A modified diatom material, and a preparation method and application thereof

Abstract

The application discloses a modified diatom material and a preparation method and application thereof, and the preparation method is as follows: taking ion type rare earth ore as raw material to co-culture diatom, and then carrying out simple impurity removal, washing and calcination on the diatom to obtain the modified diatom material; the diatom co-cultured with rare earth can adsorb rare earth elements on the shell structure of the diatom, and the shell of the diatom co-cultured with rare earth is collected to prepare a lithium ion battery negative material, which exhibits excellent electrochemical performance. The improved method is simple and easy to operate, has no pollution to the environment, is suitable for large-scale production, and in particular, the diatom shell co-cultured with rare earth extraction liquid as the lithium ion battery negative material has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of application of modified diatomaceous material in lithium ion battery negative electrode materials, and specifically relates to a rare earth co-cultured modified diatomaceous material and a preparation method and application thereof. BACKGROUND

[0002] As a traditional lithium ion battery negative electrode material, graphite has a low theoretical specific capacity (372 mAh·g -1 ) and a large irreversible capacity loss (about 10%) in the first cycle, and has been difficult to meet the demand for high capacity of new energy storage devices at present, so it is imperative to find a new graphite substitute negative electrode material. In the past 10 years, the main research work has been focused on developing Si-graphite composite materials and Si as an active negative electrode material because Si has a very high volume specific capacity and mass specific capacity, which is 10 times that of graphite. However, due to the problems of excessive volume expansion (300%-400%) and excessive formation of solid electrolyte interface layer during the cycle process, the silicon negative electrode has not been realized in commercial batteries. SiO2 has become a potential abundant and environmentally friendly negative electrode material as a substitute for Si, with a theoretical specific capacity of 1965 mAh·g -1 , and a lower volume expansion rate, and has a high application prospect. Diatom is one of the good sources of SiO2.

[0003] Diatom is a single-celled hard shell alga with strong environmental adaptability, a large number of species and quantities, and a complex layered nano-structured porous SiO2 network. Therefore, diatom is also a promising source of lithium ion battery negative electrode material, and its unique biological structure, species diversity and biological affinity have been applied in the fields of environment and medicine, but the research in the energy storage field is still in the initial stage. Although some studies have reported the influence of diatom structure on its electrochemical performance, such as the CaCO3 phase in the diatom shell which reduces the capacity, the carbonized organic matter component of diatom cells which can form a uniform carbon layer to improve the conductivity of the diatom shell, etc., as a natural material / template, the diversified structure brought by the species richness of diatom, the influence of culture conditions on biological silicification, and the use of related modification technology still need to be developed.

[0004] Therefore, it is an urgent need in the field to find a better quality and lower cost modification technology for diatom biological silicon dioxide material.

[0005] Through the literature search of the prior art, it is found that Chinese patent 201911232460.6 discloses a diatomite-based lithium ion battery negative material and a preparation method thereof. The negative material is a M-SiOx composite material formed by filling or coating porous silicon oxide material with metal by high-temperature solid-phase self-assembly synthesis method, M is one of Sn and Al, and in SiOx, 0≤x≤2. The lithium ion battery prepared by using the negative material exhibits excellent lithium storage performance, cycle life and good rate performance. However, the main disadvantage of the patent is that the metal loading is not fixed, and the experimental operation steps involve high-temperature heating of hydrogen, which is less safe.

[0006] Chinese patent CN108075110 A discloses a preparation of a lithium ion battery negative material with carbon-coated nanosilicon composite negative electrode. The main disadvantage of this patent is that the preparation steps of the composite are complicated, and the obtained target product particles are large, which is not suitable for large-scale commercial production.

[0007] Chinese patent CN110165177 A discloses a preparation method of a silicon-based composite negative material for lithium ion batteries. The method is to prepare a silicon-based composite negative material by ball milling silicon and copper oxide. The main disadvantage of this patent is that the purity of the material prepared by this method cannot be determined, and the yield is low, and there are also disadvantages such as poor controllability of morphology.

[0008] Chinese patent CN108598442 A discloses a preparation method of a silicon-based lithium ion battery negative material. The method is to wrap silicon nanoparticles with graphene oxide to form a silicon-based lithium ion battery negative material. The main disadvantage of this patent is that aniline used in the method is volatile and has high toxicity, the production cost is high, the steps are complicated, and it is not conducive to large-scale commercial production.

[0009] Chinese patent CN102983317 A discloses a silicon-carbon composite lithium ion battery negative material and a preparation method thereof. The method is to blend silicon particles and carbon precursors to obtain a mixed slurry, and then to obtain a silicon-carbon composite by high-temperature carbonization. However, the composite obtained by this production process has the disadvantages of uneven distribution of silicon and easy agglomeration. At the same time, the carbonization temperature is too high, the process is difficult, and the production cost is high. SUMMARY

[0010] The purpose of the present application is to provide a modified diatom material, a preparation method thereof and an application in lithium ion batteries, which can low-cost and simply prepare a lithium ion battery negative material with high energy density and long cycle life. The specific technical solutions are as follows:

[0011] The purpose of the present application is achieved by the following means:

[0012] A modified diatom material is obtained by culturing diatoms in a culture medium containing rare earth ions and then high-temperature calcination.

[0013] The preparation method of the modified diatom material of the present application comprises the following steps: adding rare earth ore into the diatom culture medium for co-culturing; collecting the diatom shell and high-temperature calcination, thereby obtaining the modified diatom material.

[0014] In the preparation method, the rare earth ore is wrapped with a semi-permeable membrane or prepared into a rare earth extraction solution and then added into the culture medium for diatom culture.

[0015] In the preparation method, the ratio of the semi-permeable membrane-wrapped rare earth ore to the culture medium is 0.5g-2.0g of rare earth ore: 1-2L of culture medium, and the ratio of the rare earth extraction solution to the culture medium is 5-20mL of rare earth extraction solution: 1-2L of culture medium; the inoculation amount of the diatom seed solution is 10%-20% of the amount of the culture medium.

[0016] In the preparation method, the co-culturing period is 10-14 days, the culture temperature is 22-25℃, and the light intensity is 2000-4000Lux.

[0017] In the preparation method, a semi-permeable membrane with a molecular weight cut-off of 8000D-14000D is used; an ammonium salt is used to prepare the rare earth extraction solution, and preferably, an ammonium sulfate salt is used.

[0018] In the preparation method, the rare earth extraction solution is prepared by mixing 100-200g of ionic rare earth ore with 1-2L of water, high-temperature high-pressure cooking reaction, cooling, solid-liquid separation to collect the supernatant and the precipitate, respectively, preparing a 0.5-2.5% (NH4)2SO4 solution from the supernatant, mixing with the rare earth ore precipitate, oscillating, and then centrifuging to collect the supernatant, thereby obtaining the rare earth extraction solution.

[0019] In the preparation method, after the co-culturing is completed, the algal liquid is filtered or centrifuged to obtain diatom precipitate, which is then sequentially washed with acid and ethanol, and the precipitate is collected after solid-liquid separation; the diatom precipitate is freeze-dried and high-temperature calcined to obtain the modified diatom material co-cultured with rare earth.

[0020] In the preparation method, the enriched algal liquid is acid-washed with dilute hydrochloric acid or dilute sulfuric acid; the precipitate is collected after solid-liquid separation; the acid-washed precipitate is washed with ethanol for 1-2 times until the washing liquid is colorless and transparent; the diatom precipitate is freeze-dried at -70℃ for at least 24h; the dried diatom mixture is heated to 600-900℃ at a rate of 5-10℃ / min under an argon atmosphere, and kept for 1-3h.

[0021] Further, the heating rate is preferably 5℃ / min, the calcination temperature is 600℃, and the holding time is 3h.

[0022] In the above drying and calcining process, the residual cytoplasm in diatom cells is converted into a carbon layer by calcining in an argon environment to obtain a desired REE / SiO2 / C material.

[0023] The application further provides an application of the modified diatom material prepared by the above method: preparation of a lithium ion battery negative electrode material.

[0024] The modified diatom material prepared by the application is mixed with Super P and PVDF at a mass ratio of 7:2:1, an appropriate amount of N-methyl pyrrolidone (NMP) is added, and ball milling is performed at 300-450 r / min for 1-3 h to obtain a uniformly mixed electrode slurry, the slurry is coated on a copper foil at a thickness of 25-300 μm, vacuum drying is performed at 80℃, and after cutting, an electrode sheet is obtained. Preferably, the active material: Super P: PVDF = 7:2:1, ball milling is performed at 300 r / min for 3 h, and the slurry is coated at a thickness of 50 μm.

[0025] The cut electrode sheet is placed into a battery bottom shell in an argon-filled glove box, 1-2 drops of electrolyte are added to the surface of the electrode sheet, a separator is placed thereon, 1-2 drops of electrolyte are further added, a lithium sheet is finally placed, a battery upper cover is covered, and sealing is performed on a battery packaging machine to complete battery assembly.

[0026] The difference between the application and the prior art is that: the application first uses rare earth co-cultivation diatoms, the method uses low-cost ionic rare earth minerals as raw materials instead of high-purity rare earth elements as co-cultivation raw materials, semi-permeable membranes are used to wrap ionic rare earth minerals for co-cultivation or ammonium sulfate is used to leach out abundant rare earth elements in the minerals, the rare earth extraction liquid is added to F2 culture medium for diatom cultivation, and the diatoms enrich the rare earth elements in the diatom shell structure through biomineralization in the growth and metabolism process. Unlike the traditional method of self-assembling and compounding existing diatom raw materials with other substances. Moreover, the whole operation process is simple and easy to operate, safe, low in economic cost, easy to obtain raw materials, and friendly to the ecological environment.

[0027] The technical method of the modified diatom material has the following advantages:

[0028] (1) The method uses low-cost rare earth minerals as raw materials instead of expensive high-purity rare earth elements, which is conducive to large-scale application of the method.

[0029] (2) The application is safe, environmentally friendly, and simple and easy to operate.

[0030] (3) The present application significantly improves the electrochemical performance of diatom-based silicon dioxide negative electrode material, indicating that the modification method is effective;

[0031] (4) The co-culture method of the present application improves the uneven distribution of rare earth elements caused by the direct addition of rare earth ore to the culture medium by wrapping the rare earth ore with a semi-permeable membrane or preparing a rare earth extraction solution. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 Figure 1 is a scanning electron microscope image and EDS mapping result of the diatom material of the present application Example 1; wherein a-d represent a. EDS element content spectrum of unmodified diatom material; b. SEM image; c. O element spectrum; d. High-resolution SEM image; e. Si element spectrum.

[0033] Figure 2 Figure 1 is a scanning electron microscope image and EDS mapping result of the diatom material of the present application Example 1; wherein a-d represent a. EDS element content spectrum of unmodified diatom material; b. SEM image; c. O element spectrum; d. High-resolution SEM image; e. Si element spectrum.

[0034] Figure 3 Figure 1 is a scanning electron microscope image and EDS mapping result of the diatom material of the present application Example 1; wherein a-d represent a. EDS element content spectrum of unmodified diatom material; b. SEM image; c. O element spectrum; d. High-resolution SEM image; e. Si element spectrum.

[0035] Figure 4 Figure 1 is a scanning electron microscope image and EDS mapping result of the diatom material of the present application Example 1; wherein a-d represent a. EDS element content spectrum of unmodified diatom material; b. SEM image; c. O element spectrum; d. High-resolution SEM image; e. Si element spectrum.

[0036] Figure 5 Figure 1 is a scanning electron microscope image and EDS mapping result of the diatom material of the present application Example 1; wherein a-d represent a. EDS element content spectrum of unmodified diatom material; b. SEM image; c. O element spectrum; d. High-resolution SEM image; e. Si element spectrum. DETAILED DESCRIPTION

[0037] In order to illustrate the modification method of diatom material of the present application, the following specific embodiments are combined with the drawings for further description.

[0038] Example 1: Selecting Navicula in diatom (inoculation amount is 10%) as raw material, wrapping the rare earth ore with semi-permeable membrane and placing it in diatom culture medium for co-culture:

[0039] (1) Take 2g of ionic rare earth ore as raw material, wrap it with semi-permeable membrane (material is regenerated cellulose membrane (RC membrane)) with a molecular weight cut-off of 8000D and place it in 2L culture medium for co-culture with diatom;

[0040] (2) The amount of use: 2 g of rare earth ore wrapped with semi-permeable membrane is added to 2 L of F2 medium, the culture time is 10 days, the culture temperature is 25℃, the light intensity is 4000 Lux, and the inoculation amount of diatom seed liquid is 10%;

[0041] (3) The cultured algal liquid is filtered to obtain an enriched algal liquid;

[0042] (4) Hydrochloric acid with a concentration of 1 M is added to the diatom enriched algal liquid in (3), and the hydrochloric acid and carbonate are allowed to fully react for 3 h to obtain a hydrochloric acid diatom mixture;

[0043] Amount of use: 100 mL of enriched algal liquid is added to 400 mL of dilute hydrochloric acid.

[0044] (5) The HCl diatom mixture in (4) is centrifuged at a speed of 8000 rpm for 10 min, and the supernatant is removed to obtain a diatom precipitate treated with hydrochloric acid;

[0045] (6) Ethanol is added to the diatom precipitate treated with HCl solution in (5) to extract pigments and impurity ions from diatom cells to obtain an ethanol mixture;

[0046] Amount of use: 50 mL of ethanol is added to the diatom precipitate obtained in step (5).

[0047] (7) The ethanol mixture in (6) is centrifuged at a speed of 5000 rpm for 10 min, and the supernatant is removed to obtain a diatom precipitate treated with ethanol;

[0048] (8) The diatom precipitate obtained in (7) is freeze-dried at -70℃ for 24 h to obtain a diatom material;

[0049] (9) The diatom material in (8) is heated to 600℃ at a rate of 5℃ / min under an argon atmosphere, and high-temperature calcination is performed for 3 h to obtain a modified diatom material (DBS@C-REE-2.0);

[0050] (10) After the diatom shell is gold sprayed after the copper sheet is adhered to the sample stage with conductive adhesive, the morphology and element distribution of the modified diatom material are observed by SEM-EDS, the morphology is shown in Figure 2 (b), the diatom shell structure remains intact, and the EDS results are shown in Figure 2 (a), which proves that the rare earth elements are loaded on the surface of the diatom;

[0051] (11) The modified diatomaceous material prepared in this example was mixed with Super P and PVDF at a mass ratio of 7:2:1, and an appropriate amount of N-methyl pyrrolidone (NMP) was added. The mixture was ball milled at 300 r / min for 3 h to obtain a uniformly mixed electrode slurry. The slurry was coated on a copper foil at a thickness of 50 μm, vacuum dried at 80°C, and cut into a circular electrode sheet with a diameter of 12 mm;

[0052] (12) The cut electrode sheet was placed in a battery lower shell in an argon-filled glove box, 1 drop of electrolyte was added to the surface of the electrode sheet, a separator was placed on it, and another 1 drop of electrolyte was added. Finally, a lithium sheet was placed, and the battery upper cover was covered. The battery was sealed on a button cell sealing machine, and the assembly was completed;

[0053] (13) The assembled battery was subjected to impedance spectroscopy test on a Gamry electrochemical workstation, and the test frequency range was 100 kHz-0.01 Hz. The impedance spectroscopy results are shown in Figure 5

[0054] (14) The assembled battery was subjected to cyclic charge-discharge test on a LAND battery charge-discharge test system, and the test voltage range was 0.001-3.0 V (vs. Li / Li + ). The current density was 100 mA·g -1 . The charge-discharge curve is shown in Figure 5 . The electrode has a specific capacity of ~380 mAh·g -1 after 180 cycles, and has good cycle stability.

[0055] (15) The assembled battery was subjected to cyclic voltammetry test on an electrochemical workstation, and the test voltage range was 0.001-3.0 V (vs. Li / Li + ). The cyclic voltammetry curve is shown in Figure 3 (b). An oxidation peak around 2.37 V can be observed on the cyclic voltammetry curve, indicating that the rare earth element has undergone oxidation reaction with lithium, which is beneficial to the deposition of lithium and improves the discharge specific capacity.

[0056] Example 2: The difference from Example 1 is only that:

[0057] (1) 100 g of ionic rare earth ore raw material was dissolved in 1 L of distilled water and placed in a high-pressure steam sterilizer for 121°C treatment for 20 min;

[0058] Dosage: 100 g of ionic rare earth ore, 1 L of distilled water.

[0059] (2) The mixture in (1) was centrifuged at 8000 rpm for ten minutes, and the supernatant and rare earth ore precipitate were collected;

[0060] ​(3) Prepare a 2% ammonium sulfate solution from the supernatant in (2), mix it with the rare earth ore precipitate in (2), shake at room temperature for 30 min, centrifuge at 8000 rpm for 10 min to collect the supernatant, and obtain the rare earth extract.

[0061] (4) Add 20 mL of rare earth extract to the above 2 L diatom culture medium for co-culture;

[0062] (5) The freeze-dried diatom material was heated to 600°C at a rate of 5°C / min under an argon atmosphere and calcined at high temperature for 3 hours to obtain the modified diatom material (DBS@C-REE-20).

[0063] The remaining steps are the same, and the electrochemical impedance spectroscopy results of this embodiment are as follows: Figure 5 As shown, the charge-discharge curves are as follows: Figure 5 As shown, this electrode yielded ~820 mAh·g after 35 cycles. -1 It exhibits good specific capacity and cycling stability. The cyclic voltammetry curve is shown below. Figure 3 As shown in (c), an additional reduction peak appears in the cathode scan, corresponding to the reduction reaction between rare earth elements and lithium ions; this increases the capacity of the silicon dioxide electrode.

[0064] Comparative Example 1

[0065] This comparative example provides an unmodified diatomaceous earth material, which differs from Examples 1 and 2 only in that:

[0066] No ionic rare earth minerals or rare earth extracts are added during the cultivation process; the remaining steps remain unchanged.

[0067] The electrochemical impedance spectroscopy results and charge-discharge curves of this embodiment are as follows: Figure 5 As shown, the electrode yielded ~330 mAh·g after 180 cycles. -1 Specific capacity.

[0068] The diatomaceous earth material (DBS@C) obtained in Comparative Example 1 exhibits poorer capacity and cycle stability compared to the modified diatomaceous earth materials described in Examples 1 and 2, and also has higher impedance. The modified diatomaceous earth material demonstrates excellent electrochemical performance in battery testing procedures; Example 1 shows a discharge specific capacity of approximately 380 mAh·g after 180 cycles. -1 In Example 2, the discharge specific capacity after 35 cycles was approximately 820 mAh·g. -1 All of them are higher than those of unmodified diatomaceous earth materials. Figure 5 The results of the AC impedance test showed that the electrochemical impedance of the diatom electrode obtained by rare earth co-culture was significantly lower than that of the unmodified diatom material, which demonstrated the effectiveness of this modification method.

Claims

1. Use of a modified diatomaceous material, characterized in that: The application relates to a preparation method of a modified diatom material for a lithium ion battery negative electrode material.

2. Use according to claim 1, characterized in that, The preparation method of the modified diatom material comprises the following steps: a rare earth ore is wrapped with a semi-permeable membrane or prepared into a rare earth extraction liquid form, and then added into a culture medium for diatom culture, and high-temperature calcination is conducted.

3. Use according to claim 1, characterized in that, The proportion of the semi-permeable membrane wrapped rare earth ore and the culture medium is 0.5g-2.0g of the rare earth ore: 1-2L of the culture medium, and the proportion of the rare earth extraction liquid and the culture medium is 5-20mL of the rare earth extraction liquid: 1-2L of the culture medium; the inoculation amount of the diatom seed liquid is 10%-20% of the culture medium.

4. Use according to claim 1, characterized in that, The co-culture period is 10-14 days, the culture temperature is 22-25 DEG C, and the illumination intensity is 2000Lux-4000Lux.

5. Use according to claim 4, characterized in that, The semi-permeable membrane with a molecular weight cut-off of 8000D-14000D is used; and the ammonium salt is used to prepare the rare earth extraction liquid.

6. Use according to claim 4, characterized in that, The ammonium salt is an ammonium sulfate salt.

7. Use according to claim 1, characterized in that, The preparation method of the rare earth extraction liquid comprises the following steps: 100-200g of an ionic rare earth ore is mixed with 1-2L of water according to the proportion, high-temperature high-pressure cooking reaction is conducted, and then the supernatant and the precipitate are collected after solid-liquid separation after cooling; the supernatant is configured into a 0.5-2.5% (NH4)2SO4 solution, and then mixed with the rare earth ore precipitate, and then the supernatant is collected after centrifugal collection after oscillation, so that the rare earth extraction liquid is obtained.

8. The use according to claim 1, characterized in that, After the co-culture is completed, the algal liquid is filtered or centrifuged, the diatom precipitate is obtained, and then the diatom precipitate is sequentially washed with acid and ethanol, and the precipitate is collected after solid-liquid separation; the diatom precipitate is obtained after freeze-drying and high-temperature calcination, and the modified diatom material of the rare earth co-culture is obtained. The enriched algal liquid is washed with dilute hydrochloric acid or dilute sulfuric acid; the precipitate is collected after solid-liquid separation; the precipitate after acid washing is washed with ethanol for 1-2 times until the washing liquid is colorless and transparent; the diatom precipitate is freeze-dried at-70 DEG C for at least 24h; The dried diatom mixture is heated to 600-900 DEG C at a rate of 5-10 DEG C / min under an argon atmosphere, and the temperature is kept for 1-3h.

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