A Mn2SiO4-coated diatom-based composite material, its preparation method and application

Abstract

This invention discloses a Mn2SiO4-coated diatomaceous earth-based composite material, its preparation method, and its applications. In the preparation process, a one-step hydrothermal method is used to mix diatomaceous earth powder with anhydrous ethanol and 3-aminopropyltriethoxysilane (APTES). A manganese source solution is added and stirred under heating conditions. The solid-liquid separation process collects the precipitate, which is then freeze-dried and calcined at high temperature to form a composite material with a Mn2SiO4-C-SiO2 nanostructure. This composite material is used as an active anode for lithium-ion batteries, exhibiting excellent electrochemical performance. The Mn2SiO4 coating significantly improves the conductivity, discharge specific capacity, and rate performance of the SiO2 anode material, while suppressing the volume expansion of the SiO2 anode material, thus achieving a lithium-ion battery anode material with ultra-high discharge specific capacity. This invention has the advantages of inexpensive and readily available raw materials, a simple and efficient preparation method, and low energy consumption, and has broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of diatom-based material modification technology, specifically relating to a Mn2SiO4-coated diatom-based composite material, its preparation method, and its application in lithium-ion batteries. Background Technology

[0002] The rapid development of the new energy industry has placed higher demands on all aspects of energy storage devices. Lithium-ion batteries, as the most widely used energy storage component on the market today, have seen their anode materials lag behind their cathode materials in development. Furthermore, the most widely used commercially available graphite anode material is limited by its relatively low theoretical specific capacity (372 mAh·g). -1 Excessive saturation has become insufficient to meet the demands of the current energy market, leading to the development of silicon, various metal oxides, and alloy anode materials. Silicon, in particular, is highly regarded due to its extremely high theoretical specific capacity (4200 mAh·g). -1 Silicon is considered the most promising anode material for next-generation lithium-ion batteries. However, its poor conductivity and large volume expansion (300%-400%) during cycling limit its large-scale commercial application. Furthermore, the preparation of pure silicon is an energy-intensive and carbon-emission process, while SiO2, as a substitute for Si, is abundant on Earth, although its theoretical specific capacity (1965 mAh·g) is relatively high. -1 SiO2 has a lower conductivity than silicon but still much higher conductivity than graphite, and it has smaller volume expansion and lower discharge potential. However, SiO2 anode materials also have problems such as poor conductivity and low initial coulombic efficiency. Common solutions to these problems include designing nanostructures and combining SiO2 with conductive phases. However, the design process of SiO2 nanostructures is complex and costly, making it difficult to commercialize.

[0003] Diatoms are a naturally occurring source of SiO2, capable of absorbing dissolved silicon through biomineralization and transforming it into an amorphous hydrated silica (SiO2·H2O) shell structure. Their cell walls possess a complex, layered, porous SiO2 network, effectively suppressing volume expansion during SiO2 cycling. Furthermore, diatoms are widely distributed and abundant on Earth, making them a highly promising source of silica anode materials. Currently, to address the poor conductivity of SiO2, it is common practice to composite SiO2 with conductive phases to improve conductivity and initial coulombic efficiency. Common composite methods include solid-state self-assembly, hydrothermal methods, and wet chemical methods. Commonly used composite metals include transition metals such as Fe, Co, Ni, and Mn. However, traditional composite methods suffer from low loading efficiency, uneven distribution, and easy detachment. Therefore, exploring new composite material preparation methods is an urgent need for SiO2 anodes in the application of lithium-ion battery anodes.

[0004] Chinese patent CN110165177 A discloses a method for preparing silicon-based composite anode materials for lithium-ion batteries. The method involves ball milling silicon and copper oxide to prepare silicon-based composite anode materials. The main drawbacks of this patent are that the purity of the material prepared by this method cannot be determined, the yield is low, and the morphology is poorly controllable.

[0005] Research on manganese silicate as a negative electrode material for lithium-ion batteries has also been reported. For example, Wang et al. (https: / / doi.org / 10.1016 / j.electacta.2015.11.009) prepared manganese silicate by reacting Na2SiO3·9H2O with MnCl2·4H2O. Carbon-coated manganese silicate was used as a lithium storage negative electrode material. The uniform carbon coating of manganese silicate nanoparticles as conductive materials and the formation of lithium silicate as a solid electrolyte are the reasons for its excellent performance. The manganese silicate-coated electrode material has a conductivity of 0.5 A·g -1 The discharge specific capacity after 600 cycles at a current density is 337 mAh·g. -1 However, this method is complex, and the resulting carbon-coated manganese silicate does not have structural advantages and has a low discharge specific capacity. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a simple and low-cost method for coating Mn2SiO4 onto the surface of diatom shells and the resulting composite material, and to prepare this composite material as a negative electrode material for lithium-ion batteries.

[0007] This invention is the first to coat Mn2SiO4 onto the surface of a hollow, porous diatom shell structure. Unlike traditional composite methods using metal materials, this invention utilizes Mn2SiO4 generated from aminosilane and MnCl2 to achieve uniform coating while preserving the original hollow, porous structure of the diatom shell. Simultaneously, through simple carbonization, the inexpensive organic carbon skeleton of aminosilane and the organic biomass of diatoms in the raw materials are transformed into a uniform conductive carbon layer on the SiO2 surface. The Mn2SiO4-C-SiO2 nanostructure significantly improves the conductivity of SiO2 and further suppresses the volume expansion of SiO2 during cycling, thus realizing a silicon dioxide anode material with ultra-high discharge specific capacity, opening up new prospects for the development of lithium-ion battery anode materials.

[0008] The objective of this invention is achieved through the following means:

[0009] A diatom-based composite material coated with Mn2SiO4 consists of Mn2SiO4 coated on the surface of a diatom shell, and further coated with carbon.

[0010] Furthermore, the Mn2SiO4 and carbon are generated by reacting triaminopropyltriethoxysilane (APTES) with soluble manganese source solution and diatoms, followed by calcination, preferably using MnCl2.

[0011] The present invention also provides a method for preparing the Mn2SiO4-coated diatomaceous earth composite material, comprising the following steps:

[0012] 1) Amin-functionalized diatoms: Diatom powder is mixed with solvent and triaminopropyltriethoxysilane and then dispersed.

[0013] 2) Preparation of Mn2SiO4-coated composite material: A certain amount of soluble manganese source solution was added to the mixed solution, and the mixture was heated and stirred. The precipitate was collected by solid-liquid separation. The precipitate was then freeze-dried and calcined at high temperature to obtain the final product.

[0014] Furthermore,

[0015] Step 1) Before the reaction, the diatom powder is pretreated by soaking the dried diatom powder in 2%-5% dilute acid to remove the inorganic salts and some biomass. Hydrochloric acid is preferred. After solid-liquid separation, the diatom solution is collected and washed with alcohol, preferably ethanol. After solid-liquid separation, the diatom precipitate is collected.

[0016] The addition ratio of various raw materials in steps 1) and 2) is as follows: after mixing 0.2-0.5g of diatom powder with 100-150mL of solvent, add 1-2mL of triaminopropyltriethoxysilane and disperse using ultrasonication.

[0017] Further, the mixed solution is ultrasonically dispersed for 20-30 minutes;

[0018] The solvent mentioned in step 1) includes at least one of methanol and ethanol.

[0019] Step 2) Add 20-60 mL of 0.1-0.15 M soluble manganese salt solution to the diatom mixture, heat and stir, and collect the diatom precipitate by solid-liquid separation.

[0020] The soluble manganese source mentioned in step 2) includes at least one of MnCl2, Mn(NO3)2, and MnSO4. The soluble manganese source solution is added and stirred and heated at 70-80℃ for 30-60 minutes.

[0021] Step 2) Freeze-dry the diatom precipitate at -70℃ for at least 24 hours; heat the dried diatom powder to 600-900℃; keep it at that temperature for 1-3 hours.

[0022] Step 2) Centrifuge the heated and stirred mixture at 9000-10000 r / min for at least 10 min to separate the solid and liquid and collect the precipitate.

[0023] Furthermore, the freeze-dried diatomaceous earth powder is heated at a rate of 5-10℃ / min.

[0024] The present invention also provides the application of the diatom-based composite material, namely, its use in the preparation of lithium-ion battery anode materials.

[0025] The diatom-based composite active material prepared according to this invention is mixed with Super P and PVDF at a mass ratio of 7:2:1, 7:1.5:1.5, or 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) is added, and the mixture is ball-milled at 300–450 r / min for 1–3 h to obtain a uniformly mixed electrode slurry. The slurry is coated onto copper foil with a thickness of 25–300 μm, vacuum-dried at 80 °C, and then cut to obtain electrode sheets. Preferably, the ratio of active material: Super P:PVDF = 7:2:1, ball-milled at 300 r / min for 3 h, yields a slurry coating thickness of 50 μm.

[0026] Further, in an argon-filled glove box, the cut electrode sheets are placed on the lower casing of the battery, 1-2 drops of electrolyte are added to the surface of the electrode sheets, a separator is placed on top, another 1-2 drops of electrolyte are added, and finally the lithium sheet is placed in, the battery cover is closed, and the battery is sealed on a button cell packaging machine to complete the battery assembly.

[0027] The beneficial effects of this invention are as follows: Using diatoms, a bio-based SiO2 material with a naturally regular nanostructure, as a template, this invention achieves for the first time the coating of Mn2SiO4 onto the SiO2 structure surface of the diatom shell, forming a nanostructure composed of Mn2SiO4-C-SiO2. This further enhances the conductivity of SiO2 based on existing technologies. At the same time, the Mn2SiO4 coating structure suppresses the volume expansion of SiO2 during cycling, thus realizing the development of a lithium-ion battery anode material with excellent electrochemical activity. Attached Figure Description

[0028] Figure 1 The XRD patterns of Comparative Example 1, Example 1, Example 2 and Example 3 of this invention;

[0029] In Comparative Example 1, DBS@C showed broad peaks of amorphous SiO2 and diffraction peaks of carbon. In Example 1, AFD@C-Mn-20 showed broad amorphous peaks of Mn2SiO4. In Examples 2 and 3, diffraction peaks of Mn2SiO4 were observed, proving the presence of Mn2SiO4.

[0030] Figure 2 Scanning electron microscope (SEM) and transmission electron microscope (TEM) images of Comparative Example 1, Example 1, Example 2, and Example 3;

[0031] Figure 2a shows the comparative SEM and TEM images, with a smooth, unloaded surface; Figure 2 b is the SEM and TEM image of Example 1, where a small number of Mn2SiO4 nanoclusters can be observed on the surface; Figure 2 c shows the SEM and TEM images of Example 2. The surface is rough, and a large number of Mn2SiO4 crystals can be observed to coat it. Figure 2 d shows the SEM and TEM images of Example 3. The surface is rough, and a large number of Mn2SiO4 crystals can be observed to coat it.

[0032] Figure 3 The following are SEM-EDS mapping maps for Examples 1, 2, and 3: Example 1: Figure a; Example 2: Figure b; Example 3: Figure c.

[0033] Figure 4 (a) charge-discharge long cycle curves and (b) rate cycle curves provided for Embodiments 1, 2, 3 and Comparative Example 1 of the present invention.

[0034] Figure 5 The AC impedance spectra are for Comparative Example 1, Example 1, Example 2, and Example 3.

[0035] Figure 6 The high-resolution transmission electron microscope (a) and electron diffraction pattern (b) of manganese silicate generated on the surface of diatom shells in Example 2 prove the existence of Mn2SiO4 crystals and their polycrystalline characteristics. Detailed Implementation

[0036] To explain in detail the preparation method of the material of the present invention and its application in lithium-ion battery anode materials, the following description is provided in conjunction with specific embodiments and accompanying drawings.

[0037] Example 1

[0038] (1) The dried diatom powder was washed with 5% dilute hydrochloric acid and then washed with anhydrous ethanol. After solid-liquid separation, the diatom precipitate was collected.

[0039] (2) Take 0.2g of the diatom precipitate after acid washing and alcohol washing in (1) and mix it with 100mL of anhydrous ethanol and 2mL of APTES, and sonicate for 20min.

[0040] (3) Add 20 mL of MnCl2 solution to the ultrasonicated mixture from (2), and stir and heat at 80 °C for 60 min. This allows the aminosilane to react with MnCl2. 2+ The reaction produces Mn2SiO4, which is then centrifuged at 9000 rpm for 10 min to achieve solid-liquid separation. The precipitate is collected and freeze-dried at -70℃ for 24 h to obtain a diatom mixture loaded with Mn2SiO4.

[0041] (4) The dried diatom mixture was calcined at 600℃ for 3h under an argon atmosphere at a rate of 5℃ / min. Mn2SiO4-coated diatom-based composite material was obtained.

[0042] (5) The surface structure of the diatom shell coated with Mn2SiO4 was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The elemental distribution of the diatom shell and structure surface was mapped by SEM-EDS. A small amount of amorphous Mn2SiO4 was observed on the surface of the diatom shell structure. The diatom-based composite material supported by Mn2SiO4 (AFD@C-Mn-20) was successfully synthesized.

[0043] (7) The phase composition of the diatomaceous earth composite material was analyzed by XRD, and the results are as follows: Figure 1 As shown, the composite material consists of SiO2, C and amorphous Mn2SiO4, and the desired Mn2SiO4-coated diatom-based composite material (AFD@C-Mn-20) was successfully synthesized.

[0044] (8) The active composite material was mixed with Super P and PVDF in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone (NMP) solvent was added. The mixture was ball-milled at 500 r / min for 3 h to obtain a uniformly mixed electrode slurry. The slurry was coated on copper foil with a thickness of 50 μm, dried under vacuum at 80 °C, and cut to obtain a circular electrode sheet with a diameter of 12 mm.

[0045] (9) Place the cut electrode sheet into the lower shell of the battery in an argon-filled glove box, add 1 drop of electrolyte to the surface of the electrode sheet, place the separator on it, add another drop of electrolyte, and finally put in the lithium sheet. Cover the battery with the top cover and seal it on the button battery packaging machine to complete the battery assembly.

[0046] (10) The assembled battery was subjected to impedance spectroscopy testing on a Gamry electrochemical workstation. The test frequency range was 100kHz to 10MHz. The impedance spectroscopy results are as follows: Figure 5 As shown, the charge transfer is significantly lower than that of carbon composite diatom material (DBS@C).

[0047] (11) The assembled battery was subjected to cyclic charge-discharge tests and rate performance tests on the LAND battery charge-discharge test system. The test voltage range was 0.001–3.0V (vs. Li / Li). + The current density is 100 mA·g -1 The charge / discharge curves are as follows: Figure 4 As shown, the electrode yielded 670 mAh·g after 60 cycles. -1 With its high discharge specific capacity and good cycle stability, AFD@C-Mn-20 exhibits excellent rate performance, as shown in rate test results.

[0048] Example 2

[0049] The only difference between Example 2 and Example 1 is that:

[0050] The amount of MnCl2 solution added in step (4) is 40 mL, and the remaining battery assembly and testing steps remain unchanged.

[0051] (1) The surface structure of the diatom shell coated with Mn2SiO4 was observed by SEM and TEM. The elemental distribution of the diatom shell and structure surface was mapped by SEM-EDS. A large number of crystal Mn2SiO4 were observed on the surface of the diatom shell structure. The Mn2SiO4 coated diatom composite material (AFD@C-Mn-40) was successfully synthesized.

[0052] (2) The phase composition of the diatomaceous earth composite material was analyzed by XRD, and the results are as follows: Figure 1 As shown, the composite material consists of SiO2, C, and crystalline Mn2SiO4. The desired Mn2SiO4-coated diatomaceous earth composite material (AFD@C-Mn-40) was successfully synthesized. The energy dispersive spectroscopy (EDS) results are shown below. Figure 3 As shown, C and Mn elements are uniformly distributed on the SiO2 surface.

[0053] (3) The assembled battery was subjected to cyclic charge-discharge testing on the LAND battery charge-discharge testing system, with a test voltage range of 0.001–3.0V (vs. Li / Li). + The current density is 100 mA·g -1 The charge / discharge curves are as follows: Figure 4 As shown, this electrode yielded ~962 mAh·g after 60 cycles. -1 It has good specific capacity and cycling stability. The rate curve results show that AFD@C-Mn-40 has excellent rate performance.

[0054] (4) The assembled battery was subjected to impedance spectroscopy testing on a Gamry electrochemical workstation. The test frequency range was 100kHz to 10MHz. The impedance spectroscopy results are as follows: Figure 5 As shown, it is far lower than that of carbon composite diatomaceous earth material (DBS@C).

[0055] (5) The diatom-based composite material was observed using high-resolution transmission electron microscopy (HRTEM) and zone electron diffraction (SAED). The results are as follows: Figure 6 As shown, the lattice fringes and diffraction rings of Mn2SiO4 were observed, proving the formation of Mn2SiO4 and its polycrystalline characteristics.

[0056] Example 3

[0057] The only difference between Example 3 and Examples 1 and 2 is that:

[0058] The amount of MnCl2 solution added in step (3) is 60 mL, and the rest of the battery assembly and testing steps remain unchanged.

[0059] (1) The surface structure of the diatom shell coated with Mn2SiO4 was observed by scanning electron microscopy and transmission electron microscopy, and the elemental distribution of the diatom shell and structure surface was reflected by EDS. A uniformly coated Mn2SiO4 coating was observed on the surface of the diatom shell structure, and the composite material of Mn2SiO4 coated with diatom (AFD@C-Mn-60) was successfully synthesized.

[0060] (2) The phase composition of the diatomaceous earth composite material was analyzed by XRD, and the results are as follows: Figure 1 As shown, the composite material consists of SiO2, C, and Mn2SiO4, and the desired composite material (AFD@C-Mn-60) was successfully synthesized.

[0061] (3) The assembled battery was subjected to impedance spectroscopy testing on a Gamry electrochemical workstation. The test frequency range was 100kHz to 10MHz. The impedance spectroscopy results are as follows: Figure 5 As shown, it is far lower than that of carbon composite diatomaceous earth material (DBS@C).

[0062] (4) The assembled battery was subjected to cyclic charge-discharge testing on the LAND battery charge-discharge testing system, with a test voltage range of 0.001–3.0V (vs. Li / Li). + The current density is 100 mA·g -1 The charge / discharge curves are as follows: Figure 4 As shown, this electrode yielded ~870 mAh·g after 60 cycles. -1 It has good specific capacity and cycle stability. Rate test results show that AFD@C-Mn-60 has excellent rate performance.

[0063] Comparative Example 1

[0064] The only difference between Comparative Example 1 and the Embodiment is that:

[0065] Dry diatomaceous earth powder was acid-washed and alcohol-washed, then placed directly under an argon atmosphere and calcined at 600°C for 3 hours at a rate of 5°C / min to obtain a simple diatomaceous earth-carbon composite material DBS@C. Electrode preparation, battery assembly, and electrochemical performance testing were performed using the above experimental steps as a comparative example. XRD, impedance spectroscopy, and charge-discharge results are shown below. Figure 1 , Figure 5 and Figure 4 As shown, at 100 mA·g -1 After 60 cycles, a capacity of ~407 mAh·g was obtained. -1 Specific capacity.

Claims

1. A Mn2SiO4-coated diatomaceous earth composite material, wherein Mn2SiO4 and carbon are coated on the surface of a diatom shell; the preparation method of the Mn2SiO4-coated diatomaceous earth composite material includes the following steps: 1) Amine-functionalized diatoms: diatom powder is mixed with solvent and triaminopropyltriethoxysilane and then dispersed; 2) Preparation of Mn2SiO4-coated composite material: a certain amount of soluble manganese source solution is added to the mixed solution, heated and stirred, and the precipitate is collected by solid-liquid separation; the precipitate is obtained by freeze-drying and high-temperature calcination; the addition ratio of various raw materials in steps 1) and 2) is as follows: 0.2-0.5g of diatom powder is mixed with 100-150mL of solvent and 1-2mL of triaminopropyltriethoxysilane is added, and the mixture is dispersed by ultrasonication; the mixed solution is ultrasonically dispersed for 20-30min; in step 2), 20-60mL of 0.1-0.15M soluble manganese source solution is added to the diatom mixed solution, heated and stirred, and the diatom precipitate is collected by solid-liquid separation.

2. The method for preparing the Mn2SiO4-coated diatomaceous earth composite material according to claim 1, characterized in that, Includes the following steps: 1) Amine-functionalized diatoms: Diatom powder is mixed with solvent and triaminopropyltriethoxysilane and then dispersed; 2) Preparation of Mn2SiO4-coated composite material: A certain amount of soluble manganese source solution was added to the mixed solution, and the mixture was heated and stirred. The precipitate was collected by solid-liquid separation. The precipitate was then freeze-dried and calcined at high temperature to obtain the final product.

3. The preparation method according to claim 2, characterized in that: Step 1) Before the reaction, the diatom powder is pretreated by soaking the dried diatom powder in 2%-5% dilute acid to remove the inorganic salts and some biomass. After solid-liquid separation of the acid-washed diatomaceous earth solution, the precipitate was collected and washed with alcohol. The diatom precipitate was collected after solid-liquid separation; The solvent mentioned in step 1) includes at least one of methanol and ethanol.

4. The preparation method according to claim 3, characterized in that: The dilute acid is hydrochloric acid; the alcohol is ethanol.

5. The preparation method according to claim 2, 3, or 4, characterized in that, The addition ratio of various raw materials in steps 1) and 2) is as follows: after mixing 0.2-0.5g of diatom powder with 100-150mL of solvent, add 1-2mL of triaminopropyltriethoxysilane and disperse using ultrasound; disperse the mixed solution by ultrasound for 20-30min. Step 2) Add 20-60 mL of 0.1-0.15 M soluble manganese source solution to the diatom mixture, heat and stir, and collect the diatom precipitate by solid-liquid separation.

6. The preparation method according to claim 2, 3, or 4, characterized in that, The soluble manganese source mentioned in step 2) includes at least one of MnCl2, Mn(NO3)2, and MnSO4. The soluble manganese source solution is added and stirred and heated at 70-80℃ for 30-60 minutes.

7. The preparation method according to claim 2, 3, or 4, characterized in that, Step 2) Freeze-dry the diatom precipitate at -70℃ for at least 24 h; heat the dried diatom powder to 600-900℃; keep it at that temperature for 1-3 h.

8. The preparation method according to claim 2, characterized in that, Step 2) Centrifuge the heated and stirred mixture at 9000-10000 r / min for at least 10 min to separate the solid and liquid and collect the precipitate.

9. The preparation method according to claim 2, characterized in that, The freeze-dried diatomaceous earth powder was heated at a rate of 5-10℃ / min.

10. The application of the diatomaceous earth-based composite material according to any one of claims 1-9, characterized in that, Used to prepare negative electrode materials for lithium-ion batteries.

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