Lithium-ion battery cathodes based on composite cathode active materials, their preparation methods, and applications.

Abstract

This invention discloses a lithium-ion battery cathode based on a composite cathode active material, its preparation method, and its application, relating to the field of lithium-ion battery technology. The composite cathode active material comprises LiMn. X Fe 1‑X PO4(0.4≤X≤0.6), LiMn2O4, LiNi 0.8 Co 0.1 Mn 0.1 O2, Li2Al2B2O7 and LLTO / LLZO composite materials. This invention uses LiMn X Fe 1‑X PO4 and LiMn2O4 are the main materials, combined with LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode active material composition consists of multiple positive electrode active materials, including O2, Li2Al2B2O7, and LLTO / LLZO. During battery operation, the combined use of multiple positive electrode active materials can improve ion conduction, reduce internal polarization, and suppress Mn. 2+ The leaching process optimizes the positive electrode CEI film, thereby reducing self-discharge and simultaneously improving the stability during high-temperature cycling.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium-ion battery cathode based on composite cathode active materials, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density and long cycle life, and are widely used in new energy vehicles, energy storage systems, two-wheeled vehicles, and portable electronic devices. Among them, lithium manganese iron phosphate (LMFP), as a novel cathode material, combines the high safety and long cycle life of lithium iron phosphate with the high voltage advantage of lithium manganese phosphate (LMP), and its energy density is significantly higher than that of traditional lithium iron phosphate materials, making it a research hotspot for lithium-ion battery cathode materials in recent years.

[0003] However, lithium iron phosphate (LFP) based lithium-ion batteries still face some unresolved issues in practical applications, one of which is self-discharge. The main cause of self-discharge in LFP batteries lies in the Mn content within the battery. 2+ Dissolution and instability of the positive electrode CEI film. The self-discharge caused by both leads to the battery losing its charge during storage, which not only affects the user experience but also reduces the battery's cycle stability and lifespan.

[0004] In existing technologies, methods for suppressing self-discharge in lithium-ion batteries mostly focus on the modification of single materials or the optimization of electrolytes. However, single-material modification methods often fail to balance various battery performance aspects, especially when it comes to effectively suppressing Mn while leveraging the inherent advantages of lithium manganese iron phosphate. 2+ The self-discharge problem caused by dissolution.

[0005] Based on this, a method was developed that can fully utilize the advantages of lithium manganese iron phosphate while significantly inhibiting Mn. 2+ Lithium-ion batteries that achieve the goal of reducing self-discharge through dissolution and have excellent overall performance have significant practical implications. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a lithium-ion battery cathode based on composite cathode active materials, its preparation method and application, wherein the composite cathode active materials enable the components to work synergistically to suppress Mn. 2+ The purpose of reducing self-discharge is to dissolve and optimize the CEI membrane.

[0007] To address the above technical problems, according to one aspect of the present invention, a lithium-ion battery cathode based on a composite cathode active material is provided, comprising a composite cathode active material and a conductive agent, wherein the composite cathode active material comprises: LiMn X Fe 1-X PO4, LiMn2O4, LiNi0.8 Co 0.1 Mn 0.1 O2, Li2Al2B2O7 and LLTO / LLZO composite materials, wherein 0.4≤X≤0.6;

[0008] LiMn by mass ratio X Fe 1-X PO4:LiMn2O4:LiNi 0.8 Co 0.1 Mn 0.1 The O2:Li2Al2B2O7:LLTO / LLZO composite material has a ratio of 50~80:10~45:5~30:1~10:0.5~5.

[0009] As a preferred embodiment, LiMn X Fe 1-X PO4:LiMn2O4:LiNi 0.8 Co 0.1 Mn 0.1 The mass ratio of the O2:Li2Al2B2O7:LLTO / LLZO composite material is 65:20:6:5:1.

[0010] In a preferred embodiment, the conductive agent comprises Super-P and single-walled carbon nanotubes, with a mass ratio of 1:0.99~1.01.

[0011] In a preferred embodiment, the mass ratio of LLTO to LLZO in the LLTO / LLZO composite material is 7:2.99~3.01.

[0012] As a preferred embodiment, the particle size range of the LLTO / LLZO composite material is 0.01 μm to 2 μm.

[0013] According to another aspect of the present invention, a method for preparing a lithium-ion battery cathode based on a composite cathode active material as described above is provided, comprising:

[0014] Step 1: Mix and disperse the components of the composite positive electrode active material to obtain a composite positive electrode active material mixture, and then mix and disperse the composite positive electrode active material mixture with a conductive agent to form a positive electrode material mixture;

[0015] Step 2: Mix and disperse the PVDF adhesive with N-methylpyrrolidone to form a PVDF adhesive solution;

[0016] Step 3: Mix and disperse the positive electrode material mixture with PVDF adhesive to form a slurry;

[0017] Step four: The slurry is coated onto aluminum foil, dried, and sliced ​​to form the positive electrode.

[0018] In a preferred embodiment, in step three, the mass ratio of the composite positive electrode active material mixture, conductive agent, and PVDF adhesive in the slurry is 90~97:1~2:1~2.

[0019] In a preferred embodiment, the aluminum foil thickness in step four is 10μm~12μm.

[0020] According to another aspect of the present invention, the application of the lithium-ion battery cathode based on the composite positive electrode active material described above in the preparation of lithium-ion batteries is provided.

[0021] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, a separator, and a negative electrode, wherein the positive electrode is the lithium-ion battery positive electrode based on the composite positive electrode active material described above.

[0022] The composite positive electrode active material provided by this invention uses LiMn X Fe 1-X PO4 (LMFP, 0.4≤X≤0.6) and LiMn2O4 (LMO) are the main materials, combined with LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode active material composition consists of multiple positive electrode active materials, including O2, Li2Al2B2O7, and LLTO / LLZO. During battery operation, the combined use of multiple positive electrode active materials can improve ion conduction, reduce internal polarization, and suppress Mn. 2+ The leaching process optimizes the positive electrode CEI film, thereby reducing self-discharge and simultaneously improving the stability during high-temperature cycling. Attached Figure Description

[0023] Figure 1 This is a comparison chart of the monthly self-discharge rates of lithium-ion batteries obtained in Example 1 and Comparative Examples 1-4 at 25°C.

[0024] Figure 2 These are the capacity retention curves of the lithium-ion batteries obtained in Example 2 and Comparative Examples 5-8 after cycling at 45°C.

[0025] Figure 3 The Mn content of the lithium-ion batteries obtained in Example 2 and Comparative Examples 5-8 is... 2+ Dissolution test results;

[0026] Figure 4 These are the test results of the daily self-discharge of the lithium-ion batteries obtained in Example 3 and Comparative Examples 9-12 after being fully charged. Detailed Implementation

[0027] A typical embodiment of the present invention provides a lithium-ion battery cathode based on a composite positive electrode active material, comprising a composite positive electrode active material and a conductive agent, wherein the components of the composite positive electrode active material include: LiMn X Fe 1-X PO4 (LMFP, 0.4≤X≤0.6), LiMn2O4 (LMO), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), Li2Al2B2O7 and LLTO / LLZO composite materials.

[0028] The composite cathode active material described in this embodiment is based on LMFP, laying the foundation for the safety and cycle performance of lithium-ion batteries. The composite LMO constructs a three-dimensional tunnel, which facilitates the diffusion of conductive agents and accelerates ion conduction, thereby improving rate capability and low-temperature performance. The composite NCM811 cathode material further enhances energy density. Li2Al2B2O7 is introduced as a structural stabilizer, utilizing it to construct a highly stable cathode structure system to suppress lattice distortion of LMFP and LMO during charge and discharge, and reduce Mn content. 2+ Dissolution and Li + Irreversible insertion / deintercalation suppresses self-discharge at the material level; finally, nanoscale LLTO / LLZO is added for cathode interface modification to construct a protective interface layer and suppress Jahn-Teller distortion (Mn) in LMO. 2+ (Caused by lattice volume changes), maintaining the stability of the spinel structure, improving the structural integrity of the cathode after 100 cycles by more than 40%, indirectly reducing fresh surface side reactions caused by material breakage, and inhibiting Mn 2+ Dissolution and structural distortion. Simultaneously, optimizing the interfacial compatibility of multiple materials is crucial. The significant differences in crystal structures after blending various materials easily lead to interfacial contact resistance. LLTO / LLZO can act as an interfacial bridge to reduce interfacial impedance and assist Li... + Rapid migration between different materials, avoiding local Li + Irreversible intercalation caused by concentration gradient can further reduce the self-discharge rate after 30 days of storage at room temperature.

[0029] LiMn by mass ratio X Fe 1-X The composite material of PO4 (0.4≤X≤0.6):LiMn2O4:NCM811:Li2Al2B2O7:LLTO / LLZO is 50~80:10~45:5~30:1~10:0.5~5.

[0030] For example, by mass ratio, LiMn X Fe1-X The composite material of PO4 (0.4≤X≤0.6):LiMn2O4:NCM811:Li2Al2B2O7:LLTO / LLZO is 80:10:5:1:1; or 50:40:5:1:1; or 50:45:10:10:0.5; or 70:30:30:6:5; or 65:20:6:5:1.

[0031] For example, LiMn X Fe 1-X In PO4 (0.4≤X≤0.6), X can be 0.4, 0.45, 0.5, 0.55, or 0.6.

[0032] The conductive agent comprises Super-P (SP) and single-walled carbon nanotubes (CNTs) in a mass ratio of 1:0.99~1.01. The conductive agent is a combination of Super-P and CNTs, which together construct a three-dimensional conductive network, reducing local polarization caused by uneven distribution of the conductive agent and indirectly suppressing the increase in self-discharge rate.

[0033] For example, the mass ratio of Super-P to single-walled carbon nanotubes is 1:1; 1:0.99; 1:1.01.

[0034] Among them, lithium lanthanum titanium oxide (LLTO) and lithium lanthanum zirconium oxide (LLZO) are nanoparticle-type oxide solid electrolyte materials. In the LLTO / LLZO composite material, the mass ratio of LLTO to LLZO is 7:2.99~3.01.

[0035] For example, the mass ratio of LLTO to LLZO is 7:3; 7:2.99; 7:3.01.

[0036] The preferred LLTO / LLZO composite material has a particle size range of 0.01 μm to 2 μm.

[0037] Another typical embodiment of the present invention provides a method for preparing the above-mentioned lithium-ion battery cathode based on composite cathode active material, including the following steps.

[0038] Step 1: Prepare a mixture of cathode materials

[0039] The components of the composite positive electrode active material are mixed and dispersed to obtain a composite positive electrode active material mixture, and the composite positive electrode active material mixture is mixed and dispersed with a conductive agent to form a positive electrode material mixture.

[0040] In this step, LiMn is first... X Fe 1-XPO4 (0.4≤X≤0.6), LiMn2O4, NCM811, Li2Al2B2O7, and LLTO / LLZO composite materials were mixed and dispersed evenly in a mass ratio of 50~80:10~45:5~30:1~10:0.5~5 to form a positive electrode active material mixture; then, Super P and CNT were added to the evenly mixed positive electrode active material mixture and stirred and dispersed evenly to obtain the positive electrode material mixture.

[0041] Step 2: Prepare PVDF adhesive solution

[0042] PVDF adhesive and N-methylpyrrolidone were mixed and dispersed to form a PVDF adhesive solution. The mixing ratio of the two by mass was 6%:94%.

[0043] Step 3: Mix and disperse the positive electrode material mixture with PVDF adhesive to form a slurry.

[0044] In the slurry, the mass ratio of the composite positive electrode active material mixture, conductive agent, and PVDF adhesive is 90~97:1~2:1~2.

[0045] For example, in the slurry, the mass ratio of the composite positive electrode active material mixture, the conductive agent, and the PVDF adhesive is 90:2:2; or 97:1:2; or 97:2:1; or 95:2:2.

[0046] Step 4: Prepare the positive electrode

[0047] The slurry is coated onto aluminum foil, dried, and sliced ​​to form the positive electrode.

[0048] The aluminum foil thickness is preferably 10μm~12μm.

[0049] Another typical embodiment of the present invention provides a lithium-ion battery comprising a positive electrode, a separator, and a negative electrode. The positive electrode is the lithium-ion battery positive electrode based on the composite positive electrode active material described above.

[0050] The lithium-ion battery provided in this embodiment preferably uses artificial graphite as the negative electrode, achieving an initial efficiency of ≥90%, which can reduce side reactions on the negative electrode surface and improve Li-ion efficiency. + Reversible embedding. Ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (EC / DMC / EMC) is selected as the solvent to ensure the quality of the SEI film formation, reduce electrolyte viscosity, and improve ion migration rate. LiPF6 is preferred as the electrolyte, balancing ionic conductivity and stability, and avoiding viscosity increases caused by high concentrations. The LLTO / LLZO composite material can form "micro-nano ion channels" in the electrolyte, assisting Li... + Uniform transport avoids the presence of Li in traditional liquid electrolytes +Localized accumulation due to concentration polarization reduces irreversible Li + Loss. The diaphragm is made of polyethylene (PE) substrate, and the porosity of the diaphragm is guaranteed to be 40%-50% to ensure electrolyte wettability, while avoiding micro-short circuit consequences and increased self-discharge rate caused by excessively large pore size of the diaphragm.

[0051] Graphite, conductive agent, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in proportion to form a uniform slurry. The slurry is then coated onto copper foil with a surface density of 6-12 μm, rolled, dried, and sliced ​​to form the negative electrode.

[0052] The positive electrode, separator, and negative electrode are stacked alternately. After stacking, the battery cell is subjected to tab welding and aluminum-plastic film encapsulation.

[0053] Then the battery cell is baked to remove excess moisture. After baking, electrolyte is injected, and then the cell is left to stand.

[0054] By performing pre-formation, high-temperature aging, open-circuit voltage testing (OCV testing), and room-temperature aging on the battery cells, an improved lithium-ion battery sample can be obtained.

[0055] 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 of the present invention and do not exceed the scope of the subject matter of the present invention. The scope of protection of the present invention is not limited by the embodiments. Unless otherwise specified, the materials and reagents used in this invention can be obtained from commercially available products in the art. Example 1

[0056] Step (1), LiMn X Fe 1-X PO4 (X=0.5), LiMn2O4, LiNi 0.8 Co 0.1 Mn 0.1 O2, Li2Al2B2O7, and LLTO / LLZO composite materials are stirred and dispersed evenly to form a positive electrode active material mixture; Super P and CNT are compounded and added to the evenly mixed positive electrode active material mixture, and stirred and dispersed evenly to obtain a positive electrode material mixture.

[0057] Step (2): Mix and disperse PVDF binder with N-methylpyrrolidone to form PVDF solution, add positive electrode material mixture to PVDF solution, mix and disperse for 6 hours to form slurry with solid content of 65%.

[0058] In this embodiment, LiMn X Fe 1-XPO4 (X=0.5), LiMn2O4, LiNi 0.8 Co 0.1 Mn 0.1 The mass ratio of O2, Li2Al2B2O7, LLTO / LLZO composite material, Super P, CNT, and PVDF adhesive is 80:10:5:1:1:1:1:1. In the LLTO / LLZO composite material, the mass ratio of LLTO to LLZO is 7:3.

[0059] Step (3) involves coating the slurry onto a 10μm aluminum foil to achieve a double-sided areal density of 38.2±0.6 mg / cm². 2 The positive electrode sheet is of the specified specification. The dried positive electrode sheet is then processed at 2.4 g / cm³. 3 Roll pressing is performed, followed by electrode slitting, punching, and baking processes.

[0060] Step (4): Graphite, Super P, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed in a mass ratio of 95.6:1.2:1:2.2 to make a uniformly mixed slurry. The slurry is then coated on a 6μm copper foil according to a predetermined surface density. After rolling, drying and slicing, the negative electrode sheet is made.

[0061] Step (5): A secondary lithium-ion cell is fabricated using the zig-zag stacking method; the cell is then tab-welded and encapsulated, with an aluminum-plastic film outer shell; the cell is then baked to remove water, and electrolyte is injected, followed by standing. The cell undergoes pre-formation, high-temperature aging, OCV testing, and room-temperature aging to obtain a lithium-ion battery sample, denoted as 1-a.

[0062] Comparative Example 1

[0063] The difference from Example 1 is that LiNi is not added to the positive electrode active material mixture provided in step (1). 0.8 Co 0.1 Mn 0.1 O2. The remaining steps are the same, and the resulting lithium-ion battery sample is denoted as 1-b.

[0064] Comparative Example 2

[0065] 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 denoted as 1-c.

[0066] Comparative Example 3

[0067] The difference from Example 1 is that no LLTO / LLZO composite material is 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.

[0068] Comparative Example 4

[0069] The difference from Example 1 is that LiNi is not added to the positive electrode active material mixture provided in step (1). 0.8 Co 0.1 Mn 0.1 Three positive electrode active materials were selected: O2, Li2Al2B2O7, and LLTO / LLZO. All other steps were the same, and the resulting lithium-ion battery sample was denoted as 1-e.

[0070] The five lithium-ion battery samples obtained in Example 1 and Comparative Examples 1-4 were fully charged at a charge / discharge current of 1C within the range of 3.0-4.2V, and then subjected to self-discharge tests at room temperature. The comparative data are shown in the appendix. Figure 1 As shown, the test results indicate that the lithium-ion battery prepared according to the present invention has a lower self-discharge rate. Example 2

[0071] Step (1), LiMn X Fe 1-X PO4 (X=0.5), LiMn2O4, LiNi 0.8 Co 0.1 Mn 0.1 O2, Li2Al2B2O7, and LLTO / LLZO composite materials are stirred and dispersed evenly to form a positive electrode active material mixture; Super P and CNT are compounded and added to the evenly mixed positive electrode active material mixture, and stirred and dispersed evenly to obtain a positive electrode material mixture;

[0072] Step (2): Mix and disperse PVDF adhesive with N-methylpyrrolidone to form PVDF solution, add positive electrode material mixture to PVDF solution, mix and disperse for 5 hours to form slurry with solid content of 50%.

[0073] In this embodiment, LiMn X Fe 1-X PO4 (X=0.5), LiMn2O4, LiNi 0.8 Co 0.1 Mn 0.1 The mass ratio of O2, Li2Al2B2O7, LLTO / LLZO composite material, Super P, CNT, and PVDF is 65:20:6:5:1:1:1:1. In the LLTO / LLZO composite material, the mass ratio of LLTO to LLZO is 7:3.

[0074] Step (3) involves coating the slurry onto a 12μm aluminum foil with a double-sided areal density of 38.2 ± 0.6 mg / cm². 2 The positive electrode sheet is of the specified specification. The dried positive electrode sheet is then processed at 2.4 g / cm³. 3 Roll pressing is performed, followed by electrode slitting, punching, and baking processes.

[0075] Step (4): Graphite, Super P, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed in a mass ratio of 95.6:1.2:1:2.2 to make a uniformly mixed slurry. The slurry is then coated on a 12μm copper foil according to a predetermined surface density. After rolling, drying and slicing, the negative electrode sheet is made.

[0076] Step (5): A secondary lithium-ion cell is fabricated using the zig-zag stacking method; the cell is then tab-welded and encapsulated, with an aluminum-plastic film outer shell; the cell is then baked to remove water, and electrolyte is injected, followed by standing. 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.

[0077] Comparative Example 5

[0078] The difference from Example 2 is that LiNi is not added to the positive electrode active material mixture provided in step (1). 0.8 Co 0.1 Mn 0.1 O2. The remaining steps are the same, and the resulting lithium-ion battery sample is denoted as 2-b.

[0079] Comparative Example 6

[0080] 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 denoted as 2-c.

[0081] Comparative Example 7

[0082] The difference from Example 2 is that no LLTO / LLZO composite material is 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.

[0083] Comparative Example 8

[0084] The difference from Example 2 is that LiNi is not added to the positive electrode active material mixture provided in step (1). 0.8 Co 0.1 Mn 0.1Three positive electrode active materials were selected: O2, Li2Al2B2O7, and LLTO / LLZO. All other steps were the same, and the resulting lithium-ion battery sample was denoted as 2-e.

[0085] The five lithium-ion battery samples obtained in Example 2 and Comparative Examples 5-8 were subjected to high-temperature cycling tests at a charge-discharge current of 1C within the range of 3.0-4.2V, and the Mn content of the electrodes was determined after 50 cycles. 2+ Dissolution test data are attached. Figure 2 and Figure 3 As shown, the test results indicate that the lithium-ion battery prepared in this invention has better high-temperature cycle performance and lower Mn content. 2+ Dissolution amount. Example 3

[0086] Step (1), LiMn X Fe 1-X PO4 (X = 0.5), LiMn2O4, LiNi 0.8 Co 0.1 Mn 0.1 O2, Li2Al2B2O7, and LLTO / LLZO composite materials are stirred and dispersed evenly to form a positive electrode active material mixture; Super P and CNT are compounded and added to the evenly mixed positive electrode active material mixture, and stirred and dispersed evenly to obtain a positive electrode material mixture;

[0087] Step (2): Mix and disperse PVDF adhesive with N-methylpyrrolidone to form PVDF solution, add positive electrode material mixture to PVDF solution, mix and disperse for 5 hours to form slurry with solid content of 50%.

[0088] In this embodiment, LiMn X Fe 1-X PO4 (X=0.5), LiMn2O4, LiNi 0.8 Co 0.1 Mn 0.1 The mass ratio of O2, Li2Al2B2O7, LLTO / LLZO composite material, Super P, CNT, and PVDF is 50:40:5:1:1:1:1:1. In the LLTO / LLZO composite material, the mass ratio of LLTO to LLZO is 7:3.

[0089] Step (3) involves coating the slurry onto a 12μm aluminum foil with a double-sided areal density of 38.2 ± 0.6 mg / cm². 2 The positive electrode sheet is of the specified specification. The dried positive electrode sheet is then processed at 2.4 g / cm³. 3 Roll pressing is performed, followed by electrode slitting, punching, and baking processes.

[0090] Step (4): Graphite, Super P, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed in a mass ratio of 95.6:1.2:1:2.2 to make a uniformly mixed slurry. The slurry is then coated on a 12μm copper foil according to a predetermined surface density. After rolling, drying and slicing, the negative electrode sheet is made.

[0091] Step (5): A secondary lithium-ion cell is fabricated using the zig-zag stacking method; the cell is then tab-welded and encapsulated, with an aluminum-plastic film outer shell; the cell is then baked to remove water, and electrolyte is injected, followed by standing. The cell undergoes pre-formation, high-temperature aging, OCV testing, and room-temperature aging to obtain a lithium-ion battery sample, denoted as 3-a.

[0092] Comparative Example 9

[0093] The difference from Example 3 is that LiNi is not added to the positive electrode active material mixture provided in step (1). 0.8 Co 0.1 Mn 0.1 O2. The remaining steps are the same, and the resulting lithium-ion battery sample is designated as 3-b.

[0094] Comparative Example 10

[0095] 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 denoted as 3-c.

[0096] Comparative Example 11

[0097] The difference from Example 3 is that no LLTO / LLZO composite material was 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.

[0098] Comparative Example 12

[0099] The difference from Example 3 is that LiNi is not added to the positive electrode active material mixture provided in step (1). 0.8 Co 0.1 Mn 0.1 Three positive electrode active materials were selected: O2, Li2Al2B2O7, and LLTO / LLZO. All other steps were the same, and the resulting lithium-ion battery sample was designated 3-e.

[0100] Five lithium-ion battery samples obtained in Example 3 and Comparative Examples 9-12 were charged to a full charge of 4.2V at a current of 1C within the range of 3.0-4.2V, then stored at 25°C and subjected to self-discharge monitoring. Comparative data are attached. Figure 4As shown, the test results indicate that the lithium-ion battery prepared in this invention has better self-discharge performance.

[0101] 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 lithium-ion battery cathode based on a composite cathode active material, comprising a composite cathode active material and a conductive agent, characterized in that: The composite positive electrode active material comprises: LiMn X Fe 1-X PO4, LiMn2O4, LiNi 0.8 Co 0.1 Mn 0.1 O2, Li2Al2B2O7 and LLTO / LLZO composite materials, wherein 0.4≤X≤0.6; LiMn by mass ratio X Fe 1-X PO4:LiMn2O4:LiNi 0.8 Co 0.1 Mn 0.1 The O2:Li2Al2B2O7:LLTO / LLZO composite material has a ratio of 50~80:10~45:5~30:1~10:0.5~5.

2. The lithium-ion battery cathode based on composite cathode active material according to claim 1, characterized in that: LiMn X Fe 1-X PO4:LiMn2O4:LiNi 0.8 Co 0.1 Mn 0.1 The mass ratio of the O2:Li2Al2B2O7:LLTO / LLZO composite material is 65:20:6:5:

1.

3. The lithium-ion battery cathode based on composite cathode active material according to claim 1 or 2, characterized in that: The conductive agent comprises Super-P and single-walled carbon nanotubes, with a mass ratio of 1:0.99~1.

01.

4. The lithium-ion battery cathode based on composite cathode active material according to claim 3, characterized in that: In LLTO / LLZO composite materials, the mass ratio of LLTO to LLZO is 7:2.99~3.

01.

5. The lithium-ion battery cathode based on composite cathode active material according to claim 4, characterized in that: The particle size range of LLTO / LLZO composites is 0.01 μm to 2 μm.

6. The method for preparing a lithium-ion battery cathode based on a composite cathode active material according to any one of claims 1-5, characterized in that, include: Step 1: Mix and disperse the components of the composite positive electrode active material to obtain a composite positive electrode active material mixture, and then mix and disperse the composite positive electrode active material mixture with a conductive agent to form a positive electrode material mixture; Step 2: Mix and disperse the PVDF adhesive with N-methylpyrrolidone to form a PVDF adhesive solution; Step 3: Mix and disperse the positive electrode material mixture with PVDF adhesive to form a slurry; Step four: The slurry is coated onto aluminum foil, dried, and sliced ​​to form the positive electrode.

7. The method according to claim 6, characterized in that: In step three, the mass ratio of the composite positive electrode active material mixture, conductive agent, and PVDF adhesive in the slurry is 90~97:1~2:1~2.

8. The method according to claim 6, characterized in that: In step four, the aluminum foil thickness is 10μm~12μm.

9. The application of the lithium-ion battery cathode based on composite positive electrode active material as described in any one of claims 1-5 in the preparation of lithium-ion batteries.

10. A lithium-ion battery, comprising a positive electrode, a separator, and a negative electrode, characterized in that: The positive electrode is the lithium-ion battery positive electrode based on composite positive electrode active material as described in any one of claims 1-5.

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