Lithium-ion battery and electric device comprising the same

Abstract

The application provides a lithium ion battery and an electric device comprising the same, and relates to the technical field of lithium ion batteries. The lithium ion battery adopts nitrogen and boron doped graphite material as a negative active material. The technical scheme of the above-mentioned nitrogen and boron synergistic doping can effectively improve the fast charging capacity of the graphite and enhance the interface stability. Meanwhile, the application also optimizes and adjusts the characteristic peak intensity of the negative active material through an X-ray photoelectron spectroscopy characteristic peak intensity relationship and a Raman spectrogram characteristic peak intensity relationship, effectively improving the rate charging performance, low temperature performance and cycle performance of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a lithium-ion battery and an electrical device comprising the same. Background Technology

[0002] With the rapid development of electric vehicles, smart grids, and portable electronic devices, the market has set higher standards for the performance of lithium-ion batteries, including higher energy density, faster charging speed, lower operating temperature, and longer cycle life. Graphite is currently the most widely used commercial anode material; however, it has significant performance bottlenecks under fast charging and low-temperature conditions, mainly reflected in: (1) a low lithium-ion diffusion rate, which leads to increased polarization during fast charging; (2) low electronic conductivity, which limits the efficient transport of electrons between particles; and (3) at low temperatures, lithium-ion insertion / extraction kinetics are hindered, resulting in a significant decrease in charge / discharge capacity.

[0003] To address the shortcomings of graphite's performance under fast charging and low-temperature conditions, traditional modification methods mainly focus on controlling the size and morphology of graphite particles and coating the graphite surface with a conductive carbon layer. However, while these traditional modification methods have improved graphite's fast charging and low-temperature performance to some extent, they still have some limitations. For example, excessively reducing the particle size can lead to an excessively large specific surface area, increasing side reactions; and precisely controlling the thickness of the carbon coating is quite difficult.

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

[0005] The primary objective of this invention is to provide a lithium-ion battery that, through improvements to the negative electrode active material, effectively enhances the rate charging performance, low-temperature performance, and cycle performance of the lithium-ion battery.

[0006] A second objective of the present invention is to provide an electrical device comprising the aforementioned lithium-ion battery.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0008] The present invention provides a lithium-ion battery, wherein the negative electrode active material in the negative electrode coating material of the lithium-ion battery is a nitrogen and boron doped graphite material.

[0009] The negative electrode active material simultaneously satisfies the following relationships between the characteristic peak intensities of X-ray photoelectron spectroscopy and Raman spectroscopy, wherein:

[0010] The characteristic peak intensities of the X-ray photoelectron spectroscopy of the negative electrode active material satisfy the following relationship: 0.02 ≤ I B / I C ≤0.45; 0.02≤IN / I C ≤0.4;

[0011] In the formula: I B The intensity of the B1s characteristic peak in the XPS spectrum representing the negative electrode active material; the binding energy range of the B1s characteristic peak is 186.0 eV to 196.5 eV; I N The intensity of the N1s characteristic peak in the XPS spectrum representing the active substance; the binding energy range of the N1s characteristic peak is 395.0 eV to 406.5 eV; I C The intensity of the C1s characteristic peak in the XPS spectrum representing the active substance; the binding energy range of the C1s characteristic peak is 282.0 eV to 285.5 eV.

[0012] The Raman spectrum characteristic peak intensities of the negative electrode active material satisfy the following relationship: 0.05 ≤ I D / I G ≤1.0;

[0013] In the formula: I D Raman spectra representing the negative electrode active material (1348-1353 cm⁻¹) -1 The intensity of peak D in (I); G Raman spectra representing the negative electrode active material (1578-1583 cm⁻¹) -1 The intensity of peak G in ().

[0014] Furthermore, the negative electrode active material is mainly obtained by granulation of nitrogen precursor, boron precursor and graphite;

[0015] The total amount of nitrogen precursor and boron precursor to graphite is in a mass ratio of 2 to 10:100.

[0016] The mass ratio of the nitrogen precursor to the boron precursor is 0.5-2:1, preferably 1:1.

[0017] Furthermore, the preparation method of the negative electrode active material includes: mixing nitrogen precursor, boron precursor and graphite according to the ratio, and carrying out a pyrolysis reaction at 300℃~400℃ to obtain intermediate material; then ball milling the intermediate material and graphitizing it at 2500~3000℃ to obtain the negative electrode active material.

[0018] Furthermore, the preparation method of the negative electrode active material also includes: treating the obtained negative electrode active material using a potassium hydroxide etching method to increase the number of pores.

[0019] Preferably, the potassium hydroxide etching method includes the following steps: First, the negative electrode active material (the nitrogen- and boron-doped graphite material of this application) is mixed with a 7M KOH solution and stirred at 400 rpm for 1–16 h. After vacuum drying, it is transferred to a tube furnace and pyrolyzed by step heating under nitrogen protection for 1 h. Finally, by-products are removed by water washing to obtain graphite with small changes in interlayer spacing and specific surface area and a porous structure.

[0020] Preferably, the negative electrode active material is mixed with 7M KOH solution and stirred at 400 rpm for 2-4 hours.

[0021] Furthermore, the D50 particle size of the negative electrode active material is 5–16 μm.

[0022] Furthermore, the compaction density of the negative electrode sheet is 1.2–1.75 g / cm³. 3 .

[0023] Furthermore, the raw materials for preparing the negative electrode coating material include: the above-mentioned nitrogen and boron doped graphite material, conductive agent, and binder.

[0024] Furthermore, the conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon black.

[0025] Furthermore, the adhesive includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid, and styrene-butadiene rubber.

[0026] The present invention provides an electrical device, the electrical device comprising the aforementioned lithium-ion battery.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The lithium-ion battery provided in this application uses nitrogen- and boron-doped graphite as the negative electrode active material. Nitrogen doping introduces additional electron donors, significantly improving the electronic conductivity of graphite and introducing defect sites in the graphite lattice, thereby enhancing the adsorption capacity and diffusion kinetics of lithium ions. Boron doping, by modulating the electronic structure of graphite, lowers the energy barrier for lithium-ion insertion / extraction and further optimizes the material's kinetic performance. Therefore, the nitrogen- and boron co-doping of this application not only significantly improves the fast-charging capability of graphite but also enhances its interfacial stability, demonstrating significant technical advantages and application prospects.

[0029] Meanwhile, this application also optimized and adjusted the characteristic peak intensity of the negative electrode active material through the characteristic peak intensity relationship of X-ray photoelectron energy spectrum and Raman spectrum, which effectively improved the rate charging performance, low temperature performance and cycle performance of the lithium-ion battery. Attached Figure Description

[0030] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 XPS spectrum of lithium-ion battery prepared in Example 8 of this invention;

[0032] Figure 2 The Raman spectrum of the lithium-ion battery prepared in Example 8 of this invention. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] According to one aspect of the present invention, a lithium-ion battery, wherein the negative electrode active material in the negative electrode coating material of the lithium-ion battery is a nitrogen- and boron-doped graphite material;

[0035] The negative electrode active material simultaneously satisfies the following relationships between the characteristic peak intensities of X-ray photoelectron spectroscopy and Raman spectroscopy, wherein:

[0036] The characteristic peak intensities of the X-ray photoelectron spectroscopy of the negative electrode active material satisfy the following relationship: 0.02 ≤ I B / I C ≤0.45; 0.02≤I N / I C ≤0.4;

[0037] In the formula: I B The intensity of the B1s characteristic peak in the XPS spectrum representing the negative electrode active material; the binding energy range of the B1s characteristic peak is 186.0 eV to 196.5 eV; I N The intensity of the N1s characteristic peak in the XPS spectrum representing the active substance; the binding energy range of the N1s characteristic peak is 395.0 eV to 406.5 eV; I C The intensity of the C1s characteristic peak in the XPS spectrum representing the active substance; the binding energy range of the C1s characteristic peak is 282.0 eV to 285.5 eV.

[0038] The Raman spectrum characteristic peak intensities of the negative electrode active material satisfy the following relationship: 0.05 ≤ I D / I G ≤1.0;

[0039] In the formula: I D The D peak (~1350 cm⁻¹) in the Raman spectrum representing the negative electrode active material -1 The strength of ); I G The G peak (~1580 cm⁻¹) in the Raman spectrum representing the negative electrode active material -1 The intensity of ).

[0040] The lithium-ion battery provided in this application uses nitrogen- and boron-doped graphite as the negative electrode active material. Nitrogen doping introduces additional electron donors, significantly improving the electronic conductivity of graphite and introducing defect sites in the graphite lattice, thereby enhancing the adsorption capacity and diffusion kinetics of lithium ions. Boron doping, by regulating the electronic structure of graphite, lowers the energy barrier for lithium-ion insertion / extraction and further optimizes the material's kinetic performance. The synergistic effect of nitrogen and boron doping in this application not only significantly improves the fast-charging capability of graphite but also enhances its interfacial stability, demonstrating significant technical advantages and application prospects.

[0041] Meanwhile, this application also optimized and adjusted the characteristic peak intensity of the negative electrode active material through the above-mentioned X-ray photoelectron energy spectrum characteristic peak intensity relationship and Raman spectrum characteristic peak intensity relationship, which effectively improved the rate charging performance, low temperature performance and cycle performance of the lithium-ion battery.

[0042] In a preferred embodiment of the present invention, the negative electrode active material is mainly obtained by granulation of nitrogen precursor, boron precursor and graphite;

[0043] The total amount of nitrogen precursor and boron precursor to graphite is in a mass ratio of 2 to 10:100.

[0044] The mass ratio of the nitrogen precursor to the boron precursor is 1:1.

[0045] In a preferred embodiment of the present invention, the method for preparing the negative electrode active material includes: mixing nitrogen precursor, boron precursor and graphite in a certain ratio, and carrying out a pyrolysis reaction at 300℃ to 400℃ to obtain an intermediate material; subsequently, ball milling the intermediate material and then graphitizing it at 2500℃ to 3000℃ to obtain the negative electrode active material.

[0046] In a preferred embodiment of the present invention, the method for preparing the negative electrode active material further includes: treating the obtained negative electrode active material using a potassium hydroxide etching method to increase the number of pores.

[0047] In a preferred embodiment of the present invention, the diffraction peak range corresponding to the (002) crystal plane in the X-ray diffraction (XRD) spectrum of the negative electrode active material is between 23.5° and 25.5°.

[0048] In a preferred embodiment of the present invention, the D50 particle size of the negative electrode active material is 5-16 μm.

[0049] In a preferred embodiment of the present invention, the compaction density of the negative electrode sheet is 1.2–1.75 g / cm³. 3 .

[0050] In a preferred embodiment of the present invention, the charging characteristics of the lithium-ion battery are as follows: after discharging the lithium-ion battery to 2.5V at 25°C and letting it stand for 6 hours, it is charged to 4.2V at constant current with charging rates of 1C and 10C, respectively. The corresponding constant current charging capacities are Q1 and Q10, wherein the charging capacity is maintained to satisfy Q10 / Q1≥60%.

[0051] In a preferred embodiment of the present invention, after 1000 cycles at 25°C and a 1C rate, the capacity decay rate is less than 18.5%.

[0052] In a preferred embodiment of the present invention, the lithium-ion battery exhibits an ID / IG value change rate of ≤10% after 1000 cycles at 1C.

[0053] In a preferred embodiment of the present invention, the raw materials for preparing the negative electrode coating material include: the above-mentioned nitrogen and boron doped graphite material, conductive agent and binder.

[0054] In the preferred embodiments described above, the graphite is one or more of artificial graphite, natural graphite, soft carbon, or hard carbon.

[0055] In the preferred embodiments described above, the conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon black.

[0056] In the preferred embodiments described above, the adhesive includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid, and styrene-butadiene rubber.

[0057] Furthermore, the lithium-ion battery also includes an electrolyte and a positive electrode material.

[0058] The electrolyte comprises a lithium salt, a solvent, and additives. The lithium salt comprises one or more combinations of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium difluorosulfonylimide, lithium difluorophosphate, lithium difluorooxalate borate, and lithium bis(trifluoromethanesulfonylimide); the solvent comprises one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and methyl ethyl carbonate; and the additives comprise one or more of fluoroethylene carbonate, difluoroethylene carbonate, ethylene sulfate, ethylene sulfite, vinylene carbonate, and vinyl carbonate.

[0059] The positive electrode includes a positive current collector and a positive electrode coating having at least one layer containing a positive active material; the positive active material includes lithium nickel cobalt manganese oxide (Li1Ni). x Co y Mn z M b O2) and lithium iron phosphate, wherein 0.70≤x≤0.95, 0.15≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1, and element M includes one or more of zirconium (Zr), tungsten (W), titanium (Ti), aluminum (Al), strontium (Sr), boron (B) and neodymium (Nd).

[0060] The ratio N / P of the capacity N of the negative electrode to the capacity P of the positive electrode is between 1.02 and 1.18.

[0061] According to one aspect of the present invention, an electrical device includes the aforementioned lithium-ion battery.

[0062] The electrical device provided by the present invention includes the above-mentioned lithium-ion battery. Due to the performance of the lithium-ion battery, the electrical device has better rate charging performance, low temperature performance and cycle performance.

[0063] The technical solution of the present invention will be further described below with reference to the embodiments.

[0064] Example 1

[0065] A lithium-ion battery, the method for preparing the lithium-ion battery comprising the following steps:

[0066] (1) Method for manufacturing positive electrode plates:

[0067] Take the positive electrode active material (Li1Ni) 0.8 Co 0.1 Mn 0.1O2), conductive carbon black, carbon nanotubes and polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96:1:1:2 to obtain a positive electrode coating material. The positive electrode coating material was then coated onto a 12.0 μm thick aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained.

[0068] (2) Method for manufacturing the negative electrode:

[0069] The negative electrode sheet includes a negative current collector copper foil and a negative electrode coating material coated on both sides of the copper foil. Calculated by mass percentage, the negative electrode coating material includes 96.0% nitrogen and boron co-doped graphite (graphite@NB-2%, D50 is 4.2μm), 1.5% carbon nanotubes, 1.0% thickener sodium carboxymethyl cellulose (CMC), and 1.5% binder polyacrylic acid (PAA). The above substances are added to deionized water and stirred to form the negative electrode coating material with a solid content of 40%. Then, the negative electrode coating material is coated on both sides of the negative current collector (copper foil), and after drying and cold pressing, a negative electrode sheet is formed with a compaction density of 1.5 g / cm3.

[0070] Preparation method of nitrogen and boron doped graphite (graphite@NB-2%):

[0071] 1. Preprocessing stage:

[0072] After mixing the graphite raw material needle coke and pitch at a mixing mass percentage of 100:10, the mixture is subjected to air jet milling to grind the raw and auxiliary materials with a particle size of 5-10mm to 3-10μm. The target particles are then collected using a cyclone dust collector.

[0073] 2. Granulation stage:

[0074] Pyrolysis process: Take the above materials and add nitrogen and boron doped precursors, mixing them in a mass percentage ratio of urea (N precursor): boric acid (B precursor): graphite = 1:1:100. Purge air into the reactor with nitrogen, heat to 300℃ under a certain pressure and stir for 2 hours, then continue heating to 400℃ with continuous stirring to partially decompose the N and B precursors and initially incorporate them into the carbon material, forming a material with a particle size of 10-20 mm. After cooling, an intermediate material is obtained.

[0075] Ball milling and screening process: The above materials are ground into particles of 6-10 μm using a mechanical ball mill and then screened by a screening machine.

[0076] 3. Graphitization stage: The screened materials are subjected to high-temperature graphitization (2500-3000℃). Under high temperature, N and B elements are further doped into the graphite lattice, improving the doping uniformity and the conductivity of the material.

[0077] 4. Ball milling and sieving stage: The graphitized material is physically mixed, ground and sieved. The undersize material is used as the final nitrogen and boron co-doped graphite material, namely graphite@NB-2%. Here, 2.0% represents the percentage of urea and boric acid in the total mass of graphite, urea and boric acid, and the mass percentage of urea and boric acid is 1:1.

[0078] (3) Preparation of electrolyte:

[0079] The additives are lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), and vinylene carbonate (VC).

[0080] The electrolyte is obtained by mixing the components in a mass percentage ratio of 10.0:22.0:53.0:3.0:7.0:5.0.

[0081] (4) Diaphragm:

[0082] A high-porosity membrane is selected, in which the thickness of the PE base membrane is 9μm, the thickness of the ceramic coating on both sides of the base membrane is 1.0μm, and the thickness of the PVDF coating is 1.0μm.

[0083] (5) Assembly of lithium-ion batteries:

[0084] After the positive and negative electrode sheets are rolled and slit, they are wound together with the separator according to a set process to form a 21700 cylindrical battery core. Subsequently, the battery core is fixed to a pre-made connecting piece by welding and then installed into a metal battery casing. After completing key processes such as electrolyte injection, sealing, and formation, the lithium-ion battery described in Example 1 is obtained. This lithium-ion battery uses a cylindrical casing with an external dimension of 21.0 mm in diameter and 70.0 mm in length, conforming to the 21700 standard specification.

[0085] Example 2

[0086] The difference between this embodiment and embodiment 1 is that, in step (2) during the negative electrode fabrication process, the total mass percentage of urea and boric acid added is 4%, i.e., graphite@NB-4%, while the rest is the same as in embodiment 1.

[0087] The preparation method of the nitrogen and boron doped graphite (graphite@NB-4%) is as described in Example 1.

[0088] Example 3

[0089] The difference between this embodiment and embodiment 1 is that, in step (2) during the negative electrode fabrication process, the total mass percentage of urea and boric acid added is 6%, i.e., graphite@NB-6%, while the rest is the same as in embodiment 1.

[0090] The preparation method of the nitrogen and boron doped graphite (graphite@NB-6%) is as described in Example 1.

[0091] Example 4

[0092] The difference between this embodiment and embodiment 1 is that, in step (2) during the negative electrode fabrication process, the total mass percentage of urea and boric acid added is 8%, i.e., graphite@NB-8%, while the rest is the same as in embodiment 1.

[0093] The preparation method of the nitrogen and boron doped graphite (graphite@NB-8%) is as described in Example 1.

[0094] Example 5

[0095] The difference between this embodiment and embodiment 1 is that, in step (2) of the negative electrode fabrication process, the total mass percentage of urea and boric acid added is 10%, i.e., graphite@NB-10%, while the rest is the same as in embodiment 1.

[0096] The preparation method of the nitrogen and boron doped graphite (graphite@NB-10%) is as described in Example 1.

[0097] Example 6

[0098] The difference between this embodiment and Embodiment 3 is that, in step (2) of the negative electrode fabrication process, a step is added where nitrogen and boron doped graphite (graphite@NB-4%) is treated with potassium hydroxide etching for 1 hour to increase the number of pores. That is, nitrogen and boron doped graphite (graphite@NB-4%) is added as a raw material after being treated with potassium hydroxide etching, and everything else is the same as in Embodiment 3.

[0099] The potassium hydroxide etching method involves the following steps: First, graphite@NB-4% is mixed with 7M KOH solution and stirred at 400 rpm for 1 hour. After vacuum drying, it is transferred to a tube furnace and pyrolyzed under nitrogen protection by stepwise heating for 1 hour (200℃ for dehydration, 800℃ for alkaline etching to create pores). Finally, by-products are removed by water washing, resulting in graphite with small changes in interlayer spacing and specific surface area, and a porous structure.

[0100] Principle: During heat treatment at 800℃, KOH reacts with carbon (4KOH+C→K2CO3+K2O+2H2↑), generating nanoscale pores while retaining a layered framework.

[0101] Example 7

[0102] The difference between this embodiment and embodiment 3 is that, in step (2) of the negative electrode fabrication process, a step is added to treat nitrogen and boron doped graphite (graphite@NB-4%) with potassium hydroxide etching for 2 hours to increase the number of channels. All other steps are the same as in embodiment 3.

[0103] Example 8

[0104] The difference between this embodiment and embodiment 3 is that, in step (2) of the negative electrode fabrication process, a step is added to treat nitrogen and boron doped graphite (graphite@NB-4%) with potassium hydroxide etching for 4 hours to increase the number of channels. All other steps are the same as in embodiment 3.

[0105] Example 9

[0106] The difference between this embodiment and embodiment 3 is that, in step (2) of the negative electrode fabrication process, a step is added to treat nitrogen and boron doped graphite (graphite@NB-4%) with potassium hydroxide etching for 8 hours to increase the number of channels. All other steps are the same as in embodiment 3.

[0107] Example 10

[0108] The difference between this embodiment and embodiment 3 is that, in step (2) of the negative electrode fabrication process, a step is added to treat nitrogen and boron doped graphite (graphite@NB-4%) with potassium hydroxide etching for 16 hours to increase the number of channels. All other steps are the same as in embodiment 3.

[0109] Example 11

[0110] The difference between this embodiment and Embodiment 8 is that the compaction density of the negative electrode sheet is 1.3 g / cm³. 3 Everything else is the same as in Example 8.

[0111] Example 12

[0112] The difference between this embodiment and Embodiment 8 is that the compaction density of the negative electrode sheet is 1.7 g / cm³. 3 Everything else is the same as in Example 8.

[0113] Example 13

[0114] The difference between this embodiment and Example 8 is that the D50 of the negative electrode active material graphite@NB-4% is 1.4 μm, while all other aspects are the same as in Example 8.

[0115] Example 14

[0116] The difference between this embodiment and Example 8 is that the D50 of the negative electrode active material graphite@NB-4% is 2.8 μm, while all other aspects are the same as in Example 8.

[0117] Example 15

[0118] The difference between this embodiment and Example 8 is that the D50 of the negative electrode active material graphite@NB-4% is 10.5 μm, while all other aspects are the same as in Example 8.

[0119] Example 16

[0120] The difference between this embodiment and embodiment 1 is that, in step (2) during the negative electrode fabrication process, the total mass percentage of urea and boric acid added is 12%, i.e., graphite@NB-12%, while the rest is the same as in embodiment 1.

[0121] The preparation method of the nitrogen and boron doped graphite (graphite@NB-12%) is as described in Example 1.

[0122] Example 17

[0123] The difference between this embodiment and embodiment 3 is that, in step (2) during the negative electrode fabrication process, the total mass percentage of urea and boric acid added is 6%, i.e., graphite@NB-6%, while the rest is the same as in embodiment 1.

[0124] The preparation method of the nitrogen and boron doped graphite (graphite@NB-12%) is carried out in accordance with Example 3, and the mass ratio of the nitrogen precursor to the boron precursor is 2:1.

[0125] Example 18

[0126] The difference between this embodiment and embodiment 3 is that, in step (2) during the negative electrode fabrication process, the total mass percentage of urea and boric acid added is 6%, i.e., graphite@NB-6%, while the rest is the same as in embodiment 3.

[0127] The preparation method of the nitrogen and boron doped graphite (graphite@NB-12%) is carried out in accordance with Example 1, and the mass ratio of the nitrogen precursor to the boron precursor is 1:2.

[0128] Comparative Example 1

[0129] The difference between this comparative example and Example 8 is that the graphite added was not doped with nitrogen or boron, while everything else is the same as in Example 8.

[0130] Comparative Example 2

[0131] The difference between this comparative example and Example 8 is that the graphite added is only nitrogen-doped, and the total mass percentage of urea added is 3%, i.e., graphite@N-3%. Everything else is the same as in Example 8.

[0132] Comparative Example 3

[0133] The difference between this comparative example and Example 8 is that the graphite added is only boron-doped, and the total mass percentage of boric acid added is 3%, i.e., graphite@B-3%. Everything else is the same as in Example 8.

[0134] Test methods

[0135] The specific method is as follows:

[0136] First, discharge the lithium-ion battery to a constant current of 2.5V to ensure it is in a safe state, reducing the risk of short circuits or thermal runaway during disassembly. Carefully disassemble the battery within a glove box (protected by argon or other inert atmosphere) and remove the negative electrode from the cylindrical cell. Use tweezers or a suitable tool to peel off the electrode, avoiding damage to the active material layer. Next, cut the removed positive electrode to an appropriate size and soak it in anhydrous dimethyl carbonate (DMC) solution for 30 minutes to dissolve and remove residual electrolyte and possible byproducts. After removing the electrode, gently wipe the surface with lint-free paper, then replace with fresh DMC solution, repeating the soaking-wiping process three times to ensure no residual contaminants remain on the electrode surface. Subsequently, rinse the electrode with anhydrous ethanol and wipe again to further remove solvent and impurities. After cleaning, place the electrode in a glove box and let it stand for 48 hours to ensure it is completely dry, preventing interference from residual solvent in subsequent testing. After drying, the negative electrode active material layer is gently scraped off using a plastic scraper or blade, ensuring the collected powder is uncontaminated. The scraped powder is transferred to a centrifuge tube containing anhydrous ethanol and ultrasonically dispersed for 30 minutes in an ultrasonic cleaner to further remove any possible residual electrolyte, binder, and impurities. After ultrasonic treatment, the sample is centrifuged (at 5000 rpm for 2 minutes), the supernatant is discarded, and the powder is redispersed with anhydrous ethanol, ultrasonicated again for 10 minutes, and then centrifuged again. This process is repeated three times to ensure the purity of the powder sample. Finally, the precipitate is collected and transferred to a vacuum drying oven and dried at 80°C for 12 hours to ensure complete removal of residual solvent.

[0137] After drying, the powder is placed in a sealed bag or sealed sample box, immediately removed from the glove box, and the sample is quickly subjected to XPS, Raman, XRD, and active material particle D50 tests.

[0138] 1. Specific method for determining the intensity (height) of elemental characteristic peaks in XPS spectra: XPS testing was performed using a PHI-5000 Versa Probe instrument, with Al Kα (1486.6 eV) as the X-ray source and a power of 150 W (15 kV × 10 mA). The test included full-spectrum scanning (0–1100 eV, step size 1 eV), background subtraction was performed using Shirley background correction, and C1s (284.8 eV) was used as an internal standard for data normalization and elemental quantitative analysis. Ig was calculated. B / I C Value and I N / I C value.

[0139] 2. Raman Measurement Method: A 532nm laser was used as the excitation source, with the laser power set to 1-5mW to avoid sample ablation. The sample was uniformly dispersed on a silicon substrate. Raman spectra were acquired in the range of 500-1500cm⁻¹, with a spectral resolution set to 1cm⁻¹. 3-5 scans were performed cumulatively to improve the signal-to-noise ratio. The instrument used an XYZ automatic displacement platform for precise focusing, and the silicon wafer (520.7cm⁻¹) was calibrated before testing to ensure data accuracy. I₀ was calculated. D / I G The Ig value was determined using the method described above for the initial lithium-ion battery negative electrode active material. D / I G The value and the ID / IG value after 1000 cycles.

[0140] 3. Specific methods for determining the D50 of negative electrode active material particles:

[0141] Take a small amount of powder and spread it evenly on conductive tape. Then, take clear particle images of at least 5 different regions under a scanning electron microscope (SEM). Import the images using ImageJ or Nanomeasure software, calibrate the scale, and manually or automatically measure the projected diameter of more than 200 particles. Arrange the data in ascending order and plot the cumulative distribution curve. Take the particle size value corresponding to 50% of the cumulative percentage as D50. At the same time, it is necessary to exclude the interference data of obvious agglomerates to ensure accuracy.

[0142] 4. Test method for compacted density of negative electrode sheet:

[0143] First, the negative electrode sheet, after being washed with dimethyl carbonate and vacuum dried, was cut into six standard-sized square samples (2.0cm × 2.0cm). Next, the active material on both sides of three of these square samples was removed, and they were rinsed with ethanol, dried, weighed, and their average mass M1 was calculated. Simultaneously, the average thickness L1 of the samples was measured using a micrometer. Then, the mass of the remaining three square samples was weighed, and their average mass M2 was calculated. The average thickness L2 of these samples was also measured. The electrode sheet thickness was calculated as L2 - L1 (in cm). The compaction density of the electrode sheet was also calculated. Unit: g / cm3.

[0144] 5. Ratio performance testing method:

[0145] The lithium battery was discharged to 2.5V and placed in a 25℃ constant temperature chamber for 6 hours, and then tested according to the following steps:

[0146] (1) Under 1C conditions, constant current and constant voltage charging to 4.2V, cutoff current is 0.1C, and stand for 30 minutes. The capacity of constant current charging to 4.2V is Q1.

[0147] (2) Discharge under constant current at 1C until 2.5V cutoff, with a cutoff current of 0.1C, and let stand for 30 minutes;

[0148] (3) Under 10C conditions, constant current and constant voltage charging to 4.2V, cut-off current is 0.1C, and stand for 30 minutes. The capacity meter that is constant current charged to 4.2V is Q10.

[0149] (4) Discharge under constant current at 1C until 2.5V cutoff, with a cutoff current of 0.1C, and let stand for 30 minutes;

[0150] The capacity retention rate is calculated as: Q1 / Q10×100, where C represents the charging rate.

[0151] 6. Cyclic performance testing method:

[0152] The lithium battery was placed in a 25°C constant temperature chamber for 6 hours and tested according to the following steps:

[0153] (1) First round of constant current and constant voltage charging: Charge at a constant current of 0.1C to 4.2V, then switch to constant voltage charging until the current drops to 0.1C.

[0154] (2) After charging is complete, let it stand for 30 minutes.

[0155] (3) Perform constant current discharge, and discharge to 2.5V at a rate of 0.1C.

[0156] (4) Cyclic charge and discharge process: Charge at a constant current rate of 1C to 4.2V. Let stand for 30 minutes again. Discharge at a constant current rate of 1C to 2.5V.

[0157] (5) Repeat the above charging and discharging process for a total of 1000 cycles.

[0158] Calculate the battery discharge capacity Q1 and Q1000 after 1 cycle and 1000 cycles, and calculate the battery capacity decay rate: (Q1-Q1000) / Q1×100.

[0159] The specific results are as follows:

[0160] 1. The experimental results of Examples 1 to 5 are shown in Table 1.

[0161] Table 1:

[0162]

[0163] Comparing Examples 1 to 5, it can be seen that the lithium-ion battery of Example 3 exhibits the best kinetic performance under a 10C charging rate, corresponding to I B / I C and I N / I C The values ​​are 0.16 and 0.14, respectively.

[0164] This indicates that appropriate amounts of nitrogen and boron synergistic doping can significantly optimize the high-rate charging performance of the battery. However, when I B / I C and I N / I C When the ratio deviates from this optimal range, the kinetic performance of lithium-ion batteries deteriorates significantly, specifically manifested as reduced rate performance and worsened cycle stability. This is especially true for I... B / I C >0.16 and I N / I C In the case of >0.14 (Examples 4 and 5), compared to I in Examples 1 to 3 of this application B / I C The values ​​are 0.06–0.16 and I. N / I C In embodiments with a dopant content of 0.05–0.14, the capacity decay rate after 1000 battery cycles increases significantly. This phenomenon can be attributed to the optimal threshold for nitrogen and boron doping in the graphite material.

[0165] As can be seen from Examples 1-5 above, appropriate amounts of nitrogen and boron doping in this application can not only effectively improve the conductivity of graphite, but also reduce the energy barrier for lithium-ion desolvation, thereby enhancing the diffusion kinetics of lithium ions. However, when the doping ratio exceeds a reasonable range, excessive doping can lead to lattice distortion, instability of the internal structure of the material, and exacerbation of side reactions. These negative effects can significantly damage the electrochemical performance of the material, resulting in a decrease in rate performance and a significant reduction in cycle life.

[0166] 2. Examples 6 to 10 are examples of this application that investigate the processing time of the potassium hydroxide etching method. The specific results are shown in Table 2.

[0167] Table 2:

[0168]

[0169] Comparing Examples 3 and 6-10, it can be seen that the lithium-ion battery of Example 8 exhibits the best kinetic performance under a 10C charging rate, corresponding to I D / I G The value is 0.28. Any deviation from this value, whether increased or decreased, will lead to a decrease in 10C capacity retention.

[0170] Furthermore, with I D / I G As the value of I increases, the cycle stability of lithium-ion batteries tends to decrease. This phenomenon can be explained by the fact that, within a certain range, as I increases... D / I G As the value increases, the density of defects on the graphite surface increases moderately, and these defects form more Li in the structure. + Diffusion channels, thereby promoting Li + Cross-layer transmission significantly improves Li + Diffusion rate and kinetic performance. However, when I D / I G When the value is too high, excessive defects can lead to a series of negative effects, including decreased conductivity of graphite, significantly increased electrode internal resistance, and frequent occurrence of side reactions. These adverse factors ultimately weaken the rate performance and structural stability of the battery.

[0171] Figure 1 XPS spectrum of lithium-ion battery prepared in Example 8 of this invention;

[0172] Figure 2 The Raman spectrum of the lithium-ion battery prepared in Example 8 of this invention.

[0173] 3. Examples 11 to 15 are examples of this application for investigating the compaction density of the negative electrode sheet and the D50 particle size of the active material. The specific results are shown in Table 3.

[0174] Table 3:

[0175]

[0176] Comparing Examples 8 and 11-12, it can be seen that as compaction gradually increases, the kinetic performance of the lithium battery first increases and then decreases. This is attributed to the need for the compaction density of the graphite anode sheet to balance enhanced electron conduction with impeded ion transport. Moderate compaction improves kinetic performance by optimizing particle contact and shortening diffusion paths, while excessive compaction leads to performance degradation due to structural damage and insufficient electrolyte penetration.

[0177] Comparing Examples 8 and 13-15, it can be seen that as the D50 of nitrogen and boron synergistic graphite gradually increases, the kinetic performance decreases while the cycling performance increases. This is attributed to the fact that the increase in the size of the active material will prolong the Li+ solid-phase diffusion path and reduce the kinetic performance, but it can reduce volume expansion / suppress side reactions and significantly improve cycling stability.

[0178] 4. Comparative Examples 1 to 3 are comparative examples provided in this application that do not involve nitrogen or boron doping, and those that are doped with nitrogen or boron alone. The specific results are shown in Table 4.

[0179] Table 4:

[0180]

[0181] Further comparison of Example 1 with Comparative Examples 1 to 3 revealed that the lithium-ion batteries prepared by Comparative Example 1 (without nitrogen or boron doping) and Comparative Examples 2 and 3 (with nitrogen or boron doping only) exhibited lower kinetic performance than those prepared by nitrogen and boron synergistic doping. This is attributed to the fact that nitrogen and boron synergistic doping can form appropriate structural defects and electronic localization effects in graphite, which not only optimizes the electronic conductivity of the material but also increases the Li-ion conductivity. + This significantly improves the battery's kinetic performance by optimizing the diffusion pathways and active sites.

[0182] 5. Examples 16 to 18 are examples for investigating the doping content of this application. The specific results are shown in Table 5.

[0183] Table 5:

[0184]

[0185] As can be seen from the table above, in Example 16, due to excessive total nitrogen and boron content (graphite@NB-12%), the integrity of the material structure was damaged, resulting in reduced rate performance and exacerbating electrode pulverization and interfacial side reactions during cycling, ultimately leading to rapid capacity decay.

[0186] Compared to Example 3, Example 17 has more nitrogen doping, which introduces more defects into the graphite lattice, reducing the conductivity of graphite and leading to increased polarization during charge and discharge, resulting in a decrease in rate performance and cycle stability.

[0187] Compared to Example 3, Example 18 has more boron doping, which easily leads to the formation of more BC bonds. These bonds are relatively stable but have low electron mobility. In addition, boron itself is positively charged and easily reacts with the electrolyte, resulting in unstable SEI film formation, reduced cycle life, and affected rate performance.

[0188] As can be seen from the above, Examples 1 to 18 of this application all satisfy the requirement that after 1000 cycles at 25°C and a 1C rate, the capacity decay rate is less than 18.5% and I D / I G The value change rate is ≤10%. In summary, the appropriate nitrogen and boron synergistic doping of graphite, the introduction of appropriate defects on the graphite surface, the reasonable compaction density design, and the precise control of particle size are key strategies for achieving excellent fast-charging kinetic performance and long-term cycle stability of lithium batteries. These comprehensive design strategies in this application provide a systematic theoretical basis and practical guidance for the development of high-performance lithium batteries.

[0189] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The negative electrode active material in the negative electrode coating material of the lithium-ion battery is a nitrogen- and boron-doped graphite material. The negative electrode active material simultaneously satisfies the following relationships between the characteristic peak intensities of X-ray photoelectron spectroscopy and Raman spectroscopy, wherein: The characteristic peak intensities of the X-ray photoelectron spectroscopy of the negative electrode active material satisfy the following relationship: 0.02 ≤ I B / I C ≤0.23; 0.02≤I N / I C ≤0.2; In the formula: I B The intensity of the B 1s characteristic peak in the XPS spectrum representing the negative electrode active material; the binding energy range of the B 1s characteristic peak is 186.0 eV ~ 196.5 eV; I N The intensity of the N 1s characteristic peak in the XPS spectrum representing the active substance; the binding energy range of the N 1s characteristic peak is 395.0 eV to 406.5 eV; I C The intensity of the C 1s characteristic peak in the XPS spectrum representing the active substance, with the binding energy range of the C 1s characteristic peak being 282.0 eV to 285.5 eV; The Raman spectrum characteristic peak intensities of the negative electrode active material satisfy the following relationship: 0.05 ≤ I D / I G ≤0.34; In the formula: I D The intensity of peak D in the Raman spectrum representing the negative electrode active material; I G The intensity of the G peak in the Raman spectrum representing the negative electrode active material.

2. The lithium-ion battery according to claim 1, characterized in that, The negative electrode active material is mainly obtained by granulation of nitrogen precursor, boron precursor and graphite; The total amount of nitrogen precursor and boron precursor is in a mass ratio of 2 to 10 to 100 of graphite.

3. The lithium-ion battery according to claim 2, characterized in that, The mass ratio of the nitrogen precursor to the boron precursor is 0.5-2:

1.

4. The lithium-ion battery according to claim 1, characterized in that, The preparation method of the negative electrode active material includes: Nitrogen precursor, boron precursor and graphite are mixed in a certain proportion and subjected to pyrolysis reaction at 300℃~400℃ to obtain intermediate material; then the intermediate material is ball-milled and graphitized at 2500~3000℃ to obtain negative electrode active material.

5. The lithium-ion battery according to claim 4, characterized in that, The method for preparing the negative electrode active material further includes: The process involves treating the prepared negative electrode active material using potassium hydroxide etching to increase the number of pores.

6. The lithium-ion battery according to claim 1, characterized in that, The D50 particle size of the negative electrode active material is 5~16μm.

7. The lithium-ion battery according to claim 1, characterized in that, The compacted density of the negative electrode sheet is 1.2~1.75 g / cm³. 3 .

8. The lithium-ion battery according to any one of claims 1 to 6, characterized in that, The raw materials for preparing the negative electrode coating material include: The nitrogen and boron doped graphite material, conductive agent, and binder according to any one of claims 1 to 6.

9. The lithium-ion battery according to claim 8, characterized in that, The adhesive includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid, and styrene-butadiene rubber.

10. An electrical appliance, characterized in that, The electrical device includes the lithium-ion battery as described in any one of claims 1 to 9.

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