High initial efficiency dry process composite graphite electrode

Abstract

The application discloses a high-initial-efficiency dry-method composite graphite electrode, which comprises graphite, conductive carbon material, PTFE adhesive and boron-containing lithium salt, wherein the mass ratio of the graphite, the conductive carbon material, the PTFE adhesive and the boron-containing lithium salt is X:(100-X-Y-Z):Z:Y, wherein 90<=X<98, 1<=Z<=2 and 0.2<=Y<(100-X-Z), the boron-containing lithium salt is introduced into the graphite and the PTFE adhesive, and the proportion of each component is accurately controlled, so that the dual optimization of high energy density and high initial efficiency is realized, the production cost and the process complexity are reduced, and a new efficient and low-cost idea is provided for dry-method preparation of the high-performance graphite electrode.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, specifically relating to a high-efficiency dry-process composite graphite electrode. Background Technology

[0002] With the widespread application of battery technology in various fields, the performance optimization of electrodes, as core components of batteries, has become a research hotspot. Among them, dry electrode fabrication, with its advantages of simple process flow, high production efficiency, and no need for solvents, has gradually become an important development direction for battery electrode fabrication technology. Graphite, due to its excellent pressure resistance, is considered particularly suitable for dry electrode fabrication. Therefore, the dry fabrication of negative electrode sheets using graphite as the active material has received increasing attention and application.

[0003] The sp² hybrid structure of graphite endows it with unique physical and chemical properties. Based on this structure, graphite anodes exhibit excellent cycle performance and structural stability, while also possessing high specific capacity. Combined with its voltage withstand capability, graphite can significantly improve the volumetric energy density of electrodes during dry fabrication, especially in high-graphite-content electrodes (graphite content ≥ 90%), where it demonstrates significant advantages in cycle stability and specific capacity.

[0004] However, the mixing process of graphite, the negative electrode active material, with binders (such as PTFE binders) faces challenges in actual dry preparation. Since both PTFE binders and graphite surfaces carry negative charges, they repel each other during mixing, making it difficult for the binder to effectively bond with the graphite. This problem not only reduces the initial coulombic efficiency of the negative electrode but also limits the further development of dry-process graphite negative electrodes. To address this issue, common methods include surface coating of graphite or PTFE binders or adding additives to the electrolyte to improve their compatibility. However, while these methods improve the bonding performance between PTFE binders and graphite to some extent, they also lead to problems such as reduced electrode capacity density, increased costs, and potential side reactions.

[0005] Therefore, how to effectively improve the first coulombic efficiency of graphite electrodes while fully leveraging their advantages of high stability and high energy density in dry-processed graphite electrodes has become a key research topic in current battery technology. Summary of the Invention

[0006] This invention addresses the problems in the prior art by providing a high first-efficiency dry composite graphite electrode that solves the incompatibility problem between graphite and PTFE binder, thus obtaining a high first-efficiency dry composite graphite electrode with high initial coulombic efficiency.

[0007] This invention provides a high-efficiency dry-process composite graphite electrode, comprising graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt, wherein the mass fraction ratio of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt is X:(100-XYZ):Z:Y, where 90≤X<98, 1≤Z≤2, and 0.2≤Y<(100-XZ).

[0008] As a further embodiment, in the high-efficiency dry composite graphite electrode, the mass fraction ratio of graphite, conductive carbon material, PTFE binder and boron-containing lithium salt is X:(100-XYZ):Z:Y, where 95<X<97, 1≤Z≤2, and 0.4≤Y<(100-XZ).

[0009] As a further preferred embodiment, in the high-efficiency dry composite graphite electrode, the mass fraction ratio of graphite, conductive carbon material, PTFE binder and boron-containing lithium salt is X:(100-XYZ):Z:Y, where 95<X<97, 1≤Z≤2, 0.4≤Y<(100-XZ), and Z:Y=3.8-4.2.

[0010] As a further embodiment, the conductive carbon material includes, but is not limited to, any one or more of zero-dimensional conductive carbon materials, one-dimensional conductive carbon materials, and two-dimensional conductive carbon materials.

[0011] As a further preferred option, the conductive carbon material is selected from one-dimensional conductive carbon materials.

[0012] As a further option, the boron-containing lithium salt is selected from any one or more of organic lithium borate salts and inorganic lithium borate salts.

[0013] As a further preferred option, the boron-containing lithium salt is selected from organoboronate lithium salts.

[0014] As a further option, the organoboronate lithium salt is selected from lithium oxalate borate.

[0015] As a further option, the lithium oxalate borate salt is selected from fluorine-containing and / or fluorine-free lithium oxalate borate salts.

[0016] As a further preferred embodiment, the lithium oxalate borate salt is selected from fluorine-free lithium oxalate borate salts.

[0017] As a further preferred option, the fluorine-free lithium oxalate borate salt is selected from lithium bis(oxalate borate) (LiBOB).

[0018] As a further option, the inorganic lithium borate salt is selected from fluorine-containing inorganic lithium borate salts.

[0019] As a further option, the fluorine-containing inorganic lithium borate salt is selected from lithium tetrafluoroborate.

[0020] Secondly, this solution provides a battery that uses a high-efficiency dry-process composite graphite electrode as the negative electrode.

[0021] As a further embodiment, the battery also includes a positive electrode, an electrolyte, and a separator.

[0022] As a further embodiment, the positive electrode sheet includes a positive electrode active material, a positive electrode current collector, a positive electrode conductive agent, and a positive electrode binder.

[0023] As a further option, the positive electrode conductive agent is selected from any one or more of carbon materials, metallic materials, and conductive polymers.

[0024] As a further option, the positive electrode adhesive is selected from at least one of thermoplastic resins, acrylic resins, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0025] As a further option, the electrolyte is not limited in principle. Technicians can choose a conventional basic electrolyte such as 1M LiPF6 in EC / DMC / EMC / DEC (1:1:3:1) with 2% VC added by mass.

[0026] As a further preferred embodiment, the lithium salt added to the electrolyte is preferably a mixed lithium salt of LiFSI and LiPF6.

[0027] As a further embodiment, in the mixed lithium salt, the molar ratio of LiFSI to LiPF6 is (2-5):(5-8).

[0028] As a further preferred embodiment, the molar ratio of LiFSI to LiPF6 in the mixed lithium salt is (4-5):(5-6).

[0029] As a further option, the diaphragm is not limited in principle, and technicians may choose any one of polyethylene (PE) diaphragm, polypropylene (PP) diaphragm, non-woven fabric diaphragm, aramid (Nomex) diaphragm, or polyimide (PI) diaphragm.

[0030] Compared with the prior art, the present invention has at least the following beneficial effects:

[0031] This approach significantly improves the compatibility between graphite and PTFE binders by introducing boron-containing lithium salts, solving the problem of compounding these two components in traditional dry preparation methods. The boron-containing lithium salts not only reduce electrostatic repulsion between graphite and PTFE binders but also enhance their affinity by forming multi-coordinated BF bonds. Simultaneously, they act as dispersants to inhibit graphite agglomeration, optimizing electrode uniformity and compaction density. Furthermore, the boron-containing lithium salts form a stable SEI film in situ during the first charge-discharge cycle, effectively protecting the graphite anode and optimizing the electrode's cycle stability and initial coulombic efficiency. By precisely controlling the mass fraction of each component, this approach achieves synergistic optimization of high energy density and high initial efficiency, reducing preparation costs and process complexity. It provides an efficient and low-cost solution for the dry preparation of high-performance graphite electrodes, demonstrating promising prospects for industrial application. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 middle, Figure 1 a is a microscopic image of the graphite surface after disassembly of the battery in Example 1 after formation and capacity testing. Figure 1 b is a microscopic image of the graphite surface of the battery in Comparative Example 1 after it has been disassembled and subjected to formation and capacity testing. Detailed Implementation

[0034] For ease of understanding, the present invention will be described more fully below, and embodiments of the present invention will be given, but this does not limit the scope of the present invention.

[0035] The following are descriptions of terms or words, and unless otherwise defined, all technical and scientific terms used herein have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains.

[0036] This invention provides a high-efficiency dry-process composite graphite electrode, comprising graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt, wherein the mass fraction ratio of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt is X:(100-XYZ):Z:Y, where 90≤X<98, 1≤Z≤2, and 0.2≤Y<(100-XZ).

[0037] To address the poor compatibility between graphite and PTFE binders, this solution introduces boron-containing lithium salts. Through the synergistic effect between the boron-containing lithium salts and graphite and PTFE binders, a high-efficiency dry-process composite graphite electrode is obtained. Graphite's excellent compressive strength allows it to withstand higher rolling pressures, increasing compaction density. Especially with high graphite content, the graphite electrode is expected to exhibit higher energy density. However, during the dry preparation process, the negatively charged graphite and the equally negatively charged PTFE binder repel each other, leading to a sharp decline in their compatibility. Simultaneously, the high fluorine and low wetting properties of the PTFE binder further exacerbate the incompatibility problem. Furthermore, graphite itself agglomerates under van der Waals forces, especially during solvent-free dry preparation processes, where agglomeration becomes even more severe. The extremely high graphite content makes dry-process compounding of graphite and PTFE binder extremely difficult. To address this issue, this solution introduces boron-containing lithium salts. During the dry-process preparation of graphite electrodes, the positively charged boron-containing lithium salts preferentially adsorb onto the negatively charged regions of both graphite and PTFE binder, reducing the repulsion between them and improving their compatibility. Simultaneously, during the dry-process preparation, the boron-containing lithium salts can also form multi-coordinate BF bonds with the high-fluorine-content PTFE binder, increasing the surface energy of the PTFE binder and enhancing the bonding between the PTFE binder and graphite. The affinity of the graphite is high; in addition, boron-containing lithium salts can also act as dispersants, reducing the attraction between particles by inserting into the graphite interlayer or adsorbing onto the surface, thereby preventing the graphite from agglomerating; during the first charge and discharge process, boron-containing lithium salts will passivate in situ to form an SEI film, thereby achieving effective protection of the graphite anode; furthermore, the performance optimization of high-efficiency dry composite graphite electrodes is not only the result of the compounding of graphite, PTFE binder and boron-containing lithium salts, but also requires the proportion between each substance to fully exert the compounding effect. In this scheme, we found that the addition of only a small amount of PTFE binder and boron-containing lithium salts can greatly improve the graphite anode. The dry preparation effect of graphite is achieved by using a mass fraction ratio of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt as X:(100-XYZ):Z:Y, where 90≤X<98, 1≤Z≤2, and 0.2≤Y<(100-XZ). By controlling the mass fractions of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt, this method can effectively improve the compatibility between graphite and PTFE binder while avoiding side reactions and fully optimizing the SEI film thickness to optimize the first coulombic efficiency of the high-first-efficiency dry composite graphite electrode, thus leveraging the advantages of the high-first-efficiency dry composite graphite electrode.

[0038] As examples, in the aforementioned high-efficiency dry-process composite graphite electrode, the mass fraction ratio of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt is X:(100-XYZ):Z:Y, where 95<X<97, 1≤Z≤2, and 0.4≤Y<(100-XZ). This helps to further optimize the synergistic effect among graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt, improve the compatibility between graphite and PTFE binder, thereby optimizing energy density and improving battery efficiency.

[0039] As some preferred examples, in the high first-efficiency dry composite graphite electrode, the mass fraction ratio of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt is X:(100-XYZ):Z:Y, where 95<X<97, 1≤Z≤2, 0.4≤Y<(100-XZ), and Z:Y=3.8-4.2. By further controlling the ratio of PTFE binder to boron-containing lithium salt, it is helpful to further optimize the performance of the high first-efficiency dry composite graphite electrode and improve its first coulombic efficiency.

[0040] As examples, the conductive carbon material includes, but is not limited to, any one or more of zero-dimensional conductive carbon materials, one-dimensional conductive carbon materials, and two-dimensional conductive carbon materials.

[0041] Zero-dimensional conductive carbon materials refer to conductive carbon materials whose three-dimensional spatial dimensions are all at the nanoscale. The zero-dimensional conductive carbon materials are selected from any one or more of acetylene black, Ketjen black, furnace black, and fullerene.

[0042] One-dimensional conductive carbon material refers to linear carbon material with nanoscale radial dimensions and micrometer-scale axial dimensions. The one-dimensional conductive carbon material is selected from any one or more of carbon nanotubes and carbon nanofibers.

[0043] Two-dimensional conductive carbon materials refer to sheet-like carbon materials with atomic-level thickness and macroscopic lateral dimensions. The two-dimensional conductive carbon materials are selected from any one or more of graphene, graphene oxide, and carbon nanosheets.

[0044] As some preferred examples, the conductive carbon material is selected from one-dimensional conductive carbon materials.

[0045] As examples, the boron-containing lithium salt is selected from any one or more of organic lithium borate salts and inorganic lithium borate salts.

[0046] As some preferred examples, the boron-containing lithium salt is selected from organoboronate lithium salts.

[0047] As examples, the organoboronate lithium salt is selected from lithium oxalate borate.

[0048] As examples, the lithium oxalate borate salt is selected from fluorine-containing and / or fluorine-free lithium oxalate borate salts.

[0049] As some preferred examples, the lithium oxalate borate salt is selected from fluorine-free lithium oxalate borate salts.

[0050] As some preferred examples, the fluorine-free lithium oxalate borate salt is selected from lithium bis(oxalate borate) (LiBOB).

[0051] As examples, the inorganic lithium borate salt is selected from fluorine-containing inorganic lithium borate salts.

[0052] As examples, the fluorine-containing inorganic lithium borate salt is selected from lithium tetrafluoroborate.

[0053] Secondly, this solution provides a battery that uses a high-efficiency dry-process composite graphite electrode as the negative electrode.

[0054] In some cases, the battery also includes a positive electrode, an electrolyte, and a separator.

[0055] As some examples, the positive electrode sheet includes a positive electrode active material, a positive electrode current collector, a positive electrode conductive agent, and a positive electrode binder.

[0056] As a further option, the positive electrode active material is selected from lithium iron phosphate, LiMO2, and lithium nickel cobalt manganese oxide (LiNi). x Mn y Co z O2, Lithium nickel cobalt aluminum oxide (LiNi) p Co q Al f O2, lithium-rich manganese-based cathode materials: Li 1+a Ni b Co c Mn d TM 1-b-c-d O2, lithium nickel manganese oxide (Li) k XO2, Lithium manganese iron phosphate (Li) e Mn 1-g-j Fe g Z jPO4, wherein M is selected from any one of Co, Li, and Mn; TM is selected from any one or more of nickel, cobalt, manganese, iron, titanium, chromium, vanadium, molybdenum, magnesium, and copper; X is selected from at least one of Ni, Co, and Mn; Z is selected from at least one of B, Mg, Al, Si, Ca, Ti, V, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb, and Mo, 0.1 ≤ x ≤ 0.8, 0.1 ≤ y ≤ 0.3, 0.1 ≤ z ≤ 0.3, x+y+z=1, 0.6≤ p ≤ 0.9, 0.05 ≤ q ≤ 0.2, 0.03 ≤ f ≤ 0.1, 0 <a≤0.5,0<b≤0.3,0<c≤0.3,0.2<d≤0.7,0<k<1,1-b-c-d≥0,0.8<e<1.2,0.5<1-g-j<1,0.05<g<0.5,0<j<0.2。

[0057] As a further embodiment, the positive current collector is selected from copper, aluminum, titanium, nickel, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, gold, silver, iron, platinum, chromium, tin, indium, alloys containing one or more of these, and may also be mentioned as one or more metals selected from alloys;

[0058] As some optional parameters, the positive electrode conductive agent is selected from any one or more of carbon materials, metallic materials, and conductive polymers.

[0059] As some optional parameters, the carbon material is selected from any one or more of natural graphite, carbon nanotubes, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber.

[0060] As some optional parameters, the metal material is selected from one or more of copper, nickel, aluminum, and silver.

[0061] As some optional parameters, the conductive polymer is selected from one or more of polyfluorene (PF), polyaniline (PANI), polypyrrole (PPy), polythiophene (PTh), polyethylene dioxythiophene (PEDOT), polyethylene dioxythiophene:polystyrene sulfonate (PEDOT:PSS), and polyacetylene (PA).

[0062] As some optional parameters, the positive electrode adhesive is selected from at least one of thermoplastic resins, acrylic resins, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0063] As a further embodiment, the thermoplastic resin includes at least one selected from polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of vinylidene fluoride-tetrafluoroethylene, copolymers of vinylidene fluoride-trifluoroethylene, copolymers of vinylidene fluoride-trichloroethylene, copolymers of vinylidene fluoride-fluorinated vinylidene, copolymers of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene.

[0064] As an example, the electrolyte is not limited in principle. Technicians may choose a conventional basic electrolyte such as 1M LiPF6 in EC / DMC / EMC / DEC (1:1:3:1) with 2% VC added by mass.

[0065] As some preferred examples, the lithium salt added to the electrolyte is preferably a mixed lithium salt of LiFSI and LiPF6.

[0066] As examples, in the mixed lithium salt, the molar ratio of LiFSI to LiPF6 is (2-5):(5-8).

[0067] As some preferred examples, in the mixed lithium salt, the molar ratio of LiFSI to LiPF6 is (4-5):(5-6).

[0068] As an example, the diaphragm is not limited in principle, and technicians may choose any one of polyethylene (PE) diaphragm, polypropylene (PP) diaphragm, non-woven fabric diaphragm, aramid (Nomex) diaphragm, or polyimide (PI) diaphragm.

[0069] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application and do not represent all possible embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0070] The chemical raw materials used in the following examples and comparative examples are all prior art and were obtained commercially. The experimental apparatus and testing equipment used in the following examples and comparative examples are all conventional equipment in the art, and there are no special requirements or limitations.

[0071] Example 1

[0072] Preparation of high-efficiency dry composite graphite electrodes

[0073] Graphite, carbon nanotubes, PTFE binder, and LiBF4 were mixed in a mass ratio of 96:1.5:2:0.5 and dispersed at 80℃ and 20000 rpm for 5 min. After dispersion, the mixture was passed through a 60-mesh sieve. The mixture was then extruded at 80℃ and subjected to a pressure of 30t, followed by thinning to obtain a product with a concentration of 8 mg / cm³. 2 High-efficiency dry composite graphite electrode.

[0074] Preparation of lithium iron phosphate cathode sheet

[0075] Lithium iron phosphate, carbon nanotubes, and PTFE binder were mixed at a mass ratio of 96:2:2 and dispersed at 80°C and 20,000 rpm for 5 minutes. After dispersion, the mixture was passed through a 60-mesh sieve. The mixture was then extruded at 80°C under a pressure of 30t and thinned to obtain a 20 mg / cm³ binder. 2 Lithium iron phosphate cathode.

[0076] Cell: The ratio of negative electrode capacity to positive electrode capacity is 1.1, and PE separator is selected to prepare a 1AH stacked soft pack.

[0077] Basic electrolyte: 1M LiPF6 in EC / DMC / EMC / DEC (1:1:3:1) with 2% VC added by mass.

[0078] Example 2

[0079] The synthesis and preparation methods are the same as in Example 1, except that the mass fraction ratio of graphite, carbon nanotubes, PTFE binder, and LiBF4 is 96:1.8:2:0.2.

[0080] Example 3

[0081] The synthesis and preparation methods are the same as in Example 1, except that the mass fraction ratio of graphite, carbon nanotubes, PTFE binder, and LiBF4 is 96:1.2:2:0.8.

[0082] Example 4

[0083] The synthesis and preparation methods are the same as in Example 1, except that the mass fraction ratio of graphite, carbon nanotubes, PTFE binder, and LiBF4 is 96:1:2:1.

[0084] Example 5

[0085] The synthesis and preparation methods are the same as in Example 1, except that LiDFOB is used instead of LiBF4.

[0086] Example 6

[0087] The synthesis and preparation methods are the same as in Example 1, except that LiBOB is used instead of LiBF4.

[0088] Example 7

[0089] The synthesis and preparation methods are the same as in Example 2, except that LiBOB is used to replace LiBF4, and LiPF6 in the basic electrolyte is replaced with 0.5M LiPF6 and 0.5M LiFSI.

[0090] Example 8

[0091] The synthesis and preparation methods are the same as in Example 2, except that LiBOB is used to replace LiBF4, and LiPF6 in the basic electrolyte is replaced with 0.7M LiPF6 and 0.3M LiFSI.

[0092] Example 9

[0093] The synthesis and preparation methods are the same as in Example 2, except that LiBOB is used to replace LiBF4, and LiPF6 in the basic electrolyte is replaced with 0.8M LiPF6 and 0.2M LiFSI.

[0094] Example 10

[0095] The synthesis and preparation methods are the same as in Example 1, except that LiBOB is used to replace LiBF4, and LiPF6 in the basic electrolyte is replaced with 0.5M LiPF6 and 0.5M LiFSI.

[0096] Example 11

[0097] The synthesis and preparation methods are the same as in Example 1, except that the mass fraction ratio of graphite, carbon nanotubes, PTFE binder, and LiBF4 is 90:6:2:2.

[0098] Comparative Example 1

[0099] The synthesis and preparation methods are the same as in Example 1, except that LiBF4 is not added.

[0100] Comparative Example 2

[0101] The synthesis and preparation methods are the same as in Example 1, except that the mass fraction ratio of graphite, carbon nanotubes, PTFE binder and LiBF4 is 96:1.9:2:0.1.

[0102] Comparative Example 3

[0103] The synthesis and preparation methods are the same as in Example 1, except that the mass fraction ratio of graphite, carbon nanotubes, PTFE binder, and LiBF4 is 90:4.5:5:0.5.

[0104] Comparative Example 4

[0105] The synthesis and preparation methods are the same as in Example 1, except that LiBF4 is not added to the fibrous mixture (graphite, carbon nanotubes, PTFE binder, LiBF4), but 0.2M LiBF4 is added to the electrolyte.

[0106] Comparative Example 5

[0107] The synthesis and preparation methods are the same as in Example 1, except that LiPF6 is used instead of LiBF4.

[0108] Comparative Example 6

[0109] The synthesis and preparation methods are the same as in Example 1, except that LiFSI is used instead of LiBF4.

[0110] Comparative Example 7

[0111] The synthesis and preparation methods are the same as in Example 1, except that hard carbon is used instead of graphite.

[0112] Comparative Example 8

[0113] The synthesis and preparation methods are the same as in Example 1, except that soft carbon is used instead of graphite.

[0114] Test method: Charge to 3V at 0.05C, then charge to 3.65V at a constant current and constant voltage of 0.1C, with the current limited to 0.05C. Let stand for 2 minutes, then discharge to 2.5V at a constant current of 0.2C. The initial coulombic efficiency is the ratio of discharge capacity to charge capacity.

[0115] The test results are shown in Table 1.

[0116] Table 1

[0117] First Coulomb efficiency Example 1 91.60% Example 2 87.5% Example 3 91.40% Example 4 90.70% Example 5 91.80% Example 6 92.10% Example 7 93.30% Example 8 90.70% Example 9 90.30% Example 10 96.36% Example 11 89.77% Comparative Example 1 74.60% Comparative Example 2 77.60% Comparative Example 3 80.60% Comparative Example 4 78.60% Comparative Example 5 75.10% Comparative Example 6 76.20% Comparative Example 7 77.30% Comparative Example 8 75.10%

[0118] As can be observed in Table 1, Examples 1-11 exhibit significantly higher first-cycle coulombic efficiencies than Comparative Examples 1-8. This demonstrates that introducing boron-containing lithium salts into the dry-process preparation of high-graphite electrodes effectively improves the compatibility between graphite and the PTFE binder, while avoiding graphite agglomeration during the dry process and the insufficient wettability caused by the high fluorine content of the PTFE binder. This effectively optimizes the compatibility and compounding between graphite and the PTFE binder. Furthermore, the presence of boron-containing lithium salts also helps form an SEI film during the first cycle, thereby protecting the graphite anode. Therefore, the examples demonstrate significantly higher first-cycle coulombic efficiencies than the comparative examples.

[0119] As observed in Examples 1, 1, and 4, when LiBF4 is not introduced into the high-efficiency dry composite graphite electrode (Comparative Example 1), Comparative Example 1 exhibits a significantly lower first-coulombic efficiency than Example 1. This may be because the lack of boron-containing lithium salt leads to insufficient compatibility between graphite and PTFE binder, making it difficult to form a stable SEI film during the formation process. This results in increased side reactions, causing graphite damage and partial peeling. Figure 1 Even the introduction of boron-containing lithium salts into the electrolyte was ineffective (Comparative Example 4), thus the initial coulombic efficiency of Comparative Examples 1 and 4 was affected.

[0120] Chemical reactions are affected by multiple factors such as the type and stoichiometry of substances. In Example 1 and Comparative Example 2, we discussed the effect of the mass fraction ratio of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt on their performance. It can be observed that when the mass fraction ratio of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt is not satisfied as X:(100-XYZ):Z:Y, where 90≤X<98, 1≤Z≤2, and 0.2≤Y<(100-XZ), the initial coulombic efficiency of Comparative Examples 2 and 3 is significantly affected. This may be because when X:(100-XYZ):Z:Y is not satisfied, there may be insufficient or excessive boron-containing lithium salt, which may lead to the boron-containing lithium salt not being able to fully play its role or the occurrence of side reactions, thus affecting the results of Comparative Examples 2 and 3.

[0121] In Comparative Example 3, Examples 1 and 11, we can observe that when the binder content reaches 5% and the graphite content is only 90%, the first coulombic efficiency of Comparative Example 3 is obviously lower than that of Examples 1 and 11. This may be because when the mass fraction ratio of graphite, carbon nanotubes, PTFE binder, and LiBF4 is 90:4.5:5:0.5, Comparative Example 3 has a lower graphite content and a higher PTFE binder content, which leads to a decrease in the energy density of the high first-efficiency dry composite graphite electrode, thereby affecting the coulombic efficiency.

[0122] To verify the role of boron-containing lithium salts, we replaced LiBF4 with LiPF6 and LiFSI respectively (Comparative Examples 5 and 6). The results showed that Comparative Examples 5 and 6 did not exhibit the same good results as Example 1. This may be because LiPF6 and LiFSI could not exert the same synergistic effect as LiBF4 with graphite and PTFE binders to optimize the first coulombic efficiency. Similarly, in Comparative Examples 7 and 8, we also observed that when hard carbon and soft carbon were used to replace graphite, the first coulombic efficiency in Comparative Examples 7 and 8 was below 78%, further demonstrating that without the combined effect of graphite, PTFE binders, and boron-containing lithium salts, Comparative Examples 7 and 8 could not achieve similar results to Example 1.

[0123] To further optimize the performance of the high first-efficiency dry composite graphite electrode, we further optimized the mass fraction ratio of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt. As observed in Examples 1-4, under the condition that X:(100-XYZ):Z:Y, where 90≤X<98, 1≤Z≤2, 0.2≤Y<(100-XZ), Examples 1, 3, and 4 exhibit better first-coulombic efficiency than Example 2. This may be because the ratio of graphite, carbon nanotubes, PTFE binder, and LiBF4 in Examples 1, 3, and 4 can better leverage the compounding effect between graphite, PTFE binder, and boron-containing lithium salt, thereby optimizing the first-coulombic efficiency of Examples 1, 3, and 4.

[0124] In Examples 1, 5, and 6, we can observe that Examples 5 and 6 exhibit better initial coulombic efficiency compared to Example 1. This is likely because lithium organoborate salts can better bind with graphite and PTFE binders, thereby optimizing the initial coulombic efficiency of Examples 5 and 6. Meanwhile, compared to LiDFOB (Example 5) and LiBOB (Example 6), this is likely because LiBOB can form a dense and uniform SEI film during the first cycle, thus Example 6 exhibits superior initial coulombic efficiency.

[0125] In Examples 2, 7-9, and 10, we discussed the effect of combining high-first-efficiency dry composite graphite electrodes with lithium salts in the electrolyte. It can be observed that Examples 7-10 exhibit better first-efficiency than Example 2. In Examples 7-9, Examples 7 and 10 show better results than Examples 8-9. This indicates that when the high-first-efficiency dry composite graphite electrode proposed in this scheme contains LiPF6 and LiFSI in the electrolyte, it can cooperate with the boron-containing lithium salt in the high-first-efficiency dry composite graphite electrode to construct a more stable SEI film. At the same time, when the molar ratio of LiPF6 to LiFSI is (4-5):(5-6), it helps to further optimize the combination results. Therefore, Example 7 shows the best first-coulombic efficiency.

[0126] In Examples 1 and 11, we further explored the role of graphite content. It can be observed that Example 1 exhibits a better first-time coulombic efficiency compared to Example 11. This may be because Example 1 has a better graphite content, thereby improving the energy density of the high first-time efficiency dry composite graphite electrode. It also enables it to better cooperate with conductive carbon materials, PTFE binders and boron-containing lithium salts, thereby optimizing the performance of Example 1.

[0127] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions, and variations to the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A high-efficiency dry-process composite graphite electrode, characterized in that, It includes graphite, conductive carbon material, PTFE binder and boron-containing lithium salt, wherein the mass fraction ratio of graphite, conductive carbon material, PTFE binder and boron-containing lithium salt is X:(100-XYZ):Z:Y, 90≤X<98, 1≤Z≤2, 0.2≤Y<(100-XZ); The boron-containing lithium salt is selected from any one or more of lithium oxalate borate salt and lithium tetrafluoroborate, which are fluorine-containing or / and fluorine-free.

2. The high-efficiency dry-process composite graphite electrode according to claim 1, characterized in that, In the high-efficiency dry composite graphite electrode, the mass fraction ratio of graphite, conductive carbon material, PTFE binder and boron-containing lithium salt is X:(100-XYZ):Z:Y, where 95<X<97, 1≤Z≤2, and 0.4≤Y<(100-XZ).

3. The high-efficiency dry-process composite graphite electrode according to claim 1, characterized in that, In the high-efficiency dry composite graphite electrode, the mass fraction ratio of graphite, conductive carbon material, PTFE binder and boron-containing lithium salt is X:(100-XYZ):Z:Y, where 95<X<97, 1≤Z≤2, 0.4≤Y<(100-XZ), and Z:Y=3.8-4.

2.

4. The high-efficiency dry-process composite graphite electrode according to claim 1, characterized in that, The conductive carbon material is selected from any one or more of zero-dimensional conductive carbon materials, one-dimensional conductive carbon materials, and two-dimensional conductive carbon materials.

5. The high-efficiency dry-process composite graphite electrode according to claim 1, characterized in that, The conductive carbon material is selected from one-dimensional conductive carbon materials.

6. A battery, characterized in that, The high-efficiency dry composite graphite electrode according to any one of claims 1-5 is used as the negative electrode.

7. The battery according to claim 6, characterized in that, The battery also includes a positive electrode, an electrolyte, and a separator.

8. The battery according to claim 7, characterized in that, The positive electrode sheet includes a positive electrode active material, a positive electrode current collector, a positive electrode conductive agent, and a positive electrode binder.

9. The battery according to claim 8, characterized in that, The positive electrode conductive agent is selected from any one or more of carbon materials, metallic materials, and conductive polymers; The positive electrode adhesive is selected from at least one of thermoplastic resins, acrylic resins, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

10. The battery according to claim 7, characterized in that, The lithium salt added to the electrolyte is a mixed lithium salt of LiFSI and LiPF6.

11. The battery according to claim 10, characterized in that, In the mixed lithium salt, the molar ratio of LiFSI to LiPF6 is (2-5):(5-8).

12. The battery according to claim 10, characterized in that, In the mixed lithium salt, the molar ratio of LiFSI to LiPF6 is (4-5):(5-6).

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