 μm or more, 8 μm or more, or 10 μm or more. The thickness of the coating layer 32 may be, for example, 10 μm or less, 8 μm or less, or 3 μm or less.

[0049] <Average particle size of the Li ion conductor> The coating layer 32 contains a Li-ion conductor. The Li-ion conductor is solid. The Li-ion conductor may be a group of particles. The Li-ion conductor may have an average particle size of, for example, 100 to 3000 nm, 200 to 2000 nm, or 300 to 1500 nm. When the average particle size of the Li-ion conductor is 300 to 1500 nm, improvement in cycle durability is expected. The average particle size of the Li-ion conductor may be, for example, 500 nm or more, 1000 nm or more, or 1300 nm or more. The average particle size of the Li-ion conductor may be, for example, 1300 nm or less, 1000 nm or less, or 500 nm or less.

[0050] <Li-ion conductivity of the Li-ion conductor> The Li-ion conductor has a Li-ion conductivity of 1.0×10 -13 ~2.0×10 -9 S / cm. When the Li-ion conductivity is 1.0×10 -13 ~2.0×10 -9 S / cm, improvement in cycle durability is expected. The Li-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 Li-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.

[0051] <Composition of the Li-ion conductor> As long as the Li-ion conductor has a Li-ion conductivity of 1.0×10 -13 ~2.0×10 -9 S / cm, it can have any composition. The Li-ion conductor may, for example, contain a first component, a second component, and a third component. The first component is Li.

[0052] 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 element" may include, for example, lanthanoids. The rare earth element 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.

[0053] 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.

[0054] The Li ion conductor may include, for example, a phosphate compound. The Li ion conductor may include, for example, Li3PO4.

[0055] The Li ion conductor may include, for example, a lithium phosphate nitride compound (LIPON). The Li ion conductor may have, for example, a composition represented by the following formula (1-2). Li x PO y N z …(1-2) In the above formula (1-2), x may satisfy, for example, the relationship 2 ≦ x < 3. y may satisfy, for example, the relationship 3 ≦ y < 4. z may satisfy, for example, the relationship 0.1 < z < 0.5.

[0056] The Li ion conductor may be, for example, of the NASICON type. The Li ion conductor may have, for example, a composition represented by the following formula (1-3). Li 1+x Al x M 2-x (PO4)3…(1-3) In the above formula (1-3), M is at least one selected from the group consisting of Ti and Ge. x satisfies the relationship 0 ≦ x ≦ 2.

[0057] The lithium ion conductor may have, for example, a composition represented by 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 0.3 ≦ x ≦ 0.4.

[0058] The lithium ion conductor may contain, for example, a composite oxide. The lithium ion conductor may contain at least one selected from the group consisting of, for example, LiNbO3, Li2WO4, Li3BO3, LiBO2, Li2SO4, Li2SO3, Li2TiO3, Li2Ti2O5, Li2MoO4, Li2ZrO3, and LiAlO2.

[0059] The lithium ion conductor may contain, for example, a garnet-type oxide. The lithium ion conductor may have, for example, a composition represented by the following formula (1-5). Li 7-x M 1 Zr 2-x M 2 y O 12 …(1-5) In the above formula (1-5), M 1 is a rare earth element. M 1 may be, for example, La. M 2 is at least one selected from the group consisting of, for example, Mg, Nb, and Ta. x may satisfy, for example, the relationship of 0 ≦ x ≦ 1. y may satisfy, for example, the relationship of 0 ≦ y ≦ 1.

[0060] The lithium ion conductor may contain, for example, a perovskite-type oxide. The lithium ion conductor may have, for example, a composition represented by the following formula (1-6). Li 3x La 0.66-x TiO3…(1-6) In the above formula (1-6), x may satisfy, for example, the relationship of 0 < x < 0.66.

[0061] The lithium ion conductor may, for example, have a composition represented by the following formula (1-7). Li 3x La 0.33-x NbO3…(1-7) In the above formula (1-7), x may, for example, satisfy the relationship 0 < x < 0.33.

[0062] The lithium ion conductor may, for example, contain a perovskite-type compound. The lithium ion conductor may, for example, have a composition represented by the following formula (1-8). Li 3-x (OH x )Cl …(1-8) In the above formula (1-8), x may, for example, satisfy the relationship 0 ≤ x ≤ 1.

[0063] The lithium ion conductor may, for example, be of the LISICON type. The lithium ion conductor may, for example, have a composition represented by the following formula (1-9). Li 2+2x Zn 1-x GeO4…(1-9) In the above formula (1-9), x may, for example, satisfy the relationship -0.36 < x < 0.87.

[0064] 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.

[0065] 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.

[0066] The lithium ion conductor may contain at least one selected from the group of materials described in FIGS. 7 to 11, for example.

[0067] <Method for adjusting lithium ion conductivity> Normally, 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.

[0068] FIG. 3 is a conceptual diagram showing the lithium ion conductor in the present embodiment. In FIG. 3, a cross section of the lithium ion conductor (particle 5) is conceptually shown. The particle 5 may include a central portion 1 and a surface layer portion 2. The surface layer portion 2 surrounds the central portion 1. By alternately repeating the pulverization treatment and the sintering treatment, disorder may occur in the crystallinity of the surface layer portion 2. Due to the disorder in the crystallinity of the surface layer portion 2, the lithium ion conductivity of the particle 5 may decrease. That is, the surface layer portion 2 may have lower crystallinity than the central portion 1. The crystallinity of the central portion 1 and the surface layer portion 2 can be evaluated by, for example, micro X-Ray Diffraction or the like. In the cross section of the particle 5, the surface layer portion 2 may have a width of, for example, 0.1d to 0.3d (0.1 to 0.3 times of d). "d" represents the average particle size of the lithium ion conductor.

[0069] <Binder> The coating layer 32 may further include, for example, a binder. The coating layer 32 may include, for example, a binder in a mass fraction of 50% or less, with the remainder being a Li-ion conductor. The mass fraction of the binder may be, for example, 5 to 40% or 10 to 30%. The binder may include any component. The binder may include, for example, 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.

[0070] <Porous base material> The porous substrate 31 is in the form of a film. The porous substrate 31 may have a thickness of, for example, 5 to 50 μm, or 10 to 25 μm. The porous substrate 31 may have an average pore diameter of, for example, 0.1 to 1 μm, or 0.1 to 0.5 μm. The "average pore diameter" can be measured by mercury intrusion porosimetry. The porous substrate 31 may have a pore size of, for example, 50 to 250 μm / 100 cm. 3 The "Gurley value" can be measured by the Gurley test method.

[0071] The porous substrate 31 has electrical insulation properties. The porous substrate 31 may include, for example, a resin film. The resin film may include 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 include, for example, at least one selected from the group consisting of 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.

[0072] 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.

[0073] <Negative electrode> The negative electrode 20 may be, for example, in the form of a sheet or a plate. The negative electrode 20 includes a negative electrode substrate 21. At an SOC greater than 0%, the negative electrode 20 may include a Li metal layer 22. The thickness of the Li metal layer 22 may increase as a Li metal deposition reaction (charging) occurs. The thickness of the Li metal layer 22 may decrease as a Li metal dissolution reaction (discharging) occurs.

[0074] The negative electrode substrate 21 can provide a deposition field for Li metal. The negative electrode substrate 21 is electrically conductive. 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 porous metal body, or the like. The negative electrode substrate 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 substrate 21 may include, for example, a Cu foil, a Cu alloy foil, or the like.

[0075] At 0% SOC (or before the first charge), the negative electrode 20 may include, for example, a Li foil. The Li foil may form the Li metal layer 22.

[0076] The negative electrode 20 may further include, for example, seed particles (not shown). The seed particles can serve as seeds for nucleation of Li metal during charging (precipitation). The seed particles may be disposed on the surface of the negative electrode substrate 21, for example. 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 an average particle size (D50) of, for example, 1 to 200 nm.

[0077] The negative electrode 20 may further include, for example, a negative electrode active material other than Li metal (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, for example, cycle durability. The second negative electrode active material may be, for example, particulate. The second negative electrode active material may be disposed on, for example, the surface of the negative electrode substrate 21. A negative electrode active material layer (not shown) may be formed on at least a portion of the surface of the negative electrode substrate 21. The negative electrode active material layer may include, for example, the second negative electrode active material and a binder. The binder may include, for example, CMC, SBR, etc.

[0078] The second negative electrode active material may contain at least one selected from the group consisting of, for example, natural graphite, artificial graphite, soft carbon, hard carbon, Si, SiO, Li silicate, Si-based alloy, Sn, SnO, Sn-based alloy, and Li4Ti5O 12 and may contain at least one selected from the group consisting of, for example, natural graphite, artificial graphite, soft carbon, hard carbon, Si, SiO, Li silicate, Si-based alloy, Sn, SnO, Sn-based alloy, and Li4Ti5O

[0079] "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".

[0080] Graphite may contain a dopant. The dopant may contain at least one selected from the group consisting of, for example, 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 molar fraction.

[0081] 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 at least one selected from the group consisting of, for example, P, W, Al, and O. The different material may contain at least one selected from the group consisting of, for example, Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO3, and Li3PO4.

[0082] SiO may be represented by, for example, the following formula (2-1). SiO x …(2-1) In the above formula (2-1), the relationship of 0 < x < 2 may be satisfied. For example, the relationship of 0.5 ≤ x ≤ 1.5 or 0.8 ≤ x ≤ 1.2 may be satisfied.

[0083] The Li silicate may include at least one selected from the group consisting of Li4SiO4, Li2SiO3, Li2Si2O5, and Li8SiO6. The second negative electrode active material may include 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."

[0084] 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 include, 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. 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.

[0085] The second negative electrode active material may contain two or more components. The second negative electrode active material may contain, for example, 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."

[0086] 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 referred to as a "Si-C composite material." For example, Si fine particles may be dispersed within carbon particles. For example, Si fine particles may be dispersed within graphite particles. For example, Li silicate particles may be coated with a carbon material (such as amorphous carbon). A mixture of the Si-C composite material and graphite may also be used.

[0087] <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.

[0088] 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.

[0089] 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.

[0090] 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).

[0091] 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.

[0092] 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.

[0093] The positive electrode active material may be, for example, particulate. 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, or the like. Within one particle (positive electrode active material), the composition may be uniform or non-uniform. For example, the composition may vary from the surface to the center of the particle. The composition may vary continuously or discontinuously (stepwise).

[0094] 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. 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 (3-1). Li 1-a Ni x M 1-x O2…(3-1) In the above formula (3-1), M may contain at least one selected from the group consisting of Co, Mn, and Al. For example, the relationship -0.5 ≦ a ≦ 0.5, 0 < x ≦ 1 may be satisfied. For example, the relationship -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 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.

[0095] The transition metal oxide may contain, 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.

[0096] The transition metal oxide may be represented, for example, by the following formula (3-2). The compound represented by the following formula (3-2) may also be referred to as "NCM". Li 1-a Ni x Co y Mn z O2…(3-2) In the above formula (3-2), for example, the relationships of -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 may be satisfied. For example, the relationships of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​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 It may contain at least one selected from the group consisting of O2.

[0098] The transition metal oxide may be represented by, for example, the following formula (3-3). The compound represented by the following formula (3-3) may also be referred to as "NCA". Li 1-a Ni x Co y Al z O2…(3-3) In the above formula (3-3), for example, the relationship of -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 may be satisfied. For example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x < 1 may be satisfied. For example, the relationship of 0 < y ≦ 0.1, 0.1 ≦ y ≦ 0.2, 0.2 ≦ y ≦ 0.3, 0.3 ≦ y ≦ 0.4, 0.4 ≦ y ≦ 0.5, 0.5 ≦ y ≦ 0.6, 0.6 ≦ y ≦ 0.7, 0.7 ≦ y ≦ 0.8, 0.8 ≦ y ≦ 0.9, or 0.9 ≦ y < 1 may be satisfied. For example, the relationship of 0 < z ≤ 0.1, 0.1 ≤ z ≤ 0.2, 0.2 ≤ z ≤ 0.3, 0.3 ≤ z ≤ 0.4, 0.4 ≤ z ≤ 0.5, 0.5 ≤ z ≤ 0.6, 0.6 ≤ z ≤ 0.7, 0.7 ≤ z ≤ 0.8, 0.8 ≤ z ≤ 0.9, or 0.9 ≤ z < 1 may be satisfied.

[0099] NCA may be, 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, LiNi 0.8 Co 0.17 Al 0.03 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, and at least one selected from the group consisting of LiNi 0.9 Co 0.05 Al 0.05 O2 may be included.

[0100] The positive electrode active material may include, for example, two or more types of NCM or the like. The positive electrode active material may include, for example, NCM(0.6 ≤ x) and NCM(x < 0.6). "NCM(0.6 ≤ x)" refers to a compound in which x (Ni ratio) is 0.6 or more in the above formula (3-2). NCM(0.6 ≤ x) may be referred to as, for example, a "high nickel material". NCM(0.6 ≤ x) includes, for example, LiNi 0.8 Co 0.1 Mn 0.1 O2 or the like. "NCM(x < 0.6)" refers to a compound in which x (Ni ratio) is less than 0.6 in the above formula (3-2). NCM(x < 0.6) includes, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2, 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."

[0101] 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.

[0102] The transition metal oxide may have, for example, a crystal structure belonging to the space group C2 / m. The transition metal oxide may be represented by, for example, the following formula (3-4). Li2MO3…(3-4) In the above formula (3-4), M may include, for example, at least one selected from the group consisting of Ni, Co, Mn, and Fe.

[0103] 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).

[0104] The transition metal oxide may have, for example, a crystal structure belonging to the space group Fd-3m. The transition metal oxide may be represented by, for example, the following formula (3-5). LiMn 2-x M x O4…(3-5) In the above formula (3-5), 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.

[0105] 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."

[0106] 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 (3-6) to (3-9). LiMPO4…(3-6) Li 2-x MPO4F...(3-7) Li2MSiO4…(3-8) LiMBO3…(3-9) In the above formulas (3-6) to (3-9), M may include, for example, at least one selected from the group consisting of Fe, Mn, and Co. In the above formula (3-7), for example, the relationship 0≦x≦2 may be satisfied.

[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) 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."

[0108] 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 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.

[0111] 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 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 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.

[0112] 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.

[0113] 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 (3-10). θ={I1 / (I0+I1)}×100 …(3-10) 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."

[0114] 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.).

[0115] "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."

[0116] "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.

[0117] 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.

[0118] 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.

[0119] 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."

[0120] 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).

[0121] <Electrolyte> The electrolyte is a liquid electrolyte. The electrolyte contains Li ions. The electrolyte may contain, for example, a solute and a solvent.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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."

[0128] 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".

[0129] The solvent may contain, for example, EC, FEC, EMC, DMC, and DEC. The volume ratio of each component may satisfy, for example, the relationship represented by the following formula (4-1). V EC +V FEC +V EMC +V DMC +V DEC =10 …(4-1) In the above formula (4-1), 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.

[0130] In the above formula (4-1), For example, 1 ≤ V EC ≦2, or 2≦V EC The relationship ≦3 may be satisfied. For example, 1 ≤ V FEC ≦2, or 2≦V FEC The relationship ≦4 may be satisfied. For example, 3≦V EMC ≦4 or 6≦V EMC The relationship ≦8 may be satisfied. For example, 3≦V DMC ≦4 or 6≦V DMC The relationship ≦8 may be satisfied. For example, 3≦V DEC ≦4 or 6≦V DEC The relationship ≦8 may be satisfied.

[0131] 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."

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] <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."

[0138] In this embodiment, as long as the separator 30 includes the coating layer 32 and the negative electrode 20 utilizes the dissolution and precipitation reaction of Li metal, other configurations (such as the combination of the positive electrode, negative electrode, 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]

[0139] <Test Battery Manufacturing> Test batteries (anode-free batteries) Nos. 1 to 60 were manufactured according to the following procedure. Hereinafter, for example, "test battery No. 1" may be simply referred to as "No. 1."

[0140] 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.

[0141] A resin film (thickness: 20 μm) was prepared as a porous substrate. The resin film contained an olefin-based resin. In No. 1, the porous substrate was used alone as a separator. In this example, porous substrates (resin films) of the same specifications were used in all test batteries.

[0142] 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.

[0143] 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 housed in an exterior body. An electrolyte solution was poured into the exterior body. The composition of the electrolyte solution was as follows. After the electrolyte solution was poured, the exterior body was sealed. A test battery was thus produced.

[0144] Electrolyte composition Solute: LiPF6 (1mol / L) Solvent: EC / DMC = 1 / 1 (volume ratio)

[0145] No.2 As a Li-ion conductor, commercially available Li3PO4 powder (average particle size: 300 nm, Li-ion conductivity: 1 × 10 -7 A PVDF solution was prepared. A coating material was prepared by mixing Li3PO4 powder and PVDF solution. The mixing ratio was "Li ion conductor / PVDF solution = 80 / 20 (mass ratio)." The coating material was applied to one side of the porous substrate by gravure coating to form a coating layer. The coating layer had a thickness of 10 μm. This prepared a separator. In the power generating element, the coating layer faced the negative electrode. Except for these factors, a test battery was fabricated in the same manner as No. 1.

[0146] No.3 Commercially available Li3PO4 powder (Li ion conductivity: 1 × 10) was prepared using a mechanochemical device. -7S / 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 The Li3PO4 (Li ion conductivity: 2 × 10 -9 A test cell was fabricated similar to No. 2, except that 0.15 S / cm was used as the Li-ion conductor.

[0147] No.4~No.8 FIG. 7 is Table 1 showing the evaluation results. As shown in Table 1, test batteries were manufactured in the same manner as No. 3, 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.

[0148] No.9~No.14 8 shows the evaluation results in Table 2. As shown in Table 2, test batteries were fabricated in the same manner as No. 3, except that the average particle size of Li3PO4 was changed.

[0149] No.15~No.20 9 is Table 3 showing the evaluation results. As shown in Table 3, test batteries were fabricated in the same manner as No. 3, except that the thickness of the coating layer was changed.

[0150] No.21~No.44 10 is Table 4 showing the evaluation results. Test batteries were fabricated in the same manner as No. 3, except that the Li-ion conductors listed in Table 4 were used instead of Li3PO4.

[0151] No.45~No.60 11 is Table 5 showing the evaluation results. Test batteries were fabricated in the same manner as No. 3, except that the Li-ion conductors listed in Table 5 were used instead of Li3PO4.

[0152] <Evaluation> Battery resistance 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 30°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

[0153] The battery resistances are shown in Tables 1 to 5 (Figs. 7 to 11). Each battery resistance is a normalized value, with the resistance of battery No. 1 set to "1." The smaller the value, the better the output 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.

[0154] Cycle capacity retention rate A cycle test was carried out under the following conditions: Ambient temperature: 60°C Charge / discharge method: constant current method Current rate: 1C Voltage range: 3.3~4.2V Number of cycles: 200

[0155] 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 5 (FIGS. 7 to 11). A higher cycle capacity retention rate is considered to indicate better cycle durability.

[0156] <Result> From the results of No. 1 and No. 2, it can be seen that the Li ion conductivity of ordinary Li3PO4 (Li ion conductivity: 1 × 10 -7 S / cm) is used, no improvement in cycle durability can be expected (see Figure 7).

[0157] FIG. 12 is a graph showing the evaluation results of FIG. 7. The graph of FIG. 7 is a semi-logarithmic graph. The horizontal axis is the logarithmic axis. -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), we can see a trend toward improved output performance as well as cycle durability. Li-ion rectification is also thought to be effective in reducing battery resistance.

[0159] Fig. 13 is a graph showing the evaluation results of Fig. 8. When the average particle size of the Li ion conductor is 300 to 1500 nm, there is a tendency for the cycle durability to improve significantly.

[0160] Fig. 14 is a graph showing the evaluation results of Fig. 9. When the thickness of the coating layer is 0.5 to 15 µm, there is a tendency for cycle durability to improve significantly.

[0161] 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. 10 and 11). [Explanation of symbols]

[0162] 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, 30 separator, 31 porous substrate, 31a first main surface, 31b second main surface, 32 coating layer, 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 separator includes a porous substrate and a coating layer; the porous substrate has a first major surface and a second major surface; the first main surface faces the positive electrode, the second main surface faces the negative electrode, the coating layer covers the second main surface, the coating layer contains 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 lithium ion conductor has an average particle size of 300 to 1500 nm, and The average particle size indicates a particle size at which the cumulative distribution on a volume basis measured by a laser diffraction method reaches 50%.

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

4. The coating layer has a thickness of 0.5 to 15 μm.

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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