All-solid-state lithium-ion secondary battery

Abstract

Disclosed is an all-solid-state lithium-ion secondary battery in which, by surface-treating a current collector included in a lithium-free anode with a lithiophilic material, the surface-treated material induces a uniform lithium plating reaction on the current collector even during rapid charging, thereby improving performance. The all-solid-state lithium-ion secondary battery comprises a cathode, a solid electrolyte layer, an anode current collector, and an anode active material layer disposed between the solid electrolyte layer and the anode current collector, wherein the anode current collector includes: a base material; and a lithiophilic layer positioned on the surface of the base material.

Description

All-solid-state lithium-ion secondary battery

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0167861, filed November 28, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an all-solid-state lithium-ion secondary battery including a lithium-free negative electrode, and more particularly, to an all-solid-state lithium-ion secondary battery in which a current collector included in a lithium-free negative electrode is surface-treated with a lithium-friendly material, so that the surface-treated material induces a uniform lithium plating reaction on the current collector even during rapid charging, thereby improving performance.

[0003] In terms of battery capacity, safety, output, large-scale development, and miniaturization, various batteries are being studied to overcome the limitations of lithium secondary batteries, which are currently widely commercialized. Representative examples include metal-air batteries, which have a much larger theoretical capacity than lithium secondary batteries in terms of capacity; all-solid-state batteries, which have no risk of explosion compared to lithium secondary batteries in terms of safety; super capacitors for output; sodium-sulfur batteries (NaS batteries) or redox flow batteries (RFBs) for large-scale development; and thin film batteries for miniaturization. These are all being continuously researched in academia and industry.

[0004] Among these, all-solid-state batteries are batteries that replace the liquid electrolyte used in lithium secondary batteries with a solid one. Accordingly, since flammable solvents are not used, there is no risk of fire or explosion due to decomposition reactions of conventional electrolytes, so safety can be significantly improved. Furthermore, since all-solid-state batteries can use lithium metal or a lithium alloy as the anode active material, they have the advantage of being able to dramatically improve the energy density for the mass and volume of the battery. Furthermore, the capacity density (capacity per unit weight) of lithium is approximately 10 times that of graphite, which is generally used as an anode active material. Therefore, when lithium is used as the anode active material, it is possible to increase the output of all-solid-state batteries while making them thinner.

[0005] As such a conventional all-solid-state battery, a battery is known that includes a metal layer formed of a metal that forms an alloy with lithium as an anode active material layer, and has an interface layer made of amorphous carbon on the anode active material layer. In addition, in this type of all-solid-state battery, when charging, metallic lithium is deposited between the amorphous carbon interface layer and the anode active material layer, and when discharging, the deposited metallic lithium is ionized and moves toward the cathode. However, when the all-solid-state battery as described above is repeatedly charged and discharged, the metallic lithium deposited between the amorphous carbon interface layer and the anode active material layer is ionized and dissolved, which may cause a problem in that a void is created, making it impossible to use the battery.

[0006] To address these issues, the industry has developed an all-solid-state battery comprised of a carbon-containing anode (i.e., a lithium-free anode) excluding a lithium metal layer. The anode of this all-solid-state battery does not contain lithium in the initial state or after complete discharge, and when overcharged, lithium ions moved from the positive electrode form an alloy or compound between the negative electrode current collector and the solid electrolyte, which can function as a negative electrode active material (i.e., lithium metal is plated on the surface of the negative electrode current collector during charging).

[0007] However, in this case, there is a problem that the lithium plating reaction may occur unevenly depending on the location of the current collector even under the generally applied charging current, which increases the possibility of an internal short-circuit phenomenon occurring during battery operation. In the art, to prevent this phenomenon, lithium-friendly materials such as silver (Ag), gold (Au), and silicon (Si) are included in the negative electrode active material layer (excluding lithium metal). However, as faster charging currents have been recently demanded (i.e., the need for rapid charging has increased), an all-solid-state battery that meets this requirement is required, but it is difficult to achieve the purpose by only applying the negative electrode active material layer including the lithium-friendly material as described above. Therefore, the development of a novel all-solid-state battery that can solve the above-mentioned immediate problems is urgently required.

[0008] Accordingly, an object of the present invention is to provide an all-solid-state lithium-ion secondary battery in which the surface of a current collector included in a lithium-free negative electrode is treated with a lithium-friendly material, thereby inducing a uniform lithium plating reaction on the current collector even during rapid charging, thereby improving performance.

[0009] In order to achieve the above object, the present invention provides an all-solid-state lithium ion secondary battery comprising a positive electrode, a solid electrolyte layer, a negative electrode current collector, and a negative electrode active material layer disposed between the solid electrolyte layer and the negative electrode current collector, wherein the negative electrode current collector comprises a base material; and a lithium affinity layer positioned on the surface of the base material.

[0010] According to the all-solid-state lithium-ion secondary battery of the present invention, by surface-treating the current collector included in the lithium-free negative electrode with a lithium-friendly material, the surface-treated material induces a uniform lithium plating reaction on the current collector even during rapid charging, thereby having the advantage of improved performance.

[0011] Figure 1 is a cross-sectional schematic diagram showing the configuration of an all-solid-state lithium-ion secondary battery according to one embodiment of the present invention.

[0012] Figure 2 is a cross-sectional schematic diagram showing the configuration of an all-solid-state lithium-ion secondary battery according to one embodiment of the present invention.

[0013] FIG. 3 is a schematic side cross-sectional view showing a laminated structure of a negative electrode collector (a) included in a conventional non-anode all-solid-state battery and a negative electrode collector (b) included in an all-solid-state battery according to an embodiment of the present invention.

[0014] Figure 4 is a graph showing the capacity retention rate according to the charge / discharge cycle of a battery according to one embodiment and a comparative example of the present invention.

[0015] Hereinafter, the present invention will be described in detail.

[0016] An all-solid-state lithium ion secondary battery according to the present invention includes a positive electrode, a solid electrolyte layer, a negative electrode current collector, and a negative electrode active material layer disposed between the solid electrolyte layer and the negative electrode current collector, wherein the negative electrode current collector includes a base material and a lithium affinity layer positioned on a surface of the base material.

[0017] Fig. 1 is a cross-sectional schematic diagram showing the configuration of an all-solid-state lithium-ion secondary battery according to one embodiment of the present invention. The all-solid-state lithium-ion secondary battery (100) according to one embodiment of the present invention is a so-called lithium-ion secondary battery that performs charging and discharging by lithium ions moving between a positive electrode (10) and a negative electrode (20). Specifically, as illustrated in Fig. 1, this all-solid-state lithium-ion secondary battery (100) is composed of a positive electrode (10), a negative electrode (20), and a solid electrolyte layer (30) disposed between the positive electrode (10) and the negative electrode (20).

[0018] Hereinafter, each of these will be described, and in particular, the cathode (20), which has a key feature of the present invention, will be described in more detail.

[0019] (1) Bipolar

[0020] As illustrated in Fig. 1, the positive electrode (10) includes a positive electrode active material layer (14) and a positive electrode current collector (12) sequentially arranged in the direction of the negative electrode (20). The positive electrode current collector (12) may be in a plate shape or a foil shape. The positive electrode current collector (12) may be, for example, one type of metal selected from indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, and lithium, or an alloy of two or more types of metals.

[0021] The positive electrode active material layer (14) can reversibly absorb and release lithium ions. In addition, the positive electrode active material layer (14) includes a positive electrode active material and may further include a solid electrolyte. The positive electrode active material may be a compound capable of insertion / de-insertion of lithium. Examples of the compound capable of insertion / de-insertion of lithium include Li a A 1-b B' b D'2(0.90≤a≤1.8, 0≤b≤0.5); Li a E1- b B' b O 2-c D' c(0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); LEE 2-b B' b O 4-c D' c (0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b B' c D' α (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 (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Mr b B' c D' α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b-c Mr b B' c O 2-α F' α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni b HAVE BEEN c G d O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤ 0.1); Li a Ni b Co c Mr d G e O2(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 O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a MnG bO2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4(0.90≤a≤1.8, 0.001≤b≤0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiI'O2; LiNiVO4; Li (3-f) J2(PO4)3(0≤f≤2); Li (3-f) It can be expressed as one of Fe2(PO4)3(0≤f≤2); LiFePO4.

[0022] In the above chemical formula, A is Ni, Co, Mn or a combination thereof, B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination 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, and J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0023] Specific examples of the positive electrode active material include lithium salts such as lithium cobaltate (LCO), lithium nickelate, lithium nickel cobaltate, lithium nickel cobalt aluminumate (NCA), lithium nickel cobalt manganese (NCM), lithium manganese acid, and lithium iron phosphate, and lithium sulfide. The positive electrode active material layer (14) may include only one selected from these compounds as the positive electrode active material, or may include two or more.

[0024] The above-described 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 refers to a structure in which oxygen atomic layers and metal atomic layers are alternately and regularly arranged in the direction of the cubic rock salt structure, and as a result, each atomic layer forms a two-dimensional plane. In addition, the cubic rock salt structure refers to a sodium chloride structure, which is a type of crystal structure. For example, the cubic rock salt structure refers to a structure in which face-centered cubic lattices in which cations and anions are respectively formed are arranged with a displacement of half of the edges of the unit cell.

[0025] Lithium salts of transition metal oxides having this layered rock salt structure include, for example, LiNi x Co y Al z O2(NCA) or LiNi x Co y Mn z It may be a ternary lithium transition metal oxide such as O2(NCM) (where 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1). The positive electrode active material layer (14) includes a lithium salt of a ternary transition metal oxide having such a layered rock salt structure as a positive electrode active material, thereby improving the energy density and thermal stability of an all-solid-state lithium ion secondary battery (100).

[0026] Examples of the shape of the positive electrode active material include spherical, elliptical, and spherical particle shapes. In addition, the particle size of the positive electrode active material is not particularly limited and may be within a range applicable to positive electrode active materials of a typical all-solid-state lithium-ion secondary battery. In addition, the content of the positive electrode active material in the positive electrode active material layer (14) is not particularly limited and may be within a range applicable to positive electrodes of a typical all-solid-state lithium-ion secondary battery.

[0027] In addition, the compound having a coating layer on the surface can be used, and the compound and the compound having the coating layer can be mixed and used. The coating layer can include a coating element compound of an oxide, a hydroxide, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a hydroxycarbonate of the coating element. The compounds forming these coating layers can be amorphous or crystalline. Examples of the coating elements included in the coating layer include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof, and a specific example of the coating layer includes Li2O-ZrO2, etc. The coating layer forming process can use any coating method as long as it can coat the compound with these elements in a method that does not adversely affect the properties of the positive electrode active material (for example, spray coating, dipping, etc.), and since this is well understood by those working in this field, a detailed description thereof will be omitted.

[0028] The solid electrolyte that may be further included in the positive electrode active material layer (14) may be the same as or different from the solid electrolyte included in the solid electrolyte layer (30) described below. In addition, the positive electrode active material layer (14) may be a mixture of not only the positive electrode active material and the solid electrolyte described above, but also additives such as a conductive agent, a binder, a filler, a dispersant, or an ion conductive assistant. Examples of the conductive agent include graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or metal powder. In addition, the binder is mixed with the active material and the conductive agent to bind each component and help particle growth, and examples thereof include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. In addition, the filler, dispersant, or ion conductive auxiliary agent may be exemplified by known materials commonly used in electrodes of all-solid-state lithium-ion secondary batteries. In addition, the positive electrode active material layer (14) may include the positive electrode active material, conductive material, and binder in granular form.

[0029] (2) Cathode

[0030] Next, the negative electrode (20) includes a negative electrode active material layer (24) positioned closer to the positive electrode (10) side and in contact with the solid electrolyte layer (30), and a negative electrode current collector (22) positioned at the outermost portion or the like based on the stacking direction, facing the opposite side of the negative electrode active material layer (24) that does not contact the solid electrolyte layer (30). In addition, the negative electrode may not include a separate lithium metal, except for lithium metal formed during charging.

[0031] Negative active material layer

[0032] First, the negative electrode active material layer (24) may include one or more types of negative electrode active materials capable of forming an alloy or compound with lithium. In the initial state or after complete discharge, lithium may not be included between the negative electrode current collector (22), the negative electrode active material layer (24), or the negative electrode active material layer (24) and the solid electrolyte layer (30). Fig. 2 is a cross-sectional schematic diagram showing the configuration of an all-solid-state lithium ion secondary battery according to one embodiment of the present invention.

[0033] As described below, when the all-solid-state lithium ion secondary battery (100) according to one embodiment is overcharged, the negative active material included in the negative active material layer (24) and the lithium ions that have moved from the positive electrode (10) may form an alloy or compound, so that, for example, as illustrated in FIG. 2, a metal layer (26) containing lithium as a main component may be formed (deposited) on the negative electrode (20). The metal layer (26) may be formed by being deposited between the negative current collector (22) and the negative active material layer (24), inside the negative active material layer (24), or both. When the metal layer (26) is positioned between the negative current collector (22) and the negative active material layer (24), the metal layer (26) may be formed closer to the negative current collector layer (22) than to the negative active material layer (24).

[0034] The negative electrode active material layer (24) according to one embodiment of the present invention may include at least one lithium-friendly material selected from the group consisting of silver (Ag), gold (Au), platinum (Pt), zinc (Zn), silicon (Si), magnesium (Mg), copper oxide (CuO), zinc oxide (ZnO), cobalt oxide (CoO), manganese monoxide (MnO), silicon dioxide (SiO2), titanium dioxide (TiO2), alumina (Al2O3), zinc peroxide (ZnO2), and lithium fluoride (LiF) as the negative electrode active material. In addition, it may be more preferable to apply silver (Ag) as the lithium-friendly material among these. However, the present invention is not limited thereto, and any lithium-friendly material having similar physical properties or characteristics to these may be applied without any special limitation.

[0035] Accordingly, the metal layer (26) formed during overcharge may include a Li (lithium affinity material) alloy including a γ1 phase, a βLi phase, or a combination thereof in which the lithium affinity material is dissolved in lithium. Therefore, during discharge, only Li is dissolved in the Li (lithium affinity material) alloy constituting the metal layer (26), and the dissolved lithium affinity material remains, thereby suppressing the occurrence of pores. In this case, the content of the lithium affinity material in the precipitated Li-lithium affinity material solid solution may be 60 wt% or less. Within this range, the decrease in the average discharge potential due to the influence of the lithium affinity material can be effectively suppressed. On the other hand, if the content of the lithium affinity material in the precipitated Li-lithium affinity material solid solution is too low, the amount of lithium affinity material remaining during discharge becomes small, and it may be difficult to sufficiently suppress the occurrence of pores. For this reason, the content of the lithium-affinity material in the precipitated Li-lithium-affinity material solid solution may be 20 wt% or more, for example, 40 wt% or more.

[0036] In one embodiment of the present invention, the lithium-affinity material does not necessarily need to be uniformly present in the negative electrode active material layer (24), and may be distributed in the negative electrode current collector (22) side of the negative electrode active material layer (24). In this case, lithium ions may react with the lithium-affinity material distribution layer in the negative electrode active material layer (24) that has reached the vicinity of the negative electrode current collector (22), thereby forming a Li (lithium-affinity material) alloy as a metal layer (26).

[0037] If the content of the lithium-affinity material included in the negative electrode active material layer (24) is excessively low, it may be difficult to suppress the occurrence of pores because the lithium-affinity material remaining during discharge also decreases. Therefore, the negative electrode active material layer (24) may include 10 wt% or more, preferably 20 wt% or more, of the lithium-affinity material based on 100 wt% of the total negative electrode active material included in the negative electrode active material layer (24) in the initial state before charge / discharge is performed. On the other hand, in the relationship between the reaction potential of the lithium-affinity material and Li, if the lithium-affinity material increases, the average discharge potential may decrease, which may lower the energy density of the battery. Therefore, from the viewpoint of high energy density, the upper limit of the content of the lithium-affinity material may be preferably 50 wt% or less based on 100 wt% of the total negative electrode active material included in the negative electrode active material layer (24).

[0038] In addition, in the negative electrode active material layer (24), if the content of the lithium-affinity material per unit area is excessively low when viewed in the stacking direction of the negative electrode (20), it may be difficult to suppress the occurrence of pores because the lithium-affinity material remaining during discharge also decreases. Therefore, the content of the lithium-affinity material per unit area in the negative electrode active material layer (24) is 0.05 mg / cm 2 Ideally, 0.10 mg / cm 2On the other hand, if the content of lithium-affinity material per unit area is too high, the average discharge potential may decrease, which may lower the energy density of the battery. Therefore, the upper limit of the content of lithium-affinity material per unit area is 5 mg / cm. 2 Less than or equal to 2 mg / cm 2 It could be as follows:

[0039] In addition, in the initial state before charge / discharge, the lithium-compatible material included in the negative electrode active material layer (24) may be in the form of particles or a film. When the lithium-compatible material exists in the form of particles, the average particle diameter (d50, diameter length or average diameter) of the lithium-compatible material may be 20 nm to 1 μm, but is not limited thereto.

[0040] Meanwhile, the negative electrode active material layer (24) may also include a carbon material as a negative electrode active material in addition to a lithium-friendly material. Amorphous carbon may be preferably used as the carbon material included in the negative electrode active material layer (24). Specific examples of the amorphous carbon include amorphous carbon black (amorphous acetylene black, amorphous furnace black, amorphous Ketjen black), amorphous activated carbon, amorphous graphene, and combinations thereof. However, among the negative electrode active material layers (24), by positioning a carbon material having a relatively small particle size on the interface side that comes into contact with the solid electrolyte layer (30), the interface of the negative electrode active material layer (24) that comes into contact with the solid electrolyte layer (30) can be made flatter. Based on 100 wt% of the total negative electrode active material included in the negative electrode active material layer (24), the combined negative electrode active materials other than the lithium-friendly material may be 50 wt% or more, for example, 70 wt% or more. The content of negative active material other than the lithium-compatible material can be measured using the same method as the method for measuring the content of the lithium-compatible material.

[0041] And, the carbon material included in the negative electrode active material layer (24) may contain oxygen. More specifically, the carbon material particles constituting the carbon material may contain 2 to 10 at% of oxygen. When the oxygen is included in the range of 2 to 10 at%, the surface roughness of the negative electrode active material layer and the operating characteristics of the battery may be further improved. In one embodiment of the present invention, the oxygen may exist in a form included in a functional group bonded to the carbon material particles. In addition, the functional group may include at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an ether group, an ester group, an aldehyde group, a carbonyl group, and an amide group.

[0042] The carbon material particles containing 2 to 10 at% of oxygen can be produced, for example, by a method of oxidizing the carbon material. For example, the carbon material can be treated with an acid, stirred and reacted at a temperature of 25 to 60°C, to introduce oxygen functional groups to the surface of the carbon material. The type of the acid is not particularly limited, and any acid that can introduce oxygen functional groups to the surface of the carbon material can be used. Examples of the acid include sulfuric acid, nitric acid, or mixtures thereof, and an oxidizing agent such as potassium permanganate can also be used.

[0043] The content of oxygen contained in the above carbon material particles can be measured using a photoelectron spectroscopy (XPS or ESCA). For example, it can be measured using a K-Alpha (Thermo Fisher Scientific) device. In one embodiment of the present invention, the oxygen may be present on the surface of the carbon material particles. The surface does not mean only the outer surface of the carbon material particles, but also includes, for example, the inner surface of the pores if pores exist.

[0044] And, when the carbon material contains oxygen as described above, the negative electrode active material layer (24) may contain 2 to 10 at% of oxygen, 65 to 85 at% of carbon, and 0.5 to 5 at% of silver, and preferably may contain 2.5 to 5 at% of oxygen, 74 to 85 at% of carbon, and 0.5 to 3 at% of silver. In addition, the negative electrode active material layer (24) may further contain 5 to 25 at% of fluorine (F), and preferably 10 to 20 at% of fluorine (F). In addition, the negative electrode active material layer (24) may further contain 0.01 to 1 at% of sulfur (S), and preferably 0.01 to 0.5 at% of sulfur (S). In one embodiment of the present invention, the negative active material layer (24) may include 2 to 10 at% of oxygen, 65 to 85 at% of carbon, 0.5 to 5 at% of silver, and 5 to 25 at% of fluorine, preferably 2.5 to 5 at% of oxygen, 74 to 85 at% of carbon, 0.5 to 3 at% of silver, and 10 to 20 at% of fluorine, and may further include sulfur. The above atomic composition ratios can be measured using a photoelectron spectroscopy (XPS or ESCA). For example, the composition ratios can be measured using a Nexsa4 (Thermo Fisher Scientific) device.

[0045] Meanwhile, the negative electrode active material layer (24) may further include a binder for the purpose of stabilizing the negative electrode active material layer (24) on the negative electrode current collector (22). The binder may be, for example, a resin such as styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. In addition, the negative electrode active material layer (24) may appropriately contain additives used in conventional all-solid-state batteries, such as fillers, dispersants, and ion conductive additives. Specific examples of the additives are the same as those described in the positive electrode section described above.

[0046] The total thickness of the negative electrode active material layer (24) is not particularly limited and may be, for example, 1 to 100 μm. If the thickness of the negative electrode active material layer (24) is less than 1 μm, the performance of the all-solid-state battery may not be sufficient. In addition, if the thickness of the negative electrode active material layer (24) exceeds 100 μm, the resistance of the negative electrode active material layer (24) increases, resulting in insufficient performance of the all-solid-state battery. For reference, by using the binder mentioned above, the thickness of the negative electrode active material layer (24) can be easily secured at an appropriate level.

[0047] negative current collector

[0048] The negative electrode current collector (22) may be positioned at the outermost side in the stacking direction, facing the opposite side of the negative electrode active material layer (24) that does not contact the solid electrolyte layer (30), as illustrated in FIG. 1. However, if the battery includes a structure of more than a bi-cell, it may be positioned at a location other than the outermost side in the stacking direction.

[0049] The negative electrode current collector (22) may be plate-shaped or foil-shaped. The negative electrode current collector (22) may include a material that does not react with lithium, i.e., does not form any alloy or compound with lithium. Examples of materials constituting the negative electrode current collector (22) include copper, aluminum, stainless steel, titanium, iron, cobalt, and nickel. In addition, the negative electrode current collector (22) 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.

[0050] FIG. 3 is a schematic side cross-sectional view showing a laminated structure of a negative electrode collector (a) included in a typical non-anode all-solid-state battery and a negative electrode collector (b) included in an all-solid-state battery according to an embodiment of the present invention. Meanwhile, the negative electrode collector of the present invention, as illustrated in FIG. 3, includes the base material described above and a lithium affinity layer positioned on the surface of the base material. That is, while a typical non-anode all-solid-state battery, as illustrated in FIG. 3 a, has the negative electrode collector (22) and the negative electrode active material layer (24) in direct contact with each other, the present invention, as illustrated in FIG. 3 b, includes a lithium affinity layer (23) positioned between the negative electrode collector (or base material, 22) and the negative electrode active material layer (24).

[0051] And, if the all-solid-state battery includes a bi-cell structure, the lithium affinity layer (23) can be positioned on both sides of the negative electrode current collector as shown in Fig. 3b. On the other hand, if the all-solid-state battery includes only a mono-cell structure, the lithium affinity layer (23) can be positioned only on one side of the negative electrode current collector (more precisely, one side of the negative electrode current collector in the direction of the negative electrode active material layer).

[0052] The lithium-friendly layer (23) above is a negative electrode current collector surface treatment layer including a lithium-friendly material (i.e., a material capable of forming an alloy by reacting with lithium). In addition, the lithium-friendly material may be at least one selected from the group consisting of silicon dioxide (SiO2), titanium dioxide (TiO2), alumina (Al2O3), zinc peroxide (ZnO2), and lithium fluoride (LiF). This lithium-friendly layer (23) may be a material capable of surface treatment, such as deposition, by a method selected from the group consisting of an atomic layer deposition (ALD) method, a sputtering method, and a plasma treatment method.

[0053] In addition, the lithium-affinity layer (23) may additionally include, if necessary, one or more of silver (Ag), gold (Au), zinc oxide (ZnO), cobalt oxide (CoO), manganese monoxide (MnO), and other materials that can exhibit similar or identical effects to these. In addition, the lithium-affinity layer (23) may also include a material capable of forming a compound by reacting with lithium. Examples of materials capable of forming a compound by reacting with lithium include carbon, titanium sulfide, iron sulfide, and combinations thereof.

[0054] As previously explained, the lithium-friendly material is also included in the negative electrode active material layer (24). However, as a result of repeated research from various angles, the applicant of the present invention has found that when the negative electrode current collector itself is surface-treated with a lithium-friendly material or an negative electrode active material layer containing the lithium-friendly material is additionally applied and laminated thereon (i.e., the negative electrode active material layer can be omitted in the present invention), compared to the conventional case of simply applying and laminating an negative electrode active material layer containing the lithium-friendly material on the negative electrode current collector, lithium plating on the current collector is uniformly performed even during rapid charging, and the rapid charge cycle capacity retention rate of the battery (particularly, a sulfide-based all-solid-state battery) is significantly improved. That is, the lithium-friendly layer (23) can be utilized as a layer that allows lithium metal to be evenly deposited on the surface side of the negative electrode current collector, for example, as a wetting layer.

[0055] The lithium-affinity material included in the lithium-affinity layer (23) may have an average particle diameter (D50) of 10 nm to 50 μm, preferably 10 nm to 20 μm. If the average particle diameter (D50) of the lithium-affinity material particles is less than 10 nm, the particle size may be excessively small, which may cause agglomeration problems between particles. In addition, if the average particle diameter (D50) of the lithium-affinity material particles exceeds 50 μm, the surface area of ​​the particles may become small, which may prevent the alloying reaction with lithium from proceeding smoothly.

[0056] The thickness of the lithium affinity layer (23) may be 1 to 500 nm, preferably 10 to 400 nm, and more preferably 50 to 300 nm, based on the thickness of the negative electrode current collector (or, base material) of 1 to 30 ㎛. If the thickness of the lithium affinity layer is less than 1 nm based on the thickness of the negative electrode current collector of 1 to 30 ㎛, it may be difficult to suppress the generation of pores because the lithium affinity material remaining during discharge also decreases. In addition, if the thickness of the lithium affinity layer exceeds 500 nm based on the thickness of the negative electrode current collector of 1 to 30 ㎛, cell efficiency may decrease, resulting in a decrease in energy density. In addition, it may be preferable that the lithium affinity layer (23) be formed flat on the negative electrode current collector in order to prevent the battery from cracking during the charge cycle.

[0057] In addition, the thickness ratio of the lithium affinity layer (23) and the negative electrode active material layer (24) also affects the lithium plating reaction for the current collector. The thickness ratio of the lithium affinity layer (23) and the negative electrode active material layer (24) may be 1:20 to 500, preferably 1:30 to 200. In particular, if the thickness of the lithium affinity layer is excessively thin beyond the above range, a problem may occur in which the layer cannot function as a lithium affinity layer.

[0058] Meanwhile, the lithium affinity layer (23) may also be composed of multiple layers of two or more layers. At this time, each layer includes the aforementioned lithium affinity material, and different types of lithium affinity materials may be positioned in each layer, or the same type of lithium affinity material may be positioned in each layer. For example, when the lithium affinity layer (23) is composed of two layers, the lithium affinity layer located on the base material side may include lithium fluoride (LiF), and the lithium affinity layer located on the negative electrode active material layer side may include titanium dioxide (TiO2) or lithium fluoride (LiF). At this time, there is no particular limitation on the thickness ratio between layers.

[0059] (3) Solid electrolyte layer

[0060] The above solid electrolyte layer (30) is disposed between the positive electrode (10) and the negative electrode (20) (for example, between the positive electrode active material layer (14) and the negative electrode active material layer (24)) and includes a solid electrolyte capable of moving ions. The solid electrolyte may include at least one selected from a sulfide-based solid electrolyte, a polymer-based solid electrolyte, and an oxide-based solid electrolyte, and it may be preferable to include only a sulfide-based solid electrolyte.

[0061] The above sulfide-based solid electrolyte is Li2S-P2S5, Li2S-P2S5-LiX (X=halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m and n are positive numbers, Z is one of Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, M is one of P, Si, Ge, B, Al, Ga or In), or a combination thereof. In addition, the sulfide-based solid electrolyte may include a solid electrolyte represented by the following chemical formula 1.

[0062] [Chemical Formula 1]

[0063] Li x M' y PS z A w

[0064] In the above chemical formula 1, x, y, z, and w are each independently 0 or more and 6 or less, M' is at least one selected from As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, and Ta, and A is at least one selected from F, Cl, Br, and I.

[0065] And, as the solid electrolyte, one containing sulfur (S), phosphorus (P), and lithium (Li) as constituent elements among the sulfide solid electrolyte materials can be used. For example, one containing Li2S-P2S5 can be used. When using one containing Li2S-P2S5 as the sulfide-based solid electrolyte material, the mixing molar ratio of Li2S and P2S5 can be selected from the range of, for example, Li2S:P2S5=50:50 to 90:10. In addition, the solid electrolyte may be in an amorphous state, a crystalline state, or a mixed state of amorphous and crystalline. In addition, the solid electrolyte layer (30) may further include a binder. The binder may be, for example, a resin such as styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or polyacrylic acid. In addition, the above binder may be the same as or different from the binder that may be included in each of the positive electrode active material layer (14) and the negative electrode active material layer (24).

[0066] Initial charge capacity ratio

[0067] Meanwhile, in an all-solid-state lithium ion secondary battery (100) according to one embodiment, the initial charge capacity of the positive electrode active material layer (14) may be configured to be excessively large compared to the initial charge capacity of the negative electrode active material layer (24). As described below, the all-solid-state lithium ion secondary battery (100) according to one embodiment can be used by charging (i.e., overcharging) exceeding the initial charge capacity of the negative electrode active material layer (24). In the initial stage of charging, lithium may be absorbed into the negative electrode active material layer (24). That is, the negative electrode active material may form an alloy or compound with lithium ions that have moved from the positive electrode (10). When charging is performed exceeding the initial charge capacity of the negative electrode active material layer (24), as illustrated in FIG. 2, lithium may be precipitated on the back surface of the negative electrode active material layer (24), i.e., between the negative electrode current collector (22) and the negative electrode active material layer (24), and a metal layer (26) may be formed by this lithium. The metal layer (26) may be mainly composed of lithium in which a lithium-affinity material is dissolved (i.e., lithium-affinity material-Li solid solution). This phenomenon may be caused by a material that forms an alloy or compound with the lithium-affinity material included in the negative electrode, for example. During discharge, lithium in the negative electrode active material layer (24) and the metal layer (26) may be ionized and move toward the positive electrode (10) while leaving the dissolved lithium-affinity material. Therefore, lithium can be used as the negative electrode active material in an all-solid-state lithium ion secondary battery (100). In addition, since the lithium-affinity layer (23) and the negative electrode active material layer (24) coat the metal layer (26) at the same time, they function as a protective layer for the metal layer (26) and can suppress the precipitation and growth of dendritic metallic lithium. In this way, short-circuiting and capacity reduction of the all-solid-state lithium-ion secondary battery (100) can be suppressed, and further, the characteristics of the all-solid-state lithium-ion secondary battery (100) can be improved. In addition, according to one embodiment, since the metal layer (26) is not formed in advance, there is also an advantage of being able to reduce the manufacturing cost of the all-solid-state lithium-ion secondary battery (100).

[0068] In an all-solid-state lithium-ion secondary battery (100) according to one embodiment, it is preferable that the ratio (b+c / a) of the initial charge capacity of the positive electrode active material layer (14) to the initial charge capacity of the negative electrode active material layer (24) and the lithium affinity layer (23) satisfies the following formula.

[0069] [Formula 1]

[0070] 0.01< b+c / a < 0.5

[0071] In the above formula 1, a is the initial charge capacity (mAh) of the positive electrode active material layer (14), b is the initial charge capacity (mAh) of the negative electrode active material layer (24), and c is the initial charge capacity (mAh) of the lithium affinity layer (23).

[0072] At this time, if the initial charge capacity ratio is 0.01 or less, the lithium affinity layer (23) and the negative electrode active material layer (24) may not function sufficiently as a protective layer, which may deteriorate the characteristics of the all-solid-state lithium ion secondary battery (100). For example, if the thickness of the lithium affinity layer (23) and the negative electrode active material layer (24) is very thin, the capacity ratio may become 0.01 or less. In this case, there is a concern that the lithium affinity layer (23) and the negative electrode active material layer (24) may collapse due to repeated charge and discharge, and dendritic metallic lithium may precipitate and grow. As a result, the characteristics of the all-solid-state lithium ion secondary battery (100) may deteriorate. On the other hand, if the initial charge capacity ratio is 0.5 or more, the battery capacity may decrease because the amount of lithium precipitated from the negative electrode decreases.

[0073] Manufacturing method of all-solid-state lithium-ion secondary battery

[0074] Next, a method for manufacturing the above-described all-solid-state lithium-ion secondary battery (100) will be described. An all-solid-state lithium-ion secondary battery (100) according to one embodiment can be manufactured by manufacturing a positive electrode (10), a negative electrode (20), and a solid electrolyte layer (30) separately and then laminating them.

[0075] First, the above-described positive electrode manufacturing process adds materials (positive electrode active material, binder, etc.) constituting the positive electrode active material layer (14) to a non-polar solvent to prepare a slurry (or paste), and then applies the prepared slurry onto a positive electrode current collector (12) and dries it to obtain a laminate. Then, the laminate can be pressed, for example, with hydrostatic pressure, etc., to produce a positive electrode (10). At this time, the pressing process can be omitted.

[0076] Next, the negative electrode manufacturing process adds materials constituting the negative electrode active material layer (24) (negative electrode active material including carbon material and lithium-affinity material, binder, etc.) to a polar solvent or a non-polar solvent to manufacture a slurry (or paste), and then applies the manufactured slurry onto a negative electrode current collector (22) surface-treated with a lithium-affinity material and then dries to obtain a laminate (however, it may be composed of only the negative electrode current collector surface-treated with a lithium-affinity material without the negative electrode active material layer). At this time, the process of surface-treating the negative electrode current collector with the lithium-affinity material may be by a method selected from the group consisting of an atomic layer deposition method, a sputtering method, and a plasma method. Subsequently, the laminate may be pressurized with, for example, hydrostatic pressure, etc. to manufacture the negative electrode (20). At this time, the pressurizing process may be omitted. In addition, the method of applying the slurry to the negative electrode collector (22) is not particularly limited, and for example, screen printing, metal mask printing, electrostatic painting, dip coating, spray coating, roll coating, doctor blade, gravure coating, etc. can be used.

[0077] Next, the solid electrolyte layer (30) can be manufactured using a solid electrolyte including, for example, a sulfide-based solid electrolyte material. First, starting materials (e.g., Li2S, P2S5, etc.) are processed by a melting quenching method or a mechanical milling method to obtain a sulfide-based solid electrolyte material. For example, when using a melting quenching method, starting materials are mixed in a predetermined amount, formed into pellets, reacted in a vacuum at a predetermined reaction temperature, and then rapidly cooled to manufacture a sulfide-based solid electrolyte material. In addition, the reaction temperature of the mixture of Li2S and P2S5 can be 400°C to 1000°C, for example, 800°C to 900°C. In addition, the reaction time can be 0.1 hour to 12 hours, for example, 1 hour to 12 hours. In addition, the rapid cooling temperature of the reactant may be 10℃ or lower, for example, 0℃ or lower, and the rapid cooling speed may be typically 1℃ / sec to 10000℃ / sec, for example, 1℃ / sec to 1000℃ / sec. In addition, when a mechanical milling method is used, a sulfide-based solid electrolyte material can be manufactured by stirring and reacting the starting raw materials 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 production speed of the sulfide-based solid electrolyte material can be, and the longer the stirring time, the higher the conversion rate of the raw materials into the sulfide-based solid electrolyte material can be.

[0078] Thereafter, the obtained mixed raw material (sulfide-based solid electrolyte material) is heat-treated at a predetermined temperature and then pulverized to produce a solid electrolyte in the form of particles. If the solid electrolyte has a glass transition point, it can change from an amorphous state to a crystalline state through heat treatment. Subsequently, the solid electrolyte obtained by the above method can be formed into a solid electrolyte layer (30) by forming a film using a known film forming method such as an aerosol position method, a cold spray method, or a sputtering method. In addition, the solid electrolyte layer (30) can be manufactured by pressurizing solid electrolyte particles. In addition, the solid electrolyte layer (30) can be manufactured by mixing a solid electrolyte, a solvent, and a binder, and then applying, drying, and pressurizing the mixture.

[0079] Finally, a solid electrolyte layer (30) is placed between the above-mentioned manufactured positive electrode (10) and negative electrode (20), and pressurized, for example, by hydrostatic pressure, etc., to manufacture an all-solid-state lithium ion secondary battery (100) according to one embodiment.

[0080] The all-solid-state lithium ion secondary battery (100) of the present invention can be manufactured in the form of a unit cell having a structure of anode / separator / negative electrode, a bi-cell having a structure of cathode / separator / negative electrode / separator / positive electrode, or a laminated battery having a structure of repeating unit cells. In addition, the all-solid-state lithium ion secondary battery according to the present invention can be utilized as a semi-solid battery by including a liquid electrolyte if necessary, and in this case, a separate polymer separator can be further included.

[0081] The shape of the all-solid-state lithium ion secondary battery (100) of the present invention is not particularly limited, and examples thereof include coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, and cone-shaped batteries. Furthermore, the battery can be applied to large-scale batteries used in electric vehicles, etc. For example, the all-solid-state lithium ion secondary battery (100) can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). Furthermore, it can be used in fields requiring large amounts of power storage, such as electric bicycles or power tools.

[0082] Hereinafter, preferred embodiments are presented to help understand the present invention, but these are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0083] [Manufacturing Example 1] Manufacturing of a cathode for an all-solid-state battery

[0084] First, by applying lithium fluoride (LiF) as a lithium-affinity material to the surface of a negative electrode current collector (SUS foil, thickness: 10 ㎛) using an atomic layer deposition method and drying it, a negative electrode current collector was prepared in which a lithium-affinity layer was formed with a thickness of 50 nm.

[0085] Separately, 6 g of amorphous carbon black, 2 g of Ag, 9.33 g of PVdF binder (solid content 6%), and 7.67 g of NMP solution were placed in a Thinky mixer container and mixed 12 times for 3 minutes each at 2,000 rpm. Thereafter, 5 g of NMP solution was additionally added and mixed 5 times for 3 minutes each at 2,000 rpm to prepare a negative active material slurry.

[0086] Thereafter, using a spray coating method, the manufactured negative active material slurry was applied to the surface of the lithium affinity layer of the negative electrode current collector, and then dried to obtain a laminate. Subsequently, the laminate was pressurized with hydrostatic pressure to manufacture a negative electrode for an all-solid-state battery.

[0087] [Comparative Manufacturing Example 1] Manufacturing of a Negative Electrode for an All-Solid-State Battery

[0088] An anode for an all-solid-state battery was manufactured in the same manner as in Manufacturing Example 1, except that a lithium-affinity layer was not formed on the surface of the anode current collector (i.e., a conventional bare SUS foil was applied as the anode current collector).

[0089] [Example 1, Comparative Example 1] Manufacture of an all-solid-state lithium-ion secondary battery

[0090] As a cathode, the cathode active material (lithium transition metal oxide) is placed on an aluminum current collector at 5.5 mAh / cm 2 The sulfide-based all-solid-state batteries of Example 1 and Comparative Example 1 were manufactured using the positive electrode loaded with , the negative electrodes manufactured in Manufacturing Example 1 and Comparative Manufacturing Example 1 were used as the negative electrodes, and the sulfide-based solid electrolyte (Li2S-P2S5) was used as the electrolyte.

[0091] [Experimental Example] Evaluation of Rapid Charging Performance of a Battery

[0092] Each of the sulfide-based all-solid-state batteries of Example 1 and Comparative Example 1 was operated under the following charge-discharge conditions at an operating voltage range of 4.25 V to 3.0 V and an operating temperature of 60°C to evaluate the capacity retention rate according to the charge-discharge cycle, and the results are shown in Fig. 4.

[0093] - Charging conditions: 2C, 4.25V CC / CV, 0.1C cut-off

[0094] - Discharge conditions: 0.33C, 3.0V, CC

[0095] FIG. 4 is a graph showing the capacity retention rate according to the charge / discharge cycle of batteries according to an embodiment and a comparative example of the present invention. As a result of evaluating the capacity retention rate according to the charge / discharge cycle for the sulfide-based all-solid-state batteries of Example 1 and Comparative Example 1, the battery of Example 1, in which a lithium affinity layer was formed on the surface of the negative electrode current collector, exhibited a high capacity retention rate exceeding 95% even after 80 charge / discharge cycles, as shown in FIG. 4. On the other hand, it was confirmed that the capacity retention rate of the battery of Comparative Example 1, which used a conventional negative electrode current collector without forming a lithium affinity layer, rapidly decreased from the initial charge / discharge time.

[0096] These results are attributed to the fact that the lithium-affinity material located on the surface of the negative electrode current collector induced a uniform lithium plating reaction on the current collector, and this indicates that simply including the lithium-affinity material in the negative electrode active material layer has limitations in improving rapid charging performance.

Claims

1. Comprising a positive electrode, a solid electrolyte layer, a negative electrode current collector, and a negative electrode active material layer disposed between the solid electrolyte layer and the negative electrode current collector, An all-solid-state lithium ion secondary battery comprising: the negative electrode current collector; and a lithium affinity layer positioned on the surface of the negative electrode current collector.

2. An all-solid-state lithium ion secondary battery according to claim 1, characterized in that the lithium-affinity layer includes a lithium-affinity material that reacts with lithium to form an alloy or compound.

3. In claim 2, the lithium-compatible material that reacts with lithium to form an alloy is silicon dioxide (SiO 2 ), titanium dioxide (TiO 2 ), alumina (Al 2 O 3 ), zinc peroxide (ZnO 2 ) and lithium fluoride (LiF). An all-solid-state lithium-ion secondary battery.

4. An all-solid-state lithium ion secondary battery according to claim 1, characterized in that the thickness of the lithium-affinity layer is 1 to 500 nm based on a thickness of 1 to 30 ㎛ of the base material.

5. An all-solid-state lithium ion secondary battery according to claim 1, characterized in that the thickness ratio of the lithium-affinity layer and the negative electrode active material layer is 1:20 to 500.

6. An all-solid-state lithium ion secondary battery according to claim 2, wherein the lithium-compatible material that forms an alloy by reacting with lithium has an average particle diameter (D50) of 10 nm to 50 ㎛.

7. An all-solid-state lithium ion secondary battery according to claim 1, wherein the negative electrode does not contain a separate lithium metal, except for lithium metal formed during charging.

8. An all-solid-state lithium ion secondary battery according to claim 3, characterized in that the lithium-affinity layer further includes at least one selected from the group consisting of silver (Ag), gold (Au), zinc oxide (ZnO), cobalt oxide (CoO), and manganese monoxide (MnO).

9. An all-solid-state lithium-ion secondary battery according to claim 2, characterized in that the lithium-compatible material that forms a compound by reacting with lithium is selected from the group consisting of carbon, titanium sulfide, iron sulfide, and combinations thereof.

10. An all-solid-state lithium ion secondary battery according to claim 2, characterized in that the lithium-affinity layer is composed of multiple layers, and the lithium-affinity materials included in each layer are of the same or different types.

11. In claim 1, the negative electrode active material layer comprises silver (Ag), gold (Au), platinum (Pt), zinc (Zn), silicon (Si), magnesium (Mg), copper oxide (CuO), zinc oxide (ZnO), cobalt oxide (CoO), manganese monoxide (MnO), and silicon dioxide (SiO). 2 ), titanium dioxide (TiO 2 ), alumina (Al 2 O 3 ), zinc peroxide (ZnO 2 ) and lithium fluoride (LiF). An all-solid-state lithium ion secondary battery.

12. An all-solid-state lithium ion secondary battery according to claim 11, characterized in that the negative active material contains silver (Ag).

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