A lithium / carbon monofluoride battery with a wide temperature range, a cathode material, and an electrolyte

Abstract

The present invention discloses a wide-temperature-range lithium / carbon fluoride battery, a cathode material, and an electrolyte. The battery includes a cathode, an anode, a separator, and an electrolyte. The cathode includes a carbon fluoride cathode material. The preparation method of the carbon fluoride cathode material is as follows: Place carbon fluoride in a plasma chemical vapor deposition furnace, maintain a vacuum, introduce a carbon source gas into the plasma chemical vapor deposition furnace, control the radio frequency power to be 100-200 W, the heat treatment temperature to be 550-600 °C, and the heat treatment time to be 10-20 min to obtain the carbon fluoride cathode material. The electrolyte is composed of lithium tetrafluoroborate, methyl acetate, and dimethyl sulfite. The volume ratio of methyl acetate to dimethyl sulfite is 1:1, and the concentration of lithium tetrafluoroborate is 1 mol / L. The battery of the present invention can stably operate in the range of -100 °C to 100 °C.

Description

Technical Field

[0001] The present invention belongs to the field of primary batteries, and specifically relates to a lithium / carbon fluoride battery with a wide temperature range, a cathode material, and an electrolyte solution. Background Art

[0002] Lithium / carbon fluoride (Li / CF x ) primary batteries have attracted much attention from researchers among many primary batteries due to their high theoretical energy density (2100 Wh / kg, x = 1), stable working voltage, long storage life, wide stable use range, good safety, etc., and are widely used in special national defense and military fields such as military equipment (individual combat systems, electronic test devices, missile ignition systems, submarines, etc.), deep sea / deep space exploration, polar exploration, and far space exploration. However, these fields have strict requirements for the performance of the power supply system at extreme temperatures (such as Mars exploration (~-100 °C), oil exploration (~100 °C)). Therefore, it is scientific and practical to develop lithium / carbon fluoride batteries for use at extreme temperatures.

[0003] During the discharge process of lithium / carbon fluoride batteries, the following processes occur: Li + transports in the bulk of the electrolyte; Li + is desolvated at the electrode / electrolyte interface; Li + conducts in the cathode solid electrolyte interphase (CEI); Li + diffuses between the layers of CF x ; the C-F bond breaks. At low temperatures, the ionic conductivity of the electrolyte decreases, the viscosity increases or even freezes, resulting in limited liquid-phase transport of Li + ; an unstable CEI is generated at the carbon fluoride cathode / electrolyte interface, leading to difficult desolvation of Li + and restricting ionic interface conduction; the inherent insulation of the carbon fluoride cathode material results in low ionic / electronic conductivity, which limits the solid-phase diffusion of Li + . These factors synergistically induce the accumulation of lithium fluoride generated during discharge on the surface and edges of the carbon fluoride cathode material, blocking the ion transport channels, resulting in low energy density and power density of lithium / carbon fluoride batteries. At high temperatures, due to the lack of a stable electrode / electrolyte interface, the solvent is easily decomposed to produce serious side reactions, and the solvent is easily volatilized to consume the electrolyte, causing battery failure, etc. These factors severely restrict the use of lithium / carbon fluoride batteries in a wide temperature range environment.

[0004] Based on the above analysis, the carbon fluoride cathode material and the electrolyte solution are equally important for the electrochemical performance of the battery at extreme temperatures. Therefore, how to develop a carbon fluoride cathode material and an electrolyte solution that can simultaneously take into account the high and low temperature performance of lithium / carbon fluoride batteries is of great significance for promoting the application of lithium / carbon fluoride batteries in special national defense and military fields. Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies of the prior art and provide a lithium / carbon fluoride battery, a positive electrode material and an electrolyte with a wide temperature range, which have high energy density and power density in a wide temperature range (-100 to 100 °C). At the same time, the assembled soft-pack battery with an ampere-hour level can achieve high energy densities of 470 Wh / kg and 333 Wh / kg at extremely low temperatures of -50 °C and -70 °C (based on the overall mass of the battery).

[0006] The technical solution for the present invention to solve the technical problems is as follows:

[0007] The first aspect of the present invention is to provide a lithium / carbon fluoride battery with a wide temperature range, including a positive electrode, a negative electrode, a separator and an electrolyte.

[0008] The positive electrode includes a carbon fluoride positive electrode material, and the preparation method of the carbon fluoride positive electrode material is as follows:

[0009] Place carbon fluoride in a plasma chemical vapor deposition furnace, and keep the plasma chemical vapor deposition furnace under vacuum through a vacuum pump; introduce acetylene or methane into the plasma chemical vapor deposition furnace, control the radio frequency power to be 100 - 200 W, the heat treatment temperature to be 550 - 600 °C, and the heat treatment time to be 10 - 20 min to obtain the carbon fluoride positive electrode material. The carbon fluoride positive electrode material is a thin-layer material with nano-carbon dots covering the surface and rich in mesopores. The length and width of the carbon fluoride thin-layer material are 5 - 50 μm, the thickness is 0.2 - 20 μm, the diameter of the nano-carbon dots on the surface of the thin layer is 5 - 20 nm, and the diameter of the mesopores is 2 - 50 nm.

[0010] The electrolyte is composed of lithium tetrafluoroborate, methyl acetate and dimethyl sulfite. The volume ratio of methyl acetate to dimethyl sulfite is 1:1, and the concentration of lithium tetrafluoroborate is 1 mol / L.

[0011] Further, the positive electrode is obtained by dispersing the carbon fluoride positive electrode material, conductive carbon black and binder PVDF in a mass ratio of 8 - 9:0.5 - 1:0.5 - 1 (preferably 8:1:1; for the soft-pack battery with an ampere-hour level, the ratio is 9:0.5:0.5) into N-methylpyrrolidone, fully mixing and then coating on the carbon-coated aluminum foil and drying.

[0012] Further, the negative electrode uses a lithium sheet or lithium strip with a thickness of 50 - 500 μm.

[0013] Further, the separator uses a PE separator (thickness 25 μm).

[0014] The second aspect of the present invention is to provide a cathode material for a wide-temperature-range lithium / carbon fluoride battery. The carbon fluoride cathode material is a thin-layer material with nano-carbon dots covering the surface and rich in mesopores. The length and width of the carbon fluoride thin-layer material are 5 - 50 μm, the thickness is 0.2 - 20 μm, the diameter of the nano-carbon dots on the surface of the thin layer is 5 - 20 nm, and the diameter of the mesopores is 2 - 50 nm. The preparation method is as follows: Place the carbon fluoride in a plasma chemical vapor deposition furnace, and adjust the commercial carbon fluoride cathode material to a position 10 - 50 cm away from the plasma radio frequency coil. Keep the plasma chemical vapor deposition furnace under vacuum through a vacuum pump; introduce a carbon source gas into the plasma chemical vapor deposition furnace, control the radio frequency power to be 50 - 200 W, the heat treatment temperature to be 300 - 600 °C, and the heat treatment time to be 5 - 30 min to obtain the carbon fluoride cathode material.

[0015] In the present invention, the carbon fluoride material has a large specific surface area, rich thin-layer and pore structures, which is conducive to the full infiltration of the electrolyte and promotes the rapid conduction of lithium ions. At the same time, a large number of nano-carbon dots are contained on the surface of the carbon fluoride, which improves the electronic conductivity of the material itself, reduces the polarization during the discharge process, and greatly improves the utilization rate of the carbon fluoride material at high rates and low temperatures.

[0016] Further, the carbon source gas is acetylene or methane.

[0017] Further, the radio frequency power is 100 - 200 W; the heat treatment temperature is 550 - 600 °C; the heat treatment time is 10 - 20 min. Preferably, the radio frequency power is 150 W, the heat treatment temperature is 580 °C, and the heat treatment time is 15 min.

[0018] The present invention uses plasma chemical vapor deposition technology to treat commercial carbon fluoride materials, and has the following outstanding technical effects: (1) By controlling the plasma radio frequency power, radio frequency treatment time, and heating time, a carbon fluoride material with uniform pore distribution, thinner layers, and larger specific surface area can be obtained; (2) By controlling different carrier gas components and gas flow rates, the size and quantity of carbon nano-dots on the surface of the carbon fluoride can be effectively controlled. (3) This method is simple and easy to operate, and is convenient for large-scale application. The carbon fluoride material with a large specific surface area, rich pore diameters, and a large number of carbon nano-dots coated has high ionic / electronic conductivity, effectively reduces polarization, and improves the rate performance and low-temperature performance of the carbon fluoride material.

[0019] The third aspect of the present invention is to provide an electrolyte for a wide-temperature-range lithium / carbon fluoride battery. The electrolyte is composed of lithium tetrafluoroborate, a carboxylic ester solvent, and a sulfite solvent. The carboxylic ester solvent is methyl formate, methyl acetate, ethyl acetate, methyl propionate, or ethyl propionate; the sulfite solvent is dimethyl sulfite or diethyl sulfite.

[0020] Further, the concentration of lithium tetrafluoroborate is 0.5 - 4 mol / L; the volume ratio of the carboxylic acid ester solvent to the sulfite ester solvent is 1 - 0:0 - 1.

[0021] Preferably, the concentration of lithium tetrafluoroborate is 1 mol / L, the carboxylic acid ester solvent is methyl acetate, the sulfite ester solvent is dimethyl sulfite, and the volume ratio of methyl acetate to dimethyl sulfite is 1:1.

[0022] Preferably, the method for preparing the electrolyte is as follows: First, uniformly mix the carboxylic acid ester solvent and the sulfite ester solvent to form a co-solvent; then add lithium tetrafluoroborate and dissolve it to obtain the electrolyte.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) By comparing the treatment of carbon fluoride by plasma chemical vapor deposition under different atmosphere conditions, it is found that the surface of the carbon fluoride material treated with inert gas contains a large number of pores and the specific surface area increases; the pore size / specific surface area of the carbon fluoride material treated with carbon source-containing atmosphere is further enlarged, and a large number of carbon nanodots grow on the surface of the material, significantly improving the electron / ion conductivity of the carbon fluoride material and promoting the diffusion of Li + inside the carbon fluoride at low temperature.

[0025] (2) Based on the viscosity effect and dielectric effect, the present invention selects carboxylic acid ester solvents with low viscosity and sulfite ester solvents with high dielectric constant as wide-temperature electrolytes. The carboxylic acid ester solvent has low viscosity and low freezing point, which can promote the ion diffusion of the electrolyte at low temperature. The sulfite ester solvent has a high dielectric constant and a wide liquid range, which can prevent the precipitation of salts at low temperature and the volatilization of the electrolyte at high temperature; the sulfite ester solvent with high adsorption energy and high HOMO energy level can adsorb on the surface of the carbon fluoride positive electrode and induce decomposition at high potential to generate a solid electrolyte layer rich in organic sulfur components, accelerating the Li + transport at the interface, avoiding the accumulation of lithium fluoride, and inhibiting the occurrence of side reactions; during the discharge process, this solid electrolyte layer evolves into a component rich in inorganic lithium sulfide / lithium fluoride, further accelerating the rapid conduction of Li + at the interface layer, improving the kinetic performance of the lithium / carbon fluoride battery at low temperature and its stability at high temperature; at the same time, the sulfite ester solvent with low LUMO energy level can relay the reaction at the low potential at the end of the discharge of carbon fluoride, further oxidize and decompose to provide capacity, and improve the overall energy density of the battery.

[0026] (3) Based on the carbon fluoride cathode material and electrolyte of the present invention, the lithium / carbon fluoride full battery composed by matching with a lithium metal anode has high energy density and power density in a wide temperature range (-100 to 100 °C). At the same time, the assembled Ah-level soft-pack battery can achieve high energy densities of 470 Wh / kg and 333 Wh / kg at extremely low temperatures of -50 °C and -70 °C (based on the overall mass of the battery), which is of great significance for promoting the application of lithium / carbon fluoride batteries in special defense and military fields.

[0027] (4) The preparation method of the carbon fluoride cathode material provided by the present invention has relatively mature technology and can be mass-produced in batches. The electrolyte components provided by the present invention have the advantages of low cost, easy preparation, safety and no pollution, and can be widely applied. Description of the Drawings

[0028] Figure 1 Transmission electron microscopy image of the commercial untreated carbon fluoride material in Comparative Example 1;

[0029] Figure 2 Transmission electron microscopy image of the carbon fluoride cathode material prepared in Comparative Example 2;

[0030] Figure 3 Transmission electron microscopy image of the carbon fluoride cathode material prepared in Comparative Example 3;

[0031] Figure 4 Transmission electron microscopy image of the carbon fluoride cathode material prepared in Example 1;

[0032] Figure 5 XRD comparison chart of the carbon fluoride cathode materials prepared in Example 1 and Comparative Examples 1-3;

[0033] Figure 6 BET comparison chart of the carbon fluoride cathode materials prepared in Example 1 and Comparative Examples 1-3;

[0034] Figure 7 Infrared spectrum comparison chart of the carbon fluoride cathode materials prepared in Example 1 and Comparative Examples 1-3;

[0035] Figure 8 Comparison chart of the content of semi-ionic C-F bonds in the XPS characterization of the carbon fluoride cathode materials prepared in Example 1 and Comparative Examples 1-3;

[0036] Figure 9 Discharge curve diagram of the batteries in Example 2 and Comparative Examples 4-6 at 0.1 A / g;

[0037] Figure 10 Discharge curve diagram of the batteries in Example 2 and Comparative Examples 4-6 at 5 A / g;

[0038] Figure 11XRD comparison diagrams for Example 3, Comparative Examples 7-9, and Comparative Example 1;

[0039] Figure 12 Discharge curve diagrams of the batteries of Example 4 and Comparative Examples 10-11 at a 1C rate;

[0040] Figure 13 Discharge curve diagrams of the batteries of Example 5 and Comparative Examples 12-13 at a 0.1C rate;

[0041] Figure 14 Differential scanning calorimetry comparison diagrams for Example 6 and Comparative Examples 14-17;

[0042] Figure 15 Ionic conductivity comparison diagrams for Example 6 and Comparative Examples 14-17 at different temperatures;

[0043] Figure 16 Viscosity comparison diagrams for Example 6 and Comparative Examples 14-17 at different temperatures;

[0044] Figure 17 Discharge curve diagrams of the battery of Example 7 at -100 - 100 °C;

[0045] Figure 18 Discharge curve diagrams of the battery of Example 7 at 25 °C with different current densities;

[0046] Figure 19 Discharge curve diagrams of the battery of Example 7 at -30 °C with different current densities;

[0047] Figure 20 Discharge curve diagrams of the battery of Example 7 at -50 °C with different current densities;

[0048] Figure 21 Discharge curve diagrams of the battery of Example 7 at -70 °C with different current densities;

[0049] Figure 22 Discharge curve diagrams of the battery of Example 7 at -86 °C with different current densities;

[0050] Figure 23 Discharge curve diagrams of the battery of Example 8 at -50 °C and -70 °C;

[0051] Figure 24 Content comparison diagrams of C-F bonds, S-F bonds, and LiF in the XPS characterization of the electrode sheet surface of Example 9;

[0052] Figure 25 Content comparison diagrams of Li2S and ROSOLi in the XPS characterization of the electrode sheet surface of Example 9;

[0053] Figure 26 Charge transfer impedance comparison chart of Example 10 and Comparative Example 18 at -20°C to 25°C;

[0054] Figure 27 Lithium ion desolvation energy barrier comparison chart of Example 10 and Comparative Example 18;

[0055] Figure 28 Lithium ion energy barrier comparison chart for crossing the CEI of Example 11 and Comparative Example 19;

[0056] Figure 29 Lithium ion desolvation energy barrier comparison chart of Example 11 and Comparative Example 19. Detailed implementation manners

[0057] The present invention will be further described in detail below through specific examples. The following examples are only descriptive and not restrictive, and the protection scope of the present invention cannot be limited thereby.

[0058] By comparing the morphological structures of the carbon fluoride materials of Example 1 and Comparative Examples 1 to 3, the optimal atmosphere for treating carbon fluoride by plasma chemical vapor deposition is confirmed.

[0059] Example 1

[0060] The carbon fluoride cathode material is obtained by plasma chemical vapor deposition. Specifically:

[0061] (1) Place the commercial carbon fluoride cathode material in a plasma chemical vapor deposition furnace; adjust the distance between the commercial carbon fluoride cathode material and the plasma radio frequency coil to 50 cm.

[0062] (2) Keep the plasma chemical vapor deposition furnace under vacuum by a vacuum pump.

[0063] (3) Introduce acetylene into the plasma chemical vapor deposition furnace evacuated in step (2).

[0064] (4) On the basis of step (3), turn on the radio frequency switch and heating switch of the plasma chemical vapor deposition furnace, and control the heat treatment time to obtain the carbon fluoride cathode material; the radio frequency power is 150 W, the heat treatment temperature is 580°C, and the heat treatment time is 15 min.

[0065] Comparative Example 1

[0066] Commercial untreated carbon fluoride material.

[0067] Comparative Example 2

[0068] The difference from Example 1 is that step (3) of Example 1 is omitted.

[0069] Comparative Example 3

[0070] The difference from Example 1 is that acetylene in step (3) is replaced by argon.

[0071] By performing transmission electron microscopy tests ( Figures 1 to 4 ), X-ray diffraction analysis ( Figure 5 ), BET tests ( Figure 6 ), infrared spectroscopy analysis ( Figure 7 ), and X-ray photoelectron spectroscopy analysis (XPS) ( Figure 8 ) on Example 1 and Comparative Examples 1 to 3, the morphology and structure of the carbon fluoride treated under different atmospheres are characterized.

[0072] It can be seen from Figure 1 that the surface of the untreated carbon fluoride is smooth.

[0073] It can be seen from Figure 2 that when only heat treatment is performed without passing gas, a large number of wrinkles are generated on the surface of the carbon fluoride.

[0074] It can be seen from Figure 3 that in the presence of an inert atmosphere (argon), the surface of the treated carbon fluoride is uneven and a pore-like structure is generated.

[0075] It can be seen from Figure 4 that in the presence of a carbon source atmosphere (acetylene), a rich pore structure is generated on the surface of the treated carbon fluoride, and a large number of carbon nanodots grow at the edges.

[0076] It can be seen from Figure 5 that the carbon fluoride materials obtained by plasma chemical vapor deposition technology under different atmospheres are similar in structure to commercial carbon fluoride and no obvious change occurs.

[0077] It can be seen from Figure 6 that the carbon fluoride materials obtained by plasma chemical vapor deposition technology under different atmospheres have a large specific surface area and pore size, and the effect is optimal after treatment with a carbon source atmosphere (acetylene).

[0078] It can be seen from Figure 7 and Figure 8 that the C-F bond property of the carbon fluoride materials obtained by plasma chemical vapor deposition technology under different atmospheres changes significantly, the semi-ionic bond increases, and the conductivity enhances, and the effect is optimal after treatment with a carbon source atmosphere (acetylene).

[0079] Comparative Example 4 uses untreated commercial carbon fluoride material as the positive electrode active material, and matches the electrolyte, negative electrode, and separator to form a lithium / carbon fluoride battery. Examples 2 and Comparative Examples 5-6 use carbon fluoride materials obtained by plasma chemical vapor deposition technology under different atmospheres as the positive electrode active material, and match the electrolyte, negative electrode, and separator to form a lithium / carbon fluoride battery.

[0080] Example 2

[0081] The carbon fluoride material obtained in Example 1 is used as the positive electrode active material.

[0082] Positive electrode: The carbon fluoride material, conductive carbon black (Super P), and PVDF obtained in Example 1 are mixed evenly in a mass ratio of 8:1:1, dispersed in N-methylpyrrolidone, and stirred thoroughly for 8 h until uniform to obtain a positive electrode slurry; then the positive electrode slurry is evenly coated on the carbon-coated aluminum foil, dried in an 80 °C drying oven for 12 h, and then cut into a positive electrode with a diameter of 10 mm.

[0083] Negative electrode: A lithium sheet with a diameter of 14 mm and a thickness of 500 μm is used.

[0084] Separator: A PE separator, SK innovation Co., Ltd.

[0085] The electrolyte is composed of lithium hexafluorophosphate, ethylene carbonate, and diethyl carbonate; the concentration of lithium hexafluorophosphate is 1 mol / L, and the volume ratio of ethylene carbonate to diethyl carbonate is 1:1. The specific preparation method is: first, the ethylene carbonate and diethyl carbonate solvents are evenly mixed to form a co-solvent; then lithium hexafluorophosphate is added and dissolved to obtain the electrolyte.

[0086] Battery assembly: Assemble a button battery in the order of negative electrode case - shrapnel - gasket - negative electrode - electrolyte - separator - electrolyte - positive electrode - positive electrode case, and the battery specification is 2032.

[0087] After the assembled battery is left standing for 10 h, at room temperature, a discharge test is carried out at a cut-off voltage of 1.5 V, and the discharge specific capacity of the battery is calculated using the carbon fluoride material in the positive electrode material as the active material.

[0088] Comparative Example 4

[0089] The untreated commercial carbon fluoride material in Comparative Example 1 is used as the positive electrode active material.

[0090] Positive electrode: The untreated commercial carbon fluoride material, conductive carbon black (Super P), and PVDF in Comparative Example 1 are mixed evenly in a mass ratio of 8:1:1, dispersed in N-methylpyrrolidone, and stirred thoroughly for 8 h until uniform to obtain a positive electrode slurry; then the positive electrode slurry is evenly coated on the carbon-coated aluminum foil, dried in an 80 °C drying oven for 12 h, and then cut into a positive electrode with a diameter of 10 mm.

[0091] The negative electrode, separator and electrolyte are the same as those in Example 2.

[0092] Battery assembly: The same as in Example 2.

[0093] After the assembled battery was left standing for 10 h, a discharge test was carried out at room temperature with a cut-off voltage of 1.5 V, and the discharge specific capacity of the battery was calculated based on the carbon fluoride material in the positive electrode material as the active substance.

[0094] Comparative Example 5

[0095] The carbon fluoride material obtained in Comparative Example 2 was used as the positive electrode active substance.

[0096] Positive electrode: The carbon fluoride material obtained in Comparative Example 2, conductive carbon black (Super P) and PVDF were mixed evenly in a mass ratio of 8:1:1, dispersed in N-methylpyrrolidone, and stirred thoroughly for 8 h until homogeneous to obtain a positive electrode slurry; then the positive electrode slurry was evenly coated on carbon-coated aluminum foil, dried in an oven at 80 °C for 12 h, and then cut into a positive electrode with a diameter of 10 mm.

[0097] The negative electrode, separator and electrolyte are the same as those in Example 2.

[0098] Battery assembly: The same as in Example 2.

[0099] After the assembled battery was left standing for 10 h, a discharge test was carried out at room temperature with a cut-off voltage of 1.5 V, and the discharge specific capacity of the battery was calculated based on the carbon fluoride material in the positive electrode material as the active substance.

[0100] Comparative Example 6

[0101] The carbon fluoride material obtained in Comparative Example 3 was used as the positive electrode active substance.

[0102] Positive electrode: The carbon fluoride material obtained in Comparative Example 3, conductive carbon black (Super P) and PVDF were mixed evenly in a mass ratio of 8:1:1, dispersed in N-methylpyrrolidone, and stirred thoroughly for 8 h until homogeneous to obtain a positive electrode slurry; then the positive electrode slurry was evenly coated on carbon-coated aluminum foil, dried in an oven at 80 °C for 12 h, and then cut into a positive electrode with a diameter of 10 mm.

[0103] The negative electrode, separator and electrolyte are the same as those in Example 2.

[0104] Battery assembly: The same as in Example 2.

[0105] After the assembled battery was left standing for 10 h, a discharge test was carried out at room temperature with a cut-off voltage of 1.5 V, and the discharge specific capacity of the battery was calculated based on the carbon fluoride material in the positive electrode material as the active substance.

[0106] byFigures 9 to 10 It can be seen that the carbon fluoride material obtained using Example 1 has optimal electrochemical performance. Table 1 shows the comparison of voltage and discharge specific capacity of Example 2 and Comparative Examples 4-6 at different rates.

[0107] Table 1

[0108]

[0109] As can be seen from Table 1, Example 2 has optimal electrochemical performance both at low rates and high rates. This is because the carbon fluoride corresponding to Example 1 has a large pore size / specific surface area, and a large number of carbon nanodots grow on the material surface, significantly improving the electron / ion conductivity of the carbon fluoride material, resulting in the improvement of battery performance.

[0110] Example 3 and Comparative Examples 7-9 are carbon fluoride materials obtained by plasma chemical vapor deposition technology at different temperatures, and the optimal treatment temperature is determined by characterizing their structures and electrochemical performances.

[0111] Example 3

[0112] The carbon fluoride material is obtained by plasma chemical vapor deposition, specifically:

[0113] (1) Place the commercial carbon fluoride cathode material in a plasma chemical vapor deposition furnace; adjust the distance between the commercial carbon fluoride cathode material and the plasma radio frequency coil to 40 cm.

[0114] (2) Keep the plasma chemical vapor deposition furnace under vacuum through a vacuum pump.

[0115] (3) Introduce acetylene into the plasma chemical vapor deposition furnace evacuated in step (2).

[0116] (4) On the basis of step (3), turn on the radio frequency switch and heating switch of the plasma chemical vapor deposition furnace, and control the heat treatment time to obtain the carbon fluoride cathode material; preferably, the radio frequency power is 150 W, the heat treatment temperature is 580 °C, and the heat treatment time is 15 min.

[0117] Comparative Example 7

[0118] The difference from Example 3 is that the heat treatment temperature in step (4) is 500 °C.

[0119] Comparative Example 8

[0120] The difference from Example 3 is that the heat treatment temperature in step (4) is 550 °C.

[0121] Comparative Example 9

[0122] The difference from Example 3 is that the heat treatment temperature in step (4) is 600 °C.

[0123] By performing X-ray diffraction analysis on Example 3 and Comparative Examples 7-9 ( Figure 11 ), it was found that when the heat treatment temperature reached 600 °C, the basic structure of carbon fluoride changed. Therefore, the preferred temperature range is 300-580 °C. Further, the carbon fluoride materials obtained in Example 3 and Comparative Examples 7-8 were used as the positive electrode, and a lithium / carbon fluoride battery was assembled by matching the negative electrode, separator, and electrolyte (see Example 4, Comparative Examples 10-11), and the optimal heat treatment temperature was confirmed through electrochemical performance.

[0124] Example 4

[0125] The carbon fluoride material obtained in Example 3 was used as the positive electrode active material.

[0126] Positive electrode: The carbon fluoride material obtained in Example 3, conductive carbon black (Super P), and PVDF were mixed evenly in a mass ratio of 8:1:1, dispersed in N-methylpyrrolidone, and stirred thoroughly for 8 h until homogeneous to obtain the positive electrode slurry; then the positive electrode slurry was evenly coated on the carbon-coated aluminum foil, dried in an 80 °C drying oven for 12 h, and then cut into a positive electrode with a diameter of 10 mm.

[0127] The negative electrode, separator, and electrolyte were the same as those in Example 2.

[0128] Battery assembly: The same as in Example 2.

[0129] After the assembled battery was left standing for 10 h, at room temperature, a discharge test was carried out at a cut-off voltage of 1.5 V, and the discharge specific capacity of the battery was calculated using the carbon fluoride material in the positive electrode material as the active material.

[0130] Comparative Example 10

[0131] The carbon fluoride material obtained in Comparative Example 7 was used as the positive electrode active material.

[0132] Positive electrode: The carbon fluoride material obtained in Comparative Example 7, conductive carbon black (Super P), and PVDF were mixed evenly in a mass ratio of 8:1:1, dispersed in N-methylpyrrolidone, and stirred thoroughly for 8 h until homogeneous to obtain the positive electrode slurry; then the positive electrode slurry was evenly coated on the carbon-coated aluminum foil, dried in an 80 °C drying oven for 12 h, and then cut into a positive electrode with a diameter of 10 mm.

[0133] The negative electrode, separator, and electrolyte were the same as those in Example 2.

[0134] Battery assembly: The same as in Example 2.

[0135] After the assembled battery was left standing for 10 h, at room temperature, a discharge test was carried out at a cut-off voltage of 1.5 V, and the discharge specific capacity of the battery was calculated using the carbon fluoride material in the positive electrode material as the active material.

[0136] Comparative Example 11

[0137] The carbon fluoride material obtained in Comparative Example 8 was used as the positive electrode active material.

[0138] Positive electrode: The carbon fluoride material, conductive carbon black (Super P), and PVDF obtained in Comparative Example 8 were mixed evenly at a mass ratio of 8:1:1, dispersed in N-methylpyrrolidone, and stirred thoroughly for 8 h until uniform to obtain a positive electrode slurry; then the positive electrode slurry was evenly coated on carbon-coated aluminum foil, dried in an 80°C drying oven for 12 h, and then cut into a positive electrode with a diameter of 10 mm.

[0139] The negative electrode, separator, and electrolyte were the same as those in Example 2.

[0140] Battery assembly: The same as in Example 2.

[0141] After the assembled battery was left standing for 10 h, at room temperature, a discharge test was carried out at a cut-off voltage of 1.5 V, and the discharge specific capacity of the battery was calculated using the carbon fluoride material in the positive electrode material as the active material.

[0142] From Figure 12 It can be seen that the carbon fluoride material obtained in Example 3 has the optimal electrochemical performance. It was confirmed that when the heat treatment temperature was 580°C, the carbon fluoride material obtained using plasma chemical vapor deposition technology was the best.

[0143] In Examples 5 and Comparative Examples 12 to 13, the carbon fluoride materials obtained by plasma chemical vapor deposition for different times at a heat treatment temperature of 580°C in an acetylene carbon source atmosphere were used as the positive electrode, and a lithium / carbon fluoride battery was assembled by matching the electrolyte, negative electrode, and separator, and the optimal heat treatment time was confirmed through electrochemical performance.

[0144] Example 5

[0145] The carbon fluoride material was obtained by plasma chemical vapor deposition, specifically:

[0146] (1) Place the commercial carbon fluoride positive electrode material in a plasma chemical vapor deposition furnace; adjust the distance between the commercial carbon fluoride positive electrode material and the plasma radio frequency coil to 30 cm.

[0147] (2) Keep the plasma chemical vapor deposition furnace under vacuum through a vacuum pump.

[0148] (3) Introduce acetylene into the plasma chemical vapor deposition furnace evacuated in step (2).

[0149] (4) On the basis of step (3), turn on the RF switch and heating switch of the plasma chemical vapor deposition furnace, and control the heat treatment time to obtain the carbon fluoride cathode material; the RF power is 150 W, the heat treatment temperature is 580 °C, and the heat treatment time is 15 min.

[0150] The carbon fluoride material treated in the above manner is used as the positive electrode active material.

[0151] Positive electrode: The carbon fluoride material, conductive carbon black (Super P), and PVDF obtained after the above treatment are mixed evenly in a mass ratio of 8:1:1, dispersed in N-methylpyrrolidone, and stirred thoroughly for 8 h until uniform to obtain the positive electrode slurry; then the positive electrode slurry is evenly coated on the carbon-coated aluminum foil, dried in an 80 °C drying oven for 12 h, and then cut into a positive electrode with a diameter of 10 mm.

[0152] The negative electrode, separator, and electrolyte are the same as those in Example 2.

[0153] Battery assembly: The same as in Example 2.

[0154] After the assembled battery is left standing for 10 h, at room temperature, a discharge test is carried out at a cut-off voltage of 1.5 V, and the discharge specific capacity of the battery is calculated using the carbon fluoride material in the positive electrode material as the active substance.

[0155] Comparative Example 12

[0156] The difference from Example 5 is that the heat treatment time in step (4) is 10 min.

[0157] The carbon fluoride material treated in the above manner is used as the positive electrode active material.

[0158] Positive electrode: The carbon fluoride material, conductive carbon black (Super P), and PVDF obtained after the above treatment are mixed evenly in a mass ratio of 8:1:1, dispersed in N-methylpyrrolidone, and stirred thoroughly for 8 h until uniform to obtain the positive electrode slurry; then the positive electrode slurry is evenly coated on the carbon-coated aluminum foil, dried in an 80 °C drying oven for 12 h, and then cut into a positive electrode with a diameter of 10 mm.

[0159] The negative electrode, separator, and electrolyte are the same as those in Example 2.

[0160] Battery assembly: The same as in Example 2.

[0161] After the assembled battery is left standing for 10 h, at room temperature, a discharge test is carried out at a cut-off voltage of 1.5 V, and the discharge specific capacity of the battery is calculated using the carbon fluoride material in the positive electrode material as the active substance.

[0162] Comparative Example 13

[0163] The difference from Example 5 is that the heat treatment time in step (4) is 25 min.

[0164] The carbon fluoride material processed by the above method is used as the positive electrode active material.

[0165] Positive electrode: The carbon fluoride material, conductive carbon black (Super P), and PVDF obtained after the above treatment are mixed evenly in a mass ratio of 8:1:1, dispersed in N-methylpyrrolidone, and stirred thoroughly for 8 h until uniform to obtain the positive electrode slurry; then the positive electrode slurry is evenly coated on the carbon-coated aluminum foil and dried in an oven at 80 °C for 12 h, and then cut into a positive electrode with a diameter of 10 mm.

[0166] The negative electrode, separator, and electrolyte are the same as those in Example 2.

[0167] Battery assembly: The same as in Example 2.

[0168] After the assembled battery is left standing for 10 h, at room temperature, a discharge test is carried out at a cut-off voltage of 1.5 V, and the discharge specific capacity of the battery is calculated based on the carbon fluoride material in the positive electrode material as the active material.

[0169] From Figure 13 It can be seen that Example 5 has a relatively high specific capacity and voltage, so the carbon fluoride material obtained in Example 5 has the best performance. It is confirmed that when the heat treatment temperature is 580 °C, the optimal time for treating carbon fluoride using plasma chemical vapor deposition technology is 15 min.

[0170] The optimal electrolyte composition ratio is screened by comparing the freezing points, and the ionic conductivities and viscosities at different temperatures of Example 6 and Comparative Examples 14 to 17.

[0171] Example 6

[0172] The electrolyte is composed of lithium tetrafluoroborate, methyl acetate, and dimethyl sulfite; the concentration of lithium tetrafluoroborate is 1 mol / L; the volume ratio of methyl acetate to dimethyl sulfite is 1:1.

[0173] The specific preparation method is: first, methyl acetate and dimethyl sulfite are uniformly mixed in a volume ratio of 1:1 to form a co-solvent; then lithium tetrafluoroborate is added and dissolved to obtain a uniform electrolyte with a lithium tetrafluoroborate concentration of 1 mol / L.

[0174] Comparative Example 14

[0175] The electrolyte is composed of lithium tetrafluoroborate and methyl acetate; the concentration of lithium tetrafluoroborate is 1 mol / L;

[0176] The specific preparation method is: lithium tetrafluoroborate is dissolved in methyl acetate to obtain a uniform electrolyte with a lithium tetrafluoroborate concentration of 1 mol / L.

[0177] Comparative Example 15

[0178] The electrolyte is composed of lithium tetrafluoroborate, methyl acetate and dimethyl sulfite; the concentration of lithium tetrafluoroborate is 1 mol / L; the volume ratio of methyl acetate to dimethyl sulfite is 7:3.

[0179] Comparative Example 16

[0180] The electrolyte is composed of lithium tetrafluoroborate, methyl acetate and dimethyl sulfite; the concentration of lithium tetrafluoroborate is 1 mol / L; the volume ratio of methyl acetate to dimethyl sulfite is 3:7.

[0181] Comparative Example 17

[0182] The electrolyte is composed of lithium tetrafluoroborate and dimethyl sulfite; the concentration of lithium tetrafluoroborate is 1 mol / L;

[0183] The specific preparation method is: dissolve lithium tetrafluoroborate in dimethyl sulfite to obtain a homogeneous electrolyte with a concentration of 1 mol / L of lithium tetrafluoroborate.

[0184] By performing differential scanning calorimetry ( Figure 14 ), AC impedance analysis ( Figure 15 ), and viscosity testing ( Figure 16 ) on Example 6 and Comparative Examples 14 - 17, the freezing points and ionic conductivities and viscosities of different-component electrolytes at different temperatures were characterized.

[0185] It can be seen from Figure 14 that when the volume ratio of methyl acetate to dimethyl sulfite is in the range of 0 - 7:3 - 10, the freezing point of the composed electrolyte is less than -100 °C. Combining Figures 15 to 16 , when the volume ratio of methyl acetate to dimethyl sulfite is 1:1 (Example 6), it exhibits the optimal ionic conductivity in the range of -80 to 30 °C and the lowest viscosity in the range of -40 to 30 °C, and is the electrolyte with the best comprehensive performance.

[0186] The positive electrode in Example 5 was paired with the electrolyte in Example 6, as well as the negative electrode and separator, to assemble a lithium / carbon fluoride battery, and its electrochemical performance in a wide temperature range was tested.

[0187] Example 7

[0188] Positive electrode: The same as the positive electrode in Example 5.

[0189] Electrolyte: The electrolyte in Example 6 was used.

[0190] Negative electrode, separator: The same as in Example 2.

[0191] Battery assembly: The same as in Example 2.

[0192] After the assembled battery is left standing for 10 h, for the wide temperature range test from -100 to 100 °C, the battery is discharged at a constant current density of 5 mA / g or 10 mA / g for 2 h or 4 h; for the wide temperature range test from 25 to -86 °C, the discharge test is carried out at a cut-off voltage of 1.5 V, and the discharge specific capacity of the battery is calculated based on the carbon fluoride material in the positive electrode material as the active substance.

[0193] It can be seen from Figure 17 that the positive electrode of Example 5 and the electrolyte of Example 6 can work stably in the wide temperature range from -100 to 100 °C. It can be seen from Figures 18 to 22 that the positive electrode of Example 5 and the electrolyte of Example 6 have high discharge specific capacity and rate performance in the temperature range from -86 to 25 °C. And at a small current density, a discharge specific capacity exceeding the theoretical capacity is exhibited, that is, there is a slope platform after the carbon fluoride discharge platform, corresponding to the decomposition of dimethyl sulfite, indicating that this electrolyte has a capacity contribution effect and can carry out a relay reaction after the carbon fluoride is discharged, further improving the energy density of the battery. Table 2 shows the discharge performance of the battery of Example 7 at different temperatures.

[0194] Table 2

[0195]

[0196]

[0197] It can be seen from Table 2 that Example 7 has excellent energy density and power density in the temperature range from -86 to 25 °C. Specifically, at 25 °C, the battery can work at a high current density of 50 A / g, and achieve an energy density of 1099 Wh / kg and a power density of 86 kW / kg (based on the mass of the active substance); at -30 °C, the battery can work at a high current density of 5 A / g, and achieve an energy density of 976 Wh / kg and a power density of 9220 W / kg (based on the mass of the active substance); at -50 °C, the battery can work at a high current density of 2 A / g, and achieve an energy density of 765 Wh / kg and a power density of 3567 W / kg (based on the mass of the active substance); at -70 °C, the working current density of the battery can reach 0.1 A / g, and achieve an energy density of 595 Wh / kg and a power density of 176 W / kg (based on the mass of the active substance); at -86 °C, the battery can work at a current density of 0.01 A / g, and achieve an energy density of 520 Wh / kg (based on the mass of the active substance).

[0198] Example 8

[0199] To simulate the actual use situation, a 5 Ah lithium / carbon fluoride soft-pack battery is assembled and tested under low temperature conditions.

[0200] Positive electrode: The carbon fluoride material, conductive carbon black (Super P), and PVDF obtained in Example 5 were uniformly mixed at a mass ratio of 9:0.5:0.5, dispersed in N-methylpyrrolidone, and stirred thoroughly until uniform to obtain a positive electrode slurry; then the positive electrode slurry was uniformly coated on carbon-coated aluminum foil, dried in an oven at 80 °C for 12 h, and then cut into a long strip positive electrode with a size of 66.5×6.2 cm (length×width).

[0201] Electrolyte: The electrolyte of Example 6 was used.

[0202] Negative electrode: A lithium strip with a thickness of 85 μm was cut into a long strip with a size of 70.5×6 cm (length×width).

[0203] Separator: A PE separator, SK innovation Co., Ltd. was used.

[0204] Battery assembly: The negative electrode, separator, and positive electrode were wound into a battery core with a size of 6.5×3.5 cm by winding, and then it was encapsulated with an aluminum-plastic film to obtain a 5 Ah soft-pack battery.

[0205] After the assembled battery was left standing for 24 h, it was subjected to a discharge test at a cut-off voltage of 1.5 V at different temperatures, and the discharge specific capacity of the battery was calculated using the carbon fluoride material in the positive electrode material as the active substance.

[0206] From Figure 23 It can be seen that the assembled 5 Ah soft-pack battery can achieve high energy densities of 470.6 Wh / kg and 332.7 Wh / kg based on the overall mass at -50 °C and -70 °C respectively, showing excellent application prospects at low temperatures.

[0207] During the discharge process, Li + will undergo the following processes: transport in the electrolyte bulk phase; desolvation at the electrode / electrolyte interface; conduction in the cathode solid electrolyte interphase (CEI); interlayer diffusion in CF x layer; C-F bond breakage. Among them, the desolvation of Li + at the interface and its crossing of the CEI interface layer are crucial for the low-temperature performance of the battery. Therefore, clarifying the composition and role of CEI is of great significance for the application of lithium / carbon fluoride batteries at low temperatures.

[0208] Example 9 used the same battery as Example 7. By subjecting it to different discharge depths, the positive electrode sheet was disassembled, and X-ray photoelectron spectroscopy was used to explore the changes in the CEI composition during the discharge process.

[0209] Example 9

[0210] The positive electrode, electrolyte, separator, negative electrode, and battery assembly method of the battery were the same as those of Example 7.

[0211] After the assembled battery is left standing at room temperature for 10 h, after experiencing different discharge stages at 0 °C, the battery is disassembled to obtain a carbon fluoride positive electrode.

[0212] From Figure 24 and Figure 25 It can be seen that during the discharge process of carbon fluoride in Example 9 (before 800 mAh / g), the components of the surface CEI change from the initial organic sulfur components (S-F( Figure 24 )) and ROSOLi( Figure 25 )) as the dominant components to inorganic sulfur and inorganic fluorine components (LiF( Figure 24 )) and Li2S) as the dominant components, and it remains stable during the carbon fluoride discharge stage. After the carbon fluoride discharge stage, the organic sulfur components (S-F( Figure 24 )) and ROSOLi( Figure 25 )) increase, corresponding to the decomposition of dimethyl sulfite, verifying that the electrolyte provided by this patent can indeed relay the reaction after the carbon fluoride discharge platform, further improving the battery energy density.

[0213] Example 10 and Comparative Example 18 are used to highlight the function of the CEI dominated by the organic sulfur component corresponding to the non-discharged Example 9.

[0214] Example 10

[0215] Generate a carbon fluoride positive electrode with organic sulfur as the dominant component of CEI:

[0216] The positive electrode, electrolyte, separator, negative electrode and battery assembly method of the battery are the same as those in Example 7.

[0217] After the assembled battery is left standing at room temperature for 10 h, the battery is disassembled to obtain a carbon fluoride positive electrode with organic sulfur as the dominant component of CEI.

[0218] Positive electrode: The above-obtained carbon fluoride positive electrode with organic sulfur as the dominant component of CEI

[0219] The negative electrode, separator, electrolyte and battery assembly are the same as those in Example 2.

[0220] After the assembled battery is left standing at room temperature for 10 h, an AC impedance test is carried out (-20 to 25 °C). The desolvation energy barrier of lithium ions is obtained by fitting the impedance spectrum.

[0221] Comparative Example 18

[0222] The positive electrode, electrolyte, separator, negative electrode and battery assembly method of the battery are the same as those in Comparative Example 4.

[0223] After the assembled battery is left standing at room temperature for 10 h, an AC impedance test is carried out (-20 to 25 °C). The desolvation energy barrier of lithium ions is obtained by fitting the impedance spectrum.

[0224] It can be seen that in the temperature range of -20 to 25 °C, the charge transfer impedance corresponding to Example 10 is much smaller than that of Comparative Example 18, indicating that the CEI dominated by organic sulfur generated in Example 10 promotes the Figure 26 transport of Li at the interface. Further fitting the impedance spectrum shows that ( + ) the desolvation energy barrier of Li corresponding to Example 10 is much smaller than that of Comparative Example 18, verifying that the CEI layer dominated by organic sulfur generated in Example 10 can accelerate the interfacial reaction kinetic process and improve the performance of lithium / carbon fluoride batteries at low temperatures. Figure 27 ) the desolvation energy barrier of Li corresponding to Example 10 is much smaller than that of Comparative Example 18, verifying that the CEI layer dominated by organic sulfur generated in Example 10 can accelerate the interfacial reaction kinetic process and improve the performance of lithium / carbon fluoride batteries at low temperatures. + transport of Li at the interface. Further fitting the impedance spectrum shows that (

[0225] Examples 11 and Comparative Example 19 are used to highlight the function of the CEI dominated by inorganic sulfur and inorganic fluorine components generated after discharging for a period of time in Example 9.

[0226] Example 11

[0227] The positive electrode, electrolyte, separator, negative electrode and battery assembly method of the battery are the same as those in Example 7.

[0228] After the assembled battery is left standing at room temperature for 10 h, it is discharged at a current density of 0.1 A / g at 0 °C for 1 h. Then, the battery is subjected to an AC impedance test (-70 to 25 °C). The desolvation energy barrier of lithium ions and the energy barrier for them to cross the CEI are obtained by fitting the impedance spectrum.

[0229] Comparative Example 19

[0230] The positive electrode, electrolyte, separator, negative electrode and battery assembly method of the battery are the same as those in Example 7.

[0231] After the assembled battery is left standing at room temperature for 10 h, an AC impedance test (-70 to 25 °C) is carried out. The desolvation energy barrier of lithium ions and the energy barrier for them to cross the CEI are obtained by fitting the impedance spectrum.

[0232] It can be seen that Figures 28 to 29 the desolvation energy barrier of Li corresponding to Example 11 and the energy barrier for it to cross the CEI layer are both smaller than those of Comparative Example 19, indicating that the CEI interface layer rich in inorganic sulfur and inorganic fluorine components corresponding to Example 11 can accelerate the reaction kinetic process and further improve the performance of lithium / carbon fluoride batteries at low temperatures. + transport of Li at the interface. Further fitting the impedance spectrum shows that (

[0233] Where the present invention is not described applies to the prior art.

[0234] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention.

Claims

1. A wide temperature range lithium / carbon fluoride battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte, characterized in that: The positive electrode comprises a fluorinated carbon positive electrode material, and the preparation method of the fluorinated carbon positive electrode material is: Placing carbon fluoride in a plasma chemical vapor deposition furnace, maintaining vacuum, passing acetylene or methane into the plasma chemical vapor deposition furnace, controlling the radio frequency power to be 100-200W, the heat treatment temperature to be 550-600°C, and heat treating for 10-20min to obtain a carbon fluoride positive electrode material, wherein the carbon fluoride positive electrode material is a thin layer material with a surface covered with nano-carbon dots and rich in mesopores, wherein the carbon fluoride thin layer has a length and width of 5-50 μm and a thickness of 0.2-20 μm, the diameter of the nano-carbon dots on the surface of the thin layer is 5-20 nm, and the diameter of the mesopores is 2-50 nm; The electrolyte consists of lithium tetrafluoroborate, methyl acetate and dimethyl sulfite, the volume ratio of methyl acetate to dimethyl sulfite is 1:1, and the concentration of lithium tetrafluoroborate is 1 mol / L.

2. The wide temperature range lithium / carbon fluoride battery according to claim 1, characterized in that: The positive electrode is prepared by dispersing carbon fluoride positive electrode material, conductive carbon black and binder PVDF in N-methylpyrrolidone at a mass ratio of 8-9:0.5-1:0.5-1, fully mixing, coating on carbon-coated aluminum foil, and drying.

3. The wide temperature range lithium / carbon fluoride battery according to claim 1, characterized in that: The negative electrode is made of a lithium sheet or a lithium belt with a thickness of 50 to 500 μm.

4. The wide temperature range lithium / carbon fluoride battery according to claim 1, characterized in that: The separator is a PE separator with a thickness of 25 μm.

5. A positive electrode material for a wide temperature range lithium / carbon fluoride battery, characterized in that: The carbon fluoride cathode material is a thin layer material with a surface covered with nano carbon dots and rich in mesopores, wherein the carbon fluoride thin layer material has a length and width of 5 to 50 μm, a thickness of 0.2 to 20 μm, a diameter of the nano carbon dots on the surface of the thin layer of 5 to 20 nm, and a mesopore diameter of 2 to 50 nm. The preparation method is: placing carbon fluoride in a plasma chemical vapor deposition furnace, keeping the plasma chemical vapor deposition furnace vacuum by a vacuum pump; passing a carbon source atmosphere into the plasma chemical vapor deposition furnace, controlling the radio frequency power to be 50 to 200 W, the heat treatment temperature to be 300 to 600° C., and the heat treatment time to be 5 to 30 min, to obtain the carbon fluoride cathode material.

6. The positive electrode material according to claim 5, characterized in that The carbon source atmosphere is acetylene or methane.

7. The positive electrode material according to claim 5, characterized in that The radio frequency power is 100-200W; the heat treatment temperature is 550-600°C; and the heat treatment time is 10-20min.

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