A pre-lithiation method for silicon monoxide negative electrode material

Abstract

The present invention relates to a pre-lithiation method for silicon dioxide negative electrode material, comprising the following steps: (1) pre-lithiation: crushing, pulverizing, and grinding silicon dioxide and elemental silicon to obtain particles with a diameter of 80 to 100 nanometers; mixing the nano-scale silicon dioxide and elemental silicon in a molar ratio of 90:10 to 10:90, pressing and molding the mixture, and then loading the mixture into a tube furnace; (2) disproportionation / carbon coating; and (3) electrochemical testing: preparing a slurry in NMP of pre-lithiated SiO negative electrode material, polyvinylidene fluoride, and acetylene black in a mass ratio of 80:10:10-70:15:15. The present invention introduces metallic lithium during the preparation of silicon dioxide, and silicon dioxide and elemental silicon in the high-temperature zone generate silicon dioxide under vacuum conditions, thereby greatly increasing the pre-lithiation speed, thereby increasing production efficiency, reducing production costs, and facilitating industrialization.

Description

Technical Field

[0001] The present invention belongs to the technical field of SiOx pre-lithiation, and in particular relates to a pre-lithiation method for silicon monoxide negative electrode materials. Background Art

[0002] Pre-lithiation of SiOx allows for the insertion of a small amount of lithium before the electrode undergoes formal charge-discharge cycling. This provides an additional lithium source, offsets lithium consumption in the positive electrode due to side reactions and SEI formation, improves the initial coulombic efficiency (ICE), and thus enhances battery energy density. To this end, researchers have developed a series of SiO pre-lithiation methods. A paper (Improvement of irreversible behavior of SiO anodes for lithium ion batteries by a solid-state reaction at high temperature [J]. Journal of Power Sources, 2016, 311, 159-166) reportedly increases the initial coulombic efficiency of a silicon oxide anode from 58.52% to 82.12% by calcining SiO and metallic lithium powder at 600°C. Patent CN110212183A discloses a method for pre-lithiating a silicon-based anode material using powder. This method involves immersing silicon oxide powder in a solvent containing an organic lithium salt, allowing the solution to evaporate, and then calcining the material at high temperature to produce the pre-lithiated silicon-based material. In the literature (An electrode-level prelithiation of SiO anodes withorganolithium compounds for lithium-ion batteries[J]. Journal of Power Sources, 2020, 478:229067), an organic compound (Li-9,9-dimethyl-9H-fluorenetetrahydrofuran) was synthesized to pre-lithiate the SiO electrode, increasing the initial efficiency of the full battery from 61.1% to 87.1%.

[0003] In the pre-lithiation methods mentioned in the aforementioned reports, researchers all used commercial SiO or carbon-coated SiO (SiO@C) as raw materials. While this method can effectively improve the initial Coulombic efficiency of SiO materials, the pre-lithiation process is mostly a solid-phase reaction, and the SiO is micronized, which hinders lithium migration. The reaction time is long (typically dozens of hours), making it difficult to commercialize. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for pre-lithiation of silicon monoxide negative electrode material.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for pre-lithiation of silicon monoxide negative electrode material, comprising the following steps

[0007] (1) Pre-lithiation: crush, pulverize and grind silica and elemental silicon to make the diameter of silica and elemental silicon particles between 80 and 100 nanometers. Mix the nano-scale silica and elemental silicon in a molar ratio of 90:10 to 10:90, press and form them, and then load them into a tube furnace. Turn on the tube furnace heating system, heat the high temperature zone to between 1200 and 1800°C at 8°C / min to 12°C / min, and heat the low temperature zone to between 400 and 800°C at 4°C / min to 6°C / min. Open the lithium vapor inlet valve of the low temperature zone of the tube furnace and maintain it for 4 to 6 minutes. Then turn on the vacuum system of the tube furnace and maintain the vacuum degree at -0.09 MPa to -0.07 MPa. Collect the material SiO@Li particles in the storage tank outside the tube furnace.

[0008] (2) Disproportionation / carbon coating: The SiO@Li particles obtained in step (1) are mixed evenly with coal tar pitch in a mass ratio of 90:10 to 70:30 in a mixer and then loaded into another tube furnace; the heating system is turned on and the temperature of the tube furnace is raised to 800°C-1000°C at a rate of 8°C / min-12°C / min; the temperature is maintained for 25 min-35 min, and then the heating is stopped and cooled to room temperature to obtain a pre-lithiated SiO negative electrode material;

[0009] (3) Electrochemical test: A slurry of pre-lithiated SiO2 negative electrode material, polyvinylidene fluoride, and acetylene black was prepared in NMP at a mass ratio of 80:10:10-70:15:15. The slurry was coated on a copper foil with a spatula and dried to obtain a working electrode. A lithium metal sheet was used as the counter electrode and 1 mol L-1 to 1.5 mol L-1 of LiPF6 was used as the electrolyte. The cells were assembled into CR2032 button cells in a glove box filled with high-purity argon. The cells were tested in the voltage range of 0.005 to 2.5 V.

[0010] As a preferred solution, the mixing is carried out by one or more composite methods of ball milling mixing, mechanical stirring mixing, or air flow mixing.

[0011] As a preferred solution, the mass of the lithium vapor accounts for 5% to 20% of the total mass of silicon dioxide and elemental silicon.

[0012] As a preferred solution, the SiOx@Li cluster particles have a micro-nano composite structure, the surface of the SiOx molecules inside the cluster is covered with Li atoms, and the cluster is formed in the collection tank as the temperature decreases.

[0013] Compared with existing technologies, the present invention has the following advantages: By introducing metallic lithium during the silicon oxide preparation process, elemental silicon and silicon dioxide in the high-temperature zone, under vacuum conditions, form silicon oxide. The silicon oxide then absorbs metallic lithium atoms in the low-temperature zone, forming SiO@Li clusters. Further cooling of the SiO@Li clusters results in SiO@Li particles. Within the SiO@Li clusters, SiO molecules and Li atoms can intermix at a molecular level, significantly shortening the Li+ diffusion path and significantly increasing the pre-lithiation rate. This, in turn, improves production efficiency, reduces costs, and facilitates industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0015] Figure 1 Schematic diagram of the pre-lithiation process of the present invention;

[0016] Figure 2 is the HR-TEM image of the material of Example 3 of the present invention;

[0017] Figure 3 1 is the XRD pattern of Example 3 of the present invention and the comparative example;

[0018] Figure 4 1 is the first charge and discharge curve of Example 3 of the present invention and the comparative example;

[0019] Figure 5 3 is a cycle life curve of Example 3 of the present invention and a comparative example. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to specific embodiments.

[0021] Example 1

[0022] A method for pre-lithiation of silicon monoxide negative electrode material, comprising the following steps

[0023] (1) Pre-lithiation: crush, pulverize and grind silica and elemental silicon to make the diameter of silica and elemental silicon particles 80 nanometers. Mix nano-scale silica and elemental silicon in a molar ratio of 90:10 and press them into shape before loading them into a tube furnace. Turn on the tube furnace heating system, heat the high temperature zone 1 to 1200℃ at 8℃ / min, and heat the low temperature zone 2 to 400℃ at 4℃ / min. Open the lithium vapor inlet valve 3 of the low temperature zone 2 of the tube furnace and maintain it for 4 minutes. Then turn on the vacuum system 4 of the tube furnace and maintain the vacuum degree at -0.09MPa. Collect the SiO@Li particles in the storage tank outside the tube furnace. The pre-lithiation process is as shown in the attached figure. Figure 1 As shown;

[0024] (2) Disproportionation / carbon coating: The SiO@Li particles obtained in step (1) were mixed with coal tar pitch at a mass ratio of 90:10 in a mixer and then loaded into another tube furnace; the heating system was turned on and the temperature of the tube furnace was raised to 800°C at a rate of 8°C / min; the temperature was maintained for 25 minutes, then the heating was stopped and the mixture was cooled to room temperature to obtain a pre-lithiated SiO negative electrode material;

[0025] (3) Electrochemical test: A slurry of pre-lithiated SiO2 negative electrode material, polyvinylidene fluoride, and acetylene black was prepared in NMP at a mass ratio of 80:10:10. The slurry was coated on a copper foil with a spatula and dried to obtain a working electrode. A lithium metal sheet was used as the counter electrode and 1 mol L-1 LiPF6 was used as the electrolyte. The cells were assembled into CR2032 button cells in a glove box filled with high-purity argon and tested in the 0.005 voltage range.

[0026] As a preferred solution, the mixing is carried out by one or more composite methods of ball milling mixing, mechanical stirring mixing, or air flow mixing.

[0027] As a preferred solution, the mass of the lithium vapor accounts for 5% of the total mass of silicon dioxide and elemental silicon.

[0028] As a preferred solution, the SiOx@Li cluster particles have a micro-nano composite structure, the surface of the SiOx molecules inside the cluster is covered with Li atoms, and the cluster is formed in the collection tank as the temperature decreases.

[0029] Example 2

[0030] A method for pre-lithiation of silicon monoxide negative electrode material, comprising the following steps

[0031] (1) Pre-lithiation: crush, pulverize and grind silica and elemental silicon to make the diameter of silica and elemental silicon particles 90 nanometers. Mix nano-scale silica and elemental silicon in a molar ratio of 80:20 and press them into shape before loading them into a tube furnace. Turn on the tube furnace heating system, heat the high temperature zone 1 to 1500°C at 10°C / min, and heat the low temperature zone 2 to 600°C at 5°C / min. Open the lithium vapor inlet valve 3 of the low temperature zone of the tube furnace and maintain it for 5 minutes. Then turn on the vacuum system 4 of the tube furnace and maintain the vacuum degree at -0.08MPa. Collect the SiO@Li particles in the storage tank outside the tube furnace. The pre-lithiation process is as shown in the attached figure. Figure 1 As shown;

[0032] (2) Disproportionation / carbon coating: The SiO@Li particles obtained in step (1) were mixed with coal tar pitch in a mass ratio of 80:20 in a mixer and then loaded into another tube furnace; the heating system was turned on and the temperature of the tube furnace was raised to 900°C at a rate of 10°C / min; the temperature was maintained for 30 min, then the heating was stopped and the mixture was cooled to room temperature to obtain a pre-lithiated SiO negative electrode material;

[0033] (3) Electrochemical test: A slurry of pre-lithiated SiO2 negative electrode material, polyvinylidene fluoride, and acetylene black was prepared in NMP at a mass ratio of 75:12.5:12.5. The slurry was coated on a copper foil with a spatula and dried to obtain a working electrode. A lithium metal sheet was used as the counter electrode and 1.2 mol L-1 LiPF6 was used as the electrolyte. The cells were assembled into CR2032 button cells in a glove box filled with high-purity argon and tested in the 1 V voltage range.

[0034] As a preferred solution, the mixing is carried out by one or more composite methods of ball milling mixing, mechanical stirring mixing, or air flow mixing.

[0035] As a preferred solution, the mass of the lithium vapor accounts for 15% of the total mass of silicon dioxide and elemental silicon.

[0036] As a preferred solution, the SiOx@Li cluster particles have a micro-nano composite structure, the surface of the SiOx molecules inside the cluster is covered with Li atoms, and the cluster is formed in the collection tank as the temperature decreases.

[0037] Example 3

[0038] A method for pre-lithiation of silicon monoxide negative electrode material, comprising the following steps

[0039] (1) Pre-lithiation: crush, pulverize and grind silica and elemental silicon to make the diameter of silica and elemental silicon particles within 100 nanometers. Mix nano-scale silica and elemental silicon in a molar ratio of 10:90 and press them into shape before loading them into a tube furnace. Turn on the tube furnace heating system, heat the high temperature zone 1 to 1800°C at 12°C / min, and heat the low temperature zone 2 to 800°C at 6°C / min. Open the lithium vapor inlet valve 3 of the low temperature zone of the tube furnace and maintain it for 6 minutes. Then turn on the vacuum system 4 of the tube furnace and maintain the vacuum degree at -0.07MPa. Collect the SiO@Li particles in the storage tank outside the tube furnace. The pre-lithiation process is as shown in the attached figure. Figure 1 As shown;

[0040] (2) Disproportionation / carbon coating: The SiO@Li particles obtained in step (1) were mixed with coal tar pitch in a mass ratio of 70:30 in a mixer and then loaded into another tube furnace; the heating system was turned on and the temperature of the tube furnace was raised to 1000°C at a rate of 12°C / min; the temperature was maintained for 35 minutes, and then the heating was stopped and cooled to room temperature to obtain a pre-lithiated SiO negative electrode material;

[0041] (3) Electrochemical test: A slurry of pre-lithiated SiO2 negative electrode material, polyvinylidene fluoride, and acetylene black was prepared in NMP at a mass ratio of 70:15:15. The slurry was coated on a copper foil with a spatula and dried to obtain a working electrode. A lithium metal sheet was used as the counter electrode and 1.5 mol L-1 LiPF6 was used as the electrolyte. The cells were assembled into CR2032 button cells in a glove box filled with high-purity argon and tested in the 2.5 V voltage range.

[0042] As a preferred solution, the mixing is carried out by one or more composite methods of ball milling mixing, mechanical stirring mixing, or air flow mixing.

[0043] As a preferred solution, the mass of the lithium vapor accounts for 20% of the total mass of silicon dioxide and elemental silicon.

[0044] As a preferred solution, the SiOx@Li cluster particles have a micro-nano composite structure, the surface of the SiOx molecules inside the cluster is covered with Li atoms, and the cluster is formed in the collection tank as the temperature decreases.

[0045] Comparative Example

[0046] A method for preparing silicon monoxide negative electrode material, comprising the following steps

[0047] (1) Pre-lithiation: crush, pulverize and grind silica and elemental silicon to make the diameter of silica and elemental silicon particles 20 nanometers. Mix the nano-scale silica and elemental silicon in a molar ratio of 1:1 and press them into shape before loading them into a tube furnace. Turn on the tube furnace heating system and heat the high temperature zone 1 to 1400°C at a rate of 10°C / min. Then turn on the tube furnace vacuum system 4 and maintain the vacuum degree at -0.08MPa. Collect the SiO@Li particles in the storage tank outside the tube furnace.

[0048] (2) Disproportionation / carbon coating: The SiO@Li particles obtained in step (1) were mixed with coal tar pitch in a mass ratio of 90:10 in a mixer and then loaded into another tube furnace; the heating system was turned on and the temperature of the tube furnace was raised to 1000°C at a rate of 10°C / min; the temperature was maintained for 30 min, then the heating was stopped and the mixture was cooled to room temperature to obtain a non-pre-lithiated SiO negative electrode material;

[0049] (3) Electrochemical test: A slurry of pre-lithiated SiO2 negative electrode material, polyvinylidene fluoride, and acetylene black was prepared in NMP at a mass ratio of 70:15:15. The slurry was coated on a copper foil with a spatula and dried to obtain a working electrode. A lithium metal sheet was used as the counter electrode and 1.5 mol L-1 LiPF6 was used as the electrolyte. The cells were assembled into CR2032 button cells in a glove box filled with high-purity argon and tested in the 2.5 V voltage range.

[0050] As a preferred solution, the mixing is carried out by one or more composite methods of ball milling mixing, mechanical stirring mixing, or air flow mixing.

[0051] As a preferred solution, the mass of the lithium vapor accounts for 20% of the total mass of silicon dioxide and elemental silicon.

[0052] As a preferred solution, the SiOx@Li cluster particles have a micro-nano composite structure, the surface of the SiOx molecules inside the cluster is covered with Li atoms, and the cluster is formed in the collection tank as the temperature decreases.

[0053] By the attached Figure 2 It can be seen that the grain size of nano-silicon in the generated pre-lithiation material is about 10nm. Nano-scale silicon grains can effectively alleviate the volume expansion of the material during the charge and discharge process, thereby extending the cycle life of the battery. Figure 3 The comparison of curve A of Example 3 and curve B of the comparative example shows that lithium silicate compounds are generated inside the material after pre-lithiation. This is because the pre-embedded lithium reacts with the oxygen-containing compounds inside the SiOx, consuming the oxygen content. The reduction in oxygen content can reduce the material's consumption of irreversible lithium, thereby improving battery efficiency. Figure 4 The charge capacity of the comparative curve C is 1603 mAh / g, the discharge capacity is 1194 mAh / g, and the coulombic efficiency is only 74.49%; the charge capacity of the curve D of Example 3 is 1620 mAh / g, the discharge capacity is 1487 mAh / g, and the coulombic efficiency reaches 91.79%. Figure 5 It can be seen that the capacity retention rate of curve E in Example 3 is 87.6% after 200 cycles, while the retention rate of comparative curve F after the same cycle is only 82.4%. This is because part of the internal stress of the SiOx material is released during the pre-lithiation process, so the volume expansion during the charge and discharge process is lower than that of SiOx without pre-lithiation, so its cycle performance is significantly improved.

[0054] Technical features not described in the present invention can be achieved through or by adopting existing technologies and will not be described in detail here. Of course, the above-mentioned specific implementation methods are not limitations of the present invention, and the present invention is not limited to the above-mentioned specific implementation methods. Changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A method for pre-lithiation of silicon 2 Oxide negative electrode material, characterized in that: The following steps are included (1) Pre-lithiation: crush, pulverize and grind silica and elemental silicon to make the diameter of silica and elemental silicon particles between 80 and 100 nanometers. Mix the nano-scale silica and elemental silicon in a molar ratio of 90:10 to 10:90, press and form them, and then load them into a tube furnace. Turn on the tube furnace heating system, heat the high temperature zone (1) to between 1200 and 1800°C at 8°C / min to 12°C / min, and heat the low temperature zone (2) to between 400 and 800°C at 4°C / min to 6°C / min. Open the lithium vapor (3) inlet valve of the low temperature zone (2) of the tube furnace and maintain it for 4 to 6 minutes. Then turn on the vacuum system (4) of the tube furnace and maintain the vacuum degree at -0.09 MPa to -0.07 MPa. Collect the material SiO@Li particles in the storage tank outside the tube furnace. (2) Disproportionation / carbon coating: The SiO@Li particles obtained in step (1) are mixed evenly with coal tar pitch in a mass ratio of 90:10 to 70:30 in a mixer and then loaded into another tube furnace; the heating system is turned on and the temperature of the tube furnace is raised to 800°C-1000°C at a rate of 8°C / min-12°C / min; the temperature is maintained for 25 min-35 min, and then the heating is stopped and cooled to room temperature to obtain a pre-lithiated SiO negative electrode material; (3) Electrochemical test: A slurry of pre-lithiated SiO2 negative electrode material, polyvinylidene fluoride, and acetylene black was prepared in NMP at a mass ratio of 80:10:10-70:15:

15. The slurry was coated on a copper foil with a spatula and dried to obtain a working electrode. A lithium metal sheet was used as the counter electrode and 1 mol L-1 to 1.5 mol L-1 of LiPF6 was used as the electrolyte. The cells were assembled into CR2032 button cells in a glove box filled with high-purity argon. The cells were tested in the voltage range of 0.005 to 2.5 V.

2. The pre-lithiation method of silicon 2 Oxide negative electrode material according to claim 1, characterized in that: The mixing is carried out by one or more composite methods of ball milling mixing, mechanical stirring mixing or air flow mixing.

3. The pre-lithiation method of silicon 2 Oxide negative electrode material according to claim 1, characterized in that: The mass of the lithium vapor accounts for 5% to 20% of the total mass of silicon dioxide and elemental silicon.

4. The pre-lithiation method of silicon 2 Oxide negative electrode material according to claim 1, characterized in that: The SiOx@Li cluster particles have a micro-nano composite structure, and the surface of the SiOx molecules inside the cluster is covered with Li atoms. The cluster is formed in the collection tank as the temperature decreases.

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