Negative electrode material, negative electrode plate, secondary battery and preparation method of secondary battery

Abstract

The invention discloses a negative electrode material, a negative electrode plate, a secondary battery and a preparation method of the secondary battery. The negative electrode material comprises a first substrate, a second substrate and a coating layer, the first substrate is of a porous structure, and the pore volume is V1; the second substrate is obtained by uniformly depositing the sediment I in the holes of the first substrate, the hole volume is V2, and the hole volume filling rate is P; and the coating layer is formed by uniformly depositing the sediment II on the surface of the second substrate. The expansion rate S of the negative pole piece disclosed by the invention and the pore volume filling rate P of the negative pole material meet the relational expression S = 748P2-1413P + 668. According to the invention, the concept of the pore volume filling rate P of the negative electrode material is introduced for the first time, the relational expression between the pore volume filling rate P and the expansion rate S of the prepared negative electrode plate is deduced, and accurate control of the expansion rate S of the prepared negative electrode plate is realized by controlling the pore volume filling rate P of the negative electrode material; and the silicon-carbon negative electrode material with low expansion, high cycle stability, high capacity and first efficiency is prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a negative electrode material, a negative electrode sheet, a secondary battery and a preparation method thereof. Background Art

[0002] Silicon carbon is the next generation of lithium-ion battery negative electrode material that is expected to replace graphite. Since silicon undergoes huge volume expansion / contraction during the lithium insertion / extraction process, the material becomes pulverized and loses electrical contact with the current collector, resulting in a degradation of electrochemical performance. Therefore, it is particularly important to balance the specific capacity and expansion rate of silicon-carbon negative electrode materials.

[0003] At present, most technical solutions are to prepare silicon carbon on a porous carbon substrate through a vapor deposition process. However, during the deposition process, if the deposition process parameters are not finely controlled, the pore volume filling rate of the porous carbon will be too high or too low, which will seriously affect the expansion performance of silicon carbon. When the pore volume filling rate is high, the space used to alleviate the volume expansion of silicon grains is small. The huge volume expansion produced after silicon lithiation is easy to break the material, resulting in performance deterioration; when the pore volume filling rate is low, the space used to alleviate the volume expansion of silicon grains is large. The silicon grains expand / contract at a greater rate during the lithium insertion / delithiation process. Long-term reciprocation can easily cause silicon grains to pulverize, and the low filling rate may also cause excessive electrolyte to enter the pores of the negative electrode material to cause side reactions, resulting in reduced capacity. Therefore, it is very important to effectively fill the pore volume of porous carbon, and it is particularly critical to balance the pore volume filling rate of porous carbon and the silicon carbon expansion rate.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] In view of the above problems, the present invention discloses a negative electrode material, which introduces the concept of the pore volume filling rate P of the negative electrode material for the first time, and more importantly, derives the relationship between the pore volume filling rate P and the expansion rate S of the prepared negative electrode sheet. By controlling the pore volume filling rate P of the negative electrode material, precise control of the expansion rate S of the prepared negative electrode sheet is achieved, and a silicon-carbon negative electrode material with low expansion, high cycle stability, high capacity and first efficiency is prepared.

[0006] To achieve the above purpose, the specific technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a negative electrode material, comprising a first substrate, a second substrate and a coating layer;

[0008] The first matrix is ​​a porous structure with a pore volume of V1;

[0009] The second matrix is ​​obtained by uniformly depositing the sediment I in the pores of the first matrix, the pore volume is V2, the pore volume filling rate is P, P = (V1-V2) / V1;

[0010] Among them, 0.90≤P≤0.99;

[0011] The coating layer is formed by uniformly depositing the sediment II on the surface of the second substrate.

[0012] In an optional embodiment, the pore volume V1 of the first matrix and the pore volume V2 of the second matrix satisfy at least one of the following conditions:

[0013] (1) Pore volume V1: 0.5 cm 3 / g≤V1≤2cm 3 / g;

[0014] (2) Pore volume V2: 0.005 cm 3 / g≤V2≤0.2cm 3 / g.

[0015] In an optional embodiment, the first substrate comprises a porous carbon material or a porous carbon material containing a doping element;

[0016] Optionally, the doping element is selected from one or more of nitrogen, sulfur and fluorine;

[0017] By adding doping elements, the rate performance of the prepared negative electrode material can be further improved and the initial efficiency can be increased.

[0018] In an optional embodiment, the sediment I comprises silicon grains;

[0019] In an alternative embodiment, the sediment II comprises a carbon material.

[0020] In an optional embodiment, the negative electrode material satisfies at least one of the following conditions:

[0021] (a) the silicon content in the negative electrode material is 45-50% of the total mass of the negative electrode material;

[0022] (b) the carbon content of the negative electrode material is 45-50% of the total mass of the negative electrode material;

[0023] (c) the content of the doping element in the negative electrode material is 0 to 10% of the total mass of the negative electrode material;

[0024] (d) D50: 7.5 ± 1 μm;

[0025] (e) Specific surface area: 2.5 ± 1.5 m 2 / g;

[0026] (f) Resistivity is 1 to 10 Ω-cm;

[0027] (g) Tap density: 0.95±0.15g / cm 3 .

[0028] In an optional embodiment, the negative electrode material satisfies at least one of the following conditions:

[0029] (1) Pore volume V1: 0.7 cm 3 / g≤V1≤1.3cm 3 / g; optionally, 0.8cm 3 / g≤V1≤1.0cm 3 / g; further optionally, 0.85cm 3 / g≤V1≤0.95cm 3 / g;

[0030] (2) Pore volume V2: 0.01 cm 3 / g≤V2≤0.1cm 3 / g; optionally, 0.04cm 3 / g≤V2≤0.06cm 3 / g;

[0031] (3) The pore volume filling rate is P: 0.93≤P≤0.96.

[0032] In a second aspect, the present invention further provides a method for preparing the negative electrode material, comprising:

[0033] (S1) mixing a carbon source, a crosslinking agent and an optionally added doping source, and obtaining a first matrix through pre-crosslinking, carbonization and activation processes;

[0034] (S2) uniformly depositing in the holes of the first substrate to obtain a second substrate;

[0035] (S3) uniformly depositing a coating layer on the surface of the second substrate to obtain the negative electrode material.

[0036] In step (S1):

[0037] In an optional embodiment, the carbon source is selected from one or more of phenolic resin, asphalt, and polyacrylamide;

[0038] Optionally, the carbon source is selected from phenolic resin and polyacrylamide. Experiments have shown that the battery assembled with the negative electrode material prepared by using the porous carbon prepared by the combination of the two as the substrate has better electrochemical performance.

[0039] Further optionally, the mass ratio of phenolic resin to polyacrylamide is (2-6):1;

[0040] In an optional embodiment, the cross-linking agent is selected from one or more of polyethylene glycol, propylene diamine, and tetraisocyanate;

[0041] In an optional embodiment, the pre-crosslinking temperature is 150 to 210°C;

[0042] Optionally, the pre-crosslinking time is 1 to 4 hours.

[0043] The experiment found that pre-crosslinking can improve the compressive strength of the prepared porous carbon, ensuring the low expansion rate and high cycle stability of the final negative electrode material. Without pre-crosslinking, even adding a crosslinking agent cannot significantly improve the compressive strength of the porous carbon.

[0044] In an optional embodiment, the doping source is selected from one or more of a nitrogen source, a sulfur source, and a fluorine source;

[0045] Optionally, the nitrogen source is selected from common types in the art, such as urea, melamine, etc.;

[0046] Optionally, the sulfur source is selected from common types in the art, such as thiocyanate, etc.;

[0047] Optionally, the fluorine source is selected from common types in the art, such as ammonium fluoride and the like.

[0048] Optionally, the mass ratio of the carbon source to the cross-linking agent is (10-50): (1-5);

[0049] If a doping source is added, optionally, the mass ratio of the carbon source to the doping source is (10-50): (10-50).

[0050] In an optional embodiment, the carbonization temperature is 600-800°C;

[0051] Optionally, the carbonization is carried out by heating the temperature to 600-800° C. at a heating rate of 5-10° C. / min and keeping the temperature for 5-8 hours.

[0052] In an optional embodiment, the activation agent is selected from one or more of CO, CO2, water vapor, and oxygen;

[0053] Optionally, the flow rate of the activator is 0.1-2 kg / h, the activation time is 1-24 h, and the activation temperature is 600-800°C.

[0054] Further optionally, the flow rate of the activator is 0.5 to 1.5 kg / h, and the activation time is 10 to 16 hours.

[0055] Optionally, the material prepared in step (S1) is cooled, taken out, washed, filtered and dried to obtain the first matrix.

[0056] In step (S2):

[0057] In an optional embodiment, the uniform deposition is performed at a temperature of 400 to 700° C.;

[0058] Optionally, silicon deposition is performed to uniformly deposit nano-silicon particles.

[0059] Optionally, when performing silicon deposition, the first substrate is placed in a raw material gas environment containing a silicon source gas to perform vapor deposition;

[0060] Optionally, the silicon source gas is selected from conventional types in the art, including one or more of monosilane, disilane, dichlorosilane, and trichlorosilane;

[0061] Optionally, the raw material gas containing silicon source gas has a flow rate of 1 to 60 L / h; further optionally, the flow rate is 10 to 60 L / h;

[0062] Further optionally, the flow rate is 15 to 40 L / h. Experiments have found that using this flow rate for silicon deposition can ensure that the pore volume filling rate P of the prepared second substrate is within an appropriate range, and the expansion rate S of the prepared negative electrode sheet can be controlled within a lower range.

[0063] More optionally, the flow rate is 20 L / h.

[0064] Optionally, the raw material gas containing the silicon source gas contains an inert gas, the volume percentage of which is 0 to 30%;

[0065] Optionally, it is selected from inert gases such as argon and helium.

[0066] Optionally, silicon deposition is performed for 12 to 36 hours.

[0067] Optionally, the temperature is first increased to 400-700° C. at a heating rate of 5-10° C. / min and maintained for 0.5-2 h before silicon deposition.

[0068] In step (S3):

[0069] In an optional embodiment, the uniform deposition is performed at a temperature of 500-800°C.

[0070] Optionally, a carbon coating treatment is performed to uniformly deposit a carbon coating layer.

[0071] Optionally, the carbon coating treatment is performed by placing the second substrate in a raw gas environment containing a carbon source gas to perform vapor deposition;

[0072] Optionally, the carbon source gas is selected from one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes; Optionally, C1-C4 alkanes are selected from methane, ethane, propane, and butane; Optionally, C2-C4 alkenes are selected from ethylene, propylene, butene, and 1,3-butadiene; Optionally, C2-C4 alkynes are selected from acetylene, propyne, and butyne;

[0073] Optionally, the raw gas containing the carbon source gas has a flow rate of 1 to 20 L / h;

[0074] Optionally, the carbon coating treatment is performed at a temperature of 500 to 800° C. for a time of 1 to 12 hours.

[0075] Optionally, the temperature is first increased to 500-800° C. at a heating rate of 5-10° C. / min and kept at that temperature for 0.5-2 h before the carbon coating treatment is performed.

[0076] In a third aspect, the present invention further provides a negative electrode sheet, comprising the negative electrode material, wherein the thickness of the negative electrode sheet before and after the first charge and discharge is set to T1 and T2 respectively, and the expansion rate is set to S, S=(T2-T1) / T1;

[0077] Then S and P satisfy the relationship S = 748P 2 -1413P+668(Ⅰ), in formula (Ⅰ), 0.90≤P≤0.99.

[0078] In an optional embodiment, the negative electrode plate satisfies at least one of the following conditions:

[0079] (a) The thickness of the negative electrode before the first charge and discharge is T1, 30 μm ≤ T1 ≤ 80 μm;

[0080] (b) The thickness of the negative electrode after the first charge and discharge is T2, 33mm≤T2≤240mm;

[0081] (c) Negative electrode sheet expansion rate S, 0.10≤S≤2.00.

[0082] It has been found through experiments that when the pore volume filling rate P is too low, lower than 0.90, the electrolyte will seep into the negative electrode sheet, and the influence of the electrolyte itself will be more obvious, resulting in the expansion rate S not conforming to formula (I); when the pore volume filling rate P is too high, higher than 0.99, the expansion of the negative electrode sheet cannot be buffered at all when it is basically filled, which will also cause the expansion rate S not conforming to formula (I).

[0083] It has also been found through experiments that if the compressive strength of the first matrix is ​​too low, the expansion rate S will not conform to formula (I). Therefore, it is also necessary to control the compressive strength of the first matrix to be no less than 300 MPa.

[0084] Optionally, the compression strength of the first matrix is ​​controlled to be not less than 300 MPa, and the pore volume filling rate P is controlled to be 0.93≤P≤0.96, so that the expansion rate S of the prepared negative electrode sheet can be controlled to be no more than 80%. It also has high cycle stability, high capacity and first efficiency.

[0085] In a fourth aspect, the present invention further provides a secondary battery, comprising the negative electrode plate.

[0086] Compared with the prior art, the present invention has the following beneficial results:

[0087] The invention discloses a negative electrode material, which introduces the concept of pore volume filling rate P of the negative electrode material for the first time, and more importantly, derives the relationship between the pore volume filling rate P and the expansion rate S of the negative electrode sheet.

[0088] The present invention can adjust the pore volume filling rate P of the negative electrode material by adjusting the preparation process of the negative electrode material, thereby achieving precise control of the expansion rate S of the prepared negative electrode sheet; through process optimization, the expansion rate S of the negative electrode sheet prepared by the present invention can be controlled to not exceed 80%; more preferably not exceed 70%.

[0089] The battery assembled with the negative electrode sheet prepared by the present invention has low expansion, high cycle stability, high capacity and first efficiency. DETAILED DESCRIPTION

[0091] In the description of the present invention, it should be noted that, for those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific circumstances. Below, according to the overall structure of the present invention, its embodiments are described. Unless otherwise specified, the raw materials in the embodiments of the present invention are purchased through commercial channels.

[0092] In a first aspect, the present invention provides a negative electrode material, comprising a first substrate, a second substrate and a coating layer;

[0093] The first matrix is ​​a porous structure with a pore volume of V1;

[0094] The second matrix is ​​obtained by uniformly depositing the sediment I in the pores of the first matrix, the pore volume is V2, the pore volume filling rate is P, P = (V1-V2) / V1;

[0095] Among them, 0.90≤P≤0.99;

[0096] The coating layer is formed by uniformly depositing the sediment II on the surface of the second substrate.

[0097] In an optional embodiment, the pore volume V1 of the first matrix and the pore volume V2 of the second matrix satisfy at least one of the following conditions:

[0098] (1) Pore volume V1: 0.5 cm 3 / g≤V1≤2cm 3 / g; specifically, it can be 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g, 1.5cm 3 / g, 1.6cm 3 / g, 1.7cm 3 / g, 1.8cm 3 / g, 1.9cm 3 / g, 2.0cm 3 / g or any value within the above range; Optionally, 0.7cm 3 / g≤V1≤1.3cm 3 / g; further optionally, 0.8cm 3 / g≤V1≤1.0cm 3 / g; more preferably, 0.85cm 3 / g≤V1≤0.95cm 3 / g;

[0099] (2) Pore volume V2: 0.005 cm 3 / g≤V2≤0.2cm 3 / g; specifically, it can be 0.005cm 3 / g, 0.01cm 3 / g, 0.02cm 3 / g, 0.03cm 3 / g, 0.04cm 3 / g, 0.05cm 3 / g, 0.08cm 3 / g, 0.1cm 3 / g, 0.12cm 3 / g, 0.14cm 3 / g, 0.16cm 3 / g, 0.18cm 3 / g, 0.20cm 3 / g or any value within the above range; Optionally, 0.01cm 3 / g≤V2≤0.1cm 3 / g; further optionally, 0.04cm 3 / g≤V2≤0.06cm 3 / g.

[0100] In an optional embodiment, the first substrate comprises a porous carbon material or a porous carbon material containing a doping element;

[0101] Optionally, the doping element is selected from one or more of nitrogen, sulfur and fluorine;

[0102] By adding doping elements, the rate performance of the prepared negative electrode material can be further improved and the initial efficiency can be increased.

[0103] In an optional embodiment, the sediment I comprises silicon grains;

[0104] In an alternative embodiment, the sediment II comprises a carbon material.

[0105] In an optional embodiment, the negative electrode material satisfies at least one of the following conditions:

[0106] (a) The silicon content in the negative electrode material is 45-50% of the total mass of the negative electrode material; specifically, it can be 45%, 46%, 47%, 48%, 49%, 50% or any value within the above range;

[0107] (b) the carbon content of the negative electrode material is 45-50% of the total mass of the negative electrode material; specifically, it can be 45%, 46%, 47%, 48%, 49%, 50% or any value within the above range;

[0108] (c) The content of the doping element in the negative electrode material is 0-10% of the total mass of the negative electrode material; specifically, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any value within the above range;

[0109] (d) D50 is 7.5±1 μm; specifically, it can be 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, 7.0 μm, 7.1 μm, 7.5 μm, 7.8 μm, 8.0 μm, 8.2 μm, 8.5 μm or any value within the above range;

[0110] (e) Specific surface area: 2.5 ± 1.5 m 2 / g; specifically, it can be 1m 2 / g, 1.2m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2m 2 / g, 2.2m 2 / g, 2.5m2 / g, 2.8m 2 / g, 3m 2 / g, 3.2m 2 / g, 3.5m 2 / g, 3.8m 2 / g, 4m 2 / g or any value within the above range;

[0111] (f) the resistivity is 1 to 10 Ω-cm; specifically, it can be 1 Ω-cm, 2 Ω-cm, 3 Ω-cm, 4 Ω-cm, 5 Ω-cm, 6 Ω-cm, 7 Ω-cm, 8 Ω-cm, 9 Ω-cm, 10 Ω-cm or any value within the above range;

[0112] (g) Tap density: 0.95±0.15g / cm 3 ; Specifically, it can be 0.8g / cm 3 , 0.85g / cm 3 , 0.9g / cm 3 , 0.95g / cm 3 , 1.0g / cm 3 , 1.05g / cm 3 , 1.1g / cm 3 Or any value within the above range.

[0113] In a second aspect, the present invention further provides a method for preparing the negative electrode material, comprising:

[0114] (S1) mixing a carbon source, a crosslinking agent and an optionally added doping source, and obtaining a first matrix through pre-crosslinking, carbonization and activation processes;

[0115] (S2) uniformly depositing in the holes of the first substrate to obtain a second substrate;

[0116] (S3) uniformly depositing a coating layer on the surface of the second substrate to obtain the negative electrode material.

[0117] In step (S1):

[0118] In an optional embodiment, the carbon source is selected from one or more of phenolic resin, asphalt, and polyacrylamide;

[0119] Optionally, the carbon source is selected from phenolic resin and polyacrylamide. Experiments have shown that the battery assembled with the negative electrode material prepared by using the porous carbon prepared by the combination of the two as the substrate has better electrochemical performance.

[0120] Further optionally, the mass ratio of phenolic resin to polyacrylamide is (2-6):1; specifically, it can be 2:1, 3:1, 4:1, 5:1, 6:1 or any ratio within the above range.

[0121] In an optional embodiment, the cross-linking agent is selected from one or more of polyethylene glycol, propylene diamine, and tetraisocyanate;

[0122] In an optional embodiment, the pre-crosslinking temperature is 150-210°C; specifically, it can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C or any value within the above range.

[0123] Optionally, the pre-crosslinking time is 1 to 4 hours; specifically, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours or any value within the above range.

[0124] The experiment found that pre-crosslinking can improve the compressive strength of the prepared porous carbon, ensuring the low expansion rate and high cycle stability of the final negative electrode material. Without pre-crosslinking, even adding a crosslinking agent cannot significantly improve the compressive strength of the porous carbon.

[0125] In an optional embodiment, the doping source is selected from one or more of a nitrogen source, a sulfur source, and a fluorine source;

[0126] Optionally, the nitrogen source is selected from common types in the art, such as urea, melamine, etc.;

[0127] Optionally, the sulfur source is selected from common types in the art, such as thiocyanate, etc.;

[0128] Optionally, the fluorine source is selected from common types in the art, such as ammonium fluoride and the like.

[0129] Optionally, the mass ratio of the carbon source to the cross-linking agent is (10-50):(1-5); specifically, it can be 2:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1 or any ratio within the above range.

[0130] If a doping source is added, optionally, the mass ratio of the carbon source to the doping source is (10-50):(10-50); specifically, it can be 0.2:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1 or any ratio within the above range.

[0131] In an optional embodiment, the carbonization temperature is 600-800°C; specifically, it can be 600°C, 620°C, 650°C, 680°C, 700°C, 720°C, 750°C, 780°C, 800°C or any value within the above range.

[0132] Optionally, the carbonization is carried out by heating the temperature to 600-800° C. at a heating rate of 5-10° C. / min and keeping the temperature for 5-8 hours.

[0133] In an optional embodiment, the activation agent is selected from one or more of CO, CO2, water vapor, and oxygen;

[0134] Optionally, the flow rate of the activator is 0.1-2 kg / h, specifically 0.1 kg / h, 0.2 kg / h, 0.5 kg / h, 1.0 kg / h, 1.2 kg / h, 1.5 kg / h, 2.0 kg / h or any value within the above range; further optionally, the flow rate of the activator is 0.5-1.5 kg / h.

[0135] Optionally, the activation time is 1 to 24 hours; specifically, it can be 1 hour, 2 hours, 3 hours, 5 hours, 8 hours, 12 hours, 16 hours, 20 hours, 24 hours or any value within the above range; further optionally, the activation time is 10 to 16 hours.

[0136] Optionally, the activation temperature is 600-800°C; specifically, it can be 600°C, 620°C, 650°C, 680°C, 700°C, 720°C, 750°C, 780°C, 800°C or any value within the above range.

[0137] Optionally, the material prepared in step (S1) is cooled, taken out, washed, filtered and dried to obtain the first matrix.

[0138] In step (S2):

[0139] In an optional embodiment, the uniform deposition temperature is 400-700°C; specifically, it can be 400°C, 420°C, 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C, 620°C, 650°C, 680°C, 700°C or any value within the above range.

[0140] Optionally, silicon deposition is performed to uniformly deposit nano-silicon particles.

[0141] Optionally, when performing silicon deposition, the first substrate is placed in a raw material gas environment containing a silicon source gas to perform vapor deposition;

[0142] Optionally, the silicon source gas is selected from conventional types in the art, including one or more of monosilane, disilane, dichlorosilane, and trichlorosilane;

[0143] Optionally, the raw gas containing silicon source gas has a flow rate of 1 to 60 L / h; specifically, it can be 1 L / h, 5 L / h, 10 L / h, 15 L / h, 20 L / h, 25 L / h, 30 L / h, 35 L / h, 40 L / h, 45 L / h, 50 L / h, 55 L / h, 60 L / h or any value within the above range; further optionally, the flow rate is 10 to 60 L / h; further optionally, the flow rate is 15 to 40 L / h; experiments have found that using this flow rate for silicon deposition can ensure that the pore volume filling rate P of the prepared second substrate is within an appropriate range, and the expansion rate S of the prepared negative electrode sheet can be controlled within a lower range; most optionally, the flow rate is 20 L / h.

[0144] Optionally, the raw material gas containing the silicon source gas contains an inert gas, the volume percentage of which is 0-30%; specifically, it can be 1%, 5%, 10%, 15%, 20%, 25%, 30% or any value within the above range;

[0145] Optionally, it is selected from inert gases such as argon and helium.

[0146] Optionally, silicon deposition is performed for 12 to 36 hours; specifically, it can be 12 hours, 16 hours, 20 hours, 24 hours, 28 hours, 32 hours, 36 hours or any value within the above range.

[0147] Optionally, the temperature is first increased to 400-700° C. at a heating rate of 5-10° C. / min and maintained for 0.5-2 h before silicon deposition.

[0148] In step (S3):

[0149] In an optional embodiment, the uniform deposition temperature is 500-800°C; specifically, it can be 500°C, 520°C, 550°C, 580°C, 600°C, 620°C, 650°C, 680°C, 700°C, 720°C, 750°C, 780°C, 800°C or any value within the above range.

[0150] Optionally, a carbon coating treatment is performed to uniformly deposit a carbon coating layer.

[0151] Optionally, the carbon coating treatment is performed by placing the second substrate in a raw gas environment containing a carbon source gas to perform vapor deposition;

[0152] Optionally, the carbon source gas is selected from one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes; Optionally, C1-C4 alkanes are selected from methane, ethane, propane, and butane; Optionally, C2-C4 alkenes are selected from ethylene, propylene, butene, and 1,3-butadiene; Optionally, C2-C4 alkynes are selected from acetylene, propyne, and butyne;

[0153] Optionally, the raw gas containing the carbon source gas has a flow rate of 1 to 20 L / h; specifically, it can be 1 L / h, 2 L / h, 5 L / h, 8 L / h, 10 L / h, 12 L / h, 15 L / h, 18 L / h, 20 L / h or any value within the above range;

[0154] Optionally, the carbon coating treatment is performed at a temperature of 500-800°C; specifically, it may be 500°C, 520°C, 550°C, 580°C, 600°C, 620°C, 650°C, 680°C, 700°C, 720°C, 750°C, 780°C, 800°C or any value within the above range;

[0155] Optionally, the carbon coating treatment is carried out for 1 to 12 hours; specifically, it can be 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours or any value within the above range.

[0156] Optionally, the temperature is first increased to 500-800° C. at a heating rate of 5-10° C. / min and kept at that temperature for 0.5-2 h before the carbon coating treatment is performed.

[0157] In a third aspect, the present invention further provides a negative electrode sheet, comprising the negative electrode material, wherein the thickness of the negative electrode sheet before and after the first charge and discharge is set to T1 and T2 respectively, and the expansion rate is set to S, S=(T2-T1) / T1;

[0158] Then S and P satisfy the relationship S = 748P 2 -1413P+668(Ⅰ), in formula (Ⅰ), 0.90≤P≤0.99.

[0159] In an optional embodiment, the negative electrode plate satisfies at least one of the following conditions:

[0160] (a) the thickness of the negative electrode sheet before the first charge and discharge is T1, 30 μm ≤ T1 ≤ 80 μm; specifically, it can be 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm or any value within the above range;

[0161] (b) the thickness of the negative electrode sheet after the first charge and discharge is T2, 33 mm ≤ T2 ≤ 240 mm; specifically, it can be 33 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, 220 μm, 240 μm or any value within the above range;

[0162] (c) The negative electrode sheet expansion rate S, 0.10≤S≤2.00; specifically, it can be 0.1, 0.2, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0 or any value within the above range.

[0163] It has been found through experiments that when the pore volume filling rate P is too low, lower than 0.90, the electrolyte will seep into the negative electrode sheet, and the influence of the electrolyte itself will be more obvious, resulting in the expansion rate S not conforming to formula (I); when the pore volume filling rate P is too high, higher than 0.99, the expansion of the negative electrode sheet cannot be buffered at all when it is basically filled, which will also cause the expansion rate S not conforming to formula (I).

[0164] It has also been found through experiments that if the compressive strength of the first matrix is ​​too low, the expansion rate S will not conform to formula (I). Therefore, it is also necessary to control the compressive strength of the first matrix to be no less than 300 MPa.

[0165] Optionally, the compression strength of the first matrix is ​​controlled to be not less than 300 MPa, and the pore volume filling rate P is controlled to be 0.93≤P≤0.96, so that the expansion rate S of the prepared negative electrode sheet can be controlled to be no more than 80%. It also has high cycle stability, high capacity and first efficiency.

[0166] In a fourth aspect, the present invention further provides a secondary battery, comprising the negative electrode plate.

[0167] Compared with the prior art, the present invention has the following beneficial results:

[0168] The invention discloses a negative electrode material, which introduces the concept of pore volume filling rate P of the negative electrode material for the first time, and more importantly, derives the relationship between the pore volume filling rate P and the expansion rate S of the negative electrode sheet.

[0169] The present invention can adjust the pore volume filling rate P of the negative electrode material by adjusting the preparation process of the negative electrode material, thereby achieving precise control of the expansion rate S of the prepared negative electrode sheet; through process optimization, the expansion rate S of the negative electrode sheet prepared by the present invention can be controlled to not exceed 80%; more preferably not exceed 70%.

[0170] The battery assembled with the negative electrode sheet prepared by the present invention has low expansion, high cycle stability, high capacity and first efficiency.

[0171] Example 1

[0172] (1) Polyacrylamide, phenolic resin, polyethylene glycol and urea are uniformly mixed in a mass ratio of 8:2:1:10, placed in a carbonization furnace, heated to 180°C at a heating rate of 10°C / min under an air atmosphere and kept warm for 2 hours; the obtained product is kept in a nitrogen atmosphere, the oxygen content in the carbonization furnace is controlled to be less than 20 ppm, and then heated to 700°C at a heating rate of 10°C / min and kept warm for 6 hours; after the insulation is completed, 1 kg / h of water vapor is introduced for activation for 12 hours; after the material is cooled, it is taken out, pickled, filtered and dried to obtain a first matrix.

[0173] (2) The first substrate is placed in a rotary kiln, and the oxygen content in the rotary kiln is controlled to be less than 20 ppm under a nitrogen atmosphere. The temperature is then increased to 500°C at a heating rate of 10°C / min and kept warm for 1 hour. The temperature is then kept warm for 24 hours under a monosilane gas atmosphere at a monosilane gas flow rate of 20 L / h to obtain a second substrate.

[0174] (3) In a nitrogen atmosphere, the temperature is raised to 600°C at a heating rate of 10°C / min and kept at this temperature for 1 hour; then, in an acetylene gas atmosphere, the gas flow rate is 5L / h, and the temperature is kept for 6 hours. The acetylene gas is decomposed at high temperature on the surface of the second substrate to form a carbon coating layer, thereby obtaining a negative electrode material.

[0175] Example 2

[0176] The preparation process is basically the same as that of Example 1, except that the flow rate of monosilane gas in step (2) is replaced with 10 L / h and the insulation time is replaced with 12 h.

[0177] Example 3

[0178] The preparation process is basically the same as that of Example 1, except that the flow rate of monosilane gas in step (2) is replaced with 60 L / h and the insulation time is replaced with 36 h.

[0179] Example 4

[0180] The preparation process is basically the same as that of Example 1, except that the carbon source in step (1) is replaced by polyacrylamide alone, and the mass ratio of polyacrylamide, polyethylene glycol and urea is 10:1:10.

[0181] Example 5

[0182] The preparation process is basically the same as that of Example 1, except that the carbon source in step (1) is replaced by a single phenolic resin, and the mass ratio of the phenolic resin, polyethylene glycol and urea is 10:1:10.

[0183] Example 6

[0184] The preparation process is basically the same as that of Example 1, except that the phenolic resin in step (1) is replaced by an equal mass of asphalt, that is, the mass ratio of polyacrylamide, asphalt, polyethylene glycol and urea is 8:2:1:10.

[0185] Example 7

[0186] The preparation process is basically the same as that of Example 1, except that urea is not added in step (1).

[0187] Example 8

[0188] The preparation process is basically the same as that of Example 1, except that the flow rate of water vapor in step (1) is replaced with 0.1 kg / h and the activation time is replaced with 6 h.

[0189] Example 9

[0190] The preparation process is basically the same as that of Example 1, except that the flow rate of water vapor in step (1) is replaced with 2 kg / h and the activation time is replaced with 24 h.

[0191] Comparative Example 1

[0192] (1) Polyacrylamide, phenolic resin and urea are uniformly mixed in a mass ratio of 8:2:10, placed in a carbonization furnace, maintained in a nitrogen atmosphere, and the oxygen content in the carbonization furnace is controlled to be less than 20 ppm. Then, the temperature is increased to 700°C at a heating rate of 10°C / min and kept warm for 6 hours. After the insulation is completed, 1 kg / h of water vapor is introduced for activation for 12 hours. After the material is cooled, it is taken out, pickled, filtered and dried to obtain a first matrix.

[0193] Steps (2) to (3) are exactly the same as those in Example 1.

[0194] Comparative Example 2

[0195] The preparation process is basically the same as that of Example 1, except that the flow rate of water vapor in step (1) is replaced with 0.05 kg / h and the activation time is replaced with 0.5 h.

[0196] Comparative Example 3

[0197] The preparation process is basically the same as that of Example 1, except that the flow rate of water vapor in step (1) is replaced by 4 kg / h and the activation time is replaced by 48 h.

[0198] Comparative Example 4

[0199] The preparation process is basically the same as that of Example 1, except that the flow rate of monosilane gas in step (2) is replaced with 0.5 L / h and the insulation time is replaced with 6 h.

[0200] Comparative Example 5

[0201] The preparation process is basically the same as that of Example 1, except that the flow rate of monosilane gas in step (2) is replaced with 80 L / h and the insulation time is replaced with 48 h.

[0202] The negative electrode materials prepared in Examples 1 to 9 and Comparative Examples 1 to 5 were tested for parameters such as specific surface area, pore volume, and pore volume filling rate. The specific surface area and pore volume were tested using a JW-BK300C surface analyzer and pore size analyzer. The pore volume filling rate P was calculated using the formula, and the specific values ​​are listed in Table 1 below.

[0203] Table 1

[0204]

[0205] Application Examples

[0206] Batteries were assembled using the products prepared in each embodiment and each comparative example as negative electrode materials.

[0207] The negative electrode material was mixed with carboxymethyl cellulose (CMC), acrylonitrile (LA133), single-walled carbon nanotubes (SWCNT) and carbon black (SP) in a mass ratio of 90:3.5:3.5:0.2:2.8 to prepare a slurry, evenly coated on a copper foil and dried to form a negative electrode sheet. The thickness T1 of the sheet was measured and assembled into a button cell with the negative electrode shell, electrolyte (KLD-Si01, KLD silicon-carbon button battery electrolyte), diaphragm, lithium sheet, nickel foam and positive electrode shell in an argon atmosphere glove box.

[0208] The above 14 groups of batteries were tested by the Blue Electric Battery Test System. At 25°C, they were first discharged to 0.005V at 0.05C, left to stand for 10 minutes, and then discharged to 0.001V at 0.02C and left to stand for 30 minutes; then charged to 1.5V at 0.1C, left to stand for 10 minutes, and the first charge gram capacity was recorded, and the first coulomb efficiency was calculated; then the button battery was disassembled in an argon atmosphere glove box, and the thickness T2 of the negative electrode was measured again after drying the negative electrode plate, and the expansion rate S = (T2-T1) / T1 was calculated. The above 14 groups of batteries were tested by the Blue Electric Battery Test System in the above manner. After 100 cycles, the charge and discharge capacity after 100 cycles was recorded, and the capacity retention rate after 100 cycles was calculated. The test results are shown in Table 2.

[0209] Table 2

[0210]

[0211]

[0212] Compare the data in Table 1 and Table 2.

[0213] First, the expansion rate S measured in each embodiment in Table 2 is compared with the expansion rate S calculated according to formula (I), which is relatively close, indicating that formula (I) is reasonable, and the expansion rate S of the prepared negative electrode sheet can be accurately controlled by controlling the pore volume filling rate P of the negative electrode material.

[0214] By comparing Examples 1, 8, 9 and Comparative Examples 2, 3 in Tables 1 and 2, it can be seen that the activation process parameters in the adjustment step (S1) can regulate the pore volume filling rate P and thus adjust the expansion rate S of the negative electrode sheet. When the flow rate of the activator is too low and the treatment time is too short (Comparative Example 2), the pore volume filling rate P is too high, and the space for alleviating the volume expansion of silicon particles is small. The huge volume expansion of silicon is easy to break the material, resulting in performance degradation. When the flow rate of the activator is too high and the treatment time is too long (Comparative Example 3), the pore volume filling rate P is too low, and the space for alleviating the volume expansion of silicon grains is large. The silicon particles have a greater expansion / contraction rate during the lithium insertion / delithiation process, which can easily cause the silicon particles to shatter, resulting in excessive electrolyte entering the pores of the negative electrode material to cause side reactions, resulting in reduced capacity.

[0215] By comparing Example 1 and Comparative Example 1 in Tables 1 and 2, it can be seen that if no cross-linking agent is added and no pre-cross-linking treatment is performed (Comparative Example 1), the compressive strength of the prepared first substrate is too low, resulting in an excessively high expansion rate of the prepared negative electrode sheet, leading to performance degradation.

[0216] By comparing Examples 1 to 3 and Comparative Examples 4 and 5 in Tables 1 and 2, it can be seen that adjusting the process parameters of silicon deposition in step (S2) can regulate the pore volume filling rate P and thus adjust the expansion rate S of the negative electrode sheet. When the flow rate of monosilane is too low and the deposition time is too short (Comparative Example 4), the pore volume filling rate P is too low, and the performance of the assembled battery is degraded; when the flow rate of monosilane is too high and the deposition time is too long (Comparative Example 5), the pore volume filling rate P is too high, and the performance of the assembled battery is degraded.

[0217] The above-mentioned embodiments are preferred embodiments, but the protection scope of the present invention is not limited thereto. A person skilled in the art can easily understand the spirit of the present invention based on the above-mentioned embodiments and make different extensions and changes. However, as long as they do not deviate from the spirit of the present invention, they are all within the protection scope of the present invention.

Claims

1. A negative electrode material, characterized in that: comprising a first substrate, a second substrate and a coating layer; The first matrix is ​​a porous structure with a pore volume of V1; The second matrix is ​​obtained by uniformly depositing the sediment I in the pores of the first matrix, the pore volume is V2, the pore volume filling rate is P, P = (V1-V2) / V1; Among them, 0.90≤P≤0.99; The coating layer is formed by uniformly depositing the sediment II on the surface of the second substrate.

2. The negative electrode material according to claim 1, characterized in that The pore volume V1 of the first matrix and the pore volume V2 of the second matrix satisfy at least one of the following conditions: (1) Pore volume V1: 0.5 cm 3 / g≤V1≤2cm 3 / g; (2) Pore volume V2: 0.005 cm 3 / g≤V2≤0.2cm 3 / g.

3. The negative electrode material according to claim 1, characterized in that: The first substrate comprises a porous carbon material or a porous carbon material containing a doping element; The doping element is selected from one or more of nitrogen, sulfur and fluorine; The sediment I comprises silicon grains; The sediment II includes carbon material.

4. The negative electrode material according to claim 1, characterized in that The negative electrode material satisfies at least one of the following conditions: (a) the silicon content in the negative electrode material is 45-50% of the total mass of the negative electrode material; (b) the carbon content of the negative electrode material is 45-50% of the total mass of the negative electrode material; (c) the content of the doping element in the negative electrode material is 0 to 10% of the total mass of the negative electrode material; (d) D50: 7.5 ± 1 μm; (e) Specific surface area: 2.5 ± 1.5 m 2 / g; (f) Resistivity is 1 to 10 Ω-cm; (g) Tap density: 0.95±0.15g / cm 3 .

5. The negative electrode material according to any one of claims 1 to 4, characterized in that: At least one of the following conditions is met: (1) Pore volume V1: 0.7 cm 3 / g≤V1≤1.3cm 3 / g; (2) Pore volume V2: 0.01 cm 3 / g≤V2≤0.1cm 3 / g; (3) The pore volume filling rate is P: 0.93≤P≤0.

96.

6. A method for preparing a negative electrode material according to any one of claims 1 to 5, characterized in that: include: (S1) mixing a carbon source, a crosslinking agent and an optionally added doping source, and obtaining a first matrix through pre-crosslinking, carbonization and activation processes; (S2) uniformly depositing in the holes of the first substrate to obtain a second substrate; (S3) uniformly depositing a coating layer on the surface of the second substrate to obtain the negative electrode material.

7. The method for preparing the negative electrode material according to claim 6, characterized in that: In step (S1): The carbon source is selected from one or more of phenolic resin, asphalt, and polyacrylamide; The cross-linking agent is selected from one or more of polyethylene glycol, propylene diamine, and tetraisocyanate; The doping source is selected from one or more of a nitrogen source, a sulfur source, and a fluorine source; The pre-crosslinking temperature is 150-210°C; The carbonization temperature is 600-800°C; The activation agent is selected from one or more of CO, CO2, water vapor and oxygen; In step (S2): The uniform deposition temperature is 400-700°C; In step (S3): The uniform deposition is carried out at a temperature of 500-800°C.

8. A negative electrode sheet, comprising the negative electrode material according to any one of claims 1 to 5, characterized in that: The thickness of the negative electrode sheet before and after the first charge and discharge is set to T1 and T2 respectively, and the expansion rate is set to S, S = (T2-T1) / T1; Then S and P satisfy the relationship S = 748P 2 -1413P+668(Ⅰ), in formula (Ⅰ), 0.90≤P≤0.

99.

9. The negative electrode sheet according to claim 8, characterized in that: The negative electrode sheet satisfies at least one of the following conditions: (a) The thickness of the negative electrode before the first charge and discharge is T1, 30 μm ≤ T1 ≤ 80 μm; (b) The thickness of the negative electrode after the first charge and discharge is T2, 33mm≤T2≤240mm; (c) Negative electrode sheet expansion rate S, 0.10≤S≤2.

00. 10 . A secondary battery comprising the negative electrode sheet according to claim 8 or 9 .

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