Positive electrode material for lithium-ion battery, and positive electrode and lithium-ion battery comprising same

Abstract

Disclosed in the present application are a positive electrode material for a lithium-ion battery, and a positive electrode and a lithium-ion battery comprising same. Specifically, disclosed in the present application is a positive electrode material for a lithium-ion battery. The positive electrode material comprises NCX and lithium manganese iron phosphate (LMFP), wherein the particle size distribution relationship between NCX and LMFP satisfies: D50(LMFP) / D50(NCX)≤D90(LMFP) / D90(NCX)≤0.25.

Description

Positive electrode materials for lithium-ion batteries, and positive electrodes and lithium-ion batteries containing such materials. Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically, to cathode materials for lithium-ion batteries, cathodes comprising the same, and lithium-ion batteries. Background Technology

[0002] In recent years, with the continuous advancement of electronic technology, the demand for battery devices to power electronic devices has been constantly increasing. Currently, there is a need for batteries capable of storing more electricity and outputting higher power. Traditional lead-acid and nickel-metal hydride batteries can no longer meet the demands of new electronic products. Therefore, lithium batteries have attracted widespread attention. In the development of lithium batteries, their capacity and performance have been significantly improved.

[0003] NCX materials (i.e., high-nickel cathode materials, including NCM, NCA, and NCMA) are cathode materials for lithium-ion batteries with high capacity and energy density, but they suffer from difficulty in fully utilizing their capacity in general battery systems. To address this issue, existing technologies use composite cathode materials of lithium manganese iron phosphate (LMFP) and NCX to attempt to improve the performance of NCX cathode materials. However, existing LMFP / NCX composite cathode materials still suffer from problems such as complex processing, reduced capacity, and poor rate performance.

[0004] Given the aforementioned problems, it is necessary to develop a cathode material for lithium-ion batteries, as well as a cathode and lithium-ion battery containing the cathode material, to solve the problem of poor electrochemical performance of the composite cathode material of LMFP and NCX in the prior art. Summary of the Invention

[0005] The main objective of this invention is to provide a cathode material for lithium-ion batteries, as well as a cathode and a lithium-ion battery containing the same, to solve the problem of poor electrochemical performance of composite cathode materials of LMFP and NCX in the prior art.

[0006] To achieve the above objectives, according to one aspect of the present invention, a cathode material for lithium-ion batteries is provided, the cathode material comprising NCX and lithium manganese iron phosphate (LMFP), wherein the particle size distribution relationship between NCX and LMFP satisfies D50(LMFP) / D50(NCX)≤D90(LMFP) / D90(NCX)≤0.25.

[0007] Furthermore, in the above-mentioned cathode materials for lithium-ion batteries, the molar percentage content of Ni in NCX is ≥95%.

[0008] Furthermore, in the above-mentioned cathode material for lithium-ion batteries, the particle size of NCX satisfies (D90-D10) / D50≤0.5, and 10μm≤D50≤20μm.

[0009] Furthermore, among the aforementioned cathode materials for lithium-ion batteries, NCX has a specific surface area BET of 0.3 m². 2 / g≤BET≤1m 2 / g.

[0010] Furthermore, among the aforementioned cathode materials used in lithium-ion batteries, NCX has a compaction density PD of 0 g / cm³. 3 <PD≤3.2g / cm 3 .

[0011] Furthermore, in the above-mentioned cathode materials for lithium-ion batteries, based on the total weight of NCX and LMFP, the content of LMFP satisfies 0wt% < LMFP < 15wt%.

[0012] Furthermore, the cathode material used in lithium-ion batteries also includes a conductive agent, a binder, and a dispersant.

[0013] Furthermore, in the above-mentioned cathode material for lithium-ion batteries, the conductive agent includes fibrous conductive agents and spherical conductive agents. The fibrous conductive agent includes one or more of vapor-grown carbon fiber (VGCF) and carbon nanotubes (CNT), and the spherical conductive agent includes one or more of carbon black and acetylene black.

[0014] According to another aspect of the present invention, a positive electrode for a lithium-ion battery is provided, comprising: the positive electrode material for a lithium-ion battery as described above, and a positive electrode current collector.

[0015] According to another aspect of the present invention, a lithium-ion battery is provided, comprising: a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode is the aforementioned positive electrode for a lithium-ion battery.

[0016] The present invention provides a positive electrode material for lithium-ion batteries, as well as a positive electrode and a lithium-ion battery containing the same, thereby improving the electrochemical performance, especially the capacity, of composite positive electrode materials of LMFP and NCX. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0018] Figure 1 is a schematic diagram of the structure of the NCX cathode material and the composite cathode material of LMFP and NCX of the present invention. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0020] As explained in the background section, existing composite cathode materials of LMFP and NCX suffer from poor electrochemical performance. To address this problem, according to a typical embodiment of the present invention, a cathode material for lithium-ion batteries is provided, comprising NCX and lithium manganese iron phosphate (LMFP), wherein the particle size distribution of NCX and LMFP satisfies D50(LMFP) / D50(NCX)≤D90(LMFP) / D90(NCX)≤0.25.

[0021] As mentioned above, existing composite cathode materials using LMFP and NCX suffer from poor electrochemical performance. Specifically, NCX materials are large, uniform spherical particles with a large specific surface area and low compaction density. When used alone as the active material, gaps easily form within the electrode, leading to poor electron conduction and some active material not participating in the reaction. Although this problem can be alleviated by significantly increasing the content of conductive agent, new problems arise, such as a substantial reduction in battery energy density and increased cost. Therefore, in typical electrode compositions, the amount of conductive agent needs to be strictly controlled, further increasing the difficulty of charge transport within the electrode. LMFP, as a low-cost material with a high voltage platform and high energy density, has certain advantages when used in combination with NCX. Existing technologies use composite cathode materials of LMFP and NCX to attempt to improve the performance of NCX cathode materials. However, existing composite cathode materials of LMFP and NCX still suffer from problems such as complex processing, reduced capacity, and poor rate performance. To address this issue, this invention explores the optimal particle size distribution of LMFP and NCX by mixing uniform spherical secondary particles, thus resolving the problem of ultra-high nickel NCX failing to achieve its capacity in typical battery systems. Unexpectedly, this invention reveals that in the composite cathode material of LMFP and NCX, when LMFP particles are significantly smaller than NCX particles and their particle size distribution is larger than that of NCX (i.e., D50(LMFP) / D50(NCX)≤D90(LMFP) / D90(NCX)≤0.25), LMFP is less prone to localized accumulation during the mixing process, resulting in better gap-filling performance for NCX particles. The LMFP filling the gaps in the NCX material can interact with conductive agents to form a stable three-dimensional conductive network, improving charge transport within the electrode and facilitating the full utilization of NCX capacity, thereby enhancing the electrochemical performance of the LMFP / NCX composite cathode material. The structure of the LMFP / NCX composite cathode material of this invention is shown in Figure 1.

[0022] In a preferred embodiment, the molar percentage content of Ni in NCX is ≥95%.

[0023] This invention preferably uses high-nickel NCX materials with a Ni molar percentage content ≥95%. Such high-nickel NCX materials have high theoretical capacity but are more prone to issues with capacity utilization. Therefore, using high-nickel NCX materials with a Ni molar percentage content ≥95% can further improve the performance of the cathode material in lithium-ion batteries.

[0024] In a preferred embodiment, in the above-mentioned cathode material for lithium-ion batteries, the particle size of NCX satisfies (D90-D10) / D50≤0.5, and 10μm≤D50≤20μm.

[0025] In a preferred embodiment, in the above-mentioned cathode material for lithium-ion batteries, the specific surface area (BET) of NCX satisfies 0.3 m². 2 / g≤BET≤1m 2 / g.

[0026] In a preferred embodiment, in the above-mentioned cathode material for lithium-ion batteries, the compaction density PD of NCX satisfies 0 g / cm³. 3 <PD≤3.2g / cm 3 .

[0027] This invention preferably uses NCX materials with the specific particle size distribution, specific surface area (BET), and compaction density (PD) described above. NCX materials meeting these specific conditions are more prone to capacity limitations because larger and narrower particle sizes in the electrode layer more easily create voids and gaps, leading to poor electron conduction and the non-participation of some active materials in the reaction. The low compaction density and high specific surface area further make it difficult to eliminate these gaps after rolling. Therefore, using NCX materials with the above characteristics can further improve the performance of the cathode material in lithium-ion batteries. The upper limit of D50 is specified as 20 μm because the D50 of most commonly used NCM materials on the market is less than or equal to 20 μm.

[0028] In a preferred embodiment, in the above-mentioned cathode material for lithium-ion batteries, based on the total weight of NCX and LMFP, the content of LMFP satisfies 0 wt% < LMFP < 15 wt%.

[0029] The composite cathode material of NCX and LMFP of the present invention preferably uses the specific LMFP content described above. Because high-nickel NCX materials have higher capacity and conductivity than LMFP, excessive addition of LMFP may adversely affect capacity. Therefore, using the specific LMFP content described above can further improve the performance of the cathode material for lithium-ion batteries.

[0030] In some embodiments, the cathode material for lithium-ion batteries described above also includes a conductive agent, a binder, and a dispersant.

[0031] In a preferred embodiment, the conductive agent includes fibrous conductive agents and spherical conductive agents. The fibrous conductive agent includes one or more of vapor-grown carbon fiber (VGCF) and carbon nanotubes (CNT), and the spherical conductive agent includes one or more of carbon black and acetylene black.

[0032] The use of conductive agents in cathode materials is beneficial for improving the electrochemical performance of the materials. Preferably, in the cathode material of the present invention, the use of a combination of fibrous conductive agents and spherical conductive agents facilitates the formation of a good and stable conductive network in the cathode material, further improving the performance of the cathode material of lithium-ion batteries.

[0033] According to another typical embodiment of the present invention, a positive electrode for a lithium-ion battery is provided, comprising: the positive electrode material for a lithium-ion battery as described in the above aspects, and a positive electrode current collector.

[0034] According to another typical embodiment of the present invention, a lithium-ion battery is provided, comprising: a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode is the positive electrode described above for a lithium-ion battery.

[0035] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0036] Example

[0037] In the following embodiments, the NCX material used is lithium nickel cobalt manganese oxide (NCM, LiNi) with a Ni content of 95 mol%. 0.95 Co 0.03 Mn 0.02 The LMFP material used is nano-sized lithium manganese iron phosphate particles, in which the Fe:Mn content ratio is between 40%:60% and 30%:70%; both NCX and LMFP are commercially available mass-produced cathode materials.

[0038] Lithium nickel cobalt manganese oxide is prepared using a co-precipitation method. A mixed transition sulfate solution is prepared from nickel, cobalt, and manganese raw materials. Nickel sulfate, cobalt sulfate, and manganese sulfate solutions are mixed uniformly in a specific ratio and simultaneously added to a reaction vessel along with a mixture of ammonia and sodium hydroxide for co-precipitation. The pH of the reaction solution is controlled between 11 and 12. After the co-precipitation reaction, the precipitate is washed, dried, and then mixed with lithium carbonate at high speed in a ball mill. Finally, it is calcined at a high temperature of 800-1100℃ for 24 hours. After the reaction is complete, the product is pulverized and sieved to obtain lithium nickel cobalt manganese oxide with the desired particle size.

[0039] Lithium manganese iron phosphate is prepared using a solid-state method. Raw materials, including manganese salt, iron salt, and phosphate, are prepared in a specific ratio and simultaneously added to a ball mill for mixing and grinding into powder. The powder is then sintered at high temperature in a reactor. After high-temperature sintering, the material is ground, sieved, and dried to obtain lithium manganese iron phosphate material.

[0040] Example 1

[0041] Lithium-ion batteries are prepared using the following steps.

[0042] (1) The above-mentioned lithium nickel cobalt manganese oxide and lithium manganese iron phosphate were selected for particle size selection. NCM materials with a D50 of 10 μm and a particle size distribution satisfying (D90-D10) / D50≤0.5 ((D90-D10) / D50=0.5, specific surface area BET value of 0.32m²) were selected. 2 / g, compaction density PD value is 3.15g / cm³ 3 Select LMFP materials with a D50 of less than 2.5 μm and a particle size distribution that satisfies D50(LMFP) / D50(NCX)≤D90(LMFP) / D90(NCX)≤0.25;

[0043] (2) Material mixing: The above NCM and LMFP materials are mixed in proportions of 100%:0% and 90%:10% respectively, and after thorough stirring, different mixed positive electrode active material materials are obtained;

[0044] (3) Preparation of the positive electrode sheet: The mixed positive electrode active material, conductive agent (including but not limited to one or more of vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), carbon black, and acetylene black; in the examples, the conductive agents used are vapor-grown carbon fiber (VGCF) and carbon black HS100L), binder polyvinylidene fluoride (PVDF), and dispersant polyvinylpyrrolidone (PVP) are mixed in a mass ratio of 95.5%:2%:2%:0.5%, and N-methylpyrrolidone is gradually added until the solid content reaches 65%. After thorough stirring, a positive electrode slurry is obtained. Then, the positive electrode slurry is coated onto a 12 μm thick positive electrode current collector aluminum foil and dried at 100°C by forced air drying to obtain the positive electrode sheet;

[0045] (4) Cut and roll the positive electrode sheet, and assemble it with the negative electrode sheet (which can be a common negative electrode such as graphite or lithium metal; the negative electrode used in the example is a lithium metal sheet) to form a half cell. After impregnation, aging, and formation, perform electrochemical performance testing.

[0046] Capacity testing method: Place the battery in the charging and discharging equipment channel, charge it at 0.1C at room temperature (25℃) to a voltage of 4.25V, let it stand for 3 hours, and then discharge it at 0.1C at the same environment to a voltage of 2V. The charging capacity and discharging capacity are obtained.

[0047] Example 2

[0048] Lithium-ion batteries were prepared using the same steps as in Example 1, except that the particle size distributions of the NCX and LMFP materials were different, as shown in Table 1 below.

[0049] Example 3

[0050] Lithium-ion batteries were prepared using the same steps as in Example 1, except that the particle size distributions of the NCX and LMFP materials were different, as shown in Table 1 below.

[0051] Example 4

[0052] The lithium-ion battery was prepared using the same steps as in Example 1, except that the particle size distribution of NCX and LMFP materials was different. The particle size (D90-D10) / D50 of NCX was >0.5 and D50 was <10 μm, as shown in Table 1 below.

[0053] Example 5

[0054] The lithium-ion battery was prepared using the same steps as in Example 1, except that the specific surface area (BET) of the NCX material was 0.25 m². 2 / g, compaction density PD value is 3.4g / cm³ 3 Everything else is the same as in Example 1.

[0055] Example 6

[0056] The lithium-ion battery was prepared using the same steps as in Example 1, except that the ratio of NCX to LMFP materials was 85:15, as shown in Table 1 below.

[0057] Comparative Example 1

[0058] The lithium-ion battery was prepared using the same steps as in Example 1, except that the particle size distribution of the NCX and LMFP materials was different (0.25 < D90(LMFP) / D90(NCX) < D50(LMFP) / D50(NCX)), as shown in Table 1 below.

[0059] Comparative Example 2

[0060] The lithium-ion battery was prepared using the same steps as in Example 1, except that the particle size distribution of the NCX and LMFP materials was different (0.25 < D90(LMFP) / D90(NCX) = D50(LMFP) / D50(NCX)), as shown in Table 1 below.

[0061] Comparative Example 3

[0062] The lithium-ion battery was prepared using the same steps as in Example 1, except that the particle size distribution of the NCX and LMFP materials was different (0.25 < D50(LMFP) / D50(NCX) < D90(LMFP) / D90(NCX)), as shown in Table 1 below.

[0063] Comparative Example 4

[0064] The lithium-ion battery was prepared using the same steps as in Example 1, except that the particle size distribution of the NCX and LMFP materials was different (0.25 > D50(LMFP) / D50(NCX) > D90(LMFP) / D90(NCX)), as shown in Table 1 below.

[0065] Table 1: Particle size distribution of NCX and LMFP materials and battery capacity in batteries prepared in Examples 1-5 and Comparative Examples 1-2

[0066] The test results show that the above embodiments of the present invention achieve the following technical effects:

[0067] Comparing Examples 1-6 and Comparative Examples 1-4, it can be seen that adding LMFP to the NCX cathode material, and when the particle size distribution relationship between NCX and LMFP satisfies D50(LMFP) / D50(NCX)≤D90(LMFP) / D90(NCX)≤0.25, can improve the charging capacity of the NCX cathode material. However, when the particle size distribution relationship between NCX and LMFP does not meet the above conditions, it cannot improve the charging capacity of the NCX cathode material.

[0068] Comparing Examples 1-3 and Example 4, it can be seen that when the particle size of the NCX material satisfies (D90-D10) / D50≤0.5 and D50≥10μm, it is beneficial to further improve the charging capacity of the NCX cathode material.

[0069] Comparing Examples 1-3 and Example 5, it can be seen that when the specific surface area BET of the NCX material satisfies 0.3m², 2 / g≤BET≤1m 2 / g, compaction density PD satisfies 0g / cm³ 3 <PD≤3.2g / cm 3 This is beneficial for further improving the charging capacity of NCX cathode materials.

[0070] Comparing Examples 1-3 and Example 6, it can be seen that when the content of LMFP satisfies 0wt% < LMFP < 15wt% based on the total weight of NCX and LMFP, it is beneficial to further improve the charging capacity of NCX cathode material.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cathode material for lithium-ion batteries, said cathode material comprising high-nickel cathode material NCX and lithium manganese iron phosphate (LMFP), characterized in that, The particle size distribution relationship between NCX and LMFP satisfies D50(LMFP) / D50(NCX)≤D90(LMFP) / D90(NCX)≤0.

25.

2. The positive electrode material for lithium-ion batteries according to claim 1, characterized in that, The molar percentage content of Ni in the NCX is ≥95%.

3. The positive electrode material for lithium-ion batteries according to claim 1 or 2, characterized in that, The particle size of the NCX satisfies (D90-D10) / D50≤0.5, and 10μm≤D50≤20μm.

4. The positive electrode material for lithium-ion batteries according to claim 1 or 2, characterized in that, The specific surface area (BET) of the NCX satisfies 0.3 m². 2 / g≤BET≤1m 2 / g.

5. The positive electrode material for lithium-ion batteries according to claim 1 or 2, characterized in that, The compaction density PD of the NCX satisfies 0 g / cm³. 3 <PD≤3.2g / cm 3 .

6. The positive electrode material for lithium-ion batteries according to claim 1 or 2, characterized in that, Based on the total weight of the NCX and LMFP, the content of LMFP satisfies 0 wt% < LMFP < 15 wt%.

7. The positive electrode material for lithium-ion batteries according to claim 1 or 2, characterized in that, The positive electrode material also includes a conductive agent, a binder, and a dispersant.

8. The positive electrode material for lithium-ion batteries according to claim 7, characterized in that, The conductive agent includes fibrous conductive agents and spherical conductive agents. The fibrous conductive agent includes one or more of vapor-grown carbon fiber (VGCF) and carbon nanotubes (CNT). The spherical conductive agent includes one or more of carbon black and acetylene black.

9. A positive electrode for a lithium-ion battery, characterized in that, include: The positive electrode material for lithium-ion batteries according to any one of claims 1 to 8, and Positive current collector.

10. A lithium-ion battery, characterized in that, include: positive electrode, negative electrode, Electrolyte, and Diaphragm, The positive electrode thereon is the positive electrode for a lithium-ion battery according to claim 9.

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