KR20200134126A - All solid lithium secondary battery and charging method for the same - Google Patents

Abstract

The present invention relates to an all-solid-state lithium secondary battery with excellent discharge capacity and to a charging method thereof. The all-solid-state lithium secondary battery comprises: a positive electrode active material layer; a solid electrolyte layer; and a negative electrode active material layer capable of forming an alloy or compound with lithium in an order, wherein the negative electrode active material layer includes Ag.

Description

All solid lithium secondary battery and charging method for the same

It relates to an all-solid lithium secondary battery and a charging method thereof.

Recently, an all-solid secondary battery using a solid electrolyte is attracting attention as an electrolyte. In order to improve the energy density of such an all-solid secondary battery, it has been proposed to use lithium as a negative active material. The capacity density of lithium (capacity per unit weight) is about 10 times the capacity density of graphite generally used as a negative electrode active material. Therefore, lithium is used as a negative electrode active material to increase the output while reducing the thickness of the all-solid secondary battery.

As an all-solid lithium secondary battery using lithium as a negative active material, for example, it is known that a metal layer formed of a metal forming an alloy with lithium is installed as a negative active material layer, and an interface layer made of amorphous carbon is provided on the negative active material layer. have. In this type of all-solid lithium secondary battery, metal lithium is deposited between the interface layer and the negative electrode active material layer during charging, and during discharge, the metal lithium ionizes and moves toward the positive electrode layer.

However, in the above-described all-solid lithium secondary battery, when charging and discharging are repeated, metal lithium deposited between the interface layer and the negative electrode active material layer ionizes and dissolves, thereby creating voids, which may make it impossible to use as a battery. Therefore, when this type of all-solid lithium secondary battery is actually used, it is inserted from both sides of the positive electrode current collector side and the negative electrode current collector side by using an end plate, etc. to prevent voids from being generated by charging and discharging. It is necessary to put in and apply high external pressure. However, the presence of an end plate to which an external pressure is applied may become a barrier to thinning of the solid secondary battery.

Therefore, there is no need to apply a high external pressure, and there is a growing demand for the development of an all-solid lithium secondary battery having excellent discharge capacity.

One aspect is to provide an all-solid lithium secondary battery that does not need to apply a high external pressure and has excellent discharge capacity.

Another aspect is to provide a method of charging the all-solid lithium secondary battery.

According to one aspect,

An all-solid lithium secondary battery comprising a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer capable of forming an alloy or compound with lithium in this order,

The negative active material layer is provided with an all-solid lithium secondary battery containing Ag.

The content of Ag may be 10 to 100% by weight based on 100% by weight of the total negative active material included in the negative active material layer.

The content of Ag per unit area in the negative active material layer may be 0.05 to 5 mg/cm ² .

The negative active material layer may further include at least one selected from amorphous carbon, gold, platinum, palladium, silicon, aluminum, bismuth, tin, indium, and zinc.

The negative active material layer may include Ag in the form of particles or films.

The all-solid lithium secondary battery further includes a negative electrode current collector, and a metal layer containing lithium as a main component is deposited between the negative electrode current collector and the negative electrode active material layer, inside the negative electrode active material layer, or both in an overcharged state. Can be.

The metal layer containing lithium as a main component may include a Li(Ag) alloy including a γ ₁ phase, a βLi phase, or a combination of these phases.

The solid electrolyte layer may include a sulfide-based solid electrolyte.

In use, an external pressure applied to the positive active material layer, the solid electrolyte layer, and the negative active material layer may be 1.0 Mpa or less.

According to another aspect,

It is an all-solid lithium secondary battery comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in this order,

The negative electrode layer includes a negative electrode current collector and a negative electrode active material layer,

The negative active material layer contains amorphous carbon and Ag,

An all-solid lithium secondary battery is provided in which the content of Ag is 10 to 100% by weight based on 100% by weight of the total negative active material included in the negative active material layer.

The negative electrode current collector may include a Ni foil, a Ni-coated Cu foil, a stainless steel foil, or a combination thereof.

According to another aspect,

There is provided a method for charging an all-solid lithium secondary battery in which the above-described all-solid lithium secondary battery is charged in excess of the capacity of the negative active material layer.

In the charging method of the all-solid lithium secondary battery, the charging amount may be a value of 2 to 100 times the charging capacity of the negative active material layer.

It is not necessary to apply a high external pressure, and it is possible to provide an all-solid lithium secondary battery having excellent discharge capacity.

1 is a cross-sectional view schematically showing a schematic configuration of an all-solid lithium secondary battery according to an embodiment of the present invention.
2 is a cross-sectional view showing a schematic configuration of an all-solid lithium secondary battery according to an embodiment after overcharging an anode active material layer.
3 is a cross-sectional view showing a modified example of an all-solid lithium secondary battery according to another embodiment of the present invention.
4 is a cross-sectional view showing a modified example of an all-solid lithium secondary battery according to another embodiment of the present invention.

Hereinafter, an all-solid lithium secondary battery and a charging method thereof according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. The following is presented as an example, whereby the present invention is not limited, and the present invention is only defined by the scope of the claims to be described later.

In the present specification, the term "comprising" means that other components may be further included rather than excluding other components unless otherwise stated.

In the present specification, the term "combination" includes mixtures, alloys, reaction products, and the like, unless otherwise specified. In the present specification, terms such as “first” and “second” do not indicate order, quantity, or importance, and are used to distinguish one element from another. Unless otherwise indicated herein or clearly contradicted by context, it is to be construed as including both the singular and the plural. "Or" means "and/or" unless otherwise specified. Throughout this specification, "one embodiment", "embodiment", and the like refer to specific elements described in connection with the embodiments, and are included in at least one embodiment described herein and may or may not exist in other embodiments. Means. Also, it should be understood that the described elements may be combined in any suitable manner in the various embodiments. Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in this specification contradicts or conflicts with a term in the incorporated reference, the term from this specification takes precedence over the conflicting term in the incorporated reference. While specific embodiments and implementations have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are currently unexpected or unforeseeable may occur to the applicant or skilled in the art. Accordingly, the appended claims and amendments are intended to cover all such alternatives, modifications, variations, improvements and substantial equivalents.

<1. Composition of all-solid lithium secondary battery>

1 is a cross-sectional view schematically showing a schematic configuration of an all-solid lithium secondary battery according to an embodiment of the present invention.

The all-solid lithium secondary battery 1 according to an embodiment is a so-called lithium ion secondary battery that performs charge and discharge by moving lithium ions between a positive electrode and a negative electrode. Specifically, the all-solid lithium secondary battery 1 is a solid electrolyte disposed between the anode layer 10, the cathode layer 20, and the anode layer 10 and the cathode layer 20, as shown in FIG. It is provided with a layer 30.

(1) anode layer

The positive electrode layer 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12 that are sequentially disposed toward the negative electrode layer 20.

The positive electrode current collector 11 may have a plate shape or a foil shape. The positive electrode current collector 11 is, for example, one metal selected from indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, and lithium, or an alloy of two or more metals. Can be

The positive electrode active material layer 12 may reversibly occlude and release lithium ions. The positive active material layer 12 may include a positive active material and a solid electrolyte.

The positive electrode active material may be a compound capable of intercalation/deintercalation of lithium.

Examples of the intercalation / deintercalation of the lithium compound _{is, Li a A 1 - b B} 'b D' 2 ( in the above formula, 0.90≤a≤1.8, and 0≤b≤0.5); _{Li a E 1 - b B '} b O 2 - c D' c ( wherein, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 a); _{LiE 2 - b B 'b O} 4 - c D' c ( wherein, 0≤b≤0.5, 0≤c≤0.05 a); _{Li a Ni 1 -b- c Co b} B 'c D' α ( in the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0 <α≤2); _{Li a Ni 1 -b- c Co b} B 'c O 2 - α F' α ( wherein, 0.90≤a≤1.8, 0≤b≤0.5, is 0≤c≤0.05, 0 <α <2) ; _{Li a Ni 1 -b- c Mn b} B 'c D' α ( in the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0 <α≤2); _{Li a Ni 1 -b- c Mn b} B 'c O 2 - α F' α ( wherein, 0.90≤a≤1.8, 0≤b≤0.5, is 0≤c≤0.05, 0 <α <2) ; Li _a Ni _b E _c G _d O ₂ (In the above formula, 0.90≦a≦1.8, 0≦ _b ≦0.9, 0≦ _c ≦0.5, and 0.001≦ _d ≦0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (in the above formula, 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1); Li _a NiG _b O ₂ (in the above formula, 0.90≦ _a ≦1.8 and 0.001≦ _b ≦0.1); Li _a CoG _b O ₂ (in the above formula, 0.90≦a≦1.8 and 0.001≦ _b ≦0.1); Li _a MnG _b O ₂ (in the above formula, 0.90≦ _a ≦1.8 and 0.001≦ _b ≦0.1); Li _a Mn ₂ G _b O ₄ (In the above formula, 0.90≦a≦1.8 and 0.001≦ _b ≦0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiI'O ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0≦ _f ≦2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0≦ _f ≦ ₂ ); A compound represented by any one of the formulas of LiFePO ₄ may be used.

In the above formula, A is Ni, Co, Mn, or a combination thereof; B'is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or combinations thereof; D'is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F'is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I'is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

Specific examples of the positive electrode active material include lithium cobalt acid (hereinafter referred to as LCO), nickel acid lithium, nickel cobalt oxide, nickel cobalt aluminum oxide (hereinafter referred to as NCA), nickel cobalt manganate (hereinafter referred to as NCM). ), lithium salts such as lithium manganate and lithium iron phosphate, and lithium sulfide. The positive electrode active material layer 12 may include only one type selected from these compounds as a positive electrode active material, and may also include two or more types.

The positive electrode active material may include a lithium salt of a transition metal oxide having a layered rock salt structure among the lithium salts described above. Here, the "layered rock salt structure" is a structure in which oxygen atomic layers and metal atomic layers are alternately and regularly arranged in the <111> direction of the cubic rock salt structure, and as a result, each atomic layer forms a two-dimensional plane. In addition, "cubic crystal rock salt structure" means that it is a sodium chloride type structure which is one kind of crystal structure. For example, the "cubic rock salt structure" refers to a structure in which face-centered cubic lattice formed respectively formed of positive and negative ions are shifted from each other by 1/2 of the corners of the unit lattice.

As a lithium salt of a transition metal oxide having such a layered rock salt structure, for example, LiNi _x Co _y Al _z O ₂ (NCA) or LiNi _x Co _y Mn _z O ₂ (NCM) (however, 0 <x < It may be a ternary lithium transition metal oxide such as 1, 0 <y <1, 0 <z <1, x + y + z = 1). The positive electrode active material layer 12 may improve energy density and thermal stability of the all-solid lithium secondary battery 1 by including a lithium salt of a ternary transition metal oxide having such a layered rock salt structure as a positive electrode active material.

Here, as a shape of the positive electrode active material, a particle shape, such as a spherical shape and an elliptical spherical shape, is mentioned, for example. Further, the particle diameter of the positive electrode active material is not particularly limited, and may be within a range applicable to the positive electrode active material of a typical all-solid lithium secondary battery. In addition, the content of the positive electrode active material in the positive electrode active material layer 12 is not particularly limited, and may be within a range applicable to the positive electrode layer of a typical all-solid lithium secondary battery.

Of course, one having a coating layer on the surface of the compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer may contain a coating element compound of oxide, hydroxide, oxyhydroxide of coating element, oxycarbonate of coating element, or hydroxycarbonate of coating element. The compound constituting these coating layers may be amorphous or crystalline. As a coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. The coating layer formation process may be any coating method as long as the compound can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements (e.g., spray coating, dipping method, etc.). Since the content can be well understood by those engaged in the relevant field, detailed description will be omitted. Specific examples of the coating layer may include Li ₂ O-ZrO ₂ .

The solid electrolyte included in the positive electrode active material layer 12 may be the same as or different from the solid electrolyte included in the solid electrolyte layer 30 to be described later.

In addition, the positive electrode active material layer 12 may be appropriately mixed with additives such as a conductive agent, a binder (binder), a filler, a dispersant, or an ion conductive auxiliary agent, as well as the positive electrode active material and solid electrolyte described above. have.

Examples of the conductive agent include graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or metal powder. In addition, as the binder (binder), for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. In addition, as the filler, dispersant, or ion-conducting auxiliary agent, a known material that is commonly used for an electrode of an all-solid lithium secondary battery may be used.

(2) cathode layer

The negative electrode layer 20 may include a negative electrode current collector 21 and a negative electrode active material layer 22 sequentially disposed toward the positive electrode layer 10.

The negative electrode current collector 21 may have a plate shape or a foil shape. The negative electrode current collector 21 may include a material that does not react with lithium, that is, does not form any of an alloy or compound with lithium. As a material constituting the negative electrode current collector 21, copper, stainless steel, titanium, iron, cobalt, nickel, and the like are exemplified. The negative electrode current collector 21 may be composed of one type of these metals, or may be composed of an alloy or clad material of two or more types of metals.

The negative active material layer 22 may include one or two or more negative active materials capable of forming an alloy or compound with lithium. Lithium may not be included between the negative electrode current collector 21, the negative electrode active material layer 22, or the negative electrode active material layer 22 and the solid electrolyte layer 30 in an initial state or a state after complete discharge. As described later, when the all-solid lithium secondary battery 1 according to an embodiment is overcharged, the negative active material contained in the negative active material layer 22 and the lithium ions transferred from the positive electrode layer 10 form an alloy or compound. As shown in FIG. 2, a metal layer 23 containing lithium as a main component may be formed on the negative electrode layer 20 (precipitated). As shown in FIGS. 2 to 4, the metal layer 23 may be deposited and disposed between the anode current collector and the anode active material layer, inside the anode active material layer, or both. Between the anode current collector 21 and the anode active material layer 22, the metal layer 23 containing lithium as a main component may be disposed closer to the anode current collector layer 21 than the anode active material layer 22. .

The negative active material layer 22 according to an embodiment may contain Ag as an essential negative active material. Accordingly, the metal layer 23 formed upon overcharging may include a Li(Ag) alloy including a γ ₁ phase, a βLi phase, or a combination of these phases in which Ag is dissolved in lithium. Therefore, during discharge, the generation of voids can be suppressed so that only Li is dissolved in the Li (Ag) alloy constituting the metal layer 23 and solid-solution Ag remains. In this case, the content of Ag in the precipitated Li-Ag solid solution may be 60% by weight or less. Within such a range, it is possible to effectively suppress a decrease in the average discharge potential due to the influence of Ag. On the other hand, if the amount of Ag in the precipitated Li-Ag solid solution is too small, the amount of Ag remaining at the time of discharge decreases, and generation of voids may not be sufficiently suppressed. Therefore, the content of Ag in the precipitated Li-Ag solid solution may be 20% by weight or more, for example, 40% by weight or more.

That the metal layer 23 includes at least one Li-Ag solid solution in the γ ₁ phase or the β Li phase can be confirmed by analyzing the peak position and the peak intensity ratio by XRD measurement, for example. In addition, the Ag content in the precipitated Li-Ag solid solution can be measured as follows, for example. When XRD measurement is performed, the diffraction peak position is different from that of pure metallic lithium and metallic lithium in which Ag is solid solution (Li-Ag solid solution). The diffraction peak position of metallic lithium in which Ag is solid solution approaches the peak position of pure metallic lithium as the solid solution concentration of Ag decreases. For example, in XRD measurement using a Cu target, when the solid solution concentration of Ag decreases, the diffraction peak shifts from 2θ = 37.0° to 36.5°. At this peak position, the high capacity of Ag can be estimated. In addition to this, high capacity can also be measured by ICP.

In one embodiment, Ag does not necessarily have to be uniformly present in the negative active material layer 22, and may be unevenly distributed on the negative electrode current collector 21 side of the negative active material layer 22. In this case, lithium reacted in the negative electrode layer 20 passes through the negative electrode active material layer 22 and reacts with the Ag uneven layer in the negative electrode active material layer 22 reaching the vicinity of the negative electrode current collector 21, thereby forming a Li(Ag) alloy. The silver metal layer 23 may be formed.

If Ag included in the negative electrode active material layer 22 is too small, the generation of voids may not be suppressed because Ag remaining during discharge is also reduced. Therefore, the negative active material layer 22 may contain 10% by weight or more, for example, 20% by weight or more of Ag, based on 100% by weight of the total negative active material included in the initial state without charging and discharging. I can.

Meanwhile, the upper limit of the Ag content in the negative active material layer 22 may be 100% by weight. However, in the relationship between the reaction potential between Ag and Li, if Ag increases, the average discharge potential decreases, and the energy density of the battery may also decrease. Therefore, from the viewpoint of high energy density, the content of Ag may be 80% by weight or less, for example, 50% by weight or less.

In the negative active material layer 22, the Ag content (% by weight) in which the total weight of the negative active material is 100% by weight may be measured, for example, as follows. That is, after the all-solid lithium secondary battery 1 is discharged, it is disassembled, and the negative active material layer 22 is recovered from the surface of the negative electrode layer 20. And the content of Ag in the recovered material can be determined by EDX, XRF or ICP. In addition, for example, the content of Ag can be known from SEM-EDS analysis in the cross-sectional direction.

In addition, in the negative electrode active material layer 22, when the content of Ag per unit area is too small when viewed from the stacking direction of the negative electrode layer 20, the Ag remaining at the time of discharge also decreases, making it impossible to suppress the generation of voids. There is a risk of becoming. Accordingly, the content of Ag per unit area in the negative active material layer 22 may be 0.05 mg/cm ² or more, for example, 0.10 mg/cm ^{2 or} more.

On the other hand, if the content of Ag per unit area is too large, the average discharge potential is lowered and there is a fear that the energy density of the battery is lowered. Therefore, the content of Ag per unit area may be 5.0 mg/cm ² or less, for example, 2.0 mg/cm ² or less.

The content of Ag per unit area of the negative active material layer 22 can be measured, for example, as follows. That is, the all-solid lithium secondary battery 1 is disassembled after discharging, and the content of Ag can be determined from the composition analysis in SEM-EDS from the surface or cross-sectional direction of the negative electrode layer 20. The present invention is not limited thereto, and the content of Ag can also be known in XPS and ICP.

In addition, Ag contained in the negative active material layer 22 in the initial state without charging and discharging may be in the form of particles or films. When present in the form of particles, the average particle diameter (d ₅₀ ) (diameter length or average diameter) of Ag may be 20 nm to 1 μm, but is not limited thereto.

The negative active material layer 22 is an optional negative active material other than Ag, and further includes at least one selected from, for example, amorphous carbon, Au, Pt, Pd, Si, Al, Bi, Sn, In and Zn. I can. Specific examples of amorphous carbon may include carbon black such as acetylene black, furnace black, and Ketjen black, graphene, or a combination thereof.

The negative active material layer 22 may be 50% by weight or more, for example, 70% by weight or more by adding negative active materials other than Ag, based on 100% by weight of the total negative active material it contains. The content of the negative active material other than Ag can be measured by the same method as the content of Ag.

The negative active material layer 22 may further include a binder (binder). By including a binder (binder), the negative electrode active material layer 22 can be stabilized on the negative electrode current collector 21. As a material constituting the binder (binder), for example, resin materials such as styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene can be mentioned. The binder (binder) may be composed of one or more selected from these resin materials.

In addition, the negative electrode active material layer 22 may be suitably blended with additives used in conventional all-solid lithium secondary batteries, such as a filler, a dispersant, an ion conductive agent, and the like. Specific examples of the additive are the same as those described in the above-described anode layer.

The thickness of the negative active material layer 22 is not particularly limited, but may be 1 μm to 20 μm. When the thickness of the negative active material layer 22 is less than 1 μm, the performance of the all-solid secondary battery may not be sufficiently improved. When the thickness of the negative active material layer 22 exceeds 20 μm, the resistance of the negative active material layer 22 is high, and as a result, the performance of the all-solid secondary battery may not be sufficiently improved. When the above-described binder is used, the thickness of the negative electrode active material layer 22 can be easily secured to an appropriate level.

Meanwhile, on the negative electrode current collector 21, a film including a material capable of forming an alloy or a compound with lithium may be further included, and the film may be disposed between the negative electrode current collector 21 and the negative active material layer.

Although the negative electrode current collector 21 does not react with lithium metal, it may make it difficult to deposit a smooth lithium metal layer thereon. The film may also be used as a wetting layer so that lithium metal is evenly deposited on the anode current collector 21.

The material capable of forming an alloy with the lithium metal used in the film may include silicon, magnesium, aluminum, lead, silver, tin, or a combination thereof. The material capable of forming a compound with a lithium metal used in the film may include carbon, titanium sulfide, iron sulfide, or a combination thereof. The content of the material used in the film may be a small amount within a limit that does not affect the electrochemical properties of the electrode or/and the redox potential of the electrode. The film may be applied flatly on the negative electrode current collector 21 to prevent cracking during the charging cycle of the all-solid lithium secondary battery 1. The application of the film may be a physical vapor deposition such as evaporation or sputtering, a chemical vapor deposition, or a plating method.

The thickness of the film may be 1 nm to 500 nm. The thickness of the film may be, for example, 2 nm to 400 nm. The thickness of the film may be, for example, 3 nm to 300 nm. The thickness of the film may be, for example, 4 nm to 200 nm. The thickness of the film may be, for example, 5 nm to 100 nm.

(3) solid electrolyte layer

The solid electrolyte layer 30 is disposed between the positive electrode layer 10 and the negative electrode layer 20 (eg, between the positive electrode active material layer 12 and the negative electrode active material layer 22). The solid electrolyte layer 30 includes a solid electrolyte capable of moving ions. The solid electrolyte layer 30 may include a sulfide-based solid electrolyte.

The sulfide-based solid electrolyte is Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiX (X is a halogen element), Li ₂ SP ₂ S ₅ -Li ₂ O, Li ₂ SP ₂ S ₅ -Li ₂ O- LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ SB ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m S _n (m and n are positive numbers, Z is one of Ge, Zn or Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _p MO _q (p and q are positive numbers, M is P, Si, Ge, B, Al, Ga Or one of In), or a combination thereof. The solid electrolyte may be composed of one type of material selected from these sulfide-based solid electrolyte materials, or may be composed of two or more types of materials.

The sulfide-based solid electrolyte may include a solid electrolyte represented by Formula 1:

<Formula 1>

Li _{x M'y} PS _z A _w

In Formula 1,

x, y, z, and w are each independently 0 or more and 6 or less;

M'is one or more of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta;

A is one or more of F, Cl, Br, or I.

As the solid electrolyte, one containing sulfur (S), phosphorus (P) and lithium (Li) as constituent elements of the sulfide solid electrolyte material may be used. For example, those containing Li ₂ SP ₂ S ₅ can be used. When using a sulfide-based solid electrolyte material containing Li ₂ SP ₂ S ₅ , the mixing molar ratio of Li ₂ S and P ₂ S ₅ is, for example, Li ₂ S: P ₂ S ₅ = 50: 50 to 90: It can be selected from a range of 10.

In addition, the solid electrolyte may be in an amorphous state or in a crystalline state. In addition, amorphous and crystalline may be mixed.

The solid electrolyte layer 30 may further include a binder (binder). Examples of the binder (binder) material include resins such as styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and polyacrylic acid. The binder (binder) material may be the same as or different from the material constituting the binder (binder) in the positive electrode active material layer 12 and the negative electrode active material layer 22.

(4) Initial charging capacity ratio

In the all-solid lithium secondary battery 1 according to an embodiment, the initial charging capacity of the positive active material layer 12 is excessively configured with respect to the initial charging capacity of the negative active material layer 22. As will be described later, the all-solid lithium secondary battery 1 according to the exemplary embodiment may be charged (ie, overcharged) in excess of the initial charging capacity of the negative electrode active material layer 22 to be used. Lithium may be occluded in the negative active material layer 22 at the initial stage of charging. That is, the negative active material may form lithium ions and alloys or compounds transferred from the positive electrode layer 10. When charging is performed in excess of the initial charging capacity of the negative active material layer 22, lithium is deposited between the rear surface of the negative active material layer 22, that is, between the negative electrode current collector 21 and the negative active material layer 22, as shown in FIG. Thus, the metal layer 23 can be formed by this lithium. The metal layer 23 may be mainly composed of lithium in which Ag is solid solution (ie, Ag-Li solid solution). This phenomenon may be composed of an anode active material, for example, a material forming an alloy or compound with lithium. During discharge, lithium in the negative electrode active material layer 22 and the metal layer 23 is ionized while remaining solid-solution Ag and can move toward the positive electrode layer 10. Therefore, lithium can be used as a negative electrode active material in the all-solid lithium secondary battery 1. In addition, since the negative electrode active material layer 22 coats the metal layer 23, it functions as a protective layer for the metal layer 23 and suppresses precipitation and growth of dendritic metal lithium.

In the all-solid lithium secondary battery 1 according to an embodiment, the ratio of the initial charging capacity of the positive active material layer 12 to the initial charging capacity of the negative active material layer 22, that is, the initial charging capacity ratio b/a, the following equation It is desirable to satisfy (1).

0.01< b/a< 0.5　　　（1）

(Here, a is the initial charging capacity (mAh) of the positive electrode active material layer 12, b is the initial charging capacity (mAh) of the negative electrode active material layer 22)

When the initial charging capacity ratio is 0.01 or less, there is a concern that the characteristics of the all-solid lithium secondary battery 1 may be deteriorated. The reason is that the negative electrode active material layer 22 does not sufficiently function as a protective layer. For example, when the thickness of the negative active material layer 22 is very thin, the capacity ratio may be 0.01 or less. In this case, there is a concern that the negative electrode active material layer 22 may collapse due to repeated charging and discharging, and the dendritic metal lithium may precipitate and grow. As a result, the characteristics of the all-solid lithium secondary battery 1 may be deteriorated. Therefore, the initial charging capacity ratio may be 0.01 or more. On the other hand, when the initial charging capacity ratio is 0.5 or more, the amount of lithium precipitated in the negative electrode decreases, so there is a concern that the battery capacity decreases. Therefore, the initial charging capacity ratio may be less than 0.5.

(5) Composition of all-solid lithium secondary battery

Meanwhile, the all-solid lithium secondary battery 1 is an all-solid lithium secondary battery 1 comprising a positive electrode layer 10, a solid electrolyte layer 30, and a negative electrode layer 20 in this order, and the negative electrode layer ( 20) includes an anode current collector 21 and an anode active material layer 22, the anode active material layer 22 includes amorphous carbon and Ag, and the content of Ag is included in the anode active material layer 22 It may be 10 to 100% by weight based on 100% by weight of the total negative active material.

The negative electrode current collector 21 may include a Ni foil, a Ni-coated Cu foil, a stainless steel foil, or a combination thereof. The negative electrode current collector 21 may have a further improved discharge capacity.

<2. Manufacturing method of all-solid lithium secondary battery>

Next, a method of manufacturing the all-solid lithium secondary battery 1 will be described. The all-solid lithium secondary battery 1 according to the exemplary embodiment may be obtained by preparing the positive electrode layer 10, the negative electrode layer 20, and the solid electrolyte layer 30, respectively, and then laminating each of the above layers.

(1) Anode layer manufacturing process

First, a material constituting the positive electrode active material layer 12 (a positive electrode active material, a binder (binder), etc.) is added to a non-polar solvent to prepare a slurry (or paste). Next, the obtained slurry is applied onto the prepared positive electrode current collector 11. This is dried to obtain a laminate. Subsequently, the obtained laminate is pressurized using, for example, hydrostatic pressure to obtain the anode layer 10. In addition, the pressing process is omitted.

(2) Cathode layer manufacturing process

First, a material constituting the negative electrode active material layer 22 (a negative electrode active material mainly containing Ag, a binder (binder), etc.) is added to a polar solvent or a non-polar solvent to prepare a slurry (paste may be used). Next, the obtained slurry is applied onto the prepared negative electrode current collector 21. This is dried to obtain a laminate. Subsequently, the obtained laminate is pressurized using, for example, hydrostatic pressure to produce the negative electrode layer 20. Further, the pressing step may be omitted. In addition, the method of applying the slurry to the negative electrode current collector 21 is not particularly limited, and for example, a screen printing method, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method. And a gravure coating method.

(3) Solid electrolyte layer manufacturing process

The solid electrolyte layer 30 can be made of a solid electrolyte containing a sulfide-based solid electrolyte material.

First, a starting material (eg, Li ₂ S, P ₂ S _5, etc.) is treated by a melt quenching method or a mechanical milling method to obtain a sulfide-based solid electrolyte material.

For example, in the case of using the melt quenching method, a predetermined amount of the starting material is mixed, and the pellet-formed material is reacted at a predetermined reaction temperature in a vacuum, and then rapidly cooled to prepare a sulfide-based solid electrolyte material. In addition, the reaction temperature of the mixture of Li ₂ S and P ₂ S ₅ may be 400 ℃ ~ 1000 ℃, for example 800 ℃ ~ 900 ℃. In addition, the reaction time may be 0.1 to 12 hours, for example, 1 to 12 hours. In addition, the quenching temperature of the reactant may be 10°C or less, for example, 0°C or less, and the quenching rate may be generally 1°C/sec to 10000°C/sec, for example 1°C/sec to 1000°C/sec.

Further, in the case of using a mechanical milling method, a sulfide-based solid electrolyte material can be prepared by stirring and reacting the starting material using a ball mill or the like. In addition, the stirring speed and stirring time of the mechanical milling method are not particularly limited, but the faster the stirring speed, the faster the rate of formation of the sulfide-based solid electrolyte material. You can increase it.

Thereafter, the obtained mixed raw material (sulfide-based solid electrolyte material) is heat-treated at a predetermined temperature and then pulverized to prepare a particulate solid electrolyte. When the solid electrolyte has a glass transition point, it may change from amorphous to crystalline by heat treatment.

Subsequently, the solid electrolyte obtained by the above method can be formed by using a known film forming method such as an aerosol position method, a cold spray method, and a sputtering method to form a solid electrolyte layer 30. In addition, the solid electrolyte layer 30 may be manufactured by pressing solid electrolyte particles. In addition, the solid electrolyte layer 30 may be prepared by mixing a solid electrolyte, a solvent, and a binder, followed by drying and pressing.

(4) Lamination process

A solid electrolyte layer 30 is disposed between the positive electrode layer 10 and the negative electrode layer 20 and pressurized using, for example, hydrostatic pressure to obtain an all-solid lithium secondary battery 1 according to an embodiment. I can. In addition, the all-solid lithium secondary battery 1 according to one embodiment does not need to apply a high external pressure using an end plate, etc., and when in use, the anode layer 10, the cathode layer 20, and the solid electrolyte layer ( Even if the external pressure applied to 30) is 1 MPa or less, an improved discharge capacity can be obtained.

<3. Charging method of all solid lithium secondary battery>

Next, a method of charging the all-solid lithium secondary battery 1 will be described.

The charging method of the all-solid lithium secondary battery 1 according to an embodiment may be charging (ie, overcharging) the all-solid lithium secondary battery 1 in excess of the charging capacity of the negative electrode active material layer 22.

Lithium may be occluded in the negative active material layer 22 at the beginning of charging. When charging exceeding the charging capacity of the negative active material layer 22, lithium is deposited between the rear surface of the negative active material layer 22, that is, between the negative electrode current collector 21 and the negative active material layer 22, as shown in FIG. The metal layer 23 that did not exist during manufacture may be formed by this lithium. During discharge, lithium among the negative active material layer 22 and the metal layer 23 is ionized and may move toward the positive electrode layer 10. Therefore, in the all-solid lithium secondary battery 1, lithium can be used as a negative electrode active material. In addition, since the negative electrode active material layer 22 coats the metal layer 23, it functions as a protective layer for the metal layer 23 and suppresses the deposition and growth of dendritic metal lithium. In this way, short-circuiting and capacity reduction of the all-solid lithium secondary battery 1 can be suppressed, and further, characteristics of the all-solid lithium secondary battery 1 can be improved. In addition, according to one embodiment, since the metal layer 23 is not formed in advance, it is possible to reduce the manufacturing cost of the all-solid lithium secondary battery 1.

In addition, the metal layer 23 is not limited to being formed between the negative electrode current collector 21 and the negative electrode active material layer 22 as shown in FIG. 2, but is formed inside the negative electrode active material layer 22 as shown in FIG. have. Further, as shown in FIG. 4, the metal layer 23 may be formed both between the negative electrode current collector 21 and the negative electrode active material layer 22 and inside the negative electrode active material layer 22.

The all-solid lithium secondary battery (1) is a unit cell having a structure of a positive electrode/separator/cathode, a bi-cell having a structure of a positive electrode/separator/cathode/separator/anode, or a multilayer battery structure in which the structure of the unit cell is repeated. Can be made.

The shape of the all-solid lithium secondary battery 1 is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a stacked type, a cylinder type, a flat type, and a horn type. It can also be applied to large-sized batteries used in electric vehicles. For example, the all-solid lithium secondary battery 1 may also be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, it can be used in a field requiring a large amount of power storage. For example, it can be used for electric bicycles or power tools.

Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only examples of the present invention, and the present invention is not limited to the following examples. The following 　 Examples can be implemented by adding changes within the range suitable for 　 of the invention, and they are all included in the technical scope of the present invention.

[Example]

Example One

<1. Sample production>

In the following procedure, sample No. of an all-solid lithium secondary battery containing amorphous carbon as a negative electrode active material. 1 to 37 were each produced under an argon gas atmosphere. For each of the samples, an all-solid lithium secondary battery containing amorphous carbon was fabricated in the same manner, except that the negative electrode layer was prepared by the method described in'Preparation of the negative electrode layer'.

(1) Preparation of anode layer

As a positive electrode active material, LiNi _{0 . 8} Co _{0 . 15} Al _{0 . 05} O ₂ (NCA) was prepared. Relative to the positive electrode active material such as Suzuki Naoki ^{_{"Synthesis and Electrochemical Properties of I 4 -}} - type Li 1 + 2x Zn 1 - x PS 4 Solid Electrolyte」，Chemistry of Materials, published March 9, 2018， No. 30, 2236-2244 (2018) was coated with Li ₂ O-ZrO ₂ . Further, as a solid electrolyte, Li ₆ PS ₅ Cl, which is an azirodite type crystal, was prepared. Further, as a binder, polytetrafluoroethylene (Dupont, Teflon (registered trademark)) was prepared. In addition, as a conductive agent, carbon nanofibers (CNF) were prepared. Subsequently, the materials were mixed with a positive electrode active material, a solid electrolyte, a conductive agent, and a binder in a weight ratio of 88:12:2:1.

The mixture was stretched into a sheet to prepare a positive electrode active material sheet. Then, the positive electrode active material sheet was molded into about 1.7 cm ² and pressed onto a positive electrode current collector made of an aluminum foil having a thickness of 18 μm to prepare a positive electrode layer used in Sample No. 1-37.

(2) Preparation of cathode layer

(2-1) 　 Sample 　 No. 1 and 2

A laminate (Sample No. 2) in which a 30 μm-thick Li metal foil was laminated on a negative electrode current collector made of 10 μm-thick Ni foil (Sample No. 1) and 10 μm-thick SUS304 foil was prepared. Each of these was punched to be about 2 cm ² to obtain a cathode layer. However, this negative electrode layer has a protrusion, and is used as a negative terminal of a battery as described later. In this way, the negative electrode layers used for Sample Nos. 1 and 2 were prepared.

(2-2) 　Sample Nos. 3~13 and 15~37

A binder (Kureha Corporation, # 9300) dissolved in N-methylpyrrolidone (NMP) solution was prepared. After the negative active material shown in Table 1 was added to the binder, the mixture was stirred while adding NMP little by little to the mixed solution to prepare a slurry. Then, the slurry was coated as a negative active material layer on a negative electrode current collector made of a 10 μm thick SUS304 foil by a screen printing method. Here, the content of the negative electrode active material in the negative electrode active material layer and the layer thickness of the negative electrode active material layer of each sample were set to the values shown in Table 1. In Table 1, CB is indicated as carbon black, and the content of Ag per unit area represents the content of Ag per unit area as viewed from the stacking direction of the anode layer (ie, the direction perpendicular to the surface of the slurry in the anode current collector). Then, after drying in air at about 80° C. for about 20 minutes, vacuum drying at 100° C. for about 12 hours to obtain a laminate. This laminate was punched so as to be about 2 cm ² to obtain a cathode layer. However, this negative electrode layer has a protrusion, and is used as a negative terminal of a battery as described later. In this way, negative electrode layers used for Samples Nos. 3 to 13 and 15 to 37 were prepared.

In addition, 　Sample 　No. 3~9, 11, 13, 15~37 uniformly diffused the negative electrode active material, and the slurry was coated on the negative electrode current collector in one layer. Samples 　 No. 10 and 12 were coated with a two-layered slurry on the negative electrode current collector in which the content of the negative active material was different from each other. Sample No.10 is a slurry containing only carbon black as a negative electrode active material (60% by weight based on 100% by weight of the negative electrode active material contained in the negative electrode active material layer) first, coated on the negative electrode current collector, and then negative electrode thereon. As an active material, a slurry containing carbon black (20% by weight) and Ag (20% by weight) was applied. Sample No.12 is 　a slurry containing carbon black (20% by weight) and Ag (20% by weight) as the negative electrode active material was first applied on the negative electrode current collector, and then only carbon black (60% by weight) as the negative electrode active material was applied thereon. The slurry was applied. Sample No. 14 was prepared by laminating a foil plated with Ag as a negative electrode active material on a negative electrode current collector, and a slurry containing only CB was applied thereon.

Classification Sample No.

cathode
Active material Ag
content CB
content etc
cathode
Active material
content Per unit area
Ag content cathode
Active material
Layer thickness How to make layer
rescue Remark (weight%) (weight%) (weight%) (mg/cm ² ) (㎛) Comparative example One none - - - - - - Ni
Foil Comparative example 2 none - - - - 0 - Li
Foil Example 3 CB+Ag 25 75 0 0.25 10 screen ground floor
apply Comparative example 4 CB+Zn - 75 Zn:25 - 13 screen ground floor
apply Comparative example 5 CB+Sn - 75 Sn:25 - 15 screen ground floor
apply Comparative example 6 CB+Si - 75 Si:25 - 9 screen ground floor
apply Comparative example 7 CB+Si - 90 Si:10 - 15 screen ground floor
apply Comparative example 8 CB+Al - 75 Al: 25 - 15 screen ground floor
apply Example 9 CB+Ag 25 75 - 0.25 10 screen ground floor
apply Example 10 CB+Ag 20 80 - 0.22 15 screen Double layer application ① Solid electrolyte side CB: 20% by weight, Ag: 20% by weight
② Cathode collector side
CB: 60% by weight Example 11 CB+Ag 20 80 - 0.24 15 screen One layer application Example 12 CB+Ag 20 80 - 0.20 13 screen Double layer application ① Solid electrolyte side CB: 60% by weight
② Cathode collector side
CB: 20% by weight, Ag: 20% by weight Example 13 CB+Ag 10 90 - 0.11 18 screen One layer application Example 14 CB+Ag 10 90 - 0.06 10 Plating +
screen One layer application CB is applied on Ag-plated foil Example 15 CB+Ag+Si 7.5 75 Si:17.5 0.07 14 screen One layer application Example 16 CB+Ag+Si 12.5 75 Si:12.5 0.10 12 screen One layer application Example 17 CB+Ag+Si 17.5 75 Si:7.5 0.16 12 screen One layer application Example 18 CB+Ag+Si 22.5 75 Si:2.5 0.20 11 screen One layer application Example 19 CB+Ag 25 75 - 0.25 10 screen One layer application Example 20 CB+Ag 25 75 - 1.13 45 screen One layer application Example 21 CB+Ag 25 75 - 0.83 31 screen One layer application Example 22 CB+Ag 25 75 - 0.50 19 screen One layer application Example 23 CB+Ag 25 75 - 0.25 10 screen One layer application Example 24 CB+Ag 25 75 - 0.10 5 screen One layer application Example 25 CB+Ag 25 75 - 0.05 2 screen One layer application Example 26 Ag 100 - - 2.80 10 screen One layer application Example 27 CB+Ag 83 17 - 1.83 11 screen One layer application Example 28 CB+Ag 80 20 - 1.52 10 screen One layer application Example 29 CB+Ag 75 25 - 1.13 9 screen One layer application Example 30 CB+Ag 67 33 - 0.94 9 screen One layer application Example 31 CB+Ag 50 50 - 0.60 9 screen One layer application Example 32 CB+Ag 33 67 - 0.30 9 screen One layer application Example 33 CB+Ag 25 75 - 0.25 10 screen One layer application Example 34 CB+Ag 20 80 - 0.24 15 screen One layer application Example 35 CB+Ag 17 83 - 0.19 16 screen One layer application Example 36 CB+Ag 10 90 - 0.11 18 screen One layer application Comparative example 37 CB - 100 - - 24 screen One layer application

(3) Preparation of solid electrolyte layer

1% by weight of a rubber-based binder was added to the Li ₆ PS ₅ Cl solid electrolyte based on the total 100% by weight of the solid electrolyte. The mixture was stirred while adding xylene and diethylbenzene to prepare a slurry. This slurry was applied onto a nonwoven fabric using a blade coater, and dried at 40°C in air. The laminate thus obtained was vacuum dried at 40° C. for 12 hours. This laminate was punched so as to be about 2.2 cm ² , and a solid electrolyte layer used for Sample Nos. 1 to 37 was prepared.

(4) Fabrication of all solid lithium secondary battery

The prepared positive electrode layer solid electrolyte layer and negative electrode layer were again sealed in a laminate film in vacuum in this order to prepare samples Nos. 1 to 37 of an all-solid lithium secondary battery. Here, a portion of each of the positive electrode current collector and the negative electrode current collector was protruded from the laminate film to the outside without breaking the vacuum of the battery. These protrusions were used as positive and negative terminals. In addition, this all-solid lithium secondary battery was subjected to water pressure treatment at 490 MPa for 30 minutes. Thereafter, pressure application (pressurization) was not performed on these samples either by fitting or the like by an end plate. That is, it can be said that the external pressure acting on each sample is 1 MPa or less (specifically, about atmospheric pressure).

<2. Charge/discharge test>

The battery characteristics (discharge capacity) were evaluated by carrying out a charging/discharging test for the prepared all-solid lithium secondary batteries of Sample Nos. 1 to 37 by the following experimental method.

Specifically, the prepared all-solid lithium secondary battery was placed in a thermostat at 60°C, and the battery characteristics were evaluated. In the first cycle (1 ^st cycle), charging was performed with a constant current of 0.6 mA/cm ² until the battery voltage reached 4.25 V, and a constant voltage charging of 4.25 V was performed until the current reached 0.5 mA. Thereafter, discharge was performed with a constant current of 1.2 mA/cm ² until the battery voltage became 2.5 V (0.2 C discharge). In the second cycle (Cycle 2 ^nd), and the third cycle (3 ^rd cycle), the charging was performed under the same conditions as the first cycle (1 ^st cycle). And the second cycle (2 ^nd cycle) was performed at a constant current discharge of 2.0 mA / cm ² (0.33 C discharge) until a 2.5 V battery voltage. The third cycle (3 ^rd cycle) was performed at a constant current discharge of 6.0 mA / cm ² (1 C discharging) until the battery voltage become 2.5 V. The results are shown in Table 2.

Here, those having a discharge capacity of 100 mAh/g or more in 0.2 C discharge were evaluated as having excellent discharge capacity (represented by ○ in Table 2). In addition, a discharge capacity of 100 mAh/g or more in 1 C discharge, which is most likely to affect when no external pressure is applied, was evaluated as being particularly excellent in the discharge capacity (marked by ◎ in Table 2).

Fountain classification Sample No. Charging capacity 0.2C
Discharge capacity 0.33C
Discharge capacity 1C
Discharge capacity 1C discharge capacity/
0.33C discharge capacity Discharge capacity (mAh/g) (mAh/g) (mAh/g) (mAh/g) (%) Comparative example One 235 36 One 0 22.2 X Comparative example 2 235 55 2 0 6.7 X Example 3 235 206 193 139 71.8 ◎ Comparative example 4 235 64 16 7 39.9 X Comparative example 5 235 75 25 12 46.2 X Comparative example 6 235 66 17 5 29.4 X Comparative example 7 235 53 13 4 33.3 X Comparative example 8 235 99 39 22 55.3 X Example 9 235 206 193 139 71.8 ◎ Example 10 235 206 195 138 70.8 ◎ Example 11 235 207 195 136 69.7 ◎ Example 12 235 207 194 135 69.6 ◎ Example 13 235 103 44 18 40.9 ○ Example 14 235 133 66 24 36.4 ○ Example 15 235 195 146 87 59.6 ○ Example 16 235 202 178 126 70.8 ◎ Example 17 235 204 189 133 70.4 ◎ Example 18 235 207 194 136 70.1 ◎ Example 19 235 206 193 139 71.8 ◎ Example 20 235 195 168 103 61.3 ◎ Example 21 235 201 179 125 69.8 ◎ Example 22 235 203 189 135 71.4 ◎ Example 23 235 206 193 139 71.8 ◎ Example 24 235 207 191 139 72.8 ◎ Example 25 235 208 193 - - ○ Example 26 235 150 87 11 12.9 ○ Example 27 235 188 105 33 31.4 ○ Example 28 235 201 188 131 69.7 ◎ Example 29 235 206 193 137 71.0 ◎ Example 30 235 205 193 139 72.0 ◎ Example 31 235 206 194 138 71.1 ◎ Example 32 235 205 193 139 72.3 ◎ Example 33 235 206 193 139 71.8 ◎ Example 34 235 207 195 136 69.7 ◎ Example 35 235 194 166 68 41.0 ○ Example 36 235 103 44 18 40.9 ○ Comparative example 37 235 60 14 6 42.9 X

<3. Evaluation>

As shown in Tables 1 and 2, Sample Nos. 3 and 9 to 36 are all solid lithium secondary batteries, which are examples in which the negative active material layer has Ag. It can be seen that the samples of these all-solid lithium secondary batteries all have a 0.2 C discharge capacity of 100 mAh/g or more, and exhibit excellent discharge capacity without applying a high external pressure.

Samples Nos. 9 to 12 containing carbon black and Ag as negative electrode active materials and having an Ag content of 20 to 25% by weight have a discharge capacity superior to those of Samples Nos. 13 and 14 having an Ag content of 10% by weight. It is considered that this is because, compared with Samples Nos. 13 and 14, Samples Nos. 9 to 12 have a higher content of Ag in the cathode layer, so that voids generated during discharge can be further suppressed.

Nos. 16 to 18 containing carbon black, Ag and Si as negative electrode active materials, and having a Si content of 12.5% by weight or less have a discharge capacity superior to Sample No.15, which has a Si content exceeding 12.5% by weight. This is considered to be because, when compared with Sample No. 15, Samples Nos. 16 to 18 have a large content of Ag in the cathode layer, and thus voids generated during discharge can be further suppressed.

Sample Nos. 20 to 24 containing carbon black (75% by weight) and Ag (25% by weight) as negative electrode active materials and having an Ag content of 0.1 to 2.0 mg/cm ² per unit area are Sample Nos with an Ag content of less than 0.1 per unit area It has better discharge capacity than .25. It is believed that this is because, compared with Sample No. 25, Samples Nos. 20 to 24 have a large content of Ag per unit area in the cathode layer, so that voids generated during discharge can be further suppressed.

Samples Nos. 28 to 34 containing carbon black and Ag as negative electrode active materials and having an Ag content of 20 to 80% by weight were sample Nos. 26 and 27 having an Ag content of more than 80% by weight (including 100% by weight), and It has a better discharge capacity than Samples Nos. 35 and 36 with Ag content less than 20% by weight. This is considered to be because the negative electrode layers of Samples Nos. 26 and 27 are mainly composed of Ag, and thus the negative electrode layer deteriorates due to expansion and contraction due to the reaction of Ag and Li during charge and discharge. On the other hand, since the negative electrode layers of Samples Nos. 35 and 36 with low Ag were mainly composed of CB with a large specific surface area, it is believed that the negative electrode layer deterioration occurred during charge and discharge due to insufficient strength of the negative electrode layer due to insufficient binder.

Meanwhile, Sample Nos. 1, 2, 4 to 8, and 37 are all solid-state lithium secondary batteries, which are comparative examples in which the negative active material layer does not have Ag.

All solid-state lithium secondary batteries of Samples Nos. 1 and 2 did not contain a negative active material. Therefore, in the charging and discharging of the first cycle, a void was formed in the cathode layer, so that the charging of the second cycle could not be performed.

The all-solid lithium secondary batteries of Samples Nos. 4 to 8 contain metals other than carbon black (CB) and Ag as negative electrode active materials. In addition, the all-solid lithium secondary battery of Sample No. 37 contained only carbon black (CB) as a negative electrode active material, and none of them showed excellent discharge capacity.

1: all-solid lithium secondary battery 10: anode layer
11: positive current collector 12: positive active material layer
20: negative electrode layer 21: negative electrode current collector
22: negative active material layer 23: metal layer
30: solid electrolyte layer

Claims (24)

An all-solid lithium secondary battery comprising a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer capable of forming an alloy or compound with lithium in this order,
The negative active material layer is an all-solid lithium secondary battery containing Ag. The method of claim 1,
The content of the Ag is 10 to 100% by weight based on the total 100% by weight of the negative active material included in the negative active material layer, an all-solid lithium secondary battery. The method of claim 1,
The content of the Ag is 20 to 80% by weight based on the total 100% by weight of the negative active material included in the negative electrode active material layer, an all-solid lithium secondary battery. The method of claim 1,
An all-solid lithium secondary battery having an Ag content of 0.05 to 5 mg/cm ² per unit area in the negative active material layer. The method of claim 1,
An all-solid lithium secondary battery having an Ag content of 0.1 to 2.0 mg/cm ² per unit area in the negative active material layer. The method of claim 1,
The negative active material layer further comprises at least one selected from amorphous carbon, gold, platinum, palladium, silicon, aluminum, bismuth, tin, indium, and zinc, an all-solid lithium secondary battery. The method of claim 6,
The amorphous carbon comprises carbon black, graphene, or a combination thereof, an all-solid lithium secondary battery. The method of claim 1,
The negative active material layer comprises Ag on a particle or a film, an all-solid lithium secondary battery. The method of claim 1,
The negative active material layer has a thickness of 1 to 20 μm, an all-solid lithium secondary battery. The method of claim 1,
Further comprising a negative electrode current collector,
An all-solid lithium secondary battery that does not contain lithium between the negative electrode current collector, the negative electrode active material layer, or the negative electrode active material layer and the solid electrolyte in an initial state or a state after complete discharge. The method of claim 1,
Further comprising a negative electrode current collector,
In an overcharged state, a metal layer containing lithium as a main component is deposited and disposed between the negative electrode current collector and the negative electrode active material layer, inside the negative electrode active material layer, or both. The method of claim 11,
An all-solid lithium secondary battery, wherein a metal layer containing lithium as a main component is disposed closer to the negative electrode current collector layer than the negative electrode active material layer between the negative electrode current collector and the negative electrode active material layer. The method of claim 11,
The lithium-based metal layer comprises a Li (Ag) alloy including a γ ₁ phase, a β Li phase, or a combination of these phases. The method of claim 13,
The Li (Ag) alloy comprises a Li-Ag solid solution, an all-solid lithium secondary battery. The method of claim 1,
Further comprising a negative electrode current collector,
Further comprising a film including a material capable of forming an alloy or compound with lithium on the negative electrode current collector,
The film is disposed between the negative electrode current collector and the negative electrode active material layer, an all-solid lithium secondary battery. The method of claim 15,
The thickness of the film is 1 nm to 500 nm, an all-solid lithium secondary battery. The method of claim 1,
The solid electrolyte layer comprises a sulfide-based solid electrolyte, an all-solid lithium secondary battery. The method of claim 17,
The sulfide-based solid electrolyte is Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiX (X is a halogen element), Li ₂ SP ₂ S ₅ -Li ₂ O, Li ₂ SP ₂ S ₅ -Li ₂ O- LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ SB ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m S _n (m and n are positive numbers, Z is one of Ge, Zn or Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _p MO _q (p and q are positive numbers, M is P, Si, Ge, B, Al, Ga Or one of In), or a combination of these, an all-solid lithium secondary battery. The method of claim 17,
The sulfide-based solid electrolyte includes a solid electrolyte represented by the following Formula 1, an all-solid lithium secondary battery:
<Formula 1>
Li _{x M'y} PS _z A _w
In Formula 1,
x, y, z, and w are each independently 0 or more and 6 or less;
M'is one or more of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta;
A is one or more of F, Cl, Br, or I. The method of claim 1,
In use, an all-solid lithium secondary battery in which an external pressure applied to the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer is 1.0 Mpa or less. It is an all-solid lithium secondary battery comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in this order,
The negative electrode layer includes a negative electrode current collector and a negative electrode active material layer,
The negative active material layer contains amorphous carbon and Ag,
The content of the Ag is 10 to 100% by weight based on the total 100% by weight of the negative active material included in the negative active material layer, an all-solid lithium secondary battery. The method of claim 21,
The negative electrode current collector comprises a Ni foil, a Ni-coated Cu foil, a stainless steel foil, or a combination thereof, an all-solid lithium secondary battery. A method for charging an all-solid lithium secondary battery in which the all-solid lithium secondary battery according to any one of claims 1 to 22 is charged in excess of the capacity of the negative active material layer. The method of claim 23,
A charging method of an all-solid lithium secondary battery, wherein the amount of charge is 2 to 100 times the charging capacity of the negative active material layer.

Images