CN116364878A - Silicon-based negative electrode material, preparation method of silicon-based negative electrode material and secondary battery - Google Patents
Silicon-based negative electrode material, preparation method of silicon-based negative electrode material and secondary battery Download PDFInfo
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- CN116364878A CN116364878A CN202211671725.4A CN202211671725A CN116364878A CN 116364878 A CN116364878 A CN 116364878A CN 202211671725 A CN202211671725 A CN 202211671725A CN 116364878 A CN116364878 A CN 116364878A
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- silicon
- lithium
- anode material
- carbon
- compound
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Abstract
The invention relates to the technical field of battery materials, and discloses a silicon-based negative electrode material, a preparation method of the silicon-based negative electrode material and a secondary battery. The silicon-based anode material comprises a silicon-based core and a coating layer. The silicon-based inner core comprises nano silicon and a lithium silicon oxide compound, and the coating layer at least comprises a compound with a chemical formula of aLi 2 O·MO b ·cSiO 2 Wherein a > 0, b > 0, c > 0. The preparation method of the silicon-based negative electrode material comprises the steps of preparing a pre-lithium silicon-based material and modifying and coating. The silicon-based anode material comprises a glass-like phase aLi 2 O·MO b ·cSiO 2 Can isolate water from reacting with the lithium silicon oxide compound in the silicon-based core and improve the processing performance of the material.
Description
Technical Field
The invention relates to the technical field of battery materials, in particular to a silicon-based negative electrode material, a preparation method of the silicon-based negative electrode material and a secondary battery.
Background
In secondary batteries, graphite has not been able to meet the demand for high energy density as a widely used negative electrode material. The silicon oxide material is one of the current solutions as a new generation of secondary battery negative electrode. The silica materials have a relatively high gram capacity (. Gtoreq.2000 mAh/g) and a relatively low expansion ratio (. Gtoreq.160%), but still suffer from a number of problems.
In a silicon oxide material, a higher oxygen content reduces the cyclic expansion of the material, but a large amount of lithium ions are consumed in the lithiation process, resulting in a reduction in the initial efficiency of the material. In addition, the low conductivity of the silicon oxide material leads to poor dynamic performance of the material and restricts the rate performance of the material.
In the existing solutions, pre-lithiation can raise the first effect of the silica material, but also brings about the corresponding negative effects, firstly that there are residual incompletely reacted reducing substances (e.g. lithium metal, lithium compounds, etc.) present during the pre-lithiation, most of which can be removed by washing, but still a small part remains in the material. Secondly, the metal silicate is partially soluble in water during contact with water and is strongly alkaline. These two problems will lead to a high residual alkali value in the material, and a high pH value is presented in the aqueous homogenate system, which will cause the slurry to settle, and affect the processability of the material. The residual alkali content in lithium ion battery systems also deteriorates the cycle performance of the material. Secondly, after the metal silicate is dissolved in water, the active nano silicon in the silicon oxide reacts with the water to generate gas, and the reversible capacity of the material is reduced.
Therefore, there is an urgent need to develop a silicon-based material with good processability, excellent cycle stability and rate capability, and low residual alkali content, and a preparation method thereof.
Disclosure of Invention
In view of the foregoing, an object of the present invention is to provide a silicon-based anode material and a method for producing the silicon-based anode material. The silicon-based anode material can effectively isolate the lithium silicon oxide compound in the silicon-based inner core from being dissolved in water to present strong alkalinity, simultaneously keeps the pH of a system stable, inhibits the gas production behavior of the material, avoids the slurry sedimentation in the water system homogenization process, thereby improving the processing performance of the material, and has higher reversible capacity, first coulombic efficiency and cycle performance.
To achieve the above object, a first aspect of the present invention provides a silicon-based anode material including a silicon-based core and a coating layer. The silicon-based inner core comprises nano silicon and a lithium silicon oxide compound, and the coating layer at least comprises a compound with a chemical formula of aLi 2 O·MO b ·cSiO 2 Wherein a > 0, b > 0, c > 0.
The silicon-based anode material comprises a silicon-based anode material with a chemical formula of aLi 2 O·MO b ·cSiO 2 Is coated with a coating layer. aLi 2 O·MO b ·cSiO 2 The glass-like phase compound is insoluble in water, can be used as a coating layer to isolate water from reacting with the silicon-oxygen lithium compound in the silicon-based core, prevents the silicon-oxygen lithium compound from dissolving in water to form a strong alkaline solution, and prevents nano silicon in the silicon-based core from reacting with water to generate gas, thereby improving the processing performance of the material.
In some embodiments, the nano-silicon has a grain size of 2nm to 20nm.
In some embodiments, the lithium siloxide compound comprises Li 2 SiO 3 、Li 2 Si 2 O 5 And Li (lithium) 4 SiO 4 At least one of them.
In some embodiments, M is selected from at least one of Al, ca, mg, zn, ba, cr, ti, ge, zr, sr, V, cu, fe, co, sn, Y, ge, gd and La.
In some embodiments, the silicon-based anode material has a median particle size of 2 μm to 15 μm.
In some embodiments, the silicon-based anode material has a specific surface area of 0.5m 2 /g to 5.0m 2 /g。
In some embodiments, li in the silicon-based anode material 2 CO 3 The content is less than or equal to 0.15wt percent, and the content of LiOH is less than or equal to 0.01wt percent.％。
In some embodiments, the moisture content of the silicon-based anode material is less than or equal to 0.10wt.%.
In some embodiments, the coating layer further includes a polymer of formula dLi 2 O·MO e Wherein d > 0, e > 0.dLi 2 O·MO e The lithium ion battery has the capability of rapidly conducting ions and electrons, can reduce the resistance in the lithium ion deintercalation process in the silicon-based anode material, and effectively improves the cycle performance and the multiplying power performance of the material.
In some embodiments, the coating layer includes a modified layer formed of compound a, in which compound B is dispersed.
In some embodiments, compound a comprises 0.01wt.% to 5.00wt.% of the silicon-based negative electrode material and compound B comprises 0.01wt.% to 1.00wt.% of the silicon-based negative electrode material.
In some embodiments, the sum of the M element in compound a and the M element in compound B is 0.1wt.% to 10.0wt.% of the silicon-based negative electrode material.
In some embodiments, the coating layer comprises a modified layer comprising compound a and a carbon coating layer surrounding the modified layer.
In some embodiments, the modified layer has a thickness of 20nm to 200nm.
In some embodiments, the carbon coating layer has a thickness of 5nm to 200nm.
In some embodiments, the carbon coating layer comprises 1wt.% to 20wt.% of the silicon-based negative electrode material.
The second aspect of the invention provides a preparation method of a silicon-based anode material, which comprises the steps of (I) and (II).
The step (I) of preparing the pre-lithium silicon-based material comprises the steps of mixing the silicon-based material with a lithium source, and performing a heat treatment reaction to obtain the pre-lithium silicon-based material, wherein the silicon-based material is SiO x Or carbon coated SiO x X is more than or equal to 0.5 and less than or equal to 1.5.
The step (II) of modifying and coating comprises the steps of mixing a solution containing a metal organic compound with a pre-lithium silicon-based material, drying to obtain a precursor with a metal hydroxide layer, and then carrying out heat treatment.
The preparation method of the silicon-based anode material has at least the following technical effects.
Firstly, the silicon-based material and a lithium source are subjected to heat treatment reaction, so that lithium enters the bulk phase of the silicon-based material to form a lithium silicon oxide compound, and the first coulomb efficiency of the material is improved.
Secondly, the metal organic compound is mixed with the pre-lithium silicon-based material in a solution form, namely, the liquid phase is coated on the surface of the pre-lithium silicon-based material, so that the metal organic compound can be uniformly adhered on the surface of the pre-lithium silicon-based material, then the metal organic compound can be decomposed by drying to form a uniform and compact metal hydroxide layer, finally, the metal hydroxide is converted into oxide by heat treatment and reacts with the silicon-oxygen lithium compound on the surface of the pre-lithium silicon-based material, and a glass-like phase aLi which is insoluble in water can be generated 2 O·MO b ·cSiO 2 (abbreviated as Li-M-Si-O).
Li-M-Si-O is insoluble in water and is tightly combined with the silicon-oxygen lithium compound in the silicon-based inner core to form an integrated structure, the water is isolated from reacting with the silicon-oxygen lithium compound in the silicon-based inner core, the silicon-oxygen lithium compound is prevented from being dissolved in the water to form a strong alkaline solution, and the nano silicon in the silicon-based inner core is prevented from reacting with the water to generate gas, so that the processing performance of the material is improved.
In some embodiments, the silicon-based material is carbon-coated SiO x And carbon-coated SiO x The medium carbon content accounts for 60wt.% to 100wt.% of the carbon content in the silicon-based anode material.
In some embodiments, the silicon-based material has a median particle size of 2 μm to 15 μm.
In some embodiments, the lithium source comprises at least one of lithium hydride, lithium nitride, lithium amide, lithium alkyl, and lithium metal.
In some embodiments, the lithium source comprises 5wt.% to 30wt.% of the silicon-based material.
In some embodiments, the temperature of the heat treatment in step (I) to prepare the pre-lithium silicon-based material is from 350 ℃ to 950 ℃.
In some embodiments, step (I) produces a pre-lithium silicon-based material for a time period of 2 hours to 24 hours.
In some embodiments, the heat treatment of step (I) to prepare the pre-lithium silicon-based material is performed under a non-oxidizing atmosphere comprising at least one of nitrogen, helium, neon, argon, krypton, and xenon.
In some embodiments, step (I) is followed by washing with a non-acidic solvent and drying to obtain a pre-lithium silicon-based material.
In some embodiments, li in the pre-lithium silicon-based material 2 CO 3 The content is more than or equal to 0.1wt.% and the LiOH content is more than or equal to 0.1wt.%. For example, li in the pre-lithium silicon-based material obtained after the heat treatment reaction in step (I) 2 CO 3 The content is more than or equal to 0.1wt.% and the LiOH content is more than or equal to 0.1wt.%. For example, li in the pre-lithium silicon-based material obtained by washing with a non-acidic solvent and drying after the heat treatment reaction in the step (I) 2 CO 3 The content is more than or equal to 0.1wt.% and the LiOH content is more than or equal to 0.1wt.%.
In some embodiments, the metal organic compound has the formula R-M, wherein M is selected from at least one of Al, ca, mg, zn, ba, cr, ti, ge, zr, sr, V, cu, fe, co, sn, Y, ge, gd and La, and M is selected from hydrocarbyl and/or alcoholic groups.
In some embodiments, the solution comprising the metal organic compound is prepared by dissolving the metal organic compound in an organic solvent.
In some embodiments, the solution comprising the metal organic compound is prepared by dissolving the metal organic compound in an organic solvent, and adding a templating agent to the organic solvent, the templating agent being a carboxylic acid or ester compound, the templating agent comprising 0.1wt.% to 5.0wt.% of the silicon-based material.
In some embodiments, the drying is spray drying, fluid bed drying, or agitation drying, and the temperature of the drying is above the decomposition temperature of the metal-organic compound.
In some embodiments, the temperature of the heat treatment in the modified coating of step (II) is 300 ℃ to 1000 ℃.
In some embodiments, the time for the heat treatment of the modified coating of step (II) is from 2 hours to 24 hours.
In some embodiments, the heat treatment of the modified clad of step (II) is performed under a protective atmosphere comprising at least one of nitrogen, helium, argon, neon, and xenon.
In some embodiments, the carbon coating is performed during the heat treatment of the modified coating of step (II), and the content of carbon element increased by the carbon coating is greater than 0 and less than or equal to 40wt.% of the carbon element in the silicon-based anode material.
The invention also provides application of the silicon-based anode material in anode materials. The silicon-based anode material is used as an anode active material, and can meet the use requirement of high energy density of electric tools.
The invention also provides a secondary battery, which comprises a positive electrode material and a negative electrode material, wherein the negative electrode material comprises the silicon-based negative electrode material or the silicon-based negative electrode material prepared by the preparation method of the silicon-based negative electrode material.
Drawings
FIG. 1 is a scanning electron microscope image of a silicon-based anode material of example 1;
fig. 2 is a scanning electron microscope image of the silicon-based anode material of comparative example 1.
Description of the embodiments
The silicon-based anode material can be used as an anode active material in secondary batteries (such as sodium ion batteries, lithium ion batteries or potassium ion batteries). The composite material can be used as a negative electrode active material alone or in combination with other negative electrode active materials (e.g., natural graphite, artificial graphite, soft carbon, hard carbon, etc.).
The silicon-based anode material comprises a silicon-based core and a coating layer. The median particle diameter of the silicon-based anode material is 2 μm to 15 μm, for example, 4 μm to 9 μm. As examples, the median particle diameter of the silicon-based anode material may be, but is not limited to, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm.
The specific surface area of the silicon-based anode material is 0.5m 2 /g to 5.0m 2 /g, e.g. 1.0m 2 /g to 4.0m 2 And/g. Acting asFor example, the specific surface area of the silicon-based anode material may be, but is not limited to, 0.5m 2 /g、1.0m 2 /g、1.1m 2 /g、1.2m 2 /g、1.3m 2 /g、1.4m 2 /g、1.5m 2 /g、1.8m 2 /g、2.0m 2 /g、2.5m 2 /g、3.0m 2 /g、3.5m 2 /g、4.0m 2 /g、4.5m 2 /g、5.0m 2 /g。
Li in silicon-based anode material 2 CO 3 The content is less than or equal to 0.15wt.%. As an example, li in a silicon-based anode material 2 CO 3 The content may be, but is not limited to, 0.15wt.%, 0.14wt.%, 0.13wt.%, 0.12wt.%, 0.11wt.%, 0.10wt.%, 0.08wt.%, 0.05wt.%, 0.02wt.%, 0.01wt.%, 0.005wt.%, 0. The LiOH content is less than or equal to 0.01wt.%, as an example, the LiOH content in the silicon-based negative electrode material may be, but is not limited to, less than or equal to 0.01wt.%, 0.008wt.%, 0.005wt.%, 0.003wt.%, 0.002wt.%, 0.001wt.%, 0.0005wt.%, 0.Li (Li) 2 CO 3 With LiOH in silicon-based anode materials as a by-product of the pre-lithiation process, which can adversely affect the material in subsequent use, e.g., li 2 CO 3 Is alkaline with LiOH dissolved in water, and affects the processing performance of the material in the water system homogenization process. In addition, li 2 CO 3 There is a risk of decomposition, and the generation of gas may lead to failure of the battery.
The moisture content of the silicon-based anode material is less than or equal to 0.10wt.%. As an example, the moisture content of the silicon-based anode material may be, but is not limited to, 0.10wt.%, 0.09wt.%, 0.08wt.%, 0.07wt.%, 0.06wt.%, 0.05wt.%, 0.04wt.%, 0.03wt.%, 0.02wt.%, 0.01wt.%, 0. In certain embodiments, the moisture content of the silicon-based anode material is less than or equal to 0.03wt.%. In certain embodiments, the moisture content of the silicon oxygen anode material is less than or equal to 0.03wt%.
The grain size of the nano silicon in the silicon-based core is 2nm to 20nm. By way of example, the grain size of the nano-silicon may be, but is not limited to, 2nm, 4nm, 6nm, 8nm, 10nm, 12nm, 14nm, 16nm, 18nm, 20nm. In certain embodiments, the nano-silicon has a grain size of 10nm or less.
Silica (Si-O)The lithium compound contains Li 2 SiO 3 、Li 2 Si 2 O 5 And Li (lithium) 4 SiO 4 At least one of them. In certain embodiments, the lithium siloxide compound comprises Li 2 SiO 3 Or Li (lithium) 2 SiO 3 And Li (lithium) 2 Si 2 O 5 Is a mixture of (a) and (b). The formation of lithium siloxide compounds results from the lithiation process and as the extent of lithium intercalation increases, the Li in the lithium siloxide compounds 2 Si 2 O 5 Can be converted into Li 2 SiO 3 ，Li 2 SiO 3 Can be converted into Li 4 SiO 4 。
The coating layer at least comprises a compound with a chemical formula of aLi 2 O·MO b ·cSiO 2 Wherein a > 0, b > 0, c > 0, e.g. 0<a≤3、0<b≤5、0<c is less than or equal to 5; or 0 (0)<a≤2、0<b≤4、0<c is less than or equal to 4; or 0 (0)<a≤2、0<b≤3、0<c is less than or equal to 3; or 0 (0)<a≤1、0<b≤3、0<c is less than or equal to 3; or 0 (0)<a≤1、0<b≤2、0<c is less than or equal to 2; or 0 (0)<a≤1、0<b≤1、0<c is less than or equal to 1; the time and temperature of the heat treatment will have an effect on them. M is selected from at least one of Al, ca, mg, zn, ba, cr, ti, ge, zr, sr, V, cu, fe, co, sn, Y, ge, gd and La. In certain embodiments, M is Al, a compound aLi 2 O·MO b ·cSiO 2 Is aLi 2 O·AlO 3/2 ·cSiO 2 。
The coating layer also comprises a chemical formula dLi 2 O·MO e (abbreviated as Li-M-O) wherein d > 0, e > 0, e.g. 0<d≤3、0<e is less than or equal to 5; or 0 (0) <d≤2、0<e is less than or equal to 4; or 0 (0)<d≤2、0<e is less than or equal to 3; or 0 (0)<d≤2、0<e is less than or equal to 2; or 0 (0)<d≤1、0<e is less than or equal to 2; or 0 (0)<d≤1、0<e is less than or equal to 1; the time and temperature of the heat treatment will have an effect on them. Li-M-O belongs to a fast ion conductor, can rapidly conduct ions, improves the ion conductivity of the material and improves the rate capability of the material. Li-M-O is derived from residual alkali (Li 2 CO 3 LiOH) and metal M oxide. The uniformity of Li-M-O depends on the residual alkali distribution on the surface of the pre-lithiated silicon-based material,the formation of the residual alkali and the formation of the silicon-oxygen lithium compound are synchronous, so that the residual alkali is uniformly distributed on the surface of the silicon-oxygen lithium compound. After the solid-phase heat treatment reaction, the finally formed Li-M-O is uniformly distributed in the Li-M-Si-O to form a modified layer, and the distribution can ensure that the silicon-based anode material has consistent electronic conductivity and ion conductivity in all directions, ensure consistent deintercalation depth of Li in all directions in the circulation process, and is beneficial to improving the circulation performance of the material. In certain embodiments, M is Al, i.e., compound dLi 2 O·MO e dLi of a shape of dLi 2 O·AlO 3/2 。
As an embodiment of the present invention, compound a constitutes 0.01wt.% to 5.00wt.% of the silicon-based anode material. As examples, compound a constitutes 0.01wt.%, 0.05wt.%, 0.1wt.%, 0.5wt.%, 1.00wt.%, 2.00wt.%, 3.00wt.%, 4.00wt.%, 5.00wt.% of the silicon-based anode material. Compound B constitutes 0.01wt.% to 1.00wt.% of the silicon-based anode material, as examples, 0.01wt.%, 0.03wt.%, 0.05wt.%, 0.08wt.%, 0.1wt.%, 0.5wt.%, 1.00wt.% of the silicon-based anode material.
As an embodiment of the present invention, the sum of the M element in the compound a and the M element in the compound B accounts for 0.1wt.% to 10.0wt.%, for example, 0.1wt.% to 5.0wt.% of the silicon-based anode material. As an example, the sum of the M elements constitutes 0.1wt.%, 0.2wt.%, 0.4wt.%, 0.5wt.%, 0.8wt.%, 1.0wt.%, 2.0wt.%, 3.0wt.%, 4.0wt.%, 5.0wt.%, 6.0wt.%, 7.0wt.%, 8.0wt.%, 9.0wt.%, 10 wt.% of the silicon-based anode material. Too high content of M element can affect the original high capacity and high first efficiency characteristics of the material; too low an M element content may result in failure to form a complete coating layer, which affects the processability, cycle and rate performance of the material.
As an embodiment of the present invention, the coating layer includes a modified layer including the compound a and a carbon coating layer surrounding the modified layer. The thickness of the modified layer is 20nm to 200nm, which can shorten the transmission path of electrons and ions and maintain enough strength to avoid the influence of great collision and shearing force on the structure caused by rapid mechanical stirring. By way of example, the thickness of the modified layer may be, but is not limited to, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 100nm, 120nm, 140nm, 160nm, 180nm, 200nm. In certain embodiments, the modified layer has a thickness of 30nm to 60nm.
The carbon coating layer constitutes 1wt.% to 20wt.%, for example 2.0wt.% to 5.0wt.%, as an example, the mass of the carbon coating layer constitutes 1.0wt.%, 2.0wt.%, 2.5wt.%, 3.0wt.%, 4.0wt.%, 4.5wt.%, 5.0wt.%, 7.5wt.%, 10.0wt.%, 15.0wt.%, 17.0wt.% of the silicon-based anode material.
The thickness of the carbon coating layer is 5nm to 200nm, for example 30nm to 100nm, and as an example, the thickness of the carbon coating layer may be, but not limited to, 5nm, 10nm, 15nm, 25nm, 30nm, 35nm, 50nm, 70nm, 100nm, 150nm, 200nm.
The preparation method of the silicon-based anode material comprises the steps of (I) preparing a pre-lithium silicon-based material and (II) modifying and coating.
The step (I) of preparing the pre-lithium silicon-based material comprises the steps of mixing the silicon-based material with a lithium source, and performing a heat treatment reaction to obtain the pre-lithium silicon-based material, wherein the silicon-based material is SiO x Or carbon coated SiO x And 0.5.ltoreq.x.ltoreq.1.5, wherein x may be, but is not limited to, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5.
SiO x Conventional gas phase carbon coating, liquid phase carbon coating or solid phase carbon coating may be employed and at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 93%, at least 95%, at least 97%, at least 99% of the SiO is coated x A surface. The number of cladding layers can be one, two, three, etc. Carbon coated SiO x The medium carbon content accounts for 60wt.% to 100wt.% of the carbon content in the silicon-based anode material. As an example, carbon coated SiO x The carbon content ratio in the catalyst may be, but is not limited to, 60wt.%, 70wt.%, 80wt.%, 90wt.%, 100wt.%. As an example, carbon coated SiO x The carbon content in the silicon-based anode material is only from SiO coated with carbon when the carbon content is 100 wt% x Carbon in (a) is provided.Carbon coated SiO x When the carbon content is more than or equal to 60wt.% and less than or equal to 100wt.%, the carbon content in the silicon-based anode material is partially from carbon-coated SiO x The remainder resulting from further carbon coating after coating modification. As an embodiment of the present invention, the thickness of the carbon coating layer is 5nm to 150nm. By way of example, the thickness of the carbon coating may be, but is not limited to, 5nm, 10nm, 15nm, 25nm, 30nm, 35nm, 50nm, 70nm, 100nm, 150nm.
As an embodiment of the present invention, the median particle diameter of the silicon-based material is 2 μm to 15 μm, for example 6 μm to 10 μm. By way of example, the median particle size of the silicon-based material may be, but is not limited to, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm.
As an embodiment of the present invention, the lithium source includes at least one of lithium hydride, lithium nitride, lithium amide, lithium alkyl, and lithium metal. The mass of the lithium source is 5wt.% to 30wt.%, the mass of the lithium source may be, but is not limited to, 5.0wt.%, 6.0wt.%, 7.0wt.%, 8.0wt.%, 9.0wt.%, 10.0wt.%, 10.5wt.%, 11.0wt.%, 12.0wt.%, 13.0wt.%, 15.0wt.%, 17.0wt.%, 19.0wt.%, 20 wt.%, 23.0wt.%, 26.0wt.%, 30 wt.%.
As an embodiment of the present invention, the temperature of the heat treatment is 350 ℃ to 950 ℃. The temperature of the heat treatment may be, but not limited to, 350 ℃, 400 ℃, 450 ℃, 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃, 950 ℃.
As an embodiment of the present invention, the time of the heat treatment is 2 to 24 hours. The time of the heat treatment may be, but is not limited to, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 22h, 24h. The heat treatment is performed in a non-oxidizing atmosphere including at least one of nitrogen, helium, neon, argon, krypton, and xenon.
As an embodiment of the present invention, the heat treatment reaction is followed by washing with a non-acidic solvent and drying to remove excess material from the surface of the material. The non-acidic solvent comprises water At least one of weak base water, alcohol, ether, ketone and benzene. In the washing process of the pre-lithium silicon-based material, the compound formed on the surface contains a silicon-oxygen lithium compound which is easy to dissolve in water and can be alkaline. In certain embodiments, the solvent is water or weak base water, and such solvents can dissolve the lithium source and lithium-containing compound remaining in the material, and although some of the lithium-silicon-oxygen compound is dissolved, the amount of dissolution is limited and does not affect the performance of the material. The drying temperature is 40 ℃ to 150 ℃, for example 40 ℃ to 100 ℃, and the drying temperature may be, but is not limited to, 40 ℃, 60 ℃, 80 ℃, 100 ℃, 120 ℃, 140 ℃, 150 ℃. The drying time is 6h to 48h, for example 6h to 24h, and may be, but is not limited to, 6h, 12h, 18h, 24h, 30h, 36h, 42h, 46h, 48h. As an embodiment of the invention, the atmosphere used in the drying after washing is air, nitrogen, helium, argon, neon or xenon. After washing, the material is dried, and the composition of the surface components of the material can be influenced by controlling the atmosphere in the drying process. During the drying process, if an air atmosphere is used, the dissolved lithium-silicon oxide compound will react with the CO in the air 2 React with water to produce Li 2 CO 3 And LiOH. In the presence of inert atmosphere, no CO 2 Will be present predominantly as LiOH.
In general, li 2 CO 3 Both LiOH and LiOH are harmful components in the material to be removed, and are used as a reaction matrix of the Li-M-O compound in the invention, and a certain amount of Li is initially present 2 CO 3 When the metal is reacted with LiOH, the metal is favorable for forming a Li-M-O compound by subsequent reaction with metal M oxide, the electronic and ionic conductivity of the material can be improved, and the cycle and rate capability of the material are improved. Li in pre-lithium silicon-based material (before or after washing) 2 CO 3 The content is more than or equal to 0.1wt.% and the LiOH content is more than or equal to 0.1wt.%. As an example, li in a pre-lithium silicon-based material 2 CO 3 The content may be, but is not limited to, 0.1wt.%, 0.2wt.%, 0.3wt.%, 0.4wt.%, 0.6wt.%, 0.8wt.%, 1.0wt.%, 1.2wt.%, 1.5wt.%, 1.8wt.%, 2.0wt.%. As an example, the LiOH content of the pre-lithium silicon-based material (either before or after washing) may be, but is not limited to, 0 or more.1wt.％、0.2wt.％、0.3wt.％、0.4wt.％、0.6wt.％、0.8wt.％、≥1.0wt.％、≥1.2wt.％、≥1.5wt.％、≥1.8wt.％、≥2.0wt.％。
The step (II) of modifying and coating comprises the steps of mixing a solution containing a metal organic compound with a pre-lithium silicon-based material, drying to obtain a precursor with a metal hydroxide layer, and then carrying out heat treatment.
As an embodiment of the present invention, the solution containing the metal organic compound is prepared by dissolving the metal organic compound in an organic solvent. The metal organic compound has a chemical formula of R-M, wherein M is selected from at least one of Al, ca, mg, zn, ba, cr, ti, ge, zr, sr, V, cu, fe, co, sn, Y, ge, gd and La, and M is selected from hydrocarbon groups and/or alcohol groups. By way of example, the hydrocarbyl group may be, but is not limited to, trimethyl, triethyl, tripropyl, tributyl, or trioctyl. The alcohol group may be, but is not limited to, an isopropyl alcohol group, a sec-butyl alcohol group, an n-butyl alcohol group. The organic solvent may be at least one of alcohols, benzene and benzene derivatives, esters, ketones and alicyclic hydrocarbons. By way of example, the organic solvent may be, but is not limited to, methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, pentanol, benzene, toluene, xylene, acetone, butanone, or pentanone. The mass ratio of the pre-lithium silicon-based material to the organic solvent is (0.1-1.0): 1, as examples, but not limited to, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.1:9, 1.0:1. The dissolution process of the metal organic compound may be performed in a water bath environment at a water bath temperature of 40 to 80 ℃. By way of example, the water bath temperature may be, but is not limited to, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃.
The metal organic compound is dissolved in the organic solvent, and in the drying process, the metal organic compound is decomposed to form amorphous metal M hydroxide, the particle morphology is complex, particles, irregular sheets, rods and the like are randomly presented, and the particle sizes of the formed particles are different. In order to prepare a modified layer with stable and consistent characteristics, the morphology and the particle size of the oxide of the metal M are regulated and controlled, and the template agent is added into the organic solvent to change the crystal face energy of particles and the growth rate of each crystal face so as to lead the particle shapeThe appearance is changed, and the template agent is added to enable the particles formed at one time to have isotropy (amorphous state), so that spherical nano particles are obtained, and the size and appearance of the metal M oxide can be effectively regulated and controlled. The template agent is carboxylic acid or ester compound. By way of example, the templating agent may be, but is not limited to, acetic acid, butyric acid, caprylic acid, phenylacetic acid, ethyl acetate, methyl formate, or glyceryl stearate. The templating agent comprises 0.1wt.% to 5.0wt.% of the silicon-based material. As examples, the templating agent comprises 0.1wt.%, 0.5wt.%, 1.0wt.%, 2.0wt.%, 3.0wt.%, 4.0wt.%, 5.0wt.% of the silicon-based material. In some embodiments, the templating agent comprises 0.5wt.% of the silicon-based material, and when M is Al, spherical Al having a size of 5nm to 10nm may be prepared 2 O 3 。
As an aspect of the present invention, the drying is spray drying, fluidized bed drying or agitation drying, and the drying temperature is higher than the decomposition temperature of the metal organic compound.
As an aspect of the present invention, the temperature of the heat treatment is 300 ℃ to 1000 ℃. By way of example, the temperature of the heat treatment may be, but is not limited to, 300 ℃, 400 ℃, 500 ℃, 600 ℃, 700 ℃, 800 ℃, 900 ℃, 1000 ℃. The temperature of the heat treatment is not lower than the lowest reaction temperature of the metal M oxide and the lithium silicon oxide compound, for example, the temperature is lower than the lowest reaction temperature, the Li-M-Si-O compound cannot be formed, and even if a Li-M-O layer is formed, the electron conduction and ion conduction capacity cannot be effectively reflected because the Li-M-O layer is not tightly combined with the lithium silicon oxide compound, and the cycle rate performance of the material is reduced. On the other hand, the temperature of the heat treatment is not too high, so that the active nano silicon grains are prevented from growing up rapidly, and the cycle performance is not facilitated.
The metal organic compound is dissolved in an organic solvent, and in the drying process, the metal organic compound is decomposed to form amorphous metal M hydroxide, the amorphous metal M hydroxide is converted into amorphous metal M oxide in the subsequent heat treatment process, and the amorphous metal M oxide reacts with lithium silicate and residual alkali on the surface of the pre-lithium silicon-based material to form the Li-M-Si-O, li-M-O compound.
As one technical scheme of the invention, the heat treatment time is 2 to 24 hours. As examples, the time of the heat treatment may be, but is not limited to, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 24h. The protective atmosphere used in the heat treatment process is one or at least one of nitrogen, helium, argon, neon and xenon.
As an aspect of the present invention, carbon coating is performed during heat treatment. Carbon coating is carried out in the heat treatment process, so that the carbon content in the material can be improved, the electronic conductivity of the material can be effectively improved, the electronic circulation among particles is enhanced, a stable electronic transfer route is maintained in the repeated expansion and contraction of the material, and the improvement of circulation and rate capability and the inhibition of expansion are facilitated. The carbon coating may be a conventional gas phase carbon coating, liquid phase carbon coating or solid phase carbon coating, and is at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 93%, at least 95%, at least 97%, at least 99% SiO x A surface. The number of cladding layers can be one, two, three, etc. As a technical scheme of the invention, the increment of carbon element in the carbon coating process accounts for more than 0 and less than or equal to 40wt.% of the carbon element in the silicon oxygen anode material. As an example, the incremental ratio of carbon elements in the carbon coating process may be, but is not limited to, 0.1wt.%, 0.5wt.%, 1.0wt.%, 3.0wt.%, 5.0wt.%, 7.5wt.%, 10.0wt.%, 15.0wt.%, 20.0wt.%, 25.0wt.%, 30.0wt.%, 35.0wt.%, 40.0wt.%.
For better illustrating the objects, technical solutions and advantageous effects of the present invention, the present invention will be further described with reference to examples. It should be noted that the following implementation of the method is a further explanation of the present invention and should not be taken as limiting the present invention.
Example 1
The embodiment is a preparation method of a silicon-based anode material, which comprises the following steps.
(I) Preparation of Pre-lithium silicon-based Material
Uniformly mixing 1.0kg of carbon-coated SiO (the carbon coating layer is fully coated and has the thickness of 100nm, the carbon coating layer accounts for 3.0% of the mass of the carbon-coated SiO) and lithium nitride (accounts for 14.0wt.% of the carbon-coated SiO), and placing in a box furnace in an argon atmosphere for heat preservation reaction at 800 DEG C4h, after natural cooling, placing the materials in water, mixing, stirring and washing for 2h, press-filtering to remove water, and placing in a blast drying oven at 80 ℃ for drying for 24h to obtain the pre-lithium silicon-based material (Li in the pre-lithium silicon-based material) 2 CO 3 Content was 1.56wt.%, liOH content was 1.43 wt.%.
(II) modified coating
Dissolving 30g of ethylaluminum in ethanol, stirring for 12 hours in a water bath kettle at 60 ℃, adding 1.0kg of pre-lithium silicon-based material after complete dissolution, mixing and stirring for 0.5 hours to obtain slurry, spray drying the slurry, preserving heat for 8 hours at 800 ℃ under nitrogen protection atmosphere, cooling, taking out and sieving to obtain the silicon-based anode material.
As can be seen from fig. 1, the surface of the material is smooth without obvious small particles, which indicates that the coating uniformity is better, and the modifier has penetrated into the carbon coating layer to react, and is not deposited on the surface. Through detection and calculation, the median particle diameter of the silicon-based anode material is 6.0 mu m, and the specific surface area is 1.40m 2 /g，Li 2 CO 3 The content is 0.14wt.%, the LiOH content is 0.01wt.%, the moisture content in the silicon-based negative electrode material is 0.03wt.%, and the pH is 11.21. The silicon-based anode material comprises a silicon-based core and a coating layer. The silicon-based core is composed of nano silicon (grain size is 6 nm), li 2 SiO 3 And Li (lithium) 2 Si 2 O 5 The coating layer comprises a modified layer and a carbon coating layer from inside to outside. The modified layer has a thickness of 50nm and comprises 1/2Li 2 O·AlO 3/2 ·2SiO 2 And 1/2Li 2 O·AlO 3/2 . The Al content in the silicon-based anode material is 0.63wt.%,1/2Li 2 O·AlO 3/2 ·2SiO 2 The content of (2) is 2.80wt.%,1/2Li 2 O·AlO 3/2 Is 0.57wt.%. The thickness of the carbon coating layer was 100nm, accounting for 2.50wt% of the silicon-based anode material.
The crystal structure characterization instrument adopts a Powder diffractometer of the Panalytical panaceae, netherlands, and the Xpert3Powder, and the parameters comprise 40KV of test voltage, 40mA of test current, 10-90 of scanning range, 0.008 of scanning step length and 12s of scanning time of each step.
The water test uses the karl fischer method, and the pH is obtained by testing an aqueous solution of the material with a pH meter.
The residual alkali content test comprises the following steps: 2.5g of the sample was weighed into a clean beaker, 50mL of pure water was added with a cylinder, magnetically stirred for 5min,800rpm, suction filtered, 25mL of the filtrate was then transferred into a 150mL beaker, pure water was added to 100mL of the beaker, and finally the DET-PH mode was titrated using a potentiometric titrator.
Example 2
The embodiment is a preparation method of a silicon-based anode material, which comprises the following steps.
(I) Preparation of Pre-lithium silicon-based Material
Uniformly mixing 1.0kg of carbon-coated SiO (the carbon coating layer is fully coated and has the thickness of 100nm, the carbon coating layer accounts for 3.0% of the mass of the carbon-coated SiO) and lithium nitride (accounts for 14.0wt.% of the carbon-coated SiO), placing in a box furnace with argon atmosphere, performing heat preservation reaction for 4 hours at 800 ℃, placing the materials in water after natural cooling, mixing, stirring and washing for 2 hours, performing filter pressing to remove water, and placing in an 80 ℃ air blast drying box for drying for 24 hours to obtain the pre-lithium silicon-based material (Li in the pre-lithium silicon-based material) 2 CO 3 The content was 1.48wt.%, and the LiOH content was 1.54 wt.%.
(II) modified coating
Dissolving 30g of ethylaluminum in ethanol, stirring for 12 hours in a water bath kettle at 60 ℃, adding 1.0kg of pre-lithium silicon-based material after complete dissolution, mixing and stirring for 0.5 hours to obtain slurry, adding 5g of acetic acid, mixing and stirring for 0.5 hours, spray drying the slurry, preserving heat for 8 hours at 800 ℃ under nitrogen protection atmosphere, taking out after cooling, and sieving to obtain the silicon-based anode material.
In combination with detection and calculation, the silicon-based anode material has a median particle diameter of 6.0 μm and a specific surface area of 1.4m 2 /g，Li 2 CO 3 The content is 0.09wt.%, the LiOH content is 0, the moisture content in the silicon-based negative electrode material is 0.02wt.%, and the pH is 11.10. The silicon-based anode material comprises a silicon-based core and a coating layer. The silicon-based core is composed of nano silicon (grain size is 6.0 nm), li 2 SiO 3 And Li (lithium) 2 Si 2 O 5 The coating layer comprises a modified layer and a carbon coating layer from inside to outside. The modified layer has a thickness of 50nm and comprises 1/2Li 2 O·AlO 3/2 ·2SiO 2 And 1/2Li 2 O·AlO 3/2 . The Al content in the silicon-based anode material is 0.64wt.%,1/2Li 2 O·AlO 3/2 ·2SiO 2 The content of (2) is 2.77wt.%,1/2Li 2 O·AlO 3/2 Is 0.58wt.%. The thickness of the carbon coating layer was 100nm, accounting for 2.40wt.% of the silicon-based anode material.
Example 3
The embodiment is a preparation method of a silicon-based anode material, which comprises the following steps.
(I) Preparation of Pre-lithium silicon-based Material
Uniformly mixing 1.0kg of carbon-coated SiO (the carbon coating layer is fully coated and has the thickness of 100nm, the carbon coating layer accounts for 3.0% of the mass of the carbon-coated SiO) and lithium nitride (accounts for 14.0wt.% of the carbon-coated SiO), placing in a box furnace with argon atmosphere, performing heat preservation reaction for 4 hours at 800 ℃, placing the materials in water after natural cooling, mixing, stirring and washing for 2 hours, performing filter pressing to remove water, and placing in an 80 ℃ air blast drying box for drying for 24 hours to obtain the pre-lithium silicon-based material (Li in the pre-lithium silicon-based material) 2 CO 3 The content was 1.50wt.%, and the LiOH content was 1.69 wt.%.
(II) modified coating
Dissolving 50g of aluminum isopropoxide in ethanol, stirring for 12 hours in a water bath kettle at 60 ℃, adding 1.0kg of pre-lithium silicon-based material after complete dissolution, mixing and stirring for 0.5 hours to obtain slurry, adding 5g of acetic acid, mixing and stirring for 0.5 hours, spray drying the slurry, preserving heat for 8 hours at 800 ℃ under nitrogen protection atmosphere, cooling, taking out and sieving to obtain the silicon-based anode material.
In combination with detection and calculation, the silicon-based anode material has a median particle diameter of 6.0 μm and a specific surface area of 1.45m 2 /g，Li 2 CO 3 The content is 0.08wt.%, the LiOH content is 0.01wt.%, the moisture content in the silicon-based negative electrode material is 0.02wt.%, and the pH is 11.06. The silicon-based anode material comprises a silicon-based core and a coating layer. The silicon-based core is composed of nano silicon (grain size is 6.0 nm), li 2 SiO 3 And Li (lithium) 2 Si 2 O 5 The coating layer comprises a modified layer and a carbon coating layer from inside to outside. The modified layer has a thickness of 55nm and comprises 1/2Li 2 O·AlO 3/2 ·2SiO 2 And 1/2Li 2 O·AlO 3/2 . Silicon-based negative electrodeThe Al content in the material was 0.64wt.%,1/2Li 2 O·AlO 3/2 ·2SiO 2 The content of (2) is 2.84wt.%,1/2Li 2 O·AlO 3/2 Is 0.61wt.%. The carbon coating layer had a thickness of 100nm and accounted for 2.50wt.% of the silicon-based anode material.
Example 4
The embodiment is a preparation method of a silicon-based anode material, which comprises the following steps.
(I) Preparation of Pre-lithium silicon-based Material
Uniformly mixing 1.0kg of carbon-coated SiO (the carbon coating layer is fully coated and has the thickness of 100nm, the carbon coating layer accounts for 3.0% of the mass of the carbon-coated SiO) and lithium nitride (accounts for 14.0wt.% of the carbon-coated SiO), placing in a box furnace with argon atmosphere, performing heat preservation reaction for 4 hours at 800 ℃, placing the materials in water after natural cooling, mixing, stirring and washing for 2 hours, performing filter pressing to remove water, and placing in an 80 ℃ air blast drying box for drying for 24 hours to obtain the pre-lithium silicon-based material (Li in the pre-lithium silicon-based material) 2 CO 3 The content was 1.44wt.%, and the LiOH content was 1.75 wt.%.
(II) modified coating
Dissolving 50g of aluminum isopropoxide in ethanol, stirring for 12 hours in a water bath kettle at 60 ℃, adding 1.0kg of pre-lithium silicon-based material after complete dissolution, mixing and stirring for 0.5 hours to obtain slurry, adding 5g of acetic acid, mixing and stirring for 0.5 hours, spray drying the slurry, taking ethylene as a carbon source, preserving heat for 2 hours at 850 ℃ under nitrogen protective atmosphere, taking out after cooling, and sieving to obtain the silicon-based anode material.
In combination with detection and calculation, the silicon-based anode material has a median particle diameter of 6.0 μm and a specific surface area of 1.40m 2 /g，Li 2 CO 3 The content is 0.05wt.%, the LiOH content is 0, the moisture content in the silicon-based negative electrode material is 0.02wt.%, and the pH value is 10.88. The silicon-based anode material comprises a silicon-based core and a coating layer. The silicon-based core is composed of nano silicon (grain size is 6.0 nm), li 2 SiO 3 And Li (lithium) 2 Si 2 O 5 The coating layer comprises a modified layer and a carbon coating layer from inside to outside. The modified layer has a thickness of 55nm and comprises 1/2Li 2 O·AlO 3/2 ·2SiO 2 And 1/2Li 2 O·AlO 3/2 . In silicon-based anode materialsAl content was 0.67wt.%,1/2Li 2 O·AlO 3/2 ·2SiO 2 The content of (3.09 wt.%,1/2 Li) 2 O·AlO 3/2 Is 0.54wt.%. The thickness of the carbon coating layer was 100nm, accounting for 2.35wt.% of the silicon-based anode material.
Example 5
The embodiment is a preparation method of a silicon-based anode material, which comprises the following steps.
(I) Preparation of Pre-lithium silicon-based Material
Uniformly mixing 1.0kg of carbon-coated SiO (the carbon coating layer is fully coated and has the thickness of 100nm, the carbon coating layer accounts for 3.0% of the mass of the carbon-coated SiO) and lithium nitride (accounts for 14.0wt.% of the carbon-coated SiO), placing in a box furnace with argon atmosphere, performing heat preservation reaction for 4 hours at 800 ℃, placing the materials in water after natural cooling, mixing, stirring and washing for 2 hours, performing filter pressing to remove water, and placing in an 80 ℃ air blast drying box for drying for 24 hours to obtain the pre-lithium silicon-based material (Li in the pre-lithium silicon-based material) 2 CO 3 The content was 1.44wt.%, and the LiOH content was 1.75 wt.%.
(II) modified coating
100g of aluminum isopropoxide is dissolved in ethanol, stirred for 6 hours in a water bath kettle at 80 ℃, 1.0kg of pre-lithium silicon-based material is added after complete dissolution, mixed and stirred for 0.5 hours to obtain slurry, 5g of acetic acid is added, mixed and stirred for 0.5 hours, the slurry is spray-dried, and then the temperature is kept for 12 hours at 800 ℃ under the protection of nitrogen, and after cooling, the silicon-based anode material is obtained after taking out and sieving.
In combination with detection and calculation, the silicon-based anode material has a median particle diameter of 6.0 μm and a specific surface area of 1.80m 2 /g，Li 2 CO 3 The content is 0.05wt.%, the LiOH content is 0, the moisture content in the silicon-based negative electrode material is 0.02wt.%, and the pH is 11.05. The silicon-based anode material comprises a silicon-based core and a coating layer. The silicon-based core is composed of nano silicon (grain size is 6.0 nm), li 2 SiO 3 And Li (lithium) 2 Si 2 O 5 The coating layer comprises a modified layer and a carbon coating layer from inside to outside. The modified layer has a thickness of 100nm and comprises 1/2Li 2 O·AlO 3/2 ·2SiO 2 And 1/2Li 2 O·AlO 3/2 . The Al content in the silicon-based anode material is 1.32wt.%,1/2Li 2 O·AlO 3/2 ·2SiO 2 The content of (C) was 7.39wt.%,1/2Li 2 O·AlO 3/2 Is 0.61wt.%. The thickness of the carbon coating layer was 100nm, accounting for 2.20wt.% of the silicon-based anode material.
Example 6
The embodiment is a preparation method of a silicon-based anode material, which comprises the following steps.
(I) Preparation of Pre-lithium silicon-based Material
Uniformly mixing 1.0kg of carbon-coated SiO (the carbon coating layer is fully coated and has the thickness of 100nm, the carbon coating layer accounts for 3.0% of the mass of the carbon-coated SiO) and lithium nitride (accounts for 14.0wt.% of the carbon-coated SiO), placing in a box furnace with argon atmosphere, performing heat preservation reaction for 4 hours at 800 ℃, placing the materials in water after natural cooling, mixing, stirring and washing for 2 hours, performing filter pressing to remove water, and placing in an 80 ℃ air blast drying box for drying for 24 hours to obtain the pre-lithium silicon-based material (Li in the pre-lithium silicon-based material) 2 CO 3 The content was 1.42wt.%, and the LiOH content was 1.73 wt.%.
(II) modified coating
Dissolving 50g of aluminum isopropoxide in ethanol, stirring for 12 hours in a water bath kettle at 60 ℃, adding 1.0kg of pre-lithium silicon-based material after complete dissolution, mixing and stirring for 0.5 hours to obtain slurry, adding 5g of ethyl acetoacetate, mixing and stirring for 0.5 hours, spray drying the slurry, preserving heat for 12 hours at 800 ℃ under nitrogen protection atmosphere, cooling, taking out and sieving to obtain the silicon-based anode material.
In combination with detection and calculation, the silicon-based anode material has a median particle diameter of 6.0 μm and a specific surface area of 1.40m 2 /g，Li 2 CO 3 The content is 0.07wt.%, the LiOH content is 0, the moisture content in the silicon-based negative electrode material is 0.03wt.%, and the pH is 11.12. The silicon-based anode material comprises a silicon-based core and a coating layer. The silicon-based core is composed of nano silicon (grain size is 6.0 nm), li 2 SiO 3 And Li (lithium) 2 Si 2 O 5 The coating layer comprises a modified layer and a carbon coating layer from inside to outside. The modified layer has a thickness of 50nm and comprises 1/2Li 2 O·AlO 3/2 ·2SiO 2 And 1/2Li 2 O·AlO 3/2 . The Al content in the silicon-based anode material is 0.67wt.%,1/2Li 2 O·AlO 3/2 ·2SiO 2 The content of (2) is 2.86wt.%,1/2Li 2 O·AlO 3/2 Is 0.59wt.%. The thickness of the carbon coating layer was 100nm, accounting for 2.45wt.% of the silicon-based anode material.
Example 7
The embodiment is a preparation method of a silicon-based anode material, which comprises the following steps.
(I) Preparation of silicon-based kernels
Uniformly mixing 1.0kg of carbon-coated SiO (the carbon coating layer is fully coated and has the thickness of 100nm, the carbon coating layer accounts for 3.0% of the mass of the carbon-coated SiO) and lithium nitride (accounts for 14.0wt.% of the carbon-coated SiO), placing in a box furnace in an argon atmosphere, carrying out heat preservation reaction for 4 hours at 800 ℃, placing the materials in water after natural cooling, mixing, stirring and washing for 2 hours, carrying out filter pressing to remove water, and placing in an 80 ℃ air-blast drying box for drying for 24 hours to obtain the silicon-based core (Li in the silicon-based core) 2 CO 3 The content was 1.39wt.%, and the LiOH content was 1.84 wt.%.
(II) modified coating
30g of magnesium ethoxide is dissolved in ethanol, stirred for 12 hours in a water bath kettle at 60 ℃, 1.0kg of silicon-based kernel is added after complete dissolution, mixed and stirred for 0.5 hour to obtain slurry, the slurry is spray dried, then the temperature is kept at 800 ℃ for 8 hours under the protection of nitrogen, and after cooling, the silicon-based anode material is obtained through sieving.
In combination with detection and calculation, the silicon-based anode material has a median particle diameter of 6.0 μm and a specific surface area of 1.50m 2 /g，Li 2 CO 3 The content was 1.21wt.%, the LiOH content was 1.57wt.%, the moisture content in the silicon-based negative electrode material was 0.11wt.%, and the pH was 11.81. The silicon-based anode material comprises a silicon-based core and a coating layer. The silicon-based core is composed of nano silicon (grain size is 6.0 nm), li 2 SiO 3 And Li (lithium) 2 Si 2 O 5 The coating layer comprises a modified layer and a carbon coating layer from inside to outside. The modified layer has a thickness of 40nm and comprises Li 2 O·2MgO·4SiO 2 . The silicon-based anode material contains 0.64wt.% of Mg and Li 2 O·2MgO·4SiO 2 Is 4.59wt.%. The thickness of the carbon coating layer was 100nm, accounting for 2.45wt.% of the silicon-based anode material.
Example 8
The embodiment is a preparation method of a silicon-based anode material, which comprises the following steps.
(I) Preparation of Pre-lithium silicon-based Material
Coating carbon with SiO 1.1 1.0kg (the carbon coating layer is fully coated and has the thickness of 150nm, the carbon coating layer accounts for 5.0 percent of the mass of the carbon-coated SiO) and lithium metal (accounts for 10.0 percent by weight of the carbon-coated SiO) are uniformly mixed, and are placed in a box furnace with nitrogen atmosphere for heat preservation reaction at 550 ℃ for 15 hours, after natural cooling, the materials are placed in weak alkaline water for mixing, stirring and washing for 3 hours, filter pressing is carried out to remove water, and the materials are placed in a blast drying box at 100 ℃ for drying for 20 hours to obtain the pre-lithium silicon-based material (Li in the pre-lithium silicon-based material) 2 CO 3 The content was 1.39wt.%, and the LiOH content was 1.63 wt.%.
(II) modified coating
Dissolving 30g of ethylaluminum in isopropanol, stirring for 10 hours in a water bath kettle at 75 ℃, adding 1.0kg of pre-lithium silicon-based material after complete dissolution, mixing and stirring for 1.5 hours to obtain slurry, stirring and drying the slurry, preserving heat for 8 hours at 870 ℃ under the protection of argon, cooling, and taking out and sieving to obtain the silicon-based anode material.
In combination with detection and calculation, the silicon-based anode material has a median particle diameter of 6.0 μm and a specific surface area of 1.5m 2 /g，Li 2 CO 3 The content is 0.09wt.%, the LiOH content is 0wt.%, the moisture content in the silicon-based negative electrode material is 0.03wt.%, and the pH is 11.23. The silicon-based anode material comprises a silicon-based core and a coating layer. The silicon-based core is composed of nano silicon (grain size is 6.0 nm), li 2 SiO 3 、Li 2 Si 2 O 5 And Li (lithium) 4 SiO 4 The coating layer comprises a modified layer and a carbon coating layer from inside to outside. The modified layer has a thickness of 50nm and comprises 1/2Li 2 O·AlO 3/2 ·2SiO 2 And 1/2Li 2 O·AlO 3/2 . The Al content in the silicon-based anode material is 0.66wt.%,1/2Li 2 O·AlO 3/2 ·2SiO 2 Is 2.93wt.%, dLi 2 O·AlO 2/3 Is 0.58wt.%. The carbon coating layer had a thickness of 150nm and accounted for 2.5wt.% of the silicon-based anode material.
Comparative example 1
The embodiment is a preparation method of a silicon-based anode material, which comprises the following steps.
(I) Preparation of Pre-lithium silicon-based Material
Uniformly mixing 1.0kg of carbon-coated SiO (the carbon coating layer is fully coated and has the thickness of 100nm, the carbon coating layer accounts for 3.0% of the mass of the carbon-coated SiO) and lithium nitride (accounts for 14.0wt.% of the carbon-coated SiO), placing in a box furnace with argon atmosphere, performing heat preservation reaction for 4 hours at 800 ℃, placing the materials in water after natural cooling, mixing, stirring and washing for 2 hours, performing filter pressing to remove water, and placing in an 80 ℃ air blast drying box for drying for 24 hours to obtain the pre-lithium silicon-based material (Li in the pre-lithium silicon-based material) 2 CO 3 The content was 1.39wt.%, and the LiOH content was 1.45 wt.%.
(II) modified coating
50g of aluminum oxide and 1.0kg of pre-lithium silicon-based material are put into a ball mill, ball milling is carried out for 24 hours, the temperature is kept at 800 ℃ for 8 hours under the protection of nitrogen, and after cooling, the silicon-based negative electrode material is obtained after taking out and sieving.
As can be seen in connection with fig. 2, there are many small particles on the surface of the material, and the distribution is very uneven. In combination with detection and calculation, the silicon-based anode material has a median particle diameter of 6.0 μm and a specific surface area of 1.90m 2 /g，Li 2 CO 3 The content is 0.69wt.%, the LiOH content is 0.72wt.%, the moisture content in the silicon-based negative electrode material is 0.16wt.%, and the pH is 11.85. The silicon-based anode material comprises a silicon-based core and a coating layer. The silicon-based core is composed of nano silicon (grain size is 6.0 nm), li 2 SiO 3 And Li (lithium) 2 Si 2 O 5 Composition, coating layer including small amount of 1/2Li unevenly distributed 2 O·AlO 3/2 ·2SiO 2 、1/2Li 2 O·AlO 3/2 And a carbon coating layer on which unreacted alumina particles are attached. The Al content in the silicon-based anode material was 1.31wt.%. The thickness of the carbon coating layer was 100nm, accounting for 2.40wt.% of the silicon-based anode material.
Comparative example 2
The embodiment is a preparation method of a silicon-based anode material, which comprises the following steps.
(I) Preparation of Pre-lithium silicon-based Material
Uniformly mixing 1.0kg of carbon-coated SiO (the carbon coating layer is fully coated and has the thickness of 10nm, the carbon coating layer accounts for 3.0% of the mass of the carbon-coated SiO) and lithium nitride (accounts for 14.0wt.% of the carbon-coated SiO), placing in a box furnace in an argon atmosphere, performing heat preservation reaction for 4 hours at 800 ℃, placing the materials in water after natural cooling, mixing, stirring and washing for 2 hours, performing filter pressing to remove water, and placing in an 80 ℃ air blast drying box for drying for 24 hours to obtain the pre-lithium silicon-based material (Li in the pre-lithium silicon-based material) 2 CO 3 The content was 1.33wt.%, and the LiOH content was 1.67 wt.%.
(II) modified coating
50g of magnesium oxide and 1.0kg of pre-lithium silicon-based material are put into a ball mill, ball milling is carried out for 24 hours, the temperature is kept at 800 ℃ for 8 hours under the protection of nitrogen, and after cooling, the silicon-based negative electrode material is obtained after taking out and sieving.
In combination with detection and calculation, the silicon-based anode material has a median particle diameter of 6.0 μm and a specific surface area of 1.85m 2 /g，Li 2 CO 3 The content is 1.29wt.%, the LiOH content is 1.52wt.%, the moisture content in the silicon-based negative electrode material is 0.16wt.%, and the pH is 11.79. The silicon-based anode material comprises a silicon-based core and a coating layer. The silicon-based core is composed of nano silicon (grain size is 6 nm), li 2 SiO 3 And Li (lithium) 2 Si 2 O 5 Composition, coating layer including small amount of Li unevenly distributed 2 O·2MgO·4SiO 2 And a carbon coating layer on which unreacted magnesium oxide particles are attached. The Mg content in the silicon-based anode material was 3.31wt.%. The thickness of the carbon coating layer was 100nm, accounting for 2.40wt.% of the silicon-based anode material.
Comparative example 3
The embodiment is a preparation method of a silicon-based anode material, which comprises the following steps.
(I) Preparation of Pre-lithium silicon-based Material
Uniformly mixing 1.0kg of carbon-coated SiO (the carbon coating layer is fully coated and has the thickness of 100nm, the carbon coating layer accounts for 3.0% of the mass of the carbon-coated SiO) and lithium nitride (accounts for 14.0wt.% of the carbon-coated SiO), placing in a box furnace in an argon atmosphere, carrying out heat preservation reaction for 4 hours at 800 ℃, placing the materials in dilute hydrochloric acid for mixing, stirring and washing for 1 hour after natural cooling, carrying out filter pressing to remove water, and placing in 80 DEG C Drying in a forced air drying oven for 24h to obtain the pre-lithium silicon-based material (Li in the pre-lithium silicon-based material) 2 CO 3 The content was 0.26wt.%, and the LiOH content was 0.35 wt.%.
(II) modified coating
50g of aluminum oxide and 1.0kg of pre-lithium silicon-based material are put into a ball mill, ball milling is carried out for 24 hours, the temperature is kept at 800 ℃ for 8 hours under the protection of nitrogen, and after cooling, the silicon-based negative electrode material is obtained after taking out and sieving.
In combination with detection and calculation, the silicon-based anode material has a median particle diameter of 6.0 μm and a specific surface area of 1.85m 2 /g，Li 2 CO 3 The content is 0.32wt.%, the LiOH content is 0.37wt.%, the moisture content in the silicon-based negative electrode material is 0.14wt.%, and the pH is 11.78. The silicon-based anode material comprises a silicon-based core and a coating layer. The silicon-based core is composed of nano silicon (grain size is 6.0 nm), li 2 SiO 3 And Li (lithium) 2 Si 2 O 5 Composition, coating layer including small amount of 1/2Li unevenly distributed 2 O·AlO 3/2 ·2SiO 2 、1/2Li 2 O·AlO 3/2 And a carbon coating layer on which unreacted alumina particles are attached. The Al content in the silicon-based anode material was 1.32wt.%. The thickness of the carbon coating layer was 100nm, accounting for 2.40wt.% of the silicon-based anode material.
The silicon-based anode materials prepared in examples 1 to 8 and comparative examples 1 to 3 were subjected to respective performance tests under the following test conditions, and the test results are shown in table 1.
First charge and discharge performance test: the silicon-based anode materials prepared in examples 1 to 8 and comparative examples 1 to 3 were used as active materials, respectively, mixed with an aqueous dispersion of an acrylonitrile copolymer binder (LA 132, solid content 15%) and a conductive agent (Super-P) in a mass ratio of 70:10:20, added with an appropriate amount of water as a solvent to prepare a slurry, coated on a copper foil, and vacuum-dried and rolled to prepare an anode sheet. Lithium metal was used as a counter electrode, and 1mol/L LiPF was used 6 And mixing the three components of mixed solvents according to the ratio of EC to DMC to emc=1:1:1 (v/v) to form an electrolyte, and adopting a polypropylene microporous membrane as a diaphragm to assemble the CR2032 button cell in a glove box filled with inert gas. The charge and discharge test of button cell is in Wuhan cityThe method is carried out on a battery test system of blue electronic Co., ltd, under normal temperature conditions, 0.1C constant current charge and discharge is carried out to 0.01V, then 0.02C constant current discharge is carried out to 0.005V, finally 0.1C constant current charge is carried out to 1.5V, the capacity charged to 1.5V is the first lithium intercalation capacity, and the ratio of the charging capacity to the discharging capacity is the first coulomb efficiency.
Slurry stability test: 200ml of the slurry in the first charge and discharge performance test is taken and placed in a beaker, the beaker is sealed, and whether the slurry subsides within 72 hours is observed with naked eyes. And (3) placing 5ml of slurry into a 20ml syringe, sealing the needle tube by adopting hot melt adhesive, placing the needle tube into a baking oven at 45 ℃ for storage, observing the movement condition of the syringe, and recording the time difference between the starting test time of the time interval when the syringe starts to move, thereby taking the time difference as the gas production time of the material.
And (3) testing the cycle performance: after the material is subjected to the first charge-discharge test, constant-current constant-voltage charge (0.2C) to 1.5V, constant-current discharge (0.1C) to 0.01V, and circulation for 50 weeks, and the capacity ratio of the capacity of the 50 th week discharge to 0.01V to the capacity of the 1 st week discharge to 0.01V is calculated to be the 50-week circulation retention rate.
And (3) multiplying power performance test: after the material is subjected to the first charge and discharge test, constant-current and constant-voltage discharge (0.2C, cut-off condition is 0.01C) to 0.01V, standing for 5min, constant-current charging (0.2/0.5/1/2/3C) to 1.5V, and calculating the charge capacity ratio of the charge capacity under different multiplying powers to the charge capacity under 0.2C multiplying power.
And (3) quick charge performance test: after the material is subjected to a first charge-discharge test, constant-current and constant-voltage discharge (0.2/0.5/1/2C, cut-off condition is 0.01C), standing for 5min, and then constant-current charging (0.2C) to 1.5V, and calculating the discharge capacity ratio of different multiplying powers to 0.2C.
Table 1 results of performance testing of examples and comparative examples
Table 1, below
As can be seen from the results of table 1, the silicon-based anode materials prepared in examples 1 to 8 and comparative examples 1 to 3 were high in both the first lithium intercalation capacity and the first coulombic efficiency. Compared with comparative examples 1 to 3, the silicon-based anode materials prepared in examples 1 to 8 were better in cycle performance, rate performance and quick charge performance, and the stability of the slurry was particularly remarkable. The silicon-based anode material prepared in the embodiments 1-8 mainly comprises glass-like phase Li-M-Si-O, and the Li-M-Si-O has the capability of fast conducting ions and electrons, can reduce the resistance in the lithium ion deintercalation process in the material, and effectively improves the cycle performance and the multiplying power performance of the material.
In comparative example 1, solid phase Al was mixed with solid phase Al 2 O 3 Mixing with the pre-lithium silicon-based material by a mechanical ball milling mode, and mechanically mixing Al 2 O 3 Is difficult to be uniformly mixed with the pre-lithium silicon-based material, and the silicon-oxygen lithium compound is difficult to be mixed with Al during heat treatment 2 O 3 The reaction is carried out although the lithium silicate on the surface of the pre-lithium silicon-based material and a small amount of residual alkali and Al 2 O 3 The Li-M-Si-O, li-M-O compound is generated by the reaction, but the distribution is uneven, and the coating performance is still poor.
In comparative example 2, solid-solid mixing is adopted, solid-phase MgO is mixed with a pre-lithium silicon-based material by a mechanical ball milling method, and MgO cannot form Li-M-O compounds with residual alkali, so that the material performance is poor.
Comparative example 3 the lithium-silica compound on the surface of the pre-lithium silicon-based material was rapidly dissolved by washing with dilute hydrochloric acid, so that the material performance was poor. And Li on the surface of the pre-lithium silicon-based material 2 CO 3 The residual alkali content of the surface of the pre-lithium silicon-based material is obviously reduced compared with that of the comparative example 1 by washing with water after the removal of LiOH by dilute hydrochloric acid before ball milling and mixing, thus Al is treated in the subsequent heat treatment process 2 O 3 The reaction with residual alkali does not occur to form a sufficient amount of Li-M-O compound, so that the material properties are inferior to those of comparative example 1. In additionThe residual alkali content is increased after modified coating, and due to incomplete coating, lithium siloxide compound extends to the surface of the material during coating heat treatment, and Li is regenerated after contacting with air 2 CO 3 And LiOH.
Finally, it should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the scope of the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the present invention can be modified or substituted without departing from the spirit and scope of the technical solution of the present invention.
Claims (10)
1. The silicon-based anode material is characterized by comprising a silicon-based core and a coating layer, wherein the silicon-based core comprises nano silicon and a silicon oxygen lithium compound, and the coating layer at least comprises a silicon-based material with a chemical formula of aLi 2 O·MO b ·cSiO 2 Wherein a > 0, b > 0, c > 0.
2. The silicon-based anode material according to claim 1, characterized by comprising at least one of the following features (1) to (7):
(1) the grain size of the nano silicon is 2nm to 20nm;
(2) the lithium siloxide compound comprises Li 2 SiO 3 、Li 2 Si 2 O 5 And Li (lithium) 4 SiO 4 At least one of (a) and (b);
(3) m is selected from at least one of Al, ca, mg, zn, ba, cr, ti, ge, zr, sr, V, cu, fe, co, sn, Y, ge, gd and La;
(4) the silicon-based anode material has a median particle diameter of 2-15 μm;
(5) The specific surface area of the silicon-based anode material is 0.5m 2 /g to 5.0m 2 /g；
(6) Li in the silicon-based anode material 2 CO 3 The content is less than or equal to 0.15wt percent, and the content of LiOH is less than or equal to 0.01wt percent;
(7) the moisture content of the silicon-based anode material is less than or equal to 0.10wt.%.
3. The silicon-based anode material according to claim 1, wherein the coating layer further comprises a compound of formula dLi 2 O·MO e Wherein d > 0, e > 0.
4. A silicon-based anode material according to claim 3, comprising at least one of the following features (i) to (iii):
(i) The coating layer comprises a modified layer formed by the compound A, and the compound B is dispersed in the modified layer;
(ii) The compound A accounts for 0.01 to 5.00wt.% of the silicon-based anode material, and the compound B accounts for 0.01 to 1.00wt.% of the silicon-based anode material;
(iii) The sum of the M element in the compound a and the M element in the compound B is 0.1wt.% to 10.0wt.% of the silicon-based anode material.
5. The silicon-based anode material according to claim 1, wherein the coating layer includes a modified layer containing the compound a and a carbon coating layer surrounding the modified layer.
6. The silicon-based anode material according to claim 5, comprising at least one of the following features (a) to (c):
(a) The thickness of the modified layer is 20nm to 200nm;
(b) The thickness of the carbon coating layer is 5nm to 200nm;
(c) The carbon coating layer accounts for 1wt.% to 20wt.% of the silicon-based anode material.
7. The preparation method of the silicon-based anode material is characterized by comprising the following steps:
(I) Preparation of Pre-lithium silicon-based Material
Mixing the silicon-based material with a lithium source, and performing a heat treatment reaction to obtain a pre-lithium silicon-based materialThe silicon-based material is SiO x Or carbon coated SiO x X is more than or equal to 0.5 and less than or equal to 1.5;
(II) modified coating
Mixing the solution containing the metal organic compound with the pre-lithium silicon-based material, drying to obtain a precursor with a metal hydroxide layer, and performing heat treatment.
8. The method of producing a silicon-based anode material according to claim 7, characterized by comprising at least one of the following features (1) to (17):
(1) The silicon-based material is SiO coated with carbon x And the carbon-coated SiO x The medium carbon content accounts for 60wt.% to 100wt.% of the carbon content in the silicon-based anode material;
(2) The median particle diameter of the silicon-based material is 2-15 mu m;
(3) The lithium source includes at least one of lithium hydride, lithium nitride, lithium amide, lithium alkyl, and lithium metal;
(4) The lithium source comprises 5wt.% to 30wt.% of the silicon-based material;
(5) The temperature of the heat treatment in the preparation of the pre-lithium silicon-based material in the step (I) is 350-950 ℃;
(6) The heat treatment time in the preparation of the pre-lithium silicon-based material in the step (I) is 2 to 24 hours;
(7) Step (I) preparing a pre-lithium silicon-based material wherein the heat treatment is performed under a non-oxidizing atmosphere comprising at least one of nitrogen, helium, neon, argon, krypton, and xenon;
(8) Washing and drying the material after the heat treatment reaction in the step (I) by adopting a non-acidic solvent to obtain a pre-lithium silicon-based material;
(9) Li in the pre-lithium silicon-based material 2 CO 3 The content is more than or equal to 0.1wt percent, and the content of LiOH is more than or equal to 0.1wt percent;
(10) The chemical formula of the metal organic compound is R-M, wherein M is selected from at least one of Al, ca, mg, zn, ba, cr, ti, ge, zr, sr, V, cu, fe, co, sn, Y, ge, gd and La, and M is selected from hydrocarbon groups and/or alcohol groups;
(11) The solution containing a metal organic compound is prepared by dissolving the metal organic compound in an organic solvent;
(12) The solution containing the metal organic compound is prepared by dissolving the metal organic compound in an organic solvent, and a template agent is added into the organic solvent, wherein the template agent is a carboxylic acid or ester compound, and accounts for 0.1 to 5.0wt.% of the silicon-based material;
(13) The drying in step (II) is spray drying, fluidized bed drying or agitation drying, and the temperature of the drying is higher than the decomposition temperature of the metal-organic compound;
(14) The temperature of the heat treatment in the step (II) modified coating is 300-1000 ℃;
(15) The time of the heat treatment in the step (II) modified coating is 2 to 24 hours;
(16) The heat treatment in the step (II) modified coating is carried out under a protective atmosphere, wherein the protective atmosphere comprises at least one of nitrogen, helium, argon, neon and xenon;
(17) And (2) carrying out carbon coating during the heat treatment in the step (II) modified coating, wherein the content of carbon element increased by the carbon coating accounts for more than 0 and less than or equal to 40wt.% of the carbon element in the silicon-based anode material.
9. Use of the silicon-based anode material according to any one of claims 1 to 6, or the silicon-based anode material prepared by the preparation method of the silicon-based anode material according to claim 7 or 8, in an anode material.
10. A secondary battery comprising a positive electrode material and a negative electrode material, characterized in that the negative electrode material comprises the silicon-based negative electrode material according to any one of claims 1 to 6, or the silicon-based negative electrode material produced by the production method of the silicon-based negative electrode material according to claim 7 or 8.
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| CN113437280A (en) * | 2021-08-30 | 2021-09-24 | 北京壹金新能源科技有限公司 | Slurry-stabilized lithiated silicon-based composite material and preparation method and application thereof |
| CN114388738A (en) * | 2021-12-29 | 2022-04-22 | 湖北亿纬动力有限公司 | Silicon-based negative electrode material and preparation method and application thereof |
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| CN103682279A (en) * | 2013-12-27 | 2014-03-26 | 浙江大学 | Silicon-based composite lithium ion battery negative electrode material as well as preparation method and application of silicon-based composite lithium ion battery negative electrode material |
| CN113437280A (en) * | 2021-08-30 | 2021-09-24 | 北京壹金新能源科技有限公司 | Slurry-stabilized lithiated silicon-based composite material and preparation method and application thereof |
| CN114388738A (en) * | 2021-12-29 | 2022-04-22 | 湖北亿纬动力有限公司 | Silicon-based negative electrode material and preparation method and application thereof |
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