Pre-lithiation silicon oxide material and preparation method thereof, negative electrode plate and lithium ion battery

Abstract

The present invention discloses a pre-lithiated silicon oxide material and a preparation method thereof, a negative electrode plate and a lithium ion battery. The preparation method of the pre-lithiated silicon oxide material comprises: adding a precursor to a pre-lithiated solution A, reacting under closed conditions, evaporating the obtained solution to remove the solvent after the reaction, placing the obtained product in a heating device for treatment, cooling after the treatment, and obtaining a pre-lithiated silicon oxide intermediate; adding the pre-lithiated silicon oxide intermediate to a pre-lithiated solution B, reacting under closed conditions, evaporating the obtained solution to remove the solvent after the reaction, placing the obtained product in a heating device for treatment, cooling after the treatment, and obtaining the pre-lithiated silicon oxide material. The pre-lithiated silicon oxide material does not change the morphology of material particles, maintains a high specific capacity and initial efficiency, and maintains the effect of the pre-lithiated treatment to the greatest extent.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery materials, and in particular to a pre-lithiated silicon-oxygen material and a preparation method thereof, a negative electrode plate and a lithium-ion battery. Background Art

[0002] As electrification sweeps the globe, the demand for lithium-ion battery energy density is growing more urgent, from small devices like power tools and smart homes to large vehicles like two-wheelers and four-wheelers. Consequently, the development of high-capacity lithium-ion battery cathode and anode materials is becoming increasingly important. Regarding anode materials, the specific capacity of currently used graphite-based anode materials has already approached its theoretical value (372 mAh / g), leaving little room for further improvement. Therefore, the development of new anode materials is urgent.

[0003] Silicon-based negative electrode materials have extremely high theoretical specific capacity (the theoretical specific capacity of pure silicon is about 4200mAh / g, and the theoretical specific capacity of silicon oxide is about 1700mAh / g), and therefore have become the main development direction of new negative electrode materials. Among all silicon-based materials, silicon oxide materials have a longer cycle life due to their relatively low expansion (less than 300% volume expansion rate of pure silicon), and are considered to be more easily accepted by the market and achieve mass application. However, due to the presence of some oxygen elements in silicon oxide materials, when used as negative electrode materials for lithium-ion batteries, they will consume active lithium and result in low initial efficiency. Therefore, improving the initial efficiency of silicon oxide materials is of great research significance.

[0004] Currently, pre-lithiation technology is considered the optimal method for improving the initial efficiency of silicon-oxygen materials. The essence of pre-lithiation is to utilize active lithium to react with the active oxygen in the silicon-oxygen material in advance to form lithium silicates (Li+SiO=Li4SiO4 / Li2SiO3 / Li2Si2O5). This prevents the consumption of active lithium provided by the positive electrode in the battery, thereby improving the initial efficiency. Using various pre-lithiation methods, the initial efficiency of silicon-oxygen materials can be effectively increased to >90%.

[0005] However, since the pre-lithiated silicon oxide is modified with lithium, the phases of the generated silicate are Li4SiO4, Li2SiO3 and Li2Si2O5, mainly Li2SiO3. In the process of generating silicate, volume changes will occur, destroying the carbon coating layer, exposing the silicate. The exposed Li2SiO3 will come into contact with air to generate alkaline substances LiOH and Li2CO3 (Li2SiO3+CO2=LiCO3+SiO2; Li2SiO3+H2O=2LiOH+SiO2). In addition, the exposed Li2SiO3 will partially dissolve in water, causing the solution to be alkaline. These two reasons will cause the overall alkalinity of the slurry to be high (pH greater than 11) during the conventional negative electrode water system homogenization process, destroying the binder structure in the slurry, resulting in poor slurry stability and the occurrence of gel or sedimentation. Another phenomenon is that Li2SiO3 partially dissolves in water, exposing nano-silicon embedded in the silicate matrix. Nano-silicon reacts with water under alkaline conditions to produce gas, affecting the coating uniformity and the reversible capacity of the material (Si+2H2O=SiO2+2H2).

[0006] In response to the above problems, the Chinese invention patent with application number 202011615039.6 discloses a pre-lithiation silicon-oxygen composite material, a negative electrode sheet, a lithium battery and a preparation method thereof, and specifically discloses: first, pre-lithiation is carried out, and then organic alcohols are used for soaking, washing, and reducing the surface lithium ion concentration, so that a concentration gradient appears in the radial direction of the particles. After heating, Li2Si2O5 will be formed in the surface low lithium ion concentration layer, and Li2SiO3 will be formed in the inner high lithium ion concentration layer to achieve a layered structure. The outer layer of Li2Si2O5 is used to protect the inner layer of Li2SiO3 from contacting and reacting with the outside world, thereby achieving the purpose of improving the residual alkali and optimizing the processing performance of the material. However, this implementation method is achieved by sacrificing a part of the lithium ions and reducing the degree of pre-lithiation, which results in a reduction in capacity and efficiency (capacity of about 1350mAh / g, efficiency less than 88%), and the optimal result of pre-lithiation is not achieved. Summary of the Invention

[0007] The purpose of the present invention is to provide a pre-lithiation silicon oxide material and its preparation method, a negative electrode plate and a lithium-ion battery. By adopting a graded pre-lithiation method, a layered structure can be achieved without affecting the initial efficiency improvement effect of pre-lithiation on the silicon oxide material, thereby achieving the purpose of improving residual alkali and optimizing the processing performance of the pre-lithiation silicon oxide material.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a pre-lithiated silicon-oxygen material, the method comprising the following steps:

[0010] The precursor is added to the pre-lithiation solution A and reacted under closed conditions. After the reaction is completed, the resulting solution is evaporated to remove the solvent, and the solvent can be condensed and recycled. The resulting product is placed in a heating device for treatment. After the treatment is completed, it is cooled to obtain a pre-lithiation silicon oxide intermediate;

[0011] The pre-lithiated silicon oxide intermediate is added to the pre-lithiated solution B and reacted under closed conditions. After the reaction is completed, the obtained solution is evaporated to remove the solvent. The solvent can be condensed and recycled. The obtained product is placed in a heating device for treatment. After the treatment is completed, it is cooled to obtain a pre-lithiated silicon oxide material.

[0012] Furthermore, the precursor is a carbon-coated silicon material prepared by a conventional method; the silicon in the carbon-coated silicon material is amorphous silicon, and the grain size of the silicon in the carbon-coated silicon material is 2 to 50 nm; the mass ratio of carbon to silicon particles in the carbon-coated silicon material is (1 to 10):100, and the optimal ratio is (3 to 5):100; the carbon in the carbon-coated silicon material is coated on at least 80% of the surface of the silicon particles; the carbon in the carbon-coated silicon material is any one of amorphous carbon, microcrystalline soft carbon / hard carbon, and partially crystallized graphitized carbon; the thickness of the elastic layer in the carbon-coated silicon material is 5 to 100 nm; the carbon coating methods include solid phase coating, liquid phase coating and gas phase coating, and the preparation method of the silicon particles includes: mixing silicon dioxide and silicon, evaporating at high temperature, cooling, and mechanical granulation to obtain the silicon particles.

[0013] Furthermore, the sealed condition is achieved by using a sealed reactor; the purpose of the sealed condition is mainly to prevent the reaction from being interfered with by moisture and carbon dioxide; the evaporation is achieved by vacuum distillation or atmospheric distillation;

[0014] The heating device is any one of a tubular furnace, a vacuum furnace, a rotary kiln, and a drum furnace; the heating device is a heating device capable of providing vacuum conditions or inert atmosphere conditions; the mass fractions of the pre-lithiation solution A and the pre-lithiation solution B are both 1-20%.

[0015] Furthermore, the pre-lithiation solution A is composed of organic lithium A and an organic solvent; the organic lithium A is any one of lithium-biphenyl, lithium-naphthalene, lithium-biphenyl homologues, and lithium-naphthalene homologues; the electrode potential of the organic lithium A is 0.5-1.0V; and the mass ratio of the precursor to the metallic lithium in the organic lithium A is 100:(0-4).

[0016] Furthermore, the pre-lithiation solution B is composed of an organic lithium B and an organic solvent; the organic lithium B is a lithium-biphenyl derivative or a lithium-naphthalene derivative; the electrode potential of the organic lithium B is 0-0.5V; and the mass ratio of the pre-lithiation silicon-oxygen intermediate to the metallic lithium in the organic lithium B is 100:(5-10).

[0017] Furthermore, the biphenyl derivative is obtained by grafting at least one methyl group and / or ethyl group into the ring structure of biphenyl; and the naphthalene derivative is obtained by grafting at least one methyl group and / or ethyl group into the ring structure of naphthalene.

[0018] Furthermore, the organic solvent is one or more of benzene, cyclohexane, tetrahydrofuran, ether, and petroleum ether.

[0019] In a second aspect, the present invention provides a pre-lithiated silicon-oxygen material prepared by the above method.

[0020] The pre-lithiation silicon oxide material includes three layers, namely, a Li2SiO3-rich matrix layer, a Li2Si2O5-rich matrix layer and a carbon layer from the inside to the outside. There is a relatively obvious boundary between the Li2SiO3-rich matrix layer and the Li2Si2O5-rich matrix layer. In the pre-lithiation silicon oxide material, the mass percentage of the Li2SiO3-rich matrix layer in the silicon oxide particles is 70-100%, and the mass percentage of the Li2Si2O5-rich matrix layer in the silicon oxide particles is 0-30%.

[0021] In a third aspect, the present invention provides a negative electrode plate comprising the above-mentioned pre-lithiation silicon oxide material.

[0022] The preparation method of the negative electrode plate includes: adding graphite and a conductive agent into a mixing tank, dry mixing at 1200 rpm for 10 minutes, adding an aqueous solution of a thickener CMC (carboxymethyl cellulose) after mixing, and mixing at high speed at 1600 rpm for 0.5 hours, then adding the above-mentioned pre-lithiation silicon oxide material and a binder SBR (polystyrene butadiene copolymer), and mixing at 1200 rpm for 0.5 hours to obtain a slurry containing the above-mentioned pre-lithiation silicon oxide material, uniformly coating the slurry on the surface of a metal copper foil, and obtaining a negative electrode plate containing the above-mentioned pre-lithiation silicon oxide material after vacuum drying and cutting.

[0023] In a fourth aspect, the present invention provides a lithium-ion battery comprising the above-mentioned negative electrode plate.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides a preparation method for a pre-lithiated silicon oxide material, which utilizes the difference in the electrode potential of organic lithium in different pre-lithiated reagents to achieve a multilayer structure of the pre-lithiated silicon oxide material. When metallic lithium is coordinated with biphenyl or naphthalene and its homologues to form an organic pre-lithiated reagent, due to its high electrode potential (0.5-1.0V), it basically does not react with silicon oxide, but is deposited on the surface of silicon oxide particles. During the subsequent heating process, the active lithium reacts with the silicon oxide on the surface of the silicon oxide particles to generate Li2Si2O5. When metallic lithium is coordinated with a biphenyl derivative or a naphthalene derivative to form an organic pre-lithiated reagent, due to its low electrode potential (0-0.5V), which is lower than the lithium insertion potential of the silicon oxide material, it directly diffuses into the interior of the silicon oxide particles, directly reacts with unreacted silicon oxide, and further reacts to generate Li2SiO3 under the influence of thermodynamics during the subsequent heating process. The multilayer structure of the pre-lithiated silicon oxide material is finally prepared by utilizing this electrode potential difference.

[0026] The present invention provides a method for preparing a pre-lithiation silicon oxide material, which utilizes the potential difference of a pre-lithiation reagent to achieve a multilayer structure of the pre-lithiation silicon oxide material, without affecting the final pre-lithiation effect. In addition, under the protection of the outer layer Li2Si2O5, the pre-lithiation effect can be further improved (the initial efficiency is ≥90%). The solvent in the pre-lithiation process can be evaporated and recycled for repeated use, avoiding pollution and waste. The overall process is simple and easy to mass produce.

[0027] The present invention provides a pre-lithiated silicon oxide material, comprising three layers, namely, a Li2SiO3-rich matrix layer, a Li2Si2O5-rich matrix layer, and a carbon layer, from the inside out. The present invention utilizes water-stable Li2Si2O5 to protect water-unstable Li2SiO3, thereby preventing Li2SiO3 from generating alkaline substances after direct contact with water or CO2, thereby reducing the pH of the slurry during the subsequent preparation of negative electrode sheets. In the process of preparing negative electrode sheets, the slurry prepared using the pre-lithiated silicon oxide material can maintain a long processing cycle without problems such as gelation, viscosity reduction, sedimentation, and gas production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the structure of the pre-lithiation silicon-oxygen material prepared in Examples 1 to 5 of the present invention;

[0029] Figure 2 The left is a scanning electron microscope image of the pre-lithiated silicon oxide material prepared in Example 1 of the present invention. Figure 2 The right side is a cross-sectional scanning electron microscope image of the pre-lithiated silicon oxide material prepared in Example 1 of the present invention;

[0030] Figure 3 is the XRD spectrum of the pre-lithiated silicon-oxygen material prepared in Example 1 of the present invention;

[0031] Figure 42 is the viscosity-time variation curve of the pre-lithiated silicon-oxygen material prepared in Comparative Example 2 of the present invention;

[0032] Figure 5 : is the viscosity-time variation curve of the pre-lithiated silicon-oxygen material prepared in Example 1 of the present invention;

[0033] Figure 6 These are the charge and discharge curves of the carbon-coated silicon oxide material of Comparative Example 1, the pre-lithiated silicon oxide material prepared in Comparative Example 2, and the pre-lithiated silicon oxide material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] The precursor carbon-coated silicon oxide material used in the following examples and comparative examples has a silicon grain size of 8±1 nm, a carbon coating method of vapor deposition coating, partially crystallized graphitized carbon, a mass ratio of carbon to silicon oxide particles of 3.2:100, and carbon coating on the entire surface of the silicon oxide particles.

[0036] Example 1

[0037] A method for preparing a pre-lithiated silicon-oxygen material, comprising:

[0038] Step 1: 30g of metallic lithium and 666g of biphenyl are added to 3.4kg of tetrahydrofuran in a closed reactor, mixed and stirred to dissolve to obtain a pre-lithiation solution A, and then 1.0kg of the precursor is added to the pre-lithiation solution A, and the mixture is stirred and mixed for 2h. The resulting solution is dried under reduced pressure at 60°C. The evaporated solvent can be condensed and recycled. The black solid product obtained after drying is placed in a vacuum furnace, heated to 700°C under vacuum conditions for 2h, and cooled to obtain a black pre-lithiation silicon oxide intermediate;

[0039] Step 2: Add 70g of metallic lithium and 666g of methylbiphenyl to 3.5kg of tetrahydrofuran, mix and stir to dissolve in a closed reactor to obtain a pre-lithiation solution B, then add the pre-lithiation silicon oxide intermediate obtained in step 1 to the pre-lithiation solution B, continue stirring and mixing for 6h, and then dry the resulting solution under reduced pressure at 60°C. The evaporated solvent can be condensed and recycled. The black solid product obtained after drying is placed in a vacuum furnace, heated to 600°C under vacuum conditions and kept warm for 2h, and cooled to obtain a black pre-lithiation silicon oxide material.

[0040] Example 2

[0041] A method for preparing a pre-lithiated silicon-oxygen material, comprising:

[0042] Step 1: 10g of metallic lithium and 222g of biphenyl are added to 2.5kg of tetrahydrofuran in a closed reactor, mixed and stirred to dissolve to obtain a pre-lithiation solution A, and then 1.0kg of the precursor is added to the pre-lithiation solution A, and the mixture is stirred and mixed for 2h. The resulting solution is dried under reduced pressure at 60°C. The evaporated solvent can be condensed and recycled. The black solid product obtained after drying is placed in a vacuum furnace, heated to 700°C under vacuum conditions for 2h, and cooled to obtain a black pre-lithiation silicon oxide intermediate;

[0043] Step 2: Add 90g of metallic lithium and 666g of methylbiphenyl to 3.5kg of tetrahydrofuran, mix and stir in a closed reactor to dissolve to obtain a pre-lithiation solution B, then add the pre-lithiation silicon oxide intermediate obtained in step 1 to the pre-lithiation solution B, continue stirring and mixing for 6h, and then dry the resulting solution under reduced pressure at 60°C. The evaporated solvent can be condensed and recycled. The black solid product obtained after drying is placed in a vacuum furnace, heated to 600°C under vacuum conditions and kept warm for 2h, and cooled to obtain a black pre-lithiation silicon oxide material.

[0044] Example 3

[0045] A method for preparing a pre-lithiated silicon-oxygen material, comprising:

[0046] Step 1: 30g of metallic lithium and 666g of biphenyl are added to 3.4kg of tetrahydrofuran in a closed reactor, mixed and stirred to dissolve to obtain a pre-lithiation solution A, and then 1.0kg of the precursor is added to the pre-lithiation solution A, and the mixture is stirred and mixed for 2h. The resulting solution is dried under reduced pressure at 60°C. The evaporated solvent can be condensed and recycled. The black solid product obtained after drying is placed in a vacuum furnace, heated to 700°C under vacuum conditions for 2h, and cooled to obtain a black pre-lithiation silicon oxide intermediate;

[0047] Step 2: Add 80g of metallic lithium and 666g of methylbiphenyl to 3.5kg of tetrahydrofuran, mix and stir in a closed reactor to dissolve to obtain a pre-lithiation solution B, then add the pre-lithiation silicon oxide intermediate obtained in step 1 to the pre-lithiation solution B, continue stirring and mixing for 6h, and then dry the resulting solution under reduced pressure at 60°C. The evaporated solvent can be condensed and recycled. The black solid product obtained after drying is placed in a vacuum furnace, heated to 600°C under vacuum conditions and kept warm for 2h, and cooled to obtain a black pre-lithiation silicon oxide material.

[0048] Example 4

[0049] A method for preparing a pre-lithiated silicon-oxygen material, comprising:

[0050] Step 1: 30g of metallic lithium and 553g of naphthalene are added to 3.2kg of tetrahydrofuran in a closed reactor, mixed and stirred to dissolve to obtain a pre-lithiation solution A, and then 1.0kg of the precursor is added to the pre-lithiation solution A, and the mixture is stirred and mixed for 2h. The resulting solution is dried under reduced pressure at 60°C, and the evaporated solvent can be condensed and recycled. The black solid product obtained after drying is placed in a vacuum furnace, heated to 700°C under vacuum conditions for 2h, and cooled to obtain a black pre-lithiation silicon oxide intermediate;

[0051] Step 2: Add 70g of metallic lithium and 666g of methylbiphenyl to 3.5kg of tetrahydrofuran, mix and stir to dissolve in a closed reactor to obtain a pre-lithiation solution B, then add the pre-lithiation silicon oxide intermediate obtained in step 1 to the pre-lithiation solution B, continue stirring and mixing for 6h, and then dry the resulting solution under reduced pressure at 60°C. The evaporated solvent can be condensed and recycled. The black solid product obtained after drying is placed in a vacuum furnace, heated to 600°C under vacuum conditions and kept warm for 2h, and cooled to obtain a black pre-lithiation silicon oxide material.

[0052] Example 5

[0053] A method for preparing a pre-lithiated silicon-oxygen material, comprising:

[0054] Step 1: 30g of metallic lithium and 666g of biphenyl are added to 3.4kg of tetrahydrofuran in a closed reactor, mixed and stirred to dissolve to obtain a pre-lithiation solution A, and then 1.0kg of the precursor is added to the pre-lithiation solution A, and the mixture is stirred and mixed for 2h. The resulting solution is dried under reduced pressure at 60°C. The evaporated solvent can be condensed and recycled. The black solid product obtained after drying is placed in a vacuum furnace, heated to 700°C under vacuum conditions for 2h, and cooled to obtain a black pre-lithiation silicon oxide intermediate;

[0055] Step 2: Add 70g of metallic lithium and 666g of dimethylbiphenyl to 3.5kg of tetrahydrofuran, mix and stir in a closed reactor to dissolve to obtain a pre-lithiation solution B, then add the pre-lithiation silicon oxide intermediate obtained in step 1 to the pre-lithiation solution B, continue stirring and mixing for 6h, and then dry the resulting solution under reduced pressure at 60°C. The evaporated solvent can be condensed and recycled. The black solid product obtained after drying is placed in a vacuum furnace, heated to 600°C under vacuum conditions and kept warm for 2h, and cooled to obtain a black pre-lithiation silicon oxide material.

[0056] Among the above embodiments, the pre-lithiation reagent in step 1 does not react directly with the silicon oxide particles, but is only adsorbed / loaded on the surface of the silicon oxide particles. Therefore, in order to ensure sufficient adsorption / loading, enough biphenyl / naphthalene is required, and metallic lithium and biphenyl / naphthalene are combined according to the molecular mass ratio; in order to ensure the uniformity of stirring and mixing, it is necessary to use enough tetrahydrofuran solvent, but it is sufficient to be mixed, and there is no need to add excessively, and the solid content is controlled to be about 30%; due to the high activity of the pre-lithiation reagent, it is necessary to exclude the influence of moisture and carbon dioxide in the air in a closed reactor; the temperature of reduced pressure drying is 60°C, which is close to the boiling point of tetrahydrofuran. Too low temperature will reduce the drying efficiency, and too high temperature will cause boiling, posing a safety risk; the temperature of vacuum heating is 700°C, which is too low to be conducive to the generation of Li2Si2O5, and too high temperature will cause the silicon grain size to grow, affecting performance.

[0057] The pre-lithiation reagent in step 2 has a low potential and can react directly with the silicon oxide particles. Dimethylbiphenyl and the like only serve as carriers. Metallic lithium and methylbiphenyl do not need to be combined according to the molecular weight ratio, which can reduce the amount of methylbiphenyl used. In order to ensure the uniformity of stirring and mixing, sufficient tetrahydrofuran solvent needs to be used, but it is sufficient to be mixed, and there is no need to add excessive amounts, and the solid content is controlled at around 30%. Due to the high activity of the pre-lithiation reagent, it is necessary to exclude the influence of moisture and carbon dioxide in the air in a closed reactor. The temperature for reduced pressure drying can be 60°C, which is close to the boiling point of tetrahydrofuran. Too low a temperature will reduce the drying efficiency, and too high a temperature will cause boiling, posing a safety risk. The temperature for vacuum heating is 600°C. Too low a temperature is not conducive to the formation of Li2SiO3, and too high a temperature will cause the silicon grain size to grow, affecting performance.

[0058] Comparative Example 1

[0059] Precursor carbon-coated silicon-oxygen material.

[0060] Comparative Example 2

[0061] A conventional pre-lithiated silicon oxide material with a non-multilayer structure is obtained by a one-step pre-lithiation preparation method, specifically comprising: adding 100g of metallic lithium and 666g of biphenyl to 3.5kg of tetrahydrofuran, mixing and stirring in a closed reactor to dissolve to obtain a pre-lithiated solution, then adding 1.0kg of the precursor to the pre-lithiated solution, continuing to stir and mix for 2h, and then drying the obtained solution under reduced pressure at 60°C. The evaporated solvent can be condensed and recycled for reuse. The black solid product obtained after drying is placed in a vacuum furnace, heated to 600°C under vacuum conditions and kept warm for 2h, and cooled to obtain a black pre-lithiated silicon oxide material.

[0062] Application Examples

[0063] The materials of Examples 1 to 5 and Comparative Examples 1 and 2 were used to prepare negative electrode sheets, respectively, specifically comprising: adding 80 parts of graphite and 1 part of conductive carbon black into a mixing tank, dry mixing at 1200 rpm for 10 minutes, and then adding 100 parts of an aqueous solution of a thickener CMC (carboxymethyl cellulose) (mass fraction is 2% wt), and mixing at high speed at 1600 rpm for 0.5 hours. Then, 15 parts of the materials of Examples 1 to 5 and Comparative Examples 1 and 2 and 4 parts of a binder SBR (polystyrene butadiene copolymer) emulsion (mass fraction is 50% wt) were added, and mixed at 1200 rpm for 0.5 hours to obtain a slurry (the slurrying process adjusts the order of adding the pre-lithiated silicon oxide material, reduces the contact time between the pre-lithiated silicon oxide material and water, and further optimizes the stability of the slurry). The slurry is evenly coated on the surface of a metal copper foil, and the negative electrode sheet is obtained after vacuum drying at 80°C and cutting.

[0064] Performance Testing

[0065] Figure 1 Schematic diagram of the structure of the pre-lithiation silicon-oxygen material prepared in Examples 1 to 5 of the present invention. Figure 1 It can be seen that the pre-lithiation silicon oxide material includes three layers, which are a Li2SiO3-rich matrix layer, a Li2Si2O5-rich matrix layer and a carbon layer from the inside to the outside.

[0066] The morphology and structure of the samples were observed using a Thermo Fisher Apreo C scanning electron microscope. Figure 2 The left is a scanning electron microscope image of the pre-lithiated silicon oxide material prepared in Example 1. Figure 2 The right side is a cross-sectional SEM image of the pre-lithiated silicon oxide material obtained in Example 1. Figure 2 Zuohe Figure 2 As can be seen from the right, the pre-lithiated silicon-oxygen material prepared in Example 1 maintains a relatively regular particle structure, the surface carbon coating is complete, the layered structure can be clearly seen in the cross section, and the boundary between the Li2Si2O5-rich matrix layer and the Li2SiO3-rich matrix layer is obvious.

[0067] The composition of the samples was tested using a German Bruker D8 ADVANCE X-ray diffractometer. Figure 3 The XRD spectrum of the pre-lithiated silicon-oxygen material prepared in Example 1 is shown in FIG. Figure 3 It can be seen that there are obvious peaks of Li2Si2O5 (main peak 2T = about 25°), Li2SiO3 (main peak 2T = about 27°) and silicon (main peak 2T = about 28.6°). The grain size of silicon is about 11nm after fitting calculation. Figure 2 and Figure 3 It can be confirmed that a pre-lithiated silicon-oxygen material with a multilayer structure has been successfully prepared.

[0068] Anton Paar rheometer was used to test the viscosity stability of the slurry. Figure 4 The viscosity-time curve of the pre-lithiated silicon oxide material prepared in Comparative Example 2 is shown in FIG. Figure 5 The viscosity-time curve of the pre-lithiated silicon oxide material prepared in Example 1 is shown in FIG. Figure 4 and Figure 5 It can be seen that the viscosity stability of the slurry of the pre-lithiated silicon oxide material prepared in Example 1 is significantly improved, and there is basically no significant change within 24 hours, while the viscosity stability of the slurry of the pre-lithiated silicon oxide material prepared in Comparative Example 2 is greatly reduced.

[0069] Figure 6 The charge and discharge curves of the carbon-coated silicon oxide material of Comparative Example 1, the pre-lithiated silicon oxide material prepared in Comparative Example 2, and the pre-lithiated silicon oxide material prepared in Example 1 are shown. Figure 6 It can be seen that compared with the carbon-coated silicon oxide material of Comparative Example 1, the specific capacity of the material after pre-lithiation treatment is reduced, but the first efficiency is greatly improved; compared with the pre-lithiation silicon oxide material prepared in Comparative Example 2, the layered pre-lithiation silicon oxide material prepared in Example 1 has higher specific capacity and first efficiency, and the specific capacity can reach 1401.0 mAh / g, and the first efficiency can reach 91.6%.

[0070] The specific capacity and initial efficiency of the materials of Examples 1 to 5 and Comparative Examples 1 and 2 were tested using button half cells. The test results are shown in Table 1.

[0071] Table 1 Specific capacity and initial efficiency test results of materials of Examples 1 to 5 and Comparative Examples 1 and 2

[0072]

[0073] As can be seen from Table 1, by comparing Examples 1, 2, 4 and 5, it can be found that the combination of different organic lithiums can achieve pre-lithiation of silicon oxide materials and improve the initial efficiency; by comparing Examples 1 and 2, it can be found that the distribution ratio of the two-step pre-lithiation amount will not affect the pre-lithiation effect (but will affect the improvement effect on pH, as shown in the subsequent Table 2); by comparing Examples 1 and 3, it can be seen that further increasing the amount of pre-lithiation can further improve the initial efficiency, but based on safety considerations, the amount of pre-lithiation will not be significantly increased; compared with the carbon-coated silicon oxide material of Example 1 and Comparative Example 1, the specific capacity of the material after pre-lithiation treatment is reduced, but the initial efficiency is greatly improved; by comparing Comparative Example 2 and Example 1, it can be found that the layered structure pre-lithiation material has a higher specific capacity and initial efficiency.

[0074] The pH of the materials of Examples 1 to 5 and Comparative Examples 1 and 2 was tested by testing the water washing filtrate. The specific method was as follows: 10 g of the materials of Examples 1 to 5 and Comparative Examples 1 and 2 were added to 100 g of deionized water, magnetically stirred under sealed conditions for 30 minutes, filtered, and the filtrate was taken. The pH value of the filtrate was tested using a Raman pH meter. The test results are shown in Table 2.

[0075] Table 2 pH values of the filtrates collected after washing the materials of Examples 1 to 5 and Comparative Examples 1 and 2 with water

[0076]

[0077] As can be seen from Table 2, compared with Comparative Example 1, it can be found that the pH value of the materials after pre-lithiation treatment will increase; however, compared with the materials of Examples 1 to 5 and the materials of Comparative Example 2, it can be found that the overall pH value of the pre-lithiation silicon oxide material with a layered structure is lower than that of the pre-lithiation silicon oxide material with a non-layered structure. The test results show that: the outer layer of Li2Si2O5 can play an effective protective role; compared with Examples 1 and 2, it can be found that the amount of Li2Si2O5 will have a better effect only when it is at an appropriate level; compared with Examples 1 and 3, it can be found that when the amount of pre-lithiation increases, the volume expansion is greater, and the improvement effect on pH will be reduced when there are more structural defects. In general, the pH value of the pre-lithiation silicon oxide material can be effectively optimized under the condition of reasonable control of the amount of pre-lithiation and the amount of Li2Si2O5.

[0078] The gas production of the materials of Examples 1 to 5 and Comparative Examples 1 and 2 was tested. The specific method is as follows: the materials of Examples 1 to 5 and Comparative Examples 1 and 2 were prepared into slurries according to the method of the application example, 5 mL of slurry was drawn into a 30 mL syringe, the washing liquid port was blocked with a rubber head, and then left to stand at a constant temperature of 25°C, and the piston movement position was observed and recorded at different times, wherein the gas production rate = ((piston movement position scale - 5) / 5) * 100%, and the gas production test results are shown in Table 3.

[0079] Table 3 Gas production test results of slurries prepared from materials of Examples 1 to 5 and Comparative Examples 1 and 2

[0080]

[0081] Note: "Explosion" means that the gas production is too much and exceeds the range, and the piston rushes out of the syringe tube.

[0082] As can be seen from Table 3, a comparison of Examples 1 to 5 shows that the slurry made from the pre-lithiated silicon oxide material having the Li2Si2O5 layer does not or rarely produces bubbles, while a large amount of gas is produced in Comparative Example 2. Combined with the results of Comparative Example 1, it can be clearly seen that Li2SiO3 dissolves in the water system, thereby exposing the nano-silicon grains in the matrix to react with water to produce gas. The Li2Si2O5 layer can effectively isolate the contact between water and Li2SiO3, thereby avoiding the dissolution of Li2SiO3 and causing gas production problems.

[0083] In summary, from the above experimental results, it can be seen that the pre-lithiation silicon oxide material with a multilayer structure described in the present invention can effectively solve the problems of high pH and gas production caused by pre-lithiation, and improve its stability as a negative electrode slurry. On this basis, it does not change the morphology of the material particles and maintains a high specific capacity and initial efficiency, thereby maintaining the effect of the pre-lithiation treatment to the greatest extent.

[0084] The present invention constructs a multilayer structure and utilizes the water-stable characteristics of Li2Si2O5 to protect the water-unstable Li2SiO3, thereby preventing Li2SiO3 from directly contacting water or CO2 to generate alkaline substances, thereby reducing the pH of the slurry in the subsequent preparation of the negative electrode sheet; in the process of preparing the negative electrode sheet, the slurry prepared by using pre-lithiated silicon oxide can maintain a long processing cycle and will not have problems such as gelation, viscosity reduction, sedimentation, and gas production. The construction of the multilayer structure is achieved by utilizing the potential difference of the pre-lithiation reagent, which will not affect the final pre-lithiation effect, and under the protection of the outer layer of Li2Si2O5, the pre-lithiation effect can be further improved (the first efficiency is ≥90%); the solvent in the pre-lithiation process can be evaporated and recycled for repeated use to avoid pollution and waste. The overall process is simple and easy to mass produce.

[0085] The pre-lithiated silicon oxide material of the present invention can be used to prepare negative electrode plates, and can also be used to prepare lithium-ion batteries.

[0086] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A method for preparing a pre-lithiated silicon-oxygen material, characterized in that: The method comprises the following steps: The precursor includes silicon-oxygen particles; The precursor is added to the pre-lithiation solution A and reacted under closed conditions. After the reaction is completed, the obtained solution is evaporated to remove the solvent, and the obtained product is placed in a heating device for treatment. After the treatment is completed, it is cooled and reacted on the surface of the silicon oxide particles to generate Li2Si2O5, thereby obtaining a pre-lithiation silicon oxide intermediate; The pre-lithiated silicon oxide intermediate is added to the pre-lithiated solution B and reacted under closed conditions. After the reaction is completed, the obtained solution is evaporated to remove the solvent. The obtained product is placed in a heating device for treatment. After the treatment is completed, it is cooled and reacted inside the silicon oxide particles to generate Li2SiO3, thereby finally obtaining a pre-lithiated silicon oxide material. The pre-lithiation solution A is composed of an organic lithium A and an organic solvent; the organic lithium A is any one of lithium-biphenyl, lithium-naphthalene, lithium-biphenyl homologues, and lithium-naphthalene homologues; the electrode potential of the organic lithium A is 0.5 to 1.0 V; The pre-lithiation solution B consists of an organic lithium B and an organic solvent; the organic lithium B is a lithium-biphenyl derivative or a lithium-naphthalene derivative; and the electrode potential of the organic lithium B is 0-0.5V.

2. The method for preparing the pre-lithiated silicon oxide material according to claim 1, wherein: The precursor is a carbon-coated silicon-oxygen material prepared by a conventional method; the silicon in the carbon-coated silicon-oxygen material is amorphous silicon, and the grain size of the silicon in the carbon-coated silicon-oxygen material is 2 to 50 nm; the mass ratio of carbon to silicon-oxygen particles in the carbon-coated silicon-oxygen material is (1 to 10):100; and the carbon in the carbon-coated silicon-oxygen material is coated on at least 80% of the surface of the silicon-oxygen particles.

3. The method for preparing the pre-lithiated silicon oxide material according to claim 1, wherein: The sealed condition is achieved by a closed reactor; the evaporation is performed by reduced pressure distillation or atmospheric pressure distillation; the heating device is any one of a tubular furnace, a vacuum furnace, a rotary furnace, and a drum furnace; and the mass fractions of the pre-lithiation solution A and the pre-lithiation solution B are both 1-20%.

4. The method for preparing the pre-lithiated silicon oxide material according to claim 1, wherein: The mass ratio of the precursor to the metallic lithium in the organic lithium A is 100:(0-4), excluding the endpoint value of 0.

5. The method for preparing the pre-lithiation silicon oxide material according to claim 1, wherein: The mass ratio of the pre-lithiated silicon-oxygen intermediate to the metallic lithium in the organic lithium B is 100:(5-10).

6. The method for preparing the pre-lithiated silicon oxide material according to claim 1, wherein: The biphenyl derivative is obtained by grafting at least one methyl group and / or ethyl group into the ring structure of biphenyl; the naphthalene derivative is obtained by grafting at least one methyl group and / or ethyl group into the ring structure of naphthalene.

7. The method for preparing a pre-lithiated silicon-oxygen material according to claim 1, wherein: The organic solvent is one or more of benzene, cyclohexane, tetrahydrofuran, ether and petroleum ether.

8. The pre-lithiated silicon-oxygen material prepared by the method according to any one of claims 1 to 7.

9. A negative electrode plate, characterized in that: Including the pre-lithiation silicon oxide material according to claim 8.

10. A lithium ion battery, characterized in that: Including the negative electrode sheet according to claim 9.

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