A carbon-coated low-temperature molten salt technology for preparing pre-lithiated silicon oxide and its application in energy storage batteries

Abstract

The present invention discloses a carbon-coated low-temperature molten salt technology for preparing pre-lithiated silicon oxide and its application in energy storage batteries, belonging to the field of energy storage technology. The method for preparing the carbon-coated pre-lithiated silicon oxide material of the present invention comprises the following steps: mixing silicon oxide and lithium salt, sintering molten salt to obtain the pre-lithiated silicon oxide material; mixing the pre-lithiated silicon oxide material and a solid carbon source, calcining, to obtain the carbon-coated pre-lithiated silicon oxide material. The present invention obtains the pre-lithiated silicon oxide material through the technology of low-temperature molten salt sintering, and then carbon-coates it through carbon source mixing and calcining, which effectively improves the coulombic efficiency during the first cycle of charge and discharge, thereby improving the energy density of the entire battery, and the long-cycle stability is also significantly improved.

Description

Technical Field

[0001] The present invention relates to the field of energy storage technology, and in particular to a method for preparing pre-lithiated silicon dioxide using a carbon-coated low-temperature molten salt technology and application of the carbon-coated low-temperature molten salt technology in energy storage batteries. Background Art

[0002] Lithium-ion batteries are widely used in portable electronic devices, new energy vehicles, grid energy storage and other fields due to their high energy density, long cycle life, no memory effect, wide operating temperature range and other advantages. However, with the continuous development of science and technology, people's demand for battery energy density continues to increase, and the development of lithium-ion batteries with higher energy density and long cycle life has become a research hotspot. Compared with graphite, silicon oxide as a negative electrode material for lithium-ion batteries is a mainstream research direction. It has a higher theoretical specific capacity (about 2043mAh / g), low cost and abundant reserves. It is considered to be a negative electrode material with great application prospects. More importantly, compared with nano-silicon negative electrode, silicon oxide negative electrode has a smaller volume expansion rate (volume expansion rate of about 200%) and better battery cycle performance.

[0003] However, in addition to the SEI film generated during the first charge and discharge process of silicon monoxide negative electrode materials, a large amount of irreversible phases are also formed, further aggravating the loss of active lithium and greatly limiting the commercial application of silicon monoxide negative electrodes. Further improvement is still needed. Summary of the invention

[0004] The purpose of the present invention is to provide a carbon-coated low-temperature molten salt technology for preparing pre-lithiated silicon oxide and its application in energy storage batteries. The present invention obtains pre-lithiated silicon oxide material by low-temperature molten salt sintering technology, and then carbon-coates it by mixed calcination of carbon sources, which effectively improves the coulombic efficiency during the first cycle of charge and discharge, thereby improving the energy density of the entire battery, and the long-cycle stability is also significantly improved.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention is to provide a method for preparing a carbon-coated pre-lithiated silicon dioxide material, comprising the following steps:

[0007] Mixing silicon oxide and lithium salt, and sintering the molten salt to obtain a pre-lithiated silicon oxide material;

[0008] The pre-lithiated silicon dioxide material and a solid carbon source are mixed and calcined to obtain the carbon-coated pre-lithiated silicon dioxide material.

[0009] Preferably, the lithium salt includes two or more of LiOH, LiCl, LiH, Li2CO3 and LiNO3.

[0010] Preferably, when there are two kinds of lithium salts, the mass ratio between the two kinds of lithium salts is 1-10:1-10.

[0011] The present invention selects a plurality of different lithium salts for mixed addition, and determines the lowest eutectic point through the binary phase diagram of the mixed lithium salt system, thereby reducing the sintering temperature of the molten salt.

[0012] Preferably, the size of the silicon oxide is 1-15 μm; the molar ratio of the silicon element in the silicon oxide to the lithium element in the lithium salt is 2-10:1.

[0013] Preferably, the silicon oxide and lithium salt are mixed by grinding, and the grinding time is 20-40 minutes.

[0014] Preferably, the molten salt sintering temperature is 300-750° C., the heating rate is 2-5° C. / min, the time is 4-12 hours, the atmosphere is a protective atmosphere; and the flow rate of the protective atmosphere is 50-200 sccm.

[0015] Preferably, the solid carbon source comprises asphalt, starch or graphite.

[0016] Preferably, the mass ratio of the pre-lithiated silicon dioxide material to the solid carbon source is 100:3-20.

[0017] Preferably, the pre-lithiated silicon dioxide material and the solid carbon source are mixed by grinding and mixing, and the grinding time is 20-40 minutes.

[0018] Preferably, the calcination temperature is 600-800° C., the heating rate is 2-5° C. / min, the time is 1-5 h, the atmosphere is a protective atmosphere; and the flow rate of the protective atmosphere is 50-200 sccm.

[0019] The second technical solution of the present invention is to provide a carbon-coated pre-lithiated silicon dioxide material obtained according to the above preparation method.

[0020] The third technical solution of the present invention is to provide an application of the above-mentioned carbon-coated pre-lithiated silicon dioxide material in the field of negative electrode materials for energy storage batteries.

[0021] The beneficial technical effects of the present invention are as follows:

[0022] The present invention uses silicon oxide and lithium salt to mix to prepare pre-lithiated silicon oxide material, and after carbon coating on the surface, it is applied to the field of negative electrode materials for energy storage batteries. In view of the problem of low first-cycle coulomb efficiency of silicon oxide negative electrode materials in the prior art, the present invention obtains pre-lithiated silicon oxide material through low-temperature molten salt sintering technology, embeds lithium ions into SiO material, and pre-lithiation can pre-fill the active sites in the material with lithium, ensuring that the lithium in the SiO material is fully embedded, reducing the irreversible capacity loss during the first cycle in the later stage, and improving the first-cycle coulomb efficiency; then carbon coating is performed by mixed calcination of carbon sources, and a layer of carbon is coated on the surface of the pre-lithiated material to enhance conductivity and structural stability. Carbon coating can improve the electronic conductivity of the material, relieve the stress caused by volume expansion, protect the material from side reactions with the electrolyte, and improve the overall battery performance. Finally, the coulomb efficiency is effectively improved during the first cycle of charge and discharge, thereby improving the energy density of the entire battery, and the long-cycle stability is also significantly improved.

[0023] The present invention improves the electrochemical properties of silicon dioxide electrode materials through low-temperature molten salt technology. The preparation method is simple and convenient for large-scale production. It does not require complicated preparation conditions, materials and equipment, does not generate polluting and toxic gases, is green and environmentally friendly, safe and controllable, and can be easily promoted and applied in the field of energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 The following are the cycle performance curve and coulomb efficiency curve of the battery assembled with the product of Example 1.

[0026] Figure 2 The cycle performance curve and coulombic efficiency curve of the battery assembled with the pre-lithiated silicon oxide material in Example 1 are shown.

[0027] Figure 3 The cycle performance curve and coulomb efficiency curve of the battery assembled with the product of Comparative Example 1 are shown. DETAILED DESCRIPTION

[0028] Now, various exemplary embodiments of the present invention are described in detail, and this detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention. It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention.

[0029] In addition, for the numerical range in the present invention, it is understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0030] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention pertains. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention.

[0031] The words “include,” “including,” “have,” “contain,” etc. used in the present invention are open-ended terms, meaning including but not limited to.

[0032] All raw materials used in the following examples and comparative examples of the present invention are commercially available products.

[0033] Example 1

[0034] Preparation of Carbon-Coated Pre-lithiated Silicon Oxide Materials:

[0035] (1) First weigh 10g of silicon dioxide material, then weigh Li2CO3 and LiH (the mass ratio of Li2CO3 and LiH is 2:8) according to n(Si:Li)=3:1, mix and grind for 30min, then put the materials into a crucible and transfer them to a tube furnace, and in an argon atmosphere (gas flow rate of 100sccm), heat at 2℃ / min to 550℃ and sinter in molten salt for 10h to obtain pre-lithiated silicon dioxide material.

[0036] (2) The pre-lithiated silicon dioxide material obtained in step (1) and asphalt are mixed in a mass ratio of 100:5, ground for 30 minutes, and then the material is placed in a crucible and transferred to a tubular furnace. In a nitrogen atmosphere (air flow rate of 100 sccm), the temperature is increased to 600°C at 2°C / min and calcined for 3 hours to obtain a carbon-coated pre-lithiated silicon dioxide material.

[0037] Effect verification 1

[0038] (1) Battery assembly:

[0039] The carbon-coated pre-lithiated silicon oxide material and conductive carbon black (SP), carboxymethyl cellulose (CMC), and binder (SBR) in Example 1 were weighed in a mass ratio of 80:10:5:5, and then the carbon-coated pre-lithiated silicon oxide material, conductive carbon black and carboxymethyl cellulose were mixed and ground for 30 minutes and put into a mixer. After adding 1g of distilled water for every 2g of the above materials, the mixture was rotated at a speed of 2000rpm for 30 minutes. Finally, the binder was added and the mixture was rotated at a speed of 200rpm for 5 minutes to form a black-gray slurry. The slurry was coated on a copper foil current collector at a thickness of 100μm, and vacuum dried at 110℃ for 12h. The silicon oxide electrode sheet was used as the negative electrode material of the lithium-ion battery, and the battery was assembled in an argon-filled glove box. The assembly process was as follows: the dried electrode sheet was cut into a circular electrode sheet with a diameter of 13mm by a punching machine, 1.0M LiPF6 inEC:DMC:DEC=1:1:1Vol% was used as the electrolyte, and Celgard 2400 was used as the diaphragm, a lithium sheet with a diameter of 15 mm was used as the reference electrode and the counter electrode, and CR2016 stainless steel was used as the battery shell to assemble a button-type lithium-ion negative electrode battery.

[0040] By replacing only the carbon-coated pre-lithiated silicon oxide material with the pre-lithiated silicon oxide material in Example 1, a button-type lithium-ion negative electrode battery was also assembled, and the performance was compared with that of the battery assembled with the product of Example 1.

[0041] (2) Test electrochemical performance:

[0042] After the two batteries were left to stand at 25°C for 8 hours, they were subjected to charge and discharge cycle tests at a rate of 0.1C between 0.01V and 2.0V. The cycle performance curve and Coulomb efficiency curve of the products are shown in Figure 2. Figure 1 shown.

[0043] The test results show that its first discharge specific capacity can reach 1893.8mAh / g, and the first-cycle Coulomb efficiency is as high as 93.7%. After 100 cycles, the specific capacity remains at 91.8% and the Coulomb efficiency remains at 100%.

[0044] Figure 1 The following are the cycle performance curve and coulomb efficiency curve of the battery assembled with the product of Example 1.

[0045] Figure 2 The cycle performance curve and coulombic efficiency curve of the battery assembled with the pre-lithiated silicon oxide material in Example 1 are shown.

[0046] Depend on Figure 1 and Figure 2It can be seen that the carbon-coated pre-lithiated silicon oxide material prepared by the product of Example 1 has excellent electrochemical performance when used as a negative electrode material in lithium-ion batteries; although the pre-lithiated silicon oxide material can also improve the first-cycle coulombic efficiency, the conductivity and structural stability are significantly lower than those of the battery assembled after carbon coating. It can be seen that the present invention improves the first-cycle coulombic efficiency and cycle stability of the battery made by carbon coating the material after pre-lithiation.

[0047] Example 2

[0048] Preparation of Carbon-Coated Pre-lithiated Silicon Oxide Materials:

[0049] (1) First weigh 10g of silicon dioxide material, then weigh Li2CO3 and LiNO3 (the mass ratio of Li2CO3 and LiNO3 is 5:5) according to n(Si:Li)=4:1, mix and grind for 20min, then put the materials into a crucible and transfer them to a tubular furnace, and in an argon atmosphere (air flow rate 50sccm), heat at 5℃ / min to 650℃ and sinter in molten salt for 5h to obtain pre-lithiated silicon dioxide material.

[0050] (2) The pre-lithiated silicon dioxide material obtained in step (1) and starch were mixed in a mass ratio of 100:3, ground for 40 minutes, and then the material was placed in a crucible and transferred to a tubular furnace. In a nitrogen atmosphere (air flow rate of 150 sccm), the temperature was increased to 700°C at 5°C / min and calcined for 2 hours to obtain a carbon-coated pre-lithiated silicon dioxide material.

[0051] Example 3

[0052] Preparation of Carbon-Coated Pre-lithiated Silicon Oxide Materials:

[0053] (1) First, 10 g of silicon dioxide material was weighed, and then LiCl and LiH (the mass ratio of LiCl and LiH was 3:7) were weighed according to n(Si:Li)=5:1, mixed and ground for 30 min, and then the materials were placed in a crucible and transferred to a tube furnace. In an argon atmosphere (gas flow rate of 200 sccm), the temperature was raised to 400 °C at 5 °C / min and molten salt sintered for 2 h to obtain a pre-lithiated silicon dioxide material.

[0054] (2) The pre-lithiated silicon dioxide material obtained in step (1) and starch were mixed in a mass ratio of 100:10, ground for 40 minutes, and then the material was placed in a crucible and transferred to a tubular furnace. In a nitrogen atmosphere (air flow rate of 50 sccm), the temperature was increased to 600° C. at 4° C. / min and calcined for 4 hours to obtain a carbon-coated pre-lithiated silicon dioxide material.

[0055] Example 4

[0056] Preparation of Carbon-Coated Pre-lithiated Silicon Oxide Materials:

[0057] (1) First weigh 10g of silicon dioxide material, then weigh LiNO3 and LiOH (the mass ratio of LiNO3 and LiOH is 4:6) according to n(Si:Li)=2:1, mix and grind for 40min, then put the materials into a crucible and transfer them to a tubular furnace, and in an argon atmosphere (air flow rate of 100sccm), heat to 400℃ at 4℃ / min and sinter in molten salt for 2h to obtain pre-lithiated silicon dioxide material.

[0058] (2) The pre-lithiated silicon dioxide material obtained in step (1) and starch were mixed in a mass ratio of 100:8, ground for 30 minutes, and then the materials were placed in a crucible and transferred to a tubular furnace. In a nitrogen atmosphere (air flow rate of 200 sccm), the temperature was increased to 700°C at 2°C / min and calcined for 5 hours to obtain a carbon-coated pre-lithiated silicon dioxide material.

[0059] Example 5

[0060] Preparation of Carbon-Coated Pre-lithiated Silicon Oxide Materials:

[0061] (1) First weigh 10g of silicon dioxide material, then weigh Li2CO3 and LiH (the mass ratio of Li2CO3 and LiH is 3:7) according to n(Si:Li)=10:1, mix and grind for 20min, then put the materials into a crucible and transfer them to a tube furnace, and in an argon atmosphere (air flow rate of 50sccm), heat to 700℃ at 5℃ / min and sinter in molten salt for 10h to obtain pre-lithiated silicon dioxide material.

[0062] (2) The pre-lithiated silicon dioxide material obtained in step (1) and starch were mixed in a mass ratio of 100:20, ground for 20 minutes, and then the materials were placed in a crucible and transferred to a tubular furnace. In a nitrogen atmosphere (air flow rate of 200 sccm), the temperature was increased to 800° C. at 3° C. / min and calcined for 1 hour to obtain a carbon-coated pre-lithiated silicon dioxide material.

[0063] Effect Verification 2

[0064] By modifying only the relevant reaction conditions in Example 5, different types of carbon-coated pre-lithiated silicon oxide materials were prepared, and then assembled into button-type lithium-ion negative electrode batteries by the assembly method of effect verification 1 (1), and then the electrochemical performance test was carried out by the method of effect verification 1 (2). The test results are shown in Table 1.

[0065] Table 1

[0066]

[0067] Comparative Example 1

[0068] Preparation of pre-lithiated silicon dioxide materials:

[0069] First weigh 10g of silicon dioxide material, then weigh Li2CO3 according to n(Si:Li)=3:1, mix and grind for 30 minutes, then put the materials into a crucible and transfer them to a tubular furnace. In an argon atmosphere (air flow rate of 100sccm), heat to 600℃ at 2℃ / min and sinter in molten salt for 10 hours to obtain pre-lithiated silicon dioxide material.

[0070] Comparative Example 2

[0071] Preparation of pre-lithiated silicon dioxide materials:

[0072] First weigh 10g of silicon dioxide material, then weigh LiOH according to n(Si:Li)=3:1, mix and grind for 40 minutes, then put the materials into a crucible and transfer them to a tubular furnace. In an argon atmosphere (air flow rate 150sccm), heat to 500℃ at 5℃ / min and sinter in molten salt for 5h to obtain pre-lithiated silicon dioxide material.

[0073] Effect Verification 3

[0074] The product of Comparative Example 1-2 was assembled into a button-type lithium-ion negative electrode battery according to the assembly method of Effect Verification 1 (1), and then the electrochemical performance test was carried out according to the method of Effect Verification 1 (2). The cycle performance curve and coulomb efficiency curve of the battery prepared with the product of Comparative Example 1 are shown in Figure 3 shown.

[0075] Figure 3 The cycle performance curve and coulomb efficiency curve of the battery assembled with the product of Comparative Example 1 are shown.

[0076] The test results show that the first discharge specific capacity of the battery assembled with the pre-lithiated silicon dioxide material of Comparative Example 1 is only 1514.6 mAh / g, the first cycle coulombic efficiency is 81.6%, and the specific capacity remains at 59.7% after 100 cycles.

[0077] Depend on Figure 3 It can be seen that the product prepared by the preparation method of Comparative Example 1 has a low specific capacity and a low capacity retention rate, and is not suitable for direct application in the negative electrode of a lithium-ion battery.

[0078] The first discharge specific capacity of the battery assembled with the pre-lithiated silicon dioxide material of Comparative Example 2 is only 1509.3 mAh / g, the first cycle coulombic efficiency is 77.1%, and the specific capacity remains at 56.4% after 100 cycles.

[0079] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a carbon-coated pre-lithiated silicon oxide material, characterized in that: Here are the steps: First, 10 g of silicon dioxide material was weighed, and then Li2CO3 and LiH were weighed according to n(Si:Li)=3:1, mixed and ground for 30 minutes, and then the materials were placed in a crucible and transferred to a tube furnace. In an argon atmosphere with a flow rate of 100 sccm, the temperature was raised to 550°C at 2°C / min and molten salt sintered for 10 hours to obtain a pre-lithiated silicon dioxide material; the mass ratio of Li2CO3 to LiH was 2:8; The pre-lithiated silicon dioxide material and asphalt were mixed in a mass ratio of 100:5 and ground for 30 minutes. The materials were then placed in a crucible and transferred to a tubular furnace. In a nitrogen atmosphere with a flow rate of 100 sccm, the temperature was increased to 600°C at 2°C / min and calcined for 3 hours to obtain a carbon-coated pre-lithiated silicon dioxide material.

2. A carbon-coated pre-lithiated silicon dioxide material obtained according to the preparation method of claim 1.

3. An application of the carbon-coated pre-lithiated silicon dioxide material according to claim 2 in the field of negative electrode materials for secondary energy storage batteries.

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