A modified high-initial-efficiency silicon-oxygen negative electrode material and its preparation method

Abstract

The present invention discloses a modified high-first-efficiency silicon-oxygen negative electrode material, comprising silicon oxide and pre-lithium silicon oxide, an intermediate protective layer, and a conductive layer distributed sequentially from the inside to the outside; the present invention also discloses a preparation method for the modified high-first-efficiency silicon-oxygen negative electrode material, specifically: dissolving a nano-compound and a dispersant in ethanol, adding a high-first-efficiency silicon-oxygen negative electrode precursor, stirring, spray drying, and roasting, then adding to an ethanol-graphene G dispersion, ultrasonically stirring, spray drying, and roasting to obtain the modified high-first-efficiency silicon-oxygen negative electrode material. The mutual combination of the nano-compound and the dispersant is beneficial for more uniform coating, avoiding contact between the nano-silicon generated on the surface of the material during the pre-lithium process and water, thereby stabilizing the slurry, and the dispersant plays the role of providing a partial carbon source and fixing the nano-compound; the graphene layer coated on the surface of the material significantly improves the electrical and thermal conductivity of the material, which is beneficial to the electrochemical performance of the material.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage and lithium-ion battery materials, and particularly relates to a modified high-initial-efficiency silicon-oxygen negative electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are widely used in energy storage and new energy fields due to their good environmental compatibility, long cycle life and low self-discharge rate. In order to meet the power requirements of high capacity and long endurance, the development of advanced electrode materials has been widely studied. Silicon oxide is considered to be one of the most promising high-energy density electrode materials due to its high specific capacity. However, the application of silicon oxide negative electrode materials in actual lithium-ion batteries is hindered by its low initial coulombic efficiency. Silicon oxide generates lithium oxide and lithium silicate in situ during the initial lithiation process. The generated lithium salt can act as a buffer to alleviate the large volume change of silicon oxide materials during long-term cycling. However, during the initial lithiation process, the formation of lithium salt buffers will lead to irreversible consumption of lithium ions, resulting in lithium-ion batteries with low initial coulombic efficiency and low energy density.

[0003] Pre-lithiation technology is considered one of the means to address the low initial coulombic efficiency of silicon oxide. Currently, chemical pre-lithiation, electrochemical pre-lithiation, doping with lithium additives, and direct contact with lithium are methods to improve the initial coulombic efficiency of lithium-ion batteries. Among them, high-initial efficiency silicon-oxygen anode materials can be obtained by mixing silicon oxide with lithium compounds and calcining them at high temperatures; or silicon oxide can be placed in an organic solvent containing lithium compounds to improve its initial coulombic efficiency.

[0004] However, because silicon oxide is modified with lithium or lithium compounds during pre-lithiation, a volume change occurs during the formation of silicate, destroying the carbon coating and exposing the silicate. The exposed silicate (Li2SiO3) is soluble in water, which can cause the slurry to be too alkaline during the conventional negative electrode water system homogenization process, thereby affecting the coating quality. Furthermore, some nano-silicon is generated during the pre-lithiation process. The nano-silicon exposed in the silicate matrix can react with water to produce hydrogen, which also affects the homogenization coating quality of the material. In addition, the destruction of the carbon coating and the formation of silicate on the material surface will increase the material resistivity. The above reasons have greatly hindered the large-scale application of pre-lithiation silicon oxide negative electrode materials. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a modified high-first-efficiency silicon-oxygen negative electrode material, which solves the problems of high resistivity and poor slurrying stability of existing high-first-efficiency silicon-oxygen negative electrode materials.

[0006] Another object of the present invention is to provide a modified high-first-efficiency silicon-oxygen negative electrode material prepared by the above preparation method.

[0007] The technical solution adopted by the present invention is a modified high-first-efficiency silicon-oxygen negative electrode material, including silicon oxide and pre-lithium silicon oxide, an intermediate protective layer and a conductive layer distributed in sequence from the inside to the outside; the silicon oxide and pre-lithium silicon oxide include silicon monoxide, silicon and lithium silicate; the lithium silicate is Li2SiO3, Li2Si2O5 or a mixture of the above two; the intermediate protective layer is a composite layer of an organic carbon layer and a nano-compound formed after high-temperature calcination of the nano-compound and the dispersant; the conductive layer is a graphene coating layer.

[0008] Another technical solution adopted by the present invention is a method for preparing a modified high-initial-efficiency silicon-oxygen negative electrode material, which is specifically implemented according to the following steps:

[0009] Step 1: dissolving the nanocompound and the dispersant in ethanol, then adding the high-first-efficiency silicon-oxygen anode precursor to form a dispersed slurry, stirring evenly, spray drying the slurry, and then calcining the slurry under protective gas to obtain a high-first-efficiency silicon-oxygen anode intermediate;

[0010] Step 2: Add the high first-efficiency silicon-oxygen negative electrode intermediate to the ethanol-graphene G dispersion to prepare a silicon-oxygen-graphene spray slurry, spray-dry it after ultrasonic stirring, and then calcine it under protective gas to obtain a modified high first-efficiency silicon-oxygen negative electrode material.

[0011] The present invention is also characterized in that:

[0012] In step 1, the nanocompound is any one or more of aluminum oxide, zirconium oxide, and titanium dioxide; and the dispersant is any one or more of polymethyl methacrylate, polyvinyl pyrrolidone, and dopamine.

[0013] In step 1, the mass ratio of the high first-effect silicon oxide precursor, the nanocompound and the dispersant is 1:0.001-0.1:0.05-0.5.

[0014] In step 1, the protective gas is an inert gas or nitrogen; the roasting temperature is 450-700° C.; and the roasting holding time is 1-10 hours.

[0015] In step 2, the ethanol-graphene G dispersion is prepared by mixing ethanol and graphene G; the graphene G is graphene or graphene oxide.

[0016] In step 2, the mass ratio of the high first-efficiency silicon-oxygen negative electrode intermediate to graphene G is 1:0.005-0.2; and the ultrasonic stirring time is 5-180 min.

[0017] In step 2, the protective gas is an inert gas or nitrogen; the roasting temperature is 400-700° C.; and the roasting holding time is 1-6 hours.

[0018] The beneficial effects of the present invention are that the modified high-first-efficiency silicon-oxygen negative electrode material provided by the present invention has the characteristics of low resistivity and good slurry stability; the preparation process adopts the combination of nano-compounds and dispersants, which is conducive to more uniform coating, avoids the contact of nano-silicon generated on the surface of the material during the pre-lithiation process with water, and makes the slurry stable, and the dispersant plays the role of providing part of the carbon source and fixing the nano-compound; the graphene layer coated on the surface of the material significantly improves the electrical and thermal conductivity of the material, which is beneficial to the electrochemical performance of the material; the process of the present invention is suitable for existing production and manufacturing equipment, and the process is simple, reliable, and easy to scale up, which is conducive to industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of a modified high first-efficiency silicon-oxygen negative electrode material of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] The present invention provides a modified high-initial-efficiency silicon-oxygen negative electrode material, such as Figure 1 As shown, it includes silicon oxide and pre-lithium silicon oxide 1-2, an intermediate protection layer 1-1 and a conductive layer 1-3 distributed sequentially from the inside to the outside;

[0022] Silicon oxides and pre-lithium silicon oxides include silicon monoxide, silicon, and lithium silicate salts;

[0023] The lithium silicate salt is Li2SiO3, Li2Si2O5 or a mixture of the two;

[0024] The middle protective layer is a composite layer of an organic carbon layer and a nano compound formed by calcining the nano compound and the dispersant at high temperature; the conductive layer is a graphene coating layer;

[0025] The present invention provides a method for preparing a modified high-initial-efficiency silicon-oxygen negative electrode material, which is specifically implemented according to the following steps:

[0026] Step 1: dissolving the nanocompound and the dispersant in ethanol, then adding the high-first-efficiency silicon-oxygen anode precursor to form a dispersed slurry, stirring evenly, spray drying the slurry, and then calcining the slurry under protective gas to obtain a high-first-efficiency silicon-oxygen anode intermediate;

[0027] The nanocompound is any one or more of aluminum oxide, zirconium oxide, and titanium dioxide;

[0028] The dispersant is any one or more of polymethyl methacrylate, polyvinyl pyrrolidone, and dopamine;

[0029] The solid content in the dispersed slurry is 1 to 50%;

[0030] The high first-efficiency silicon-oxygen negative electrode precursor is prepared by pre-lithiation by high-temperature calcination of silicon dioxide and lithium compounds, or pre-lithiation by liquid phase environment of silicon dioxide and aromatic lithium compounds, or by pre-lithiation by half-cell-like electrochemical method;

[0031] The mass ratio of the high first-effect silicon oxide precursor, the nano compound and the dispersant is 1:0.001-0.1:0.05-0.5;

[0032] The protective gas is inert gas or nitrogen; the roasting temperature is 450-700°C; the roasting holding time is 1-10 hours;

[0033] Step 2: adding the high first-efficiency silicon-oxygen anode intermediate to the ethanol-graphene G dispersion to prepare a silicon-oxygen-graphene spray slurry, spray-drying the slurry after ultrasonic stirring, and then calcining the slurry under protective gas to obtain a modified high first-efficiency silicon-oxygen anode material;

[0034] The solid content of the silicon-graphene spray slurry is 1 to 50%;

[0035] The ethanol-graphene G dispersion is prepared by mixing ethanol and graphene G; the graphene G is graphene or graphene oxide;

[0036] The mass ratio of the high first-efficiency silicon-oxygen negative electrode intermediate to graphene G is 1:0.005-0.2;

[0037] Ultrasonic stirring time is 5 to 180 minutes;

[0038] The protective gas is an inert gas or nitrogen; the roasting temperature is 400-700°C; and the roasting holding time is 1-6 hours.

[0039] Example 1

[0040] The present invention provides a method for preparing a modified high-initial-efficiency silicon-oxygen negative electrode material, which is specifically implemented according to the following steps:

[0041] Nano-zirconia and polyvinyl pyrrolidone were dissolved in ethanol, and then a high-first-efficiency silicon-oxygen anode precursor was added to form a dispersed slurry. The mass ratio of the high-first-efficiency silicon-oxygen anode precursor, nano-zirconia, and polyvinyl pyrrolidone was 1:0.05:0.5. The solid content was adjusted to 25%. After stirring evenly, the mixture was spray-dried and then calcined at 680°C for 3.5 hours under an argon atmosphere to obtain a high-first-efficiency silicon-oxygen anode intermediate.

[0042] A high-first-efficiency silicon-oxygen anode intermediate was added to an ethanol-based graphene dispersion to prepare a silicon-oxygen-graphene spray slurry. The mass ratio of the high-first-efficiency silicon-oxygen anode intermediate to graphene was 1:0.01, and the solid content was adjusted to 20%. After ultrasonic stirring for 120 minutes, the slurry was spray-dried and then calcined at 400°C for 1 hour under an argon atmosphere to obtain a modified high-first-efficiency silicon-oxygen anode material.

[0043] The modified high-first-efficiency silicon-oxygen negative electrode material was used to prepare a button battery with metallic lithium as the electrode. By observing the first-week charge and discharge curve, the initial coulomb efficiency was 90.3%, the gram capacity was 1480 mAh / g, and the slurry had good stability after homogenization.

[0044] Example 2

[0045] The present invention provides a method for preparing a modified high-initial-efficiency silicon-oxygen negative electrode material, which is specifically implemented according to the following steps:

[0046] Nano-alumina and polyvinyl pyrrolidone were dissolved in ethanol, and then a high-first-efficiency silicon-oxygen anode precursor was added to form a dispersed slurry. The mass ratio of the high-first-efficiency silicon-oxygen anode precursor, nano-alumina, and polyvinyl pyrrolidone was 1:0.001:0.5. The solid content was adjusted to 10%. After stirring evenly, the mixture was spray-dried and then calcined at 700°C for 1 hour under a nitrogen atmosphere to obtain a high-first-efficiency silicon-oxygen anode intermediate.

[0047] A high-first-efficiency silicon-oxygen anode intermediate was added to an ethanol-based graphene dispersion to prepare a silicon-oxygen-graphene spray slurry. The mass ratio of the high-first-efficiency silicon-oxygen anode intermediate to graphene was 1:0.2, and the solid content was adjusted to 50%. After ultrasonic stirring for 180 minutes, the slurry was spray-dried and then calcined at 700°C under a nitrogen atmosphere for 6 hours to obtain a modified high-first-efficiency silicon-oxygen anode material.

[0048] The modified high-first-efficiency silicon-oxygen negative electrode material was used to prepare a button battery with metallic lithium as the electrode. By observing the first-week charge and discharge curve, the initial coulomb efficiency was 90.0%, the gram capacity was 1405 mAh / g, and the slurry had good stability after homogenization.

[0049] Example 3

[0050] The present invention provides a method for preparing a modified high-initial-efficiency silicon-oxygen negative electrode material, which is specifically implemented according to the following steps:

[0051] Nano-alumina and polymethyl methacrylate were dissolved in ethanol, and then a high-first-efficiency silicon-oxygen anode precursor was added to form a dispersed slurry. The mass ratio of the high-first-efficiency silicon-oxygen anode precursor, nano-alumina, and polymethyl methacrylate was 1:0.01:0.1. The solid content was adjusted to 50%. After stirring evenly, the mixture was spray-dried and then calcined at 600°C for 2.5 hours under an argon atmosphere to obtain a high-first-efficiency silicon-oxygen anode intermediate.

[0052] A high-first-efficiency silicon-oxygen anode intermediate was added to an ethanol-based graphene oxide dispersion to prepare a silicon-oxygen-graphene spray slurry. The mass ratio of the high-first-efficiency silicon-oxygen anode intermediate to graphene oxide was 1:0.005, and the solid content was adjusted to 1%. After ultrasonic stirring for 5 minutes, the slurry was spray-dried and then calcined at 600°C for 1 hour under an argon atmosphere to obtain a modified high-first-efficiency silicon-oxygen anode material.

[0053] The modified high-first-efficiency silicon-oxygen negative electrode material was used to prepare a button battery with metallic lithium as the electrode. By observing the first-week charge and discharge curve, the initial coulomb efficiency was 90.8%, the gram capacity was 1462 mAh / g, and the slurry had good stability after homogenization.

[0054] Example 4

[0055] The present invention provides a method for preparing a modified high-initial-efficiency silicon-oxygen negative electrode material, which is specifically implemented according to the following steps:

[0056] Nano-titanium dioxide and dopamine were dissolved in ethanol, and then a high-first-efficiency silicon-oxygen negative electrode precursor was added to form a dispersed slurry. The mass ratio of the high-first-efficiency silicon-oxygen negative electrode precursor, nano-titanium dioxide, and dopamine was 1:0.1:0.05. The solid content was adjusted to 1%. After stirring evenly, the mixture was spray-dried and then calcined at 450°C for 10 hours under a nitrogen atmosphere to obtain a high-first-efficiency silicon-oxygen negative electrode intermediate.

[0057] A high-first-efficiency silicon-oxygen anode intermediate was added to an ethanol-based graphene oxide dispersion to prepare a silicon-oxygen-graphene spray slurry. The mass ratio of the high-first-efficiency silicon-oxygen anode intermediate to graphene oxide was 1:0.03, and the solid content was adjusted to 18%. After ultrasonic stirring for 35 minutes, the slurry was spray-dried and then calcined at 550°C for 3.5 hours under an argon atmosphere to obtain a modified high-first-efficiency silicon-oxygen anode material.

[0058] The modified high-first-efficiency silicon-oxygen negative electrode material was used to prepare a button battery with metallic lithium as the electrode. By observing the first-week charge and discharge curve, the initial coulomb efficiency was 90.2%, the gram capacity was 1457 mAh / g, and the slurry had good stability after homogenization.

[0059] Comparative Example 1

[0060] Nano-alumina and polyvinyl pyrrolidone were dissolved in ethanol, and then a high-first-efficiency silicon-oxygen anode precursor was added to form a dispersed slurry. The mass ratio of the high-first-efficiency silicon-oxygen anode precursor, nano-alumina, and polyvinyl pyrrolidone was 1:0.001:0.5. The solid content was adjusted to 10%. After stirring evenly, the mixture was spray-dried and then calcined at 700°C for 1 hour under a nitrogen atmosphere to obtain a modified high-first-efficiency silicon-oxygen anode material.

[0061] The modified high-first-efficiency silicon-oxygen negative electrode material was used to prepare a button battery with metallic lithium as the electrode. By observing the first-week charge and discharge curve, the initial coulomb efficiency was 90.2%, the gram capacity was 1411 mAh / g, and the slurry had good stability after homogenization.

[0062] Comparative Example 2

[0063] A high-first-efficiency silicon oxide precursor was added to an ethanol-based single-walled graphene dispersion to prepare a silicon oxide-graphene spray slurry. The mass ratio of the high-first-efficiency silicon oxide negative electrode intermediate to graphene was 1:0.01, and the solid content was adjusted to 20%. After ultrasonic stirring for 120 minutes, the mixture was spray-dried and then calcined at 680°C for 2.5 hours under an argon atmosphere to obtain a modified high-first-efficiency silicon oxide negative electrode material.

[0064] The modified high-first-efficiency silicon-oxygen negative electrode material was used to prepare a button battery with metallic lithium as the electrode. By observing the first-week charge and discharge curves, the initial coulombic efficiency was 90.2%, the gram capacity was 1493 mAh / g, and the slurry stability was poor after homogenization.

[0065] Comparative Example 3

[0066] A button battery with metallic lithium as the counter electrode was made using a high-initial-efficiency silicon-oxygen precursor. By observing the charge-discharge curve in the first week, the initial coulombic efficiency was 90.1%, the gram capacity was 1445 mAh / g, and the slurry stability was poor after homogenization.

[0067] It can be seen from Table 1 that, compared with Examples 1 to 5, after the material is modified, the pH of the slurry is significantly reduced, the gas production is small or no gas is produced, and the resistivity is significantly lower; compared with Example 2 and Comparative Examples 1 to 3, it can be clearly found that the intermediate protective layer coating can significantly improve the slurry stability, and the conductive layer coating significantly reduces the material resistivity.

[0068] Table 1 Example material performance test results

[0069]

[0070]

[0071] Note: "Gushing" means that the slurry produces a large amount of gas in the container within 12 hours after slurrying, causing the liquid level to rise significantly.

[0072] The modified high-first-efficiency silicon-oxygen negative electrode material of the present invention adds a dispersant and a nano-compound in the middle protective layer to isolate the nano-silicon on the surface of the material from water and improve the stability of the material slurry; the function of the dispersant is to improve the dispersibility of the nano-compound and make the coating uniform. In addition, the dispersant can form organic carbon after calcination, which can fix the nano-compound and prevent it from falling off easily; the function of the nano-compound is to fill the defects of the carbon layer on the surface of the material and prevent the nano-silicon on the surface of the material from reacting with water.

Claims

1. A modified high first-efficiency silicon-oxygen negative electrode material, characterized in that: The invention comprises silicon oxide and pre-lithium silicon oxide, an intermediate protective layer and a conductive layer distributed sequentially from the inside to the outside; the silicon oxide and pre-lithium silicon oxide comprise silicon monoxide, silicon and lithium silicate; the lithium silicate is Li2SiO3, Li2Si2O5 or a mixture of the two above; The intermediate protective layer is a composite layer of an organic carbon layer and a nano compound formed by calcining the nano compound and the dispersant at high temperature; the conductive layer is a graphene coating layer; The preparation method of the modified high-first-efficiency silicon-oxygen negative electrode material is specifically implemented according to the following steps: Step 1: dissolving the nanocompound and the dispersant in ethanol, then adding the high-first-efficiency silicon-oxygen anode precursor to form a dispersed slurry, stirring evenly, spray drying the slurry, and then calcining the slurry under protective gas to obtain a high-first-efficiency silicon-oxygen anode intermediate; The nanocompound is any one or more of aluminum oxide, zirconium oxide, and titanium dioxide; the dispersant is any one or more of polymethyl methacrylate, polyvinyl pyrrolidone, and dopamine; The protective gas is inert gas or nitrogen; the roasting temperature is 450~700℃; the roasting holding time is 1~10h; Step 2: adding the high first-efficiency silicon-oxygen anode intermediate to the ethanol-graphene G dispersion to prepare a silicon-oxygen-graphene spray slurry, spray-drying the slurry after ultrasonic stirring, and then calcining the slurry under protective gas to obtain a modified high first-efficiency silicon-oxygen anode material; The ethanol-graphene G dispersion is prepared by mixing ethanol and graphene G; the graphene G is graphene or graphene oxide; The protective gas is inert gas or nitrogen; the roasting temperature is 400~700℃; and the roasting holding time is 1~6h.

2. The modified high first-efficiency silicon-oxygen negative electrode material according to claim 1, characterized in that: In the step 1, the mass ratio of the high first-efficiency silicon oxide precursor, the nanocompound, and the dispersant is 1: 0.001-0.1: 0.05-0.

5.

3. The modified high first-efficiency silicon-oxygen negative electrode material according to claim 1, characterized in that: In the step 2, the mass ratio of the high first-efficiency silicon-oxygen negative electrode intermediate to the graphene G is 1:0.005-0.2; and the ultrasonic stirring time is 5-180 min.

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