Manganese-doped polyvinyl alcohol-based carbon-coated carbon fluoride cathode material and preparation method thereof

Abstract

The present application discloses a manganese-doped polyvinyl alcohol-based carbon-coated carbon fluoride cathode material and a preparation method thereof, belonging to the materials for primary lithium batteries; the preparation process of the cathode material is as follows: a dispersant is used to hydrophilize the CF x material, and then polyvinyl alcohol is used as the carbon source. First, a mixed solution containing a manganese source and polyvinyl alcohol is coated on the surface of the CF x material by a suction filtration method, and then a carbon fluoride material containing both carbon and manganese on the surface is prepared by a high-temperature carbonization method. The preparation process is simple, without using any toxic reagents, low in cost and environmentally friendly. The prepared manganese-doped carbon-coated carbon fluoride cathode material can better improve its rate performance, discharge platform and discharge specific capacity.

Description

Technical Field

[0001] The present invention belongs to the technical field of primary lithium battery materials, and particularly relates to a carbon-coated graphite fluoride cathode material based on polyvinyl alcohol doped with manganese oxide and a preparation method thereof. Background Art

[0002] Currently, civil, military, medical and other devices have increasingly high requirements for the performance of electrochemical power sources, such as energy density and storage life. Compared with other primary and secondary batteries, lithium carbon fluoride (Li / CF x ) batteries have the advantages of high theoretical energy density, low self-discharge rate, high storage life, and applicability to extreme temperatures. However, factors such as the C–F characteristic covalent bond of the carbon fluoride material itself and the surface inert –CF2 group result in insufficient intrinsic conductivity. At the same time, the in-situ generated LiF on the surface during the lithiation of carbon fluoride causes passivation of the electrochemical interface. These adverse factors exacerbate the polarization during the discharge process of lithium carbon fluoride batteries, resulting in a decrease in the voltage platform and a decline in rate performance.

[0003] To improve the rate performance of lithium carbon fluoride batteries, researchers have tried to start from the perspective of the conductivity of carbon fluoride, such as using high-conductivity carbon sources, surface coating, composite cathodes, etc. Among them, carbon coating is the most commonly used. However, the improvement effect of a single carbon coating modification method on electrochemical performance is not prominent. In particular, the low voltage platform and voltage hysteresis phenomenon still restrict the improvement of rate performance. Therefore, it is necessary to simultaneously introduce manganese oxide for multi-component and multi-mechanism synergistic enhancement.

[0004] In the prior art CN105140520A, researchers used the complex coacervation method to coat a layer of gum arabic gelatin on the surface of carbon fluoride, and then formed a carbon-coated carbon fluoride (CF x @C) structure through a carbonization process. The discharge specific capacity of CF x @C at a 1C rate is 531 mAh g -1 , but its discharge platform is relatively low and the voltage hysteresis phenomenon is obvious. In 2020, Luo et al. in-situ coated MnO2 nanowires (CF x ) on the surface of CF x @MnO2), and the discharge specific capacities of CF x @MnO2 and the original CF x at 1C are 631 mAh g -1 and 540 mAh g -1 respectively, and the discharge platforms are both 2.2V. It can be seen that the voltage hysteresis phenomenon is improved after coating, but the discharge platform has not been increased. Therefore, the coating of a single carbon or MnO2 component is not sufficient to meet the performance requirements of carbon fluoride electrodes. Summary of the Invention

[0005] To solve the problems of insufficient rate performance and relatively low voltage plateau of lithium carbon fluoride batteries, the present invention provides a low-cost and simple-process polyvinyl alcohol-based carbon-coated carbon fluoride cathode material doped with manganese oxide, which meets the needs of social production, so as to simultaneously achieve the purposes of increasing the discharge plateau, improving voltage hysteresis, and enhancing rate performance.

[0006] The technical solution adopted by the present invention is as follows:

[0007] On the one hand, the present invention provides a preparation method of a polyvinyl alcohol-based carbon-coated carbon fluoride cathode material doped with manganese oxide, which is characterized by including the following steps:

[0008] (1) Add carbon fluoride particles to a mixed solution of a manganese source, polyvinyl alcohol, and a dispersant, mix evenly, and then centrifuge or filter to obtain CF material with a mixture containing the manganese source and polyvinyl alcohol coated on its surface; x Material;

[0009] (2) Carry out carbonization treatment on the CF material obtained in step 1 under an inert gas atmosphere, and then cool down; x Material for carbonization treatment, and cool down;

[0010] (3) Carry out high-temperature oxidation on the carbonized CF material obtained in step 2 under an oxygen atmosphere to obtain a polyvinyl alcohol-based carbon-coated carbon fluoride material doped with manganese oxide, namely CF@C-MnO; x Material for high-temperature oxidation under an oxygen atmosphere to obtain a polyvinyl alcohol-based carbon-coated carbon fluoride material doped with manganese oxide, namely CF@C-MnO; x @C-MnO X .

[0011] Furthermore: The carbon fluoride particles are at least one of carbon fluoride coke, carbon fluoride graphite, carbon fluoride graphene, and carbon fluoride nanotube particle materials.

[0012] Furthermore: The dispersant is at least one of OP-10, Tween-80, and BYK-190.

[0013] Furthermore: The manganese source is at least one of Mn(NO3)2, MnSO4, and KMnO4.

[0014] Furthermore: The dosage ratio of the carbon fluoride, manganese source, and polyvinyl alcohol is 1 g:(0.251 - 1.255) g:(0.044 - 0.22) g.

[0015] Furthermore: The carbonization temperature in step (2) is 350°C - 450°C, and the high-temperature oxidation temperature in step (3) is 350°C - 450°C.

[0016] Furthermore: The heating rate is controlled at 1 - 5°C / min during the carbonization and high-temperature oxidation processes. The holding time during the carbonization and high-temperature oxidation processes is 3 - 9 h, preferably 6 h.

[0017] On the other hand, the present invention provides a manganese oxide-doped polyvinyl alcohol-based carbon-coated graphite fluoride cathode material, which is characterized in that it is prepared by the above preparation method.

[0018] The beneficial effects of the present invention are as follows: The present invention uses polyvinyl alcohol as a carbon source, and at the same time dopes manganese oxide to modify the carbon fluoride material. After carbonization and oxidation treatment, as can be seen from the SEM in Figure 3 b, an amorphous carbon layer with relatively high conductivity is coated on the material surface (compared with the SEM in Figure 3 a, it can be seen that the layered structure of the carbon fluoride after coating is not obvious, and the color around the material is dark black). A conductive layer is provided outside the carbon fluoride, shortening the lithium ion diffusion distance, thereby reducing the battery polarization and significantly improving the voltage platform and discharge specific capacity. At the same time, the introduction of manganese oxide helps to improve the voltage platform at the initial stage of discharge and improve the voltage hysteresis phenomenon. In addition, the preparation process of the present invention is environmentally friendly, non-toxic and harmless, the process is simple, and it can be quickly synthesized for mass production. Description of the Drawings

[0019] Figure 1 is the rate-specific capacity diagram of the cathode material prepared in Example 1 and the carbon fluoride battery prepared by blank control at 1C, 2C, 4C, and 6C;

[0020] Figure 2 (a, b) are the constant current discharge curves of the cathode material prepared by blank control and the carbon fluoride battery prepared in Example 1 at 1C, 2C, 4C, and 6C respectively;

[0021] Figure 3 (a, b) are the scanning electron microscope diagrams of the cathode material prepared by blank control and the carbon fluoride prepared in Example 1 respectively. Detailed Embodiments

[0022] The present invention will be further described in detail with reference to the accompanying drawings of the specification through examples, but it is not a limitation to the present invention.

[0023] Example 1

[0024] The preparation method of the manganese oxide-doped polyvinyl alcohol-based carbon-coated graphite fluoride cathode material in this example is specifically as follows:

[0025] Step 1) Coating: Add 1 g of carbon fluoride nanotubes to 20 mL of a mixed solution containing manganese source Mn(NO3)2 and polyvinyl alcohol with 20 μL of dispersant OP-10 added dropwise. The mass of the manganese source in the mixed solution of the manganese source and polyvinyl alcohol is 1.013 g, and the mass of polyvinyl alcohol is 0.15 g. Mix evenly, and then use centrifugation and suction filtration to obtain CF x material with a mixed solution containing manganese source and polyvinyl alcohol coated on its surface;

[0026] Step 2) Carbonization + Oxidation: Under an argon atmosphere, a CF material coated with a mixed solution of a manganese source and polyvinyl alcohol on the surface of Step 1 x is subjected to carbonization treatment. The carbonization temperature is 400 °C, the heating rate is 5 °C / min, and the heat preservation time is 6 h, and then it is naturally cooled; under an oxygen atmosphere, oxygen is introduced into the CF material that has been carbonized for high-temperature oxidation. The oxidation temperature is 400 °C, the heating rate is 5 °C / min, and the heat preservation time is 6 h, and then it is naturally cooled to obtain a CF x @C-MnO x material. X

[0027] Example 2

[0028] The preparation method of the doped manganese oxide-based polyvinyl alcohol carbon-coated fluorinated graphite cathode material in this example is as follows:

[0029] Step 1) Coating: Add 1 g of fluorinated coke to 20 mL of a mixed solution of a manganese source MnSO4 and polyvinyl alcohol with 20 μL of a dispersant Tween-80 added dropwise. The mass of the manganese source in the mixed solution of the manganese source and polyvinyl alcohol is 0.251 g, and the mass of polyvinyl alcohol is 0.044 g. Mix evenly, and then use the centrifugation and suction filtration method to obtain a CF x material;

[0030] Step 2) Carbonization + Oxidation: Under an argon atmosphere, a CF material coated with a mixed solution of a manganese source and polyvinyl alcohol on the surface of Step 1 x is subjected to carbonization treatment. The carbonization temperature is 350 °C, the heating rate is 1 °C / min, and the heat preservation time is 3 h, and then it is naturally cooled; under an oxygen atmosphere, oxygen is introduced into the CF material that has been carbonized for high-temperature oxidation. The oxidation temperature is 350 °C, the heating rate is 1 °C / min, and the heat preservation time is 3 h, and then it is naturally cooled to obtain a CF x @C-MnO x material. X

[0031] Example 3

[0032] The preparation method of the doped manganese oxide-based polyvinyl alcohol carbon-coated fluorinated graphite cathode material in this example is as follows:

[0033] ​​Step 1) Coating: 1 g of graphite fluoride was added to 20 mL of a mixed solution of manganese source KMnO4 and polyvinyl alcohol with 20 μL of dispersant BYK-19 dropped in. The mass of the manganese source in the mixed solution of manganese source and polyvinyl alcohol was 1.255 g, and the mass of polyvinyl alcohol was 0.22 g. After mixing evenly, a CF material with a mixed solution of manganese source and polyvinyl alcohol coated on its surface was obtained by centrifugation and suction filtration. x Material;

[0034] Step 2) Carbonization + Oxidation: The CF material with a mixed solution of manganese source and polyvinyl alcohol coated on its surface obtained in Step 1 was carbonized under an argon atmosphere. The carbonization temperature was 450 °C, the heating rate was 3 °C / min, and the holding time was 9 h, and then it was cooled naturally; the carbonized CF material was passed through oxygen for high-temperature oxidation under an oxygen atmosphere. The oxidation temperature was 450 °C, the heating rate was 3 °C / min, and the holding time was 9 h, and then it was cooled naturally, obtaining a CF@C-MnO material. x Material. x x @C-MnO X Material.

[0035] Comparative Example 1

[0036] Comparative Example 1. In 2016, Zhu Ling published a doctoral thesis "Research on the Surface Modification of Carbon Fluoride Materials and Their Applications in Lithium Batteries". The difference is that polyvinylpyrrole was used to replace polyvinyl alcohol herein. The author coated a polyvinylpyrrole film on the surface of graphite fluoride particles by chemical oxidation in-situ polymerization method, and then physically mixed it with MnO2 (MnO2 and CF@PPy mixed material). x @PPy mixed material).

[0037] Comparative Example 2

[0038] Comparative Example 2. In 2009, Zhang et al. published a paper "Carbothermal treatment for the improved discharge performance of primary Li / CF battery", reference (Journal of Power Sources, 2009, 191(2): 648 - 652.). x battery》, reference (Journal of Power Sources, 2009, 191(2): 648 - 652.)

[0039] The preparation method of the positive electrode material in this comparative example was basically the same as that in Example 1. The difference was that the manganese source was replaced with polyvinylidene fluoride.

[0040] Blank control

[0041] The blank control used untreated carbon fluoride material.

[0042] The positive electrode materials prepared in the above-mentioned examples, comparative examples, and the blank control were respectively subjected to electrochemical performance tests. The specific method was as follows: Grind the positive electrode materials evenly, weigh 0.08 g, and then weigh 0.01 g of Super P and 0.01 g of PVDF according to the ratio of positive electrode material:Super P:PVDF = 8:1:1. Mix the above three materials evenly, put them into a defoamer and rotate at a speed of 1500 r / min for 30 min. Coating the adjusted slurry on the aluminum foil, then drying, cutting into pieces to make battery electrode sheets. Assemble into a button-type lithium battery LIR2032 type button battery in a glove box filled with argon. The negative electrode is a lithium sheet, the electrolyte solute is 1 mol / L LiPF6, the electrolyte solvent is 3:4:3 EC (ethylene carbonate):EMC (ethyl methyl carbonate):DMC (dimethyl carbonate), and a polyethylene single-layer separator is selected.

[0043] Perform electrochemical testing on the LIR2032 type button batteries assembled from the above-mentioned examples, comparative examples, and blank controls. Perform constant current discharge under the conditions of (1C, 2C, 4C, 6C) respectively. The cut-off voltage of the battery discharge is set to 1.5 V (vs. Li / Li + ).

[0044] Figure 2 The discharge curves of the lithium / carbon fluoride batteries of Example 1 and the blank control are shown. The discharge curve rules of Example 2 and Example 3 are the same as those of Example 1 and will not be elaborated here; Figure 1 Shown as CF x @C-MnO X The line comparison chart of the discharge specific capacity of the material applied in the lithium / carbon fluoride battery and the original carbon fluoride battery at different discharge rates.

[0045] As Figure 1 , shown in Figure 2: CF x @C-MnO X The material, especially at high rates of 2C, 4C, and 6C, has a higher discharge specific capacity than the original carbon fluoride. Compared with the original carbon fluoride, CF x @C-MnO X The material has a 0.15 V increase in the discharge plateau at 1C, which indicates that the C-Mn-based composite coating can significantly improve the discharge specific capacity at high rates, and the discharge plateau has also been significantly improved. Furthermore, the rate performance of the primary lithium carbon fluoride battery has been improved.

[0046] Compared with the original carbon fluoride, CF x @C-MnO XThe discharge platform of the material at 1C has increased by 0.15V. At 1C, 2C, 4C, and 6C, the discharge specific capacities of the carbon fluoride-coated materials are 638 mAh / g, 560 mAh / g, 400 mAh / g, and 291 mAh / g respectively, while the discharge specific capacities of the original carbon fluoride are 576 mAh / g, 450 mAh / g, 300 mAh / g, and 178 mAh / g respectively. In addition to being coated with a layer of carbon, manganese oxide is doped on the surface of the carbon fluoride, which has an obvious effect on improving the battery voltage hysteresis phenomenon. At the same time, increasing the discharge platform voltage and improving the battery voltage hysteresis benefit from the synergistic effect of polyvinyl alcohol and manganese oxide doping.

[0047] In Comparative Example 1, MnO2 and CF x @PPy hybrid material and CF in this patent x @C-MnO X The discharge specific capacities of the materials at 1C are 205 mAh g -1 and 631 mAh g -1 , The discharge specific capacity of the modified carbon fluoride in Comparative Example 1 has decreased compared with that of the original carbon fluoride. The discharge specific capacity of CF x @C-MnO X material has increased a lot compared with the original carbon fluoride. It can be seen that changing the carbon source does not have as good an improvement effect on the electrochemical performance (discharge specific capacity) as in the examples.

[0048] In Comparative Example 2, the discharge platform of the modified carbon fluoride at 0.2C has increased by 95 mV compared with the original carbon fluoride, and the discharge specific capacity has not increased significantly. In this patent, compared with the original carbon fluoride, CF x @C-MnO X The discharge platform of the material at 1C has increased by 0.15V, and the discharge specific capacity has also increased significantly. It can be seen that changing the manganese source does not have as good an improvement effect on the electrochemical performance (discharge specific capacity, discharge platform) as in the examples.

[0049] The above has described the embodiments of the present invention in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made according to the purpose of the invention of the present invention. Any changes, modifications, substitutions, combinations, or simplifications made based on the spirit and principle of the technical solution of the present invention shall be equivalent replacement methods. As long as they meet the purpose of the invention of the present invention and do not deviate from the technical principle and inventive concept of the present invention, they all belong to the protection scope of the present invention.

Claims

1. Preparation method of a manganese-doped manganese oxide-based polyvinyl alcohol carbon-coated fluorinated graphite cathode material, characterized in that: Including the following steps: (1) Using polyvinyl alcohol as the carbon source and the manganese source being at least one of Mn(NO3)2, MnSO4, and KMnO4, add carbon fluoride particles to the mixed solution of the manganese source, polyvinyl alcohol, and dispersant, mix evenly, and then centrifuge or filter by suction to obtain CF with a mixture containing the manganese source and polyvinyl alcohol coated on its surface. x Material; (2) Carbonize the CF obtained in step 1 under an inert gas atmosphere, with the carbonization temperature being 350°C - 450°C, and then cool down; x ​ (3) High-temperature oxidize the carbonized CF obtained in step 2 in an oxygen atmosphere, and the high-temperature oxidation temperature is 350°C - 450°C to obtain a polyvinyl alcohol-based carbon-coated carbon fluoride material CF x doped with manganese oxide x @C-MnO X .

2. The preparation method of the manganese-doped polyethylene glycol-based carbon-coated fluorinated graphite cathode material according to claim 1, characterized in that: The carbon fluoride particles are at least one of fluorinated coke, fluorinated graphite, fluorinated graphene, and fluorinated carbon nanotube particulate materials.

3. The preparation method of the manganese-doped oxide-doped polyvinyl alcohol-based carbon-coated fluorinated graphite cathode material according to claim 1, wherein: The dispersant is at least one of OP-10, Tween-80, and BYK-190.

4. The preparation method of the manganese-doped polyethylene glycol-based carbon-coated fluorinated graphite cathode material according to claim 1, characterized in that: The dosage ratio of the carbon fluoride, manganese source, and polyvinyl alcohol is 1 g : (0.251 - 1.255) g : (0.044 - 0.22) g.

5. The preparation method of the manganese-doped polyvinyl alcohol-based carbon-coated graphite fluoride cathode material according to claim 1, characterized in that: The heating rate during the carbonization and high-temperature oxidation processes is controlled at 1 - 5 °C / min.

6. According to the preparation method of the doped manganese oxide-based polyvinyl alcohol-based carbon-coated fluorinated graphite cathode material of claim 1 or as described above, it is characterized in that: The heat preservation time during both the carbonization and high-temperature oxidation processes is 3 - 9 h.

7. A manganese-doped oxide polyvinyl alcohol-based carbon-coated fluorinated graphite cathode material, characterized in that: Obtained by using the preparation method according to any one of claims 1 - 6.

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