Preparation method of sodium bis(oxalatoborate) and obtained product

Abstract

The present invention provides a preparation method of sodium bis(oxalatoborate) and the resulting product, belonging to the technical field of electrochemical materials. The preparation method of sodium bis(oxalatoborate) provided by the present invention comprises the following steps: preparing a sodium bis(oxalatoborate) mixed precursor; pressing the obtained sodium bis(oxalatoborate) mixed precursor into tablets, and placing the tabletted precursor in a hydrothermal reactor for high-temperature calcination, using the water vapor and pressure changes generated by the calcination reaction itself to accelerate the reaction to obtain a white solid; ball milling the obtained white solid, washing the crushed solid powder with a solvent, and placing it in a rotary evaporator for rotary evaporation and drying to obtain high-purity sodium bis(oxalatoborate). The method provided by the present invention has a simple process route and a short time consumption. Compared with the traditional solid phase method, oxalic acid does not need to be excessive, the cost is low, the product quality is good, and the yield is high, which can solve the defects in the solid phase method for synthesizing NaBOB.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical materials, and in particular relates to a preparation method of sodium bis(oxalatoborate) and the obtained product. Background Art

[0002] As an important component of sodium-ion batteries, the performance of electrolyte sodium salt affects the battery's specific energy, safety performance, cycle performance, rate performance and battery cost. At present, the main electrolyte for commercial sodium-ion batteries is sodium hexafluorophosphate (NaPF6), but it is easily hydrolyzed and has poor thermal stability. It will immediately generate HF when in contact with moisture in the air and residual moisture in the solvent, which limits its further use in sodium battery systems. Other sodium salt additives need to be added to improve the high-temperature performance and stability characteristics of the sodium battery system. Lithium bis(oxalatoborate) (NaBOB) has a high decomposition temperature (≥300°C) and better high-temperature stability than NaPF6. It can assist in the formation of a stable SEI film in the electrolyte, effectively inhibiting the direct contact between the electrolyte and the electrode surface, inhibiting electrolyte corrosion, and passivating aluminum foil.

[0003] At present, as sodium ion batteries are in the initial stage of the market, there are few patent reports on sodium ion batteries, especially sodium salt additives, and the only reported method for preparing NaBOB is mainly a solid phase synthesis method, which draws on the synthesis route of LiBOB products. As mentioned in CN110305153A, by mixing and tableting boric acid, oxalic acid and sodium compounds, solid-solid reaction is carried out under high temperature conditions, extraction is carried out in a non-aqueous solvent, and the extract is evaporated and crystallized to obtain the final product NaBOB. However, the defects of this method are: oxalic acid needs to be excessive to offset the loss of oxalic acid sublimation during high temperature calcination, and the product cost is high; the yield of the solid phase method is low, and the product purity is low. Therefore, it is urgent to find a simple, efficient and fast preparation method with excellent product performance to solve the defects in the solid phase synthesis of NaBOB process. Summary of the invention

[0004] The invention provides a preparation method of sodium bis(oxalatoborate) and the obtained product. The method has a simple process route and is time-saving. Compared with a traditional solid-phase method, the method does not require excessive oxalic acid, has low cost, good product quality and high yield, and can solve the defects existing in the solid-phase method for synthesizing NaBOB.

[0005] In order to achieve the above object, the present invention provides a method for preparing sodium bis(oxalatoborate), comprising the following steps:

[0006] preparing a sodium bis(oxalatoborate) mixed precursor;

[0007] The obtained sodium bis(oxalatoborate) mixed precursor is pressed into tablets, and the pressed precursor is placed in a hydrothermal reactor for high-temperature calcination, and the water vapor and pressure change generated by the calcination reaction itself are used to accelerate the reaction to obtain a white solid;

[0008] The obtained white solid is subjected to ball milling treatment, the crushed solid powder is washed with a solvent, and is placed in a rotary evaporator for rotary evaporation and drying to obtain high-purity sodium bis(oxalatoborate).

[0009] Compared with the traditional solid phase method, the above-mentioned preparation method adopted by the present invention has the advantages that: the uniformly mixed precursor is pressed into a sheet and placed in a closed hydrothermal reactor environment for calcination synthesis reaction, and the oxalic acid sublimated at high temperature will not be lost and volatilized, and will continue to participate in the NaBOB synthesis reaction as a reaction raw material in a closed system; at the same time, a large amount of water vapor will be generated during the synthesis reaction, further increasing the pressure in the reaction system, the reaction materials will not disperse rapidly, the contact between the materials will be closer, the product will have a higher mixing uniformity and better purity. In addition, the water vapor generated by the process reaction will be removed after the subsequent product washing and drying, and will not have any effect on the reaction.

[0010] Preferably, the preparation of the sodium bis(oxalatoborate) mixed precursor is as follows:

[0011] A sodium source, a boron source and oxalic acid are added into a sealed ball mill at a time according to a theoretical molar ratio, and the ball milling speed is controlled to be 100-600 r / min for 10-60 min to prepare a mixed precursor of sodium bis(oxalyl)borate.

[0012] Preferably, the feeding environment of the sodium source, boron source and oxalic acid is a half-cell assembly glove box or a drying room with a dew point below -50°C. It is understandable that the feeding environment is limited because oxalic acid and the sodium source are easy to absorb water when placed in the air, and are easy to produce large agglomerated particles in the subsequent ball milling mixing process, which is not conducive to the uniform mixing of the raw material precursors. After controlling the moisture, the raw materials will not agglomerate into blocks during the ball milling process, and the mixing uniformity of the precursors will be higher.

[0013] Preferably, the boron source is boric acid, and the sodium source is selected from at least one of sodium chloride, sodium nitrate, sodium hydroxide, sodium carbonate, sodium oxalate, sodium sulfate and sodium cobaltate.

[0014] Preferably, the molar ratio of the added oxalic acid, boron source, and sodium source is (2-2.8): 1: 1. It is understandable that if the amount of oxalic acid added is too much, the product quality and yield will be less affected, but the more excess oxalic acid, the greater the loss, and the cost of the product will increase; and if the amount of oxalic acid added is too little, more boron-containing impurities will be generated, and the purity of the product will be reduced.

[0015] Preferably, the obtained sodium bis(oxalatoborate) mixed precursor is pressed into tablets as follows:

[0016] The obtained sodium bis(oxalatoborate) mixed precursor is pressed into tablets at a pressure of 1-10 MPa, and the weight of a single tablet is 5 g / tablet.

[0017] Preferably, the solvent used is at least one selected from ether, acetone and ethanol.

[0018] Preferably, the calcination temperature of high temperature calcination is 120-280°C, and the calcination time is 2-8h; the drying temperature of the rotary evaporator is 60°C-180°C, and the drying time is 2-20h. It can be understood that in this scheme, the calcination temperature and time of high temperature calcination can be adjusted according to actual conditions. For example, the calcination temperature can be 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280°C or any point value within the above range, and the calcination time can be 2, 3, 4, 5, 6, 7, 8h or any point in the above range; similarly, the drying temperature can be 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180°C or any point in the above range, and the drying time can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20h or any point in the above range.

[0019] Preferably, the yield of the obtained sodium bis(oxalatoborate) is ≥95% and the purity is ≥99.5%.

[0020] The present invention also provides an electrolyte for a sodium ion battery, comprising sodium bis(oxalatoborate) prepared by the preparation method described in any one of the above technical solutions.

[0021] Compared with the prior art, the advantages and positive effects of the present invention are:

[0022] The present invention relates to a preparation technology of sodium salt electrolyte for sodium ion batteries, and specifically to a preparation method of sodium bis(oxalatoborate) (NaBOB). The method comprises the following steps: uniformly mixing materials such as a sodium source, a boron source, and oxalic acid, and then pressing the mixture into a sheet, which is then placed in a closed hydrothermal reactor for high-temperature calcination, and utilizing the water vapor and pressure changes generated by the calcination reaction itself to accelerate the reaction, and crushing the crude NaBOB obtained by calcination, washing with an organic solvent, and drying to obtain a NaBOB product. The method of the present invention has a simple process route and is relatively short in time. Compared with the traditional solid phase method, no excessive oxalic acid is required, the cost is relatively low, the product quality is relatively good, the yield is relatively high, and it is conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the infrared test spectrum of sodium bis(oxalatoborate) NaBOB prepared in Example 1;

[0024] Figure 2 This is the XRD test spectrum of sodium bis(oxalylborate) NaBOB prepared in Example 1. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] Oxalic acid, boric acid and sodium hydroxide were added into a sealed ball mill at a molar ratio of 2:1:1 (the addition should be carried out in a half-cell assembly glove box or a dry room with a dew point below -50°C), and the ball milling speed was set to 500r / min, and the ball milling time was controlled to 10min to generate a mixed precursor of NaBOB;

[0028] The mixed precursor is placed in a tablet press and pressed into tablets, wherein the weight of a single mixed tablet is 5 g / tablet and the pressure is 7 MPa;

[0029] The pressed mixture tablets are placed in a hydrothermal reactor, and then placed in an oven or a muffle furnace for high-temperature calcination, and the water vapor and pressure changes generated by the calcination reaction are used to accelerate the reaction to obtain a white solid, wherein the calcination temperature is 150° C. and the calcination time is 6 hours;

[0030] The obtained white solid is crushed, and the crushed solid powder is washed with anhydrous ethanol, and then filtered to obtain a reaction residue;

[0031] The obtained filter residue was placed in a rotary evaporator for drying at a temperature of 60°C, a drying time of 20 h, and a rotary vacuum of 0.1 MPa;

[0032] After drying, high-purity sodium bis(oxalatoborate) is obtained, wherein the NaBOB yield can reach 95.7% and the purity can reach 99.93%. The infrared test spectrum of the obtained high-purity sodium bis(oxalatoborate) is as follows: Figure 1 As shown, such as 820cm -1 , 1776cm -1 (C=O vibration coupling), 1372cm -1 The peaks at positions such as (COBOC stretching vibration) are consistent with those in the standard infrared spectrum of NaBOB; the XRD test spectrum is as follows Figure 2As shown, the strongest peaks appear at 21.96°, 37.34° and 41.50°, and the second strongest peaks appear at 13.94° and 26.82°, and their peak positions are consistent with the NaBOB standard spectrum.

[0033] Example 2

[0034] Oxalic acid, boric acid and sodium hydroxide were added into a sealed ball mill at a molar ratio of 2.8:1:1 (the addition should be carried out in a half-cell assembly glove box or a dry room with a dew point below -50°C), and the ball milling speed was set to 350r / min, and the ball milling time was controlled to 25min to generate a mixed precursor of NaBOB;

[0035] The mixed precursor is placed in a tablet press and pressed into tablets, wherein the weight of a single mixed tablet is 5 g / tablet and the pressure is 7 MPa;

[0036] The pressed mixture tablets are placed in a hydrothermal reactor, and then placed in an oven or a muffle furnace for heating, and the water vapor and pressure changes generated by the calcination reaction are used to accelerate the reaction to obtain a white solid, wherein the calcination temperature is 120°C and the calcination time is 6 hours;

[0037] The obtained white solid is crushed to obtain a reaction residue;

[0038] The obtained filter residue was placed in a rotary evaporator for drying at a temperature of 180°C, a drying time of 3 h, and a rotary vacuum of 0.1 MPa;

[0039] After drying, high-purity sodium bis(oxalatoborate) is obtained, wherein the NaBOB yield can reach 96.4% and the purity can reach 99.79%.

[0040] Example 3

[0041] Oxalic acid, boric acid and sodium hydroxide were added into a sealed ball mill at a molar ratio of 2.3:1:1 (the addition should be carried out in a half-cell assembly glove box or a dry room with a dew point below -50°C), and the ball milling speed was set to 160r / min, and the ball milling time was controlled to 45min to generate a mixed precursor of NaBOB;

[0042] The mixed precursor is placed in a tablet press and pressed into tablets, wherein the weight of a single mixed tablet is 5 g / tablet and the pressure is 7 MPa;

[0043] The pressed mixture tablets are placed in a hydrothermal reactor, and then placed in an oven or a muffle furnace for heating, and the water vapor and pressure changes generated by the calcination reaction are used to accelerate the reaction to obtain a white solid, wherein the calcination temperature is 200°C and the calcination time is 4h;

[0044] The obtained white solid is crushed, and the crushed solid powder is washed with anhydrous ethanol, and then filtered to obtain a reaction residue;

[0045] The obtained filter residue was placed in a rotary evaporator for rotary drying at a drying temperature of 80°C, a drying time of 16 h, and a rotary vacuum degree of 0.1 MPa.

[0046] After drying, high-purity sodium bis(oxalatoborate) is obtained, wherein the NaBOB yield can reach 95.8% and the product purity can reach 99.81%.

[0047] Example 4

[0048] Oxalic acid, boric acid and sodium hydroxide were added into a sealed ball mill at a molar ratio of 2.5:1:1 (the addition should be carried out in a half-cell assembly glove box or a dry room with a dew point below -50°C), and the ball milling speed was set to 100 r / min and the ball milling time was controlled to 60 min to generate a mixed precursor of NaBOB;

[0049] The mixed precursor is placed in a tablet press and pressed into tablets, wherein the weight of a single mixed tablet is 5 g / tablet and the pressure is 7 MPa;

[0050] The pressed mixture tablets are placed in a hydrothermal reactor, and then placed in an oven or a muffle furnace for heating, and the water vapor and pressure changes generated by the calcination reaction are used to accelerate the reaction to obtain a white solid, wherein the calcination temperature is 280°C and the calcination time is 2h;

[0051] The obtained white solid is crushed, and the crushed solid powder is washed with anhydrous ethanol, and then filtered to obtain a reaction residue;

[0052] The obtained filter residue was placed in a rotary evaporator for rotary drying at a drying temperature of 120°C, a drying time of 8 hours, and a rotary vacuum degree of 0.1 MPa.

[0053] After drying, high-purity sodium bis(oxalatoborate) is obtained, wherein the NaBOB yield can reach 96.5% and the product purity can reach 99.52%.

[0054] Comparative Example 1

[0055] The preparation method is the same as that of Example 2, except that the calcination temperature is 80°C.

[0056] The yield of the obtained high-purity sodium bis(oxalatoborate) can reach 93.2%, and the purity can reach 91.3%.

[0057] Comparative Example 2

[0058] The preparation method is the same as that of Example 2, except that the calcination temperature is 360°C.

[0059] The yield of the obtained high-purity sodium bis(oxalatoborate) can reach 90.2%, and the purity can reach 92.3%.

[0060] Comparative Example 3 (Preparation of NaBOB by Traditional Method)

[0061] The preparation method is the same as that of Example 1, except that: 1) oxalic acid, boric acid and sodium hydroxide are directly mixed in air; and 2) the pressed mixture sheet is placed in an ordinary crucible, and the crucible is placed in a muffle furnace for heating.

[0062] The yield of the obtained high-purity sodium bis(oxalatoborate) can reach 87%, and the purity can reach 83.2%.

Claims

1. A method for preparing sodium bis(oxalatoborate), characterized in that: The following steps are involved: Sodium hydroxide, boric acid and oxalic acid are added into a sealed ball mill at a molar ratio of (2-2.8): 1:1 at once, and the ball milling speed is controlled to be 100-600 r / min for 10-60 min to prepare a mixed precursor of sodium bis(oxalatoborate); The obtained sodium bis(oxalatoborate) mixed precursor is pressed into tablets, and the pressed precursor is placed in a hydrothermal reactor and calcined at 120-280° C. for 2-8 hours, and the water vapor and pressure change generated by the calcination reaction itself are used to accelerate the reaction to obtain a white solid; The obtained white solid is subjected to ball milling treatment, and the crushed solid powder is washed with a solvent and placed in a rotary evaporator for rotary evaporation to obtain high-purity sodium bis(oxalatoborate). The yield of the obtained sodium bis(oxalatoborate) is ≥95%, and the purity is ≥99.5%.

2. The preparation method according to claim 1, characterized in that: The feeding environment of sodium hydroxide, boric acid and oxalic acid is in a half-cell assembly glove box or a dry room with a dew point below -50°C.

3. The preparation method according to claim 1, characterized in that: The obtained sodium bis(oxalatoborate) mixed precursor is pressed into tablets as follows: The obtained sodium bis(oxalatoborate) mixed precursor is pressed into tablets at a pressure of 1-10 MPa, and the weight of a single tablet is 5 g / tablet.

4. The preparation method according to claim 1, characterized in that: The solvent used is selected from at least one of ether, acetone and ethanol.

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