Positive electrode and lithium-ion battery

Abstract

The application provides a positive electrode sheet and a lithium ion battery. The positive electrode sheet comprises a current collector and a positive electrode active layer, and the material of the positive electrode active layer comprises lithium cobaltate, a positive electrode dispersant, a positive electrode conductive agent and a positive electrode binder; wherein the positive electrode dispersant comprises fluorinated acrylic rubber. The fluorinated acrylic rubber can provide good dispersion stability in the slurry process of the positive electrode material. In the charging and discharging process of the positive electrode sheet, the fluorinated acrylic rubber is not easy to decompose at high voltage. The presence of the fluorinated acrylic rubber not only helps to improve the dispersity of each component, but also helps to improve the high-voltage resistance of the positive electrode sheet. Moreover, the fluorine ion is inert by itself, and even if oxidation decomposition occurs, the formed fluorocarbon is difficult to be oxidized in one step, thereby helping to further reduce the risk of gas production.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and more specifically, to a positive electrode and a lithium-ion battery. Background Technology

[0002] Lithium cobalt oxide cathode materials, with their outstanding high compaction density, exhibit exceptional energy density. Their superior cycle life and safety performance have led to their widespread and dominant use in consumer product batteries. However, the increasing demand for longer battery life in portable devices necessitates further improvements in cell energy density without increasing cell size.

[0003] Lithium cobalt oxide with a charging cutoff voltage of 4.2V only achieves half of its theoretical capacity in practical applications (theoretical capacity 270mAh·g). -1 Only half of Li + This has been applied. Therefore, further increasing the cutoff voltage can improve Li + Utilization rate, meaning more electricity, is an effective way to increase the energy density of lithium cobalt oxide. However, with the development of Li... + The large-scale extraction of lithium cobalt oxide causes extensive collapse of the lithium cobalt oxide structure, thereby losing the ability to repeatedly insert and extract lithium, resulting in rapid capacity decay and low cycle life. Therefore, the application of high-voltage lithium-ion batteries with lithium cobalt oxide cathodes requires solving problems such as the structural stability of lithium cobalt oxide, oxygen defects, and cobalt dissolution under high voltage.

[0004] In addition, the negative electrode material of lithium-ion batteries can also determine the performance of high-voltage lithium-ion batteries; untreated graphite negative electrodes have poor lithium-ion migration kinetics and are prone to lithium plating during high-current charging, which poses a safety hazard; the low compaction and specific capacity of graphite negative electrodes cannot contribute to volumetric energy density.

[0005] This demonstrates that existing lithium-ion battery materials cannot meet the requirements for cycle life and charging speed of lithium-ion batteries at high voltages (≥4.48V). Therefore, improving existing lithium cobalt oxide cathode battery materials and enhancing the structural stability of lithium cobalt oxide under high voltage and long-cycle conditions to meet the demands of fast charging is of great significance. Summary of the Invention

[0006] The main objective of this application is to provide a positive electrode and a lithium-ion battery to solve the problem of poor high-voltage resistance in existing lithium-ion batteries.

[0007] To achieve the above objectives, according to one aspect of this application, a positive electrode sheet is provided, comprising a current collector and a positive electrode active layer, wherein the material of the positive electrode active layer comprises lithium cobalt oxide, a positive electrode dispersant, a positive electrode conductive agent, and a positive electrode binder; wherein the positive electrode dispersant comprises fluorinated acrylate rubber.

[0008] Furthermore, the above-mentioned positive electrode dispersant also includes hydrogenated nitrile butadiene rubber; further, the mass percentage of hydrogenated segments in the hydrogenated nitrile butadiene rubber is 3-9%; and / or, the mass percentage of fluorinated segments in the fluorinated acrylate rubber is 3-9%; and / or, the weight-average molecular weight of the hydrogenated nitrile butadiene rubber is 10,000-700,000 g / mol; and / or, the weight-average molecular weight of the fluorinated acrylate rubber is 5,000-200,000 g / mol.

[0009] Furthermore, the above-mentioned positive electrode dispersant is a combination of hydrogenated nitrile butadiene rubber and fluorinated acrylate rubber, and the mass ratio of hydrogenated nitrile butadiene rubber to fluorinated acrylate rubber is 1 to 20:1.

[0010] Furthermore, the mass ratio of the above-mentioned lithium cobalt oxide, positive electrode dispersant, positive electrode conductive agent, and positive electrode binder is (96-99):(0.01-0.1):(0.5-1.5):(0.5-1.5).

[0011] Further, the aforementioned lithium cobalt oxide is modified lithium cobalt oxide; further, the preparation method of modified lithium cobalt oxide includes: step S1, mixing raw materials including a first cobalt salt and a first aluminum salt and then sequentially performing a first co-precipitation and a first heat treatment to obtain a first aluminum-doped cobalt tetroxide; step S2, mixing raw materials including a second cobalt salt and a second aluminum salt and then sequentially performing a second co-precipitation and a second heat treatment to obtain a second aluminum-doped cobalt tetroxide; step S3, mixing raw materials including a first lithium source, the first aluminum-doped cobalt tetroxide, and a first additive... After mixing the raw materials, a first calcination is performed to obtain first lithium cobalt oxide; in step S4, the raw materials including a second lithium source, second aluminum-doped cobalt tetroxide, and a second additive are mixed and then subjected to a second calcination to obtain second lithium cobalt oxide; in step S5, the raw materials including first lithium cobalt oxide, second lithium cobalt oxide, and a third additive are mixed and then subjected to a third calcination to obtain modified lithium cobalt oxide; wherein, the median particle size of the first aluminum-doped cobalt tetroxide is 3-5 μm; and / or, the median particle size of the second aluminum-doped cobalt tetroxide is 15-18 μm.

[0012] Further, in step S1 above, the mass ratio of the first cobalt salt to the first aluminum salt is 1:0.005 to 0.015; and / or, the temperature of the first co-precipitation is 25 to 45°C; and / or, the time of the first co-precipitation is 10 to 18 hours; and / or, the temperature of the first heat treatment is 600 to 800°C; and / or, the time of the first heat treatment is 4 to 8 hours; and / or, in step S2, the mass ratio of the second cobalt salt to the second aluminum salt is 1:0.005 to 0.015; and / or, the temperature of the second co-precipitation is 25 to 45°C; and / or, the time of the second co-precipitation is 10 to 18 hours; and / or, the temperature of the second heat treatment is 600 to 800°C; and / or, the time of the second heat treatment is 3 to 6 hours.

[0013] Further, in step S3 above, the mass ratio of the first lithium source, the first aluminum-doped cobalt tetroxide, and the first additive is 1:(2.1~2.5):(0.005~0.01); and / or, the first calcination temperature is 700~1000℃; and / or, the first calcination time is 6~10h; and / or, in step S4, the mass ratio of the second lithium source, the second aluminum-doped cobalt tetroxide, and the second additive is 1:(2.1~2.5):(0.005~0.01); and / or, the second calcination temperature is 700~900℃; and / or, the second calcination time is 6~10h.

[0014] Further, in step S5 above, the mass ratio of the first lithium cobalt oxide, the second lithium cobalt oxide, and the third additive is 1:(0.2~0.3):(0.005~0.01); and / or, the third calcination temperature is 400~600℃; and / or, the third calcination time is 4~6h.

[0015] Further, the first additive and the second additive are each independently selected from any one or more of the first Mg source, the first Al source, the first Co source, the first Ti source, the first Zr source, the first Y source, and the first La source; and / or, the third additive is selected from any one or more of the second Mg source, the second Al source, the second Ti source, the second Zr source, the second Y source, the second La source, the P source, the F source, and the second Co source; further, the first additive is a combination of the first Mg source and the first Y source, and the mass ratio of the first Mg source to the first Y source is 1:0.1 to 0.5; and / or, the second additive is a combination of the first Co source and the first Ti source, and the mass ratio of the first Co source to the first Ti source is 1:0.1 to 1; and / or, the third additive is a combination of the second Al source and the F source, and the mass ratio of the second Al source to the F source is 1:0.1 to 1.

[0016] According to another aspect of this application, a lithium-ion battery is provided, comprising a positive electrode, an electrolyte, and a negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0017] By applying the technical solution of this application, fluorinated acrylate rubber can provide good dispersion stability during the slurry preparation process of the positive electrode material. During the charge and discharge process of the positive electrode sheet, the fluorinated acrylate rubber is not easily decomposed under high voltage. The presence of fluorinated acrylate rubber not only helps improve the dispersibility of each component but also helps improve the high voltage resistance of the positive electrode sheet. Furthermore, the inertness of fluoride ions means that even if oxidative decomposition occurs, the resulting fluorinated hydrocarbons are difficult to be oxidized in one step, thus further reducing the risk of gas generation. Therefore, the dispersant containing fluorinated acrylate rubber in the positive electrode sheet helps reduce the risk of dispersant decomposition and gas generation under high voltage, thereby improving the high voltage resistance of the positive electrode sheet and ultimately improving the safety and electrochemical performance of the battery under high voltage. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0019] As analyzed in the background section of this application, existing lithium-ion batteries have the problem of poor high-voltage resistance. In order to solve this problem, this application provides a positive electrode and a lithium-ion battery.

[0020] In a typical embodiment of this application, a positive electrode sheet is provided, including a current collector and a positive electrode active layer. The material of the positive electrode active layer includes lithium cobalt oxide, a positive electrode dispersant, a positive electrode conductive agent, and a positive electrode binder; wherein the positive electrode dispersant includes fluorinated acrylate rubber.

[0021] Fluorinated acrylate rubber provides excellent dispersion stability during the cathode material slurry preparation process. During charge-discharge of the cathode, fluorinated acrylate rubber is not easily decomposed at high voltages. The presence of fluorinated acrylate rubber not only helps improve the dispersibility of each component but also enhances the high-voltage resistance of the cathode. Furthermore, the inertness of fluoride ions means that even if oxidative decomposition occurs, the resulting fluorinated hydrocarbons are difficult to oxidize in one step, further reducing the risk of gas generation. Therefore, dispersants containing fluorinated acrylate rubber in the cathode help reduce the risk of dispersant decomposition and gas generation at high voltages, thereby improving the high-voltage resistance of the cathode and ultimately enhancing the safety and electrochemical performance of the battery at high voltages.

[0022] To further improve the high voltage resistance of the positive electrode, in one embodiment of this application, the positive electrode dispersant further includes hydrogenated nitrile butadiene rubber; in one embodiment of this application, the mass percentage of hydrogenated segments in the hydrogenated nitrile butadiene rubber is 3-9%; and / or, the mass percentage of fluorinated segments in the fluorinated acrylate rubber is 3-9%; and / or, the weight-average molecular weight of the hydrogenated nitrile butadiene rubber is 10,000-700,000 g / mol; and / or, the weight-average molecular weight of the fluorinated acrylate rubber is 5,000-200,000 g / mol.

[0023] The aforementioned hydrogenated nitrile butadiene rubber and fluorinated acrylate rubber can be purchased from Shenzhen Haodian Technology Co., Ltd. or Zeon Co., Ltd.

[0024] In one embodiment of this application, the above-mentioned positive electrode dispersant is a combination of hydrogenated nitrile butadiene rubber and fluorinated acrylate rubber, and the mass ratio of hydrogenated nitrile butadiene rubber to fluorinated acrylate rubber is 1 to 20:1.

[0025] Hydrogenated nitrile butadiene rubber (HNBR) and fluorinated acrylate rubber have different rheological properties. Controlling the mass ratio of HNBR to fluorinated acrylate rubber within the aforementioned range helps optimize the rheological properties of the slurry, ensuring better stability and uniformity during mixing and coating. Both HNBR and fluorinated acrylate rubber possess unique high-pressure resistance characteristics. HNBR reduces unsaturated double bonds and improves oxidative stability through hydrogenation; fluorinated acrylate rubber increases electronegativity and reduces double bond reactivity through fluorinated segments. Mixing them in the aforementioned ratio enhances their synergistic effect, thereby improving the stability of the dispersant under high-voltage conditions and reducing the risk of dispersant decomposition and gas generation.

[0026] In one embodiment of this application, the mass ratio of the lithium cobalt oxide, positive electrode dispersant, positive electrode conductive agent, and positive electrode binder is (96-99):(0.01-0.1):(0.5-1.5):(0.5-1.5).

[0027] Lithium cobalt oxide is the active component in cathode materials, responsible for the insertion and extraction of lithium ions during the battery's charging and discharging process. Excessive content of cathode dispersant, while improving the stability of the cathode slurry, can affect the migration rate of lithium ions; insufficient content of cathode dispersant fails to provide adequate dispersion, impacting coating quality. Controlling the mass ratio of lithium cobalt oxide, cathode dispersant, cathode conductive agent, and cathode binder within the aforementioned range helps improve the rate performance and cycle stability of the cathode sheet at high voltages.

[0028] In one embodiment of this application, the aforementioned lithium cobalt oxide is modified lithium cobalt oxide; in one embodiment of this application, the preparation method of modified lithium cobalt oxide includes: step S1, mixing raw materials including a first cobalt salt and a first aluminum salt and then sequentially performing a first co-precipitation and a first heat treatment to obtain a first aluminum-doped cobalt tetroxide; step S2, mixing raw materials including a second cobalt salt and a second aluminum salt and then sequentially performing a second co-precipitation and a second heat treatment to obtain a second aluminum-doped cobalt tetroxide; step S3, mixing raw materials including a first lithium source and the first aluminum-doped cobalt tetroxide... After mixing with the raw material containing the first additive, a first calcination is performed to obtain the first lithium cobalt oxide; in step S4, the raw material including the second lithium source, the second aluminum-doped cobalt tetroxide, and the second additive is mixed and then calcined to obtain the second lithium cobalt oxide; in step S5, the raw material including the first lithium cobalt oxide, the second lithium cobalt oxide, and the third additive is mixed and then calcined to obtain the modified lithium cobalt oxide; wherein, the median particle size of the first aluminum-doped cobalt tetroxide is 3-5 μm; and / or, the median particle size of the second aluminum-doped cobalt tetroxide is 15-18 μm.

[0029] Incorporating aluminum into the cobalt tetroxide precursor stage helps stabilize the layered structure of lithium cobalt oxide, reducing structural damage caused by the extensive lithium deintercalation and deintercalation at high voltages. Aluminum doping helps suppress irreversible phase transitions, improves the cycling stability of the material at high voltages, and reduces capacity decay and structural collapse. The addition of the first and second additives helps improve the structural stability of lithium cobalt oxide, promotes lithium cobalt oxide crystal growth, and enhances its conductivity. The addition of the third additive helps form a solid solution on the lithium cobalt oxide surface, repairing the surface, improving the structural stability of excessive delithiation at the lithium cobalt oxide interface, and reducing direct contact between the electrolyte and the cathode material. Controlling the median particle size of the first and second aluminum-doped cobalt tetroxide within the aforementioned ranges helps increase the compaction density of lithium cobalt oxide, thereby further improving the stability of the cathode sheet at high voltages.

[0030] In one embodiment of this application, in step S1, the mass ratio of the first cobalt salt to the first aluminum salt is 1:0.005 to 0.015; and / or, the temperature of the first co-precipitation is 25 to 45°C; and / or, the time of the first co-precipitation is 10 to 18 hours; and / or, the temperature of the first heat treatment is 600 to 800°C; and / or, the time of the first heat treatment is 4 to 8 hours; and / or, in step S2, the mass ratio of the second cobalt salt to the second aluminum salt is 1:0.005 to 0.015; and / or, the temperature of the second co-precipitation is 25 to 45°C; and / or, the time of the second co-precipitation is 10 to 18 hours; and / or, the temperature of the second heat treatment is 600 to 800°C; and / or, the time of the second heat treatment is 3 to 6 hours.

[0031] Controlling the mass ratio of the first cobalt salt to the first aluminum salt, and the mass ratio of the second cobalt salt to the second aluminum salt, within the aforementioned ranges helps control the amount of aluminum doping, thereby improving the structural stability of lithium cobalt oxide. Controlling the temperature and time of the first co-precipitation, and the temperature and time of the second co-precipitation, within the aforementioned ranges helps control the size of the aluminum-doped cobalt tetroxide within a suitable range, thereby improving the compaction density of lithium cobalt oxide. Controlling the temperature and time of the first heat treatment, and the temperature and time of the second heat treatment, within the aforementioned ranges helps improve the crystallinity of the aluminum-doped cobalt tetroxide, thereby improving the electrical conductivity of lithium cobalt oxide.

[0032] In one embodiment of this application, in step S3 above, the mass ratio of the first lithium source, the first aluminum-doped cobalt tetroxide, and the first additive is 1:(2.1~2.5):(0.005~0.01); and / or, the first calcination temperature is 700~1000℃; and / or, the first calcination time is 6~10h; and / or, in step S4, the mass ratio of the second lithium source, the second aluminum-doped cobalt tetroxide, and the second additive is 1:(2.1~2.5):(0.005~0.01); and / or, the second calcination temperature is 700~900℃; and / or, the second calcination time is 6~10h.

[0033] Controlling the mass ratios of the first lithium source, the first aluminum-doped cobalt tetroxide, and the first additive, as well as the mass ratios of the second lithium source, the second aluminum-doped cobalt tetroxide, and the second additive, within the aforementioned ranges helps to form lithium cobalt oxide with a stable structure and low impurity content. Excessively high calcination temperatures may lead to sintering of the material, affecting the lithium-ion migration channels; excessively low temperatures may prevent sufficient lithiation. Controlling the temperature and time of the first calcination, and the temperature and time of the second calcination, within the aforementioned ranges helps to improve the crystallinity of lithium cobalt oxide, thereby contributing to improved cycle stability of the cathode at high voltages.

[0034] In one embodiment of this application, step S3 further includes pulverizing and sieving the product after the first calcination to obtain a first lithium cobalt oxide with a median particle size of 16-18 μm.

[0035] In one embodiment of this application, step S4 further includes pulverizing and sieving the product after the second calcination to obtain a second lithium cobalt oxide with a median particle size of 3 to 5 μm.

[0036] In one embodiment of this application, in step S5 above, the mass ratio of the first lithium cobalt oxide, the second lithium cobalt oxide, and the third additive is 1:(0.2~0.3):(0.005~0.01); and / or, the third calcination temperature is 400~600℃; and / or, the third calcination time is 4~6h.

[0037] Controlling the mass ratio of the first lithium cobalt oxide, the second lithium cobalt oxide, and the third additive within the aforementioned range helps to form a composite modified layer, reduces direct contact between the electrolyte and the active material, suppresses side reactions, and simultaneously enhances lithium-ion migration kinetics, improving the material's conductivity and cycle life. Controlling the temperature and time of the third calcination within the aforementioned range helps to promote the chemical reaction between the third additive and the lithium cobalt oxide, forming a solid solution on the lithium cobalt oxide surface, which helps to improve the material's structure and electrochemical performance.

[0038] In one embodiment of this application, step S5 further includes pulverizing and sieving the product after the third calcination to obtain modified lithium cobalt oxide with a median particle size of 14-17 μm.

[0039] In one embodiment of this application, the first additive and the second additive are each independently selected from any one or more of the first Mg source, the first Al source, the first Co source, the first Ti source, the first Zr source, the first Y source, and the first La source; and / or, the third additive is selected from any one or more of the second Mg source, the second Al source, the second Ti source, the second Zr source, the second Y source, the second La source, the P source, the F source, and the second Co source; in one embodiment of this application, the first additive is a combination of the first Mg source and the first Y source, and the mass ratio of the first Mg source to the first Y source is 1:0.1 to 0.5; and / or, the second additive is a combination of the first Co source and the first Ti source, and the mass ratio of the first Co source to the first Ti source is 1:0.1 to 1; and / or, the third additive is a combination of the second Al source and the F source, and the mass ratio of the second Al source to the F source is 1:0.1 to 1.

[0040] Controlling the types of the first, second, and third additives within the aforementioned range helps to further improve the cycle stability of the cathode material under high voltage while enriching material selectivity. The first additive is a combination of a first Mg source and a first Y source. Mg and Y elements can form structures conducive to lithium-ion diffusion and electron transport during doping, and they also help stabilize the crystal structure of lithium cobalt oxide, suppressing harmful phase transitions and oxygen evolution under high voltage. The second additive is a combination of a first Co source and a first Ti source. Co elements can repair structural defects on the surface of lithium cobalt oxide and consume residual lithium on the surface, while the added Ti elements can inhibit further crystal growth of lithium cobalt oxide during secondary sintering. The third additive is a combination of a second Al source and a F source. The lower temperature of the third calcination makes it difficult for the surface-coated Al elements to diffuse into the inner layer, thus playing a stabilizing role on the surface structure. The presence of F elements replaces oxygen sites in lithium cobalt oxide, helping to suppress oxygen release during the phase transition process.

[0041] Including but not limited to, the first Mg source and the second Mg source are each independently selected from any one or more of MgO, MgF2 and Mg(OH)2;

[0042] Including but not limited to, the first Al source and the second Al source mentioned above are each independently Al2O3 and / or AlF3;

[0043] Including but not limited to, the first Ti source and the second Ti source mentioned above are each independently TiO2 and / or Ti2O3;

[0044] Including but not limited to, the first Zr source and the second Zr source are each independently selected from any one or more of ZrO2, Zr(OH)4 and ZrF4;

[0045] Including but not limited to, the first Y source and the second Y source mentioned above are each independently Y2O3;

[0046] Including but not limited to, the first La source and the second La source are each independently selected from any one or more of La2O3, La2(CO3)3, La(OH)3 and LaF3;

[0047] Including but not limited to, the above-mentioned P source is selected from any one or more of P2O3, NH4H2PO4 and (NH4)2HPO4;

[0048] Including but not limited to, the aforementioned F source is NH4HF2;

[0049] Including but not limited to, the first Co source and the second Co source mentioned above are each independently Co(OH)2 and / or Co3O4;

[0050] Including but not limited to, the first cobalt salt and the second cobalt salt are each independently selected from any one or more of Co(NO3)2, CoCl2 and CoSO4;

[0051] Including but not limited to, the first aluminum salt and the second aluminum salt are each independently selected from any one or more of Al(NO3)3, AlCl3 and Al2(SO4)3;

[0052] Including but not limited to, the first lithium source and the second lithium source mentioned above are each independently selected from any one or more of LiOH, Li2CO3, LiNO3 and CH3COOLi.

[0053] In another typical embodiment of this application, a lithium-ion battery is provided, including a positive electrode, an electrolyte, and a negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0054] Because the lithium-ion battery contains the positive electrode of this application, it has excellent cycle stability at high voltage.

[0055] In one embodiment of this application, the negative electrode sheet includes a current collector and a negative electrode active layer. The material of the negative electrode active layer includes a negative electrode active material, a negative electrode conductive agent, a negative electrode dispersant, and a negative electrode binder. In one embodiment of this application, the mass ratio of the negative electrode active material, the negative electrode conductive agent, the negative electrode dispersant, and the negative electrode binder is (95-99):(0.1-1.5):(0.5-1.5):(0.5-1.5).

[0056] Including but not limited to, the aforementioned negative electrode active material is carbon-coated graphite and / or silicon-based graphite; the negative electrode active material being carbon-coated graphite can meet the battery's fast charging capability; the negative electrode active material being silicon-based negative electrode graphite helps to further improve the battery's energy density.

[0057] Including but not limited to, the above-mentioned negative electrode dispersant is sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose;

[0058] Including but not limited to the aforementioned negative electrode binders, polystyrene butadiene and / or polyacrylic acid;

[0059] Including but not limited to, the positive electrode conductive agent and the negative electrode conductive agent mentioned above are each independently selected from any one or more of conductive carbon black, conductive graphite, carbon nanotubes and graphene.

[0060] The above-mentioned method for preparing lithium-ion batteries includes: Step 1: Weigh out the positive electrode binder according to the measured amount and dissolve it in N-methylpyrrolidone to prepare a positive electrode solution. Add measured amounts of lithium cobalt oxide, positive electrode dispersant, and positive electrode conductive agent to the positive electrode solution and stir to prepare a positive electrode slurry. Weigh out the negative electrode dispersant according to the measured amount and dissolve it in deionized water to prepare a negative electrode solution. Take 25% to 35% of the negative electrode solution and add measured amounts of negative electrode active material to knead it. Add the remaining negative electrode solution, negative electrode binder, and negative electrode conductive agent and stir to prepare a negative electrode slurry. Step 2: Coat the positive electrode slurry and negative electrode slurry evenly onto the positive electrode current collector and negative electrode current collector respectively according to the requirements of the coating structure. Roll press, slitting, tab welding, and adhesive bonding are performed to obtain positive electrode sheets and negative electrode sheets. The coating structure includes single-layer coating and double-layer coating. Step 3: The positive and negative electrode sheets are separated by a separator, stacked or wound to form a bare cell and packaged. After vacuum baking, electrolyte is injected, the cell is left to stand, formed under high temperature and pressure, sealed by vacuuming, capacity testing, and then tested to obtain a lithium-ion battery.

[0061] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0062] Example 1

[0063] 1) Preparation of modified lithium cobalt oxide:

[0064] In step S2, CoCl2 and AlCl3 are dissolved in deionized water at a mass ratio of 1:0.005 and subjected to a first co-precipitation and a first heat treatment. After crushing, a first aluminum-doped cobalt tetroxide with a median particle size of 3 μm is obtained. The first co-precipitation temperature is 25℃ and the first co-precipitation time is 18 h. The first heat treatment temperature is 600℃ and the first heat treatment time is 8 h. In step S3, CoCl2 and AlCl3 are dissolved in deionized water at a mass ratio of 1:0.005 and subjected to a second co-precipitation and a second heat treatment. After crushing, a second aluminum-doped cobalt tetroxide with a median particle size of 15 μm is obtained. The second co-precipitation temperature is 25℃ and the second co-precipitation time is 18 h. The second heat treatment temperature is 600℃ and the second heat treatment time is 6 h. In step S4, LiOH, the first aluminum-doped cobalt tetroxide, and a first additive are mixed and then subjected to a first calcination to obtain first lithium cobalt oxide. The first additive is MgO and Y2O3 in a mass ratio of 1:0.1. The mass ratio of LiOH, the first aluminum-doped cobalt tetroxide, and the first additive is 1:2.1:0.01. The first calcination temperature is 700℃, and the first calcination time is 10h. In step S4, Li2CO3, the second aluminum-doped cobalt tetroxide, and the second additive are mixed and then subjected to a second calcination to obtain the second lithium cobalt oxide. The second additive is Co(OH)2 and TiO2 in a mass ratio of 1:0.1. The ratio of the first lithium cobalt oxide to the second lithium cobalt oxide is 1:2.1:0.01, the second calcination temperature is 700℃, and the second calcination time is 10h; in step S5, the first lithium cobalt oxide, the second lithium cobalt oxide, and the third additive are mixed and then subjected to a third calcination to obtain modified lithium cobalt oxide. The third additive is Al2O3 and NH4HF2 in a mass ratio of 1:0.1. The mass ratio of the first lithium cobalt oxide, the second lithium cobalt oxide, and the third additive is 1:0.2:0.01. The third calcination temperature is 400℃, and the third calcination time is 6h.

[0065] 2) Preparation of the positive electrode:

[0066] The positive electrode binder was added to N-methylpyrrolidone and mixed to obtain a 7% (w / w) positive electrode binder solution. The modified lithium cobalt oxide, positive electrode conductive agent, and positive electrode dispersant were then added to the solution and stirred to obtain a positive electrode slurry. The mass ratio of the modified lithium cobalt oxide, positive electrode dispersant, positive electrode conductive agent, and positive electrode binder was 98:0.02:1.18:0.8. The dispersant consisted of hydrogenated nitrile butadiene rubber and fluorinated acrylate rubber from Shenzhen Haodian Technology Co., Ltd. The weight-average molecular weight of the hydrogenated nitrile butadiene rubber was 10000 g / mol, and the weight-average molecular weight of the fluorinated acrylate rubber was 5000 g / mol. The mass percentage of hydrogenated segments in the hydrogenated nitrile butadiene rubber was 6%, and the mass percentage of fluorinated segments in the fluorinated acrylate rubber was 6%. The mass ratio of hydrogenated nitrile butadiene rubber to fluorinated acrylate rubber was 10:1. The positive electrode conductive agent was conductive carbon black. The positive electrode slurry is evenly coated on both sides of the aluminum foil, and then baked, rolled, die-cut, tab welded, and glued to obtain the positive electrode sheet.

[0067] Example 2

[0068] The difference from Example 1 is that the mass percentage of hydrogenated segments in the hydrogenated nitrile rubber is 3%, and the mass percentage of fluorinated segments in the fluorinated acrylate rubber is 9%, ultimately yielding a positive electrode sheet.

[0069] Example 3

[0070] The difference from Example 1 is that the mass percentage of hydrogenated segments in the hydrogenated nitrile rubber is 9%, and the mass percentage of fluorinated segments in the fluorinated acrylate rubber is 3%, ultimately yielding a positive electrode sheet.

[0071] Example 4

[0072] The difference from Example 1 is that the mass percentage of hydrogenated segments in the hydrogenated nitrile rubber is 2%, and the mass percentage of fluorinated segments in the fluorinated acrylate rubber is 2%, ultimately yielding a positive electrode sheet.

[0073] Example 5

[0074] The difference from Example 1 is that the weight-average molecular weight of the hydrogenated nitrile rubber is 700,000 g / mol, and the weight-average molecular weight of the fluorinated acrylate rubber is 200,000 g / mol, ultimately yielding a positive electrode sheet.

[0075] Example 6

[0076] The difference from Example 1 is that the weight-average molecular weight of the hydrogenated nitrile rubber is 1,000,000 g / mol, and the weight-average molecular weight of the fluorinated acrylate rubber is 300,000 g / mol, ultimately yielding a positive electrode sheet.

[0077] Example 7

[0078] The difference from Example 1 is that the mass ratio of hydrogenated nitrile rubber to fluorinated acrylate rubber is 20:1, resulting in a positive electrode sheet.

[0079] Example 8

[0080] The difference from Example 1 is that the mass ratio of hydrogenated nitrile rubber and fluorinated acrylate rubber is 1:1, resulting in a positive electrode sheet.

[0081] Example 9

[0082] The difference from Example 1 is that hydrogenated nitrile rubber was omitted, resulting in a positive electrode sheet.

[0083] Example 10

[0084] The difference from Example 1 is that the mass ratio of modified lithium cobalt oxide, positive electrode dispersant, positive electrode conductive agent and positive electrode binder is 96:0.1:0.5:1.5, and the positive electrode sheet is finally obtained.

[0085] Example 11

[0086] The difference from Example 1 is that the mass ratio of modified lithium cobalt oxide, positive electrode dispersant, positive electrode conductive agent, and positive electrode binder is 99:0.01:1.5:0.5, and a positive electrode sheet is finally obtained.

[0087] Example 12

[0088] The difference from Example 1 is that the mass ratio of modified lithium cobalt oxide, positive electrode dispersant, positive electrode conductive agent, and positive electrode binder is 99:0.005:2:0.3, and a positive electrode sheet is finally obtained.

[0089] Example 13

[0090] The difference from Example 1 is that the mass ratio of LiOH, the first aluminum-doped cobalt tetroxide, and the first additive is 1:2.5:0.005, the mass ratio of Li2CO3, the second aluminum-doped cobalt tetroxide, and the second additive is 1:2.5:0.005, and the mass ratio of the first lithium cobalt oxide, the second lithium cobalt oxide, and the third additive is 1:0.3:0.005, thus obtaining the positive electrode sheet.

[0091] Example 14

[0092] The difference from Example 1 is that the mass ratio of LiOH, the first aluminum-doped cobalt tetroxide, and the first additive is 1:1.5:0.01, the mass ratio of Li2CO3, the second aluminum-doped cobalt tetroxide, and the second additive is 1:1.5:0.01, and the mass ratio of the first lithium cobalt oxide, the second lithium cobalt oxide, and the third additive is 1:1.5:0.01, thus obtaining the positive electrode sheet.

[0093] Example 15

[0094] The difference from Example 1 is that the first additive is MgO and Y2O3 in a mass ratio of 1:0.5, the second additive is Co(OH)2 and TiO2 in a mass ratio of 1:1, and the third additive is Al2O3 and NH4HF2 in a mass ratio of 1:1, and finally a positive electrode is obtained.

[0095] Example 16

[0096] The difference from Example 1 is that the first additive is MgO and Y2O3 in a mass ratio of 1:0.05, the second additive is Co(OH)2 and TiO2 in a mass ratio of 1:0.05, and the third additive is Al2O3 and NH4HF2 in a mass ratio of 1:0.05, and finally a positive electrode is obtained.

[0097] Comparative Example 1

[0098] The difference from Example 1 is that the positive electrode dispersant is polyvinylpyrrolidone, and the final positive electrode sheet is obtained.

[0099] Preparation of negative electrode:

[0100] The mass ratio of carbon-coated graphite, graphene, sodium carboxymethyl cellulose, and polystyrene butadiene is 97:0.4:1.1:1.5. Sodium carboxymethyl cellulose is dispersed in deionized water to form a slurry. Carbon-coated graphite and graphene are added to the slurry and stirred. Then, sodium carboxymethyl cellulose is added to obtain the negative electrode slurry. The negative electrode slurry is uniformly coated on both sides of a copper foil, and after baking, rolling, die-cutting, tab welding, and adhesive bonding, the negative electrode sheet is obtained.

[0101] Battery manufacturing:

[0102] The positive electrode, separator, and negative electrode prepared in the examples and comparative examples are stacked in sequence to obtain a bare cell. The cell is then packaged in an aluminum-plastic film of suitable size, baked, injected with electrolyte, and subjected to high-temperature and high-pressure formation, vacuum sealing, and capacity testing to obtain a high-voltage lithium cobalt oxide battery.

[0103] Performance testing

[0104] Capacity retention after 500 cycles at 45°C: After placing the battery in a 45°C oven for 2 hours, perform the following charge-discharge cycles for 500 cycles: charge at 1C constant current to 4.53V, stop at 0.05C constant voltage; rest for 10 minutes; discharge at 0.7C to 3.0V, and rest for 10 minutes.

[0105] Cobalt leaching from the negative electrode after 500 cycles at 45℃: The negative electrode sheet was removed from the battery after 500 cycles and baked in an oven at 45℃ for 6 hours. The baked electrode sheet was then processed using a circular stamping machine to achieve a fixed area of ​​5.02 cm². 2The wafers were punched, weighed, and then acid-digested and diluted to the cobalt working curve range of 10ppm to 2000ppm before ICP-OES determination of the cobalt content. This value represents the cobalt content dissolved from the positive electrode to the negative electrode.

[0106] The capacity retention rate and cobalt dissolution of the negative electrode of the lithium cobalt oxide battery prepared above were tested after 500 cycles at 45℃. The test results are shown in Table 1.

[0107] Table 1

[0108]

[0109]

[0110] As can be seen from the above description, the embodiments of this application achieve the following technical effects:

[0111] Fluorinated acrylate rubber provides excellent dispersion stability during the cathode material slurry preparation process. During charge-discharge of the cathode, fluorinated acrylate rubber is not easily decomposed at high voltages. The presence of fluorinated acrylate rubber not only helps improve the dispersibility of each component but also enhances the high-voltage resistance of the cathode. Furthermore, the inertness of fluoride ions means that even if oxidative decomposition occurs, the resulting fluorinated hydrocarbons are difficult to oxidize in one step, further reducing the risk of gas generation. Therefore, dispersants containing fluorinated acrylate rubber in the cathode help reduce the risk of dispersant decomposition and gas generation at high voltages, thereby improving the high-voltage resistance of the cathode and ultimately enhancing the safety and electrochemical performance of the battery at high voltages.

[0112] The above are merely embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode sheet comprising a current collector and a positive electrode active layer, characterized by, The material of the positive electrode active layer comprises lithium cobaltate, a positive electrode dispersant, a positive electrode conductive agent and a positive electrode binder; wherein the positive electrode dispersant comprises fluorinated acrylate rubber; the positive electrode dispersant further comprises hydrogenated nitrile rubber, and the mass percentage of hydrogenated segments in the hydrogenated nitrile rubber is 3-9%.

2. The positive electrode sheet according to claim 1, characterized by The mass percentage of fluorinated segments in the fluorinated acrylate rubber is 3-9%; and / or, the weight average molecular weight of the hydrogenated nitrile rubber is 10000-700000 g / mol; and / or, the weight average molecular weight of the fluorinated acrylate rubber is 5000-200000 g / mol.

3. The positive electrode sheet according to claim 2, characterized by The positive electrode dispersant is a combination of the hydrogenated nitrile rubber and the fluorinated acrylate rubber, and the mass ratio of the hydrogenated nitrile rubber to the fluorinated acrylate rubber is 1-20:

1.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized by, The mass ratio of the lithium cobaltate, the positive electrode dispersant, the positive electrode conductive agent and the positive electrode binder is (96-99):(0.01-0.1):(0.5-1.5):(0.5-1.5).

5. The positive electrode sheet according to any one of claims 1 to 3, characterized by The lithium cobaltate is modified lithium cobaltate; The preparation method of the modified lithium cobaltate comprises: Step S1, mixing raw materials comprising a first cobalt salt and a first aluminum salt, and then sequentially performing first co-precipitation and first heat treatment to obtain first aluminum-doped tricobalt tetroxide; Step S2, mixing raw materials comprising a second cobalt salt and a second aluminum salt, and then sequentially performing second co-precipitation and second heat treatment to obtain second aluminum-doped tricobalt tetroxide; Step S3, mixing raw materials comprising a first lithium source, first aluminum-doped tricobalt tetroxide and a first additive, and then performing first calcination to obtain first lithium cobaltate; Step S4, mixing raw materials comprising a second lithium source, second aluminum-doped tricobalt tetroxide and a second additive, and then performing second calcination to obtain second lithium cobaltate; Step S5, mixing raw materials comprising first lithium cobaltate, second lithium cobaltate and a third additive, and then performing third calcination to obtain modified lithium cobaltate; In the step S1, the mass ratio of the first cobalt salt to the first aluminum salt is 1:0.005-0.015; and / or, the temperature of the first co-precipitation is 25-45℃; and / or, the time of the first co-precipitation is 10-18h; and / or, the temperature of the first heat treatment is 600-800℃; and / or, the time of the first heat treatment is 4-8h; 6. The positive electrode sheet according to claim 5, characterized by In the step S2, the mass ratio of the second cobalt salt to the second aluminum salt is 1:0.005-0.015; and / or, the temperature of the second co-precipitation is 25-45℃; and / or, the time of the second co-precipitation is 10-18h; and / or, the temperature of the second heat treatment is 600-800℃; and / or, the time of the second heat treatment is 3-6h. ​ 7. The positive electrode sheet according to claim 5, characterized by In the step S3, the mass ratio of the first lithium source, the first aluminum-doped cobalt oxide and the first additive is 1:(2.1-2.5):(0.005-0.01); and / or, the temperature of the first calcination is 700-1000℃; and / or, the time of the first calcination is 6-10h. In the step S4, the mass ratio of the second lithium source, the second aluminum-doped cobalt oxide and the second additive is 1:(2.1-2.5):(0.005-0.01); and / or, the temperature of the second calcination is 700-900℃; and / or, the time of the second calcination is 6-10h.

8. The positive electrode sheet according to claim 5, characterized by In the step S5, the mass ratio of the first lithium cobalt oxide, the second lithium cobalt oxide and the third additive is 1:(0.2-0.3):(0.005-0.01); and / or, the temperature of the third calcination is 400-600℃; and / or, the time of the third calcination is 4-6h.

9. The positive electrode sheet according to claim 5, characterized by The first additive and the second additive are each independently selected from any one or more of a first Mg source, a first Al source, a first Co source, a first Ti source, a first Zr source, a first Y source and a first La source; The third additive is selected from any one or more of a second Mg source, a second Al source, a second Ti source, a second Zr source, a second Y source, a second La source, a P source, a F source and a second Co source.

10. The positive electrode sheet according to claim 9, characterized by The first additive is a combination of the first Mg source and the first Y source, and the mass ratio of the first Mg source and the first Y source is 1:0.1-0.5; The second additive is a combination of the first Co source and the first Ti source, and the mass ratio of the first Co source and the first Ti source is 1:0.1-1; The third additive is a combination of the second Al source and the F source, and the mass ratio of the second Al source and the F source is 1:0.1-1.

11. A lithium-ion battery comprising a positive electrode sheet, an electrolyte, and a negative electrode sheet, characterized by, The positive electrode sheet is the positive electrode sheet of any one of claims 1-10.

Images