High-strength long-circulation silicon-carbon negative electrode material and preparation method thereof

Abstract

The application belongs to the technical field of negative electrode materials, and particularly relates to a high-strength long-cycle silicon-carbon negative electrode material and a preparation method thereof. A high-strength carbon component is obtained by designing the molecular structure of a carbon precursor; through double-layer carbon coating treatment on silicon particles, a dense outer layer carbon with low specific surface area is used to improve electronic conductivity and form a stable interface, and a high-strength porous inner layer carbon is used to limit the volume expansion of the silicon particles, so that a silicon-carbon negative electrode material with stable cycle performance is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of negative electrode materials, and particularly relates to a high-strength long-cycle silicon-carbon negative electrode material and a preparation method thereof. BACKGROUND

[0002] Silicon has become an important high-performance negative electrode material for current high-energy-density lithium-ion batteries due to its high theoretical specific capacity, low lithium intercalation / deintercalation potential, and abundant reserves, but the large volume expansion effect and low electrical conductivity of the silicon negative electrode limit the further application of the silicon negative electrode in commerce. At present, the most commonly used method to improve the performance of the silicon negative electrode is to composite the silicon negative electrode material with a carbon material, and the characteristics of the carbon material are used to absorb the mechanical stress caused by the volume expansion of silicon, establish a rapid transmission channel for ions and electrons to increase the electrical conductivity, or avoid direct contact between silicon and electrolyte to maintain chemical stability.

[0003] A wide variety of carbon materials have different structures, from traditional graphite to later carbon nanotubes, graphene, and graphdiyne, and new carbon materials are developing rapidly. Researchers try different combination methods and different combination structures to well control the volume and interface problems of the composite silicon-carbon negative electrode. At present, although the overall performance of the silicon-carbon negative electrode is good, it is a type of material that is closest to industrialization for the silicon negative electrode, but its commercialization process is still slow. The main reason is that the strength of the carbon component for maintaining the stability of the silicon particles is not enough, and it is difficult to limit the volume expansion of the silicon particles to maintain the structural stability.

[0004] The type of carbon source precursor seriously affects the structural characteristics of the carbon material, so the molecular structure design of the carbon precursor is particularly important. At present, the carbon source used for silicon material compounding is mainly pitch and phenolic resin, and the strength of the prepared carbon component is insufficient, so it is urgent to optimize the molecular structure of the carbon precursor in the silicon-carbon composite material to meet the demand of limiting the volume expansion of the silicon particles. SUMMARY

[0005] In view of the problem of insufficient strength of the carbon component in the silicon-carbon negative electrode material, the application provides a high-strength long-cycle silicon-carbon negative electrode material and a preparation method thereof. The molecular structure of the carbon precursor is designed to obtain a high-strength carbon component; the silicon particles are subjected to double-layer carbon coating treatment, the low specific surface area of the dense outer layer carbon is used to improve the electrical conductivity and form a stable interface, and the high-strength porous inner layer carbon is used to limit the volume expansion of the silicon particles, so as to obtain a silicon-carbon negative electrode material with stable cycle performance.

[0006] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0007] A high-strength long-cycle silicon-carbon negative electrode material is prepared by grinding micron silicon with a sand mill to obtain a nano silicon slurry, coating the nano silicon with a resin in a liquid phase, grinding again, then coating with pitch in a solid phase, and finally carbonizing to obtain the silicon-carbon negative electrode material.

[0008] Preferably, the silicon particles account for 40-70% by mass, the resin carbon accounts for 10-40% by mass, and the pitch carbon accounts for 5-20% by mass in the silicon-carbon negative electrode material.

[0009] Preferably, the nano silicon particles have a size of 50-200 nm.

[0010] The preparation method of the high-strength long-cycle silicon-carbon negative electrode material comprises the following steps:

[0011] (1) Grinding: micron coarse silicon and isopropyl alcohol organic solvent are coarsely ground together, then a surfactant is added for fine grinding to obtain a nano silicon slurry;

[0012] (2) Resin coating: a certain amount of resorcinol, a secondary primary amine and formaldehyde are added to the nano silicon slurry, which is stirred uniformly and then heated for polymerization to obtain a block material, which is crushed and sieved to obtain a resin-coated nano silicon material;

[0013] (3) Pitch coating: the resin-coated nano silicon material of step (2) is uniformly mixed with high-temperature pitch powder, and vacuum hot pressing is performed in a hot press to obtain a pitch-coated material;

[0014] (4) Carbonization: the material of step (3) is heated and carbonized in an inert atmosphere, and then crushed and sieved to obtain a silicon-carbon negative electrode material.

[0015] Further, the surfactant of step (1) is one or more of cetyltrimethylammonium bromide, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium stearate, octadecylamine and sodium oleate.

[0016] Further, the secondary primary amine of step (2) is one or more of hexanediamine, butanediamine, pentanediamine, ethylenediamine and octanediamine.

[0017] Further, the mass ratio of resorcinol to nano silicon in step (2) is 1:(5-10), the molar ratio of resorcinol to formaldehyde is 1:2, the molar ratio of resorcinol to secondary primary amine is (30-50):1, and the heating temperature is 50-90℃.

[0018] Further, the high-temperature pitch of step (3) is one or more of petroleum pitch, coal pitch and biomass pitch with a softening point >150℃, and the mass ratio of high-temperature pitch powder to resin-coated nano silicon powder is 1:(5-15).

[0019] Further, the hot-pressing temperature of step (3) is 200-300 DEG C, and the hot-pressing time is 0.5-2 h.

[0020] Further, the carbonization temperature in step (4) is 900-1200 DEG C, and the carbonization time is 1-4 h.

[0021] Advantages of the present application:

[0022] 1. Using phenol, aldehyde and diamine as raw materials, the difference in reactivity between benzoxazine system and phenolic system is utilized, the sequence reaction process is designed, the assembly process of phenolic aldehyde amine and phenolic pre-polymer is guided by hydrogen bond, and the structural skeleton resin cross-linked with each other is formed on the surface of silicon particles. The introduction of diamine not only greatly accelerates the reaction and synthesis speed, but also introduces flexible long chain in the carbon precursor, greatly improves the strength of the inner carbon material, and is beneficial to limit the volume change of silicon particles.

[0023] 2. Structure design of double-layer soft and hard carbon matrix on the surface of nano silicon particles: the dense outer layer soft carbon improves the conductivity of the material and stabilizes the electrolyte interface, the porous inner layer hard carbon adapts to the volume change, and the mechanical and chemical synergies between the two carbon layers with different structures make the silicon-carbon particles have high densification and anti-cracking performance.

[0024] 3. By synchronous carbonization of resin and pitch, cross-linking reaction of resin and pitch occurs at high temperature, forming a soft and hard carbon combined interface, eliminating the influence of different carbon component interfaces, and improving the conductivity and structural stability of the material.

[0025] 4. The obtained silicon-carbon composite negative electrode material has excellent electrochemical performance, the reversible capacity is more than 1800 mAh / g, the initial efficiency is > 87%, and the capacity is maintained at more than 80% after 1000 cycles. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Structure schematic diagram of the silicon-carbon negative electrode material prepared in the embodiment of the present application;

[0027] Figure 2 Cross-sectional SEM picture of the silicon-carbon negative electrode material prepared in Example 1 of the present application;

[0028] Figure 3 Cycle performance diagram of the materials in Example 1 and Comparative Example 1 of the present application. SPECIFIC IMPLEMENTATION METHOD

[0029] The present application is further described in detail by the following examples, so that those skilled in the art can better understand the present application, but the present application is not limited to the following examples.

[0030] Example 1

[0031] A preparation method of a high-strength long-cycle silicon-carbon negative electrode material, comprising the following steps:

[0032] (1) micron coarse silicon and isopropyl alcohol are loaded into a sand mill at a ratio of 1:6, coarse grinding is performed by the sand mill, then hexadecyl trimethyl ammonium bromide is added as a surfactant to modify the surface, fine grinding is continuously performed in the sand mill, and a nano silicon mixed slurry with a particle size of about 80 nm is obtained;

[0033] (2) then 100 g of the slurry containing nano silicon is taken, 10 g of resorcinol, 2.5 g of hexanediamine and 13 g of formaldehyde are sequentially added, stirring is uniformly performed, and then block carbon is obtained after reaction at 50°C for 2 h, and after crushing and screening, a resin-coated nano silicon material is obtained;

[0034] (3) the resin-coated nano silicon material is uniformly mixed with high-temperature petroleum pitch powder with a softening point of 230°C at a mass ratio of 10:1, and is placed into a hot press for vacuum hot pressing treatment at 260°C for 0.5 h, and then pitch-coated material is obtained.

[0035] (4) the material of step (3) is carbonized at 1000°C for 2 h under a nitrogen atmosphere, and after crushing and screening, a silicon-carbon negative electrode material is obtained.

[0036] Figure 1 A structure schematic diagram of the silicon-carbon negative electrode material prepared in the embodiment is shown; Figure 2 The nano silicon particles in the silicon-carbon negative electrode material prepared in embodiment 1 are uniformly dispersed in the carbon matrix, the double-layer carbon component only wraps the nano silicon particles, and there is no obvious hole in the material; Figure 3 The cycle performance of the silicon-carbon material prepared in embodiment 1 is shown, and the capacity retention rate after 1000 cycles is 83.5%, and the structure parameters and electrochemical performance of the material prepared in the embodiment are shown in table 1.

[0037] Embodiment 2

[0038] A preparation method of a high-strength long-cycle silicon-carbon negative electrode material, comprising the following steps:

[0039] (1) micron coarse silicon and isopropyl alcohol are loaded into a sand mill at a ratio of 1:6, coarse grinding is performed by the sand mill, then sodium dodecyl benzene sulfonate is added as a surfactant to modify the surface, fine grinding is continuously performed in the sand mill, and a nano silicon mixed slurry with a particle size of about 50 nm is obtained;

[0040] (2) then 100 g of the slurry containing nano silicon is taken, 10 g of resorcinol, 2.5 g of hexanediamine and 13 g of formaldehyde are sequentially added, stirring is uniformly performed, and then block carbon is obtained after reaction at 50°C for 2 h, and after crushing and screening, a resin-coated nano silicon material is obtained;

[0041] (3) The resin-coated nanosilicon material is mixed with high-temperature petroleum pitch powder with a softening point of 160°C at a mass ratio of 15:1, and is placed in a hot press for vacuum hot pressing treatment at 200°C for 2h to obtain pitch-coated material.

[0042] (4) The material of step (3) is carbonized at 1200°C for 1h under an argon atmosphere, and after crushing and screening, a silicon-carbon negative electrode material is obtained.

[0043] Example 3

[0044] A preparation method of a high-strength long-cycle silicon-carbon negative electrode material includes the following steps:

[0045] (1) Micron coarse silicon and isopropyl alcohol are placed in a sand mill at a ratio of 1:6, and coarse grinding is performed by the sand mill. Then, sodium stearate is added as a surfactant to modify the surface, and fine grinding is continued in the sand mill to obtain nanosilicon mixed slurry with a particle size of about 200nm;

[0046] (2) Then, 100g of nanosilicon slurry is taken, and 10g of resorcinol, 4.0g of pentanediamine, and 13g of formaldehyde are added in sequence. After stirring uniformly, block carbon is obtained by reacting at 90°C for 0.5h, and after crushing and screening, resin-coated nanosilicon material is obtained;

[0047] (3) The resin-coated nanosilicon material is mixed with high-temperature petroleum pitch powder with a softening point of 260°C at a mass ratio of 5:1, and is placed in a hot press for vacuum hot pressing treatment at 300°C for 2h to obtain pitch-coated material.

[0048] (4) The material of step (3) is carbonized at 900°C for 4h under an argon atmosphere, and after crushing and screening, a silicon-carbon negative electrode material is obtained.

[0049] Comparative Example 1 - Inner layer carbon is phenolic resin precursor

[0050] The other steps and process parameters are the same as those of Example 1, except that NaOH is used instead of a binary primary amine as a catalyst in step (2) to form nanosilicon coated with phenolic resin, and after carbonization, a phenolic resin-based inner layer carbon is obtained. Comparative Example 2 - No pitch-based outer layer carbon coating

[0051] Comparative Example 3 - Single-component pitch-based carbon coating

[0052] A preparation method of a high-strength long-cycle silicon-carbon negative electrode material includes the following steps:

[0053] (1) The micron coarse silicon and isopropyl alcohol are loaded into a sand mill at a ratio of 1:6, and coarse grinding is performed by the sand mill. Then, cetyltrimethylammonium bromide is added as a surfactant to modify the surface, and fine grinding is continued in the sand mill to obtain a nano silicon mixed slurry with a particle size of about 80 nm;

[0054] (2) The nano silicon mixed slurry is spray dried, and then mixed with high-temperature petroleum asphalt powder with a softening point of 230°C at a mass ratio of 1:1 to obtain an asphalt-coated nano silicon material.

[0055] (3) The material of step (2) is carbonized at 1000°C for 2h under a nitrogen atmosphere, and after crushing and screening, a silicon-carbon negative electrode material is obtained.

[0056] Comparative Example 4 - Resin and asphalt carbonized separately

[0057] The other steps and process parameters are the same as those of Example 1, except that step (4) is performed after step (2), and step (4) is performed after step (3), i.e., the resin and asphalt are carbonized separately.

[0058] The silicon-carbon negative electrode materials obtained in the examples and comparative examples are assembled into coin-type half-cells according to conventional methods, and their electrochemical performance is tested, including initial specific capacity, first charge-discharge efficiency, and cycle performance.

[0059] Table 1 Comparison of structure and performance of negative electrode materials prepared in each example and comparative example

[0060]

Claims

1. A method for preparing a high-strength long-cycling silicon-carbon anode material, characterized in that, It comprises the following steps: (1) grinding: micron coarse silicon and isopropanol organic solvent together with coarse grinding, and then adding a surfactant, fine grinding, to obtain a nanosilicon slurry; (2) resin coating: a certain amount of resorcinol, binary primary amine and formaldehyde are added to the nanosilicon slurry, stirred uniformly, and then heated to polymerize to obtain a bulk material, which is crushed and sieved to obtain a resin-coated nanosilicon material; (3) asphalt coating: the resin-coated nanosilicon material of step (2) is mixed with high-temperature asphalt powder uniformly, and then vacuum hot pressing treatment is carried out in a hot press to obtain an asphalt-coated material; (4) carbonization: the material of step (3) is heated and carbonized under an inert atmosphere, and then crushed and sieved to obtain a silicon-carbon negative electrode material; The silicon-carbon negative electrode material has a mass of 100%, and the mass of silicon particles accounts for 40-70%, the mass of resin carbon accounts for 10-40%, and the mass of asphalt carbon accounts for 5-20%.

2. The production method according to claim 1, characterized by, The nanosilicon particle size in the nanosilicon slurry of step (1) is 50-200 nm.

3. The preparation method according to claim 1, characterized in that, The surfactant of step (1) is one or more of cetyltrimethylammonium bromide, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium stearate, octadecylamine, and sodium oleate.

4. The method of claim 1, wherein, The binary primary amine of step (2) is one or more of hexanediamine, butanediamine, pentanediamine, ethylenediamine, and octanediamine.

5. The preparation method according to claim 1, characterized in that, The heating temperature in step (2) is 50-90℃.

6. The method of claim 1, wherein, The high-temperature asphalt of step (3) is one or more of petroleum asphalt, coal tar pitch, and biomass pitch with a softening point > 150℃, and the mass ratio of high-temperature asphalt powder to resin-coated nanosilicon powder is 1:(5-15).

7. The preparation method according to claim 1, characterized in that, The hot pressing temperature of step (3) is 200-300℃, and the hot pressing time is 0.5-2h.

8. The production method according to any one of claims 1 to 7, characterized by, The carbonization temperature in step (4) is 900-1200℃, and the carbonization time is 1-4h.

9. A high-strength long-cycling silicon-carbon anode material, characterized in that, The silicon-carbon negative electrode material prepared by the preparation method of any one of claims 1-8.

10. The silicon-carbon negative electrode material of claim 9 as a battery negative electrode.

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