Negative electrode slurry and preparation method and application thereof
By designing a layered structure consisting of a core coating layer, an intermediate buffer layer, and an outer skeleton reinforcement layer on the lithium-ion battery anode material, the problems of lithium plating, volume expansion, and SEI film rupture during fast charging were solved, resulting in a significant improvement in battery life.
Patent Information
- Application Number
- CN202511390358.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-25
- Publication Date
- 2025-12-23
AI Technical Summary
Lithium-ion battery anodes face problems such as lithium plating, volume expansion, and SEI film rupture during fast charging, leading to shortened battery life. Existing technologies, such as increasing conductivity or using composite carbon nanotubes, have failed to effectively solve these problems.
The system employs a layered structure consisting of a core coating layer, an intermediate buffer layer, and an exoskeleton reinforcement layer. The content of the conductive agent gradually decreases, forming a stable three-layer gradient conductive network that buffers volume expansion and optimizes ion transport and interface stability.
It significantly improves the fast-charging lifespan of lithium-ion batteries by stabilizing the conductive network, graded buffering of volume expansion, and optimizing the SEI film, thereby enhancing the structural integrity and interface stability of the battery.
Smart Images
Figure CN121192146A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of battery negative electrode slurry, and in particular to a negative electrode slurry, a preparation method and application thereof. BACKGROUND
[0002] With the increasing demand for fast charging of electric vehicles (≥3C), lithium ion batteries, especially the negative electrode that undertakes the task of fast charging, faces three failure challenges: 1. Critical point migration of lithium precipitation: the accumulation rate of lithium ions on the surface of the negative electrode is higher than the embedding rate under a large current, the electronic transmission of the traditional homogeneous conductive network lags behind, leading to the intensification of local polarization (experiments show that the negative electrode polarization voltage can reach 120 mV at 5C rate), and the risk of lithium dendrite growth is triggered; 2. Volume expansion chain reaction: anisotropic expansion (>13%) of graphite particles occurs during fast charging, the homogeneous conductive network is broken due to the lack of a buffer layer, and the interruption of the electronic path triggers the failure of the active material; 3. Continuous rupture of the interface SEI film: repeated volume changes consume a large amount of lithium source for SEI film repair, and the uneven distribution of CMC in the traditional slurry leads to a decrease in adhesion, accelerating the peeling of the active material (the negative electrode thickness expansion rate is >35% after 500 cycles).
[0003] In the prior art, the conductivity is improved mainly by increasing the total amount of conductive agent (such as >3wt%) or compounding carbon nanotubes (CNT), but there are obvious defects: the one-time addition of the conductive agent leads to insufficient coverage of the negative electrode material surface, and the bottleneck of electronic transmission in the edge area is prominent under high rate; carbon nanotubes cannot effectively isolate the active material due to the shielding effect of graphite particles when mixed directly; and the failure of the negative electrode becomes the primary factor restricting the fast charging life of the battery (industry shows that >70% of capacity decay is due to the collapse of the negative electrode structure). SUMMARY
[0004] Therefore, the present application aims to provide a negative electrode slurry, a preparation method and application thereof, which can effectively improve the fast charging life of lithium ion batteries.
[0005] In order to achieve the above-mentioned application purpose, the present application provides the following technical scheme: The present application provides a negative electrode slurry, comprising a dispersant and a dispersion medium, wherein the dispersant comprises a negative electrode active material, and an inner core coating layer, an intermediate buffer layer and an outer skeleton strengthening layer successively coated on the surface of the negative electrode active material. The inner core coating layer, the intermediate buffer layer and the outer skeleton strengthening layer independently comprise a conductive agent and a high molecular thickening agent. The content of the conductive agent in the inner core coating layer, the intermediate buffer layer and the outer skeleton strengthening layer decreases successively.
[0006] Preferably, the negative electrode active material comprises one or more of graphite, hard carbon, silicon-carbon composite material and silicon-oxygen composite material.
[0007] Preferably, the conductive agent includes one or more of acetylene black, conductive carbon black, carbon nanotubes, carbon nanofibers, and graphene.
[0008] Preferably, the conductive carbon black has a DBP value of 50~800 mL / 100 g and a specific surface area of 10~2000 m². 2 / g; The carbon nanotubes have a diameter of 1-20 nm, a length of 0.5-50 μm, an aspect ratio ≥100, and a specific surface area of 100-300 m². 2 / g; The carbon nanofibers have a diameter of 100~500nm, a length of 5~100μm, and an aspect ratio of >50; The graphene has 1 to 10 layers, a sheet diameter of 5 to 100 μm, and a carbon-to-oxygen ratio of 30 to 70.
[0009] Preferably, the polymeric thickener includes carboxymethyl cellulose thickeners and / or polyacrylic acid thickeners.
[0010] Preferably, the carboxymethyl cellulose thickener has a degree of substitution of 0.8 to 1.5, a molecular weight of 50,000 to 300,000, and heavy metal residue of <50 ppm; The polyacrylic thickener includes one or more of polyacrylic acid, polyacrylate, polyacrylate and acrylic copolymers.
[0011] Preferably, the mass ratios of the conductive agent and the polymeric thickener in the core coating layer, the intermediate buffer layer, and the outer skeleton reinforcement layer are denoted as X, Y, and Z, respectively. The ratio of X to Y is (1~6):1; The ratio of Y to Z is (1~6):1.
[0012] Preferably, when the conductive agent in the exoskeleton reinforcing layer includes carbon nanotubes and / or carbon nanofibers, the carbon nanotubes and / or carbon nanofibers are distributed in the exoskeleton reinforcing layer, and are also distributed in the negative electrode slurry and connected to the dispersion in the negative electrode slurry.
[0013] The present invention also provides a method for preparing the negative electrode slurry described in the above technical solution, comprising the following steps: After mixing the negative electrode active material and the first conductive agent, it is mixed with the first thickener adhesive to obtain the first slurry; the dispersed phase in the first slurry is the negative electrode active material coated with a core coating layer; The first slurry, the second conductive agent, and the second thickener are mixed to obtain a second slurry; the dispersed component in the second slurry is a negative electrode active material and a core coating layer and an intermediate buffer layer sequentially coated on the surface of the negative electrode active material. The second slurry, the third conductive agent, and the third thickener are mixed together to obtain the negative electrode slurry.
[0014] The present invention also provides the application of the negative electrode slurry described in the above technical solution or the negative electrode slurry prepared by the preparation method described in the above technical solution in lithium-ion batteries.
[0015] This invention provides a negative electrode slurry, comprising a dispersion phase and a dispersion medium. The dispersion phase includes a negative electrode active material, and a core coating layer, an intermediate buffer layer, and an exoskeleton reinforcement layer sequentially coated on the surface of the negative electrode active material. Each of the core coating layer, intermediate buffer layer, and exoskeleton reinforcement layer independently includes a conductive agent and a polymeric thickener. The content of the conductive agent in the core coating layer, intermediate buffer layer, and exoskeleton reinforcement layer decreases sequentially. This three-layer gradient coating structure of "core-buffer-exoskeleton" is designed to precisely and layer-by-layer address several fundamental challenges faced by lithium-ion battery negative electrode materials during charge and discharge processes, thereby achieving a leap in overall performance.
[0016] Its advantages are mainly reflected in the following aspects: 1. Constructing a stable and efficient "three-in-one" conductive network. This gradient conductive design, from the inside out (core dedicated channel → outer skeleton highway) and from point to surface (single particle → overall electrode), is more uniform, stable, and efficient than physically mixed conductive networks, and can significantly reduce electrode impedance; 2. Graded buffering of volume expansion to maintain structural integrity. When the active material expands due to lithiation, it will first be squeezed outward. The rigid outer skeleton reinforcement layer provides strong constraint, inhibiting the unlimited expansion of the particles. At this time, the buffer layer in the middle deforms like a "spring" or "air cushion," absorbing and dissipating most of the mechanical stress. This process avoids stress concentration that could cause the particles to break directly, and also protects the outer skeleton layer from being torn apart. During delithiation shrinkage, the elasticity of the buffer layer can help the particles recover their shape, preventing the active material from detaching from the coating layer. This "rigid-flexible" layered structure (core conductivity + exoskeleton constraint + intermediate buffer) greatly improves the anode material's tolerance to volume expansion, thereby significantly enhancing the battery's cycle life. 3. Optimized ion transport and stable solid-liquid interface (SEI film): The robust exoskeleton reinforcement layer provides a stable "outer surface" for the electrode material. This outer structure is relatively stable and does not change drastically with the expansion and contraction of the core, thus allowing the formation of a thinner, more stable, and denser SEI film on its surface. This SEI film is less prone to breakage, reducing repeated regeneration during cycling, lowering electrolyte consumption, and ensuring long-term interface stability. In summary, this invention achieves precise functional allocation and synergistic effects through a "core-shell" layered design. Attached Figure Description
[0017] Figure 1 This is a schematic diagram of the structure of the dispersed phase in the negative electrode slurry of the present invention, wherein 101 is the outer skeleton reinforcement layer, 102 is the intermediate buffer layer, 103 is the core coating layer, 104 is the negative electrode active material, and 105 is carbon nanotubes and / or carbon nanofibers. Figure 2 This is an enlarged structural diagram of the dispersed phase in the negative electrode slurry of the present invention, wherein 104 is the negative electrode active material and 107 is the conductive agent. Detailed Implementation
[0018] like Figure 1 As shown, the present invention provides a negative electrode slurry, comprising a dispersion and a dispersion medium, wherein the dispersion comprises a negative electrode active material (104), and a core coating layer (103), an intermediate buffer layer (102) and an exoskeleton reinforcement layer (101) sequentially coating the surface of the negative electrode active material. The core coating layer, intermediate buffer layer, and exoskeleton reinforcement layer each independently include a conductive agent (such as...). Figure 2 (as shown) and polymeric thickener; The content of conductive agent in the core coating layer, intermediate buffer layer and exoskeleton reinforcement layer decreases sequentially.
[0019] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.
[0020] In this invention, the negative electrode active material preferably includes one or more of graphite, hard carbon, silicon-carbon composite material, and silicon-oxygen composite material; the graphite is preferably artificial graphite and / or natural graphite; the mass ratio of silicon to carbon in the silicon-carbon composite material is preferably (50~55):(50~45), more preferably 50:50; the chemical composition of the silicon-oxygen composite material is preferably SiO2. x / C, wherein the value range of x is preferably 0 < x < 2.05, more preferably 1.95~2.05, and most preferably 1.98~2.02; the SiO x The mass ratio of C to the anode material is preferably less than 1. When the anode material is two or more of the specific choices mentioned above, the present invention does not impose any special limitation on the ratio of the specific substances, and they can be mixed in any ratio. In the embodiments of the present invention, the anode active material can be artificial graphite, natural graphite, or a composite material of natural graphite and silicon-carbon (the mass ratio of silicon-carbon is 50:50).
[0021] In this invention, the particle size of the negative electrode active material is preferably 5-25 micrometers, more preferably 8-20 micrometers. In embodiments of this invention, the particle size of the negative electrode active material can be 10 micrometers, 15 micrometers, or 20 micrometers.
[0022] In this invention, the core coating layer, the intermediate buffer layer, and the exoskeleton reinforcement layer each independently include a conductive agent and a polymer thickener.
[0023] In this invention, the conductive agent preferably includes one or more of acetylene black, conductive carbon black, carbon nanotubes, carbon nanofibers, and graphene; the DBP value of the conductive carbon black is preferably 50~800mL / 100g, and the specific surface area of the conductive carbon black is preferably 10~2000m². 2 / g; the conductive carbon black is preferably one or more of Super P, Litx series, and Ketjen Black ECP; the Litx series is preferably one or more of Litx-50, Litx-100, and Litx300, and the Ketjen Black ECP is preferably one or more of ECP300J, ECP900JD, and ECP600JD; the carbon nanotubes preferably have a diameter of 1~20nm, a length of 0.5~50μm, an aspect ratio of ≥100, and a specific surface area of 100~300m². 2 / g; the carbon nanotubes are preferably one or more of SWCNTs, MWCNTs and FWCNTs; the diameter of the carbon nanofibers is preferably 100~500nm, the length is preferably 5~100μm, and the aspect ratio is preferably >50; the carbon nanofibers are preferably VGCF and / or VGNF; the number of graphene layers is preferably 1~10 layers, the sheet diameter is preferably 5~100μm, and the carbon-oxygen ratio is preferably 30~70, more preferably 40~60; when the conductive agent is two or more of the above-mentioned specific selections, the present invention does not have any special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio.
[0024] In this invention, the polymeric thickener preferably includes carboxymethyl cellulose thickeners and / or polyacrylic acid thickeners; the degree of substitution of the carboxymethyl cellulose thickener is preferably 0.8-1.5, the molecular weight is preferably 50,000-300,000, and the heavy metal residue is preferably <50 ppm; the polyacrylic acid thickener preferably includes one or more of polyacrylic acid, polyacrylate, polyacrylate ester, and acrylic copolymers; the polyacrylate preferably includes sodium polyacrylate and / or lithium polyacrylate; the polyacrylate preferably includes polymethyl acrylate and / or polyethyl acrylate; the acrylic copolymer preferably includes acrylic acid-acrylamide copolymer; when the polymeric thickener is two or more of the above-mentioned specific selections, this invention does not have any special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. In this invention, the degree of substitution can be understood as the numerical value of hydroxyl groups being replaced by carboxymethyl groups.
[0025] In this invention, the polymer thickener not only thickens the slurry and provides cohesive force to the particles in the core-shell structure, but more importantly, it carries different gradients of electrical conductivity in different shell layers.
[0026] In this invention, the thickness of the core coating layer is preferably 10-70 nm, more preferably 30-50 nm. In embodiments of this invention, the thickness of the core coating layer can be 30 nm, 40 nm, or 50 nm.
[0027] In this invention, the mass ratio of the conductive agent to the polymeric thickener in the core coating layer is denoted as X, and the value of X preferably ranges from 0.1 to 10, more preferably from 0.3 to 5. In embodiments of this invention, the mass ratio of the conductive agent to the polymeric thickener in the core coating layer can be 3, 4, or 0.4. In embodiments of this invention, the conductive agent in the core coating layer can be acetylene black or Super P; the polymeric thickener in the core coating layer can be carboxymethyl cellulose (CMC).
[0028] In this invention, the core coating layer provides the initial conductive network basis and effective coating of the negative electrode active material.
[0029] In this invention, the thickness of the intermediate buffer layer is preferably 30-90 nm, more preferably 50-70 nm. In embodiments of this invention, the thickness of the intermediate buffer layer can be 50 nm, 60 nm, or 70 nm.
[0030] In this invention, the mass ratio of the conductive agent to the polymeric thickener in the intermediate buffer layer is denoted as Y, and the value of Y is preferably 0.1~10, more preferably 0.3~5. In this invention, the ratio of X to Y is preferably (1~6):1, more preferably 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, or 6:1. In embodiments of this invention, the mass ratio of the conductive agent to the polymeric thickener in the core coating layer can be 1.4, 1.75, or 0.5:1.3; the ratio of X to Y can be 2.14:1, 2.29:1, or 1.04:1; the conductive agent in the core coating layer can be acetylene black or SuperP; the polymeric thickener in the core coating layer can be carboxymethyl cellulose (CMC) or a mass ratio of carboxymethyl cellulose and polyacrylic acid of 0.3:8.3.
[0031] In this invention, the intermediate buffer layer serves to connect the inner and outer layers and to provide stress buffering and transition.
[0032] In this invention, the thickness of the exoskeleton reinforcement layer is preferably 40-120 nm, more preferably 60-100 nm. In embodiments of this invention, the thickness of the exoskeleton reinforcement layer can be 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm.
[0033] In this invention, the mass ratio of the conductive agent to the polymeric thickener in the exoskeleton reinforcing layer is denoted as Z, and the value of Z preferably ranges from 0.1 to 10, more preferably from 0.3 to 5. In this invention, the ratio of Y to Z is preferably (1-6):1, more preferably 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, or 6:1. In embodiments of this invention, the mass ratio of the conductive agent to the polymeric thickener in the exoskeleton reinforcing layer can be 0.8, 1.67, or 0.2; the ratio of Y to Z can be 1.05, 1.75, or 1.92; the conductive agent in the exoskeleton reinforcing layer can be Super P; and the polymeric thickener in the exoskeleton reinforcing layer can be carboxymethyl cellulose (CMC).
[0034] In this invention, when the conductive agent in the exoskeleton reinforcing layer includes carbon nanotubes and / or carbon nanofibers, the carbon nanotubes and / or carbon nanofibers are distributed in the exoskeleton reinforcing layer, and preferably also distributed in the negative electrode slurry and connected to the dispersed phase (structure as shown in the diagram) in the negative electrode slurry. Figure 1 (The positional relationship is shown in 105). The carbon nanotubes and / or carbon nanofibers can be interconnected and penetrate the layer. This interconnected carbon nanotube network structure can significantly enhance the electronic conductivity within the core-shell composite particles and between different core-shell composite particles. On the other hand, by tightly bonding with the outer matrix rich in polymer thickener, it greatly enhances the structural cohesion of the core-shell composite particles themselves and the bonding strength between the particles and other components in the slurry (such as the binder network).
[0035] In this invention, the exoskeleton reinforcing layer has a relatively high content of polymer thickener, providing structural strength and adhesion.
[0036] In this invention, the dispersion medium is preferably water.
[0037] In this invention, the negative electrode slurry preferably further includes N-methylpyrrolidone and SBR. In this invention, the preferred mass ratio of the negative electrode active material, N-methylpyrrolidone, and SBR is (93~95):3:(0.5~1.5). In embodiments of this invention, the mass ratio of the negative electrode active material, N-methylpyrrolidone, and SBR can be 94.8:3:1.50, 94.1:3:1.50, or 93.5:3:0.50.
[0038] In this invention, the solid content of the negative electrode slurry is preferably 1-10%, more preferably 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%. In an embodiment of this invention, the solid content of the negative electrode slurry can be 3.5%.
[0039] The present invention also provides a method for preparing the negative electrode slurry described in the above technical solution, comprising the following steps: After mixing the negative electrode active material and the first conductive agent, it is mixed with the first thickener adhesive to obtain the first slurry; the dispersed phase in the first slurry is the negative electrode active material coated with a core coating layer; The first slurry, the second conductive agent, and the second thickener are mixed to obtain a second slurry; the dispersed component in the second slurry is a negative electrode active material and a core coating layer and an intermediate buffer layer sequentially coated on the surface of the negative electrode active material. The second slurry, the third conductive agent, and the third thickener are mixed together to obtain the negative electrode slurry.
[0040] In this invention, the negative electrode active material and the first conductive agent are first mixed, and then the mixture is secondly mixed with the first thickener adhesive to obtain a first slurry; the dispersed phase in the first slurry is the negative electrode active material coated with a core coating layer.
[0041] In this invention, the solvent of the first thickener solution is preferably water, more preferably deionized water, and the type of thickener in the first thickener solution is preferably the type of thickener described in the above technical solution, which will not be repeated here.
[0042] In this invention, the first thickener solution is preferably prepared in advance or preferably formed during the second mixing process.
[0043] In this invention, when the first thickener solution is preferably prepared in advance, the preferred method of preparation is to mix the thickener with water. This mixing is preferably carried out under mechanical stirring conditions. The revolution speed of the mechanical stirring is preferably 15-40 rpm, more preferably 15 rpm, 20 rpm, 25 rpm, 30 rpm, 35 rpm, or 40 rpm; the rotation speed is preferably 500-3000 rpm, more preferably 500 rpm, 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, or 3000 rpm; and the time is preferably 30-400 min, more preferably 30 min, 60 min, 100 min, 140 min, 180 min, 240 min, 300 min, 350 min, or 400 min. In embodiments of this invention, the revolution speed of the mechanical stirring can be 35 rpm or 20 rpm, the rotation speed can be 1500 rpm or 1000 rpm, and the time can be 240 min or 180 min.
[0044] In this invention, the mass ratio of thickener to water in the first thickener solution is preferably 0.001~0.05:1, more preferably 0.01~0.02:1. In an embodiment of this invention, the mass ratio of thickener to water in the first thickener solution can be 1.2:65.5.
[0045] In this invention, the types of the negative electrode active material and the first conductive agent are preferably the same as those described in the above technical solution, and will not be repeated here.
[0046] In this invention, the mass ratio of the negative electrode active material to the first conductive agent is preferably 30-150:1, more preferably 40-120:1. In embodiments of this invention, the mass ratio of the negative electrode active material to the first conductive agent can be 94.8:1.8, 94.1:2, or 93.5:1.
[0047] In this invention, the first mixing method is preferably mechanical stirring. The revolution speed of the mechanical stirring is preferably 10-50 rpm, more preferably 10 rpm, 20 rpm, 30 rpm, 40 rpm, or 50 rpm; the rotation speed is preferably 500-2000 rpm, more preferably 500 rpm, 800 rpm, 1000 rpm, 1300 rpm, 1600 rpm, or 2000 rpm; and the time is preferably 20-80 min, more preferably 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, or 80 min. In an embodiment of this invention, the revolution speed of the mechanical stirring can be 40 rpm or 30 rpm, the rotation speed can be 1000 rpm or 800 rpm, and the time can be 30 min or 60 min.
[0048] In this invention, the second mixing method is preferably mechanical stirring, wherein the revolution speed of the mechanical stirring is preferably 5-20 rpm, more preferably 5 rpm, 10 rpm, 15 rpm or 20 rpm; and the time is preferably 60-240 min, more preferably 60 min, 90 min, 120 min, 150 min, 180 min, 210 min or 240 min. In an embodiment of this invention, the revolution speed of the mechanical stirring can be 15 rpm or 10 rpm, and the time can be 90 min, 120 min or 150 min.
[0049] In this invention, the solid content of the first slurry is preferably 60-80%, more preferably 60%, 63%, 65%, 68%, 70%, 73%, 75%, 78%, or 80%. In embodiments of this invention, the solid content of the first slurry can be 65±1%, 75.5±1%, or 75±1%.
[0050] In this invention, when the slurry obtained by the second mixing does not meet the above-mentioned solid content range, it is preferable to add deionized water during the second mixing process to adjust it to meet the above-mentioned solid content range.
[0051] After obtaining the first slurry, the present invention mixes the first slurry, the second conductive agent, and the second thickener adhesive to obtain the second slurry.
[0052] In this invention, the type of the second conductive agent is preferably the same as that described in the above technical solution, and will not be repeated here.
[0053] In this invention, the second thickener solution is preferably prepared in advance or preferably formed during the third mixing process.
[0054] In this invention, when the second thickener solution is preferably prepared in advance, the preparation process of the first thickener solution described above is preferred and will not be repeated here.
[0055] In this invention, the type of thickener in the second thickener solution preferably refers to the type of thickener described in the above-described technical solution, and will not be repeated here. In this invention, the solvent in the second thickener solution is preferably water, more preferably deionized water. In the embodiments of this invention, the thickener in the second thickener solution can be CMC or a mixture of CM and polyacrylic acid (PAA) in a mass ratio of 0.3:8.3.
[0056] In this invention, the mass ratio of thickener to water in the second thickener solution is preferably 0.001~0.5:1, more preferably 0.01~0.4:1. In embodiments of this invention, the mass ratio of thickener to water in the second thickener solution can be 1.2:65.5, 0.3:16.4, or 8.6:24.9.
[0057] In this invention, the mass ratio of the negative electrode active material and the second conductive agent in the first slurry is preferably 50~300:1, more preferably 100~200:1. In embodiments of this invention, the mass ratio of the negative electrode active material and the second conductive agent in the first slurry can be 94.8:0.5, 94.1:0.7, or 93.5:0.5.
[0058] In this invention, the mass ratio of the thickener in the second conductive agent and the second thickener adhesive is preferably 0.01~5:1, more preferably 0.05~3:1. In embodiments of this invention, the mass ratio of the thickener in the second conductive agent and the second thickener adhesive can be 0.5:8.6, 0.7:0.39, or 0.5:0.35.
[0059] In this invention, the third mixing method is preferably mechanical stirring. The revolution speed of the mechanical stirring is preferably 10-70 rpm, more preferably 10 rpm, 20 rpm, 30 rpm, 40 rpm, 50 rpm, 60 rpm, or 70 rpm; the rotation speed is preferably 200-1500 rpm, more preferably 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, or 1500 rpm; the time is preferably 30-240 min, more preferably 30 min, 60 min, 90 min, 120 min, 150 min, 180 min, 210 min, or 240 min. In an embodiment of this invention, the revolution speed of the mechanical stirring can be 50 rpm or 40 rpm, the rotation speed can be 500 rpm or 800 rpm, and the time can be 90 min or 120 min.
[0060] In this invention, the solid content of the second slurry is preferably 50-70%, more preferably 50%, 55%, 60%, 65% or 70%. In embodiments of this invention, the solid content of the second slurry can be 65±1%, 64.8±1% or 55±1%.
[0061] In this invention, when the solid content of the second slurry does not meet the above requirements, it is preferable to adjust it by adding deionized water to ensure that the solid content of the obtained second slurry is within the above range.
[0062] After obtaining the second slurry, the present invention mixes the second slurry, the third conductive agent and the third thickener adhesive to obtain the negative electrode slurry.
[0063] In this invention, the type of the third conductive agent is preferably the same as that described in the above technical solution, and will not be repeated here.
[0064] In this invention, the third thickener solution is preferably prepared in advance or preferably formed during the fourth mixing process.
[0065] In this invention, when the third thickener solution is preferably prepared in advance, the preparation process of the first thickener solution described above is preferred and will not be repeated here.
[0066] In this invention, the type of thickener in the third thickener solution is preferably the type of thickener described in the above-described technical solution, and will not be repeated here. In this invention, the solvent in the third thickener solution is preferably water, more preferably deionized water. In embodiments of this invention, the thickener in the third thickener solution can be CMC.
[0067] In this invention, the mass ratio of thickener to water in the third thickener solution is preferably 0.01~0.5:1, more preferably 0.015~0.3:1. In an embodiment of this invention, the mass ratio of thickener to water in the third thickener solution can be 1.2:65.5.
[0068] In this invention, the mass ratio of the negative electrode active material to the third conductive agent in the second slurry is preferably 50-1000:1, more preferably 100-600:1. In embodiments of this invention, the mass ratio of the negative electrode active material to the third conductive agent in the second slurry can be 94.8:0.2, 94.1:0.3, or 93.5:0.5.
[0069] In this invention, the mass ratio of the third conductive agent to the thickener in the third thickener adhesive is preferably 0.1 to 10:1, more preferably 0.5 to 8:1. In embodiments of this invention, the mass ratio of the third conductive agent to the thickener in the third thickener adhesive can be 0.2:0.25, 0.3:0.30, or 0.5:0.075.
[0070] In this invention, the fourth mixing method is preferably mechanical stirring. The revolution speed of the mechanical stirring is preferably 10-60 rpm, more preferably 10 rpm, 20 rpm, 30 rpm, 40 rpm, 50 rpm, or 60 rpm; the rotation speed is preferably 1000-3500 rpm, more preferably 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, or 3500 rpm; and the time is preferably 1-3 hours, more preferably 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours. In an embodiment of this invention, the revolution speed of the mechanical stirring can be 40 rpm or 50 rpm, the rotation speed can be 2500 rpm or 3000 rpm, and the time can be 2 hours.
[0071] In this invention, the solid content of the slurry obtained by the fourth mixing is preferably 45-65%, more preferably 45%, 50%, 55%, 60% or 65%. In embodiments of this invention, the solid content of the slurry obtained by the fourth mixing can be 50±1%, 58.6±1% or 60±1%.
[0072] In this invention, when the solid content of the slurry obtained by the fourth mixing does not meet the above requirements, this invention preferably adjusts the solid content of the obtained slurry by adding deionized water to ensure that the solid content is within the above range.
[0073] After the fourth mixing is completed, the present invention preferably includes a slurry forming and viscosity adjustment process; the slurry forming and viscosity adjustment process preferably includes: mixing the slurry obtained from the fourth mixing, N-methylpyrrolidone, SBR dispersion and water to obtain the negative electrode slurry.
[0074] In this invention, the solid content of the SBR dispersion is preferably 35-50%, more preferably 35%, 40%, 45% or 50%. In an embodiment of this invention, the solid content of the SBR dispersion can be 45%.
[0075] In this invention, the water is preferably deionized water.
[0076] In this invention, the preferred mass ratio of the negative electrode active material, N-methylpyrrolidone, and SBR in the SBR dispersion in the slurry obtained by the fourth mixing is (93~95):3:(0.5~1.5). In embodiments of this invention, the mass ratio of the negative electrode active material, N-methylpyrrolidone, and SBR in the SBR dispersion in the slurry obtained by the fourth mixing can be 94.8:3:1.50, 94.1:3:1.50, or 93.5:3:0.50.
[0077] In this invention, the mass ratio of negative electrode active material to water in the slurry obtained by the fourth mixing is preferably 1~10:1, more preferably 2~8:1; in the embodiments of this invention, the mass ratio of negative electrode active material to water in the slurry obtained by the fourth mixing can be 94.8:25.8, 94.1:16.3 or 93.5:41.7.
[0078] In this invention, the slurry preparation and viscosity adjustment process preferably includes the addition of a conductive slurry. The solid content of the conductive slurry is preferably 1% to 5%, more preferably 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. In an embodiment of this invention, the solid content of the conductive slurry can be 3.5%. In this invention, the conductive agent in the conductive slurry is preferably carbon nanotubes, more preferably multi-walled carbon nanotubes. In this invention, the mass ratio of N-methylpyrrolidone to the conductive slurry is preferably 0.1 to 5:1, more preferably 0.3 to 3:1. In an embodiment of this invention, the mass ratio of N-methylpyrrolidone to the conductive slurry can be 3:5.71 or 3:2.86.
[0079] In this invention, the slurry preparation and viscosity adjustment process is preferably carried out under vacuum and mechanical stirring conditions, wherein the vacuum degree is preferably ≤95%. In this invention, the revolution speed of the mechanical stirring is preferably 10~50 rpm, more preferably 10 rpm, 20 rpm, 30 rpm, 40 rpm, or 50 rpm; the rotation speed is preferably 100~1000 rpm, more preferably 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, or 1000 rpm; the time is preferably 10~200 min, more preferably 10 min, 30 min, 50 min, 70 min, 90 min, 110 min, 130 min, 150 min, 170 min, or 200 min. In an embodiment of this invention, the revolution speed of the mechanical stirring can be 30 rpm, the rotation speed can be 500 rpm, and the time can be 30 min.
[0080] This invention also provides the application of the negative electrode slurry described in the above-described technical solutions or the negative electrode slurry prepared by the preparation method described in the above-described technical solutions in lithium-ion batteries. This invention does not impose any special limitations on the method of application; any method well-known to those skilled in the art can be used.
[0081] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0082] Example 1 1.2 kg of CMC and 65.5 kg of deionized water were mechanically mixed (revolution speed of 35 rpm, rotation speed of 1500 rpm, time of 240 min) to obtain CMC adhesive solution; 94.8 kg of artificial graphite (D 50 =11μm) and 1.8kg of Super P were mechanically mixed (revolution speed 40rpm, rotation speed 1000rpm, time 30min), and then 33.3kg of the CMC adhesive was added and mechanically mixed (revolution speed 15rpm, rotation speed 3000rpm, time 90min) to obtain the first slurry (solid content 75±1%, core coating thickness 40nm, X value in core coating 3:1); The first slurry, 0.5 kg of Super P and 19.44 kg of the CMC adhesive were mechanically stirred and mixed (revolution speed of 50 rpm, rotation speed of 500 rpm, time of 90 min) to obtain the second slurry (solid content of 65±1%, thickness of intermediate buffer layer of 25 nm, Y value of 1.4:1 and X:Y=2.14 in intermediate buffer layer). The second slurry, 0.2 kg of Super P and 13.9 g of the CMC adhesive were mechanically mixed (revolution speed of 40 rpm, rotation speed of 2500 rpm, time of 2 h, vacuum degree ≤95%) to obtain the third slurry (solid content of 60±1%, thickness of the outer skeleton reinforcement layer of 60 nm, Z value of 0.8:1, Y:Z=1.75 in the outer skeleton reinforcement layer). The third slurry, 3 kg of N-methylpyrrolidone, 3.33 kg of SBR dispersion (solid content 45%) and 25.8 kg of deionized water were mechanically mixed (revolution speed 30 rpm, rotation speed 500 rpm, time 30 min, vacuum degree ≤95%) to obtain the negative electrode slurry.
[0083] Example 2 1.2 kg of CMC and 65.5 kg of deionized water were mechanically mixed (revolution speed of 35 rpm, rotation speed of 1500 rpm, time of 240 min) to obtain CMC adhesive solution; 94.1 kg of natural graphite (D 50 =8~20μm) and 2kg of Super P were mechanically mixed (revolution speed 30rpm, rotation speed 800rpm, time 30min), and then 27.3kg of the CMC adhesive was added and mechanically mixed (revolution speed 10rpm, rotation speed 2500rpm, time 120min) to obtain the first slurry (solid content 75.5±1%, core coating thickness 30nm, X value in core coating 4:1); The first slurry, 0.7 kg of Super P and 21.88 kg of the CMC adhesive were mechanically stirred and mixed (revolution speed of 50 rpm, rotation speed of 500 rpm, time of 90 min) to obtain the second slurry (solid content of 64.8±1%, thickness of intermediate buffer layer of 50 nm, Y value of 1.75:1, X:Y=2.29 in intermediate buffer layer). The second slurry, 0.3 kg of Super P, and 16.4 kg of the CMC adhesive were mechanically mixed (revolution speed of 40 rpm, rotation speed of 2500 rpm, time of 2 h, vacuum degree ≤95%) to obtain the third slurry (solid content of 58.6±1%, thickness of the outer skeleton reinforcement layer of 60 nm, Z value of 1.67:1, Y:Z=1.05 in the outer skeleton reinforcement layer). The third slurry, 3 kg of N-methylpyrrolidone, 3.33 kg of SBR dispersion (solid content 45%), 16.3 kg of deionized water, and 5.71 kg of MWCNT conductive slurry with a solid content of 3.5% were mechanically stirred (revolution speed 30 rpm, rotation speed 500 rpm, time 30 min, vacuum degree ≤95%) to obtain the negative electrode slurry.
[0084] Example 3 0.3 kg of CMC and 16.4 kg of deionized water were mechanically mixed (revolution speed of 20 rpm, rotation speed of 1000 rpm, time of 180 min) to obtain CMC adhesive solution; 18.7 kg of silicon-carbon composite material (SiC) and 74.8 kg of artificial graphite (D) were used. 50 =8~20μm) and 1kg of acetylene black were mechanically mixed (revolution speed 40rpm, rotation speed 1000rpm, time 60min), then 20.83kg of PAA and 30kg of deionized water were added and mechanically mixed (revolution speed 15rpm, rotation speed 2000rpm, time 150min) to obtain the first slurry (solid content 65±1%, core coating thickness 50nm, X value in core coating 1:2.5). The first slurry, 0.5 kg of acetylene black, 16.7 kg of the CMC adhesive, 8.3 kg of PAA, and 8.5 kg of deionized water were mechanically mixed (revolution speed 40 rpm, rotation speed 800 rpm, time 1200 min) to obtain the second slurry (solid content 55±1%, intermediate buffer layer thickness 70 nm, Y value of 0.5:1.3, X:Y=1.04 in the intermediate buffer layer); The second slurry, 0.5 kg of acetylene black, 4.17 kg of the CMC adhesive and 15 kg of deionized water were mechanically mixed (revolution speed of 50 rpm, rotation speed of 3000 rpm, time of 2 h, vacuum degree ≤95%) to obtain the third slurry (solid content of 50±1%, thickness of the outer skeleton reinforcement layer of 100 nm, Z value of 0.1:0.5, Y:Z=1.92 in the outer skeleton reinforcement layer). The third slurry, 3 kg of N-methylpyrrolidone, 1.11 kg of SBR dispersion (solid content 45%), 41.7 kg of deionized water, and 2.86 kg of MWCNT conductive slurry with a solid content of 3.5% were mechanically stirred (revolution speed 30 rpm, rotation speed 500 rpm, time 30 min, vacuum degree ≤95%) to obtain the negative electrode slurry.
[0085] Comparative Example 1 0.76 kg of CMC and 41.43 kg of deionized water were mechanically mixed (revolution speed of 20 rpm, rotation speed of 1000 rpm, time of 180 min) to obtain CMC solution. 16.878 kg of the CMC adhesive solution, 1.582 kg of Super P and 13.061 kg of deionized water were mechanically stirred (revolution speed of 10 rpm, rotation speed of 1500 rpm, time of 30 min) to obtain the first slurry; The first slurry and 60 kg of artificial graphite were mechanically stirred and mixed (revolution speed of 15 rpm, rotation speed of 2000 rpm, time of 60 min) to obtain the second slurry; The second slurry and 4.954 kg of deionized water were mechanically mixed (pressure -50 kPa, revolution speed 20 rpm, rotation speed 2200 rpm, time 60 min) to obtain the third slurry; The third slurry and 25.316 kg of the CMC adhesive were mechanically stirred and mixed (vacuum degree ≤95%, revolution speed 25 rpm, rotation speed 2500 rpm, time 120 min) to obtain the fourth slurry; The fourth slurry, 1.899 kg of N-methylpyrrolidone, 2.11 kg of SBR dispersion (solid content 45%), and 4.504 kg of deionized water were mechanically mixed (vacuum degree ≤95%, revolution speed 30 rpm, rotation speed 500 rpm, time 30 min) to obtain the negative electrode slurry.
[0086] Comparative Example 2 0.76 kg of CMC and 41.43 kg of deionized water were mechanically mixed (revolution speed of 20 rpm, rotation speed of 1000 rpm, time of 180 min) to obtain CMC solution. 16.878 kg of the CMC adhesive solution, 1.582 kg of Super P and 13.061 kg of deionized water were mechanically stirred (revolution speed of 10 rpm, rotation speed of 1500 rpm, time of 30 min) to obtain the first slurry; The first slurry, 12 kg SiC and 48 kg artificial graphite were mechanically stirred and mixed (revolution speed of 15 rpm, rotation speed of 2000 rpm, time of 60 min) to obtain the second slurry; The second slurry and 14.954 kg of deionized water were mechanically mixed (pressure: -50 kPa, revolution speed: 20 rpm, rotation speed: 2200 rpm, time: 60 min) to obtain the third slurry. The third slurry and 3.316 kg of the CMC adhesive were mechanically stirred and mixed (vacuum degree ≤95%, revolution speed 25 rpm, rotation speed 2500 rpm, time 120 min) to obtain the fourth slurry; The fourth slurry, 1.899 kg of N-methylpyrrolidone, 2.11 kg of SBR dispersion (solid content 45%), and 14.324 kg of deionized water were mechanically stirred (vacuum degree ≤95%, revolution speed 30 rpm, rotation speed 500 rpm, time 30 min) to obtain the negative electrode slurry.
[0087] Test case The negative electrode slurry described in Examples 1-3 and Comparative Examples 1-2 was coated onto the surface of a negative electrode current collector (copper foil), and dried to obtain a negative electrode; A lithium-ion battery is assembled using lithium-nickel-cobalt-manganese-oxygen ternary material as the positive electrode, the above-mentioned negative electrode as the negative electrode, organic solvent and several additives as the electrolyte, and PE composite coating as the separator. The cycle performance, storage performance, rate performance and high and low temperature resistance of the lithium-ion battery were tested. The test conditions for the cycle performance are as follows: charge and discharge cycles are performed under 5C (charge) / 10C (discharge) conditions, with a 15-minute rest between charge and discharge, and the number of cycles is recorded when the output performance is 80% SOH (State of Health). The test conditions for the storage performance are: the capacity retention rate after storage at 85°C for 4 hours (referred to as storage 1) or the capacity retention rate after storage at 60°C for 30 days (referred to as storage 2). The test conditions for the rate performance are: capacity retention rate after discharge at 10C. The test conditions for the high and low temperature resistance performance are: under discharge conditions of -40℃ and 0.5C, the output performance is the trough voltage; The test results are shown in Table 1: Table 1. Electrochemical performance of lithium-ion batteries prepared in Examples 1-3 and Comparative Examples 1-2
[0088] As shown in Table 1, the negative electrode slurry of the present invention has a more uniform, stable and efficient conductive network due to its special "core-buffer-exoskeleton" coating structure, which can significantly reduce the click impedance. At the same time, the layered structure of the coating layer greatly improves the tolerance of the negative electrode material to volume expansion, thereby significantly improving the cycle performance of the battery.
[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A negative electrode slurry, characterized in that, It includes a dispersion phase and a dispersion medium, wherein the dispersion phase includes a negative electrode active material, and a core coating layer, an intermediate buffer layer and an exoskeleton reinforcement layer sequentially coated on the surface of the negative electrode active material; The core coating layer, intermediate buffer layer, and exoskeleton reinforcement layer each independently include a conductive agent and a polymer thickener; The content of conductive agent in the core coating layer, intermediate buffer layer and exoskeleton reinforcement layer decreases sequentially.
2. The negative electrode slurry as described in claim 1, characterized in that, The negative electrode active material includes one or more of graphite, hard carbon, silicon-carbon composite materials, and silicon-oxygen composite materials.
3. The negative electrode slurry as described in claim 1, characterized in that, The conductive agent includes one or more of acetylene black, conductive carbon black, carbon nanotubes, carbon nanofibers, and graphene.
4. The negative electrode slurry as described in claim 3, characterized in that, The conductive carbon black has a DBP value of 50~800 mL / 100 g and a specific surface area of 10~2000 m². 2 / g; The carbon nanotubes have a diameter of 1-20 nm, a length of 0.5-50 μm, an aspect ratio ≥100, and a specific surface area of 100-300 m². 2 / g; The carbon nanofibers have a diameter of 100~500nm, a length of 5~100μm, and an aspect ratio of >50; The graphene has 1 to 10 layers, a sheet diameter of 5 to 100 μm, and a carbon-to-oxygen ratio of 30 to 70.
5. The negative electrode slurry as described in claim 1, characterized in that, The polymeric thickener includes carboxymethyl cellulose thickeners and / or polyacrylic acid thickeners.
6. The negative electrode slurry as described in claim 5, characterized in that, The carboxymethyl cellulose thickener has a degree of substitution of 0.8 to 1.5, a molecular weight of 50,000 to 300,000, and heavy metal residue of <50 ppm; The polyacrylic thickener includes one or more of polyacrylic acid, polyacrylate, polyacrylate and acrylic copolymers.
7. The negative electrode slurry as described in claim 1, characterized in that, The mass ratios of conductive agent and polymeric thickener in the core coating layer, intermediate buffer layer and outer skeleton reinforcement layer are denoted as X, Y and Z, respectively. The ratio of X to Y is (1~6):1; The ratio of Y to Z is (1~6):
1.
8. The negative electrode slurry according to any one of claims 1 to 7, characterized in that, When the conductive agent in the exoskeleton reinforcement layer includes carbon nanotubes and / or carbon nanofibers, the carbon nanotubes and / or carbon nanofibers are distributed in the exoskeleton reinforcement layer, and are also distributed in the negative electrode slurry and connected to the dispersion in the negative electrode slurry.
9. A method for preparing the negative electrode slurry according to any one of claims 1 to 8, characterized in that, Includes the following steps: After mixing the negative electrode active material and the first conductive agent, it is mixed with the first thickener adhesive to obtain the first slurry; the dispersed phase in the first slurry is the negative electrode active material coated with a core coating layer; The first slurry, the second conductive agent, and the second thickener are mixed to obtain a second slurry; the dispersed component in the second slurry is a negative electrode active material and a core coating layer and an intermediate buffer layer sequentially coated on the surface of the negative electrode active material. The second slurry, the third conductive agent, and the third thickener are mixed together to obtain the negative electrode slurry.
10. The application of the negative electrode slurry according to any one of claims 1 to 8 or the negative electrode slurry prepared by the preparation method according to claim 9 in lithium-ion batteries.