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

Abstract

The application belongs to the technical field of silicon-carbon negative electrode of lithium ion battery, and relates to a preparation method of a roller pressure resistant and low temperature resistant silicon-carbon negative electrode material, comprising the following steps: (1) mixing linear phenolic resin, phenolic hydroxyl containing aromatic aldehyde and curing agent uniformly to perform first stage cross-linking reaction; then adding dialdehyde group polyethylene glycol to perform second stage cross-linking reaction to obtain high-strength and high-toughness phenolic resin; (2) carbonizing the high-strength and high-toughness phenolic resin under inert atmosphere to obtain a porous carbon precursor; (3) expanding the porous carbon precursor through activation to obtain porous carbon; and (4) sequentially depositing silicon and coating carbon on the porous carbon to obtain the roller pressure resistant and low temperature resistant silicon-carbon negative electrode material. The application introduces phenolic hydroxyl containing aromatic aldehyde and dialdehyde group polyethylene glycol in the curing process to perform two-step cross-linking reaction, forms a compact and stable body network structure, and then carbonizes to form high-strength and high-toughness porous carbon, so that the prepared silicon-carbon negative electrode material has excellent roller pressure resistance and low temperature resistance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of silicon-carbon negative electrode of lithium ion battery, and particularly relates to a preparation method of a roll-pressing-resistant and low-temperature-resistant silicon-carbon negative electrode material. BACKGROUND

[0002] The energy density of lithium ion battery has approached the theoretical limit of traditional graphite negative electrode (372 mAh / g), while the theoretical specific capacity of silicon-based negative electrode is as high as 4200 mAh / g, which has become the core direction to break through the bottleneck. However, silicon expands seriously in the charging and discharging process, which leads to easy pulverization of the electrode sheet and poor cycle performance. In the prior art, the problem is solved by chemical vapor deposition of silicon atoms into the internal pores of porous carbon to form a silicon-carbon composite negative electrode material, and the volume expansion of silicon is relieved by the "spatial confinement" effect of the pores of the porous carbon.

[0003] The strength of the silicon-carbon composite negative electrode material mainly depends on the skeleton strength of the porous carbon, and the skeleton strength of the porous carbon is often insufficient in practical application, especially the porous carbon prepared by a resin-based carbon source. The reason is that the macromolecular chains of the conventional resin-based carbon source are broken and small molecule gases (such as aromatic, CO, CO2, hydrogen, etc.) are released in the pyrolysis process, and the carbon atoms recombine to form disordered graphite crystallites. This process is accompanied by the formation of pores and the shrinkage of the carbon matrix, which causes local stress concentration of the carbon skeleton and further weakens the skeleton strength of the porous carbon. When the strength of the porous carbon is insufficient, the skeleton of the porous carbon is prone to collapse or breakage in the process of repeated lithium ion intercalation / deintercalation, 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 skeleton also causes the exposure of silicon, which in turn causes a side reaction with the electrolyte. Therefore, the problem of insufficient strength of the porous carbon restricts the application potential of the silicon-carbon composite negative electrode material in high energy density and long cycle scenarios; especially in low temperature cycle scenarios, because in a low temperature environment, the carbon skeleton itself becomes more fragile, the physical constraint force limiting the expansion of silicon particles decreases, and low temperature exacerbates the inhomogeneity of silicon expansion. The improvement strategies for optimizing the porous carbon such as core-shell structure and three-dimensional ordered skeleton can alleviate some problems, but the preparation process is complex and not suitable for large-scale production, and the cost is high.

[0004] CN119517968 A discloses a silicon-carbon composite material and its preparation method, application and battery, which comprises: a porous carbon matrix; a metal plating layer on the pore wall of the porous carbon matrix; silicon alloy particles on the surface of the metal plating layer; amorphous silicon particles grown epitaxially along the silicon alloy particles; and a carbon coating layer on the outer layer. The invention is to deposit a metal plating layer on the pore wall of the porous carbon matrix by gas phase deposition reaction, then prepare metal-silicon alloy particles on the surface of the metal plating layer, and in the subsequent silicon deposition process, the metal-silicon alloy particles are used as deposition anchors, and amorphous silicon is deposited and grown epitaxially along them, so that the active material and the carbon matrix can form a more close connection, and the stability of the overall structure of the negative electrode material is improved. Therefore, the prepared silicon-carbon composite material has a unique three-dimensional structure design, which improves the specific capacity and high-low temperature cycle stability of the electrode material. However, the invention does not involve improving the intrinsic strength of the porous carbon skeleton, and its room temperature cycle stability and low temperature cycle stability still need to be further improved. SUMMARY

[0005] In view of the problem that the insufficient strength of the porous carbon skeleton in the prior art restricts the application of the silicon-carbon composite negative electrode material in high energy density, long cycle scenarios, especially in low temperature cycle scenarios, the present application provides a preparation method of a roll-pressing-resistant and low-temperature-resistant silicon-carbon negative electrode material. The present application improves the intrinsic strength and toughness of the porous carbon skeleton, so that the silicon-carbon negative electrode material prepared by silicon deposition and carbon coating of the high-strength and high-toughness porous carbon has excellent roll-pressing resistance and low-temperature resistance, and meets the application in high energy density, long cycle scenarios, especially in low temperature and long cycle scenarios.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A preparation method of a roll-pressing-resistant and low-temperature-resistant silicon-carbon negative electrode material, comprising the following steps:

[0008] (1) uniformly mix linear phenolic resin, phenolic hydroxyl-containing aromatic aldehyde and curing agent, and perform first stage crosslinking reaction; then add dialdehyde-based polyethylene glycol, and perform second stage crosslinking reaction to obtain high-strength and high-toughness phenolic resin;

[0009] (2) carbonize the high-strength and high-toughness phenolic resin under an inert atmosphere, and crush to obtain a porous carbon precursor;

[0010] (3) activate the porous carbon precursor to obtain a porous carbon;

[0011] (4) sequentially perform silicon deposition and carbon coating on the porous carbon to obtain a roll-pressing-resistant and low-temperature-resistant silicon-carbon negative electrode material.

[0012] Further, in step (1), the mass ratio of the linear phenolic resin, the aromatic aldehyde containing phenolic hydroxyl group, the curing agent, and the dialdehyde-based 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 group, the dialdehyde-based polyethylene glycol, and the curing agent, the linear phenolic resin generates cross-linking reaction when heat-cured, forming a body network structure.

[0013] Further, in step (1), the aromatic aldehyde containing phenolic hydroxyl group is at least one selected from 3-hydroxybenzaldehyde, 3,4-dihydroxybenzaldehyde, 3,5-dihydroxybenzaldehyde, and 3,4,5-trihydroxybenzaldehyde; preferably, the aromatic aldehyde containing phenolic hydroxyl group is 3,5-dihydroxybenzaldehyde.

[0014] Further, in step (1), the number average molecular weight of the polyethylene glycol segment of the dialdehyde-based polyethylene glycol is 400-800.

[0015] Further, 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 at least one selected from trimethylhexamethylene diamine, diethylaminopropylamine, and hexamethyltetramine.

[0016] Further, in step (1), the first stage cross-linking reaction is carried out at a temperature of 130-160℃ for 30-60 min, and the second stage cross-linking reaction is carried out at a temperature of 200-250℃ for 30-60 min.

[0017] Preferably, in step (1), the pressure of the system is controlled at 0.3-1 Mpa during the first stage cross-linking reaction and the second stage cross-linking reaction. Under the pressurized condition, the close arrangement of the molecular chains of the phenolic resin is promoted, and the structural strength defects caused by chain segment relaxation in the subsequent pyrolysis process are inhibited.

[0018] The application introduces the aromatic aldehyde containing phenolic hydroxyl and the dialdehyde group polyethylene glycol to participate in the crosslinking reaction during the curing process of the linear phenolic resin to prepare the high-strength and high-toughness phenolic resin. The possible reasons are as follows. On the one hand, the aromatic aldehyde containing phenolic hydroxyl contains aldehyde group and phenolic hydroxyl, has double reaction sites, the aldehyde group has high activity, participates in the crosslinking reaction on the linear phenolic resin, and thus the phenolic resin forms a dense network structure during the curing process. Meanwhile, the phenolic hydroxyl in the aromatic aldehyde containing phenolic hydroxyl can strongly activate the ortho and para C-H bonds of the hydroxyl on the aromatic ring, that is, the ortho and para active hydrogens can further participate in crosslinking condensation by reacting with formaldehyde generated by the curing agent. The molecule itself can be deeply integrated into the network as a multifunctional crosslinking point to form a more dense and highly branched network structure, and ordinary aromatic aldehyde is difficult to form a highly branched network. On the other hand, the aromatic aldehyde containing phenolic hydroxyl has relatively high thermal stability due to the conjugated system, and the introduction of the aromatic aldehyde structure makes the phenolic resin form a more stable carbonized structure during pyrolysis. On the third hand, the introduction of the aromatic aldehyde containing phenolic hydroxyl also makes the network too rigid, which can cause microcracks due to stress release during the carbonization stage. Therefore, the application also adds the dialdehyde group polyethylene glycol. The dialdehyde group polyethylene glycol is a long molecular chain aliphatic aldehyde containing aldehyde groups at both ends, which can react with the phenolic resin. Through the synergistic effect of the aromatic aldehyde containing phenolic hydroxyl and the dialdehyde group polyethylene glycol, the toughness of the crosslinking network is improved, a dense and stable network structure with high toughness is formed, and the high-strength and high-toughness phenolic resin is obtained. The high-strength and high-toughness porous carbon is obtained after the high-strength and high-toughness phenolic resin is carbonized and activated. On the fourth hand, the aromatic aldehyde containing phenolic hydroxyl and the dialdehyde group polyethylene glycol are crosslinked at different stages. The aromatic aldehyde containing phenolic hydroxyl and the curing agent are introduced at a slightly lower temperature to perform the first stage crosslinking reaction, and a preliminary stable crosslinking network is formed. Then the dialdehyde group polyethylene glycol is introduced at a slightly higher temperature to perform the second stage crosslinking reaction, the crosslinking density is strengthened, the toughness of the network structure is improved, and a dense and stable network structure is formed. The gradient reaction matching the activity of the substance can avoid uneven crosslinking caused by local overheating, thereby avoiding stress concentration. In the preferred technical scheme of the application, the crosslinking reaction is carried out under pressure, which can promote the close arrangement of the molecular chains of the phenolic resin, and is beneficial to further improving the skeleton strength of the carbonized porous carbon. In summary, through the staged crosslinking, the aromatic aldehyde containing phenolic hydroxyl provides high crosslinking density and thermal stability, the dialdehyde group polyethylene glycol provides flexible segments and further crosslinking, and the two synergistically form a stable and dense network structure to obtain high-strength and high-toughness phenolic resin, thereby greatly improving the strength of the carbon skeleton.

[0019] Further, in step (2), the inert atmosphere is nitrogen, argon or helium; the carbonization condition is 450-700℃ for 4-6h; and the crushing is crushed to a median particle size D50 of 3-15μm.

[0020] Further, in step (3), the reagent for the activation treatment is at least one of carbon dioxide, water vapor, ammonia, hydrogen sulfide; and the activation treatment is performed at a temperature of 850-1000 DEG C for 5-10 hours.

[0021] Further, in step (3), the specific surface area of the porous carbon is 2300-2800 m 2 / g, the pore volume is 0.9-1.1 m 3 / g, and the pore size distribution is as follows: micropores (<2 nm) account for 89-95%, pores larger than 10 nm account for <3%, and the rest are mesopores of 2-10 nm.

[0022] The silicon deposition and carbon coating in step (4) are known to those skilled in the art and are not particularly limited. For example, silicon is deposited by vapor deposition using an organosilicon source gas selected from at least one of silane, dichlorodihydrogen silane, trichlorosilane, silicon tetrachloride, silicon tetrafluoride, disilane, etc., under the protection of an inert gas at 400-650 DEG C for 2-4 hours, the inert gas is nitrogen and / or argon, the ratio of the amount of porous carbon to silane gas is 1 kg:500-800 L, and the flow ratio of the inert gas to silane gas is 5-10:1. For example, carbon is coated by using a carbon source gas selected from at least one of C1-4 alkane, C2-4 alkene, C2-4 alkyne, under the protection of an inert gas at 500-700 DEG C for 1-3 hours, the ratio of the amount of porous carbon to the gas-phase carbon source is 1 kg:250-350 L.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] 1. In the present application, phenolic hydroxyl-containing aromatic aldehyde and dialdehyde-based polyethylene glycol are introduced in the on-line phenolic resin curing process for step-by-step crosslinking, the phenolic hydroxyl-containing aromatic aldehyde provides a highly branched network and thermal stability, and the flexible long chain of the dialdehyde-based polyethylene glycol effectively enhances the toughness of the crosslinked network, the synergistic effect of the two forms a high-strength and high-toughness phenolic resin, which further forms a high-strength porous carbon (the compressive strength is higher than 360 MPa, showing excellent structural stability) in the pyrolysis process; the silicon-carbon negative electrode material prepared by chemically depositing silicon and coating carbon on the high-strength porous carbon has excellent roll pressure resistance and low-temperature resistance, and breaks through the low-temperature performance bottleneck of the silicon-carbon negative electrode.

[0025] 2, The lithium battery assembled by the roll-pressing and low-temperature-resistant silicon-carbon negative electrode material prepared from the roll-pressing and low-temperature-resistant silicon-carbon negative electrode material has high initial coulombic efficiency and specific capacity, and more significantly, excellent roll-pressing resistance and low-temperature cycle performance, wherein the capacity attenuation rate after 10t roll-pressing is not more than 3%, the cycle capacity retention rate after 100 cycles at 25 DEG C is more than 91%, and the cycle capacity retention rate after 100 cycles at 0 DEG C is also more than 83%. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 SEM image of the porous carbon prepared in step (3) of Example 1;

[0027] Figure 2 X-ray diffraction spectrum of the porous carbon prepared in step (3) of Example 1;

[0028] Figure 3 The first charge-discharge diagram of the lithium battery assembled by the roll-pressing and low-temperature-resistant silicon-carbon negative electrode material of Example 1. DETAILED DESCRIPTION

[0029] The application will be further described in conjunction with specific examples, but the application is not limited to the following examples.

[0030] In the following examples, the experimental methods are conventional methods unless otherwise specified; and the reagents and materials are commercially available unless otherwise specified.

[0031] The linear phenolic resin is selected from Shandong Laiwu Run Da New Material Co., Ltd., and has a softening point of about 108 DEG C and a number average molecular weight of about 5000.

[0032] The dialdehyde-based polyethylene glycol CHO-PEG400-CHO and CHO-PEG800-CHO are both selected from Guangzhou Carbohydrate Technology Co., Ltd., and the number average molecular weight of the polyethylene glycol segment in each is 400 and 800, respectively.

[0033] Example 1

[0034] (1) 10 kg of linear phenolic resin, 0.3 kg of 3,5-dihydroxybenzaldehyde, and 0.8 kg of methenamine are mixed uniformly in a high-speed mixer to obtain a mixture, and the mixture is put into a rotary furnace, and reacted at 150 DEG C under 0.5 Mpa for 50 min; then 0.1 kg of dialdehyde-based polyethylene glycol CHO-PEG800-CHO is added, and reacted at 230 DEG C under 0.5 Mpa for 50 min to obtain a high-strength and high-toughness phenolic resin;

[0035] (2) The high-strength and high-toughness phenolic resin is kept in the rotary furnace, and heated to 600 DEG C at a heating rate of 8 DEG C / min under a nitrogen atmosphere, and kept for 5 h, and then cooled to room temperature, and crushed to D50 of about 7.1 μm to obtain a porous carbon precursor.

[0036] (3) Take 2 kg of porous carbon precursor into the activation furnace, and heat to 950℃ at a heating rate of 8℃ / min under nitrogen atmosphere, and then keep for 25 min. After that, turn off the nitrogen and continuously input CO2 gas at a flow rate of 14 L / min for 7 h. After the activation, switch to nitrogen atmosphere until the furnace body cools to room temperature, and then take out the material, to obtain the porous carbon;

[0037] (4) Take 500 g of the porous carbon into the CVD furnace, and input nitrogen at a flow rate of 6 L / min, and then heat to 550℃. Keep the nitrogen flow rate and input silane gas at a flow rate of 3 L / min for 3 h, so that the formed amorphous silicon particles are deposited in the pores of the porous carbon material, to obtain a silicon-carbon composite material. Then, continuously keep the silicon-carbon composite material in the CVD furnace, continuously input nitrogen at a flow rate of 6 L / min, and input acetylene gas at a flow rate of 2.5 L / min, and keep at 650℃ for 2 h, to realize carbon coating of the silicon-carbon composite material. Cool to room temperature to obtain a roll-pressing-resistant and low-temperature-resistant silicon-carbon negative electrode material.

[0038] The SEM image of the porous carbon prepared in step (3) is shown in Figure 1 , and the X-ray diffraction spectrum is shown in Figure 2 .

[0039] Example 2

[0040] The rest is the same as example 1, the difference is that the amount of raw materials in step (1) is different, specifically: 10 kg of linear phenolic resin, 0.2 kg of 3,5-dihydroxybenzaldehyde, 0.6 kg of methenamine, 50 g of dialdehyde-based polyethylene glycol CHO-PEG800-CHO.

[0041] Example 3

[0042] The rest is the same as example 1, the difference is that the amount of raw materials in step (1) is different, specifically: 10 kg of linear phenolic resin, 0.3 kg of 3,5-dihydroxybenzaldehyde, 0.6 kg of methenamine, 0.1 kg of dialdehyde-based polyethylene glycol CHO-PEG800-CHO.

[0043] Example 4

[0044] The rest is the same as example 1, the difference is that the amount of raw materials in step (1) is different, specifically: 10 kg of linear phenolic resin, 0.4 kg of 3,5-dihydroxybenzaldehyde, 0.8 kg of methenamine, 0.15 kg of dialdehyde-based polyethylene glycol CHO-PEG800-CHO.

[0045] Example 5

[0046] The rest is the same as example 1, the difference is that the amount of raw materials in step (1) is different, specifically: 10 kg of linear phenolic resin, 0.4 kg of 3,5-dihydroxybenzaldehyde, 1.0 kg of methenamine, 0.2 kg of dialdehyde-based polyethylene glycol CHO-PEG800-CHO.

[0047] Example 6

[0048] The rest is the same as example 1, the difference is that 3-hydroxybenzaldehyde is used instead of 3,5-dihydroxybenzaldehyde in step (1), and dialdehyde-based polyethylene glycol CHO-PEG400-CHO is used instead of CHO-PEG800-CHO.

[0049] Example 7

[0050] The rest is the same as example 1, the difference is that 3,4,5-trihydroxybenzaldehyde is used instead of 3,5-dihydroxybenzaldehyde in step (1).

[0051] Example 8

[0052] The rest is the same as example 1, the difference is that dialdehyde-based polyethylene glycol CHO-PEG400-CHO is used instead of CHO-PEG800-CHO in step (1).

[0053] Example 9

[0054] The rest is the same as example 1, the difference is that no pressure is added during the crosslinking reaction in step (1), specifically:

[0055] (1) 10 kg of linear phenolic resin, 0.3 kg of 3,4-dihydroxybenzaldehyde, 0.8 kg of methenamine are added into a high-speed mixer and mixed uniformly to obtain a mixture, then the mixture is put into a rotary furnace and reacted at 150°C under normal pressure for 50 min; then 0.1 kg of dialdehyde-based polyethylene glycol CHO-PEG800-CHO is added, and the reaction is carried out at 230°C under normal pressure for 50 min to obtain a high-strength and high-toughness phenolic resin;

[0056] (2) The same as example 1;

[0057] (3) The same as example;

[0058] (4) The same as example.

[0059] Comparative example 1

[0060] The rest is the same as example 1, the difference is that no dialdehyde-based polyethylene glycol is used for the second stage of crosslinking reaction in step (1), specifically:

[0061] (1) 10 kg of linear phenol formaldehyde resin, 0.4 kg of 3,4-dihydroxybenzaldehyde, and 0.8 kg of methenamine were mixed in a high-speed mixer to obtain a mixture, and the mixture was put into a rotary furnace to react at 150°C for 50 min under 0.5 MPa to obtain the crosslinked phenol formaldehyde resin;

[0062] (2) The same as in Example 1;

[0063] (3) The same as in Example 1;

[0064] (4) The same as in Example 1.

[0065] Comparative Example 2

[0066] The rest was the same as in Example 1, except that no aromatic aldehyde containing phenolic hydroxyl group was used in step (1) for the first stage of crosslinking reaction, specifically:

[0067] (1) 10 kg of linear phenol formaldehyde resin, 0.8 kg of methenamine, and 0.4 kg of dialdehyde-based polyethylene glycol CHO-PEG800-CHO were mixed in a high-speed mixer to obtain a mixture, and the mixture was put into a rotary furnace to react at 230°C for 50 min under 0.5 MPa to obtain the crosslinked phenol formaldehyde resin;

[0068] (2) The same as in Example 1;

[0069] (3) The same as in Example 1;

[0070] (4) The same as in Example 1.

[0071] Comparative Example 3

[0072] Compared with Example 1, the difference lies in that the aromatic aldehyde containing phenolic hydroxyl group and the dialdehyde-based polyethylene glycol in step (1) are synchronously added for reaction, specifically:

[0073] (1) 10 kg of linear phenol formaldehyde resin, 0.3 kg of 3,4-dihydroxybenzaldehyde, 0.8 kg of methenamine, and 0.1 kg of dialdehyde-based polyethylene glycol CHO-PEG800-CHO were mixed in a high-speed mixer to obtain a mixture, and the mixture was put into a rotary furnace to react at 200°C for 100 min under 0.5 MPa to obtain the crosslinked phenol formaldehyde resin;

[0074] (2) The same as in Example 1;

[0075] (3) The same as in Example 1;

[0076] (4) The same as in Example 1.

[0077] Comparative Example 4

[0078] Compared with Example 1, the difference is that: benzaldehyde is used instead of phenolic hydroxyl-containing aromatic aldehyde in step (1).

[0079] Test and analysis

[0080] 1) Test the compressive strength and pore size distribution of the porous carbon

[0081] Compressive strength test: the single particle compressive strength of the porous carbon prepared in the examples and comparative examples was tested by using the single particle mechanical property testing system (SPFT) of Yuaneng Technology (Xiamen), and the specific data are shown in Table 1.

[0082] Pore size distribution determination: according to GB / T19587-2017 gas adsorption BET method, the Tristar II 3020 type full-automatic specific area and pore size analyzer produced by Micromeritics Instrument Corporation of the United States was used to carry out low-temperature nitrogen adsorption experiment on the porous carbon prepared in the examples and comparative examples, and the pore size distribution was determined, and the specific data are shown in Table 1.

[0083] Table 1 Pore size distribution and compressive strength of the porous carbon

[0084] .

[0085] As can be seen from Table 1, the porous carbon prepared in the examples of the present application has high structural strength, and the compressive strength is all above 360Mpa.

[0086] 2) Electrochemical performance test

[0087] The silicon-carbon negative electrode material prepared above is applied to the negative electrode of a lithium ion battery, assembled into a lithium battery, and its electrochemical performance is tested. The specific method is as follows: the silicon-carbon negative electrode material, Super P, carboxymethyl cellulose (CMC) and butadiene rubber (SBR) to form a composite binder (the mass ratio of CMC and SBR is 1:1) are mixed in a mass ratio of 8:1:1 to form a slurry, and the slurry is coated on a copper foil by using a 200μm thick doctor blade, and then vacuum dried for 12h to prepare a silicon-carbon negative electrode sheet; then, metal lithium is used as the counter electrode, polyolefin is used as the separator, 1mol / L LiPF6 (the solvent is a mixture of EC (ethylene carbonate) and DMC (dimethyl carbonate) in a volume ratio of 1:1) is used as the electrolyte, and the volume fraction of VC (vinylene carbonate) and FEC (fluorinated ethylene carbonate) added in the electrolyte is 2% and 5% respectively, and a button cell is assembled in a German Braun inert gas glove box in an argon atmosphere.

[0088] a) Pressure resistance performance test: the roller pressure was set to 10 t, and after the electrode sheet was pressed at a constant speed, the specific capacity after being subjected to 10 t pressure and recovering from the pressure was tested. The capacity loss rate after 10 t roller pressure was calculated according to the following formula, and the lower the capacity loss rate, the better the pressure resistance performance. The specific test results are shown in Table 2.

[0089] Capacity loss rate = (Initial specific capacity - Specific capacity after 10 t roller pressure) / Initial specific capacity x 100%

[0090] b) Initial reversible specific capacity and initial coulombic efficiency: the above assembled battery was subjected to charge and discharge test on a LAND charge and discharge tester at 25°C, and the charge and discharge interval was 50 mV~1.5 V. The compaction density was 1.1 g / cm 3 After three times of charge and discharge at a current density of 0.1C (1C = 1500 mA / g), the capacity, initial coulombic efficiency of the material were obtained, and the specific results are shown in Table 2. The first cycle charge and discharge curve of the lithium battery assembled by the low-temperature cycle-resistant silicon-carbon negative electrode material of Example 1 at 0.1C rate is shown in Figure 3

[0091] c) Normal temperature and low temperature cycle performance test: the battery was cycled at 0.1C current density at 25°C and 0°C respectively, and the capacity retention rate after 100 cycles was tested. The test results are shown in Table 2.

[0092] Table 2 Electrochemical performance

[0093] .

[0094] From the data in Table 2, it can be clearly seen that the silicon-carbon negative electrode material prepared by the method of the present application exhibits excellent pressure resistance and low temperature resistance. When used as the negative electrode of a lithium battery, the capacity loss rate after 10 t roller pressure is not more than 3%, preferably not more than 2% in the preferred embodiment; at low temperature, it still has good cycle stability, and the capacity retention rate after 100 cycles at low temperature 0°C can also reach more than 83%. The specific capacity and initial coulombic efficiency of the lithium battery in Comparative Examples 1-3 are relatively high, but the cycle performance and pressure resistance performance are significantly poorer than those of the examples, especially the low temperature cycle performance is significantly worse than that of the examples. The pressure resistance performance of the lithium battery in Comparative Example 4 is lower than that of the examples, and especially the low temperature cycle performance is also poor.​​

Claims

1. A method for preparing a roller-pressed low-temperature-resistant silicon-carbon negative electrode material, characterized in that, The method comprises the following steps: (1) mixing linear phenolic resin, phenolic hydroxyl-containing aromatic aldehyde and curing agent uniformly to perform first-stage crosslinking reaction; then adding dialdehyde-based polyethylene glycol to perform second-stage crosslinking reaction, thereby obtaining high-strength and high-toughness phenolic resin; (2) carbonizing the high-strength and high-toughness phenolic resin under inert atmosphere, and crushing to obtain porous carbon precursor; (3) performing activation treatment on the porous carbon precursor to obtain porous carbon; (4) sequentially performing silicon deposition and carbon coating on the porous carbon to obtain roll-pressing-resistant and low-temperature-resistant silicon-carbon negative electrode material.

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

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

4. The method of claim 1, wherein, In step (1), the phenolic hydroxyl-containing aromatic aldehyde is 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 phenolic hydroxyl-containing aromatic aldehyde is 3,5-dihydroxybenzaldehyde.

6. The method of claim 1, wherein, In step (1), the number-average molecular weight of the polyethylene glycol segment of the dialdehyde-based 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 at least one of trimethylhexamethylene diamine, diethylamino propylamine and hexamethylene tetramine.

8. The method of claim 1, wherein, In step (1), the first-stage crosslinking reaction is performed at a temperature of 130-160℃ for 30-60min; and the second-stage crosslinking reaction is performed at a temperature of 200-250℃ for 30-60min.

9. The method of claim 1, wherein, In step (1), the pressure of the system is controlled at 0.3-1Mpa during the first-stage crosslinking reaction and the second-stage crosslinking reaction.

10. The method of claim 1, wherein, In step (2), the inert atmosphere is nitrogen, argon or helium; the carbonization is performed at 450-700℃ for 4-6h; and the crushing is performed to a median particle size D50 of 3-15μm. In step (3), the activation treatment reagent is at least one of carbon dioxide, water vapor, ammonia and hydrogen sulfide; and the activation treatment is performed at a temperature of 850-1000℃ for 5-10h. ​

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