Modified negative electrode material and preparation method thereof, negative electrode plate and secondary battery

Abstract

The invention discloses a modified negative electrode material and a preparation method thereof, a negative plate and a secondary battery, the modified negative electrode material comprises a negative electrode active material and a modified layer on the modified surface of the negative electrode active material, the modified layer comprises cinnamic acid, and the cinnamic acid is connected with an oxygen-containing functional group on the surface of the negative electrode active material through dehydration condensation. The negative electrode material has the beneficial effects that the negative electrode material is modified by using the cinnamic acid as the modification layer, so that the slope capacity improvement and relatively high first coulombic efficiency of the negative electrode material can be balanced, and on one hand, carboxylic acid groups of the cinnamic acid can be connected with oxygen-containing functional groups on the surface of the negative electrode active material through dehydration condensation; the surface electrolyte affinity of the negative electrode active material is enhanced, and transmission of alkali metal ions is promoted; on the other hand, conjugated double bonds of the cinnamic acid enhance the interface bonding force through pi-pi interaction, and meanwhile, the aromatic structure of the cinnamic acid can also improve the electrochemical stability of the negative electrode active material.

Description

Technical Field

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

[0002] As global energy demand continues to rise and sustainable energy development strategies advance, sodium-ion batteries, with their abundant resources and low costs, are showing broad application prospects in portable electronic devices, electric vehicles, and large-scale energy storage. As the core component of sodium-ion batteries, the performance of the anode material directly determines the battery's energy density, charge-discharge efficiency, cycle life, and safety.

[0003] Currently, hard carbon, alloys, transition metal oxides, and silicon-oxygen materials are the most widely used anode materials for sodium-ion batteries. Hard carbon materials have attracted considerable attention due to their high theoretical specific capacity, low cost, and environmental friendliness. However, they suffer from low initial coulombic efficiency, poor rate performance, and poor cycling stability, which severely restrict their large-scale commercial application.

[0004] To optimize the electrochemical performance of hard carbon anode materials, researchers have conducted research on surface treatment, activation, composite formation, and element doping. For example, graphene coating can increase hard carbon's specific capacity and conductivity, improving rate performance; while the introduction of surface oxygen-containing functional groups such as carbonyl and carboxyl groups can enhance electron mobility. These modification methods primarily focus on manipulating the material's specific surface area, pore structure, and oxygen-containing functional group content.

[0005] Currently, research on hard carbon anode materials for sodium-ion batteries focuses on improving first coulombic efficiency, rate performance, and reducing costs. Researchers are exploring performance optimization paths by analyzing the sodium storage processes (intercalation, adsorption, and nanopore filling) in hard carbon materials. However, existing technologies for improving the slope region and rate performance of hard carbon still have significant drawbacks: the preparation process is complex and poorly controllable, resulting in insufficient consistency and reproducibility in material performance; the high cost of preparing high-performance hard carbon materials limits their commercialization; and, furthermore, an increase in slope region capacity is often accompanied by a decrease in first coulombic efficiency, making it difficult to achieve a balance between the two.

[0006] Therefore, there is an urgent need to develop a new method for modifying hard carbon materials to simultaneously improve the slope region capacity, rate performance and safety of hard carbon materials. Summary of the Invention

[0007] The purpose of the present invention is to provide a modified negative electrode material to increase the initial coulombic efficiency of the negative electrode material and improve the rate performance and structural stability of the negative electrode material.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A modified negative electrode material comprises a negative electrode active material and a modified layer for modifying the surface of the negative electrode active material. The modified layer comprises cinnamic acid, and the cinnamic acid is connected to oxygen-containing functional groups on the surface of the negative electrode active material through dehydration condensation.

[0010] Preferably, the negative electrode active material includes one or more of hard carbon, nano-silicon particles, porous silicon, silicon-carbon composite materials, and soft carbon.

[0011] Preferably, the mass percentage of the cinnamic acid in the negative electrode active material is 2 to 15%.

[0012] The present invention also provides a method for preparing a modified negative electrode material, comprising the following steps:

[0013] Step 1: Mix cinnamic acid and solvent evenly, add negative electrode active material, and disperse evenly to obtain a mixed solution;

[0014] Step 2: heating and stirring the mixed solution until dry to obtain a powdery solid;

[0015] Step 3: vacuum drying the powdered solid and cooling it to obtain a modified negative electrode material.

[0016] Preferably, in the step 1, the volume ratio of the mass of the cinnamic acid to the solvent is 1-5 g:160-200 ml.

[0017] Preferably, in step 1, the solvent is at least one of N-methylpyrrolidone, ethanol, methanol, chloroform and glacial acetic acid.

[0018] Preferably, in step 2, the heating temperature is 50-80°C.

[0019] Preferably, in step three, the vacuum drying temperature is 110-150° C., and the time is 10-15 hours.

[0020] The present invention also provides a negative electrode sheet, comprising the modified negative electrode material or the modified negative electrode material prepared by the preparation method.

[0021] The present invention also provides a secondary battery comprising the above-mentioned negative electrode sheet.

[0022] The beneficial effects of the present invention are:

[0023] (1) The present invention uses cinnamic acid as a modification layer to modify the negative electrode material, thereby balancing the slope capacity improvement and the high first coulombic efficiency of the negative electrode material. Among them, the carboxylic acid group of cinnamic acid can, on the one hand, enhance the electrophilicity of the surface of the negative electrode active material through dehydration condensation with the oxygen-containing functional groups on the surface of the negative electrode active material, thereby promoting the transmission of alkali metal ions; on the other hand, the conjugated double bonds of cinnamic acid enhance the interfacial bonding force through π-π interaction. At the same time, the aromatic structure of cinnamic acid can also improve the electrochemical stability of the negative electrode active material.

[0024] (2) Placing cinnamic acid as a modified layer on the surface of the negative electrode active material improves the first coulombic efficiency of the negative electrode material, balances the capacity improvement and the first coulombic efficiency in the slope region, and also improves the structural stability of the negative electrode material.

[0025] (3) The modified negative electrode material of the present invention has a simple preparation process, low cost, obvious effect, no side effects, and great application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The first cycle charge and discharge curves of Example 1 and Comparative Example 1 of the present invention are shown;

[0027] Figure 2 The capacity curves of the slope region after 30 cycles of Example 1 and Comparative Example 1 of the present invention are shown;

[0028] Figure 3 1 is a rate performance diagram of Example 1 of the present invention and Comparative Example 1;

[0029] Figure 4 This is a long cycle performance diagram at 10C for Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0030] To make the technical solutions and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0031] According to a first aspect of the present invention, a modified negative electrode material is provided, comprising a negative electrode active material and a modified layer for modifying the surface of the negative electrode active material, the modified layer comprising cinnamic acid, which is bonded to oxygen-containing functional groups on the surface of the negative electrode active material by dehydration condensation. The present invention modifies the negative electrode material using cinnamic acid as the modified layer. The carboxylic acid groups of the cinnamic acid can, on the one hand, bond to the oxygen-containing functional groups on the surface of the negative electrode active material by dehydration condensation to form covalent bonds, thereby modifying the surface of the negative electrode active material. This can enhance the electrolytic affinity of the surface of the negative electrode active material, promote the transport of alkali metal ions, and passivate the active sites on the hard carbon surface, reducing electrolyte decomposition. Furthermore, the conjugated double bonds of the cinnamic acid enhance interfacial bonding through π-π interactions, while the aromatic structure of the cinnamic acid can also enhance the electrochemical stability of the negative electrode material.

[0032] Setting cinnamic acid as a modified layer on the surface of the negative electrode active material improves the first coulombic efficiency of the negative electrode material, balances the capacity improvement and the first coulombic efficiency in the slope region, and also improves the structural stability of the negative electrode material.

[0033] The modified negative electrode material of the present invention has simple preparation process, low cost, obvious effect, no side effects, and great application value.

[0034] In one embodiment according to the present invention, the negative electrode active material includes one or more of hard carbon, nano-silicon particles, porous silicon, silicon-carbon composite materials, and soft carbon.

[0035] When the carboxylic acid silicon-based negative electrode of cinnamic acid reacts with the hydroxyl groups on the silicon surface, a stable interface layer can be formed, alleviating the problem of volume expansion of silicon-based materials after application; at the same time, the conjugated structure of cinnamic acid can increase and enhance electron conduction; the modification of cinnamic acid can inhibit the pulverization of silicon-based negative electrodes from the root and improve the rate performance of secondary batteries. The silicon-based negative electrode materials are nano-silicon particles, porous silicon, and silicon-carbon composite materials.

[0036] When the negative electrode active material is soft carbon or disordered carbon, cinnamic acid and the surface of the soft carbon or disordered carbon undergo an esterification reaction to regulate the distribution of surface functional groups, which can optimize the behavior of the alkali metal storage element and thus improve the first coulombic efficiency and rate performance of the secondary battery.

[0037] In the selection of negative electrode active materials, the most preferred is hard carbon material. Cinnamic acid and oxygen-containing functional groups such as hydroxyl (-OH) and epoxy (COC) on the surface of hard carbon undergo esterification or condensation reaction to form covalent bonds such as ester bonds RO-CO-R, etc.; the polarity of the carboxylic acid group of cinnamic acid will enhance the electrolytic affinity of the hard carbon surface, which is beneficial to promote the transmission of alkali metal ions. In addition, the carboxylic acid group can also passivate the active sites on the hard carbon surface, reduce the decomposition of the electrolyte, and inhibit the excessive growth of the SEI film during the secondary battery reaction. This is beneficial for the hard carbon to maintain the original first coulombic efficiency while increasing the capacity in the slope zone, and can achieve both the capacity in the slope zone and the first coulombic efficiency.

[0038] In one embodiment of the present invention, the mass percentage of cinnamic acid in the negative electrode active material is 2-15%. If the mass percentage of cinnamic acid in the negative electrode active material is higher than 15%, the excess cinnamic acid covers the surface of the negative electrode active material, which will hinder the electron transmission path, increase the interface impedance, and thus reduce the conductivity; and the large molecular cinnamic acid may block the microporous structure of the negative electrode active material, reduce the sodium ion diffusion channel, and reduce the rate performance; in addition, the excess carboxylic acid may trigger side reactions (such as self-polymerization), forming an inactive coating, which weakens the sodium storage activity. When the mass percentage of cinnamic acid in the negative electrode active material is lower than 2%, cinnamic acid cannot form a complete modified layer on the surface of the negative electrode active material, and the improvement of the negative electrode material cannot achieve the purpose. Therefore, the mass percentage of cinnamic acid in the negative electrode active material of the present invention is controlled to be 2-15% to achieve the modification effect of the present invention.

[0039] In a second aspect of the present invention, a method for preparing a modified negative electrode material is provided, comprising the following steps:

[0040] Step 1: Mix cinnamic acid and solvent evenly, add negative electrode active material, and disperse evenly to obtain a mixed solution;

[0041] Step 2: heating and stirring the mixed solution until dry to obtain a powdery solid;

[0042] Step 3: vacuum drying the powdered solid and cooling it to obtain a modified negative electrode material.

[0043] The preparation method of the modified negative electrode material provided by the present invention is simple to operate, has a concise process, is low in cost, is very suitable for large-scale application, and has great commercial value and prospects.

[0044] In one embodiment of the present invention, in step 1, the mass ratio of cinnamic acid to solvent is 1-5 g: 160-200 ml. Within this range, the cinnamic acid can be dissolved without wasting raw materials.

[0045] In one embodiment according to the present invention, in step 1, the solvent is at least one of N-methylpyrrolidone, ethanol, methanol, chloroform and glacial acetic acid.

[0046] In one embodiment according to the present invention, in step 2, the heating temperature is 50-80°C, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C. Low-temperature drying can slowly evaporate NMP, reduce solvent residue, and avoid high-temperature-induced decomposition of grafted molecules (such as cinnamate bonds) or oxidation of the hard carbon surface. Excessively high heating temperatures may cause desorption of grafted cinnamic acid molecules or breakage of chemical bonds. The present invention selects a heating temperature of 50-80°C to balance drying efficiency and structural protection.

[0047] In one embodiment according to the present invention, in step three, the vacuum drying temperature is 110-150° C., and the time is 10-15 hours.

[0048] In a third aspect of the present invention, a negative electrode sheet is provided, comprising the modified negative electrode material described above or the modified negative electrode material prepared by the preparation method described above. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode active material layer comprises the modified negative electrode material described above or the modified negative electrode material prepared by the preparation method described above, and the negative electrode current collector is preferably aluminum foil.

[0049] In a fourth aspect, the present invention also provides a secondary battery comprising the aforementioned negative electrode sheet. The secondary battery comprises a negative electrode sheet, a positive electrode sheet, a separator, and the electrolyte described in any of the above paragraphs. The positive electrode sheet, separator, and negative electrode sheet are sequentially stacked and wound or laminated to form a bare cell. The cell is then placed in a shell and filled with electrolyte. The sodium ion battery is then produced through formation and capacity separation processes.

[0050] The positive electrode includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector. The positive electrode active material used in the positive electrode active material layer may include, but is not limited to, one or more of Na, Na, CoO2, NaxMnO2 and its doped compounds, polyanionic compounds, NaFePO4, NASICON-type phosphate Na3V2(PO4)3, LiCoO2, LiMnO2, LiMn2O4, etc. The positive electrode current collector is preferably aluminum foil.

[0051] The separator can be selected from various separators used in secondary batteries known to those skilled in the art, such as polyethylene, polypropylene, PE / PP composite multi-layer microporous membrane, and PI / PE composite membrane.

[0052] In order to make the technical solutions and advantages of the present invention more clear, the present invention will be further described below through specific embodiments.

[0053] Example 1

[0054] This embodiment provides a modified negative electrode material, including a negative electrode active material and a modified layer for modifying the surface of the negative electrode active material, wherein the modified layer includes cinnamic acid, and the cinnamic acid is dehydrated and condensed with oxygen-containing functional groups on the surface of the negative electrode active material, wherein the negative electrode active material is hard carbon.

[0055] Preparation of modified negative electrode materials:

[0056] Step 1: Mix cinnamic acid and N-methylpyrrolidone evenly, add hard carbon material, stir and disperse evenly for 3 hours to obtain a mixed solution, wherein the mass ratio of cinnamic acid and hard carbon material is 10%, and the ratio of cinnamic acid and N-methylpyrrolidone is 6g:180ml.

[0057] Step 2: Heat and stir the mixed solution until dry to obtain a powdery solid, wherein the heating temperature is 60°C.

[0058] Step 3: Dry the powdered solid at 130° C. in vacuum for 12 h and cool to obtain a modified negative electrode material.

[0059] Preparation of secondary batteries:

[0060] The modified negative electrode material, binder and conductive agent were prepared into a slurry in a ratio of 8:1:1 and coated on aluminum foil to obtain a negative electrode sheet. In an anhydrous and oxygen-free environment, the battery was assembled in the order of negative electrode shell, spring, gasket, negative electrode sheet, separator, positive electrode sheet, and positive electrode shell. During the assembly process, 100 μL of electrolyte was injected and the battery was encapsulated to obtain a 2032-type button battery.

[0061] Example 2

[0062] Different from Example 1, the negative electrode active material used in this example is silicon nanoparticles;

[0063] The rest is the same as in Example 1 and will not be described again here.

[0064] Example 3

[0065] Different from Example 1, the negative electrode active material used in this example is soft carbon;

[0066] The rest is the same as in Example 1 and will not be described again here.

[0067] Example 4

[0068] Different from Example 1, the mass ratio of cinnamic acid to modified negative electrode material in this example is 15%;

[0069] The rest is the same as in Example 1 and will not be described again here.

[0070] Example 5

[0071] Different from Example 1, the mass ratio of cinnamic acid to modified negative electrode material in this example is 2%;

[0072] The rest is the same as in Example 1 and will not be described again here.

[0073] Comparative Example 1

[0074] Different from Example 1, the negative electrode material of this embodiment adopts commercially available unmodified hard carbon material;

[0075] The rest is the same as in Example 1 and will not be described again here.

[0076] Comparative Example 2

[0077] Different from Example 1, the negative electrode material of this embodiment adopts commercially available unmodified silicon-based negative electrode material;

[0078] The rest is the same as in Example 1 and will not be described again here.

[0079] Comparative Example 3

[0080] Different from Example 1, the negative electrode material of this embodiment adopts commercially available unmodified soft carbon material;

[0081] The rest is the same as in Example 1 and will not be described again here.

[0082] Performance testing:

[0083] The secondary batteries of the above examples and comparative examples were subjected to electrochemical performance tests, and the test results are as follows: Figures 1 to 4 As shown in Table 2.

[0084] Table 2

[0085]

[0086]

[0087] As shown in Table 1, the experimental data of Examples 1 to 5 are all better than those of Comparative Examples 1 to 3, indicating that cinnamic acid can significantly improve the electrochemical performance, especially the rate performance, of various negative electrode materials through a reasonable design of surface modification strategy.

[0088] Comparing Example 1 with Comparative Example 1, the electrochemical performance data of Example 1 is better than that of Comparative Example 1, indicating that the formation of a cinnamic acid modified layer on the hard carbon surface can improve the first coulombic efficiency and rate performance of the battery.

[0089] Based on the disclosure and teachings of the above description, those skilled in the art will be able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments. Any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention fall within the scope of protection of the present invention. In addition, although certain specific terms are used in this description, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A modified negative electrode material, characterized in that The invention comprises a negative electrode active material and a modified layer for modifying the surface of the negative electrode active material. The modified layer comprises cinnamic acid, and the cinnamic acid is connected to the oxygen-containing functional groups on the surface of the negative electrode active material through dehydration condensation.

2. The modified negative electrode material according to claim 1, characterized in that The negative electrode active material includes one or more of hard carbon, nano silicon particles, porous silicon, silicon-carbon composite materials, and soft carbon.

3. The modified negative electrode material according to claim 1, characterized in that The mass percentage of the cinnamic acid in the negative electrode active material is 2 to 15%.

4. A method for preparing a modified negative electrode material, characterized in that: The following steps are involved: Step 1: Mix cinnamic acid and solvent evenly, add negative electrode active material, and disperse evenly to obtain a mixed solution; Step 2: heating and stirring the mixed solution until dry to obtain a powdery solid; Step 3: vacuum drying the powdered solid and cooling it to obtain a modified negative electrode material.

5. The method for preparing the modified negative electrode material according to claim 4, wherein: In the step 1, the volume ratio of the mass of the cinnamic acid to the solvent is 1-5 g:160-200 ml.

6. The method for preparing the modified negative electrode material according to claim 4, wherein: In the step 1, the solvent is at least one of N-methylpyrrolidone, ethanol, methanol, chloroform and glacial acetic acid.

7. The method for preparing a modified negative electrode material according to claim 4, wherein: In the step 2, the heating temperature is 50-80°C.

8. The method for preparing a modified negative electrode material according to claim 4, wherein: In the step three, the vacuum drying temperature is 110-150° C. and the time is 10-15 hours.

9. A negative electrode sheet, characterized in that: The modified negative electrode material comprises the modified negative electrode material according to any one of claims 1 to 3 or the modified negative electrode material prepared by the preparation method according to any one of claims 4 to 8.

10. A secondary battery, characterized in that: Including the negative electrode sheet according to claim 9.

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