Preparation method of rolling-resistant and low-temperature-resistant silicon-carbon negative electrode material

Abstract

The invention belongs to the technical field of lithium ion battery silicon-carbon negative electrodes, and relates to a preparation method of a rolling-resistant low-temperature-resistant silicon-carbon negative electrode material, which comprises the following steps: (1) uniformly mixing linear phenolic resin, phenolic hydroxyl group-containing aromatic aldehyde and a curing agent, and carrying out a first-stage cross-linking reaction; then adding dialdehyde polyethylene glycol, and carrying out second-stage cross-linking reaction to obtain the high-strength and high-toughness phenolic resin. (2) carbonizing the high-strength and high-toughness phenolic resin in an inert atmosphere to obtain a porous carbon precursor; (3) activating and chambering the porous carbon precursor to obtain porous carbon; and (4) sequentially carrying out silicon deposition and carbon coating on the porous carbon to prepare the rolling-resistant and low-temperature-resistant silicon-carbon negative electrode material. According to the invention, phenolic hydroxyl group-containing aromatic aldehyde and dialdehyde polyethylene glycol are introduced in the curing process, and a two-step cross-linking reaction is carried out to form a compact and stable three-dimensional network structure, so that high-strength and high-toughness porous carbon is formed through carbonization, and the prepared silicon-carbon negative electrode material has excellent rolling resistance and low temperature resistance.

Description

Technical Field

[0001] This invention belongs to the field of silicon-carbon anode technology for lithium-ion batteries, specifically relating to a method for preparing a silicon-carbon anode material that is resistant to rolling and low temperature. Background Technology

[0002] The energy density of lithium-ion batteries has approached the theoretical limit of traditional graphite anodes (372 mAh / g), while silicon-based anodes boast a theoretical specific capacity as high as 4200 mAh / g, making them a core direction for overcoming bottlenecks. However, silicon experiences severe volume expansion during charging and discharging, leading to easy pulverization of the electrode sheets and poor cycle performance. Current technologies primarily address this issue by depositing silicon atoms into the internal pores of porous carbon through chemical vapor deposition to form silicon-carbon composite anode materials. The porous carbon mitigates the volume expansion of silicon through the "spatial confinement" effect of its pores.

[0003] The strength of silicon-carbon composite anode materials mainly depends on the strength of the porous carbon framework. In practical applications, the framework strength of porous carbon is often insufficient, especially for porous carbon prepared from resin-based carbon sources. This is because during the pyrolysis of conventional resin-based carbon sources, the macromolecular chains break down and release small molecule gases (such as aromatics, CO, CO2, hydrogen, etc.), and carbon atoms recombine to form disordered graphite microcrystals. This process is accompanied by the drastic shrinkage of the carbon matrix and the formation of pores, resulting in local stress concentration in the carbon framework, which weakens the framework strength of the porous carbon. When the strength of the porous carbon is insufficient, the framework is prone to collapse or breakage during repeated lithium-ion insertion / extraction, leading to electrode pulverization, loss of active material, and thus rapid capacity decay. At the same time, the collapse or breakage of the porous carbon framework can also expose silicon, resulting in side reactions with the electrolyte. Therefore, the insufficient strength of porous carbon limits the application potential of silicon-carbon composite anode materials in high-energy-density, long-cycle scenarios; its application in low-temperature cycling scenarios is particularly limited, because at low temperatures, the carbon framework itself becomes more fragile, its physical constraint on silicon particle expansion decreases, and low temperatures exacerbate the non-uniformity of silicon expansion. While optimization strategies for porous carbon, such as core-shell structures and three-dimensional ordered frameworks, can alleviate some of these problems, their preparation processes are complex and unsuitable for large-scale production, and their costs are high.

[0004] CN119517968 A discloses a silicon-carbon composite material, its preparation method, application, and battery. The silicon-carbon composite material includes: a porous carbon matrix; a metal coating located on the pore walls of the porous carbon matrix; silicon alloy particles located on the surface of the metal coating; amorphous silicon particles growing epitaxially along the silicon alloy particles; and a carbon coating layer located on the outer layer. This invention involves depositing a metal coating on the pore walls of a porous carbon matrix via vapor deposition, followed by the preparation of metal-silicon alloy particles on the surface of the metal coating. During subsequent silicon deposition, the metal-silicon alloy particles serve as deposition anchors, and amorphous silicon grows epitaxially along their edges. This allows for a tighter connection between the active material and the carbon matrix, improving the overall structural stability of the anode material. Therefore, the prepared silicon-carbon composite material possesses a unique three-dimensional structural design, which improves the specific capacity and high / low temperature cycling stability of the electrode material. However, this invention does not address the improvement of the intrinsic strength of the porous carbon framework; its cycling stability at both room temperature and low temperature still needs further improvement. Summary of the Invention

[0005] Given that the insufficient strength of the porous carbon framework in existing technologies restricts the application of silicon-carbon composite anode materials in high-energy-density, long-cycle scenarios, especially in low-temperature cycling scenarios, this invention provides a method for preparing a roll-press resistant and low-temperature resistant silicon-carbon anode material. This invention improves the intrinsic strength and toughness of the porous carbon framework, enabling the silicon-carbon anode material prepared from this high-strength, high-toughness porous carbon through silicon deposition and carbon coating to possess excellent roll-press resistance and low-temperature resistance, meeting the requirements for high-energy-density, long-cycle applications, especially in low-temperature, long-cycle scenarios.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a roll-press resistant and low-temperature resistant silicon-carbon anode material includes the following steps: (1) Linear phenolic resin, aromatic aldehyde containing phenolic hydroxyl groups and curing agent are mixed evenly and the first stage crosslinking reaction is carried out; then dialdehyde polyethylene glycol is added and the second stage crosslinking reaction is carried out to obtain high strength and high toughness phenolic resin. (2) The high-strength and high-toughness phenolic resin was carbonized under an inert atmosphere and then pulverized to obtain a porous carbon precursor. (3) Porous carbon is obtained by activating the porous carbon precursor; (4) Porous carbon is successively deposited with silicon and coated with carbon to obtain a silicon-carbon anode material that is resistant to rolling and low temperature.

[0007] Further, in step (1), the mass ratio of the linear phenolic resin, the aromatic aldehyde containing phenolic hydroxyl groups, the curing agent, and the dialdehyde polyethylene glycol is 100:(2~4):(6~10):(0.5~2), preferably 100:(3~4):(6~8):(1~1.5). Under the combined action of the aromatic aldehyde containing phenolic hydroxyl groups, the dialdehyde polyethylene glycol, and the curing agent, the linear phenolic resin undergoes a cross-linking reaction during thermosetting, forming a three-dimensional network structure.

[0008] Further, in step (1), the aromatic aldehyde containing phenolic hydroxyl groups is selected from at least one of 3-hydroxybenzaldehyde, 3,4-dihydroxybenzaldehyde, 3,5-dihydroxybenzaldehyde, and 3,4,5-trihydroxybenzaldehyde; preferably, the aromatic aldehyde containing phenolic hydroxyl groups is 3,5-dihydroxybenzaldehyde.

[0009] Further, in step (1), the number average molecular weight of the polyethylene glycol segments of the dialdehyde polyethylene glycol is 400~800.

[0010] Further, in step (1), the linear phenolic resin has a softening point of 100~120℃ and a number average molecular weight of 3000~6000; the curing agent is selected from at least one of trimethylhexamethylenediamine, diethylaminopropylamine, and hexamethylenetetramine.

[0011] Further, the conditions for the first stage crosslinking reaction in step (1) are: temperature 130~160℃, time 30~60min; the conditions for the second stage crosslinking reaction are: temperature 200~250℃, time 30~60min.

[0012] Preferably, in step (1), the system pressure is controlled at 0.3~1 MPa during the first stage crosslinking reaction and the second stage crosslinking reaction. Under pressure, the molecular chains of phenolic resin can be tightly arranged, and structural strength defects caused by chain segment relaxation during subsequent pyrolysis can be suppressed.

[0013] This invention introduces aromatic aldehydes containing phenolic hydroxyl groups and dialdehyde polyethylene glycol into the crosslinking reaction during the curing process of linear phenolic resin to prepare high-strength and high-toughness phenolic resin. The possible reasons are twofold: First, aromatic aldehydes containing phenolic hydroxyl groups contain both aldehyde and phenolic hydroxyl groups, possessing dual reaction sites. The aldehyde group exhibits high activity, participating in the crosslinking reaction on the linear phenolic resin, thereby forming a dense network structure during curing. Simultaneously, the phenolic hydroxyl groups in these aromatic aldehydes can strongly activate the ortho and para-CH bonds of their aromatic rings, meaning their own active hydrogen at the ortho and para positions can react with formaldehyde produced by the decomposition of the curing agent, further participating in crosslinking condensation. This allows the molecule itself to act as a multifunctional crosslinking point, deeply integrating into the network and forming a denser, more branched three-dimensional network structure, which is difficult for ordinary aromatic aldehydes to form highly branched networks. Second, aromatic aldehydes containing phenolic hydroxyl groups exhibit relatively high thermal stability due to their conjugated system. The introduction of the aromatic aldehyde structure allows the phenolic resin to form a more stable carbonized structure during pyrolysis. Thirdly, the introduction of aromatic aldehydes containing phenolic hydroxyl groups can make the network too rigid, causing microcracks to form during the carbonization stage due to the inability to release stress. Therefore, this invention also adds dialdehyde polyethylene glycol, which is a long-chain aliphatic aldehyde with aldehyde groups at both ends. It can crosslink with phenolic resin. Through the synergistic effect of aromatic aldehydes containing phenolic hydroxyl groups and dialdehyde polyethylene glycol, the toughness of the crosslinked network is improved, forming a dense, stable and tough three-dimensional network structure, thus obtaining a high-strength and high-toughness phenolic resin. After carbonization and activation, the high-strength and high-toughness phenolic resin yields high-strength and high-toughness porous carbon. Fourthly, this invention involves crosslinking a phenolic hydroxyl-containing aromatic aldehyde and a dialdehyde-based polyethylene glycol at different stages. First, a more reactive phenolic hydroxyl-containing aromatic aldehyde and a curing agent are introduced at a slightly lower temperature for a first-stage crosslinking reaction, forming a preliminarily stable crosslinked network. Subsequently, dialdehyde-based polyethylene glycol is introduced at a slightly higher temperature for a second-stage crosslinking reaction, enhancing the crosslinking density and improving the toughness of the network structure, thereby forming a tight and stable three-dimensional network structure. This gradient reaction, matched to the activity of the substances, avoids uneven crosslinking caused by localized overheating, thus preventing stress concentration. In a preferred embodiment of this invention, using pressurized conditions for the crosslinking reaction further promotes the tight arrangement of the phenolic resin molecular chains, which is beneficial for further improving the strength of the carbonized porous carbon skeleton. In summary, through staged crosslinking, the phenolic hydroxyl-containing aromatic aldehyde provides high crosslinking density and thermal stability, while the dialdehyde-based polyethylene glycol provides flexible segments and further crosslinking. The two work synergistically to form a stable and dense three-dimensional network structure, resulting in a high-strength and high-toughness phenolic resin, thereby significantly improving the strength of the carbon skeleton.

[0014] Further, in step (2), the inert atmosphere is nitrogen, argon or helium; the carbonization conditions are 450~700℃ for 4~6h; and the pulverization is pulverization to a median particle size D50 of 3~15μm.

[0015] Further, in step (3), the reagent for activation treatment is at least one of carbon dioxide, water vapor, ammonia, and hydrogen sulfide; the conditions for activation treatment are: temperature 850℃~1000℃, time 5h~10h.

[0016] Furthermore, in step (3), the specific surface area of ​​the porous carbon is 2300~2800 m². 2 / g, pore volume 0.9~1.1m 3 / g, pore size distribution is as follows: micropores (<2nm) account for 89~95%, pores larger than 10nm account for <3%, and the rest are mesopores of 2~10nm.

[0017] The silicon deposition and carbon coating techniques described in step (4) are well known to those skilled in the art and are not particularly limited. For example, silicon can be deposited in the vapor phase using an organosilicon source gas. The organosilicon source gas is selected from at least one of silane, dichlorosilane, trichlorosilane, silicon tetrachloride, silicon tetrafluoride, and disilane. The conditions for silicon deposition are as follows: under inert gas protection, silane gas is introduced and kept at 400~650℃ for 2~4h. The inert gas is nitrogen and / or argon. The ratio of porous carbon to silane gas is 1kg:500~800L, and the flow rate ratio of inert gas to silane gas is 5~10:1. For example, carbon source gas is used for carbon coating. The carbon source gas is selected from at least one of C1-4 alkanes, C2-4 alkenes, and C2-4 alkynes. The carbon coating conditions are as follows: under inert gas protection, gaseous carbon source is introduced and kept at 500~700℃ for 1~3h. The ratio of porous carbon to gaseous carbon source is 1kg:250~350L.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention introduces aromatic aldehydes containing phenolic hydroxyl groups and dialdehyde polyethylene glycol for stepwise crosslinking during the online curing process of phenolic resin. The aromatic aldehydes containing phenolic hydroxyl groups provide a highly branched network and thermal stability, while the flexible long chains of dialdehyde polyethylene glycol effectively enhance the toughness of the crosslinked network. The two work synergistically to form a high-strength and high-toughness phenolic resin, which then forms high-strength porous carbon during pyrolysis (with compressive strengths all exceeding 360 MPa, exhibiting excellent structural stability). The silicon-carbon anode material prepared by chemically depositing silicon and coating carbon with the high-strength porous carbon has excellent resistance to rolling pressure and low temperature, breaking through the low-temperature performance bottleneck of silicon-carbon anodes.

[0019] 2. The lithium battery assembled from the roll-press resistant and low-temperature resistant silicon-carbon anode material prepared by this invention not only has high initial coulombic efficiency and specific capacity, but also exhibits excellent roll-press resistance and low-temperature cycling performance. The capacity decay rate after 10t roll pressing is no more than 3%, the cycle capacity retention rate after 100 cycles at 25℃ is more than 91%, and the capacity retention rate after 100 cycles at 0℃ is also more than 83%. Attached Figure Description

[0020] Figure 1 The image shows the SEM image of the porous carbon obtained in step (3) of Example 1. Figure 2 The X-ray diffraction pattern of the porous carbon obtained in step (3) of Example 1; Figure 3 This is a diagram of the first charge and discharge cycle of a lithium battery assembled from the roll-press-resistant and low-temperature-resistant silicon-carbon anode material of Example 1. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0022] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0023] The linear phenolic resin was selected from Shandong Laiwu Runda New Material Co., Ltd., with a softening point of approximately 108℃ and a number-average molecular weight of approximately 5000.

[0024] The dialdehyde polyethylene glycol CHO-PEG400-CHO and CHO-PEG800-CHO were both selected from Guangzhou Carbon Water Technology Co., Ltd., and the number average molecular weights of the polyethylene glycol segments were 400 and 800, respectively.

[0025] Example 1 (1) 10 kg of linear phenolic resin, 0.3 kg of 3,5-dihydroxybenzaldehyde and 0.8 kg of hexamethylenetetramine were added to a high-speed mixer and mixed evenly to obtain a mixture. The mixture was then placed in a rotary kiln and reacted at 150°C under 0.5 MPa for 50 min. Then 0.1 kg of dialdehyde polyethylene glycol CHO-PEG800-CHO was added, and the mixture was reacted at 230°C under 0.5 MPa for 50 min to obtain a high-strength and high-toughness phenolic resin. (2) The high-strength and high-toughness phenolic resin was kept in a rotary kiln and heated to 600℃ in a nitrogen atmosphere at a heating rate of 8℃ / min and held for 5h. After cooling to room temperature, it was pulverized to a D50 of about 7.1μm to obtain a porous carbon precursor. (3) Take 2 kg of porous carbon precursor and place it in an activation furnace. Under nitrogen atmosphere, heat it to 950°C at a heating rate of 8°C / min, hold it for 25 min, then turn off the nitrogen and continuously introduce CO2 gas at a flow rate of 14 L / min for 7 h. After activation, switch to nitrogen atmosphere until the furnace cools down to room temperature, take out the material, and you will get porous carbon. (4) Take 500g of porous carbon and put it into the CVD furnace. Nitrogen gas is introduced at a flow rate of 6L / min and the temperature is raised to 550℃. Then, the flow rate of nitrogen gas is maintained and silane gas is introduced at a flow rate of 3L / min for 3h. The amorphous silicon particles formed are deposited in the pores of the porous carbon material to obtain silicon-carbon composite material. Then, the silicon-carbon composite material is kept in the CVD furnace and nitrogen gas is continuously introduced at a flow rate of 6L / min. Then, acetylene gas is introduced at a flow rate of 2.5L / min and kept at 650℃ for 2h to achieve carbon coating of silicon-carbon composite material. Cool to room temperature to obtain roll-press resistant and low-temperature resistant silicon-carbon anode material.

[0026] The SEM image of the porous carbon obtained in step (3) is shown below. Figure 1 As shown, the X-ray diffraction pattern is as follows: Figure 2 As shown.

[0027] Example 2 The rest is the same as in Example 1, except that the amount of raw materials used in step (1) is different, specifically: 10kg linear phenolic resin, 0.2kg 3,5-dihydroxybenzaldehyde, 0.6kg hexamethylenetetramine, and 50g dialdehyde polyethylene glycol CHO-PEG800-CHO.

[0028] Example 3 The rest is the same as in Example 1, except that the amount of raw materials used in step (1) is different, specifically: 10kg linear phenolic resin, 0.3kg 3,5-dihydroxybenzaldehyde, 0.6kg hexamethylenetetramine, and 0.1kg dialdehyde polyethylene glycol CHO-PEG800-CHO.

[0029] Example 4 The rest is the same as in Example 1, except that the amount of raw materials used in step (1) is different, specifically: 10kg linear phenolic resin, 0.4kg 3,5-dihydroxybenzaldehyde, 0.8kg hexamethylenetetramine, and 0.15kg dialdehyde polyethylene glycol CHO-PEG800-CHO.

[0030] Example 5 The rest is the same as in Example 1, except that the amount of raw materials used in step (1) is different, specifically: 10kg linear phenolic resin, 0.4kg 3,5-dihydroxybenzaldehyde, 1.0kg hexamethylenetetramine, and 0.2kg dialdehyde polyethylene glycol CHO-PEG800-CHO.

[0031] Example 6 The rest is the same as in Example 1, except that: in step (1), 3-hydroxybenzaldehyde is used to replace 3,5-dihydroxybenzaldehyde by mass, and dialdehyde polyethylene glycol CHO-PEG400-CHO is used to replace CHO-PEG800-CHO by mass.

[0032] Example 7 The rest is the same as in Example 1, except that in step (1), 3,4,5-trihydroxybenzaldehyde is used to replace 3,5-dihydroxybenzaldehyde by mass.

[0033] Example 8 The rest is the same as in Example 1, except that in step (1), CHO-PEG800-CHO is replaced by dialdehyde polyethylene glycol CHO-PEG400-CHO.

[0034] Example 9 The rest is the same as in Example 1, except that no pressure is applied during the crosslinking reaction in step (1), specifically: (1) 10 kg of linear phenolic resin, 0.3 kg of 3,4-dihydroxybenzaldehyde and 0.8 kg of hexamethylenetetramine were added to a high-speed mixer and mixed evenly to obtain a mixture. The mixture was then placed in a rotary kiln and reacted at 150°C under normal pressure for 50 min. Then 0.1 kg of dialdehyde polyethylene glycol CHO-PEG800-CHO was added and reacted at 230°C under normal pressure for 50 min to obtain high-strength and high-toughness phenolic resin. (2) Same as Example 1; (3) Same as the embodiment; (4) Same as the example.

[0035] Comparative Example 1 The rest is the same as in Example 1, except that: in step (1), dialdehyde polyethylene glycol is not used for the second-stage crosslinking reaction, specifically: (1) 10 kg of linear phenolic resin, 0.4 kg of 3,4-dihydroxybenzaldehyde and 0.8 kg of hexamethylenetetramine were added to a high-speed mixer and mixed evenly to obtain a mixture. The mixture was then placed in a rotary kiln and kept at 150°C for 50 min at 0.5 MPa to obtain cross-linked phenolic resin. (2) Same as Example 1; (3) Same as Example 1; (4) Same as Example 1.

[0036] Comparative Example 2 The rest is the same as in Example 1, except that: in step (1), aromatic aldehydes containing phenolic hydroxyl groups are not used for the first stage of cross-linking reaction, specifically: (1) 10 kg of linear phenolic resin, 0.8 kg of hexamethylenetetramine and 0.4 kg of dialdehyde polyethylene glycol CHO-PEG800-CHO were added to a high-speed mixer and mixed evenly to obtain a mixture. The mixture was then placed in a rotary kiln and kept at 230°C for 50 min at 0.5 MPa to obtain cross-linked phenolic resin. (2) Same as Example 1; (3) Same as Example 1; (4) Same as Example 1.

[0037] Comparative Example 3 Compared with Example 1, the difference is that in step (1), the aromatic aldehyde containing phenolic hydroxyl groups and the dialdehyde polyethylene glycol are added simultaneously for reaction, specifically: (1) 10 kg of linear phenolic resin, 0.3 kg of 3,4-dihydroxybenzaldehyde, 0.8 kg of hexamethylenetetramine, and 0.1 kg of dialdehyde polyethylene glycol CHO-PEG800-CHO were added to a high-speed mixer and mixed evenly to obtain a mixture. The mixture was then placed in a rotary kiln and reacted at 200°C for 100 min at 0.5 MPa to obtain cross-linked phenolic resin. (2) Same as Example 1; (3) Same as Example 1; (4) Same as Example 1.

[0038] Comparative Example 4 Compared with Example 1, the difference is that in step (1), benzaldehyde is used in equimolar substitution for aromatic aldehydes containing phenolic hydroxyl groups.

[0039] Testing and Analysis 1) Test the compressive strength and pore size distribution of porous carbon. Compressive strength test: The single-particle compressive strength of the porous carbon prepared in the examples and comparative examples was tested using the single-particle mechanical property testing system (SPFT) of Yuaneng Technology (Xiamen). The specific data are shown in Table 1.

[0040] Pore ​​size distribution determination: According to GB / T19587—2017 Gas Adsorption BET Method, the porous carbon prepared in the examples and comparative examples was subjected to low-temperature nitrogen adsorption experiments using a Tristar II 3020 fully automatic specific area and pore size analyzer manufactured by Micromeritics Instrument Corporation, USA, and its pore size distribution was determined. The specific data are shown in Table 1.

[0041] Table 1. Pore size distribution and compressive strength of porous carbon .

[0042] As can be seen from Table 1, the porous carbon prepared in the embodiments of the present invention has high structural strength, and its compressive strength is above 360 ​​MPa.

[0043] 2) Electrochemical performance testing The silicon-carbon anode material prepared above was applied to the anode of a lithium-ion battery to assemble a lithium battery, and its electrochemical performance was tested. Specific method: A composite binder formed by silicon-carbon anode material, Super P, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) (CMC and SBR mass ratio 1:1) was mixed at a mass ratio of 8:1:1 to form a slurry. This slurry was coated onto copper foil using a 200 μm thick scraper, and then vacuum dried for 12 h to prepare the silicon-carbon anode sheet. Then, lithium metal was used as the counter electrode, polyolefin as the separator, and 1 mol / L LiPF6 (a mixture of EC (ethylene carbonate) and DMC (dimethyl carbonate) in a volume ratio of 1:1) as the electrolyte. 2% VC (ethylene carbonate) and 5% FEC (fluoroethylene carbonate) were added to the electrolyte. A coin cell was assembled in an argon-atmosphere Braun inert gas glove box in Germany.

[0044] a) Pressure resistance test: The roller pressure is set to 10t. After the electrode is pressed at a constant speed, the specific capacity after being subjected to 10t pressure and then released is tested. Compared with the first reversible capacity, the capacity loss rate after 10t roller pressure is calculated according to the following formula. The lower the capacity loss rate, the better the pressure resistance performance. The specific test results are shown in Table 2.

[0045] Capacity loss rate = × 100% b) Initial reversible specific capacity and initial coulombic efficiency: The assembled battery was tested on a LAND charge-discharge tester at 25°C, with a charge-discharge range of 50mV to 1.5V and a compaction density of 1.1g / cm³. 3 After three charge-discharge cycles at a current density of 0.1C (1 C = 1500 mA / g), the capacity and initial coulombic efficiency of the material were obtained, and the specific results are shown in Table 2. The first charge-discharge curve of the lithium battery assembled from the low-temperature cycling-resistant silicon-carbon anode material of Example 1 at a 0.1C rate is shown in Table 2. Figure 3 As shown.

[0046] c) Cycling performance test at room temperature and low temperature: The battery was cycled at 25°C and 0°C at a current density of 0.1C, and the capacity retention rate after 100 cycles was tested. The test results are shown in Table 2.

[0047] Table 2 Electrochemical performance .

[0048] As can be clearly seen from the data in Table 2, the silicon-carbon anode material prepared by the method of this invention exhibits excellent rolling resistance and low-temperature performance. When used as the anode in lithium-ion battery assemblies, the capacity loss rate after 10t rolling is no more than 3%, and in the preferred embodiment, no more than 2%. It also maintains good cycle stability at low temperatures, retaining over 83% of its capacity after 100 cycles at 0°C. While the lithium-ion batteries in Comparative Examples 1-3 have higher specific capacity and initial coulombic efficiency, their cycle performance and rolling resistance are significantly worse than those of the examples, especially their low-temperature cycle performance. The lithium-ion battery in Comparative Example 4 exhibits lower rolling resistance than the examples, and its low-temperature cycle performance is also poor.

Claims

1. A method for preparing a roll-press resistant and low-temperature resistant silicon-carbon anode material, characterized in that, Includes the following steps: (1) Linear phenolic resin, aromatic aldehyde containing phenolic hydroxyl groups and curing agent are mixed evenly and the first stage crosslinking reaction is carried out; then dialdehyde polyethylene glycol is added and the second stage crosslinking reaction is carried out to obtain high strength and high toughness phenolic resin. (2) The high-strength and high-toughness phenolic resin was carbonized under an inert atmosphere and then pulverized to obtain a porous carbon precursor. (3) Porous carbon is obtained by activating the porous carbon precursor; (4) Porous carbon is successively deposited with silicon and coated with carbon to obtain a silicon-carbon anode material that is resistant to rolling and low temperature.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of the linear phenolic resin, the aromatic aldehyde containing phenolic hydroxyl groups, the curing agent, and the dialdehyde polyethylene glycol is 100:(2~4):(6~10):(0.5~2).

3. The preparation method according to claim 2, characterized in that, In step (1), the mass ratio of the linear phenolic resin, the aromatic aldehyde containing phenolic hydroxyl groups, the curing agent, and the dialdehyde polyethylene glycol is 100:(3~4):(6~8):(1~1.5).

4. The preparation method according to claim 1, characterized in that, In step (1), the aromatic aldehyde containing phenolic hydroxyl groups is selected from at least one of 3-hydroxybenzaldehyde, 3,4-dihydroxybenzaldehyde, 3,5-dihydroxybenzaldehyde, and 3,4,5-trihydroxybenzaldehyde.

5. The preparation method according to claim 4, characterized in that, In step (1), the aromatic aldehyde containing phenolic hydroxyl groups is 3,5-dihydroxybenzaldehyde.

6. The preparation method according to claim 1, characterized in that, In step (1), the number average molecular weight of the polyethylene glycol segments of the dialdehyde polyethylene glycol is 400~800.

7. The preparation method according to claim 1, characterized in that, In step (1), the softening point of the linear phenolic resin is 100~120℃ and the number average molecular weight is 3000~6000; the curing agent is selected from at least one of trimethylhexamethylenediamine, diethylaminopropylamine, and hexamethylenetetramine.

8. The preparation method according to claim 1, characterized in that, In step (1), the conditions for the first stage crosslinking reaction are: temperature 130~160℃, time 30~60min; the conditions for the second stage crosslinking reaction are: temperature 200~250℃, time 30~60min.

9. The preparation method according to claim 1, characterized in that, In step (1), the system pressure is controlled at 0.3~1 MPa during the first stage crosslinking reaction and the second stage crosslinking reaction.

10. The preparation method according to claim 1, characterized in that, In step (2), the inert atmosphere is nitrogen, argon or helium; the carbonization conditions are to keep warm at 450~700℃ for 4~6h; the pulverization is to pulverize to a median particle size D50 of 3~15μm; and / or In step (3), the reagent for activation treatment is at least one of carbon dioxide, water vapor, ammonia, and hydrogen sulfide; the activation treatment conditions are: temperature 850℃~1000℃, time 5h~10h.

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