Application of a new negative electrode additive in improving negative electrode gradient porosity and preparation method thereof

Abstract

The application discloses application of a novel negative electrode additive in improvement of negative electrode gradient porosity and a preparation method thereof, and belongs to the technical field of electrodes including active materials. In the preparation process of the negative electrode sheet, a perforated carbon ball with a perforated structure is used as the negative electrode additive, the perforated carbon ball is coated on the surface of the un-compacted negative electrode sheet, and the perforated carbon ball penetrates into the gap of the surface layer particles of the negative electrode sheet by capillary action. Through the special hollow structure of the perforated carbon ball, even in the case of overpressure of the negative electrode surface, a lithium ion channel can be effectively constructed, and the penetration ability of lithium ions in the low-porosity surface layer is effectively improved. Meanwhile, the method can effectively improve the lithium precipitation and service life problems caused by the aggregation of lithium ions in the surface layer in the long-period rate cycle process, and improves the safety and cycle life of the battery.

Description

Technical Field

[0001] This invention relates to the field of electrode technology, including active materials, and particularly to the application of a novel negative electrode additive in improving the gradient porosity of the negative electrode and its preparation method. Background Technology

[0002] As the number of electric vehicle users increases, their demand for charging speed is also rising. Traditional slow charging takes a long time to complete, while fast charging can significantly shorten charging time, improving vehicle availability and user experience. Therefore, the demand for fast charging in new energy vehicles is mainly driven by the desire to complete charging faster, saving time and improving efficiency.

[0003] While providing high-speed charging, fast charging technology must also ensure the safety of the charging process. High temperatures and high pressures may occur during charging, therefore appropriate safety measures are essential to ensure the stability and reliability of the charging process. New energy vehicle users' demands for fast charging also include safety requirements for charging equipment and systems; they hope to use equipment that has undergone rigorous testing and certification to avoid potential safety risks.

[0004] Anode materials play a crucial role in the fast-charging performance of batteries. Their structure, surface properties, and electrochemical characteristics all influence lithium-ion diffusion, electrochemical reactions, and electrolyte wettability during the fast-charging process. Optimizing the performance of anode materials can improve the fast-charging performance of batteries, meeting the fast-charging requirements of new energy vehicles. After years of research on fast-charging anodes, most improvements have reached bottlenecks, and there are still few solutions to improve the gradient porosity of anodes. Summary of the Invention

[0005] In view of the above-mentioned deficiencies of the prior art, in a first aspect of the present invention, a method for improving the gradient porosity of a negative electrode is provided, comprising the following steps: during the preparation of the negative electrode sheet, using perforated carbon balls with a perforated structure as a negative electrode additive, coating the perforated carbon balls on the surface of the uncompacted negative electrode sheet, so that the perforated carbon balls can penetrate into the gaps of the surface particles of the negative electrode sheet by capillary action.

[0006] Gradient porosity in the negative electrode can improve the charge / discharge rate of a battery. During rapid charge / discharge of a battery, lithium ions need to enter and exit the negative electrode material as quickly as possible. However, in regions with low porosity, the diffusion rate of lithium ions may be limited, thus restricting the charge / discharge rate of the battery. Gradient porosity in the negative electrode can provide more active surface area, allowing lithium ions to enter and exit the negative electrode material more easily, while reducing the mechanical stress on the negative electrode material during charge / discharge, thereby improving the charge / discharge performance of the battery. This invention, through the special hollow structure of perforated carbon spheres, can effectively construct a lithium ion pathway even under overpressure conditions on the negative electrode surface, effectively improving the penetration ability of lithium ions in the low-porosity surface layer. At the same time, this method can effectively improve the lithium plating and lifespan problems caused by lithium ion accumulation on the surface during long-cycle rate cycling, improving battery safety and cycle life.

[0007] Preferably, the perforated carbon spheres are prepared as follows:

[0008] S1. Dissolve the polymer in an organic solvent to obtain the corresponding central liquid and external liquid, and set them aside.

[0009] S2. Using a coaxial electrospinning process, the central liquid and the outer liquid are coaxially electrospinned to obtain core-shell structured fiber filaments for later use.

[0010] S3. Add the fiber to an organic solvent to dissolve the core layer while retaining the shell layer. Collect the filter cake by filtration and dry it to obtain carbon sphere fiber body for later use.

[0011] S4. The carbon sphere fiber body is pre-sintered in an air atmosphere, and then carbonized under inert gas protection to obtain perforated carbon spheres.

[0012] More preferably, in S1, the polymer in the central liquid includes at least one of polymethyl methacrylate, polyethylene, polystyrene, and polyvinyl acetate.

[0013] Furthermore, the concentration of the central liquid is 5 wt.% to 10 wt.%.

[0014] More preferably, in step S1, the polymer in the external liquid includes at least one of polyamide, polyacrylonitrile, polyvinyl alcohol, and polyvinyl chloride.

[0015] Furthermore, the concentration of the external liquid is 5 wt.% to 15 wt.%.

[0016] Based on the type of polymer in the central and external liquids, suitable organic solvents in the art can be used to dissolve them. Furthermore, the organic solvent includes at least one of N,N-dimethylformamide, dimethyl furan, dimethyl sulfoxide, and N-methylpyrrolidone.

[0017] Heating and stirring help to fully dissolve the polymer, resulting in a uniform and stable central and external liquid. More preferably, in step S1, the dissolution is promoted by heating and stirring at a temperature of 60–100°C, a stirring rate of 500–2000 rpm, and a processing time of 5–60 min.

[0018] More preferably, in step S2, the parameters of the coaxial electrospinning are as follows: voltage of 10-30kV, central liquid propulsion rate of 20-500mL / min, external liquid propulsion rate of 25-250mL / min, and electrode distance of 15-30cm.

[0019] The ratio of the propulsion rates of the central liquid to the external liquid affects the performance of the finished product. The smaller this ratio, the greater the weight proportion of the external liquid polymer, the smaller the perforations, the fewer the active surfaces, and the better the cycle performance. Furthermore, the ratio of the propulsion rates of the central liquid to the external liquid is 0.2 to 2.0.

[0020] The organic solvent in step S3 can also be of a type suitable in the art. More preferably, in S3, the organic solvent includes at least one of toluene, tetrahydrofuran, xylene, and amyl acetate. Similarly, mixing can be carried out by heating and stirring. More preferably, in S3, mixing is promoted by heating and stirring at a temperature of 60–100°C, a stirring rate of 200–1000 rpm, and a processing time of 1–5 hours.

[0021] More preferably, in step S4, the pre-sintering temperature is 200–400°C, and the processing time is 1–5 hours.

[0022] More preferably, in step S4, the carbonization temperature is 1200–1500°C, and the processing time is 1–6 hours.

[0023] Preferably, the specific operation of the method for improving the gradient porosity of the negative electrode is as follows: In the preparation process of the negative electrode sheet, perforated carbon balls with perforated structures are used as negative electrode additives. The perforated carbon balls are mixed with conductive agents and binders to form an additive slurry. The additive slurry is coated on the surface of the uncompacted negative electrode sheet, so that the perforated carbon balls can penetrate into the gaps of the surface particles of the negative electrode sheet by capillary action. After compaction, the improvement of the gradient porosity of the negative electrode is completed.

[0024] The selection and ratio of conductive agents and binders are diverse, and commercially available types commonly used in the field can be adopted, among which SP carbon black and SBR binder are particularly suitable conductive agent and binder types, respectively.

[0025] Coating using a wire rod is a simple and quick operation, and the amount of coating on the surface can be controlled by adjusting the mesh spacing of the wire rod. More preferably, the additive slurry is coated onto the surface of the uncompacted negative electrode sheet using a wire rod, with the wire rod mesh spacing being 6–30 μm.

[0026] Based on the above technical solutions, the method for improving the gradient porosity of the negative electrode in this invention uses perforated carbon spheres with perforated structures as a novel negative electrode additive. The perforations through which the electrolyte enters the center of the carbon spheres provide more effective active surfaces and lithium-ion channels. After coating, the lithium ions penetrate into the surface negative electrode through capillary action. Because the carbon spheres are rigid enough, they will not deform under cold pressure, effectively constructing a lithium-ion pathway and improving the penetration ability of lithium ions in the low-porosity surface layer. The construction of the surface lithium-ion pathway can also effectively improve the lithium plating and lifespan problems caused by the accumulation of lithium ions on the surface during long-cycle rate cycling, thereby improving the safety and cycle life of the battery.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] This invention provides a method for improving the gradient porosity of the negative electrode. The method uses a perforated structure as a novel negative electrode additive in the preparation of the negative electrode, which optimizes the performance of the negative electrode material and thus improves the fast charging performance of the battery. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope (SEM) cross-sectional image of the electrode prepared using perforated carbon spheres in Example 2. Detailed Implementation

[0030] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0031] Example 1

[0032] A method for improving negative electrode gradient porosity, comprising the following steps:

[0033] In the preparation of the negative electrode sheet, perforated carbon spheres (90 wt.%) with perforated structure are mixed with SP carbon black (5 wt.%) and SBR binder (5 wt.%) to form an additive slurry. The additive slurry is coated onto the surface of the uncompacted negative electrode sheet using a wire rod with a mesh size of 6 μm, so that the perforated carbon spheres can penetrate into the gaps between the particles on the surface of the negative electrode sheet through capillary action. After compaction, a perforated carbon sphere negative electrode sheet is obtained.

[0034] The method for preparing perforated carbon spheres in this embodiment is as follows:

[0035] S1. Add polymethyl methacrylate to N,N-dimethylformamide and heat and stir at 500 rpm at 60°C for 60 min to obtain a central liquid with a concentration of 5 wt.%; add polyamide to N,N-dimethylformamide and heat and stir at 500 rpm at 60°C for 60 min to obtain an external liquid with a concentration of 5 wt.%, for later use.

[0036] S2. Using a coaxial electrospinning device, the voltage is set to 10kV, the propulsion rate of the central liquid is 50mL / min, and the propulsion rate of the external liquid is 250mL / min, so that the ratio of the two propulsion rates is controlled to 0.2, and the electrode distance is 30cm. Core-shell structured fiber filaments are obtained by coaxial electrospinning and are ready for use.

[0037] S3. Add the fiber to excess toluene, stir at 200 rpm for 1 hour at 100°C to dissolve the core, filter through a vacuum filter and collect the filter cake, dry the filter cake to obtain carbon ball fiber body for later use.

[0038] S4. In an air atmosphere, the carbon ball fiber body is pre-sintered at 200°C for 5 hours, and then carbonized at 1200°C for 6 hours under nitrogen protection. After cooling, perforated carbon balls are obtained.

[0039] Example 2

[0040] A method for improving negative electrode gradient porosity, comprising the following steps:

[0041] In the preparation of the negative electrode sheet, perforated carbon spheres (90 wt.%) with perforated structure are mixed with SP carbon black (5 wt.%) and SBR binder (5 wt.%) to form an additive slurry. The additive slurry is coated onto the surface of the uncompacted negative electrode sheet using a wire bar with a mesh size of 15 μm, allowing the perforated carbon spheres to penetrate into the gaps between the surface particles of the negative electrode sheet through capillary action. After compaction, a perforated carbon sphere negative electrode sheet is obtained.

[0042] The method for preparing perforated carbon spheres in this embodiment is as follows:

[0043] S1. Polyethylene is added to dimethylfuran and heated and stirred at 1000 rpm at 80°C for 30 min to obtain a central liquid with a concentration of 8 wt.%; polyacrylonitrile is added to dimethylfuran and heated and stirred at 1000 rpm at 80°C for 30 min to obtain an external liquid with a concentration of 10 wt.%, which is set aside for later use.

[0044] S2. Using a coaxial electrospinning device, the voltage is set to 20kV, the propulsion rate of the central liquid is 50mL / min, the propulsion rate of the external liquid is 50mL / min, the ratio of the two propulsion rates is controlled to 1.0, and the electrode distance is 20cm. Core-shell structured fibers are obtained by coaxial electrospinning and are ready for use.

[0045] S3. Add the fiber to excess tetrahydrofuran, stir at 600 rpm for 3 hours at 80°C to dissolve the core, filter through a vacuum filter and collect the filter cake, dry the filter cake to obtain carbon ball fiber body for later use.

[0046] S4. In an air atmosphere, the carbon sphere fiber body is pre-sintered at 300°C for 3 hours, and then carbonized at 1300°C for 3 hours under argon protection. After cooling, perforated carbon spheres are obtained.

[0047] The cross-sectional morphology of the perforated carbon sphere negative electrode sheet was observed using scanning electron microscopy (SEM), such as... Figure 1 As shown in the figure, the dimensions marked in the figure indicate that the perforated carbon spheres have effectively penetrated into the gaps of the negative electrode graphite, increasing the porosity of the graphite surface layer, thereby creating a gradient porosity and improving the electrical performance of the electrode.

[0048] Example 3

[0049] A method for improving negative electrode gradient porosity, comprising the following steps:

[0050] In the preparation of the negative electrode sheet, perforated carbon spheres (90 wt.%) with perforated structure are mixed with SP carbon black (5 wt.%) and SBR binder (5 wt.%) to form an additive slurry. The additive slurry is coated onto the surface of the uncompacted negative electrode sheet using a wire rod with a mesh size of 30 μm, allowing the perforated carbon spheres to penetrate into the gaps between the surface particles of the negative electrode sheet through capillary action. After compaction, a perforated carbon sphere negative electrode sheet is obtained.

[0051] The method for preparing perforated carbon spheres in this embodiment is as follows:

[0052] S1. Add polystyrene to N-methylpyrrolidone and heat and stir at 1500 rpm for 5 min at 100°C to obtain a central liquid with a concentration of 10 wt.%; add polyvinyl alcohol to N-methylpyrrolidone and heat and stir at 1500 rpm for 5 min at 100°C to obtain an external liquid with a concentration of 15 wt.%, for later use.

[0053] S2. Using a coaxial electrospinning device, the voltage is set to 30kV, the propulsion rate of the central liquid is 50mL / min, and the propulsion rate of the external liquid is 25mL / min, so that the ratio of the two propulsion rates is controlled to 2.0. The electrode distance is 15cm. Core-shell structured fiber filaments are obtained by coaxial electrospinning and are ready for use.

[0054] S3. Add the fiber to excess xylene and stir at 1000 rpm for 5 hours at 60°C to dissolve the core. Filter the mixture through a vacuum filter and collect the filter cake. Dry the filter cake to obtain carbon ball fiber body for later use.

[0055] S4. In an air atmosphere, the carbon sphere fiber body is pre-sintered at 400°C for 1 hour, and then carbonized at 1500°C for 1 hour under nitrogen protection. After cooling, perforated carbon spheres are obtained.

[0056] Compare with Example 1

[0057] The negative electrode used in this comparative example is the same as the one used in the previous example, without any other processing.

[0058] Compare with Example 2

[0059] The negative electrode used in this comparative example is replaced with hard carbon with a D50 of 2.3 μm, and the same coating process is used.

[0060] This study investigates the effect of the perforated carbon sphere negative electrode sheets prepared in Examples 1-3 of this invention on improving the rate performance of batteries. Comparative Example 1 uses the untreated negative electrode sheet as described in the examples. Comparative Example 2 uses hard carbon instead of perforated carbon spheres, mixed with conductive agent SP (90 wt.%) and binder SBR (5 wt.%), and coated onto the surface of an uncompacted negative electrode sheet using a wire rod with a 15 μm mesh pattern. After compaction, the negative electrode sheet is obtained. Comparative Examples 1 and 2 serve as control groups. The negative electrode sheets prepared in Examples 1-3, along with those in Examples 1-3, are used to manufacture 505070 soft-pack batteries (1.7 Ah). Commercially available lithium iron phosphate positive electrodes are used. The positive and negative electrode formulations and process parameters of all samples are kept consistent, resulting in the corresponding soft-pack batteries to be tested. The D50 of the perforated carbon spheres or hard carbon is tested using a laser particle size analyzer, and the rate performance of the resulting soft-pack batteries is tested. The results are shown in Table 1.

[0061] Table 1:

[0062]

[0063] Comparing the examples and comparative examples, it can be seen that after overpressure, the rate performance and cycle performance of the examples are significantly higher than those of the control example. It can be observed that the perforated carbon spheres in the examples effectively expand the graphite, providing a high porosity level on the graphite surface. Even under overpressure conditions, effective ion channels can be constructed.

[0064] Comparing the examples and Comparative Example 2, it can be seen that although hard carbon also has the function of expanding graphite, its performance degradation under overpressure conditions is greater than that of the examples because there are no channels in the middle of the carbon spheres. This indicates that the perforated channels in the middle of the perforated carbon spheres play a core role in transporting lithium ions.

[0065] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for improving negative electrode gradient porosity, characterized in that, The process includes the following steps: during the preparation of the negative electrode sheet, perforated carbon balls with a perforated structure are used as negative electrode additives. The perforated carbon balls are coated on the surface of the uncompacted negative electrode sheet, allowing the perforated carbon balls to penetrate into the gaps between the surface particles of the negative electrode sheet through capillary action. The perforated carbon balls have sufficient rigidity and will not deform under cold pressing.

2. The method according to claim 1, characterized in that, The perforated carbon spheres are prepared as follows: S1. Dissolve the polymer in an organic solvent to obtain the corresponding central liquid and external liquid, and set them aside. S2. Using a coaxial electrospinning process, the central liquid and the outer liquid are coaxially electrospinned to obtain core-shell structured fiber filaments for later use. S3. Add the fiber to an organic solvent to dissolve the core layer while retaining the shell layer. Collect the filter cake by filtration and dry it to obtain carbon sphere fiber body for later use. S4. The carbon sphere fiber body is pre-sintered in an air atmosphere, and then carbonized under inert gas protection to obtain perforated carbon spheres.

3. The method according to claim 2, characterized in that: In step S1, the polymer in the central liquid includes at least one of polymethyl methacrylate, polyethylene, polystyrene, and polyvinyl acetate; the polymer in the external liquid includes at least one of polyamide, polyacrylonitrile, polyvinyl alcohol, and polyvinyl chloride; and the organic solvent includes at least one of N,N-dimethylformamide, dimethyl furan, dimethyl sulfoxide, and N-methylpyrrolidone.

4. The method according to claim 3, characterized in that: The concentration of the central liquid is 5 wt.% to 10 wt.%, and the concentration of the external liquid is 5 wt.% to 15 wt.%.

5. The method according to claim 2, characterized in that: In step S1, the dissolution is promoted by heating and stirring. The heating and stirring temperature is 60~100℃, the stirring rate is 500~2000rpm, and the processing time is 5~60min.

6. The method according to claim 2, characterized in that: In step S2, the parameters of the coaxial electrospinning are as follows: voltage is 10~30kV, the propulsion rate of the central liquid is 20~500mL / min, the propulsion rate of the external liquid is 25~250mL / min, the ratio of the propulsion rates of the central liquid to the external liquid is 0.2~2.0, and the electrode distance is 15~30cm.

7. The method according to claim 2, characterized in that: In step S3, the organic solvent includes at least one of toluene, tetrahydrofuran, xylene, and amyl acetate; the mixing is promoted by heating and stirring, with the heating and stirring temperature being 60~100℃, the stirring rate being 200~1000rpm, and the processing time being 1~5h.

8. The method according to claim 2, characterized in that: In step S4, the pre-sintering temperature is 200~400℃ and the processing time is 1~5h; the carbonization temperature is 1200~1500℃ and the processing time is 1~6h.

9. The method according to claim 1, characterized in that, The specific operation is as follows: In the preparation process of the negative electrode sheet, perforated carbon balls with perforated structure are used as negative electrode additives. The perforated carbon balls are mixed with conductive agents and binders to form an additive slurry. The additive slurry is coated on the surface of the uncompacted negative electrode sheet, so that the perforated carbon balls can penetrate into the gaps of the surface particles of the negative electrode sheet by capillary action. After compaction, the improvement of the gradient porosity of the negative electrode is completed.

10. The method according to claim 9, characterized in that: The additive slurry is coated onto the surface of the uncompacted negative electrode sheet using a wire rod, with the wire rod mesh being 6~30μm.

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