Negative plate and battery
By setting a combination of graphite and silicon-carbon layers on the surface of the negative electrode current collector, the problem of current collector breakage caused by the expansion of high-silicon negative electrode sheets is solved, thereby improving the battery's lifespan and energy density.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-24
- Publication Date
- 2026-03-13
AI Technical Summary
The expansion of the silicon-carbon layer in the high-silicon anode sheet can cause the current collector to break, leading to a sharp decline in battery capacity.
A first graphite layer, a silicon-carbon layer, and a second graphite layer are sequentially disposed on the surface of the negative electrode current collector, with the silicon-carbon layer located between the two layers to buffer the stress generated by silicon expansion. The stress is absorbed and dispersed through the first and second graphite layers.
It reduces the probability of negative electrode breakage, improves battery life and energy density, and extends battery cycle life.
Smart Images
Figure CN121662741A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of battery technology, specifically to a negative electrode and a battery. Background Technology
[0002] To improve battery energy density, cathode materials are being developed towards high-nickel ternary materials, while anode materials are being developed towards high-silicon materials. The use of high-silicon materials also leads to increased battery material activity and side reactions. Currently, the anode sheet structure consists of a silicon-carbon layer and a graphite layer sequentially placed on the surface of the anode current collector, away from the current collector. When the silicon-carbon layer expands, it exerts significant stress on the anode current collector, causing localized fracture of the current collector, which in turn leads to a broken anode sheet and a sharp decrease in battery capacity. Therefore, overcoming these technical problems and defects is a key issue that needs to be addressed. Summary of the Invention
[0003] To address the problem of excessive expansion of the silicon-carbon layer in the negative electrode of high-silicon battery systems, which easily leads to electrode breakage, this invention provides a negative electrode and a battery.
[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: The present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector; along the direction away from the negative electrode current collector, the negative electrode active material layer comprises a first graphite layer, a silicon-carbon layer and a second graphite layer stacked sequentially; the silicon-carbon layer comprises silicon-carbon material, with the total weight of the silicon-carbon layer being 100%, and the percentage content of the silicon-carbon material in the total weight of the silicon-carbon layer being 3%-30%.
[0005] Optionally, the silicon-carbon layer further includes a third graphite material, a third binder, and a conductive agent; taking the total weight of the silicon-carbon layer as 100%, the third graphite material accounts for 66%-93% of the total weight of the silicon-carbon layer; the third binder accounts for 2%-5% of the total weight of the silicon-carbon layer; and the conductive agent accounts for 0.1%-2% of the total weight of the silicon-carbon layer.
[0006] Optionally, the first graphite layer includes a first graphite material and a first binder; taking the total weight of the first graphite layer as 100%, the first graphite material accounts for 97%-99% of the total weight of the first graphite layer; and the first binder accounts for 1%-3% of the total weight of the first graphite material.
[0007] Optionally, the second graphite layer includes a second graphite material and a second binder; taking the total weight of the second graphite layer as 100%, the second graphite material accounts for 97%-99% of the total weight of the second graphite layer; and the second binder accounts for 1%-3% of the total weight of the second graphite material.
[0008] Optionally, the first graphite material, the second graphite material, and the third graphite material are each individually selected from one or more of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, and organic polymer compound carbon.
[0009] Optionally, the first adhesive, the second adhesive, and the third adhesive are each individually selected from one or more of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, styrene-butadiene rubber, and polyacrylates.
[0010] Optionally, the conductive agent is selected from one or more of conductive carbon black, acetylene black, Ketjen black, conductive carbon fiber, carbon nanotubes, graphene, and carbon fiber.
[0011] Optionally, the silicon-carbon material is a vapor-deposited silicon-carbon material.
[0012] Optionally, the thickness of the negative electrode active material layer is H, the thickness of the first graphite layer is H1, the thickness of the silicon-carbon layer is H2, and the thickness of the second graphite layer is H3. The thicknesses of H, H1, H2, and H3 satisfy the following relationships: 10% ≤ H1 / H ≤ 20%; 50% ≤ H2 / H ≤ 80%; 10% ≤ H3 / H ≤ 30%.
[0013] In another aspect, the present invention provides a battery comprising the negative electrode sheet described above.
[0014] According to the negative electrode sheet provided by the present invention, a first graphite layer, a silicon-carbon layer and a second graphite layer are sequentially disposed on the surface of the negative electrode current collector; the silicon-carbon layer is located between the first graphite layer and the second graphite layer. When the silicon-carbon layer expands, the first graphite layer and the second graphite layer play a buffering role on the silicon-carbon layer, absorbing and dispersing the stress generated by the silicon expansion; the negative electrode sheet has a small K value and a reduced probability of breakage, thereby improving the service life of the battery. Attached Figure Description
[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0016] Figure 1This is a schematic diagram of the structure of a negative electrode sheet provided in an embodiment of the present invention; The reference numerals in the accompanying drawings are as follows: 1-Negative electrode current collector; 2-Negative electrode active material layer; 21-First graphite layer; 22-Silicon-carbon layer; 23-Second graphite layer. Detailed Implementation
[0017] To make the technical problems solved, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.
[0018] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.
[0019] like Figure 1 As shown, in one embodiment, the present invention provides a negative electrode sheet, including a negative electrode current collector 1 and a negative electrode active material layer 2 disposed on the surface of the negative electrode current collector 1; along the direction away from the negative electrode current collector 1, the negative electrode active material layer 2 includes a first graphite layer 21, a silicon carbon layer 22 and a second graphite layer 23 stacked sequentially; the silicon carbon layer 22 includes silicon carbon material, and the percentage of silicon carbon material in the total weight of the silicon carbon layer 22 is 3%-30%, with the total weight of the silicon carbon layer 22 being 100%.
[0020] Specifically, the percentage of silicon-carbon material in the total weight of silicon-carbon layer 22 is any one value or a range of any two values from 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%; in a preferred embodiment, the percentage of silicon-carbon material in the total weight of silicon-carbon layer 22 is 15%-20%.
[0021] When the percentage of silicon-carbon material in the total weight of silicon-carbon layer 22 is 3%-30%, it can significantly improve the battery energy density and extend the battery's range. The carbon matrix can act as a "buffer," absorbing and dispersing the stress generated by silicon expansion, limiting the expansion range of silicon, preventing electrode structure cracking, and improving battery cycle life. When the percentage of silicon-carbon material in the total weight of silicon-carbon layer 22 is less than 3%, it will result in a lower battery energy density. When the percentage of silicon-carbon material in the total weight of silicon-carbon layer 22 is greater than 30%, it will cause the negative electrode active material to fall off, the electrode structure to crack, the SEI film to become unstable, and the battery cycle life to decrease.
[0022] If the structure of the negative electrode sheet has a silicon-carbon layer and a graphite layer sequentially disposed on the surface of the negative electrode current collector along the direction away from the negative electrode current collector; when the silicon-carbon layer expands, the stress on the negative electrode current collector is large, which leads to local fracture of the current collector, and then to the breakage of the negative electrode sheet, resulting in a sharp decrease in battery capacity. If the structure of the negative electrode sheet is such that a graphite layer and a silicon-carbon layer are sequentially disposed on the surface of the negative electrode current collector in a direction away from the negative electrode current collector; the silicon-carbon material in the silicon-carbon layer expands significantly during battery cycling, causing the silicon-carbon layer structure to crack, and irregular particles and burrs to pierce the separator, resulting in a large K value of the battery. This invention sequentially deposits a first graphite layer 21, a silicon-carbon layer 22, and a second graphite layer 23 on the surface of the negative electrode current collector 1. The silicon-carbon layer 22 is located between the first graphite layer 21 and the second graphite layer 23. When the silicon-carbon layer 22 expands, the first graphite layer 21 and the second graphite layer 23 act as a buffer for the silicon-carbon layer 22, absorbing and dispersing the stress generated by the silicon expansion. The negative electrode sheet has a small K value and a lower probability of breakage, thus improving the battery's lifespan.
[0023] like Figure 1 As shown, in one embodiment, the silicon-carbon layer 22 further includes a third graphite material, a third binder, and a conductive agent; taking the total weight of the silicon-carbon layer 22 as 100%, the third graphite material accounts for 66%-93% of the total weight of the silicon-carbon layer 22; the third binder accounts for 2%-5% of the total weight of the silicon-carbon layer 22; and the conductive agent accounts for 0.1%-2% of the total weight of the silicon-carbon layer 22.
[0024] Specifically, the percentage of the third graphite material in the total weight of the silicon-carbon layer 22 is any one value or a range of any two values from 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, or 93%; in a preferred embodiment, the percentage of the third graphite material in the total weight of the silicon-carbon layer 22 is 75%-85%.
[0025] When the percentage of the third graphite material in the total weight of the silicon-carbon layer 22 is 66%-93%, the third graphite material can buffer the expansion of silicon material, absorbing and dispersing the stress generated by silicon expansion; the K value of the negative electrode is small, and the probability of breakage is reduced; when the percentage of the third graphite material in the total weight of the silicon-carbon layer 22 is less than 66%, the silicon content is high, which will lead to the shedding of the negative electrode active material and the cracking of the electrode structure; the SEI film is unstable, and the cycle life of the battery is reduced; when the percentage of the third graphite material in the total weight of the silicon-carbon layer 22 is greater than 93%, the silicon content is low, and the energy density of the battery is low.
[0026] Specifically, the percentage of the third adhesive in the total weight of the silicon carbide layer 22 is any one value or a range of any two values from 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%; in a preferred embodiment, the percentage of the third adhesive in the total weight of the silicon carbide layer 22 is 3%-4%.
[0027] When the third binder accounts for 2%-5% of the total weight of the silicon-carbon layer 22, it can ensure good adhesion between the silicon-carbon layer 22 and the first graphite layer 21, as well as between the silicon-carbon layer 22 and the second graphite layer 23. When the third binder accounts for less than 2% of the total weight of the silicon-carbon layer 22, the adhesion between the silicon-carbon layer 22 and the first graphite layer 21 and the second graphite layer 23 will be weak, and the silicon-carbon layer 22 and the second graphite layer 23 are prone to detachment during cycling. When the third binder accounts for more than 5% of the total weight of the silicon-carbon layer 22, the content of the third binder in the silicon-carbon layer 22 will be too high, reducing the energy density of the battery.
[0028] Specifically, the percentage of the conductive agent in the total weight of the silicon-carbon layer 22 is any one value or a range of any two values from 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%. In a preferred embodiment, the percentage of the first binder in the total mass of solid matter in the first negative electrode slurry is 0.8%-1.2%.
[0029] When the percentage of conductive agent in the total weight of silicon-carbon layer 22 is 0.1%-2%, it can construct an efficient conductive network, improve battery rate performance and cycle stability, and balance energy density and cost. When the percentage of conductive agent in the total weight of silicon-carbon layer 22 is less than 0.1%, it will lead to an incomplete conductive network, poor battery rate performance, and poor battery cycle performance. When the percentage of conductive agent in the total weight of silicon-carbon layer 22 is greater than 2%, it will reduce the electrode energy density.
[0030] like Figure 1 As shown, in one embodiment, the first graphite layer 21 includes a first graphite material and a first binder; taking the total weight of the first graphite layer 21 as 100%, the first graphite material accounts for 97%-99% of the total weight of the first graphite layer 21; and the first binder accounts for 1%-3% of the total weight of the first graphite material.
[0031] Specifically, the percentage content of the first graphite material in the total weight of the first graphite layer 21 is any one value or any two values from 97%, 97.5%, 98%, 98.5% or 99%; in a preferred embodiment, the percentage content of the first graphite material in the total weight of the first graphite layer 21 is 97.5%-98.5%.
[0032] When the first graphite material accounts for 97%-99% of the total weight of the first graphite layer 21, it exhibits high reversible specific capacity and stable cycling. Graphite exhibits minimal volume change during charging and discharging, effectively buffering stress and maintaining the integrity of the electrode structure. As the bottom layer, it provides mechanical support and a flat substrate for the upper silicon-carbon layer 22, suppressing electrode warping or peeling caused by silicon expansion. Graphite itself has good conductivity, and its high proportion helps to construct an efficient electron transport network and reduce electrode internal resistance. When the first graphite material accounts for less than 97% of the total weight of the first graphite layer 21, it leads to excessive inactive materials and reduced battery energy density. When the first graphite material accounts for more than 99% of the total weight of the first graphite layer 21, it results in a lack of necessary binder, poor adhesion, and potential defects such as cracks and edge effects during coating. If the conductive agent content is too low (<1%), it is difficult to form an efficient and continuous electronic pathway, resulting in an imperfect conductive network and a significantly shortened battery cycle life.
[0033] Specifically, the percentage of the first binder in the total weight of the first graphite material is any one value or a range of any two values from 1%, 1.5%, 2%, 2.5% or 3%; in a preferred embodiment, the percentage of the first binder in the total weight of the first graphite material is 1.5%-2.5%.
[0034] When the first binder accounts for 1%-3% of the total weight of the first graphite material, it can ensure good adhesion between the silicon carbon layer 22 and the first graphite layer 21. When the first binder accounts for less than 1% of the total weight of the first graphite material, it will result in weak adhesion between the silicon carbon layer 22 and the first graphite layer 21, and the silicon carbon layer 22 and the second graphite layer 23 are prone to detachment during cycling. When the first binder accounts for more than 3% of the total weight of the first graphite material, it will result in an excessively high content of the first binder in the first graphite layer 21, reducing the energy density of the battery.
[0035] like Figure 1As shown, in one embodiment, the second graphite layer 23 includes a second graphite material and a second binder; taking the total weight of the second graphite layer 23 as 100%, the second graphite material accounts for 97%-99% of the total weight of the second graphite layer 23; and the second binder accounts for 1%-5% of the total weight of the second graphite material.
[0036] Specifically, the percentage content of the second graphite material in the total weight of the second graphite layer 23 is any one value or any two values from 97%, 97.5%, 98%, 98.5% or 99%; in a preferred embodiment, the percentage content of the second graphite material in the total weight of the second graphite layer 23 is 97.5%-98.5%.
[0037] When the second graphite material accounts for 97%-99% of the total weight of the second graphite layer 23, it exhibits high reversible specific capacity and stable cycling. Graphite exhibits minimal volume change during charging and discharging, effectively buffering stress and maintaining the integrity of the electrode structure. As the bottom layer, it provides mechanical support and a flat substrate for the upper silicon-carbon layer 22, suppressing electrode warping or peeling caused by silicon expansion. Graphite itself has good conductivity, and its high proportion helps to build an efficient electron transport network and reduce electrode internal resistance. When the second graphite material accounts for less than 97% of the total weight of the second graphite layer 23, it leads to excessive inactive materials and reduced battery energy density. When the second graphite material accounts for more than 99% of the total weight of the second graphite layer 23, it results in a lack of necessary binder, poor adhesion, and potential defects such as cracks and edge effects during coating. If the conductive agent content is too low (<1%), it is difficult to form an efficient and continuous electronic pathway, resulting in an imperfect conductive network and a significantly shortened battery cycle life.
[0038] Specifically, the percentage of the second binder in the total weight of the second graphite material is any one value or a range of any two values from 1%, 1.5%, 2%, 2.5% or 3%; in a preferred embodiment, the percentage of the second binder in the total weight of the second graphite material is 1.5%-2.5%.
[0039] When the second binder accounts for 1%-3% of the total weight of the second graphite material, it can ensure good adhesion between the silicon carbon layer 22 and the second graphite layer 23. When the second binder accounts for less than 1% of the total weight of the second graphite material, it will result in weak adhesion between the silicon carbon layer 22 and the second graphite layer 23, and the silicon carbon layer 22 and the second graphite layer 23 are prone to detachment during cycling. When the second binder accounts for more than 3% of the total weight of the second graphite material, it will result in an excessively high content of the second binder in the second graphite layer 23, reducing the energy density of the battery.
[0040] like Figure 1As shown, in one embodiment, the first graphite material, the second graphite material, and the third graphite material are each individually selected from one or more of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, and organic polymer compound carbon; they have high reversible specific capacity and stable cycling; the graphite material has small volume change during charging and discharging, which can effectively buffer stress and maintain the integrity of the electrode structure; the graphite material itself has good conductivity, and its high proportion helps to build an efficient electron transport network and reduce the internal resistance of the electrode.
[0041] like Figure 1 As shown, in one embodiment, the first binder, the second binder, and the third binder are each individually selected from one or more of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, styrene-butadiene rubber, and polyacrylate; this can make the negative electrode slurry uniformly dispersed.
[0042] like Figure 1 As shown, in one embodiment, the silicon-carbon material is a vapor-deposited silicon-carbon material.
[0043] Specifically, the silicon-carbon material used in this invention is a vapor-deposited silicon-carbon material. The CVD method can grow silicon or silicon oxide in situ on or inside a carbon matrix (such as porous graphite, carbon microspheres, carbon nanotubes, etc.), achieving a highly controllable composite structure with flexible structural design. It can effectively suppress silicon pulverization and repeated rupture of the SEI film, significantly improving cycle stability. During the CVD process, silicon and the carbon matrix form chemical bonds or strong physical bonds, and the interfacial bonding force is much higher than that of mechanical mixing. The CVD method can achieve uniform deposition of silicon on the carbon matrix by controlling parameters such as gas flow rate, temperature, and pressure. The CVD method can effectively solve the silicon expansion problem.
[0044] like Figure 1 As shown, in one embodiment, the conductive agent is selected from one or more of conductive carbon black, acetylene black, Ketjen black, conductive carbon fiber, carbon nanotubes, graphene, and carbon fiber; it can be fully dispersed to form a continuous electronic conduction pathway between silicon particles and a carbon matrix (such as graphite or amorphous carbon) to construct a highly efficient conductive network.
[0045] like Figure 1 As shown, in one embodiment, the thickness of the negative electrode active material layer 2 is H, the thickness of the first graphite layer 21 is H1, the thickness of the silicon-carbon layer 22 is H2, and the thickness of the second graphite layer 23 is H3. H, H1, H2, and H3 satisfy the following relationships: 10%≤H1 / H≤20%; 50%≤H2 / H≤80%; 10%≤H3 / H≤30%.
[0046] Specifically, the value range of H1 / H is any one value or any two values from 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%; in a preferred embodiment, the value range of H1 / H is 12%≤H1 / H≤18%.
[0047] When the value of H1 / H is in the range of 10%≤H1 / H≤20%, graphite has small volume change during charging and discharging, which can effectively buffer stress and maintain the integrity of the electrode structure. As the bottom layer, it provides mechanical support and a flat substrate for the upper silicon-carbon layer 22, suppressing electrode warping or peeling caused by silicon expansion. Graphite itself has good conductivity, and its high proportion helps to build an efficient electron transport network and reduce the internal resistance of the electrode. When H1 / H≤10%, it cannot effectively suppress electrode warping or peeling caused by silicon expansion, the K value is large, and the probability of breakage is high. When 20%≤H1 / H, the silicon-carbon layer 22 is thin and cannot effectively improve the energy density of the battery.
[0048] Specifically, the value of H2 / H is any one point or any two points from 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, or 80%; in a preferred embodiment, the value of H2 / H is 60% ≤ H2 / H ≤ 70%.
[0049] When the value of H2 / H is within the range of 50%≤H2 / H≤80%, the battery energy density can be significantly improved, and the battery range can be enhanced. When H2 / H≤50%, the silicon-carbon layer 22 will be too thin, and the battery energy density cannot be effectively improved. When 80%≤H2 / H, the first graphite layer 21 and the second graphite layer 23 will be too thin, and the electrode warping or peeling caused by silicon expansion cannot be effectively suppressed. The K value is large, and the probability of breakage is high.
[0050] Specifically, the value range of H3 / H is any one point or any two points from 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%; in a preferred embodiment, the value range of H3 / H is 15% ≤ H3 / H ≤ 25%.
[0051] When the value of H3 / H is in the range of 10%≤H3 / H≤30%, the graphite has a small volume change during charging and discharging, which can effectively buffer stress and maintain the integrity of the electrode structure. As the upper layer, it provides a buffer for the lower silicon-carbon layer 22, suppressing electrode warping or peeling caused by silicon expansion. When H3 / H≤10%, it cannot effectively suppress electrode warping or peeling caused by silicon expansion, the K value is large, and the probability of breakage is high. When 30%≤H3 / H, the silicon-carbon layer 22 is thin and cannot effectively improve the battery energy density.
[0052] In another aspect, the present invention provides a battery comprising the aforementioned negative electrode.
[0053] In some embodiments, the battery can be a secondary battery, which can be a lithium-ion battery. Typically, a battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. In the actual battery manufacturing process, firstly, the positive electrode, separator, negative electrode, and separator are sequentially stacked and assembled to obtain a bare cell. The assembly method can be, for example, stacking or winding. Then, electrolyte is injected into the dry bare cell, and after formation and aging, a secondary battery is obtained. The negative electrode is the negative electrode described in the above embodiments. The positive electrode includes a positive current collector and a positive active material layer coated on the positive current collector. Specifically, the positive active material layer can include a positive active material, a conductive agent, and a binder. The positive active material can include, for example, at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt manganese aluminum oxide; the conductive agent can include, for example, at least one of conductive carbon black, carbon nanotubes, and acetylene black; the binder can include, for example, polyvinylidene fluoride (PVDF). The separator can be, for example, a polyethylene membrane, a polypropylene membrane, a PVDF membrane, or a non-woven fabric. Electrolytes may include, for example, lithium salts and solvents. The types of lithium salts and solvents are not specifically limited and can be selected according to actual needs.
[0054] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.
[0055] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Materials not specified in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.
[0056] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.
[0057] In the following embodiments, the reagents, materials and instruments used, unless otherwise specified, are commercially available or can be obtained through synthesis methods known in the art.
[0058] Table 1. Design of negative electrode parameters for Examples 1-6 and Comparative Examples 1-5; Example 1 This embodiment illustrates the negative electrode sheet and battery disclosed in this invention; it includes the following operational steps: Preparation of negative electrode: The first graphite material, graphite, and the first binder, SBR, are mixed in a ratio of 98:2 to prepare the first negative electrode slurry. The second graphite material, graphite, and the second binder, SBR, are mixed in a ratio of 98:2 to prepare the second negative electrode slurry. A third negative electrode slurry is prepared by mixing vapor-deposited silicon-carbon material, third graphite material graphite, third binder SBR and conductive agent conductive carbon black in a ratio of 10:87:3:1. The first negative electrode slurry, the third negative electrode slurry, and the second negative electrode slurry are sequentially coated onto the copper foil of the negative electrode current collector on a coating machine. After drying, rolling, die cutting and other processes, the negative electrode sheet is obtained. At this time, the thickness ratio of the first graphite layer, the silicon carbon layer and the second graphite layer is 2:6:2.
[0059] Preparation of positive electrode: Lithium cobalt oxide, single-walled carbon nanotubes, conductive carbon black SP, and binder PVDF are mixed in a ratio of 98:0.5:0.5:1.0 to prepare a positive electrode slurry. The positive electrode slurry is then coated onto the surface of the positive electrode current collector on a coating machine. After drying, rolling, die-cutting, and other processes, a positive electrode sheet that meets the requirements is obtained.
[0060] Electrolyte preparation: Lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 1:2:1 to obtain an electrolyte with a concentration of 1 mol / L.
[0061] Preparation of the diaphragm: PE porous polymer film is used as the membrane substrate; Battery manufacturing: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then stacked in the same manner to form a battery cell. The battery cell is placed into a pre-formed battery casing, and the electrolyte is injected into the baked and dried battery cell. After vacuum sealing, settling, and formation processes, the battery is obtained.
[0062] Examples 2-6 Examples 2-6 illustrate the negative electrode sheet and battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences: The parameters of the negative electrode shown in Table 1 are used.
[0063] Comparative Examples 1-5 Comparative Examples 1-5 are used to illustrate the negative electrode sheet and battery disclosed in this invention, including most of the operating steps in Example 1, the difference being: The parameters of the negative electrode shown in Table 1 are used.
[0064] Performance testing The following performance tests were performed on the batteries prepared in Examples 1-6 and Comparative Examples 1-5: Battery cell performance testing method: Charge the battery cell at 3C constant current and constant voltage to 4.5V, cut off at 0.05C, discharge at 0.5C, and after 1000 cycles, measure the thickness of the battery cell at the bottom and compare it with the initial thickness. The ratio is the thickness expansion.
[0065] K-value test: K value = (voltage 1 - voltage 2) / time.
[0066] Energy density: Energy density = Capacity * Nominal capacity / Cell volume The test results are shown in Table 2.
[0067] Table 2 Battery Electrochemical Performance Comparing Examples 1-3 and Comparative Examples 1-2, it can be seen that when the percentage of silicon-carbon material in the total weight of the silicon-carbon layer is 3%-30%, the K-value of the battery can be significantly reduced. After 1000 cycles, the battery has a high energy density, a low thickness expansion rate, and no breakage occurs. When the percentage of silicon-carbon material in the total weight of the silicon-carbon layer is less than 3%, the K-value of the battery is low, and the battery energy density is low. When the percentage of silicon-carbon material in the total weight of the silicon-carbon layer is greater than 30%, the K-value of the battery is large, the thickness expansion rate is high after 1000 cycles, and breakage is more likely to occur. Comparing Examples 1 and 4-6, it can be seen that when H1, H2, and H3 satisfy the relationship (10-20): (50-80): (10-30), the K value and energy density of the battery can be significantly reduced. After 1000 cycles, the thickness expansion rate of the battery is low and no breakage occurs. When the above relationship is not satisfied, the energy density of the battery is low.
[0068] Comparing Example 1 with Comparative Examples 3-5, it can be seen that when there is no first graphite layer in the negative electrode, the battery is prone to breakage; when there is no second graphite layer in the negative electrode, the K value of the battery is larger or the thickness expansion rate is higher after 1000 cycles.
[0069] This invention sequentially sets a first graphite layer, a silicon-carbon layer, and a second graphite layer on the surface of the negative electrode current collector; with the silicon-carbon layer located between the first and second graphite layers, when the silicon-carbon layer expands, the first and second graphite layers act as a buffer, absorbing and dispersing the stress generated by the silicon expansion; the negative electrode sheet has a small K value and a reduced probability of breakage, thus improving the battery's lifespan.
[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A negative electrode sheet, characterized in that: It includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector; along the direction away from the negative electrode current collector, the negative electrode active material layer includes a first graphite layer, a silicon carbon layer and a second graphite layer stacked sequentially; the silicon carbon layer includes silicon carbon material, with the total weight of the silicon carbon layer being 100%, and the percentage content of the silicon carbon material in the total weight of the silicon carbon layer being 3%-30%.
2. The negative electrode sheet according to claim 1, characterized in that: The silicon-carbon layer further includes a third graphite material, a third binder, and a conductive agent; taking the total weight of the silicon-carbon layer as 100%, the third graphite material accounts for 66%-93% of the total weight of the silicon-carbon layer; the third binder accounts for 2%-5% of the total weight of the silicon-carbon layer; and the conductive agent accounts for 0.1%-2% of the total weight of the silicon-carbon layer.
3. The negative electrode sheet according to claim 2, characterized in that: The first graphite layer comprises a first graphite material and a first binder; taking the total weight of the first graphite layer as 100%, the first graphite material accounts for 97%-99% of the total weight of the first graphite layer; the first binder accounts for 1%-3% of the total weight of the first graphite material.
4. The negative electrode sheet according to claim 3, characterized in that: The second graphite layer comprises a second graphite material and a second binder; taking the total weight of the second graphite layer as 100%, the second graphite material accounts for 97%-99% of the total weight of the second graphite layer; the second binder accounts for 1%-3% of the total weight of the second graphite material.
5. The negative electrode sheet according to claim 4, characterized in that: The first graphite material, the second graphite material, and the third graphite material are each individually selected from one or more of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, and organic polymer compound carbon.
6. The negative electrode sheet according to claim 4, characterized in that: The first adhesive, the second adhesive, and the third adhesive are each individually selected from one or more of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, styrene-butadiene rubber, and polyacrylates.
7. The negative electrode sheet according to claim 2, characterized in that: The conductive agent is selected from one or more of conductive carbon black, acetylene black, Ketjen black, conductive carbon fiber, carbon nanotubes, graphene, and carbon fiber.
8. The negative electrode sheet according to claim 1, characterized in that: The silicon-carbon material is a vapor-deposited silicon-carbon material.
9. The negative electrode sheet according to claim 1, characterized in that: The thickness of the negative electrode active material layer is H, the thickness of the first graphite layer is H1, the thickness of the silicon-carbon layer is H2, and the thickness of the second graphite layer is H3. The H, H1, H2, and H3 satisfy the following relationships: 10%≤H1 / H≤20%; 50%≤H2 / H≤80%; 10%≤H3 / H≤30%.
10. A battery, characterized in that: Includes the negative electrode sheet as described in any one of claims 1-9.