High-first-effect dry-method composite graphite electrode

Abstract

The invention discloses a high-first-effect dry-process composite graphite electrode which comprises graphite, a conductive carbon material, a PTFE adhesive and boron-containing lithium salt, the mass fraction ratio of the graphite to the conductive carbon material to the PTFE adhesive to the boron-containing lithium salt is X: (100-X-Y-Z): Z: Y, X is larger than or equal to 90 and smaller than 98, Z is larger than or equal to 1 and smaller than or equal to 2, and Y is larger than or equal to 0.2 and smaller than (100-X-Z). According to the preparation method, the high-performance graphite electrode is prepared through the dry method, the proportion of all the components is accurately regulated and controlled, dual optimization of high energy density and high first efficiency is achieved, meanwhile, the production cost and the process complexity are reduced, and an efficient and low-cost new thought is provided for dry preparation of the high-performance graphite electrode.

Description

Technical Field

[0001] The present invention belongs to the field of lithium - ion batteries, and particularly relates to a high - first - efficiency dry - composite graphite electrode. Technical Background

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

[0003] The sp 2 hybrid structure of graphite endows it with unique physical and chemical properties. Based on this structure, the graphite negative electrode sheet exhibits excellent cycle performance and structural stability, and at the same time has a high specific capacity. Combining its pressure - resistant performance, graphite can significantly improve the volumetric energy density of the electrode during the dry - method preparation process. Especially in electrodes with a high graphite content (graphite content ≥ 90%), it shows significant advantages in terms of cycle stability and specific capacity.

[0004] However, in the actual dry - method preparation process, the mixing process of the negative - electrode active material graphite and the binder (such as PTFE binder) faces challenges. Since both the PTFE binder and the graphite surface carry negative charges, they repel each other during the mixing process, resulting in the binder being difficult to effectively bond to the graphite. This problem not only reduces the first - coulomb efficiency of the negative electrode sheet but also limits the further development of the dry - method preparation of graphite negative electrodes. To solve this problem, the common current methods are to perform surface coating treatment on graphite or the PTFE binder, or to add additives to the electrolyte to improve the compatibility between the two. However, although these methods improve the bonding performance between the PTFE binder and graphite to a certain extent, they also bring problems such as a decrease in the capacity density of the electrode sheet, an increase in cost, and possible side reactions.

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

[0006] In view of the problems in the prior art, the present invention provides a high - first - efficiency dry - composite graphite electrode, which solves the problem of incompatibility between graphite and the PTFE binder and obtains a high - first - coulomb - efficiency high - first - efficiency dry - composite graphite electrode.

[0007] The present invention provides a high-first-efficiency dry-composite graphite electrode, which comprises graphite, a conductive carbon material, a PTFE binder, and a boron-containing lithium salt. Among them, the mass fraction ratio of graphite, the conductive carbon material, the PTFE binder, and the boron-containing lithium salt is X:(100-X-Y-Z):Z:Y, where 90≤X<98, 1≤Z≤2, and 0.2≤Y<(100-X-Z).

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

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

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

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

[0012] As a further solution, the boron-containing lithium salt is selected from any one or several of organic lithium borates and inorganic lithium borates.

[0013] As a further preferred solution, the boron-containing lithium salt is selected from organic lithium borates.

[0014] As a further solution, the organic lithium borate is selected from lithium oxalate borate.

[0015] As a further solution, the lithium oxalate borate is selected from lithium oxalate borate containing fluorine or / and without fluorine.

[0016] As a further preferred solution, the lithium oxalate borate is selected from lithium oxalate borate without fluorine.

[0017] As a further preferred solution, the lithium oxalate borate without fluorine is selected from lithium bis(oxalato)borate (LiBOB).

[0018] As a further solution, the inorganic lithium borate is selected from inorganic lithium borates containing fluorine.

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

[0020] In a second aspect, the present solution provides a battery that uses a high first-efficiency dry-composite graphite electrode as the negative electrode.

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

[0022] As a further solution, 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 solution, the positive electrode conductive agent is selected from any one or several of carbon materials, metal materials, and conductive polymers.

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

[0025] As a further solution, the electrolyte is not limited in principle, and those skilled in the art can select a conventional basic electrolyte such as: 1M LiPF6 in EC / DMC / EMC / DEC (1:1:3:1) with 2% by mass of VC added.

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

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

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

[0029] As a further solution, the separator is not limited in principle, and those skilled in the art can select any one of polyethylene (PE) separators, polypropylene (PP) separators, non-woven fabric separators, aramid (Nomex) separators, and polyimide (PI) separators.

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

[0031] By introducing boron-containing lithium salts, this solution significantly improves the compatibility between graphite and PTFE binder, solving the problem of compounding these two components in traditional dry preparation methods. Boron-containing lithium salts can not only reduce the electrostatic repulsion between graphite and PTFE binder, but also enhance their affinity by forming multi-coordinated B-F bonds. At the same time, as a dispersant, it inhibits the agglomeration of graphite, optimizing the uniformity and compaction density of the electrode. In addition, boron-containing lithium salts form a stable SEI film in-situ during the first charge-discharge process, effectively protecting the graphite anode and optimizing the cycle stability and first Coulombic efficiency of the electrode. By precisely controlling the mass fractions of each component, this solution achieves the synergistic optimization of high energy density and high first efficiency, reducing the preparation cost and process complexity, providing an efficient and low-cost solution for the dry preparation of high-performance graphite electrodes, and having good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the accompanying drawings required for the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0033] Figure 1 Among them, Figure 1 a is a microscopic image of the graphite surface after disassembling the battery of Example 1 after formation and formation capacity testing, Figure 1 b is a microscopic image of the graphite surface after disassembling the battery of Comparative Example 1 after formation and formation capacity testing. DETAILED DESCRIPTION OF THE EMBODIMENTS

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

[0035] The following are explanations of terms or words, and unless otherwise defined, all technical and scientific terms used herein have the meanings commonly understood by those skilled in the art to which the present invention belongs.

[0036] The present invention provides a high first-efficiency dry composite graphite electrode, including graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt. Among them, the mass fraction ratio of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt is X:(100-X-Y-Z):Z:Y, where 90≤X<98, 1≤Z≤2, 0.2≤Y<(100-X-Z).

[0037] To solve the problem of poor compatibility between graphite and PTFE binder, this solution introduces a boron-containing lithium salt. Through the mutual cooperation among the boron-containing lithium salt, graphite, and PTFE binder, a dry-process composite graphite electrode with high initial efficiency is obtained. Graphite has good pressure resistance, enabling it to withstand higher rolling pressure and thus improve the compaction density. Especially in the case of high graphite content, the graphite electrode is expected to exhibit a higher energy density. However, during the dry preparation process, the negatively charged graphite repels the equally negatively charged PTFE binder, resulting in a sharp decline in the compatibility between graphite and PTFE binder. At the same time, the high-fluorine and low-wetting characteristics of the PTFE binder further exacerbate the deterioration of the compatibility between graphite and PTFE binder. Moreover, graphite itself will agglomerate under the action of van der Waals forces, especially in the solvent-free dry preparation process, where the agglomeration phenomenon will be more serious. Coupled with the ultra-high graphite content, it is extremely difficult to achieve a suitable dry-process compounding between graphite and PTFE binder. To solve this problem, this solution introduces a boron-containing lithium salt. During the dry preparation of the graphite electrode, the positively charged boron-containing lithium salt will preferentially adsorb on the negatively charged regions of graphite and PTFE binder, reducing the repulsive force between graphite and PTFE binder and enhancing the compatibility between them. At the same time, during the dry preparation process, the boron-containing lithium salt can also form multi-coordinated B-F bonds with the highly fluorinated PTFE binder, increasing the surface energy of the PTFE binder and enhancing the affinity between the PTFE binder and graphite. In addition, the boron-containing lithium salt may also act as a dispersant, reducing the attraction between particles by inserting into the graphite interlayer or adsorbing on the surface, thereby avoiding the agglomeration of graphite. During the first charge and discharge process, the boron-containing lithium salt will in-situ passivate to form a SEI film, thus effectively protecting the graphite negative electrode. In addition, the optimization of the performance of the dry-process composite graphite electrode with high initial efficiency is not only the result of the compounding of graphite, PTFE binder, and boron-containing lithium salt, but also requires the cooperation of the ratios among various substances to fully exert the compounding effect. In this solution, we found that the addition of only a small amount of PTFE binder and boron-containing lithium salt can greatly improve the dry preparation effect of graphite. The mass fraction ratio of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt is X:(100-X-Y-Z):Z:Y, where 90≤X<98, 1≤Z≤2, 0.2≤Y<(100-X-Z). By controlling the mass fractions of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt, this solution can effectively improve the compatibility between graphite and PTFE binder while avoiding side reactions and fully optimizing the thickness of the SEI film to fully optimize the initial Coulomb efficiency of the dry-process composite graphite electrode with high initial efficiency and give full play to the advantages of the dry-process composite graphite electrode with high initial efficiency.

[0038] As some cases, in the high first-efficiency dry-compounded graphite electrode, the mass fraction ratio of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt is X:(100-X-Y-Z):Z:Y, where 95 < X < 97, 1 ≤ Z ≤ 2, 0.4 ≤ Y < (100-X-Z), which helps to further optimize the cooperation among graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt, improve the compatibility between graphite and PTFE binder, thereby optimizing the energy density and enhancing the first efficiency of the battery.

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

[0040] As some cases, 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 with all three spatial dimensions in the nanoscale. The zero-dimensional conductive carbon materials are selected from any one or more of acetylene black, Ketjen black, furnace black, and fullerenes.

[0042] One-dimensional conductive carbon materials refer to linear carbon materials with nanoscale radial dimensions and micron-scale axial dimensions. The one-dimensional conductive carbon materials are selected from any one or more of carbon nanotubes and carbon nanofibers.

[0043] Two-dimensional conductive carbon materials refer to sheet-structured carbon materials with atomic-scale 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 cases, the conductive carbon material is selected from one-dimensional conductive carbon materials.

[0045] As some cases, the boron-containing lithium salt is selected from any one or more of organic lithium borates and inorganic lithium borates.

[0046] As some preferred cases, the boron-containing lithium salt is selected from organic lithium borates.

[0047] As some cases, the organic lithium borate is selected from lithium oxalate borate.

[0048] As some examples, the lithium oxalate borate salt is selected from fluorine-containing or / and 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(oxalato)borate (LiBOB).

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

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

[0053] In a second aspect, the present solution provides a battery, which uses a high first-cycle efficiency dry composite graphite electrode as the negative electrode.

[0054] As some examples, the battery further includes a positive electrode sheet, 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 solution, the positive electrode active material is selected from lithium iron phosphate, LiMO2, lithium nickel cobalt manganese oxide LiNi x Mn y Co z O2, lithium nickel cobalt aluminate LiNi p Co q Al f O2, lithium-rich manganese-based positive electrode material: 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 electrode current collector is selected from copper, aluminum, titanium, nickel, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, gold, silver, iron, platinum, chromium, tin, indium, an alloy containing one or more of these, and 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, metal materials, and conductive polymers.

[0059] As some optional parameters, the carbon materials are 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 materials are selected from any one or more of copper, nickel, aluminum, and silver.

[0061] As some optional parameters, the conductive polymers are selected from one or more of polyfluorene (PF), polyaniline (PANI), polypyrrole (PPy), polythiophene (PTh), poly(ethylenedioxythiophene) (PEDOT), poly(ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), and polyacetylene (PA).

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

[0063] As a further solution, the thermoplastic resin includes at least one of polyvinylidene fluoride, copolymer of vinylidene fluoride, polytetrafluoroethylene, copolymer of vinylidene fluoride - hexafluoropropylene, copolymer of tetrafluoroethylene - hexafluoropropylene, copolymer of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymer of ethylene - tetrafluoroethylene, copolymer of vinylidene fluoride - tetrafluoroethylene, copolymer of vinylidene fluoride - trifluoroethylene, copolymer of vinylidene fluoride - trichloroethylene, copolymer of vinylidene fluoride - fluoroethylene, copolymer of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene.

[0064] As some cases, the electrolyte is not limited in principle, and those skilled in the art can select a conventional basic electrolyte such as: 1M LiPF6 in EC / DMC / EMC / DEC(1:1:3:1) with 2% by mass of VC added.

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

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

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

[0068] As some cases, the separator is not limited in principle, and those skilled in the art can select any one of polyethylene (PE) separator, polypropylene (PP) separator, non - woven fabric separator, aramid (Nomex) separator, and polyimide (PI) separator.

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

[0070] The chemical raw materials involved in the following examples and comparative examples are all prior arts and are obtained through commercial purchase. The experimental devices, testing devices, etc. involved in the following examples and comparative examples are all conventional devices in the art without special requirements and limitations.

[0071] Example 1

[0072] Preparation of a high - first - efficiency dry - compounded graphite electrode

[0073] Mix graphite, carbon nanotubes, PTFE binder, and LiBF4 in a mass fraction ratio of 96:1.5:2:0.5, disperse them at 80 °C and 20,000 rpm for 5 min, and pass through a 60-mesh sieve after dispersion. At an extrusion temperature of 80 °C, roll them under a pressure of 30 t, and then obtain a high-first-efficiency dry-composite graphite electrode with a thickness of 8 mg / cm 2 by thinning.

[0074] Preparation of Lithium Iron Phosphate Cathode Sheet

[0075] Mix lithium iron phosphate, carbon nanotubes, and PTFE binder in a mass fraction ratio of 96:2:2, disperse them at 80 °C and 20,000 rpm for 5 min, and pass through a 60-mesh sieve after dispersion. At an extrusion temperature of 80 °C, roll them under a pressure of 30 t, and then obtain a lithium iron phosphate cathode sheet with a thickness of 20 mg / cm 2 by thinning.

[0076] Cell: The ratio of the capacity of the anode sheet to the capacity of the cathode sheet is 1.1. Select a PE separator and fabricate a 1-Ah laminated soft package.

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

[0078] Example 2

[0079] The synthesis and preparation methods are the same as those 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 those 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 those 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 those in Example 1, except that LiDFOB is used to replace LiBF4.

[0086] Example 6

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

[0088] Example 7

[0089] The synthesis and preparation methods are the same as those 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 those 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 those 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 those 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 those 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 those in Example 1, except that LiBF4 is not added.

[0100] Comparative Example 2

[0101] The synthesis and preparation methods are the same as those 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 those 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 those in Example 1, except that LiBF4 is not added to the fibrillated mixture (graphite, carbon nanotubes, PTFE binder, LiBF4), and 0.2 M LiBF4 is added to the electrolyte.

[0106] Comparative Example 5

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

[0108] Comparative Example 6

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

[0110] Comparative Example 7

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

[0112] Comparative Example 8

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

[0114] Test method: Charge at 0.05C to 3V, charge at 0.1 constant current and constant voltage to 3.65V, limit the current to 0.05C, let it stand for 2 minutes, and discharge at 0.2C constant current to 2.5V. The initial Coulombic efficiency is the ratio of the discharge capacity to the charge capacity.

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

[0116] Table 1

[0117] Initial 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] It can be observed from Table 1 that Examples 1 - 11 exhibit far better initial Coulombic efficiency than Comparative Examples 1 - 8, indicating that the method of introducing boron-containing lithium salts into the dry preparation of high-graphite electrodes can effectively improve the compatibility between graphite and PTFE binder, while avoiding the agglomeration of graphite during the dry process and the problem of insufficient wettability caused by the high fluorine content of PTFE binder, thereby effectively optimizing the compatibility and compounding between graphite and PTFE binder; at the same time, the presence of boron-containing lithium salts also helps to form a SEI film during the first cycle, thus achieving the protection of the graphite negative electrode. Therefore, the examples exhibit better initial Coulombic efficiency than the comparative examples.

[0119] It can be observed from Example 1, Comparative Example 1, and Comparative Example 4 that when LiBF4 is not introduced into the high-first-efficiency dry composite graphite electrode (Comparative Example 1), Comparative Example 1 shows a first Coulombic efficiency far lower than that of Example 1. This may be because the lack of boron-containing lithium salt will lead to insufficient compatibility between graphite and PTFE binder, making it difficult to form a stable SEI film during formation, resulting in an increase in the degree of side reactions, thus causing damage to graphite and partial peeling ( Figure 1 ). Even when a boron-containing lithium salt is introduced into the electrolyte, it is difficult to achieve the effect (Comparative Example 4). Therefore, the first Coulombic efficiencies of Comparative Example 1 and Comparative Example 4 are both affected.

[0120] Chemical reactions are affected by multiple factors such as the types and stoichiometry of substances. In Example 1 and Comparative Example 2, we discussed the influence of the mass fraction ratios of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt on their performance. It can be observed that when the mass fraction ratios of graphite, conductive carbon material, PTFE binder, and boron-containing lithium salt do not satisfy X:(100-X-Y-Z):Z:Y, where 90≤X<98, 1≤Z≤2, 0.2≤Y<(100-X-Z), the first Coulombic efficiencies of Comparative Example 2 and Comparative Example 3 are both greatly affected. This may be because when the ratio does not satisfy X:(100-X-Y-Z):Z:Y, where 90≤X<98, 1≤Z≤2, 0.2≤Y<(100-X-Z), there may be a shortage or excess of boron-containing lithium salt, resulting in the boron-containing lithium salt being unable to play its role fully or side reactions occurring, thus affecting the results of Comparative Example 2 and Comparative Example 3.

[0121] In Comparative Example 3, Example 1, and Example 11, it can be observed that when the binder ratio reaches 5% and the graphite ratio is only 90%, the first Coulombic efficiency of Comparative Example 3 is significantly lower than that of Example 1 and Example 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 ratio, resulting in a decrease in the energy density of the high-first-efficiency dry composite graphite electrode, thus affecting the Coulombic efficiency.

[0122] To verify the role of the boron-containing lithium salt, we replaced LiBF4 with LiPF6 and LiFSI respectively (Comparative Example 5 and Comparative Example 6). As a result, it was observed that Comparative Example 5 and Comparative Example 6 did not show good results like Example 1. This may be because LiPF6 and LiFSI cannot play the synergistic role with graphite and PTFE binder to optimize the first Coulombic efficiency. Similarly, in Comparative Example 7 and Comparative Example 8, it was also observed that when hard carbon and soft carbon were used to replace graphite, the first Coulombic efficiency of Comparative Example 7 and Comparative Example 8 was lower than 78% after the first cycle. It was also proved that when the combined action of graphite, PTFE binder, and boron-containing lithium salt is lacking, it is difficult for Comparative Example 7 and Comparative Example 8 to achieve a similar effect to Example 1.

[0123] To further optimize the performance of the high-first-efficiency dry-compounded graphite electrode, we further optimized the mass fraction ratios of graphite, conductive carbon materials, PTFE binder, and boron-containing lithium salts. From Examples 1-4, we can observe that on the basis of satisfying X:(100-X-Y-Z):Z:Y, where 90≤X<98, 1≤Z≤2, 0.2≤Y<(100-X-Z), Examples 1, 3, and 4 exhibit better initial Coulombic efficiency than Example 2. This may be because the ratios of graphite, carbon nanotubes, PTFE binder, and LiBF4 in Examples 1, 3, and 4 can better exert the compounding effect among graphite, PTFE binder, and boron-containing lithium salts, thus optimizing the initial Coulombic efficiency of Examples 1, 3, and 4.

[0124] In Examples 1, 5, and 6, we can observe that compared with Example 1, Examples 5 and 6 exhibit better initial Coulombic efficiency. This may be because the organoboron lithium salt can better combine with graphite and PTFE binder, thus optimizing the initial Coulombic efficiency of Examples 5 and 6. At the same time, compared with LiDFOB (Example 5), LiBOB (Example 6), this may be because during the first cycle, LiBOB can form a dense and uniform SEI film, so Example 6 shows better initial Coulombic efficiency.

[0125] In Examples 2, 7-9, and 10, we discussed the compounding effect of the high-first-efficiency dry-compounded graphite electrode and lithium salts in the electrolyte. It can be observed that Examples 7-10 show better first efficiency than Example 2. Among Examples 7-9, Examples 7 and 10 show better results than Examples 8-9, indicating that the high-first-efficiency dry-compounded graphite electrode proposed in this scheme can cooperate with the boron-containing lithium salts in the electrolyte to construct a more stable SEI film when the electrolyte contains LiPF6 and LiFSI. At the same time, when the molar ratio of LiPF6 and LiFSI is (4-5):(5-6), it helps to further optimize the compounding result, so Example 7 exhibits the optimal initial Coulombic efficiency.

[0126] In Examples 1 and 11, we further explored the role of the graphite content. It can be observed that compared with Example 11, Example 1 exhibits better initial Coulombic efficiency. This may be because Example 1 has a better graphite content, which improves the energy density of the high-first-efficiency dry-compounded graphite electrode and enables it to better cooperate with conductive carbon materials, PTFE binder, and boron-containing lithium salts, thus optimizing the performance of Example 1.

[0127] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention. In addition, without mutual contradiction, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples.

Claims

1. A high initial efficiency dry composite graphite electrode, characterized in that: It includes graphite, conductive carbon material, PTFE adhesive and boron-containing lithium salt, wherein the mass fraction ratio of graphite, conductive carbon material, PTFE adhesive and boron-containing lithium salt is X:(100-XYZ):Z:Y, 90≤X<98, 1≤Z≤2, 0.2≤Y<(100-XZ).

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

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

2.

4. The high initial efficiency dry 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 material, one-dimensional conductive carbon material, and two-dimensional conductive carbon material. Preferably, the conductive carbon material is selected from one-dimensional conductive carbon material.

5. The high initial efficiency dry composite graphite electrode according to claim 1, characterized in that: The boron-containing lithium salt is selected from any one or more of organic borate lithium salts and inorganic borate lithium salts; Preferably, the boron-containing lithium salt is selected from organic borate lithium salts; Preferably, the organic borate lithium salt is selected from oxalate borate lithium salt; Preferably, the lithium oxalate borate salt is selected from fluorine-containing or / and fluorine-free lithium oxalate borate salts; Preferably, the lithium oxalate borate salt is selected from a lithium oxalate borate salt that does not contain fluorine; Preferably, the fluorine-free lithium oxalatoborate salt is selected from lithium bis(oxalatoborate).

6. The high initial efficiency dry composite graphite electrode according to claim 5, characterized in that: The organic lithium borate salt is selected from lithium oxalate borate; the lithium oxalate borate salt is selected from fluorine-containing and / or fluorine-free lithium oxalate borate; the fluorine-free lithium oxalate borate salt is selected from lithium bis(oxalatoborate); the inorganic lithium borate salt is selected from fluorine-containing inorganic lithium borate salt; preferably, the fluorine-containing inorganic lithium borate salt is selected from lithium tetrafluoroborate.

7. A battery, characterized in that: Using the high initial efficiency dry composite graphite electrode described in any one of claims 1 to 6 as the negative electrode; Preferably, the battery further comprises a positive plate, an electrolyte, and a diaphragm; Preferably, the positive electrode sheet includes a positive electrode active material, a positive electrode current collector, a positive electrode conductor, and a positive electrode binder.

8. The battery according to claim 7, characterized in that The battery also includes a positive plate, an electrolyte, and a diaphragm; The positive electrode sheet comprises a positive electrode active material, a positive electrode current collector, a positive electrode conductive agent, and a positive electrode adhesive; The positive electrode conductive agent is selected from any one or more of carbon materials, metal materials, and conductive polymers; Preferably, the positive electrode binder is selected from at least one of thermoplastic resin, acrylic resin, sodium carboxymethyl cellulose and styrene butadiene rubber.

9. 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.

10. The battery according to claim 9, characterized in that In the mixed lithium salt, the molar ratio of LiFSI to LiPF6 is (2-5): (5-8); Preferably, in the mixed lithium salt, the molar ratio of LiFSI to LiPF6 is (4-5): (5-6).

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