Modification method of carbon fluoride, modified carbon fluoride and lithium / carbon fluoride battery

Abstract

The invention belongs to the technical field of batteries, and provides a carbon fluoride modification method, modified carbon fluoride and a lithium / carbon fluoride battery, and the modification method comprises the following steps: mixing a carbon fluoride material, acid anhydride and a solvent, and carrying out modification treatment to obtain the modified carbon fluoride. From the perspective of improving the stability of the carbon fluoride material, the solution system containing the anhydride compound is formed by using the anhydride and the solvent to modify the carbon fluoride material, and free fluorine and active fluorocarbon bonds in the carbon fluoride material are effectively removed, so that the stability of the carbon fluoride material is improved, and the service life of the carbon fluoride material is prolonged. The problem of side reaction between the carbon fluoride and the electrolyte is solved, so that the storage stability of the carbon fluoride battery is improved.

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 by 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, and 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 decay 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 trishydroxymethylaminomethane (Tris) as a buffer, first obtains a polydopamine fluorinated carbon composite material through a self-polymerization reaction of dopamine hydrochloride, and then the composite material is subjected to high-temperature calcination under an inert atmosphere, and finally obtains 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 multiple steps are required, 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 effect on the battery performance, and the control difficulty is relatively large, which easily leads to performance differences between batches.

[0005] CN114175320A discloses an electrolyte composition of an electrochemical cell comprising a lithium anode, which is formed by adding a certain proportion of fluorocarbonate, such as fluoroethylene carbonate (FEC) or fluoropropylene carbonate (FPC) to the electrolyte, so that the introduction of fluorocarbonate can form a dense solid electrolyte interface film (SEI film) on the surface of metallic lithium, thereby effectively inhibiting the side reaction of metallic lithium and electrolyte, reducing the self-discharge rate of the battery, and improving the storage stability of the battery. In addition, fluorocarbonate also has high oxidation stability, which can prevent the decomposition of the electrolyte at high temperature to a certain extent, and further improve the high temperature performance of the battery. However, the oxidation potential of phosphate additives is higher than the open circuit voltage of lithium / fluorinated carbon batteries, 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 (producing 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 during 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 solve the adverse reactions that occur or are caused by carbon fluoride materials, thereby improving the stability of the battery and extending its service life. Summary of the invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for modifying carbon fluoride, modified carbon fluoride and lithium / carbon fluoride battery, wherein the modification method comprises mixing carbon fluoride material, acid anhydride and solvent, and performing modification treatment to obtain modified carbon fluoride. From the perspective of improving the stability of the carbon fluoride material itself, the present invention uses an acid anhydride and solvent to form a solution system containing anhydride compounds 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 uses anhydride as an electrophilic reagent, which has a strong ability to capture free fluorine and can effectively remove free fluorine in the fluorinated carbon material. The anhydride as an electrophilic reagent can have an electrophilic effect with the fluorine in the active carbon-fluorine bond, and also has a removal effect on the unstable carbon-fluorine bond in the fluorinated carbon, thereby facilitating the improvement of the chemical stability of the fluorinated carbon material itself, solving the problem of the side reaction between the fluorinated carbon and the electrolyte, and thus effectively improving the storage stability of the lithium / fluorinated carbon battery. The modification method of the present invention is simple and 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 be limitations of 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 phenyl maleic 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, etc. Preferably, it 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 are 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 unlisted values ​​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 100-1000r / min, for example, 100r / min, 150r / min, 200r / min, 250r / min, 300r / min, 350r / min, 400r / min, 450r / min, 500r / min, 550r / min, 600r / min, 650r / min, 700r / min, 750r / min, 800r / min, 850r / min, 900r / min, 950r / min or 1000r / min, etc., but are 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 prior art solutions, the present invention has at least the following beneficial effects:

[0028] The present invention performs a modification reaction in a liquid phase system formed by an acid anhydride and a solvent to achieve pretreatment, which can effectively remove free fluorine and active carbon-fluorine bonds in the carbon fluoride material, thereby improving the chemical stability of the carbon fluoride material; during the storage process of the lithium / carbon fluoride battery containing the prepared modified carbon fluoride, the problem of battery capacity loss caused by the reaction between the electrolyte and the positive electrode carbon fluoride can be effectively improved and alleviated, thereby improving the storage stability of the lithium / carbon fluoride battery. In addition, the modification method of the present invention is simple and convenient, has low cost, and is 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 clear 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 500r / min, and modification treatment is carried out at 50°C for 5h, and finally solid-liquid separation is carried out, the separated product is placed in a blast oven for drying, and finally a powder disperser is used to disperse the dried modified carbon fluoride particles 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 its speed 300r / min, and modification treatment is carried out at 60°C for 5h, and finally solid-liquid separation is carried out, the separated product is placed in a blast oven for drying, and finally a powder disperser is used to disperse the dried modified carbon fluoride particles 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 solvent ethanol 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 its speed 300r / min, and modification treatment is carried out at 25°C for 10h, and finally solid-liquid separation is carried out, the separated product is placed in a blast oven for drying, and finally a powder disperser is used to disperse the dried modified carbon fluoride particles to obtain modified carbon fluoride powder.

[0040] Example 4

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

[0044] Example 6

[0045] This embodiment provides a method for modifying fluorinated carbon, wherein the acid anhydride is replaced by citraconic anhydride from 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 carbon fluoride, 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 fluorinated carbon, 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] Embodiment 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] Embodiment 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 500r / min, and modification treatment is carried out at 50°C for 5h, and finally solid-liquid separation is carried out, the separated product is placed in a blast oven for drying, and finally a powder disperser is used to disperse the dried modified carbon fluoride particles 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 are used as active materials to make carbon fluoride positive electrode sheets, and then the carbon fluoride positive electrode sheets, metal lithium negative electrode sheets and separators are assembled into battery cells by stacking, and a primary lithium carbon fluoride battery electrolyte is injected into the battery cells, the electrolyte composition is PC / DME / LiBF4, wherein the volume ratio of PC (propylene carbonate) to DME (ethylene glycol dimethyl ether) is 1 / 1, and LiBF4 is 1 mol / L, and a lithium / carbon fluoride battery is obtained after sealing.

[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. The storage stability of the batteries was evaluated, and the discharge rate was controlled to 0.01C. The results are shown in Table 1.

[0065] Table 1

[0066]

[0067] It can be seen from Table 1 that:

[0068] By comparing Examples 1-6 with Comparative Example 1, it is found that the stability of the carbon fluoride material is significantly improved after being washed with anhydride, and the capacity retention rate of the prepared battery after storage is 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 excess anhydride will remain in the fluorinated carbon material and cannot be 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 little, the solvent has insufficient wettability on 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 much, the storage stability of the battery cell is no longer improved, and there is no need to introduce excessive solvent, which increases the difficulty and cost of processing.

[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 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; the 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, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope 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 suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0074] In addition, 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 fluorinated carbon material, acid anhydride and solvent are mixed and modified to obtain modified fluorinated carbon.

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, etc.; preferably at least one of maleic anhydride, phthalic anhydride, succinic anhydride or NA-anhydride.

3. The method for modifying carbon fluoride according to claim 1 or 2, characterized in that: The solvent comprises at least one of an alcohol solvent, an ether solvent, a carboxylate solvent or a carbonate solvent, preferably an ether solvent; Preferably, the alcohol solvent includes at least one of methanol, ethanol or propanol; Preferably, the ether solvent includes tetrahydrofuran and / or ethylene glycol dimethyl ether; Preferably, the carboxylate solvent includes at least one of ethyl formate, ethyl acetate or propyl acetate; Preferably, the carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate.

4. The method for modifying carbon fluoride according to any one of claims 1 to 3, characterized in that: The mass of the acid anhydride accounts for 0.1% to 5% of the total mass of the acid anhydride and the solvent.

5. The method for modifying fluorinated carbon according to any one of claims 1 to 4, characterized in that: 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).

6. The method for modifying fluorinated carbon according to any one of claims 1 to 4, characterized in that: The temperature of the modification treatment is 0 to 90°C, preferably 30 to 60°C; Preferably, the modification treatment time is >5 min, preferably 1 to 10 h; Preferably, the modification treatment is carried out under stirring, and the stirring speed is 100-1000 r / min.

7. The method for modifying fluorinated carbon according to any one of claims 1 to 4, characterized in that: The modification method comprises 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.

8. A modified fluorinated carbon, characterized in that: Prepared according to the modification method according to any one of claims 1 to 7.

9. A positive electrode sheet, characterized in that: The active material of the positive electrode sheet includes the modified fluorinated carbon as claimed in claim 8.

10. A lithium / carbon fluoride battery, characterized in that: Contains the modified fluorinated carbon according to claim 8 or contains the positive electrode sheet according to claim 9.

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