Lithium silicate coated lithium copper doped silicon carbon composite material and preparation method thereof

Abstract

The preparation method comprises the steps that an oxide layer on the surface of foamy copper is removed, then a carbon source, a lithium source and a silicon source are sequentially introduced through a vapor deposition method to obtain a silicon-carbon precursor, then carbon source gas is introduced for surface passivation, pre-lithiation and amorphous carbon coating, and the lithium silicate-coated lithium-copper-doped silicon-carbon composite material is obtained. The lithium silicate coated lithium copper doped silicon carbon composite material is obtained. According to the obtained material, the electronic conductivity of the material is improved through lithium-doped foamy copper, the first efficiency is improved, the ionic conductivity is improved, and the rate capability is improved through coating of lithium silicate on the outer layer; meanwhile, a layered structure is formed by depositing the carbon source, the lithium source, the silicon source and the carbon source in stages, so that the specific capacity of the material is improved, and the expansion is reduced.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material preparation, specifically a lithium silicate-coated lithium copper-doped silicon-carbon composite material and its preparation method. Background Technology

[0002] Silicon-carbon materials are composed of porous carbon and deposited nano-silicon, coated with amorphous carbon. The poor electronic conductivity of the porous carbon core and the amorphous carbon shell, formed by low-temperature carbonization, result in high impurity content and the presence of chemical bonds such as CH, leading to high electronic impedance. The interaction between the core and shell causes deviations in the material's power performance. To improve the power performance of silicon-carbon materials, it is necessary to improve the electronic and ionic conductivity of both the core and shell. While some researchers have improved the electronic conductivity by doping the core with metals or non-metals, or by coating the shell with lithium fast-ion conductors, for example, patent application CN202210567480.4 discloses a core-shell silicon-carbon composite material, its preparation method, and its applications. The core is a composite material comprising hard carbon, amorphous carbon, and silicon-based materials, and the shell is a fast-ion conductor. Although the fast-charging performance and initial efficiency of the material are improved, the poor compatibility between the inorganic fast-ion conductor in the coating layer and the electrolyte limits the improvement in initial efficiency and low-temperature performance. Therefore, it is necessary to double-coat the material and improve its core to further enhance its fast-charging performance and low-temperature performance. Summary of the Invention

[0003] The present invention aims to at least partially solve one of the technical problems in the related art.

[0004] To improve the fast-charging performance and low-temperature performance of silicon-carbon materials, this invention prepares a lithium copper-doped silicon-carbon precursor material. The precursor is obtained by sequentially introducing a carbon source, a lithium source, and a silicon source through vapor deposition. Then, carbon source gas is introduced for surface passivation, pre-lithiation, and amorphous carbon coating to prepare a lithium silicate-coated lithium copper-doped silicon-carbon composite material, which has the advantages of good power performance, high initial efficiency, and low expansion.

[0005] The purpose of this invention is to propose a lithium silicate-coated lithium copper-doped silicon-carbon composite material, characterized in that the composite material has a core-shell structure, with the core being lithium-doped foamed copper silicon-carbon material, the middle layer being lithium silicate, and the outer layer being amorphous carbon; wherein the thickness ratio of the core:middle layer:outer layer is 70-90:5-15:5-15.

[0006] The present invention also aims to provide a method for preparing a lithium silicate-coated lithium copper-doped silicon-carbon composite material, characterized by comprising the following steps:

[0007] Step S1:

[0008] The modified copper foam was soaked in 0.1 mol / L hydrochloric acid for 24 h, and then added to an ethanol / deionized water mixture and ultrasonically dispersed for 24 h to obtain the modified copper foam.

[0009] Step S2:

[0010] The modified copper foam was transferred to a rotary kiln, and lithium copper-doped silicon-carbon precursor material was prepared by chemical vapor deposition. Specifically, the rotary kiln was heated to 700-1100℃, and carbon source gas was introduced at a flow rate of 50-500 SCCM for 30-300 min. Then the temperature was adjusted to 850-950℃, and lithium source gas was introduced at a flow rate of 10-100 SCCM for 30-300 min. Then the temperature was lowered to 450-550℃, and silane gas was introduced at a flow rate of 50-500 SCCM for 30-300 min to obtain lithium copper-doped silicon-carbon precursor material.

[0011] Step S3:

[0012] Under an inert atmosphere, the lithium copper-doped silicon-carbon precursor material is transferred to a rotary kiln, and then an oxygen / nitrogen mixed gas is introduced with a volume ratio of oxygen:nitrogen = 1-5:10. The gas is introduced at a flow rate of 100-500 SCCM for 30-300 min to obtain the silicon-oxygen coated lithium copper-doped silicon-carbon precursor material.

[0013] Step S4:

[0014] The silicon-oxygen coated lithium copper-doped silicon-carbon precursor material and the organic lithium compound were mixed uniformly according to a mass ratio of 100:5-10. The mixture was then heated to 50-400℃ under an inert atmosphere to melt and held for 3-9 hours. After that, the temperature was raised to 700-1000℃, and a carbon source gas was introduced at a flow rate of 100-500 SCCM for 30-300 minutes to perform amorphous carbon coating, thus obtaining a lithium silicate coated lithium copper-doped silicon-carbon composite material.

[0015] Further, in step S2, the carbon source gas is at least one of acetylene, ethylene, propyne, methane, and ethane; the lithium source gas is lithium hydride; and the silane gas is at least one of silane, disilane, dichlorosilane, and methyldichlorosilane.

[0016] Further, in step S4, the organolithium compound is at least one of lithium formate, lithium acetate, lithium propionate, lithium butyrate, and lithium isobutyrate.

[0017] Furthermore, in step S4, the carbon source gas is at least one of acetylene, propane, cyclohexane, methane, and benzene.

[0018] This application optimizes the sequence of "carbon source → lithium source → silicon source," first constructing a conductive framework with a carbon source, then inserting a lithium source into the pores of copper foam to form ion conduction channels, and finally depositing silicon to fill the pores, forming a synergistic structure of "conductive network-ion channels-active material," significantly improving the electronic and ion conduction coupling efficiency of the material. Furthermore, the deposition temperatures used in each process—carbon source deposition (700-1100℃) → lithium source deposition (850-950℃) → silicon source deposition (450-550℃)—are controlled by a cooling gradient to regulate the deposition sequence and interfacial bonding of each component. This avoids damage to the carbon framework caused by high-temperature lithium sources, while low-temperature silicon deposition reduces silicon agglomeration, better ensuring the uniformity of each layer and interfacial compatibility. This results in an initial efficiency improvement of over 93% and a reduction in the full-charge expansion rate to 86.5%–92.4%. Carbon source deposition is used to construct a conductive framework and reduce powder resistivity; lithium source deposition is used to improve ion conduction and reduce DCR; silicon source deposition is used to provide high capacity, with a specific capacity of 1878.5–2003.7 mAh / g; lithium silicate layer is used to reduce electrolyte side reactions; and amorphous carbon coating is used to seal the surface and suppress expansion.

[0019] Beneficial effects:

[0020] 1. Depositing amorphous carbon and lithium in copper foam improves the electronic and ionic conductivity of the material, and depositing nano-silicon in its porous copper improves both the specific capacity and the electronic conductivity of the material.

[0021] 2. The lithium copper-doped silicon-carbon precursor material is oxidized to obtain a silicon-oxygen coated lithium copper-doped silicon-carbon precursor material, which is then reacted with an organolithium compound to generate lithium silicate coated lithium copper-doped silicon-carbon, thereby improving the first-pass efficiency of the material and restricting its expansion, thus enhancing its cycle performance. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The image shows a SEM image of the lithium silicate-coated lithium copper-doped silicon-carbon composite material prepared in Example 1. Detailed Implementation

[0024] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0025] With regard to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0026] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0027] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0028] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0029] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0030] Example 1

[0031] A method for preparing a lithium silicate-coated lithium copper-doped silicon-carbon composite material includes the following steps:

[0032] Step S1:

[0033] 100g of copper foam was soaked in 500g of 0.1mol / L hydrochloric acid for 24h, and then added to an ethanol / deionized water mixture for ultrasonic dispersion for 24h to obtain modified copper foam.

[0034] Step S2:

[0035] The modified copper foam was transferred to a rotary kiln and then heated to 900°C by vapor deposition. Ethylene gas was introduced at a flow rate of 300 SCCM for 150 min. The temperature was then maintained at 900°C, and lithium hydride gas was introduced at a flow rate of 50 SCCM for 150 min. The temperature was then lowered to 500°C, and silane gas was introduced at a flow rate of 300 SCCM for 150 min to obtain lithium copper doped silicon carbon precursor material.

[0036] Step S3:

[0037] Under an inert argon atmosphere, the lithium copper-doped silicon-carbon precursor material was transferred to a rotary kiln, and then an oxygen / nitrogen mixed gas (volume ratio: oxygen: nitrogen = 3:10) was introduced at a flow rate of 300 SCCM for 150 min to obtain the silicon-oxygen coated lithium copper-doped silicon-carbon precursor material.

[0038] Step S4:

[0039] 100g of silicon-oxygen coated lithium copper-doped silicon-carbon precursor material was mixed with 8g of lithium formate and heated to 80℃ under an inert atmosphere to melt and hold for 6h. Then the temperature was raised to 850℃ and acetylene gas was introduced. Amorphous carbon coating was carried out at a flow rate of 300SCCM for 120min to obtain lithium silicate coated lithium copper-doped silicon-carbon composite material.

[0040] Example 2

[0041] A method for preparing a lithium silicate-coated lithium copper-doped silicon-carbon composite material includes the following steps:

[0042] Step S1:

[0043] 100g of copper foam was soaked in 500g of 0.1mol / L hydrochloric acid for 24h, and then added to an ethanol / deionized water mixture for ultrasonic dispersion for 24h to obtain modified copper foam.

[0044] Step S2:

[0045] The modified copper foam was transferred to a rotary kiln and then subjected to vapor deposition. The temperature was raised to 700°C and ethylene gas was introduced at a flow rate of 50 SCCM for 300 min. The temperature was then raised to 850°C and lithium hydride gas was introduced at a flow rate of 10 SCCM for 300 min. The temperature was then lowered to 450°C and silane gas was introduced at a flow rate of 500 SCCM for 300 min to obtain lithium copper doped silicon carbon precursor material.

[0046] Step S3:

[0047] Under an inert atmosphere, the lithium copper-doped silicon-carbon precursor material was transferred to a rotary kiln, and then an oxygen / nitrogen mixed gas (volume ratio: oxygen: nitrogen = 1:10) was introduced at a flow rate of 100 SCCM for 300 min to obtain the silicon-oxygen coated lithium copper-doped silicon-carbon precursor material.

[0048] Step S4:

[0049] 100g of silicon-oxygen coated lithium copper-doped silicon-carbon precursor material was mixed evenly with 5g of lithium acetate, heated to 150℃ under an argon inert atmosphere and held for 3h. Then the temperature was raised to 700℃ and propane gas was introduced. Amorphous carbon coating was carried out at a flow rate of 100SCCM for 180min to obtain lithium silicate coated lithium copper-doped silicon-carbon composite material.

[0050] Example 3

[0051] A method for preparing a lithium silicate-coated lithium copper-doped silicon-carbon composite material includes the following steps:

[0052] Step S1:

[0053] 100g of copper foam was soaked in 500g of 0.1mol / L hydrochloric acid for 24h, and then added to an ethanol / deionized water mixture for ultrasonic dispersion for 24h to obtain modified copper foam.

[0054] Step S2:

[0055] The modified copper foam was transferred to a rotary kiln and then subjected to vapor deposition. The temperature was raised to 1100℃ and methane gas was introduced at a flow rate of 500 SCCM for 30 min. The temperature was then adjusted to 950℃ and lithium hydride gas was introduced at a flow rate of 100 SCCM for 30 min. The temperature was then lowered to 550℃ and dichlorosilane gas was introduced at a flow rate of 500 SCCM for 30 min to obtain lithium copper doped silicon carbon precursor material.

[0056] Step S3:

[0057] Under an inert atmosphere, the lithium copper-doped silicon-carbon precursor material was transferred to a rotary kiln, and then an oxygen / nitrogen mixed gas (volume ratio: oxygen: nitrogen = 5:10) was introduced at a flow rate of 500 SCCM for 30 min to obtain the silicon-oxygen coated lithium copper-doped silicon-carbon precursor material.

[0058] Step S4:

[0059] 100g of silicon-oxygen coated lithium copper-doped silicon-carbon precursor material was mixed evenly with 10g of lithium propionate, and heated to 400℃ under an argon inert atmosphere to melt and hold for 3h. Then the temperature was raised to 1000℃ and cyclohexane gas was introduced at a flow rate of 500SCCM for 30min to perform amorphous carbon coating, thus obtaining lithium silicate coated lithium copper-doped silicon-carbon composite material.

[0060] Comparative Example 1:

[0061] Unlike Example 1, porous carbon (manufacturer: Kuraray Co., Ltd., Japan; model: YP-80F) was used instead of copper foam, otherwise it was the same as Example 1.

[0062] Comparative Example 2:

[0063] Unlike Example 1, lithium hydride gas is not introduced in step S2; otherwise, it is the same as Example 1.

[0064] Comparative Example 3:

[0065] Unlike Example 1, the silicon-oxygen coated lithium copper-doped silicon-carbon precursor material in step S3 is used as the negative electrode.

[0066] (1) SEM testing

[0067] Figure 1 The image shows a SEM image of the lithium silicate-coated lithium copper-doped silicon-carbon composite material prepared in Example 1. As can be seen from the image, the material exhibits a granular structure with a particle size between 5 and 10 μm.

[0068] (2) Physicochemical performance testing:

[0069] The specific surface area of ​​each silicon-carbon composite material was tested according to the national standard GB / T 38823-2020 "Silicon-Carbon"; the powder resistivity of each composite material was tested using a four-probe tester; and the gas production of the powder material was tested (45℃, 48h). The test results are shown in Table 1 below.

[0070] (3) Button cell battery test:

[0071] The silicon-carbon composite materials corresponding to Examples 1-3 and Comparative Examples 1-3 were used as negative electrode materials for lithium-ion batteries to prepare coin cells according to the following method:

[0072] A binder, conductive agent, and solvent were added to the corresponding silicon-carbon composite materials, stirred to form a slurry, coated onto copper foil, and dried and rolled to obtain a negative electrode sheet. The binder used was LA132, the conductive agent was SP (conductive carbon black), and the solvent was NMP. The ratio of composite material, SP, LA132, and NMP was 95g:1g:4g:220mL. The electrolyte was a solution with LiPF6 as the electrolyte and a concentration of 1mol / L. The solvent was a mixture of EC and DEC with a volume ratio of 1:1. The lithium metal sheet was used as the counter electrode, and the separator was a polypropylene (PP) membrane.

[0073] Each coin cell was assembled in an argon-filled glove box, and then its electrochemical performance was tested. Specifically, the electrochemical performance was tested on a Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.005V to 2.0V and a charge / discharge rate of 0.1C. The initial discharge specific capacity and initial efficiency of the material were tested. At the same time, the charge DCR (0.1C, 50% SOC) and cycle performance (0.1C / 0.1C, 100 cycles) of the coin cells were tested. The full charge expansion of the coin cells was also tested. The test results are shown in Table 1 below.

[0074] Table 1

[0075]

[0076] As can be seen from the data in Table 1 above, the specific capacity and first-time efficiency of the novel silicon-carbon composite materials prepared in Examples 1-3 of this application are significantly better than those of Comparative Examples 1-3. The reason may be that: the irreversible capacity is reduced by depositing lithium hydride in the core of the silicon-carbon material, and the electronic conductivity of the material is improved by the porous foam copper, the impedance is reduced and the first-time efficiency is improved, and the powder resistivity of the material is reduced.

[0077] (4) Soft package performance test:

[0078] The silicon-carbon composite materials corresponding to Examples 1-3 and Comparative Examples 1-3, with 90% doped artificial graphite, were used as negative electrode materials (i.e., negative electrode sheets). These were then assembled with ternary positive electrode materials (LiNi1 / 3Co1 / 3Mn1 / 3O2), electrolyte, and separator to form a 5Ah pouch battery. The separator was Celegard 2400, and the electrolyte was a LiPF6 solution (the solvent was a 1:1 volume ratio of EC and DEC, and the concentration of LiPF6 was 1.1 mol / L).

[0079] The following performance tests were performed on each pouch battery:

[0080] The test conditions for the cyclic performance test are as follows:

[0081] The charge / discharge voltage range is 2.5~4.2V, the temperature is 25±3.0℃, the charge / discharge rate is 1.0C / 1.0C, and the cycle count is 500.

[0082] The test conditions for the ratio test are as follows:

[0083] The constant current ratio of each pouch cell under 2C conditions is calculated as: 2C constant current capacity / (2C constant current capacity + 0.1C constant voltage capacity); the test results are shown in Table 2 below.

[0084] Table 2

[0085] Example Capacity retention rate (%) after 500 cycles 2C constant current ratio Example 1 94.5 90.8％ Example 2 94.0 89.9％ Example 3 95.1 91.3％ Comparative Example 1 92.8 87.6％ Comparative Example 2 91.4 86.5％ Comparative Example 3 93.1 88.2％

[0086] As shown in Table 2, the rate capability and cycle performance of the soft-pack lithium-ion batteries prepared using the silicon-carbon composite materials provided in Examples 1-3 are significantly better than those of Comparative Examples 1-3. This is because the materials in the examples have low powder resistivity, which reduces DCR and increases the constant current ratio of the materials; at the same time, the materials in the examples have high specific surface area, which improves the liquid retention performance of the materials and improves the cycle performance.

[0087] In summary, the following conclusions can be drawn: The three-dimensional porous structure of copper foam significantly improves the material's conductivity and expansion suppression capability. Lithium doping further reduces impedance. The "carbon source → lithium source → silicon source" sequence optimizes the ion and electron conduction pathways, increasing the initial efficiency to over 93%. The lithium silicate layer effectively reduces electrolyte side reactions and improves cycle stability. Capacity retention after 100 cycles is significantly improved, high-temperature molten organic lithium compounds improve lithium distribution uniformity, and the outer amorphous carbon layer reduces interfacial impedance and improves rate performance.

[0088] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0089] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0090] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A lithium silicate-coated lithium copper-doped silicon-carbon composite material, characterized in that, The composite material has a core-shell structure, with the core being lithium-doped foamed copper silicon-carbon material, the middle layer being lithium silicate, and the outer layer being amorphous carbon; wherein the thickness ratio of the core:middle layer:outer layer is 70-90:5-15:5-15.

2. The method for preparing a lithium silicate-coated lithium copper-doped silicon-carbon composite material according to claim 1, characterized in that, Includes the following steps: Step S1: The modified copper foam was soaked in 0.1 mol / L hydrochloric acid for 24 h, and then added to an ethanol / deionized water mixture and ultrasonically dispersed for 24 h to obtain the modified copper foam. Step S2: The modified copper foam was transferred to a rotary kiln, and lithium copper-doped silicon-carbon precursor material was prepared by chemical vapor deposition. Specifically, the rotary kiln was heated to 700-1100℃, and carbon source gas was introduced at a flow rate of 50-500 SCCM for 30-300 min. Then the temperature was adjusted to 850-950℃, and lithium source gas was introduced at a flow rate of 10-100 SCCM for 30-300 min. Then the temperature was lowered to 450-550℃, and silane gas was introduced at a flow rate of 50-500 SCCM for 30-300 min to obtain lithium copper-doped silicon-carbon precursor material. Step S3: Under an inert atmosphere, the lithium copper-doped silicon-carbon precursor material is transferred to a rotary kiln, and then an oxygen / nitrogen mixed gas is introduced with a volume ratio of oxygen:nitrogen = 1-5:

10. The gas is introduced at a flow rate of 100-500 SCCM for 30-300 min to obtain the silicon-oxygen coated lithium copper-doped silicon-carbon precursor material. Step S4: The silicon-oxygen coated lithium copper-doped silicon-carbon precursor material and the organic lithium compound were mixed uniformly according to a mass ratio of 100:5-10. The mixture was then heated to 50-400℃ under an inert atmosphere to melt and held for 3-9 hours. After that, the temperature was raised to 700-1000℃, and a carbon source gas was introduced at a flow rate of 100-500 SCCM for 30-300 minutes to perform amorphous carbon coating, thus obtaining a lithium silicate coated lithium copper-doped silicon-carbon composite material.

3. The method for preparing lithium silicate-coated lithium copper-doped silicon-carbon composite material according to claim 2, characterized in that, In step S2, the carbon source gas is at least one of acetylene, ethylene, propyne, methane, and ethane; the lithium source gas is lithium hydride; and the silane gas is at least one of methylsilane, disilane, dichlorosilane, and methyldichlorosilane.

4. The method for preparing lithium silicate-coated lithium copper-doped silicon-carbon composite material according to claim 2, characterized in that, In step S4, the organolithium compound is at least one of lithium formate, lithium acetate, lithium propionate, lithium butyrate, and lithium isobutyrate.

5. The method for preparing lithium silicate-coated lithium copper-doped silicon-carbon composite material according to claim 2, characterized in that, In step S4, the carbon source gas is at least one of acetylene, propane, cyclohexane, methane, and benzene.

Images