Negative pole piece of lithium ion battery, lithium ion battery comprising negative pole piece and electric device comprising negative pole piece

Abstract

The invention provides a lithium ion battery negative pole piece, a lithium ion battery comprising the same and an electric device, and relates to the technical field of lithium ion batteries. The negative electrode coating material of the lithium ion battery is a silicon-carbon composite material and meets the following X-ray diffraction characteristic peak intensity relational expression: ISi / IGr is more than or equal to 0.05 and less than or equal to 0.6, and D is more than or equal to 10.0 and less than or equal to 70.0; wherein IGr represents the characteristic diffraction peak intensity of the crystal face of the carbon raw material in the silicon-carbon composite material in an XRD spectrogram; iSi represents the characteristic diffraction peak intensity of a silicon raw material in the silicon-carbon composite material in an XRD spectrogram; d is the grain size of the silicon raw material in the silicon-carbon composite material. By optimizing and adjusting the X-ray diffraction characteristic peak intensity relational expression of the silicon-carbon composite material and limiting the grain size of the silicon raw material in the silicon-carbon composite material, the rate charging performance, the low-temperature performance and the cycle performance of the lithium ion battery are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a lithium-ion battery negative electrode plate, a lithium-ion battery comprising the same, and an electrical device. Background Art

[0002] Lithium-ion batteries (LIBs) have been widely used in consumer electronics, electric vehicles, and energy storage due to their high energy density, long cycle life, and environmental friendliness. However, the performance of LIBs remains significantly limited under high-rate charge / discharge conditions and at low temperatures. Traditional graphite anode materials offer excellent cycle stability and low expansion, but their rate and low-temperature performance are limited. This is primarily due to the significant reduction in the lithium-ion diffusion rate of graphite anode materials at low temperatures, resulting in a significant decrease in charge / discharge efficiency and rate performance.

[0003] In contrast, silicon has attracted considerable attention due to its ultra-high theoretical specific capacity, making it a promising material for improving the energy density of lithium-ion batteries. However, silicon undergoes a volume change of over 300% during lithium insertion / extraction. This dramatic expansion leads to damage to the electrode structure, increased electrolyte decomposition, and instability of the solid electrolyte interface (SEI) film, significantly limiting its practical application in terms of cycle life and rate performance.

[0004] To combine the advantages of graphite and silicon, researchers have proposed combining graphite with silicon, leveraging graphite's structural stability with silicon's high capacity to achieve a balance between rate capability, low-temperature performance, and cycling performance. However, the composite's overall performance is significantly impacted by the ratio of graphite to silicon-carbon, the adjustment of graphite interlayer spacing, the design of particle size, and the optimization of the anode compaction density. Prior art has yet to establish a systematic optimization strategy for regulating these key parameters.

[0005] Therefore, there is an urgent need for a systematic approach to achieve an optimal balance between rate performance, low-temperature performance and cycle performance by optimizing the ratio of graphite to silicon and their structural properties, so as to provide theoretical guidance and practical solutions for the design of high-performance lithium-ion batteries.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The first object of the present invention is to provide a lithium-ion battery negative electrode plate, which uses a silicon-carbon composite material as the negative electrode coating material, thereby effectively improving the rate performance, low temperature performance and cycle performance of the lithium-ion battery.

[0008] A second object of the present invention is to provide a lithium ion battery.

[0009] A third object of the present invention is to provide an electrical device.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0011] The present invention provides a lithium-ion battery negative electrode plate, which is composed of a current collector and a negative electrode coating material coated on at least one surface thereof;

[0012] The negative electrode coating material is a silicon-carbon composite material, and the X-ray diffraction (XRD) characteristic peak intensity of the silicon-carbon composite material satisfies the following relationship:

[0013] 0.05≤I Si / I Gr ≤0.6, and 10.0≤D≤70.0; where:

[0014] I Gr The characteristic diffraction peak intensity of the carbon raw material crystal plane in the silicon-carbon composite material in the XRD spectrum is represented, and the corresponding 2θ angle range is usually 25.0° to 27.0°;

[0015] I Si Represents the characteristic diffraction peak intensity of the silicon raw material in the silicon-carbon composite material in the XRD spectrum, and the corresponding 2θ angle range is usually 27.5° to 28.8°;

[0016] D is the grain size of the silicon raw material in the silicon-carbon composite material, in nm.

[0017] Furthermore, the X-ray diffraction (XRD) characteristic peak intensity of the negative electrode coating material satisfies the following relationship:

[0018] 0.06≤I Si / I Gr ≤0.19, and 10.3≤D≤50.8.

[0019] Furthermore, the interlayer spacing d of the carbon raw material in the silicon-carbon composite material is 002 =0.335~0.35nm.

[0020] Furthermore, the compaction density of the negative electrode sheet is 1.2 to 1.6 g / cm 3 .

[0021] Furthermore, the raw materials for preparing the negative electrode coating material include: silicon raw material, carbon raw material, conductive agent, thickener and binder.

[0022] Furthermore, the negative electrode coating material includes, by mass percentage, 5-48% silicon raw material, 44-86% carbon raw material, 0.5-2.0% conductive agent, 0.5-1.5% thickener and 0.5-2.0% binder.

[0023] Preferably, the negative electrode coating material comprises, by mass percentage, 20% silicon raw material, 76% carbon raw material, 1.5% conductive agent, 1.0% thickener and 1.5% binder.

[0024] Furthermore, the carbon raw material includes at least one of artificial graphite, natural graphite, soft carbon or hard carbon;

[0025] The silicon raw material includes at least one of deposited silicon carbon and crystalline silicon.

[0026] Furthermore, the conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black;

[0027] The thickener includes one or more of pre-lithiated sodium carboxymethyl cellulose, sodium carboxymethyl cellulose and hydroxypropyl methyl cellulose;

[0028] The binder includes one or more of polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid and styrene-butadiene rubber.

[0029] The present invention provides a lithium-ion battery, which includes the above-mentioned negative electrode plate.

[0030] The present invention provides an electrical device, which includes the above-mentioned lithium-ion battery or the above-mentioned negative electrode plate.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention provides a lithium ion battery negative electrode plate, wherein the negative electrode coating material of the negative electrode plate is a silicon-carbon composite material and satisfies the following X-ray diffraction (XRD) characteristic peak intensity relationship: 0.05≤I Si / I Gr ≤0.6, and 10.0≤D≤70.0; where: I Gr Represents the characteristic diffraction peak intensity of the carbon raw material crystal plane in the silicon-carbon composite material in the XRD spectrum, and the corresponding 2θ angle range is usually 25.0° to 27.0°; I Si represents the characteristic diffraction peak intensity of the silicon raw material in the silicon-carbon composite material in the XRD spectrum, and its corresponding 2θ angle range is usually 27.5° to 28.8°; D is the grain size of the silicon raw material in the silicon-carbon composite material, in nm.

[0033] The present invention effectively improves the rate charging performance, low temperature performance and cycle performance of the lithium-ion battery by optimizing and adjusting the X-ray diffraction characteristic peak intensity relationship of the silicon-carbon composite material and limiting the grain size of the silicon raw material in the silicon-carbon composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 This is the X-ray diffraction (XRD) characteristic peak diagram provided by Example 1 of the present invention. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0037] According to one aspect of the present invention, a negative electrode plate for a lithium-ion battery is provided, wherein the negative electrode plate comprises a current collector and a negative electrode coating material coated on at least one surface thereof;

[0038] The negative electrode coating material is a silicon-carbon composite material, and the X-ray diffraction (XRD) characteristic peak intensity of the silicon-carbon composite material satisfies the following relationship:

[0039] 0.05≤I Si / I Gr ≤0.6, and 10.0≤D≤70.0; where:

[0040] I Gr The characteristic diffraction peak intensity of the carbon raw material crystal plane in the silicon-carbon composite material in the XRD spectrum is represented, and the corresponding 2θ angle range is usually 25.0° to 27.0°;

[0041] I Si Represents the characteristic diffraction peak intensity of the silicon raw material in the silicon-carbon composite material in the XRD spectrum, and the corresponding 2θ angle range is usually 27.5° to 28.8°;

[0042] D is the grain size of the silicon raw material in the silicon-carbon composite material, in nm.

[0043] The present invention provides a lithium-ion battery negative electrode plate, wherein the negative electrode coating material of the negative electrode plate is composed of a silicon-carbon composite material and satisfies the aforementioned X-ray diffraction characteristic peak intensity relationship formula for the silicon-carbon composite material. By optimizing and adjusting the X-ray diffraction characteristic peak intensity relationship formula for the silicon-carbon composite material and limiting the grain size of the silicon raw material in the silicon-carbon composite material, the present invention effectively improves the rate charging performance, low-temperature performance, and cycle performance of the lithium-ion battery.

[0044] It should be noted that, in this application, D is the grain size of the silicon raw material (deposited silicon carbon or silicon), in nm, according to the Scherrer Equation:

[0045] D = (K × λ) / Bcosθ is calculated, K is the Scherrer constant (usually 0.89 for spherical nanoparticles), λ is the wavelength of X-rays (Cu Kα target is ); B: diffraction peak half-width (FWHM, needs to be converted into radians); θ: diffraction angle half-value.

[0046] In a preferred embodiment of the present invention, the X-ray diffraction (XRD) characteristic peak intensity of the negative electrode coating material satisfies the following relationship: 0.06≤I Si / I Gr ≤0.19, and 10.3≤D≤50.8.

[0047] Preferably, the X-ray diffraction (XRD) characteristic peak intensity of the negative electrode coating material satisfies the following relationship: 0.11≤I Si / I Gr ≤0.19, and 10.3≤D≤50.8.

[0048] In a preferred embodiment of the present invention, the interlayer spacing d of the carbon raw material in the silicon-carbon composite material is 002 =0.335~0.35nm.

[0049] It should be noted that the above d 002 The diffraction peak position corresponding to the (002) crystal plane in the XRD spectrum is fitted by a Gaussian function, according to the Bragg's equation: Calculated, n is the first order diffraction, θ is the half value of the diffraction angle, λ is the wavelength of X-ray (Cu Kα target is ).

[0050] In a preferred embodiment of the present invention, the Raman spectrum of the negative electrode active material is between 1335 and 1365 cm -1 and 1560~1590cm -1 Characteristic peaks appear.

[0051] In a preferred embodiment of the present invention, the compaction density of the negative electrode sheet is 1.2 to 1.6 g / cm 3 .

[0052] In a preferred embodiment of the present invention, the raw materials for preparing the negative electrode coating material include: silicon raw material, carbon raw material, conductive agent, thickener and binder.

[0053] In the above preferred embodiment, the negative electrode coating material includes, by mass percentage, 5-48% silicon raw material, 44-86% carbon raw material, 0.5-2.0% conductive agent, 0.5-1.5% thickener and 0.5-2.0% binder.

[0054] It should be noted that the present invention proposes a method for comprehensively optimizing the rate performance, low-temperature performance and cycle performance of lithium-ion batteries by studying the ratio of graphite (carbon raw material) and deposited silicon-carbon / silicon (silicon raw material) composite materials and the interaction between the above-mentioned particle size, compaction density and graphite interlayer spacing, providing a feasible solution for the design and industrial application of lithium battery materials.

[0055] Among them, the proportion of the silicon raw material can be but not limited to 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 48%, or any proportion between 5% and 48%. The proportion of the carbon raw material can be but not limited to 44%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 86%, or any proportion between 44% and 86%. The proportion of the conductive agent can be but not limited to 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8% or 2.0%, or any proportion between 0.5% and 2.0%. The proportion of the thickener can be but not limited to 0.5%, 0.8%, 1.0%, 1.2%, 1.4% or 1.5%, or any proportion between 0.5% and 1.5%. The proportion of the binder may be, but is not limited to, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8% or 2.0%, or any proportion between 0.5% and 2.0%.

[0056] Preferably, the negative electrode coating material comprises, by mass percentage, 20% silicon raw material, 76% carbon raw material, 1.5% conductive agent, 1.0% thickener and 1.5% binder.

[0057] Preferably, the carbon raw material comprises at least one of artificial graphite, natural graphite, soft carbon or hard carbon;

[0058] Preferably, the silicon raw material includes at least one of deposited silicon carbon and crystalline silicon.

[0059] Preferably, the conductive agent comprises one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black;

[0060] Preferably, the thickener comprises one or more of pre-lithiated sodium carboxymethyl cellulose, sodium carboxymethyl cellulose and hydroxypropyl methyl cellulose;

[0061] Preferably, the binder includes one or more of polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid and styrene-butadiene rubber.

[0062] According to one aspect of the present invention, a lithium-ion battery comprises the above-mentioned negative electrode plate.

[0063] The charging characteristics of the lithium-ion battery provided by the present invention are as follows: after the lithium-ion battery is discharged to 2.5V at 25°C and left to stand for 6 hours, it is charged to 4.2V at a constant current of 1C and 10C respectively. The corresponding constant current section charging capacities are Q1 and Q2. 10 , where the charge capacity is maintained to satisfy Q 10 / Q1≥70%.

[0064] Preferably, the charging characteristics of the lithium-ion battery are as follows: after the lithium-ion battery is discharged to 2.5V at 25°C and left to stand at -40°C for 6 hours, it is charged to 4.2V at a constant current of 1C and 5C charging rates, respectively. The corresponding constant current section charging capacities are Q1 and Q5, and the charging capacity is maintained to meet Q5 / Q1≥50%.

[0065] The lithium ion battery provided by the present invention has a capacity attenuation rate of less than 20% after being cycled 1000 times at a rate of 1C at 25°C.

[0066] After the lithium ion battery provided by the present invention is cycled 1000 times at 1C, the change rate of the ISi / IGr value is ≤5%.

[0067] According to one aspect of the present invention, an electrical device includes the above-mentioned lithium-ion battery or the above-mentioned negative electrode plate.

[0068] The above-mentioned lithium-ion battery negative electrode plate provided by the present invention can be widely used in the preparation process of lithium-ion batteries and electrical devices. Determined by the performance of the negative electrode plate of the present application, the lithium-ion batteries and electrical devices containing it have excellent rate performance, low temperature performance and cycle performance.

[0069] The technical solution of the present invention will be further described below with reference to embodiments.

[0070] Example 1

[0071] A lithium-ion battery, wherein the preparation method of the lithium-ion battery comprises the following steps:

[0072] (1) Method for making positive electrode sheet:

[0073] Take the positive electrode active material (Li1Ni 0.8 Co 0.1 Mn 0.1 O2), conductive carbon black, carbon nanotubes and polyvinylidene fluoride (PVDF) are thoroughly stirred and mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96:1:1:2 to obtain a positive electrode coating material, and then the positive electrode coating material is coated on a 12.0 μm thick aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained;

[0074] (2) Negative electrode production method:

[0075] The negative electrode sheet includes the negative electrode current collector copper foil and the negative electrode coating material coated on both sides of the copper foil. Calculated by mass percentage, the negative electrode coating material includes:

[0076] 20.0% of deposited silicon carbon (D value is 25.5nm, the grain size is calculated according to Scherrer formula), 76.0% of graphite (interlayer spacing d 002 The interlayer spacing is 0.35 nm, calculated according to the Bragg formula; the graphite is treated by low-temperature bromine intercalation method), 1.5% carbon nanotubes, 1.0% thickener sodium carboxymethyl cellulose (CMC) and 1.5% binder polyacrylic acid (PAA);

[0077] The above substances were added to deionized water and stirred to form a negative electrode coating material with a solid content of 42%. The negative electrode coating material was then coated on both sides of the negative electrode current collector (copper foil). After drying and cold pressing, a negative electrode sheet was formed with a compaction density of 1.5 g / cm 3 ;

[0078] The low-temperature bromine intercalation method operates as follows: First, graphite and excess Br are sealed in a glass tube and reacted at a constant temperature of 60°C for 2 hours (Br diffuses and inserts into the interlayer to form a CBr intercalation compound). Then, the reaction is quickly transferred to a 200°C tubular furnace, purged with nitrogen, and heat treated for 30 minutes. Br is vaporized by heat to generate pressure, and the distance between graphite layers increases.

[0079] (3) Preparation of electrolyte: lithium salt lithium hexafluorophosphate (LiPF6), organic solvent ethylene carbonate (EC), dimethyl carbonate (DMC), first type additive fluoroethylene carbonate (FEC), second additive ethylene sulfate (DTD) and third type additive vinylene carbonate (VC) are mixed in a mass percentage of 10.0:22.0:53.0:3.0:7.0:5.0 to obtain electrolyte.

[0080] (4) Diaphragm: A high-porosity diaphragm is selected. The thickness of the base film PE in the diaphragm is 9 μm, the thickness of the ceramic coating on both sides of the base film is 1.0 μm, and the thickness of the PVDF coating is 1.0 μm.

[0081] (5) Assembly of lithium-ion batteries: After the positive and negative electrode sheets are rolled and slit, they are wound together with the separator according to the set process to form a 21700 cylindrical battery core. Subsequently, the battery core is fixed to the prefabricated connecting piece by welding and loaded into the metal battery shell. After completing the key processes such as electrolyte injection, sealing and formation, the lithium-ion battery described in Example 1 is obtained. The lithium-ion battery adopts a cylindrical shell with an external dimension of 21.0 mm in diameter and 70.0 mm in length, which meets the 21700 standard specifications.

[0082] Figure 1 This is the X-ray diffraction (XRD) characteristic peak diagram provided by Example 1 of the present invention.

[0083] Example 2

[0084] The difference between this embodiment and embodiment 1 is that the ratio of the main materials of the negative electrode coating is adjusted to 7.0% of deposited silicon carbon and 89.0% of graphite, and the rest is the same as embodiment 1.

[0085] Example 3

[0086] The difference between this embodiment and embodiment 1 is that the ratio of the main materials of the negative electrode coating is adjusted to 12.0% of deposited silicon carbon and 84.0% of graphite, and the rest is the same as embodiment 1.

[0087] Example 4

[0088] The difference between this embodiment and embodiment 1 is that the ratio of the main materials of the negative electrode coating is adjusted to 17.0% of deposited silicon carbon and 79.0% of graphite, and the rest is the same as embodiment 1.

[0089] Example 5

[0090] The difference between this embodiment and embodiment 1 is that the ratio of the main materials of the negative electrode coating is adjusted to 25.0% of deposited silicon carbon and 71.0% of graphite, and the rest is the same as embodiment 1.

[0091] Example 6

[0092] The difference between this embodiment and embodiment 1 is that the ratio of the main materials of the negative electrode coating is adjusted to 32.0% of deposited silicon carbon and 64.0% of graphite, and the rest is the same as embodiment 1.

[0093] Example 7

[0094] The difference between this embodiment and embodiment 1 is that the ratio of the main materials of the negative electrode coating is adjusted to 35.0% of deposited silicon carbon and 61.0% of graphite, and the rest is the same as embodiment 1.

[0095] Example 8

[0096] The difference between this embodiment and embodiment 1 is that the ratio of the main materials of the negative electrode coating is adjusted to 42.0% of deposited silicon carbon and 35.0% of graphite, and the rest is the same as embodiment 1.

[0097] Example 9

[0098] The difference between this embodiment and embodiment 1 is that the deposited silicon carbon in embodiment 1 is replaced by deposited silicon carbon with a D value of 10.3 nm, and the rest is the same as embodiment 1.

[0099] Example 10

[0100] The difference between this embodiment and embodiment 1 is that the deposited silicon carbon in embodiment 1 is replaced by deposited silicon carbon with a D value of 50.8 nm, and the rest is the same as embodiment 1.

[0101] Example 11

[0102] The difference between this embodiment and embodiment 1 is that the deposited silicon carbon in embodiment 1 is replaced by deposited silicon carbon with a D value of 85.7 nm, and the rest is the same as embodiment 1.

[0103] Example 12

[0104] A lithium-ion battery, wherein the preparation method of the lithium-ion battery comprises the following steps:

[0105] (1) Method for manufacturing the positive electrode sheet: same as in Example 1.

[0106] (2) Negative electrode production method:

[0107] The negative electrode sheet includes the negative electrode current collector copper foil and the negative electrode coating material coated on both sides of the copper foil. Calculated by mass percentage, the negative electrode coating material includes:

[0108] 20.0% deposited silicon carbon (D value is 25.5nm, the grain size is calculated according to the Scherrer formula), 76.0% graphite (interlayer spacing d002 is 0.335nm, the interlayer spacing is calculated according to the Bragg formula), 1.5% carbon nanotubes, 1.0% thickener sodium carboxymethyl cellulose (CMC) and 1.5% binder polyacrylic acid (PAA);

[0109] The above substances were added to deionized water and stirred to form a negative electrode coating material with a solid content of 42%. The negative electrode coating material was then coated on both sides of the negative electrode current collector (copper foil). After drying and cold pressing, a negative electrode sheet was formed with a compaction density of 1.5 g / cm 3 ;

[0110] (3) Preparation of electrolyte: same as in Example 1.

[0111] (4) Diaphragm: Same as in Example 1.

[0112] (5) Assembly of lithium-ion battery: same as in Example 1.

[0113] The difference between this embodiment and embodiment 1 is that the added graphite (d002 is 0.335 nm) has not been treated by the low-temperature bromine intercalation method, and the other aspects are the same as those of embodiment 1.

[0114] Example 13

[0115] A lithium-ion battery, wherein the preparation method of the lithium-ion battery comprises the following steps:

[0116] (1) Method for manufacturing the positive electrode sheet: same as in Example 1.

[0117] (2) Negative electrode production method:

[0118] The negative electrode sheet includes the negative electrode current collector copper foil and the negative electrode coating material coated on both sides of the copper foil. Calculated by mass percentage, the negative electrode coating material includes:

[0119] 20.0% deposited silicon carbon (D value is 25.5nm, the grain size is calculated according to the Scherrer formula), 76.0% graphite (interlayer spacing d002 is 0.40nm, the interlayer spacing is calculated according to the Bragg formula; the graphite is treated by low-temperature bromine intercalation method), 1.5% carbon nanotubes, 1.0% thickener sodium carboxymethyl cellulose (CMC) and 1.5% binder polyacrylic acid (PAA);

[0120] The above substances were added to deionized water and stirred to form a negative electrode coating material with a solid content of 42%. The negative electrode coating material was then coated on both sides of the negative electrode current collector (copper foil). After drying and cold pressing, a negative electrode sheet was formed with a compaction density of 1.5 g / cm 3 ;

[0121] The low-temperature bromine intercalation method operates as follows: First, graphite and excess Br are sealed in a glass tube and reacted at a constant temperature of 60°C for 2 hours (Br diffuses and inserts into the interlayer to form a CBr intercalation compound). Then, the reaction is quickly transferred to a 200°C tubular furnace, purged with nitrogen, and heat treated for 30 minutes. Br is vaporized by heat to generate pressure, and the distance between graphite layers increases.

[0122] (3) Preparation of electrolyte: same as in Example 1.

[0123] (4) Diaphragm: Same as in Example 1.

[0124] (5) Assembly of lithium-ion battery: same as in Example 1.

[0125] The difference between this embodiment and embodiment 1 is that the treatment time of the added graphite (d002 is 0.40 nm) by the low-temperature bromine intercalation method is extended by 3 times, and the other aspects are the same as those in embodiment 1.

[0126] Example 14

[0127] The difference between this embodiment and embodiment 1 is that the compaction of the negative electrode sheet is 1.35g / cm 3 , and the rest are the same as in Example 1.

[0128] Example 15

[0129] The difference between this embodiment and embodiment 1 is that the compaction of the negative electrode sheet is 1.65g / cm 3 , and the rest are the same as in Example 1.

[0130] Comparative Example 1

[0131] The difference between this comparative example and Example 1 is that the proportion of the main material of the negative electrode coating is adjusted to 96.0% graphite, and no deposited silicon carbon is added. Other aspects are the same as Example 1.

[0132] Comparative Example 2

[0133] The difference between this comparative example and Example 1 is that the added deposited silicon carbon is deposited silicon carbon with a D value of 378 nm, and the other aspects are the same as Example 1.

[0134] Comparative Example 3

[0135] The difference between this comparative example and Example 1 is that the compaction of the negative electrode sheet is 1.75g / cm 3 , and the rest are the same as in Example 1.

[0136] Test Method

[0137] The specific method is as follows:

[0138] First, discharge the lithium-ion battery at a constant current to 2.5V to ensure it is in a safe state to reduce the risk of short circuit or thermal runaway during disassembly. In a glove box (argon or other inert atmosphere protection), carefully disassemble the battery and remove the negative electrode of the cylindrical cell. Use tweezers or suitable tools to peel off the electrode and avoid damaging the active material layer. Next, cut the removed negative electrode into appropriate sizes and soak it in an anhydrous dimethyl carbonate (DMC) solution for 30 minutes to dissolve and remove residual electrolyte and possible by-products. After removing the electrode, gently wipe the surface with a dust-free wipe, then replace it with fresh DMC solution and repeat the soak-wipe process three times to ensure that there are no residual contaminants on the surface of the electrode. Subsequently, rinse the electrode with anhydrous ethanol and wipe it again to further remove the solvent and impurities. After cleaning, place the electrode in the glove box and let it stand for 48 hours to ensure that the electrode is completely dry to prevent subsequent testing from being interfered with by solvent residues. After drying, use a plastic scraper or blade to gently scrape the negative electrode active material layer of the electrode to ensure that the collected powder is not contaminated. The scraped powder is transferred to a centrifuge tube containing anhydrous ethanol and deionized water (v / v=1:1) and ultrasonically dispersed in an ultrasonic cleaner for 30 minutes to further remove possible residual electrolyte, binder and impurities. After ultrasonic treatment, the sample is centrifuged (the speed is set at 5000rpm for 2 minutes), the supernatant is discarded, and the powder is redispersed with anhydrous ethanol and deionized water (v / v=1:1), ultrasonicated again for 10 minutes, and then centrifuged again. Repeat this process three times to ensure the purity of the powder sample. Finally, the precipitate is collected and transferred to a vacuum drying oven and dried at 80°C for 12 hours to ensure complete removal of residual solvent.

[0139] The dried powder was placed in a sealed bag or sealed sample box, immediately taken out of the glove box, and the sample was quickly tested by XRD, Raman and X-ray fluorescence spectroscopy (XRF).

[0140] 1. XRD specific measurement method: using copper target X-ray diffractometer (Cu-Kα radiation, The sample was evenly dispersed on a silicon substrate (tube voltage 40 kV, tube current 40 mA), and XRD spectra were acquired in the range of 2θ = 15° to 70° at a scanning rate of 2° / min.

[0141] I is calculated based on the intensity of the characteristic diffraction peak (25.0°~27.0°) IGr and the intensity of the characteristic diffraction peak (27.5°~28.8°) ISi in the XRD pattern. Si / I Gr value.

[0142] The D value was calculated from the half-peak width of the diffraction peak (27.5° to 28.8°) in the XRD pattern according to the Scherrer equation: K is the Scherrer constant (usually 0.89 for quasi-spherical nanoparticles), λ is the wavelength of the X-ray; B is the half-maximum width of the diffraction peak (FWHM, which needs to be converted into radians); θ is the half-maximum value of the diffraction angle.

[0143] The graphite interlayer spacing d(002) is calculated based on the diffraction peak position (25.0°~27.0°) corresponding to the (002) crystal plane in the XRD pattern according to the Bragg's equation: n is the first order of diffraction, θ is the half value of the diffraction angle, and λ is the wavelength of X-rays.

[0144] Figure 1 This is the X-ray diffraction (XRD) characteristic peak diagram provided by Example 1 of the present invention.

[0145] 2. Raman measurement method: A 532nm laser was used as the excitation light source, with a laser power of 1-5mW to avoid sample ablation. The sample was evenly dispersed on a silicon substrate. Raman spectra were collected in the range of 500-1700cm⁻¹, with a spectral resolution of 1cm⁻¹, and 3-5 cumulative scans were performed to improve the signal-to-noise ratio. The instrument utilized an automated XYZ stage for precise focusing, and silicon wafer calibration (520.7cm⁻¹) was performed before testing to ensure data accuracy.

[0146] 3. Specific method for XRF determination of the mass percentage of silicon and carbon in the negative electrode active material: First, based on the possible content range of silicon and carbon in the material to be tested, select known standard samples (such as national standard materials) to establish standard calibration curves for silicon and carbon. Subsequently, use an XRF instrument to excite the sample under optimized excitation voltage, current, and filtering conditions, and record the intensity signals of the characteristic X-rays of silicon and carbon elements (such as SiKα and CKα). The characteristic X-ray intensities of silicon and carbon in the sample are compared with the standard curve to calculate the mass percentages of the two. To improve accuracy, matrix effect correction (such as the ZAF correction method) and background subtraction should be considered.

[0147] 4. Test method for the compaction density of the negative electrode: First, cut the negative electrode sheet that has been rinsed with dimethyl carbonate and vacuum dried into 6 square samples of standard size (2.0 cm × 2.0 cm); then, wipe off the active material on the front and back of 3 of the square samples, rinse with ethanol, dry, weigh, and calculate the average mass M1. At the same time, use a screw micrometer to measure the average thickness L1 of the sample; then, weigh the mass of the other 3 square samples and calculate the average mass M2. At the same time, measure the average thickness L2 of the sample, and calculate the thickness of the electrode sheet: L2-L1, unit: cm; calculate the compaction density of the electrode sheet: Unit: g / cm 3 .

[0148] 5. Rate performance test method:

[0149] Discharge the lithium battery to 2.5V and place it in a 25℃ constant temperature box for 6 hours and test it according to the following steps:

[0150] (a) Charge to 4.2V at 1C constant current and constant voltage, with a cutoff current of 0.1C and let stand for 30 minutes. The capacity at 4.2V is Q1 (constant current stage capacity).

[0151] (b) Discharge at a constant current of 1C to a cutoff of 2.5V, with a cutoff current of 0.1C, and then let it stand for 30 minutes;

[0152] (c) Charge the battery to 4.2 V at 10 C with a constant current and constant voltage, a cutoff current of 0.1 C, and let it rest for 30 min. The capacity at which the battery is charged to 4.2 V with constant current is Q10.

[0153] (d) Discharge at a constant current of 1C to a cutoff of 2.5V, with a cutoff current of 0.1C, and then let it stand for 30 minutes;

[0154] The calculation method for the capacity retention rate of lithium batteries at 25°C is: Q1 / Q10×100.

[0155] 6. Low temperature rate performance test method: Discharge the lithium battery to 2.5V at 25℃, place it in a -40℃ constant temperature box for 6 hours and then test it according to the following steps:

[0156] (a) Charge to 4.2V at 1C constant current and constant voltage, with a cutoff current of 0.1C and let stand for 30 minutes. The capacity at 4.2V is Q1 (constant current stage capacity).

[0157] (b) Discharge at a constant current of 1C to a cutoff of 2.5V, with a cutoff current of 0.1C, and then let it stand for 30 minutes;

[0158] (c) Charge to 4.2V at 5C constant current and constant voltage, with a cut-off current of 0.1C, and let stand for 30 minutes. The capacity when charged to 4.2V at constant current is Q5.

[0159] (d) Discharge at a constant current of 1C to a cutoff of 2.5V, with a cutoff current of 0.1C, and then let it stand for 30 minutes;

[0160] The calculation method for the capacity retention rate of -40℃ lithium battery is: Q1 / Q5×100.

[0161] 7. Cycle performance test method: Place the battery in a 25°C constant temperature box for 6 hours and test it according to the following steps:

[0162] (a) First cycle constant current constant voltage charging: charging at a constant current of 0.1C to 4.2V, then switching to constant voltage charging until the current drops to 0.01C.

[0163] (b) After charging is complete, let it sit for 30 minutes.

[0164] (c) Perform constant current discharge at a rate of 0.1C to 2.5V.

[0165] (d) Cyclic charge and discharge process: Charge at a constant current rate of 1C to 4.2V. Let it rest for 30 minutes. Discharge at a constant current rate of 1C to 2.5V.

[0166] (e) Repeat the above charge and discharge process for a total of 1000 cycles.

[0167] The discharge capacity Q1 and Q1000 of the battery after 1 cycle and 1000 cycles are calculated, and the capacity attenuation rate of the battery is calculated as: (Q1-Q1000) / Q1×100.

[0168] The specific results are as follows:

[0169] 1. The experimental results of Examples 1 to 8 are shown in Table 1.

[0170] Table 1:

[0171]

[0172]

[0173] As shown in Table 1, it can be seen from the comparative examples 1 to 8 that I Si / I Gr When the value approaches 0.19, the 10C capacity retention rate (25℃) and 5C capacity retention rate (-40℃) of the lithium battery are the highest. Deviating from this value will lead to a decrease in the capacity retention rate. Si / I Gr 0.11-0.19 has the best technical effect.

[0174] In addition, when I Si / I Gr When the capacitance is >0.24, the capacity attenuation rate of the lithium battery increases significantly after 1000 cycles at 1C. This phenomenon is attributed to the coordinated effect of deposited silicon carbon and graphite forming a three-dimensional conductive network:

[0175] When I Si / I Gr When the ratio is <0.19, a high proportion of graphite and a small proportion of deposited silicon carbon play a complementary role. The high conductivity of graphite ensures the electron transmission channel, and its layered structure helps to buffer the stress generated during the charge and discharge process of the deposited silicon carbon and maintain structural stability. Nano-silicon has a short lithium ion diffusion path and excellent kinetic performance.

[0176] When I S i / I Gr When the silicon ratio is >0.19, it will significantly affect the continuity of the conductive network. Due to the low conductivity of silicon itself and the significant volume expansion effect, it is easy to cause mechanical stress accumulation and structural damage within the material, resulting in a significant increase in interfacial impedance during charge and discharge. In addition, side reactions on the silicon surface (such as the formation and rupture of the SEI film) will also exacerbate interfacial instability, further increasing internal resistance, especially at high rate and low temperature conditions.

[0177] When I Si / I Gr When the Si content is >0.24, the significant volume expansion effect and stress accumulation caused by the excessively high silicon content are further aggravated, leading to mechanical fracture and interface instability of the active material, and the cycle stability is significantly reduced.

[0178] 2. The experimental results of Examples 9 to 11 are shown in Table 2.

[0179] Table 2:

[0180]

[0181] Comparing Example 1 with Examples 9-11, it can be seen that the room-temperature rate performance and low-temperature rate performance of the lithium battery show a significant downward trend as the size of the deposited silicon carbon increases. This is attributed to the fact that the diffusion path of lithium ions within the deposited silicon carbon becomes longer, and its solid-phase diffusion internal resistance increases, thereby limiting the ability of lithium ions to quickly insert and extract. In particular, when the D value in Example 11 exceeds the range of 10.3 to 50.8, the room-temperature rate performance and low-temperature rate performance of the lithium battery are significantly reduced.

[0182] 3. The experimental results of Examples 12 to 14 are shown in Table 3.

[0183] Table 3:

[0184]

[0185]

[0186] By comparing Example 1 with Examples 12 and 13, it can be seen that the room temperature rate performance and low temperature rate performance of the lithium battery show a certain upward trend with the increase of the graphite interlayer spacing. This is attributed to the fact that the increase in the graphite interlayer spacing can effectively reduce the insertion and deintercalation energy barrier of lithium ions, thereby improving the diffusion rate and kinetic performance of lithium ions.

[0187] Comparing Example 1 with Examples 14 and 15, it can be seen that when the compaction of the negative electrode sheet is too high (1.65 g / cm 3), the room temperature and low temperature rate performance and cycle stability of lithium batteries have been greatly reduced. This is attributed to the fact that excessive compaction will significantly compress the pore structure of the electrode, reduce the permeability of the electrolyte and the number of effective ion channels, increase the pore impedance of the diffusion of lithium ions in the electrode, and seriously affect the rate performance; excessive compaction will also cause the silicon particles to break, and the solid electrolyte interface film will be significantly thickened during the cycle, thereby worsening the cycle performance.

[0188] 4. The experimental results of Comparative Examples 1 to 3 are shown in Table 4.

[0189] Table 4:

[0190]

[0191] By comparing Example 1 with Comparative Examples 1 to 3, it can be seen that when no deposited silicon carbon is added to the negative electrode active material, the size of the deposited silicon carbon is increased to 378 nm, and the compaction is as high as 1.75 g / cm3, the room temperature and low temperature rate performance of the lithium battery is greatly reduced.

[0192] These phenomena can be explained by the lack of synergistic effect of graphite and deposited silicon-carbon materials, which leads to limited specific capacity and lithium insertion kinetics; the increase in particle size prolongs the diffusion path of lithium ions inside silicon-carbon, while aggravating the conductive network breakage caused by volume expansion; the excessively high compaction density significantly increases the interfacial impedance and reduces the electrolyte permeability and structural stability.

[0193] In summary, the appropriate ratio of graphite and deposited silicon carbon, optimized deposited silicon carbon size, expanded graphite interlayer spacing and appropriate compaction are the keys to improving lithium ion rate performance and low temperature performance as well as balanced cycle performance.

[0194] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium-ion battery negative electrode plate, characterized in that: The negative electrode plate is composed of a current collector and a negative electrode coating material coated on at least one surface thereof, wherein the negative electrode coating material is a silicon-carbon composite material; The X-ray diffraction (XRD) characteristic peak intensity of the silicon-carbon composite material satisfies the following relationship: 0.05≤I Si / I Gr ≤0.6, and 10.0≤D≤70.0; Among them: I Gr The characteristic diffraction peak intensity of the carbon raw material crystal plane in the silicon-carbon composite material in the XRD spectrum is represented, and the corresponding 2θ angle range is usually 25.0° to 27.0°; I Si Represents the characteristic diffraction peak intensity of the silicon raw material in the silicon-carbon composite material in the XRD spectrum, and the corresponding 2θ angle range is usually 27.5° to 28.8°; D is the grain size of the silicon raw material in the silicon-carbon composite material, in nm.

2. The negative electrode plate of a lithium-ion battery according to claim 1, characterized in that: The X-ray diffraction (XRD) characteristic peak intensity of the negative electrode coating material satisfies the following relationship: 0.06 ≤ I Si / I Gr ≤0.19, and 10.3≤D≤50.

8.

3. The negative electrode plate of a lithium-ion battery according to claim 1, characterized in that: The interlayer spacing d of the carbon raw material in the silicon-carbon composite material 002 =0.335~0.35nm.

4. The negative electrode plate of a lithium-ion battery according to claim 1, characterized in that: The compaction density of the negative electrode plate is 1.2 to 1.6 g / cm 3 .

5. The negative electrode sheet for a lithium-ion battery according to any one of claims 1 to 3, characterized in that: The raw materials for preparing the negative electrode coating material include: silicon raw material, carbon raw material, conductive agent, thickener and binder.

6. The negative electrode plate of a lithium-ion battery according to claim 5, characterized in that: Measured by mass percentage, the negative electrode coating material includes: 5-48% silicon raw material, 44-86% carbon raw material, 0.5-2.0% conductive agent, 0.5-1.5% thickener and 0.5-2.0% binder; Preferably, the negative electrode coating material comprises, by mass percentage, 20% silicon raw material, 76% carbon raw material, 1.5% conductive agent, 1.0% thickener and 1.5% binder.

7. The negative electrode plate of a lithium-ion battery according to claim 6, characterized in that: The carbon raw material includes at least one of artificial graphite, natural graphite, soft carbon or hard carbon; The silicon raw material includes at least one of deposited silicon carbon and crystalline silicon.

8. The negative electrode plate of a lithium-ion battery according to claim 6, characterized in that: The conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black; The thickener includes one or more of pre-lithiated sodium carboxymethyl cellulose, sodium carboxymethyl cellulose and hydroxypropyl methyl cellulose; The binder includes one or more of polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid and styrene-butadiene rubber.

9. A lithium-ion battery, characterized in that: The lithium-ion battery comprises the negative electrode sheet according to any one of claims 1 to 8.

10. An electrical device, characterized in that: The electrical device comprises the lithium-ion battery according to claim 9 or the negative electrode sheet according to any one of claims 1 to 8.

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