Negative electrode material, preparation method and application thereof

Abstract

The application relates to the technical field of lithium ion batteries, and discloses a negative electrode material and a preparation method and application thereof, wherein the negative electrode material is a core-shell structure, the inner core is a silicon-based particle, and the shell comprises a first coating layer and a second coating layer; the first coating layer is attached outside the inner core, and the second coating layer is attached outside the first coating layer; the first coating layer comprises a carbon-nitrogen compound, and the second coating layer comprises a phosphate salt. The negative electrode material provided by the application takes a silicon-based particle as the inner core, and the carbon-nitrogen coating layer and the phosphate coating layer are attached outside the inner core in sequence; under the action of the double coating layers, the lithium ion conduction capacity and the electrochemical performance of the negative electrode material are effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] In recent years, lithium ion batteries (LIBs) are not only required to have long cycle life and green environmental protection, but also need to have high energy / power density. The theoretical lithium intercalation capacity of the current graphite negative electrode is only 372 mAh / g, which seriously limits the further improvement of the energy density of lithium ion batteries and cannot meet the market demand of rapid development. Therefore, it is necessary to develop a negative electrode material with high energy density, strong durability and long cycle life.

[0003] Silicon-based materials are considered to be one of the most attractive negative electrode materials for lithium ion batteries, because silicon-based materials have a very high theoretical capacity (up to 3579 mAh / g, about 10 times that of graphite), and the content of silicon element is very rich and the raw material is relatively cheap. However, silicon has a large volume expansion (about 300%) during lithiation and delithiation, which will cause the solid electrolyte interface (SEI) film to be continuously broken and reformed, the particles to be broken and even crushed during the cycle process, so it greatly leads to the low first coulombic efficiency, fast capacity decay and poor cycle stability of silicon-based materials.

[0004] The first coulombic efficiency (referred to as first efficiency) is an important indicator to measure the charging and discharging capacity of lithium ion batteries. With the increase of the content of silicon, the first efficiency will be lower and lower, and the effective method to improve the first efficiency is pre-lithiation, that is, a small amount of lithium is added in advance in the negative electrode to supplement the lithium consumed in the process of side reaction and solid electrolyte interface (SEI) film formation. However, to achieve high capacity pre-lithiation in lithium batteries, a very thin lithium foil (thickness less than 5 μm) needs to be made, which brings great technical difficulty, and when using a thin lithium foil for pre-lithiation, the utilization efficiency of lithium metal is not high, and lithium metal fragments may be produced, affecting the performance and service life of the battery.

[0005] In order to solve the above problems, a coating process is adopted for the substrate material. The currently reported coating process is mostly limited to single-layer coating, and usually ignores the design of the mechanical properties (elasticity, rigidity, toughness, etc.) of the coating layer, while the mechanical properties of the coating layer are particularly important for the regulation of stress and strain of the electrode. The design ignoring the mechanical properties leads to poor mechanical properties of the coating layer, which cannot adapt to the severe stress and strain in the lithiation / delithiation process, and the coated electrode material exhibits unsatisfactory electrochemical performance.

[0006] Therefore, it is urgent to provide a negative electrode material with excellent mechanical properties, which can resist the stress caused by the volume expansion of the silicon-based negative electrode material during lithiation, improve the structural stability of the SEI film, and thus improve the initial coulombic efficiency, capacity attenuation performance and cycle stability of the material. SUMMARY

[0007] The purpose of the present application is to overcome the problems of poor mechanical properties of silicon-based materials in the prior art, which cannot adapt to the severe stress generated by the volume expansion of silicon during lithiation and delithiation, leading to the rupture or crushing of the SEI film, resulting in low initial coulombic efficiency, fast capacity attenuation and poor cycle stability of the silicon-based negative electrode material.

[0008] To achieve the above-mentioned purpose, the first aspect of the present application provides a negative electrode material, wherein the negative electrode material is of a core-shell structure, the inner core is a silicon-based particle, and the outer shell comprises a first coating layer and a second coating layer.

[0009] The first coating layer is attached to the outside of the inner core, and the second coating layer is attached to the outside of the first coating layer.

[0010] The first coating layer comprises a carbon-nitrogen compound, and the second coating layer comprises a phosphate.

[0011] The second aspect of the present application provides a preparation method of a negative electrode material, wherein the method comprises the following steps:

[0012] (1) In an organic solvent, mix silicon-based particles, a dopant, an oxidizing agent and a nitrogen-containing heterocyclic compound monomer, and perform drying treatment to obtain a gray-brown powder;

[0013] (2) In an acidic solution, heat treat the gray-brown powder with a phosphate to obtain a negative electrode material.

[0014] The third aspect of the present application provides a negative electrode material prepared by the method of the present application.

[0015] The fourth aspect of the present application provides the application of the negative electrode material of the present application in lithium ion batteries.

[0016] Through the above technical solution, the present application achieves the following beneficial technical effects:

[0017] (1) The silicon-based particles used in the present application are micron-sized, and the preparation process is simpler and the cost is lower compared to nanoscale silicon-based particles.

[0018] (2) The negative electrode material provided by the application has a silicon-based particle as a core, and a carbon-nitrogen coating layer and a lithium phosphate coating layer are sequentially attached outside the core, wherein the carbon-nitrogen coating layer has strong flexibility and adhesion, can absorb residual stress transmitted by the rigid coating layer, and further improves the stability of the structure; the lithium phosphate coating layer has excellent mechanical properties, improves the cycle stability of the negative electrode material, and can ensure the rapid transmission of ions / electrons and improve the rate performance of the negative electrode material. Under the action of the double coating layers, the lithium ion conduction capacity and the electrochemical performance of the negative electrode material are effectively improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 are scanning electron microscope (SEM) images of the negative electrode materials A1 and B1-B3 prepared in Example 1 and Comparative Examples 1-3, respectively;

[0020] Figure 1 a-1d correspond to the samples of Si@NC@LPO in Example 1, Si@NC in Comparative Example 1, Si@LPO in Comparative Example 2, and Si@LPO@NC in Comparative Example 3, respectively.

[0021] Figure 2 are energy X-ray spectroscopy (EDS) images of the negative electrode materials A1 and B1-B3 prepared in Example 1 and Comparative Examples 1-3, respectively;

[0022] Figure 2 a-2d correspond to the samples of Si@NC@LPO in Example 1, Si@NC in Comparative Example 1, Si@LPO in Comparative Example 2, and Si@LPO@NC in Comparative Example 3, respectively.

[0023] Figure 3 are the first cycle charge-discharge curves of the coin batteries C1, D1-D3 prepared by taking the negative electrode materials A1 and B1-B3 prepared in Example 1 and Comparative Examples 1-3 as negative electrode active materials under 0.01-1.5V, 0.1C;

[0024] Figure 3 a-3d correspond to the coin batteries C1 and D1-D3 prepared by taking Si@NC@LPO in Example 1, Si@NC in Comparative Example 1, Si@LPO in Comparative Example 2, and Si@LPO@NC in Comparative Example 3 as negative electrode active materials, respectively.

[0025] Figure 4 are the charge-discharge cycle curves of the coin batteries C1, D1-D3 prepared by taking the negative electrode materials A1 and B1-B3 prepared in Example 1 and Comparative Examples 1-3 as negative electrode active materials under 0.01-1.5V, 1C;

[0026] Figure 4a-4d correspond to the coin batteries C1 and D1-D3 prepared with Si@NC@LPO in Example 1, Si@NC in Comparative Example 1, Si@LPO in Comparative Example 2, Si@LPO@NC in Comparative Example 3 as negative active material, respectively.

[0027] Figure 5 is a scanning electron microscope (SEM) image of the micron silicon particles in Comparative Example 4.

[0028] Figure 6 is the first cycle charge-discharge curve of the coin battery D4 prepared with the micron silicon in Comparative Example 4 as negative active material, cycled at 0.01-1.5V, 0.1C.

[0029] Figure 7 is the charge-discharge cycle curve of the coin battery D4 prepared with the micron silicon in Comparative Example 4 as negative active material, cycled at 0.01-1.5V, 1C. DETAILED DESCRIPTION

[0030] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the invention. Any numeric range recited is intended to include all values from the lower value to the upper value. For values which are not numeric, the recited range is intended to include all values between the recited values. Numeric ranges can be combined with other ranges or values to form new ranges, which are to be construed in accordance with the above.

[0031] The first aspect of the present application provides a negative electrode material, wherein the negative electrode material is a core-shell structure, the inner core is a silicon-based particle, and the shell comprises a first coating layer and a second coating layer.

[0032] The first coating layer is attached outside the inner core, and the second coating layer is attached outside the first coating layer.

[0033] The first coating layer comprises a carbon-nitrogen compound, and the second coating layer comprises a phosphate.

[0034] According to some embodiments of the present application, the particle size of the silicon-based particle is 1-5 μm.

[0035] According to some embodiments of the present application, the phosphate is selected from lithium phosphate and / or lithium dihydrogen phosphate, and preferably is lithium phosphate.

[0036] In the present application, the type of phosphate meets the above range, which can provide a coating layer with certain rigidity and improve the mechanical properties of the coating layer.

[0037] In the present application, the carbon-nitrogen compound is prepared by carbonization of a polymer.

[0038] Preferably, the polymer is selected from at least one of polypyrrole and / or polyaniline, more preferably polypyrrole.

[0039] In the present application, the negative electrode material takes silicon-based particles as the inner core, and has carbon-nitrogen coating layer and lithium phosphate coating layer attached outside the inner core in sequence, wherein the carbon-nitrogen coating layer serves as a flexible layer, has strong flexibility and adhesion, can absorb residual stress transmitted by the rigid coating layer, and further improves the stability of the structure; the lithium phosphate coating layer serves as a rigid layer, has excellent mechanical properties, can resist the stress caused by the volume expansion of the silicon-based negative electrode during lithiation, further improves the stability of the material structure, thereby improving the first cycle efficiency; at the same time, the irreversible deformation and fracture of the SEI film are avoided, the integrity of the SEI film structure is maintained, the lithium ion conduction capacity of the material in the charging and discharging process is improved, thereby improving the rate performance of the material. Under the action of the double coating layers, the lithium ion conduction capacity of the negative electrode material and the electrochemical performance of the negative electrode material are effectively improved.

[0040] The second aspect of the present application provides a preparation method of a negative electrode material, wherein the method comprises the following steps:

[0041] (1) mixing silicon-based particles, a dopant, an oxidizing agent and a pyrrole monomer in an organic solvent, and performing drying treatment to obtain a gray-brown powder;

[0042] (2) performing heat treatment on the gray-brown powder and a phosphate in an acidic solution to obtain a negative electrode material.

[0043] According to some embodiments of the present application, the molar ratio of the dopant, the nitrogen-containing heterocyclic compound and the oxidizing agent is 1:(1-3):(6-9).

[0044] According to some embodiments of the present application, the nitrogen-containing heterocyclic compound is selected from pyrrole and / or aniline, and is preferably pyrrole.

[0045] According to some embodiments of the present application, the organic solvent is anhydrous ethanol.

[0046] According to some embodiments of the present application, the dopant is selected from at least one of sodium p-toluenesulfonate, sodium dodecyl sulfonate and sodium dodecyl benzene sulfonate, and is preferably sodium p-toluenesulfonate.

[0047] According to some embodiments of the present application, the oxidizing agent is selected from iron chloride and / or ferrous chloride, and is preferably iron chloride.

[0048] In the present application, the silicon-based particle powder is used as raw material, sodium toluenesulfonate is used as dopant, and ferric chloride is used as oxidant to initiate in-situ polymerization of pyrrole monomer to generate polypyrrole, which is attached to the outer surface of the silicon-based particle, and then heat treatment is performed to carbonize the polypyrrole into a carbon-nitrogen coating layer uniformly attached to the silicon-based particle, thereby providing a carbon-nitrogen coating layer with flexibility and adhesion, and improving the stability of the structure of the negative electrode material.

[0049] According to some embodiments of the present application, the acidic solution is a mixed solution of formic acid and water.

[0050] Preferably, the volume ratio of formic acid to water is (1-5):100.

[0051] According to some embodiments of the present application, the mass ratio of the silicon-based particle to the phosphate is (5-25):1.

[0052] According to some embodiments of the present application, in step (1), the mixing method comprises magnetic stirring under ice bath conditions.

[0053] Preferably, the temperature of the ice bath is 0-3℃, and the conditions of magnetic stirring include a rotation speed of 200-300r / min and a time of 6-8h.

[0054] According to some embodiments of the present application, in step (1), the drying treatment is performed at a temperature of 60-80℃ for a time of 11-12h.

[0055] In the present application, in step (2), before heat treatment, heating and grinding treatment are further included, and the specific method comprises mixing and dispersing the grayish brown powder and the phosphate in the acidic solution, heating to dryness under magnetic stirring, collecting the solid product for grinding to obtain dark brown powder.

[0056] According to some embodiments of the present application, in step (2), the heat treatment method comprises heating to 300-500℃ at a heating rate of 5-10℃ / min in an argon atmosphere, and heat treatment is performed for 3-6h.

[0057] In the present application, the above method can adjust the inner and outer sequences of the carbon-nitrogen coating layer and the phosphate coating layer attached to the shell of the silicon-based material, forming a coating layer with "soft inside and hard outside", which effectively avoids particle breakage of the silicon-based negative electrode material in the cycle process due to its unique double energy absorption mechanism, improves the structural stability of the negative electrode material in the cycle process, and thereby improves the first cycle efficiency of the negative electrode material.

[0058] The third aspect of the present application provides a negative electrode material prepared by the method of the present application.

[0059] The fourth aspect of the present application provides application of the negative electrode material in the lithium ion battery.

[0060] The present application will be described in detail below through examples.

[0061] Unless otherwise specified, the materials are commercially available.

[0062] Example 1

[0063] (1) 0.5 g of micron silicon powder (particle size of 1 μm) was dispersed in 40 mL of anhydrous ethanol, and the silicon powder dispersion was placed in an ice bath, and sodium p-toluenesulfonate, pyrrole monomer, and anhydrous ferric chloride were added, respectively, and stirred at 0°C for 6 h (rotational speed of 250 r / min), and after centrifugation at 6000 r / min, a Si@PPy precursor was obtained, and the Si@PPy precursor was dried at 80°C for 12 h to obtain a grayish brown powder, i.e., Si@PPy powder;

[0064] The molar ratio of sodium p-toluenesulfonate, pyrrole monomer, and anhydrous ferric chloride is 1:3:9.

[0065] (2) 2 g of Si@PPy powder and 0.1 g of lithium phosphate were added to a mixed solution of 1000 μL of formic acid and 100 mL of water (volume ratio of formic acid to water of 1:100), and after thorough mixing, the solution was stirred at 80°C until it was evaporated, and the solid product was collected and ground to obtain a dark brown powder;

[0066] (3) The above dark brown powder was transferred to a tube furnace, and heated to 400°C at a rate of 5°C / min under an argon atmosphere, and heat-treated for 6 h to obtain Si@NC@LPO powder, i.e., the negative electrode material A1 was prepared;

[0067] The negative electrode material A1 prepared has a carbon-nitrogen coating layer and a lithium phosphate coating layer attached to the outside of the silicon-based particles in sequence.

[0068] Comparative Example 1

[0069] (1) 0.5 g of silicon powder was dispersed in 40 mL of ethanol, and sodium p-toluenesulfonate and pyrrole monomer were added, respectively, and ultrasonicated for 10 min, and FeCl3 was dissolved in 20 mL of ethanol, and the silicon powder dispersion was stirred in an ice bath, and the FeCl3 ethanol solution was added, and stirred at 0°C for 6 h (rotational speed of 250 r / min), and after centrifugation at 6000 r / min, a Si@PPy precursor was obtained, and the Si@PPy precursor was dried at 80°C for 12 h to obtain a grayish brown powder, i.e., Si@PPy powder;

[0070] The molar ratio of sodium p-toluenesulfonate, pyrrole monomer, and anhydrous ferric chloride is 1:3:9.

[0071] (2) The above grayish-brown powder was transferred to a tube furnace, heated to 400°C at 5°C / min under an argon atmosphere, and heat-treated for 6h to obtain Si@NC powder, i.e., to prepare the negative electrode material B1;

[0072] The negative electrode material B1 prepared has only a carbon-nitrogen coating layer attached to the outside of the silicon-based particles.

[0073] Comparative Example 2

[0074] (1) In a mixed solution of 1000μL formic acid and 100ml water (volume ratio of formic acid to water 1:100), 2g micron silicon powder and 0.1g lithium phosphate were added, and after being mixed thoroughly, magnetic stirring was performed at 80°C until the solution was evaporated to dryness, and the solid product was collected and ground to obtain a dark brown powder;

[0075] (2) The above dark brown powder was transferred to a tube furnace, heated to 400°C at 5°C / min under an argon atmosphere, and heat-treated for 6h to obtain Si@LPO powder, i.e., to prepare the negative electrode material B2;

[0076] The negative electrode material B2 prepared has only a lithium phosphate coating layer attached to the outside of the silicon-based particles.

[0077] Comparative Example 3

[0078] (1) In a mixed solution of 1000μL formic acid and 100ml water (volume ratio of formic acid to water 1:100), 2g micron silicon powder and 0.1g lithium phosphate were added, and after being mixed thoroughly, magnetic stirring was performed at 80°C until the solution was evaporated to dryness, and the solid product was collected, ground and dried at 80°C for 12h to obtain a dark brown powder, i.e., Si@LPO powder;

[0079] (2) 0.5g of the dark brown powder was dispersed in 40mL anhydrous ethanol, and sodium p-toluenesulfonate and pyrrole monomer were added respectively, and ultrasonic treatment was performed for 10min, FeCl3was dissolved in 20mL ethanol, and the silicon powder dispersion was stirred under ice bath conditions, and the FeCl3ethanol solution was added, and stirring was performed at 0°C for 6h (rotational speed 250r / min), and after centrifugation at 6000r / min, Si@LPO@PPy precursor was obtained;

[0080] The molar ratio of sodium p-toluenesulfonate, pyrrole monomer and anhydrous ferric chloride was 1:3:9;

[0081] (3) The above Si@LPO@PPy precursor was transferred to a tube furnace, heated to 400°C at 5°C / min under an argon atmosphere, and heat-treated for 6h to obtain Si@LPO@NC powder, i.e., to prepare the negative electrode material B3;

[0082] The prepared negative electrode material B3 has a lithium phosphate coating layer and a carbon-nitrogen coating layer attached to the silicon-based particles in sequence.

[0083] Comparative Example 4

[0084] The micron silicon particles (particle size 1 μm) were used as the negative electrode material B4, and the silicon-based particles had no coating layer.

[0085] Test Example 1

[0086] The negative electrode materials A1 and B1-B4 (Si@NC@LPO, Si@NC, Si@LPO, Si@LPO@NC and micron silicon particles) in Example 1 and Comparative Examples 1-4 were used as the negative electrode active material, Super P was used as the conductive agent, and PAA-Li was used as the binder. The three were mixed in a mass ratio of 8:1:1, water was used as the solvent, and the mixture was ground in a marquise mortar for 30 min to obtain an electrode slurry. The copper foil was used as the current collector, the electrode slurry was coated on the copper foil, and then transferred to a vacuum drying oven. After vacuum drying at 80°C for 12 h, the copper foil was taken out, and a punching machine was used to punch a circular electrode with a diameter of 11 mm. The prepared electrode was used as the negative electrode, lithium foil was used as the counter electrode, celgard 2500 was used as the separator, and the organic solvent containing 1 mol / L LiPF6, EC+DMC (volume ratio 1:1) and 5% FEC was used as the electrolyte. CR2032 button cells C1, D1-D4 were assembled in an argon-filled glove box.

[0087] The above CR2032 button cells C1, D1-D4 were subjected to scanning electron microscopy (SEM) test and energy dispersive X-ray spectroscopy (EDS) test, and the assembled batteries were subjected to electrochemical performance test on a LAND battery test system. The results are shown in Figures 1-7

[0088] Energy dispersive X-ray spectroscopy (EDS) test: Oxford energy dispersive X-ray fluorescence spectrometer produced by Oxford Company was used, and the instrument model was Oxford X-MAX.

[0089] Figure 1 The scanning electron microscopy (SEM) images of the negative electrode materials A1 and B1-B3 prepared in Example 1 and Comparative Examples 1-3 are shown in Figure 1 a-1d correspond to the scanning electron microscopy (SEM) images of the Si@NC@LPO in Example 1, Si@NC in Comparative Example 1, Si@LPO in Comparative Example 2, and Si@LPO@NC in Comparative Example 3, respectively. As shown in Figure 1 ​​

[0090] Figure 2 The images show the energy X-ray energy dispersive spectroscopy (EDS) spectra of the negative electrode materials A1 and B1-B3 prepared in Example 1 and Comparative Examples 1-3, respectively. Figure 2 a-2d correspond to the energy X-ray energy dispersive spectroscopy (EDS) spectra of the Si@NC@LPO samples in Example 1, Si@NC samples in Comparative Example 1, Si@LPO samples in Comparative Example 2, and Si@LPO@NC samples in Comparative Example 3, respectively. Figure 2 As shown, each element in each sample is uniformly dispersed on the surface of the negative electrode material, indicating that the coating effect of the four samples in Example 1 and Comparative Examples 1-3 is good.

[0091] Figure 3 The first-cycle charge-discharge curves of button batteries C1 and D1-D3 prepared using the negative electrode materials A1 and B1-B3 obtained in Example 1 and Comparative Examples 1-3 as negative electrode active materials were obtained under a voltage window of 0.01-1.5V and a current density of 0.1C (1C current density is 2000mA / g). Figure 3 a- Figure 3 d corresponds to the first-cycle charge-discharge curves of button batteries C1 and D1-D3 prepared using Si@NC@LPO in Example 1, Si@NC in Comparative Example 1, Si@LPO in Comparative Example 2, and Si@LPO@NC in Comparative Example 3 as the negative electrode active materials, respectively. Figure 3 It can be seen that the button cell prepared using the Si@NC@LPO sample in Example 1 as the negative electrode active material has a discharge specific capacity of 3222.6 mAh / g and a charge specific capacity of 2772.1 mAh / g in the first cycle, with a coulombic efficiency of 86.0% in the first cycle; the button cell prepared using the Si@NC sample in Comparative Example 1 as the negative electrode active material has a discharge specific capacity of 3308.1 mAh / g and a charge specific capacity of 2888.8 mAh / g in the first cycle, with a coulombic efficiency of 87%. The discharge specific capacity and charge specific capacity of the button cell prepared using the Si@LPO sample in Comparative Example 2 as the negative electrode active material were 3295.6 mAh / g and 2934.7 mAh / g, respectively, and the coulombic efficiency of the first cycle was 89.1%. The discharge specific capacity and charge specific capacity of the button cell prepared using the Si@LPO@NC sample in Comparative Example 3 as the negative electrode active material were 3277.2 mAh / g and 2823.4 mAh / g, respectively, and the coulombic efficiency of the first cycle was 86.2%.

[0092] Figure 4 The figures show the charge-discharge cycle curves of button batteries C1 and D1-D3 prepared using the negative electrode materials A1 and B1-B3 obtained in Example 1 and Comparative Examples 1-3 as negative electrode active materials, respectively, at 1C for 100 cycles within a voltage window of 0.01-1.5V. Figure 4a-4d respectively correspond to the first cycle charge-discharge curves of the button cell C1 and D prepared by taking Si@NC@LPO in Example 1, Si@NC in Comparative Example 1, Si@LPO in Comparative Example 2, and Si@LPO@NC in Comparative Example 3 as the negative active material 1- The charge-discharge cycle data of D3, obtained by Figure 4 It can be seen that the reversible specific capacity of the Si@NC@LPO electrode in Example 1, the Si@NC electrode in Comparative Example 1, the Si@LPO electrode in Comparative Example 2, and the Si@LPO@NC electrode in Comparative Example 3 is 1609.6 mAh / g, 1410.5 mAh / g, 1357.4 mAh / g, and 1328.0 mAh / g, respectively, after 100 stable cycles; the capacity retention rate is 91.1%, 98.9%, 88.9%, and 100%, respectively, from the 20th cycle.

[0093] Figure 5 is a scanning electron microscope (SEM) image of the micron silicon particles in Comparative Example 4. It can be seen from Figure 5 that the particle size of the micron silicon particles is uneven, and is basically distributed in 1-5 μm, the particle surface is rough, and agglomeration exists.

[0094] Figure 6 is the first cycle charge-discharge curve of the button cell D4 prepared by taking the micron silicon in Comparative Example 4 as the negative active material, cycled at 0.01-1.5 V and 0.1 C. It can be seen from Figure 6 that the discharge specific capacity and the charge specific capacity of the button cell prepared by taking the micron silicon as the negative active material are 3211.6 mAh / g and 2568.7 mAh / g, respectively, in the first cycle, and the first cycle coulombic efficiency is only 80.0%.

[0095] Figure 7 is the charge-discharge cycle curve of the button cell D4 prepared by taking the micron silicon in Comparative Example 4 as the negative active material, cycled at 0.01-1.5 V and 1 C. It can be seen from Figure 7 that the reversible specific capacity of the button cell prepared by taking the micron silicon as the negative active material is 1016.5 mAh / g after 100 stable cycles, and the capacity retention rate is 89.6%.

[0096] In summary, the negative electrode material prepared by the method of the present application has a carbon-nitrogen coating layer and a lithium phosphate coating layer attached in sequence outside the silicon-based material, and the reversible specific capacity of the negative electrode material is higher after long cycle.

[0097] The above describes the preferred embodiments of the present application in detail, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application, and all fall within the protection scope of the present application.

Claims

1. A negative electrode material, characterized by, The negative electrode material is a core-shell structure, the inner core is a silicon-based particle, and the shell comprises a first coating layer and a second coating layer; The first coating layer is attached to the outside of the inner core, and the second coating layer is attached to the outside of the first coating layer; The first coating layer comprises a carbon-nitrogen compound, and the second coating layer comprises a phosphate; The phosphate is selected from lithium phosphate and / or lithium dihydrogen phosphate; The particle size of the silicon-based particle is 1-5 μm.

2. The negative electrode material of claim 1, wherein, The phosphate is lithium phosphate.

3. A method for producing the negative electrode material according to claim 1 or 2, characterized by, The method comprises the following steps: (1) In an organic solvent, mix silicon-based particles, a dopant, an oxidizing agent, and a nitrogen-containing heterocyclic compound monomer, dry-treat to obtain a grayish brown powder; (2) In an acidic solution, heat-treat the grayish brown powder with a phosphate to obtain a negative electrode material.

4. The method of claim 3, wherein, The molar ratio of the dopant, the nitrogen-containing heterocyclic compound, and the oxidizing agent is 1:(1-3):(6-9); And / or, the nitrogen-containing heterocyclic compound is selected from pyrrole and / or aniline.

5. The method of claim 4, wherein, The nitrogen-containing heterocyclic compound is pyrrole.

6. The method of claim 3, wherein, The organic solvent is anhydrous ethanol; And / or, the dopant is selected from at least one of sodium p-toluenesulfonate, sodium dodecyl sulfonate, and sodium dodecyl benzene sulfonate; And / or, the oxidizing agent is selected from iron chloride and / or ferrous chloride.

7. The method of claim 6, wherein, The dopant is sodium p-toluenesulfonate.

8. The method of claim 6, wherein, The oxidizing agent is iron chloride.

9. The method of any of claims 3-8, wherein, The acidic solution is a mixed solution of formic acid and water.

10. The method of claim 9, wherein, The volume ratio of the formic acid to water is (1-5):

100.

11. The method of any one of claims 3-8, wherein, The mass ratio of the silicon-based particles to the phosphate is (5-25):

1.

12. The method of any one of claims 3-8, wherein, In step (1), the mixing method comprises: under ice bath conditions, magnetic stirring.

13. The method of claim 12, wherein, The temperature of the ice bath is 0-3℃, and the conditions of the magnetic stirring comprise: a rotation speed of 200-300 r / min and a time of 6-8 h.

14. The method of any one of claims 3-8, wherein, In step (1), the dry-treating temperature is 60-80℃, and the time is 11-12 h; And / or, in step (2), the heat-treating method comprises: under an argon atmosphere, heating at a heating rate of 5-10℃ / min to 300-500℃, and heat-treating for 3-6 h.

15. A negative electrode material prepared by the method of any one of claims 3-14.

16. The use of the negative electrode material of claim 15 in a lithium ion battery.

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