A method for preparing silicon negative electrode material modified by lithium silicate in situ

Abstract

A lithium silicate in-situ modified silicon negative electrode material and a preparation method thereof, wherein a silicon raw material is mixed with an oxidant, a lithium source, a carbon source, and an additive auxiliary material, followed by a hydrothermal reaction, and finally subjected to high-temperature carbonization to obtain a lithium silicate in-situ modified silicon-carbon composite negative electrode material. The composite material is composed of a silicon core and a carbon shell modified in situ by lithium silicate, and a carbon coating layer with a thickness of 20-30 nm is generated on the silicon surface. This method adheres to the principles of green environmental protection in both the selection of raw materials and the preparation process, does not generate toxic waste, and meets the requirements of sustainable development. The prepared finished material has high purity, which helps to improve battery performance and extend its service life. The preparation process of this method is simple, the required equipment is easy to operate, the manufacturing cost is relatively low, and it is suitable for industrial large-scale production.

Description

Technical Field

[0001] The invention relates to a silicon composite negative electrode material that can be used for lithium secondary batteries and a preparation method thereof, and belongs to the field of electrochemical power sources. Background Art

[0002] Amid the rapid expansion of the global electric vehicle and energy storage industries, lithium-ion batteries (LIBs), the core of electric vehicle power and energy storage systems, have a significant impact on vehicle safety, range, and durability. To alleviate the range concerns of electric vehicles and improve the energy density of energy storage systems, one effective approach is to employ high-capacity electrode materials. Currently, the graphite anode materials used in most electric vehicle and energy storage system batteries have a low specific capacity (theoretical value: 372 mAh / g), which limits the range of electric vehicles, the energy density of energy storage systems, and their economic practicality. Silicon-based anode materials, with their excellent specific capacity (theoretical value: 3579 mAh / g) and moderate lithium insertion potential (0.2–0.4 V), are considered promising next-generation battery anode materials. However, silicon materials experience significant volume expansion (over 300%) during lithiation, which can lead to electrode cracking, structural damage, increased interfacial impedance, and degradation of electrical performance, posing a threat to battery safety. Summary of the Invention

[0003] In order to optimize the electrochemical performance of silicon materials and reduce side reactions, surface modification techniques such as carbon layer coverage and inorganic compound coating are widely used.

[0004] This study proposes an innovative artificial solid electrolyte modification structure for silicon surfaces. Silicon powder, commonly used industrial oxidants such as hydrogen peroxide (H2O2) and potassium permanganate, and lithium sources such as lithium acetate (CH3COOLi·2H2O) and lithium carbonate serve as modifiers. This mixture, along with carbon sources such as glucose and sucrose, serves as the raw materials for a hydrothermal reaction. After the hydrothermal reaction, a lithium silicate protective layer is in situ formed on the surface of the silicon anode material. A carbon-coated lithium silicate-in-situ modified silicon composite is then prepared through a low-temperature heat treatment process. This preparation method is simple, environmentally friendly, and safe. The prepared composite effectively mitigates the volume expansion of the silicon material during lithiation, slowing the electrode degradation rate and improving the cycling stability of the material. Currently, there is limited research on silicon-based composites with carbon-coated lithium silicate-in-situ modified silicon, and even fewer studies on silicon surface modification and carbon coating using a one-step process. Based on these analyses, it is of great significance to develop cost-effective and industrial-scale preparation techniques for carbon-coated lithium silicate-in-situ modified silicon composite anode materials.

[0005] The present invention aims to propose a lithium silicate in-situ modified silicon-carbon anode material (Si@LSO@C) and a new preparation method thereof, which has simple operation, environmentally friendly manufacturing process, low manufacturing cost, and good prospects for industrial mass production.

[0006] The specific technical solutions of the present invention are described below.

[0007] The present invention mixes silicon powder with an oxidant, a lithium source, a carbon source, and additive auxiliary materials, then conducts a hydrothermal reaction, and finally carbonizes at high temperature to obtain a lithium silicate in-situ modified silicon-carbon composite negative electrode material.

[0008] This study proposes an innovative method to prepare silicon-carbon composite materials for battery anode materials. The core of this method is to oxidize silicon, modify it in situ with lithium silicate, and then combine it with graphite to form a composite material in a one-step hydrothermal reaction.

[0009] Specifically, the composite material consists of a silicon core in situ modified with lithium silicate and a carbon shell.

[0010] In the hydrothermal reaction stage, the patent of this invention describes in detail the formula parameters of various raw materials, the types of raw materials and the proportions of raw materials.

[0011] The silicon raw material includes micron silicon, nano silicon powder, or a mixture of micron silicon and nano silicon powder. The oxidant includes one or a combination of hydrogen peroxide (H2O2), potassium permanganate (KMnO4), potassium perchlorate (KClO4), and the like. The lithium source includes one or more lithium hydroxide (LiOH), lithium acetate (CH3COOLi), lithium carbonate (Li2CO2), and the like. The carbon source includes one or more glucose, sucrose, chitosan, asphalt, and the like. Additives include cetyltrimethylammonium bromide (CTAB), polyvinylpyrrolidone (PVP), and oxalic acid (H2C2O2).

[0012] In addition, the patent describes in detail the hydrothermal reaction process parameters, including reaction temperature and reaction time. The temperature is between 101-300°C, preferably between 150-199°C, and the reaction time is between 8-48 hours, preferably between 10-24 hours.

[0013] In addition, the patent describes in detail the carbonization process parameters, including reaction temperature and reaction time. The temperature is between 350-1500°C, preferably between 550-950°C, and the reaction time is between 3-48 hours, preferably between 5-12 hours.

[0014] The patent of this invention describes in detail the mass ratio of raw materials, silicon: oxidant: lithium source: carbon source: additive auxiliary material = (50~95): (0.1~20): (0.1-10): (0.1-50): (1~10).

[0015] Through these detailed steps and parameters, this study aims to provide an efficient and reproducible method to prepare lithium silicate in situ modified silicon-carbon composite anode materials to meet the demand for high-performance anode materials in modern battery technology.

[0016] Compared with the existing silicon-carbon composite anode material preparation technology, this study proposed a novel method, which is unique in the following aspects:

[0017] (1) In the composite material prepared by this method, a hydrothermal synthesis method is used to obtain a lithium silicate coating on the surface of the silicon material in a one-pot process. Although hydrothermal synthesis methods are widely used in material synthesis, there are relatively few reports in the literature on the synthesis of a lithium silicate coating layer in situ modified on the surface of elemental silicon without an oxide layer by a one-pot method. This coating layer has the properties of a solid electrolyte, that is, it is insulating to electrons but permeable to ions.

[0018] (2) This method adheres to green environmental protection principles in the selection and preparation of raw materials, does not produce toxic waste, and meets the requirements of sustainable development. The finished material has high purity, which helps improve battery performance and extend its service life. The preparation process of this method is simple, the required equipment is easy to operate, and the manufacturing cost is relatively low, making it suitable for industrial large-scale production.

[0019] Through these innovations, this study aims to provide a new economical and environmentally friendly approach for the preparation of battery anode materials to meet the growing demand for energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 : X-ray diffraction patterns of Si@LSO@C composite materials.

[0021] Figure 2 : High-resolution transmission electron microscopy (TEM) images of Si@LSO@C composite materials.

[0022] Figure 3 : Cycling performance curves of Si@LSO@C composite material and pure silicon anode. DETAILED DESCRIPTION

[0023] This article will explain the technical details of the present invention in detail, including examples and control groups, to demonstrate the characteristics and advantages of the lithium silicate in-situ modified silicon-carbon composite material (Si@LSO@C) involved in the present invention. Please note that the examples mentioned do not cover all possible scenarios, and any other non-innovative examples proposed based on the examples of the present invention should also be considered within the scope of protection of the present invention. To more clearly demonstrate the advantages of the present invention, Examples 2-3 mainly adjust the raw materials used in preparing Si@LSO@C in Example 1, Examples 4-5 mainly adjust the raw material ratios used in preparing Si@LSO@C in Example 1, and Example 6 mainly adjusts some process parameters used in preparing Si@LSO@C in Example 1. Example 7 mainly tests and analyzes the electrochemical performance of the Si@LSO@C prepared in Examples 1-6. Control groups 1 to 4 do not contain an oxidant, auxiliary materials, lithium source, or carbon source, respectively.

[0024] Example 1

[0025] 5 g of micronized silicon (particle size D50 between 1 and 20 μm) was added to a hydrothermal reactor containing 100 g of water. After stirring with a magnetic stirrer for 30 minutes, 3 g of 35 wt.% hydrogen peroxide solution and 0.1 g of lithium carbonate were added, along with 0.3 g of glucose as a carbon source. Additives included 0.1 g of cetyltrimethylammonium bromide (CTAB), 0.1 g of polyvinylpyrrolidone (PVP), and 0.1 g of oxalic acid (H₂C₂O₂). The ratio of silicon: oxidant: lithium source: carbon source: additives was 50:10.5:1:3:3. The hydrothermal reaction was performed at 180°C for 12 hours. After hydrothermal reaction, the product was filtered and dried in an oven at 60°C for 24 hours. The carbonization temperature was 650°C for 6 hours.

[0026] The sample Si@LSO@C in this example was analyzed by X-ray diffraction (XRD), and the diffraction peaks of silicon and lithium silicate were detected. The XRD spectrum is shown in Figure 1 In addition, the transmission electron microscope (TEM) analysis of the Si@LSO@C sample of this embodiment shows that a carbon coating layer with a thickness of about 25 nm is generated on the silicon surface. The TEM image is shown in Figure 2 .

[0027] Example 2

[0028] 5 g of nanosilicon (particle size D50 between 10-500 nm) was added to a hydrothermal reactor containing 100 g of water. After stirring with a magnetic stirrer for 30 minutes, 1.05 g of potassium permanganate, 0.1 g of lithium carbonate, and 0.3 g of sucrose (carbon source) were added. Additives and auxiliary materials included 0.1 g of cetyltrimethylammonium bromide (CTAB), 0.1 g of polyvinylpyrrolidone (PVP), and 0.1 g of oxalic acid (H2C2O2). The ratio of silicon: oxidant: lithium source: carbon source: additives and auxiliary materials was 50:10.5:1:3:3. The hydrothermal reaction temperature was 180°C for 12 hours. After hydrothermal reaction, the product was filtered and dried in an oven at 60°C for 24 hours. The carbonization temperature was 650°C for 6 hours.

[0029] Example 3

[0030] 5 g of micronized silicon (particle size D50 between 1 and 20 μm) was added to a hydrothermal reactor containing 100 g of water. After stirring with a magnetic stirrer for 30 minutes, 3 g of 35 wt.% hydrogen peroxide solution and 0.1 g of lithium carbonate were added, along with 0.3 g of glucose and 0.3 g of cetyltrimethylammonium bromide (CTAB) as carbon sources. The silicon:oxidant:lithium source:carbon source:additives and auxiliary materials ratio was 50:10.5:1:3:3. The hydrothermal reaction was carried out at 180°C for 12 hours. After hydrothermal reaction, the product was filtered and dried in an oven at 60°C for 24 hours. The carbonization temperature was 650°C for 6 hours.

[0031] Example 4

[0032] 5 g of micronized silicon (particle size D50 between 1 and 20 μm) was added to a hydrothermal reactor containing 100 g of water. After stirring with a magnetic stirrer for 30 minutes, 1 g of 35 wt.% hydrogen peroxide solution and 0.05 g of lithium carbonate were added, along with 0.1 g of glucose as a carbon source. Additives included 0.1 g of cetyltrimethylammonium bromide (CTAB), 0.1 g of polyvinylpyrrolidone (PVP), and 0.1 g of oxalic acid (H₂C₂O₂). The ratio of silicon: oxidant: lithium source: carbon source: additives was 50:3.5:0.5:1:3. The hydrothermal reaction was performed at 180°C for 12 hours. After hydrothermal reaction, the product was filtered and dried in an oven at 60°C for 24 hours. The carbonization temperature was 650°C for 6 hours.

[0033] Example 5

[0034] 5 g of micronized silicon (particle size D50 between 1 and 20 μm) was added to a hydrothermal reactor containing 100 g of water. After stirring with a magnetic stirrer for 30 minutes, 1 g of a 35 wt.% hydrogen peroxide solution and 0.05 g of lithium carbonate were added, along with 0.1 g of glucose as a carbon source. Additives and auxiliary materials included 0.1 g of cetyltrimethylammonium bromide (CTAB) and 0.1 g of polyvinylpyrrolidone (PVP). The ratio of silicon: oxidant: lithium source: carbon source: additives and auxiliary materials was 50:3.5:0.5:1:2. The hydrothermal reaction was carried out at 180°C for 12 hours. After hydrothermal reaction, the product was filtered and dried in an oven at 60°C for 24 hours. The carbonization temperature was 650°C for 6 hours.

[0035] Example 6

[0036] 5 g of micronized silicon (particle size D50 between 1 and 20 μm) was added to a hydrothermal reactor containing 100 g of water. After magnetic stirring for 30 minutes, 3 g of 35 wt.% hydrogen peroxide solution and 0.1 g of lithium carbonate were added, along with 0.3 g of glucose as a carbon source. Additives included 0.1 g of cetyltrimethylammonium bromide (CTAB), 0.1 g of polyvinylpyrrolidone (PVP), and 0.1 g of oxalic acid (H₂C₂O₂). The ratio of silicon: oxidant: lithium source: carbon source: additives was 50:10.5:1:3:3. The hydrothermal reaction was carried out at 200°C for 16 hours. After hydrothermal reaction, the product was filtered and dried in an oven at 60°C for 24 hours. The carbonization temperature was 850°C for 12 hours.

[0037] Example 7

[0038] The samples of Examples 1-6 were subjected to button cell tests to evaluate their capacity and charge-discharge cycle characteristics. The button cell preparation steps for all samples in the present invention are as follows: the active material, acetylene black (CB) and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 70:20:10 and dissolved in N-methylpyrrolidone (NMP) to form a slurry. Subsequently, the slurry is evenly coated on the surface of the copper foil and dried in a vacuum environment for 12 hours. Metal lithium foil is used as the negative electrode, and a polypropylene separator (PP, 20 microns) and an electrolyte (the solvent ratio is DMC:EMC:EC=5:3:2, the LiPF6 concentration is 1.1M, and FEC accounts for 1.5% of the total volume of the electrolyte) are assembled into a 2025-type button cell. When performing the charge and discharge test, the current density is set to 1 A / g and the voltage window is set between 0.01 and 1.5V. The test results are shown in Figure 3 Compared with other embodiments, the material cycle stability of embodiment 1 is significantly improved.

[0039] Comparative Example 1

[0040] The reaction materials were similar to those in Example 1, except that no oxidant was added. Specifically, 5 grams of micronized silicon (particle size D50 between 1 and 20 μm) was added to a hydrothermal reactor containing 100 grams of water. After stirring with a magnetic stirrer for 30 minutes, 0.1 grams of battery-grade lithium source Li2CO3 and 0.3 grams of glucose as a carbon source were added. Additives and auxiliary materials included 0.1 grams of cetyltrimethylammonium bromide (CTAB), 0.1 grams of polyvinylpyrrolidone (PVP), and 0.1 grams of oxalic acid (H2C2O2). The ratio of silicon: oxidant: lithium source: carbon source: additives and auxiliary materials was 50:10.5:1:3:3. The hydrothermal reaction temperature was 180°C for 12 hours. After hydrothermal reaction, the mixture was filtered and dried in an oven at 60°C for 24 hours. The carbonization temperature was 850°C for 12 hours.

[0041] Comparative Example 2

[0042] The reaction materials were similar to those in Example 1, except that no auxiliary materials were added. Specifically, 5 grams of micronized silicon (particle size D50 between 1 and 20 μm) was added to a hydrothermal reactor containing 100 grams of water. 3 grams of a 35 wt.% hydrogen peroxide solution was then added. After stirring with a magnetic stirrer for 30 minutes, 0.1 grams of lithium carbonate and 0.3 grams of glucose, a carbon source, were added. The ratio of silicon: oxidant: lithium source: carbon source: additives and auxiliary materials was 50:10.5:1:3:3. The hydrothermal reaction temperature was 180°C for 12 hours. After hydrothermal reaction, the mixture was filtered and dried in an oven at 60°C for 24 hours. The carbonization temperature was 850°C for 12 hours.

[0043] Comparative Example 3

[0044] The reaction materials were similar to those in Example 1, except that no lithium source was added. Specifically, 5 grams of micronized silicon (particle size D50 between 1 and 20 μm) was added to a hydrothermal reactor containing 100 grams of water. 3 grams of a 35 wt.% hydrogen peroxide solution was then added. After stirring with a magnetic stirrer for 30 minutes, 0.3 grams of glucose (carbon source) and 0.1 grams of additives (cetyltrimethylammonium bromide (CTAB), 0.1 grams of polyvinylpyrrolidone (PVP), and 0.1 grams of oxalic acid (H₂C₂O₂)) were added. The ratio of silicon:oxidant:lithium source:carbon source:additives was 50:10.5:1:3:3. The hydrothermal reaction was performed at 180°C for 12 hours. After hydrothermal reaction, the mixture was filtered and dried in an oven at 60°C for 24 hours. The carbonization temperature was 850°C for 12 hours.

[0045] Comparative Example 4

[0046] The reaction ingredients were similar to those in Example 1, except that no carbon source was added. Specifically, 5 grams of micronized silicon (particle size D50 between 1 and 20 μm) was added to a hydrothermal reactor containing 100 grams of water. 3 grams of a 35 wt.% hydrogen peroxide solution (oxidant) was then added and stirred with a magnetic stirrer for 30 minutes. 0.1 grams of lithium carbonate and auxiliary additives included 0.1 grams of cetyltrimethylammonium bromide (CTAB), 0.1 grams of polyvinylpyrrolidone (PVP), and 0.1 grams of oxalic acid (H₂C₂O₂). The ratio of silicon: oxidant: lithium source: carbon source: auxiliary additive was 50:10.5:1:3:3. The hydrothermal reaction temperature was 180°C for 12 hours. After hydrothermal reaction, the product was filtered and dried in an oven at 60°C for 24 hours. The carbonization temperature was 850°C for 12 hours.

Claims

1. A method for preparing a lithium silicate in-situ modified silicon negative electrode material, characterized in that: The silicon raw material is mixed with an oxidant, a lithium source, a carbon source, and an additive auxiliary material, followed by a hydrothermal reaction, and finally subjected to high-temperature carbonization to obtain a lithium silicate in-situ modified silicon-carbon composite negative electrode material. The composite material is composed of a silicon core and a carbon shell modified with lithium silicate in-situ, and a carbon coating layer with a thickness of 20-30 nm is formed on the silicon surface; the composite material has characteristic peaks at approximately 24°, approximately 24.5°, approximately 25°, approximately 28°, and approximately 44°; The silicon raw material includes micron silicon, nano silicon powder, or a mixture of micron silicon and nano silicon powder; The oxidant includes one or a combination of hydrogen peroxide, potassium permanganate, and potassium perchlorate oxidants; The additive excipients include one or more of cetyltrimethylammonium bromide, polyvinylpyrrolidone, and oxalic acid; The hydrothermal reaction temperature is between 101-300°C; the reaction time is between 8-48 hours; The high-temperature carbonization temperature is between 550-850° C.; and the reaction time is between 3-48 hours.

2. The method for preparing a lithium silicate in-situ modified silicon negative electrode material according to claim 1, characterized in that: The mass ratio of silicon: oxidant: lithium source: carbon source: additive auxiliary material is (50~95): (0.1~20): (0.1-10): (0.1-50): (1~10).

3. The method for preparing a lithium silicate in-situ modified silicon negative electrode material according to claim 1, characterized in that: The lithium source includes one or more of lithium hydroxide, lithium acetate, and lithium carbonate; The carbon source includes one or more of glucose, sucrose, chitosan and asphalt.

4. The method for preparing a lithium silicate in-situ modified silicon negative electrode material according to claim 1, wherein: The hydrothermal reaction temperature is between 150-199° C.; the reaction time is between 10-24 hours.

5. The method for preparing a lithium silicate in-situ modified silicon negative electrode material according to claim 1, characterized in that: The high-temperature carbonization reaction time is between 5 and 12 hours.

6. A lithium-ion battery, characterized in that: The invention relates to a silicon negative electrode material in situ modified with lithium silicate prepared by the method according to any one of claims 1 to 5.

7. A button battery, characterized in that: The invention relates to a silicon negative electrode material in situ modified with lithium silicate prepared by the method according to any one of claims 1 to 5.

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