Method for preparing all-solid-state electrolyte and secondary battery using same

Abstract

The present invention relates to a method for preparing a ceramic solid electrolyte, the method comprising: a liquid precursor preparation step of preparing a liquid precursor slurry by introducing, into a co-precipitation reactor, a La(NO3)3‧6H2O aqueous solution and a ZrOCl2‧8H2O aqueous solution together with a complexing agent and a pH adjusting agent and performing a co-precipitation reaction at 20-40°C for 2-5 hours; a liquid precursor drying step of drying the liquid precursor slurry at 110-130°C for 22-26 hours; a solid precursor preparation step of mixing the dried precursor with a doping agent capable of providing a dopant selected from Al, Ga, Nb, and Ta and a lithium source capable of providing lithium and performing a solid-phase reaction to prepare a solid-phase precursor; and a solid-phase precursor sintering step of sintering the solid-phase precursor at 800-1200°C for 2-4 hours to prepare a ceramic solid electrolyte.

Description

Method for manufacturing an all-solid-state electrolyte and a secondary battery utilizing the same

[0001] The present invention relates to a method for manufacturing an all-solid-state electrolyte. More specifically, the present invention relates to a method for manufacturing a ceramic solid electrolyte (also simply referred to as a "ceramic electrolyte"). According to the method for manufacturing a ceramic solid electrolyte of the present invention, a ceramic solid electrolyte having a uniform particle size, a uniform shape, and high ionic conductivity can be obtained. A secondary battery utilizing the ceramic solid electrolyte of the present invention has a high energy density, a long lifespan, and improved stability.

[0002] Liquid electrolytes remain the most widely used electrolyte for lithium-ion secondary batteries. These batteries are assembled by placing a separator between the positive and negative electrodes, then injecting the liquid electrolyte into this assembly. Liquid electrolyte secondary batteries have the advantage of high ionic conductivity. However, they also have the disadvantages of being prone to explosion and leakage. Solid electrolyte secondary batteries are designed to overcome these drawbacks. Solid electrolytes can be broadly categorized into polymer electrolytes and ceramic electrolytes.

[0003] Polymer electrolytes are electrolytes that transport ions through the movement of polymer segments. Initially, attempts were made to use pure polymers. However, the ionic conductivity of polymers was so low that a polymer electrolyte made from pure polymers could not replace a liquid electrolyte. Therefore, research is being conducted to maximize the liquid electrolyte content in polymer electrolytes to increase their low ionic conductivity while minimizing problems such as explosion or leakage.

[0004] Initially, research was conducted to determine which polymers and which liquid electrolytes would work best together. Then, by mixing a small amount of ceramic particles into a polymer electrolyte, either embedding the ceramic particles within the polymer or allowing the ceramic particles to exist between the polymers, creating microscopic holes, grooves, or gaps in the polymer, and then adding a liquid electrolyte, it was discovered that the polymer electrolyte could contain significantly more liquid electrolyte than when the liquid electrolyte was added to the polymer electrolyte without mixing the ceramic particles, while also resolving some of the problems of explosion and leakage. Another attempt to maximize the inclusion of liquid electrolyte in polymer electrolytes led to the development of gel polymer electrolytes. Gel polymer electrolytes are a swelling polymer in which the liquid electrolyte is embedded within the three-dimensional structure of a cross-linkable polymer. There have also been attempts to mix ceramic particles into gel polymer electrolytes to increase the inclusion of liquid electrolyte in the gel polymer.

[0005] Ceramic electrolytes utilize the principle of ion migration between ceramic particles in contact. Research into ceramic electrolytes has focused on developing new ceramic materials with high ionic conductivity that can replace liquid electrolytes. Ceramic electrolytes are produced using either solid-state or wet methods. The solid-state method involves mixing the starting materials for the ceramic electrolyte in a solid state and repeatedly sintering them. Wet methods include spray pyrolysis and coprecipitation. Spray pyrolysis involves dissolving the raw materials in a solvent, spraying them into fine droplets, evaporating the solvent, and pyrolyzing the precipitated precursor to obtain ceramic particles. Coprecipitation involves simultaneously precipitating multiple ions from an aqueous or non-aqueous solution. Specifically, coprecipitation involves mixing the starting materials for the ceramic electrolyte, dissolving them in water or a non-aqueous solvent, adding a complexing agent and a pH regulator, and coprecipitating the starting materials. The coprecipitated precipitate is then dried to produce the ceramic electrolyte.

[0006] Ceramic electrolytes are typically manufactured using either the solid-state method (dry method) or the wet method. Both the solid-state and wet methods have their advantages and disadvantages, including production costs, yields, electrolyte properties, and battery characteristics. The solid-state method offers the advantages of simple manufacturing, low manufacturing costs, and high reproducibility. However, the solid-state method has drawbacks: it is difficult to form a solid solution of solid phases, many impurities are introduced when mixing solid phases, particle size control is difficult, high temperatures are required, and the manufacturing process takes a long time. Among wet methods, the coprecipitation method offers the advantage of controlling the constituent elements of the ceramic electrolyte down to the atomic scale and producing uniform, spherical particles. However, the coprecipitation method has drawbacks: if the amount of coprecipitant and the control of the reaction environment are uncertain, non-uniform coprecipitation results in a powder mixture rather than a compound, making mass production difficult.

[0007] The present invention provides a novel manufacturing method for producing a ceramic electrolyte using both a co-precipitation method and a solid-state method. The manufacturing method of the present invention can overcome the shortcomings of the conventional solid-state method or co-precipitation method by producing a primary precursor by a co-precipitation method and a secondary precursor by a solid-state method. Specifically, the present invention comprises: producing a precipitate of a primary precursor by a co-precipitation method; washing, drying, and pulverizing the precipitate to produce a primary precursor powder; mixing the primary precursor powder with a lithium source powder and a dopant powder to produce a secondary precursor powder; and heat-treating the secondary precursor powder to produce a final ceramic electrolyte. The co-precipitation method can be performed using a Couette-Taylor reactor. The dopant added to the primary precursor may be Ga, Nb, Sn, Al, Ta, or the like.

[0008] According to the present invention, a primary precursor having a stable and intended stoichiometric ratio is prepared through a co-precipitation method, and then a lithium source, an electrolyte, and a dopant for improving battery characteristics are added through a solid-state method to prepare a secondary precursor, thereby producing an electrolyte having a stable structure and high purity. According to the present invention, an all-solid-state electrolyte layer can be made thin, dense, and has a void-free structure. According to the present invention, a secondary battery having high energy density, long life, high output, and safety can be manufactured. According to the present invention, the interface between the all-solid-state electrolyte layer and the positive electrode layer and the interface between the all-solid-state electrolyte layer and the negative electrode layer can be easily removed, and dendrite control is possible. According to the present invention, a secondary battery having excellent cycle life characteristics and rate characteristics can be manufactured.

[0009] Figure 1 is a graph showing the capacity retention rate during 60 cycles of charging and discharging of the secondary batteries of Example 3, Comparative Example 3, and Comparative Example 7 at a charging rate of 0.2 C and a discharging rate of 1.0 C.

[0010] Figure 2 is a graph showing the change in specific capacity during 18 charge / discharge cycles, 3 times each, of the secondary batteries of Example 3, Comparative Example 3, and Comparative Example 7 sequentially at a charge / discharge rate of 0.2C, a charge / discharge rate of 0.5C, a charge / discharge rate of 1.0C, a charge / discharge rate of 2.0C, a charge / discharge rate of 3.0C, and finally a charge / discharge rate of 0.2C.

[0011] Figure 3 is a graph showing the results of crystal phase analysis of the ceramic solid electrolyte of Example 3 and Comparative Example 3 using X-ray diffraction (XRD).

[0012] Figures 4, 5, and 6 are graphs showing the particle size distribution of the ceramic solid electrolytes of Example 3, Comparative Example 3, and Comparative Example 7 measured using a PSA particle size analyzer.

[0013] Figures 7, 8, and 9 are SEM photographs of the surfaces of the ceramic solid electrolytes of Example 2, Comparative Example 2, and Comparative Example 6, magnified 10,000 times.

[0014] According to the present invention, a lithium lanthanum zirconium oxide (LLZO) oxide all-solid electrolyte having a garnet structure containing at least one type of Al, Ga, Nb, Sn, and Ta dopant can be manufactured. First, a primary precursor (LZO precursor) can be synthesized by a co-precipitation method. The synthesized primary precursor can be washed and dried to obtain a primary precursor powder. Subsequently, the primary precursor powder can be mixed with a Li source and a dopant in a solid state to produce a secondary precursor powder. The ceramic electrolyte of the present invention can be manufactured by heat-treating the secondary precursor powder at a high temperature to sinter the secondary precursor powder.

[0015] One aspect of the present invention is a method for manufacturing a new ceramic solid electrolyte. This method comprises a liquid precursor manufacturing step of introducing an aqueous solution of lanthanum (III) nitrate hexahydrate (La(NO3)3ㆍ6H2O) and an aqueous solution of zirconyl chloride octahydrate (ZrOCl2ㆍ8H2O) into a co-precipitation reactor together with a complexing agent and a pH regulator and performing a co-precipitation reaction at 20℃-40℃ for 2-5 hours to manufacture a liquid precursor slurry.

[0016] A liquid precursor drying step of drying the above liquid precursor slurry at 110°C-130°C for 22-26 hours,

[0017] A solid-state precursor manufacturing step of manufacturing a solid-state precursor by mixing a dopant capable of providing a dopant selected from Al, Ga, Nb, and Ta and a lithium source capable of providing lithium to the dried precursor and performing a solid-state reaction, and

[0018] A solid precursor firing step for producing a ceramic solid electrolyte by firing the above solid precursor at 800°C-1,200°C for 2-4 hours.

[0019] may include.

[0020] The temperature of the above coprecipitation reaction may be 20-25°C, 20-30°C, 20-35°C, 25-30°C, 25-35°C, 25-40°C, 30-35°C, 30-40°C, or 35-40°C depending on the substance. The coprecipitation reaction time may be 2 hours-3 hours, 2 hours-4 hours, 2 hours-5 hours, 3 hours-4 hours, 3 hours-5 hours, or 4 hours-5 hours depending on the substance. The temperature at which the above liquid precursor slurry is dried may be 110°C-115°C, 110°C-120°C, 110°C-125°C, 110°C-130°C, 115°C-120°C, 115°C-125°C, 115°C-130°C, 120°C-125°C, 120°C-130°C, depending on the material.

[0021] Another aspect of the present invention is characterized in that the solid precursor in the method for manufacturing the ceramic solid electrolyte is a material represented by the following chemical formula.

[0022] Li x X y La z Zr p O 12

[0023] In the above formula, X is Al, Ga, Nb or Ta. In the above formula, 5≤x≤6, 5≤x≤7, 5≤x≤8, 5≤x<9, 6≤x≤7, 6≤x≤8, 6≤x<9, 7≤x≤8, 7≤x<9, 8≤x<9. In the above formula, 0 <y≤1일 수 있다. 상기 식에서 2≤z≤3, 2≤z≤4, 3≤z≤4일 수 있다. 상기 식에서 1≤p≤2, 1≤p≤3, 2≤p≤3일 수 있다.

[0024] Another embodiment of the present invention is characterized in that the lithium source and the doping agent are mixed in a ratio of 5-6:0-1, 5-7:0-1, 5-8:0-1, 5-9:0-1 in the method for manufacturing the ceramic solid electrolyte.

[0025] Another embodiment of the present invention is characterized in that, in the method for producing the ceramic solid electrolyte, the pH adjusting agent is NaOH, and the pH adjusting agent is introduced into a co-precipitation reactor to adjust the pH of the co-precipitation reactor to 10-12. The pH of the co-precipitation reactor may be 10-11, 10-12, or 11-12.

[0026] Another embodiment of the present invention is characterized in that, in the method for producing the ceramic solid electrolyte, the complexing agent is NH4OH, and the complexing agent is introduced into the co-precipitation reactor at a weight ratio of 150-160, 150-170, 150-180, 160-170, 160-180, or 170-180 with respect to 100 parts by weight of an aqueous solution of lanthanum (III) nitrate hexahydrate (La(NO3)3ㆍ6H2O) and an aqueous solution of zirconyl chloride octahydrate (ZrOCl2ㆍ8H2O).

[0027] Another aspect of the present invention is a method for manufacturing a novel secondary battery. This manufacturing method

[0028] A liquid precursor manufacturing step in which an aqueous solution of lanthanum (III) nitrate hexahydrate (La(NO3)3ㆍ6H2O) and an aqueous solution of zirconyl chloride octahydrate (ZrOCl2ㆍ8H2O) are introduced into a co-precipitation reactor together with a complexing agent and a pH regulator, and a co-precipitation reaction is performed at 20℃-40℃ for 2-5 hours to manufacture a liquid precursor slurry.

[0029] A liquid precursor drying step of drying the above liquid precursor slurry at 110°C-130°C for 22-26 hours,

[0030] A solid-state precursor manufacturing step of manufacturing a solid-state precursor by mixing a dopant capable of providing a dopant selected from Al, Ga, Nb, and Ta and a lithium source capable of providing lithium to the dried precursor and performing a solid-state reaction,

[0031] A solid precursor firing step for producing a ceramic solid electrolyte by firing the above solid precursor at 800°C-1,200°C for 2-4 hours,

[0032] A step for manufacturing a ceramic solid electrolyte sheet by mixing the above ceramic solid electrolyte with a polymer electrolyte in a weight ratio of 60-90:10-40 and manufacturing it in the form of a sheet, and

[0033] A secondary battery manufacturing step for manufacturing a secondary battery by placing and laminating the above ceramic solid electrolyte sheet between the positive and negative electrodes.

[0034] It is characterized by including.

[0035] The temperature of the above coprecipitation reaction may be 20-25°C, 20-30°C, 20-35°C, 25-30°C, 25-35°C, 25-40°C, 30-35°C, 30-40°C, or 35-40°C depending on the substance. The coprecipitation reaction time may be 2 hours-3 hours, 2 hours-4 hours, 2 hours-5 hours, 3 hours-4 hours, 3 hours-5 hours, or 4 hours-5 hours depending on the substance. The temperature at which the above liquid precursor slurry is dried may be 110°C-115°C, 110°C-120°C, 110°C-125°C, 110°C-130°C, 115°C-120°C, 115°C-125°C, 115°C-130°C, 120°C-125°C, 120°C-130°C, depending on the material.

[0036] The mixing ratio of the above ceramic solid electrolyte and the above polymer electrolyte is 60-70:10-20, 60-70:10-30, 60-70:10-40, 60-70:20-30, 60-70:20-40, 60-70:30-40, 60-80:10-20, 60-80:10-30, 60-80:10-40, 60-80:20-30, 60-80:20-40, 60-80:30-40, 60-90:10-20, 60-90:10-30, 60-90:10-40, 60-90:20-30, 60-90 : 20-40, 60-90 : 30-40, 70-80 : 10-20, 70-80 : 10-30, 70-80 : 10-40, 70-80 : 20-30, 70-80 : 20-40, 70-80 : 30-40, 70-90 : 10-20, 70-90 : 10-30, 70-90 : 10-40, 70-90 : 20-30, 70-90 : 20-40, 70-90 : 30-40, 80-90 : 10-20, 80-90 : 10-30, 80-90 : 10-40, 80-90 : 20-30, It could be 80-90:20-40, 80-90:30-40.

[0037] Another embodiment of the present invention is a method for manufacturing a secondary battery, wherein the polymer electrolyte is a polyvinylidene fluoride (PVdF)-based polymer or a copolymer thereof, a poly[(vinylidene fluoride-co-trifluoroethylene]-based polymer or a copolymer thereof, a polyethylene glycol (PEO)-based polymer or a copolymer thereof, a polyacrylonitrile (PAN)-based polymer or a copolymer thereof, a poly(methyl methacrylate) (PMMA)-based polymer or a copolymer thereof, a polyvinyl chloride-based polymer or a copolymer thereof, a polyvinylpyrrolidone (PVP)-based polymer or a copolymer thereof, a polyimide (PI)-based polymer or a copolymer thereof, a polyethylene (PE)-based polymer or a copolymer thereof, a polyurethane (PU)-based polymer or a copolymer thereof, a polypropylene (PP)-based polymer or a copolymer thereof, a poly(propylene oxide) (PPO)-based polymer or a copolymer thereof, a poly(ethylene imine) (PEI)-based polymer or a copolymer thereof, a poly(ethylene It is characterized by being a poly(ethylene succinate) (PES)-based or copolymer thereof, a poly(vinyl acetate) (PVAc)-based or copolymer thereof, a poly(ethylene succinate) (PESc)-based or copolymer thereof, a polyester-based or copolymer thereof, a polyamine-based or copolymer thereof, a polysulfide-based or copolymer thereof, a siloxane-based or copolymer thereof, a styrene butadiene rubber (SBR)-based or copolymer thereof, a carboxymethyl cellulose (CMC)-based or copolymer thereof, or a derivative thereof, or a combination thereof.

[0038] Another aspect of the present invention is a secondary battery manufactured using the method for manufacturing the secondary battery.

[0039] A method for synthesizing the above-mentioned primary precursor by co-precipitation is described in detail. First, the starting material is dissolved in distilled water to create an aqueous starting material solution. The starting material consists of a lanthanum source and a zirconium source. The lanthanum source is, for example, La(NO3). 3ㆍ 6H2O, and the zirconium source is ZrOCl 2ㆍIt can be 8H2O. Next, prepare a complexing agent, and mix the starting material aqueous solution and the complexing agent in a co-precipitation reactor to co-precipitate the starting material and the complexing agent. For example, ammonia water (NH4OH) can be used as the complexing agent. And, as a pH adjuster for controlling the pH of the reactor, an aqueous sodium hydroxide solution prepared by dissolving sodium hydroxide (NaOH) powder in distilled water can be used. The pH of the co-precipitation reactor can be controlled to a level of 9-13, 10-13, 11-13, 12-13, 9-12, 10-12, 11-12, 9-11, or 10-11. Even after the co-precipitation reaction is completed, the impeller inside the co-precipitation reactor can continue to rotate to perform additional stirring for a certain period of time. The primary precursor thus produced can be washed, dried, and pulverized to produce primary precursor powder. For example, the precipitate produced in the coprecipitation reaction can be washed with distilled water, and this washing can be performed multiple times until the pH reaches 7-8. The washed precipitate can be dried overnight in a dryer to produce the primary precursor powder. The drying temperature can be set to 100-150°C, 110-140°C, or 120-130°C. The primary precursor powder does not yet contain Li. The coprecipitation process can be performed in a Couette-Taylor reactor. The coprecipitation process can also be performed using a homogenizer or a planetary mixer.

[0040] The solid-state method of the present invention is a process for introducing lithium into a primary precursor powder. The primary precursor powder and the lithium source powder are measured at a certain ratio and then uniformly mixed using, for example, a planetary ball mill or a double cone mixer to form a secondary precursor powder. The secondary precursor powder is heat-treated at a high temperature and sintered to obtain a final ceramic electrolyte. The sintering temperature can be any temperature between 600 and 1,200°C. The sintering temperature can be, for example, 600°C, 700°C, 800°C, 900°C, 1,000°C, 1,100°C, or 1,200°C. The crystal structure of the ceramic electrolyte can vary depending on the sintering temperature. The sintering time can be any time between 2 and 4 hours. The sintering time can be, for example, 2 hours, 3 hours, or 4 hours. The preferred firing method is a conventional firing method using a conventional heating element. The fired ceramic electrolyte can be finely divided into particles using a ball mill, air jet mill, fluidized bed jet mill, cutter mill, or other similar equipment. The use of an air jet mill is preferred.

[0041] An electrolyte sheet can be made by mixing 10-40 wt% of a polymer electrolyte with 60-90 wt% of the ceramic electrolyte powder of the present invention manufactured in this way. The amount of the ceramic electrolyte powder can be 60-80 wt%, 60-70 wt%, 70-80 wt%, 70-90 wt%, or 80-90 wt%. The amount of the polymer electrolyte can be 20-40 wt%, 30-40 wt%, 20-30 wt%, 10-30 wt%, or 10-20 wt%.

[0042] Separately from the above electrolyte sheet, a cathode layer sheet and a cathode layer sheet can be manufactured. The cathode layer sheet may be a sheet in which an NCM cathode active material layer is formed on an Al current collector. The cathode layer sheet may be a sheet in which a Li-metal anode active material layer is formed on a Cu current collector. A secondary battery can be manufactured by inserting and then laminating the electrolyte sheet layer of the present invention between the cathode layer and the cathode layer. Polymer electrolyte is polyvinylidene fluoride (PVdF) type or its copolymer, poly[(vinylidene fluoride-co-trifluoroethylene] type or its copolymer, polyethylene glycol (PEO) type or its copolymer, polyacrylonitrile (PAN) type or its copolymer, poly(methyl methacrylate) (PMMA) type or its copolymer, polyvinyl chloride type or its copolymer, polyvinylpyrrolidone (PVP) type or its copolymer, polyimide (PI) type or its copolymer, polyethylene (PE) type or its copolymer, polyurethane (PU) type or its copolymer, polypropylene (PP) type or its copolymer, poly(propylene oxide) (PPO) type or its copolymer, poly(ethylene imine) (PEI) type or its copolymer, poly(ethylene sulfide) (PES) type or its copolymer, poly(vinyl It may be a poly(ethylene succinate) (PVAc)-based or copolymer thereof, a poly(ethylene succinate) (PESc)-based or copolymer thereof, a polyester-based or copolymer thereof, a polyamine-based or copolymer thereof, a polysulfide-based or copolymer thereof, a siloxane-based or copolymer thereof, a styrene butadiene rubber (SBR)-based or copolymer thereof, a carboxymethyl cellulose (CMC)-based or copolymer thereof, or a derivative thereof, or a combination thereof.

[0043] The present invention describes a method for producing Ta-LLZO doped with Ta. The present invention is not limited to this description. First, a primary precursor consisting of La and Zr starting materials is synthesized by a co-precipitation method. It is preferable to utilize a Couette-Taylor reactor capable of continuous reaction and precursor production. Starting materials La(NO3)3ㆍ6H2O, ZrOCl2ㆍ8H2O, a complexing agent NH4OH, and a pH adjuster NaOH are introduced into the reactor to produce a liquid precursor by the co-precipitation method. The pH of the solution is adjusted to 10-12. The prepared precursor is sufficiently dried at 120°C. It is recommended to dry for more than 24 hours. Next, Ta-LLZO is synthesized by a solid-state method. The primary precursor LaZrO is mixed with a lithium source and a Ta doping agent and a solid-state reaction is performed. It is preferable to use Ta2O5 as the Ta doping agent and LiOHㆍH2O as the Li source. A mixed powder is prepared by mixing the primary precursor powder, Ta2O5 powder, and LiOHㆍH2O powder. The powder thus prepared is fired at 800-1,000℃ for 2-4 hours to obtain a final ceramic electrolyte in a crystalline phase.

[0044] The present invention describes a method for producing Ga-doped Ga-LLZO. The present invention is not limited to this description. First, a primary precursor consisting of La and Zr starting materials is synthesized by a co-precipitation method. It is preferable to utilize a Couette-Taylor reactor capable of continuous reaction and precursor production. Starting materials La(NO3)3ㆍ6H2O, ZrOCl2ㆍ8H2O, a complexing agent NH4OH, and a pH adjuster NaOH are introduced into the reactor to produce a liquid precursor by the co-precipitation method. The pH of the solution is adjusted to 10-12. The prepared precursor is sufficiently dried at 120°C. It is recommended to dry for more than 24 hours. Next, Ga-LLZO is synthesized by a solid-state method. The primary precursor LaZrO is mixed with a Li source and a Ga doping agent and a solid-state reaction is performed. It is preferable to use gallium oxide (Ga2O3) as the Ga doping agent and LiOHㆍH2O as the Li source. A mixed powder is prepared by mixing the primary precursor powder, Ga2O3 powder, and LiOHㆍH2O powder. The powder thus prepared is fired at 800-1,000℃ for 2-4 hours to obtain a final ceramic electrolyte in a crystalline phase.

[0045] The present invention describes a method for producing Al-doped Al-LLZO. The present invention is not limited to this description. First, a primary precursor consisting of La and Zr starting materials is synthesized by a co-precipitation method. It is preferable to utilize a Couette-Taylor reactor capable of continuous reaction and precursor production. Starting materials La(NO3)3ㆍ6H2O, ZrOCl2ㆍ8H2O, a complexing agent NH4OH, and a pH adjuster NaOH are introduced into the reactor to produce a liquid precursor by the co-precipitation method. The pH of the solution is adjusted to 10-12. The prepared precursor is sufficiently dried at 120°C. Drying for more than 24 hours is recommended. Next, Al-LLZO is synthesized by a solid-state method. The primary precursor LaZrO is mixed with a lithium source and an aluminum doping agent and a solid-state reaction is performed. It is preferable to use aluminum oxide (Al2O3) as the aluminum doping agent and LiOHㆍH2O as the lithium source. A mixed powder is prepared by mixing the primary precursor powder, Al2O3 powder, and LiOHㆍH2O powder. The powder thus prepared is fired at 800-1,000℃ for 2-4 hours to obtain a final ceramic electrolyte in a crystalline phase.

[0046] The present invention describes a method for producing Nb-doped Nb-LLZO. The present invention is not limited to this description. First, a primary precursor consisting of La and Zr starting materials is synthesized by a co-precipitation method. It is preferable to utilize a Couette-Taylor reactor capable of continuous reaction and precursor production. Starting materials La(NO3)3ㆍ6H2O, ZrOCl2ㆍ8H2O, a complexing agent NH4OH, and a pH adjuster NaOH are introduced into the reactor to produce a liquid precursor by the co-precipitation method. The pH of the solution is adjusted to 10-12. The prepared precursor is sufficiently dried at 120°C. It is recommended to dry for more than 24 hours. Next, Nb-LLZO is synthesized by a solid-state method. The primary precursor LaZrO is mixed with a lithium source and a Nb doping agent and a solid-state reaction is performed. It is preferable to use niobium oxide (Nb12O5) as the Nb doping agent and LiOHㆍH2O as the Li source. A mixed powder is prepared by mixing the primary precursor powder, NbI2O5 powder, and LiOHㆍH2O powder. The powder thus prepared is fired at 800-1,000℃ for 2-4 hours to obtain a final ceramic electrolyte in a crystalline phase.

[0047] Example 1

[0048] A 1 molar aqueous solution of La(NO3)3ㆍ6H2O and a 1 molar aqueous solution of ZrOCl2ㆍ8H2O were prepared as starting materials. A 0.6 M aqueous solution of NH4OH was prepared as a complexing agent. A 1 M aqueous solution of NaOH was prepared as a pH regulator. The NaOH aqueous solution was added to the Couette-Taylor reactor at a rate of 2.7 mL / min, and distilled water was added at a rate of 2.3 mL / min, thereby adjusting the pH level in the Couette-Taylor reactor to approximately 11. The rotation speed of the Couette-Taylor reactor was set to approximately 1,000 rpm. The La(NO3)3ㆍ6H2O starting material aqueous solution was added to the Couette-Taylor reactor at a rate of 1.7 mL / min, the ZrOCl2ㆍ8H2O starting material aqueous solution was added to the Couette-Taylor reactor at a rate of 1.65 mL / min, and the NH4OH complexing agent aqueous solution was added to the Couette-Taylor reactor at a rate of 1.85 mL / min. The coprecipitation reaction was carried out for 4 hours. After the coprecipitation reaction was completed, the Couette-Taylor reactor was further rotated at 1,000 rpm for 24 hours. The precipitate generated in the Couette-Taylor reactor was then continuously washed with distilled water until the pH level reached 7. The precipitate was then dried at 120°C for 48 hours. The dried precipitate was ground using an air jet mill to obtain 100 g of fine powder. 30 g of Ta2O5 was ground using a planetary ball mill to obtain 25 g of fine powder. 25 g of LiOHㆍH2O was ground using an air jet mill to obtain 20 g of fine powder. 100 g of precipitate powder, 25 g of Ta2O5 powder, and 20 g of LiOHㆍH2O powder were mixed in a mixer. The mixed powder was calcined at 1,000°C for 3 hours to obtain 100 g of the final ceramic electrolyte Ta-LLZO in the crystalline phase.

[0049] A 1M LiPF6 solution in EC / DMC (ethyl carbonate / dimethyl carbonate, 1:1 vol) was prepared as a liquid electrolyte. 5 g of the liquid electrolyte was mixed with 30 g of the Ta-LLZO powder prepared above to produce an electrolyte sheet. A cathode layer composed of NCM cathode active material purchased from POSCO Chemical and an Al current collector was produced. A negative electrode layer composed of Li metal purchased from Honjo Metal and a Cu current collector was produced. The electrolyte sheet layer was placed between the cathode and anode layers and laminated to produce a secondary battery.

[0050] Example 2

[0051] A 1 molar aqueous solution of La(NO3)3ㆍ6H2O and a 1 molar aqueous solution of ZrOCl2ㆍ8H2O were prepared as starting materials. A 0.6 M aqueous solution of NH4OH was prepared as a complexing agent. A 1 M aqueous solution of NaOH was prepared as a pH regulator. The NaOH aqueous solution was added to the Couette-Taylor reactor at a rate of 2.7 mL / min, and distilled water was added at a rate of 2.3 mL / min, thereby adjusting the pH level in the Couette-Taylor reactor to approximately 11. The rotation speed of the Couette-Taylor reactor was set to approximately 1,000 rpm. The La(NO3)3ㆍ6H2O starting material aqueous solution was added to the Couette-Taylor reactor at a rate of 1.7 mL / min, the ZrOCl2ㆍ8H2O starting material aqueous solution was added to the Couette-Taylor reactor at a rate of 1.63 mL / min, and the NH4OH complexing agent aqueous solution was added to the Couette-Taylor reactor at a rate of 1.85 mL / min. The coprecipitation reaction was carried out for 4 hours. After the coprecipitation reaction was completed, the Couette-Taylor reactor was further rotated at 1,000 rpm for 24 hours. The precipitate generated in the Couette-Taylor reactor was then continuously washed with distilled water until the pH level reached 7. The precipitate was then dried at 120°C for 48 hours. The dried precipitate was ground with an air jet mill to obtain 200 g of fine powder. 30 g of Ga2O3 was ground with a planetary ball mill to obtain 25 g of fine powder. 25 g of LiOHㆍH2O was ground with an air jet mill to obtain 20 g of fine powder. 100 g of precipitate powder, 25 g of Ga2O3 powder, and 20 g of LiOHㆍH2O powder were mixed in a mixer. The mixed powder was calcined at 1,000°C for 3 hours to obtain 100 g of the final ceramic electrolyte Ga-LLZO in the crystalline phase.

[0052] A 1M LiPF6 solution in EC / DMC (ethyl carbonate / dimethyl carbonate, 1:1 vol) was prepared as a liquid electrolyte. 5 g of the liquid electrolyte was mixed with 30 g of the Ga-LLZO powder prepared above to produce an electrolyte sheet. A cathode layer composed of NCM cathode active material purchased from POSCO Chemical and an Al current collector was produced. A negative electrode layer composed of Li metal purchased from Honjo Metal and a Cu current collector was produced. The electrolyte sheet layer was placed between the cathode and anode layers and laminated to produce a secondary battery.

[0053] Example 3

[0054] A 1 molar aqueous solution of La(NO3)3ㆍ6H2O and a 1 molar aqueous solution of ZrOCl2ㆍ8H2O were prepared as starting materials. A 0.6 M aqueous solution of NH4OH was prepared as a complexing agent. A 1 M aqueous solution of NaOH was prepared as a pH regulator. The NaOH aqueous solution was added to the Couette-Taylor reactor at a rate of 2.7 mL / min, and distilled water was added at a rate of 2.3 mL / min, thereby adjusting the pH level in the Couette-Taylor reactor to approximately 11. The rotation speed of the Couette-Taylor reactor was set to approximately 1,000 rpm. The La(NO3)3ㆍ6H2O starting material aqueous solution was added to the Couette-Taylor reactor at a rate of 1.7 mL / min, the ZrOCl2ㆍ8H2O starting material aqueous solution was added to the Couette-Taylor reactor at a rate of 1.63 mL / min, and the NH4OH complexing agent aqueous solution was added to the Couette-Taylor reactor at a rate of 1.85 mL / min. The coprecipitation reaction was carried out for 4 hours. After the coprecipitation reaction was completed, the Couette-Taylor reactor was further rotated at 1,000 rpm for 24 hours. The precipitate generated in the Couette-Taylor reactor was then continuously washed with distilled water until the pH level reached 7. The precipitate was then dried at 120°C for 48 hours. The dried precipitate was ground using an air jet mill to obtain 100 g of fine powder. 30 g of Al2O3 was ground using a planetary ball mill to obtain 25 g of fine powder. 25 g of LiOHㆍH2O was ground using an air jet mill to obtain 20 g of fine powder. 100 g of precipitate powder, 25 g of Al2O3 powder, and 20 g of LiOHㆍH2O powder were mixed in a mixer. The mixed powder was calcined at 1,000°C for 3 hours to obtain 100 g of the final ceramic electrolyte Al-LLZO in the crystalline phase.

[0055] A 1M LiPF6 solution in EC / DMC (ethyl carbonate / dimethyl carbonate, 1:1 vol) was prepared as a liquid electrolyte. 5 g of the liquid electrolyte was mixed with 30 g of the Al-LLZO powder prepared above to produce an electrolyte sheet. A cathode layer composed of NCM cathode active material purchased from POSCO Chemical and an Al current collector was produced. A negative electrode layer composed of Li metal purchased from Honjo Metal and a Cu current collector was produced. The electrolyte sheet layer was placed between the cathode and anode layers and laminated to produce a secondary battery.

[0056] Example 4

[0057] A 1 molar aqueous solution of La(NO3)3ㆍ6H2O and a 1 molar aqueous solution of ZrOCl2ㆍ8H2O were prepared as starting materials. A 0.6 M aqueous solution of NH4OH was prepared as a complexing agent. A 1 M aqueous solution of NaOH was prepared as a pH regulator. The NaOH aqueous solution was added to the Couette-Taylor reactor at a rate of 2.7 mL / min, and distilled water was added at a rate of 2.3 mL / min, thereby adjusting the pH level in the Couette-Taylor reactor to approximately 11. The rotation speed of the Couette-Taylor reactor was set to approximately 1,000 rpm. The La(NO3)3ㆍ6H2O starting material aqueous solution was added to the Couette-Taylor reactor at a rate of 1.7 mL / min, the ZrOCl2ㆍ8H2O starting material aqueous solution was added to the Couette-Taylor reactor at a rate of 1.63 mL / min, and the NH4OH complexing agent aqueous solution was added to the Couette-Taylor reactor at a rate of 1.85 mL / min. The coprecipitation reaction was carried out for 4 hours. After the coprecipitation reaction was completed, the Couette-Taylor reactor was further rotated at 1,000 rpm for 24 hours. The precipitate generated in the Couette-Taylor reactor was then continuously washed with distilled water until the pH level reached 7. The precipitate was then dried at 120°C for 48 hours. The dried precipitate was ground using an air jet mill to obtain 200 g of fine powder. 30 g of Nb2O5 was ground using a planetary ball mill to obtain 25 g of fine powder. 25 g of LiOHㆍH2O was ground using an air jet mill to obtain 20 g of fine powder. 100 g of precipitate powder, 25 g of Nb2O5 powder, and 20 g of LiOHㆍH2O powder were mixed in a mixer. The mixed powder was calcined at 1,000°C for 3 hours to obtain 100 g of the final ceramic electrolyte Nb-LLZO in the crystalline phase.

[0058] A 1M LiPF6 solution in EC / DMC (ethyl carbonate / dimethyl carbonate, 1:1 vol) was prepared as a liquid electrolyte. 5 g of the liquid electrolyte was mixed with 30 g of the Nb-LLZO powder prepared above to produce an electrolyte sheet. A cathode layer composed of NCM cathode active material purchased from POSCO Chemical and an Al current collector was produced. A negative electrode layer composed of Li metal purchased from Honjo Metal and a Cu current collector was produced. The electrolyte sheet layer was placed between the cathode and anode layers and laminated to produce a secondary battery.

[0059] Comparative Example 1

[0060] Unlike the above example, Ta-LLZO was synthesized by a co-precipitation method.

[0061] A 51 molar aqueous solution of tantalum nitrate Ta(NO3), a 1 molar aqueous solution of lanthanum(III) nitrate hexahydrate (La(NO3)3ㆍ6H2O), and a 1 molar aqueous solution of zirconyl chloride octahydrate ZrOCl2ㆍ8H2O were prepared as starting materials. A 0.6 M aqueous solution of NH4OH was prepared as a complexing agent. A 1 M aqueous solution of NaOH was prepared as a pH regulator. The NaOH aqueous solution was added to the Couette-Taylor reactor at a rate of 2.7 mL / min, and distilled water was added at a rate of 2.3 mL / min, to adjust the pH level in the Couette-Taylor reactor to approximately 11. The rotation speed of the Couette-Taylor reactor was set to approximately 1,000 rpm. The above Ta(NO3)5 starting material aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.2 mL / min, the above La(NO3)3ㆍ6H2O starting material aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.7 mL / min, the above ZrOCl2ㆍ8H2O starting material aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.63 mL / min, and the above complexing agent NH4OH aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.85 mL / min. The coprecipitation reaction was carried out for 4 hours. After the coprecipitation reaction was completed, the Couette-Taylor reactor was additionally rotated at a speed of 1,000 rpm for 24 hours. Thereafter, the precipitate generated in the Couette-Taylor reactor was continuously washed with distilled water until the pH level became 7. 100 g of the above precipitate and 25 g of lithium powder (LiOHㆍH2O) were uniformly mixed using a planetary ball mill to obtain a precursor powder having Li introduced into the precipitate. This precursor powder was calcined at 1,000°C for 3 hours to obtain the final ceramic electrolyte Ta-LLZO in crystalline form.

[0062] A 1M LiPF6 solution in EC / DMC (ethyl carbonate / dimethyl carbonate, 1:1 vol) was prepared as a liquid electrolyte. 5 g of the liquid electrolyte was mixed with 30 g of the Ta-LLZO powder prepared above to produce an electrolyte sheet. A cathode layer composed of NCM cathode active material purchased from POSCO Chemical and an Al current collector was produced. A negative electrode layer composed of Li metal purchased from Honjo Metal and a Cu current collector was produced. The electrolyte sheet layer was placed between the cathode and anode layers and laminated to produce a secondary battery.

[0063] Comparative Example 2

[0064] Unlike the above example, Ga-LLZO was synthesized by a co-precipitation method.

[0065] As starting materials, a 1 molar aqueous solution of gallium(III) nitrate hydrate Ga(NO3)3ㆍxH2O, a 1 molar aqueous solution of lanthanum(III) nitrate hexahydrate (La(NO3)3ㆍ6H2O), and a 1 molar aqueous solution of zirconyl chloride octahydrate ZrOCl2ㆍ8H2O were prepared. A 0.6 M aqueous NH4OH solution was prepared as a complexing agent. A 1 M aqueous NaOH solution was prepared as a pH regulator. The NaOH aqueous solution was added to the Couette-Taylor reactor at a rate of 2.7 mL / min, and distilled water was added at a rate of 2.3 mL / min, to adjust the pH level in the Couette-Taylor reactor to approximately 11. The rotation speed of the Couette-Taylor reactor was set to approximately 1,000 rpm. The above Ga(NO3)3ㆍxH2O starting material aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.2 mL / min, the above La(NO3)3ㆍ6H2O starting material aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.7 mL / min, the above ZrOCl2ㆍ8H2O starting material aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.63 mL / min, and the above complexing agent NH4OH aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.85 mL / min. The coprecipitation reaction was carried out for 4 hours. After the coprecipitation reaction was completed, the Couette-Taylor reactor was additionally rotated at a speed of 1,000 rpm for 24 hours. Thereafter, the precipitate generated in the Couette-Taylor reactor was continuously washed with distilled water until the pH level became 7. 100 g of the above precipitate and 25 g of lithium powder (LiOHㆍH2O) were uniformly mixed using a planetary ball mill to obtain a precursor powder in which Li was introduced into the precipitate. This precursor powder was calcined at 1,000°C for 3 hours to obtain the final ceramic electrolyte Ga-LLZO in crystalline form.

[0066] A 1M LiPF6 solution in EC / DMC (ethyl carbonate / dimethyl carbonate, 1:1 vol) was prepared as a liquid electrolyte. 5 g of the liquid electrolyte was mixed with 30 g of the Ga-LLZO powder prepared above to produce an electrolyte sheet. A cathode layer composed of NCM cathode active material purchased from POSCO Chemical and an Al current collector was produced. A negative electrode layer composed of Li metal purchased from Honjo Metal and a Cu current collector was produced. The electrolyte sheet layer was placed between the cathode and anode layers and laminated to produce a secondary battery.

[0067] Comparative Example 3

[0068] Unlike the above example, Al-LLZO was synthesized by a co-precipitation method.

[0069] As starting materials, 1 molar aqueous solution of aluminum nitrate Al(NO3), 1 molar aqueous solution of lanthanum(III) nitrate hexahydrate (La(NO3)3ㆍ6H2O), and 1 molar aqueous solution of zirconyl chloride octahydrate ZrOCl2ㆍ8H2O were prepared. A 0.6 M aqueous solution of NH4OH was prepared as a complexing agent. A 1 M aqueous solution of NaOH was prepared as a pH regulator. The NaOH aqueous solution was added to the Couette-Taylor reactor at a rate of 2.7 mL / min, and distilled water was added at a rate of 2.3 mL / min, to adjust the pH level in the Couette-Taylor reactor to approximately 11. The rotation speed of the Couette-Taylor reactor was set to approximately 1,000 rpm. The above Al(NO3)3 starting material aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.15 mL / min, the above La(NO3)3ㆍ6H2O starting material aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.7 mL / min, the above ZrOCl2ㆍ8H2O starting material aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.63 mL / min, and the complexing agent NH4OH aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.85 mL / min. The coprecipitation reaction was carried out for 4 hours. After the coprecipitation reaction was completed, the Couette-Taylor reactor was additionally rotated at a speed of 1,000 rpm for 24 hours. Thereafter, the precipitate generated in the Couette-Taylor reactor was continuously washed with distilled water until the pH level became 7. 100 g of the above precipitate and 25 g of lithium powder (LiOHㆍH2O) were uniformly mixed using a planetary ball mill to obtain a precursor powder in which Li was introduced into the precipitate. This precursor powder was calcined at 1,000°C for 3 hours to obtain the final ceramic electrolyte Al-LLZO in crystalline form.

[0070] A 1M LiPF6 solution in EC / DMC (ethyl carbonate / dimethyl carbonate, 1:1 vol) was prepared as a liquid electrolyte. 5 g of the liquid electrolyte was mixed with 30 g of the Al-LLZO powder prepared above to produce an electrolyte sheet. A cathode layer composed of NCM cathode active material purchased from POSCO Chemical and an Al current collector was produced. A negative electrode layer composed of Li metal purchased from Honjo Metal and a Cu current collector was produced. The electrolyte sheet layer was placed between the cathode and anode layers and laminated to produce a secondary battery.

[0071] Comparative Example 4

[0072] Unlike the above example, Nb-LLZO was synthesized by a co-precipitation method.

[0073] As starting materials, a 1 mol aqueous solution of niobium oxynitrate NbO(NO3), a 1 mol aqueous solution of lanthanum(III) nitrate hexahydrate (La(NO3)3ㆍ6H2O), and a 1 mol aqueous solution of zirconyl chloride octahydrate ZrOCl2ㆍ8H2O were prepared. A 0.6 M aqueous NH4OH solution was prepared as a complexing agent. A 1 M aqueous NaOH solution was prepared as a pH regulator. The NaOH aqueous solution was added to the Couette-Taylor reactor at a rate of 2.7 mL / min, and distilled water was added at a rate of 2.3 mL / min, to adjust the pH level in the Couette-Taylor reactor to approximately 11. The rotation speed of the Couette-Taylor reactor was set to approximately 1,000 rpm. The above NbO(NO3)3 starting material aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.25 mL / min, the above La(NO3)3ㆍ6H2O starting material aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.7 mL / min, the above ZrOCl2ㆍ8H2O starting material aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.63 mL / min, and the above complexing agent NH4OH aqueous solution was introduced into the Couette-Taylor reactor at a rate of 1.85 mL / min. The coprecipitation reaction was carried out for 4 hours. After the coprecipitation reaction was completed, the Couette-Taylor reactor was additionally rotated at a speed of 1,000 rpm for 24 hours. Thereafter, the precipitate generated in the Couette-Taylor reactor was continuously washed with distilled water until the pH level became 7. 100 g of the above precipitate and 25 g of lithium powder (LiOHㆍH2O) were uniformly mixed using a planetary ball mill to obtain a precursor powder having Li introduced into the precipitate. This precursor powder was calcined at 1,000°C for 3 hours to obtain the final ceramic electrolyte Nb-LLZO in crystalline form.

[0074] A 1M LiPF6 solution in EC / DMC (ethyl carbonate / dimethyl carbonate, 1:1 vol) was prepared as a liquid electrolyte. 5 g of the liquid electrolyte was mixed with 30 g of the Nb-LLZO powder prepared above to produce an electrolyte sheet. A cathode layer composed of NCM cathode active material purchased from POSCO Chemical and an Al current collector was produced. A negative electrode layer composed of Li metal purchased from Honjo Metal and a Cu current collector was produced. The electrolyte sheet layer was placed between the cathode and anode layers and laminated to produce a secondary battery.

[0075] Comparative Example 5

[0076] Unlike the above example, Ta-LLZO was synthesized using a solid-state method.

[0077] Starting materials, 10 g of tantalum oxide (Ta2O3), 60 g of lanthanum oxide (La2O3), and 40 g of zirconia oxide (ZrO2) were placed in a ball mill, deionized water (Di water) was added, and ball milling was performed to synthesize a primary precursor. 100 g of this primary precursor and 70 g of lithium powder (LiOHㆍH2O) were uniformly mixed using a planetary ball mill to obtain 160 g of a secondary precursor powder in which Li was introduced into the primary precursor. This secondary precursor powder was calcined at 1,000°C for 3 hours to obtain a final ceramic electrolyte Ta-LLZO in a crystalline phase.

[0078] A 1M LiPF6 solution in EC / DMC (ethyl carbonate / dimethyl carbonate, 1:1 vol) was prepared as a liquid electrolyte. 5 g of the liquid electrolyte was mixed with 30 g of the Ta-LLZO powder prepared above to produce an electrolyte sheet. A cathode layer composed of NCM cathode active material purchased from POSCO Chemical and an Al current collector was produced. A negative electrode layer composed of Li metal purchased from Honjo Metal and a Cu current collector was produced. The electrolyte sheet layer was placed between the cathode and anode layers and laminated to produce a secondary battery.

[0079] Comparative Example 6

[0080] Unlike the above example, Ga-LLZO was synthesized using a solid-state method.

[0081] Starting materials, 10 g of gallium oxide (Ga2O3), 60 g of lanthanum oxide (La2O3), and 40 g of zirconia oxide (ZrO2) were placed in a ball mill, deionized water (Di water) was added, and ball milling was performed to synthesize a primary precursor. 100 g of this primary precursor and 70 g of lithium powder (LiOHㆍH2O) were uniformly mixed using a planetary ball mill to obtain 150 g of a secondary precursor powder in which Li was introduced into the primary precursor. This secondary precursor powder was calcined at 1,000°C for 3 hours to obtain a final ceramic electrolyte Ga-LLZO in a crystalline phase.

[0082] A 1M LiPF6 solution in EC / DMC (ethyl carbonate / dimethyl carbonate, 1:1 vol) was prepared as a liquid electrolyte. 5 g of the liquid electrolyte was mixed with 30 g of the Ga-LLZO powder prepared above to produce an electrolyte sheet. A cathode layer composed of NCM cathode active material purchased from POSCO Chemical and an Al current collector was produced. A negative electrode layer composed of Li metal purchased from Honjo Metal and a Cu current collector was produced. The electrolyte sheet layer was placed between the cathode and anode layers and laminated to produce a secondary battery.

[0083] Comparative Example 7

[0084] Unlike the above example, Al-LLZO was synthesized using a solid-state method.

[0085] Starting materials, 12 g of aluminum oxide (Al2O3), 60 g of lanthanum oxide (La2O3), and 40 g of zirconia oxide (ZrO2) were placed in a ball mill, deionized water (Di water) was added, and ball milling was performed to synthesize a primary precursor. 110 g of this primary precursor and 70 g of lithium powder (LiOHㆍH2O) were uniformly mixed using a planetary ball mill to obtain 150 g of a secondary precursor powder in which Li was introduced into the primary precursor. This secondary precursor powder was calcined at 1,000°C for 3 hours to obtain a final ceramic electrolyte Al-LLZO in a crystalline phase.

[0086] A 1M LiPF6 solution in EC / DMC (ethyl carbonate / dimethyl carbonate, 1:1 vol) was prepared as a liquid electrolyte. 5 g of the liquid electrolyte was mixed with 30 g of the Al-LLZO powder prepared above to produce an electrolyte sheet. A cathode layer composed of NCM cathode active material purchased from POSCO Chemical and an Al current collector was produced. A negative electrode layer composed of Li metal purchased from Honjo Metal and a Cu current collector was produced. The electrolyte sheet layer was placed between the cathode and anode layers and laminated to produce a secondary battery.

[0087] Comparative Example 8

[0088] Unlike the above example, Nb-LLZO was synthesized using a solid-state method.

[0089] Starting materials, 10 g of niobium oxide (Nb2O5), 60 g of lanthanum oxide (La2O3), and 40 g of zirconia oxide (ZrO2) were placed in a ball mill, deionized water (Di water) was added, and ball milling was performed to synthesize a primary precursor. 105 g of this primary precursor and 70 g of lithium powder (LiOHㆍH2O) were uniformly mixed using a planetary ball mill to obtain 160 g of a secondary precursor powder in which Li was introduced into the primary precursor. This secondary precursor powder was calcined at 1,000°C for 3 hours to obtain a final ceramic electrolyte Nb-LLZO in a crystalline phase.

[0090] A 1M LiPF6 solution in EC / DMC (ethyl carbonate / dimethyl carbonate, 1:1 vol) was prepared as a liquid electrolyte. 5 g of the liquid electrolyte was mixed with 30 g of the Nb-LLZO powder prepared above to produce an electrolyte sheet. A cathode layer composed of NCM cathode active material purchased from POSCO Chemical and an Al current collector was produced. A negative electrode layer composed of Li metal purchased from Honjo Metal and a Cu current collector was produced. The electrolyte sheet layer was placed between the cathode and anode layers and laminated to produce a secondary battery.

[0091] Capacity retention rate evaluation

[0092] The secondary batteries of Example 3, Comparative Example 3, and Comparative Example 7 were subjected to 60 cycles of 0.2C charging and 1.0C discharging to evaluate capacity retention. The results are shown in Fig. 1. Example 3 exhibited a capacity retention rate of 89.2%, Comparative Example 3 exhibited a capacity retention rate of 88.7%, and Comparative Example 7 exhibited a capacity retention rate of 78.2%. Example 3 exhibited the best capacity retention rate.

[0093] Output Characteristics Evaluation (C-RATE Evaluation)

[0094] The capacity change rate according to the charge / discharge rate was evaluated for the secondary batteries of Example 3, Comparative Example 3, and Comparative Example 7. The results are shown in Fig. 2. Example 3 was the best at all charge / discharge rates. For example, when the charge / discharge rate was 3.0C (charge / discharge rate 20 min), Example 3 showed a capacity retention rate of 85%, Comparative Example 3 showed 80%, and Comparative Example 7 showed 77%. Therefore, Example 3 showed a capacity retention rate improvement of 6-10% compared to Comparative Example 3 or Comparative Example 7.

[0095] Evaluation of crystal phase by XRD analysis

[0096] The ceramic solid electrolytes of Example 3 and Comparative Example 3 were subjected to crystal phase analysis using X-ray diffraction (XRD). The results are shown in Fig. 3. The ceramic solid electrolyte of Example 3 was found to have a single LLZO crystal phase with almost no impurities. In contrast, the ceramic solid electrolyte of Comparative Example 3 had an LZO impurity phase peak observed at 2 Theta / degree. From this, it was found that the ceramic solid electrolyte of Comparative Example 3 had a mixture of a cubic crystal phase and a tetragonal crystal phase.

[0097] Ionic conductivity evaluation

[0098] The ionic conductivity of Examples 1 to 8 is shown in Table 1 below. The ionic conductivity of Example 1 was higher than that of Comparative Example 1 or Comparative Example 5. The ionic conductivity of Example 2 was higher than that of Comparative Example 2 or Comparative Example 6. The ionic conductivity of Example 3 was higher than that of Comparative Example 3 or Comparative Example 7. The ionic conductivity of Example 4 was higher than that of Comparative Example 4 or Comparative Example 8. In particular, Examples 1 to 4 had at least 30% higher ionic conductivity than Comparative Examples 5 to 8.

[0099]

[0100] Comparison of particle size distributions

[0101] The particle size distributions of the ceramic solid electrolytes of Example 3, Comparative Example 3, and Comparative Example 7 were compared. The results are shown in Figs. 4, 5, and 6. The D50 of Example 3, Comparative Example 3, and Comparative Example 7 were 2 μm, 5 μm, and 9 μm, respectively. Example 3 was capable of achieving 22%-40% finer particle size than Comparative Example 3 or Comparative Example 7. It was confirmed that the improvement in ionic conductivity evaluated above could be achieved due to this difference in particle size distribution.

[0102] Microsurface structure by SEM analysis

[0103] The surfaces of the Ga-doped ceramic solid electrolytes of Example 2, Comparative Example 2, and Comparative Example 6 were observed using SEM (X10 magnification). The SEM images are shown in Figs. 7, 8, and 9. The ceramic solid electrolyte of Example 2 had a smooth surface, no defects, and a uniform, spherical shape. On the other hand, the ceramic solid electrolyte of Comparative Example 2 had an uneven surface and coagulation between particles. The ceramic solid electrolyte of Comparative Example 6 had a considerably rough surface, many defects on the surface, and an uneven particle shape. From this, it was found that when a ceramic solid electrolyte is manufactured by the method of the present invention, a uniform crystal phase can be obtained and electrochemical characteristics are also improved.

Claims

1. A liquid precursor manufacturing step in which an aqueous solution of lanthanum (III) nitrate hexahydrate (La(NO3)3ㆍ6H2O) and an aqueous solution of zirconyl chloride octahydrate (ZrOCl2ㆍ8H2O) are introduced into a co-precipitation reactor together with a complexing agent and a pH regulator, and a co-precipitation reaction is performed at 20℃-40℃ for 2-5 hours to manufacture a liquid precursor slurry. A liquid precursor drying step of drying the above liquid precursor slurry at 110°C-130°C for 22-26 hours, A solid-state precursor manufacturing step of manufacturing a solid-state precursor by mixing a dopant capable of providing a dopant selected from Al, Ga, Nb, and Ta and a lithium source capable of providing lithium to the dried precursor and performing a solid-state reaction, and A solid precursor firing step for producing a ceramic solid electrolyte by firing the above solid precursor at 800°C-1,200°C for 2-4 hours. A method for producing a ceramic solid electrolyte, characterized in that it comprises:

2. A method for producing a ceramic solid electrolyte, characterized in that the solid precursor in the first paragraph is composed of the following chemical formula. Li x X y La z Zr p O 12 (X is Al, Ga, Nb or Ta, 5≤x<9, 0 <y≤1, 2≤z≤4, 1≤p≤3 이다.) 3. A method for producing a ceramic solid electrolyte, characterized in that in paragraph 1, the lithium source and the doping agent are formed in a ratio of 5-9:0-1.

4. A method for producing a ceramic solid electrolyte, characterized in that in the first paragraph, the pH adjusting agent is NaOH and is introduced into a co-precipitation reactor to adjust the pH of the co-precipitation reactor to 10-12.

5. A method for producing a ceramic solid electrolyte, characterized in that in the first paragraph, the complexing agent is NH4OH and is introduced into a co-precipitation reactor at a weight ratio of 150-180 with respect to 100 parts by weight of an aqueous solution of lanthanum (III) nitrate hexahydrate (La(NO3)3ㆍ6H2O) and an aqueous solution of zirconyl chloride octahydrate (ZrOCl2ㆍ8H2O).

6. A liquid precursor manufacturing step in which an aqueous solution of lanthanum (III) nitrate hexahydrate (La(NO3)3ㆍ6H2O) and an aqueous solution of zirconyl chloride octahydrate (ZrOCl2ㆍ8H2O) are introduced into a co-precipitation reactor together with a complexing agent and a pH regulator, and a co-precipitation reaction is performed at 20℃-40℃ for 2-5 hours to manufacture a liquid precursor slurry. A liquid precursor drying step of drying the above liquid precursor slurry at 110°C-130°C for 22-26 hours, A solid-state precursor manufacturing step of manufacturing a solid-state precursor by mixing a dopant capable of providing a dopant selected from Al, Ga, Nb, and Ta and a lithium source capable of providing lithium to the dried precursor and performing a solid-state reaction, A solid precursor firing step for producing a ceramic solid electrolyte by firing the above solid precursor at 800°C-1,200°C for 2-4 hours, A step for manufacturing a ceramic solid electrolyte sheet by mixing the above ceramic solid electrolyte with a liquid electrolyte in a weight ratio of 60-90:10 to 40 and manufacturing it in the form of a sheet, and A secondary battery manufacturing step for manufacturing a secondary battery by placing and laminating the above ceramic solid electrolyte sheet between the positive and negative electrodes. A method for manufacturing a secondary battery, characterized in that it includes:

7. In paragraph 6, the polymer electrolyte is a polyvinylidene fluoride (PVdF) type or a copolymer thereof, a poly[(vinylidene fluoride-co-trifluoroethylene] type or a copolymer thereof, a polyethylene glycol (PEO) type or a copolymer thereof, a polyacrylonitrile (PAN) type or a copolymer thereof, a poly(methyl methacrylate) (PMMA) type or a copolymer thereof, a polyvinyl chloride type or a copolymer thereof, a polyvinylpyrrolidone (PVP) type or a copolymer thereof, a polyimide (PI) type or a copolymer thereof, a polyethylene (PE) type or a copolymer thereof, a polyurethane (PU) type or a copolymer thereof, a polypropylene (PP) type or a copolymer thereof, a poly(propylene oxide) (PPO) type or a copolymer thereof, a poly(ethylene imine) (PEI) type or a copolymer thereof, a poly(ethylene sulfide) (PES) type or a copolymer thereof. A method for manufacturing a secondary battery, characterized in that the secondary battery is a copolymer, a poly(vinyl acetate) (PVAc) type or a copolymer thereof, a poly(ethylene succinate) (PESc) type or a copolymer thereof, a polyester type or a copolymer thereof, a polyamine type or a copolymer thereof, a polysulfide type or a copolymer thereof, a siloxane-based type or a copolymer thereof, a styrene butadiene rubber (SBR) type or a copolymer thereof, a carboxymethyl cellulose (CMC) type or a copolymer thereof, or a derivative thereof, or a combination thereof.

8. A secondary battery manufactured by the method of clause 6 or 7.

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