Graphite-based potassium ion battery composite negative electrode and preparation method and application thereof

Abstract

The invention provides a graphite-based potassium ion battery composite negative electrode and a preparation method and application thereof, and belongs to the technical field of potassium ion battery negative electrode materials. The composite negative electrode is a composite material obtained by mechanically mixing graphite and lamellar iron-doped graphite phase carbon nitride; wherein the mass ratio of the graphite to the lamellar iron-doped graphite phase carbon nitride is (4-20): 1; the lamellar iron-doped graphite phase carbon nitride is Fe-g-C3N4 (ferrum-doped graphite phase carbon nitride); the graphite is natural graphite of 300 to 800 meshes. The graphite and the lamellar iron-doped graphite phase carbon nitride are mechanically mixed to obtain the composite negative electrode, and the composite negative electrode has high reversible specific capacity, excellent cycle performance and excellent rate capability when being used as the negative electrode of the potassium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of potassium ion battery negative electrode materials, and in particular to a graphite-based potassium ion battery composite negative electrode, a preparation method thereof, and applications thereof. Background Art

[0002] Rechargeable lithium-ion batteries have high reversible specific capacity and good cycle stability, and are one of the most important portable commercial energy storage systems currently. Among them, lithium iron phosphate or nickel-cobalt-manganese ternary positive electrodes are one of the important components of lithium-ion batteries. However, due to the extremely high prices of lithium, nickel and cobalt sources, the current preparation cost of lithium batteries is extremely high. Finding low-cost alternatives to lithium batteries is one of the important tasks in the current industry. Currently, low-cost secondary batteries as alternatives to lithium-ion batteries have become a research hotspot in the industry. Potassium-ion batteries have received widespread attention in recent years due to their similar physical properties to lithium.

[0003] Graphite has the advantages of high capacity, low charge and discharge platform, excellent conductivity and easy processing. It is currently one of the most ideal low-cost secondary energy storage battery negative electrode materials. Compared with sodium-ion batteries, one of the advantages of potassium-ion batteries is that multi-stage potassium-carbon compounds can be formed through intercalation reactions in the graphite negative electrode to achieve reversible insertion / extraction. However, the graphite negative electrode causes a large volume change during the insertion / extraction of potassium ions, which in turn affects the structural stability of the graphite negative electrode and ultimately leads to poor cycle performance. At the same time, the slow potassiumization kinetics of the graphite negative electrode limits its rate performance. How to improve its structural stability and improve its cycle and rate performance when used as the negative electrode of potassium ion batteries is an important research hotspot in the current field of potassium ion batteries.

[0004] Currently, the main modification schemes for graphite negative electrodes include the following: 1. Improving the transport capacity of potassium ions and electrons by constructing different coating layers on the graphite surface; 2. Composite graphite with other negative electrode materials, combining the advantages of each material to achieve high capacity or fast kinetics to improve the overall rate and cycle performance; 3. Optimizing the components of the electrolyte, including solvents, potassium salts and additives, to regulate the transport kinetics of potassium ions and the stability of the interface; 4. Regulating the structure of the graphite material itself, such as constructing a porous structure, expanding the interlayer spacing, etc., to construct a smoother potassium ion transmission channel, alleviate the volume change during the charge and discharge process, and thereby improve the structural stability of graphite. Among the above four methods, the composite negative electrode strategy is relatively simpler and easier to control, has better effects, and is easier to achieve industrial promotion. Therefore, finding a suitable composite negative electrode strategy is the key to improving graphite as a negative electrode material for potassium ion batteries. Summary of the Invention

[0005] To address the aforementioned issues with existing technologies, the present invention provides a graphite-based composite anode for potassium-ion batteries, its preparation method, and its application. By mechanically mixing graphite with lamellar iron-doped graphite-phase carbon nitride, the resulting composite anode exhibits high reversible specific capacity, excellent cycling performance, and superior rate capability when used as a potassium-ion battery anode.

[0006] The technical solutions of the present invention are as follows:

[0007] The present invention first provides a graphite-based potassium ion battery composite negative electrode, wherein the composite negative electrode is a composite material obtained by mechanically mixing graphite and lamellar iron-doped graphite phase carbon nitride; wherein the mass ratio of graphite to lamellar iron-doped graphite phase carbon nitride is 4-20:1; and the lamellar iron-doped graphite phase carbon nitride is Fe-g-C3N4.

[0008] Furthermore, the ratios of graphite to iron-doped graphitic carbon nitride are 9.5:0.5, 9:1, 8.5:1.5, and 8:2. This design combines graphite with a small amount of iron-doped graphitic carbon nitride. By adjusting the ratio of iron-doped graphitic carbon nitride to graphite, the composition of the composite material can be precisely controlled, thereby achieving customized preparation of the target material.

[0009] Preferably, the graphite is 300-800 mesh natural graphite.

[0010] The present invention also provides a method for preparing the lamellar iron-doped graphite-phase carbon nitride, comprising the following steps:

[0011] S1. Weigh urea and NaCl in a mass ratio of 1:2-3 and dissolve them in deionized water; after ultrasonication for 30-60 minutes, dry at 60-80°C for 12-15 hours to obtain a precursor product;

[0012] S2. The obtained precursor product is then heated in a muffle furnace at 500-550° C. for 1.5-2.5 h to obtain the desired graphite phase carbon nitride g-C3N4; after grinding, the obtained sample is passed through a 200-300 mesh sieve;

[0013] S3. Disperse the sieved g-C3N4 in a methanol solution, and add polyether F127 and melamine in a mass ratio of 1:1:1-1.3 to obtain a uniform dispersion by ultrasonication. Stir for 10-15 hours, and slowly add FeCl3 to the solution. After drying, obtain a carbonized sample.

[0014] S4. The obtained carbonized sample was kept at 800-850℃ in a tube furnace under argon atmosphere for 2-3h to obtain a carbonized sample, and then 5mol·L -1The obtained product was etched with HNO3 solution for 20-24h; after filtration and drying, lamellar iron-doped graphite carbon nitride Fe-g-C3N4 was obtained.

[0015] Preferably, in step S1, when 3 g of urea is used, 30-50 ml of deionized water is required.

[0016] Preferably, in step S3, when the amount of graphite carbon nitride used is 300 mg, the amount of methanol required is 30-50 ml, and the amount of FeCl3 required is 0.2-0.4 mmol.

[0017] Preferably, in step S3, the drying is performed at 60-80° C. for 12-15 hours.

[0018] Preferably, in step S4, the drying temperature is 60-80° C. and the drying time is 6-12 hours.

[0019] The present invention further provides a method for mechanically mixing graphite and lamellar iron-doped graphite-phase carbon nitride, which specifically comprises the following steps: placing the graphite and the lamellar iron-doped graphite-phase carbon nitride in a ball mill, adding ethanol and performing ball milling to obtain a mixture; and drying and fully grinding the mixture to obtain the composite negative electrode material for potassium ion batteries.

[0020] Preferably, during the ball milling treatment, the mass ratio of the sum of the mass of graphite and iron-doped graphite-phase carbon nitride to ethanol is 1:2-3; the rotation speed of the ball mill is 250-300 r / min, the ball milling time is 1-2 h; and the ball-to-material ratio is 1:1-2.

[0021] Preferably, the drying is carried out in a drying oven at 60-80° C. for 12-15 hours.

[0022] Furthermore, the ball milling beads used are alumina ball milling beads.

[0023] The present invention further provides an application of the composite negative electrode, that is, the composite negative electrode is mixed with PVDF, conductive carbon black, and NMP to obtain a slurry with suitable viscosity, which is then coated on a current collector and dried to obtain a potassium ion battery negative electrode.

[0024] The beneficial technical effects of the present invention are:

[0025] 1. The present invention combines a small amount of iron-doped graphite with a graphite negative electrode to obtain a potassium ion battery negative electrode material with high reversible specific capacity, high cycle stability, and high rate performance. Compared with a single graphite negative electrode and an iron-doped graphite phase carbon nitride single-phase negative electrode, the composite negative electrode has better performance, reflecting the synergistic effect of the two:

[0026] (1) First, due to its large specific surface area, iron-doped graphite-phase carbon nitride has a strong adsorption capacity, and its porous structure can also become a potassium storage site. However, the large specific surface area makes it not easy to process as a negative electrode material, which will cause the electrode structure to be too loose, and the phenomenon of powder falling and cracking will occur. In addition, as a semiconductor material, its electron conduction ability is limited. Therefore, its performance is poor when used alone as a negative electrode material. For graphite, its disadvantage is that there is a high contact resistance between particles and poor potassium storage kinetics. However, when compounded with natural graphite and fully dispersed, iron-doped graphite-phase carbon nitride sheets can help the graphite negative electrode better build a conductive network, using its sp 2 The hybridization forms a highly delocalized π-conjugated system, which forms an electron conduction bridge between graphite particles and reduces the contact resistance between graphite particles.

[0027] (2) Secondly, there is a potential difference between the iron-doped graphitic carbon nitride that adsorbs potassium ions and the unpotassium-doped graphite. This potential difference can provide additional electric field force, which helps potassium ions diffuse from the iron-doped graphitic carbon nitride to the nearest neighboring graphite, providing faster potassium storage kinetics and achieving excellent rate performance. At the same time, the cycling test results show that the synergistic effect between the two phases can also achieve high cycling stability.

[0028] (3) Third, iron-doped graphite-phase carbon nitride is prone to agglomeration due to electrostatic effects, while graphite with good conductivity can serve as a conductive component to reduce the surface resistance of the powder, accelerate charge transfer, avoid the agglomeration of iron-doped graphite-phase carbon nitride, and achieve good dispersion.

[0029] 2. The present invention does not require complex modification of the graphite negative electrode. Instead, it only requires mechanical mixing of the graphite negative electrode with iron-doped graphite carbon nitride. This results in a simple process and controllable composition. The manganese-based potassium ion battery negative electrode material prepared by the method of the present invention is a low-cost battery material, and the required iron-doped graphite carbon nitride content is extremely low. It has the advantages of readily available raw materials, low cost, simple composition, and no pollution to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a SEM image of the iron-doped graphite-phase carbon nitride prepared in Example 1;

[0031] Figure 2 This is an SEM image of the graphite and iron-doped graphite-phase carbon nitride composite negative electrode sheet of Example 1;

[0032] Figure 3 This is the EIS graph of the composite potassium ion battery negative electrode material prepared in Example 1;

[0033] Figure 4 This is a graph showing the cycle performance test results of the composite potassium ion battery negative electrode material prepared in Example 1;

[0034] Figure 5 This is a graph showing the cycle performance test results of the composite potassium ion battery negative electrode material prepared in Example 1 under high current density conditions;

[0035] Figure 6 This is a graph showing the cycle performance test results of the single-phase graphite potassium ion battery negative electrode material in Comparative Example 1;

[0036] Figure 7 Graph showing the cycling performance test results of the single-phase graphite potassium ion battery negative electrode material in Comparative Example 1 at high current density;

[0037] Figure 8 This is the EIS graph of the single-phase graphite potassium ion battery negative electrode material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0038] The present invention is described in detail below with reference to the accompanying drawings and embodiments. It is apparent that the embodiments described are only a portion of the embodiments of the present invention, rather than all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0039] Example 1:

[0040] The potassium ion battery negative electrode material prepared in this embodiment is graphite / iron-doped graphite phase carbon nitride, and the preparation method includes the following steps:

[0041] S1. Weigh 3 g of urea and 6 g of sodium chloride in a mass ratio of 1:2 and dissolve them in 30 ml of deionized water.

[0042] S2, after 30 min of ultrasonication and drying at 60 °C for 12 h, the precursor product was obtained;

[0043] S3, then heating the obtained sample in a muffle furnace at 520 degrees Celsius for 1.5 hours;

[0044] S4, after grinding, passing through a 200 mesh sieve to obtain the desired graphite phase carbon nitride g-C3N4;

[0045] S5, taking 300 mg of the obtained g-C3N4 and dispersing it in 30 ml of methanol solution;

[0046] S6. Polyether F127 and melamine were added in a mass ratio of 1:1:1 of graphite carbon nitride: polyether F127: melamine. After ultrasonication for 1 hour, the mixture was stirred for 10 hours. At the same time, 0.3 mmol of FeCl3 was slowly added to the above solution using a peristaltic pump (all subsequent examples were slowly added using a peristaltic pump).

[0047] S7, drying at 60°C for 12 h to obtain a precursor sample;

[0048] S8, the dried sample was placed in a tube furnace under argon at 800 ° C for 2 h to obtain a carbonized sample;

[0049] S9, the obtained product was treated with 5 mol·L -1 Etching with HNO3 solution for 24h;

[0050] S10, after filtration and drying at 60°C for 10 h, lamellar iron-doped graphite phase carbon nitride was obtained;

[0051] S11. Weigh 800-mesh natural graphite and lamellar iron-doped graphite-phase carbon nitride in a mass ratio of 9.5:0.5 in a ball mill;

[0052] S12, adding ethanol at a mass ratio of active material to ethanol of 1:2; ball milling at 200 rpm for 1 hour at a ball-to-material ratio of 1:1.2 to obtain a mixture; wherein the active material is a mixture of a graphite negative electrode and lamellar iron-doped graphite carbon nitride;

[0053] S13, drying the mixture at 60°C for 6h;

[0054] S14, after sufficient grinding, the composite potassium ion battery negative electrode material is obtained.

[0055] The SEM diffraction pattern of the iron-doped graphite phase carbon nitride prepared in this example is as follows: Figure 1 As shown by Figure 1 It can be seen that the prepared iron-doped graphite phase carbon nitride is a clustered lamellar structure with a cluster size of about 1-5 microns. When mechanically mixed with graphite, the cluster structure is destroyed and dispersed, becoming nano-sized flakes dispersed between graphite particles and attached to graphite particles. Since the size of the flakes is an order of magnitude different from that of the graphite particles, the SEM image after the two are mixed and prepared into a pole piece (as shown in FIG. Figure 2 No obvious flake iron-doped graphite carbon nitride is seen in the graphite negative electrode sheet, making the SEM image of the composite negative electrode sheet very close to the SEM image of the graphite negative electrode sheet.

[0056] The specific surface area of ​​the prepared iron-doped graphite carbon nitride is 480.3 m 2 ·g -1 , much larger than the graphite phase carbon nitride without iron doping (46.87m 2 ·g -1 ) and natural graphite (1-20m 2 ·g -1 The specific surface area of ​​the composite material obtained by mixing graphite and iron-doped graphite carbon nitride is also much larger than that of graphite. Figure 3 and Figure 8From the EIS test, it can be seen that the composite negative electrode mixed with graphite and iron-doped graphite-phase carbon nitride has a smaller impedance than the single-phase graphite negative electrode, indicating that the composite negative electrode sheet forms a better conductive network than the single-phase negative electrode sheet, which means better kinetic performance.

[0057] The graphite / iron-doped graphite phase carbon nitride (CPN) anode material for potassium ion batteries prepared in this example was mixed with PVDF, conductive carbon black, and NMP in a mass ratio of 8:1:1:20 to obtain a slurry with suitable viscosity. The slurry was then coated on copper foil and dried to obtain a battery negative electrode sheet. The slurry was then assembled into a 2032 button cell and tested.

[0058] The low current density cycle performance test results and high current density cycle performance test results of the obtained potassium ion battery negative electrode material are shown in Figure 2. Figure 4 and Figure 5 As shown by Figure 4 and Figure 5 It can be seen that the potassium ion battery negative electrode material prepared in this embodiment has a high current density (50 mA g -1 ) The first cycle discharge capacity is up to 400mAh g -1 Above, and at 500mA·g -1 Under the current density condition of 300mAh·g -1 The capacity retention rate is as high as 80% after 500 cycles.

[0059] The negative electrode material is at 100mA·g -1 After 800 cycles at the same current density, the capacity retention rate is still close to 75%. The above data are much higher than the graphite negative electrode (278mAh·g -1 ) capacity (J.Am.Chem.Soc.2015,137,11566-11569) and cycle performance. Figure 6 As shown in the figure, the first cycle discharge capacity of the single-phase graphite potassium ion battery negative electrode material in Comparative Example 1 is only 250 mAh g -1 After 100 cycles, the capacity is only 100 mAh g -1 .pass Figure 7 It can be seen that the capacity of the single-phase graphite negative electrode is less than 40 mAh g under high current density conditions. -1 , which is similar to the results reported in the literature (J.Am.Chem.Soc.2015,137,11566-11569), but far inferior to the composite negative electrode in Example 1.

[0060] Example 2:

[0061] S1. Weigh 3 g of urea and 6 g of sodium chloride in a mass ratio of 1:2 and dissolve them in 30 ml of deionized water.

[0062] S2, after 30 min of ultrasonication and drying at 60 °C for 12 h, the precursor product was obtained;

[0063] S3, then heating the obtained sample in a muffle furnace at 550 degrees Celsius for 1.5 hours;

[0064] S4, after grinding and passing through a 250-mesh sieve, the desired graphite phase carbon nitride g-C3N4 is obtained;

[0065] S5, taking 300 mg of the obtained g-C3N4 and dispersing it in 50 ml of methanol solution;

[0066] S6. According to the mass ratio of graphite carbon nitride: polyether F127: melamine of 1:1:1.3, polyether F127 and melamine were continued to be added and stirred for 10 hours. At the same time, 0.2 mmol FeCl3 was slowly added to the above solution;

[0067] S7, drying at 60°C for 13 h to obtain a precursor sample;

[0068] S8, the dried sample was kept in a tube furnace at 850°C for 3 h under argon to obtain a carbonized sample;

[0069] S9, the obtained product was treated with 5 mol·L -1 Etching with HNO3 solution for 20h;

[0070] S10, after filtration and drying at 60°C for 12h, lamellar iron-doped graphite phase carbon nitride was obtained;

[0071] S11. Weigh 500-mesh natural graphite and lamellar iron-doped graphite-phase carbon nitride in a mass ratio of 9:1 in a ball mill;

[0072] S12, adding ethanol at a ratio of active substance to ethanol of 1:2; ball milling at 200 rpm for 1 hour at a ball-to-material ratio of 1:1.2 to obtain a mixture;

[0073] S13, drying the mixture at 60°C for 6h;

[0074] S14, after sufficient grinding, the composite potassium ion battery negative electrode material is obtained.

[0075] The potassium ion battery negative electrode material prepared in this example has a low current density (50 mA·g -1 ) The first cycle discharge capacity is up to 400mAh g -1 Above, and at 500mA·g -1 Under the current density condition of 300mAh·g -1 The capacity retention rate is as high as 78% after 500 cycles.

[0076] Example 3:

[0077] S1. Weigh 3 g of urea and 7.5 g of sodium chloride in a mass ratio of 1:2.5 and dissolve them in 40 ml of deionized water.

[0078] S2, after 45 min of ultrasonic treatment and drying at 70 °C for 13 h, the precursor product was obtained;

[0079] S3, then heating the obtained sample in a muffle furnace at 510 degrees Celsius for 2.4 hours;

[0080] S4, after grinding, passing through a 300 mesh sieve to obtain the desired graphite phase carbon nitride g-C3N4;

[0081] S5, take 300 mg of the obtained g-C3N4 and disperse it in 45 ml of methanol solution;

[0082] S6. According to the mass ratio of graphite carbon nitride: polyether F127: melamine of 1:1:1.2, polyether F127 and melamine were continued to be added and stirred for 13 hours. At the same time, 0.4 mmol FeCl3 was slowly added to the above solution;

[0083] S7, drying at 80°C for 15h to obtain a precursor sample;

[0084] S8, the dried sample was kept in a tube furnace at 835°C under argon for 2.5 h to obtain a carbonized sample;

[0085] S9, the obtained product was treated with 5 mol·L -1 Etching with HNO3 solution for 22h;

[0086] S10, after filtration and drying at 70°C for 8h, lamellar iron-doped graphite phase carbon nitride was obtained;

[0087] S11. Weigh 300-mesh natural graphite and lamellar iron-doped graphite-phase carbon nitride in a mass ratio of 8.5:1.5 in a ball mill;

[0088] S12, adding ethanol at a ratio of active substance to ethanol of 1:2.5; ball milling at 280 rpm for 1.5 hours at a ball-to-material ratio of 1:1.5 to obtain a mixture;

[0089] S13, drying the mixture at 70°C for 13h;

[0090] S14, after sufficient grinding, the composite potassium ion battery negative electrode material is obtained.

[0091] The potassium ion battery negative electrode material prepared in this example has a low current density (50 mA·g -1 ) The first cycle discharge capacity is up to 400mAh g -1 Above, and at 500mA·g-1 Under the current density condition of 300mAh·g -1 The capacity retention rate is as high as 79% after 500 cycles.

[0092] Example 4:

[0093] S1. Weigh 3 g of urea and 9 g of sodium chloride in a mass ratio of 1:3 and dissolve them in 50 ml of deionized water.

[0094] S2, after 60 min of ultrasonication and drying at 80 °C for 15 h, the precursor product was obtained;

[0095] S3, then heating the obtained sample in a muffle furnace at 550 degrees Celsius for 2.5 hours;

[0096] S4, after grinding, passing through a 300 mesh sieve to obtain the desired graphite phase carbon nitride g-C3N4;

[0097] S5, taking 300 mg of the obtained g-C3N4 and dispersing it in 50 ml of methanol solution;

[0098] S6. According to the mass ratio of graphite phase carbon nitride: polyether F127: melamine of 1:1:1.3, polyether F127 and melamine were continued to be added and stirred for 15 hours. At the same time, 0.4 mmol FeCl3 was slowly added to the above solution;

[0099] S7, drying at 70°C for 15 h to obtain a precursor sample;

[0100] S8, the dried sample was kept in a tube furnace at 850°C for 3 h under argon to obtain a carbonized sample;

[0101] S9, the obtained product was treated with 5 mol·L -1 Etching with HNO3 solution for 24h;

[0102] S10, after filtration and drying at 80°C for 6h, lamellar iron-doped graphite phase carbon nitride was obtained;

[0103] S11. Graphite and lamellar iron-doped graphite-phase carbon nitride are weighed in a mass ratio of 8:2 in a ball mill;

[0104] S12, adding ethanol at a ratio of active substance to ethanol of 1:3; ball milling at 300 rpm for 2 hours at a ball-to-material ratio of 1:2 to obtain a mixture;

[0105] S13, drying the mixture at 80°C for 15h;

[0106] S14, after sufficient grinding, the composite potassium ion battery negative electrode material is obtained.

[0107] The potassium ion battery negative electrode material prepared in this example has a low current density (50 mA·g -1 ) The first cycle discharge capacity is up to 400mAh g -1 Above, and at 500mA·g -1 Under the current density condition of 300mAh·g -1 The capacity retention rate is as high as 75% after 500 cycles.

[0108] Comparative Example 1:

[0109] This comparative example is a graphite single-phase negative electrode, comprising the following steps:

[0110] The 800-mesh single-phase natural graphite negative electrode was mixed with PVDF, conductive carbon black, and NMP in a mass ratio of 8:1:1:20 to obtain a slurry with appropriate viscosity, which was then coated on aluminum foil. After drying, the battery negative electrode sheet was obtained, which was then assembled into a 2032 button battery and tested.

[0111] The cycle performance test results of potassium ion battery negative electrode materials are shown in Figure 2. Figure 6 and Figure 7 As shown by Figure 6 and Figure 7 It can be seen that the first cycle discharge capacity of the potassium ion battery negative electrode material prepared in this comparative example is only 80 mAh g -1 About 300mA·g -1 There is almost no discharge capacity at this current density.

[0112] The EIS impedance results of the material obtained in this comparative example 1 and the material obtained in Example 1 are as follows: Figure 8 and 2 As shown, by comparison, it can be seen that the potassium ion battery negative electrode material prepared by the method of Example 1 has higher impedance.

[0113] The potassium ion battery negative electrode material prepared in this comparative example has a low current density (50 mA·g -1 ) The first cycle discharge capacity is 250mAh g -1 About 500mA·g -1 Under the current density condition of only 30mAh·g -1 capacity.

[0114] Comparative Example 2:

[0115] The potassium ion battery composite negative electrode material prepared in this comparative example is an iron-doped graphite phase carbon nitride single-phase negative electrode, and the preparation method includes the following steps:

[0116] S1. Weigh 3 g of urea and 6 g of sodium chloride in a mass ratio of 1:2 and dissolve them in 30 ml of deionized water.

[0117] S2, after 30 min of ultrasonication and drying at 60 °C for 12 h, the precursor product was obtained;

[0118] S3, then heating the obtained sample in a muffle furnace at 520 degrees Celsius for 1.5 hours;

[0119] S4, after grinding, passing through a 200-mesh sieve to obtain the desired graphite phase carbon nitride g-C3N4;

[0120] S5, taking 300 mg of the obtained g-C3N4 and dispersing it in 30 ml of methanol solution;

[0121] S6. According to the mass ratio of graphite carbon nitride: polyether F127: melamine of 1:1:1, polyether F127 and melamine were added continuously, ultrasonicated for 1 hour, stirred for 10 hours, and 0.1 mmol FeCl3 was slowly added to the above solution;

[0122] S7, drying at 60°C for 12 h to obtain a precursor sample;

[0123] S8, the dried sample was placed in a tube furnace under argon at 800 ° C for 2 h to obtain a carbonized sample;

[0124] S9, the obtained product was treated with 5 mol·L -1 HNO3 etching for 24h;

[0125] S10, after filtration and drying at 60°C for 6 hours, lamellar iron-doped graphite phase carbon nitride was obtained.

[0126] The single-phase iron-doped graphite-phase carbon nitride negative electrode was mixed with PVDF, conductive carbon black, and NMP in a mass ratio of 8:1:1:20 to obtain a slurry with appropriate viscosity, which was then coated on aluminum foil. After drying, the battery negative electrode sheet was obtained, which was then assembled into a 2032 button battery and tested.

[0127] After testing, the material's first cycle discharge capacity is 400mAh g -1 However, the cycle performance is poor under high current density conditions, with only 30% capacity retention after 500 cycles.

[0128] Comparative Example 3:

[0129] The negative electrode material of the potassium ion battery prepared in this comparative example is a graphite / hard carbon composite negative electrode, and the preparation method includes the following steps:

[0130] S1. Weigh 800 mesh natural graphite and Type 2 Kuraray hard carbon anode in a ball mill at a mass ratio of 9.5:0.5;

[0131] S2. Add ethanol at a ratio of active substance to ethanol of 1:2; ball mill at 200 rpm for 1 hour at a ball-to-material ratio of 1:1.2 to obtain a mixture; the active substance is a mixture of graphite and hard carbon;

[0132] S3, drying the mixture at 60°C for 6h;

[0133] S4. After sufficient grinding, the composite potassium ion battery negative electrode material is obtained.

[0134] The graphite / hard carbon composite potassium ion battery negative electrode material prepared in this comparative example was mixed with PVDF, conductive carbon black, and NMP in a mass ratio of 8:1:1:20 to obtain a slurry with appropriate viscosity, which was then coated on aluminum foil and dried to obtain a battery negative electrode sheet, which was then assembled into a 2032 button battery and tested.

[0135] The test results show that the reversible capacity of the prepared material is 260 mAh g -1 , at 500mA·g -1 The current density is only 50 mAh g -1 The capacity is much worse than that of Example 1, which proves that the graphite / iron-doped graphite phase carbon nitride composite negative electrode has better performance and is a better solution.

[0136] Comparative Example 4:

[0137] The negative electrode material of the potassium ion battery prepared in this comparative example is a graphite / nickel selenide composite negative electrode, and the preparation method includes the following steps:

[0138] S1. Weigh 800 mesh natural graphite and commercial 99.9% nickel selenide in a ball mill at a mass ratio of 9.5:0.5;

[0139] S2. Add ethanol at a ratio of active substance to ethanol of 1:2; ball mill at 200 rpm for 1 hour at a ball-to-material ratio of 1:1.2 to obtain a mixture; the active substance is a mixture of graphite and nickel selenide;

[0140] S3, drying the mixture at 60°C for 6h;

[0141] S4. After sufficient grinding, the composite potassium ion battery negative electrode material is obtained.

[0142] The graphite / nickel selenide composite potassium ion battery negative electrode material prepared in this comparative example was mixed with PVDF, conductive carbon black, and NMP in a mass ratio of 8:1:1:20 to obtain a slurry with appropriate viscosity, which was then coated on aluminum foil and dried to obtain a battery negative electrode sheet, which was then assembled into a 2032 button battery and tested.

[0143] The test results show that the reversible capacity of the prepared material is 300 mAh g -1 , at 500mA·g-1 The current density is only 70 mAh·g -1 The capacity is much worse than that of Example 1, which proves that the graphite / iron-doped graphite phase carbon nitride composite negative electrode has better performance and is a better solution.

[0144] Comparative Example 5:

[0145] The potassium ion battery negative electrode material prepared in this comparative example is a graphite / graphene composite negative electrode, and the preparation method includes the following steps:

[0146] S1. Weigh 800-mesh natural graphite and 5-8 layers of graphene with a diameter less than 10 μm in a mass ratio of 9.5:0.5 in a ball mill;

[0147] S2. Add ethanol at a ratio of active substance to ethanol of 1:2; ball mill at 200 rpm for 1 h at a ball-to-material ratio of 1:1.2 to obtain a mixture;

[0148] S3, drying the mixture at 60°C for 6h;

[0149] S4. After sufficient grinding, the composite potassium ion battery negative electrode material is obtained.

[0150] The graphite / graphene composite potassium ion battery negative electrode material prepared in this comparative example was mixed with PVDF, conductive carbon black, and NMP in a mass ratio of 8:1:1:20 to obtain a slurry with appropriate viscosity, which was then coated on aluminum foil and dried to obtain a battery negative electrode sheet, which was then assembled into a 2032 button battery and tested.

[0151] The test results show that the reversible capacity of the prepared material is 295 mAh g -1 , at 500mA·g -1 The current density is only 150 mAh g -1 The capacity is much worse than that of Example 1, which proves that the graphite / iron-doped graphite phase carbon nitride composite negative electrode has better performance and is a better solution.

[0152] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, for those of ordinary skill in the art, various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A graphite-based potassium ion battery composite negative electrode, characterized in that The composite negative electrode is a composite material obtained by mechanically mixing graphite and lamellar iron-doped graphite-phase carbon nitride; the mass ratio of graphite to lamellar iron-doped graphite-phase carbon nitride is 4-20:1; and the lamellar iron-doped graphite-phase carbon nitride is Fe-g-C3N4.

2. The composite negative electrode according to claim 1, characterized in that The graphite is 300-800 mesh natural graphite.

3. The composite negative electrode according to claim 2, characterized in that The preparation method of the lamellar iron-doped graphite phase carbon nitride comprises the following steps: S1. Weigh urea and NaCl in a mass ratio of 1:2-3 and dissolve them in deionized water; after ultrasonication for 30-60 minutes, dry at 60-80°C for 12-15 hours to obtain a precursor product; S2. The obtained precursor product is then heated in a muffle furnace at 500-550° C. for 1.5-2.5 h to obtain the desired graphite phase carbon nitride g-C3N4; after grinding, the obtained sample is passed through a 200-300 mesh sieve; S3. Disperse the sieved g-C3N4 in a methanol solution, and add polyether F127 and melamine in a mass ratio of 1:1:1-1.3 to obtain a uniform dispersion by ultrasonication. Stir for 10-15 hours, and slowly add FeCl3 to the solution. After drying, obtain a carbonized sample. S4. The obtained carbonized sample was kept at 800-850℃ in a tube furnace under argon atmosphere for 2-3h to obtain a carbonized sample, and then 5mol·L -1 The HNO3 solution was etched for 20-24 hours; after filtration and drying, lamellar iron-doped graphite carbon nitride Fe-g-C3N4 was obtained; In step S1, when 3 g of urea is used, 30-50 ml of deionized water is required.

4. The composite negative electrode according to claim 1, characterized in that In step S3, when the amount of graphite carbon nitride used is 300 mg, the amount of methanol required is 30-50 ml, and the amount of FeCl3 required is 0.2-0.4 mmol.

5. The composite negative electrode according to claim 1, characterized in that In step S3, the drying is performed at 60-80° C. for 12-15 hours.

6. The composite negative electrode according to claim 1, characterized in that In step S4, the drying temperature is 60-80° C. and the drying time is 6-12 hours.

7. The composite negative electrode according to claim 1, characterized in that The method for mechanically mixing graphite and lamellar iron-doped graphite phase carbon nitride comprises the following steps: placing the graphite and the lamellar iron-doped graphite phase carbon nitride in a ball mill, adding ethanol and performing ball milling to obtain a mixture; and drying and fully grinding the mixture to obtain the potassium ion battery composite negative electrode material.

8. The composite negative electrode according to claim 7, characterized in that During the ball milling treatment, the mass ratio of the sum of the mass of graphite and iron-doped graphite phase carbon nitride to ethanol is 1:2-3; the rotation speed of the ball mill is 250-300 r / min, the ball milling time is 1-2 hours; and the ball-to-material ratio is 1:1-2.

9. The composite negative electrode according to claim 7, characterized in that The drying step is to dry the mixture in a drying oven at 60-80° C. for 12-15 hours.

10. Use of the composite negative electrode according to any one of claims 1 to 9, characterized in that: The composite negative electrode is mixed with PVDF, conductive carbon black and NMP to obtain a slurry with suitable viscosity, which is then coated on a current collector and dried to obtain a potassium ion battery negative electrode.

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