RU2720349C1 - Method of producing solid electrolyte - Google Patents

Abstract

FIELD: physics.SUBSTANCE: invention relates to methods of producing solid electrolyte with high ionic conductivity at ambient temperatures and can be used in production of electrochemical current sources, sensors, ion sources and other devices. Method of producing solid electrolyte based on tetra-silver-cesium pentahalides involves annealing a mixture of bromides and cesium and silver iodides with intermediate homogenisation, wherein the silver compound used is AgBrIcomplex silver bromide-iodide, where 0.25≤y≤0.375, with weight ratio of cesium iodide : complex silver bromide-iodide equal to 24.03÷24.29 : 75.71÷75.97, wherein the ratio of total amount of cesium and silver ions is equal to 1:4, and annealing is carried out with compaction of mixture at temperature 160–170 °C in vacuum at residual pressure of 10÷10atm with not less than threefold intermediate homogenisation.EFFECT: technical result is simplification of technology of producing solid electrolyte, providing the possibility of scaling and using only standard laboratory equipment.1 cl, 2 ex

Description

The method of obtaining solid electrolyte

The invention relates to methods for producing a solid electrolyte with high ionic conductivity at ambient temperatures and can be used in the manufacture of electrochemical current sources, sensors, ion sources and other devices.

Known mechanochemical method for the synthesis of tetra-silver-cesium pentahalides CsAg ₄ Br _3-x I _{2 + x} (0.25≤x≤1), which consists in mixing stoichiometric amounts of CsI, AgI and AgBr in an agate mortar for 5 minutes, moving the reaction mixture into an agate container with agate grinding media, evacuating the container followed by filling with argon and the subsequent mechanochemical treatment in a planetary mill for 3 hours at a rotation speed of 450 rpm. The resulting product consisted of an almost single-phase solid solution of CsAg ₄ Br _3-x I _{2 + x} with trace amounts of the starting AgI reagent and intermediate CsAgBr ₂ (W. Zuo, V. Pelenovich, A. Tolstogouzov, X. Zeng, Z. Wang, X. Song, SI Gusev, C. Tian, D. Fu. Mechano-chemical synthesis of crystalline superionic conductor CsAg ₄ Br _3-x I _{2 + x} (x = 0.32) and its application for Ag ⁺ ion-beam generation. J AlloysandCompounds, 2019, V. 790, p. 109-116).

The disadvantages of this method include the inability to obtain a single-phase product without impurities of the starting materials and intermediate phases. In addition, its implementation requires expensive equipment - a planetary mill, containers and grinding bodies made of agate or other inert ceramic material, moreover, the design of the containers must contain a protective clamping device and ensure gas impermeability while maintaining an inert gas atmosphere inside the container during synthesis.

A known method of producing tetra-silver-cesium pentahalides of the general formula CsAg ₄ Br _3-x I _{2 + x} , where 0.25≤x≤1, by directional crystallization from a melt, comprising mixing bromides and iodides of cesium and silver with a ratio of total amounts of salts cesium and silver 1: 4, fusion in a quartz ampoule at 320 ^о С in an inert atmosphere (Ar), stirring, crystallization at room temperature, homogenization by grinding in a mortar, pressing and annealing at a temperature below the melting temperature (which is 165-175 ^о C depending on the state Ava) (Patent RU 1 697 573 C, IPC H01M 6/18, 1995) (prototype).

The disadvantages of the known production method include, firstly, its duration, since due to the incongruent nature of the melting of α-CsAg ₄ Br _3-x I _{2 + x} solid solutions, uncontrolled phase formation with crystallization of not only α-CsAg ₄ Br occurs upon cooling of the melt _3-x I _{2 + x} , but also of other peritectic reaction products in a three-component system, moreover, the composition of impurities at different points in the volume of the melt will inevitably differ due to uneven cooling. Consequently, subsequent annealing crushed smelt lead to avoid the formation of liquid phase at temperatures considerably below its melting temperature, given the inevitable appearance of one or two eutectics at temperatures of 125 ± ⁵ ° and 155 ± 5 ^{° C,} which increases the duration of the heat treatment. Secondly, the disadvantage is the complexity, since the operation of homogenization of partially crystallized and partially vitrified melt requires considerable effort. As a consequence, the disadvantage of this method is the impossibility of scaling it to obtain significant quantities of solid electrolyte.

Thus, the authors were faced with the task of developing a more technologically advanced and scalable method for producing a solid electrolyte based on tetra-silver-cesium pentahalides.

The problem is solved in the proposed method for producing a solid electrolyte based on tetra-silver-cesium pentahalides, including annealing a mixture of cesium and silver bromides and iodides with intermediate homogenization, in which silver bromide iodide of the composition AgBr _1-y I _{y is} used as a silver compound , where 0.25≤y≤0.375, with the mass ratio of cesium iodide: complex bromide-silver iodide equal to 24.03 ÷ 24.29: 75.71 ÷ 75.97, while the ratio of the total number of cesium and silver ions is 1: 4, and annealing is carried out with compaction of the mixture at a pace Aturi 160-170 ^{° C} under vacuum at a residual pressure of 10 ^-2 ÷ 10 ^-3 atm with at least triply intermediate homogenisation.

Currently, from the patent and scientific and technical literature, there is no known method for producing a solid electrolyte based on tetra-silver-cesium pentahalides using silver bromide-iodide compound AgBr _1-y I _y as the starting silver compound, where 0.25≤y ≤0.375, in terms of the process proposed by the authors.

Studies conducted by the authors revealed that the annealing temperature solid phase reaction mixture can be as close as possible to the temperature of the solid electrolyte melting at atmospheric pressure (165 ± 5 ° ^C) without the risk of formation of liquid phases owing to the phase transition displacement at vacuumizing toward higher temperatures in the case of using CsI iodide CsI and a solid solution based on silver bromide-iodide composition AgBr _1-y I _y as starting materials.

At the same time, all operations to obtain solid electrolyte can be performed using standard laboratory equipment, which, when scaled, can easily be replaced by a more productive one.

Proposed authors method involves a significant decrease in the temperature of the heat treatment of the primary reaction mixture (from 320 to 165 ± 5 ° ^C), deletion (in the case of use of inert atmosphere) complicating the synthesis operations by producing an inert atmosphere and bubbling an inert gas through the melt for its stirring, exclusion of unproductive and the time-consuming operation of primary grinding of melt, while the proposed method ensures the achievement of high ionic (up to 0.2 Ohm ^-1 · cm ^-1 ) and low electron (~ 10 ^-9 Ohm ^-1 · cm ^-1 ) st at room temperature and maintaining high transport characteristics of the electrolyte upon cooling to minus 50 ^about C.

The task can be solved only if the conditions of the process proposed by the authors are observed. So, with the mass ratio of cesium iodide: complex silver bromide-iodide, the appearance of by-products due to violation of stoichiometry is observed beyond the reduced range of values 24.03 ÷ 24.29: 75.71 ÷ 75.97. Reducing the annealing temperature below 160 ^{° C} leads to an increase in annealing time and number of intermediate homogenisation. Raising the annealing temperature above 170 ^{° C} leads to incongruent melting with decomposition and formation of a dense solid monolith.

The proposed method for producing solid electrolyte can be carried out as follows.

Prepare a reaction mixture of CsI and AgBr _1-y I _y , where 0.25≤y≤0.375, with a mass ratio of cesium iodide: complex silver bromide-iodide equal to 24.03 ÷ 24.29: 75.71 ÷ 75.97, while the ratio of the total number of cesium ions and silver is 1: 4. Homogenized in an agate mortar and transferred to a quartz glass seal was placed in the evacuated oven or reactor is evacuated to a residual pressure of 10 ^-2 ÷ 10 ^-3 atm, and then subjected to annealing in the temperature range 160-170 ^{° C} with not less than threefold intermediate homogenization, for ⁓ 160-190 hours. Get tetra-silver-cesium pentahalide composition CsAg ₄ Br _3-x I _{2 + x} , where 0.25≤x≤0.5. The composition of the final product is controlled by x-ray diffraction and thermal analysis methods. The ionic conductivity of the final product is measured in a symmetric two-probe two-electrode cell with reversible or blocking electrodes by the method of electrochemical impedance. The electronic component of conductivity is determined by the Habb-Wagner polarization method in an asymmetric two-probe two-electrode cell with blocking (carbon) and reversible (silver) electrodes according to the method described in the well-known source (N. Valverde. Thermodynamic stabilization of the solid electrolyte RbAg ₄ I _5. J. Electrochem. Soc.: Solid State Science and Technology, 1980, V.127, No. 11, p. 2425-2429).

The essence of the invention is illustrated by the following examples of specific performance.

Example 1. Prepare a reaction mixture of 2.7670 g of CsI and 8.7500 g of a solid solution of AgBr _0.625 I _0.375 , which corresponds to the mass ratio of cesium iodide: complex bromide-silver iodide equal to 24.03: 75.97, while the ratio of the total number of cesium ions and silver is 1: 4. Homogenized in an agate mortar for 30 min, transferred to a quartz glass capacity of 250 ml, compacted, placed in a sealed stainless steel reactor volume 400 cm ^3, is evacuated to a residual pressure of 10 ^-2 atm, and then subjected to calcination at 170 ° ^C with intermediate homogenization after 24 hours, 48 hours, 48 hours and final homogenization after 48 hours with a total annealing time of 168 hours. After each stage of annealing, the reactor is cooled to room temperature, the residual pressure is monitored with a vacuum gauge (to make sure it is unchanged), the valve is opened to establish atmospheric pressure, and the beaker with the reaction mixture is removed. Next, intermediate homogenization of the material in an agate mortar is carried out for 30 minutes, it is again loaded into a quartz glass, compacted, placed in a reactor, the reactor is evacuated, placed in an oven and annealing is continued. The resulting product is homogenized in an agate mortar, placed in a dark glass jar and a sample is taken to control the phase composition. All operations are carried out in a dark room with red lighting. The product is stored in isolation from light.

Prepared well otkristallizovanny single-phase powder of a given composition CsAg ₄ Br _2.5 I _2.5 cubic cell parameter a = 10,957 Å (which corresponds to data ICDDPDF-2 [46-50]) and a melting onset temperature of 179 ^{° C} (other effects on the thermogram lacking). Yield 97-98%. Ionic conductivity at 25 ^about C is 0.28 Ohm ^-1 · cm ^-1 ; the electronic component of conductivity is 8 × 10 ^-9 Ohm ^-1 · cm ^-1 .

Example 2. Prepare a reaction mixture of 2.5981 g CsI and 8.0974 g of a solid solution of AgBr _0.688 I _0.312 , which corresponds to the mass ratio of cesium iodide: complex bromide-silver iodide equal to 24.29: 75.71, while the ratio of the total number of cesium and silver ions equal to 1: 4. Homogenize in an agate mortar for 30 minutes, transfer to a quartz glass with a capacity of 250 ml, compact, place in a sealed stainless steel reactor with a volume of 400 cm ³ , vacuum to a residual pressure of 10 ^-3 atm, and then calcine at 160 with intermediate homogenization after 48 hours, 48 hours, 48 hours and final homogenization after 48 hours with a total annealing time of 192 hours. After each stage of annealing, the reactor is cooled to room temperature, the residual pressure is monitored with a vacuum gauge (to make sure it remains unchanged), the valve is opened to establish atmospheric pressure, and the beaker with the reaction mixture is removed. Next, intermediate homogenization of the material in an agate mortar is carried out for 30 minutes, it is again loaded into a quartz glass, compacted, placed in a reactor, the reactor is evacuated, placed in an oven and annealing is continued. The resulting product is homogenized in an agate mortar, placed in a dark glass jar and a sample is taken to control the phase composition. All operations are carried out in a dark room with red lighting. The product is stored in isolation from light.

Prepared well otkristallizovanny single-phase powder of a given composition CsAg ₄ Br _2.75 I _2.25 with a cubic cell parameter a = 10.924 Å (which corresponds to data ICDDPDF-2 [46-50]) and a melting onset temperature of 179 ^{° C} with an admixture of trace amounts CsAgBr _2. Yield 97-98%. Ionic conductivity at 25 ^about C is 0.25 Ohm ^-1 · cm ^-1 ; the electronic component of conductivity is 8 × 10 ^-9 Ohm ^-1 · cm ^-1 .

Thus, the authors propose a method for producing a solid electrolyte with high conductivity on silver cations at ambient temperatures, eliminating the stages of charge melting, melt mixing, crystallization and disaggregation of solidified melt, due to a decrease in the annealing temperature, which simplifies the production technology, providing the possibility of scaling and use only standard laboratory equipment.

Claims (1)

A method for producing a solid electrolyte based on tetra-silver-cesium pentahalides, comprising annealing a mixture of cesium and silver bromides and iodides with intermediate homogenization, characterized in that a silver bromide-iodide of the composition AgBr _1-y I _{y is} used as a silver compound, where 0 , 25≤y≤0.375, in the mass ratio of cesium iodide: complex silver bromide-iodide, equal to 24.03

24.29: 75.71

75.97, while the ratio of the total amounts of cesium and silver ions is 1: 4, and annealing are sealingly mixture at a temperature ^of 160-170 C in a vacuum at a residual pressure of 10 ^-2

10 ^-3 atm with at least three times intermediate homogenization.