A method for modifying carbon fluoride, modified carbon fluoride and lithium / carbon fluoride battery

Abstract

The present invention belongs to the field of battery technology and provides a method for modifying carbon fluoride, modified carbon fluoride, and a lithium / carbon fluoride battery. The modification method comprises mixing a carbon fluoride material, an acid anhydride, and a solvent, and performing a modification treatment to obtain the modified carbon fluoride. The present invention improves the stability of the carbon fluoride material itself by using an acid anhydride and a solvent to form a solution system containing an acid anhydride compound to modify the carbon fluoride material. This effectively removes free fluorine and active carbon-fluorine bonds in the carbon fluoride material, thereby improving the stability of the carbon fluoride material, resolving the problem of side reactions between the carbon fluoride and the electrolyte, and further improving the storage stability of the carbon fluoride battery.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to a carbon fluoride modification method, modified carbon fluoride and a lithium / carbon fluoride battery. Background Art

[0002] Li / CF x (Lithium / carbon fluoride) battery is a non-aqueous primary battery with lithium metal as the negative electrode and carbon fluoride material as the positive electrode. Due to its advantages such as high energy density, long life, good storage stability and wide operating temperature range, Li / CF x Batteries are widely used in military, aerospace, medical equipment, and portable electronic devices.

[0003] The chemical structure of carbon fluoride materials is usually represented as CF x , where the x value is usually between 0.5 and 1.0. In fluorinated carbon materials, the bonding forms between carbon atoms and fluorine atoms are diverse, including CF single bonds, CF double bonds and CF triple bonds. These different bonding forms give fluorinated carbon materials unique electrochemical properties. However, some unstable carbon-fluorine bonds in fluorinated carbon materials are prone to homolytic or heterolytic cleavage at high temperatures or during long-term storage, producing carbon radicals, fluorine radicals or carbon cations, fluoride ions. These highly chemically active intermediate species will trigger the decomposition of the electrolyte and generate by-products inside the battery, further leading to rapid attenuation of the battery capacity, thereby affecting the overall performance of the battery.

[0004] CN114628670A discloses a nitrogen-doped-carbon-coated fluorinated carbon for use in lithium / fluorinated carbon batteries, which uses an aqueous solution of tris(hydroxymethylaminomethane) (Tris) as a buffer solution, first obtains a polydopamine fluorinated carbon composite material through the self-polymerization reaction of dopamine hydrochloride, and then calcines the composite material at high temperature under an inert atmosphere to finally obtain a nitrogen-doped-carbon-coated fluorinated carbon electrode material. The nitrogen-doped-carbon coating layer can not only effectively block the direct contact between the electrolyte and the fluorinated carbon material, reduce the self-discharge phenomenon of the battery, but also improve the high-temperature shelf performance of the battery. However, the preparation process of the nitrogen-doped-carbon-coated fluorinated carbon material is relatively complicated and requires multiple steps, including self-polymerization reaction, high-temperature calcination, etc., which undoubtedly greatly increases the production cost and is particularly unfavorable for large-scale industrial production. In addition, the thickness and uniformity of the nitrogen-doped-carbon coating layer have a significant impact on the battery performance, are difficult to control, and easily lead to performance differences between batches.

[0005] CN114175320A discloses an electrolyte composition for an electrochemical cell comprising a lithium anode, which is prepared by adding a certain proportion of fluorocarbonates, such as fluoroethylene carbonate (FEC) or fluoropropylene carbonate (FPC), to the electrolyte so that the introduction of the fluorocarbonates can form a dense solid electrolyte interface film (SEI film) on the surface of the metallic lithium, thereby effectively inhibiting the side reactions between the metallic lithium and the electrolyte, reducing the self-discharge rate of the battery, and improving the storage stability of the battery. In addition, the fluorocarbonates also have high oxidation stability, which can prevent the decomposition of the electrolyte at high temperatures to a certain extent, further improving the high temperature performance of the battery. However, the oxidation potential of the phosphate additive is higher than the open circuit voltage of the lithium / fluorinated carbon battery, and the battery needs to be pre-charged to form a passivation layer of cyclic phosphate at the positive electrode, and the charging process may also affect the safety performance of the battery (generating lithium dendrites and piercing the diaphragm). Moreover, the optimization method from the electrolyte side cannot completely solve the problem of the reaction between the positive electrode carbon fluoride and the electrolyte. The unstable carbon-fluorine bonds in the carbon fluoride material will still react with the electrolyte at high temperature or long-term storage, resulting in a decrease in battery capacity. It can be seen that it does not solve the storage stability problem of carbon fluoride batteries from the root.

[0006] Therefore, there is still a need to optimize and improve carbon fluoride and lithium / carbon fluoride batteries to avoid or resolve adverse reactions caused by carbon fluoride materials, thereby improving the stability of the batteries and extending their service life. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention aims to provide a method for modifying carbon fluoride, a modified carbon fluoride, and a lithium / carbon fluoride battery. The modification method comprises mixing a carbon fluoride material, an acid anhydride, and a solvent, and performing a modification treatment to obtain the modified carbon fluoride. The present invention improves the stability of the carbon fluoride material itself by using an acid anhydride and a solvent to form a solution system containing an acid anhydride compound to modify the carbon fluoride material, thereby improving the stability of the carbon fluoride material and the storage stability of the carbon fluoride battery.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for modifying carbon fluoride, comprising: mixing a carbon fluoride material, an acid anhydride and a solvent, and performing a modification treatment to obtain modified carbon fluoride.

[0010] The present invention utilizes an acid anhydride as an electrophilic reagent, which has a strong ability to capture free fluorine and can effectively remove free fluorine from the fluorinated carbon material. Furthermore, the acid anhydride, as an electrophilic reagent, can react electrophilically with the fluorine in the activated carbon-fluorine bond and also remove unstable carbon-fluorine bonds in the fluorinated carbon. This helps improve the chemical stability of the fluorinated carbon material itself, resolves the problem of side reactions between the fluorinated carbon and the electrolyte, and effectively improves the storage stability of the lithium / fluorinated carbon battery. The modification method of the present invention is simple, feasible, easy to implement, and suitable for large-scale production.

[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0012] As a preferred technical solution of the present invention, the acid anhydride includes at least one of phenylmaleic anhydride, maleic anhydride, phthalic anhydride, 2,3-pyridinedicarboxylic anhydride (PDA), succinic anhydride, biphenyl anhydride, glutaric anhydride, adipic anhydride, benzoic anhydride, citraconic anhydride, phenoxyacetic anhydride, phenylsuccinic anhydride, or NA-anhydride. Preferably, the acid anhydride is at least one of maleic anhydride, phthalic anhydride, succinic anhydride, or NA-anhydride.

[0013] As a preferred technical solution of the present invention, the solvent includes at least one of an alcohol solvent, an ether solvent, a carboxylate solvent or a carbonate solvent, preferably an ether solvent.

[0014] As a preferred technical solution of the present invention, the alcohol solvent includes at least one of methanol, ethanol or propanol.

[0015] As a preferred technical solution of the present invention, the ether solvent includes tetrahydrofuran and / or ethylene glycol dimethyl ether.

[0016] As a preferred technical solution of the present invention, the carboxylate solvent includes at least one of ethyl formate, ethyl acetate or propyl acetate.

[0017] As a preferred technical solution of the present invention, the carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate.

[0018] As a preferred technical solution of the present invention, the mass of the acid anhydride accounts for 0.1% to 5% of the total mass of the acid anhydride and the solvent, for example, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8% or 5%, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0019] As a preferred technical solution of the present invention, the ratio of the mass of the fluorinated carbon material to the total mass of the acid anhydride and the solvent is 1:(1-10), for example, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9, 1:9.5 or 1:10, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0020] As a preferred technical solution of the present invention, the temperature of the modification treatment is 0 to 90°C, for example, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C, etc., preferably 30 to 60°C, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0021] As a preferred technical solution of the present invention, the time of the modification treatment is greater than 5 min, for example, 5.5 min, 8 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h or 10 h, etc., preferably 1 to 10 h, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0022] As a preferred technical solution of the present invention, the modification treatment is carried out under stirring, and the stirring speed is 100 to 1000 r / min, for example, 100 r / min, 150 r / min, 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min, 500 r / min, 550 r / min, 600 r / min, 650 r / min, 700 r / min, 750 r / min, 800 r / min, 850 r / min, 900 r / min, 950 r / min or 1000 r / min, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0023] As a preferred technical solution of the present invention, the modification method includes first preparing the acid anhydride and the solvent into an acid anhydride solution, then mixing the carbon fluoride material with the acid anhydride solution, performing the modification treatment, and then sequentially performing solid-liquid separation, washing, baking and dispersion to obtain the modified carbon fluoride.

[0024] In a second aspect, the present invention provides a modified fluorinated carbon, which is prepared according to the modification method described in the first aspect.

[0025] In a third aspect, the present invention provides a positive electrode plate, wherein the active material of the positive electrode plate includes the modified fluorinated carbon described in the second aspect.

[0026] In a fourth aspect, the present invention provides a lithium / carbon fluoride battery comprising the modified carbon fluoride described in the second aspect or the positive electrode sheet described in the third aspect.

[0027] Compared with the existing technical solutions, the present invention has at least the following beneficial effects:

[0028] The present invention pre-treats the carbon fluoride material by subjecting it to a modification reaction in a liquid phase system formed by an acid anhydride and a solvent. This effectively removes free fluorine and active carbon-fluorine bonds from the carbon fluoride material, thereby improving the chemical stability of the carbon fluoride material. During storage, lithium / carbon fluoride batteries containing the modified carbon fluoride are effectively mitigated and alleviated from the problem of battery capacity loss caused by the reaction between the electrolyte and the positive electrode carbon fluoride, thereby improving the storage stability of the lithium / carbon fluoride battery. Furthermore, the modification method of the present invention is simple, convenient, and low-cost, making it very suitable for large-scale production. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0030] It should be apparent to those skilled in the art that the embodiments are only intended to help understand the present invention and should not be considered as specific limitations of the present invention.

[0031] Example 1

[0032] This embodiment provides a method for modifying carbon fluoride, comprising:

[0033] First, maleic anhydride is added to a solvent of ethylene glycol dimethyl ether and stirred evenly to obtain an anhydride solution, wherein the mass ratio of maleic anhydride to ethylene glycol dimethyl ether is 2:98; then, a carbon fluoride material is added to the anhydride solution so that the solid-liquid mass ratio of the carbon fluoride material to the anhydride solution is 1:3, stirring is started to make its speed 500 r / min, and modification treatment is carried out at 50° C. for 5 hours, and finally, solid-liquid separation is performed, and the separated product is placed in a blast oven for drying, and finally, the dried modified carbon fluoride particles are dispersed using a powder disperser to obtain modified carbon fluoride powder.

[0034] Example 2

[0035] This embodiment provides a method for modifying carbon fluoride, comprising:

[0036] First, succinic anhydride is added to a solvent tetrahydrofuran and stirred evenly to obtain an anhydride solution, wherein the mass ratio of succinic anhydride to tetrahydrofuran is 5:95; then, a carbon fluoride material is added to the anhydride solution so that the solid-liquid mass ratio of the carbon fluoride material to the anhydride solution is 1:3, stirring is started to make the speed 300 r / min, and modification treatment is carried out at 60° C. for 5 hours, and finally, solid-liquid separation is performed, and the separated product is placed in a blast oven for drying, and finally, the dried modified carbon fluoride particles are dispersed by a powder disperser to obtain modified carbon fluoride powder.

[0037] Example 3

[0038] This embodiment provides a method for modifying carbon fluoride, comprising:

[0039] First, succinic anhydride is added to an ethanol solvent and stirred evenly to obtain an anhydride solution, wherein the mass ratio of succinic anhydride to ethanol is 5:95; then, a carbon fluoride material is added to the anhydride solution so that the solid-liquid mass ratio of the carbon fluoride material to the anhydride solution is 1:3, stirring is started to make the stirring rate 300 r / min, and the modification treatment is carried out at 25°C for 10 hours. Finally, solid-liquid separation is carried out, and the separated product is placed in a blast oven for drying. Finally, the dried modified carbon fluoride particles are dispersed by a powder disperser to obtain modified carbon fluoride powder.

[0040] Example 4

[0041] This embodiment provides a method for modifying carbon fluoride, wherein the acid anhydride is replaced by adipic anhydride instead of maleic anhydride. Except for the above, other conditions are exactly the same as those in Example 1.

[0042] Example 5

[0043] This embodiment provides a method for modifying fluorinated carbon, wherein the acid anhydride is replaced by 2,3-pyridinedicarboxylic anhydride instead of maleic anhydride. Except for the above, other conditions are exactly the same as those in Example 1.

[0044] Example 6

[0045] This example provides a method for modifying fluorinated carbon, wherein the anhydride is replaced by citraconic anhydride instead of maleic anhydride. Except for the above, other conditions are exactly the same as those in Example 1.

[0046] Example 7

[0047] This embodiment provides a method for modifying fluorinated carbon, wherein the mass ratio of maleic anhydride to ethylene glycol dimethyl ether is adjusted from 2:98 to 0.1:99.9. Except for the above, other conditions are exactly the same as those in Example 1.

[0048] Example 8

[0049] This embodiment provides a method for modifying carbon fluoride, wherein the mass ratio of maleic anhydride to ethylene glycol dimethyl ether is adjusted from 2:98 to 1:99. Except for the above, other conditions are exactly the same as those in Example 1.

[0050] Example 9

[0051] This embodiment provides a method for modifying carbon fluoride, wherein the mass ratio of maleic anhydride to ethylene glycol dimethyl ether is adjusted from 2:98 to 5:95. Except for the above, other conditions are exactly the same as those in Example 1.

[0052] Example 10

[0053] This embodiment provides a method for modifying carbon fluoride, wherein the mass ratio of maleic anhydride to ethylene glycol dimethyl ether is adjusted from 2:98 to 7:93. Except for the above, other conditions are exactly the same as those in Example 1.

[0054] Example 11

[0055] This embodiment provides a method for modifying carbon fluoride, wherein the solid-liquid mass ratio of the carbon fluoride material to the acid anhydride solution is adjusted from 1:3 to 1:0.7. Except for the above, other conditions are exactly the same as those in Example 1.

[0056] Example 12

[0057] This embodiment provides a method for modifying carbon fluoride, wherein the solid-liquid mass ratio of the carbon fluoride material to the acid anhydride solution is adjusted from 1:3 to 1:1. Except for the above, other conditions are exactly the same as those in Example 1.

[0058] Example 13

[0059] This embodiment provides a method for modifying carbon fluoride, wherein the solid-liquid mass ratio of the carbon fluoride material to the acid anhydride solution is adjusted from 1:3 to 1:7. Except for the above, other conditions are exactly the same as those in Example 1.

[0060] First, maleic anhydride is added to a solvent of ethylene glycol dimethyl ether and stirred evenly to obtain an anhydride solution, wherein the mass ratio of maleic anhydride to ethylene glycol dimethyl ether is 2:98; then, a carbon fluoride material is added to the anhydride solution so that the solid-liquid mass ratio of the carbon fluoride material to the anhydride solution is 1:3, stirring is started to make its speed 500 r / min, and modification treatment is carried out at 50° C. for 5 hours, and finally, solid-liquid separation is performed, and the separated product is placed in a blast oven for drying, and finally, the dried modified carbon fluoride particles are dispersed using a powder disperser to obtain modified carbon fluoride powder.

[0061] Comparative Example 1

[0062] This comparative example uses the fluorinated carbon material in Example 1 for subsequent testing, without using anhydride and solvent for modification.

[0063] The modified carbon fluoride powder obtained in the embodiment and the unmodified carbon fluoride material in comparative example 1 were used as active materials to make carbon fluoride positive electrode sheets, and then the carbon fluoride positive electrode sheets, the metal lithium negative electrode sheets and the separator were assembled into battery cells by lamination, and a primary lithium carbon fluoride battery electrolyte was injected into the battery cells. The electrolyte composition was PC / DME / LiBF4, wherein the volume ratio of PC (propylene carbonate) to DME (ethylene glycol dimethyl ether) was 1 / 1, and LiBF4 was 1 mol / L. After sealing, a lithium / carbon fluoride battery was obtained.

[0064] The prepared batteries were stored at 70°C for 1 month, and the capacity retention rates of the new batteries and the batteries after storage were tested respectively to evaluate the storage stability of the batteries. The discharge rate was controlled at 0.01C, and the results are shown in Table 1.

[0065] Table 1

[0066]

[0067] As can be seen from Table 1:

[0068] By comparing Examples 1-6 with Comparative Example 1, it was found that the stability of the carbon fluoride material was significantly improved after being cleaned with anhydride, and the capacity retention rate of the prepared battery after storage was increased from 94.1% of the comparative example to more than 97%.

[0069] In Comparative Examples 1 and 7-10, as the anhydride concentration / content decreases, the capacity retention rate of the battery cell decreases, indicating that when the anhydride concentration is low, the anhydride has limited processing capacity for the fluorinated carbon material; when the anhydride content / concentration is too high, the storage stability of the battery cell deteriorates. The main reason is that excessive anhydride will remain in the fluorinated carbon material and cannot be completely removed during the cleaning process, causing the anhydride in the material to be released into the battery cell, corroding the electrolyte and metallic lithium, resulting in a decrease in the storage stability of the battery cell.

[0070] In Comparative Examples 1 and 11-13, when the solvent content is too low, the solvent has insufficient wettability for the carbon fluoride material, resulting in the inability to completely remove the free carbon fluoride material by the acid anhydride; when the solvent content is too high, the storage stability of the battery cell is no longer improved, and there is no need to introduce excessive solvent, which increases the processing difficulty and processing cost.

[0071] In summary, the present invention can effectively remove free fluorine and active carbon-fluorine bonds in the carbon fluoride material by subjecting the carbon fluoride material to a reaction pretreatment in a liquid phase system formed by an acid anhydride and a solvent, thereby improving the chemical stability of the carbon fluoride material and alleviating the problem of battery capacity loss caused by the reaction between the electrolyte and the positive electrode carbon fluoride during the storage process of the lithium carbon fluoride battery; this reaction pretreatment method of the carbon fluoride material is simple, convenient, low-cost, and very suitable for large-scale production.

[0072] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0073] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0074] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for modifying carbon fluoride, characterized in that: include: The carbon fluoride material, acid anhydride and solvent are mixed and modified to obtain modified carbon fluoride.

2. The method for modifying carbon fluoride according to claim 1, characterized in that: The acid anhydride includes at least one of phenyl maleic anhydride, maleic anhydride, phthalic anhydride, 2,3-pyridinedicarboxylic anhydride, succinic anhydride, biphenyl anhydride, glutaric anhydride, adipic anhydride, benzoic anhydride, citraconic anhydride, phenoxyacetic anhydride, phenylsuccinic anhydride or NA-anhydride.

3. The method for modifying carbon fluoride according to claim 2, characterized in that: The acid anhydride is at least one of maleic anhydride, phthalic anhydride, succinic anhydride or NA-anhydride.

4. The method for modifying carbon fluoride according to claim 1, wherein: The solvent includes at least one of an alcohol solvent, an ether solvent, a carboxylate solvent or a carbonate solvent.

5. The method for modifying carbon fluoride according to claim 4, characterized in that: The solvent is an ether solvent.

6. The method for modifying carbon fluoride according to claim 4, characterized in that: The alcohol solvent includes at least one of methanol, ethanol or propanol.

7. The method for modifying carbon fluoride according to claim 4 or 5, characterized in that: The ether solvent includes tetrahydrofuran and / or ethylene glycol dimethyl ether.

8. The method for modifying carbon fluoride according to claim 4, characterized in that: The carboxylate solvent includes at least one of ethyl formate, ethyl acetate or propyl acetate.

9. The method for modifying carbon fluoride according to claim 4, characterized in that: The carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate.

10. The method for modifying carbon fluoride according to claim 1, wherein: The mass of the acid anhydride accounts for 0.1% to 5% of the total mass of the acid anhydride and the solvent.

11. The method for modifying carbon fluoride according to claim 1, wherein: The ratio of the mass of the carbon fluoride material to the total mass of the acid anhydride and the solvent is 1:(1-10).

12. The method for modifying carbon fluoride according to claim 1, wherein: The temperature of the modification treatment is 0-90°C.

13. The method for modifying carbon fluoride according to claim 12, characterized in that: The temperature of the modification treatment is 30-60°C.

14. The method for modifying carbon fluoride according to claim 1, wherein: The modification treatment time is greater than 5 minutes.

15. The method for modifying carbon fluoride according to claim 14, characterized in that: The modification treatment time is 1 to 10 hours.

16. The method for modifying carbon fluoride according to claim 1, wherein: The modification treatment is carried out under stirring, and the stirring speed is 100-1000 r / min.

17. The method for modifying carbon fluoride according to claim 1, wherein: The modification method includes preparing the acid anhydride and the solvent into an acid anhydride solution, mixing the carbon fluoride material with the acid anhydride solution, performing the modification treatment, and then sequentially performing solid-liquid separation, washing, baking and dispersion to obtain the modified carbon fluoride.

18. A modified fluorinated carbon, characterized in that: Prepared according to the modification method according to any one of claims 1 to 17.

19. A positive electrode plate, characterized in that: The active material of the positive electrode sheet includes the modified fluorinated carbon according to claim 18.

20. A lithium / carbon fluoride battery, characterized in that: Containing the modified fluorinated carbon according to claim 18 or the positive electrode sheet according to claim 19.

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