Modified graphite negative electrode material and preparation method thereof, negative electrode and lithium ion battery

Abstract

The invention relates to a modified graphite negative electrode material and a preparation method thereof, a negative electrode and a lithium ion battery. The modified graphite negative electrode material comprises graphite particles and an SEI precursor layer which is uniformly coated on the surface of each graphite particle and is constructed by lithium salt, wherein the lithium salt is of a crystalline state structure, and the thickness of the SEI precursor layer is 1-500 nm; during the first charging and discharging process of the battery, the lithium salt of the SEI precursor layer is subjected to electrochemical reaction prior to electrolyte, and an inorganic phase SEI with LiF and / or Li3PO4 as a main component is formed on the surface of graphite particles in situ. The negative electrode material disclosed by the invention realizes active formation and uniform distribution of SEI, even in a thick electrode, a continuous SEI layer can be formed on the surface of a deep graphite particle in the first charge-discharge and cycle process of a battery, the first-cycle coulombic efficiency is remarkably improved, the cycle life is remarkably prolonged, and the low-temperature and rate performance is improved; in addition, the electrolyte can more easily infiltrate the electrode, so that Li < + > is more smoothly transmitted in the thick electrode, and the electrochemical performance of the electrode is improved.

Description

Technical Field

[0001] This invention relates to the field of graphite anode material technology, and in particular to a modified graphite anode material, its preparation method, anode, and lithium-ion battery. Background Technology

[0002] Graphite is currently the most commonly used anode material in commercial lithium-ion batteries, possessing a low lithium intercalation potential, a stable charge-discharge platform, and reversible lithium-ion insertion / extraction capabilities. Furthermore, graphite resources are abundant and inexpensive, making it suitable for large-scale applications. With the rapid development of the electronic equipment and new energy vehicle industries, the demand for lithium-ion batteries with high energy density and fast-charging performance is constantly increasing. Using graphite to prepare thick electrodes can accommodate more active material, thereby significantly improving battery energy density. However, as the thickness of the anode sheet increases, the transport distance of lithium ions within the electrode becomes longer, leading to a decrease in ion migration efficiency and an exacerbation of polarization, which in turn affects the battery's charge-discharge performance and cycle life. Current technologies struggle to achieve a balance between the high energy density of thick electrodes and good ion transport performance.

[0003] For the fabrication and optimization of thick electrodes, existing published literature has proposed a variety of technical solutions.

[0004] CN118676296A discloses a negative electrode sheet and its preparation method, which introduces an electrolyte salt on the side of a thick electrode sheet away from the current collector to improve the electrolyte distribution in that region. However, the electrolyte salt in this method consists of particles of 1–250 μm, and its main function is to improve ion contact at the macroscopic level on the surface of one side of the thick electrode sheet. The interfacial properties of the deep graphite particles inside the thick electrode remain uneven, and the method does not fundamentally improve the ion transport efficiency and cycle stability of the thick electrode.

[0005] CN119695084A proposes to prepare thick electrodes by forming a porous structure in the negative electrode slurry, thereby reducing the tortuosity of the lithium-ion migration path inside the electrode and improving the lithium-ion conduction rate and cell rate performance. However, this method mainly relies on optimizing the slurry pore structure and graphite particle gradation. The porous structure primarily improves the wetting and ion transport of the electrode surface particles. The interfacial properties of the deep graphite particles inside the thick electrode remain uneven. Furthermore, the porous structure can cause fluctuations in the slurry rheology, affecting coating uniformity. Therefore, this technology cannot fundamentally improve the SEI uniformity of each graphite particle surface and the overall ion transport efficiency inside the thick electrode.

[0006] CN118763284A enhances fast-charging rate performance by adding low-viscosity additives, such as propionitrile, butyronitrile, FEC, and ODA, to the electrolyte to improve the desolvation capability of lithium ions. However, this approach relies on the diffusion of additives in the electrolyte to the surface of graphite particles during charge and discharge to form an SEI film. For thick electrodes, the deep graphite particles are far from the liquid phase of the electrolyte, limiting additive diffusion and making it difficult to form a uniform and continuous SEI layer on the surface of each particle. Therefore, this technology cannot fundamentally guarantee the interfacial stability and high-rate cycling performance of the deep particles inside thick electrodes.

[0007] CN118983399A improves the power output of conventional lithium batteries by introducing modified porous alumina into the negative electrode slurry. However, this method mainly improves overall conductivity and structural stability, and the continuity of ion transport channels inside the thick electrode remains limited. Furthermore, the additional introduction of porous alumina occupies part of the active material volume, reducing the energy density of the thick electrode. Therefore, this technology cannot fundamentally improve the uniform formation of the SEI on the surface of each graphite particle inside the thick electrode and the overall ion transport efficiency.

[0008] In summary, while existing technologies have improved lithium-ion transport on the surface or overall structure of thick electrodes, problems such as insufficient wetting of deep graphite particles inside the thick electrode, uneven interfacial properties, and low ion transport efficiency still exist. Furthermore, the porous structures or auxiliary materials introduced by some methods to improve ion transport can affect the rheology of the slurry or occupy the volume of the active material, making it difficult to simultaneously achieve high energy density and cycle stability in thick electrodes. Summary of the Invention

[0009] The purpose of this invention is to address the deficiencies of existing technologies by providing a modified graphite anode material and its preparation method, as well as an anode and a lithium-ion battery. This invention achieves the active formation and uniform distribution of SEI (Sediment-Insulated Layer). Even in thick electrodes, a continuous SEI layer can be formed on the surface of deep graphite particles during the first charge-discharge and cycle of the battery, significantly improving the first-cycle coulombic efficiency and cycle life, and enhancing low-temperature and rate performance.

[0010] To achieve the above objectives, in a first aspect, the present invention provides a modified graphite anode material, comprising: graphite particles and a solid electrolyte interface (SEI) precursor layer constructed from lithium salt uniformly coated on the surface of each of the graphite particles; The lithium salt has a crystalline structure, and the thickness of the SEI precursor layer is 1–500 nm. During the first charge and discharge of the battery, the lithium salt preferentially undergoes an electrochemical reaction with the electrolyte, forming an inorganic SEI phase with LiF and / or Li3PO4 as the main components in situ on the surface of the graphite particles.

[0011] Preferably, the lithium salt comprises one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium nitrate (LiNO3), or lithium dioxolaneborate (LiBOB).

[0012] Preferably, in the SEI precursor layer, the lithium salt is distributed on the surface of the graphite particles in an island-like crystalline structure and / or a continuous and dense crystalline coating structure.

[0013] Preferably, the SEI precursor layer is constructed by incorporating lithium salt during the negative electrode slurry preparation stage and then crystallizing in situ onto the surface of each graphite particle during the electrode drying stage as the solvent evaporates.

[0014] Preferably, the modified graphite anode material is used for a thick electrode, the thickness of which ranges from 100 to 300 micrometers.

[0015] In a second aspect, embodiments of the present invention provide a method for preparing the modified graphite anode material described in the first aspect above, comprising: A negative electrode slurry is prepared by mixing and stirring graphite particles, conductive agent, binder and solvent. Lithium salt is added to the negative electrode slurry and stirring is continued to make the lithium salt uniformly dispersed in the negative electrode slurry to form a modified slurry; The modified slurry is coated onto the surface of the negative electrode current collector and dried. During the drying process, the solvent evaporates, and the lithium salt crystallizes in situ on the surface of the graphite particles to form a uniform SEI precursor layer that coats the surface of each graphite particle.

[0016] Preferably, the drying time is 1 to 12 hours and the temperature is 60 to 120°C.

[0017] Preferably, the lithium salt comprises one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium nitrate (LiNO3), or lithium dioxolaneborate (LiBOB); The amount of lithium salt added is 0.1 to 20 wt% of the sum of the mass of the graphite particles, conductive agent, and binder.

[0018] Preferably, the conductive agent includes one or more of the following: conductive carbon black, conductive graphite, conductive carbon nanotubes, carbon fibers, or conductive carbon composite materials; The adhesive includes one or more of sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), or copolymers thereof; The solvent includes one or more of water, N-methylpyrrolidone (NMP), ethanol, isopropanol, or a mixture thereof.

[0019] Thirdly, embodiments of the present invention provide a negative electrode, comprising the modified graphite negative electrode material described in the first aspect above.

[0020] Fourthly, embodiments of the present invention provide a lithium-ion battery comprising the modified graphite anode material described in the first aspect above, or the anode material described in the third aspect above.

[0021] The modified graphite anode material provided in this invention achieves particle-level interface control of the anode material by forming a crystalline lithium salt SEI precursor layer on the surface of each graphite particle. The SEI precursor layer has controllable thickness and uniform distribution, and can preferentially decompose before the electrolyte during the first charge-discharge process to generate an inorganic SEI phase rich in LiF and / or Li3PO4, thereby improving interface stability and mechanical strength. The particle surface coating of this invention can significantly reduce the Li content inside the electrode. + Migration resistance, accelerate ion transport rate, and optimize desolvation process.

[0022] In thick electrode applications, due to the high compaction density and complex pores of the electrodes, traditional methods struggle to ensure electrolyte wetting of deep particles and the formation of a uniform interface. This invention addresses this by in-situ crystallization deposition of lithium salt during the slurry preparation stage and drying process. This ensures that all graphite particles in the thick electrode have a dense and continuous SEI precursor layer, effectively improving electrolyte wetting, ion channel continuity, and overall ion transport efficiency. Furthermore, by adjusting the amount of lithium salt added and the drying conditions, the thickness of the SEI precursor layer (1-500 nm) can be controlled, achieving island-like and / or continuous crystalline coating, thus balancing the energy density and high-rate charge / discharge performance of the thick electrode.

[0023] The modified graphite anode material provided by this invention can not only improve the initial coulombic efficiency, cycle stability and low-temperature discharge performance of the electrode, but also significantly enhance the fast charging capability, enabling the thick electrode system to maintain good ion transport efficiency and structural stability under high rate conditions, thereby comprehensively improving the overall electrochemical performance of lithium-ion batteries. Attached Figure Description

[0024] Figure 1 is a structural comparison diagram of SEI formed by the modified graphite anode material provided by the present invention and SEI formed by conventional methods in the prior art; Figure 2 The elemental distribution diagram of LiTFSI-coated graphite particles provided in Embodiment 1 of the present invention is shown in the transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS). Figure 3 This is a high-resolution transmission electron microscope (HRTEM) image of LiTFSI-coated graphite particles provided in Embodiment 1 of the present invention; Figure 4 This is a comparison chart of the rate performance of a graphite anode with 2% LiTFSI added and a pure graphite anode provided in Embodiment 1 of the present invention. Figure 5 This is a comparison chart of the rate performance of the graphite anode with 2% LiNO3 added and the pure graphite anode provided in Embodiment 2 of the present invention. Figure 6 This is a comparison chart of the rate performance of the graphite anode with 2% LiBOB added and the pure graphite anode provided in Embodiment 3 of the present invention. Figure 7 This is a comparison chart of the rate performance of the graphite anode with 2% LiOP2F2 added and the pure graphite anode provided in Embodiment 4 of the present invention. Figure 8 This is a comparison chart of the rate performance of a graphite anode with 1.5% LiTFSI and 0.5% LiOP2F2 added and a pure graphite anode provided in Embodiment 5 of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0026] This invention provides a modified graphite anode material, its preparation method, an anode, and a lithium-ion battery.

[0027] The modified graphite anode material proposed in this invention includes: graphite particles and a solid electrolyte interface (SEI) precursor layer constructed from lithium salt uniformly coated on the surface of each graphite particle.

[0028] The lithium salt is in a crystalline state and includes one or more of the following: lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium nitrate (LiNO3), or lithium dioxolaneborate (LiBOB).

[0029] The SEI precursor layer is constructed by incorporating lithium salt during the negative electrode slurry preparation stage and then crystallizing in situ onto the surface of each graphite particle during the electrode drying stage as the solvent evaporates. This in-situ formed lithium salt SEI precursor coating exhibits strong polarity and excellent wettability to commercial electrolytes such as carbonates and carboxylic esters. This characteristic is particularly crucial in thick electrode systems, effectively promoting rapid and uniform wetting of the electrolyte into the depths of the electrode pores, ensuring that all graphite particles are in full contact with the electrolyte, constructing continuous ion transport channels, and significantly reducing Li-induced degradation. + The transport resistance inside the electrode accelerates Li + The migration rate ensures the high-rate performance of thick electrodes.

[0030] The thickness of the SEI precursor layer is positively correlated with the amount of lithium salt added. In this invention, the thickness of the SEI precursor layer is preferably 1–500 nm. This is because although the lithium salt coating can effectively promote electrolyte wetting into the depths of the electrode pores, allowing all graphite particles to fully contact the electrolyte and form continuous ion transport channels, an excessively thick coating may cause excess lithium salt to randomly crystallize or form free particles inside the electrode, failing to further improve interface performance. Therefore, the thickness of the SEI precursor layer is preferably 1–500 nm.

[0031] In the SEI precursor layer, lithium salts are distributed on the surface of graphite particles in the form of island-like crystalline structures and / or continuous, dense crystalline coating structures. Specifically, island-like coatings are predominant in the thickness range of 1–100 nm, while continuous coatings are predominant in the thickness range of 100–500 nm.

[0032] During the initial charge-discharge cycle of the battery, the lithium salt preferentially undergoes an electrochemical reaction before the electrolyte, forming an inorganic SEI phase primarily composed of LiF and / or Li3PO4 on the surface of the graphite particles. This inorganic SEI phase not only possesses high mechanical stability and chemical inertness, effectively inhibiting the continuous decomposition of the electrolyte, but also optimizes the Li-ion exchange process. + The desolvation process accelerates Li + The migration and intercalation from the electrolyte into the graphite bulk phase comprehensively improves the electrochemical performance of the electrode.

[0033] The modified graphite anode material proposed in this invention can be used for thick electrodes with a thickness range of 100-300 micrometers.

[0034] Figure 1 is a structural comparison diagram of the SEI (b) formed by the modified graphite anode material provided by the present invention and the SEI (a) formed by conventional means in the prior art.

[0035] pass Figure 1a As can be seen, during the charging process of existing thick electrode negative electrodes, SEI is mainly passively generated by additives in the electrolyte. The graphite particles that reach the surface first form SEI, while the diffusion of deep graphite particles is limited by the electrolyte and additives, resulting in incomplete SEI film formation or uneven thickness. This leads to low ion transport efficiency inside the thick electrode, which easily generates concentration polarization and limits the high rate performance and cycle stability of the electrode.

[0036] And through Figure 1b As shown, this invention forms an SEI precursor coating by uniformly coating lithium salt onto the surface of each graphite particle during the slurry preparation stage. After battery assembly, the precursor is preferentially decomposed before the electrolyte to generate inorganic SEI, fundamentally ensuring that the surface of each graphite particle inside the thick electrode has a uniform, continuous, and dense interface film.

[0037] The modified graphite anode material of the present invention can be prepared by the following preparation method.

[0038] Step 1: Mix and stir graphite particles, conductive agent, binder and solvent to obtain negative electrode slurry.

[0039] Specifically, conductive agents include one or more of the following: conductive carbon black, conductive graphite, conductive carbon nanotubes, carbon fibers, or conductive carbon composite materials. The binders include one or more of the following: sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), or copolymers thereof; Solvents include one or more of the following: water, N-methylpyrrolidone (NMP), ethanol, isopropanol, or mixed solvent systems thereof.

[0040] In the following specific embodiments, the present invention will be mainly described using water as the solvent.

[0041] Mixing and stirring can be performed using standard equipment and process parameters commonly used in the industry for electrode slurry mixing.

[0042] Step 2: Add lithium salt to the negative electrode slurry and continue stirring to make the lithium salt evenly dispersed in the negative electrode slurry to form a modified slurry.

[0043] In subsequent specific embodiments of the present invention, lithium salts are selected as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium nitrate (LiNO3), and lithium dioxalate borate (LiBOB) because the slurry preparation in the embodiments uses deionized water as a solvent. Therefore, the lithium salts selected need to be stable in aqueous solution and not undergo hydrolysis reaction.

[0044] Therefore, those skilled in the art will understand from this specification that the selection of lithium salts simply requires following industry-standard knowledge and selecting accordingly based on the type of solvent in the slurry. For example, LiTFSI and LiBOB can also be used in PVDF / NMP organic system slurries. Furthermore, if a water-sensitive lithium salt is selected for a specific application, an organic solvent can be selected accordingly. The subsequent specific embodiments of this invention do not limit the preparation method to using only aqueous solvents and corresponding lithium salts.

[0045] Preferably, the amount of lithium salt added is 0.1 to 20 wt% of the sum of the mass of graphite particles, conductive agent, and binder.

[0046] Step 3: The modified slurry is coated onto the surface of the negative electrode current collector and dried. During the drying process, the solvent evaporates and the lithium salt crystallizes in situ on the surface of the graphite particles, forming a uniform SEI precursor layer that coats the surface of each graphite particle.

[0047] Specifically, the drying time is 1 to 12 hours, and the temperature is 60 to 120°C.

[0048] The drying time of the electrode affects the crystallinity of lithium salt on the surface of graphite particles. If the drying time is less than 1 hour, the crystallinity is poor. If the drying time is greater than 1 hour, the lithium salt can form a stable crystal structure. A drying time of about 6 hours is optimal.

[0049] The modified graphite anode material provided in this invention achieves particle-level interface control of the anode material by forming a crystalline lithium salt SEI precursor layer on the surface of each graphite particle. The SEI precursor layer has controllable thickness and uniform distribution, and can preferentially decompose before the electrolyte during the first charge-discharge process to generate an inorganic SEI phase rich in LiF and / or Li3PO4, thereby improving interface stability and mechanical strength. The particle surface coating of this invention can significantly reduce the Li content inside the electrode. + Migration resistance, accelerating ion transport rate, and reducing Li in the electrolyte. + By removing the energy barrier of solvent molecules, the intercalation efficiency is improved, and the desolvation process is optimized, thereby improving fast-charging performance and interface uniformity. In thick electrode applications, due to the high compaction density and complex pores of the electrodes, traditional methods struggle to ensure electrolyte wetting of deep particles and the formation of a uniform interface. This invention addresses this by in-situ crystallization deposition of lithium salt during the slurry preparation stage and drying process. This ensures that all graphite particles in the thick electrode have a dense and continuous SEI precursor layer, effectively improving electrolyte wetting, ion channel continuity, and overall ion transport efficiency. Furthermore, by adjusting the amount of lithium salt added and the drying conditions, the thickness of the SEI precursor layer (1-500 nm) can be controlled, achieving island-like and / or continuous crystalline coating, thus balancing the energy density and high-rate charge / discharge performance of the thick electrode.

[0050] The modified graphite anode material provided by this invention can not only improve the initial coulombic efficiency, cycle stability and low-temperature discharge performance of the electrode, but also significantly enhance the fast charging capability, enabling the thick electrode system to maintain good ion transport efficiency and structural stability under high rate conditions, thereby comprehensively improving the overall electrochemical performance of lithium-ion batteries.

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0052] Example 1 Step A) Mix graphite particles (Gr), conductive carbon black, CMC-Na, and SBR in deionized water at a mass ratio of 90:3:3.5:3.5 to form a uniform slurry; Step B) Add 2 wt% LiTFSI to the slurry obtained in step A) and mix thoroughly to form a mixed slurry; Step C): The mixed slurry obtained in step B) is coated onto the copper current collector, dried at 80°C for 6 hours, and then rolled to achieve an electrode compaction density of 0.9 g / cm³. -3 A modified graphite electrode with a thickness of 200 micrometers (excluding the current collector thickness) was obtained.

[0053] Example 2 Step A) Mix graphite particles (Gr), conductive carbon black, CMC-Na, and SBR in deionized water at a mass ratio of 90:3:3.5:3.5 to form a uniform slurry; Step B) Add 2 wt% LiNO3 to the slurry obtained in step A) and mix thoroughly to form a mixed slurry; Step C): The mixed slurry obtained in step B) is coated onto the copper current collector, dried at 80°C for 6 hours, and then rolled to achieve an electrode compaction density of 0.9 g / cm³. -3 A modified graphite electrode with a thickness of 200 micrometers (excluding the current collector thickness) was obtained.

[0054] Example 3 Step A) Mix graphite particles (Gr), conductive carbon black, CMC-Na, and SBR in deionized water at a mass ratio of 90:3:3.5:3.5 to form a uniform slurry; Step B) Add 2 wt% LiBOB to the slurry obtained in step A) and mix thoroughly to form a mixed slurry; Step C): The mixed slurry obtained in step B) is coated onto the copper current collector, dried at 80°C for 6 hours, and then rolled to achieve an electrode compaction density of 0.9 g / cm³. -3 A modified graphite electrode with a thickness of 200 micrometers (excluding the current collector thickness) was obtained.

[0055] Example 4 Step A) Mix graphite particles (Gr), conductive carbon black, CMC-Na, and SBR in deionized water at a mass ratio of 90:3:3.5:3.5 to form a uniform slurry; Step B) Add 2 wt% LiOP2F2 to the slurry obtained in step A), mix well, and form a mixed slurry; Step C): The mixed slurry obtained in step B) is coated onto the copper current collector, dried at 80°C for 6 hours, and then rolled to achieve an electrode compaction density of 0.9 g / cm³. -3 A modified graphite electrode with a thickness of 200 micrometers (excluding the current collector thickness) was obtained.

[0056] Example 5 Step A) Mix graphite particles (Gr), conductive carbon black, CMC-Na, and SBR in deionized water at a mass ratio of 90:3:3.5:3.5 to form a uniform slurry; In step B), 1.5 wt% LiTFSI and 0.5 wt% LiOP2F2, accounting for 1.5 wt% of the total mass of the slurry, are added to the slurry obtained in step A) and mixed evenly to form a mixed slurry. Step C): The mixed slurry obtained in step B) is coated onto the copper current collector, dried at 80°C for 6 hours, and then rolled to achieve an electrode compaction density of 0.9 g / cm³. -3 A modified graphite electrode with a thickness of 200 micrometers (excluding the current collector thickness) was obtained.

[0057] Example 6 Step A) Graphite particles (Gr), conductive carbon black, PVDF, and SBR are mixed in NMP at a mass ratio of 90:3:3.5:3.5 to form a uniform slurry; Step B) Add 2 wt% LiTFSI to the slurry obtained in step A) and mix thoroughly to form a mixed slurry; Step C): The mixed slurry obtained in step B) is coated onto the copper current collector, dried at 90°C for 5 hours, and then rolled to achieve an electrode compaction density of 0.9 g / cm³. -3 A modified graphite electrode with a thickness of 100 micrometers (excluding the current collector thickness) was obtained.

[0058] Example 7 Step A) Graphite particles (Gr), conductive carbon black, PVDF, and SBR are mixed in NMP at a mass ratio of 90:3:3.5:3.5 to form a uniform slurry; Step B) Add 2 wt% LiBOB to the slurry obtained in step A) and mix thoroughly to form a mixed slurry; Step C): The mixed slurry obtained in step B) is coated onto the copper current collector, dried at 60°C for 10 hours, and then rolled to achieve an electrode compaction density of 0.9 g / cm³. -3 A modified graphite electrode with a thickness of 300 micrometers (excluding the current collector thickness) was obtained.

[0059] Comparative Example 1 Step A) Mix graphite particles (Gr), conductive carbon black, CMC-Na, and SBR in deionized water at a mass ratio of 90:3:3.5:3.5 to form a uniform slurry; Step B): The mixed slurry obtained in step A) is coated onto the copper current collector, dried at 80°C for 6 hours, and then rolled to achieve an electrode compaction density of 0.9 g / cm³. -3 A graphite electrode with a thickness of 200 micrometers (excluding the current collector thickness) was obtained.

[0060] Full cells were assembled for Examples 1-5 and Comparative Example 1 to test the performance of the electrodes.

[0061] The negative electrode sheets obtained in Examples 1-5 and Comparative Example 1 were cut into electrode sheets with a diameter of 14 mm, and then dried in a vacuum oven at 120°C for 6 hours to remove moisture.

[0062] The full cell was assembled in an argon-filled glove box. The positive electrode was an NCM811 electrode (13mm in diameter, N / P ratio 1.2 compared to the negative electrode), the separator was Celgard 2500 (polypropylene (PP) material), and the electrolyte was a 1 mol / L LiPF6 solution of dimethyl carbonate: ethylene carbonate: ethyl methyl carbonate (DMC:EC:EMC) = 1:1:1 Vol.

[0063] The assembled full cells were first placed at 45°C for 15 hours, then converted at a rate of 0.2C for 5 weeks, and the rate performance was tested at room temperature.

[0064] Figure 2 This is a high-resolution transmission electron microscope (HRTEM) image of LiTFSI-coated graphite particles provided in Example 1 of the present invention. It can be seen that the EDS elemental distribution test results show that the surface of the LiTFSI-coated graphite particles in Example 1 has a corresponding distribution of C, O, N, F, and S elements. Elements specific to LiTFSI, such as N and S, also show a uniform distribution, indicating that the lithium salt is uniformly coated on the surface of the graphite particles.

[0065] Figure 3 This is a high-resolution transmission electron microscope (HRTEM) image of the LiTFSI-coated graphite particles provided in Example 1 of the present invention. It can be seen that the HRTEM test shows that the surface of the LiTFSI-coated graphite particles in Example 1 has a distribution of LiTFSI crystals, corresponding to the characteristic crystal planes (315), (122), and (217). This proves that the method yields a lithium salt coating with good crystallinity.

[0066] Figure 4This is a comparison chart of the rate performance of the modified graphite anode with 2% LiTFSI and the pure graphite anode provided in Example 1 of this invention. It can be seen that the modified graphite anode of Example 1 has better fast-charging performance. Under 5C conditions, the modified anode with graphite particles (Gr) + 2% LiTFS retains a discharge specific capacity of 123.4 mAh / g, while the graphite anode without LiTFSI only has a discharge specific capacity of 76.3 mAh / g.

[0067] Figure 5 This is a comparison chart of the rate performance of the modified graphite anode with 2% LiNO3 and the pure graphite anode provided in Example 2 of the present invention. It can be seen that the modified graphite anode of Example 2 has better fast-charging performance. Under 5C conditions, the modified anode with graphite particles (Gr) + 2% LiNO3 can retain a discharge specific capacity of 89.5 mAh / g, while the graphite anode without LiNO3 only has a discharge specific capacity of 76.3 mAh / g.

[0068] Figure 6 This is a comparison chart of the rate performance of the modified graphite anode with 2% LiBOB and the pure graphite anode provided in Example 3 of the present invention. It can be seen that the modified graphite anode of Example 3 has better fast charging performance. Under 5C conditions, the modified anode with graphite particles (Gr) + 2% LiBOB can retain a discharge specific capacity of 113.5 mAh / g, while the graphite anode without LiBOB only has a discharge specific capacity of 76.3 mAh / g.

[0069] Figure 7 This is a comparison chart of the rate performance of the modified graphite anode with 2% LiOP2F2 and the pure graphite anode provided in Example 4 of the present invention. It can be seen that the modified graphite anode of Example 4 has better fast-charging performance. Under 5C conditions, the modified anode with graphite particles (Gr) + 2% LiOP2F2 can retain a discharge specific capacity of 121.1 mAh / g, while the graphite anode without LiOP2F2 only has a discharge specific capacity of 76.3 mAh / g.

[0070] Figure 8 This is a comparison chart of the rate performance of the modified graphite anode with added 1.5% LiTFSI and 0.5% LiOP2F2 and the pure graphite anode provided in Example 5 of the present invention. It can be seen that the modified graphite anode of Example 5 has better fast charging performance. Under 5C conditions, the modified anode with graphite particles (Gr) + 1.5% LiTFSI + 0.5% LiOP2F2 can retain a discharge specific capacity of 129.6 mAh / g, while the graphite anode without added LiTFSI and LiOP2F2 only has a discharge specific capacity of 76.3 mAh / g.

[0071] As can be seen from the comparison of Examples 1-5 and Comparative Example 1, the modified graphite anode of the present invention exhibits significant advantages over the unmodified pure graphite anode in thick electrode systems: the in-situ uniformly coated SEI precursor coating of lithium salt on the surface of each graphite particle preferentially decomposes to form a stable SEI rich in inorganic components during the first charge-discharge cycle, improving cycle stability, first coulombic efficiency, and low-temperature discharge capability; simultaneously, it can rapidly and uniformly improve electrolyte wetting and ion transport, significantly reducing the internal Li content of the electrode. + Reduced transmission resistance, improved high-rate performance. The preparation process proposed in this invention is simple and easy to implement, fully integrates with existing negative electrode slurry preparation processes, and can effectively improve performance.

[0072] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A modified graphite anode material, characterized in that, The negative electrode material includes: graphite particles and a solid electrolyte interface (SEI) precursor layer constructed from lithium salt uniformly coated on the surface of each graphite particle; The lithium salt has a crystalline structure, and the thickness of the SEI precursor layer is 1–500 nm. During the first charge and discharge of the battery, the lithium salt preferentially undergoes an electrochemical reaction with the electrolyte, forming an inorganic SEI phase with LiF and / or Li3PO4 as the main components in situ on the surface of the graphite particles.

2. The modified graphite anode material according to claim 1, characterized in that, The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium nitrate (LiNO3), or lithium dioxolaneborate (LiBOB).

3. The modified graphite anode material according to claim 1, characterized in that, In the SEI precursor layer, the lithium salt is distributed on the surface of the graphite particles in the form of an island-like crystalline structure and / or a continuous and dense crystalline coating structure.

4. The modified graphite anode material according to claim 1, characterized in that, The SEI precursor layer is constructed by incorporating lithium salt during the negative electrode slurry preparation stage and then crystallizing in situ onto the surface of each graphite particle during the electrode drying stage as the solvent evaporates.

5. The modified graphite anode material according to claim 1, characterized in that, The modified graphite anode material is used for a thick electrode, the thickness of which ranges from 100 to 300 micrometers.

6. A method for preparing the modified graphite anode material according to any one of claims 1 to 5, characterized in that, The preparation method includes: A negative electrode slurry is prepared by mixing and stirring graphite particles, conductive agent, binder and solvent. Lithium salt is added to the negative electrode slurry and stirring is continued to make the lithium salt uniformly dispersed in the negative electrode slurry to form a modified slurry; The modified slurry is coated onto the surface of the negative electrode current collector and dried. During the drying process, the solvent evaporates, and the lithium salt crystallizes in situ on the surface of the graphite particles to form a uniform SEI precursor layer that coats the surface of each graphite particle.

7. The preparation method according to claim 6, characterized in that, The drying time is 1 to 12 hours, and the temperature is 60 to 120°C.

8. The preparation method according to claim 6, characterized in that, The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium nitrate (LiNO3), or lithium dioxolaneborate (LiBOB); The amount of lithium salt added is 0.1 to 20 wt% of the sum of the mass of the graphite particles, conductive agent, and binder. The conductive agent includes one or more of the following: conductive carbon black, conductive graphite, conductive carbon nanotubes, carbon fibers, or conductive carbon composite materials. The adhesive includes one or more of the following: sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), or copolymers thereof; The solvent includes one or more of the following: water, N-methylpyrrolidone (NMP), ethanol, isopropanol, or a mixture thereof.

9. A negative electrode, characterized in that, The negative electrode comprises the modified graphite negative electrode material according to any one of claims 1 to 5.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the modified graphite anode material according to any one of claims 1 to 5, or includes the anode material according to claim 9.

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