RU2805519C1 - Method for producing thin films of complex oxide systems from dry nanocrystalline powder for electrochemical devices - Google Patents

Abstract

FIELD: thin films.

SUBSTANCE: method for producing thin films (0.1-100 mcm) of complex oxide systems that can be used in the manufacture of various electrochemical devices: solid oxide fuel cells, solid-state batteries, etc. The effect is achieved by the fact that formation of films occurs by spraying an aerosol with a dry nanocrystalline powder with a crystallite size of up to 100 nm, collected into soft agglomerates up to 100 mcm in size, onto a substrate under low vacuum (100-1000 Pa) and room temperature.

EFFECT: increased density, density uniformity, ionic and/or electronic conductivity of the formed films of complex oxide systems, reduced sintering temperature, and increased deposition productivity.

1 cl, 4 dwg, 3 ex

Description

The invention relates to a method for producing thin films (0.1-100 microns) of complex oxide systems, and can be used in the manufacture of various electrochemical devices: solid oxide fuel cells, solid-state batteries, etc.

It is known that complex oxide systems are used as electrode and electrolyte materials for various electrochemical devices, for example, solid oxide fuel cells and solid-state batteries. The main requirements for functional films of electrochemical devices are high ionic and/or electronic conductivity, controlled porosity or its absence.

There is a known method for producing a solid electrolyte based on stabilized zirconium dioxide (patent RU 2592936 C2), in which the formation of a thin film is carried out by casting a slip onto a moving belt, followed by drying and annealing at a temperature of 1500°C. The thickness of the formed films is 5-300 microns.

The disadvantage of the proposed method is the use of a solvent, the evaporation of which during the drying process leads to the formation of voids in the formed layer and a small contact area of the grains, which ultimately leads to the need for high sintering temperatures. Another disadvantage of this method is the difficulty of producing films with a thickness of less than 20 microns and the impossibility of producing gas-tight films with a thickness of less than 5 microns.

There is a known method for producing solid electrolyte by magnetron sputtering (patent EP 2083466 A1). In this method, atomic sputtering of a target occurs, followed by the deposition of atoms onto the substrate and the formation of a film. The films formed by this method have a gas-tight structure. The thickness of the formed films is up to 15 microns.

The disadvantages of this method are the low productivity of oxide deposition, the complexity of deposition of composite materials, the complexity of organizing continuous production due to high vacuum requirements, as well as the difficulty of forming oxide films in the required stoichiometry, leading to the need for firing in an air or oxygen atmosphere. In addition, obtaining films with controlled porosity is a difficult task.

The closest analogue, taken as a prototype, is the method (US patent 7,993,701 B2). In this method, polycrystalline powder particles with a size of 0.1-5 microns are deposited at room temperature and low vacuum (100-1000 Pa) by acceleration with a carrier gas and collision with the substrate, while the particles are crushed or deformed with the formation of fresh surfaces and a decrease in size crystallite, fresh surfaces are bonded together to form a film structure characterized by high hardness and density.

The disadvantage of this approach is that the formed films have low conductivity due to the presence of a developed and highly defective grain boundary (Jorg Exner, Jaroslaw Kita, Ralf Moos. In-and through-plane conductivity of 8YSZ films produced at room temperature by aerosol deposition // Journal of Materials Science, 2019, V54, No. 21, pp. 13619-13634). To eliminate defects in the grain boundaries of the films being formed, thermal treatment of the films is required. During the annealing process, the resulting films in many cases undergo cracking and high residual porosity (Jong-Jin Choi, Joon-Hwan Choi, Jungho Ryu, Byung-Dong Hahn, Jong-Woo Kim, Cheol-Woo Ahn, Woon-Ha Yoon, Dong- Soo Park. Microstructural evolution of YSZ electrolyte aerosol-deposited on porous NiO-YSZ // Journal of the European Ceramic Society, 2012, V 32, No. 12, pp. 3249-3254) due to the high degree of uneven density of the initial layer associated including the presence of strongly bound but not crushed agglomerates in the films.

The technical result of this invention is to increase the density, density uniformity, ionic and/or electronic conductivity of the formed films of complex oxide systems, reduce the sintering temperature, and increase the deposition productivity.

The technical result is achieved by the fact that the formation of films occurs by spraying an aerosol with a dry nanocrystalline powder with a crystallite size of up to 100 nm, collected into soft agglomerates up to 100 microns in size, onto a substrate under conditions of low vacuum (100-1000 Pa) and room temperature. When colliding with a substrate, soft agglomerates are destroyed completely and/or partially to their constituent crystallites, while unbroken agglomerates are soft and have low adhesion to the film, but have a larger cross-sectional area than their constituent crystallites, and they are blown away by tangential gas flows formed naturally by colliding the carrier gas with the substrate and/or by tilting the nozzle relative to the substrate. Due to the high density of the resulting layer, nanocrystalline structure and high density uniformity, sintering temperatures are significantly reduced compared to methods involving the use of solvents.

Figure 1 shows a schematic diagram of how the method works. A method for producing thin oxide films from dry nanocrystalline powder may include preparing the powder in a planetary ball mill by grinding the powder in ethyl alcohol to a grain size of less than 100 nm, and evaporating the ethyl alcohol. Mandatory includes mixing the powder with nitrogen gas or dry air in an aerosol generator (1) and spraying the resulting aerosol from a nozzle (2) onto a substrate (3) attached to linear motion modules (4) and located in a low vacuum atmosphere of 100-1000 Pa deposition chamber (5). The vacuum in the deposition chamber is maintained using a pump group (6). The film deposition area is moved by the movement of the substrate provided by the movement of the movement modules. The use of powder with a grain size of up to 100 nm results in the powder being soft agglomerates, which are then sprayed onto the substrate and subsequently broken down into their constituent grains. In this case, there is no reduction in grain or crystallite size. After deposition, the films are subjected to temperature annealing, the annealing temperature depends on the required percentage of porosity. The thickness of the formed films is 0.1-100 microns

Examples of specific performance.

Example 1.

Powder (Y ₂ O ₃ ) _0.08 (ZrO ₂ ) _0.92 with a grain size of 20-50 nm, collected in soft agglomerates, is placed in a steel cylindrical vessel, to which a nitrogen supply is organized from a cylinder with a reducer and aerosol removal from the upper zone of the cylinder. The cylindrical vessel is placed on a vibration table, the vibration frequency is 600 rpm. The cylindrical vessel, vibrating table and cylinder with reducer in this example constitute an aerosol generator. The resulting aerosol of nitrogen gas and dry powder enters a tapering nozzle with an outlet diameter of 2 mm. From the nozzle, the aerosol is sprayed into the deposition chamber onto the substrate located at a distance of 10 mm from the nozzle. The pressure in the deposition chamber is set at 800 Pa, the pressure in front of the nozzle is maintained at 150 kPa. The nozzle is directed at an angle of 60° relative to the substrate (90° is perpendicular to the direction of the nozzle). The substrate is attached to the motion modules. The substrate movement speed is 1 mm/s. The resulting film (Y ₂ O ₃ ) _0.08 (ZrO ₂ ) _0.92 is fired at a temperature of 1200-1300°C for 1 hour. Porosity percentage <1%. An image of the surface of the resulting film is shown in Fig. 2.

Example. 2

Powder Gd _0.1 Ce _0.9 O _1.95 with a grain size of 20-50 nm is placed in a steel cylindrical vessel, to which a nitrogen supply is organized from a cylinder with a reducer and aerosol removal from the upper zone of the cylinder. The cylindrical vessel is placed on a vibration table, the vibration frequency is 600 rpm. The cylindrical vessel, vibrating table and cylinder with reducer in this example constitute an aerosol generator. The resulting aerosol of nitrogen gas and dry powder enters a tapering nozzle with an outlet diameter of 2 mm. From the nozzle, the aerosol is sprayed into the deposition chamber onto the substrate located at a distance of 10 mm from the nozzle. The pressure in the deposition chamber is set at 400 Pa, the pressure in front of the nozzle is maintained at 100 kPa. The nozzle is directed at an angle of 90° relative to the substrate (90° is perpendicular to the direction of the nozzle). The substrate is attached to the motion modules. The substrate movement speed is 1 mm/s. The resulting Gd _0.1 Ce _0.9 O _1.95 film is fired at a temperature of 950-1100°C for 1 hour. Porosity percentage <1%. An image of the surface of the resulting film is shown in Fig. 3.

Example 3

NiO/(Y ₂ O ₃ ) _0.08 (ZrO ₂ ) _0.92 (50/50 m%) composite powder with a grain size of 50-100 nm, collected into soft agglomerates, is placed in a steel cylindrical vessel, to which a nitrogen supply is organized from a cylinder with gearbox and removal of aerosol from the upper zone of the cylinder. The cylindrical vessel is placed on a vibration table, the vibration frequency is 600 rpm. The cylindrical vessel, vibrating table and cylinder with reducer in this example constitute an aerosol generator. The resulting aerosol of nitrogen gas and dry powder enters a tapering nozzle with an outlet diameter of 2 mm. From the nozzle, the aerosol is sprayed into the deposition chamber onto the substrate located at a distance of 10 mm from the nozzle. The pressure in the deposition chamber is set at 400 Pa, the pressure in front of the nozzle is maintained at 100 kPa. The nozzle is directed at an angle of 90° relative to the substrate (90° is perpendicular to the direction of the nozzle). The substrate is attached to the motion modules. The substrate movement speed is 1 mm/s. The resulting film (Y ₂ O ₃ ) _0.08 (ZrO ₂ ) _0.92 is fired at a temperature of 1100-1200°C for 1 hour. Porosity percentage 30-50%. An image of the surface of the resulting film is shown in Fig. 4.

Claims (1)

A method for producing thin films of complex oxide systems from dry nanocrystalline powder for electrochemical devices, including spraying an aerosol from a dry powder onto a substrate under conditions of low vacuum (100-1000 Pa) and room temperature, characterized in that crystallites up to 100 in size are used as powder particles nm, collected into soft agglomerates up to 100 microns in size.