Artificial SEI (Solid Electrolyte Interphase) film layer applied to fast-charging negative electrode material as well as preparation method and application of artificial SEI film layer

Abstract

The invention provides an artificial SEI film layer applied to a fast-charging negative electrode material and a preparation method and application of the artificial SEI film layer. The material of the artificial SEI film layer comprises a polymer with a three-dimensional interpenetrating network structure, and the structure of the polymer comprises a combination of a nitro group, a furan group and an imidazolone group. The artificial SEI film layer provided by the invention has good mechanical property and chemical stability, and can significantly relieve the volume change of an internal inorganic material and improve the ion transmission rate, thereby improving the electrochemical performance of the fast-charging negative electrode material under high voltage.

Description

Technical Field

[0001] The present invention belongs to the field of battery technology, and specifically relates to an artificial SEI film layer used for fast-charging negative electrode materials, and a preparation method and application thereof. Background Art

[0002] Silicon-based anode materials have become an important research direction in the field of lithium-ion batteries due to their high specific capacity, abundant resources, and environmental friendliness. Among them, the biggest advantage of silicon-based anode materials is that their theoretical specific capacity is much higher than that of traditional graphite anode materials. Specifically, the theoretical specific capacity of silicon is as high as 4200mAh / g, which is more than 10 times that of graphite (372mAh / g). This characteristic makes silicon-based anode materials have significant potential in improving the energy density of lithium-ion batteries, especially in the fields of new energy vehicles and portable electronic devices.

[0003] Despite the many advantages of silicon-based anode materials, they still face some technical challenges in practical applications. The main issues include the following two aspects: (1) Silicon undergoes a huge volume change during the charge and discharge process (expansion rate is as high as 300% to 400%), and the SEI film on the surface of the silicon-based material is unable to adapt to the volume change of the anode, has low structural strength and is prone to rupture, which in turn affects the cycle life and capacity of lithium-ion batteries; (2) The low conductivity of pure silicon results in a high interfacial resistance between the electrolyte and the anode, and the ion transfer rate is limited, thereby reducing the fast charging performance and overall cycle efficiency of lithium-ion batteries.

[0004] To address these issues, researchers have proposed a variety of improvement measures, such as coating the surface of silicon-based anode materials with a stable material to effectively inhibit the excessive growth of the SEI film and improve its stability, or introducing additives into the electrolyte to improve the chemical composition and structure of the SEI film, thereby improving its stability and conductivity. Although these technical measures can alleviate the problem to a certain extent, they are currently unable to fundamentally and completely solve all technical problems.

[0005] Therefore, how to provide a silicon-based negative electrode material with good interface stability and efficient ion transport properties between it and the electrolyte is crucial to meet the needs of developing high-performance lithium-ion batteries. Summary of the Invention

[0006] In response to the shortcomings of the prior art, the present invention aims to provide an artificial SEI film layer for fast-charging negative electrode materials, as well as its preparation method and application. The artificial SEI film layer provided by the present invention has good mechanical properties and chemical stability, and can significantly reduce the volume change of the internal inorganic material and increase the ion transmission rate, thereby improving the electrochemical performance of the fast-charging negative electrode material at high voltage.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides an artificial SEI film layer for fast-charging negative electrode materials, wherein the material of the artificial SEI film layer includes a polymer having a three-dimensional interpenetrating network structure, and the structure of the polymer contains a combination of nitro groups, furan groups and imidazolidone groups.

[0009] First, the artificial SEI film provided by the present invention possesses a certain degree of flexibility, effectively overcoming the deformation and stress issues caused by volume expansion of silicon-based anode materials. Furthermore, the furan groups in the polymer structure possess a certain degree of rigidity and strength. Therefore, the artificial SEI film containing furan groups can enhance the structural strength of silicon-based anode materials, reducing the pulverization and shedding of electrode materials caused by volume changes during charge and discharge, thereby improving the cycling stability of silicon-based anode materials.

[0010] Secondly, the nitro group can interact with the ions in the electrolyte, optimizing the interface structure between the electrolyte and the negative electrode material, thereby reducing the interfacial resistance between the two and increasing the ion migration rate. In addition, the nitro group (-NO2) can produce a synergistic effect with the imidazolone group (-NH-CO-NH-), promoting rapid ion conduction through dipole-ion interaction, thereby further reducing the interfacial impedance between the negative electrode material and the electrolyte, thereby comprehensively improving the fast charging performance of silicon-based negative electrode materials.

[0011] Finally, the present invention forms a three-dimensional interpenetrating network structure by designing polymers, thereby improving the mechanical properties and acid and alkali resistance of the artificial SEI film layer, thereby enhancing the fast charging stability of silicon-based negative electrode materials in complex environments.

[0012] Preferably, the monomers forming the polymer include compounds containing a combination of at least one unsaturated double bond, at least one nitro group, at least one furan group, and at least one imidazolone group.

[0013] Preferably, the monomers forming the polymer include compounds containing a combination of at least one alkenyl group, at least one nitrofuran group, and at least one imidazolidiones group.

[0014] Preferably, the monomers forming the polymer include 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione.

[0015] The present invention preferably uses 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione as a polymerization monomer, thereby being able to better balance the mechanical properties and interfacial properties of the artificial SEI film layer, so that the mechanical properties of the artificial SEI film layer are significantly improved while having excellent ionic conductivity, thereby effectively coping with the stress generated by the huge volume change of the silicon-based negative electrode material, thereby improving the cycle life and the first coulombic efficiency of the secondary battery.

[0016] Specifically, the furan group and the nitro group in the monomer structure of 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione are in a suitable conjugated position, which is conducive to electron delocalization and enhances the interaction between the nitro group and the ions in the electrolyte. In addition, the position of unsaturated bonds such as alkenyl groups and carbon-nitrogen double bonds affects the degree of cross-linking and flexibility of the polymer. When they are distributed at specific positions on the polymer backbone, they can form a stable and flexible three-dimensional interpenetrating network structure, thereby better buffering the volume expansion of silicon-based negative electrode materials.

[0017] Further preferably, the ratio of the number of furan groups, nitro groups, amino groups, unsaturated hydrocarbon groups and imidazolinone groups in the monomer structure forming the polymer is (1-4):(1-4):(0.5-3):(1-3):(1-5).

[0018] The present invention optimizes the overall performance of the artificial SEI film by regulating the quantitative ratio of the aforementioned different types of groups in the polymerized monomer structure. At this quantitative ratio, the groups work synergistically. Specifically, the nitro and imidazolone groups perform best in terms of ion conductivity, the furan group is most effective in enhancing the structural strength of the silicon-based negative electrode material, and the unsaturated hydrocarbon groups can form a stable three-dimensional interpenetrating network structure when participating in the polymerization reaction. Through the combination of these different types of groups, the fast-charging performance of the silicon-based negative electrode material is effectively improved.

[0019] Preferably, the number average molecular weight of the polymer is 10,000 Da to 50,000 Da, preferably 22,000 Da to 40,000 Da, for example, it can be 10,000 Da, 15,000 Da, 20,000 Da, 22,000 Da, 25,000 Da, 30,000 Da, 35,000 Da, 40,000 Da, 45,000 Da or 50,000 Da, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] The present invention regulates the number-average molecular weight of the polymer to an appropriate range, resulting in an artificial SEI film layer with good mechanical strength, ionic conductivity, and chemical stability. If a polymer with a lower number-average molecular weight is used, the mechanical strength and chemical stability of the polymer may be insufficient, and it may not effectively protect the fast-charging negative electrode material. If a polymer with a higher number-average molecular weight is used, the viscosity of the polymer solution increases, which is not conducive to uniform coating and may increase the interfacial impedance between the SEI film and the fast-charging negative electrode material, ultimately reducing the charge and discharge performance of the secondary battery.

[0021] In a second aspect, the present invention provides a method for preparing an artificial SEI film layer for a fast-charging negative electrode material according to the first aspect, the method comprising the following steps:

[0022] A monomer comprising at least one unsaturated double bond, at least one nitro group, at least one furan group and at least one imidazolone group, an initiator and an organic solvent are mixed, and after a polymerization reaction, an artificial SEI film layer applied to a fast-charging negative electrode material is obtained.

[0023] Preferably, the polymerization reaction temperature is 60°C to 80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0024] Preferably, the polymerization reaction time is 8 h to 12 h, for example, 8 h, 9 h, 10 h, 11 h or 12 h, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] In the present invention, the polymerization reaction is carried out under an inert atmosphere, which exemplarily includes argon and / or nitrogen.

[0026] In the present invention, the initiator exemplarily includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, or dibenzoyl peroxide (BPO). Furthermore, based on the total mass of the monomers as 100%, the mass percentage of the initiator is 0.5% to 1.5%, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, or 1.5%, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0027] In the present invention, the organic solvent illustratively includes at least one of benzene, tetrahydrofuran (THF), N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF).

[0028] In the present invention, after the polymerization reaction, the following steps are further included: adding the reaction solution after the polymerization reaction into a precipitation solvent to obtain a polymer precipitate, and then washing and drying the polymer precipitate to obtain the polymer.

[0029] In the present invention, the precipitation solvent illustratively includes at least one of propanol, isopropanol or acetone.

[0030] In a third aspect, the present invention provides a fast-charging negative electrode material, which includes a silicon-carbon material matrix and an artificial SEI film layer arranged on the surface of the silicon-carbon material matrix, and the artificial SEI film layer includes the artificial SEI film layer applied to the fast-charging negative electrode material according to the first aspect.

[0031] Preferably, the average particle size of the silicon-carbon material matrix is ​​4μm to 8μm, for example, it can be 4μm, 4.2μm, 4.5μm, 4.8μm, 5μm, 5.2μm, 5.5μm, 5.8μm, 6μm, 6.2μm, 6.5μm, 6.8μm, 7μm, 7.2μm, 7.5μm, 7.8μm or 8μm, etc., not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] The present invention facilitates subsequent processing and improves the ion transport performance of silicon-based anode materials by regulating the average particle size of the silicon-carbon material. Using a silicon-carbon material with a smaller average particle size makes it difficult to disperse the particles during the subsequent homogenization process. Using a silicon-carbon material with a larger average particle size degrades the ion transport performance of the resulting silicon-based anode material, and the rate performance of the resulting secondary battery deteriorates accordingly.

[0033] Preferably, the specific surface area of ​​the silicon-carbon material matrix is ​​1m 2 / g~8m 2 / g, for example, 1m 2 / g, 1.2m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2m 2 / g, 2.2m 2 / g, 2.5m 2 / g, 2.8m 2 / g、3m 2 / g, 3.2m 2 / g, 3.5m 2 / g, 3.8m 2 / g、4m 2 / g, 4.2m 2 / g, 4.5m 2 / g, 4.8m2 / g、5m 2 / g, 5.2m 2 / g, 5.5m 2 / g, 5.8m 2 / g、6m 2 / g, 6.2m 2 / g, 6.5m 2 / g, 6.8m 2 / g、7m 2 / g, 7.2m 2 / g, 7.5m 2 / g、7.8m 2 / g or 8m 2 / g, etc., are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] Preferably, the mass percentage of silicon material in the silicon-carbon material matrix is ​​40% to 59%, for example, it can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58% or 59%, etc., not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0035] By regulating the mass percentage of silicon material in the silicon-carbon matrix, the present invention achieves a high gram capacity and a high first coulombic efficiency while minimizing volume expansion. Using a silicon-carbon matrix with a lower silicon content results in lower gram capacity and first coulombic efficiency; using a silicon-carbon matrix with a higher silicon content results in greater volume expansion.

[0036] Preferably, based on the total mass of the fast-charging negative electrode material as 100%, the mass percentage of the artificial SEI film layer is 1% to 4%, for example, it can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8% or 4%, etc., not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0037] The present invention regulates the mass percentage of the material of the artificial SEI film layer, thereby ensuring the mechanical strength and chemical stability of the film and maintaining a low interface impedance.

[0038] Preferably, the thickness of the artificial SEI film layer is 20 nm to 90 nm, for example, it can be 20 nm, 22 nm, 25 nm, 28 nm, 30 nm, 32 nm, 35 nm, 38 nm, 40 nm, 42 nm, 45 nm, 48 nm, 50 nm, 52 nm, 55 nm, 58 nm, 60 nm, 62 nm, 65 nm, 68 nm, 70 nm, 72 nm, 75 nm, 78 nm, 80 nm, 82 nm, 85 nm, 88 nm or 90 nm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] The present invention regulates the thickness of the artificial SEI membrane to ensure both good structural stability and high ionic conductivity, thereby comprehensively improving the cycle performance and rate performance of the assembled secondary battery. A thinner artificial SEI membrane would have lower mechanical strength, making it difficult to effectively suppress the volume expansion of the silicon-based negative electrode material. A thicker artificial SEI membrane would have poor ion transport performance and increased interfacial impedance, which would reduce the cycle performance and rate performance of the assembled secondary battery.

[0040] The present invention also provides a method for preparing the fast-charging negative electrode material, which comprises the following steps:

[0041] The silicon-carbon material matrix and the solution containing the artificial SEI film layer applied to the fast-charging negative electrode material according to the first aspect are mixed, and after spray drying, the fast-charging negative electrode material is obtained.

[0042] Preferably, the mass concentration of the solution containing the artificial SEI film layer for fast-charging negative electrode materials according to the first aspect is 4% to 15%, for example, it can be 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, etc., not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0043] In the present invention, the solution containing the artificial SEI film layer applied to the fast-charging negative electrode material according to the first aspect includes an artificial SEI film layer applied to the fast-charging negative electrode material and a solvent, and the solvent exemplarily includes at least one of benzene, tetrahydrofuran (THF), N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF).

[0044] Preferably, the mixing temperature is 70°C to 100°C, for example, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0045] Preferably, the mixing time is 5 h to 10 h, for example, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0046] Preferably, the inlet temperature of the spray drying is 100°C to 200°C, for example, it can be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0047] Preferably, the outlet temperature of the spray drying is 60°C to 90°C, for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0048] In a fourth aspect, the present invention provides a negative electrode sheet, which includes a negative electrode active material, and the negative electrode active material includes the fast-charging negative electrode material according to the third aspect.

[0049] In a fifth aspect, the present invention provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the negative electrode sheet is the negative electrode sheet according to the fourth aspect.

[0050] The present invention improves the ion conductivity and electrode interface stability of the negative electrode material by regulating the structure and composition thereof, thereby significantly improving the fast charging performance of the secondary battery assembled therefrom.

[0051] In the present invention, the lithium salt in the electrolyte can be selected from the types of lithium salts commonly used in the art, for example, it can be at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroborate (LiBF6), lithium bis(difluorosulfonyl imide) (LiFSI) or lithium bis(oxalatoborate) (LiBOB).

[0052] In the present invention, the electrolyte further includes a lithium salt additive, and the lithium salt additive is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0053] In the present invention, the LiTFSI lithium salt additive can form a coordination bond with the nitro group in the polymer structure, thereby accelerating the dissociation of the lithium salt and improving the ionic conductivity.

[0054] Furthermore, the mass percentage of the lithium salt additive in the electrolyte is 0.5% to 3%, for example, it can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8% or 3%, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0055] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] The present invention provides an artificial SEI film layer for fast-charging anode materials. First, it exhibits a certain degree of flexibility, effectively overcoming the deformation and stress problems caused by volume expansion of silicon-based anode materials. Furthermore, the furan groups in the polymer structure possess a certain degree of rigidity and strength. Therefore, the artificial SEI film layer containing furan groups can enhance the structural strength of silicon-based anode materials, reduce the pulverization and shedding of electrode materials caused by volume changes during the charge and discharge process, and thus improve the cyclic stability of silicon-based anode materials.

[0058] Secondly, the nitro group can interact with the ions in the electrolyte, optimizing the interface structure between the electrolyte and the negative electrode material, thereby reducing the interfacial resistance between the two and increasing the ion migration rate. In addition, the nitro group (-NO2) can produce a synergistic effect with the imidazolone group (-NH-CO-NH-), promoting rapid ion conduction through dipole-ion interaction, thereby further reducing the interfacial impedance between the negative electrode material and the electrolyte, thereby comprehensively improving the fast charging performance of silicon-based negative electrode materials.

[0059] Finally, the present invention forms a three-dimensional interpenetrating network structure by designing polymers, thereby improving the mechanical properties and acid and alkali resistance of the artificial SEI film layer, thereby enhancing the fast charging stability of silicon-based negative electrode materials in complex environments. DETAILED DESCRIPTION

[0060] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0061] Example 1

[0062] This embodiment provides an artificial SEI film layer suitable for a fast-charging negative electrode material. The artificial SEI film layer is coated on the surface of a silicon-carbon material, thereby obtaining a fast-charging negative electrode material.

[0063] Among them, the material of the artificial SEI film layer includes poly 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione with a number average molecular weight of 30,000Da. The thickness of the artificial SEI film layer is 55nm, and the mass percentage of the artificial SEI film layer is 2.5% based on the total mass of the fast-charging negative electrode material as 100%. The average particle size of the silicon-carbon material is 6μm and the specific surface area is 4.5m 2 / g, and the mass percentage of silicon material in the silicon-carbon material is 50%.

[0064] This embodiment provides the above-mentioned artificial SEI film layer suitable for fast-charging negative electrode materials and a method for preparing the fast-charging negative electrode material, which includes the following steps:

[0065] 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione was added to a tetrahydrofuran solvent, and then azobisisobutyronitrile was added as an initiator. The mixture was heated to 70° C. under an argon atmosphere to carry out a polymerization reaction for 10 hours to obtain a reaction solution.

[0066] The reaction solution is added to a propanol solvent to precipitate a polymer, and the polymer precipitate is washed and dried to obtain a polymer;

[0067] The polymer was dissolved in tetrahydrofuran solvent to obtain a polymer solution with a mass concentration of 10%. The silicon-carbon material was added to the polymer solution and stirred at 85°C for 7 hours to obtain a mixed solution. The mixed solution was spray-dried at an inlet temperature of 150°C and an outlet temperature of 75°C to obtain a fast-charging negative electrode material.

[0068] Example 2

[0069] This embodiment provides an artificial SEI film layer suitable for a fast-charging negative electrode material. The artificial SEI film layer is coated on the surface of a silicon-carbon material, thereby obtaining a fast-charging negative electrode material.

[0070] Among them, the material of the artificial SEI film layer includes poly 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione with a number average molecular weight of 40,000Da. The thickness of the artificial SEI film layer is 85nm, and the mass percentage of the artificial SEI film layer is 3.5% based on the total mass of the fast-charging negative electrode material as 100%. The average particle size of the silicon-carbon material is 6μm and the specific surface area is 4.5m 2 / g, and the mass percentage of silicon material in the silicon-carbon material is 55%.

[0071] This embodiment provides the above-mentioned artificial SEI film layer suitable for fast-charging negative electrode materials and a method for preparing the fast-charging negative electrode material, which includes the following steps:

[0072] 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione was added to a tetrahydrofuran solvent, and then azobisisobutyronitrile was added as an initiator. The mixture was heated to 75° C. under an argon atmosphere to carry out a polymerization reaction for 9 hours to obtain a reaction solution;

[0073] The reaction solution is added to a propanol solvent to precipitate a polymer, and the polymer precipitate is washed and dried to obtain a polymer;

[0074] The polymer was dissolved in tetrahydrofuran solvent to obtain a polymer solution with a mass concentration of 13%. The silicon-carbon material was added to the polymer solution and stirred at 85°C for 7 hours to obtain a mixed solution. The mixed solution was spray-dried at an inlet temperature of 150°C and an outlet temperature of 75°C to obtain a fast-charging negative electrode material.

[0075] Example 3

[0076] This embodiment provides an artificial SEI film layer suitable for a fast-charging negative electrode material. The artificial SEI film layer is coated on the surface of a silicon-carbon material, thereby obtaining a fast-charging negative electrode material.

[0077] Among them, the material of the artificial SEI film layer includes poly 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione with a number average molecular weight of 25000Da. The thickness of the artificial SEI film layer is 25nm, and the mass percentage of the artificial SEI film layer is 2% based on the total mass of the fast-charging negative electrode material as 100%. The average particle size of the silicon-carbon material is 6μm and the specific surface area is 4.5m 2 / g, and the mass percentage of silicon material in the silicon-carbon material is 40%.

[0078] This embodiment provides the above-mentioned artificial SEI film layer suitable for fast-charging negative electrode materials and a method for preparing the fast-charging negative electrode material, which includes the following steps:

[0079] 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione was added to a tetrahydrofuran solvent, and then azobisisobutyronitrile was added as an initiator. The mixture was heated to 65° C. under an argon atmosphere to carry out a polymerization reaction for 10 hours to obtain a reaction solution.

[0080] The reaction solution is added to a propanol solvent to precipitate a polymer, and the polymer precipitate is washed and dried to obtain a polymer;

[0081] The polymer was dissolved in tetrahydrofuran solvent to obtain a polymer solution with a mass concentration of 5%. The silicon-carbon material was added to the polymer solution and stirred at 85°C for 7 hours to obtain a mixed solution. The mixed solution was spray-dried at an inlet temperature of 150°C and an outlet temperature of 75°C to obtain a fast-charging negative electrode material.

[0082] Example 4

[0083] This embodiment provides an artificial SEI film layer suitable for a fast-charging negative electrode material. The artificial SEI film layer is coated on the surface of a silicon-carbon material, thereby obtaining a fast-charging negative electrode material.

[0084] Among them, the material of the artificial SEI film layer includes poly 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione with a number average molecular weight of 10,000Da. The thickness of the artificial SEI film layer is 20nm, and the mass percentage of the artificial SEI film layer is 1% based on the total mass of the fast-charging negative electrode material as 100%. The average particle size of the silicon-carbon material is 4μm and the specific surface area is 8m 2 / g, and the mass percentage of silicon material in the silicon-carbon material is 40%.

[0085] This embodiment provides the above-mentioned artificial SEI film layer suitable for fast-charging negative electrode materials and a method for preparing the fast-charging negative electrode material, which includes the following steps:

[0086] 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione was added to a tetrahydrofuran solvent, and then azobisisobutyronitrile was added as an initiator. The mixture was heated to 60° C. under an argon atmosphere to carry out a polymerization reaction for 12 hours to obtain a reaction solution.

[0087] The reaction solution is added to a propanol solvent to precipitate a polymer, and the polymer precipitate is washed and dried to obtain a polymer;

[0088] The polymer was dissolved in tetrahydrofuran solvent to obtain a polymer solution with a mass concentration of 4%. The silicon-carbon material was added to the polymer solution and stirred at 85°C for 7 hours to obtain a mixed solution. The mixed solution was spray-dried at an inlet temperature of 150°C and an outlet temperature of 75°C to obtain a fast-charging negative electrode material.

[0089] Example 5

[0090] This embodiment provides an artificial SEI film layer suitable for a fast-charging negative electrode material. The artificial SEI film layer is coated on the surface of a silicon-carbon material, thereby obtaining a fast-charging negative electrode material.

[0091] Among them, the material of the artificial SEI film layer includes poly 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione with a number average molecular weight of 50,000Da. The thickness of the artificial SEI film layer is 90nm, and the mass percentage of the artificial SEI film layer is 4% based on the total mass of the fast-charging negative electrode material as 100%. The average particle size of the silicon-carbon material is 8μm and the specific surface area is 1m 2 / g, and the mass percentage of silicon material in the silicon-carbon material is 59%.

[0092] This embodiment provides the above-mentioned artificial SEI film layer suitable for fast-charging negative electrode materials and a method for preparing the fast-charging negative electrode material, which includes the following steps:

[0093] 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione was added to a tetrahydrofuran solvent, and then azobisisobutyronitrile was added as an initiator. The mixture was heated to 80° C. under an argon atmosphere to carry out a polymerization reaction for 8 hours to obtain a reaction solution;

[0094] The reaction solution is added to a propanol solvent to precipitate a polymer, and the polymer precipitate is washed and dried to obtain a polymer;

[0095] The polymer was dissolved in tetrahydrofuran solvent to obtain a polymer solution with a mass concentration of 15%. The silicon-carbon material was added to the polymer solution and stirred at 85°C for 7 hours to obtain a mixed solution. The mixed solution was spray-dried at an inlet temperature of 150°C and an outlet temperature of 75°C to obtain a fast-charging negative electrode material.

[0096] Example 6

[0097] The difference between this embodiment and embodiment 1 is that the number average molecular weight of the polymer is 5000 Da, wherein the change of the number average molecular weight of the polymer is achieved by adjusting the temperature and time of the polymerization reaction. The rest is the same as embodiment 1.

[0098] Example 7

[0099] The difference between this embodiment and embodiment 1 is that the number average molecular weight of the polymer is 80,000 Da, wherein the change in the number average molecular weight of the polymer is achieved by adjusting the temperature and time of the polymerization reaction. The rest is the same as embodiment 1.

[0100] Example 8

[0101] The difference between this embodiment and embodiment 1 is that the thickness of the artificial SEI film layer is 10 nm, which is obtained by specifically controlling the following parameters: the polymer is dissolved in tetrahydrofuran solvent to obtain a polymer solution with a mass concentration of 2%. Other parameters are the same as those in embodiment 1.

[0102] Example 9

[0103] The difference between this embodiment and embodiment 1 is that the thickness of the artificial SEI film layer is 110 nm, which is obtained by specifically controlling the following parameters: the polymer is dissolved in tetrahydrofuran solvent to obtain a polymer solution with a mass concentration of 25%. Other parameters are the same as those in embodiment 1.

[0104] Example 10

[0105] The difference between this embodiment and embodiment 1 is that the mass percentage of silicon material in the silicon-carbon material is 30%, and the rest is the same as embodiment 1.

[0106] Comparative Example 1

[0107] The difference between this comparative example and Example 1 is that the silicon-carbon material is not subjected to artificial SEI film coating treatment, and only one silicon-carbon material is provided, and the average particle size, specific surface area and mass percentage of the provided silicon-carbon material are the same as those in Example 1.

[0108] Comparative Example 2

[0109] The difference between this comparative example and Example 1 is that 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione is replaced with an equal amount of 4-(5-nitrofuran-2-yl)but-3-en-2-one monomer (CAS No.: 3455-61-6), and the rest are the same as Example 1.

[0110] Comparative Example 3

[0111] The difference between this comparative example and Example 1 is that 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione is replaced with an equal amount of 4-(2-furyl)-3-butene-2-one monomer (CAS No.: 623-15-4), and the rest are the same as Example 1.

[0112] Comparative Example 4

[0113] The difference between this comparative example and Example 1 is that 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione is replaced with an equal amount of 1-allylimidazolidine-2,4-dione (CAS No.: 3366-93-6), and the rest are the same as Example 1.

[0114] Comparative Example 5

[0115] The difference between this comparative example and Example 1 is that 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione is replaced by an equal amount of (E)-2-(5-nitro-2-furyl)ethyleneamine (CAS No.: 758635-45-9), and the rest are the same as Example 1.

[0116] Application Examples 1-10 and Comparative Application Examples 1-5

[0117] The silicon-carbon negative electrode materials provided in Examples 1 to 10 and Comparative Examples 1 to 5 were used to prepare negative electrode sheets, and then assembled to obtain lithium-ion batteries. The specific preparation method is as follows:

[0118] Preparation of negative electrode sheet:

[0119] The silicon-carbon negative electrode material, conductive carbon black Super-P, single-walled carbon nanotubes (SWCNTs) and polyacrylic acid binder (PAA) provided in the above embodiments and comparative examples were mixed and stirred uniformly with water in a mass ratio of 80:9:1:10 to obtain a negative electrode slurry, and the solid content was controlled to be 30%. The negative electrode slurry was then coated on a copper foil current collector through a coating process, and then vacuum dried and cold pressed to obtain a negative electrode sheet.

[0120] Preparation of positive electrode:

[0121] The ternary cathode material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 The active material O2, polyvinylidene fluoride binder (PVDF) and conductive carbon black Super-P are mixed and stirred evenly with N-methylpyrrolidone solvent in a mass ratio of 96:2:2 to obtain a positive electrode slurry, and then the positive electrode slurry is coated on an aluminum foil through a coating process, and then dried and cold pressed to obtain a positive electrode sheet.

[0122] Electrolyte:

[0123] Ethylene carbonate, dimethyl carbonate, diethyl carbonate, and fluoroethylene carbonate are mixed in a volume ratio of 20:40:30:10 to prepare an organic solvent. Thoroughly dried lithium salt LiPF6 is then dissolved in the organic solvent to prepare an electrolyte solution with a lithium salt concentration of 1 mol / L. The electrolyte also includes a LiTFSI lithium salt additive, with the weight percentage of the LiTFSI lithium salt additive being 1.5% based on the total weight of the electrolyte being 100%.

[0124] Preparation of lithium-ion batteries:

[0125] The positive electrode sheet, separator (including a polyethylene-based film and a ceramic coating provided on one side of the polyethylene-based film) and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare battery cell; the bare battery cell is placed in an outer packaging shell, dried, and then injected with electrolyte, and after vacuum packaging, standing, forming and shaping processes, a lithium-ion battery is obtained.

[0126] Comparative Application Example 6

[0127] The difference between this comparative application example and application example 1 is that all the LiTFSI lithium salt additives are replaced with LiPF6 lithium salt of equal content, and the rest are the same as application example 1.

[0128] Test conditions

[0129] The lithium-ion batteries provided in Application Examples 1 to 10 and Comparative Application Examples 1 to 6 were subjected to performance tests. The rate performance of the batteries was tested under lithium-ion battery test conditions. The tests were conducted on the LAND battery test system of Wuhan Jinnuo Electronics Co., Ltd. at room temperature (25°C). The charge and discharge voltages were limited to 2.5V to 4.3V. The test conditions are as follows:

[0130] (1) First Coulombic efficiency

[0131] At 25°C, the lithium-ion battery was charged to 4.3V at a constant current and constant voltage rate of 0.33C and allowed to stand for 10 minutes. Then, the lithium-ion battery was discharged to 2.5V at a constant current rate of 0.33C and allowed to stand for 10 minutes. The first coulombic efficiency of the lithium-ion battery was calculated.

[0132] First coulombic efficiency (%)=(first discharge total capacity of the lithium-ion battery at a rate of 0.33C / first charge total capacity of the lithium-ion battery at a rate of 0.33C)×100%.

[0133] (2) Capacity retention after 1000 cycles at 1C / 2C at room temperature

[0134] At 25°C, the lithium-ion battery is charged to 4.3V at a constant current and constant voltage rate of 1C, with a cut-off current of 0.05C, and allowed to stand for 10 minutes. Then, the lithium-ion battery is discharged to 2.5V at a constant current rate of 2C and allowed to stand for 10 minutes. This is considered one charge and discharge cycle. The lithium-ion battery is charged and discharged 1200 times according to the above method. The capacity retention rate of the lithium-ion battery after 1000 charge and discharge cycles at 1C / 2C is calculated.

[0135] Capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0136] (3) Room temperature 6C rate performance - constant current charging ratio

[0137] At 25°C, the lithium-ion battery was discharged at a constant current rate of 1C to 2.5V and allowed to stand for 10 minutes. The lithium-ion battery was then charged at a constant current and constant voltage rate of 6C to 4.3V with a cut-off current of 0.05C and allowed to stand for 10 minutes. The constant current charging capacity Q1 and the total constant current and constant voltage charging capacity Q2 of the lithium-ion battery were recorded. The constant current charging ratio of the 6C rate charging was calculated according to the following formula: 6C rate charging constant current charging ratio = (constant current charging capacity Q1 / total constant current and constant voltage charging capacity Q2) × 100%.

[0138] (4) 1C / 8C discharge capacity retention rate at room temperature

[0139] At 25°C, the divided lithium-ion battery is charged to 4.3V at a constant current and constant voltage rate of 1C, with a cut-off current of 0.05C; it is left to stand for 10 minutes; then the lithium-ion battery is discharged to 2.5V at a constant current rate of 1C, and its discharge capacity Q is recorded. 1C As the initial discharge capacity; then at 25 ℃, the lithium ion battery is charged to 4.3V at a constant current and constant voltage rate of 1C, with a cut-off current of 0.05C; let it stand for 10 minutes; then the fully charged battery is discharged to 2.5V at a constant current rate of 8C, and its discharge capacity Q is recorded. 8C ; Calculate the discharge capacity retention rate (%) of lithium-ion batteries at 1C / 8C rate = (discharge capacity Q at 8C rate) 8C / Discharge capacity Q at 1C rate 1C )×100%.

[0140] (5) Initial expansion rate of negative electrode

[0141] ① Before assembling the lithium-ion battery, use a micrometer to measure the initial thickness of the negative electrode sheet and record it as h1. The thickness of the negative electrode current collector is recorded as h0.

[0142] ② Fully charged: At 25°C, after assembling the battery cells, charge the lithium-ion battery at a constant current and constant voltage rate of 0.33C to 4.3V, with a cut-off current of 0.05C, and let it stand for 120 minutes;

[0143] ③ Disassemble the fully charged lithium-ion battery to obtain the negative electrode sheet, clean the negative electrode sheet with dimethyl carbonate, and measure the thickness of the cleaned negative electrode sheet, which is recorded as h2;

[0144] ④The initial expansion rate of the negative electrode is: (h2-h1) / (h1-h0)×100%.

[0145] The test results are shown in Table 1:

[0146] Table 1

[0147]

[0148]

[0149] As can be seen from Table 1, compared to Comparative Application Example 1, the artificial SEI film provided by Application Examples 1 to 5 of the present invention not only has suitable mechanical strength, thereby effectively overcoming the deformation and stress problems caused by the volume expansion of the silicon-carbon negative electrode material, but also can further reduce the interfacial impedance between the silicon-carbon negative electrode material and the electrolyte. In addition, the polymer designed in the present invention forms a three-dimensional interpenetrating network structure, which jointly improves the mechanical properties and acid and alkali resistance of the artificial SEI film, thereby comprehensively improving the fast charging stability of the silicon-carbon negative electrode material.

[0150] By comparing Application Example 1, Application Example 6 and Application Example 7, it can be seen that the present invention optimizes the number average molecular weight range of the polymer so that the artificial SEI film layer has good mechanical strength, interface performance and chemical stability, thereby being able to fully exert the protective effect on the silicon-carbon negative electrode material and reduce the interface resistance, and ultimately comprehensively improve the cycle performance and fast charging performance of the lithium-ion battery.

[0151] By comparing Application Example 1, Application Example 8 and Application Example 9, it can be seen that the present invention optimizes the thickness of the artificial SEI film layer to ensure that it has both good structural stability and ion transport performance, thereby improving the overall performance of the lithium-ion battery.

[0152] Comparing Application Example 1 and Application Example 10, it can be seen that the present invention optimizes the mass percentage of silicon material in the silicon-carbon material matrix, so that the silicon-carbon material matrix not only has a higher gram capacity and a higher first coulombic efficiency, but also has a smaller volume expansion.

[0153] From Comparative Application Examples 1, 2 to 5, it can be seen that the present invention further enhances the mechanical strength, chemical stability and ion transport performance of the artificial SEI film layer by optimizing the structure of the polymerized monomers, thereby improving the overall performance of the lithium-ion battery.

[0154] Comparison of Application Examples 1 and 6 demonstrates the synergistic effect of the artificial SEI layer and the lithium bis(trifluoromethanesulfonyl)imide additive in the electrolyte. By optimizing the electrolyte additive composition, the present invention accelerates lithium salt dissociation and enhances ionic conductivity, ultimately improving the cycling performance and fast-charging performance of lithium-ion batteries.

[0155] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. An artificial SEI film layer used for fast charging negative electrode materials, characterized in that: The material of the artificial SEI film layer includes a polymer having a three-dimensional interpenetrating network structure, and a combination of a nitro group, a furan group and an imidazolone group in the structure of the polymer.

2. The artificial SEI film layer for fast-charging negative electrode materials according to claim 1, characterized in that: The monomers forming the polymer include compounds containing a combination of at least one unsaturated double bond, at least one nitro group, at least one furan group, and at least one imidazolone group; Preferably, the monomers forming the polymer include a compound containing a combination of at least one alkenyl group, at least one nitrofuran group, and at least one imidazoledione group; Preferably, the monomers forming the polymer include 1-((3-(5-nitrofuran-2-yl)allylidene)amino)imidazolidine-2,4-dione.

3. The artificial SEI film layer for fast-charging negative electrode materials according to claim 1 or 2, characterized in that: The number average molecular weight of the polymer is 10,000 Da to 50,000 Da, preferably 22,000 Da to 40,000 Da.

4. A method for preparing an artificial SEI film layer for fast-charging negative electrode materials according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: A monomer comprising at least one unsaturated double bond, at least one nitro group, at least one furan group and at least one imidazolone group, an initiator and an organic solvent are mixed, and after a polymerization reaction, an artificial SEI film layer applied to a fast-charging negative electrode material is obtained.

5. The method according to claim 4, characterized in that The polymerization reaction temperature is 60°C to 80°C; Preferably, the polymerization reaction time is 8 h to 12 h.

6. A fast-charging negative electrode material, characterized in that: The fast-charging negative electrode material includes a silicon-carbon material matrix and an artificial SEI film layer arranged on the surface of the silicon-carbon material matrix, and the artificial SEI film layer includes the artificial SEI film layer applied to the fast-charging negative electrode material according to any one of claims 1-3.

7. The fast-charging negative electrode material according to claim 6, characterized in that: The average particle size of the silicon-carbon material matrix is ​​4 μm to 8 μm; Preferably, the specific surface area of ​​the silicon-carbon material matrix is ​​1m 2 / g~8m 2 / g; Preferably, the mass percentage of silicon material in the silicon-carbon material matrix is ​​40% to 59%.

8. The fast-charging negative electrode material according to claim 6 or 7, characterized in that: Based on the total mass of the fast-charging negative electrode material as 100%, the mass percentage of the artificial SEI film layer is 1% to 4%; Preferably, the thickness of the artificial SEI film layer is 20 nm to 90 nm.

9. A negative electrode sheet, characterized in that: The negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes the fast-charging negative electrode material according to any one of claims 6 to 8.

10. A secondary battery, characterized in that: The secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, and the negative electrode sheet is the negative electrode sheet according to claim 9.

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