Lithium carbon monofluoride battery electrode additive, positive electrode and battery

Abstract

This invention relates to the field of lithium fluoride carbon batteries, and particularly to a lithium fluoride carbon battery electrode additive, a positive electrode, and a battery. The lithium fluoride carbon battery electrode additive is iron fluoride. This invention employs a heterogeneous nucleation-induced strategy to reduce the exothermic behavior caused by LiF crystallization, solving the problem of guiding low-temperature nucleation growth of LiF, thereby effectively addressing the Li / CF... x The thermal runaway problem in lithium-carbon fluoride batteries caused by the violent crystallization of LiF during discharge increases the Li / CF ratio. x The thermal stability and electrochemical performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium fluoride carbon batteries, and particularly to a lithium fluoride carbon battery electrode additive, a positive electrode, and a battery. Background Technology

[0002] With advancements in technologies such as mobile communications, aerospace, transportation, and military equipment, the development of high-power-density and high-energy-density batteries has become an urgent need for the national economy. Due to the high negative electrode potential of lithium metal, lithium primary batteries, including Li / MnO2, Li / SO2, and Li / SOCl2 batteries, have received increasing attention. Among these primary batteries, lithium / carbon fluoride (Li / CF4) batteries are particularly promising. x The battery has the highest specific energy, reaching 2180Wh·kg⁻¹. -1 Compared to other primary lithium batteries, Li / CF x The battery exhibits excellent electrochemical performance, such as long lifespan, wide operating temperature range, and high reliability. However, Li / CF... x Batteries have consistently faced the problem of thermal runaway during discharge due to excessive heat generation, which severely impacts their safety and stability. Researchers have attempted various methods to reduce heat generation during discharge, but the results have been less than ideal. How to better address the thermal runaway problem of lithium-carbon fluoride batteries, reduce heat generation during discharge, and enhance battery safety remains a pressing technical challenge. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a lithium fluoride carbon battery electrode additive, a positive electrode, and a battery. Employing a heterogeneous nucleation-induced strategy, and by optimizing the selection and mechanism design of the positive electrode additive, it solves the problem of guiding the low-temperature nucleation growth of LiF, thereby effectively addressing the Li / CF... x The thermal runaway problem in lithium-carbon fluoride batteries caused by the violent crystallization of LiF during discharge increases the Li / CF ratio. x The thermal stability and electrochemical performance of the battery.

[0004] In a first aspect, the present invention provides a lithium fluorinated carbon battery electrode additive, wherein the lithium fluorinated carbon battery electrode additive is iron fluoride.

[0005] This invention addresses the Li / CF problem through a pre-nucleation strategy. xThe thermal runaway problem of batteries. Before discharge, a small number of stable crystal nuclei with high binding energy to LiF are pre-generated through a chemical reaction. These nuclei act as seeds for LiF crystallization and growth, promoting the crystallization and growth of newly formed LiF on their surface during discharge, thereby reducing the entropy increase associated with LiF nucleation. By using trivalent iron fluoride as an additive to the electrode active material of lithium-carbon fluoride batteries, in the initial stage of discharge, lithium and iron fluoride will first discharge to generate LiFeF4, which then becomes the nucleus for LiF. This not only effectively reduces the Li / CF ratio... x The heat generated during battery discharge also increases the Li / CF ratio. x The thermal stability and electrochemical performance of the battery.

[0006] In a second aspect, the present invention provides a positive electrode for a lithium fluoride carbon battery, wherein the electrode active material in the positive electrode includes fluoride carbon, a conductive agent, a binder and iron fluoride; the mass ratio of the fluoride carbon, the conductive agent and the binder is (5-10):(0.1-5):(0.1-5).

[0007] The positive electrode of the lithium fluoride carbon battery of the present invention uses a certain proportion of fluorinated carbon, conductive agent and binder, and iron fluoride (FeF3) can be oxidized to [FeF3] during the initial stage of discharge. + The lower valence state of iron makes it easier to adsorb free F ions, and the amorphous LiFeF4 generated in the initial stage of discharge can serve as an active site for LiF crystallization. Lower valence state iron cannot form amorphous LiFeF3 and cannot provide nucleation sites for lithium fluoride. Furthermore, calculations show that the binding energy between FeF2 and LiF is much lower than that of LiFeF4, so it also cannot provide nucleation sites for LiF. This invention utilizes the characteristic of amorphous LiFeF4 generated in the first stage of the lithium iron fluoride battery discharge process, making it an active site for the crystal growth of lithium fluoride, a discharge product of lithium carbon fluoride batteries. This reduces the heat generated during the lithium fluoride crystallization process and amorphizes the lithium fluoride product.

[0008] Preferably, the iron fluoride accounts for 0.1% to 20% of the total mass of the electrode active material; for example, 0.1%, 0.5%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, etc.

[0009] More preferably, the iron fluoride accounts for 1 to 10% of the total mass of the electrode active material.

[0010] Further preferably, the conductive agent is selected from one or more of conductive carbon black, graphene, conductive graphite, carbon nanotubes, acetylene black, and Ketjen black, with conductive carbon black being the most preferred.

[0011] More preferably, the adhesive is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose, with polyvinylidene fluoride being the most preferred.

[0012] Thirdly, the present invention provides a method for preparing the positive electrode of a lithium fluoride carbon battery, comprising: mixing fluoride carbon, a conductive agent, a binder, iron fluoride, and a first solvent to obtain a mixed slurry, and then using the mixed slurry to prepare a positive electrode sheet. The present invention obtains a high-performance positive electrode for a lithium fluoride carbon battery by mixing fluoride carbon, a conductive agent, a binder, iron fluoride, and an organic solvent to prepare an electrode sheet, and the method of the present invention is simple.

[0013] Preferably, the first solvent is selected from one or more of N-methylpyrrolidone, ethanol, and methanol, with N-methylpyrrolidone being the most preferred. The preparation method employed in this invention involves dissolving preferred raw materials such as fluorinated carbon, conductive carbon black, polyvinylidene fluoride, and iron fluoride in N-methylpyrrolidone and mixing them uniformly. The mixture is then coated into an electrode film with a thickness of 0.1-0.2 mm using a wet film preparation device. After vacuum drying, the film is cut into electrode sheets with a diameter of 10-20 mm using a slicing machine. This method effectively prepares the positive electrode for lithium fluoride carbon batteries and significantly reduces the Li / CF ratio. x The heat generated during battery discharge increases the Li / CF ratio. x The thermal stability and electrochemical performance of the battery.

[0014] Fourthly, the present invention provides a lithium fluoride carbon battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the positive electrode is the lithium fluoride carbon battery positive electrode described above or the lithium fluoride carbon battery positive electrode obtained by the above preparation method. In the lithium fluoride carbon battery system of the present invention, the positive electrode, negative electrode, separator, and electrolyte interact, and the optimized lithium fluoride carbon battery positive electrode effectively solves the aforementioned technical problems, significantly reducing the Li / CF ratio. x The heat generated during battery discharge significantly increases the Li / CF ratio. x The thermal stability and electrochemical performance of the battery.

[0015] Preferably, the lithium fluoride carbon battery operates at a temperature of -40 to 150°C.

[0016] Preferably, the lithium fluoride carbon battery is allowed to discharge at a rate of 0.01 to 10C during operation.

[0017] Preferably, the electrolyte comprises a lithium salt and a second solvent; preferably, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, and lithium hexafluoroarsenate; and / or, the second solvent is selected from at least one of dimethyl carbonate, propylene carbonate, ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene glycol dimethyl ether, tetrahydrofuran, 1,2-dimethoxyethylene, 1,4-dioxocyclohexane, diethylene glycol dimethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; and / or, the molar concentration of the lithium salt in the lithium fluoride carbon battery electrolyte is 0.01~10M.

[0018] Preferably, the negative electrode is a lithium negative electrode.

[0019] Preferably, the diaphragm includes at least one of modified polypropylene diaphragm, modified polyethylene diaphragm, polyethylene diaphragm, polypropylene diaphragm, polytetrafluoroethylene diaphragm, and organic-inorganic composite diaphragm.

[0020] The beneficial effects of this invention are at least as follows: By introducing FeF3 as an electrode additive for lithium fluoride carbon batteries, this invention induces the amorphous LiF to discharge into Li in the first stage. x Fe y F3 surface growth significantly reduces heat generation during battery discharge. This invention achieves the generation of amorphous LiFeF4 nuclei in the early stages of discharge; induces ordered crystallization of LiF, avoiding the formation of high-temperature hot spots; significantly reduces heat release during discharge, improving thermal stability; and enhances the Li / CF ratio. x Overall electrochemical performance of the battery. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0022] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0023] Unless otherwise specified, specific techniques or conditions in the embodiments of this invention shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Devices, instruments, reagents, etc., used without a specified manufacturer are all conventional products that can be purchased through legitimate channels. The raw materials and reagents in the embodiments of this invention were all purchased commercially.

[0024] The analytical method in the embodiments of this application is as follows: Electrochemical testing of the assembled flow-type supercapacitor is performed using a Landian constant current charge-discharge instrument. The equipment used is a CT2001A battery testing system, manufactured by Wuhan Landian Electronics Co., Ltd.

[0025] Example 1 This embodiment provides a lithium fluoride carbon battery electrode additive, wherein the lithium fluoride carbon battery electrode additive is iron fluoride (FeF3).

[0026] This embodiment provides a positive electrode for a lithium fluoride carbon battery. In the positive electrode of the lithium fluoride carbon battery, the electrode active material is fluoride carbon, conductive carbon black, PVDF and iron fluoride in a mass ratio of 7:1:1:1 (the mass of iron fluoride accounts for 2.5% of the total mass of the electrode active material). The positive electrode of the lithium fluoride carbon battery is an electrode sheet with a thickness of 0.15 mm and a diameter of 14 mm.

[0027] This embodiment also provides a method for preparing the positive electrode of the lithium fluoride carbon battery, including: dissolving fluoride carbon, conductive carbon black, PVDF, and iron fluoride in N-methylpyrrolidone at a mass ratio of 7.75:1:1:0.25 (the mass of iron fluoride accounts for 2.5% of the total mass of the electrode active material) and mixing them evenly. The mixture is then coated into an electrode film with a thickness of 0.15 mm using a wet film preparation device. After vacuum drying, the film is cut into electrode sheets with a diameter of 14 mm using a slicer. The weight of the active material is then weighed and the mass of the active material is calculated.

[0028] The lithium fluoride carbon battery provided in this embodiment uses the positive electrode of the lithium fluoride carbon battery provided in this embodiment, with a lithium sheet as the negative electrode, Celgard 2500 as the separator, and 70 μL of electrolyte (the lithium fluoride carbon battery electrolyte includes: dimethyl carbonate, propylene carbonate, and ethylene glycol dimethyl ether in a volume ratio of 1:1:1, and LiClO4, with the ratio of LiClO4 to the mixed solvent being 1 mol:1 L). The assembly process of the lithium fluoride carbon battery includes: the positive electrode of the lithium fluoride carbon battery uses the electrode sheet provided in this embodiment, with a lithium sheet as the negative electrode, and Celgard 2500 as the separator. A 2500-mesh separator was used, and 70 μL of electrolyte was added (the preparation method of this lithium fluoride carbon battery electrolyte includes: mixing dimethyl carbonate, propylene carbonate, and ethylene glycol dimethyl ether in a volume ratio of 1:1:1 to obtain a mixed solvent; weighing 1 L of the mixed solvent and adding 1 mol of LiClO4, stirring to dissolve). The battery was assembled into a button cell in an argon-filled glove box, and electrochemical and temperature tests were performed on the above lithium fluoride carbon battery. The battery was discharged at a 5C rate to 1V. A temperature sensor was attached to the center of the positive electrode side of the button cell to sense the battery temperature change. During the test, the battery discharge capacity and the surface temperature of the positive electrode casing at the moment of discharge completion were recorded. The assembled button cell had a discharge capacity of 779 mAh / g, and the battery positive electrode casing temperature was 50.1℃.

[0029] Example 2 Following the method and requirements of Example 1, without changing other conditions, the only difference is that the amount of iron fluoride added is changed from 2.5% to 1% of the total mass of the electrode active material. The assembled coin cell has a discharge capacity of 777 mAh / g and a positive electrode casing temperature of 55.5°C.

[0030] Example 3 Following the method and requirements of Example 1, without changing other conditions, the only difference is that the amount of iron fluoride added is changed from 2.5% to 10% of the total mass of the electrode active material. The assembled coin cell has a discharge capacity of 774 mAh / g and a positive electrode casing temperature of 55.7°C.

[0031] Example 4 Following the method and requirements of Example 1, without changing other conditions, the only difference is that the amount of iron fluoride added is changed from 2.5% to 0.1%. The assembled button cell has a discharge capacity of 771 mAh / g and a positive electrode casing temperature of 61.3°C.

[0032] Example 5 Following the method and requirements of Example 1, without changing other conditions, the only difference was that the amount of iron fluoride added was changed from 2.5% to 20%. The assembled button cell had a discharge capacity of 764 mAh / g and a positive electrode casing temperature of 61.6°C.

[0033] Comparative Example 1 Following the method and requirements of Example 1, without changing other conditions, the only difference being the absence of added iron fluoride. The assembled button cell has a discharge capacity of 699 mAh / g and a positive electrode casing temperature of 85.1°C.

[0034] By comparing Example 1 and Comparative Example 1, it was found that without the addition of iron fluoride, the goal of promoting LiF prenucleation could not be achieved, and the heat generation of the battery could not be reduced.

[0035] Comparative Example 2 Following the method and requirements of Example 1, without changing other conditions, the only difference is that the amount of iron fluoride added is changed from 2.5% to 25%. The assembled button cell has a discharge capacity of 672 mAh / g and a positive electrode casing temperature of 79.3°C.

[0036] Comparative Example 3 Following the method and requirements of Example 1, without changing other conditions, the only difference is that ferric fluoride is replaced with ferrous fluoride (divalent). The assembled button cell has a discharge capacity of 661 mAh / g and a positive electrode casing temperature of 79.5°C.

[0037] Comparative Example 4 Following the method and requirements of Example 1, without changing other conditions, the only difference is that iron fluoride is replaced with cobalt fluoride (trivalent). The assembled button cell has a discharge capacity of 659 mAh / g and a positive electrode casing temperature of 80.6°C.

[0038] As shown in Comparative Examples 2-4, only trivalent iron fluoride can initially generate Li in the initial stage of discharge. x Fe y F3 becomes the nucleus for LiF crystals, greatly reducing the heat generated during the LiF crystallization process. Other compounds cannot generate corresponding nuclei at high potentials (initial stage of discharge), especially comparative example 4, where cobalt fluoride (trivalent) cannot be converted to [CoF3] at the initial stage of discharge. + It cannot adsorb free fluoride ions, nor can it assist in the growth of LiF crystals, thus failing to solve the thermal runaway problem of the battery. Furthermore, in Comparative Example 2, the excessive addition of iron fluoride led to increased battery polarization and Joule heating, resulting in increased heat generation during battery discharge. In Comparative Example 3, the low valence state of iron in divalent ferrous fluoride prevented it from promoting the pre-nucleation process, resulting in no significant reduction in battery heat generation.

[0039] Comparative Example 5 Following the method and requirements of Example 1, without changing other conditions, the only difference is that, during the preparation of the fluorinated carbon electrode, the same amount of iron fluoride was added to the electrolyte as in Example 1, and iron fluoride was not added during the preparation of the electrode active material. The assembled coin cell has a discharge capacity of 655 mAh / g and a positive electrode casing temperature of 81.7°C.

[0040] As shown in Comparative Example 5, the assembled coin cell exhibited a significant decrease in specific capacity and generated substantial heat during discharge during the fabrication of the fluorinated carbon electrode. This was due to the formation of a large amount of high-resistivity LiFeF4 in the electrolyte during the initial discharge stage, which severely hindered lithium-ion transport and significantly increased the resistance of the electrode active material. Ultimately, this resulted in substantial heat generation during battery discharge.

[0041] Unless otherwise specified, all figures appearing in this application specification and claims, such as temperature and time values, should not be construed as absolutely precise values. Due to the standard deviation of measurement techniques, the measured values ​​inevitably contain a certain degree of experimental error.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium fluoride carbon battery electrode additive, characterized in that, The electrode additive for the lithium fluoride carbon battery is iron fluoride.

2. A positive electrode for a lithium fluoride carbon battery, characterized in that, The electrode active material in the positive electrode of the lithium fluoride carbon battery includes fluorinated carbon, conductive agent, binder and iron fluoride; the mass ratio of fluorinated carbon, conductive agent and binder is (5-10):(0.1-5):(0.1-5).

3. The positive electrode of a lithium fluoride carbon battery according to claim 2, characterized in that, The iron fluoride accounts for 0.1% to 20% of the total mass of the electrode active material; Preferably, the iron fluoride accounts for 1 to 10% of the total mass of the electrode active material.

4. The positive electrode of a lithium fluoride carbon battery according to claim 2 or 3, characterized in that, The conductive agent is selected from one or more of conductive carbon black, graphene, conductive graphite, carbon nanotubes, acetylene black, and Ketjen black. And / or, the adhesive is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose.

5. The method for preparing the positive electrode of a lithium fluoride carbon battery according to any one of claims 2 to 4, characterized in that, include: Fluorinated carbon, conductive agent, binder, iron fluoride and a first solvent are mixed to obtain a mixed slurry, and then the positive electrode sheet is prepared using the mixed slurry.

6. The preparation method according to claim 5, characterized in that, The first solvent is selected from one or more of N-methylpyrrolidone, ethanol, and methanol, preferably N-methylpyrrolidone.

7. A lithium fluoride carbon battery, characterized in that, The lithium fluoride carbon battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the positive electrode is the lithium fluoride carbon battery positive electrode according to any one of claims 2 to 4 or the lithium fluoride carbon battery positive electrode obtained by the preparation method according to any one of claims 5 or 6.

8. The lithium fluoride carbon battery according to claim 7, characterized in that, The operating temperature of the lithium fluoride carbon battery is -40~150℃.

9. The lithium fluoride carbon battery according to claim 7 or 8, characterized in that, The allowable discharge rate of the lithium fluoride carbon battery during operation is 0.01~10C.

10. The lithium fluoride carbon battery according to any one of claims 7 to 9, characterized in that, The electrolyte comprises a lithium salt and a second solvent; preferably, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, and lithium hexafluoroarsenate; and / or, the second solvent is selected from at least one of dimethyl carbonate, propylene carbonate, ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene glycol dimethyl ether, tetrahydrofuran, 1,2-dimethoxyethylene, 1,4-dioxane, diethylene glycol dimethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; and / or, the molar concentration of the lithium salt in the lithium fluoride carbon battery electrolyte is 0.01~10M; And / or, the negative electrode is a lithium negative electrode; And / or, the diaphragm includes at least one of modified polypropylene diaphragm, modified polyethylene diaphragm, polyethylene diaphragm, polypropylene diaphragm, polytetrafluoroethylene diaphragm, and organic-inorganic composite diaphragm.