A lithium oxalate, its preparation method and uses

Abstract

The present invention provides a lithium oxalate, a preparation method thereof and uses thereof. In the preparation method, granular or slurry-form oxalic acid is added to a lithium hydroxide solution at least in two portions until the pH is stabilized at 2-3, and then the separated liquid obtained after solid-liquid separation is subjected to evaporation crystallization to obtain a part of lithium oxalate, and at the same time, the obtained separated solid is dried to obtain another part of lithium oxalate. By improving the process route, the present invention does not need to dissolve oxalic acid. After adding granular or slurry-form oxalic acid to lithium hydroxide, the obtained mother liquor can be directly subjected to evaporation crystallization to obtain a part of lithium oxalate without recovery treatment. The preparation method can obtain high-purity lithium oxalate at room temperature, greatly reducing the energy cost and improving the production efficiency.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of lithium oxalate, and relates to a lithium oxalate, a preparation method thereof and a use thereof. Background Art

[0002] In recent years, with the rapid development of the lithium-ion battery industry, the research and development of its electrolyte lithium salts have become increasingly hot, and new lithium salts with new structures and functions have been continuously reported. At present, considering various aspects such as performance, price, and process, the most representative and promising lithium salt in the market is lithium difluoro(oxalato)borate (LiODFB). It combines the advantages of lithium tetrafluoroborate (LiBF4) and lithium bis(oxalato)borate (LiBOB), has a high thermal decomposition temperature of up to 240 °C, has basically no corrosion to electrode materials, has good cycle performance, low moisture sensitivity, good high and low temperature performance, rate performance, and positive and negative electrode compatibility, etc. Its various performances are superior to those of lithium hexafluorophosphate used in current lithium-ion batteries, and it may replace it as the main salt of lithium battery electrolytes in the future.

[0003] The raw material for preparing lithium difluoro(oxalato)borate is lithium oxalate. The purity and performance indicators of lithium oxalate affect the quality of lithium difluoro(oxalato)borate, and thus have a direct impact on the lithium-ion battery capacity, cycle times, and safety performance of the lithium difluoro(oxalato)borate electrolyte system. For this reason, it is very necessary to produce high-purity lithium oxalate with excellent performance.

[0004] At present, the traditional method for preparing lithium oxalate is mainly to neutralize lithium carbonate or lithium hydroxide with oxalic acid. The process control is not easy, it is not suitable for large-scale production, and it cannot meet the demand for producing lithium difluoro(oxalato)borate. Moreover, this traditional process requires oxalic acid to have a relatively high solubility at high temperatures. Therefore, it is necessary to first heat and dissolve it in water and then mix it with a lithium hydroxide solution. For example, CN105859542A discloses a method for preparing high-purity lithium oxalate, in which oxalic acid is dissolved in water at high temperature, and impurities are removed by adding the oxalic acid solution and the lithium hydroxide solution to each other, and finally high-purity lithium oxalate is obtained; when this process is applied to large-scale industrial production, heat preservation pipelines or heat preservation facilities are required in this process so that the whole process can be carried out under heating conditions, which requires high equipment heat preservation performance, consumes a large amount of energy, and the heating process takes a long time, greatly increasing the production cost and reducing the production efficiency.

[0005] Therefore, it is still necessary to develop a new preparation scheme for lithium oxalate. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to provide a lithium oxalate, a preparation method thereof and a use thereof. In the preparation method, granular or slurry-form oxalic acid is added to a lithium hydroxide solution at least in two portions until the pH is stabilized at 2-3, and then the separated liquid obtained after solid-liquid separation is subjected to evaporation crystallization to obtain a part of lithium oxalate, and at the same time, the separated solid obtained is dried to obtain another part of lithium oxalate. By improving the process route, the present invention does not need to dissolve oxalic acid, and the mother liquor obtained after adding granular or slurry-form oxalic acid to lithium hydroxide does not need to be recycled and treated, but can be directly subjected to evaporation crystallization to obtain a part of lithium oxalate. The preparation method can obtain high-purity lithium oxalate at normal temperature, greatly reducing the cost and improving the production efficiency.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a preparation method of lithium oxalate, comprising the following steps:

[0009] Prepare granular or slurry-form oxalic acid, and add it to a lithium hydroxide solution at least in two portions until the pH is stabilized at 2-3. After solid-liquid separation, the separated liquid obtained is subjected to evaporation crystallization to obtain a part of lithium oxalate, and at the same time, the separated solid obtained is dried to obtain another part of lithium oxalate.

[0010] The biggest difference between the method of the present invention and the prior art is that the present invention does not need to dissolve lithium oxalate, thus omitting the equipment, site, personnel and high-temperature energy consumption costs in the process of preparing or dissolving a lithium oxalate solution. By using granular or slurry-form oxalic acid and adding it to the lithium hydroxide solution in multiple small portions, the system state is stabilized, and on the premise that basically all the oxalic acid added each time reacts, the pH fluctuation is reduced, and thus the target product can be prepared at normal temperature. It can be seen that the preparation method of the present invention can effectively reduce the energy cost and economic cost, effectively improve the production efficiency, and is more suitable for large-scale industrial production.

[0011] In the present invention, the pH is stabilized at 2-3, for example, it can be 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0012] In the present invention, the pH value needs to be at a relatively low level to ensure the conversion rate of lithium hydroxide to lithium oxalate. However, too low a pH means that more oxalic acid is added, which will cause waste of oxalic acid and residual oxalic acid solids in the product.

[0013] The following are the preferred technical solutions of the present invention, but not the limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0014] As a preferred technical solution of the present invention, the oxalic acid includes oxalic acid dihydrate.

[0015] Preferably, the purity of the oxalic acid is greater than or equal to 99.5%.

[0016] As a preferred technical solution of the present invention, the particle size of the granular oxalic acid is 1 - 500 μm, such as 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, 20 μm, 30 μm, 50 μm, 70 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, 220 μm, 240 μm, 260 μm, 280 μm, 300 μm, 320 μm, 340 μm, 360 μm, 380 μm, 400 μm, 420 μm, 440 μm, 460 μm, 480 μm or 500 μm, etc., preferably 1 - 200 μm, but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0017] Preferably, the method for preparing the granular oxalic acid includes subjecting the oxalic acid to any one or a combination of at least two of ball milling, sand milling, mechanical grinding or jet milling. Typical but non-limiting examples of the combination include the combination of ball milling and sand milling, the combination of ball milling and mechanical grinding, the combination of mechanical grinding and ball milling, the combination of mechanical grinding and jet milling, preferably mechanical grinding, to obtain solid particles.

[0018] Preferably, the solid content in the slurry-like oxalic acid is 5 - 50 wt%, such as 5 wt%, 8 wt%, 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt%, 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, 30 wt%, 32 wt%, 34 wt%, 36 wt%, 38 wt%, 40 wt%, 42 wt%, 44 wt%, 46 wt%, 48 wt% or 50 wt%, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0019] Preferably, the particle size of oxalic acid in the slurry - like oxalic acid is 0.05 - 50 μm, such as 0.05 μm, 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, etc. Preferably, it is 0.1 - 10 μm, but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0020] Preferably, the method for preparing the slurry - like oxalic acid includes ball - milling and / or sand - milling oxalic acid with water and / or lithium oxalate solution.

[0021] As a preferred technical solution of the present invention, the lithium hydroxide used to prepare the lithium hydroxide solution includes industrial - grade monohydrate lithium hydroxide.

[0022] Preferably, the purity of the industrial - grade monohydrate lithium hydroxide is greater than or equal to 99%.

[0023] Preferably, before preparing the lithium hydroxide solution, the industrial - grade monohydrate lithium hydroxide is mechanically ground to obtain particles and / or powders.

[0024] Preferably, the saturation of the lithium hydroxide solution is 50% - 100%, such as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 85% or 100%, etc. But it is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0025] Exemplarily, when preparing with monohydrate lithium hydroxide, the mass ratio of monohydrate lithium hydroxide to water is 1:(5 - 10). When it is 1:5, a saturated solution is obtained; when it is 1:10, a solution with a saturation of 50% is obtained. The saturated solution obtained at 1:5 is generally slightly turbid and has insoluble small particles. Therefore, in actual production, it is preferably to reduce the concentration. However, if the concentration is too low, it will affect production efficiency, and when there is too much water, it is easy to cause an increase in the dissolution of lithium oxalate dissolved in water, and in addition, more energy consumption is required for evaporation and crystallization.

[0026] Preferably, the temperature for preparing the lithium hydroxide solution is room temperature.

[0027] As a preferred technical solution of the present invention, the amount of oxalic acid added each time is equal or decreases successively.

[0028] Preferably, the granular or slurry - like oxalic acid is equally divided into five parts and added to the lithium hydroxide solution successively.

[0029] Preferably, each time oxalic acid is added to the lithium hydroxide solution, after the pH of the system is stable, the next addition is carried out.

[0030] In the present invention, preferably, the addition amount of oxalic acid is in excess relative to lithium hydroxide to ensure the full reaction of lithium hydroxide. However, an excessive amount of lithium oxalate will waste more oxalic acid.

[0031] Preferably, when the pH is stabilized at 2 - 3, continue stirring for 0.5 - 2 h, such as 0.5 h, 0.8 h, 1.1 h, 1.4 h, 1.7 h or 2 h, etc., but not limited to the listed values. Other unlisted values within the above value range are equally applicable.

[0032] As a preferred technical solution of the present invention, the method for solid-liquid separation includes any one or a combination of at least two of pressure filtration, suction filtration or centrifugation. Typical but non-limiting examples of the combination include the combination of pressure filtration and suction filtration, the combination of pressure filtration and centrifugation, or the combination of suction filtration and centrifugation.

[0033] Preferably, before the solid-liquid separation, the preparation method is carried out at room temperature.

[0034] As a preferred technical solution of the present invention, the drying temperature is 190 - 220 °C, such as 190 °C, 192 °C, 196 °C, 200 °C, 204 °C, 208 °C, 212 °C, 216 °C or 220 °C, etc., but not limited to the listed values. Other unlisted values within the above value range are equally applicable.

[0035] Preferably, the drying is carried out in a rotary kiln.

[0036] Preferably, the rotary kiln is provided with a gas recovery device for collecting the volatilized oxalic acid.

[0037] Preferably, the temperature for evaporation crystallization is 190 - 220 °C, such as 190 °C, 192 °C, 196 °C, 200 °C, 204 °C, 208 °C, 212 °C, 216 °C or 220 °C, etc., but not limited to the listed values. Other unlisted values within the above value range are equally applicable.

[0038] Oxalic acid will undergo thermal decomposition at 190 °C to generate carbon monoxide, carbon dioxide and water. In order to prevent the obtained lithium oxalate from containing oxalic acid impurities, a higher temperature is required to completely remove it. Since the total amount of oxalic acid added in this application is preferably in excess, therefore, for the separated liquid, a higher temperature is required for evaporation crystallization to remove the excess oxalic acid and obtain lithium oxalate with higher purity. The temperature should be higher than 190 °C, preferably 200 °C.

[0039] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0040] (1) Mechanically grind solid oxalic acid dihydrate with a purity of greater than or equal to 99.5% to grind large lumps into solid particles with a particle size of 1 - 500 μm to obtain granular oxalic acid. Alternatively, ball mill the solid oxalic acid dihydrate with a small amount of water or lithium oxalate solution to make the particle size of oxalic acid reach 0.05 - 50 μm and disperse to form a slurry with a solid content of 5 - 50 wt% to obtain slurry-like oxalic acid. Meanwhile, mechanically grind industrial-grade lithium hydroxide monohydrate solid with a purity of greater than or equal to 99% to grind large lumps into granular form, and then mix the industrial-grade lithium hydroxide monohydrate with water in a reaction kettle at room temperature in a mass ratio of 1:(5 - 10) and mix evenly to obtain a lithium hydroxide solution;

[0041] (2) Divide the granular or slurry-like oxalic acid obtained in step (1) into five equal parts and add them to the obtained lithium hydroxide solution in sequence at room temperature. Each time oxalic acid is added to the lithium hydroxide solution, wait until the pH of the system stabilizes, and then carry out the next addition. After the pH stabilizes at 2 - 3, continue stirring for 0.5 - 2 h to obtain a solid-liquid mixture;

[0042] Perform solid-liquid separation on the obtained solid-liquid mixture by at least one of pressure filtration, suction filtration, or centrifugation. Evaporate and crystallize the obtained separated liquid at 190 - 220 °C to obtain a part of lithium oxalate. At the same time, dry the obtained separated solid in a rotary kiln at 190 - 220 °C. The rotary kiln is provided with a gas recovery device to recover the mixed water vapor and oxalic acid to obtain another part of lithium oxalate.

[0043] In the second aspect, the present invention provides a lithium oxalate obtained by using the preparation method described in the first aspect.

[0044] In the third aspect, the present invention provides a battery lithium supplement agent containing the lithium oxalate described in the second aspect or prepared by using the lithium oxalate described in the second aspect.

[0045] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0046] (1) The preparation method of the present invention does not require dissolving oxalic acid, but can use granular or slurry-like oxalic acid to prepare lithium oxalate through solid-liquid reaction at room temperature. Compared with the existing method of dissolving oxalic acid at high temperature and then reacting, it greatly reduces the time and energy consumption required for the reactant preparation process, simplifies the equipment, greatly reduces the preparation cost, and improves the production efficiency;

[0047] (2) The preparation method of the present invention further utilizes the characteristic that the sublimation temperature of oxalic acid is relatively low. After solid-liquid separation, the separated solid is dried to volatilize and remove oxalic acid, thus overcoming the problem of insufficient reaction of solid-phase reactants caused by dissolving lithium oxalate in the prior art, and there will be no residue of lithium hydroxide or oxalic acid;

[0048] (3) In the preparation method of the present invention, there is no need to dissolve oxalic acid. Instead, granular or slurry-like oxalic acid is added to the lithium hydroxide solution in small amounts and multiple times. After solid-liquid separation, the separated liquid can be directly evaporated and crystallized without recovery, obtaining a part of lithium oxalate, which improves the yield of lithium oxalate. Detailed implementation manners

[0049] The technical solutions of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0050] Example 1

[0051] This example provides a method for preparing lithium oxalate, which includes the following steps:

[0052] (1) Mechanically grind the solid of dihydrate oxalic acid with a purity of greater than or equal to 99.5% to grind the large agglomerates into solid particles with a particle size of 100 μm; at the same time, mechanically grind the solid of industrial-grade monohydrate lithium hydroxide with a purity of greater than or equal to 99%, grind the large agglomerates into granular form, and then mix the industrial-grade monohydrate lithium hydroxide with water in a reaction kettle at room temperature in a mass ratio of 1:6 to mix evenly to obtain a lithium hydroxide solution;

[0053] (2) Divide the granular or slurry-like oxalic acid obtained in step (1) into five equal parts, and add them to the obtained lithium hydroxide solution in sequence at room temperature. Each time the oxalic acid is added to the lithium hydroxide solution, wait until the pH of the system is stable, and then perform the next addition until the pH is stable at 2.6, and continue stirring for 1 h to obtain a solid-liquid mixture;

[0054] Perform solid-liquid separation on the obtained solid-liquid mixture by at least one of pressure filtration, suction filtration or centrifugation. Evaporate and crystallize the obtained separated liquid at 200 °C to obtain a part of lithium oxalate. At the same time, dry the obtained separated solid in a rotary kiln at 200 °C. The rotary kiln is provided with a gas recovery device to recover the mixed water vapor and oxalic acid to obtain another part of lithium oxalate.

[0055] Example 2

[0056] This example provides a method for preparing lithium oxalate, which includes the following steps:

[0057] (1) Use a small amount of water to ball-mill the solid of dihydrate oxalic acid with a purity of greater than or equal to 99.5% to disperse it into a slurry with a particle size of 0.5 μm and a solid content of 30 wt% to obtain slurry-like oxalic acid; at the same time, mechanically grind the solid of industrial-grade monohydrate lithium hydroxide with a purity of greater than or equal to 99%, grind the large agglomerates into granular form, and then mix the industrial-grade monohydrate lithium hydroxide with water in a reaction kettle at room temperature in a mass ratio of 1:5 to mix evenly to obtain a lithium hydroxide solution;

[0058] (2) Divide the granular or slurry oxalic acid obtained in step (1) into five equal parts, and sequentially add them to the obtained lithium hydroxide solution at room temperature. Each time the oxalic acid is added to the lithium hydroxide solution, wait until the pH of the system stabilizes, and then perform the next addition until the pH stabilizes at 2, and continue stirring for 2 h to obtain a solid-liquid mixture;

[0059] Perform solid-liquid separation on the obtained solid-liquid mixture by at least one of pressure filtration, suction filtration, or centrifugation. Evaporate and crystallize the obtained separated liquid at 180 °C to obtain a part of lithium oxalate. At the same time, dry the obtained separated solid in a rotary kiln at 180 °C. The rotary kiln is provided with a gas recovery device to recover the mixed water vapor and oxalic acid to obtain another part of lithium oxalate.

[0060] Example 3

[0061] This example provides a method for preparing lithium oxalate, including the following steps:

[0062] (1) Perform air flow pulverization on solid oxalic acid dihydrate with a purity of greater than or equal to 99.5%, and grind large agglomerates into solid particles with a particle size of 10 μm; at the same time, mechanically grind industrial-grade lithium hydroxide monohydrate solid with a purity of greater than or equal to 99% into granular form, and then mix the industrial-grade lithium hydroxide monohydrate with water in a reaction kettle at room temperature according to a mass ratio of 1:10 and mix evenly to obtain a lithium hydroxide solution;

[0063] (2) Divide the granular or slurry oxalic acid obtained in step (1) into five equal parts, and sequentially add them to the obtained lithium hydroxide solution at room temperature. Each time the oxalic acid is added to the lithium hydroxide solution, wait until the pH of the system stabilizes, and then perform the next addition until the pH stabilizes at 3, and continue stirring for 0.5 h to obtain a solid-liquid mixture;

[0064] Perform solid-liquid separation on the obtained solid-liquid mixture by at least one of pressure filtration, suction filtration, or centrifugation. Evaporate and crystallize the obtained separated liquid at 220 °C to obtain a part of lithium oxalate. At the same time, dry the obtained separated solid in a rotary kiln at 220 °C. The rotary kiln is provided with a gas recovery device to recover the mixed water vapor and oxalic acid to obtain another part of lithium oxalate.

[0065] Example 4

[0066] This embodiment provides a preparation method of lithium oxalate. Except that in step (1), slurry-shaped oxalic acid is used instead of granular oxalic acid, and the slurry-shaped oxalic acid is prepared by ball-milling solid dihydrate oxalic acid with a purity of greater than or equal to 99.5% with a small amount of water, so that the particle size (D50) of the oxalic acid is 50 μm and it is dispersed to form a slurry with a solid content of 30 wt%, other conditions are exactly the same as those in Example 1.

[0067] Example 5

[0068] This embodiment provides a preparation method of lithium oxalate. Except that in step (2), the total amount of oxalic acid added is controlled so that the pH is adjusted from being stable at 2.6 to being stable at 2, other conditions are exactly the same as those in Example 1.

[0069] Example 6

[0070] This embodiment provides a preparation method of lithium oxalate. Except that in step (2), the total amount of oxalic acid added is controlled so that the pH is adjusted from being stable at 2.6 to being stable at 3, other conditions are exactly the same as those in Example 1.

[0071] Example 7

[0072] This embodiment provides a preparation method of lithium oxalate. Except that in step (2), the drying temperature of the separated solid is adjusted from 200 °C to 180 °C, and the evaporation and crystallization temperature of the separated liquid is adjusted from 200 °C to 180 °C, other conditions are exactly the same as those in Example 1.

[0073] Example 8

[0074] This embodiment provides a preparation method of lithium oxalate. Except that in step (2), the drying temperature of the separated solid is adjusted from 200 °C to 190 °C, and the evaporation and crystallization temperature of the separated liquid is adjusted from 200 °C to 190 °C, other conditions are exactly the same as those in Example 1.

[0075] Example 9

[0076] This embodiment provides a preparation method of lithium oxalate. Except that in step (2), the drying temperature of the separated solid is adjusted from 200 °C to 220 °C, and the evaporation and crystallization temperature of the separated liquid is adjusted from 200 °C to 220 °C, other conditions are exactly the same as those in Example 1.

[0077] Example 10

[0078] This embodiment provides a method for preparing lithium oxalate. The total amount of oxalic acid used in this preparation method is the same as that in Example 1. However, in step (2), the oxalic acid is equally divided into two parts and added to the obtained lithium hydroxide solution successively at room temperature. Each time the oxalic acid is added to the lithium hydroxide solution, the next addition is carried out after the pH of the system stabilizes until the pH of the system finally stabilizes, obtaining a solid-liquid mixture. In addition, other conditions are exactly the same as those in Example 1.

[0079] Example 11

[0080] This embodiment provides a method for preparing lithium oxalate. The total amount of oxalic acid used in this preparation method is the same as that in Example 1. However, in step (2), the oxalic acid is equally divided into three parts and added to the obtained lithium hydroxide solution successively at room temperature. Each time the oxalic acid is added to the lithium hydroxide solution, the next addition is carried out after the pH of the system stabilizes until the pH of the system finally stabilizes, obtaining a solid-liquid mixture. In addition, other conditions are exactly the same as those in Example 1.

[0081] Example 12

[0082] This embodiment provides a method for preparing lithium oxalate. The total amount of oxalic acid used in this preparation method is the same as that in Example 1. However, in step (2), the oxalic acid is equally divided into four parts and added to the obtained lithium hydroxide solution successively at room temperature. Each time the oxalic acid is added to the lithium hydroxide solution, the next addition is carried out after the pH of the system stabilizes until the pH of the system finally stabilizes, obtaining a solid-liquid mixture. In addition, other conditions are exactly the same as those in Example 1.

[0083] Example 13

[0084] This embodiment provides a method for preparing lithium oxalate. Except that in step (1), the particle size of the mechanically ground oxalic acid particles is adjusted from 100 μm to 0.05 μm, other conditions are exactly the same as those in Example 1.

[0085] Example 14

[0086] This embodiment provides a method for preparing lithium oxalate. Except that in step (1), the particle size of the mechanically ground oxalic acid particles is adjusted from 100 μm to 1 μm, other conditions are exactly the same as those in Example 1.

[0087] Example 15

[0088] This embodiment provides a method for preparing lithium oxalate. Except that in step (1), the particle size of the mechanically ground oxalic acid particles is adjusted from 100 μm to 50 μm, other conditions are exactly the same as those in Example 1.

[0089] Example 16

[0090] This example provides a preparation method of lithium oxalate. Except that in step (1), the particle size of the oxalic acid particles obtained by mechanical grinding is adjusted from 100 μm to 200 μm, other conditions are exactly the same as those in Example 1.

[0091] Example 17

[0092] This example provides a preparation method of lithium oxalate. Except that in step (1), the particle size of the oxalic acid particles obtained by mechanical grinding is adjusted from 100 μm to 350 μm, other conditions are exactly the same as those in Example 1.

[0093] Example 18

[0094] This example provides a preparation method of lithium oxalate. Except that in step (1), the particle size of the oxalic acid particles obtained by mechanical grinding is adjusted from 100 μm to 500 μm, other conditions are exactly the same as those in Example 1.

[0095] Example 19

[0096] This example provides a preparation method of lithium oxalate. Except that in step (1), the particle size of the oxalic acid particles obtained by mechanical grinding is adjusted from 100 μm to 700 μm, other conditions are exactly the same as those in Example 1.

[0097] Example 20

[0098] This example provides a preparation method of lithium oxalate. Except that in step (1), the mass ratio of industrial-grade lithium hydroxide monohydrate to water in the reaction kettle is adjusted from 1:6 to 1:5, other conditions are exactly the same as those in Example 1.

[0099] Example 21

[0100] This example provides a preparation method of lithium oxalate. Except that in step (1), the mass ratio of industrial-grade lithium hydroxide monohydrate to water in the reaction kettle is adjusted from 1:6 to 1:8, other conditions are exactly the same as those in Example 1.

[0101] Example 22

[0102] This example provides a preparation method of lithium oxalate. Except that in step (1), the mass ratio of industrial-grade lithium hydroxide monohydrate to water in the reaction kettle is adjusted from 1:6 to 1:10, other conditions are exactly the same as those in Example 1.

[0103] Example 23

[0104] This embodiment provides a method for preparing lithium oxalate. Except that in step (1), the mass ratio of industrial-grade lithium hydroxide monohydrate to water in the reaction kettle is adjusted from 1:6 to 1:11, other conditions are exactly the same as those in Embodiment 1.

[0105] Example 24

[0106] This embodiment provides a method for preparing lithium oxalate. Except that in step (1), the mass ratio of industrial-grade lithium hydroxide monohydrate to water in the reaction kettle is adjusted from 1:6 to 1:15, other conditions are exactly the same as those in Embodiment 1.

[0107] Comparative Example 1

[0108] This comparative example uses the method for preparing high-purity lithium oxalate disclosed in CN105859542A to prepare lithium oxalate.

[0109] Comparative Example 2

[0110] This comparative example provides a method for preparing lithium oxalate. The total amount of oxalic acid used in the method is the same as that in Embodiment 1, but in step (2), the obtained granular or slurry-like oxalic acid is not divided into multiple parts, but is all added to the lithium hydroxide solution at one time until the pH is stable, and a solid-liquid mixture is obtained. Except for this, other conditions are exactly the same as those in Embodiment 1.

[0111] Comparative Example 3

[0112] This comparative example provides a method for preparing lithium oxalate. Except that in step (2), the total amount of oxalic acid added is controlled so that the pH is adjusted from being stable at 2.6 to being stable at 3.5, other conditions are exactly the same as those in Embodiment 1.

[0113] Comparative Example 4

[0114] This comparative example provides a method for preparing lithium oxalate. Except that in step (2), the total amount of oxalic acid added is controlled so that the pH is adjusted from being stable at 2.6 to being stable at 5, other conditions are exactly the same as those in Embodiment 1.

[0115] Comparative Example 5

[0116] This comparative example provides a method for preparing lithium oxalate. Except that in step (2), the total amount of oxalic acid added is controlled so that the pH is adjusted from being stable at 2.6 to being stable at 7, other conditions are exactly the same as those in Embodiment 1.

[0117] Comparative Example 6

[0118] This comparative example provides a method for preparing lithium oxalate. Except that in step (2), the total amount of oxalic acid added is controlled so that the pH is adjusted from being stable at 2.6 to being stable at 7.5, other conditions are exactly the same as those in Example 1.

[0119] Since the oxalate in the unreacted oxalic acid is reducing and will interfere with the determination of the purity of lithium oxalate by the oxide titration method, first, the saturation solution pH value method is used to measure the oxalic acid residue in the lithium oxalate obtained in the examples and comparative examples, and then the acidic potassium permanganate titration method is used to measure the purity of the obtained lithium oxalate;

[0120] The saturation solution pH value method is as follows: Dissolve 6 g of the obtained lithium oxalate sample in 50 g of distilled water. After fully dissolving until it is clear, measure its pH value. The compliance requirement is between 7 and 8.5;

[0121] The acidic potassium permanganate titration method is as follows: Weigh 0.15 g of the sample, accurate to 0.0001 g, dissolve it in 100 mL of water containing 8 mL of sulfuric acid. When titrating to the end point with a potassium permanganate standard titration solution [c(1 / 5KMnO4) = 0.1 mol / L], heat it to 65 °C, continue titrating until the solution turns pink and remains so for 30 s, and at the same time, conduct a blank experiment;

[0122] The mass fraction of lithium oxalate is w = (V1 - V2)cM / (m * 1000) * 100%;

[0123] V1: The volume of the potassium permanganate standard titration solution consumed in the sample experiment (mL);

[0124] V2: The volume of the potassium permanganate standard titration solution consumed in the blank experiment (mL);

[0125] c: The concentration of the potassium permanganate standard titration solution (mol / L);

[0126] M: The molar mass of lithium oxalate (g / mol) [M(1 / 2Li2C2O4) = 50.95 g / mol]; m: The mass of the sample (g);

[0127] The above results are recorded in Table 1.

[0128] Table 1

[0129] Project Purity (%) pH of Saturated Solution Example 1 99.9 7.65 Example 2 99.9 7.80 Example 3 99.9 7.95 Example 4 99.9 8.42 Example 5 99.9 8.32 Example 6 99.9 7.52 Example 7 99.9 7.66 Example 8 99.9 7.54 Example 9 99.9 8.08 Example 10 99.9 5.86 Example 11 99.9 7.61 Example 12 99.9 8.43 Example 13 99.9 4.68 Example 14 99.9 8.32 Example 15 99.9 7.65 Example 16 99.9 8.19 Example 17 99.9 7.94 Example 18 99.9 7.85 Example 19 99.9 4.37 Example 20 97.6 10.37 Example 21 99.9 7.88 Example 22 99.9 8.01 Example 23 99.9 7.96 Example 24 99.9 8.29 Comparative Example 1 99.9 8.45 Comparative Example 2 99.9 4.52 Comparative Example 3 99.5 7.54 Comparative Example 4 99.0 7.52 Comparative Example 5 98.6 9.13 Comparative Example 6 98.2 10.47

[0130] It can be seen from Table 1 that:

[0131] The purity of the lithium oxalate samples prepared in Examples 1 - 3 and the pH value of the saturation solution are both within the required ranges.

[0132] From the comparison between Example 1 and Example 4, it can be seen that the state (granular or slurry) of the oxalic acid during the reaction has no effect on the quality of the finished product within the preferred range;

[0133] Comparing Example 1 with Examples 5 - 6 and Comparative Examples 3 - 6, it can be seen that the reaction end point (pH value after reaction) has a great influence on the quality of the finished product. If the pH value is too high, lithium hydroxide residue will occur and the purity will decrease; if it is too low, oxalic acid will be wasted.

[0134] Comparing Example 1 with Examples 7 - 9, it can be seen that within the preferred range and with sufficient drying time, the drying temperature has little influence on the product purity.

[0135] Comparing Example 1 with Examples 10 - 12 and Comparative Example 2, it can be seen that the number of times of adding oxalic acid in batches has a certain influence on the product purity. If the number of times is small, the reaction of oxalic acid will be incomplete and the pH value of the product saturated solution will be relatively low.

[0136] Comparing Example 1 with Examples 13 - 19, it can be seen that if the particle size of oxalic acid is too large or too small, the reaction of oxalic acid will be incomplete. This is because when the particle size of oxalic acid is too small, it is easy to agglomerate in the solution and adhere to the inside of the lithium oxalate particles generated by the reaction, and finally remain in the product; when the particle size of oxalic acid is too large, it is difficult to dissolve and is easy to remain after being coated by lithium oxalate.

[0137] Comparing Example 1 with Examples 20 - 24, it can be seen that the concentration of lithium hydroxide has a great influence on the purity and yield of the product. When the concentration of lithium hydroxide reaches the theoretical saturation (lithium hydroxide monohydrate: water = 1:5) and reacts with oxalic acid particles, the pH value of the product saturated solution is alkaline, indicating that there is still undissolved lithium hydroxide remaining in the product at this concentration; too low concentration of lithium hydroxide has no influence on the product purity, but will affect the production efficiency.

[0138] Comparing Example 1 with Comparative Example 1, it can be seen that compared with the traditional method, there is no obvious difference in the purity of lithium oxalate obtained by using the preparation method of the present invention, but the preparation method described in the present invention is significantly simpler and easier to implement.

[0139] The present invention uses the above - mentioned examples to illustrate the detailed structural features of the present invention, but the present invention is not limited to the above - mentioned detailed structural features, that is, it does not mean that the present invention must rely on the above - mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the components selected by the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

[0140] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above - mentioned embodiments. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0141] In addition, it should be noted that, for the various specific technical features described in the above specific embodiments, they can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0142] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A preparation method of lithium oxalate, characterized in that, It includes the following steps: Prepare granular or slurry oxalic acid. The particle size of the granular oxalic acid is 1 - 500 μm, and the particle size of the oxalic acid in the slurry oxalic acid is 0.05 - 50 μm. Add it to the lithium hydroxide solution at least in two portions. The saturation of the lithium hydroxide solution is 50% - 100%. Until the pH stabilizes at 2 - 3, after solid-liquid separation, evaporate and crystallize the obtained separated liquid to obtain a part of lithium oxalate. At the same time, dry the obtained separated solid to obtain another part of lithium oxalate.

2. The preparation method according to claim 1, characterized in that, The oxalic acid includes oxalic acid dihydrate.

3. The preparation method according to claim 1, wherein, The purity of the oxalic acid is greater than or equal to 99.5%.

4. The preparation method according to claim 1, characterized in that, The particle size of the granular oxalic acid is 1 - 200 μm.

5. The preparation method according to claim 1, wherein The method for preparing the granular oxalic acid includes any one or a combination of at least two of ball milling, sand milling, mechanical grinding, or jet milling of oxalic acid to obtain solid particles.

6. The preparation method according to claim 1, wherein, The solid content in the slurry oxalic acid is 5 - 50 wt%.

7. The preparation method according to claim 1, characterized in that, The particle size of the oxalic acid in the slurry oxalic acid is 0.1 - 10 μm.

8. The preparation method according to claim 1, characterized in that, The method for preparing the slurry oxalic acid includes ball milling and / or sand milling of oxalic acid with water and / or lithium oxalate solution.

9. The preparation method according to claim 1, characterized in that The lithium hydroxide used for preparing the lithium hydroxide solution includes industrial-grade lithium hydroxide monohydrate.

10. The preparation method according to claim 9, characterized in that, The purity of the industrial-grade lithium hydroxide monohydrate is greater than or equal to 99%.

11. The preparation method according to claim 9 or 10, characterized in that, Before preparing the lithium hydroxide solution, mechanically grind the industrial-grade lithium hydroxide monohydrate to obtain particles and / or powders.

12. The preparation method according to claim 9 or 10, characterized in that, The temperature for preparing the lithium hydroxide solution is room temperature.

13. The preparation method according to claim 1, characterized in that, The amount of oxalic acid added each time is equal or decreases successively.

14. The preparation method according to claim 1, characterized in that, Divide the granular or slurry oxalic acid into five equal portions and add them to the lithium hydroxide solution in sequence.

15. The preparation method according to claim 1, characterized in that, Each time oxalic acid is added to the lithium hydroxide solution, wait until the pH of the system stabilizes, and then add it next time.

16. The preparation method according to claim 1, characterized in that, When the pH stabilizes at 2 - 3, continue stirring for 0.5 - 2 h.

17. The preparation method according to claim 1, wherein The method for solid-liquid separation includes any one or a combination of at least two of pressure filtration, suction filtration, or centrifugation.

18. The preparation method according to claim 1, characterized in that, Before the solid-liquid separation, the preparation method is carried out at room temperature.

19. The preparation method according to claim 1, characterized in that, The drying temperature is 190 - 220 °C.

20. The preparation method according to claim 1, characterized in that The drying is carried out in a rotary kiln.

21. The preparation method according to claim 20, characterized in that, The rotary kiln is provided with a gas recovery device for collecting the volatilized oxalic acid.

22. The preparation method according to claim 1, characterized in that, The evaporation and crystallization temperature is 190 - 220 °C.

23. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Mechanically grind the solid oxalic acid dihydrate with a purity greater than or equal to 99.5% to grind the large agglomerates into solid particles with a particle size of 1 - 500 μm to obtain granular oxalic acid. Or, ball mill the solid oxalic acid dihydrate with a small amount of water or lithium oxalate solution to make the particle size of the oxalic acid reach 0.05 - 50 μm and disperse to form a slurry with a solid content of 5 - 50 wt% to obtain slurry oxalic acid. At the same time, mechanically grind the industrial-grade lithium hydroxide monohydrate solid with a purity greater than or equal to 99% to grind the large agglomerates into particles, and then mix the industrial-grade lithium hydroxide monohydrate with water in a reaction kettle at room temperature in a mass ratio of 1:(5 - 10) and mix evenly to obtain a lithium hydroxide solution; (2) Divide the granular or slurry-like oxalic acid obtained in step (1) into five equal parts, and sequentially add them to the obtained lithium hydroxide solution at room temperature. Each time the oxalic acid is added to the lithium hydroxide solution, wait until the pH of the system stabilizes, and then carry out the next addition. After the pH stabilizes at 2-3, continue stirring for 0.5-2 h to obtain a solid-liquid mixture; Perform solid-liquid separation on the obtained solid-liquid mixture by at least one of pressure filtration, suction filtration or centrifugation. Evaporate and crystallize the obtained separated liquid at 190-220 °C to obtain a part of lithium oxalate. At the same time, dry the obtained separated solid in a rotary kiln at 190-220 °C. The rotary kiln is provided with a gas recovery device to recover the mixed water vapor and oxalic acid to obtain another part of lithium oxalate. Remove iron from all the lithium oxalate, and continue to use the recovered oxalic acid.