Cathode for all-solid-state battery, and all-solid-state battery comprising same

Abstract

Disclosed are a cathode for an all-solid-state battery, and an all-solid-state battery comprising same, the cathode having physically-optimized cathode physical properties that directly affect the lifespan and capacity expression of a battery, and thus can improve performance of the battery. The cathode for an all-solid-state battery comprises a cathode active material, a solid electrolyte and a binder, wherein the amount of the cathode active material exceeds 70 wt%.

Description

Cathode for all-solid-state battery and all-solid-state battery containing same

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0130763, filed September 27, 2023, and Korean Patent Application No. 10-2024-0121373, filed September 6, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an all-solid-state battery positive electrode having a tensile strength within a specific range while containing components in a predetermined ratio, and an all-solid-state battery including the same, and more particularly, to an all-solid-state battery positive electrode capable of improving the performance of a battery by physically optimizing the properties of the positive electrode that directly affect the lifespan and capacity development of the battery, and an all-solid-state battery including the same.

[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, unlike lithium secondary batteries, have no risk of explosion 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 replace the liquid electrolyte used in lithium secondary batteries with a solid one. Consequently, they eliminate the use of flammable solvents, eliminating the risk of ignition or explosion due to electrolyte decomposition reactions, as was the case with conventional batteries. This significantly improves safety. Furthermore, all-solid-state batteries can utilize lithium metal or lithium alloys as their anode materials, offering the advantage of dramatically improving energy density relative to the battery's mass and volume.

[0005] Meanwhile, solid electrolytes of all-solid-state batteries can be broadly classified into organic (polymer) solid electrolytes and inorganic solid electrolytes, and among these, inorganic solid electrolytes can be divided into sulfide and oxide. In addition, the solid electrolyte that has undergone the most technological development is the sulfide solid electrolyte, and its development has progressed to the point where its ionic conductivity is close to that of organic electrolytes. In this way, the sulfide solid electrolyte is ranked 10th among solid electrolytes. -3 10 inland -2 Not only does it have a high ionic conductivity of S / cm, but it also has the advantage of being malleable, making good contact with the interface and thus improving resistance.

[0006] In sulfide-based all-solid-state batteries containing these sulfide-based solid electrolytes, the characteristics of the cathode, in particular, directly impact the battery's lifespan and capacity development. Therefore, research is being conducted on structural improvements to reduce resistance within the cathode, as well as on improving cathode properties, particularly ionic and electrical conductivity. However, these improvements remain unsatisfactory, and thus, more fundamental solutions are needed to optimize cathode properties and enhance battery performance.

[0007] Accordingly, the purpose of the present invention is to provide a positive electrode for an all-solid-state battery and an all-solid-state battery including the same, which can improve the performance of a battery by physically optimizing the properties of the positive electrode that directly affect the lifespan and capacity development of the battery.

[0008] To achieve the above object, the present invention provides a positive electrode for an all-solid-state battery, which comprises a positive electrode active material, a solid electrolyte, and a binder, and in which the content of the positive electrode active material exceeds 70 wt%.

[0009] In addition, the present invention provides an all-solid-state battery including a positive electrode; a negative electrode; and an electrolyte for the all-solid-state battery.

[0010] The positive electrode for an all-solid-state battery according to the present invention and the all-solid-state battery including the same have the advantage of improving the performance of the battery by physically optimizing the properties of the positive electrode that directly affect the lifespan and capacity development of the battery.

[0011] Figure 1 is a stress-strain curve for confirming the tensile strength of the positive electrode manufactured in the examples and comparative examples of the present invention.

[0012] Figure 2 is a graph showing the life characteristics and capacity retention rate of a battery according to one embodiment and a comparative example of the present invention.

[0013] Hereinafter, the present invention will be described in detail.

[0014] The positive electrode for an all-solid-state battery according to the present invention comprises a positive electrode active material, a solid electrolyte, and a binder, and is characterized in that the content of the positive electrode active material exceeds 70 wt%.

[0015] All-solid-state batteries replace the liquid electrolyte used in lithium secondary batteries with a solid one. Because they do not use flammable solvents, there is no risk of fire or explosion due to electrolyte decomposition, which is common in conventional batteries. Furthermore, all-solid-state batteries can use lithium metal or lithium alloys as anode materials, which allows for a dramatic increase in energy density relative to the mass and volume of the battery. Sulfide-based solid electrolytes are currently the most developed solid electrolytes, and their ionic conductivity has reached levels approaching that of organic electrolytes. Furthermore, sulfide-based solid electrolytes are malleable, allowing for good contact with interfaces, which is beneficial for improving resistance.

[0016] In sulfide-based all-solid-state batteries containing these sulfide-based solid electrolytes, the characteristics of the cathode, in particular, directly impact the battery's lifespan and capacity development. Therefore, structural research is being conducted to reduce resistance within the cathode, and in particular, to improve the cathode's physical properties, such as ionic and electrical conductivity. However, these efforts have not yet reached a satisfactory level. Therefore, the present applicant has invented a method to improve battery performance by physically optimizing the properties of the cathode, which directly impact the battery's lifespan and capacity development.

[0017] Hereinafter, the present invention will be described in more detail.

[0018] First, the positive electrode active material included in the positive electrode for the all-solid-state battery may be a compound capable of reversibly absorbing and releasing lithium ions and 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); Lia MnG b O2(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.

[0019] 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.

[0020] 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 manganate, and lithium iron phosphate, and lithium sulfide. The positive electrode active material may include only one selected from these compounds, or may include two or more.

[0021] 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.

[0022] 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) (wherein 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1). The cathode active material may include a lithium salt of a ternary transition metal oxide having such a layered rock salt structure as a cathode active material, thereby improving the energy density and thermal stability of an all-solid-state battery.

[0023] In addition, the compound mentioned above can be used when it has a coating layer on the surface, 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 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 skilled in the art, a detailed description thereof will be omitted.

[0024] Examples of the shape of the positive electrode active material include spherical, elliptical, and other 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 typical all-solid-state lithium-ion secondary batteries. However, when the particle size (D50) of the positive electrode active material is 1 to 10 μm, preferably 3 to 8 μm, and more preferably 4 to 6 μm, the effects according to the present invention can be maximized.

[0025] The content of the positive electrode active material is one of the key features of the present invention, and is greater than 70 wt%, preferably greater than 70 wt% and less than or equal to 95 wt%, more preferably 73 to 89 wt%, and most preferably 78 to 88 wt%, based on the total weight of the positive electrode. If the content of the positive electrode active material is less than 70 wt%, there is a problem that the energy density of the cell itself, which is one of the important factors in evaluating the performance of the battery, is significantly reduced.

[0026] In particular, in the case of all-solid-state batteries, there is an advantage of high energy density compared to existing lithium-ion batteries, but this reduction in positive electrode active material lowers the energy density, which is a factor that significantly reduces the competitiveness of all-solid-state batteries against lithium-ion batteries. In addition, since the cost of the solid electrolyte is the highest among the materials in the positive electrode, in order to be competitive in terms of price compared to lithium-ion batteries, the content of the positive electrode active material must be increased as mentioned above in order to be competitive. In addition, since the optimal tensile strength of the electrode itself changes when the content of the positive electrode active material is reduced, even if the positive electrode is adjusted to the tensile strength according to the present invention under a composition in which the content of the positive electrode active material is 70 wt% or less, the performance results of the cell similar to the present invention cannot be achieved.

[0027] Next, the solid electrolyte included in the positive electrode for the all-solid-state battery of the present invention 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. In addition, the sulfide-based solid electrolyte is a liquid in which a solid sulfide-based electrolyte is dissolved, and is impregnated between particles such as positive electrode active material particles and positive electrode binder particles, and then cured through drying, thereby coating the surfaces of the particles and positioning between the particles. In other words, the solid electrolyte included in the positive electrode may include a solid electrolyte that is coated and positioned on the surfaces of the particles; and a solid electrolyte that is impregnated and positioned between the particles.

[0028] The above sulfide-based solid electrolyte may include a lithium salt, and the lithium salt is an ionizable lithium salt such as Li + X - It can be expressed as . The anion of this lithium salt is not particularly limited, but F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C -, (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - Examples include:

[0029] In addition, the sulfide-based solid electrolyte contains sulfur (S) and has the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and may include Li-PS-based glass or Li-PS-based glass ceramic. Non-limiting examples of such sulfide-based solid electrolytes include Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-LiCl-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, and Li2S-GeS2-ZnS, and the sulfide-based solid electrolyte may include any one or more thereof.

[0030] The content of the solid electrolyte included in the positive electrode is 0.1 to 29 wt%, preferably 5 to 19 wt%, and more preferably 7 to 20 wt%, based on the total weight of the positive electrode. If the content of the solid electrolyte included in the positive electrode is less than 0.1 wt%, lithium ion conduction within the positive electrode may not be smooth, which may cause problems in cell operation. In addition, if the content of the solid electrolyte included in the positive electrode exceeds 29 wt%, the loading amount of the positive electrode active material is relatively reduced, so the capacity of the cell decreases, which results in a decrease in the energy density, which is one of the important performances of the battery.

[0031] Continuing, the positive electrode binder included in the positive electrode for the all-solid-state battery of the present invention is mixed with the positive electrode active material and the solid electrolyte included in the positive electrode described above, and serves to bind each component, thereby assisting particle growth. In particular, since the sulfide-based solid electrolyte is sensitive to moisture, such as generating hydrogen sulfide (H2S) gas upon contact with moisture, it is desirable to exclude moisture as much as possible from the initial addition.

[0032] Such a positive electrode binder may be an organic binder, and the organic binder means a binder that is dissolved or dispersed in an organic solvent, particularly N-methylpyrrolidone (NMP), and is distinguished from an aqueous binder that uses water as a solvent or dispersion medium. For example, the binder may be selected from the group consisting of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyimide, polyamideimide, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butylene rubber, and fluororubber, but is not limited thereto.

[0033] The content of the positive electrode binder is 0.1 to 5 wt%, preferably 0.2 to 2 wt%, and more preferably 0.3 to 1 wt%, based on the total weight of the positive electrode. If the content of the positive electrode binder is less than 0.1 wt%, the binder may be insufficient to maintain the electrode structure, which may cause a problem in that it is difficult to manufacture the electrode itself. In addition, if the content of the positive electrode binder exceeds 5 wt%, the binder acts as a resistance component within the electrode, which may cause the cell resistance to increase, thereby reducing the output and life characteristics of the cell.

[0034] Meanwhile, the positive electrode for an all-solid-state battery according to the present invention may further include one or more additives such as a conductive agent, a filler, a dispersant, and an ion-conductive aid, as needed. Examples of the conductive agent include carbon nanotubes, graphite, carbon black, carbon fiber, and metal powder. Examples of the filler, dispersant, and ion-conductive aid include known materials typically used in electrodes of all-solid-state lithium-ion secondary batteries. In addition, the positive electrode active material may include the above positive electrode active material, a binder, and a conductive agent in a granular form.

[0035] Meanwhile, the conductive material may include at least one of linear particles and dot-shaped particles. In addition, when both linear and dot-shaped conductive materials are used together, only the advantages of applying the conductive material as a linear conductive material and the advantages of applying the dot-shaped conductive material can be expressed, thereby facilitating the manufacture of electrodes and batteries and improving the performance of the batteries. The linear conductive material may be a carbon nanofiber (CNF) composed of linear particles or a carbon nanotube (CNT) composed of linear particles. Among carbon nanotubes, a single-walled carbon nanotube (SWCNT) composed of linear particles may be more preferable. In these cases, there is an advantage of improved electrical conductivity and an improved migration phenomenon of the conductive material. As the dot-shaped conductive agent, carbon black (CB) can be exemplified, and in addition, any material having a shape and properties similar to or identical to those of carbon black particles can be used as the dot-shaped conductive agent. Using such a dot-shaped conductive agent enables the formation of a uniform surface, thereby improving the adhesion with the solid electrolyte in contact with the electrode. In other words, the dot-shaped conductive agent can be incorporated into the pores between linear conductive agents to flatten the surface of the anode. In addition, multi-walled carbon nanotubes (MWCNT), activated carbon, and mesoporous carbon can also be used as the dot-shaped conductive agent.

[0036] If the conductive material is included in the positive electrode of the present invention, the content of the conductive material is 0.001 to 5 wt%, preferably 0.05 to 2 wt%, and more preferably 0.1 to 1 wt%, based on the total weight of the positive electrode. If the content of the conductive material is less than 0.001 wt%, the benefits that can be obtained by using the conductive material may be minimal. In addition, if the content of the conductive material exceeds 5 wt%, side reactions with the electrolyte and the surface increase significantly, which may cause significant problems in the life performance of the cell.

[0037] As described above, the anode for an all-solid-state battery of the present invention is characterized by containing the constituent components within the anode in a predetermined ratio and possessing a specific range of tensile strength. Furthermore, through the combination of these components, the physical properties of the anode, which directly affect the battery's lifespan and capacity development, can be physically optimized, thereby improving battery performance (particularly ionic conductivity and electrical conductivity).

[0038] The tensile strength of the positive electrode for an all-solid-state battery according to the present invention is 0.01 to 1.0 MPa, preferably 0.03 to 0.7 MPa, and more preferably 0.1 to 0.5 MPa. If the tensile strength of the positive electrode is not within the above range, the synergistic effect with the advantages according to the composition and composition ratio of the components in the positive electrode does not occur. Conversely, even if the tensile strength of the positive electrode is within the above range, if the composition and composition ratio of the components in the positive electrode are not within the scope of the present invention, the synergistic effect similarly does not occur, making it difficult to improve the performance of the electrode and the battery.

[0039] More specifically, if the tensile strength of the positive electrode is less than 0.01 Mpa, the strength of the electrode is greatly reduced, which may cause problems during the electrode manufacturing and cell assembly processes. In addition, if the tensile strength of the positive electrode exceeds 1.0 Mpa, the resistance of the cell may greatly increase, which may cause problems with the lifespan and output characteristics of the cell. The tensile strength of the positive electrode of the present invention is lower than that of a typical positive electrode, and a high tensile strength means that the binder covers a relatively larger portion of the surface of the active material and solid electrolyte within the positive electrode. In other words, as the tensile strength increases, the resistance due to the binder increases, which inevitably leads to a deterioration in the performance of the battery.

[0040] Next, a method for manufacturing a positive electrode for an all-solid-state battery according to the present invention will be described. The method for manufacturing the positive electrode for an all-solid-state battery can be performed by manufacturing a positive electrode active material, a solid electrolyte, and a binder in the form of granules, etc., applying them onto a positive electrode metal current collector, and then rolling them to manufacture a positive electrode in the form of a sheet, etc. In this case, a conductive material may be further used in addition to the positive electrode active material, solid electrolyte, and binder. However, this is merely an example, and it should be noted that the positive electrode can be manufactured using various methods known in the art.

[0041] Next, an all-solid-state battery according to the present invention will be described. The all-solid-state battery includes the positive electrode, negative electrode, and electrolyte for the all-solid-state battery described above. The electrolyte is preferably a solid electrolyte, and the solid electrolyte is positioned as a layered membrane between the positive electrode and the negative electrode, and is physically separated from the solid electrolyte included in the positive electrode. The solid electrolyte positioned between the positive electrode and the negative electrode can simultaneously perform a role similar to a separator in a general lithium secondary battery (i.e., electrically insulating the negative electrode and the positive electrode while simultaneously allowing lithium ions to pass through). In addition, the solid electrolyte is preferably a sulfide-based solid electrolyte, and therefore, the all-solid-state battery is preferably a sulfide-based all-solid-state battery.

[0042] As for the sulfide-based solid electrolyte, it may be the same as the sulfide-based solid electrolyte exemplified in the positive electrode section above, but among the exemplified ones, the solid electrolyte included in the positive electrode and the solid electrolyte positioned between the positive electrode and the negative electrode may be different. Meanwhile, the above-mentioned all-solid-state battery may be utilized as a semi-solid battery by including a liquid electrolyte if necessary, in which case a separate polymer separator may be additionally required.

[0043] The above negative electrode may include a negative electrode active material usable in a lithium ion secondary battery. For example, the negative electrode active material may include carbon such as non-graphitizable carbon, graphite carbon, etc.; Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me' y O z(Me: Mn,Fe,Pb,Ge; Me': Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni계 재료; 티타늄 산화물; 리튬 티타늄 산화물; 등에서 선택된 어느 하나 이상을 포함한 것일 수 있는 등, 전고체 전지 분야에서 통용되는 다양한 음극이 적용될 수 있다.

[0044] Meanwhile, the negative electrode may not contain separate lithium metal except for lithium metal formed during charging (i.e., corresponding to a non-anode all-solid-state battery).

[0045] That is, lithium may not be included between the negative electrode current collector, the negative electrode active material layer, or the negative electrode active material layer and the solid electrolyte layer in the initial state or after complete discharge.

[0046] For example, when an all-solid-state battery including such a negative electrode is overcharged, the negative electrode active material included in the negative electrode active material layer and lithium ions that have moved from the positive electrode may form an alloy or compound, so that a metal layer with lithium as a main component may be formed (deposited) on the negative electrode. The metal layer may be formed by depositing between the negative electrode current collector and the negative electrode active material layer, inside the negative electrode active material layer, or both. When the metal layer is positioned between the negative electrode current collector and the negative electrode active material layer, the metal layer may be formed closer to the negative electrode current collector layer than to the negative electrode active material layer.

[0047] In an embodiment of the present invention, the negative electrode active material layer in the non-anode all-solid-state battery 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). 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 special limitation.

[0048] Therefore, the metal layer 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, 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.

[0049] In one embodiment of the present invention, the lithium-affinity material need not necessarily be uniformly present in the negative electrode active material layer, and may be distributed unevenly toward the negative electrode current collector side among the negative electrode active material layers. In this case, when lithium ions reach the vicinity of the negative electrode current collector and react with the lithium-affinity material distribution layer in the negative electrode active material layer, a Li (lithium-affinity material) alloy can be formed as a metal layer.

[0050] In addition, in the initial state before charge / discharge, the lithium-compatible material included in the negative electrode active material layer 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, but is not limited to, 20 nm to 1 μm.

[0051] Meanwhile, the negative electrode active material layer may also include a carbon material as a negative electrode active material in addition to the lithium-friendly material. Amorphous carbon may be preferably used as the carbon material included in the negative electrode active material layer. 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, by positioning a carbon material having a relatively small particle size on the interface side in contact with the solid electrolyte layer, the interface of the negative electrode active material layer in contact with the solid electrolyte layer can be made flatter. Based on 100 wt% of the total negative electrode active material included in the negative electrode active material layer, the combined amount of 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 the negative electrode active material other than the lithium-friendly material may be measured using the same method as the method for measuring the content of the lithium-friendly material.

[0052] Meanwhile, the negative electrode current collector may be positioned at the outermost side based on the stacking direction, facing the opposite side of the negative electrode active material layer that does not come into contact with the solid electrolyte layer. 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 based on the stacking direction.

[0053] The negative electrode current collector may be plate-shaped or foil-shaped. The negative electrode current collector may include a material that does not react with lithium, i.e., does not form any alloys or compounds with lithium. Examples of materials constituting the negative electrode current collector include copper, aluminum, stainless steel, titanium, iron, cobalt, and nickel. In addition, the negative electrode current collector may be composed of one type of these metals, or may be composed of an alloy of two or more types of metals or a clad material.

[0054] Meanwhile, in a non-anode all-solid-state battery according to one embodiment, the initial charge capacity of the positive electrode active material layer may be configured to be excessively large compared to the initial charge capacity of the negative electrode active material layer. The non-anode all-solid-state battery according to one embodiment can be used by charging (i.e., overcharging) exceeding the initial charge capacity of the negative electrode active material layer. In the initial stage of charging, lithium may be absorbed in the negative electrode active material layer. That is, the negative electrode active material may form an alloy or compound with lithium ions that have migrated from the positive electrode. When charging is performed exceeding the initial charge capacity of the negative electrode active material layer, lithium may be precipitated on the back of the negative electrode active material layer, that is, between the negative electrode current collector and the negative electrode active material layer, and a metal layer may be formed by the lithium. The metal layer 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 lithium-affinity material included in the negative electrode, for example, a material that forms an alloy or compound with lithium. During discharge, lithium in the negative electrode active material layer and the metal layer can be ionized and move to the positive electrode while leaving the lithium-affinity material it has incorporated in the solution. Therefore, lithium can be used as the negative electrode active material in an all-solid-state battery. In addition, since the lithium-affinity layer and the negative electrode active material layer simultaneously coat the metal layer, they function as a protective layer for the metal layer and can suppress the precipitation and growth of dendritic metallic lithium. This suppresses short-circuiting and capacity degradation of the all-solid-state battery, and further improves the characteristics of the all-solid-state battery. In addition, according to one embodiment, since the metal layer is not formed in advance, there is also an advantage of reducing the manufacturing cost of the all-solid-state battery.

[0055] The present invention as described above provides a battery module including the all-solid-state battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include, but are not limited to, a power tool that is powered by an electric motor; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc.; an electric two-wheeled vehicle including an electric bicycle (E-bike) and an electric scooter (E-scooter); an electric golf cart; and a power storage system.

[0056] 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.

[0057]

[0058] [Example 1] Manufacturing of a positive electrode for an all-solid-state battery

[0059] First, LiNi as the active material 0.8 Co 0.1 Mn 0.1O2 powder and lithium argyrodite-type solid electrolyte Li6PS5Cl were mixed in a mixer at room temperature, and the electrolyte was coated on the surface of the positive electrode active material. Thereafter, carbon nanofibers (CNF) and polytetrafluoroethylene (PTFE) were sequentially mixed and then vigorously mixed to prepare an electrode dough. Subsequently, the electrode dough was sheeted to make it thin, thereby preparing an all-solid-state battery positive electrode containing 85 wt% of the active material, 14 wt% of the solid electrolyte, 0.5 wt% of the binder, and 0.5 wt% of the conductive agent. At this time, the tensile strength of the manufactured positive electrode was adjusted to be approximately 0.25 MPa.

[0060] Meanwhile, the anode used in the tensile strength test was a rectangular specimen measuring 3 × 7 cm in length and width and 150 ㎛ in thickness, and the tensile speed was set to 5 mm / min for the test. Fig. 1 is a stress-strain curve for confirming the tensile strength of the anodes manufactured in the examples and comparative examples of the present invention, and shows the extent to which the tensile strength (or stress, Stress (Mpa)) of the anodes of Example 2 and Comparative Example 1, which will be described later, changes according to the strain (Strain, %), etc. in addition to the anode of Example 1.

[0061] [Example 2] Manufacturing of a positive electrode for an all-solid-state battery

[0062] A positive electrode for an all-solid-state battery was manufactured in the same manner as in Example 1, except that the tensile strength of the positive electrode was adjusted to approximately 1.0 MPa.

[0063] [Comparative Example 1] Manufacturing of a positive electrode for an all-solid-state battery

[0064] A positive electrode for an all-solid-state battery was manufactured in the same manner as in Example 1, except that the tensile strength of the positive electrode was adjusted to approximately 1.2 MPa.

[0065] [Experimental Example 1] Evaluation of the physical properties of the anode

[0066] The electrical conductivity and ionic conductivity of the positive electrodes manufactured in Examples 1 and 2 and Comparative Example 1 were measured, and the results are shown in Table 1 below.

[0067] Electrical Conductivity (S / cm) Ionic Conductivity (S / cm) Example 11.7.E-04 8.3.E-05 Example 22.5.E-04 9.5.E-05 Comparative Example 11.3.E-04 4.1.E-05

[0068] As a result of measuring the electrical conductivity and ionic conductivity of the positive electrodes manufactured in Examples 1, 2 and Comparative Example 1 as described above, both Examples 1 and 2, in which the tensile strength of the positive electrode was within the range of 0.01 to 1.0 Mpa, exhibited significantly higher ionic conductivity than Comparative Example 1, which was outside the above range, and in the case of Example 2, it was confirmed that the electrical conductivity was also significantly higher than that of Comparative Example 1.

[0069] [Examples 3, 4 and Comparative Example 2] Manufacture of all-solid-state batteries

[0070] First, 6 g of carbon black, 2 g of Ag, 9.33 g of PVdF binder, 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. Then, 5 g of NMP solution was additionally added and mixed 5 times for 3 minutes each at 2,000 rpm to prepare a slurry of negative active material, which was then applied to a SUS foil and dried to prepare a negative electrode.

[0071] Next, each of the positive electrodes manufactured in Examples 1 and 2 and Comparative Example 1 was positioned to face each of the negative electrodes manufactured above, and a sulfide-based solid electrolyte (Li2S-P2S5) was interposed therebetween to manufacture an all-solid-state battery. Thereafter, the manufactured cell was pressurized under conditions of 500 Mpa for 30 minutes using an isotropic pressurizing device (Warm Isostatic Pressure).

[0072] [Experimental Example 2] Performance Evaluation of All-Solid-State Battery

[0073] The solid-state batteries manufactured in Examples 3 and 4 and Comparative Example 2 were operated under the following charge and discharge conditions at an operating voltage range of 4.25 V to 3.0 V and an operating temperature of 60°C, and their performances were evaluated for 100 cycles, and the results are shown in Fig. 2.

[0074] - Charging conditions: 0.1C, 4.25V CC / CV, 0.05C cut-off

[0075] - Discharge conditions: 0.1C, 3.0V, CC

[0076] FIG. 2 is a graph showing the life characteristics and capacity retention rate of batteries according to an embodiment and a comparative example of the present invention, wherein FIG. 2 a corresponds to Example 3, FIG. 2 b corresponds to Example 4, and FIG. 2 c corresponds to Comparative Example 2. As a result of evaluating the performance of the all-solid-state batteries manufactured in Examples 3 and 4 and Comparative Example 2, it was confirmed that the batteries of Examples 3 and 4 maintained their capacities at levels close to the initial levels even after 100 charge and discharge cycles, whereas the battery of Comparative Example 2 showed a rapid decrease in capacity from the beginning of charge and discharge. Therefore, it can be seen that even if the composition of the positive electrode is the same, if the tensile strength of the positive electrode is outside the scope of the present invention, it is impossible to achieve the purpose.

Claims

1. A positive electrode for an all-solid-state battery comprising a positive electrode active material, a solid electrolyte and a binder, wherein the content of the positive electrode active material exceeds 70 wt%.

2. A positive electrode for an all-solid-state battery, characterized in that the tensile strength of the positive electrode is 0.01 to 1.0 Mpa in claim 1.

3. A positive electrode for an all-solid-state battery, characterized in that, in claim 1, the content of the solid electrolyte is 0.1 to 29 wt% and the content of the binder is 0.1 to 5 wt% with respect to the total weight of the positive electrode.

4. A positive electrode for an all-solid-state battery, characterized in that the positive electrode further comprises a conductive material according to claim 1.

5. A positive electrode for an all-solid-state battery, characterized in that the conductive material comprises at least one of linear particles and dot-shaped particles according to claim 4.

6. A positive electrode for an all-solid-state battery, characterized in that, in claim 5, the conductive material composed of linear particles is carbon nanofibers or single-walled carbon nanotubes, and the conductive material composed of dot-shaped particles is carbon black.

7. A positive electrode for an all-solid-state battery, characterized in that the content of the conductive material in claim 4 is 0.001 to 5 wt% based on the total weight of the positive electrode.

8. A positive electrode for an all-solid-state battery, characterized in that the content of the positive electrode active material in claim 1 is more than 80 wt% and less than or equal to 95 wt% based on the total weight of the positive electrode.

9. A positive electrode for an all-solid-state battery, characterized in that the solid electrolyte according to claim 1 is a sulfide-based solid electrolyte.

10. An all-solid-state battery comprising the positive electrode; negative electrode; and electrolyte of claim 1.

11. An all-solid-state battery according to claim 10, characterized in that the electrolyte is a solid electrolyte positioned as a layered film between the positive and negative electrodes.

12. An all-solid-state battery according to claim 10, characterized in that the all-solid-state battery is a semi-solid-state battery including a liquid electrolyte.

13. An all-solid-state battery according to claim 10, characterized in that the all-solid-state battery is a sulfide-based all-solid-state battery.

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