Press sintering method for all-solid-state battery comprising amorphous solid electrolyte

Abstract

According to one embodiment of the present disclosure, provided is a method for manufacturing a laminated ceramic all-solid-state battery, the method comprising the steps of: sequentially laminating a first current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a second current collector layer to produce a sheet laminate, wherein the negative electrode active material layer includes graphite, and the positive electrode active material layer includes a lithium compound; and sintering the sheet laminate under a reducing atmosphere and a pressure of 5 to 25 ton / cm2. According to the method, a laminated ceramic all-solid-state battery can be manufactured in an energy-efficient manner while minimizing damage to the ceramic constituting the all-solid-state battery, and the ionic conductivity of the laminated ceramic all-solid-state battery can be improved.

Description

Pressure sintering method of an all-solid-state battery containing an amorphous solid electrolyte

[0001] This invention relates to a pressure sintering method for an all-solid-state battery containing an amorphous solid electrolyte.

[0002] All-solid-state batteries using oxide-based solid electrolytes have the advantage of high stability compared to conventional lithium-ion batteries using liquid electrolytes, can produce high output even in a small volume, allowing for miniaturization, and can be directly mounted on a printed circuit board (PBC). Recently, with the increasing demand for wearable devices such as smartwatches, earbuds, and smart rings, there is a growing demand to develop high-output, ultra-small stacked ceramic all-solid-state batteries by fabricating these batteries in a stacked form, and to replace existing liquid electrolyte-based coin cells.

[0003] To manufacture a multilayer ceramic all-solid-state battery, a composite cathode composed of a positive active material and a solid electrolyte, a composite negative electrode composed of a negative active material and a solid electrolyte, and a solid electrolyte and a transition metal current collector must be stacked in multiple layers at once and then sintered simultaneously. Typically, high temperatures of 1000°C or higher are required for the sintering of ceramics; however, at such high temperatures, problems such as volatilization or damage to the ceramics constituting the all-solid-state battery may occur, so it is important to control the conditions of the sintering process.

[0004] The present disclosure aims to provide a method for manufacturing a multilayer ceramic all-solid-state battery by simultaneously sintering a positive electrode active material, a negative electrode active material, and a solid electrolyte at a temperature significantly lower than the conventional ceramic sintering temperature.

[0005] According to one aspect of the present disclosure, a method for manufacturing a multilayer ceramic all-solid-state battery is provided, the method comprising: stacking a first current collector layer, a positive active material layer, a solid electrolyte layer, a negative active material layer, and a second current collector layer in sequence to form a sheet laminate, wherein the negative active material layer comprises graphite and the positive active material layer comprises a lithium compound; and the sheet laminate in a reducing atmosphere and 5 to 25 ton / cm² 2 It includes a step of sintering under pressure.

[0006] According to one embodiment, the positive active material layer may include a lithium-based oxide.

[0007] According to one embodiment, the solid electrolyte layer may include Li-Si-based amorphous glass.

[0008] According to one embodiment, the first and second current collector layers may include Cu, Li, Al, or a combination thereof.

[0009] According to one embodiment, the partial pressure of oxygen in the reducing atmosphere is 10 -18 to 10 -7 It could be an ATM.

[0010] According to one embodiment, the nitrogen fraction in the reducing atmosphere may be 99.4 to 99.8%.

[0011] According to one embodiment, the hydrogen fraction in the reducing atmosphere may be 0.1 to 0.5%.

[0012] According to one embodiment, the water temperature in the reducing atmosphere may be 40 to 70°C.

[0013] According to one embodiment, the sintering step can be performed at a temperature of 200 to 350 ℃.

[0014] According to the present disclosure, a multilayer ceramic all-solid-state battery can be manufactured by sintering a sheet laminate at a low temperature while minimizing volatilization and interfacial reactions of ceramic elements constituting the all-solid-state battery, and high ionic conductivity of the multilayer ceramic all-solid-state battery can be achieved.

[0015] Figure 1 is an X-ray diffraction pattern showing a phase change according to the pressurized sintering temperature of a solid electrolyte according to one embodiment.

[0016] FIGS. 2a to 2f are scanning electron microscope (SEM) images showing changes in microstructure according to the pressure sintering temperature of a solid electrolyte according to one embodiment.

[0017] FIG. 3 is an impedance spectroscopic curve showing the change in microstructure according to the pressurized sintering temperature of a solid electrolyte according to one embodiment.

[0018] The objects, advantages, and features of the present disclosure will become more apparent from the following detailed description and preferred embodiments in conjunction with the accompanying drawings, but the present disclosure is not necessarily limited thereto. Furthermore, in describing the present disclosure, detailed descriptions of related prior art are omitted where it is determined that such detailed descriptions may unnecessarily obscure the essence of the present disclosure.

[0019] According to one aspect of the present disclosure, a method for manufacturing a multilayer ceramic all-solid-state battery is provided, the method comprising the step of stacking a first current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a second current collector layer in sequence to form a sheet laminate, wherein the negative electrode active material layer comprises graphite and the positive electrode active material layer comprises a lithium compound; and the sheet laminate is placed in a reducing atmosphere and 5 to 25 ton / cm² 2 It includes a step of sintering under pressure.

[0020] The first and second current collector layers are layers that perform the function of transferring electrons from the outside to the active material (first current collector layer) or releasing electrons from the active material to the outside (second current collector layer) so that electrochemical reactions can occur within the battery when charging or discharging the battery. In the above-described multilayer ceramic all-solid-state battery, the first and second current collector layers are stacked adjacent to the positive active material layer and the negative active material layer, respectively, and perform the function of transferring electrons to the positive active material layer and the negative active material layer or releasing electrons from them during charging or discharging. The first and second current collector layers include metal, and since metal has high electrical conductivity, it can facilitate the movement of electrons through the current collector layers.

[0021] In one embodiment, the first and second current collector layers may include Cu, Li, Al, or a combination thereof. The metal included in the current collector layer must have high electrical conductivity, and in this regard, Cu, Li, Al, or a combination thereof is suitable for use as a current collector. In addition, the metal also has an advantage in terms of cost. Specifically, when comprehensively considering electrical conductivity, cost, and oxidation stability, it may be advantageous to include Cu and Al in the current collector layer. The positive active material layer refers to a layer containing a positive active material that receives electrons from the first current collector layer and is reduced along with cations when the battery is charged. When charging the battery, electrons are supplied to the positive active material layer, causing the positive active material to be reduced and cations to be released into the electrolyte layer, and the released cations subsequently generate electricity in the negative active material layer. The positive active material layer affects the capacity and output of the battery, and in particular, since the cations released from the positive active material layer play a role in generating electricity, it is advantageous to include a material that facilitates the generation of cations during charging in the positive active material layer.

[0022] In one embodiment, the positive electrode active material layer may include a lithium-based oxide. Since the positive electrode active material layer containing highly diffusible lithium cations facilitates cation generation and diffusion into the solid electrolyte layer during charging, the battery capacity and output can be improved. The lithium-based oxide included in the positive electrode active material layer may be, for example, LiCoO2 (LCO), Li(Ni,Co,Mn)O2 (NCM), Li(Ni,Co,Al)O2 (NCA), LiMn2O4 (LMO), or LiFePO4 (LFP), and it may be advantageous to use LCO when simultaneously considering battery life, output, and ease of subsequent low-temperature sintering.

[0023] The solid electrolyte layer described above serves to transfer cations released from the positive electrode active material layer to the negative electrode active material layer during battery charging. Unlike liquid electrolytes, using a solid electrolyte does not require a separate separator to separate the electrolyte from the electrode, allowing for a more compact battery manufacturing process that increases battery capacity per unit volume and offers advantages in terms of stability compared to batteries using liquid electrolytes. The solid electrolyte layer may include any material capable of densifying with adjacent positive and negative electrode active material layers through sintering without limitation, and may include, for example, a ceramic containing Li oxide.

[0024] In one embodiment, the solid electrolyte layer may include Li-Si-based amorphous glass. Unlike conventional ceramics, which are typically sintered at high temperatures of about 800°C or higher, Li-Si-based amorphous glass can be sintered at low temperatures of 600°C or lower, thus having the advantage of being sinterable even in the low-temperature simultaneous sintering step of the present disclosure. Furthermore, while conventional ceramics require high-temperature conditions for sintering because ionic conductivity is achieved only in a crystallized state, the Li-Si-based amorphous glass can achieve ionic conductivity even in an amorphous state, and thus can exhibit sufficient ionic conductivity to be used as an electrolyte for an all-solid-state battery even when sintered at a temperature of 350°C or lower as described below.

[0025] The above-mentioned negative electrode active material layer receives and stores cations released from the positive electrode active material layer and moving through the solid electrolyte layer during battery charging, and then generates electricity by releasing these cations through the solid electrolyte layer and transferring them back to the positive electrode active material layer during battery discharge. The above-mentioned negative electrode active material layer comprises graphite, which has a structure in which multiple graphene layers are stacked. Electricity is generated through a process in which cations are stored in the spaces between each graphene layer within the graphite during charging and then discharged back into the solid electrolyte layer during battery discharge; due to the aforementioned stacked graphene structure, the graphite possesses a high battery capacity.

[0026] In the lamination step, the above layers are laminated in the order of a first current collector layer, an anode active material layer, a solid electrolyte layer, a cathode active material layer, and a second current collector layer to form a sheet laminate.

[0027] Since sulfide-based and polymer-based all-solid-state batteries are manufactured by a lamination process rather than sintering, conductive binders are included as conductive materials in the anode, cathode, and electrolyte; whereas the laminated ceramic all-solid-state battery of the present disclosure does not include separate additives such as binders, it possesses higher stability and reliability compared to sulfide-based and polymer-based all-solid-state batteries.

[0028] The above method involves the sheet laminate in a reducing atmosphere and 5 to 25 ton / cm 2 The method includes a step of sintering under pressure. As previously described, the positive active material layer, the solid electrolyte layer, and the negative electrolyte layer of the sheet laminate comprise ceramic materials, and typically, the sintering of ceramic materials is performed at a high temperature of approximately 800°C or higher. However, the sheet laminate comprises graphite as the negative active material, and since graphite has the characteristic of volatilizing in the atmosphere at a temperature of approximately 500°C, volatilization may occur if the reaction temperature is set to 800°C or higher for the sintering of the sheet laminate. The method enables the sheet laminate to be sintered at a temperature lower than the usual sintering temperature by controlling the sintering atmosphere to a reducing atmosphere. Here, "reducing atmosphere" refers to an atmosphere within the reactor in which the sheet laminate is sintered that is capable of donating hydrogen or electrons to the sheet laminate, specifically referring to a state in which the partial pressure of hydrogen is increased compared to the atmosphere. In the absence of a reducing atmosphere, the graphite of the negative active material layer and the metals of the first and second laminates may volatilize. In addition, the sintering step is 5 to 25 ton / cm 2It is performed under pressure, and such pressurized conditions allow the sheet laminate to be densified even at relatively low sintering temperatures. By making the sheet laminate more densified compared to sintering without pressure at the same sintering temperature, it can improve the ion conductivity of the multilayer ceramic all-solid-state battery. The pressure during the sintering step is 5 ton / cm² 2 If it is less than, the sheet laminate may not densify at a relatively low sintering temperature, thereby requiring a higher temperature for the sintering of the sheet laminate. The pressure during the sintering step is 25 ton / cm² 2 If exceeded, the sheet laminate may be excessively pressed, causing deformation or damage, which may consequently result in a decrease in the ion conductivity of the multilayer ceramic all-solid-state battery. In one embodiment, the sintering step is specifically 7.5 to 20 ton / cm 2 , more specifically 10 to 15 ton / cm 2 It can be performed under the pressure of the above. The above method provides a method for simultaneously sintering each layer of a sheet laminate under the aforementioned atmosphere and pressure, thereby allowing the ceramic materials used in ceramic all-solid-state batteries to be diversified into two or more types without an adhesive or a corresponding buffer layer between each layer, and can simplify the process configuration.

[0029] In one embodiment, the partial pressure of oxygen in the reducing atmosphere is 10 -18 to 10 -7 It can be atm. The partial pressure of oxygen in a reducing atmosphere is 10 -18 If the pressure is below atm, phase collapse may occur due to the volatilization of specific components within the positive active material layer and solid electrolyte layer, particularly Li, which can significantly degrade battery performance, and if the partial pressure of oxygen in the reducing atmosphere is 10 -7 If the pressure exceeds atm, rapid volatilization due to oxidation of graphite within the cathode active material layer may occur. Specifically, the partial pressure of oxygen in the reducing atmosphere is 10 -15Up to 5×10 -8 atm, more specifically 10 -12 to 10 -5 It could be an ATM.

[0030] In one embodiment, the nitrogen fraction in the reducing atmosphere may be 99.4 to 99.8%. If the nitrogen fraction in the reducing atmosphere is less than 99.4% and greater than 99.8%, a problem may occur in which the graphite and solid electrolyte layer contained in the negative active material layer of the sheet laminate volatilize at the sintering temperature.

[0031] In one embodiment, the hydrogen fraction in the reducing atmosphere may be 0.1 to 0.5%. If the hydrogen fraction in the reducing atmosphere is less than 0.1%, a problem may occur in which the positive electrode active material layer and the solid electrolyte layer are oxidized during the sintering process, and if the hydrogen fraction in the reducing atmosphere is greater than 0.5%, the positive electrode and negative electrode active material layers may volatilize during the sintering process.

[0032] In one embodiment, the wetter temperature in the reducing atmosphere may be 40 to 70 °C. As used in this disclosure, the term “wetter temperature” refers to the temperature of a tank containing water (H2O) used to control the partial pressure of oxygen in the aforementioned reducing atmosphere. Specifically, the partial pressure of oxygen in the reducing atmosphere is determined by the equilibrium of the following chemical formula.

[0033] H2(g) + 1 / 2O2(g) → H2O(g)

[0034] Here, when the water vapor partial pressure in the reducing atmosphere increases as the water temperature rises, a reverse reaction proceeds to achieve equilibrium, increasing the oxygen partial pressure; and when the water temperature falls, the water vapor partial pressure decreases, a forward reaction proceeds to achieve equilibrium, decreasing the oxygen partial pressure. If the water temperature in the reducing atmosphere is below 40°C or above 70°C, the oxygen partial pressure in the reducing atmosphere described above is not satisfied, and thus, during the sintering stage, a degradation in battery performance may occur due to the volatilization of one or more of the positive active material layer, the solid electrolyte layer, and the negative active material layer.

[0035] In one embodiment, the sintering step may be performed at a temperature of 200 to 350 °C. As previously mentioned, sintering of conventional ceramic materials is performed at a high temperature of about 800 °C or higher; however, since the sintering step of the sheet laminate of the present disclosure is performed under a reducing atmosphere and pressurized conditions, it may be performed at a temperature of 200 to 350 °C, which is significantly lower than the conventional ceramic sintering temperature. If the sintering step is performed at a temperature below 200 °C, the sheet laminate may not be sufficiently densified, which may result in a decrease in the ion conductivity of the all-solid-state battery. In one embodiment, the sintering step may be performed specifically at a temperature of 200 to 300 °C, more specifically at a temperature of 200 to 250 °C.

[0036] Preferred embodiments are provided below to aid in understanding the present disclosure, but the following embodiments are provided only to facilitate a better understanding of the present invention and are not intended to limit the present disclosure.

[0037] Experimental Example 1 - Phase change of solid electrolyte according to changes in sintering atmosphere and sintering temperature

[0038] Seven solid electrolyte samples were prepared by molding Li-Si-based amorphous oxide-based solid electrolyte powder (hereinafter LBA) into disc shapes with a diameter of 10 mm. Six disc-shaped solid electrolytes were 10 -10A reducing atmosphere (Wetter) containing an oxygen partial pressure atm, a nitrogen fraction of 99.5%, and a hydrogen fraction of 0.04%, and 12.5 ton / cm² 2 Sintering was performed under pressure at temperatures of 200, 350, 400, 450, 500, 550, and 600 °C. Subsequently, the phase changes of these seven LBA solid electrolytes according to the change in sintering temperature were confirmed by analyzing the X-ray diffraction patterns. The results are as shown in Fig. 1. Referring to Fig. 1, when the sintering temperature was 500 °C or higher, crystallized peaks of the solid electrolyte were observed at diffraction angles (2θ) of approximately 22, 35, and 36 degrees, but when the sintering temperature was 450 °C or lower, these crystalline phase peaks were not observed. From this, it can be inferred that when the sintering temperature is 450 °C or lower under the above reducing atmosphere and pressurized conditions, the LBA solid electrolyte exists in an amorphous state.

[0039] Experimental Example 2 - Microstructural changes in the solid electrolyte layer according to changes in sintering temperature

[0040] Among the seven sintered solid electrolytes of Experimental Example 1, the microstructures of five solid electrolytes sintered at temperatures of 200, 350, 400, 450, and 500 °C were examined using a scanning electron microscope. SEM images for examining the microstructures of each solid electrolyte are shown in Figures 2a to 2e. Additionally, an SEM image of the solid electrolyte sintered at 500 °C without pressure is shown in Figure 2f. As a result of microstructure analysis, it was confirmed that the solid electrolytes pressure-sintered at low sintering temperatures of 200 °C to 450 °C exhibited a superior degree of densification, while the solid electrolytes pressure-sintered at 500 °C were in an under-sintered state. Furthermore, it was confirmed that the solid electrolyte pressure-sintered at a sintering temperature of 200 °C exhibited a superior degree of densification compared to the solid electrolyte sintered at 500 °C without pressure.

[0041] In other words, it can be inferred that the above-mentioned solid electrolyte can have a densified structure while remaining in an amorphous state by being pressure-sintered at a low temperature.

[0042] Experimental Example 3 - Measurement of Change in Ionic Conductivity of Solid Electrolyte According to Sintering Temperature

[0043] Among the seven sintered solid electrolytes of Experimental Example 1, the impedance was measured for three solid electrolytes sintered at sintering temperatures of 200, 350, and 500 °C. Specifically, after clamping each specimen in a pressure jig, the impedance as a function of frequency was measured using an impedance analyzer from the terminals of both ends in accordance with the method described in Journal of Applied Physics, 66, 3850 (1989) (DC Sinclair and AR West). The measurement results are shown in Fig. 3. The measured impedance is a complex impedance, consisting of an imaginary part and a real part, with the imaginary part plotted on the y-axis of the graph in Fig. 3 and the real part on the x-axis of the graph in Fig. 3.

[0044] Referring to Fig. 3, the x-intercept at the point where the semicircular portion of the graph for each sample meets the x-axis by extrapolation represents the insulation resistance of each sample, from which the conductivity of each sample can be calculated. Since these samples have an electronic conductivity close to zero, the conductivity can be specified as ionic conductivity. From Fig. 3, it can be confirmed that the insulation resistance of the solid electrolyte sintered at 200 ℃ is the lowest, and thus the ionic conductivity is the highest. It can also be confirmed that the ionic conductivity of the solid electrolyte sintered at 350 ℃ is significantly high, although it does not reach that of the solid electrolyte sintered at 200 ℃. Furthermore, it can be confirmed that the ionic conductivity of the solid electrolyte sintered at 500 ℃ is significantly lower when compared to the ionic conductivity of the solid electrolytes sintered at 200 ℃ and 350 ℃. From this, it can be inferred that sintering a solid electrolyte under a reducing atmosphere and pressurized conditions is effective at a low temperature of less than 500°C in terms of improving the ionic conductivity of the solid electrolyte. In addition, as mentioned in Experimental Example 1, it can be confirmed that a solid electrolyte pressure-sintered at temperatures of 200 and 350°C, where the solid electrolyte exists in an amorphous state, exhibits superior ionic conductivity compared to a solid electrolyte in a crystallized state pressure-sintered at a temperature of 500°C.

[0045] Experimental Example 4 - Changes in Ionic Conductivity of Solid Electrolyte and Composite Anode According to Pressurization Conditions and Sintering Temperature

[0046] Four samples were prepared by molding Li-Si-based amorphous oxide-based solid electrolyte powder (LBA) into 10 mm diameter discs. Additionally, four composite cathode samples were prepared by mixing LBA powder with the cathode active material LiCO2 (LCO) in a 1:1 ratio and molding them into 10 mm diameter discs. Subsequently, four composite anode samples were prepared by mixing LBA powder with the anode active material graphite in a 1:1 ratio and molding them into 10 mm diameter discs. These 12 samples were 1.8 × 10⁻⁶ -10 Sintering was performed under a reducing atmosphere containing an oxygen partial pressure of atm, a nitrogen fraction of 99.5%, and a hydrogen fraction of 0.4%, with different applied pressures and sintering temperatures. After sintering, the ionic conductivity of these samples was measured in the same manner as in Experimental Example 3, and the measurement results are as shown in Table 1.

[0047]

[0048] As shown in Table 1, the LBA solid electrolyte is 12.5 ton / cm 2 12.5 ton / cm² when sintered at temperatures of 200 and 350 ℃ under pressurized conditions 2 It exhibited higher ionic conductivity than when sintered at a temperature of 500 ℃ under pressure conditions. In addition, it was confirmed that sintering with pressure at the same sintering temperature resulted in higher ionic conductivity compared to sintering without pressure.

[0049] In the case of composite anodes and cathodes, it was confirmed that sintering at a low temperature of 200°C under pressurized conditions resulted in higher ionic conductivity compared to sintering at a high temperature of 500°C, and that sintering with pressurization at the same sintering temperature resulted in higher ionic conductivity compared to sintering without pressurization.

[0050] From this, it can be inferred that, from the perspective of improving the performance of all-solid-state batteries, it is desirable to apply pressure and perform low-temperature sintering during the sintering of the solid electrolyte, composite anode, and composite cathode.

[0051] The present disclosure has been described in detail through specific embodiments. The embodiments are intended to specifically explain the present disclosure and are not limited thereto. It will be apparent that modifications or improvements can be made by those skilled in the art within the technical scope of the present disclosure.

[0052] All simple variations or modifications of the present disclosure fall within the scope of the present disclosure, and the specific scope of protection of the present disclosure will be clarified by the appended claims.

Claims

1. As a method for manufacturing a stacked ceramic all-solid-state battery: A step of stacking a first current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a second current collector layer in sequence to produce a sheet laminate, wherein the negative electrode active material layer comprises graphite and the positive electrode active material layer comprises a lithium compound; and The above sheet laminate is subjected to a reducing atmosphere and 5 to 25 ton / cm 2 A method for manufacturing a multilayer ceramic all-solid-state battery, comprising the step of sintering under pressure.

2. In Claim 1, A method for manufacturing a multilayer ceramic all-solid-state battery, wherein the positive electrode active material layer comprises a lithium-based oxide.

3. In Claim 1, A method for manufacturing a multilayer ceramic all-solid-state battery, wherein the solid electrolyte layer comprises Li-Si-based amorphous glass.

4. In Claim 1, A method for manufacturing a multilayer ceramic all-solid-state battery, wherein the first and second current collector layers comprise Cu, Ni, Al, or a combination thereof.

5. In Claim 1, The partial pressure of oxygen in a reducing atmosphere is 10 -18 to 10 -7 A method for manufacturing a stacked ceramic all-solid-state battery.

6. In Claim 1, A method for manufacturing a multilayer ceramic all-solid-state battery in which the nitrogen fraction in the reducing atmosphere is 99.4 to 99.8%.

7. In Claim 1, A method for manufacturing a multilayer ceramic all-solid-state battery in which the hydrogen fraction in a reducing atmosphere is 0.1 to 0.5%.

8. In Claim 1, A method for manufacturing a multilayer ceramic all-solid-state battery, wherein the wetter temperature in a reducing atmosphere is 40 to 70 ℃.

9. In Claim 1, A method for manufacturing a multilayer ceramic all-solid-state battery, wherein the above sintering step is performed at a temperature of 200 to 350 ℃.

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