A positive electrode material composition, a positive electrode sheet, and a preparation method and application thereof

Abstract

The application provides a positive electrode material composition, a positive electrode sheet and a preparation method and application thereof. The positive electrode material composition comprises a positive electrode material, a mixed conductive agent and a binder, the positive electrode material has surface cracks, at least part of the mixed conductive agent is filled in the surface cracks, the mixed conductive agent comprises at least one halide and a conductive carbon material, the general formula of the halide is AX, wherein A is selected from one of IA group elements; X is halogen; and the conductive carbon material is selected from one or more of carbon nanotubes, acetylene black and carbon black. The mixed conductive agent in the application is embedded in the cracks of the positive electrode material, and can strengthen the deintercalation of lithium ions during the charge-discharge cycle of the battery. The halide in the mixed conductive agent can fill the part of the coating crack, can block the contact between the positive electrode material and the electrolyte, reduce the occurrence of side reactions, improve the conductivity and safety of lithium ions, and stabilize the deintercalation of lithium ions during the charge-discharge cycle of the large current.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically, to a positive electrode material composition, a positive electrode sheet, a method for preparing the same, and its applications. Background Technology

[0002] Currently, lithium-ion batteries are developing rapidly. Common cathode materials for lithium-ion batteries typically include ternary cathode materials such as NCM, NCA, lithium manganese oxide (LMO), and lithium iron phosphate (LFP). Lithium manganese oxide batteries offer good safety, but their relatively low specific capacity limits their application. While lithium nickel cobalt manganese oxide has a higher specific capacity, its safety is poor. Lithium iron phosphate offers high cycle performance and safety, but its energy density is low and its low-temperature performance is poor.

[0003] High-capacity lithium-ion batteries have poor charge-discharge cycle performance under high current, and tool-type batteries that can be used with high current generally have low capacity. Therefore, improving the charge-discharge cycle performance of high-capacity lithium-ion batteries under high current and ensuring their safety are the current research priorities. Summary of the Invention

[0004] The main objective of this invention is to provide a positive electrode material composition, a positive electrode sheet, a method for preparing the same, and its application, so as to solve the problem that high-capacity lithium-ion batteries in the prior art are difficult to balance conductivity and safety.

[0005] To achieve the above objectives, according to one aspect of the present invention, a positive electrode material composition is provided, the positive electrode material composition comprising a positive electrode material, a mixed conductive agent and a binder, wherein the positive electrode material has surface gaps, at least partially filled with the mixed conductive agent, the mixed conductive agent comprising at least one halide and a conductive carbon material, the general formula of the halide being AX, wherein A is selected from one of group IA elements; X is a halogen; and the conductive carbon material is selected from one or more of carbon nanotubes, acetylene black, and carbon black.

[0006] Furthermore, the mixed conductive agent includes at least two halides, preferably iodides.

[0007] Furthermore, the mass ratio of halide to conductive carbon material in the mixed conductive agent is 3-5:100, and the mass ratio of positive electrode material to mixed conductive agent is 95.8:0.5-98.3:0.6; the positive electrode material composition also includes optional activated carbon, and the mass content of activated carbon in the positive electrode material composition is 0-1.5%.

[0008] Furthermore, the cathode material is selected from one or more of ternary cathode materials, lithium manganese oxide, and lithium iron phosphate; the binder is preferably polyvinylidene fluoride and / or polyvinylidene fluoride.

[0009] To achieve the above objectives, according to one aspect of the present invention, a positive electrode sheet is provided, the positive electrode sheet comprising a current collector and a positive electrode layer, the positive electrode layer comprising the above-mentioned positive electrode material composition, preferably having a thickness of 190 to 210 μm.

[0010] According to another aspect of the present invention, a method for preparing the above-mentioned positive electrode sheet is provided, the method comprising: step S1, mixing materials including positive electrode material, optional activated carbon, binder, conductive carbon material and halide to obtain positive electrode slurry; step S2, coating the positive electrode slurry onto a current collector and drying it to obtain a positive electrode sheet.

[0011] Further, the mixing in step S1 is a first stirring mixing, which is carried out in a stirring device. The stirring device is equipped with a stirring paddle and a dispersing disk, which are arranged side by side. The stirring paddle and the dispersing disk revolve around the axis of the stirring device at a first speed, and the dispersing disk rotates on its own axis in the horizontal direction at a second speed. Preferably, the first speed is 30 to 60 rpm, the second speed is 1000 to 6000 rpm, and the first stirring time is 1 to 4 hours. Preferably, the solid content of the positive electrode slurry is 70% to 80%.

[0012] Furthermore, the material in step S1 also includes a solvent, which is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide.

[0013] Furthermore, prior to step S1, the preparation method also includes a process of mixing conductive carbon material, halide and solvent to form a mixed conductive agent solution.

[0014] Furthermore, the mixing used to form the mixed conductive agent solution is a second stirring, which is carried out in a stirring device equipped with a stirring paddle and a dispersing disk. The stirring paddle and the dispersing disk are arranged side by side. The stirring paddle and the dispersing disk revolve around the axis of the stirring device at a third speed, and the dispersing disk rotates on its own axis in the horizontal direction at a fourth speed. Preferably, the third speed is 40 to 80 rpm, the fourth speed is 4000 to 10000 rpm, and the second stirring time is 0.5 to 2 hours.

[0015] Furthermore, the mass ratio of the positive electrode material, the mixed conductive agent, the optional activated carbon, and the binder is 95.8:0.5:1.5:2.2 to 98.3:0.6:0:1.1.

[0016] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises the aforementioned positive electrode sheet, and preferably the thickness of the positive electrode sheet is 130-160 μm.

[0017] Furthermore, the electrolyte includes lithium salt and halide; the lithium salt is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, lithium hexafluorophosphate, phosphorus pentafluoride and hydrofluoric acid; the halide is 1 to 3% of the mass of the lithium salt in the electrolyte.

[0018] By applying the technical solution of this invention, the mixed conductive agent in this application is embedded in the cracks of the positive electrode material, which can enhance the lithium-ion insertion / extraction during battery charge-discharge cycles. Specifically, the mixed conductive agent contains halides. The interaction between the halogen anions and metal ions in the halides is weak, resulting in good lithium-ion conductivity. Secondly, the halogen ions have a large radius, which is beneficial for lithium-ion migration. Moreover, the halides have good stability in the electrolyte, facilitating the formation of stable and robust connections. At the same time, the halides dispersed in the cracks of the positive electrode material can fill and cover the cracked parts, thereby blocking the contact between the positive electrode material and the electrolyte, reducing the occurrence of side reactions, and thus improving the conductivity and safety of lithium ions, stabilizing the lithium-ion insertion / extraction during high-current charge-discharge cycles. Detailed Implementation

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

[0020] As analyzed in the background section, existing lithium-ion batteries suffer from the problem of balancing conductivity and safety. To address this issue, this application provides a positive electrode material composition, a positive electrode sheet, a method for preparing the same, and its applications.

[0021] In one typical embodiment of this application, a positive electrode material composition is provided. The positive electrode material composition includes a positive electrode material, a mixed conductive agent, and a binder. The positive electrode material has surface gaps, and at least part of the mixed conductive agent fills the surface gaps. The mixed conductive agent includes at least one halide and a conductive carbon material. The general formula of the halide is AX, where A is selected from one of the elements in group IA; X is a halogen; and the conductive carbon material is selected from one or more of carbon nanotubes (CNTs), acetylene black, and carbon black.

[0022] The hybrid conductive agent in this application, embedded in the cracks of the positive electrode material, can enhance the insertion and extraction of lithium ions during battery charge-discharge cycles. Specifically, the hybrid conductive agent contains halides. The interaction between the halogen anions and metal ions in the halides is weak, resulting in good lithium-ion conductivity. Secondly, the large radius of halogen ions facilitates lithium-ion migration. Moreover, the halides exhibit good stability in the electrolyte, facilitating the formation of stable and robust connections. Simultaneously, the halides dispersed in the cracks of the positive electrode material can fill and cover the cracked areas, thereby blocking contact between the positive electrode material and the electrolyte, reducing the occurrence of side reactions, and thus improving the conductivity and safety of lithium ions, stabilizing lithium-ion insertion and extraction during high-current charge-discharge cycles.

[0023] The aforementioned mixed conductive agent comprises at least two halides. When a mixture of at least two halides is used, the cycle life and rate discharge performance are significantly improved. Iodides are preferred as the halides. When the halides are iodides, the chemical bond strength of the formed lithium halide gradually changes with increasing halogen atomic number. The higher the halogen atomic number, the greater the covalent bond component of the halide with lithium atoms, resulting in a corresponding increase in its solubility in nonpolar solvents.

[0024] To effectively improve the conductivity of the positive electrode while avoiding excessive lithium-ion insertion / extraction paths due to excessive mixed conductive agents, which would affect charge / discharge efficiency, the mass ratio of halide to conductive carbon material in the mixed conductive agent is controlled at 3–5:100, and the mass ratio of positive electrode material to mixed conductive agent is 95.8:0.5–98.3:0.6. In some embodiments, the above-mentioned positive electrode material composition also includes optional activated carbon, with an activated carbon content of 0–1.5% in the positive electrode material composition. The use of activated carbon relatively reduces the specific capacity of the positive electrode material composition, but significantly improves the specific power and cycle performance, thus making it more suitable for high-power batteries.

[0025] The cathode material composition of this application has good applicability and can be used in commonly used lithium-ion battery cathode materials in the art. There are no particular limitations on the type of binder. Referring to commonly used binders in the art, in some embodiments, the cathode material is selected from one or more of ternary cathode materials, lithium manganese oxide (LMO), and lithium iron phosphate (LFP); the ternary cathode material can be NCM or NCA, and the binder is polyvinylidene fluoride and / or polyvinylidene fluoride.

[0026] In another typical embodiment of this application, a positive electrode sheet is provided, which includes a current collector and a positive electrode layer, the positive electrode layer comprising the aforementioned positive electrode material composition. Preferably, the thickness of the positive electrode sheet is 190–210 μm. The positive electrode sheet having the positive electrode material composition of this application has higher conductivity and safety, and more stable lithium-ion insertion / extraction during high-current charge-discharge cycles.

[0027] In another typical embodiment of this application, a method for preparing the above-mentioned positive electrode sheet is provided. The method includes: step S1, mixing materials containing positive electrode material, optional activated carbon, binder, conductive carbon material and halide to obtain positive electrode slurry; step S2, coating the positive electrode slurry onto a current collector and drying it to obtain a positive electrode sheet.

[0028] The preparation method of this application is simple. A uniform dispersion of conductive carbon material, halide, and cathode material is obtained through mixing. Then, in the cathode sheet prepared after drying, the mixed conductive agent is embedded in the cracks of the cathode material, which can enhance the lithium-ion insertion / extraction during battery charge-discharge cycles. Specifically, the mixed conductive agent contains halide. The interaction between the halide anions and metal ions in the halide is weak, resulting in good lithium-ion conductivity. Secondly, the large radius of halide ions is beneficial to lithium-ion migration. Moreover, the halide has good stability in the electrolyte, facilitating the formation of stable and strong connections. The halide dispersed in the cracks of the cathode material can fill and cover the cracked parts, thereby blocking the contact between the cathode material and the electrolyte, reducing the occurrence of side reactions, and thus improving the conductivity and safety of lithium ions, stabilizing lithium-ion insertion / extraction during high-current charge-discharge cycles. After mixing with the conductive carbon material, the halide can more easily enter the cracks of the spherical cathode material.

[0029] When activated carbon is used, it can improve specific power and cycle performance, so the resulting positive electrode sheet is suitable for high-power batteries.

[0030] To ensure thorough dispersion of the materials, in some embodiments, the mixing in step S1 is a first stirring mixture. This first stirring is carried out in a stirring device equipped with a stirring paddle and a dispersing disc, arranged side-by-side. The stirring paddle and dispersing disc revolve around the axis of the stirring device at a first speed, while the dispersing disc rotates horizontally at a second speed. Preferably, the first speed is 30–60 rpm, and the second speed is 1000–6000 rpm, preferably 4000–6000 rpm. The first stirring time is 1–4 hours, and the solid content of the positive electrode slurry is preferably 70%–80%. This application combines two stirring methods. The stirring paddle has a larger diameter, which can effectively mix and disperse the components, while the dispersing disc has a smaller diameter, allowing for rapid and uniform mixing of the components. Furthermore, the high-speed rotation of the dispersing disc impacts the positive electrode material, which is more conducive to forming cracks on the surface of the positive electrode material. Simultaneously, the conductive carbon material and halides enter the cracks in a filamentous manner under the action of the dispersing disc, better filling the cracks.

[0031] During the mixing process, depending on the fluidity of each component after mixing, the mixing speed can be increased when there is a large amount of dry material to avoid damage to the equipment.

[0032] When the conductive carbon material is carbon nanotubes (such as CNTs30N, CNTs40N), since carbon nanotubes are usually stored in solvents, such as N-methylpyrrolidone, N,N-dimethylformamide, or dimethyl sulfoxide, no additional solvent needs to be added when using carbon nanotubes as the conductive carbon material. When the conductive carbon material is acetylene black or carbon black, a solvent needs to be added in step S1. The solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide.

[0033] To ensure uniform dispersion of the conductive carbon material and halide, and to facilitate their co-filling within the gaps of the cathode material, in some embodiments, prior to step S1, the preparation method further includes a process of mixing the conductive carbon material, halide, and solvent to form a mixed conductive agent solution. The solvent used here is the same as described above.

[0034] In some embodiments, the mixing used to form the mixed conductive agent solution is a second stirring, which is carried out in a stirring device equipped with a stirring paddle and a dispersing disk arranged side by side. The stirring paddle and the dispersing disk revolve around the axis of the stirring device at a third speed, and the dispersing disk rotates horizontally at a fourth speed. Preferably, the third speed is 40-80 rpm and the fourth speed is 4000-10000 rpm. The second stirring time is 0.5-2 hours. During the second stirring process, the conductive carbon material and the halide can be fully mixed, which is beneficial for them to form filaments and then enter the cracks of the positive electrode material after subsequent incorporation.

[0035] In some embodiments, to ensure thorough mixing of the components, the positive electrode material NCM, the mixed conductive agent, activated carbon, and the binder PVDF are weighed in a mass ratio of 95.8:0.5:1.5:2.2. 50% of the total binder and 50% of the total solvent are mixed with the NCM and activated carbon and stirred to obtain a first slurry. The stirring speed is 30-40 rpm, the dispersion plate speed is 1000-3000 rpm, and the stirring time is 60-80 min. The first slurry and the mixed conductive agent are then mixed and stirred at a stirring speed of 40-50 rpm and a dispersion plate speed of 4000-5000 rpm for 60-80 min to obtain a second slurry. The remaining binder, the remaining solvent, and the second slurry are then mixed and stirred at a stirring speed of 50-60 rpm and a dispersion plate speed of 5000-6000 rpm for 60-80 min to obtain a positive electrode slurry. Finally, the positive electrode slurry is defoamed for 60 min.

[0036] To effectively improve the conductivity of the positive electrode sheet, while avoiding excessive mixing of conductive agents which would lead to excessively long lithium-ion insertion / extraction paths and affect charge / discharge efficiency, the mass ratio of positive electrode material, mixed conductive agent, optional activated carbon, and binder is controlled to be 95.8:0.5:1.5:2.2 to 98.3:0.6:0:1.1.

[0037] In another typical embodiment of this application, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises the aforementioned positive electrode sheet, preferably with a thickness of 130–160 μm. The lithium-ion battery of this application exhibits excellent charge-discharge cycle performance.

[0038] To prevent the shuttle effect of lithium ions between the positive and negative electrodes, the electrolyte includes a lithium salt and a halide; the lithium salt is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, lithium hexafluorophosphate, phosphorus pentafluoride, and hydrofluoric acid; the halide accounts for 1-3% of the mass of the lithium salt in the electrolyte. The halide in the electrolyte and the halide in the aforementioned positive electrode can be the same or different, but preferably the same.

[0039] 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.

[0040] Example 1

[0041] (1) Add anhydrous lithium iodide to CNT dispersion (where the dispersant is N-methylpyrrolidone) to obtain a mixed conductive agent solution. The mixed conductive agent is subjected to a second stirring and high-speed dispersion in a stirrer. The mixed conductive agent solution is then stored under vacuum. The mass of anhydrous lithium iodide is 3% of CNT, the third speed is 55 rpm, the fourth speed is 8000 rpm, and the second stirring time is 1 h.

[0042] (2) The positive electrode material NCM: mixed conductive agent: activated carbon: binder PVDF are stirred in a mass ratio of 95.8:0.5:1.5:2.2 to obtain a positive electrode slurry. The solid content of the positive electrode slurry is adjusted to 70% by controlling the amount of N-methylpyrrolidone. The first speed is 30 rpm, the second speed is 4000 rpm, and the first stirring time is 4h.

[0043] (3) The positive electrode slurry is coated on Al foil and rolled horizontally into the drying oven for drying. When the positive electrode slurry is coated on only one side of Al foil, the drying temperature is set to 90℃; when the positive electrode slurry is coated on the other side of Al foil, the temperature is set to 100℃ to obtain the positive electrode sheet with a thickness of 190μm~210μm. The positive electrode sheet is then vacuum stored.

[0044] (4) Mix artificial graphite (silicon suboxide doped): activated carbon: CMC: SBR in a mass ratio of 95.2:1.5:1.5:1.8 to obtain a negative electrode slurry; coat the negative electrode slurry on Cu foil and roll it horizontally into a drying oven for drying. When the negative electrode slurry is coated on only one side of Al foil, set the drying temperature to 55℃. When the negative electrode slurry is coated on the other side of Al foil, set the temperature to 70℃ to obtain a negative electrode sheet with a thickness of 150-200μm. Store the negative electrode sheet under vacuum.

[0045] (5) The above positive electrode and negative electrode are cold-pressed and then assembled with a polyolefin separator to form a battery cell. At this time, the thickness of the positive electrode is 130-160 μm and the thickness of the negative electrode is 90-140 μm.

[0046] (6) Under vacuum, anhydrous lithium iodide is added to the electrolyte. The main components of the electrolyte are 1M LiPF6, EC:DEC (1:1 vol%). The mass of anhydrous lithium iodide is 1% of the lithium salt in the electrolyte. After mixing evenly, the electrolyte is stored under vacuum to obtain the electrolyte. The electrolyte is then injected into the above-mentioned battery cell and sealed to obtain a lithium-ion battery.

[0047] Example 2

[0048] Unlike Example 1, the mass of anhydrous lithium iodide was 5% of CNTs.

[0049] Example 3

[0050] Unlike Example 1, the mass of anhydrous lithium iodide was 10% of CNTs.

[0051] Example 4

[0052] Unlike Example 1, the mass of anhydrous lithium iodide was 1% of CNTs.

[0053] Example 5

[0054] Unlike Example 1, in step (1), anhydrous lithium iodide, carbon black, and N-methylpyrrolidone are subjected to a second stirring and high-speed dispersion to obtain a mixed conductive agent solution.

[0055] Example 6

[0056] Unlike Example 1, in step (1), lithium bromide is added to CNT to obtain a mixed conductive agent solution.

[0057] Example 7

[0058] Unlike Example 1, in step (6), the mass of anhydrous lithium iodide in the electrolyte is 3% of the lithium salt in the electrolyte.

[0059] Example 8

[0060] Unlike Example 1, in step (6), the mass of anhydrous lithium iodide in the electrolyte is 6% of the lithium salt in the electrolyte.

[0061] Example 9

[0062] Unlike Example 1, in step (2), the positive electrode material NCM: mixed conductive agent: activated carbon: binder PVDF are mixed in a mass ratio of 98.3:0.6:0:1.1.

[0063] Example 10

[0064] Unlike Example 1, in step (2), the positive electrode material NCM: mixed conductive agent: activated carbon: binder PVDF are mixed in a mass ratio of 96.2:0.1:1.5:2.2.

[0065] Example 11

[0066] Unlike Example 1, in step (2), the positive electrode material NCM: mixed conductive agent: activated carbon: binder PVDF are mixed in a mass ratio of 95.5:0.8:1.5:2.2.

[0067] Example 12

[0068] (1) The positive electrode material NCM, anhydrous lithium iodide, CNT dispersion, activated carbon, and binder PVDF are mixed. The mass ratio of NCM, (anhydrous lithium iodide + CNT), activated carbon, and binder PVDF is 95.8:0.5:1.5:2.2. The mixture is stirred for the first time to obtain the positive electrode slurry. In the mixed conductive agent, the mass of anhydrous lithium iodide is 3% of that of CNT. During the first stirring, the first speed is increased from 40 rpm to 60 rpm at a rate of 10 rpm / h, and the second speed is increased from 0 rpm to 5000 rpm at a rate of 1000 rpm / h. After the first and second speeds are stable, the stirring time is maintained for 4 hours.

[0069] Example 13

[0070] Unlike Example 1, the first speed is 60 rpm and the second speed is 6000 rpm.

[0071] Example 14

[0072] Unlike Example 1, the second speed in the first stirring was 580 rpm.

[0073] Example 15

[0074] Unlike Example 1, the third speed is 40 rpm and the fourth speed is 4000 rpm.

[0075] Example 16

[0076] Unlike Example 1, the fourth speed is 3000 rpm.

[0077] Example 17

[0078] Unlike Example 1, no activated carbon is added in step (2).

[0079] Example 18

[0080] Unlike Example 1, in step (1), anhydrous sodium iodide and lithium bromide were mixed in a 1:1 ratio and added to the CNT dispersion instead of anhydrous lithium iodide.

[0081] Example 19

[0082] (1) Anhydrous lithium iodide was added to CNT dispersion (where the dispersant was N-methylpyrrolidone) to obtain a mixed conductive agent solution. The mixed conductive agent was subjected to a second stirring and high-speed dispersion in a stirrer. The mixed conductive agent solution was then stored under vacuum. The mass of anhydrous lithium iodide was 3% of that of CNTs. The third speed was 55 rpm, the fourth speed was 8000 rpm, and the second stirring time was 4 h.

[0083] (2) The positive electrode material NCM: mixed conductive agent: activated carbon: binder PVDF are stirred in a mass ratio of 95.8:0.5:1.5:2.2 to obtain a positive electrode slurry. The solid content of the positive electrode slurry is adjusted to 70% by controlling the amount of N-methylpyrrolidone. The first speed is 30 rpm, the second speed is 4000 rpm, and the first stirring time is 4h.

[0084] (3) The positive electrode slurry is coated on Al foil and rolled horizontally into the drying oven for drying. When the positive electrode slurry is coated on only one side of Al foil, the drying temperature is set to 90℃; when the positive electrode slurry is coated on the other side of Al foil, the temperature is set to 100℃ to obtain the positive electrode sheet with a thickness of 190μm~210μm. The positive electrode sheet is then vacuum stored.

[0085] (4) Mix artificial graphite (silicon suboxide doped): activated carbon: CMC: SBR in a mass ratio of 95.2:1.5:1.5:1.8 to obtain a negative electrode slurry; coat the negative electrode slurry on Cu foil and roll it horizontally into a drying oven for drying. When the negative electrode slurry is coated on only one side of Al foil, set the drying temperature to 55℃. When the negative electrode slurry is coated on the other side of Al foil, set the temperature to 70℃ to obtain a negative electrode sheet with a thickness of 150-200μm. Store the negative electrode sheet under vacuum.

[0086] (5) The above positive electrode and negative electrode are cold-pressed and then assembled with the separator to form a battery cell. At this time, the thickness of the positive electrode is 130-160 μm and the thickness of the negative electrode is 90-140 μm.

[0087] (6) The main components of the electrolyte are 1M LiPF6, EC:DEC (1:1 vol%). The electrolyte is injected into the above-mentioned cell and then sealed to obtain a lithium-ion battery.

[0088] The lithium-ion batteries prepared in Examples 1 to 19 were subjected to charging tests:

[0089] A. Precharge the battery at 0.05C for 3 minutes.

[0090] B. After standing for 10-24 hours, perform formation by charging at a constant current of 0.05C for 2 hours, at a constant current of 0.1C for 2 hours, and at a constant current of 0.2C for 3 hours.

[0091] C. After standing for 24-48 hours, perform the following steps: charge at 0.2C constant current and constant voltage for 3 hours to 4.2V, cut off current of 0.01C, discharge at 0.2C constant current to 2.5V, and charge at 0.5C constant current and constant voltage for 3 hours to 4.2V to perform capacity testing.

[0092] D. Perform charge-discharge cycles at 1C / 20A.

[0093] The test results are shown in Table 1. The capacity of the 18650 cylindrical battery discharged at standard 1C to 2.5V is 3100-3300mAh.

[0094] Example 20

[0095] (1) Add anhydrous lithium iodide to CNT to obtain a mixed conductive agent solution. The mixed conductive agent is subjected to a second stirring and high-speed dispersion in a stirrer. The mixed conductive agent solution is then stored under vacuum. The mass of anhydrous lithium iodide is 3% of CNT, the third speed is 55 rpm, the fourth speed is 8000 rpm, and the second stirring time is 1 h.

[0096] (2) The positive electrode material LFP, mixed conductive agent, activated carbon and binder are stirred in a mass ratio of 95.8:0.5:1.5:2.2 to obtain a positive electrode slurry with a solid content of 70%. The first speed is 30 rpm and the second speed is 4 h.

[0097] (3) The positive electrode slurry is coated on Al foil and rolled horizontally into the drying oven for drying. When the positive electrode slurry is coated on only one side of Al foil, the drying temperature is set to 90℃; when the positive electrode slurry is coated on the other side of Al foil, the temperature is set to 100℃ to obtain the positive electrode sheet with a thickness of 190μm~210μm. The positive electrode sheet is then vacuum preserved.

[0098] (4) Mix artificial graphite, activated carbon, CMC and SBR in a mass ratio of 95.2:1.5:1.5:1.8 to obtain a negative electrode slurry; coat the negative electrode slurry on Cu foil and roll it horizontally into a drying oven for drying. When the negative electrode slurry is coated on only one side of Al foil, set the drying temperature to 55℃. When the negative electrode slurry is coated on the other side of Al foil, set the temperature to 70℃ to obtain a negative electrode sheet with a thickness of 150-200μm. Store the negative electrode sheet under vacuum.

[0099] (5) The above positive electrode and negative electrode are cold-pressed and then assembled with the separator to form a battery cell. At this time, the thickness of the positive electrode is 130-160 μm and the thickness of the negative electrode is 90-140 μm.

[0100] (6) Under vacuum, anhydrous lithium iodide was added to the electrolyte at a mass of 1% of the lithium salt in the electrolyte. After mixing evenly, the mixture was stored under vacuum to obtain the electrolyte. The main components of the electrolyte were 1M LiPF6, EC:DEC (1:1 vol%). The electrolyte was injected into the above-mentioned battery cell and then sealed to obtain a lithium-ion battery.

[0101] Charging tests were performed on the aforementioned lithium-ion batteries:

[0102] A. Precharge the battery at 0.05C for 3 minutes.

[0103] B. After standing for 10-24 hours, perform formation by charging at a constant current of 0.05C for 2 hours, at a constant current of 0.1C for 2 hours, and at a constant current of 0.2C for 3 hours.

[0104] C. After standing for 24-48 hours, perform the following steps to divide the capacity: charge at 0.2C constant current and constant voltage for 3 hours to 3.65V, cut off current of 0.01C, discharge at 0.2C constant current to 2.0V, and charge at 0.5C constant current and constant voltage for 3 hours to 3.65V.

[0105] D. Perform charge-discharge cycles at 1C / 20A.

[0106] The test results are shown in Table 1. The capacity of the 18650 cylindrical battery discharged at standard 1C to 2.0V is 1800-2000mAh.

[0107] Comparative Example 1

[0108] (1) The positive electrode material NCM:CNT:activated carbon:binder was stirred in a mass ratio of 95.8:0.5:1.5:2.2 to obtain a positive electrode slurry; the speed of the stirring paddle in the first stirring was 30 rpm, the speed of the dispersion plate was 4000 rpm, and the stirring time was 4 h.

[0109] (2) The positive electrode slurry is coated on Al foil and rolled horizontally into the drying oven for drying. When the positive electrode slurry is coated on only one side of Al foil, the drying temperature is set to 90℃; when the positive electrode slurry is coated on the other side of Al foil, the temperature is set to 100℃ to obtain the positive electrode sheet with a thickness of 190μm~210μm. The positive electrode sheet is then vacuum stored.

[0110] (3) Mix artificial graphite (silicon suboxide doped): activated carbon: CMC: SBR in a mass ratio of 95.2:1.5:1.5:1.8 to obtain a negative electrode slurry; coat the negative electrode slurry on Cu foil and roll it horizontally into a drying oven for drying. When the negative electrode slurry is coated on only one side of Al foil, set the drying temperature to 55℃. When the negative electrode slurry is coated on the other side of Al foil, set the temperature to 70℃ to obtain a negative electrode sheet with a thickness of 150-200μm. Store the negative electrode sheet under vacuum.

[0111] (4) The above positive electrode and negative electrode are cold-pressed and then assembled with the separator to form a battery cell. At this time, the thickness of the positive electrode is 130-160 μm and the thickness of the negative electrode is 90-140 μm.

[0112] (5) Under vacuum, anhydrous lithium iodide was added to the lithium hexafluorophosphate electrolyte. The mass of the anhydrous lithium iodide was 1% of the lithium salt in the electrolyte. After mixing evenly, the electrolyte was stored under vacuum to obtain the electrolyte. The main components of the electrolyte were 1M LiPF6, EC:DEC (1:1 vol%). The electrolyte was injected into the above-mentioned battery cell and then sealed to obtain a lithium-ion battery.

[0113] The lithium-ion battery prepared in Comparative Example 1 was subjected to a charging test:

[0114] A. Precharge the battery at 0.05C for 3 minutes.

[0115] B. After standing for 10-24 hours, perform formation by charging at a constant current of 0.05C for 2 hours, at a constant current of 0.1C for 2 hours, and at a constant current of 0.2C for 3 hours.

[0116] C. After standing for 24-48 hours, perform the following steps: charge at 0.2C constant current and constant voltage for 3 hours to 4.2V, cut off current of 0.01C, discharge at 0.2C constant current to 2.5V, and charge at 0.5C constant current and constant voltage for 3 hours to 4.2V to perform capacity testing.

[0117] D. Perform charge-discharge cycles at 1C / 20A.

[0118] The test results are shown in Table 1.

[0119] Table 1

[0120]

[0121]

[0122] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: the mixed conductive agent in this application is embedded in the gaps of the positive electrode material bonding, which can enhance the lithium ion insertion / extraction during battery charge-discharge cycles. Specifically, the mixed conductive agent contains halides, and the interaction between the halogen anions and metal ions in the halides is weak, resulting in good lithium ion conductivity; secondly, the halogen ions have a large radius, which is beneficial to the migration of lithium ions; moreover, the halides have good stability in the electrolyte, which facilitates the formation of stable and firm connections; at the same time, the halides dispersed in the gaps of the positive electrode material can fill the cracked parts, thereby blocking the contact between the positive electrode material and the electrolyte, reducing the occurrence of side reactions, thereby improving the conductivity and safety of lithium ions, and stabilizing the lithium ion insertion / extraction during high-current charge-discharge cycles.

[0123] 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 positive electrode material composition, characterized in that, The positive electrode material composition includes a positive electrode material, a mixed conductive agent, and a binder. The positive electrode material has surface gaps, and at least a portion of the mixed conductive agent fills the surface gaps. The mixed conductive agent includes at least one halide and a conductive carbon material. The general formula of the halide is AX, where A is selected from one of the elements in group IA; X is a halogen; and the conductive carbon material is selected from one or more of carbon nanotubes and carbon black.

2. The cathode material composition according to claim 1, characterized in that, The mixed conductive agent comprises at least two halides.

3. The cathode material composition according to claim 2, characterized in that, The halide is an iodide.

4. The cathode material composition according to claim 1, characterized in that, The mass ratio of the halide to the conductive carbon material in the mixed conductive agent is 3~5:100, and the mass ratio of the positive electrode material to the mixed conductive agent is 95.8:0.5~98.3:0.

6.

5. The cathode material composition according to claim 4, characterized in that, The cathode material composition also includes activated carbon, and the activated carbon in the cathode material composition has a mass content of 0~1.5%.

6. The cathode material composition according to claim 1, characterized in that, The cathode material is selected from one or more of ternary cathode materials, lithium manganese oxide, and lithium iron phosphate.

7. The cathode material composition according to claim 6, characterized in that, The adhesive is polyvinylidene fluoride and / or polyvinylidene fluoride.

8. A positive electrode sheet, said positive electrode sheet comprising a current collector and a positive electrode layer, characterized in that, The positive electrode layer comprises the positive electrode material composition according to any one of claims 1 to 7.

9. The positive electrode sheet according to claim 8, characterized in that, The thickness of the positive electrode sheet is 190~210μm.

10. A method for preparing a positive electrode sheet as described in claim 8 or 9, characterized in that, The preparation method includes: Step S1: Mix the materials containing positive electrode material, binder, conductive carbon material and halide to obtain positive electrode slurry; Step S2: The positive electrode slurry is coated onto the current collector and dried to obtain the positive electrode sheet.

11. The preparation method according to claim 10, characterized in that, The material also includes activated carbon.

12. The preparation method according to claim 10 or 11, characterized in that, The mixing in step S1 is a first stirring mixing, which is carried out in a stirring device. The stirring device is equipped with a stirring paddle and a dispersing disk. The stirring paddle and the dispersing disk are arranged side by side. The stirring paddle and the dispersing disk revolve around the axis of the stirring device at a first speed, and the dispersing disk rotates on its own axis in the horizontal direction at a second speed.

13. The preparation method according to claim 12, characterized in that, The first speed is 30~60 rpm, the second speed is 1000~6000 rpm, and the first stirring time is 1~4 hours.

14. The preparation method according to claim 12, characterized in that, The solid content of the positive electrode slurry is 70%~80%.

15. The preparation method according to claim 10 or 11, characterized in that, The material in step S1 also includes a solvent, which is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide.

16. The preparation method according to claim 10 or 11, characterized in that, Prior to step S1, the preparation method further includes a process of mixing the conductive carbon material, the halide, and the solvent to form a mixed conductive agent solution.

17. The preparation method according to claim 16, characterized in that, The mixing used to form the mixed conductive agent solution is a second stirring, which is carried out in a stirring device. The stirring device is equipped with a stirring paddle and a dispersing disk. The stirring paddle and the dispersing disk are arranged side by side. The stirring paddle and the dispersing disk revolve around the axis of the stirring device at a third speed, and the dispersing disk rotates on its own axis in the horizontal direction at a fourth speed.

18. The preparation method according to claim 17, characterized in that, The third speed is 40~80 rpm, the fourth speed is 4000~10000 rpm, and the second stirring time is 0.5~2h.

19. The preparation method according to claim 11, characterized in that, The mass ratio of the positive electrode material, the mixed conductive agent, the activated carbon, and the binder is 95.8:0.5:1.5:2.2 to 98.3:0.6:0:1.

1.

20. A lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The positive electrode comprises the positive electrode sheet as described in claim 8 or 9.

21. The lithium-ion battery according to claim 20, characterized in that, The thickness of the positive electrode sheet is 130~160μm.

22. The lithium-ion battery according to claim 20, characterized in that, The electrolyte comprises lithium salt and halide; the lithium salt is selected from lithium hexafluorophosphate; the halide is 1 to 3% of the mass of the lithium salt in the electrolyte.

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