Modified conductive carbon, slurry, positive electrode, battery, and method for manufacturing the same

Abstract

The application provides a modified conductive carbon, a slurry, a positive electrode, a battery and a preparation method thereof, the modified conductive carbon, wherein 0.05wt%-0.1wt% of F elements are doped. Compared with unmodified conductive carbon, the modified conductive carbon has an open pore structure. The modified conductive carbon is prepared by fluorination treatment of graphene oxide with sodium 2,2,3,3-tetrafluoropropionate as a fluorine source and phosphoric acid immersion treatment. The application improves the problem of water introduction in the positive electrode slurry, can stabilize the viscosity of the positive electrode slurry in air, and improves the electrical properties such as the resistance, charge and discharge life of the battery, and improves the chemical stability of the positive electrode slurry of the sodium ion battery in air.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to a modified conductive carbon, a slurry, a positive electrode, a battery, and a method for preparing the same. Background Technology

[0002] Because the layered oxides and polyanions in sodium-ion cathode materials are micron- or nano-sized solids, they readily absorb moisture from the air. Water acts as a bridge, causing the cathode material to react with carbon dioxide (CO2) and oxygen (O2) in the air, leading to acidification and oxidation failures and the production of residual alkali. This further increases the pH value of the slurry, causing a sharp increase in the viscosity of the cathode slurry, even gelling. Specifically, in acidification failure, the presence of CO2 alters the Na... + / H + The balance of exchange leads to the formation of NaHCO3 or Na2CO3. Figure 1 a); In oxidative degradation, when O2 and H2O coexist, low-valence transition metals (such as Ni) are activated. 2+ ) oxidized to a higher oxidation state (Ni) 4+ High-valence nickel is unstable and readily undergoes a reduction reaction with H2O on its surface, leading to the release of lattice oxygen and surface reconstruction into rock salt phase NiO; the coexisting H2O and O2 generate OH- through the oxidation of transition metal ions in the layered oxides. - ( Figure 1 b); In addition, the free basic groups -OH in the slurry attack the CH and CF bonds of the binder polyvinylidene fluoride (PVDF), causing an elimination reaction to form C=C and HF. The C=C double bonds produce chemical cross-links. Due to the high regularity of the PVDF polymer chain, continuous elimination reactions easily occur, eventually leading to gelation ( Figure 1 c). HF corrodes the transition metal ions at the interface between the positive electrode and the electrolyte, causing these ions to dissolve into the electrolyte and deposit in the membrane. In severe cases, this can turn the membrane surface pale yellow, ultimately hindering normal ion transport. Furthermore, the organic reagent N-methylpyrrolidone (NMP) used in the homogenization process contains polar amide groups (O=CN) in its molecular structure. Due to the principle of "like dissolves like," it readily absorbs water and forms hydrogen bonds. Excessive water content in the solvent also reduces the solubility of the positive electrode binder, polyvinylidene fluoride (PVDF), causing the slurry to gel and form a jelly-like consistency, which is detrimental to the viscosity stability of the positive electrode slurry.

[0003] The adverse effects of water can lead to the leaching of transition metal ions, deactivation of active materials, increased pH and decreased fluidity of the slurry, and subsequent slurry gelation, making coating and processing difficult, resulting in decreased cathode capacity and battery performance. Transition metal ions are oxidized to a highly oxidized state, and lattice oxygen loses its cation barrier and repulses, resulting in both exhibiting high surface activity. This easily triggers surface structure rearrangement, leading to problems such as transition metal dissolution and oxygen evolution. Simultaneously, optimizing the composition of the cathode interface film, enriching it with inorganic compounds like NaF to enhance its thermal stability and density, is crucial. Without stable CEI protection on the cathode surface, these side reactions will be further accelerated. Dissolved metal ions and released oxygen will further oxidize the electrolyte, participating in its decomposition reaction and causing irreversible damage to the cathode. This process continues, leading to deterioration of material performance. In existing technologies, adding acid to the electrode slurry is a feasible method to suppress gelation problems. Many weak acids have been developed, such as anhydrous oxalic acid and citric acid. However, directly adding phosphoric acid to oil-based cathodes has not been attempted, possibly because the preparation process of solid phosphoric acid is complex and not cost-effective. Therefore, most commercially available products are 85% phosphoric acid solutions. If an 85% phosphoric acid solution is added directly to the cathode slurry, the PVDF cathode adhesive will directly absorb water and swell, causing the cathode slurry to immediately lose its adhesiveness.

[0004] Based on this, it is necessary to propose a modified conductive carbon, slurry, positive electrode, battery and its preparation method to solve the problems existing in the prior art. Summary of the Invention

[0005] In order to improve the introduction of water into the positive electrode slurry, stabilize the viscosity of the positive electrode slurry in the air, and improve the electrical performance of the battery such as resistance and charge-discharge life, this invention provides a modified conductive carbon, slurry, positive electrode, battery and its preparation method, so as to improve the chemical stability of the positive electrode slurry of sodium-ion battery in air.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] In a first aspect, a modified conductive carbon is provided, wherein 0.05 wt% to 0.1 wt% of element F is doped. In some embodiments, the modified conductive carbon is doped with 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, or 0.1 wt% of element F.

[0008] In some embodiments, the modified conductive carbon has an open pore structure compared to unmodified conductive carbon.

[0009] In some embodiments, the modified conductive carbon is prepared by fluorinating graphene oxide with sodium 2,2,3,3-tetrafluoropropionate as a fluorine source, followed by immersion in phosphoric acid.

[0010] In some embodiments, the fluorination treatment refers to hydrothermal fluorination treatment or heating annealing fluorination treatment.

[0011] In some embodiments, the preparation process of the modified conductive carbon specifically includes:

[0012] Step a1: Graphene oxide is coated onto a foil to form a graphene oxide film;

[0013] Step a2: After pretreatment by immersing the graphene oxide film in an aqueous solution of sodium 2,2,3,3-tetrafluoropropionate, the graphene oxide film is obtained by hydrothermal fluorination, washing, and drying.

[0014] Step a3: The fluorinated graphene oxide film is immersed in a phosphoric acid solution for immersion treatment, washed, vacuum dried, and the modified conductive carbon is scraped off from the foil to obtain the modified conductive carbon.

[0015] In some embodiments, the graphene oxide film preparation process is as follows:

[0016] (1) Graphene oxide was dispersed in deionized water and ultrasonically treated to obtain a graphene oxide suspension;

[0017] (2) A graphene oxide suspension is coated onto a foil and dried to obtain a graphene oxide film.

[0018] In some embodiments, the preparation process of the modified conductive carbon specifically includes:

[0019] Step b1: Graphene oxide and sodium 2,2,3,3-tetrafluoropropionate are mixed and ground to obtain a solid mixture;

[0020] Step b2: Place the solid mixture in an inert atmosphere, heat and anneal for fluorination, and then wash and dry to obtain fluorinated graphene oxide;

[0021] Step b3: Fluorinated graphene oxide is immersed in phosphoric acid solution, washed, and dried to obtain modified conductive carbon.

[0022] In some embodiments, the graphene oxide is used after pretreatment. The pretreatment process is as follows: the graphene oxide is immersed in anhydrous ethanol and ultrasonically treated, then rinsed with water and dried to complete the pretreatment.

[0023] In some embodiments, the foil is at least one selected from aluminum foil, tin foil, composite aluminum foil, and copper foil. The thickness of the foil can be any one of 10µm, 12µm, and 16µm.

[0024] In some embodiments, the drying temperature is 40~70℃, and the drying time is 4~10h. Preferably, the drying temperature is any one of 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, or any two of the above values. Preferably, the drying time is any one of 4h, 5h, 6h, 7h, 8h, 9h, 10h, or any two of the above values.

[0025] In some embodiments, the vacuum drying temperature is 90~110℃, and the vacuum drying time is 15~20h. Preferably, the drying temperature is any one of 90℃, 95℃, 100℃, 105℃, 110℃, or any two of the above values. Preferably, the vacuum drying time is any one of 15h, 16h, 17h, 18h, 19h, 20h, or any two of the above values.

[0026] In some embodiments, the concentration of the graphene oxide suspension is 30-60 mg / mL. Preferably, the concentration of the graphene oxide suspension is any one of the following ranges: 30 mg / mL, 35 mg / mL, 40 mg / mL, 45 mg / mL, 50 mg / mL, 55 mg / mL, 60 mg / mL, or any two of the above values.

[0027] In some embodiments, the concentration of the sodium 2,2,3,3-tetrafluoropropionate aqueous solution is 10-20 mg / mL. Preferably, the concentration is 10 mg / mL, 15 mg / mL, 20 mg / mL, or any two of the above values ​​forming any one of the ranges.

[0028] In some embodiments, the preprocessing time in step a2 is 1 to 3 hours, preferably any one of the ranges of 1 hour, 2 hours, 3 hours, or any two of the above values.

[0029] In some embodiments, in step a2, the hydrothermal fluorination is maintained at 160~200℃ for 12~24h. Preferably, the temperature of the hydrothermal fluorination is any one of the following ranges: 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, or any two of the above values. Preferably, the time of the hydrothermal fluorination is any one of the following ranges: 12h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 22h, 24h, or any two of the above values.

[0030] In some embodiments, the mass fraction of the phosphoric acid solution is 50-85%. Preferably, the mass fraction of the phosphoric acid solution is any one of the following ranges: 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, and any two of the above values.

[0031] In some embodiments, in step a3, the volume ratio of the fluorinated graphene oxide film to the phosphoric acid solution is 1:(3~10), preferably 1:2, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, or any two of the above values ​​forming a range.

[0032] In some embodiments, the soaking time in the phosphoric acid solution is 3 to 10 days, preferably any one of the following ranges: 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 9 days, 10 days, or any two of the above values.

[0033] In some embodiments, in step b1, the mass ratio of graphene oxide to sodium 2,2,3,3-tetrafluoropropionate is (8~12):1, preferably 8:1, 9:1, 10:1, 11:1, 12:1, or any two of the above values ​​forming a range.

[0034] In some embodiments, during step b2, the fluorination process involves heating to 100-600°C for pyrolysis for 20-60 minutes. After annealing, the device is removed when the displayed temperature is no greater than 50°C. Preferably, the pyrolysis temperature is any one of the following ranges: 160°C, 100°C, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, or any two of these values. Preferably, the pyrolysis time is any one of the following ranges: 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, or any two of these values.

[0035] In some embodiments, in step b3, the volume ratio of the fluorinated graphene oxide to the phosphoric acid solution is 1:3 to 1:10, preferably 1:2, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, or any two of the above values ​​forming a range.

[0036] In a second aspect, a slurry is provided, comprising the modified conductive carbon described in this invention.

[0037] In some embodiments, the slurry includes a positive electrode carbon layer functional layer slurry, a positive electrode colloidal carbon functional layer slurry, or a positive electrode active layer slurry.

[0038] In some embodiments, the preparation process of the positive electrode adhesive carbon functional layer slurry is as follows: PVDF is dissolved in NMP to prepare an adhesive solution; the modified conductive carbon of the present invention is added to obtain the adhesive solution.

[0039] In some embodiments, the mass fraction concentration of modified conductive carbon in the positive electrode adhesive carbon functional layer slurry is 20-40%. Preferably, the mass fraction concentration of modified conductive carbon in the positive electrode adhesive carbon functional layer slurry is any one of 20%, 25%, 30%, 35%, 40%, or any two of the above values.

[0040] In some embodiments, the preparation process of the positive electrode carbon layer functional layer slurry is as follows: the modified conductive carbon of the present invention is added to an aqueous ethanol solution.

[0041] In some embodiments, the mass fraction concentration of modified conductive carbon in the positive electrode carbon layer functional layer slurry is 20-40%. Preferably, the mass fraction concentration of modified conductive carbon in the positive electrode carbon layer functional layer slurry is any one of 20%, 25%, 30%, 35%, 40%, or any two of the above values.

[0042] In some embodiments, the positive electrode active layer slurry includes a positive electrode active material, the modified conductive carbon described in this invention, and a binder.

[0043] In some embodiments, the positive electrode active layer slurry comprises, by weight percentage, 94-96% positive electrode active material, 1-8% of the modified conductive carbon of the present invention, and 1-6% binder.

[0044] In some embodiments, the positive electrode active layer slurry comprises, by weight percentage, 95% positive electrode active material, 2.5% modified conductive carbon as described in this invention, and 2.5% binder.

[0045] In some embodiments, the positive electrode active material is one of O3-type layered oxide, P2-type layered oxide, or phosphate-based polyanions.

[0046] In some embodiments, the adhesive is either PVDF or sodium alginate.

[0047] Thirdly, a positive electrode sheet is provided, comprising the slurry described in this invention or the modified conductive carbon described in this invention.

[0048] In some embodiments, the positive electrode sheet includes a positive electrode functional layer containing the modified conductive carbon of the present invention and a positive electrode active layer containing the modified conductive carbon of the present invention.

[0049] The positive electrode functional layer is selected from the positive electrode liquid carbon functional layer or the positive electrode carbon layer functional layer.

[0050] In some embodiments, the preparation process of the slurry for the positive electrode adhesive carbon functional layer is as follows: PVDF is dissolved in NMP to prepare an adhesive solution; the modified conductive carbon described in this invention is added to obtain the slurry.

[0051] In some embodiments, the mass fraction concentration of modified conductive carbon in the slurry of the positive electrode adhesive carbon functional layer is 20-40%. Preferably, the mass fraction concentration of modified conductive carbon in the slurry of the positive electrode adhesive carbon functional layer is any one of 20%, 25%, 30%, 35%, 40%, or any two of the above values.

[0052] In some embodiments, the slurry preparation process of the positive electrode carbon layer functional layer is as follows: the modified conductive carbon of the present invention is added to an aqueous ethanol solution.

[0053] In some embodiments, the mass fraction concentration of modified conductive carbon in the slurry of the positive electrode carbon layer functional layer is 20-40%. Preferably, the mass fraction concentration of modified conductive carbon in the slurry of the positive electrode carbon layer functional layer is any one of 20%, 25%, 30%, 35%, 40%, or any two of the above values.

[0054] Fourthly, a method for preparing a positive electrode sheet is provided, comprising: coating a positive electrode functional layer slurry onto a current collector, drying it, coating a positive electrode active layer slurry, and drying it to obtain a positive electrode sheet.

[0055] In some embodiments, a positive electrode functional layer slurry is coated onto one surface of a current collector; after drying, a positive electrode active layer slurry is coated onto the positive electrode functional layer, and then dried to obtain a positive electrode sheet. This is manifested in that the positive electrode coating is divided into a primary coating and a secondary coating; the primary coating forms the positive electrode functional layer, and the secondary coating forms the positive electrode active layer.

[0056] Fifthly, a battery is provided, comprising the positive electrode sheet described in this invention.

[0057] In some embodiments, "room temperature" refers to room temperature of 10~40℃, preferably 20~30℃ or 25℃.

[0058] Compared with the prior art, one of the above technical solutions has the following advantages or beneficial effects:

[0059] The modified conductive carbon provided by this invention is an F-doped nanoscale conductive carbon treated with phosphoric acid solution. Because F has the strongest electronegativity and stable electrochemical properties, it can replace some O2. -The provided slurry not only resists the formation of residual alkali but also reduces the introduction of water from the air, thereby stabilizing the viscosity of the cathode slurry in the air to facilitate subsequent coating processes. It also improves the battery's cycle life and reduces its DC internal resistance. This cathode slurry preparation method provides valuable insights for industrial production. Attached Figure Description

[0060] Figure 1 This diagram illustrates the failure principle of the positive electrode slurry in air. Reaction (a) represents the acidification failure of the layered oxides; reaction (b) represents the oxidative degradation failure of the layered oxides; and (c) represents the PVDF gel failure.

[0061] Figure 2 This is a diagram illustrating the preparation process of the positive electrode sheet in this application. (a) shows a single coating; (b) a double coating, where the first layer is the positive electrode adhesive carbon functional layer and the second layer is the positive electrode active layer; and (c) a double coating, where the first layer is the positive electrode carbon functional layer and the second layer is the positive electrode active layer.

[0062] Figure 3 The images show scanning electron microscope (SEM) images of different conductive carbon samples in Example 1. (a) GO sample; (b) GO-1 sample; (c) GO-2 sample.

[0063] Figure 4 The images show the EDS elemental mappings of different conductive carbon samples in Example 1. (a) shows sample GO-1 and (b) shows sample GO-2.

[0064] Figure 5 The graph shows the viscosity changes of different cathode slurry samples in air in Example 2. Among them, (a) is a trend graph of the viscosity of the cathode slurry changing over time, and (b) is a comparison graph of the viscosity growth of the cathode slurry.

[0065] Figure 6 The figures show the results of moisture tests on different positive electrode sheets in Example 2. (a) Comparison of moisture content of the positive electrode sheets; (b) Moisture absorption of the positive electrode sheets after exposure to air.

[0066] Figure 7 The following are comparative graphs of electrochemical tests on different positive electrode plates in Example 2. Among them, (a) is a comparison graph of charge-discharge capacity curves of different batteries; (b) is a comparison graph of specific capacity and first efficiency (ICE) of different batteries.

[0067] Figure 8 This is a comparison chart of the DC internal resistance (DCIR) of different batteries during charging and discharging in Example 2.

[0068] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Detailed Implementation

[0069] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0070] I. Chemicals and Instruments

[0071] Phosphoric acid solution (H3PO4, 85%) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; sodium 2,2,3,3-tetrafluoropropionate (C3HF4NaO2, 98%) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; graphene oxide (GO) was provided by Xiamen Kaina Graphene Technology Co., Ltd.; polyvinylidene fluoride (PVDF, 5130) was purchased from Guangdong Zhuguang New Energy Technology Co., Ltd.; N-methylpyrrolidone (NMP) was provided by Chongqing Zhongrun New Materials Co., Ltd.; and positive electrode layered oxide (CFM003S) was purchased from Zhongke Haina Technology Co., Ltd.

[0072] Field emission scanning electron microscopy (SEM) was performed on a Zeiss Sigma 300 to analyze the microstructure of the material, and high-resolution X-ray energy dispersive spectroscopy (EDS) was also performed to test the mapping surface scan.

[0073] The following equipment was purchased: a high-temperature tube furnace (OTF-1200X-II) and a vacuum stirrer (SFM-7) from Hefei Kejing Materials Technology Co., Ltd.; a Karl Fischer moisture analyzer (C10S) from Changzhou Mettler Toledo Precision Instruments Co., Ltd.; a digital viscometer (NDJ-5S) from Shanghai Nirun Intelligent Technology Co., Ltd.; a battery tester (CT-4008-5VA-SI) from Shenzhen Xinwei Electronics Co., Ltd.; an electrochemical workstation (CHI660E) from Shanghai Chenhua Instrument Technology Co., Ltd.; a vacuum oven (DZF-6020BZ) from Shanghai Yixin Scientific Instruments Co., Ltd.; aqueous mixed membrane filter paper (PTFE 100mm × 0.45µm) and a 500 mL sand core filtration device from Haining Delu New Materials Technology Co., Ltd.; glass fiber (GF / D Whatman); and a complete set of CR2032 button battery accessories from Dongguan Kelude Innovation Technology Co., Ltd.

[0074] II. The standard operating procedure is as follows:

[0075] 1. Preparation of positive electrode slurry

[0076] A. Special treatment of conductive carbon:

[0077] A1 conductive carbon GO-1

[0078] (1) Soak graphene oxide (GO) in anhydrous ethanol solution and sonicate for 1-2 hours, then rinse with water, remove the supernatant, and dry;

[0079] (2) A certain amount of GO was uniformly dispersed in deionized water in a beaker, and after ultrasonic treatment for 5-8 hours, a GO suspension with a concentration of 30-60 mg / mL was obtained.

[0080] (3) Use a scraper to coat the GO suspension onto an aluminum foil to form a graphene oxide film. The aluminum foil thickness can be any one of 10µm, 12µm, or 16µm. The graphene oxide film is dried on a hot plate at a temperature of 40~70℃ for 4~10h.

[0081] (4) The graphene oxide film was immersed in a sodium 2,2,3,3-tetrafluoropropionate aqueous solution (15 mg / mL) (the solid-liquid volume ratio of the two is 20:1) for 1-3 h, and then transferred to a 50 mL hydrothermal reactor and kept at 160-200 °C for 12-24 h. After hydrothermal treatment, it was washed with deionized water 3-5 times and then dried in a vacuum oven for 6-8 h at a temperature of 45-65 °C to obtain the fluorinated graphene oxide film.

[0082] (5) The fluorinated graphene oxide film is immersed in a phosphoric acid solution with a mass fraction of 50-85%, the volume ratio of solid to liquid is 1:3-1:10, the immersion time is 3-10 days, after immersion, it is washed with deionized water and filtered 2-5 times, and then the resulting mixed solid material is placed in a glass dish and vacuum dried at 100 °C for 15-20 h. Finally, the material is scraped off the foil and used for later use. The obtained material is modified conductive carbon and is labeled as GO-1.

[0083] A2 conductive carbon GO-2

[0084] (1) Graphene oxide (GO) was soaked in anhydrous ethanol solution and sonicated for 1-2 hours, then rinsed with water, the supernatant was removed, and dried.

[0085] (2) Graphene oxide (GO) and sodium 2,2,3,3-tetrafluoropropionate were ground in a mortar for 10-20 min at a mass ratio of 10:1. The solid mixture was placed in a porcelain boat and placed in a muffle furnace. Argon gas was passed through the apparatus for 20-30 min, and then the heating rate was set to 5 °C / min. The temperature was raised to 100-600 °C for pyrolysis and held for 20-60 min. Annealing was performed. When the temperature displayed on the apparatus was no greater than 50 °C, the obtained material was taken out. The material was washed with deionized water and vacuum filtered 2-5 times. The filter paper used was an aqueous mixed membrane (PTFE polytetrafluoroethylene) to remove sodium salt impurities and obtain fluorinated graphene oxide.

[0086] (3) The obtained fluorinated graphene oxide is then soaked in a phosphoric acid solution with a mass fraction of 85%. The volume ratio of solid to liquid is 1:3 to 1:10, and the soaking time is 3 to 10 days. After soaking, it is washed with deionized water and filtered 2 to 5 times. The resulting mixed solid material is then placed in a glass dish and dried under vacuum at 100 °C for 15 to 20 h. The resulting mixed solid material is modified conductive carbon and is labeled as GO-2.

[0087] A3 conductive carbon GO

[0088] Graphene oxide (GO) is immersed in anhydrous ethanol solution and sonicated for 1-2 hours, then rinsed with water to remove the supernatant, and dried for later use.

[0089] B. Baking preparation: The active material positive electrode material is vacuum dried at 100~130 ℃ for 6~10 h to bake away the surface moisture, and the binder is baked at 70~90 ℃ for 3~5 h to keep its surface dry.

[0090] C. The pulping process adopts dry pulping: the positive electrode active material, conductive carbon and binder are mixed and stirred at a speed of 2 rpm. After 10 min, NMP is added. The resulting slurry has a dispersed solids content of 60~65%, a dispersion speed of 10 rpm, and an output solids content of 50~55%.

[0091] The positive electrode active material used is one of the following: O3-type layered oxide, P2-type layered oxide, or phosphate-based polyanionic oxide. The conductive carbon can be graphene oxide (GO), GO-2 treated with high-temperature pyrolysis fluorination and phosphoric acid solution, or GO-1 scraped from the initial positive electrode of phosphoric acid-treated fluorinated graphene oxide prepared by hydrothermal method. The binder is one of PVDF or sodium alginate.

[0092] Positive electrode colloid carbon functional layer slurry: PVDF is dissolved in NMP to prepare a 2% colloid, and conductive carbon with a mass fraction of 30% of the total mass is added and dispersed in the 2% PVDF colloid.

[0093] Positive electrode carbon layer functional layer slurry: Conductive carbon is dispersed in a 2% aqueous ethanol solution to prepare a conductive carbon slurry with a mass fraction of 30% of the total mass.

[0094] Positive electrode active layer slurry: A slurry prepared from positive electrode active material, conductive carbon, and binder, using NMP as the solvent. The mass ratios of active material, conductive carbon, and binder are 94-96%, 1-8%, and 1-6%, respectively.

[0095] D. Coating:

[0096] First coating: A glass rod is used to apply the slurry onto a 16 µm aluminum foil, and a 100 µm-side scraper is used to coat the foil evenly. The conductive carbon can be graphene oxide (GO), GO-1 obtained through high-temperature hydrothermal doping, or GO-2 obtained through high-temperature pyrolysis doping. Then, it is vacuum dried and cut into round wafers. Next, the first coating process is as follows... Figure 2 Figure a shows a coating process, where the slurry is the positive electrode active layer slurry.

[0097] Secondary coating can be ( Figure 2 (b) Following a single coating process, the first layer is the positive electrode adhesive carbon functional layer, a slurry coated on the positive electrode current collector, denoted as Slurry A. The conductive carbon used is one of graphene oxide (GO), GO-1 obtained through high-temperature hydrothermal doping, or GO-2 obtained through high-temperature pyrolysis doping. Following a single coating process, the second layer is the positive electrode active layer, a slurry coated on the positive electrode current collector, denoted as Slurry B. After the two coatings are completed, vacuum drying is performed, and the material is cut into wafers.

[0098] Secondary coating can also be ( Figure 2 c): Following a single coating process, the first layer is the positive electrode carbon functional layer, a slurry coated on the positive electrode current collector, denoted as slurry C, where the conductive carbon is GO-1. Following the same process, the second layer is the positive electrode active layer, a slurry coated on the positive electrode current collector. This active layer is composed of active material, positive electrode adhesive, and conductive carbon, which can be GO, GO-1, or GO-2, and is coated onto the first functional layer using a doctor blade. After the two coating processes are completed, vacuum drying is followed by cutting into round slices.

[0099] All of the above coating processes are single-sided coatings, meaning the uncoated side is the bare aluminum foil. The variables in the comparative example are the positions of the conductive carbon and the positive electrode functional layer.

[0100] 2. Battery preparation and testing

[0101] In a glove box (where water and oxygen levels are both less than 0.1 ppm), stack the positive electrode shell, positive electrode plate, separator, composite sodium plate, gasket, spring sheet, and negative electrode shell in that order from bottom to top. Add the electrolyte dropwise after covering the separator, at a rate of 200-300 µL. The negative electrode sodium plate should face and cover the positive electrode plate. Seal at 500 MPa for 3-5 seconds. Wipe away any electrolyte from the battery and sealing mold surfaces with a lint-free paper towel.

[0102] (1) Slurry viscosity test: rotation speed is 10 rpm, measurement time is 10 min, and constant temperature is 25.0±0.5℃.

[0103] (2) Moisture content test of positive electrode: The positive electrode was placed in air with a humidity of 50-70% for 2 hours, and the moisture content before and after exposure to air was tested. The ambient temperature of the instrument was 25 ± 1 ℃ and the relative humidity was 15 ± 2%. The moisture content of the sample was measured according to the steps of blank determination, drift determination, reagent calibration and sample moisture determination. The drift time was 10 min. The sample used for calibration was deionized water with a mass of 10 ± 0.2 mg. The calibration was performed 5 times. The sample addition time was 2 min. The electrode sample was cut into strips of 3×0.5 cm and evenly spread on the sample tray. The sample amount was 10 ± 0.2 g. The heating temperature was set to 150˚C.

[0104] (3) Charge-discharge cycle test:

[0105] Step 1: Let stand for 6 hours;

[0106] Step 2: Constant current charging, cutoff voltage 4.2 V, current 0.1 C;

[0107] Step 3: Let stand for 10 minutes;

[0108] Step 4: Constant current discharge to 2.5 V, current 0.1C;

[0109] Step 5: Let stand for 10 minutes;

[0110] Step 6: Repeat 100 times, from Steps 2 to 5.

[0111] The effective active mass of the electrode measured was 2 mg, the standard capacity was 105 mAh / g, and the current at 0.1 C was 0.021 mA.

[0112] Example 1

[0113] 1. Preparation and coating of positive electrode slurry

[0114] (A) Conductive carbon GO

[0115] (1) Soak graphene oxide (GO) in anhydrous ethanol solution and sonicate for 2 h, then rinse with deionized water, remove the supernatant, and dry;

[0116] (2) Disperse the dried GO evenly in deionized water in a beaker, and after ultrasonic treatment for 5-8 h, obtain a GO suspension with a concentration of 50 mg / mL;

[0117] (3) Use a scraper to coat the GO suspension onto aluminum foil to form a graphene oxide film. The aluminum foil is 16 μm thick, cut to a width of 6 cm and a length of 6 cm. Then dry the graphene oxide film on a hot plate in an oven at 50°C for 6 hours. Set aside for later use. Scrape the conductive carbon material off the foil of the graphene oxide film and set aside for later use. This conductive carbon is labeled as GO.

[0118] (B) Conductive carbon GO-1

[0119] (1) Disperse sodium 2,2,3,3-tetrafluoropropionate in deionized water to prepare a 15 mg / mL aqueous solution; soak the dried graphene oxide film in sodium 2,2,3,3-tetrafluoropropionate solution (volume ratio of the two is 20:1) for 2 h, then transfer it to a 50 mL hydrothermal reactor and keep it at 190 °C for 16 h. After hydrothermal treatment, wash it three times with deionized water and dry it in a vacuum oven for 7 h at a temperature of 50 °C to obtain the fluorinated graphene oxide film.

[0120] (2) The fluorinated graphene oxide film was immersed in an 85% phosphoric acid solution with a solid-to-liquid volume ratio of 1:5 for 7 days. After immersion, the film was washed with deionized water and filtered three times to remove impurities. The resulting mixed solid material was then placed in a glass dish and vacuum dried at 100 °C for 18 h. The conductive carbon material was scraped off the foil from the graphene oxide film for later use. This conductive carbon was labeled GO-1.

[0121] (C) Conductive carbon GO-2

[0122] (1) The above-mentioned dried GO and sodium 2,2,3,3-tetrafluoropropionate were ground in a mortar for 15 min at a mass ratio of 10:1. The solid mixture was placed in a porcelain boat and placed in a muffle furnace. Argon gas was passed through the device for 20 min. Then the heating rate was set to 5 °C / min and the temperature was raised to 350 °C for pyrolysis. The temperature was held for 40 min and annealed. When the temperature displayed on the device was no more than 50 °C, the obtained material was taken out. The material was washed with deionized water and filtered three times to remove impurities. The filter paper used was an aqueous mixed membrane (PTFE polytetrafluoroethylene) to remove sodium salt impurities and obtain fluorinated graphene oxide.

[0123] (2) The obtained fluorinated graphene oxide was soaked in a phosphoric acid solution with a mass fraction of 85%, the volume ratio of solid to liquid was 1:5, the soaking time was 7 days, after soaking, it was washed with deionized water and filtered to remove impurities 3 times, and then the obtained mixed solid material was put into a glass dish and vacuum dried at 100 °C for 18 h. Finally, the material was scraped off the foil for use. This conductive carbon was marked as GO-2.

[0124] (D) Characterization of conductive carbon samples

[0125] (1) The microstructure of the three conductive carbon samples was characterized using scanning electron microscopy (SEM). The results are as follows: Figure 3 As shown.

[0126] from Figure 3 It can be found that, Figure 3 The image shows the disordered stacking of the original GO carbon nanosheets, which are thin and wrinkled, forming a translucent film structure with obvious curling. Figure 3 b and Figure 3 c indicates that the morphology of GO changed after chemical doping. Figure 3 b shows that the thickness of GO-1 carbon nanosheets is greater than that of GO, while retaining the previous sheet-like morphology, and the carbon nanosheets are more stretched. The morphological change is more obvious in GO-2, where the area of ​​the carbon nanosheets has become smaller, and the sheets are significantly stretched to form an open porous structure. Figure 3 The results show that the morphology and structure of GO can be adjusted by hydrothermal or high-temperature annealing.

[0127] The chemical composition of materials GO-1 and GO-2 was characterized using X-ray energy-dispersive spectroscopy (EDS). The results are as follows: Figure 4 As shown.

[0128] like Figure 4 As shown, C and O are well distributed in the material, and F can be detected in both in the EDS elemental mapping. Figure 4 a shows that the distribution density of F element in GO-1 carbon nanosheets is not as high as Figure 4 b shows the distribution density of fluorine (F) in the GO-2 carbon nanosheets. The detection data indicates that the F content in GO-1 is 0.05 wt%, and the F content in GO-2 is 0.08 wt%. This demonstrates that F was successfully doped into GO. The presence of F in conductive carbon promotes the formation of inorganic-rich NaF on the cathode surface, protecting the cathode and preventing excessive dissolution in the electrolyte, which could cause side reactions. Simultaneously, it releases O2, which is beneficial to the stability of the cathode.

[0129] (F) Preparation of slurry

[0130] (1) The active material positive electrode was vacuum dried at 120 °C for 8 h to remove surface moisture, and the binder was baked at 80 °C for 5 h to keep its surface dry. Unless otherwise specified, the positive electrode was prepared in an environment with a relative humidity of less than 10%. The positive active material used was a P2 type layered oxide.

[0131] (2) The pulping process adopts dry pulping: the mass ratios of positive electrode active material, conductive carbon, and binder are 95%, 2.5%, and 2.5%, respectively. The positive electrode active material used is a P2 type layered oxide; the conductive carbons are GO, GO-1, and GO-2. The binder is PVDF. Positive electrode active layer slurry: the positive electrode active material, conductive carbon, and PVDF are mixed at a stirring speed of 2 rpm, and NMP is added after 10 min. The solid content of the material after dispersion is 65%, the dispersion speed is 10 rpm, and the solid content of the output is 50%, thus obtaining the positive electrode active layer slurry. The slurries prepared with conductive carbons GO, GO-1, and GO-2 are labeled as slurry No. 1, slurry No. 2, and slurry No. 3, respectively.

[0132] (G) Coating:

[0133] (1) Single coating: The positive electrode active layer slurry was dipped into a glass rod and applied to a 16 µm aluminum foil. The slurry was then uniformly coated onto the aluminum foil using a 100 µm-side scraper. The foil was then vacuum dried at 100 °C for 3 h and cut into circular pieces with a radius of 7 mm. All prepared positive electrode sheets were single-sided coated and are designated as Positive Electrode Sheet 1, Positive Electrode Sheet 2, and Positive Electrode Sheet 3.

[0134] (2) Slurry viscosity test: The rotation speed was 10 rpm, the measurement time was 10 min, the constant temperature was 25.0±0.5℃, and the viscosity value was recorded every 20 min. The results are as follows: Figure 5 As shown.

[0135] Depend on Figure 5 As can be seen from a, the viscosity of the positive electrode slurry increased over time after being exposed to air. Overall, the growth trajectory showed a phenomenon of rapid increase at first, followed by slow increase. The slurry with the fastest growth rate was No. 1. Figure 5b indicates that the viscosity of slurry No. 1 increased by 4540 mPa·s within 2 hours, while the viscosity increases of slurries No. 2 and No. 3 were 1660 mPa·s and 1906 mPa·s, respectively. This shows that the addition of modified conductive carbon (GO-1, GO-2) effectively suppressed the rapid viscosity increase of the cathode slurry in air. This may be because the modified conductive carbon (GO-1, GO-2) was treated with sodium 2,2,3,3-tetrafluoropropionate, and the presence of fluorine (F) on the carbon material surface gives it a certain degree of hydrophobicity. Alternatively, it may have been treated with phosphoric acid solution, which stabilizes the cathode gel and slows down its failure side reactions in an alkaline environment (where there is residual alkali on the cathode material surface). The cathode slurry prepared in this application has less water intrusion, thus reducing the reaction between residual alkali and water on the cathode material surface to form alkaline salts, thereby controlling the attack of alkaline groups in the alkaline salts on PVDF and promoting its crosslinking. Therefore, the cathode slurry prepared in this application effectively improves the introduction of water, stabilizes the viscosity of the cathode slurry, and enhances the chemical stability of the slurry, which is beneficial for subsequent improvements in battery resistance and charge / discharge life.

[0136] (H) Moisture content test of positive electrode sheet:

[0137] The positive electrode sheet was taken freshly coated and dried at 100℃ for 3 min (simulating the drying of the electrode sheet in industrial coating). The electrode sheet that was visually dry was then placed in air with a humidity of 50-70% for 2 h. The moisture value before and after exposure to air was recorded, as well as the moisture value after baking at 150℃ for 4 h. Four parallel experiments were set up for each group as shown in Table 1.

[0138] Table 1. Record of moisture values ​​for positive electrode sheets

[0139]

[0140] From Table 1 and Figure 6 As can be seen from point a, the moisture values ​​of the freshly coated positive electrode plates two and three are lower than those of positive electrode plate one. This indicates that less moisture intrusion occurred during the initial slurry preparation process. This conclusion is consistent with the findings in the "Slurry Viscosity Test". Figure 5 The viscosity increases of slurries No. 2 and No. 3 in sample a are slow and consistent. All positive electrode sheets showed varying degrees of moisture increase after exposure to air, due to the porous nature of the conductive carbon, which readily absorbs moisture from the air. The highest moisture content was observed in positive electrode sheet No. 1, ranging from 756.5 to 776.9 ppm; while the moisture content of positive electrode sheets No. 2 and No. 3 were 442.6–462.3 ppm and 481.2–513.9 ppm, respectively. The average difference in moisture content before and after air exposure for the positive electrode sheets is shown below. Figure 6As shown in b, the average water absorption values ​​of positive electrode plates 1, 2, and 3 after exposure were 499.0 ppm, 243.9 ppm, and 257.7 ppm, respectively. Compared to the average water absorption value of positive electrode plate 1, the values ​​of positive electrode plates 2 and 3 are significantly reduced, indicating that positive electrode plates 2 and 3 have a certain degree of water resistance. This may be due to the fact that the conductive carbons GO-1 and GO-2 were treated with sodium 2,2,3,3-tetrafluoropropionate, and the presence of fluorine (F) on the surface of the carbon material gives it a certain degree of hydrophobicity; or it may be due to treatment with phosphoric acid solution, which can stabilize the positive electrode gel and slow down its failure side reactions in an alkaline environment (where there is residual alkali on the surface of the positive electrode material).

[0141] Example 2

[0142] 1. Preparation of positive electrode slurry

[0143] PVDF was dissolved in NMP to prepare a 2% solution. GO, GO-1, and GO-2, each with a mass fraction of 30% of the total mass, were added to obtain GO solution, GO-1 solution, and GO-2 solution, which were used as the first positive electrode carbon functional layer slurry and denoted as slurry A.

[0144] GO-1 was dissolved in a 2% ethanol aqueous solution to obtain a GO-1 solution with a mass fraction of 30% of the total mass. This solution was used as the first positive electrode carbon layer functional layer slurry and was denoted as slurry C.

[0145] The positive electrode active layer slurry prepared in Example 1 is used as the second positive electrode active layer slurry.

[0146] Second coating-1 ( Figure 2 b): The first positive electrode carbon functional layer slurry (slurry A) is coated onto aluminum foil using a scraper. After drying at 100°C for 2 minutes, the second positive electrode active layer slurry (denoted as slurry B (i.e., slurry No. 2 in Example 1)) is coated. Then, it is vacuum dried at 100°C for 2-3 hours and cut into circular pieces with a radius of 7 mm. The resulting electrode pieces are named positive electrode A, positive electrode B, and positive electrode C, respectively, corresponding to GO, GO-1, and GO-2 slurries in the first positive electrode carbon functional layer slurry.

[0147] Second coating-2 ( Figure 2 c): The first layer is the positive electrode carbon functional layer, which is a conductive carbon GO-1 ethanol aqueous solution coated on the positive electrode current collector, denoted as C slurry. The second layer is the positive electrode active layer, which is coated on the other side of the positive electrode current collector with a second positive electrode active layer slurry (referred to as B slurry in the figure, which is also slurry No. 1, No. 2, and No. 3 in Example 1)). It is prepared by active material, positive electrode adhesive, and conductive carbon. The conductive carbon can be GO, GO-1, or GO-2. Then, it is vacuum dried at 100 °C for 2-3 h and cut into circular pieces with a radius of 7 mm. The resulting electrode pieces are named D positive electrode piece, E positive electrode piece, and F positive electrode piece, respectively.

[0148] The second positive electrode is a single-coated electrode prepared in Example 1.

[0149] Table 2. Coating details of the positive electrode structure

[0150]

[0151] 2. Electrochemical testing comparison of positive electrode plates

[0152] To investigate the impact of the position and composition of the positive electrode functional layer on the battery's electrical performance, positive electrode sheets A, B, C, D, E, and F were assembled into coin cells, corresponding to battery numbers A, B, C, D, E, and F. Their first-cycle capacity, first-cycle efficiency, and capacity retention were tested, and their DC resistance during charging and discharging was monitored simultaneously. As a comparison, a coin cell assembled with positive electrode sheet 2 from Example 1 was used.

[0153] like Figure 7 a. As shown in Table 3, the battery assembled with the positive electrode sheet prepared by single coating (Battery No. 1) has lower specific capacity, initial efficiency, and 200-cycle 0.1C capacity retention rate than all batteries assembled with positive electrode sheets prepared by double coating. This indicates that double coating is more effective than single coating. In double coating, the battery assembled with a positive electrode sheet whose first layer is a positive carbon functional layer performs better than the battery assembled with a positive electrode sheet whose first layer is a positive adhesive carbon functional layer. Specifically, compared to Battery No. 1, the capacity and initial efficiency of Batteries A, B, C, D, E, and F are all improved. This may be because the doping of fluorine in the conductive carbon reduces irreversible sodium loss to some extent, resulting in a slight increase in discharge capacity. Furthermore, from... Figure 7 In b, it was found that the capacity of batteries A, B, and C was slightly lower than that of batteries D, E, and F. This may be because the carbon layer and the current collector have good contact, and the loose and porous structure inside can accommodate more sodium ions, resulting in a higher electron transfer rate between carbon layers. In contrast, the presence of non-conductive PVDF in the positive electrode gel carbon functional layer increases the resistance and electrochemical polarization to some extent, leading to a slight increase in capacity, but it is still lower than that of batteries with a positive electrode carbon layer functional layer.

[0154] from Figure 8The comparison of DC resistance of different batteries shows that battery 1 has the highest DC resistance, while batteries D, E, and F have the lowest DC resistance. This indicates that the positive electrode carbon layer can effectively reduce the internal resistance of the battery. Table 3 shows that batteries D, E, and F have the best capacity retention rates, with capacity retention rates of 93.36%, 94.69%, and 94.11% respectively after 200 cycles at 0.1C. Compared to battery 1's capacity retention rate of only 87.21%, these batteries exhibit excellent room temperature cycling performance.

[0155] This study compares the first-cycle capacity, first-cycle efficiency, and capacity retention of batteries assembled from cathode sheets prepared using different treatment methods for conductive carbon GO. Among batteries A, B, and C, battery B is the best; and among batteries D, E, and F, battery E is the best. All batteries used conductive carbon GO-1 prepared via a hydrothermal method. This indicates that in this experiment, the hydrothermal treatment of conductive carbon GO is more effective than the high-temperature pyrolysis treatment. Based on this, adjusting the high-temperature pyrolysis temperature and annealing time may improve the electrical properties of conductive carbon; therefore, the modification of conductive carbon includes, but is not limited to, this.

[0156] In the preparation of positive electrode sheets, the coating method is not limited to single coating or double coating.

[0157] Table 3 Comparison of battery electrochemical performance

[0158]

[0159] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A modified conductive carbon, characterized in that, It is doped with 0.05wt%~0.1wt% of F element; The modified conductive carbon is prepared by fluorinating graphene oxide with sodium 2,2,3,3-tetrafluoropropionate as a fluorine source, followed by immersion in phosphoric acid. The preparation process of the modified conductive carbon is as follows: Step a1: Graphene oxide is coated onto a foil to form a graphene oxide film; Step a2: After pretreatment by immersing the graphene oxide film in an aqueous solution of sodium 2,2,3,3-tetrafluoropropionate, the graphene oxide film is obtained by hydrothermal fluorination, washing, and drying. Step a3: The fluorinated graphene oxide film is immersed in a phosphoric acid solution, washed, vacuum dried, and the modified conductive carbon is scraped off from the foil to obtain the modified conductive carbon; Alternatively, the preparation process of the modified conductive carbon is specifically as follows: Step b1: Graphene oxide and sodium 2,2,3,3-tetrafluoropropionate are mixed and ground to obtain a solid mixture; Step b2: Place the solid mixture in an inert atmosphere, heat and anneal for fluorination, and then wash and dry to obtain fluorinated graphene oxide; Step b3: Fluorinated graphene oxide is immersed in phosphoric acid solution, washed, and dried to obtain modified conductive carbon.

2. The modified conductive carbon according to claim 1, characterized in that, The drying temperature is 40~70℃ and the drying time is 4~10h; or, the vacuum drying temperature is 90~110℃ and the vacuum drying time is 15~20h. Alternatively, the concentration of the sodium 2,2,3,3-tetrafluoropropionate aqueous solution is 10~20 mg / mL; Alternatively, the preprocessing time in step a2 is 1~3 hours; Alternatively, in step a2, the hydrothermal fluorination is maintained at 160~200℃ for 12~24h; Alternatively, the mass fraction of the phosphoric acid solution is 50-85%; Alternatively, in step a3, the volume ratio of the fluorinated graphene oxide film to the phosphoric acid solution is 1:(3~10). Alternatively, the phosphoric acid treatment soaking time is 3 to 10 days; Alternatively, in step b1, the mass ratio of the graphene oxide to sodium 2,2,3,3-tetrafluoropropionate is (8~12):1; Alternatively, in step b2, during the heating annealing fluorination process, heat to 100~600℃ for pyrolysis for 20~60 minutes, and remove the device when the temperature displayed on the device is no greater than 50℃ after annealing; Alternatively, in step b3, the volume ratio of the fluorinated graphene oxide to the phosphoric acid solution is 1:(3~10).

3. A slurry, characterized in that, Includes the modified conductive carbon according to any one of claims 1 to 2.

4. The slurry according to claim 3, characterized in that, The slurry includes a positive electrode carbon layer functional layer slurry, a positive electrode colloidal carbon functional layer slurry, or a positive electrode active layer slurry; Alternatively, the preparation process of the positive electrode adhesive carbon functional layer slurry is as follows: PVDF is dissolved in NMP to prepare an adhesive solution; modified conductive carbon is added to obtain the final product. Alternatively, the mass fraction concentration of modified conductive carbon in the positive electrode adhesive carbon functional layer slurry is 20-40%; Alternatively, the preparation process of the positive electrode carbon layer functional layer slurry is as follows: the modified conductive carbon according to any one of claims 1 to 2 is added to an aqueous ethanol solution to obtain the slurry; Alternatively, the mass fraction concentration of modified conductive carbon in the positive electrode carbon layer functional layer slurry is 20-40%; Alternatively, the positive electrode active layer slurry includes a positive electrode active material, modified conductive carbon, and a binder; Alternatively, the positive electrode active material is one of O3-type layered oxide, P2-type layered oxide, or phosphate-based polyanion; Alternatively, the adhesive may be either PVDF or sodium alginate.

5. A positive electrode sheet, characterized in that, It includes the slurry according to any one of claims 3 to 4 or the modified conductive carbon according to any one of claims 1 to 2.

6. The positive electrode sheet according to claim 5, characterized in that, The positive electrode sheet includes a positive electrode functional layer containing the modified conductive carbon according to any one of claims 1 to 2 and a positive electrode active layer containing the modified conductive carbon according to any one of claims 1 to 2; The positive electrode functional layer is selected from the positive electrode liquid carbon functional layer or the positive electrode carbon layer functional layer.

7. A method for preparing the positive electrode sheet according to claim 5, characterized in that, include: The positive electrode functional layer slurry is coated onto the current collector, dried, and then the positive electrode active layer slurry is coated and dried to obtain the positive electrode sheet.

8. A battery comprising the positive electrode sheet as described in claim 5.

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