An anode sheet and application thereof

Abstract

The application discloses a negative pole piece and application thereof, and belongs to the technical field of battery materials. The negative pole piece comprises first pole piece active substances and second pole piece active substances; the first pole piece active substances and the second pole piece active substances satisfy the relationship: 1<=L*Xc / H<=25; L represents the OI value of the first pole piece active substances, Xc represents the crystallinity of the second pole piece active substances, and H is the thickness of the anode active substances. The application sets the characteristic parameters of the first pole piece active substances and the second pole piece active substances to satisfy a specific relationship, solves the problem that the volume expansion of silicon leads to the performance failure of a battery, and simultaneously improves the conductivity and energy density of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a negative electrode sheet and its application. Background Technology

[0002] Lithium-ion batteries possess outstanding advantages such as high energy density, no memory effect, long cycle life, rapid charging and discharging, and low self-discharge, making them widely used in consumer electronics, electric vehicles, and energy storage. As market demands for higher energy density and charging rates from lithium-ion batteries continue to increase...

[0003] Currently, a common method to improve energy density is to dope silicon-based materials into the negative electrode active material. However, during charge and discharge, lithium ions are inserted and extracted into the silicon-doped negative electrode active material, causing the silicon material to expand and contract in volume. This significant volume change during cycling leads to a series of consequences, including material pulverization, electrode damage, and electrolyte drying, ultimately resulting in poor cycle performance. As the proportion of silicon in the negative electrode material gradually increases, the expansion of silicon leads to a large thickness expansion rate during battery cycling, severely impacting the overall performance of the device.

[0004] Therefore, there is an urgent need to find an anode active material to solve the problems of silicon volume expansion leading to battery performance failure in the existing technologies. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a negative electrode sheet that solves the problem of battery performance failure caused by silicon volume expansion, while also improving battery conductivity and energy density.

[0006] The present invention also provides a battery including the negative electrode.

[0007] According to an embodiment of the first aspect of the present invention, the negative electrode sheet is provided to include a first electrode active material and a second electrode active material;

[0008] The first electrode active material and the second electrode active material satisfy the following relationship: 1≤L*Xc / H≤25; L represents the OI value of the first electrode active material, Xc represents the crystallinity of the second electrode active material, and H is the thickness of the anode active material.

[0009] The negative electrode sheet according to embodiments of the present invention has at least the following beneficial effects:

[0010] The negative electrode of this invention comprises a first electrode active material and a second electrode active material. By setting the characteristic parameters (such as the OI value of graphite and the crystallinity of silicon) of the first electrode active material (graphite) and the second electrode active material (amorphous crystalline silicon-based material) to satisfy a specific relationship, the volume expansion of the anode material during lithium-ion insertion and extraction is effectively reduced, especially the expansion in the thickness direction. By controlling the OI value of graphite, its lattice expansion in the XYZ axis directions is dispersed, reducing the performance degradation of the battery caused by expansion and improving the cycle life of the battery. If the OI value of graphite is small, the expansion generated during charge and discharge cycles is smaller. This is because during lithium insertion, lithium ions are inserted into the interlayer spacing of graphite, causing the interlayer spacing to expand and resulting in graphite expansion; and isotropic graphite material undergoes lattice expansion in multiple directions, thus dispersing the expansion of the battery in the thickness direction. When the OI value is within the range defined by this invention and satisfies the relationship, the expansion difference of the negative electrode active layer is moderate, which can improve the electrolyte wetting of the negative electrode, reduce cell expansion, and improve battery performance.

[0011] This invention controls the crystallinity of the second electrode active material to maintain good volume change stability while also possessing a certain degree of electronic conductivity. The second electrode active material has a relatively large critical fracture size for the lithiation reaction, effectively addressing the volume expansion issue of silicon materials during charge and discharge, while maintaining moderate conductivity. This balances electronic conduction and lithium-ion diffusion characteristics, improving the overall electrochemical performance of the battery. In crystalline silicon, silicon atoms are arranged in a long-range ordered manner, resulting in high anisotropy in lithium diffusion paths and interphase deformation. In contrast, in amorphous silicon, silicon atoms are arranged in a long-range disordered manner, leading to a much larger critical fracture size for the lithiation reaction compared to crystalline silicon. The isotropy of amorphous silicon helps address the volume change problem in lithium alloying, but this long-range disordered structure results in a much lower electronic conductivity than crystalline silicon. Lithium-ion battery materials need to possess both electronic and lithium-ion conduction properties. Therefore, this invention balances this relationship by controlling the crystallinity of amorphous crystalline silicon particles to achieve moderate electronic conductivity and isotropic characteristics.

[0012] This invention limits the OI value of the graphite active material of the first electrode and the crystallinity of the silicon-based material of the second electrode active material to work synergistically within a limited range. The pore structure of the electrode is optimized, and the electrolyte can better penetrate into the negative electrode active material layer, improving the wettability of the electrode, thereby improving the charge and discharge efficiency of the battery and reducing the increase in resistance caused by electrolyte accumulation on the electrode surface.

[0013] Where OI=I(004) / I(110), I(004) is the integral area of ​​the diffraction peak of the (004) crystal plane, and I(110) is the integral area of ​​the diffraction peak of the (110) crystal plane.

[0014] Xc=Ic / (Ic+Ia), where Ic is the diffraction integral intensity of the crystalline part and Ia is the scattering integral intensity of the amorphous part.

[0015] According to some embodiments of the present invention, the active material of the first electrode is graphite.

[0016] According to some embodiments of the present invention, the graphite includes at least one of artificial graphite and natural graphite.

[0017] According to some embodiments of the present invention, the second electrode active material is an amorphous crystalline silicon-based material.

[0018] According to some embodiments of the present invention, the amorphous crystalline silicon-based material includes at least one of silicon, silicon-carbon, silicon-oxygen, and silicon alloys.

[0019] According to some embodiments of the present invention, L is 2 to 12, for example, it can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12.

[0020] According to some embodiments of the present invention, Xc is 20.6% to 62.8%.

[0021] Preferably, the Xc is 29.8% to 62.8%.

[0022] According to some embodiments of the present invention, H is 25–70 μm.

[0023] Preferably, H is 35–50 μm.

[0024] According to some embodiments of the present invention, the particle size D50 of the first electrode active material is 11-17 μm.

[0025] Preferably, the particle size D50 of the first electrode active material is 15-17 μm.

[0026] According to some embodiments of the present invention, the particle size D50 of the second electrode active material is 5.5 to 11 μm.

[0027] Preferably, the particle size D50 of the second electrode active material is 8–10 μm.

[0028] According to some embodiments of the present invention, the difference in particle size D50 between the first electrode active material and the second electrode active material is 2 to 8 μm, and the particle size of the first electrode active material is larger than that of the second electrode active material.

[0029] When used in combination, the active material of the second electrode can effectively fill the voids in the active material of the first electrode, increasing the compaction density of the negative electrode. This not only increases the volumetric energy density of the electrode but also reduces compaction rebound, thereby improving the battery's energy output. If the graphite particle size is smaller than that of silicon particles, the graphite particles are embedded between the silicon particles, failing to effectively restrict the lithium intercalation expansion of the silicon particles. Furthermore, the compaction density of small-diameter graphite is relatively low, which is detrimental to the battery's energy density.

[0030] According to some embodiments of the present invention, the anode active material comprises, by mass percentage: 70% to 97% of the first electrode active material and 3% to 30% of the second electrode active material.

[0031] According to some embodiments of the present invention, the mass ratio of the first electrode active material to the second electrode active material is 9:1 to 7:3; for example, it can be 9:1, 8:2, or 7:3.

[0032] According to some embodiments of the present invention, the grain size of the second electrode active material is 10-17 nm.

[0033] The grain size of this invention affects charge-discharge performance. Smaller grains result in shorter lithium-ion insertion channels, which is more conducive to the alloying of silicon and lithium, allowing them to quickly reach a fully intercalated lithium state and thus exhibiting better charge-discharge performance. Grain size also affects cycle performance. Smaller grains can exhibit better electrochemical performance, slowing down the volume expansion and contraction of silicon particles during lithium intercalation and deintercalation, avoiding material crack propagation and pulverization, and thus affecting cycle life.

[0034] According to some embodiments of the present invention, the full width at half maximum (FWHM) of the XRD (111) diffraction peak of the second electrode active material is 0.4 to 0.75.

[0035] The full width at half maximum (FWHM) of a crystal diffraction peak mainly relates to the crystallinity of the material; the smaller the FWHM, the higher the crystallinity.

[0036] According to some embodiments of the present invention, the negative electrode further includes a current collector disposed between the active materials of the first electrode and the active materials of the second electrode.

[0037] According to an embodiment of a second aspect of the present invention, a lithium-ion battery is provided, comprising the aforementioned negative electrode sheet.

[0038] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0039] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0040] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0041] Figure 1 This is a structural diagram of the active material of the electrode in Example 1 of the present invention. Detailed Implementation

[0042] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0043] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0044] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0045] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0046] In this invention, in order to achieve a specific crystallinity of the amorphous silicon-based material for the second electrode active material and the OI value of the first anode active material, the following preparation and control methods were adopted:

[0047] In practice, the preparation method for silicon-based materials is not strictly limited, and various methods well-known to those skilled in the art can be used, including but not limited to chemical vapor deposition, mechanical alloying, solution methods, high-temperature pyrolysis, and mechanical ball milling. The following is a specific example of preparation and control:

[0048] Polyphenolic resin was dissolved in acetone at a ratio of 50:50. An 85% (w / w) aqueous solution of phosphoric acid was added to the solution and shaken. The reaction solution was placed at 55°C for 12 hours, then cured at 120°C for 6 hours, followed by pyrolysis carbonization at 800°C under nitrogen protection. The carbonized carbon matrix was then activated under nitrogen protection by heating to 800°C at a rate of 150°C / h and introducing steam (0.3–5 mL / min) for 80–100 minutes. The particle size was adjusted using a crusher according to the target material size to obtain a carbon matrix of a specific particle size. The carbon matrix was placed in a tube furnace, and silane gas was introduced, with nitrogen used as a carrier gas and dilution gas. The carbon matrix was decomposed at 400–800°C to produce gaseous silicon, yielding silicon-based materials. Different degrees of crystallinity in silicon-based materials can be obtained by adjusting the decomposition temperature.

[0049] In practice, the OI value of graphite is controlled during the secondary particle coating stage at the supplier.

[0050] Example 1

[0051] This embodiment provides a negative electrode sheet, the active material of which has the following characteristics:

[0052] L represents the OI value of the first electrode active material as 2; Xc represents the crystallinity of the second electrode active material as 29.8; H represents the thickness of the anode active material as 35 μm; satisfying L*Xc / H=1.70;

[0053] The first electrode active material is graphite with a particle size D50 of 15 μm, and the second electrode active material is silicon with a particle size D50 of 8 μm; the results for the electrode active materials are as follows: Figure 1 As shown.

[0054] This embodiment also provides a method for preparing the above-mentioned negative electrode sheet: the electrode active material, conductive agent (SP and CNT mixed in a mass ratio of 0.45:0.05), and binder (SBR and PAALi mixed in a mass ratio of 0.5:1.8) are mixed in a weight ratio of 97.7:1.1:1.2 to obtain an anode active material slurry that is uniformly coated on both sides of the negative current collector, and then cold-pressed and slit to obtain the negative electrode sheet.

[0055] This embodiment also provides a lithium-ion battery, the specific preparation method of which includes:

[0056] Positive electrode sheet: The cathode active material LiCoO2, conductive agent acetylene black, conductive carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are fully dispersed and uniformly coated on both sides of the positive electrode current collector in an N-methylpyrrolidone solvent system at a weight ratio of 97.6:0.5:0.6:1.3.

[0057] Separator: A ceramic mixture is coated on the PE surface to serve as a separator.

[0058] Electrolyte: Ethyl carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed in a volume ratio of 1.2:1:4:4. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare the electrolyte.

[0059] Full cell preparation: The above-mentioned positive electrode sheet, separator, and negative electrode sheet are wound or stacked to make a bare cell, and then packaged and injected with electrolyte to make a finished lithium-ion battery.

[0060] The characteristics of the active materials of the electrodes in Examples 2-8 and Comparative Examples 1-4 are shown in Table 1, and the rest are the same as in Example 1.

[0061] Table 1. Characteristics of the active materials in the electrode sheets of Examples 2-8 and Comparative Examples 1-4

[0062]

[0063]

[0064] Performance testing:

[0065] Compacted density:

[0066] The electrode sheet is placed in a rolling mill, and the thickness of the electrode sheet is adjusted by adjusting the rolling pressure. The compaction density is β, the mass of the negative electrode active material is M, the force-bearing area of ​​the negative electrode active material is S, and the thickness of the electrode sample after rolling is H. The formula for calculating the compaction density is as follows: β=M / (S×H).

[0067] Loop testing method:

[0068] In a 25℃ environment, perform cyclic testing according to the following methods: charging mode: 2.8C CC to 4.25V, 2C CC to 4.35V, CV to 1.8C, 1.8C CC to 4.4V, CV to 1.5C, 1.5C CC to 4.5V, CV to 1.2C, 1.2C CC to 4.55V, CV to 0.26C; discharging mode: 0.7C DC to 3.0V.

[0069] Where Fading is the capacity retention rate and Swelling is the thickness expansion rate; the calculation formula is as follows:

[0070] 500-week Fading = Discharge capacity in week 500 / Discharge capacity in week 1 * 100%;

[0071] 500-week Swelling = Discharge thickness in week 500 / Discharge thickness in week 1 * 100%;

[0072] DCR test:

[0073] The battery was charged to 4.5V at 0.5C, with a cutoff current of 0.02C, and left to stand for 5 minutes; then discharged at 1A for 500ms.

[0074] DCR = (Voltage before discharge - Voltage after discharge) / Current;

[0075] The performance test results of the embodiments and comparative examples of the present invention are shown in Table 2.

[0076] Table 2 Performance test results of the examples and comparative examples

[0077]

[0078]

[0079] As shown in Table 2, the lithium-ion batteries of the embodiments of the present invention exhibit good performance in terms of capacity retention (fading) and battery swelling (swelling) during 500-cycle testing. For example, the swelling of Example 10 after 500 cycles is 7.77%, and the fading is 89.34%. Compared with the poor performance of the comparative examples (e.g., the swelling of Comparative Example 7 is 20.57%, and the fading is 72.55%), this indicates that the active material combination of the present invention can effectively suppress battery capacity decay and swelling. The present invention maintains good resistance characteristics while improving cycle performance. The relatively low DCR test results in the embodiments indicate that, based on the optimized design of the negative electrode material, the internal resistance can be effectively reduced, ensuring the performance stability of the battery under high power conditions. By controlling the particle size and coating thickness of the materials, the compaction density of the present invention is between 1.6 and 1.72 g / cm³. 3 Compared to the comparative example, this invention achieves a higher energy density, indicating that it not only optimizes cycle stability but also improves the battery's energy storage capacity. Experiments demonstrate that the L*Xc / H ratio of the anode active material significantly impacts the final battery performance, and the appropriate L*Xc / H ratios in the examples (such as 3.53 in Example 7 and 7.15 in Example 10) resulted in better electrochemical performance.

[0080] Therefore, it can be seen that the anode active material of the present invention can significantly improve the cycle performance of lithium-ion batteries in the negative electrode sheet, solve the battery failure problem caused by the expansion and deformation of the negative electrode sheet, and the battery cell also has good conductivity and good energy density.

[0081] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode includes a first electrode active material and a second electrode active material; The first electrode active material and the second electrode active material satisfy the following relationship: 1≤L*Xc / H≤25; L represents the OI value of the first electrode active material, Xc represents the crystallinity of the second electrode active material, and H is the thickness of the anode active material; L is 2~12; Xc is 20.6%~62.8%; the particle size D50 of the first electrode active material is 11~17μm; the particle size D50 of the second electrode active material is 5.5~11μm; the first electrode active material is graphite; the second electrode active material is an amorphous crystalline silicon-based material.

2. The negative electrode sheet according to claim 1, characterized in that, The amorphous crystalline silicon-based material includes at least one of silicon, silicon-carbon, silicon-oxygen, and silicon alloys.

3. The negative electrode sheet according to claim 1, characterized in that, The H value is 25~70μm.

4. The negative electrode sheet according to claim 1, characterized in that, The difference in particle size D50 between the first electrode active material and the second electrode active material is 2~8μm, and the particle size of the first electrode active material is larger than that of the second electrode active material.

5. The negative electrode sheet according to claim 1, characterized in that, The anode active material comprises, by mass percentage: 70% to 97% of the first electrode active material and 3% to 30% of the second electrode active material.

6. The negative electrode sheet according to claim 1 or 2, characterized in that, The grain size of the second electrode active material is 10~17nm.

7. The negative electrode sheet according to claim 1, characterized in that, The negative electrode also includes a current collector coated with the active material of the first electrode and the active material of the second electrode.

8. A lithium-ion battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1 to 7.

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