Electrode composite for all-solid-state battery and manufacturing method therefor

Abstract

The present invention relates to an electrode composite for an all-solid-state battery and a manufacturing method therefor. More specifically, disclosed is an electrode composite for an all-solid-state battery, having a core-shell structure comprising: active material particles; and a sulfide solid electrolyte layer coated on the surfaces of the active material particles by a mechanical coating process, wherein the solid electrolyte layer has a non-fully cover shell structure including a region partially uncoated with a solid electrolyte, and thus provides an ion transfer path formed by a coated region of the solid electrolyte layer and an electron transfer path formed by an uncoated region thereof, thereby improving electronic contact and ionic contact at the interface of the composite.

Description

Electrode composite for all-solid-state batteries and method for manufacturing the same

[0001] The present invention relates to a method for manufacturing an electrode composite for an all-solid-state battery, and more specifically, to a method for manufacturing an electrode composite for an all-solid-state battery in which the electron contact and ion contact at the interface of the composite are improved by partially coating a soft sulfide solid electrolyte on the surface of an active material using a dry mechanical coating process.

[0002] With the advent of the eco-friendly electric vehicle era aimed at resolving the global climate crisis, rechargeable batteries are garnering attention as a clean power source, leading to an expansion of the related market. To popularize electric vehicles and replace internal combustion engine vehicles, the energy density limitations and safety issues of current lithium-ion batteries (LIBs) must be addressed. While various next-generation batteries with high energy density, such as Li-metal, Li-S, and Li-O2, are being researched to overcome the limitations of existing LIBs, they fundamentally present safety concerns due to the use of flammable liquid electrolytes.

[0003] Accordingly, active development is underway for sulfide electrolyte-based all-solid-state batteries (ASSBs) that can guarantee both cell performance and safety by utilizing sulfide solid electrolytes (SEs) that are non-volatile, non-explosive, and possess high ionic conductivity similar to liquid electrolytes. However, conventional simple mixing processes make it difficult to secure an electrochemical reaction surface area through effective contact between the sulfide solid electrolyte and the active material, to secure lithium ion transport pathways through effective connections between solid electrolytes within the electrode, and to secure electron transport pathways between cathode active materials mediated by conductive materials. Furthermore, friction between active materials during electrode compression makes it difficult to improve electrode packing density, and consequently, it is difficult to eliminate pores that hinder the flow of electrons and ions. These issues lead to problems such as reduced energy density due to decreased active material utilization, limitations in high-rate performance due to increased electron and ion transport resistance, and long-term performance degradation caused by interfacial separation and the formation of additional pores resulting from volume changes of the active material during charging and discharging.

[0004] To improve interfacial contact between the active material and the solid electrolyte, some manufacturing technologies for core-shell structured electrode composites, in which the solid electrolyte surrounds the surface of the active material, are being studied. The core-shell structured powder of such electrode composites can be manufactured through a wet coating process in which the solid electrolyte is dissolved in a solution and then coated onto the surface, and a dry coating process in which a flexible solid electrolyte is mechanically coated onto the active material using devices such as a blade mill, twin screw, or ball mill.

[0005] In the case of conventional simple mixing processes, the solid electrolyte is unevenly distributed within the electrode, making it difficult to secure sufficient ion and electron conduction pathways. Furthermore, it is difficult to effectively remove pores during compression, which presents a problem in achieving expected battery characteristics such as energy density, rate capability, and lifespan. Although wet coating processes are being attempted to improve this, the solid electrolyte solution can be uniformly distributed on the surface of the active material or inside the electrode by coating particles with a solution containing dissolved solid electrolyte or filling the pores of the electrode with the solution. However, uneven distribution of the solid electrolyte may occur during the process of removing the solvent to precipitate the solid electrolyte. Additionally, the precipitated amorphous solid electrolyte has low ion conductivity and is ineffective for ion conduction. Moreover, the heat treatment process to restore the ion conductivity of this solid electrolyte is difficult to apply up to crystallization temperatures of 400 degrees or higher due to side reactions with the active material, making it unsuitable for sufficiently improving battery performance.

[0006] On the other hand, the dry coating process uses shear and compressive forces to directly coat a soft sulfide solid electrolyte onto the surface of the active material, thereby mitigating the degradation of the solid electrolyte caused by dissolution and drying that occurs in the wet process, and also allows for controlling the coating thickness and solid electrolyte content of the composite with a controlled amount of solid electrolyte, so unlike the simple mixing process or wet coating process, improved battery performance can be expected.

[0007] However, in this coating process, if a solid electrolyte is coated thickly and uniformly on the surface of the active material for the purpose of improving interfacial contact, the active material may become isolated, which can hinder the electron conduction pathway. Although the possibility of contact between active materials mediated by a conductive material can be expected along with an improvement in electrode packing density due to the flexible solid electrolyte coating layer during the compression process, electrode composites with such a uniform and thick coating layer have problems that impair battery performance, such as energy density and rate capability, due to reduced utilization rate caused by the isolation of the active material and low electron conductivity.

[0008] Accordingly, the inventors confirmed that by manufacturing an electrode composite with a controlled surface coating rate of a solid electrolyte, cell performance can be improved by simultaneously securing an ion transport pathway through the coated region and an electron transport pathway through the uncoated region, while also enhancing the packing density of the electrode, and thus completed the present invention.

[0009] Accordingly, the present invention provides a technical solution to the problem of providing an electrode composite for an all-solid-state battery in which a sulfide solid electrolyte coating layer including a partially uncoated region is formed on an active material particle, thereby simultaneously securing an ion transport pathway through the coated region and an electron transport pathway through the uncoated region.

[0010] In addition, another technical problem of the present invention is to provide a method for manufacturing an electrode composite for an all-solid-state battery, wherein a sulfide solid electrolyte coating layer including partially uncoated regions is formed on active material particles using a dry mechanical coating process, thereby simultaneously securing an ion transport pathway through the coated region and an electron transport pathway through the uncoated region.

[0011] In addition, the present invention has as another technical problem to solve the provision of an electrode for an all-solid-state battery comprising the aforementioned electrode composite and an all-solid-state battery comprising the same.

[0012] In order to solve the above technical problem, the present invention,

[0013] Active material particles;

[0014] The electrode composite having a core-shell structure comprising a sulfide solid electrolyte layer coated on the surface of the active material particles by a mechanical coating process, and

[0015] The above solid electrolyte layer has a non-fully cover shell structure including a region where the solid electrolyte is partially uncoated,

[0016] The present invention provides an electrode composite for an all-solid-state battery characterized by providing an ion transfer pathway through a coated region of the solid electrolyte layer and an electron transfer pathway through an uncoated region, thereby improving electron contact and ion contact at the interface of the composite.

[0017] In the present invention, the coating area is characterized by exceeding 50% of the surface area of ​​the active material particle.

[0018] In addition, in the present invention, the sulfide solid electrolyte is characterized by being one or more selected from the group consisting of LGPS-based solid electrolytes, LPSX(X=Cl, Br, I)-based solid electrolytes, and thio-LISICON-based solid electrolytes.

[0019] In addition, the active material in the present invention is characterized as being a positive electrode active material which is a lithium metal oxide, or one or more negative electrode active materials selected from silicon-based, tin-based, or carbon-based active materials.

[0020] In addition, the present invention is characterized in that the active material particles have a buffer layer coated with a lithium ion conductive oxide formed on the surface of the positive active material particles.

[0021] In order to solve the aforementioned other technical problems, the present invention,

[0022] Step of preparing active material powder; and

[0023] A core-shell structured electrode composite is manufactured by including the step of mixing sulfide solid electrolyte powder with the above active material powder, and then forming a sulfide solid electrolyte layer coated by a mechanical coating process.

[0024] The above solid electrolyte layer has a non-fully cover shell structure including a region where the solid electrolyte is partially uncoated,

[0025] The present invention provides a method for manufacturing an electrode composite for an all-solid-state battery, characterized by providing an ion transfer pathway through a coated region of the solid electrolyte layer and an electron transfer pathway through an uncoated region to improve electron contact and ion contact at the interface of the composite. The composite manufactured by the above method is characterized as being the electrode composite described above.

[0026] In the present invention, the thickness of the coating region of the solid electrolyte layer is characterized as being 200 to 800 nm.

[0027] In addition, the present invention is characterized in that, when forming the sulfide solid electrolyte layer, the sulfide solid electrolyte is mixed such that the weight ratio of the active material to the sulfide solid electrolyte is 80:20 to 95:5.

[0028] In addition, to solve the aforementioned other technical problem, the present invention provides an electrode for an all-solid-state battery characterized by having an improved filling density by including an electrode composite.

[0029] In addition, to solve the above-mentioned other technical problem, the present invention provides an all-solid-state battery characterized by including the electrode.

[0030] The electrode composite for an all-solid-state battery according to the present invention is partially coated with a sulfide solid electrolyte on the surface of an active material, thereby securing a sufficient lithium ion pathway at the interface between the active material and the solid electrolyte layer, while simultaneously securing electron conduction pathways between the active materials within the electrode and ion conduction pathways between the solid electrolyte. Furthermore, the electrode comprising the composite of the present invention has an improved packing density and can enhance cell performance by minimizing voids within the electrode due to the flexibility of the partially coated solid electrolyte. Since this electrode composite of the present invention is manufactured using a dry process, it offers the benefits of process simplification and cost reduction.

[0031] Figure 1 shows the manufacturing process of an electrode composite for an all-solid-state battery according to the present invention and the simulation results of the electrode composite according to the thickness of the solid electrolyte layer coating.

[0032] FIG. 2(a) shows the electron and ion transport pathways of an electrode composite according to one embodiment of the present invention, and FIG. 2(b) and (c) show SEM and EDS mapping images confirming the surface coating of the electrode composite according to the example and comparative example.

[0033] FIG. 3 shows (a) the amount of solid electrolyte coating and the surface coverage rate (%) of an electrode composite according to one embodiment of the present invention, and (b) a blade mill photograph after the MM process.

[0034] Figure 4 shows SEM and EDS mapping images of (a) pristine NCM811 positive electrode active material particles, (b) LNO-coated NCM811 positive electrode active material particles, (c) HM NCM@10SE electrode composite coated with 10 wt% SE via the HM process, (d) MM NCM@10SE electrode composite coated with 10 wt% SE via the MM process, and (e) MM NCM@23SE electrode composite coated with 23 wt% SE via the MM process.

[0035] Figure 5 shows (a) XRD and (b) XPS spectra of LPSCl, NCM, NCM@10SE(MM), and NCM@23SE(MM) samples, (c) cross-sectional SEM images of NCM, NCM@10SE(MM), and NCM@23SE(MM) samples, and (d) PSA results of bare NCM, HM, and MM samples with different SE contents (the numbers in parentheses in the legend indicate the average particle diameter of the sample based on the large peak, and the small peaks indicate residual SE).

[0036] Figure 6 shows (a) SEM and EDS images of the HM23, MM10, and MM23 electrode composites, (b) low-magnification and high-magnification CP-SEM images of the cross-section, (c) ionic conductivity measurement results by EIS spectrum measurement, (d) electronic conductivity measurement results by DC polarization, (e) 3D electrode structures with different coating weight ratios of SE and NCM, and (f) contact area ratios for NCM, VGCF, and SE, respectively.

[0037] Figure 7 shows the cycling performance and voltage profiles of HM23, MM10, and MM23 cells.

[0038] The present invention will be described in detail below.

[0039] Furthermore, throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0040] The present invention relates to a method for manufacturing an electrode composite for an all-solid-state battery through a dry coating process capable of mass production and commercialization, particularly a mechanical coating process. In this regard, FIG. 1 shows the manufacturing process of an electrode composite for an all-solid-state battery according to the present invention and simulation results of the electrode composite according to the coating thickness of the solid electrolyte layer. As shown in FIG. 1, the electrode composite of the present invention is composed of a solid electrolyte layer that includes an uncoated region that is partially uncoated, while the solid electrolyte is coated on the surface of the active material particles forming the core.

[0041] In one embodiment, the present invention relates to an electrode composite having a core-shell structure comprising: active material particles; and a sulfide solid electrolyte layer coated on the surface of the active material particles by a mechanical coating process; wherein the solid electrolyte layer has a non-fully cover shell structure including a region where the solid electrolyte is partially uncoated, thereby providing an ion transport pathway through the coated region of the solid electrolyte layer and an electron transport pathway through the uncoated region, thereby improving electron contact and ion contact at the interface of the composite.

[0042] The electrode composite of the present invention is formed by coating soft sulfide solid electrolyte particles onto the surface of active material particles using shear and compressive forces via a mechanical coating process utilizing a blade mill or mechanofusion method. However, if the composite is formed by coating uniformly in a core-shell structure to completely cover the surface, the insulating properties of the sulfide solid electrolyte particles forming the coating layer may hinder electron transfer, thereby impairing cell performance. Accordingly, the present invention is characterized in that the sulfide solid electrolyte layer on the surface of the active material particles in the core-shell structured electrode composite has a non-fully cover shell structure that includes a region where the solid electrolyte is partially uncoated, so that electron transfer can occur while sufficiently securing an ion transfer pathway through the solid electrolyte coating. As a result, by providing an ion transfer pathway through the coated region of the solid electrolyte layer and an electron transfer pathway through the uncoated region, it is possible to improve electron contact and ion contact at the interface of the electrode composite.

[0043] Figure 2(a) shows the ion transfer and electron transfer characteristics of the electrode composite of the present invention compared with those of an electrode composite manufactured by a simple mixing process. In the electrode composite of the present invention, which is manufactured by a mechanical coating process to form a non-complete cover shell, electron transfer (indicated in red) can occur in the uncoated region. However, in the electrode composite manufactured by a simple mixing process, the solid electrolyte is aggregated on the surface of the active material particles, making it difficult to secure an electron transfer path and causing voids between particles to form, making interfacial contact difficult.

[0044] In this regard, FIG. 2(b) shows SEM and EDS mapping images of a composite formed by a mechanical coating process in one embodiment of the present invention, and FIG. 2(c) shows a composite formed by a simple mixing process. Referring to these images, the composite of the present invention has a solid electrolyte uniformly coated on NCM particles (Fig. 2b), whereas the composite formed by the simple mixing process as shown in FIG. 2(a) is found to have uneven aggregation on the surface, which can be confirmed to result in poor formation of ion transport pathways as well as electron transport.

[0045] As such, the electrode composite of the present invention is formed by a sulfide solid electrolyte layer having a non-complete cover shell structure on the surface of active material particles through a mechanical coating process, and it is preferable that the coating area exceeds 50% of the surface area of ​​the active material particles. This is because if the solid electrolyte coating area is less than the above range, the effect of forming an ion transfer pathway by the solid electrolyte is reduced, and ion contact and electron contact at the particle interface cannot be improved due to the non-uniform coating layer.

[0046] In addition, in the present invention, the sulfide solid electrolyte forming the solid electrolyte layer may be one or more selected from the group consisting of LGPS-based solid electrolyte, LPSX(X=Cl, Br, I)-based solid electrolyte, LPS-based solid electrolyte, and thio-LISICON-based solid electrolyte.

[0047] In addition, the above active material may be a positive electrode active material that is a lithium metal oxide. Examples of lithium metal oxides include lithium nickel cobalt manganese (NCM) based, lithium cobalt oxide (LCO) based, lithium nickel cobalt aluminum (NCA), lithium nickel cobalt manganese aluminum (NCMA) based, lithium iron phosphate (LFP) based, and lithium manganese (LMO) based active materials. In a preferred embodiment of the present invention, a lithium nickel cobalt manganese (NCM) based positive electrode active material was used.

[0048] More preferably, the cathode active material may have a buffer layer formed by coating a lithium ion-conducting oxide on the surface of lithium metal oxide particles. When the buffer layer is formed on the surface of the cathode active material particles, side reactions between the cathode active material and the solid electrolyte are suppressed, and low interfacial resistance is achieved, thereby improving cell capacity, rate capability, and cycle stability. Preferably, the lithium ion-conducting oxide forming the buffer layer is, for example, LiNbO3, Li2SiO3, or Li4Ti5O. 12 , Li 3x La 2 / 3-x It may be at least one from the group consisting of TiO3, Li2ZrO3, LiAlO2, Li3BO3, Li3PO4, LiNbO3, and LiTaO3.

[0049] In addition, the above active material may be one or more negative active materials selected from silicon-based, tin-based, or carbon-based active materials. Examples of silicon-based negative active materials include Si, SiOx, Si / C, Si / Metal, etc. Examples of tin-based negative active materials include Sn, SnOx, Sn / C, Sn / Metal, etc. Examples of carbon-based negative active materials include C, C / Si, C / Metal, etc.

[0050] As such, the electrode composite for an all-solid-state battery according to the present invention is manufactured by controlling the core-shell structure to form a non-complete cover shell with a surface coverage rate of less than 100% while forming a solid electrolyte layer on the surface of the active material particles, thereby maintaining contact between the active material and a conductive material or other active material, thereby simultaneously securing electron and ion transfer pathways.

[0051] Accordingly, in another aspect, the present invention relates to a method for manufacturing an electrode composite for an all-solid-state battery, comprising the steps of: preparing an active material powder; and mixing a sulfide solid electrolyte powder with the active material powder, and then forming a coated sulfide solid electrolyte layer by a mechanical coating process; wherein the solid electrolyte layer has a non-fully cover shell structure including a region where the solid electrolyte is partially uncoated, thereby providing an ion transport pathway through the coated region of the solid electrolyte layer and an electron transport pathway through the uncoated region, thereby improving the electron contact and ion contact at the interface of the composite. Preferably, the electrode composite for an all-solid-state battery described above can be manufactured.

[0052] According to the method of the present invention, a sulfide solid electrolyte layer is formed on the surface of active material particles, particularly through a mechanical coating process, and is formed as a non-completely covered shell structure that includes an uncoated region where the solid electrolyte is not coated. That is, it is important to control the mechanical coating process so that the surface coverage rate does not become 100%.

[0053] Preferably, the coating process is carried out by adding and mixing a sulfide solid electrolyte to the prepared active material powder, and then performing a mechanical mixing process. Preferably, a blade mill or mechanofusion method may be used for the mechanical mixing process. For example, the positive electrode active material and the sulfide solid electrolyte may be mixed for 10 minutes using a mixing mixer, and then a solid electrolyte layer may be formed through dry mechanical coating using a blade mill. At this time, the inner rotor of the blade mill rotates at a speed of 1,000 to 10,000 rpm, and the positive electrode active material and the sulfide solid electrolyte are in close contact with the narrow gap between the inner rotor of the blade mill and the inner wall of the chamber, subjected to shear stress and compressive stress, thereby manufacturing a positive electrode composite (see Fig. 1). In a preferred embodiment of the present invention, the positive electrode composite was manufactured by repeating a cycle consisting of 60 seconds of operation and 90 seconds of rest 15 times while controlling the equipment temperature to 15°C to prevent overheating of all particles.

[0054] In addition, in the present invention, the coating region of the solid electrolyte layer may be formed with a thickness of 200 to 800 nm. If the thickness is less than 200 nm, it may be somewhat insufficient to form an ion transport path, and if it exceeds 800 nm, the solid electrolyte having insulating properties is formed too thickly on the surface of the active material, isolating the active material and limiting the formation of an electron transport path.

[0055] At this time, the thickness of the coating area is determined according to the amount of solid electrolyte coating, and accordingly, the surface coverage rate (%) is determined as shown in FIG. 3(a). In order to form a non-completely covered coating layer with a surface coverage rate of less than 100% by controlling process variables in the mechanical coating process of the present invention, it is important to perform the mechanical coating process by mixing the sulfide solid electrolyte such that the ratio of the active material to the sulfide solid electrolyte is 80:20 to 95:5 during the solid electrolyte layer formation step. This is because, as shown in FIG. 3(b), some of the solid electrolyte remains after the mechanical coating process due to process control. If the range is exceeded, the surface coverage rate becomes 50% or less, or becomes 100% due to complete coverage, making it difficult to form an ion transfer pathway or an electron transfer pathway.

[0056] In addition, when manufacturing electrodes, an active material is mixed with a binder or conductive material in a wet or dry manner to form a composite, which is then coated or bonded onto a current collector in the form of a thin film, and subsequently pressure is applied to manufacture the electrode. In the case of all-solid-state batteries, if the charging is not done properly, pores are formed within the electrode, which prevents proper electron and ion contact at the particle interface, thereby causing a problem of performance degradation. Accordingly, the present invention is characterized by manufacturing a shell-structured composite that is not completely covered with a solid electrolyte on the surface of active material particles through a mechanical coating process as described above, thereby forming an ion transport pathway through the coated region and an electron transport pathway through the uncoated region. The electrode utilizing the electrode composite of the present invention improves electron and ion contact at the composite interface, thereby improving the charging density.

[0057] Accordingly, in another aspect, the present invention relates to an electrode for an all-solid-state battery comprising the electrode composite and an all-solid-state battery manufactured including the same.

[0058] According to the present invention, a composite is formed in which a solid electrolyte is coated on the surface of a positive electrode active material without the occurrence of solid electrolyte aggregation, and thus, an increased packing density can be achieved due to the effect of reducing frictional force between active materials by the flexible solid electrolyte surface. In addition, by controlling the content of the solid electrolyte and the coating process of the solid electrolyte layer, a composite with a shell structure that is not completely covered by the solid electrolyte on the surface of active material particles is manufactured, thereby simultaneously securing ion transport pathways through the coated area and electron transport pathways through the uncoated area, and the packing density of the electrode applied thereto can be improved, thereby solving the problems of energy density, rate capability, and long-term durability required in all-solid-state batteries.

[0059] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

[0060] Ingredients

[0061] * Li metal foil (thickness: 20μm): Honjo (Japan)

[0062] * Stainless Steel Foil (SS Foil, Thickness: 10 μm) : MTI Korea

[0063] * Li2S(99.98%), P2S5(99%), LiCl(99%) : Sigma-Aldrich (USA)

[0064] * LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM, Diameter: 13.5 μm) : EcoPro BM (Korea)

[0065] * LiNbO3 Coated NCM (LNO-NCM): Wonik P&E (Korea)

[0066] * Argyrodite solid electrolyte Li6PS5Cl (LPSCl) with average particle size of 1μm: POSCO-JK Solid Solution (Korea)

[0067] * Vapor-Growthed Carbon Fiber (VGCF): Resonac Packaging Corporation (Japan)

[0068] <Example 1> Preparation of Anode Composite (MM10)

[0069] First, LNO-NCM and 1 μm LPSCl particles were mixed for 10 minutes using an acoustic mixer (PharmaRAM1, Resodyn, USA). Then, using a blade mill system (KBM-L, KM Tech, Korea), a total weight of 40 g (volume of approximately 50 mL) was loaded into a chamber with a weight ratio of 90:10 between the host powder and the guest powder, using rigid, large-particle NCM and relatively flexible, small-particle LPSCl as the host and guest materials, respectively. Next, the chamber was sealed in a glove box filled with argon, and a dry mechanical mixing (MM) process was performed to coat the LPSCl particles and prepare an anode composite.

[0070] During the MM process, all particles were propelled in close contact with the inner wall of the chamber while the equipment temperature was controlled to 15°C to prevent overheating. Due to the centrifugal force generated by a chopper rotating at 4000 rpm, the particles received significant mechanical energy from shear and compressive forces as they passed through the narrow space between the press head and the inner wall of the chamber. This process was repeated 15 times, with each cycle consisting of 60 seconds of operation and 90 seconds of rest.

[0071] <Comparative Examples 1 to 3> Preparation of Anode Composite (MM23 / HM10 / HM23)

[0072] Comparative Example 1 prepared an anode composite (MM23) in the same manner as Example 1, except that the host powder and guest powder were mixed in a weight ratio of 77:23 instead of 90:10.

[0073] Comparative Examples 2 and 3 prepared an anode composite (HM10 / HM23) in the same manner as Example 1, except that instead of a blade mill device, a simple mixing process was used to hand-mix LNO-NCM and LPSCl in weight ratios of 90:10 and 77:23 in a glove box filled with Ar for 40 minutes.

[0074] <Test Example 1> Evaluation of Anode Composite Characteristics

[0075] Morphological analysis of the anode complex was performed using field emission SEM (FE-SEM, S-4800, Hitachi, Japan) and energy dispersive X-ray spectroscopy (EDS, Sirion, FEI, USA).

[0076] The X-ray diffraction (XRD) pattern of the anode complex was obtained using an X-ray diffraction analyzer (X'pert Pro, PANalytical, Netherlands) using Cu-Kα radiation (λ = 0.15406 nm). In particular, a gas-state XRD holder (Netherlands, PANalytical) was used to prevent the reactive sample from being exposed to air.

[0077] The chemical composition and bonding characteristics of the anode composite were analyzed using a glove-box connected X-ray photoelectron spectrometer (XPS, Ax-Supra, Kratos, Japan) using monochromatic Al-Kα as an X-ray light source.

[0078] For the analysis of the cross-sectional morphology of the anode composite, cross-sectional samples were prepared using a cross-section grinder (CP, Model 1061 SEM Mill, Picione Instruments, USA) and characterized using SEM-EDS (Gemini 500 SEM, Ultim Extreme detector, Zeiss, Germany).

[0079] The actual amount of solid electrolyte coated on the surface of the cathode active material was calculated through the mass loss of the complex before and after washing in a polar ethanol solvent.

[0080] <Test Example 2> Anode Manufacturing and Performance Evaluation

[0081] Anode manufacturing

[0082] A positive electrode was prepared by adding 2 wt% of vapor-grown carbon fiber (VGCF) as a conductive material to the positive electrode composite of Example 1 and Comparative Examples 1 to 3 to form an electron transmission path, and by adding 3 μm of sulfide solid electrolyte to control the total sulfide solid electrolyte content in the electrode to 23%.

[0083] Performance evaluation

[0084] Morphological analysis of the anode electrode was performed using a field emission SEM (FE-SEM, S-4800, Hitachi, Japan) and an energy dispersive X-ray spectrometer (EDS, Sirion, FEI, USA).

[0085] The ionic conductivity of the positive electrode was measured by preparing an electron blocking cell and then performing electrochemical impedance spectroscopy (EIS) analysis. The electrochemical impedance spectroscopy (EIS) analysis was performed using a VSP tester (Biologic, France) at 25°C in a frequency range of 10 MHz to 7 MHz.

[0086] The electronic conductivity of the positive electrode was obtained by preparing an ion-blocking cell and then using a direct current (DC) polarization technique.

[0087] <Test Example 3> Manufacturing of All-Solid State Battery and Cell Performance Evaluation

[0088] Solid-state battery manufacturing

[0089] A test cell was fabricated using the anode electrode prepared above, pelletized LPSCl as the solid electrolyte layer, and a dendrite-free In-Li alloy with interfacial stability as the reference / counter electrode. The final weight ratio of NCM, LPSCl, and VGCF in the anode composite was controlled to 75:23:2.

[0090] Cell performance evaluation

[0091] Cell tests were performed at 55°C using a battery cycler (WBCS3000L, Wonatech, Korea). For cycling performance tests, the In-Li anode cells used galvanostatic charge / discharge modes and Li / Li+ at current densities of 0.1 and 0.3C in a voltage range of 2.38–3.68 V. For graphite-protected lithium and sandwich SE layer cells, the voltage range was controlled at 1°C to 3.0–4.3 V versus Li / Li+, and the cells were precycled for one cycle at 0.1°C prior to the cell test to create a stable interface.

[0092] For speed performance testing, the unit cell was set to 0.1 ~ 4C (1C = 200mAg -1 Charged and discharged at the C-rate of ).

[0093] The test results according to the above examples and comparative examples are shown in FIGS. 2 to 8.

[0094] Figure 2(a) shows the electron and ion transport pathways of electrode composites prepared according to the MM and HM processes, and Figures 2(b) and (c) show SEM and EDS mapping images confirming the surface coating of electrode composites according to Example 1 (MM-NCM@10SE, MM10) and Comparative Example 2 (HM-NCM@10SE, HM10). Referring to this, in the MM10 composite, after the mechanical mixing process, the pores between NCM particles disappeared and the surface of the NCM became smooth, and S elements originating from the solid electrolyte coating layer were detected throughout the particles. However, in the HM10 composite formed by the simple mixing process, S elements were detected unevenly despite having the same solid electrolyte content as in Example 1. This indicates that the elements are unevenly aggregated on the surface, implying that when prepared by simple mixing, the formation of ion transport pathways as well as electron transport may be poor. Therefore, it can be confirmed that by manufacturing through a mechanical mixing process, a uniform coating is possible in which the solid electrolyte is uniformly distributed on the surface of LNO-NCM particles compared to simple hand mixing.

[0095] Figure 3 shows (a) the amount of solid electrolyte coating and the surface coverage rate (%) of the electrode composite, and (b) a blade mill photograph after the MM process. By controlling the MM process so that the surface is not completely covered by the solid electrolyte, the solid electrolyte remaining in the blade mill can be observed. In fact, when examining the weight change before and after the ethanol washing process of Example 1, it was confirmed that although Example 1 was prepared by adding 10 wt% sulfide solid electrolyte, 8.56 wt% of the solid electrolyte was coated through the mass loss change due to ethanol washing. Additionally, by referring to the high-magnification SEM and EDS images of Example 1 (Figure 4d), it can be confirmed that the sulfide solid electrolyte does not completely cover the entire surface of the cathode active material. This indicates that, as shown in Figure 3(b), a 100% completely covered coating layer was not formed because the sulfide solid electrolyte adhered to the inner wall of the chamber during the mechanical mixing process, resulting in some loss.

[0096] Figure 4 shows SEM and EDS mapping images of (a) pristine NCM811 cathode active material particles, (b) LNO-coated NCM811 cathode active material particles, (c) an electrode composite coated with 10 wt% SE via the HM process (HM NCM@10SE), (d) an electrode composite coated with 10 wt% SE via the MM process (MM NCM@10SE), and (e) an electrode composite coated with 23 wt% SE via the MM process (MM NCM@23SE). Comparing Figure 4(a) and (b), it was confirmed that Nb, Ni, and Co were more present on the surface of the cathode active material particles due to the LNO coating, and the surface of the particles was also found to be smoother. Comparing Figures 4(c) and (d), it can be seen that when the coating layer is formed by the HM process, uncoated solid electrolyte remains, and the solid electrolyte is coated in an aggregated form on the surface of the active material particles, showing an uneven distribution. In contrast, when the coating layer is formed by the MM process, the solid electrolyte is coated evenly on the surface of the active material particles without aggregation, and uncoated areas where NCM is exposed on the surface are formed. Additionally, comparing Figures 4(d) and (e), when the amount of solid electrolyte coating is increased to 23%, a relatively large amount of residual solid electrolyte that is not formed as a coating layer is observed between the NCM particles; it is determined that this occurs when the amount of solid electrolyte exceeds a certain ratio and aggregates.

[0097] Figure 5 shows (a) XRD and (b) XPS spectra of samples LPSCl, NCM, NCM@10SE (Example 1), and NCM@23SE (Comparative Example 1); (c) cross-sectional SEM images of samples NCM, NCM@10SE (Example 1), and NCM@23SE (Comparative Example 1); and (d) PSA results of bare NCM, HM, and MM samples with different SE contents (the numbers in parentheses in the legend indicate the average particle diameter of the sample based on the large peak, and the small peak indicates residual SE).

[0098] Referring to Fig. 5(a), as the solid electrolyte content increases, the peak associated with NCM decreases and the peak assigned to LPSCl relatively increases, confirming that the solid electrolyte is coated on the NCM without structural degradation. Furthermore, no peak associated with side reactions with increasing solid electrolyte content was detected in Fig. 5(a), and no noticeable peak change was observed in the XPS spectrum after the mechanical mixing process in Fig. 5(b). Thus, it can be confirmed that the anode composite of Example 1 has interface stability between the solid electrolyte and the anode active material, and can form a solid electrolyte coating layer without interface or structural damage in a dry mechanical mixing process environment. FIG. 5(c) shows the cross-sectional SEM analysis results of the cathode active material (LNO-NCM), Example 1, and Comparative Example 1, which were side-cut using a cross-sectional polisher (CP). It was found that Example 1 had a solid electrolyte coating layer of 300 to 400 nm, whereas Comparative Example 1 had a thick and non-uniform coating thickness of 400 to 1200 nm. The thickness of Comparative Example 1 corresponds to a thickness that makes it difficult to form an electron conduction path, as the NCM particles are completely covered by a thick insulating solid electrolyte layer and separated from each other.

[0099] Figure 5(d) shows the change in solid electrolyte coating thickness according to the amount of solid electrolyte used in the MM process as a result of particle size analysis (PSA). The large peak is related to the main particle size, and the small peak represents the uncoated residual solid electrolyte. Although the solid electrolyte particle size increased when using the MM process compared to the HM process, a distribution was observed where the residual solid electrolyte was more abundant when using the HM process at approximately 1 μm. In other words, since larger particle sizes and less residual solid electrolyte were observed when using the MM process, it implies that the NCM surface can form a solid electrolyte coating layer with relatively less residue through the MM process. Accordingly, a larger amount of solid electrolyte can be directly coated onto active material particles by a mechanical coating process. This allows a dry mechanical coating method based on shear and compressive force in an Ar atmosphere to minimize interfacial side reactions that commonly occur in wet-based processes, reduce the amount of residual solid electrolyte, and produce active material particles with a more uniformly coated solid electrolyte compared to the existing simple mixing process.

[0100] FIG. 6 shows (a) SEM and EDS images of the HM23 (Comparative Example 3), MM10 (Example 1), and MM23 (Comparative Example 1) electrodes, (b) low-magnification and high-magnification CP-SEM images of the cross-section, (c) ionic conductivity measurement results by EIS spectrum measurement, (d) electron conductivity measurement results by DC polarization, (e) 3D electrode structures with different coating weight ratios of SE and NCM, and (f) contact area ratios for NCM, VGCF, and SE, respectively. As shown in FIGS. 6(a) and 6(b), in Comparative Example 3, HM23, the NCM particles were not sufficiently covered with solid electrolyte, and many voids were observed between the particles; in Example 1, MM10, the NCM particles were uniformly coated with solid electrolyte, and additional solid electrolyte filled the empty spaces, reducing the voids; and in Comparative Example 1, MM23, isolated NCM particles could be observed even after uniaxial pressing due to the thick solid electrolyte layer on the NCM surface. That is, as the distribution of electrode composite particles changed due to this solid electrolyte coating, in MM10, electron and ion transfer occurred sufficiently with a high packing density, resulting in high values ​​(4.13 mS / cm) for both ionic and electronic conductivity, whereas in MM23, the packing density was lowered due to the thick solid electrolyte insulating layer, resulting in the lowest values ​​(3.34 mS / cm) for both ionic and electronic conductivity. In HM23 containing the same solid electrolyte, the ionic conductivity is higher than that of MM23 due to the low-density composite structure with many voids, and the electrical conductivity is the highest (6.2 mS / cm) due to the additional solid electrolyte present in the voids.

[0101] In this regard, Figure 6(e) visualizes a 3D electrode structure, where VGCF, a conductive material, creates an electron conduction path throughout the electrode. During the compression process in electrode manufacturing, the particles intersect to form a contact interface between the active NCM and inactive composites such as VGCF and SE. At this time, the contact area is calculated using the spherical cap surface area equation and represented as the NCM surface area as shown in Figure 6(f). That is, the electron conductivity of the electrode can vary depending on the contact conditions between the conductive agent, the active material, and the current collector. As the contact area between NCM and VGCF increases, electron transport within the composite becomes more efficient, and as the contact area between SE and NCM increases, more active sites are provided for lithium ion transport, thereby reducing the ionic resistance of the composite and increasing ionic conductivity. Accordingly, as shown in Figures 6(e) and 6(f), HM23 formed a low-density composite structure and exhibited a high contact area ratio, while MM23 exhibited a higher charge transfer resistance than HM23 because the thick SE layer completely covering the NCM particles acted as an electronic insulating layer that hindered charge transfer, resulting in a much higher charge transfer resistance. Furthermore, MM10 directly coated SE onto the NCM particles, and it can be confirmed that the contact area with VGCF and SE was increased by including uncoated regions. This indicates that when a non-complete cover shell is formed with surface coverage of less than 100%, a portion of the NCM surface is exposed and can come into contact with a conductive material, thereby facilitating electron transfer. Therefore, to improve electrode performance, it is important to optimize the SE coating weight ratio and thickness according to the NCM surface coverage.

[0102] Figure 7 shows the cycling performance and voltage profiles of the HM23 (Comparative Example 3), MM10 (Example 1), and MM23 (Comparative Example 1) cells. Referring to Figure 7(a), 0.3 C and 10 mg cm⁻¹ -2 Under the test conditions, MM23 and HM23 were 108 and 173 mAh g, respectively. -1 It exhibited an initial discharge capacity of and showed capacity retention rates of 30.6% and 26.8%, respectively, over 400 cycles. The reason for the low capacity of MM23 is that it exhibited low ionic and electronic conductivity due to poor contact between cathode active material particles caused by the thickly coated solid electrolyte layer. On the other hand, MM10 had an initial capacity of 188 mAhg -1 It showed excellent capacity retention rates of 86.3% and 53.2% during 400 and 1000 cycles, respectively.

[0103] Also, referring to Fig. 7(b), the smallest charge and discharge overpotentials were observed in MM23, which is because the resistance increases to a minimum during cycling.

[0104] Also, referring to Fig. 7(c), as the C-rate increases, the HM23 and MM23 cells each have 17 mAh g -1 and showed a capacity close to zero, and the MM10 cell maintained 35mAh g, corresponding to 20% capacity compared to 0.1 C, even when the current density increased 40-fold. -1 It exhibited the lowest charge / discharge overpotential by displaying a capacity. In particular, the MM23 cell showed 0 mAh g only at 2 C due to relatively low ionic and electronic conductivity caused by the thickly coated solid electrolyte layer and poor contact between the cathode active material and the cell. -1 It showed a capacity close to [value]. From these results, it can be confirmed that by coating a solid electrolyte on the surface of an active material through a mechanical process and controlling the coating rate of the surface to include uncoated areas, ion and electron transfer pathways can be secured and improved rate capability performance can be exhibited due to improved inter-particle contact.

[0105] From the results of the above examples and test examples, it can be confirmed that the present invention can effectively apply as an electrode composite to a sulfide solid electrolyte battery by manufacturing a core-shell structured electrode composite in which a solid electrolyte layer is formed on the surface of active material particles by a mechanical coating process, and by having a non-complete cover shell structure including an uncoated region where the solid electrolyte is partially not coated, thereby providing an ion transport pathway through the coated region of the solid electrolyte layer and an electron transport pathway through the uncoated region, thereby improving electron and ion contact at the interface of the composite and improving cell performance by having a dense packing density.

[0106] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not to limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by such embodiments. The scope of protection of the present invention shall be interpreted by the claims, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

Claims

1. Active material particles; The electrode composite having a core-shell structure comprising a sulfide solid electrolyte layer coated on the surface of the active material particles by a mechanical coating process, and The above solid electrolyte layer has a non-fully cover shell structure including a region where the solid electrolyte is partially uncoated, An electrode composite for an all-solid-state battery, characterized by providing an ion transfer pathway through a coated region of the solid electrolyte layer and an electron transfer pathway through an uncoated region to improve electron contact and ion contact at the interface of the composite.

2. In Paragraph 1, An electrode composite for an all-solid-state battery, characterized in that the coating region thickness of the solid electrolyte layer is 200 to 800 nm.

3. In Paragraph 2, An electrode composite for an all-solid-state battery, characterized in that the coating area exceeds 50% of the surface area of ​​the active material particle.

4. In Paragraph 1, The above active material is, An electrode composite for an all-solid-state battery, characterized by having a positive electrode active material which is a lithium metal oxide, or one or more negative electrode active materials selected from silicon-based, tin-based, or carbon-based active materials.

5. In Paragraph 4, The above active material particles are characterized by having a buffer layer coated with a lithium ion conductive oxide formed on the surface of the positive active material particles, forming an electrode composite for an all-solid-state battery.

6. Step of preparing active material powder; and A core-shell structured electrode composite is manufactured by including the step of mixing sulfide solid electrolyte powder with the above active material powder, and then forming a sulfide solid electrolyte layer coated with a uniform thickness by a mechanical coating process. The above solid electrolyte layer has a partial shell structure in which a coating layer is formed only on a portion of the surface area of ​​the active material particles, including a partially uncoated area. Characterized by providing an ion transfer path through a coated region of the solid electrolyte layer and an electron transfer path through an uncoated region, thereby improving electron contact and ion contact at the composite interface. Method for manufacturing an electrode composite for an all-solid-state battery.

7. In Paragraph 6, A method for manufacturing an electrode composite for an all-solid-state battery, characterized in that the electrode composite is an electrode composite according to any one of claims 1 to 5.

8. In Paragraph 6, A method for manufacturing an electrode composite for an all-solid-state battery, characterized in that the above-mentioned sulfide solid electrolyte is one or more selected from the group consisting of LGPS-based solid electrolytes, LPSX(X=Cl, Br, I)-based solid electrolytes, LPS-based solid electrolytes, and thio-LISICON-based solid electrolytes.

9. In Paragraph 6, A method for manufacturing an electrode composite for an all-solid-state battery, characterized in that, when forming the sulfide solid electrolyte layer, the sulfide solid electrolyte is mixed such that the weight ratio of the active material to the sulfide solid electrolyte is 80:20 to 95:

5.

10. An electrode for an all-solid-state battery characterized by having an improved filling density, comprising an electrode composite according to any one of claims 1 to 5.

11. An all-solid-state battery characterized by including an electrode according to claim 11.

Images