Lithium ion secondary battery positive electrode material, and preparation method and application thereof

Abstract

The application discloses a lithium ion secondary battery positive electrode material and a preparation method and application thereof, and belongs to the technical field of secondary batteries. Lithium benzenetetracarboxylate is mixed with active material lithium iron phosphate by ball milling to obtain a precursor, the precursor is mixed with carbon nanotubes, PVDF and NMP and is ground, and then is rolled and dried to obtain the lithium ion secondary battery positive electrode material; based on the total mass of the lithium ion secondary battery positive electrode material, the content of the lithium benzenetetracarboxylate is 3-5%, the content of the lithium iron phosphate is 70-80%, the content of the carbon nanotubes is 2-8%, the content of the PVDF is 2-5%, and the balance is NMP. The positive electrode material prepared by the method is used in a lithium ion secondary battery, and can significantly improve the initial efficiency, capacity and cycle performance of the lithium battery, overcome the problem of gas generation of the positive electrode material, and improve the safety performance of the battery.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, specifically to a lithium-ion secondary battery cathode material, its preparation method, and its application. Background Technology

[0002] With the continuous expansion of lithium-ion battery applications, especially in new energy vehicles and energy storage, increasingly higher demands are being placed on battery performance, such as energy density and cycle life. With the research and application of new high-capacity anode materials such as silicon-based anodes, the lithium loss problem during battery charging and discharging is becoming increasingly prominent, leading to the development of lithium replenishment technology. During the first charge of a lithium-ion battery, a series of complex electrochemical reactions occur, resulting in lithium loss. On the anode surface, the electrolyte reacts with the anode material to form a solid electrolyte interphase (SEI) film. This process consumes lithium ions, and once these lithium ions participate in the reaction, they cannot return to the battery's normal cycle, causing irreversible lithium loss. Solving the problem of active lithium loss during the first charge and discharge process through lithium replenishment technology can improve the battery's initial efficiency, capacity, and cycle performance.

[0003] Lithium replenishment technology can be divided into positive electrode lithium replenishment and negative electrode lithium replenishment. Negative electrode lithium replenishment involves the use of flammable and explosive metallic lithium, posing a high safety risk, and is also complex and costly. Positive electrode lithium replenishment, on the other hand, has advantages such as high safety and no need to change existing battery manufacturing processes, making it a "new favorite" in the industry. Currently, mainstream positive electrode lithium replenishing agents include lithium-rich nickel oxide (Li2NiO2, LNO) and lithium-rich lithium iron oxide (Li5FeO4, LFO), but these have limitations such as complex processes (requiring high-temperature sintering or coating modification), high costs, and insufficient conductivity.

[0004] Existing lithium iron phosphate (LFP) cathode materials without lithium replenishment agents suffer from low initial efficiency due to irreversible lithium loss, which also reduces battery capacity and cycle performance. Cathode materials with lithium replenishment agents such as lithium iron phosphate / lithium nickel phosphate not only have complex manufacturing processes and high costs, but also suffer from severe gas generation problems. Therefore, there is an urgent need to develop a lithium battery cathode material that, by adding novel lithium replenishment agents, can improve the initial efficiency, capacity, and cycle performance of lithium batteries while overcoming the gas generation problem and enhancing battery safety. Summary of the Invention

[0005] The purpose of this invention is to provide a positive electrode material for lithium-ion secondary batteries, its preparation method, and its application. When the positive electrode material prepared by this method is used in lithium-ion secondary batteries, it can significantly improve the first-time efficiency, capacity, and cycle performance of lithium batteries, while also overcoming the problem of gas generation in positive electrode materials and improving the safety performance of batteries.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a positive electrode material for a lithium-ion secondary battery, comprising the following steps: ball milling and mixing lithium phenyltetracarboxylate, a lithium supplement agent, with lithium iron phosphate, an active material, to obtain a precursor; mixing and grinding the precursor with carbon nanotubes, polyvinylidene fluoride (hereinafter referred to as PVDF) and N-methylpyrrolidone (hereinafter referred to as NMP); and then rolling and drying the mixture to obtain the positive electrode material for a lithium-ion secondary battery.

[0007] The lithium phenyltetracarboxylate has a purity of 99.9% and a particle size of 5-10 μm.

[0008] Based on the total mass of the cathode material for lithium-ion secondary batteries, the content of lithium phenyltetracarboxylate (lithium supplementer) is 3-5%, lithium iron phosphate is 70-80%, carbon nanotubes are 2-8%, PVDF is 2-5%, and the balance is NMP.

[0009] The ball milling time for lithium phenyltetracarboxylate and lithium iron phosphate is 10-12 hours, and the mixing and grinding time for the precursor with carbon nanotubes and PVDF is 30-40 minutes.

[0010] Secondly, the present invention provides a lithium-ion secondary battery cathode material prepared by the above-described preparation method.

[0011] Thirdly, the present invention provides an application of the above-mentioned lithium-ion secondary battery cathode material in lithium-ion secondary batteries.

[0012] The embodiments of this application have at least the following beneficial effects: Currently, the mainstream lithium replenishing agents on the market are lithium-rich nickel oxide and lithium-rich iron oxide. These are unstable under high voltage and high current conditions, causing gas production in the battery and affecting battery safety. Lithium phenylene oxide, due to its chemically stable benzene ring, remains stable under high voltage and high current conditions and does not produce gas, thus solving the safety issues associated with lithium replenishing agents. Furthermore, because lithium phenylene oxide has a high unit lithium replenishment capacity, cathode materials containing lithium phenylene oxide as a lithium replenishing agent are more effective in improving the initial efficiency, capacity, and cycle performance of lithium batteries. The cathode material of this invention, used in lithium-ion secondary batteries, achieves an initial efficiency of 89.4-92.5%, a 5C discharge battery capacity of 185.2-190.9 mAh / g, a capacity retention of 90.1-92.7% after 1000 cycles at 25℃, and a gas production of 0.6-0.8 ml. Detailed Implementation

[0013] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0014] The lithium-ion secondary battery cathode material in this embodiment is described in detail below.

[0015] First, it should be noted that the lithium supplementer added to the positive electrode material in this embodiment is lithium phenyltetracarboxylate, with a purity of 99.9% and a particle size of 5-10 μm.

[0016] The following will describe the preparation method of the lithium-ion secondary battery cathode material and the battery in this embodiment.

[0017] The lithium-ion secondary battery includes: a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte.

[0018] positive electrode: In this embodiment of the invention, based on the total mass of the cathode material, the active material in the cathode is lithium iron phosphate, with a content of 70-80%; the conductive agent is carbon nanotubes, with a content of 2-8%; the binder is PVDF, with a content of 2-5%; the lithium supplementer is lithium phenyltetracarbonate, with a content of 3-5%; and the balance is NMP.

[0019] negative electrode: In this embodiment of the invention, the negative electrode material may be selected from at least one of artificial graphite, natural graphite, hard carbon, silicon-based negative electrode material and tin-based negative electrode material.

[0020] Diaphragm: Understandably, a diaphragm is usually sandwiched between the positive and negative electrodes to prevent short circuits. The diaphragm used in this embodiment of the invention is one of polyolefins including polyethylene, polypropylene, and polytetrafluoroethylene.

[0021] Electrolyte: The electrolyte of this invention is a non-aqueous electrolyte, which is composed of lithium salt, non-aqueous solvent, and additives.

[0022] In one embodiment, the non-aqueous solvent is selected from at least one of propylene carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, difluoroethyl acetate, and ethyl 2,2,2-trifluoroethyl acetate. The content of the non-aqueous solvent is 70-90%, based on the total mass of the non-aqueous electrolyte.

[0023] In one embodiment, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalate phosphate, lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate, and lithium difluorosulfonylimide. The lithium salt content is 5-15%, based on the total mass of the non-aqueous electrolyte.

[0024] The additive is one or a combination of several of vinylene carbonate, fluorovinyl carbonate, and 1,3-propanesulfonate lactone, with a content of 5-10%.

[0025] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0026] Unless otherwise specified, all materials, reagents and instruments used in the following embodiments are commercially available. Examples 1-6 and Comparative Examples 1-3

[0027] The lithium-ion secondary batteries of Examples 1-6 and Comparative Examples 1-3 were prepared according to the following method.

[0028] (1) Preparation of positive electrode The lithium supplement lithium phenyltetracarboxylate and the active material lithium iron phosphate were ball-milled and mixed for 10-12 hours to obtain a precursor. The precursor was then mixed with carbon nanotubes, PVDF and NMP and ground for 30-40 minutes, followed by roll pressing and drying to prepare a lithium-ion secondary battery cathode material. Based on the total mass of the cathode material for lithium-ion secondary batteries, the content of lithium phenyltetracarboxylate (lithium phenylene oxide) is 3-5%; the content of lithium iron phosphate is 70-80%; the content of carbon nanotubes is 2-8%; the content of PVDF is 2-5%; and the balance is NMP.

[0029] (2) Preparation of negative electrode sheet Graphite is mixed with conductive agent Super P, thickener CMC, and binder SBR (styrene-butadiene rubber latex), deionized water is added, and the mixture is stirred evenly under vacuum. The mixed slurry is then evenly coated onto copper foil, dried, and cold-pressed and slit to obtain the negative electrode sheet.

[0030] (3) Electrolyte preparation In an argon atmosphere glove box with a water content of <10ppm and an oxygen content of <10ppm, ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC of 1:1:1. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent, and then additives were added. After mixing evenly, an electrolyte was obtained.

[0031] (4) Preparation of the separating membrane A 15μm thick polyethylene film (purchased from Celgard) was selected.

[0032] (5) Preparation of lithium-ion secondary batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell, which is placed in an aluminum-plastic film casing. Electrolyte is injected and the casing is sealed. After processes such as settling, formation, final sealing, and capacity testing, a lithium-ion secondary battery is obtained.

[0033] In Table 1 below, the lithium replenishing agent in Examples 1-6 is lithium phenyltetracarboxylate, the lithium replenishing agent in Comparative Example 1 is lithium-rich nickel oxide, the lithium replenishing agent in Comparative Example 2 is lithium-rich lithium ferrite, and there is no lithium replenishing agent in Comparative Example 3.

[0034] Table 1: Composition and content (%) of cathode materials in Examples 1-6 and Comparative Examples 1-3 Example 1 3 70 5 6 16 Example 2 4 75 2 8 11 Example 3 5 80 3 2 10 Example 4 3 72 2 3 20 Example 5 4 72 4 5 15 Example 6 5 76 3 4 12 Comparative Example 1 4 75 2 8 11 Comparative Example 2 4 75 2 8 11 Comparative Example 3 / 79 2 8 11

[0035] The lithium-ion batteries prepared in the above embodiments and comparative examples were tested for their first efficiency, capacity, cycle performance, and gas production. The test results are shown in Table 2.

[0036] In Table 2 below, the lithium supplementer added to the cathode material in Examples 1-6 is lithium phenyltetracarbonate, the lithium supplementer added to the cathode material in Comparative Example 1 is lithium-rich nickel oxide, the lithium supplementer added to the cathode material in Comparative Example 2 is lithium-rich lithium iron oxide, and no lithium supplementer was added to the cathode material in Comparative Example 3.

[0037] Table 2: Performance test results of Examples 1-6 and Comparative Examples 1-3 Example 1 89.4 185.2 90.1 0.8 Example 2 92.5 190.9 92.7 0.6 Example 3 91.3 186.4 91.1 0.8 Example 4 90.3 186.6 90.2 0.7 Example 5 91.7 189.2 92.4 0.7 Example 6 90.8 185.7 90.8 0.7 Comparative Example 1 87.5 172.2 87.7 2.5 Comparative Example 2 87.2 171.5 87.2 2.3 Comparative Example 3 79.8 157.4 82.5 0.5 According to the test results in Table 2, after adding lithium phenyltetracarboxylate as a lithium supplement to the cathode materials in Examples 1-6, the batteries outperformed those of Comparative Example 1 (cathode material with lithium-rich lithium nickel oxide), Comparative Example 2 (cathode material with lithium-rich lithium ferrite), and Comparative Example 3 (cathode material without lithium supplement), in terms of initial efficiency, capacity, and cycle performance. The performance of the formulation in Example 2 was particularly excellent. Furthermore, the gas production of the batteries with lithium phenyltetracarboxylate as a lithium supplement was significantly lower than that of Comparative Example 1 (cathode material with lithium-rich lithium nickel oxide) and Comparative Example 2 (cathode material with lithium-rich lithium ferrite), and only slightly higher than that of the batteries without lithium supplement. This demonstrates that cathode materials containing lithium phenyltetracarboxylate as a lithium supplement can significantly improve battery performance and produce less gas compared to currently commercially available cathode materials with lithium-rich lithium nickel oxide / lithium-rich lithium nickel oxide as a lithium supplement. This is because lithium phenyltetracarboxylate has a higher theoretical lithium supplement capacity and stability.

[0038] The technical solutions provided by the embodiments of this application have been described in detail above. Specific examples have been used in this document to illustrate the principles and implementation methods of the embodiments of this application. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the embodiments of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing a positive electrode material for a lithium-ion secondary battery, characterized in that, Includes the following steps: The lithium supplement lithium benzoate and the active material lithium iron phosphate were ball-milled and mixed to obtain a precursor. The precursor was then mixed with carbon nanotubes, polyvinylidene fluoride and N-methylpyrrolidone and ground. Subsequently, the mixture was rolled and dried to obtain the positive electrode material for lithium-ion secondary batteries.

2. The method for preparing the positive electrode material of a lithium-ion secondary battery according to claim 1, characterized in that, The lithium phenyltetracarboxylate has a purity of 99.9% and a particle size of 5-10 μm.

3. The method for preparing the positive electrode material of a lithium-ion secondary battery according to claim 1, characterized in that, Based on the total mass of the positive electrode material for lithium-ion secondary batteries, the content of lithium phenyltetracarboxylate (lithium supplementer) is 3-5%, lithium iron phosphate is 70-80%, carbon nanotubes are 2-8%, polyvinylidene fluoride is 2-5%, and the balance is N-methylpyrrolidone.

4. The method for preparing the positive electrode material of a lithium-ion secondary battery according to claim 1, characterized in that, The lithium phenylenetetracarboxylate and lithium iron phosphate are ball-milled for 10-12 hours, and the precursor is mixed with carbon nanotubes, polyvinylidene fluoride and N-methylpyrrolidone and then ground for 30-40 minutes.

5. A positive electrode material for a lithium-ion secondary battery, characterized in that, The lithium-ion secondary battery cathode material is prepared by the preparation method according to any one of claims 1-4.

6. An application of a positive electrode material for lithium-ion secondary batteries, characterized in that, The lithium-ion secondary battery cathode material according to claim 5 is applied in a lithium-ion secondary battery.