Cerium-doped diatom-based silicon-carbon negative electrode material, and preparation method and application thereof

Abstract

This invention discloses a cerium-doped diatom-based silicon-carbon anode material, its preparation method, and its application, belonging to the technical field of lithium battery anode materials and their preparation. Using a diatom shell as a framework, a bio-doping method is employed. When the diatoms grow to the early logarithmic phase in a culture medium, cerium ammonium nitrate is added to the diatom culture medium for co-cultivation. The co-cultivated diatom shells are then calcined at high temperature to obtain the cerium-doped diatom-based silicon-carbon anode material. This invention employs a two-stage cultivation strategy, introducing cerium ammonium nitrate after the diatoms have reached the early logarithmic phase to avoid toxic inhibition during the growth-sensitive period. Simultaneously, it utilizes the efficient absorption and doping capabilities of diatoms during the active biomineralization phase, achieving a balance between high doping efficiency and structural integrity. This method utilizes the biomineralization capabilities of diatoms to achieve uniform elemental doping, resulting in a simple, low-cost, and environmentally friendly process; providing a new approach for the development of high-performance silicon-carbon anode materials.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery anode materials and their preparation technology. Specifically, it relates to a cerium-doped diatom-based silicon-carbon anode material, its preparation method, and its application. Background Technology

[0002] With the rapid expansion of the new energy vehicle market, the requirements for lithium battery performance are becoming increasingly stringent. As one of the most important energy storage devices in today's new energy market, the performance of lithium-ion batteries is closely related to electrode materials. Among various anode materials, silicon-based anode materials are considered one of the most promising anode materials for next-generation lithium-ion batteries due to their high theoretical specific capacity (4300 mAh / g, more than 10 times that of traditional graphite anode materials), abundant reserves, and operating potential. However, silicon-based materials still face two major challenges in commercial applications.

[0003] 1) Huge volume expansion effect: During charging and discharging, the volume expansion of silicon-based anode materials can reach 300%. This repeated and drastic volume change will cause the active material to pulverize, thereby destroying the integrity of the electrode structure and causing the battery capacity to decay rapidly.

[0004] 2) Poor electronic conductivity and ion diffusion: Silicon, as a semiconductor, has a room temperature electronic conductivity of approximately 10. -4 The low S / cm ratio hinders electron conduction, making it difficult to form an effective conductive network inside the electrode, thus impeding electron transfer during charging and discharging. Furthermore, the slow insertion and extraction kinetics of lithium ions in silicon particles further exacerbate electrode polarization, thereby reducing the battery's charge / discharge efficiency and cycle stability.

[0005] Diatoms, a widely distributed marine single-celled algae, possess a cell wall that is a naturally porous nano-silica structure. Compared to elemental silicon, SiO2 has a lower volume expansion rate, and its natural three-dimensional porous structure provides more active sites and increases the contact area with the electrolyte when used as an anode material, thus facilitating the rapid transport of lithium ions. Based on these characteristics, existing research has directly used diatom shells as anode materials for lithium-ion batteries.

[0006] For example, Chinese patent CN117720111A discloses a method for preparing materials by modifying diatom shells through rare earth co-cultivation. This method uses ionic rare earth mineral extracts to co-cultivate diatoms throughout the entire process, but it still has the following limitations: First, the doping elements are complex, and the use of mixed rare earth sources leads to uncontrollable doping composition, making it difficult to achieve precise doping of a single element; second, the doping timing is coarse, failing to optimize the timing for key stages of diatom biomineralization, resulting in limited doping efficiency; third, there is a risk of growth inhibition, as premature or excessive introduction of rare earth elements can easily affect the normal growth of diatoms and the integrity of the shell structure. Consequently, its electrical properties have not seen a significant breakthrough.

[0007] Therefore, directly applying natural diatom shells to high-performance lithium-ion battery anodes still faces many challenges, such as: the difficulty in effectively controlling the relationship between the structural diversity of diatom shells and their electrochemical performance; the complexity of the biosilicification process, making precise modification difficult; and the high energy consumption and complex process flow of traditional modification methods, which are not conducive to large-scale application. Summary of the Invention

[0008] The purpose of this invention is to provide a novel cerium-doped diatom-based silicon-carbon anode material, its preparation method, and its application. It aims to develop a modification method for diatom-based anode materials that features a single doping element, precise doping timing, high doping efficiency, and is friendly to diatom growth. This method combines the advantages of high efficiency, low cost, and simple process, and is of great significance for promoting the practical application of bio-silicon-based materials in lithium-ion batteries.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A method for preparing a cerium-doped diatom-based silicon-carbon anode material, characterized by comprising the following steps:

[0011] 1) When diatoms are placed in the culture medium and grow to the early logarithmic phase, cerium source is added to the diatom culture medium for co-culture;

[0012] 2) The co-cultured diatom shells are calcined at high temperature to obtain the cerium-doped diatom-based silicon-carbon anode material.

[0013] This invention employs a two-stage cultivation strategy, introducing a cerium source after the diatoms have grown to the early logarithmic phase, thus avoiding toxic inhibition during the growth-sensitive period. At the same time, it utilizes the diatoms' efficient absorption and doping capabilities of cerium during the active biomineralization phase to achieve a balance between high doping efficiency and structural integrity.

[0014] This invention utilizes the metabolism of diatoms themselves to add Ce to the cerium source in the culture medium. 4+ Loaded onto a diatom shell, thus obtaining a Ce-doped material. 4+Bio-based silicon materials. These are obtained by in-situ doping of cerium into the diatom shell using the biomineralization process of diatoms, followed by high-temperature calcination.

[0015] Step 1) Continue culturing for at least 5 days after adding the cerium source.

[0016] Step 1) The diatom culture medium includes F / 2 culture medium, and the diatom type is Cryptomona cryptica.

[0017] Step 1) The conditions for diatom cultivation include: a temperature of 22-25℃, a light intensity of 2000-4000 lux, a light duration of 12-14 hours / day, and an inoculum size of 8-10%.

[0018] Step 1) The cerium source is cerium ammonium nitrate, preferably with a concentration of at least 200 μmol / L.

[0019] The selection of diatom type, the selection of cerium source type, and the control of cerium source concentration also have an important impact on the effectiveness of this invention, especially their synergistic effect is significant.

[0020] The preparation method described in this invention divides the diatom cultivation cycle into two stages.

[0021] Phase 1: Diatoms are cultured normally using artificial seawater culture medium F / 2 until they reach the early logarithmic growth phase. This is generally around day 5-6 of the culture period.

[0022] Phase 2: Add cerium ammonium nitrate to the diatom culture medium in the early logarithmic phase to make the concentration of cerium ammonium nitrate in the culture medium reach 200 μmol / L. Place the diatom cells in the culture medium with added cerium ammonium nitrate and culture them for about 11-12 days.

[0023] Furthermore, in the preparation method described above, step 2) before high-temperature calcination also includes pretreatment of diatom cells, the pretreatment comprising the following steps: (1) centrifuging the diatom culture medium after the culture is completed to separate the diatoms from the culture medium and obtain diatom cell precipitate; (2) washing the centrifuged diatom cells with deionized water and collecting the precipitate by solid-liquid separation; (3) acid soaking the diatom cells with hydrochloric acid and then collecting the precipitate by solid-liquid separation; (4) washing the diatom cells with deionized water until neutral and collecting the precipitate by solid-liquid separation; (5) washing the diatom cells with anhydrous ethanol until colorless and transparent and collecting the precipitate by solid-liquid separation; (6) freeze-drying the precipitate.

[0024] Step (3) Use hydrochloric acid with a concentration of 0.5-0.8M to acid-soak the diatom cells, and freeze-dry the precipitate at -70℃ to -80℃ and 25-40Pa for at least 24 hours.

[0025] It is preferred to use 0.6 M hydrochloric acid to acid-soak diatom cells, and then freeze-dry the precipitate at -80°C and 30 Pa for 24 hours.

[0026] Step 2) The diatom shells are calcined at 600-800℃ under an inert atmosphere by heating at a rate of 5-10℃ / min.

[0027] Preferably, the freeze-dried shell is calcined at 700°C under an inert atmosphere at a rate of 10°C / min.

[0028] A second objective of this invention is to provide a cerium-doped diatom-based silicon-carbon anode material prepared by the method described above.

[0029] A third objective of this invention is to provide the application of the aforementioned cerium-doped diatom-based silicon-carbon anode material for the preparation of anode materials for lithium-ion batteries.

[0030] Specifically, the steps include the following:

[0031] The Ce-modified biosilicon-based material obtained in this invention is mixed with carbon black and PVDF in a ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone is added. The mixture is then ball-milled at 500 r / min for 3 h using a planetary ball mill to obtain a uniformly mixed electrode slurry. This slurry is then coated onto the rough surface of a copper foil with a thickness of about 50 μm and subsequently dried in a vacuum oven at 90 °C.

[0032] The dried electrode sheets are punched to the specified size using a coin cell slicing machine. In a vacuum glove box filled with argon, they are assembled together with the separator, lithium sheet, nickel foam and electrolyte to form a CR2032 coin cell. Finally, the cells are packaged on a battery packaging machine.

[0033] The beneficial effects of this invention lie in proposing a solution using in-situ biomineralization doping. By intervening in the biomineralization of diatoms during the shell synthesis process, a novel two-stage diatom cultivation method is proposed. During the critical period (stage two) of diatom cell shell construction, a functional metal salt (cerium ammonium nitrate) is introduced. Utilizing the diatoms' own metabolic and biomineralization mechanisms, cerium is in-situ and uniformly fixed into the newly generated silica network. The doping modification method used in this invention is highly efficient, low-cost, and simple, possessing the potential for industrial production and market application.

[0034] Compared with other metal modification and doping methods, the main technical advantage of this invention is that it uses a bio-mineralization method to uniformly fix the metal element Ce in situ within the SiO2 network of diatom shells. This not only achieves truly nanoscale uniform doping and unifies the material structure from the source, but also preserves the integrity of the natural porous structure of diatom shells to the greatest extent. It combines the material synthesis and modification steps into one, simplifies the process, reduces energy consumption and cost, and significantly improves the performance of the prepared anode material. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the growth curves of diatoms in Embodiment 1, Comparative Example 1, Comparative Example 2, and Comparative Example 4 of the present invention.

[0036] Figure 2 The images show scanning electron microscope (SEM) images and EDS mapping results of diatom shells in the cerium ammonium nitrate addition group in Comparative Example 1 of this invention. Figure 2 a: EDS elemental content spectrum; Figure 2 b: SEM image; Figure 2 c: Elemental spectrum of Si; Figure 2 d represents the spectrum of Ce element.

[0037] Figure 3 The images show scanning electron microscope (SEM) images and EDS mapping results of the diatom shells in the two-stage cerium ammonium nitrate group of Example 1 of this invention. Figure 3 a: EDS elemental content spectrum; Figure 3 b: SEM image; Figure 3 c: Elemental spectrum of Si; Figure 3 d represents the spectrum of Ce element.

[0038] Figure 4 The images show scanning electron microscope images and EDS mapping results of the diatom shells in the blank control group of Comparative Example 4 of this invention. Figure 4 a: EDS elemental content spectrum; Figure 4 b: SEM image; Figure 4 c: Elemental spectrum of Si; Figure 4 d represents the spectrum of Ce element.

[0039] Figure 5 Fourier transform infrared spectra of diatom shells and calcined silicon-carbon materials in Examples 1 and 4 of this invention.

[0040] Figure 6 The above are the charge-discharge test curves of Embodiment 1 and Comparative Examples 1, 2, 3, and 4 of the present invention. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] The diatom species used in this embodiment is *Cyclotella cryptica*, belonging to the phylum Cyclotella, class Cyclothales, order Cyclothales, family Cyclothaceae, and genus *Cyclotella*. After centrifuging the algal cells, the cell pellet was collected, washed 2-3 times with sterile culture medium, and then inoculated into 50 mL of F / 2 culture medium for expansion culture to obtain diatom seed culture medium.

[0044] The diatoms were cultured in a light incubator with a culture medium volume of 2.5 L (F / 2). The culture temperature was 25℃, the light intensity was 3500 lux, and the light duration was 12 hours / day. The diatom inoculum was 10% (of which the concentration of diatoms in the seed culture medium was approximately 2 × 10⁻⁶). 6 Cell / mL, culture period is 12 days.

[0045] To avoid inhibiting diatom growth by introducing cerium source too early, and to fully utilize the efficient absorption capacity of diatoms for cerium during the active biomineralization period, this invention adopts a two-stage cultivation strategy. The specific cultivation steps are as follows:

[0046] Phase 1 (Post-inoculation to Day 6): Diatoms were cultured normally using F / 2 medium until they reached the early logarithmic growth phase. Phase 2 (Days 6-12): On day 6, cerium ammonium nitrate was added to the culture medium to reach a final concentration of 200 μmol / L. Culture was continued for another 6 days to allow the diatoms to complete cerium doping during the plateau phase. Figure 1 As shown in the growth curves, under the condition of cerium ammonium nitrate concentration of 200 μmol / L, the two-stage culture strategy described above can significantly reduce the toxic inhibitory effect of cerium ammonium nitrate on Cyclocarya cryptotavia.

[0047] Comparative Example 1

[0048] The only difference from Example 1 is that instead of dividing the culture into two stages, cerium ammonium nitrate (i.e., Ce-full addition group) was added during the initial stage of culture (day 1) and cultured for 12 days.

[0049] Comparative Example 2

[0050] The difference from Example 1 is that the cerium source is changed from cerium ammonium nitrate to CeO. 2，The diatoms were cultured in a two-stage manner under the same conditions as in Example 1, with a CeO2 concentration of 200 μmol / L.

[0051] Comparative Example 3

[0052] The difference from Example 1 is that the rare earth element used for biological doping is replaced with a mixed rare earth element and co-cultured with diatoms instead of a single cerium source. The specific culture method is as follows: 2g of ionic rare earth mineral raw material (the upper limit of the threshold at which diatoms are basically not poisoned) is weighed, wrapped with a semi-permeable membrane (made of regenerated cellulose membrane (RC membrane)) with a molecular weight cutoff of 8000D, and placed in 2L of culture medium for co-culture with diatoms.

[0053] Comparative Example 4

[0054] This control example is a blank control group, meaning no foreign metal reagents were added.

[0055] To verify the protective effect of the cerium ammonium nitrate two-stage culture strategy on diatom growth and its positive impact on doping efficiency, this application systematically set up multiple comparative experiments. The diatoms in each group were grown for 12 days under the same culture conditions, and their key growth kinetic parameters are shown in Table 1:

[0056]

[0057] Note: Growth rate calculation formula: Specific growth rate of diatoms (rate of change in cell number per unit time, μ (specific growth rate) = [ln(t)] a )-ln(t b )] / day a-day b, where the breeding cycle is 12 days, and the unit of time is d -1 ).

[0058] As shown in Table 1, the growth rate of Comparative Example 1 (with cerium ammonium nitrate added throughout the entire culture period) was only 0.087 days. -1 (As shown in Table 1), the growth rate was significantly lower than that of the blank control group in Stage 1, indicating that the early continuous addition of cerium ammonium nitrate significantly inhibited diatom growth. SEM images showed obvious shrinkage and pore collapse in the diatom shell structure, with poor integrity. EDS surface scan results showed weak Ce element signal, and the calculated relative Ce content was only 0.1% (e.g., ...). Figure 2 As shown in the figure, this indicates that the effective doping rate of cerium is also suppressed under conditions where growth is continuously suppressed.

[0059] Meanwhile, in Comparative Example 2, cerium dioxide was used as the cerium source for two-stage culture. Although the growth rate in the first stage was close to that of the blank control group, the growth of diatoms was still inhibited in the second stage, indicating that different cerium sources still have different effects on the later physiological development of diatoms.

[0060] In contrast, the two-stage culture method described in this invention (Example 1) has a growth rate of 0.212 days. -1 The growth rate was comparable to the blank control group, indicating that its critical logarithmic growth phase was not disturbed. After the introduction of cerium ammonium nitrate in stage two, the diatom growth entered a plateau phase, and the growth rate was also close to that of the blank control group, indicating that the two-stage cultivation method can effectively mitigate the physiological toxicity of the external metal source to diatoms. SEM images showed that the diatom shell maintained a well-preserved natural porous three-dimensional structure with clear channels and complete morphology. EDS surface scanning showed a strong and uniform Ce element signal distributed throughout the shell, and the calculated relative Ce content reached 2.5%, achieving efficient and uniform cerium doping. Figure 3 .

[0061] Fourier transform infrared spectroscopy analysis of diatom shells before and after pyrolysis revealed (e.g.) Figure 5 As shown), in Example 1, compared to the blank control group (Comparative Example 4), it showed improvement at 500 cm⁻¹. -1 and 1000cm -1 A distinct characteristic absorption peak attributable to the Ce-O-Ce bond was observed, which corresponds to the EDS results, confirming that cerium has been successfully incorporated into the silica network through chemical bonding.

[0062] In summary, the cultivation strategy of this invention, which combines cerium ammonium nitrate with two-stage time-controlled cultivation, successfully achieves efficient and uniform cerium doping while effectively avoiding the toxic inhibition of cerium on the critical growth period of diatoms. This provides a reliable basis for obtaining structurally complete and controllable doping bio-silicon-carbon anode materials.

[0063] The culture medium of diatoms was centrifuged, and the precipitate was collected for preliminary enrichment and salt removal. The centrifuged diatom cells were washed with deionized water to completely remove soluble salts and obtain diatom cells. The precipitate was then soaked in 0.6 mol / L dilute hydrochloric acid solution for 5 hours to remove organic matter and metal oxides, and the precipitate was collected after solid-liquid separation. The precipitate was washed with deionized water until neutral to remove acid and soluble products, and the precipitate was collected after solid-liquid separation. The precipitate was then washed with anhydrous ethanol until colorless and transparent to complete dehydration and displacement, and the precipitate was collected after solid-liquid separation. Finally, the precipitate was freeze-dried at -80℃ and 30 Pa for 24 hours, and then the dried shell was calcined at 700℃ for 3 hours under an argon inert atmosphere at a rate of 10℃ / min to obtain the bio-silicon-based anode material.

[0064] The materials prepared in the examples and comparative examples were mixed with carbon black and PVDF in a ratio of 7:2:1, and a certain amount of N-methylpyrrolidone was added. The mixture was then ball-milled using a planetary ball mill at 500 r / min for approximately 3 hours to obtain a uniformly mixed electrode slurry. This slurry was coated onto copper foil to a thickness of approximately 50 μm, and then dried in a vacuum oven at 90°C for approximately 12 hours. The dried electrode sheets were then punched using a coin cell slicing machine. The cut electrode sheets were placed in a vacuum glove operating box, and the battery casing, negative electrode sheet, separator, lithium separator, nickel foam, and electrolyte were assembled. Finally, the assembly was completed using a coin cell packaging machine.

[0065] The electrochemical performance of the cerium ammonium nitrate dual-stage doped diatom-based silicon-carbon anode material prepared in this invention and four comparative examples was systematically evaluated in the form of coin cells. The assembled cells were placed on a LAND battery charge-discharge testing system, and the test voltage was 0.001-3.0V (vs. Li / Li). + The current density is 100 mA·g ‐1 Perform long-cycle charge-discharge tests.

[0066] Test results show that the cerium-doped bio-silicon carbon material (Example 1) provided by this invention exhibits excellent cycling stability and capacity enhancement characteristics, as shown in Table 2 and... Figure 6 As shown, its charge / discharge specific capacity increases with the number of cycles from the initial 798.2 mAh·g. ‐1 Increased to 932.8 mAh·g on the 200th cycle. ‐1 The capacity retention rate was as high as 116.9%, with a corresponding negative capacity decay coefficient (-0.078% / cycle), indicating that the material underwent continuous electrochemical activation during cycling. In contrast, the bio-silicon carbon materials in the comparative examples all exhibited varying degrees of capacity decay, and their specific capacity was significantly lower than that of Example 1. In Comparative Example 1, the shell structure defects caused by growth inhibition (such as...) Figure 1 (As shown) This gives it an initial capacity of 912.8 mAh·g ‐1 After 200 cycles, it rapidly decreased to 286.4 mAh·g. ‐1 The capacity retention rate was only 31.4%, and the decay coefficient was as high as 0.580% / cycle. The capacity retention rates of Comparative Example 2 (CeO2 two-stage addition) and Comparative Example 4 (blank undoped) were 44.6% and 33.9%, respectively, and their cycle stability was much lower than that of Example 1. Comparative Example 3 (mixed rare earth doping) showed a higher initial coulombic efficiency and relatively smooth decay, but its initial and final specific capacity were both lower than that of Example 1, and its overall performance was limited.

[0067]

[0068] In summary, this invention successfully prepared cerium-doped diatom-based silicon-carbon composite materials by combining cerium ammonium nitrate with a two-stage cultivation strategy. While ensuring a high average coulombic efficiency, it achieved a significant increase in specific capacity and stable and superior long-cycle performance during cycling, demonstrating that this material has good application potential in lithium battery anode materials.

Claims

1. A method for preparing a cerium-doped diatom-based silicon-carbon anode material, characterized in that, Includes the following steps: 1) When diatoms are placed in the culture medium and grow to the early logarithmic phase, cerium source is added to the diatom culture medium for co-culture; 2) The co-cultured diatom shells are calcined at high temperature to obtain the cerium-doped diatom-based silicon-carbon anode material.

2. The preparation method according to claim 1, characterized in that, Step 1) Continue culturing for at least 5 days after adding the cerium source.

3. The preparation method according to claim 1, characterized in that, Step 1) The diatom culture medium includes F / 2 culture medium, and the diatom type is Cryptomona cryptica.

4. The preparation method according to claim 1, characterized in that, Step 1) The conditions for diatom cultivation include: a temperature of 22-25℃, a light intensity of 2000-4000 lux, a light duration of 12-14 hours / day, and an inoculum size of 8-10%.

5. The preparation method according to claim 1, characterized in that, Step 1) The cerium source is cerium ammonium nitrate, preferably with a concentration of at least 200 μmol / L.

6. The preparation method according to claim 1, characterized in that, Step 2) Before the high-temperature calcination, the diatom cells are pretreated. The pretreatment includes the following steps: (1) centrifuging the diatom culture medium after the culture is completed to separate the diatoms from the culture medium and obtain diatom cell precipitate; (2) washing the centrifuged diatom cells with deionized water and collecting the precipitate by solid-liquid separation; (3) acid soaking the diatom cells with hydrochloric acid and then collecting the precipitate by solid-liquid separation; (4) washing the diatom cells with deionized water until neutral and collecting the precipitate by solid-liquid separation; (5) washing the diatom cells with anhydrous ethanol until colorless and transparent and collecting the precipitate by solid-liquid separation; (6) freeze-drying the precipitate.

7. The preparation method according to claim 6, characterized in that, Step (3) Use hydrochloric acid with a concentration of 0.5-0.8 M to acid-soak the diatom cells, and freeze-dry the precipitate at -70℃ to -80℃ and 25-40 Pa for at least 24 hours.

8. The preparation method according to claim 1, characterized in that, Step 2) The diatom shells are calcined at 600-800℃ under an inert atmosphere by heating at a rate of 5-10℃ / min.

9. The cerium-doped diatom-based silicon-carbon anode material prepared by the method according to any one of claims 1-8.

10. The application of the cerium-doped diatom-based silicon-carbon anode material according to claim 9, characterized in that, Anode materials used in the preparation of lithium-ion batteries.

Images