A positive electrode sheet and a lithium ion battery thereof

Abstract

This invention belongs to the field of battery technology, and particularly relates to a positive electrode sheet and its lithium-ion battery, comprising a first delithiable material and a second delithiable material; the first delithiable material has a coin cell initial charge specific capacity of C1 mAh / g and a particle size D50 of D50-1; the second delithiable material has a coin cell initial charge specific capacity of C2 mAh / g and a particle size D50 of D50-2; the positive electrode sheet also contains a conductive material with a length of L and a diameter of S in the width direction, and an average L / S ratio of 100~2000; wherein C1 / C2>2, L>D50-2 or L>D50-1, and the conductive material surrounds the first delithiable material to form a conductive bridge. Compared with the prior art, this invention can effectively improve the subsequent gas generation problem of the lithium replenishment agent, improve the lithium replenishment capacity, and significantly improve the kinetics of the system.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and particularly relates to a positive electrode sheet and its lithium-ion battery. Background Technology

[0002] Lithium replenishing agents for positive electrodes are typically used as additives, directly mixed with the positive electrode active material to form a slurry, which is then coated onto the electrode sheet. However, due to the material's high internal resistance and insufficient conductivity, complete lithium removal occurs during the initial formation process. As a result, the lithium replenishing agent continues to add lithium during later battery use, leading to battery swelling. Therefore, improving the conductivity of the lithium replenishing agent is crucial to fully realize its lithium replenishing effect (i.e., complete lithium removal).

[0003] Furthermore, as battery energy density increases and electrode thickness increases, electrode resistance also increases. If the lithium replenishing agent is simply physically mixed with the positive electrode material and coated to form the electrode under such a thick electrode design, the polarization of the lithium replenishing agent will be further aggravated, leading to a higher risk of gas generation during later battery use.

[0004] Furthermore, the reason why lithium replenishing agents can replenish lithium is that most of the lithium remains at the negative electrode during the initial charge, compensating for the consumption of active lithium at the positive electrode by the SEI and the subsequent lithium consumption during cycling. This also causes the lithium replenishing agent particles to shrink within the crystal lattice, resulting in smaller particles. If the lithium replenishing agent particles cannot be completely filled with conductive agent or active material around them, gaps will appear in the thickness direction of the electrode, increasing resistance.

[0005] To address the aforementioned technical challenges, existing innovative solutions primarily focus on the coating and doping processes of the materials themselves, particle size adjustment, and optimization of battery formation processes. However, these existing technologies are costly, involve complex procedures, have long verification cycles, and still cannot completely resolve the existing problems of this lithium replenishment agent.

[0006] In view of this, the present invention aims to provide a positive electrode sheet and its lithium-ion battery, which utilizes the difference between high lithium replenishment agent and active material particles, and adjusts the amount of lithium replenishment agent to make the lithium replenishment agent uniformly distributed or embedded in the electrode sheet, and combined with ultra-long conductive paths and highly conductive materials, and adjusts the amount of lithium replenishment agent to form a uniform conductive network around the three, so that even if the lithium replenishment agent lattice shrinks, it can still maintain a high conductivity, and form conductive bridges around the lithium replenishment agent particles, so that even if gaps occur, they will not affect the resistance of the entire electrode sheet and particles. Summary of the Invention

[0007] To address the shortcomings of existing technologies, a positive electrode and its battery are provided. By adjusting the particles of high-capacity lithium replenishing agent and active material, large lithium replenishing agent particles are evenly distributed or embedded in the electrode, avoiding large local gaps caused by the shrinkage of lithium replenishing agent particles due to detachment from the crystal lattice, which would lead to a series of side reactions later. At the same time, a special conductive agent is introduced to form conductive bridges around the lithium replenishing agent particles, so that even if gaps occur, the resistance of the entire electrode and particles is not affected.

[0008] To solve the above problems, the technical solution of the present invention is as follows: A positive electrode of a lithium-ion battery includes a first delithiable material and a second delithiable material. The first lithium-delithiable material has a coin cell initial charge capacity of C1 mAH / g and a particle size D50 of D50-1. The first charge capacity of the second lithium-depletable material is C2 mAh / g, and the particle size D50 is D50-2. The mass of the first delithiable substance is M1, and the mass of the second delithiable substance is M2; The positive electrode also contains a conductive material with a length of L and a diameter of S in the width direction, and the average value of L / S is 100~2000. The conductive material with this characteristic can form a coating on the surface of the lithium replenishing agent, acting as a bridge. Even if the lithium replenishing agent delithiates, the crystal lattice shrinks, and there are gaps in the particles, it still achieves a conductive connection effect.

[0009] Where C1 / C2>2, L>D50-2 or L>D50-1, the conductive material forms a conductive bridge around the first delithiable material. The higher the capacity of the lithium replenishing agent (i.e., the first delithiable material), the more lithium it will remove during the first charge, resulting in greater lattice shrinkage and a greater negative impact on the overall internal resistance of the electrode. When its capacity ratio to the active material is greater than 2, this invention can achieve significant effects. In this invention, the first delithiable material acts as a lithium replenishing agent, and its specific capacity is much higher than that of the main material (the second delithiable material), thus achieving a lithium replenishment effect. Simultaneously, by selecting the particle size of the lithium replenishing agent and the main material, synergistic effects with the conductive material are achieved, resulting in a bridging effect.

[0010] Preferably, the particle size D90 of the first delithiable material is D90-1, and the particle size D90 of the second delithiable material is D90-2; L>D90-2 or L>D90-1. Material blends with the above parameter relationships can achieve better results.

[0011] As an improvement to the positive electrode sheet of the lithium-ion battery of the present invention, the mass of the first lithium-deintercalatable substance is M1, and the mass of the second lithium-deintercalatable substance is M2; the weight of the conductive substance is M3, and M3 / M1 > 1 / 20, and 0.5% < M1 / M2 < 3.5%. This is because if the amount of the first lithium-deintercalatable substance M1 is too small and the lithium supplementing agent is too little, there is not much room for the electrode sheet itself to improve the resistance, and the effect of the present invention is not significant. If the content of the first lithium-deintercalatable substance is too high, it is also difficult for the conductive substance to play an obvious improvement role. Because the conductive substance cannot be increased infinitely. Excessive conductive substance will increase the processing difficulty, and if it is not evenly dispersed, it will instead play a negative role.

[0012] As an improvement to the positive electrode sheet of the lithium-ion battery of the present invention, the conductive substance is at least one of conductive carbon fiber, conductive carbon black, and conductive carbon nanotubes. Utilize the conductivity of carbon materials such as carbon nanotubes to improve the conductivity of the lithium supplementing agent and reduce the internal resistance, so as to fully exert the lithium supplementing effect.

[0013] As an improvement to the positive electrode sheet of the lithium-ion battery of the present invention, the conductive substance is single-walled carbon nanotubes. The single-walled carbon nanotubes have a larger aspect ratio and better conductive effect.

[0014] As an improvement to the positive electrode sheet of the lithium-ion battery of the present invention, the first lithium-deintercalatable substance is Li x M y O z , where 0 < x ≤ 6, 0 < y ≤ 3, 0 < z ≤ 4, and M is at least one of Fe, Co, Ni, Mn, C, and Si.

[0015] As an improvement to the positive electrode sheet of the lithium-ion battery of the present invention, the second lithium-deintercalatable substance is at least one of LFP (lithium iron phosphate), LFMP (lithium manganese iron phosphate), NCM (nickel cobalt manganese ternary material), lithium cobaltate, and lithium-rich manganese-based cathode material.

[0016] As an improvement to the positive electrode sheet of the lithium-ion battery of the present invention, the positive electrode sheet further includes a dispersant with a mass percentage of 0.02% - 0.2% and a binder with a mass percentage of 0.8% - 2.5%.

[0017] As an improvement to the positive electrode sheet of the lithium-ion battery of the present invention, the preparation method of the positive electrode sheet at least includes the following steps: The first step is to prepare a suspension solution with a solid content of 1% - 8% (the solvent is NMP) from the conductive substance to make a uniformly dispersed conductive paste; The second step is to prepare a uniformly dispersed liquid with a solid content of 5 - 15% (the solvent is NMP) from the dispersant to make a uniformly dispersed dispersant solution; The third step is to prepare a first positive electrode paste from the conductive paste in the first step and the first lithium-deintercalatable substance; The fourth step involves adding the dispersant solution from the second step and the second delithiable substance to the positive electrode slurry according to the metering ratio, dispersing them evenly, and adjusting the viscosity to obtain a coating-ready positive electrode slurry. The fifth step is to coat the positive electrode slurry onto the current collector, bake it to remove the solvent, and obtain the positive electrode sheet.

[0018] The present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode is the positive electrode described in the present invention.

[0019] Compared to existing technologies, this invention primarily addresses the issue of high-capacity lithium replenishing agents and active materials by adjusting the particle size distribution of large lithium replenishing agent particles, allowing them to be evenly distributed or embedded within the electrode. This avoids large localized gaps caused by the shrinkage of aggregated lithium replenishing agent particles due to lattice detachment, which could lead to a series of subsequent side reactions. Simultaneously, a special conductive agent is introduced to form conductive bridges around the lithium replenishing agent particles, ensuring that even with gaps, the overall resistance of the electrode and particles remains unaffected. This invention effectively improves the subsequent gas generation problem of the lithium replenishing agent, enhances lithium replenishment capacity, and significantly improves the system's kinetics. Attached Figure Description

[0020] Figure 1 This is a SEM image of a carbon nanotube-coated first lithium-depletable material in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Example 1

[0022] This embodiment provides a positive electrode for a lithium-ion battery, comprising a first delithitable material, lithium iron phosphate (Li5FeO4), and a second delithitable material, lithium iron phosphate (LFP). The first delithitable material has a first charge specific capacity of 760 mAh / g and a particle size D50 of D50-1 (specifically 5.6 μm). The second delithitable material has a first charge specific capacity of 158 mAh / g and a particle size D50 of D50-2 (specifically 1.8 μm). The first delithitable material has a mass of 28 g, and the second delithitable material has a mass of 1400 g. The positive electrode also contains conductive carbon nanotubes with a length L of 2.4 μm and a diameter S in the width direction, and the average value of L / S is about 200. The weight M3 of the conductive material is 2 g, and M3 / M1 = 1 / 14.

[0023] The positive electrode sheet also includes a dispersant and a binder, wherein the dispersant is a polyamide ester with a mass of 2.2g; and the binder is PVDF with a mass of 16g.

[0024] The preparation method of this positive electrode sheet includes at least the following steps: The first step involves adding a conductive material to NMP to prepare a uniformly dispersed conductive slurry with a solid content of 5%; the SEM image of this conductive slurry is shown below. Figure 1 As shown; The second step is to add the dispersant to NMP to prepare a uniform liquid with a solid content of 10%, thus creating a uniformly dispersed dispersant solution. The third step is to prepare positive electrode paste one by combining the conductive paste from the first step with the first lithium-depleting material. The fourth step involves adding the dispersant solution from the second step and the second delithiable substance to the positive electrode slurry according to the metering ratio, dispersing them evenly, and adjusting the viscosity to obtain a coating-ready positive electrode slurry. The fifth step is to coat the positive electrode slurry onto the current collector, bake it to remove the solvent, and obtain the positive electrode sheet.

[0025] The fourth step is to coat the positive electrode slurry onto the current collector, bake it to remove the solvent, and obtain the positive electrode sheet. Example 2

[0026] Unlike Example 1, L>D50-1 (instead of L>D50-2), and L is specifically 6.6 μm. L / S=700.

[0027] The rest is the same as in Example 1, and will not be repeated here. Example 3

[0028] Unlike Example 1, the conductive material is specifically a mixture of carbon nanotubes and superconducting carbon (SP) in a mass ratio of 1:1. The weight of the carbon nanotubes is 2g.

[0029] The rest is the same as in Example 1, and will not be repeated here. Example 4

[0030] Unlike Example 1, M3 is 1g.

[0031] The rest is the same as in Example 1, and will not be repeated here. Example 5

[0032] Unlike Example 1, the first delithiable material is a mixture of lithium iron ferrite and lithium nickel ferrite in a mass ratio of 8:2, and the average D50-1 of the mixture of the two lithium replenishing agents is 6.7 μm.

[0033] The rest is the same as in Example 1, and will not be repeated here. Example 6

[0034] Unlike Example 1, the first delithiable material is lithium-rich nickel oxide, and the second delithiable material is a mixture of LFP and NCM in a mass ratio of 1:9. The average particle size of the two active materials is 4.2 μm, the D50-1 of lithium-rich nickel oxide is 8.4 μm, and the L is 6.6 μm.

[0035] The rest is the same as in Example 1, and will not be repeated here. Example 7

[0036] Unlike Example 1, the conductive material is a single-arm carbon nanotube.

[0037] The rest is the same as in Example 1, and will not be repeated here. Example 8

[0038] This embodiment provides a positive electrode for a lithium-ion battery, comprising a first delithitable material Li2NiO2 and a second delithitable material, a nickel-cobalt-manganese ternary material; the first delithitable material has a first charge specific capacity of 430 mAh / g and a particle size D50 of D50-1 (specifically 8.4 μm); the second delithitable material has a first charge specific capacity of 188 mAh / g and a particle size D50 of D50-2 (specifically 4.6 μm); the first delithitable material has a mass of 28 g, and the second delithitable material has a mass of 1400 g; The positive electrode also contains a single-arm carbon nanotube (which can be a single-arm carbon nanotube, or a mixture of single-arm, multi-arm, or oligo-arm carbon nanotubes). Its length L is 12 μm, L>D50-1, its diameter in the width direction is S, and the average value of L / S is 1500. The weight M3 of the conductive material is 4 g, and M3 / M1=1 / 7.

[0039] The positive electrode sheet also includes a dispersant and a binder, wherein the dispersant is a polyamide ester with a mass of 2.8g; and the binder is PVDF with a mass of 16g.

[0040] The rest is the same as in Example 1, and will not be repeated here. Comparative Example 1

[0041] This comparative example provides a positive electrode sheet for a lithium-ion battery, including LFP, lithium iron phosphate rich in lithium, and SP, with LFP weighing 1400g, Li5FeO4 weighing 28g, and SP weighing 220g. Comparative Example 2

[0042] This comparative example provides a positive electrode sheet for a lithium-ion battery, including LFP, lithium iron phosphate, lithium nickel oxide 8:2, and SP, with the same mass as above. LFP is 1400g, of which Li5FeO4 is 22.4g, Li2NiO2 is 5.6g, and SP is 220g.

[0043] The positive and negative electrode sheets, electrolytes, and separators from Examples 1-7 and Comparative Examples 1-2 were assembled into coin cells. Their initial charge specific capacity, gas production / cell expansion rate (60℃, 100% SOC, 30D storage), and DC internal resistance (mohm) at 50% SOC of the fresh battery over 10 seconds were tested. The results are shown in Table 1. Table 1: Experimental data of batteries including Examples 1-7 and Comparative Examples 1-2

[0044] As can be seen from Table 1: Examples 1 and 2 illustrate that the solution of this invention can significantly improve the internal resistance of the battery cell, reduce gas production, and improve lithium replenishment capability, especially with longer tube diameters. Examples 7 and 8 further demonstrate that the effect is more pronounced when using a single arm with stronger conductivity and a larger tube diameter ratio. Example 4 shows that when the amount of conductive material meeting the size requirements is too small, the improvement effect is not obvious. Example 3 further illustrates that when a certain amount of conductive material meeting the tube diameter ratio or length requirements is maintained, it can also have a certain effect when combined with conductive carbon black, achieving synergy between surface and point paths. Examples 5, 6, and 8 demonstrate that the solution of this invention still has significant effects when using different lithium replenishment agent systems or main material systems. The prior art has shown that a mixture of lithium-rich lithium nickel oxide and lithium ferrite is better than using lithium-rich lithium ferrite alone, which is why the gas production of Comparative Example 2 is less than that of Comparative Example 1.

[0045] In summary, this invention primarily addresses the issue of high-capacity lithium replenishing agent and active material particle size distribution by adjusting the size of the lithium replenishing agent particles. This allows for the uniform distribution or embedding of large lithium replenishing agent particles within the electrode, preventing large-area gaps caused by lattice contraction and subsequent side reactions. Simultaneously, a special conductive agent is introduced to form conductive bridges around the lithium replenishing agent particles, ensuring that even with gaps, the overall resistance between the electrode and the particles remains unaffected. This invention effectively improves the subsequent gas generation problem of the lithium replenishing agent, enhances lithium replenishment capacity, and significantly improves the system's kinetics.

[0046] In other words, this invention utilizes the difference between high lithium replenishment agent and active material particles, and adjusts the amount of lithium replenishment agent to make the lithium replenishment agent uniformly distributed or embedded in the electrode, and combines it with ultra-long conductive paths and highly conductive materials, adjusting the amount of lithium replenishment agent and the three to form a uniform conductive network around them, so that even if the lithium replenishment agent lattice shrinks, it can still maintain a high conductivity.

[0047] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A positive electrode sheet of a lithium ion battery, characterized by: Including a first delithiable material and a second delithiable material; The first lithium-delithiable material has a coin cell initial charge capacity of C1 mAH / g and a particle size D50 of D50-1. The first charge capacity of the second lithium-depletable material is C2 mAh / g, and the particle size D50 is D50-2. The positive electrode also contains a conductive material with a length of L and a diameter of S in the width direction, and the average value of L / S is 100~2000. Where C1 / C2>2, L>D50-2 or L>D50-1, the conductive material surrounds the first delithiable material to form a conductive bridge.

2. The positive electrode sheet of the lithium-ion battery according to claim 1, characterized by: The particle size D90 of the first delithiable material is D90-1, and the particle size D90 of the second delithiable material is D90-2; L>D90-2 or L>D90-1.

3. The positive electrode sheet of the lithium-ion battery according to claim 1, characterized in that: The mass of the first delithiable material is M1, the mass of the second delithiable material is M2, the weight of the conductive material is M3, and M3 / M1>1 / 20, and 0.5%< M1 / M2<3.5%.

4. The positive electrode sheet of the lithium-ion battery according to claim 1, characterized by: The conductive material is at least one of conductive carbon fiber, conductive carbon black, and conductive carbon nanotubes.

5. The positive electrode sheet of the lithium-ion battery according to claim 4, characterized in that: The conductive material is a single-arm carbon nanotube.

6. The positive electrode sheet of the lithium-ion battery according to claim 1, characterized in that: The first delithiation-resistant material is Li x M y O z , 0 < x < 6, 0 < y < 3, 0 < z < 4, wherein M is at least one of Fe, Co, Ni, Mn, C, and Si.

7. The positive electrode sheet of the lithium-ion battery according to claim 1, characterized in that: The second delithiable material is at least one of LFP, LFMP, NCM, lithium cobalt oxide, and lithium-rich manganese-based cathode materials.

8. The positive electrode of the lithium-ion battery according to claim 1, characterized in that: The positive electrode sheet also includes a dispersant of 0.02% to 0.2% by mass and a binder of 0.8% to 2.5% by mass.

9. The positive electrode of the lithium-ion battery according to claim 8, characterized in that: The method for preparing the positive electrode sheet includes at least the following steps: The first step is to prepare a conductive material into a suspension solution with a solid content of 1% to 8%, and then make a uniformly dispersed conductive slurry. The second step is to prepare the dispersant into a uniform liquid with a solid content of 5-15%, thus creating a uniformly dispersed dispersant solution. The third step is to prepare positive electrode paste one by combining the conductive paste from the first step with the first lithium-depleting material. The fourth step involves adding the dispersant solution from the second step and the second delithiable substance to the positive electrode slurry according to the metering ratio, dispersing them evenly, and adjusting the viscosity to obtain a coating-ready positive electrode slurry. The fifth step is to coat the positive electrode slurry onto the current collector, bake it to remove the solvent, and obtain the positive electrode sheet.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that, The positive electrode is the positive electrode as described in any one of claims 1-9.

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