CN114430042B

CN114430042B - Lithium alginate for lithium battery additive and preparation method and application thereof

Info

Publication number: CN114430042B
Application number: CN202011091081.2A
Authority: CN
Inventors: 张丝雨; 董文芊; 高焕新; 孙赛; 张同宝
Original assignee: China Petroleum and Chemical Corp; Sinopec Shanghai Research Institute of Petrochemical Technology
Current assignee: China Petroleum and Chemical Corp; Sinopec Shanghai Research Institute of Petrochemical Technology
Priority date: 2020-10-13
Filing date: 2020-10-13
Publication date: 2023-09-29
Anticipated expiration: 2040-10-13
Also published as: CN114430042A

Abstract

The invention discloses lithium alginate for a lithium battery additive, wherein the sodium content in the lithium alginate is less than 20mg/g. The invention also discloses a preparation method of the lithium alginate, which comprises the following steps: acidifying sodium alginate solution to obtain jelly, pretreating with saturated saline water, and washing to remove impurity ions; then mixing and reacting with a lithium source, and drying to obtain the product lithium alginate. The lithium alginate prepared by the method has lower content of sodium, calcium and other hetero ions, can be used as an additive for preparing positive and negative electrode materials of lithium batteries, and improves the comprehensive performance of the electrode materials.

Description

Lithium alginate for lithium battery additive and preparation method and application thereof

Technical Field

The invention relates to lithium alginate which can be used as an additive of a lithium battery and a preparation method thereof.

Background

With the gradual exhaustion of fossil fuels, the development of new energy fields is increasingly emphasized, and the application of organic lithium salts in batteries is also becoming wider. The organic lithium salt can be used as a binder of an electrode material and also can be used as an additive in the preparation process of the electrode material. When additives are used to improve battery performance, the introduction of impurity ions can affect battery performance. Because of the large radius of sodium ions and large resistance of intercalation/deintercalation, for the common cathode materials (such as graphite) of lithium batteries, sodium easily causes volume expansion of electrode materials, material breakage and difficult deintercalation of the intercalated sodium ions in the intercalation/deintercalation process, thereby increasing irreversible capacity loss of the battery. Therefore, in lithium batteries, it is desirable to minimize the introduction of sodium.

The organolithium salts currently on the market are generally prepared by a process of neutralizing an organic acid with a lithium salt to convert the same into an organolithium salt. Sodium-containing substances such as sodium carbonate and other raw materials are generally added in the preparation process of the organic acid, the introduced impurities are difficult to completely remove in the subsequent treatment, and lithiation is incomplete, so that the purity of an organic lithium salt product is low, and the lithium salt product can influence the performance of a battery as an additive of the lithium battery. Because most of the preparation technologies of the organic lithium salt are still immature, the reaction period is long, and the production process of the organic sodium salt is relatively more mature, so that the organic sodium salt can be selected to be lithiated to obtain the organic lithium salt meeting the requirements.

Therefore, how to effectively reduce the sodium content in organolithium salt products is a continuing technical problem in the art.

Disclosure of Invention

Aiming at the technical problems in the prior art, the invention provides lithium alginate for a lithium battery additive, and a preparation method and application thereof. The lithium alginate has very low content of impurity ions such as Na, ca, al and the like, and can be used as a high-quality lithium battery electrode material. The preparation method of the organic lithium salt is simple to operate and does not need complex equipment.

In a first aspect the invention provides a lithium alginate for use in a lithium battery additive, said lithium alginate having a sodium content of less than 20mg/g, preferably less than 12mg/g.

In the technical scheme, the Ca content in the lithium alginate is less than 1mg/g.

In the technical scheme, the content of Al in the lithium alginate is less than 1mg/g.

In a second aspect, the present invention provides a method for preparing lithium alginate for a lithium battery additive, comprising:

(1) Acidifying sodium alginate solution to obtain jelly, pretreating with saturated saline water, and washing to remove impurity ions;

(2) And (3) mixing the material obtained in the step (1) with a lithium source for reaction, and drying to obtain the product lithium alginate.

In the technical scheme, in the sodium alginate in the step (1), the calcium content is below 100 mg/g.

In the technical scheme, in the sodium alginate in the step (1), the aluminum content is below 20mg/g.

In the above technical scheme, the mass fraction of the sodium alginate solution in the step (1) is 2% -20%, for example 2%, 4%, 6%, 8%, 10%, 15%, 20% and so on. The solvent is any one of water and water-alcohol mixed solution with any proportion, wherein the alcohol is at least one of ethanol and isopropanol.

In the above technical scheme, in the step (1), the acid used for the acidification treatment is any one or more of hydrochloric acid, acetic acid, citric acid, sulfuric acid, nitric acid and phosphoric acid. The concentration of the acid is 0.5mol/L to 5.0mol/L. The acidification is adjusted to a pH of the solution of less than 6, preferably ph=3 to 5.

In the above technical scheme, the conditions for pretreatment with saturated saline solution in step (1) are as follows: the treatment temperature is 20-50 ℃, the treatment time is 0.5-4.0 h, the consumption of saturated saline water each time is 0.5-2 times of the total volume of the jelly, and the pretreatment times are 1-5 times. The pretreatment method is that the jelly and the saturated saline water are mixed and stirred. After each pretreatment, solid-liquid separation is needed, and then saturated saline water is adopted to pretreat the solid phase for the next time. Solid-liquid separation is carried out by suction filtration, centrifugation, dialysis and the like, and then the filtrate is washed by water (preferably deionized water) until the filtrate is neutral.

In the above technical solution, the lithium source in step (2) accounts for 5% -40% of the mass of the sodium alginate, for example, 5%, 8%, 10%, 20%, 30%, 40% and so on.

In the above technical solution, the lithium source in step (2) may be one or more selected from lithium carbonate, lithium acetate, lithium hydroxide and lithium oxide, and more preferably any one of lithium carbonate and lithium hydroxide.

In the above technical scheme, the conditions of the mixing reaction in the step (2) are as follows: the temperature is 20-50 ℃ and the stirring time is 0.1-6.0 h.

In the above technical solution, the drying conditions in step (2) are as follows: freeze drying or vacuum drying at 60-100 deg.c.

In the technical scheme, the sodium content in the lithium alginate obtained in the step (2) is less than 20mg/g, preferably less than 12mg/g.

In the technical scheme, the content of Ca in the lithium alginate obtained in the step (2) is less than 1mg/g.

In the technical scheme, the content of Al in the lithium alginate obtained in the step (2) is less than 1mg/g.

In the technical scheme, the calcium content in the lithium alginate product obtained in the step (1) is lower than that in the sodium alginate product obtained in the step (1).

In the technical scheme, the aluminum content of the product lithium alginate obtained in the step (1) is lower than that of the sodium alginate obtained in the step (1).

The third aspect of the invention provides application of the lithium alginate in a lithium ion battery.

Compared with the prior art, the invention has the following technical effects:

1. compared with the commercial product, the lithium alginate has lower content of impurity ions such as sodium, calcium, aluminum and the like, and can obviously improve the first coulombic efficiency of the anode material and improve the cycling stability of the material when being used as the additive of the lithium ion battery.

2. The sodium content of the lithium alginate obtained by the method is far lower than that of similar products sold in the market, and the lithium alginate is used as a complexing agent for preparing ternary anode materials, so that the use amount of ammonia water can be reduced, the emission of three wastes in the process is reduced, and meanwhile, the hetero elements such as nitrogen, phosphorus and the like contained in a polymer can realize hetero atom doping of the materials, so that the electrochemical performance of the materials is improved.

3. The lithium alginate obtained by the invention can be used as a film coating agent for coating lithium metal, inhibit lithium dendrite formed in the repeated charge and discharge process of the lithium metal electrode, and improve the safety and stability of the lithium metal electrode.

4. The inventors have unexpectedly found that in the preparation method of the lithium alginate, sodium alginate is acidified and then added with saturated saline water for pretreatment, so that insoluble organic acid and lithium alginate are better separated, subsequent removal of impurity ions such as sodium, calcium, aluminum and the like is facilitated, and the content of sodium impurities in the lithium alginate product is not increased due to a large amount of sodium ions introduced by the saturated saline water. In addition, the impurity ions such as sodium, calcium, aluminum and the like can be easily removed in the subsequent deionized water washing process, so that the residues of the impurity ions such as sodium, calcium, aluminum and the like in the lithium alginate product in the lithium alginate are reduced. The lithiation step is preferably lithium carbonate, which facilitates determination of the end point of the reaction (whether or not bubbles are evolved).

5. The lithium alginate obtained by the invention is suitable for lithium batteries. The cycling stability of the material can be improved when the material is used for the negative electrode; when the method is used for preparing the positive electrode material, the method can be used as a complexing agent to prepare a ternary material precursor, so that the prior art is simplified.

Drawings

FIG. 1 is a comparison of the solutions of example 1 before and after acidification of sodium alginate;

FIG. 2 is a graph showing the cycle stability test of the lithium alginate battery of application example 1;

fig. 3 is a cycle stability test curve of the lithium alginate battery in application example 1 without the addition of the lithium alginate.

Detailed Description

In order to facilitate understanding of the present invention, examples are set forth below. It will be apparent to those skilled in the art that the examples are merely to aid in the understanding of the present invention and should not be construed as a specific limitation thereof.

All publications, patent applications, patents, and other references mentioned in this specification are herein incorporated by reference in their entirety. Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art. In case of conflict, the present specification, definitions, will control.

In the context of this specification, any two or more aspects of the invention may be combined arbitrarily, and the resulting solution is part of the original disclosure of the specification, while also falling within the scope of the invention.

In the present invention, the content of each element in lithium alginate was measured by ICP. The test method is as follows: 3g of the sample was dispersed in 200mL of pure water, and then diluted 1000-fold, and the elemental content of the sample was analyzed by ICP-OES internal standard method. The instrument model is a Thermo company iCAP 7600 type inductively coupled plasma emission spectrometer.

Unless explicitly indicated, all percentages, parts, ratios, etc. mentioned in this specification are by weight unless otherwise clear to the routine knowledge of a person skilled in the art.

Example 1

(1) 20g of sodium alginate (the mass content of Ca is 98.2mg/g, the mass content of Al is less than 1 mg/g) is taken, water is added to prepare a solution with the mass fraction of 8%, 100mL of hydrochloric acid with the concentration of 1mol/L is added to adjust the pH to be 3, and flocculent gel appears in the solution at the moment, so that a jelly is obtained. 200mL of saturated saline was added to the gum at 25℃and allowed to stand after stirring for 2 hours, the liquid was allowed to separate, the liquid was removed by filtration, and the procedure was repeated three times (the total amount of saturated saline was 1.67 times the total volume of the gum). And then washing the gel with deionized water until the filtrate is neutral, thereby obtaining the alginic acid.

(2) 100g of deionized water was added to the alginic acid obtained in the step (1), and 4g of lithium carbonate was added while stirring, and stirring was performed for 4 hours, to obtain a lithium alginate solution.

(3) Vacuum drying at 80 deg.c to eliminate water and obtain solid lithium alginate.

Table 1 shows the content of each element in lithium alginate obtained in example 1 as measured by ICP. As can be seen from Table 1, the Na content in the obtained material was 10.3mg/g, ca content was less than 1mg/g, al content was less than 1mg/g and Al content in sodium alginate, and the impurity element content was significantly reduced as compared with the commercial product.

Fig. 1 is a comparison of the solutions before and after acidification of sodium alginate in example 1, wherein the left graph shows sodium alginate solution, the middle shows acidified jelly, and the right graph shows the mixed solution after addition of saturated saline. As can be seen from FIG. 1, insoluble flocculent gel appears in the acidified solution, and obvious delamination phenomenon appears after saturated saline water is added, which is helpful for separation between alginic acid and the solution.

Example 2

(1) 20g of sodium alginate (the mass content of Ca is 98.2mg/g, the mass content of Al is less than 1 mg/g) is taken, water is added to prepare a solution with the mass fraction of 2%, 100mL of hydrochloric acid with the concentration of 1mol/L is added to adjust the pH to be=5, and flocculent gel appears in the solution at the moment, so that a jelly is obtained. 200mL of saturated saline was added to the jelly at 25℃and allowed to stand after stirring for 30 minutes, the liquid was allowed to separate, and the separation was repeated three times (the total amount of saturated saline was 0.5 times the total volume of the jelly). And then washing the gel with deionized water until the filtrate is neutral, thereby obtaining the alginic acid.

(3) Vacuum drying at 80 deg.c to eliminate water and obtain solid lithium alginate. Wherein, the content of each element in the obtained lithium alginate is shown in Table 1.

Example 3

(1) 20g of sodium alginate (the mass content of Ca is 98.2mg/g, the mass content of Al is less than 1 mg/g) is taken, water is added to prepare a solution with the mass fraction of 10%, and 200mL of hydrochloric acid with the concentration of 1mol/L is added to adjust the pH to be=3. At this point, a flocculent gel appeared in the solution, yielding a gum. 200mL of saturated saline was added to the jelly at 25℃and allowed to stand after stirring for 4 hours, the liquid was allowed to separate, the liquid was removed by filtration, and the procedure was repeated three times (the total amount of saturated saline was 1 time the total volume of the jelly). And then washing the gel with deionized water until the filtrate is neutral, thereby obtaining the alginic acid.

(2) 100g of deionized water was added to the alginic acid obtained in the step (1), 8g of lithium carbonate was added while stirring, and stirring was performed for 1 hour, to obtain a lithium alginate solution.

Example 4

(1) 20g of sodium alginate (the mass content of Ca is 98.2mg/g, the mass content of Al is less than 1 mg/g) is taken, water is added to prepare a solution with the mass fraction of 8%, and 20mL of hydrochloric acid with the concentration of 5mol/L is added to adjust the pH to be=3. At this point, a flocculent gel appeared in the solution, yielding a gum. 200mL of saturated saline was added to the gum at 25℃and stirred for 2 hours, then allowed to stand, the liquid was separated into layers, and the liquid was removed by filtration. This procedure was performed once (total amount of saturated saline was 0.7 times of total volume of jelly). And then washing the gel with deionized water until the filtrate is neutral, thereby obtaining the alginic acid.

(2) 100g of deionized water was added to the alginic acid obtained in the step (1), and 4g of lithium carbonate was added while stirring, and stirring was performed for 1 hour, to obtain a lithium alginate solution.

Example 5

(1) 20g of sodium alginate (the mass content of Ca is 98.2mg/g, the mass content of Al is less than 1 mg/g) is taken, water is added to prepare a solution with the mass fraction of 20%, and 200mL of hydrochloric acid with the concentration of 0.5mol/L is added to adjust the pH to be=5. At this point, a flocculent gel appeared in the solution, yielding a gum. 200mL of saturated saline was added to the gum at 25℃and allowed to stand after stirring for 4 hours, the liquid was allowed to separate, the liquid was removed by filtration, and the process was repeated twice (the total amount of saturated saline was 2 times the total volume of the gum). And then washing the gel with deionized water until the filtrate is neutral, thereby obtaining the alginic acid.

Comparative example 1

(1) 20g of sodium alginate (the mass content of Ca is 98.2mg/g, the mass content of Al is less than 1 mg/g) is taken, water is added to prepare a solution with the mass fraction of 8%, 100mL of hydrochloric acid with the concentration of 1mol/L is added to adjust the pH to be 3, and flocculent gel appears in the solution at the moment, so that a jelly is obtained. Filtering to remove water, washing with deionized water until the filtrate is neutral, and obtaining alginic acid.

Application example 1

The lithium alginate obtained in example 1 was used as a silicon carbon material additive (silicon carbon material) in the form of a 1mol/L LiPF using a commercially available silicon carbon material (S-500, bei Terui) and a metallic lithium sheet as a positive electrode and a negative electrode ₆ The solution (the mixture of ethylene carbonate and diethyl carbonate in the volume ratio of 3:7 is used as a solvent) is used as an electrolyte, the polypropylene microporous membrane is used as a diaphragm, and the CR2016 button cell is assembled, so that the cycling stability of the silicon-carbon negative electrode material is characterized. Fig. 2 shows the cycling stability of the battery at 0.5C discharge rate, and it can be seen from fig. 2 that the capacity retention of the material after 160 cycles is greater than 80% for the resulting battery.

Compared with application example 1, the lithium alginate obtained in example 1 was used as a positive electrode and a negative electrode by using a commercially available silicon carbon material (S-500, bei Terui) and a metallic lithium sheet without adding lithium alginate, and LiPF of 1mol/L was used ₆ The solution (the mixture of ethylene carbonate and diethyl carbonate in the volume ratio of 3:7 is used as a solvent) is used as an electrolyte, the polypropylene microporous membrane is used as a diaphragm, and the CR2016 button cell is assembled, so that the cycling stability of the silicon-carbon negative electrode material is characterized. Fig. 3 shows the cycling stability of the battery at 0.5C discharge rate, and it can be seen from fig. 3 that the capacity retention of the material after 160 cycles of the resulting battery is less than 10%.

Application example 2

1) According to Ni: co: mn=0.6:0.2:0.2 (molRatio), nickel sulfate, cobalt sulfate and manganese sulfate are used as raw materials, deionized water is used as a solvent, and total metal ions (Ni) are prepared ²⁺ 、Co ²⁺ 、Mn ²⁺ ) A solution with a concentration of 1 mol/L.

2) 10g of the lithium alginate obtained in example 1 was taken and deionized water was used as a solvent to prepare an aqueous solution of 8% by mass of lithium alginate.

3) By Li ⁺ Ion concentration: preparing a lithium alginate/Ni/Co/Mn solution in a ratio of total metal ion concentration=1.5:1 (molar concentration ratio), mechanically and fully stirring, and drying the obtained mixture at 120 ℃ for 2 hours to obtain the NCM-622 ternary positive electrode material precursor.

4) And 3) placing the precursor obtained in the step 3) into a tube furnace, heating to 550 ℃ at a speed of 2 ℃/min, preserving heat for 10 hours, continuously heating to 800 ℃, preserving heat for 8 hours, and naturally cooling and drying to obtain the NCM-622 ternary positive electrode material. The obtained NCM-622 ternary positive electrode material is taken as a positive electrode, a metal lithium sheet is taken as a negative electrode, 1mol/L LiPF6 solution is taken as electrolyte, a polypropylene microporous membrane is taken as a diaphragm, and the CR2016 button cell is assembled. The electrical properties of the cell were characterized. The primary reversible charge capacity of the obtained NCM-622 ternary positive electrode material is 181 mAh.g ^-1 The first coulombic efficiency was 88%.

The NCM-622 ternary positive electrode material is prepared by taking the lithium alginate obtained in the embodiment 1 as a lithium source, so that a tedious and time-consuming coprecipitation process is avoided, and the production efficiency is greatly improved.

Table 1 shows the content of each impurity element in the product obtained in each example, and the content of each impurity element in the commercially available lithium alginate as a comparison.

Table 1 elemental content in the product

Sample of	Li(mg/g)	Na(mg/g)	Ca(mg/g)	Al(mg/g)
					Example 1	1015.2	10.3	<1	<1
Example 2	986.5	9.6	<1	<1
					Example 3	1132.5	11.7	<1	<1
Example 4	997.4	15.5	<1	<1
					Example 5	1005.4	19.6	<1	<1
Comparative example 1	959.1	80.4	<1	<1
					Commercial lithium alginate	930.1	178.2	98.2	<1

The above describes in detail the specific embodiments of the present invention, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.

Claims

1. A method for preparing lithium alginate for a lithium battery additive, the sodium content in the lithium alginate being less than 20mg/g, the method comprising:

(1) Acidifying sodium alginate solution to obtain jelly, pretreating with saturated saline water, and washing to remove impurity ions; the mass fraction of the sodium alginate solution is 2% -20%;

(2) Mixing the material obtained in the step (1) with a lithium source for reaction, and drying to obtain a product lithium alginate;

wherein the acid used for the acidification treatment is one or more of hydrochloric acid, acetic acid, citric acid, sulfuric acid, nitric acid and phosphoric acid; the concentration of the acid is 0.5mol/L to 5.0mol/L; the pH value of the solution is adjusted to be less than 6 by the acidification treatment;

the pretreatment method adopting saturated saline water comprises the steps of mixing and stirring jelly and saturated saline water, and pretreating for 1-5 times, wherein the pretreatment conditions are as follows: the treatment temperature is 20-50 ℃, the treatment time is 0.5-4.0 h, and the consumption of the saturated saline water is 0.5-2.0 times of the total volume of the jelly.

2. The method according to claim 1, wherein the sodium alginate has a calcium content of 100mg/g or less and/or an aluminum content of 20mg/g or less.

3. The preparation method of claim 1, wherein the mass fraction of the sodium alginate solution is 2% -10%.

4. The method according to claim 1, wherein the acidification treatment is carried out to a pH value of the solution=3 to 5.

5. The method of claim 1, wherein the washing to remove ions is performed with deionized water until the filtrate is neutral.

6. The preparation method according to claim 1, wherein the lithium source in the step (2) accounts for 5% -40% of the mass of the sodium alginate, and the lithium source is one or more selected from lithium carbonate, lithium acetate, lithium hydroxide and lithium oxide.

7. The method according to claim 1, wherein the lithium source is any one of lithium carbonate and lithium hydroxide.

8. The process according to claim 1, wherein the conditions of the mixing reaction in step (2) are as follows: the temperature is 20-50 ℃ and the stirring time is 0.1-6.0 h;

and/or, the drying conditions in the step (2) are as follows: freeze drying or vacuum drying at 60-100 ℃.

9. The method according to claim 1, wherein the sodium content of the lithium alginate is less than 12mg/g.

10. The method according to claim 1, wherein the Ca content in the lithium alginate is less than 1mg/g.

11. The method according to claim 1, wherein the content of Al in the lithium alginate is less than 1mg/g.

12. Lithium alginate produced by the production method of any one of claims 1 to 11.

13. Use of lithium alginate as defined in any one of claims 1 to 11 in a lithium ion battery.