Modified silicon negative electrode material and preparation method and application thereof

Abstract

The invention provides a modified silicon negative electrode material and a preparation method and application thereof. The modified silicon negative electrode material sequentially comprises a silicon-based material core and a first coating layer covering the surface of the silicon-based material core from inside to outside, the material of the first coating layer comprises a polymer, and the structure of the polymer comprises a combination of a pyridine group and a carboxyl group. According to the invention, the electronic conductivity of the silicon-based negative electrode material is comprehensively improved, the stability of an interfacial film is enhanced, and meanwhile, the volume expansion phenomenon of the silicon material can be effectively buffered, so that the charge-discharge performance of the assembled secondary battery under high rate is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a modified silicon negative electrode material and a preparation method and application thereof. Background Art

[0002] With continuous technological breakthroughs and growing market demand, the requirements for lithium-ion batteries' charge and discharge performance at high rates (high current densities) are increasing. This is especially true in areas such as electric vehicles, drones, and portable electronic devices, where rapid charge and discharge capabilities have become key performance indicators. To further improve the electrochemical performance of lithium-ion batteries at high rates, it is necessary to comprehensively consider multiple aspects, including electrode materials, electrolytes, and battery structure. For example, by optimizing the electronic and ionic conductivity of electrode materials, selecting a suitable electrolyte system, and rationally designing the battery structure, the rate performance of lithium-ion batteries can be significantly improved to meet the needs of high-performance applications.

[0003] Among them, silicon-based negative electrode materials have become extremely promising electrode materials due to their high theoretical specific capacity. However, silicon-based negative electrode materials face many challenges in practical applications. For example, silicon undergoes huge volume changes (greater than 300%) during the charge and discharge process, which leads to material pulverization, structural collapse, and electrical contact failure, which in turn causes battery capacity decay. In addition, it is difficult for silicon-based negative electrode materials to form a stable SEI film during the cycle process. Due to the volume expansion phenomenon, the SEI film will continue to rupture and regenerate, resulting in continuous consumption of electrolyte and loss of active lithium, further exacerbating capacity decay, and the above problems are particularly significant during high-rate charge and discharge, thereby affecting the rate performance and fast charging performance of lithium ions.

[0004] Currently, existing technologies disclose some improvement methods, including simple physical mixing or the use of traditional coating materials. While these methods can improve the electrochemical performance of silicon-based anode materials to a certain extent, the technical effects achieved are limited. In fact, traditional coating materials cannot fully address the technical problems of poor conductivity and insufficient interfacial stability of silicon-based anode materials. This results in rapid capacity decay during high-rate lithium-ion charge and discharge, making it difficult to meet practical application requirements.

[0005] Therefore, in this field, there is an urgent need to develop a silicon-based negative electrode material with good fast charging capability to solve the above technical problems. Summary of the Invention

[0006] To address the shortcomings of the prior art, the present invention aims to provide a modified silicon anode material, its preparation method, and its application. This invention comprehensively improves the electronic conductivity of silicon-based anode materials and enhances the stability of the interfacial film. It also effectively mitigates the volume expansion of the silicon material, thereby enhancing the charge-discharge performance of the assembled secondary battery at high rates.

[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 a modified silicon negative electrode material, wherein the modified silicon negative electrode material comprises, from the inside to the outside, a silicon-based material core and a first coating layer covering the surface of the silicon-based material core;

[0009] The material of the first coating layer includes a polymer, and the polymer structure includes a combination of a pyridine group and a carboxyl group.

[0010] The present invention utilizes a polymer structured as a combination of pyridine and carboxyl groups as the coating material for the first coating layer. The pyridine nitrogen functional group has high electronic conductivity, significantly increasing the electron transfer rate of the silicon-based negative electrode material at high current densities. This improves the rate performance of the assembled secondary battery and significantly reduces capacity decay during high-current charge and discharge. Furthermore, the carboxyl groups in the polymer structure can form ester bonds with the hydroxyl groups on the surface of the silicon-based negative electrode material, further enhancing the structural stability of the interfacial film while reducing the loss of active lithium and extending the cycle life of the secondary battery.

[0011] Preferably, the monomers forming the polymer include compounds containing a combination of at least one carbon-carbon double bond, at least one pyridine group, and at least one carboxyl group.

[0012] Preferably, the monomers forming the polymer are selected from (E)-3-(6-aminopyridin-3-yl)acrylic acid (CAS No.: 167837-43-6).

[0013] In the present invention, the preferred (E)-3-(6-aminopyridin-3-yl) acrylic acid polymer monomer achieves a better coating effect. This is because the presence of an amino group ortho and a carboxyl group para to the pyridine group, respectively, is more conducive to improving the electronic conductivity and enhancing the stability of the interface film. In addition, the ortho amino group and the para carboxyl group can produce a synergistic effect with the pyridine nitrogen atom, thereby promoting the transport of lithium ions. The para carboxyl group also helps to form a more stable ester bond structure on the surface of the silicon-based negative electrode material.

[0014] Preferably, the number average molecular weight of the polymer is 10,000 Da to 50,000 Da, preferably 22,000 Da to 43,000 Da, for example, it can be 10,000 Da, 12,000 Da, 15,000 Da, 18,000 Da, 20,000 Da, 22,000 Da, 25,000 Da, 28,000 Da, 30,000 Da, 32,000 Da, 35,000 Da, 38,000 Da, 40,000 Da, 42,000 Da, 43,000 Da, 45,000 Da, 48,000 Da or 50,000 Da, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0015] The present invention achieves excellent processing properties, mechanical strength, and interfacial compatibility by regulating the number-average molecular weight of the polymer. Using a polymer with a lower number-average molecular weight results in poor film-forming properties and structural stability, making it ineffective in improving the electronic conductivity of silicon-based negative electrode materials and the stability of the interfacial film. Using a polymer with a higher number-average molecular weight results in poor solubility, hindering the coating process and potentially increasing interfacial internal resistance, ultimately affecting the electrochemical performance of the resulting secondary battery.

[0016] Preferably, the thickness of the first coating layer is 30nm to 80nm, for example, it can be 30nm, 32nm, 35nm, 38nm, 40nm, 42nm, 45nm, 48nm, 50nm, 52nm, 55nm, 58nm, 60nm, 62nm, 65nm, 68nm, 70nm, 72nm, 75nm, 78nm or 80nm, etc., and is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] The present invention regulates the thickness of the first coating layer 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 first coating layer can easily break, leading to loss of active lithium. A thicker first coating layer can result in poor ion transport performance, and the cycle performance and rate performance of the assembled secondary battery can be reduced.

[0018] Preferably, based on the total mass of the silicon-based material core including the first coating layer as 100%, the mass percentage of the material of the first coating layer is 1% to 5%, 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%, 4%, 4.2%, 4.5%, 4.8% or 5%, etc., not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0019] The present invention regulates the mass percentage of the material of the first coating layer to form a coating layer with suitable thickness and uniform composition, thereby avoiding local current concentration, further optimizing interface stability and ion conductivity, and reducing the occurrence of electrolyte decomposition and side reactions.

[0020] Preferably, the modified silicon negative electrode material further includes a second coating layer, and the second coating layer is arranged on the surface of the first coating layer.

[0021] Preferably, the material of the second coating layer includes metal oxide.

[0022] The present invention significantly improves the durability and stability of silicon-based negative electrode materials by placing a metal oxide coating layer on the outermost layer of the silicon-based material comprising the first coating layer. Due to its excellent chemical stability, the metal oxide coating layer is resistant to corrosion and oxidation by the electrolyte. Furthermore, the metal oxide coating layer exhibits excellent lithium ion diffusion properties, providing more transport channels for lithium ions and successfully suppressing the volume expansion of the silicon material during charge and discharge.

[0023] Preferably, the metal oxide comprises titanium dioxide.

[0024] Preferably, based on the total mass of the silicon-based material core including the first coating layer as 100%, the mass percentage of the material of the second coating layer is 5% to 15%, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5% or 15%, etc., not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0025] By regulating the mass percentage of the material of the second coating layer, the present invention enables the modified silicon anode material to possess suitable mechanical strength, high ionic conductivity, and high electronic conductivity, thereby better resisting the volume expansion of the silicon material during the charge and discharge process and improving the battery's rate performance. If a lower mass percentage of the second coating layer material is used, the second coating layer has poor rigidity, which is not conducive to suppressing the volume expansion of the silicon-based anode material. If a higher mass percentage of the second coating layer material is used, the ionic and electronic conductivity of the second coating layer is reduced, resulting in a lower initial coulombic efficiency and poor rate performance of the assembled secondary battery.

[0026] In the present invention, the silicon-based material core exemplarily includes a silicon oxide material core and / or a silicon-carbon material core.

[0027] In the present invention, the average particle size of the silicon-carbon material core is 4μm to 12μm, 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, 8μm, 8.2μm, 8.5μm, 8.8μm, 9μm, 9.2μm, 9.5μm, 9.8μm, 10μm, 10.5μm, 11μm, 11.5μm or 12μm, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] The present invention regulates the average particle size of the silicon-carbon material core, facilitating subsequent processing and improving the ion transport performance of the silicon-based anode material. Using a silicon-carbon material core with a smaller average particle size makes it difficult to disperse the silicon-carbon material particles during the subsequent homogenization process. Using a silicon-carbon material core 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 is subsequently impaired.

[0029] In the present invention, the specific surface area of ​​the silicon-carbon material core 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, 4.8m 2 / 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, 7.5m2 / 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.

[0030] In the present invention, the mass percentage of silicon material in the silicon-carbon material core is 40% to 55%, for example, it can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54% or 55%, etc., and is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] By regulating the mass percentage of silicon in the silicon-carbon core, the present invention achieves a high gram capacity and high initial coulombic efficiency while minimizing volume expansion. Using a silicon-carbon core with a lower silicon content results in lower gram capacity and initial coulombic efficiency; using a silicon-carbon core with a higher silicon content results in greater volume expansion.

[0032] In a second aspect, the present invention provides a method for preparing the modified silicon negative electrode material according to the first aspect, the method comprising the following steps:

[0033] The modified silicon negative electrode material is obtained by mixing a silicon-based material with a polymer solution containing a combination of pyridine groups and carboxyl groups in its structure and performing a first spray drying process.

[0034] Preferably, the mass concentration of the polymer solution is 5% to 20%, for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0035] In the present invention, the polymer solution includes a polymer and a solvent, and the solvent illustratively includes at least one of benzene, tetrahydrofuran (THF), N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF).

[0036] Preferably, the method for preparing the polymer in the polymer solution comprises the following steps:

[0037] A monomer comprising at least one carbon-carbon double bond, at least one pyridine group and at least one carboxyl group, an initiator and an organic solvent are mixed, and the polymer is obtained after a polymerization reaction.

[0038] Preferably, the polymerization reaction is carried out under an inert atmosphere.

[0039] In the present invention, the inert atmosphere illustratively includes argon and / or nitrogen.

[0040] Preferably, the polymerization reaction temperature is 60°C to 100°C, for example, it can be 60°C, 65°C, 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 this numerical range are also applicable.

[0041] Preferably, the polymerization reaction time is 5 h to 12 h, for example, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h or 12 h, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0042] In the present invention, the initiator illustratively 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%, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%, etc., and is not limited to the values ​​listed above. Other values ​​not listed within this numerical range are also applicable.

[0043] In the present invention, the organic solvent illustratively includes at least one of benzene, tetrahydrofuran (THF), N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF).

[0044] 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.

[0045] In the present invention, the precipitation solvent illustratively includes at least one of propanol, isopropanol or acetone.

[0046] Preferably, the mixing temperature is 60°C to 100°C, for example, it can be 60°C, 65°C, 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 this numerical range are also applicable.

[0047] 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.

[0048] Preferably, the inlet temperature of the first spray drying is 100°C to 200°C, for example, 100°C, 120°C, 150°C, 180°C or 200°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0049] Preferably, the outlet temperature of the first 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.

[0050] Preferably, after the first spray drying process is completed, the following steps are further included:

[0051] A first dispersion containing a silicon-based material whose surface is coated with a polymer is mixed with a second dispersion containing a metal oxide to obtain a mixed dispersion; the mixed dispersion is subjected to a second spray drying process to obtain the modified silicon negative electrode material.

[0052] In the present invention, the preparation method of the first dispersion liquid of the silicon-based material whose surface is coated with a polymer includes the following steps: stirring and dispersing the silicon-based material whose surface is coated with a polymer with deionized water for 1 hour to 2 hours to ensure that the silicon-based material is fully dispersed to obtain the first dispersion liquid of the silicon-based material whose surface is coated with a polymer.

[0053] In the present invention, the preparation method of the second dispersion containing metal oxides comprises the following steps: dispersing nano-metal oxides in deionized water, adding an appropriate amount of dispersant (such as polyvinyl pyrrolidone), and ultrasonically dispersing for 30 to 60 minutes to form a uniform and stable second dispersion containing metal oxides.

[0054] In the present invention, ultrasonic dispersion can effectively break up the agglomerates of metal oxides and improve their dispersibility in the solution.

[0055] Preferably, based on the total mass of the silicon-based material whose surface is coated with a polymer as 100%, the mass percentage of the metal oxide is 5% to 15%, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5% or 15%, etc., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0056] Preferably, the inlet temperature of the second spray drying is 150°C to 200°C, for example, it can be 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.

[0057] Preferably, the outlet temperature of the second spray drying is 80°C to 120°C, for example, it can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0058] In a third aspect, the present invention provides a negative electrode plate, wherein the negative electrode plate includes a negative electrode active material, and the negative electrode active material includes the modified silicon negative electrode material according to the first aspect.

[0059] In a fourth 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 third aspect.

[0060] 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(oxalatoborate) (LiBOB) or lithium bis(trifluoromethanesulfonyl imide) (LiTFSI).

[0061] In the present invention, the electrolyte further includes a lithium salt additive, and the lithium salt additive is lithium bis(difluorosulfonylimide) (LiFSI).

[0062] Furthermore, the mass percentage of the LiFSI lithium salt additive in the electrolyte is 1% to 5%, 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%, 4%, 4.2%, 4.5%, 4.8% or 5%, etc., not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0063] In the present invention, due to the synergistic effect between the LiFSI lithium salt additive and the material of the first coating layer, the LiFSI lithium salt additive can increase the lithium ion concentration in the electrolyte in the presence of the polymer of the first coating layer, thereby improving the ionic conductivity of the secondary battery and further improving the constant current charging ratio when charging at a 6C rate.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] The present invention provides a modified silicon negative electrode material, which has the following technical effects:

[0066] On one hand, the present invention utilizes a polymer structured as a combination of pyridine and carboxyl groups as the coating material for the first coating layer. The pyridine nitrogen functional group has high electronic conductivity, significantly increasing the electron transfer rate of the silicon-based negative electrode material at high current densities, thereby improving the rate performance of the assembled secondary battery and significantly reducing its capacity decay during high-current charge and discharge. Furthermore, the carboxyl groups in the polymer structure can form ester bonds with the hydroxyl groups on the surface of the silicon-based negative electrode material, further enhancing the structural stability of the interfacial film while reducing the loss of active lithium and extending the cycle life of the secondary battery.

[0067] Furthermore, the present invention also incorporates a metal oxide coating layer on the outermost layer of the silicon-based material comprising the first coating layer. Due to its excellent chemical stability, the metal oxide coating layer is resistant to corrosion and oxidation by the electrolyte, significantly improving the durability and stability of the silicon-based negative electrode material. Furthermore, the metal oxide coating layer exhibits excellent lithium ion diffusion properties, providing more transport channels for lithium ions and successfully suppressing the volume expansion of the silicon material during charge and discharge, further enhancing the overall performance of the secondary battery. DETAILED DESCRIPTION

[0068] 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.

[0069] Example 1

[0070] This embodiment provides a modified silicon negative electrode material, which includes a silicon-carbon material core, a first coating layer and a second coating layer from the inside to the outside. The material of the first coating layer includes poly (E) -3- (6-aminopyridin-3-yl) acrylic acid (number average molecular weight of 30000 Da), and the material of the second coating layer includes nano titanium dioxide.

[0071] Among them, the thickness of the first coating layer is 50nm, and the mass percentage of the material of the first coating layer is 3% based on the total mass of the silicon-carbon material including the first coating layer is 100%; the mass percentage of the material of the second coating layer is 10% based on the total mass of the silicon-carbon material including the first coating layer is 100%.

[0072] The average particle size of the silicon carbon material core is 8μm and the specific surface area is 4.5m 2 / g, and the mass percentage of silicon material in the silicon-carbon material core is 47%.

[0073] This embodiment also provides a method for preparing the modified silicon negative electrode material, the preparation method comprising the following steps:

[0074] S1. (E)-3-(6-aminopyridin-3-yl)acrylic acid was added to tetrahydrofuran solvent, and then azobisisobutyronitrile was added as an initiator. The mixture was heated to 80° C. under an argon atmosphere for polymerization reaction for 8 h to obtain a reaction solution.

[0075] 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;

[0076] The polymer was dissolved in tetrahydrofuran solvent to obtain a polymer solution with a mass concentration of 12%. The silicon-carbon material was added to the polymer solution and stirred at 80°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 silicon-based material with a surface coated with the polymer.

[0077] S2. The surface of the polymer-coated silicon-based material and deionized water were stirred and dispersed for 1.5h to obtain a first dispersion containing a surface of a polymer-coated silicon-based material;

[0078] Dispersing nano-titanium dioxide in deionized water, adding an appropriate amount of polyvinyl pyrrolidone dispersant (the mass percentage of polyvinyl pyrrolidone dispersant is 3% based on the total mass of nano-titanium dioxide as 100%), and ultrasonically dispersing for 50 minutes to form a uniform and stable second dispersion containing nano-titanium dioxide;

[0079] A first dispersion containing a polymer-coated silicon-based material and a second dispersion containing nano-titanium dioxide were mixed for 1.5 hours to obtain a mixed dispersion. The mixed dispersion was then sprayed into a drying chamber via a nozzle using a spray dryer in the form of droplets. The inlet temperature of the drying chamber was controlled at 180°C, and the outlet temperature was controlled at 100°C. Water from the droplets evaporated rapidly in the drying chamber, yielding the modified silicon anode material.

[0080] Example 2

[0081] This embodiment provides a modified silicon negative electrode material, which includes a silicon-carbon material core, a first coating layer and a second coating layer from the inside to the outside. The material of the first coating layer includes poly (E) -3- (6-aminopyridin-3-yl) acrylic acid (number average molecular weight of 40000 Da), and the material of the second coating layer includes nano titanium dioxide.

[0082] Among them, the thickness of the first coating layer is 70nm, and the mass percentage of the material of the first coating layer is 4.5% based on the total mass of the silicon-carbon material including the first coating layer is 100%; the mass percentage of the material of the second coating layer is 10% based on the total mass of the silicon-carbon material including the first coating layer is 100%.

[0083] The average particle size of the silicon carbon material core is 8μm and the specific surface area is 4.5m 2 / g, and the mass percentage of silicon material in the silicon-carbon material core is 53%.

[0084] This embodiment also provides a method for preparing the modified silicon negative electrode material, the preparation method comprising the following steps:

[0085] S1. (E)-3-(6-aminopyridin-3-yl)acrylic acid was added to tetrahydrofuran solvent, and then azobisisobutyronitrile was added as an initiator. The mixture was heated to 90° C. under an argon atmosphere for polymerization for 6 h to obtain a reaction solution.

[0086] 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;

[0087] 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 80°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 silicon-based material with a surface coated with the polymer.

[0088] S2. The surface of the polymer-coated silicon-based material and deionized water were stirred and dispersed for 1.5h to obtain a first dispersion containing a surface of a polymer-coated silicon-based material;

[0089] Dispersing nano-titanium dioxide in deionized water, adding an appropriate amount of polyvinyl pyrrolidone dispersant (the mass percentage of polyvinyl pyrrolidone dispersant is 3% based on the total mass of nano-titanium dioxide as 100%), and ultrasonically dispersing for 50 minutes to form a uniform and stable second dispersion containing nano-titanium dioxide;

[0090] A first dispersion containing a polymer-coated silicon-based material and a second dispersion containing nano-titanium dioxide were mixed for 1.5 hours to obtain a mixed dispersion. The mixed dispersion was then sprayed into a drying chamber via a nozzle using a spray dryer in the form of droplets. The inlet temperature of the drying chamber was controlled at 180°C, and the outlet temperature was controlled at 100°C. Water from the droplets evaporated rapidly in the drying chamber, yielding the modified silicon anode material.

[0091] Example 3

[0092] This embodiment provides a modified silicon negative electrode material, which includes a silicon-carbon material core, a first coating layer and a second coating layer from the inside to the outside. The material of the first coating layer includes poly (E) -3- (6-aminopyridin-3-yl) acrylic acid (number average molecular weight of 25000 Da), and the material of the second coating layer includes nano titanium dioxide.

[0093] Among them, the thickness of the first coating layer is 45nm, and the mass percentage of the material of the first coating layer is 2% based on the total mass of the silicon-carbon material including the first coating layer is 100%; the mass percentage of the material of the second coating layer is 8% based on the total mass of the silicon-carbon material including the first coating layer is 100%.

[0094] The average particle size of the silicon carbon material core is 8μm and the specific surface area is 4.5m 2 / g, and the mass percentage of silicon material in the silicon-carbon material core is 42%.

[0095] This embodiment also provides a method for preparing the modified silicon negative electrode material, the preparation method comprising the following steps:

[0096] S1. (E)-3-(6-aminopyridin-3-yl)acrylic acid was added to tetrahydrofuran solvent, and then azobisisobutyronitrile was added as an initiator. The mixture was heated to 70° C. under an argon atmosphere for polymerization reaction for 10 h to obtain a reaction solution.

[0097] 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;

[0098] The polymer was dissolved in tetrahydrofuran solvent to obtain a polymer solution with a mass concentration of 8%. The silicon-carbon material was added to the polymer solution and stirred at 80°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 silicon-based material with a surface coated with the polymer.

[0099] S2. The surface of the polymer-coated silicon-based material and deionized water were stirred and dispersed for 1.5h to obtain a first dispersion containing a surface of a polymer-coated silicon-based material;

[0100] Dispersing nano-titanium dioxide in deionized water, adding an appropriate amount of polyvinyl pyrrolidone dispersant (the mass percentage of polyvinyl pyrrolidone dispersant is 3% based on the total mass of nano-titanium dioxide as 100%), and ultrasonically dispersing for 50 minutes to form a uniform and stable second dispersion containing nano-titanium dioxide;

[0101] A first dispersion containing a polymer-coated silicon-based material and a second dispersion containing nano-titanium dioxide were mixed for 1.5 hours to obtain a mixed dispersion. The mixed dispersion was then sprayed into a drying chamber via a nozzle using a spray dryer in the form of droplets. The inlet temperature of the drying chamber was controlled at 180°C, and the outlet temperature was controlled at 100°C. Water from the droplets evaporated rapidly in the drying chamber, yielding the modified silicon anode material.

[0102] Example 4

[0103] The difference between this embodiment and embodiment 1 is that the entire process of step S2 is not performed, and the silicon-based material with the surface coated with a polymer is used as the final modified silicon negative electrode material. The rest is the same as embodiment 1.

[0104] Example 5

[0105] The difference between this embodiment and embodiment 1 is that (E)-3-(6-aminopyridin-3-yl)acrylic acid is replaced with an equal amount of (E)-3-(6-chloropyridin-3-yl)acrylic acid monomer, and the rest is the same as embodiment 1.

[0106] Example 6

[0107] 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.

[0108] Example 7

[0109] The difference between this embodiment and embodiment 1 is that the mass percentage of the material of the first coating layer is 0.5%, and the mass percentage of the material of the second coating layer is 20%. The rest is the same as embodiment 1.

[0110] Example 8

[0111] The difference between this embodiment and embodiment 1 is that the mass percentage of the material of the first coating layer is 10%, and the mass percentage of the material of the second coating layer is 2%. The rest is the same as embodiment 1.

[0112] Comparative Example 1

[0113] The difference between this comparative example and Example 1 is that no coating treatment is performed on the silicon-carbon material, only one silicon-carbon material is provided, and the average particle size, specific surface area and mass percentage of the silicon material provided are the same as those in Example 1.

[0114] Comparative Example 2

[0115] The difference between this comparative example and Example 1 is that the first coating layer coating treatment is not performed, that is, only the silicon-carbon negative electrode material is directly coated with nano-titanium dioxide, wherein the method and steps of the nano-titanium dioxide coating treatment are the same as step S2, and step S1 is not performed. The rest are the same as Example 1.

[0116] Comparative Example 3

[0117] The difference between this comparative example and Example 1 is that (E)-3-(6-aminopyridin-3-yl)acrylic acid is replaced by an equal amount of 4-dimethylaminopyridine monomer, and the rest is the same as Example 1.

[0118] Comparative Example 4

[0119] The difference between this comparative example and Example 1 is that the material of the first coating layer is replaced with graphene with the same content, and the rest is the same as Example 1.

[0120] Application Examples 1-8 and Comparative Application Examples 1-4

[0121] The silicon-based negative electrode materials provided in Examples 1 to 8 and Comparative Examples 1 to 4 were used to prepare negative electrode sheets, and then assembled to obtain lithium-ion batteries. The specific preparation method is as follows:

[0122] Preparation of negative electrode sheet:

[0123] The silicon-based 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.

[0124] Preparation of positive electrode sheet:

[0125] 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.

[0126] Electrolyte:

[0127] Ethylene carbonate, dimethyl carbonate, diethyl carbonate and fluoroethylene carbonate are mixed in a volume ratio of 20:40:30:10 to obtain an organic solvent, and then the fully dried lithium salt LiPF6 and LiFSI lithium salt additive are dissolved in the organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L. The mass percentage of the LiFSI lithium salt additive is 3% based on the total mass of the electrolyte as 100%.

[0128] Preparation of lithium-ion batteries:

[0129] 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.

[0130] Comparative Application Example 5

[0131] The difference between this comparative application example and application example 1 is that all the LiFSI lithium salt additives are replaced with LiPF6 lithium salt of equal content, and the rest are the same as application example 1.

[0132] Test conditions

[0133] The lithium-ion batteries provided in Application Examples 1 to Application Examples 8 and Comparative Application Examples 1 to Comparative Application Examples 5 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 4.2V. The test conditions are as follows:

[0134] (1) First Coulombic efficiency

[0135] At 25°C, the lithium-ion battery was charged to 4.2V 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.

[0136] 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%.

[0137] (2) Capacity retention after 1000 cycles at 1C / 2C at room temperature

[0138] At 25°C, the lithium-ion battery is charged to 4.2V 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.

[0139] 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.

[0140] (3) Room temperature 6C rate performance - constant current charging ratio

[0141] 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 4.2V 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%.

[0142] (4) 1C / 8C discharge capacity retention rate at room temperature

[0143] At 25°C, the divided lithium-ion battery is charged to 4.2V 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 4.2V 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%.

[0144] (5) Initial expansion rate of negative electrode

[0145] 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.

[0146] 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 4.2V, with a cut-off current of 0.05C, and let it stand for 120 minutes;

[0147] 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;

[0148] ④The initial expansion rate of the negative electrode is: (h2-h1) / (h1-h0)×100%.

[0149] The test results are shown in Table 1:

[0150] Table 1

[0151]

[0152]

[0153] As can be seen from Table 1, compared to Comparative Application Examples 1-2, the modified silicon negative electrode materials provided in Application Examples 1-4 of the present invention use a polymer comprising a combination of pyridine groups and carboxyl groups as the coating material of the first coating layer. This not only significantly improves the electron transfer rate of the silicon-carbon negative electrode material at high current density, thereby better improving the rate performance of the assembled lithium-ion battery, but also enhances the structural stability of the interface film, while reducing the loss of active lithium and extending the cycle life of the lithium-ion battery. Application Example 4 shows that the preferred provision of a second coating layer can comprehensively improve the mechanical strength, ionic conductivity, and chemical stability of the modified silicon negative electrode material, thereby better resisting the volume expansion of the silicon-carbon negative electrode material during the charge and discharge process and the corrosion and oxidation of the electrolyte.

[0154] By comparing Application Example 1 with Application Example 5, it can be seen that the ortho-positioned amino group and the para-positioned carboxyl group in the (E)-3-(6-aminopyridin-3-yl) acrylic acid monomer can produce a synergistic effect with the pyridine nitrogen atom, thereby promoting the transmission of lithium ions, thereby achieving a better coating effect and helping to improve the charge and discharge performance of lithium-ion batteries under high current.

[0155] Comparing Application Example 1 with Application Example 6, it can be seen that the present invention achieves good processing performance, mechanical strength, and interfacial compatibility in the first coating layer by regulating the number average molecular weight of the polymer. If a polymer with a lower number average molecular weight is used, the film-forming performance and structural stability of the polymer are both poor, and thus the electronic conductivity of the silicon-carbon negative electrode material and the stability of the interfacial film cannot be effectively improved, and the overall performance of the lithium-ion battery will also be deteriorated.

[0156] By comparing Application Example 1, Application Example 7 and Application Example 8, it can be seen that the content of the first coating layer and the second coating layer has an important influence on the interface stability, ion conductivity and chemical stability of the modified silicon negative electrode material. By setting the content of the two coating layers within a specific range, the volume expansion of the silicon material during the charge and discharge process can be better resisted and the first coulombic efficiency, cycle performance and high-rate performance of the lithium-ion battery can be improved.

[0157] From Comparative Application Examples 1, 3 and 4, it can be seen that if (E)-3-(6-aminopyridin-3-yl) acrylic acid is replaced with other pyridine monomers containing amino groups or conductive carbon materials, the interface stability and electronic conductivity of the silicon-carbon negative electrode material cannot be taken into account, and therefore the full technical effects of the technical solution of the present invention cannot be achieved.

[0158] Comparing Application Examples 1 and 5, it can be seen that there is a synergistic effect between the LiFSI lithium salt additive and the polymer material of the first coating layer. In the presence of the polymer of the first coating layer, the LiFSI lithium salt additive can improve the ionic conductivity of the lithium-ion battery and further improve the constant current charging ratio when charging at a 6C rate.

[0159] The applicant states that while the above-described embodiments illustrate the process of the present invention, the present invention is not limited to the above-described process steps, nor does it imply that the present invention must rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A modified silicon negative electrode material, characterized in that: The modified silicon negative electrode material comprises, from the inside to the outside, a silicon-based material core and a first coating layer covering the surface of the silicon-based material core; The material of the first coating layer includes a polymer, and the polymer structure includes a combination of a pyridine group and a carboxyl group.

2. The modified silicon negative electrode material according to claim 1, characterized in that The monomers forming the polymer include compounds containing a combination of at least one carbon-carbon double bond, at least one pyridine group, and at least one carboxyl group; Preferably, the monomers forming the polymer are selected from (E)-3-(6-aminopyridin-3-yl)acrylic acid.

3. The modified silicon negative electrode material 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 43,000 Da.

4. The modified silicon negative electrode material according to any one of claims 1 to 3, characterized in that The thickness of the first coating layer is 30nm to 80nm; Preferably, based on the total mass of the silicon-based material core including the first coating layer being 100%, the mass percentage of the material of the first coating layer is 1% to 5%.

5. The modified silicon negative electrode material according to any one of claims 1 to 4, characterized in that: The modified silicon negative electrode material further includes a second coating layer, and the second coating layer is arranged on the surface of the first coating layer; Preferably, the material of the second coating layer includes metal oxide; Preferably, the metal oxide comprises titanium dioxide; Preferably, based on the total mass of the silicon-based material core including the first coating layer being 100%, the mass percentage of the material of the second coating layer is 5% to 15%.

6. A method for preparing the modified silicon negative electrode material according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: The modified silicon negative electrode material is obtained by mixing a silicon-based material with a polymer solution containing a combination of pyridine groups and carboxyl groups in its structure and performing a first spray drying process.

7. The method according to claim 6, characterized in that The mass concentration of the polymer solution is 5% to 20%; Preferably, the method for preparing the polymer in the polymer solution comprises the following steps: Mixing a monomer comprising at least one carbon-carbon double bond, at least one pyridine group, and at least one carboxyl group, an initiator, and an organic solvent, and performing a polymerization reaction to obtain the polymer; Preferably, the polymerization reaction is carried out under an inert atmosphere; Preferably, the polymerization reaction temperature is 60°C to 100°C; Preferably, the polymerization reaction time is 5h to 12h; Preferably, the mixing temperature is 60°C to 100°C; Preferably, the mixing time is 5h to 10h; Preferably, the inlet temperature of the first spray drying is 100°C to 200°C; Preferably, the outlet temperature of the first spray drying is 60°C to 90°C.

8. The method according to claim 6 or 7, characterized in that After the first spray drying process is completed, the following steps are further included: Mixing a first dispersion containing a silicon-based material whose surface is coated with a polymer with a second dispersion containing a metal oxide to obtain a mixed dispersion; spray drying the mixed dispersion for a second time to obtain the modified silicon negative electrode material; Preferably, the mass percentage of the metal oxide is 5% to 15% based on the total mass of the silicon-based material whose surface is coated with the polymer as 100%; Preferably, the inlet temperature of the second spray drying is 150°C to 200°C; Preferably, the outlet temperature of the second spray drying is 80°C to 120°C.

9. A negative electrode plate, characterized in that: The negative electrode plate includes a negative electrode active material, and the negative electrode active material includes the modified silicon negative electrode material according to any one of claims 1 to 5.

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.

Images