A multi-component positive electrode active material, a lithium ion battery positive electrode, a preparation method thereof and a long-life lithium ion battery

Abstract

The application discloses a multi-component positive electrode active material, a lithium ion battery positive electrode and a preparation method thereof and a long-life lithium ion battery, and relates to the technical field of lithium ion batteries. The multi-component positive electrode active material comprises a material main body and a composite lithium supplement agent, and the mass ratio of the material main body and the composite lithium supplement agent is 86-95:2-8. The material main body comprises lithium iron manganese phosphate and Li2MnO4, and the composite lithium supplement agent comprises Li5AlO4, Li6MnO4 and Li2Al2B2O7. The positive electrode material is optimized in the formula, Li5AlO4, Li6MnO4 and Li2Al2B2O7 with a specific composition are used as the composite lithium supplement agent, lithium ions can be released in a controllable manner during the charging and discharging process of the LMFP-based lithium ion battery, lithium loss of the lithium ion battery is compensated, and the decomposition products can protect the positive electrode material and inhibit the surface side reaction of the positive electrode.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a multi-component positive electrode active material, a lithium-ion battery positive electrode and its preparation method, and a long-life lithium-ion battery. Background Technology

[0002] Lithium manganese iron phosphate (LMFP) has become an important cathode material in the fields of power batteries and energy storage batteries due to its excellent safety performance and cost advantages. However, LMFP-based lithium-ion batteries still face key bottlenecks in practical applications: on the one hand, an SEI film forms on the negative electrode during the first charge and discharge cycle, causing irreversible loss of some lithium ions and affecting battery capacity output; on the other hand, Mn is prone to forming on the LMFP surface during cycling. 2+ Dissolution, lattice structure distortion, and insufficient conductivity and structural stability of traditional electrode systems limit battery cycle life and rate performance.

[0003] In the existing technology, although a single lithium replenishing agent (such as Li2O or Li4SiO4) can make up for some lithium loss, it has no surface protection function after decomposition and cannot solve the structural degradation problem of LMFP. At the same time, an unreasonable combination of conductive agent and binder will lead to high internal resistance of electrode and poor interfacial bonding, further deteriorating battery performance.

[0004] Therefore, developing an electrode system that integrates lithium replenishment, surface protection, and structural enhancement is of great significance for improving the cycle performance of LMFP-based lithium-ion batteries. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a multi-component positive electrode active material, a lithium-ion battery positive electrode and its preparation method, and a long-life lithium-ion battery. By optimizing the positive electrode material formulation, a synergistic effect of lithium replenishment, surface protection and structural enhancement is achieved, thereby improving the cycle life of the battery.

[0006] To solve the above technical problems, according to one aspect of the present invention, a multi-component positive electrode active material is provided, comprising a material body and a composite lithium supplement agent;

[0007] The main material comprises lithium manganese iron phosphate and Li2MnO4, with a mass ratio of 5:5 to 7:3.

[0008] The composite lithium supplement includes Li5AlO4, Li6MnO4 and Li2Al2B2O7, with a mass ratio of 3:3:2.

[0009] The mass ratio of the main material to the composite lithium supplement is 86-95:2-8.

[0010] According to another aspect of the present invention, a lithium-ion battery positive electrode is provided, comprising the multi-component positive electrode active material, conductive agent and binder described above.

[0011] As a preferred embodiment, the mass ratio of the multi-component positive electrode active material, conductive agent, and binder is 94-97:1.5-4:1.5-3.

[0012] According to another aspect of the present invention, a method for preparing the above-mentioned lithium-ion battery cathode is provided, comprising:

[0013] Step 1: Mix and disperse the components of the multi-component positive electrode active material and the conductive agent to form a positive electrode material mixture;

[0014] Step 2: The positive electrode material mixture is mixed and dispersed with PVDF adhesive to form a slurry;

[0015] Step 3: The slurry is coated onto aluminum foil, dried, and sliced ​​to form the positive electrode of a lithium-ion battery.

[0016] In a preferred embodiment, the conductive agent is superconducting carbon black.

[0017] In a preferred embodiment, the PVDF adhesive is stirred and dispersed with N-methylpyrrolidone to form the PVDF adhesive solution described in step two.

[0018] In a preferred embodiment, the aluminum foil thickness in step three is 10μm~12μm.

[0019] According to another aspect of the present invention, the application of the above-described lithium-ion battery cathode in the preparation of lithium-ion batteries is provided.

[0020] According to another aspect of the present invention, a long-life lithium-ion battery is provided, comprising a positive electrode, a separator, a liquid electrolyte, and a negative electrode, wherein the positive electrode is the positive electrode of the lithium-ion battery described above.

[0021] This invention optimizes the formulation of the cathode material by using a specific composition of Li5AlO4, Li6MnO4, and Li2Al2B2O7 as a composite lithium replenishing agent. During the charging and discharging process of LMFP-based lithium-ion batteries, the lithium ions are released in a controlled manner to compensate for the lithium loss of the lithium-ion battery. The decomposition products can protect the cathode material and suppress the surface side reactions of the cathode.

[0022] The lithium-ion battery prepared by this invention has the advantages of long cycle life and good safety performance, with a capacity retention rate of ≥88% after 1000 cycles at 1C rate. Attached Figure Description

[0023] Figure 1 This is a comparison of the capacity data of lithium-ion batteries prepared in Example 1 and Comparative Examples 1, 2, and 3 of the present invention;

[0024] Figure 2 This is a comparison of the room-temperature cycling capacity retention rates of lithium-ion batteries prepared in Example 2 and Comparative Examples 4, 5, and 6 of the present invention.

[0025] Figure 3 This is a comparison of the performance data of lithium-ion batteries prepared in Example 3 and Comparative Examples 7, 8 and 9 of the present invention at different discharge rates. Detailed Implementation

[0026] A typical embodiment of the present invention provides a multi-component positive electrode active material, comprising a material body and a composite lithium supplement agent.

[0027] The main components of the material include lithium manganese iron phosphate and Li₂MnO₄. Li₂MnO₄ has the general formula LiMn. x Fe 1-x PO4, 0.4≤X≤0.6, is abbreviated as LMFP; Li2MnO4 is a spinel oxide material, abbreviated as LMO.

[0028] The mass ratio of lithium manganese iron phosphate to Li2MnO4 is 5:5 to 7:3; in some embodiments, the mass ratio can be 5:5, 7:3, 6:4, etc.

[0029] The composite lithium supplement includes Li5AlO4, Li6MnO4 and Li2Al2B2O7, with a mass ratio of 3:3:2.

[0030] The mass ratio of the main material to the composite lithium supplement is 86-95:2-8. In some embodiments, the mass ratio of the main material to the composite lithium supplement can be 86:2, 86:8, 95:2, 95:8, 88:5, 90:4, 92:6, etc.

[0031] The multi-component positive electrode active material described in this embodiment is based on lithium manganese iron phosphate (LMFP) and spinel Li2MnO4 (LMO), compounded with Li5AlO4, Li6MnO4 and Li2Al2B2O7. Li5AlO4, Li6MnO4 and Li2Al2B2O7 serve as composite lithium replenishing agents, which can controllably decompose and release lithium ions during the charging and discharging process of lithium-ion batteries to compensate for lithium loss in lithium-ion batteries. In addition, the decomposition products of composite lithium replenishing agents form a protective film, which plays a structural support role, suppresses side reactions and volume expansion on the surface of LMFP, and achieves a significant improvement in cycle stability.

[0032] Another typical embodiment of the present invention provides a lithium-ion battery cathode prepared based on the multi-component active material described above, the preparation method of which includes the following steps.

[0033] Step 1: Prepare a mixture of cathode materials

[0034] The components of a multi-component positive electrode active material and a conductive agent are mixed and dispersed to form a positive electrode material mixture.

[0035] The conductive agent is preferably a superconducting carbon black conductive agent (SP).

[0036] In this step, LMFP, LMO, Li5AlO4, Li6MnO4, and Li2Al2B2O7 are first stirred and dispersed evenly to form a positive electrode active material mixture. Then, this positive electrode active material mixture and the conductive agent are stirred and dispersed to form a positive electrode material mixture.

[0037] Step 2: Prepare the positive electrode slurry

[0038] The positive electrode material mixture is mixed and dispersed with PVDF adhesive to form a slurry with a solid content of 50% to 65%.

[0039] The PVDF adhesive is prepared by mixing PVDF binder and N-methylpyrrolidone in a mass ratio of 6:94.

[0040] The mass ratio of the multi-component positive electrode active material, conductive agent, and PVDF adhesive is 94-97:1.5-4:1.5-3. In some embodiments, the mass ratio of the multi-component positive electrode active material, conductive agent, and PVDF adhesive can be 94:4:3, 97:1.5:1.5, or 95:3:2.

[0041] Step 3: Prepare the positive electrode for lithium-ion batteries

[0042] The positive electrode slurry is dried and sliced ​​on aluminum foil with a thickness of 10μm to 12μm to form the positive electrode of a lithium-ion battery.

[0043] Another typical embodiment of the present invention provides a lithium-ion battery, which includes a positive electrode, a separator, a liquid electrolyte, and a negative electrode.

[0044] The positive electrode is a lithium-ion positive electrode prepared based on multi-component positive electrode active materials according to the present invention.

[0045] Graphite, conductive agent, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in a certain proportion to form a uniform slurry. The slurry is then coated, rolled, dried, and sliced ​​onto a 6-12μm copper foil to form a negative electrode.

[0046] The positive electrode, separator, and negative electrode are stacked in an alternating sequence of positive electrode, separator, negative electrode, and positive electrode, or the stacked separator, positive electrode, separator, and negative electrode are wound to form a battery cell. Then, the battery cell is subjected to tab welding and aluminum-plastic film encapsulation.

[0047] The purpose of baking the battery cell is to remove excess moisture inside. After baking, electrolyte is injected, and then the cell is left to stand after injection.

[0048] Finally, by performing pre-formation, high-temperature aging, OCV testing, and room-temperature aging on the battery cells, an improved battery sample can be obtained.

[0049] The technical solutions claimed in this invention will be further described below through some embodiments. However, the embodiments and comparative examples are for explaining the implementation schemes of this invention and do not exceed the scope of the subject matter of this invention. The scope of protection of this invention is not limited by the embodiments. Unless otherwise specified, the materials and reagents used in this invention are all available from commercially available products in the art. Example 1

[0050] Step (1): LMFP, LMO, Li5AlO4, Li6MnO4, and Li2Al2B2O7 are stirred and dispersed evenly to form a positive electrode active material mixture; conductive agent SP is added to the positive electrode active material mixture and stirred and dispersed evenly to obtain a positive electrode material mixture.

[0051] Step (2): Mix the PVDF binder with N-methylpyrrolidone to obtain a PVDF solution. Add the cathode material mixture to the PVDF solution and disperse it evenly for 5 hours to form a cathode slurry with a solid content of 50%.

[0052] The mass ratio of LMFP, LMO, Li5AlO4, Li6MnO4, Li2Al2B2O7, conductive agent SP, and PVDF adhesive mentioned above is 43:43:3:3:2:4:2.

[0053] Step (3) involves coating the positive electrode slurry onto a 10 μm aluminum foil to achieve a double-sided areal density of 35.2 ± 0.6 mg / cm². 2 Positive electrode sheet of specified specifications; the dried positive electrode sheet is priced at 2.4 g / cm³. 3 Roll forming is performed, followed by electrode slitting, punching, baking, and other processes.

[0054] Step (4): Graphite, SP, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed in a mass ratio of 95.8:1.0:1.2:2.0 to form a uniformly mixed slurry. The slurry is then coated on a 6μm copper foil, rolled, dried and sliced ​​to form a negative electrode sheet.

[0055] Step (5): The secondary lithium-ion battery cell pack is fabricated using a stacking method, and the tabs are welded and packaged. The packaging shell can be an aluminum-plastic film shell. The cell is baked to remove excess internal moisture. After baking, electrolyte is injected, and then the cell is allowed to stand after electrolyte injection. Finally, the cell is subjected to pre-formation, high-temperature aging, OCV testing, and room-temperature aging to obtain a lithium-ion battery sample, denoted as 1-a.

[0056] Comparative Example 1

[0057] The difference from Example 1 is that Li5AlO4 is not added to the positive electrode active material mixture provided in step (1). The remaining steps are the same, and the obtained lithium-ion battery sample is denoted as 1-b.

[0058] Comparative Example 2

[0059] The difference from Example 1 is that Li6MnO4 is not added to the positive electrode active material mixture provided in step (1). The remaining steps are the same, and the obtained lithium-ion battery sample is recorded as 1-c.

[0060] Comparative Example 3

[0061] The difference from Example 1 is that Li2Al2B2O7 is not added to the positive electrode active material mixture provided in step (1). The remaining steps are the same, and the obtained lithium-ion battery sample is recorded as 1-d.

[0062] The liquid lithium battery samples obtained in Example 1 and Comparative Examples 1, 2, and 3 were fully charged within the range of 3.0-4.2V at charging currents of 0.01C, 0.02C, 0.05C, and 0.1C, respectively. They were then discharged at a 0.1C discharge current, and the 0.1C discharge capacity was recorded. After being charged to 3.7V at a 0.1C current, the batteries were placed at room temperature. Comparative data are shown below. Figure 1 As shown, the results indicate that the liquid lithium-ion battery provided by the present invention has better high capacity. Example 2

[0063] Step (1): LMFP, LMO, Li5AlO4, Li6MnO4, and Li2Al2B2O7 are stirred and dispersed evenly to form a positive electrode active material mixture; conductive agent SP is added to the positive electrode active material mixture and stirred and dispersed evenly to obtain a positive electrode material mixture.

[0064] Step (2): Mix the PVDF binder with N-methylpyrrolidone to obtain a PVDF solution. Add the cathode material mixture to the PVDF solution and disperse it evenly for 6 hours to form a cathode slurry with a solid content of 65%.

[0065] The mass ratio of the above-mentioned LMFP, LMO, Li5AlO4, Li6MnO4, Li2Al2B2O7, conductive agent SP, and PVDF adhesive is 66.5:28.5:0.75:0.75:0.5:1.5:1.5.

[0066] Step (3) involves coating the positive electrode slurry onto a 12μm aluminum foil to achieve a double-sided areal density of 35.2±0.6 mg / cm². 2 Positive electrode sheet of specified specifications; the dried positive electrode sheet is priced at 2.4 g / cm³. 3 Roll forming is performed, followed by electrode slitting, punching, baking, and other processes.

[0067] Step (4): Graphite, SP, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed in a mass ratio of 95.8:1.0:1.2:2.0 to form a uniformly mixed slurry. The slurry is then coated on a 12μm copper foil, rolled, dried and sliced ​​to form a negative electrode sheet.

[0068] Step (5): A secondary lithium-ion battery cell pack is fabricated using a winding method, and the tabs are welded and packaged. The packaging shell can be an aluminum-plastic film shell. The cell is baked to remove excess internal moisture. After baking, electrolyte is injected, and then the cell is allowed to stand after electrolyte injection. Finally, the cell undergoes pre-formation, high-temperature aging, OCV testing, and room-temperature aging to obtain a lithium-ion battery sample, denoted as 2-a.

[0069] Comparative Example 4

[0070] The difference from Example 2 is that Li5AlO4 is not added to the positive electrode active material mixture provided in step (1). The remaining steps are the same, and the obtained lithium-ion battery sample is designated as 2-b.

[0071] Comparative Example 5

[0072] The difference from Example 2 is that Li6MnO4 is not added to the positive electrode active material mixture provided in step (1). The remaining steps are the same, and the obtained lithium-ion battery sample is denoted as 2-c.

[0073] Comparative Example 6

[0074] The difference from Example 2 is that Li2Al2B2O7 is not added to the positive electrode active material mixture provided in step (1). The remaining steps are the same, and the obtained lithium-ion battery sample is recorded as 2-d.

[0075] The liquid lithium battery samples obtained in Example 2 and Comparative Examples 4, 5, and 6 were subjected to cycle tests at a charge-discharge current of 1C within the range of 3.0-4.2V. The comparative data are as follows: Figure 2As shown, the results indicate that the liquid lithium-ion battery provided by this invention has better cycle stability, achieving ≥88% after 1000 cycles at 1C. Example 3

[0076] Step (1): LMFP, LMO, Li5AlO4, Li6MnO4, and Li2Al2B2O7 are stirred and dispersed evenly to form a positive electrode active material mixture; conductive agent SP is added to the positive electrode active material mixture and stirred and dispersed evenly to obtain a positive electrode material mixture.

[0077] Step (2): Mix the PVDF binder with N-methylpyrrolidone to obtain a PVDF solution. Add the cathode material mixture to the PVDF solution and disperse it evenly for 5 hours to form a cathode slurry with a solid content of 55%.

[0078] The mass ratio of LMFP, LMO, Li5AlO4, Li6MnO4, Li2Al2B2O7, conductive agent SP, and PVDF adhesive mentioned above is 54:36:1.5:1.5:1:3:3.

[0079] Step (3) involves coating the positive electrode slurry onto an 11 μm aluminum foil to achieve a double-sided areal density of 35.2 ± 0.6 mg / cm². 2 Positive electrode sheet of specified specifications; the dried positive electrode sheet is priced at 2.4 g / cm³. 3 Roll forming is performed, followed by electrode slitting, punching, baking, and other processes.

[0080] Step (4): Graphite, SP, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed in a mass ratio of 95.8:1.0:1.2:2.0 to form a uniformly mixed slurry. The slurry is then coated on an 8μm copper foil, rolled, dried and sliced ​​to form a negative electrode sheet.

[0081] Step (5): The secondary lithium-ion battery cell pack is fabricated using a stacking method, and the tabs are welded and packaged. The packaging shell can be an aluminum-plastic film shell. The cell is baked to remove excess internal moisture. After baking, electrolyte is injected, and then the cell is allowed to stand after electrolyte injection. Finally, the cell is subjected to pre-formation, high-temperature aging, OCV testing, and room-temperature aging to obtain the lithium-ion battery sample, denoted as 3-a.

[0082] Comparative Example 7

[0083] The difference from Example 3 is that Li5AlO4 is not added to the positive electrode active material mixture provided in step (1). The remaining steps are the same, and the obtained lithium-ion battery sample is designated as 3-b.

[0084] Comparative Example 8

[0085] The difference from Example 3 is that Li6MnO4 is not added to the positive electrode active material mixture provided in step (1). The remaining steps are the same, and the obtained lithium-ion battery sample is denoted as 3-c.

[0086] Comparative Example 9

[0087] The difference from Example 3 is that Li2Al2B2O7 is not added to the positive electrode active material mixture provided in step (1). The remaining steps are the same, and the obtained lithium-ion battery sample is recorded as 3-d.

[0088] The liquid lithium battery samples obtained in Example 3 and Comparative Examples 7, 8, and 9 were subjected to cycle tests at a charge-discharge current of 1C within the range of 3.0-4.2V. The comparative data are as follows: Figure 3 As shown, the results indicate that the liquid lithium-ion battery provided by this invention has better cycle stability, achieving ≥88% after 1000 cycles at 1C.

[0089] The scope of protection claimed by this invention is not limited to the specific embodiments described above. For those skilled in the art, this invention can have various modifications and alterations. Any modifications, improvements, and equivalent substitutions made within the concept and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A multi-component cathode active material, characterized by, Including the main material and the composite lithium supplement; The main material comprises lithium manganese iron phosphate and Li2MnO4, with a mass ratio of 5:5 to 7:

3. The composite lithium supplement includes Li5AlO4, Li6MnO4 and Li2Al2B2O7, with a mass ratio of 3:3:

2. The mass ratio of the main material to the composite lithium supplement is 86-95:2-8.

2. A lithium-ion battery cathode, characterized by: It includes the multi-component positive electrode active material, conductive agent, and binder as described in claim 1.

3. The lithium-ion battery cathode of claim 2, wherein: The mass ratio of the multi-component positive electrode active material, conductive agent and binder is 94-97:1.5-4:1.5-3.

4. The method of making a lithium-ion battery cathode of claim 2, wherein, include: Step 1: Mix and disperse the components of the multi-component positive electrode active material and the conductive agent to form a positive electrode material mixture; Step 2: The positive electrode material mixture is mixed and dispersed with PVDF adhesive to form a slurry; Step 3: The slurry is coated onto aluminum foil, dried, and sliced ​​to form the positive electrode of a lithium-ion battery.

5. The method for preparing the positive electrode of a lithium-ion battery according to claim 4, characterized in that: The conductive agent is superconducting carbon black.

6. The method for preparing a lithium-ion battery cathode according to claim 4 or 5, characterized in that: The PVDF adhesive is stirred and dispersed with N-methylpyrrolidone to form the PVDF adhesive solution described in step two.

7. The method for preparing the positive electrode of a lithium-ion battery according to claim 6, characterized in that: In step three, the aluminum foil thickness is 10μm~12μm.

8. The application of the lithium-ion battery cathode according to any one of claims 2 and 3 in the preparation of lithium-ion batteries.

9. A long-life lithium-ion battery, comprising a positive electrode, a separator, a liquid electrolyte, and a negative electrode, characterized in that: The positive electrode is the positive electrode of the lithium-ion battery according to any one of claims 2 and 3.

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