Solid electrolyte, method for manufacturing same, and battery cell manufactured thereby

Abstract

The present invention relates to a solid electrolyte, a method for manufacturing same, and a battery cell manufactured thereby. According to one aspect of the present invention, the solid electrolyte comprises lithium, phosphorus, and sulfur, and has a residual solvent content of greater than 100 ppmw and less than 500 ppmw.

Description

Solid electrolyte, method for manufacturing the same, and battery cell manufactured thereby

[0001] The present invention relates to a solid electrolyte, a method for manufacturing the same, and a battery cell manufactured through the same, and more specifically, to a sulfide-based solid electrolyte, a method for manufacturing the same, and a battery cell manufactured through the same.

[0002] Currently, despite the many advantages of lithium-ion batteries, such as high energy density and long lifespan, their use is limited due to safety issues like explosions and ignition. In particular, short circuits, overheating, and overcharging that can occur within lithium-ion batteries act as risk factors that can lead to explosions or fires. Various research and technological developments are actively underway to address these safety issues.

[0003] All-solid-state batteries are batteries in which all components of lithium-ion batteries are composed in a solid state. They are a next-generation battery technology that solves the safety issues associated with the aforementioned lithium-ion batteries and are one of the fields currently undergoing extensive research.

[0004] In particular, sulfide-based solid electrolytes maintain high ionic conductivity at room temperature, supporting efficient ion conduction between electrodes and significantly improving energy transfer performance. Furthermore, compared to liquid electrolytes, they offer superior compatibility with electrodes and possess high chemical and thermal stability, which can greatly enhance battery safety.

[0005] Since the electrical characteristics of a battery cell can be improved as the contact area of ​​the solid electrolyte with the electrode active material increases, it is common practice to perform a grinding process to atomize the solid electrolyte before applying it to a battery cell. However, since residues remain in the solid electrolyte during the grinding process, they can degrade the electrical characteristics of the battery cell.

[0006] Accordingly, there is a need to develop technology that does not degrade the characteristics of battery cells despite the micronization process of solid electrolytes.

[0007] Meanwhile, the aforementioned background technology is technical information that the inventor possessed for the derivation of the present invention or acquired during the process of deriving the present invention, and it cannot be considered as prior art disclosed to the general public prior to the filing of the present invention.

[0008] One embodiment of the present invention aims to provide a solid electrolyte in which the electrical characteristics of a battery cell are maintained despite the incorporation of residues due to a micronization process, a method for manufacturing the same, and a battery cell manufactured through the same.

[0009] As a technical means for achieving the technical problem described above, according to one aspect of the present invention, the solid electrolyte of the present invention comprises lithium, phosphorus, and sulfur, and has a residual solvent content of more than 100 ppmw and less than 500 ppmw.

[0010] According to another aspect of the present invention, the solid electrolyte is Li a P b S c X d It can have the composition of. (where X is a Group 17 element and 0 <a≤10, 0<b≤10, 0<c≤15 및 0<d≤20 임)

[0011] As a technical means for achieving the technical problem described above, according to another aspect of the present invention, a method for manufacturing a solid electrolyte of the present invention comprises a step of providing a solid electrolyte pretreatment material that provides a solid electrolyte pretreatment material comprising lithium, phosphorus, and sulfur, and a solvent control step that controls the solvent content of the solid electrolyte pretreatment material, wherein the solvent control step is performed such that the solvent content of the pretreatment material is greater than 100 ppmw and less than 500 ppmw.

[0012] According to another aspect of the present invention, the step of providing a solid electrolyte pretreatment material may include a solid-state synthesis step of synthesizing a solid electrolyte pretreatment material by stirring a precursor comprising lithium, phosphorus, and sulfur in a solid state.

[0013] According to another aspect of the present invention, the step of providing a solid electrolyte pretreatment material may include a liquid synthesis step of synthesizing a solid electrolyte pretreatment material by stirring a precursor containing lithium, phosphorus, and sulfur in a liquid state.

[0014] According to another aspect of the present invention, the step of providing a solid electrolyte pretreatment material may include a step of forming a mixed solution by stirring a precursor containing lithium, phosphorus, and sulfur in a liquid state to form a mixed solution of said precursor, and a step of synthesizing the solid electrolyte pretreatment material by spraying said mixed solution.

[0015] According to another aspect of the present invention, after the step of providing a solid electrolyte pretreatment material, a first heat treatment step in which the solid electrolyte pretreatment material is crystallized is further included, and the solvent control step may be performed after the first heat treatment step.

[0016] According to another aspect of the present invention, after the solvent control step, a second heat treatment step may be further included in which the pretreated material of the solvent-controlled solid electrolyte is crystallized.

[0017] According to another aspect of the present invention, after the step of providing a solid electrolyte pretreatment material, a grinding step in which the solid electrolyte pretreatment material is atomized is further included, and the solvent control step may be performed after the grinding step.

[0018] As a technical means for achieving the technical problem described above, according to another aspect of the present invention, the battery cell of the present invention comprises an electrode composite comprising an electrode active material and a solid electrolyte, wherein the solid electrolyte has a residual solvent content of more than 100 ppmw and less than 500 ppmw.

[0019] According to another aspect of the present invention, the porosity of the electrode composite may be 20% or less.

[0020] According to another aspect of the present invention, the density of the electrode composite is 2.9 g / cm³ 3 It could be more than that.

[0021] According to another aspect of the present invention, the first Coulomb efficiency, which is the ratio of the first discharge capacity (mAh / g) to the first charge capacity (mAh / g) of the battery cell manufactured from the electrode composite, may be 80% or more.

[0022] According to another aspect of the present invention, when a battery cell manufactured from the electrode composite is charged and discharged 50 times, the capacity retention rate (%), which is the ratio of the 50th discharge capacity (mAh / g) to the 1st discharge capacity (mAh / g), may be 88% or more.

[0023] According to any one of the means for solving the problem of the present invention described above, the solid electrolyte of the present invention has a residual solvent content of more than 100 ppmw and less than 500 ppmw, so both ionic conductivity and electronic conductivity can be excellent.

[0024] According to any one of the means for solving the problem of the present invention described above, the residual solvent content in the solid electrolyte is controlled to be greater than 100 ppmw and less than 500 ppmw, so as the porosity of the solid electrolyte is reduced, the filling rate of the battery cell can be improved, and as stress can be relieved or absorbed due to the appropriate amount of residual solvent, the mechanical properties of the solid electrolyte can be improved.

[0025] According to any one of the means for solving the problem of the present invention described above, the residual solvent content in the solid electrolyte is controlled to be greater than 100 ppmw and less than 500 ppmw; thus, due to the appropriate content of residual solvent, defects caused by stress due to volume expansion of the cathode active material can be prevented despite repeated charge-discharge cycles. In addition, since the formation of by-products due to by-reactions in the residual solvent in the solid electrolyte is suppressed, ionic conductivity can be maintained. Accordingly, a high capacity retention rate can be maintained.

[0026] According to any one of the means for solving the problem of the present invention described above, the residual solvent content in the solid electrolyte is controlled to be greater than 100 ppmw and less than 500 ppmw. Since the formation of voids in the solid electrolyte is suppressed due to the appropriate amount of residual solvent, an excellent filling rate can be maintained. In addition, the formation of carbonized material in the solid electrolyte is suppressed, and ion conductivity can be improved. Accordingly, the Coulomb efficiency of the battery cell can be improved.

[0027] The effects obtainable from the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description below.

[0028] FIG. 1 is a flowchart of a method for manufacturing a solid electrolyte according to one embodiment of the present invention.

[0029] FIG. 2 is a flowchart of a method for manufacturing a solid electrolyte according to another embodiment of the present invention.

[0030] FIG. 3 is a flowchart of a method for manufacturing a solid electrolyte according to another embodiment of the present invention.

[0031] FIG. 4 is a flowchart of a method for manufacturing a solid electrolyte according to another embodiment of the present invention.

[0032] Figure 5 is a conceptual diagram of the cross-sectional structure of the battery cell of the present invention.

[0033] Figure 6 is a Scanning Electron Microscope (SEM) image of a solid electrolyte according to embodiments of the present invention.

[0034] Figure 7 shows the first discharge capacity (mAh / g) measurement result of a battery cell manufactured using a solid electrolyte according to embodiments of the present invention.

[0035] Figure 8 shows the results of measuring the discharge capacity (%) according to the number of charge and discharge cycles of a battery cell manufactured using a solid electrolyte according to embodiments of the present invention.

[0036] Embodiments of the present invention are described below with reference to the attached drawings so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification are denoted by similar reference numerals.

[0037] Throughout the specification, when a part is described as being "connected" to another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" with other members or elements interposed between them. Furthermore, 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.

[0038] The present invention will be described in detail below with reference to the attached drawings.

[0039] The solid electrolyte of the present invention, the method for manufacturing the same, and the battery cell manufactured thereby have the advantage of being able to improve the packing density of the solid electrolyte by controlling the residual solvent content of the solid electrolyte, and to improve the cell characteristics and lifespan of the battery cell.

[0040] FIG. 1 is a flowchart of a method for manufacturing a solid electrolyte according to one embodiment of the present invention.

[0041] Referring to FIG. 1, the method for manufacturing a solid electrolyte according to the present invention includes the step of providing a pretreatment material of a solid electrolyte containing lithium, phosphorus and sulfur (S110) and the step of controlling the solvent content of the pretreatment material of the solid electrolyte (S120).

[0042] First, the step of providing a pre-treated solid electrolyte (S110) means a step of providing a pre-treated solid electrolyte to which an additional process, including a subsequent solvent control step (S120), can be performed.

[0043] Here, the pretreatment material of the solid electrolyte is a pretreatment material containing a seed material that forms the basic framework of the solid electrolyte, and may be, for example, an electrolyte material containing a sulfide-based seed material with an argyrodite structure.

[0044] The pretreatment material of the solid electrolyte of the present invention may be provided in a solid form or in a liquid form dissolved in a solvent.

[0045] The step of providing a solid electrolyte according to the present invention may include, in addition to the step of directly synthesizing and providing a solid electrolyte, a step of obtaining and providing a solid electrolyte that has already been synthesized.

[0046] If the pretreatment material of the solid electrolyte is directly synthesized and provided, the pretreatment material of the solid electrolyte can be synthesized and provided through various methods such as the solid-phase method, the liquid-phase method, or the gas-phase method.

[0047] The solid-state method is a method of synthesizing a final product by reacting starting materials in a solid state, and may be a method of synthesizing a pre-treated solid electrolyte by stirring a precursor, which is a starting material for the solid electrolyte, under specific conditions.

[0048] The liquid phase method may be a method for synthesizing pre-treated materials for solid electrolytes by inducing chemical reactions of precursors dissolved in a solvent. By controlling conditions such as solvent characteristics, precursor concentration, temperature, and pressure, the liquid phase method allows for the control of reaction rate and selectivity, thereby enabling the control of the characteristics of the pre-treated material for solid electrolytes.

[0049] The vapor phase method may be a method for synthesizing a pre-treated solid electrolyte by spraying a precursor in a gaseous or aerosol state and then applying energy. The vapor phase method can control the characteristics of the pre-treated solid electrolyte by controlling the droplet size of the precursor, the spray pressure, and the amount of applied energy.

[0050] After the step of providing a pretreatment material for the solid electrolyte (S110), a solvent control step (S120) may be performed.

[0051] The solvent control step (S120) may be a step of controlling the content of the solvent remaining in the pretreated material of the solid electrolyte to a certain level.

[0052] In this case, the solvent is not particularly limited as long as it is a solvent used in the process of synthesizing the pretreatment material of the solid electrolyte. For example, the solvent may be water (H2O), alcohol (C2O). n H 2n+1It may be one or a mixture of two or more selected from the group comprising OH, 1≤n≤20), formic acid, and acetic acid, tetrahydrofuran, dimethylformamide, acetonitrile, dimethyl sulfoxide, acetone, ethyl acetate, dimethoxy ethane, 1,3-dioxolane, N-methylpyrrolidinone, N-methylformamide, diethyl carbonate, ethylmethyl carbonate, and dimethyl carbonate.

[0053] The solvent control step (S120) can be any method that allows the residual solvent to be controlled to a desired level. For example, drying, evaporation, depressurization, heating, gasification, extraction, distillation, and adsorption methods may be used.

[0054] To perform the solvent control step (S120), various solvent control devices may be used, and the solvent control devices may be rotary evaporators, vacuum evaporators, rotary evaporators, cooling towers, heating baths, dryers, fractional distillation devices, air blow systems, etc.

[0055] In some embodiments, an evaporation method may be used to perform the solvent control step (S120). In this case, preferably, a rotary evaporator may be used to control the residual solvent in the pretreated solid electrolyte.

[0056] A rotary evaporator is a device that places a solution into a rotating flask and heats it to evaporate the solvent. By applying a vacuum to lower the vapor pressure of the solvent, the rotary evaporator can promote evaporation even at low temperatures, allowing for the effective removal of the solvent and the concentration of the remaining substance.

[0057] Specifically, the solvent can be controlled using a rotary evaporator as follows. First, the solution is placed in a flask inside the rotary evaporator, and evaporation can be induced by setting the temperature. Then, the boiling point can be lowered under vacuum, and the rotation speed can be adjusted to ensure that the solvent evaporates uniformly.

[0058] At this time, the temperature can be set between 40°C and 60°C. Preferably, a range of 50°C to 55°C may be suitable. The vacuum condition can be set to 20 to 100 mbar. The rotation speed is set between 50 and 150 rpm, and generally, about 100 rpm may be suitable. The evaporation time can be adjusted from 30 minutes to within 2 hours.

[0059] In addition, in some embodiments, the solvent of the pretreated solid electrolyte can be controlled by combining a heating method and a depressurization method. Here, the heating method is a method of controlling the amount of solvent to a certain level by heating the solvent. The depressurization method is a method of lowering the boiling point of the solvent by lowering the pressure. The aforementioned combined method can perform depressurization and heating simultaneously to heat the solvent at a lower temperature.

[0060] For example, the reduced pressure atmosphere may be at a pressure lower than atmospheric pressure. For example, it may be from 0.01 Pa to 10 Pa.

[0061] In addition, the heating temperature may be 50°C to 300°C and may be 30 minutes to 12 hours.

[0062] In addition, heating can be carried out in two stages, including a low-temperature heating stage and a high-temperature heating stage, by setting different temperatures. Specifically, it can be carried out in such a way that a low-boiling point solvent is first controlled at a low temperature from a pre-treated solid electrolyte, and then a high-boiling point solvent is controlled at a high temperature.

[0063] Specifically, the low-temperature heating step can be performed at a temperature level at which the low-boiling point solvent can be controlled. For example, the low-temperature heating step can be performed at 50°C to 120°C. The heating atmosphere can be an inert atmosphere, a reduced-pressure atmosphere, or a vacuum atmosphere. The low-temperature heating time can be 10 minutes to 2 hours.

[0064] The high-temperature heating step can be performed at a temperature higher than the low-temperature heating step, at a level where the high-boiling point solvent can be controlled. For example, it can be from 130°C to 300°C. The heating atmosphere can be an inert atmosphere, a reduced-pressure atmosphere, or a vacuum atmosphere. The high-temperature heating time can be from 30 minutes to 12 hours.

[0065] Through any one of the methods described above, the solvent in the pretreated material of the solid electrolyte can be controlled to more than 100 ppmw and less than 800 ppmw, and preferably to more than 100 ppmw and less than 500 ppmw.

[0066] If the solvent in the pre-treated material of the solid electrolyte is less than 100 ppmw, the porosity of the solid electrolyte may increase as there is insufficient solvent to fill the voids between the particles of the pre-treated material. As the porosity of the solid electrolyte increases, the packing density decreases, making it difficult to achieve capacitance. Furthermore, due to the lack of residual solvent, high concentrations of ions within the solid electrolyte may migrate to the electrode active material, which may reduce ion conductivity and cause a decrease in initial charge / discharge capacity. Additionally, if charge / discharge cycles are repeated for a long time, volume expansion of the electrode active material may occur. The stress caused by this volume expansion may lead to defects within the solid electrolyte, and since these defects can hinder ion movement, they may reduce the capacity retention rate of the battery cell.

[0067] Meanwhile, if the solvent concentration in the pretreatment material of the solid electrolyte exceeds 500 ppmw, the solid electrolyte may carbonize due to carbon components in the residual solvent. Consequently, in a battery cell manufactured with the solid electrolyte, the movement of ions is inhibited by the carbonized material, and the ion conductivity may decrease. As a result, the initial charge / discharge capacity of the battery cell manufactured using the solid electrolyte may decrease. Furthermore, if charge / discharge cycles are repeated for a long time, the ion conductivity may decrease due to by-products resulting from side reactions in the residual solvent. Consequently, the capacity retention rate of the battery cell may decrease.

[0068] Through the step of providing the pretreatment material of the solid electrolyte described above (S110) and the step of controlling the solvent of the pretreatment material of the solid electrolyte (S120), the solid electrolyte can be finally obtained.

[0069] The solid electrolyte of the present invention is Li a P b S c X d(where X is a Group 17 element and 0 <a≤10, 0<b≤10, 0<c≤15 및 0<d≤20 임)의 조성을 갖는 화합물일 수 있다.

[0070] For example, the solid electrolyte may include any one of Li2S-SiS2, Li2S-P2S5, Li2S-GeS2, Li2S-B2S3, Li2S-Ga2S3, Li2S-Al2S3, Li2S-GeS2-P2S5, Li2S-Al2S3-P2S5, Li2S-P2S3, Li2S-P2S3-P2S5, LiX-Li2S-P2S5, LiX-Li2S-SiS2, LiX-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, LiX-Li2S-P2O5, and LiX-Li3PO4-P2S5 (X: any one of I, Br, and Cl).

[0071] The solid electrolyte of the present invention has the characteristic of having a residual solvent content of more than 100 ppmw and less than 500 ppmw.

[0072] In addition, the porosity of the solid electrolyte of the present invention may be greater than 2% and less than 4%.

[0073] In addition, the ionic conductivity of the solid electrolyte of the present invention may be 3.3 mS / cm or higher.

[0074] In addition, the electronic conductivity of the solid electrolyte of the present invention is 5×10 -9 Exceeding S / cm by 8×10 -7 It may be less than S / cm.

[0075] FIG. 2 is a flowchart of a method for manufacturing a solid electrolyte according to another embodiment of the present invention.

[0076] The method for manufacturing a solid electrolyte of FIG. 2 is substantially the same as the method for manufacturing a solid electrolyte of FIG. 1, except that the step (S110) of providing a pre-treated material of the solid electrolyte includes a step of synthesizing the pre-treated material of the solid electrolyte and further includes a heat treatment step. Accordingly, the description of the overlapping steps will be omitted.

[0077] Referring to FIG. 2, the step (S110) of providing a pre-treated solid electrolyte may include the step of synthesizing the pre-treated solid electrolyte by any one of the solid-phase method, liquid-phase method and gas-phase method.

[0078] When the step of providing a pretreatment material for a solid electrolyte of the present invention includes the step of synthesizing a solid electrolyte according to a solid-state method, the step of providing a pretreatment material for a solid electrolyte involves synthesizing a pretreatment material for a solid electrolyte (S210) by stirring a precursor containing lithium, phosphorus, and sulfur in a solid state.

[0079] To provide a detailed explanation of this, first, a solid-state precursor can be prepared.

[0080] As a starting material for a solid electrolyte containing lithium, phosphorus, and sulfur, any precursor capable of forming an azirodite structure may be used. When a precursor is used alone, a precursor containing all of the lithium, phosphorus, and sulfur elements may be selected.

[0081] For example, precursors are Li3PS4, Li4P2S6, Li8P2S9, Li7PS6, and Li7P3S 11 It could be the back.

[0082] When the precursor consists of two or more, a precursor containing at least some of lithium, phosphorus, and sulfur and a precursor containing other elements may be selected.

[0083] For example, when the precursor is composed of two or more, it may be selected from Li2S, Li2S3, Li2S4, Li2S6, Li2S8, Li3PS4, Li2CO3, LiOH, Li2O, Li2SO4, LiCl, LiClO4, LiNO3, P2S5, P2S3, Li3P, Li3PO4, PI3, PCl3, POCl3, P2O5, PBr3, POBr3, etc. However, the types of precursors of the present invention are not limited to the examples described above.

[0084] Subsequently, the above precursor is stirred to synthesize a pre-treated solid electrolyte.

[0085] The above stirring step is a method for synthesizing a pretreated solid electrolyte through stirring of the precursor in a solid state, and may be referred to as grinding or mixing.

[0086] The stirring step can be performed using a stirring device. For example, one or more or multiple methods among various milling devices such as planetary ball mills, bead mills, ball mills, cutter mills, hammer mills, and jet mills may be used. Among these devices, using a planetary ball mill or a bead mill may be particularly desirable in terms of being able to perform mechanical processing simultaneously.

[0087] When mechanical processing is performed in a planetary ball mill or a bead mill, it is preferable that the size of the grinding device used has a diameter of 0.01 mm or more, more preferably 0.1 mm or more, and typically 50 mm or less. The materials for the grinding device include zirconia, zircon, menow, alumina, tungsten carbide, iron, stainless steel, glass, etc., and these materials may be useful for performing mechanical processing and grinding processing simultaneously. In addition, considering wear caused by the device, it may be particularly preferable to use zirconia or alumina as the grinding device.

[0088] A solid electrolyte pretreatment material can be obtained through the stirring step described above, and in some embodiments, a post-treatment step of washing and calcining the obtained solid electrolyte pretreatment material may be further performed.

[0089] Meanwhile, if the step of providing a pretreatment material for a solid electrolyte according to the present invention includes the step of synthesizing a solid electrolyte according to a liquid phase method, the step of providing a pretreatment material for a solid electrolyte involves synthesizing a pretreatment material for a solid electrolyte (S310) by stirring a precursor containing lithium, phosphorus, and sulfur in a liquid state.

[0090] First, the precursor and solvent are prepared.

[0091] As a starting material for a solid electrolyte comprising lithium, phosphorus, and sulfur, the same precursor as the provided precursor may be used in the synthesis step of a pretreatment of a solid electrolyte according to the solid-state method described above.

[0092] The solvent is not particularly limited and can be freely used as long as it can provide an environment for the precursor to react through a liquid-phase reaction. For example, it may include at least one of tetrahydrofuran, acetonitrile, ethyl pentanoate, ethyl acetate, 1,2-dimethoxyethane, dimethyl carbonate, methyl propyl ketone, N-methylformamide, dimethyl sulfoxide, propylene carbonate, dichloromethane, N-methylmorpholine, 1,2-dimethoxyethane, acetone, anhydrous hydrrazine, pyridine, and anisole. Preferably, it may include at least one selected from the group consisting of acetonitrile, tetrahydrofuran, hexane, acetone, dimethyl ether, and ethyl acetate, and more preferably, it may include at least one selected from the group consisting of acetonitrile, tetrahydrofuran, and ethyl acetate.

[0093] Subsequently, a pretreatment material for a solid electrolyte is synthesized by mixing the prepared precursor and the solvent.

[0094] The above mixing is a method of synthesizing a pretreatment material of a solid electrolyte in a liquid state, and may be referred to as grinding or stirring.

[0095] The mixing device is not particularly limited as long as it is a device that allows the precursor to be well mixed in the solvent, and for example, heating mixing devices such as hot plates, ultrasonic mixing devices, ball mills, bead mills, planetary mixers, blade mixers, roll mills, kneaders, thin film rotary high-speed mixers, high-speed rotary stirring devices, and disc mills, etc., whichever device is capable of mixing in a liquid state can be appropriately selected.

[0096] The mixing step can be performed in a temperature range of 30°C to 70°C, preferably in a temperature range of 45°C to 55°C, but the temperature range during mixing can be freely selected based on the amount of precursor introduced, the amount of solvent, and the volume of the processing vessel, and is not limited thereto.

[0097] In addition, the mixing step can be carried out for an appropriate amount of time so that the product has a sufficiently small particle size and is formed sufficiently uniformly. For example, the mixing step can be carried out for 48 hours or more.

[0098] In some embodiments, after obtaining a pretreated solid electrolyte by a liquid phase method, a heat treatment step may be performed. In this case, the heat treatment step may be referred to as a drying step for removing the solvent from the obtained solid electrolyte. The heat treatment step may be performed at a temperature of 100°C to 500°C. If the temperature of the heat treatment step is below 100°C, the evaporation of the solvent may not be sufficient, and if the temperature of the heat treatment step exceeds 500°C, aggregation between solid electrolyte particles may occur, and the shape of the solid electrolyte particles may become non-uniform.

[0099] Meanwhile, if the step of providing a pretreatment material for a solid electrolyte according to the present invention includes the step of synthesizing a solid electrolyte according to a vapor phase method, the step of providing a pretreatment material for a solid electrolyte involves stirring a precursor containing lithium, phosphorus, and sulfur in a liquid state to form a mixed solution (S411), and synthesizing a pretreatment material for a solid electrolyte by spraying the formed mixed solution (S413).

[0100] The method of forming a mixed solution (S411) by mixing a precursor and a solvent may be the same as the method of preparing the mixed solution provided in the synthesis step (S310) of the pretreatment material of the solid electrolyte according to the liquid phase method described above.

[0101] After the preparation of the mixed solution is completed, for the synthesis of the pretreatment material of the solid electrolyte (S413), the mixed solution can first be atomized and sprayed.

[0102] A spray device may be used to form droplets. Any device capable of forming droplets may be used as the spray device. For example, ultrasonic spray devices, air nozzle spray devices, ultrasonic nozzle spray devices, filter expansion aerosol generators (FEAGs), electrostatic spray devices, etc. may be included.

[0103] Afterward, the sprayed droplets are heat-treated to synthesize a pre-treated solid electrolyte. The synthesis of the pre-treated solid electrolyte through heat treatment can be carried out at a temperature above 100°C. If the heat treatment temperature is below 100°C, the solvent may not evaporate sufficiently, making it difficult to grow solid electrolyte crystals.

[0104] In some embodiments, the synthesis of a pre-treated solid electrolyte through heat treatment can be carried out in an inert gas atmosphere such as CO, H2, N2, Ar, He, Ne, etc. Specifically, under the aforementioned inert gas atmosphere, the synthesis of a pre-treated solid electrolyte through heat treatment can be carried out by spraying a mixed solution at a temperature of 450°C or higher and 600°C or lower for 1 hour to 24 hours.

[0105] Referring again to FIG. 2, after synthesizing the pretreatment material of the solid electrolyte, a first heat treatment step (S220) may be performed before the solvent control step (S230) is performed.

[0106] The first heat treatment step (S220) can be performed to heal defects in the pretreated material of the solid electrolyte and to improve the degree of crystallinity. The physical properties and uniformity of the solid electrolyte after undergoing the first heat treatment step (S220) can be improved.

[0107] The first heat treatment step (S220) can be performed using a heat treatment device, and the heat treatment device is not particularly limited as long as it can perform heat treatment at a specific temperature. For example, a rotary kiln, a tube furnace, a batch oven, an electric furnace, a vacuum furnace, a lifting batch kiln, etc., may be used.

[0108] The heat treatment temperature may preferably be between 350°C and 480°C. If the heat treatment temperature is below 350°C, the halogen in the argyrodite-type crystal structure increases, and the crystal structure may become unstable. Additionally, if the heat treatment temperature exceeds 480°C, the crystal structure may become unstable as the halogen is released.

[0109] Afterwards, a solvent control step (S230) for removing residual solvent from the heat-treated solid electrolyte pretreatment material may be performed.

[0110] Through the first heat treatment step (S220), some of the solvent within the solid electrolyte may evaporate, but residual solvent may remain between the particles of the solid electrolyte. The method for manufacturing a solid electrolyte according to the present invention can further control the residual solvent of the pretreated material of the heat-treated solid electrolyte by performing a solvent control step (S230) after the first heat treatment step (S220).

[0111] The solvent control step (S230) may be substantially the same as the solvent control step described with reference to FIG. 1, and may be performed so that the residual solvent content in the solid electrolyte is greater than 100 ppmw and less than 500 ppmw.

[0112] FIG. 3 is a flowchart of a method for manufacturing a solid electrolyte according to another embodiment of the present invention.

[0113] The method for manufacturing a solid electrolyte of FIG. 3 is substantially the same as the method for manufacturing a solid electrolyte according to FIG. 2, except that the order of the solvent control step and the heat treatment step is reversed. Accordingly, redundant descriptions will be omitted.

[0114] First, as described with reference to FIG. 2, a pretreatment material of the solid electrolyte is synthesized (S210, S310, S410), and the residual solvent content in the pretreatment material of the solid electrolyte is controlled (S330).

[0115] The residual solvent content in the solid electrolyte pretreatment material can be controlled to be greater than 100 ppmw and less than 500 ppmw.

[0116] Afterwards, the pretreated solid electrolyte with controlled residual solvent is subjected to a second heat treatment (S340).

[0117] The second heat treatment step (S340) can be performed in substantially the same way as the first heat treatment step (S220) described with reference to FIG. 2. However, since the second heat treatment step (S340) of FIG. 3 is performed on a pre-treated solid electrolyte with controlled residual solvent, the temperature or time of the second heat treatment step (S340) can be controlled so that the residual solvent of the solid electrolyte is not reduced to less than 100 ppmw.

[0118] The method for manufacturing a solid electrolyte according to the present invention may perform a second heat treatment step (S340) after the solvent control step (S330). Accordingly, in the second heat treatment step (S340), problems such as carbonization of the solid electrolyte caused by residual solvent or issues affecting the color and electronic conductivity of the solid electrolyte powder can be prevented in advance.

[0119] FIG. 4 is a flowchart of a method for manufacturing a solid electrolyte according to another embodiment of the present invention.

[0120] The method for manufacturing a solid electrolyte of FIG. 4 is substantially the same as the method for manufacturing a solid electrolyte according to FIG. 2, except that a grinding step (S420) is added before the solvent control step (S430). Accordingly, redundant descriptions will be omitted.

[0121] First, as described with reference to FIG. 2, a pretreatment material of a solid electrolyte is synthesized (S210, S310, S410), and the pretreatment material of a solid electrolyte is crushed (S420).

[0122] The grinding step (S420) is a step of micronizing the pre-treated solid electrolyte to increase reactivity or forming particles of a certain size to make it suitable for subsequent processes, and may be a step of increasing the surface area by crushing or grinding the pre-treated solid electrolyte using mechanical force.

[0123] The grinding device used in the grinding step (S420) may be a ball mill, bead mill, vibratory mill, turbo mill, mechanofusion, disc mill, roll mill, etc. Among these, a ball mill and a bead mill may be suitable as grinding devices capable of efficiently generating impact energy. In addition, rotary and impact grinding devices, such as roll mills, rock drills, vibratory drills, and impact drivers, as well as high-pressure gliding rolls, roller-type male mills, or ball-type male mills, may be preferred as devices with excellent continuous productivity.

[0124] The grinding step (S420) can be performed to a size that optimizes the ion conductivity and chemical reaction efficiency of the pretreated solid electrolyte while ensuring there are no issues with physical properties. For example, the pretreated solid electrolyte can be ground to a D50 particle size of 0.5 μm or less.

[0125] However, if the material is ground into particles that are too small, handling the pre-treated solid electrolyte may be difficult, and when applied to a battery cell later, molding may be difficult due to poor aggregation.

[0126] Afterwards, the solvent in the pretreated solid electrolyte after the grinding step (S420) is completed can be controlled (S430).

[0127] Since the aforementioned grinding step (S420) can be performed in a wet state, residual solvent may remain between the particles of the solid electrolyte through the grinding step (S420). The method for manufacturing a solid electrolyte according to the present invention can further control residual solvent of the pretreated material of the heat-treated solid electrolyte by performing a solvent control step (S430) after the grinding step (S420).

[0128] The solvent control step (S430) may be substantially the same as the solvent control step described with reference to FIG. 1, and may be performed so that the residual solvent content in the solid electrolyte is greater than 100 ppmw and less than 500 ppmw.

[0129] Through the method described above, a solid electrolyte with controlled residual solvent content can be obtained, and an all-solid-state battery cell can be manufactured using this.

[0130] FIG. 5 is a conceptual diagram of the cross-sectional structure of a battery cell of the present invention. Specifically, FIG. 5(a) is a conceptual diagram of the cross-sectional structure of a battery cell composed of a positive electrode composite (510), a separator (520), and a negative electrode composite (530), and FIG. 5(b) is a conceptual diagram of the cross-sectional structure of a battery cell composed of a positive electrode (540), an electrolyte (550), a separator (560), and a negative electrode (570).

[0131] Referring to FIG. 5 (a), the positive electrode composite (510) is a composite that functions as a positive electrode in a battery cell.

[0132] The cathode composite may include a cathode active material, an electrolyte, a conductive material, and a binder, etc.

[0133] The cathode active material is a substance that inserts or emits ions at the cathode and can be composed of materials with high energy density and stability. For example, LiCoO2, LiFePO4, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, LiNiO2, Li4Ti5O 12 It can be LiFeMnPO4, etc.

[0134] The electrolyte constituting the anode composite (510) may be the solid electrolyte of the present invention.

[0135] The conductive material constituting the positive electrode composite (510) is not particularly limited as long as it is conductive without causing chemical changes in the battery cell. For example, carbon powder such as carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0136] The separator (520) may be a membrane capable of physically separating the positive electrode composite (510) and the negative electrode composite (530). Any membrane that prevents a fire or explosion caused by a short circuit resulting from contact between the positive electrode composite (510) and the negative electrode composite (530) may be used as the separator (520).

[0137] The cathode active material constituting the cathode composite (530) is a material that emits or inserts ions at the cathode and can be composed of a material that requires high charge capacity and fast charge speed. For example, it may be C (graphite or nanostructured carbon), Si, Li, LiX (lithium alloy), Nb2O5, P, etc.

[0138] The electrolyte constituting the cathode composite (530) is not particularly limited as long as it is a medium that moves ions to transmit current, and may be the same as the electrolyte constituting the anode composite (510).

[0139] The conductive material constituting the negative electrode composite (530) is not particularly limited as long as it is conductive without causing chemical changes in the battery cell, and may be the same as the conductive material constituting the positive electrode composite (510).

[0140] The positive electrode composite (510) and negative electrode composite (530) of the present invention may be collectively referred to as an electrode composite.

[0141] The porosity of the electrode composite of the present invention may be less than 20%. The porosity of the electrode composite may be greater than the porosity of the solid electrolyte. This is believed to be due to the difference in particle size of the aforementioned materials, as the electrode composite contains other materials such as an electrode active material, a conductive material, and a binder in addition to the solid electrolyte.

[0142] The density of the electrode composite of the present invention is 2.9 g / cm³ 3 It could be more than that.

[0143] Meanwhile, the battery cell of the present invention may be composed of a positive electrode (540), an electrolyte (550), a separator (560), and a negative electrode (570), as shown in FIG. 5 (b). The battery cell of FIG. 5 (b) may be substantially identical to the battery cell described in FIG. 5 (a), except that the positive electrode composite (510) is divided into the positive electrode (540) and the electrolyte (550) and the negative electrode composite (530) is divided into the negative electrode (570) and the electrolyte (550), compared to the battery cell of FIG. 5 (a).

[0144] Specifically, the positive electrode (540) may be an electrode made of the positive active material described in (a) of FIG. 5.

[0145] The separator (560) may be a membrane capable of physically separating the positive electrode (540) and the negative electrode (570).

[0146] The negative electrode (570) may be an electrode made of the negative active material described in Fig. 5 (a).

[0147] The electrolyte is a medium that moves ions to transmit electric current, and may be a layer made of the same material as the solid electrolyte described with reference to Figure 5 (a).

[0148] The battery cell of the present invention comprises a solid electrolyte in which the residual solvent content is controlled to be greater than 100 ppmw and less than 500 ppmw, thereby having excellent initial charge and discharge capacities and excellent Coulomb efficiency. For example, the first charge capacity of the battery cell of the present invention may be 218 mAh / g or more, the first discharge capacity may be 180 mAh / g or more, and the first Coulomb efficiency may be 80% or more. Here, the first Coulomb efficiency (%) refers to the value obtained by converting the value of [first discharge capacity (mAh / g) / first charge capacity (mAh / g)] into a percentage.

[0149] In addition, the battery cell of the present invention may have an excellent capacity retention rate. For example, the capacity retention rate (%) of the battery cell of the present invention may be 88% or higher. Here, the capacity retention rate (%) refers to a value converted into a percentage of [50th discharge capacity (mAh / g) / 1st discharge capacity (mAh / g)].

[0150] The excellent cell characteristics of the battery cell of the present invention are achieved by controlling the residual solvent content of the solid electrolyte. Below, the effect of improving the cell characteristics of the battery cell according to the solid electrolyte and the method of manufacturing the same according to the present invention will be explained in more detail through experimental examples.

[0151] <Preparation Example 1> Preparation of Solid Electrolyte

[0152] First, for Examples 1 to 8, 3.4497 g of Li2S and 55.6129 g of P2S were selected as the first precursor, ethyl acetate was selected as the first solvent, and the first precursor and the first solvent were mixed to prepare a first precursor solution. 1.7248 g of Li2S and 2.6502 g of LiCl were selected as the second precursor, ethanol was selected as the second solvent, and the second precursor and the second solvent were mixed to prepare a second precursor solution.

[0153] A mixed solution was prepared by mixing the first precursor solution and the second precursor solution described above. Subsequently, droplets were formed using the mixed solution, and then the droplets were sprayed into a heating furnace and heat-treated under the conditions of [Table 1] below to synthesize a pre-treated solid electrolyte. Subsequently, a solid electrolyte was obtained by controlling the solvent under the conditions of [Table 2] below.

[0154] Common Conditions Mixed Solution Heating Furnace Temperature: 200–300°C Carrier Gas Type: Nitrogen (N2) or Argon (Ar) Flow Rate: 5–20 L / min

[0155] Residual solvent (ppm) Example 1 19 Example 2 1 13 Example 3 2 47 Example 4 3 21 Example 5 4 23 Example 6 5 38 Example 7 6 21 Example 8 7 53

[0156]

[0157] <Experimental Example 1 - Calculation of Porosity of Solid Electrolyte>

[0158] First, the porosity of the solid electrolytes obtained in Examples 1 to 8 was measured. The porosity of a solid electrolyte is the ratio of empty voids within the solid, calculated by dividing the void volume by the total volume and converting it into a percentage. [Table 3] below shows the measured porosity of the solid electrolyte prepared according to Preparation Example 1.

[0159] Residual Solvent (ppm) Porosity (%) Example 1 196.36 Example 2 1133.31 Example 3 2473.24 Example 4 3213.01 Example 5 4232.42 Example 6 5382.89 Example 7 6213.31 Example 8 7532.95

[0160] As can be seen by referring to [Table 3], in Examples 2 to 8, when the residual solvent content exceeds 100 ppmw, the porosity of the solid electrolyte is maintained at 2% to 4%. In addition, in Example 1, the porosity of the solid electrolyte is 6% or higher. This is because, in Example 1, as the residual solvent content in the pre-treated material of the solid electrolyte is negligible at 19 ppmw, there is insufficient solvent to fill the pores between the particles of the pre-treated material of the solid electrolyte, and as a result, the porosity increases.

[0161]

[0162] <Experimental Example 2 - Measurement of Ionic Conductivity of Solid Electrolyte>

[0163] In order to compare and evaluate the ionic conductivity of the solid electrolyte of the present invention, the ionic conductivity was measured.

[0164] To evaluate ionic conductivity, electrochemical impedance spectra (EIS) were measured using an AC impedance spectroscopy instrument (Biologic SP-300). Measurements were conducted under conditions of a frequency of 1 Hz to 7 MHz and an AC amplitude of 20 mV. The measured impedance values ​​were analyzed using the EIS (Electrochemical impedance spectroscopy) method, Nyquist plot, and equivalent circuit. Additionally, ionic conductivity was measured using the following relationship based on the bulk resistance values ​​obtained from plotting and the dimensions of the LPSCl pellet produced through a pressurized cell.

[0165] σ = t / (A×R),

[0166] In this case, ionic conductivity (σ) refers to the thickness (t) of the pellet, the measured ionic resistance (R), and the area (A) of the pellet.

[0167] Table 4 below shows the ionic conductivity of solid electrolytes according to embodiments of the present invention.

[0168] Residual Solvent (ppm) Ionic Conductivity (mS / cm) Example 1 19 3.42 Example 2 11 3 3.38 Example 3 2 47 3.39 Example 4 3 2 13.45 Example 5 4 2 3 3.48 Example 6 5 38 3.11 Example 7 6 2 13.04 Example 8 7 5 32.89

[0169] As can be seen by referring to [Table 4], it can be observed that the ionic conductivity of the solid electrolytes in Examples 1 to 8 tends to increase as the residual solvent content of the solid electrolyte is controlled more. In particular, in Examples 1 to 5, where the residual solvent content was controlled to a level of less than 500 ppmw, a high ionic conductivity of 3.38 mS / cm or higher was observed. This suggests that as the residual solvent content is controlled more, the ionic conductivity improves as the hindrance to ion movement caused by the residual solvent decreases.

[0170]

[0171] <Experimental Example 3 - Measurement of Electronic Conductivity of Solid Electrolytes>

[0172] In order to compare and evaluate the electronic conductivity of the solid electrolyte of the present invention, the electronic conductivity was measured.

[0173] [Table 5] below shows the electronic conductivity of solid electrolytes according to embodiments of the present invention.

[0174] Residual solvent (ppm) Electronic conductivity (S / cm) Example 1 194.3 x 10⁻⁶ -9 Example 21131.8 x 10 -8 Example 32475.4 x 10 -8 Example 43219.1 x 10 -8 Example 54231.3 x 10 -7 Example 65388.6 x 10 -7 Example 76211.2 x 10 -6 Example 87535.8 x 10 -6

[0175] As can be seen by referring to [Table 5], the electron conductivity of the solid electrolytes of Examples 1 to 8 tends to increase as the solvent in the solid electrolyte is less controlled. This is believed to be because carbonization of the solid electrolyte is induced by the carbon component in the residual solvent within the solid electrolyte, and a large amount of carbonized material with high electron conductivity is produced, thereby increasing the electron conductivity.

[0176]

[0177] <Experimental Example 4 - SEM Measurement of Solid Electrolyte>

[0178] To compare the solid electrolytes obtained in Examples 1 to 5, particles were photographed using a scanning electron microscope (SEM).

[0179] The result is as shown in Fig. 6.

[0180] Figure 6 is a Scanning Electron Microscope (SEM) image of a solid electrolyte according to embodiments of the present invention.

[0181] As can be seen by referring to Figure 6 and [Table 3] of Experimental Example 1, it can be seen that in Example 1 (residual solvent controlled to less than 100 ppmw), a large amount of white areas presumed to be pores are observed compared to other examples. This suggests that in Example 1, as the residual solvent is controlled to less than 100 ppmw, the pores between the solid electrolyte particles are not well filled by the residual solvent. On the other hand, in Examples 2 to 5 (residual solvent controlled to greater than 100 ppmw and less than 500 ppmw), white areas are not well observed compared to Example 1 (residual solvent controlled to less than 100 ppmw). This is believed to be because, as the residual solvent in the solid electrolyte is controlled to greater than 100 ppmw and less than 500 ppmw, the pores between the solid electrolyte particles are filled by the residual solvent.

[0182]

[0183] <Manufacturing Example 2> Battery cell manufacturing

[0184] For Examples 1 to 8, battery cells containing a solid electrolyte prepared through Preparation Example 1 were manufactured. At this time, an electrode composite was prepared by mixing an electrode active material, a solid electrolyte, a conductive material, and a binder. Depending on the type of electrode active material, the electrode composite is divided into a positive electrode composite and a negative electrode composite, respectively, with a separator as the boundary.

[0185] In Preparation Example 2, NCM811 as the cathode active material, LPSCl as the solid electrolyte, and VGCF as the conductive material were mechanically mixed, and then mixed and dispersed in a heptane solvent to produce a slurry. Subsequently, the slurry was cast onto an aluminum current collector to produce a cathode composite. Here, NCM811 refers to a cathode active material prepared with a ratio of nickel, cobalt, and manganese elements of 8:1:1, LPSCl refers to a solid electrolyte composed of lithium, phosphorus, sulfur, and chlorine elements, and VGCF (Vapor-Grown Carbon Fiber) refers to a carbon fiber produced by a vapor phase method.

[0186]

[0187] <Experimental Example 5 - Calculation of Porosity of Electrode Composite>

[0188] The porosity was calculated for comparison of the electrode composite prepared according to Preparation Example 2.

[0189] To calculate the porosity of the electrode composite, the density of the electrode composite was first measured. Specifically, the density of the electrode composite was determined by taking a sample of the electrode composite of a specific area, measuring its mass and thickness, and subtracting the mass and thickness of the electrode composite substrate of the same area—namely, a metal such as copper or aluminum—from each of these values. The porosity of the electrode composite was calculated by subtracting the density of the electrode composite obtained from the sample of the specific area from the density of the electrode composite, dividing this value by the density of the electrode composite excluding the substrate, and converting the result into a percentage.

[0190] Table 6 below shows the porosity of the electrode composite according to the embodiments of the present invention.

[0191] Residual Solvent (ppm) Electrode Composite Porosity (%) Example 1 19 18.6 Example 2 113 16.8 Example 3 24 7 13.7 Example 4 32 112 Example 5 42 39.7 Example 6 53 814 Example 7 62 115.1 Example 8 75 315.4

[0192] As can be seen by referring to [Table 6], when the residual solvent content in the solid electrolyte is controlled to exceed 100 ppmw, the porosity of the electrode composite is maintained at less than 17%, and the packing efficiency of the electrode composite is excellent. In particular, in the case of Example 5 (controlled to a residual solvent of 423 ppmw), the porosity of the electrode composite is 9.7%, indicating the best packing efficiency. On the other hand, in the case of Example 1, the porosity increases as the solvent available to fill the voids between the solid electrolyte particles becomes insufficient. Additionally, when the solvent in the solid electrolyte is controlled to exceed 500 ppmw, the porosity saturates at the 15% level.

[0193]

[0194] <Experimental Example 6 - Measurement of Electrode Composite Density>

[0195] [Table 7] below shows the measured density of the electrode composite prepared according to Preparation Example 2.

[0196] Specifically, the method for measuring the density of the electrode composite involved taking a sample of the electrode composite of a specific area, measuring its mass and thickness, and obtaining the value by subtracting the mass and thickness of the electrode composite substrate of the same area, i.e., a metal such as copper or aluminum, from each of these values.

[0197] Residual solvent (ppm) Electrode complex density (g / cm³) 3 Example 1 19 2.85 Example 2 11 32.91 Example 3 24 7 3.02 Example 4 32 13.08 Example 5 42 33.16 Example 6 53 83.01 Example 76 212.97 Example 8 75 32.96

[0198] As can be seen by referring to [Table 7], as in Examples 2 to 5, when the residual solvent content in the solid electrolyte is controlled to be greater than 100 ppmw and less than 500 ppmw, the density of the electrode composite is 2.9 g / cm³ 3 It can be seen that it is maintained at an excessively high density. On the other hand, in the case of Example 1, where the solvent in the solid electrolyte is controlled to less than 100 ppmw, the density is 2.85 g / cm³. 3 It can be seen that... This is believed to be because the porosity increased and the density of the solid electrolyte decreased as the solvent capable of filling the voids between the solid electrolyte particles became insufficient. Accordingly, it is believed that the density of the electrode composite prepared containing the solid electrolyte also decreased. In particular, in the case of Example 5 (residual solvent controlled at 423 ppmw), the density of the electrode composite was 3.16 g / cm³ 3 As a result, it can be seen that it has a high density. In addition, when the solvent in the solid electrolyte is controlled to exceed 500 ppmw, the density of the solid electrolyte is 3 g / cm³. 3 It can be seen that it converges to.

[0199]

[0200] <Experimental Example 7 - 1st Coulomb Efficiency of Battery Cell>

[0201] Table 8 below measures the first charge capacity (mAh / g) and first discharge capacity (mAh / g) of the battery cell manufactured according to Manufacturing Example 2. Here, the first Coulomb efficiency (%) refers to the value of [first discharge capacity (mAh / g) / first charge capacity (mAh / g)] converted into a percentage.

[0202] Figure 7 shows the first discharge capacity (mAh / g) measurement result of a battery cell manufactured using a solid electrolyte according to embodiments of the present invention.

[0203] Residual Solvent (ppm) 1st Charge Capacity (mAh / g) 1st Discharge Capacity (mAh / g) 1st Coulomb Efficiency (%) Example 1 19 219.9 174.3 79.3 Example 2 113 218.2 180.8 82.8 Example 3 24 7218.3 181.1 82.9 Example 4 3 212 20.5 184.6 83.7 Example 5 4 23 21.6 186.3 84.1 Example 6 5 38 215.4 154.1 71.6 Example 7 6 212 18.3 158.1 72.4 Example 8 7 53 215.8 150.4 69.7

[0204] As can be seen by referring to [Table 8], the battery cells of Examples 2 to 5 exhibit a high first charge capacity of 218 mAh / g or higher and a high first discharge capacity of 180 mAh / g or higher as the solvent in the solid electrolyte is controlled to be greater than 100 ppmw and less than 500 ppmw, thereby maintaining a good first Coulomb efficiency of greater than 82%. This is believed to be a phenomenon resulting from the residual solvent in the solid electrolyte being controlled to an appropriate content. Specifically, since the residual solvent content of the solid electrolytes of Examples 2 to 5 is controlled to a certain level (controlled to be greater than 100 ppmw), the voids between the solid electrolyte particles are sufficiently filled and an excellent filling rate can be maintained. Furthermore, since the residual solvent in the solid electrolyte is sufficiently low (controlled to be less than 500 ppmw), the carbonization phenomenon of the solid electrolyte caused by carbon components in the residual solvent can be suppressed, and it is believed that this is realized as the first charge capacity and discharge capacity of the battery cell. Accordingly, it is believed that the first Coulomb efficiency of the battery cell is excellent.

[0205] On the other hand, in the case of Example 1, where the solvent in the solid electrolyte is controlled to less than 100 ppmw, it can be seen that the first charge capacity is 219.9 mAh / g and the first discharge capacity is 174.3 mAh / g, and the first Coulomb efficiency is 79.3%, which is lower than that of Examples 2 to 5. This is believed to be because the solid electrolyte in Example 1 has an excessively low residual solvent content, which increases the porosity. Specifically, as the solvent capable of filling the voids between the solid electrolyte particles becomes insufficient, the porosity increases and the filling rate decreases, which is believed to cause the first charge capacity and discharge capacity of the battery cell to drop, and the first Coulomb efficiency to drop.

[0206] Meanwhile, in Examples 6 to 8 (residual solvent controlled to exceed 500 ppmw), where the solvent in the solid electrolyte is controlled to exceed 500 ppmw, it can be seen that the first charge capacity exceeds 215 mAh / g, and with reference to FIG. 7, the first discharge capacity has a value of less than 159 mAh / g, and the first Coulomb efficiency is less than 73%, indicating a lower first Coulomb efficiency compared to Examples 2 to 5. This is believed to be due to the carbonization phenomenon of the solid electrolyte caused by an excess of residual solvent in the solid electrolyte. Specifically, the solid electrolyte may be carbonized due to carbon components in the residual solvent. Consequently, in a battery cell manufactured with the above solid electrolyte, the generation or movement of ions is inhibited by the carbonized material, and the ion conductivity may decrease. Accordingly, it is believed that the first discharge capacity of the battery cell decreases and the first Coulomb efficiency decreases.

[0207]

[0208] <Experimental Example 8 - Capacity Retention Rate of Battery Cells>

[0209] Table 9 below measures the 1st discharge capacity (mAh / g) and 50th discharge capacity (mAh / g) of the battery cell manufactured according to Manufacturing Example 2. Here, the capacity retention rate (%) refers to the value converted into a percentage of [50th discharge capacity (mAh / g) / 1st discharge capacity (mAh / g)].

[0210] Figure 8 shows the results of measuring the discharge capacity (%) according to the number of charge and discharge cycles of a battery cell manufactured using a solid electrolyte according to embodiments of the present invention.

[0211] Residual Solvent (ppm) 1st Cycle Discharge Capacity (mAh / g) 50th Cycle Discharge Capacity (mAh / g) Capacity Retention Rate (%, @ 50 cycle) Example 1 19 174.1 163.9 94.1 Example 2 113 179.8 171.8 95.6 Example 3 24 7180.4 170 94.2 Example 4 3 21184 175.1 95.2 Example 5 4 23 185.4 178.7 96.4 Example 6 5 38154.3 135.2 87.6 Example 7 6 21156.2 134.7 86.2 Example 8 7 53 150.2 127.8 85.1

[0212] As can be seen by referring to [Table 9] and Fig. 8, the battery cells of Examples 2 to 5 exhibit a high first discharge capacity of 179 mAh / g or higher and a high 50th discharge capacity of 170 mAh / g or higher as the solvent in the solid electrolyte is controlled to be greater than 100 ppmw and less than 500 ppmw, thereby maintaining a good capacity retention rate of 94.2% or higher. This is believed to be a phenomenon resulting from the residual solvent in the solid electrolyte being controlled to an appropriate content. Specifically, since the residual solvent content of the solid electrolytes of Examples 2 to 5 is controlled to a specific content, they can be filled with a sufficiently excellent density when implemented as an electrode composite, and this is believed to have been realized as the first discharge capacity of the battery cell. In addition, since the residual solvent in the solid electrolyte is sufficiently low, side reactions caused by the residual solvent can be suppressed even when the battery cell is used for a long time. Since the residual solvent in the solid electrolyte has a constant content exceeding 100 ppmw, even if the positive electrode active material expands due to repeated use of the battery cell, the residual solvent can alleviate or absorb the stress caused by the expansion of the positive electrode active material, thereby suppressing the occurrence of defects in the solid electrolyte and maintaining the 50th discharge capacity at a constant level. Accordingly, the capacity retention rate of the battery cell can be maintained excellently.

[0213] On the other hand, in the case of Example 1, where the solvent in the solid electrolyte is controlled to less than 100 ppmw, it can be seen that the 1st discharge capacity is 174.1 mAh / g and the 50th discharge capacity is 163.9 mAh / g, indicating a lower capacity retention rate compared to Examples 2 to 5. This is believed to be because the mechanical properties of the solid electrolyte in Example 1 deteriorate during repeated charge-discharge cycles due to the excessively low residual solvent content. Specifically, as repeated charge-discharge cycles proceed, volume expansion of the cathode active material is induced, and this volume expansion of the cathode active material can induce continuous stress in the solid electrolyte within the electrode composite. Since the residual solvent content of the solid electrolyte in Example 1 is less than 100 ppmw, the material properties are relatively brittle, and defects within the solid electrolyte can be easily induced due to stress caused by the volume expansion of the cathode active material. It is believed that such defects can hinder ion movement within the electrode complex and reduce the capacity retention rate of the battery cell.

[0214] Meanwhile, as charging and discharging progress, in Examples 6 to 8 (residual solvent controlled to exceed 500 ppmw), it can be observed that the discharge capacity decreases steeply. Since the 1st discharge capacity is less than 157 mAh / g and the 50th discharge capacity is less than 136 mAh / g, it can be seen that the capacity retention rate has a value of less than 88%. This is believed to be a phenomenon caused by side reactions resulting from an excess of residual solvent in the solid electrolyte in the case of Examples 6 to 8, where the solvent in the solid electrolyte is controlled to exceed 500 ppmw. Specifically, it is believed that when charging and discharging are repeated for a long time, side reactions caused by residual solvent may occur, and the generation or movement of ions is hindered by the side reaction products, thereby reducing the capacity retention rate of the battery cell.

[0215] As described above, the solid electrolyte of the present invention contains an appropriate amount of residual solvent, thereby providing sufficient residual solvent to fill the voids and increasing the filling rate. Accordingly, the realization of capacitance in the battery cell can be facilitated. Furthermore, the phenomenon of carbonization of the solid electrolyte due to carbon components in the residual solvent of the solid electrolyte can be suppressed. Therefore, as the generation or movement of ions is not hindered by carbonized material and becomes easier, ion conductivity increases, and the realization of capacitance can be facilitated.

[0216] Since the solid electrolyte of the present invention contains an appropriate amount of residual solvent, defects caused by stress due to volume expansion of the cathode active material can be prevented even as repeated charge-discharge cycles proceed. Accordingly, interference with ion movement caused by defects can be minimized. Furthermore, side reactions in the residual solvent within the solid electrolyte that may occur during repeated charge-discharge cycles are minimized, and inhibition of ion generation or interference with movement by side reaction products can be minimized. Consequently, a high capacity retention rate can be maintained despite repeated charge-discharge cycles.

[0217] Meanwhile, since the solid electrolyte of the present invention contains an appropriate amount of residual solvent, the mechanical properties of the solid electrolyte can be improved by the residual solvent. That is, since an appropriate residual solvent within the solid electrolyte can absorb or relieve stress, the toughness of the material can be improved. In addition, since the pores within the solid electrolyte can be filled by the residual solvent, the filling rate of the solid electrolyte is improved, and the overall capacity of the battery cell can be enhanced.

[0218] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0219] The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

[0220] The present invention is a method for manufacturing a sulfide electrolyte and can be widely utilized in industries where secondary batteries are used. For example, the present invention can be widely used in small electronic devices as well as medium-to-large devices such as electric vehicles, and can be applied to various fields such as home appliances, medical devices, robots, aerospace, energy storage systems, wearable devices, IoT devices, etc.

Claims

1. Contains lithium, phosphorus, and sulfur, Residual solvent content greater than 100 ppmw and less than 500 ppmw, Solid electrolyte.

2. In Paragraph 1, The above solid electrolyte is Li a P b S c X d A solid electrolyte characterized by having the composition of (where X is a Group 17 element and 0 <a≤10, 0<b≤10, 0<c≤15 및 0<d≤20 임) 3. A step of providing a solid electrolyte pretreatment material that provides a solid electrolyte pretreatment material including lithium, phosphorus, and sulfur; and It includes a solvent control step for controlling the solvent content of the pretreated material of the above-mentioned solid electrolyte, and The solvent control step is performed such that the solvent content of the pretreated material is greater than 100 ppmw and less than 500 ppmw. Method for manufacturing solid electrolyte.

4. In Paragraph 3, The above step of providing a solid electrolyte pretreatment material is, A solid-state synthesis step comprising synthesizing a pretreatment product of the solid electrolyte by stirring the precursor containing the lithium, phosphorus, and sulfur in a solid state. Method for manufacturing solid electrolyte.

5. In Paragraph 3, The above step of providing a solid electrolyte pretreatment material is, A liquid-phase synthesis step comprising synthesizing a pretreatment product of the solid electrolyte by stirring the precursor containing the lithium, phosphorus, and sulfur in a liquid state. Method for manufacturing solid electrolyte.

6. In Paragraph 3, The above step of providing a solid electrolyte pretreatment material is, A mixed solution forming step of forming a mixed solution of the precursors by stirring the precursors containing the lithium, phosphorus, and sulfur in a liquid state; and A gas phase synthesis step comprising synthesizing the solid electrolyte pretreatment product by spraying the above mixed solution, Method for manufacturing solid electrolyte.

7. In Paragraph 3, After the step of providing the solid electrolyte pretreatment material mentioned above, The above-mentioned solid electrolyte pretreatment material further includes a first heat treatment step in which it crystallizes, and The solvent control step is performed after the first heat treatment step, Method for manufacturing solid electrolyte.

8. In Paragraph 3, After the above solvent control step, A second heat treatment step in which the pretreatment material of the solvent-controlled solid electrolyte is crystallized is further included. Method for manufacturing solid electrolyte.

9. In Paragraph 3, After the above-mentioned solid electrolyte pretreatment step, The method further includes a grinding step in which the pretreated material of the above-mentioned solid electrolyte is micronized, and The above solvent control step is performed after the above grinding step, Method for manufacturing solid electrolyte.

10. An electrode composite comprising an electrode active material and a solid electrolyte, and The above solid electrolyte has a residual solvent content of more than 100 ppmw and less than 500 ppmw, Battery cell.

11. In Paragraph 10, The above electrode composite has a porosity of 20% or less, Battery cell.

12. In Paragraph 10, The density of the above electrode composite is 2.9 g / cm³ 3 Lee Sang-in, Battery cell.

13. In Paragraph 10, The first Coulomb efficiency, which is the ratio of the first discharge capacity (mAh / g) to the first charge capacity (mAh / g) of the battery cell manufactured from the above electrode composite, is 80% or higher, Battery cell.

14. In Paragraph 10, When the battery cell manufactured from the above electrode composite has been charged and discharged 50 times, A capacity retention rate (%) of 88% or higher, which is the ratio of the 50th discharge capacity (mAh / g) to the 1st discharge capacity (mAh / g), Battery cell.

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