Positive electrode slurry and preparation method thereof, positive plate and lithium ion battery
By blending NCM main material with lithium iron phosphate in lithium-ion batteries and optimizing the preparation process of cathode slurry, the performance degradation problem of lithium-ion batteries in low-temperature environments was solved, and higher discharge and charge power performance, capacity and energy efficiency were achieved.
Patent Information
- Application Number
- CN202511514639.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-22
- Publication Date
- 2025-12-16
AI Technical Summary
Lithium-ion batteries experience performance degradation at low temperatures, limiting their application in cold regions, especially in the temperature range below 0–45°C, which affects charge-discharge characteristics, capacity characteristics, and cycle performance.
By blending NCM main material with lithium iron phosphate, and combining it with a specific ratio of conductive agent and binder, the dispersion and uniformity of the cathode slurry are improved through optimized preparation process, thus producing cathode sheets and lithium-ion batteries suitable for low-temperature environments.
It significantly improves the discharge and charging power performance of lithium-ion batteries in low-temperature environments, and increases the available capacity and energy ratio, especially under low-temperature conditions of -45℃ to 0℃.
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Figure CN121149232A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of energy storage batteries, in particular to a positive electrode slurry, a preparation method thereof, a positive electrode sheet and a lithium ion battery. BACKGROUND
[0002] The battery is the power source of the pure electric vehicle, and the performance of the battery directly determines the performance of the vehicle. There are many types of electric vehicle batteries, including lead-acid batteries, nickel-hydrogen batteries, lithium ion batteries, lithium polymer batteries and super capacitors. Among them, the lithium ion battery is the most ideal battery selection for electric vehicles at present due to its high energy density, no memory effect, long cycle life, low self-discharge and other characteristics. The best working temperature range of the lithium ion battery is generally 20-30℃, and it is relatively comfortable within 0-45℃. When the temperature is lower than 0℃, the charge-discharge characteristics, capacity characteristics and cycle performance of the battery will be reduced. Due to the influence of low temperature on the performance of the lithium ion battery, the use range is limited. For example, in the relatively cold northeast, the audience of pure electric vehicles is small. Once the low-temperature barrier is broken, the lithium battery has great potential in the northern market. SUMMARY
[0003] The purpose of the present application is to overcome the deficiencies and defects of the prior art, and to provide a positive electrode slurry, a preparation method thereof, a positive electrode sheet and a lithium ion battery.
[0004] In order to achieve the above-mentioned purpose, the following solutions are adopted in the present application:
[0005] A positive electrode slurry, comprising the following components by mass:
[0006] NCM main material: 86-92 parts;
[0007] Lithium iron phosphate: 2-10 parts,
[0008] Conductive agent: 1-1.5 parts of powder conductive agent and 0.5-1 part of slurry conductive agent;
[0009] Binder: PVDF 1-1.5 parts
[0010] and solvent.
[0011] Preferably, the following components by mass are included:
[0012] NCM main material: 92.64 parts;
[0013] Lithium iron phosphate: 3.86 parts;
[0014] Conductive agent: 1.5 parts of powder conductive agent and 0.6 parts of slurry conductive agent;
[0015] Binder: PVDF 1.4 parts;
[0016] and solvent.
[0017] Preferably, the particle size of the NCM main material is D50 N ; the particle size of the lithium iron phosphate is D50 P , 0.5≤D50 N / D50 P ≤1.5; preferably, 0.8≤D50 N / D50 P ≤1.2; more preferably, D50 N is 3.9um, and D50 P is 4.4um.
[0018] The PVDF has a weight average molecular weight (Da) of ≥900,000 and a rotational viscosity (mPa.s) of 4000-8000.
[0019] The NCM main material is a lithium cobalt manganese oxide ternary system; preferably, the powder conductive agent is conductive carbon black; the slurry conductive agent is CNT; and preferably, the solvent is NMP or water.
[0020] The application also includes a preparation method of the positive electrode slurry, comprising the following steps:
[0021] 1) The binder and the slurry conductive agent CNT are first added to a mixer, and a high-speed dispersion and slow stirring mode is started, and stirring is performed for 30-50min, and the powder conductive agent is added, and stirring is continued for 60-90min; preferably, the slow stirring speed is 10-20rpm, and the high-speed dispersion speed is 2000-3000rpm;
[0022] 2) The NCM main material is evenly divided into three equal parts, and the first time of adding is simultaneously with the addition of all the lithium iron phosphate, and a high-speed dispersion and slow stirring mode is started, and the high-speed dispersion speed is reduced to 400rpm, and stirring is performed for 10-30min;
[0023] 3) The remaining two parts of the NCM main material are added twice, and the stirring speed and time are the same as step 2);
[0024] 4) After the main material is added, a high-speed dispersion is started, and the speed is increased to 2000-3000rpm, and stirring is performed for 120-150min;
[0025] 5) Finally, the solvent is added for viscosity adjustment, vacuum is extracted, slurry preparation is completed, and the discharge viscosity is 8000-10000cp.
[0026] The application also includes a positive electrode sheet, comprising the positive electrode slurry and a positive electrode current collector.
[0027] The application also includes a lithium ion battery, comprising the positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.
[0028] The negative electrode sheet comprises a negative electrode slurry and a negative electrode current collector; the negative electrode slurry comprises a negative electrode main material, a negative electrode conductive agent and a negative electrode binder;
[0029] Preferably, the negative electrode main material comprises primary particle carbonized products and primary particle graphitized products; preferably, the complexing ratio of the primary particle carbonized products and the primary particle graphitized products is 65:35, the D50 particle size of the primary particle carbonized products is 11.5 um, and the range is 11.5±2, the D50 particle size of the primary particle graphitized products is 8.1 um, and the particle size tolerance is 8±2;
[0030] or comprises secondary particle graphitized products and primary particle carbonized products; the complexing ratio is 35:65, the D50 of the secondary particle graphitized products is 12.2 um, and the range is 12±2 um; the D50 of the primary particle carbonized products is 11.5 um, and the range is 11.5±2,
[0031] or secondary particle carbonized products and primary particle carbonized products, the complexing ratio is 35:65, the D50 of the secondary particle carbonized products is 14.28 um, and the range is 14±2 um; the D50 of the primary particle carbonized products is 11.5 um, and the range is 11.5±2.
[0032] The electrolyte comprises a lithium salt and a solvent;
[0033] The lithium salt is LiPF6 and LiFSI, the mass ratio of LiPF6 is 10-15%, preferably 13%, the mass ratio of LiFSI is 1-3%, preferably 2%;
[0034] The solvent comprises 1-3% of fluorine reagent, 1-3% of sulfite, 55-80% of carbonate, and 5-10% of carboxylate; preferably, the fluorine reagent is fluoroethylene carbonate, the sulfite is propylene sulfite, the carbonate is methyl ethyl carbonate, and the carboxylate is ethyl acetate;
[0035] The separator comprises a base film and a functional layer arranged on both sides of the separator; the functional layer comprises a ceramic layer close to the base film and a glue layer away from the base film; preferably, the base film is a PE film; the thickness of the ceramic layer is 1.5 um; the thickness of the glue layer is 2 um; the ceramic layer comprises Al2O3 or boehmite.
[0036] The application also comprises a lithium ion battery, which is applied to a low-temperature environment, preferably, the low-temperature environment is-45℃ to 0°.
[0037] Compared with the prior art, the application has the following beneficial effects:
[0038] The technical scheme of the present application mixes lithium iron phosphate in the NCM main material, and the prepared battery can effectively improve the low-temperature discharge power performance in the interval above 30%~100% SOC and the low-temperature charging power performance in the interval of 0~100% SOC. BRIEF DESCRIPTION OF DRAWINGS
[0039] Figure 1 The charging curve and the discharging curve of pure ternary and ternary mixed with 4% lithium iron at room temperature, the charging process is 1C constant current constant voltage charging to 4.4V, and the cut-off is 0.05C, the discharging process is 1C constant current constant voltage discharging to 2.8V.
[0040] Figure 2 The curves obtained by adjusting the load to different SOC electrical states at-20℃ and performing constant power discharge for pure ternary and ternary mixed with 4% lithium iron. DETAILED DESCRIPTION
[0041] The present application will be further described in detail below in combination with the drawings and specific examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.
[0042] Example 1
[0043] 1. The positive electrode slurry comprises NCM main material: 92.64 parts; lithium iron phosphate: 3.86 parts; conductive agent: powder conductive agent SP 1.5 parts and slurry conductive agent CNT 0.6 parts; binder: PVDF 1.4 parts (PVDF weight average molecular weight (Da) ≥ 900,000, rotary viscosity (mPa.s) 7000); PVDF glue selects homopolymer with medium viscosity, which reduces the "jelly" and "agglomeration" problems of the slurry and improves the dispersibility of the slurry. The particle size of the NCM main material is D50 N ; the particle size of the lithium iron phosphate is D50 P , D50 N is 3.9um, and D50 P is 4.4um. The D50 size of lithium iron phosphate is selected to be as close as possible to the size of the ternary system, which is more conducive to the uniform dispersion of lithium iron particles in the ternary particles and avoids the agglomeration phenomenon.
[0044] The preparation method of the positive electrode slurry comprises the following steps:
[0045] 1) First, add the binder and the slurry conductive agent CNT in the mixer, start the high-speed dispersion and slow stirring mode, stir for 30~50min, add the powder conductive agent, and continue to stir for 60~90min; the slow stirring speed is 10~20rpm, and the high-speed dispersion speed is 2000~3000rpm;
[0046] 2) Divide the NCM main material into 3 equal parts and add it at the same time as all the lithium iron phosphate when adding it for the first time. Simultaneously turn on the high-speed dispersion and slow stirring mode, reduce the high-speed dispersion speed to 400 rpm, and stir for 10 to 30 minutes.
[0047] 3) Add the remaining two portions of the three main ingredients in two batches, stirring at the same speed and time as in step 2);
[0048] 4) After all the main ingredients are added, turn on the high-speed dispersing function and increase the speed to 2000-3000 rpm, and stir for 120-150 minutes;
[0049] 5) Finally, add solvent to adjust viscosity, vacuum, and the pulping is complete. The output viscosity is 8000-10000cp.
[0050] The positive electrode homogenization double planetary conductive adhesive process, with the feeding sequence of (A+B)+B+B, can improve the uniformity of lithium iron phosphate dispersion in ternary slurry.
[0051] 2. Preparation of positive electrode sheet: The positive electrode slurry prepared in step 1 is coated onto the positive electrode current collector to obtain the positive electrode sheet.
[0052] 3. Preparation of the negative electrode sheet: The negative electrode slurry includes the negative electrode main material, the negative electrode conductive agent, and the negative electrode binder; the ratio of the negative electrode main material, the negative electrode conductive agent, and the negative electrode binder is 96.8:0.8:2.4; the negative electrode main material includes primary granular carbide and primary granular graphitized material; the compounding ratio of primary granular carbide and primary granular graphitized material is 65:35, the primary granular carbide has a D50 particle size of 11.5 μm with a range of 11.5 ± 2 μm, and the primary granular graphitized material has a particle size of 8.1 μm with a particle size tolerance of 8 ± 2 μm; the negative electrode conductive agent is conductive carbon black, and the negative electrode binder is a mixture of styrene-butadiene rubber and CMC with a ratio of 1.1:1.3.
[0053] 4. Lithium-ion battery fabrication: Positive electrode, negative electrode, separator, and electrolyte are assembled into a pouch cell. To improve the quality of the SEI (solid electrolyte interface) membrane, the semi-finished battery undergoes a high-temperature settling and high-temperature venting process after electrolyte injection. The high-temperature (settling / venting) temperature is 35–45°C, and the settling time is 12–24 hours. The SOC after high-temperature venting is 45%–55%. The vented cells then undergo room-temperature capacity testing and aging processes to obtain the finished battery.
[0054] The electrolyte comprises lithium salt and solvent; the lithium salt is LiPF6 and LiFSI, with LiPF6 accounting for 13% by mass and LiFSI accounting for 2% by mass; the solvent comprises 1.3% fluoroethylene carbonate, 1.3% propylene sulfite, 53% methyl ethyl carbonate, 21.2% propylene carbonate, and 8.2% ethyl acetate.
[0055] The separator comprises a PE base film and functional layers disposed on both sides of the separator; the functional layers comprise a ceramic layer close to the base film and an adhesive layer away from the base film; the thickness of the ceramic layer is 1.5 μm; the thickness of the adhesive layer is 2 μm; the ceramic layer comprises Al2O3.
[0056] Comparative Example 1
[0057] The difference between Comparative Example 1 and Example 1 is that lithium iron phosphate is not added, and the positive electrode slurry includes NCM main material: 96.5 parts; lithium iron phosphate: 0 parts; conductive agent: powder conductive agent SP 1.5 parts and slurry conductive agent CMC 0.6 parts; binder: PVDF 1.4 parts and solvent.
[0058] Resistance tests were performed on the ternary electrodes doped with 4% lithium iron phosphate in Comparative Example 1 and Example 1. The results showed that the electrode prepared by the formulation in step 1 and the homogenization process in step 2 had an interfacial resistance 0.018 ohms-cm lower than that of the pure ternary electrode. 2 This indicates that the addition of lithium iron phosphate reduces the interfacial resistance of the electrode.
[0059] Table 1
[0060] Interfacial resistivity / ohm-cm2 Comparative Example 1 0.158 Example 1 0.140
[0061] Resistance tests were performed on the ternary electrodes of Comparative Example 1 and Example 1, which were doped with 4% lithium iron phosphate. Standard 1C / 1C charge-discharge tests were conducted at 25°C from 2.8V to 4.4V. Results... Figure 1 The comparison of charge-discharge curves shows that the voltage in each SOC range of the ternary lithium-ion battery is always lower than that of the pure ternary lithium-ion battery. This is because the voltage in each SOC range of the lithium-ion lithium-ion battery system is lower than that of the ternary lithium-ion battery. The addition of 4% lithium-ion lithium to the ternary lithium-ion battery system causes the voltage of the entire system to shift downward.
[0062] Constant power discharge test under the same conditions, such as Figure 2 As shown, a higher termination voltage indicates better discharge power performance. With increasing State of Charge (SOC), the power advantage of ternary lithium iron phosphate (LFP) batteries becomes increasingly apparent. Until SOC > 30%, the power performance of ternary lithium batteries with 4% LFP is essentially on par with pure ternary lithium batteries. As SOC continues to rise, the power performance of ternary lithium batteries with 4% LFP outperforms that of pure ternary lithium batteries. In constant power charging tests, a lower termination voltage indicates better charging power performance. Through constant power charging tests at -20℃ with different SOCs, the termination voltage of ternary lithium batteries with 4% LFP is consistently lower than that of pure ternary lithium batteries, indicating that the power performance of ternary lithium batteries with 4% LFP is superior to that of pure ternary lithium batteries.
[0063] Table 2 shows the WLTC (World Light Vehicle Test Procedure) test results at -20℃. Under the same operating conditions, the usable capacity of the ternary lithium battery with 4% lithium iron phosphate is 4% higher than that of the pure ternary lithium battery, and the usable energy is 3% higher than that of the pure ternary lithium battery.
[0064] Example 2-3
[0065] Meanwhile, this application tested different lithium iron phosphate doping amounts. Example 2 used 3% (NCM main material 93.61 parts; lithium iron phosphate: 2.90 parts; conductive agent: powder conductive agent SP 1.5 parts and slurry conductive agent CNT 0.6 parts; binder: PVDF 1.4 parts), and Example 3 used 9% (NCM main material 87.82 parts; lithium iron phosphate: 8.69 parts; conductive agent: powder conductive agent SP 1.5 parts and slurry conductive agent CNT 0.6 parts; binder: PVDF 1.4 parts). The test results are shown in Table 2. The results show that by increasing the mass ratio of lithium iron phosphate in the system, the usable capacity ratio and usable energy ratio at -20℃ can be improved.
[0066] Table 2
[0067]
[0068] In summary, the technical solution of this application, by mixing lithium iron phosphate into the NCM main material, can effectively improve the low-temperature discharge power performance in the range of 30% to 100% SOC and the low-temperature charging power performance in the range of 0 to 100% SOC, and improve the usable capacity ratio and usable energy ratio at -20℃.
[0069] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.
[0070] Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.
[0071] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A positive electrode slurry, characterized in that, Includes the following components by weight: NCM main material: 86-92 parts; Lithium iron phosphate: 2-10 parts, Conductive agent: 1-1.5 parts of powdered conductive agent and 0.5-1 part of slurry conductive agent; Adhesive: 1-1.5 parts PVDF And solvents.
2. The positive electrode slurry according to claim 1, characterized in that, Includes the following components by weight: NCM main material: 92.64 parts; Lithium iron phosphate: 3.86 parts; Conductive agent: 1.5 parts powdered conductive agent and 0.6 parts slurry conductive agent; Adhesive: 1.4 parts PVDF; And solvents.
3. The positive electrode slurry according to claim 1, characterized in that, The particle size of the NCM main material is D50. N The lithium iron phosphate has a particle size of D50. P 0.5≤D50 N / D50 P ≤1.5; preferably 0.8≤D50 N / D50 P ≤1.2; more preferably, D50 N It is 3.9um, D50 P It is 4.4um.
4. The positive electrode slurry according to claim 1, characterized in that, The PVDF has a weight-average molecular weight (Da) ≥ 900,000 and a rotational viscosity (mPa.s) of 4000-8000.
5. The positive electrode slurry according to claim 1, characterized in that, The NCM main material is a lithium cobalt manganese oxide ternary system; preferably, the powder conductive agent is conductive carbon black; the slurry conductive agent is CNT; preferably, the solvent is NMP or water.
6. A method for preparing the positive electrode slurry according to any one of claims 1-5, characterized in that, Includes the following steps: 1) First add the binder and CNT conductive agent to the mixer, turn on the high-speed dispersion and slow stirring mode, stir for 30 to 50 minutes, add the powdered conductive agent, and continue stirring for 60 to 90 minutes; preferably, the slow stirring speed is 10 to 20 rpm, and the high-speed dispersion speed is 2000 to 3000 rpm. 2) Divide the NCM main material into 3 equal parts and add it at the same time as all the lithium iron phosphate when adding it for the first time. Simultaneously turn on the high-speed dispersion and slow stirring mode, reduce the high-speed dispersion speed to 400 rpm, and stir for 10 to 30 minutes. 3) Add the remaining two portions of the three main ingredients in two batches, stirring at the same speed and time as in step 2); 4) After all the main ingredients are added, turn on the high-speed dispersing function and increase the speed to 2000-3000 rpm, and stir for 120-150 minutes; 5) Finally, add solvent to adjust viscosity, vacuum, and the pulping is complete. The output viscosity is 8000-10000cp.
7. A positive electrode plate, characterized in that, Includes the positive electrode slurry and positive electrode current collector as described in any one of claims 1-5.
8. A lithium-ion battery, characterized in that, Includes the positive electrode, negative electrode, separator, and electrolyte as described in claim 7; The negative electrode sheet includes a negative electrode slurry and a negative electrode current collector; the negative electrode slurry includes a negative electrode main material, a negative electrode conductive agent, and a negative electrode binder; Preferably, the negative electrode material comprises primary granular carbide and primary granular graphitized material; preferably, the compounding ratio of primary granular carbide and primary granular graphitized material is 65:35, the primary granular carbide has a D50 particle size of 11.5 μm with a range of 11.5 ± 2 μm, and the primary granular graphitized material has a particle size of 8.1 μm with a particle size tolerance of 8 ± 2 μm. Alternatively, it may include secondary particulate graphitized products and primary particulate carbides; the compounding ratio is 35:65, the secondary particulate graphitized product has a D50 of 12.2 μm, ranging from 12 ± 2 μm; the primary particulate carbides have a D50 of 11.5 μm, ranging from 11.5 ± 2 μm. Alternatively, a mixture of secondary and primary particulate carbonized products can be prepared in a ratio of 35:
65. The secondary particulate carbonized product has a D50 of 14.28 μm, ranging from 14 ± 2 μm; the primary particulate carbonized product has a D50 of 11.5 μm, ranging from 11.5 ± 2 μm.
9. The lithium-ion battery according to claim 8, characterized in that, The electrolyte includes lithium salt and solvent; The lithium salt is LiPF6 and LiFSI, with LiPF6 accounting for 10-15% by mass, preferably 13%; and LiFSI accounting for 1-3% by mass, preferably 2%. The solvent comprises 1-3% fluorine reagent, 1-3% sulfites, 55-80% carbonates, and 5-10% carboxylic acid esters; preferably, the fluorine reagent is fluoroethylene carbonate, the sulfites are propylene sulfites, the carbonates are methyl ethyl carbonate, and the carboxylic acid esters are ethyl acetate. The diaphragm includes a base membrane and functional layers disposed on both sides of the diaphragm; the functional layers include a ceramic layer close to the base membrane and an adhesive layer away from the base membrane; preferably, the base membrane is a PE membrane; the thickness of the ceramic layer is 1.5 μm; the thickness of the adhesive layer is 2 μm; the ceramic layer includes Al2O3 or boehmite.
10. A lithium-ion battery according to claims 8-9, characterized in that, For use in low-temperature environments, preferably, the low-temperature environment is -45°C to 0°C; more preferably, it is -20°C.