Positive electrode material, positive electrode plate and lithium ion battery

Abstract

The composite particle size D of the positive electrode material is introduced into the positive electrode material, the composite particle size D is related to the D10 of the positive electrode material, the D50 of the positive electrode material and the D90 of the positive electrode material, and the composite particle size D is associated with the average direct-current internal resistance DCRav reflecting the dynamic working state of the battery, namely, the average direct-current internal resistance DCRav of the positive electrode material is related to the D10 of the positive electrode material, the D50 of the positive electrode material and the D90 of the positive electrode material. And an incidence relation is constructed between the material physical property parameters and the battery performance, so that effective theoretical guidance and performance prediction are carried out on material development.

Description

Technical Field

[0001] This application relates to the technical field of batteries, specifically to a positive electrode material, a positive electrode sheet, and a lithium-ion battery. Background Technology

[0002] Lithium manganese iron phosphate (LiMn) x Fe 1-x PO4 (LMFP), a novel olivine-structured cathode material, boasts a high voltage plateau of 4.1V and an energy density approximately 15%–20% higher than traditional lithium iron phosphate (LFP), making it a valuable complement to ternary materials and lithium iron phosphate battery systems. However, LMFP materials exhibit low intrinsic ionic conductivity, only about 10⁻⁶. -13 S / cm, much lower than LFP (approximately 10). -9 S / cm) and ternary materials (approximately 10 -3 The S / cm ratio severely limits its application in high-rate charging and discharging scenarios.

[0003] Currently, the industry typically uses methods such as carbon coating, element doping, and nano-sizing to improve the electronic and ionic conductivity of LMFP materials in order to meet the 3C~5C fast charging requirements.

[0004] However, the evaluation of the rate performance of LMFP materials mainly relies on direct rate charge and discharge tests, and there is a lack of effective theoretical guidance and performance prediction methods for the development of LMFP materials. Summary of the Invention

[0005] This application provides a cathode material, a cathode sheet, and a lithium-ion battery, aiming to construct a correlation model between the physical properties of LMFP materials and the DC internal resistance of the battery, so as to more effectively provide theoretical guidance and performance prediction for LMFP materials.

[0006] In a first aspect, embodiments of this application provide a positive electrode material, wherein the composite particle size D of the positive electrode material is related to the average DC internal resistance DCR. av The fitted curves show a negative correlation; The composite particle size D of the cathode material is related to the D10, D50 and D90 of the cathode material.

[0007] Optionally, in some embodiments of this application, the composite particle size D of the cathode material satisfies the formula shown in Equation I, along with the D10, D50, and D90 of the cathode material: D=1 / (D10×D50) 2 ×D90) Formula I.

[0008] Optionally, in some embodiments of this application, the value of D10 ranges from 0.25 μm to 0.40 μm; and / or The value of D50 ranges from 0.50 μm to 1.10 μm; and / or The value of D90 ranges from 8μm to 15μm.

[0009] Optionally, in some embodiments of this application, DCR and SOC satisfy a quadratic function as shown in Equation II: y=a1X 2 +b1X+c1 Form II; in, y is the DCR value; The value of X ranges from 40% SOC to 80% SOC.

[0010] Optionally, in some embodiments of this application, the value of a1 is greater than 0 and less than or equal to 0.1; The value of b1 is greater than or equal to -4 and less than or equal to 0; The value of c1 is greater than or equal to 0 and less than or equal to 200.

[0011] Optionally, in some embodiments of this application, the average DC internal resistance DCR av With DCR min DCR 40%SOC and DCR 80%SOC Satisfy the formula shown in Equation III: DCR av =(DCR min +DCR 40%SOC +DCR 80%SOC ) / 3-type III.

[0012] Optionally, in some embodiments of this application, the composite particle size D of the positive electrode material is related to the average DC internal resistance DCR. av Satisfy the formula shown in Equation IV: DCR av =a2D+b2 equation IV; in, The range of values ​​for a2 is greater than or equal to -20 and less than or equal to 0; The value of b2 is greater than or equal to 50 and less than or equal to 100.

[0013] Secondly, embodiments of this application provide a positive electrode sheet, which includes the positive electrode material as described above.

[0014] Thirdly, embodiments of this application provide a lithium-ion battery, the lithium-ion battery including the positive electrode sheet as described above.

[0015] In this application embodiment, the cathode material introduces a composite particle size D, which is related to the D10, D50, and D90 of the cathode material. Furthermore, the composite particle size D is correlated with the average DC internal resistance DCR, which reflects the dynamic operating state of the battery. av Correlation is established, that is, a correlation is constructed between material properties and battery performance, so as to provide effective theoretical guidance and performance prediction for material development. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a simulated curve of DCR versus composite particle size D provided by an exemplary embodiment of this disclosure; Figure 2 These are the DCR-SOC curves provided in Embodiments 3 and 4 of this disclosure; Figure 3 This is a simulated curve of the capacity retention rate versus DCR of a battery provided by an exemplary embodiment of this disclosure. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] Direct Current Resistance (DCR) refers to the total internal resistance of a battery under direct current, including ohmic resistance, charge transfer impedance, and polarization resistance, reflecting the dynamic impedance characteristics of the battery under actual operating conditions.

[0020] During high-rate charging and discharging, voltage rise or drop occurs due to impedance such as polarization, resulting in a reduction in actual usable capacity.

[0021] The particle size of LMFP has the following effects on the ion diffusion path: if the particle size is too large, the diffusion path of lithium ions inside the lithium iron phosphate particles increases, resulting in an increase in impedance DCR; if the particle size is too small, the specific surface area will increase, leading to an increase in side reactions.

[0022] According to a first aspect of the embodiments of this application, a positive electrode material is provided, the positive electrode material having an average DC internal resistance DCR av The fitting curve of the composite particle size D of the cathode material shows a negative correlation; Among them, the composite particle size D of the cathode material is related to the D10, D50 and D90 of the cathode material.

[0023] When considering the rate performance of LMFP materials, it is necessary to consider not only the average particle size D50 of the cathode material, but also the influence of small particle size D10 and large particle size D90 on performance such as DCR. Under the same process, the particle size of LMFP can be adjusted to control DCR, thereby improving the rate performance of LMFP materials.

[0024] In this application embodiment, the cathode material introduces a composite particle size D, which is related to the D10, D50, and D90 of the cathode material. Furthermore, the composite particle size D is correlated with the average DC internal resistance DCR, which reflects the dynamic operating state of the battery. av Correlation is established, that is, a correlation is constructed between material properties and battery performance, so as to provide effective theoretical guidance and performance prediction for material development.

[0025] In some embodiments of this application, the composite particle size D of the cathode material satisfies the formula shown in Equation I, along with the cathode material's D10, D50, and D90: D=1 / (D10×D50) 2 ×D90) Formula I.

[0026] By adopting the above solution, the D50 2 The maximum weight of the composite particle size D in the cathode material indicates its dominant influence on the ion diffusion path and ohmic resistance. D10 and D90 represent the contributions of small and large particles, respectively. Too many small particles increase side reactions, while too many large particles prolong the ion diffusion path, both leading to increased internal resistance. A comprehensive index is constructed using the relationship between the product and its reciprocal in Equation I: when the composite particle size D is relatively concentrated and moderate, the D value is large; when the composite particle size D is unevenly distributed (with too many small or large particles), the D value decreases.

[0027] Formula I can be modified by using different combinations, such as D10×D50×D90 or D10×D50. 2 Each of ×D90 yields D, which is then fitted with DCR. The result is shown in Equation I, which yields the highest correlation.

[0028] In some embodiments of this application, the value of D10 ranges from 0.25 μm to 0.40 μm. Exemplarily, D10 can be 0.25 μm, 0.27 μm, 0.29 μm, 0.31 μm, 0.33 μm, 0.35 μm, 0.38 μm, 0.40 μm, or any value between two adjacent values ​​mentioned above.

[0029] In some embodiments of this application, the value of D50 ranges from 0.50 μm to 1.10 μm. Exemplarily, D50 can be 0.50 μm, 0.55 μm, 0.60 μm, 0.65 μm, 0.70 μm, 0.75 μm, 0.80 μm, 0.85 μm, 0.90 μm, 0.95 μm, 1.0 μm, 1.05 μm, 1.10 μm, or any value between two adjacent values ​​mentioned above.

[0030] In some embodiments of this application, the value of D90 ranges from 8 μm to 15 μm. Exemplarily, D90 can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any value between two adjacent values ​​mentioned above.

[0031] By adopting the above scheme, D10, D50, and D90, within the aforementioned ranges, help achieve the optimal balance between ion diffusion kinetics, active material filling density, and interface stability, thereby ensuring battery cycle life and safety performance while reducing DCR. D10 should not be too small, as this helps prevent excessively fine powder from causing an excessively large specific surface area and a surge in side reactions; D50 should not be too large, as this effectively controls the solid-state diffusion distance of lithium ions within the particles, avoiding a significant increase in concentration polarization due to excessively long paths; D90 should not be too large or too small, as this helps maintain a different distribution width of the cathode material, preventing the presence of oversized particles from becoming a performance bottleneck and significantly increasing the battery's DCR.

[0032] In some embodiments of this application, DCR and SOC satisfy a quadratic function as shown in Equation II: y=a1X 2 +b1X+c1 Form II; in, y is the DCR value; The value of X ranges from 40% SOC to 80% SOC, preferably from 50% SOC to 70% SOC.

[0033] By adopting the above scheme, the polarization of the battery changes with the state of charge (SOC) in accordance with a quadratic function as shown in Equation II. Setting X in the range of 40% SOC to 80% SOC helps to more stably characterize the overall impedance characteristics in this range.

[0034] In some embodiments of this application, the value of a1 is greater than 0 and less than or equal to 0.1. For example, a1 can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, and any value between two adjacent values ​​mentioned above.

[0035] In some embodiments of this application, the value of b1 is greater than or equal to -4 and less than or equal to 0. For example, b1 can be -4, -3, -2, -1, 0, or any value between two adjacent values ​​mentioned above.

[0036] In some embodiments of this application, the value of c1 is greater than or equal to 0 and less than or equal to 200. For example, c1 can be 0, 50, 100, 150, 200, or any value between two adjacent values ​​mentioned above.

[0037] By adopting the above scheme, and selecting the above ranges for a1, b1, and c1, it is helpful to improve the DCR. av The correlation with D is higher. If a1, b1, and c1 are outside the above range, the desired rate performance cannot be obtained.

[0038] In some embodiments of this application, the average DC internal resistance DCR av With DCR min DCR 40%SOC and DCR 80%SOC Satisfy the formula shown in Equation III: DCR av =(DCR min +DCR 40%SOC +DCR 80%SOC ) / 3-type III.

[0039] By adopting the above-described scheme, the embodiments of this application introduce the average DC internal resistance (DCR). av The concept is to extract the minimum DCR value within the interval, i.e., DCRmin, to represent the ideal dynamic state; and to extract the two endpoint values, 40% SOC and 80% SOC, to represent the polarization at the interval boundary. By averaging these three values, the average DC internal resistance DCR within a certain SOC interval can be obtained. av This helps to more comprehensively characterize the impedance characteristics of this SOC range.

[0040] Formula III is derived by fitting the DCR and SOC curves of the cathode material obtained by HPPC testing. The correlation of the formula is higher in the range of 40% SOC to 80% SOC.

[0041] In some embodiments of this application, the composite particle size D of the positive electrode material is related to the average DC internal resistance DCR.av Satisfy the formula shown in Equation IV: DCR av =a2D+b2 equation IV; in, The range of values ​​for a2 is greater than or equal to -20 and less than or equal to 0; The value of b2 is greater than or equal to 50 and less than or equal to 100.

[0042] By adopting the above scheme, the embodiments of this application address the relationship between the composite particle size D of the cathode material and the average DC internal resistance DCR of the battery. av Following the formula shown in Equation III above, where a2 is a negative number, the key physical parameters of the material (composite particle size D) are combined with the core electrical performance of the battery (average DC internal resistance DCR). av The reverse correlation is established, that is, a clear and highly directional mathematical relationship is constructed between material properties and battery performance, thereby providing efficient performance prediction for the development of LMFP materials with low internal resistance and high rate performance.

[0043] Figure 1 DCR is one of the embodiments of this application. av Fitting curve of composite particle size D. Figure 1 It can be seen that DCR av It exhibits a linear inverse correlation with the composite particle size D. That is, as the composite particle size D gradually increases, the DCR... av Gradually decreasing.

[0044] Secondly, embodiments of this application provide a positive electrode sheet, which includes the positive electrode material as described above.

[0045] By adopting the above-described solution, the positive electrode sheet of this application embodiment includes all the beneficial effects of the aforementioned positive electrode material, such as having a specific particle size distribution and low DCR. av The characteristic positive electrode material helps to ensure that the electrode has an excellent conductive network and ion transport channels, which directly translates into lower polarization and faster reaction kinetics of the electrode during high-rate charge and discharge, thus enabling the battery to exhibit outstanding high-rate capacity retention.

[0046] Thirdly, embodiments of this application provide a lithium-ion battery, which includes a positive electrode as described above.

[0047] By adopting the above-mentioned scheme, the lithium-ion battery of this application embodiment includes all the beneficial effects of the aforementioned positive electrode sheet. For example, the lithium-ion battery has a lower DC internal resistance and excellent rate performance, and achieves a capacity retention rate that is significantly higher than that of conventional LMFP batteries under high-rate charging conditions such as 3C, thus meeting the stringent requirements of battery performance for application scenarios such as fast charging and high power of electric vehicles.

[0048] The present application will be specifically described below through specific embodiments. These embodiments are only some embodiments of the present application and are not intended to limit the present application. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.

[0049] Example 1 Preparation of cathode materials: Configure the cathode material according to the particle size shown in Table 1; Preparation of positive electrode sheet: Positive electrode active material LMFP(Li 1.01 Fe 0.5 Mn 0.5 PO4, conductive agent acetylene black, dispersant and binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) in a mass ratio of 94:2:1:3 to prepare a positive electrode slurry. The positive electrode slurry is coated on the surface of aluminum foil and vacuum dried and then cold pressed. After edge cutting, cutting and slitting, positive electrode sheets are made, which are then assembled into soft-pack batteries for testing.

[0050] Examples 2 to 8 Except for configuring the cathode material according to the particle size shown in Table 1, the remaining steps and processes are consistent with those in Example 1.

[0051] Comparative Examples 1 to 3 Except for configuring the cathode material according to the particle size shown in Table 1, the remaining steps and processes are consistent with those in Example 1.

[0052] Table 1

[0053] Performance testing: 1. Particle size test: (a) 0.2 g of sample was added to a 100 mL beaker and the powder was sonicated for 5 min; (b) Malvern particle size analyzer was used with the refractive index set to 1.74, absorptivity to 1.0, and occlusion to 8%-12%; (c) the test was started and particle sizes D10, D50, and D90 were obtained. 2. Capacity retention test: (a) At 25°C, charge at 0.5C to 4.2V, then discharge to 2.5V, repeat 3 times; (b) Charge 0.5 Q0 to 4.2V at 25°C; (c) Constant current charging / discharging at different rates, cutoff voltage 2.5V, charging capacity Q1 (0.1C charging capacity Q0). (d) Capacity retention rate = Q1 / Q0.

[0054] Table 2

[0055] Combining Examples 1-8 with Comparative Examples 1-3, it can be seen that D10, D50, and D90 of the cathode materials in Examples 1-8 are within a specific range, while D10 of the cathode material in Comparative Example 1 exceeds the specific range, D50 of the cathode material in Comparative Example 2 exceeds the specific range, and D90 of the cathode material in Comparative Example 3 exceeds the specific range. Referring to Table 2, it can be seen that the composite particle size D of the cathode materials in Examples 1-8 has a higher correlation with DCRav after fitting, and a1, b1, and c1 all fall within the selectable range. This establishes a correlation between material properties and battery performance, enabling effective theoretical guidance and performance prediction for material development.

[0056] Figure 2 These are fitting curves of DCR-SOC for Embodiments 3 and 4 of this application. Figure 2 It can be seen that on the DCR-SOC curves fitted in Examples 3 and 4, a1 is greater than 0 and less than or equal to 0.1, b1 is greater than or equal to -4 and less than or equal to 0, and c1 is greater than or equal to 0 and less than or equal to 200.

[0057] Figure 3 These are simulated curves showing the capacity retention rate versus DCR of the battery in some embodiments of this application. The cathode materials of Examples 1-8 meet the requirements. Figure 3 The fitted curve is obtained, thereby enabling effective theoretical guidance and performance prediction of the battery.

[0058] The above provides a detailed description of a positive electrode material, a positive electrode sheet, and a lithium-ion battery provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A positive electrode material, characterized in that, The composite particle size D and average DC internal resistance DCR of the positive electrode material av The fitted curves show a negative correlation; The composite particle size D of the cathode material is related to the D10, D50 and D90 of the cathode material.

2. The cathode material according to claim 1, characterized in that, The composite particle size D of the cathode material satisfies the formula shown in Equation I, along with the cathode material's D10, D50, and D90: D=1 / (D10×D50) 2 ×D90) Formula I.

3. The cathode material according to claim 1 or 2, characterized in that, The value of D10 ranges from 0.25 μm to 0.40 μm; The value of D50 ranges from 0.50 μm to 1.10 μm; The value of D90 ranges from 8μm to 15μm.

4. The cathode material according to claim 1, characterized in that, DCR and SOC satisfy a quadratic function as shown in Equation II: y = a1X 2 + b1X + c1, Formula II; in, y is the DCR value; The value of X ranges from 40% SOC to 80% SOC.

5. The positive electrode material according to claim 4, characterized in that, The value of a1 is greater than 0 and less than or equal to 0.1; The value of b1 is greater than or equal to -4 and less than or equal to 0; The value of c1 is greater than or equal to 0 and less than or equal to 200.

6. The cathode material according to claim 1, characterized in that, The average DC internal resistance DCR av With DCR min DCR 40%SOC and DCR 80%SOC Satisfy the formula shown in Equation III: DCR av = (DCR min + DCR 40%SOC + DCR 80%SOC ) / 3 Formula III 7. The cathode material according to any one of claims 1 to 6, characterized in that, The composite particle size D and average DC internal resistance DCR of the positive electrode material av Satisfy the formula shown in Equation IV: DCR av =a2D+b2 equation IV; in, The range of values ​​for a2 is greater than or equal to -20 and less than or equal to 0; The value of b2 is greater than or equal to 50 and less than or equal to 100.

8. The positive electrode material according to claim 1, characterized in that, The molecular formula of the cathode material is Li. a M b (PO4) c M is Fe 1-x Mn x ; The Li / P ratio ranges from 0.95 to 1.

10. The value of M / P ranges from 0.9 to 1.15; The value of Li / M ranges from 1.01 to 1.

10.

9. A positive electrode sheet, characterized in that, The positive electrode sheet includes the positive electrode material as described in any one of claims 1 to 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode as described in claim 9.

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