CN115924931B - Compound lithium sodium borate, preparation method and application - Google Patents

Abstract

The present invention provides a compound sodium lithium borate, a preparation method and a use thereof. The compound has a chemical formula of Li _1.45 Na _7.55 B ₂₁ O ₃₆ , a molecular weight of 986.65, belongs to a hexagonal system, has a space group of P 6 ₃ / mcm , unit cell parameters of a=9.3446Å, b=9.3446Å, c=20.2013Å, α=β=90°, γ=120°, a unit cell volume of 1527.68Å ³ , and is prepared by a solid phase synthesis method, a high temperature melt method, a hydrothermal method or a room temperature solution method. The sodium lithium borate of the present invention does not deliquesce in the air, is stable within 732°C, has an ultraviolet absorption edge shorter than 200nm, has a one-dimensional lithium ion channel structure in the structure, and can be used as a lithium ion battery electrode material.

Description

A compound sodium lithium borate and its preparation method and use

Technical Field

The invention relates to a preparation method and application of a compound sodium lithium borate, belonging to the field of new materials.

Background technique

Borates are widely used in optoelectronic materials, glass materials, ceramic materials, fireproof materials and additive materials due to their rich structures and excellent performance. According to previous research, two-thirds of borates have isolated anionic groups, while less than 10% of borates have one-dimensional chain anionic groups. Among the many borate groups, the twelve-membered ring boron twelve oxygen twenty-tetradecanoic group is a common anionic group, but its potential application has not yet been discovered. Lithium-ion batteries are widely used in mobile phones, notebooks and other electronic products batteries and new energy vehicle batteries due to their high energy density, high average output voltage, low self-discharge, no memory effect, wide operating temperature range, excellent cycle performance, fast charging and discharging, high charging efficiency, high output power, long service life, and no toxic and harmful substances. However, they also have disadvantages such as easy aging, low recovery rate, and intolerance to overcharge and over-discharge. Lithium-ion batteries are closely related to the performance of lithium electrode electrolyte materials of batteries, so new high-performance lithium-ion battery materials are urgently needed.

Summary of the invention

The present invention aims to provide a new compound, sodium lithium borate, which has a chemical formula of Li _1.45 Na _7.55 B ₂₁ O ₃₆ , a molecular weight of 986.65, belongs to the hexagonal system, has a space group of P6 ₃ /mcm, and a unit cell parameter of α＝β＝90°，γ＝120°，the unit cell volume is The compound sodium lithium borate is prepared by solid phase synthesis, high temperature melt method, hydrothermal method or room temperature solution method. The compound sodium lithium borate of the present invention is expected to be used as a lithium ion battery material.

The compound sodium lithium borate is characterized in that it is prepared by solid phase synthesis method, high temperature melt method, hydrothermal method or room temperature solution method.

The solid phase synthesis method is used to prepare the compound sodium lithium borate, and the specific operation is carried out according to the following steps:

The Li-containing compound, the Na-containing compound and the B-containing compound are uniformly mixed at a molar ratio of Li:Na:B=0.5-3:5-7:15-25, and the mixture is put into a ceramic crucible, and then placed in a muffle furnace, and the temperature is raised to 500-700°C, and the temperature is kept constant for 3-96 hours to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ ; the Li-containing compound is LiBO ₂ , Li ₂ CO ₃ , LiNO ₃ , LiHCO ₃ , LiOH or CH ₃ COOLi; the Na-containing compound is a compound NaBO ₂ , Na ₂ CO ₃ , NaNO ₃ , NaHCO ₃ , NaOH or CH ₃ COONa; the B-containing compound is H ₃ BO ₃ , B ₂ O ₃ or HBO ₂ ;

The high temperature melt method for preparing the compound sodium lithium borate is specifically carried out in the following steps:

a. Mix the Li-containing compound, the Na-containing compound and the B-containing compound in a molar ratio of Li:Na:B=0.5-3:5-7:15-25, put them into a ceramic crucible, and then put them into a muffle furnace, heat them to 500-700°C, and keep them at this temperature for 3-96 hours to obtain polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ ; the Li-containing compound is LiBO ₂ , Li ₂ CO ₃ , LiNO ₃ , LiHCO ₃ , LiOH or CH ₃ COOLi; the Na-containing compound is NaBO ₂ , Na ₂ CO ₃ , NaNO ₃ , NaHCO ₃ , NaOH or CH ₃ COONa; the B-containing compound is H ₃ BO ₃ , B ₂ O ₃ or HBO ₂ ;

b. The polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in step a is uniformly mixed with a flux in a molar ratio of 1:0.1-0.5, and then put into a clean platinum crucible, and the temperature is increased to 600-850°C at a rate of 35-45°C/h, and kept at a constant temperature for 7-15 hours to obtain a mixed melt; the Li-containing compound is LiBO ₂ , Li ₂ CO ₃ , LiNO ₃ , LiHCO ₃ , LiOH or CH ₃ COOLi; the Na-containing compound is NaBO ₂ , Na ₂ CO ₃ , NaNO ₃ , NaHCO ₃ , NaOH or CH ₃ COONa; the B-containing compound is H ₃ BO ₃ , B ₂ O ₃ or HBO ₂ ; the flux is H ₃ BO ₃ , B ₂ O ₃ , HBO ₂ , PbO or PbF ₂ ;

c. placing the mixed melt obtained in step b in a single crystal furnace, then cooling the temperature to 600-750°C at a rate of 0.1-0.5°C/h, cooling the temperature to 550-650°C at a rate of 0.2-0.6°C/h, and then cooling the temperature to 30°C at a rate of 3-10°C/h to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ ;

The hydrothermal method for preparing the compound sodium lithium borate is specifically carried out in the following steps:

a. Mix a Li-containing compound, a Na-containing compound and a B-containing compound in a molar ratio of Li:Na:B=0.5-3:5-7:15-25, put them into a ceramic crucible, and then put them into a muffle furnace, heat them to 500-700°C, and keep them at this temperature for 3-96 hours to obtain a product of Li _1.45 Na _7.55 B ₂₁ O ₃₆ polycrystalline powder; the Li-containing compound is LiBO ₂ , Li ₂ CO ₃ , LiNO ₃ , LiHCO ₃ , LiOH or CH ₃ COOLi; the Na-containing compound is a compound NaBO ₂ , Na ₂ CO ₃ , NaNO ₃ , NaHCO ₃ , NaOH or CH ₃ COONa; the B-containing compound is H ₃ BO ₃ , B ₂ O ₃ or HBO ₂ ;

b. The polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in step a is placed in 5-30 mL of deionized water to dissolve, and the incompletely dissolved mixture is subjected to ultrasonic treatment at a temperature of 20-50° C. for 5-30 minutes to fully mix and dissolve;

c. Transfer the mixed solution obtained in step b into the liner of a clean, pollution-free autoclave with a volume of 100 mL, and tighten and seal the autoclave;

d. Place the autoclave in a thermostatic box, raise the temperature to 150-350°C at a rate of 5-50°C/h, keep the temperature constant for 3-15 days, and then cool it down to room temperature at a rate of 5-30°C/day to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ ;

The room temperature solution method is used to prepare the compound sodium lithium borate, and the specific operation is carried out according to the following steps:

a. Mix a Li-containing compound, a Na-containing compound and a B-containing compound in a molar ratio of Li:Na:B=0.5-3:5-7:15-25, put them into a ceramic crucible, and then put them into a muffle furnace, heat them to 500-700°C, and keep them at this temperature for 3-96 hours to obtain a product of Li _1.45 Na _7.55 B ₂₁ O ₃₆ polycrystalline powder; the Li-containing compound is LiBO ₂ , Li ₂ CO ₃ , LiNO ₃ , LiHCO ₃ , LiOH or CH ₃ COOLi; the Na-containing compound is a compound NaBO ₂ , Na ₂ CO ₃ , NaNO ₃ , NaHCO ₃ , NaOH or CH ₃ COONa; the B-containing compound is H ₃ BO ₃ , B ₂ O ₃ or HBO ₂ ;

b. Place the polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in step a into a clean glass container, add 20-100 mL of deionized water, and then treat with ultrasound for 5-60 minutes to fully mix and dissolve it, and then add HF and NaOH to adjust the pH value of the solution to 8-11;

c. Seal the container containing the solution in step b with weighing paper, place it in a static environment without shaking, pollution, and air convection, pierce the seal with a small hole to control the evaporation rate to 0.2-2 mL/day, and let it stand at room temperature for 5-20 days;

d. Waiting for the solution in step c to grow crystal particles at the bottom of the container until the size of the crystal particles no longer changes significantly, the growth is completed, and a seed crystal is obtained;

e. Filter the remaining solution with qualitative filter paper to remove the crystals and other impurities in the solution, select seed crystals with good quality, fix the seed crystals with platinum wire, suspend them in the filtered solution, pierce the seal with small holes to control the evaporation rate to 0.2-2 mL/day, and let it stand and grow at room temperature for 10-30 days to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ .

The preparation method of the compound sodium lithium borate Li _1.45 Na _7.55 B ₂₁ O ₃₆ of the present invention, the sodium lithium borate polycrystalline powder used in preparing the mixed melt or the mixed solution can also be replaced by directly weighed raw materials, that is, the Li-containing compound, the Na-containing compound and the B-containing compound are weighed and mixed uniformly at a molar ratio of Li:Na:B=0.5-3:5-7:15-25, the Li-containing compound is LiBO ₂ , Li ₂ CO ₃ , LiNO ₃ , LiHCO ₃ , LiOH or CH ₃ COOLi; the Na-containing compound is a compound NaBO ₂ , Na ₂ CO ₃ , NaNO ₃ , NaHCO ₃ , NaOH or CH ₃ COONa; the B-containing compound is H ₃ BO ₃ , B ₂ O ₃ or HBO ₂ .

The preparation method of the compound sodium lithium borate of the present invention comprises a platinum crucible, a ceramic crucible, a quartz tube, a conical flask, a beaker, and a hydrothermal kettle lined with polytetrafluoroethylene or a stainless steel liner equipped with a platinum sleeve. When the container is a quartz tube, it needs to be vacuumed before sealing to prevent the quartz tube from bursting due to volatilization of the raw materials during the reaction. When the container is a conical flask or a beaker, the container must be cleaned with acid first, then rinsed with deionized water, and dried.

In the preparation method of the compound sodium lithium borate of the present invention, the resistance furnace used in the preparation process is a muffle furnace or a drying box.

The compound sodium lithium borate described in the present invention is expected to be used as a lithium ion battery material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a structural diagram of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ of the present invention, wherein the anion group is composed of a one-dimensional chain-like boron-oxygen structure;

FIG2 is a powder XRD spectrum of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ of the present invention, which is consistent with the theoretical XRD spectrum, proving the existence of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ , measured from the powder obtained in Example 1;

FIG3 is an EDS spectrum of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ of the present invention, and the spectrum shows that the element types of the experiment and the theory are consistent, proving the rationality of the elements of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ , which is measured from the powder obtained in Example 3;

FIG. 4 is a test graph of the electrical conductivity of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ of the present invention, measured from the powder obtained in Example 4.

Detailed ways

The present invention is further described below in conjunction with examples. It should be noted that the present invention is not limited to the examples listed, and any improvements made on the basis of the present invention do not violate the spirit of the present invention. The raw materials or equipment used in the present invention, unless otherwise specified, are all commercially available.

Example 1

The compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ was prepared by solid phase synthesis;

The compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ was synthesized by solid phase synthesis according to the reaction 1.45LiBO ₂ +7.55NaBO ₂ +12H ₃ BO ₃ →Li _1.45 Na _7.55 B ₂₁ O ₃₆ :

LiBO ₂ , NaBO ₂ and B ₂ O ₃ were mixed evenly in a molar ratio of 3:15:12, placed in a clean, pollution-free platinum crucible of 28 mL, heated to 500° C., and kept at this temperature for 96 hours to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ ;

A portion of the sample powder was taken for powder XRD test, and the test results are shown in FIG2 .

Example 2

The compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ was prepared by solid phase synthesis;

The compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ was synthesized by solid phase synthesis according to the reaction 1.45LiBO ₂ +7.55NaBO ₂ +6B ₂ O ₃ →Li _1.45 Na _7.55 B ₂₁ O ₃₆ :

LiBO ₂ , NaBO ₂ and B ₂ O ₃ were mixed uniformly in a molar ratio of 3:15:12, placed in a clean, pollution-free platinum crucible of 28 mL, heated to 700° C. and kept at this temperature for 3 hours to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ .

Example 3

Preparation of compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ by high temperature melt method;

The Li _1.45 Na _7.55 B ₂₁ O ₃₆ polycrystalline powder obtained in Example 1 was mixed evenly with flux H ₃ BO ₃ at a molar ratio of 1:0.3, and then placed in a clean platinum crucible, and heated to 700°C at a rate of 40°C/h and kept at this temperature for 10 hours to obtain a mixed melt;

The prepared mixed melt was placed in a single crystal furnace, and then cooled to 700°C at a rate of 0.3°C/h, then cooled to 600°C at a rate of 0.3°C/h, and then cooled to 30°C at a rate of 5°C/h to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ .

Example 4

Preparation of compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ by high temperature melt method;

The compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ polycrystalline powder obtained in Example 2 is uniformly mixed with flux B ₂ O ₃ , HBO ₂ , PbO or PbF ₂ at a molar ratio of 1:0.5, and then put into a clean platinum crucible, and the temperature is increased to 720°C at a rate of 35°C/h, and kept at this temperature for 9 hours to obtain a mixed melt;

The prepared mixed melt was placed in a single crystal furnace, then cooled to 720°C at a rate of 0.4°C/h, cooled to 600°C at a rate of 0.4°C/h, and then cooled to 30°C at a rate of 3°C/h to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ .

Example 5

The high temperature melt method for preparing the compound sodium lithium borate is specifically carried out in the following steps:

The polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in Example 1 was mixed evenly with flux HBO ₂ at a molar ratio of 1:0.2, and then placed in a clean platinum crucible, and heated to 600° C. at a rate of 38° C./h, and kept at this temperature for 7 hours to obtain a mixed melt;

The obtained mixed melt was placed in a single crystal furnace, and then cooled to 600°C at a rate of 0.2°C/h, cooled to 550°C at a rate of 0.3°C/h, and then cooled to 30°C at a rate of 7°C/h to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ ;

Example 6

The high temperature melt method for preparing the compound sodium lithium borate is specifically carried out in the following steps:

The polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in Example 2 was mixed evenly with flux PbO at a molar ratio of 1:0.4, and then placed in a clean platinum crucible, and heated to 800° C. at a rate of 42° C./h, and kept at this temperature for 10 hours to obtain a mixed melt;

The obtained mixed melt was placed in a single crystal furnace, and then cooled to 650°C at a rate of 0.4°C/h, cooled to 600°C at a rate of 0.4°C/h, and then cooled to 30°C at a rate of 7°C/h to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ ;

Example 7

The high temperature melt method for preparing the compound sodium lithium borate is specifically carried out in the following steps:

The polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in Example 1 was mixed evenly with flux PbF ₂ at a molar ratio of 1:0.5, and then placed in a clean platinum crucible, and heated to 850° C. at a rate of 45° C./h, and kept at this temperature for 15 hours to obtain a mixed melt;

The obtained mixed melt was placed in a single crystal furnace, and then cooled to 750°C at a rate of 0.5°C/h, cooled to 650°C at a rate of 0.6°C/h, and then cooled to 30°C at a rate of 10°C/h to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ ;

Example 8

The hydrothermal method for preparing the compound sodium lithium borate is specifically carried out in the following steps:

The polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in Example 1 was placed in 5 mL of deionized water for dissolution, and the incompletely dissolved mixture was subjected to ultrasonic treatment at a temperature of 20° C. for 30 minutes to fully mix and dissolve;

The obtained mixed solution was transferred into the liner of a clean, non-polluting autoclave with a volume of 100 mL, and the autoclave was tightened and sealed;

The autoclave was placed in a thermostatic box, and the temperature was raised to 350°C at a rate of 5°C/h, kept constant for 3 days, and then cooled to room temperature at a rate of 5°C/day, to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ .

Example 9

The hydrothermal method for preparing the compound sodium lithium borate is specifically carried out in the following steps:

The polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in Example 2 was placed in 10 mL of deionized water for dissolution, and the incompletely dissolved mixture was subjected to ultrasonic treatment at a temperature of 30° C. for 20 minutes to fully mix and dissolve;

The obtained mixed solution was transferred into the liner of a clean, non-contaminated high-pressure reactor with a volume of 100 mL, and the reactor was tightened and sealed;

The autoclave was placed in a thermostatic box, heated to 300°C at a rate of 10°C/h, kept at the constant temperature for 8 days, and then cooled to room temperature at a rate of 10°C/day, to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ .

Example 10

The hydrothermal method for preparing the compound sodium lithium borate is specifically carried out in the following steps:

The polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in Example 2 was placed in 15 mL of deionized water for dissolution, and the incompletely dissolved mixture was subjected to ultrasonic treatment at a temperature of 25° C. for 25 minutes to fully mix and dissolve;

The obtained mixed solution was transferred into the liner of a clean, non-polluting autoclave with a volume of 100 mL, and the autoclave was tightened and sealed;

The autoclave was placed in a thermostatic box, heated to 200°C at a rate of 25°C/h, kept at the constant temperature for 10 days, and then cooled to room temperature at a rate of 25°C/day, to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ .

Embodiment 11

The hydrothermal method for preparing the compound sodium lithium borate is specifically carried out in the following steps:

The polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in Example 1 was placed in 30 mL of deionized water for dissolution, and the incompletely dissolved mixture was subjected to ultrasonic treatment at a temperature of 50° C. for 5 minutes to fully mix and dissolve;

The obtained mixed solution was transferred into the liner of a clean, non-polluting autoclave with a volume of 100 mL, and the autoclave was tightened and sealed;

The autoclave was placed in a thermostatic box, heated to 350°C at a rate of 50°C/h, kept at the constant temperature for 15 days, and then cooled to room temperature at a rate of 30°C/day, to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ .

Example 12

The room temperature solution method is used to prepare the compound sodium lithium borate, and the specific operation is carried out according to the following steps:

The polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in Example 1 was placed in a clean glass container, 20 mL of deionized water was added, and then ultrasonic treatment was performed for 5 minutes to fully mix and dissolve the powder, and then HF and NaOH were added to adjust the pH value of the solution to 8;

Seal the container containing the solution with weighing paper, place it in a static environment without shaking, pollution, or air convection, pierce a small hole in the seal to control the evaporation rate to 0.2 mL/day, and leave it at room temperature for 5 days;

Wait for the solution to grow crystal particles at the bottom of the container until the size of the crystal particles no longer changes significantly, and the growth is completed to obtain a seed crystal;

The remaining solution was filtered with qualitative filter paper to remove the crystals and other impurities in the solution. Seed crystals with better quality were selected and fixed with platinum wire. The seed crystals were suspended in the filtered solution. The seal was pierced with small holes to control the evaporation rate to 0.2 mL/day. The compound was grown at room temperature for 10 days to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ .

Example 13

The room temperature solution method is used to prepare the compound sodium lithium borate, and the specific operation is carried out according to the following steps:

The polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in Example 1 was placed in a clean glass container, 40 mL of deionized water was added, and then ultrasonic treatment was performed for 20 minutes to fully mix and dissolve the powder, and then HF and NaOH were added to adjust the pH value of the solution to 9;

Seal the container containing the solution with weighing paper, place it in a static environment without shaking, pollution, or air convection, pierce a small hole in the seal to control the evaporation rate to 0.5 mL/day, and leave it at room temperature for 10 days;

Wait for the solution to grow crystal particles at the bottom of the container until the size of the crystal particles no longer changes significantly, and the growth is completed to obtain a seed crystal;

The remaining solution was filtered with qualitative filter paper to remove the crystals and other impurities in the solution. Seed crystals with better quality were selected and fixed with platinum wire. The seed crystals were suspended in the filtered solution. The seal was pierced with small holes to control the evaporation rate to 0.5 mL/day. The solution was allowed to grow at room temperature for 15 days to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ .

Embodiment 14

The room temperature solution method is used to prepare the compound sodium lithium borate, and the specific operation is carried out according to the following steps:

The polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in Example 2 was placed in a clean glass container, 70 mL of deionized water was added, and then ultrasonic treatment was performed for 40 minutes to fully mix and dissolve it, and then HF and NaOH were added to adjust the pH value of the solution to 10;

Seal the container containing the solution with weighing paper, place it in a static environment without shaking, pollution, or air convection, pierce a small hole in the seal to control the evaporation rate to 1 mL/day, and leave it at room temperature for 15 days;

Wait for the solution to grow crystal particles at the bottom of the container until the size of the crystal particles no longer changes significantly, and the growth is completed to obtain a seed crystal;

The remaining solution was filtered with qualitative filter paper to remove the crystals and other impurities in the solution. Seed crystals with better quality were selected and fixed with platinum wire. The seed crystals were suspended in the filtered solution. The seal was pierced with small holes to control the evaporation rate to 1 mL/day. The compound was allowed to grow at room temperature for 25 days to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ .

Embodiment 15

The room temperature solution method is used to prepare the compound sodium lithium borate, and the specific operation is carried out according to the following steps:

The polycrystalline powder of the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ obtained in Example 1 was placed in a clean glass container, 100 mL of deionized water was added, and then ultrasonic treatment was performed for 60 minutes to fully mix and dissolve the powder, and then HF and NaOH were added to adjust the pH value of the solution to 11;

Seal the container containing the solution with weighing paper, place it in a static environment without shaking, pollution, or air convection, pierce a small hole in the seal to control the evaporation rate to 2 mL/day, and leave it at room temperature for 20 days;

Wait for the solution to grow crystal particles at the bottom of the container until the size of the crystal particles no longer changes significantly, and the growth is completed to obtain a seed crystal;

The remaining solution was filtered with qualitative filter paper to remove the crystals and other impurities in the solution. Seed crystals with better quality were selected and fixed with platinum wire. The seed crystals were suspended in the filtered solution. The seal was pierced with small holes to control the evaporation rate to 2 mL/day. The solution was allowed to grow at room temperature for 30 days to obtain the compound Li _1.45 Na _7.55 B ₂₁ O ₃₆ .

Claims (3)

1. A compound lithium sodium borate, which is characterized in that the chemical formula of the compound is Li _1.45Na_7.55B₂₁O₃₆, the molecular weight of the compound is 986.65, the compound belongs to a hexagonal system, the space group is P6 ₃/mcm, the unit cell parameters are a= 9.3446 a, b= 9.3446 a, c= 20.2013 a, α=β=90°, γ=120°, and the unit cell volume is 1527.68 a ³.

2. A method for preparing the compound lithium sodium borate as claimed in claim 1, wherein the compound lithium sodium borate is prepared by a solid phase synthesis method, a high Wen Rongye method, a hydrothermal method or a room temperature solution method;

the solid phase synthesis method for preparing the compound lithium sodium borate comprises the following steps:

Uniformly mixing a Li-containing compound, a Na-containing compound and a B-containing compound according to a chemical formula of Li _1.45Na_7.55B₂₁O₃₆, putting the mixture into a ceramic crucible, then putting the ceramic crucible into a muffle furnace, heating to 500-700 ℃, and keeping the temperature for 3-96 hours to obtain a compound Li _1.45Na_7.55B₂₁O₃₆; the Li-containing compound is LiBO ₂、Li₂CO₃、LiNO₃、LiHCO₃, liOH or CH ₃ COOLi; na-containing is a compound NaBO ₂、Na₂CO₃、NaNO₃、NaHCO₃, naOH or CH ₃ COONa; the compound containing B is H ₃BO₃、B₂O₃ or HBO ₂;

the preparation method of the compound sodium lithium borate by the high-temperature melt method comprises the following specific operations:

a. Uniformly mixing a Li-containing compound, a Na-containing compound and a B-containing compound according to a chemical formula of Li _1.45Na_7.55B₂₁O₃₆, putting the mixture into a ceramic crucible, then putting the ceramic crucible into a muffle furnace, heating to 500-700 ℃, and keeping the temperature for 3-96 hours to obtain polycrystalline powder of the compound Li _1.45Na_7.55B₂₁O₃₆; the Li-containing compound is LiBO ₂、Li₂CO₃、LiNO₃、LiHCO₃, liOH or CH ₃ COOLi; na-containing is a compound NaBO ₂、Na₂CO₃、NaNO₃、NaHCO₃, naOH or CH ₃ COONa; the compound containing B is H ₃BO₃、B₂O₃ or HBO ₂;

b. Uniformly mixing polycrystalline powder of the compound Li _1.45Na_7.55B₂₁O₃₆ obtained in the step a with a fluxing agent according to the mol ratio of 1:0.1-0.5, then placing the mixture into a cleaned platinum crucible, heating to 600-850 ℃ at the speed of 35-45 ℃/h, and keeping the temperature for 7-15 hours to obtain a mixed solution;

c. Placing the mixed solution prepared in the step b into a single crystal furnace, then cooling to 600-750 ℃ at the cooling rate of 0.1-0.5 ℃/h, cooling to 550-650 ℃ at the cooling rate of 0.2-0.6 ℃/h, and then cooling to 30 ℃ at the cooling rate of 3-10 ℃/h to obtain a compound Li _1.45Na_7.55B₂₁O₃₆;

the preparation of the compound sodium lithium borate by the hydrothermal method comprises the following steps:

a. Uniformly mixing a Li-containing compound, a Na-containing compound and a B-containing compound according to a chemical formula of Li _1.45Na_7.55B₂₁O₃₆, putting the mixture into a ceramic crucible, then putting the ceramic crucible into a muffle furnace, heating to 500-700 ℃, and keeping the temperature for 3-96 hours to obtain a product of Li _1.45Na_7.55B₂₁O₃₆ polycrystalline powder; the Li-containing compound is LiBO ₂、Li₂CO₃、LiNO₃、LiHCO₃, liOH or CH ₃ COOLi; na-containing is a compound NaBO ₂、Na₂CO₃、NaNO₃、NaHCO₃, naOH or CH ₃ COONa; the compound containing B is H ₃BO₃、B₂O₃ or HBO ₂;

b. C, putting the compound Li _1.45Na_7.55B₂₁O₃₆ polycrystalline powder obtained in the step a into 5-30mL of deionized water for dissolution, and performing ultrasonic treatment on the incompletely dissolved mixture at 20-50 ℃ for 5-30 minutes to enable the incompletely dissolved mixture to be fully mixed and dissolved;

c. Transferring the mixed solution obtained in the step b into a clean and pollution-free lining of a high-pressure reaction kettle with the volume of 100mL, and screwing and sealing the reaction kettle;

d. Placing the high-pressure reaction kettle in a constant temperature box, heating to 150-350 ℃ at the speed of 5-50 ℃/h, keeping the temperature for 3-15 days, and cooling to room temperature at the cooling speed of 5-30 ℃/day to obtain a compound Li _1.45Na_7.55B₂₁O₃₆;

the method for preparing the compound sodium lithium borate by the room-temperature solution method comprises the following steps:

a. Uniformly mixing a Li-containing compound, a Na-containing compound and a B-containing compound according to a chemical formula of Li _1.45Na_7.55B₂₁O₃₆, putting the mixture into a ceramic crucible, then putting the ceramic crucible into a muffle furnace, heating to 500-700 ℃, and keeping the temperature for 3-96 hours to obtain a product of Li _1.45Na_7.55B₂₁O₃₆ polycrystalline powder; the Li-containing compound is LiBO ₂、Li₂CO₃、LiNO₃、LiHCO₃, liOH or CH ₃ COOLi; na-containing is a compound NaBO ₂、Na₂CO₃、NaNO₃、NaHCO₃, naOH or CH ₃ COONa; the compound containing B is H ₃BO₃、B₂O₃ or HBO ₂;

b. placing the compound Li _1.45Na_7.55B₂₁O₃₆ polycrystalline powder obtained in the step a into a cleaned glass container, adding 20-100mL of deionized water, performing ultrasonic treatment for 5-60 minutes to fully mix and dissolve the deionized water, and then adding HF and NaOH to adjust the pH value of the solution to 8-11;

c. Sealing the container filled with the solution in the step b by using weighing paper, placing the container in a static environment without shaking, pollution and air convection, sealing small holes to control the evaporation rate to be 0.2-2 mL/day, and standing for 5-20 days at room temperature;

d. c, growing crystal particles on the bottom of the container until the crystal particle size is not changed obviously, and obtaining seed crystals after the growth is finished;

e. Filtering the residual solution with qualitative filter paper, selecting seed crystal with better quality, fixing the seed crystal with platinum wire, suspending the seed crystal in the filtered solution, sealing small holes to control the evaporation rate to 0.2-2 mL/day, standing at room temperature for 10-30 days, and obtaining the compound Li _1.45Na_7.55B₂₁O₃₆.

3. Use of the compound lithium sodium borate of claim 1 in lithium ion battery electrode materials.