A method for preparing nanoscale lithium-silicon alloy and its application

Abstract

This invention belongs to the field of materials preparation technology, specifically relating to a method for preparing nanoscale lithium-silicon alloys and their applications. The invention involves injecting a mixture of silane gas and dilution gas into a plasma thermal field generated by a radio frequency plasma generator to produce silicon atoms. Subsequently, an inert gas is used as a carrier gas to send a lithium source into the plasma thermal field to generate lithium atom vapor. The two are then alloyed in a high-temperature thermal field. Driven by a cooling airflow, the lithium-silicon alloy particles pass through high-temperature and low-temperature cooling zones and enter a cyclone classification chamber. Unreacted lithium sources and large-diameter lithium-silicon alloy particles remain in the cyclone classification chamber, while small-diameter lithium-silicon alloy particles are carried into a collection chamber and adsorbed onto the filter surface. These particles are then blown off by periodic backflushing airflow to obtain the lithium-silicon alloy powder to be coated. Finally, the nanoscale lithium-silicon alloy to be coated is introduced into a fluidized bed, and silicon and carbon coating is performed using vapor deposition to prepare a lithium-silicon alloy with an inner coating layer of element-doped silicon and an outer coating layer of carbon. This alloy can be used as a negative electrode material for thermal batteries, solid-state batteries, and as a lithium replenishing agent for liquid lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation technology, specifically relating to a method for preparing nanoscale lithium-silicon alloys and their applications. Background Technology

[0002] With the increasing demand for high-energy-density lithium-ion batteries, silicon doping of graphite anodes has become an inevitable trend. Silicon anodes have a theoretical capacity of up to 4200 mAh / g, and their lithium intercalation potential is higher than that of graphite, which can effectively solve the problems of low lithium intercalation potential and easy lithium deposition in graphite.

[0003] Silicon-carbon anodes have high specific capacity; however, the silicon in the anode undergoes significant volume expansion during lithium alloying. This high expansion rate continuously damages the solid electrolyte interphase (SEI) film on the anode surface, causing the lithium-ion battery to constantly damage or repair the SEI film during charge and discharge. This leads to the consumption of electrolyte and active lithium ions, resulting in poor battery cycle stability and consistency. (Lithium-silicon alloy Li...) x Si (x < 3.75 at room temperature), as a novel pre-lithiation anode material, exhibits significantly improved ionic and electronic conductivity compared to pure silicon anodes. Li x The lithium in the Si alloy can also replenish the lithium lost during cycling, which can significantly improve the battery's first efficiency and energy density, and has extremely high practical application value.

[0004] Patents CN 114335492 A and CN 112928242 B describe a method for forming a lithium-silicon alloy. This method involves contacting a mixture containing lithium and silicon under specific conditions to form a molten precursor, which is then centrifugally distributed and solidified using a centrifugal atomizing reactor. The resulting lithium-silicon alloy particles are negative electrode materials with a D50 diameter of 1–30 μm. Similarly, patents CN 209578165 U and CN 109482892 B disclose a method and apparatus for producing a lithium-silicon alloy. This method involves separately melting silicon powder and lithium particles in a crucible, heating and stirring at a certain temperature to fully mix and melt the silicon and lithium into an alloy, transferring the melted alloy to a heat-insulating crucible, and finally atomizing the molten alloy into fine droplets using high-pressure inert gas. After cooling, the resulting lithium-silicon alloy powder has a particle size of 40–300 mesh (approximately 44–420 μm). CN 117525377A discloses "a micro / nano structured lithium-silicon alloy anode material and its preparation method and application." This method involves mixing lithium metal and silicon at an atomic ratio of 99.5:0.5 to 97.5:1.5, placing the mixture into the chamber of a melting and spinning equipment, and melting the raw materials into a liquid alloy by heating. The liquid alloy is then spray-cast and collected by copper rollers. The product collected on the copper rollers is rolled into a thin sheet with a thickness of 100–300 μm, which is then cut to obtain the micro / nano structured lithium-silicon alloy anode material. The above methods involve precise control of multiple steps, including the mixing of lithium and silicon, temperature, and pressure. The process is relatively complex, requiring high-precision, high-temperature resistant equipment and strict process control, which increases production costs and difficulty.

[0005] CN 117248133 A discloses "a lithium-silicon alloy and its preparation method and application." The method involves mixing lithium flakes and silicon powder at a mass ratio of 0.2–1.1 in a reactor vessel, heating and reacting under inert gas protection to obtain alloy powder. Subsequently, the alloy powder is mixed with polytetrafluoroethylene at a mass ratio of 10–20, ball-milled, and reacted to obtain a micron-sized lithium-silicon alloy with lithium fluoride, carbon, and fluorinated carbon adhering to its surface. This method is only suitable for laboratory sample preparation and is not applicable to industrial-scale production.

[0006] CN 113437282 B discloses "A nanoscale lithium-silicon alloy material and its preparation method and uses." This method involves dissolving metallic lithium in an organic solvent to form a solution, then adding nanoscale silicon or doped nanoscale silicon material to the lithiumized solution and stirring at a certain temperature to allow the lithium and silicon to react and form an alloy. The alloying reaction takes 10–48 hours. Finally, the mixture is cleaned and dried with an organic solvent to obtain 1–500 nm nanoscale lithium-silicon alloy powder. While this method avoids the harsh conditions of traditional high-temperature, high-pressure, or long-term sintering, achieving the preparation of nanoscale lithium-silicon alloys under relatively mild conditions, the alloying reaction between nanoscale silicon and lithium is an outside-in reaction process. For large-particle-size nanoscale silicon, it is difficult to form a bulk-uniform lithium-silicon alloy. Furthermore, the organic solvents used in this method (such as dimethyl ether, diethyl ether, etc.) must be strictly anhydrous and oxygen-free, placing extremely high demands on the production environment and increasing process complexity and cost.

[0007] In summary, there are currently two main methods for preparing lithium-silicon alloy powder: one involves mechanically mixing and melting high-purity lithium metal with silicon powder, then mechanically pulverizing and grinding the resulting lithium-silicon alloy ingot to obtain lithium-silicon alloy powder; the other involves mixing high-purity lithium powder and silicon powder in a certain proportion, sintering under high temperature or high pressure, and then mechanically pulverizing and grinding to obtain lithium-silicon alloy powder, as shown in CN 115763771B. The lithium-silicon alloy particles prepared by these two methods are generally at the micrometer scale or larger. Furthermore, traditional smelting methods for preparing lithium-silicon alloys suffer from problems such as floating molten lithium blocks, difficulties in the eutectic of silicon and lithium, and uneven bulk phase distribution of the lithium-silicon alloy. These methods are highly complex, have high production costs, low batch-to-batch consistency, and are unsuitable for mass production. Therefore, providing an in-situ method for preparing nano-lithium-silicon alloys is a technical challenge that urgently needs to be addressed by those skilled in the art. Summary of the Invention

[0008] In view of this, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing nanoscale lithium-silicon alloys and their applications. This method for preparing nanoscale lithium-silicon alloy materials is simple, inexpensive, continuous, and suitable for large-scale application. The nanoscale lithium-silicon alloy materials prepared by this invention can be used as negative electrode materials for lithium-ion batteries, all-solid-state batteries, and as lithium replenishing agents for lithium-ion battery negative electrodes.

[0009] It should be noted that this invention discloses a method for preparing nanoscale lithium-silicon alloy. First, silane gas and dilution gas are mixed and injected into the plasma thermal field generated by a radio frequency plasma generator to generate silicon atoms. Then, lithium source is sent into the plasma thermal field using an inert gas as a carrier gas to generate lithium atom vapor. The two are alloyed in a high-temperature thermal field. Driven by a cooling airflow, the lithium-silicon alloy particles pass through high-temperature and low-temperature cooling zones and enter a cyclone classification chamber. Unreacted lithium source and large-diameter lithium-silicon alloy particles remain in the cyclone classification chamber, while small-diameter lithium-silicon alloy particles are carried into a collection chamber and adsorbed on the filter surface. They are then blown off by a periodic backflushing airflow to obtain the lithium-silicon alloy powder to be coated. Finally, the nanoscale lithium-silicon alloy to be coated is introduced into a fluidized bed and coated with silicon and carbon using a vapor deposition method to prepare a lithium-silicon alloy with an inner coating layer of element-doped silicon and an outer coating layer of carbon. This alloy can be used as a negative electrode material for thermal batteries, solid-state batteries, and a lithium replenishing agent for liquid lithium-ion batteries.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] The first technical objective of this invention is to provide a method for preparing nanoscale lithium-silicon alloys, comprising the following steps:

[0012] (1) Preparations:

[0013] Argon gas is used to flush and leak-check the entire pyrolysis system. After leak detection, the central gas and sheath gas are introduced into the plasma reactor at a certain flow rate. After excitation, a stable high-temperature plasma with a predetermined power is formed. A compressor is used to introduce a high-temperature circulating cooling gas into the primary high-temperature cooling zone and a low-temperature circulating cooling gas into the secondary low-temperature cooling zone. The central gas is argon with a flow rate of 5–100 slpm. The sheath gas is a mixture of argon and hydrogen, with an argon flow rate of 20–250 slpm and a hydrogen flow rate of 0–30 slpm.

[0014] (2) Preparation and collection of lithium-silicon alloys:

[0015] The lithium source is placed in the feeder, and nitrogen gas is introduced to flush the feeder, ensuring the oxygen content is less than 50 ppm. Next, the feed probe is opened, and silicon source gas is injected into the plasma thermal field generated by the RF plasma generator under a dilution gas flow for pyrolysis, producing silicon atoms. Then, carrier gas is introduced into the feeder, and the feeder is started, allowing the lithium source to pass through the high-temperature plasma at a certain rate under the action of the carrier gas and be delivered into the reaction chamber. At this point, the lithium source rapidly pyrolyzes into lithium atoms in the plasma thermal field. The pyrolyzed lithium atoms mix and collide with silicon atoms in the plasma thermal field, undergoing an alloying reaction, and are then cooled by the gas flow. Driven by the process, the lithium-silicon alloy particles are formed after passing through a primary high-temperature cooling zone and a secondary low-temperature cooling zone. Simultaneously, the lithium-silicon alloy particles are continuously carried into the cyclone classification chamber by the cooling airflow. The coarser lithium-silicon alloy particles and unreacted lithium source remain in the cyclone classification chamber, while the finer lithium-silicon alloy particles are carried into the collection chamber by the airflow, blocked by the filter and adhered to the filter surface. After being blown off by the periodic backflushing airflow, lithium-silicon alloy powder is collected. After continuously introducing silicon source gas and lithium source into the radio frequency plasma reactor and continuously working and reacting for 4 to 24 hours, the powder collection tank is replaced, the reactor is stopped, and the powder is collected to obtain the nano-sized lithium-silicon alloy to be coated.

[0016] (3) Coating of lithium-silicon alloy

[0017] Nitrogen gas is introduced into the fluidized bed to clean the interior and ensure that the oxygen content is less than 50 ppm. Next, the lithium silicon alloy powder prepared in step (2) is transported into the fluidized bed through nitrogen gas. The furnace is kept under a slight positive pressure. Then, the furnace body is heated to 480-700°C. Nitrogen gas, silicon source gas, and doping gas are introduced at a certain flow rate to coat the surface of the lithium silicon alloy with silicon in the fluidized bed. The coating time is T1. After the coating is completed, the silicon source gas and doping gas are stopped. The furnace body is heated to 550-1000°C. Carbon source gas is introduced at a certain flow rate to coat the surface of the lithium silicon alloy with carbon so that a carbon layer is formed on the surface. The coating time is T2. After the coating is completed, the carbon source gas is stopped and the heating device is turned off. When the fluidized bed cools to room temperature, the nano-lithium silicon alloy particles coated on the surface are taken out.

[0018] Optionally, in step (1), the central gas is argon with a flow rate of 5 to 100 slpm; the sheath gas is a mixture of argon and hydrogen, with the argon flow rate in the sheath gas being 20 to 250 slpm and the hydrogen flow rate in the sheath gas being 0 to 30 slpm.

[0019] The high-temperature circulating cooling gas is a mixture of argon and hydrogen, with a temperature of 300–800°C and a flow rate of 800–5000 slpm; the low-temperature circulating cooling gas is a mixture of argon and hydrogen, with a temperature of 15–35°C and a flow rate of 3000–25000 slpm.

[0020] Furthermore, the purity of hydrogen is 99.999%, and the purity of argon is 99.999%.

[0021] Furthermore, the plasma reactor has a power of 80–200 kW and a system operating pressure of 14–17 psig; the volume ratio of argon to hydrogen in the high-temperature circulating cooling gas and the low-temperature circulating cooling gas is (10%–90%):(10%–90%).

[0022] Optionally, in step (2), the silicon source gas is one or a mixture of two of silane and disilane in any proportion, and the purity of the silicon source gas is 99.999%; the flow rate of the silicon source gas is 5 to 120 slpm; the dilution gas flow is argon, and the flow rate is 50 to 200 slpm.

[0023] Further, in step (2), the lithium source is lithium powder or lithium hydride; the lithium powder has a purity of ≥99% and a medium particle size of 40-50 μm; the lithium hydride has a purity of 99.99% and a medium particle size of 1-10 μm; the carrier gas of the lithium source is argon, the gas flow rate is 1-10 slpm, and the feeding rate of the lithium source raw material is 0.2-200 g / min.

[0024] Furthermore, the lithium-silicon alloy powder to be coated prepared in step (2) is Li x Si, where x ranges from 0.5 to 4.4, specifically LiSi, Li 12 Si7, Li2Si, Li 13 Si4, Li 15 Si4 and Li 22 Any one of Si5; the particle size of the lithium silicon alloy powder to be coated prepared in step (2) is 60-150 nm, and the production capacity of the lithium silicon alloy powder is 1.0-9.0 kg / h.

[0025] The lithium-silicon alloy powder in step (2) is the lithium-silicon alloy powder to be coated, which can be used in solid-state batteries and thermal batteries.

[0026] Optionally, in step (3), the mass of the lithium-silicon alloy powder to be coated introduced into the fluidized bed is 0.5 to 2 kg, the mass of the silicon coating layer accounts for 1 wt.% to 5 wt.% of the mass of the lithium-silicon alloy, the mass of the doped atoms accounts for 0.01 wt.% to 5.0 wt.% of the mass of the silicon coating layer, and the mass of the carbon coating layer accounts for 2 wt.% to 10 wt.% of the mass of the lithium-silicon alloy.

[0027] Further, in step (3), the silicon source gas is one or a mixture of two of silane and disilane in any proportion, and the purity of the silicon source gas is 99.999%; the doping gas is one or a mixture of one or more of diborane, phosphine, germanane, and arsine in any proportion, and the purity of the doping gas is 99.999%; the carbon source gas is one or a mixture of any of methane, acetylene, propyne, ethylene, and cyclohexane in any proportion.

[0028] Furthermore, in step (3), the flow rate of nitrogen is 8-20 slpm, the flow rate of silicon source gas is 0.2-1 slpm, the flow rate of doping gas is 0.2-100 sccm, the flow rate of carbon source gas is 1-5 slpm, the coating time of silicon T1 is 0.5-3h, and the coating time of carbon T2 is 2-6h.

[0029] It should be noted that the particle size of the lithium silicon alloy powder coated with silicon and carbon in step (3) is 80-200 nm.

[0030] The second technical objective of this invention is to provide an application of the nanoscale lithium-silicon alloy prepared by the method described above in thermal batteries, solid-state batteries, and liquid lithium-ion batteries.

[0031] Specifically, the prepared nanoscale lithium-silicon alloy is used as an active material for the negative electrode of thermal batteries, liquid lithium-ion batteries, solid lithium-ion batteries, and lithium replenishment agent for the negative electrode of lithium-ion batteries.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] (1) This invention employs a radio frequency plasma method to prepare nanoscale lithium-silicon alloys. At high temperatures, silicon-containing gas and lithium source gas undergo thermal decomposition in a plasma thermal field, followed by an alloying reaction under a plasma thermal field of approximately 10000 K, resulting in the in-situ formation of lithium-silicon alloys. This method overcomes the problem of lithium evaporation caused by the higher melting temperature of silicon (1414℃) compared to the boiling point of lithium (1342℃) in traditional melt-processing methods. It also solves the problem caused by the low density of silicon (2.329 g / cm³). 3 ) and the density of lithium (0.534 g / cm³) 3 Significant differences can lead to gravity separation, such as floating molten lithium blocks, difficulties in the eutectic melting of silicon and lithium, and uneven bulk phase distribution of lithium-silicon alloys.

[0034] The lithium-silicon alloy prepared by this method has good bulk phase uniformity; it can realize long-term, continuous and batch production of nanoscale lithium-silicon alloys, thereby reducing the unit production cost of materials.

[0035] (2) This invention discloses a method for preparing nanoscale lithium-silicon alloy. By adjusting the ratio of lithium source and silicon source in the raw materials, the proportion of lithium-silicon alloy in the product can be adjusted. At the same time, the cooling rate of the cooling gas can be adjusted to control the particle size and distribution of the lithium-silicon alloy. In addition, this invention uses a vapor deposition method to dope the lithium-silicon alloy with elemental silicon nano-silicon and carbon coating to prepare a lithium-silicon alloy with an inner layer of elemental doped nano-silicon coating and an outer layer of carbon coating. This solves the problems of high reactivity, poor air stability, and poor conductivity of lithium-silicon alloy, as well as the problems of low initial efficiency, low cycle performance, and poor rate capability when used in lithium-ion batteries. This improves the practicality and feasibility of lithium-silicon alloy as a negative electrode material and negative electrode lithium replenishment agent for lithium-ion batteries.

[0036] The nanoscale lithium-silicon alloy prepared by the method of this invention can be used as a negative electrode material for thermal batteries and solid-state batteries, as well as a lithium replenishing agent for liquid lithium-ion batteries. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the apparatus for preparing nanoscale lithium-silicon alloys by inductive plasma pyrolysis.

[0039] The diagram is labeled as follows: 1-Inductive plasma generator, 2-Lithium source, 3-Center gas, 4-Sheath gas, 5-Feed probe, 6-Silicon source gas, 7-Dilution gas, 8-Primary high-temperature cooling zone, 9-High-temperature circulating cooling airflow inlet, 10-Low-temperature circulating cooling airflow inlet, 11-Nitrogen cooling airflow inlet, 12-Secondary low-temperature cooling zone, 13-Cyclone classifier, 14-Powder collection tank 1, 15-Powder collection tank 2, 16-Collection chamber, 17-Filter, 18-Compressor, 19-Water-cooled heat exchanger, 20-Electric heating tube, 21-Tail gas treatment device.

[0040] Figure 2 These are the first charge-discharge curves of the coin cells prepared in Example 3 and Comparative Example 2.

[0041] Figure 3These are the first charge-discharge curves of the coin cells prepared in Example 1 and Comparative Example 2.

[0042] Figure 4 This is a comparison chart of the 0.5C cycling of coin cells prepared in Example 1 and Comparative Example 2.

[0043] Figure 5 This is a schematic diagram of a lithium-silicon alloy structure. Detailed Implementation

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0045] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in the embodiments of this application, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in this application is merely for describing particular implementations and is not intended to limit the scope of this disclosure.

[0046] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; other experimental methods and technical means not specifically mentioned herein refer to experimental methods and technical means commonly used by one of ordinary skill in the art.

[0047] To better illustrate the content of this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail in order to highlight the main points of this application.

[0048] Without conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solution belongs to the content disclosed in the embodiments of this application.

[0049] This invention discloses a method for preparing nanoscale lithium-silicon alloys and their applications.

[0050] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0051] Example 1

[0052] A method for preparing a lithium-silicon alloy and its application, specifically including the following steps:

[0053] (1) Preparations:

[0054] The entire pyrolysis system was flushed and leak-checked using argon gas. A center gas (argon) of 60 slpm and a sheath gas (a mixture of 150 slpm argon and 30 slpm hydrogen) were introduced into the induction plasma generator. The induction plasma was then activated, and the system pressure was adjusted to 16.5 psi, with the induction plasma generator power set to 120 kW. The compressor was then started, and a high-temperature circulating cooling gas flow of 4500 slpm and 680°C was introduced into the primary high-temperature cooling zone. A low-temperature circulating cooling gas flow of 9500 slpm and 25°C and a nitrogen cooling gas flow of 500 slpm were introduced into the secondary low-temperature cooling zone. The volume ratio of argon to hydrogen in the high-temperature and low-temperature circulating cooling gases was 80%:20%.

[0055] (2) Preparation and collection of lithium-silicon alloys

[0056] Lithium metal with a particle size of 40 μm was placed into a feeder, and nitrogen gas was introduced to flush the feeder, ensuring that the oxygen content was less than 50 ppm. Next, the feed probe was opened, and silane was injected into the plasma thermal field generated by the RF plasma generator under the influence of a dilution gas flow. The silane flow rate was 60 slpm, and the dilution gas flow was argon with a flow rate of 50 slpm. Then, a carrier gas was introduced into the feeder, and the feeder was started, allowing the lithium powder to pass through the high-temperature plasma at a rate of 60.2 g / min under the action of the carrier gas and be fed into the reaction chamber. At this time, the lithium powder was... Lithium atoms are rapidly pyrolyzed in the plasma thermal field. The pyrolyzed lithium atoms mix and collide with silicon atoms in the plasma thermal field, undergoing an alloying reaction. Driven by the cooling airflow, they pass through a primary high-temperature cooling zone and a secondary low-temperature cooling zone, forming lithium-silicon alloy particles. Simultaneously, the lithium-silicon alloy particles are continuously carried by the cooling airflow into the cyclone classification chamber. Coarser lithium-silicon alloy particles and unreacted lithium remain in the cyclone classification chamber, while finer lithium-silicon alloy particles are carried by the airflow into the collection chamber, where they are blocked by the filter and adhere to the filter surface. Periodic backflushing airflow blows them off, obtaining lithium-silicon alloy powder. After continuously introducing silicon source gas and lithium source into the radio frequency plasma reactor and reacting continuously for 8 hours, the powder collection tank was replaced, and the reactor was shut down for collection, yielding 42.2 kg of nano-sized Li to be coated. 13 Si4 lithium-silicon alloy, with a particle size of 90nm.

[0057] (3) Coating of lithium-silicon alloy

[0058] Nitrogen gas was introduced into the fluidized bed to clean the interior and ensure that the oxygen content was less than 50 ppm. Next, 2 kg of lithium-silicon alloy powder prepared in step (2) was transported into the fluidized bed using nitrogen gas. A slight positive pressure was maintained inside the furnace. The furnace was then heated to 540°C, and nitrogen, silicon source gas, and doping gas were introduced. The flow rate of nitrogen was 20 slpm, the flow rate of silicon source gas was 1 slpm, the flow rate of borane gas was 7 sccm, and the flow rate of phosphine gas was 4.8 sccm. The surface of the lithium-silicon alloy was coated with silicon in the fluidized bed for 1.5 hours. After the coating time was completed, the silicon source gas and doping gas were stopped. Then, the furnace was heated to 600°C, and acetylene was introduced at a flow rate of 3 slpm to carbon-coat the surface of the lithium-silicon alloy, so that a carbon layer was formed on its surface. The coating time was T2, which was 3.0 hours. After the coating time was completed, the acetylene was stopped and the heating device was turned off. After the fluidized bed cooled to room temperature, the surface-coated lithium-silicon alloy particles were removed.

[0059] This embodiment prepares a lithium-silicon alloy by surface coating a nanoscale lithium-silicon alloy, resulting in an inner layer of boron- and phosphorus-doped silicon coating and an outer layer of carbon coating. The core Li... 13 The mass ratio of Si4 to silicon coating and carbon coating is 100%:5%:5%, and its particle size is 120nm.

[0060] (4) Applications in lithium-ion batteries

[0061] The prepared coated lithium-silicon alloy was used as a lithium replenishing agent for the silicon-carbon anode to prepare coin-type lithium-ion batteries (coin-type all-electric batteries). The preparation method is as follows:

[0062] Preparation of the positive electrode sheet: The positive electrode active material lithium nickel cobalt manganese oxide (NCM523), conductive carbon black, conductive carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) are thoroughly stirred in a mass ratio of 97.5:0.3:1.2:1 to obtain a positive electrode slurry. The prepared slurry is coated onto aluminum foil, dried, and rolled to obtain the positive electrode sheet. Subsequently, it is cut into diameters... The electrodes were dried in a vacuum drying oven at 120°C for 24 hours. The dried electrodes were then transferred to a glove box for later use.

[0063] Preparation of the negative electrode: The silicon-carbon negative electrode (450 mAh / g reversible specific capacity) was mixed with the lithium-silicon alloy coated in this embodiment at a mass ratio of 100%:3%. The specific formula and usage method are as follows:

[0064] Silicon-carbon anode material, conductive carbon black, conductive carbon nanotubes (SWCNTs), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and coated lithium-silicon alloy were thoroughly mixed in a ratio of 96.0:0.9:0.1:1.20:1.80:2.80 to obtain a negative electrode slurry. The prepared slurry was coated onto copper foil, and after drying and rolling, a negative electrode sheet was obtained. Subsequently, it was cut into diameters... The electrodes were dried in a vacuum drying oven at 120°C for 24 hours. The dried electrodes were then transferred to a glove box for later use.

[0065] Fabrication of button-type all-electric devices:

[0066] The positive electrode, negative electrode, separator, and electrolyte are combined and assembled into a button cell battery with the model number 2032.

[0067] Test conditions:

[0068] The test conditions for the button cell are as follows: The initial charge and discharge method is as follows: charge to 3.00V at 0.02C, charge to 3.80V at 0.05C, charge to 4.20V at 0.08C, and charge to 4.40V at 0.1C constant current and constant voltage, with a cutoff current of 0.02C. Then, discharge at 0.1C, followed by a cycle test. The cycle test method is as follows: cycle test at a current rate of 0.5C, with a charge and discharge voltage range of 3.00 to 4.40V.

[0069] Example 2

[0070] A method for preparing nanoscale lithium-silicon alloy and its application, specifically including the following steps:

[0071] (1) Preparations:

[0072] The entire pyrolysis system was flushed and leak-checked using argon gas. A center gas (argon) of 30 slpm and a sheath gas (a mixture of 60 slpm argon and 30 slpm hydrogen) were introduced into the induction plasma generator. The induction plasma was then excited, the system pressure was adjusted to 14.5 psi, and the power of the induction plasma generator was set to 80 kW. The compressor was then started, and a high-temperature circulating cooling gas of 1500 slpm and 750°C was introduced into the primary high-temperature cooling zone. A low-temperature circulating cooling gas of 6500 slpm and 28°C and a nitrogen cooling gas of 250 slpm were introduced into the secondary low-temperature cooling zone. The volume ratio of argon to hydrogen in the high-temperature and low-temperature circulating cooling gases was 60%:40%.

[0073] (2) Preparation and collection of lithium-silicon alloys

[0074] Lithium hydride particles with a medium particle size of 10 μm were placed into a feeder, and nitrogen gas was introduced to flush the feeder, ensuring an oxygen content of less than 50 ppm. Next, the feed probe was opened, and silane was injected into the plasma thermal field generated by the RF plasma generator under a dilution gas flow. The silane flow rate was 26 slpm, and the dilution gas was argon with a flow rate of 35 slpm. Then, a carrier gas was introduced into the feeder, and the feeder was started, allowing the lithium hydride to pass through the high-temperature plasma at a rate of 41.5 g / min under the action of the carrier gas and be delivered into the reaction chamber. At this point, the lithium hydride was in the plasma... In the plasma thermal field, lithium atoms and hydrogen gas are rapidly pyrolyzed. The pyrolyzed lithium atoms mix and collide with silicon atoms in the plasma thermal field to undergo an alloying reaction. Driven by the cooling airflow, they pass through a primary high-temperature cooling zone and a secondary low-temperature cooling zone to form lithium-silicon alloy particles. Simultaneously, the lithium-silicon alloy particles are continuously carried by the cooling airflow into the cyclone classification chamber. Coarser lithium-silicon alloy particles and unreacted lithium hydride remain in the cyclone classification chamber, while finer lithium-silicon alloy particles are carried by the airflow into the collection chamber, blocked by the filter and adhered to the filter surface. They are then blown off by periodic backflushing airflow to obtain lithium-silicon alloy powder. After continuously introducing silicon source gas and lithium source into the radio frequency plasma reactor and reacting continuously for 9 hours, the powder collection tank is replaced, the reactor is shut down, and the powder is collected, yielding 25.5 kg of nano-sized Li to be coated. 22 Si5 lithium-silicon alloy, with a particle size of 120nm.

[0075] (3) Coating of lithium-silicon alloy

[0076] Nitrogen gas was introduced into the fluidized bed to clean the interior and ensure that the oxygen content was less than 50 ppm. Next, 1.2 kg of lithium silicon alloy powder prepared in step (2) was transported into the fluidized bed through nitrogen gas. The furnace was kept under a slight positive pressure. The furnace body was then heated to 540°C. Nitrogen gas, silicon source gas, and doping gas were then introduced. The flow rate of nitrogen gas was 20 slpm, the flow rate of silicon source gas was 0.5 slpm, and the flow rate of phosphine gas was 2.5 sccm. The surface of the lithium silicon alloy was coated with silicon in the fluidized bed for 1.5 h. After the coating time was completed, the introduction of silicon source gas and doping gas was stopped. Then, the furnace body was heated to 700°C, and acetylene was introduced at a flow rate of 2.0 slpm to carbon coat the surface of the lithium silicon alloy, so that a carbon layer was formed on its surface. The coating time was T2, which was 5.2 h. After the coating time was completed, the introduction of acetylene was stopped and the heating device was turned off. When the fluidized bed cooled to room temperature, the coated lithium silicon alloy particles were removed.

[0077] This embodiment prepares a lithium-silicon alloy with an inner phosphorus-doped silicon coating layer and an outer carbon coating layer by surface coating of a nanoscale lithium-silicon alloy. The core Li... 22The mass ratio of Si5 to silicon coating and carbon coating is 100%:8%:10%, and its particle size is 180nm.

[0078] (4) Applications in lithium-ion batteries

[0079] The prepared coated lithium-silicon alloy was used as a lithium supplement for silicon-carbon anode to prepare button cells. The preparation and testing methods were the same as in Example 1, except that the silicon-carbon anode (450mAh / g reversible specific capacity) and the coated lithium-silicon alloy of this example were mixed at a mass ratio of 100%:2% to finally prepare the anode sheet.

[0080] Example 3

[0081] A method for preparing nanoscale lithium-silicon alloy and its application, specifically including the following steps:

[0082] (1) Preparations:

[0083] The entire pyrolysis system was flushed and leak-checked using argon gas. A center gas (argon) of 80 slpm and a sheath gas (a mixture of 120 slpm argon and 10 slpm hydrogen) were introduced into the induction plasma generator. Induction plasma was then activated, and the system pressure was adjusted to 16 psi, with the induction plasma generator power set to 150 kW. The compressor was then started, introducing a high-temperature circulating cooling gas flow of 5000 slpm at 500°C into the primary high-temperature cooling zone, and a low-temperature circulating cooling gas flow of 20000 slpm at 20°C into the secondary low-temperature cooling zone. The volume ratio of argon to hydrogen in both the high-temperature and low-temperature circulating cooling gases was 75%:25%.

[0084] (2) Preparation and collection of lithium-silicon alloys:

[0085] Lithium metal with a particle size of 45 μm was placed into a feeder, and nitrogen gas was introduced to flush the feeder, ensuring an oxygen content of less than 50 ppm. Next, the feed probe was opened, and silane was injected into the plasma thermal field generated by the RF plasma generator under a dilution gas flow. The silane flow rate was 106 slpm, and the dilution gas was argon with a flow rate of 200 slpm. Then, a carrier gas was introduced into the feeder, and the feeder was started, allowing the lithium powder to pass through the high-temperature plasma at a rate of 65.9 g / min under the action of the carrier gas and be fed into the reaction chamber. At this time, the lithium powder was... Lithium atoms are rapidly pyrolyzed in the plasma thermal field. The pyrolyzed lithium atoms mix and collide with silicon atoms in the plasma thermal field to undergo an alloying reaction. Driven by the cooling airflow, they pass through a primary high-temperature cooling zone and a secondary low-temperature cooling zone to form lithium-silicon alloy particles. Simultaneously, the lithium-silicon alloy particles are continuously carried by the cooling airflow into the cyclone classification chamber. The coarser lithium-silicon alloy particles and unreacted metallic lithium remain in the cyclone classification chamber, while the finer lithium-silicon alloy particles are carried by the airflow into the collection chamber, blocked by the filter and adhered to the filter surface. They are then blown off by periodic backflushing airflow to obtain lithium-silicon alloy powder. After continuously introducing silicon source gas and lithium source into the radio frequency plasma reactor and reacting continuously for 12 hours, the powder collection tank is replaced, the reactor is shut down, and the powder is collected to obtain 8.3 kg of nano-sized Li2Si lithium-silicon alloy to be coated. The particle size of the lithium-silicon alloy is 90 nm.

[0086] (3) Coating of lithium-silicon alloy

[0087] Nitrogen gas was introduced into the fluidized bed to clean the interior and ensure that the oxygen content was less than 50 ppm. Next, 2.5 kg of lithium-silicon alloy powder prepared in step (2) was transported into the fluidized bed using nitrogen gas. A slight positive pressure was maintained inside the furnace. The furnace body was then heated to 540°C, and nitrogen, silicon source gas, and doping gas were introduced. The flow rate of nitrogen was 20 slpm, the flow rate of silicon source gas was 0.3 slpm, the flow rate of borane gas was 20 sccm, and the flow rate of germanane gas was 20 sccm. The surface of the lithium-silicon alloy was coated with silicon in a fluidized bed for 2.2 hours. After the coating time was completed, the silicon source gas and doping gas were stopped. Then, the furnace was heated to 700°C, and acetylene was introduced at a flow rate of 2.0 slpm to carbon coat the surface of the lithium-silicon alloy, so that a carbon layer was formed on its surface. The coating time was T2, which was 6.1 hours. After the coating time was completed, the acetylene was stopped and the heating device was turned off. When the fluidized bed cooled to room temperature, the surface-coated lithium-silicon alloy particles were removed.

[0088] In this embodiment, a lithium-silicon alloy with a boron and germanium ion-doped silicon coating layer as the inner layer and a carbon coating layer as the outer layer is prepared by surface coating of nanoscale lithium-silicon alloy. The mass ratio of the core Li2Si to the silicon coating layer and the carbon coating layer is 100%:2%:6%, and the particle size is 120nm.

[0089] (4) Applications in lithium-ion batteries

[0090] The prepared coated lithium-silicon alloy was used as a lithium supplement for the silicon-carbon anode to prepare a coin cell. The preparation and testing methods were the same as in Example 1, except that the silicon-carbon anode (450 mAh / g reversible specific capacity) and the coated lithium-silicon alloy of this example were mixed at a mass ratio of 100%:5% to finally prepare the anode sheet. Simultaneously, the prepared silicon-carbon electrode sheet was used as the positive electrode, with metallic lithium as the counter electrode, and combined with a separator and a self-made electrolyte to assemble a 2032 type coin cell.

[0091] The test conditions for button cell half-cells are as follows: discharge at 0.1C to 0.010V, discharge at 0.01C to 0.005V, stand for 5 minutes, and charge at 0.1C to 1.50V.

[0092] To further demonstrate the beneficial effects of the present invention and to better understand it, the technical features disclosed in the present invention are further illustrated by the following comparative examples, but these should not be construed as limiting the present invention. Other improvements made by those skilled in the art based on the above description of the invention, without inventive effort, are also considered to fall within the protection scope of the present invention.

[0093] Comparative Example 1

[0094] This comparative example is a repetition of Example 1, but differs from Example 1 in that:

[0095] Step (4) The coated lithium-silicon alloy prepared in Example 1 was used as the active material to prepare a coin cell and tested.

[0096] Specifically, the coated lithium-silicon alloy was prepared according to the following formula: the ratio of coated lithium-silicon alloy, conductive carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) was 85.0:5.0:4.0:6.0. The resulting slurry was then prepared to form an electrode sheet. Subsequently, the prepared lithium-silicon alloy electrode sheet was used as the positive electrode, and lithium metal was used as the counter electrode. The electrode sheet was combined with a separator and a self-made electrolyte to form a 2032 type button cell. The test method was the same as that used for the button half-cell in Example 3.

[0097] Comparative Example 2

[0098] This comparative example is the preparation of a coin cell. A silicon-carbon anode (450mAh / g reversible specific capacity) and a positive electrode active material lithium nickel cobalt manganese oxide (NCM523) were used as active materials to prepare a coin cell and test it. The preparation steps and testing methods were carried out in step (4) of Example 1. However, it should be noted that no coated lithium silicon alloy was added to the anode sheet.

[0099] Meanwhile, this comparative example also uses the prepared silicon-carbon electrode as the positive electrode and lithium metal as the counter electrode, and combines it with a separator and a self-made electrolyte to assemble a 2032 type button half cell. The specific assembly and testing methods refer to the preparation and testing methods of button half cells in Example 3.

[0100] Comparative Example 3

[0101] This comparative example is a repetition of Example 3, except that:

[0102] In step (3), the lithium-silicon alloy to be coated was only coated with carbon, and finally a lithium-silicon alloy with a core of lithium-silicon alloy and an outer coating layer of carbon was obtained. The mass ratio of the core Li2Si to the carbon coating layer was 100%:6%, and its particle size was 100nm.

[0103] Step (4) The carbon-coated lithium-silicon alloy prepared in this comparative example and lithium nickel cobalt manganese oxide (NCM523) as the positive electrode active material were used to prepare coin cells and tested. The specific preparation process and testing methods are as described in Example 1.

[0104] Meanwhile, the silicon-carbon electrode prepared in this comparative example is used as the positive electrode, and lithium metal is used as the counter electrode. It is then combined with a separator and a self-made electrolyte to assemble a 2032 type button half-cell. The test method is the same as the test method for button half-cells in Example 3.

[0105] Table 1. Basic performance of coin cell all-electric and half-electric cells prepared in each embodiment.

[0106]

[0107] Table 1 shows that comparing the coin cell results of Examples 1-2 with Comparative Example 2, the coin cell with added lithium-silicon alloy as a lithium replenisher exhibits better initial efficiency and specific capacity than that without a lithium replenisher (Comparative Example 2). Furthermore, comparing the coin cell and half-cell results of Comparative Example 2 with those of Example 3, the addition of lithium-silicon alloy as a lithium replenisher to the silicon-carbon anode improves the initial charge-discharge performance of both the coin cell and half-cell. Comparing the coin cell results of Example 3 with those of Comparative Example 3, Comparative Example 3 only contains a carbon coating layer, while the lithium-silicon alloy in Example 3 has an additional doped nano-silicon coating layer. This coating layer increases the conductivity between the lithium-silicon alloy and the carbon coating layer, thus improving the electrochemical performance of the lithium-silicon alloy as a lithium replenisher for silicon-based anodes.

[0108] In summary, the nanoscale lithium-silicon alloy material prepared by this invention has broad application prospects. It can be used not only as a negative electrode material for thermal and solid-state batteries, but also as a lithium replenisher for liquid lithium-ion batteries. Although this invention only provides a specific embodiment of lithium-silicon alloy as a lithium replenisher for liquid lithium-ion batteries, the invention is not limited thereto, and the lithium-silicon alloy material is also applicable to negative electrode materials in other battery systems.

[0109] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for producing a nanoscale lithium-silicon alloy, characterized by, The method comprises the following steps: (1) Preparation: The whole pyrolysis system is flushed with argon and leak tested; after the leak testing is completed, central gas and sheath gas are introduced into the plasma reactor at a certain flow rate to form a predetermined power, stable high-temperature plasma after excitation, a compressor is used to introduce high-temperature circulating cooling gas into the first-stage high-temperature cooling area and low-temperature circulating cooling gas into the second-stage low-temperature cooling area; wherein the central gas is argon, and the flow rate is 5-100 slpm; the sheath gas is a mixture of argon and hydrogen, the argon flow rate in the sheath gas is 20-250 slpm, and the hydrogen flow rate in the sheath gas is 0-30 slpm; (2) Preparation and collection of lithium-silicon alloy: The lithium source is placed in a feeder, nitrogen is introduced, and the feeder is flushed with nitrogen to ensure that the oxygen content is less than 50 ppm; secondly, the silicon source gas is injected into the plasma thermal field generated by the radio frequency plasma generator under the wrapping of the dilution gas stream to produce silicon atoms by opening the feeding probe; then, the carrier gas is introduced into the feeder, and the feeder is started to make the lithium source pass through the high-temperature plasma at a certain rate under the action of the carrier gas and enter the reaction chamber; at this time, the lithium source is rapidly pyrolyzed into lithium atoms in the plasma thermal field, the pyrolyzed lithium atoms and silicon atoms mix and collide in the plasma thermal field to perform alloying reaction, and the lithium-silicon alloy particles are formed under the driving of the cooling gas through the first-stage high-temperature cooling area and the second-stage low-temperature cooling area; at the same time, the lithium-silicon alloy particles are continuously driven into the cyclone classification chamber by the cooling gas stream, the relatively coarse lithium-silicon alloy particles and unreacted lithium source are retained in the cyclone classification chamber, the relatively fine lithium-silicon alloy particles are brought into the collection chamber by the gas stream, and are blocked and adhered to the surface of the filter by the filter, and are blown off by the periodic back-blowing gas stream to collect the lithium-silicon alloy powder; after continuous introduction of the silicon source gas and lithium source into the radio frequency plasma reactor for 4-24 hours, the powder collection tank is replaced, and the lithium-silicon alloy to be coated is collected after the machine is stopped; (3) Coating of lithium-silicon alloy: Nitrogen is introduced into the fluidized bed to clean the inside and ensure that the oxygen content is less than 50 ppm; secondly, the lithium-silicon alloy powder prepared in step (2) is delivered to the fluidized bed by nitrogen, the furnace is kept at a slight positive pressure, and then the furnace body is heated to 480-700 ℃, nitrogen, silicon source gas and doping gas are introduced at a certain flow rate to perform silicon coating on the surface of the lithium-silicon alloy in the fluidized bed, and the coating time is T1; After the coating is completed, the introduction of the silicon source gas and the doping gas is stopped; the furnace body is heated to 550-1000 ℃, the carbon source gas is introduced at a certain flow rate to perform carbon coating on the surface of the lithium-silicon alloy to form a carbon layer on the surface, and the coating time is T2; after the coating is completed, the introduction of the carbon source gas is stopped, and the heating device is turned off; when the fluidized bed is cooled to room temperature, the surface-coated nanometer lithium-silicon alloy particles are taken out.

2. The method for preparing nanoscale lithium-silicon alloy as described in claim 1, characterized in that, In step (1), the central gas is argon, and the flow rate is 5-100 slpm; the sheath gas is a mixture of argon and hydrogen, the argon flow rate in the sheath gas is 20-250 slpm, and the hydrogen flow rate in the sheath gas is 0-30 slpm. The high-temperature circulating cooling gas flow is a mixture of argon and hydrogen, the temperature of the high-temperature circulating cooling gas flow is 300-800℃, and the flow rate is 800-5000 slpm; the low-temperature circulating cooling gas flow is a mixture of argon and hydrogen, the temperature of the low-temperature circulating cooling gas flow is 15-35℃, and the flow rate is 3000-25000 slpm; The purity of the hydrogen is 99.999%, and the purity of the argon is 99.999%.

3. The method for preparing nanoscale lithium-silicon alloy as described in claim 1 or 2, characterized in that, The power of the plasma reactor is 80-200 KW, and the system working pressure is 14-17 psig; in the high-temperature circulating cooling gas and the low-temperature circulating cooling gas, the volume ratio of argon to hydrogen is (10%-90%):(10%-90%).

4. The method for preparing nanoscale lithium-silicon alloy as described in claim 1, characterized in that, In step (2), the silicon source gas is one or a mixture of both of silane and disilane in any ratio, and the purity of the silicon source gas is 99.999%; the flow rate of the silicon source gas is 5-120 slpm; and the dilution gas flow is argon, and the flow rate is 50-200 slpm.

5. The method for preparing nanoscale lithium-silicon alloy as described in claim 1 or 4, characterized in that, In step (2), the lithium source is lithium powder or lithium hydride; the purity of the lithium powder is ≥99%, and the medium particle size is 40-50 μm; the purity of the lithium hydride is 99.99%, and the medium particle size is 1-10 μm; the carrier gas of the lithium source is argon, the gas flow rate is 1-10 slpm, and the feeding rate of the lithium source raw material is 0.2-200 g / min.

6. The method of claim 5, wherein the lithium-silicon alloy is prepared at a temperature of 400 to 600 °C. The lithium-silicon alloy powder prepared in the step (2) is Li x Si, wherein x is 0.5 to 4.4, specifically LiSi, Li 12 Si7, Li2Si, Li 13 Si4, Li 15 Si4, and Li 22 Si5; the particle size of the lithium-silicon alloy powder prepared in the step (2) is 60-150 nm, and the production capacity of the lithium-silicon alloy powder is 1.0-9.0 kg / h.

7. The method for preparing nanoscale lithium-silicon alloy as described in claim 1, characterized in that, In step (3), the mass of the lithium-silicon alloy powder to be coated in the fluidized bed is 0.5-2 kg, the mass of the silicon coating layer accounts for 1 wt.%-5 wt.% of the mass of the lithium-silicon alloy, and the mass of the doped atoms accounts for 0.01 wt.%-5.0 wt.% of the mass of the silicon coating layer; the mass of the carbon coating layer accounts for 2 wt.%-10 wt.% of the mass of the lithium-silicon alloy.

8. The method for preparing nanoscale lithium-silicon alloy as described in claim 1 or 7, characterized in that, In step (3), the silicon source gas is one or a mixture of both of silane and disilane in any ratio, and the purity of the silicon source gas is 99.999%; the doping gas is one or a mixture of more than one of diborane, phosphine, germane, and arsine in any ratio, and the purity of the doping gas is 99.999%; and the carbon source gas is one or a mixture of more than one of methane, acetylene, propyne, ethylene, and cyclohexane in any ratio.

9. The method of claim 8, wherein the lithium-silicon alloy is prepared at a temperature of 400 to 600 °C. In step (3), the flow rate of the nitrogen is 8-20 slpm, the flow rate of the silicon source gas is 0.2-1 slpm, the flow rate of the doping gas is 0.2-100 sccm; the flow rate of the carbon source gas is 1-5 slpm; the coating time of silicon T1 is 0.5-3 h; and the coating time of carbon T2 is 2-6 h.

10. The application of the nanoscale lithium-silicon alloy prepared by the method of claim 1 in thermal batteries, solid-state batteries, and liquid lithium-ion batteries.

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